Secondary battery and electronic device

Abstract

The present invention belongs to the technical field of batteries, and provides a secondary battery and an electronic device. The secondary battery comprises a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises silicon-containing active particles, and the spherization degree of the silicon-containing active particles is A; and the electrolyte contains fluoroethylene carbonate, and based on the mass of the electrolyte, the mass percentage content of fluoroethylene carbonate is B%, with A and B satisfying: 1.6≤(B / A)≤29.4. In this way, the synergistic effect between the spheroidization degree of the silicon material particles and the content of fluoroethylene carbonate can be fully exerted, and the crushing of the silicon particles and side reactions with the electrolyte are reduced, thereby improving the initial coulombic efficiency and cycle performance of the secondary battery and enhancing the over-discharge gas production resistance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of secondary batteries, and specifically relates to a secondary battery and an electronic device. BACKGROUND

[0002] Silicon, as a material with abundant resources and high theoretical specific capacity, has great application potential in secondary battery negative electrodes. However, silicon-containing negative electrodes undergo volume swelling and contraction during intercalation and deintercalation of active materials, which easily leads to stress concentration in electrode materials and cracking of silicon nanoparticles. The cracked silicon nanoparticles continuously undergo side reactions with electrolytes to form a solid electrolyte interface film, resulting in capacity loss and rapid cycling performance decrease of secondary batteries.

[0003] The prior art proposes adding an additive to an electrolyte to improve the performance of a solid electrolyte interface film and reduce side reactions between the electrolyte and silicon nanoparticles. However, the use of the additive brings problems such as reduced active ion concentration in the electrolyte, increased electrolyte viscosity, and increased secondary battery impedance, which still affect the initial efficiency and cycling performance of a secondary battery to a certain extent. SUMMARY

[0004] In view of this, the present application provides a secondary battery, aiming to solve the problem in the prior art that silicon particles are prone to break so as to undergo side reactions, thereby improving the coulombic efficiency, capacity retention rate and over-discharge resistance of the secondary battery. On the other hand, the present application further provides an electronic device including the above secondary battery.

[0005] According to a first aspect, the present application provides a secondary battery, including a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode active material layer. The negative electrode active material layer includes silicon-containing active particles. The sphericity of the silicon-containing active particles is A. The electrolyte contains fluoroethylene carbonate (FEC). Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is B%; where A and B satisfy: 1.6'"" (B A)" 29.4. The present application adds the fluoroethylene carbonate to the electrolyte and closely matches the sphericity of the silicon-containing active particles with the mass percentage of the fluoroethylene carbonate in the electrolyte, so that a solid electrolyte interface (SEI) film formed by the decomposition of the fluoroethylene carbonate can effectively cover a silicon-containing fresh interface exposed after the silicon-containing active particles are broken, reducing side reactions between exposed active silicon and the electrolyte. The secondary battery has lower internal resistance, thereby improving the coulombic efficiency and cycling capacity retention rate of the secondary battery and enabling the secondary battery to have better over-discharge resistance.

[0006] In some embodiments, 0.65<A<1. When the sphericity of the silicon-containing active particles is within this range, there are fewer sharp corners on the surface. In conjunction with the above relationship between the sphericity and fluoroethylene carbonate content, the side reactions between active silicon and the electrolyte can be further reduced, the coulombic efficiency of the secondary battery can be further improved and over-discharge resistance thereof can be enhanced. In some embodiments, 0.71<A<1.

[0007] In some embodiments, 1.1<B<20. When the mass percentage of the fluoroethylene carbonate is within this range, the increase in internal resistance of the secondary battery caused by the generated SEI film can be reduced or avoided, the initial coulombic efficiency of the secondary battery can be further improved and over-discharge resistance thereof can be enhanced.

[0008] In some embodiments, 2<B<7. The quality of the SEI film can be maximized, further enhancing the over-discharge resistance of the secondary battery.

[0009] In some embodiments, a minimum angle of cross-sectional profiles of silicon-containing active particles with a diameter greater than 10 gm is C°, and 96<C<180. When the minimum angle of the cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 gm satisfies the above range, it indicates that the edges and corners of the silicon-containing active particles are gentle, which can reduce the breakage of the silicon-containing active particles, further improve the coulombic efficiency of the secondary battery and enhance cycling performance and over-discharge resistance thereof.

[0010] In some embodiments, a sphericity A of the silicon-containing active particles, a minimum angle C° of cross-sectional profiles of silicon-containing active particles with a diameter greater than 10 gm, and the mass percentage B% of the additive fluoroethylene carbonate satisfy: 45.28<(AxC-B)<176.0. By controlling the sphericity of the silicon-containing active particles, the shape characteristics of the minimum angle of the cross-sectional profiles, and the mass percentage of the fluoroethylene carbonate to satisfy the above relationship, the SEI film formed by fluoroethylene carbonate can be further ensured to cover the broken surface of the silicon-containing active particles, optimizing the cycling performance and overdischarge resistance of the secondary battery and improving the initial coulombic efficiency and cycling capacity retention rate thereof.

[0011] In some embodiments, A, B and C satisfy: 60^(AXC-B)< 120, further improving and optimizing the cycling performance and over-discharge resistance of the secondary battery.

[0012] In some embodiments, the silicon-containing active particles include a porous carbon matrix and nano-silicon, and the nano-silicon is distributed inside and on a surface of the porous carbon matrix.

[0013] In some embodiments, based on a mass of the silicon-containing active particles, a mass fraction of element Si is 42%-55%.

[0014] In some embodiments, based on a mass of the negative electrode active material layer, a mass fraction of element Si is 2.1%-22%. In some embodiments, based on the mass of the negative electrode active material layer, a mass percentage of the silicon-containing active particles is 5-40%.

