Electrolyte additive and lithium-ion battery electrolyte and lithium-ion battery using the same

Abstract

The present invention provides an electrolyte additive, a lithium-ion battery electrolyte, and a lithium-ion battery using the same, relating to the field of battery material technology. The electrolyte additive is made from an propylene ester additive with a specific structure, vinylene carbonate, fluoroethylene carbonate, and a lithium salt additive. When applied to an electrolyte, the electrolyte additive can effectively improve the electrolyte's ionic conductivity, cycling performance, and high-voltage resistance. Furthermore, when applied to a lithium-ion battery system, the electrolyte additive can also promote the formation of a dense and stable passivation film on the surfaces of the positive and negative electrodes, thereby improving the electrochemical performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials and relates to an electrolyte additive and a lithium ion battery electrolyte and a lithium ion battery using the electrolyte additive. Background Art

[0002] With the vigorous development of the global new energy industry, a green, low-carbon, circular economic system is gradually taking shape. Lithium-ion batteries, due to their high energy density, low self-discharge, long life, environmental friendliness, and reasonable cost, have become the preferred choice for the automotive industry in producing pure electric vehicles (EVs). However, charging time for EVs remains a major limitation to their practical application. Achieving fast charging for EVs can effectively eliminate range anxiety and holds broad commercial promise. To achieve effective EV range and alleviate range anxiety, fast-charging systems combining high-nickel ternary materials with silicon-based anodes have gradually become a research hotspot within the industry.

[0003] The main challenge of fast charging comes from Li + Non-equilibrium diffusion on the anode side. Lithium battery fast charging electrolyte determines the Li + Diffusion in the electrolyte and electrode / electrolyte interface. Side reactions caused by rapid charging can reduce electrolyte stability and lead to heat generation and lithium deposition, worsening electrolyte conductivity and limiting the battery's usable capacity. Therefore, the development of fast-charging and safe electrolytes is essential.

[0004] At present, many energy companies and research institutes have conducted research on fast-charging electrolytes for lithium batteries. For example, CN114614096A discloses a fast-charging electrolyte and its application in lithium-ion batteries. The electrolyte uses fluorine-substituted isoxazole and its derivatives as the main solvent. It is applied to a lithium-ion battery system with graphite as the negative electrode, showing good fast-charging characteristics. At the same time, it shows the characteristics of high power, long cycle and large capacity under a wide temperature range. However, as the main solvent, fluorine-substituted substances are expensive and have a narrow practical application range. Moreover, the application of this electrolyte in fast-charging silicon-based negative electrode system lithium batteries is unclear. CN114566710A discloses a non-aqueous electrolyte for lithium-ion batteries and lithium-ion batteries for fast charging. The non-aqueous electrolyte for lithium-ion batteries includes a lithium salt, a non-aqueous organic solvent and an additive. The additive includes a thiouracil compound and a nitrile compound. The organic combination of the thiouracil compound and the nitrile compound can significantly improve the fast charging cycle performance and high-temperature storage performance of the lithium cobalt oxide battery. However, the application of this electrolyte in high-nickel ternary system lithium batteries is also unclear. CN111934009A discloses a high-voltage fast-charging lithium-ion battery electrolyte, a preparation method, and an application thereof. The electrolyte includes an electrolyte salt, an organic solvent, a functional lithium salt containing fluorine or boron, and a phenol derivative containing at least one substituent. The first additive is a functional lithium salt containing fluorine and boron, and the second additive is a phenol derivative containing at least one substituent. The electrolyte can solve the problem of making the positive electrode-electrolyte interface film (CEI) more dense, stable, and complete, and can also solve the problem of phase transition at the positive electrode electrolyte interface, while improving the cycle performance and rate performance of the lithium-ion secondary battery under high voltage conditions. However, the stability of the SEI film generated by the electrolyte is poor, and the cycle performance of lithium ions needs to be further improved.

[0005] In summary, the existing technology still lacks a fast-charging lithium-ion battery electrolyte that can be applied to high-nickel ternary and silicon-based negative electrode systems. Summary of the Invention

[0006] In view of the shortcomings and defects of the existing technology, the present invention aims to provide an electrolyte additive and a lithium-ion battery electrolyte and a lithium-ion battery using the same; the electrolyte additive is made of an propylene ester additive with a specific structure and vinylene carbonate, fluoroethylene carbonate and a lithium salt additive. When the electrolyte additive is applied to the electrolyte, the electrolyte can have higher ion conductivity, good cycle performance and high-voltage resistance, so it has good application prospects in fast-charging lithium-ion battery systems.

[0007] In order to achieve the above purpose, the following technical solutions are adopted:

[0008] The present invention provides an electrolyte additive, including vinylene carbonate, fluoroethylene carbonate, a lithium salt additive, and an acrylate additive, wherein the acrylate additive includes one or a combination of at least two of the compounds shown in Formula 1, the compound shown in Formula 2, or the compound shown in Formula 3:

[0009]

[0010] Among them, R1, R2 and R3 are each independently selected from one of a halogen atom, a C1-C20 alkoxy group or a halogenated alkoxy group, a C1-C20 siloxy group, a C1-C20 alkyleneoxy group, a C1-C20 hydrocarbon group or a halogenated hydrocarbon group, a C1-C20 isocyanate group, a C1-C20 aniline group, a C1-C20 amino group, a C1-C20 acyl group or a C1-C20 ether group.

