Electrolyte compositions, electrolytes and their preparation methods, and lithium-ion batteries

Abstract

This invention relates to the field of lithium-ion battery technology, disclosing an electrolyte composition, an electrolyte, a method for preparing the same, and a lithium-ion battery. The composition contains a lithium salt, a film-forming additive, an organic solvent, and an auxiliary agent; wherein, based on the total weight of the electrolyte, the lithium salt content is 6-20 wt%, the film-forming additive content is 2-6 wt%, the organic solvent content is 75-90 wt%, and the auxiliary agent content is 2-10 wt%; the auxiliary agent is a combination of 4-iodophthalonitrile and 6-fluoro-nicotinamide in a mass ratio of 1:0.5-2. The electrolyte prepared from the electrolyte composition provided by this invention, when applied to a lithium-ion battery system with a single-particle graphite anode, can significantly improve the interfacial stability of the single-particle graphite anode at high temperatures, suppress the increase in anode polarization and gas generation problems; and can significantly improve the high-temperature cycle life and high-temperature rate performance of the lithium-ion battery.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to electrolyte compositions, electrolytes and their preparation methods, and lithium-ion batteries. Background Technology

[0002] To promote the integration and application of renewable energy sources such as wind and solar power, equipping devices with electrochemical energy storage systems, represented by lithium iron phosphate batteries, has become a trend. To improve the operational lifespan of lithium iron phosphate battery energy storage systems, using single-particle graphite anodes with smaller specific surface areas is currently the mainstream strategy. However, in actual energy storage system operation, the heat generated inside the battery is difficult to release, easily leading to temperature increases. This severely affects the stability of the graphite anode / electrolyte interface, resulting in problems such as battery bulging and capacity decay. Simply reducing the specific surface area with single-particle graphite is insufficient to meet these requirements.

[0003] Improving the thermal stability of the graphite anode / electrolyte interface through high-temperature electrolyte additives is an effective supplementary approach. However, currently used mainstream high-temperature additives (such as 1,3-propanesulfonate lactone and methylene methane disulfonate) are still not ideal, and side reactions at the anode / electrolyte interface continue to occur in practical applications, leading to a significant drop in battery capacity. Furthermore, due to the high film-forming impedance of 1,3-propanesulfonate lactone and methylene methane disulfonate, they exacerbate heat generation during cycling in high-rate testing, further deteriorating the battery's high-temperature performance. To address these issues, there is an urgent need to develop a high-temperature electrolyte that can form high thermal stability and low impedance on the graphite anode surface.

[0004] CN117832630A discloses a suitable electrolyte and lithium battery for lithium manganese iron phosphate batteries. The electrolyte includes lithium salt, organic solvent, and additives. The lithium salt includes lithium difluorosulfonylimide and lithium hexafluorophosphate. The organic solvent includes ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate. The additives include vinylene carbonate, 1,3-propanesulfonate lactone, ethylene sulfate, lithium difluorophosphate, and tris(trimethylsilyl)phosphate. This technical solution has good effects on interface improvement, gas generation suppression, and cycle optimization; however, it still suffers from insufficient long-term negative electrode interface stability and poor high-temperature rate performance. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of poor high-temperature interface stability, rapid high-temperature cycling capacity decay, and poor high-temperature rate performance of single-particle graphite anodes in the prior art.

[0006] To achieve the above objectives, a first aspect of the present invention provides an electrolyte composition comprising a lithium salt, a film-forming additive, an organic solvent, and an auxiliary agent;

[0007] Based on the total weight of the electrolyte, the lithium salt content is 6-20 wt%, the film-forming additive content is 2-6 wt%, the organic solvent content is 75-90 wt%, and the auxiliary agent content is 2-10 wt%.

[0008] The additive is a combination of 4-iodophthalonitrile and 6-fluoro-nicotinonitrile in a mass ratio of 1:0.5-2.

