An electrolyte and a battery comprising the same

Abstract

This invention provides an electrolyte and a battery comprising the electrolyte, wherein the electrolyte contains Ag. + and NO 3‑ When Ag + and NO 3‑ When Ag enters the electrolyte system, it alters the original solvation structure of the electrolyte. + As a comparison with Li + Stronger Lewis acids are more likely to bind with Lewis base solvent molecules, making exposed Li₂ more likely to form a free radical. + The increased number of NO molecules makes the desolvation process easier, thus reducing electrochemical impedance. Similarly, NO... 3‑ After participating in the solvation structure, an nitrogen-containing SEI film is formed on the negative electrode surface, which plays a role in stabilizing the interface and reducing the SEI film impedance. When the electrolyte is used in lithium-ion batteries, the low-temperature kinetic performance is improved and the room-temperature cycling stability is also enhanced due to the significant reduction in electrochemical impedance.

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] Since the commercialization of lithium ion batteries in the 1990s, great progress has been made in the application of lithium ion batteries in the fields of digital, electric vehicles and energy storage. However, with the expansion and subdivision of application fields, people have put forward higher requirements for the performance of lithium ion batteries, such as low-temperature performance and fast-charging performance.

[0003] It is well known that the low-temperature performance and fast-charging performance of lithium ion batteries are closely related to electrochemical polarization, because temperature reduction and large-rate charging will cause the electrochemical impedance to increase rapidly, not only deteriorating the performance of the battery, but also generating lithium precipitation, thereby causing safety hazards. Therefore, the methods for improving the low-temperature performance and fast-charging performance in the industry generally focus on how to reduce the electrochemical impedance. Improving the impedance of the battery can be approached from many aspects, and the improvement of the electrolyte has always been an important content.

[0004] The electrolyte, as one of the main materials of lithium ion batteries, greatly affects the performance of lithium ion batteries. The lithium salt, solvent and additive in the electrolyte will affect the solvation structure, which further affects the SEI film. The solvation and the SEI film greatly affect the electrochemical impedance, especially the solvation and desolvation, which are generally considered as key factors affecting the electrochemical impedance. Therefore, reducing the electrochemical impedance by regulating the solvation structure is one of the means to improve the low-temperature performance and fast-charging performance. SUMMARY

[0005] 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, wherein the electrolyte contains AgNO3 and tetraethylene glycol dimethyl ether (G4), and the combination of the two changes the solvation structure of the electrolyte, improves the film formation and reduces the desolvation impedance, so that the low-temperature performance of the battery is improved; at the same time, due to the more stable SEI film, the room temperature cycle performance (such as capacity retention rate and thickness expansion rate) of the battery is also greatly improved.

[0006] The purpose of the present application is achieved by the following technical scheme:

[0007] An electrolyte, comprising an electrolyte salt, an organic solvent and an additive, wherein the additive comprises AgNO3 and tetraethylene glycol dimethyl ether (G4).

[0008] According to the embodiments of the present application, the introduction of AgNO3 makes the electrolyte system contain Ag + and NO 3- . On the one hand, Ag +The combination with solvent molecules makes the exposed Li + The increased number reduces the energy consumption of desolvation, making the desolvation process easier, and part of the Ag + The reduction of nano-sized Ag particles on the surface of the negative electrode also enhances the conductivity; on the other hand, the NO 3- The participation of the solvation structure makes the N-containing SEI film generated on the surface of the negative electrode, which can also accelerate the Li + The SEI film reduces the impedance of the SEI film. The introduction of tetraethylene glycol dimethyl ether can improve the solubility of AgNO3 in ester solvents.

[0009] According to an embodiment of the present application, the electrolyte is an electrolyte containing an AgNO3 / tetraethylene glycol dimethyl ether (G4) additive.

[0010] According to an embodiment of the present application, the electrolyte salt is selected from at least one of electrolyte lithium salts, electrolyte sodium salts, electrolyte magnesium salts, etc.

[0011] 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).

