Secondary battery and electric device

Abstract

Provided are a secondary battery and an electric device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte; a positive electrode film layer in the positive electrode sheet comprises an iron-lithium based positive electrode active material, and a negative electrode film layer in the negative electrode sheet comprises a silicon-based material and a carbon-based material; and a solvent of the electrolyte comprises a cyclic ester solvent and a chain ester solvent. The secondary battery uses the iron-lithium based positive electrode active material, and has good cycle performance and a long service life while having relatively high energy density.

Description

Secondary battery and electric device

[0001] Related applications

[0002] The present application claims priority to the Chinese patent application No. 2024110351027, filed on July 30, 2024, entitled "Secondary battery and electric device", the contents of which are hereby incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, in particular to a secondary battery and an electric device. BACKGROUND

[0004] In recent years, the application range of secondary batteries such as lithium ion batteries is more and more extensive, which has been widely applied in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles and the like. Since the secondary battery has achieved great development, higher requirements have been put forward for its energy density, cycle performance and safety performance and the like.

[0005] Iron lithium type positive active material is one of the main types of secondary battery positive active material, and the improvement of its energy density faces technical bottlenecks. The volume energy density of the secondary battery using traditional iron lithium type positive active material is difficult to break through 450 Wh / L, which will seriously limit the application of the battery using iron lithium type positive active material in, for example, vehicles with high endurance mileage requirements and the like. Some methods make the secondary battery have higher energy density by using high coating weight or high compaction density, but such methods will reduce the cycle performance and service life of the secondary battery. SUMMARY

[0006] Based on this, the present application provides a secondary battery in one aspect, which uses iron lithium type positive active material and has high energy density, good cycle performance and long service life. The present application also provides an electric device comprising the secondary battery in another aspect.

[0007] The present application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte. The positive electrode film layer in the positive electrode sheet comprises iron lithium type positive active material, the negative electrode film layer in the negative electrode sheet comprises silicon-based material and carbon-based material, and the solvent of the electrolyte comprises cyclic ester solvent and chain ester solvent.

[0008] The present application is directed to the battery system of iron lithium type positive active material, and by introducing silicon-based material and carbon-based material in the negative electrode film layer and using cyclic ester solvent and chain ester solvent as the solvent in the electrolyte, the secondary battery has high volume energy density, good cycle performance and long service life.

[0009] In some embodiments, the mass ratio of the cyclic ester solvent and the chain ester solvent is (0.1-1):1. Reasonable control of the mass ratio of the cyclic ester solvent and the chain ester solvent can reasonably regulate the viscosity of the electrolyte and the dissociation degree of the lithium salt, and improve the cycle performance of the secondary battery. Further, the mass ratio of the cyclic ester solvent and the chain ester solvent is (0.2-0.5):1.

[0010] In some embodiments, the cyclic ester solvent comprises one or more of vinyl carbonate, propylene carbonate and fluoro-vinyl carbonate; and / or the chain ester solvent comprises one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, methyl acetate, ethyl propionate and methyl propionate.

[0011] In some embodiments, the cyclic ester solvent comprises one or more of vinyl carbonate and fluoro-vinyl carbonate; and / or the chain ester solvent comprises one or both of ethyl acetate and methyl acetate.

[0012] In some embodiments, the mass percentage of the chain ester solvent in the electrolyte is 30%-80%. Reasonable control of the proportion of the chain ester solvent can effectively alleviate the hindering effect of the solid-liquid contact interface, reduce the deterioration of the interface and the consumption of the active material by the side reaction, and achieve better cycle life.

[0013] In some embodiments, the conductivity of the electrolyte is 12 mS / cm-18 mS / cm. For the battery system of the iron-lithium positive active material system, reasonable control of the conductivity of the electrolyte can reduce polarization, alleviate the interface reaction, reduce the consumption and deterioration of the active material, and comprehensively improve the cycle life.

[0014] In some embodiments, the compaction density of the positive electrode sheet is 2.5 g / cm 3 -2.9 g / cm 3 , the chain ester solvent comprises one or both of ethyl acetate and methyl acetate, and the conductivity of the electrolyte is 12 mS / cm-16 mS / cm. In the case of a higher compaction density, reasonable control of the conductivity of the electrolyte can better support the ion migration kinetics in the charging and discharging process, and alleviate the hindering effect of the solid-liquid contact interface.

[0015] In some embodiments, the mass percentage of the silicon-based material in the negative electrode film layer is 3%-15%. Reasonable control of the proportion of the silicon-based material in the negative electrode film layer can reduce the thickness of the electrode sheet, improve the polarization of the system, improve the ion transport kinetics, reduce the volume effect of the silicon-based material, improve the interface stability between materials, reduce the consumption of the active material, and thus improve the life of the secondary battery.

[0016] In some embodiments, the silicon-based material has a Dv50 of 5-15 μm.

[0017] In some embodiments, the silicon-based material comprises a silicon-carbon material, which comprises a porous carbon matrix and silicon material disposed within pores of the porous carbon matrix. The pores of the porous carbon matrix can effectively alleviate the volume change of the silicon material during lithium extraction and insertion, and thus reduce the damage to the interface and the electrode sheet.

[0018] In some embodiments, the silicon-based material has a specific discharge capacity of 1200-2000 mAh / g.

[0019] In some embodiments, the electrolyte comprises an additive, which comprises a carbonic acid ester compound and a sulfuric acid ester compound. The use of the carbonic acid ester compound and the sulfuric acid ester compound as electrolyte additives can alleviate the volume effect of the material and improve the interface stability of the material, and thus improve the cycle performance of the battery system.

