An electrolyte and a battery comprising the same

Abstract

The application provides an electrolyte and a battery comprising the electrolyte. The electrolyte contains a benzene ring-containing nitrate compound. The additive is more difficult to lose electrons due to the strong electron-withdrawing nitrate group, has strong oxidation stability and is more resistant to high pressure. Meanwhile, the N and O atoms in the nitrate group also contain lone pair electrons, which is beneficial to accelerate the transmission of lithium ions, thereby reducing the impedance of the lithium ion battery and enhancing the kinetic performance. When the electrolyte is used in a battery, the high-temperature stability, cycle performance and low-temperature performance of the high-voltage battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrolyte and a battery comprising the same, and belongs to the technical field of lithium ion batteries, in particular to the field of development of electrolytes for lithium ion batteries. BACKGROUND

[0002] In recent years, with the development of the electric vehicle industry and the energy storage field, the research and application of lithium ion batteries have attracted more and more attention. In particular, high-energy-density lithium ion batteries have always been the focus of research. Generally, to improve the energy density, the battery operating voltage is usually increased, and the compaction density of the positive and negative electrode main materials is increased. However, increasing the compaction density of the main materials will affect the liquid retention and electrolyte infiltration of the battery, and increasing the battery operating voltage requires a high-voltage-resistant and more stable electrolyte to match.

[0003] At present, the most commonly used electrolyte in the industry is formed by dissolving lithium salt (mainly lithium hexafluorophosphate) in organic carbonate (ethylene carbonate, etc.). This type of electrolyte basically meets the charging and discharging requirements, but also has some shortcomings. For example, lithium hexafluorophosphate has poor thermal stability and is easily decomposed under high temperature and high pressure, which will cause various side reactions with the electrolyte and the positive and negative electrodes, affecting the cycle stability and safety performance of the battery. At the same time, the solvents used in the electrolyte also have similar problems. Therefore, the development of a high-voltage-resistant (above 4.45V) electrolyte system has always been an important research topic for lithium ion batteries. SUMMARY

[0004] In order to improve the deficiencies of the prior art, the purpose of the present application is to provide an electrolyte and a battery comprising the same. The first additive of the electrolyte is selected from a nitrate compound containing a benzene ring, and the introduction of the first additive can improve the oxidation stability of the electrolyte under high voltage (such as 4.55-5.0V), which can improve the high-temperature storage performance, room-temperature cycle performance, thickness change rate, and low-temperature performance of the battery while improving the energy density of the battery.

[0005] The purpose of the present application is achieved by the following technical solutions:

[0006] An electrolyte, comprising an electrolyte salt, an organic solvent, and a first additive, wherein the first additive comprises a nitrate compound containing a benzene ring.

[0007] According to an embodiment of the present application, the nitrate compound containing a benzene ring comprises a benzene ring and a nitrate group, and the benzene ring and the nitrate group are directly connected or connected through an alkylene group.

[0008] According to an embodiment of the present application, the nitrate compound containing a benzene ring is selected from at least one of the compounds shown in Formula 1:

[0009]

[0010] In formula 1, n is an integer between 0 and 4; m1 is an integer between 0 and 5; R is halogen, -CN, -NR1R2, hydroxyl, carboxyl, aldehyde, substituted or unsubstituted alkyl, if substituted, the substituent is alkyl or halogen, R1, R2 are the same or different and are independently selected from alkyl.

[0011] According to an embodiment of the present application, n is 0, 1, 2, 3 or 4; m1 is 0, 1, 2, 3, 4 or 5; R is halogen, -CN, -NR1R2, hydroxyl, carboxyl, aldehyde, substituted or unsubstituted C 1-6 alkyl, if substituted, the substituent is C 1-6 alkyl or halogen, R1, R2 are the same or different and are independently selected from C 1-6 alkyl.

[0012] According to an embodiment of the present application, the nitrate compound containing benzene ring is selected from at least one of compound A to compound D:

[0013]

[0014]

[0015] According to an embodiment of the present application, the mass of the nitrate compound containing benzene ring accounts for 3wt% to 15wt% of the total mass of the electrolyte, for example, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0016] According to an embodiment of the present application, the introduction of nitrate group in the nitrate compound containing benzene ring enhances the electron-withdrawing ability on one hand, improves the oxidation stability of the electrolyte system, improves the voltage endurance of the battery, improves the energy density of the battery, and improves the high-temperature performance and cycle performance of the battery; on the other hand, the N and O atoms in the nitrate group also provide certain lone pair of electrons, which can coordinate with lithium ions during use, accelerate the transmission of lithium ions, improve the lithium ion conductivity, reduce the electrochemical impedance of the battery system, and thus improve the low-temperature performance of the battery.

