High-temperature-resistant electrolyte and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a high-temperature-resistant electrolyte and a lithium ion battery. The high-temperature-resistant electrolyte comprises a lithium salt, an organic solvent, a film-forming additive and a high-temperature-resistant additive; based on the total mass of the high-temperature-resistant electrolyte being 100%, the content of the high-temperature-resistant additive is 1-5%; the high-temperature-resistant additive is selected from a combination of diphenylphosphonyl hydroxylamine and phenylphosphonyl nitrile. The high-temperature-resistant additive is introduced into the high-temperature-resistant electrolyte provided by the invention, so that a stable and compact SEI film can be formed on the surface of a negative electrode, dendritic crystal growth is inhibited, active lithium loss is reduced, meanwhile, a high-temperature-resistant protective layer is generated on the positive electrode side, and the anti-oxidation stability of a positive electrode interface is effectively improved, so that the electrode interface has compactness and heat resistance; and the interface stability at high temperature is obviously improved, so that the battery applying the composite material has excellent high-temperature cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more particularly to a high-temperature resistant electrolyte and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries, as the most representative rechargeable battery system, play a core role in new energy vehicles, smart grids, and portable electronic products due to their high specific energy, long cycle life, and excellent energy conversion efficiency.

[0003] However, as its applications gradually expand to extreme environments and high-load scenarios, such as power system operation in high-temperature climates, deep oil and gas well exploration, and aerospace equipment power supply, the stability and safety issues of batteries under high-temperature conditions are becoming increasingly prominent. Especially in environments exceeding 60°C, traditional carbonate-based electrolyte systems generally face multiple challenges: First, the thermal decomposition reaction of conventional solvents intensifies, easily generating gases and byproducts, leading not only to abnormal changes in electrolyte viscosity and conductivity but also potentially inducing thermal runaway risks; second, commonly used lithium salts such as lithium hexafluorophosphate decompose easily at high temperatures, and the generated corrosive substances such as HF damage the electrode / electrolyte interface, significantly shortening battery life; third, the negative electrode SEI film is unstable at high temperatures, prone to cracking and repeated repair cycles, resulting in continuous consumption of active lithium, while the surface of the positive electrode material may also undergo electrolyte oxidation reactions, forming a high-resistivity layer that severely hinders lithium-ion transport and energy efficiency. The combination of these problems not only reduces the cycle stability of the battery but also poses a threat to the safe operation of large-scale energy storage and power battery systems.

[0004] Therefore, developing novel high-temperature electrolyte systems has become a common direction for both research and industrial demand. Currently, feasible improvement strategies include: (1) introducing solvents with higher thermal decomposition temperatures and better chemical inertness through molecular design to fundamentally improve the thermal stability of the electrolyte; (2) screening and optimizing high-temperature resistant lithium salts to ensure long cycle life and safe operation of the battery; and (3) constructing a dense and heat-resistant interfacial film on the electrode surface by adding film-forming agents and high-temperature functional additives to effectively suppress side reactions and stabilize the interfacial structure. Although some studies have explored the application of additives such as fluorinated solvents and dianionic salts, there are still problems such as high cost, insufficient system compatibility, or poor long-term thermal stability.

[0005] Therefore, how to achieve excellent interfacial stability and resistance to thermal decomposition while maintaining high ionic conductivity, and how to construct a new electrolyte system for high-temperature applications, has become a key issue that urgently needs to be addressed. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a high-temperature resistant electrolyte and a lithium-ion battery. The high-temperature resistant electrolyte provided by this invention incorporates high-temperature resistant additives, enabling the formation of a stable and dense SEI film on the negative electrode surface. This inhibits dendrite growth and reduces active lithium loss. Simultaneously, a high-temperature resistant protective layer is generated on the positive electrode side, effectively improving the oxidation stability of the positive electrode interface. Thus, the electrode interface possesses both density and heat resistance, significantly improving interface stability at high temperatures, and enabling batteries using this electrolyte to exhibit excellent high-temperature cycle performance.

