Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device. The secondary battery comprises a positive pole piece, a negative pole piece and an electrolyte, a positive electrode film layer in the positive electrode plate comprises an iron-lithium positive electrode active material, and a negative electrode film layer in the negative electrode plate comprises a silicon-based material and a carbon-based material; a solvent of the electrolyte comprises a cyclic ester solvent and a chain ester solvent. The secondary battery adopts an iron-lithium type positive electrode active material, has relatively high energy density, and is good in cycle performance and long in service life.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] In recent years, the application scope of secondary batteries such as lithium-ion batteries has become increasingly wide, and they have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles and other fields. As secondary batteries have made great progress, higher requirements have been put forward for their energy density, cycle performance and safety performance.

[0004] Iron-lithium cathode active materials are one of the main types of cathode active materials for secondary batteries. The improvement of their energy density faces a technical bottleneck. The volume energy density of traditional secondary batteries using iron-lithium cathode active materials is difficult to exceed 450Wh / L, which will seriously limit the application of batteries with iron-lithium cathode active material systems in vehicles with high mileage requirements. Some methods use high coating weight or high compaction density to make them have higher energy density, but such methods will cause secondary batteries to face a decline in cycle performance and life. Summary of the invention

[0005] Based on this, the present application provides a secondary battery, which uses an iron-lithium positive electrode active material and has high energy density, good cycle performance and long life. The present application also provides an electrical device including the secondary battery.

[0006] The present application provides a secondary battery, comprising a positive electrode plate, a negative electrode plate and an electrolyte; the positive electrode film layer in the positive electrode plate comprises an iron-lithium positive electrode active material, and the negative electrode film layer in the negative electrode plate comprises a silicon-based material and a carbon-based material; the solvent of the electrolyte comprises a cyclic ester solvent and a chain ester solvent.

[0007] The present application is directed to a battery system with iron-lithium positive electrode active materials. By introducing silicon-based materials and carbon-based materials into the negative electrode film layer for combination, and using cyclic ester solvents and chain ester solvents as solvents in the electrolyte, the secondary battery has a high volume energy density as well as good cycle performance and a long life.

[0008] In some embodiments, the mass ratio of the cyclic ester solvent to the chain ester solvent is (0.1-1):1. Reasonable control of the mass ratio of the cyclic ester solvent to the chain ester solvent can reasonably regulate the viscosity of the electrolyte and the degree of dissociation of the lithium salt, thereby improving the cycle performance of the secondary battery. Furthermore, the mass ratio of the cyclic ester solvent to the chain ester solvent is (0.2-0.5):1.

[0009] In some embodiments, the cyclic ester solvent includes one or more of ethylene carbonate, propylene carbonate and fluoroethylene carbonate; and / or the chain ester solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl acetate, ethyl propionate and methyl propionate.

[0010] In some embodiments, the cyclic ester solvent includes one or more of ethylene carbonate and fluoroethylene carbonate; and / or the chain ester solvent includes one or both of ethyl acetate and methyl acetate.

[0011] In some embodiments, in the electrolyte, the mass percentage of the chain ester solvent is 30% to 80%. Reasonable control of the proportion of the chain ester solvent can effectively alleviate the obstruction of the solid-liquid contact interface, reduce the deterioration of the interface caused by side reactions and the consumption of active materials, and achieve a better cycle life.

[0012] In some embodiments, the conductivity of the electrolyte is 12mS / cm to 18mS / cm. For a battery system with an iron-lithium positive electrode active material system, reasonable control of the conductivity of the electrolyte can reduce polarization while alleviating interface reactions, reduce the deterioration of active material consumption, and comprehensively improve cycle life.

[0013] In some embodiments, the compaction density of the positive electrode sheet is 2.5-2.9 g / cm 3 The chain ester solvent includes one or both of ethyl acetate and methyl acetate, and the conductivity of the electrolyte is 12mS / cm to 16mS / cm. Under the condition of high compaction density, reasonable control of the conductivity of the electrolyte can better support the ion migration dynamics during the charge and discharge process and alleviate the obstruction of the solid-liquid contact interface.