[0015] In some embodiments, a specific surface area of the silicon-containing active particles is 0.5 m2 / g-5 m2 / g. When the specific surface area of the silicon-containing active particles is within the above range, the initial coulombic efficiency of the secondary battery can be further improved.

[0016] In some embodiments, a conductivity of the electrolyte is 6.5 mS / cm-11 mS / cm. By controlling the conductivity within the above range, the transport of active ions can be promoted, so that the secondary battery has improved cycling performance and over-discharge resistance.

[0017] In some embodiments, a hydrofluoric acid content in the electrolyte is <83 pg / g, which can further improve the kinetic performance of the secondary battery.

[0018] According to a second aspect, the present application further provides an electronic device including any one of the above secondary batteries.

[0019] Based on the secondary battery of the present application, the beneficial effects include: by controlling the sphericity of the silicon-containing active particles to match with the content of the fluoroethylene carbonate in the electrolyte to generate a synergistic effect in the present application, the fluoroethylene carbonate can form a low-impedance SEI film, which can effectively cover the active surface generated by the breakage of the silicon-containing active particles, thereby reducing or avoiding side reactions between the silicon-containing active particles and the electrolyte, reducing the consumption of the electrolyte and silicon-containing active particles caused by the side reactions, improving the initial efficiency and cycling performance of the secondary battery, reducing gas generated by the side reactions, and improving the over-discharge resistance of the secondary battery. Further, the present application defines the synergistic coordination among the sphericity of the silicon-containing active particles, the minimum angle of the particle cross-sectional profiles, and the fluoroethylene carbonate in the electrolyte, thereby further optimizing the initial efficiency and cycling performance of the secondary battery. In addition, the secondary battery produces less gas during over-discharge and therefore has higher over-discharge resistance. BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a backscattered SEM image of a cross section of a negative electrode sheet in a thickness direction in a secondary battery of Example 1 of the present application; and

[0021] FIG. 2 is a schematic diagram of determining a minimum angle of crosssectional profiles of silicon-containing active particles with a diameter greater than 10 gm according to embodiments of the present application. DETAILED DESCRIPTION

[0022] In order to make the purpose, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0023] For the sake of brevity, the present application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unrecorded range. Any lower limit can be combined with other lower limits to form an unrecorded range. Similarly, any upper limit can be combined with any other upper limit to form an unrecorded range. In addition, each individually disclosed point or single numerical value itself can be used as a lower limit or upper limit to be combined with any other point or single numerical value or with other lower limits or upper limits to form an unrecorded range.

[0024] In the description of the present application, unless otherwise specified, "above" and "below" include the number itself.

[0025] Unless otherwise specified, the terms used in the present application have the well-known meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values of the parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the embodiments of the present application).

[0026] In the present application, the term "silicon-containing active particles" refers to a negative electrode material containing silicon element in a solid particle state. For example, it can be a silicon-carbon composite material in a solid particle state. In some exemplary embodiments, the silicon-containing active particles include porous carbon particles having pores, and silicon formed inside the porous carbon particles and / or on the surface of the porous carbon particles. The silicon-containing active particles in the embodiments of the present application can better cooperate with fluoroethylene carbonate in the electrolyte through shape characteristics such as sphericity. This helps the secondary battery to achieve higher initial efficiency and cycling performance and improved over-discharge resistance.

[0027] The present application is further illustrated below in conjunction with specific embodiments. It should be understood that these specific embodiments are used to only illustrate the present application and are not used to limit the scope of the present application.

[0028] In order to solve the problem of side reactions between silicon nanoparticles and an electrolyte, the present application has found that when fresh silicon interfaces generated from breakage are protected by adding FEC to an electrolyte, an excess of the FEC additive lead to problems such as reduced active ion concentration in the electrolyte, increased electrolyte viscosity and increased electrode impedance, thereby affecting performance such as the coulombic efficiency and capacity retention rate of a secondary battery.

[0029] In view of this, the present application provides a secondary battery, including a negative electrode sheet and an electrolyte, the negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes silicon-containing active particles. A sphericity of the silicon-containing active particles is A, and the electrolyte includes fluoroethylene carbonate. Based on a mass of the electrolyte, a mass percentage of the fluoroethylene carbonate is B%; where A and B satisfy: 1.6" (B A)" 29.4. By making the sphericity of the negative electrode silicon material particles and the content of the fluoroethylene carbonate in the electrolyte satisfy the above relationship in the present application, the synergistic effect between the sphericity of the material particles and the content of the fluoroethylene carbonate is fully utilized to reduce or avoid the problem that sharp corners of the silicon material particles of the secondary battery are crushed during the negative electrode rolling process or during charging and discharging, thereby enabling the SEI film formed by the fluoroethylene carbonate to effectively cover the silicon-containing fresh interface exposed after the silicon-containing active particles are broken. This reduces side reactions between the exposed active silicon and the electrolyte, and ensures that the SEI film on the surface of the silicon-containing active particles has low impedance, so that the secondary battery has low internal resistance, thereby improving the capacity exertion and coulombic efficiency of the secondary battery and enhances the over-discharge resistance of the secondary battery.

[0030] In some embodiments, the ratio B / A of the mass percentage B% of the additive fluoroethylene carbonate to the sphericity A of the silicon-containing active particles may be 1.6, 2.9, 4, 4.4, 4.9, 5.1, 5.9, 6.2, 7.3, 8.8, 9.8, 10.1, 10.3, 16.2, 18.3, 22.0, 23.5, 24.4, 29.4 or a value within a range composed of any two of these values. When B / A<1.6, the SEI film formed by the fluoroethylene carbonate cannot effectively cover the silicon-containing fresh interface generated by particle breakage, which will eventually cause the exposed active silicon to persistently consume the electrolyte, resulting in a decrease in the coulombic efficiency of the secondary battery. When B / A>29.4, an excessively high content of the additive fluoroethylene carbonate causes the impedance of the formed SEI film to increase, thereby causing the internal resistance of the secondary battery to increase and reducing the initial coulombic efficiency performance of the secondary battery.