[0009] Preferably, based on the total weight of the electrolyte, the lithium salt content is 10-15 wt%, the film-forming additive content is 3-5 wt%, the organic solvent content is 80-83 wt%, and the auxiliary agent content is 2-5 wt%.

[0010] Preferably, the lithium salt is selected from at least two of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, and lithium nitrate.

[0011] In a preferred embodiment, the lithium salt is a combination of lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalate)borate, and lithium bis(trifluoromethylsulfonyl)imide in a mass ratio of 2-3:1:1-2.

[0012] Preferably, the film-forming additive is selected from at least three of the following: fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, 1,3,6-hexanetrionitrile, methanedisulfonate, tri(allyl) phosphite, triargyl phosphite, and di(trimethylsilyl) fluorophosphite.

[0013] Preferably, the film-forming additive is a combination of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, methylene disulfonate, and di(trimethylsilyl) fluorophosphite in a mass ratio of 1:1-3:0.5-1.5:0.2-0.7:0.2-0.7.

[0014] In a preferred embodiment, the organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0015] A second aspect of the present invention provides a method for preparing an electrolyte, the method comprising: contact mixing the electrolyte described in the first aspect with the components of a composition under a protective atmosphere to obtain an electrolyte.

[0016] A third aspect of the invention provides an electrolyte prepared by the method of claim 8.

[0017] A fourth aspect of the present invention provides a lithium-ion battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte;

[0018] The electrolyte is the electrolyte described in the third aspect.

[0019] Through the above technical solution, the present invention has at least the following advantages:

[0020] The electrolyte composition provided by this invention can be used in lithium-ion battery systems with single-particle graphite anodes. It can not only significantly improve the interfacial stability of single-particle graphite anodes at high temperatures and suppress the increase of anode polarization and gas generation, but also significantly improve the high-temperature cycle life and high-temperature rate performance of lithium-ion batteries. Attached Figure Description

[0021] Figure 1 These are the high-temperature cycling test results of the electrolytes prepared in Example 1 and Comparative Example 1 of the present invention;

[0022] Figure 2 These are the high-temperature rate test results of the electrolyte prepared in Example 1 of this invention;

[0023] Figure 3 This is the high-temperature rate charge-discharge curve of the electrolyte prepared in Example 1 of the present invention. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] As previously described, a first aspect of the present invention provides an electrolyte composition comprising a lithium salt, a film-forming additive, an organic solvent, and an auxiliary agent;

[0026] Based on the total weight of the electrolyte, the lithium salt content is 6-20 wt%, the film-forming additive content is 2-6 wt%, the organic solvent content is 75-90 wt%, and the auxiliary agent content is 2-10 wt%.

[0027] The additive is a combination of 4-iodophthalonitrile and 6-fluoro-nicotinonitrile in a mass ratio of 1:0.5-2.

[0028] During their research, the inventors of this invention discovered that a mixture of 4-iodophthalonitrile and 6-fluoro-nicotinonitrile was specifically chosen as an additive. The two additives can work synergistically to form a highly thermally stable, low-impedance negative electrode / electrolyte interface through the cyano and fluorine atoms they contain. At the same time, this additive works in conjunction with lithium salt, film-forming additives, and organic solvents to obtain the electrolyte described in this invention. This electrolyte can maintain the stable operation of the battery during high-temperature cycling, suppress capacity decay and increased polarization, and ultimately improve the high-temperature cycle life and rate performance of the single-particle graphite negative electrode.

[0029] Preferably, based on the total weight of the electrolyte, the lithium salt content is 8-20 wt%, the film-forming additive content is 2-6 wt%, the organic solvent content is 76-83 wt%, and the auxiliary agent content is 2-5 wt%.

[0030] Preferably, based on the total weight of the electrolyte, the lithium salt content is 10-15 wt%, the film-forming additive content is 3-5 wt%, the organic solvent content is 80-83 wt%, and the auxiliary agent content is 2-5 wt%.