[0020] In some embodiments, the carbonic acid ester compound has the structural characteristics shown in the following formula (I):

[0021] The sulfuric acid ester compound has the structural characteristics shown in the following formula (II):

[0022] wherein R1, R2, R3, R4 each independently comprises H, F, C1-C4 alkyl or C1-C4 fluoroalkyl.

[0023] In some embodiments, the mass percentage of the vinylene carbonate in the electrolyte is 1-10%, and / or the mass percentage of the vinyl sulfates in the electrolyte is 0.1-3%.

[0024] In some embodiments, the mass percentage of the silicon-based material in the negative electrode film layer and the mass ratio of the carbonic acid ester compound to the sulfuric acid ester compound satisfy one of the following conditions:

[0025] (1) the mass percentage of the silicon-based material in the negative electrode film layer is P1, 3%≤P1≤6%, and the mass ratio of the carbonic acid ester compound to the sulfuric acid ester compound is M1, 2:1≤M1≤5:1;

[0026] (2) the mass percentage of the silicon-based material in the negative electrode film layer is P2, 6%<P2≤15%, and the mass ratio of the carbonic acid ester compound to the sulfuric acid ester compound is M2, 5:1<M2≤10:1.

[0027] According to the mass percentage of the silicon-based material in the negative electrode film layer, the proportion of the additive is reasonably controlled, which can further improve the cycle performance and storage life of the battery.

[0028] In some embodiments, the volume energy density of the secondary battery is ≥420 Wh / L.

[0029] The application also provides a power-using device. The power-using device comprises the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the present application, the drawings used in the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of the drawings.

[0031] In order to better describe and illustrate the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any one of the disclosed applications, the presently described embodiments or examples, and the best mode presently understood of these applications. Moreover, the same reference numerals are used to represent the same components in all the drawings. In the drawings:

[0032] Figure 1 is a schematic diagram of a secondary battery according to an embodiment of the present application.

[0033] Figure 2 is an exploded view of the secondary battery shown in Figure 1 according to an embodiment of the present application.

[0034] Figure 3 is a schematic diagram of a power-using device using the secondary battery as a power source according to an embodiment of the present application.

[0035] Legend of reference numerals: 1, secondary battery; 11, shell; 12, electrode assembly; 13, cover plate; 2, power-using device. DETAILED DESCRIPTION

[0036] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are shown in the drawings. However, the present application can be implemented in many different forms, and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0037] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0038] "ranges" disclosed herein can be defined with endpoints by selecting a lower limit and an upper limit and defining the range as the values between the lower and upper limits. Ranges defined using endpoints can include the endpoint values or exclude the endpoint values, and ranges excluding the endpoint values can be combined with other ranges to form a range that excludes either or both of the excluded endpoint values. For example, if a range of 60-120 and a range of 80-110 are listed, it is understood that a range of 60-110 and a range of 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 are listed, and if a maximum range value of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, a numerical range "a-b" indicates a shorthand way of describing each and every numerical value within the range. For example, the numerical range "0-5" indicates that all real numbers between 0 and 5 have been listed herein. The numerical range "0-5" is merely a shorthand way of describing each and every numerical value within the range. Additionally, when a parameter is stated to be an integer ≥ 2, it is equivalent to listing the parameter as, for example, integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is stated to be an integer selected from "2-10", it is equivalent to listing the parameter as integer 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0039] As used herein, the singular forms "a", "an" and "the" include plural referents unless the context clearly dictates otherwise. As used herein, the term "or" means any one member of a logical disjunction, unless stated otherwise. As used herein, "comprise", "comprises" and "comprising" or "include", "includes" and "including" are inclusive (i.e. they mean "including, but not limited to") unless the context clearly dictates otherwise. As used herein, the term "plurality" means two or more, unless the context clearly dictates otherwise.

[0040] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, unless otherwise specified.

[0041] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the application. The appearances of the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive or alternative embodiments. It is expressly understood that the embodiments described herein are merely examples from a whole class of comparable embodiments which those skilled in the art will readily synthesize without being actively dependent on the examples described herein. Reference herein to "an implementation" has a similar understanding.

[0042] Those skilled in the art can understand that the order of writing each step in the method of each embodiment or example does not mean a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0043] In the present application, A (such as B) means that B is one non-limiting example of A, and it can be understood that A is not limited to B.

[0044] In the present application, "optionally", "optional" and "optional" mean that it can or can not exist, that is, it means to select any one from the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, and there is no special description, and there is no contradictory or mutual restrictive relationship, each "option" is independent.

[0045] In the present application, "alkyl" refers to a saturated hydrocarbon monovalent radical generated by losing one hydrogen atom, which contains primary (normal) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof. The phrase containing this term, for example, "C1-C4 alkyl" refers to an alkyl group containing 1-4 carbon atoms, which can be C1 alkyl, C2 alkyl, C3 alkyl or C4 alkyl independently of each other. Suitable examples include but are not limited to: methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -CH(CH3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3). "Fluoroalkyl" refers to "alkyl" in which at least one H is replaced by F.

