Secondary battery and electric device

Abstract

The invention discloses a secondary battery and an electric device, and belongs to the technical field of batteries. According to the secondary battery provided by the invention, a specific type of substance is selected as an organic solvent, meanwhile, an appropriate type of electrolyte additive is selected, and further, the mass percent of cyclic carbonate, linear carbonate, a compound A, a compound B and a compound C in the electrolyte is established, so that the mass percent of the compound A, the compound B and the compound C is increased; the relationship between the electrolyte retention coefficient of the electrolyte and the addition amount of the silicon-based material makes the secondary battery satisfy 43 < = (alpha + beta) * ln (sigma * x + 2gamma) * 2 / min (x * v, sigma w / v, w * alpha / beta) < = 1090; the obtained secondary battery has excellent high-temperature cycle and storage stability, and the obtained secondary battery has excellent thermal shock resistance.

Description

Technical Field

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

[0002] Among the various commercially available graphite materials, graphite has essentially reached its theoretical capacity limit (372 mAh / g). Simply increasing the capacity of graphite alone is ineffective in increasing the capacity of the negative electrode. Silicon doping of the negative electrode is currently one of the most effective methods for increasing its capacity. Silicon has a theoretical capacity of up to 4200 mAh / g, far exceeding that of graphite (372 mAh / g). Therefore, doping a certain proportion of silicon into the negative electrode can significantly increase its capacity. However, the introduction of silicon into the negative electrode significantly reduces the battery's initial coulombic efficiency (ICE), impacting its full capacity. To address this issue, lithium-rich ferrite (Li5FeO4) can be incorporated into the battery to effectively improve its ICE. Currently, lithium-rich ferrite (Li5FeO4) is the most commercially promising lithium-rich ferrite material. Its use as a lithium-rich ferrite material requires no major changes to production lines or processes, resulting in a relatively low cost. However, it also presents a number of challenges, such as cell gassing at high voltages, intense gassing during high-temperature storage, and a significant deterioration in thermal shock resistance.

[0003] Therefore, there is an urgent need to develop an electrolyte that is suitable for the high-voltage lithium cobalt oxide + Li5FeO4-graphite / silicon mixed negative electrode system, which can suppress the gas production problem of the system and improve the thermal shock resistance of the battery cell. Summary of the Invention

[0004] The purpose of the present application is to provide a secondary battery and an electrical device to solve the problem that the prior art cannot solve that a silicon-containing battery system using lithium cobalt oxide as the positive electrode active material and lithium ferrite (Li5FeO4) as a lithium supplement will cause high-temperature storage and circulation gas production and thermal shock failure temperature is too low.

[0005] To achieve the above objectives, in a first aspect, the present application provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the electrolyte comprises an organic solvent, an additive A, and a lithium salt, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector;

[0006] The organic solvent includes cyclic carbonate substances and linear carbonate substances;

[0007] The additive A includes compound A, compound B and compound C;

[0008] The positive electrode active material layer includes lithium cobalt oxide, Li5FeO4, a positive electrode conductor and a positive electrode binder;

[0009] The negative electrode active material layer includes a silicon-based material, graphite, a negative electrode conductor, a thickener and a negative electrode binder;

[0010] The structural formulas of the compounds A to C are shown in Formulas I to III, respectively:

[0011]

[0012] Wherein, R1 is selected from fluorinated or non-fluorinated alkyl, alkenyl, alkynyl, and aromatic groups;

[0013] R2 to R6 are each independently selected from substituted or unsubstituted alkyl, alkenyl, alkynyl, and alkoxy;

[0014] R7 is selected from substituted or unsubstituted fluorinated aromatic groups;

[0015] R8~R 10 Each is independently selected from substituted or unsubstituted aromatic groups;

[0016] The secondary battery satisfies 43≤Y≤1090,

[0017] Among them, Y=(α+β)*ln(σ*x+2γ)*2 / min(x*v,σw / v,w*α / β);

[0018] α% is the mass percentage of cyclic carbonate based on the total mass of the electrolyte;

[0019] β% is the mass percentage of linear carbonate based on the total mass of the electrolyte;

[0020] γ% is the mass percentage of compound A based on the total mass of the electrolyte;

[0021] w% is the mass percentage of compound B based on the total mass of the electrolyte;

[0022] x% is the mass percentage of compound C based on the total mass of the electrolyte;

[0023] σg / Ah is the electrolyte retention coefficient;

[0024] v% is the mass percentage of the silicon-based material based on the total mass of the negative electrode active material layer.

[0025] As an embodiment of the present application, the secondary battery satisfies 115≤Y≤326.

[0026] As an embodiment of the present application, the mass percentage α% of the cyclic carbonate is 1% to 20% based on the total mass of the electrolyte.

