Lithium battery electrolyte and application thereof

Abstract

The application provides a lithium battery electrolyte and application thereof, the lithium battery electrolyte comprises a lithium salt, an organic solvent and a high-temperature additive, the lithium salt comprises a main salt and an auxiliary salt, and the high-temperature additive comprises a nitrile compound.The lithium battery electrolyte is compounded by the lithium salt, the organic solvent and the high-temperature additive, has good high-temperature resistance, can inhibit the problems of gas production and thickness increase of the lithium battery under high-temperature conditions, and improves the high-temperature storage stability of the lithium battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a lithium battery electrolyte and its application. Background Technology

[0002] Lithium-ion batteries are widely used in automobiles, home appliances, and portable electronic products. As the demand for lithium-ion batteries increases, so too does the demand for their performance and safety. Lithium-ion batteries suffer from poor high-temperature resistance. For example, primary batteries, such as lithium / manganese dioxide batteries, exhibit poor discharge and significant thickness expansion at high temperatures, severely limiting their application and posing certain safety hazards. The electrolyte, as a crucial component of the lithium-ion battery system, has a significant impact on the battery's energy density, voltage, and temperature resistance. Designing and optimizing the electrolyte can effectively improve the temperature resistance of lithium-ion batteries.

[0003] CN103858268A discloses an electrolyte for lithium batteries and a lithium battery using the electrolyte. The electrolyte contains a quaternary ammonium salt ionic liquid, which includes cations and anions. The cation is an N-alkyl quaternary ammonium salt; the anion is one of the following: halide salt ion, tetrafluoroborate anion, hexafluorophosphate anion, di(trifluoromethanesulfonyl)imide anion, lactate anion, p-toluenesulfonate anion, acetylsulimide anion, saccharin anion, amino acid anion, sulfate ester anion, diisooctyl succinate sulfonate anion, 4,5-dinitroimidazole anion, and 5-nitrotetrazole anion. This technical solution provides an electrolyte for lithium batteries that uses a quaternary ammonium salt ionic liquid as an additive, enabling the lithium battery to maintain consistent high-performance discharge capability from room temperature to high temperature. However, it does not mention improving the thickness expansion problem of lithium batteries at high temperatures.

[0004] CN114520371A discloses a non-aqueous electrolyte and a lithium-ion battery containing the same. The non-aqueous electrolyte comprises, by mass percentage: 5-25% cyclic carbonate solvent, 30-50% chain carboxylic acid ester solvent, 5-20% fluorinated chain carboxylic acid ester, 1-5% nitrile compound, 0.1-15% film-forming additive, and at least one lithium salt. The non-aqueous electrolyte provided by this technical solution does not decompose under high pressure, avoiding excessive consumption of conductive lithium salts and gas generation, significantly improving the cycle performance, high-temperature storage stability, and low-temperature electrical performance of the lithium battery. However, the applicable temperature range of the electrolyte still needs to be further expanded.

[0005] CN110148784A discloses an electrolyte comprising a non-aqueous organic solvent and a conductive lithium salt. The electrolyte further comprises, by weight, 0.1% to 10% of a negative electrode film-forming additive, 0.1% to 10% of a positive electrode film-forming additive, 0.1% to 5% of a gas-inhibiting additive, and 0.1% to 10% of a low-resistance additive. The gas-inhibiting additive in the electrolyte provided by this technical solution can reduce the risk of gas generation during battery cycling and storage. The combined use of these four types of additives can give the lithium battery superior electrical performance; however, the high-temperature resistance of the electrolyte still needs further improvement.

[0006] Therefore, it is necessary to develop a lithium battery electrolyte that can suppress the thickness expansion of lithium batteries at high temperatures and has good stability, so as to broaden the applicable temperature range of lithium batteries. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a lithium battery electrolyte and its applications. The described lithium battery electrolyte exhibits good high-temperature resistance, suppressing gas generation and thickness increases under high-temperature conditions, thus enabling the lithium battery to possess excellent high-temperature storage stability.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a lithium battery electrolyte, the lithium battery electrolyte comprising a lithium salt, an organic solvent and a high-temperature additive, wherein the lithium salt comprises a main salt and an auxiliary salt.

[0010] The high-temperature additive includes nitrile compounds represented by Formula I.

