Secondary batteries and their use

Abstract

The present application belongs to the technical field of batteries, and more specifically, to a secondary battery. The secondary battery according to the present application includes a positive electrode plate, a negative electrode plate, and an electrolyte, the electrolyte includes an organic solvent, the organic solvent includes a cyclic ester solvent and a chain ester solvent, and the parameters of the secondary battery satisfy the following relational expression (1). The secondary battery has good dynamic characteristics at low temperatures by adjusting the electrolyte and the negative electrode plate to make them act synergistically, and has good capacity retention and low impedance under low temperature conditions.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from a Chinese patent application bearing application number 202211260215.8 and entitled "Secondary Battery" filed with the State Intellectual Property Office of the People's Republic of China on October 14, 2022, the entire contents of which are incorporated herein by reference. [Technical Field]

[0002] The present application belongs to the technical field of batteries, and more particularly to secondary batteries. [Background technology]

[0003] Secondary batteries, such as lithium-ion batteries, have become the most popular energy storage systems due to their characteristics of high specific energy, long life, and environmental friendliness, and are currently widely used in the fields of home appliances, electric vehicles, energy storage, etc. With the popularity of new energy vehicles and the rapid development of the energy storage market, the performance requirements for lithium-ion batteries are constantly improving, and the development of low-cost, highly safe, and widely applicable lithium-ion batteries is currently an urgent need in the development of the lithium battery industry.

[0004] Secondary batteries have drawbacks such as low capacity retention and high impedance in low-temperature environments, limiting their large-scale use. Therefore, it is necessary to improve the dynamic characteristics of secondary batteries at low temperatures. Summary of the Invention [Problem to be solved by the invention]

[0005] Therefore, the technical problem to be solved by the present application is to provide a lithium ion battery that overcomes the drawbacks of the prior art, such as poor dynamic characteristics at low temperatures of lithium ion batteries. [Means for solving the problem]

[0006] For this reason, the present application provides the following technical solutions:

[0007] The present application provides a secondary battery including a positive electrode plate, a negative electrode plate, and an electrolyte, wherein the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the electrolyte includes an organic solvent, and the organic solvent includes a cyclic ester solvent and a chain ester solvent, A secondary battery is provided that satisfies the following relational expression (1):

number

[0008] Preferably, the secondary battery comprises: (1) the mass ratio β of the cyclic ester solvent to the chain ester solvent is 0.25 to 0.85, preferably 0.33 to 0.82; (2) The conductivity σ of the electrolyte solution is 9 to 13, preferably 9.5 to 12.5; (3) The viscosity η of the electrolyte solution is 2 to 5, preferably 2.5 to 4.5; (4) At least one of the following conditions is satisfied: the weight value Mel. of the electrolyte is 11 to 16, preferably 13 to 15.

[0009] Preferably, the PD value is 1.1 to 1.65, preferably 1.2 to 1.6.

[0010] Preferably, the chain ester solvent comprises at least one of a chain carbonate and a chain carboxylate, the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; The chain carboxylate includes at least one of ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0011] Preferably, the cyclic ester solvent includes at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0012] Preferably, the electrolyte further comprises an additive, and the additive comprises at least one of a silicon-containing additive, a cyclic carbonate additive, or a sulfur-containing additive.

[0013] Preferably, the additive is (a) the silicon-containing additive includes at least one of tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, trimethylfluorosilane, and heptamethyldisilazane, and the silicon-containing additive is 0.1 to 4 mass% with respect to the mass of the electrolytic solution; (b) the cyclic carbonate additive includes at least one of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate, and the amount of the cyclic carbonate additive is 0.05 to 3 mass% relative to the mass of the electrolytic solution; (c) The sulfur-containing additive contains at least one of 1,3-propane sultone and vinyl sulfate, and the amount of the sulfur-containing additive is 0.05 to 3 mass % relative to the mass of the electrolyte.

[0014] Preferably, the electrolyte additive comprises a silicon-containing additive and a sulfur-containing additive, and the content of the silicon-containing additive relative to the mass of the electrolyte is W si %, and the content of the sulfur-containing additive is W s %, and 0.3≦W si +W s ≦4, 0.1≦W si / W s Satisfies ≦5.

[0015] Preferably, the electrolyte solution further comprises a lithium salt additive, and the lithium salt additive comprises at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorooxalate phosphate; The lithium salt additive in the electrolytic solution is 0.1 to 5% by mass.

