Electrochemical devices and electronic devices

Abstract

The application provides an electrochemical device and an electronic device, and belongs to the technical field of electrochemistry. The electrochemical device comprises a positive electrode, a negative electrode and an electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode composite layer arranged on at least one surface of the positive electrode current collector. The positive electrode composite layer comprises a first polymer and carbon nanotubes. The first polymer comprises nitrogen, oxygen and carbon. The positive electrode composite layer has characteristic peaks of cyanide and carbonyl in an infrared spectrum. The characteristic peak of cyanide is located at 2235cm ‑1 to 2250cm ‑1 , and the characteristic peak of carbonyl is located at 1675cm ‑1 to 1700cm ‑1 . The peak intensity ratio of the characteristic peaks of cyanide and carbonyl is A, and 1≤A≤4. The aspect ratio of the carbon nanotubes is B, and 10≤B≤500. The application can improve the floating charge performance of the electrochemical device, and improve the high-temperature safety performance and the puncture safety performance.

Description

Technical Field

[0001] This application belongs to the field of electrochemical technology, specifically relating to an electrochemical device and an electronic device. Background Technology

[0002] With the continuous development of the portable electronic devices and electric vehicle markets, higher demands are being placed on the energy density and charging efficiency of rechargeable batteries. This trend has driven a significant increase in battery voltage and charging rate to meet the urgent need for longer battery life and shorter charging times for electronic devices.

[0003] However, under high voltage or float charging conditions, complex electrochemical reactions accelerate within the secondary battery, limiting its efficiency and lifespan. Especially in float charging mode, where the battery remains near full charge for extended periods without complete discharge, the internal chemical imbalance intensifies, affecting the battery's stability and safety. Therefore, improving the stability and safety of secondary batteries has become a critical technical challenge that urgently needs to be addressed in the current secondary battery field. Summary of the Invention

[0004] In view of this, this application provides an electrochemical device and an electronic device, which can improve the float charging performance of the electrochemical device by adjusting the positive electrode mixture layer to include a first polymer and carbon nanotubes, while also improving high-temperature safety performance and puncture safety performance.

[0005] In a first aspect, this application provides an electrochemical device, including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode additive layer disposed on at least one surface of the positive electrode current collector. The positive electrode additive layer includes a first polymer and carbon nanotubes. The first polymer includes nitrogen, oxygen, and carbon. The infrared spectrum of the positive electrode additive layer includes characteristic peaks of cyano and carbonyl groups, with the characteristic peak of cyano located at 2235 cm⁻¹. -1 Up to 2250cm -1 The characteristic peak of the carbonyl group is located at 1675 cm⁻¹. -1 Up to 1700cm -1 The peak intensity ratio of the characteristic peaks of cyano and carbonyl groups is A, where 1 ≤ A ≤ 4; the aspect ratio of the carbon nanotubes is B, where 10 ≤ B ≤ 500. This application controls the positive electrode complex layer to include a first polymer and carbon nanotubes, wherein the first polymer has cyano and carbonyl groups. By controlling the peak intensity ratio of the cyano and carbonyl groups to match the aspect ratio of the carbon nanotubes, electrostatic attraction between the first polymer and the carbon nanotubes can be promoted, thereby forming a conductive three-dimensional network of first polymer-positive electrode active material-carbon nanotubes on the surface of the positive electrode active material. This improves the complexation effect of the positive electrode, thereby reducing the breakage of the positive electrode active material and side reactions with the electrolyte under float charging, high temperature, or puncture conditions, and improving the float charging performance, high temperature safety performance, and puncture safety performance of the electrochemical device.

[0006] In some embodiments, the electrochemical device satisfies at least one of the following conditions: (1) 150 ≤ A × B ≤ 400; (2) 1 ≤ A ≤ 2; (3) 100 ≤ B ≤ 300. Adjusting the peak intensity ratio of cyano and carbonyl groups and the aspect ratio of carbon nanotubes to satisfy the above conditions can promote better cooperation between the first polymer and carbon nanotubes, further improving the float charging performance, high-temperature safety performance and puncture safety performance of the electrochemical device.

[0007] In some embodiments, the positive electrode mixture layer further includes lithium cobalt oxide. Based on the total number of particles in the positive electrode mixture layer, the particle number ratio of the first polymer is K1%, and the particle number ratio of lithium cobalt oxide is K2%, where 33 ≤ K2 / K1 ≤ 10000. The inventors have found that under float charging, high temperature, or puncture conditions, the lithium cobalt oxide in the positive electrode easily undergoes rapid heat and gas generation reactions with the electrolyte, affecting the float charging performance and safety performance of the electrochemical device. This application, by controlling the particle numbers of lithium cobalt oxide and the first polymer to satisfy the above relationship, can improve the complexation effect of the conductive three-dimensional network of the first polymer-lithium cobalt oxide-carbon nanotubes, reduce the breakage of lithium cobalt oxide under the above conditions and its side reactions with the electrolyte, and further improve the float charging performance, high temperature safety performance, and puncture safety performance of the electrochemical device.

