Non-aqueous electrolyte and lithium ion battery containing same

Abstract

The invention provides a non-aqueous electrolyte and a lithium ion battery containing the non-aqueous electrolyte. The non-aqueous electrolyte comprises a non-aqueous organic solvent, an electrolyte salt and an additive. The additive comprises a compound A and a compound B, the compound A is vinylene carbonate, and the structural formula of the compound B is shown in the formula 1. The electrolyte additive disclosed by the invention contains vinylene carbonate and a compound B shown as a formula I, and through combination of the vinylene carbonate and the compound B, the battery can have relatively good cycle and high-temperature performance, and the low-temperature performance can be further improved. # imgabs0 #

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a non-aqueous electrolyte and a lithium ion battery containing the non-aqueous electrolyte. Background Art

[0002] With the rapid development of mobile communications and portable appliances in modern society, the use of lithium-ion batteries is constantly expanding. The technology of lithium-ion batteries is also constantly improving, and adding some additives to the electrolyte, which is the "blood" of lithium-ion batteries, can improve many performances of the battery. Among them, vinylene carbonate (VC) is the most widely used electrolyte additive for lithium-ion batteries, which can form a solid electrolyte interface film (SEI) on the surface of the negative electrode. At the same time, VC can produce synergistic effects with various additives such as FEC and PS. As a common organic film-forming additive and overcharge protection agent in the electrolyte, it has good high and low temperature performance and imitation gas expansion function, which can increase the stability of the solvent, effectively inhibit the decomposition of the solvent, promote the formation of the SEI film, and improve the cycle performance of the battery.

[0003] However, since vinylene carbonate contains double bonds, it is polymerizable and oxidizable, and is easy to deteriorate. It is easy to polymerize or oxidize during the distillation process, so the yield is not high and the purity is not too high. At the same time, in actual production applications, in order to prevent VC from being oxidized and polymerized during long-term storage, affecting product quality, 2,6-di-tert-butyl-p-cresol (BHT) is usually added as an inhibitor to extend the shelf life of VC. The addition of BHT will increase the internal resistance of the battery and reduce the battery discharge efficiency under low temperature conditions, so the amount of BHT added must be strictly controlled.

[0004] In addition, VC is not only easily oxidized during long-term storage, but also has insufficient antioxidant properties in the electrolyte of the high-voltage system, making it easy to decompose under high voltage, and it will reduce the oxidative decomposition potential of non-aqueous organic solvents (such as carbonates, etc.), making it difficult to use in electrolytes such as lithium cobalt oxide high-voltage electrolytes, lithium-rich manganese high-voltage electrolytes, 5V-level high-voltage electrolytes, and high-nickel ternary systems. The SEI film formed during the formation of VC contains polyvinyl carbonate components, which contain carbon-carbon double bonds and polymers, and the outer surface of the SEI film has polyethylene, which will peel off at high temperatures, affecting its storage stability, and thus has poor high-temperature performance. Summary of the invention

[0005] In view of the above problems, an object of the present invention is to provide a non-aqueous electrolyte and a lithium ion battery containing the non-aqueous electrolyte, which can not only exert the cycle performance of vinylene carbonate but also make up for the defect of poor high temperature performance.

[0006] To achieve the above-mentioned purpose, the first aspect of the present invention provides a non-aqueous electrolyte, comprising a non-aqueous organic solvent, an electrolyte salt and an additive, wherein the additive comprises compound A and compound B, wherein compound A is vinylene carbonate, and the structural formula of compound B is shown in formula 1.

[0007]

[0008] The additive in the non-aqueous electrolyte of the present invention contains vinylene carbonate and compound B as shown in Formula 1. The solid electrolyte interface film formed by vinylene carbonate on the surface of the negative electrode can effectively improve the cycle performance. Although there is a problem that the stability under high temperature and high pressure is poor and affects the high temperature performance, this problem can be overcome by adding compound B as shown in Formula 1. Specifically, the carbon-carbon double bond in the ring of compound B is relatively easy to produce a polymerization effect. When the battery is in the formation stage, a free radical polymerization reaction can occur on the surface of the negative electrode material to generate a polyalkyl carbonate compound, that is, to form a solid electrolyte interface film (SEI film), thereby effectively inhibiting the co-insertion reaction of solvent molecules. Due to the presence of a bicyclic sulfide symmetrical structure, this film has a stable structure, a strong bond energy of the sulfur bond, and a uniform force on the intermolecular force formed. Therefore, compared with the film formed by VC, it is denser, has stronger protection performance, is more solid at high temperature, can better inhibit a series of adverse reactions occurring at the electrolyte electrode interface during the charge and discharge process, and can make up for the defect of poor high temperature performance of vinylene carbonate. Furthermore, the carbonyl group of the symmetrical structure outside the ring of compound B has high conductivity and strong electrical conductivity, and the formed film has low impedance, which can also improve the low-temperature performance of the battery. Therefore, the electrolyte additive of the present application contains vinylene carbonate and compound B as shown in formula 1. Through the combination of the two, not only can the battery have better cycle and high-temperature performance, but also the low-temperature performance can be further improved.