[0007] In a first aspect, the present invention provides a high-temperature resistant electrolyte, the high-temperature resistant electrolyte comprising lithium salt, organic solvent, film-forming additive and high-temperature resistant additive; Based on the total mass of the high-temperature resistant electrolyte as 100%, the content of the high-temperature resistant additive is 1-5%, such as 1%, 2%, 3%, 4%, 5%, etc. The high-temperature resistant additive is selected from a combination of diphenylphosphonohydroxylamine and phenylphosphononitrile.

[0008] The high-temperature resistant electrolyte provided by this invention exhibits excellent high-temperature stability. Diphenylphosphonic hydroxylamine forms a stable and dense SEI film on the negative electrode surface, inhibiting dendrite growth and reducing active lithium loss. Meanwhile, phenylphosphonic nitrile generates a high-temperature resistant protective layer on the positive electrode side, effectively improving the oxidation stability of the positive electrode interface. The synergistic effect of these two components gives the electrode interface both density and heat resistance, thus significantly improving interface stability at high temperatures. Furthermore, the high-temperature resistant additives provided by this invention synergistically inhibit electrolyte decomposition and byproduct accumulation at high temperatures, reduce interfacial impedance growth, and ensure the reversible migration efficiency of lithium ions. This results in batteries using this electrolyte exhibiting excellent high-temperature cycle performance, solving the problems of existing lithium-ion battery electrolytes such as easy decomposition at high temperatures, unstable interfacial films, short cycle life, and low energy efficiency.

[0009] As a preferred embodiment of the present invention, the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile is 1:(0.8-1.5), for example, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, etc.

[0010] The high-temperature resistant electrolyte provided by this invention simultaneously introduces diphenylphosphonohydroxylamine and phenylphosphononitrile. Diphenylphosphonohydroxylamine primarily acts on the negative electrode, forming a dense and stable SEI film on its surface, thereby effectively suppressing lithium dendrite formation. Phenylphosphononitrile primarily acts on the positive electrode; its high-temperature resistance helps construct a stable antioxidant film, significantly improving the thermal stability of the positive electrode interface. By controlling the ratio of these two components within the aforementioned range, the resulting interfacial film exhibits both high density and excellent heat resistance, effectively suppressing side reactions at the electrode / electrolyte interface under high-temperature conditions and improving the battery's cycle life and energy efficiency in high-temperature environments.

[0011] As a preferred embodiment of the present invention, the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile is 1:(1-1.2).

[0012] As a preferred embodiment of the present invention, the film-forming additive includes any one or more of fluoroethylene carbonate, vinylene carbonate, ethylene sulfate, and lithium difluorophosphate.

[0013] The film-forming additive provided by this invention can work synergistically with high-temperature resistant additives to construct a dense and heat-resistant interfacial film on the electrode surface, thereby effectively suppressing side reactions and stabilizing the interfacial structure.

[0014] As a preferred embodiment of the present invention, the film-forming additive is selected from a combination of vinylene carbonate, lithium difluorophosphate and fluoroethylene carbonate.

[0015] As a preferred embodiment of the present invention, the mass ratio of vinylene carbonate, lithium difluorophosphate and fluoroethylene carbonate is 1:(0.5-1):(0.5-1), for example 1:0.5:0.5, 1:0.8:0.6, 1:0.6:0.8, 1:1:1, etc.

[0016] As a preferred embodiment of the present invention, the content of the film-forming additive is 2-6%, for example, 2%, 3%, 4%, 5%, 6%, etc., based on the total mass of the high-temperature resistant electrolyte as 100%.

[0017] As a preferred embodiment of the present invention, the lithium salt includes any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, and lithium difluorosulfonylimide.

[0018] As a preferred embodiment of the present invention, the lithium salt content is 11-15% based on the total mass of the high-temperature resistant electrolyte as 100%, for example, 11%, 12%, 13%, 14%, 15%, etc.

[0019] As a preferred embodiment of the present invention, the organic solvent includes any one or more of ethyl acetate, propyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate.

[0020] As a preferred embodiment of the present invention, the content of the organic solvent is 75-85%, for example, 75%, 78%, 80%, 82%, 85%, etc., based on the total mass of the high-temperature resistant electrolyte as 100%.

