A compound, an electrolyte and its application

Abstract

This invention discloses a compound, an electrolyte, and their applications. The compound has the structure shown in Formula I. The electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the lithium salt includes LiPF6, and the additive includes the compound shown in Formula I. The compound of this invention uses pyridine as the parent compound, wherein N has weak basicity, which can moderately suppress the acidity of the electrolyte and reduce the generation of HF; in combination with phosphoric acid oxygen and saturated or unsaturated alkyl groups, under certain conditions, through an acid-base coordination reaction, it can neutralize PF5 derived from the decomposition products of LiPF6, stabilize the decomposition product PF5, and rapidly form a stable protective film, while ensuring low resistance. It can be used as an electrolyte for lithium-ion batteries, improving the high-temperature cycle performance and high-temperature storage performance of the battery, and reducing the DCR growth in the later stages of battery cycling.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and specifically to a compound, an electrolyte, and their applications. Background Technology

[0002] Lithium-ion batteries are a key driving force in modern technology, not only because of their high energy density (approximately 240 Wh / kg) and high operating voltage (approximately 3.6 V), but also because of their low self-discharge loss, long cycle life, and most importantly, their environmental friendliness. Their performance is crucial for ultra-portable electronic products such as mobile phones, tablets, laptops, smartwatches, and other digital devices. Two other high-potential application areas include energy storage at various capacity levels, from home to grid-scale, and power sources for electric vehicles. Currently, research on lithium-ion battery materials has been ongoing for several years, with battery performance and safety being the primary concerns.

[0003] With the increasing demands of new energy policies and the growing market need for high-performance batteries, improving battery energy density and safety has become a major focus. Nickel-rich cathode materials are key materials for high-energy-density lithium-ion batteries in next-generation energy storage devices. Among nickel-rich cathode materials, high-nickel ternary cathode materials (such as NCM811, chemical formula LiNi) are particularly important. 0.8 Co 0.1 Mn 0.1 O2 has attracted widespread attention from researchers due to its advantages such as large charge / discharge capacity, high operating voltage, high lifespan, long cycle life, and low cost. However, compared with cathode materials with low Ni content, some defects limit its widespread development in lithium-ion batteries. Taking NCM811 as an example, its defects are listed as follows: (1) Oxygen element instability: Oxygen elements in the layered structure of NCM811 are easily precipitated under cycling or high temperature, and oxygen defects produce lattice defects, causing safety hazards. (2) High surface alkali content: Lithium residues on the surface of NCM811 will react with H2O and CO2 in the air to generate LiOH and Li2CO3. The generated impurities can accelerate the decomposition of electrolyte to generate HF, and the transition metals in NCM811 are easily dissolved by HF. (3) Structural instability: During charge / discharge cycles, the insertion and extraction of lithium ions cause lattice expansion or contraction, and lead to particle breakage. NCM811 changes from a layered structure to a spinel structure, and Ni 4+ It can be easily reduced to Ni by gaining electrons. 2+ .

[0004] Materials with high nickel content, such as NCM811, operate at higher voltages, typically between 4.2V and 4.4V. Under high temperature and high pressure, they are prone to interface degradation, particle breakage, and electrolyte oxidation, leading to a rapid decline in battery life at high temperatures. Simultaneously, excessively rapid increases in the battery's discharge rate (DCR) can cause battery failure. Therefore, from an electrolyte perspective, it is necessary to develop positive electrode electrolyte additives that can passivate the positive electrode interface and form a stable CEI protective film at high temperatures.

[0005] In recent years, numerous studies have reported on the practical application of electrolyte additives in lithium-ion batteries, focusing on improving battery charge / discharge capacity, cycle life, storage durability, and overcharge safety. CN103022561A discloses an electrolyte that improves the high-temperature cycling and storage performance of lithium-ion batteries. This electrolyte comprises lithium salts, organic solvents, and additives. It also contains a high-temperature film-forming agent, which is one or any combination of δ-valerolactone, γ-valerolactone, γ-caprolactone, and ε-caprolactone. The high-temperature film-forming agent accounts for 0.5% to 15% of the total electrolyte mass. By adding a high-temperature film-forming agent to the lithium-ion battery electrolyte, a passivation film with excellent thermal stability can be formed on the surface of the positive electrode of the lithium-ion battery. This improves the interface between the positive electrode and the electrolyte, suppresses the decomposition reaction of the electrolyte on the positive electrode material at high temperatures, and overcomes the shortcomings of existing lithium-ion batteries, such as rapid capacity loss, low recovery rate, and rapid battery thickness expansion under high-temperature conditions. This improves the high-temperature cycling and storage characteristics of the battery. CN115579523A discloses an electrolyte for improving the cycle performance and high-temperature storage performance of lithium-ion batteries. The electrolyte comprises an electrolyte lithium salt, an organic solvent, and composite additives. The composite additives include fluoroethylene carbonate, propylene sulfite, and at least one of compounds I and II. This invention, based on the first two additives, combines the synergistic effect of the latter two, thereby improving the battery's cycle performance and high-temperature storage performance. It is particularly beneficial for lithium-ion batteries with graphite, composites of monocrystalline silicon and graphite, or composites of silicon suboxide and graphite as the negative electrode material, providing them with high safety, excellent cycle stability, and high-temperature storage performance. CN109818064A discloses a high-temperature, high-voltage non-aqueous electrolyte and a lithium-ion battery containing the non-aqueous electrolyte. The high-temperature, high-voltage non-aqueous electrolyte comprises a lithium salt, a non-aqueous solvent, and additives. The additives include a first type of borate additive, a second type of nitrogen-containing lithium salt additive, a third type of silicon-nitrogen-based additive, and a fourth type of mixed additive of sulfonates and sulfates. By combining various additives in appropriate proportions, their respective advantages can be brought into play while suppressing each other's disadvantages. Through their synergistic effect, the high-temperature storage performance of the battery is improved, and the high-temperature cycle performance of the battery is enhanced, showing good application prospects under high temperature and high voltage conditions.

