Electrolyte additive, electrolyte and battery

Abstract

The invention relates to the field of batteries, and provides an electrolyte additive, an electrolyte and a battery. The electrolyte additive comprises a siloxane compound, vinylene carbonate and fluoroethylene carbonate, the siloxane compound is at least one of compounds as shown in a formula 1, in the formula 1, m represents any integer from 1 to 12, R1, R2 and R3 are the same or different and are independently C1-C8 alkyl groups, C1-C8 alkoxy groups and the like, and one or two of R1, R2 and R3 are C1-C8 alkoxy groups. The electrolyte additive can improve the electrochemical performance of the battery. # imgabs0 #

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to an electrolyte additive, an electrolyte, and a battery. Background Art

[0002] Lithium-ion batteries have a profound impact on our lives today. Mobile devices like smartphones, tablets, and laptops have become ubiquitous. These devices have become an integral part of our daily lives, transforming how we work, communicate, and entertain ourselves.

[0003] Lithium-ion batteries, as the primary power source for electric vehicles, have driven their rise. The widespread adoption of electric vehicles can reduce dependence on traditional oil, reduce environmental pollution, and transform transportation. Furthermore, lithium-ion batteries are widely used for renewable energy storage. With the increasing popularity of renewable energy sources like solar and wind power, lithium-ion batteries can help store this energy and release it when needed, improving energy efficiency.

[0004] Typically, the electrolyte of a lithium-ion battery consists primarily of a solvent, a lithium salt, and electrolyte additives. Adding these additives can effectively improve the battery's film-forming properties and overcharge performance. However, current electrolyte additives still present some challenges in practical applications, impacting the battery's electrochemical performance.

[0005] Therefore, it is necessary to further improve the battery system. Summary of the Invention

[0006] The present application aims to solve one of the technical problems in the related art at least to a certain extent.

[0007] The present application aims to provide an electrolyte additive, an electrolyte and a battery. The electrolyte comprising the electrolyte additive can improve the high-temperature cycle stability of the battery.

[0008] A first aspect of the present application provides an electrolyte additive, comprising a siloxane compound, vinylene carbonate (VC) and fluoroethylene carbonate (FEC), wherein the siloxane compound is at least one of the compounds represented by Formula 1:

[0009]

[0010] wherein m represents any integer from 1 to 12, R1, R2 and R3 are the same or different and are each independently a C1-C8 alkyl, a C1-C8 alkoxy, a C2-C8 alkenyl or a C2-C8 alkynyl, and one or two of R1, R2 and R3 are a C1-C8 alkoxy.

[0011] In the electrolyte additives of the present application, the siloxane compound is used in combination with VC and FEC to improve the high-temperature cycle stability of the battery, inhibit the dissolution of metal ions in the positive electrode material and reduce the amount of metal ions deposited on the negative electrode. Specifically, VC can promote the formation of a dense solid electrolyte interface (SEI) film on the surface of the negative electrode. The passivation film is beneficial to prevent the deposition of metal ions on the negative electrode, but VC usually also reduces the oxidative decomposition potential of the electrolyte, which has the risk of promoting the dissolution of metal ions; FEC has a similar structure to VC. It not only has a film-forming function similar to VC, but also has a higher oxidation potential, which can reduce the risk of metal ion dissolution to a certain extent. However, FEC has poor high-temperature stability and is easily reduced to produce gas and release hydrofluoric acid, which in turn accelerates the dissolution of metal ions. The introduced siloxane compound can reduce or prevent the formation of hydrofluoric acid and avoid hydrofluoric acid corrosion of the positive electrode material: The one or two Si-O bonds in the molecular structure of these siloxane compounds are easily destroyed by hydrofluoric acid, forming more stable Si-F bonds, thereby reducing the impact of HF on the positive electrode material. Compared with siloxanes with three Si-O bonds or silanes without Si-O bonds, the combination of one or two Si-O bonds and alkyl / alkenyl / alkynyl groups provides better steric hindrance and does not significantly reduce the Li+ migration rate. In addition, the isocyanate group (-NCO) attached to Si acts as an electron donor, attracting decomposition products of electrolytes (such as LiPF6) in the electrolyte to form a complex, thereby inhibiting the formation of acids generated by the hydrolysis of the decomposition products and further suppressing the dissolution of transition metal ions. Furthermore, FEC can promote the formation of an excellent positive electrode passivation film by these siloxane compounds, improving the stability of the positive electrode interface.

[0012] In some embodiments of the present application, one of R1, R2 and R3 is a C1-C8 alkyl group, and the other two are C1-C8 alkoxy groups.

[0013] Optionally, one of R1, R2 and R3 is a C1-C4 alkyl group, and the other two are C1-C4 alkoxy groups.

[0014] In some embodiments of the present application, one of R1, R2 and R3 is a C2-C8 alkenyl group or a C2-C8 alkynyl group, and the other two are C1-C8 alkoxy groups.

[0015] Optionally, one of R1, R2 and R3 is a C2-C4 alkenyl group or a C2-C4 alkynyl group, and the other two are C1-C4 alkoxy groups.

[0016] In some embodiments of the present application, two of R1, R2 and R3 are C1-C8 alkyl groups, and the remaining one is C1-C8 alkoxy group.

[0017] Optionally, two of R1, R2 and R3 are C1-C4 alkyl groups, and the remaining one is C1-C4 alkoxy group.

