Squaric acid derivative compounds, methods of making the same, and use in batteries

Abstract

The application provides a squaric acid derivative compound and a preparation method and application in a battery. The structural formula of the squaric acid derivative compound is shown in formula I, formula II, formula III or formula IV, X is selected from SO2, SO, CO, B-R, P-R, PO-R or Si-R2, Y is selected from B-R2, P-R2, PO-R2 or P-R4, Z is selected from SO, C or P-R, W is selected from B, P or P-R2, and R is hydrogen, halogen or C1-C3 alkyl. The squaric acid derivative compound can be directly used in an electrolyte as a functional additive, can inhibit the oxidation decomposition of the electrolyte caused by the dissolution of metal ions in the positive electrode material, and can improve the high-temperature storage and high-temperature cycle performance of the battery. Moreover, the lithium salt of the novel squaric acid derivative compound can also be used as an electrolyte salt, thereby playing a lithium supplementing role.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of material synthesis, in particular to a compound applied in a battery, more particularly to a squaraine derivative compound and a preparation method thereof, and application in a battery. BACKGROUND

[0002] In recent years, with the rapid development of new energy vehicles, portable electronic products, unmanned aerial vehicles, distributed energy storage and smart grids, higher requirements are put forward for the performance of batteries, among which the requirement for improving the energy density of the battery is particularly urgent. At present, the energy density of the battery is mainly improved by the following methods. (1) Using positive electrode materials with higher energy density such as high-nickel ternary positive electrode materials (NCM, NCA). (2) Using high-capacity silicon, tin-based alloy as negative electrode active material. (3) Optimizing the battery structure to improve the energy density of the battery, such as blade battery technology. (4) Using battery lithium supplement technology to improve the energy density of the battery. Due to the formation of a nano-structured SEI film on the surface of the negative electrode during the formation of the lithium ion battery, a part of the active lithium is consumed, resulting in a loss of battery capacity. The irreversible capacity loss of the most widely used graphite negative electrode is 6%, while the irreversible capacity loss of high specific capacity silicon-based and tin-based alloy negative electrodes is as high as 10-20%. Therefore, the lithium supplement technology can effectively improve the initial efficiency of the battery, improve the energy density of the battery and prolong the cycle life.

[0003] The lithium supplement technology can be divided into positive electrode lithium supplement and negative electrode lithium supplement. The negative electrode lithium supplement technology is researched earlier, including physical mixing lithium supplement of metal lithium, chemical lithium supplement, and electrochemical lithium supplement. However, due to the activity of metal lithium material, the process is very difficult, and it has not been widely used at present. In recent years, the positive electrode lithium supplement technology has attracted widespread attention and research. The positive electrode lithium supplement technology adds lithium supplement material to the positive electrode material of the lithium battery. The positive electrode lithium supplement material has the advantages of stable chemical properties and easy synthesis. Moreover, the positive electrode lithium supplement material can be directly added in the homogenization process of the positive electrode slurry, and the preparation process is simple and the cost is low. It is the most promising lithium supplement technology at present. At present, some manufacturers use lithium squarate as a positive electrode lithium supplement additive. It can be used as a sacrificial lithium salt to supplement the irreversible capacity loss of lithium ions, thereby improving the cycle performance of the lithium ion battery. At present, the application of squaric acid in batteries is mainly to neutralize it with alkali metal compounds to become lithium salt or sodium salt as a positive electrode material lithium / sodium supplement additive. However, the conductivity and ion transference rate of lithium squarate are very low, which increases the internal resistance of the positive electrode plate, affects the performance of the electrode material, and the electrochemical activity is poor, which cannot fully play the effect of lithium / sodium supplement, thereby limiting its application in positive electrode lithium supplement technology. SUMMARY

