Battery electrolyte film-forming additive, battery electrolyte and application thereof

Abstract

The application provides a battery electrolyte film-forming additive, a battery electrolyte and application thereof. The battery electrolyte film-forming additive is one or more of alkyl phosphonate alkoxysilane compounds, the compound has a chemical structure shown in formula (I), wherein R1, R2, R3, R4 and R5 are each independently selected from one of C1-C10 alkyl, 1<=n<=10, and n is an integer. In the formula, P with electrophilic characteristics shows a high reduction potential; the reaction of oxygen atoms and silicon negative active points can reduce the activity of the passivation film layer; the high bond energy of Si-O bonds and the alkyl structure can make the passivation film have flexibility and stability. Under the synergistic cooperation of the above structure, the battery electrolyte film-forming additive can generate a passivation film layer with compactness, flexibility and stability on the silicon negative electrode, inhibit the continuous consumption of the battery electrolyte caused by the expansion of silicon particles in the cycle process, reduce the interface impedance, and improve the battery performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a battery electrolyte film-forming additive, a battery electrolyte and applications thereof. Background Art

[0002] Lithium-ion batteries, due to their high operating voltage, high specific energy density, long cycle life, and environmentally friendly design, have become an indispensable and important chemical energy source for applications such as digital electronics, electric vehicles, energy storage, and aerospace. The electrolyte in lithium-ion batteries is a crucial component, often referred to as the battery's "blood." Typically composed of lithium salts, solvents, and additives, it significantly impacts the battery's cycle performance, rate capability, and safety.

[0003] The most promising direction for high-energy-density lithium-ion battery applications is the silicon-carbon material system. However, silicon-carbon anodes also have many problems: the volume expansion and contraction of silicon particles during intercalation and deintercalation leads to particle pulverization, shedding, and electrochemical performance failure; the continuous growth of the solid electrolyte layer (SEI) on the surface of silicon particles due to continuous side reactions with the electrolyte, resulting in poor cycling performance of high-energy-density batteries using silicon-carbon anode materials.

[0004] In the existing method, the cycle stability performance of lithium-ion batteries can be further improved by adding battery electrolyte film-forming additives to the battery electrolyte. Existing commonly used battery electrolyte film-forming additives include vinylene carbonate (VC), fluoroethylene carbonate (FEC), propylene sulfate (PCS), etc. Adding them to the electrolyte has a certain effect on improving battery performance. However, the film layer formed by traditional battery electrolyte film-forming additives is not flexible and stable enough, and may also bring safety, cost and environmental problems. These shortcomings limit their application in the new generation of high-energy-density lithium-ion batteries, especially they cannot meet the ideal application effect in silicon-carbon negative electrode battery systems.

[0005] When traditional battery electrolyte film-forming additives are applied to silicon-carbon anode lithium-ion batteries formed from silicon-carbon material systems, the formed film layer is prone to rupture during cycling, leading to continuous decomposition of the electrolyte and consumption of active lithium in the electrolyte, increasing impedance and reducing the battery's cycling stability and energy density. The characteristics of silicon-carbon anode materials require that the formed film layer not only have good stability but also high flexibility to accommodate the volume expansion and contraction of silicon particles during charge and discharge. However, the films formed by traditional additives are often relatively rigid and cannot meet this basic requirement.

[0006] Therefore, developing new battery electrolyte additives that can form more stable and flexible battery electrolytes and applying them to silicon-carbon negative electrode lithium-ion batteries is an important research direction in the field of lithium-ion batteries. Summary of the Invention

[0007] The main purpose of the present invention is to provide a battery electrolyte film-forming additive, a battery electrolyte and its application, so as to solve the problems in the prior art caused by the poor stability and flexibility of the battery electrolyte film-forming additive and the problem that it cannot be applied to silicon-carbon negative electrode lithium-ion batteries with higher requirements for stability and flexibility.

[0008] In order to solve the above problems, the present invention provides a battery electrolyte film-forming additive, wherein the battery electrolyte film-forming additive is one or more alkylphosphonate alkoxysilanes, and the alkylphosphonate alkoxysilane has a chemical structure shown in the following formula (I): Wherein, R1, R2, R3, R4, and R5 are each independently selected from one of C1 to C10 alkyl groups, 1≤n≤10, and n is an integer. The use of the above-mentioned battery electrolyte film-forming additive can effectively form a passivation film layer with a dense structure and both flexible and stable properties. The presence of this passivation film layer can inhibit the continuous consumption of battery electrolyte caused by silicon particle expansion during cycling, and can also reduce interfacial impedance, thereby improving the cycling stability of lithium-ion batteries with silicon-carbon negative electrode cell systems.

[0009] Furthermore, R1, R2, and R3 are each independently selected from a C1-C5 alkyl group, R4 and R5 are each independently selected from a C1-C10 alkyl group, 1 ≤ n ≤ 3, and n is an integer. Preferably, R1, R2, and R3 are each independently selected from a C1-C10 alkyl group, R4 and R5 are each independently selected from a C1-C2 alkyl group, 1 ≤ n ≤ 3, and n is an integer. The above limitations can further enhance the effectiveness of the battery electrolyte film-forming additive.