[0031] In some embodiments, when the B / A value satisfies 6.2<(B / A)C16.2, the cooperation of the fluoroethylene carbonate and the sphericity of the silicon-containing active particles enables the secondary battery to exhibit higher initial coulombic efficiency and capacity retention rate, as well as more excellent overdischarge resistance.

[0032] In some embodiments, the conductivity of the electrolyte is 6.5 mS / cm-11 mS / cm. By controlling the conductivity within the above range, the transport of active ions can be promoted, so that the secondary battery has improved cycling performance and over-discharge resistance.

[0033] In some embodiments, the hydrofluoric acid content in the electrolyte is <83 gg / g, which can further improve the kinetic performance of the secondary battery.

[0034] In some embodiments, 0.65<A<1. For example, the sphericity A of the silicon-containing active particles may be 0.65, 0.68, 0.71, 0.79, 0.82, 0.91, 1 or a value within a range composed of any two of these values. The silicon-containing active particles with the sphericity within this range have fewer sharp corners on the surface, which can reduce or avoid the crushing of the silicon-containing active particles during cold pressing of the electrode sheet, and reduce the exposure of active silicon. In conjunction with the above relationship between sphericity and fluoroethylene carbonate content, this can further reduce side reactions between active silicon and the electrolyte, further improve the coulombic efficiency of the secondary battery and enhance over-discharge resistance thereof. In some embodiments, 0.71<A<1 can further improve the coulombic efficiency of the secondary battery and enhance over-discharge resistance thereof.

[0035] In some embodiments, 1.1<B<20. For example, B may be 1.1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 or a value within a range composed of any two of these values. On the basis of the coordination relationship between the sphericity of the silicon-containing active particles and the content of the fluoroethylene carbonate, further regulating the mass percentage of the fluoroethylene carbonate can reduce or avoid the increase in internal resistance of the secondary battery caused by the generated SEI film, and further improve the initial coulombic efficiency of the secondary battery. In some embodiments, 2<B<7. By further controlling the mass percentage of the fluoroethylene carbonate, the quality improvement of the SEI film can be maximized, while the silicon-containing active particles are protected, the kinetic performance of the secondary battery can be improved, and the over-discharge resistance thereof can be enhanced.

[0036] In some embodiments, a minimum angle of cross-sectional profiles of silicon-containing active particles with a diameter greater than 10 gm is C°, and 96<C<180. For example, C may be 96, 100, 110, 120, 129, 135, 140, 150, 160, 170, 180 or a value within a range composed of any two of these values. When the minimum angle of the cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 gm satisfies the above range, it indicates that the edges and corners of the silicon-containing active particles are gentle, which is beneficial to applying a uniform force on the silicon-containing active particles in the negative electrode active material layer. This reduces the breakage of the silicon-containing active particles, improves the active ion transport, further improves the coulombic efficiency of the secondary battery and enhances cycling performance and over-discharge resistance thereof. In the present application, the diameter of the silicon-containing active particles is the longest distance between any two points on the cross-sectional profiles of the silicon-containing active particles.

[0037] In some embodiments, the sphericity A of the silicon-containing active particles, the minimum angle C° of the cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 gm, and the mass percentage B% of the additive fluoroethylene carbonate satisfy: 45.28<(A*C- B)<176.0. For example, AxC-B may be 45.28, 45.3, 67.72, 63.4, 69.8, 70.59, 71.72, 76.72, 79.85, 80.72, 83.72, 85.72, 86.62, 86.72, 89.8, 90.8, 97.8, 97.91, 98.8, 101.78, 113.39, 151.5, 176.0 or a value within a range composed of any two of these values. By controlling the sphericity of the silicon-containing active particles, the shape characteristics of the minimum angle of the cross-sectional profiles, and the mass percentage of the fluoroethylene carbonate to satisfy the above relationship, the SEI film formed by the fluoroethylene carbonate can be further ensured to cover the broken surface of the silicon-containing active particles, reducing the internal impedance of the secondary battery, optimizing the cycling performance and overdischarge resistance of the secondary battery, and improving the initial coulombic efficiency and cycling capacity retention rate thereof. In some embodiments, A, B and C satisfy: 60<(A*C-B)<120, further improving and optimizing the cycling performance and over-discharge resistance of the secondary battery.

[0038] In some embodiments, a specific surface area of the silicon-containing active particles is 0.5 m2 / g-5 m2 / g. In some embodiments, the specific surface area of the silicon-containing active particles is 0.5 m2 / g-2.8 m2 / g. When the specific surface area of the silicon-containing active particles is within the above range, the transport and diffusion rate of active ions can be ensured while reducing side reactions with the electrolyte, further improving the initial coulombic efficiency of the secondary battery.

[0039] In some embodiments, a gram capacity of the silicon-containing active particles is 1621 mAh / g-1796 mAh / g, and initial coulombic efficiency of the silicon-containing active particles is 75.3%-83.5%.

[0040] In some embodiments, the silicon-containing active particles provided by the present application are prepared by a method including the following steps: Step S100. Perform gradient heating and heat preservation treatment on a mixture of a carbon source and a base to obtain a porous carbon material. Step S200. Introduce silane gas into the porous carbon material under an inert gas atmosphere for reaction to obtain the silicon-containing active particles. This method helps to obtain the silicon-containing active particles including porous carbon particles and silicon formed inside the porous carbon particles and / or on the surface of the porous carbon particles, thereby better cooperating with the fluoroethylene carbonate in the electrolyte through shape characteristics.

[0041] In some embodiments, the gradient heating and heat preservation treatment includes: heating the mixture of the carbon source and the base to 350°C-550°C for heat preservation treatment for 15 min-45 min, and then heating it to 600°C-900°C for heat preservation treatment for 0.5 h-2 h.

