Positive active material for lithium secondary battery and lithium secondary battery including the same
阅读说明：本技术 用于锂二次电池的正极活性材料以及包括其的锂二次电池 (Positive active material for lithium secondary battery and lithium secondary battery including the same ) 是由 卢美正 金直洙 金相墣 崔智勋 韩国炫 于 2019-04-10 设计创作，主要内容包括：用于锂二次电池的正极活性材料,包括：在具有特定式的锂金属氧化物颗粒的表面上形成的锂-铝-钛氧化物。即使在高温条件下,该正极活性材料也可以具有改善的结构稳定性。(A positive active material for a lithium secondary battery, comprising: lithium-aluminum-titanium oxide formed on the surface of lithium metal oxide particles having a specific formula. The positive active material may have improved structural stability even under high temperature conditions.)
1. A positive active material for a lithium secondary battery, comprising:
lithium metal oxide particles formed of crystals of a compound represented by the following formula 1; and
lithium-aluminum-titanium oxide formed on at least a portion of the surface of the lithium metal oxide particles:
[ formula 1]
LiαNiyMzO2-β
Wherein, in the above formula 1, M is at least one element selected from the group consisting of Co, Mn, Ti, Zr, Al and B, and α, β, y and z are in the ranges of 0.7. ltoreq. α.ltoreq.1.1, -0.1. ltoreq. β.ltoreq.0.5, 0.7. ltoreq. y.ltoreq.0.95 and 0.95< y + z. ltoreq.1.1, respectively.
2. The positive active material for a lithium secondary battery according to claim 1, wherein the lithium-aluminum-titanium oxide is represented by the following formula 2:
[ formula 2]
LiγAlvTiwOx
Wherein, in the above formula 2, γ, v, w and x are respectively in the ranges of 0.8< γ ≦ 1.2, 0< v ≦ 1, 0< w ≦ 1, 0.98 ≦ v + w ≦ 1.02 and 1.5 ≦ x ≦ 4.
3. Use according to claim 1 forA positive electrode active material for a lithium secondary battery, wherein, in the above formula 1, MzIs CoaMnbM’cM' is at least one element selected from the group consisting of Ti, Zr, Al and B, and a, B, c and y are 0.05. ltoreq. a.ltoreq.0.2, 0.03. ltoreq. b.ltoreq.0.2 and 0.95, respectively<y + a + b + c is less than or equal to 1.1.
4. The positive electrode active material for a lithium secondary battery according to claim 3, wherein, in the above formula 1, a, b and y are in the ranges of 0.8. ltoreq. y.ltoreq.0.88, 0.09. ltoreq. a.ltoreq.0.1 and 0.03. ltoreq. b.ltoreq.0.1, respectively.
5. The positive active material for a lithium secondary battery according to claim 1, further comprising Al formed on the surface of the lithium metal oxide particles2O3And LiAlO2At least one of (1).
6. The positive active material for a lithium secondary battery according to claim 1, further comprising LiTiO formed on the surface of the lithium metal oxide particles2。
7. The positive active material for a lithium secondary battery according to claim 1, further comprising a zirconium-containing oxide formed on the surface of the lithium metal oxide particles.
8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein the zirconium-containing oxide comprises AlZrO.
9. The positive active material for a lithium secondary battery according to claim 1, further comprising a boron-containing oxide formed on the surface of the lithium metal oxide particles.
10. The positive active material for a lithium secondary battery according to claim 9, wherein the boron-containing oxide comprises a boron-containing oxide selected from the group consisting of B4O10、AlBO3And Li2B4O7At least one of the group consisting of.
11. The positive active material for a lithium secondary battery according to claim 1, wherein the lithium-aluminum-titanium oxide is prepared by mixing lithium metal oxide particles with Al having a particle diameter of 30nm to 70nm, respectively, under a high temperature condition2O3And TiO2Dry-mixed and then oxidized.
12. The positive active material for a lithium secondary battery according to claim 11, wherein the positive active material is prepared by further comprising ZrO2And H3BO3At least one of (a) and (b).
13. The positive active material for a lithium secondary battery according to claim 12, wherein Al is based on the weight of the lithium metal oxide particles2O3、TiO2、ZrO2And H3BO3In amounts of 2500ppm to 3500ppm, 500ppm to 1500ppm, 300ppm to 700ppm and 300ppm to 700ppm, respectively.
14. The positive electrode active material for a lithium secondary battery according to claim 12, wherein ZrO2Has a particle diameter of 70nm to 130 nm.