[0008] In some embodiments, 0.01 ≤ K1 ≤ 1; and / or, 98 ≤ K2 ≤ 99. When the particle ratio of the first polymer and lithium cobalt oxide is controlled within the above range, the synergistic effect of the first polymer and lithium cobalt oxide can be improved, thereby better improving the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0009] In some embodiments, to improve the float charging performance, high temperature safety performance and puncture safety performance of the electrochemical device, based on the total mass of carbon, nitrogen and oxygen, the first polymer satisfies at least one of the following conditions: (1) the mass percentage of nitrogen is H1%, 5≤H1≤20; (2) the mass percentage of oxygen is H2%, 5≤H2≤20; (3) the mass percentage of carbon is H3%, 60≤H3≤90.

[0010] In some embodiments, the first polymer includes a first monomer, a second monomer, and a third monomer; the first monomer is selected from at least one of acrylonitrile or methacrylonitrile; the second monomer is selected from at least one of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, isobutyl acrylate, tert-butyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, or 2-ethylhexyl methacrylate; the third monomer is selected from at least one of acrylic acid, methacrylic acid, lithium acrylate, sodium acrylate, lithium methacrylate, or sodium methacrylate.

[0011] In this application, the first polymer comprising a first monomer, a second monomer, and a third monomer means that the first polymer is obtained by copolymerizing monomers comprising the first monomer, the second monomer, and the third monomer. Taking the first monomer as an example, based on the mass of the first polymer, the mass percentage of the first monomer refers to the mass percentage of the unit formed after the polymerization of the first monomer in the first polymer.

[0012] In some embodiments, based on the mass of the first polymer, the first polymer satisfies at least one of the following conditions: (1) the mass percentage of the first monomer is M1%, 50≤M1≤90; (2) the mass percentage of the second monomer is M2%, 1≤M2≤30; (3) the mass percentage of the third monomer is M3%, 5≤M3≤30. This application regulates the mass percentage of each monomer in the first polymer to satisfy the above ranges, wherein the first monomer can dominate the complexation with the transition metal of the positive electrode active material, reducing the impact and damage of high voltage on the positive electrode particles; the second monomer can provide adhesive force, so that the polymer can interact with the positive electrode particles with a relatively strong physical adhesive effect; the third monomer can enhance the flexibility of the molecule, so that when the electrode sheet is subjected to greater pressure during cold pressing, the positive electrode particles will not be crushed but will have a certain buffer. Through the mutual cooperation between the monomers, the float charging performance, high temperature safety performance and puncture safety performance of the electrochemical device are further improved.

[0013] In some embodiments, the first polymer further includes a fourth monomer, which is selected from at least one of acrylamide, N-methylacrylamide, N-ethylacrylamide, or 2-methylacrylamide. Based on the mass of the first polymer, the mass percentage of the fourth monomer is M4%, with 0.01 ≤ M4 ≤ 15, preferably 1 ≤ M4 ≤ 15. This application regulates the further addition of a fourth monomer to the first polymer and controls the mass percentage of the fourth monomer to meet the above range. The amide can undergo a certain π-π attraction with the nitriles in the first monomer, and after combining with carbon nanotubes, it can expand to form a larger positive electrode attraction and conductive network, giving the positive electrode material better high-voltage and high-temperature resistance, further improving the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0014] In some embodiments, the maximum particle size of the first polymer is D μm, 15 ≤ D ≤ 100; preferably 15 ≤ D ≤ 50. When the maximum particle size of the first polymer is within the above range, it can be close to the size of the positive electrode material particles, and the elements of the polymer can interact with the positive electrode elements on the same scale. Furthermore, at the above size, it can match the size of the electrode sheet, reducing particle breakage caused by the cold pressing process of the electrode sheet, which is beneficial to improving the stability of the first polymer particles, and can also optimize the coating effect on the positive electrode active material particles, reduce the occurrence of side reactions, thereby further improving the float charging performance, high temperature safety performance, and puncture safety performance of the electrochemical device.