[0011]

[0012] Where R is -CH2-CH2-, -CH2-CH2-CH2-CH2-, Any one of them.

[0013] In this invention, "high temperature" means 45°C to 80°C. The same expression used below has the same meaning.

[0014] In this invention, the high-temperature resistance of the lithium battery electrolyte is improved by compounding lithium salt, organic solvent, and high-temperature additives. The high-temperature additives include nitrile compounds represented by Formula I, which possess carbon-nitrogen triple bond functional groups. These compounds effectively remove trace amounts of water and acidic byproducts formed by the high-temperature decomposition of the electrolyte. Their strong oxidation resistance effectively inhibits electrolyte decomposition, stabilizes the structure of the positive electrode material, and reduces side reactions at the electrode interface, thereby suppressing problems such as gas generation, bulging, and increased thickness of the lithium battery under high-temperature conditions.

[0015] Preferably, the main salt comprises lithium perchlorate.

[0016] Preferably, the auxiliary salt is selected from any one or a combination of at least two of lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonylimide, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, lithium bis(oxalate-borate) or lithium difluorooxalate-borate.

[0017] In this invention, the lithium salt includes a main salt and an auxiliary salt. This is because the performance of a single lithium salt is limited. By using a mixture of two lithium salts, the conductivity of the electrolyte can be improved while the high and low temperature resistance can be enhanced, which can significantly improve the discharge performance of the lithium battery.

[0018] Preferably, the organic solvent includes any one or a combination of at least two of cyclic ester organic solvents, linear ester organic solvents, ether organic solvents, or sulfone organic solvents.

[0019] Preferably, the cyclic ester organic solvent is selected from any one or a combination of at least two of ethylene carbonate, propylene carbonate, or 1,4-butyrolactone.

[0020] Preferably, the linear ester organic solvent is selected from any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, or ethyl propionate.

[0021] Preferably, the ether organic solvent is selected from any one or a combination of at least two of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, 1,3-dioxopentane, 1,3-dioxane, 1,4-dioxane, or tetrahydrofuran.

[0022] Preferably, the sulfone organic solvent is selected from any one or a combination of at least two of vinyl sulfone, dimethyl sulfoxide, or sulfolane.

[0023] Preferably, the lithium battery electrolyte comprises the following components by mass percentage: 1-27% lithium salt (e.g., 1%, 3%, 6%, 9%, 12%, 15%, 18%, 21%, 24%, or 27%), 63-92% organic solvent (e.g., 63%, 65%, 70%, 75%, 80%, 85%, 90%, or 92%), and 0.01-10% high-temperature additive (e.g., 0.01%, 0.05%, 1%, 3%, 5%, 6%, 7%, 8%, 9%, or 10%).

[0024] Preferably, based on the total mass of the lithium battery electrolyte, the mass percentage of the high-temperature additive is 0.5% to 4%, for example, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, or 4%.

[0025] In this invention, the mass percentage of the high-temperature additive is preferably 0.5-4%, because when the content of the high-temperature additive is too low, the Lewis acid generated inside the electrolyte cannot be completely neutralized, and the effect of inhibiting electrolyte decomposition under high temperature and high voltage is not good; when the content of the high-temperature additive is too high, the cost of the electrolyte will increase, and there is no significant improvement in the high-temperature storage stability of the battery.

[0026] Preferably, based on the total mass of the lithium battery electrolyte, the mass percentage of the main salt is 0.1% to 18%, for example, 0.1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, or 18%.

[0027] Preferably, based on the total mass of the lithium battery electrolyte, the mass percentage of the auxiliary salt is 0.1% to 10%, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0028] Preferably, based on the total mass of the lithium battery electrolyte (100%), the mass percentage of the cyclic ester organic solvent is 10-40% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, or 40%), the mass percentage of the linear ester organic solvent is 5-60% (e.g., 5%, 10%, 15%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%), the mass percentage of the ether organic solvent is 0-50% (e.g., 0%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%), and the mass percentage of the sulfone organic solvent is 0-20% (e.g., 0%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, or 20%).

