Negative electrode lithium replenishment method, negative electrode lithium replenishment device, negative electrode and battery

Abstract

The embodiments of the present application provide a negative electrode lithium replenishment method, a negative electrode lithium replenishment device, a negative electrode and a battery, wherein the negative electrode lithium replenishment method comprises sequentially passing the negative electrode through a first lithium replenishment stage and a second lithium replenishment stage; the lithium replenishment current of the first lithium replenishment stage is greater than the lithium replenishment current of the second lithium replenishment stage. The negative electrode lithium replenishment method adopts a staged lithium replenishment method, wherein the first lithium replenishment stage can quickly replenish lithium for the negative electrode and improve the lithium replenishment efficiency of the negative electrode, and the second lithium replenishment stage can accurately control the lithium replenishment degree of the negative electrode, thereby ensuring the uniformity of lithium replenishment and avoiding local excessive or insufficient lithium replenishment. Moreover, the first lithium replenishment stage and the second lithium replenishment stage generate a structurally stable SEI film to ensure the structural stability of the negative electrode, and on the basis of improving the initial efficiency of the negative electrode, effectively suppress the volume expansion of the active component layer in the negative electrode.

Description

Technical Field

[0001] The present application belongs to the technical field of battery materials. Specifically, the present application relates to a negative electrode lithium replenishment method, a negative electrode lithium replenishment device, a negative electrode and a battery. Background Art

[0002] As people's environmental awareness continues to increase, electric vehicles have gradually entered people's lives. As the main power component of electric vehicles, lithium-ion batteries provide a guarantee for the operation of electric vehicles.

[0003] Currently, most lithium-ion batteries used in the market use graphite as the negative electrode material. Graphite has the characteristics of stable structure, good rate performance, high and low temperature performance and good cycle performance. However, the specific capacity of graphite can only reach up to 372mAh / g, which greatly limits the improvement of the energy density of lithium-ion batteries.

[0004] In addition to graphite materials, there are some materials with high theoretical specific capacity that are expected to be used in lithium-ion battery negative electrodes, such as silicon, tin, aluminum, zinc, germanium, antimony and other elements and their oxides, nitrides, sulfides, phosphides, etc. However, the initial charge and discharge efficiency of these materials is low, and the silicon negative electrode will experience a dramatic volume expansion during the lithium insertion / extraction process, causing the silicon negative electrode particles to be easily pulverized and out of electrical contact, which in turn causes the battery capacity to decay, reducing the battery life of the lithium-ion battery. Summary of the invention

[0005] One purpose of the embodiments of the present application is to provide a negative electrode lithium replenishment method, a negative electrode lithium replenishment device, a negative electrode and a new technical solution for a battery.

[0006] According to a first aspect of an embodiment of the present application, a method for replenishing lithium of a negative electrode is provided, comprising:

[0007] The negative electrode is sequentially passed through a first lithium replenishment stage and a second lithium replenishment stage, so that the lithium replenishment electrode sheet replenishes lithium for the negative electrode;

[0008] The lithium replenishment current in the first lithium replenishment stage is greater than the lithium replenishment current in the second lithium replenishment stage;

[0009] After the first lithium supplementation stage, the first efficiency of the negative electrode is a first target first efficiency, and after the second lithium supplementation stage, the first efficiency of the negative electrode is a second target first efficiency;

[0010] The difference between the first target first efficiency and the first efficiency of the negative electrode without lithium supplementation is the first lithium supplementation efficiency, the difference between the second target first efficiency and the first efficiency of the negative electrode without lithium supplementation is the second lithium supplementation efficiency, and the first lithium supplementation efficiency is 80%-90% of the second lithium supplementation efficiency.

[0011] Optionally, the current rate range of the first lithium replenishment stage is 0.1C-0.8C.

[0012] Optionally, the current rate range of the second lithium replenishment stage is 0.01C-0.08C.

[0013] Optionally, the first lithium replenishment stage includes placing the negative electrode in an electrolyte containing an additive, and the additive in the first lithium replenishment stage includes at least one of LiPO2F2, LiBF4, LiDFOB, LiBOB, FSI, TFSI, LiTDI, LiPDI, LiHDI and DFOP, so that the negative electrode forms an inorganic component on its surface.

[0014] Optionally, the concentration of the additive in the first lithium supplementation stage in the electrolyte is in the range of 0.1-20%.

[0015] Optionally, the second lithium replenishment stage includes placing the negative electrode in an electrolyte containing additives, and the additives in the second lithium replenishment stage include at least one of VC, VEC, FEC, FEMC, TFEC, TEP, TAP, TMSB, TMB, PS, PES and DTD, so that the negative electrode forms an organic component on its surface.

