Non-aqueous electrolyte and lithium ion battery thereof

Abstract

The application provides a non-aqueous electrolyte and a lithium ion battery thereof. The non-aqueous electrolyte comprises a lithium salt, an organic solvent and an additive, the additive comprises trimethylsilyl phosphate and a compound A shown in formula I or formula II, wherein R1 and R2 are selected from C1-C12 alkyl groups. The additive of the application comprises trimethylsilyl phosphate and an alkenyl-containing succinic anhydride compound, and through the synergistic effect of the two substances, the stability of the positive electrode material can be effectively improved, the problem of volume expansion of the negative electrode interface can be improved, and the high-temperature storage performance and high-temperature cycle performance of the lithium ion battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, in particular to a non-aqueous electrolyte and a lithium ion battery thereof. BACKGROUND

[0002] Pure electric vehicles (BEV) have become the future development trend of the automobile industry, and the endurance mileage has become a development obstacle restricting the current electric vehicles. In order to solve the mileage anxiety, the main improvement direction of the material end is to use higher capacity density single cell, such as high-nickel positive electrode and silicon-carbon negative electrode. The electrolyte, as the only liquid substance in the battery, plays a very important role in the development of the energy density of the two materials, such as: 1. How to improve the volume expansion of the silicon-carbon negative electrode from the electrolyte end, 2. How to relieve the high catalytic reaction activity of the high-nickel positive electrode in the cycle process from the electrolyte end, etc. These problems restrict the development of high-energy density electrolyte, and also limit the development of high-energy density batteries.

[0003] Therefore, it is urgent to develop an effective electrolyte to solve the problems existing in the prior art. SUMMARY

[0004] The purpose of the present application is to provide a non-aqueous electrolyte and a lithium ion battery thereof, which includes trimethylsilyl phosphate and a butane anhydride compound containing an alkenyl group. Through the synergistic effect between the two substances, the stability of the positive electrode material can be effectively improved, thereby improving the high-temperature cycle performance of the battery. At the same time, the problem of volume expansion of the negative electrode interface can also be relieved, thereby improving the high-temperature storage performance of the lithium ion battery.

[0005] To achieve the above purpose, the present application provides a non-aqueous electrolyte, which includes a lithium salt, an organic solvent and an additive, characterized in that the additive includes trimethylsilyl phosphate and a compound A as shown in formula I or formula II:

[0006]

[0007] Wherein, R1, R2 is selected from C1-C12 alkyl.

[0008] Compared with the prior art, the application introduces an olefin-containing succinic anhydride compound and trimethylsilyl phosphate into a non-aqueous electrolyte, wherein the olefin-containing succinic anhydride compound can form a good interface protection layer on the surface of the positive electrode material due to the presence of succinic anhydride, thereby reducing the dissolution of active nickel and active oxygen and reducing the probability of oxidation of the electrolyte, thereby improving the stability of the positive electrode side and further improving the cycle stability of the battery. Meanwhile, the double bond olefin group can undergo a double bond polymerization reaction at the negative electrode interface. Compared with a single olefin group, the olefin group is provided with a relatively large anhydride functional group, thereby reducing the polymerization degree and reducing the overall battery internal resistance (compared with a single olefin-containing substance), reducing the risk of lithium precipitation at the negative electrode interface, and matching the trimethylsilyl phosphate. The trimethylsilyl phosphate can effectively reduce the battery interface resistance. When the two are used together, the hydrogen absorption effect between the P=O bond of the trimethylsilyl phosphate and the C=O in the anhydride reduces the presence of acidic substances generated by the C=O in the anhydride used alone, significantly improves the stability of the non-aqueous electrolyte, reduces the influence of the acid value on the interface film components, and further improves the battery storage stability. Therefore, the non-aqueous electrolyte can maintain a stable SEI film under long-term cycle conditions, inhibit the oxidative decomposition of the non-aqueous electrolyte, thereby reducing the decomposition of the organic electrolyte, and further improving the high-temperature cycle and high-temperature storage performance of the lithium ion battery and relieving the expansion of the negative electrode interface volume.