[0011] Furthermore, based on the above technical solution of the present invention, in the structure of the acrylic ester additive, at least one group among R1, R2 and R3 is selected from C1-C20 siloxy groups or C1-C20 isocyanate groups.

[0012] Furthermore, based on the above technical solution of the present invention, the acrylic ester additive includes at least one of additive A, additive B, additive C, additive D, additive E or additive F having the following structure:

[0013]

[0014]

[0015] Furthermore, based on the above technical solution of the present invention, the acrylic ester additive includes additive A, additive B and additive C; or, the acrylic ester additive includes additive D, additive E and additive F.

[0016] Furthermore, based on the above technical solution of the present invention, the lithium salt additive includes at least one of lithium difluorophosphate, lithium bis(oxalatoborate), lithium bis(fluorooxalatoborate) or lithium bis(fluorooxalatophosphate).

[0017] The mass ratio of the vinylene carbonate, fluoroethylene carbonate, lithium salt additive and propylene ester additive is (0.5-1.5):(3-7):(0.5-1.5):(1-3).

[0018] The present invention also provides a lithium ion battery electrolyte, which comprises the following components in the following mass fractions, calculated as 100% by mass:

[0019] 15-25% lithium salt, 70-80% organic solvent and 1.0-10.0% electrolyte additive;

[0020] Wherein, the electrolyte additive is the above electrolyte additive.

[0021] Furthermore, based on the above technical solution of the present invention, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0022] Furthermore, based on the above technical solution of the present invention, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

[0023] The present invention also provides a lithium-ion battery, characterized in that it comprises the above-mentioned lithium-ion battery electrolyte;

[0024] The lithium-ion battery is a high-nickel ternary / silicon-based negative electrode system battery.

[0025] Compared with the prior art, the technical solution of the present invention has at least the following technical effects:

[0026] (1) The present invention provides an electrolyte additive, which is prepared by using an propylene ester additive with a specific structure, vinylene carbonate, fluoroethylene carbonate and a lithium salt additive. When the electrolyte additive is applied to the electrolyte, the ion conductivity, cycle performance and high-voltage resistance of the electrolyte can be effectively improved; at the same time, when the electrolyte additive is applied to the lithium-ion battery system, it can also promote the formation of a dense and stable passivation film on the surface of the positive and negative electrodes, which is beneficial to the improvement of the electrochemical performance of the lithium-ion battery.

[0027] (2) The present invention provides a lithium-ion battery electrolyte, comprising a lithium salt, an organic solvent and the above-mentioned electrolyte additive. In view of the advantages of the above-mentioned electrolyte additive, the electrolyte using it has high ion conductivity, good cycle performance and high-voltage resistance, so that the electrolyte has good application prospects in fast-charging lithium-ion battery systems.

[0028] (3) The present invention provides a lithium-ion battery, comprising the above-mentioned lithium-ion battery electrolyte. In view of the advantages of the above-mentioned lithium-ion battery electrolyte, the lithium-ion battery has good rate performance and cycle performance. Experimental verification shows that the lithium-ion battery (high nickel ternary / silicon-based negative electrode system battery) can achieve a 3C capacity retention rate of more than 91% at 25°C, a 5C capacity retention rate of more than 84% at 25°C, and a capacity retention rate of more than 80% after 860 cycles of 3C / 1C at 25°C. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. The process parameters for which specific conditions are not specified in the following examples are generally in accordance with conventional conditions.

[0030] The endpoints of the ranges and any values 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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values can be combined with each other to form one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed in the present invention.

[0031] electrolyte additives

[0032] The present invention provides an electrolyte additive, including vinylene carbonate, fluoroethylene carbonate, a lithium salt additive, and an acrylate additive. The acrylate additive includes one or a combination of at least two of the compounds shown in Formula 1, Formula 2, or Formula 3:

[0033]

[0034] Among them, R1, R2, and R3 are each independently selected from a halogen atom, a C1-C20 alkoxy group or a halogenated alkoxy group, a C1-C20 siloxy group, a C1-C20 alkyleneoxy group, a C1-C20 hydrocarbon group or a halogenated hydrocarbon group, a C1-C20 isocyanate group, a C1-C20 aniline group, a C1-C20 amino group, a C1-C20 acyl group, or a C1-C20 ether group.

[0035] In the present invention, a mixture of vinylene carbonate and fluoroethylene carbonate is used as the main additive. The polycarbonate formed by reduction is very stable at high temperatures. The polycarbonate can effectively inhibit the continuous growth of the SEI film on the surface of the negative electrode (silicon-based) material, thereby improving the high temperature performance and cycle performance of the battery.

[0036] Lithium salt additives are mainly used to improve the conductivity, high and low temperature performance and hydrolysis resistance of the electrolyte.

