An electrochemical pre-lithiation method, a pre-lithiation negative electrode, and a lithium battery

Abstract

This application provides an electrochemical pre-lithiation method, a pre-lithiated negative electrode, and a lithium battery. The method includes: providing a negative electrode to be pre-lithiated; heat-treating the negative electrode in a reducing gas environment; and performing electrochemical pre-lithiation treatment on the negative electrode after heat treatment. In this application, heat-treating the negative electrode in a reducing gas environment not only removes adsorbed hydrophilic oxide groups from the electrode surface and creates wrinkles and etched channels, deepening electrolyte immersion and pre-lithiation uniformity, but also reacts with the negative electrode surface to generate reducing groups, improving the affinity between the electrolyte and the electrode material, thereby increasing lithium source utilization and saving pre-lithiation costs. Simultaneously, by adjusting the gas source ventilation time, the degree of etching on the electrode surface can be precisely controlled, increasing the lithium replenishment amount and intensity of the electrode while ensuring the surface pretreatment effect.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to an electrochemical pre-lithiation method, a pre-lithiation negative electrode, and a lithium battery. Background Technology

[0002] Silicon, as the anode material for next-generation high-capacity lithium-ion batteries, suffers from significant volume expansion and substantial capacity decay during lithium delithiation / intercalation, leading to instability in the solid electrolyte interphase (SEI) film. A stable SEI film is a key factor in extending battery cycle life. However, the formation and breakdown of the SEI film during charging and discharging continuously consume lithium ions, resulting in low initial coulombic efficiency and short cycle life in lithium-ion batteries.

[0003] To address the aforementioned issues, a relatively effective method currently is to pre-add a small amount of lithium source to the negative electrode using electrochemical lithium replenishment technology before the electrode undergoes formal charge-discharge cycles. This balances the excess lithium consumed during the reaction, replenishes the lithium consumed by the cathode during side reactions and SEI film formation, thereby improving the initial coulombic efficiency, extending battery cycle life, and mitigating volume expansion.

[0004] Although electrochemical lithium replenishment technology can achieve lithium replenishment of the negative electrode to a certain extent, its lithium replenishment effect is not ideal due to the limited number of active sites on the surface of the negative electrode particles that can adsorb lithium ions, the relatively dense particles, poor conductivity, and the difficulty in electrolyte penetration.

[0005] Therefore, existing technologies still need improvement. Summary of the Invention

[0006] The technical problem to be solved by this application is to provide an electrochemical pre-lithiation method, a pre-lithiated negative electrode sheet, and a lithium battery, so as to solve the problem that the existing technology of pre-lithiation of negative electrode sheets by electrochemical pre-lithiation treatment has poor lithium replenishment effect.

[0007] To solve the above problems, this application provides the following technical solution:

[0008] This application proposes an electrochemical pre-lithiation method, comprising:

[0009] Provide negative electrode sheets for pre-lithiation;

[0010] The negative electrode is heat-treated in a reducing gas environment;

[0011] After heat treatment, the negative electrode sheet undergoes electrochemical pre-lithiation treatment.

[0012] Furthermore, in the method, the reducing gas includes at least one of NH3, H2, CH4, and CO.

[0013] Furthermore, in the method, the reducing gas includes NH3 and H2.

[0014] Furthermore, in the method, the flow rate ratio of NH3 to H2 in the reducing gas is 1:4 to 4:1.

[0015] Furthermore, in the method described, during the plasma treatment of the negative electrode, the flow rate ratio of NH3 to H2 in the reducing gas is 1:2 to 2:1.

[0016] Furthermore, in the method, the heat treatment temperature is 100℃~800℃, and the time is 0.5~2h.

[0017] Furthermore, in the method, before heat-treating the negative electrode sheet in a reducing gas environment, the method further includes:

[0018] The negative electrode sheet is baked in an oxygen-free environment.

[0019] Furthermore, in the method, the baking temperature is 100℃~800℃ and the time is 30s~30min.

[0020] This application also provides a pre-lithiated anode sheet, which is obtained by the method described above.

[0021] This application also provides a lithium battery, which includes a pre-lithiated negative electrode as described above.

[0022] Compared with the prior art, the embodiments of this application have the following advantages:

[0023] In this embodiment, the provided electrochemical pre-lithiation method first heat-treats the negative electrode sheet to be pre-lithiated in a reducing gas environment; then, after heat treatment, electrochemical pre-lithiation is performed on the negative electrode sheet. The heat treatment of the negative electrode sheet in a reducing gas environment not only removes adsorbed hydrophilic oxide groups from the electrode surface and creates wrinkles and etched channels, deepening electrolyte immersion and improving the uniformity of pre-lithiation, but also reacts with the negative electrode surface to generate reducing groups, increasing the affinity between the electrolyte and the electrode material, thereby improving lithium source utilization and saving pre-lithiation costs.