15. The positive active material for a lithium secondary battery according to claim 12, wherein the lithium-aluminum-titanium oxide is formed by: reacting the lithium metal oxide particles with Al at elevated temperature2O3、TiO2And ZrO2Dry-blended and oxidized, and then further dry-blended under high temperature conditions3BO3And oxidation is carried out.
16. The positive active material for a lithium secondary battery according to claim 15, wherein Al is doped2O3、TiO2And ZrO2Mixing at 600-800 deg.C, and adding H3BO3Mixing at a temperature of 250 ℃ to 330 ℃.
17. The positive active material for a lithium secondary battery according to claim 1, wherein the lithium metal oxide particles and the lithium-aluminum-titanium oxide are formed by: under the condition of high temperature, the composite metal salt compound, the lithium salt compound and Al with the grain diameter of 30nm to 70nm respectively2O3And TiO2Dry-mixed and oxidized.
18. The positive active material for a lithium secondary battery according to claim 1, wherein at least a portion of the surface of the lithium metal oxide particles is coated with lithium-aluminum-titanium oxide.
19. A lithium secondary battery comprising:
an electrode assembly comprising a positive electrode made of the positive electrode active material for a lithium secondary battery according to any one of claims 1 to 18, a negative electrode, and a separation film disposed between the positive electrode and the negative electrode;
a case in which the electrode assembly is accommodated; and
an electrolyte in which the electrode assembly is impregnated in the case.
Technical Field
The present invention relates to a positive electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same, and particularly, to a positive electrode active material based on a lithium metal oxide and a lithium secondary battery comprising the same.
Background
The secondary battery is a battery that can be repeatedly charged and discharged. With the rapid development of the information and communication industry and the display industry, secondary batteries have been widely used as power sources for various portable telecommunication electronic devices, such as camcorders, mobile phones, laptop computers. Recently, a battery pack including a secondary battery has also been developed and applied as a power source to an environmentally friendly automobile such as a hybrid vehicle.
Examples of the secondary battery may include a lithium secondary battery, a nickel cadmium battery, and a nickel hydrogen battery. Among them, the lithium secondary battery has a high operating voltage and a high energy density per unit weight, and has advantages in terms of charging speed and light weight. In view of this, lithium secondary batteries have been actively developed and used as power sources.
For example, the lithium secondary battery may include: an electrode assembly including a positive electrode, a negative electrode, and a separation film (separator); and an electrolyte in which the electrode assembly is impregnated. The lithium secondary battery may further include a sheath, for example, in the form of a pouch, in which the electrode assembly and the electrolyte are accommodated.
In the lithium secondary battery, a lithium metal oxide is used as a positive electrode active material, and preferably has high capacity, high output, and long life characteristics. Therefore, there is a need for: chemical stability is maintained even when the lithium metal oxide is repeatedly charged and discharged.
However, when the lithium metal oxide is exposed to the atmosphere or is in contact with an electrolyte, a by-product of lithium or nickel may be generated due to a side reaction on the surface of the lithium metal oxide particles. In this case, the life span and operational stability of the lithium secondary battery may be deteriorated.
For example, korean patent laid-open publication No. 10-2017-0093085 discloses a positive electrode active material including a transition metal compound and an ion-adsorbing binder, but as described above, there is a limitation in ensuring sufficient operational stability of the positive electrode active material.
Disclosure of Invention
According to an aspect of the present invention, there is provided a positive active material for a lithium secondary battery having improved electrical and mechanical reliability and stability.
According to an aspect of the present invention, there is provided a lithium secondary battery having improved electrical and mechanical reliability and stability.
According to an exemplary embodiment, a positive active material for a lithium secondary battery includes: lithium metal oxide particles formed of crystals of a compound represented by the following formula 1; and lithium-aluminum-titanium oxide formed on at least a portion of the surface of the lithium metal oxide particle:
[ formula 1]
LiαNiyMzO2-β
(wherein, in the above formula 1, M is at least one element selected from the group consisting of Co, Mn, Ti, Zr, Al and B, and α, β, y and z are in the ranges of 0.7. ltoreq. α.ltoreq.1.1, -0.1. ltoreq. β.ltoreq.0.5, 0.7. ltoreq. y.ltoreq.0.95 and 0.95< y + z. ltoreq.1.1, respectively).