[0037] Acrylate additives have the chemical structure shown in Formula 1, Formula 2, or Formula 3 above. "C1-C20" refers to a group with 1 to 20 carbon atoms, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 carbon atoms. "C1-C20 alkoxy or haloalkoxy" refers to an unsubstituted alkoxy group (such as methoxy, ethoxy, etc.) with 1 to 20 carbon atoms or a haloalkoxy group with 1 to 20 carbon atoms. A haloalkoxy group refers to an alkoxy group substituted with a halogen. Similarly, "C1-C20 hydrocarbon group or halohydrocarbon group" refers to an unsubstituted hydrocarbon group with 1 to 20 carbon atoms or a halohydrocarbon group with 1 to 20 carbon atoms. A halohydrocarbon group refers to a hydrocarbon group substituted with a halogen. A hydrocarbon group can be an alkyl, alkenyl, or alkynyl group. Halogenated hydrocarbon groups include, but are not limited to, halogenated alkyl groups, for example, CH3F, C2H5F, wait.

[0038] When the propylene ester additive provided by the present invention (chemical structure as shown in formula 1, formula 2 or formula 3) is added to the electrolyte and applied to the lithium ion battery system, the propylene ester additive has a certain effect of promoting the formation of a dense and stable passivation film on the surface of the positive and negative electrodes. Specifically, the S-sulfoxide structure (-S=O) in formula 1 can promote the formation of a flexible SEI film on the surface of the negative electrode, and can slow down the damage of the SEI film in the system (especially the silicon-containing system) during the expansion and contraction process; while the phosphorus (P) in formula 2 and the boron (B) in formula 3 can promote the formation of the CEI film on the surface of the positive electrode, prevent the dissolution of the positive electrode metal in the system (especially the high nickel system), and the P and B atoms can react with the PF 6- Coordination forms a more stable lithium salt complex, improving the ionic conductivity of the electrolyte. At the same time, P and B are more easily oxidized to form soluble phosphates and borates, which can effectively inhibit the decomposition of carbonates and further improve the cycle performance of the electrolyte. In addition, the cyclic structures in Formulas 1, 2, and 3 have a certain degree of rigidity, which can improve the protection of free radical cations from further reaction and enhance the high-voltage resistance of the electrolyte.

[0039] The structure of the acrylic ester additive has been further optimized. As an optional embodiment of the present invention, in the structure of the acrylic ester additive, R1, R2, and R3 are each independently selected from a halogen atom, a C1-C20 haloalkoxy group, a C1-C20 silanoxy group, a C1-C20 isocyanate group, or a C1-C20 hydrocarbon group; more preferably, at least one of R1, R2, and R3 is selected from a C1-C20 silanoxy group or a C1-C20 isocyanate group.

[0040] As a preferred embodiment of the present invention, the acrylic ester additive includes at least one of additive A, additive B, additive C, additive D, additive E or additive F having the following structure:

[0041]

[0042] In additives A, additives B and additives C, R1 in the structural unit is a halogenated alkoxy group, R2 is a silanoloxy group, and R3 is an alkyl group. Among them, when R1 is a halogenated (fluoro) alkoxy group, it can form a self-assembled polyfluoroalkyl chain layer as a solvent-repellent layer, effectively inhibiting the decomposition of the electrolyte solvent and promoting the formation of the SEI film on the negative electrode surface. The generated SEI film has low impedance and can effectively improve the high-rate fast charging performance of the lithium-ion battery system (especially the high-nickel ternary / silicon-based negative electrode system); when R2 is a silanoloxy group, it can remove trace water and HF in the electrolyte, prevent the SEI / CEI film from being destroyed, improve the stability of the positive and negative electrodes, and improve the high-temperature storage and cycle performance; when R3 is an alkyl group, it can be Li in the negative electrode SEI film + It provides space for transmission, enhances the ionic conductivity of the SEI membrane, and improves fast charging performance.

[0043] In Additives D, E, and F, R1 in the structural unit is fluorine, R2 is an isocyanate group, and R3 is a hydrocarbon group. When R1 is a fluorine atom, it decomposes on the negative electrode surface to produce LiF, which acts as a bond between the negative electrode material and the SEI film, reducing the formation of microcracks, thereby improving the stability of the negative electrode SEI film and cycling performance. When R2 is an isocyanate group, it can remove trace water and HF from the electrolyte, preventing damage to the SEI / CEI film, improving the stability of the positive and negative electrodes, and improving high-temperature storage and cycling performance. When R3 is a hydrocarbon group, it and the sulfoxide group promote the formation of a flexible and rigid SEI film, thereby improving the stability of the SEI film.

[0044] Preferably, the acrylic ester additive includes one or a combination of at least two of additive A, additive B and additive C, and more preferably includes additive A, additive B and additive C.

[0045] Preferably, the acrylic ester additive includes one of additive D, additive E and additive F, or a combination of at least two of them, and more preferably includes additive D, additive E and additive F.

[0046] Experiments have found that when the propylene ester additive is a combination of additive A, additive B and additive C, or a combination of additive D, additive E and additive F, the electrochemical performance of the corresponding lithium-ion battery system is better.

[0047] The preparation methods of additives A, B and C can be further defined.

