Acetal compound, preparation method and electrolyte thereof

Abstract

The invention discloses an acetal compound, a preparation method and an electrolyte thereof. The acetal compound has a structure as shown in a formula I, and R is selected from C1-C6 alkyl, C2-C6 alkenyl or C1-C6 halogenated alkyl. The acetal compound can be used as an electrolyte additive with excellent performance, an electrolyte containing the acetal compound is applied to a secondary battery, a good protective film can be formed on an interface of a positive electrode material and a negative electrode material, and the acetal compound has relatively small internal resistance so as to improve the rate and low-temperature performance of the battery. Formula I.

Description

Technical Field

[0001] This invention relates to the field of materials synthesis technology, and more particularly to a compound used in batteries, and even more particularly to an acetal compound, its preparation method and electrolyte. Background Technology

[0002] Electrolyte is the lifeblood of lithium-ion batteries, playing a crucial role in transferring lithium ions between the positive and negative electrode materials and the separator. Furthermore, it significantly influences the formation of the SEI and CEI at the interface between the positive and negative electrode materials, as well as their impedance. With the rapid development of pure electric vehicles and hybrid electric vehicles, the requirements for energy density, long cycle life, rate performance, and safety of lithium-ion batteries are constantly increasing. The positive electrode material for lithium-ion batteries has shifted from lithium iron phosphate and lithium manganese oxide systems to ternary material systems. In traditional electrolyte systems, ternary materials undergo significant interfacial catalytic reactions under high voltage and high temperature conditions, leading to electrolyte decomposition and gas production, which compromises battery life and safety. Studies have reported that adding additives that can form films at the interface of ternary positive electrode materials (such as organic additives VC, PS, DTD, TMSP; and inorganic additives LiPO2F2, LiFSI, LiTFSI, LiPF2(C2O4)2, LiBOB, etc.) can effectively protect the positive electrode, improve the electrolyte's voltage withstand window, and enhance battery cycle life. Studies have found that these additives can form a CEI film not only at the cathode material interface but also a SEI film at the graphite anode interface, leading to increased internal resistance and affecting the battery's rate capability and low-temperature performance. Given the shortcomings of currently available commercial electrolyte additives, it is necessary to develop new additives to address the deficiencies of existing technologies. Summary of the Invention

[0003] In view of the above problems, the purpose of the present invention is to provide an acetal compound, a preparation method thereof, and an electrolyte thereof. The acetal compound can be used as a high-performance electrolyte additive. When the electrolyte containing the acetal compound is applied to a secondary battery, it can form a good protective film at the interface of the positive and negative electrode materials and has a small internal resistance, thereby improving the rate performance and low-temperature performance of the battery.

[0004] To achieve the above objectives, the present invention provides an acetal compound having the structure shown in Formula I.

[0005] Formula I R is selected from C1-C6 alkyl, C2-C6 alkenyl or C1-C6 haloalkyl.

[0006] Compared with the prior art, the acetal compounds of the present invention have the structure shown in Formula I. The compounds include alkyl, haloalkyl or alkenyl substituents and an erythritol skeleton, which have the advantages of both substituents and erythritol skeleton. They can form a good protective film at the interface of positive and negative electrode materials and have low internal resistance, so as to improve the rate and low temperature performance of the battery and have good application prospects.

[0007] As a preferred technical solution, R is selected from C1-C4 alkyl, C2-C4 alkenyl or C1-C4 haloalkyl.

[0008] As a preferred technical solution, the acetal compound is at least one of compound 1 to compound 4.

[0009] Compound 1, Compound 2, Compound 3, Compound 4.

[0010] A second aspect of the present invention provides a method for preparing the aforementioned acetal compound, comprising the steps of: (1) The polyol compound shown in Formula II, the acid catalyst, and the first solvent are mixed at a certain temperature to form a first solution, and the aldehyde compound shown in Formula III is mixed with the second solvent to form a second solution; (2) The second solution is added dropwise to the first solution to react and the product is obtained. The product is then purified and dried.