[0024] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the electrochemical pre-lithiation device in the embodiments of this application;

[0026] Figure 2This is a flowchart of the electrochemical pre-lithiation method provided in the embodiments of this application;

[0027] Figure 3 This is a schematic diagram of the negative electrode surface after plasma treatment in an embodiment of this application;

[0028] Figure 4 This is a schematic diagram of the system structure for performing the electrochemical pre-lithiation method in an embodiment of this application. Detailed Implementation

[0029] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Currently, commercially available lithium-ion batteries mainly use graphite as the anode material. The theoretical specific capacity of graphite is 372 mAh / g, while high-end graphite materials on the market can reach 360-365 mAh / g. Therefore, the potential for increasing the energy density of lithium-ion batteries using graphite as the anode material is very limited, and there is an urgent need to find new anode materials to replace traditional graphite-based carbon anode materials.

[0031] Research has revealed that active materials that can replace graphite as lithium-ion battery anodes include elements such as Mg, Al, Sb, Sn, Ti, and Si, as well as their oxides, nitrides, sulfides, and phosphides. The theoretical capacity of these materials is much greater than that of graphite.

[0032] Among the many alternative materials, silicon is expected to become the anode material for the next generation of high-capacity lithium-ion batteries. As the most abundant non-gaseous element in the Earth's crust, silicon has advantages such as low price and environmental friendliness. Moreover, silicon has a higher lithium intercalation platform than graphite, so lithium ions will not be deposited on the electrode surface during charging and discharging, avoiding the formation of lithium dendrites and ensuring high safety performance.

[0033] However, silicon undergoes significant volume expansion (300%) and substantial capacity decay during lithium delithiation / intercalation, directly leading to instability of the solid electrolyte interphase (SEI) film. A stable SEI film is a major factor in extending battery cycle life. Furthermore, the formation and destruction of the SEI film during the charging and discharging process of lithium-ion batteries continuously consume lithium ions, resulting in low initial coulombic efficiency (SiO initial efficiency is only about 70%) and short cycle life of lithium-ion batteries.

[0034] To address the aforementioned issues, the most effective solution currently available is to employ pre-lithiation technology, which involves adding a small amount of lithium source before the electrode undergoes its formal charge-discharge cycle. This balances the excess lithium consumed during the reaction, replenishes the lithium consumed by the cathode during side reactions and SEI film formation, thereby improving the initial coulombic efficiency, extending battery cycle life, alleviating volume expansion to some extent, and improving the overall performance of lithium-ion batteries.

[0035] Electrochemical lithium replenishment technology is a key pre-lithiation technology. This technology typically involves placing the negative electrode A1 (requiring lithium replenishment), lithium source L1, and separator S1 into the electrolyte E1. The negative electrode A1 and lithium source L1 need to be connected via an external circuit, such as... Figure 1 As shown, this successfully establishes both electronic and ion pathways between the negative electrode and the lithium source, thereby enabling lithium replenishment of the negative electrode.

[0036] However, this method of pre-lithiation of negative electrode sheets has the following drawbacks: 1. The principle of electrochemical pre-lithiation is that the active particles react with Li ions or undergo a phase change to form an SEI film on the particle surface to achieve pre-lithiation. However, there are few active sites on the particle surface that can adsorb Li ions, which greatly reduces the utilization rate of the Li source; 2. After the electrode sheet is pressed, the surface particles are relatively dense, which greatly reduces the effective contact area between the active material and the electrolyte, affecting the final pre-lithiation effect; 3. There are few adsorption groups on the electrode surface that can be affinity-bonded with the electrolyte, so the wettability with the electrolyte is poor, which is not conducive to the formation of a uniform electronic pathway and ion pathway during the electrochemical lithium replenishment process; 4. In the conventional negative electrode coating process, the electrode sheet needs to be dried in the air at a certain temperature (around 100°C). This results in a large number of oxide layers on the surface of the coated negative electrode sheet. The presence of the oxide layer will hinder the affinity between the active material and the electrolyte, and these oxides may even directly undergo side reactions, causing byproducts to cover the electrode sheet, making it more difficult for the electrolyte to penetrate.

[0037] Addressing the issue of poor lithium replenishment effects in existing electrochemical pre-lithiation treatments of negative electrode sheets, this application provides an electrochemical pre-lithiation method, such as... Figure 2 As shown, steps S100 to S300 are included:

[0038] Step S100: Provide the negative electrode sheet to be pre-lithiated.

[0039] In step S100 above, the negative electrode sheet to be pre-lithiated is the negative electrode sheet that needs to be supplemented with lithium. Specifically, the negative electrode active material, conductive agent, and binder are first dissolved in a solvent in a certain proportion and mixed into a slurry. Then, the slurry is coated on a wide conductive substrate, dried, rolled, and slit to obtain the above-mentioned negative electrode sheet.

[0040] The drying and rolling conditions can adopt conventional techniques. The temperature for drying the negative electrode sheet is 60-150℃, preferably 80-110℃, and the drying time is 0.5-5 hours.

[0041] In this embodiment, the materials of the negative electrode are not specifically limited.

[0042] In the aforementioned negative electrode sheet, the negative electrode active material includes all negative electrode materials that can be used as lithium-ion batteries, such as 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, as well as one or more of their oxides, nitrides, sulfides and phosphides.

