Secondary battery, manufacturing method therefor and electronic apparatus

Abstract

The present application belongs to the technical field of batteries. Provided are a secondary battery and an electronic apparatus. The secondary battery of the present application comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising silicon-containing active particles, the aspect ratio of the silicon-containing active particles being A, the compaction density of the negative electrode active material layer being B, and A and B satisfying: 1.83≤(A×B)≤2.89. By controlling the synergistic relationship between the aspect ratio of the silicon-containing active particles and the compaction density of the negative electrode active material layer in the negative electrode sheet, the synergistic effect between the shapes of the silicon-containing active particles and the processing pressure is fully exerted, thus reducing the cracking of the silicon-containing active particles, and reducing side reactions between the silicon-containing active particles and an electrolyte, thereby improving the cycle performance and safety of secondary batteries.

Description

Secondary battery, preparation method thereof, and electronic device

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on March 25, 2024, with application number 202410346719.4 and invention name “A Secondary Battery and Electronic Device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the field of battery technology, and specifically relates to a secondary battery and an electronic device. Background Art

[0003] With the rapid development of electric vehicles, portable electronic devices and other fields, the demand for higher performance batteries is growing. Silicon-containing negative electrodes have a high active material embedding / de-embedding capacity (3579mAh / g). Compared with traditional carbon negative electrode materials (372mAh / g), the specific capacity of silicon-containing negative electrodes can be several times higher, or even more. This means that at the same volume and weight, silicon-doped batteries can store more lithium ions and provide a higher energy storage density. However, due to the problems of large volume changes and high electrochemical activity of silicon-containing negative electrodes in actual applications, they are prone to react with electrolytes to cause capacity loss, which restricts the development and application of silicon-containing negative electrodes.

[0004] Existing technology proposes depositing nano-silicon in porous carbon materials, using porous carbon to provide expansion space for silicon particles, and combining with the smaller volume change rate of nano-silicon materials to improve the volume effect of silicon-containing negative electrodes to a certain extent, but the cycle performance of secondary batteries still needs further improvement. Summary of the Invention

[0005] In view of this, the present application provides a secondary battery to solve the problem of poor cycle performance of secondary batteries with silicon-containing negative electrodes in the prior art, and also has higher safety performance. In a second aspect, the present application provides an electronic device including the secondary battery.

[0006] To address the above-mentioned problems, the present application provides, in a first aspect, a secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer; the negative electrode active material layer comprising silicon-containing active particles; the aspect ratio of the silicon-containing active particles is A, the compaction density of the negative electrode active material layer is B g / cc, and A and B satisfy the following: 1.83≤(A×B)≤2.89. By controlling the aspect ratio of the silicon-containing active particles in the negative electrode plate and coordinating it with the compaction density of the negative electrode active material layer, the synergistic effect of the two reduces the breakage of the silicon-containing active particles during the rolling process of the negative electrode plate and the charging expansion process, resulting in a lower specific surface area of ​​the silicon-containing active particles, reducing side reactions between the silicon-containing active particles and the electrolyte, thereby reducing the loss of active material, and further helping to reduce the internal resistance and heat generation of the secondary battery, thereby improving the cycle performance of the secondary battery and having higher safety and reliability.

[0007] More preferably, 1.0≤A≤1.7. On the basis of satisfying the above A×B relationship, controlling the range of the aspect ratio of the silicon-containing active particles and reducing the anisotropy of the particles can promote uniform stress on the silicon-containing active particles during rolling, further reducing the cracking or breakage of the particles, thereby reducing the exposure of the internal active silicon after particle breakage and the side reaction with the electrolyte, which is conducive to maintaining a high capacity retention rate of the secondary battery.

[0008] More preferably, 1.70 ≤ B ≤ 1.83. While satisfying the aforementioned A × B relationship, controlling the compaction density of the negative electrode active material layer ensures sufficient contact between the components in the active material layer, further reducing breakage of the silicon-containing active particles and improving the cycle performance and safety of the secondary battery. Furthermore, 1.75 ≤ B ≤ 1.80 ensures even better cycle performance and safety.

[0009] More preferably, A and B satisfy: 1.83≤(A×B)≤2.14. Secondary batteries within this range can further improve the cycle performance and safety performance of secondary batteries by coordinating the aspect ratio of the silicon-containing active particles with the compaction density of the negative electrode active material layer.

[0010] More preferably, the sphericity of silicon-containing active particles with a diameter greater than 10 μm is between 0.81 and 0.98. By controlling the sphericity of the silicon-containing active particles, in conjunction with their aspect ratio and the compaction density of the negative electrode active material layer, the present invention can further ensure that the silicon-containing active particles are uniformly stressed within the negative electrode active material layer, reducing or avoiding the problem of uneven stress and easy crushing when stressed, and further optimizing the cycle performance and safety performance of the secondary battery.

[0011] More preferably, the mass fraction of Si element is 43% to 55% based on the silicon-containing active particles. In some embodiments, the mass fraction of Si element is 2.1% to 22% based on the negative electrode active material layer.