[0016] Preferably, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, the positive electrode active material layer including a positive electrode active material, The positive electrode active material is Li a Fe 1-y Mn y Contains PO4 (0.9≦a≦1.1, 0≦y≦1).

[0017] The active material layer in the negative electrode plate contains at least one of graphite and silicon-based materials.

[0018] The present application also provides an electric device including the above secondary battery. [Effects of the Invention]

[0019] The technical solution of this application has the following advantages: The secondary battery according to the present application comprises a positive electrode plate, a negative electrode plate, and an electrolyte, the electrolyte containing an organic solvent, the organic solvent including a cyclic ester solvent and a chain ester solvent, and the secondary battery satisfies the following relational expression (1). By optimizing the composition and content of the electrolyte and adjusting the active material layer of the negative electrode plate, the secondary battery exhibits good dynamic characteristics at low temperatures, good capacity retention and low impedance under low-temperature conditions, and generally does not suffer from lithium elution. The electrolyte is one of the main components of a lithium-ion battery and is one of the factors that affect the performance of the secondary battery. The solvent is an important component of the electrolyte and significantly affects the performance of the secondary battery, such as its cycle life, impedance, and dynamic characteristics. The present application optimizes the electrolyte, negative electrode plate, and battery capacity, and comprehensively designs parameters such as the electrolyte solvent composition, electrolyte viscosity, electrical conductivity, and battery capacity, thereby significantly improving the low-temperature dynamic characteristics of the secondary battery, reducing the impedance of the secondary battery, and increasing the low-temperature capacity retention. Among these, cyclic ester solvents have a high dielectric constant and a high viscosity, while chain ester solvents have a low dielectric constant and a low viscosity. Controlling the ratio of the cyclic ester solvent to the chain ester solvent within an appropriate range contributes to improving the dynamic characteristics of secondary batteries. In the secondary battery according to the present application, the viscosity of the electrolyte affects the migration speed of lithium ions in the electrolyte, and if the viscosity of the electrolyte is within the range of the present application, the transport of lithium ions is further improved, the impedance of the secondary battery is reduced, and the cycle characteristics of the battery are improved. In addition to satisfying the following relational expression (1), the low viscosity of the electrolyte promotes the transport of lithium ions in the electrolyte, further improving the dynamic characteristics. By limiting the conductivity of the electrolyte, it is possible to more reliably prevent phenomena such as lithium elution during high current operation. The amount of electrolyte injected into a secondary battery is affected by the design capacity of the battery. If the amount injected is too small, it will be difficult to completely impregnate the positive and negative electrodes, which will affect the degree of lithium ion deintercalation during the charge and discharge process, and will affect the impedance, capacity, cycle life, lithium elution, and other issues of the secondary battery. If the amount injected is too large, side reactions will increase, causing gas generation and swelling. If the packing density PD of the negative electrode active material layer in the negative electrode plate is too low, the battery's energy density will be affected and the negative electrode slurry application process will be difficult to control. If the packing density PD is too high, the electrolyte will not easily penetrate the negative electrode active material layer, which will affect the battery's dynamic characteristics. By setting an appropriate packing density PD, the battery's dynamic characteristics and energy density can be further improved. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following examples are provided for a better understanding of the present application, and are not limited to the best embodiment, and do not limit the content and protection scope of the present application. Any products identical or similar to the present application that someone obtains based on the present application or as a result of combining the features of the present application with other prior art shall fall within the protection scope of the present application.

[0021] The present application provides a battery including a positive electrode plate, a negative electrode plate, and an electrolyte solution, the negative electrode plate including a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the electrolyte solution including an organic solvent, the organic solvent including a cyclic ester solvent and a chain ester solvent, A secondary battery is provided that satisfies the following relational expression (1):

number

[0022] In some embodiments of the present application,

number

[0023] In some embodiments of the present application, the mass ratio β of the cyclic ester solvent to the chain ester solvent is 0.25 to 0.85. For example, it may be 0.25, 0.30, 0.33, 0.35, 0.38, 0.40, 0.43, 0.45, 0.47, 0.50, 0.53, 0.55, 0.57, 0.60, 0.63, 0.65, 0.67, 0.70, 0.72, 0.74, 0.78, 0.80, 0.82, 0.85, or a range consisting of any two of these values. When the mass ratio P of the cyclic ester solvent to the chain ester solvent is within the above range, the viscosity and conductivity of the electrolyte are relatively stable, lithium ion diffusion at low temperatures is facilitated, the dynamic behavior of lithium ions is maintained, and the risk of lithium elution is reduced.

