Secondary battery and electric device

Abstract

The invention provides a secondary battery and an electric device, and belongs to the technical field of electrochemical energy storage. The secondary battery comprises a negative electrode plate, wherein the negative electrode plate comprises a negative electrode current collector, a negative electrode active layer and an aerogel layer; the negative electrode active layer and the aerogel layer are arranged on at least one side surface of the negative electrode current collector; the negative electrode active layer is positioned between the negative electrode current collector and the aerogel layer; the aerogel layer comprises SiO2 (at) HAP aerogel, and the mass percentage content of the SiO2 (at) HAP aerogel in the aerogel layer is 80 to 99 percent. The secondary battery provided by the invention has excellent thermal safety and cycle performance.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, specifically to secondary batteries and electrical devices. Background Technology

[0002] Currently, secondary batteries using lithium metal as the positive electrode are widely used in electric vehicles, 3C consumer batteries, and energy storage due to their advantages such as high energy density, long cycle life, and high voltage. However, they are troubled by the unfavorable electrolyte-lithium metal interface, which leads to uneven metal deposition and instability of the solid-electrolyte interface (SEI). The SEI is a layer of lithium salt on the lithium surface, which is generated by the decomposition of the electrolyte at low voltage. Under the huge interfacial flow and large volume change of the lithium negative electrode, the SEI is mechanically unstable and continuously consumes electrolyte during cycling. In actual batteries, in order to improve energy density, the amount of electrolyte contained in the battery is limited. Therefore, the unstable SEI will cause additional electrolyte loss, resulting in a sharp decline in the thermal stability and cycle performance of the secondary battery. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the prior art and provide a secondary battery and an electrical device.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: In the first aspect, a secondary battery is provided, including a negative electrode sheet, wherein the negative electrode sheet includes a negative current collector and a negative active layer and an aerogel layer disposed on at least one side surface of the negative current collector; The negative electrode active layer is located between the negative electrode current collector and the aerogel layer; The aerogel layer contains SiO2@HAP aerogel, and the mass percentage of SiO2@HAP aerogel in the aerogel layer is 80-99%.

[0005] In some embodiments, the SiO2@HAP aerogel contains 60-90% SiO2 by mass and 10-40% HAP by mass.

[0006] In some embodiments, the porosity of the SiO2@HAP aerogel is 80-99.8%.

[0007] In some embodiments, the particle size Dv50 of HAP in the SiO2@HAP aerogel is 20~200nm.

[0008] In some embodiments, the thickness of the SiO2@HAP aerogel layer is 0.5~5μm.

[0009] In some embodiments, the aerogel layer comprises a binder, the binder including styrene-butadiene rubber and sodium carboxymethyl cellulose.

[0010] In some embodiments, the styrene-butadiene rubber has a mass percentage of 55-80% based on the mass of the binder; and the sodium carboxymethyl cellulose has a mass percentage of 20-45%.

[0011] In some embodiments, the thickness of the negative electrode active layer is 40~60μm.

[0012] In some embodiments, the negative electrode active layer includes a negative electrode active material, which includes a carbon material.

[0013] Secondly, an electrical device is provided, including the aforementioned secondary battery.

[0014] Compared with the prior art, the beneficial effects of this application are as follows: In this application, the aerogel layer plays a role in isolating the internal heat conduction of the secondary battery, solving the safety problem caused by internal heat diffusion in the secondary battery; the porous structure in SiO2@HAP aerogel is conducive to lithium ion transport, reducing the internal resistance of the secondary battery, and also reducing the weight of the secondary battery and increasing its energy density; the PO4 in HAP 3- OH - The functional groups can provide raw materials for the SEI membrane of secondary batteries, reduce electrolyte consumption during the formation process, improve the film density and stability of SEI, continuously repair damaged SEI membranes during cycling without side reactions with electrolyte, thereby improving the cycle stability of secondary batteries. Detailed Implementation

[0015] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0016] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0017] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0018] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1~5” is disclosed, the described range should be interpreted as including ranges “1~4”, “1~3”, “1~2”, “1~2 and 4~5”, “1~3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0019] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0020] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has 'a' parts by mass and component B has 'b' parts by mass, it means that the mass ratio of component A to component B is a:b. It is important to understand that, unlike mass percentage content, the sum of the mass parts of all components is not limited to 100 parts.

[0021] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0022] A first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet including a negative electrode current collector and a negative electrode active layer and an aerogel layer disposed on at least one side surface of the negative electrode current collector; The negative electrode active layer is located between the negative electrode current collector and the aerogel layer; The aerogel layer contains SiO2@HAP aerogel, and the mass percentage of SiO2@HAP aerogel in the aerogel layer is 80-99%.

