Lithium ion battery and electronic equipment

Abstract

The invention discloses a lithium ion battery and electronic equipment. The lithium ion battery comprises a pre-lithiated negative plate and an electrolyte, the electrolyte comprises a lithium salt and an ionic liquid solvent; the pre-lithiated negative electrode plate is obtained by carrying out pre-lithiation treatment on a negative electrode plate by adopting a pre-lithiation agent; wherein the pre-lithiation agent comprises a lithium salt and a nonionic liquid solvent. The lithium ion battery disclosed by the invention also has excellent rate capability and relatively high first efficiency on the basis of remarkably improving the cycling stability.

Description

Technical Field

[0001] The invention relates to a lithium ion battery and electronic equipment. Background Art

[0002] Currently, most commercial lithium-ion battery anode materials are graphite (theoretical specific capacity: 372 mAh / g). However, the capacity of these lithium-ion batteries is relatively low and no longer sufficient for daily use, especially in electric vehicles. Silicon materials have a theoretical specific capacity of up to 4200 mAh / g, and their discharge plateau is slightly higher than that of carbon materials. Lithium-ion batteries made from silicon materials are less susceptible to the formation of lithium dendrites during charge and discharge. Therefore, using silicon materials as anode materials for lithium-ion batteries can improve their safety performance and is considered a potential alternative to graphite anode materials. However, silicon materials suffer from a significant initial irreversible capacity loss and experience dramatic volume expansion and contraction (approximately 300%) during charge and discharge, which can damage the electrode structure and lead to poor cycling stability. Research has shown that using an electrolyte containing an ionic liquid solvent in combination with a silicon-based anode material can effectively improve the cycling stability of the anode material (DOI: 10.1016 / j.ensm.2019.09.035). Summary of the Invention

[0003] To overcome the drawback of prior art techniques for improving the cycle stability of lithium-ion batteries while failing to balance rate performance and initial efficiency, the present invention provides a lithium-ion battery and electronic device. The lithium-ion battery of the present invention has high cycle stability, excellent rate performance, and high initial efficiency.

[0004] The present invention solves the above technical problems through the following technical solutions.

[0005] In a first aspect, the present invention provides a lithium-ion battery comprising a pre-lithiated negative electrode sheet and an electrolyte; the electrolyte comprises a lithium salt and an ionic liquid solvent; the pre-lithiated negative electrode sheet is obtained by pre-lithiating the negative electrode sheet using a pre-lithiating agent; wherein the pre-lithiating agent comprises a lithium salt and a non-ionic liquid solvent.

[0006] In a second aspect, the present invention provides an electronic device comprising the lithium-ion battery as described above.

[0007] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0008] The reagents and raw materials used in the present invention are commercially available.

[0009] The positive progress effect of the present invention is:

[0010] The present invention uses a pre-lithiation agent including a non-ionic liquid solvent to pre-lithiate the negative electrode sheet to obtain a pre-lithiated negative electrode sheet, and uses it in combination with a lithium-ion battery prepared by using an electrolyte including an ionic liquid solvent. This can achieve both excellent rate performance and high initial efficiency while improving cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The figures are the cycle performance test data of the lithium ion batteries prepared in Example 1 and Comparative Examples 1 and 2.

[0012] Figure 2 The figures are the rate cycle performance test data of the lithium ion batteries prepared in Example 1 and Comparative Example 2. DETAILED DESCRIPTION

[0013] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0014] lithium-ion batteries

[0015] In the lithium-ion battery described in the first aspect of the present invention, it includes a pre-lithiated negative electrode sheet and an electrolyte; the electrolyte includes a lithium salt and an ionic liquid solvent; the pre-lithiated negative electrode sheet is obtained by pre-lithiating the negative electrode sheet using a pre-lithiating agent; wherein the pre-lithiating agent includes a lithium salt and a non-ionic liquid solvent.

[0016] The ionic liquid solvent itself has a very high viscosity, resulting in poor electrochemical rate performance of lithium-ion batteries using electrolytes containing ionic liquid solvents at room temperature, which cannot meet the current demand for fast charging of lithium-ion batteries. Currently, in order to improve the problem of poor rate performance of lithium-ion batteries using electrolytes containing ionic liquid solvents, high-temperature testing methods are usually used. Therefore, how to improve the rate performance of lithium-ion batteries using electrolytes containing ionic liquid solvents at room temperature has become a top priority in current research.