In some embodiments, the lithium-aluminum-titanium oxide may be represented by
[ formula 2]
LiγAlvTiwOx
(wherein, in the
In some embodiments, in formula 1 above, MzMay be CoaMnbM’cM' may be at least one element selected from the group consisting of Ti, Zr, Al and B, and a, B, c and y are 0.05. ltoreq. a.ltoreq.0.2, 0.03. ltoreq. b.ltoreq.0.2 and 0.95, respectively<y + a + b + c is less than or equal to 1.1.
In some embodiments, in formula 1 above, a, b, and y are in the ranges of 0.8 ≦ y ≦ 0.88, 0.09 ≦ a ≦ 0.1, and 0.03 ≦ b ≦ 0.1, respectively.
In some embodiments, the positive active material for a lithium secondary battery may further include Al formed on the surface of the lithium metal oxide particles2O3And LiAlO2At least one of (1).
In some embodiments, the positive active material for a lithium secondary battery may further include LiTiO formed on the surface of the lithium metal oxide particle2。
In some embodiments, the positive active material for a lithium secondary battery may further include a zirconium (Zr) -containing oxide formed on the surface of the lithium metal oxide particle.
In some embodiments, the zirconium-containing oxide may include AlZrO.
In some embodiments, the positive active material for a lithium secondary battery may further include a boron (B) -containing oxide formed on the surface of the lithium metal oxide particle.
In some embodiments, the boron-containing oxide may include a boron selected from the group consisting of B4O10、AlBO3And Li2B4O7At least one of the group consisting of.
In some embodiments, the lithium-aluminum-titanium oxide may be prepared by mixing lithium metal oxide particles with Al having a particle size of 30nm to 70nm, respectively, under high temperature conditions2O3And TiO2Dry-mixed and then oxidized.
In some embodiments, by further comprising ZrO2And H3BO3Is dry-mixed.
In some embodiments, Al is based on the weight of the lithium metal oxide particles2O3、TiO2、ZrO2And H3BO3In amounts of 2500ppm (parts per million) to 3500ppm, 500ppm to 1500ppm, 300ppm to 700ppm and 300ppm to 700ppm, respectively.
In some embodiments, ZrO2May have a particle size of 70nm to 130 nm.
In some embodiments, the lithium-aluminum-titanium oxide may be formed by: reacting lithium metal oxide particles with Al at elevated temperature2O3、TiO2And ZrO2Dry-blended and oxidized, and then further dry-blended under high temperature conditions3BO3And oxidation is carried out.
In some embodiments, Al may be added2O3、TiO2And ZrO2Mixing at 600-800 deg.C, and optionally adding H3BO3Mixing at a temperature of 250 ℃ to 330 ℃.
In some embodiments, the lithium metal oxide particles and lithium-aluminum-titanium oxide may be formed by: under the condition of high temperature, the composite metal salt compound, the lithium salt compound and Al with the grain diameter of 30nm to 70nm respectively2O3And TiO2Dry-mixed and oxidized.
In some embodiments, at least a portion of the surface of the lithium metal oxide particles may be coated with lithium-aluminum-titanium oxide.
According to an exemplary embodiment, a lithium secondary battery includes an electrode assembly, a positive electrode made of a positive active material for a lithium secondary battery according to the above embodiment, a negative electrode, and a separation film disposed between the positive electrode and the negative electrode; a case in which the electrode assembly is accommodated; and an electrolyte, the electrode assembly being impregnated in the dielectric in the case.
The positive active material for a lithium secondary battery according to an exemplary embodiment may include a lithium-aluminum-titanium oxide formed on the surface of lithium metal oxide particles including crystals having a specific formula. The positive electrode active material may have improved stability at a high temperature by the lithium-aluminum-titanium oxide.
The lithium-aluminum-titanium oxide may also include oxides containing aluminum, titanium, or boron. The stability of the positive active material under high temperature conditions may be improved, so that the lithium secondary battery including the above-described oxide may have an improved life span under high temperature conditions.
Lithium-aluminum-titanium oxide can be produced by reacting lithium metal oxide particles with Al at high temperature2O3、TiO2、ZrO2And/or H3BO3Mixing under dry conditions. Thereby, a lithium-aluminum-titanium oxide firmly bonded to the lithium metal oxide particles may be formed, so that the lithium secondary battery may have further improved stability and life at high temperatures.