[0017] According to an embodiment of the present application, the nitrate compound containing benzene ring can be prepared by the following method:

[0018] Step 1: at room temperature, add equimolar ratio of HNO3 and raw material a into a nitration reactor, and then stir for 30-60 min after evacuating for 5 min by blowing in inert gas at a stirring speed of 100 rad / min;

[0019] Step two: add a certain amount of catalyst H2SO4 into the reactor at room temperature, and stir for 8-15 min.

[0020] The stirring speed is unchanged;

[0021] Step three: slowly raise the temperature of the reactor to 70-85℃, and stir for at least 2h, and the stirring speed is unchanged;

[0022] Step four: after the reaction is completed, first stop stirring, and then stop aeration after the temperature drops to room temperature; after the condensation product is layered, first wash with alkali, and then wash with water until neutral and dry to collect the product.

[0023] The concentration of nitric acid in step one is preferably above 65wt%. More preferably, it is 69.8wt%.

[0024] The inert gas in step one is preferably nitrogen or argon. More preferably, it is nitrogen, and the stirring time is 45 min.

[0025] Preferably, the concentration of catalyst H2SO4 is 98wt%, and the addition amount is 5wt%-10wt% of the total mass, more preferably 8wt%. At the same time, the stirring time is preferably 10 min.

[0026] The reaction temperature in step three is preferably 80℃, and the stirring time is 4h.

[0027] Preferably, the alkali for washing the product in step four is Na2CO3 or K2CO3, more preferably Na2CO3.

[0028] According to an embodiment of the present application, the structural formula of the raw material a is shown as formula a:

[0029]

[0030] According to an embodiment of the present application, the electrolyte salt is selected from at least one of electrolyte lithium salts.

[0031] According to an embodiment of the present application, the electrolyte lithium salt is selected from any one or a combination of at least two of LiPF6, LiBOB, LiODFB, LiFSI, LiTFSI, LiBF4, LiPO2F2, LiNO3, LiN(SO2F)2, LiN(SO2F)(SO2CF3), LiC(SO2CF3)3, LiPF2(C2O4), and LiPF4(C2O4).

[0032] According to an embodiment of the present application, the mass of the electrolyte salt accounts for 8wt%-17wt% of the total mass of the electrolyte, for example, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, or 16wt%, etc.

[0033] According to embodiments of the present application, the electrolyte lithium salt is selected from a combination of LiPF6and at least one of the following other lithium salts: LiBOB, LiODFB, LiFSI, LiTFSI, LiBF4, LiPO2F2, LiNO3, LiN(SO2F)2, LiN(SO2F)(SO2CF3), LiC(SO2CF3)3, LiPF2(C2O4), and LiPF4(C2O4).

[0034] Preferably, the mass of the other lithium salt is 0.3wt% to 2wt% of the total mass of the electrolyte, such as 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, or 1.9wt%, and the like.

[0035] According to embodiments of the present application, the electrolyte further comprises a second additive selected from at least one of the following compounds: methanedisulfonic acid methylene ester, vinyl carbonate, 1,3-propane sulfonic acid lactone (PS), fluoroethylene carbonate (FEC), vinyl ethylene carbonate, 1,4-butane sulfonic acid lactone, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, ethylene glycol bispropionitrile ether, tris(2,2,2-trifluoroethyl)phosphite, 1,4-dicyano-2-butene, ethylene sulfite, 1,3,6-hexanetricarbonitrile, citric anhydride, fluorobenzene, boron trifluoride tetrahydrofuran, pentafluoro(phenoxy)cyclotriphosphazene, citraconic anhydride, ethylene sulfate, 1,3-propene sulfonic acid lactone, and 4-methyl ethylene sulfite.

[0036] According to embodiments of the present application, the mass of the second additive is 4wt% to 15wt% of the total mass of the electrolyte, such as 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, or 14wt%, and the like.

[0037] According to embodiments of the present application, the organic solvent is selected from any one or a combination of at least two of the following: vinyl carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propyl propionate, ethyl propionate, propyl acetate, butyl butyrate, and ethyl butyrate.

