Secondary battery and electronic device

Abstract

The present application provides a secondary battery and an electronic device. The secondary battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte; and when the secondary battery is charged to 3.6 V, the XRD diffraction pattern of the positive electrode sheet has a characteristic peak A in the range of 18° to 19°, a characteristic peak B in the range of 15° to 16°, and a characteristic peak C in the range of 44° to 46°. The electrolyte comprises a first additive, and the first additive comprises at least one of compounds represented by formula I, formula II, formula III, and formula IV; and on the basis of the mass of the electrolyte, the mass percentage content of the first additive is M%, wherein 0.02≤M≤6. The positive electrode sheet having the described characteristics ensures high structural stability of the positive electrode sheet, and moreover, the electrolyte containing the first additive and the value of M being regulated within the described range improve the high-temperature storage performance, the high-temperature cycling performance, and the float charging performance of the secondary battery.

Description

Secondary battery and electronic device Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, have attracted widespread attention due to their high energy density, low maintenance, relatively low self-discharge, long cycle life, lack of memory effect, stable operating voltage, and environmental friendliness. They are widely used in portable electronic devices, power tools, and electric vehicles. However, with the rapid development of technology and the diversification of market demands, people are also placing more demands on secondary batteries that power electronic products, such as thinner and lighter weight, more diverse form factors, improved safety, higher power, and longer service life.

[0003] The dissolution of transition metals in the positive electrode and the oxygen released by the positive electrode catalyzing the decomposition of the electrolyte will affect the high-temperature storage performance of lithium-ion batteries. How to improve the high-temperature storage performance of lithium-ion batteries has become an urgent problem that needs to be solved.

[0004] Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and an electronic device to improve the high-temperature storage performance of the secondary battery. The specific technical solution is as follows:

[0006] A first aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte; when the secondary battery is charged to 3.6V, an XRD diffraction spectrum of the positive electrode sheet exhibits a characteristic peak A within a range of 18° to 19°, a characteristic peak B within a range of 15° to 16°, and a characteristic peak C at 44° to 46°; the electrolyte comprises a first additive, the first additive comprising at least one compound represented by Formula I, Formula II, Formula III, or Formula IV;

[0007] wherein R1 to R4 are each independently selected from C1 to C4 alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, C1 to C4 alkoxy, C2 to C4 alkenyloxy, C2 to C4 alkynyloxy or phenyl groups which are unsubstituted or substituted with fluorine atoms; R5 to R8 are each independently selected from hydrogen atoms, fluorine atoms or methyl groups; Y is selected from nitrogen atoms or CR 15 , R 15 is selected from a hydrogen atom, a fluorine atom, a methyl group which is unsubstituted or substituted by a fluorine atom; R9 is selected from a C1 to C5 alkyl group which is unsubstituted or substituted by a fluorine atom, a C2 to C4 alkenyl group, a C2 to C4 alkynyl group, a phenyl group or a benzyl group; X is selected from a vinylene group, R10 to R 14 Each of the first additives is independently selected from a hydrogen atom, a fluorine atom, or a C1 to C4 alkyl group. Based on the mass of the electrolyte, the mass percentage of the first additive is M%, 0.02≤M≤6, preferably 0.06≤M≤0.6. For example, the value of M can be 0.02, 0.05, 0.08, 0.1, 0.3, 0.5, 0.6, 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, or a range consisting of any two of these values.

[0008] The inventors have discovered that when the positive electrode sheet has the above characteristics and the electrolyte includes the first additive shown in Formula I, the silicon-containing group in Formula I can combine with the hydrofluoric acid generated by the electrolyte during the cycle, reducing the damage of hydrofluoric acid to the positive and negative electrode materials, reducing the dissolution of transition metals from the positive electrode and the precipitation of transition metals on the negative electrode, protecting the negative electrode solid electrolyte interface film (SEI film), thereby improving the high-temperature storage performance, high-temperature cycle performance, and float charge performance of the secondary battery. When the positive electrode sheet has the above characteristics and the electrolyte includes at least one of the first additives shown in Formula II, Formula III, or Formula IV, the structure of the above substance contains a double bond, which can be electronically reduced on the negative electrode surface before the solvent in the electrolyte to form a dense SEI film, reducing the formation of the solvent in the electrolyte on the negative electrode, and at the same time reducing the possibility of transition metals dissolved from the positive electrode being electronically reduced on the negative electrode surface to form transition metal dendrites, thereby facilitating the protection of the interface between the negative electrode sheet and the electrolyte. At the same time, the double bonds in the above substances are easily polymerized into a film on the surface of the positive electrode under a higher voltage (for example, ≥2.8V), reducing the possibility of contact between the solvent in the electrolyte and the high-valent positive electrode metal, reducing the oxidation and decomposition of the solvent in the electrolyte to produce gas, thereby improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery. When the value of M is too small, for example, less than 0.02, it is not conducive to the first additive to play the above-mentioned role, and it is impossible to improve the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery; when the value of M is too large, for example, greater than 6, it will cause too many side reactions to occur in the electrolyte during the circulation of the secondary battery, which is not conducive to improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery. Therefore, regulating the value of M within the scope of this application is conducive to improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery. Therefore, the positive electrode plate has the above-mentioned characteristics, which can make the positive electrode plate have higher structural stability. At the same time, the electrolyte includes the first additive and the value of the first additive content M is regulated within the above-mentioned range. The first additive can polymerize into a film on the surface of the positive electrode plate and the negative electrode plate, thereby improving the interface stability of the positive electrode plate and the negative electrode plate. Combined with the positive electrode plate with the above-mentioned characteristics, the first additive can passivate the oxygen element and transition metal element in the positive electrode plate, delay the decomposition of the electrolyte, and improve the high-temperature storage gas production problem of the secondary battery, thereby improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery.

