阅读说明：本技术 一种锂电池及其制备方法 (Lithium battery and preparation method thereof ) 是由 阳晓霞 冯辉 段征 于 2019-09-29 设计创作，主要内容包括：本发明公开锂电池,包括正极(1)、复合型负极(2),正极(1)包括形成在正极集流体(6)上的正极涂层(7)；复合型负极(2)包括形成在负极集流体(10)上的碳多孔电极层(8)、金属锂平板电极层(9)；碳多孔电极层(8)与正极涂层(7)的可逆脱嵌锂的容量比值范围为0.1～0.9,金属锂平板电极层(9)是在电池化成激活阶段采用双向脉冲循环充电方式在碳多孔电极层(8)表面电沉积一层致密金属锂形成。本发明公开锂电池制备方法,在电池激活阶段采用双向脉冲循环充电方式,在负极的碳多孔电极层上沉积一层致密的金属锂层,从而获得复合型负极。本发明锂电池兼具了更高比能量、可大倍率放电、长循环特性和优异的存储性能。(The invention discloses a lithium battery, which comprises an anode (1) and a composite cathode (2), wherein the anode (1) comprises an anode coating (7) formed on an anode current collector (6); the composite negative electrode (2) comprises a carbon porous electrode layer (8) and a metal lithium flat electrode layer (9) which are formed on a negative electrode current collector (10); the ratio of the reversible lithium-releasing capacity to the lithium-releasing capacity of the carbon porous electrode layer (8) and the positive electrode coating (7) is 0.1-0.9, and the metal lithium flat electrode layer (9) is formed by electrodepositing a layer of compact metal lithium on the surface of the carbon porous electrode layer (8) in a bidirectional pulse cyclic charging mode in the activation stage of battery formation. The invention discloses a preparation method of a lithium battery, which adopts a bidirectional pulse cycle charging mode at the activation stage of the battery, and a compact metal lithium layer is deposited on a carbon porous electrode layer of a negative electrode, so that a composite negative electrode is obtained. The lithium battery has the advantages of higher specific energy, capability of discharging at a large rate, long cycle characteristic and excellent storage performance.)

1. A lithium battery is characterized by comprising a positive electrode (1) and a composite negative electrode (2), wherein the positive electrode (1) comprises a positive electrode coating (7) formed on a positive electrode current collector (6); the composite negative electrode (2) comprises a carbon porous electrode layer (8) which is formed on a negative electrode current collector (10) and can reversibly release and insert lithium, and a metal lithium flat electrode layer (9); the ratio of the reversible lithium-releasing capacity of the porous carbon electrode layer (8) to the reversible lithium-releasing capacity of the anode coating (7) is 0.1-0.9, and the metal lithium flat electrode layer (9) is formed by releasing lithium in an anode active material in a bidirectional pulse cycle charging mode at the battery formation activation stage, firstly inserting the lithium into a carbon layer in the composite cathode (2), and then depositing a compact lithium layer on the surface of the lithium-releasing porous carbon electrode.

2. The lithium battery according to claim 1, wherein the ratio of the capacity of reversibly deintercalating lithium of the carbon porous electrode layer (8) to the positive electrode coating (7) is in the range of 0.5 to 0.66.

3. The lithium battery according to claim 1, wherein the carbon porous electrode layer (8) is formed by uniformly mixing an active material carbon, a conductive agent and a binder in a solvent and then coating both sides of the negative electrode current collector (10).

4. A lithium battery as claimed in claim 1, characterized in that the carbon of the reversibly deintercalated lithium in the carbon porous electrode layer (8) comprises one or more of natural graphite, artificial graphite, hard carbon, soft carbon, etc.

5. The lithium battery of claim 1, wherein the carbon porous electrode layer has a thickness of 50 μm to 150 μm.

6. A lithium battery according to claim 1, characterized in that the positive electrode active material forming the positive electrode coating (7) is composed of one or more lithium-containing metal composite oxides; the metal element in the lithium-containing metal oxide comprises one or more of nickel Ni, cobalt Co, manganese Mn, aluminum Al, magnesium Mn, zirconium Zr and the like.

