Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention provides a lithium ion battery electrolyte, the lithium ion battery electrolyte comprises an organic solvent, a lithium salt and an electrolyte additive, and the electrolyte additive comprises carbodiimide and isocyanate. The electrolyte additive can react with other substances in the electrolyte to form a dense SEI film with moderate thickness, and meanwhile, the moisture in a pole core can be reduced, so that the capacity and the cycle and storage performance of the lithium ion battery are improved. When the lithium ion battery electrolyte is applied to the lithium ion battery, the lithium ion battery with both long periodicity and low impedance performance can be obtained. The invention also provides electric equipment comprising the lithium ion battery.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery electrolyte and a lithium-ion battery. Background Art

[0002] There is a small amount of cuprous oxide on the surface of the copper foil of the negative electrode material of the lithium-ion battery. After the electrolyte is soaked for a period of time, the trace water in the electrode core will slowly release into the electrolyte, and the reaction will continuously generate Cu + and water. On the one hand, Cu + It is preferentially reduced to metallic copper on the negative electrode, and the copper dendrites formed penetrate the diaphragm, causing the battery's self-discharge to increase. The water continuously released from the electrode may also increase the side reactions inside the battery, thereby increasing the battery's self-discharge and reducing the battery's storage performance and quality. On the other hand, a small amount of water will also participate in the formation of the battery's solid electrolyte interface film, namely the SEI film, causing the SEI film to increase in thickness and the battery's impedance. At the same time, it will consume the active lithium released from the positive electrode, resulting in a reduction in battery capacity and poor cycle and storage performance.

[0003] In addition, the SEI film formed by the existing conventional SEI film-forming additives is relatively loose, and when the added amount is small, the formed SEI film is thinner, resulting in poor long-term room temperature cycle stability and high temperature performance of the battery; when the added amount is large, the formed SEI film is thicker and the battery impedance is large, resulting in poor high-rate power performance and low-temperature discharge performance of the battery. Summary of the invention

[0004] In view of this, the present application provides a lithium-ion battery electrolyte, which includes an organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive includes carbodiimide and isocyanate. The electrolyte additive can react with other substances in the electrolyte to form a SEI film of moderate thickness and density, and can also reduce the moisture in the pole core, thereby improving the capacity and cycle and storage performance of the lithium-ion battery. The lithium-ion battery electrolyte is applied to a lithium-ion battery to obtain a lithium-ion battery that takes into account both long-cycle performance and low-impedance performance. The present application also provides electrical equipment including the lithium-ion battery.

[0005] In a first aspect, the present application provides a lithium ion battery electrolyte, the lithium ion battery electrolyte comprising an organic solvent, a lithium salt and an electrolyte additive, the electrolyte additive comprising a carbodiimide as shown in formula (I) and an isocyanate as shown in formula (II), the mass ratio of the carbodiimide to the isocyanate being 1:0.25-4;

[0006]

[0007]

[0008] Wherein, R1 and R2 are selected from any one of isopropyl, tert-butyl, cyclohexyl and phenyl;

[0009] R3 is selected from a monovalent, divalent or trivalent substituted or unsubstituted hydrocarbon group or a sulfone group;

[0010] n is 1, 2 or 3.

[0011] In the embodiment of the present application, in the lithium-ion battery electrolyte, the carbodiimide includes one or more of N,N' diisopropylcarbodiimide, N,N' di-tert-butylcarbodiimide, N,N' dicyclohexylcarbodiimide and N,N' diphenylcarbodiimide.

[0012] In the embodiment of the present application, in the lithium-ion battery electrolyte, the isocyanate includes monoisocyanate, diisocyanate and triisocyanate; the monoisocyanate includes p-toluenesulfonyl isocyanate, the diisocyanate includes isophorone diisocyanate, diphenylmethane diisocyanate and lysine diisocyanate, and the triisocyanate includes 4,4',4" triphenylmethane triisocyanate.

[0013] In the embodiment of the present application, in the lithium-ion battery electrolyte, the sum of the mass percentages of the carbodiimide and the isocyanate in the lithium-ion battery electrolyte is 0.5%-3%.

[0014] In an embodiment of the present application, the lithium-ion battery electrolyte further includes a SEI film-forming additive, and the SEI film-forming additive includes one or more of vinylene carbonate, fluoroethylene carbonate, propylene sulfite and methylene methanedisulfonate.

[0015] In the embodiment of the present application, in the lithium ion battery electrolyte, the organic solvent includes one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, N-methylformamide, N-methylacetamide, acetonitrile, N,N-dimethylformamide, cyclopentane, dimethyl sulfoxide, dimethyl sulfite and other fluorine-containing, sulfur-containing or unsaturated bond-containing cyclic or chain organic esters.

