Application of trifluoromethyl pyrazolyl dimethyl phosphonate isomer compound in electrolyte, electrolyte additive and lithium ion battery electrolyte

Abstract

The invention relates to application of a trifluoromethyl pyrazolyl dimethyl phosphonate isomer compound in an electrolyte, an electrolyte additive and a lithium ion battery electrolyte, relates to the technical field of lithium ion batteries, and provides application of the trifluoromethyl pyrazolyl dimethyl phosphonate isomer compound in the electrolyte. And the lithium ion battery has a wide application prospect in the field of lithium ion batteries, and makes up for the defects in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion batteries, and in particular to the application of trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compounds in electrolytes, electrolyte additives and lithium ion battery electrolytes. Background Art

[0002] With the rapid development of modern science and technology, lithium-ion batteries, as an efficient and lightweight energy storage device, have shown an irreplaceable role in many fields. From portable electronic devices such as smartphones and tablets to large-scale application scenarios such as electric vehicles and energy storage systems, the requirements for the performance of lithium-ion batteries are increasing. Among them, long cycle performance is one of the key indicators to measure the quality and practicality of lithium-ion batteries. In actual use, both consumers and industrial applications expect lithium-ion batteries to maintain high capacity and stable performance after multiple charge and discharge cycles to reduce the cost and resource waste caused by frequent battery replacement.

[0003] During the charge and discharge cycle of lithium-ion batteries, electrode materials undergo complex physical and chemical changes. Taking graphite negative electrodes as an example, the repeated insertion and extraction of lithium ions causes the distance between graphite layers to change continuously. Long-term cycles will cause the destruction of the graphite layered structure, causing the electrode material to gradually pulverize. Positive electrode materials also face structural stability issues. Especially during high-potential charge and discharge, the crystal structure may undergo phase changes and lattice distortion, affecting the diffusion channels and insertion sites of lithium ions, thereby reducing the capacity and performance of the battery.

[0004] On the negative electrode surface, when lithium ions are embedded, the solvent molecules and salt anions in the electrolyte react with the electrode surface to form a solid electrolyte interface (SEI) film. However, during long-term cycling, the SEI film is not stable and will continue to grow, rupture and repair. This dynamic change process will continuously consume the active ingredients and lithium ions in the electrolyte, while increasing the internal resistance of the battery. On the positive electrode side, under high potential conditions, redox reactions are likely to occur between the positive electrode material and the electrolyte, resulting in damage to the positive electrode surface structure and the generation of gas, which in turn affects the internal pressure and chemical stability of the battery.

[0005] As the number of charge and discharge cycles increases, the properties of the electrolyte itself will also change. For example, the decomposition of lithium salts, the volatilization and polymerization of solvents will cause the ionic conductivity of the electrolyte to decrease, the number of lithium ion migration will decrease, and further affect the charge and discharge performance and cycle life of the battery.

[0006] At present, researchers have tried many methods to improve the long-cycle performance of lithium-ion batteries. For example, electrode materials are modified, including element doping, surface coating and other technologies, but these methods are often complex and costly, and may have a certain impact on the bulk performance of electrode materials. In terms of electrolytes, although there are some conventional electrolyte formulas, their stability in the long-term cycle process still needs to be improved, and it is difficult to meet the growing demand for high-performance lithium-ion batteries.

[0007] As a relatively simple and effective means, electrolyte additives provide a new way to improve the long-cycle performance of lithium-ion batteries. By adding a small amount of specific compounds to the electrolyte, it is possible to specifically solve the electrode-electrolyte interface problem, inhibit the structural changes of the electrode material, and improve the performance of the electrolyte itself. Different types of additives, such as film-forming additives, overcharge protection additives, ion transport promoter additives, and gas inhibition additives, each have a unique mechanism of action and can improve the long-cycle performance of lithium-ion batteries from different angles. However, the current research on new and efficient electrolyte additives is still in the stage of continuous exploration and improvement, and further in-depth research is needed to develop technical solutions that are more suitable for commercial applications.

[0008] In summary, from the perspective of electrolyte additives, studying methods to improve the long-cycle performance of lithium-ion batteries has important theoretical and practical application value and is one of the current research hotspots in the field of lithium-ion battery technology. Summary of the invention

[0009] In order to solve the above problems, the present invention provides the use of trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compounds in electrolytes, electrolyte additives and lithium ion battery electrolytes.

[0010] In a first aspect, the present invention provides the use of trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compounds in an electrolyte.

[0011] Furthermore, the chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound is as shown in Formula I;

[0012] The formula I: Wherein: R1, R2 and R3 are each independently a hydrogen atom or dimethyl phosphonate, and only one of R1, R2 and R3 contains dimethyl phosphonate.

