Electrolyte for eliminating overcharge lithium precipitation, manufacturing method and lithium ion battery

Abstract

The invention provides an electrolyte for eliminating overcharge lithium precipitation, a manufacturing method and a lithium ion battery, and relates to the technical field of lithium battery electrolytes.According to the electrolyte for eliminating overcharge lithium precipitation, from the perspective of eliminating overcharge lithium precipitation, a compound with complex ions containing [Fe (CN) 6] 3 <-> is introduced to serve as an additive for eliminating overcharge lithium precipitation, and the electrolyte is prepared; the lithium metal precipitated on the negative electrode during overcharge is oxidized, so that lithium dendrites formed on the negative electrode react to form Li < + >, and the lithium dendrites are eliminated, so that the problem of lithium precipitation during overcharge is effectively solved, the process is simple, and the cost is low.

Description

Technical Field

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

[0002] Lithium iron phosphate batteries have been widely used in the energy storage and power battery industries due to their high safety, high temperature resistance and low cost. However, despite the good safety performance of lithium iron phosphate batteries, when overcharged and abused, serious lithium precipitation will occur at the negative electrode of the battery. The precipitated lithium metal will penetrate the diaphragm, causing a short circuit in the battery and thermal runaway, which may lead to serious battery fire safety accidents.

[0003] In the prior art, the prevention of lithium deposition in batteries generally adopts modification treatment of graphite negative electrode, such as coating, doping, alloying or deposition, to improve the anti-lithium deposition ability of graphite negative electrode. For example, by depositing a metal layer with a nanometer thickness on the surface of the negative electrode, the overpotential of lithium metal deposition can be increased and the driving force of lithium metal growth can be weakened, thereby achieving the purpose of improving lithium deposition; by doping the end surface of the graphite material with nickel and depositing an amorphous silicon oxide coating on the surface, the mass transfer kinetics and the potential of silicon-lithium alloying can be improved, thereby inhibiting the negative electrode from reaching the lithium deposition potential.

[0004] However, the graphite negative electrode modification treatment method used in the prior art has a preventive effect on lithium deposition during normal battery charging, but cannot effectively prevent severe lithium deposition during overcharging, and the effect is limited, and it will still cause a short circuit in the battery and thermal runaway. In addition, the prior art has the disadvantages of complex processing technology, high equipment requirements, and high cost investment. Summary of the invention

[0005] The present application provides an electrolyte, a preparation method and a lithium ion battery for eliminating overcharging lithium deposition, so as to solve the current problem that serious lithium deposition during overcharging cannot be effectively prevented and the effect is limited.

[0006] In the first aspect, the present application provides an electrolyte for eliminating overcharge lithium deposition, which is used to eliminate overcharge lithium deposition in lithium-ion batteries. The components of the electrolyte include: a lithium salt, a solvent, a film-forming additive and an additive for eliminating overcharge lithium deposition. The additive for eliminating overcharge lithium deposition is a material containing [Fe(CN)6] 3- The complex ion compound, wherein the weight percentage of the overcharge elimination lithium additive in the electrolyte is 0.5wt%-5wt%.

[0007] Through the above scheme, from the perspective of eliminating overcharge lithium precipitation, the introduction of [Fe(CN)6] 3-The complex ion compound is used as an additive to eliminate overcharge lithium precipitation. The principle is that the iron ion in this complex is in the +3 oxidation state and has an oxidizing, strongly oxidizing anionic group [Fe(CN)6] 3- It will undergo a chemical oxidation reaction with the lithium metal precipitated on the negative electrode, oxidizing Li into Li + The reaction equation is Li+[Fe(CN)6] 3- =Li + +[Fe(CN)6] 4- This effectively solves the problem of overcharging and lithium deposition, and the process is simple and low-cost.

[0008] In a possible design, the additive for eliminating overcharge lithium precipitation is composed of one or more of lithium ferrocyanide, ferric ferrocyanide, ferrous ferrocyanide, potassium ferrocyanide, calcium ferrocyanide, and sodium ferrocyanide.