[0012] More preferably, the silicon-containing active particles are prepared by a method comprising the following steps: step S100, subjecting a mixture of a carbon source and an alkali to a gradient temperature increase and insulation treatment to obtain a porous carbon material; step S200, introducing silane gas into the porous carbon material under an inert gas atmosphere to react, thereby obtaining silicon-containing active particles.

[0013] More preferably, the gradient temperature rising and heat preservation treatment comprises: heating the mixture of the carbon source and the alkali to 350° C. to 550° C. and heat preservation treatment for 15 min to 45 min, and then heating to 600° C. to 900° C. and heat preservation treatment for 0.5 h to 2 h.

[0014] More preferably, the carbon source is selected from at least one of phenolic resin, coal, biomass material, and petroleum coke.

[0015] More preferably, the aspect ratio of the carbon source is 1.0 to 1.8.

[0016] More preferably, the secondary battery satisfies at least one of conditions a to c: condition a, the Dv50 particle size of the silicon-containing active particles satisfies: 5.6μm≤Dv50≤10.4μm; condition b, the true density of the silicon-containing active particles is 1.853g / cc~2.108g / cc; condition c, the negative electrode active material layer also includes a carbon material; the carbon material includes artificial graphite and / or natural graphite. Among them, the present application controls the Dv50 particle size of the silicon-containing active particles within a suitable range, which can ensure that lithium ions and electrons have a suitable transmission distance in the particles, while reducing the outer surface of the silicon-containing active particles, further reducing side reactions with the electrolyte, and ensuring the coulombic efficiency and cycle performance of the secondary battery. On the other hand, the present application controls the true density of the silicon-containing active particles to provide them with suitable pores, thereby accommodating the volume expansion of the internal nano-silicon and ensuring a high silicon content to improve the energy density of the secondary battery.

[0017] In a second aspect, the present application further provides an electronic device comprising any one of the above-mentioned secondary batteries.

[0018] Based on the secondary battery provided by the present application, by limiting the synergistic relationship between the aspect ratio A of the silicon-containing active particles and the compaction density B of the negative electrode active material layer, the synergistic effect between the shape of the silicon-containing active particles and the processing pressure is fully utilized to avoid the secondary battery from being crushed due to the silicon material particles in the negative electrode rolling process, so that the active silicon inside the silicon-containing active particles is exposed and undergoes side reactions with the air or electrolyte, resulting in loss of active materials, thereby improving the capacity retention rate and cycle performance of the secondary battery. Reducing side reactions can also reduce the internal resistance and internal heat generation of the secondary battery, so that the secondary battery has higher safety performance. The present application further controls the sphericity of the silicon-containing active particles with a diameter greater than 10 μm in combination with the above parameters, which can avoid the silicon-containing active particles from being broken due to uneven force in the negative electrode active material layer, thereby further improving the cycle performance and safety performance of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] FIG1 is a SEM image of silicon-containing active particles provided in Example 1 of the present application. DETAILED DESCRIPTION

[0020] In order to make the purpose, 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 embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0021] For the sake of clarity, this application only specifically discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0022] In the description of the present application, unless otherwise specified, “above” and “below” include the number.

[0023] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0024] In this application, a list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0025] As used herein, the term "silicon-containing active particles" refers to anode materials containing silicon in a solid particle state, such as 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 within and / or on the surface of the porous carbon particles.

[0026] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0027] Silicon-containing negative electrodes have higher specific capacity and can therefore provide higher electrical energy storage density. However, during actual processing, the compaction density of silicon-containing negative electrodes is lower than that of traditional graphite negative electrodes, which makes it impossible to fully utilize the high capacity advantage of silicon negative electrodes, resulting in limited improvement in the volume energy density of secondary batteries.

[0028] During their research, the inventors of this application discovered that because the silicon negative electrode's deformation ability during compaction is weaker than that of graphite, and because conventional silicon negative electrode particles are irregular in shape, the silicon negative electrode particles are easily broken due to uneven force when the rolling pressure increases. Before the secondary battery is assembled, the broken silicon negative electrode particles react with moisture or oxygen in the air, reducing the capacity of the silicon negative electrode. After the secondary battery is assembled, they react irreversibly with the electrolyte, consuming the electrolyte's solvent and lithium salts, and may produce trace amounts of water, gas, and other harmful substances. Furthermore, the side reaction layer generated on the surface of the silicon particles and insufficient electrolyte can significantly increase the internal resistance of the secondary battery, generating more Joule heat when the positive and negative electrodes are short-circuited, thereby increasing the safety risks of the secondary battery.

[0029] In order to solve the problem that silicon negative electrode particles are easily broken during rolling, the inventors of this application found that when reducing the negative electrode rolling pressure, optimizing the particle size distribution and reducing the silicon doping amount in graphite, reducing the rolling pressure and silicon doping amount will cause the volume capacity of the negative electrode to decrease and ultimately lead to a decrease in the volume energy density of the secondary battery. Optimizing the particle size distribution can only reduce the number of broken silicon particles and cannot completely solve the problem.