Drawings
The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
fig. 1 is a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment;
fig. 2A is a time-of-flight secondary ion mass spectrometry (TOF-SIMS) image showing the surface of a positive electrode prepared using the positive electrode active material for a lithium secondary battery of example 7;
FIG. 2B is a diagram illustrating LiTiAl in the image of FIG. 2A+Images of compound distribution;
FIG. 2C is a graph showing contrast to LiTiAl in a region corresponding to the image of FIG. 2B+A graph of the results of the analysis of the compound content;
fig. 3A is a TOF-SIMS image showing the surface of a cathode prepared using the cathode active material for a lithium secondary battery of example 23;
FIG. 3B is a diagram illustrating LiTiAl in the image of FIG. 3A+Graph of the distribution of the CompoundsAn image;
FIG. 4 is a view showing the presence of LiTiAl on the surface of a positive electrode prepared using the positive electrode active material of comparative example 1+A graph of the results of the analysis of the compound content;
fig. 5A is a TOF-SIMS image of the surface of a cathode prepared using the cathode active material for a lithium secondary battery of comparative example 36;
FIG. 5B is a diagram illustrating LiTiAl in the image of FIG. 5A+Images of compound distribution;
FIG. 5C is a graph showing contrast to LiTiAl in a region corresponding to the image of FIG. 5B+A graph of the results of the analysis of the compound content;
fig. 6A is a Scanning Electron Microscope (SEM) image showing a cross section of the positive electrode active material for a lithium secondary battery of example 7;
fig. 6B is an SEM image showing a cross section of the positive electrode active material for a lithium secondary battery of example 7 after charge-discharge for 350 cycles at a temperature of 60 ℃;
fig. 6C is an enlarged SEM image showing the rectangular area in fig. 6B;
fig. 7A is an SEM image showing a cross section of the positive electrode active material of comparative example 1 after charge-discharge for 350 cycles at a temperature of 60 ℃;
fig. 7B is an enlarged SEM image showing the rectangular area in fig. 7A;
fig. 8A is an SEM image showing a cross section of the positive electrode active material of comparative example 36 after charge-discharge for 350 cycles at a temperature of 60 ℃; and
fig. 8B is an enlarged SEM image showing the rectangular area in fig. 8A.
Detailed Description
According to an exemplary embodiment of the present invention, there is provided a positive electrode active material for a lithium secondary battery including a lithium-aluminum-titanium oxide formed on a surface of a lithium metal oxide particle having a specific formula, thereby improving structural stability even under high temperature conditions, and a lithium secondary battery including the same.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, since the drawings of the present disclosure are only for illustrating one of preferred various embodiments of the present invention for easily understanding the technical spirit of the present invention having the above-described invention, it should not be construed as being limited to such description illustrated in the drawings.
Fig. 1 is a schematic cross-sectional view illustrating a lithium secondary battery according to an exemplary embodiment.
Referring to fig. 1, the lithium secondary battery of the present invention may include a cathode 130, an anode 140, and a separation film 150 interposed between the cathode and the anode.
The positive electrode 130 may include a positive electrode current collector 110 and a positive electrode active material layer 115 formed by coating a positive electrode active material on the positive electrode current collector 110.
According to an exemplary embodiment, the cathode active material may include lithium metal oxide particles formed of crystals of a compound represented by formula 1 below.
[ formula 1]
LiαNiyMzO2-β
In the above formula 1, M is at least one element selected from the group consisting of Co, Mn, Ti, Zr, Al and B, and α, β, y and z may be in the ranges of 0.7. ltoreq. α.ltoreq.1.1, -0.1. ltoreq. β.ltoreq.0.5, 0.7. ltoreq. y.ltoreq.0.95 and 0.95< y + z. ltoreq.1.1, respectively.
The term "excess" as used herein means to include at the maximum content or molar ratio of metals other than lithium. The term "content" or "concentration" as used herein may refer to the molar ratio of lithium metal oxide.
For example, nickel may be provided as a metal related to the capacity of a lithium secondary battery. The higher the nickel content, the better the capacity and output of the lithium secondary battery. However, if the content of nickel is excessively increased, the life of the lithium secondary battery may be reduced, and may be disadvantageous in terms of mechanical and electrical stability. For example, when the content of nickel is excessively increased, failures such as fire, short circuit, and the like may not be sufficiently suppressed when puncture caused by an external object occurs. Thus, according to an exemplary embodiment, manganese (Mn) may be distributed therewith as a whole to compensate for chemical and mechanical instability caused by nickel.
In addition, manganese (Mn) may be provided as a metal associated with mechanical and electrical stability of the lithium secondary battery. For example, manganese can suppress or reduce failures such as fire, short circuit, and the like that occur when the positive electrode is pierced by an external object. Thus, the life span of the lithium secondary battery can be increased. In addition, cobalt (Co) may be a metal related to the conductivity or resistance of the lithium secondary battery.