[0046] It is a great challenge to improve the cycle and life of secondary batteries with iron-lithium-based positive active material systems with a volume energy density of ≥450 Wh / L, and there is a huge application market. However, the traditional way of high coating weight (for example, positive electrode ≥25.9 mg / cm 2 , negative electrode ≥12.3 mg / cm 2 ) or high compaction density (for example, negative electrode PD ≥1.75 g / cm 3 ) usually reduces the cycle and life of the secondary battery, which may be due to the following reasons: for the way of high coating weight, the increase of coating weight, the coating weight of which needs to be increased synchronously with the same kind of active material, the corresponding electrode sheet thickness increases, the electrode sheet kinetics deteriorates, the fast charging performance decreases, the risk of lithium precipitation increases, and it is found through research that it also makes the lithium distribution in the thickness direction of the negative electrode sheet uneven, and the state of charge (SOC state) gradually decreases from the surface to the inside. The SOC of the surface layer is too high, which increases the side reaction and further deteriorates the storage life; for the way of high compaction density, the porosity of the electrode sheet decreases, the liquid retention capacity weakens, the kinetics further deteriorates, and at the same time, more active material particles are broken, the reaction sites increase, the first lithium consumption increases, and the cycle storage also deteriorates.

[0047] In addition, for the battery system with ternary material as the positive electrode material, there is a method to improve the overall capacity of the battery by using silicon-based material in the negative electrode, but there is less research on the application of silicon-based material in the battery system with iron-lithium-based positive active material. The possible reason is that the silicon-based material has a low first efficiency, which consumes a lot of active lithium in the first charge and discharge process, and the gram capacity of the iron-lithium-based positive active material is low, which makes the positive and negative electrode mismatch.

[0048] Considering the above factors, an embodiment of the present application provides a secondary battery, which comprises a positive electrode sheet, a negative electrode sheet and an electrolyte; the positive electrode film layer in the positive electrode sheet comprises an iron-lithium-based positive active material, the negative electrode film layer in the negative electrode sheet comprises a silicon-based material and a carbon-based material; and the solvent of the electrolyte comprises a cyclic ester solvent and a chain ester solvent.

[0049] The application is directed to a battery system of iron-lithium type positive active material, by introducing silicon-based material and carbon-based material in the negative electrode film layer, the high specific capacity silicon-based material can effectively reduce the load of the negative electrode sheet in the battery system, reduce the compaction density of the negative electrode sheet, improve the life deterioration caused by uneven lithium distribution in the thickness direction of the electrode sheet, and correspondingly, the use of cyclic ester solvents and chain ester solvents as solvents in the electrolyte can make the electrolyte have suitable viscosity and dissociation property to electrolyte salt, increase the active lithium content and transmission, so as to better adapt to the negative electrode sheet compounded by silicon-based material and carbon-based material and the positive electrode sheet of iron-lithium type positive active material, and improve the cycle performance of the secondary battery. In this way, the above-mentioned battery system of iron-lithium type positive active material has high volume energy density, and also has good cycle performance and long service life.

[0050] In some embodiments, the compaction density of the negative electrode sheet is 1.4 g / cm 3 ~ 1.7 g / cm 3 .

[0051] In some embodiments, the volume energy density (VED) of the secondary battery is ≥420 Wh / L.

[0052] In some embodiments, the iron-lithium type positive active material includes one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite material of lithium manganese iron phosphate and carbon.

[0053] In some embodiments, the mass ratio of the cyclic ester solvent and the chain ester solvent is (0.1-1):1. Reasonably controlling the mass ratio of the cyclic ester solvent and the chain ester solvent can reasonably regulate the viscosity of the electrolyte and the degree of dissociation of lithium salt, and improve the cycle performance of the secondary battery. Specifically, the mass ratio of the cyclic ester solvent and the chain ester solvent includes but is not limited to 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1, 0.4:1, 0.45:1, 0.5:1, 0.55:1, 0.6:1, 0.65:1, 0.7:1, 0.75:1, 0.8:1, 0.85:1, 0.9:1, 0.95:1, 1:1 or a range between any two of the foregoing. Further, the mass ratio of the cyclic ester solvent and the chain ester solvent is (0.2-0.5):1. Still further, the mass ratio of the cyclic ester solvent and the chain ester solvent is (0.3-0.4):1.

[0054] Without limitation, the cyclic ester-based solvent includes one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. Further, the cyclic ester-based solvent includes one or more of ethylene carbonate and fluoroethylene carbonate.

[0055] Without limitation, the chain ester-based solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl acetate, ethyl propionate, and methyl propionate. Further, the chain ester-based solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate, and methyl acetate. Still further, the chain ester-based solvent includes one or both of ethyl acetate and methyl acetate.

[0056] In some embodiments, the electrolyte has an electrical conductivity of 12 milli- Siemens per centimeter (mS / cm) to 18 mS / cm. For battery systems of iron-lithium based cathode active material systems, reasonable control of the electrical conductivity of the electrolyte can alleviate interfacial reactions while reducing polarization, reducing active material consumption deterioration and gas production, and overall improving cycle life. Specifically, the electrolyte has an electrical conductivity including, but not limited to, 12 mS / cm, 13 mS / cm, 14 mS / cm, 15 mS / cm, 16 mS / cm, 17 mS / cm, 18 mS / cm, or a range between any two of the foregoing.

[0057] In some embodiments, the cathode electrode has a compacted density of 2.5 g / cm 3 to 2.9 g / cm 3 A cathode electrode with a higher compacted density can use a higher active material coating weight and reduce the increase in thickness, further improving the volumetric energy density of the secondary battery. Further, the chain ester-based solvent includes a first chain ester-based solvent including ethyl acetate and / or methyl acetate, and the electrolyte has an electrical conductivity of 12 mS / cm to 16 mS / cm. With a higher compacted density, by using ethyl acetate and / or methyl acetate as a chain ester-based solvent and reasonably controlling the electrical conductivity of the electrolyte, ion migration kinetics during charging and discharging can be better supported, and the hindering effect of the solid-liquid contact interface can be alleviated, to better adapt to the design of high-pressure dense cathode electrodes under high energy density conditions.