[0043] In the aforementioned negative electrode sheet, the binder can be any binder known in the art, such as one or more of polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, and polyacrylate. The binder content is 0.1–15 wt% of the negative electrode active material, preferably 1–7 wt%. The conductive agent can be any conductive agent known in the art, such as one or more of graphite, carbon fiber, carbon black, metal powder, metal oxide, and fiber.

[0044] In the above-mentioned negative electrode sheet, the content of the conductive agent is 0.1 to 20 wt% of the negative electrode active material, preferably 1 to 10 wt%.

[0045] Specifically, the negative electrode sheet can be prepared using various methods commonly used in the art. For example, a solvent can be used to prepare a slurry from the negative electrode active material, binder, and conductive agent. The amount of solvent added is known to those skilled in the art and can be flexibly adjusted according to the viscosity and operability requirements of the slurry to be prepared for coating. Then, the prepared negative electrode material slurry is coated onto the current collector, dried, pressed, and then cut to obtain the negative electrode sheet.

[0046] The drying temperature is typically 120°C, and the drying time is typically 5 hours. The solvent used for the negative electrode slurry can be any solvent available in the prior art, such as one or more selected from N-methylpyrrolidone (NMP), dimethylformamide (DMF), diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, and alcohols. The amount of solvent used is sufficient to coat the slurry onto the conductive substrate. For example, the amount of solvent used results in the content of the positive electrode active material in the slurry being 20–90 wt%, preferably 40–85 wt%.

[0047] Step S200: Heat-treat the negative electrode in a reducing gas environment.

[0048] In step S200 above, before the negative electrode is formally immersed in the electrolyte for electrochemical pre-lithiation, the negative electrode is first heat-treated in a reducing gas environment.

[0049] In this process, a reducing gas reacts with the electrode surface to remove the oxide layer, generating reducing electrolyte-loving groups. Simultaneously, the electrode surface material is etched to a certain extent, forming pits, channels, and wrinkles. The reducing groups significantly improve the affinity between the electrolyte and the electrode material, the wrinkles increase the specific surface area for the electrode surface to react with the electrolyte, and the pits and channels greatly enhance the efficiency of electrolyte penetration. Therefore, using a pre-lithiated negative electrode can significantly improve the pre-lithiation efficiency and uniformity.

[0050] High-temperature baking can increase the kinetic energy of gas molecules, reduce the reaction barrier of reducing gas etching the carbon layer on the electrode surface, and make the reaction easier to proceed.

[0051] In step S200 above, only a high-temperature baking step and an air source outlet need to be added to the existing production line structure. It does not require too many changes to the original traditional structure and has the natural advantage of being compatible with the original structure.

[0052] In step S200 above, under high temperature conditions, a suitable reducing gas and airflow velocity are used to reduce and etch the surface of the negative electrode.

[0053] In step S200 above, the reducing gas includes at least one of NH3, H2, CH4, and CO. The presence of the reducing gas removes the oxide layer and surface groups with poor affinity to the electrolyte from the electrode surface, thereby improving the wettability of the electrode and the electrolyte, enhancing the pre-lithiation uniformity of the electrode, and also etching the electrode surface material to a certain extent, forming etching pits, channels, and wrinkles. These wrinkles increase the specific surface area for the electrode surface to react with the electrolyte, while the etching pits and channels significantly improve the efficiency of electrolyte penetration into the material, greatly increasing the pre-lithiation efficiency. Simultaneously, the presence of the reducing gas causes the electrode surface material to react with the reducing gas to generate reducing groups, which greatly improves the affinity between the electrolyte and the electrode material, thus effectively improving the pre-lithiation uniformity of the electrode and the utilization rate of the lithium source, saving pre-lithiation costs.

[0054] The reducing gas mentioned above can be a mixture of multiple gases, such as a mixture of NH3 and H2, a mixture of CH4 and H2, a mixture of CO and H2, etc.

[0055] Optionally, in one embodiment, the reducing gas is composed of NH3 and H2, that is, the reducing gas is a mixture of NH3 and H2.

[0056] Among them, NH3 can provide nitrogen element while achieving the reducing effect, which can better perform nitriding on the surface of the negative electrode. By utilizing the delocalized electrons of nitrogen element, the conductivity of the electrode can be improved, the electrolyte wetting process can be promoted, and more active sites can be provided for lithium ion adsorption, thereby improving the electrochemical pre-lithiation effect. In addition, due to the presence of reducing gas NH3, the material on the electrode surface reacts with it to generate reducing groups such as C≡N, which can greatly improve the affinity between the electrolyte and the electrode material, thereby effectively improving the pre-lithiation uniformity of the electrode and the utilization rate of lithium source, and saving pre-lithiation cost.

[0057] Meanwhile, since a single NH3 gas source has high reducing power, it is not easy to control the etching effect on the electrode. However, hydrogen has weaker reducing power than ammonia. Combining the two can adjust the overall reducing power of the gas source, thereby adjusting the final etching degree of the electrode.

