Lithium secondary battery
阅读说明：本技术 锂二次电池 (Lithium secondary battery ) 是由 严仁晟 权要翰 朴恩囧 李在宪 张民哲 孙炳国 河性珉 于 2019-10-30 设计创作，主要内容包括：本发明涉及一种锂二次电池,其被制造为无负极电池并且具有通过充电在负极集电器上形成的锂金属,并且使用含有牺牲盐的电解质。所述锂二次电池在与大气隔绝的状态下形成锂金属,从而从根本上改善由于锂金属的高反应性而引起的现有的问题,并且通过在所述电解质中含有所述牺牲盐,减少由负极中的不可逆反应引起的锂的消耗,这可以防止电池的容量和寿命特性的劣化。(The present invention relates to a lithium secondary battery which is manufactured as a non-anode battery and has lithium metal formed on an anode current collector by charging, and uses an electrolyte containing a sacrificial salt. The lithium secondary battery forms lithium metal in a state of being sealed from the atmosphere, thereby fundamentally improving the existing problems due to high reactivity of lithium metal, and reduces consumption of lithium caused by an irreversible reaction in the negative electrode by containing the sacrificial salt in the electrolyte, which can prevent deterioration of capacity and life characteristics of the battery.)
1. A lithium secondary battery, comprising:
a positive electrode;
a negative electrode; and
an electrolyte disposed between the two electrodes and having a dielectric layer,
wherein lithium metal is formed on the negative electrode current collector from lithium ions that migrate by charging; and is
The electrolyte includes a sacrificial salt having an oxidation potential of 5V or less with respect to lithium.
2. The lithium secondary battery according to claim 1, wherein the sacrificial salt has an oxidation potential ranging from 3V to 4.8V with respect to lithium.
3. The lithium secondary battery according to claim 1, wherein the sacrificial salt has an irreversible capacity of 100mAh/g to 600 mAh/g.
4. The lithium secondary battery of claim 1, wherein the sacrificial salt comprises lithium.
5. The lithium secondary battery of claim 1, wherein the sacrificial salt comprises a salt selected from the group consisting of LiN3、Li2C2O4、Li2C4O4、Li2C3O5、Li2C4O6、LiCF3CO2、LiC2F5CO2At least one of the group consisting of LitC, LiVFB, LiBBB and LiBFB.
6. The lithium secondary battery according to claim 1, wherein the sacrificial salt is included in an amount of 0.1 to 30 wt% based on the total 100 wt% of the electrolyte.
7. The lithium secondary battery according to claim 1, wherein the electrolyte further comprises a lithium salt and an organic solvent.
8. The lithium secondary battery according to claim 7, wherein the lithium salt comprises one or more compounds selected from the group consisting of LiCl, LiBr, LiI, and LiClO4、LiBF4、LiB10Cl10、LiPF6、LiCF3SO3、LiCF3CO2、LiC4BO8、LiAsF6、LiSbF6、LiAlCl4、CH3SO3Li、CF3SO3Li、(CF3SO2)2NLi、(C2F5SO2)2NLi、(SO2F)2NLi and (CF)3SO2)3At least one of the group consisting of CLi.
9. The lithium secondary battery according to claim 1, wherein the lithium ions are derived from the positive electrode or the electrolyte.
10. The lithium secondary battery according to claim 1, wherein the lithium metal is formed by first charging in a voltage range of 4.8V to 2.5V.
11. The lithium secondary battery according to claim 1, wherein the positive electrode comprises at least one positive electrode active material selected from the group consisting of: LiCoO2；LiNiO2；LiMnO2；LiMn2O4；Li(NiaCobMnc)O2(0 < a < 1, 0 < b < 1, 0 < c < 1 and a + b + c ═ 1); LiNi1-YCoYO2，LiCo1-YMnYO2，LiNi1-YMnYO2(here, 0. ltoreq. Y < 1); li (Ni)aCobMnc)O4(0 < a < 2, 0 < b < 2, 0 < c < 2 and a + b + c 2); LiMn2-zNizO4，LiMn2-zCozO4(here, 0 < Z < 2); lixMyMn2-yO4-zAz(where 0.9. ltoreq. x. ltoreq.1.2, 0<y<2，0≤z<0.2, M ═ one or more of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti, and Bi, and a is one or more anions having a valence of-1 or-2); li1+aNibM'1-bO2-cA'c(0≤a≤0.1，0≤b≤0.8，0≤c<0.2, M' is a structure selected from octahedral stabilising elements such as Mn, Co, Mg or AlAnd A' is one or more anions having a valence of-1 or-2); LiCoPO4(ii) a And LiFePO4。
12. The lithium secondary battery according to claim 1, wherein the positive electrode further comprises a lithium metal compound represented by any one of the following chemical formulas 1 to 8:
[ chemical formula 1]
Li2Ni1-aM1 aO2
In the formula, 0. ltoreq. a < 1, and M1Is at least one element selected from the group consisting of Mn, Fe, Co, Cu, Zn, Mg and Cd;
[ chemical formula 2]
Li2+bNi1-cM2 cO2+d
In the formula, b is more than or equal to-0.5 and less than or equal to 0.5, c is more than or equal to 0 and less than or equal to 1, d is more than or equal to 0 and less than 0.3, and M2Is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo, and Cd;
[ chemical formula 3]
LiM3 eMn1-eO2
In the formula, 0. ltoreq. e < 0.5, and M3Is at least one element selected from the group consisting of Cr, Al, Ni, Mn and Co;
[ chemical formula 4]
Li2M4O2
In the formula, M4Is at least one element selected from the group consisting of Cu and Ni;
[ chemical formula 5]
Li3+fNb1-gM5 gS4-h
In the formula, f is-0.1. ltoreq. f.ltoreq.1, g is 0. ltoreq. g.ltoreq.0.5, h is-0.1. ltoreq. h.ltoreq.0.5, and M5Is at least one element selected from the group consisting of Mn, Fe, Co, Cu, Zn, Mg and Cd;
[ chemical formula 6]
LiM6 iMn1-iO2
In the formula, i is 0.05. ltoreq.i < 0.5, and M6Is at least one element selected from the group consisting of Cr, Al, Ni, Mn and Co;
[ chemical formula 7]
LiM7 2jMn2-2jO4
In the formula, j is 0.05. ltoreq.j < 0.5, and M7Is at least one element selected from the group consisting of Cr, Al, Ni, Mn and Co; and
[ chemical formula 8]
Lik-M8 m-Nn
In the formula, M8Represents an alkaline earth metal, k/(k + m + n) is 0.10 to 0.40, m/(k + m + n) is 0.20 to 0.50, and n/(k + m + n) is 0.20 to 0.50.
13. The lithium secondary battery according to claim 1, wherein the anode further comprises a protective film on a surface in contact with the separator.
14. The lithium secondary battery according to claim 13, wherein the protective film comprises at least one selected from the group consisting of a lithium ion-conductive polymer and an inorganic solid electrolyte.
15. The lithium secondary battery of claim 14, wherein the lithium ion conducting polymer comprises a material selected from the group consisting of polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyvinylidene fluoride-hexafluoropropylene, LiPON, Li3N、LixLa1-xTiO3(0<x<1) And Li2S-GeS-Ga2S3At least one of the group consisting of.
16. The lithium secondary battery of claim 14, wherein the inorganic solid electrolyte comprises a material selected from the group consisting of thio-LISICON (Li)3.25Ge0.25P0.75S4)；Li2S-SiS2；LiI-Li2S-SiS2；LiI-Li2S-P2S5；LiI-Li2S-P2O5；LiI-Li3PO4-P2S5；Li2S-P2S5；Li3PS4；Li7P3S11；Li2O-B2O3；Li2O-B2O3-P2O5；Li2O-V2O5-SiO2；Li2O-B2O3；Li3PO4；Li2O-Li2WO4-B2O3；LiPON；LiBON；Li2O-SiO2；LiI；Li3N；Li5La3Ta2O12；Li7La3Zr2O12；Li6BaLa2Ta2O12；Li3PO(4-3/2w)Nw(w is w < 1); and Li3.6Si0.6P0.4O4At least one of the group consisting of.