[0004] Based on the above problems, the purpose of the present application is to provide a new squaraine derivative compound and a preparation method thereof, which can be directly used as a functional additive in an electrolyte, can inhibit the dissolution of metal ions in the positive electrode material to cause the oxidative decomposition of the electrolyte, thereby improving the high-temperature storage and high-temperature cycle performance of the battery, and the lithium salt of the new squaraine derivative compound can also be used as an electrolyte salt, thereby playing a role of supplementing lithium.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a squaraine derivative compound, the structural formula of which is shown in Formula I, Formula II, Formula III or Formula IV, X is selected from SO2, SO, CO, B-R, P-R, PO-R or Si-R2, Y is selected from B-R2, P-R2, PO-R2 or P-R4, Z is selected from SO, C or P-R, W is selected from B, P or P-R2, and R is hydrogen, halogen or C1-C3 alkyl.

[0006]

[0007] The left squaraine structure in the squaraine derivative compound of the present application has high stability and conjugate structure, can form a complex with the positive electrode metal ion to stabilize the structure. On the other hand, the right half structure of the squaraine derivative compound can introduce heteroatoms to form S=O, C=O, P-R, B-R, Si-R, etc. bonds, which can increase the solubility of the squaraine derivative compound in the electrolyte, and at the same time, can form a stable SEI film during the cycle of the battery, which can inhibit the dissolution of metal ions in the positive electrode material to cause the oxidative decomposition of the electrolyte. Therefore, after adding the squaraine derivative compound containing the squaraine derivative compound to the non-aqueous electrolyte of the secondary battery, the high-temperature storage and high-temperature cycle performance of the secondary battery under high voltage can be improved.

[0008] As a technical solution of the present application, the squaraine derivative compound includes at least one of Compound I to Compound VIII.

[0009]

[0010] The second aspect of the present application provides a preparation method of the squaraine derivative compound, which includes the following steps:

[0011] (1) mixing the squaraine and a solvent to form a first solution;

[0012] (2) adding an electrophilic reagent to the first solution to perform a substitution reaction, or first adding a salt to the first solution and then adding an electrophilic reagent to perform a substitution reaction, the electrophilic reagent is a silicon halide, a phosphorus halide, a boron halide, a sulfur halide or an ester compound, and the salt is a lithium salt or a sodium salt;

[0013] (3) purifying and drying after the reaction.

[0014] The preparation method of the present application is simple, and the substitution reaction of squaric acid and electrophilic reagents such as silicon halide, phosphorus halide, boron halide, sulfur halide, ester compound, etc. can obtain squaric acid derivative compounds as described in Formula I or Formula III. The substitution reaction of squaric acid and electrophilic reagents such as silicon halide, phosphorus halide, boron halide, sulfur halide, ester compound, etc. under the action of salt can obtain squaric acid derivative compounds as described in Formula II or Formula IV. The prepared squaric acid derivative compounds can improve the high-temperature storage and high-temperature cycle performance of the battery.

[0015] As a technical solution of the present application, the solvent includes at least one of halogenated hydrocarbon solvents, aliphatic hydrocarbons, ether solvents, ketone solvents, ester solvents, and nitrile solvents.

[0016] As a technical solution of the present application, the reaction temperature of the substitution reaction is -20-90°C.

[0017] As a technical solution of the present application, the molar ratio of the squaric acid to the electrophilic reagent is 1:0.5-2.1.

[0018] As a technical solution of the present application, between step (2) and step (3), an oxidation step is further included to oxidize the product of the substitution reaction.

[0019] As a technical solution of the present application, the electrophilic reagent is selected from at least one of silicon tetrachloride, trimethylchlorosilane, dimethylchlorosilane, monomethylchlorosilane, chlorosulfoxide, phosphorus trichloride, phosphorus pentachloride, phosphorus tribromide, phosphorus pentabromide, boron trichloride, boron trifluoride, boron trifluoride diethyl ether complex, dimethyl carbonate complex, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, and the salt is selected from lithium hexafluorophosphate, lithium tetrafluoroborate, sodium hexafluorophosphate, or sodium tetrafluoroborate.

[0020] The third aspect of the present application provides the application of squaric acid derivative compounds in secondary batteries.