[0009] As a technical solution of the present invention, the sum of the masses of the non-aqueous organic solvent, the electrolyte salt and the additive is m, the mass of the compound A is n, and n / m is 0.1 to 2.0%.

[0010] As a technical solution of the present invention, the sum of the masses of the non-aqueous organic solvent, the electrolyte salt and the additive is m, the mass of the compound B is p, and p / m is 0.5 to 2.5%.

[0011] As a technical solution of the present invention, the electrolyte salt accounts for 5 to 20% of the total mass of the non-aqueous organic solvent, the electrolyte salt and the additive.

[0012] As a technical solution of the present invention, the electrolyte salt is a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonyl imide, lithium bis(oxalatoborate), lithium difluorophosphate, lithium difluorooxalatoborate, lithium difluorobis(oxalatophosphate) and lithium bis(fluorosulfonyl imide).

[0013] As a technical solution of the present invention, the non-aqueous organic solvent accounts for 80-95% of the total mass of the non-aqueous organic solvent, the electrolyte salt and the additive.

[0014] As a technical solution of the present invention, the non-aqueous organic solvent includes at least one of a linear carbonate, a cyclic carbonate and a carboxylic acid ester.

[0015] As a technical solution of the present invention, the non-aqueous organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, propyl propionate, ethyl propionate and ethyl butyrate.

[0016] The second aspect of the present invention provides a lithium ion battery, comprising a positive electrode material, a negative electrode material and a non-aqueous electrolyte. The lithium ion battery has better cycle, high temperature and low temperature performance, which is conducive to the further industrial development of lithium ion batteries.

[0017] As a technical solution of the present invention, the maximum charging voltage of the lithium-ion battery is greater than 4.3V. DETAILED DESCRIPTION

[0018] The present invention mainly provides a non-aqueous electrolyte, which can be used in lithium ion batteries, sodium ion batteries, etc., preferably lithium ion batteries. Of course, in addition to the non-aqueous electrolyte, the lithium ion battery can also include positive electrode materials and negative electrode materials.

[0019] The positive electrode material is a positive electrode active material with a maximum charging voltage greater than 4.3V. For example, high voltage lithium cobalt oxide Li 1-x M x CoO2, 0<x≤0.05, M includes one or more of Al, Mg, Ti, Sn, V, Cu, Zn, Zr, Cr, Mn, Ni, Co, Fe, Ga, Mo, Sb, W, Y and Nb, or is a high voltage ternary positive electrode material Li x Ni a Mn b Co c N dO2, wherein 1.03<x≤1.30, 0.50≤a≤0.85, 0.05≤b≤0.30, 0.05≤b≤0.30, a+b+c+d=1.0, 0≤d≤0.025, and N includes one or more of Al, Mg, Ti, Sn, V, Cu, Zn, Zr, Cr, Fe, Ga, Mo, Sb, W, Y and Nb. Of course, the positive electrode material of the present application may also use other high-voltage positive electrode active materials or use conventional materials that can produce ion deintercalation with lithium ions instead of high-voltage materials. The negative electrode material includes at least one of a carbon-based material, a titanium-based compound and an alloy material. Furthermore, the negative electrode material may include hard carbon, soft carbon, lithium titanate, Sb alloy, Sn alloy, potassium alloy, aluminum alloy, copper alloy, molybdenum alloy, etc.

[0020] The nonaqueous electrolyte of the present invention includes a nonaqueous organic solvent, an electrolyte salt and an additive.

