High voltage lithium ion battery electrolyte additive and electrolyte and battery

Abstract

The application relates to a high-voltage lithium ion battery electrolyte additive and electrolyte and battery. The high-voltage lithium ion battery electrolyte additive comprises a first additive, and the first additive is a cyanosiloxane compound. The scheme provided by the application can improve the cycle performance of the battery under high temperature and high voltage, and improve the high-temperature cycle life and high-temperature storage performance of the battery through the action of the cyanosiloxane compound.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a high-voltage lithium ion battery electrolyte additive and electrolyte and battery. BACKGROUND

[0002] Lithium ion batteries have the advantages of high working voltage, long cycle life, low self-discharge, no memory effect, etc., and are widely used in portable electronic devices, electric vehicles and other products. One of the important directions for the development of lithium ion batteries in the future is to improve the energy density of the battery by increasing the battery voltage or the capacity of the positive and negative electrode materials. However, the increase of the battery voltage or the capacity will accelerate the decomposition of the electrolyte.

[0003] In related technologies, using film-forming additives is a common means to alleviate electrolyte decomposition. However, current room temperature film-forming additives are difficult to simultaneously consider high and low temperature performance. For example, vinylene carbonate VC can form a stable SIE film at the negative electrode to improve high-temperature cycle performance, but the film-forming impedance is large, and the lithium precipitation window of the battery will deteriorate. Vinyl sulfonate DTD can reduce impedance to improve battery dynamics, but it has poor thermal stability, is prone to discoloration during storage, and increases the acidity of the electrolyte.

[0004] Therefore, it is crucial to provide an electrolyte additive that can be applied to high-energy-density batteries to expand the use range of lithium ion batteries. SUMMARY

[0005] To solve or partially solve the problems in the related art, the present application provides a high-voltage lithium ion battery electrolyte additive and electrolyte and battery, which can improve the cycle performance of the battery at high temperature and high voltage, and improve the high-temperature cycle life and high-temperature storage performance of the battery through the action of cyanosiloxane compounds.

[0006] The first aspect of the present application provides a high-voltage lithium ion battery electrolyte additive, comprising a first additive, the first additive is a cyanosiloxane compound, and the structure formula of the first additive is as follows:

[0007]

[0008] In formula I, R1-R4 are independently selected from H, halogen, C1-C6 alkyl, C5-C12 substituted or unsubstituted cycloalkyl, C6-C24 substituted or unsubstituted aryl, heteroaryl or fused ring aryl.

[0009] As an optional embodiment, the first additive comprises at least one of the following compounds:

[0010]

[0011]

[0012] As an optional embodiment, the first additive accounts for 0.1% to 5% of the mass percentage of the electrolyte.

[0013] As an optional embodiment, the first additive accounts for 0.5% to 1% of the mass percentage of the electrolyte.

[0014] As an optional embodiment, the electrolyte additive further comprises a second additive, and the second additive is a nitrile compound.

[0015] As an optional embodiment, the second additive comprises at least one of the following compounds:

[0016]

[0017] As an optional embodiment, the second additive accounts for 0.5% to 3% of the mass percentage of the electrolyte.

[0018] As an optional embodiment, the second additive accounts for 0.5% to 2% of the mass percentage of the electrolyte.

[0019] The second aspect of the present application provides a high-voltage lithium ion battery electrolyte, comprising an electrolyte salt, an organic solvent and an additive, and the additive comprises the electrolyte additive described above.

[0020] The third aspect of the present application provides a high-voltage lithium ion battery comprising the high-voltage lithium ion battery electrolyte described above.

[0021] The technical solution provided by the present application can include the following beneficial effects:

[0022] The first additive in the present application is a cyano siloxane compound, which can better match the negative electrode. The -Si-O- group contained therein can preferentially undergo redox reaction over the solvent during battery charging, forming a protective film with a three-dimensional cross-linked organic polymer network structure containing -Si-O-Si- bonds on the negative electrode surface, improving the mechanical strength and flexibility of the negative electrode protective film to adapt to the stress concentration during the huge volume expansion and contraction of the silicon material in the cycle process, reducing the continuous interfacial reaction of the electrolyte during long-term cycling, and improving the cycle performance of the battery at high temperature and high voltage. Furthermore, the -Si-O- group has similar properties to crown ethers and sandwich compounds in forming complexes with metal cations, can coordinate with Li+, participate in the solvation structure of Li+, and the compound containing -Si-O-F- bonds formed can participate in the film formation on the positive and negative electrode surfaces, so that the three-dimensional cross-linked organic polymer network protective film is rich in LiF, which can greatly reduce the electrolyte decomposition of the silicon-based battery system and help to form a more stable protective film.