[0016] In an embodiment of the present application, in the lithium-ion battery electrolyte, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate and bis(fluorosulfonyl)imide lithium salt.

[0017] The second aspect of the present application provides a lithium-ion battery, the lithium-ion battery comprising a battery housing and a positive electrode, a negative electrode, a separator and an electrolyte contained in the battery housing. The electrolyte comprises the lithium-ion battery electrolyte provided in the first aspect of the present application.

[0018] In the embodiment of the present application, the room temperature DC internal resistance of the lithium ion battery is 0.4mΩ-0.6mΩ; the cycle capacity retention rate after 1000 cycles at 60°C is 85%-90%; and the storage capacity residual rate after storage at 60°C for 28 days is 95%-97%.

[0019] A third aspect of the present application provides an electrical device, which includes the lithium-ion battery provided in the second aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic diagram of the structure of a lithium-ion battery provided in one embodiment of the present application;

[0021] Figure 2 A schematic diagram of the structure of an electrical device provided in one embodiment of the present application.

[0022] Description of Figure Numbers

[0023] 100-lithium-ion battery; 101-lithium-ion battery electrolyte; 102-diaphragm; 103-positive electrode; 104-negative electrode; 105-battery casing; 200-electric vehicle; 201-lithium-ion battery. DETAILED DESCRIPTION

[0024] The present application is further described in detail below in conjunction with preferred embodiments, but the protection scope of the present application is not limited to the following specific embodiments.

[0025] In the present application, all professional terms have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0026] There is a small amount of cuprous oxide on the surface of the copper foil of the negative electrode material of the lithium-ion battery. After the electrolyte is soaked for a period of time, the trace water in the electrode core will slowly release into the electrolyte, and the reaction will continuously generate Cu + and water. On the one hand, Cu +On the negative electrode, it is first reduced to metallic copper, and the copper dendrites formed penetrate the diaphragm, causing the battery's self-discharge to increase. The water continuously released from the electrode may also increase the side reactions inside the battery, thereby increasing the battery's self-discharge and reducing the battery's storage performance and quality. On the other hand, a small amount of water will also participate in the formation of the SEI film, causing the thickness of the SEI film to increase, the impedance of the battery to increase, and at the same time consume the active lithium released by the positive electrode, resulting in a decrease in battery capacity and poor cycle and storage performance.

[0027] There are two main methods commonly used to remove moisture from the electrode core. One is to change the baking process conditions by increasing the baking temperature, extending the baking time, and reducing the baking furnace pressure, but these methods will greatly increase the energy loss of the battery, thereby increasing the production cost of the battery; in addition, higher temperatures and longer baking times may also cause the diaphragm to wrinkle, thereby affecting the performance of the battery. The second is to replace the PE diaphragm with a PP diaphragm to slow down the effect of the infiltration rate on copper precipitation, but there is also the risk of diaphragm wrinkling and the improvement effect in actual application is not obvious.

[0028] In addition, the SEI film formed by the existing conventional SEI film-forming additives is relatively loose, and when the added amount is small, the formed SEI film is thinner, resulting in poor long-term room temperature cycle stability and high temperature performance of the battery; when the added amount is large, the formed SEI film is thicker and the battery impedance is large, resulting in poor high-rate power performance and low-temperature discharge performance of the battery.

[0029] In view of the above problems, the present application provides a lithium-ion battery electrolyte, which includes an organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive can react with other substances in the electrolyte to form a SEI film of moderate thickness and density, and can also reduce the moisture in the pole core, thereby improving the capacity and cycle and storage performance of the lithium-ion battery. The electrolyte to which the electrolyte additive is added is applied to a lithium-ion battery, and a lithium-ion battery with both long cycle performance and low impedance performance can be obtained.

[0030] The present application provides a lithium ion battery electrolyte, which includes an organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive includes a carbodiimide as shown in formula (I) and an isocyanate as shown in formula (II), and the mass ratio of the carbodiimide to the isocyanate is 1:0.25-4;

[0031]

[0032] Wherein, R1 and R2 are selected from any one of isopropyl, tert-butyl, cyclohexyl and phenyl;

[0033] R3 is selected from a monovalent, divalent or trivalent substituted or unsubstituted hydrocarbon group or a sulfone group;

[0034] n is 1, 2 or 3.