[0058] Optionally, the flow rate ratio of NH3 to H2 in the aforementioned reducing gases is 1:4 to 4:1. If the flow rate of NH3 is too high and the flow rate of H2 is too low, the overall reducing power of the gas source may be too strong, making it difficult to control the etching effect on the electrode during plasma treatment. Conversely, if the flow rate of NH3 is too low and the flow rate of H2 is too high, the overall reducing power of the gas source may be insufficient, making it impossible to effectively etch the surface of the electrode through plasma treatment. Preferably, the flow rate ratio of NH3 to H2 is 0.5:1.

[0059] Specifically, the H2 flow rate can be fixed at 3.6 mol / min, and the NH3 flow rate can be adjusted so that the ratio of NH3 to H2 flow rates is 1:2 to 2:1.

[0060] During the heat treatment process described above, the degree of etching on the electrode surface can be precisely controlled by adjusting the gas supply time, ensuring the surface pretreatment effect while taking into account the amount and strength of the negative electrode coating.

[0061] The heat treatment temperature is 100℃~800℃, and the treatment time is 0.5~2h, that is, the negative electrode is kept in an environment of 100℃~800℃ with a reducing gas for 0.5~2h. After the above heat treatment, the electrode retains a good morphology, the degree of etching is moderate, and some of the etching pits become larger and interconnected, achieving a better treatment effect.

[0062] Among the aforementioned reducing gases, appropriately adjusting the overall reducing properties of the gas to match the applied heat treatment temperature can achieve a better etching effect. For example, when the heat treatment temperature is between 100℃ and 800℃, introducing a mixture of NH3 and H2, and controlling the flow rate ratio of NH3 to H2 to be 0.5:1, can achieve a better etching effect on the negative electrode.

[0063] Step S300: After heat treatment, the negative electrode sheet undergoes electrochemical pre-lithiation treatment.

[0064] In step S300 above, the negative electrode sheet processed in step S200 is subjected to conventional electrochemical pre-lithiation treatment to obtain a pre-lithiation negative electrode sheet.

[0065] Specifically, in step S300 above, such as Figure 1 As shown, the negative electrode A1, separator S1, and lithium source L1 are stacked in sequence, and then the electrolyte E1 is placed in it. Then, an external power supply is connected, and the negative electrode A1 is connected to the negative terminal of the power supply and the lithium source L1 is connected to the positive terminal of the power supply. A certain voltage is applied between the negative electrode A1 and the lithium source L1 to achieve electron and ion conduction and to replenish lithium to the negative electrode A1.

[0066] In step S300 above, the lithium source can be a self-supporting lithium plate or a lithium foil attached to other thin film materials. The lithium plate can be manufactured by die casting. For example, a die of a certain size is selected, and a lithium ingot is die-cast into the die through a cold rolling process. After die casting, a demolding operation is performed to obtain a lithium plate that can be used for electrochemical lithium replenishment.

[0067] The length and width of the lithium plate are not specifically required and can be adjusted according to the lithium replenishment device and the size of the electrode requiring lithium replenishment. The thickness of the lithium plate is generally 1mm to 5cm, preferably 3mm to 4cm. Lithium foil attached to other foil materials can be obtained through various methods. For example, the lithium plate can be obtained by dispersing lithium metal powder or lithium metal powder in an organic solvent such as hexane and then uniformly coating it onto one side of various thin film materials; the lithium plate can also be obtained by heating lithium metal to a molten state and directly coating it onto one side of various thin film materials; the lithium plate can also be obtained by vapor deposition of lithium onto one side of various thin film materials; the lithium plate can also be obtained by roll forming of lithium metal onto one side of various thin film materials. The aforementioned thin film materials can be metal thin film materials, such as copper foil, aluminum foil, nickel foil, iron foil, tin foil, or their alloys or composites; the aforementioned thin film materials can also be plastic or polymer thin film materials, such as polyethylene film, polypropylene film, polypropylene film, polyvinylidene fluoride film, PET film material, PI film material, or their modified or composite materials. The thickness of the lithium foil is generally 1μm to 1mm, preferably 3μm to 200μm.

[0068] In step S300 above, the liquid electrolyte is a non-aqueous electrolyte, which is a solution of lithium electrolyte salt in a non-aqueous solvent. Conventional non-aqueous electrolytes known to those skilled in the art can be used.

[0069] For example, the electrolyte lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorosilicate (LiSiF6), lithium tetraphenylborate (LiB(C6H5)4), lithium chloride (LiCl), lithium bromide (LiBr), lithium chloroaluminate (LiAlCl4), and lithium fluorocarbon sulfonate (LiC(SO2CF3)3), LiCH3SO3, LiN(SO2CF3)2, and LiN(SO2C2F5)2.

[0070] The non-aqueous solvent can be selected from a mixed solution of linear esters and cyclic esters. The linear esters can be one or more of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), dipropyl carbonate (DPC), and other linear organic esters containing fluorine, sulfur, or unsaturated bonds. The cyclic esters can be one or more of ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), γ-butyrolactone (γ-BL), sulfolactone, and other cyclic organic esters containing fluorine, sulfur, or unsaturated bonds.