[0048] As an optional embodiment of the present invention, additive A can be prepared using the following raw materials (the raw materials can be obtained by searching the structural formula on Gaide Chemical Network) according to the following synthetic route:

[0049]

[0050] As an optional embodiment of the present invention, the synthesis route of additive B is as follows:

[0051]

[0052] Additive B is obtained by replacing the substituents on the basis of formula (B). For the specific replacement of the substituents, please refer to the synthetic route of additive A (replacement of the substituents in formula (A)).

[0053] As an optional embodiment of the present invention, the synthetic route of additive C is as follows:

[0054]

[0055] Additive C is obtained by replacing the substituents on the basis of formula (C). For the specific replacement of the substituents, please refer to the synthetic route of additive A (replacement of the substituents in formula (A)).

[0056] Similarly, the preparation methods of Additive D, Additive E, and Additive F may be further defined. As an optional embodiment of the present invention, Additive D may be prepared using the following raw materials (the raw materials can be obtained by searching the structural formula on Gaide Chemical Network) according to the following synthetic route:

[0057]

[0058] The synthetic route of additive E is as follows:

[0059]

[0060] Additive E is obtained by replacing the substituents on the basis of formula (E). For the specific replacement of the substituents, please refer to the synthetic route of additive D (replacement of the substituents in formula (A)).

[0061] The synthetic route of additive F is as follows:

[0062]

[0063] Additive F is obtained by replacing substituents based on formula (F). For specific replacement of substituents, refer to the synthetic route of additive D (replacement of substituents in formula (A)). In addition to optimizing the structure of the acrylate additive, the type of lithium salt additive can also be further limited. As an optional embodiment of the present invention, the lithium salt additive includes at least one of lithium difluorophosphate, lithium bisoxalatoborate, lithium bisfluorooxalatoborate, or lithium bisfluorooxalatophosphate.

[0064] In addition to optimizing the specific types of the above-mentioned acrylate additives and lithium salt additives, there are also certain restrictions on the usage of each component of the electrolyte additive.

[0065] As an optional embodiment of the present invention, the mass ratio of vinylene carbonate, fluoroethylene carbonate, lithium salt additive and propylene ester additive is (0.5-1.5):(3-7):(0.5-1.5):(1-3), and typical but non-limiting mass ratios include 0.5:3:0.5:1, 0.5:5:0.5:1, 0.5:7:0.5:1, 0.5:3:0.8:1, 0.5:5:1:1, 0.5:7:1.5:1, 0.5:3:0.5:2, 0.5:5:0.5:2, 0.5:7:0.5:3, 0.8:3:0.5:1, 1:5:0.5:1, 1:5:1:1, 1:5:1:1.5, 1:5:1:3, or 1.5:7:0.5:1.

[0066] Lithium-ion battery electrolyte

[0067] Based on the above electrolyte additive, the present invention also provides a lithium-ion battery electrolyte. The electrolyte comprises the following components in the following mass fractions, calculated as 100% by mass:

[0068] 15-25% lithium salt, 70-80% organic solvent and 1.0-10.0% of the above electrolyte additives.

[0069] The specific type of lithium salt is not limited, and common types in the art may be selected, such as lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, or bis(oxalatoboric acid). Typical but non-limiting mass fractions of the lithium salt in the electrolyte are 15%, 16%, 18%, 20%, 22%, 24%, or 25%.

[0070] The specific type of organic solvent is not limited, and common solvent types in the art can be selected, such as ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, or propylene carbonate. Typical but non-limiting mass fractions of the organic solvent in the electrolyte are 70%, 72%, 74%, 75%, 76%, 78%, or 80%.

[0071] The electrolyte additive is the electrolyte additive provided by the present invention. It should be noted that there are certain restrictions on the amount of electrolyte additives used. If the mass fraction of the electrolyte additive is too high (higher than 10%), it will continuously consume the active Li components in the battery, causing the capacity of the lithium-ion battery to decay faster. If the mass fraction of the electrolyte additive is too low (lower than 1%), it will not achieve the purpose of optimizing the CEI and SEI membranes and improving the performance of the battery cell. Therefore, the amount of the electrolyte additive should be controlled within a certain numerical range. Typical but non-restrictive mass fractions of electrolyte additives are 1%, 2%, 4%, 5%, 6%, 8% or 10%.

[0072] The lithium-ion battery electrolyte provided by the present invention adopts a specific type of electrolyte additive in combination with lithium salts and organic solvents, so that when applied to a battery (high-nickel ternary / silicon-based negative electrode system battery) system, the electrolyte can promote the formation of more stable CEI / SEI films at the positive and negative electrodes, thereby significantly improving the battery's rate performance and cycle performance.

[0073] The specific types and dosages of lithium salts have been further optimized.

[0074] As an optional embodiment of the present invention, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide;

[0075] Preferably, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is (6-10):(2-6), with typical but non-limiting mass ratios being 6:2, 6:4, 6:5, 6:6, 7:2, 7:4, 7:5, 7:6, 8:2, 8:4, 8:5, 8:6, 10:2, 10:4, or 10:6. Experimental results show that a mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide of 7:4 achieves better results.

[0076] As an optional embodiment of the present invention, the concentration of the lithium salt in the electrolyte is 1-3 mol / L. Typical but non-limiting concentrations of the lithium salt are 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.5 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.8 mol / L or 3.0 mol / L.

