A lithium-ion battery electrolyte for silicon negative electrode and its application

Abstract

The present invention belongs to the technical field of lithium-ion batteries and relates to a lithium-ion battery electrolyte for a silicon negative electrode and its application. The present invention discovers a first additive rarely reported in lithium-ion batteries, and at the same time utilizes the synergistic effect of a second additive and optimizes the composition of lithium salts, solvents, and additives. Through the mechanism of forming a low-impedance, high-stability SEI film on the surface of the silicon negative electrode, the battery cycle performance is improved, and both high and low temperature performance are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium ion battery electrolyte for a silicon negative electrode and applications thereof. Background Art

[0002] Lithium-ion batteries, with their advantages of high energy density, long cycle life, low self-discharge, and wide operating temperature range, have experienced significant development since their introduction in 1991, becoming widely used in mobile portable devices, electric vehicles, energy storage systems, and other fields. To further expand the application of lithium-ion batteries, there is an urgent need for lithium-ion batteries with higher energy density, longer cycle life, and improved safety.

[0003] Silicon anode materials, due to their high theoretical specific capacity (3579 mAh / g) and low reaction potential (0.4 V vs Li / Li⁺), show great potential in lithium-ion batteries. They hold broad application prospects in electric vehicles, consumer electronics, and energy storage systems, significantly improving battery energy density and fast-charging performance. However, silicon anodes also face numerous challenges, such as significant volume expansion (approximately 300%), poor interfacial stability, and easily ruptured SEI films, resulting in shortened cycle life. To address these issues, researchers have made significant progress through nano-scaling, composite materials, and electrolyte optimization. As technology matures and costs decrease, silicon anodes are expected to become the mainstream choice for next-generation battery anode materials, driving further advancements in battery technology.

[0004] Since the volume of the silicon-carbon anode expands during charging and contracts during discharge, the SEI film on the surface of the silicon anode continues to form and is in an unstable state during the cycle, and it also continuously consumes electrolyte and lithium ions, resulting in low initial efficiency, slow reaction kinetics, poor cycling, poor rate performance, and poor high and low temperature performance. Therefore, it is urgent to solve the volume expansion and contraction problem of the silicon anode. Summary of the Invention

[0005] The present invention discovers a first additive that has rarely been reported in lithium-ion batteries. It also utilizes the synergistic effect of a second additive and optimizes the composition of lithium salts, solvents, and additives. By forming a low-impedance, high-stability SEI film on the surface of the silicon negative electrode, the battery cycle performance is improved while also having high and low temperature performance.

[0006] The present invention aims to provide a silicon negative electrode lithium ion battery electrolyte, wherein the designed electrolyte has a cycle performance superior to conventional electrolytes.

[0007] Another object of the present invention is to apply the above electrolyte to lithium-ion batteries to improve the energy density, cycle life, and wide temperature performance of lithium-ion batteries.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A lithium-ion battery electrolyte for a silicon negative electrode, comprising an organic solvent, a lithium salt, and additives; the additives comprising a first additive and a second additive; the first additive comprising 2-(trimethylsilylmethyl)allyl acetate; the second additive being a cyclic compound; the cyclic compound comprising one or more of the following structures:

[0010]

[0011] Formula I,

[0012]

[0013] Formula II.

[0014] Preferably, in the structure of the cyclic compound, R1 and R2 contain at least one sulfur atom; in the structure of the cyclic compound, R1, R2, R3, and R4 are each independently selected from one or more of the following structures:

[0015]

[0016] Formula III,

[0017]

[0018] Formula IV.

[0019] Preferably, the cyclic compound includes one or more of the following compounds:

[0020]

[0021] Compound a1,

[0022]

[0023] Compound a2,

[0024]

[0025] Compound a3,

[0026]

[0027] Compound a4.

[0028] Preferably, among the additives, the mass ratio of the first additive to the second additive is 1-2:1.

[0029] Preferably, the mass fraction of the additive in the lithium-ion battery electrolyte is 0.5-10%.

[0030] Preferably, the raw materials include the following parts by weight:

[0031] 75-90 parts of the organic solvent

[0032] 10 to 15 parts of the lithium salt

[0033] The additive is 0.5 to 10 parts.

[0034] Preferably, the organic solvent includes a carbonate solvent and a carboxylate solvent mixed in a mass ratio of 20-80:5-20; the carbonate solvent includes one or more of cyclic carbonates and linear carbonates; the carboxylate solvent includes one or more of ethyl acetate, ethyl propionate, and propyl propionate; the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate; the linear carbonate includes one or more of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the lithium salt includes one or more of lithium hexafluorophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium difluorophosphate.

