A prelithiated negative active material and device

Abstract

The application relates to the technical field of batteries, in particular to a pre-lithiation negative electrode active material and device. The pre-lithiation negative electrode active material comprises negative electrode active material particles and a first SEI film, and the first SEI film is wrapped on the surface of the negative electrode active material particles. The application solves the problems of incomplete pre-lithiation of a conventional metal lithium source lithium supplementing mode and low lithium source utilization rate. Generally, SEI is formed in a full battery, which simultaneously influences the positive electrode and the negative electrode. The method of the application preferentially forms the SEI film outside the full battery, is not limited by battery materials, improves the initial efficiency and energy density of the battery, and improves the cycle life of the battery.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a pre-lithiated negative electrode active material and device. BACKGROUND

[0002] In recent years, the rapid development of portable electronic products and new energy vehicles has continuously put forward higher requirements for the performance of lithium ion batteries, among which the improvement of battery energy density is the most urgent. Under the existing lithium ion battery system, the battery structure is optimized, the positive and negative electrode materials are iterated, such as using high-nickel ternary and high-voltage nickel-manganese materials for the positive electrode, using high-capacity silicon and tin-based alloy negative electrode for the negative electrode, and using lithium ion battery lithium supplement technology to improve the initial efficiency of the battery, which is an effective way to improve the energy density of the battery.

[0003] During the first charge and discharge process of the battery, a solid electrolyte interface (SEI) is formed on the negative electrode side. The irreversible capacity loss of the most widely used graphite negative electrode is more than 6%, while for silicon-based and tin-based alloy negative electrodes with high specific capacity, the irreversible capacity loss is even as high as 10% to 20% or more, which reduces the overall energy density of the battery. Lithium supplement technology can improve the short board of low initial efficiency and fully exert the advantages of high capacity, which is an effective means to solve this problem.

[0004] The negative electrode side lithium supplement technology includes metal lithiumization physical lithiumization, chemical lithiumization, and electrochemical pre-lithiation. The current process lithium supplement method involves rolling the metal lithium foil to a thickness of several microns, then compounding and rolling it with the negative electrode. After the battery is filled with liquid, these metal lithiums quickly react with the negative electrode and are embedded in the negative electrode material, thereby improving the initial efficiency of the material. This lithium supplement method is simple and efficient, but the utilization rate of lithium source is often less than 65%, which easily forms "dead lithium" to hinder the diffusion and mass transfer of lithium ions, leading to larger polarization of the battery and lithium precipitation phenomenon, making it impossible to be applied on a large scale; the application of lithium supplement technology not only improves the capacity of lithium ion batteries, but also improves the cycle life of the battery, but the additional lithium supplement material reduces the proportion of active materials in the electrode.

[0005] Therefore, how to achieve non-damage pre-lithiation is a challenging problem. Developing high-safety and low-cost lithium supplement technology to improve the energy density and cycle life of lithium ion batteries is crucial for the development of lithium ion batteries. SUMMARY

[0006] Therefore, the present application provides a pre-lithiated negative electrode active material and device. The pre-lithiated negative electrode active material is used to improve the initial efficiency of the battery, fully exert the capacity of the battery, improve the cycle life and electrochemical performance of the battery, and can also be well compatible with the existing battery manufacturing process, which opens up a new way for commercial application.

[0007] To achieve the above-mentioned object, the present application provides the following technical solutions.

[0008] The present application provides a pre-lithiated negative active material, which comprises negative active material particles and a first SEI film, and the first SEI film is wrapped on the surface of the negative active material particles.

[0009] In the embodiments provided by the present application, the negative active material particles are primary particles or secondary particles.

[0010] The "primary particles" in the present application are un-agglomerated particles. The "secondary particles" in the present application are agglomerated particles.

[0011] In the embodiments provided by the present application, the secondary particles are agglomerates of at least 2 primary particles, or agglomerates of at least 2 primary particles with a second SEI film wrapped on the surface.

[0012] As preferred, the particle size D 50 of the primary particles is 3-15 μm.

[0013] As preferred, the particle size D 50 of the secondary particles is 6-30 μm.

[0014] In the embodiments provided by the present application, when the negative active material particles are primary particles or agglomerates of at least 2 primary particles, the pre-lithiated negative active material comprises the first SEI film and does not comprise the second SEI film, and the thickness of the first SEI film is 2-4 nm.