If the lower limit of the nickel concentration is less than about 0.7, the capacity and output of the lithium secondary battery may be excessively reduced. If the upper limit of the nickel concentration exceeds about 0.95, it may result in shortened lifetime and increased mechanical instability.
According to some embodiments, in formula 1 above, MzMay be CoaMnbM’cM' may be at least one element selected from the group consisting of Ti, Zr, Al and B, and a, B, c and y may be respectively 0.05. ltoreq. a.ltoreq.0.2, 0.03. ltoreq. b.ltoreq.0.2 and 0.95<y + a + b + c is less than or equal to 1.1. Therefore, the compound represented by formula 1 is an NCM active material having nickel, cobalt, and manganese as main components, and may exhibit balanced characteristics in terms of output, capacity, life, and stability.
Preferably, in the above formula 1, a, b and y may be controlled within the ranges of 0.8. ltoreq. y.ltoreq.0.88, 0.09. ltoreq. a.ltoreq.0.1 and 0.03. ltoreq. b.ltoreq.0.1, respectively. Therefore, the compound represented by formula 1 may be an NCM compound having a Ni molar ratio of 80% or more while exhibiting high density energy characteristics.
In some embodiments, the lithium metal oxide particles may have a single particle structure. The single grain structure may include a single crystal structure.
In some embodiments, the lithium metal oxide particles may have a secondary particle structure formed by agglomeration of primary particles (e.g., crystals of the compound represented by formula 1). Average particle diameter (D) of lithium metal oxide particles50) Can be about 6 μm to about 25 μm, preferably about 10 μm to 16 μm.
For example, lithium nickel oxide exposed to the surface of lithium metal oxide particles may react with air or moisture and then decompose into lithium hydroxide, lithium carbonate, nickel oxide, and the like, thereby generating byproducts. In addition, nickel ions exposed to the surface of the lithium metal oxide particles may react with the electrolyte, thereby causing phase change and crystal structure deformation in the surface layer of the particles.
In an exemplary embodiment, the lithium metal oxide particles may include lithium-aluminum-titanium oxide on at least a portion of the surface thereof.
In an exemplary embodiment, the lithium-aluminum-titanium oxide may form an oxide coating layer coating at least a portion of the surface of the lithium metal oxide particle. The oxide coating layer may include a structure in which lithium-aluminum-titanium oxide continuously covers at least a portion of the surface of the lithium metal oxide, or a structure in which lithium-aluminum-titanium oxide exists separately from each other as a plurality of islands.
The lithium-aluminum-titanium oxide may include, for example, oxides of Al, Ti, Zr, or B and alloys thereof. These oxides may be used alone, or two or more kinds thereof may be used in combination.
The lithium-metal oxide particles are passivated by lithium-aluminum-titanium oxide, so that puncture stability and life can be further improved, and structural stability of the particles can be ensured.
In some embodiments, an element, an alloy, or an oxide of the above-described lithium-aluminum-titanium oxide may be intercalated as a dopant in the lithium metal oxide particles.
In an exemplary embodiment, the lithium-aluminum-titanium oxide may be formed as a separate layer with respect to the surface of the lithium metal oxide particle as a boundary, and may be formed by penetrating the surface of the lithium metal oxide particle to a predetermined depth. For example, the oxide coating may have a thickness of 90nm to 200nm and a penetration depth of 90nm to 200 nm.
Generally, Al, Ti, and Zr are similar to transition metals of Ni, Co, and Mn in terms of ionic radius, and have an oxidation number of +3 or +4, which is similar to that of the transition metals. Therefore, these metals can be easily doped into vacancies of transition metals in the structure.
Al exists as an oxide or a lithium composite oxide on the surface of the lithium metal oxide particle to prevent the surface structure of the positive electrode active material from collapsing due to a side reaction with the electrolyte during the electrochemical reaction, and a portion thereof may react with the electrolyte to form another stable surface layer (e.g., AlF)3). Therefore, Al can be effectively used as a material for a coating layer on the particle surface and as a doping layer.
Ti and Zr are materials having an oxidation number of +4, and can be obtained by substituting Mn in a lithium metal oxide having a high Ni content4+The oxidation number is balanced so that the oxidation number of Ni can be kept at + 2. Therefore, Ni can be increased2+Resulting in an increase in battery capacity. In addition, Ti can suppress the occupation of Li by Ti+Ni of site2+The resulting output decreases. In addition, since Zr has a strong binding force with oxygen, it is possible to prevent structural changes caused by oxygen desorption during electrochemical reactions at room temperature and high temperature, thereby improving life stability of the positive electrode active material.