[0014] In some embodiments, the mass percentage of the silicon-based material in the negative electrode film layer is 3% to 15%. Reasonable control of the proportion of silicon-based materials in the negative electrode film layer can improve the polarization of the system, enhance the ion transfer kinetics, reduce the volume effect of silicon-based materials, enhance the interface stability between materials, reduce the consumption of active materials, and thus extend the life of the secondary battery while reducing the thickness of the electrode.

[0015] In some embodiments, the Dv50 of the silicon-based material is 5 μm to 15 μm.

[0016] In some embodiments, the silicon-based material includes a silicon-carbon material, and the silicon-carbon material includes a porous carbon matrix and a silicon material disposed in the pores of the porous carbon matrix. The pores of the porous carbon matrix can effectively alleviate the damage to the interface and the pole piece caused by the volume change of the silicon material during the lithium insertion and extraction process.

[0017] In some embodiments, the discharge specific capacity of the silicon-based material is 1200 mAh / g to 2000 mAh / g.

[0018] In some embodiments, the electrolyte includes an additive, and the additive includes a carbonate ester compound and a sulfate ester compound. The carbonate ester compound and the sulfate ester compound are used as electrolyte additives to alleviate the volume effect of the material and improve the interface stability of the material, thereby improving the cycle performance of the battery system.

[0019] In some embodiments, the carbonate ester compound has a structural feature shown in the following formula (I):

[0020] (I)

[0021] The sulfate compound has a structural feature shown in the following formula (II):

[0022] (II)

[0023] Wherein, R1, R2, R1, R2 each independently include H, F, C1~C4 alkyl or C1~C4 fluoroalkyl.

[0024] In some embodiments, 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%.

[0025] 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 to the sulfate compound meet one of the following conditions:

[0026] (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 ester compound to the sulfate ester compound is M1, 2:1≤M1≤5:1;

[0027] (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 ester compound to the sulfate ester compound is M2, 5:1<M2≤10:1.

[0028] According to the mass percentage of the silicon-based material in the negative electrode film layer, the proportion of the additives can be reasonably controlled to further improve the cycle performance and storage life of the battery.

[0029] In some embodiments, the volume energy density of the secondary battery is ≥420Wh / L.

[0030] The present application also provides an electric device, wherein the electric device comprises the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

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

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

[0034] Figure 3 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0035] Description of reference numerals:

[0036] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. DETAILED DESCRIPTION

[0037] In order to facilitate the 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 given 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.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0039] The "range" disclosed in the present application can be limited in the form of a lower limit and an upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The range limited in this way can be including or excluding end values, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents the abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0040] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0041] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0042] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0043] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0044] In this application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. If there is no other explanation, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A includes not only a1, a2 and a3, but also other members".

[0045] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0046] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0047] In the present application, "alkyl" refers to a monovalent residue formed by the loss of a hydrogen atom from a saturated hydrocarbon containing a primary (normal) carbon atom, a secondary carbon atom, a tertiary carbon atom, a quaternary carbon atom, or a combination thereof. Phrases containing this term, for example, "C1-C4 alkyl" refers to an alkyl containing 1 to 4 carbon atoms, and each occurrence may be independently C1 alkyl, C2 alkyl, C3 alkyl or C4 alkyl. 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" means that at least one H in "alkyl" is replaced by F.