[0012] According to an embodiment of the present application, the mass of the electrolyte salt accounts for 8wt% to 17wt% of the total mass of the electrolyte, for example, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, or 16wt%, etc.

[0013] According to an embodiment of the present application, the electrolyte lithium salt is selected from a combination of at least one of LiPF6 and 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).

[0014] Preferably, the mass of the other lithium salt accounts for 0.3wt% to 2wt% of the total mass of the electrolyte, for example, 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%, etc.

[0015] According to embodiments of the present application, the organic solvent is selected from any one or a combination of at least two of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl propionate, ethyl propionate, propyl acetate, butyl butyrate and ethyl butyrate.

[0016] According to embodiments of the present application, the mass of the organic solvent accounts for 50wt% to 85wt% of the total mass of the electrolyte, for example 52wt%, 55wt%, 58wt%, 60wt%, 62wt%, 65wt%, 68wt%, 70wt%, 72wt%, 75wt%, 78wt%, 80wt% or 82wt% and the like.

[0017] According to embodiments of the present application, the mass of the tetraethylene glycol dimethyl ether (G4) 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% or 14wt% and the like.

[0018] According to embodiments of the present application, the mass of the AgNO3 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% or 14wt% and the like.

[0019] The present application also provides a battery comprising the electrolyte described above.

[0020] According to embodiments of the present application, the battery is a lithium ion battery.

[0021] According to embodiments of the present application, the battery comprises a positive electrode sheet, a negative electrode sheet and a separator.

[0022] Preferably, the positive electrode sheet comprises a current collector and a positive electrode coating layer on the surface of the current collector.

[0023] 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.

[0024] Preferably, the positive electrode coating layer contains a positive electrode active material and an additive.

[0025] Preferably, the positive electrode active material is at least one of lithium iron phosphate, a ternary positive electrode material and lithium cobaltate.

[0026] 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.

[0027] According to an embodiment of the present application, the positive electrode sheet is prepared by a method comprising the following steps:

[0028] (1) mixing positive electrode active material, conductive agent and positive electrode binder uniformly to obtain positive electrode slurry;

[0029] (2) coating the positive electrode slurry on the surface of the current collector, and baking to obtain the positive electrode sheet.

[0030] According to an embodiment of the present application, the mass ratio of positive electrode active material, conductive agent and positive electrode binder is not particularly limited, and the mass ratio known in the art can be used. For example, the mass ratio of positive electrode active material, conductive agent and positive electrode binder can be 96.2:2:1.8; for example, the mass ratio of lithium cobaltate, carbon black and PVDF is 96.2:2:1.8.

[0031] Preferably, the negative electrode sheet comprises a current collector and a negative electrode coating layer on the surface of the current collector.

[0032] Preferably, the current collector in the negative electrode sheet is single-facet copper foil, double-facet copper foil or porous copper foil.

[0033] Preferably, the negative electrode coating layer contains negative electrode active material and additive.

[0034] Preferably, the negative electrode active material is one of natural graphite, artificial graphite, silicon, silicon-carbon, hard carbon, soft carbon and lithium titanate.

[0035] Preferably, the additive comprises 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 is 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).

[0036] According to an embodiment of the present application, the negative electrode sheet is prepared by a method comprising the following steps:

[0037] (1) mixing negative electrode active material, conductive agent, negative electrode binder and dispersing agent uniformly to obtain negative electrode slurry;

[0038] (2) coating the negative electrode slurry on the surface of the current collector, and baking to obtain the negative electrode sheet.

[0039] According to the embodiments of the present application, the mass ratio of the negative active material, the conductive agent, the negative binder and the dispersing agent is not particularly limited, and the mass ratio known in the art can be used. For example, the mass ratio of the negative active material, the conductive agent, the negative binder and the dispersing agent can be 96.5:1:1.5:1; and exemplarily, the mass ratio of the graphite, the carbon black, the SBR and the CMC is 96.5:1:1.5:1.

[0040] According to the embodiments of the present application, the separator is an oily separator commonly used in the industry.