[0023] In this application, the aerogel layer serves to isolate internal heat conduction in the secondary battery, solving the safety issues caused by internal heat diffusion. The porous structure in SiO2@HAP aerogel facilitates lithium-ion transport, reduces the internal resistance of the secondary battery, and also reduces the weight and increases the energy density of the secondary battery; the PO4 in HAP... 3- OH - The functional groups can provide raw materials for the SEI membrane of secondary batteries, reduce electrolyte consumption during the formation process, improve the film density and stability of SEI, continuously repair damaged SEI membranes during cycling without side reactions with electrolyte, thereby improving the cycle stability of secondary batteries.

[0024] Specifically, HAP refers to hydroxyapatite.

[0025] Specifically, in SiO2@HAP, "@" means "and", referring to a mixture of SiO2 and hydroxyapatite.

[0026] In this application, inductively coupled plasma atomic emission spectrometry (ICP-OES) is used to test the mass percentage content of SiO2@HAP aerogel in the aerogel layer, specifically including the following steps: (1) First, crush, sieve and mix the solid material of the aerogel layer; weigh 5.0g of sample, add nitric acid and hydrogen peroxide to digest, and then measure after adjusting the volume; (2) Turn on the ICP-OES power supply and set the power parameters to 1300W, plasma gas flow rate to 15.0L / min, auxiliary gas flow rate to 0.20L / min, and atomizing gas flow rate, etc. (3) Use standard solutions to plot calibration curves, dilute the mixed standard solutions into different concentration series, import them into ICP-OES to measure spectral intensity, and establish intensity-concentration relationship curves; (4) Introduce the prepared sample solution into ICP-OES to determine the spectral intensity; calculate the concentration of elements in each sample according to the standard curve; (5) Calculate the silicon content ratio based on the concentration to obtain the mass ratio of SiO2@HAP aerogel in the aerogel layer.

[0027] Specifically, the mass percentage of SiO2@HAP aerogel in the aerogel layer can be a range of 80%, 82%, 84%, 86%, 88%, 90%, 92%, 95%, 97%, 99%, or any combination of two of these values.

[0028] In some embodiments, the SiO2@HAP aerogel contains 60-90% SiO2 by mass and 10-40% HAP by mass.

[0029] In this application, the mass percentages of SiO2 and HAP in the SiO2@HAP aerogel are within the above-mentioned range, which is beneficial to enhancing the compactness and structural stability of the SEI film, as well as reducing electrolyte consumption and side reactions, and further improving the cycle stability of the secondary battery.

[0030] In this application, inductively coupled plasma atomic emission spectrometry (ICP-OES) is used to determine the mass percentage content of SiO2 and HAP in SiO2@HAP aerogel, specifically including the following steps: (1) First, crush, sieve and mix the SiO2@HAP aerogel solid material; weigh 5.0g of sample, add nitric acid and hydrogen peroxide to digest, and make up to volume before testing; (2) Turn on the ICP-OES power supply and set the power parameters to 1300W, plasma gas flow rate to 15.0L / min, auxiliary gas flow rate to 0.20L / min, and atomizing gas flow rate, etc. (3) Use standard solutions to plot calibration curves, dilute the mixed standard solutions into different concentration series, import them into ICP-OES to measure spectral intensity, and establish intensity-concentration relationship curves; (4) Introduce the prepared sample solution into ICP-OES to determine the spectral intensity; calculate the concentration of elements in each sample according to the standard curve; (5) Calculate the ratio of silicon and calcium elements based on the concentration to obtain the mass percentage of SiO2 and HAP in SiO2@HAP aerogel.

[0031] Specifically, the mass percentage of SiO2 in the SiO2@HAP aerogel can be a range of 60%, 62%, 65%, 67%, 70%, 73%, 75%, 78%, 80%, 82%, 85%, 87%, and 90%, or any combination of two of these values. In some embodiments, the mass percentage of SiO2 in the SiO2@HAP aerogel is 75-90%.

[0032] Specifically, the mass percentage of HAP in the SiO2@HAP aerogel can be a range of 10%, 12%, 15%, 17%, 20%, 23%, 25%, 28%, 30%, 32%, 35%, 37%, or 40%, or any combination of both. In some embodiments, the mass percentage of HAP in the SiO2@HAP aerogel is 10-25%.

[0033] In some embodiments, the porosity of the SiO2@HAP aerogel is 80-99.8%; for example, it can be a range of one or any two of 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 99.8%.

[0034] In this application, the porosity of SiO2@HAP aerogel is within the above-mentioned range, which is beneficial to increase the number of lithium-ion conduction channels, improve lithium-ion transport efficiency, and prevent lithium deposition on the surface of the aerogel layer during cycling. This can simultaneously improve the safety and electrochemical performance of lithium-ion batteries.