[0029] In this invention, the organic solvent of the lithium battery electrolyte includes 10-40% by mass of cyclic ester organic solvent, 5-60% by mass of linear ester organic solvent, 0-50% by mass of ether organic solvent, and 0-20% by mass of sulfone organic solvent. This is because a single cyclic ester organic solvent has excessively high viscosity, making its application in electrolytes difficult. Compared to using a single type of organic solvent, combining linear ester organic solvent, cyclic ester organic solvent, optional ether organic solvent, and optional sulfone organic solvent as the organic solvent for the lithium battery electrolyte reduces viscosity. This combination improves the electrolyte conductivity while maintaining its performance at low temperatures and high-temperature storage stability, increasing the flash point of the electrolyte. The lithium battery electrolyte prepared using the combined organic solvent exhibits better overall performance.

[0030] In a second aspect, the present invention provides an electrochemical device comprising a lithium battery electrolyte as described in the first aspect.

[0031] Preferably, the electrochemical energy storage device includes a lithium battery.

[0032] Preferably, the lithium battery is a primary lithium-manganese battery.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The lithium battery electrolyte provided by this invention, through the design and component compounding of a lithium salt, organic solvent, and high-temperature additive system, makes the electrolyte less prone to decomposition at high temperatures, suppresses battery failure caused by gas production, stabilizes the structure of the positive electrode material, reduces discharge reduction due to side reactions at the electrode interface, and improves the service life of lithium batteries using this electrolyte at high temperatures. The electrolyte exhibits good stability at high temperatures (45–80°C), reducing problems such as bulging, gas expansion, and thickness increase during high-temperature storage of lithium batteries, and expanding the operating temperature range of lithium batteries. Detailed Implementation

[0035] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0036] The raw materials involved in the following embodiments and comparative examples of the present invention are shown below:

[0037] High-temperature additive a has the following structural formula:

[0038]

[0039] High-temperature additive b has the following structural formula:

[0040]

[0041] High-temperature additive C has the following structural formula:

[0042]

[0043] High-temperature additive d has the following structural formula:

[0044]

[0045] Example 1

[0046] This embodiment provides a lithium battery electrolyte. The amount of each component added to the lithium battery electrolyte is calculated as a percentage of the total mass of the lithium battery electrolyte. The preparation method is as follows:

[0047] The preparation process of the lithium battery electrolyte is carried out in a glove box filled with argon gas, where the moisture content is <0.01ppm and the oxygen concentration is <0.01ppm. 30.5% propylene carbonate, 25% dimethyl carbonate, 20% ethylene glycol dimethyl ether, 10% sulfolane, and 0.5% high-temperature additive a are mixed. 13% lithium perchlorate is added to the mixed solution and stirred until homogeneous. After the solution temperature drops to room temperature, 1% lithium trifluoromethanesulfonate is added. After complete dissolution, the mixture is stirred for 4 hours to obtain the lithium battery electrolyte.

[0048] Experimental Examples 2-16 and Comparative Examples 1-5 used the same preparation method as Example 1, except for the raw materials and their contents, as detailed in Tables 1, 2 and 3.

[0049] Table 1

[0050]

[0051]

[0052] Table 2

[0053]

[0054] Table 3

[0055]

[0056]

[0057] In Tables 2 and 3, "-" indicates that the component was not added.

[0058] The moisture and acidity of the lithium battery electrolytes provided in the examples and comparative examples were measured to ensure that the moisture content was <20 ppm and the acidity was <50 ppm for the preparation and performance testing of the lithium manganese battery.

[0059] The lithium battery electrolytes provided in the examples and comparative examples were used to prepare primary lithium manganese batteries. The preparation method is as follows: MnO2 was used as the positive electrode material and a positive electrode sheet was made using general technology. Lithium metal was used as the negative electrode material and a negative electrode lithium sheet was made using general technology. A lithium battery-specific separator was inserted between the positive and negative electrodes. The positive and negative electrode sheets were stacked to form a battery cell. The battery cell was sealed with an aluminum-plastic film to form a CP223830 model soft-pack battery cell. The lithium battery electrolytes provided in the examples and comparative examples were injected respectively. After being sealed by a hand-press sealing machine, the cells were left to stand for 24 hours to obtain primary lithium manganese batteries. The following performance tests were performed.

