Secondary battery and electronic device

Abstract

The secondary battery comprises a positive electrode, a negative electrode and an electrolyte, the negative electrode comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer comprises a negative electrode material, the negative electrode current collector is a copper foil, the content of an oxygen element in the negative electrode material is X1%, the content of the oxygen element in the pressurized negative electrode material is X2%, and 0.5 < = X2-X1 < = 1.4, in the pressurization treatment, the intensity of pressure applied to the negative electrode material is 127 Mpa, and the pressure maintaining time is 60 seconds; the electrolyte comprises an ether nitrile compound. According to the present invention, the negative electrode material satisfies 0.5 < = X2-X1 < = 1.4, and the electrolyte comprises the ether nitrile compound, such that the rate performance and the cycle capacity retention performance of the secondary battery can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of energy storage, and particularly relates to a secondary battery and an electronic device. BACKGROUND

[0002] The secondary battery, also known as a rechargeable battery or a storage battery, has a working principle based on a reversible chemical reaction, and realizes the storage and release of electric energy through the reactivation of active substances by charging, and is widely applied in the fields of electric vehicles, renewable energy storage and portable electronic devices.

[0003] However, in the charging and discharging process of the secondary battery, the negative electrode material in the negative electrode material layer will change in volume, causing extrusion and damage to the structure in the secondary battery, thereby reducing the electrical performance of the secondary battery. The above-mentioned problems need to be solved in the field. SUMMARY

[0004] Therefore, the application provides a secondary battery, which can improve the rate performance and cycle capacity retention performance of the secondary battery by making the negative electrode material satisfy 0.5≤X2-X1≤1.4 and making the electrolyte include an ether nitrile compound.

[0005] In a first aspect, the application provides a secondary battery, which includes a positive electrode, a negative electrode and an electrolyte, the negative electrode includes a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector, the negative electrode material layer includes a negative electrode material, the negative electrode current collector is a copper foil, the content of oxygen element in the negative electrode material is X1 %, the content of oxygen element in the negative electrode material after pressure treatment is X2 %, 0.5≤X2-X1≤1.4, in the pressure treatment, the pressure applied to the negative electrode material is 127Mpa, and the pressure holding time is 60 seconds; the electrolyte includes an ether nitrile compound. The application makes the negative electrode material satisfy 0.5≤X2-X1≤1.4, which is conducive to making the surface of the negative electrode material include a coating layer with high mechanical strength, and can constrain the volume change of the negative electrode material during the charging and discharging of the secondary battery, thereby reducing the pulverization and falling off of the negative electrode material layer. However, at this time, the coating layer is relatively dense, and lithium ions are difficult to migrate efficiently in the coating layer, so the electrolyte includes an ether nitrile compound, which is conducive to introducing an appropriate amount of flexible components into the SEI film, and helps to improve the thickness uniformity, elasticity and lithium ion conductivity of the SEI film, and can improve the migration efficiency of lithium ions between the electrolyte and the negative electrode material, thereby improving the rate performance and cycle capacity retention performance of the secondary battery.