7. A method for preparing a lithium battery, which is used for preparing the battery as claimed in any one of claims 1 to 6, characterized in that in the activation stage of battery formation, pulse charging and pulse discharging are alternately and cyclically used for charging until a set charging termination voltage or constant voltage charging current is reached, so that a layer of compact metal lithium is electrodeposited on the surface of the carbon porous electrode layer (8) to form a metal lithium flat electrode layer (9); wherein the charging pulse width is greater than the discharging pulse width.

8. The method for preparing a lithium battery according to claim 7, wherein the pulse width for pulse charging is 0.1 to 5 seconds, and the pulse width for pulse discharging is 0.01 to 1 second.

9. The method for manufacturing a lithium battery as claimed in claim 7, wherein the end-of-charge voltage is 3.9V to 4.35V.

10. The method of manufacturing a lithium battery as claimed in claim 7, wherein the pulsed charging and discharging regime includes constant current charging and discharging, constant power charging and discharging; the current density ranges of constant current charging and constant current discharging are 0.1mA/cm ²～10mA/cm ²(ii) a The power density of constant power charging and constant power discharging is 0.3mW/cm ²～30mW/cm ²。

Technical Field

The invention relates to the technical field of lithium batteries, in particular to a lithium battery and a preparation method thereof.

Background

The lithium ion battery has high self-discharge rate, namely, the electric energy difference of stored charge, and the typical monthly capacity loss is 3 to 5 percent. Compared with a lithium ion battery, the monthly capacity loss of the traditional lithium primary battery is generally not more than 0.5%, but the rate performance of the lithium primary battery is poorer than that of the lithium ion battery, even if the lithium primary battery is a power type lithium primary battery, the discharge rate of the lithium primary battery does not exceed 1 hour rate, and the working voltage platform of the lithium primary battery is low, so that the output power is low, and the defects limit many applications of the traditional lithium primary battery.

The key difference between lithium ion batteries and lithium primary batteries is the negative electrode. The lithium ion battery cathode is a porous carbon electrode, and the lithium primary battery cathode is a flat lithium metal electrode. The porous electrode has a much larger reaction area than a flat electrode, and the concentration polarization is small, so that the electrochemical reaction is facilitated, and the rate performance of the porous carbon electrode is obviously superior to that of a metal lithium electrode. However, the porous electrode has many side reaction interfaces, and particularly, when the negative electrode is in a fully charged state, the lithium-embedded carbon has extremely high activity, and can react with an electrolyte to form a Solid Electrolyte Interface (SEI) film, but the SEI film has large area and poor stability, so that the storage performance of the lithium ion battery is poor.

The lithium metal has high activity, but a thin and compact passive film can be easily formed in air and electrolyte, and the chemical and electrochemical stability of the passive film can be kept. At present, some technologies can transfer lithium ions in a positive electrode to a negative copper foil in a battery formation stage in a constant-current charging mode, and a layer of metal lithium is formed through electrodeposition, but the metal lithium layer has poor compactness, high charging capacity loss and incapability of being cycled for many times, otherwise lithium dendrites are easily formed, so that capacity attenuation is fast, and even potential safety hazards exist.

Disclosure of Invention

The invention aims to provide a lithium battery and a preparation method thereof, which solve the technical problems that the storage performance of the conventional lithium battery is poor and the primary lithium battery cannot discharge at a large multiplying power, solve the problem that lithium dendrite is easy to generate during the deposition of metal lithium by adopting a composite negative electrode design and considering the high multiplying power performance and adopting a special charging mode of bidirectional pulse cycle charging, and can realize long cycle life.

The invention provides a lithium battery which comprises a positive electrode (1), a composite negative electrode (2), a diaphragm (3), a non-aqueous electrolyte (4) and a shell (5).

The positive electrode (1) consists of a positive electrode current collector (6) and a positive electrode coating (7), the positive electrode coating (7) consists of an active substance, a conductive agent and a binder, the positive electrode current collector is an aluminum foil, and the thickness of the aluminum foil is 8-30 microns.