[0060] (1) High-temperature storage performance test: The initial thickness of primary lithium-manganese batteries prepared using the lithium battery electrolytes provided in the examples and comparative examples was tested. After recording the data, the primary lithium-manganese batteries were placed in constant temperature ovens at 60℃ and 80℃ respectively. Thickness tests were performed once per 7-day cycle, and data were recorded for 4 cycles. Before testing the thickness, the batteries were placed in a constant temperature chamber at 25℃ for 24 hours to cool down. The formula for calculating the thickness change rate is as follows:

[0061] Thickness change rate (%) after three weeks of storage at 60℃ = 100% × (thickness at 60℃ in the third week - initial thickness) / initial thickness

[0062] Thickness change rate (%) after four weeks of storage at 60℃ = 100% × (thickness at 60℃ in the fourth week - initial thickness) / initial thickness

[0063] Thickness change rate (%) after storage at 80℃ for three weeks = 100% × (thickness at 80℃ in the third week - initial thickness) / initial thickness

[0064] Thickness change rate (%) after four weeks of storage at 80℃ = 100% × (thickness at 80℃ in the fourth week - initial thickness) / initial thickness

[0065] (2) Battery capacity retention test: Primary lithium-manganese batteries prepared using the lithium battery electrolytes provided in the examples and comparative examples were stored in ovens at 60°C and 80°C for 30 days, respectively. After 30 days, they were removed, cooled to room temperature, and discharged using a 1.5kΩ constant resistance discharge method. The discharge capacity after 30 days of storage at 60°C and 80°C was measured. Primary lithium-manganese batteries that were not stored at high temperatures were also discharged using a 1.5kΩ constant resistance discharge method, and the discharge capacity before storage was measured. The formula for calculating the battery capacity retention rate is as follows:

[0066] Battery capacity retention rate at 60℃ (%) = (Discharge capacity after 30 days of storage at 60℃ / Discharge capacity without storage) × 100%

[0067] Battery capacity retention rate at 80℃ (%) = (Discharge capacity after 30 days of storage at 80℃ / Discharge capacity before storage) × 100%

[0068] The test results are shown in Tables 4, 5 and 6.

[0069] Table 4

[0070]

[0071]

[0072] Table 5

[0073]

[0074]

[0075] Table 6

[0076]

[0077]

[0078] According to the data in Tables 4, 5, and 6, the thickness change rate of the primary lithium-manganese batteries prepared with the lithium battery electrolytes provided in Examples 1-16 was 5.9%-12.4% after three weeks of storage at 60°C, and 9.2%-18.4% after four weeks of storage at 60°C. The thickness change rate of the primary lithium-manganese batteries prepared with the lithium battery electrolytes provided in Examples 1-16 was 13.2%-19.5% after three weeks of storage at 80°C, and 17.8%-24.5% after four weeks of storage at 80°C. After 30 days of storage at 60°C, the capacity retention rate of the primary lithium-manganese batteries prepared with the lithium battery electrolytes provided in Examples 1-16 was 90.2%-92.7%; after 30 days of storage at 80°C, the capacity retention rate was 84.3%-87.9%. Under the same storage time, compared with the primary lithium-manganese batteries stored at 60°C, the primary lithium-manganese batteries stored at 80°C showed a greater thickness increase; the higher the temperature, the greater the thickness increase and the lower the capacity retention rate. The test results from Examples 1-3 and Examples 4-6 show that when adding a high-temperature additive of the same structure at a concentration of 1%, the effect on inhibiting battery thickness growth is most significant, and the discharge capacity after high-temperature storage is improved, which is beneficial to the normal performance of the capacity. Compared with Examples 1-6, the lithium battery electrolyte prepared using a combination of four high-temperature additive structures (Examples 7 and 8) has a more significant effect on inhibiting battery thickness growth and also has a higher battery capacity retention rate.

[0079] Compared with Example 1, if high-temperature additive a is not added and 31% propylene carbonate (Comparative Example 1) is added, the resulting lithium battery electrolyte will have increased thickness, lower capacity retention, and poor high-temperature resistance when assembled with it under high-temperature storage.

[0080] Compared with Example 1, if no auxiliary salt (lithium trifluoromethanesulfonate) is added and 14% lithium perchlorate (Comparative Example 2) is added, the prepared lithium battery electrolyte will have a greater thickness increase, lower battery capacity retention, insufficient discharge, and poor high temperature resistance when the primary lithium manganese battery assembled with it is stored at high temperature.