[0058] Further, in the electrolyte, the mass percentage of the first chain ester solvent is 30% to 80%. Reasonably controlling the proportion of the first chain ester solvent can effectively alleviate the hindering effect of the solid-liquid contact interface, reduce the deterioration of the interface and the consumption of the active material by the side reaction, and achieve better cycle life. Specifically, the mass percentage of the first chain ester solvent includes but is not limited to 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a range between any two of the foregoing. Further, the mass percentage of the first chain ester solvent is 30% to 60%. Without limitation, in addition to the first chain ester solvent, the mass percentage of other chain ester solvents in the electrolyte can be 5% to 30%. Specifically, the mass percentage of other chain ester solvents in the electrolyte includes but is not limited to 5%, 10%, 15%, 20%, 25%, 30%, or a range between any two of the foregoing.

[0059] In addition, in some embodiments, the mass percentage of the silicon-based material in the negative electrode film layer is 3% to 15%. Reasonably controlling the proportion of the silicon-based material in the negative electrode film layer can reduce the thickness of the electrode sheet, improve the polarization of the system, improve the ion transport kinetics, reduce the volume effect of the silicon-based material, improve the interface stability between materials, reduce the consumption of the active material, and thus improve the life of the secondary battery. Specifically, the mass percentage of the silicon-based material in the negative electrode film layer includes but is not limited to 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range between any two of the foregoing.

[0060] Without limitation, the silicon-based material can include one or more of elemental silicon, silicon oxide compounds, silicon-carbon materials, silicon-nitrogen compounds, and silicon alloys.

[0061] In some embodiments, the silicon-based material includes a silicon-carbon material. Further, the silicon-carbon material includes a porous carbon matrix and a silicon material arranged in the pores of the porous carbon matrix. Utilizing the pores of the porous carbon matrix can effectively alleviate the damage to the interface and the electrode sheet caused by the volume change of the silicon material during the deintercalation of lithium. Without limitation, the silicon material is nanosilicon, and the material of the porous carbon matrix is hard carbon.

[0062] In some embodiments, the silicon-based material has a discharge specific capacity of 1500 milliampere-hour per gram (mAh / g) to 2300 mAh / g. Specifically, the silicon-based material has a discharge specific capacity including, but not limited to, 1500 mAh / g, 1600 mAh / g, 1700 mAh / g, 1800 mAh / g, 1900 mAh / g, 2000 mAh / g, 2100 mAh / g, 2200 mAh / g, 2300 mAh / g, or a range between any two of the foregoing. Reasonably controlling the discharge specific capacity of the silicon-based material can reduce the problems of poor stability and life deterioration caused by material expansion while obtaining a higher initial efficiency. Further, the silicon-based material has a discharge specific capacity of 1700 mAh / g to 1900 mAh / g.

[0063] Without limitation, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon, and hard carbon.

[0064] In some embodiments, the electrolyte includes an additive including one or both of a carbonic acid ester compound and a sulfuric acid ester compound. Further, the additive includes both the carbonic acid ester compound and the sulfuric acid ester compound. Using the carbonic acid ester compound and the sulfuric acid ester compound as electrolyte additives can alleviate the volume effect of the material and improve the interface stability of the material, thereby improving the cycle performance of the battery system.

[0065] In some embodiments, the carbonic acid ester compound has a structural feature as shown in the following formula (I):

[0066] wherein R1, R2 each individually includes H, F, C1-C4 alkyl, or C1-C4 fluoroalkyl.

[0067] In some embodiments, the carbonic acid ester compound includes one or more of vinylene carbonate, propylene carbonate, butylene carbonate, and dimethyl vinylene carbonate.

[0068] In some embodiments, the carbonate compound comprises vinylene carbonate. Vinylene carbonate is a cyclic unsaturated bond-containing film-forming additive that can generate organic and polymeric interfacial films during charge and discharge, and has good adaptability to volume effects of the deintercalation / intercalation of lithium. Further, the mass percentage of the vinylene carbonate in the electrolyte is 1% to 10%. Specifically, the mass percentage of the vinylene carbonate includes, but is not limited to, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 8%, 9%, 10%, or a range between any two of the foregoing. Further, the mass percentage of the vinylene carbonate in the electrolyte is 2% to 6%.

[0069] In some embodiments, the sulfate compound has a structural feature shown in the following formula (II):

[0070] wherein R1, R2, R3, R4 each independently includes H, F, C1-C4 alkyl, or C1-C4 fluoroalkyl.

[0071] In some embodiments, the sulfate compound includes one or more of vinyl sulfate, propylene sulfate, and dimethyl vinyl sulfate.

[0072] In some embodiments, the sulfate compound includes vinyl sulfate. Vinyl sulfate can participate in reactions at the interface to generate sulfate and sulfite substances, effectively improving the thermal stability and chemical stability of the interface. Further, the mass percentage of the vinyl sulfate in the electrolyte is 0.1% to 3%. Specifically, the mass percentage of the vinyl sulfate includes, but is not limited to, 0.1%, 0.3%, 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 2%, 2.5%, 3%, or a range between any two of the foregoing. Further, the mass percentage of the vinyl sulfate in the electrolyte is 0.3% to 1%.