17. The lithium secondary battery according to claim 13, wherein the protective film has a thickness of 10nm to 50 μm.
Technical Field
The present application claims the benefit of priority based on korean patent application No. 10-2018-.
The present invention relates to a lithium secondary battery having a structure without a negative electrode using an electrolyte containing a sacrificial salt.
Background
With the rapid development of the electrical, electronic, communication, and computer industries, the demand for high-performance and high-stability secondary batteries has recently increased rapidly. In particular, with the trend toward lighter, thinner, smaller, and portable batteries and electronic products, weight reduction and miniaturization have also been required for secondary batteries, which are key components. Further, as the demand for new energy supply has increased due to environmental pollution problems and fossil depletion, the necessity of developing electric vehicles capable of solving such problems has increased. Among various secondary batteries, lithium secondary batteries that are lightweight, exhibit high energy density and operating potential, and have a long cycle life have recently received attention.
A lithium secondary battery has a structure in which an electrode assembly including a cathode, an anode, and a separator disposed between the cathode and the anode is laminated or wound, and is formed by inserting the electrode assembly into a battery case and injecting a nonaqueous electrolytic solution thereinto. At this time, the capacity of the lithium secondary battery may vary according to the type of the electrode active material, and commercialization has not been achieved because sufficient capacity as theoretical capacity cannot be secured during actual driving.
In order to obtain a high capacity of a lithium secondary battery, a metal-based material having a high storage capacity property by an alloying reaction with lithium, such as silicon (4200mAh/g) or tin (990mAh/g), has been used as a negative active material. However, when a metal such as silicon or tin is used as an anode active material, the volume significantly expands to about 4 times during charging for alloying with lithium, and shrinks during discharging. Since such a large change in volume of the electrode repeatedly occurs during charge and discharge, the active material is gradually micronized and is exfoliated from the electrode, resulting in a rapid decrease in capacity, and thus commercialization has not been achieved since stability and reliability cannot be ensured.
Lithium metal has an excellent theoretical capacity of 3860mAh/g, compared to the above negative active material, and has a very low standard reduction potential of-3.045V (with respect to a Standard Hydrogen Electrode (SHE)), thereby enabling realization of a battery having a high capacity and a high energy density, and thus extensive research has been conducted on a Lithium Metal Battery (LMB) using lithium metal as a negative active material of a lithium secondary battery.
However, when lithium metal is used as the negative electrode of a battery, the battery is generally manufactured by attaching lithium foil to a planar current collector. And since lithium as an alkali metal having high reactivity is explosively reacted with water and easily reacts with oxygen in the atmosphereAnd therefore, it is difficult to manufacture and use under general circumstances. In particular, when lithium metal is exposed to the atmosphere, such as LiOH, Li are formed on the surface due to oxidation2O or Li2CO3Oxide layer (native layer). Such an oxide layer serves as an insulating film that lowers conductivity and suppresses lithium ion migration, and a problem occurs in that the internal resistance of the battery is increased.
Due to such high instability of lithium metal, a lithium metal battery using lithium metal as a negative electrode has not been commercialized yet.
Accordingly, various methods for commercializing the lithium metal battery by improving the above problems have been studied.
As an example, korean patent No. 10-0635684 relates to a method of forming a lithium electrode having a glass protective layer, and discloses a method of preparing a lithium electrode by forming a protective layer on a substrate (PET) on which a release agent layer is deposited, depositing lithium on the protective layer, and then depositing a current collector on the lithium.
Although the prior art documents improve the problem of forming an oxide layer due to the reactivity of lithium metal to some extent by performing a vacuum deposition process when forming a lithium negative electrode, since the electrode is still exposed to the atmosphere during the battery assembly process, the fundamental suppression of the formation of the oxide layer has not been achieved. Therefore, there has been a need to develop a lithium metal battery capable of increasing energy density by using lithium metal while solving the problem of high lithium reactivity and further simplifying the process.
[ Prior art documents ]
[ patent document ]
Korean patent No. 10-0635684 (2006, 10/11/10), Encoated LITHIUM ELECTRODES HAVING GLASS PROTECTIVE LAYERS AND METHOD FOR the same electrode (ENCAPSULATED LITHIUM electrode with glass PROTECTIVE layer and METHOD FOR preparing the same).
Disclosure of Invention
[ problem ] to provide a method for producing a semiconductor device
As a result of extensive studies in view of the above circumstances, the inventors of the present invention have devised a structure of a non-anode battery capable of forming lithium metal on an anode current collector using lithium ions transferred by charging after assembling the battery while fundamentally preventing contact between the lithium metal and the atmosphere at the time of assembling the battery, have confirmed that the battery capacity and life are improved by improving the reactivity and stability of the lithium metal by including a sacrificial salt as an additive in an electrolyte, and have completed the present invention.
Accordingly, an aspect of the present invention provides a lithium secondary battery having improved performance and life span by solving the problems caused by the high reactivity of lithium metal.
[ technical solution ] A
According to an aspect of the present invention, there is provided a lithium secondary battery comprising a cathode, an anode, and an electrolyte interposed between the cathode and the anode, wherein lithium metal is formed on an anode current collector from lithium ions that migrate by charging, and the electrolyte comprises a sacrificial salt having an oxidation potential of 5V or less with respect to lithium.
The sacrificial salt may have an oxidation potential in a range of 3V to 4.8V with respect to lithium.
The sacrificial salt may have an irreversible capacity of 100mAh/g to 600 mAh/g.
The sacrificial salt may comprise lithium.
The sacrificial salt may comprise a compound selected from the group consisting of LiN3、Li2C2O4、Li2C4O4、Li2C3O5、Li2C4O6、LiCF3CO2、LiC2F5CO2At least one of the group consisting of LitC, LiVFB, LiBBB and LiBFB.
The sacrificial salt may be included in an amount of 0.1 to 30 wt% based on a total of 100 wt% of the electrolyte.
The electrolyte may further include a lithium salt and an organic solvent.
The lithium ions may be derived from the positive electrode or the electrolyte.
The lithium metal may be formed by first charging in a voltage range of 4.8V to 2.5V.
The negative electrode may further include a protective film on a surface in contact with the separator.
[ PROBLEMS ] the present invention
The lithium secondary battery according to the present invention is coated while being isolated from the atmosphere through the process of forming lithium metal on the anode current collector, and thus can suppress the formation of a surface oxide layer on the lithium metal caused by oxygen and moisture in the atmosphere, and thus obtain the effect of improving cycle life characteristics. In particular, by including a sacrificial salt in the electrolyte, the battery capacity can be maximized by preventing irreversible capacity loss from occurring during charge and discharge, and a long life can be obtained.
Drawings
Fig. 1 is a schematic view of a lithium secondary battery manufactured according to an embodiment of the present invention.
Fig. 2 is a view illustrating lithium ions (Li) when a lithium secondary battery manufactured according to an embodiment of the present invention is initially charged+) Schematic representation of migration.
Fig. 3 is a schematic view after completing initial charging of a lithium secondary battery manufactured according to an embodiment of the present invention.
Fig. 4 is a schematic view of a lithium secondary battery manufactured according to another embodiment of the present invention.
Fig. 5 is a view illustrating lithium ions (Li) when a lithium secondary battery manufactured according to another embodiment of the present invention is initially charged+) Schematic representation of migration.
Fig. 6 is a schematic view after completing initial charging of a lithium secondary battery manufactured according to another embodiment of the present invention.
Detailed Description
Hereinafter, the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily practice the invention. However, the present invention may be embodied in various forms and is not limited to the present specification.