[0042] In some embodiments, the carbon source is at least one selected from the group consisting of phenolic resin, coal, biomass material, and petroleum coke.

[0043] In some embodiments, a sphericity of the carbon source is 0.68-1. For example, it may be 0.68, 0.70, 0.74, 0.78, 0.82, 0.92, 0.93, 0.96, 1 or a value within a range of any two of these values. The sphericity of the silicon-containing active particles in the present application can be regulated by controlling the sphericity of the carbon source. Using the carbon source with the above sphericity in conjunction with gradient heating and heat preservation treatment can obtain silicon-containing active particles with higher sphericity. After cooperating with FEC, this is beneficial to further improving the kinetic performance of the secondary battery and enhancing the over-discharge resistance.

[0044] In some embodiments, a minimum angle of cross-sectional profiles of the carbon source is 105°-180°. For example, it may be 105°, 113°, 121°, 130°, 136°, 146°, 152°, 167°, 172°, 175°, 180° or a value within a range of any two of these values. The minimum angle of the cross-sectional profiles of the silicon-containing active particles in the present application can be regulated by controlling the minimum angle of the cross-sectional profiles of the carbon source. Using the carbon source with the above minimum angle of the cross-sectional profiles in conjunction with gradient heating and heat preservation treatment can obtain silicon-containing active particles with a higher minimum angle of cross-sectional profiles. After cooperating with its sphericity and FEC in the electrolyte, this is beneficial to further optimizing the cycling performance and over-discharge resistance of the secondary battery, and improving the initial coulombic efficiency and cycling capacity retention rate thereof.

[0045] In some embodiments, after the reaction of the introduced silane gas in step S200 is completed, alkyne gas is also introduced into the porous carbon material to ensure the purity of the silicon particles deposited in the porous carbon.

[0046] In some specific embodiments, the preparation method of the silicon-containing active particles includes the following steps:

[0047] Step S100. Mix phenolic resin microspheres and potassium hydroxide in a ratio of alkali to carbon (1-4):(1-2), first treat them in a rotary kiln at 300°C to 400°C for 20 min to 40 min, then raise the temperature of the rotary kiln to 600°C to 800°C and hold at that temperature for 20 min to 50 min, and acid-wash, water-wash and dry the obtained product to obtain a porous carbon material.

[0048] Step S200. Take the above porous carbon material and add it to a fluidized bed reactor for heating to 400°C to 550°C under a nitrogen atmosphere of 7 L / min to 14 L / min and hold at that temperature for 1 h to 3 h; then introduce 1.5 L / min to 3.5 L / min of silane gas for 200 min to 400 min; after stopping the introduction of silane, heat the fluidized bed reactor to 400°C to 550°C and hold at that temperature for 0.5 h to 2.5 h; and then introduce 3.5 L / min to 6 L / min of acetylene gas for 250 min to 350 min. After the reaction is completed, silicon-containing active particles are obtained. In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, poly(1,1-difluoroethylene), polyethylene, polypropylene, styrene-butadiene rubber, acrylated or acrylate-modified styrene-butadiene rubber, epoxy resin or nylon, or the like.

[0049] In some embodiments, the conductive agent includes, but is not limited to: carbon-based material, metal-based material, conductive polymer and a mixture thereof. In some embodiments, the carbon-based material is selected from the group consisting of carbon black, acetylene black, ketjen black, carbon fiber and any combination thereof. In some embodiments, the metal-based material is selected from the group consisting of metal powder, metal fiber, copper, nickel, aluminum and silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0050] The secondary battery of the present application further includes a positive electrode, the positive electrode includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material, a binder and a conductive agent.

[0051] According to some embodiments of the present application, the positive electrode current collector may use a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, and the like) on a polymer substrate.

[0052] According to some embodiments of the present application, the positive electrode active material includes at least one selected from the group consisting of lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganate, spinel lithium nickel manganate, and lithium titanate. In some embodiments, the binder includes a binder polymer, such as at least one selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber and polyurethane. In some embodiments, the polyolefin binder includes at least one selected from the group consisting of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol and polyacrylic acid. In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, or silver; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.

[0053] The secondary battery of the present application further includes a separator. The separator used in the secondary battery of the present application is not limited to a particular material and shape, and it may be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer is at least one selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be selected.

[0054] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder. The inorganic particles are at least one selected from the group consisting 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-carbon composite material, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is at least one selected from the group consisting of polyvinylidene fluoride, a copolymer of vinylidene fluoridehexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is at least one selected from the group consisting of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0055] The secondary battery of the present application further includes an electrolyte. The electrolyte in the present application includes an organic solvent, a lithium salt and an optional additive. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate. In some embodiments, the organic solvent includes an ether solvent, for example, including at least one selected from the group consisting of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one selected from the group consisting of an organic lithium salt and an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate    (LiPO2F2),    lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalato)borate LiB(C2O4)2 (LiBOB) or lithium difluoro(oxalato)borate LiBF2(C2O4) (LiDFOB). The additive may be an electrolyte additive known in the prior art.

[0056] According to some embodiments of the present application, the secondary battery of the present application includes, but is not limited to: a lithium-ion battery or a sodium ion battery. In some embodiments, the secondary battery includes a lithium-ion battery.

[0057] The present application further provides an electronic device including the secondary battery of the first aspect of the present application.

[0058] The electronic equipment or device of the present application is not particularly limited. In some embodiments, the electronic equipment of the present application includes but is not limited to notebook computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game machines, clocks, electric tools, flashlights, cameras, large household batteries, lithium ion capacitors, and the like.