[0009] As a preferred technical solution, R1 and R2 are each independently selected from C1-C6 linear or branched alkyl. Specifically, the C1-C6 alkyl refers to alkyl with a carbon atom number of 1-6, which can be linear or branched. Further, the C1-C6 linear alkyl specifically refers to alkyl with carbon atoms connected in a straight line, such as methyl (CH3-), ethyl (CH3CH2-), propyl (CH3CH2CH2-), butyl (CH3CH2CH2CH2-), pentyl (CH3(CH2)3-) and hexyl (CH3(CH2)4-). The C1-C6 branched alkyl refers to alkyl with a branched carbon atom based on linear alkyl. For example, isopropyl ((CH3)2CH-), isobutyl (CH3CH(CH3)CH2-), sec-butyl (CH3CH2CH(CH3)-), tert-butyl ((CH3)3C-), etc.

[0010] As a preferred technical solution, the compound A of the application is selected from at least one of compound 1 to compound 6:

[0011]

[0012] As a preferred technical solution, the mass percentage of the compound A in the non-aqueous electrolyte is 0.05% to 2.0%. Further, the mass percentage of the compound A in the non-aqueous electrolyte is about 0.1% to 1.0%, or about 0.1% to 0.5%. As an example, the mass percentage of the compound A in the non-aqueous electrolyte can be, but is not limited to, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, or 2.0%.

[0013] As a preferred technical solution, the mass percentage of the trimethylsilyl phosphate (TMSP) in the non-aqueous electrolyte is 0.05% to 2.0%. Further, the mass percentage of the trimethylsilyl phosphate in the non-aqueous electrolyte is about 0.1% to 1.5%, or about 0.5% to 1.0%. As an example, the mass percentage of the trimethylsilyl phosphate in the non-aqueous electrolyte can be, but is not limited to, 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, or 2.0%.

[0014] As a preferred technical solution, the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium trifluoromethylsulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(CF3SO2)2), lithium bis(oxalato)borate (C4BLiO8), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (C2BF2LiO4), lithium difluoro(bisoxalato)phosphate (LiDFBP), and lithium bis(fluorosulfonyl)imide (LiFSI).

[0015] As a preferred technical solution, the mass percentage of the lithium salt in the non-aqueous electrolyte is 5% to 20%. Further, the mass percentage of the lithium salt in the non-aqueous electrolyte is 6% to 15%. As an example, the mass percentage of the lithium salt in the non-aqueous electrolyte can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%.

[0016] As a preferred technical solution, the organic solvent is selected from at least one of a carbonate-based organic solvent, a carboxylate-based organic solvent, and an ether-based organic solvent.

[0017] Specifically, the carbonate-based organic solvent can be, but is not limited to, a chain carbonate, a cyclic carbonate, a fluorinated carbonate. As an example, the carbonate-based organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), pentylene carbonate, vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and the like; the carboxylic acid ester-based organic solvent includes, but is not limited to, a fluorinated carboxylic acid ester, butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), propyl propionate (n-PP), ethyl propionate (EP), and ethyl butyrate (Eb), and the like; the ether-based organic solvent includes, but is not limited to, a fluorinated ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyl tetrahydrofuran, diphenyl ether, and a crown ether, and the like.

[0018] As a preferred technical solution, the mass percentage of the organic solvent in the non-aqueous electrolyte is 60% to 90%. Further, the mass content of the organic solvent in the non-aqueous electrolyte is 70% to 85%. As an example, the mass percentage of the organic solvent in the non-aqueous electrolyte can be, but is not limited to, 60, 65%, 70%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%.

[0019] In another aspect, the present application provides a lithium ion battery, comprising a positive electrode material and a negative electrode material, and further comprising the non-aqueous electrolyte described above.

[0020] As a preferred technical solution, the positive electrode material of the present application is selected from a nickel-cobalt-manganese oxide material, and the chemical formula of the nickel-cobalt-manganese oxide material is LiNi x Co y Mn (1xy) M z O2, 0.6≤x≤0.9, x+y<1, 0≤z<0.08, and M is one of Al, Mg, Zr, and Ti. Preferably, x=0.6, y=0.2, M is Zr, and z=0.03, or x=0.8, y=0.1, M is Zr, and z=0.02.

[0021] As a preferred technical solution, the negative electrode material of the present application is selected from a silicon-carbon negative electrode material. Specifically, the weight percentage of silicon to carbon in the silicon-carbon negative electrode material can be 1:9. DETAILED DESCRIPTION

[0022] To better illustrate the purpose, technical solutions and beneficial effects of the present application, the present application will be further described below in conjunction with specific examples. It should be noted that the following implementation of the method is a further explanation and description of the present application, and should not be regarded as a limitation of the present application.