[0024] In some embodiments of the present application, the mass ratio β of the cyclic ester solvent to the chain ester solvent is 0.33 to 0.82.

[0025] In some embodiments of the present application, the conductivity σ of the electrolyte solution is 9 to 13. For example, it may be 9, 9.3, 9.5, 9.7, 10.0, 10.4, 10.7, 11.0, 11.3, 11.5, 11.7, 12.0, 12.2, 12.4, 12.5, 12.7, 13.0, or a range consisting of any two of these values. When the conductivity of the electrolyte solution is in the above range, lithium ions in the electrolyte solution diffuse rapidly, and lithium ions desorbed from the positive electrode reach the negative electrode more quickly, thereby increasing the potential of the negative electrode, effectively improving the dynamic properties of the lithium ions, and further improving lithium elution at low temperatures.

[0026] In some embodiments of the present application, the electrolytic solution has a conductivity σ value of 9.5 to 12.5.

[0027] The conductivity of the electrolyte can be measured using a DDSJ-308A type conductivity meter.

[0028] In some embodiments of the present application, the viscosity η of the electrolyte solution is 2 to 5. For example, the viscosity η may be 2, 2.2, 2.4, 2.6, 2.8, 3.0, 3.3, 3.5, 3.7, 3.9, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, or a range consisting of any two of these values. When the viscosity η of the electrolyte solution is within the above range, the larger the η, the higher the viscosity of the electrolyte solution, which adversely affects the diffusion of lithium ions at low temperatures, reduces the dynamic behavior of lithium ions, and poses a risk of lithium elution.

[0029] In some embodiments of the present application, the viscosity η of the electrolyte solution is 2.5 to 4.5.

[0030] In this application, the viscosity of the electrolyte may be measured using an 1835 Ubbelohde viscometer.

[0031] In some embodiments of the present application, the weight value of the electrolyte, Mel. teeth The weight of the electrolyte is 11 to 16. For example, it may be 11, 11.2, 11.5, 11.7, 12, 12.2, 12.4, 12.8, 13, 13.3, 13.5, 13.7, 14, 14.3, 14.5, 14.7, 15, 15.5, 16, or a range consisting of any two of these values. When the weight of the electrolyte is within the above range, the amount of circulating gas generated by the battery is within an appropriate range, preventing an excessive increase in the internal pressure of the battery, which could cause the explosion-proof valve to burst and lead to battery failure, and also reducing black spots of bubbles generated at the interface of the negative electrode plate. Furthermore, the electrolyte allows for good mobility of lithium ions, improving the cycle characteristics and dynamic characteristics of the battery.

[0032] In some embodiments of the present application, the weight value Mel. of the electrolyte is 13 to 15. When Mel. is in this range, the electrolyte can transfer lithium ions more efficiently, while the amount of gas generated by the battery is reduced, resulting in better overall battery performance.

[0033] In some embodiments of the present application, the Mel. / Cap. value is 3-6.

[0034] In some embodiments of the present application, the value of PD is 1.1 to 1.65. When PD is in the above range, the packed density affects the movement of lithium ions in the negative electrode, and if the packed density is too high, the diffusion rate of lithium ions decreases, which affects low-temperature performance, particularly at low temperatures, and causes lithium elution. Furthermore, if the packed density is too high, it affects the impregnation of the electrolyte.

[0035] In some embodiments of the present application, the value of PD is 1.2 to 1.6.

[0036] In some embodiments herein, the linear ester solvent comprises at least one of a linear carbonate and a linear carboxylate.

[0037] In some embodiments of the present application, the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate.

[0038] In some embodiments of the present application, the linear carboxylate comprises at least one of ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

[0039] In some embodiments herein, the cyclic ester solvent comprises at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

[0040] In some embodiments herein, the electrolyte further comprises an additive, and the additive comprises at least one of a silicon-containing additive, a cyclic carbonate additive, or a sulfur-containing additive.

[0041] In some embodiments herein, the silicon-containing additive comprises at least one of tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, trimethylfluorosilane, or heptamethyldisilazane.

[0042] In some embodiments of the present application, the silicon-containing additive is present in an amount of 0.1 to 4% by mass relative to the mass of the electrolyte.

[0043] In some embodiments herein, the cyclic carbonate additive comprises at least one of vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, or difluoroethylene carbonate.