[0035] In the embodiment of the present application, the carbodiimide and isocyanate in the lithium-ion battery electrolyte are a special SEI film-forming additive. Different from the commonly used SEI film-forming additives containing carbon-carbon double bonds, carbon-oxygen double bonds and sulfur-oxygen double bonds, the electrolyte additives in the lithium-ion battery electrolyte provided by the present application include both carbodiimide and isocyanate. Lithium-ion battery formation refers to the process of charging the lithium-ion battery for the first time, the purpose of which is to form a layer of solid electrolyte interface film, i.e., SEI film, on the surface of the negative electrode. In the embodiment of the present application, in the early stage of lithium-ion battery formation, carbodiimide and isocyanate can react with solvent molecules and lithium salts in the electrolyte to generate a cyclic polymer with a dense structure, thereby obtaining a dense SEI film of moderate thickness. Specifically, the unsaturated double bonds containing N atoms in carbodiimide and isocyanate, the above unsaturated double bonds under low current (i.e., battery formation stage), each undergoes a ring-opening reaction and interconnects to form a new cyclic polymer, the cyclic polymer is a six-membered ring, the structure is more stable, and it also contains nitrogen atoms, which is conducive to coordination with lithium ions to form a stable and dense SEI film. The dense SEI film can effectively prevent the solvent from reacting with the negative electrode active material, allowing lithium ions to be deintercalated, thereby improving the electrochemical performance of the lithium ion battery. In addition, the thickness of the dense SEI is moderate, which not only avoids the problem of poor long-term room temperature cycle performance and high temperature performance of the battery caused by the SEI film being too thin, but also avoids the problem of large battery impedance and poor rate performance caused by the SEI film being too thick. The embodiment of the present application obtains a lithium ion battery electrolyte that takes into account the long-term performance and low impedance performance of the lithium ion battery by selecting a two-component electrolyte additive of carbodiimide and isocyanate.

[0036] In the embodiment of the present application, the carbodiimide includes one or more of N,N' diisopropylcarbodiimide, N,N' di-tert-butylcarbodiimide, N,N' dicyclohexylcarbodiimide and N,N' diphenylcarbodiimide. Preferably, the carbodiimide includes at least one of N,N' diisopropylcarbodiimide and N,N' di-tert-butylcarbodiimide. There is a small amount of cuprous oxide on the negative electrode material of the lithium-ion battery. After the electrolyte is infiltrated for a period of time, the trace moisture in the electrode core will slowly release into the electrolyte, and the reaction will continuously generate Cu + and water. On the one hand, Cu +It is preferentially reduced to metallic copper on the negative electrode, and the formed copper dendrites pass through the diaphragm, causing the self-discharge of the battery to increase. The water continuously released from the electrode may also increase the side reactions inside the battery, thereby increasing the self-discharge of the battery and reducing the storage performance and quality of the battery. On the other hand, a small amount of water will also participate in the formation of the SEI film, resulting in an increase in the thickness of the SEI film and an increase in the impedance of the battery. At the same time, it will consume the active lithium released by the positive electrode, resulting in a decrease in battery capacity and poor cycle and storage performance. The carbodiimide in the lithium-ion battery electrolyte of the present application can react with the lithium-ion battery electrode and trace water in the electrolyte to form urea, thereby achieving the purpose of removing trace water in the electrode core. In some embodiments, the carbodiimide in the electrolyte additive is selected from N, N'diisopropylcarbodiimide, and N, N'diisopropylcarbodiimide reacts with trace water to form 1,3 diisopropyl urea. On the one hand, N,N'-diisopropylcarbodiimide is a liquid at room temperature and is easily dispersed evenly after being added to the electrolyte; on the other hand, the generated 1,3-diisopropylurea can be dissolved in the organic solvent of the electrolyte and will not decompose at 100°C, thereby ensuring the stability of the electrochemical performance of the battery. In other embodiments, the carbodiimide in the electrolyte additive is selected from N,N'-di-tert-butylcarbodiimide, which reacts with trace amounts of water to generate 1,3-di-tert-butylurea, which can also be dissolved in the organic solvent of the electrolyte. While removing trace amounts of water in the electrode core, the products generated by the reaction will not have a negative impact on the electrochemical performance of the battery.

[0037] In some embodiments of the present application, R3 is selected from substituted or unsubstituted hydrocarbon groups, and the hydrocarbon group can be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group can be an alkyl group, and the alkyl group can be a linear alkyl group or a cycloalkyl group, wherein the substituted alkyl group can be an arylalkyl group. The arylalkyl group is, for example, a phenylalkyl group. The aromatic hydrocarbon group can be, for example, an aryl group or a heteroaryl group, and the aryl group can be, for example, a phenyl group, an alkylphenyl group, or a biphenyl group. The number of carbon atoms of the substituted or unsubstituted hydrocarbon group is 1-30, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30.