[0021] In a second aspect, the present invention provides a lithium-ion battery, the lithium-ion battery comprising the high-temperature resistant electrolyte described in the first aspect.

[0022] The technical solution provided by the embodiments of the present invention has the following advantages compared with the prior art: 1. The high-temperature resistant electrolyte provided by this invention introduces high-temperature resistant additives, which can form a stable and dense SEI film on the negative electrode surface, inhibit dendrite growth and reduce active lithium loss. At the same time, a high-temperature resistant protective layer is generated on the positive electrode side, which effectively improves the oxidation stability of the positive electrode interface. Thus, the electrode interface has both density and heat resistance, significantly improving the interface stability at high temperatures, and enabling the battery using it to have excellent high-temperature cycle performance.

[0023] 2. The high-temperature resistant additives provided by this invention can inhibit the decomposition of electrolyte and the accumulation of by-products at high temperatures, reduce the growth of interfacial impedance, and ensure the reversible migration efficiency of lithium ions, thereby significantly improving the cycle life and energy efficiency of batteries using them in high-temperature environments. Detailed Implementation

[0024] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0025] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0026] Unless otherwise specified, the raw materials and equipment used in the following examples are all commercially available, and the solvents used are all analytical grade. Some of the raw materials are sourced as shown below: Lithium difluorosulfonylimide, Suzhou Duoduo Chemical Technology Co., Ltd.; Lithium hexafluorophosphate, Suzhou Duoduo Chemical Technology Co., Ltd. Propyl acetate, Shanghai Adamas Reagent Co., Ltd.; Dimethyl carbonate, Suzhou Duoduo Chemical Technology Co., Ltd.; Ethyl carbonate, Suzhou Duoduo Chemical Technology Co., Ltd.; Ethyl methyl carbonate, Suzhou Duoduo Chemical Technology Co., Ltd. Ethylene carbonate, Shanghai Maclean Biochemical Technology Co., Ltd.; Lithium difluorophosphate, Shanghai Maclean Biochemical Technology Co., Ltd.; Fluorinated ethylene carbonate, Suzhou Duoduo Chemical Technology Co., Ltd. Diphenylphosphonohydroxylamine, Suzhou Haofan Biotechnology Co., Ltd.; Phenylephosphononitrile, Suzhou Duoduo Chemical Technology Co., Ltd.; Lithium iron phosphate, Hunan Yuneng New Energy Battery Materials Co., Ltd.; Ketjen Black conductive carbon, Shanghai Huiping New Energy Co., Ltd.; Graphite, Hunan Zhongke Xingcheng Graphite Co., Ltd.; Sodium carboxymethyl cellulose, Changshu Weiyi Technology Co., Ltd. Styrene-butadiene rubber latex, Shanghai Daoying Industrial Co., Ltd.

[0027] Example 1 This embodiment provides a high-temperature resistant electrolyte, including lithium salt, organic solvent, film-forming additive, and high-temperature resistant additive; The organic solvent is a mixture of propyl acetate, dimethyl carbonate, ethylene carbonate, and ethyl methyl carbonate, with a mass ratio of 1:1:2:4. The organic solvent accounts for 80% of the total mass of the electrolyte. The lithium salt is a mixture of lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate in a mass ratio of 7:6, and the lithium salt accounts for 13% of the total mass of the electrolyte. The film-forming additive is a mixture of vinylene carbonate, lithium difluorophosphate, and fluoroethylene carbonate, with a mass ratio of 1:0.5:0.5. The film-forming additive accounts for 4% of the total mass of the electrolyte. The high-temperature resistant additive is a mixture of diphenylphosphonohydroxylamine and phenylphosphononitrile, with a mass ratio of 1:1.1. The high-temperature resistant additive accounts for 3% of the total mass of the electrolyte.

[0028] The electrolyte was prepared in an argon-protected glove box (water and oxygen content were both less than 0.1 ppm). Lithium salt was added to the organic solvent, followed by film-forming additives and high-temperature resistant additives. The mixture was stirred at room temperature for 12 h to obtain the high-temperature resistant electrolyte.