[0009] According to the above scheme, since lithium ferrocyanide, ferric ferrocyanide, ferrous ferrocyanide, potassium ferrocyanide, calcium ferrocyanide, and sodium ferrocyanide all have anionic groups [Fe(CN)6] 3- , which can undergo a chemical oxidation reaction with the lithium metal deposited on the negative electrode, oxidizing Li into Li+, thereby effectively inhibiting the lithium deposition phenomenon during overcharging.

[0010] In a possible design, the additive for eliminating overcharge lithium precipitation is potassium ferrocyanide, and the weight percentage of potassium ferrocyanide is 2wt%.

[0011] According to the above scheme, the amount of potassium ferrocyanide added to the electrolyte is 2wt%, which means that the mass of potassium ferrocyanide is 2g in 100g of electrolyte. This amount of addition can effectively reduce the lithium precipitation phenomenon during overcharging, reduce the risk of short circuit in the battery and improve the safety of the battery.

[0012] In a possible design, in the 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 close to 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 lithium ion transmission, film-forming additives help form a stable SEI film, and eliminating overcharge lithium additives improves battery safety. The weight percentage of each component needs to be optimized according to the specific battery design and usage conditions to achieve optimal battery performance and safety.

[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 salts include lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which are all commonly used lithium salts in lithium-ion batteries and have good ionic conductivity and electrochemical stability. LiFSI has high stability, excellent low-temperature performance and environmental friendliness. LiPF6 has good comprehensive performance, LiTFSI has suitable conductivity, high thermal stability and electrochemical stability, and the probability of side reactions is small, and no corrosive gases are produced. 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 a possible design, the lithium salt is composed of lithium hexafluorophosphate and lithium bisfluorosulfonyl imide, and the concentration ratio of lithium hexafluorophosphate to lithium bisfluorosulfonyl imide is 10:2; 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.

[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 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 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] The solvents include 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), which are used as carriers 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 salts 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.

[0019] 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.

[0020] 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 expensive, while DMC and EMC are relatively cheap. This mixing method allows the solvent to ensure the chemical stability and thermal stability of the electrolyte while maintaining good conductivity.

[0021] 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.

[0022] 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.

[0023] In a second aspect, the present application provides a method for preparing an electrolyte for eliminating overcharge lithium precipitation, comprising the steps of: preparing a carbonate solvent; forming a solution, adding a lithium salt to the carbonate solvent, and fully dissolving the lithium salt to form a solution; forming an electrolyte, adding a film-forming additive accounting for 0.5% to 5% of the mass ratio of the carbonate solvent and a liquid containing [Fe(CN)6] accounting for 0.5% to 5% of the mass ratio of the carbonate solvent to the solution; 3- A compound of complexing ions.

[0024] Through the above scheme, the lithium salt has a sufficiently high solubility in the organic solvent to ensure that the electrolyte has a high conductivity. Sufficient stirring is performed to ensure that the lithium salt is completely dissolved to form a uniform solution. The amount of film-forming additives added is 0.5%-5% of the mass ratio of the carbonate solvent. They help to form a stable SEI film on the electrode surface and improve the cycle stability and safety of the battery. At the same time, a mixture containing [Fe(CN)6] 3- The complex ion compounds, such as lithium ferrocyanide (Li3[Fe(CN)6]), ferric ferrocyanide (Fe[Fe(CN)6]), etc., are used as additives to eliminate overcharge lithium precipitation. The amount of these compounds added accounts for 0.5%-5% of the mass ratio of carbonate solvents. 3-The complex ion compound has strong oxidizing properties and will undergo chemical oxidation reaction with the lithium metal precipitated on the negative electrode, oxidizing Li to Li + The reaction equation is Li+[Fe(CN)6] 3- =Li + +[Fe(CN)6] 4- The appropriate amount of overcharge lithium deposition additives can effectively inhibit the lithium deposition phenomenon during overcharge and improve the safety of the battery.

[0025] In a third 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 electrolytes.

[0026] The beneficial effects of the lithium-ion battery provided in the third aspect and each possible design of the third aspect can be referred 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.

[0027] 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

[0028] 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.

[0029] Figure 1 This is a rendering showing that the graphite negative electrode of the battery in Example 2 of the present application has no lithium deposition after an overcharge test.