[0018] In some embodiments of the present application, two of R1, R2 and R3 are C2-C8 alkenyl or C2-C8 alkynyl, and the remaining one is C1-C8 alkoxy.

[0019] Optionally, two of R1, R2 and R3 are C2-C4 alkenyl groups or C2-C4 alkynyl groups, and the remaining one is C1-C4 alkoxy group.

[0020] In some embodiments of the present application, R1, R2 and R3 are each independently methyl, ethyl, n-propyl, n-butyl, vinyl, ethynyl, methoxy or ethoxy.

[0021] In some embodiments of the present application, the siloxane compound is selected from at least one of compounds 1 to 8 shown below:

[0022]

[0023] In some embodiments of the present application, the mass ratio of vinylene carbonate, fluoroethylene carbonate and the siloxane compound is a / b / 1, wherein a is 0.2-10 and b is 0.4-20.

[0024] In some embodiments of the present application, the electrolyte additive further includes an ester additive, and the ester additive is at least one of methylene methanedisulfonate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

[0025] Optionally, the mass ratio of the ester additive to the siloxane compound is c / 1, where c is 0.1-5.

[0026] The second aspect of the present application provides an electrolyte comprising the electrolyte additive described in the first aspect of the present application. The electrolyte can improve the high-temperature cycle stability of the battery.

[0027] In some embodiments of the present application, the mass content of the siloxane compound in the electrolyte is 0.1% to 5%. Thus, the siloxane compound can play a role in removing acid and water while minimizing the increase in battery impedance caused by isocyanate group polymerization that may be caused by excessive siloxane content.

[0028] Furthermore, in the electrolyte, the mass content of the siloxane compound is 0.5% to 2%.

[0029] In some embodiments of the present application, the mass content of vinylene carbonate in the electrolyte is 0.3% to 5%, thereby promoting the effective formation of a passivation film while reducing the increase in battery impedance that may be caused by excessive VC content.

[0030] Furthermore, in the electrolyte, the mass content of vinylene carbonate is 0.5% to 3%.

[0031] In some embodiments of the present application, the electrolyte contains 0.3% to 5% by weight of fluoroethylene carbonate, thereby effectively forming a passivation film while reducing the risk of decomposition and gas generation during high-temperature storage of the battery due to excessive FEC content.

[0032] Furthermore, in the electrolyte, the mass content of fluoroethylene carbonate is 0.5% to 3%.

[0033] In some embodiments of the present application, the electrolyte additive further includes an ester additive, wherein the ester additive is at least one of methylene methanedisulfonate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate. This helps maintain the high-temperature stability of the electrolyte.

[0034] Optionally, in the electrolyte, the mass content of the ester additive is 0.05% to 2%.

[0035] Furthermore, the mass content of the ester additive in the electrolyte is 0.05-0.5%, thereby improving the high-temperature cycle stability of the battery and further reducing the deposition of transition metals (such as Mn) on the negative electrode.

[0036] In some embodiments of the present application, the mass content of the electrolyte additive in the electrolyte is 1% to 10%.

[0037] In some embodiments of the present application, the electrolyte further includes a lithium salt, and the lithium salt includes at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4.

[0038] Optionally, in the electrolyte, the mass content of the lithium salt is 8% to 20%.

[0039] In some embodiments of the present application, the electrolyte further includes an organic solvent, and the organic solvent is a cyclic organic solvent and / or a chain organic solvent.

[0040] Optionally, the cyclic organic solvent is at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone and sulfolane.

[0041] Optionally, the chain organic solvent is at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 2,2-difluoroethyl acetate.

[0042] The third aspect of the present application provides a battery comprising the electrolyte additive described in the first aspect of the present application or the electrolyte described in the second aspect of the present application. The battery has high high-temperature cycle stability.

[0043] In some embodiments of the present application, the battery further comprises a positive electrode plate, the positive electrode plate comprising a positive electrode current collector and a positive electrode film layer located on at least one side surface of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material.

[0044] Optionally, the positive electrode active material includes lithium transition metal oxide and / or lithium-containing phosphate.

[0045] More optionally, the lithium transition metal oxide contains manganese, and the lithium-containing phosphate contains manganese. In particular, the electrolyte can more effectively inhibit the dissolution of manganese ions in such manganese-based positive electrode materials, reduce their deposition on the negative electrode, fully utilize their high safety characteristics, and enable the battery to maintain high cycle stability even at high temperatures.

[0046] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become obvious from the description below, or will be learned through practice of the present application. DETAILED DESCRIPTION

[0047] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and should not be understood as limiting the present application.

[0048] Lithium-ion batteries are developing in the direction of high capacity, low price and greater safety. The positive electrode materials of the battery usually include oxides and phosphates containing lithium and transition metals. As the battery is charged and discharged, the transition metals in the positive electrode material react easily to form metal ions and dissolve into the electrolyte, and then deposit on the negative electrode, affecting the performance of the battery. In particular, manganese-based positive electrode materials (such as lithium iron manganese phosphate and lithium nickel manganese oxide) have potential applications due to their high safety and low price. However, during the cycle, compared with other transition metals, manganese (Mn) is more easily deposited on the surface of the negative electrode material (such as graphite), resulting in continuous decomposition and regeneration of the SEI film on the negative electrode surface, and continuous consumption of active lithium. Polarization loss caused by reasons such as SEI film thickening, electrolyte consumption and by-products blocking the lithium insertion and deintercalation channels. At the same time, the positive electrode material produces manganese-deficient phases and Mn due to the dissolution of manganese. 3+ The Jan-Taylor effect leads to lattice distortion and reduced structural stability, hindering the diffusion of lithium ions during subsequent charge and discharge, increasing battery polarization and capacity loss. Suppressing Mn dissolution and deposition to achieve high cycle and storage performance is a challenge that must be addressed for the further commercialization of manganese-based materials.

