A battery electrolyte overcharge protection additive based on a carbazole ring derivative and its preparation and application

Abstract

The present invention discloses a battery electrolyte overcharge protection additive based on a carbazole ring derivative, and its preparation and application. The overcharge protection additive r-mPh-BCz of the present invention has a relatively high redox potential, and a redox reaction occurs in the voltage range of 3.5 to 4.5 V. Moreover, r-mPh-BCz exhibits reversibility of the redox reaction and good stability of the reaction intermediate. When r-mPh-BCz is added to the electrolyte as an overcharge protection additive, when the battery charging voltage exceeds 4.2 V, the r-mPh-BCz in the electrolyte preferentially undergoes a redox reaction to inhibit the decomposition of the electrolyte itself, and avoid capacity attenuation of the battery caused by electrolyte decomposition and even trigger battery thermal runaway. The overcharge protection additive of the present invention effectively improves the cycle stability and safety of the battery without affecting the energy density of the battery, and its preparation process is simple, pollution-free, and has a low cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of electrolyte additives for batteries, and particularly relates to a small-ring organic molecule overcharge protection electrolyte additive based on a redox mechanism for bin-carbazole, specifically an overcharge protection additive for a battery electrolyte based on a bin-carbazole cyclic derivative, and its preparation and application. Background Art

[0002] With the development of modern society, especially the rapid development of electronic technology and information industry, higher requirements are put forward for chemical power sources - high energy, miniaturization, light weight, long service time, long working life, maintenance-free... Compared with other secondary battery systems, lithium-ion batteries have the advantages of high voltage (average working voltage 3.5 - 3.7V), high specific energy (above 100Wh / kg), low self-discharge, long cycle life (>1000 times), low cost and less pollution, and are green batteries meeting the modernization requirements. Now they have become the secondary batteries with the fastest development and the most extensive use. The safety of lithium-ion batteries has always been a concern in the development of electric vehicles and is an important factor restricting the actual production and use of high-capacity power lithium-ion batteries. When lithium batteries came out, internal short circuits caused by lithium dendrites led to battery combustion and explosion, thus hindering the further development of lithium batteries. In lithium-ion batteries, lithium always exists in the form of lithium ions, so it has relatively high safety compared with lithium batteries. However, since a fully charged battery itself is an energy storage device and the electrolyte used in lithium-ion batteries is an organic solution containing fluorinated lithium salts, it has the conditions for combustion and corrosion. When the battery is overcharged (V>4.2V), the electrolyte will decompose, causing gas expansion inside the battery and posing an explosion risk, with a considerable potential safety hazard. At present, the overcharge protection of lithium-ion batteries is achieved by adding a dedicated protection circuit, a gas release valve or a PTC element (positive temperature coefficient switch) externally, which will increase the cost of the battery pack. Achieving overcharge protection of the battery by adding electrolyte additives is of great significance for simplifying the battery manufacturing process and reducing the battery production cost.

[0003] Common overcharge protection additives are mainly of two types: redox pair additives and electro-polymerization additives. The working principle of redox pair additives is that no electrochemical reaction occurs at the normal voltage of the lithium-ion battery. However, when the battery is overcharged, the additive is oxidized near the positive electrode to form active molecules, which then diffuse to the negative electrode and are reduced to form neutral molecules, and then diffuse back to the positive electrode, repeating this cycle to achieve the purpose of overcharge protection. Adding overcharge protection additives to the electrolyte is a classic method to deal with overcharge problems, and almost all electrolytes for consumer batteries and power batteries contain overcharge protection additives. However, searching for and designing overcharge additives that are both safe and effective, have no negative impact on battery performance, and have low cost is a very challenging task. Summary of the Invention

[0004] The first object of the present invention is to provide, in view of the deficiencies of the prior art, a redox couple overcharge prevention additive based on a carbazole-based small-ring organic molecule, which can effectively prevent the battery from overcharging, has no negative impact on the battery performance, has a low cost, and has a simple and pollution-free preparation process.