[0038] In some embodiments of the present application, R3 is selected from substituted or unsubstituted sulfone groups, wherein the substituted sulfone groups can be alkylsulfone groups, phenylsulfone groups, alkylphenylsulfone groups, phenylalkylsulfone groups. The number of carbon atoms of the substituted or unsubstituted sulfone groups is 1-30, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30.

[0039] Specifically, in some embodiments, when R3 is a monovalent group, the corresponding isocyanate is a monoisocyanate. In some embodiments, R3 can be a p-toluenesulfonyl group. When R3 is a divalent group, the corresponding isocyanate is a diisocyanate. In some embodiments, R3 can be a diphenylmethyl group. When R3 is a trivalent group, the corresponding isocyanate is a triisocyanate. In some embodiments, R3 can be a triphenylmethyl group.

[0040] In the embodiment of the present application, the isocyanate may be one or more of monoisocyanate, diisocyanate, and triisocyanate; wherein the monoisocyanate may be p-toluenesulfonyl isocyanate, the diisocyanate may be one or more of isophorone diisocyanate, diphenylmethane diisocyanate, and lysine diisocyanate, and the triisocyanate includes 4,4',4" triphenylmethane triisocyanate. Isocyanate has high activity and can react with trace amounts of moisture to generate amines and CO2 gas. When the amount of isocyanate added is large and the activity is large, the generated amine can further generate urea. In some embodiments, the isocyanate in the electrolyte additive is p-toluenesulfonyl isocyanate. P-toluenesulfonyl isocyanate Cyanate is a highly efficient dehydrating agent that reacts with trace amounts of water in an electrolyte to generate p-toluenesulfonamide and carbon dioxide gas. The carbon dioxide gas is pumped away by negative pressure during the subsequent formation of the lithium-ion battery; p-toluenesulfonamide can be dissolved in the organic solvent of the electrolyte, and has stable performance during the charging and discharging process of the lithium-ion battery, and will not be electrochemically oxidized or reduced to other substances, and has no significant effect on the electrochemical performance of the battery. In other embodiments, the isocyanate in the electrolyte additive is isophorone diisocyanate. Isophorone diisocyanate has two isocyanate groups, reacts with water at a moderate rate in the absence of a catalyst, and reacts with trace amounts of water to generate isophorone diamine that can be dissolved in an organic solvent.

[0041] In the embodiment of the present application, the carbodiimide and isocyanate in the lithium ion battery electrolyte can be used as dewatering additives in the electrolyte, respectively, to remove trace moisture from the pole core. Carbodiimide reacts with trace moisture to form urea, and isocyanate reacts with trace moisture to form amine or further reacts to form urea. The product obtained by the reaction is easily dissolved in the organic solvent of the electrolyte and maintains excellent stability during the battery charge and discharge process. In addition, carbodiimide and isocyanate are added together, which can be used as a special SEI film-forming additive. Compared with conventional carbon SEI film-forming additives, carbodiimide and isocyanate can react with other substances in the electrolyte to form cyclic polymers, forming a dense and moderately thick SEI film, and obtaining an electrolyte additive that takes into account the long-cycle performance and low impedance performance of lithium ion batteries.

[0042] In the embodiment of the present application, the mass ratio of carbodiimide to isocyanate in the lithium ion battery electrolyte is 1:0.25-4. In some embodiments, the mass ratio of carbodiimide to isocyanate in the lithium ion battery electrolyte can be 1:0.25, 1:0.33, 1:0.5, 1:1, 1:2, 1:3, 1:4. The present application adjusts the component ratio of carbodiimide and isocyanate so that the lithium ion battery electrolyte takes into account both the relatively excellent water removal performance and SEI film forming performance. In some embodiments, when the addition amount of the electrolyte additive is the same, the lithium ion battery prepared by adding carbodiimide and isocyanate within a suitable ratio range in the present application has a lower internal resistance than the lithium ion battery prepared by adding carbodiimide or isocyanate alone, and has better cycle performance and storage performance. That is, when the electrochemical performance of the prepared lithium ion battery is equivalent, the total addition amount of carbodiimide and isocyanate added in a suitable ratio is less than the addition amount of carbodiimide or isocyanate added alone.