[0010] Furthermore, R1, R2, R3, R4, and R5 are each independently selected from methyl, ethyl, propyl, and butyl, 3≤n≤5, and n is an integer. Selecting the above specific types of structures can further enhance the effectiveness of the battery electrolyte film-forming additive, thereby improving the cycle stability of the battery.

[0011] Furthermore, the battery electrolyte film-forming additive is selected from one or more of the following structures:

[0012] Preferably, the battery electrolyte film-forming additive is a compound of compound S1 and compound S4, and the weight ratio of the two is (1-3):2; alternatively, the battery electrolyte film-forming additive is a compound of compound S3 and compound S4, and the weight ratio of the two is 2:(3-5); alternatively, the battery electrolyte film-forming additive is a compound of compound S2 and compound S3, and the weight ratio of the two is 1:(1-3). Compounding the battery electrolyte film-forming additive in the above manner can make the obtained mixed battery electrolyte film-forming additive have better system miscibility characteristics, which is beneficial to make the passivation film layer formed in the battery have better density, stability and flexibility.

[0013] According to another aspect of the present invention, a battery electrolyte is provided, comprising a lithium salt, an organic solvent, and the aforementioned battery electrolyte film-forming additive. Application of the aforementioned battery electrolyte additive to the battery electrolyte is beneficial for reducing the internal resistance of the battery and improving the cycling stability of the lithium battery.

[0014] Furthermore, by weight, the battery electrolyte comprises 7-16% lithium salt, 0.5-9% battery electrolyte film-forming additive, and the balance is an organic solvent. Preferably, by weight, the battery electrolyte comprises 10-15% lithium salt, 0.5-3% battery electrolyte film-forming additive, and the balance is an organic solvent. Controlling the ratio of lithium salt, battery electrolyte film-forming additive, and organic solvent in the battery electrolyte within the above range ensures that the battery electrolyte has good conductivity and electrochemical stability while also ensuring good compatibility among the above components, thereby further improving the performance of the battery electrolyte.

[0015] Furthermore, the organic solvent is one or more of an organic carbonate, an ionic liquid, a polyether, an aromatic ether, a C1-C40 alkyl ether, a cyclic ether, a carboxylate, a sulfone, a nitrile, a dinitrile, and a polynitrile; preferably, the organic solvent is one or more of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate; preferably, the lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium bis(fluorosulfonylimide), lithium difluoro(bisoxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate; further preferably, the lithium salt is lithium hexafluorophosphate. The above-mentioned types of lithium salts and the battery electrolyte film-forming additive of the present invention can better exert a synergistic effect.

[0016] Furthermore, the battery electrolyte film-forming additive is a compound of compound S1 and compound S4, the organic solvent is dimethyl sulfoxide, and the lithium salt is lithium difluorooxalatoborate; or, the battery electrolyte film-forming additive is a compound of compound S3 and compound S4, the organic solvent is aromatic polyoxyethylene ether, and the lithium salt is lithium trifluoromethanesulfonate; or, the battery electrolyte film-forming additive is a compound of compound S2 and compound S3, the organic solvent is hexanetrinitrile, and the lithium salt is bis(fluorosulfonyl imide) lithium; wherein the structural formulas of compound S1, compound S2, compound S3, and compound S4 are as follows:

[0017] Using them in the above manner is beneficial to further improve the stability and flexibility of the passivation film layer formed during the battery cycle.

[0018] According to a third aspect of the present invention, a silicon-carbon anode lithium-ion battery is provided, comprising the above-mentioned battery electrolyte. Introducing the above-mentioned battery electrolyte film-forming additive into the silicon-carbon anode lithium-ion battery is beneficial for improving the cycle stability of the battery.

[0019] Furthermore, the silicon-carbon negative electrode lithium-ion battery also includes a positive electrode containing a cathode active material, a negative electrode containing an anode active material, and a battery separator; preferably, the cathode active material is a material capable of releasing lithium ions; further preferably, the cathode active material is one or more of transition metal phosphates, transition metal oxide lithium salts, and metal sulfides; preferably, the anode active material is a material capable of receiving lithium ions; further preferably, the anode active material is one or more of silicon material, silicon-carbon material, a composite material of silicon monoxide and graphite, or a composite material of silicon-carbon and silicon monoxide; preferably, the battery separator is at least one of a polyimide separator, a polyethylene separator, a polypropylene separator, and a polyethylene terephthalate separator; further preferably, the battery separator is a polyethylene separator or a polypropylene separator. Selecting the above-mentioned types of cathode, anode, and separator materials can further improve the cycle stability performance of the silicon-carbon negative electrode lithium-ion battery.