[0005] The present invention provides a redox couple overcharge prevention additive r-mPh-BCz based on a carbazole-based small-ring organic molecule, and its structural general formula is as follows:

[0006]

[0007] wherein R1, R2, R3, and R4 are each independently one of H, Me, Et, iPr, tBu, OMe, and OEt; Ar =

[0008] The overcharge prevention additive r-mPh-BCz has a relatively high redox potential, and a redox reaction occurs in the voltage range of 3.5 - 4.5V, and the redox reaction of r-mPh-BCz is reversible, and the reaction intermediate is stable.

[0009] When r-mPh-BCz is added to the electrolyte as an overcharge protection additive, when the battery charging voltage exceeds 4.2V, the r-mPh-BCz in the electrolyte preferentially undergoes a redox reaction to inhibit the decomposition of the electrolyte itself, and avoid capacity attenuation or even short-circuit thermal runaway of the battery caused by the decomposition of the electrolyte, effectively improving the cycle stability and safety of the battery.

[0010] Meanwhile, the occurrence of the redox reaction of the r-mPh-BCz does not affect the electrochemical process of the positive electrode material itself, and can provide capacity for the battery.

[0011] Preferably, the structural formula of the overcharge prevention additive r-mPh-BCz is one of the following:

[0012]

[0013] The second object of the present invention is to provide a preparation process for the redox couple overcharge prevention additive r-mPh-BCz based on a carbazole-based small-ring organic molecule, specifically:

[0014]

[0015] Compound I, Compound II, cesium carbonate, palladium acetate, 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl and toluene were added to a reaction vessel, and oxygen was removed through a freeze-vacuum-thaw cycle. Then, the mixture was refluxed, condensed, and stirred at a certain temperature for a period of time. After the obtained crude product was cooled to room temperature, it was washed, filtered, and purified with triethylamine, methanol, and water, and then fractionally purified through a sublimator to collect the corresponding dimer product, which was the target product.

[0016] Preferably, the molar ratio of Compound I to Compound II is 1:1; the ratio of Compound I, cesium carbonate, palladium acetate, and 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl is 5:15:0.4:0.8.

[0017] Preferably, the reaction temperature is 100 °C and the reaction time is 12 hours.

[0018] The third object of the present invention is to provide an application of r-mPh-BCz as an overcharge protection additive in a lithium-ion battery, specifically as follows:

[0019] The overcharge protection additive r-mPh-BCz was added in a certain amount to a conventional electrolyte to be fully dissolved in the conventional electrolyte, and an electrolyte with the overcharge protection additive r-mPh-BCz was prepared.

[0020] Preferably, the conventional electrolyte includes an electrolyte salt and a solvent; the solvent includes, but is not limited to, one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, triethylene glycol dimethyl ether, dimethyl sulfone, dimethyl ether, vinylene sulfite, etc., and the electrolyte salt includes, but is not limited to, one or more of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)amide, lithium tetrafluoroborate, lithium bis(oxalato)borate.

[0021] Preferably, the concentration of the conventional electrolyte is 1 mol / L.

[0022] Preferably, the dosage of the overcharge protection additive r-mPh-BCz is 0.01% - 5% of the mass of the electrolyte, and more preferably 0.5% - 3%.

[0023] Preferably, the positive electrode material of the lithium-ion battery includes, but is not limited to, ternary materials or organic positive electrode materials, and the ternary materials include lithium cobaltate, lithium manganate, and nickel cobalt manganese ternary materials; the negative electrode material includes, but is not limited to, graphite or organic negative electrode materials.

[0024] Preferably, the separator of the lithium-ion battery includes, but is not limited to, ion-conducting thin films such as Celgard 2500 or PP film.

