Lithium ion battery electrolyte and lithium ion battery containing same

Abstract

The invention provides a lithium ion battery electrolyte and a lithium ion battery containing the same. The lithium ion battery electrolyte comprises an electrolyte, a non-aqueous organic solvent and an additive, the additive comprises a film-forming additive and at least one compound A, and the compound A has a structure as shown in any one of formulas I-V. By adding the compound A, a layer of protective film can be formed on the surface of the negative electrode, and meanwhile, water and HF acid in the electrolyte can be removed, so that the stability of the electrolyte is greatly improved, and the safety and high-temperature performance of the lithium ion battery are improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of lithium ion batteries, and particularly relates to a non-aqueous electrolyte and a lithium ion battery containing the same. BACKGROUND

[0002] To adapt to the rapidly growing electric vehicle market, the use environment puts forward higher requirements. Especially under high temperature conditions, the acceleration of the internal chemical reaction of the battery and the increase of the side reaction. Under high temperature, the hydrolysis rate of lithium hexafluorophosphate in the electrolyte is accelerated, and the HF acid generated by hydrolysis increases rapidly. In this case, the SEI film will be unstable, decomposed and thickened. In order to repair the damaged film, the battery will consume a large amount of active lithium and electrolyte, resulting in loss of active lithium and increase of impedance, and safety problems.

[0003] The present application proposes a cyclic phosphoric anhydride type water and acid removing film forming additive, which can quickly react with water and HF in the electrolyte, and at the same time form a protective film on the negative electrode surface. On the one hand, it reduces the HF and water in the electrolyte, improves the stability of the electrolyte, reduces the corrosion of the SEI film, and on the other hand, the film forming of the positive and negative electrodes can better protect the electrode material, improve the performance and safety of the lithium ion battery under high temperature. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a lithium ion battery non-aqueous electrolyte and a lithium ion battery to solve the high temperature storage performance and gas production of the current silicon negative electrode lithium ion battery, and further improve the performance and safety of the lithium ion battery.

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a lithium ion battery non-aqueous electrolyte and a lithium ion battery. In order to achieve this purpose, the present application adopts the following technical solutions: In a first aspect, the present application provides a lithium ion battery electrolyte, the lithium ion battery electrolyte comprising an electrolyte, a non-aqueous organic solvent and an additive, the additive comprising a film forming additive and at least one compound A, the compound A having a structure represented by any one of the following formulae I-V: ; wherein R1, R2, R3, R4 and R5 are independently selected from C1-C5 (e.g. C1, C2, C3, C4 or C5) alkyl, fluorinated C1-C5 (e.g. C1, C2, C3, C4 or C5) alkyl, fluorine-substituted or unsubstituted phenyl, sulfonic acid group.

[0006] In the present application, by using a cyclic phosphoric anhydride compound additive in the electrolyte, the lithium ion battery has good high temperature storage and high temperature cycle performance.

[0007] The anhydride group in the cyclic phosphoric anhydride compound can react with water and HF, greatly reducing the content of water acid in the electrolyte, thus the substance has a strong function of stabilizing the electrolyte. Meanwhile, the substance can also form a film on the surface of the negative electrode, improving the high-temperature performance of the lithium ion battery.

[0008] Preferably, the mass percentage of the compound A is 0.05%-5%, such as 0.05%, 0.1%, 0.3%, 0.6%, 0.8%, 1%, 1.2%, 1.8%, 2%, 2.4%, 3.5%, 4.7% or 5%, preferably 0.05%-3%, based on 100% of the mass of the lithium ion battery electrolyte.

[0009] Preferably, R1, R2, R3, R4 and R5 are independently selected from methyl, ethyl or phenyl.

[0010] Preferably, the compound A is any one of the following compounds: ; Further preferably, the compound A is compound 1.

[0011] Preferably, the film-forming additive comprises any one of the ester-based additives or a combination of at least two thereof. Preferably, the ester-based additive comprises any one of the following or a combination of at least two thereof: vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, methylene methane disulfonate, vinyl sulfate, tris(trimethylsilyl)borate or tris(trimethylsilyl)phosphate.

[0012] Preferably, the mass percentage of the ester-based additive is 1-20%, such as 1%, 3%, 5%, 7%, 9%, 12%, 15%, 17%, 18% or 20%, etc., based on 100% of the mass of the lithium ion battery electrolyte.

[0013] Preferably, the electrolyte is a lithium salt.