[0044] In some embodiments of the present application, the cyclic carbonate additive is present in an amount of 0.05 to 3% by mass relative to the mass of the electrolyte solution.

[0045] In some embodiments herein, the sulfur-containing additive comprises at least one of 1,3-propane sultone or vinyl sulfate.

[0046] In some embodiments of the present application, the sulfur-containing additive is present in an amount of 0.05 to 3% by weight relative to the weight of the electrolyte.

[0047] In some embodiments of the present application, the electrolyte additive comprises a silicon-containing additive and a sulfur-containing additive, and the content of the silicon-containing additive relative to the mass of the electrolyte is W. si %, and the content of the sulfur-containing additive is W s %, and 0.3≦W si +W s ≦4. When the electrolyte solution contains both a silicon-containing additive and a sulfur-containing additive, they can form an SEI film with a relatively low impedance, allowing lithium ions to pass through the SEI film quickly. When the total content of both additives is within the above range, the film formation state is better, and the formed protective film has good quality and thickness, improving the diffusibility of lithium ions.

[0048] In some embodiments of the present application, the electrolyte additive comprises a silicon-containing additive and a sulfur-containing additive, and the content of the silicon-containing additive relative to the mass of the electrolyte is W. si %, and the content of the sulfur-containing additive is W s %, and 0.1≦W si / W s ≦5. W si / W s When the value is within the above range, the composition and thickness of the protective film to be formed can be further optimized, and the overall characteristics of the battery can be improved.

[0049] In some embodiments of the present application, the electrolyte solution further comprises a lithium salt additive, and the lithium salt additive comprises at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorooxalate phosphate. When the electrolyte solution comprises the lithium salt additive, the impedance of the film can be further reduced, the stability of the film formation can be improved, the diffusibility of lithium ions can be improved, and cycle characteristics can also be taken into consideration.

[0050] In some embodiments of the present application, the lithium salt additive in the electrolyte solution is 0.1 to 5% by mass.

[0051] In some embodiments of the present application, the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, The positive electrode active material is Li a Fe 1-y Mn y Contains PO4 (0.9≦a≦1.1, 0≦y≦1).

[0052] In some embodiments of the present application, the positive electrode active material may further include a doping element. The type of the doping element is not limited as long as it can improve the performance of the positive electrode active material.

[0053] In some embodiments of the present application, the positive electrode active material has a coating layer on its surface.

[0054] In some embodiments of the present application, the coating layer includes a coating element, and the coating element is not limited as long as it can improve the stability of the positive electrode active material.

[0055] In some embodiments of the present application, a carbon material layer is included on a surface of the positive electrode active material, and the carbon material layer includes amorphous carbon.

[0056] Phosphate-based positive electrode active materials are widely used in lithium batteries due to their advantages of low cost and high safety. However, because phosphate-based positive electrode active materials have poor low-temperature mechanical properties, the combination of a phosphate-based positive electrode active material with the electrolyte and negative electrode plate of the present application can significantly improve the low-temperature performance of the battery. The electrolyte of the present application, the phosphate-based positive electrode active material, and the negative electrode plate all have good compatibility, and the impedance of the formed film can be reduced, stability can be improved, and cycle characteristics can be taken into consideration, and lithium elution at low temperatures can be effectively improved.

[0057] If specific experimental steps or conditions are not described in the examples, they can be carried out according to the procedures or conditions of conventional experimental steps described in the literature in the field. If the manufacturers of the reagents or instruments used are not specified, they are all ordinary reagent products that can be purchased on the market. Example 1