[0030] Figure 2 This is a rendering showing that the graphite negative electrode of the battery in comparative example 1 of the present application produces severe lithium deposition after an overcharge test.

[0031] Figure 3 This is a schematic diagram of the overcharge SOC and battery temperature results of the battery in the overcharge test of Example 2 of the present application.

[0032] Figure 4 This is a schematic diagram of the overcharge SOC and battery temperature results of the battery in the overcharge test of Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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).

[0038] Lithium deposition refers to the phenomenon that during the charging process of lithium-ion batteries, due to certain abnormal conditions, lithium ions cannot be embedded in the negative electrode and can only obtain electrons on the surface of the negative electrode, thereby forming metallic lithium. This phenomenon usually occurs in a low temperature environment or during repeated charging and discharging of the battery, resulting in the inability of lithium ions deintercalated from the positive electrode to be normally embedded in the negative electrode, but deposited on the surface of the negative electrode to form solid metallic lithium, namely lithium dendrites. The growth of lithium dendrites will increase the internal resistance of the battery, reduce the energy density and charge and discharge efficiency. Lithium dendrites may damage the solid electrolyte interface (SEI) film and battery separator, causing internal short circuits in the battery, generating a large amount of heat and current, which may cause safety problems such as fire or explosion.

[0039] Overcharge lithium deposition refers to the phenomenon that occurs when a lithium-ion battery is fully charged but the charging voltage exceeds its upper cut-off voltage and continues to charge. In this case, excess lithium ions will be embedded in the negative electrode, forming metallic lithium on the surface of the negative electrode, namely lithium dendrites.

[0040] As can be seen from the background technology, in the current production of lithium iron phosphate batteries, there is a preventive effect on lithium deposition during normal charging of the battery, but it is unable to effectively prevent severe lithium deposition during overcharging.

[0041] In the related art, the graphite negative electrode is modified, such as coating, doping, alloying or deposition, to improve the resistance of the graphite negative electrode to lithium precipitation. For example, by depositing a metal layer with a nanometer thickness on the surface of the negative electrode, the overpotential of lithium metal precipitation can be increased and the driving force of lithium metal growth can be weakened, thereby achieving the purpose of improving lithium precipitation; by nickel doping on the end surface of the graphite material and depositing an amorphous silicon oxide coating on the surface, the mass transfer kinetics and the potential of silicon-lithium alloying can be improved, thereby inhibiting the negative electrode from reaching the lithium precipitation potential. However, it has a preventive effect on lithium precipitation during normal battery charging, but cannot effectively prevent severe lithium precipitation during overcharging. The effect is limited and will still cause short circuits in the battery and thermal runaway.

[0042] In view of this, the present invention provides an electrolyte, a preparation method and a lithium ion battery for eliminating overcharge lithium precipitation. From the perspective of eliminating overcharge lithium precipitation, an electrolyte containing [Fe(CN)6] 3- The complex ion compound is used as an additive to eliminate overcharge lithium precipitation, oxidizing the lithium metal precipitated on the negative electrode during overcharge, so that the lithium dendrites formed on the negative electrode react to Li + , thereby eliminating lithium dendrites, which effectively solves the problem of overcharging and lithium precipitation, and the process is simple and low-cost.

[0043] 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.

[0044] Example 1

[0045] The present embodiment provides an electrolyte for eliminating overcharge lithium deposition, which is used to eliminate overcharge lithium deposition in lithium-ion batteries. The components of the electrolyte include: lithium salt, solvent, film-forming additive and overcharge lithium deposition eliminating additive. The overcharge lithium deposition eliminating additive is a compound having a complex ion containing [Fe(CN)6]n-, wherein the weight percentage of the overcharge lithium deposition eliminating additive in the electrolyte is 0.5wt%-5wt%.

[0046] Lithium salt, as a basic component of electrolyte, is used to provide lithium ions to maintain the battery's charge and discharge cycle.