[0016] Optionally, the concentration of the additive in the second lithium supplementation stage in the electrolyte is in the range of 0.1-20%.

[0017] According to a second aspect of an embodiment of the present application, a negative electrode lithium replenishing device is provided, wherein the negative electrode lithium replenishing method according to the first aspect is adopted in the lithium replenishing device, comprising:

[0018] A first lithium replenishing unit and a second lithium replenishing unit;

[0019] The first lithium replenishment unit and the second lithium replenishment unit are both provided with lithium replenishment pole pieces;

[0020] The negative electrode is disposed in the first lithium replenishment unit and the second lithium replenishment unit, and the lithium replenishment electrode sheet is configured to replenish lithium for the negative electrode;

[0021] The lithium replenishment current of the first lithium replenishment unit is greater than the lithium replenishment current of the second lithium replenishment unit.

[0022] Optionally, the first lithium replenishing unit and the second lithium replenishing unit are both filled with an electrolyte, and the electrolyte is a solution of electrolyte lithium salt in a non-aqueous solvent.

[0023] According to a third aspect of an embodiment of the present application, a negative electrode is provided. The negative electrode is obtained by using the negative electrode lithium replenishment method described in the first aspect.

[0024] According to a fourth aspect of the embodiments of the present application, a battery is provided, comprising a positive electrode, a separator and the negative electrode according to the third aspect;

[0025] The positive electrode and the negative electrode are respectively disposed on both sides of the separator.

[0026] One technical effect of the embodiment of the present application is:

[0027] The embodiment of the present application provides a method for replenishing lithium of a negative electrode, wherein the method for replenishing lithium of the negative electrode adopts a staged lithium replenishment method, wherein the first lithium replenishment stage can quickly replenish lithium for the negative electrode, thereby improving the lithium replenishment efficiency of the negative electrode, and the second lithium replenishment stage can accurately control the degree of lithium replenishment of the negative electrode, thereby ensuring the uniformity of lithium replenishment and avoiding local excessive or insufficient lithium replenishment. Moreover, the first lithium replenishment stage and the second lithium replenishment stage generate a structurally stable SEI film to ensure the structural stability of the negative electrode, and on the basis of improving the initial efficiency of the negative electrode, effectively suppress the volume expansion of the active component layer in the negative electrode.

[0028] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0030] Figure 1 A schematic diagram of a negative electrode lithium replenishing device provided in an embodiment of the present application.

[0031] in:

[0032] 1-negative electrode; 2-lithium supplement electrode;

[0033] 100-first lithium replenishing unit; 200-second lithium replenishing unit. DETAILED DESCRIPTION

[0034] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0035] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0036] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0037] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0038] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0039] The embodiment of the present application provides a method for replenishing lithium of a negative electrode, and the method for replenishing lithium of a negative electrode comprises:

[0040] The negative electrode is sequentially passed through a first lithium replenishment stage and a second lithium replenishment stage, so that the lithium replenishment electrode sheet replenishes lithium for the negative electrode;

[0041] The lithium replenishment current of the first lithium replenishment stage is greater than the lithium replenishment current of the second lithium replenishment stage, that is, the first lithium replenishment stage can quickly replenish lithium for the active component layer of the negative electrode, thereby improving the lithium replenishment efficiency of the active component layer of the negative electrode, while the second lithium replenishment stage can accurately control the degree of lithium replenishment of the active component layer of the negative electrode to ensure the structural stability of the active component layer of the negative electrode. After the first lithium replenishment stage, the first efficiency of the active component layer of the negative electrode is the first target first efficiency, and after the second lithium replenishment stage, the first efficiency of the active component layer of the negative electrode is the second target first efficiency.

[0042] The difference between the first target first efficiency and the first efficiency of the active component layer of the negative electrode without lithium replenishment is the first lithium replenishment efficiency, the difference between the second target first efficiency and the first efficiency of the active component layer of the negative electrode without lithium replenishment is the second lithium replenishment efficiency, and the first lithium replenishment efficiency is 80%-90% of the second lithium replenishment efficiency.

[0043] Specifically. Taking the silicon oxide-based active component layer attached to the negative electrode as an example, the first efficiency of the silicon oxide-based active component layer before lithium replenishment can be 70%. Assuming that the second target first efficiency is 95%, that is, the first efficiency of the silicon oxide-based active component layer after two-stage lithium replenishment reaches 95%; the first lithium replenishment efficiency is 80% of the second lithium replenishment efficiency. Since the first lithium replenishment stage and the second lithium replenishment stage increase the first efficiency of the silicon oxide-based active component layer by 95%-70%=25%, that is, the second lithium replenishment efficiency is 25%, then the first lithium replenishment efficiency is 25%*80%=20%, so that after the silicon oxide-based active component layer passes through the first lithium replenishment stage, the first efficiency of the silicon oxide-based active component layer reaches 70%+20%=90%, and after the silicon oxide-based active component layer passes through the second lithium replenishment stage, the first efficiency of the silicon oxide-based active component layer reaches 95%.