[0031] Preferably, the lithium salt is selected from at least two of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, and lithium nitrate.

[0032] In a preferred embodiment, the lithium salt is a combination of lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalate)borate, and lithium bis(trifluoromethylsulfonyl)imide in a mass ratio of 2-3:1:1-2. The inventors of this invention have discovered that, in this preferred embodiment, the high-temperature rate performance of the lithium-ion battery can be further improved.

[0033] Preferably, the film-forming additive is selected from at least three of the following: fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, 1,3,6-hexanetrionitrile, methanedisulfonate, tri(allyl) phosphite, triargyl phosphite, and di(trimethylsilyl) fluorophosphite.

[0034] Preferably, the film-forming additive is a combination of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, methylene disulfonate, and di(trimethylsilyl) fluorophosphite in a mass ratio of 1:1-3:0.5-1.5:0.2-0.7:0.2-0.7. In this preferred embodiment, the high-temperature cycle life of the lithium-ion battery can be significantly improved.

[0035] In a preferred embodiment, the organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0036] As previously described, a second aspect of the present invention provides a method for preparing an electrolyte, the method comprising: contact mixing the electrolyte described in the first aspect with the components of a composition under a protective atmosphere to obtain an electrolyte.

[0037] Preferably, the protective atmosphere is selected from at least one of nitrogen, argon and helium.

[0038] More preferably, in the protective atmosphere, the content of water and oxygen is each independently less than 0.1 ppm.

[0039] It should be noted that the present invention does not have specific requirements for the contact mixing time and temperature, and any conditions known in the art can be used. According to a particularly preferred embodiment, the contact mixing conditions include: a temperature of 10-30°C and a time of 6-24 hours.

[0040] As previously stated, a third aspect of the present invention provides an electrolyte prepared by the method of claim 8.

[0041] As mentioned above, a fourth aspect of the present invention provides a lithium-ion battery comprising: a positive electrode, a negative electrode, a separator, and an electrolyte;

[0042] The electrolyte is the electrolyte described in the third aspect.

[0043] Preferably, the positive electrode is a lithium iron phosphate electrode sheet, the negative electrode is a single-particle graphite electrode sheet, and the separator is a polyolefin separator.

[0044] It should be noted that the present invention does not have any special requirements on the content of the electrolyte in the lithium-ion battery, and any electrolyte known in the art can be used.

[0045] The present invention will be described in detail below through examples. In the following examples, unless otherwise specified, all raw materials used are commercially available products.

[0046] Lithium difluorosulfonylimide was purchased from Bailingwei Technology Co., Ltd., CAS No. 171611-11-3;

[0047] Lithium difluorooxalate boronate was purchased from Bailingwei Technology Co., Ltd., CAS No. 409071-16-5;

[0048] Lithium bis(trifluoromethanesulfonylimide) was purchased from Bailingwei Technology Co., Ltd., CAS No. 90076-65-6;

[0049] Fluorinated vinyl carbonate, purchased from Bailingwei Technology Co., Ltd., CAS No. 114435-02-8;

[0050] Vinylene carbonate, purchased from Bailingwei Technology Co., Ltd., CAS No. 872-36-6;

[0051] Vinyl sulfate, purchased from Bailingwei Technology Co., Ltd., CAS No. 1072-53-3;

[0052] Methylene methane disulfonate, purchased from Bailingwei Technology Co., Ltd., CAS No. 99591-74-9;

[0053] Di(trimethylsilyl) fluorophosphite was purchased from Bailingwei Technology Co., Ltd., CAS No. 36198-87-5;

[0054] 4-Iodophthalonitrile, purchased from Bailingwei Technology Co., Ltd., CAS No. 69518-17-8;

[0055] 6-Fluoro-nicotinonitrile, purchased from Bailingwei Technology Co., Ltd., CAS No. 1020253-14-8;

[0056] Fluoroacetonitrile, purchased from Bailingwei Technology Co., Ltd., CAS No. 503-20-8;

[0057] The lithium metal flakes were purchased from Tianjin Zhongneng Lithium Industry Co., Ltd., with a purity of 99.9%.

