A lithium-ion battery electrolyte for high-voltage lithium cobalt oxide positive electrode material and its application

Abstract

The present invention belongs to the technical field of lithium-ion batteries and relates to an electrolyte for lithium-ion batteries with high-voltage lithium cobalt oxide positive electrode materials and applications thereof. The present invention is based on solving the problem of instability of the lithium cobalt oxide interface caused by high voltage. A propylene sulfonamide additive rarely reported in lithium-ion batteries is discovered. The additive can produce a synergistic effect with other additives and optimize the composition of lithium salts, solvents, and additives. Through the mechanism of forming low-impedance, high-stability CEI and SEI films on the surfaces of the positive and negative electrodes, the high-voltage resistance and cycle performance of the battery are improved, making it have both high and low-temperature performance.

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 high-voltage lithium cobalt oxide positive electrode material and an application 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] The theoretical density of lithium cobalt oxide is about 5.06g / cm3, which is higher than that of NCM ternary materials, lithium iron phosphate, lithium manganese oxide, etc. After complete delithiation, the theoretical specific capacity is 274mAh / g, and the actual compaction density can reach 4.2g / cm3. It has extremely high volume energy density and is the most widely used positive electrode material in the consumer electronics field.

[0004] However, the actual specific capacity of lithium cobalt oxide is only 135-140 mAh / g, and only 50% of the lithium can be reversibly released, making it difficult to meet the requirements of high energy density. Studies have shown that by increasing the charge cut-off voltage, lithium cobalt oxide can release more lithium to participate in the redox reaction, thereby increasing the specific capacity. For example, increasing the upper limit voltage of lithium cobalt oxide from 4.2V to 4.45V can increase the discharge specific capacity from 140mAh / g to 180mAh / g (an increase of about 28.6%), and the discharge platform from 3.70V to 3.87V (an increase of about 4.6%). Therefore, increasing the upper limit voltage of lithium cobalt oxide is one of the most effective ways to increase the energy density of batteries.

[0005] When the charging voltage exceeds 4.2 V, LCO will begin to dissolve Co and precipitate oxygen (oxygen radicals or oxygen). Side reactions will occur between LCO and the electrolyte, causing electrochemical performance degradation, which may cause serious safety problems. Currently, there are three main methods to improve the problems caused by high voltage: bulk doping of lithium cobalt oxide, surface coating of lithium cobalt oxide, and optimization of high-voltage electrolytes. Compared with bulk doping and surface coating, electrolyte optimization is a simple, effective and low-cost method. The use of a small amount of additives can greatly optimize the performance of the electrolyte. High-voltage lithium cobalt oxide additives mainly improve battery performance from the aspects of optimizing the positive electrode interface properties, limiting cobalt dissolution, and inhibiting the generation of HF. Summary of the Invention

[0006] The present invention aims to solve the problem of instability of the lithium cobalt oxide interface caused by high voltage. It discovers an additive called propenylsulfonamide, which has rarely been reported in lithium-ion batteries. It can also produce synergistic effects with other additives and optimize the composition of lithium salts, solvents, and additives. Through the mechanism of forming low-impedance, high-stability CEI and SEI films on the surfaces of the positive and negative electrodes, the battery's high-voltage resistance and cycle performance are improved, making it have both high and low-temperature performance.

[0007] The object of the present invention is to provide a high-voltage lithium cobalt oxide positive electrode material lithium ion battery electrolyte, the designed electrolyte has better cycle performance than conventional electrolytes.

[0008] 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.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] A lithium-ion battery electrolyte for high-voltage lithium cobalt oxide positive electrode materials comprises an organic solvent, a lithium salt and an additive; the additive comprises acrylsulfonamide.

[0011] Preferably, the mass fraction of the additive in the lithium-ion battery electrolyte is 0.5-10%.

[0012] Preferably, the additive further comprises a cyclic compound; the cyclic compound comprises one or more of the following structures:

[0013]

[0014] Formula I,

[0015]

[0016] Formula II.