In the drawings, for clarity of description of the present invention, portions irrelevant to the description are not included, and the same reference numerals are used for the same elements throughout the specification. Further, the sizes and relative sizes of the constituent elements shown in the drawings are not related to an actual scale, and may be reduced or enlarged for clarity of description.
The terms or words used in the present specification and claims should not be construed as limited to general or dictionary meanings, but interpreted as meanings and concepts conforming to the technical idea of the present disclosure on the basis of the principle that the inventor can appropriately define the concept of the term to describe the invention in the best possible manner.
The term "non-negative electrode (non-anode) battery" used in the present invention generally refers to a lithium secondary battery comprising a negative electrode having a form in which a negative electrode mixture contained in the negative electrode is formed by charge and discharge of the battery. At this time, the anode and the negative electrode have the same meaning.
In other words, in the present invention, an anodeless battery is a concept including both an anodeless battery in which an anode is not formed on an anode current collector at the time of initial assembly of the battery or a battery in which an anode may be formed on an anode current collector depending on use.
Further, in the anode of the present invention, the form of lithium metal formed as an anode on the anode current collector includes both a form in which lithium metal is formed as a layer and a structure in which lithium metal is not formed as a layer (for example, a structure in which lithium metal is aggregated in the form of particles).
Hereinafter, the present invention will be described based on the form of a lithium metal layer in which lithium metal is formed as a layer, however, it is apparent that such description does not exclude a structure in which lithium metal is not formed as a layer.
Fig. 1 is a sectional view of a lithium secondary battery manufactured according to an embodiment of the present invention, and includes: a positive electrode comprising a positive electrode current collector (11) and a positive electrode mixture (13); a negative electrode including a negative electrode current collector (21), a first protective layer (25), and a second protective layer (27); and a separator (30) and an electrolyte (not shown) interposed therebetween.
In a general lithium secondary battery, an anode includes an anode current collector and an anode mixture formed on the anode current collector. However, in the present invention, a non-anode battery structure is assembled using only an anode current collector, and then, lithium ions deintercalated from a cathode mixture by charging form lithium metal as an anode mixture on the anode current collector, and thereby an anode having a known configuration of an anode current collector and an anode mixture is formed to obtain the configuration of a general lithium secondary battery.
Fig. 2 is a view illustrating lithium ions (Li) when a lithium secondary battery manufactured according to an embodiment of the present invention is initially charged+) A schematic diagram of migration, and fig. 3 is a schematic diagram after completion of initial charging of a lithium secondary battery manufactured according to an embodiment of the present invention.
According to fig. 2 and 3, when a lithium secondary battery having a non-negative electrode battery structure is charged by applying a voltage above a certain level, lithium ions generated from a cathode mixture (13) or an electrolyte (not shown) in a cathode (10) migrate toward a negative electrode current collector (21) side after passing through a separator (30), and lithium metal (23) entirely formed of lithium is formed on the negative electrode current collector (21) to form a negative electrode (20).
Such formation of lithium metal (23) by charging has an advantage of being able to form a thin film layer and very easily adjust interfacial properties when compared with an existing anode obtained by sputtering lithium metal (23) on an anode current collector (21) or laminating a lithium foil and an anode current collector (21). Further, since the bonding strength of the lithium metal (23) laminated on the negative electrode current collector (21) is large and stable, the lithium metal does not suffer from removal from the negative electrode current collector (21) caused by returning to an ionized state by discharge.
Further, when forming a non-negative electrode battery structure, lithium metal is not exposed to the atmosphere at all during battery assembly, which fundamentally prevents the existing problems such as formation of an oxide layer on the surface and the resulting reduction in the life of the lithium secondary battery caused by the high reactivity of lithium itself.
In particular, in order to improve the problems of high chemical reactivity and electrochemical reactivity of lithium metal and to ensure the effect of improving battery performance and life, the lithium secondary battery according to the present invention includes a sacrificial salt having low oxidation stability as an additive in an electrolyte.
As described above, lithium metal has high reactivity and is therefore very susceptible in terms of stability. In addition, in a lithium secondary battery including lithium metal as a negative electrode, lithium reacts with some components forming an electrolyte during initial charge and discharge to form a passivation layer (solid electrolyte interphase; SEI) on the surface to prevent side reactions between the negative electrode and the electrolyte and to stably drive by reversibly maintaining the amount of lithium ions in the electrolyte. However, since a certain amount of lithium is inevitably consumed in forming the passivation layer, the amount of reversible lithium is inevitably reduced as compared to the initial design. Lithium consumed in such irreversible reaction serves as irreversible capacity, thereby reducing the capacity of the battery. Further, such a passivation layer is continuously formed during charge and discharge, which continuously consumes lithium metal and gradually reduces the amount of reversible lithium, and thus charge and discharge efficiency is reduced.
In view of the above, the present invention prevents irreversible capacity loss caused by the formation of a passivation layer during initial charge and discharge by including a sacrificial salt having low oxidation stability. In other words, the sacrificial salt may be dissociated, moved to the anode, and reduced to be obtained as charge and discharge capacity, and thus battery capacity and life characteristics may be improved by reducing the amount of lithium consumed during charge and discharge.
Specifically, the sacrificial salt contained in the electrolyte of the present invention is dissociated during charge and discharge of the lithium secondary battery, thereby irreversibly providing an excess amount of lithium ions, and such lithium ions may be reduced to lithium metal after migrating to the negative electrode. Accordingly, the sacrificial salt may provide lithium ions that are irreversibly consumed in forming the passivation layer during initial charge and discharge, or function as a lithium source that compensates for the amount of lithium ions that have been consumed in forming the passivation layer, or function as both, and thus may prevent irreversible capacity loss of the battery that inevitably accompanies formation of the passivation layer.
In the present invention, the sacrificial salt may have an oxidation potential of 5V or less, and preferably in the range of 3V to 4.8V, with respect to lithium. By making the oxidation potential of the sacrificial salt with respect to lithium correspond to the above range, the sacrificial salt is oxidized at the initial charge voltage of the battery, and at this time, lithium ions may be reduced in the anode current collector to form a lithium metal anode.
Further, the sacrificial salt is capable of irreversibly providing an excessive amount of lithium ions during the first charge and discharge cycle, and an irreversible capacity of the first charge and discharge cycle of the sacrificial salt (first cycle charge capacity-first cycle discharge capacity) may be 100mAh/g to 600mAh/g, and preferably 200mAh/g to 570 mAh/g. When the irreversible capacity of the sacrificial salt is less than the above range, the amount to be added to the electrolytic solution increases, and a problem of volume expansion of the battery may occur due to gas generated during charge and discharge. In contrast, when the irreversible capacity is greater than the above range, elements other than lithium forming the sacrificial salt increase, resulting in an increase in the amount of gas generated during charge and discharge, and as in the case where the irreversible capacity is less than the above range, a problem of volume expansion of the battery may occur.
The sacrificial salt is not limited as long as it is a material corresponding to the above potential and irreversible capacity ranges, and may contain, for example, lithium as a cation.
For example, the sacrificial salt may comprise a salt selected from the group consisting of LiN3、Li2C2O4、Li2C4O4、Li2C3O5、Li2C4O6、LiCF3CO2、LiC2F5CO2Lithium thiocyanate (Litc), LiVFB (lithium 1, 2-ethyleneglycoldifluoroborate (rate (1-), [1, 2-ethylendioloto (2-) - κ O)1,κO2]difluoro-, lithium (1:1), (T-4) -), bis [1,2-benzenediol (2-) -O, O']Lithium borate (lithium-bis [1, 2-benzanediatoto (2-) -O, O']Borate) (LiBBB)) and bis [ perfluoro-1,2-benzenediPhenol to (2-) -O, O']Lithium borate (lithium-bis [ perfluoro-1, 2-benzanediatoo (2-) -O, O']Rate (libfb)). Preferably, the sacrificial salt may be selected from the group consisting of LiN3At least one of the group consisting of LiVFB and LiBBB.