[0021] The fourth aspect of the present application provides an electrolyte solution, which includes a non-aqueous organic solvent, an electrolyte salt, and an additive, the additive includes the aforementioned squaric acid derivative compound, and the squaric acid derivative compound accounts for 0.01-2.00% of the mass of the electrolyte solution.

[0022] As a technical solution of the present application, the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium difluoro oxalate borate, lithium bis oxalate borate, lithium difluorophosphate, and lithium difluoro bis-oxalate phosphate, and the non-aqueous organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, butyl propionate, and ethyl butyrate. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 Mass spectrum of compound five in Example 4.

[0024] Figure 2 Mass spectrum of compound six in Example 5.

[0025] Figure 3 Mass spectrum of compound seven in Example 6. DETAILED DESCRIPTION

[0026] The squaraine derivative compounds of the present application can be used in material synthesis, secondary batteries. In particular, the squaraine derivative compounds are used in secondary batteries such as lithium ion batteries or sodium ion batteries, and the squaraine derivative compounds can be used as electrolyte additives to improve the high-temperature storage and high-temperature cycle performance of the secondary batteries.

[0027] The secondary battery includes a positive electrode active material, a negative electrode active material, and an electrolyte. If used in a lithium ion battery, the positive electrode active material can be a layered transition metal lithium oxide. The layered transition metal lithium oxide can be, but is not limited to, a lithium cobalt oxide (such as LiCoO2) and a coating and a dopant of the lithium cobalt oxide. If the secondary battery is a sodium ion battery, the positive electrode active material can be a layered transition metal sodium oxide. The layered transition metal sodium oxide can be, but is not limited to, a sodium cobalt oxide (such as NaCoO2) and a coating and a dopant of the sodium cobalt oxide. The negative electrode active material includes at least one of a carbon-based material, a silicon-based material, lithium titanate, and a tin-based material. 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 mesocarbon microbeads. The silicon-based material can be, but is not limited to, at least one of silicon single substance, silicon-oxygen composite material, silicon-carbon composite material, and silicon alloy material. The tin-based material can include tin single substance, tin-carbon composite material, tin-oxygen composite material, and tin alloy compound.

[0028] The electrolyte includes an electrolyte salt, a non-aqueous organic solvent, and an additive.

[0029] The electrolyte salt can be, but is not limited to, at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium difluoro-oxalato-borate, lithium bis-oxalato-borate, lithium difluorophosphate, and lithium difluoro-bis-oxalato-phosphate.

[0030] The non-aqueous organic solvent is selected from carbonates and / or carboxylic acid esters. Further, the non-aqueous organic solvent is selected from at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), propylene carbonate (PC), butyl acetate, γ-butyrolactone, propyl propionate, butyl propionate, and ethyl butyrate.

[0031] The additive is a squaraine derivative compound, and further, the additive is a squaraine derivative compound having a structure as shown in Formula I, Formula II, Formula III, or Formula IV. X is selected from SO2, SO, CO, B-R, P-R, PO-R, or Si-R2, Y is selected from B-R2, P-R2, PO-R2, or P-R4, Z is selected from SO, C, or P-R, W is selected from B, P, or P-R2, and R is hydrogen, halogen, or C1-C3 alkyl.

[0032]

[0033]

[0034] Further, the squaraine derivative compound includes at least one of Compound I to Compound VIII.

[0035]

[0036] The squaraine derivative compound accounts for 0.01-2.00% of the mass of the electrolyte. As an example, the proportion of the squaraine derivative compound can be, but is not limited to, 0.01%, 0.03%, 0.05%, 0.08%, 0.10%, 0.30%, 0.50%, 0.80%, 1.00%, 1.20%, 1.40%, 1.60%, 1.80%, or 2.00%.

[0037] The preparation method of the squaraine derivative compound includes the following steps.

[0038] (1) mixing the squaraine and a solvent to form a first solution.