[0017] In the present invention, the pre-lithiation negative electrode sheet preferably includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; a pre-lithiation layer is disposed on the negative electrode material layer.

[0018] In the present invention, the thickness of the pre-lithiation layer may be 0.1-120 nm.

[0019] In the present invention, the pre-lithiation layer may include one or more of Li2O, LiF, LiCl, Li2CO3, and LiCO2-R, wherein R may include one or more of hydroxyl, carboxyl, and alkyl.

[0020] In the present invention, after the pre-lithiation treatment, a post-treatment step may be further included; the post-treatment may be performed using a post-treatment method conventionally selected in the art, preferably including cleaning and drying.

[0021] In the present invention, the lithium salt in the pre-lithiation agent may be a lithium salt conventionally used in the art, preferably including one or more of LiFSI, LiPF6, LiTFSI and LiBF4.

[0022] In the present invention, the concentration of the lithium salt in the pre-lithiation agent can be selected to be 0.5-2.0 mol / L, for example, 1 mol / L, wherein the concentration is calculated as the number of moles of lithium salt / volume of the non-ionic liquid solvent.

[0023] In the present invention, the non-ionic liquid solvent may be a non-ionic liquid solvent conventionally used in the art, preferably including one or more of EC, DMC, THF, DEC and DME, more preferably THF, DME or EC / DMC.

[0024] In the present invention, the pre-lithiation agent includes a non-ionic liquid solvent. This is because compared with ionic liquid solvents, non-ionic solvents have lower viscosity, which is conducive to forming a denser and thinner SEI film on the surface of the negative electrode sheet, thereby improving the first efficiency and rate performance of the lithium-ion battery.

[0025] In an optional embodiment of the present invention, the pre-lithiation treatment is short-circuit pre-lithiation, which includes the following steps: pressing a negative electrode sheet to which the pre-lithiation agent is applied together with a lithium sheet, wherein the side of the negative electrode sheet to which the pre-lithiation agent is applied is in contact with the lithium sheet. The pressing pressure is preferably 1-5 kPa, for example, 2 kPa or 3 kPa; and the amount of the pre-lithiation agent used is preferably 10-60 μL, more preferably 30-50 μL.

[0026] In an optional embodiment of the present invention, the pre-lithiation treatment is performed by electrochemical pre-lithiation, comprising the following steps: assembling the negative electrode sheet, lithium sheet, and separator into a half-cell, injecting the pre-lithiation agent, and performing charge-discharge cycling and / or lithium insertion. The charge-discharge cycle voltage is preferably 0.005-2V; the number of charge-discharge cycles is preferably 2-5, for example, 3 cycles; and the lithium insertion process is performed at a charging rate not exceeding 1C.

[0027] In the present invention, the pre-lithiation degree of the pre-physicalized negative electrode sheet is less than 100%. If the degree is too high, it will lead to the risk of lithium deposition. Specifically, the pre-lithiation degree can be avoided by controlling the OCV at 0.2-0.8V.

[0028] In the present invention, the lithium salt in the electrolyte may include one or more of LiPF6, LiBF4, LiTFSI and LiFSI. Considering the solubility of the lithium salt in the ionic liquid solvent, LiPF6, LiTFSI or LiFSI is preferred.

[0029] In the present invention, the concentration of the lithium salt in the electrolyte can be selected to be 0.5-3 mol / L, preferably 0.8-2 mol / L, for example 1 mol / L, wherein the concentration is calculated as the number of moles of lithium salt / volume of the ionic liquid solvent.

[0030] In the present invention, the ionic liquid solvent may include a pyrrole ionic liquid or a phosphorus ionic liquid. 13 TFSI, Py 13 FSI, Py 14 TFSI, Py 14 FSI, Py 13 PF6, Py 14 PF6, Py 14 BF4 and Py 13 One or more of BF4. The pyrrole ionic liquid is preferably an anion of TFSI - or FSI - of ionic liquids, which is considered to be different from other anions such as BP4 - or PF6 - Compared with ionic liquids, the two have better rate performance and cycle performance, and are more suitable for silicon and carbon systems.