[0049] To this end, in a first aspect, the present application provides an electrolyte additive, comprising a siloxane compound, vinylene carbonate (VC) and fluoroethylene carbonate (FEC), wherein the siloxane compound is at least one of the compounds represented by Formula 1:

[0050]

[0051] wherein m represents any integer from 1 to 12, R1, R2 and R3 are the same or different and are each independently a C1-C8 alkyl, a C1-C8 alkoxy, a C2-C8 alkenyl or a C2-C8 alkynyl, and one or two of R1, R2 and R3 are a C1-C8 alkoxy.

[0052] In the electrolyte additives of the present application, VC, FEC and the siloxane compound are used in combination to improve the high-temperature cycle stability of the battery, inhibit the dissolution of metal ions in the positive electrode material and reduce the amount of deposition on the negative electrode. Specifically, VC can promote the formation of a dense solid electrolyte interface (SEI) film at the negative electrode. The passivation film is beneficial to prevent the deposition of metal ions on the negative electrode, but VC usually also reduces the oxidative decomposition potential of the electrolyte, which has the risk of promoting the dissolution of metal ions; FEC has a similar structure to VC. It not only has a film-forming function similar to VC, but also has a higher oxidation potential, which can reduce the risk of metal ion dissolution to a certain extent. However, FEC has poor high-temperature stability and is easy to reduce and produce gas and release hydrofluoric acid, which in turn accelerates the dissolution of metal ions. The introduced siloxane compound can reduce or prevent the formation of hydrofluoric acid (HF) and avoid HF corrosion of the positive electrode material: The compound has one or two silicon-oxygen (Si-O) bonds in its molecular structure, which are easily destroyed by HF, forming more stable silicon-fluorine (Si-F) bonds, thereby reducing the impact of HF on the positive electrode material. Compared with three silicon-oxygen bonds or no silicon-oxygen bonds, one or two silicon-oxygen bonds and alkyl / alkenyl / alkyne groups have better steric hindrance and will not reduce the Li+ migration rate too much. In addition, the isocyanate group (-NCO) is connected to Si, which acts as an electron donor and can attract the decomposition products of the electrolyte (such as LiPF6) in the electrolyte to form a complex, thereby inhibiting the formation of acid generated by the hydrolysis of the decomposition products and further inhibiting the dissolution of transition metal ions. Furthermore, FEC can also promote the formation of an excellent positive electrode passivation film by the siloxane compound, improving the stability of the positive electrode interface.

[0053] In the present application, m in Formula 1 represents the number of alkylene groups (-CH2-). Specifically, m can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.

[0054] As some examples, m is any integer from 1 to 6.

[0055] In this application, a C1-C8 alkyl group refers to a saturated hydrocarbon group having 1 to 8 carbon atoms. The number of carbon atoms in the alkyl group may be 1, 2, 3, 4, 5, 6, 7, or 8. Specific examples of the alkyl group include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, n-pentyl, isopentyl, n-hexyl, heptyl, n-octyl, and the like.

[0056] In the present application, a C1-C8 alkoxy group can be represented by -OR, wherein R represents a C1-C8 alkyl group, and the explanation of the C1-C8 alkyl group is as described above. Specific examples of alkoxy groups include, but are not limited to, methoxy and ethoxy.

[0057] In this application, a C2-C8 alkenyl group refers to an unsaturated hydrocarbon group having 2 to 8 carbon atoms and at least one carbon-carbon double bond. The number of carbon atoms in an alkenyl group can be 2, 3, 4, 5, 6, 7, or 8. Specific examples of alkenyl groups include, but are not limited to, ethenyl, propenyl, allyl, 1-butenyl, 2-butenyl, and the like.

[0058] In this application, a C2-C8 alkynyl group refers to an unsaturated hydrocarbon group having 2 to 8 carbon atoms and at least one carbon-carbon triple bond. The number of carbon atoms in an alkynyl group may be 2, 3, 4, 5, 6, 7, or 8. Specific examples of alkynyl groups include, but are not limited to, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, and the like.

[0059] In some embodiments, two of R1, R2, and R3 are C1-C8 alkoxy groups.

[0060] In some specific embodiments, one of R1, R2 and R3 is a C1-C8 alkyl group, and the other two are C1-C8 alkoxy groups.

[0061] Furthermore, one of R1, R2 and R3 is a C1-C4 alkyl group, and the other two are C1-C4 alkoxy groups.

[0062] As other specific embodiments, one of R1, R2 and R3 is a C2-C8 alkenyl group or a C2-C8 alkynyl group, and the other two are C1-C8 alkoxy groups.

[0063] Furthermore, one of R1, R2 and R3 is a C2-C4 alkenyl group or a C2-C4 alkynyl group, and the other two are C1-C4 alkoxy groups.