[0011] Formula II Formula III R is selected from C1-C6 alkyl, C2-C6 alkenyl or C1-C6 haloalkyl.

[0012] Compared with existing technologies, the preparation method of this invention uses substituted aldehyde compounds to modify erythritol biomolecules as shown in Formula II to synthesize a series of acetal compounds with novel structures. This preparation method uses readily available raw materials, has a simple process, high yield, high purity, good atom economy, and is easy to industrialize. The obtained acetal compounds can effectively improve the low-temperature and rate performance of batteries.

[0013] As a preferred technical solution, the first solvent and the second solvent are each independently selected from at least one of nitrile solvents, ether solvents, ester solvents, ketone solvents and aromatic hydrocarbon solvents.

[0014] As a preferred technical solution, the acidic catalyst is selected from at least one of dilute sulfuric acid, dilute hydrochloric acid, and p-toluenesulfonic acid.

[0015] As a preferred technical solution, the specified temperature is -10℃ to 120℃, and the mixing time at the specified temperature is 10 min to 120 min.

[0016] As a preferred technical solution, the molar ratio of the polyol compound represented by Formula II to the aldehyde compound represented by Formula III is 1:2.0~2.5.

[0017] As a preferred technical solution, the amount of the acidic catalyst is 1% to 20% of the sum of the mass of the polyol compound represented by Formula II, the aldehyde compound represented by Formula III, and the acidic catalyst.

[0018] As a preferred technical solution, the reaction temperature is -10℃ to 30℃, and the reaction time is 1h to 24h.

[0019] As a preferred technical solution, the purification includes filtration and / or washing.

[0020] As a preferred technical solution, the drying temperature is 35℃~120℃, and the drying time is 1h~24h.

[0021] A third aspect of this invention provides an electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and an additive, wherein the additive comprises the aforementioned acetal compound or an acetal compound prepared by the aforementioned method. Applying the electrolyte containing the acetal compound of this invention to a secondary battery can effectively reduce the battery's internal resistance and improve the rate capability and low-temperature performance of the lithium-ion battery. Detailed Implementation

[0022] The acetal compounds of the present invention can be used as intermediates to synthesize electroplating additives, polycarbonate fire retardants, lubricating grease thickeners, polypropylene antistatic agents, polyethyleneimine crosslinking agents, etc. They can also be used as electrolyte additives. Applying electrolytes containing these acetal compounds to secondary batteries can effectively improve the low-temperature, rate, and other electrochemical performance of lithium-ion batteries.

[0023] A secondary battery comprises a positive electrode active material, a negative electrode active material, and an electrolyte. The positive electrode active material can be a layered transition metal lithium oxide or an olivine-type lithium compound. Specifically, the positive electrode active material can be, but is not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (with the chemical formula LiNi). x Co y Mn (1-x-y) M zO2, where 0.1 < x < 0.9, x + y < 1, 0 ≤ z < 0.08, and M is at least one of Al, Mg, Zr, and Ti), and the coatings and dopants of the above materials. It is particularly suitable for ternary lithium nickel cobalt manganese oxide materials. These cathode active materials can be used alone or in combination of two or more.

[0024] The anode active material includes at least one of carbon-based materials, silicon-based materials, and tin-based materials. Among them, the carbon-based material can be, but is not limited to, at least one of artificial graphite, natural graphite, hard carbon, soft carbon, graphene, and mesophase carbon microspheres. The silicon-based material can be, but is not limited to, at least one of elemental silicon, silicon-oxygen composite materials, silicon-carbon composite materials, and silicon alloy materials. The tin-based material can include elemental tin, tin-carbon composite materials, tin-oxygen composite materials, and tin alloy compounds.

[0025] The electrolyte includes an electrolyte salt, a non-aqueous organic solvent, and an additive.