[0071] The non-aqueous solvent can also be selected from chain ether and cyclic ether solutions or mixed solutions, wherein the cyclic ether can be one or more of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF), 1,3-dioxolane (DOL), and 4-methyl-1,3-dioxolane (4-MeDOL), as well as other fluorine-containing, sulfur-containing, or unsaturated chain organic esters. Chain ethers mainly include dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), 1,2-dimethoxypropane (DMP), and diethylene glycol dimethyl ether (DG), as well as one or more of other fluorine-containing, sulfur-containing, or unsaturated chain organic esters.

[0072] In the non-aqueous electrolyte, the concentration of the electrolyte lithium salt is 0.1–15 mol / L, preferably 1–10 mol / L.

[0073] In step S300, since the negative electrode sheet has already undergone step S200, a large number of etched pits, wrinkles, etc. have been formed on its surface, and the surface condition of the negative electrode sheet is as follows: Figure 3 As shown, this can increase the specific surface area of ​​the electrode surface reacting with the electrolyte, greatly improving the efficiency of electrolyte immersion in the material and significantly increasing the pre-lithiation efficiency.

[0074] The electrochemical pre-lithiation method provided in this application first heat-treats the negative electrode sheet to be pre-lithiated in a reducing gas environment; then, after heat treatment, electrochemical pre-lithiation is performed on the negative electrode sheet. The heat treatment of the negative electrode sheet in a reducing gas environment not only removes adsorbed hydrophilic oxide groups from the electrode surface and creates wrinkles and etched channels, deepening electrolyte immersion and pre-lithiation uniformity, but also reacts with the negative electrode surface to generate reducing groups, improving the affinity between the electrolyte and the electrode material, thereby increasing lithium source utilization and saving pre-lithiation costs. Simultaneously, by adjusting the gas supply time, the degree of etching on the electrode surface can be precisely controlled, increasing the amount and intensity of lithium replenishment while ensuring the surface pretreatment effect.

[0075] Optionally, in one embodiment, the electrochemical pre-lithiation method provided in this application further includes step S101 before step S200:

[0076] Step S101: Bake the negative electrode sheet in an oxygen-free environment.

[0077] In step S101 above, the anaerobic environment can be a nitrogen environment, an inert gas environment, or an H2 environment.

[0078] In the above embodiments, before the pre-lithiated negative electrode sheet is formally immersed in the electrolyte for electrochemical pre-lithiation, the negative electrode sheet is first subjected to a brief high-temperature baking treatment, and then a reducing gas is introduced into the negative electrode sheet for pretreatment in a high-temperature environment. Among them, high-temperature baking can remove hydrophilic groups such as -OH adsorbed on the surface of the electrode sheet, clean impurities on the surface of the negative electrode sheet, and at the same time, it plays an activating role in the etching reaction of the reducing gas.

[0079] Optionally, the baking process described above can be carried out at a temperature of 100℃ to 800℃ for a time of 30s to 30min, which can achieve better results in removing impurities from the surface of the negative electrode and activating the negative electrode.

[0080] Please see Figure 4 The diagram illustrates a system structure schematic for performing the electrochemical pre-lithiation method in an embodiment of this application. Figure 4 As shown, the negative electrode sheet to be pre-lithiated is first placed in the heat treatment zone and baked at high temperature in an oxygen-free environment to remove surface impurities and activate it. Then, a reducing gas source is introduced to etch the surface. The treated negative electrode sheet, separator, and lithium source are then stacked in sequence and placed in the electrolyte. An external power supply is then connected, and the negative electrode sheet is connected to the negative terminal of the power supply, and the lithium source is connected to the positive terminal of the power supply. This applies a certain voltage between the negative electrode sheet and the lithium source L1, enabling electron and ion conduction and thus replenishing lithium to the negative electrode sheet.

[0081] This application also provides a pre-lithiated anode sheet, which is obtained by the method described above. The pre-lithiated anode sheet has a higher and more concentrated pre-lithiation load, which can balance the excess lithium consumed in the lithium battery reaction for a longer period, replenish the lithium consumed in the side reactions and SEI film formation process, improve the initial coulombic efficiency, extend the battery cycle life, alleviate volume expansion to some extent, and improve the overall performance of the lithium-ion battery.

[0082] This application also provides a lithium battery, which includes the pre-lithiated negative electrode sheet as described above, i.e., the pre-lithiated negative electrode sheet is used as the negative electrode of the lithium battery.

[0083] The present application will be described in detail below through embodiments.

[0084] Battery cycle life and energy density testing methods:

[0085] The charging and discharging voltage range is 3V to 4.5V, and the charging and discharging regime is 0.7C constant current to charge to the upper voltage limit and 0.2C constant current to discharge to the lower voltage limit.