[0015] In the embodiments provided by the present application, when the negative active material particles are agglomerates of at least 2 primary particles with a second SEI film wrapped on the surface, the pre-lithiated negative active material comprises the first SEI film and the second SEI film, the thickness of the first SEI film is 2-3 nm, and the thickness of the second SEI film is 2-4 nm.

[0016] As preferred, the first SEI film or the second SEI film comprises a lithium-containing compound; the lithium-containing compound comprises one or more of Li2CO3, LiF, Li2O, LiOH, ROCO2Li, ROLi, (ROCO2Li)2, wherein R is an alkyl group.

[0017] As preferred, the molar ratio of the negative active material to the lithium-containing compound is 1:(3-10); preferably 1:(3-6).

[0018] As preferred, in the first SEI film or the second SEI film, the mass percentage of Li2CO3 is 20%-40%, and the mass percentage of LiF is 10%-20%.

[0019] In the embodiments provided in the present application, the mass percentage of Li2O is 5% to 10%.

[0020] In the embodiments provided in the present application, the mass percentage of LiOH is 5% to 10%.

[0021] In the embodiments provided in the present application, the mass percentage of ROCO2Li is 5% to 10%.

[0022] In the embodiments provided in the present application, the mass percentage of ROLi is 5% to 10%.

[0023] In the embodiments provided in the present application, the mass percentage of (ROCO2Li)2 is 4% to 8%.

[0024] Preferably, the specific surface area of the pre-lithiated negative active material is 1 to 15 m 2 / g.

[0025] Preferably, the negative active material is one or more of graphite, hard carbon, silicon negative material, titanium-based material, silicon-based material, and tin-based material.

[0026] In the embodiments provided in the present application, the first formation efficiency of the pre-lithiated negative active material is greater than 94%.

[0027] The present application also provides a preparation method of the pre-lithiated negative active material, which comprises: performing pre-lithiation treatment on the negative active material particles by using an electrochemical pre-lithiation technology in a reducing gas atmosphere to obtain the pre-lithiated negative active material.

[0028] In the embodiments provided in the present application, the electrolytic device used in the electrochemical pre-lithiation technology uses lithium foil as a reference electrode and a counter electrode, and an ion-conducting diaphragm is arranged between the anode and the cathode as a barrier; the electrolytic device is connected with a constant potential instrument.

[0029] Preferably, the solute of the electrolyte used in the electrochemical pre-lithiation technology is one or more of LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiN(CF3SO2)2, LiNO3, LiPF6, and LiTFSI.

[0030] Preferably, the solute of the electrolyte is a mixture of LiNO3 and LiTFSI, or LiPF6.

[0031] Preferably, when the solute of the electrolyte is a mixture of LiNO3 and LiTFSI, the concentration of LiNO3 is 5 to 10 mol / L, and the concentration of LiTFSI is 10 to 100 mol / L.

[0032] In the embodiment of the present application, when the solute of the electrolyte is a mixture of LiNO3 and LiTFSI, the concentration of LiNO3 is 8 mol / L and the concentration of LiTFSI is 40 mol / L.

[0033] Preferably, the solute of the electrolyte is LiPF6, and the concentration of LiPF6 is 10-50 mol / L.

[0034] In the embodiment of the present application, the solute of the electrolyte is LiPF6, and the concentration of LiPF6 is 24 mol / L.

[0035] Preferably, the solvent of the electrolyte is one or more of EC, EMC, DEC, PC, DMC, DME and 1,3-dioxolane.

[0036] Preferably, the solvent of the electrolyte is 1,3-dioxolane or a mixture of EC and EMC.

[0037] Preferably, the solvent of the electrolyte is a mixture of EC and EMC, and the volume ratio of EC to EMC is (1-10):(1-10).

[0038] Preferably, the flow rate of the electrolyte is 5-20 mL / min.

[0039] Preferably, the flow rate of the electrolyte is 10 mL / min. Too fast flow rate affects the formation of SEI film.

[0040] Preferably, the voltage window of the electrolytic device is 0.005-2.000 V (vs. Li+ / Li).

[0041] Preferably, the current density of the potentiostat is 0.01-0.1 C.

[0042] Preferably, the current density of the potentiostat is 0.06-0.1 C.

[0043] More preferably, the current density of the potentiostat is 0.06 C.

[0044] In the embodiment of the present application, the ion-conducting separator is polytetrafluoroethylene (PTFT).