[0043] In the embodiment of the present application, the sum of the mass percentages of carbodiimide and isocyanate in the lithium ion battery electrolyte is 0.5%-3%. In some embodiments, the sum of the mass percentages of carbodiimide and the isocyanate in the lithium ion battery electrolyte can be 0.5%, 0.75%, 1%, 1.25%, 1.5%, 1.75%, 2%, 2.25%, 2.5%, 2.75%, 3%. The present application controls the thickness of the SEI film within a suitable range by controlling the sum of the mass percentages of carbodiimide and isocyanate in the lithium ion battery electrolyte within the range of 0.5%-3%, thereby avoiding the problem of poor long-term room temperature cycle performance and high temperature performance of the lithium ion battery caused by the SEI film being too thin, and avoiding the problem of poor high-rate power performance and low-temperature discharge performance of the lithium ion battery caused by the SEI film being too thick, thereby ensuring a significant improvement in the electrochemical performance of the lithium ion battery while reducing the cost as much as possible.

[0044] In the embodiment of the present application, the organic solvent in the lithium ion battery electrolyte includes one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, N-methylformamide, N-methylacetamide, acetonitrile, N,N-dimethylformamide, cyclopentane, dimethyl sulfoxide, dimethyl sulfite and other fluorine-containing, sulfur-containing or unsaturated bond-containing cyclic or chain organic esters. The above organic solvent can dissolve the product of the reaction of carbodiimide and isocyanate with water while dissolving the lithium salt. Selecting a suitable organic solvent can improve the conductivity and physicochemical stability of the electrolyte. In some embodiments of the present application, the solvent is selected from ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate. In some embodiments, the mass ratio of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate and dimethyl carbonate is 34:35:13:18.

[0045] In the embodiment of the present application, the lithium salt in the lithium ion battery electrolyte includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium difluorophosphate and bis(fluorosulfonyl)imide lithium salt. As a provider of lithium ions in the lithium ion battery electrolyte, the lithium salt is one of the necessary components in the electrolyte. The above-mentioned lithium salt and the organic solvent described above can react with the carbodiimide in the electrolyte additive to form a dense SEI film.

[0046] In an embodiment of the present application, the lithium ion battery electrolyte also includes a SEI film-forming additive, and the SEI film-forming additive includes one or more of vinylene carbonate, fluoroethylene carbonate, propylene sulfite and methylene disulfonate. The SEI film-forming additive is a double bond substance containing carbon-carbon double bonds, carbon-oxygen double bonds or sulfur-oxygen double bonds, and has a high reduction potential. In the early stage of battery formation, electrons are preferentially reduced and combined with lithium ions to form an inorganic composition of the SEI film. The SEI film-forming additive can react with organic solvents, lithium salts and carbodiimides and isocyanates in the lithium ion electrolyte to form a dense SEI film. In some embodiments of the present application, the SEI film-forming additive is vinylene carbonate. In some embodiments, the mass ratio of vinyl carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate and vinylene carbonate is 34:35:13:18:3.

[0047] The lithium-ion battery electrolyte provided by the present application is obtained by adding electrolyte additives carbodiimide and isocyanate to the electrolyte. In the early stage of the lithium-ion battery formation, the carbodiimide and isocyanate react with the solvent molecules, lithium salts and SEI film-forming additives in the electrolyte to obtain a moderately thick and dense SEI film. The dense SEI film can effectively prevent the solvent from reacting with the negative electrode active material, allowing lithium ions to pass through for deintercalation, thereby improving the electrochemical performance of the lithium-ion battery. The thickness of the dense SEI is moderate, which not only avoids the problems of poor long-term room temperature cycle performance and high temperature performance caused by the SEI film being too thin, but also avoids the problems of large battery impedance and poor rate performance caused by the SEI film being too thick. In addition, carbodiimide and isocyanate can also reduce the moisture in the pole core. The lithium-ion battery electrolyte is applied to a lithium-ion battery to obtain a lithium-ion battery that takes into account both long-cycle performance and low impedance performance.

[0048] like Figure 1As shown, the present application also provides a lithium-ion battery, the lithium-ion battery 100 includes a battery housing 105 and a lithium-ion battery electrolyte 101, a separator 102, a positive electrode 103 and a negative electrode 104 contained in the battery housing 105, and the lithium-ion battery electrolyte 101 and the separator 102 are located between the positive electrode 103 and the negative electrode 104. Among them, the separator 102 is a polymer film; the positive electrode 103 includes a current collector aluminum foil and a positive electrode active material disposed on the current collector aluminum foil; the negative electrode 104 includes a current collector copper foil and a negative electrode active material disposed on the current collector copper foil; the battery housing 105 includes but is not limited to materials such as steel shell, aluminum shell, nickel-plated iron shell or aluminum-plastic film.