The sacrificial salt may be included in an amount of 0.1 to 30 wt%, and preferably 2 to 15 wt%, based on the total 100 wt% of the electrolyte. The inclusion of the sacrificial salt less than the above range may have a problem of shortening the battery life due to insufficient formation of lithium of the negative electrode. In contrast, the inclusion of the sacrificial salt more than the above range increases the viscosity of the electrolyte, decreases the lithium ion conductivity of the electrolyte, and may cause a problem in the safety of the battery due to gas generated during charging.
The electrolyte of the present invention contains an electrolyte salt, and the electrolyte salt is used for electrochemically reducing lithium ions generated by oxidation during charging in the negative electrode.
The electrolyte may be a non-aqueous electrolyte formed of a non-aqueous organic solvent that does not react with lithium metal and an electrolyte salt, and in addition, may further include an organic solid electrolyte or an inorganic solid electrolyte, however, the electrolyte is not limited thereto.
As the nonaqueous organic solvent, those generally used in an electrolyte solution for a lithium secondary battery may be used without limitation, and for example, ethers, esters, amides, chain carbonates, cyclic carbonates, and the like may be used each alone or as a mixture of two or more. Among these, ether compounds may be generally included.
The ether compound may include acyclic ethers and cyclic ethers.
For example, as the acyclic ether, at least one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, dimethoxyethane, diethoxyethane, methoxyethoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol methyl ethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol methyl ethyl ether, tetraethylene glycol dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene glycol methyl ethyl ether, polyethylene glycol dimethyl ether, polyethylene glycol diethyl ether and polyethylene glycol methyl ethyl ether may be used, however, the acyclic ether is not limited thereto.
Examples of the cyclic ether include cyclic ethers selected from the group consisting of 1, 3-dioxolane, 4, 5-dimethyl-dioxolane, 4, 5-diethyl-dioxolane, 4-methyl-1, 3-dioxolane, 4-ethyl-1, 3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 2, 5-dimethyltetrahydrofuran, 2, 5-dimethoxytetrahydrofuran, 2-ethoxytetrahydrofuran, 2-methyl-1, 3-dioxolane, 2-vinyl-1, 3-dioxolane, 2-dimethyl-1, 3-dioxolane, 2-methoxy-1, 3-dioxolane, 2-ethyl-2-methyl-1, 3-dioxolane, tetrahydropyran, 1, 4-bisAt least one of the group consisting of alkane, 1, 2-dimethoxybenzene, 1, 3-dimethoxybenzene, 1, 4-dimethoxybenzene and isosorbide dimethyl ether, however, the cyclic ether is not limited thereto.
As the ester in the organic solvent, any one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, γ -valerolactone, γ -caprolactone, σ -valerolactone and ∈ -caprolactone, or a mixture of two or more thereof may be used, however, the ester is not limited thereto.
Specific examples of the chain carbonate compound may generally include any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, Ethyl Methyl Carbonate (EMC), propyl methyl carbonate and propyl ethyl carbonate, or a mixture of two or more thereof, however, the chain carbonate compound is not limited thereto.
In addition, specific examples of the cyclic carbonate compound may include any one selected from the group consisting of Ethylene Carbonate (EC), Propylene Carbonate (PC), 1, 2-butylene carbonate, 2, 3-butylene carbonate, 1, 2-pentylene carbonate, 2, 3-pentylene carbonate, vinylene carbonate, ethylene carbonate, and halides thereof, or a mixture of two or more thereof. Examples of the halide thereof may include fluoroethylene carbonate (FEC) and the like, but are not limited thereto.
The electrolyte salt contained in the nonaqueous electrolyte is a lithium salt. The lithium salt may be used without limitation as long as it is generally used for an electrolyte for a lithium secondary battery. For example, the anion of the lithium salt may comprise a compound selected from the group consisting of F-、Cl-、Br-、I-、NO3 -、N(CN)2 -、BF4 -、ClO4-、PF6 -、(CF3)2PF4 -、(CF3)3PF3 -、(CF3)4PF2 -、(CF3)5PF-、(CF3)6P-、CF3SO3 -、CF3CF2SO3 -、(CF3SO2)2N-、(FSO2)2N-、CF3CF2(CF3)2CO-、(CF3SO2)2CH-、(SF5)3C-、(CF3SO2)3C-、CF3(CF2)7SO3 -、CF3CO2 -、CH3CO2 -、SCN-And (CF)3CF2SO2)2N-Any one of the group or two or more thereof.
For example, the lithium salt may include one or more selected from the group consisting of LiCl, LiBr, LiI and LiClO4、LiBF4、LiB10Cl10、LiPF6、LiCF3SO3、LiCF3CO2、LiC4BO8、LiAsF6、LiSbF6、LiAlCl4、CH3SO3Li、CF3SO3Li、(CF3SO2)2NLi、(C2F5SO2)2NLi、(SO2F)2NLi and (CF)3SO2)3At least one of the group consisting of CLi.
The concentration of the lithium salt may be appropriately determined in consideration of ion conductivity, solubility, and the like, and may be, for example, 0.1M to 4.0M, and preferably 0.5M to 2.0M.
When the concentration of the lithium salt is less than the above range, it is difficult to ensure ion conductivity suitable for battery driving, whereas when the concentration is greater than the above range, the viscosity of the electrolyte increases, thereby decreasing the lithium ion mobility, and the battery performance may be degraded due to an increase in decomposition reaction of the lithium salt itself, and thus the concentration is appropriately adjusted within the above range.
For improving charge and discharge properties, flame retardancy and the like, for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, (glycidyl) glymes, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substitutedOxazolidinone, N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, and the like are added to the nonaqueous electrolyte. In some cases, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may also be included to provide incombustibility, and carbon dioxide gas may also be included to improve high-temperature storage properties.
The nonaqueous electrolytic solution may be injected at an appropriate stage in the electrochemical device manufacturing process, depending on the manufacturing process and the desired properties of the final product. In other words, the nonaqueous electrolytic solution may be used at a stage before the electrochemical device is assembled or at a final stage of the electrochemical device assembly.
As the organic solid electrolyte, for example, a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, a polyallylamine, a polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, a polymer containing an ionic dissociation group, or the like can be used.
As the inorganic solid electrolyte, for example, a nitride, a halide, or sulfuric acid of Li can be usedSalts and the like, e.g. Li3N、LiI、Li5NI2、Li3N-LiI-LiOH、LiSiO4、LiSiO4-LiI-LiOH、Li2SiS3、Li4SiO4、Li4SiO4-LiI-LiOH or Li3PO4-Li2S-SiS2。
In the present invention, the anode current collector (21) may have lithium metal (23) formed by charging, and is not particularly limited as long as it has conductivity without causing chemical changes of the lithium secondary battery. Examples thereof may include copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., aluminum-cadmium alloy, etc.
At this time, in order to increase the adhesive strength with the anode active material, the anode current collector (21) may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, or a non-woven fabric, with fine irregularities formed on the surface.
Preferably, the anode current collector (21) has a three-dimensional structure form with pores formed therein, and may have a thickness of 20 to 200 μm, preferably 50 to 150 μm, and more preferably 80 to 120 μm. When the thickness of the anode current collector (21) is less than the above range, lithium metal formed in the anode current collector (21) may be formed outside the porous current collector, so that the lithium dendrite suppression effect may be reduced, and the battery performance may be degraded. When the thickness is more than the above range, the battery thickness may become large, which may be disadvantageous for commercialization.
The anode current collector (21) may have a porosity of 50% to 90%, preferably 60% to 85%, and more preferably 70% to 85%. When the porosity of the anode current collector (21) is less than the above range, lithium metal formed in the anode current collector may be formed outside the porous current collector, thereby reducing the lithium dendrite suppression effect, and when the porosity is greater than the above range, the anode current collector (21) may have unstable strength, thereby making the battery manufacturing process difficult.