[0059] The solution of the present application is described below by taking a lithium-ion battery as an example and in combination with the following specific examples and comparative examples. In the following examples and comparative examples, the reagents, materials and instruments used can be commercially obtained unless otherwise specified.

[0060] Example 1

[0061] The lithium-ion battery of this example included a negative electrode sheet and an electrolyte, the negative electrode sheet included a negative electrode active material layer, and the negative electrode active material layer included silicon-containing active particles. A sphericity A of the silicon-containing active particles was 0.68. The electrolyte contained FEC, and based on a mass of the electrolyte, a mass percentage B% of FEC was 1.1%, where A and B satisfied: B / A=1.6.

[0062] A minimum angle C° of cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 pm was 129°, and (A*C-B)=86.62.

[0063] The lithium-ion battery of this example was prepared by a method including the following steps:

[0064] <Preparation of porous carbon>

[0065] 1000 g of thermoplastic linear phenolic resin and 120 g of a curing agent hexamethylenetetramine were dissolved in 2.5 L of methanol at a dissolution temperature of 50°C for a dissolution time of 1 h. Then the methanol solvent was removed by vacuum distillation to obtain a uniform mixture of phenolic resin and hexamethylenetetramine.

[0066] An aqueous solution of sodium dodecyl sulfate with a concentration of 0.15 mol / L was prepared in an autoclave, and the above uniform mixture of phenolic resin and hexamethylenetetramine was dissolved therein. The temperature of the autoclave was raised to 130°C and held at that temperature for 30 min. After the autoclave was cooled, phenolic resin microspheres were obtained. A sphericity of the phenolic resin microspheres was 0.72, and a minimum angle of cross-sectional profiles thereof was 136°.

[0067] The phenolic resin microspheres and potassium hydroxide were mixed in a ratio of alkali to carbon of 3:1, and first treated in a rotary kiln at 400°C for 30 min. Then the temperature of the rotary kiln was raised to 750°C and held at that temperature for 45 min. The obtained product was acid-washed, water-washed and dried to obtain a porous carbon material.

[0068] <Preparation of silicon-containing active particles>

[0069] 1000 g of the above porous carbon was taken and added to a fluidized bed reactor, heated to 480°C under a 10 L / min nitrogen atmosphere and held at that temperature for 2 h. Then 2.5 L / min of monosilane gas was introduced for 300 min. After stopping the introduction of silane, the fluidized bed was heated to 500°C and held at that temperature for 1 h. Then 5 L / min of acetylene gas was introduced for 300 min. After the reaction was completed, silicon-containing active particles were obtained.

[0070] A specific surface area of the silicon-containing active particles was 2.80 m2 / g, and based on a mass of the silicon-containing active particles, a mass fraction of element Si was 46.2%.

[0071] <Preparation of negative electrode sheet>

[0072] Negative electrode active materials (silicon-containing active particles and graphite mixed in a mass ratio of 1:9), carbon nanotubes, lithium carboxymethyl cellulose, and lithium polyacrylate were mixed in a mass ratio of 97.4:0.2:0.4:2, and a solvent deionized water was added. A negative electrode slurry was obtained under the action of a vacuum mixer, where a solid content of the negative electrode slurry was 45wt%, and the viscosity was 6000 mPa.s. The negative electrode slurry was uniformly applied on one surface of a negative electrode current collector copper foil with a thickness of 6 gm. The copper foil was dried at 80°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side with a coating weight of 100.1 mg / 1540.25 mm2. Then the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with the negative electrode material layer on both sides. After cold pressing, slicing and slitting, a negative electrode sheet with a size of 661 mm*78 mm was obtained.

[0073] FIG. 1 is a backscattered SEM image of a cross section of a negative electrode sheet in a thickness direction in a lithium-ion battery of Example 1 of the present application, where based on a mass of a negative electrode active material layer, a mass fraction of element Si is 4.5%.

[0074] <Preparation of positive electrode sheet>

[0075] A positive electrode active material LiCoO2, a conductive agent conductive carbon black, and a binder polyvinylidene fluoride were mixed in a mass ratio of 96.7:1.7:1.6, and N-methylpyrrolidone (NMP) was added, to obtain a positive electrode slurry under the action of a vacuum mixer, where a solid content of the positive electrode slurry was 76wt%. The positive electrode slurry was uniformly applied on one surface of a positive electrode current collector aluminum foil with a thickness of 9 gm. The aluminum foil was dried at 120°C to obtain a positive electrode sheet coated with a positive electrode material layer on one side with a coating weight of 260 mg / 1540.25 mm2. Then the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated with the positive electrode material layer on both sides. After cold pressing, slicing and slitting, a positive electrode sheet with a size of 661 mm*76.5 mm was obtained.

[0076] <Preparation of electrolyte>

[0077] In a glove box with an argon atmosphere with a water content of less than 10 ppm, EC, PC, EP and PP were mixed in a mass ratio of 17:25:40:18 to obtain an organic solvent, and then a lithium salt LiPF6 and FEC were added to the organic solvent to obtain an electrolyte. Based on a mass of the electrolyte, a mass percentage of the lithium salt LiPF6 was 12.5%, a mass percentage of FEC was 1.1%, a conductivity of the electrolyte was 7.83 mS / cm, and a hydrofluoric acid content thereof was 28.2 pg / g.

[0078] <Separator>

[0079] A porous polyethylene film with a thickness of 10 pm (provided by Celgard) was used.

[0080] <Preparation of lithium-ion battery>

[0081] The positive electrode sheet, separator and negative electrode sheet prepared above were stacked in order, so that the separator was in the middle of the positive electrode sheet and the negative electrode sheet for separation, and were wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum-plastic film packaging bag, and dried, followed by electrolyte injection, and processes such as vacuum packaging, standing, formation, degassing, and edge trimming to obtain a lithium-ion battery.