[0020] The present invention provides a battery electrolyte film-forming additive, a battery electrolyte, and applications thereof. The battery electrolyte film-forming additive is composed of an alkylphosphonate alkoxysilane, the component structure of which contains not only Si-O bonds and chain alkyl ((CH2)n) structures with high bond energy, but also P atoms with good electrophilic properties. The electrophilic P in the structure exhibits a high reduction potential, allowing the battery to preferentially form a dense and stable passivation film on the silicon negative electrode during the formation process. The oxygen atoms in the structure react with the active points of the silicon negative electrode to reduce the activity of the passivation film layer, thereby further inhibiting decomposition of the battery electrolyte at the active points of the silicon negative electrode during circulation. The high bond energy Si-O bonds and chain alkyl ((CH2)n) structures in the structure make the passivation film more flexible and stable. Under the synergistic effect of the above-mentioned structural features, alkyl phosphonate alkoxysilane can be used as a film-forming additive for battery electrolyte to effectively form a passivation film layer with a dense structure and both flexible and stable properties on the silicon negative electrode. The presence of this passivation film layer can inhibit the continuous consumption of battery electrolyte caused by the expansion of silicon particles during the cycle, and can also reduce the interfacial impedance, thereby improving the cycle stability of lithium-ion batteries with silicon-carbon negative electrode cell systems. DETAILED DESCRIPTION

[0021] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0022] As mentioned in the background technology section, conventional battery electrolyte film-forming additives, when applied to silicon-carbon negative-electrode lithium-ion batteries using silicon-carbon material systems, can easily cause the film formed to break during cycling. This leads to continuous decomposition of the battery electrolyte and consumption of active lithium in the battery electrolyte, increasing impedance and, in turn, reducing the battery's cycling stability and energy density. Therefore, finding a battery electrolyte film-forming additive that can form a film with both stability and flexibility is key to solving this problem.

[0023] In order to solve the above problems, the present invention provides a battery electrolyte film-forming additive, wherein the battery electrolyte film-forming additive is one or more alkylphosphonate alkoxysilanes, and the alkylphosphonate alkoxysilane has a chemical structure shown in the following formula (I):

[0024]

[0025] Wherein, R1, R2, R3, R4 and R5 are each independently selected from one of C1 to C10 alkyl groups, 1≤n≤10, and n is an integer.

[0026] The component structure of the alkylphosphonate alkoxysilane in the aforementioned battery electrolyte film-forming additive contains not only P atoms with excellent electrophilic properties, but also high-energy Si-O bonds and chain alkyl ((CH2)n) structures. The electrophilic P in the structure exhibits a high reduction potential, allowing a dense and stable passivation film to preferentially form on the silicon anode during the battery formation process. The oxygen atoms in the structure react with the active sites of the silicon anode, reducing the activity of the passivation film, thereby further inhibiting decomposition at the active sites of the silicon anode during battery electrolyte circulation. The high-energy Si-O bonds and chain alkyl ((CH2)n) structures make the passivation film more flexible and stable. Under the synergistic effect of the above-mentioned structural features, alkylphosphonate alkoxysilanes as battery electrolyte film-forming additives can effectively form a passivation film layer with a dense structure and both flexible and stable characteristics on the silicon negative electrode. The presence of this passivation film layer can inhibit the continuous consumption of battery electrolyte caused by the expansion of silicon particles during the cycle, and can also reduce the interfacial impedance, thereby improving the cycle stability of lithium-ion batteries with silicon-carbon negative electrode battery cells. In addition, the alkyl substituents R1, R2, R3, R4 and R5 in the alkylphosphonate alkoxysilane are each independently selected from one of the C1 to C10 alkyl groups, and 1≤n≤10 is controlled, and n is an integer. The above-mentioned structural features can further improve the flexibility of the formed passivation film layer. Controlling the component structure of the battery electrolyte film-forming additive within the above-mentioned range can not only make it have good system compatibility, but also make the passivation film layer formed by the battery electrolyte film-forming additive during use have better flexibility and stability, effectively improving the use effect of the battery electrolyte film-forming additive.

[0027] In a preferred embodiment, R1, R2 and R3 are each independently selected from one of C1 to C5 alkyl groups, R4 and R5 are each independently selected from one of C1 to C10 alkyl groups, 1≤n≤3, and n is an integer. By making the component structure of the battery electrolyte film-forming additive within the above range, the battery electrolyte film-forming additive can better participate in the battery system, and the passivation film layer formed has better stability and flexibility. Preferably, R1, R2 and R3 are each independently selected from one of C1 to C10 alkyl groups, R4 and R5 are each independently selected from one of C1 to C2 alkyl groups, 1≤n≤3; and n is an integer. The above characteristics of the alkyl chain can further enhance the use effect of the battery electrolyte film-forming additive.

[0028] In a preferred embodiment, R1, R2, R3, R4, and R5 are each independently selected from methyl, ethyl, propyl, and butyl, with 3≤n≤5, and n being an integer. Selecting the substituents R1, R2, R3, R4, and R5 in the alkylphosphonate alkoxysilane from the specific types described above, and controlling the number of chain alkyl groups within the above range, can further enhance the stability and flexibility of the battery electrolyte film-forming additive, effectively improving the cycling stability of the battery.

[0029] In a preferred embodiment, the battery electrolyte film-forming additive is selected from one or more of the following structures:

[0030] Preferably, the battery electrolyte film-forming additive is a compound of compound S1 and compound S4, and the weight ratio of the two is (1 to 3): 2; or, the battery electrolyte film-forming additive is a compound of compound S3 and compound S4, and the weight ratio of the two is 2: (3 to 5); or, the battery electrolyte film-forming additive is a compound of compound S2 and compound S3, and the weight ratio of the two is 1: (1 to 3). In particular, after a large number of experiments, the present invention creatively discovered that the above-mentioned battery electrolyte film-forming additives can be compounded and used in the above-mentioned proportions to obtain better results. This may be because after mixing the above-mentioned battery electrolyte film-forming additives with chain alkyl groups of different lengths and substituent side chains of different lengths, the obtained mixed battery electrolyte film-forming additive has better system mutual solubility characteristics, and the passivation film layer formed in the battery has better density, stability and flexibility, which can further improve the cycle stability of the battery.