[0009] In this application, there is no particular restriction on the charge rate for "charging the secondary battery to 3.6V", as long as the purpose of this application can be achieved. For example, the charge rate can be 0.1C to 2C, for example, the charge rate can be 0.1C, 0.2C, 0.5C, 0.8C, 1C, 1.2C, 1.5C, 1.8C, 2C or a range consisting of any two values ​​therein. In this application, "high temperature" means greater than or equal to 45°C.

[0010] In some embodiments of the present application, Formula I includes at least one of the following compounds:

[0011] When the positive electrode plate has the above characteristics and the electrolyte includes the first additive shown in Formula I, the silicon-containing group in Formula I can combine with the hydrofluoric acid generated in the electrolyte system during the circulation process, which is more conducive to reducing the damage of hydrofluoric acid to the positive electrode material and the negative electrode material, reducing the dissolution of transition metals from the positive electrode and the precipitation at the negative electrode, and better protecting the negative electrode solid electrolyte interface film (SEI film), thereby further improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery.

[0012] In some embodiments of the present application, Formula II includes at least one of the following compounds:

[0013] In some embodiments of the present application, Formula III includes at least one of the following compounds:

[0014] In some embodiments of the present application, Formula IV includes at least one of the following compounds:

[0015] When the positive electrode has the above-mentioned characteristics and the electrolyte includes at least one of the first additives represented by Formula II, Formula III, or Formula IV, the structure of the above-mentioned substance contains a double bond, which can be reduced by electrons on the surface of the negative electrode before the solvent in the electrolyte to form a dense SEI film. This is more conducive to reducing the formation of a film on the negative electrode by the solvent in the electrolyte. It can also reduce the possibility of transition metals dissolved from the positive electrode being reduced by electrons on the negative electrode surface to form transition metal dendrites, thereby facilitating the protection of the interface between the negative electrode and the electrolyte. In addition, the substance containing a double bond is more likely to polymerize and form a film on the surface of the positive electrode at higher voltages, thereby reducing the possibility of contact between the solvent in the electrolyte and the high-valent positive electrode metal, reducing the oxidative decomposition and gas production of the solvent in the electrolyte, and further improving the high-temperature storage performance, high-temperature cycling performance, and floating charge performance of the secondary battery.

[0016] In some embodiments of the present application, when the secondary battery is charged to 3.6V, the XRD diffraction spectrum of the positive electrode piece has a characteristic peak D in the range of 36° to 38°. In addition to the characteristic peak A, characteristic peak B, and characteristic peak C in the XRD diffraction spectrum of the positive electrode piece, the XRD diffraction spectrum of the positive electrode piece also has the above-mentioned characteristic peak D, which is beneficial to further improve the stability of the positive electrode piece and reduce the dissolution of transition metals in the positive electrode piece, thereby further improving the high-temperature storage performance, high-temperature cycle performance, and float charge performance of the secondary battery.

[0017] In some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, the positive electrode material layer including a first positive electrode active material and a second positive electrode active material; the first positive electrode active material is a lithium manganese composite oxide, for example, including but not limited to LiMnO2, Li 0.95 MnO 1.95 F 0.05 The second positive electrode active material includes lithium cobalt oxide (LiCoO2), lithium iron phosphate (LiFePO4), lithium iron manganese phosphate (LiMn 0.5 Fe 0.5 PO4) or at least one of lithium nickel cobalt manganese oxide. Lithium nickel cobalt manganese oxide may include but is not limited to LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523),LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333) or LiNi 0.9 Co 0.05 Mn 0.05 At least one of O2 (NCM955). The positive electrode sheet includes the first positive electrode active material and the second positive electrode active material. When the two materials are used at the same time, the Mn element in the delithiation product of the first positive electrode active material can be mostly in the form of Mn 4+ The presence of the first positive electrode active material and the second positive electrode active material can reduce the Mn dissolution caused by the Jahn-Teller effect, reduce the risk of the dissolved Mn element damaging the SEI film, and further improve the stability of the positive electrode sheet. At the same time, the first positive electrode active material and the second positive electrode active material have good compatibility, which is beneficial to reducing the side reactions between the first positive electrode active material and the second positive electrode active material, thereby being more conducive to improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery.