[0031] In some optional embodiments, the lithium-ion battery includes the pre-lithiated negative electrode sheet and an electrolyte, and further includes a lithium sheet and a separator.

[0032] negative electrode

[0033] In some optional embodiments, the negative electrode sheet can be prepared using conventional methods in the art. For example, the following method can be used: after mixing the negative electrode active material, binder, and conductive agent in a certain weight ratio, a solvent is added and mixed uniformly to obtain a negative electrode slurry; the negative electrode slurry is then evenly coated on the negative electrode current collector; and the negative electrode sheet is prepared through drying, rolling, cutting, and other processes. The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector.

[0034] The negative electrode active material may be a negative electrode active material conventionally used in the art for preparing negative electrode sheets, and may be one or more of graphene, artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microbeads, silicon oxide, and silicon carbon.

[0035] Among them, the binder plays a role in improving the bonding effect between the negative electrode active materials and the adhesion effect between the negative electrode active materials and the negative electrode current collector. The type of the binder is not particularly limited. Specific examples of the binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0036] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. Examples include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black (Super P), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0037] As for the negative electrode current collector, the negative electrode current collector can be a current collector conventionally used for negative electrodes in the art, and can be a common current collector or a composite current collector. The negative electrode current collector can use, without restriction, a material that does not cause chemical changes and has conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon or aluminum-cadmium alloy, or copper, stainless steel or aluminum-cadmium alloy surface-treated with carbon, nickel, titanium or silver can be used. In addition, in order to enhance the adhesion of the negative electrode active material, micro-embossing can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh or porous body.

[0038] In some embodiments, the thickness of the negative electrode current collector may be 5-10 μm.

[0039] In some specific embodiments, the negative electrode current collector is a copper foil with a thickness of 6 μm.

[0040] Lithium tablets

[0041] In some embodiments, the thickness of the lithium sheet may be 100-500 μm.

[0042] diaphragm

[0043] In some embodiments, the separator can be made of polypropylene film or polyethylene film.

[0044] The thickness of the diaphragm may be 12 μm.

[0045] The air permeability of the diaphragm may be 180-380s / 100mL.

[0046] The porosity of the diaphragm may be 30%-50%.

[0047] In a specific embodiment, the separator is a polypropylene film; the thickness of the separator is 12 μm; the air permeability of the separator is 230 s / 100 mL; and the porosity of the separator is 40%.

[0048] In the present invention, the preparation method of the lithium-ion battery can be a conventional preparation method in the art, which can be to assemble the lithium sheet, the pre-lithiated negative electrode sheet and the separator into a battery and inject an electrolyte to prepare a half-cell.

[0049] electronic devices

[0050] In the electronic device described in the second aspect of the present invention, it includes the lithium-ion battery described above.

[0051] Exemplarily, the electronic devices described in the present invention may be, but are not limited to, mobile devices (such as mobile phones, tablet computers, laptop computers, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0052] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0053] In Examples 1-8 and Comparative Examples 1-4, the carbon is cracked carbon obtained by carbonizing asphalt; the thickness of the copper foil is 6 μm; the thickness of the lithium sheet is 500 μm; the diaphragm is a polypropylene film; the thickness of the diaphragm is 12 μm; the air permeability of the diaphragm is 230 s / 100 mL; and the porosity of the diaphragm is 40%.

[0054] Example 1

[0055] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water are added to obtain a negative electrode slurry. The negative electrode slurry is coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 2.3 mg / cm 2 .

[0056] (2) Preparation of pre-lithiation agent: In a glove box, 1 mol / L LiPF6 was dissolved in EC / DMC (volume ratio of 3:7) solution as a pre-lithiation agent.