[0044] When the ratio of the first lithium replenishment efficiency to the second lithium replenishment efficiency is too small, that is, the first lithium replenishment stage is short, which is not conducive to the rapid lithium replenishment of the active component layer of the negative electrode; when the ratio of the first lithium replenishment efficiency to the second lithium replenishment efficiency is too large, the lithium replenishment process left for the first lithium replenishment stage is short. Since the lithium replenishment speed of the first lithium replenishment stage is relatively high, it is difficult to accurately control the lithium replenishment degree of the active component layer of the negative electrode, which reduces the structural stability of the active component layer of the negative electrode.

[0045] Specifically, the active component layer of the negative electrode may include a negative electrode active material, a binder and a conductive agent. Among them, the negative electrode active material may include carbon materials, silicon-based materials, tin-based materials, metal oxide materials and lithium titanate materials. Specifically, it may be natural graphite, artificial graphite, hard carbon, soft carbon, lithium titanate, iron oxide, lithium titanium phosphate, titanium dioxide, silicon, tin, aluminum, zinc, germanium, antimony and other elements and one or more mixtures of oxides, nitrides, sulfides and phosphides of silicon, tin, aluminum, zinc, germanium and antimony.

[0046] The binder can be one or more combinations of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber and polyacrylate. The content of the binder is 0.1-15wt% of the total mass of the active component layer, preferably 1-7wt%. The conductive agent can be one or more combinations of graphite, carbon fiber, carbon black, metal powder, metal oxide and fiber. The content of the conductive agent is 0.1-20wt% of the total mass of the active component layer, preferably 1-10wt%.

[0047] The active component layer also needs to add a solvent during the preparation process, and the solvent can be selected from one or more combinations of N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water and alcohols. The amount of solvent is such that the slurry of the active component layer can be coated on the current collector layer. The ratio of the amount of solvent to the total mass of the active component layer is in the range of 20-90wt%, preferably 40-85wt%.

[0048] The lithium replenishment method of the negative electrode provided in the embodiment of the present application adopts a staged lithium replenishment method, specifically, the lithium replenishment process of the negative electrode sequentially passes through the first lithium replenishment stage and the second lithium replenishment stage. Since the lithium replenishment current of the first lithium replenishment stage is greater than the lithium replenishment current of the second lithium replenishment stage, the first lithium replenishment stage can quickly replenish lithium for the active component layer of the negative electrode, thereby improving the lithium replenishment efficiency of the active component layer of the negative electrode. The second lithium replenishment stage can accurately control the degree of lithium replenishment of the active component layer of the negative electrode, thereby ensuring the uniformity of lithium replenishment and avoiding excessive or insufficient local lithium replenishment. Moreover, the lithium replenishment process of the first lithium replenishment stage and the second lithium replenishment stage can form a structurally stable SEI film, and the composition of the SEI film is controllable. After the negative electrode is applied to the battery, the structural stability of the active component layer of the negative electrode can be guaranteed. On the basis of improving the initial efficiency of the negative electrode, the volume expansion of the active component layer in the negative electrode is effectively suppressed, thereby ensuring the cycle retention rate of the battery.

[0049] In addition, the staged lithium replenishment method of the negative electrode can also be carried out in three stages, four stages or more stages to improve the controllability of the lithium replenishment of the active component layer of the negative electrode, and enhance the structural stability of the SEI film formed on the surface of the active component layer of the negative electrode, thereby increasing the capacity of the battery. Moreover, the present application forms a structurally stable SEI film on the surface of the active component layer when the negative electrode is prepared, which can ensure the electrode stability during the battery charging and discharging process. The SEI film on the surface of the traditional negative electrode is formed during the battery charging and discharging process, and it is difficult to control the structure of the SEI film. Moreover, the volume change of the active material on the negative electrode during the charging and discharging process will cause the SEI film to be destroyed. The instability of the SEI film will continuously consume electrolyte to repair it, causing the battery to produce gas, increase impedance and maintain a decrease in capacity, which significantly reduces the battery's charging and discharging performance.

[0050] Optionally, the current rate range of the first lithium replenishment stage is 0.1C-0.8C, preferably 0.2C-0.6C.