[0017] 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:

[0018]

[0019] Formula III,

[0020]

[0021] Formula IV.

[0022] Preferably, the cyclic compound includes one or more of the following compounds:

[0023]

[0024] Compound a1,

[0025]

[0026] Compound a2,

[0027]

[0028] Compound a3,

[0029]

[0030] Compound a4.

[0031] Preferably, in the additive, the mass ratio of the acrylsulfonamide to the cyclic compound is 1-3:1.

[0032] Preferably, the raw materials include the following parts by weight:

[0033] 75-90 parts of the organic solvent

[0034] 10 to 15 parts of the lithium salt

[0035] The additive is 0.5 to 10 parts.

[0036] A high-voltage lithium cobalt oxide positive electrode material lithium-ion battery electrolyte comprises an organic solvent, a lithium salt, and an additive. The organic solvent accounts for 75% to 90% of the total weight of the lithium-ion battery electrolyte, the lithium salt accounts for 10% to 15% of the total weight of the lithium-ion battery electrolyte, and the additive accounts for 0.5% to 10% of the total weight of the lithium-ion battery electrolyte.

[0037] 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.

[0038] In the above-mentioned lithium-ion battery electrolyte, the organic solvent is a mixture of carbonate and carboxylate solvents in a certain proportion, wherein the carbonate solvent accounts for 20-80% of the total weight of the lithium-ion battery electrolyte, and the carboxylate solvent accounts for 5-20% of the total weight of the lithium-ion battery electrolyte. The carbonate solvent includes cyclic carbonates and linear carbonates, wherein the cyclic carbonate includes at least one of ethylene carbonate (EC) and propylene carbonate (PC); the linear carbonate includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). The carboxylate solvent includes at least one of ethyl acetate (EA), ethyl propionate (EP), and propyl propionate (PP).

[0039] The lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), and lithium difluorophosphate (LiPO2F2), and the lithium salt accounts for 10-15% of the total weight of the lithium-ion battery electrolyte.

[0040] An application of the lithium ion battery electrolyte for high-voltage lithium cobalt oxide positive electrode material is used to prepare lithium ion batteries.

[0041] A lithium ion battery obtained by the above application.

[0042] Preferably, it includes the lithium-ion battery electrolyte, positive electrode, negative electrode, diaphragm, and shell; the positive electrode includes lithium cobalt oxide; the negative electrode includes one or more of graphite, silicon carbon, and lithium metal; 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.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] As a new additive, acrylsulfonamide has a unique atomic composition and chemical structure, containing carbon, nitrogen, sulfur, and oxygen atoms, forming structures such as acryl and sulfonamide. Its unique structure and steric hindrance are achieved through a special connection method. The additive acrylsulfonamide has strong reducing and oxidizing activities, forming insoluble cross-linked polymer deposits on the negative electrode surface, improving the stability of the SEI film. It also preferentially forms a CEI film on the positive electrode. The cross-linked polymer deposits are highly tough, have low membrane impedance, and are more stable, preventing the dissolution of transition metals.

[0045] 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≤3, 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 decomposition products of the first additive and the second additive are cross-linked to form a more stable CEI film, preventing the dissolution of metal ions in the positive electrode active material layer. On the other hand, the first additive and the second additive jointly participate in the negative electrode film formation to form a stable SEI film. Since the second additive has poor compatibility with the negative electrode, when the content is added in large amounts, the negative electrode film formation effect is poor. Therefore, when the first additive and the second additive are added in a ratio of 1 to 3, it is possible to improve the negative electrode film formation effect, reduce the interfacial impedance of the battery, and improve the high and low temperature cycle performance of the battery while ensuring the stability of the positive electrode of the battery.

[0046] 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

[0047] Figure 1 It is the chemical structure of the additive acrylsulfonamide in the present invention.