[0064] In some embodiments, one of R1, R2 and R3 is a C1-C8 alkoxy group.

[0065] As some specific embodiments, two of R1, R2 and R3 are C1-C8 alkyl groups, and the remaining one is C1-C8 alkoxy group.

[0066] Furthermore, two of R1, R2 and R3 are C1-C4 alkyl groups, and the remaining one is a C1-C4 alkoxy group.

[0067] As other specific embodiments, two of R1, R2 and R3 are C2-C8 alkenyl or C2-C8 alkynyl, and the remaining one is C1-C8 alkoxy.

[0068] Furthermore, two of R1, R2 and R3 are C2-C4 alkenyl or C2-C4 alkynyl, and the remaining one is C1-C4 alkoxy.

[0069] Optionally, R1, R2 and R3 are each independently methyl, ethyl, n-propyl, n-butyl, vinyl, ethynyl, methoxy or ethoxy, thereby reducing the steric hindrance of the compound and improving the structural stability.

[0070] In some embodiments, the siloxane compound is selected from at least one of compounds 1 to 8 shown below:

[0071]

[0072]

[0073] In addition, the compound 1 is methyl-(3-isocyanatepropyl)dimethylsilane, abbreviated as CFS-720; the compound 5 is 3-isocyanatepropylmethyldiethoxysilane, abbreviated as CFS-280.

[0074] In some embodiments, the mass ratio of vinylene carbonate, fluoroethylene carbonate and silicone compound is a / b / 1, wherein a is 0.2-10 and b is 0.4-20.

[0075] As some examples, a may be 0.2, 0.4, 0.5, 0.6, 1, 2, 2.1, 3, 4, 5, 6, 7, 8, 9, 10, etc. Optionally, a is 0.5-5.

[0076] As some examples, b can be 0.4, 0.5, 0.6, 1, 1.3, 1.8, 2, 3, 4, 5, 6, 8, 10, 11, 13, 15, 17, 18, 20, etc. Optionally, b is 1-6.

[0077] In some embodiments, the electrolyte additive further includes an ester additive, wherein the ester additive is at least one of methylene methanedisulfonate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate. Introducing such an additive is beneficial for further maintaining the high-temperature stability of the electrolyte.

[0078] Optionally, the mass ratio of the ester additive to the siloxane compound is c / 1, where c is 0.1 to 5. As some examples, c can be 0.1, 0.2, 0.4, 0.5, 0.6, 0.8, 1, 2, 3, 4, 5, etc.

[0079] In a second aspect, the present application provides an electrolyte comprising the electrolyte additive described in the first aspect of the present application. The electrolyte can improve the high-temperature cycle stability of the battery.

[0080] In some embodiments, the mass content of the siloxane compound in the electrolyte may be 0.1% to 5%, for example, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, etc. In this case, the siloxane compound can play a role in removing acid and water while minimizing the increase in battery impedance that may be caused by excessive content.

[0081] Optionally, in the electrolyte, the mass content of the siloxane compound is 0.5% to 2%.

[0082] In some embodiments, the mass content of vinylene carbonate in the electrolyte is 0.3% to 5%, for example, 0.3%, 0.5%, 0.1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, etc. In this case, the electrolyte can promote the effective formation of a passivation film while reducing the increase in battery impedance that may be caused by excessive VC content.

[0083] Optionally, in the electrolyte, the mass content of vinylene carbonate is 0.5% to 3%.

[0084] In some embodiments, the mass content of vinylene carbonate in the electrolyte is 0.3% to 5%, for example, 0.3%, 0.5%, 0.1%, 1.5%, 2%, 2.5%, 3%, 4%, 5%, etc. In this case, a passivation film can be effectively formed while reducing the risk of decomposition and gassing of the battery during high-temperature storage due to excessive FEC content.

[0085] Optionally, in the electrolyte, the mass content of fluoroethylene carbonate is 0.5% to 3%.

[0086] In some embodiments, the electrolyte additive further includes the ester additive.

[0087] Optionally, in the electrolyte, the mass content of the ester additive is 0.05% to 2%, for example, 0.05%, 0.1%, 0.3%, 0.5%, 0.7%, 0.8%, 1%, 2%, etc.

[0088] Furthermore, the mass content of the ester additive in the electrolyte is 0.05-0.5%, thereby improving the high-temperature cycle stability of the battery and further reducing the deposition of transition metals (such as Mn) on the negative electrode.

[0089] In some embodiments, the electrolyte contains the electrolyte additive in an amount of 1% to 10% by weight, such as 1%, 1.5%, 2.5%, 3%, 4%, 5%, 6%, 7%, 8%, 10%, etc.

[0090] Optionally, the electrolyte contains the electrolyte additive in an amount of 2% to 6% by weight. In this case, the SEI film formed can have an appropriate thickness, minimizing the risk of the SEI film being too thin (which would prevent the dissolution of transition metals (such as Mn) in the positive electrode material) due to a low additive content, and the risk of the SEI film being too thick (which would increase impedance and affect battery capacity retention) due to a high additive content.

[0091] In the present application, the electrolyte may generally further include a lithium salt as an electrolyte.

