Overcharge safety electrolyte for lithium ion battery and lithium ion battery

Abstract

The invention provides an overcharge safety electrolyte for a lithium ion battery and the lithium ion battery, and relates to the technical field of lithium battery electrolytes. The overcharge safe electrolyte for the lithium ion battery comprises the following components: lithium salt, a solvent, a film-forming additive and an overcharge-preventing additive, the overcharge-preventing additive is a compound with a cyclohexyl organic functional group, and the weight percentage of the overcharge-preventing additive in the overcharge safe electrolyte is 0.5 wt%-5wt%. The electrolyte using the compound with the cyclohexyl organic functional group as the anti-overcharge additive can effectively protect the lithium ion battery under the overcharge condition, and the internal resistance of the battery is rapidly increased to enable the voltage to rapidly rise to the overcharge cut-off voltage in a short time, so that the temperature rise of the battery caused by long-time overcharge can be avoided, and the service life of the lithium ion battery is prolonged. Therefore, the thermal runaway problem is considered from the temperature perspective, and the safety of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of lithium battery electrolytes, and in particular to an overcharge safety electrolyte for lithium ion batteries and a lithium ion battery. Background Art

[0002] Lithium iron phosphate batteries have the advantages of safety, high temperature resistance, and low cost, and have been widely used in the fields of energy storage and power batteries. However, despite the good safety of lithium iron phosphate batteries, when they are overcharged or subjected to electrical abuse, the battery cells still have the risk of thermal runaway. This risk is more prominent in large-capacity lithium iron phosphate square shell batteries, leading to serious battery fire safety accidents.

[0003] In the prior art, improving the overcharge resistance of lithium iron phosphate batteries is generally achieved by adding anti-overcharge additives to the electrolyte. Common anti-overcharge additives mainly include redox pairs, such as ferrocene, polypyridine, dimethylhydroxybenzene, etc., which can be oxidized at the positive electrode under high voltage, and the oxidation products diffuse to the negative electrode and are reduced, and the reduction products diffuse to the negative electrode and are oxidized. The working principle of the redox reaction is to form a circuit inside the battery, consume the excess charge accumulated on the electrode, thereby limiting the increase of the battery voltage, keeping the battery voltage constant, and achieving the purpose of protecting the battery from overcharging.

[0004] However, although the redox pair anti-overcharge additives used in the prior art provide overcharge protection by consuming charge and limiting voltage increase, the temperature will still rise during actual use and thermal runaway may still occur. Therefore, the current lithium ion overcharge protection effect needs further study. Summary of the invention

[0005] The present application provides an overcharge safety electrolyte for lithium ion batteries and a lithium ion battery, so as to solve the problem that the current anti-overcharge additives cannot well achieve anti-overcharge protection.

[0006] In a first aspect, the present application provides an overcharge safety electrolyte for a lithium-ion battery, wherein the components of the overcharge safety electrolyte include: a lithium salt, a solvent, a film-forming additive and an anti-overcharge additive, wherein the anti-overcharge additive is a compound having a cyclohexyl organic functional group, wherein the weight percentage of the anti-overcharge additive in the overcharge safety electrolyte is 0.5wt%-5wt%.

[0007] Through the above scheme, the compound with cyclohexyl organic functional group undergoes ring-opening polymerization under overcharge conditions. This polymerization reaction causes the polymerization product to adhere to the electrode surface, thereby increasing the internal resistance of the battery. Since the polymerization product adheres to the electrode surface, the internal resistance of the battery is increased, which helps to suppress the current and prevent the battery from continuing to absorb more charge under overcharge conditions, thereby avoiding safety problems caused by overcharge. Since the internal resistance of the battery can increase rapidly, the battery voltage will increase rapidly in a short period of time and reach the overcharge cut-off protection voltage, which can avoid long-term overcharging causing the battery temperature to rise. By quickly reaching the overcharge protection voltage, the battery temperature can be prevented from rising sharply due to charging for too long, thereby solving the thermal runaway problem caused by the sharp rise in battery temperature and better protecting the safety of lithium-ion batteries.

[0008] In a possible design, the overcharge prevention additive is composed of one or more of cyclohexyl dimethyl phosphate, cyclohexyl diethyl phosphoramidite, cyclohexyl dicarboxylic acid dimethyl ester, and cyclohexyl ethyl acetate.

[0009] Through the above scheme, any one of cyclohexyl dimethyl phosphate, cyclohexyl diethyl aminophosphorate, cyclohexyl dimethyl carboxylate, and cyclohexyl ethyl acetate contains a cyclohexyl organic functional group. According to different situations, any one or a combination of them can be selected to form an anti-overcharge additive. The cyclic group in the anti-overcharge additive can undergo a ring-opening polymerization reaction under overcharge conditions, and the polymerization product is attached to the electrode surface, increasing the internal resistance of the battery, thereby suppressing the current and solving the safety problem caused by overcharge. At the same time, this reaction can quickly increase the internal resistance of the battery, so that the battery voltage rises rapidly in a short time to reach the overcharge cut-off protection voltage, avoiding the temperature rise caused by charging for too long, thereby solving the problem of thermal runaway caused by the rapid rise in battery temperature, and better achieving the purpose of protecting the safety of lithium-ion batteries.

[0010] In a possible design, the overcharge prevention additive is cyclohexyl dimethyl phosphate, and the weight percentage of cyclohexyl dimethyl phosphate is 2 wt %.