[0013] Further, the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound includes trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 1, trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 2 or trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 3;

[0014] The chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 1 is:

[0015]

[0016] The chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 2 is:

[0017]

[0018] The chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 3 is:

[0019]

[0020] In a second aspect, the present invention provides an electrolyte additive, wherein the electrolyte additive is the isomer compound of dimethyl trifluoromethylpyrazolylphosphonate as described in any one of the first aspects.

[0021] In a third aspect, the present invention provides a lithium-ion battery electrolyte, wherein the lithium-ion battery electrolyte comprises the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound as described in any one of the first aspects.

[0022] Furthermore, the lithium-ion battery electrolyte comprises a lithium salt, an anhydrous organic solvent, the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound according to any one of the first aspects, and a second additive;

[0023] The molar concentration of the lithium salt in the lithium ion battery electrolyte is 0.8M-1.4M;

[0024] In terms of weight percentage, the amount of the anhydrous organic solvent accounts for 60 to 80% of the total weight of the lithium ion battery electrolyte;

[0025] In terms of weight percentage, the amount of the dimethyl trifluoromethyl pyrazolylphosphonate isomer compound is 0.1 to 10% of the total weight of the lithium ion battery electrolyte;

[0026] In terms of weight percentage, the amount of the second additive is 0.1 to 20% of the total weight of the lithium ion battery electrolyte;

[0027] The second additive includes at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfite, ethylene sulfate, lithium bis(oxalatoborate), lithium difluoro(oxalatoborate), tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

[0028] Furthermore, in terms of weight percentage, the amount of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound is 0.1-5% of the total weight of the lithium ion battery electrolyte, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the anhydrous organic solvent includes at least one of carbonate and carboxylic acid ester; the carbonate includes at least one of propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate; the carboxylic acid ester includes at least one of ethyl propionate, ethyl acetate, methyl acetate, propyl propionate and propyl acetate.

[0029] Furthermore, in terms of weight percentage, the amount of the dimethyl trifluoromethylpyrazolylphosphonate isomer compound is 0.1-1% of the total weight of the lithium ion battery electrolyte.

[0030] The above technical solution provided by the embodiment of the present invention has at least the following advantages compared with the prior art:

[0031] The present invention provides the use of trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compounds in electrolytes, which can significantly improve the long cycle performance of lithium-ion batteries, have broad application prospects in the field of lithium-ion batteries, and make up for the shortcomings of the prior art. Specifically:

[0032] (1) Reaction activity and side reaction control

[0033] Advantages of structural functional groups: The phosphonate functional groups in the isomers of trifluoromethylpyrazolylphosphonic acid dimethyl ester have certain chemical stability. The PO bond and CP bond of the phosphonate group are relatively stable, making it difficult for the compound to undergo unnecessary chemical bond breakage and reaction in the electrolyte environment. At the same time, the pyrazole ring structure also increases the stability of the molecule, and its conjugated system can disperse the charge and reduce the reactivity of the molecule.

[0034] Mode of action: In the electrolyte, this compound can occupy certain reactive sites through its stable structure, preventing other highly reactive compounds from approaching and causing side reactions. It can form relatively stable complexes with active intermediates in the electrolyte, thereby inhibiting these intermediates from further inducing side reactions, reducing the generation of impurities, and maintaining the purity and stability of the electrolyte.

[0035] (2) Volatile substance management

[0036] Advantages of structural functional groups: The trifluoromethyl group in the molecule increases the molecular weight and intermolecular forces of the compound. The trifluoromethyl group has a large steric hindrance and strong electronegativity, which enhances the van der Waals force between molecules and reduces the volatility of the compound.

[0037] Mode of action: During long-term cycling in a high-temperature environment, dimethyl trifluoromethyl pyrazolylphosphonate isomers can stably exist in the electrolyte. It is not as easy to volatilize and lose as low-molecular-weight volatile substances, thereby maintaining the stability of the electrolyte composition ratio. This helps maintain the original performance of the electrolyte and ensures that the lithium ion transmission efficiency is not affected by changes in composition.

[0038] (3) Electrode material compatibility

[0039] Advantages of structural functional groups: Phosphonate groups and pyrazolyl groups may have good electrode affinity. Phosphonate functional groups can interact with metal ions (such as lithium ions) on the surface of electrode materials to a certain extent to form a stable adsorption layer. The nitrogen atom of the pyrazolyl group can also participate in this interaction and regulate the properties of the electrode-electrolyte interface.

[0040] Mode of action: During long-term cycling, the compound can form a uniform and stable interface layer on the electrode surface, reducing the increase in interface resistance. It can inhibit electrode polarization through good interaction with electrode materials, reduce battery energy loss, thereby improving battery charge and discharge efficiency and improving long-cycle performance.

[0041] (4) Compatibility between additives

[0042] Structural functional group advantages: The chemical structure of trifluoromethylpyrazolylphosphonic acid dimethyl ester isomers is relatively stable, and its functional groups have certain selective reaction characteristics. The reactivity of phosphonate groups and pyrazolyl groups is relatively low, and it is not easy to have violent chemical reactions with other additives.