[0058] The single-particle graphite anode was purchased from Shenzhen Kejing Zhida Technology Co., Ltd., CAS No. 7782-42-5.

[0059] In the following examples, room temperature refers to a temperature of 23±2℃.

[0060] In the following examples, organic solvent I is a combination of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a mass ratio of 1:1:1.08;

[0061] Lithium salt I is a combination of lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalate boron) and lithium bis(trifluoromethylsulfonyl)imide in a mass ratio of 5:2:3;

[0062] Lithium salt II is a combination of lithium difluorosulfonylimide and lithium difluorooxalate boron in a mass ratio of 1:5;

[0063] Film-forming additive I is a combination of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, methylene disulfonate and fluorophosphite di(trimethylsilyl) ester in a mass ratio of 1:2:1:0.5:0.5.

[0064] Film-forming additive II is a combination of fluoroethylene carbonate, vinylene carbonate and vinyl sulfate in a mass ratio of 1:2:2;

[0065] Additive I is a combination of 4-iodophthalonitrile and 6-fluoro-nicotinonitrile in a mass ratio of 1:2;

[0066] Additive II is a combination of 4-iodophthalonitrile and 6-fluoro-nicotinonitrile in a mass ratio of 2:1;

[0067] Additive III is 4-iodophthalonitrile;

[0068] Additive IV is 6-fluoro-nicotinonitrile;

[0069] Additive V is a combination of 4-iodophthalonitrile and fluoroacetonitrile in a mass ratio of 1:2.

[0070] Example 1

[0071] In an argon-protected glove box (H2O and O2 contents are both less than 0.1ppm), lithium salt, film-forming additives, organic solvents and auxiliaries are contact-mixed (temperature 25℃, time 6h), and stirred at room temperature for 24h to obtain electrolyte.

[0072] The specific types and amounts of raw materials used in Example 1 are shown in Table 1. Unless otherwise specified, the other examples follow the same process as Example 1, except for the raw materials and proportions used, as detailed in Table 1.

[0073] Table 1

[0074]

[0075]

[0076] Example 4

[0077] This embodiment uses a method similar to that of Example 1, except that in this embodiment, film-forming additive II of equal mass is used to replace film-forming additive I in Example 1 to obtain an electrolyte.

[0078] Example 5

[0079] This embodiment uses a method similar to that of Example 1, except that lithium salt I in Example 1 is replaced with lithium salt II of equal mass to obtain the electrolyte.

[0080] Comparative Example 1

[0081] This comparative example was conducted using a method similar to that of Example 1. The difference is that no additives were added in this comparative example, and the amount of organic solvent was adjusted to 8.45g. The type of organic solvent remained unchanged, and an electrolyte was obtained.

[0082] Comparative Example 2

[0083] This comparative example was conducted using a method similar to that of Example 1. The difference is that in this comparative example, an equal mass of additive III was used to replace additive I in Example 1 to obtain the electrolyte.

[0084] Comparative Example 3

[0085] This comparative example was conducted using a method similar to that of Example 1. The difference is that in this comparative example, an equal mass of additive IV was used to replace additive I in Example 1 to obtain the electrolyte.

[0086] Comparative Example 4

[0087] This comparative example was conducted using a method similar to that of Example 1. The difference is that in this comparative example, an equal mass of additive V was used to replace additive I in Example 1 to obtain the electrolyte.

[0088] Test case

[0089] The electrolytes prepared in the above examples were subjected to performance tests, including rate performance and cycle performance.