[0049] In the embodiment of the present application, the room temperature DC internal resistance of the lithium ion battery is 0.4mΩ-0.6mΩ; the cycle capacity retention rate after 1000 cycles at 60°C is 85%-90%; the storage capacity residual rate after 28 days of storage at 60°C is 95%-97%. In some embodiments, the room temperature DC internal resistance of the lithium ion battery can be 0.5mΩ-0.6mΩ; the cycle capacity retention rate after 1000 cycles at 60°C can be 85%-89%; the storage capacity residual rate after 28 days of storage at 60°C can be 96%-97%.

[0050] The present application also provides an electrical device, which includes the lithium-ion battery described above. The electrical device may be, for example, an electric car, a mobile phone, a tablet computer, a laptop computer, a wearable device (a watch, a bracelet), a digital camera, etc. Figure 2 The electric device may be an electric car 200. The electric car 200 includes the lithium-ion battery 201 described above in the present application.

[0051] The present application is further described below in multiple embodiments:

[0052] Example 1

[0053] Ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate, N,N'-diisopropylcarbodiimide, p-toluenesulfonyl isocyanate and 1 mol / L lithium hexafluorophosphate in a mass ratio of 34:35:13:14.5:3:0.25:0.25 are prepared to obtain a lithium ion battery electrolyte, and the total injection amount of the electrolyte is 430 g; lithium iron phosphate, acetylene black and polyvinylidene fluoride are dissolved in N-methylpyrrolidone in a mass ratio of 90:5:5 to form a battery slurry with a solid content of 58 wt%, and the positive electrode slurry obtained after stirring is coated on The two sides of an aluminum foil with a thickness of 13 μm are coated and baked at 100°C ± 5°C, and then rolled and vacuum dried to form a material layer with a thickness of 130 μm ± 5 μm to obtain a positive electrode sheet; asphalt-coated natural graphite with an asphalt coating amount of 2%, conductive carbon black, styrene-butadiene rubber and carboxymethyl cellulose are dispersed in deionized water at a mass ratio of 95:1:1.1:2.3 to obtain a negative electrode slurry with a solid content of 60wt%, and the negative electrode slurry obtained after uniform stirring is coated on both sides of a copper foil with a thickness of 8 μm, and baked at 100°C ± 5°C to obtain a negative electrode sheet;

[0054] The prepared positive electrode plate, negative electrode plate and a polyethylene diaphragm with a thickness of 9 μm were stacked to obtain a square lithium-ion movement, which was loaded into an aluminum shell with a size of 550 mm×100 mm×19.5 mm and the shell cover was welded to form a battery cell. It was then baked in a tunnel furnace at a temperature of 100°C±5°C for 10 h±0.5 h. After baking, the moisture content of the positive and negative electrode combination was tested by the Karl Fischer method and was 112 ppm.

[0055] The prepared lithium-ion battery electrolyte is injected into the baked battery cell, the cap is welded and sealed, and the lithium-ion battery is prepared through the steps of formation, charging, high-temperature aging, capacity division and the like.

[0056] Example 2

[0057] Ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate, N,N'-diisopropylcarbodiimide, p-toluenesulfonyl isocyanate and 1 mol / L lithium hexafluorophosphate in a mass ratio of 34:35:13:14:3:0.5:0.5 were prepared to obtain a lithium ion battery electrolyte, and the total injection volume of the electrolyte was 430 g; the preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0058] Example 3

[0059] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate, N,N'-diisopropylcarbodiimide and p-toluenesulfonyl isocyanate in a mass ratio of 34:35:13:13.5:3:0.5:1 and 1 mol / L lithium hexafluorophosphate. The total injection volume of the electrolyte was 430 g. The preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0060] Example 4

[0061] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate, N,N'-diisopropylcarbodiimide and p-toluenesulfonyl isocyanate in a mass ratio of 34:35:13:13.5:3:1:0.5 and 1 mol / L lithium hexafluorophosphate. The total injection volume of the electrolyte was 430 g. The preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0062] Example 5

[0063] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate, N,N'-diisopropylcarbodiimide and p-toluenesulfonyl isocyanate in a mass ratio of 34:35:13:12:3:1.5:1.5 and 1 mol / L lithium hexafluorophosphate. The total injection volume of the electrolyte was 430 g. The preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0064] Comparative Example 1

[0065] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate and vinylene carbonate in a mass ratio of 34:35:13:15:3 and 1 mol / L lithium hexafluorophosphate, and the total injection amount of the electrolyte was 430 g; the preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0066] Comparative Example 2

[0067] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate and N,N'-diisopropylcarbodiimide in a mass ratio of 34:35:13:13.5:3:1.5 and 1 mol / L lithium hexafluorophosphate. The total injection volume of the electrolyte was 430 g. The preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0068] Comparative Example 3