[0092] The present application does not particularly limit the lithium salt, and can be selected with reference to existing lithium ion electrolytes. In some embodiments, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiB(C2O4)2), lithium difluorooxalatoborate (LiBF2C2O4), lithium bis(fluorosulfonyl)imide (LiN(SO2F)2), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatophosphate (LiPF2(C2O4)2), and lithium tetrafluorooxalatophosphate (LiPF4C2O4).

[0093] As some specific embodiments, the lithium salt includes lithium hexafluorophosphate. Usually during the operation of the battery, the lithium hexafluorophosphate in the electrolyte will decompose to form phosphorus pentafluoride (PF5), and phosphorus pentafluoride will usually hydrolyze with trace water in the system to form hydrofluoric acid (HF) (LiPF6→PF5+LiF, PF5+H2O→POF3+HF). In the electrolyte provided by the present application, the -NCO provided by the siloxane compound as an electrolyte additive component will form a complex with phosphorus pentafluoride: the N in -NCO is Lewis basic and can preferentially react with Lewis-acidic phosphorus pentafluoride. Therefore, the isocyanate functional group stabilizes and inactivates phosphorus pentafluoride, thereby reducing the hydrolysis of phosphorus pentafluoride and reducing the formation of HF, thereby further inhibiting the decomposition of the electrolyte and the dissolution of transition metal ions.

[0094] In some embodiments, the mass content of the lithium salt is 8% to 20%, for example, 8%, 10%, 12%, 13%, 14%, 15%, 16%, 18%, 20%, etc.

[0095] In the present application, the electrolyte may further include a solvent. The solvent may include a non-aqueous organic solvent, such as a cyclic organic solvent and / or a chain organic solvent.

[0096] Optionally, the cyclic organic solvent is at least one of ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone, sulfolane and fluoroethylene carbonate.

[0097] Optionally, the chain organic solvent is at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methylpropyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 2,2-difluoroethyl acetate.

[0098] As an example, the organic solvent includes EC and EMC, and the mass ratio of EC to EMC is, for example, 3:7.

[0099] In some embodiments, the mass content of the organic solvent in the electrolyte is 70% to 92%, for example, 70%, 80%, 90%, 92%, etc.

[0100] In a third aspect, the present application provides a battery comprising the electrolyte described in the first aspect of the present application or the electrolyte described in the second aspect of the present application. The battery has high high-temperature cycling stability. The battery may be a lithium-ion battery.

[0101] In general, in addition to the electrolyte, the battery also includes a positive electrode sheet, a negative electrode sheet, and a separator. During the battery's charge and discharge processes, active ions are embedded in and released from the positive and negative electrodes. The electrolyte conducts ions between the positive and negative electrodes. The separator is located between the positive and negative electrodes, primarily preventing short circuits between the positive and negative electrodes while allowing ions to pass through.

[0102] In the present application, the positive electrode plate may include a positive electrode current collector and a positive electrode active material layer located on at least one side of the positive electrode plate. The positive electrode active material layer includes a positive electrode active material.

[0103] In some embodiments, the positive electrode active material comprises a lithium transition metal oxide and / or a lithium-containing phosphate. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as NCM111, NCM523, NCM811), and lithium-rich manganese-based. Examples of lithium-containing phosphates include, but are not limited to, lithium iron phosphate (such as LFP), lithium manganese phosphate (such as LiMnPO4), and lithium manganese iron phosphate (LMFP).

[0104] Optionally, the lithium transition metal oxide contains manganese, and the lithium-containing phosphate contains manganese. In particular, the electrolyte can more effectively inhibit the dissolution of manganese ions in such manganese-based positive electrode materials, reduce their deposition on the negative electrode, and fully utilize their high safety characteristics, enabling the battery to maintain high cycle stability even at high temperatures.

[0105] In some embodiments, the positive electrode active material layer may further include a binder, and specific examples of the binder include, but are not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer.

[0106] In some embodiments, the positive electrode active material layer may further include a conductive agent, and specific examples of the conductive agent include, but are not limited to, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and the like.

[0107] In some embodiments, the positive electrode current collector may be a metal foil, such as aluminum foil.

[0108] In the present application, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0109] In some embodiments, the negative electrode active material may include at least one of graphite, a silicon-based material, and lithium titanate.

[0110] In some embodiments, the negative electrode active material layer may further include a binder, and specific examples of the binder include, but are not limited to, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylamide (PAM).

[0111] In some embodiments, the negative electrode active material layer may further include a conductive agent, and specific examples of the conductive agent include, but are not limited to, superconducting carbon, acetylene black, carbon black, graphene, and the like.

[0112] In some embodiments, the negative active material layer may further include a thickener, such as sodium carboxymethylcellulose (CMC-Na).

[0113] The present application has no particular restrictions on the type of diaphragm. Various porous structure diaphragms with good stability can be selected, such as one or more of polyethylene diaphragms, polypropylene diaphragms, PE ceramic coated diaphragms, aromatic polyamide diaphragms, polytetrafluoroethylene diaphragms, and polyethersulfone diaphragms. The specific selection can be made according to needs.

[0114] The battery of the present application can be in the form of a battery cell, a battery module or a battery pack, which can be selected according to the application of the battery. Generally, the battery module can be formed by assembling battery cells, and the battery pack can be assembled from the battery modules.

[0115] The present invention will be described below by way of specific examples. It should be noted that the following examples are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. Where specific techniques or conditions are not specified in the examples, they are determined according to the techniques or conditions described in the literature in this area or according to the product specifications. Reagents or instruments not specified by manufacturer are all commercially available conventional products.