[0045] The present application also provides a negative electrode material, which comprises the pre-lithiated negative electrode active material described above.

[0046] In the embodiment of the present application, the negative electrode material further comprises a conductive agent and / or a binder.

[0047] In the embodiment of the present application, the conductive agent is selected from one or more of conductive carbon black, carbon fiber, ketjen black, acetylene black, carbon nanotube and graphene.

[0048] In specific embodiments of the application, the binder is selected from one or more of polyvinylidene fluoride, styrene butadiene latex, polyacrylic acid, polytetrafluoroethylene, polyethylene oxide.

[0049] The application also provides a negative electrode sheet, comprising the negative electrode material described above.

[0050] In specific embodiments of the application, the negative electrode sheet further comprises a current collector.

[0051] In specific embodiments of the application, the current collector of the negative electrode sheet is a copper foil.

[0052] In specific embodiments of the application, the thickness of the copper foil is 2-12 μm.

[0053] The application also provides an electrochemical device comprising a positive electrode and a negative electrode, the negative electrode comprising the pre-lithiated negative electrode active material described above.

[0054] As a preference, the electrochemical device is a battery cell.

[0055] In specific embodiments of the application, the battery cell further comprises a separator.

[0056] In specific embodiments of the application, the positive electrode active material of the positive electrode is selected from one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium titanate, ternary positive electrode material.

[0057] In specific embodiments of the application, the current collector of the positive electrode is an aluminum foil.

[0058] In specific embodiments of the application, the thickness of the aluminum foil is 2-12 μm.

[0059] In specific embodiments of the application, the battery cell is one of a conventional jelly-roll, a jelly-roll with tabs in the middle, a jelly-roll with multiple tabs, a stacked structure.

[0060] The application also provides an electronic device comprising the electrochemical device described above.

[0061] In specific embodiments of the application, the electronic device is a battery.

[0062] In specific embodiments of the application, the battery further comprises a housing and an electrolyte.

[0063] Compared with the prior art, the application has the beneficial effects of:

[0064] The application proposes pre-lithiation of graphite powder from the perspective of lithium source / negative electrode interface, adjusts the initial contact state of lithium source and negative electrode, and makes the electronic path dominate the conversion of lithium source, so that lithium is directly supplemented on the surface of graphite powder to compensate for the first cycle capacity loss of lithium ion battery. Since the SEI film is formed on the graphite negative electrode in advance, the initial efficiency of the battery is improved. By adjusting the parameters and structure of the flowing electrolytic cell, the performance of the pre-lithiated graphite can be further improved.

[0065] The method can directly compensate Li for graphite powder, without a complex graphite electrode preparation process, and is easy to scale up in industry, in addition, the method can be extended to next-generation lithium ion battery negative materials such as Si, Sn, etc., and can be well compatible with existing lithium ion battery manufacturing processes, and opens up a new way for improving the energy density of lithium ion batteries and realizing commercial application.

[0066] The application solves the problems of incomplete prelithiation and low lithium source utilization rate of the conventional metal lithium source lithium compensation method, and the general SEI is formed in the full battery, which will simultaneously affect the positive electrode and the negative electrode, the method of the application preferentially forms the SEI film outside the full battery, and is not limited by the battery material, improves the cycle life of the battery while improving the initial efficiency and energy density of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0067] Figure 1 A graphite pre-film forming mechanism is provided for the application;

[0068] Figure 2 A prelithiated graphite SEM graph is provided for the application, wherein a-c: original graphite powder; d-f: graphite powder after prelithiation;

[0069] Figure 3 An electrochemical performance CV curve graph of pre-SEI graphite is provided for the application;

[0070] Figure 4 A first week charge-discharge curve schematic diagram is provided for the application;

[0071] Figure 5 A cycle curve of the battery of the application is provided;

[0072] Figure 6 A structure schematic diagram of the prelithiated negative active material is provided, Figure 6-1 The inner core is a primary particle, Figure 6-2 The inner core is an agglomerate of a plurality of primary particles, Figure 6-3 The inner core is an agglomerate of a plurality of primary particles wrapped with a second SEI film.