[0057] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform short-circuit pre-lithiation to obtain an intermediate pre-lithiation negative electrode sheet; cleaning the intermediate pre-lithiation negative electrode sheet with a cleaning agent, and then drying the intermediate pre-lithiation negative electrode sheet to obtain a pre-lithiation negative electrode sheet;

[0058] The amount of the pre-lithiation agent added was 30 μL, the pressure was 2 KPa, and the pre-lithiation treatment time was 10 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0059] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0060] The lithium salt of the electrolyte is 1 mol / L LiFSI, and the ionic liquid solvent is Py 13 FSI.

[0061] Example 2

[0062] (1) Preparation of negative electrode sheet: Carbon-coated silicon oxide (coated with 30% carbon, the percentage is the mass percentage of carbon to the sum of the mass of carbon and silicon oxide) (SiO / C), conductive carbon black (CNT), and binder (PVDF) were mixed in a mass ratio of 8:1:1 (a total of 100 parts by mass), and 80 parts by mass of deionized water were added to obtain a negative electrode slurry. The negative electrode slurry was coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet was 2.5 mg / cm 2 .

[0063] (2) Preparation of a pre-lithiation agent: In a glove box, LiTFSI was dissolved in THF and stirred to obtain a solution with a concentration of 1.0 mol / L, which was used as a pre-lithiation agent.

[0064] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform a short-circuit pre-lithiation treatment to obtain an intermediate pre-lithiation negative electrode sheet; using a cleaning agent to clean the intermediate pre-lithiation negative electrode sheet, and then drying it to obtain a pre-lithiation negative electrode sheet;

[0065] The amount of the pre-lithiation agent added was 50 μL, the pressure was 5 KPa, and the pre-lithiation treatment time was 15 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0066] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0067] The lithium salt of the electrolyte is 1 mol / L LiTFSI, and the ionic liquid solvent is Py 14 TFSI.

[0068] Example 3

[0069] (1) Preparation of negative electrode sheet: Carbon-coated silicon oxide (coated with 30% carbon, the percentage is the mass percentage of carbon to the sum of the mass of carbon and silicon oxide) (SiO / C), conductive carbon black (SP), and binder (CMC to SBR mass ratio of 3:7) were mixed in a mass ratio of 8:1:1 (a total of 100 parts by mass), and 80 parts by mass of deionized water were added to obtain a negative electrode slurry. The negative electrode slurry was coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet was 2.5 mg / cm 2 .

[0070] (2) Preparation of pre-lithiation agent: In a glove box, 2 mol / L LiBF4 was dissolved in DMC to serve as the pre-lithiation agent.

[0071] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform a short-circuit pre-lithiation treatment to obtain an intermediate pre-lithiation negative electrode sheet; using a cleaning agent to clean the intermediate pre-lithiation negative electrode sheet, and then drying it to obtain a pre-lithiation negative electrode sheet;

[0072] The amount of the pre-lithiation agent added was 50 μL, the pressure was 5 KPa, and the pre-lithiation treatment time was 10 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0073] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0074] The lithium salt of the electrolyte is 1 mol / L LiTFSI, and the ionic liquid solvent is Py 14 FSI.

[0075] Example 4

[0076] (1) Preparation of negative electrode sheet: Hard carbon (HC), conductive carbon black (SP), and binder (CMC and SBR with a mass ratio of 5:5) were mixed in a mass ratio of 93:3:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water were added to obtain a negative electrode slurry. The negative electrode slurry was coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet was 2.4 mg / cm 2 .

[0077] (2) Preparation of pre-lithiation agent: In a glove box, LiFSI was dissolved in DME and stirred to obtain a solution with a concentration of 2.0 mol / L, which was used as a pre-lithiation agent.

[0078] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform a short-circuit pre-lithiation treatment to obtain an intermediate pre-lithiation negative electrode sheet; using a cleaning agent to clean the intermediate pre-lithiation negative electrode sheet, and then drying it to obtain a pre-lithiation negative electrode sheet;

[0079] The amount of the pre-lithiation agent added was 50 μL, the pressure was 3 KPa, and the pre-lithiation treatment time was 15 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0080] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0081] The lithium salt of the electrolyte is 1 mol / L LiTFSI, and the ionic liquid solvent is Py 14 FSI.