[0014] Preferably, the lithium salt is selected from one of the following or a combination of at least two thereof: lithium hexafluorophosphate, lithium difluoro(oxalato)borate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium nitrate.

[0015] Preferably, the mass percentage of the electrolyte is 2-22%, such as 2%, 4%, 6%, 8%, 10%, 12%, 16%, 18%, 20% or 22%, etc., based on 100% of the mass of the lithium ion battery electrolyte.

[0016] Preferably, the non-aqueous organic solvent comprises a carbonate-based organic solvent or a carboxylate-based organic solvent.

[0017] Preferably, the carbonate-based organic solvent comprises a cyclic carbonate and / or a chain carbonate.

[0018] Preferably, the cyclic carbonate comprises any one or a combination of at least two of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0019] Preferably, the chain carbonate comprises any one or a combination of at least two of diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, or methyl propyl carbonate.

[0020] Preferably, the carboxylic acid ester-based organic solvent comprises at least one of ethyl propionate, propyl propionate, ethyl acetate, ethyl n-butyrate, methyl acetate, propyl acetate, methyl propionate, or gamma-butyrolactone.

[0021] Preferably, the mass percentage content of the non-aqueous organic solvent is 75% to 94%, for example, 75%, 77%, 79%, 80%, 82%, 84%, 86%, 88%, 90%, 92%, or 94%, and the like, based on 100% of the mass of the lithium ion battery electrolyte.

[0022] In the present application, the preparation method of the lithium ion battery electrolyte comprises, first, adding a lithium salt to a solvent to dissolve, then adding a film-forming additive and compound A, and mixing uniformly.

[0023] On the other hand, the present application provides a lithium ion battery comprising the lithium ion battery electrolyte as described in the first aspect.

[0024] Preferably, the lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet.

[0025] Preferably, the positive electrode sheet comprises a positive electrode active material, and the positive electrode active material is at least one of LiNi x Co y Mn z L (1-x-y-z) O2, LiNi x’ L’ y’ Mn (2-x’-y’) O4; wherein L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; 0.5≤x≤1, 0≤y<1, 0≤z≤1, 0<x+y+z≤1, 0<x’≤1, 0.01≤y’≤0.2, L’ is at least one of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe; Preferably, the negative electrode sheet comprises a negative active material selected from one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, mesocarbon microbeads, graphene, graphyne, metallic lithium, nanocarbon, carbon nanotube, elemental silicon, silicon oxide compound, silicon / copper oxide composite, AG composite, silicon alloy, elemental tin, tin oxide compound, tin / carbon composite, tin alloy, or lithium titanate.

[0026] Preferably, the material of the separator comprises one of polyethylene, polypropylene, or composite ceramic film.

[0027] Compared with the prior art, the present application has the following beneficial effects: Lithium hexafluorophosphate (LiPF6) is the most commonly used electrolyte for lithium ion batteries, but it is extremely sensitive to water at high temperatures and will react to generate HF. HF is a strong corrosive acid that will corrode the positive electrode material, causing transition metal ions to dissolve out and destroy the material structure, resulting in capacity decay. HF will also corrode the SEI film of the negative electrode, causing similar damage effects as water. Lewis acid will catalyze the decomposition of electrolyte, increasing the side reactions of electrolyte. The cyclic phosphoric anhydride will preferentially react with these water and HF, eliminating the adverse factors brought by them. By removing HF and water, a clean environment is created for the formation of a more stable and denser SEI film and CEI film. In addition to this, this type of compound will decompose EC in advance and form an SEI film at the negative electrode, thereby improving the safety and electrochemical performance of lithium ion batteries under high temperature conditions. DETAILED DESCRIPTION

[0028] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations on the present application.

[0029] Examples 1-14 and Comparative Examples 1-3 provide a non-aqueous electrolyte, the composition of which is shown in Table 1.

[0030] Table 1 The structure of the cyclic phosphoric nitrile in Comparative Example 4 is as follows: .

[0031] Examples 1-9 and Comparative Examples 1-3 In Examples 1-9 and Comparative Examples 1-3, a secondary lithium ion battery is respectively provided, the lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the electrolyte being the electrolyte provided in Examples 1-9 and Comparative Examples 1-3, respectively.