[0030] In view of this, the present application provides a secondary battery comprising a negative electrode plate, the negative electrode plate comprising a negative electrode active material layer; the negative electrode active material layer comprising silicon-containing active particles; the silicon-containing active particles having an aspect ratio A, the compaction density of the negative electrode active material layer having a compaction density B, and A and B satisfying the following conditions: 1.83 ≤ (A × B) ≤ 2.89. By defining a synergistic relationship between the aspect ratio A of the silicon-containing active particles and the rolling density B during negative electrode processing, the present application fully utilizes the synergistic effect between material shape and processing pressure, thereby preventing the secondary battery from being crushed by silicon material particles during the negative electrode rolling process, reducing the internal resistance and heat generation of the secondary battery, and improving the safety performance of the secondary battery. Furthermore, by reducing the exposure of active silicon within the silicon particles, side reactions with air or electrolyte can be reduced, thereby improving the initial efficiency of the secondary battery and ensuring the capacity retention rate of the secondary battery during the cycle.

[0031] In some embodiments, 1.83≤(A×B)≤2.14, which can further improve the cycle performance and safety performance of the secondary battery. In some embodiments, the product of the aspect ratio A of the silicon-containing active particles and the negative electrode compaction density B can be 1.83, 1.93, 2.04, 2.06, 2.10, 2.14, 2.16, 2.18, 2.20, 2.49, 2.89 or a value within the range of any two of these values. When (A×B)>2.89, the silicon-containing active particles will break during negative electrode rolling. The fresh interface produced by the breakage contains a large amount of highly active nano-silicon. A series of side reactions of the nano-silicon (reaction with air, electrolyte, etc.) will lead to an increase in irreversible electrochemical reactions. The large amount of non-conductive byproducts accumulated on the electrode surface will increase the internal resistance of the secondary battery and generate more Joule heat, thereby deteriorating the coulombic efficiency of the secondary battery and significantly deteriorating the cycle performance and safety performance capacity retention rate of the secondary battery. When (A×B)<1.83, insufficient contact points between the active material layer particles will occur, the resistance of the negative electrode coating will increase, and the negative electrode conductivity, electron and ion transport performance will decrease, thereby reducing the various charging and discharging performances of the secondary battery.

[0032] In some embodiments, the aspect ratio A of the silicon-containing active particles is in the range of 1.0 ≤ A ≤ 1.7. For example, A can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, or a range consisting of any two of these values. When the aspect ratio of the silicon-containing active particles is greater than 1.7, the anisotropy of the silicon-containing active particles increases, making them susceptible to rupture due to uneven force during rolling. After the particles are ruptured by pressure, the active silicon inside the silicon-containing particles is exposed and undergoes side reactions with the electrolyte, affecting the cycle performance of the secondary battery.

[0033] In some embodiments, the compaction density B of the negative electrode active material layer is in the range of 1.70 g / cc ≤ B ≤ 1.83 g / cc. For example, B can be 1.70, 1.71, 1.72, 1.73, 1.74, 1.75, 1.76, 1.77, 1.78, 1.79, 1.80, 1.81, 1.82, 1.83, or a value within the range of any two of these values. Controlling the compaction density of the negative electrode active material layer can ensure sufficient contact between the components in the active material layer, facilitate ion or electron transport, improve the kinetic performance of the secondary battery, reduce the damage of silicon-containing active particles, improve the negative electrode lithium storage capacity, and further improve the cycle performance and safety performance of the secondary battery. In some embodiments, 1.75 ≤ B ≤ 1.80 can further improve the cycle performance and safety performance of the secondary battery.

[0034] In some embodiments, the sphericity of the silicon-containing active particles with a diameter greater than 10 μm is 0.81 to 0.98. For example, the sphericity of the silicon-containing active particles with a diameter greater than 10 μm can be 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, or a value within a range consisting of any two of these values. By controlling the sphericity of the silicon-containing active particles with a diameter greater than 10 μm, in combination with their aspect ratio and the compaction density of the negative electrode active material layer, the cycle performance and safety performance of the secondary battery can be further improved. In some embodiments, the Dv50 particle size of the silicon-containing active particles satisfies the following: 5.6 μm ≤ Dv50 ≤ 10.4 μm. When Dv50 is too low, the silicon-containing active particles have a large external surface area. The SEI film formed on these external surfaces will cause more irreversible side reactions and consume more electrolyte, thereby affecting the coulombic efficiency and cycle performance of the secondary battery. When Dv50 is too high, the transmission distance of lithium ions and electrons in the particles increases, which will slow the charge and discharge speed of the secondary battery.