[0029] Example 2 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Example 1. The difference is that the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile in the high-temperature resistant additive in this embodiment is 1:1.

[0030] Example 3 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Example 1. The difference is that the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile in the high-temperature resistant additive in this embodiment is 1:1.2.

[0031] Example 4 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Example 1. The difference is that the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile in the high-temperature resistant additive in this embodiment is 1:0.8.

[0032] Example 5 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Example 1. The difference is that the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile in the high-temperature resistant additive in this embodiment is 1:1.5.

[0033] Example 6 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Example 1. The difference is that the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile in the high-temperature resistant additive in this embodiment is 1:2.

[0034] Example 7 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Example 1. The difference is that the mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile in the high-temperature resistant additive in this embodiment is 1:0.5.

[0035] Example 8 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Embodiment 1. The difference is that in this embodiment, the high-temperature resistant additive accounts for 1% of the total mass of the electrolyte, and the organic solvent accounts for 82% of the total mass of the electrolyte.

[0036] Example 9 This embodiment provides a high-temperature resistant electrolyte with the same composition as in Embodiment 1. The difference is that in this embodiment, the high-temperature resistant additive accounts for 5% of the total mass of the electrolyte, and the organic solvent accounts for 78% of the total mass of the electrolyte.

[0037] Comparative Example 1 This comparative example provides an electrolyte with the same composition as in Example 1, except that no high-temperature resistant additives are added in this comparative example, and the organic solvent accounts for 83% of the total mass of the electrolyte.

[0038] Comparative Example 2 This comparative example provides an electrolyte with the same composition as in Example 1. The difference is that the high-temperature resistant additive in this comparative example is only diphenylphosphinohydroxylamine, which accounts for 3% of the total mass of the electrolyte.

[0039] Comparative Example 3 This comparative example provides an electrolyte with the same composition as Example 1, except that the high-temperature resistant additive in this comparative example is only phenylphosphonic nitrile, which accounts for 3% of the total mass of the electrolyte.

[0040] Comparative Example 4 This comparative example provides an electrolyte comprising a lithium salt and an organic solvent. The lithium salt is lithium hexafluorophosphate, and the organic solvent is a mixed solution of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a mass ratio of 1:1:1. The concentration of the lithium salt is 1 mol / L.

[0041] Comparative Example 5 This comparative example provides an electrolyte with the same composition as in Example 1, except that the high-temperature resistant additive accounts for 8% of the total mass of the electrolyte and the organic solvent accounts for 75% of the total mass of the electrolyte.

[0042] Application examples The electrolytes provided in the examples and comparative examples were used to assemble batteries.

[0043] (1) Positive electrode: Lithium iron phosphate, Ketjen Black conductive carbon, and polytetrafluoroethylene are added to 2 mL of water in a mass ratio of 8:1:1. N The positive electrode slurry with a solid content of 33.3% was obtained by thoroughly stirring the methylpyrrolidone dispersion. The slurry was coated onto an aluminum foil with a thickness of 15 µm, baked at 60°C for 12 h, and then cut into discs with a diameter of 12 mm to obtain the lithium iron phosphate positive electrode sheet. (2) Negative electrode sheet: Graphite, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene copolymer were added to 5 mL of ultrapure water at a mass ratio of 8:0.5:0.5:1 and stirred at high speed for 8 h to obtain a negative electrode slurry with a solid content of 16.7%. The above slurry was coated on a copper foil with a thickness of 9 µm, vacuum baked at 100℃ for 12 h, and then cut into round sheets with a diameter of 14 mm to obtain a graphite negative electrode sheet; (3) Add 60 μL of the electrolyte provided in the example or comparative example between the negative electrode and the positive electrode, and then assemble the negative electrode according to the negative electrode shell. negative electrode sheet diaphragm Positive electrode film gasket shrapnel Assemble the CR2032 coin cell in sequence with the positive electrode casing.

[0044] Performance testing The batteries assembled for the corresponding use cases were tested: Battery high-temperature cycle performance test: The Wuhan Land charge and discharge tester was used for charge and discharge test. Specifically, within the voltage range of 2.5-3.65 V, the battery was first activated three times at a rate of 0.1 C, and then charged and discharged 100 times at a rate of 0.5 C at a high temperature of 45℃.