[0058] This embodiment provides a lithium ion secondary battery, which has a designed theoretical capacity Cap. of 3.5 Ah and includes a positive electrode plate, a negative electrode plate, and an electrolyte. Positive electrode plate: Positive electrode active material LiFePO4, conductive agent SP, and binder PVDF (HSV900 manufactured by Arkema, same below) were mixed in a mass ratio of 96:2:2, NMP was added, and the mixture was stirred under vacuum until the system became homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then applied to an aluminum foil positive electrode current collector, baked, and cold-pressed to a compact density of 2.45 g / cm. 3 A positive electrode plate having the positive electrode active material layer was obtained. Negative electrode plate: Graphite, conductive agent SP, thickener CMC, and binder SBR (Zeon Corporation 451B, same below) were mixed in a mass ratio of 96.2:1.2:1.2:1.4, deionized water was added, and the mixture was stirred under vacuum until the system became homogeneous to obtain a negative electrode slurry. The negative electrode slurry was then applied to a copper foil negative electrode current collector, dried, and cold-pressed to a compact density of 1.55 g / cm. 3 Thus, a negative electrode plate having the negative electrode active material layer formed thereon was obtained. Electrolyte: Ethylene carbonate (EC, cyclic ester solvent), methyl ethyl carbonate (EMC, linear carbonate solvent), and dimethyl carbonate (DMC, linear carbonate solvent) were mixed in a 30:40:30 ratio to obtain an organic solvent. LiPF6 was added to the organic solvent and mixed uniformly. After that, vinylene carbonate, vinyl sulfate, lithium difluorophosphate, and tris(trimethylsilyl)phosphate were added to obtain an electrolyte. The LiPF6 content was 12% by mass, vinylene carbonate content was 1% by mass, vinyl sulfate content was 1.5% by mass, lithium difluorophosphate content was 0.5% by mass, and tris(trimethylsilyl)phosphate content was 1% by mass. The mass ratio β of the cyclic ester solvent to the linear ester solvent was 0.43. The electrolyte conductivity was 11.28 mS / cm, and the viscosity of the electrolyte was 3.46 mPa s. A positive electrode plate, a separator (14PP manufactured by Star Yuan Materials Co., Ltd.), and a negative electrode plate were stacked in this order, and the separator was interposed between the positive and negative electrodes. The stack was then wound to obtain an electrode assembly. The electrode assembly was packaged in aluminum plastic film, dried, and filled with 14 g of electrolyte. The assembly was then packaged, left to stand, formed, and hot-pressed to obtain a secondary battery. Example 2

[0059] The compressed density of the negative electrode active material layer is 1.6 g / cm 3 Other than that, the results were the same as in Example 1. Example 3

[0060] The compressed density of the negative electrode active material layer is 1.45 g / cm 3 Other than that, the results were the same as in Example 1. Example 4

[0061] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), dimethyl carbonate (DMC, a chain carbonate solvent), and ethyl acetate (EA, a chain carboxylate solvent) in a ratio of 30:30:30:10. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.43, the conductivity of the electrolyte solution was 11.44 mS / cm, and the viscosity of the electrolyte solution was 3.32 mPa s. Example 5

[0062] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 27:40:33. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.37, the conductivity of the electrolyte solution was 11.09 mS / cm, and the viscosity of the electrolyte solution was 3.37 mPa s. Example 6

[0063] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 25:45:30. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.33, the conductivity of the electrolyte solution was 10.75 mS / cm, and the viscosity of the electrolyte solution was 3.3 mPa s. Example 7

[0064] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 32:40:28. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.47, the conductivity of the electrolyte solution was 11.52 mS / cm, and the viscosity of the electrolyte solution was 3.48 mPa s. Example 8

[0065] In the production method, the electrolyte did not contain vinyl sulfate, and the obtained electrolyte had a mass ratio β of the cyclic ester solvent to the chain ester solvent of 0.43, a conductivity of 11.18 mS / cm, and a viscosity of 3.34 mPa s, which were the same as in Example 1. Example 9

[0066] In the production method, the electrolyte did not contain vinyl sulfate or tris(trimethylsilyl)phosphate, and the obtained electrolyte had a mass ratio β of cyclic ester solvent to chain ester solvent of 0.43, a conductivity of 11.02 mS / cm, and a viscosity of 3.4 mPa s, which were the same as in Example 1. Example 10

[0067] In the production method, the electrolyte did not contain vinyl sulfate, lithium difluorophosphate, or tris(trimethylsilyl) phosphate, and the obtained electrolyte had a mass ratio β of cyclic ester solvent to chain ester solvent of 0.43, a conductivity of 10.85 mS / cm, and a viscosity of 3.42 mPa s, which were the same as in Example 1. Example 11

[0068] In the production method, the electrolyte solution was specifically added with 0.5% lithium difluorophosphate, 1% tris(trimethylsilyl) phosphate, and 1.5% vinyl sulfate. The obtained electrolyte solution had a mass ratio β of the cyclic ester solvent to the chain ester solvent of 0.43, a conductivity of 11.12 mS / cm, and a viscosity of 3.39 mPa s, which were the same as in Example 1. Example 12