[0041] According to the embodiments 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 an electric core by the winding or the stacking commonly used in the industry, and then packaged by an aluminum plastic film, and then sequentially subjected to the processes of baking, injecting electrolyte, formation and double sealing to obtain the lithium ion battery.

[0042] The present application has the following beneficial effects:

[0043] The present application provides an electrolyte and a battery comprising the electrolyte, wherein the electrolyte contains Ag + and NO 3- When Ag + and NO 3- enter the electrolyte system, the original solvation structure of the electrolyte is changed. Ag + as a stronger Lewis acid than Li + is more likely to combine with the Lewis base solvent molecules, so that the number of exposed Li + increases, making the desolvation process easier, thus reducing the electrochemical impedance. Similarly, NO 3- participates in the solvation structure to generate an N-containing SEI film on the negative electrode surface, which stabilizes the interface and reduces the impedance of the SEI film. When the electrolyte is applied to a lithium ion battery, the electrochemical impedance is greatly reduced, the low-temperature kinetic performance is improved, and the room-temperature cycle stability is also improved. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 EIS (alternating impedance) of the batteries of Example 1 and Comparative Example 1 at 25℃ 50% SOC. DETAILED DESCRIPTION

[0045] The present application will be further described in detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of protection intended by the present application.

[0046] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples are commercially available unless otherwise specified.

[0047] 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.

[0048] Example 1

[0049] The electrolyte is configured as follows: in an argon-filled glove box (O2<2ppm, H2O<3ppm), ethylene carbonate and dimethyl carbonate are mixed uniformly according to a mass ratio of 1:1 to prepare a solvent, then 67wt% of the total mass of the solvent is taken, 9wt% of the total mass of AgNO3 is added to the solvent, and at the same time, 9wt% of the total mass of G4 is added to the solvent to obtain a mixed solution; then 15wt% of the total mass of lithium salt is slowly added to the mixed solution, the lithium salt is a mixture of 14wt% of the total mass of lithium hexafluorophosphate (LiPF6), 0.5wt% of the total mass of lithium difluoro(oxalato)borate (LiODFB), and 0.5wt% of the total mass of lithium difluorophosphate (LiPO2F2);

[0050] The positive electrode active material lithium cobaltate, the binder PVDF and the conductive agent conductive carbon black are dispersed in N-methyl pyrrolidone, and after stirring, a uniformly dispersed positive electrode slurry is obtained, wherein the solid content includes 96.2wt% of lithium cobaltate, 1.8wt% of PVDF and 2wt% of conductive carbon black, the solid content of the positive electrode slurry is 67.5wt%, and the viscosity is 21745mPa·s. The positive electrode slurry is uniformly coated on both sides of an aluminum foil, dried at 100-130℃ for 4h, and compacted by a rolling machine, and the compacted density is 2.6-3.2g / cm 3 , to obtain a positive electrode sheet;

[0051] The negative electrode active material graphite, the binder SBR, the dispersant CMC and the conductive agent conductive carbon black are mixed and dispersed in deionized water to obtain a negative electrode slurry, wherein the solid content includes 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 is 44-46wt%, and the viscosity is 6561mPa·s. The slurry is uniformly coated on both sides of a copper foil, dried at 70-100℃ for 5h, and compacted by a rolling machine, and the compacted density is 1.4-1.7g / cm 3 , to obtain a negative electrode sheet;

[0052] The positive electrode sheet, the negative electrode sheet and the separator (PP / PE / PP composite film, thickness 8 μm, porosity 42%) were wound and packaged into an electric core, and then injected with electrolyte, and after formation, hot pressing and two-sealing, a lithium ion battery was obtained.

[0053] Examples 2-5 and Comparative Examples 1-6

[0054] The batteries of Examples 2-5 and Comparative Examples 1-6 were substantially the same as Example 1, except that the composition of the additives of the electrolyte was different, as described in Table 1.