In addition, the oxide containing Ti has excellent conductivity. Therefore, when the surface of the lithium metal oxide particle is coated with an oxide containing Ti, an increase in resistance due to the coating can be minimized, thereby suppressing a decrease in output characteristics.
In the present invention, the lithium-aluminum-titanium oxide may refer to an oxide containing lithium, aluminum, and titanium as metal elements, and to an oxide in which the sum of the number of moles of aluminum and the number of moles of titanium is substantially the same as the number of moles of lithium. In addition, oxygen contained in the oxide may have a mole number that compensates for the oxidation number of the metal element. According to some embodiments, the lithium-aluminum-titanium oxide may be a material consisting of lithium, aluminum, titanium, and oxygen.
The lithium-aluminum-titanium oxide containing aluminum and titanium may enhance structural stability of the lithium metal oxide particles and improve output characteristics and capacity characteristics. Therefore, the structural stability of the lithium metal oxide particles as well as the output characteristics and capacity characteristics can be maintained even when stored or operated under high temperature conditions.
In some embodiments, the lithium-aluminum-titanium oxide may be represented by
[ formula 2]
LiγAlvTiwOx
In the
According to an exemplary embodiment, in the
In exemplary embodiments, the lithium metal oxide particles may further include at least one of an aluminum (Al) containing oxide and a titanium (Ti) containing oxide on the surface thereof. For example, the aluminum-containing oxide may include Al2O3And LiAlO2And the titanium-containing oxide may include LiTiO2. When at least one of an aluminum-containing oxide and a titanium-containing oxide is formed on the lithium metal oxide, the surface structure stability of the lithium metal oxide and the output characteristics and capacity characteristics can be simultaneously improved.
In some embodiments, the lithium metal oxide particles may also include a zirconium (Zr) containing oxide on the surface thereof. For example, the zirconium-containing oxide may include AlZrO. When the zirconium-containing oxide is formed on the positive electrode active material, the structural stability of the positive electrode active material can be improved.
According to some embodiments, the lithium metal oxide particles may further comprise a boron-containing (B) oxide on the surface thereof. For example, the boron-containing oxide may include B4O10、AlBO3Or Li2B4O7. The boron-containing oxide may be filled in the concave-convex portion formed on the surface of the lithium metal oxide particle, and the lithium metal oxide particleMay be at least partially smooth. Accordingly, the surface area of the lithium metal oxide particles may be slightly reduced, thereby reducing side reactions between the lithium metal oxide and the electrolyte when the battery is operated.
Hereinafter, a method of manufacturing the positive electrode active material according to the above-described embodiment of the present invention will be provided.
According to an exemplary embodiment, a metal salt of an active material may be prepared. The metal salts of the active material may include nickel salts, manganese salts, and cobalt salts. Examples of the nickel salt may include nickel sulfate, nickel hydroxide, nickel nitrate, nickel acetate, hydrates thereof, and the like. Examples of the manganese salt may include manganese sulfate, manganese acetate, hydrates thereof, and the like. Examples of the cobalt salt may include cobalt sulfate, cobalt nitrate, cobalt carbonate, hydrates thereof, and the like.
The metal salt may be mixed with a precipitant and/or a chelating agent in a ratio satisfying the content of each metal or the concentration ratio described with reference to formula 1 to prepare an aqueous solution. The aqueous solution may be co-precipitated in a reactor to produce a composite metal salt compound (e.g., NCM precursor).
The precipitating agent may include an alkaline compound, such as sodium hydroxide (NaOH), sodium carbonate (Na)2CO3) And the like. The chelating agent may include, for example, ammonia (e.g., NH)3H2O), ammonium carbonate (e.g. NH)3HCO3) And the like.
Thereafter, the lithium salt compound may be mixed with the composite metal salt compound and reacted by coprecipitation to prepare lithium metal oxide particles. The lithium salt compound may include, for example, lithium carbonate, lithium nitrate, lithium acetate, lithium oxide, lithium hydroxide, and the like. These compounds may be used alone, or two or more thereof may be used in combination.
For example, Al having a particle size of about 30nm to 70nm may be used2O3And TiO2Al and Ti surface treatments were performed on the lithium metal oxide particles. When Al is present2O3And TiO2When the particle diameter of (b) is within the above range, the lithium-aluminum-titanium oxide can be more densely formed, thereby improving the protective property for the internal structure of the cathode active material. In the comparative example, ifAl2O3And TiO2If the particle diameter of (b) is outside the above range, lithium-aluminum-titanium oxide may not be formed.