[0011] Through the above scheme, cyclohexyl dimethyl phosphate is used as an anti-overcharge additive. Its working principle is that when the battery is overcharged, the cyclic group undergoes a ring-opening polymerization reaction, and the generated polymer adheres to the electrode surface, increasing the internal resistance of the battery, thereby suppressing the current and preventing the battery from overcharging. This ring-opening polymerization reaction can quickly increase the internal resistance of the battery, so that the battery voltage can quickly increase in a short period of time to reach the overcharge cut-off protection voltage, avoiding the temperature rise caused by charging for too long, thereby solving the problem of thermal runaway caused by a sharp rise in battery temperature, and better achieving the purpose of protecting the safety of lithium-ion batteries. In the overcharge safety electrolyte, the addition amount of cyclohexyl dimethyl phosphate is 2wt%, which means that in 100 grams of electrolyte, the mass of cyclohexyl dimethyl phosphate is 2 grams. This addition amount can ensure that the battery is adequately protected when overcharged, and will not have a negative impact on the normal charge and discharge performance of the battery.

[0012] In a possible design, in the overcharge safety electrolyte, the weight percentage of lithium salt is 5wt%-30wt%, the weight percentage of solvent is 70wt%-90wt%, and the weight percentage of film-forming additive is 0.5wt%-5wt%.

[0013] Through the above scheme, the weight percentage of each component should add up to nearly 100% to ensure that the total weight of the electrolyte is 100%. Such a design aims to balance the electrochemical performance, safety and cost-effectiveness of the electrolyte. Lithium salts provide the necessary lithium ions, solvents provide a medium for ion migration, film-forming additives improve the electrode interface, and anti-overcharge additives provide overcharge protection. By precisely controlling the proportion of each component, the performance of the electrolyte can be optimized to ensure that the battery maintains good performance and safety under normal working and overcharge conditions.

[0014] In a possible design, the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0015] Through the above scheme, lithium hexafluorophosphate is the most widely used lithium salt in lithium-ion battery electrolyte, with good ionic conductivity and electrochemical stability. LiFSI has high stability, excellent low-temperature performance and environmental friendliness. LiTFSI has suitable conductivity, high thermal stability and electrochemical stability, and has a low probability of side reactions and does not produce corrosive gases. Selecting one or more of them as lithium salts can provide the main lithium ion component for the electrolyte, which is responsible for supporting the battery's charge and discharge chemical reactions.

[0016] In one possible design, the lithium salt is composed of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the concentration ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 10:2.

[0017] Through the above scheme, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) are selected to form lithium salts, and the synergistic effect of the two lithium salts is taken into account. Lithium hexafluorophosphate (LiPF6) is the most commonly used lithium salt in lithium-ion batteries and is widely used due to its good ionic conductivity and cost-effectiveness. However, LiPF6 is not stable enough at high temperatures and may react with water to generate harmful hydrofluoric acid (HF). Lithium bis(fluorosulfonyl)imide (LiFSI) is known for its better thermal and electrochemical stability, but may be corrosive to aluminum current collectors. Mixed lithium salt electrolytes will improve the electrochemical performance of the battery, such as reducing charge transfer resistance and reducing self-discharge, thereby improving the efficiency and cycle stability of the battery. The addition of LiFSI may help reduce the generation of gas at high temperatures and improve the safety of the battery. At the same time, the SEI film formed by LiFSI may be thinner and more uniform, which helps to reduce the damage of dendrites to the battery structure and improve stability. By mixing LiPF6 and LiFSI in a ratio of 10:2, it is expected that the high stability of LiFSI can be used to make up for the deficiency of LiPF6 at high temperatures while maintaining the cost-effectiveness of LiPF6. This ratio may help improve the overall performance of the electrolyte without sacrificing too much cost.

[0018] In one possible design, the solvent includes one or more of cyclic ethylene carbonate, cyclic propylene carbonate, chain dimethyl carbonate, chain ethyl methyl carbonate, chain diethyl carbonate, ethyl acetate, and methyl butyrate.

[0019] Through the above scheme, the solvent selection includes one or more of cyclic ethylene carbonate (EC), cyclic propylene carbonate (PC), chain dimethyl carbonate (DMC), chain ethyl methyl carbonate (EMC), chain diethyl carbonate (DEC), ethyl acetate (EA), and methyl butyrate (MB), as a carrier for transporting lithium ions, solvating the electrolyte salt to ensure the transmission of lithium ions. Among them, EC is a cyclic carbonate with a high dielectric constant, which makes lithium salt more soluble. In lithium battery electrolytes, EC can be used as a high-permittivity electrolyte component and mixed with other solvents such as DMC, EMC, and DEC to reduce viscosity and melting point. PC is also a cyclic carbonate, and compared with EC, PC has a higher dielectric constant and chemical stability. PC can improve the stability of the cathode surface in the electrolyte, has a strong dissolving effect on lithium salts, and has a good passivation effect on the anode surface. DMC is a chain carbonate with low viscosity and good electrochemical stability. DMC can be mixed with a variety of lithium salts to form a stable electrolyte solution, and can reduce the viscosity of the electrolyte and increase the energy density of the battery. EMC combines the characteristics of cyclic and chain carbonates and has good comprehensive performance. DEC is a chain carbonate with low viscosity and good low-temperature performance. EA is a commonly used organic solvent with good solubility and electrochemical properties. MB, as a carboxylic acid ester solvent, can be used in electrolytes to improve the conductivity of the electrolyte and battery performance.

[0020] In a possible design, the solvent consists of cyclic ethylene carbonate, chain ethyl methyl carbonate and chain dimethyl carbonate, and the concentration ratio of the cyclic ethylene carbonate, chain ethyl methyl carbonate and chain dimethyl carbonate is 3:3:4.