[0023] In addition, in the cyano siloxane compound of the present application, the cyano group is connected to the C element and then connected to the O element. The compound formed by the indirect connection between the cyano group and the O element is more stable, less flammable, and less sensitive to water than the compound formed by the direct connection between the cyano group and the O element, and is less likely to combine with water to form an acid and destroy the SEI film.

[0024] It should be understood that the general description above and the following detailed description are only exemplary and explanatory, and are not limiting to the present application. DETAILED DESCRIPTION

[0025] Embodiments of the present application will be described in more detail by way of specific examples. Although the following examples show the embodiments of the present application, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments described herein. Rather, these embodiments are provided so that the present application is more complete and complete, and the scope of the present application is fully conveyed to those skilled in the art.

[0026] The terms used in the present application are only for the purpose of describing specific embodiments, and are not intended to limit the present application. The singular forms "a", "an" and "the" used in the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein means and includes any or all possible combinations of one or more associated listed items.

[0027] It should be understood that although the terms "first", "second", "third" and the like can be used in the present application to describe various information, these information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, the first information can also be referred to as the second information, and similarly, the second information can also be referred to as the first information without departing from the scope of the present application. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more features. In the description of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0028] In the related art, the use of film-forming additives is a common means to alleviate electrolyte decomposition, but it is difficult for current room temperature film-forming additives to simultaneously consider high and low temperature performance. For example, vinyl carbonate VC can form a stable SIE film at the negative electrode to improve high temperature cycle performance, but the film-forming impedance is large, and the lithium precipitation window of the battery will deteriorate; vinyl sulfate DTD can reduce impedance to improve battery dynamics, but its thermal stability is poor, it is easy to discolor during storage, and the electrolyte acidity is increased.

[0029] Therefore, it is important to provide an electrolyte additive capable of being applied to a high-energy-density battery to broaden the application range of lithium-ion batteries.

[0030] To solve the above problems, the embodiment of the present application provides a high-voltage lithium-ion battery electrolyte additive, which improves the cycle performance of the battery at high temperature and high voltage, and improves the high-temperature and high-voltage cycle life and high-temperature storage performance of the battery through the action of a cyanosiloxane compound.

[0031] The embodiment of the present application provides a high-voltage lithium-ion battery electrolyte additive, which comprises a first additive, the first additive is a cyanosiloxane compound, and the structural formula of the first additive is as follows:

[0032]

[0033] In formula I, R1-R4 are independently selected from H, halogen, C1-C6 alkyl, C5-C12 substituted or unsubstituted cycloalkyl, C6-C24 substituted or unsubstituted aryl, heteroaryl or fused ring aryl.

[0034] The first additive in the embodiment of the present application is a cyanosiloxane compound, which can better match the negative electrode. The -Si-O- group contained in the cyanosiloxane compound can preferentially undergo an oxidation-reduction reaction (decomposition reaction) than the solvent during battery charging, and itself crosslinks on the negative electrode surface to form a protective film with a three-dimensional cross-linked organic polymer network structure containing -Si-O-Si- bonds, thereby improving the mechanical strength and flexibility of the negative electrode protective film to adapt to the stress concentration when the silicon material undergoes huge volume expansion and contraction during the cycle process, reducing the continuous interfacial reaction of the electrolyte during long-term cycling, and improving the cycle performance of the battery at high temperature and high voltage. Secondly, the -Si-O- group has similar properties to crown ethers and sandwich compounds in forming complexes with metal cations, can coordinate with Li+, participate in the solvation structure of Li+, and the -Si-O- bond can also combine with free F in the electrolyte to generate a compound containing -Si-O-F- bonds, which can participate in the film formation on the positive and negative electrode surfaces, so that the three-dimensional cross-linked organic polymer network protective film is rich in LiF, which can greatly reduce the electrolyte decomposition of the silicon-based battery system and help to form a more stable protective film. Furthermore, the cyan group contained therein has a strong complexation with the transition metal on the surface of the positive electrode material, can form a stable CEI film to protect the positive electrode material, and inhibit the dissolution of transition metal elements, thereby reducing the side reaction of the positive electrode and the electrolyte, can inhibit the high-temperature storage gas production, and the battery has good high-temperature storage performance.