[0045] Battery high-temperature cycle capacity retention rate = discharge capacity of the 100th high-temperature cycle / discharge capacity of the 1st high-temperature cycle. The test results are shown in Table 1.

[0046] Battery high-temperature energy efficiency test: The Wuhan Land charge and discharge tester was used for charge and discharge test. Specifically, within the voltage range of 2.5-3.65 V, the battery was first activated three times at a rate of 0.1 C, and then cycled three times at a rate of 1 C. The average energy efficiency at the 1 C rate was calculated.

[0047] Energy efficiency = total discharge energy / total charge energy. The test results are shown in Table 1.

[0048] Table 1

[0049] As can be seen from the comparison of the examples and comparative examples in Table 1, the high-temperature resistant electrolyte provided by the present invention exhibits significant advantages in terms of cycle stability. The improvement effect is mainly attributed to the synergistic effect of diphenylphosphonohydroxylamine and phenylphosphononitrile. When the two are in an appropriate ratio, they can form a dense and thermally stable protective layer at the interface between the negative electrode and the positive electrode, thereby effectively suppressing high-temperature side reactions.

[0050] A comparison between Example 1 and Comparative Example 5 reveals that when the content of the high-temperature resistant additive is too high, the SEI film on the negative electrode surface will become excessively thick, leading to an increase in interfacial impedance and restricted ion migration, thereby reducing electrochemical efficiency. A comparison between Example 1 and Comparative Example 1 reveals that when no high-temperature resistant additive is added, the interfacial protection is insufficient, making it difficult to effectively suppress dendrite growth and positive electrode oxidation side reactions, which will also cause a decrease in cycle performance.

[0051] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0052] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A high-temperature resistant electrolyte, characterized in that, The high-temperature resistant electrolyte includes lithium salt, organic solvent, film-forming additive, and high-temperature resistant additive; Based on the total mass of the high-temperature resistant electrolyte being 100%, the content of the high-temperature resistant additive is 1-5%; The high-temperature resistant additive is selected from a combination of diphenylphosphonohydroxylamine and phenylphosphononitrile.

2. The high-temperature resistant electrolyte according to claim 1, characterized in that, The mass ratio of diphenylphosphonohydroxylamine to phenylphosphononitrile is 1:(0.8-1.5), preferably 1:(1-1.2).

3. The high-temperature resistant electrolyte according to claim 1 or 2, characterized in that, The film-forming additive includes any one or more of fluoroethylene carbonate, vinylene carbonate, vinyl sulfate, and lithium difluorophosphate.

4. The high-temperature resistant electrolyte according to claim 3, characterized in that, The film-forming additive is selected from a combination of vinylene carbonate, lithium difluorophosphate and fluoroethylene carbonate; Preferably, the mass ratio of vinylene carbonate, lithium difluorophosphate, and fluoroethylene carbonate is 1:(0.5-1):(0.5-1).

5. The high-temperature resistant electrolyte according to any one of claims 1-4, characterized in that, Based on the total mass of the high-temperature resistant electrolyte being 100%, the content of the film-forming additive is 2-6%.

6. The high-temperature resistant electrolyte according to any one of claims 1-5, characterized in that, The lithium salt includes any one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalate borate, lithium difluorodioxalate phosphate, and lithium difluorosulfonylimide.

7. The high-temperature resistant electrolyte according to any one of claims 1-6, characterized in that, Based on the total mass of the high-temperature resistant electrolyte being 100%, the lithium salt content is 11-15%.

8. The high-temperature resistant electrolyte according to any one of claims 1-7, characterized in that, The organic solvent includes any one or more of ethyl acetate, propyl acetate, butyl acetate, dimethyl carbonate, diethyl carbonate, ethylene carbonate, and methyl ethyl carbonate.

9. The high-temperature resistant electrolyte according to any one of claims 1-8, characterized in that, Based on the total mass of the high-temperature resistant electrolyte being 100%, the content of the organic solvent is 75-85%.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes the high-temperature resistant electrolyte as described in any one of claims 1-9.

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