[0035] In this application, the porosity of SiO2@HAP aerogel is determined using microscopic analysis, including the following steps: A composite electrode sample is obtained using a cutting machine, and a 30*15mm insert is fabricated using a cold-mounting method (mixing curing agent in the mold). The insert is then pre-ground with coarse and fine sandpaper, followed by coarse and fine polishing with a polishing cloth and diamond spray polishing agent to obtain a smooth and glossy SiO2@HAP composite coating observation surface. The prepared sample is placed under a microscope, and appropriate magnification parameters are selected to observe and capture cross-sectional images. The pore area and cross-sectional area of ​​the sample are measured using the instrument's image analysis software. The porosity of the SiO2@HAP aerogel is calculated using the formula: Porosity = Pore Area / Cross-sectional Area * 100%.

[0036] In some embodiments, the particle size Dv50 of HAP in the SiO2@HAP aerogel is 20~200nm; for example, it can be a range of one or any combination of 20nm, 40nm, 60nm, 80nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm.

[0037] In this application, the particle size Dv50 of HAP in SiO2@HAP aerogel is within the above-mentioned range. The nanoscale material has a large specific surface area, and the HAP material with a large specific surface area can efficiently provide PO4 for the reconstruction and repair of SEI film. 3- OH - Group raw materials.

[0038] In this application, the particle size Dv50 of HAP in SiO2@HAP aerogel can be detected by the following method: The particle size of HAP in SiO2@HAP aerogel is measured using a scanning electron microscope (SEM). First, the sample is brittlely fractured under liquid nitrogen conditions to form a natural fracture surface. The conductivity is enhanced by gold plating or low vacuum mode. Then, high-resolution images are acquired under appropriate accelerating voltage and magnification. Multiple regions are randomly sampled, and the average particle size and distribution are statistically analyzed to obtain the particle size Dv50 of HAP in SiO2@HAP aerogel.

[0039] In some embodiments, the thickness of the SiO2@HAP aerogel layer is 0.5~5μm; for example, it can be a range of one or any combination of two of the following: 0.5μm, 0.7μm, 1μm, 1.2μm, 1.5μm, 1.7μm, 2μm, 2.3μm, 2.5μm, 2.8μm, 3μm, 3.2μm, 3.5μm, 3.7μm, 4μm, 4.3μm, 4.5μm, 4.8μm, and 5μm.

[0040] In this application, the thickness of the SiO2@HAP aerogel layer is within the above-mentioned range, which is beneficial to increase the thickness and structural stability of the SEI film, while reducing the products of electrolyte decomposition and side reactions, thereby improving the cycle stability of the secondary battery.

[0041] Specifically, the thickness of the SiO2@HAP aerogel layer can be measured using the following method: the thickness of the SiO2@HAP aerogel layer is measured using a scanning electron microscope (SEM), the sample is cut using an ultrathin slicer to form a cross-section to expose the cross-section of the SiO2@HAP aerogel layer, the conductivity is enhanced by gold plating or low vacuum mode, and then high-resolution images are acquired under appropriate accelerating voltage and magnification. Multiple areas are randomly sampled, and the thickness and distribution of the SiO2@HAP aerogel layer are statistically analyzed to obtain the thickness of the SiO2@HAP aerogel layer.

[0042] In some embodiments, the preparation method of the SiO2@HAP aerogel includes the following steps: The SiO2 aerogel was ultrasonically cleaned in anhydrous ethanol to remove surface impurities, and then dried to obtain the pretreated SiO2 aerogel. The pretreated SiO2 aerogel was placed in an aminosilane coupling agent solution for coupling reaction. The product obtained from the reaction was washed and dried to obtain amino-modified SiO2 aerogel. The modified SiO2 aerogel was placed in an aqueous solution of hydroxyapatite for chemical cross-linking reaction. The resulting product was washed and freeze-dried to obtain SiO2@HAP aerogel.

[0043] In this application, SiO2@HAP aerogel is prepared by modifying SiO2 aerogel with an aminosilane coupling agent and by chemical crosslinking through directional pre-freezing. HAP is deposited on the surface and in the pores of SiO2@HAP aerogel, which improves the crosslinking density and compatibility of SiO2@HAP aerogel and is beneficial to improving the cycle performance of secondary batteries.

[0044] Specifically, the aminosilane coupling agent solution includes an aminosilane coupling agent and an ethanol / water solution; based on the mass of the aminosilane coupling agent solution, the mass percentage of the aminosilane coupling agent is 5-10%, for example, it can be a range of one or any two of 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%.

[0045] Specifically, the ethanol / water solution contains 90-98% ethanol by mass, for example, a range of values ​​consisting of one or any two of 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, and 98%.