[0035] In addition, in the cyano siloxane compound of the embodiments of the present application, the cyano group in the structural formula is connected to the C element and then connected to the O element. The compound formed by the indirect connection between the cyano group and the O element is more stable, less flammable, and less sensitive to water than the compound formed by the direct connection between the cyano group and the O element, and is less likely to combine with water to form an acid and destroy the SEI film.

[0036] As an optional embodiment, the first additive comprises at least one of the following compounds:

[0037]

[0038]

[0039] In the embodiments of the present application, R2 to R3 of the compounds 1-1 to 1-11 are selected from an alkyl group with one carbon atom, and R1 is selected from different groups.

[0040] R1 of the compound 1-1 is selected from -CL. Such a compound has a high DN value (a measure of the solvent's ability to dissolve cations and Lewis acids), has the ability to coordinate with Li+ and is more likely to appear in the first solvation shell, and is therefore more likely to be "dragged" into the double layer near the negative electrode together with Li+, and then decomposed to form a Li x C-rich SEI film. The compound has a strong adsorption with the Si negative electrode, is difficult to migrate to the positive electrode to be oxidized, but is easily combined with water to form an acid to destroy the negative electrode SEI film.

[0041] R1 of the compound 1-2 is selected from H, R1 of the compound 1-3 is selected from an alkyl group with one carbon atom, and R1 of the compound 1-4 is selected from an alkyl group with multiple carbon atoms. The compounds 1-2 to 1-4 are all cyano siloxane compounds containing saturated chains. Such a compound has a high thermal decomposition temperature, can maintain structural stability in a wide temperature range, and can flexibly control the physical properties such as hardness, elasticity, and adhesion of the material by changing the chain length, functional groups, and fine-tuning of the molecular structure to meet the specific needs of different application scenarios.

[0042] R1 of the compound 1-5 is selected from a saturated six-membered ring, R1 of the compound 1-6 is selected from a saturated five-membered ring, and R1 of the compound 1-7 is selected from a saturated eight-membered ring. These compounds are all cyano siloxane compounds containing saturated ring structures. Such a compound has good oxidation resistance, but has poor coordination ability with Li ions.

[0043] R1 of compound 1-8 is selected from phenyl, R1 of compound 1-9 is selected from heteroaryl (pyridyl group), R1 of compound 1-10 is selected from methoxyphenyl, and R1 of compound 1-11 is selected from fused ring aryl (fused ring formed by a five-membered aromatic ring and a saturated five-membered ring), all of which are cyano siloxane compounds containing unsaturated ring structure, and such compounds have high DN value (a measure of the ability of a solvent to dissolve cations and Lewis acids), have the ability to coordinate with Li+ to make it more likely to appear in the first solvation shell, and thus more likely to be "dragged" into the double layer near the negative electrode together with Li+, and then decomposed to form SEI film rich in Li x C. However, such compounds have weak oxidation resistance.

[0044] The above compounds can be used alone or in combination in the embodiments of the present application, which can improve the film stability and oxidation resistance.

[0045] As an optional embodiment, the first additive accounts for 0.1% to 5% of the mass percentage of the electrolyte.

[0046] In the embodiments of the present application, the first additive can account for 0.1%, 0.5%, 1%, 2%, 5% or any value within the above defined range of the mass percentage of the electrolyte, which is not limited in the present application.

[0047] If the content of the first additive is too high, the positive electrode film forming impedance of the lithium ion battery increases, and the high temperature cycle performance is deteriorated; if the content of the first additive is too low, the positive electrode film stability is poor, the complexation with transition metals of the positive electrode is weakened, and the high temperature storage performance of the lithium ion battery is deteriorated.