[0047] The weight percentage of lithium salt is 5wt%-30wt%. Lithium salt provides necessary lithium ions. When the weight percentage of lithium salt is lower than 5wt%, it cannot provide enough lithium ions for lithium ion batteries. When the weight percentage of lithium salt is higher than 30wt%, it will lead to excessive lithium ion content in lithium ion batteries, which is not conducive to the effectiveness of the battery.

[0048] The solvent in this embodiment is a carbonate solvent, and the solvent provides a transmission medium for lithium ions. The weight percentage of the solvent is 70wt%-90wt%. When the weight percentage of the solvent is lower than 70wt%, it cannot provide a sufficient medium for the transmission of lithium ions.

[0049] In this embodiment, the weight percentage of the film-forming additive is 0.5 wt %-5 wt %. The weight percentages of the lithium salt and the solvent should be close to 100% to ensure that the total weight of the electrolyte is 100%.

[0050] Film-forming additives help form a stable SEI film, while eliminating overcharge lithium additives improves battery safety. The weight percentage of each component needs to be optimized according to the specific battery design and usage conditions to achieve the best battery performance and safety.

[0051] In this embodiment, from the perspective of eliminating overcharge lithium precipitation, a material containing [Fe(CN)6] 3- The complex ion compound is used as an additive to eliminate overcharge lithium precipitation. The principle is that the strong oxidizing anion group [Fe(CN)6] 3- It will undergo a chemical oxidation reaction with the lithium metal precipitated on the negative electrode, oxidizing Li into Li + The reaction equation is Li+[Fe(CN)6] 3- =Li + +[Fe(CN)6] 4- This effectively solves the problem of overcharging and lithium deposition, and the process is simple and low-cost.

[0052] In this embodiment, the lithium salt may include any one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which are all commonly used lithium salts in lithium-ion batteries and have good ionic conductivity and electrochemical stability. LiFSI has high stability, excellent low-temperature performance and environmental friendliness. LiPF6 has good comprehensive performance, LiTFSI has suitable conductivity, high thermal stability and electrochemical stability, and the probability of side reactions is small, and no corrosive gas is generated. 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 charge and discharge chemical reactions of the battery.

[0053] In this embodiment, the additive for eliminating overcharge lithium precipitation may be composed of one or more of lithium ferrocyanide, ferric ferrocyanide, ferrous ferrocyanide, potassium ferrocyanide, calcium ferrocyanide, and sodium ferrocyanide.

[0054] According to the above scheme, since lithium ferrocyanide, ferric ferrocyanide, ferrous ferrocyanide, potassium ferrocyanide, calcium ferrocyanide, and sodium ferrocyanide all have anionic groups [Fe(CN)6] 3- , which can undergo a chemical oxidation reaction with the lithium metal deposited on the negative electrode, oxidizing Li into Li+, thereby effectively inhibiting the lithium deposition phenomenon during overcharging.

[0055] In this embodiment, the additive for eliminating overcharge lithium precipitation is potassium ferrocyanide, and the weight percentage of potassium ferrocyanide is 2wt%. In the electrolyte, the addition amount of potassium ferrocyanide is 2wt%, which means that in 100 grams of electrolyte, the mass of potassium ferrocyanide is 2 grams. This addition amount can effectively reduce the lithium precipitation phenomenon during overcharge, reduce the risk of short circuit in the battery and improve the safety of the battery.

[0056] 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; 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.

[0057] 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) has better thermal stability and electrochemical stability. 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 can be 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.

[0058] In this embodiment, the solvent may include 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 salts 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.

[0059] 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.

[0060] 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 expensive, while DMC and EMC are relatively cheap. This mixing method allows the solvent to ensure the chemical stability and thermal stability of the electrolyte while maintaining good conductivity.

[0061] In this embodiment, the film-forming additive includes one or more of vinylene carbonate, vinyl ethylene carbonate, vinyl sulfite, propylene sulfite, γ-butyrolactone, and adiponitrile.

[0062] 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 surface of the battery electrode, which helps to improve the battery's charge and discharge efficiency, cycle stability and safety. 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.

[0063] 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.

[0064] GBL acts as a film-forming additive in lithium batteries, helping to form a stable SEI layer and improve battery performance.

[0065] 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.