[0073] The reference signs are as follows:

[0074] 1 shows the negative active material particle, 2 shows the first SEI film, and 3 shows the second SEI film. DETAILED DESCRIPTION

[0075] The present application discloses a kind of prelithiation negative active material and device, and those skilled in the art can learn from the content herein, and process parameters are appropriately improved to realize.In particular, it needs to be pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are all regarded as included in the present application.The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0076] The present application prelithiation graphite negative electrode preparation includes the following steps:

[0077] Prelithiation graphite is prepared in a flowing electrolytic cell, and the electrolytic cell is connected to a potentiostat. The pre-film forming mechanism of graphite is as follows: Figure 1 150mg graphite powder is dispersed into an electrolytic cell containing electrolyte solution flow. Lithium foil is used as reference electrode and counter electrode, and 1mm thick polytetrafluoroethylene (PTFE) diaphragm is used as barrier between cathode and anode for ion conduction only; The electrolytic cell device is placed in a glove box to ensure operation in a reducing gas. The solution in the electrolytic cell is connected by an external pump and continuously stirred to ensure uniform dispersion of graphite particles in the electrolyte and avoid any sedimentation. The electrolyte solution is circulated for 30 minutes before prelithiation to ensure the wettability of the potentiostat. The voltage window of the electrolytic cell during prelithiation is between 0.005V and 2.000V (vs. Li + / Li), simulating the SEI formation process of graphite in the battery. When the graphite particles come into contact with the cathode, they will get electrons and start to form SEI when the voltage is below 1.0V. The lithium intercalation state of graphite can be controlled by controlling the cycle time and current density. After the formation of SEI, the graphite powder is separated and washed using a centrifuge to obtain graphite powder with Li2CO3 / LiF as the main SEI film component, which is stable in air and does not affect the performance.

[0078] The present application lithium ion battery preparation method includes the following steps:

[0079] a: The prelithiation negative electrode powder (positive active material) prepared in the above electrolytic cell is mixed with conductive agent and adhesive in a mass ratio of 0.8:0.1:0.1, and a certain proportion of solvent is added and stirred for 60 minutes using a high-speed mixer to dissolve. The active material slurry is coated on the copper (aluminum) foil by conventional or zebra coating method to obtain negative (positive) electrode sheet;

[0080] b: The negative (positive) electrode sheet is rolled after being baked in an oven at 80-150℃, and the electrode sheet is cut to obtain a single negative (positive) electrode sheet structure by laser cleaning / scraping / die cutting method;

[0081] c: the positive electrode sheet / negative electrode sheet and the separator are assembled into a roll core, electrolyte is added, and lithium ion batteries are prepared after formation and capacity distribution.

[0082] The reagents and materials used in the present application can be obtained through commercial channels.

[0083] The present application is further described below in conjunction with examples:

[0084] Example 1

[0085] (1) The pre-lithiated graphite in this example was prepared in a flowing electrolytic cell connected to a potentiostat. 150 mg of graphite powder was dispersed in an electrolyte solution. The 50 mL electrolyte solution contained 2 mol of LiTFSI (lithium bis(trifluoromethanesulfonyl) imide) and 0.4 mol of LiNO3, and the solvent was 1,3-dioxolane. Lithium foil was used as the reference electrode and the counter electrode, and the device was placed in a glove box. The solution in the electrolytic cell was connected to an external pump and continuously stirred to ensure uniform dispersion of the graphite particles in the electrolyte. The electrolyte solution was circulated at a flow rate of 10 mL / min for 30 minutes before pre-lithiation to ensure the wettability of the potentiostat. The current of the potentiostat was 0.06C, and the voltage window was between 0.005V and 2.000V (vs. Li+ / Li), and the negative electrode formed a SEI film <1.0V; after the formation of the SEI, the graphite powder was separated and washed using a centrifuge to obtain pre-lithiated graphite;

[0086] The pre-lithiated graphite was subjected to scanning electron microscopy (SEM) detection, as shown in Figure 2 , wherein Figure 2 a / b / c is the surface morphology of the graphite before pre-lithiation, and d / e / f is the surface morphology of the graphite after pre-lithiation. The results show that the morphology of the pre-formed graphite becomes more porous and rough, and the surface of the pre-lithiated graphite indeed forms a SEI; the structural diagram of the pre-lithiated graphite is shown in Figure 6 .