[0048] As a preferred embodiment, the first additive accounts for 0.5% to 1% of the mass percentage of the electrolyte.

[0049] In the embodiments of the present application, the first additive can account for 0.5%, 0.8%, 1% or any value within the above defined range of the mass percentage of the electrolyte, which is not limited in the present application.

[0050] The first additive in the preferred range of the embodiments of the present application is used, and the obtained electrolyte has better high temperature cycle stability and high temperature storage performance.

[0051] As an optional embodiment, the electrolyte additive further includes a second additive, and the second additive is a nitrile compound.

[0052] When the first additive migrates to the positive electrode, due to its lower cyan group content, the protection of the positive electrode is weak, and the positive electrode is easily oxidized at high voltage, accelerating the dissolution of transition metals in the positive electrode. When the second additive is added, the carbon-nitrogen triple bond in the second additive has high bond energy and is not easily oxidized. In addition, nitrile compounds have good stability on the positive electrode and strong oxidation resistance, and can form a stable CEI film on the positive electrode to avoid decomposition of the first additive. Therefore, the second additive of the embodiment of the present application can effectively improve the stability of the positive electrode, and synergistically act with the cyanosiloxane compound to effectively balance the transmission rate of lithium ions, effectively improve the gas generation problem prone to occur in the high-low voltage system, and improve the cycle life and storage performance of the battery.

[0053] As a preferred embodiment, the second additive comprises at least one of the following compounds:

[0054]

[0055] In the embodiment of the present application, the second additive is a multi-nitrile compound, which is rich in -CN functional groups and is more likely to accumulate on the positive electrode surface, thereby reducing the side reaction of the positive electrode and the electrolyte, making the battery have good high-temperature performance, and inhibiting high-temperature storage gas generation.

[0056] As a preferred embodiment, the mass percentage of the second additive in the electrolyte is 0.5% to 3%.

[0057] In the embodiment of the present application, the mass percentage of the second additive in the electrolyte can be 0.5%, 1%, 1.5%, 2%, 3% or any value within the above limited range, which is not limited by the present application.

[0058] The second additive has poor compatibility with the negative electrode. When the content of the second additive increases, the stability of the negative electrode interface becomes poor, and too much cyan group can react with the metal at the negative electrode, causing self-discharge of the lithium ion battery. When the content of the second additive is too low, the dissolution of transition metal ions in the positive electrode cannot be effectively inhibited, and the SEI film formed at the negative electrode is unstable.

[0059] Further, the mass percentage of the second additive in the electrolyte is 0.5% to 2%.

[0060] In the embodiment of the present application, the mass percentage of the second additive in the electrolyte can be 0.5%, 1%, 1.5%, 2% or any value within the above limited range, which is not limited by the present application.

[0061] The second additive of the embodiment of the present application is used in the preferred range with the first additive, and the obtained electrolyte has better high-temperature cycle stability and high-temperature storage performance.

[0062] Corresponding to the foregoing application function implementation method embodiments, the application further provides a high-voltage lithium ion battery electrolyte, a high-voltage lithium ion battery and corresponding embodiments.

[0063] The application embodiment provides a high-voltage lithium ion battery electrolyte, which comprises an electrolyte salt, an organic solvent and an additive, and the additive comprises the foregoing electrolyte additive.

[0064] In the application embodiment, the electrolyte salt comprises one or more of lithium hexafluorophosphate LiPF6, lithium difluoro(oxalato)borate LiODFB, lithium bis(oxalato)borate LiBOB, lithium difluorophosphate LiDFOP, lithium tetrafluoroborate LiBF4, lithium bis(trifluoromethylsulfonyl)imide LiTFSI, lithium bis(fluorosulfonyl)imide LiFSI and lithium difluorophosphate LiPOF2.

[0065] In the application embodiment, the organic solvent comprises two or more of ethylene carbonate EC, propylene carbonate PC, diethyl carbonate DEC, ethyl methyl carbonate EMC, ethyl propionate EP, propyl propionate PP, ethyl fluoroacetate DFEA, fluoroethyl methyl carbonate FEMC, fluorodimethyl carbonate FDMC and fluoropropylene carbonate FPC.

