An electrochemical pre-lithiation method, system, pre-lithiated negative electrode sheet and lithium battery

Abstract

The application provides an electrochemical pre-lithiation method, system, pre-lithiated negative electrode sheet and lithium battery. The method comprises the following steps: performing plasma treatment on a negative electrode sheet to be pre-lithiated in a nitrogen-containing reducing gas environment; and performing electrochemical pre-lithiation treatment on the negative electrode sheet after the plasma treatment. In the application, the plasma treatment can not only remove the hydrophilic oxide groups adsorbed on the surface of the electrode sheet, generate wrinkles and etching channels, and improve the uniformity of electrolyte immersion and pre-lithiation, but also can perform nitrogen doping on the surface of the negative electrode, improve the conductivity of the electrode sheet, improve the utilization rate of the lithium source, and save the pre-lithiation cost.

Description

Technical Field

[0001] This application relates to the field of lithium battery technology, and in particular to an electrochemical pre-lithiation method, system, pre-lithiation negative electrode and 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, system, pre-lithiation negative electrode and lithium battery, so as to solve the problem that the existing technology of pre-lithiation of negative electrode 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 sheet is subjected to plasma treatment in a nitrogen-containing reducing gas environment;

[0011] After plasma treatment, the negative electrode is subjected to electrochemical pre-lithiation treatment.

[0012] Furthermore, in the method, the nitrogen-containing reducing gas includes NH3.

[0013] Furthermore, in the method, the nitrogen-containing reducing gas also includes N2.

[0014] Furthermore, in the method, the flow rate ratio of NH3 to N2 in the nitrogen-containing reducing gas is 0.25:1 to 4:1.

[0015] Furthermore, in the method described, during the plasma treatment of the negative electrode, the flow rate of the nitrogen-containing reducing gas is 50 sccm to 300 sccm, and the moving speed of the negative electrode is 5 m / min to 20 m / min.

[0016] This application also provides a pre-lithiated anode sheet, which is obtained by the method described above.

[0017] This application also provides a lithium battery, which includes a pre-lithiated negative electrode as described above.

[0018] This application also provides an electrochemical pre-lithiation system, wherein the electrochemical pre-lithiation method described above is implemented;

[0019] The system includes a negative electrode plasma treatment device and an electrochemical pre-lithiation device;

[0020] The negative electrode plasma treatment device is used to perform plasma treatment on the negative electrode to be pre-lithiated in a nitrogen-containing reducing gas environment.

[0021] The electrochemical pre-lithiation device is used to perform electrochemical pre-lithiation treatment on the negative electrode sheet after plasma treatment.

[0022] The negative electrode plasma processing device includes: a plasma discharge tube, a first insulating plug, a second insulating plug, a first electrode, a second electrode, and a power supply;

[0023] The first insulating plug and the second insulating plug are respectively disposed at both ends of the plasma discharge tube;

[0024] The first electrode is arranged along the axial direction of the plasma discharge tube, and the first electrode is electrically connected to the power supply;

[0025] The second electrode is disposed on the wall of the plasma discharge tube, and the second electrode is grounded;

[0026] The plasma discharge tube is provided with an air inlet for allowing nitrogen-containing reducing gas to enter.

[0027] The lower part of the first insulating plug and / or the lower part of the second insulating plug are provided with a first through hole for the nitrogen-containing reducing gas to flow out;

[0028] The upper parts of the first insulating plug and the upper parts of the second insulating plug are provided with a second through hole, which is used for the negative electrode sheet to be processed to pass through.

[0029] Furthermore, in the system, the first electrode penetrates the plasma discharge tube, and both ends of the first electrode are fixed to the first insulating plug and the second insulating plug, respectively; both ends of the first electrode are electrically connected to the power supply; both ends of the first electrode are electrically connected to the power supply.

[0030] Furthermore, in the system described above, the plasma discharge tube is a hollow quartz tube.

[0031] Compared with the prior art, the embodiments of this application have the following advantages:

[0032] The electrochemical pre-lithiation method provided in this application first involves plasma treatment of the negative electrode sheet to be pre-lithiated in a nitrogen-containing reducing gas environment; then, after plasma treatment, the negative electrode sheet undergoes electrochemical pre-lithiation treatment. The plasma treatment 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 nitrogen doping the negative electrode surface improves electrode conductivity, increases lithium source utilization, and reduces pre-lithiation costs.