[0015] In some embodiments, the electrolyte includes linear carbonates, including ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. This application further controls the electrolyte to include ethylene carbonate, propylene carbonate, and fluoroethylene carbonate, which can promote electrostatic coupling between polar functional groups of the electrolyte and the polymer, thereby softening the solid polymer to a certain extent under the action of the electrolyte. The softened polymer has a larger contact area with the positive electrode particles, and the contact effect is improved to a certain extent, further improving the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0016] Secondly, this application provides an electronic device, including any of the above-mentioned electrochemical devices. Attached Figure Description

[0017] Figure 1 The infrared spectrum of the positive electrode mixture layer in the electrochemical device of Example 1-1 of this application;

[0018] Figure 2 This is a scanning electron microscope image of the first polymer of this application. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0020] In a first aspect, this application provides an electrochemical device, including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode additive layer disposed on at least one surface of the positive electrode current collector. The positive electrode additive layer includes a first polymer and carbon nanotubes. The first polymer includes nitrogen, oxygen, and carbon. The infrared spectrum of the positive electrode additive layer includes characteristic peaks of cyano and carbonyl groups, with the characteristic peak of cyano located at 2235 cm⁻¹. -1 Up to 2250cm -1 The characteristic peak of the carbonyl group is located at 1675 cm⁻¹. -1 Up to 1700cm -1 The peak intensity ratio of the characteristic peaks of cyano and carbonyl groups is A, where 1 ≤ A ≤ 4; the aspect ratio of the carbon nanotubes is B, where 10 ≤ B ≤ 500. This application controls the positive electrode complex layer to include a first polymer and carbon nanotubes, wherein the first polymer has cyano and carbonyl groups. By controlling the peak intensity ratio of the cyano and carbonyl groups to match the aspect ratio of the carbon nanotubes, electrostatic attraction between the first polymer and the carbon nanotubes can be promoted, thereby forming a conductive three-dimensional network of first polymer-positive electrode active material-carbon nanotubes on the surface of the positive electrode active material. This improves the complexation effect of the positive electrode, thereby reducing the breakage of the positive electrode active material and side reactions with the electrolyte under float charging, high temperature, or puncture conditions, and improving the float charging performance, high temperature safety performance, and puncture safety performance of the electrochemical device.

[0021] In some embodiments, 150 ≤ A × B ≤ 400; for example, the value of A × B is 150, 160, 170, 200, 230, 240, 250, 270, 300, 320, 330, 360, 370, 400, or a value within the range of any two of these values. Adjusting the peak intensity ratio of cyano and carbonyl groups and the aspect ratio of carbon nanotubes to satisfy the above relationship can further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0022] In some embodiments, 1 ≤ A ≤ 4, preferably 1 ≤ A ≤ 2. For example, A is a value within the range of 1, 1.2, 1.3, 1.5, 1.8, 2.1, 2.3, 2.6, 2.8, 3.0, 3.1, 3.4, 3.7, 4, or any combination of these values. Adjusting the peak intensity ratio of the cyano and carbonyl groups to meet the above conditions can further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0023] In some embodiments, 10 ≤ B ≤ 500, preferably 100 ≤ B ≤ 300. For example, B is a value within the range of 10, 70, 110, 150, 160, 200, 250, 280, 330, 360, 400, 450, 490, 500, or any combination of these values. Adjusting the aspect ratio of carbon nanotubes to meet the above conditions can further improve the float charging performance, high-temperature safety performance, and puncture safety performance of electrochemical devices.

[0024] In some embodiments, the positive electrode mixture layer further includes lithium cobalt oxide. Based on the total number of particles in the positive electrode mixture layer, the particle number ratio of the first polymer is K1%, and the particle number ratio of lithium cobalt oxide is K2%, where 33 ≤ K2 / K1 ≤ 10000. For example, the value of K2 / K1 is 33, 462, 1029, 2242, 2353, 3291, 4016, 5090, 5897, 6820, 7469, 7776, 8695, 9407, 10000, or a value within the range of any two of these values. By controlling the particle numbers of lithium cobalt oxide and the first polymer to satisfy the above relationship, this application can improve the complexation effect of the conductive three-dimensional network of the first polymer-lithium cobalt oxide-carbon nanotube, reduce the breakage of lithium cobalt oxide under the above conditions and the side reactions with the electrolyte, and further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0025] In some embodiments, 0.01 ≤ K1 ≤ 1, for example, the value of K1 is 0.01, 0.09, 0.16, 0.22, 0.25, 0.35, 0.43, 0.49, 0.62, 0.64, 0.74, 0.82, 0.86, 0.99, 1, or a value within any two of these ranges. When the proportion of particles of the first polymer is controlled within the above range, the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device can be better improved.

[0026] In some embodiments, 98 ≤ K2 ≤ 99, for example, K2 is a value within the range of 98, 98.04, 98.10, 98.22, 98.26, 98.34, 98.43, 98.48, 98.57, 98.62, 98.71, 98.80, 98.89, 98.93, 99, or any combination of these values. When the proportion of lithium cobalt oxide particles is controlled within the above range, the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device can be better improved.