[0046] Specifically, the temperature of the coupling reaction is 50~70℃, for example, it can be one or any combination of 50℃, 52℃, 55℃, 57℃, 60℃, 63℃, 65℃, 68℃, 70℃.

[0047] Specifically, the coupling reaction time is 3 to 5 hours, for example, it can be one of 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours or any combination of two of them.

[0048] Specifically, the drying temperature is 40~100℃, for example, it can be a range of one or any combination of 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, and 100℃.

[0049] Specifically, the drying time is 10 to 18 hours, for example, a range of one or any combination of 10 hours, 12 hours, 14 hours, 16 hours, and 18 hours.

[0050] Specifically, the temperature of the chemical cross-linking reaction is 35~40℃, for example, it can be one or any combination of 35℃, 36℃, 37℃, 38℃, 39℃, and 40℃.

[0051] Specifically, the chemical cross-linking reaction time is 20 to 30 hours, for example, it can be one or any combination of 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, and 30 hours.

[0052] Specifically, the freeze-drying temperature is -50℃ to -80℃, for example, it can be one or any combination of -50℃, -55℃, -60℃, -65℃, -70℃, -75℃, and -80℃.

[0053] In this application, the mass percentage of SiO2 and HAP in SiO2@HAP aerogel and the porosity of SiO2@HAP aerogel can be changed by adjusting the mass ratio of SiO2 to HAP in the raw materials; for example, when the mass percentage of HAP is 40%, the porosity of SiO2@HAP is 80%.

[0054] In some embodiments, the aerogel layer comprises a binder, the binder including styrene-butadiene rubber and sodium carboxymethyl cellulose.

[0055] In some embodiments, the styrene-butadiene rubber has a mass percentage of 55-80% based on the mass of the binder; and the sodium carboxymethyl cellulose has a mass percentage of 20-45%.

[0056] Specifically, based on the mass of the adhesive, the mass percentage of the styrene-butadiene rubber can be a range of one or any two of the following: 55%, 57%, 60%, 63%, 65%, 68%, 70%, 72%, 75%, 77%, and 80%.

[0057] Specifically, based on the mass of the binder, the mass percentage of sodium carboxymethyl cellulose can be a range of one or any two of the following: 20%, 22%, 25%, 27%, 30%, 33%, 35%, 37%, 40%, 43%, and 45%.

[0058] In some embodiments, the thickness of the negative electrode active layer is 40~60μm; for example, it can be a range of one or any combination of 40μm, 42μm, 44μm, 46μm, 48μm, 50μm, 52μm, 54μm, 56μm, 58μm, 60μm.

[0059] In this application, the thickness of the negative electrode active layer is within the above-mentioned range, which is beneficial to balancing the fast charging performance and cycle life of the battery.

[0060] In this application, the thickness of the negative electrode active layer can be detected by the following method: the thickness of the negative electrode active layer is measured using a scanning electron microscope (SEM), the sample is cut using an ultrathin slicer to form a cut surface to expose the cross-section of the negative electrode active layer, the conductivity is enhanced by gold plating or low vacuum mode, and then high-resolution images are acquired under appropriate accelerating voltage and magnification. Multiple areas are randomly sampled, and the thickness and distribution of the negative electrode active layer are statistically analyzed to obtain the thickness of the negative electrode active layer.

[0061] In some embodiments, the negative electrode active layer includes a negative electrode active material, which includes a carbon material.

[0062] In some embodiments, the carbon material has a mass percentage of 90-97%, based on the mass percentage of the negative electrode active material.

[0063] In some embodiments, the carbon material includes at least one of natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, and mesophase carbon microspheres (MCMB). The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for secondary batteries.

[0064] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil or a carbon-coated copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0065] In some embodiments, the conductive layer may include at least one of graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon.

[0066] In some embodiments, the negative electrode conductive agent may include at least one selected from graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon. The negative electrode conductive agent of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0067] In some embodiments, the secondary battery further includes a positive electrode, a separator, and an electrolyte.

[0068] In some embodiments, the positive electrode may include a positive current collector and a layer of positive active material disposed on at least one side of the positive current collector.

[0069] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is an aluminum foil or a carbon-coated aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0070] In some embodiments, the conductive layer may include at least one of graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon.

[0071] In some embodiments, the positive electrode active material layer may include a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent.

[0072] In some embodiments, the positive electrode active material may be, but is not limited to, a chemical formula such as Li a Ni x Co y M z O 2-b Nb (where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The cathode active material can be one or more of the following: O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The cathode active material can also be modified. Methods for modifying the cathode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the cathode active material. The materials used for modification can be one or more of the following: Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W.