[0018] In some embodiments of the present application, based on the mass of the positive electrode material layer, the content of the lithium manganese composite oxide material is P%, 1≤P≤30, 1≤P / M≤300, preferably 10≤P / M≤100, and 2≤P≤20. For example, the value of P can be 1, 3, 5, 8, 10, 13, 15, 17, 20, 22, 25, 26, 28, 30, or a range consisting of any two values ​​thereof, and the value of P / M can be 1, 3, 5, 8, 10, 13, 15, 20, 22, 25, 28, 30, 50, 80, 100, 130, 150, 200, 220, 250, 270, 300, or a range consisting of any two values ​​thereof. By regulating the values ​​of P and P / M within the above range, the synergistic effect between the first positive electrode active material and the first additive can be better exerted, the transition metal elements and oxygen elements in the positive electrode plate at high potential can be stabilized, a positive electrode solid electrolyte interface film (CEI film) with good performance can be formed on the surface of the positive electrode plate, and a SEI film with good performance can be formed on the surface of the negative electrode plate, thereby reducing the dissolution of the Mn element in the first positive electrode active material and its deposition on the surface of the negative electrode plate, thereby better improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery.

[0019] In some embodiments of the present application, based on the mass of the positive electrode material layer, the mass percentage of the second positive electrode active material is Q%, and 60≤Q≤95. For example, the value of Q can be 60, 63, 66, 68, 70, 72, 75, 78, 80, 83, 85, 88, 90, 93, 95, or a range consisting of any two values ​​therein. By regulating the value of Q within the above range, it is beneficial to improve the stability of the positive electrode sheet while achieving better compatibility between the second positive electrode active material and the first positive electrode active material, and is more conducive to reducing the side reactions between the first positive electrode active material and the second positive electrode active material while increasing the amount of active lithium, thereby further improving the high temperature storage performance, high temperature cycle performance, and floating charge performance of the secondary battery.

[0020] In some embodiments of the present application, the electrolyte further includes a second additive, the second additive including at least one of 1,3-propane sultone (PS), 1,3-propylene sultone (PES), vinyl sulfate (DTD), 1,3-propylene glycol sulfate (PCS), 2,4-butane sultone (BS), or methylene methanedisulfonate (MMDS). Based on the mass of the electrolyte, the mass percentage of the second additive is N%, 0.01≤N≤3, preferably 0.1≤N≤1. For example, the value of N can be 0.01, 0.03, 0.05, 0.08, 0.1, 0.3, 0.5, 0.6, 0.8, 1, or a range consisting of any two of these values. On the basis of the electrolyte including the first additive, a second additive is further introduced and the value of N is regulated within the above range. The second additive can undergo an oxidation reaction at the positive electrode before the first additive, which can further improve the stability of the CEI film and reduce the side reaction between the positive electrode sheet and the electrolyte, thereby making the secondary battery have good high-temperature cycle performance while further improving its high-temperature storage performance and floating charge performance.

[0021] The electrolyte of the present application also includes a lithium salt. The present application does not particularly limit the type of lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include but is not limited to at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalatoborate) (LiBOB) or lithium difluorooxalatoborate (LiDFOB). The present application does not particularly limit the content of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. Exemplarily, based on the mass of the electrolyte, the mass percentage of the lithium salt is 8% to 15%, for example, the mass percentage of the lithium salt can be 8%, 9%, 10%, 11%, 13%, 15% or a range consisting of any two of these values.

[0022] The electrolyte of the present application also includes a non-aqueous solvent. The present application does not particularly limit the type of non-aqueous solvent, as long as the purpose of the present application can be achieved. For example, it may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound or other non-aqueous solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a chain carbonate compound or a cyclic carbonate compound. The above-mentioned chain carbonate compound may include but is not limited to at least one of dimethyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate or methylethyl carbonate. The above-mentioned cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate or vinyl ethylene carbonate. The above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate, γ-butyrolactone, decanolactone, valerolactone or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of ethylene glycol dimethyl ether, dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other non-aqueous solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved. Exemplarily, based on the mass of the electrolyte, the mass percentage of the non-aqueous solvent is 76% to 91.98%. For example, the mass percentage of the non-aqueous solvent can be 76%, 78%, 79%, 80%, 82%, 85%, 86%, 87.5%, 90%, 91%, 91.98% or a range consisting of any two of these values.