[0021] Through the above scheme, the solvent is composed of cyclic ethylene carbonate (EC), chain ethyl methyl carbonate (EMC) and chain dimethyl carbonate (DMC), and their concentration ratio is 3:3:4. The design of this mixed solvent system takes into account the characteristics of different carbonates to achieve the purpose of optimizing the performance of the electrolyte. Cyclic ethylene carbonate (EC) has a high dielectric constant and ionic conductivity, which helps to increase the lithium ion migration number of the electrolyte, thereby improving the charge and discharge efficiency of the battery. Cyclic carbonates such as EC can form a stable SEI film on the surface of the negative electrode, which is crucial for protecting the electrode and improving the cycle stability of the battery. Chain carbonates such as DMC and EMC have low viscosity and good electrochemical stability, which helps to improve the low temperature performance of the electrolyte and the safety of the battery. By adjusting the ratio of EC, EMC and DMC, the cost can be balanced while maintaining the high performance of the electrolyte. EC is usually more expensive, while DMC and EMC are relatively low in price, and the cost can be controlled through reasonable proportioning. At the same time, this mixed solvent system can combine the advantages of cyclic and chain carbonates to improve the battery's charge and discharge performance, cycle stability and safety performance.

[0022] In a possible design, the film-forming additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, vinyl sulfite, propylene sulfite, γ-butyrolactone, and adiponitrile.

[0023] Through the above scheme, the film-forming additive includes one or more of vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfite (ES), propylene sulfite (PS), γ-butyrolactone (GBL) and adiponitrile (GN), which can form a protective film on the electrode surface of the battery, which helps to improve the charge and discharge efficiency, cycle stability and safety of the battery. VC is a widely used film-forming additive that can form a stable phase interface (SEI) layer on the anode surface to improve the electrochemical reaction performance. As a film-forming additive, ES has good film-forming ability and has a significant effect on improving the low-temperature performance of lithium-ion batteries. It is also used as a film-forming additive for all-solid-state lithium-ion batteries. PS is a sulfur-containing organic solvent, which has stronger reducibility at the graphite negative electrode interface than the corresponding carbonate, and the reduction potential of PS is also significantly higher, which helps to form a stable SEI layer. GBL, as a film-forming additive in lithium batteries, helps to form a stable SEI layer and improve battery performance. GN, as an additive, can effectively stabilize the interface between lithium metal anode and nickel-rich NCM cathode and improve battery performance. The film-forming additive can be selected and optimized according to the specific needs and performance goals of the battery.

[0024] In a second aspect, the present application provides a lithium-ion battery, comprising a positive electrode material, a negative electrode material, a diaphragm material, and any of the above-mentioned overcharge safety electrolytes.

[0025] The beneficial effects of the lithium-ion battery provided in the second aspect and each possible design of the second aspect can refer to the beneficial effects brought about by the first aspect and each possible implementation method of the first aspect, which will not be repeated here.

[0026] The above description is only an overview of the technical solution of the embodiment of the present application. In order to more clearly understand the technical means of the embodiment of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the embodiment of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is a schematic diagram of voltage and temperature results in the battery test in Example 2 of the present application.

[0029] Figure 2 This is a schematic diagram of voltage and temperature results in the battery test in Comparative Example 2 of the present application. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used in the specification of the application are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification, claims and drawings of this application are intended to cover non-exclusive inclusions.

[0032] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase "embodiments" in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0033] The term "and / or" in this article is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0034] In the description of the present application, unless otherwise specified, "plurality" means more than two (including two), and similarly, "multiple groups" means more than two groups (including two).

[0035] As can be seen from the background technology, the overcharge protection performance of the battery needs to be considered in the production of lithium iron phosphate batteries, so as to improve the safety of the battery.

[0036] In the related art, the anti-overcharge additives used can consume charge through redox reactions, thereby limiting the increase in battery voltage. However, this limitation will cause the battery voltage to remain constant, making it difficult to reach the cutoff protection voltage for battery charging. Moreover, under a constant high voltage, the redox pair will undergo a persistent redox reaction, thereby generating a large amount of reaction heat, causing the battery temperature to rise sharply and trigger thermal runaway. Therefore, the redox pair anti-overcharge additives only limit the increase in battery voltage, but do not fully consider the changes in battery temperature. In the related art, there are also some electropolymerization additives that form a polymer film by undergoing an electropolymerization reaction on the electrode surface at a certain voltage. The film covers the electrode surface to isolate the electrode. Electrons can pass through the polymer film, but lithium ions cannot pass through the polymer film, thereby limiting the charging current to achieve the purpose of protecting the battery from overcharging. However, current electropolymerization additives cannot prevent thermal runaway very well.

[0037] In view of this, the embodiment of the present application provides an overcharge safety electrolyte and a lithium ion battery for lithium ion batteries, wherein the overcharge safety electrolyte includes a compound having a cyclohexyl organic functional group, and the compound having a cyclohexyl organic functional group undergoes a ring-opening polymerization reaction under overcharge conditions. This polymerization reaction causes the polymer product to adhere to the electrode surface, thereby increasing the internal resistance of the battery, which helps to suppress the current and prevent the battery from continuing to absorb more charge under overcharge conditions, thereby avoiding safety problems caused by overcharge. In addition, the compound having a cyclohexyl organic functional group allows the internal resistance of the battery to increase rapidly, and correspondingly, the battery voltage will rise rapidly in a short time to reach the overcharge cut-off protection voltage, which can avoid long-term overcharging causing the battery temperature to rise, thereby avoiding thermal runaway, thereby greatly improving the safety of the battery. Therefore, the compound having a cyclohexyl organic functional group in this embodiment is used as an anti-overcharge additive to protect the battery from both current and temperature perspectives, thereby achieving battery safety.

[0038] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings.