[0006] However, higher-performance electrolyte additives are urgently needed to prepare an electrolyte that can combine high-temperature cycling and storage performance while ensuring a smaller increase in DCR in the later stages of battery cycling. Summary of the Invention

[0007] To address the aforementioned technical problems in the existing technology, the present invention aims to provide a compound, an electrolyte, and their applications. The electrolyte of the present invention not only improves the high-temperature storage performance and high-temperature cycling performance of the battery, but also ensures a smaller increase in DCR (Discharge Rate) in the later stages of battery cycling, resulting in excellent overall battery performance. To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a compound having the structure shown in Formula I:

[0009]

[0010] R1-R4 are independently selected from any one of saturated alkyl or unsaturated alkyl groups.

[0011] The compounds of this invention use pyridine as the parent compound, wherein N has weak basicity and can moderately suppress the acidity of the electrolyte; in combination with phosphate oxygen and saturated or unsaturated alkyl groups, under certain conditions, through acid-base coordination reaction, they can neutralize PF5 derived from the decomposition products of LiPF6, stabilize the decomposition product PF5, and quickly form a stable protective film, while ensuring low resistance. They can be used in electrolytes for lithium-ion batteries, improving the high-temperature cycle performance and high-temperature storage performance of the battery, and reducing the DCR growth in the later stages of battery cycling.

[0012] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0013] Preferably, R1-R4 are linear alkyl groups.

[0014] Preferably, the saturated alkyl group has the general formula C2. n H 2n+1 , 1≤n≤3.

[0015] Preferably, the unsaturated alkyl group has the general formula C2. n H 2n , 2≤n≤3, the unsaturated alkyl group includes carbon-carbon double bonds.

[0016] Preferably, R1 and R3 are the same, and R2 and R4 are the same.

[0017] Preferably, R1-R4 are all propylene-based.

[0018] In a second aspect, the present invention provides a method for preparing the compound as described in the first aspect, the method comprising the following steps:

[0019] Synthesis of 1,2,6-dihydroxypyridine: Starting material a reacts to yield product A. The reaction process is as follows:

[0020]

[0021] II. Synthesis of 2,6-dichloropyridine: Product A reacts to give product B, and the reaction process is as follows:

[0022]

[0023]

[0024] III. Synthesis of tetraalkylpyridine-2,6-dimethylphosphonate: Product B reacts with raw material b to obtain product C, wherein raw material b is a trialkyl phosphite.

[0025] As a preferred embodiment of the preparation method described in this invention, in step I, the reaction is carried out in a solvent, wherein the solvent is anhydrous tetrahydrofuran (THF).

[0026] Preferably, in step I, the reaction is carried out in the presence of a catalyst, preferably lithium aluminum hydride (LiAlH4). Under the action of the catalyst, the carbonyl group in the carboxyl group is reduced to an alkyl group.

[0027] Preferably, 2,6-pyridinedicarboxylic acid is dissolved in anhydrous tetrahydrofuran and cooled. More preferably, the cooling temperature is 0°C and the cooling time is 10 min to 30 min.

[0028] Preferably, the molar ratio of 2,6-pyridinedicarboxylic acid and lithium aluminum hydride is less than 1:1, for example, it can be 59.8:116.

[0029] Preferably, in step I, the reaction is carried out under reflux stirring, and the reflux stirring temperature is 50℃-70℃, for example, it can be 50℃, 52℃, 55℃, 56℃, 58℃, 60℃, 62℃, 63℃, 65℃, 68℃ or 70℃, etc.; the reflux stirring time is 18h-30h, for example, it can be 18h, 20h, 21h, 22h, 24h, 25h, 28h or 30h, etc.

[0030] Preferably, before the reflux stirring, room temperature stirring is performed first, and the room temperature stirring time is preferably 20 min to 45 min, for example, it can be 20 min, 22 min, 23 min, 24 min, 25 min, 26 min, 28 min, 30 min, 32 min, 33 min, 35 min, 36 min, 37 min, 38 min, 40 min, 43 min or 45 min, etc.

[0031] In this invention, room temperature refers to 20 to 28°C, such as 20°C, 21°C, 22°C, 23°C, 24°C, 25°C, 26°C, 27°C, or 28°C.

[0032] Preferably, after reflux and stirring, the mixture is cooled and extracted to obtain a crude product, which is then purified to obtain the intermediate product 2,5-dihydroxypyridine.

[0033] As a preferred embodiment of the preparation method described in this invention, in step II, the reaction is carried out in a solvent, wherein the solvent is dichloromethane (CH2Cl2).

[0034] Preferably, in II, the reaction is carried out in the presence of thionyl chloride (SOCl2).

[0035] Preferably, the molar ratio of 2,6-dihydroxypyridine to thionyl chloride is 1:(2-4), for example, it can be 1:2, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.7, 1:2.8, 1:3, 1:3.2, 1:3.3, 1:3.5, 1:3.6, 1:3.8 or 1:4, etc.

[0036] Preferably, in step II, the reaction is carried out under stirring at room temperature.

[0037] Preferably, in II, the reaction time is 8h to 12h, for example, it can be 8h, 8.2h, 8.5h, 8.7h, 8.8h, 9h, 9.3h, 9.6h, 9.8h or 10h.

[0038] Preferably, in step III, the reaction process is as follows:

[0039]

[0040] R5, R6, and R′ are independently selected from any one of saturated alkyl or unsaturated alkyl groups;

[0041] As a preferred embodiment of the preparation method described in this invention, in step III, the reaction is carried out in a solvent, wherein the solvent is N,N-dimethylformamide (DMF).

[0042] Preferably, in step III, the molar ratio of product B to raw material b is 1 to 1.2, for example, it can be 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.14, 1.15, 1.16, 1.18 or 1.2, etc.

[0043] Preferably, in step III, the reaction is carried out under the protection of a protective gas, which includes at least one of nitrogen, helium, and argon.

[0044] Preferably, in step III, the reaction temperature is 160℃ to 180℃, for example, it can be 160℃, 163℃, 165℃, 167℃, 168℃, 170℃, 172℃, 174℃, 175℃, 177℃ or 180℃, etc.; the reaction time is 6h to 8h, for example, it can be 6h, 6.2h, 6.4h, 6.5h, 6.6h, 6.8h, 7h, 7.3h, 7.6h, 7.8h or 8h, etc.