[0039] (2) adding an electrophilic reagent to the first solution to perform a substitution reaction, or first adding a salt to the first solution and then adding an electrophilic reagent to perform a substitution reaction.

[0040] (3) purifying and drying after the reaction.

[0041] In step (1), the solvent includes at least one of a halogenated hydrocarbon solvent, an aliphatic hydrocarbon solvent, an ether solvent, a ketone solvent, an ester solvent, and a nitrile solvent. Further, the halogenated hydrocarbon solvent can be dichloromethane, trichloromethane, 1,2-dichloroethane, or tetrachloroethane, the aliphatic hydrocarbon solvent can be n-hexane or cyclohexane, the ether solvent can be diethyl ether, methyl tert-butyl ether, ethylene glycol dimethyl ether, tetrahydrofuran, or dioxane, the ketone solvent can be acetone, cyclohexanone, or 4-methyl-2-pentanone, the ester solvent can be dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl acetate, ethyl acetate, or propyl acetate, and the nitrile solvent can be acetonitrile. The squaraine and the solvent are mixed uniformly to form a clear and transparent solution or a suspension.

[0042] In step (2), the electrophilic reagent is a silicon halide, phosphorus halide, boron halide, sulfur halide or ester compound. Further, the electrophilic reagent is selected from at least one of silicon tetrachloride, trimethylchlorosilane, dimethylchlorosilane, monomethylchlorosilane, sulfuric chloride, phosphorus trichloride, phosphorus pentachloride, phosphorus tribromide, phosphorus pentabromide, boron trichloride, boron trifluoride, boron trifluoride diethyl ether complex, dimethyl carbonate complex, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. The salt is a lithium salt or a sodium salt, and further, the salt is selected from lithium hexafluorophosphate, lithium tetrafluoroborate, sodium hexafluorophosphate or sodium tetrafluoroborate. The substitution reaction using squaric acid and the electrophilic reagent can obtain the squaric acid derivative compound as described in Formula I or Formula III. The substitution reaction using squaric acid and the electrophilic reagent in the presence of the salt can obtain the squaric acid derivative compound as described in Formula II or Formula IV, which is a salt and can be used as an additive to improve the performance of the battery, or can replace part of the lithium salt to serve as an electrolyte component.

[0043] The reaction temperature of the substitution reaction is -20-90°C, and as an example, the reaction temperature can be but is not limited to -20°C, -10°C, 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C. The reaction time of the substitution reaction is 2-24h, and as an example, the reaction time can be but is not limited to 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, 24h. The molar ratio of squaric acid and the electrophilic reagent is 1:0.5-2.1, and as an example, the molar ratio of the two can be but is not limited to 1:0.5, 1:0.7, 1:1.0, 1:1.2, 1:1.5, 1:1.8, 1:2.0, 1:2.1. In order to obtain the high-oxidizing squaric acid derivative compound, an oxidation step can also be included between step (2) and step (3), and the product of the substitution reaction is oxidized. For example, to obtain compound I, squaric acid-cyclic sulfite compound can be prepared first, and then sodium hypochlorite or ozone is used for oxidation to obtain squaric acid-cyclic sulfate compound. After synthesizing compound III, sodium hypochlorite or ozone can also be used for oxidation to obtain compound IV.

[0044] In step (3), the purification method is washing, filtration or recrystallization. The washing can be carried out with hydrochloric acid aqueous solution, saturated brine or water and multiple washing. The filtration can be carried out by centrifugal separation, reduced pressure filtration or general filtration. The recrystallization can be carried out using a mixed solvent of ethanol / water, and the drying can be carried out by vacuum drying in an oven. The temperature of the vacuum drying can be 40-120°C, and as an example, the temperature can be but is not limited to 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C.

[0045] For better illustrating the purpose, technical scheme and beneficial effects of the present application, the present application will be further explained in combination with specific examples. It should be noted that the following implementation of the method is a further explanation of the present application, and should not be regarded as a limitation of the present application.