[0086] Example 1

[0087] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0088] The negative electrode slurry, obtained by mixing the negative electrode active material (carbon-coated silicon suboxide), conductive agent (Super P), and binder (a mixture of SBR and CMC) in a mass ratio of 90:5:5, is coated onto copper foil and then dried and rolled to obtain the negative electrode sheet A1 to be replenished with lithium.

[0089] (2) High-temperature reducing gas surface-treated negative electrode A1:

[0090] The lithium anode sheet A1 to be supplemented was baked at high temperature in a nitrogen environment at 300℃ for 10 min. The baked A1 electrode sheet was then etched with a reducing gas to obtain a pretreated electrode sheet with good morphology, moderate etching degree, and some etch pits enlarged and interconnected. The reducing gas was a mixture of NH3 and H2, with an H2 flow rate of 3.6 mol / min and an NH3 / H2 flow rate ratio of 0.5. The electrode sheet was left to stand for 1 h.

[0091] (3) Adopt Figure 1 The electrochemical lithium replenishment device shown above replenishes lithium to the surface-pretreated negative electrode A1, wherein the lithium source is a lithium plate, and the power supply voltage between the negative electrode A1 and the lithium source is 0.5V; after the lithium replenishment is completed, the negative electrode is washed with organic solvent and dried to obtain the lithium-replenished negative electrode.

[0092] (4) Preparation of full cells:

[0093] A positive electrode slurry, prepared by mixing positive electrode active material (LiCoO2), conductive agent (Super P), and binder (PVDF) in a mass ratio of 96:2:2, is coated onto both sides of an aluminum foil. After drying and pressing, a positive electrode sheet is obtained. This positive electrode sheet, along with a separator and the aforementioned lithium-added negative electrode sheet, are stacked sequentially to form a battery cell. The battery cell is housed in a battery casing, and a 1 mol / L LiPF6 EC+DEC mixed electrolyte is injected, wherein the volume ratio of EC to DEC is 1:1. The battery casing is then sealed to obtain a full cell.

[0094] (5) Preparation of half-cell:

[0095] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0096] Example 2

[0097] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0098] The negative electrode slurry, obtained by mixing the negative electrode active material (carbon-coated silicon suboxide), conductive agent (Super P), and binder (a mixture of SBR and CMC) in a mass ratio of 90:5:5, is coated onto copper foil and then dried and rolled to obtain the negative electrode sheet A1 to be replenished with lithium.

[0099] (2) High-temperature reducing gas surface-treated negative electrode A1:

[0100] The lithium anode sheet A1 to be supplemented was baked at high temperature in a hydrogen environment at 500℃ for 1 minute. The baked A1 electrode sheet was then etched with a reducing gas to obtain a pretreated electrode sheet with good morphology, moderate etching degree, and some etch pits that were enlarged and interconnected. The reducing gas was a mixture of NH3 and H2, with an H2 flow rate of 3.6 mol / min and an NH3 / H2 flow rate ratio of 0.5. The electrode sheet was left to stand for 1 hour.

[0101] (3) Adopt Figure 1 The electrochemical lithium replenishment device shown above replenishes lithium to the surface-pretreated negative electrode A1, wherein the lithium source is a lithium plate, and the power supply voltage between the negative electrode A1 and the lithium source is 0.5V; after the lithium replenishment is completed, the negative electrode is washed with organic solvent and dried to obtain the lithium-replenished negative electrode.

[0102] (4) Preparation of full cells:

[0103] A positive electrode slurry, prepared by mixing positive electrode active material (LiCoO2), conductive agent (Super P), and binder (PVDF) in a mass ratio of 96:2:2, is coated onto both sides of an aluminum foil. After drying and pressing, a positive electrode sheet is obtained. This positive electrode sheet, along with a separator and the aforementioned lithium-added negative electrode sheet, are stacked sequentially to form a battery cell. The battery cell is housed in a battery casing, and a 1 mol / L LiPF6 EC+DEC mixed electrolyte is injected, wherein the volume ratio of EC to DEC is 1:1. The battery casing is then sealed to obtain a full cell.

[0104] (5) Preparation of half-cell:

[0105] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0106] Example 3

[0107] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0108] The negative electrode slurry, obtained by mixing the negative electrode active material (carbon-coated silicon suboxide), conductive agent (Super P), and binder (a mixture of SBR and CMC) in a mass ratio of 90:5:5, is coated onto copper foil and then dried and rolled to obtain the negative electrode sheet A1 to be replenished with lithium.

[0109] (2) High-temperature reducing gas surface-treated negative electrode A1:

[0110] The lithium anode sheet A1 to be supplemented was baked at high temperature in a nitrogen atmosphere at 300℃ for 10 min. The baked A1 electrode sheet was then etched with a reducing gas to obtain a pretreated electrode sheet with good morphology, moderate etching degree, and some etch pits enlarged and interconnected. The reducing gas selected was NH3 with a flow rate of 5.4 mol / min, and the electrode sheet was left to stand for 1 h.