[0038] According to embodiments of the present application, the mass of the organic solvent is 50wt% to 85wt% of the total mass of the electrolyte, such as 52wt%, 55wt%, 58wt%, 60wt%, 62wt%, 65wt%, 68wt%, 70wt%, 72wt%, 75wt%, 78wt%, 80wt%, or 82wt%, and the like.

[0039] The application also provides a battery comprising the electrolyte.

[0040] According to an embodiment of the application, the battery is a lithium ion battery.

[0041] According to an embodiment of the application, the battery comprises a positive electrode sheet, a negative electrode sheet and a separator.

[0042] Preferably, the positive electrode sheet comprises a current collector and a positive electrode coating layer on the surface of the current collector.

[0043] Preferably, the current collector in the positive electrode sheet is a single-surface aluminum foil, a double-surface aluminum foil or a porous aluminum foil.

[0044] Preferably, the positive electrode coating layer contains a positive electrode active material and an additive.

[0045] Preferably, the positive electrode active material is at least one of lithium iron phosphate, a ternary positive electrode material and lithium cobaltate.

[0046] Preferably, the additive comprises a conductive agent and / or a positive electrode binder, for example, the conductive agent is at least one of graphite, carbon black, acetylene black, graphene and carbon nanotubes; for example, the positive electrode binder can be at least one of PVDF, polyacrylate and polyacrylic acid, preferably PVDF.

[0047] According to an embodiment of the application, the positive electrode sheet is prepared by a method comprising the following steps:

[0048] (1) mixing a positive electrode active material, a conductive agent and a positive electrode binder uniformly to obtain a positive electrode slurry;

[0049] (2) coating the positive electrode slurry on the surface of the current collector, and baking to obtain the positive electrode sheet.

[0050] According to an embodiment of the application, the mass ratio of the positive electrode active material, the conductive agent and the positive electrode binder is not particularly limited, and a mass ratio known in the art can be used. For example, the mass ratio of the positive electrode active material, the conductive agent and the positive electrode binder can be 96.2:2:1.8; illustratively, the mass ratio of lithium cobaltate, carbon black and PVDF is 96.2:2:1.8.

[0051] Preferably, the negative electrode sheet comprises a current collector and a negative electrode coating layer on the surface of the current collector.

[0052] Preferably, the current collector in the negative electrode sheet is a single-surface copper foil, a double-surface copper foil or a porous copper foil.

[0053] Preferably, the negative electrode coating layer contains a negative electrode active material and an additive.

[0054] Preferably, the negative active material is one of natural graphite, artificial graphite, silicon, silicon-carbon, hard carbon, soft carbon, and lithium titanate.

[0055] Preferably, the additive includes a conductive agent, a negative electrode binder, and a dispersing agent; for example, the conductive agent is at least one of graphite, carbon black, acetylene black, graphene, and carbon nanotubes; for example, the negative electrode binder can be at least one of SBR, polyacrylate, and polyacrylic acid, preferably SBR; for example, the dispersing agent is at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose, preferably sodium carboxymethyl cellulose (CMC).

[0056] According to an embodiment of the present application, the negative electrode sheet is prepared by a method comprising the following steps:

[0057] (1) mixing the negative active material, the conductive agent, the negative electrode binder, and the dispersing agent uniformly to obtain a negative electrode slurry;

[0058] (2) coating the negative electrode slurry on the surface of the current collector, and baking to obtain the negative electrode sheet.

[0059] According to an embodiment of the present application, the mass ratio of the negative active material, the conductive agent, the negative electrode binder, and the dispersing agent is not particularly limited, and a mass ratio known in the art can be used. For example, the mass ratio of the negative active material, the conductive agent, the negative electrode binder, and the dispersing agent can be 96.5:1:1.5:1; for example, the mass ratio of graphite, carbon black, SBR, and CMC is 96.5:1:1.5:1.

[0060] According to an embodiment of the present application, the lithium ion battery is assembled from the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte. For example, the positive electrode sheet, the negative electrode sheet, and the separator are assembled into a cell by winding or stacking commonly used in the industry, and then packaged by an aluminum plastic film, and then sequentially subjected to baking, electrolyte injection, formation, and second sealing processes to obtain the lithium ion battery.

[0061] According to an embodiment of the present application, the charging cutoff voltage of the lithium ion battery is 4.45-5.0 V, preferably 4.55 V.