[0077] The present invention selects lithium hexafluorophosphate with good electrochemical stability and lithium bis(fluorosulfonyl)imide with strong thermal stability as solutes, and the high concentration of lithium salt improves the ion conductivity of the electrolyte.

[0078] The specific type and dosage of organic solvents have been further optimized.

[0079] As an optional embodiment of the present invention, the organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate;

[0080] Preferably, the volume ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate is (25-45):(50-60):(5-15):(1-10), and typical but non-limiting volume ratios are 25:50:5:1, 25:55:5:1, 25:60:5:1, 25:50:8:1, 25:55:10:1, 25:60:15:1, 25:50:5:4, 25:55:5:5, 25:60:5:10, 30:50:5:1, 30:55:10:5, 35:55:5:5, 40:60:5:1 or 45:60:5:1. Among them, when the volume ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate is 30:55:10:5, the effect is better.

[0081] The present invention selects a mixed solvent of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate to reduce the melting point and viscosity of the electrolyte and improve the ion transmission performance of the electrolyte.

[0082] The lithium-ion battery electrolyte provided by the present invention can be prepared using common preparation methods in the art.

[0083] As an optional embodiment of the present invention, a method for preparing a lithium-ion battery electrolyte includes the following steps: uniformly mixing a lithium salt, an organic solvent, and an electrolyte additive to obtain a lithium-ion battery electrolyte.

[0084] When mixing the above raw materials, the temperature, humidity, oxygen content and water content of the environment need to be controlled. As an optional embodiment of the present invention, the temperature of the environment is 10-20°C, the humidity is ≤1%, the oxygen content is ≤1ppm, and the water content is ≤0.1ppm.

[0085] By limiting the above temperature, humidity, oxygen content and water content, the purity of the organic solvent and the electrochemical stability window are ensured to prevent the decomposition of the lithium salt and the failure of the electrolyte.

[0086] lithium-ion batteries

[0087] The present invention also provides a lithium-ion battery, comprising the above-mentioned lithium-ion battery electrolyte; the lithium-ion battery is a high-nickel ternary / silicon-based negative electrode system battery.

[0088] In view of the advantages of the above-mentioned lithium-ion battery electrolyte, the lithium-ion battery has good high and low temperature rate performance and cycle performance.

[0089] As an optional embodiment of the present invention, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator and the above-mentioned lithium-ion battery electrolyte.

[0090] As an optional embodiment of the present invention, the raw material of the positive electrode plate includes a high-nickel ternary positive electrode active material;

[0091] Preferably, the high nickel ternary positive electrode active material includes lithium nickel cobalt manganese oxide Li (Ni x Co y Mn z )O2 (abbreviated as NCM) or lithium nickel cobalt aluminum oxide Li (Ni x Co y Al z )O2 (abbreviated as NCA), where x≥0.6, 0 <y≤0.2,0<z≤0.2,x+y+z=1。

[0092] In the general structural formula of lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide, the value of x can be, for example, 0.6, 0.7, 0.8 or 0.9, the value of y can be, for example, 0.1, 0.15 or 0.2, and the value of z can be, for example, 0.1, 0.15 or 0.2.

[0093] As an optional embodiment of the present invention, the raw material of the negative electrode plate includes a silicon-containing negative electrode active material;

[0094] Preferably, the negative electrode active material comprises any one of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compounds, or silicon carbon compounds, or a combination of at least two thereof. Typical but non-limiting examples of such combinations include: a combination of soft carbon and hard carbon, a combination of hard carbon and artificial graphite, a combination of artificial graphite and natural graphite, a combination of natural graphite and silicon, a combination of silicon and silicon oxide compounds, a combination of silicon oxide compounds and silicon carbon compounds, or a combination of silicon carbon compounds. For example, SiC (or SiO) / graphite, wherein the mass ratio of SiC (or SiO) to graphite is (3-20): (80-97).

[0095] As an optional embodiment of the present invention, the application temperature of the lithium ion battery is -40 to 55° C. The lithium ion battery has good electrochemical performance at both high and low temperatures.

[0096] The present invention will be further described in detail below with reference to specific examples and comparative examples.

[0097] Example 1

[0098] This embodiment provides a lithium-ion battery electrolyte, which includes the following components in the following mass fractions, calculated as 100% by mass:

[0099] Lithium salt 18.5%, organic solvent 73% and electrolyte additive 8.5%.

[0100] The organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate. Based on the total volume of the organic solvent as 100%, the mass ratio of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate: propylene carbonate is 30:55:10:5.

[0101] The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Based on 100% of the mass of the lithium salt, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 7:4.

[0102] The electrolyte additives include vinylene carbonate, fluoroethylene carbonate, lithium salt additives and propylene ester additives, and the mass ratio of the four is 1:5:1:1.5; wherein the lithium salt additive includes lithium difluorophosphate and lithium difluorooxalatoborate (the mass ratio of the two is 1:1), and the propylene ester additive includes additive A, additive B and additive C having the following structure (the mass ratio of the three is 1:1:1):

[0103]

[0104] The synthetic route of additive A is as follows:

[0105]

[0106] The synthetic route of additive B is as follows:

[0107]

[0108] Additive B is obtained by replacing the substituents on the basis of formula (B). For the specific replacement of the substituents, please refer to the synthetic route of additive A (replacement of the substituents in formula (A)).