[0031] It should be noted that the present invention provides a simpler and more convenient method for preparing a film-forming additive for battery electrolytes. The method uses Bu3N as a catalyst, selects a corresponding substituted alkenylphosphonic acid diester and a corresponding alkyl and methoxy-substituted silane in a molar ratio of 1: (8-16), adds the above two raw materials and the catalyst to anhydrous ethanol, reacts the mixed system at 60-80°C for 8-14 hours, and then uses reduced pressure distillation to remove the anhydrous ethanol solvent and unreacted silane raw material to obtain a battery electrolyte film-forming additive. This method is simple to operate, especially with convenient post-processing, and is a method that can be used for large-scale production.

[0032] According to another aspect of the present invention, a battery electrolyte is provided, comprising a lithium salt, an organic solvent, and the aforementioned battery electrolyte film-forming additive. When applied to the battery electrolyte, the battery electrolyte additive forms a passivation film layer having a dense structure, flexibility, and stability during cycling. The presence of the passivation film layer can suppress the continuous consumption of the battery electrolyte during cycling, reduce the internal resistance of the battery, and improve the cycling stability of the lithium battery.

[0033] In a preferred embodiment, by weight percentage, the lithium salt in the battery electrolyte is 7-16%, the battery electrolyte film-forming additive is 0.5-9%, and the balance is an organic solvent. By controlling the ratio of lithium salt, battery electrolyte film-forming additive and organic solvent in the battery electrolyte within the above range, the battery electrolyte can have good conductivity and electrochemical stability while also having good compatibility of the above components, further reducing the internal resistance of the battery and improving the cycle stability of the lithium battery. Preferably, by weight percentage, the lithium salt in the battery electrolyte is 10-15%, the battery electrolyte film-forming additive is 0.5-3%, and the balance is an organic solvent. The above effect is better when the components in the battery electrolyte are controlled within the above preferred range.

[0034] By way of example but not limitation, the organic solvent is one or more of an organic carbonate, an ionic liquid, a polyether, an aromatic ether, a C1-C40 alkyl ether, a cyclic ether, a carboxylate, a sulfone, a nitrile, a dinitrile and a polynitrile. The organic solvent in the battery electrolyte can act as a mixed system, and the above-mentioned types of organic solvents and lithium salts and battery electrolyte film-forming additives all have good compatibility. Preferably, the organic solvent is one or more of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate. The above-mentioned types of organic solvents are more common in actual use and have better effects. Also by way of example but not limitation, the lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium trifluoromethylsulfonate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium bis(fluorosulfonylimide), lithium difluoro(bis(oxalato)phosphate and lithium tetrafluoro(oxalato)phosphate. The aforementioned types of lithium salts and the battery electrolyte film-forming additives described herein all exhibit excellent synergistic effects. Further preferably, the lithium salt is lithium hexafluorophosphate, which is more common in practice and exhibits better results. The organic solvents ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate can be mixed in any proportion. In the embodiments of the present invention, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate are mixed in a mass ratio of 3:3:4.

[0035] In a preferred embodiment, the battery electrolyte film-forming additive is a compound of compound S1 and compound S4, the organic solvent is dimethyl sulfoxide, and the lithium salt is lithium difluorooxalatoborate; or, the battery electrolyte film-forming additive is a compound of compound S3 and compound S4, the organic solvent is aromatic polyoxyethylene ether, and the lithium salt is lithium trifluoromethanesulfonate; or, the battery electrolyte film-forming additive is a compound of compound S2 and compound S3, the organic solvent is hexanetrinitrile, and the lithium salt is bis(fluorosulfonyl imide) lithium; wherein the structural formulas of compound S1, compound S2, compound S3, and compound S4 are as follows:

[0036] During the experiment, the inventors found that according to the above-mentioned combination method, the mixed battery electrolyte film-forming additive, lithium salt and organic solvent have a better combination effect. This may be because, under the above-mentioned combination method, there is a certain synergistic effect between the battery electrolyte film-forming additive and the lithium salt and organic solvent, which will affect the compatibility between the three and the stability and flexibility of the passivation film layer formed during the battery cycle, making it have a better effect.

[0037] According to the third aspect of the present invention, a silicon-carbon negative electrode lithium-ion battery is also provided, which includes the above-mentioned battery electrolyte. During the charge and discharge process of the silicon-carbon negative electrode, the volume expansion and contraction of silicon particles during deintercalation lead to particle pulverization, shedding and electrochemical performance failure, and the continuous side reaction with the battery electrolyte causes the continuous growth of the solid electrolyte layer (SEI) on the surface of the silicon particles. After the battery electrolyte film-forming additive proposed by the present invention is introduced into the silicon-carbon negative electrode lithium-ion battery, the above-mentioned problems can be effectively suppressed, thereby reducing the irreversible consumption of the negative electrode surface, reducing the internal resistance of the silicon-carbon negative electrode lithium ion battery, and improving the coulombic efficiency and cycle stability characteristics of the silicon-carbon negative electrode lithium ion battery. In addition, the battery electrolyte additive also has good electrochemical stability, can maintain the stability of the battery electrolyte in a wider voltage range, further enhances the safety performance of the battery, and improves the operating temperature range of the battery.