[0035] In some embodiments, the true density of the silicon-containing active particles is between 1.853 g / cc and 2.108 g / cc. When the true density is too low, the silicon-containing active particles contain a large number of pores, reducing the amount of material participating in the electrochemical reaction per unit volume, resulting in insufficient secondary battery capacity density. When the true density is too high, the silicon-containing active particles have fewer pores and are too dense. The volume expansion caused by the expansion of the internal nano-silicon embedded with lithium may not be absorbed by the pores, affecting the structural stability of the silicon-containing active particles.

[0036] In some embodiments, the gram capacity of the silicon-containing active particles is 1485.5 mAh / g to 1804.2 mAh / g, and the first coulombic efficiency of the silicon-containing active particles is 79.2% to 87.7%.

[0037] In some embodiments, the silicon-containing active particles provided in the present application are prepared by a method comprising the following steps: step S100, subjecting a mixture of a carbon source and an alkali to a gradient temperature increase and insulation treatment to obtain a porous carbon material; step S200, introducing silane gas into the porous carbon material under an inert gas atmosphere to react, thereby obtaining silicon-containing active particles.

[0038] In some embodiments, the aspect ratio of the carbon source is 1.0 to 1.8, for example, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, or a value within a range consisting of any two of these values. The aspect ratio of the silicon-containing active particles in the present application can be regulated by controlling the aspect ratio of the carbon source. Using a carbon source with the aforementioned aspect ratio in combination with a gradient temperature increase and insulation treatment can produce silicon-containing active particles with a higher aspect ratio, which, when combined with the compaction density of the negative electrode active material layer, produces a synergistic effect, thereby further improving the cycle performance and safety performance of the secondary battery.

[0039] In some embodiments, after the reaction of introducing silane gas in step S200 is completed, the step further includes introducing acetylene gas into the porous carbon material to ensure the purity of silicon particles deposited in the porous carbon.

[0040] In some embodiments, the preparation method of silicon-containing active particles includes the following steps: Step S100, 1000g of phenolic resin microspheres and potassium hydroxide are mixed in an alkali-carbon ratio of 3:1, and the mixture is then subjected to a gradient temperature increase and heat preservation treatment, the gradient temperature increase and heat preservation treatment comprising: first, treating the mixture in a rotary kiln at 450°C for 30 minutes, then raising the rotary kiln temperature to 750°C and holding it for 45 minutes. After the gradient temperature increase and heat preservation treatment, the obtained product is acid-washed, washed with water, and dried to obtain a porous carbon material. Step S200, take the above-mentioned 1000g porous carbon and add it to a fluidized bed reactor, heat it to 480°C under a 10L / min nitrogen atmosphere and hold it for 4 hours, then introduce 2.5L / min of silane gas for 280 minutes. After stopping the introduction of silane, the fluidized bed reactor is heated to 500°C and held for 1 hour, and then acetylene gas is introduced at 5L / min for 300 minutes. After the reaction is completed, silicon-containing active particles can be obtained.

[0041] In some embodiments, the negative electrode active material layer further comprises a carbon material; the carbon material comprises artificial graphite and / or natural graphite. Optionally, the mass ratio of the silicon-containing active particles to the graphite in the negative electrode active material layer is 1:(5-12), preferably 1:(8-10).

[0042] In some embodiments, the negative electrode sheet is prepared by a method comprising the following steps: mixing the negative electrode active material (silicon-containing active particles and graphite in a mass ratio of 1:9, and the mixed gram capacity of the negative electrode active material is controlled to be 480 mAh / g), carbon nanotubes, lithium carboxymethyl cellulose, and lithium polyacrylate in a mass ratio of 97.4:0.2:0.4:2, adding deionized water as a solvent, and obtaining a negative electrode slurry under the action of a vacuum mixer, wherein the solid content of the negative electrode slurry is 45wt% and the viscosity is 6000mPa.s. The negative electrode slurry is coated on one surface of a negative electrode current collector copper foil of a certain thickness, and the copper foil is dried at 80°C to obtain a coating weight of 100.1mg / 1540.25mm 2 The negative electrode sheet is coated on one side with a negative electrode material layer. The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. After cold pressing, cutting, and slitting, a negative electrode sheet with a size of 661mm x 78mm is obtained.

[0043] In some embodiments, the negative electrode active material layer further includes a binder and / or a conductive agent. In some embodiments, the binder in the negative electrode active material layer includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, vinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic acid or acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0044] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0045] The secondary battery of the present application further includes a positive electrode, which includes a positive electrode current collector and a positive electrode active material layer, which includes a positive electrode active material, a binder, and a conductive agent.

[0046] According to some embodiments of the present application, the positive electrode current collector may be 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, etc.) on a polymer substrate.

[0047] According to some embodiments of the present application, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, 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 manganese oxide, spinel lithium nickel manganese oxide and lithium titanate. In some embodiments, in the positive electrode active material layer, the binder includes a binder polymer such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid. In some embodiments, the conductive agent includes a carbon-based material such as carbon black, acetylene black, ketjen black or carbon fiber; a metal-based material such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof.