[0027] As an embodiment of the present application, the mass percentage β% of the linear carbonate is 0.4% to 10% based on the total mass of the electrolyte.

[0028] As an embodiment of the present application, the mass percentage γ% of compound A is 0.3% to 3% based on the total mass of the electrolyte.

[0029] As an embodiment of the present application, based on the total mass of the electrolyte, the mass percentage w% of compound B is 0.3% to 3%.

[0030] As an embodiment of the present application, the mass percentage x% of compound C is 0.3% to 3% based on the total mass of the electrolyte.

[0031] As an embodiment of the present application, the electrolyte has a liquid retention coefficient σ of 1.0 to 1.3 g / Ah.

[0032] As an embodiment of the present application, the mass percentage v% of the silicon-based material is 3% to 20% based on the total mass of the negative electrode active material layer.

[0033] As an embodiment of the present application, the compound A includes at least one of 4-methoxyphenyl trifluoromethanesulfonate and p-tolyl trifluoromethanesulfonate.

[0034] As an embodiment of the present application, the compound B includes at least one of 3,5-bis(trifluoromethyl)benzeneacetonitrile and 2-trifluoromethylbenzonitrile.

[0035] As an embodiment of the present application, the compound C includes at least one of 4-fluorophenylboronic anhydride and 2,4,6-tris(3,4,5-trifluorophenyl)boroxine.

[0036] As an embodiment of the present application, the cyclic carbonate includes at least one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), bisfluoroethylene carbonate, and 3,3,3-trifluoropropylene carbonate.

[0037] As an embodiment of the present application, the linear carbonate includes at least one of dimethyl carbonate (DMC) and diethyl carbonate (DEC).

[0038] As an embodiment of the present application, the electrolyte further includes an additive B, and the additive B includes at least one of 1,3-propane sultone (PS), dithiothreitol (DTD), tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

[0039] As an embodiment of the present application, the mass percentage of the additive B is 0.1% to 20% based on the total mass of the electrolyte.

[0040] As an embodiment of the present application, the mass percentage of the lithium salt is 8% to 25% based on the total mass of the electrolyte.

[0041] As an embodiment of the present application, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, and lithium bisfluorosulfonyl imide.

[0042] As an embodiment of the present application, the silicon-based material includes at least one of silicon carbon and silicon oxygen.

[0043] As an embodiment of the present application, the organic solvent further includes at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, methyl butyrate, butyl butyrate, and ethyl difluoroacetate.

[0044] In a second aspect of the present application, the present application provides an electrical device, which includes the secondary battery described in the present application.

[0045] Compared with the prior art, the present invention has the following advantages:

[0046] The present application provides a secondary battery by selecting a specific type of substance as an organic solvent and selecting a suitable type of electrolyte additive. Furthermore, the present application establishes the relationship between the mass percentages of cyclic carbonate, linear carbonate, compound A, compound B and compound C in the electrolyte, the liquid retention coefficient of the electrolyte and the mass percentage of the silicon-based material, so that the secondary battery satisfies 43≤(α+β)*ln(σ*x+2γ)*2 / min(x*v,σw / v,w*α / β)≤1090; the obtained secondary battery can effectively solve the problem of serious gas generation during storage or circulation at high temperature in silicon-containing system batteries using lithium cobalt oxide and lithium ferrite lithium supplements as positive electrode active materials; that is, the obtained secondary battery has excellent high-temperature cycling and storage stability, and the obtained secondary battery has excellent thermal shock resistance. DETAILED DESCRIPTION

[0047] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0048] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0049] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0050] The reagents and instruments used in this application without manufacturer indication are all conventional products that can be purchased commercially.

[0051] In one embodiment of the present application, the present application provides a secondary battery, the secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, the electrolyte comprising an organic solvent, an additive A and a lithium salt, the positive electrode sheet comprising a positive electrode collector and a positive electrode active material layer disposed on at least one surface of the positive electrode collector, the negative electrode sheet comprising a negative electrode collector and a negative electrode active material layer disposed on at least one surface of the negative electrode collector;

[0052] The organic solvent includes cyclic carbonate substances and linear carbonate substances;

[0053] The additive A includes compound A, compound B and compound C;

[0054] The positive electrode active material layer includes lithium cobalt oxide, Li5FeO4, a positive electrode conductor and a positive electrode binder;

[0055] The negative electrode active material layer includes a silicon-based material, graphite, a negative electrode conductor, a thickener and a negative electrode binder;

[0056] The structural formulas of the compounds A to C are shown in Formulas I to III, respectively:

[0057]