[0062] The present application has the following advantages:

[0063] The application provides an electrolyte and a battery comprising the electrolyte. The electrolyte comprises a nitrate compound containing a benzene ring. The additive is more difficult to lose electrons due to the strong electron-withdrawing nitrate group, and has strong oxidation stability and high pressure resistance. At the same time, the N and O atoms in the nitrate group also contain lone pair electrons, which is beneficial to accelerate the transmission of lithium ions, thereby reducing the impedance of the lithium ion battery and enhancing the kinetic performance. When the electrolyte is used in a battery, the high-temperature stability, cycle performance and low-temperature performance of the high-voltage battery can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0064] Figure 1 Test chart of cycle performance of the battery of Example 1 and Comparative Example 1.

[0065] Figure 2 Test chart of 70 DEG C high-temperature storage of the battery of Example 1 and Comparative Example 1.

[0066] Figure 3 Test chart of 25 DEG C 100% SOC EIS of the battery of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0067] The application will be described in further detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application. Any technology achieved based on the above description of the application is included in the scope of protection intended by the application.

[0068] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0069] The cycle performance involved in the following examples and comparative examples is measured by using the Land battery test system of Wuhan Lan Electric Company, and the process is as follows:

[0070] The cycle test voltage range is 4.55V-3.0V

[0071] 1. 0.5C discharge to the lower limit cutoff voltage;

[0072] 2. Put into a 25 DEG C incubator and stand for 15 min;

[0073] 3. 1C charge to the upper limit cutoff voltage, constant voltage to 0.05C cutoff;

[0074] 4. Stand for 5 min;

[0075] 5. 1C discharge to the lower limit cutoff voltage;

[0076] 6. Stand for 5 min;

[0077] 7. 3-6 cycles 250 times;

[0078] 8. Calculate the capacity retention rate after 250 cycles, and the test results are shown in Table 2 and Figure 1 .

[0079] 9. Calculate the percentage of thickness increase value of the battery after 250 times and the original thickness, and the test results are shown in Table 2.

[0080] The following examples and comparative examples involve high-temperature storage performance at 70°C, which is tested according to the following procedure:

[0081] 1. At (25±2) °C, standard constant current discharge to the end-of-discharge voltage, and stand for 30 min; then standard constant current and constant voltage charge to the charge limit voltage, with a cutoff current of 0.05C, and stand for 30 min; standard constant current discharge to the end-of-discharge voltage, and the initial capacity of the battery cell C1 is obtained; stand for 30 min;

[0082] 2. According to the standard charging method, fully charge with constant current and constant voltage, and then stand open-circuit at 70°C for 24 hours;

[0083] 3. Take out every 2h, stand for 1h at (25±2) °C, measure the internal resistance, thickness, residual capacity Cn1, and recovery capacity Cn2, and the test results are shown in Table 2. Figure 2 .

[0084] The electrochemical impedance involved in the following examples and comparative examples is measured by an electrochemical workstation (model CHI600E) produced by Shanghai Chenhua, the test frequency is 10KHz-0.01Hz, and the alternating current amplitude is 5mV, and the test results are shown in Table 2. Figure 3 .

[0085] The following examples and comparative examples involve the test process of low-temperature performance as follows:

[0086] -20°C discharge: fully charged battery is placed in a low-temperature box at -20°C, and discharged at 0.2C, and the discharge capacity retention rate is calculated, and the test results are shown in Table 2.

[0087] Example 1

[0088] Electrolyte configuration: in an argon-filled glove box (O2<2ppm, H2O<3ppm), ethylene carbonate, propylene carbonate, propyl propionate, dimethyl carbonate were mixed uniformly according to a mass ratio of 2:2:4:2 to prepare a solvent, then 67wt% of the total mass of the solvent was taken, 11wt% of the total mass of the electrolyte was added to FEC, and 7wt% of the total mass of the electrolyte was added to the first additive shown in formula 1 to obtain a mixed solution; then 15wt% of the total mass of the electrolyte was slowly added to the mixed solution, and the lithium salt was a mixture of 14wt% of the total mass of the electrolyte as lithium hexafluorophosphate (LiPF6), 0.5wt% of the total mass of the electrolyte as lithium difluoro(oxalato)borate (LiODFB), and 0.5wt% of the total mass of the electrolyte as lithium difluorophosphate (LiPO2F2);