The active material is composed of one or more lithium-containing metal composite oxides; the metal element in the lithium-containing metal oxide comprises one or more of nickel Ni, cobalt Co, manganese Mn, aluminum Al, magnesium Mn, zirconium Zr and the like.

The conductive agent comprises at least one of carbon black, Ketjen black, activated carbon, carbon nanotube CNTs, carbon fiber VGCF, Graphene and graphite conductive agent.

The binder comprises one or more of styrene butadiene latex (SBR), sodium carboxymethylcellulose (CMC), Polyacrylate (PAA), modified polyacrylate, polyacrylonitrile, polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride and Polytetrafluoroethylene (PTFE).

The total thickness of the positive electrode is 70-300 μm, and the total thickness is preferably 70-150 μm.

The composite negative electrode (2) consists of a carbon porous electrode layer (8) capable of reversibly releasing and inserting lithium, a metal lithium flat electrode layer (9) and a negative current collector (10); the ratio of the reversible lithium-intercalated capacity of the carbon porous electrode layer (8) to the reversible lithium-intercalated capacity of the anode coating (7) is 0.1-0.9, and the ratio is preferably 0.5-0.66; the negative current collector is a copper foil, and the thickness of the copper foil is 6-30 mu m.

The carbon porous electrode layer (8) is composed of carbon, a conductive agent and a binder, wherein the carbon comprises natural graphite, artificial graphite, hard carbon, soft carbon and the like; the conductive additive comprises at least one of carbon black, Ketjen black, activated carbon, carbon nanotube CNTs, carbon fiber VGCF, Graphene and graphite conductive agent; the binder comprises one or more of styrene butadiene latex (SBR), sodium carboxymethylcellulose (CMC), Polyacrylate (PAA), modified polyacrylate, polyacrylonitrile, polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride and Polytetrafluoroethylene (PTFE); the thickness of the carbon porous electrode layer is 50 to 150 μm, and the preferable thickness is 50 to 80 μm.

The lithium metal flat electrode (9) is formed by electrodeposition on the surface of the carbon porous electrode in a bidirectional pulse cyclic charging mode at the activation stage of the battery.

The matrix material of the diaphragm (3) comprises various organic films which can be used for lithium batteries, such as Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), Polyimide (PI), and the like; the structure form of the ceramic coating comprises a substrate single-surface ceramic coating layer and a substrate double-surface ceramic coating layer, wherein the substrate single-surface ceramic coating layer and an organic binder are mixed and coated, the substrate double-surface ceramic coating layer and an organic binder are mixed and coated, the substrate surface is sequentially coated with the ceramic coating layer and the organic binder coating layer, and the like, but the ceramic coating is not limited to the substrate single-surface ceramic coating layer and; the total thickness of the diaphragm ranges from 8 mu m to 50 mu m, and the preferred total thickness ranges from 12 mu m to 20 mu m.

The nonaqueous electrolyte (4) is composed of a lithium salt, a solvent and an additive.

The kind of the lithium salt includes lithium hexafluorophosphate LiPF ₆Lithium tetrafluoroborate (LiBF) ₄Lithium perchlorate LiClO ₄Lithium oxalyldifluoroborate LiODFB, lithium bis (trifluoromethylsulfonyl) imide LiTFSI, and lithium difluorophosphate LiPF ₂O ₂One or more of the following; the molar concentration of lithium salt in the electrolyte is 0.8-2.0 mol/L.

The types of the solvent comprise two or more of propylene carbonate PC, ethylene carbonate EC, methyl ethyl carbonate EMC, diethyl carbonate DEC, dimethyl carbonate DMC, ethyl acetate EA, ethyl propionate EP, ethyl butyrate EB, propyl propionate PP and the like;

the additives include fluoroethylene carbonate FEC, propylene sulfite PS, 1, 3-propane sultone PST, ethylene sulfate DTD, methylene methanedisulfonate MMDS, 1, 2-vinylene carbonate VC, ethylene carbonate VEC, fluorobenzene FB, biphenyl BP, cyclohexylbenzene CHB, adiponitrile AND, succinonitrile SN, phosphazene flame retardant additives AND the like, but are not limited thereto.