[0048] Improving the cycle and life of secondary batteries with iron-lithium cathode active material systems with a volume energy density of ≥450Wh / L is a major challenge and has a huge application market. However, the traditional high coating weight (for example, positive electrode ≥25.9mg / cm², negative electrode ≥12.3mg / cm²) or high compaction density (for example, negative electrode PD ≥1.75g / cm³) methods usually reduce the cycle and life of secondary batteries. The possible reasons are: for the high coating weight method, the coating weight increases, and the coating weight also needs to increase synchronously when the type of active material remains unchanged. The corresponding electrode thickness increases, which deteriorates the electrode dynamics, reduces the fast charging performance, and increases the risk of lithium precipitation. It has been found that it will also cause uneven lithium distribution in the thickness direction of the negative electrode, and the state of charge (SOC) will gradually decrease from the surface to the inside. Excessive surface SOC will increase side reactions, thereby deteriorating the storage life; for the high compaction density method, the porosity of the electrode will be reduced, the liquid retention capacity will be weakened, the dynamics will be further deteriorated, and more active material particles will be broken, the reaction sites will increase, the first cycle lithium consumption will increase, and the cycle storage will also be deteriorated.

[0049] In addition, for battery systems using ternary materials as positive electrode materials, there are methods to increase the overall capacity of the battery by using silicon-based materials in the negative electrode. However, there is less research on the application of silicon-based materials in battery systems using iron-lithium positive electrode active materials. The possible reasons are: the initial efficiency of silicon-based materials is low, and more active lithium is consumed during the first charge and discharge process. The gram capacity of iron-lithium positive electrode active materials themselves is low, resulting in poor matching between the positive and negative electrodes.

[0050] Taking the above factors into consideration, one embodiment of the present application provides a secondary battery, including a positive electrode plate, a negative electrode plate and an electrolyte; the positive electrode film layer in the positive electrode plate contains an iron-lithium positive electrode active material, and the negative electrode film layer in the negative electrode plate contains a silicon-based material and a carbon-based material; the solvent of the electrolyte includes a cyclic ester solvent and a chain ester solvent.

[0051] The present application is directed to a battery system of iron-lithium positive electrode active materials. By introducing silicon-based materials and carbon-based materials into the negative electrode film layer for coordination, the silicon-based materials with high specific capacity can effectively reduce the load of the negative electrode plate in the battery system while making the battery system have better energy density, reduce the compaction density of the negative electrode plate, and improve the deterioration of the life due to the uneven distribution of lithium in the thickness direction of the plate. Accordingly, cyclic ester solvents and chain ester solvents are used as solvents in the electrolyte to make the electrolyte have a suitable viscosity and dissociation of electrolyte salts, increase the active lithium content and transmission, so that the negative electrode plate of the silicon-based material and the carbon-based material composite and the positive electrode plate of the iron-lithium positive electrode active material can be better adapted, and the cycle performance of the secondary battery can be improved. In this way, the battery system of the iron-lithium positive electrode active material has a high volume energy density while also having good cycle performance and a long life.

[0052] In some embodiments, the compaction density of the negative electrode sheet is 1.4 g / cm 3 ~1.7g / cm 3 .

[0053] In some embodiments, the volume energy density (VED) of the secondary battery is ≥420Wh / L.

[0054] In some embodiments, the iron-lithium positive electrode 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 iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0055] In some embodiments, the mass ratio of the cyclic ester solvent to the chain ester solvent is (0.1~1):1. Reasonable control of the mass ratio of the cyclic ester solvent to the chain ester solvent can reasonably regulate the viscosity of the electrolyte and the degree of dissociation of the lithium salt, thereby improving the cycle performance of the secondary battery. Specifically, the mass ratio of the cyclic ester solvent to 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 to the chain ester solvent is (0.2~0.5):1. Furthermore, the mass ratio of the cyclic ester solvent to the chain ester solvent is (0.3~0.4):1.

[0056] Without limitation, the cyclic ester solvent includes one or more of ethylene carbonate, propylene carbonate and fluoroethylene carbonate. Further, the cyclic ester solvent includes one or more of ethylene carbonate and fluoroethylene carbonate.

[0057] Without limitation, the chain ester 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 solvent includes one or more of dimethyl carbonate, ethyl methyl carbonate, ethyl acetate and methyl acetate. Further, the chain ester solvent includes one or both of ethyl acetate and methyl acetate.