[0089] The positive active material lithium cobaltate, the binder PVDF and the conductive carbon black were dispersed in N-methyl pyrrolidone, and after stirring, a uniformly dispersed positive electrode slurry was obtained, wherein the solid content included 96.2wt% of lithium cobaltate, 1.8wt% of PVDF and 2wt% of conductive carbon black, the solid content of the positive electrode slurry was 67.5wt%, and the viscosity was 21745mPa·s. The positive electrode slurry was uniformly coated on both sides of the aluminum foil, dried at 100-130℃ for 4h, and compacted by a roll press machine, and the compacted density was 2.6-3.2g / cm 3 , to obtain a positive electrode sheet;

[0090] The graphite, the binder SBR, the thickening agent CMC and the conductive agent conductive carbon black were mixed and dispersed in deionized water to obtain a negative electrode slurry, wherein the solid content included 96.5wt% of graphite, 1wt% of CMC, 1wt% of conductive carbon black and 1.5wt% of SBR, the solid content of the negative electrode slurry was 44-46wt%, and the viscosity was 6561mPa·s. The slurry was uniformly coated on both sides of the copper foil, dried at 70-100℃ for 5h, and compacted by a roll press machine, and the compacted density was 1.4-1.7g / cm 3 , to obtain a negative electrode sheet;

[0091] The positive electrode sheet, the negative electrode sheet and the separator (PP / PE / PP composite film, thickness 8μm, porosity 42%) were wound and packaged into a battery cell, then the electrolyte was injected, and after formation, hot pressing and two-sealing, a lithium ion battery was obtained.

[0092] Examples 2-9 and Comparative Examples 1-3

[0093] The batteries of Examples 2-9 and Comparative Examples 1-3 were basically the same as Example 1, except that the composition and content of the additives of the electrolyte were different, as described in Table 1.

[0094] Table 1 Composition of electrolyte of lithium ion battery of Comparative Example 1 and Examples 1-9

[0095]

[0096]

[0097] By Figure 1 It can be seen that the cycle retention rate and capacity of the battery in Example 1 are improved relative to Comparative Example 1 by introducing the nitrate compound containing a benzene ring. It is shown that the introduction of the nitrate compound containing a benzene ring is beneficial to the cycle stability at high pressure. By Figure 2 It can be seen that the nitrate compound containing a benzene ring can improve the high-temperature storage performance at full charge state at high pressure and reduce the expansion rate; By Figure 3 It can be seen that the resistance of the lithium ion battery is reduced and the kinetic performance is improved after adding the nitrate compound containing a benzene ring.

[0098] It can be seen from Table 2 that the performance of the battery added with the nitrate compound containing a benzene ring is superior to that of the battery without addition and the battery added with an alkyl nitrate in terms of 0.2C discharge capacity retention rate at -20℃, 1C charge-discharge cycle capacity retention rate at normal temperature for 250T, expansion rate at normal temperature, and lithium precipitation performance at low temperature.

[0099] Table 2 Performance test results of lithium ion batteries of Comparative Examples 1-3 and Examples 1-9

[0100]

[0101] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A lithium ion battery comprising an electrolyte, characterized in that, The electrolyte comprises an electrolyte salt, an organic solvent, a first additive and a second additive, the first additive comprises a nitrate compound containing a benzene ring; The nitrate compound containing a benzene ring is selected from at least one of the compounds shown in Formula 1: Formula 1 In Formula 1, n is an integer between 0 and 4; m1 is an integer between 1 and 5; R is -CN; The second additive is selected from fluoroethylene carbonate; The organic solvent is selected from propyl propionate and a combination of at least one of the following components: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl propionate, propyl acetate, butyl butyrate or ethyl butyrate; The electrolyte salt is selected from an electrolyte lithium salt, the electrolyte lithium salt is selected from a combination of LiPF6, lithium difluoro(oxalato)borate and lithium difluorophosphate; The charging cut-off voltage of the lithium ion battery is 4.45-5.0V; The mass of the nitrate compound containing a benzene ring accounts for 3wt%-15wt% of the total mass of the electrolyte; The mass of the second additive accounts for 4wt%-15wt% of the total mass of the electrolyte.

2. The lithium-ion battery of claim 1, wherein, The nitrate compound containing a benzene ring is selected from at least one of compounds B-D: Compound B; Compound C; Compound D.

3. The lithium-ion battery of claim 1, wherein, The mass of the electrolyte salt accounts for 8wt%-17wt% of the total mass of the electrolyte.

4. The lithium-ion battery of claim 3, wherein, The mass of lithium difluoro(oxalato)borate and lithium difluorophosphate accounts for 0.3wt%-2wt% of the total mass of the electrolyte.

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