[0051] Specifically, C is used to represent the battery charge and discharge rate, which is charge and discharge rate = charge and discharge current / rated capacity; for example, when a battery with a rated capacity of 100A·h is discharged at 20A, its discharge rate is 0.2C. Among the battery discharge rates, 1C, 2C, and 0.2C are all battery discharge rates, which represent a measure of how fast the battery discharges. The capacity of a battery is discharged in 1 hour, which is called 1C discharge; if it is discharged in 5 hours, it is called 1 / 5=0.2C discharge, that is, the greater the charge and discharge rate, the higher the charge and discharge current of the battery. The first lithium replenishment stage uses a larger current rate, which can shorten the lithium replenishment time of the active component layer of the negative electrode and improve the lithium replenishment efficiency of the active component layer of the negative electrode.

[0052] Optionally, the current rate range of the second lithium replenishment stage is 0.01C-0.08C, preferably 0.02C-0.06C.

[0053] Specifically, since the traditional lithium replenishment process uses one-time lithium replenishment, and in order to control the time of lithium replenishment, high-current lithium replenishment is required. Based on the lithium replenishment in the first lithium replenishment stage, the present application uses a small-current lithium replenishment process in the second lithium replenishment stage to ensure the uniformity of lithium replenishment, avoid local excessive lithium replenishment or local insufficient lithium replenishment, shorten the lithium replenishment time while ensuring the uniformity of lithium replenishment, and accurately regulate the SEI film composition on the surface of the active component layer of the negative electrode.

[0054] Optionally, the first lithium replenishment stage includes placing the negative electrode in an electrolyte containing additives, and the additives in the first lithium replenishment stage include at least one of LiPO2F2 (lithium difluorophosphate), LiBF4 (lithium tetrafluoroborate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bis(oxalate borate), FSI (lithium bis(fluorosulfonyl)imide), TFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTDI (lithium 4,5-dicyano-2-(trifluoromethyl)isopyrazole), LiPDI (lithium 4,5-dicyano-2-(hexafluoroethyl)isopyrazole), LiHDI (lithium 4,5-dicyano-2-(nonafluoropropyl)isopyrazole) and DFOP (lithium bis(oxalate difluorophosphate)), so that the active component layer of the negative electrode forms an inorganic component on its surface.

[0055] Specifically, when the negative electrode is replenishing lithium, the active component layer on the negative electrode needs to be replenished with lithium through the lithium replenishing pole piece, and the negative electrode and the lithium replenishing pole piece are generally arranged in the electrolyte. The additives in the first lithium replenishing stage are added to the electrolyte. When the active component layer on the negative electrode is replenishing lithium, due to the large lithium replenishing current in the first lithium replenishing stage, the additives represented by LiPO2F2, LiBF4 and LiDFOB tend to undergo a two-electron reduction reaction, thereby forming the inorganic component on the surface of the active component layer of the negative electrode. The inorganic component can specifically include Li2CO3, LiF and Li2O. Li2CO3, LiF and Li2O can be used as part of the SEI film to ensure the ion conductivity of the negative electrode.

[0056] Optionally, the concentration of the additive in the first lithium supplementation stage in the electrolyte is in the range of 0.1%-20%, preferably 0.5%-5%.

[0057] Specifically, when the negative electrode is replenishing lithium, the negative electrode and the lithium replenishing electrode plate can be placed together in the electrolyte, and then the additive of the first lithium replenishing stage is added to the electrolyte, and the concentration of the additive of the first lithium replenishing stage in the electrolyte is specifically the mass concentration. When the concentration of the additive of the first lithium replenishing stage in the electrolyte is too low, it is difficult to effectively form a film on the surface of the active component layer of the negative electrode, which is not conducive to the structural stability and capacity retention of the negative electrode; and when the concentration of the additive of the first lithium replenishing stage in the electrolyte is too high, the film forming speed and thickness on the surface of the active component layer will be too large, which is not conducive to the charge and discharge of the negative electrode, and reduces the charge and discharge efficiency of the negative electrode.

[0058] Optionally, the additives in the second lithium supplementation stage include at least one of VC (vinylene carbonate), VEC (ethylene carbonate), fluorinated additives, phosphorus-containing additives, boron-containing additives and sulfur-containing additives. Among them, the fluorinated additives may include FEC (fluoroethylene carbonate), FEMC (fluoroethyl methyl carbonate) and TFEC (bis (2,2,2-trifluoroethyl) carbonate), etc.; the phosphorus-containing additives may include TEP (triethyl phosphate) and TAP (triallyl phosphate), etc.; the boron-containing additives may include TMSB (tri (trimethylsilane) borate) and TMB (trimethyl borate), etc.; the sulfur-containing additives may include PS (1,3-propane sultone), PES (1,3-propylene sultone) and DTD (ethylene sulfate), etc., so that the active component layer of the negative electrode forms an organic component on its surface.