[0043] Mode of action: In the electrolyte additive combination, this compound can coexist peacefully with other additives. It will not easily generate undesirable byproducts with other additives, which is conducive to maintaining the performance stability of the electrolyte. In addition, it can promote the synergistic effect between additives through its own stable structure, such as helping to form a uniform protective film to avoid hindering the transmission of lithium ions, thereby improving the battery cycle performance.

[0044] (5) Electrode corrosion protection

[0045] Advantages of structural functional groups: The phosphonate group has a certain antioxidant effect and protective effect on electrode materials. It can form a protective film on the electrode surface to prevent the corrosive components in the electrolyte from contacting the electrode material. The pyrazole group can also enhance the stability of this protective film, and its conjugated structure can provide electron delocalization, making the protective film denser.

[0046] Mode of action: During long-term cycling, the protective film formed by dimethyl trifluoromethylpyrazolylphosphonate isomers on the electrode surface can effectively isolate the electrolyte from the electrode material, especially protecting the negative electrode material. This can prevent the electrode surface structure from being destroyed, maintain the stability of the electrode, reduce the problems of active material shedding and electrode surface area reduction, thereby slowing down the battery capacity attenuation and internal resistance increase, which is conducive to the improvement of long-cycle performance.

[0047] (6) Prevention of hydrolysis problems

[0048] Advantages of structural functional groups: The structure of the phosphonate group in this compound is relatively stable and less sensitive to moisture. Compared with some easily hydrolyzed organophosphorus compounds, the electron cloud distribution and chemical bond properties in its molecular structure make it difficult for hydrolysis to occur.

[0049] Mode of action: During battery production and long-term cyclic use, even if the ambient humidity changes slightly, dimethyl trifluoromethyl pyrazolylphosphonate isomers are not prone to hydrolysis. This can avoid the formation of substances that affect the pH and ion conductivity of the electrolyte, maintain the chemical balance of the electrolyte, reduce the cumulative damage to battery performance, and ensure long-cycle performance.

[0050] (7) Solubility issues

[0051] Advantages of structural functional groups: Functional groups such as trifluoromethyl and pyrazolyl in the molecule can improve the solubility of the compound. The polarity and steric hindrance of the trifluoromethyl group can regulate the interaction between the molecule and the solvent molecules, and the pyrazolyl group can also form hydrogen bonds and other interactions with the solvent in the electrolyte through its heterocyclic structure to increase solubility.

[0052] Mode of action: During long-term battery cycling, especially in low-temperature environments, dimethyl trifluoromethyl pyrazolylphosphonate isomers can maintain good solubility and are not easy to precipitate. This helps maintain the uniformity and ion conductivity of the electrolyte, avoids the obstruction of ion transmission due to precipitation accumulation, thereby ensuring the performance of the battery during low-temperature cycling and has a positive impact on long-cycle performance.

[0053] (8) Migration and aggregation phenomena

[0054] Advantages of structural functional groups: The structural characteristics of the compound make it have good dispersibility in the electrolyte. The presence of trifluoromethyl and pyrazolyl groups gives the molecule a certain degree of steric hindrance, preventing the molecules from getting too close and aggregating. At the same time, its interaction with the electrolyte also helps to maintain the uniform distribution of the molecules.

[0055] Mode of action: During the battery cycle, dimethyl trifluoromethyl pyrazolylphosphonate isomers can be evenly distributed on the electrode surface to avoid migration and aggregation. This can ensure the uniformity and stability of film formation, making the embedding and extraction of lithium ions on the electrode surface smoother, reducing the increase in battery internal resistance and reducing the fluctuation of battery performance during long cycles.

[0056] (9) Optimization of ion transmission

[0057] Advantages of structural functional groups: The molecular structure design of this compound can avoid increasing the viscosity of the electrolyte to a certain extent. Its functional group will not produce large intermolecular forces like some additives, leading to increased electrolyte viscosity. Moreover, it may help to regulate the microstructure of the electrolyte and optimize the solvation environment of the ions.

[0058] Mode of action: During the long-term battery cycle, dimethyl trifluoromethyl pyrazolylphosphonate isomers can ensure the formation of a good interface film without reducing the migration rate of ions. It can promote the transmission of lithium ions, reduce the increase of battery internal resistance, and improve the charge and discharge rate performance, which helps to improve the long-cycle performance of the battery.

[0059] (10) Influence of interfacial film

[0060] Advantages of structural functional groups: The phosphonate group can participate in the formation of the interfacial film and can regulate the growth of the interfacial film. It can interact with lithium ions to form a thin and dense interfacial film. The pyrazole group can also modify the structure of the interfacial film to give it a better lithium ion conduction channel.