[0025] The beneficial effects of the present invention are:

[0026] The overcharge protection additive r-mPh-BCz of the present invention introduces a carbazole-based small-ring organic molecule, which has a relatively high redox potential, and redox reactions occur in the voltage range of 3.5 - 4.5V. Moreover, r-mPh-BCz exhibits the reversibility of the redox reaction and good stability of the reaction intermediate. When r-mPh-BCz is added to the electrolyte as an overcharge protection additive, when the battery charging voltage exceeds 4.2V, r-mPh-BCz in the electrolyte preferentially undergoes a redox reaction to inhibit the decomposition of the electrolyte itself, avoiding capacity attenuation of the battery caused by electrolyte decomposition and even triggering battery thermal runaway. The overcharge protection additive of the present invention effectively improves the cycle stability and safety of the battery without affecting the energy density of the battery, and its preparation process is simple, pollution-free, and has a relatively low cost. Description of the Drawings

[0027] The present invention will be further described in the form of exemplary embodiments, and these exemplary embodiments will be described in detail through the drawings. These embodiments are not restrictive. In these embodiments, the same numbers represent the same structures, where:

[0028] Figure 1 is the mass spectrum of r-2Ph-BCz.

[0029] Figure 2 is the mass spectrum of r-SPh-BCz.

[0030] Figure 3 is the charge-discharge curve of r-2Ph-BCz.

[0031] Figure 4 is the charge-discharge curve of r-SPh-BCz. Detailed Embodiments

[0032] As mentioned above, in view of the deficiencies of the prior art, the inventors of this case have proposed the technical solution of the present invention through long-term research and a large number of practices. The main basis includes at least:

[0033] In order to make the objectives, technical solutions, and advantages of the present invention clearer, the following further details the present invention in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] In a first aspect, an overcharge protection additive r-mPh-BCz based on a redox couple of a carbazole-based small-ring organic molecule is provided, and its structural formula is as follows:

[0035]

[0036] wherein R1, R2, R3, and R4 are each independently one of H, Me, Et, iPr, tBu, OMe, and OEt; Ar =

[0037] In a second aspect, a preparation process of a redox couple overcharge prevention additive r-mPh-BCz based on a carbazole-based small-ring organic molecule is provided, specifically:

[0038]

[0039] Add compound I, compound II, cesium carbonate, palladium acetate, 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl, and toluene into a reaction vessel, remove oxygen through a freeze-vacuum-thaw cycle, and then reflux and condense and stir the mixture at 100 °C for 12 hours; after the obtained crude product is cooled to room temperature, wash, filter, and purify it with triethylamine, methanol, and water, and then fractionally purify it through a sublimator to collect the corresponding dimer product, which is the target product.

[0040] Preferably, the molar ratio of compound I to compound II is 1:1; the ratio of compound I, cesium carbonate, palladium acetate, and 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl is 5:15:0.4:0.8.

[0041] When R1, R2, R3, R4 = H, Ar = the structural formula of the overcharge prevention additive r-1Ph-BCz is as follows:

[0042]

[0043] The synthesis route of the r-1Ph-BCz is as follows, and the specific synthesis steps are:

[0044]

[0045] Add 1,4-dibromobenzene (1.18 g, 5 mmol), 3,3′-bicarbazole (1.66 g, 5 mmol), cesium carbonate (4.89 g, 15 mmol), palladium acetate (89.80 mg, 0.4 mmol), 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (381.4 mg, 0.8 mmol), and 25 mL of toluene into a 100 mL two-neck reaction flask, remove oxygen through a freeze-vacuum-thaw cycle 3 times, and then reflux and condense and stir the mixture at 100 °C for 12 hours. After the obtained crude product is cooled to room temperature, wash, filter, and purify it with triethylamine (50 mL), methanol (50 mL), and water (50 mL), and then fractionally purify it through a sublimator to collect the corresponding dimer product, which is the target product r-1Ph-BCz.