[0055] Table 1 Composition of the electrolyte of the lithium ion batteries of Comparative Examples 1-6 and Examples 1-5

[0056]

[0057]

[0058] Test Example 1

[0059] The batteries prepared from the examples and comparative examples were subjected to performance testing, and the test items included low temperature performance (12℃ 3C lithium precipitation, -20℃ discharge) and cycle retention rate, and the testing process was as follows:

[0060] Low temperature performance: -20℃ discharge: the full battery was placed in a low temperature box at -20℃, and discharged at 0.2C, and the discharge capacity retention rate was calculated.

[0061] 12℃ 3C lithium precipitation: the battery was placed in a low temperature box at 12℃, and discharged at 0.5C to 3V, and then charged at 3C to 4.48V, and the current was cut off at 0.05C. After 20 cycles, the battery was disassembled and the interface condition was observed.

[0062] Normal temperature cycle retention rate: at normal temperature 25℃, 1C charge-discharge was cycled for 250 times, and the capacity retention rate after 250 times was calculated.

[0063] Normal temperature cycle expansion rate: at normal temperature 25℃, 1C charge-discharge was cycled for 250 times, and the percentage of the thickness increase value of the battery after 250 times to the original thickness was calculated.

[0064] From the above data, it can be seen that the EIS impedance of the battery in Example 1 was reduced due to the introduction of AgNO3. Figure 1 It can be seen that, in Example 1, due to the introduction of AgNO3, the EIS impedance of the battery was reduced. This indicates that Ag + and NO 3- reduced the electrochemical polarization of the battery, and reduced Rct. At the same time, the cosolvent effect of tetraethylene glycol dimethyl ether further enhanced the kinetic performance of the battery.

[0065] The batteries of the above examples and comparative examples were subjected to electrical performance tests, and the results are shown in Table 2. As can be seen from Table 2, the batteries of the examples in which the functional additive (AgNO3 / G4) was added had more advantages than the comparative examples in terms of lithium precipitation at 12°C 3C, discharge at -20°C, cycle retention rate at room temperature, and expansion rate. In particular, the performance of Example 1 was the best.

[0066] Table 2 Performance test results of lithium ion batteries of Comparative Examples 1 to 6 and Examples 1 to 5

[0067]

[0068]

[0069] 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 principle of the present application should be included in the scope of protection of the present application.

Claims

1. A lithium ion battery, said battery comprising a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, characterized in that, The electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive being AgNO3 and tetraethylene glycol dimethyl ether; the negative electrode sheet comprises a current collector and a negative electrode coating layer on the surface of the current collector, the negative electrode coating layer containing a negative electrode active material, the negative electrode active material being one of natural graphite, artificial graphite, silicon, silicon-carbon, hard carbon, soft carbon and lithium titanate; The mass of the tetraethylene glycol dimethyl ether accounts for 8wt%-15wt% of the total mass of the electrolyte; the mass of the AgNO3 accounts for 3wt%-10wt% of the total mass of the electrolyte.

2. The lithium-ion battery of claim 1, wherein, The electrolyte salt is selected from electrolyte lithium salts, the mass of the electrolyte salt accounting for 8wt%-17wt% of the total mass of the electrolyte.

3. The lithium-ion battery of claim 2, wherein, The electrolyte lithium salt is selected from the combination of LiPF6 and 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).

4. The lithium-ion battery of claim 3, wherein, The mass of the other lithium salt accounts for 0.3wt%-2wt% of the total mass of the electrolyte.

5. The lithium-ion battery of claim 1, wherein, The organic solvent is selected from any one or a combination of at least two of the following: ethylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, propyl propionate, ethyl propionate, propyl acetate, butyl butyrate and ethyl butyrate.

6. The lithium-ion battery of claim 1 or 5, wherein, The mass of the organic solvent accounts for 50wt%-85wt% of the total mass of the electrolyte.

7. The lithium-ion battery of claim 1, wherein, The positive electrode sheet comprises a current collector and a positive electrode coating layer on the surface of the current collector, the positive electrode coating layer containing a positive electrode active material, the positive electrode active material being at least one of lithium iron phosphate, a ternary positive electrode material and lithium cobaltate.

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