[0046] First part: preparation of squaric acid derivative compound

[0047] Example 1

[0048] This example is to prepare compound one, the synthesis reaction formula is as follows, and the preparation method comprises the following steps.

[0049]

[0050] (1) In a 500ml three-necked flask, 11.4g of squaric acid and 88g of anhydrous acetonitrile were added and stirred to form a first solution.

[0051] (2) Then 12.5g of chlorosulfoxide was slowly added and a substitution reaction was carried out at 35℃ for 7.5h to obtain a pre-solution of squaric acid-cyclic sulfoxide, and then the pre-solution was concentrated and cooled to crystallize to obtain 14.4g of squaric acid-cyclic sulfoxide crude product. The obtained squaric acid-cyclic sulfoxide crude product was put into a new three-necked flask, 80g of acetonitrile and 14g of sodium bicarbonate aqueous solution were added, the temperature was controlled at-20℃, and sodium hypochlorite aqueous solution 67g was added dropwise to carry out oxidation reaction to obtain acetonitrile solution containing squaric acid-cyclic sulfate compound.

[0052] (3) Then concentrated and crystallized, vacuum dried at 50℃ to obtain 13.8g of compound one, with a yield of 87%.

[0053] Example 2

[0054] This example is to prepare compound two, the synthesis reaction formula is as follows, and the preparation method comprises the following steps.

[0055]

[0056] (1) In a 500ml three-necked flask, 11.4g of squaric acid and 34.2g of methanol were added and stirred to form a first solution.

[0057] (2) Then 45.6g of dimethyl carbonate and 0.02g of potassium carbonate were slowly added and a substitution reaction was carried out at 75℃ under reflux for 12h until the solution was clear.

[0058] (3) Then concentrated and crystallized, filtered, and vacuum dried at 80℃ to obtain 12.3g of compound two, with a yield of 88%.

[0059] Example 3

[0060] This example is for preparing compound three and compound four, the reaction formula is as follows, and the preparation method comprises the following steps.

[0061]

[0062] (1) In a 500ml three-necked flask, 11.4g of squaric acid, 89g of anhydrous acetonitrile were added and stirred to form a first solution.

[0063] (2) Then 13.7g of phosphorus trichloride was slowly added dropwise, and a substitution reaction was carried out at 35°C for 7.0h. During the reaction, sodium hydroxide was used to absorb the generated acid. After the reaction was completed, the mother liquor was concentrated, filtered, and dried at 60°C to obtain 16g of squaric acid-cyclic chlorophosphite compound. The obtained 16g of squaric acid-cyclic chlorophosphite compound was continuously put into a new anhydrous reaction container, 80g of anhydrous acetonitrile and 10.4g of anhydrous potassium fluoride were added, and a reflux reaction was carried out at 80°C for 24h. After the reaction was completed, the mother liquor was filtered, concentrated, filtered, washed, and dried at 60°C under vacuum to obtain 13.1g of compound three, with a yield of 90%.

[0064] The obtained 13.1g of compound three was added into a new anhydrous reaction container, 72g of toluene was added, the reaction temperature was set to 40°C, then oxygen was introduced into the container for reaction, the progress of the reaction was monitored by LCMS, and the oxygen was stopped after the raw material peak disappeared. Then the mother liquor was concentrated, crystallized, and dried at 50°C under vacuum to obtain 12.4g of compound four, with a yield of 86%.

[0065] Example 4

[0066] This example is for preparing compound five, the reaction formula is as follows, and the preparation method comprises the following steps.

[0067]

[0068] (1) In a 500ml three-necked flask, 11.4g of squaric acid, 15.1g of lithium hexafluorophosphate, 113g of methyl ethyl carbonate were added and stirred to form a first solution.

[0069] (2) Then 8.5g of silicon tetrachloride was slowly added dropwise, and a substitution reaction was carried out at 35°C for 5.5h.

[0070] (3) The reaction solution was vacuumed to remove acid, concentrated, crystallized, filtered, and dried at 60°C under vacuum to obtain 21.5g of compound five, with a yield of 95%. The mass spectrum of the prepared compound five is shown in Figure 1 It can be seen from the mass spectrum that compound five can be synthesized.