[0109] The synthetic route of additive C is as follows:

[0110]

[0111] Additive C is obtained by replacing the substituents on the basis of formula (C). For the specific replacement of the substituents, please refer to the synthetic route of additive A (replacement of the substituents in formula (A)).

[0112] Example 2

[0113] This embodiment provides a lithium-ion battery electrolyte, which includes the following components in the following mass fractions, calculated as 100% by mass:

[0114] Lithium salt 18.50%, organic solvent 71.5% and electrolyte additive 10%.

[0115] The organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate. Based on the total volume of the organic solvent as 100%, the mass ratio of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate: propylene carbonate is 30:55:10:5.

[0116] The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Based on 100% of the mass of the lithium salt, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 7:4.

[0117] The electrolyte additives include vinylene carbonate, fluoroethylene carbonate, lithium salt additives and propylene ester additives, and the mass ratio of the four is 1:5:1:3; among them, the lithium salt additive includes lithium difluorophosphate and lithium difluorooxalatoborate (the mass ratio of the two is 1:1), and the propylene ester additive includes additive A, additive B and additive C (the mass ratio of the three is 1:1:1). The structures and synthesis methods of additives A, additive B and additive C are shown in Example 1.

[0118] Example 3

[0119] This embodiment provides a lithium-ion battery electrolyte, which includes the following components in the following mass fractions, calculated as 100% by mass:

[0120] Lithium salt 18.50%, organic solvent 73.5% and electrolyte additive 8%.

[0121] The organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate. Based on the total volume of the organic solvent as 100%, the mass ratio of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate: propylene carbonate is 30:55:10:5.

[0122] The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Based on 100% of the mass of the lithium salt, the mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 7:4.

[0123] The electrolyte additives include vinylene carbonate, fluoroethylene carbonate, lithium salt additives and propylene ester additives, and the mass ratio of the four is 1:5:1:1; among them, the lithium salt additive includes lithium difluorophosphate and lithium difluorooxalatoborate (the mass ratio of the two is 1:1), and the propylene ester additive includes additive A, additive B and additive C (the mass ratio of the three is 1:1:1). The structures and synthesis methods of additives A, additive B and additive C are shown in Example 1.

[0124] Example 4

[0125] This embodiment provides a lithium-ion battery electrolyte. Except that the propylene ester additives are replaced by additives A, additives B and additives C with additives D, additives E and additives F (the mass ratio of the three is 1:1:1), the types and amounts of other raw materials are the same as those in Example 1.

[0126] The structural formulas of additives D, E and F are as follows:

[0127]

[0128] The synthetic route of additive D is as follows:

[0129]

[0130] The synthetic route of additive E is as follows:

[0131]

[0132] Additive E is obtained by replacing the substituents on the basis of formula (E). For the specific replacement of the substituents, please refer to the synthetic route of additive D (replacement of the substituents in formula (A)).

[0133] The synthetic route of additive F is as follows:

[0134]

[0135] Additive F is obtained by replacing the substituents on the basis of formula (F). For the specific replacement of the substituents, please refer to the synthetic route of additive D (replacement of the substituents in formula (A)).

[0136] Example 5

[0137] This embodiment provides a lithium-ion battery electrolyte. Except that the composition of the propylene ester additive is replaced from Additive A: Additive B: Additive C = 1:1:1 to Additive A: Additive B = 1:1, the total amount of the propylene ester additive remains unchanged, and the types and amounts of other raw materials are the same as those in Example 1.

[0138] Example 6

[0139] This embodiment provides a lithium-ion battery electrolyte, except that the composition of the propylene ester additive is replaced from Additive A: Additive B: Additive C = 1:1:1 to only Additive A, the total amount of the propylene ester additive remains unchanged, and the types and amounts of other raw materials are the same as those in Example 1.

[0140] Example 7

[0141] This embodiment provides a lithium-ion battery electrolyte, except that the composition of the propylene ester additive is replaced from Additive A: Additive B: Additive C = 1:1:1 to only Additive B, the total amount of the propylene ester additive remains unchanged, and the types and amounts of other raw materials are the same as those in Example 1.

[0142] Example 8

[0143] This embodiment provides a lithium-ion battery electrolyte, except that the composition of the propylene ester additive is replaced from Additive A: Additive B: Additive C = 1:1:1 to only Additive C, the total amount of the propylene ester additive remains unchanged, and the types and amounts of other raw materials are the same as those in Example 1.

[0144] Example 9

[0145] This embodiment provides a lithium-ion battery electrolyte, which includes the following components in the following mass fractions, calculated as 100% by mass:

[0146] Lithium salt 20%, organic solvent 70% and electrolyte additive 10%.

[0147] The organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate. Based on the total volume of the organic solvent as 100%, the mass ratio of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate: propylene carbonate is 30:55:10:5.

[0148] The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Based on 100% of the mass of the lithium salt, the mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is 10:2.