[0082] Example 5

[0083] (1) Preparation of negative electrode sheet: artificial graphite, binder, and conductive agent were mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water were added to obtain a negative electrode slurry. The negative electrode slurry was coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet was 3.0 mg / cm 2 .

[0084] (2) Preparation of pre-lithiation agent: In a glove box, 0.5 mol / L LiPF6 was dissolved in EC / DMC (volume ratio of 3:7) solution as a pre-lithiation agent.

[0085] (3) Pre-lithiation method of negative electrode sheet: assemble the negative electrode sheet, lithium sheet and separator in step (1) into a battery and inject a pre-lithiation agent to make a half-cell, perform three charge and discharge cycles and then disassemble; use a cleaning agent to clean the intermediate pre-lithiation negative electrode sheet, and then dry it to obtain a pre-lithiation negative electrode sheet; wherein the applied voltage range during the charge and discharge cycle is 0.005-2V.

[0086] The cleaning agent is DMC, and the cleaning time is 5 minutes.

[0087] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0088] The lithium salt of the electrolyte is 1 mol / L LiPF6, and the ionic liquid solvent is Py 14 PF6.

[0089] Example 6

[0090] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water are added to obtain a negative electrode slurry. The negative electrode slurry is coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 2.3 mg / cm 2 .

[0091] (2) Preparation of pre-lithiation agent: In a glove box, 1 mol / L LiPF6 was dissolved in THF solution to serve as a pre-lithiation agent.

[0092] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform short-circuit pre-lithiation to obtain an intermediate pre-lithiation negative electrode sheet; cleaning the intermediate pre-lithiation negative electrode sheet with a cleaning agent, and then drying the intermediate pre-lithiation negative electrode sheet to obtain a pre-lithiation negative electrode sheet;

[0093] The amount of the pre-lithiation agent added was 30 μL, the pressure was 2 KPa, and the pre-lithiation treatment time was 10 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0094] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0095] The lithium salt of the electrolyte is 1 mol / L LiFSI, and the ionic liquid solvent is Py 13 FSI.

[0096] Example 7

[0097] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water are added to obtain a negative electrode slurry. The negative electrode slurry is coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 2.3 mg / cm 2 .

[0098] (2) Preparation of pre-lithiation agent: In a glove box, 1 mol / L LiPF6 was dissolved in DME solution to serve as the pre-lithiation agent.

[0099] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform short-circuit pre-lithiation to obtain an intermediate pre-lithiation negative electrode sheet; cleaning the intermediate pre-lithiation negative electrode sheet with a cleaning agent, and then drying the intermediate pre-lithiation negative electrode sheet to obtain a pre-lithiation negative electrode sheet;

[0100] The amount of the pre-lithiation agent added was 30 μL, the pressure was 2 KPa, and the pre-lithiation treatment time was 10 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0101] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0102] The lithium salt of the electrolyte is 1 mol / L LiFSI, and the ionic liquid solvent is Py 13 FSI.

[0103] Example 8

[0104] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water are added to obtain a negative electrode slurry. The negative electrode slurry is coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 2.3 mg / cm 2 .

[0105] (2) Preparation of pre-lithiation agent: In a glove box, 1 mol / L LiPF6 was dissolved in EC / DEC (volume ratio of 3:7) solution as a pre-lithiation agent.

[0106] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform short-circuit pre-lithiation to obtain an intermediate pre-lithiation negative electrode sheet; cleaning the intermediate pre-lithiation negative electrode sheet with a cleaning agent, and then drying the intermediate pre-lithiation negative electrode sheet to obtain a pre-lithiation negative electrode sheet;

[0107] The amount of the pre-lithiation agent added was 30 μL, the pressure was 2 KPa, and the pre-lithiation treatment time was 10 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0108] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0109] The lithium salt of the electrolyte is 1 mol / L LiFSI, and the ionic liquid solvent is Py 13 FSI.

[0110] Comparative Example 1

[0111] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water are added to obtain a negative electrode slurry. The negative electrode slurry is coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 2.3 mg / cm 2 .

[0112] (2) Preparation of lithium-ion battery: The negative electrode sheet, lithium sheet and separator obtained in step (1) are assembled into a battery and an electrolyte is injected into the battery to prepare a half-cell.