[0071] Example 5

[0072] This embodiment is to prepare compound six, and the reaction formula is as follows, and the preparation method comprises the following steps.

[0073]

[0074] (1) 22.8 g of squaric acid, 15.1 g of lithium hexafluorophosphate and 113 g of methyl ethyl carbonate were added into a 500 ml three-necked flask and stirred to form a first solution.

[0075] (2) 17.0 g of silicon tetrachloride was slowly added dropwise, and a substitution reaction was carried out at 35 °C for 7.5 h.

[0076] (3) The reaction solution was vacuumized to remove acid, concentrated, crystallized, filtered, and vacuum dried at 60 °C to obtain 28.2 g of compound six, with a yield of 94 %. The mass spectrum of the prepared compound six is shown in Figure 2 It can be seen from the mass spectrum that compound six can be synthesized.

[0077] Example 6

[0078] This embodiment is to prepare compound seven, and the reaction formula is as follows, and the preparation method comprises the following steps.

[0079]

[0080] (1) 11.4 g of squaric acid, 9.4 g of lithium tetrafluoroborate and 84 g of dimethyl carbonate were added into a 500 ml three-necked flask and stirred to form a first solution.

[0081] (2) 8.5 g of silicon tetrachloride was slowly added dropwise, and a substitution reaction was carried out at 35 °C for 2.5 h, and then the temperature was increased to 60 °C for reaction for 4.5 h.

[0082] (3) The reaction solution was vacuumized to remove acid, concentrated, crystallized, filtered, and vacuum dried at 120 °C to obtain 15.1 g of compound seven, with a yield of 90 %. The mass spectrum of the prepared compound seven is shown in Figure 3 It can be seen from the mass spectrum that compound seven can be synthesized.

[0083] Example 7

[0084] This embodiment is to prepare compound eight, and the reaction formula is as follows, and the preparation method comprises the following steps.

[0085]

[0086] (1) 11.4 g of squaric acid and 85 g of tetrahydrofuran were added into a 500 ml three-necked flask and stirred to form a first solution.

[0087] (2) Slowly add 12.9 g of dimethyldichlorosilane, 11 g of triethylamine, and raise the temperature to 70°C to reflux for 24 h.

[0088] (3) Remove acid by vacuum extraction, concentrate, crystallize, filter, and dry at 60°C under vacuum to obtain 15.5 g of compound eight with a yield of 91%.

[0089] Second part: Application of squaric acid derivative compounds in batteries

[0090] 1.1 Preparation of non-aqueous electrolyte

[0091] In a glove box filled with nitrogen (water content ≤1 ppm, oxygen content ≤1 ppm), dehydrate vinyl carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) to make the water content of the solution ≤1 ppm (add 5% solution mass of activated 4A molecular sieves), then configure a mixed solution 87 g with a mass ratio of EC: EMC: DEC = 1: 1: 1 and stir uniformly, then slowly add lithium hexafluorophosphate 12.9 g to the mixed solution, stir uniformly to make it completely dissolved, then add compound one 0.1 g, stir uniformly to make it completely dissolved, to form non-aqueous electrolyte 1#.

[0092] 1.2 Preparation of positive electrode sheet

[0093] Mix lithium cobaltate, adhesive PVDF, and conductive agent SuperP in a mass ratio of 95:1.5:3.5 to make a certain viscosity of lithium ion battery positive electrode slurry, coat on the current collector aluminum foil, cold press, edge cutting, sheet cutting, and striping to make the required lithium ion battery positive electrode sheet.

[0094] 1.3 Preparation of negative electrode sheet

[0095] Mix artificial graphite, conductive agent SuperP, thickening agent CMC, and adhesive SBR (styrene-butadiene rubber emulsion) in a mass ratio of 95:2:1:2 to make a slurry, mix uniformly, coat on both sides of the copper foil with the mixed slurry, and then dry and roll to obtain a negative electrode sheet, to make the required lithium ion battery negative electrode sheet.