[0026] The electrolyte salt can be, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium methyl sulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(oxalato)borate (C4BLiO8), lithium difluoro(oxalato)borate (C2BF2LiO4), lithium difluorophosphate (LiPO2F2), and lithium difluoro(bis(oxalato)phosphate) (LiDFBP). The non-aqueous organic solvent is selected from carbonate esters and / or carboxylic acid esters. Further, the non-aqueous organic solvent is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), methyl acetate (MA), ethyl acetate (EA), propyl acetate, butyl acetate (BAC), ethyl propionate (EP), propyl propionate (PP), and butyl propionate (PRB).

[0027] The additive can at least include the acetal compounds shown in Formula I of the present invention.

[0028] Formula I Among them, R is selected from C1-C6 alkyl, C2-C6 alkenyl, or C1-C6 haloalkyl. Further, R is selected from C1-C6 alkyl, C2-C6 alkenyl, or C1-C6 haloalkyl. Preferably, the acetal compound can be at least one of Compound 1 to Compound 4.

[0029] Compound 1 Compound 2 Compound 3 Compound 4.

[0030] The acetal compounds of this invention account for 0.1% to 2.5% of the total mass of the electrolyte. Preferably, the acetal compounds of this invention account for 0.5% to 1.5% of the total mass of the electrolyte. As an example, the acetal compounds account for 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.3%, 2.4%, and 2.5% of the total mass of the electrolyte.

[0031] The method for preparing the acetal compounds of the present invention may include the following steps: (1) The polyol compound shown in Formula II, the acid catalyst, and the first solvent are mixed at a certain temperature to form a first solution, and the aldehyde compound shown in Formula III is mixed with the second solvent to form a second solution; (2) The second solution is added dropwise to the first solution to carry out the reaction and obtain the product. The product is then purified and dried.

[0032] Formula II Formula III Wherein, R is selected from C1-C6 alkyl, C2-C6 alkenyl, or C1-C6 haloalkyl. Preferably, the aldehyde compound is at least one selected from methacrolein, n-butyl aldehyde, chloroethyl aldehyde, and bromoethyl aldehyde.

[0033] Specifically, the first solvent and the second solvent are each independently selected from at least one of nitrile solvents, halogenated hydrocarbon solvents, ether solvents, ester solvents, ketone solvents, and aromatic hydrocarbon solvents. Further, the first solvent and the second solvent are each independently selected from at least one of acetonitrile, butyronitrile, n-hexane, cyclohexane, dichloromethane, trichloromethane, 1,2-dichloroethane, tetrachloroethane, methyl tert-butyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, dioxane, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, propyl acetate, acetone, cyclohexanone, 4-methyl-2-pentanone, benzene, xylene, and toluene. The first solvent and the second solvent may be the same or different.

[0034] The acidic catalyst is selected from at least one of dilute sulfuric acid, dilute hydrochloric acid, and p-toluenesulfonic acid. Preferably, the acidic catalyst is selected from p-toluenesulfonic acid.

[0035] The polyol compound shown in Formula II, the acidic catalyst, and the first solvent need to be mixed at a certain temperature, which is -10℃ to 120℃, preferably -10℃ to 50℃. As an example, the certain temperature can be, but is not limited to, -10℃, -8℃, -5℃, -2℃, 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, or 120℃. The mixing time at the certain temperature is 10 min to 120 min. As an example, the mixing time at the certain temperature can be, but is not limited to, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, or 120 min.

[0036] The molar ratio of the polyol compound shown in Formula II to the aldehyde compound shown in Formula III is 1:2.0 to 2.5. For example, the molar ratio may be, but is not limited to, 1:2.0, 1:2.1, 1:2.2, 1:2.3, 1:2.4, or 1:2.5. The amount of acidic catalyst used is 1% to 20% of the sum of the mass of the polyol compound shown in Formula II, the aldehyde compound shown in Formula III, and the acidic catalyst. Preferably, the amount of acidic catalyst used is 1% to 5%. For example, the amount of acidic catalyst used may be, but is not limited to, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 14%, 15%, 16%, 18%, or 20%.