[0113] The lithium salt of the electrolyte is 1 mol / L LiFSI, and the ionic liquid solvent is Py 13 FSI.

[0114] Comparative Example 2

[0115] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water are added to obtain a negative electrode slurry. The negative electrode slurry is coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 2.3 mg / cm 2 .

[0116] (2) Pre-lithiation of the negative electrode sheet: adding a pre-lithiation agent to the negative electrode sheet in step (1), placing lithium foil on the negative electrode sheet, and performing a short-circuit pre-lithiation treatment to obtain a pre-lithiation negative electrode sheet;

[0117] The amount of the pre-lithiation agent added was 30 μL, the pressure was 2 KPa, and the pre-lithiation treatment time was 10 min.

[0118] (3) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0119] Among them, the pre-lithiation agent and electrolyte are both LiFSI with a lithium salt of 1 mol / L, and the solvent is Py 13 FSI.

[0120] Comparative Example 3

[0121] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), 80 parts by mass of deionized water are added to obtain a negative electrode slurry, the negative electrode slurry is coated on Cu foil, and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 3.3 mg / cm 2 .

[0122] (2) Pre-lithiation: adding electrolyte to the negative electrode sheet in step (1), placing lithium foil on the sheet, and performing short-circuit pre-lithiation treatment to obtain a pre-lithiated negative electrode sheet;

[0123] The amount of electrolyte added was 30 μL, the pressure was 2 KPa, and the pre-lithiation treatment time was 10 min.

[0124] (3) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0125] Among them, the lithium salt of the electrolyte is 1 mol / L LiPF6, the solvent is EC / DMC, and the volume ratio is 3:7.

[0126] Comparative Example 4

[0127] (1) Preparation of negative electrode sheet: Silicon oxide doubly coated with carbon and graphene (coated with 10% carbon and 5% graphene, the percentage is the mass percentage of the mass of each component to the sum of the mass of carbon, graphene and silicon oxide) (SiO / C / G), conductive carbon black (SP), and binder (the mass ratio of CMC to SBR is 3:7) are mixed in a mass ratio of 92:4:4 (a total of 100 parts by mass), and 80 parts by mass of deionized water are added to obtain a negative electrode slurry. The negative electrode slurry is coated on Cu foil and dried to obtain a negative electrode sheet. The surface density of the negative electrode sheet is 2.3 mg / cm 2 .

[0128] (2) Preparation of pre-lithiation agent: In a glove box, 1 mol / L LiFSI was dissolved in Py 13 In FSI, it is used as a pre-lithiation agent.

[0129] (3) A method for pre-lithiation of a negative electrode sheet: dripping the pre-lithiation agent of step (2) onto the negative electrode sheet of step (1), and then placing lithium foil on the negative electrode sheet to perform short-circuit pre-lithiation to obtain an intermediate pre-lithiation negative electrode sheet; cleaning the intermediate pre-lithiation negative electrode sheet with a cleaning agent, and then drying the intermediate pre-lithiation negative electrode sheet to obtain a pre-lithiation negative electrode sheet;

[0130] The amount of the pre-lithiation agent added was 30 μL, the pressure was 2 KPa, and the pre-lithiation treatment time was 10 min. The cleaning agent was DMC, and the cleaning treatment time was 5 min.

[0131] (4) Preparation of lithium-ion battery: The pre-lithiated negative electrode sheet, lithium sheet and separator obtained in step (3) are assembled into a battery and injected with electrolyte to form a half-cell.

[0132] The lithium salt of the electrolyte is 1 mol / L LiPF6, and the solvent is EC / DMC (volume ratio is 3:7).

[0133] Effect Example 1

[0134] The lithium ion batteries prepared in Examples 1-8 and Comparative Examples 1-4 were tested as follows:

[0135] (1) Open circuit voltage OCV (V) test method

[0136] The open circuit voltage is tested using a multimeter.

[0137] The lower the OCV, the higher the degree of pre-lithiation (ICE). The present invention ensures that the first efficiency is less than 100% by controlling the OCV within the range of 0.2-0.8V.