The lithium secondary battery having a structure without an anode can be obtained using various methods, but in the present invention, it can be ensured by controlling the composition used in the cathode mixture (13).
As the cathode mixture (13), various cathode active materials can be used according to the type of battery, and the cathode active material used in the present invention is not particularly limited as long as it is a material capable of intercalating or deintercalating lithium ions, however, lithium transition metal oxides are generally used at present as cathode active materials capable of obtaining batteries having excellent life characteristics and charge and discharge efficiencies.
As the lithium transition metal oxide, a layered compound containing two or more transition metals, such as lithium cobalt oxide (LiCoO), may be contained2) Or lithium nickel oxide (LiNiO)2) And may be replaced, for example, by more than one transition metal; lithium manganese oxides, lithium nickel-based oxides, spinel-based lithium nickel manganese composite oxides in which some Li in the chemical formula is replaced with an alkaline earth metal, olivine-based lithium metal phosphates, etc., which are substituted with one or more transition metals, however, the lithium transition metal oxides are not limited thereto.
The lithium transition metal oxide is preferably used as the positive electrode active material, and for example, at least one selected from the group consisting of: LiCoO2、LiNiO2、LiMnO2、LiMn2O4、Li(NiaCobMnc)O2(0 < a < 1, 0 < b < 1, 0 < c < 1 and a + b + c ═ 1), LiNi1-YCoYO2、LiCo1-YMnYO2、LiNi1-YMnYO2(where 0. ltoreq. Y < 1), Li (Ni)aCobMnc)O4(0 < a < 2, 0 < b < 2, 0 < c < 2 and a + b + c ═ 2), LiMn2-zNizO4、LiMn2-zCozO4(Here, 0 < Z < 2), LixMyMn2-yO4-zAz(where 0.9. ltoreq. x. ltoreq.1.2, 0<y<2，0≤z<0.2, M is one or more of Al, Mg, Ni, Co, Fe, Cr, V, Ti, Cu, B, Ca, Zn, Zr, Nb, Mo, Sr, Sb, W, Ti and Bi, and A is one or moreAnions of the above-1 or-2 valences), Li1+aNibM'1-bO2-cA'c(0≤a≤0.1，0≤b≤0.8，0≤c<0.2, and M 'is one or more selected from the group consisting of octahedral stabilizing elements such as Mn, Co, Mg or Al and A' is one or more anions of-1 or-2 valences), LiCoPO4And LiFePO4. In addition to these oxides, sulfides, selenides, halides, and the like may also be used.
The lithium transition metal oxide can be used as a positive electrode active material in the positive electrode mixture (13) together with a binder, a conductive material, and the like. In the non-negative battery structure of the present invention, the lithium source for forming the lithium metal (23) is changed to a sacrificial salt of a lithium transition metal oxide or electrolyte. In other words, when charging is performed in a specific voltage range, lithium ions in the lithium transition metal oxide are released in the positive electrode, thereby forming lithium metal (23) on the negative electrode current collector (21).
However, in practice, with respect to lithium ions in the lithium transition metal oxide, at the above-described operating voltage level, there is no lithium capable of forming a lithium negative electrode other than the capacity obtained at the time of charge and discharge, thereby making it difficult to form lithium metal (23), and even at the time of formation, the amount is insufficient, thereby reducing the battery life characteristics. Therefore, when only the lithium transition metal oxide is used, irreversible capacity is greatly reduced, thereby causing a problem that life characteristics of the lithium secondary battery are reduced.
In view of the above, a lithium metal compound, which is a highly irreversible material having a difference between a charge capacity and a discharge capacity (irreversible capacity) of 200mAh/g or more or an initial irreversibility of 25% or more when first charged at 0.01C to 0.2C in a voltage range of 4.8V to 2.5V, is used together in the present invention as an additive capable of providing a lithium source to a lithium transition metal oxide.
The term "highly irreversible material" referred to in the present invention can be used in the same manner as "large-capacity irreversible material" in another term, and this means a material in which the irreversible capacity ratio of the first charge and discharge cycle is high, i.e., (first cycle charge capacity-first cycle discharge capacity)/first cycle charge capacity "is high. In other words, the highly irreversible material can irreversibly supply excess lithium ions during the first charge and discharge cycle. For example, among lithium transition metal compounds capable of intercalating and deintercalating lithium ions, a positive electrode material having a large irreversible capacity of the first charge and discharge cycle (first cycle charge capacity — first cycle discharge capacity) is considered.
The irreversible capacity of the cathode active material generally used is about 2% to 10% with respect to the initial charge capacity, but in the present invention, it is preferably 25% or more and more preferably 50% or more with respect to the initial charge capacity, and a lithium metal compound having an initial charge capacity of 200mAh/g or more and preferably 230mAh/g or more is used as the highly irreversible material of the present invention. The use of such a lithium metal compound can function as a lithium source capable of forming the lithium metal (23) while increasing the irreversible capacity of the lithium transition metal oxide as a positive electrode active material.
As the lithium metal compound provided in the present invention, compounds represented by the following chemical formulae 1 to 8 may be used:
[ chemical formula 1]
Li2Ni1-aM1 aO2
(in the formula, 0. ltoreq. a < 1, and M1Is at least one element selected from the group consisting of Mn, Fe, Co, Cu, Zn, Mg and Cd);
[ chemical formula 2]
Li2+bNi1-cM2 cO2+d
(in the formula, -0.5. ltoreq. b<0.5, 0. ltoreq. c.ltoreq.1, 0. ltoreq. d.ltoreq.0.3, and M2Is at least one element selected from the group consisting of P, B, C, Al, Sc, Sr, Ti, V, Zr, Mn, Fe, Co, Cu, Zn, Cr, Mg, Nb, Mo, and Cd);
[ chemical formula 3]
LiM3 eMn1-eO2
(in the formula, 0. ltoreq. e < 0.5, and M3At least one element selected from the group consisting of Cr, Al, Ni, Mn and Co);
[ chemical formula 4]
Li2M4O2
(in the formula, M4Is at least one element selected from the group consisting of Cu and Ni);
[ chemical formula 5]
Li3+fNb1-gM5 gS4-h
(in the formula, -0.1. ltoreq. f.ltoreq.1, 0. ltoreq. g.ltoreq.0.5, -0.1. ltoreq. h.ltoreq.0.5, and M5Is at least one element selected from the group consisting of Mn, Fe, Co, Cu, Zn, Mg and Cd);
[ chemical formula 6]
LiM6 iMn1-iO2
(in the formula, 0.05. ltoreq. i < 0.5, and M6Is at least one element selected from the group consisting of Cr, Al, Ni, Mn, and Co);
[ chemical formula 7]
LiM7 2jMn2-2jO4
(in the formula, j is 0.05. ltoreq. j < 0.5, and M7Is at least one element selected from the group consisting of Cr, Al, Ni, Mn, and Co); and
[ chemical formula 8]
Lik-M8 m-Nn
(in the formula, M8Represents an alkaline earth metal, k/(k + m + n) is 0.10 to 0.40, m/(k + m + n) is 0.20 to 0.50, and n/(k + m + n) is 0.20 to 0.50).
The lithium metal compounds of chemical formulas 1 to 8 are different in irreversible capacity according to the structure. These may be used alone or as a mixture, and function to increase the irreversible capacity of the positive electrode active material.
As an example, the highly irreversible materials represented by chemical formulas 1 and 3 have different irreversible capacities depending on types, and as an example, have values as listed in table 1 below.
[ TABLE 1]
Further, the lithium metal compound of chemical formula 2 may preferably belong to the space group Immm, and among this group, a Ni and M composite oxide forming a planar tetrahedral (Ni, M) O4, in which the planar tetrahedral structure forms a main chain while sharing opposite sides (sides formed of O — O), may be more preferable. The compound of chemical formula 2 may preferably have A 90, β 90 and γ 90 lattice constants.