[0116] Example 1

[0117] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a mass ratio of 3:7 to obtain an organic solvent. Lithium salt LiPF6, electrolytic additives VC, FEC, and compound 1 (CFS-720) were added to the organic solvent and stirred to obtain an electrolyte. The addition amounts (in mass percentages) of the components in the electrolyte were as follows:

[0118] LiPF6 13%, VC 1%, FEC 2%, CFS-720 0.5%, and the rest are organic solvents.

[0119] Examples 2-6

[0120] The electrolyte was prepared according to the method of Example 1, except that the amount of VC was adjusted, and the amount of organic solvent was adjusted accordingly, so that the contents of other components in the electrolyte remained unchanged.

[0121] Examples 7-11

[0122] The electrolyte was prepared according to the method of Example 1, except that the amount of FEC was adjusted, and the amount of organic solvent was adjusted accordingly, so that the mass contents of the other components in the electrolyte remained unchanged.

[0123] Examples 12-16

[0124] The electrolyte was prepared according to the method of Example 1, except that the amount of CFS-720 was adjusted, and the amount of the organic solvent was adjusted accordingly, so that the mass contents of the other components in the electrolyte remained unchanged.

[0125] Example 17

[0126] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), EC and EMC were mixed in a mass ratio of 3:7 to obtain an organic solvent. Lithium salt LiPF6 and electrolytic additives VC, FEC, and CFS-720 were added to the organic solvent and stirred thoroughly to obtain an electrolyte. The addition amounts of each component in the electrolyte (in mass percentage) are as follows:

[0127] LiPF6 16%, VC 1.5%, FEC 1.5%, CFS-720 0.7%, and the rest are organic solvents.

[0128] Example 18

[0129] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), EC and EMC were mixed in a mass ratio of 3:7 to obtain an organic solvent. Lithium salt LiPF6 and electrolytic additives VC, FEC, CFS-720, and methylene disulfonate (abbreviated as "Z1" in Table 1) were added to the organic solvent and stirred thoroughly to obtain an electrolyte. The addition amounts of each component in the electrolyte (in mass percentage) are as follows:

[0130] LiPF6 13%, VC 1%, FEC 2%, CFS-720 0.5%, methylene methanedisulfonate 0.3%, and the rest are organic solvents.

[0131] Examples 19-22

[0132] An electrolyte was prepared according to the method of Example 18, except that the amount of methylene methanedisulfonate was adjusted, and the amount of organic solvent was adjusted accordingly to keep the mass contents of the remaining components in the electrolyte unchanged.

[0133] Example 23

[0134] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), EC and EMC were mixed in a mass ratio of 3:7 to prepare an organic solvent. Lithium salt LiPF6 and electrolytic additives VC, FEC, CFS-720, and methylene methanedisulfonate were added to the organic solvent and stirred thoroughly to prepare an electrolyte. The addition amounts of each component in the electrolyte (in mass percentage) are as follows:

[0135] LiPF6 16%, VC 1.5%, FEC 1.5%, CFS-720 0.7%, methylene methanedisulfonate 0.3%, and the rest are organic solvents.

[0136] Examples 24-25

[0137] The electrolyte was prepared according to the method of Example 18, except that methylene methanedisulfonate was replaced by tris(trimethylsilyl)borate (abbreviated as "Z2" in Table 1) and tris(trimethylsilyl)phosphate (abbreviated as "Z3" in Table 1), respectively.

[0138] Examples 26-32

[0139] The electrolyte was prepared according to the method of Example 1, except that Compound 1 was replaced by Compounds 2 to 8, respectively.

[0140] Example 33

[0141] An electrolyte was prepared according to the method of Example 18, except that Compound 1 was replaced by Compound 4.

[0142] Comparative Example 1

[0143] The electrolyte was prepared according to the method of Example 1, except that no electrolyte additive was added and the amount of the organic solvent was adjusted accordingly to keep the mass contents of the remaining components in the electrolyte unchanged.

[0144] Comparative Examples 2-7

[0145] The electrolyte was prepared according to the method of Example 1, except that one or two components of the electrolyte additive were not added, and the amount of the organic solvent was adjusted accordingly to keep the mass contents of the remaining components in the electrolyte unchanged.

[0146] Comparative Examples 8-9

[0147] The electrolyte was prepared according to the method of Example 1, except that CFS-720 was replaced by trimethylsilyl isocyanate (abbreviated as "D1" in Table 1) and 3-isocyanatepropyltrimethoxysilane (abbreviated as "D2" in Table 1).

[0148] Comparative Examples 10-12

[0149] An electrolyte was prepared according to the method of Example 18, except that one component of the electrolyte additive was not added, and the amount of the organic solvent was adjusted accordingly to keep the mass contents of the remaining components in the electrolyte unchanged.

[0150] The specific compositions of the electrolytes in the above examples and comparative examples are shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154]

[0155] Note: “Mass ratio (a / b / 1)” refers to the mass ratio of VC / FEC / silicone additives, and “mass ratio (c / 1)” refers to the mass ratio of ester additives / silicone additives.

[0156] Test Case

[0157] The test examples are used to illustrate the performance of the electrolytes of the embodiments and comparative examples.