[0027] In some embodiments, the first polymer includes a first monomer, a second monomer, and a third monomer; the first monomer is selected from at least one of acrylonitrile or methacrylonitrile; the second monomer is selected from at least one of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, isobutyl acrylate, tert-butyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, or 2-ethylhexyl methacrylate; the third monomer is selected from at least one of acrylic acid, methacrylic acid, lithium acrylate, sodium acrylate, lithium methacrylate, or sodium methacrylate.

[0028] In some embodiments, based on the mass of the first polymer, the first polymer satisfies at least one of the following conditions: (1) the mass percentage of the first monomer is M1%, 50 ≤ M1 ≤ 90, for example, the value of M1 is 50, 52, 55, 57, 61, 63, 68, 71, 73, 77, 78, 84, 86, 87, 90 or a value within the range of any two of these values; (2) the mass percentage of the second monomer is M2%, 1 ≤ M2 ≤ 30, for example, the value of M2 is 1, 2, 4, 6, 9, 11, 12, 15, 17, ... 19, 22, 24, 26, 29, 30 or any two of these values; (3) The mass percentage of the third monomer is M3%, 5≤M3≤30, for example, the value of M3 is 5, 8, 9, 12, 15, 15, 17, 19, 21, 24, 26, 28, 29, 30 or any two of these values; This application regulates the mass percentage of each monomer in the first polymer to meet the above range, which can further improve the float charging performance, high temperature safety performance and puncture safety performance of the electrochemical device.

[0029] In some embodiments, the first polymer further includes a fourth monomer selected from at least one of acrylamide, N-methylacrylamide, N-ethylacrylamide, or 2-methylacrylamide. Based on the mass of the first polymer, the mass percentage of the fourth monomer is M4%, where 1 ≤ M4 ≤ 15. For example, the value of M4 is 1, 2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 14, 15, or any combination thereof. By controlling the inclusion of a fourth monomer in the first polymer and adjusting its mass percentage to satisfy the above range, this application can further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0030] In this application, the first polymer is prepared by a method comprising the following steps: under an inert gas atmosphere, a first monomer, a second monomer, and a third monomer are added to a dispersion medium (if a fourth monomer is present, it may also be added in this step), the temperature is raised to 55–80°C, and then an initiator is added to carry out a copolymerization reaction for 3–10 hours to obtain the first polymer. To better utilize the effect of the first polymer, it can be neutralized to a pH of 7–7.8, and then dried and pulverized.

[0031] This application does not have special requirements for the dispersion medium, as long as it can dissolve or disperse the monomers in this application, such as water or organic solvents.

[0032] In some specific embodiments, the first polymer can be prepared by a method including the following steps: At room temperature, a solvent is placed in a 2000L reactor, and nitrogen gas with a purity ≥99.9% is introduced while stirring at 100-300 rpm at a flow rate controlled at 2000-4000 L / H. After purging for 1 hour, water-soluble oxygen is removed, and 60% acrylic acid, 20% methyl acrylate, and 20% methacrylic acid are added by mass percentage. Under a nitrogen atmosphere, the solution is heated to 65°C at a heating rate of 1-2°C / min, and 0.1 wt% ammonium persulfate is added. The temperature is kept stable, and the reaction is carried out for 5 hours to copolymerize and obtain the first polymer. Then, at 60°C, the solution is neutralized to pH 7.5 with an alkaline aqueous solution to obtain a film. The film is then dried in an oven at 120°C for 24 hours. The dried film is transferred to a FRITSCH grinder and ground into powder at a speed of 400 rpm.

[0033] In some embodiments, the maximum particle size of the first polymer is D μm, where 15 ≤ D ≤ 100; preferably, 15 ≤ D ≤ 50, for example, D is a value within the range of 15, 17, 25, 33, 38, 45, 50, 55, 66, 68, 76, 81, 88, 99, 100, or any combination thereof. When the maximum particle size of the first polymer is within the above range, the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device can be further improved.

[0034] In this application, the positive electrode includes a positive electrode current collector and a positive electrode additive layer disposed on at least one surface of the positive electrode current collector. The aforementioned "positive electrode additive layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode additive layer can be located on one surface of the positive electrode current collector along its thickness direction, or on two surfaces of the positive electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive electrode current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the positive electrode current collector, as long as the purpose of this application is achieved. For example, the positive electrode current collector can contain aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). In this application, the positive electrode active material can also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0035] In this application, the positive electrode binder layer may further include a positive electrode adhesive. This application does not impose any particular limitation on the type of positive electrode adhesive in the positive electrode binder layer, as long as it achieves the purpose of this application. For example, the positive electrode adhesive may include, but is not limited to, at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified styrene-butadiene rubber (SBR), or polyurethane. In some embodiments, the polyolefin adhesive includes at least one of polyethylene, polypropylene, polyolefin ester, polyenol, or polyacrylic acid. This application does not impose any particular limitation on the thickness of the positive electrode binder layer, as long as it achieves the purpose of this application. For example, the thickness of the positive electrode binder layer may be from 3 μm to 15 μm.