[0045] Preferably, in step III, extraction and purification are performed after the reaction.

[0046] Thirdly, the present invention provides an electrolyte comprising an organic solvent, a lithium salt, and an additive, wherein the lithium salt comprises LiPF6, and the additive comprises a compound represented by Formula I as described in the first aspect.

[0047] LiPF6, a common lithium salt in electrolyte, is an unstable compound that will undergo side reactions as shown in equations (1) to (5) inside the battery. The decomposition products PF5 and HF will react with the components of the SEI and CEI films on the surfaces of the positive and negative electrodes, causing damage to the CEI and SEI films, continuously consuming electrolyte and affecting battery performance.

[0048] LiPF6 → LiF↓ + PF5 Equation (1)

[0049] HF + ROCOOLi → LiF↓ + ROCOOH (Equation 2)

[0050] HF + Li2CO3 → LiF↓ + H2O + CO2↑ Formula (3)

[0051] 2ROCOOLi + PF5 + H2O → 2LiF + 2ROCOOH + PF3O (Equation 4)

[0052] Li2CO3 + PF5 → 2LiF↓ + PF3O + CO2↑ Equation (5)

[0053] This invention adds the compound shown in Formula I to the electrolyte as an additive. During the pre-charging process, the phosphate oxygen in the additive molecule preferentially participates in the reaction, neutralizing the PF5 derived from the decomposition products of LiPF6 through acid-base coordination reaction, stabilizing the decomposition product PF5, and finally generating a complex covering the electrode surface, rapidly forming a stable solid electrolyte interphase (CEI) film. This film can passivate the positive electrode interface and form a stable protective film, thus avoiding the side reactions of lithium salt LiPF6 decomposition. At the same time, the amine groups in the additive combine with HF, reducing the impact of HF on the battery. The stable SEI film can also improve the high-temperature cycle performance and high-temperature storage performance of the battery, and reduce the DCR growth in the later stages of battery cycling.

[0054] Taking the compound shown in Formula I, where R1-R4 are all propenyl groups, as an example, we will use it as a model substance to illustrate the specific mechanism of action:

[0055]

[0056] Preferably, R1-R4 are linear alkyl groups.

[0057] Preferably, the saturated alkyl group has the general formula C2. n H 2n+1 , 1≤n≤3.

[0058] Preferably, the unsaturated alkyl group has the general formula C2. n H 2n , 2≤n≤3, the unsaturated alkyl group includes carbon-carbon double bonds.

[0059] In this invention, by limiting the chain lengths of saturated and unsaturated alkyl groups, film formation can be better controlled and impedance reduced.

[0060] Preferably, R1 and R3 are the same, and R2 and R4 are the same.

[0061] Preferably, R1-R4 are all propylene-based. In this case, due to the presence of propylene groups, the compound shown in Formula I can polymerize during the pre-charge process, forming a uniform and thin CEI film that covers the surfaces of the positive and negative electrode materials, improving the stability of the battery under high voltage conditions, increasing the battery cycle life and storage life, while reducing DCR growth in the later stages of cycling.

[0062] As a preferred embodiment of the electrolyte of the present invention, the mass fraction of the compound represented by Formula I is 0.01% to 5% based on the total mass of the electrolyte as 100%. For example, it can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.1% to 2%.

[0063] As a preferred embodiment of the electrolyte of the present invention, the additives further include high-temperature additives.

[0064] Preferably, the high-temperature additive comprises any one or a combination of at least two of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, tris(trimethylsilane)borate, or tris(trimethylsilane)phosphate. Typical but non-limiting examples of such combinations include: a combination of vinylene carbonate and vinyl ethylene carbonate, a combination of vinyl ethylene carbonate and fluoroethylene carbonate, and a combination of 1,3-propanesulfonate lactone and tris(trimethylsilane)borate. Preferably, it is 1,3-propanesulfonate lactone.

[0065] Preferably, based on the total mass of the electrolyte (100%), the mass fraction of the high-temperature additive is 0.01% to 2.5%, for example, it can be 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, or 2.5%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 0.1% to 1.5%.

[0066] As a preferred embodiment of the electrolyte of the present invention, the lithium salt mainly includes lithium hexafluorophosphate.

[0067] Preferably, the mass fraction of lithium hexafluorophosphate is 10% to 15% based on the total mass of the electrolyte (100%), for example, it can be 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, or 15%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0068] Preferably, the lithium salt further includes lithium difluorophosphate and / or lithium bisfluorosulfonylimide.

[0069] Preferably, the mass fraction of lithium difluorophosphate is 0.5% to 1%, based on the total mass of the electrolyte as 100%. For example, it can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1%, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0070] Preferably, the mass fraction of lithium bisfluorosulfonylimide is 0.1% to 10% based on the total mass of the electrolyte (100%). For example, it can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, or 10%, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0071] As a preferred embodiment of the electrolyte of the present invention, the organic solvent includes cyclic carbonate 60-90 esters and chain esters.

[0072] Preferably, the volume ratio of the cyclic carbonate to the chain ester is (10-40):(60-90), wherein the cyclic carbonate is selected from "10-40", for example, it can be 10, 12, 14, 15, 16, 18, 20, 23, 25, 26, 28, 30, 32, 34, 35, 36, 38 or 40, etc.; the chain ester is selected from "60-90", for example, it can be 60, 65, 70, 75, 80, 85 or 90, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably (15-40):(60-85).

[0073] Preferably, the cyclic carbonate comprises any one or a combination of at least two of ethylene carbonate, propylene carbonate, or butene carbonate. Typical but non-limiting examples of such combinations include combinations of ethylene carbonate and propylene carbonate, and combinations of propylene carbonate and butene carbonate.