[0058] Wherein, R1 is selected from fluorinated or non-fluorinated alkyl, alkenyl, alkynyl, and aromatic groups;

[0059] R2 to R6 are each independently selected from substituted or unsubstituted alkyl, alkenyl, alkynyl, and alkoxy;

[0060] R7 is selected from substituted or unsubstituted fluorinated aromatic groups;

[0061] R8~R 10Each is independently selected from substituted or unsubstituted aromatic groups;

[0062] The secondary battery satisfies 43≤Y≤1090,

[0063] Among them, Y=(α+β)*ln(σ*x+2γ)*2 / min(x*v,σw / v,w*α / β);

[0064] α% is the mass percentage of cyclic carbonate based on the total mass of the electrolyte;

[0065] β% is the mass percentage of linear carbonate based on the total mass of the electrolyte;

[0066] γ% is the mass percentage of compound A based on the total mass of the electrolyte;

[0067] w% is the mass percentage of compound B based on the total mass of the electrolyte;

[0068] x% is the mass percentage of compound C based on the total mass of the electrolyte;

[0069] σg / Ah is the electrolyte retention coefficient;

[0070] v% is the mass percentage of the silicon-based material based on the total mass of the negative electrode active material layer.

[0071] The present application has found that a secondary battery provided by the present application selects a specific type of substance as an organic solvent and a suitable type of electrolyte additive. Furthermore, the present application establishes the relationship between the mass percentages of cyclic carbonate, linear carbonate, compound A, compound B, and compound C in the electrolyte, the liquid retention coefficient of the electrolyte, and the amount of silicon-based material added, so that the secondary battery satisfies 43≤(α+β)*ln(σ*x+2γ)*2 / min(x*v,σw / v,w*α / β)≤1090; the obtained secondary battery can effectively solve the problem of severe gas generation during storage or circulation at high temperatures of silicon-containing batteries using lithium cobalt oxide as the positive electrode active material and adding lithium ferrite as a lithium supplement; that is, the obtained secondary battery has excellent high-temperature cycling and storage stability, and the obtained secondary battery has excellent thermal shock resistance. Specifically, if the value in the relationship satisfied by the secondary battery is less than 43, the electrolyte will not have sufficient protective effect on the positive and negative active materials, and will not be able to effectively suppress the side reactions of the secondary battery. The gas production problem will be more serious, and the secondary battery's thermal shock resistance will also be poor; if the value in the relationship satisfied by the secondary battery is greater than 1090, the thickness of the SEI film formed will be too thick, which will not only cause the initial impedance of the secondary battery to be higher, but also the impedance growth rate during the cycle will be faster, resulting in deterioration of the cycle performance, but also slow down the migration rate of lithium ions in the SEI film, deteriorating the rate performance and low-temperature discharge performance of the secondary battery.

[0072] Specifically, the compound A of the present application is a sulfonic acid ester compound, which has a lower HOMO energy and can be oxidized on the positive electrode surface in preference to the electrolyte solvent in the formation stage, which helps to reduce the electrolyte solvent consumption in the formation stage, while improving the stability of the positive electrode surface, reducing the structural collapse under high voltage and the transition metal ion dissolution caused by it, and a series of negative effects; it can also preferentially form a film on the negative electrode surface and cover the surface of the negative electrode active material, effectively blocking the electrolyte and the active material, and suppressing the side reaction between the two. The compound B selected by the present application is a nitrile compound, which can be adsorbed on the surface of the positive electrode active material, and the cyano group has a lone pair of electrons, which can be effectively complexed with transition metal ions, thereby effectively suppressing the transition metal ion dissolution of the positive terminal, while occupying the outermost empty orbit of the transition metal ion, suppressing its catalytic electrolyte decomposition, and the HOMO energy of the nitrile compound is relatively low, and the stability under high voltage is higher, which helps to improve the stability of the electrolyte under high voltage and improve the cycle performance of the secondary battery. The compound C provided in the present application is a boroxine compound. Compound A is introduced into the electrolyte. Its HOMO has a high energy and poor oxidation resistance. It is easy to decompose on the surface of the positive electrode. The product will cover the surface of the positive electrode. The product contains compounds with high bond energy and stability such as BO, BF, and BH-Al, which can effectively improve the heat resistance of the CEI film on the positive electrode surface. At the same time, due to the electron-deficient structure of B, it is easy to react with F and PF6 in the lithium salt compound. - Or other anionic groups can be combined to induce the formation of LiPO-rich x F y , LiF and other inorganic components, while alleviating the defects caused by the introduction of compound A, it improves the surface stability of the positive electrode and ensures that the CEI layer on the positive electrode surface has a high Li + The migration number can significantly improve the high temperature resistance of lithium-ion batteries while ensuring that the rate performance and low temperature discharge performance are not deteriorated.