[0158] 1. Battery preparation

[0159] Preparation of positive electrode sheet: lithium manganese iron phosphate material LMFP, conductive agent SuperP, adhesive PVDF and solvent NMP are mixed in a mass ratio of 97.5:1.5:1 to form a positive electrode slurry with a certain viscosity, which is then coated on both surfaces of the positive electrode current collector aluminum foil, dried at 85°C and cold pressed. The coating amount is 250g / m 2 (excluding solvent), compacted density is 2.2g / cm 3 ; Then, trimming, cutting and stripping are carried out. After stripping, it is dried at 85℃ for 4 hours under vacuum conditions, and the tabs are welded to make the positive electrode sheets.

[0160] Preparation of negative electrode sheet: artificial graphite, conductive agent SuperP, thickener CMC, adhesive SBR (styrene-butadiene rubber emulsion) are mixed evenly with solvent water at a mass ratio of 95:1.5:1:2.5 to form a negative electrode slurry of a certain viscosity. The negative electrode slurry is coated on both sides of the negative electrode current collector copper foil, dried at 85°C and then cold pressed. The coating amount is 154g / m 2 (excluding solvent), compacted density is 1.6g / cm 3 ; Trim, cut, and slit, and then dry at 85°C for 4 hours under vacuum conditions to obtain the negative electrode.

[0161] The positive electrode sheet, negative electrode sheet and separator (using a 16 μm thick polypropylene porous membrane as the separator) prepared according to the above process are laminated to form a lithium-ion battery with a thickness of 4.7 mm, a width of 55 mm and a length of 60 mm, with a capacity of 1300 mAh. The battery is vacuum-baked at 85°C for 48 hours and the above electrolyte is injected to complete the battery production.

[0162] 2. Battery test

[0163] 1) High temperature cycle performance test

[0164] At 45°C, charge the battery at a constant current of 1.0C to 4.25V, charge it at a constant voltage to a cutoff current of 0.05C, and then discharge it at a constant current of 1.0C. The discharge capacity is recorded as C0. Repeat the charge and discharge steps for 1000 cycles to obtain the discharge capacity C0 at the 1000th cycle. 1000 , capacity retention rate = (C1000 / C0)×100%.

[0165] 2) Measurement of manganese deposition:

[0166] Disassemble the battery after 1000 cycles and remove the negative electrode. Rinse the negative electrode three times with an excess of DMC. Then soak the negative electrode in plenty of water until the negative electrode material falls off the copper foil. Discard the copper foil, filter, and dry the negative electrode material.

[0167] Weigh 0.5 g of the negative electrode material and place it in a 300 mL glass beaker. Slowly add 10 mL of 65 wt% nitric acid and 10 mL of 98 wt% sulfuric acid. Place it on an electric furnace, cover with a watch glass and heat until the sample is dissolved (turns milky white), remove and cool, add 10 mL of 36 wt% hydrochloric acid and heat until the salts are dissolved (the solution is clear), remove and cool, and filter with medium-speed quantitative filter paper. Rinse the filter paper and beaker and transfer to a 250 mL volumetric flask to make up the volume. Then, perform ICP injection testing. Specifically, an inductively coupled plasma emission spectrometer (Agilent ICP-OES 5110) is used to directly read the manganese content in the negative electrode material.

[0168] The test results are shown in Table 2.

[0169] Table 2

[0170]

[0171]

[0172] In combination with Table 1 and Table 2, by comparing Examples 1-33 with Comparative Examples 1-12, it can be seen that the use of VC, FEC and the siloxane compound with the structure shown in Formula 1 in Examples 1-33 as electrolyte additives can effectively improve the high-temperature cycle stability of the battery, inhibit the dissolution of manganese in the positive electrode material and reduce its deposition on the negative electrode.

[0173] It can be seen from Examples 1-16 that when VC, FEC and the siloxane compound are used as electrolyte additives, controlling the mass content of the three in the electrolyte to 0.5% to 3%, 0.5% to 3% and 0.5% to 2%, respectively, can further improve the high temperature cycle stability of the battery and at the same time reduce the amount of manganese deposition on the negative electrode.

[0174] Comparing Example 1 with Examples 18-25, it can be seen that the further introduction of the ester additive on the basis of VC, FEC and siloxane compounds can also enable the battery to maintain a relatively high high-temperature cyclability; in particular, when the content of the ester additive is controlled at 0.05% to 0.5%, while improving the high-temperature cyclability of the battery, it can also maintain a relatively low manganese deposition amount.

[0175] Comparing Example 1 with Comparative Example 1, it can be seen that when no electrolyte additive is added, the high-temperature cycle stability of the battery is very poor, and the amount of manganese deposition is also very high; comparing Example 1 with Comparative Examples 2-7, in which only one or two of VC, FEC, and the siloxane compounds are introduced, although the addition of some additives can improve the performance of the battery, the degree of improvement is limited; comparing Example 1 with Comparative Examples 8-9, it can be seen that, when silicon-containing additives are also introduced, the performance of the battery can be significantly improved by controlling the presence of one or two Si-O bonds in such additives; comparing Examples 1 and 18 with Comparative Examples 10-12, it can be seen that even if ester additives are introduced, the improvement in battery performance is very limited when the components of the electrolyte additives of the present application are not contained.

[0176] In summary, the electrolyte additive provided in the present application is used in the electrolyte, which can improve the high-temperature cycle stability of the battery and effectively reduce the manganese deposition amount of the negative electrode.