[0074] Preferably, the chain ester comprises any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, or propyl acetate. Typical but non-limiting examples of such combinations include: combinations of dimethyl carbonate and diethyl carbonate, combinations of methyl ethyl carbonate and methyl propyl carbonate, combinations of ethyl propyl carbonate and methyl formate, combinations of methyl formate and ethyl formate, combinations of propyl formate and methyl acetate, and combinations of ethyl acetate and propyl acetate. A combination of methyl ethyl carbonate and dimethyl carbonate is preferred.

[0075] Preferably, the organic solvent has a mass fraction of 70% to 85% based on the total mass of the electrolyte (100%). For example, it can be 70%, 72%, 73%, 74%, 75%, 76%, 78%, 80%, 82%, 83%, 84%, or 85%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0076] The organic solvent in this invention can better avoid the damage of water to the electrolyte, and at the same time promotes the more complete dissolution of each component in the electrolyte, thereby improving the synergy between the components and obtaining an electrolyte with excellent electrochemical performance.

[0077] Thirdly, the present invention provides a lithium-ion battery, wherein the lithium-ion battery contains the electrolyte described in the second aspect.

[0078] The lithium-ion battery of the present invention further includes a positive electrode, a negative electrode, and a separator, wherein the separator is located between the positive electrode and the negative electrode.

[0079] Preferably, the positive electrode active material in the positive electrode sheet includes lithium transition metal oxides and / or lithium transition metal phosphate compounds.

[0080] Preferably, the lithium transition metal oxide includes LiCoO2 and LiNi. x Co y Mn z O2 (0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), LiNi x Mn y O2 (0≤x≤1, 0≤y≤1, x+y=1), LiMn2O4, LiMnO2, or Li2MnO4, or a combination of at least two of these. Typical but non-limiting examples of such combinations include LiCoO2 and LiNi. x Co y Mn z O2 combination, LiNi x Mn y Combinations of O2 and LiMn2O4, combinations of LiMnO2 and Li2MnO4, etc. For example, the value of x can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1; the value of y can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1; the value of z can be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1, etc., but is not limited to the listed values; other unlisted values ​​within the above ranges also apply. It should be noted that LiNi... xCo y Mn z O2 and LiNi x Mn y In O2, the value of x can be the same or different, and similarly, the value of y can be the same or different.

[0081] Preferably, the lithium transition metal phosphate compound mainly includes any one or a combination of at least two of LiFePO4, LiMnPO4, or LiCoPO4. Typical but non-limiting examples of such combinations include combinations of LiFePO4 and LiMnPO4, and combinations of LiMnPO4 and LiCoPO4.

[0082] Preferably, the negative electrode active material in the negative electrode sheet includes any one or a combination of at least two of carbonaceous materials, alloy materials, or lithium-containing metal composite materials. Typical but non-limiting examples of such combinations include: combinations of carbonaceous materials and alloy materials, combinations of alloy materials and lithium-containing metal composite materials, or combinations of carbonaceous materials and lithium-containing metal composite materials, etc.

[0083] Preferably, the negative electrode active material in the negative electrode sheet includes any one or a combination of at least two of natural graphite, artificial graphite, soft carbon, hard carbon, and lithium titanate. Typical but non-limiting examples of such combinations include: combinations of natural graphite and artificial graphite, combinations of artificial graphite and soft carbon, combinations of soft carbon and hard carbon, and combinations of hard carbon and lithium titanate.

[0084] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0085] Compared with existing technologies, the present invention has the following beneficial effects:

[0086] The compounds of this invention use pyridine as the parent compound, wherein N has weak basicity and can moderately suppress the acidity of the electrolyte; in combination with phosphate oxygen and saturated or unsaturated alkyl groups, under certain conditions, through acid-base coordination reaction, they can neutralize PF5 derived from the decomposition products of LiPF6, stabilize the decomposition product PF5, and quickly form a stable protective film, while ensuring low resistance. They can be used in electrolytes for lithium-ion batteries, improving the high-temperature cycle performance and high-temperature storage performance of the battery, and reducing the DCR growth in the later stages of battery cycling. Detailed Implementation

[0087] The technical solution of the present invention will be further illustrated below through specific embodiments.

[0088] The compounds with structures shown in Formula 1-1, Formula 1-2, and Formula 1-3 used in this embodiment were all prepared by the following method, which includes the following steps:

[0089] 1) 2,6-Pyridinedicarboxylic acid (10 g, 59.8 mmol) was dissolved in 800 mL of anhydrous tetrahydrofuran. After cooling at 0 °C for 20 min, lithium aluminum hydride (LiAlH4) (4.4 g, 116 mmol) was added, and the mixture was stirred at room temperature for 30 min. The mixture was then heated to 60 °C and refluxed for 24 h. The mixture was then cooled to 0 °C, and water was added to cool the reaction. The mixture was extracted with ethyl acetate five times, each time with 200 mL of ethyl acetate. The extract was dried over anhydrous sodium sulfate and concentrated. The crude product was purified by silica gel column chromatography using chloroform / ethanol (20:1 v / v) as the eluent to give the intermediate 2,5-dihydroxypyridine.

[0090] 2) Dissolve 2,6-dihydroxypyridine (1.44 g, 0.01 mol) in 20 mL of dichloromethane, and then slowly add thionyl chloride (3.57 g, 0.03 mol) dropwise under nitrogen protection. Stir at room temperature for 10 h to obtain 2,6-dichloromethylpyridine.

[0091] 3) Dissolve 2,6-dichloromethylpyridine (1.74 g, 0.01 mol) in N,N-dimethylformamide (DMF), add trialkyl phosphite (1.36 g, 0.011 mol), stir for 7 h under nitrogen protection at 170 °C, treat excess DMF with distilled water, extract with ethyl acetate, and purify by rotary evaporation on silica gel column to obtain the final product tetraalkylpyridine-2,6-dimethyldimethylphosphonate, with a mass of 2.818 g (0.008 mol) (yield: 73.48%).

[0092] The compound prepared by the above method has the structure shown in Formula I:

[0093]

[0094] R1-R4 are independently selected from any one of saturated alkyl or unsaturated alkyl groups.