[0073] For example, A can be any point value or any two point range values ​​between 43 and 1090, such as 43, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1090, etc.

[0074] In one embodiment, the secondary battery satisfies 115≤Y≤326. For example, A can be 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300, 310, 320, 326, etc.

[0075] The present application study found that when Y is further selected between 115 and 326, the resulting secondary battery has better stability at high temperatures, better high-temperature storage and cycle performance, and stronger resistance to thermal shock.

[0076] In one embodiment, based on the total mass of the electrolyte, the mass percentage α% of the cyclic carbonate is 1% to 20%.

[0077] It should be noted that the mass percentage α% of the cyclic carbonate based on the total mass of the electrolyte is obtained by gas chromatography (GC) testing.

[0078] Exemplarily, α can be any point value or any two-point range value between 1 and 20, such as 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 20, etc.

[0079] In one embodiment, based on the total mass of the electrolyte, the mass percentage β% of the linear carbonate is 0.4% to 10%.

[0080] It should be noted that the mass percentage β% of the linear carbonate, based on the total mass of the electrolyte, is obtained by gas chromatography (GC) testing.

[0081] Exemplarily, β can be any point value or any two point range values ​​between 0.4 and 10, such as 0.4, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc.

[0082] The present study found that by selecting appropriate mass percentages of cyclic carbonates and linear carbonates in the electrolyte, the two can interact with each other and with other components, thereby effectively improving the stability of the electrolyte, reducing the gas production of the battery at high temperature and high pressure, thereby improving the high-temperature storage and cycle performance of the secondary battery, and also improving the thermal shock resistance of the secondary battery.

[0083] In one embodiment, based on the total mass of the electrolyte, the mass percentage γ% of compound A is 0.3% to 3%.

[0084] It should be noted that the mass percentage γ% of compound A based on the total mass of the electrolyte is obtained by gas chromatography (GC) testing.

[0085] Exemplarily, γ can be any point value between 0.3 and 3 or any two point range values, such as 0.3, 0.5, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, etc.

[0086] In one embodiment, based on the total mass of the electrolyte, the mass percentage (w%) of compound B is 0.3% to 3%.

[0087] It should be noted that the mass percentage (w%) of compound B based on the total mass of the electrolyte is obtained by gas chromatography (GC) testing.

[0088] Exemplarily, w can be any point value between 0.3 and 3 or any two point range values, such as 0.3, 0.5, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, etc.

[0089] In one embodiment, based on the total mass of the electrolyte, the mass percentage x% of compound C is 0.3% to 3%.

[0090] It should be noted that the mass percentage x% of compound C based on the total mass of the electrolyte is obtained by gas chromatography (GC) testing.

[0091] Exemplarily, x can be any point value or any two point range values ​​between 0.3 and 3, such as 0.3, 0.5, 0.8, 1, 1.2, 1.4, 1.6, 1.8, 2, 2.2, 2.4, 2.6, 2.8, 3, etc.

[0092] The research in this application found that by introducing compound A, compound B and compound C with specific structures as additives, the interaction between the three can effectively improve the high-temperature stability of the silicon-doped lithium-supplemented system, significantly improve the gas production problem of the battery, and enhance the thermal stability of the battery; thereby effectively improving the thermal shock resistance of the secondary battery as well as the storage and cycle performance at high temperatures.

[0093] In one embodiment, the electrolyte has a liquid retention coefficient σg / Ah of 1.0 g / Ah to 1.3 g / Ah.

[0094] Exemplarily, the electrolyte retention coefficient σ can be any point value or any two point range values ​​between 1.0 and 1.3, for example, it can be 1.0, 1.02, 1.04, 1.06, 1.08, 1.1, 1.120, 1.14, 1.16, 1.18, 1.2, 1.22, 1.24, 1.26, 1.28, 1.3, etc.

[0095] The present study found that the electrolyte retention coefficient will affect the electrolyte's wetting effect on the positive and negative electrodes, thereby affecting the performance of the secondary battery. When the electrolyte retention coefficient σ is further selected to be within the above range, the overall performance of the secondary battery obtained is better.

[0096] It should be noted that the electrolyte retention coefficient can be altered by adjusting parameters during the secondary battery manufacturing process, such as changing the rest time after injection. For example, increasing the rest time after injection can increase the electrolyte retention coefficient; decreasing it can decrease it. Alternatively, the electrolyte retention coefficient can be altered by adjusting the platen pressure or vacuum time during secondary sealing.

[0097] In one embodiment, based on the total mass of the negative electrode active material layer, the mass percentage (v%) of the silicon-based material is 3% to 20%.