The shell 5 comprises various materials such as stainless steel, aluminum alloy, aluminum-plastic composite films and the like.

The structural form of the lithium battery comprises a cylinder, a square, an airfoil shape, a special shape and the like.

The preparation method of the lithium battery comprises the following main steps:

the first step is as follows: preparing a positive electrode: one or more lithium-containing metal composite oxides, a conductive agent and a binder are fully mixed according to a certain proportion and then coated on a positive current collector, and then the positive electrode is prepared by the working procedures of rolling, cutting, drying, tab welding and the like;

the second step is that: preparing a carbon porous electrode, namely fully mixing one or more carbon materials, a conductive agent and a binder according to a certain proportion, coating the mixture on a negative current collector, and then performing the working procedures of rolling, cutting, drying, lug welding and the like to prepare the carbon porous electrode;

the third step: preparing a pole group: winding or stacking the positive electrode, the carbon porous electrode and the diaphragm according to structural design requirements in a winding or laminating mode to obtain a battery pole group;

the fourth step: assembling the battery: putting the electrode assembly into a shell, drying, injecting liquid and sealing;

the fifth step: standing the battery: the electrolyte fully infiltrates the electrode and the diaphragm;

and a sixth step: and (3) battery activation: performing bidirectional pulse cyclic charging to obtain a composite cathode;

the seventh step: aging the battery;

eighth step: and (4) screening the batteries.

In the sixth step, the bidirectional pulse cyclic charging is to perform charging by adopting pulse charging and pulse discharging in an alternating cyclic manner until a set charging termination voltage or constant voltage charging current is reached, wherein the pulse width (time) is greater than the discharging pulse width (time); the pulse width (time) of pulse charging is 0.1-5 seconds, and the pulse width (time) of pulse discharging is 0.01-1 second; the charge termination voltage is 3.9V to 4.35V, preferably 4.0V to 4.1V.

The charging and discharging can be in various forms including constant current, constant power and the like; the current densities of the constant current charging and the constant current discharging can be the same or different, and the current density range is 0.1mA/cm ²～10mA/cm ²(ii) a The power densities of the constant power charging and the constant power discharging can be the same or different, and the power density range is 0.3mW/cm ²～30mW/cm ²。

According to the technical scheme, the lithium battery provided by the invention adopts the special design that the reversible lithium intercalation capacity of a carbon material in the negative electrode is lower than the reversible lithium deintercalation capacity of an active substance in the positive electrode, adopts a bidirectional pulse cycle charging mode in a formation activation stage, and deposits a compact metal lithium layer on a carbon porous electrode layer of the negative electrode so as to obtain a composite negative electrode, so that the specific energy of the battery is improved, and the storage and rate capability are considered; meanwhile, the problem that lithium dendrite is easily generated during charging is solved by a bidirectional pulse cyclic charging formation mode, and long cycle life can be realized.

Drawings

Fig. 1 is a schematic structural diagram of a lithium battery provided by the present invention;

FIG. 2 is a flow chart of a method for preparing a lithium battery according to the present invention;

FIG. 3 is a graph showing a comparison of cycle trends of a cylindrical battery;

fig. 4 is a graph comparing the cycling profiles of flexible packaged batteries.

Detailed Description

In order that those skilled in the art will better understand the technical solution of the present invention, the following detailed description of the present invention is provided in conjunction with the accompanying drawings and embodiments.

Referring to fig. 1, the lithium battery provided by the invention comprises a positive electrode (1), a composite negative electrode (2), a diaphragm (3), a non-aqueous electrolyte (4) and a shell (5).

Specifically, the positive electrode (1) is composed of a positive electrode current collector (6) and a positive electrode coating (7), wherein the positive electrode coating (7) is formed by mixing a positive electrode active substance, a conductive agent and a binder according to a certain proportion, is uniformly mixed in a solvent, is coated on two sides of the positive electrode current collector (6), and meets a set surface density value. And rolling the positive coating layer to reduce the porosity, wherein the total thickness of the rolled positive coating layer is 70-300 mu m, and the preferred total thickness is 70-150 mu m.