[0073] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0074] In some embodiments, the positive electrode conductive agent may include at least one selected from graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0075] In some embodiments, the diaphragm porous substrate comprises woven or nonwoven polymer fibers. In some embodiments, the porous substrate is a nonwoven material comprising polymer fibers.

[0076] In some embodiments, the porous substrate is, but is not limited to, at least one of polyolefin, polyester, polyacetal, polyamide, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate.

[0077] Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0078] In some embodiments, the thickness of the separator is from 4 μm to 10 μm, for example, but not limited to 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, or within any two of the above values. A separator thickness within this range not only allows the separator to possess higher puncture strength to better suppress lithium dendrites, but also maintains lower internal resistance and higher energy density.

[0079] In some embodiments, the porosity of the separator is 30% to 70%, for example, but not limited to 30%, 32%, 35%, 37%, 40%, 43%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 63%, 65%, 68%, or 70%, or within any two of the above values. A porosity within this range not only facilitates the separator having more ion channels, thereby reducing internal resistance and improving charge / discharge efficiency and high-rate discharge capability, but also gives the separator higher mechanical strength, thus reducing the risk of lithium dendrite penetration.

[0080] In some embodiments, the diaphragm includes an inorganic coating disposed on at least one side of the surface of the porous substrate.

[0081] In some embodiments, the inorganic coating includes inorganic fillers, which may include boehmite, ceramic fibers, Al2O3, SiO, SiO2, CaO, ZnO, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, BaTi2O5, BaTiO3, TiN, AlN, Na2O·mTiO2 (m is 3 or 6), K2O·nTiO2 (n is 1, 2, 4, 6 or 8), BaO x(x is 1 or 2), MTiO3 (M is Ba, Sr or Ca). In some embodiments, the inorganic filler includes at least one of silica particles, barium disitinathate particles, zirconium dioxide particles, alumina particles, barium metatitanate particles, barium sulfate particles, tin oxide particles, titanium nitride particles, aluminum nitride particles, silica particles, calcium oxide particles, magnesium oxide particles, magnesium hydroxide particles, zinc oxide particles, titanium dioxide particles, boehmite particles, hydrated alumina particles, and ceramic particles.

[0082] This application does not impose any particular restrictions on the shape of the inorganic filler, as long as it can achieve the purpose of this application.

[0083] Inorganic fillers can be spherical, rod-shaped, sheet-shaped, disc-shaped, needle-shaped, cylindrical, irregular, or other known particle shapes. In some embodiments, the inorganic material is not spherical, rod-shaped, sheet-shaped, disc-shaped, needle-shaped, cylindrical, or irregular. In some embodiments, the inorganic filler is spherical. Spherical particles have a higher packing density, can form a continuous thermally conductive network, reduce the risk of local thermal runaway, and have a smaller surface curvature, a lower contact angle with the electrolyte, higher liquid absorption, and better wettability.

[0084] In some embodiments, the electrolyte may also include a non-aqueous solvent and a lithium salt.

[0085] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate.

[0086] In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds.

[0087] In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds.

[0088] In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (EMC), and combinations thereof.

[0089] In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof.

[0090] In some embodiments, the fluorinated carbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethyl ethylene carbonate.

[0091] In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonic acid lactone, caprolactone, and methyl formate.

[0092] In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0093] In some embodiments, the non-aqueous solvent may further include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate ester.

[0094] In a second aspect, there is provided an electrical device including the secondary battery described above.

[0095] The electrical device of the present application is not particularly limited and may be any electrical device known in the prior art.

[0096] In some embodiments, the electrical device includes, but is not limited to, mobile phones, mobile telephones, smart phones, laptop computers, tablet computers, wearable devices, smart watches, smart bracelets, smart glasses, mobile power supplies, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio speakers, household appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robotic dogs, industrial robots, embodied robots, etc.

[0097] Example 1 <Preparation of SiO2@HAP Aerogel> The SiO2 aerogel was placed in absolute ethanol and ultrasonically cleaned for 30 min to remove surface impurities. After drying in a vacuum drying oven at 60 °C for 12 h, the pretreated SiO2 aerogel was obtained; A solution of aminosilane coupling agent was obtained by mixing 3-aminopropyltriethoxysilane (APTES), anhydrous ethanol and water in a mass ratio of 1:9:0.5. The pretreated SiO2 aerogel was immersed in an aminosilane coupling agent solution and sonicated for 1 hour, then reacted at 60°C for 4 hours. The product obtained was washed three times with anhydrous ethanol and dried in a vacuum drying oven at 60°C for 12 hours to obtain amino-modified SiO2 aerogel. Amino-modified SiO2 aerogel was immersed in an aqueous solution of hydroxyapatite (HAP) and reacted at 37°C for 24 h to induce HAP deposition on the surface and pores of the amino-modified SiO2 aerogel. The product obtained was washed three times with deionized water and freeze-dried at -60°C for 24 h to obtain SiO2@HAP aerogel. The mass percentage of SiO2 in the SiO2@HAP aerogel was 75%, the mass percentage of HAP was 25%, the particle size Dv50 of HAP was 80 nm, and the porosity was 90%.