[0061] Mode of action: During the long-term battery cycle, the interfacial film formed by the isomer of trifluoromethylpyrazolylphosphonic acid dimethyl ester will not grow excessively or deteriorate in structure. It can ensure the smooth insertion and extraction of lithium ions, maintain the reversible capacity of the battery, and reduce capacity decay. In addition, its interaction with other components in the electrolyte is also conducive to maintaining the performance of the interfacial film, further enhancing the battery's capacity retention ability, and playing an important role in improving long-cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0063] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0064] Figure 1 This is the NMR characterization diagram of compound 1 provided in the example of the present invention.

[0065] Figure 2 This is the NMR characterization diagram of compound 2 provided in the example of the present invention.

[0066] Figure 3 This is the NMR characterization diagram of compound 3 provided in the example of the present invention. DETAILED DESCRIPTION

[0067] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0068] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0069] The present invention aims to solve the technical problems faced by lithium-ion batteries, mainly involving the following aspects:

[0070] (1) Reactivity and side reaction control: Some compounds in the electrolyte are highly reactive and prone to side reactions with other components. For example, during long-term battery cycling, highly reactive compounds continue to react to produce impurities, which can affect the purity and stability of the electrolyte. As the number of cycles increases, more and more impurities accumulate, interfering with the normal electrochemical processes inside the battery, causing the battery performance to gradually decline. Moreover, the long-term effects of these side reactions are difficult to predict and control. How to suppress these unnecessary side reactions is one of the key technical issues faced in improving long-cycle performance.

[0071] (2) Management of volatile substances: Some low molecular weight electrolyte components are volatile. During the long-term cycle of the battery, especially in a high temperature environment, these volatile substances will gradually evaporate and be lost. This will change the composition ratio of the electrolyte, causing the originally optimized electrolyte formula to lose balance. Changes in the electrolyte composition directly affect its improvement effect on battery performance, such as reduced lithium ion transmission efficiency. How to prevent or reduce the loss of these volatile substances during long cycles and maintain the stability of the electrolyte composition is a technical problem that needs to be solved.

[0072] (3) Electrode material compatibility: There may be compatibility issues between the electrolyte and the positive or negative electrode materials. During long-term cycling, this incompatibility will cause the interface resistance to gradually increase. For example, when the battery is repeatedly charged and discharged, the interface resistance increases, the electrode polarization phenomenon intensifies, the battery's energy loss increases, and the battery's charge and discharge efficiency continues to decrease, ultimately affecting the long-cycle performance. Moreover, as the number of cycles increases, the interface may undergo structural changes or accumulation of side reaction products due to poor compatibility, further deteriorating the battery performance.

[0073] (4) Compatibility between additives: There may also be compatibility issues with the combination of additives in the electrolyte. Different additives may react chemically during long-term storage or circulation to generate undesirable byproducts. These byproducts will contaminate the electrolyte and affect the performance stability of the electrolyte. For example, when the synergistic effect between additives cannot be effectively exerted or even has a negative effect, such as the formation of an uneven protective film on the electrode surface, it will hinder the transmission of lithium ions and lead to a decrease in battery cycle performance.

[0074] (5) Electrode corrosion protection: Some electrolyte components will corrode the electrode materials (especially the negative electrode materials) during long-term cycling. The electrode surface structure is destroyed, making the electrode less stable. As the number of cycles increases, the performance of the electrode material gradually decays, such as the shedding of active substances and the reduction of electrode surface area. This will cause the battery's capacity to decay faster, the internal resistance to increase, and seriously affect the battery's long-cycle performance. Therefore, how to reduce the corrosion of the electrolyte to the electrode is a technical problem that must be overcome to improve long-cycle performance.

[0075] (6) Prevention of hydrolysis problems: Some organic phosphorus compounds in the electrolyte are sensitive to moisture and are prone to hydrolysis. During battery production and long-term circulation, even if the environmental humidity is slightly improperly controlled, hydrolysis may occur. Substances generated by hydrolysis will affect the pH and ionic conductivity of the electrolyte. For example, substances such as phosphoric acid generated may react with other electrolyte components or change the ion balance of the electrolyte. As the number of cycles increases, this effect will continue to accumulate and reduce battery performance, so preventing hydrolysis is a technical problem that needs to be solved to improve long-cycle performance.

[0076] (7) Solubility issues: Some electrolyte additives have limited solubility in the electrolyte, or their solubility varies greatly at different temperatures. During long-term battery cycling, especially in low-temperature environments, additives may precipitate to form precipitates. Precipitation affects the uniformity and ion conductivity of the electrolyte, causing battery performance to deteriorate during low-temperature cycling. Moreover, as the number of cycles increases, precipitation may accumulate inside the battery, further hindering ion transport and affecting long-cycle performance.