[0035] An application of the lithium ion battery electrolyte for silicon negative electrode is used to prepare lithium ion batteries.

[0036] A lithium ion battery obtained by the above application.

[0037] Preferably, it includes the lithium-ion battery electrolyte, positive electrode, negative electrode, diaphragm, and shell; the positive electrode includes one or more of lithium cobalt oxide, lithium iron phosphate, and NCM ternary materials; the negative electrode includes a silicon negative electrode; the diaphragm includes one or more of a polypropylene film and a polypropylene coated alumina ceramic film; the shell includes one or more of a steel shell cylindrical shell, a square soft package shell, and a steel shell button battery shell.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 2-(Trimethylsilylmethyl)allyl acetate, a novel additive, possesses a unique atomic composition and chemical structure, containing carbon, silicon, and oxygen atoms, forming trimethylsilane, allyl, and ester structures. This unique structure and steric hindrance are achieved through a unique connection method. The additive, 2-(trimethylsilylmethyl)allyl acetate, exhibits strong reduction and oxidation activity, forming a composite SEI film on the surface of a silicon anode. This film, containing both insoluble inorganic components and highly elastic organic components, provides a more stable SEI film with high mechanical strength. It also preferentially forms a CEI film on the positive electrode, exhibiting suitable steric hindrance, resulting in low film impedance and enhanced stability.

[0040] In addition, the inventors have found through extensive research that by regulating the mass percentage of the first additive and the second additive to meet the condition 1≤a / b≤2, the lithium-ion battery has the best high-temperature and low-temperature cycle performance. It is speculated that the first additive and the second additive are added in a specific ratio, and the two cooperate with each other. On the one hand, the first additive can form a high-strength, low-impedance SEI film on the silicon negative electrode. On the other hand, the first additive and the second additive jointly participate in the positive electrode film formation to form a stable CEI film. Since the second additive has poor compatibility with the positive electrode, when the content is added in large amounts, the positive electrode film formation effect is poor. Therefore, when the first additive and the second additive are added in a ratio of 1 to 2, it can improve the positive electrode film formation effect on the basis of ensuring the stability of the silicon negative electrode, inhibit the dissolution of transition metals, reduce interfacial impedance, and improve the high and low temperature cycle performance of the battery.

[0041] The lithium-ion battery electrolyte of the present invention can simultaneously form a low-impedance interface film on the surfaces of the positive and negative electrodes, thereby improving interface stability. When applied to lithium-ion batteries, better cycle stability and life can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is the chemical structure of the first additive in the present invention. DETAILED DESCRIPTION

[0043] The present invention is further described below with reference to the examples and accompanying drawings, but the embodiments of the present invention are not limited thereto. Where specific conditions are not specified in the examples, the experiments were carried out under conventional conditions or the conditions recommended by the manufacturer. Reagents or instruments used, where the manufacturer is not specified, are commercially available conventional products.

[0044] Unless otherwise specified, all reagents used in the Examples and Comparative Examples can be purchased from the market.

[0045] The lithium cobalt oxide / silicon anode batteries assembled in the examples and comparative examples used 2016 model battery cases. The positive electrode had no gasket or spring plate, while the negative electrode used a stainless steel gasket. The diameter of the lithium cobalt oxide and silicon anode electrodes was 14 mm; the gasket thickness was 1 mm. The amount of electrolyte used was 50 μL, and the separator used was a PP material separator with a diameter of 19 mm and a thickness of 25 μm.

[0046] Example 1

[0047] This embodiment provides an electrolyte for a silicon negative electrode lithium ion battery and its application. The electrolyte comprises the following components, calculated by mass percentage: 12.5% ​​LiPF6 / LiODFB / LiBOB (8 / 1 / 1); 85.5% PC / EC / EMC / DMC / EP (2 / 2 / 2 / 2 / 2); 1% first additive; and 1% second additive. This embodiment also provides an electrolyte for a silicon negative electrode lithium ion battery and its application, and the preparation steps are as follows:

[0048] S1. In a glove box filled with high-purity argon, the moisture and oxygen contents in the glove box were controlled to be below 0.1ppm, and the above mass percentages of the components were weighed;

[0049] S2. First, the organic solvent is mixed and stirred to form a uniform organic solvent;

[0050] S3. The lithium salt is then dissolved in an organic solvent and stirred to form a uniform solution;

[0051] S4. The first additive and the second additive are added to the uniform solution of step S3 and stirred to obtain the electrolyte;

[0052] S5. Assemble a lithium cobalt oxide / silicon negative electrode button cell using the electrolyte obtained in S4. The cell was allowed to stand for 12 hours and activated for three cycles at a rate of 0.1C to form a film. Then, a long charge-discharge cycle test was performed at a rate of 1C to evaluate the cycling stability of the lithium-ion battery containing this electrolyte.