[0073] Further, the particle size distribution of the silicon-based material and the mass percentage of the silicon-based material in the negative electrode film layer are related to the specific surface area, and also affect the characteristics of the solid-liquid reaction interface. In some embodiments, the mass ratio of the carbonate compound and the sulfate compound in the electrolyte is reasonably controlled according to the particle size distribution of the silicon-based material and the mass percentage of the silicon-based material in the negative electrode film layer. The carbonate compound generates organic interface components, and the sulfate compound is inclined to generate inorganic sulfate. The two are compounded in a certain mass ratio, which can better adapt to the volume effect of the silicon-based material in the negative electrode film layer and the high reactivity of the interface under high temperature and high SOC environment, improve the stability of the solid-liquid interface performance, and thus improve the service life of the secondary battery.

[0074] In some embodiments, the Dv50 of the silicon-based material is 5 microns (pm) to 15 pm. Specifically, the Dv50 of the silicon-based material includes but is not limited to 5 pm, 6 pm, 7 pm, 8 pm, 9 pm, 10 pm, 11 pm, 12 pm, 13 pm, 13 pm, 15 pm, or a range between any two of the foregoing. Further, the Dv50 of the silicon-based material is 7 pm to 12 pm.

[0075] In addition, according to the mass percentage of the silicon-based material in the negative electrode film layer, the proportion of the additive is reasonably controlled, which can further improve the cycle performance and storage life of the battery. In some embodiments, the mass percentage of the silicon-based material in the negative electrode film layer and the mass ratio of the carbonate compound and the sulfate compound satisfy one of the following conditions:

[0076] (1) The mass percentage of the silicon-based material in the negative electrode film layer is P1, 3%≤P1≤6%, and the mass ratio of the carbonate compound and the sulfate compound is M1, 2:1≤M1≤5:1. Specifically, the mass percentage of the silicon-based material in the negative electrode film layer includes but is not limited to 3%, 4%, 5%, 6%, or a range between any two of the foregoing. The mass ratio of the carbonate compound and the sulfate compound includes but is not limited to 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 5:1, or a range between any two of the foregoing;

[0077] (2) the mass percentage of the silicon-based material in the negative electrode film layer is P2, 6% < P2≤ 15%, and the mass ratio of the carbonate compound to the sulfate compound is M2, 5:1 < M2≤ 10:1; specifically, the mass percentage of the silicon-based material in the negative electrode film layer includes but is not limited to 6.1%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range between any two of the foregoing; and the mass ratio of the carbonate compound to the sulfate compound includes but is not limited to 5.1:1, 5.5:1, 6:1, 7:1, 9:1, 10:1, or a range between any two of the foregoing.

[0078] Further, in some embodiments, the electrolyte further includes a lithium salt. Without limitation, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium difluoro-bis-oxalato-phosphate (LiDFOP), and lithium tetrafluoro-oxalato-phosphate (LiTFOP). Further, the lithium salt includes one or both of lithium hexafluorophosphate and lithium bisfluorosulfonylimide. Without limitation, the concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L. Specifically, the concentration of the lithium salt includes but is not limited to 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.1 mol / L, 1.5 mol / L, 1.7 mol / L, 2 mol / L. Further, the concentration of the lithium salt in the electrolyte is 0.8 mol / L to 1.1 mol / L.

[0079] Without limitation, the secondary battery of the present application is further described below with appropriate reference to the accompanying drawings.

[0080] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted into and extracted from the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly serves to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0081] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including a positive electrode active material.

[0082] As a non-limiting example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material layer is disposed on either one or both of the two surfaces of the positive electrode current collector.

[0083] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base material. Non-limiting examples of the metal material in the positive electrode current collector can include one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. Non-limiting examples of the polymer material base material in the positive electrode current collector can include one or more of a polypropylene (PP) base material, a polyethylene terephthalate (PET) base material, a polybutylene terephthalate (PBT) base material, a polystyrene (PS) base material, a polyethylene (PE) base material, and the like.

[0084] In some embodiments, the positive electrode active material includes an iron lithium-based positive electrode active material. In addition, the positive electrode active material can further include other positive electrode active materials for a battery as known in the art. As a non-limiting example, the positive electrode active material can further include one or more of lithium transition metal oxides and respective modified compounds thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for a battery can be used. These positive electrode active materials can be used alone or in combination of two or more. Examples of the lithium transition metal oxide can include, but are not limited to, one or more of lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof. Non-limiting examples of the lithium cobalt oxide can include LiCoO2; non-limiting examples of the lithium nickel oxide can include LiNiO2; non-limiting examples of the lithium manganese oxide can include LiMnO2, LiMn2O4, and the like; non-limiting examples of the lithium nickel cobalt manganese oxide can include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to as NCM 211 ), LiNi0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 ), etc. Non-limiting examples of lithium nickel cobalt aluminum oxides can include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0085] In some embodiments, the positive electrode film layer further optionally includes a binder. As non-limiting examples, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0086] In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As non-limiting examples, the conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained. The type of the solvent can be selected from, but is not limited to, any of the aforementioned embodiments, such as N-methyl pyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40% to 80% by mass (i.e., 40 wt% to 80 wt%). The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 millipascal seconds (mPa s) to 25000 mPa s. When coating the positive electrode slurry, the coating unit area density, by dry weight (excluding the solvent), can be 15 milligrams per square centimeter (mg / cm 2 ) to 35 mg / cm 2 .

[0088] The negative electrode tab includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material.