[0082] Example 2

[0083] The lithium-ion battery of this example differed from Example 1 only in that, based on the mass of the electrolyte, the mass percentage of FEC was 2%; where B / A=2.9.

[0084] Example 3

[0085] The lithium-ion battery of this example differed from Example 1 only in that, based on the mass of the electrolyte, the mass percentage of FEC was 4%; where B / A=5.9.

[0086] Example 4

[0087] The lithium-ion battery of this example differed from Example 1 only in that, based on the mass of the electrolyte, the mass percentage of FEC was 7%; where B / A=10.3.

[0088] Example 5

[0089] The lithium-ion battery of this example differed from Example 1 only in that, based on the mass of the electrolyte, the mass percentage of FEC was 11%; where B / A=16.2.

[0090] Example 6

[0091] The lithium-ion battery of this example differed from Example 1 only in that, based on the mass of the electrolyte, the mass percentage of FEC was 16%; where B / A=23.5.

[0092] Example 7

[0093] The lithium-ion battery of this example differed from Example 1 only in that, based on the mass of the electrolyte, the mass percentage of FEC was 20%; where B / A=29.4.

[0094] Example 8

[0095] The lithium-ion battery of this example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 0.79, and based on the mass of the electrolyte, the mass percentage of FEC was 4%; where B / A=5.1.

[0096] Example 9

[0097] The lithium-ion battery of this example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 0.82, and based on the mass of the electrolyte, the mass percentage of FEC was 4%; where B / A=4.9.

[0098] Example 10

[0099] The lithium-ion battery of this example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 0.91, and based on the mass of the electrolyte, the mass percentage of FEC was 4%; where B / A=4.4.

[00100] Example 11

[00101] The lithium-ion battery of this example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 0.65, and based on the mass of the electrolyte, the mass percentage of FEC was 4%; where B / A=6.2.

[00102] Example 12

[00103] The lithium-ion battery of this example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 0.68, and based on the mass of the electrolyte, the mass percentage B% of FEC was 20%; where B / A=29.4, the minimum angle C° of the cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 ^m was 96°, and (AxC-B)=45.28.

[00104] Example 13

[00105] The lithium-ion battery of this example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 1, and based on the mass of the electrolyte, the mass percentage B% of FEC was 4%; where B / A=4, the minimum angle C° of the cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 pm was 180°, and (A*C-B)=176.0.

[00106] Comparative Example 1

[00107] The lithium-ion battery of this comparative example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 0.68, and based on the mass of the electrolyte, the mass percentage of FEC was 1%; where B / A=1.5.

[00108] Comparative Example 2

[00109] The lithium-ion battery of this comparative example differed from Example 1 only in that the sphericity A of the silicon-containing active particles was 0.71, and based on the mass of the electrolyte, the mass percentage of FEC was 21%; where B / A=29.6.

[00110] Test example

[00111] The following test methods are used to test various parameters or performance of the lithium-ion batteries provided in the examples and comparative examples of the present application:

[00112] 1. Sphericity test

[00113] The sphericity of the silicon-containing active particles was tested by the equivalent diameter method. The test method was to use a ZEISS-SEM (sigma-0233) scanning electron microscope to observe the silicon-containing active particles in the silicon-containing active particle powder or the negative electrode sheet, eliminate incomplete particles, and calculate the perimeter equivalent diameters and the particle area equivalent diameters of the complete particles.

[00114] Sphericity=perimeter equivalent diameter / area equivalent diameter.

[00115] 2. Minimum angle of cross-sectional profiles of particles with diameter greater than 10 pm

[00116] 0.47 g of the silicon-containing active particles and 0.396 g of polyacrylic acid were dispersed in water. They were mixed uniformly in a homogenizer, and applied on the surface of copper foil with a doctor blade, dried, and then sliced using a Japanese electronic ion polisher (model: IB-09010CP). A ZEISS-SEM (sigma-0233) was used to take cross-sectional microscopic images of the silicon-containing active particles. The cross-sectional profiles of silicon-containing active particles with a diameter greater than 10 pm were selected for analysis. FIG. 2 shows a schematic diagram of determining a minimum angle of cross-sectional profiles of silicon-containing active particles with a diameter greater than 10 pm. As shown in FIG. 2, the outline of the silicon-containing active particles was traced, then tangents were drawn along the edges on two sides of the sharp corner, and the included angle between the two tangents was measured. The values of the measured angles were compared in magnitudes, and the minimum value was taken as the minimum angle value of the cross-sectional profiles of the particles (as shown in the schematic diagram of FIG. 2, angle 1 was 115°, angle 2 was 105°, angle 3 was 142°, angle 4 was 140°, and angle 2 was recorded as the minimum angle of the cross-sectional profiles of the silicon-containing active particles, that is, the minimum angle of the cross-sectional profiles of the silicon-containing active particles was 105°). The degrees of the minimum angles in the cross-sectional profiles of at least 20 silicon-containing active particles were collected and averaged as the minimum angle of the cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 pm in this batch.

[00117] 3. Test for specific surface area

[00118] 2.0 g of silicon-containing active particles was weighed and placed in a sample tube. The sample tube was installed at the degassing station port. The heating temperature was set to 200°C for degassing for 120 min. Nitrogen was introduced into the sample tube, and the adsorption partial pressure was directly measured by controlling the equilibrium pressure in the sample tube. The adsorption amount at the partial pressure point was obtained from the gas state equation. During the measurement, the adsorbate gas was gradually increased to gradually increase the adsorption equilibrium pressure, and finally an adsorption isotherm was obtained. The adsorption equilibrium pressure was reduced by gradually pumping away the adsorbate gas to obtain a desorption isotherm. Finally, the specific surface area of the silicon-containing active particles was calculated using the BJH (Barrett-Joyner-Halenda) theory.