[0058] In some embodiments, the conductivity of the electrolyte is 12mS / cm~18mS / cm. For a battery system with an iron-lithium positive electrode active material system, reasonable control of the conductivity of the electrolyte can reduce polarization while alleviating interfacial reactions, reduce deterioration of active material consumption and gas production, and comprehensively improve cycle life. Specifically, the conductivity of the electrolyte includes but is not limited to: 12mS / cm, 13mS / cm, 14mS / cm, 15mS / cm, 16mS / cm, 17mS / cm, 18mS / cm or a range between any two of the foregoing.

[0059] In some embodiments, the compaction density of the positive electrode sheet is 2.5 g / cm 3 ~2.9g / cm 3. The use of a positive electrode plate with a higher compaction density can use a higher active material coating weight and reduce the increase in thickness, further improving the volume energy density of the secondary battery. Furthermore, the chain ester solvent includes a first chain ester solvent, the first chain ester solvent includes ethyl acetate and / or methyl acetate, and the conductivity of the electrolyte is 12mS / cm~16mS / cm. In the case of a higher compaction density, by using ethyl acetate and / or methyl acetate as the chain ester solvent and reasonably controlling the conductivity of the electrolyte, it is possible to better support the ion migration dynamics during the charge and discharge process and alleviate the obstruction of the solid-liquid contact interface, so as to better adapt to the high-pressure and high-density positive electrode plate design under high energy density conditions.

[0060] Further, in the electrolyte, the mass percentage of the first chain ester solvent is 30% to 80%. Reasonable control of the proportion of the first chain ester solvent can effectively alleviate the obstruction of the solid-liquid contact interface while reducing the deterioration of the interface by side reactions and the consumption of active materials, thereby achieving a 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 the 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 the range between any two of the foregoing.

[0061] In addition, in some embodiments, the mass percentage of the silicon-based material in the negative electrode film layer is 3% to 15%. Reasonable control of the proportion of silicon-based materials in the negative electrode film layer can improve the polarization of the system, enhance the ion transfer kinetics, reduce the volume effect of silicon-based materials, enhance the interface stability between materials, reduce the consumption of active materials, and thus increase the life of the secondary battery while reducing the thickness of the pole piece. 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.

[0062] Without limitation, the silicon-based material may include one or more of elemental silicon, silicon-oxygen compounds, silicon-carbon materials, silicon-nitrogen compounds, and silicon alloys.

[0063] 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 disposed in the pores of the porous carbon matrix. By utilizing the pores of the porous carbon matrix, the damage to the interface and the pole piece caused by the volume change of the silicon material during the lithium insertion and extraction process can be effectively alleviated. Without limitation, the silicon material is nano-silicon, and the material of the porous carbon matrix is ​​hard carbon.

[0064] In some embodiments, the specific discharge capacity of the silicon-based material is 1500mAh / g~2300mAh / g. Specifically, the specific discharge capacity of the silicon-based material includes but is not limited to: 1500mAh / g, 1600mAh / g, 1700mAh / g, 1800mAh / g, 1900mAh / g, 2000mAh / g, 2100mAh / g, 2200mAh / g, 2300mAh / g, or a range between any two of the foregoing. Reasonably control the specific discharge capacity of the silicon-based material to obtain a higher first effect while reducing problems such as poor stability and deterioration of life caused by material expansion. Further, the specific discharge capacity of the silicon-based material is 1700mAh / g~1900mAh / g.

[0065] Without limitation, the carbon-based material includes one or more of artificial graphite, natural graphite, soft carbon and hard carbon.

[0066] In some embodiments, the electrolyte includes an additive, and the additive includes one or both of a carbonate ester compound and a sulfate ester compound. Further, the additive includes a carbonate ester compound and a sulfate ester compound. The use of carbonate ester compounds and sulfate ester compounds 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.

[0067] In some embodiments, the carbonate ester compound has a structural feature shown in the following formula (I):

[0068]

[0069] Wherein, R1 and R2 each independently include H, F, C1~C4 alkyl or C1~C4 fluoroalkyl.