[0023] Unless otherwise specified in the examples, the implementation is carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0024] Example 1

[0025] (1) Preparation of non-aqueous electrolyte: In a nitrogen-filled glove box (O2< 2 ppm, H2O < 3 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed in a weight ratio of EC:DEC:EMC = 1:2:1 to obtain 83.8 g of organic solvent, followed by the addition of 0.2 g of Compound 1 and 1 g of TMSP, dissolution and thorough stirring, and then the addition of 15 g of lithium hexafluorophosphate. After mixing uniformly, a non-aqueous electrolyte was obtained.

[0026] (2) Preparation of positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 Zr 0.03 O2, adhesive PVDF and conductive agent SuperP were mixed in a mass ratio of 97:1:2 to form a lithium ion battery positive electrode slurry with a certain viscosity. After coating the mixed slurry on both sides of the aluminum foil, drying and rolling, a positive electrode sheet was obtained.

[0027] (3) Preparation of negative electrode: A slurry was prepared by mixing silicon-carbon negative electrode material (10 wt.%Si), conductive agent SuperP, thickening agent CMC, and adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 96:1:1:2. After coating the mixed slurry on both sides of the copper foil, drying and rolling, a negative electrode sheet was obtained.

[0028] (4) Preparation of lithium ion battery: The positive electrode sheet, separator and negative electrode sheet were stacked in a laminated manner to form a square cell. The cell was packaged with a polymer, filled with the prepared lithium ion battery non-aqueous electrolyte, and then subjected to formation, capacity distribution and other processes to obtain a lithium ion battery with a capacity of 1400 mAh.

[0029] The non-aqueous electrolyte formulations of Examples 1-13 and Comparative Examples 1-6 are shown in Table 1. Among them, the steps of configuring the electrolyte and making the battery of Examples 2-13 and Comparative Examples 1-6 are the same as those of Example 1.

[0030] Table 1: Electrolyte components of each example and comparative example

[0031]

[0032]

[0033] The lithium ion batteries prepared according to Examples 1-13 and Comparative Examples 1-6 were subjected to high-temperature cycle performance test, high-temperature storage performance test and thickness expansion rate, respectively, under the following conditions, and the test results are shown in Table 2.

[0034] (1) High-temperature cycle performance

[0035] The lithium ion battery was placed in a 45°C thermostat for 30 minutes to allow the lithium ion battery to reach a constant temperature. The battery was charged at 2C constant current to a voltage of 4.45V, then charged at 4.45V constant voltage to a current of 0.05C, and then discharged at 1C constant current to a voltage of 3.0V. The first cycle discharge capacity of the battery was recorded as C0. This was one charge-discharge cycle. Then the battery was subjected to 1C / 1C charging and discharging at 45°C for 300 cycles, and the discharge capacity was recorded as C1.

[0036] Capacity retention rate = C1 / C0*100%

[0037] (2) High-temperature storage test

[0038] The lithium ion battery was subjected to one 0.3C / 0.3C charge and discharge (the battery discharge capacity was recorded as C0) at room temperature (25°C), with an upper voltage of 4.45V. Then the battery was charged to 4.45V at 0.3C constant current and constant voltage, and the thickness of the battery was measured (the thickness was recorded as D0). The battery was placed in a 60°C oven for 30D, removed and the thickness of the battery was measured (the thickness was recorded as D1). The battery was placed in a 25°C environment and discharged at 0.3C. The discharge capacity was recorded as C1. Then the lithium ion battery was subjected to one 0.3C / 0.3C charge and discharge (the battery discharge capacity was recorded as C2). The capacity retention rate, capacity recovery rate and thickness expansion rate of the lithium ion battery were calculated using the following formula:

[0039] Capacity retention rate = C1 / C0*100%

[0040] Capacity recovery rate = C2 / C0*100%

[0041] Thickness expansion rate = D1 / D0*100%

[0042] Table 2 Test results of lithium ion battery performance

[0043]

[0044]

[0045] Table 3 Test results of electrolyte acid value stability performance

[0046]

[0047]

[0048] From the results of Table 2, based on Comparative Examples 1-6, it can be seen that Examples 1-13 of the present application, which are based on TMSP in combination with Compound A, can improve the high-temperature storage and high-temperature cycling performance of high-nickel ternary cathode material system batteries at high voltage, and can reduce the gas production of the battery. Further comparison of Examples 1-6 shows that when Compound 6 is used in combination with TMSP, the performance is the best, which may be because the branched structure functional group contained therein affects the degree of polymerization of the double bond, thereby affecting the performance of the acid anhydride film-forming effect of the structural material, and further affecting the high-temperature performance of the battery and the gas production performance of the battery.