[0096] 1.4 Preparation of lithium ion battery

[0097] Stack the positive electrode sheet, separator, and negative electrode sheet to make a square cell, use polymer packaging, then vacuum dry at 60°C for 12 h, then inject non-aqueous electrolyte into the cell in the glove box, and then go through formation, capacity distribution, etc. to make a lithium ion battery 1# with a capacity of 1000 mAh.

[0098] The squaric acid derivative compounds in Examples 2-7 were substituted for the squaric acid derivative compound in Example 1 to prepare nonaqueous electrolytes 2#-16#, and a nonaqueous electrolyte 17# was prepared without adding a squaric acid derivative compound. The compositions of the nonaqueous electrolytes 2#-17# are shown in Table 1. Lithium ion batteries 2#-17# were prepared using the same positive and negative electrode sheets and lithium ion battery preparation method as in 1.1-1.4.

[0099] Table 1 Compositions of nonaqueous electrolytes 2#-17#

[0100] Group Non-aqueous organic solvent / g Lithium salt / g Additive / g Non-aqueous electrolyte 1 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.9 Compound 1 / 0.1 Non-aqueous electrolyte 2 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.7 Compound 1 / 0.3 Non-aqueous electrolyte 3 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.9 Compound 2 / 0.1 Non-aqueous electrolyte 4 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.7 Compound 2 / 0.3 Non-aqueous electrolyte 5 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.9 Compound 3 / 0.1 Non-aqueous electrolyte 6 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.7 Compound 3 / 0.3 Non-aqueous electrolyte 7 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.9 Compound 4 / 0.1 Non-aqueous electrolyte 8 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.7 Compound 4 / 0.3 Non-aqueous electrolyte 9 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.9 Compound 5 / 0.1 Non-aqueous electrolyte 10 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.7 Compound 5 / 0.3 Non-aqueous electrolyte 11 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.9 Compound 6 / 0.1 Non-aqueous electrolyte 12 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.7 Compound 6 / 0.3 Non-aqueous electrolyte 13 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.7 Compound 7 / 0.1 Non-aqueous electrolyte 14 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 / 12.9 Compound 7 / 0.3 Non-aqueous electrolyte 15 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 12.7 Compound 8 / 0.1 Non-aqueous electrolyte 16 EC:EMC:DEC = 1:1:1 / 87.0 LiPF6 12.9 Compound 8 / 0.3 Non-aqueous electrolyte 17 EC:EMC:DEC = 1:1:1 / 87.0 LiPF613.0 /

[0101] The lithium ion batteries 2#-17# were subjected to high-temperature storage performance tests and high-temperature fast-charging cycle performance tests under the following test conditions, and the test results are shown in Table 2.

[0102] High-temperature storage performance test: The lithium ion battery was subjected to one 0.3C / 0.3C charge and discharge at room temperature (25°C) and an upper limit voltage of 4.53 V, and the discharge capacity was recorded as C0. Then the battery was placed in an oven at 60°C for 7 days, and after the battery temperature was reduced to 25°C, 0.3C discharge was performed, and the discharge capacity was recorded as C1. Then the lithium ion battery was subjected to one 0.3C / 0.3C charge and discharge, and the discharge capacity was recorded as C2.

[0103] Capacity retention rate = C1 / C0 * 100%

[0104] Capacity recovery rate = C2 / C0 * 100%

[0105] High-temperature fast-charging cycle performance test: The lithium ion battery was placed in a 45°C constant-temperature oven and allowed to stand for 30 min to bring the lithium ion battery to a constant temperature. The battery was charged at 2C constant current to a voltage of 4.53 V, then charged at 4.53 V constant voltage to a current of 0.05C, and then discharged at 1C constant current to a voltage of 3.0 V. The first-cycle discharge capacity of the battery was recorded as C0. This was one charge and discharge cycle. Then the battery was subjected to 2C / 1C charge and discharge at 45°C for 300 cycles, and the discharge capacity was recorded as C1.