[0069] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate and N,N'-diisopropylcarbodiimide in a mass ratio of 34:35:13:14.5:3:0.5 and 1 mol / L lithium hexafluorophosphate. The total injection volume of the electrolyte was 430 g. The preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0070] Comparative Example 4

[0071] Ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate and N,N'-diisopropylcarbodiimide in a mass ratio of 34:35:13:14:3:1 and 1 mol / L lithium hexafluorophosphate are configured to obtain a lithium ion battery electrolyte, and the lithium ion battery electrolyte is obtained by configuring according to the mass ratio, and the total injection amount of the electrolyte is 430 g; the preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery are the same as in Example 1.

[0072] Comparative Example 5

[0073] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate and p-toluenesulfonyl isocyanate in a mass ratio of 34:35:13:13.5:3:1.5 and 1 mol / L lithium hexafluorophosphate. The total injection volume of the electrolyte was 430 g. The preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0074] Comparative Example 6

[0075] Ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate and p-toluenesulfonyl isocyanate in a mass ratio of 34:35:13:14.5:3:0.5 and 1 mol / L lithium hexafluorophosphate were prepared to obtain a lithium ion battery electrolyte, and the total injection volume of the electrolyte was 430 g; the preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0076] Comparative Example 7

[0077] Ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate and p-toluenesulfonyl isocyanate in a mass ratio of 34:35:13:14:3:1 and 1 mol / L lithium hexafluorophosphate were prepared to obtain a lithium ion battery electrolyte, and the total injection volume of the electrolyte was 430 g; the preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0078] Comparative Example 8

[0079] A lithium ion battery electrolyte was prepared by mixing ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, vinylene carbonate, N,N'-diisopropylcarbodiimide and 1 mol / L lithium hexafluorophosphate of p-toluenesulfonyl isocyanate in a mass ratio of 34:35:13:12.75:3:0.25:2, and the total injection volume of the electrolyte was 430 g; the preparation of the positive electrode material, the negative electrode material and the assembly preparation of the lithium ion battery were the same as in Example 1.

[0080] The lithium ion batteries prepared in the above Examples 1-5 and Comparative Examples 1-8 were tested as follows:

[0081] (1) Capacity test

[0082] The lithium-ion battery was loaded into the battery performance tester BS-9300, and charged at a current of 0.5C with an upper voltage of 3.8V at a room temperature of 25°C, and then discharged at a current of 1 / 3C with a lower voltage of 2.0V. The charge and discharge were performed three times, and the average value of the three discharge capacities was taken as the capacity value of the lithium-ion battery. The results are shown in Table 1.

[0083] (2) Normal temperature DC internal resistance test

[0084] At room temperature of 25°C, the lithium-ion battery was adjusted to a 25% SOC state. A DC internal resistance meter was used to perform a discharge test of the lithium-ion battery at a current of 1.5C for 10S at room temperature of 25°C. The ratio of the voltage difference before and after discharge to the current value was taken as the room-temperature DC internal resistance of the lithium-ion battery. The results are shown in Table 1.

[0085] (3) Low temperature DC internal resistance test

[0086] At room temperature of 25°C, the lithium-ion battery was adjusted to a 25% SOC state. A DC internal resistance meter was used to perform a discharge test of the lithium-ion battery at a current of 1.5C for 10S at a low temperature of -10°C. The ratio of the voltage difference before and after discharge to the current value was taken as the low-temperature DC internal resistance of the lithium-ion battery. The results are shown in Table 1.

[0087] (4) 60℃ Cycle Capacity Retention Test

[0088] The lithium-ion battery was loaded into the battery performance tester BS-9300, and charged and discharged at a current of 0.5C at a temperature of 60°C, with an upper limit voltage of 3.8V and a lower limit voltage of 2.0V for 1000 cycles. The ratio of the discharge capacity of 1000 times to the discharge capacity of the first time is the 60°C cycle capacity retention rate of the battery. The results are shown in Table 1.

[0089] (5) 60℃ storage capacity remaining rate test

[0090] The lithium-ion battery was loaded into the battery performance tester BS-9300, and charged to 3.8V at a current of 0.5C at a room temperature of 25°C. The charging capacity was recorded. The battery was then stored at a high temperature of 60°C for 28 days, then taken out and discharged to 2.0V at a current of 0.5C at a room temperature of 25°C. The ratio of the discharged capacity to the charged capacity is the capacity residual rate. The results are shown in Table 1.