[0036] In some embodiments, the electrolyte includes ethylene carbonate, propylene carbonate, and fluoroethylene carbonate. This application further controls the inclusion of ethylene carbonate, propylene carbonate, and fluoroethylene carbonate in the electrolyte, which can further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0037] According to some embodiments of this application, the electrolyte further includes lithium salts and non-aqueous solvents. The lithium salts may include, but are not limited to, at least one of: lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB), LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, and Li2SiF6. This application does not limit the content of lithium salts in the electrolyte, as long as the purpose of this application is achieved. This application does not particularly limit the non-aqueous solvents, as long as the purpose of this application is achieved. For example, the non-aqueous solvents may include, but are not limited to, at least one of cyclic carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned cyclic carbonate compounds and carboxylic acid ester compounds include at least one of methyl formate, methyl acetate, methyl propionate, methyl butyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, propyl formate, propyl acetate, propyl propionate, propyl butyrate, butyl butyrate, butyl propionate, and pentyl propionate. The aforementioned ether compounds may include, but are not limited to, at least one of 1,3-dioxopentane (DOL), ethylene glycol dimethyl ether (1,2-dimethoxyethane, DME), dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The other organic solvents mentioned above may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.

[0038] This application does not impose any particular limitation on the negative electrode sheet, as long as the purpose of this application can be achieved. For example, the negative electrode sheet includes a negative current collector and a negative electrode additive layer disposed on at least one surface of the negative current collector. In this application, the negative electrode additive layer can be disposed on one surface or two surfaces in the thickness direction of the negative current collector. It should be noted that "surface" here can be the entire area of ​​the negative current collector or a part of the negative current collector; this application does not impose any particular limitation, as long as the purpose of this application can be achieved. This application does not impose any particular limitation on the negative current collector, as long as the purpose of this application can be achieved. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, or composite current collectors (e.g., carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). In this application, there are no particular limitations on the thickness of the negative current collector, the negative electrode additive layer, and the negative electrode sheet, as long as the purpose of this application can be achieved.

[0039] The negative electrode mixture layer of this application includes a negative electrode active material, which may include, but is not limited to, graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, and SiO2. x (0.5 < x < 1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel-structured lithium titanate lithiation TiO2-Li4Ti5O 12 At least one of Li-Al alloy and metallic lithium.

[0040] The negative electrode mixture layer in this application may further include a negative electrode binder and a negative electrode conductive agent, or the negative electrode mixture layer may further include a negative electrode binder, a negative electrode conductive agent, and a thickener. This application does not particularly limit the types of negative electrode binders and negative electrode conductive agents, as long as they achieve the purpose of this application. For example, the negative electrode binder may include, but is not limited to, at least one of the aforementioned positive electrode binders, and the negative electrode conductive agent may include, but is not limited to, at least one of the aforementioned positive electrode conductive agents. This application does not particularly limit the types of thickeners, as long as they achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or carboxymethyl cellulose. This application does not particularly limit the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode binder, and thickener in the negative electrode mixture layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0041] The electrochemical device of this application may also include a separator membrane. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. The type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, and spun membrane. For example, the separator membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is disposed 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 mixture of polymer and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. This application does not have any particular limitation on the inorganic particles, which may include at least one of alumina, 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. This application does not have any particular limitation on the binder, which may include at least one of the above-mentioned positive electrode binders. The polymer layer contains a polymer. This application does not have any particular limitation on the polymer, which may include at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene). In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application. For example, the thickness of the separator may be from 5 μm to 500 μm.

[0042] The electrochemical device of this application also includes a packaging bag for containing the positive electrode, negative electrode, diaphragm, and electrolyte, as well as other components known in the art in the electrochemical device. This application does not limit the scope of these other components. This application does not impose any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it achieves the purpose of this application.

[0043] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the electrochemical device may include, but is not limited to, lithium-ion batteries, sodium-ion batteries, etc.

[0044] This application does not impose any particular limitation on the preparation method of the electrochemical device. For example, it may include the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device; or stacking the positive electrode, the separator, and the negative electrode in sequence, and then fixing the four corners of the entire stacked structure to obtain a stacked electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the electrochemical device.

[0045] Secondly, this application provides an electronic device, including any of the above-mentioned electrochemical devices.

[0046] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0047] The following uses a lithium-ion battery as an example to illustrate the solution of this application with specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available products, and the devices or equipment used are all purchased from conventional market sales channels.