[0048] The secondary battery of the present application also includes an isolation membrane. The material and shape of the isolation membrane used in the secondary battery of the present application are not particularly limited, and it can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes a polymer or inorganic substance formed from a material that is stable to the electrolyte of the present application. For example, the isolation membrane may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0049] 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 a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from 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, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0050] The secondary battery of the present application also includes an electrolyte. The electrolyte in the present application includes an organic solvent, a lithium salt and optional additives. 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 of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or 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(oxalatoborate) LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0051] 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.

[0052] The present application further provides an electronic device, which includes the secondary battery of the present application.

[0053] The electronic devices or devices of the present application are not particularly limited. In some embodiments, the electronic devices of the present application include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0054] The present invention is described below using lithium-ion batteries as an example in conjunction with the following specific examples and comparative examples. In the following examples and comparative examples, all reagents, materials, and instruments used are commercially available unless otherwise specified.

[0055] Example 1

[0056] The lithium-ion battery of this embodiment includes a negative electrode plate, which includes a negative electrode active material layer; the negative electrode active material layer includes silicon-containing active particles; the aspect ratio A of the silicon-containing active particles is 1.2, the compaction density B of the negative electrode active material layer is 1.70 g / cc, and A×B=2.04.

[0057] The lithium-ion battery of this embodiment is prepared by a method comprising the following steps:

[0058] <Preparation of Porous Carbon>

[0059] Phenolic resin microspheres with an aspect ratio of 1.3 were used as a carbon source. 1000g of the phenolic resin microspheres were mixed with potassium hydroxide at an alkali-to-carbon ratio of 3:1. The mixture was first heated in a rotary kiln at 450°C for 30 minutes, then the kiln temperature was raised to 750°C and held there for 45 minutes. The resulting product was then acid-washed, washed with water, and dried to obtain a porous carbon material.

[0060] <Preparation of Silicon-Containing Active Particles>

[0061] Take the above 1000g porous carbon and add it to a fluidized bed reactor, heat it to 480℃ under a 10L / min nitrogen atmosphere and keep it warm for 4h, then introduce 2.5L / min of monosilane gas for 280min. After stopping the introduction of silane gas, heat the fluidized bed reactor to 500℃ and keep it warm for 1h, then introduce 5L / min of acetylene gas for 300min, and after the reaction is completed, silicon-containing active particles with an aspect ratio A of 1.2 can be obtained. Figure 1 is an SEM image of the silicon-containing active particles provided in Example 1 of the present application, wherein the sphericity of the silicon-containing active particles with a diameter greater than 10μm is 0.81, the Dv50 particle size of the silicon-containing active particles is 7.8μm, and the true density of the silicon-containing active particles is 2.040g / cc. Based on the silicon-containing active particles, the mass fraction of the Si element is 46.2%.

[0062] <Preparation of negative electrode sheet>

[0063] The negative electrode active material (silicon-containing active particles and graphite are mixed in a mass ratio of 1:9, and the mixed gram capacity of the negative electrode active material is controlled to be 480 mAh / g), carbon nanotubes, lithium carboxymethyl cellulose, and lithium polyacrylate are mixed in a mass ratio of 97.4:0.2:0.4:2, and deionized water is added as a solvent. A negative electrode slurry is obtained under the action of a vacuum mixer. The solid content of the negative electrode slurry is 45wt% and the viscosity is 6000mPa.s. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 6μm. The copper foil is dried at 80°C to obtain a coating weight of 100.1mg / 1540.25mm 2A negative electrode sheet coated on one side with a negative electrode material layer is produced. The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet coated on both sides with a negative electrode material layer. During the cold pressing process, the compaction density of the negative electrode active material layer is controlled to 1.70 g / cc. After cutting and slitting, a negative electrode sheet with a size of 661 mm x 78 mm is obtained.

[0064] In the negative electrode active material layer, the mass fraction of Si element was 4.5% based on the negative electrode active material layer.

[0065] <Preparation of positive electrode sheet>

[0066] The positive electrode active material LiCoO2, the conductive agent conductive carbon black, and the 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. The positive electrode slurry had a solid content of 76 wt %. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 9 μm. The aluminum foil was dried at 120°C to obtain a coating weight of 260 mg / 1540.25 mm 2 The positive electrode sheet is coated on one side with a positive electrode material layer. The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet coated on both sides with a positive electrode material layer. After cold pressing, cutting, and slitting, a positive electrode sheet with a size of 661 mm x 76.5 mm is obtained.

[0067] <Preparation of Electrolyte>

[0068] In an argon atmosphere glove box with a water content of less than 10 ppm, FEC, EC, PC, EMC, and DEC were mixed in a mass ratio of 5:10:15:20:50 to obtain an organic solvent. LiPF6 was then added to the organic solvent and mixed thoroughly to obtain an electrolyte solution. The mass percentage of LiPF6 was 12.5%.

[0069] <Isolation Film>

[0070] A porous polyethylene film with a thickness of 10 μm (supplied by Celgard) was used.

[0071] <Preparation of lithium-ion batteries>

[0072] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide insulation, and then wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. The lithium-ion battery is then produced through vacuum packaging, resting, formation, degassing, and trimming.