[0037] The second solution is added dropwise to the first solution to control the reaction rate. The reaction temperature is -10℃ to 30℃, preferably -10℃ to 10℃. More preferably, the reaction temperature can be, but is not limited to, -10℃, -8℃, -5℃, -2℃, 0℃, 10℃, 20℃, or 30℃. The reaction time is 1 to 24 hours. As an example, the reaction time can be, but is not limited to, 1 hour, 3 hours, 5 hours, 7 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours. Purification includes filtration and / or washing. Filtration can be performed by centrifugation, vacuum filtration, or ordinary filtration. Washing can be performed multiple times with dichloromethane, tetrahydrofuran, or water. Drying can be carried out using forced-air drying, with a drying temperature of 35~120℃. For example, the temperature can be, but is not limited to, 35℃, 45℃, 55℃, 65℃, 75℃, 85℃, 95℃, 105℃, 110℃, 115℃, and 120℃. The drying time is 1~24 hours, but is not limited to 1 hour, 3 hours, 5 hours, 7 hours, 9 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, and 24 hours.

[0038] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0039] Part 1: Preparation of Acetal Compounds Example 1 This embodiment describes the preparation of acetal compounds, and the preparation method includes the following steps.

[0040] (1) Stir 30.0g erythritol, 1.3g p-toluenesulfonic acid and 150g n-hexane at 0℃ for 10 min to form the first solution, and mix 35g methacrolein and 80g n-hexane evenly to form the second solution; (2) The second solution was added dropwise to the first solution and reacted at 0°C for 20 h to obtain the product. The product was filtered, washed with dichloromethane, and dried under vacuum at 60°C for 10 h to obtain 47.4 g of compound 1.

[0041] The yield of compound 1 was 85.4%, and the purity was 99%. Compound 1... 1 ¹H NMR (400MHz, CDCl₃, ppm): δ 1.79 (s, 6H), 3.62–3.87 (m, 4H), 3.92–4.06 (dt, 2H), 5.18 (s, 2H), 5.32 (s, 2H), 5.63 (s, 2H). Compound 1... 13 C-NMR (100MHz, CDCl3, ppm): δ15.6, 68.5, 80.5, 117.7, 117.9, 140.4.

[0042] The reaction formula for preparing compound 1 in this embodiment is as follows: .

[0043] Example 2 This embodiment describes the preparation of acetal compounds, and the preparation method includes the following steps.

[0044] (1) Stir 30.0g erythritol, 1.3g p-toluenesulfonic acid and 150g n-hexane at 0℃ for 10min to form the first solution, and mix 35.4g n-butyraldehyde and 80g n-hexane evenly to form the second solution.

[0045] (2) The second solution was added dropwise to the first solution and reacted at 0°C for 20 h to obtain the product. The product was filtered, washed with dichloromethane, and dried under vacuum at 60°C for 10 h to obtain 50.4 g of compound 2.

[0046] The yield of compound 2 was 89.3%, and the purity was 99%. Compound 2... 1 ¹H NMR (400MHz, CDCl₃, ppm): δ 0.90 (t, 6H), 1.32 (tq, 4H), 1.58 (dt, 4H), 3.62–3.87 (m, 4H), 3.92–4.06 (dt, 2H), 5.45 (t, 2H). Compound 2... 13 C-NMR (100 MHz, CDCl3, ppm): δ13.1, 14.4, 36.2, 65.3, 80.0, 109.5.

[0047] The reaction formula for preparing compound 2 in this embodiment is as follows: .

[0048] Example 3 This embodiment describes the preparation of acetal compounds, and the preparation method includes the following steps.

[0049] (1) Stir 30.0g erythritol, 1.3g p-toluenesulfonic acid and 100g cyclohexane at 0℃ for 10min to form the first solution, and mix 38.5g chloroacetaldehyde and 70g cyclohexane evenly to form the second solution.

[0050] (2) The second solution was added dropwise to the first solution and reacted at 5°C for 2 hours to obtain the product. The product was filtered, washed with tetrahydrofuran, and dried under vacuum at 70°C for 8 hours to obtain 54.8 g of compound 3.