[0077] (8) Migration and aggregation: Additives may migrate or aggregate during the battery cycle, resulting in uneven distribution on the electrode surface. This uneven distribution will affect the uniformity and stability of film formation, causing battery performance to fluctuate during long cycles. For example, an uneven protective film will affect the embedding and extraction process of lithium ions on the electrode surface, increase the internal resistance of the battery, and reduce the long-cycle performance of the battery.

[0078] (9) Optimization of ion transport: Although some electrolyte additives help to form the solid electrolyte interface (SEI) and the positive electrode electrolyte interface (CEI), some additives may increase the viscosity of the electrolyte, thereby reducing the migration rate of ions. During the long-term cycle of the battery, the reduction in ion transport efficiency will lead to an increase in the internal resistance of the battery and a decrease in the charge and discharge rate performance. This effect may be more obvious when the additive is added in high concentration or the molecular structure is large. How to optimize ion transport while ensuring other performance is a technical difficulty in improving long-cycle performance.

[0079] (10) Influence of interfacial film: The interfacial film formed by electrolyte additives may hinder the insertion and extraction of lithium ions to a certain extent. During the long-term cycle of the battery, if the interfacial film grows too thick or the structure is not ideal, the reversible capacity of the battery will decrease. As the number of cycles increases, the capacity decay will become more and more serious, affecting the long-cycle performance of the battery. Moreover, the performance changes of the interfacial film may interact with other components in the electrolyte, further reducing the battery's capacity retention ability.

[0080] The technical solution provided by the present invention is as follows:

[0081] The invention provides an electrolyte additive; the additive is a trifluoromethyl pyrazolyl phosphonic acid dimethyl ester isomer as shown in formula I.

[0082]

[0083] in:

[0084] R1, R2 and R3 independently represent a hydrogen atom and dimethyl phosphonate.

[0085] One and only one of R1, R2 and R3 contains dimethyl phosphonate.

[0086] According to some embodiments of the present invention, the isomers of dimethyl trifluoromethylpyrazolylphosphonate represented by the general formula (I) include the following compounds:

[0087]

[0088]

[0089] The present invention discloses a lithium ion battery electrolyte containing trifluoromethyl pyrazolyl phosphonic acid dimethyl ester isomers. The components of the electrolyte include lithium salt, an anhydrous organic solvent and an electrolyte additive. The amount of trifluoromethyl pyrazolyl phosphonic acid dimethyl ester isomers in the electrolyte is 0.1%-10%, preferably 0.1%-5%, and more preferably 0.1%-1% of the total mass of the electrolyte.

[0090] The isomers of dimethyl trifluoromethyl pyrazolylphosphonate have many advantages in improving the shortcomings of battery electrolytes and improving long-cycle performance. Structurally, the phosphonate functional group and pyrazole ring structure are stable, the PO bond and CP bond of the phosphonate are stable, and the pyrazole ring conjugated system disperses the charge, reduces the reaction activity, occupies the active site, inhibits side reactions, reduces impurities, and maintains the purity and stability of the electrolyte. In terms of volatility management, the trifluoromethyl group increases the molecular weight and intermolecular forces, and its large steric hindrance and strong electronegativity enhance the van der Waals force, reduce volatility, and maintain the stability of the electrolyte composition ratio during long-term high-temperature cycles to ensure the efficiency of lithium ion transmission. For electrode material compatibility, the phosphonate group and the pyrazolyl group have good electrode affinity. The phosphonate can interact with the metal ions on the electrode surface, and the pyrazolyl nitrogen atom participates to form a stable adsorption layer. In long-term cycles, it can reduce the increase in interface resistance, inhibit electrode polarization, reduce energy loss, and improve charge and discharge efficiency. In terms of additive compatibility, its chemical structure is stable, the functional group has low reactivity, and it is not easy to react violently with other additives. It can promote the synergistic effect, avoid the formation of by-products, maintain the stability of the electrolyte performance, and facilitate the formation of a uniform protective film to ensure lithium ion transmission and battery cycle performance. In terms of electrode corrosion protection, the phosphonate group is antioxidant and can form a protective film on the electrode surface. The pyrazolyl group enhances the stability of the film. It can isolate the electrolyte and electrode materials during long-term circulation, protect the negative electrode, prevent electrode structure damage, active material shedding and surface area reduction, and slow down capacity decay and internal resistance increase. In terms of prevention of hydrolysis problems, the phosphonate group has a stable structure in the molecule, low sensitivity to moisture, and is not easy to hydrolyze. During battery production and long-term use, even if the humidity changes, it can avoid the generation of substances that affect the pH and ionic conductivity of the electrolyte, maintain chemical balance, and ensure long-cycle performance. In terms of solubility, trifluoromethyl and pyrazolyl can improve solubility. The trifluoromethyl group regulates the interaction between the molecule and the solvent, and the pyrazolyl group forms a hydrogen bond with the solvent. It can maintain good solubility in low-temperature environments, avoid precipitation, maintain electrolyte uniformity and ionic conductivity, and ensure low-temperature cycle performance. In response to the migration and aggregation phenomena, the molecular structure enables it to have good dispersibility in the electrolyte. The steric hindrance of the trifluoromethyl and pyrazolyl groups prevents molecular aggregation, and the interaction with the electrolyte facilitates uniform distribution. It can be evenly distributed on the electrode surface during the cycle, ensuring uniform and stable film formation, which is conducive to the insertion and removal of lithium ions, reducing the increase in internal resistance and performance fluctuations. In terms of ion transport optimization, the molecular structure will not increase the viscosity of the electrolyte, but can also adjust the microstructure and optimize the ion solvation environment. In long-term cycles, it ensures the formation of a good interface film while not reducing the ion migration rate, reducing internal resistance and improving charge and discharge rate performance. As for the influence on the interface film, the phosphonate group participates in and regulates the growth of the interface film, reacts with lithium ions to form a thin and dense film, and the pyrazolyl modifies the membrane structure, ensuring smooth insertion and removal of lithium ions during long-term cycles, maintaining reversible capacity, reducing capacity attenuation, interacting with other components to maintain membrane performance, and enhancing capacity retention, which is of great significance to the improvement of long-cycle performance.In short, this isomer provides new possibilities for solving battery electrolyte problems and improving long-cycle performance.