[0070] In some embodiments, the carbonate compound includes one or more of vinylene carbonate, propylene carbonate, butylene carbonate and dimethyl vinylene carbonate.

[0071] In some embodiments, the carbonate compound includes vinylene carbonate. Vinylene carbonate is a cyclic film-forming additive containing unsaturated bonds. It can generate organic and polymeric interface films during the charge and discharge process and has good adaptability to the volume effect of the lithium extraction / insertion process. Further, in the electrolyte, the mass percentage of the vinylene carbonate is 1%~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. Furthermore, in the electrolyte, the mass percentage of the vinylene carbonate is 2%~6%.

[0072] In some embodiments, the sulfate compound has a structural feature shown in the following formula (II):

[0073]

[0074] Wherein, R1, R2, R1, R2 each independently include H, F, C1~C4 alkyl or C1~C4 fluoroalkyl.

[0075] In some embodiments, the sulfate ester compound includes one or more of vinyl sulfate, propylene sulfate and bis(methylvinyl sulfate).

[0076] In some embodiments, the sulfate ester compound includes vinyl sulfate. Vinyl sulfate can participate in the reaction at the interface to generate sulfate and sulfite substances, effectively improving the thermal stability and chemical stability of the interface. Further, in the electrolyte, the mass percentage of vinyl sulfate is 0.1%~3%. Specifically, the mass percentage of 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. Furthermore, in the electrolyte, the mass percentage of vinyl sulfate is 0.3%~1%.

[0077] Furthermore, the particle size distribution of silicon-based materials and the mass percentage of silicon-based materials in the negative electrode film layer are related to the reaction specific surface area, and also affect the characteristics of the solid-liquid reaction interface. In some embodiments, the mass ratio of carbonate compounds and sulfate compounds in the electrolyte is reasonably controlled according to the particle size distribution of silicon-based materials and the mass percentage of silicon-based materials in the negative electrode film layer. Carbonate compounds generate organic interface components, and sulfate compounds tend to generate inorganic sulfates. The two are compounded in a certain mass ratio, which can better adapt to the volume effect of silicon-based materials in the negative electrode film layer and the high reactivity of the interface under high temperature and high SOC environment, improve the stability of solid-liquid interface performance, and thus improve the life of the secondary battery.

[0078] In some embodiments, the Dv50 of the silicon-based material is 5 μm to 15 μm. Specifically, the Dv50 of the silicon-based material includes but is not limited to: 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 13 μm, 15 μm or a range between any two of the foregoing. Further, the Dv50 of the silicon-based material is 7 μm to 12 μm.

[0079] In addition, according to the mass percentage of the silicon-based material in the negative electrode film layer, the proportion of the additives can be reasonably controlled to 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 to the sulfate compound meet one of the following conditions:

[0080] (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 ester compound to the sulfate ester 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 ester compound to the sulfate ester 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;

[0081] (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 ester compound to the sulfate ester 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; the mass ratio of the carbonate ester compound to the sulfate ester 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.

[0082] In addition, 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 bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorobis(oxalate phosphate) (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP). Further, the lithium salt includes one or two of lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide salt. Without limitation, in the electrolyte, the concentration of the lithium salt 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, in the electrolyte, the concentration of the lithium salt is 0.8 mol / L to 1.1 mol / L.

[0083] Without limitation, the secondary battery of the present application will be further described below with reference to the accompanying drawings as appropriate.

[0084] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0085] 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, wherein the positive electrode film layer includes a positive electrode active material.

[0086] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0087] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may 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 may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0088] In some embodiments, the positive electrode active material includes an iron-lithium positive electrode active material. In addition, the positive electrode active material may also include other positive electrode active materials for batteries known in the art. As a non-limiting example, the positive electrode active material may also include one or more of the following materials: lithium transition metal oxides and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as 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 their modified compounds. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may 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 referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0089] In some of the embodiments, the positive electrode film layer may also optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0090] In some embodiments, the positive electrode film layer may further include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0091] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt%~80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s~25000mPa·s. When applying the positive electrode slurry, the coating unit surface density based on dry weight (excluding solvent) can be 15 mg / cm 2 ~35mg / cm 2 .