[0038] In a preferred embodiment, the silicon-carbon negative electrode lithium ion battery further comprises a positive electrode containing a cathode active material, a negative electrode containing an anode active material and a battery separator; preferably, the cathode active material is a material capable of releasing lithium ions; further preferably, the cathode active material is one or more of transition metal phosphates, transition metal oxide lithium salts and metal sulfides; preferably, the anode active material is a material capable of receiving lithium ions; further preferably, the anode active material is one or more of silicon material, silicon-carbon material, a composite material of silicon monoxide and graphite, and a composite material of silicon-carbon and silicon monoxide; preferably, the battery separator is at least one of a polyimide separator, a polyethylene separator, a polypropylene separator and a polyethylene terephthalate separator; further preferably, the battery separator is a polyethylene separator or a polypropylene separator. In the process of preparing silicon-carbon negative electrode lithium-ion batteries, by selecting the above-mentioned types of cathode, anode and diaphragm materials, they can better interact with the battery electrolyte containing the battery electrolyte film-forming additive proposed in the present invention, thereby significantly improving the energy density of the silicon-carbon negative electrode lithium-ion battery, further reducing the internal stress problem of the battery caused by volume change of the silicon-carbon negative electrode material during the charging and discharging process, and improving the cycle stability performance of the silicon-carbon negative electrode lithium-ion battery.

[0039] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0040] Example 1

[0041] (1) Preparation of battery electrolyte film-forming additives

[0042] Diethyl propenylphosphonate and methyltrimethoxysilane were added to anhydrous ethanol in a molar ratio of 1:10 and mixed evenly. Bu3N was added as a catalyst, and the mixture was reacted at 70°C for 12 hours. After the reaction was completed, the reaction mixture was distilled under reduced pressure to remove the anhydrous ethanol and unreacted methyltrimethoxysilane, yielding the battery electrolyte film-forming additive S1. The chemical reaction formula is shown below:

[0043]

[0044] (2) Preparation of battery electrolyte

[0045] In an argon-filled glove box (water content in the glove box is less than 0.1 ppm, oxygen content is less than 0.1 ppm), ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 3:3:4, and then lithium hexafluorophosphate (LiPF6) is slowly added. After the lithium salt is completely dissolved, a battery electrolyte film-forming additive S1 is added, and the mixture is stirred to obtain a battery electrolyte. In the above battery electrolyte, the organic solvent accounts for 87.5%, the lithium salt accounts for 12%, and the battery electrolyte film-forming additive S1 accounts for 0.5%, by weight.

[0046] (3) Preparation of battery positive electrode

[0047] According to weight percentage, 92% NCM811, 4% acetylene black and 4% PVDF binder were added to N-methylpyrrolidone to prepare a slurry, and the obtained slurry was coated on a 12-micron thick aluminum foil, dried and rolled to obtain a battery positive electrode sheet.

[0048] (4) Preparation of battery negative electrode

[0049] By weight percentage, 87% silicon carbon, 9% acetylene black and 4% SBR binder were mixed, deionized water was added thereto, and then the slurry was coated on 8-micron copper foil, dried and rolled to obtain the battery negative electrode.

[0050] (5) Preparation of batteries

[0051] The leakage point is controlled in a dry environment below -50°C, and the battery positive electrode sheet, battery separator (model 92233), and battery negative electrode sheet are stacked in order to make a battery cell. The stacking process must ensure that the separator completely separates the positive electrode sheets and the negative electrode completely covers the positive electrode. Then, use the glue-coated tabs to encapsulate them in an aluminum-plastic film of a fixed size to form a soft-pack battery to be filled with liquid. Then, the battery electrolyte is injected into the soft-pack battery, and then it is sealed, formed, aged, and sealed again to obtain an experimental battery for testing.

[0052] Example 2

[0053] The difference between Example 2 and Example 1 is that the prepared battery electrolyte film-forming additives are different, and when preparing the battery electrolyte, the addition ratios of the organic solvent, lithium salt and the battery electrolyte film-forming additive are different.

[0054] (1) Preparation of battery electrolyte film-forming additives

[0055] Dimethyl vinylphosphonate and methyltriethoxysilane were added to anhydrous ethanol in a molar ratio of 1:8 and mixed evenly. Bu3N was added as a catalyst, and the mixture was reacted at 60°C for 10 hours. After the reaction was completed, the reaction mixture was distilled under reduced pressure to remove the anhydrous ethanol and unreacted methyltriethoxysilane, yielding the battery electrolyte film-forming additive S2. The chemical reaction formula is shown below:

[0056]

[0057] (2) Preparation of battery electrolyte

[0058] In an argon-filled glove box (water content in the glove box is less than 0.1 ppm, oxygen content is less than 0.1 ppm), ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate are uniformly mixed in a mass ratio of 3:3:4. Lithium hexafluorophosphate is then slowly added to the mixture. After the lithium salt is completely dissolved, a battery electrolyte film-forming additive S1 is added, and the mixture is stirred to obtain a battery electrolyte. The battery electrolyte comprises, by weight, 87% organic solvent, 12% lithium salt, and 1% battery electrolyte film-forming additive S2.