[0033] 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

[0034] Figure 1 This is a schematic diagram of the electrochemical pre-lithiation device in the embodiments of this application;

[0035] Figure 2 This is a flowchart of the electrochemical pre-lithiation method provided in the embodiments of this application;

[0036] Figure 3 This is a schematic diagram of the negative electrode surface after plasma treatment in an embodiment of this application;

[0037] Figure 4 This is a schematic diagram of the negative electrode plasma processing device provided in the embodiments of this application;

[0038] Figure 5 This is a schematic diagram of the interface of the first insulating plug in an embodiment of this application. Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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 an electronic pathway and an ion pathway between the negative electrode and the lithium source, thereby achieving lithium replenishment of the negative electrode.

[0046] 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. Due to the poor conductivity of SiO, the circuit conduction in the electrode sheet pre-lithiation process relies entirely on the C skeleton in the electrode sheet. However, due to the influence of binders, the size of the gaps between particles, and other factors, the overall conductivity of the electrode sheet is still insufficient, resulting in an unsatisfactory pre-lithiation effect; 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. In fact, these oxides may directly undergo side reactions, causing byproducts to cover the electrode sheet, making it more difficult for the electrolyte to penetrate.

[0047] 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 S101 to S102 are included:

[0048] Step S101: In a nitrogen-containing reducing gas environment, the negative electrode sheet to be pre-lithiated is subjected to plasma treatment.

[0049] In step S101 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.

[0050] 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.

[0051] In this embodiment, the materials of the negative electrode are not specifically limited.

[0052] 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.

[0053] 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.

[0054] 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%.

[0055] 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.

[0056] 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%.

[0057] In step S101 above, before the negative electrode is formally immersed in the electrolyte for electrochemical pre-lithiation, the electrode is first subjected to room-temperature plasma gas treatment. Plasma is an ionized gas composed of negative ions, positive ions, and neutral particles, and is electrically neutral overall. Because plasma can interact physically and chemically with the surface matrix molecules, it implants functional groups on the surface and produces etching and chemical modification, changing the surface state of the electrode to improve its wettability with the electrolyte and allowing for appropriate etching and nitriding.

[0058] In step S101 above, only a plasma discharge tube needs to be added to the existing production line structure, a high-frequency voltage is applied, and air is circulated for plasma treatment. There is no need to make too many changes to the original traditional structure, which has the natural advantage of being compatible with the original structure.

[0059] In step S101 above, under normal temperature and pressure conditions, a suitable nitrogen-containing reducing gas, negative electrode moving speed, and airflow velocity are used to generate plasma-state gas through high-frequency voltage, which reacts with the surface of the negative electrode to perform nitriding and etching on the surface of the negative electrode. Here, normal pressure is one standard atmosphere, i.e., 101 kPa, and normal temperature is 25–27°C.

[0060] The presence of reducing gas removes the oxide layer and surface groups with poor affinity to the electrolyte from the electrode surface, improving the wettability of the electrode and electrolyte, and enhancing the pre-lithiation uniformity. It also etches 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 electrolyte penetration efficiency, greatly increasing pre-lithiation efficiency. Simultaneously, the presence of reducing gas causes the electrode surface material to react and generate reducing groups, greatly improving the affinity between the electrolyte and the electrode material, thus effectively improving pre-lithiation uniformity and lithium source utilization, and saving pre-lithiation costs. Furthermore, the nitriding effect of the plasma gas on the surface generates a large amount of pyridine nitrogen and pyrrole nitrogen, producing sp... 2 CN, sp 3 Incorporating elements such as CN can significantly improve the conductivity and structural stability of materials. Furthermore, incorporating nitrogen into the C framework can promote the electrolyte wetting process and provide more active sites for lithium ion adsorption.

[0061] Optionally, in one embodiment, in step S101 above, the nitrogen-containing reducing gas includes NH3, which can provide N element while achieving the reducing effect, thereby better performing nitriding on the surface of the negative electrode. This utilizes the delocalized electrons of N element to improve the conductivity of the electrode, promote the electrolyte wetting process, and provide more active sites for lithium ion adsorption, thus improving the electrochemical pre-lithiation effect. In addition, due to the presence of the 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 the lithium source, and saving pre-lithiation costs.