[0048] Figure 2 is the chemical structure of the comparative additive propylsulfonamide in the present invention. DETAILED DESCRIPTION

[0049] 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.

[0050] Unless otherwise specified, the reagents used in the examples and comparative examples can be purchased from the market.

[0051] The lithium cobalt oxide (LCO) / lithium half-cells assembled in the Examples and Comparative Examples used a 2016 model battery case. The positive electrode had no gasket or spring, and the negative electrode used a stainless steel gasket. The LCO positive electrode had a diameter of 14 mm; the lithium sheet had the same diameter as the stainless steel gasket (16 mm), with a thickness of 1 mm and a gasket of 0.5 mm. The electrolyte volume used was 50 μL, and the separator used was a PP membrane with a diameter of 19 mm and a thickness of 25 μm.

[0052] Example 1

[0053] This embodiment provides an electrolyte for a high-voltage lithium cobalt oxide positive electrode material lithium ion battery and its application, which includes the following components, calculated by mass percentage: LiPF6 / LiODFB / LiBOB (8 / 1 / 1) 12.5%; PC / EC / EMC / DMC / EP (2 / 2 / 2 / 2 / 2) 85.5%; propenylsulfonamide (structure as shown in FIG Figure 1 This embodiment also provides an electrolyte for a high-voltage lithium cobalt oxide positive electrode material lithium ion battery and its application preparation steps, which are as follows:

[0054] 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;

[0055] S2. First, the organic solvent is mixed and stirred to form a uniform organic solvent;

[0056] S3. The lithium salt is then dissolved in an organic solvent and stirred to form a uniform solution;

[0057] S4. The propenylsulfonamide was added to the uniform solution in step S3 and stirred to obtain the electrolyte;

[0058] S5. Assemble LCO / lithium button cells using the electrolyte obtained in S4. Allow to stand for 12 hours, perform three cycles of activation at a 0.1C rate to form a film, and then perform a long charge-discharge cycle test at a 1C rate to evaluate the cycling stability of the lithium-ion battery containing this electrolyte.

[0059] Comparative Example 1

[0060] This embodiment provides an electrolyte for a high-voltage lithium cobalt oxide positive electrode material lithium ion battery and its application, which includes the following components by mass percentage: LiPF6 / LiODFB / LiBOB (8 / 1 / 1) 12.5%; PC / EC / EMC / DMC / EP (2 / 2 / 2 / 2 / 2) 85.5%; propyl sulfonamide (structure as shown in FIG Figure 2 This embodiment also provides an electrolyte for a high-voltage lithium cobalt oxide positive electrode material lithium ion battery and its application preparation steps, which are as follows:

[0061] 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;

[0062] S2. First, the organic solvent is mixed and stirred to form a uniform organic solvent;

[0063] S3. The lithium salt is then dissolved in an organic solvent and stirred to form a uniform solution;

[0064] S4. The propenylsulfonamide was added to the uniform solution in step S3 and stirred to obtain the electrolyte;

[0065] S5. Assemble LCO / lithium button cells using the electrolyte obtained in S4. Allow to stand for 12 hours, perform three cycles of activation at a 0.1C rate to form a film, and then perform a long charge-discharge cycle test at a 1C rate to evaluate the cycling stability of the lithium-ion battery containing this electrolyte.

[0066] Example 2

[0067] This embodiment provides an electrolyte for a high-voltage lithium cobalt oxide positive electrode material lithium ion battery and its application. The electrolyte comprises the following components, calculated by mass percentage: LiPF6 / LiODFB / LiBOB (8 / 1 / 1) 12.5%; PC / EC / EMC / DMC / EP (2 / 2 / 2 / 2 / 2) 85.5%; a first additive of acrylsulfonamide 1%; a second additive of a cyclic compound 1%; This embodiment also provides an electrolyte for a high-voltage lithium cobalt oxide positive electrode material lithium ion battery and its application, and the preparation steps are as follows:

[0068] 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;

[0069] S2. First, the organic solvent is mixed and stirred to form a uniform organic solvent;

[0070] S3. The lithium salt is then dissolved in an organic solvent and stirred to form a uniform solution;

[0071] S4. The first additive and the second additive are added to the uniform solution of step S3 and stirred to obtain the electrolyte;

[0072] S5. Assemble LCO / lithium button cells using the electrolyte obtained in S4. Allow to stand for 12 hours, perform three cycles of activation at a 0.1C rate to form a film, and then perform a long charge-discharge cycle test at a 1C rate to evaluate the cycling stability of the lithium-ion battery containing this electrolyte.

[0073] Effect Example 1

[0074] The secondary battery for the blank control was prepared similarly to that of Example 1, except that no additives were added, as detailed in Table 1. The button cells assembled in Example 1, Comparative Example 1, and the blank control were all subjected to constant current charge-discharge tests at 0°C, 25°C, and 45°C using a Xinwei test system to evaluate cycling stability. The constant current charge-discharge tests were conducted over a voltage range of 2.3V-4.55V. The first three cycles were activated at 0.1C, followed by long-term cycling at 1C. The test results are shown in Table 1.

[0075] Table 1 Test results of Example 1, Comparative Example 1, and Blank Control

[0076]

[0077] As shown in Table 1, although propylsulfonamide and acrylsulfonamide have a partially similar structure, the battery's capacity retention rate after using propylsulfonamide is around 30%, and the cycle performance is poor. The difference with the blank control is not significant, and there is basically no improvement. After replacing it with acrylsulfonamide, the battery's capacity retention rate jumped to around 60%, and the cycle performance was greatly improved.

[0078] Effect Example 2

[0079] The secondary batteries of Example 2-17 and Comparative Example 2-7 were prepared in a similar manner to the secondary battery of Example 1, except that the composition and parameters of the additives, solvent, and lithium salt in the electrolyte were adjusted, as shown in Table 2.

[0080] The button batteries assembled in the examples and comparative examples were tested using a Xinwei test system and subjected to constant current charge and discharge tests 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. 0.1C was used for the first three activation cycles, and then 1C was used for long cycles. The test results are shown in Table 2.

[0081] Table 2 Test results of Examples 2-17 and Comparative Examples 3-8

[0082]

[0083] The test results in Table 2 show that the addition of the first and second additives both improves cycling performance at 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 ≤ 3) is even more significant, boosting the battery's capacity retention to over 80%. In particular, a comparison of Example 11 with Comparative Example 3 reveals a surprising improvement in cycling performance at room temperature of approximately 50%, and in cycling performance at both high and low temperatures of approximately 70%, with even greater improvements at both high and low temperatures.

[0084] 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 high voltage lithium cobalt oxide positive electrode material, characterized in that: The invention comprises an organic solvent, a lithium salt and an additive; the additive comprises acrylsulfonamide; the mass fraction of the additive in the lithium-ion battery electrolyte comprises 0.5 to 10%; the additive further comprises 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; In the additive, the mass ratio of the acrylsulfonamide to the cyclic compound is 1-3:

1.

2. The lithium-ion battery electrolyte for high-voltage lithium cobalt oxide positive electrode material 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 high-voltage lithium cobalt oxide positive electrode material according to claim 1, characterized in that: 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.

4. The lithium-ion battery electrolyte for high-voltage lithium cobalt oxide positive electrode material 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.

5. A use of the lithium ion battery electrolyte for high voltage lithium cobalt oxide positive electrode material as claimed in claim 1, characterized in that: Used to prepare lithium-ion batteries.

6. A lithium-ion battery obtained by the application of claim 5, characterized in that: It includes the lithium-ion battery electrolyte, positive electrode, negative electrode, diaphragm, and shell; the positive electrode includes lithium cobalt oxide; the negative electrode includes one or more of graphite, silicon carbon, and lithium metal; 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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