Further, in the lithium metal compound of chemical formula 8, the content of the alkaline earth metal may be 30 atomic% to 45 atomic%, and the content of nitrogen may be 30 atomic% to 45 atomic%. At this time, when the alkaline earth metal content and the nitrogen content are within the above ranges, the compound of chemical formula 1 has excellent thermal properties and lithium ion conductive properties. In chemical formula 8, k/(k + m + n) may be 0.15 to 0.35 and, for example, 0.2 to 0.33, m/(k + m + n) may be 0.30 to 0.45 and, for example, 0.31 to 0.33, and n/(k + m + n) may be 0.30 to 0.45 and, for example, 0.31 to 0.33.
According to one embodiment, in the electrode active material of chemical formula 1, a may be 0.5 to 1, b may be 1, and c may be 1.
In the positive electrode mixture (13) according to the present invention, it is necessary to limit the respective contents of the positive electrode active material and the lithium metal compound. In other words, the parameter affected by the content of the lithium metal compound may include the thickness of the lithium metal (23) and the loading amount of the positive electrode active material, and both are in a trade-off relationship with each other.
With increasing lithium metal (23) thickness, the lifetime characteristics are generally improved. Therefore, when the content of the lithium metal compound as a lithium source is high, the advantage of increasing the thickness of the lithium metal (23) formed on the negative electrode current collector (21) can be secured, however, there is a problem that the loading amount of the positive electrode active material loaded in the entire positive electrode mixture is reduced. Such a reduced loading of the positive electrode active material may result in a reduction in the overall battery capacity. On the other hand, when the content of the lithium metal compound is low, the load of the positive electrode active material is high, but there is a disadvantage that the irreversible property cannot be sufficiently compensated. However, the lithium metal (23) can be formed relatively thinner than a commercially available lithium foil, and thinning and weight reduction of the battery can be achieved.
For this reason, in the positive electrode mixture (13) provided in the present invention, the positive electrode active material and the lithium metal compound (positive electrode active material: lithium metal compound) may be used in a weight ratio of 5:95 to 100:0, preferably 10:90 to 90:10, and more preferably 30:70 to 70:30, and even more preferably, the lithium metal compound may be advantageously used at 70% or less with respect to the total weight of the positive electrode mixture. Specifically, the positive electrode active material lithium metal compound may be preferably used in a weight ratio range of 95:5 to 30: 70. With such a content range, the positive electrode mixture of the present invention may have 1mAh/cm2～10mAh/cm2Preferably 2mAh/cm2～10mAh/cm2And more preferably 3mAh/cm2～10mAh/cm2The amount of the supported catalyst. Further, by the lithium secondary battery of the present invention using such a cathode mixture, a secondary battery in which lithium is formed on the anode current collector after the first charge can be formed.
The lithium metal compounds of chemical formulas 1 to 8 can form lithium metal on the negative electrode without reducing the battery capacity by adjusting the irreversible capacity of the positive electrode. The lithium metal compound is a material capable of deintercalating 1 mole or more of lithium ions during first-cycle charging and capable of intercalating and deintercalating 1 mole or less of lithium ions from first-cycle discharging and thereafter cycles. Therefore, when the lithium metal compound is added to the positive electrode, lithium is formed in the negative electrode as much as the irreversible capacity of the positive electrode, and thus excess lithium (excess Li) having the target capacity may be formed in the first cycle.
The cathode active material according to the present invention includes a lithium transition metal oxide and a lithium metal compound of chemical formula 1 to chemical formula 8, and the form at this time is not particularly limited as long as lithium can be irreversibly deintercalated from the lithium metal compound.
As an example, the positive electrode active material and the lithium metal compound may be dispersed in the positive electrode mixture (13) in a form of being mixed with each other or may form a core-shell structure. In the core-shell structure, the core may be a positive electrode active material or a lithium metal compound, and the shell may be a lithium metal or a positive electrode active material. Further, each of the core and the shell may be formed in a mixture form thereof, as necessary. Further, the shell may be formed as a single layer or as multiple layers of more than one layer. Preferably, when the lithium metal compound is formed in the shell, lithium ions can be easily deintercalated from the lithium metal compound by charging the battery.
In one embodiment, the lithium metal compound may be coated on the current collector while being mixed with the positive electrode active material.
In another embodiment, a first coating layer including a cathode active material is coated on the current collector, and a coating layer including a lithium metal compound may be coated on the first coating layer.
Specifically, the first coating layer is formed of a positive electrode active material and a conductive material and a binder, the second coating layer is formed of a lithium metal compound and a conductive material and a binder, and the lithium metal compound of the second coating layer may serve as a protective layer of the first coating layer by being converted into an irreversible state during activation of the secondary battery.
In other words, the second coating layer has a metal compound form in which lithium has been removed from the lithium metal compound, and is thus thermally and electrochemically stable, and thus the first coating layer can be protected by suppressing a side reaction or the like between the electrode and the electrolyte.
Such a simply mixed or core-shell structured positive electrode active material may be used according to the above content.
Further, in the positive electrode mixture (13) according to the present invention, a known material capable of increasing irreversible capacity, for example, such as Li, may be additionally usedxVO3(1≤x≤6)、Li3Fe2(PO4)3、Li3Fe2(SO4)3Or Li3V(PO4)3Of a material such as MnO2、MoO3、VO2、V2O5、V6O13、Cr3O8、CrO2、Al2O3、ZrO2、AlPO4、SiO2、TiO2Or a material of MgO.
The material is used at 60 parts by weight or less, 50 parts by weight or less, and preferably 40 parts by weight or less with respect to 100 parts by weight of the positive electrode active material.
In the present invention, the charging for forming the lithium metal (23) is performed in a voltage range of 4.8V to 2.5V. When charging is performed at a voltage level less than the above range, it is difficult to form the lithium metal (23), and when the voltage level is greater than the above range, the battery (single cell) is damaged, and charging and discharging cannot be performed properly after over-discharge occurs.
The lithium metal (23) formed as described above forms a uniform continuous layer or a discontinuous layer on the negative electrode current collector (21). As an example, when the anode current collector (21) has a foil form, a continuous film form may be obtained, and when the anode current collector (21) has a three-dimensional porous structure, the lithium metal (23) may be discontinuously formed. In other words, the discontinuous layer means a form in which a discontinuous distribution of a region having the lithium metal (23) and a region having no lithium metal (23) exists in a specific region, and since the region having no lithium metal (23) is distributed to isolate, break or separate the region having the lithium compound into an island type, the region having the lithium metal (23) is discontinuously distributed.
The lithium metal (23) formed by such charge and discharge has a minimum thickness of 50nm or more, 100 μm or less, and preferably 1 μm to 50 μm to be used as a negative electrode. When the thickness is less than the above range, the charge and discharge efficiency of the battery is rapidly reduced. In contrast, when the thickness is greater than the above range, the life characteristics and the like are stable, however, there is a problem that the energy density of the battery is lowered.
In particular, by being manufactured as a non-negative electrode battery without lithium metal at the time of assembling the battery, an oxide layer generated during the assembly due to high reactivity of lithium is not formed or hardly formed on the lithium metal (23) provided in the present invention, as compared to the conventional lithium secondary battery assembled using a lithium foil. Therefore, the life deterioration of the battery caused by the oxide layer can be prevented.
Further, the lithium metal (23) is formed of lithium ions formed by charging of a highly irreversible material or decomposition of a sacrificial salt, and this can form a more stable lithium metal (23) than the lithium metal (23) formed on the positive electrode. When lithium metal is attached to the positive electrode, a chemical reaction may occur between the positive electrode and the lithium metal.