[0023] In some embodiments, the electrolyte includes a first additive, a lithium salt and a non-aqueous solvent, the mass percentages of the first additive and the lithium salt are as described above, the mass percentage of the non-aqueous solvent can be 79% to 91.98%, and the secondary battery includes the above electrolyte, which can improve the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery.

[0024] In some embodiments, the electrolyte includes a first additive, a second additive, a lithium salt and a non-aqueous solvent, the mass percentages of the first additive, the second additive and the lithium salt are as described above, the mass percentage of the non-aqueous solvent can be 76% to 91.97%, and the secondary battery includes the above electrolyte, which can further improve the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery.

[0025] In the present application, the positive electrode material layer can be arranged on one surface in the thickness direction of the positive electrode current collector, or on two surfaces in the thickness direction of the positive electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a partial area of ​​the surface of the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the positive electrode current collector may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). This application has no special restrictions on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 20μm, and the thickness of the single-sided positive electrode material layer is 30μm to 120μm.

[0026] The cathode material layer of the present application may further include a conductive agent and a binder. The present application has no particular restrictions on the conductive agent, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and conductive carbon black may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powder and / or metal fibers, and specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the binder, as long as the purpose of the present application can be achieved. For example, the binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyamide-imide, styrene-butadiene rubber, or polyvinylidene fluoride (PVDF). The present application has no particular restrictions on the mass percentages of the conductive agent and the binder in the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, based on the mass of the positive electrode material layer, the mass percentage of the conductive agent may be 0% to 5%, and the mass percentage of the binder may be 1.0% to 5%.

[0027] In the present application, there is no particular limitation on the preparation method of the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, it can be prepared by the following method: a first positive electrode active material, a second positive electrode active material, a conductive agent, and a binder are mixed, N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry with a solid content of 65wt% to 85wt%. The positive electrode slurry is evenly coated on one surface of the positive electrode collector, and after drying, a positive electrode sheet coated with a positive electrode material layer on one side is obtained. Then, the above coating steps are repeated on the other surface of the positive electrode collector, and after drying, a positive electrode sheet coated with a positive electrode material layer on both sides is obtained. After coating is completed, the positive electrode sheet is obtained by cold pressing and cutting.

[0028] The present application has no special restrictions on the negative electrode plate, as long as the purpose of the present application can be achieved. For example, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. In the present application, the negative electrode material layer can be provided on one surface in the thickness direction of the negative electrode current collector, or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector. The present application has no special restrictions, as long as the purpose of the present application can be achieved. The negative electrode material layer of the present application includes negative electrode active materials. The present application has no special restrictions on the type of negative electrode active materials, as long as the purpose of the present application can be achieved. For example, the negative electrode active material can include natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, SiO x (0<x≤2), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structure lithium titanate Li4Ti5O 12 At least one of lithium-ion battery, lithium-alloy, or metallic lithium. In this application, there are no particular restrictions on the thickness of the negative electrode current collector and negative electrode material layer, as long as they can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 to 12 μm, and the thickness of the single-sided negative electrode material layer is 30 to 160 μm.

[0029] The negative electrode material layer of the present application may further comprise a conductive agent, a binder, and a dispersant. The present application does not particularly limit the mass ratio of the negative electrode active material, the conductive agent, and the binder in the negative electrode material layer, as long as the purpose of the present application can be achieved. The present application does not particularly limit the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the conductive agent and the binder may be at least one of the conductive agents in the above-mentioned positive electrode material layer. The thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0030] In the present application, there is no particular limitation on the method for preparing the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, it can be prepared by the following method: a negative electrode active material, a binder, and a thickener are mixed, deionized water is added and stirred evenly, and a negative electrode slurry with a solid content of 40wt% to 65wt% is obtained. The negative electrode slurry is evenly coated on one surface of the negative electrode current collector, and after drying, a negative electrode sheet coated with a negative electrode material layer on one side is obtained. Then, the above coating steps are repeated on the other surface of the negative electrode current collector, and after drying, a negative electrode sheet coated with a negative electrode material layer on both sides is obtained. After coating, the negative electrode sheet is obtained by cold pressing and cutting.

[0031] The secondary battery of the present application also includes a separator. The present application has no particular restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include, but is not limited to, polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or at least one of aramid. The type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane. In some embodiments, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, a membrane or a composite membrane having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. In some embodiments, the inorganic layer includes inorganic particles and a binder. The application is not particularly limited to inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The application is not particularly limited to the binder. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0032] The secondary battery also includes a shell for accommodating the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the above-mentioned other components. This application does not particularly limit the shell, and it can be a shell known in the art, as long as it can achieve the purpose of this application. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal. This application does not limit the type of metal. A metal hard shell known in the art can be used, as long as it can achieve the purpose of this application. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0033] The present application does not particularly limit the type of secondary battery, which may include any device that generates an electrochemical reaction. For example, secondary batteries may include but are not limited to lithium-ion batteries, sodium-ion batteries, lithium polymer secondary batteries, and lithium-ion polymer secondary batteries.