[0090] The testing method is as follows:

[0091] A coin cell half-cell was assembled using a single-particle graphite negative electrode as the working electrode and a lithium metal sheet as the counter electrode. The specific assembly sequence was as follows: positive electrode shell - single-particle graphite negative electrode - electrolyte - separator - electrolyte - lithium metal sheet - gasket - spring sheet - negative electrode shell. After assembly, the battery was activated at 0.1C for 3 weeks, and then cycled at 1C for 100 cycles at 45℃. The discharge specific capacity was recorded. The discharge specific capacity was also tested at 0.1C, 0.5C, 1C, 2C, and 3C. The test results are shown in Table 2.

[0092] Table 2

[0093]

[0094] The present invention is exemplarily described in Figure 1 The high-temperature cycling test results of the electrolytes prepared in Example 1 and Comparative Example 1 are provided; through Figure 1 The results show that the electrolyte prepared by this invention can significantly improve the cycle life of the battery at a high temperature of 45°C.

[0095] The present invention is exemplarily described in Figure 2 The results of high-temperature rate testing of the electrolyte prepared in Example 1 are provided; and in Figure 3 The high-temperature rate charge-discharge curves of the electrolyte prepared in Example 1 are provided; through Figure 2 , Figure 3 The results show that the electrolyte prepared by this invention can form a graphite anode interface with both high stability and low polarization, thereby significantly improving the rate performance of the battery at high temperatures.

[0096] The results above show that the electrolyte prepared by the electrolyte composition provided by the present invention, when applied to a lithium-ion battery system with a single-particle graphite anode, can have a higher high-temperature cycle discharge specific capacity and a higher high-temperature rate discharge specific capacity compared to the comparative example, and can significantly improve the cycle life and rate performance of the single-particle graphite anode at high temperatures.

[0097] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A composition for use in an electrolyte, characterized in that, The composition contains lithium salt, film-forming additives, organic solvents, and auxiliaries; Based on the total weight of the electrolyte, the lithium salt content is 6-20 wt%, the film-forming additive content is 2-6 wt%, the organic solvent content is 75-90 wt%, and the auxiliary agent content is 2-10 wt%. The additive is a combination of 4-iodophthalonitrile and 6-fluoro-nicotinonitrile in a mass ratio of 1:0.5-2.

2. The composition according to claim 1, wherein, Based on the total weight of the electrolyte, the lithium salt content is 10-15 wt%, the film-forming additive content is 3-5 wt%, the organic solvent content is 80-83 wt%, and the auxiliary agent content is 2-5 wt%.

3. The composition according to claim 1 or 2, wherein, The lithium salt is selected from at least two of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethyl)sulfonyl)imide, lithium tetrafluoroborate, lithium di(oxalate)borate, lithium di(fluorooxalate)borate, and lithium nitrate.

4. The composition according to claim 3, wherein, The lithium salt is a combination of lithium bis(fluorosulfonyl)imide, lithium bis(fluorooxalate boron) and lithium bis(trifluoromethylsulfonyl)imide in a mass ratio of 2-3:1:1-2.

5. The composition according to claim 1 or 2, wherein, The film-forming additive is selected from at least three of the following: fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, 1,3-propanesulfonate lactone, 1,3,6-hexanetrionitrile, methanedisulfonate, tri(allyl) phosphite, triargyl phosphite, and di(trimethylsilyl) fluorophosphite.

6. The composition according to claim 5, wherein, The film-forming additive is a combination of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, methylene disulfonate, and di(trimethylsilyl) fluorophosphite in a mass ratio of 1:1-3:0.5-1.5:0.2-0.7:0.2-0.

7.

7. The composition according to claim 1 or 2, wherein, The organic solvent is selected from at least one of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

8. A method for preparing an electrolyte, characterized in that, The method includes: under a protective atmosphere, contact mixing the electrolyte according to any one of claims 1-7 with the components in the composition to obtain an electrolyte.

9. The electrolyte prepared by the method of claim 8.

10. A lithium-ion battery, characterized in that, The battery includes: a positive electrode, a negative electrode, a separator, and an electrolyte; The electrolyte is the electrolyte according to claim 9.

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