[0048] Test methods

[0049] Carbon nanotube aspect ratio test

[0050] Use SEM to observe the positive electrode plate, count the length and diameter of at least 20 carbon nanotubes, calculate the average length and diameter, and then calculate the aspect ratio of the carbon nanotubes based on the average length and diameter.

[0051] Particle Count Test

[0052] The positive electrode was observed using a scanning electron microscope (SEM) in backscatter mode, with a total area of ​​2000 μm. 2 The area to be tested is the region to be tested. Based on the ratio of the number of lithium cobalt oxide particles to the number of first polymer particles in the region to be tested, the arithmetic mean is calculated to obtain the final particle number ratio.

[0053] Maximum particle size test

[0054] In SEM backscatter mode, observe the first polymer particles separated from the positive electrode or observe the first polymer in the positive electrode. Select the first polymer material with the largest longest diameter in the field of view. The longest diameter of the first polymer material is the maximum particle size of the first polymer. Figure 2 The image shows a scanning electron microscope (SEM) image of the first polymer of this application. As shown in the figure, the maximum particle size of this batch of first polymer particles is 32.0 μm. When observing the positive electrode, the actual area corresponding to the total field of view should be greater than 2000 μm. 2 .

[0055] Float charging test

[0056] (1) Place the lithium-ion battery in an environment of 45°C and let it stand for 5 minutes;

[0057] (2) Charge the battery at a constant current of 0.7C to a full charge voltage of 4.53V, and charge it at a constant voltage of 60mA at the maximum voltage; test the initial thickness d0 of the lithium-ion battery.

[0058] (3) Charge the battery at a constant voltage of 4.53V for 70 days and charge it to 100mA; (4) Every 4 days, use the test probe of the voltage internal resistance meter to directly connect to the positive and negative terminals of the lithium-ion battery to measure the voltage internal resistance of the lithium-ion battery (1KHz frequency), and use a flat plate thickness gauge (with 500g pressure) to measure the battery thickness d1. The thickness growth rate = battery thickness d1 / initial thickness d0 × 100%. When the battery thickness growth rate exceeds 40% compared to the initial value, stop the test.

[0059] (5) The thickness growth rate on day 32 is defined as the float charge performance characterization point, that is, the float charge thickness growth rate = battery thickness d1 on day 32 / initial thickness d0 × 100%.

[0060] Puncture safety test

[0061] (1) Place the lithium-ion battery in an environment of 25°C and let it stand for 5 minutes.

[0062] (2) Discharge the battery at a constant current of 0.2C until the voltage reaches 3.0V, and let it stand for 10 minutes.

[0063] (3) Charge the battery at a constant current of 0.7C to a full charge voltage of 4.53V, and charge at a constant voltage at the maximum voltage until the current is 0.025C. Let it stand for 10 minutes.

[0064] (4) Take a picture of the lithium-ion battery and use the test probe of the voltage internal resistance meter to directly connect to the positive and negative terminals of the lithium-ion battery to measure the voltage internal resistance of the lithium-ion battery (1kHz frequency).

[0065] (5) Attach the temperature sensing wire to the surface of the lithium-ion battery. In a test environment of 20±5℃, place the lithium-ion battery on the test platform and use a 3mm diameter straight nail at a speed of 150mm / s to test from the center of the lithium-ion battery. The lithium-ion battery should be completely pierced by the straight nail. After holding the test for 30 minutes, take a picture and measure the internal resistance of the lithium-ion battery again using a voltage internal resistance meter. If the battery does not catch fire or explode before the nail is removed, it indicates that the lithium-ion battery has passed the nail penetration performance test, recorded as P (Pass). In the test results, 3 / 10P means that 3 out of 10 products passed the test, and 0 / 10P means that 0 out of 10 products passed the test.

[0066] The high-temperature safety test (i.e., hot chamber test) procedure is as follows:

[0067] (I) Adjust the furnace temperature to 25°C, place the lithium-ion battery to be tested into the heating furnace and let it stand for 5 minutes;

[0068] (II) 0.2C constant current discharge (DC) to 3.0V;

[0069] (III) Let stand for 10 minutes;

[0070] (IV) Charge at a constant current of 0.7C (CC) to 4.53V, then charge at a constant voltage (CV) to 0.025C;

[0071] (V) Let stand for 10 minutes.

[0072] Before testing, take photos, measure the internal resistance, and attach the temperature sensing wire to the battery surface. Place the sample in the heating furnace chamber and heat it to 130℃ (or 132℃) at a heating rate of 5±2℃ / min, maintaining this temperature for 60 minutes. After the test, take photos and measure the internal resistance again. If the battery does not catch fire or explode, it has passed the heating chamber test and is recorded as P (Pass). In the test results, 3 / 5P indicates that 3 out of 5 products passed the test, and 0 / 5P indicates that 0 out of 5 products passed the test.