[0111] (3) Adopt Figure 1 The electrochemical lithium replenishment device shown above replenishes lithium to the surface-pretreated negative electrode A1, wherein the lithium source is a lithium plate, and the power supply voltage between the negative electrode A1 and the lithium source is 0.5V; after the lithium replenishment is completed, the negative electrode is washed with organic solvent and dried to obtain the lithium-replenished negative electrode.

[0112] (4) Preparation of full cells:

[0113] A positive electrode slurry, prepared by mixing positive electrode active material (LiCoO2), conductive agent (Super P), and binder (PVDF) in a mass ratio of 96:2:2, is coated onto both sides of an aluminum foil. After drying and pressing, a positive electrode sheet is obtained. This positive electrode sheet, along with a separator and the aforementioned lithium-added negative electrode sheet, are stacked sequentially to form a battery cell. The battery cell is housed in a battery casing, and a 1 mol / L LiPF6 EC+DEC mixed electrolyte is injected, wherein the volume ratio of EC to DEC is 1:1. The battery casing is then sealed to obtain a full cell.

[0114] (5) Preparation of half-cell:

[0115] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0116] Example 4

[0117] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0118] The negative electrode slurry, obtained by mixing the negative electrode active material (carbon-coated silicon suboxide), conductive agent (Super P), and binder (a mixture of SBR and CMC) in a mass ratio of 90:5:5, is coated onto copper foil and then dried and rolled to obtain the negative electrode sheet A1 to be replenished with lithium.

[0119] (2) High-temperature reducing gas surface-treated negative electrode A1:

[0120] The lithium anode sheet A1 to be supplemented was baked at high temperature in a nitrogen atmosphere at 300℃ for 10 min. The baked A1 electrode sheet was then etched with a reducing gas to obtain a pretreated electrode sheet with good morphology, moderate etching degree, and some etch pits that were enlarged and interconnected. The reducing gas was a CH4 / H2 mixture with an H2 flow rate of 3.6 mol / min and a CH4 / H2 flow rate ratio of 0.5. The electrode sheet was left to stand for 1 h.

[0121] (3) Adopt Figure 1 The electrochemical lithium replenishment device shown above replenishes lithium to the surface-pretreated negative electrode A1, wherein the lithium source is a lithium plate, and the power supply voltage between the negative electrode A1 and the lithium source is 0.5V; after the lithium replenishment is completed, the negative electrode is washed with organic solvent and dried to obtain the lithium-replenished negative electrode.

[0122] (4) Preparation of full cells:

[0123] A positive electrode slurry, prepared by mixing positive electrode active material (LiCoO2), conductive agent (Super P), and binder (PVDF) in a mass ratio of 96:2:2, is coated onto both sides of an aluminum foil. After drying and pressing, a positive electrode sheet is obtained. This positive electrode sheet, along with a separator and the aforementioned lithium-added negative electrode sheet, are stacked sequentially to form a battery cell. The battery cell is housed in a battery casing, and a 1 mol / L LiPF6 EC+DEC mixed electrolyte is injected, wherein the volume ratio of EC to DEC is 1:1. The battery casing is then sealed to obtain a full cell.

[0124] (5) Preparation of half-cell:

[0125] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0126] Example 5

[0127] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0128] The negative electrode slurry, obtained by mixing the negative electrode active material (carbon-coated silicon suboxide), conductive agent (Super P), and binder (a mixture of SBR and CMC) in a mass ratio of 90:5:5, is coated onto copper foil and then dried and rolled to obtain the negative electrode sheet A1 to be replenished with lithium.

[0129] (2) High-temperature reducing gas surface-treated negative electrode A1:

[0130] The lithium anode sheet A1 to be supplemented was baked at high temperature in a nitrogen environment at 300℃ for 10 min. The baked A1 electrode sheet was then etched with a reducing gas to obtain a pretreated electrode sheet with good morphology, moderate etching degree, and some etch pits that were enlarged and interconnected. The reducing gas was a CO / H2 mixture with an H2 flow rate of 3.6 mol / min and a CO / H2 flow rate ratio of 0.5. The electrode sheet was left to stand for 1 h.

[0131] (3) Adopt Figure 1 The electrochemical lithium replenishment device shown above replenishes lithium to the surface-pretreated negative electrode A1, wherein the lithium source is a lithium plate, and the power supply voltage between the negative electrode A1 and the lithium source is 0.5V; after the lithium replenishment is completed, the negative electrode is washed with organic solvent and dried to obtain the lithium-replenished negative electrode.

[0132] (4) Preparation of full cells:

[0133] A positive electrode slurry, prepared by mixing positive electrode active material (LiCoO2), conductive agent (Super P), and binder (PVDF) in a mass ratio of 96:2:2, is coated onto both sides of an aluminum foil. After drying and pressing, a positive electrode sheet is obtained. This positive electrode sheet, along with a separator and the aforementioned lithium-added negative electrode sheet, are stacked sequentially to form a battery cell. The battery cell is housed in a battery casing, and a 1 mol / L LiPF6 EC+DEC mixed electrolyte is injected, wherein the volume ratio of EC to DEC is 1:1. The battery casing is then sealed to obtain a full cell.