[0053] Effect Example 1

[0054] The secondary batteries of Examples 2-18 and Comparative Examples 1-10 were prepared in a similar manner to the secondary battery of Example 1, except that the composition and parameters of the additives, solvents, and lithium salts in the electrolyte were adjusted, as shown in Table 1.

[0055] The button batteries assembled in the embodiment were all tested using the Xinwei test system, and constant current charge and discharge tests were performed at 0°C, 25°C and 45°C to evaluate the cycle stability. The voltage range of the constant current charge and discharge test was: 2.3V-4.55V. First, 0.1C was used for the first three cycles of activation, and then 1C was used for long cycles. The test results are shown in Table 1.

[0056] Table 1 Test results of the embodiments and comparative examples

[0057]

[0058] The test results in Table 1 show that the addition of the first and second additives can improve cycling performance at both room temperature (25°C), high temperature (45°C), and low temperature (0°C). The synergistic effect (the ratio a of the first additive and the ratio b of the second additive satisfying 1 ≤ a / b ≤ 2) is even more significant, boosting the battery's capacity retention to around 80%. In particular, a comparison of Example 11 with Comparative Example 4 reveals a surprising improvement in cycling performance at room temperature of approximately 30%, high temperature cycling performance of approximately 60%, and low temperature cycling performance of approximately 40%, relative to Comparative Example 4. The improvements are greater at both high and low temperatures, with the high temperature performance improvement being particularly significant.

[0059] The above disclosure is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A lithium ion battery electrolyte for a silicon negative electrode, characterized in that: The invention comprises an organic solvent, a lithium salt and an additive; the additive comprises a first additive and a second additive; the first additive comprises 2-(trimethylsilylmethyl)allyl acetate; the second additive is a cyclic compound; the cyclic compound comprises one or more of the following structures: Formula I, Formula II; In the structure of the cyclic compound, R1 and R2 contain at least one sulfur atom; in the structure of the cyclic compound, R1, R2, R3, and R4 are each independently selected from one or more of the following structures: Formula III, Formula IV; Among the additives, the mass ratio of the first additive to the second additive is 1-2:

1.

2. The lithium-ion battery electrolyte for silicon negative electrode according to claim 1, characterized in that: The cyclic compound includes one or more of the following compounds: Compound a1, Compound a2, Compound a3, Compound a4.

3. The lithium-ion battery electrolyte for silicon negative electrode according to claim 1, characterized in that: The mass fraction of the additive in the lithium ion battery electrolyte is 0.5-10%.

4. The lithium-ion battery electrolyte for silicon negative electrode according to claim 1, wherein: Including the following raw materials by weight: 75-90 parts of the organic solvent 10 to 15 parts of the lithium salt The additive is 0.5 to 10 parts.

5. The lithium-ion battery electrolyte for silicon negative electrode according to claim 1, characterized in that: The organic solvent includes a carbonate solvent and a carboxylate solvent mixed in a mass ratio of 20-80:5-20; the carbonate solvent includes one or more of cyclic carbonates and linear carbonates; the carboxylate solvent includes one or more of ethyl acetate, ethyl propionate, and propyl propionate; the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate; the linear carbonate includes one or more of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium difluorophosphate.

6. A use of the lithium-ion battery electrolyte for silicon negative electrode according to claim 1, characterized in that: Used to prepare lithium-ion batteries.

7. A lithium-ion battery obtained by the application as claimed in claim 6.

8. The lithium-ion battery according to claim 7, wherein: It includes the lithium-ion battery electrolyte, positive electrode, negative electrode, diaphragm, and shell; the positive electrode includes one or more of lithium cobalt oxide, lithium iron phosphate, and NCM ternary materials; the negative electrode includes a silicon negative electrode; the diaphragm includes one or more of polypropylene film and polypropylene coated alumina ceramic film; the shell includes one or more of a steel shell cylindrical shell, a square soft package shell, and a steel shell button battery shell.

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