[0073] Example 2

[0074] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that, during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.72 g / cc.

[0075] Example 3

[0076] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that, during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.75 g / cc.

[0077] Example 4

[0078] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that, during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.78 g / cc.

[0079] Example 5

[0080] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that, during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.80 g / cc.

[0081] Example 6

[0082] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that, during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.83 g / cc.

[0083] Example 7

[0084] The lithium-ion battery of this embodiment differs from that of Example 1 only in that the aspect ratio of the prepared silicon-containing active particles is 1.0, and during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.83 g / cc.

[0085] Example 8

[0086] The lithium-ion battery of this embodiment differs from that of Example 1 only in that the aspect ratio of the prepared silicon-containing active particles is 1.1, and during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.75 g / cc.

[0087] Example 9

[0088] The lithium-ion battery of this embodiment differs from that of Example 1 only in that the aspect ratio of the prepared silicon-containing active particles is 1.4, and during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.78 g / cc.

[0089] Example 10

[0090] The lithium-ion battery of this embodiment differs from that of Example 1 only in that the aspect ratio of the prepared silicon-containing active particles is 1.7. During the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is the same as that of Example 1, both being 1.7 g / cc.

[0091] Example 11

[0092] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that the sphericity of the silicon-containing active particles with a diameter greater than 10 μm is 0.87.

[0093] Example 12

[0094] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that the sphericity of the silicon-containing active particles having a diameter greater than 10 μm is 0.95.

[0095] Example 13

[0096] The lithium-ion battery of this embodiment differs from that of embodiment 1 only in that the sphericity of the silicon-containing active particles with a diameter greater than 10 μm is 0.98.

[0097] Comparative Example 1

[0098] The lithium-ion battery of this comparative example differs from that of Example 1 only in that the aspect ratio of the prepared silicon-containing active particles is 1.7, and during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.82 g / cc.

[0099] Comparative Example 2

[0100] The lithium ion battery of this comparative example is different from that of Example 5 only in that the aspect ratio of the prepared silicon-containing active particles is 1.8.

[0101] Comparative Example 3

[0102] The lithium-ion battery of this comparative example is different from that of Example 6 only in that the aspect ratio of the prepared silicon-containing active particles is 1.8.

[0103] Comparative Example 4

[0104] The lithium-ion battery of this comparative example differs from that of Example 1 only in that the aspect ratio of the prepared silicon-containing active particles is 2.3. During the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is the same as that of Example 1, both being 1.7 g / cc.

[0105] Comparative Example 5

[0106] The lithium-ion battery of this comparative example is different from that of Example 7 only in that, during the cold pressing of the negative electrode sheet, the compaction density of the negative electrode active material layer is 1.68 g / cc.

[0107] Comparative Example 6

[0108] The lithium ion battery of this comparative example is different from that of Example 1 only in that the aspect ratio of the prepared silicon-containing active particles is 1.5.

[0109] Test example

[0110] The following test methods were used to test various parameters or performances of the lithium-ion batteries of the examples and comparative examples of the present application:

[0111] 1. Particle aspect ratio test

[0112] The particles were photographed using a scanning electron microscope, and the longest diameter L (the distance between the two farthest points on the edge of the particle projection surface) and the longest diameter W on the particle projection surface perpendicular to the longest diameter L were measured on the particle projection surface. The aspect ratio of the particles was obtained by calculating the L / W ratio.

[0113] 2. Sphericity test

[0114] The sphericity of the material is tested using the equivalent diameter method. The test method is to use a ZEISS-SEM (sigma-02-33) scanning electron microscope to observe the silicon-containing active particles in the powder or electrode, remove incomplete particles, and calculate the equivalent diameter of the circumference of the complete particles and the equivalent diameter of the particle area.

[0115] Sphericity = circumference equivalent diameter / area equivalent diameter.

[0116] 3. True density test

[0117] Based on the Archimedean principle and the Bohr law of small helium molecules under certain conditions (PV=nRT), the true volume of the material being tested is accurately measured to obtain its true density. The test equipment used is the AccuPyc II1340 true density tester.

[0118] 4. Diameter of silicon-containing active particles

[0119] Image analysis was used to test the active silicon particles in the powder or electrode using a ZEISS-SEM (Sigma-02-33) scanning electron microscope in backscattered mode. ImageJ software was used to identify the edges of the active silicon particles in the images. The equivalent projected area of ​​each particle was then calculated. The equivalent diameter of each particle was then calculated based on the equivalent projected area, yielding the diameter of the active silicon particles.

[0120] 5. Gram capacity test

[0121] Silicon-containing active particles, a conductive agent (conductive carbon black, SP), a binder (lithiated polyacrylic acid, 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 produce a negative electrode slurry with a solid content of 48%. The slurry was then evenly mixed and applied to copper foil. The negative electrode sheet was then dried, cold pressed, and punched.