[0039] Example 1

[0040] The present embodiment provides an overcharge safety electrolyte for a lithium-ion battery. The components of the overcharge safety electrolyte include: a lithium salt, a solvent, a film-forming additive and an anti-overcharge additive. The anti-overcharge additive is a compound having a cyclohexyl organic functional group. The weight percentage of the anti-overcharge additive in the overcharge safety electrolyte is 0.5wt%-5wt%.

[0041] Overcharge safety electrolyte is an electrolyte designed specifically to improve the safety of lithium-ion batteries. It prevents battery overcharge by adding specific anti-overcharge additives, thereby avoiding possible safety problems.

[0042] In this embodiment, the compound of the cyclohexyl organic functional group in the anti-overcharge additive undergoes a ring-opening polymerization reaction under overcharge conditions. This polymerization reaction causes the polymerization product to adhere to the electrode surface, thereby increasing the internal resistance of the battery. Since the polymerization product adheres to the electrode surface, the internal resistance of the battery is increased, which helps to suppress the current and prevent the battery from continuing to absorb more charge under overcharge conditions, thereby avoiding safety problems caused by overcharging. Since the internal resistance of the battery can increase rapidly, correspondingly, the battery voltage will rise rapidly in a short period of time and reach the overcharge cut-off protection voltage, which can avoid long-term overcharging causing the battery temperature to rise. By quickly reaching the overcharge protection voltage, a sharp rise in battery temperature due to excessively long-term charging can be avoided, thereby solving the thermal runaway problem caused by a sharp rise in battery temperature and better protecting the safety of lithium-ion batteries.

[0043] The overcharge prevention additive may be composed of one or more of cyclohexyl dimethyl phosphate, cyclohexyl diethyl phosphoramidite, cyclohexyl dicarboxylic acid dimethyl ester, and ethyl cyclohexyl acetate.

[0044] Through the above scheme, any one of cyclohexyl dimethyl phosphate, cyclohexyl diethyl aminophosphorate, cyclohexyl dimethyl carboxylate, and cyclohexyl ethyl acetate contains a cyclohexyl organic functional group. According to different situations, any one or a combination of them can be selected to form an anti-overcharge additive. The cyclic group in the anti-overcharge additive can undergo a ring-opening polymerization reaction under overcharge conditions, and the polymerization product is attached to the electrode surface, increasing the internal resistance of the battery, thereby suppressing the current and solving the safety problem caused by overcharge. At the same time, this reaction can quickly increase the internal resistance of the battery, so that the battery voltage rises rapidly in a short time to reach the overcharge cut-off protection voltage, avoiding the temperature rise caused by charging for too long, thereby solving the problem of thermal runaway caused by the rapid rise in battery temperature, and better achieving the purpose of protecting the safety of lithium-ion batteries.

[0045] In this embodiment, the overcharge prevention additive is cyclohexyl dimethyl phosphate, and the weight percentage of cyclohexyl dimethyl phosphate is 2 wt %.

[0046] Through the above scheme, cyclohexyl dimethyl phosphate is used as an anti-overcharge additive. Its working principle is that when the battery is overcharged, the cyclic group undergoes a ring-opening polymerization reaction, and the generated polymer adheres to the electrode surface, increasing the internal resistance of the battery, thereby suppressing the current and preventing the battery from overcharging. This ring-opening polymerization reaction can quickly increase the internal resistance of the battery, so that the battery voltage can quickly increase in a short period of time to reach the overcharge cut-off protection voltage, avoiding the temperature rise caused by charging for too long, thereby solving the problem of thermal runaway caused by a sharp rise in battery temperature, and better achieving the purpose of protecting the safety of lithium-ion batteries. In the overcharge safety electrolyte, the addition amount of cyclohexyl dimethyl phosphate is 2wt%, which means that in 100 grams of electrolyte, the mass of cyclohexyl dimethyl phosphate is 2 grams. This addition amount can ensure that the battery is adequately protected when overcharged, and will not have a negative impact on the normal charge and discharge performance of the battery.

[0047] In this embodiment, in the overcharge safety electrolyte, the weight percentage of lithium salt is 5wt%-30wt%, the weight percentage of solvent is 70wt%-90wt%, and the weight percentage of film-forming additive is 0.5wt%-5wt%.

[0048] Through the above scheme, the weight percentage of each component should add up to nearly 100% to ensure that the total weight of the electrolyte is 100%. Such a design aims to balance the electrochemical performance, safety and cost-effectiveness of the electrolyte. Lithium salts provide the necessary lithium ions, solvents provide a medium for ion migration, film-forming additives improve the electrode interface, and anti-overcharge additives provide overcharge protection. By precisely controlling the proportion of each component, the performance of the electrolyte can be optimized to ensure that the battery maintains good performance and safety under normal working and overcharge conditions.

[0049] The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0050] Through the above scheme, lithium hexafluorophosphate is the most widely used lithium salt in lithium-ion battery electrolyte, with good ionic conductivity and electrochemical stability. LiFSI has high stability, excellent low-temperature performance and environmental friendliness. LiTFSI has suitable conductivity, high thermal stability and electrochemical stability, and has a low probability of side reactions and does not produce corrosive gases. Selecting one or more of them as lithium salts can provide the main lithium ion component for the electrolyte, which is responsible for supporting the battery's charge and discharge chemical reactions.

[0051] In this embodiment, the lithium salt is composed of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the concentration ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide is 10:2.