[0034] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheets, the separator and the negative electrode sheets in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly with a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. may be placed in the shell to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0035] The second aspect of the present application provides an electronic device comprising the secondary battery provided in the first aspect of the present application. The secondary battery provided in the first aspect of the present application has good high-temperature storage performance, high-temperature cycle performance, and float charge performance, thereby providing the electronic device of the present application with a long service life and good performance.

[0036] The present application does not particularly limit the type of electronic device, and the electronic device may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0037] Beneficial effects of this application:

[0038] The present application provides a secondary battery and an electronic device. The secondary battery includes a positive electrode, a negative electrode, and an electrolyte. When the secondary battery is charged to 3.6V, the XRD diffraction spectrum of the positive electrode exhibits a characteristic peak A within the range of 18° to 19°, a characteristic peak B within the range of 15° to 16°, and a characteristic peak C at 44° to 46°. The electrolyte includes a first additive, the first additive comprising at least one compound represented by Formula I, Formula II, Formula III, or Formula IV. The mass percentage of the first additive is M%, based on the mass of the electrolyte, and 0.02≤M≤6. The positive electrode plate has the above-mentioned characteristics, which can make the positive electrode plate have higher structural stability. At the same time, the electrolyte includes a first additive and the value of M is regulated within the above-mentioned range. The first additive can polymerize into a film on the surface of the positive electrode plate and the negative electrode plate, thereby improving the interface stability of the positive electrode plate and the negative electrode plate. Combined with the positive electrode plate with the above-mentioned characteristics, the first additive can passivate the oxygen element and transition metal element in the positive electrode plate, delay the decomposition of the electrolyte, and improve the high-temperature storage gas production problem of the secondary battery, thereby improving the high-temperature storage performance, high-temperature cycle performance and floating charge performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute improper limitations on the present application.

[0040] FIG1 is an X-ray diffraction spectrum of the positive electrode sheet of Example 1-1;

[0041] FIG2 is an X-ray diffraction spectrum of the positive electrode sheet of Example 1-48. DETAILED DESCRIPTION

[0042] To make the objectives, technical solutions, and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and examples. It is apparent that the described examples are only a portion of the embodiments of this application, rather than all of them. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0043] It should be noted that in the following description, the present application is explained using a lithium-ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0044] Example

[0045] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0046] Test methods and equipment:

[0047] X-ray diffraction (XRD) test:

[0048] The lithium-ion battery was charged to 3.6V at 1C and then disassembled. The positive electrode was taken out and the positive electrode sample was obtained after cleaning and drying. The XRD spectrum of the positive electrode sample was measured using an X-ray diffraction tester (PANalytical, the Netherlands, XPert Pro MPD), and the test conditions were set as: Cu Kα radiation The working current was 250 mA, continuous scanning was adopted, the working voltage was 40 kV, the scanning range 2θ was 10° to 70°, the step length was 0.1°, and the scanning speed was 0.2 s / step.

[0049] Test of the content of each component in the electrolyte:

[0050] The lithium-ion battery was discharged at a constant current of 1C to 2.5V and then disassembled to collect the electrolyte. The positive electrode sheet, negative electrode sheet, and separator were centrifuged, and the liquid obtained after centrifugation was mixed with the above electrolyte. Then, the components in the electrolyte were obtained and their contents were tested using a gas chromatography-mass spectrometer (instrument model: Agilent 8890) and an ion chromatography (instrument model: AQUION ion chromatography).

[0051] High temperature storage performance test:

[0052] At 25°C, the lithium-ion battery was charged at a constant current of 0.5C to 3.6V, then charged at a constant voltage to a current of 0.05C. The thickness of the lithium-ion battery was measured and recorded as D0. Finally, the lithium-ion battery was placed in a 60°C oven for 180 days and then removed. The thickness at this time was monitored and recorded as D. The thickness expansion rate (%) of the lithium-ion battery during storage at 60°C = (D - D0) / D0 × 100%.

[0053] High temperature cycle performance test:

[0054] At 45°C, a lithium-ion battery is charged to 3.6V at 1C, then charged to 0.05C at 3.6V, and then discharged to 2.5V at a constant current of 1C. This is one cycle process. The first discharge capacity is recorded as C1. Repeat the charge and discharge cycle for 1000 cycles, and the discharge capacity at the 1000th cycle is recorded as C2. The lithium-ion battery's 45°C / 1000 cycle capacity retention rate (%) = C2 / C1×100%.