[0066] Based on the above embodiment, this embodiment also provides a method for preparing an electrolyte for eliminating overcharge lithium precipitation, comprising the steps of: preparing a carbonate solvent; forming a solution, adding a lithium salt to the carbonate solvent, and fully dissolving the lithium salt to form a solution; forming an electrolyte, adding a film-forming additive accounting for 0.5%-5% of the mass ratio of the carbonate solvent and a liquid containing [Fe(CN)6] accounting for 0.5%-5% of the mass ratio of the carbonate solvent to the solution. 3- By adding a compound containing [Fe(CN)6] 3- The complex ion compounds are used as additives to eliminate overcharge lithium precipitation. The addition amount of these compounds accounts for 0.5%-5% of the mass ratio of carbonate solvent. 3- The complex ion compound has strong oxidizing properties and will undergo chemical oxidation reaction with the lithium metal precipitated on the negative electrode, oxidizing Li to Li + The reaction equation is Li+[Fe(CN)6] 3- =Li + +[Fe(CN)6] 4-The appropriate amount of overcharge lithium deposition additives can effectively inhibit the lithium deposition phenomenon during overcharge and improve the safety of the battery.

[0067] Based on the above embodiments, the present application provides a lithium-ion battery, including a positive electrode material, a negative electrode material, a diaphragm material and any of the above electrolytes.

[0068] It is understood that there is a liquid injection coefficient between the lithium-ion battery and the electrolyte, and the liquid injection coefficient refers to the mass of electrolyte required for the battery per unit capacity. The liquid injection 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 liquid injection coefficient is 3g / Ah to 3.5g / Ah. A suitable liquid injection coefficient can improve the performance and life of the lithium-ion battery.

[0069] Since the composition and beneficial effects of the electrolyte have been described in detail in the previous embodiments, the present application will not repeat them here.

[0070] Example 2

[0071] The electrolyte for lithium-ion batteries in this embodiment includes components such as lithium salt, solvent, film-forming additive and additive for eliminating overcharge lithium deposition.

[0072] The lithium salt consists of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI).

[0073] The solvent is composed of cyclic ethylene carbonate (EC), chain ethyl methyl carbonate (EMC) and chain dimethyl carbonate (DMC).

[0074] The film-forming additive is vinylene carbonate (VC).

[0075] The additive to eliminate lithium precipitation caused by overcharging is potassium ferrocyanide.

[0076] The proportion of the electrolyte in this embodiment is as follows: 1 mol / L LiPF6 + 0.2 mol / L LiFSI + 1 LEC / EMC / DMC (30:30:40 vol%) + 3 wt% VC + 2 wt% K3[Fe(CN)6]

[0077] The preparation method of the electrolyte comprises:

[0078] 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 potassium ferrocyanide were added thereto at a mass ratio of 3% and 2% of the carbonate solvent, respectively.

[0079] Example 3

[0080] The difference between Example 3 and Example 2 is that the amount of potassium ferrocyanide added in Example 3 is 4 wt %, while the amount of potassium ferrocyanide added in Example 2 is 2 wt %.

[0081] The proportion of the electrolyte in this embodiment is as follows: 1 mol / L LiPF6 + 0.2 mol / L LiFSI + 1 LEC / EMC / DMC (30:30:40 vol%) + 3 wt% VC + 4 wt% K3[Fe(CN)6]

[0082] The preparation method of the electrolyte comprises:

[0083] 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 concentrations of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved, a solution was formed, and VC and potassium ferrocyanide were added thereto at a mass ratio of 3% and 4% of the carbonate solvent, respectively.

[0084] Example 4

[0085] The difference between Example 4 and Example 2 is that the amount of potassium ferrocyanide added in Example 4 is 1 wt %, while the amount of potassium ferrocyanide added in Example 2 is 2 wt %.

[0086] The proportion of the electrolyte in this embodiment is as follows: 1 mol / L LiPF6 + 0.2 mol / L LiFSI + 1 LEC / EMC / DMC (30:30:40 vol%) + 3 wt% VC + 1 wt% K3[Fe(CN)6]

[0087] The preparation method of the electrolyte comprises:

[0088] 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 potassium ferrocyanide were added thereto at a mass ratio of 3% and 1% of the carbonate solvent, respectively.