[0069] In the production method, the electrolyte solution was specifically prepared by adding 1.0% vinylene carbonate, 0.5% lithium difluorophosphate, 0.2% vinyl sulfate, and 1% tris(trimethylsilyl)phosphate. The obtained electrolyte solution had a mass ratio β of the cyclic ester solvent to the chain ester solvent of 0.43, a conductivity of 11.14 mS / cm, and a viscosity of 3.41 mPa s, which were the same as those in Example 1. Example 13

[0070] In the manufacturing method, the electrolyte solution specifically contained 1.0% vinylene carbonate, 0.5% lithium difluorophosphate, 0.7% vinyl sulfate, and 1.6% tris(trimethylsilyl)phosphate. The resulting electrolyte solution had a mass ratio β of the cyclic ester solvent to the chain ester solvent of 0.43, a conductivity of 11.25 mS / cm, and a viscosity of 3.38 mPa s, similar to those in Example 1. Example 14

[0071] In the production method, the electrolyte solution was specifically added with 1.0% vinylene carbonate, 0.5% lithium difluorophosphate, 2% vinyl sulfate, and 0.15% tris(trimethylsilyl)phosphate. The obtained electrolyte solution had a mass ratio β of cyclic ester solvent to chain ester solvent of 0.43, a conductivity of 11.21 mS / cm, and a viscosity of 3.36 mPa s, which were the same as those in Example 1. Example 15

[0072] In the production method, the electrolyte solution was specifically prepared by adding 1.0% vinylene carbonate, 0.5% lithium difluorophosphate, 1.5% vinyl sulfate, and 3% tris(trimethylsilyl)phosphate. The obtained electrolyte solution had a mass ratio β of cyclic ester solvent to chain ester solvent of 0.43, a conductivity of 11.33 mS / cm, and a viscosity of 3.33 mPa s, which were the same as those in Example 1. Example 16

[0073] In the production method, the electrolyte solution was specifically added with 1.0% vinylene carbonate, 0.5% lithium difluorophosphate, 2.5% vinyl sulfate, and 3% tris(trimethylsilyl)phosphate. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.43, the conductivity of the electrolyte solution was 11.32 mS / cm, and the viscosity of the electrolyte solution was 3.35 mPa s. Example 17

[0074] The manufacturing method was the same as in Example 1 except that the mass of the electrolyte was different, specifically, the amount of electrolyte injected was 13 g. Example 18

[0075] The manufacturing method was the same as in Example 1, except that the amount of electrolyte injected was specifically 16 g. Example 19

[0076] The manufacturing method differs in the compressed density of the negative electrode. Specifically, the density of the negative electrode active material layer is 1.68 g / cm 3 Other than that, the results were the same as in Example 1. Comparative Example 1

[0077] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 40:30:30. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.67, the conductivity of the electrolyte solution was 12.01 mS / cm, and the viscosity of the electrolyte solution was 3.74 mPa s. Comparative Example 2

[0078] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 40:40:20. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.67, the conductivity of the electrolyte solution was 11.84 mS / cm, and the viscosity of the electrolyte solution was 4.05 mPa s. Comparative Example 3

[0079] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 40:15:45. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.67, the conductivity of the electrolyte solution was 12.19 mS / cm, and the viscosity of the electrolyte solution was 3.66 mPa s. Comparative Example 4

[0080] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 48:26:26. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.92, the conductivity of the electrolyte solution was 12.13 mS / cm, and the viscosity of the electrolyte solution was 4.43 mPa s. Comparative Example 5

[0081] In the production method, the electrolyte solution specifically contained 3.5% vinylene carbonate, 0.5% lithium difluorophosphate, 1% tris(trimethylsilyl)phosphate, and 1.5% vinyl sulfate. The resulting electrolyte solution had a mass ratio β of the cyclic ester solvent to the chain ester solvent of 0.43, a conductivity of 10.97 mS / cm, and a viscosity of 3.68 mPa s, similar to those in Example 12. Comparative Example 6

[0082] The manufacturing method was the same as in Example 1 except that the mass of the electrolyte was different, specifically, the amount of electrolyte injected was 10 g. Comparative Example 7