In terms of uniformity of surface treatment, Al having particle diameters similar to each other is used2O3And TiO2May be advantageous. By the surface treatment of Al and Ti, lithium-aluminum-titanium oxide can be uniformly formed on the surface of the lithium metal oxide particle.
In addition, in some embodiments, ZrO having a particle size of about 70nm to 130nm in the surface treatment2May be used together with Al and Ti. Therefore, the lithium-aluminum-titanium oxide is formed together with at least one of Zr and a Zr-containing oxide (e.g., AlZrO), so that the strength of the oxide coating can be improved.
Al can be added by high-speed rotating equipment2O3、TiO2And ZrO2Coated on the surface of the active material and then subjected to high temperature heat treatment to form an oxide coating or achieve doping.
In some embodiments, the heat treatment may be performed at a temperature of about 600 ℃ to 800 ℃.
According to some embodiments, LiOH and Li remaining in an oxide coating layer formed on a lithium metal oxide or in a surface thereof2CO3Can be removed by washing with aqueous or organic solvents. In this case, a region where a side reaction may occur when operating the battery may be increased, and additional coating may be performed using boron to suppress the side reaction.
E.g. H3BO3Can be dry mixed with the lithium metal oxide particles at an elevated temperature and oxidized to form a boron-containing oxide on the surface of the lithium metal oxide particles. For example, dry blending may be carried out at an elevated temperature of 250 ℃ to 330 ℃. The boron-containing oxide may at least partially cover the lithium metal oxide particles, and the boron-containing oxide may be integrated with the lithium-aluminum-titanium oxide to form an oxide coating. For example, the boron-containing oxide may be present in a doped form within the lithium-aluminum-titanium oxide coating.
In some embodiments, the lithium-aluminum-titanium oxide may use only Al2O3And TiO2Form, and preferably, ZrO may be2Or H3BO3Used therewith to form an oxide on the surface of the lithium metal oxide particles.
In some embodiments, Al2O3、TiO2、ZrO2And H3BO3The oxide may be formed by a thermal dry mixing process. In some embodiments, Al is formed from Al by a first hot dry mixing process2O3、TiO2And ZrO2After forming the first oxide, H3BO3The second oxide is formed by a second hot dry mixing process. The first oxide and the second oxide may be provided as separate layers (a first oxide coating and a second oxide coating), and the second oxide coating may penetrate into the first oxide coating to be integrated therewith, so that it may be provided as one layer.
According to an exemplary embodiment, Al is based on the weight of the lithium metal oxide particles2O3、TiO2、ZrO2And H3BO3May be used in amounts of 2500ppm to 3500ppm, 500ppm to 1500ppm, 300ppm to 700ppm and 300ppm to 700ppm, respectively. If the amount is less than the above range, the oxide is not properly formed. When the amount thereof exceeds the above range, the oxide may be formed too thick, thereby degrading the electrical characteristics of the positive electrode active material.
When Al is used2O3、TiO2、ZrO2And H3BO3When all of them are formed into an oxide, it is possible to form a lithium-aluminum-titanium oxide more efficiently, and thus to improve the structural stability (particularly at high temperatures) and the life of the positive electrode active material.
According to some embodiments, the lithium metal oxide particles and oxides may be prepared by combining a metal salt compound, a lithium salt compound, Al under high temperature conditions2O3And TiO2Dry blended and oxidized. In addition, ZrO2Or H3BO3May be simultaneously reacted with Al2O3And TiO2Are mixed together.
By compounding a metal salt compound, a lithium salt compound and Al under high temperature conditions2O3And TiO2Dry blending and oxidation, the two-step process for preparing lithium metal oxide particles and then forming the oxide can be integrated into a one-step process, so that economic advantages and efficiency can be improved.
The slurry may be prepared by mixing and stirring the positive electrode active material with the binder, the conductive material, and/or the dispersant in the solvent. The slurry may be coated on the positive electrode current collector 110, and then compressed and dried to manufacture the positive electrode 130.
The positive current collector 110 may include, for example, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably includes aluminum or an aluminum alloy.
The binder may be selected, for example, from organic binders such as vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, and the like; or an aqueous binder such as styrene-butadiene rubber (SBR), and may be used with a thickener such as carboxymethylcellulose (CMC).