[0089] As a non-limiting example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative active material layer is disposed on either one or both of the two surfaces of the negative current collector.

[0090] In some embodiments, the negative current collector can employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be obtained by forming a metal material on a polymer material base layer. Non-limiting examples of the metal material in the negative current collector can include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like. Non-limiting examples of the polymer material base layer in the negative current collector can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0091] In some embodiments, the negative active material includes a silicon-based material and a carbon-based material. In addition, the negative active material can further include other negative active materials for batteries known in the art. As a non-limiting example, the negative active material can further include one or more of a tin-based material and lithium titanate, and the like. The tin-based material can include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as negative active materials for batteries can also be used. These negative active materials can be used alone or in combination with two or more.

[0092] In some embodiments, the negative film layer can further optionally include a binder. The binder can include one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0093] In some embodiments, the negative film layer can further optionally include a conductive agent. The conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some embodiments, the negative film layer can further optionally include other auxiliary agents, such as a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

[0095] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector, and after processes such as drying, cold pressing, etc., the negative electrode sheet can be obtained. The surface of the negative electrode current collector coated with the negative electrode slurry can be on a single surface of the negative electrode current collector, or on both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40% to 60% by mass (i.e., 40 wt% to 60 wt%). The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa s to 10000 mPa s. When coating the negative electrode slurry, the coating unit area density (excluding the solvent) can be 75 g / m 2 2

[0096] The electrolyte has the function of conducting ions between the positive electrode sheet and the negative electrode sheet.

[0097] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous structure separator having good chemical stability and mechanical stability can be used.

[0098] In some embodiments, the material of the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0099] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and can be 12 μm to 20 μm.

[0100] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to prepare an electrode assembly by a winding process or a stacking process.

[0101] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-mentioned electrode assembly and the electrolyte.

[0102] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0103] ​​The secondary battery includes at least one battery cell. The secondary battery can include one or more battery cells.

[0104] In the present application, a "battery cell" refers to a basic unit capable of converting chemical energy and electrical energy to each other, and further, generally includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. During charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct the active ions between the positive electrode sheet and the negative electrode sheet.

[0105] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, FIG. 1 is a secondary battery 1 of a square structure as an example.

[0106] In some embodiments, referring to FIG. 2, the outer package can include a housing 11 and a cover plate 13. The housing 11 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be provided on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form an electrode assembly 12 through a winding process or a stacking process. The electrode assembly 12 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, which can be selected by a person skilled in the art according to actual needs.

[0107] The secondary battery can be a battery module or a battery pack.

[0108] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0109] In the battery module, the plurality of battery cells can be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells can be fixed by fasteners.

[0110] Optionally, the battery module can further include a housing having a receiving space, and the plurality of battery cells are received in the receiving space.

[0111] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0112] A battery pack can include a battery case and a plurality of battery modules disposed in the battery case. The battery case includes an upper case and a lower case, and the upper case is capable of being disposed on the lower case and forms an enclosed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery case in any manner.

[0113] In addition, the application also provides a power consuming device. The power consuming device includes the above-mentioned secondary battery. The secondary battery can be used as a power supply of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. The mobile device can be a mobile phone, a notebook computer, etc., for example; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0114] As the power consuming device, the secondary battery can be selected according to the use requirement thereof.

[0115] FIG. 3 is a power consuming device 2 as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power consuming device, a battery pack or a battery module can be used.

[0116] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and the secondary battery can be used as a power supply.

[0117] In order to make the technical problems, technical solutions and beneficial effects solved by the application clearer, the application will be further described in detail below in combination with embodiments and drawings. Obviously, the described embodiments are only a part of the embodiments of the application, rather than all the embodiments. The description of the at least one exemplary embodiment below is actually only illustrative, but not as any limitation on the application and its application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the application.

[0118] Unless otherwise specified in the embodiments, the technology or conditions are carried out according to the technology or conditions described in the literature in the art or according to the product manual. Unless otherwise specified, the reagents or instruments used are conventional products that can be obtained from the market.

[0119] Embodiment 1

[0120] 1) Preparation of positive electrode sheet

[0121] Lithium iron phosphate, conductive carbon black SP and binder PVDF were dispersed into solvent NMP in a weight ratio of 98%:1%:1% to mix uniformly to obtain a positive electrode slurry; the positive electrode slurry was uniformly coated on the double-sided surfaces of a positive electrode current collector aluminum foil, and after drying, cold pressing, a positive electrode sheet was obtained, wherein the coating amount per unit area of the double sides was 0.27 g / 1540.25 mm 2 , and the compacted density was 2.8 g / cm 3 .

[0122] 2) Preparation of a negative electrode sheet

[0123] The negative electrode active material natural graphite, silicon-carbon material (commercial product, hard carbon with nano-silicon deposited in pores, specific discharge capacity of 1600 mAh / g, Dv50 of 10 μm), thickening agent sodium carboxymethyl cellulose, adhesive styrene-butadiene rubber, and conductive agent acetylene black were mixed in a mass ratio of 93%:4%:1%:1%:1%, deionized water was added, and a negative electrode slurry was obtained under the action of a vacuum stirrer; the negative electrode slurry was uniformly coated on the double-sided surfaces of a copper foil; the copper foil was dried at room temperature, then transferred to a 120°C oven for drying for 1 h, and then cold pressed, cut to obtain a negative electrode sheet, wherein the coating amount per unit area of the double sides was 0.17 g / 1540.25 mm 2 , and the compacted density was 1.5 g / cm 3 .