[0062] Optionally, in one embodiment, the nitrogen-containing reducing gas further includes N2, that is, the nitrogen-containing reducing gas is an NH3 / N2 mixture. Since a single NH3 gas source has high reducing power, it is difficult to control the etching effect on the electrode. Incorporating neutral gas N2 can adjust the overall reducing power of the gas source, thereby adjusting the final etching degree of the electrode. Furthermore, incorporating different gases can increase the nitrogen source for the nitrogen doping reaction, which is beneficial for nitrogen doping on the electrode surface.

[0063] Optionally, the flow rate ratio of NH3 to N2 in the aforementioned nitrogen-containing reducing gas is 0.25:1 to 4:1. If the flow rate of NH3 is too high and the flow rate of N2 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 N2 is too high, the overall reducing power of the gas source may be insufficient, making it difficult to effectively etch the surface of the electrode through plasma treatment. Preferably, the flow rate ratio of NH3 to N2 is 1:1.

[0064] In the plasma treatment process described above, by adjusting the gas source airflow rate and power frequency, the degree of nitriding and etching on the electrode surface can be precisely controlled, ensuring the surface pretreatment effect while taking into account the amount and strength of the negative electrode coating.

[0065] Optionally, during the plasma treatment of the negative electrode, the flow rate of the nitrogen-containing reducing gas is controlled to be 50 sccm to 300 sccm, such as 50 sccm, 100 sccm, 200 sccm, 300 sccm, etc., preferably 200 sccm.

[0066] Optionally, during the plasma treatment of the negative electrode, the moving speed of the negative electrode is controlled to be 5 m / min to 20 m / min, such as 5 m / min, 10 m / min, 20 m / min, etc., preferably 10 m / min.

[0067] Since the above step S101 can be carried out under normal temperature and pressure, there is no need to build an additional closed system. It is only necessary to prepare a quartz tube that can generate plasma, allow nitrogen-containing reducing gas to pass through, and allow the negative electrode to pass through. The equipment can be recycled. In particular, by designing multiple channels in the insulating plug of the above quartz tube for the electrode to pass through, energy consumption can be reduced, gas utilization can be improved, and pretreatment efficiency can be improved.

[0068] Step S102: After plasma treatment, the negative electrode is subjected to electrochemical pre-lithiation treatment.

[0069] In step S102 above, the negative electrode sheet that has been processed in step S101 is subjected to conventional electrochemical pre-lithiation treatment to obtain a pre-lithiation negative electrode sheet.

[0070] Specifically, in step S102 above, as follows: 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.

[0071] In step S102 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.

[0072] 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-5cm, preferably 3mm-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-1mm, preferably 3μm-200μm.

[0073] In step S102 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] In the non-aqueous electrolyte, the concentration of the electrolyte lithium salt is 0.1–15 mol / L, preferably 1–10 mol / L.

[0078] In step S102, since the negative electrode has already been processed in step S101, a large number of etched pits, wrinkles, and conductive groups (sp) have been formed on its surface. 2 CN, sp 3 CN, etc., surface morphology of the negative electrode plate, such as Figure 3 As shown, this can increase the specific surface area of ​​the electrode surface reacting with the electrolyte, improve the conductivity and structural stability of the material, greatly enhance the efficiency of electrolyte immersion in the material, and significantly improve the pre-lithiation efficiency.

[0079] The electrochemical pre-lithiation method provided in this application first performs plasma treatment on the negative electrode sheet to be pre-lithiated in a nitrogen-containing reducing gas environment; then, after plasma treatment, the negative electrode sheet undergoes electrochemical pre-lithiation treatment. The plasma treatment 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 nitrogen-dops the negative electrode surface, improving electrode conductivity, increasing lithium source utilization, and saving pre-lithiation costs. Simultaneously, by adjusting the gas source flow rate and power frequency, the degree of nitrogen diffusion and etching on the electrode surface can be precisely controlled, thus ensuring the surface pretreatment effect while considering the amount and intensity of lithium replenishment on the negative electrode sheet.

[0080] This application also provides an electrochemical pre-lithiation system for implementing the electrochemical pre-lithiation method as described above;

[0081] The system includes a negative electrode plasma treatment device and an electrochemical pre-lithiation device; the negative electrode plasma treatment device is used to perform plasma treatment on the negative electrode to be pre-lithiated in a nitrogen-containing reducing gas environment; the electrochemical pre-lithiation device is used to perform electrochemical pre-lithiation treatment on the negative electrode after plasma treatment.