[0098] It should be noted that the mass percentage v% of the silicon-based material, based on the total mass of the negative electrode active material layer, is obtained through inductively coupled plasma spectrometry (ICP) testing.

[0099] Exemplarily, v can be any point value or any two point range value between 3 and 20, such as 3, 5, 7, 9, 10, 12, 14, 16, 18, 20, etc.

[0100] It should be noted that the mass percentage of silicon-based materials in the negative electrode active material layer will not only affect the stability of the negative electrode plate, but also affect the cycle performance and thermal shock resistance of the secondary battery at high temperature. When the mass percentage of silicon-based materials in the negative electrode active material layer is further selected to be within the range given in this application, the comprehensive performance of the secondary battery obtained is even better.

[0101] In one embodiment, the compound A includes at least one of 4-methoxyphenyl trifluoromethanesulfonate (CAS: 66107-29-7) and p-tolyl trifluoromethanesulfonate (CAS: 29540-83-8).

[0102] In one embodiment, the compound B includes at least one of 3,5-bis(trifluoromethyl)benzeneacetonitrile (CAS: 85068-32-2) and 2-trifluoromethylbenzonitrile (CAS: 447-60-9).

[0103] In one embodiment, the compound C includes at least one of 4-fluorophenylboronic anhydride (CAS: 448-59-9) and 2,4,6-tris(3,4,5-trifluorophenyl)boroxine (CAS: 223440-94-6).

[0104] In one embodiment, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and 3,3,3-trifluoropropylene carbonate.

[0105] In one embodiment, the linear carbonate includes at least one of dimethyl carbonate and diethyl carbonate.

[0106] The present application study found that when compound A, compound B, compound C, cyclic carbonate and linear carbonate are further selected as the above substances, the gas production of the secondary battery under high temperature and high pressure can be better reduced, and the thermal shock resistance and storage and cycle performance of the secondary battery under high temperature can be improved.

[0107] In one embodiment, the electrolyte further includes an additive B, and the additive B includes at least one of 1,3-propane sultone (PS), dithiothreitol (DTD), tris(trimethylsilyl)borate (TMSB), and tris(trimethylsilyl)phosphate (TMSP).

[0108] The additive B provided in this application is a film-forming additive. The selection of the above-mentioned type of film-forming additive can better cooperate with compound A, compound B, compound C, cyclic carbonate, and linear carbonate to improve the overall performance of the secondary battery.

[0109] In one embodiment, the mass percentage of the additive B is 0.1% to 20% based on the total mass of the electrolyte.

[0110] It should be noted that the mass percentage of additive B based on the total mass of the electrolyte is obtained by gas chromatography (GC) testing.

[0111] Illustratively, based on the total mass of the electrolyte, the mass percentage of additive B can be any point value between 0.1% and 20% or any two point range values, such as 0.1%, 1%, 3%, 5%, 7%, 9%, 10%, 12%, 14%, 16%, 18%, 20%, etc.

[0112] In one embodiment, the mass percentage of the lithium salt is 8% to 25% based on the total mass of the electrolyte.

[0113] It should be noted that the mass percentage of the lithium salt based on the total mass of the electrolyte is obtained through ion chromatography (IC) testing.

[0114] Illustratively, based on the total mass of the electrolyte, the mass percentage of the lithium salt can be any point value between 8% and 25% or any two points in the range, such as 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 25%, etc.

[0115] In one embodiment, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiODFP), lithium tetrafluorooxalatophosphate (LiOTFP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI) and lithium bis(fluorosulfonyl imide) (LiFSI).

[0116] In one embodiment, the silicon-based material includes silicon carbon (SiC), silicon oxide (SiO x ) at least one of.

[0117] In one embodiment, the organic solvent further comprises at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, methyl butyrate, butyl butyrate, and ethyl difluoroacetate.

[0118] The present application has no restrictions on the selection of the positive electrode conductive agent, and the positive electrode conductive agent conventionally used in the art can be selected, such as at least one of SuperP, carbon nanotubes, and graphene.

[0119] The present application has no restrictions on the selection of positive electrode binders, and positive electrode binders commonly used in the art can be selected, such as at least one of PVDF, PTFE, CMC, and SBR.

[0120] The present application has no restrictions on the selection of the negative electrode conductive agent, and the negative electrode conductive agent conventionally used in the art can be selected, such as at least one of CNT, acetylene black, and Ketjen black.

[0121] The present application has no restrictions on the selection of thickeners, and thickeners commonly used in the art, such as sodium carboxymethyl cellulose, can be selected.

[0122] The present application has no restrictions on the selection of negative electrode binders, and negative electrode binders commonly used in the art can be selected, such as at least one of PVDF, PTFE, PAALi, CMC, and SBR.