[0138] (2) Charging capacity (mAh / g) test method

[0139] During the cycle, it was charged with a current of 0.05C until the capacity at 0.05V was reached.

[0140] (3) Discharge capacity (mAh / g) test method

[0141] Discharge with a current of 0.05C until the capacity reaches 2V.

[0142] (4) Cycle number (capacity retention rate is 80%) test method

[0143] At 25°C, in the voltage range of 0.005-2V, charge and discharge at 0.05C / 0.05C in the first cycle, and 1C / 1C in the second cycle. The capacity of the second cycle is the standard capacity, and the number of cycles when the capacity reaches or falls below the cut-off capacity is the number of cycles (cut-off capacity = standard capacity × 80%).

[0144] The cycle performance of the lithium ion batteries in Example 1 and Comparative Examples 1-2 was tested and the results were as follows: Figure 1 ,Depend on Figure 1 It can be seen that under the same number of cycles, the gram capacity in Example 1 is higher. Therefore, compared with Comparative Examples 1-2, the cycle stability of the lithium ion battery in Example 1 is higher.

[0145] The lithium ion batteries in Example 1 and Comparative Example 2 were subjected to rate cycle performance tests, and the results were as follows: Figure 2 ,Depend on Figure 2 It can be seen that at the same 1C cycle, the gram capacity obtained in Example 1 is higher, and in the cycle process of 0.2C discharge and finally charging to 0.2C, the gram capacity in Example 1 is better recovered. Therefore, compared with Comparative Example 2, the lithium ion battery in Example 1 has excellent rate performance.

[0146] The relevant parameters and test results of Examples 1-8, Comparative Examples 1-4 and Effect Example 1 are shown in Table 1. Wherein, first effect / (%)=discharge capacity / charge capacity×100%.

[0147] Table 1

[0148]

[0149]

[0150] According to Table 1, Examples 1-8 of the present invention use a pre-lithiation agent including a non-ionic liquid solvent to pre-lithiate the negative electrode sheet, which can form a thin and dense SEI film on the surface of the negative electrode sheet. When the obtained pre-lithiated negative electrode sheet is used in combination with an electrolyte including an ionic liquid solvent for the preparation of a lithium-ion battery, the first efficiency can reach more than 85%, or even more than 95%, and the number of cycles can reach 310 cycles or more when the capacity retention rate is 80%. It can be seen that the use of the pre-lithiated negative electrode sheet of the present invention can effectively improve the cycle stability of the lithium-ion battery while taking into account the first efficiency.

[0151] Compared with Examples 1-8, the difference of Comparative Example 1 is that only ionic liquid solvent is used, and no pre-lithiation agent is used to pre-lithiate the negative electrode sheet, that is, no pre-lithiated negative electrode sheet is used, and the first efficiency and cycle number of the obtained lithium-ion battery are significantly reduced. This may be because the pre-lithiation agent is not used for pre-lithiation treatment, resulting in the inability to form an SEI film on the surface of the negative electrode sheet, thereby failing to reduce the loss of active lithium, thereby reducing the first efficiency, and the direct contact of the negative electrode sheet surface with the electrolyte is not conducive to improving the cycle stability. It can be seen that the use of pre-lithiated negative electrode sheets in combination with ionic liquids can give both a higher first efficiency and better cycle stability.

[0152] Comparing Comparative Example 2 with Examples 1-8, the only difference is that the negative electrode sheet was pre-lithiated using an ionic liquid solvent instead of a non-ionic liquid. The initial efficiency and cycle number of the lithium-ion battery prepared using the obtained negative electrode sheet and the ionic liquid solvent were significantly reduced. This shows that only by using a pre-lithiated negative electrode sheet using a non-ionic liquid solvent as the pre-lithiation agent and the ionic liquid can both achieve a high initial efficiency and good cycling stability.

[0153] Compared with Examples 1-8, Comparative Example 3 differs in that a lithium-ion battery is prepared using an electrolyte comprising a non-ionic liquid solvent instead of an ionic liquid solvent. The first efficiency of the lithium-ion battery prepared by using the obtained negative electrode sheet and the ionic liquid solvent is slightly reduced, while the number of cycles is significantly reduced. It can be seen that the use of a pre-lithiated negative electrode sheet can ensure a higher first efficiency of the lithium-ion battery, but only when used with an electrolyte comprising an ionic liquid solvent can better cycle stability be achieved.