[0066] In the application embodiment, the mass percentage of the organic solvent in the electrolyte is 20% to 70%.

[0067] The additive includes fluoroethylene carbonate FEC.

[0068] The application embodiment further provides a high-voltage lithium ion battery, which comprises a positive electrode, a negative electrode, a separator and the foregoing high-voltage lithium ion battery electrolyte.

[0069] In the application embodiment, the positive electrode active material comprises lithium cobaltate, lithium iron phosphate, lithium manganate and lithium nickel cobalt manganate; preferably, the positive electrode material is lithium cobaltate or a nickel cobalt manganate ternary material.

[0070] In the application embodiment, the negative electrode active material comprises at least one of graphite, hard carbon, silicon, silicon oxide and silicon carbide; preferably, the negative electrode active material is silicon carbide.

[0071] In order to further understand the application, the application is described below in combination with embodiments, which are only used to illustrate the application and do not limit the scope of the application.

[0072] I. Preparation of a lithium ion battery

[0073] (1) Preparation of a positive electrode sheet:

[0074] The positive active material lithium cobaltate LCO, conductive agent CNT, and adhesive PVDF are mixed in a weight ratio of 97:1.5:1.5 in a NMP solvent, and stirred sufficiently to form a uniform positive electrode slurry. The slurry is coated on an aluminum foil with a safety primer, and subjected to processes such as drying, cold pressing, slitting, sheet making, welding of tabs, and gluing, to produce a positive electrode sheet that meets the requirements for winding.

[0075] (2) Production of the negative electrode sheet:

[0076] The negative active material silicon particles (SiC content 12%), artificial graphite, conductive agent SP, thickening agent CMC, and adhesive SBR are mixed in a mass ratio of 12:84.3:1:1.2:1.5 in a suitable amount of deionized water solvent, and stirred sufficiently to form a uniform negative electrode slurry. The slurry is coated on a negative current collector Cu foil, and subjected to processes such as drying, cold pressing, slitting, sheet making, welding of tabs, and gluing, to produce a negative electrode sheet that meets the requirements for winding.

[0077] (3) Preparation of the electrolyte:

[0078] In an argon environment with a water content <10 ppm, EC / PC / EP / PP are mixed in a glove box in a ratio of 1.5:1.5:4:3, LiPF6 is added, 10% of fluoroethylene carbonate FEC is added based on the total mass of the electrolyte, and first and second additives are added according to the amounts in Table 1, to obtain the electrolytes of the examples and the comparative examples.

[0079] (4) Production of the lithium ion battery:

[0080] The above positive electrode sheet, separator, and negative electrode sheet are wound to obtain a bare cell. The bare cell is placed in an aluminum-plastic film that has been punched, to complete the top side sealing. The lithium ion battery of each example and the comparative example is produced by processes such as high-temperature baking, injection of the electrolyte of each example and the comparative example, standing, formation, capacity grading, and detection.

[0081] II. Performance test of the lithium ion battery

[0082] The lithium ion batteries produced in the above examples and the comparative examples are subjected to corresponding performance tests according to the following methods, and the test data in Table 2 are calculated and obtained.

[0083] (1) 45°C cycle test:

[0084] At 45℃, rest for 4h, charge to 4.53V at 1C, cut-off current 0.05C, rest for 10min, test initial internal resistance R0, full charge thickness and charge capacity, discharge to 3.0V at 0.5C, record discharge capacity C0 as initial, repeat 400 cycles, test full charge internal resistance and full charge thickness every 100 cycles. Finally get the capacity C400, internal resistance R400 after 400 cycles, calculate capacity retention rate = C400 / C0, internal resistance growth rate = R400 / R0.

[0085] (2) 80℃ 6h storage test:

[0086] Charge to 4.53V at 25℃ with 0.8C constant current and constant voltage, cut-off current 0.05C, rest for 10min, test cell thickness H0, then store at 85±2℃ for 6h, measure thickness H6, thickness expansion rate = (H6-H0) / H0.