[0089] Example 5

[0090] The difference between Example 5 and Example 2 is that the overcharge lithium deposition additive in Example 5 is ferric ferrocyanide, while the overcharge lithium deposition additive in Example 2 is potassium ferrocyanide.

[0091] The proportion of the electrolyte in this embodiment is as follows: 1 mol / L LiPF6 + 0.2 mol / L LiFSI + 1 LEC / EMC / DMC (30:30:40 vol%) + 3 wt% VC + 2 wt% Fe[Fe(CN)6]

[0092] The preparation method of the electrolyte comprises:

[0093] 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 ferric ferrocyanide were added thereto at a mass ratio of 3% and 2% of the carbonate solvent, respectively.

[0094] Example 6

[0095] The difference between Example 6 and Example 3 is that the overcharge lithium deposition additive in Example 6 is ferric ferrocyanide, while the overcharge lithium deposition additive in Example 3 is potassium ferrocyanide.

[0096] The proportion of the electrolyte in this embodiment is as follows: 1 mol / L LiPF6 + 0.2 mol / L LiFSI + 1 LEC / EMC / DMC (30:30:40 vol%) + 3 wt% VC + 4 wt% Fe[Fe(CN)6]

[0097] The preparation method of the electrolyte comprises:

[0098] 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 ferric ferrocyanide were added thereto at a mass ratio of 3% and 4% of the carbonate solvent, respectively.

[0099] Example 7

[0100] The difference between Example 7 and Example 4 is that the overcharge lithium deposition additive in Example 7 is ferric ferrocyanide, while the overcharge lithium deposition additive in Example 4 is potassium ferrocyanide.

[0101] The proportion of the electrolyte in this embodiment is as follows: 1 mol / L LiPF6 + 0.2 mol / L LiFSI + 1 LEC / EMC / DMC (30:30:40 vol%) + 3 wt% VC + 1 wt% Fe[Fe(CN)6]

[0102] The preparation method of the 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 then VC and ferric ferrocyanide were added thereto at a mass ratio of 3% and 1% of the carbonate solvent, respectively.

[0104] Comparative Example 1

[0105] 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: in Comparative Example 1, no overcharge lithium additive is used, while in Example 2, the overcharge lithium additive used is potassium ferrocyanide.

[0106] The proportion of the electrolyte in this embodiment is as follows: 1 mol / L LiPF6 + 0.2 mol / L LiFSI + 1 LEC / EMC / DMC (30:30:40 vol%) + 3 wt% VC

[0107] The preparation method of the electrolyte comprises:

[0108] 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 concentrations of 1 mol / L and 0.2 mol / L, respectively. After fully dissolved to form a solution, VC accounting for 3% of the mass ratio of the carbonate solvent was added thereto.

[0109] Performance Testing:

[0110] In this application, 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. Subsequently, the large-capacity battery is overcharged: National Standard GB / T-36276-2023: overcharge at 0.5C constant current to 5.475V or stop when the time reaches 1h, the results are shown in Table 1.

[0111] Among them, the overcharge capacity (SOC) refers to the percentage of the remaining power of the battery to its total power. During the charging and discharging process of the battery, the change in SOC can be calculated by multiplying the current I by the charging time t. The battery temperature is the temperature of the battery when the cut-off voltage reaches 5.475V.

[0112] Table 1:

[0113]