A positive electrode mixture (13) including a positive electrode active material and a lithium metal compound is formed, and here, the positive electrode mixture (13) may further include a conductive material, a binder, and other additives generally used in lithium secondary batteries.
The conductive material serves to further improve the conductivity of the electrode active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical changes of the corresponding battery, and for example, graphite such as natural graphite or artificial graphite; carbon blacks such as super-P, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fibers or metal fibers; carbon fluoride; metal powders such as nickel powder and aluminum powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; polyphenylene derivatives, and the like.
A binder may also be included for binding the positive electrode active material, the lithium metal compound, and the conductor and for binding with the current collector. The binder may comprise a thermoplastic resin or a thermosetting resin. For example, polyethylene, polypropylene, Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic acid copolymer, etc. may be used alone or as a mixture, however, the binder is not limited thereto, and those that can be used as a binder in the art may be used.
Examples of other additives may include fillers. The filler is selectively used as a component for inhibiting the expansion of the electrode, and is not particularly limited as long as it is a fibrous material that does not cause chemical changes of the corresponding battery. For example, olefin-based polymers such as polyethylene or polypropylene; or fibrous materials such as glass fibers or carbon fibers.
The positive electrode mixture (13) may be formed on the positive electrode current collector (11).
The positive electrode current collector is generally prepared to a thickness of 3 to 500 μm. Such a positive electrode collector (11) is not particularly limited as long as it has high conductivity without causing chemical changes of the lithium secondary battery, and, for example, copper, stainless steel, aluminum, nickel, titanium, palladium, calcined carbon, copper or stainless steel whose surface is treated with carbon, nickel, silver, or the like, aluminum-cadmium alloy, or the like can be used.
At this time, in order to increase the adhesive strength with the cathode active material, the cathode current collector (11) may be used in various forms such as a film, a sheet, a foil, a mesh, a porous body, a foam, or a non-woven fabric, with fine irregularities formed on the surface.
The method of coating the positive electrode mixture (13) on the positive electrode current collector (11) may include a method of distributing an electrode mixture slurry on the current collector and uniformly dispersing the resultant using a doctor blade or the like, a die casting method, a comma coating method, a screen printing method, or the like. In addition, the electrode mixture slurry may be bonded to the current collector using a pressing or laminating method after being formed on a separate substrate, however, the method is not limited thereto.
Meanwhile, as shown in the structure of fig. 3, the lithium secondary battery according to the present invention includes a positive electrode (10), a negative electrode (20), and a separator (30) and an electrolyte (not shown) interposed therebetween, and may not include the separator (30) according to the battery type.
The separator (30) may be formed of a porous substrate, and as the porous substrate, a porous substrate generally used for electrochemical devices may be used. Examples thereof may include, but are not limited to, polyolefin-based porous films or nonwoven fabrics.
The separator (30) according to the present invention is not particularly limited in terms of material, and may be used without particular limitation as long as it is generally used as a separator (30) in a lithium secondary battery and is a material that physically separates a positive electrode and a negative electrode and has electrolyte and ion permeability. However, as the porous, non-conductive or insulating material, those having excellent electrolyte moisturizing ability while having low resistance to ion migration of the electrolyte are preferable. For example, a polyolefin-based porous film or nonwoven fabric may be used, however, the separator is not particularly limited thereto.
Examples of the polyolefin-based porous film may include using a polyolefin-based polymer alone, such as polyethylene, e.g., high-density polyethylene, linear low-density polyethylene, and ultrahigh-molecular-weight polyethylene; polypropylene, polybutylene and polypentene or a film formed of a polymer using a mixture thereof.
As the nonwoven fabric other than the above polyolefin based nonwoven fabric, there may be included, for example, a nonwoven fabric formed of a polymer using a single polyphenylene ether, polyimide, polyamide, polycarbonate, polyester such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate, polyphenylene sulfide, polyacetal, polyether sulfone, polyether ether ketone or the like or using a mixture thereof. Such nonwoven fabrics have the form of fibers forming a porous web and comprise a spunbond or meltblown form formed from long fibers.
The thickness of the separator (30) is not particularly limited, but is preferably in the range of 1 μm to 100 μm, and more preferably in the range of 5 μm to 50 μm. When the thickness of the separator (30) is less than 1 μm, mechanical properties may not be maintained, and when the thickness is greater than 100 μm, the separator (30) acts as a resistance layer, thereby reducing battery performance.
The pore diameter and porosity of the separator (30) are not particularly limited, however, the pore diameter is preferably 0.1 to 50 μm, and the porosity is preferably 10 to 95%. When the pore diameter of the separator (30) is less than 0.1 μm or the porosity is less than 10%, the separator (30) functions as a resistive layer, and when the pore diameter is greater than 50 μm or the porosity is greater than 95%, mechanical properties may not be maintained.
The lithium secondary battery according to the present invention may be subjected to lamination (stacking) and folding processes of a separator and an electrode, in addition to winding as a general process.
The shape of the lithium secondary battery is not particularly limited, and various shapes such as a cylindrical type, a laminate type, or a coin type may be used.
Meanwhile, a lithium secondary battery according to another embodiment of the present invention may have a protective film (55) on a surface of the anode current collector (51) in contact with the separator (60).
In other words, when the protective film (55) is formed, as shown in fig. 4, lithium ions transferred from the cathode mixture (43) pass through the protective film (55), and the lithium metal (23) is formed on the anode current collector (51).
Any material may be used as the protective film (55) as long as it can smoothly transfer lithium ions, and materials for a lithium ion conductive polymer and/or an inorganic solid electrolyte may be used. A lithium salt may be further included, as necessary.
Examples of the lithium ion conductive polymer may include a polymer selected from the group consisting of polyethylene oxide (PEO), Polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), LiPON, Li3N、LixLa1-xTiO3(0<x<1) And Li2S-GeS-Ga2S3Any one of the group consisting of, or two or more thereofThe above mixture, however, the lithium ion conducting polymer is not limited thereto, and a polymer having lithium ion conductivity may be used without limitation.
As for the formation of the protective film (55) using the lithium ion conductive polymer in the present invention, a coating solution obtained by dissolving or swelling the lithium ion conductive polymer in a solvent may be prepared and then coated on the anode current collector (51).
At this time, the coating method may be selected from known methods in consideration of material properties and the like, or an appropriate new method may be used. For example, it is preferable that the polymer protective film composition is distributed on the current collector and then uniformly dispersed using a doctor blade or the like. In some cases, a method of achieving distribution and dispersion in one process may also be used. In addition, dip coating, gravure coating, slot die coating, spin coating, comma coating, bar coating, reverse roll coating, screen printing, cap coating, and the like can be used. At this time, the negative electrode current collector (51) is the same as described above.
Thereafter, the protective film (55) formed on the negative electrode current collector (51) may be subjected to a drying process, and at this time, the drying process may be performed at a temperature of 80 to 120 ℃ using a heating process, hot air drying, or the like, depending on the type of solvent used for the lithium ion conductive polymer.
The solvent used herein preferably has a solubility index similar to that of the lithium ion conducting polymer and has a low boiling point. This is due to the fact that the mixing can be homogeneous and that the solvent can be easily removed afterwards. Specifically, N-dimethylacetamide (DMAc), Dimethylsulfoxide (DMSO), N-Dimethylformamide (DMF), acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), cyclohexane, water, or a mixture thereof may be used as the solvent.
In order to further increase the lithium ion conductivity when a lithium ion conductive polymer is used, a material for this purpose may be further contained.
For example, the composition may further contain a lithium salt such as LiCl, LiBr, or the like,LiI、LiClO4、LiBF4、LiB10Cl10、LiPF6、LiCF3SO3、LiCF3CO2、LiAsF6、LiSbF6、LiAlCl4、CH3SO3Li、CF3SO3Li、LiSCN、LiC(CF3SO2)3、(CF3SO2)2NLi、(FSO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium tetraphenylborate or lithium iminate.