[0082] The structure of the above-mentioned electrochemical pre-lithiation device is as follows: Figure 1 As shown;

[0083] The aforementioned negative electrode plasma processing device 40, such as Figures 4-5 As shown, it includes a plasma discharge tube 41, a first insulating plug 42, a second insulating plug 43, a first electrode 44, a second electrode 45, and a power supply 46;

[0084] The first insulating plug 42 and the second insulating plug 43 are respectively disposed at both ends of the plasma discharge tube 41;

[0085] The first electrode 44 is arranged along the axial direction of the plasma discharge tube 41 and is electrically connected to the power supply 46; the second electrode 45 is arranged on the tube wall of the plasma discharge tube 41 and is grounded.

[0086] The plasma discharge tube 41 is provided with an air inlet 47 for supplying nitrogen-containing reducing gas; the lower part of the first insulating plug 42 and / or the lower part of the second insulating plug 43 are provided with a first through hole 48 for supplying nitrogen-containing reducing gas; the first through hole 48 can be circular or square.

[0087] A second through hole 49 is provided opposite to the upper part of the first insulating plug 42 and the upper part of the second insulating plug 43. The second through hole 49 is used for the negative electrode sheet to be processed to pass through. The second through hole 49 is square to match the shape of the electrode sheet.

[0088] In the system provided in this embodiment, the first insulating plug 42 and the second insulating plug 43 are respectively disposed at both ends of the plasma discharge tube 41, that is, the two ends of the plasma discharge tube 41 are blocked by the first insulating plug 42 and the second insulating plug 43. The plasma discharge tube 41 can be a hollow quartz tube with a straight cylindrical shape to facilitate the passage of the electrode.

[0089] The first electrode 44 is arranged along the axial direction of the plasma discharge tube 41 and electrically connected to the power supply 46, while the second electrode 45 is disposed on the tube wall of the plasma discharge tube 41 and grounded. This allows a high voltage to be generated between the first electrode 44 and the second electrode 45, facilitating the electron interaction of the flowing gas to form plasma gas. The power supply 46 has a power of 0–500 W, a frequency of 10–20 kHz, and a voltage of 0–10 kV.

[0090] The upper parts of the first insulating plug 42 and the upper parts of the second insulating plug 43 are respectively provided with second through holes 49 for the negative electrode sheet 50 to be processed to pass through. This allows the negative electrode sheet 50 to enter the plasma discharge tube 41 through the second through hole 49 on the first insulating plug 42, then pass through the plasma discharge tube 41, and then exit the plasma discharge tube 41 through the second through hole 49 on the second insulating plug 43. At the same time, because the plasma discharge tube 41 is provided with an inlet 47 for nitrogen-containing reducing gas to enter, and the lower parts of the first insulating plug 42 and / or the lower parts of the second insulating plug 43 are provided with first through holes 48 for nitrogen-containing reducing gas to flow out, the formed plasma gas can be forced to have a longer contact distance with the negative electrode sheet 50, prolonging the nitriding and etching process, thereby improving the pretreatment effect on the negative electrode sheet 50.

[0091] Optionally, the aforementioned negative electrode plasma processing device 40 further includes a support 51, on which the plasma discharge tube 41 is disposed. Fixed pulleys 52 are provided at both ends of the support 51. The fixed pulleys 52 are used to wind and support the negative electrode 50 as it enters the plasma discharge tube 41 from the first insulating plug 42 and as it exits the plasma discharge tube 41 from the second insulating plug 43. To achieve automated movement of the negative electrode, the device further includes a winding machine 53, which is connected to the negative electrode and used to wind and drive the negative electrode 50 through the second through hole 49 into the plasma discharge tube 41.

[0092] Optionally, the first electrode 44 penetrates the plasma discharge tube 41, and the two ends of the first electrode 44 are respectively fixed to the first insulating plug 42 and the second insulating plug 43. The first insulating plug 42 and the second insulating plug 43 are provided with a third through hole 54 for mounting and fixing the first electrode 44. The first electrode 44 is cylindrical, and the third through hole 54 can be set to be circular to match the shape of the first electrode 44.