[0122] In a glove box with a water and oxygen content of less than 10 ppm, ethyl methyl carbonate (EMC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a 1:1:1 mass ratio to form a mixed solvent. LiPF6 and fluoroethylene carbonate (FEC) were then added and mixed thoroughly to form an electrolyte. The mass percentage of the lithium salt LiPF6 was 12.5% ​​and the mass percentage of FEC was 4% based on the mass of the electrolyte.

[0123] In a glove box with a water and oxygen content of less than 10 ppm, the above-mentioned negative electrode plate, the counter electrode metal lithium plate, the polypropylene (PP) separator and the above-mentioned electrolyte were assembled into a button battery.

[0124] Gram Capacity Test: After standing for 6 hours at 25°C, the button cell was discharged at 0.05C to 5mV. Next, it was discharged at 50μA to 5mV. After standing for 5 minutes, it was discharged again at 10μA to 5mV. After standing for 5 minutes, it was charged at 0.05C to 0.8V. The discharge capacity is recorded as G0, and the charge capacity is recorded as G1.

[0125] Among them, gram capacity = G1; first coulombic efficiency = G1 / G0×100%.

[0126] 6. Lithium-ion battery cycle performance and thickness expansion rate test

[0127] Place the lithium-ion battery in a 25°C constant temperature test chamber and let it rest for 30 minutes to allow the lithium-ion battery to reach a constant temperature of 25°C. Charge it at a constant current of 1C to 4.53V, then charge it at a constant voltage to a current of 0.025C. Let it rest for 5 minutes, then discharge it at a constant current of 0.5C to 3.0V. Record the initial discharge capacity as C0. Repeat this cycle for 400 cycles, and record the discharge capacity after 400 cycles as C1.

[0128] After 400 cycles, the capacity retention rate = C1 / C0×100%.

[0129] 7. Compaction density test of negative electrode active material layer

[0130] Use a micrometer to measure the thickness of the negative electrode sheet obtained after rolling, and measure the thickness of any 12 different positions to calculate the average value to obtain the thickness value h3 of the negative electrode sheet. Use a circular cutter to punch out the negative electrode sheet after formation to an area of ​​1540.25mm 2 The disc is weighed on a balance with a resolution of 1 / 10,000. Repeat the punching / weighing steps 5 times and take the average of the weights to get the disc weight m3. Take pure copper foil and use the same method to get the thickness h2 and area of ​​pure copper foil of 1540.25mm 2 The weight of the pure copper foil disc is m2.

[0131] The compaction density of the negative electrode active material layer is Q1 = (m3 - m2) / (h3 - h2) / 1540.25.

[0132] 8. Lithium-ion battery short circuit test

[0133] Place 10 lithium-ion batteries in a 25°C constant temperature test chamber and let them sit for 30 minutes to allow the lithium-ion batteries to reach a constant temperature of 25°C. Charge them at a constant current of 1C to 4.53V, then charge them at a constant voltage to a current of 0.02C and let them sit for 5 minutes. Use an 80±20mΩ load resistor to short-circuit the positive and negative terminals of the lithium-ion batteries and observe the appearance and temperature changes of the lithium-ion batteries. If all 10 lithium-ion batteries do not leak, smoke, catch fire, or explode, and the surface temperature of the battery cell does not exceed 150°C, they pass the short-circuit test. If any lithium-ion battery does not meet the above indicators, it will fail the short-circuit test.

[0134] The parameters and performance characterization results of the lithium-ion batteries of Examples 1 to 10 and Comparative Examples 1 to 6 provided in this application obtained through the above tests are shown in Table 1 below.

[0135] Table 1

[0136] From the performance characterization results in Table 1, it can be seen that Examples 1 to 10 control the aspect ratio A of the silicon-containing active particles in the negative electrode sheet and the compaction density B of the negative electrode active material layer to meet 1.83≤(A×B)≤2.89, and the capacity retention rate of the lithium-ion battery after 400 cycles can reach 89.6% to 94.5%, and all pass the short-circuit test. In contrast, when the A×B values ​​of Comparative Examples 1 to 6 exceed the limit range, the capacity retention rate is only 76.5% to 88.7%, and they cannot pass the short-circuit test. Among them, the A×B values ​​in Comparative Examples 1 to 4 exceed the limit range, resulting in a significant deterioration in the capacity retention rate of the lithium-ion battery after 400 cycles. This is mainly because an excessively high aspect ratio or a too high compaction density will cause a large number of silicon-containing active particles to be crushed, and a large number of side reactions will occur on the fresh interfaces produced after the rupture, causing the active silicon and electrolyte to be rapidly consumed. At the same time, a large number of byproducts generated by the reaction between the electrolyte and the active silicon will increase the impedance of the negative electrode, generating a large amount of Joule heat under the high current of the short-circuit test, causing the internal temperature of the battery to be too high and leading to safety failure. The A×B values ​​in Comparative Examples 5 to 6 are lower than the specified range, resulting in loose contact between the particles in the negative electrode active material layer, causing the negative electrode to be unable to effectively exert its capacity due to increased impedance, so the capacity retention rate of the lithium-ion battery will also be low after 400 cycles. It can be seen that the present application controls the aspect ratio of the silicon-containing active particles in the negative electrode sheet, and the compaction density of the negative electrode active material layer to meet 1.83≤(A×B)≤2.89, so that the two work together to effectively improve the cycle performance and safety performance of the lithium-ion battery.