[0021] Among them, the non-aqueous organic solvent accounts for 80-95% of the sum of the mass of the non-aqueous organic solvent, the electrolyte salt and the additive, preferably 85%-90%. As an example, the proportion of the non-aqueous organic solvent can be, but is not limited to, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%. The non-aqueous organic solvent is at least one of a chain carbonate, a cyclic carbonate and a carboxylate. Preferably, the non-aqueous organic solvent includes a mixture of a chain carbonate and a cyclic carbonate. As an example, the non-aqueous organic solvent includes at least one of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), butyl acetate (n-Ba), γ-butyrolactone (γ-Bt), propyl propionate (n-Pp), ethyl propionate (EP) and ethyl butyrate (Eb).

[0022] The electrolyte salt accounts for 5-20% of the sum of the mass of the non-aqueous organic solvent, the electrolyte salt and the additive, preferably 7-16%. As an example, the proportion of the electrolyte salt can be, but is not limited to, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%. The electrolyte salt is a lithium salt, and the lithium salt includes at least one of lithium hexafluorophosphate (NaPF6), lithium perchlorate (NaClO4), lithium tetrafluoroborate (NaBF4), lithium trifluoromethylsulfonate (NaCF3SO3), lithium bistrifluoromethylsulfonyl imide (NaN(CF3SO2)2), lithium bisoxalate borate (C4BLiO8), lithium difluorophosphate (NaPO2F2), lithium difluorooxalate borate (C2BF2NaO4), lithium difluorobisoxalate phosphate (NaDFBP) and lithium bisfluorosulfonyl imide (NaFSI).

[0023] The additive includes compound A and compound B, compound A is vinylene carbonate, and the structural formula of compound B is shown in formula 1.

[0024]

[0025] The sum of the masses of the non-aqueous organic solvent, electrolyte salt and additives in the electrolyte is m. The mass of compound A is n, and n / m is 0.1-2.0%. As an example, n / m can be, but is not limited to, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%. The mass of compound B is p, and p / m is 0.5-2.5%. As examples, p / m can be, but is not limited to, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%.

[0026] In order to better illustrate the purpose, technical scheme and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0027] Where specific conditions are not specified in the examples, the experiments can be carried out under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specifying the manufacturer are all conventional products available from the market.

[0028] Example 1

[0029] (1) Preparation of non-aqueous electrolyte: Under an argon atmosphere, the electrolyte is prepared in a vacuum glove box with an oxygen content of less than 1 ppm and a moisture content of less than 1 ppm. In a dry argon atmosphere glove box, propylene carbonate PC, ethylene carbonate EC and diethyl carbonate DEC are mixed in a weight ratio of PC:EC:DEC=1:1:1, and then compound A and compound B are added. After dissolving and stirring, lithium hexafluorophosphate is added and mixed evenly to obtain an electrolyte.

[0030] (2) Preparation of positive electrode: Nickel cobalt lithium manganese oxide ternary material NaNi 0.8 Co 0.1 Mn 0.1O2, adhesive PVDF and conductive agent SuperP are evenly mixed in a mass ratio of 95:1:4 to form a lithium-ion battery positive electrode slurry with a certain viscosity. The mixed slurry is coated on both sides of an aluminum foil, and then dried and rolled to obtain a positive electrode sheet.

[0031] (3) Preparation of lithium-ion button cells: A lithium sheet is used as the counter electrode and assembled with the positive electrode sheet into a button cell and the electrolyte is injected.

[0032] The electrolyte formulas of Examples 1 to 8 and Comparative Examples 1 to 3 are shown in Table 1. The steps of preparing the electrolytes and batteries of Examples 2 to 8 and Comparative Examples 1 to 3 are the same as those of Example 1.

[0033] Table 1 Electrolyte components of various embodiments and comparative examples

[0034]

[0035]

[0036] The electrochemical performance tests were conducted on the lithium ion batteries prepared in Examples 1 to 8 and Comparative Examples 1 to 3. The specific test conditions are as follows. The test results are shown in Table 2.

[0037] (1) Lithium-ion battery room temperature cycle test

[0038] Place the lithium-ion battery in a 25℃ constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge at a constant current of 0.5C to a voltage of 4.3V, with a cut-off current of 0.02C, and then discharge at a constant current of 0.5C to a voltage of 2.8V. Record the first cycle discharge capacity of the battery. This is a charge and discharge cycle. Repeat this cycle for 200 weeks, record the first cycle discharge capacity and the last cycle discharge capacity, and calculate the capacity retention rate according to the following formula.