[0093] Optionally, both ends of the first electrode 44 are electrically connected to the power supply 46. While improving the stability of the first electrode 44, it can also allow the first electrode 44 to come into contact with more reducing gases, forming more plasma gas. This allows more plasma gas to pass through the negative electrode, prolonging the nitriding and etching process, thereby improving the pretreatment effect on the negative electrode.

[0094] 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.

[0095] 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.

[0096] The present application will be described in detail below through embodiments.

[0097] Battery cycle life and energy density testing methods:

[0098] The charging and discharging voltage range is 3V-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.

[0099] Example 1

[0100] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0101] 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.

[0102] (2) Room temperature plasma gas surface treatment:

[0103] pass Figure 4 A NH3 / N2 mixture is introduced through the central air inlet 47 at a flow ratio of 1:1 and a gas velocity of 200 sccm, filling the plasma discharge tube with the reducing mixture; then the circuit is opened. Figure 4 The power supply 46 is set to a voltage of 250V to rapidly plasma-encode the reducing mixed gas entering the discharge tube; the winding machine is started to begin surface pretreatment, with the winding speed set to 10m / min, thereby obtaining a negative electrode sheet with a surface treated by plasma gas, moderate etching degree, and nitrogen doping.

[0104] (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.

[0105] (4) Preparation of full cells:

[0106] 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.

[0107] (5) Preparation of half-cell:

[0108] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0109] Example 2

[0110] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0111] 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.

[0112] (2) Room temperature plasma gas surface treatment:

[0113] pass Figure 4 NH3 is introduced through the central air inlet 47 at a flow rate of 200 sccm, filling the plasma discharge tube with NH3; then the circuit is opened. Figure 4 The power supply 46 is set to a voltage of 250V to rapidly plasma-encode the reducing mixed gas entering the discharge tube; the winding machine is started to begin surface pretreatment, with the winding speed set to 10m / min, thereby obtaining a negative electrode sheet with a surface treated by plasma gas, moderate etching degree, and nitrogen doping.

[0114] (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.

[0115] (4) Preparation of full cells:

[0116] 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.

[0117] (5) Preparation of half-cell:

[0118] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0119] Example 3

[0120] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0121] 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.

[0122] (2) Room temperature plasma gas surface treatment:

[0123] pass Figure 4 N2 is introduced through the central air inlet 47 at a flow rate of 200 sccm, filling the plasma discharge tube with N2; then the circuit is opened. Figure 4 The power supply 46 is set to a voltage of 250V to rapidly plasma-encode the reducing mixed gas entering the discharge tube; the winding machine is started to begin surface pretreatment, with the winding speed set to 10m / min, thereby obtaining a negative electrode sheet with a surface treated by plasma gas, moderate etching degree, and nitrogen doping.

[0124] (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.

[0125] (4) Preparation of full cells:

[0126] 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.

[0127] (5) Preparation of half-cell:

[0128] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0129] Example 4

[0130] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0131] 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.

[0132] (2) Room temperature plasma gas surface treatment:

[0133] pass Figure 4 An NH3 / N2 mixture is introduced through the central air inlet 47 at a flow ratio of 0.5:1 and a gas velocity of 200 sccm, filling the plasma discharge tube with the reducing mixture; then the circuit is opened. Figure 4 The power supply 46 is set to a voltage of 250V to rapidly plasma-encode the reducing mixed gas entering the discharge tube; the winding machine is started to begin surface pretreatment, with the winding speed set to 10m / min, thereby obtaining a negative electrode sheet with a surface treated by plasma gas, moderate etching degree, and nitrogen doping.

[0134] (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.

[0135] (4) Preparation of full cells:

[0136] 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.

[0137] (5) Preparation of half-cell:

[0138] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0139] Example 5

[0140] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0141] 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.

[0142] (2) Room temperature plasma gas surface treatment:

[0143] pass Figure 4 A mixture of NH3 / N2 gas is introduced through the central air inlet 47 at a flow ratio of 2:1 and a gas velocity of 200 sccm, filling the plasma discharge tube with the reducing mixture; then the process is initiated. Figure 4 The power supply 46 is set to a voltage of 250V to rapidly plasma-encode the reducing mixed gas entering the discharge tube; the winding machine is started to begin surface pretreatment, with the winding speed set to 10m / min, thereby obtaining a negative electrode sheet with a surface treated by plasma gas, moderate etching degree, and nitrogen doping.