[0123] The present application has no limitation on the diaphragm, and the diaphragm conventionally used in the art can be selected; for example, the material of the diaphragm can be polypropylene, polyethylene, or a composite of polypropylene and polyethylene, etc.

[0124] In a second aspect of the present application, the present application provides an electrical device comprising the secondary battery described in the present application.

[0125] Example 1

[0126] An embodiment of the present application provides a secondary battery, wherein a method for preparing the secondary battery comprises the following steps:

[0127] (1) Preparation of negative electrode sheet

[0128] Graphite, silicon-based material (SiC), conductive agent (carbon nanotubes CNT), thickener (sodium carboxymethyl cellulose), and negative electrode binder (lithium polyacrylate PAALi) are mixed according to the mass ratio of silicon-based material (SiC), conductive agent (carbon nanotubes CNT), thickener (sodium carboxymethyl cellulose), and negative electrode binder (polyacrylate PAA) of 97:0.8:1.2:1, and the mass ratio of graphite to silicon-based material is 5.64:1. Then, the mixture is added to deionized water, stirred thoroughly, and coated on copper foil. After drying, rolling, and slitting, the negative electrode sheet is obtained;

[0129] (2) Preparation of positive electrode sheet

[0130] The positive electrode material lithium cobalt oxide, lithium supplement agent (Li5FeO4), positive electrode conductive agent (Super P), and positive electrode binder (polyvinylidene fluoride PVDF) are thoroughly stirred and mixed in N-methylpyrrolidone at a mass ratio of 97:1.5:0.5:1, and then coated on aluminum foil. After drying, rolling, and slitting, the positive electrode sheet is obtained;

[0131] (3) Preparation of electrolyte

[0132] In a glove box filled with argon, various solvents are mixed and then mixed with lithium salts. During the mixing process, cooling measures are used to keep the temperature of the mixture below 10°C. After sufficient mixing, additives are added and mixed evenly to obtain an electrolyte;

[0133] The cyclic carbonates are ethylene carbonate (EC) and propylene carbonate (PC), the linear carbonate is diethyl carbonate (DEC), and propyl propionate (PP) is added in a ratio of 7:7:2.8:83.2. Compound A is 4-methoxyphenyl trifluoromethanesulfonate, added at 1%; Compound B is 3,5-bis(trifluoromethyl)benzeneacetonitrile, added at 1.5%; Compound C is 4-fluorophenylboric anhydride, added at 0.8%; Additive B is 1,3-propane sultone (PS), added at 10%; and the lithium salt is lithium hexafluorophosphate, added at 15%.

[0134] (5) Preparation of secondary batteries

[0135] The prepared positive electrode sheet, negative electrode sheet, separator (polypropylene porous polymer film) and other battery components are assembled, and a secondary battery is obtained through processes such as shaping, baking, packaging, liquid injection, formation, and capacity division.

[0136] Examples 2 to 4

[0137] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the cyclic carbonate is changed by adjusting the amount of the cyclic carbonate added.

[0138] Examples 5 to 7

[0139] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the linear carbonate is changed by adjusting the amount of the linear carbonate added.

[0140] Examples 8 to 10

[0141] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of compound A is changed by adjusting the addition amount of compound A.

[0142] Examples 11 to 13

[0143] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of compound B is changed by adjusting the addition amount of compound B.

[0144] Examples 14 to 16

[0145] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of compound C is changed by adjusting the addition amount of compound C.

[0146] Examples 17-18

[0147] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the electrolyte retention coefficient is changed by adjusting the amount of substance (lithium salt) added to the electrolyte.

[0148] Examples 19 to 21

[0149] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the mass percentage of the silicon-based material is changed by adjusting the addition amount of the silicon-based material.

[0150] Example 22

[0151] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the types of compound A, compound B, and compound C are adjusted.

[0152] Example 23

[0153] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 lies in that the types of cyclic carbonate and linear carbonate are adjusted.

[0154] Example 24

[0155] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the type and amount of additive B are adjusted.

[0156] Example 25

[0157] The embodiment of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that the type and addition amount of the lithium salt are adjusted.

[0158] Comparative Examples 1-2

[0159] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and Example 1 is that the amount of substances added in the electrolyte and the amount of silicon-based materials added are adjusted to achieve the parameters in Tables 1 and 2.

[0160] Comparative Example 3

[0161] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and the embodiment 1 is that no cyclic carbonate is added.

[0162] Comparative Example 4

[0163] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and Example 1 is that no linear carbonate is added.

[0164] Comparative Example 5

[0165] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and Example 1 is that compound A is not added.

[0166] Comparative Example 6

[0167] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and Example 1 is that compound B is not added.