[0055] Float charge performance test:

[0056] The lithium-ion battery was discharged at 0.5C to 2.5V at 25°C, then charged at 1C to 3.6V, and then charged at a constant voltage of 3.6V to 0.05C. The thickness of the lithium-ion battery was measured and recorded as D2. The battery was placed in a 45°C oven and charged at a constant voltage of 3.6V for 50 days. The thickness change during this time was monitored and recorded as D3. The 45°C float charge thickness expansion rate (%) of the lithium-ion battery was (D3-D2) / D2×100%. The test was stopped if the thickness expansion rate was greater than 50%.

[0057] Example 1-1

[0058] <Preparation of Electrolyte>

[0059] In an argon atmosphere glove box with a water content of <10 ppm, the non-aqueous solvents ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were uniformly mixed in a mass ratio of 1:1:1:1:1. The lithium salt LiPF6 was then dissolved in the non-aqueous solvent. Finally, the first additive of formula III-3 was added and mixed uniformly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of the lithium salt was 12.5%, the mass percentage of the first additive was as shown in Table 1, and the remainder was the non-aqueous solvent.

[0060] <Preparation of positive electrode sheet>

[0061] The first positive electrode active material LiMnO2, the second positive electrode active material LiFePO4, the binder PVDF and the conductive agent conductive carbon black were mixed in a mass ratio of 6:90.4:2.1:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, a positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm and dried at 120℃ to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer was 267.8mg / 1540mm 2 After cold pressing, cutting, and welding the tabs, a positive electrode sheet with a size of 74mm x 867mm was obtained for use. The thickness of the single-sided positive electrode material layer was 42μm.

[0062] <Preparation of negative electrode sheet>

[0063] The negative electrode active material artificial graphite, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) were mixed in a weight ratio of 97.4:1.4:1.2, and deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. After stirring evenly with a vacuum mixer, the negative electrode slurry was obtained. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6 μm and dried at 120°C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 142 mg / 1540 mm 2 After cold pressing, cutting, and welding the tabs, a negative electrode sheet with a size of 78mm x 875mm was obtained for use. The thickness of the negative electrode material layer on a single side was 54.5μm.

[0064] <Preparation of Separator>

[0065] PVDF and alumina ceramic were mixed in a 9:1 mass ratio, and deionized water was added as a solvent to prepare a ceramic layer slurry with a solid content of 25wt%. The mixture was then stirred evenly. The slurry was evenly coated on one surface of a 12μm thick polyethylene porous film substrate. After drying, a separator membrane with a 2μm alumina ceramic layer coated on one side was obtained. The above coating steps were then repeated on the other surface of the substrate to obtain a separator membrane with a 2μm alumina ceramic layer coated on both sides. The porosity of the separator membrane was 39%.

[0066] <Preparation of lithium-ion batteries>

[0067] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electronic component; after welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, placed in an 85°C vacuum oven to dry for 12 hours to remove moisture, and injected with the above-prepared electrolyte. After vacuum packaging, standing, formation, shaping, capacity testing, secondary packaging and other processes, a lithium-ion battery is obtained. Among them, the formation process is as follows: the first cycle of charge and discharge is carried out at 45±5°C, and the process is as follows: first, charge at a constant current rate of 0.1C for 10 minutes, then charge at a constant current rate of 0.5C to a specified voltage of 4.6V, then charge at a constant voltage until the current is less than or equal to 0.05C, and then discharge at a constant current rate of 0.5C to 2.5V.

[0068] Example 1-2 to Example 1-61

[0069] The parameters are adjusted according to Table 1, and the rest are the same as Example 1-1. When the mass percentage of the first additive and the mass percentage of the non-aqueous solvent are changed, the mass percentage of the lithium salt remains unchanged.

[0070] Example 2-1 to Example 2-17

[0071] Except for adjusting the parameters according to Table 2, the rest is the same as Example 1-1.

[0072] Example 3-1 to Example 3-16

[0073] Except for adjusting the parameters according to Table 3, the rest is the same as Example 1-56.

[0074] Example 4-1 to Example 4-11

[0075] The process was the same as Example 1-1, except that the second additive was added in the preparation of the electrolyte and the parameters were adjusted according to Table 4. While the weight percentages of the second additive and the non-aqueous solvent were changed, the weight percentages of the first additive and the lithium salt remained unchanged.

[0076] Comparative Example 1

[0077] Except that the first additive is not added in the preparation of the electrolyte, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 1-1.

[0078] Comparative Example 2

[0079] Except that the first positive electrode active material is not added in the <Preparation of Positive Electrode Sheet>, the mass percentage of the second positive electrode active material is changed accordingly, and the mass percentages of the binder and the conductive agent remain unchanged, the rest is the same as Example 1-1.

[0080] Comparative Example 3

[0081] The process is the same as that of Comparative Example 2 except that the first additive is not added in the preparation of the electrolyte, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged.