[0095] By replacing the trialkyl phosphite in the above preparation method with trimethyl phosphite, triethyl phosphite, and tripropyl phosphite, respectively, compounds with the structures shown in Formula 1-1, Formula 1-2, and Formula 1-3 are obtained, with the specific structures as follows:

[0096]

[0097] Example 1

[0098] This embodiment provides a non-aqueous electrolyte, comprising a lithium salt, additives, and a solvent. The lithium salt comprises lithium hexafluorophosphate and lithium difluorophosphate. The additives comprise compounds having the structure shown in Formula 1-1 (tetrapropylenepyridine-2,6-dimethyldimethylphosphonate), 1,3-propanesulfonate lactone, and vinyl sulfate. The solvent is specifically composed of vinyl carbonate, ethyl methyl carbonate, and dimethyl carbonate in a mass ratio of 30:30:40.

[0099] The contents of all the following components are based on 100% of the total mass of the non-aqueous electrolyte. Specifically:

[0100] The mass fraction of lithium hexafluorophosphate is 12.5%, and the mass fraction of lithium difluorophosphate is 1%.

[0101] The mass fraction of the compound having the structure shown in Formula 1-1 is 0.5%, the mass fraction of 1,3-propanesulfonic acid lactone is 0.5%, and the mass fraction of vinyl sulfate is 1%.

[0102] The solvent has a mass fraction of 84.5%.

[0103] This embodiment also provides a method for preparing the above-mentioned non-aqueous electrolyte, which includes the following steps:

[0104] When the oxygen content is <0.1ppm and the water content is <0.1ppm, the above components are mixed according to the formula amount and stirred evenly to obtain the non-aqueous electrolyte.

[0105] Example 2

[0106] This embodiment provides a non-aqueous electrolyte, which differs from Example 1 in that the compound having the structure shown in Formula 1-1 is replaced with the compound having the structure shown in Formula 1-2, while all other aspects are the same as in Example 1.

[0107] Example 3

[0108] This embodiment provides a non-aqueous electrolyte. The difference between this embodiment and Embodiment 1 is that the content of all components below is based on the total mass of the non-aqueous electrolyte being 100%. Specifically:

[0109] The mass fraction of lithium hexafluorophosphate is 14%, and the mass fraction of lithium difluorophosphate is 0.4%.

[0110] The compound having the structure shown in Formula 1-1 has a mass fraction of 0.5%, 1,3-propanesulfonic acid lactone has a mass fraction of 1%, and vinyl sulfate has a mass fraction of 0.1%.

[0111] The solvent has a mass fraction of 84%.

[0112] Everything else is the same as in Example 1.

[0113] Example 4

[0114] This embodiment provides a non-aqueous electrolyte. The difference between this embodiment and Embodiment 1 is that the content of all components below is based on the total mass of the non-aqueous electrolyte being 100%. Specifically:

[0115] The mass fraction of lithium hexafluorophosphate is 11%, and the mass fraction of lithium difluorophosphate is 0.4%.

[0116] The mass fraction of the compound having the structure shown in Formula 1-1 is 0.5%, the mass fraction of 1,3-propanesulfonate lactone is 1%, and the mass fraction of vinyl sulfate is 1%.

[0117] The solvent has a mass fraction of 86.5%.

[0118] Everything else is the same as in Example 1.

[0119] Example 5

[0120] This embodiment provides a non-aqueous electrolyte. The difference between this embodiment and Embodiment 1 is that vinyl sulfate is replaced with an equal amount of vinylene carbonate, while all other aspects are the same as in Embodiment 1.

[0121] Example 6

[0122] The difference between this embodiment and Example 1 is that the solvent composition is ethylene carbonate and methyl ethyl carbonate in a mass ratio of 3:7, while all other aspects are the same as in Example 1.

[0123] Example 7

[0124] This embodiment provides a non-aqueous electrolyte, which differs from Example 1 in that the compound having the structure shown in Formula 1-1 is replaced with the compound having the structure shown in Formula 1-3, while all other aspects are the same as in Example 1.

[0125] Example 8

[0126] The difference between this embodiment and Embodiment 1 is that lithium difluorophosphate is replaced with an equal amount of lithium hexafluorophosphate; otherwise, they are the same as in Embodiment 1.

[0127] Example 9

[0128] The difference between this embodiment and Example 1 is that 1,3-propanesulfonic acid lactone and vinyl sulfate are replaced with equal amounts of compounds having the structures shown in Formulas 1-2, while everything else is the same as in Example 1.

[0129] Example 10

[0130] This embodiment provides a non-aqueous electrolyte comprising a lithium salt, additives, and a solvent. The lithium salt includes lithium hexafluorophosphate, lithium difluorosulfonylimide, and lithium difluorophosphate. The additives include compounds having the structure shown in Formula 1-1 (tetrapropylenepyridine-2,6-dimethyldimethylphosphonate), 1,3-propanesulfonate lactone, and vinyl sulfate. The solvent is specifically composed of vinyl carbonate, ethyl methyl carbonate, and dimethyl carbonate in a mass ratio of 30:30:40.

[0131] The contents of all the following components are based on 100% of the total mass of the non-aqueous electrolyte. Specifically:

[0132] The mass fraction of lithium hexafluorophosphate is 15%, the mass fraction of lithium difluorosulfonyl imide is 5%, and the mass fraction of lithium difluorophosphate is 0.7%.

[0133] The compound having the structure shown in Formula 1-1 has a mass fraction of 1.8%, a mass fraction of 1,3-propanesulfonic acid lactone of 0.3%, and a mass fraction of vinyl sulfate of 0.2%.

[0134] The solvent has a mass fraction of 77%.

[0135] Everything else is the same as in Example 1.

[0136] Example 11

[0137] The difference between this comparative example and Example 1 is that the content of the compound having the structure shown in Formula 1-1 is 3%, and the content of the solvent is adjusted so that the mass fraction of the total system is 100%. Everything else is the same as in Example 1.

[0138] Comparative Example 1

[0139] The difference between this comparative example and Example 1 is that no compound having the structure shown in Formula 1-1 is added, and the solvent content is adjusted so that the mass fraction of the total system is 100%. Everything else is the same as in Example 1.