[0059] Specifically, when the negative electrode is replenishing lithium, the additives of the second lithium replenishing stage are added to the electrolyte. When the active component layer on the negative electrode is replenishing lithium, since the lithium replenishing current of the second lithium replenishing stage is small, the additives represented by FEC, VC, PS, VEC and DTD tend to undergo a single-electron reduction reaction, thereby forming the organic component on the surface of the active component layer. The organic component may specifically include Poly VC (poly VC), Oligo-VC (VC oligomer or VC oligomer), ROCO2Li (R is olefin, alkane or a carbon chain with its group), RSO3Li (R is olefin, alkane or a carbon chain with its group), etc. Poly VC, Oligo-VC, ROCO2Li and RSO3Li can be used as part of the SEI film, and the organic component can be combined with the inorganic component formed in the first lithium replenishing stage to form a SEI film with high strength, good elasticity and good ion conductivity.

[0060] The structure of Poly VC and Oligo-VC is shown in the following structural formula:

[0061]

[0062] Optionally, the concentration of the additive in the second lithium supplementation stage in the electrolyte is in the range of 0.1%-20%, preferably 0.5%-5%.

[0063] After the negative electrode completes the first lithium replenishment stage, the inorganic component is formed on the surface of the active component layer of the negative electrode, and the inorganic component can be used as a part of the SEI film; and the organic component formed after the additive in the second lithium replenishment stage is added can be combined with the inorganic component formed in the first lithium replenishment stage to form a SEI film with high strength, good elasticity and good ion conductivity, thereby ensuring the capacity of the negative electrode. In the case of small current lithium replenishment in the second lithium replenishment stage, the additive and solvent in the second lithium replenishment stage tend to undergo a single electron reduction reaction, and the organic component of the SEI film can be formed on the surface of the active component layer. The organic component is combined with the inorganic component formed in the first lithium replenishment stage to form a SEI film with high strength, good elasticity and good ion conductivity. Since the SEI film has a certain strength, the volume expansion of the active component layer can be suppressed during the lithium replenishment process, and the dense SEI film can make the battery with the negative electrode more stable during the charge and discharge process, avoiding reaction with the electrolyte components during the battery cycle. At the same time, because the SEI film has a certain elasticity, it can avoid the SEI film from rupturing during the volume change of the active component layer, effectively isolate the active component layer from the electrolyte, prevent the electrolyte from undergoing redox reactions on the active component layer and corroding the negative electrode, avoid battery failure during the charge and discharge cycle, and ensure the cycle quality of the battery.

[0064] See also Figure 1 The embodiment of the present application further provides a negative electrode lithium replenishing device using the negative electrode lithium replenishing method, comprising:

[0065] A first lithium replenishing unit 100 and a second lithium replenishing unit 200;

[0066] The first lithium replenishment unit 100 and the second lithium replenishment unit 200 are both provided with a lithium replenishment electrode 2;

[0067] The negative electrode 1 is disposed in the first lithium replenishment unit 100 and the second lithium replenishment unit 200, and the lithium replenishment electrode sheet 2 is configured to replenish lithium for the negative electrode 1;

[0068] The lithium replenishment current of the first lithium replenishment unit 100 is greater than the lithium replenishment current of the second lithium replenishment unit 200 .

[0069] Specifically, the first lithium replenishment unit 100 and the second lithium replenishment unit 200 may both be lithium replenishment cells, the negative electrode 1 and the lithium replenishment electrode sheet 2 are both disposed in the lithium replenishment cell, the lithium replenishment cell is filled with electrolyte, and additives are added to the electrolyte.

[0070] The lithium replenishment device provided in the embodiment of the present application replenishes lithium for the negative electrode 1 in stages. Specifically, the lithium replenishment process of the negative electrode 1 sequentially goes through a first lithium replenishment stage and a second lithium replenishment stage. Since the lithium replenishment current of the first lithium replenishment stage is greater than the lithium replenishment current of the second lithium replenishment stage, the first lithium replenishment stage can quickly replenish lithium for the active component layer, thereby improving the lithium replenishment efficiency of the active component layer. The second lithium replenishment stage can accurately control the lithium replenishment degree of the active component layer of the lithium replenishment method, thereby ensuring the uniformity of lithium replenishment, avoiding local excessive lithium replenishment or local insufficient lithium replenishment, and ensuring the cycle retention rate of the battery.