[0049] From the test results in Table 3, it can be seen that when TMSP and Compound A are both contained in the non-aqueous electrolyte, the acid value stability of the electrolyte is significantly improved and maintained at a relatively low level.

[0050] The non-aqueous electrolyte of the present application contains both an olefin-containing succinic anhydride compound and a trimethylsilyl phosphate, wherein the olefin-containing succinic anhydride compound contains succinic anhydride, which can form a good interfacial protective layer on the surface of the cathode material, thereby reducing the dissolution of active nickel and active oxygen and reducing the probability of electrolyte oxidation, thereby improving the stability of the cathode side and further improving the cycle stability of the battery. At the same time, the double bond olefin can undergo a double bond polymerization reaction at the negative electrode interface. Compared with a single olefinic substance, the olefin has a relatively large anhydride functional group, which reduces the degree of polymerization, thereby reducing the overall battery internal resistance (compared with a pure olefinic substance) and reducing the risk of lithium precipitation at the negative electrode interface. At the same time, the trimethylsilyl phosphate is matched. The trimethylsilyl phosphate can effectively reduce the battery interface resistance. When both are used together, the P=O bond of the trimethylsilyl phosphate and the C=O in the anhydride are used to reduce the acidic substances produced by the C=O in the anhydride alone, significantly improving the stability of the non-aqueous electrolyte, reducing the effect of acid value on the components of the interfacial film, and further achieving the effect of improving the storage stability of the battery. Therefore, the non-aqueous electrolyte of the present application can maintain a stable SEI film under long-term cycling conditions, inhibit the oxidative decomposition of the non-aqueous electrolyte, thereby reducing the decomposition gas of the organic electrolyte, and further improving the high-temperature cycling and high-temperature storage performance of the lithium ion battery and relieving the volume expansion of the negative electrode interface.

[0051] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application, and although the present application has been described in detail with reference to the preferred embodiments, it is not limited to the listed in the embodiments, and those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A non-aqueous electrolyte comprising a lithium salt, an organic solvent and an additive, characterized in that: The additive includes trimethylsilyl phosphate and a compound A as shown in Formula 1 or Formula 2: Wherein, R1 and R2 are each independently selected from C1 to C12 alkyl groups.

2. The non-aqueous electrolyte according to claim 1, characterized in that The compound A is selected from at least one of compounds 1 to 6:

3. The non-aqueous electrolyte according to claim 1, wherein The mass percentage of the compound A in the non-aqueous electrolyte is 0.05% to 2.0%.

4. The non-aqueous electrolyte according to claim 1, wherein The mass percentage of the trimethylsilyl phosphate in the non-aqueous electrolyte is 0.05% to 2.0%.

5. The non-aqueous electrolyte according to claim 1, characterized in that The lithium salt is selected from at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonyl imide, lithium bisoxalatoborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium difluorobisoxalatophosphate and lithium bisfluorosulfonyl imide.

6. The non-aqueous electrolyte according to claim 1, wherein The mass percentage of the lithium salt in the non-aqueous electrolyte is 5% to 20%.

7. The non-aqueous electrolyte according to claim 1, characterized in that The organic solvent is selected from at least one of carbonate organic solvents, carboxylate organic solvents and ether organic solvents.

8. A lithium-ion battery comprising a positive electrode material and a negative electrode material, characterized in that: Also included is the non-aqueous electrolyte according to any one of claims 1 to 7.

9. The lithium-ion battery according to claim 8, characterized in that The positive electrode material is selected from nickel-cobalt-manganese oxide material, and the chemical formula of the nickel-cobalt-manganese oxide material is LiNi x Co y Mn (1xy) M z O2, 0.6≤x≤0.9, x+y<1, 0≤z<0.08, M is one of Al, Mg, Zr and Ti.

10. The lithium-ion battery according to claim 8, characterized in that The negative electrode material is selected from silicon-carbon negative electrode materials.

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