[0140] Comparative Example 2

[0141] The difference between this comparative example and Example 1 is that the compound having the structure shown in Formula 1-1 is replaced with an equal amount of fluoroethylene carbonate, while all other aspects are the same as in Example 1.

[0142] Comparative Example 3

[0143] The difference between this comparative example and Example 1 is that the compound having the structure shown in Formula 1-1 is replaced with an equal amount of tris(trimethylsilane)phosphonate, while all other aspects are the same as in Example 1.

[0144] The electrolytes of Examples 1-11 and Comparative Examples 1-3 were assembled into lithium-ion batteries, including the following steps:

[0145] (1) Preparation of the positive electrode sheet for lithium-ion secondary batteries:

[0146] Lithium nickel cobalt manganese oxide (LiNi) is used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2), conductive agent Super-P, and binder PVDF were dissolved in N-methylpyridinone solvent at a mass ratio of 95.8:2.2:2.0 and mixed evenly to prepare the positive electrode slurry. The positive electrode slurry was then uniformly coated onto the current collector aluminum foil with a coating amount of 18 mg / cm². 2 After drying at 90°C, the material is cold-pressed, trimmed, cut into pieces, and slit. Then, it is dried under vacuum at 90°C for 4 hours, and the tabs are welded to produce the positive electrode sheet of a lithium-ion secondary battery that meets the requirements.

[0147] (2) Preparation of the negative electrode sheet for lithium-ion secondary batteries:

[0148] Artificial graphite (negative electrode active material), Super-P (conductive agent), CMC (thickener), and SBR (binder) were dissolved in deionized water at a mass ratio of 96.5:1.0:1.0:1.5 and mixed thoroughly to form a negative electrode slurry. This slurry was then uniformly coated onto the copper foil current collector, with a coating weight of 8.9 mg / cm². 2 After drying at 90℃, the material is cold-pressed, trimmed, cut into pieces, and slit. Then, it is dried under vacuum at 110℃ for 4 hours, and the tabs are welded to produce the negative electrode sheet of a lithium-ion secondary battery that meets the requirements.

[0149] (3) Preparation of lithium-ion batteries:

[0150] The positive electrode, negative electrode, and separator (PE film) of the lithium-ion secondary battery prepared according to the aforementioned process are stacked to form a battery with a thickness of 8 mm, a width of 60 mm, and a length of 130 mm. The battery is then vacuum baked at 90°C for 10 h, injected with the electrolytes from Examples 1-11 and Comparative Examples 1-3, and left to stand for 24 h. After that, it is charged to 4.4 V with a constant current of 0.1 C (200 mA), then charged at a constant voltage of 4.4 V until the current drops to 0.05 C (100 mA), then discharged to 2.8 V with a constant current of 0.1 C (200 mA), and this charge-discharge cycle is repeated twice. Finally, it is charged to 3.8 V with a constant current of 0.1 C (200 mA), thus completing the preparation of the lithium-ion secondary battery.

[0151] The lithium-ion secondary batteries corresponding to Examples 1-11 and Comparative Examples 1-3 (the lithium-ion secondary batteries are numbered Application Examples 1-11 and Comparative Examples 1-3, respectively) were tested for high-temperature storage performance, high-temperature cycle performance, high-temperature cycle discharge DCR growth rate, and high-temperature storage gas generation performance. The test methods are as follows:

[0152] (1) High-temperature storage performance test of lithium-ion secondary batteries:

[0153] At 25℃, the lithium-ion secondary battery was first charged to 4.35V with a constant current of 0.05C, then further charged to 0.05C with a constant voltage of 4.35V, and then discharged to 2.8V with a constant current of 0.5C. This discharge capacity is the discharge capacity of the lithium-ion secondary battery before high-temperature storage. Then, the lithium-ion secondary battery was charged to 4.35V with a constant current of 0.5C, and stored at 60℃ for 30 days. After storage, the lithium-ion secondary battery was placed at 25℃, and then discharged to 2.8V with a constant current of 0.5C. This process was repeated, and the lithium-ion secondary battery was charged to 4.35V with a constant current of 0.5C, then further charged to 0.05C with a constant voltage of 4.35V, and then discharged to 2.8V with a constant current of 0.5C. This final discharge capacity is the discharge capacity of the lithium-ion secondary battery after high-temperature storage. Capacity retention rate (%) of lithium-ion secondary battery after high-temperature storage = [Discharge capacity of lithium-ion secondary battery after high-temperature storage / Discharge capacity of lithium-ion secondary battery before high-temperature storage] × 100%.

[0154] (2) High-temperature cycle performance test of lithium-ion secondary batteries:

[0155] The high-temperature cycle performance of the prepared lithium-ion secondary batteries was tested. The specific method was as follows: at 45℃, the lithium-ion secondary batteries were first charged to 4.35V with a constant current of 0.5C, then charged to the cutoff current of 0.05C with a constant voltage of 4.35V, and finally discharged to 2.8V with a constant current of 0.5C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The lithium-ion secondary batteries were subjected to charge-discharge tests in the above manner, and the discharge capacity of the 1000th cycle was recorded. The capacity retention rate (%) of the lithium-ion secondary battery after 1000 cycles = [Discharge capacity of the 1000th cycle / Discharge capacity of the first cycle] × 100%.

[0156] (3) High-temperature cycle discharge DCR growth rate test of lithium-ion secondary batteries:

[0157] The high-temperature cycle performance of the prepared lithium-ion secondary batteries was tested. The specific method was as follows: at 45℃, the lithium-ion secondary batteries were first charged to 4.35V with a constant current of 0.5C, then charged to the cutoff current of 0.05C with a constant voltage of 4.35V. Next, the lithium-ion secondary batteries were discharged for 1 hour with a constant current of 0.5C to 50% SOC. At 50% SOC, the batteries were discharged at 1C for 30 seconds. The voltage before and after discharge was recorded. Dividing this voltage by the discharge current yielded the discharge DCR during this discharge process. This discharge DCR is the discharge DCR before the cycle. The lithium-ion secondary batteries were subjected to cycle charge-discharge tests in the above manner, and the battery after 1000 cycles was used. The discharge DCR growth rate (%) of the lithium-ion secondary battery after 1000 cycles = [Discharge DCR of the 1000th cycle / Discharge DCR growth before the cycle] × 100% - 100%.