[0059] Example 3

[0060] The difference between Example 3 and Example 1 is that the prepared battery electrolyte film-forming additives are different, and when preparing the battery electrolyte, the addition ratios of the organic solvent, lithium salt and the battery electrolyte film-forming additive are different.

[0061] (1) Preparation of battery electrolyte film-forming additives

[0062] Diethyl vinylphosphonate and ethyltripropoxysilane were added to anhydrous ethanol in a molar ratio of 1:8 and mixed evenly. Bu3N was added as a catalyst, and the mixture was reacted at 80°C for 8 hours. After the reaction was completed, the reaction mixture was distilled under reduced pressure to remove the anhydrous ethanol and unreacted ethyltripropoxysilane, yielding the battery electrolyte film-forming additive S3. The chemical reaction formula is shown below:

[0063]

[0064] (2) Preparation of battery electrolyte

[0065] In an argon-filled glove box (water content in the glove box is less than 0.1 ppm, oxygen content is less than 0.1 ppm), ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate are uniformly mixed in a mass ratio of 3:3:4. Lithium hexafluorophosphate is then slowly added to the mixture. After the lithium salt is completely dissolved, a battery electrolyte film-forming additive S1 is added, and the mixture is stirred to obtain a battery electrolyte. The battery electrolyte comprises, by weight, 86.5% organic solvent, 12% lithium salt, and 1.5% battery electrolyte film-forming additive S2.

[0066] Example 4

[0067] The difference between Example 4 and Example 1 is that the prepared battery electrolyte film-forming additives are different, and when preparing the battery electrolyte, the addition ratios of the organic solvent, lithium salt and the battery electrolyte film-forming additive are different.

[0068] (1) Preparation of battery electrolyte film-forming additives

[0069] Dimethyl propenylphosphonate and ethyltributoxysilane were added to anhydrous ethanol in a molar ratio of 1:16 and mixed evenly. Bu3N was added as a catalyst, and the mixture was reacted at 75°C for 14 hours. After the reaction was completed, the reaction mixture was distilled under reduced pressure to remove the anhydrous ethanol and unreacted ethyltributoxysilane, yielding the battery electrolyte film-forming additive S4. The chemical reaction formula is shown below:

[0070]

[0071] (2) Preparation of battery electrolyte

[0072] In an argon-filled glove box (water content in the glove box is less than 0.1 ppm, oxygen content is less than 0.1 ppm), ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate are uniformly mixed in a mass ratio of 3:3:4. Lithium hexafluorophosphate is then slowly added to the mixture. After the lithium salt is completely dissolved, a battery electrolyte film-forming additive S1 is added, and the mixture is stirred to obtain a battery electrolyte. The battery electrolyte comprises, by weight, 86% organic solvent, 12% lithium salt, and 2% battery electrolyte film-forming additive S2.

[0073] Example 5

[0074] The difference between Example 5 and Example 1 is that, in the prepared battery electrolyte, the organic solvent accounts for 92.5%, the lithium salt accounts for 7%, and the battery electrolyte film-forming additive S1 accounts for 0.5% by weight.

[0075] Example 6

[0076] The difference between Example 6 and Example 1 is that, in the prepared battery electrolyte, the organic solvent accounts for 75%, the lithium salt accounts for 16%, and the battery electrolyte film-forming additive S1 accounts for 9% by weight.

[0077] Example 7

[0078] The main difference between Example 7 and Example 1 is that, in the prepared battery electrolyte, the organic solvent accounts for 87%, the lithium salt accounts for 10%, and the battery electrolyte film-forming additive S1 accounts for 3%, by weight percentage.

[0079] Example 8

[0080] The main difference between Example 8 and Example 1 is that in the prepared battery electrolyte, the organic solvent accounts for 84.5%, the lithium salt accounts for 15%, and the battery electrolyte film-forming additive S1 accounts for 0.5% by weight.

[0081] Example 9

[0082] The difference between Example 9 and Example 1 is that in the battery electrolyte, the battery electrolyte film-forming additive is compound S1 and compound S4 mixed in a mass ratio of 1:2, the organic solvent is dimethyl sulfoxide (DMSO), and the lithium salt is lithium difluorooxalatoborate (LiBF2(C2O4)).

[0083] Example 10

[0084] The difference between Example 10 and Example 1 is that in the battery electrolyte, the battery electrolyte film-forming additive is compound S1 and compound S4 mixed in a mass ratio of 3:2, the organic solvent is dimethyl sulfoxide, and the lithium salt is lithium difluorooxalatoborate.

[0085] Example 11

[0086] The difference between Example 11 and Example 1 is that in the battery electrolyte, the battery electrolyte film-forming additive is compound S3 and compound S4 mixed in a mass ratio of 2:3, the organic solvent is aromatic polyoxyethylene ether, and the lithium salt is lithium trifluoromethanesulfonate (LiCF3SO3).