[0092] The negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material.

[0093] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0094] In some of the embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0095] In some embodiments, the negative electrode active material includes a silicon-based material and a carbon-based material. In addition, the negative electrode active material may also include other negative electrode active materials for batteries known in the art. As a non-limiting example, the negative electrode active material may also include one or more of the following materials: tin-based materials and lithium titanate, etc. Tin-based materials may 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 traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0096] In some embodiments, the negative electrode film layer may further include a binder. The binder may 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).

[0097] In some embodiments, the negative electrode film layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0098] In some of the embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0099] In some of the embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 40wt%~60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s~10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 ~220g / m 2 .

[0100] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode.

[0101] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0102] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0103] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0104] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0105] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0106] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging 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 plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0107] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0108] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0109] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 1 The secondary battery 1 is a square structure as an example.

[0110] In some of these embodiments, reference Figure 2 , the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity. The shell 11 has an opening connected to the accommodating cavity, and the cover plate 13 can be covered on the opening to close the accommodating cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the accommodating cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to actual needs.

[0111] The secondary battery may be a battery module or a battery pack.

[0112] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0113] In the battery module, the plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0114] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells are accommodated in the accommodation space.

[0115] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0116] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0117] In addition, another embodiment of the present application provides an electrical device. The electrical device includes the above-mentioned secondary battery. The secondary battery can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited to these. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, 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 are not limited to these.

[0118] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0119] Figure 3 The power consumption device 2 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0120] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0121] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0122] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0123] Example 1

[0124] 1) Preparation of positive electrode

[0125] Lithium iron phosphate, conductive carbon black SP and binder PVDF were dispersed in a solvent NMP at a weight ratio of 98%:1%:1% and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry was evenly coated on both sides of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode sheet was obtained, wherein the coating amount per unit area on both sides was 0.27g / 1540.25mm 2 , compacted density is 2.8g / cm 3 .

[0126] 2) Preparation of negative electrode sheet

[0127] The negative electrode active material natural graphite, silicon-carbon material (commercially available product, hard carbon with nano-silicon deposited in the pores, discharge specific capacity of 1600mAh / g, Dv50 of 10μm), thickener sodium carboxymethyl cellulose, adhesive styrene-butadiene rubber, conductive agent acetylene black are mixed in a mass ratio of 93%:4%:1%:1%:1%, deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on both sides of the copper foil; the copper foil is dried at room temperature and then transferred to a 120°C oven for drying for 1h, and then super-cold pressed and cut to obtain a negative electrode sheet, wherein the coating amount per unit area on both sides is 0.17g / 1540.25mm 2 , compacted density is 1.5g / cm 3 .

[0128] 3) Isolation film

[0129] A 12μm thick polypropylene isolation film was selected.

[0130] 4) Preparation of electrolyte

[0131] The organic solvent is a mixture of ethylene carbonate, ethyl acetate, and dimethyl carbonate in a mass ratio of 25%:55%:20%. In an argon atmosphere glove box with a water content of <10ppm, fully dried lithium salt LiPF6 and additives are dissolved in the organic solvent and mixed evenly to obtain an electrolyte with a conductivity of 15 mS / cm. Among them, the concentration of the lithium salt is 1 mol / L, and the additives are 2.5% by mass of vinyl carbonate in the electrolyte and 1% by mass of vinyl sulfate in the electrolyte.

[0132] 5) Preparation of batteries

[0133] The positive electrode sheet, isolation film, and negative electrode sheet are stacked in order, so that the isolation film is placed between the positive and negative electrode sheets to play an isolating role. Then, they are wound into a square bare battery cell, loaded with aluminum-plastic film, and then baked at 80°C to remove water. After that, 10g of the corresponding non-aqueous electrolyte is injected and sealed. After standing, hot and cold pressing, formation, clamping, capacity division and other processes, a finished battery with a capacity of 4000mAh is obtained.