[0168] Comparative Example 7

[0169] The comparative example of the present application provides a secondary battery. The difference between the secondary battery and Example 1 is that the compound C is not added.

[0170] Comparative Example 8

[0171] The comparative example of the present application provides a secondary battery, which differs from Example 1 in that no silicon-based material is added.

[0172] The values ​​of α%, β%, γ%, w%, x%, σ, v%, A, compound A, compound B, compound C, cyclic carbonate, linear carbonate, additive B and mass percentage m%, and lithium salt and mass percentage n% in the secondary batteries in the Examples and Comparative Examples are shown in Tables 1 to 2.

[0173] Table 1

[0174]

[0175]

[0176] Table 2

[0177]

[0178]

[0179]

[0180] The high temperature storage performance, cycle performance and thermal shock resistance of the secondary batteries prepared in the examples and comparative examples are shown in Table 3. The test method includes the following steps:

[0181] (1) Normal temperature cycle performance test: In a 25°C environment, the divided secondary battery is charged to 4.55V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 400 cycles of charge and discharge, the capacity retention rate at the 400th week is calculated. The calculation formula is as follows:

[0182] 400th cycle capacity retention rate (%) = (400th cycle discharge capacity / first cycle discharge capacity) × 100%;

[0183] Thickness growth rate at the 400th cycle = (thickness at the 400th cycle at full charge / thickness at the first cycle at full charge) × 100%;

[0184] (2) High temperature cycle performance test: In a 45°C environment, the divided secondary battery is charged to 4.55V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. After 300 cycles of charge and discharge, the capacity retention rate at the 300th week is calculated. The calculation formula is as follows:

[0185] 300th cycle capacity retention rate (%) = (300th cycle discharge capacity / first cycle discharge capacity) × 100%;

[0186] Thickness growth rate at the 300th cycle (%) = (thickness at the 300th cycle in full charge state / thickness at the first cycle in full charge state) × 100%;

[0187] (3) 85℃ / 24h high temperature storage test: The secondary battery was placed at room temperature and charged and discharged once at 0.5C (3.0V-4.55V), and the discharge capacity C0 of the secondary battery before storage was recorded. The secondary battery was then charged to a full charge state of 4.55V (100% SOC) at constant current and constant voltage. The thickness d1 of the battery before high temperature storage was measured using a PPG battery thickness gauge (600g). The secondary battery was placed in an 85℃ constant temperature box and stored for 24h. After the storage was completed, the secondary battery was taken out and the thermal thickness d2 of the battery after storage was measured. The thickness expansion rate of the secondary battery after storage at 85℃ for 24h was calculated. After the secondary battery was cooled at room temperature for 24h, the secondary battery was again discharged to 3.0V at 0.5C and then charged to 4.55V at 0.5C constant current and constant voltage. The discharge capacity C1 and charge capacity C2 of the secondary battery after storage were recorded. The capacity remaining rate and recovery rate of the secondary battery after storage at 85℃ for 24h were calculated as follows:

[0188] Thickness expansion ratio after storage at 85℃ for 24h = (d2-d1) / d1*100%;

[0189] Capacity retention after storage at 85°C for 24 hours = C1 / C0*100%;

[0190] After storage at 85°C for 24 hours, the capacity recovery rate = C2 / C0*100%.

[0191] (4) Thermal shock performance: Under 25°C ambient conditions, discharge the battery to 3.0V at a given current of 0.2C; let it sit for 5 minutes; charge it to 4.55V at a charging current of 0.2C. When the secondary battery voltage reaches 4.55V, change to 4.55V constant voltage charging until the charging current ≤ the cut-off current of 0.05C; after leaving it for 1 hour, place the secondary battery in an oven, increase the oven temperature to 135±2°C at a rate of 5±2°C / min, and keep it for 60 minutes before stopping. The judgment standard is that the secondary battery does not catch fire or explode.

[0192] Table 3

[0193]

[0194]

[0195] As can be seen from Table 3, the secondary battery prepared by the method provided in the present application has excellent room temperature cycle performance, high temperature cycle and storage performance, and excellent thermal shock resistance; specifically, the capacity retention rate of the obtained secondary battery at the 400th cycle is above 81.9%, the thickness growth rate at the 400th cycle is above 16.6%, the capacity retention rate at the 300th cycle is above 77.5%, the thickness growth rate at the 300th cycle is above 19.6%, the thickness expansion rate after storage at 85°C for 24 hours is below 19.6%, the capacity retention rate after storage at 85°C for 24 hours is above 80.1%, the capacity recovery rate after storage at 85°C for 24 hours is above 85.1%, and the 135°C thermal shock pass rate is above 4 / 6;

[0196] It can be seen from Examples 1 to 25 and Comparative Examples 1 to 2 that when (α+β)*ln(σ*x+2γ)*2 / min(x*v,σw / v,w*α / β) does not meet the range of 43 to 1090, the comprehensive performance of the obtained secondary battery is significantly reduced, and the effect of the present application cannot be achieved; it can be seen from Examples 1 to 25 and Comparative Examples 3 to 8 that when any substance specified in the present application is not added to the secondary battery, the comprehensive performance of the obtained secondary battery also shows a significant downward trend.