[0114] Please refer to Figure 1 , Figure 1 This is a rendering of the battery in Example 2 after an overcharge test, showing that there is no lithium deposition on the graphite negative electrode. Figure 2 This is a rendering of the battery in Comparative Example 1, which shows severe lithium deposition at the graphite negative electrode after an overcharge test. Figure 3 Schematic diagram of overcharge SOC and battery temperature results of the battery in Example 2 during overcharge test. Figure 4 This is a schematic diagram of the overcharge SOC and battery temperature results of the battery in the overcharge test of Comparative Example 1. Please refer to Figures 1 to 4 It can be seen that after the overcharge test, the battery with K3[Fe(CN)6] additive has no lithium precipitation phenomenon in the graphite negative electrode ( Figure 1 ), no overcharge short circuit occurs ( Figure 3 ), the overcharge SOC was 114%, the battery temperature was 47°C, no thermal runaway occurred, and the test passed. However, after the overcharge test, the battery without K3[Fe(CN)6] additive had serious lithium deposition on the graphite negative electrode ( Figure 2 ), overcharge short circuit occurs ( Figure 4 ), the overcharge SOC is 116%, the battery temperature is 110°C, thermal runaway occurs, and the test fails. This is because the strong oxidizing anion [Fe(CN)6] of the K3[Fe(CN)6] additive 3- It will undergo a chemical oxidation reaction with the lithium metal precipitated on the negative electrode, oxidizing Li into Li + , eliminate lithium plating.

[0115] The comparison results of Example 2 and Example 3 show that the effect of 2wt% K3[Fe(CN)6] additive is better than that of 1wt%. The graphite negative electrode of the battery with 1wt% addition has a slight lithium precipitation phenomenon, which is because the low content of K3[Fe(CN)6] cannot react with a large amount of lithium metal for oxidation, and the effect is limited.

[0116] The comparison results of Example 2 and Example 4 show that the effect of the 2wt% K3[Fe(CN)6] additive is consistent with that of the 4wt% additive, and the graphite negative electrode has no lithium precipitation phenomenon, no overcharge short circuit, no thermal runaway, and the test passed. This shows that the effect of the 2wt% addition is obvious, and further increasing the addition amount has limited effect on eliminating lithium precipitation, and the risk of battery electrical performance loss increases with the increase of additive content.

[0117] The test results of Examples 5, 6 and 7 correspond to the test results of Examples 2, 3 and 4. Since ferric ferrocyanide and potassium ferrocyanide both contain [Fe(CN)6] 3- Compounds with anionic groups. When overcharged to produce lithium deposition, the strongly oxidizing anionic group [Fe(CN)6] 3-It will react chemically with the lithium dendrites precipitated on the negative electrode to oxidize Li into Li + The reaction equation is Li+[Fe(CN)6] 3- =Li + +[Fe(CN)6] 4- . Thus, lithium dendrites are eliminated, which effectively solves the problem of overcharge and lithium precipitation, and the process is simple and low-cost.

[0118] 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 electrolyte for eliminating overcharge lithium deposition, used for eliminating overcharge lithium deposition in lithium ion batteries, the components of the electrolyte comprising: Lithium salt, solvent, film-forming additive and overcharge elimination lithium additive, characterized in that: the overcharge elimination lithium additive is a material containing [Fe(CN)6] 3- The compound comprises a complex ion, wherein the weight percentage of the overcharge elimination lithium precipitation additive in the electrolyte is 0.5wt%-5wt%.

2. The electrolyte according to claim 1, characterized in that The additive for eliminating overcharge lithium precipitation is composed of one or more of lithium ferrocyanide, ferric ferrocyanide, ferrous ferrocyanide, potassium ferrocyanide, calcium ferrocyanide and sodium ferrocyanide.

3. The electrolyte according to claim 2, characterized in that The additive for eliminating overcharge lithium precipitation is potassium ferrocyanide, and the weight percentage of the potassium ferrocyanide is 2wt%.

4. The electrolyte according to claim 2, characterized in that The electrolyte according to claim 1 is characterized in that, in the 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 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; 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.

6. The 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 electrolyte according to claim 5, 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.

8. The electrolyte according to claim 7, 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.

9. A method for preparing an electrolyte for eliminating overcharge lithium precipitation, characterized in that: Includes steps: Preparation of carbonate solvents; forming a solution, adding a lithium salt to the carbonate solvent and fully dissolving the lithium salt to form a solution; An electrolyte is formed, and a film-forming additive accounting for 0.5% to 5% of the mass ratio of the carbonate solvent and a solvent containing [Fe(CN)6] accounting for 0.5% to 5% of the mass ratio of the carbonate solvent are added to the solution. 3- A compound of complexing ions.

10. A lithium ion battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material, a diaphragm material and the electrolyte according to any one of claims 1 to 8.

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