[0134] (5) Preparation of half-cell:

[0135] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0136] Comparative Example 1

[0137] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0138] The negative electrode slurry, obtained by mixing the negative electrode active material (carbon-coated silicon suboxide), conductive agent (Super P), and binder (a mixture of SBR and CMC) in a mass ratio of 90:5:5, is coated onto copper foil and then dried and rolled to obtain the negative electrode sheet A1 to be replenished with lithium.

[0139] (2) Adopt Figure 1 The electrochemical lithium replenishment device shown above replenishes lithium to the surface-pretreated negative electrode A1, wherein the lithium source is a lithium plate, and the power supply voltage between the negative electrode A1 and the lithium source is 0.5V; after the lithium replenishment is completed, the negative electrode is washed with organic solvent and dried to obtain the lithium-replenished negative electrode.

[0140] (3) Preparation of full cells:

[0141] A positive electrode slurry, prepared by mixing positive electrode active material (LiCoO2), conductive agent (Super P), and binder (PVDF) in a mass ratio of 96:2:2, is coated onto both sides of an aluminum foil. After drying and pressing, a positive electrode sheet is obtained. This positive electrode sheet, along with a separator and the aforementioned lithium-added negative electrode sheet, are stacked sequentially to form a battery cell. The battery cell is housed in a battery casing, and a 1 mol / L LiPF6 EC+DEC mixed electrolyte is injected, wherein the volume ratio of EC to DEC is 1:1. The battery casing is then sealed to obtain a full cell.

[0142] (4) Preparation of half-cell:

[0143] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0144] Sample performance testing:

[0145] The cycle life and energy density of the full cells prepared in each of the above embodiments were tested sequentially, and the first-cycle coulombic efficiency of the half cells prepared in each of the above embodiments was tested sequentially. The full cell test was performed by charging at 0.2C to 4.45V and discharging at 0.2C to 2.75V; the half cell test was performed by charging at 0.1C to 4.5V and discharging at 0.1C to 3V. The test results are shown in Table 1 below.

[0146] Based on the sample performance test results of Examples 1-5 and Comparative Example 1 in Table 1, compared with Comparative Example 1 which did not undergo high-temperature reducing gas surface pretreatment before lithium replenishment, Examples 1-5 of this application all underwent surface pretreatment with reducing gas at high temperature before lithium replenishment, which improved the lithium replenishment effect of the negative electrode. Correspondingly, the electrochemical performance of the battery made from the negative electrode with plasma surface treatment is better.

[0147] Furthermore, a comparison of the results between Example 1 and Example 2 shows that hydrogen gas is more effective than nitrogen gas in cleaning oxygen-containing groups and oil stains at high temperatures.

[0148] By comparing Example 1 and Example 3, it can be seen that introducing a mixed gas has a better etching effect than introducing a single gas.

[0149] By comparing Example 1 with Examples 4 and 5, it can be seen that using NH3 / H2 mixed gas as a reducing gas has moderate reducing properties, which can better improve the lithium replenishment effect of the negative electrode and improve the electrochemical performance of the battery.

[0150] Table 1

[0151]

[0152] In summary, in this embodiment, the negative electrode sheet to be pre-lithiated is first heat-treated in a reducing gas environment; then, after heat treatment, the negative electrode sheet is subjected to electrochemical pre-lithiation treatment, which can effectively solve the technical problem of poor lithium replenishment effect of existing electrochemical pre-lithiation treatment for negative electrode sheets.

[0153] Although preferred embodiments of the present application have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the embodiments of the present application.

[0154] The above provides a detailed description of the electrochemical pre-lithiation method, pre-lithiation negative electrode, and lithium battery provided in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the method and its core ideas. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. An electrochemical pre-lithiation method, characterized in that, include: Provide negative electrode sheets for pre-lithiation; In a reducing gas environment, the negative electrode is heat-treated to remove the oxide layer on the surface of the negative electrode, generate reducing electrophilic groups, and form at least one of the following on the surface of the negative electrode: etching pits, channels, and wrinkles. After heat treatment, the negative electrode sheet undergoes electrochemical pre-lithiation treatment; The reducing gas consists of NH3 and H2; In the reducing gas, the flow rate ratio of NH3 to H2 is 1:4 to 4:

1.

2. The method according to claim 1, characterized in that, During the heat treatment of the negative electrode, the flow rate ratio of NH3 to H2 in the reducing gas is 1:2 to 2:

1.

3. The method according to claim 1, characterized in that, The heat treatment temperature is 100℃~800℃, and the time is 0.5~2h.

4. The method according to claim 1, characterized in that, Before heat treatment of the negative electrode sheet in a reducing gas environment, the method further includes: The negative electrode sheet is baked in an oxygen-free environment.

5. The method according to claim 4, characterized in that, The baking process is carried out at a temperature of 100℃ to 800℃ for a time of 30 seconds to 30 minutes.

6. A pre-lithiated anode sheet, characterized in that, Obtained by processing using the method described in any one of claims 1 to 5.

7. A lithium battery, characterized in that, Including the pre-lithiated anode as described in claim 6.

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