[0046] When R1, R2, R3, R4 = H and Ar = the structural formula of r-2Ph-BCz is as follows:

[0047]

[0048] The synthetic route of the said r-2Ph-BCz is as follows. The specific synthesis steps are:

[0049]

[0050] Add 4,4'-dibromobiphenyl (1.56 g, 5 mmol), 3,3'-bicarbazole (1.66 g, 5 mmol), cesium carbonate (4.89 g, 15 mmol), palladium acetate (90 mg, 0.4 mmol), 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (381.4 mg, 0.8 mmol) and 25 mL of toluene into a 100 mL two-neck reaction flask. Remove oxygen by freeze-vacuum-melt cycle 3 times, and then reflux and condense the mixture at 100 °C with stirring for 12 hours. After the obtained crude product is cooled to room temperature, it is washed, filtered and purified with triethylamine (50 mL), methanol (50 mL) and water (50 mL), and then fractionally purified by a sublimator to collect the corresponding dimer product, which is the target product r-2Ph-BCz.

[0051] When R1, R2, R3, R4 = tBu and Ar = the structural formula of r-SPh-BCz is as follows:

[0052]

[0053] The synthetic route of the said r-SPh-BCz is as follows. The specific synthesis steps are:

[0054]

[0055] Add 4,4'-dibromodiphenyl sulfide (1.72 g, 5 mmol), 6,6'-di-tert-butyl-3,3'-bicarbazole (2.22 g, 5 mmol), palladium acetate (90 mg, 0.4 mmol), 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (381 mg, 0.8 mmol) and 25 mL of toluene into a 100 mL two-neck reaction flask. Remove oxygen by freeze-vacuum-melt cycle 3 times, and then reflux and condense the mixture at 100 °C with stirring for 12 hours. After the obtained crude product is cooled to room temperature, it is washed, filtered and purified with triethylamine (50 mL), methanol (50 mL) and water (50 mL), and then fractionally purified by a sublimator to collect the corresponding dimer product, which is the target product r-SPh-BCz.

[0056] In a third aspect, an application of r-mPh-BCz as an overcharge protection additive in a lithium-ion battery is provided, specifically as follows:

[0057] Add a certain amount of the overcharge protection additive r-mPh-BCz to a conventional electrolyte solution to make it fully dissolve in the conventional electrolyte solution, and prepare an electrolyte solution with the overcharge protection additive r-mPh-BCz.

[0058] Preferably, the conventional electrolyte solution includes an electrolyte salt and a solvent; wherein the solvent includes, but is not limited to, one or a mixture of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, triethylene glycol dimethyl ether, dimethyl sulfone, dimethyl ether, vinylene sulfite, etc., and the electrolyte salt includes, but is not limited to, one or a mixture of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)amide, lithium tetrafluoroborate, lithium bis(oxalato)borate.

[0059] Preferably, the concentration of the conventional electrolyte solution is 1 mol / L.

[0060] Preferably, the dosage of the overcharge protection additive r-mPh-BCz is 0.01%-5% of the mass of the electrolyte solution, and more preferably 0.5%-3%.

[0061] Preferably, the positive electrode material of the lithium-ion battery includes, but is not limited to, ternary materials or organic positive electrode materials, and the ternary materials include lithium iron phosphate, lithium cobaltate, lithium manganate, nickel cobalt manganese ternary materials; the negative electrode material includes, but is not limited to, graphite or organic negative electrode materials.

[0062] Preferably, the separator of the lithium-ion battery includes, but is not limited to, ion-conducting thin films such as Celgard 2500 or PP films.

[0063] The following description is for enabling a person of ordinary skill in the art to make and use the present invention, and this description is provided in the context of a specific application and its requirements. For a person of ordinary skill in the art, it is obvious that various changes can be made to the disclosed embodiments. Additionally, without departing from the spirit and scope of the present invention, the general principles defined in the present invention can be applied to other embodiments and application scenarios. Therefore, the present invention is not limited to the disclosed embodiments, but should be given the broadest scope consistent with the scope of the invention patent.