[0083] In the manufacturing method, the electrolyte solution was specifically a mixture of ethylene carbonate (EC, a cyclic ester solvent), methyl ethyl carbonate (EMC, a chain carbonate solvent), and dimethyl carbonate (DMC, a chain carbonate solvent) in a ratio of 20:40:40. The obtained electrolyte solution was the same as in Example 1, except that the mass ratio β of the cyclic ester solvent to the chain ester solvent was 0.25, the conductivity of the electrolyte solution was 10.48 mS / cm, and the viscosity of the electrolyte solution was 3.11 mPa s. In each of the Examples and Comparative Examples, the conductivity of the electrolyte solution is measured at 25°C using a conductivity meter, and the viscosity of the electrolyte solution is measured at 25°C using a viscometer. Test Example

[0084] This test example provides performance test results of the lithium ion secondary batteries according to the examples and comparative examples, and is specifically as follows. Test method for battery capacity retention rate: The battery was fully charged to the upper limit voltage and discharged to the lower limit voltage at a discharge current of 1C at a temperature of 25°C, and the discharge capacity was taken as C0. The battery was again fully charged to the upper limit voltage at 25°C, and the temperature was adjusted to -20°C, and the battery was discharged to the lower limit voltage at a discharge current of 1C, and the discharge capacity was taken as C1. The capacity retention rate of a lithium-ion secondary battery at -20°C is C1 / C0. Battery DCR (impedance) test method: Adjust the remaining capacity to 50% SOC at 25℃ with a discharge current of 1C, adjust the temperature to -25℃, discharge at 0.36C for 10 seconds, and calculate the discharge DCR at -25℃ using the formula △U / I, where △U is the change in voltage before and after discharge, and I is the discharge current. Battery lithium elution test method: Adjust the temperature to -10℃, charge to the upper voltage limit with a charging current of 0.13C, discharge to the lower voltage limit with a discharging current of 1C, perform 10 charge and discharge cycles, adjust the temperature to 25℃, charge to the upper voltage limit with a charging current of 1C, disassemble the battery, and observe whether lithium elution occurs at the interface. If the area of ​​the lithium eluted area on the negative plate surface is less than 2%, it is considered to be no lithium elution; if the area of ​​the lithium eluted area on the negative plate surface is 2% or more but less than 5%, it is considered to be slight lithium elution; if the area of ​​the lithium eluted area on the negative plate surface is 5% to 50%, it is considered to be lithium elution; and if the area of ​​the lithium eluted area on the negative plate surface is more than 50%, it is considered to be serious lithium elution. [Table 1] TIFF0007778234000005.tif167170

[0085] From the experimental results shown in Table 1, when the parameters of the organic solvent, negative electrode plate, and electrode assembly in the secondary battery satisfy a specific relationship, the secondary battery has a good capacity retention rate and low impedance under low temperature conditions, and the lithium elution phenomenon hardly occurs, although slight lithium elution was observed individually (Example 15).

[0086] Specifically, when comparing Comparative Example 1, Examples 4 to 6, and Comparative Example 4,

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[0087] Compared with Example 1,

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[0088] Comparing Examples 1 to 3 with Example 19, when the compression density is too high,

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[0089] In Examples 17 to 18 and Comparative Example 6, the change in the amount of electrolyte injected is different from that in Example 1. When the amount of injection is too low,

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[0090] The data from Example 1, Examples 8 to 16, and Comparative Example 5 show that the difference in additives does not have a significant effect on the viscosity and conductivity of the electrolyte, and that even when a certain additive is used in excess, lithium dissolution occurs, as in Comparative Example 5. Secondary batteries manufactured with different additive systems do not essentially dissolve lithium at low temperatures, but their capacity retention rates and impedances are different. Furthermore, under the cooperative action of the cyclic carbonate ester additive, silicon-containing additive, sulfonate ester-based additive, and lithium salt-type additive, parameters such as the weight of the electrolyte, the active material layer of the negative electrode plate, and the electrolyte in the secondary battery are rationally designed and rationally quantified.

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[0091] From the data of Example 1 and Examples 12 to 16, it is clear that 0.3≦W si +W s ≦4, 0.1≦W si / W s If ≦5, the secondary battery has better overall performance.

[0092] Obviously, the above examples are merely illustrative examples for the purpose of clarity and are not intended to limit the embodiments. Those skilled in the art may make other different modifications or changes based on the above description. It is not necessary and cannot be possible to cover all the embodiments here. Any obvious modifications or changes thus made are also included in the scope of protection of the present application.