The positive active material is composed of one or more lithium-containing metal composite oxides; the metal element in the lithium-containing metal oxide comprises one or more of nickel Ni, cobalt Co, manganese Mn, aluminum Al, magnesium Mn, zirconium Zr and the like.

The conductive agent comprises at least one of carbon black, Ketjen black, activated carbon, carbon nanotube CNTs, carbon fiber VGCF, Graphene and graphite conductive agent.

The binder comprises one or more of styrene butadiene latex (SBR), sodium carboxymethylcellulose (CMC), Polyacrylate (PAA), modified polyacrylate, polyacrylonitrile, polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride and Polytetrafluoroethylene (PTFE).

The positive current collector is an aluminum foil, and the thickness of the aluminum foil is 8-30 mu m.

In particular, the composite negative electrode (2) is composed of a carbon porous electrode layer (8), a metal lithium flat electrode layer (9) and a negative electrode current collector (10). The carbon porous electrode layer is formed by uniformly mixing active substance carbon, a conductive agent and a binder in a solvent and then coating the mixture on two sides of a negative current collector (10); the ratio of the reversible lithium-intercalated capacity of the carbon porous electrode layer (8) to the reversible lithium-intercalated capacity of the anode coating (7) is 0.1-0.9, and the preferable ratio is 0.5-0.66. The metal lithium flat plate electrode (9) is formed by taking out lithium in a positive active material by adopting a bidirectional pulse cycle charging mode during formation, firstly embedding the lithium into a carbon layer in a composite negative electrode, and then depositing a compact lithium layer on the surface of a carbon porous electrode embedded with lithium.

The carbon porous electrode layer (8) is composed of carbon, a conductive agent and a binder, wherein the carbon comprises natural graphite, artificial graphite, hard carbon, soft carbon and the like; the conductive additive comprises at least one of carbon black, Ketjen black, activated carbon, carbon nanotube CNTs, carbon fiber VGCF, Graphene and graphite conductive agent; the kinds of the binder include: one or more of styrene butadiene latex (SBR), sodium carboxymethylcellulose (CMC), Polyacrylate (PAA), modified polyacrylate, polyacrylonitrile, polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride and Polytetrafluoroethylene (PTFE); the thickness of the carbon porous electrode layer is 50 to 150 μm, and the preferable thickness is 50 to 80 μm.

The negative current collector (10) is a copper foil, and the thickness of the copper foil is 6-30 microns.

In particular, the preparation method of the lithium battery comprises the following main steps:

the first step is as follows: preparation of the Positive electrode

Firstly, one or more lithium-containing metal composite oxides, a conductive agent and a binder are fully mixed in a solvent according to a certain proportion, then the uniformly mixed slurry is coated on the upper surface and the lower surface of a positive current collector according to a certain surface density requirement, and simultaneously the solvent in the mixture is dried to obtain a formed semi-finished pole piece. Rolling the semi-finished product of the pole piece according to a certain compaction density, cutting the pole piece according to a certain width, drying the pole piece under a vacuum condition at a proper temperature and time, and finally welding one or more drainage pole lugs to prepare the positive pole;

the second step is that: preparation of carbon porous electrode

The method comprises the steps of fully mixing one or more carbon materials, a conductive agent and a binder in a solvent according to a certain proportion, and then carrying a negative electrode material with a certain surface density on a negative electrode current collector by adopting the same method as that for preparing a positive electrode to prepare the carbon porous electrode, wherein the ratio of the reversible capacity of the carbon porous electrode to the reversible capacity of the positive electrode is 0.1-0.9, preferably 0.5-0.66.

The third step: preparation of electrode sets

The dried positive electrode, the carbon porous electrode and the diaphragm can be wound or stacked mutually in different structural forms such as winding, lamination and the like to obtain a battery pole group. The diaphragm is positioned between the anode and the carbon porous electrode, and the length and the width of the diaphragm are both larger than those of the carbon porous electrode, and the carbon porous electrode is larger than or equal to the anode.