[0082] Comparative Example 4 to Comparative Example 5

[0083] Except that the mass percentage of the first additive is adjusted according to Table 1, the mass percentage of the non-aqueous solvent is changed accordingly, and the mass percentage of the lithium salt remains unchanged, the rest is the same as Example 1-1.

[0084] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0085] Table 1

[0086] Note: In Table 1, “\” means there is no relevant parameter or the corresponding substance does not exist.

[0087] It can be seen from Example 1-1 to Example 1-61 that the XRD diffraction spectrum of the positive electrode sheet has a characteristic peak A in the range of 18° to 19°, a characteristic peak B in the range of 15° to 16°, and a characteristic peak C at 44° to 46°. At the same time, the electrolyte includes the first additive and the value of M is regulated within the scope of this application. The lithium-ion battery has a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion battery has better high-temperature storage performance, high-temperature cycle performance, and float charge performance. The electrolyte of Comparative Example 1 does not include the first additive, the positive electrode sheet of Comparative Example 2 does not have the above-mentioned characteristic peak in its XRD spectrum, the electrolyte of Comparative Example 3 does not include the first additive and the XRD spectrum of its positive electrode sheet does not have the above-mentioned characteristic peak, the values ​​of M in Comparative Examples 4 and 5 are not within the scope of this application, and the lithium-ion batteries of the above-mentioned comparative examples have a higher 60°C storage thickness expansion rate, a lower 45°C / 1000 cycle capacity retention rate, and a higher 45°C float charge thickness expansion rate, indicating that the high-temperature storage performance, high-temperature cycle performance, and float charge performance of the lithium-ion batteries are worse.

[0088] The type of first additive typically affects the high-temperature storage performance, high-temperature cycling performance, and float charge performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-51, selecting a first additive within the scope of this application can result in lithium-ion batteries having a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion batteries have good high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0089] The value of M usually affects the high-temperature storage performance, high-temperature cycle performance and float charge performance of the lithium-ion battery. It can be seen from Example 1-1, Example 1-52 to Example 1-61, Comparative Example 4 and Comparative Example 5 that when the value of M is too small, such as Comparative Example 4, when the value of M is too large, such as Comparative Example 8, the lithium-ion batteries of the above comparative examples have a higher 60°C storage thickness expansion rate, a lower 45°C / 1000 cycle capacity retention rate and a higher 45°C float charge thickness expansion rate, indicating that when the value of M is not within the scope of this application, the high-temperature storage performance, high-temperature cycle performance and float charge performance of the lithium-ion battery are worse. Therefore, by regulating the value of M within the scope of this application, the lithium-ion battery can have a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion battery has good high-temperature storage performance, high-temperature cycle performance and float charge performance.

[0090] The type of first positive electrode active material generally affects the high-temperature storage performance, high-temperature cycling performance, and float charge performance of a lithium-ion battery. As can be seen from Examples 1-1 and 1-51, selecting a first positive electrode active material within the scope of this application can result in a lithium-ion battery having a low 60°C storage thickness expansion rate, a high 45°C / 1000 cycle capacity retention rate, and a low 45°C float charge thickness expansion rate, demonstrating that the lithium-ion battery has good high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0091] As can be seen from Figure 1, in the XRD diffraction spectrum of the positive electrode sheet of Example 1-1, there is a characteristic peak A in the range of 18° to 19°, a characteristic peak B in the range of 15° to 16°, and a characteristic peak C in the range of 44° to 46°.

[0092] As can be seen from Figure 2, in the XRD diffraction spectrum of the positive electrode sheet of Example 1-48, there is a characteristic peak A in the range of 18° to 19°, a characteristic peak B in the range of 15° to 16°, and a characteristic peak C in the range of 44° to 46°.

[0093] Table 2

[0094] Note: “\” in Table 2 means there is no relevant parameter or the corresponding substance does not exist.

[0095] The inclusion of characteristic peak D in the positive electrode sheet generally affects the high-temperature storage performance, high-temperature cycling performance, and float charge performance of the lithium-ion battery. As can be seen from Examples 1-1, 1-6, 1-19, and 2-1 to 1-17, the inclusion of characteristic peak D in the positive electrode sheet can result in the lithium-ion battery having a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion battery has good high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0096] The type of second positive electrode active material generally affects the high-temperature storage performance, high-temperature cycling performance, and float charge performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-3, 2-7, 2-11, and 2-15, selecting a second positive electrode active material within the scope of this application can result in a lithium-ion battery having a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion battery has good high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0097] Table 3

[0098] The values ​​of P and Q generally affect the high-temperature storage performance, high-temperature cycling performance, and float charge performance of lithium-ion batteries. As can be seen from Examples 1-1 and 3-1 to 3-16, regulating the values ​​of P and Q within the scope of this application can result in lithium-ion batteries having a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion battery has good high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0099] The P / M value generally affects the high-temperature storage performance, high-temperature cycling performance, and float charge performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-52 to 1-61, and 3-1 to 3-16, regulating the P / M value within the scope of this application can result in lithium-ion batteries having a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion battery has good high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0100] Table 4

[0101] Note: “\” in Table 4 means there is no relevant parameter or the corresponding substance does not exist.