[0158] (4) High-temperature storage gas generation performance test of lithium-ion secondary batteries:

[0159] At 25°C, the prepared lithium-ion secondary battery was first charged to 4.35V with a constant current of 0.5C, then further charged to the current cutoff point of 0.05C with a constant voltage of 4.35V. Next, the lithium-ion secondary battery was discharged to 2.8V with a constant current of 0.5C. This discharge capacity represents the discharge capacity of the lithium-ion secondary battery before high-temperature storage. Then, the lithium-ion secondary battery was charged to 4.35V with a constant current of 0.5C, and then charged to the current cutoff point of 0.05C with a constant voltage of 4.35V, fully charging the lithium-ion battery. The battery volume was tested using the water displacement method, and the battery thickness was measured using a micrometer.

[0160] The lithium-ion batteries were then stored at 60°C for 90 days. After storage, the rechargeable lithium-ion batteries were placed at 25°C, and their volume was tested using the water displacement method. Specifically, a beaker containing pure water was first placed on a balance and weighed, recorded as reading 1. Then, the battery before storage (fresh battery) or after storage was immersed in the water in the beaker and weighed, recorded as reading 2. Reading 2 minus reading 1 gives the volume of the battery before or after storage. Since the density of water is 1 mg / mL, a reading of 1 mL corresponds to a volume of 1 mL for either the battery before or after storage. Therefore, the battery immersed in water is the battery before storage, and reading 2 minus reading 1 gives the battery's volume before storage; the battery immersed in water is the battery after storage, and reading 2 minus reading 1 gives the battery's volume after storage. The ratio of the volume after storage to the volume before storage is the battery's volume after storage. The thickness of the battery was measured using a micrometer. The lithium-ion battery was then discharged to 2.8V at a constant current of 0.5C, followed by charging to 4.35V at a constant current of 0.5C. It was then further charged at a constant voltage of 4.35V to a current of 0.05C, and finally discharged to 2.8V at a constant current of 0.5C. The final discharge capacity is the discharge capacity of the lithium-ion battery after high-temperature storage. Battery volume expansion rate (%) = (volume after storage / volume before storage - 1) × 100%.

[0161] The test results are shown in Table 1:

[0162] Table 1. Performance test results of lithium-ion batteries with different electrolytes

[0163]

[0164] As can be seen from the table above, compared with Comparative Example 1), with the addition of compounds having the structures shown in Formula 1-1, Formula 1-2 or Formula 1-3, the capacity retention rate of lithium-ion secondary batteries at 60°C increases, storage gas production decreases, the capacity retention rate at 45°C high-temperature cycling improves, and the DCR growth in the later stage of cycling is also lower, which is beneficial to improving battery life.

[0165] Meanwhile, a comparison of Examples 1, 2 and 7 shows that the compound with the structure shown in Formula 1-3 has a more significant improvement in battery performance compared to the compounds with the structures shown in Formula 1-1 and Formula 1-2. This is mainly because: due to the presence of the propylene group, the compound shown in Formula I can polymerize during the pre-charge process, forming a uniform and thin CEI film that covers the surface of the positive and negative electrode materials, improving the stability of the battery under high voltage conditions, increasing the battery cycle life and storage life, and reducing the DCR growth in the later stages of the cycle.

[0166] A comparison between Example 1 and Example 6 shows that Example 1 has a higher content of dimethyl carbonate, which has low viscosity and high conductivity, and is therefore more conducive to improving battery performance.

[0167] A comparison of Examples 1 and 8 shows that, in the electrolyte system of the present invention, the combination of lithium hexafluorophosphate and lithium difluorophosphate is more beneficial to improving battery performance than lithium hexafluorophosphate alone.

[0168] A comparison between Example 1 and Example 9 shows that using a combination of additives is beneficial to battery performance.

[0169] A comparison between Example 1 and Example 11 shows that the amount of the novel additive (tetraalkylpyridine-2,6-dimethylphosphonate) shown in Formula I used in this patent is preferably less than 2%. Excessive addition will increase battery impedance and affect battery performance.

[0170] A comparison of Example 1 and Comparative Example 2 shows that the novel additive tetraalkylpyridine-2,6-dimethylphosphonate used in this patent is superior to the traditional additive fluoroethylene carbonate in improving battery performance.

[0171] The comparison between Example 1 and Comparative Example 3 shows that the novel additive tetraalkylpyridine-2,6-dimethylphosphonate used in this patent is superior to the traditional additive tris(trimethylsilane)phosphonate in improving battery performance.

[0172] The applicant declares that the detailed method of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed method, that is, it does not mean that the present invention must rely on the above detailed method to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A compound, characterized in that, The compound has the structure shown in Formula I: Among them, R1-R4 are all propylene-based.

2. A method for preparing the compound as described in claim 1, characterized in that, The preparation method includes the following steps: Synthesis of 1,2,6-dihydroxypyridine: Starting material a reacts to yield product A. The reaction process is as follows: II. Synthesis of 2,6-dichloropyridine: Product A reacts to give product B, and the reaction process is as follows: III. Synthesis of tetraalkylpyridine-2,6-dimethylphosphonate: Product B reacts with starting material b to obtain the compound shown in Formula I of claim 1, wherein starting material b is tripropylene phosphite.

3. The preparation method according to claim 2, characterized in that, In I, the reaction is carried out in a solvent, which is anhydrous tetrahydrofuran.

4. The preparation method according to claim 2, characterized in that, In I, the reaction is carried out in the presence of a catalyst, which is lithium aluminum hydride.

5. The preparation method according to claim 2, characterized in that, 2,6-pyridinedicarboxylic acid was dissolved in anhydrous tetrahydrofuran and then cooled.

6. The preparation method according to claim 2, characterized in that, In step I, the reaction is carried out under reflux stirring at a temperature of 50°C to 70°C for a duration of 18 to 30 hours.