[0087] (2) The pre-lithiated graphite powder, Super P, polyvinylidene fluoride, and N-methyl pyrrolidone were mixed in a mass ratio of 0.8:0.1:0.1:10, stirred in a high-speed blender for 60 minutes, and then coated on a copper foil to obtain a negative electrode sheet;

[0088] The positive active material lithium cobaltate, Super P, polyvinylidene fluoride, and N-methyl pyrrolidone were mixed in a mass ratio of 0.8:0.1:0.1:10, stirred in a high-speed blender for 60 minutes, and then coated on an aluminum foil to obtain a positive electrode sheet;

[0089] (3) Preparation of electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed uniformly in a mass ratio of EC:PC:EMC:DEC = 10:30:30:30, followed by the addition of 2% fluoroethylene carbonate and 2% 1,3-propane sultone. After dissolution and thorough stirring, lithium salt LiPF6 was added, and the mixture was uniformly mixed to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L.

[0090] (4) The obtained positive electrode sheet, separator, and negative electrode sheet were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a barrier, and then wound to obtain a bare battery. The bare battery was placed in an outer packaging foil aluminum plastic film, electrolyte was injected, and the battery was subjected to a process flow of vacuum packaging, standing, and formation to obtain a lithium ion battery.

[0091] Example 2

[0092] This example is similar to Example 1, except that 50 mL of electrolyte solution contains 1.2 mol of LiPF6, and the solvent is EC / EMC (volume ratio 1:1).

[0093] Example 3

[0094] This example is similar to Example 2, except that the constant potential instrument current is 0.1C.

[0095] Comparative Example 1

[0096] In this comparative example, a negative electrode sheet was prepared using graphite powder that was not pre-lithiated, and the specific steps were as follows:

[0097] (1) The graphite powder (not pre-lithiated), Super P, polyvinylidene fluoride, and N-methyl pyrrolidone were mixed in a mass ratio of 0.8:0.1:0.1:10, stirred with a high-speed mixer for 60 min, and then coated on a copper foil to obtain a negative electrode sheet;

[0098] The positive active material lithium cobaltate, Super P, polyvinylidene fluoride, and N-methyl pyrrolidone were mixed in a mass ratio of 0.8:0.1:0.1:10, stirred with a high-speed mixer for 60 min, and then coated on an aluminum foil to obtain a positive electrode sheet;

[0099] (2) Electrolyte preparation: In a dry argon-atmospheric glove box, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed evenly in a mass ratio of EC:PC:EMC:DEC = 10:30:30:30. Then, 2% fluoroethylene carbonate and 2% 1,3-propanesulfonyl lactone were added, dissolved, and stirred thoroughly. Lithium salt LiPF6 was then added and mixed evenly to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L.

[0100] (3) Stack the obtained positive electrode, separator and negative electrode in order, so that the separator is between the positive electrode and the negative electrode to play the role of isolation, and then wind them to obtain a bare battery; place the bare battery in the outer packaging foil aluminum-plastic film, inject electrolyte, and obtain a lithium-ion battery through vacuum sealing, standing, formation and other processes.

[0101] Performance testing

[0102] 1. Cyclic Voltammetry (CV) Test

[0103] The experimental parameters are as follows: voltage range: 0~2V; initial scan polarity: negative; step interval: 0.001mv / s; number of scan segments: 2.

[0104] like Figure 3 The CV curves of graphite before and after pre-lithiation are shown. Compared with unlithiated graphite, the peak potential of prelithiated graphite is at 0.5V (vs. Li). + Around / Li), the electrolyte decomposes to form an SEI film.

[0105] 2. First week charge / discharge test

[0106] The experimental method is as follows: Take the formed lithium-ion battery, first charge it to 4.45V at 0.02C to obtain the first week's charging capacity, and then discharge it to 3.0V at 0.02C to obtain the first week's discharging capacity.

[0107] like Figure 4 As shown, the pre-lithiated negative electrode graphite exhibits less first-week discharge capacity loss compared to cells made from conventional graphite powder.

[0108] 3. Cyclic performance test

[0109] The experimental method is as follows:

[0110] ① Resting: Rest for 10 minutes at 25℃±2℃;

[0111] ② Initial capacity test:

[0112] Discharge to the lower limit voltage at 0.2C and let stand for 10 minutes;

[0113] 0.7C charge to upper voltage limit, current cut-off at specification;

[0114] 0.2C discharge to lower voltage limit;

[0115] 3. rest for 10 min;

[0116] 4. charge to upper voltage limit at specification, current cut-off, rest for 10 min;

[0117] 5. 0.7C discharge to 3.0V, 8-9 step cycles for 600 times;

[0118] Repeat steps 4-5 for 100 times to test the capacity. After the cycle, measure the data at full charge state, voltage, internal resistance, thickness, DC internal resistance.