[0006] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) 3.0 ≤ X1 ≤ 4.0; (2) 3.5 ≤ X2 ≤ 5.4; (3) 0.7 ≤ X2 - X1 ≤ 1.1. By making the secondary battery satisfy at least one of the above conditions, this application can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0007] In some embodiments, the porosity of the negative electrode material layer is K%, where 30 ≤ K ≤ 40, and preferably, 33 ≤ K ≤ 37. By controlling the value of K to meet the above range, this application can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0008] In some embodiments, in the XRD diffraction pattern of the negative electrode, a first characteristic peak exists in the range of 43~44°, with a peak area of ​​A, where 3987≤A≤15013; and a second characteristic peak exists in the range of 50~51°, with a peak area of ​​B, where 1.55≤A / B≤1.75, preferably 1.6≤A / B≤1.7. This application, by controlling the value of A / B to meet the above range, can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0009] In some embodiments, the ether nitrile compound includes a class of ether nitrile compounds, which includes at least one of the compounds shown in Formulas 1-1 to 1-3: Formula 1-1 Formula 1-2 Equation 1-3; Based on the mass of the electrolyte, the mass percentage of a certain type of ether nitrile compound is E1%, where 0.1 ≤ E1 ≤ 3.5, and preferably 0.5 ≤ E1 ≤ 2.4. This application, by adjusting the value of E1 to meet the above range, can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0010] In some embodiments, the ether nitrile compound includes a class of ether nitrile compounds, which include at least one of the compounds shown in Formulas 2-1 to 2-3: Formula 2-1 Equation 2-2 Equation 2-3; Based on the mass of the electrolyte, the mass percentage of the second-class ether nitrile compound is E2%, where 0.05 ≤ E2 ≤ 2, and preferably 0.1 ≤ E2 ≤ 0.9. This application, by adjusting the value of E2 to fall within the above range, can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0011] In some embodiments, the ether nitrile compound includes a first-class ether nitrile compound and a second-class ether nitrile compound. Based on the mass of the electrolyte, the mass percentage of the first-class ether nitrile compound is E1%, and the mass percentage of the second-class ether nitrile compound is E2%, with 1.3 ≤ E1 / E2 ≤ 8, preferably 2 ≤ E1 / E2 ≤ 6. By controlling the value of E1 / E2 to meet the above range, this application can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0012] In some embodiments, the electrolyte comprises a primary ester and a secondary ester. The primary ester includes at least one of methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, or methyl acetate. The secondary ester includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate, propylene carbonate, or ethylene carbonate. Based on the mass of the electrolyte, the primary ester accounts for Z% of the mass, and the secondary ester accounts for Y% of the mass, with 5 ≤ Y ≤ 27 and 2 ≤ Z / Y ≤ 6. Preferably, 2.5 ≤ Z / Y ≤ 4. By controlling the T / Y value to meet the above range, this application can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0013] In some embodiments, the diesters include fluorinated diesters and non-fluorinated diesters. Fluorinated diesters include at least one of fluoroethylene carbonate (FEC), difluoroethylene carbonate, or trifluoromethylethylene carbonate, and non-fluorinated diesters include at least one of propylene carbonate (PC) or ethylene carbonate (EC). Based on the mass of the electrolyte, the mass percentage of fluorinated diesters is Y1%, and the mass percentage of non-fluorinated diesters is Y2%, with 0.6 ≤ Y2 / Y1 ≤ 2.6, preferably 0.8 ≤ Y2 / Y1 ≤ 2. By controlling the value of Y2 / Y1 to meet the above range, this application can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0014] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) the negative electrode material layer further includes a binder, the binder being at least one of polyacrylate, polyacrylic acid, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, or potassium hydroxymethyl cellulose; (2) the negative electrode material layer further includes a conductive agent, the conductive agent being at least one of conductive carbon black, carbon nanotubes, or sheet graphene, the carbon nanotubes being at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes; (3) the negative electrode material includes silicon-based particles, the silicon-based particles being at least one of silicon-carbon particles or silicon-oxygen particles; (4) the negative electrode material includes silicon-based particles, the silicon-based particles being silicon-carbon particles, the silicon-carbon particles being porous carbon, silicon particles at least partially located in the pores inside the porous carbon, and a carbon layer located on the surface of the silicon-carbon particles. By enabling the secondary battery to satisfy at least one of the above conditions, this application can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0015] Secondly, this application also provides an electronic device including the secondary battery described in the first aspect above. Detailed Implementation

[0016] 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.

[0017] In a first aspect, this application provides a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode current collector and a negative electrode material layer located on at least one surface of the negative electrode current collector. The negative electrode material layer comprises a negative electrode material. The negative electrode current collector is copper foil. The negative electrode material has an oxygen content of X1%, and after pressure treatment, the oxygen content in the negative electrode material is X2%, with 0.5 ≤ X2 - X1 ≤ 1.4, preferably 0.7 ≤ X2 - X1 ≤ 1.1. During the pressure treatment, the pressure applied to the negative electrode material is 127 MPa, and the pressure holding time is 60 seconds. The value of X2 - X1 can be a value within the range of 0.5, 0.7, 0.9, 1.0, 1.1, 1.4, or any two of these values. The electrolyte comprises an ether nitrile compound. This application improves the rate performance and cycle capacity retention performance of secondary batteries by making the negative electrode material satisfy 0.5≤X2-X1≤1.4 and the electrolyte include ether nitrile compounds.

[0018] During the charging and discharging process of a secondary battery, the negative electrode material undergoes volume changes, causing the negative electrode material layer to pulverize and detach, which severely reduces the cycle capacity retention performance and rate performance of the secondary battery.