[0052] Through the above scheme, lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide are selected to form lithium salts, and the synergistic effect of the two lithium salts is taken into account. Lithium hexafluorophosphate (LiPF6) is the most commonly used lithium salt in lithium-ion batteries and is widely used due to its good ionic conductivity and cost-effectiveness. However, LiPF6 is not stable enough at high temperatures and may react with water to generate harmful hydrofluoric acid (HF). Lithium bis(fluorosulfonyl)imide (LiFSI) is known for its better thermal and electrochemical stability, but may be corrosive to aluminum current collectors. Mixed lithium salt electrolytes may improve the electrochemical performance of batteries, such as reducing charge transfer resistance and reducing self-discharge, thereby improving battery efficiency and cycle stability. The addition of LiFSI may help reduce gas generation at high temperatures and improve battery safety. At the same time, the SEI film formed by LiFSI may be thinner and more uniform, which helps to reduce the damage of dendrites to the battery structure and improve stability. By mixing LiPF6 and LiFSI in a ratio of 10:2, it is expected to use the high stability of LiFSI to make up for the shortcomings of LiPF6 at high temperatures while maintaining the cost-effectiveness of LiPF6. This ratio helps improve the overall performance of the electrolyte without sacrificing too much cost.

[0053] The solvent includes one or more of cyclic ethylene carbonate, cyclic propylene carbonate, chain dimethyl carbonate, chain ethyl methyl carbonate, chain diethyl carbonate, ethyl acetate, and methyl butyrate.

[0054] Through the above scheme, the solvent selection includes one or more of cyclic ethylene carbonate (EC), cyclic propylene carbonate (PC), chain dimethyl carbonate (DMC), chain ethyl methyl carbonate (EMC), chain diethyl carbonate (DEC), ethyl acetate (EA), and methyl butyrate (MB), as a carrier for transporting lithium ions, solvating the electrolyte salt to ensure the transmission of lithium ions. Among them, EC is a cyclic carbonate with a high dielectric constant, which makes lithium salt more soluble. In lithium battery electrolytes, EC can be used as a high-permittivity electrolyte component and mixed with other solvents such as DMC, EMC, and DEC to reduce viscosity and melting point. PC is also a cyclic carbonate, and compared with EC, PC has a higher dielectric constant and chemical stability. PC can improve the stability of the cathode surface in the electrolyte, has a strong dissolving effect on lithium salts, and has a good passivation effect on the anode surface. DMC is a chain carbonate with low viscosity and good electrochemical stability. DMC can be mixed with a variety of lithium salts to form a stable electrolyte solution, and can reduce the viscosity of the electrolyte and increase the energy density of the battery. EMC combines the characteristics of cyclic and chain carbonates and has good comprehensive performance. DEC is a chain carbonate with low viscosity and good low-temperature performance. EA is a commonly used organic solvent with good solubility and electrochemical properties. MB, as a carboxylic acid ester solvent, can be used in electrolytes to improve the conductivity of the electrolyte and battery performance.

[0055] In this embodiment, the solvent consists of cyclic ethylene carbonate, chain ethyl methyl carbonate and chain dimethyl carbonate, and the concentration ratio of the cyclic ethylene carbonate, chain ethyl methyl carbonate and chain dimethyl carbonate is 3:3:4.

[0056] Through the above scheme, the solvent is composed of cyclic ethylene carbonate (EC), chain ethyl methyl carbonate (EMC) and chain dimethyl carbonate (DMC), and their concentration ratio is 3:3:4. The design of this mixed solvent system takes into account the characteristics of different carbonates to achieve the purpose of optimizing the performance of the electrolyte.

[0057] Cyclic ethylene carbonate (EC) has a high dielectric constant and ionic conductivity, which helps to increase the lithium ion migration number of the electrolyte, thereby improving the charge and discharge efficiency of the battery. Cyclic carbonates such as EC can form a stable SEI film on the surface of the negative electrode, which is essential for protecting the electrode and improving the cycle stability of the battery. Chain carbonates such as DMC and EMC have low viscosity and good electrochemical stability, which help to improve the low-temperature performance of the electrolyte and the safety of the battery. By adjusting the ratio of EC, EMC and DMC, the cost can be balanced while maintaining the high performance of the electrolyte. EC is usually more expensive, while DMC and EMC are relatively cheap, and the cost can be controlled through a reasonable ratio. At the same time, this mixed solvent system can combine the advantages of cyclic and chain carbonates to improve the charge and discharge performance, cycle stability and safety performance of the battery.

[0058] The film-forming additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, vinyl sulfite, propylene sulfite, γ-butyrolactone, and adiponitrile.

[0059] Through the above scheme, the film-forming additive includes one or more of vinyl carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfite (ES), propylene sulfite (PS), γ-butyrolactone (GBL) and adiponitrile (GN), which can form a protective film on the electrode surface of the battery, which helps to improve the charge and discharge efficiency, cycle stability and safety of the battery. The film-forming additive in this embodiment is vinyl carbonate (VC), which is a widely used film-forming additive that can form a stable phase interface (SEI) layer on the anode surface to improve the electrochemical reaction performance. ES, as a film-forming additive, has good film-forming ability and has a significant effect on the improvement of the low-temperature performance of lithium-ion batteries.

[0060] PS is a sulfur-containing organic solvent, and its reducing property at the graphite negative electrode interface is stronger than that of the corresponding carbonate. The high reduction potential of PS helps to form a stable SEI layer.

[0061] GBL acts as a film-forming additive in lithium batteries, helping to form a stable SEI layer and improve battery performance.

[0062] As an additive, GN can effectively stabilize the electrode interface and improve battery performance. Film-forming additives can be selected and optimized according to the specific needs and performance goals of the battery.

[0063] Based on the above embodiments, a lithium-ion battery is also provided in this embodiment, including a positive electrode material, a negative electrode material, a diaphragm material and any one of the above overcharge safety electrolytes.

[0064] It is understandable that there is a filling coefficient between lithium-ion batteries and overcharge safety electrolytes, and the filling coefficient refers to the mass of electrolyte required for a battery per unit capacity. The filling coefficient is usually expressed in grams per ampere-hour (g / Ah), indicating the mass (g) of electrolyte required per ampere-hour (Ah) of the battery. In this embodiment, the filling coefficient is 3g / Ah to 3.5g / Ah, and a suitable filling coefficient can improve the performance and life of lithium-ion batteries.