[0091] Synthesis method:

[0092] In a dry reaction vessel, 10 mmol of 1-tert-butylpyrazole was dissolved in 50 ml of dichloromethane, and then 15 mmol of potassium carbonate was added and stirred well.

[0093] Under stirring, slowly drop 20 mmol of boron trifluoride ether complex into the reaction system. During the dropwise addition, the dropwise addition speed should be controlled to prevent the reaction from being too violent. After the dropwise addition is completed, continue to stir the reaction at room temperature for 6-12 hours to allow the reaction to proceed fully.

[0094] After the reaction is completed, the reaction mixture is filtered to remove insoluble solid impurities. The filtrate is then concentrated to obtain a crude product. The crude product is purified by column chromatography using a suitable eluent (such as a mixed solvent of petroleum ether and ethyl acetate), and the fractions containing the target product are collected to finally obtain 1-tert-butyl-3,4,5-trifluoropyrazole.

[0095] In a dry reaction container (such as a three-necked flask), add 10 mmol of 1-tert-butyl-3,4,5-trifluoropyrazole and 50-100 mL of anhydrous tetrahydrofuran, and start stirring to fully dissolve the solid.

[0096] Next, 15-20 mmol of triethylamine was slowly added dropwise under ice-bath cooling (0-5° C.), and the mixture was stirred for 10-15 minutes after the addition was complete.

[0097] While maintaining a low temperature (0-5°C) and stirring, 12-15 mmol of dimethylphosphonyl chloride is slowly added dropwise to the reaction system. After the addition is complete, the reaction system is slowly heated to room temperature and stirred at room temperature for 12-24 hours to allow the reaction to proceed fully.

[0098] After the reaction is completed, the reaction mixture is filtered to remove the triethylamine hydrochloride precipitate generated during the reaction. The filtrate is transferred to a separatory funnel and washed with an appropriate amount of water (50 mL) to remove unreacted raw materials and other water-soluble impurities. The organic phase is dried over anhydrous sodium sulfate overnight to remove residual moisture.

[0099] After filtering and removing the desiccant, the solvent tetrahydrofuran is removed by reduced pressure distillation to obtain a crude product. The crude product is purified by silica gel column chromatography, using a suitable eluent (such as a petroleum ether-ethyl acetate mixed solvent), and the target product fractions are collected to finally obtain a 1-tert-butyl-3,4,5-trifluoropyrazole product containing a dimethyl phosphonate group.

[0100] The NMR characterization of compound 1 prepared by the above method is as follows Figure 1 shown.

[0101] The NMR characterization of compound 2 prepared by the above method is as follows Figure 2 shown.

[0102] The NMR characterization of compound 3 prepared by the above method is as follows Figure 3 shown.

[0103] The invention discloses a lithium ion battery electrolyte containing trifluoromethyl pyrazolyl phosphonic acid dimethyl ester isomers, wherein the additive accounts for 0.1% to 20% of the total mass of the lithium ion battery electrolyte.

[0104] The additive is selected from at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), vinyl sulfite (ES), ethylene sulfate (DTD), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiDFOB), tris(trimethylsilyl)borate (TMSB), and tris(trimethylsilyl)phosphate (TMSP).

[0105] The invention discloses a lithium ion battery electrolyte containing dimethyl trifluoromethyl pyrazolyl phosphonate isomers, wherein the concentration of lithium salt in the electrolyte is 0.8M-1.4M.

[0106] The lithium salt is selected from at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide.