For example, PVDF-based binders can be used as the positive electrode-forming binders. In this case, the amount of the binder used to form the positive electrode active material layer may be reduced, and the amount of the positive electrode active material may be relatively increased, thereby improving the output and capacity of the secondary battery.
A conductive material may be included to facilitate electron transfer between active material particles. For example, the conductive material may include: carbon-based conductive materials, e.g. graphite, carbon black, graphene or carbon nanotubes, and/or metal-based conductive materials, e.g. tin, tin oxide, titanium oxide or materials such as LaSrCoO3And LaSrMnO3The perovskite material of (a).
According to an exemplary embodiment, the anode 140 may include an anode current collector 120 and an anode active material layer 125 formed by coating the anode current collector 120 with an anode active material.
The anode active material that can be used in the present invention is not particularly limited, and may include any material known in the related art as long as it can absorb and desorb lithium ions. For example, it is possible to use: carbon-based materials such as crystalline carbon, amorphous carbon, carbon composite, carbon fiber, and the like; a lithium alloy; silicon or tin. Examples of the amorphous carbon may include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500 ℃ or less, mesophase pitch-based carbon fibers (MPCF), and the like. The crystalline carbon may include graphite-based carbons such as natural graphite, graphite coke, graphite MCMB, graphite MPCF, and the like. Other elements included in the lithium alloy may include: such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, indium, and the like.
The anode current collector 120 may include, for example, gold, stainless steel, nickel, aluminum, titanium, copper, or an alloy thereof, and preferably includes copper or a copper alloy.
In some embodiments, the slurry may be prepared by mixing and stirring the negative active material with the binder, the conductive material, and/or the dispersant in the solvent. The slurry may be coated on the anode current collector 120, and then compressed and dried to manufacture the anode 140.
As the binder and the conductive material, substantially the same or similar materials as those described above can be used. In some embodiments, the binder used to form the negative electrode may include, for example, an aqueous binder such as styrene-butadiene rubber (SBR) to conform to the carbon-based active material, and may be used with a thickener such as carboxymethyl cellulose (CMC).
The separation film 150 may be interposed between the positive electrode 130 and the negative electrode 140. The separation membrane 150 may include a porous polymer membrane made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene/butene copolymer, ethylene/hexene copolymer, ethylene/methacrylate copolymer. The separation film may include a non-woven fabric made of glass fiber having a high melting point, polyethylene terephthalate, or the like.
In some embodiments, the area and/or volume of the negative electrode 140 (e.g., the contact area with the separator 150) may be greater than the area and/or volume of the positive electrode 130. Thus, for example, lithium ions generated from the cathode 130 can smoothly move to the anode 140 without being precipitated in the middle. Therefore, the effect of improving both output and stability by using the above-described cathode active material can be more easily achieved.
According to an exemplary embodiment, the electrode unit 160 is defined by the positive electrode 130, the negative electrode 140, and the separation film 150, and a plurality of electrode units 160 are stacked to form, for example, a jelly-roll type electrode assembly. For example, the electrode assembly may be formed by winding, laminating, folding, or the like of the separation film.
The electrode assembly is accommodated in the outer case 170 together with an electrolyte, so that a lithium secondary battery may be defined. According to an exemplary embodiment, a non-aqueous electrolyte may be used as the electrolyte.
The non-aqueous electrolyte includes a lithium salt and an organic solvent as an electrolyte. Lithium salts, e.g. made of Li+X-Represents, and may include 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-、(CF3CF2SO2)2N-Etc. as examples.
Examples of the organic solvent may use any one of Propylene Carbonate (PC), Ethylene Carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), methylpropyl carbonate, dipropyl carbonate, dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, vinylene carbonate, sulfolane (sulfolane), γ -butyrolactone, propylene sulfite, and tetrahydrofuran, or a mixture of two or more thereof. These compounds may be used alone, or two or more thereof may be used in combination.
The electrode tabs may be respectively formed of the positive and negative current collectors 110 and 120 belonging to each electrode unit, and may extend to one side of the case 170. The electrode tabs may be fused together with one side of the outer casing 170 to form electrode leads that extend to or are exposed outside of the outer casing 170.
The lithium secondary battery may be manufactured, for example: cylindrical, square, bag-shaped or button-shaped cans are used.
Hereinafter, preferred embodiments are presented to more specifically describe the present invention. However, the following examples are only illustrative of the present invention and will be apparent to those skilled in the art: various changes and modifications may be made within the scope and spirit of the present invention. Such changes and modifications are properly included in the appended claims.
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