[0197] Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. A secondary battery, comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator, wherein the electrolyte comprises an organic solvent, an additive A, and a lithium salt; the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector; and the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector; It is characterized by: The organic solvent includes cyclic carbonate substances and linear carbonate substances; The additive A includes compound A, compound B and compound C; The positive electrode active material layer includes lithium cobalt oxide, Li5FeO4, a positive electrode conductor and a positive electrode binder; The negative electrode active material layer includes a silicon-based material, graphite, a negative electrode conductor, a thickener and a negative electrode binder; The structural formulas of the compounds A to C are shown in Formulas I to III, respectively: Wherein, R1 is selected from fluorinated or non-fluorinated alkyl, alkenyl, alkynyl, and aromatic groups; R2 to R6 are each independently selected from substituted or unsubstituted alkyl, alkenyl, alkynyl, and alkoxy; R7 is selected from substituted or unsubstituted fluorinated aromatic groups; R8~R 10 Each is independently selected from substituted or unsubstituted aromatic groups; The secondary battery satisfies 43≤Y≤1090, Among them, Y=(α+β)*ln(σ*x+2γ)*2 / min(x*v,σw / v,w*α / β); α% is the mass percentage of cyclic carbonate based on the total mass of the electrolyte; β% is the mass percentage of linear carbonate based on the total mass of the electrolyte; γ% is the mass percentage of compound A based on the total mass of the electrolyte; w% is the mass percentage of compound B based on the total mass of the electrolyte; x% is the mass percentage of compound C based on the total mass of the electrolyte; σg / Ah is the electrolyte retention coefficient; v% is the mass percentage of the silicon-based material based on the total mass of the negative electrode active material layer.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies 115≤Y≤326.

3. The secondary battery according to claim 1, wherein Meet at least one of the following: 1) Based on the total mass of the electrolyte, the mass percentage α% of the cyclic carbonate is 1% to 20%; 2) Based on the total mass of the electrolyte, the mass percentage β% of the linear carbonate is 0.4% to 10%; 3) Based on the total mass of the electrolyte, the mass percentage γ% of compound A is 0.3% to 3%; 4) Based on the total mass of the electrolyte, the mass percentage (w%) of compound B is 0.3% to 3%; 5) Based on the total mass of the electrolyte, the mass percentage x% of compound C is 0.3% to 3%; 6) The electrolyte has a liquid retention coefficient σg / Ah of 1.0 g / Ah to 1.3 g / Ah; 7) Based on the total mass of the negative electrode active material layer, the mass percentage (v%) of the silicon-based material is 3% to 20%.

4. The secondary battery according to claim 1, wherein The compound A includes at least one of 4-methoxyphenyl trifluoromethanesulfonate and p-tolyl trifluoromethanesulfonate; And / or, the compound B includes at least one of 3,5-bis(trifluoromethyl)benzeneacetonitrile and 2-trifluoromethylbenzonitrile; And / or, the compound C includes at least one of 4-fluorophenylboronic anhydride and 2,4,6-tris(3,4,5-trifluorophenyl)boroxine.

5. The secondary battery according to claim 1, wherein The cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, and 3,3,3-trifluoropropylene carbonate; And / or, the linear carbonate includes at least one of dimethyl carbonate and diethyl carbonate.

6. The secondary battery according to claim 1, wherein The electrolyte further includes an additive B, wherein the additive B includes at least one of 1,3-propane sultone, vinyl sulfate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate; And / or, based on the total mass of the electrolyte, the mass percentage of additive B is 0.1% to 20%.

7. The secondary battery according to claim 1, wherein The mass percentage of the lithium salt is 8% to 25% based on the total mass of the electrolyte; And / or, the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, and lithium bisfluorosulfonyl imide.

8. The secondary battery according to claim 1, wherein The silicon-based material includes at least one of silicon carbon and silicon oxygen.

9. The secondary battery according to claim 1, wherein The organic solvent further comprises at least one of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ethyl butyrate, methyl butyrate, butyl butyrate, and ethyl difluoroacetate.

10. An electrical device, characterized in that: The electric device includes the secondary battery according to any one of claims 1 to 9.

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