[0107] The invention discloses a lithium ion battery electrolyte containing trifluoromethyl pyrazolyl phosphonic acid dimethyl ester isomers, wherein the anhydrous organic solvent in the electrolyte accounts for 60% to 80% of the total mass of the lithium ion battery electrolyte.

[0108] Preferably, the anhydrous organic solvent comprises any one of carbonate esters and carboxylates or a mixture of two of them.

[0109] Preferably, the carbonate mainly includes propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate.

[0110] Preferably, the carboxylic acid esters mainly include ethyl propionate, ethyl acetate, methyl acetate, propyl propionate and propyl acetate.

[0111] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually measured according to national standards. If there is no corresponding national standard, then the conditions recommended by the manufacturer are followed.

[0112] Example 1

[0113] The positive active material of the lithium ion battery used in the embodiment of the present invention is lithium iron phosphate material (LiFePO4), the negative electrode material is artificial graphite, and the electrolyte usage is 2.3±0.5g / Ah. A lithium ion battery assembled with a lithium ion battery electrolyte containing trifluoromethyl pyrazolyl phosphonic acid dimethyl ester isomers is selected as an embodiment, and a lithium ion battery assembled with a conventional electrolyte not containing trifluoromethyl pyrazolyl phosphonic acid dimethyl ester isomers is selected as a comparative example.

[0114] The specific steps for preparing lithium-ion battery electrolyte in a glove box (H2O < 5ppm) are as follows:

[0115] (1) dehydrating an anhydrous organic solvent molecular sieve under the protection of nitrogen or inert gas to obtain an anhydrous organic solvent;

[0116] (2) adding an appropriate amount of lithium salt to an anhydrous organic solvent, stirring and cooling to obtain a mixed solution;

[0117] (3) Add appropriate amount of additives to the mixed solution to obtain 2000 g of electrolyte, which is placed in a fluorination bottle.

[0118] The electrolyte is used to assemble a lithium-ion battery. The positive electrode material of the lithium-ion battery is a ternary material (LiFePO4), the negative electrode material is artificial graphite, the designed capacity is 60Ah, and the injection amount is 2.3±0.5g / Ah.

[0119] Comparative Example 1:

[0120] The non-aqueous organic solvent used is: EC:PC:DMC:EMC=30:5:10:55; lithium salt: the concentration is 1.2M lithium hexafluorophosphate (LiPF6).

[0121] Comparative Example 2:

[0122] The non-aqueous organic solvent used is: EC:PC:DMC:EMC=30:5:10:55; lithium salt: the concentration is 0.8M lithium hexafluorophosphate (LiPF6), the concentration is 0.4M lithium bis(fluorosulfonyl)imide (LiFSI).

[0123] Comparative Example 3:

[0124] The non-aqueous organic solvent used is: EC:PC:DMC:EMC=30:5:10:55; lithium salt: 0.8M lithium hexafluorophosphate (LiPF6), 0.4M lithium bis(fluorosulfonyl)imide (LiFSI). Additives: 2.5wt.% VC, 1wt.% FEC, 0.5wt.% PS, 0.5wt.% ES, 1wt.% DTD, 0.5wt.% LiDFOB, 0.5wt.% TMSP.

[0125] Embodiment 1:

[0126] The non-aqueous organic solvent used was: EC:PC:DMC:EMC=30:5:10:55; lithium salt: 0.8M lithium hexafluorophosphate (LiPF6), 0.4M lithium bis(fluorosulfonyl)imide (LiFSI). Additives: 2.5wt.% VC, 1wt.% FEC, 0.5wt.% PS, 0.5wt.% ES, 1wt.% DTD, 0.5wt.% LiDFOB, 0.5wt.% TMSP. The addition amount of compound 1 was 8%.

[0127] Embodiment 2:

[0128] The non-aqueous organic solvent used was: EC:PC:DMC:EMC=30:5:10:55; lithium salt: 0.8M lithium hexafluorophosphate (LiPF6), 0.4M lithium bis(fluorosulfonyl)imide (LiFSI). Additives: 2.5wt.% VC, 1wt.% FEC, 0.5wt.% PS, 0.5wt.% ES, 1wt.% DTD, 0.5wt.% LiDFOB, 0.5wt.% TMSP. The addition amount of compound 1 was 4%.

[0129] Embodiment 3:

[0130] The non-aqueous organic solvent used was: EC:PC:DMC:EMC=30:5:10:55; lithium salt: 0.8M lithium hexafluorophosphate (LiPF6), 0.4M lithium bis(fluorosulfonyl)imide (LiFSI). Additives: 2.5wt.% VC, 1wt.% FEC, 0.5wt.% PS, 0.5wt.% ES, 1wt.% DTD, 0.5wt.% LiDFOB, 0.5wt.% TMSP. The addition amount of compound 1 was 0.5%.