[0102] The electrolyte further includes a second additive and the value of N generally affects the high-temperature storage performance, high-temperature cycling performance, and float charge performance of the lithium-ion battery. As can be seen from Examples 1-1, 4-1, and 4-7, further introducing a second additive into the electrolyte and regulating the value of N within the scope of this application can enable the lithium-ion battery to have a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, indicating that the lithium-ion battery has good high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0103] The type of second additive typically affects the high-temperature storage performance, high-temperature cycling performance, and float charge performance of lithium-ion batteries. As can be seen from Examples 4-1, 4-8, and 4-11, selecting a second additive within the scope of this application can result in lithium-ion batteries having a lower 60°C storage thickness expansion rate, a higher 45°C / 1000 cycle capacity retention rate, and a lower 45°C float charge thickness expansion rate, demonstrating that the lithium-ion batteries have excellent high-temperature storage performance, high-temperature cycling performance, and float charge performance.

[0104] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte; When the secondary battery is charged to 3.6V, in the XRD diffraction spectrum of the positive electrode sheet, there is a characteristic peak A in the range of 18° to 19°, a characteristic peak B in the range of 15° to 16°, and a characteristic peak C at 44° to 46°; The electrolyte includes a first additive, wherein the first additive includes at least one compound represented by Formula I, Formula II, Formula III or Formula IV; in, R1 to R4 are each independently selected from C1 to C4 alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, unsubstituted or substituted by fluorine atoms, C1 to C4 alkoxy, C2 to C4 alkenyloxy, C2 to C4 alkynyloxy or phenyl; R5 to R8 are each independently selected from a hydrogen atom, a fluorine atom or a methyl group; Y is selected from a nitrogen atom or CR 15 , R 15 A methyl group selected from a hydrogen atom, a fluorine atom, and an unsubstituted or fluorine-substituted methyl group; R9 is selected from C1 to C5 alkyl, C2 to C4 alkenyl, C2 to C4 alkynyl, phenyl or benzyl groups which are unsubstituted or substituted by fluorine atoms; X is selected from vinylene, R 10 to R 14 are each independently selected from a hydrogen atom, a fluorine atom or a C1 to C4 alkyl group; Based on the mass of the electrolyte, the mass percentage of the first additive is M%, and 0.02≤M≤6.

2. The secondary battery according to claim 1, wherein The formula I comprises at least one of the following compounds: The formula II comprises at least one of the following compounds: The formula III comprises at least one of the following compounds: The formula IV comprises at least one of the following compounds:

3. The secondary battery according to claim 1, wherein 0.06≤M≤0.6。 4. The secondary battery according to any one of claims 1 to 3, wherein When the secondary battery is charged to 3.6V, a characteristic peak D exists in the range of 36° to 38° in the XRD diffraction spectrum of the positive electrode.

5. The secondary battery according to any one of claims 1 to 3, wherein The positive electrode sheet includes a positive electrode current collector and a positive electrode material layer provided on at least one surface of the positive electrode current collector, wherein the positive electrode material layer includes a first positive electrode active material and a second positive electrode active material; The first positive electrode active material is a lithium manganese composite oxide; the second positive electrode active material includes at least one of lithium cobalt oxide, lithium iron phosphate, lithium iron manganese phosphate or lithium nickel cobalt manganese oxide.

6. The secondary battery according to claim 5, wherein Based on the mass of the positive electrode material layer, the content of the lithium manganese composite oxide material is P%, 1≤P≤30; 1≤P / M≤300. 7 . The secondary battery according to claim 6 , which satisfies at least one of the following characteristics: (a) 10≦P / M≦100; (b) 2≦P≦20.

8. The secondary battery according to claim 5, wherein Based on the mass of the positive electrode material layer, the mass percentage of the second positive electrode active material is Q%, and 60≤Q≤95.

9. The secondary battery according to any one of claims 1 to 3, wherein The electrolyte further includes a second additive, wherein the second additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, vinyl sulfate, 1,3-propylene glycol sulfate, 2,4-butane sultone or methylene methanedisulfonate. Based on the mass of the electrolyte, the mass percentage of the second additive is N%, and 0.01≤N≤3.

10. The secondary battery according to claim 9, wherein 0.1≤N≤1。 11 . An electronic device comprising the secondary battery according to claim 1 .

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