[0051] The yield of compound 3 was 92.1 g, with a purity of 99%. Compound 3... 1 ¹H NMR (400MHz, CDCl₃, ppm): δ 3.48–3.69 (m, 4H), 3.62–3.81 (m, 4H), 4.02 (t, 2H), 5.87 (t, 2H). Compound 3... 13 C-NMR (100 MHz, CDCl3, ppm): δ50.8, 64.5, 79.2, 116.0.

[0052] The reaction formula for preparing compound 3 in this embodiment is as follows: .

[0053] Example 4 This embodiment describes the preparation of acetal compounds, and the preparation method includes the following steps.

[0054] (1) Stir 30.0g erythritol, 1.3g p-toluenesulfonic acid and 100g cyclohexane at 10℃ for 20min to form the first solution, and mix 60.3g bromoacetaldehyde and 80g cyclohexane evenly to form the second solution.

[0055] (2) The second solution was added dropwise to the first solution and reacted at 10°C for 16 h to obtain the product. The product was filtered, washed with dichloromethane, and dried under vacuum at 60°C for 10 h to obtain 76.1 g of compound 4.

[0056] The yield of compound 4 was 93.6%, and the purity was 99%. Compound 4... 1 ¹H NMR (400MHz, CDCl₃, ppm): δ 3.48–3.73 (m, 4H), 3.62–3.87 (m, 4H), 4.02 (t, 2H), 5.97 (t, 2H). Compound 4... 13 C-NMR (100MHz, CDCl3, ppm): δ32.6, 64.3, 79.0, 117.0.

[0057] The reaction formula for preparing compound 4 in this embodiment is as follows: .

[0058] Part Two: Applications of Acetal Compounds in Batteries 1.1 Preparation of non-aqueous electrolyte In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), 86 g of a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) at a mass ratio of 1:1 was used as the organic solvent. Then, 1.5 g of the acetal compounds prepared in Examples 1-4 were added to each to obtain a mixed solution. The mixed solutions were sealed and packaged, and frozen in a freezer (-4°C) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After uniform mixing, non-aqueous electrolytes 1-4# were prepared.

[0059] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), 85.5 g of a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) at a mass ratio of 1:1 was used as the organic solvent. Then, 2.0 g of the acetal compound prepared in Example 1 was added to each solvent to obtain a mixed solution. The mixed solution was sealed and packaged, and frozen in a freezer (-4°C) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After uniform mixing, non-aqueous electrolyte 5# was prepared.

[0060] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), 85 g of a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) at a mass ratio of 1:1 was used as the organic solvent. Then, 2.5 g of the acetal compound prepared in Example 1 was added to each solvent to obtain a mixed solution. The mixed solution was sealed and packaged, and frozen in a freezer (-4°C) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After uniform mixing, non-aqueous electrolyte 6# was prepared.

[0061] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), 86.5 g of a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) at a mass ratio of 1:1 was used as the organic solvent. Then, 1.0 g of the acetal compound prepared in Example 1 was added to each solvent to obtain a mixed solution. The mixed solution was sealed and packaged, and frozen in a freezer (-4°C) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After uniform mixing, non-aqueous electrolyte 7# was prepared.

[0062] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), 87 g of a mixed solvent obtained by uniformly mixing diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) at a mass ratio of 1:1 was used as the organic solvent. Then, 0.5 g of the acetal compound prepared in Example 1 was added to each solvent to obtain a mixed solution. The mixed solution was sealed and packaged, and frozen in a freezer (-4°C) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After uniform mixing, non-aqueous electrolyte #8 was prepared.

[0063] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 1:1 to obtain a mixed solvent of 87.5 g, which was then used as the organic solvent. The organic solvent was sealed and packaged, then frozen in a freezer (-4℃) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), and mixed thoroughly to prepare non-aqueous electrolyte #9.