[0065] Since the composition and beneficial effects of the overcharge safety electrolyte of the lithium-ion battery have been described in detail in the previous embodiments, the present application will not repeat them here.

[0066] Example 2

[0067] The overcharge safety electrolyte for lithium-ion batteries in this embodiment includes components such as lithium salt, solvent, film-forming additive and overcharge prevention additive.

[0068] The lithium salt consists of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0069] The solvent is composed of cyclic ethylene carbonate (EC), chain ethyl methyl carbonate (EMC) and chain dimethyl carbonate (DMC).

[0070] The film-forming additive is vinylene carbonate (VC).

[0071] The anti-overcharge additive is cyclohexyl dimethyl phosphate.

[0072] The ratio of the overcharge prevention safety electrolyte in this embodiment is as follows:

[0073] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC(30:30:40vol%)+3wt%VC+2wt%cyclohexyl dimethyl phosphate.

[0074] The preparation method of the overcharge safety electrolyte comprises:

[0075] EC, EMC and DMC were mixed in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, and then LiPF6 and LiFSI were added to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved, a solution was formed, and then VC and cyclohexyl dimethyl phosphate were added thereto at a mass ratio of 3% and 2% of the carbonate solvent, respectively.

[0076] Example 3

[0077] The overcharge safety electrolyte for lithium-ion batteries in this embodiment includes components such as lithium salt, solvent, film-forming additive and overcharge prevention additive.

[0078] The lithium salt consists of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0079] The solvent is composed of cyclic ethylene carbonate (EC), chain ethyl methyl carbonate (EMC) and chain dimethyl carbonate (DMC).

[0080] The film-forming additive is vinylene carbonate (VC).

[0081] The anti-overcharge additive is cyclohexyl dimethyl phosphate.

[0082] The ratio of the overcharge prevention safety electrolyte in this embodiment is as follows:

[0083] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC(30:30:40vol%)+3wt%VC+4wt%cyclohexyl dimethyl phosphate.

[0084] The preparation method of the overcharge safety electrolyte comprises:

[0085] EC, EMC and DMC were mixed in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, and then LiPF6 and LiFSI were added to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved, a solution was formed, and then VC and cyclohexyl dimethyl phosphate were added thereto at a mass ratio of 3% and 4% of the carbonate solvent, respectively.

[0086] The difference between Example 3 and Example 2 is that the amount of cyclohexyl dimethyl phosphate added in Example 3 is 4 wt %, while the amount of cyclohexyl dimethyl phosphate added in Example 2 is 2 wt %.

[0087] Example 4

[0088] The overcharge safety electrolyte for lithium-ion batteries in this embodiment includes components such as lithium salt, solvent, film-forming additive and overcharge prevention additive.

[0089] The lithium salt consists of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0090] The solvent is composed of cyclic ethylene carbonate (EC), chain ethyl methyl carbonate (EMC) and chain dimethyl carbonate (DMC).

[0091] The film-forming additive is vinylene carbonate (VC).

[0092] The anti-overcharge additive is cyclohexyl dimethyl phosphate.

[0093] The ratio of the overcharge prevention safety electrolyte in this embodiment is as follows:

[0094] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC(30:30:40vol%)+3wt%VC+0.5wt%cyclohexyl dimethyl phosphate.

[0095] The preparation method of the overcharge safety electrolyte comprises:

[0096] EC, EMC and DMC were mixed in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, and then LiPF6 and LiFSI were added to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved, a solution was formed, and then VC and cyclohexyl dimethyl phosphate were added thereto at a mass ratio of 3% and 0.5 of the carbonate solvent, respectively.

[0097] The difference between Example 4 and Example 2 is that the amount of cyclohexyl dimethyl phosphate added in Example 4 is 0.5 wt %, while the amount of cyclohexyl dimethyl phosphate added in Example 2 is 2 wt %.

[0098] Example 5

[0099] The overcharge safety electrolyte for lithium-ion batteries in this embodiment includes: lithium salt, solvent, film-forming additive and overcharge prevention additive. The difference between Example 5 and Example 2 is that the overcharge prevention additive used in Example 5 is cyclohexyl diethyl aminophosphorate, and the overcharge prevention additive used in Example 2 is cyclohexyl dimethyl phosphate.

[0100] The ratio of the overcharge prevention safety electrolyte in this embodiment is as follows:

[0101] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC(30:30:40vol%)+3wt%VC+2wt%cyclohexylaminophosphoric acid diethyl ester.

[0102] The preparation method of the overcharge safety electrolyte comprises:

[0103] EC, EMC and DMC were mixed in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, and then LiPF6 and LiFSI were added to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved, a solution was formed, and VC and cyclohexylaminophosphodiester were added thereto at a mass ratio of 3% and 2% of the carbonate solvent, respectively.

[0104] Example 6

[0105] The overcharge safety electrolyte for lithium ion batteries in this embodiment includes: lithium salt, solvent, film-forming additive and overcharge prevention additive. The difference between Example 6 and Example 3 is that the overcharge prevention additive used in Example 6 is cyclohexyl diethyl aminophosphorate, and the overcharge prevention additive used in Example 3 is cyclohexyl dimethyl phosphate.

[0106] The ratio of the overcharge prevention safety electrolyte in this embodiment is as follows:

[0107] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC(30:30:40vol%)+3wt%VC+4wt%cyclohexylaminophosphoric acid diethyl ester.