Claims

1. A lithium ion secondary battery including a positive electrode plate, a negative electrode plate, and an electrolyte solution, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the electrolytic solution includes an organic solvent, and the organic solvent includes a cyclic ester solvent and a chain ester solvent, A secondary battery characterized by satisfying the following relational expression (1): [Equation 1] (where Mel. is the weight of the electrolyte in the secondary battery, and the unit of weight is g, σ is the conductivity value of the electrolyte, and the unit of conductivity is mS / cm. Cap. is the value of the theoretical capacity designed for the secondary battery, and the unit of the designed theoretical capacity is Ah, PD is the value of the compressed density of the negative electrode active material layer, and the unit of compressed density is g / cm ３ and η is the viscosity value of the electrolyte, and the viscosity unit is mPa s. β is the mass ratio of the cyclic ester solvent to the chain ester solvent in the electrolyte solution, The conductivity of the electrolyte solution is measured at 25°C, and the viscosity of the electrolyte solution is measured at 25°C.

2. (1) the mass ratio β of the cyclic ester solvent to the chain ester solvent is 0.25 to 0.85; (2) The conductivity σ of the electrolyte is 9 to 13; (3) the viscosity η of the electrolyte is 2 to 5; (4) The lithium ion secondary battery according to claim 1, wherein the weight value Mel. of the electrolyte is 11 to 16.

3. 2. The lithium ion secondary battery according to claim 1, wherein the mass ratio β of the cyclic ester solvent to the chain ester solvent is 0.33 to 0.

82.

4. 2. The lithium ion secondary battery according to claim 1, wherein the value of the conductivity σ of the electrolyte is 9.5 to 12.

5.

5. 2. The lithium ion secondary battery according to claim 1, wherein the viscosity η of the electrolyte is 2.5 to 4.

5.

6. 2. The lithium ion secondary battery according to claim 1, wherein the weight value Mel. of the electrolyte is 13 to 15.

7. 2. The lithium ion secondary battery according to claim 1, wherein the PD value is 1.1 to 1.

65.

8. the chain ester solvent contains at least one of a chain carbonate and a chain carboxylate; the chain carbonate includes at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate; 2. The lithium ion secondary battery according to claim 1, wherein the chain carboxylate includes at least one of ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl butyrate.

9. 2. The lithium ion secondary battery according to claim 1, wherein the cyclic ester solvent contains at least one of ethylene carbonate, propylene carbonate, and butylene carbonate.

10. 2. The lithium ion secondary battery according to claim 1, wherein the electrolyte further comprises an additive, and the additive comprises at least one of a silicon-containing additive, a cyclic carbonate additive, or a sulfur-containing additive.

11. The additive is (a) the silicon-containing additive includes at least one of tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, trimethylfluorosilane, or heptamethyldisilazane, and the silicon-containing additive is 0.1 to 4 mass% relative to the mass of the electrolyte; (b) the cyclic carbonate additive includes at least one of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate, and the cyclic carbonate additive is present in an amount of 0.05 to 3 mass% relative to the mass of the electrolyte; (c) the sulfur-containing additive includes at least one of 1,3-propane sultone and vinyl sulfate, and the sulfur-containing additive is present in an amount of 0.05 to 3 mass% relative to the mass of the electrolyte solution. The lithium ion secondary battery according to claim 10,

12. The additives of the electrolyte solution include a silicon-containing additive and a sulfur-containing additive, and the content of the silicon-containing additive relative to the mass of the electrolyte solution is W ｓｉ %, and the content of the sulfur-containing additive is W ｓ %, and 0.3≦W ｓｉ +W ｓ ≦4, 0.1≦W ｓｉ / W ｓ 11. The lithium ion secondary battery according to claim 10, wherein the following condition is satisfied: ≦5.

13. the electrolyte solution further comprises a lithium salt additive, the lithium salt additive comprising at least one of lithium bisfluorosulfonylimide, lithium bistrifluoromethanesulfonylimide, lithium difluorooxalate borate, lithium difluorophosphate, and lithium difluorooxalate phosphate; 2. The lithium ion secondary battery according to claim 1, wherein the lithium salt additive in the electrolyte is 0.1 to 5 mass %.

14. the positive electrode plate includes a positive electrode current collector and a positive electrode active material layer provided on the positive electrode current collector, the positive electrode active material layer including a positive electrode active material; The positive electrode active material is Li ａ Fe １－ｙ Mn ｙ P.O. ４ 2. The lithium ion secondary battery according to claim 1, wherein a is a group of atoms having a valence number a and y is a group of atoms having a valence number y.

15. An electrical device comprising the lithium ion secondary battery according to any one of claims 1 to 14.

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