[0149] The electrolyte additives include vinylene carbonate, fluoroethylene carbonate, lithium salt additives and propylene ester additives, and the mass ratio of the four is 2:6:1:1; among them, the lithium salt additive includes lithium difluorophosphate and lithium difluorooxalatoborate (the mass ratio of the two is 1:1), and the propylene ester additive includes additive A, additive B and additive C having the following structure (the mass ratio of the three is 1:1:1). The structures and synthesis methods of additives A, additive B and additive C are shown in Example 1.

[0150] Example 10

[0151] This embodiment provides a lithium-ion battery electrolyte, which includes the following components in the following mass fractions, calculated as 100% by mass:

[0152] Lithium salt 15%, organic solvent 80% and electrolyte additive 5%.

[0153] The organic solvent includes ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate. Based on the total volume of the organic solvent as 100%, the mass ratio of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate: propylene carbonate is 30:55:10:5.

[0154] The lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide. Based on 100% of the mass of the lithium salt, the mass ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is 1:1.

[0155] The electrolyte additives include vinylene carbonate, fluoroethylene carbonate, lithium salt additives and propylene ester additives, and the mass ratio of the four is 0.5:3:0.5:1; among them, the lithium salt additive includes lithium difluorophosphate and lithium difluorooxalatoborate (the mass ratio of the two is 1:1), and the propylene ester additive includes additive A, additive B and additive C having the following structure (the mass ratio of the three is 1:1:1). The structures and synthesis methods of additives A, additive B and additive C are shown in Example 1.

[0156] Example 11

[0157] This embodiment provides a lithium-ion battery electrolyte. Except that the composition of the propylene ester additive is replaced from Additive D: Additive E: Additive F = 1:1:1 to Additive D: Additive E = 1:1, the total amount of the propylene ester additive remains unchanged, and the types and amounts of other raw materials are the same as those in Example 4.

[0158] Example 12

[0159] This embodiment provides a lithium-ion battery electrolyte, except that the composition of the propylene ester additive is replaced from Additive D: Additive E: Additive F = 1:1:1 to only Additive D, the total amount of the propylene ester additive remains unchanged, and the types and amounts of other raw materials are the same as those in Example 4.

[0160] Comparative Example 1

[0161] This comparative example provides a lithium-ion battery electrolyte, except that the mass ratio of vinylene carbonate, fluoroethylene carbonate, lithium salt additive and propylene ester additive in the electrolyte additive is replaced from 1:5:1:1.5 to 0.5:3:1:4, and the types and amounts of other raw materials are the same as those in Example 1.

[0162] Comparative Example 2

[0163] This comparative example provides a lithium-ion battery electrolyte, which contains only additive A except that the propylene ester additive contains only additive A, and the mass ratio of vinylene carbonate, fluoroethylene carbonate, lithium salt additive and propylene ester additive in the electrolyte additive is replaced from 1:5:1:1.5 to 1.5:5:1.5:0.5. The types and amounts of other raw materials are the same as those in Example 1.

[0164] Comparative Example 3

[0165] This comparative example provides a lithium-ion battery electrolyte. Except that the propylene ester additive composition is replaced by tris(trimethylsilyl) phosphate, propylene sulfate and 1,3-propane sultone (mass ratio is 1:1:1), the other raw material types and amounts are the same as those in Example 1.

[0166] Comparative Example 4

[0167] This comparative example provides a lithium-ion battery electrolyte, except that no propylene ester additive is added to the electrolyte, that is, the electrolyte is composed of vinylene carbonate, fluoroethylene carbonate and lithium salt additive, and the mass ratio of vinylene carbonate, fluoroethylene carbonate and lithium salt additive is 1.5:5:2. The types and amounts of other raw materials are the same as those in Example 1.

[0168] Comparative Example 5

[0169] This comparative example provides a lithium-ion battery electrolyte, except that no propylene ester additive is added to the electrolyte, that is, the electrolyte is composed of vinylene carbonate, fluoroethylene carbonate and lithium salt additive, the mass ratio of vinylene carbonate, fluoroethylene carbonate and lithium salt additive is 1:5:1, and the types and amounts of other raw materials are the same as those in Example 1.

[0170] Comparative Example 6

[0171] This comparative example provides a lithium-ion battery electrolyte, except that the mass fraction of the electrolyte additive is adjusted from 8.5% to 11% and the mass fraction of the organic solvent is adjusted from 73% to 70.5%. The other raw material types and amounts are the same as those in Example 1.

[0172] Comparative Example 7

[0173] This comparative example provides a lithium-ion battery electrolyte, except that the mass fraction of the electrolyte additive is adjusted from 8.5% to 0.5% and the mass fraction of the organic solvent is adjusted from 73% to 81%. The remaining raw material types and amounts are the same as those in Example 1.

[0174] In order to compare the technical effects of the above embodiments and comparative examples, the following experimental examples are specially set up.

[0175] Experimental Example 1

[0176] Soft-pack 505060 lithium-ion batteries were respectively manufactured using the electrolytes in Examples 1-12 and Comparative Examples 1-7 by adopting a soft-pack lamination process.