[0032] The method for preparing a lithium ion battery comprises the following steps: (1) Preparation of the positive electrode sheet: Polyvinylidene fluoride (PVDF) was uniformly dissolved in N-methyl pyrrolidone (NMP), then conductive agent Super P was added, mixed thoroughly, and then positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O2 powder was gradually added, wherein the mass ratio of LiNi 0.8 Co 0.1 Mn 0.1 O2 powder, PVDF and conductive agent Super P was 97.4:1.3:1.3, to obtain positive electrode slurry (the solid content of the output of the positive electrode slurry was 63.1%), which was coated on the current collector, and then dried, rolled, and slitted to obtain the positive electrode sheet which can be directly laminated.

[0033] (2) Preparation of the negative electrode sheet: Artificial graphite, conductive carbon, silicon oxide powder and sodium carboxymethyl cellulose with a mass ratio of 80.9:2.9:15:1.2 were premixed, stirred at a speed of 250 rpm for 140 min, then transferred to deionized water for dispersion, mixed uniformly, and then sieved, and finally the sieved negative electrode slurry (solid content 94.5%) was coated on the negative electrode current collector, and then dried, rolled, and slitted to obtain the negative electrode sheet which can be laminated.

[0034] (3) Preparation of the electrolyte: Ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed in a mass ratio of EC: EMC = 3:7 (vol / vol), and then film-forming additive and additive A were added into the mixed solvent, and then lithium hexafluorophosphate (LiPF6) was added to a molar concentration of 1 M.

[0035] (4) Preparation of the battery cell: The slitted positive electrode sheet and negative electrode sheet were laminated on a laminator, the separator was PP / PE / PP three-layer material, and a soft-pack battery cell was formed.

[0036] (5) Liquid injection, formation and aging: After the battery cell was dried at high temperature, the electrolyte of the example and the comparative example was injected into the soft-pack battery cell. After the electrolyte was injected, the lithium battery was subjected to the first packaging, surface cleaning and other processes to complete the preliminary work, and was placed at room temperature for one day. The formation was carried out by step formation method, the first step formation current was 0.05 C, and the constant current was charged for 2 h, and the second step formation current was 0.1 C, and the constant current was charged until the voltage reached 3.7 V. After formation, it was subjected to 45℃ aging treatment for one day, cooled to room temperature and finally sealed.

[0037] Performance test After the battery was assembled, the electrolyte was fully infiltrated between the electrolyte and the battery electrode sheet for 10 h at room temperature, and then the following tests were carried out.

[0038] (1) High temperature storage performance - the method for testing the capacity retention rate, capacity recovery rate and volume expansion rate of the battery after 30 days of storage at 60°C: The battery after formation is charged at 1 C constant current and constant voltage to 4.2 V at room temperature, the cut-off current is 0.05C, then discharged at 1C constant current to 2.75 V, measure the initial discharge capacity of the battery, then charged at 1C constant current and constant voltage to 4.2 V, the cut-off current is 0.05C, measure the initial volume of the battery, then store the battery at 60°C for 30 days, measure the volume of the battery, then discharge at 1C constant current to 2.75 V, measure the retention capacity of the battery, then charged at 1C constant current and constant voltage to 4.2 V, the cut-off current is 0.05C, then discharged at 1C constant current to 2.75 V, measure the recovery capacity.

[0039] The calculation formula of capacity retention rate, capacity recovery rate, thickness expansion is as follows: Battery capacity retention rate (%) = retention capacity / initial capacity x 100%; Battery capacity recovery rate (%) = recovery capacity / initial capacity x 100%; Battery volume expansion rate (%) = (volume after 30 days-initial volume) / initial volume x 100%; (1) 45°C high temperature cycle test: constant current charge and discharge at 1C current density of rated capacity in 45°C constant temperature room, cycle times is 800 times, test voltage range is 2.75V-4.2V, charge cut-off current is 0.05C, after the test, according to the first discharge capacity, calculate the 400th cycle capacity retention rate.

[0040] The calculation formula of 400th cycle capacity retention rate is as follows: 400th cycle capacity retention rate (%) = (400th cycle discharge capacity at room temperature / first discharge capacity) x 100%.

[0041] The test results are shown in Table 2.

[0042] Table 2 Through the high-temperature storage performance test of the lithium battery prepared by the above-mentioned embodiments, it is found that the lithium battery prepared by using the electrolyte of the present application can improve the high-temperature performance of the battery. The cyclic phosphoric acid anhydride compound with 0.1% can reduce the high-temperature storage volume expansion rate, and even can control the volume expansion rate below 3%. Adding a small amount of the substance can improve the high-temperature storage retention rate and recovery rate and the capacity retention rate of high-temperature cycle. After high-temperature storage for 30 days, the capacity retention rate is much higher than that of the comparative examples and the BASE group, and the retention rate is basically maintained at 90%, and the recovery rate is above 90%. After high-temperature cycle for 400 weeks, the capacity retention rate of the examples containing the substance is greater than that of the BASE group. Therefore, the electrolyte of the present application applied to the ion battery greatly improves the charge-discharge cycle performance and safety performance of the lithium ion battery.