[0039] Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%

[0040] (2) High temperature cycle test of lithium-ion batteries

[0041] Place the lithium-ion battery in a 45℃ constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge at a constant current of 0.5C to a voltage of 4.3V, with a cut-off current of 0.02C, and then discharge at a constant current of 0.5C to a voltage of 2.8V. Record the first cycle discharge capacity of the battery. This is a charge and discharge cycle. Repeat this cycle for 100 weeks, record the first cycle discharge capacity and the last cycle discharge capacity, and calculate the capacity retention rate according to the following formula.

[0042] Capacity retention rate = discharge capacity of the last cycle / discharge capacity of the first cycle × 100%

[0043] (3) Lithium-ion battery high temperature storage test

[0044] Place the lithium-ion battery in a 25℃ constant temperature box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge at a constant current of 0.5C to a voltage of 4.3V, with a cut-off current of 0.02C, then discharge at a constant current of 0.5C to a voltage of 2.8V, record the first cycle discharge capacity of the battery, store at a high temperature of 45℃ for 14 days, then discharge at a constant current of 0.5C at 25℃ to a voltage of 2.8V, then perform a 0.5C / 0.02C charge and discharge at 25℃, record the recovery capacity, and calculate the capacity recovery rate according to the following formula.

[0045] Capacity recovery rate = recovery capacity / first cycle discharge capacity × 100%

[0046] (4) Low temperature discharge test

[0047] At room temperature (25°C), the lithium-ion battery was charged and discharged at 0.5C / 0.5C, and the first cycle discharge capacity of the battery was recorded. The upper limit voltage was 4.3V. The battery was then placed in a -10°C low temperature box for 4 hours, and then discharged at a constant current of 0.1C to a voltage of 2.0V. The discharge capacity of the battery was recorded and the capacity retention rate was calculated.

[0048] Capacity retention rate = discharge capacity / first cycle discharge capacity × 100%

[0049] Table 2 Performance test results of lithium ion batteries of various embodiments and comparative examples

[0050]

[0051] From the results in Table 2, it can be seen that the room temperature cycle performance, high temperature cycle performance, high temperature storage performance and low temperature performance of the lithium ion batteries in Examples 1 to 8 are better than those in Comparative Examples 1 to 3. This is because the electrolyte additive of the present application contains vinylene carbonate and compound B as shown in Formula 1. Through the combination of the two, not only can the battery have better cycle and high temperature performance, but also the low temperature performance can be further improved. However, there is no compound B in Comparative Example 2, which cannot make up for the poor high temperature performance of VC. There is no VC in Comparative Example 3, and the cycle performance is significantly deteriorated.

[0052] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A non-aqueous electrolyte comprising a non-aqueous organic solvent, an electrolyte salt and an additive, characterized in that: The additive comprises compound A and compound B, wherein compound A is vinylene carbonate, and the structural formula of compound B is as shown in formula 1:

2. The non-aqueous electrolyte according to claim 1, characterized in that The sum of the masses of the non-aqueous organic solvent, the electrolyte salt and the additive is m, the mass of the compound A is n, and n / m is 0.1 to 2.0%.

3. The non-aqueous electrolyte according to claim 2, characterized in that The sum of the masses of the non-aqueous organic solvent, the electrolyte salt and the additive is m, the mass of the compound B is p, and p / m is 0.5 to 2.5%.

4. The non-aqueous electrolyte according to claim 1, characterized in that The electrolyte salt accounts for 5 to 20% of the total mass of the non-aqueous organic solvent, the electrolyte salt and the additive.

5. The non-aqueous electrolyte according to claim 1, characterized in that The electrolyte salt is a lithium salt, and the lithium salt includes 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, characterized in that The non-aqueous organic solvent accounts for 80 to 95% of the total mass of the non-aqueous organic solvent, the electrolyte salt and the additive.

7. The non-aqueous electrolyte according to claim 1, characterized in that The non-aqueous organic solvent includes at least one of a chain carbonate, a cyclic carbonate, and a carboxylic acid ester.

8. The non-aqueous electrolyte according to claim 7, characterized in that The non-aqueous organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, propyl propionate, ethyl propionate and ethyl butyrate.

9. A lithium ion battery comprising a positive electrode material, a negative electrode material and the non-aqueous electrolyte according to any one of claims 1 to 8.

10. The lithium ion battery according to claim 9, characterized in that: The maximum charging voltage is greater than 4.3V.

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