[0124] 3) Isolation film

[0125] A 12 μm thick polypropylene isolation film was selected.

[0126] 4) Preparation of an electrolyte

[0127] The organic solvent was a mixture containing ethylene carbonate, ethyl acetate and dimethyl carbonate in a mass ratio of 25%:55%:20%. In an argon glove box with a water content of <10 ppm, a fully dried lithium salt LiPF6 and an additive were dissolved in the organic solvent to mix uniformly to obtain an electrolyte with a conductivity of 15 mS / cm. The concentration of the lithium salt was 1 mol / L, the additive was vinylene carbonate with a mass percentage of 2.5% in the electrolyte, and vinyl ethyl sulfate with a mass percentage of 1% in the electrolyte.

[0128] 5) Preparation of a battery

[0129] The positive electrode sheet, the isolation film and the negative electrode sheet were stacked in order, with the isolation film between the positive and negative electrode sheets to play a role of isolation, then wound into a square bare cell, and then placed in an aluminum plastic film, and then baked at 80°C to remove water, then injected with 10 g of the corresponding non-aqueous electrolyte, sealed, and then subjected to processes of standing, hot and cold pressing, formation, clamping and capacity distribution to obtain a finished battery with a capacity of 4000 mAh.

[0130] The secondary battery of Examples 2-3 was prepared in the same manner as Example 1, with the main difference being that the mass ratio of the cyclic ester solvent and the chain ester solvent was changed.

[0131] The secondary battery of Examples 4-5 was prepared in the same manner as Example 1, with the main difference being that the mass percentage of ethyl acetate in the electrolyte was changed, and the mass percentage of dimethyl carbonate was increased or decreased accordingly so that the mass ratio of the cyclic ester solvent and the chain ester solvent remained unchanged.

[0132] The secondary battery of Example 6 was prepared in the same manner as Example 1, with the main difference being that ethyl acetate in the electrolyte was replaced with methyl acetate, and the mass percentage was changed, and the mass percentage of dimethyl carbonate was increased accordingly so that the mass ratio of the cyclic ester solvent and the chain ester solvent remained unchanged.

[0133] The secondary battery of Examples 7-12 was prepared in the same manner as Example 1, with the main difference being that the composition of the additive was changed.

[0134] The secondary battery of Example 13 was prepared in the same manner as Example 1, with the main difference being that no additive was used.

[0135] The secondary battery of Comparative Example 1 (D1) was prepared in the same manner as Example 1, with the main difference being that no silicon-carbon material was used, i.e., the negative active material natural graphite, the thickening agent sodium carboxymethyl cellulose, the binder styrene-butadiene rubber, and the conductive agent acetylene black were mixed in a mass ratio of 97%:1%:1%:1%.

[0136] The secondary battery of Comparative Example 2 (D2) was prepared in the same manner as Example 1, with the main difference being that no chain ester solvent was used, i.e., the organic solvent was only ethylene carbonate.

[0137] The secondary battery of Comparative Example 3 (D3) was prepared in the same manner as Example 1, with the main difference being that no cyclic ester solvent was used, i.e., the organic solvent was a mass ratio of 73%:27% ethyl acetate and dimethyl carbonate.

[0138] The preparation parameters of the secondary batteries of Examples 1-13 and Comparative Examples 1-3 are shown in Table 1 below.

[0139] Table 1

[0140] Test Example

[0141] (1) Volumetric energy density

[0142] The positive electrode sheet, the separator, and the negative electrode sheet were stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to function as a separator, and then wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum case (V = 0.411 L) having a thickness of 28.5 mm, a width of 148 mm, and a height of 97.5 mm, with a case entry allowance of 92%, and after drying, an electrolyte was injected. The battery was subjected to a vacuum packaging process, a standing process, a formation process, a shaping process, and the like, to obtain a secondary battery.

[0143] The secondary battery was charged at 0.33C to 3.8V at 25°C, and then held at 3.8V at 0.05C. After 10 minutes of standing, the battery was discharged at 0.33C to 2.0V, and then held for 10 minutes. The above steps were repeated three times. The energy W (unit: Wh) at the time of the last discharge at 0.33C to 2V was extracted, and then the energy density VED was calculated as VED = W / V (unit: Wh / L).

[0144] (2) Cycle performance

[0145] The secondary battery prepared in each example and comparative example was charged at 0.5C to 3.8V at 45°C, and then charged at a constant voltage until the current was less than or equal to 0.05C. After 5 minutes of standing, the battery was discharged at 0.33C to 2V, and then held for 5 minutes. This was one charge-discharge cycle. The battery was subjected to a cycle charge-discharge test according to this method, and the capacity retention rate after 1000 cycles was calculated.

[0146] (3) Storage life

[0147] The secondary battery prepared in each example and comparative example was charged at 0.5C to 3.8V at 25°C, and then charged at a constant voltage until the current was less than or equal to 0.05C. After 5 minutes of standing, the battery was discharged at 0.33C to 2V, and then held for 5 minutes. This was one charge-discharge cycle.

[0148] The battery was then charged at 0.5C to 3.8V, and then charged at a constant voltage until the current was less than or equal to 0.05C. After 300 days of storage at 60°C, the battery was subjected to a cycle charge-discharge test according to the above method, and the capacity retention rate after 300 days of storage was calculated.

[0149] The test results are shown in Table 2.

[0150] Table 2

[0151] By comparing between the examples 1-13 and the comparative example 1, it can be seen that the examples can improve the volumetric energy density of the battery by using carbon-based materials and silicon-based materials as negative active materials, while maintaining high cycle performance and storage life.