[0091] Table 1 Relevant electrochemical performance test data of lithium ion batteries of Examples 1-5 and Comparative Examples 1-8

[0092]

[0093] It can be seen from the data of the above-mentioned Examples 1-5 and Comparative Examples 1-8 that, compared with Comparative Example 1 in which carbodiimide and isocyanate are not added and Examples 2-7 in which only a single component of carbodiimide or isocyanate is added, the electrolyte of Examples 1-5 is prepared by adding two components of carbodiimide and isocyanate at the same time. The battery has a capacity that is roughly the same, and the DC resistance at room temperature and low temperature is significantly reduced, and the reduction in low-temperature DC resistance is more obvious. And compared with Comparative Example 8, Examples 1-5 of the present application can further reduce the resistance of the battery and improve the cycle performance of the battery by controlling the mass ratio of carbodiimide and isocyanate within a suitable range. In addition, the 60°C cycle capacity retention rate of the battery is increased by more than 5%, and the 60°C storage capacity residual rate is also improved to a certain extent. Therefore, the lithium-ion battery prepared by using the lithium-ion battery electrolyte containing carbodiimide and isocyanate provided by the present application has better electrochemical performance than the lithium-ion battery obtained by adding only conventional additives or only adding a single component of additives.

[0094] The preferred embodiments are described in detail above, but the present invention is not limited to the above-mentioned specific implementation modes. Under the guidance of the present application, technicians in this field can also make various specific changes without departing from the scope of protection of the present application, which all fall within the scope of protection of the present invention.

Claims

1. A lithium ion battery electrolyte, characterized in that: The lithium-ion battery electrolyte comprises an organic solvent, a lithium salt and an electrolyte additive, wherein the electrolyte additive comprises a carbodiimide as shown in formula (I) and an isocyanate as shown in formula (II), and the mass ratio of the carbodiimide to the isocyanate is 1:0.25-4; Wherein, R1 and R2 are selected from any one of isopropyl, tert-butyl, cyclohexyl and phenyl; R3 is selected from a monovalent, divalent or trivalent substituted or unsubstituted hydrocarbon group or a sulfone group; n is 1, 2 or 3.

2. The lithium ion battery electrolyte according to claim 1, characterized in that The carbodiimide includes one or more of N,N'-diisopropylcarbodiimide, N,N'-di-tert-butylcarbodiimide, N,N'-dicyclohexylcarbodiimide and N,N'-diphenylcarbodiimide.

3. The lithium ion battery electrolyte according to claim 1 or 2, characterized in that: The isocyanate includes one or more of monoisocyanate, diisocyanate and triisocyanate; the monoisocyanate includes p-toluenesulfonyl isocyanate; the diisocyanate includes one or more of isophorone diisocyanate, diphenylmethane diisocyanate and lysine diisocyanate; the triisocyanate includes 4,4',4" triphenylmethane triisocyanate.

4. The lithium ion battery electrolyte according to any one of claims 1 to 3, characterized in that The sum of the mass percentages of the carbodiimide and the isocyanate in the lithium ion battery electrolyte is 0.5%-3%.

5. The lithium ion battery electrolyte according to any one of claims 1 to 4, characterized in that: The lithium ion battery electrolyte further includes a SEI film-forming additive, wherein the SEI film-forming additive includes one or more of vinylene carbonate, fluoroethylene carbonate, propylene sulfite and methylene methanedisulfonate.

6. The lithium ion battery electrolyte according to any one of claims 1 to 5, characterized in that: The organic solvent includes one or more of γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, dipropyl carbonate, N-methylformamide, N-methylacetamide, acetonitrile, N,N-dimethylformamide, sulfolane, dimethyl sulfoxide, dimethyl sulfite and other fluorine-containing, sulfur-containing or unsaturated bond-containing cyclic or chain organic esters.

7. The lithium ion battery electrolyte according to any one of claims 1 to 6, characterized in that: The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium difluorophosphate and bis(fluorosulfonyl)imide lithium salt.

8. A lithium ion battery, characterized in that: The lithium-ion battery comprises a battery housing and a positive electrode, a negative electrode, a separator and an electrolyte contained in the battery housing, wherein the electrolyte comprises the lithium-ion battery electrolyte according to any one of claims 1 to 7.

9. The lithium ion battery according to claim 8, characterized in that The room temperature DC internal resistance of the lithium ion battery is 0.4 mΩ-0.6 mΩ; the cycle capacity retention rate after 1000 cycles at 60°C is 85%-90%; and the storage capacity residual rate after 28 days of storage at 60°C is 95%-97%.

10. An electrical device, characterized in that: The electrical device comprises the lithium-ion battery as claimed in claim 8 or 9.

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