[0137] As a preferred embodiment, Examples 1 to 4 and Examples 7 to 8 control A and B to satisfy: 1.83≤(A×B)≤2.14, thereby reducing the breakage of the silicon-containing active particles during the rolling and expansion processes, and enabling the capacity retention rate of the lithium-ion battery after 400 cycles to reach 91.3% to 94.5%, further improving the cycle performance of the lithium-ion battery.

[0138] In the present application, the side reactions of the silicon-containing active particles are significantly suppressed by coordinating the aspect ratio of the silicon-containing active particles with the compaction density of the negative electrode active material layer, and the impedance increase phenomenon of the negative electrode is controlled, thereby improving the capacity retention rate of the lithium-ion battery after cycling. In addition, the Joule heat generated during the short-circuit test is limited, and the safety performance of the lithium-ion battery is better.

[0139] The parameters and performance characterization results of the lithium-ion batteries of Examples 1 and 11 to 13 provided in this application obtained through the above tests are shown in Table 2 below.

[0140] Table 2

[0141] As shown in Table 2, the lithium-ion batteries of Examples 1 and 11-13 further optimize the sphericity of the silicon-containing active particles with diameters greater than 10 μm. This shape feature, combined with the aspect ratio and the compaction density of the negative electrode active material layer, further ensures uniform stress distribution within the negative electrode active material layer, reducing or avoiding the problem of uneven stress and easy crushing when subjected to stress. The resulting lithium-ion batteries exhibited a capacity retention rate of 93.8% to 95.2% after 400 cycles, demonstrating excellent cycling performance. Specifically, Examples 11-13, in addition to optimizing the aspect ratio A of the silicon-containing active particles in the negative electrode sheet and the compaction density B of the negative electrode active material layer, further optimize the sphericity of the silicon-containing active particles with diameters greater than 10 μm to 0.87 to 0.98, further improving the cycling performance of the lithium-ion batteries while ensuring their safety.

Claims

1. A secondary battery comprising a negative electrode plate, characterized in that: The negative electrode plate includes a negative electrode active material layer; the negative electrode active material layer includes silicon-containing active particles; The aspect ratio of the silicon-containing active particles is A, the compaction density of the negative electrode active material layer is B g / cc, and A and B satisfy the following: 1.83≤(A×B)≤2.

89.

2. The secondary battery according to claim 1, wherein 1.0≤A≤1.7。 3. The secondary battery according to claim 1 or 2, characterized in that 1.70≤B≤1.83。 4. The secondary battery according to any one of claims 1 to 3, characterized in that 1.75≤B≤1.80。 5. The secondary battery according to any one of claims 1 to 4, characterized in that A and B satisfy: 1.83≤(A×B)≤2.

14.

6. The secondary battery according to any one of claims 1 to 5, characterized in that The sphericity degree of the silicon-containing active particles with a diameter greater than 10 μm is 0.81 to 0.

98.

7. The secondary battery according to any one of claims 1 to 6, characterized in that Based on the silicon-containing active particles, the mass fraction of Si element is 43% to 55%.

8. The secondary battery according to any one of claims 1 to 7, characterized in that The secondary battery satisfies at least one of conditions a to c: Condition a: The Dv50 particle size of the silicon-containing active particles satisfies the following conditions: 5.6 μm ≤ Dv50 ≤ 10.4 μm; Condition b: the true density of the silicon-containing active particles is 1.853 g / cc to 2.108 g / cc; Condition c: the negative electrode active material layer further comprises a carbon material; the carbon material comprises artificial graphite and / or natural graphite.

9. A method for preparing a secondary battery according to any one of claims 1 to 8, characterized in that: The method for preparing the silicon-containing active particles comprises the following steps: Step S100, subjecting a mixture of a carbon source and an alkali to a gradient temperature increase and heat preservation treatment to obtain a porous carbon material; Step S200 : introducing silane gas into the porous carbon material under an inert gas atmosphere to carry out a reaction, thereby obtaining the silicon-containing active particles.

10. The preparation method according to claim 9, characterized in that The gradient temperature rise and insulation treatment comprises: heating the mixture of the carbon source and the alkali to 350° C. to 550° C. and insulation treatment for 15 min to 45 min, then heating the mixture to 600° C. to 900° C. and insulation treatment for 0.5 h to 2 h; and / or, The carbon source is selected from at least one of phenolic resin, coal, biomass material, and petroleum coke; and / or, The aspect ratio of the carbon source is 1.0 to 1.

9.

11. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 1 to 8 or the secondary battery prepared by the preparation method according to claim 9 or 10.

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