[0152] By comparing between the examples 1-13 and the comparative examples 2 and 3, it can be seen that the examples can effectively improve the cycle performance and storage life of the battery by using a combination of cyclic ester solvents and chain ester solvents as solvents.

[0153] By comparing between the examples 1-3, it can be seen that reasonable adjustment of the mass ratio of cyclic ester solvents and chain ester solvents can further improve the cycle performance and storage life of the battery.

[0154] By comparing between the examples 1 and 4-5, it can be seen that reasonable adjustment of the mass percentage of the first chain ester solvent in the electrolyte can further improve the cycle performance and storage life of the battery.

[0155] By comparing between the examples 1 and 6, it can be seen that using ethyl acetate as the first chain ester solvent can further improve the cycle performance and storage life of the battery.

[0156] By comparing between the examples 1 and 7-10, it can be seen that reasonable adjustment of the proportion of two additives in the electrolyte according to the mass percentage of the silicon-based material in the negative electrode film layer can further improve the cycle performance and storage life of the battery.

[0157] By comparing between the examples 1 and 11-12, it can be seen that compared to using only an ester carbonate compound or a sulfate compound as an additive, the combination of the two can better improve the cycle performance and storage life of the battery.

[0158] By comparing between the examples 1 and 11-13, it can be seen that using an ester carbonate compound and / or a sulfate compound as an additive can further improve the cycle performance and storage life of the battery.

[0159] The technical features of the above-described examples can be combined in any way. To make the description concise, not all possible combinations of the technical features in the above-described examples are described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

[0160] The above-described embodiments are merely illustrative of several embodiments of the present application, which are described in more detail and in a specific manner, but should not be construed as limiting the scope of the patent. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte; wherein the positive electrode film in the positive electrode comprises a lithium iron phosphate active material, and the negative electrode film in the negative electrode comprises a silicon-based material and a carbon-based material; and the electrolyte solvent comprises a cyclic ester solvent and a chain ester solvent.

2. The secondary battery according to claim 1, wherein, The mass ratio of the cyclic ester solvent to the chain ester solvent is (0.1 to 1):

1.

3. The secondary battery according to claim 2, wherein, The mass ratio of the cyclic ester solvent to the chain ester solvent is (0.2–0.5):

1.

4. The secondary battery according to any one of claims 1 to 3, wherein, The cyclic ester solvents include one or more of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate; and / or The chain-like ester solvents include one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethyl acetate, ethyl propionate, and methyl propionate.

5. The secondary battery according to claim 4, wherein, The cyclic ester solvents include one or more of ethylene carbonate and fluoroethylene carbonate; and / or The chain-like ester solvent includes one or both of ethyl acetate and methyl acetate.

6. The secondary battery according to claim 5, wherein, In the electrolyte, the mass percentage of the chain ester solvent is 30% to 80%.

7. The secondary battery according to any one of claims 1 to 6, wherein, The conductivity of the electrolyte is 12 mS / cm to 18 mS / cm.

8. The secondary battery according to claim 7, wherein, The compaction density of the positive electrode sheet is 2.5–2.9 g / cm³. 3 The chain-like ester solvent includes one or both of ethyl acetate and methyl acetate, and the conductivity of the electrolyte is 12 mS / cm to 16 mS / cm.

9. The secondary battery according to any one of claims 1 to 8, wherein, The mass percentage of the silicon-based material in the negative electrode film is 3% to 15%.

10. The secondary battery according to any one of claims 1 to 9, wherein, The Dv50 of the silicon-based material is 5μm to 15μm.

11. The secondary battery according to any one of claims 1 to 10, wherein, The silicon-based material includes silicon-carbon material, which includes a porous carbon matrix and silicon material disposed within the pores of the porous carbon matrix.

12. The secondary battery according to any one of claims 1 to 11, wherein, The specific discharge capacity of the silicon-based material is 1200mAh / g to 2000mAh / g.

13. The secondary battery according to any one of claims 1 to 12, wherein, The electrolyte includes additives, which include carbonate esters and sulfate esters.

14. The secondary battery according to claim 13, wherein, The carbonate ester compounds have the structural features shown in formula (I): The sulfate ester compound has the structural features shown in formula (II): R1, R2, R3, and R4 each individually include H, F, C1-C4 alkyl, or C1-C4 fluoroalkyl.

15. The secondary battery according to claim 13 or 14, wherein, In the electrolyte, the mass percentage of the vinylene carbonate is 1% to 10%; and / or In the electrolyte, the mass percentage of the vinyl sulfate is 0.1% to 3%.

16. The secondary battery according to any one of claims 13 to 15, wherein, The mass percentage of the silicon-based material in the negative electrode film and the mass ratio of the carbonate ester compound to the sulfate ester compound satisfy one of the following conditions: (1) The mass percentage of the silicon-based material in the negative electrode film is P1, 3%≤P1≤6%, and the mass ratio of the carbonate ester compound to the sulfate ester compound is M1, 2:1≤M1≤5:1; (2) The mass percentage of the silicon-based material in the negative electrode film is P2, 6% < P2 ≤ 15%, and the mass ratio of the carbonate ester compound to the sulfate ester compound is M2, 5:1 < M2 ≤ 10:

1.

17. The secondary battery according to any one of claims 1 to 16, wherein, The volumetric energy density of the secondary battery is ≥420Wh / L.

18. An electrical device comprising a secondary battery as described in any one of claims 1 to 17.

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