[0144] (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.

[0145] (4) Preparation of full cells:

[0146] 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.

[0147] (5) Preparation of half-cell:

[0148] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0149] Comparative Example 1

[0150] (1) Preparation of the negative electrode A1 to be lithium supplemented:

[0151] 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.

[0152] (2) Adopt Figure 1 The electrochemical lithium replenishment device shown replenishes lithium on the negative electrode A1 to be replenished, 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.

[0153] (3) Preparation of full cells:

[0154] 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.

[0155] (4) Preparation of half-cell:

[0156] The lithium-added negative electrode sheet and the lithium metal sheet are assembled into a coin cell to obtain a half cell.

[0157] Sample performance testing:

[0158] 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 to 4.45V at 0.2C and discharging to 2.75V at 0.2C. The half cell test was performed by charging to 4.5V at 0.1C and discharging to 3V at 0.1C. The test results are shown in Table 1 below.

[0159] 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 room temperature plasma gas surface pretreatment before lithium replenishment, Examples 1-5 of this application all used N-containing gas plasma for surface pretreatment before lithium replenishment of the negative electrode, 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.

[0160] In addition, a comparison of the results of Example 1 and Example 2 shows that, compared with a single gas source, the mixed gas has advantages such as moderate reducing properties and richer nitrogen source, which can achieve better etching and nitrogen doping effects, thereby improving the pre-lithiation effect.

[0161] By comparing Example 1 with Examples 3-5, it can be seen that when the ratio of NH3 / N2 mixed gas is 1:1, the surface pretreatment effect can be better achieved, the lithium replenishment effect of the negative electrode can be improved, and the electrochemical performance of the battery can be improved.

[0162] Table 1

[0163]

[0164] In summary, in this embodiment, the negative electrode sheet to be pre-lithiated is first subjected to plasma treatment in a nitrogen-containing reducing gas environment; then, after plasma 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.

[0165] 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.

[0166] The above provides a detailed description of the electrochemical pre-lithiation method, apparatus, 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 core ideas of this application. 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: In a nitrogen-containing reducing gas environment, the negative electrode sheet to be pre-lithiated is subjected to plasma treatment; After plasma treatment, the negative electrode sheet undergoes electrochemical pre-lithiation treatment. The nitrogen-containing reducing gas includes NH3 and N2, and the flow rate ratio of NH3 to N2 is 0.25:1 to 4:

1.

2. The method according to claim 1, characterized in that, During the plasma treatment of the negative electrode, the flow rate of the nitrogen-containing reducing gas is 50 sccm to 300 sccm, and the moving speed of the negative electrode is 5 m / min to 20 m / min.

3. The method according to any one of claims 1 to 2, characterized in that, The electrochemical pre-lithiation method is implemented using the following electrochemical pre-lithiation system; The electrochemical pre-lithiation system includes a negative electrode plasma treatment device and an electrochemical pre-lithiation device. The negative electrode plasma treatment device is used to perform plasma treatment on the negative electrode to be pre-lithiated in a nitrogen-containing reducing gas environment. The electrochemical pre-lithiation device is used to perform electrochemical pre-lithiation treatment on the negative electrode after plasma treatment. The negative electrode plasma processing device includes a plasma discharge tube, a first insulating plug, a second insulating plug, a first electrode, a second electrode, and a power supply; The first insulating plug and the second insulating plug are respectively disposed at both ends of the plasma discharge tube; The first electrode is arranged along the axial direction of the plasma discharge tube, and the first electrode is electrically connected to the power supply; The second electrode is disposed on the wall of the plasma discharge tube, and the second electrode is grounded; The plasma discharge tube is provided with an air inlet for allowing nitrogen-containing reducing gas to enter. The lower part of the first insulating plug and / or the lower part of the second insulating plug are provided with a first through hole for the nitrogen-containing reducing gas to flow out; The upper parts of the first insulating plug and the upper parts of the second insulating plug are provided with a second through hole, which is used for the negative electrode sheet to be processed to pass through.

4. The method according to claim 3, characterized in that, The first electrode passes through the plasma discharge tube, and its two ends are fixed to the first insulating plug and the second insulating plug, respectively; both ends of the first electrode are electrically connected to the power supply.

5. The method according to claim 3, characterized in that, The plasma discharge tube is a hollow quartz tube.

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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