[0154] Comparative Example 4 is compared with Examples 1-8 in that a pre-lithiation treatment is performed using a pre-lithiation agent comprising an ionic liquid solvent to obtain a pre-lithiation negative electrode sheet, and an electrolyte comprising a non-ionic liquid solvent is used. The first efficiency and number of cycles of the lithium-ion battery obtained are significantly reduced. This may be because the SEI film formed by the ionic liquid electrolyte itself is thicker and cannot effectively improve its rate performance. It can be seen that only by using a pre-lithiation agent comprising a non-ionic liquid solvent to obtain a pre-lithiation negative electrode sheet, and using an electrolyte comprising an ionic liquid solvent, can the lithium-ion battery obtained have both a high first efficiency and excellent cycle stability.

[0155] By comparing Example 1 and Example 8, it can be seen that when the non-ionic liquid solvent is EC / DMC, the lithium-ion battery has a higher first efficiency and better cycle stability than EC / DEC. This may be because EC / DMC has a higher dielectric constant, better conductivity, and lower viscosity, and is therefore more conducive to improving the electrochemical performance of the battery.

[0156] By comparing Examples 6-7 with Example 8, it can be seen that when the non-ionic liquid solvent is THF or DME, the lithium-ion battery has a higher first efficiency and better cycle stability than EC / DEC. This may be because when THF or DME is used, the solvent has a higher dielectric constant, better conductivity, and lower viscosity, which is more advantageous. It will improve the overall charge and discharge efficiency and reduce energy loss.

[0157] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A lithium-ion battery, characterized in that: It includes a pre-lithiated negative electrode sheet and an electrolyte; the electrolyte includes a lithium salt and an ionic liquid solvent; The pre-lithiation negative electrode sheet is obtained by pre-lithiation treatment of the negative electrode sheet using a pre-lithiation agent; wherein the pre-lithiation agent includes a lithium salt and a non-ionic liquid solvent.

2. The lithium-ion battery according to claim 1, wherein The pre-lithiation negative electrode sheet comprises a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector; a pre-lithiation layer is disposed on the negative electrode material layer.

3. The lithium-ion battery according to claim 1, wherein The lithium salt includes one or more of LiFSI, LiPF6, LiTFSI and LiBF4.

4. The lithium-ion battery according to claim 1, wherein The non-ionic liquid solvent includes one or more of EC, DMC, THF, DEC and DME.

5. The lithium-ion battery according to claim 1, wherein The concentration of the lithium salt in the pre-lithiation agent is 0.5-2.0 mol / L.

6. The lithium-ion battery according to claim 1, wherein The pre-lithiation treatment method is short-circuit pre-lithiation, which includes the following steps: pressing the negative electrode sheet applied with the pre-lithiation agent together with a lithium sheet, wherein the side of the negative electrode sheet applied with the pre-lithiation agent is in contact with the lithium sheet.

7. The lithium-ion battery according to claim 1, wherein The pre-lithiation treatment is performed by electrochemical pre-lithiation, which includes the following steps: assembling the negative electrode sheet, lithium sheet and separator into a half-cell, injecting the pre-lithiation agent, and performing charge-discharge cycles and / or lithium insertion.

8. The lithium-ion battery according to claim 1, wherein In the electrolyte, the electrolyte satisfies one or both of the following conditions (a)-(b): (a) the concentration of lithium salt in the electrolyte is 0.5-3 mol / L; (b) The ionic liquid solvent is a pyrrole ionic liquid or a phosphorus ionic liquid.

9. The lithium-ion battery according to claim 8, wherein The pyrrole ionic liquid includes Py 13 TFSI, Py 13 FSI, Py 14 TFSI, Py 14 FSI, Py 13 PF6, Py 14 PF6, Py 14 BF4 and Py 13 One or more of BF4.

10. An electronic device, characterized in that: It comprises the lithium ion battery according to any one of claims 1 to 9.

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