[0177] The specific method is as follows: an NCM811 positive electrode sheet, a silicon-based graphite negative electrode sheet (the mass ratio of SiO to graphite is 10:90) and a polyethylene separator (for example, PE+OBS separator) are stacked and assembled and then baked until the moisture content is qualified, the electrolyte of the embodiment or comparative example is injected, and the battery is packaged after hot pressing and high-temperature standing. After volume separation, the battery is stood at room temperature to obtain a soft-pack 505060 finished battery. The above electrolyte is tested for HF content and conductivity, and the above battery is tested for electrochemical performance.

[0178] HF content test: After the prepared electrolyte was stored at 45°C for 0 and 30 days, the electrolyte was dissolved in ice water and titrated with 0.01 mol / L sodium hydroxide standard solution to obtain the HF content of the electrolyte stored at 45°C for 0 and 30 days (see Table 1).

[0179] Conductivity test: The conductivity of the electrolyte was tested using a conductivity meter at a test temperature of -10°C. Each sample was measured three times, and the average value was taken as the result, see Table 1.

[0180] Cycling performance: Tested at 25°C on an electrochemical workstation battery test system with a charge and discharge current density of 3C / 1C and a charge and discharge voltage window of 2.75V to 4.2V. See Table 1.

[0181] Rate performance: Tested at 25°C on an electrochemical workstation battery test system at current densities of 1C / 1C, 1C / 3C, and 1C / 5C. The discharge capacities at 3C and 5C rates were calculated by dividing the discharge capacity at 1C rate. The obtained percentage values are the 3C capacity retention rate and 5C capacity retention rate, respectively. The charge and discharge voltage window is 2.75V to 4.2V, as shown in Table 1.

[0182] Table 1

[0183]

[0184]

[0185] Combining the HF content data for Examples 1-12 and Comparative Examples 1-7 in Table 1, it can be seen that the acrylic ester additives of the present invention can react with trace amounts of water in the electrolyte and active hydrogen on the surfaces of the positive and negative electrodes of the battery through isocyanate or siloxy groups, preventing the HF generated by the decomposition of LiPF6 from causing SEI film decomposition. Combining Example 1 with Comparative Examples 1-7, as the content of the acrylic ester additive in the electrolyte of the present invention increases, the detected HF value shows a downward trend. Combining the conductivity data in Table 1, it can be seen that the conductivity of the electrolyte increases with the lithium salt content, and high concentrations of lithium salts improve the ionic conductivity of the electrolyte.

[0186] Combining the cycle test and rate test data in Table 1, it can be seen that when the lithium battery is cycled to 80% SOH (State of Health), Example 1 has the most cycles, the best cycle stability, and the best capacity retention under 3C and 5C discharge. Compared with Comparative Examples 1-7, the various electrical properties of the lithium battery prepared by Example 1 are higher than those of Comparative Examples 1-7, indicating that when the addition amounts of lithium salt, organic solvent, and additives are within the preferred range, the performance is more excellent, and when vinylene carbonate, fluoroethylene carbonate, lithium salt additive, and propylene ester additive are present together, the performance of the resulting battery is optimal.

[0187] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are within the scope of protection of the pending claims of the present invention.

Claims

1. An electrolyte additive, characterized in that It includes vinylene carbonate, fluoroethylene carbonate, lithium salt additive and acrylic ester additive, wherein the acrylic ester additive includes a compound represented by Formula 1, a compound represented by Formula 2 and a compound represented by Formula 3: wherein R1, R2 and R3 are each independently selected from one of a halogen atom, a C1-C20 alkoxy group or a halogenated alkoxy group, a C1-C20 siloxy group, a C1-C20 hydrocarbon group or a halogenated hydrocarbon group, and a C1-C20 isocyanate group; The mass ratio of the vinylene carbonate, fluoroethylene carbonate, lithium salt additive and propylene ester additive is (0.5-1.5):(3-7):(0.5-1.5):(1-3).

2. The electrolyte additive according to claim 1, characterized in that In the structure of the acrylic ester additive, at least one group among R1, R2 and R3 is selected from C1-C20 silanoxy groups or C1-C20 isocyanate groups.

3. The electrolyte additive according to claim 1, characterized in that The acrylic ester additive includes at least one of additive A, additive B, additive C, additive D, additive E or additive F having the following structure:

4. The electrolyte additive according to claim 3, characterized in that The acrylic ester additives include additive A, additive B and additive C; or, the acrylic ester additives include additive D, additive E and additive F.

5. The electrolyte additive according to claim 1, characterized in that The lithium salt additive includes at least one of lithium difluorophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate or lithium difluorooxalatophosphate.

6. A lithium ion battery electrolyte, characterized in that: Taking the mass fraction as 100%, it includes the following components in mass fraction: 15-25% lithium salt, 70-80% organic solvent and 1.0-10.0% electrolyte additive; Wherein, the electrolyte additive is the electrolyte additive according to any one of claims 1 to 5; and the organic solvent comprises ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and propylene carbonate.

7. The lithium-ion battery electrolyte according to claim 6, characterized in that The lithium salts include lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

8. A lithium-ion battery, characterized in that: Containing the lithium ion battery electrolyte according to claim 6 or 7; The lithium-ion battery is a high-nickel ternary / silicon-based negative electrode system battery.

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