[0131] Comparative Example 4:

[0132] The difference between this example and implementation test example 3 is that the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound is replaced by the compound represented by formula (II) (CAS registration number is 140374-07-8);

[0133] The formula (II):

[0134] The lithium-ion batteries assembled in the comparative example and the embodiment were placed in an environment of 25° C. and cycled at 1C charge and 1C discharge to test the capacity retention rate in a voltage range of 2.5 to 3.65 V. The results are shown in Table 1.

[0135] Table 1 Normal temperature cycle performance test

[0136] Test samples 1000 laps 2000 laps 4000 laps 6000 laps 8000 laps Comparative Example 1 20.4％ 15.4％ 5.4％ 0.0％ 0.0％ Comparative Example 2 55.3％ 50.3％ 40.3％ 25.3％ 5.3％ Comparative Example 3 99.9％ 97.9％ 92.9％ 77.9％ 47.9％ Comparative Example 4 99.5％ 97.5％ 92.5％ 77.5％ 47.5％ Example 1 98.9％ 96.9％ 94.9％ 82.9％ 80.9％ Example 2 100.0％ 98.0％ 96.0％ 84.0％ 82.0％ Example 3 100.7％ 98.7％ 96.7％ 84.7％ 82.7％

[0137] The lithium-ion batteries assembled in the comparative example and the embodiment were placed in an environment of 45°C and cycled at 1C charge and 1C discharge to test the capacity retention rate in a voltage range of 2.5 to 3.65V. The results are shown in Table 2.

[0138] Table 2 High temperature cycle performance test

[0139] Test samples 1000 laps 2000 laps 3000 laps 4000 laps Comparative Example 1 29.9％ 19.9％ 0.0％ 0.0％ Comparative Example 2 65.4％ 55.4％ 35.4％ 5.4％ Comparative Example 3 92.8％ 82.8％ 54.8％ 24.8％ Comparative Example 4 92.5％ 82.5％ 54.5％ 24.5％ Example 1 95.2％ 92.2％ 89.2％ 80.2％ Example 2 97.0％ 94.0％ 91.0％ 82.0％ Example 3 97.5％ 94.5％ 91.5％ 82.5％

[0140] It can be seen from the results that the lithium ion battery electrolyte containing trifluoromethylpyrazolylphosphonic acid dimethyl ester isomers can improve the cycle performance of lithium ion batteries and has a good application prospect.

[0141] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. Application of dimethyl trifluoromethylpyrazolylphosphonate isomers in electrolytes.

2. The use according to claim 1, characterized in that: The chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound is shown in Formula I; The formula I: Wherein: R1, R2 and R3 are each independently a hydrogen atom or dimethyl phosphonate, and only one of R1, R2 and R3 contains dimethyl phosphonate.

3. The use according to claim 1, characterized in that: The trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound includes trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 1, trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 2 or trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 3; The chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 1 is: The chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 2 is: The chemical structural formula of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound 3 is:

4. An electrolyte additive, characterized in that: The electrolyte additive is the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound according to any one of claims 1 to 3.

5. A lithium ion battery electrolyte, characterized in that: The lithium-ion battery electrolyte comprises the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound according to any one of claims 1 to 3.

6. The lithium ion battery electrolyte according to claim 5, characterized in that: The lithium-ion battery electrolyte comprises a lithium salt, an anhydrous organic solvent, the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound according to any one of claims 1 to 3, and a second additive; The molar concentration of the lithium salt in the lithium ion battery electrolyte is 0.8M-1.4M; In terms of weight percentage, the amount of the anhydrous organic solvent accounts for 60-80% of the total weight of the lithium ion battery electrolyte; In terms of weight percentage, the amount of the dimethyl trifluoromethyl pyrazolylphosphonate isomer compound is 0.1 to 10% of the total weight of the lithium ion battery electrolyte; In terms of weight percentage, the amount of the second additive is 0.1 to 20% of the total weight of the lithium ion battery electrolyte; The second additive includes at least one of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl sulfite, ethylene sulfate, lithium bis(oxalatoborate), lithium difluoro(oxalatoborate), tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

7. The lithium ion battery electrolyte according to claim 6, characterized in that: In terms of weight percentage, the amount of the trifluoromethylpyrazolylphosphonic acid dimethyl ester isomer compound is 0.1-5% of the total weight of the lithium ion battery electrolyte, the lithium salt includes at least one of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, the anhydrous organic solvent includes at least one of carbonate and carboxylic acid ester; the carbonate includes at least one of propylene carbonate, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate and ethylene carbonate; the carboxylic acid ester includes at least one of ethyl propionate, ethyl acetate, methyl acetate, propyl propionate and propyl acetate.

8. The lithium ion battery electrolyte according to claim 6, characterized in that: In terms of weight percentage, the amount of the dimethyl trifluoromethyl pyrazolylphosphonate isomer compound is 0.1-1% of the total weight of the lithium ion battery electrolyte.

Images