[0108] The preparation method of the overcharge safety electrolyte comprises:

[0109] EC, EMC and DMC were mixed in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, and then LiPF6 and LiFSI were added to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved, a solution was formed, and then VC and cyclohexylaminophosphodiester were added thereto at a mass ratio of 3% and 4% of the carbonate solvent, respectively.

[0110] Example 7

[0111] The overcharge safety electrolyte for lithium ion batteries in this embodiment includes: lithium salt, solvent, film-forming additive and overcharge prevention additive. The difference between Example 7 and Example 4 is that the overcharge prevention additive used in Example 7 is cyclohexyl diethyl aminophosphorate, and the overcharge prevention additive used in Example 4 is cyclohexyl dimethyl phosphate.

[0112] The ratio of the overcharge prevention safety electrolyte in this embodiment is as follows:

[0113] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC(30:30:40vol%)+3wt%VC+0.5wt%cyclohexylaminophosphoric acid diethyl ester.

[0114] The preparation method of the overcharge safety electrolyte comprises:

[0115] EC, EMC and DMC were mixed in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, and then LiPF6 and LiFSI were added to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved, a solution was formed, and VC and cyclohexylaminophosphodiester were added thereto at a mass ratio of 3% and 0.5 of the carbonate solvent, respectively.

[0116] Comparative Example 1

[0117] An electrolyte is provided, the components of which include: a lithium salt, a solvent, and a film-forming additive. The difference between Comparative Example 1 and Example 2 is that: No overcharge prevention additive is used in Comparative Example 1, and the overcharge prevention additive used in Example 2 is cyclohexyl dimethyl phosphate.

[0118] Its ingredients include:

[0119] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC (30:30:40vol%)+3wt%VC.

[0120] The preparation method includes: mixing EC, EMC and DMC in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, then adding LiPF6 and LiFSI to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L respectively, forming a solution after being fully dissolved, and then adding VC accounting for 3% of the mass ratio of the carbonate solvent.

[0121] Comparative Example 2

[0122] An electrolyte is provided, the components of which include: a lithium salt, a solvent, a film-forming additive and polypyridine. The difference between Comparative Example 2 and Example 2 is that the anti-overcharge additive used in Comparative Example 2 is a redox pair (polypyridine), and the anti-overcharge additive used in Example 2 is cyclohexyl dimethyl phosphate.

[0123] Its ingredients include:

[0124] 1mol / LLiPF6+0.2mol / LLiFSI+1LEC / EMC / DMC(30:30:40vol%)+3wt%VC+2wt%polypyridine.

[0125] The preparation method includes: mixing EC, EMC and DMC in a volume percentage ratio of 30:30:40 to form 1L of carbonate solvent, then adding LiPF6 and LiFSI to the carbonate solvent at a concentration of 1 mol / L and 0.2 mol / L respectively, forming a solution after being fully dissolved, and then adding VC and polypyridine in a mass ratio of 3% and 2% of the carbonate solvent respectively.

[0126] Performance Test:

[0127] The overcharge time is the time required for charging to reach the cut-off voltage. If the time required is too long, the temperature of the battery will be too high, resulting in thermal runaway. The battery temperature is the temperature of the battery when the cut-off voltage is reached. The higher the battery temperature, the more likely it is to cause thermal runaway. The overcharge capacity (SOC) refers to the percentage of the remaining battery capacity in the total capacity. During the charging and discharging process of the battery, the change in SOC can be calculated by the product of the current I and the charging time t.

[0128] In this application, whether the test is passed is evaluated by the comprehensive situation of overcharge SOC / %, overcharge time / s and battery temperature / °C.

[0129] The above electrolyte is injected into a square-shell lithium iron phosphate battery. The positive electrode material of the lithium iron phosphate battery is lithium iron phosphate, the negative electrode material is graphite, and the diaphragm material is polyethylene. After the battery cell is activated, it is fully charged and the battery capacity is 300Ah. National standard GB / T-36276-2023: Stop charging when the battery is overcharged to 5.475V at a constant current of 0.5C or the time reaches 1h. Observe for 1h to observe whether the battery catches fire, explodes, or ruptures at locations other than the explosion-proof valve or pressure relief point. Test the overcharge capacity (SOC) / %, overcharge time / s and battery temperature / ℃. The results are shown in Table 1.

[0130] Table 1:

[0131] Group Overcharge SOC / % Overcharge time / s Battery temperature / ℃ Test pass status Example 2 110 720 50 pass Example 3 112 864 60 pass Example 4 116 1152 90 pass Example 5 113 936 70 pass Example 6 115 1080 85 pass Example 7 118 1296 95 pass Comparative Example 1 120 1440 110 Not passed Comparative Example 2 124 1728 140 Not passed

[0132] It can be seen from Table 1 that:

[0133] The comparison results of Example 2 and Comparative Example 1 show that no anti-overcharge additive is added in Comparative Example 1. Therefore, the overcharge time of Comparative Example 1 is 1440s, the battery temperature is 110°C, and the overcharge SOC is 120%, which can be used as a critical point for comparison. In Example 2, due to the addition of cyclohexyl dimethyl phosphate additive, the overcharge SOC of the battery is significantly reduced by 10%, the overcharge time is reduced by 720s, and the battery temperature is reduced by 60°C. This is because the ring-opening polymerization product of cyclohexyl dimethyl phosphate increases the internal resistance of the battery, causing the battery voltage to rise rapidly in a short period of time and reach the overcharge cut-off protection voltage.

[0134] Figure 1 This is a schematic diagram of voltage and temperature results during the battery test in Example 2. Figure 2 This is a schematic diagram of the voltage and temperature results during the battery test in Comparative Example 2.