[0064] Example 1: Synthesis of the overcharge protection additive r-2Ph-BCz and its electrochemical performance test

[0065] 1.1 Synthesis of r-2Ph-BCz

[0066] 4,4'-Dibromobiphenyl (1.56 g, 5 mmol), 3,3′-bicarbazole (1.66 g, 5 mmol), cesium carbonate (4.89 g, 15 mmol), palladium acetate (90 mg, 0.4 mmol), 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (381 mg, 0.8 mmol) and 25 mL of toluene were added to a 100 mL two-neck reaction flask. The oxygen was removed 3 times by freeze-vacuum-melt cycle, and then the mixture was refluxed, condensed and stirred at 100 °C for 12 hours. After the obtained crude product was cooled to room temperature, it was washed, filtered and purified with triethylamine (50 mL), methanol (50 mL) and water (50 mL), and then fractionally purified by a sublimator to collect the corresponding dimer product, which was the target product r-2Ph-BCz. Its mass spectrometry data is as Figure 1 shown.

[0067] The synthesis route is as follows:

[0068]

[0069] 1.2 Electrochemical performance test of r-2Ph-BCz

[0070] Using r-2Ph-BCz as the positive electrode active material, it was mixed with a conductive agent and a binder in a certain mass ratio (6-9: 0.5-3: 0.5-3), added to the solvent N,N-dimethylpyrrolidone solvent (NMP) and mixed evenly, and coated on the positive electrode current collector with a certain thickness (30-100 um) and dried. After drying, it was cut into electrode sheets of appropriate size as the r-2Ph-BCz electrode sheet; using the r-2Ph-BCz electrode sheet as the positive electrode, lithium metal as the negative electrode, a solution of 1 M lithium hexafluorophosphate in EC:DEC = 1:1 as the electrolyte, and Celgard 2500 film as the separator, a button cell was assembled; in the Blue Electric test system, the electrochemical performance of the battery was tested at a rate of 2C.

[0071] Figure 3 is the charge-discharge curve of r-2Ph-BCz. The overcharge prevention additive r-2Ph-BCz has a relatively high redox potential and has stable and reversible redox reaction properties in the voltage range of 3.5-4.5 V. At the same time, while protecting the electrode material as an overcharge protection agent, it can provide a certain reversible charge-discharge capacity and improve the overall energy density of the battery.

[0072] Example 2: Synthesis and electrochemical performance test of overcharge prevention additive r-SPh-BCz

[0073] 2.1 Synthesis of r-SPh-BCz

[0074] 4,4'-Dibromodiphenyl sulfide (1.72 g, 5 mmol), 6,6′-di-tert-butyl-3,3′-bicarbazole (2.22 g, 5 mmol), cesium carbonate (4.89 g, 15 mmol), palladium acetate (90 mg, 0.4 mmol), 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (381 mg, 0.8 mmol) and 25 mL of toluene were added to a 100 mL two-necked reaction flask. The oxygen was removed 3 times through the freeze-vacuum-melt cycle, and then the mixture was refluxed and condensed with stirring at 100 °C for 12 hours. After the obtained crude product was cooled to room temperature, it was washed, filtered and purified with triethylamine (50 mL), methanol (50 mL) and water (50 mL), and then fractionally purified by a sublimator to collect the corresponding dimer product, which was the target product r-SPh-BCz. Its mass spectrometry data is as Figure 2 shown.

[0075] The synthesis route is as follows:

[0076]

[0077] 2.2 Electrochemical performance test of r-SPh-BCz

[0078] Using r-SPh-BCz as the positive electrode active material, it was mixed with a conductive agent and a binder in a certain mass ratio (6-9: 0.5-3: 0.5-3), added to the solvent N,N-dimethylpyrrolidone solvent (NMP) and mixed evenly, and coated on the positive electrode current collector with a certain thickness (30-100 um) and dried. After drying, it was cut into electrode sheets of appropriate size as the r-SPh-BCz electrode sheet; using the r-SPh-BCz electrode sheet as the positive electrode, lithium metal as the negative electrode, a solution of 1M lithium hexafluorophosphate in EC:DEC = 1:1 as the electrolyte, and Celgard 2500 film as the separator, a button cell was assembled; in the BlueTEC test system, the electrochemical performance of the battery was tested at a rate of 2C.

[0079] Figure 4 is the charge-discharge curve of r-SPh-BCz. As an overcharge prevention additive, r-SPh-BCz has a relatively high redox potential and has stable and reversible redox reaction properties in the voltage range of 3.5-4.5 V. At the same time, as an overcharge protection agent, it can protect the electrode material and provide a certain reversible charge-discharge capacity, improving the overall energy density of the battery.