The diaphragm is made of Polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), Polyimide (PI) and other various organic films which can be used for lithium batteries; the structure form of the ceramic coating comprises a substrate single-surface ceramic coating layer and a substrate double-surface ceramic coating layer, wherein the substrate single-surface ceramic coating layer and an organic binder are mixed and coated, the substrate double-surface ceramic coating layer and an organic binder are mixed and coated, the substrate surface is sequentially coated with the ceramic coating layer and the organic binder coating layer, and the like, but the ceramic coating is not limited to the substrate single-surface ceramic coating layer and; the total thickness of the diaphragm ranges from 8 mu m to 50 mu m, and the preferred total thickness ranges from 12 mu m to 20 mu m.

The laminated structure comprises Z-shaped laminated sheets, winding laminated sheets and other common structures.

The fourth step: assembling the battery: putting the electrode assembly into a shell, drying, injecting liquid and sealing;

an aluminum plastic packaging bag or a metal shell (such as stainless steel, aluminum and aluminum alloy) is used as the shell, and the shape of the shell can be a cylinder, a square or a special-shaped structure. And (3) putting the electrode group into a shell, respectively sealing by adopting hot melt adhesive sealing, laser welding and other modes, and reserving a liquid injection hole for injecting liquid.

Drying the electrode group in a vacuum environment at a certain temperature and time before liquid injection, injecting liquid after the water content meets a certain control value, controlling the liquid injection amount to meet a design value, and then standing in vacuum at negative pressure to enable the electrolyte to enter the electrode group.

For the aluminum plastic film flexible package battery, vacuum degassing is carried out, and then hot melting sealing is carried out; for the metal shell battery, according to the process design requirements, temporary sealing can be carried out by adopting a mode of sticking a sealing sheet, and permanent sealing can also be carried out by adopting a mode of mechanical sealing or ball smashing and the like.

The fifth step: battery rest

Under the condition of high temperature or room temperature, certain pressure can be applied to the flexible package battery, and the injected electrolyte is fully soaked into the electrode and the diaphragm after a period of time.

And a sixth step: battery activation

And (2) transferring lithium in the lithium-containing metal oxide in the positive electrode to the negative electrode by adopting a charge-discharge formation device to set a bidirectional pulse cycle charging system, embedding lithium with carbon in the negative electrode, and then uniformly depositing a metal lithium layer on the surface of the completely lithium-embedded carbon, thereby preparing the composite negative electrode and activating the battery.

The bidirectional pulse cyclic charging is to perform charging by adopting pulse charging and pulse discharging in an alternating cyclic manner until a set charging termination voltage or constant-voltage charging current is reached, wherein the pulse width (time) is greater than the discharging pulse width (time); the pulse width (time) of pulse charging is 0.1-5 seconds, and the pulse width (time) of pulse discharging is 0.01-1 second; the charge termination voltage is 3.9V to 4.35V, preferably 4.0V to 4.1V.

The charging and discharging modes comprise various modes such as constant current and constant power; the current densities of the constant current charging and the constant current discharging can be the same or different, and the current density range is 0.1mA/cm ²～10mA/cm ²(ii) a The power densities of the constant power charging and the constant power discharging can be the same or different, and the power density range is 0.3mW/cm ²～30mW/cm ²。

The seventh step: aging of battery

And (3) placing the activated battery at a high temperature or room temperature for a period of time, respectively measuring parameters of the battery such as voltage, internal resistance and weight before and after placing, and observing the appearance of the battery.

Eighth step: and (4) screening the batteries.

According to the data change before and after aging laying, sorting out the batteries with abnormal voltage reduction, abnormal internal resistance increase, liquid leakage, swelling and the like.

The following will describe a method for preparing a lithium battery according to the present invention, a specific process for preparing a lithium battery according to the present invention, and advantages of the prepared lithium battery, with reference to specific examples, comparative examples, and test examples.