[0087] Example 12

[0088] The difference between Example 12 and Example 1 is that in the battery electrolyte, the battery electrolyte film-forming additive is compound S3 and compound S4 in a mass ratio of 2:5, the organic solvent is aromatic polyoxyethylene ether, and the lithium salt is lithium trifluoromethanesulfonate.

[0089] Example 13

[0090] The difference between Example 13 and Example 1 is that in the battery electrolyte, the battery electrolyte film-forming additive is compound S2 and compound S3 mixed in a mass ratio of 1:1, the organic solvent is hexanetrionitrile, and the lithium salt is lithium bis(fluorosulfonyl imide) (Li[(CF3SO2)2N]).

[0091] Example 14

[0092] The difference between Example 14 and Example 1 is that in the battery electrolyte, the battery electrolyte film-forming additive is compound S2 and compound S3 mixed in a mass ratio of 1:3, the organic solvent is hexanetrionitrile, and the lithium salt is lithium bis(fluorosulfonyl imide).

[0093] Example 15

[0094] The difference between Example 15 and Example 4 is that the amount of the battery electrolyte film-forming additive added to the battery electrolyte is 0.3%.

[0095] Example 16

[0096] The difference between Example 16 and Example 4 is that the amount of the battery electrolyte film-forming additive added to the battery electrolyte is 10%.

[0097] Comparative Example 1

[0098] The difference from Example 1 is that the film-forming additive in the battery electrolyte is 2% fluoroethylene carbonate (FEC).

[0099] Comparative Example 2

[0100] The difference from Example 1 is that the film-forming additive in the battery electrolyte is 1% vinylene carbonate (VC).

[0101] Comparative Example 3

[0102] The difference from Example 1 is that the film-forming additive in the battery electrolyte is 1% diethyl sulfate (DTD).

[0103] Comparative Example 4

[0104] The difference from Example 1 is that no battery electrolyte film-forming additives are added during the process of preparing the battery electrolyte.

[0105] In order to facilitate intuitive comparison of the compositions of the battery electrolytes prepared in the examples and comparative examples, the components of the battery electrolytes are summarized here. The results are shown in Table 1. It should be noted that the data in the table involve ratios that refer to their mass ratios.

[0106] Table 1

[0107]

[0108]

[0109] The batteries prepared in the above examples and comparative examples were tested for relevant performance, and the results are shown in Table 2. The specific testing methods are as follows:

[0110] The above-mentioned soft-pack batteries were formed and capacity-scaled using a battery test cabinet. The formation process was a 0.03C constant-current charge to 3.0V, a 0.05C constant-current charge to 3.4V, and a 0.1C constant-current charge to 3.7V. The aging process was a 12-hour aging process at 45°C. The capacity-scaled process was a 0.33C constant-current and constant-voltage charge to 4.25V, a cutoff current of 0.05C, and a 0.33C constant-current discharge to 2.75V, repeated three times. The batteries were then cycled at room temperature at a constant current and constant voltage of 1C / 1C for 1000 cycles, with a voltage range of 2.75-4.25V, to test their initial coulombic efficiency and capacity retention. The impedance of the battery was tested before and after 1000 cycles using an internal resistance meter. The internal resistance growth rate was equal to the difference before and after the cycle divided by the internal resistance of the battery before the cycle. The thickness of the battery was tested before and after 1000 cycles using a vernier caliper. The thickness growth rate was equal to the difference in battery thickness before and after the cycle divided by the battery thickness before the cycle.

[0111] Table 2

[0112]

[0113]

[0114] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0115] In Examples 1 to 16, when the battery electrolyte film-forming additive described herein was used in batteries, battery cycle testing demonstrated significant improvements in initial coulombic efficiency and capacity retention after 1000 cycles, with significant reductions in internal resistance and battery thickness during cycling. In particular, controlling the amount of the battery electrolyte film-forming additive in the battery electrolyte within a preferred range further enhanced these effects. Compounding the prepared battery electrolyte additive in appropriate proportions, along with the appropriate lithium salt and organic solvent, further improved the overall performance of the battery.

[0116] In contrast, in Comparative Examples 1 to 3, conventional battery electrolyte film-forming additives are used. Although the battery performance is improved compared to Comparative Example 4 in which no battery electrolyte film-forming additive is used, the effect is not ideal, and is far from the effect of using the battery electrolyte film-forming additive prepared by the present invention.

[0117] In summary, the battery electrolyte additive of alkyl phosphonate alkoxysilane provided by the present invention can significantly improve the initial charge and discharge coulombic efficiency and capacity retention rate in the battery cycle test, and can also effectively reduce the internal resistance and battery thickness, inhibit the impedance growth caused by the reaction of the battery electrolyte with the lithiated silicon negative electrode during the cycle, and at the same time protect the silicon negative electrode from repeated lithium insertion and deintercalation caused by particle breakage and differentiation, which is beneficial to improving the cycle stability of the battery.

[0118] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A battery electrolyte film-forming additive for silicon-carbon negative electrode lithium ion battery, characterized in that: The battery electrolyte film-forming additive is one or more alkylphosphonate alkoxysilanes, and the alkylphosphonate alkoxysilane has a chemical structure shown in the following formula (I): Formula (I), Wherein, R1, R2, R3, R4 and R5 are each independently selected from one of C1 to C10 alkyl groups, 1≤n≤10, and n is an integer.