[0043] The applicant declares that the lithium ion battery electrolyte and lithium ion battery containing the same of the present application are illustrated by the above-mentioned embodiments, but the present application is not limited to the above-mentioned embodiments, that is, it does not mean that the present application must rely on the above-mentioned embodiments to be implemented. It should be understood by those skilled in the art that any improvement of the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific mode, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A lithium-ion battery electrolyte, characterized in that, The lithium-ion battery electrolyte comprises an electrolyte, a non-aqueous organic solvent, and additives. The additives include a film-forming additive and at least one compound A, wherein compound A has a structure shown in any one of formulas I-V: ； R1, R2, R3, R4 and R5 are independently selected from C1-C5 alkyl, fluorinated C1-C5 alkyl, fluorinated or unsubstituted phenyl, sulfonic acid group.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that, Based on the mass of the lithium-ion battery electrolyte as 100%, the mass percentage of compound A is 0.05% to 5%, preferably 0.05% to 3%.

3. The lithium-ion battery electrolyte according to claim 1 or 2, characterized in that, R1, R2, R3, R4, and R5 are independently selected from methyl, ethyl, or phenyl.

4. The lithium-ion battery electrolyte according to any one of claims 1-3, characterized in that, Compound A is any one of the following compounds: ； More preferably, compound A is compound 1.

5. The lithium-ion battery electrolyte according to any one of claims 1-4, characterized in that, The film-forming additive includes any one or a combination of at least two ester additives; Preferably, the ester additives include any one or a combination of at least two of the following: vinylene carbonate, fluorovinyl carbonate, 1,3-propanesulfonate lactone, methanedisulfonate, vinyl sulfate, tris(trimethylsilane)borate, or tris(trimethylsilane)phosphate. Preferably, the ester additive has a mass percentage content of 1-20% based on the mass of the lithium-ion battery electrolyte (100%).

6. The lithium-ion battery electrolyte according to any one of claims 1-5, characterized in that, The electrolyte is a lithium salt; Preferably, the lithium salt is selected from one or a combination of at least two of lithium hexafluorophosphate, lithium difluorooxalate borate, lithium tetrafluoroborate, lithium dioxalate borate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, and lithium nitrate.

7. The lithium-ion battery electrolyte according to any one of claims 1-6, characterized in that, With the mass of the lithium-ion battery electrolyte being 100%, the mass percentage of the electrolyte is 2-22%.

8. The lithium-ion battery electrolyte according to any one of claims 1-7, characterized in that, The non-aqueous organic solvents include carbonate organic solvents or carboxylic acid ester organic solvents; Preferably, the carbonate organic solvent includes cyclic carbonates and / or chain carbonates; Preferably, the cyclic carbonate includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, and butene carbonate; Preferably, the chain carbonate includes any one or a combination of at least two of diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, or methyl propyl carbonate. Preferably, the carboxylic acid ester organic solvent includes at least one of ethyl propionate, propyl propionate, ethyl acetate, ethyl butyrate, methyl acetate, propyl acetate, methyl propionate, or γ-butyrolactone. Preferably, the non-aqueous organic solvent has a mass percentage content of 75% to 94% based on the mass of the lithium-ion battery electrolyte being 100%.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-ion battery electrolyte according to any one of claims 1-7.

10. The lithium-ion battery according to claim 9, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; Preferably, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material is LiNi. x Co y Mn z L (1-x-y-z) O2, LiNi x’ L' y’ Mn (2-x’-y’) At least one of O4; wherein L is at least one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, and Fe; 0.5≤x≤1, 0≤y<1, 0≤z≤1, 0<x+y+z≤1, 0<x'≤1, 0.01≤y'≤0.2, and L' is at least one of Co, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, and Fe; Preferably, the negative electrode sheet includes a negative electrode active material, which is selected from one or a combination of at least two of the following: natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, graphene, graphynylene, lithium metal, nano-carbon, carbon nanotubes, elemental silicon, silicon oxide, silicon / copper oxide composite, AG composite, silicon alloy, elemental tin, tin oxide, tin-carbon composite, tin alloy, or lithium titanate.

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