[0064] In a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 1:1. 87.5 g of the resulting mixed solvent was used as the organic solvent. Then, 1.5 g of compound A was added. The organic solvent was sealed and packaged, then frozen in a freezer (-4°C) for 2 hours. After removal, 12.5 g of lithium hexafluorophosphate (LiPF6) was slowly added to the mixed solution in a nitrogen-filled glove box (O2 < 1 ppm, H2O < 1 ppm). After thorough mixing, non-aqueous electrolyte 10# was prepared. The structural formula of compound A is shown below:

[0065] Compound A 1.2 Preparation of the positive electrode sheet Ternary material LiNi 0.5 Co 0.2 Mn 0.3 Zr 0.03 O2, conductive agent SuperP, binder PVDF and carbon nanotubes (CNT) are mixed evenly in a mass ratio of 96.5:1.5:1:1 to prepare a lithium-ion battery positive electrode slurry of a certain viscosity. After being coated on both sides of aluminum foil, the slurry is dried and rolled to obtain a positive electrode sheet, thus producing a lithium-ion battery positive electrode sheet that meets the requirements.

[0066] 1.3 Preparation of negative electrode sheet Artificial graphite, conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber latex) are mixed in a mass ratio of 95:1.5:1.0:2.5 to form a slurry. The mixture is then coated on both sides of a copper foil, dried, and rolled to obtain a negative electrode sheet, thus producing a lithium-ion battery negative electrode sheet that meets the requirements.

[0067] 1.4 Preparation of Lithium-ion Batteries The positive electrode, negative electrode, and separator prepared according to the above process are stacked to form lithium-ion batteries with a thickness of 4.7 mm, a width of 55 mm, a length of 60 mm, and a total capacity of 2 Ah. These batteries are then vacuum-baked at 75°C for 10 h and injected with non-aqueous electrolytes #1 to #5. After standing for 24 h, they are charged to 3.65 V using a constant current of 0.1 C (200 mA), then charged at a constant voltage of 3.65 V until the current drops to 0.05 C (100 mA). They are then discharged to 2.5 V using 0.2 C (400 mA), and this charge-discharge cycle is repeated twice. Finally, the batteries are charged to 3.65 V using 0.1 C (200 mA), completing the fabrication of lithium-ion batteries #1 to #10.

[0068] Performance tests were conducted on lithium-ion batteries #1 to #10. The test results are shown in Table 1. The test conditions are as follows.

[0069] (1) High-rate cycling performance test Under normal temperature (25℃) conditions, the lithium-ion battery was subjected to one 3.0 C / 3.0 C charge and discharge cycle (the battery discharge capacity was recorded as C0), with an upper limit voltage of 4.5V; then, it was subjected to 500 cycles of 3.0 C / 3.0 C charge and discharge, and the capacity retention rate was calculated.

[0070] Capacity retention rate = (Battery capacity after 500 cycles C1 / Initial battery capacity C0) × 100% (2) Low-temperature discharge test Under normal temperature (25℃) conditions, a lithium-ion battery was subjected to a single 0.5 C / 0.5 charge-discharge cycle (battery cutoff voltage 3.0 V, discharge capacity C0), with an upper limit voltage of 4.5 V (cutoff current 0.05 C). The battery was then fully charged to 4.5 V at 0.5 C at 25℃ (cutoff current 0.05 C), and then transferred to -20℃ for 4 hours. It was then discharged at 0.5 C to 3.0 V, with a discharge capacity of C1. The capacity retention rate was calculated.

[0071] Capacity retention rate = (C1 / C0) × 100% (3) Internal resistance test After capacity testing, the lithium-ion batteries were placed in a 25°C constant temperature chamber and left to stand for 30 minutes to allow them to reach a constant temperature. They were then charged at a constant current of 1C until the voltage reached 4.5V, followed by constant voltage charging at 4.5V until the current reached 0.05C. Next, they were discharged at a constant current of 1C until the voltage reached 3V. The first discharge capacity of the battery was recorded as C0. This constitutes one charge-discharge cycle. Then, at 25°C, the batteries were charged and discharged at 1C / 1C for three cycles. The batteries were discharged to 0.5C0, and the DC internal resistance R was measured.

[0072] Table 1. Electrochemical performance test results for each example.