[0081] Compared with Example 1, if lithium perchlorate is not added and 14% lithium trifluoromethanesulfonate (Comparative Example 3) is added, the conductivity of the prepared lithium battery electrolyte is too low, which affects the normal discharge of the primary lithium manganese battery and results in low battery capacity retention.

[0082] Compared with Example 1, if the high-temperature additive a is replaced with the same mass percentage of acrylonitrile (Comparative Example 4), the lithium battery electrolyte prepared using it will have a greater increase in thickness when stored at high temperature, indicating that when the carbon chain is too short or the number of carbon-nitrogen triple bonds is small, it will not have a significant effect.

[0083] Compared with Example 1, if the high-temperature additive a is replaced with the same mass percentage of glutaronitrile (Comparative Example 5), the resulting lithium battery electrolyte exhibits a greater increase in thickness at high temperatures, a lower battery capacity retention rate, and poorer high-temperature resistance in primary lithium-manganese batteries assembled with it.

[0084] In summary, this invention, through the compounding of lithium salt, organic solvent, and high-temperature additives, enables the lithium battery electrolyte to effectively suppress gas generation and thickness increase in lithium batteries under high-temperature conditions (45℃~80℃), thereby improving the high-temperature storage stability of lithium batteries.

[0085] The applicant declares that this invention illustrates a lithium battery electrolyte and its application through the above embodiments, but the invention is not limited to the above embodiments, that is, it does not mean that the invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to this invention, equivalent substitutions of the raw materials of the product, addition of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of this invention.

Claims

1. A primary lithium-manganese battery, characterized by comprising: The primary lithium-manganese battery includes an electrolyte, which includes lithium salt, organic solvent and high-temperature additive, wherein the lithium salt includes a main salt and an auxiliary salt. The high-temperature additive is composed of a combination of high-temperature additive a, high-temperature additive b, high-temperature additive c, and high-temperature additive d; The high-temperature additive a has the following structural formula: The high-temperature additive b has the following structural formula: The high-temperature additive c has the following structural formula: The high-temperature additive d has the following structural formula: The main salt includes lithium perchlorate; The auxiliary salt is selected from any one or a combination of at least two of lithium trifluoromethanesulfonate, lithium bistrifluoromethanesulfonylimide, lithium tetrafluoroborate, lithium bisfluorosulfonylimide, lithium bis(oxalate)borate, or lithium difluorooxalateborate. Based on the total mass of the electrolyte as 100%, the organic solvents include 10-40% by mass of cyclic ester organic solvents, 5-60% by mass of linear ester organic solvents, 10-50% by mass of ether organic solvents, and 1-20% by mass of sulfone organic solvents.

2. The primary lithium-manganese battery according to claim 1, characterized in that, The cyclic ester organic solvent is selected from any one or a combination of at least two of ethylene carbonate, propylene carbonate, or 1,4-butyrolactone.

3. The primary lithium-manganese battery according to claim 1, characterized in that, The linear ester organic solvent is selected from any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, or ethyl propionate.

4. The primary lithium-manganese battery according to claim 1, characterized in that, The ether organic solvent is selected from any one or a combination of at least two of ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol methyl ethyl ether, 1,3-dioxopentane, 1,3-dioxane, 1,4-dioxane, or tetrahydrofuran.

5. The primary lithium-manganese battery according to claim 1, characterized in that, The sulfone organic solvent is selected from any one or a combination of at least two of vinyl sulfone, dimethyl sulfoxide, or sulfolane.

6. The primary lithium-manganese battery according to claim 1, characterized in that, The electrolyte comprises the following components by mass percentage: 1-27% lithium salt, 63-92% organic solvent and 0.01-10% high-temperature additive.

7. The primary lithium-manganese battery according to claim 1, characterized in that, Based on the total mass of the electrolyte being 100%, the mass percentage of the high-temperature additive is 0.5-4%.

8. The primary lithium-manganese battery according to claim 1, characterized in that, Based on the total mass of the electrolyte being 100%, the mass percentage of the main salt is 0.1% to 18%.

9. The primary lithium-manganese battery according to claim 1, characterized in that, Based on the total mass of the electrolyte being 100%, the mass percentage of the auxiliary salt is 0.1-10%.

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