[0073] Example 1-1

[0074] The lithium-ion battery of this embodiment includes a positive electrode, a negative electrode and an electrolyte. The positive electrode includes a positive electrode current collector and a positive electrode additive layer disposed on at least one surface of the positive electrode current collector. The positive electrode additive layer includes a first polymer and carbon nanotubes. Figure 1 The infrared spectrum of the positive electrode mixture layer is shown, revealing characteristic peaks for cyano and carbonyl groups. The characteristic peak of the cyano group is located at 2235 cm⁻¹. -1 Up to 2250cm -1 The characteristic peak of the carbonyl group is located at 1675 cm⁻¹. -1 Up to 1700cm -1The peak intensity ratio of the characteristic peaks of cyano and carbonyl groups is A, where A = 1.6; the aspect ratio of carbon nanotubes is B, where B = 150, and A × B = 240.

[0075] The positive electrode additive layer also includes lithium cobalt oxide. Based on the total number of particles in the positive electrode additive layer, the particle count of the first polymer (K1%) is 2.88%, the particle count of lithium cobalt oxide (K2%) is 95%, and K2 / K1 = 33. The first polymer includes a first monomer, a second monomer, and a third monomer. The first monomer is acrylonitrile, with a mass percentage (M1%) of 60%, the second monomer is methyl acrylate, with a mass percentage (M2%) of 10%, and the third monomer is acrylic acid, with a mass percentage (M3%) of 30%. The maximum particle size (Dμm) of the first polymer is 110μm.

[0076] Preparation of negative electrode

[0077] Graphite particles (negative electrode active material), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) were thoroughly mixed in deionized water at a weight ratio of 97.4:1.4:1.2 to form a uniform negative electrode slurry (42% solid content). The negative electrode slurry was uniformly coated onto a 5µm thick copper foil negative electrode current collector, dried, and cold-pressed to form a 110µm negative electrode active material layer. After cutting and welding the tabs, the negative electrode sheet was obtained.

[0078] Preparation of positive electrode

[0079] Lithium cobalt oxide (CCO), acetylene black (CCO), polyvinylidene fluoride (PVDF), and a first polymer were mixed in a mass ratio of 97.2:1.3:1.3:0.2 in N-methylpyrrolidone (NMP) solvent and stirred thoroughly under vacuum to obtain a CCO slurry (69% solids content). This CCO slurry was coated onto a 10µm thick aluminum foil current collector, dried, and cold-pressed to form an approximately 80µm thick CCO active material layer. After cutting and welding the tabs, the CCO sheet was obtained.

[0080] Preparation of electrolyte

[0081] In a dry argon-atmospheric glove box, ethylene carbonate (EC) and propylene carbonate (PC) were mixed thoroughly at a mass ratio of EC:PC = 55:45. Then, fluoroethylene carbonate was added, dissolved, and stirred completely. Lithium salt LiPF6 was then added and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentage of LiPF6 was 12.5%, and the mass percentage of fluoroethylene carbonate was 5%.

[0082] Preparation of the separating membrane

[0083] Polyethylene (PE) porous polymer film is used as the separator.

[0084] Preparation of lithium-ion batteries

[0085] The obtained positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. Then, they are wound to obtain a bare battery. The bare battery is placed in an outer packaging foil aluminum-plastic film, and electrolyte is injected. After vacuum sealing, settling, and formation processes, a lithium-ion battery is obtained.

[0086] The lithium-ion batteries in the examples and comparative examples in Table 1 differ from those in Examples 1-1 mainly in that the peak intensity ratio A of the characteristic peaks of cyano and carbonyl groups, the aspect ratio B of carbon nanotubes, and the types and mass proportions of each monomer of the first polymer are adjusted according to Table 1. The specific adjustment parameters and performance test results are shown in Table 1.

[0087] Table 1

[0088]

[0089]

[0090] Note: The values ​​in parentheses represent the mass percentage of each monomer in the first polymer.

[0091] As shown in Table 1, this application improves the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device by adjusting the peak intensity ratio of amino and carbonyl groups in the first polymer of the positive electrode binder layer in conjunction with the aspect ratio of the carbon nanotubes. In particular, when the peak intensity ratio of cyano and carbonyl groups and the aspect ratio of the carbon nanotubes are adjusted to meet the above-mentioned ranges, the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device can be further improved.

[0092] Specifically, when the types and mass ratios of the first, second, and third monomers in the first polymer are controlled within the aforementioned ranges, the synergistic effect between the monomers can further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device. In particular, when the first polymer also includes the aforementioned fourth monomer, controlling the mass ratio of the fourth monomer within the aforementioned range allows it to combine with carbon nanotubes, thereby enabling the electrochemical device to exhibit even superior float charging performance, high-temperature safety performance, and puncture safety performance.