[0098] <Preparation of Negative Electrode Sheets> Artificial graphite, super P, CMC, and SBR were added to a deionized water solvent in a mass ratio of 95:1:1.6:2.4 and stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry was then coated onto a copper foil and dried to obtain a negative electrode active layer with a thickness of 50 μm. SiO2@HAP aerogel, binder, and deionized water were mixed evenly at a mass ratio of 8.5:1.5:90 to obtain an aerogel slurry. The binder consisted of CMC and SBR, with a mass ratio of CMC to SBR of 65:35. The aerogel slurry was then sprayed onto the surface of the negative electrode active layer using ultrasonic atomization. The ultrasonic atomization conditions were as follows: ultrasonic frequency of 80kHz, power of 30W, carrier gas pressure of 0.3MPa, and spraying distance of 3cm. After spraying, the aerogel layer with a thickness of 5μm was obtained. Subsequently, the aerogel was rolled, cut, and the negative electrode tabs were cut from the corresponding positions of the empty foil area of ​​the copper foil to obtain the negative electrode sheet.

[0099] <Preparation of the positive electrode> Lithium iron phosphate, super P, and PVDF were added to NMP solvent in a mass ratio of 97:1:2 and stirred thoroughly to form a positive electrode slurry with a solid content of 58% and a viscosity of 4000 mPa·s. The slurry was then coated onto aluminum foil, dried, rolled, and cut into sheets. Positive electrode tabs were obtained by cutting from the corresponding positions of the empty foil area of ​​the aluminum foil. <Preparation of Electrolyte> Lithium hexafluorophosphate was dissolved in a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 30:5:10:55 to obtain an electrolyte, wherein the molar concentration of lithium hexafluorophosphate was 1.02 mol / L.

[0100] <Preparation of Secondary Batteries> A 20μm thick polypropylene film was used as the separator. The prepared positive electrode, separator, and negative electrode were stacked in sequence, with the separator positioned between the positive and negative electrodes. After winding, hot pressing and shaping, and electrode tab welding, a bare cell was obtained. The bare cell was placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above was injected into the dried battery. After standing, formation, and capacity testing, the secondary battery was completed. The theoretical capacity of the secondary battery is 61.5Ah.

[0101] Example 2 Except for the difference in the mass percentage of SiO2 and HAP in the SiO2@HAP aerogel compared to Example 1, the rest is the same as in Example 1; the mass percentage of SiO2 in the SiO2@HAP aerogel of this example is 73%, and the mass percentage of HAP is 27%.

[0102] Example 3 Except for the difference in the mass percentage of SiO2 and HAP in the SiO2@HAP aerogel compared to Example 1, the rest is the same as in Example 1; in this example, the mass percentage of SiO2 in the SiO2@HAP aerogel is 85%, and the mass percentage of HAP is 15%.

[0103] Example 4 Except for the difference in the mass percentage of SiO2 and HAP in the SiO2@HAP aerogel compared to Example 1, the rest is the same as in Example 1; in this example, the mass percentage of SiO2 in the SiO2@HAP aerogel is 90%, and the mass percentage of HAP is 10%.

[0104] Example 5 Except for the difference in the mass percentage of SiO2 and HAP in the SiO2@HAP aerogel compared to Example 1, the rest is the same as in Example 1; in this example, the mass percentage of SiO2 in the SiO2@HAP aerogel is 60%, and the mass percentage of HAP is 40%.

[0105] Example 6 Except for the difference in the mass percentage of SiO2@HAP aerogel layer compared to Example 1, the rest is the same as in Example 1. In this example, the mass percentage of SiO2@HAP aerogel layer is 95%.

[0106] Example 7 Except for the difference in the mass percentage of SiO2@HAP aerogel layer compared to Example 1, the rest is the same as in Example 1. In this example, the mass percentage of SiO2@HAP aerogel layer is 80%.

[0107] Example 8 Except for the difference in the mass percentage of SiO2@HAP aerogel layer compared to Example 1, the rest is the same as in Example 1. In this example, the mass percentage of SiO2@HAP aerogel layer is 99%.

[0108] Example 9 Except for the thickness of the SiO2@HAP aerogel layer, which differs from that in Example 1, the rest is the same as in Example 1. The thickness of the SiO2@HAP aerogel layer in this example is 4 μm.