[0071] In addition, the lithium supplement electrode 2 can be a lithium plate, for example, the electrode material of waste lithium batteries or lithium-containing electrolyte is used as the lithium source, and a lithium-plated metal sheet is obtained by electroplating, and the lithium-plated metal sheet is used as the lithium source. Or a lithium plate formed by die casting, the thickness of the lithium plate can be 0.1-5cm, preferably 0.3-4cm.

[0072] Alternatively, the lithium supplement electrode 2 may be a lithium foil attached to other foil materials, and metallic lithium powder may be prepared, or metallic lithium powder may be dispersed in an organic solvent such as hexane, and then evenly coated on one side of various thin film materials; metallic lithium may be heated to a molten state and directly coated on one side of a variety of thin film materials; lithium may be evaporated on one side of a variety of thin film materials by an evaporation method; or metallic lithium may be deposited on one side of a variety of thin film materials by a rolling method.

[0073] The above-mentioned film material can be a metal film material, such as copper foil, aluminum foil, nickel foil, iron foil, tin foil or alloys or composites thereof; it can also be a plastic or polymer film material, such as polyethylene film, polypropylene film, polypropylene film, polyvinylidene fluoride film, PET film material, PI film material or modified or composites thereof. The thickness of the lithium foil can be 1 μm-1000 μm, preferably 3 μm-200 μm.

[0074] Optionally, the first lithium replenishing unit 100 and the second lithium replenishing unit 200 are both filled with an electrolyte, and the electrolyte is a solution of electrolyte lithium salt in a non-aqueous solvent.

[0075] Specifically, the electrolyte can be a non-aqueous electrolyte, that is, a solution of an electrolyte lithium salt in a non-aqueous solvent. The electrolyte lithium salt can be selected from one or more combinations of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorosilicate (LiSiF6), lithium tetraphenylborate (LiB(C6H5)4), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl4), lithium fluoroalkylsulfonate (LiC(SO2CF3)3), LiCH3SO3, LiN(SO2CF3)2 and LiN(SO2C2F5)2. The non-aqueous solvent can be selected from a mixed solution of a chain acid ester or a cyclic acid ester, wherein the chain acid ester can be dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC) and one or more combinations of chain organic esters containing fluorine, sulfur or unsaturated bonds. The cyclic acid ester can be ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), sultone and one or more combinations of cyclic organic esters containing fluorine, sulfur or unsaturated bonds. The non-aqueous solvent can also be selected from chain ethers, cyclic ether solutions or mixed solutions of the two, wherein the cyclic ether can be tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), 4-methyl-1,3-dioxolane (4-MeDOL) and one or more combinations of chain organic esters containing fluorine, sulfur or unsaturated bonds. Chain ethers can include dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), diethylene glycol dimethyl ether (DG), and one or more combinations of chain organic esters containing fluorine, sulfur or unsaturated bonds. In addition, in the non-aqueous electrolyte, the concentration of the electrolyte lithium salt may be 0.1-15 mol / L, preferably 1-10 mol / L.

[0076] Reference Figure 1, an embodiment of the present application provides a negative electrode 1, and the negative electrode 1 is obtained by using the lithium supplementation method.

[0077] Specifically, the negative electrode 1 includes a current collector layer and an active component layer attached to the surface of the current collector layer, the active component layer is an active component layer that has been replenished with lithium, and the lithium replenishment process of the active component layer includes a first lithium replenishment stage and a second lithium replenishment stage.

[0078] The lithium replenishment current of the first lithium replenishment stage is greater than the lithium replenishment current of the second lithium replenishment stage, that is, the first lithium replenishment stage can quickly replenish lithium for the active component layer and improve the lithium replenishment efficiency of the active component layer, while the second lithium replenishment stage can accurately control the lithium replenishment degree of the active component layer to ensure the structural stability of the active component layer. After the first lithium replenishment stage, the first efficiency of the active component layer is the first target first efficiency, and after the second lithium replenishment stage, the first efficiency of the active component layer is the second target first efficiency.

[0079] The negative electrode 1 provided in the embodiment of the present application adopts a staged lithium replenishment method, specifically, the lithium replenishment process of the negative electrode 1 sequentially passes through the first lithium replenishment stage and the second lithium replenishment stage. Since the lithium replenishment current of the first lithium replenishment stage is greater than the lithium replenishment current of the second lithium replenishment stage, the first lithium replenishment stage can quickly replenish lithium for the active component layer of the negative electrode 1, thereby improving the lithium replenishment efficiency of the active component layer of the negative electrode 1. The second lithium replenishment stage can accurately control the lithium replenishment degree of the active component layer of the negative electrode 1, thereby ensuring the uniformity of lithium replenishment and avoiding excessive or insufficient local lithium replenishment. Moreover, the lithium replenishment process of the first lithium replenishment stage and the second lithium replenishment stage can form a structurally stable SEI film, and the composition of the SEI film is controllable.