[0019] The inventors of this application have discovered that having the negative electrode material satisfy 0.5≤X2-X1≤1.4 is beneficial for including a coating layer with high mechanical strength on the surface of the negative electrode material, which can constrain the volume change of the negative electrode material during the charging and discharging of the secondary battery, thereby reducing the pulverization and shedding of the negative electrode material layer. However, at this time, the coating layer is relatively dense, making it difficult for lithium ions to migrate efficiently within the coating layer. Therefore, including ether nitrile compounds in the electrolyte at the same time is beneficial for introducing an appropriate amount of flexible components into the SEI film, which helps to improve the thickness uniformity, elasticity and lithium ion conductivity of the SEI film, and can improve the migration efficiency of lithium ions between the electrolyte and the negative electrode material. When X2-X1≤0.5, the coating layer on the surface of the negative electrode material is relatively dense, making it difficult for the electrolyte to diffuse within the negative electrode material layer and contact the negative electrode material. This results in low migration efficiency of lithium ions between the electrolyte and the negative electrode material. Even if the electrolyte is made to include ether nitrile compounds to introduce flexible components into the SEI film to increase the lithium ion conductivity, it is still insufficient to enable efficient migration of lithium ions between the electrolyte and the negative electrode material. This also increases the lithium ion concentration on the surface of the negative electrode material and causes lithium metal to deposit on the surface of the negative electrode material, increasing the consumption of active lithium ions. When 1.4≤X2-X1, the mechanical strength of the coating layer on the surface of the negative electrode material is low. The volume change during lithium insertion / extraction of the negative electrode material causes repeated cracking and repair of the coating layer, increasing the consumption of electrolyte and active lithium ions. It also increases the side reactions between the negative electrode material and the electrolyte, and thickens the SEI film, which is not conducive to the migration of lithium ions between the electrolyte and the negative electrode material. In summary, this application improves the rate performance and cycle capacity retention performance of secondary batteries by ensuring that the negative electrode material satisfies 0.5≤X2-X1≤1.4 and that the electrolyte includes ether nitrile compounds.

[0020] In this application, the method of controlling the values ​​of X2-X1 is not limited, as long as it can achieve the purpose of this application.

[0021] The negative electrode material in this application can be obtained by a preparation method including the following steps: S1. Mix graphite raw materials and coating agents to obtain a mixture. Based on the mass of the mixture, the mass percentage of the coating agent is W%. Heat the mixture to T1 ℃ in an inert gas protective atmosphere and keep it at that temperature for t1 h to obtain graphite particles, where 1≤W≤5, 750≤T1≤1000, and 5≤t1≤7. The coating agent includes at least one of asphalt or petroleum coke, wherein the density of the asphalt is 1.0-1.1 g / cc and the aromatic hydrocarbon content is 40-60%, and the density of the petroleum coke is 1.9-2.1 g / cc and the aromatic hydrocarbon content is 70-90%. S2. At T2 ℃, hydrocarbon gas is introduced into a silicon-carbon matrix with a silicon content of S% and the reaction is maintained at this temperature for t2 h to obtain silicon-based particles. The hydrocarbon gas includes alkynes, alkanes and alkenes. Based on the volume of the hydrocarbon gas, the volume ratio of alkynes is V1%, the sum of the volume ratios of alkanes and alkenes is V2%, 40≤S≤70, 560≤T2≤700, 3≤t2≤5, 35≤V1≤50, 50≤V2≤65, and the volume ratio of alkanes to alkenes is 1:1. S3. Mix graphite particles and silicon-based particles at a mass ratio to obtain the negative electrode material.

[0022] Based on the above preparation method, a negative electrode material satisfying the range of 0.5 ≤ X2 - X1 ≤ 1.4 can be obtained. Increasing the temperature T1 or T2 within the range provided in this application can reduce the value of X2 - X1; increasing the volume percentage V1 of alkynes within the range provided in this application can also reduce the value of X2 - X1.

[0023] Secondary batteries There are no particular limitations on the secondary battery described in this application. It is classified into various categories based on the type of electron transport medium. For example, when the electron transport medium is lithium (Li, including ions), the secondary battery is a lithium-ion battery; when the electron transport medium is sodium (Na, including ions), the secondary battery is a sodium-ion battery.

[0024] According to one embodiment of this application, a secondary battery may include a battery cell and an electrolyte. The battery cell may include packaging material and an electrode assembly disposed within the packaging material, and the electrolyte may fill the internal space formed by the packaging material. The packaging material may protect the electrode assembly from external impacts and prevent electrolyte leakage to the outside. Depending on the shape of the packaging material, the battery cell may be prismatic, cylindrical, or pouch-type.