[0177] Unless otherwise specified, all technical and scientific terms used in this application have the same meanings as commonly understood by those skilled in the art to which this application belongs. All patents and publications referred to in this application are incorporated herein by reference in their entirety. The terms "comprising" or "including" are open-ended expressions, meaning that they include the contents specified in this application but do not exclude contents elsewhere.

[0178] In the description of this specification, the descriptions with reference to the terms "some embodiments", "other embodiments", etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory.

[0179] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. An electrolyte additive, characterized in that It includes siloxane compounds, vinylene carbonate and fluoroethylene carbonate, wherein the siloxane compound is at least one of the compounds shown in Formula 1: wherein m represents any integer from 1 to 12, R1, R2 and R3 are the same or different and are each independently a C1-C8 alkyl, a C1-C8 alkoxy, a C2-C8 alkenyl or a C2-C8 alkynyl, and one or two of R1, R2 and R3 are a C1-C8 alkoxy.

2. The electrolyte additive according to claim 1, characterized in that One of R1, R2 and R3 is a C1-C8 alkyl group, and the other two are C1-C8 alkoxy groups; or One of R1, R2 and R3 is a C2-C8 alkenyl group or a C2-C8 alkynyl group, and the other two are C1-C8 alkoxy groups; Optionally, one of R1, R2 and R3 is a C1-C4 alkyl group, and the other two are C1-C4 alkoxy groups; Optionally, one of R1, R2 and R3 is a C2-C4 alkenyl group or a C2-C4 alkynyl group, and the other two are C1-C4 alkoxy groups.

3. The electrolyte additive according to claim 1, characterized in that Two of R1, R2 and R3 are C1-C8 alkyl groups, and the remaining one is a C1-C8 alkoxy group; or Two of R1, R2 and R3 are C2-C8 alkenyl or C2-C8 alkynyl, and the remaining one is C1-C8 alkoxy; Optionally, two of R1, R2 and R3 are C1-C4 alkyl groups, and the remaining one is a C1-C4 alkoxy group; Optionally, two of R1, R2 and R3 are C2-C4 alkenyl or C2-C4 alkynyl, and the remaining one is C1-C4 alkoxy.

4. The electrolyte additive according to claim 1, characterized in that R1, R2 and R3 are each independently methyl, ethyl, n-propyl, n-butyl, vinyl, ethynyl, methoxy or ethoxy.

5. The electrolyte additive according to claim 1, characterized in that The siloxane compound is selected from at least one of compounds 1 to 8 whose structures are shown below:

6. The electrolyte additive according to any one of claims 1 to 5, characterized in that: The mass ratio of vinylene carbonate, fluoroethylene carbonate and the silicone compound is a / b / 1, wherein a is 0.2-10 and b is 0.4-20.

7. The electrolyte additive according to any one of claims 1 to 5, characterized in that Also included is an ester additive, wherein the ester additive is at least one of methylene methanedisulfonate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate; Optionally, the mass ratio of the ester additive to the siloxane compound is c / 1, where c is 0.1-5.

8. An electrolyte, characterized in that The electrolyte additive comprises the electrolyte additive according to any one of claims 1 to 7.

9. The electrolyte according to claim 8, characterized in that In the electrolyte, the mass content of the siloxane compound is 0.1% to 5%, and can be optionally 0.5% to 2%; and / or, in the electrolyte, the mass content of vinylene carbonate is 0.3% to 5%, and can be optionally 0.5% to 3%; and / or, in the electrolyte, the mass content of fluoroethylene carbonate is 0.3% to 5%, and can be optionally 0.5% to 3%.

10. The electrolyte according to claim 8, characterized in that The electrolyte additive further includes an ester additive, wherein the ester additive includes at least one of methylene methanedisulfonate, tris(trimethylsilyl)borate and tris(trimethylsilyl)phosphate; Optionally, in the electrolyte, the mass content of the ester additive is 0.05% to 2%, and optionally 0.05 to 0.5%.

11. The electrolyte according to any one of claims 8 to 10, characterized in that: In the electrolyte, the total mass content of the electrolyte additive is 1% to 10%.

12. The electrolyte according to any one of claims 8 to 10, characterized in that Also included is a lithium salt, the lithium salt including at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4; Optionally, in the electrolyte, the mass content of the lithium salt is 8% to 20%.

13. The electrolyte according to any one of claims 8 to 10, characterized in that Also included is an organic solvent, wherein the organic solvent is a cyclic organic solvent and / or a chain organic solvent; Optionally, the cyclic organic solvent is at least one of ethylene carbonate, propylene carbonate, γ-butyrolactone and sulfolane; Optionally, the chain organic solvent is at least one of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methylpropyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether and 2,2-difluoroethyl acetate.

14. A battery, characterized in that: The electrolyte additive comprises the electrolyte additive according to any one of claims 1 to 7 or the electrolyte according to any one of claims 8 to 13.

15. The battery according to claim 14, characterized in that Also included is a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer located on at least one side of the positive electrode current collector, the positive electrode film layer comprising a positive electrode active material; Optionally, the positive electrode active material includes a lithium transition metal oxide and / or a lithium-containing phosphate; More optionally, the lithium transition metal oxide contains manganese, and the lithium-containing phosphate contains manganese.

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