[0134] The secondary battery preparation process of Examples 2-3 is the same as that of Example 1, with the main difference being that the mass ratio of the cyclic ester solvent to the chain ester solvent is changed.

[0135] The secondary battery preparation process of Examples 4-5 is the same as that of Example 1, with the main difference being that the mass percentage of ethyl acetate in the electrolyte is changed, and the mass percentage of dimethyl carbonate is increased or decreased accordingly to keep the mass ratio of the cyclic ester solvent to the chain ester solvent unchanged.

[0136] The secondary battery preparation process of Example 6 is the same as that of Example 1, with the main difference being that ethyl acetate in the electrolyte is replaced with methyl acetate, and the mass percentage is changed, and the mass percentage of dimethyl carbonate is increased accordingly to keep the mass ratio of cyclic ester solvents to chain ester solvents unchanged.

[0137] The secondary battery preparation process of Examples 7 to 12 is the same as that of Example 1, with the main difference being that the composition of the additives is changed.

[0138] The secondary battery preparation process of Example 13 is the same as that of Example 1, with the main difference being that no additive is used.

[0139] The secondary battery preparation process of Comparative Example 1 (D1) is the same as that of Example 1, except that no silicon-carbon material is used, that is, the negative electrode active material natural graphite, the thickener sodium carboxymethyl cellulose, the adhesive styrene-butadiene rubber, and the conductive agent acetylene black are mixed in a mass ratio of 97%:1%:1%:1%.

[0140] The secondary battery preparation process of Comparative Example 2 (D2) is the same as that of Example 1, with the main difference being that no chain ester solvent is used, that is, the organic solvent is only ethylene carbonate.

[0141] The secondary battery preparation process of Comparative Example 3 (D3) is the same as that of Example 1, except that no cyclic ester solvent is used, that is, the organic solvent is ethyl acetate and dimethyl carbonate in a mass ratio of 73%:27%.

[0142] The preparation parameters of the secondary batteries of Examples 1 to 13 and Comparative Examples 1 to 3 are summarized in Table 1 below.

[0143] Table 1

[0144]

[0145] Test Case

[0146] (1) Volumetric energy density

[0147] The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, and the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role. The electrode assembly is then wound and placed in an aluminum shell (V=0.411L) with a thickness of 28.5mm, a width of 148mm, and a height of 97.5mm. The shell group margin is 92%. After drying, the electrolyte is injected, and a secondary battery is obtained through vacuum packaging, standing, formation, shaping and other processes.

[0148] Place the secondary battery in a 25°C environment, charge it to 3.8V at a rate of 0.33C, hold it at a constant voltage of 3.8V to 0.05C, let it rest for 10 minutes, then discharge it to 2.0V at a rate of 0.33C and let it rest for 10 minutes. Repeat the above steps 3 times, extract the energy W (unit: Wh) of the last discharge at 0.33C to 2V, and then calculate the energy density VED, VED=W / V (unit: Wh / L).

[0149] (2) Cycle performance

[0150] At 45°C, the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 0.5 C to a charge cut-off voltage of 3.8V, then charged at a constant voltage to a current of ≤0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33 C to a discharge cut-off voltage of 2V, left to stand for 5 minutes. This was a charge and discharge cycle. The battery was subjected to a cyclic charge and discharge test according to this method, and the capacity retention rate of the lithium-ion battery after 1000 cycles was calculated.

[0151] (3) Storage life

[0152] At 25°C, the secondary batteries prepared in the embodiments and comparative examples were charged at a constant current of 0.5 C to a charge cut-off voltage of 3.8 V, then charged at a constant voltage to a current ≤ 0.05 C, left standing for 5 min, and then discharged at a constant current of 0.33 C to a discharge cut-off voltage of 2 V, left standing for 5 min. This was one charge and discharge cycle.