[0080] In the following Application Examples 1-6, the electrolyte is 1 mole of lithium hexafluorophosphate dissolved in a 1L solution of ethylene carbonate and diethyl carbonate with a volume ratio of 1:1. The positive electrode is lithium iron phosphate: conductive carbon black: PVDF binder with a mass ratio of 7:2:1. An appropriate amount of the solvent N,N-dimethylpyrrolidone is added and mixed into a uniform slurry, which is then scraped onto the current collector aluminum foil. After drying, it is cut into circular pieces as the positive electrode. The negative electrode is a lithium foil. The separator is a Celgard 2500 separator.

[0081] Example 2: Synthesis of overcharge prevention additive r-1Ph-BCz

[0082]

[0083] 1,4-Dibromobenzene (1.18 g, 5 mmol), 3,3′-bicarbazole (1.66 g, 5 mmol), cesium carbonate (4.89 g, 15 mmol), palladium acetate (89.80 mg, 0.4 mmol), 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl (381.4 mg, 0.8 mmol) and 25 mL of toluene were added to a 100 mL two-neck reaction flask. Oxygen was removed by freeze-vacuum-thaw cycle 3 times, and then the mixture was refluxed and stirred at 100 °C for 12 hours. After the obtained crude product was cooled to room temperature, it was washed, filtered and purified with triethylamine (50 mL), methanol (50 mL) and water (50 mL), and then fractionally purified by a sublimator to collect the corresponding dimer product, which is the target product r-1Ph-BCz.

[0084] Application Example 1: Application of overcharge prevention additive r-2Ph-BCz in lithium-ion batteries

[0085] Weigh an amount of r-2Ph-BCz synthesized in Example 1 with a mass fraction of 1% in the electrolyte and add it to the conventional electrolyte for miscibility to prepare an electrolyte containing an overcharge prevention additive r-2Ph-BCz with a mass fraction of 1%; assemble the battery with the miscible electrolyte containing r-2Ph-BCz with a mass fraction of 1%, the positive and negative electrodes and the separator together.

[0086] Application Example 2: Application of overcharge prevention additive r-2Ph-BCz in lithium-ion batteries

[0087] Weigh an amount of r-2Ph-BCz synthesized in Example 1 with a mass fraction of 2% in the electrolyte and add it to the conventional electrolyte for miscibility to prepare an electrolyte containing an overcharge prevention additive r-2Ph-BCz with a mass fraction of 2%; assemble the battery with the miscible electrolyte containing r-2Ph-BCz with a mass fraction of 2%, the positive and negative electrodes and the separator together.

[0088] Application Example 3: Application of overcharge prevention additive r-2Ph-BCz in lithium-ion batteries

[0089] Weigh out the amount of r-2Ph-BCz synthesized in Example 1 with a mass fraction of 3% in the electrolyte and add it to the conventional electrolyte for miscibility to prepare an electrolyte containing an overcharge prevention additive of r-2Ph-BCz with a mass fraction of 3%; assemble a battery together with the miscible electrolyte containing r-2Ph-BCz with a mass fraction of 3%, the positive and negative electrodes, and the separator.

[0090] Application Example 4: Application of the overcharge prevention additive r-SPh-BCz in a lithium-ion battery

[0091] Weigh out the amount of r-SPh-BCz synthesized in Example 2 with a mass fraction of 1% in the electrolyte and add it to the conventional electrolyte for miscibility to prepare an electrolyte containing an overcharge prevention additive of r-SPh-BCz with a mass fraction of 1%; assemble a battery together with the miscible electrolyte containing r-SPh-BCz with a mass fraction of 1%, the positive and negative electrodes, and the separator.