[0119] Figure 5 The initial cyclic voltammetry (CV) curves between graphite and Pre-SEI graphite are shown. Compared with the original graphite anode, the cathode peak of Pre-SEI graphite is greatly reduced at around 0.5V (vs. Li + / Li), which is believed to be the formation of SEI with the decomposition of electrolyte. The reduced double-layer charge in the CV curve from Pre-SEI graphite indicates the formation of SEI layer on the graphite surface, as the pre-formed SEI layer reduces the surface area of the graphite powder.

[0120] 4. First week discharge capacity test

[0121] The experimental method is: take the lithium ion battery after formation, first charge to 4.45V at 0.02C to get the first week charge capacity, then discharge to 3.0V at 0.02C to get the first week discharge capacity.

[0122] 5. Capacity loss test

[0123] The capacity loss is the difference between the discharge capacity of each week and the discharge capacity of the previous week.

[0124] 6. Energy density test

[0125] The experimental method is: charge the lithium ion battery to 4.45V at a rate of 0.2C, then charge to 0.025C at a constant voltage to complete the full charge of the lithium ion battery; next, discharge at a rate of 0.2C until the voltage of the lithium ion battery decreases to 3.87V, record the total capacity C discharged during the discharge process, and calculate the actual volume V of the lithium ion battery;

[0126] ED = discharge capacity C * voltage platform / cell volume V

[0127] The platform voltage of 4.45V system is usually 3.87V.

[0128] ED loss rate = ED difference / initial ED * 100%

[0129] The first week discharge capacity, capacity loss, energy density test results are as follows:

[0130] Table 1 ED comparison

[0131]

[0132] Table 1 results show that the pre-lithiation treated negative electrode graphite, compared with the conventional graphite powder prepared battery, the first week discharge capacity loss is reduced, and the energy density loss is reduced.

[0133] The above only is the preferred embodiment of the present application, it should be pointed out that, for the ordinary skilled in the art, without departing from the principles of the present application, can also make a number of improvements and refinements, these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A negative electrode sheet, characterized in that, The negative electrode sheet includes a pre-lithiated negative electrode active material, which includes negative electrode active material particles and a first SEI film. The first SEI film is coated on the surface of the negative electrode active material particles. The negative electrode active material particles are secondary particles. The secondary particles are aggregates of at least two primary particles whose surfaces are coated with a second SEI film. The pre-lithiated negative electrode active material is prepared by dispersing negative electrode active material particles into an electrolytic cell containing an electrolyte solution. The electrolytic cell is connected to a potentiostat, with lithium foil as the reference electrode and counter electrode. A diaphragm is used as a barrier between the anode and cathode. The process is carried out in a reducing gas and electrolyzed within a voltage window of 0.005V to 2.000V.

2. The negative electrode sheet according to claim 1, characterized in that, The particle size D of the primary particles 50 The particle size D of the secondary particles is 3~15μm. 50 The value is 6~30μm.

3. The negative electrode sheet according to claim 1, characterized in that, The thickness of the first SEI film is 2~3nm, and the thickness of the second SEI film is 2~4nm.

4. The negative electrode sheet according to claim 1, characterized in that, The first SEI film or the second SEI film comprises a lithium-containing compound; The lithium-containing compound includes one or more of Li2CO3, LiF, Li2O, LiOH, ROCO2Li, ROLi, and (ROCO2Li)2, wherein R is an alkyl group.

5. The negative electrode sheet according to claim 4, characterized in that, The molar ratio of the negative electrode active material to the lithium-containing compound is 1:(3~10).

6. The negative electrode sheet according to claim 4, characterized in that, In the first SEI film or the second SEI film, the mass percentage of Li2CO3 is 20%~40% and the mass percentage of LiF is 10%~20%.

7. The negative electrode sheet according to claim 1, characterized in that, The specific surface area of ​​the pre-lithiated negative electrode active material is 1~15 m². 2 / g.

8. The negative electrode sheet according to any one of claims 1-7, characterized in that, The negative electrode active material is one or more of graphite, hard carbon, silicon negative electrode material, titanium-based material, silicon-based material, and tin-based material.

9. An electrochemical device, characterized in that, It includes a positive electrode and a negative electrode as described in any one of claims 1-8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.

Images