[0153] Then the battery was charged at a constant current of 0.5 C rate to a charge cut-off voltage of 3.8 V, and then charged at a constant voltage to a current ≤ 0.05C. After the battery was stored at 60°C for 300 days, the battery was subjected to a cyclic charge and discharge test according to the above method, and the capacity retention rate of the lithium-ion battery after 300 days of storage was calculated.

[0154] The test results are shown in Table 2.

[0155] Table 2

[0156]

[0157] By comparing Examples 1 to 13 with Comparative Example 1, it can be seen that the examples can improve the volume energy density of the battery by combining carbon-based materials and silicon-based materials as negative electrode active materials, while also maintaining high cycle performance and storage life.

[0158] By comparing Examples 1 to 13 with 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 cyclic ester solvent and a chain ester solvent as a solvent.

[0159] From the comparison between Examples 1 to 3, it can be seen that the reasonable regulation of the mass ratio of the cyclic ester solvent to the chain ester solvent can further improve the cycle performance and storage life of the battery.

[0160] By comparing Examples 1 with Examples 4 to 5, it can be seen that the reasonable regulation 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.

[0161] From the comparison between 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.

[0162] By comparing Examples 1 with 7 to 10, it can be seen that the cycle performance and storage life of the battery can be further improved by rationally adjusting the proportions of the two additives in the electrolyte according to the mass percentage of the silicon-based material in the negative electrode film layer.

[0163] By comparing Examples 1 with Examples 11-12, it can be seen that, compared with using only carbonate compounds or sulfate compounds as additives, the synergy of the two can better improve the cycle performance and storage life of the battery.

[0164] By comparing Examples 1 with Examples 11 to 13, it can be seen that using carbonate compounds and / or sulfate compounds as additives can further improve the cycle performance and storage life of the battery.

[0165] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0166] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations 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 shall be subject to the attached claims.

Claims

1. A secondary battery, characterized in that: It includes a positive electrode plate, a negative electrode plate and an electrolyte; the positive electrode film layer in the positive electrode plate contains an iron-lithium positive electrode active material, and the negative electrode film layer in the negative electrode plate contains a silicon-based material and a carbon-based material; the solvent of the electrolyte includes a cyclic ester solvent and a chain ester solvent.

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

1.

3. The secondary battery according to claim 2, characterized in that: 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, characterized in that: The cyclic ester solvent includes one or more of ethylene carbonate, propylene carbonate and fluoroethylene carbonate; and / or The chain ester solvent includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, methyl acetate, ethyl propionate and methyl propionate.

5. The secondary battery according to claim 4, characterized in that: The cyclic ester solvent includes one or more of ethylene carbonate and fluoroethylene carbonate; and / or The chain ester solvent includes one or both of ethyl acetate and methyl acetate.

6. The secondary battery according to claim 5, characterized in that: 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, characterized in that: The conductivity of the electrolyte is 12mS / cm~18mS / cm.

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

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

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

11. The secondary battery according to any one of claims 1 to 10, characterized in that: The silicon-based material includes a silicon-carbon material, and the silicon-carbon material includes a porous carbon matrix and a silicon material disposed in pores of the porous carbon matrix.

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

13. The secondary battery according to any one of claims 1 to 12, characterized in that: The electrolyte includes additives, and the additives include carbonate ester compounds and sulfate ester compounds.

14. The secondary battery according to claim 13, characterized in that: The carbonate compound has the structural characteristics shown in the following formula (I): （I） The sulfate compound has a structural feature shown in the following formula (II): (II) Wherein, R1, R2, R1, R2 each independently include H, F, C1~C4 alkyl or C1~C4 fluoroalkyl.

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

16. The secondary battery according to any one of claims 13 to 15, characterized in that: The mass percentage of the silicon-based material in the negative electrode film layer and the mass ratio of the carbonate ester compound to the sulfate ester compound meet one of the following conditions: (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 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 layer 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, characterized in that: The volume energy density of the secondary battery is ≥420Wh / L.

18. An electrical device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 1 to 17.

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