[0080] The embodiment of the present application provides a battery, including a positive electrode, a separator and the negative electrode 1;

[0081] The positive electrode and the negative electrode 1 are respectively arranged on both sides of the separator.

[0082] Specifically, the negative electrode 1 of the battery adopts a staged lithium replenishment method, specifically, the lithium replenishment process of the negative electrode 1 sequentially passes through the first lithium replenishment stage and the second lithium replenishment stage. Since the lithium replenishment current of the first lithium replenishment stage is greater than the lithium replenishment current of the second lithium replenishment stage, the first lithium replenishment stage can quickly replenish lithium for the active component layer, thereby improving the lithium replenishment efficiency of the active component layer. The second lithium replenishment stage can accurately control the lithium replenishment degree of the active component layer, thereby ensuring the uniformity of lithium replenishment and avoiding excessive or insufficient local lithium replenishment. Moreover, the lithium replenishment process of the first lithium replenishment stage and the second lithium replenishment stage can form a structurally stable SEI film, and the composition of the SEI film is controllable, thereby ensuring the structural stability of the battery and the active component layer. On the basis of improving the initial efficiency of the negative electrode 1, the volume expansion of the active component layer in the negative electrode 1 is effectively suppressed, thereby ensuring the cycle retention rate of the battery.

[0083] The negative electrode and the battery of the present application are described in detail below through examples and comparative examples;

[0084] Among them, the negative electrodes of the embodiments and comparative examples are prepared by dissolving the negative electrode active material, conductive agent, and binder in a solvent in a certain proportion and mixing them into a slurry, which is then coated on a wide conductive substrate, and then dried, rolled and cut to obtain the negative electrode pole piece.

[0085] The drying temperature ranges from 60 to 150° C., preferably from 80 to 110° C., and the drying time ranges from 0.5 to 5 hours.

[0086] The batteries of the embodiments and comparative examples are prepared by winding or laminating the positive electrode, the separator, and the negative electrode in sequence to form a battery core, and then placing the battery core in a battery shell and sealing it to obtain a battery.

[0087] Example 1

[0088] The silicon oxide-based active component layer of the negative electrode was replenished with lithium to the first target initial efficiency using a current rate of 0.4C, with 5% LiPO2F2 as a film-forming additive and a non-aqueous electrolyte of lithium hexafluorophosphate in dimethyl carbonate;

[0089] The active component layer of the negative electrode was replenished with lithium to the second target first efficiency (target first efficiency was 95%) using a current rate of 0.04C, with 5% PS as a film-forming additive and the electrolyte being a non-aqueous electrolyte of lithium hexafluorophosphate in dimethyl carbonate;

[0090] Wherein, the first lithium replenishment efficiency is 80% of the second lithium replenishment efficiency.

[0091] Example 2

[0092] The first lithium replenishment efficiency is 85% of the second lithium replenishment efficiency, The rest is the same as Example 1.

[0093] Example 3

[0094] The first lithium replenishment efficiency is 90% of the second lithium replenishment efficiency, The rest is the same as Example 1.

[0095] Comparative Example 1

[0096] The silicon oxide-based active component layer of the negative electrode was replenished with lithium to an initial efficiency of 90% using a current rate of 0.4C, and the electrolyte was a non-aqueous electrolyte of lithium hexafluorophosphate in dimethyl carbonate.

[0097] Comparative Example 2

[0098] The silicon oxide-based active component layer of the negative electrode replenishes lithium to an initial efficiency of 95% , the rest is the same as Comparative Example 1.

[0099] Comparative Example 3

[0100] The silicon oxide-based active component layer of the negative electrode was replenished with lithium to an initial efficiency of 90% using a current rate of 0.04C, and the electrolyte was a non-aqueous electrolyte of lithium hexafluorophosphate in dimethyl carbonate.

[0101] Comparative Example 4

[0102] The silicon oxide-based active component layer of the negative electrode replenishes lithium to an initial efficiency of 95% , the rest is the same as Comparative Example 3.

[0103] Comparative Example 5

[0104] The silicon oxide-based active component layer of the negative electrode is not replenished with lithium.

[0105] The negative electrodes of the above-mentioned embodiments and comparative examples were prepared into corresponding batteries according to the above-mentioned battery preparation method, and charge and discharge cycle tests were performed on each battery.