[0093] The main difference between the lithium-ion batteries in the embodiments and comparative examples in Table 2 and those in Examples 1-5 is that the particle number percentage K1% of the first polymer, the particle number percentage K2% of the lithium cobalt oxide, and the maximum particle size Dμm of the first polymer were adjusted according to Table 2. The specific adjustment parameters and performance test results are shown in Table 2.

[0094] Table 2

[0095]

[0096]

[0097] As shown in Table 2, the particle counts and relationships of the first polymer and lithium cobalt oxide in the positive electrode mixture layer, as described in this application, fall within the aforementioned ranges, which can further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device. In particular, when the maximum particle size Dμm of the first polymer is controlled within the aforementioned range, it is beneficial to further improve the float charging performance, high-temperature safety performance, and puncture safety performance of the electrochemical device.

[0098] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the principles of this application should be included within the protection scope of this application.

Claims

1. An electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, characterized in that, The positive electrode includes a positive electrode current collector and a positive electrode additive layer disposed on at least one surface of the positive electrode current collector. The positive electrode additive layer includes a first polymer and carbon nanotubes. The first polymer includes nitrogen, oxygen and carbon elements. The infrared spectrum of the positive electrode mixture layer includes characteristic peaks of cyano and carbonyl groups, with the characteristic peak of the cyano group located at 2235 cm⁻¹. -1 Up to 2250 cm -1 The characteristic peak of the carbonyl group is located at 1675 cm⁻¹. -1 Up to 1700 cm -1 The peak intensity ratio of the characteristic peaks of the cyano group and the carbonyl group is A, where 1 ≤ A ≤ 2. The aspect ratio of the carbon nanotube is B, where 10 ≤ B ≤ 300; Furthermore, the electrochemical device satisfies the following condition: 150 ≤ A × B ≤ 400; The positive electrode mixture layer further includes lithium cobalt oxide. Based on the total number of particles in the positive electrode mixture layer, the particle count of the first polymer is K1%, the particle count of the lithium cobalt oxide is K2%, and the electrochemical device satisfies at least one of the following conditions: (1) 33≤K2 / K1≤10000; （2）0.01≤K1≤1； （3）98≤K2≤99。 2. The electrochemical device according to claim 1, characterized in that, The electrochemical device satisfies the following condition: 100≤B≤300.

3. The electrochemical device according to claim 1, characterized in that, Based on the total mass of the carbon, nitrogen, and oxygen elements, the first polymer satisfies at least one of the following conditions: (1) The mass percentage of nitrogen is H1%, 5≤H1≤20; (2) The mass percentage of oxygen is H2%, 5≤H2≤20; (3) The mass percentage of the carbon element is H3%, 60≤H3≤90.

4. The electrochemical device according to any one of claims 1 to 3, characterized in that, The first polymer comprises a first monomer, a second monomer, and a third monomer; The first monomer is selected from at least one of acrylonitrile or methacrylonitrile; The second monomer is selected from at least one of methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, isobutyl acrylate, tert-butyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, isoamyl methacrylate, n-hexyl methacrylate, or 2-ethylhexyl methacrylate; The third monomer is selected from at least one of acrylic acid, methacrylic acid, lithium acrylate, sodium acrylate, lithium methacrylate, or sodium methacrylate.

5. The electrochemical device according to claim 4, characterized in that, Based on the mass of the first polymer, the first polymer satisfies at least one of the following conditions: (1) The mass percentage of the first monomer is M1%, and 50 ≤ M1 ≤ 90; (2) The mass percentage of the second monomer is M2%, 1≤M2≤30; (3) The mass percentage of the third monomer is M3%, and 5≤M3≤30.

6. The electrochemical device according to claim 4, characterized in that, The first polymer further includes a fourth monomer, which is selected from at least one of acrylamide, N-methylacrylamide, N-ethylacrylamide or 2-methylacrylamide; Based on the mass of the first polymer, the mass percentage of the fourth monomer is M4%, where 0.01 ≤ M4 ≤ 15.

7. The electrochemical device according to claim 6, characterized in that, 1≤M4≤15。 8. The electrochemical device according to any one of claims 1 to 3, characterized in that, The maximum particle size of the first polymer is D μm, where 15 ≤ D ≤ 100; The electrolyte includes ethylene carbonate, propylene carbonate, and fluoroethylene carbonate.

9. The electrochemical device according to claim 8, characterized in that, 15≤D≤50。 10. An electronic device, characterized in that, The electrochemical device includes any one of claims 1 to 9.

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