[0092] Application Example 5: Application of the overcharge prevention additive r-SPh-BCz in a lithium-ion battery

[0093] Weigh out the amount of r-SPh-BCz synthesized in Example 2 with a mass fraction of 2% in the electrolyte and add it to the conventional electrolyte for miscibility to prepare an electrolyte containing an overcharge prevention additive of r-SPh-BCz with a mass fraction of 2%; assemble a battery together with the miscible electrolyte containing r-SPh-BCz with a mass fraction of 2%, the positive and negative electrodes, and the separator.

[0094] Application Example 6: Application of the overcharge prevention additive r-SPh-BCz in a lithium-ion battery Weigh out the amount of r-SPh-BCz synthesized in Example 2 with a mass fraction of 3% in the electrolyte and add it to the conventional electrolyte for miscibility to prepare an electrolyte containing an overcharge prevention additive of r-SPh-BCz with a mass fraction of 3%; assemble a battery together with the miscible electrolyte containing r-SPh-BCz with a mass fraction of 3%, the positive and negative electrodes, and the separator.

Claims

1. An overcharge prevention electrolyte additive r-mPh-BCz based on carbazole-based small-ring organic molecules, with a dosage of 0.01% - 5% of the mass of the electrolyte when in use, characterized in that, The general structural formula of r-mPh-BCz is as follows: ； wherein each of R1, R2, R3, and R4 is independently one of H, Me, Et, iPr, tBu, OMe, and OEt; Ar = or or .

2. The overcharge prevention electrolyte additive r-mPh-BCz based on a carbazole-based small-ring organic molecule according to claim 1, characterized in that, One of the general structural formulas of r-mPh-BCz is as follows: 、 、 。 3. Preparation method of redox couple overcharge prevention electrolyte additive r-mPh-BCz based on carbazole-based small-ring organic molecules, characterized in that Specifically, the method is as follows: ； Compound I, Compound II, cesium carbonate, palladium acetate, 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl and toluene are added to a reaction vessel, and oxygen is removed through a freeze-vacuum-thaw cycle. Then, the mixture is refluxed, condensed and stirred at a certain temperature for a period of time. After the obtained crude product is cooled to room temperature, it is washed, filtered and purified with triethylamine, methanol and water, and then fractionally purified by a sublimator to collect the corresponding dimer product, which is the target product.

4. The method according to claim 3, characterized in that The molar ratio of Compound I to Compound II is 1:1; the molar ratio of Compound I, cesium carbonate, palladium acetate, and 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl is 5:15:0.4:0.

8.

5. The method according to claim 3 or 4, characterized in that The reaction temperature is 100 °C and the reaction time is 12 hours.

6. The application of the overcharge protection electrolyte additive r-mPh-BCz based on carbazole-based small-ring organic molecules according to claim 1 or 2 in a lithium-ion battery.

7. The application according to claim 6, wherein Specifically, the r-mPh-BCz described in claim 1 or 2 is added to a conventional electrolyte to make it fully dissolved, and an electrolyte with an overcharge protection electrolyte additive is prepared.

8. The application according to claim 7, wherein The dosage of the overcharge protection electrolyte additive r-mPh-BCz is 0.01%-5% of the mass of the electrolyte.

9. The application according to claim 8, wherein The dosage of the overcharge protection electrolyte additive r-mPh-BCz is 0.5%-3% of the mass of the electrolyte.

10. The application according to claim 7, characterized in that The conventional electrolyte includes an electrolyte salt and a solvent; the solvent includes one or a mixture of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, triethylene glycol dimethyl ether, dimethyl sulfone, dimethyl ether, vinylene sulfite, etc., and the electrolyte salt includes one or a mixture of lithium hexafluorophosphate, lithium perchlorate, lithium bis(trifluoromethylsulfonyl)amide, lithium tetrafluoroborate, lithium bis(oxalato)borate, etc.; The positive electrode material of the lithium-ion battery includes a ternary material or an organic positive electrode material, and the ternary material includes one or a mixture of lithium cobaltate, lithium manganate, nickel cobalt manganese ternary materials; the negative electrode material includes graphite or an organic negative electrode material; The separator of the lithium-ion battery includes Celgard 2500 or a PP membrane.

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