[0109] Example 10 Except for the thickness of the SiO2@HAP aerogel layer, which differs from that in Example 1, the rest is the same as in Example 1. The thickness of the SiO2@HAP aerogel layer in this example is 2 μm.

[0110] Example 11 Except for the thickness of the SiO2@HAP aerogel layer, which differs from that in Example 1, the rest is the same as in Example 1. The thickness of the SiO2@HAP aerogel layer in this example is 0.5 μm.

[0111] Example 12 Except for the thickness of the SiO2@HAP aerogel layer, which differs from that in Example 1, the rest is the same as in Example 1. The thickness of the SiO2@HAP aerogel layer in this example is 7 μm.

[0112] Example 13 Except for the particle size Dv50 of HAP in SiO2@HAP aerogel, which is different from that in Example 1, the rest is the same as in Example 1. The particle size Dv50 of HAP in SiO2@HAP aerogel in this example is 150nm.

[0113] Example 14 Except for the particle size Dv50 of HAP in SiO2@HAP aerogel, which is different from that in Example 1, the rest is the same as in Example 1. The particle size Dv50 of HAP in SiO2@HAP aerogel in this example is 20nm.

[0114] Example 15 Except for the particle size Dv50 of HAP in SiO2@HAP aerogel, which is different from that in Example 1, the rest is the same as in Example 1. The particle size Dv50 of HAP in SiO2@HAP aerogel in this example is 200nm.

[0115] Example 16 Except for the porosity of the SiO2@HAP aerogel, which differs from that of Example 1, the rest is the same as in Example 1. The porosity of the SiO2@HAP aerogel in this example is 80%.

[0116] Example 17 Except for the porosity of the SiO2@HAP aerogel, which differs from that of Example 1, the rest is the same as in Example 1. The porosity of the SiO2@HAP aerogel in this example is 99.8%.

[0117] Example 18 Except for the porosity of the SiO2@HAP aerogel, which differs from that of Example 1, the rest is the same as in Example 1. The porosity of the SiO2@HAP aerogel in this example is 75%.

[0118] Comparative Example 1 Except for the structure of the negative electrode sheet, which is different from that of this embodiment, the rest is the same as that of Example 1. The negative electrode sheet of this comparative example does not include the SiO2@HAP aerogel layer.

[0119] Comparative Example 2 Except for the difference in the mass percentage of SiO2@HAP aerogel layer compared to Example 1, the rest is the same as Example 1. The mass percentage of SiO2@HAP aerogel layer in this comparative example is 75%.

[0120] Table 1 shows some parameters of the secondary batteries in Examples 1-18 and Comparative Examples 1-2.

[0121] Performance testing (1) The thickness of the SEI film: The physical thickness of the SEI film was measured by directly observing the cross-section of the SEI film through a transmission electron microscope (TEM); (2) Electrolyte composition: The composition of the electrolyte was tested using inductively coupled plasma atomic emission spectrometry (ICP-OES). The intensity of the elemental characteristic spectral lines was determined, and the content was calculated using a standard curve. (3) Hot needle puncture: Fix a fully charged battery on the test stand, and puncture the battery vertically with a 5mm steel needle at a speed of 0.1~1mm / s, and observe for one hour. Observe whether the battery catches fire, explodes, or emits smoke; (4) Thermal diffusion: Five fully charged batteries are placed face to face with a 0.8mm air gap in between, and named from left to right as batteries 1, 2, 3, 4, and 5. A high-power heating element is placed on one of the large faces of battery 3, and the battery in the center is the thermal trigger battery. The voltage values ​​of the five batteries are measured at different times to see if they drop to zero, and whether there is any fire, smoke, or explosion. If the voltage values ​​of the five batteries do not drop to zero, and there is no fire, smoke, or explosion, it proves that the battery is safe and is marked as PASS. (5) Battery cycle performance: The secondary battery was placed in a charge and discharge test cabinet at a constant temperature of 25°C. The charging rate was 0.33C, the charging cut-off voltage was 3.6V, the discharging rate was 1C, and the discharging cut-off voltage was 2.5V. The capacity retention rate was recorded after 2000 cycles.

[0122] The test results are shown in Table 2.

[0123] Table 1 Table 2 As can be seen from the experimental data in Tables 1 and 2, after 2000 cycles, the thickness of the SEI film in the secondary battery of this application is >60nm, the HF content in the electrolyte is <0.85%, and the capacity retention rate is >80%. This indicates that the aerogel layer in the negative electrode sheet of this application can improve the film density and stability of SEI, reduce electrolyte consumption, and improve the cycle performance of the secondary battery.