7. The preparation method according to claim 6, characterized in that, Before the reflux stirring, the mixture is stirred at room temperature.

8. The preparation method according to claim 7, characterized in that, The stirring time at room temperature is 20 min to 45 min.

9. The preparation method according to claim 6, characterized in that, After reflux and stirring, the mixture is cooled and extracted to obtain a crude product. The crude product is then purified to obtain the intermediate product 2,5-dihydroxypyridine.

10. The preparation method according to claim 2, characterized in that, In II, the reaction is carried out in a solvent, namely dichloromethane.

11. The preparation method according to claim 2, characterized in that, In II, the reaction is carried out in the presence of thionyl chloride.

12. The preparation method according to claim 11, characterized in that, The molar ratio of the 2,6-dihydroxypyridine to the thionyl chloride is 1:(2-4).

13. The preparation method according to claim 2, characterized in that, In II, the reaction is carried out under stirring at room temperature.

14. The preparation method according to claim 2, characterized in that, In II, the reaction time is 8 h to 12 h.

15. The preparation method according to claim 2, characterized in that, In step III, the reaction is carried out in a solvent, namely N,N-dimethylformamide.

16. The preparation method according to claim 2, characterized in that, In section III, the molar ratio of product B to raw material b is 1 to 1.

2.

17. The preparation method according to claim 2, characterized in that, In step III, the reaction is carried out under the protection of a protective gas, which includes at least one of nitrogen, helium, and argon.

18. The preparation method according to claim 2, characterized in that, In step III, the reaction temperature is 160℃~180℃, and the reaction time is 6h~8h.

19. The preparation method according to claim 2, characterized in that, In step III, after the reaction, extraction and purification are performed.

20. An electrolyte, characterized in that, The electrolyte comprises an organic solvent, a lithium salt, and an additive, wherein the lithium salt comprises LiPF6, and the additive comprises a compound represented by Formula I; R1-R4 are independently selected from any one of saturated alkyl or unsaturated alkyl groups; The general formula of the saturated alkyl group is C2. n H 2n+1 , 1≤n≤3; the general formula of the unsaturated alkyl group is C n H 2n , 2≤n≤3, the unsaturated alkyl group is a carbon-carbon double bond.

21. The electrolyte according to claim 20, characterized in that, Based on the total mass of the electrolyte as 100%, the mass fraction of the compound represented by Formula I is 0.01% to 5%.

22. The electrolyte according to claim 21, characterized in that, Based on the total mass of the electrolyte (100%), the mass fraction of the compound represented by Formula I is 0.1% to 2%.

23. The electrolyte according to claim 20, characterized in that, In Equation I, R1 and R3 are the same, and R2 and R4 are the same.

24. The electrolyte according to claim 20, characterized in that, In Formula I, R1-R4 are all propene groups.

25. The electrolyte according to claim 20, characterized in that, The additives also include high-temperature additives.

26. The electrolyte according to claim 25, characterized in that, The high-temperature additive includes any one or a combination of at least two of the following: vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propanesulfonate lactone, tris(trimethylsilane)borate, or tris(trimethylsilane)phosphate.

27. The electrolyte according to claim 26, characterized in that, The high-temperature additive is 1,3-propanesulfonic acid lactone.

28. The electrolyte according to claim 25, characterized in that, Based on the total mass of the electrolyte (100%), the mass fraction of the high-temperature additive is 0.01% to 2.5%.

29. The electrolyte according to claim 28, characterized in that, Based on the total mass of the electrolyte (100%), the mass fraction of the high-temperature additive is 0.1% to 1.5%.

30. The electrolyte according to claim 20, characterized in that, The lithium salts mainly include lithium hexafluorophosphate.

31. The electrolyte according to claim 30, characterized in that, Based on the total mass of the electrolyte being 100%, the mass fraction of lithium hexafluorophosphate is 10% to 15%.

32. The electrolyte according to claim 30, characterized in that, The lithium salt also includes lithium difluorophosphate and / or lithium difluorosulfonylimide.

33. The electrolyte according to claim 32, characterized in that, Based on the total mass of the electrolyte (100%), the mass fraction of lithium difluorophosphate is 0.5% to 1%.

34. The electrolyte according to claim 32, characterized in that, Based on the total mass of the electrolyte (100%), the mass fraction of lithium difluorosulfonylimide is 0.1% to 10%.

35. The electrolyte according to claim 20, characterized in that, The organic solvents include cyclic carbonates and chain esters.

36. The electrolyte according to claim 35, characterized in that, The volume ratio of the cyclic carbonate to the chain ester is (10-40):(60-90).

37. The electrolyte according to claim 36, characterized in that, The volume ratio of the cyclic carbonate to the chain ester is (15-40):(60-85).

38. The electrolyte according to claim 35, characterized in that, The cyclic carbonates include any one or a combination of at least two of ethylene carbonate, propylene carbonate, or butene carbonate.

39. The electrolyte according to claim 35, characterized in that, The chain esters include any one or a combination of at least two of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, or propyl acetate.

40. The electrolyte according to claim 39, characterized in that, The chain ester is a combination of ethyl methyl carbonate and dimethyl carbonate.

41. The electrolyte according to claim 20, characterized in that, Based on the total mass of the electrolyte (100%), the mass fraction of the organic solvent is 70% to 85%.

42. A lithium-ion battery, characterized in that, The lithium-ion battery contains the electrolyte according to any one of claims 20-41.

43. The lithium-ion battery according to claim 42, characterized in that, The lithium-ion battery also includes a positive electrode, a negative electrode, and a separator, with the separator located between the positive electrode and the negative electrode.

44. The lithium-ion battery according to claim 43, characterized in that, The positive electrode active material in the positive electrode sheet includes lithium transition metal oxides and / or lithium transition metal phosphate compounds.

45. The lithium-ion battery according to claim 43, characterized in that, The negative electrode active material in the negative electrode sheet includes any one or a combination of at least two of the following: carbonaceous materials, alloy materials, or lithium-containing metal composite materials.

Images