[0135] Combined with Table 1 reference Figure 1 and Figure 2, the comparison between Example 2 and Comparative Example 2 shows that the battery containing polypyrrole additive in Comparative Example 2, because polypyrrole is a redox pair, will undergo a persistent redox reaction, thereby generating a large amount of reaction heat, causing the battery temperature to rise sharply, and it will cause the battery voltage to remain constant, making it difficult to reach the cut-off protection voltage of battery charging, which will make the charging time too long, and during this period, the temperature will also rise. Therefore, this situation does not take into account the change of battery temperature, resulting in test failure. The battery containing cyclohexyl dimethyl phosphate additive in Example 2 has a significantly reduced overcharge SOC of 14%, a reduced overcharge time of 1008s, and a reduced battery temperature of 90°C. This is because cyclohexyl dimethyl phosphate will undergo a ring-opening polymerization reaction of cyclic groups under high voltage, and the high-impedance polymerization product adheres to the electrode surface, increasing the internal resistance of the battery, causing the battery voltage to rise rapidly to the overcharge cut-off voltage of 5.475V in a short time, and the overcharge test stops, so the overcharge SOC and overcharge time of Example 2 are shorter. At the same time, no large amount of reaction heat will be generated, and no heat will be accumulated by charging all the time, so the battery temperature is lower.

[0136] The comparison results of Example 2 and Example 3 show that the effect of 2wt% addition of cyclohexyl dimethyl phosphate is better than that of 4wt%, and its overcharge SOC is reduced by 2%, the overcharge time is reduced by 144s, and the battery temperature is reduced by 10°C. This shows that the effect of further increasing the addition amount on overcharge improvement is limited, and even deterioration occurs. This is because the high content of cyclohexyl dimethyl phosphate has a large number of ring-opening polymerization products, which are enough to penetrate the diaphragm to form a conductive bridge between the positive and negative electrodes, causing an internal micro-short circuit, thereby reducing the increase in battery voltage.

[0137] The comparison results of Example 2 and Example 4 show that the effect of 2wt% addition of cyclohexyl dimethyl phosphate is significantly better than that of 0.5wt%, and its overcharge SOC is reduced by 6%, the overcharge time is reduced by 432s, and the battery temperature is reduced by 40°C. This is because the polymerization product of low-content cyclohexyl dimethyl phosphate has limited increase in battery internal resistance.

[0138] Example 5, Example 6 and Example 7 correspond to the test results of Example 2, Example 3 and Example 4, respectively, because cyclohexyl diethyl aminophosphorate and cyclohexyl dimethyl phosphate are both compounds with cyclohexyl organic functional groups, and ring-opening polymerization occurs under overcharge conditions. This polymerization reaction causes the polymerization product to adhere to the electrode surface, thereby increasing the internal resistance of the battery. Since the polymerization product adheres to the electrode surface, the internal resistance of the battery is increased, which helps to suppress the current and prevent the battery from continuing to absorb more charge under overcharge conditions, thereby avoiding safety problems caused by overcharge. Since the internal resistance of the battery can increase rapidly, the battery voltage will increase rapidly in a short time and reach the overcharge cut-off protection voltage, which can avoid long-term overcharging causing the battery temperature to rise. By quickly reaching the overcharge protection voltage, the battery temperature can be prevented from rising sharply due to charging for too long, thereby solving the thermal runaway problem caused by the sharp rise in battery temperature and better protecting the safety of lithium-ion batteries.

[0139] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. An overcharge safety electrolyte for a lithium ion battery, the components of the overcharge safety electrolyte comprising: Lithium salt, solvent, film-forming additive and anti-overcharge additive, characterized in that: the anti-overcharge additive is a compound with a cyclohexyl organic functional group, wherein the weight percentage of the anti-overcharge additive in the overcharge safety electrolyte is 0.5wt%-5wt%.

2. The overcharge safety electrolyte according to claim 1, characterized in that: The overcharge prevention additive is composed of one or more of cyclohexyl dimethyl phosphate, cyclohexyl diethyl phosphoramidite, cyclohexyl dimethyl carboxylate, and ethyl cyclohexyl acetate.

3. The overcharge safety electrolyte according to claim 2, characterized in that: The anti-overcharge additive is cyclohexyl dimethyl phosphate, and the weight percentage of the cyclohexyl dimethyl phosphate is 2wt%.

4. The overcharge safety electrolyte according to claim 2, characterized in that: The overcharge safety electrolyte according to claim 1 is characterized in that, in the overcharge safety electrolyte, the weight percentage of the lithium salt is 5wt%-30wt%; the weight percentage of the solvent is 70wt%-90wt%; and the weight percentage of the film-forming additive is 0.5wt%-5wt%.

5. The overcharge safety electrolyte according to claim 2, characterized in that: The lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

6. The overcharge safety electrolyte according to claim 5, characterized in that: The lithium salt consists of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, and the concentration ratio of the lithium hexafluorophosphate to the lithium bis(fluorosulfonyl)imide is 10:

2.

7. The overcharge safety electrolyte according to claim 2, characterized in that: The solvent includes one or more of cyclic ethylene carbonate, cyclic propylene carbonate, chain dimethyl carbonate, chain ethyl methyl carbonate, chain diethyl carbonate, ethyl acetate, and methyl butyrate.

8. The overcharge safety electrolyte according to claim 7, characterized in that: The solvent consists of cyclic ethylene carbonate, chain ethyl methyl carbonate and chain dimethyl carbonate, and the concentration ratio of the cyclic ethylene carbonate, chain ethyl methyl carbonate and chain dimethyl carbonate in the solvent is 3:3:

4.

9. The overcharge safety electrolyte according to claim 2, characterized in that: The film-forming additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, vinyl sulfite, propylene sulfite, γ-butyrolactone, and adiponitrile.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material, a diaphragm material and the overcharge safety electrolyte according to any one of claims 1 to 9.

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