[0124] The experimental data from Examples 1-5 show that when the mass percentage of SiO2 in the SiO2@HAP aerogel is 75-90%, the thickness of the SEI film after 2000 cycles of the secondary battery is ≥99nm, the HF content in the electrolyte is ≤0.32%, and the capacity retention rate is >88%. This indicates that when the mass percentage of SiO2 in the SiO2@HAP aerogel is 75-90%, the thickness of the SEI film can be further increased, the electrolyte consumption can be reduced, and the cycle performance of the secondary battery can be improved.

[0125] The experimental data from Examples 1 and 6-8 show that when the mass percentage of SiO2@HAP aerogel in the aerogel layer is 85-95%, the thickness of the SEI film after 2000 cycles of the secondary battery is ≥99nm, the HF content in the electrolyte is ≤0.32%, and the capacity retention rate is >88%. This indicates that when the mass percentage of SiO2@HAP aerogel in the aerogel layer is 85-95%, the thickness of the SEI film can be further increased, the electrolyte consumption can be reduced, and the cycle performance of the secondary battery can be improved.

[0126] The experimental data from Examples 1 and 9-12 show that when the thickness of the aerogel layer is 0.5-5 μm, the thickness of the SEI film after 2000 cycles of the secondary battery is ≥90 nm, the HF content in the electrolyte is ≤0.40%, and the capacity retention rate is >84%. This indicates that when the thickness of the aerogel layer is 0.5-5 μm, the thickness of the SEI film can be further increased, reducing electrolyte consumption and improving the cycle performance of the secondary battery.

[0127] The experimental data from Examples 1 and 13-15 show that when the particle size Dv50 of HAP in SiO2@HAP aerogel is 80-150 nm, the thickness of the SEI film after 2000 cycles of the secondary battery is ≥99 nm, the HF content in the electrolyte is ≤0.32%, and the capacity retention rate is >88%. This indicates that when the particle size Dv50 of HAP in SiO2@HAP aerogel is 80-150 nm, the thickness of the SEI film can be further increased, the electrolyte consumption can be reduced, and the cycle performance of the secondary battery can be improved.

[0128] The experimental data from Examples 1 and 16-18 show that when the porosity of SiO2@HAP aerogel is 80-90%, the thickness of the SEI film after 2000 cycles of the secondary battery is ≥88nm, the HF content in the electrolyte is ≤0.54%, and the capacity retention is >83%. This indicates that when the porosity of SiO2@HAP aerogel is 80-90%, the thickness of the SEI film can be further increased, the electrolyte consumption can be reduced, and the cycle performance of the secondary battery can be improved.

[0129] The experimental data from Examples 1 and Comparative Examples 1-2 show that when the negative electrode does not include an aerogel layer or the mass percentage of SiO2@HAP aerogel in the aerogel layer is less than 80%, the thickness of the SEI film after 2000 cycles of the secondary battery is ≤56nm, the HF content in the electrolyte is ≥0.90%, and the capacity retention rate is <74%. This indicates that when the negative electrode does not include an aerogel layer or the mass percentage of SiO2@HAP aerogel in the aerogel layer is less than 80%, the thickness of the SEI film will be reduced and the side reactions of the electrolyte will be increased, thereby leading to a decrease in the cycle performance of the secondary battery.

[0130] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery, characterized in that, The negative electrode includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active layer and an aerogel layer disposed on at least one side surface of the negative electrode current collector. The negative electrode active layer is located between the negative electrode current collector and the aerogel layer; The aerogel layer contains SiO2@HAP aerogel, and the mass percentage of SiO2@HAP aerogel in the aerogel layer is 80-99%.

2. The secondary battery as described in claim 1, characterized in that, The SiO2@HAP aerogel contains 60-90% SiO2 by mass and 10-40% HAP by mass.

3. The secondary battery as described in claim 1, characterized in that, The thickness of the aerogel layer is 0.5~5μm.

4. The secondary battery as described in claim 1, characterized in that, The particle size Dv50 of HAP in the SiO2@HAP aerogel is 20~200nm.

5. The secondary battery as described in claim 1, characterized in that, The porosity of the SiO2@HAP aerogel is 80~99.8%.

6. The secondary battery as described in claim 1, characterized in that, The aerogel layer contains an adhesive, which includes styrene-butadiene rubber and sodium carboxymethyl cellulose.

7. The secondary battery as described in claim 6, characterized in that, Based on the quality of the binder, the styrene-butadiene rubber has a mass percentage of 55-80%; the sodium carboxymethyl cellulose has a mass percentage of 20-45%.

8. The secondary battery as described in claim 1, characterized in that, The thickness of the negative electrode active layer is 40~60μm.

9. The secondary battery as described in claim 1, characterized in that, The negative electrode active layer includes a negative electrode active material, which includes a carbon material.

10. An electrical device, characterized in that, Includes the secondary battery as described in any one of claims 1 to 9.

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