[0087] Table 1 Formulation Table

[0088]

[0089]

[0090] Table 2 Performance Test Results

[0091]

[0092]

[0093] In combination with the data in Table 1 and Table 2, by comparing Examples 1-11, and Comparative Example 1 and Comparative Example 5, it is found that after adding the first additive with structural formula I, the cycle performance of the battery is improved, and further comparing Examples 1-11, it is found that when the first additive is selected from compounds 1-4, 1-6, 1-8, 1-9, 1-1, especially selected from compound 1-9, it has excellent film forming stability, can form a stable film on the positive and negative electrodes, and significantly improves the cycle and storage performance of the battery; further comparing Example 9, Examples 12-16, and Comparative Example 4, it is found that when the mass percentage of the first additive in the electrolyte is 0.1% to 5%, the battery has stable high-temperature cycle performance and high-temperature storage performance. And when the mass percentage of the first additive in the electrolyte is 0.5% to 1%, the high-temperature cycle performance and high-temperature storage performance of the battery are better.

[0094] By comparing Example 9 and Examples 17-21, and comparing Examples 4, 6, 8, 9, 11 and Examples 18, 22-25, it is found that the first additive and the second additive have a synergistic effect, which can significantly improve the high-temperature performance of the battery cell; further comparing Examples 18, 26-28 and Comparative Examples 6-9, it is found that when the first additive accounts for 0.1% to 5% by mass of the electrolyte, and the second additive accounts for 0.5% to 3% by mass of the electrolyte, the two have a good synergistic effect, and the battery cell exhibits excellent high-temperature cycling and high-temperature storage performance. And when the first additive accounts for 0.5% to 1% by mass of the electrolyte, and the second additive accounts for 0.5% to 2% by mass of the electrolyte, the battery has better high-temperature cycling and high-temperature storage performance.

[0095] Although the present application has been described with reference to preferred embodiments, those skilled in the art will understand that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the present application. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the present application without departing from the essential scope thereof. Therefore, the present application is not intended to be limited to the particular embodiments disclosed as the best mode contemplated for carrying out the present application, but it will include all embodiments falling within the scope of the appended claims.

[0096] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are combinable with the ranges.

[0097] The various embodiments of the present application have been described above, the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes are obvious to those skilled in the art without departing from the scope and spirit of the described embodiments. The choice of terms used herein is intended to best explain the principles, practical applications, or improvements to the technology in the market, or to enable other ordinary skilled persons in the art to understand the embodiments disclosed herein.

Claims

1. A high voltage lithium ion battery electrolyte, characterized in that: The electrolyte includes an electrolyte salt, an organic solvent, and an additive, the additive including a first additive, the first additive being a cyanosiloxane compound, and the first additive having a structural formula as follows: Formula I In Formula I, R1-R4 are each independently selected from H, halogen, C1-C6 alkyl, C5-C12 substituted or unsubstituted cycloalkyl, C6-C24 substituted or unsubstituted aryl, heteroaryl, or fused ring aryl.

2. The electrolyte according to claim 1, characterized in that, The first additive includes at least one of the following compounds: Compound 1-1 Compound 1-2 Compound 1-3 Compound 1-4 Compound 1-5 Compound 1-6 Compound 1-7 Compound 1-8 Compound 1-9 Compound 1-10 Compound 1-11.

3. The electrolyte of claim 1, wherein The first additive accounts for 0.1% to 5% of the mass percentage of the electrolyte.

4. The electrolyte according to claim 3, characterized in that The first additive accounts for 0.5% to 1% of the mass percentage of the electrolyte.

5. The electrolyte of claim 1, wherein The electrolyte additive further includes a second additive, the second additive being a nitrile compound.

6. The electrolyte of claim 5, wherein, The second additive includes at least one of the following compounds: Compound 2-1 Compound 2-2 Compound 2-3 Compound 2-4 Compound 2-5.

7. The electrolyte of claim 5, wherein The second additive accounts for 0.5% to 3% of the mass percentage of the electrolyte.

8. The electrolyte of claim 7, wherein, The second additive accounts for 0.5% to 2% of the mass percentage of the electrolyte.

9. A high voltage lithium ion battery, characterized in that, A high-voltage lithium ion battery electrolyte according to any one of claims 1 to 8.

Images