[00119] 4. Test for hydrofluoric acid content in electrolyte

[00120] 100 g of ice-water mixture was taken in a plastic beaker, 10 drops of bromothymol blue indicator with a concentration of 1 g / L were added and stirred evenly. Titration was performed with a 0.01 mol / L NaOH standard solution until the ice-water mixture turned blue. The standard volume V0 (ml) of the NaOH standard solution consumed at the titration endpoint was recorded.

[00121] An ice-water mixture and a bromothymol blue indicator mixed solution were prepared by the same method as above, and 20 g of the electrolyte under test was added. The added mass m (g) of the electrolyte under test was recorded. Titration was performed with a 0.01 mol / L NaOH standard solution until the icewater mixture turned blue. The standard volume V1 (ml) of the NaOH standard solution consumed at the titration endpoint was recorded.

[00122] Finally, the content of hydrofluoric acid in the electrolyte under test was calculated using the following formula: HF (^g / g)=(Vi-Vo)x2OO / m.

[00123] 5. Test for electrolyte conductivity

[00124] The test was performed with reference to the method for determining conductivity in lithium hexafluorophosphate electrolyte in HG / T 4067-2015. The selected electrode was a DJS-1C platinum black electrode.

[00125] 6. Test for gram capacity of silicon-containing active particles

[00126] Silicon-containing active particles, a conductive agent (SP), a binder (PAA-Li), carbon nanotubes (CNTs), and a dispersant (CMC) were mixed in a mass ratio of 84:10:5:0.4:0.6, and deionized water was added to obtain a negative electrode slurry with a solid content of 48%. The negative electrode slurry was mixed evenly and then applied on copper foil. After drying, cold pressing and punching, a negative electrode sheet was obtained.

[00127] In a glove box with water and oxygen contents both less than 10 ppm, ethyl methyl carbonate (EMC), ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, then FEC accounting for 10% of the volume fraction of the above mixed solvent was added, and finally a lithium salt LiPF6 was added to obtain an electrolyte. The concentration of the lithium salt LiPF6 was 1 mol / L.

[00128] In a glove box with water and oxygen contents both less than 10 ppm, the above negative electrode sheet, a counter electrode metal lithium sheet, a polypropylene (PP) separator and the above electrolyte were assembled into a button cell.

[00129] Test of gram capacity of silicon-containing active particles: the above button cell was left standing for 6 h in a 25°C environment, discharged to 5 mV at a current of 0.05C, then discharged to 5 mV at a current of 50 pA, left standing for 5 min, then discharged to 5 mV at a current of 10 pA, left standing for 5 min, and then charged to 0.8 V at a rate of 0.05C. The above discharge capacity was recorded as G0, and the charge capacity was recorded as G1.

[00130] Gram capacity of silicon-containing active particles=G1; and initial coulombic efficiency of silicon-containing active particles=G1 / G0x100%.

[00131] 7. Test for initial discharge capacity and initial coulombic efficiency of lithium-ion battery

[00132] In a 25°C normal pressure environment, the newly prepared lithium-ion battery was charged at a constant current of 0.5C to 4.53 V, and then charged at a constant voltage to 0.05C, and left standing for 5 min. The charge capacity at this step was recorded as C1. It was discharged at a constant current of 0.2C to 3.0 V, and the discharge capacity at this step was recorded as C2. C2 was the initial discharge capacity of the lithium-ion battery.

[00133] Initial coulombic efficiency of lithium-ion battery=C2 / C1x100%.

[00134] 8. Test for cycling performance of lithium-ion battery

[00135] The lithium-ion battery was placed in a 25°C thermostatic chamber and left standing for 30 min to bring the lithium-ion battery to a constant temperature state of 25°C; and was charged at a constant current of 1C to 4.53 V, charged at a constant voltage until the current is 0.025C, left standing for 5 min, and discharged at a constant current of 0.5C to 3.0 V. The initial discharge capacity was recorded as C0. The above step was repeated for 400 cycles, and the discharge capacity after 400 cycles was recorded as C1.

[00136] Capacity retention rate after 400 cyclesC1 C0,x 100%.

[00137] 9. Test for over-discharge resistance

[00138] The test temperature was 25°C. It was charged and discharged at a constant current of 0.2C to 3.0 V, left standing for 5 minutes, then discharged at a constant current of 10 mA to 0.1 V, left standing for 30 minutes, and then discharged at a constant current of 1 mA to 0.1 V. An online thickness measuring device was used to test the thickness of the lithium-ion battery. The thickness measuring weight was 300 g, and the sampling time interval was 10 s. The initial thickness of the lithium-ion battery was recorded as T1, the thickness after discharge was recorded as T2, and the voltage of the lithium-ion battery was recorded.

[00139] The voltage value when (T2-T1) / T1x100% equaled 10% was recorded as the over-discharge gas production test voltage of the lithium-ion battery. A lower value of the over-discharge gas production test voltage means higher over-discharge resistance of the lithium-ion battery.

[00140] The parameters and performance characterization results of the lithium-ion batteries of Examples 1 to 13 and Comparative Examples 1 and 2 provided by the present application obtained through the above tests are shown in Table 1 below. Table 1 Group Sphericity A Mass percentage B of FEC (%) B / A Minimum angle C of particles with diameter>10 gm (°) A^C-B Initial coulombic efficiency of lithium-ion battery Capacity retention rate after 400 cycles Overdischarge gas production test voltage (V) Example 1 0.68 1.1 1.6 129 86.62 86.6% 92.3% 2.30 Example 2 0.68 2 2.9 129 85.72 88.4% 93.5% 2.15 Example 3 0.68 4 5.9 129 83.72 88.7% 94.8% 2.07 Example 4 0.68 7 10.3 129 80.72 89.4% 95.9% 1.99 Example 5 0.68 11 16.2 129 76.72 88.2% 93.4% 2.18 Example 6 0.68 16 23.5 129 71.72 87.8% 92.9% 2.22 Example 7 0.68 20 29.4 129 67.72 87.1% 92.5% 2.26 Example 8 0.79 4 5.1 129 97.91 89.6% 96.1% 1.93 Example 9 0.82 4 4.9 129 101.78 89.8% 96.7% 1.90 Example 10 0.91 4 4.4 129 113.39 90.2% 96.9% 1.89 Example 11 0.65 4 6.2 129 79.85 87.9% 93.1% 2.20 Example 12 0.68 20 29.4 96 45.28 86.4% 92.0% 2.31 Example 13 1 4 4 180 176.0 90.7% 97.2% 1.91 Comparative Example 1 0.68 1 1.5 129 86.72 85.4% 88.6% 2.58 Comparative Example 2 0.71 21 29.6 129 70.59 83.2% 89.7% 2.47