The inorganic solid electrolyte is a ceramic-based material, and a crystalline material or an amorphous material may be used, and a material such as thio-LISICON (Li) may be used3.25Ge0.25P0.75S4)、Li2S-SiS2、LiI-Li2S-SiS2、LiI-Li2S-P2S5、LiI-Li2S-P2O5、LiI-Li3PO4-P2S5、Li2S-P2S5、Li3PS4、Li7P3S11、Li2O-B2O3、Li2O-B2O3-P2O5、Li2O-V2O5-SiO2、Li2O-B2O3、Li3PO4、Li2O-Li2WO4-B2O3、LiPON、LiBON、Li2O-SiO2、LiI、Li3N、Li5La3Ta2O12、Li7La3Zr2O12、Li6BaLa2Ta2O12、Li3PO(4-3/2w)Nw(w is w < 1) or Li3.6Si0.6P0.4O4The inorganic solid electrolyte of (1). Here, when the inorganic solid electrolyte is used, a lithium salt may be further included as necessary.
The inorganic solid electrolyte may be used in the form of a thick film by paste coating after being mixed with a known material such as a binder. Further, the thin film form may be used by a deposition process such as sputtering, as needed. The type of slurry coating used herein may be appropriately selected based on the coating method, the drying method, and the solvent as described in the lithium ion conductive polymer.
The protective film (55) comprising the above-described lithium ion-conductive polymer and/or inorganic solid electrolyte is capable of ensuring the effect of suppressing or preventing the generation of lithium dendrites generated when a lithium metal (23)/anode current collector (51) is used as an anode while easily forming the lithium metal (23) by increasing the lithium ion transfer rate.
In order to ensure the above effect, the thickness of the protective film (55) needs to be limited.
The protective film (55) having a small thickness is advantageous for the output characteristics of the battery, however, the protective film needs to be formed to a thickness or more to suppress side reactions between lithium subsequently formed on the anode current collector (51) and the electrolyte, and furthermore, dendrite growth can be effectively prevented. In the present invention, the protective film (55) preferably has a thickness of 10nm to 50 μm. When the thickness of the protective film (55) is less than the above range, side reactions between lithium and an electrolyte, which increase under overcharge or high-temperature storage conditions, may not be effectively suppressed, and thus safety may not be improved, whereas when the thickness is greater than the above range, in the case of a lithium ion conductive polymer, it takes a long time for an electrolyte solution to infiltrate or swell the protective film (55) composition, and lithium ion migration is reduced, thereby causing a concern of a decrease in overall battery performance.
In a lithium secondary battery of another embodiment of the present invention, the configuration other than the protective film (55) follows the description provided in the one embodiment.
In addition, the present invention provides a battery module including the lithium secondary battery as a unit cell.
The battery module may be used as a power source for medium to large-sized devices requiring high-temperature stability, long cycle performance, and high-capacity performance.
Examples of the middle-to large-sized device may include a power tool operated by receiving power from a battery motor; electric vehicles including Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and the like; an electric two-wheeled vehicle including an electric bicycle (e-bike) and an electric scooter (e-scooter); an electric golf cart; a system for storing power, and the like, but is not limited thereto.
[ EXAMPLES OF THE INVENTION ]
Hereinafter, preferred embodiments will be provided to illustrate the present invention, however, the following embodiments are only for illustrative purposes, and it will be apparent to those skilled in the art that various changes and modifications may be made within the scope and technical concept of the present invention and also fall within the scope of the appended claims.
Examples and comparative examples
[ example 1]
Using LiCoO in N-methyl-2-pyrrolidone2(LCO) as a positive electrode active material, a conductive material (super-P), a binder (PVdF) were mixed at a weight ratio of 95:2.5:2.5, and then L2N (Li) was added thereto in such a manner that the weight ratio to LCO was 20%2NiO2) And the resultant was mixed for 30 minutes using a paste mixer to prepare a positive electrode slurry composition.
The slurry composition prepared above was dried at 130 ℃ for 12 hours on an aluminum foil having a thickness of 20 μm as a positive electrode current collector to prepare a positive electrode having 4mAh/cm2The amount of the positive electrode.
As a negative electrode, a copper foil having a thickness of 100 μm was prepared as a negative electrode current collector.
Between the cathode and anode current collectors prepared as described above, a polyethylene separator was disposed to prepare an electrode assembly, and the electrode assembly was placed inside a case.
Subsequently, LiPF as a lithium salt was injected thereinto at a concentration of 1.0M6And 1% by weight of LiN as a sacrificial salt3(oxidation potential with respect to lithium: 3.7V) electrolyte (100. mu.l) dissolved in an organic solvent in which ethylene carbonate, diethyl carbonate and dimethyl carbonate were mixed in a volume ratio of 1:2:1 to produce a non-negative electrodeA lithium secondary battery.
[ example 2]
Except that LiN is used in preparing the electrolyte3Except that the content of (b) was changed to 5 wt%, a non-anode lithium secondary battery was manufactured in the same manner as in example 1.
[ example 3]
Except that LiN is used in preparing the electrolyte3A non-anode lithium secondary battery was manufactured in the same manner as in example 1, except that the content of (d) was changed to 10% by weight.
Comparative example 1
A non-anode lithium secondary battery was manufactured in the same manner as in example 1, except that a sacrificial salt was not used in preparing an electrolyte.
Comparative example 2
Except that LiN is used in preparing the electrolyte3Except that the content of (b) was changed to 35% by weight, a non-anode lithium secondary battery was manufactured in the same manner as in example 1.
Comparative example 3
A non-negative electrode lithium secondary battery was manufactured in the same manner as in example 1, except that 10 wt% of fluoroethylene carbonate (FEC) was used instead of the sacrificial salt in manufacturing the electrolyte.
Experimental example 1: evaluation of lithium Secondary Battery Performance
Each of the non-anode lithium secondary batteries manufactured in examples and comparative examples was charged once at CC/CV (5% current cutoff at 1C) of 0.1C and 4.25V to manufacture a lithium secondary battery formed with lithium metal.
Each of the lithium secondary batteries was charged and discharged under the conditions of 0.2C charging and 0.5C discharging using a charge and discharge measuring device (product of PNE SOLUTION ltd.), and the number of cycles when the capacity retention rate with respect to the initial discharge capacity reached 80% was measured, and the results obtained here are shown in table 2.
[ TABLE 2]
When referring to table 2, it was confirmed that the non-anode lithium secondary batteries according to the examples had excellent capacity and life characteristics compared to the non-anode lithium secondary batteries according to the comparative examples. Specifically, as shown in table 2, it was confirmed that in examples 1 to 3 in which a certain content of sacrificial salt was contained in the electrolyte, the number of cycles at a capacity retention rate of 80% with respect to the initial discharge capacity was 10 cycles or more, and the number of cycles increased as the content of sacrificial salt increased. On the other hand, in comparative example 1 containing no sacrificial salt and comparative example 3 containing a conventional electrolyte additive, the number of cycles when the capacity retention rate with respect to the initial discharge capacity was 80% was less than 10 cycles, and since the decrease in capacity rapidly proceeded, it was difficult to maintain the capacity retention rate, resulting in poor life characteristics. Further, in comparative example 2 containing an excessive amount of sacrificial salt, the sacrificial salt was not completely dissolved in the electrolyte, and the number of cycles at a capacity retention rate of 80% with respect to the initial discharge capacity could not be measured.
From these results, it was confirmed that the non-anode lithium secondary battery according to the present invention including a sacrificial salt according to the present application has an excellent capacity retention rate and thus has improved life characteristics.
[ description of reference numerals ]
10. 40: positive electrode
11. 41: positive electrode current collector
13. 43: positive electrode mixture
20. 50: negative electrode
21. 51: negative electrode current collector
23. 53: lithium metal
30. 60: diaphragm