[0106] Capacity retention rate = C1 / C0 * 100%

[0107] Table 2 High-temperature storage performance and high-temperature fast-charging cycle performance test results for lithium ion batteries 2#-17#

[0108]

[0109]

[0110] The results in Table 2 show that lithium-ion batteries 1# to 16# exhibit superior high-temperature storage performance and high-temperature fast-charge cycling performance to lithium-ion battery 17#. This is due to the inclusion of squaric acid derivatives as additives in lithium-ion batteries 1# to 16#. The squaric acid structure on the left side has high stability and a conjugated structure, which can complex with the positive electrode metal ions to stabilize the structure. Furthermore, the right half of the squaric acid derivative structure can introduce heteroatoms to form bonds such as S=O, C=O, PR, BR, and Si-R, increasing the solubility of the squaric acid derivative in the electrolyte. Furthermore, during battery cycling, a robust SEI film can be formed, inhibiting the dissolution of metal ions from the positive electrode material and leading to oxidative decomposition of the electrolyte. This can improve the high-temperature storage and high-temperature cycling performance of the secondary battery at high voltages.

[0111] Furthermore, a comparison of lithium-ion batteries 1# to 16# reveals that lithium-ion batteries 1# to 2# and lithium-ion batteries 9# to 10# perform better. This is because the right-hand side structure of compound 1 is a cyclic structure similar to vinyl sulfate, which combines the dual effects of squaric acid and vinyl sulfate to achieve a synergistic effect. The right-hand side structure of compound 5 contains a large number of PF bonds. The cleavage of these PF bonds during the battery formation stage allows the SEI film formed to contain a large amount of LiF, making the SEI film more stable and significantly improving the battery's high-temperature performance.

[0112] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A squaric acid derivative compound, characterized in that The structural formula is shown in Formula 1, X is selected from SO2, PR or Si-R2, R is hydrogen, halogen or C1~C3 alkyl, Formula 1.

2. The squaraine derivative compound according to claim 1, characterized in that including at least one of compound 1, compound 3 and compound 8, Compound 1, Compound 3, Compound 8.

3. The method for preparing a squaric acid derivative compound according to claim 2, wherein: Including steps: (1) mixing squaric acid and a solvent to form a first solution; (2) adding an electrophilic reagent to the first solution to carry out a substitution reaction, wherein the electrophilic reagent is dimethylchlorosilane, thionyl chloride or phosphorus trichloride; (3) Purify and dry after the reaction.

4. The method for preparing a squaric acid derivative compound according to claim 3, wherein: The reaction temperature of the substitution reaction is -20~90°C.

5. The method for preparing a squaric acid derivative compound according to claim 3, wherein: The molar ratio of the squaric acid to the electrophilic reagent is 1:0.5-2.

1.

6. The method for preparing a squaric acid derivative compound according to claim 3, wherein: An oxidation step is also included between step (2) and step (3) to oxidize the product of the substitution reaction.

7. Use of the squaric acid derivative compound according to claim 1 or 2, or the squaric acid derivative compound prepared by the method for preparing the squaric acid derivative compound according to any one of claims 3 to 6, in a secondary battery.

8. An electrolyte comprising a non-aqueous organic solvent, an electrolyte salt and an additive, characterized in that: The additive includes the squaric acid derivative compound according to claim 1 or 2, or a squaric acid derivative compound prepared by the preparation method of the squaric acid derivative compound according to any one of claims 3 to 7, and the squaric acid derivative compound accounts for 0.01 to 2.00% by mass of the electrolyte.

9. The electrolyte according to claim 8, characterized in that The electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium difluorooxalatoborate, lithium bis(oxalatoborate), lithium difluorophosphate and lithium difluorobis(oxalatophosphate), and the non-aqueous organic solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, butyl acetate, γ-butyrolactone, propyl propionate, butyl propionate and ethyl butyrate.

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