[00141] As can be seen from Table 1, the lithium-ion batteries of Examples 1 to 13 control the sphericity A of the silicon-containing active particles and the mass percentage B% of FEC in the electrolyte to satisfy 1.6<(B / A)<29.4, their initial coulombic efficiency reaches 86.4%-90.7%, and their capacity retention rate after 400 cycles reaches 92.0%-97.2%, showing high initial efficiency and cycling performance. In addition, the over-discharge gas production test voltage of the lithium-ion batteries of Examples 1 to 13 can reach 1.85 V-2.31 V. It can be seen that the lithium-ion batteries of the embodiments of the present application can reach a lower discharge voltage when producing the same volume of gas, indicating that the lithium-ion batteries of the embodiments of the present application produce less gas during discharge and have higher over-discharge resistance.

[00142] In contrast, when the B / A value of the lithium-ion batteries of Comparative Examples 1 and 2 is outside the defined range, the initial coulombic efficiency is 83.2%-85.4%, the capacity retention rate after 400 cycles is 88.6%-89.7%, and the over-discharge gas production test voltage can be 2.47 V-2.58 V. The reason may be that the fresh interface generated when the silicon-containing active particles are stressed cannot be covered by a dense SEI film, resulting in persistent side reactions between the active silicon and the electrolyte, and seriously deteriorated performance of the lithium-ion battery.

[00143] When the sphericity A of the silicon-containing active particles is controlled to be 0.65-1, the initial efficiency, cycling performance and overdischarge resistance of the lithium-ion battery can be further improved.

[00144] It can be seen from Examples 1 to 7 that FEC can form a dense and low-impedance SEI film on the surface of the silicon-containing active particles, which can prevent side reactions of active silicon and further decomposition of the electrolyte, thereby allowing more active silicon to participate in alloying / dealloying reactions, thereby improving the initial coulombic efficiency of the lithium-ion battery and the capacity retention rate after 400 cycles, reducing its over-discharge gas production test voltage, and improving the cycling performance of the lithium-ion battery. Further controlling the mass percentage B% of FEC to be 2<B<7 results in higher initial coulombic efficiency and cycling capacity retention rate of the lithium-ion battery, and a lower discharge voltage when swelling occurs during the over-discharge gas production test. This indicates that the lithium-ion battery produces less gas during over-discharge and has higher over-discharge resistance.

[00145] Compared among Examples 8 to 11, the FEC content is the same, but the sphericity of the silicon-containing active particles changes. Examples 8 to 10 further optimize the shape characteristics of sphericity on the basis of satisfying the B / A range, so that the sphericity of the silicon-containing active particles is above 0.79, which has higher initial efficiency, cycling performance and over-discharge resistance than Example 11.

[00146] In Examples 1 to 13, by controlling the sphericity A of the silicon-containing active particles, the minimum angle C of the cross-sectional profiles of the silicon-containing active particles with a diameter greater than 10 gm, and the mass percentage B% of FEC in the electrolyte to satisfy 45.28<(AxC-B)<176.0, the lithium-ion battery has significantly improved initial efficiency and cycling capacity retention rate and significantly improved cycling performance and over-discharge resistance. When A, B, and C satisfy 60^(AX C-B)< 120, the performance of the secondary battery can be further improved, showing better cycling performance and over-discharge resistance.

Claims

1. A secondary battery, comprising a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material layer, the negative electrode active material layer comprises silicon-containing active particles, and a sphericity of the silicon-containing active particles is A; andthe electrolyte comprises fluoroethylene carbonate, and based on a mass of the electrolyte, a mass percentage of the fluoroethylene carbonate is B%;wherein 1.6<(B / A)<29.4.

2. The secondary battery according to claim 1, wherein 0.65<A<1.

3. The secondary battery according to claim 1 or 2, wherein 1.1<B<20.

4. The secondary battery according to any one of claims 1 to 3, wherein 2<B<7.

5. The secondary battery according to any one of claims 1 to 4, wherein a minimum angle of cross-sectional profiles of silicon-containing active particles with a diameter greater than 10 gm is C°, and 96<C<180.

6. The secondary battery according to claim 5, wherein 45.28<(A*C-B)<176.0.

7. The secondary battery according to claim 5 or 6, wherein 60<(A*C-B)<120.

8. The secondary battery according to any one of claims 1 to 7, wherein the silicon-containing active particles comprise a porous carbon matrix and nano-silicon, and the nano-silicon is distributed inside and on a surface of the porous carbon matrix.

9. The secondary battery according to any one of claims 1 to 8, wherein the secondary battery satisfies at least one selected from the group consisting of the following conditions:(1) based on a mass of the silicon-containing active particles, a mass fraction of element Si is 42%-55%;(2) a specific surface area of the silicon-containing active particles is 0.5 m2 / g-5 m2 / g; and(3) an electrical conductivity of the electrolyte is 6.5 mS / cm-11 mS / cm.

10. An electronic device, comprising the secondary battery according to any oneof claims 1 to 9.

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