[0073] As shown in Table 1, lithium-ion batteries #1-8 exhibit better rate performance and low-temperature performance than lithium-ion battery #9. This is because lithium-ion batteries #1-8 use acetal compounds as additives. Acetal compounds consist of a five-membered ring ether structure formed by substituent groups on aldehydes and erythritol. This structure can form a good protective film at the interface between the positive and negative electrode materials and has low internal resistance, thus improving the battery's rate performance and low-temperature performance. Lithium-ion battery #10 uses compound A with a triacetal structure as an additive. Its internal resistance, rate performance, and low-temperature performance are inferior to those of lithium-ion batteries #1-8 of this invention. This may be because compound A with a triacetal structure has a relatively large overall molecular weight, and the additive molecule contains three functionalized benzene ring groups, resulting in poor overall solubility. Consequently, the electrolyte using compound A with a triacetal structure as an additive shows relatively poor rate performance and low-temperature performance.

[0074] Further testing results from lithium-ion batteries #1 to #8 show that lithium-ion battery #1 exhibits the best performance. This may be because, compared to the other additives, the acetal compound 1, with its carbon-carbon double bond functional group, performs better than the electron-withdrawing branched chains of compounds 3 and 4. Compound 2, due to its longer substituent branches, does not perform as well as compound 1 when prepared as an electrolyte. Furthermore, based on lithium-ion batteries #1, #5, and #8, it is evident that when the mass of compound 1 in the electrolyte is 1.5g, its performance is optimal.

[0075] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An acetal compound, characterized in that, It has the structure shown in Formula I. Formula I R is selected from C1-C6 alkyl, C2-C6 alkenyl or C1-C6 haloalkyl.

2. The acetal compound as described in claim 1, characterized in that, R is selected from C1-C4 alkyl, C2-C4 alkenyl, or C1-C4 haloalkyl.

3. The acetal compound as described in claim 1, characterized in that, It is at least one of compound 1 to compound 4. Compound 1, Compound 2, Compound 3, Compound 4.

4. A method for preparing an acetal compound as described in any one of claims 1 to 3, characterized in that, Including the following steps: (1) The polyol compound shown in Formula II, the acid catalyst, and the first solvent are mixed at a certain temperature to form a first solution, and the aldehyde compound shown in Formula III is mixed with the second solvent to form a second solution; (2) The second solution is added dropwise to the first solution to react and the product is obtained. The product is then purified and dried. Formula II Formula III R is selected from C1-C6 alkyl, C2-C6 alkenyl or C1-C6 haloalkyl.

5. The method for preparing acetal compounds as described in claim 4, characterized in that, The first solvent and the second solvent are each independently selected from at least one of nitrile solvents, ether solvents, ester solvents, ketone solvents and aromatic hydrocarbon solvents, and the acidic catalyst is selected from at least one of dilute sulfuric acid, dilute hydrochloric acid and p-toluenesulfonic acid.

6. The method for preparing acetal compounds according to claim 4, characterized in that, The specified temperature is -10℃ to 120℃, and the mixing time at the specified temperature is 10 min to 120 min.

7. The method for preparing acetal compounds according to claim 4, characterized in that, The molar ratio of the polyol compound represented by Formula II to the aldehyde compound represented by Formula III is 1:2.0~2.5, and the amount of the acidic catalyst is 1%~20% of the sum of the mass of the polyol compound represented by Formula II, the aldehyde compound represented by Formula III, and the acidic catalyst.

8. The method for preparing acetal compounds as described in claim 4, characterized in that, The reaction temperature is -10℃ to 30℃, and the reaction time is 1 hour to 24 hours.

9. The method for preparing acetal compounds according to claim 4, characterized in that, The purification includes filtration and / or washing, the drying temperature is 35℃~120℃, and the drying time is 1h~24h.

10. An electrolyte comprising a non-aqueous organic solvent, an electrolyte salt, and additives, characterized in that, The additive includes acetal compounds as described in any one of claims 1 to 3 or acetal compounds prepared by the method described in any one of claims 4 to 9.

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