[0106] The specific test temperature is 25°C, and the test process includes:

[0107] The battery is charged to 4.1V with a 1.3C current and a constant voltage charge to a current of 1.0C; the battery is charged to 4.2V with a 1.0C current and a constant voltage charge to a current of 0.7C; the battery is charged to 4.3V with a 0.7C current and a constant voltage charge to a current of 0.4C; the battery is charged to 4.48V with a 0.4C current and a constant voltage charge to a current of 0.025C; the battery is discharged to 3.0V with a 0.2C constant current. The discharge capacity is recorded and compared with the design capacity to obtain the following data.

[0108] Table 1

[0109]

[0110]

[0111] It can be seen from Table 1 that by replenishing lithium in stages through the negative electrode of the embodiment of the present application, the capacity retention rate of the battery prepared by the negative electrode can reach more than 97.1% after 50 cycles, and the capacity retention rate can reach more than 85.5% after 500 cycles.

[0112] However, since the negative electrode in the comparative example did not use lithium replenishment in batches or did not replenish lithium at all, the capacity retention rate of the battery prepared with the negative electrode of the comparative example was less than 95.4% after 50 cycles and less than 67.9% after 500 cycles.

[0113] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A method for replenishing lithium in a negative electrode, characterized in that: include: The negative electrode is sequentially passed through a first lithium replenishment stage and a second lithium replenishment stage, so that the lithium replenishment electrode sheet replenishes lithium for the negative electrode; The lithium replenishment current in the first lithium replenishment stage is greater than the lithium replenishment current in the second lithium replenishment stage; After the first lithium supplementation stage, the first efficiency of the negative electrode is a first target first efficiency, and after the second lithium supplementation stage, the first efficiency of the negative electrode is a second target first efficiency; The difference between the first target first efficiency and the first efficiency of the negative electrode without lithium supplementation is the first lithium supplementation efficiency, the difference between the second target first efficiency and the first efficiency of the negative electrode without lithium supplementation is the second lithium supplementation efficiency, and the first lithium supplementation efficiency is 80%-90% of the second lithium supplementation efficiency; The current rate range of the first lithium replenishment stage is 0.4C-0.8C; The current rate range of the second lithium replenishment stage is 0.01C-0.08C.

2. The lithium supplementation method according to claim 1, characterized in that: The first lithium replenishment stage includes placing the negative electrode in an electrolyte containing an additive, and the additive in the first lithium replenishment stage includes at least one of LiPO2F2, LiBF4, LiDFOB, LiBOB, FSI, TFSI, LiTDI, LiPDI, LiHDI and DFOP, so that the negative electrode forms an inorganic component on its surface.

3. The lithium supplementation method according to claim 2, characterized in that: The concentration of the additive in the first lithium supplementation stage in the electrolyte is in the range of 0.1-20%.

4. The lithium supplementation method according to claim 2, characterized in that: The second lithium replenishment stage includes placing the negative electrode in an electrolyte containing an additive, and the additive in the second lithium replenishment stage includes at least one of VC, VEC, FEC, FEMC, TFEC, TEP, TAP, TMSB, TMB, PS, PES and DTD, so that the negative electrode forms an organic component on its surface.

5. The lithium supplementation method according to claim 4, characterized in that: The concentration of the additive in the second lithium supplementation stage in the electrolyte is in the range of 0.1-20%.

6. A lithium replenishing device for a negative electrode, characterized in that: The lithium replenishment device adopts the lithium replenishment method according to any one of claims 1 to 5, and the lithium replenishment device comprises: A first lithium replenishing unit (100) and a second lithium replenishing unit (200); The first lithium replenishment unit (100) and the second lithium replenishment unit (200) are both provided with lithium replenishment pole pieces (2); The negative electrode (1) is arranged in the first lithium replenishment unit (100) and the second lithium replenishment unit (200), and the lithium replenishment electrode sheet (2) is configured to replenish lithium for the negative electrode (1); The lithium replenishment current of the first lithium replenishment unit (100) is greater than the lithium replenishment current of the second lithium replenishment unit (200).

7. The lithium replenishing device according to claim 6, characterized in that: The first lithium replenishment unit (100) and the second lithium replenishment unit (200) are both filled with an electrolyte, and the electrolyte is a solution formed by an electrolyte lithium salt in a non-aqueous solvent.

8. A negative electrode (1), characterized in that The negative electrode (1) is obtained by the lithium replenishment method according to any one of claims 1 to 5.

9. A battery, characterized in that: comprising a positive electrode, a separator and the negative electrode (1) according to claim 8; The positive electrode and the negative electrode (1) are respectively arranged on both sides of the separator.

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