2. The battery electrolyte film-forming additive according to claim 1, characterized in that The R1, the R2 and the R3 are each independently selected from one of C1 to C5 alkyl groups, the R4 and the R5 are each independently selected from one of C1 to C10 alkyl groups, 1≤n≤3, and n is an integer.

3. The battery electrolyte film-forming additive according to claim 2, characterized in that The R1, the R2 and the R3 are each independently selected from one of C1 to C10 alkyl groups, the R4 and the R5 are each independently selected from one of C1 to C2 alkyl groups, 1≤n≤3; and n is an integer.

4. The battery electrolyte film-forming additive according to claim 1, characterized in that The R1, the R2, the R3, the R4 and the R5 are each independently selected from a methyl group, an ethyl group, a propyl group and a butyl group, 3≤n≤5; and n is an integer.

5. The battery electrolyte film-forming additive according to any one of claims 1 to 4, characterized in that The battery electrolyte film-forming additive is selected from one or more of the following structures: ， ， ， 。 6. The battery electrolyte film-forming additive according to claim 5, characterized in that The battery electrolyte film-forming additive is a compound of compound S1 and compound S4, and the weight ratio of the two is (1~3):2; alternatively, the battery electrolyte film-forming additive is a compound of compound S3 and compound S4, and the weight ratio of the two is 2:(3~5); alternatively, the battery electrolyte film-forming additive is a compound of compound S2 and compound S3, and the weight ratio of the two is 1:(1~3).

7. A battery electrolyte for a silicon-carbon negative electrode lithium ion battery, characterized in that: The battery electrolyte comprises a lithium salt, an organic solvent, and the battery electrolyte film-forming additive according to any one of claims 1 to 6.

8. The battery electrolyte according to claim 7, characterized in that In terms of weight percentage, the lithium salt in the battery electrolyte is 7-16%, the battery electrolyte film-forming additive is 0.5-9%, and the balance is the organic solvent.

9. The battery electrolyte according to claim 8, characterized in that In terms of weight percentage, the lithium salt in the battery electrolyte is 10-15%, the battery electrolyte film-forming additive is 0.5-3%, and the balance is the organic solvent.

10. The battery electrolyte according to any one of claims 7 to 9, characterized in that The organic solvent is one or more of organic carbonate, ionic liquid, polyether, aromatic ether, C1-C40 alkyl ether, cyclic ether, carboxylate, sulfone, nitrile, dinitrile and polynitrile.

11. The battery electrolyte according to claim 10, characterized in that The organic solvent is one or more of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.

12. The battery electrolyte according to claim 10, characterized in that The lithium salt is one or more of lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium trifluoromethanesulfonate, lithium bis(pentafluoroethylsulfonylimide), lithium bis(trifluoromethylsulfonylimide), lithium bis(fluorosulfonylimide), lithium difluoro(bisoxalato)phosphate and lithium tetrafluoro(oxalato)phosphate.

13. The battery electrolyte according to claim 12, characterized in that The lithium salt is lithium hexafluorophosphate.

14. The battery electrolyte according to claim 7, characterized in that The battery electrolyte film-forming additive is a compound of compound S1 and compound S4, the organic solvent is dimethyl sulfoxide, and the lithium salt is lithium difluorooxalatoborate; or The battery electrolyte film-forming additive is a compound of compound S3 and compound S4, the organic solvent is an aromatic polyoxyethylene ether, and the lithium salt is lithium trifluoromethanesulfonate; or The battery electrolyte film-forming additive is a compound of compound S2 and compound S3, the organic solvent is hexanetrinitrile, and the lithium salt is lithium bis(fluorosulfonyl imide); The structural formulas of the compound S1, the compound S2, the compound S3, and the compound S4 are as follows: ， ， ， 。 15. A silicon-carbon negative electrode lithium ion battery, characterized in that: The silicon-carbon negative electrode lithium-ion battery comprises the battery electrolyte described in any one of claims 7 to 14.

16. The silicon-carbon negative electrode lithium ion battery according to claim 15, characterized in that: The silicon-carbon negative electrode lithium ion battery further comprises a positive electrode containing a cathode active material, a negative electrode containing an anode active material and a battery separator.

17. The silicon-carbon negative electrode lithium ion battery according to claim 16, characterized in that: The cathode active material is a material capable of releasing lithium ions.

18. The silicon-carbon negative electrode lithium ion battery according to claim 17, characterized in that: The cathode active material is one or more of transition metal phosphates, transition metal oxides, lithium salts, and metal sulfides.

19. The silicon-carbon negative electrode lithium ion battery according to claim 16, characterized in that: The anode active material is a material capable of accepting lithium ions.

20. The silicon-carbon negative electrode lithium ion battery according to claim 19, characterized in that: The anode active material is one or more of a silicon material, a silicon-carbon material, a composite material of silicon monoxide and graphite, and a composite material of silicon-carbon and silicon monoxide.

21. The silicon-carbon negative electrode lithium ion battery according to claim 16, characterized in that: The battery separator is at least one of a polyimide separator, a polyethylene separator, a polypropylene separator and a polyethylene terephthalate separator.

22. The silicon-carbon negative electrode lithium ion battery according to claim 21, characterized in that The battery separator is a polyethylene separator or a polypropylene separator.

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