[0025] The electrode assembly includes a positive electrode, a negative electrode, and a separator, as well as other components known in the art for use in secondary batteries. This application does not limit the scope of these other components. The separator may be located between the positive and negative electrodes.

[0026] This application does not impose any particular limitation on the preparation method of the secondary battery. For example, it may include the following steps: stacking the positive electrode, separator and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain an electrode assembly; placing the electrode assembly into packaging material; injecting electrolyte into the packaging material and sealing it to obtain a secondary battery.

[0027] positive electrode In this application, there are no particular limitations on the positive electrode, as long as the purpose of this application can be achieved. The positive electrode includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector; the aforementioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be located on one surface of the positive electrode current collector along its own thickness direction, or it can be located on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode current collector, or it can be a part of the surface of the positive electrode current collector. This application has no particular limitations, as long as the purpose of this application can be achieved.

[0028] This application does not impose any particular restrictions on the type, size, or shape of the positive electrode current collector, as long as it does not cause chemical changes in the battery cell and has electrical conductivity. For example, the positive electrode current collector can be made of materials such as stainless steel, aluminum, nickel, titanium, calcined carbon, or a substance that has been surface-treated with carbon, nickel, titanium, or silver on aluminum or stainless steel. In this application, the positive electrode current collector may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0029] The positive current collector can have an appropriate thickness as needed. Although there are no particular limitations, the positive current collector can have a thickness in the range of 1 μm to 500 μm, or a thickness in the range of 1 μm to 300 μm, or a thickness in the range of 1 μm to 100 μm, or a thickness in the range of 1 μm to 50 μm, or a thickness in the range of 1 μm to 20 μm.

[0030] Unless otherwise specified, the terms thickness (or height), width, and length used in this invention refer to average values ​​and can be measured by a measuring instrument capable of measuring thickness (or height), width, and length separately and in accordance with methods in the art.

[0031] The positive electrode current collector can have fine irregularities formed on its surface, thereby further enhancing its adhesion to the positive electrode material layer. For example, the positive electrode current collector can be selected from one or more of the following: membrane, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0032] In this application, there are no particular restrictions on the thickness of the positive current collector and the positive electrode material layer, as long as the purpose of this application can be achieved.

[0033] In some embodiments, the positive electrode material layer may further include a positive electrode binder. This application does not particularly limit the type of positive electrode binder, as long as it achieves the purpose of this application. For example, the positive electrode binder 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, polyolefin binders include at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0034] In some embodiments, the positive electrode material layer may further include a conductive agent. This application does not impose any particular limitation on the type of conductive agent in the positive electrode material layer, as long as it achieves the purpose of this application. In some exemplary embodiments, the conductive agent includes carbon-based materials, such as graphite (natural or artificial graphite), carbon black (acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, etc.), or carbon fibers; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or mixtures formed by any combination of these substances.

[0035] In this application, the positive electrode material layer can be formed by coating a positive electrode slurry onto at least one side of the positive electrode current collector and drying it, and calendering can be performed after drying if necessary. The positive electrode slurry includes the aforementioned positive electrode material and a positive electrode binder, and may further include a conductive agent if necessary. In addition, the positive electrode slurry may also contain a solvent. This application does not have any particular limitation on the type of solvent, as long as it can achieve the purpose of this application. For example, the solvent may be an organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, methyl propionate, alcohol, or ethyl propionate, or an aqueous solvent such as water, or a mixed solvent composed of two or more of the above solvents.

[0036] This application does not impose any particular restrictions on the mass ratio of the positive electrode material, conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. These mass ratios can be those that are known to be applicable.

[0037] negative electrode This application does not impose any particular limitation on the negative electrode, as long as the purpose of this application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. In this application, the negative electrode material layer can be disposed on one surface or on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of ​​the negative electrode current collector or a part of the negative electrode current collector; this application does not impose any particular limitation, as long as the purpose of this application can be achieved.

[0038] The negative electrode material layer of this application includes a negative electrode material.

[0039] In some embodiments, 3.0≤X1≤4.0, and the value of X1 can be a value within the range of 3.0, 3.3, 3.4, 3.9, 4.0 or any two thereof. By making the value of X1 satisfy the above range, the oxygen content of the negative electrode material satisfies the above range, which is beneficial to further make the surface of the negative electrode material have a coating layer with suitable mechanical strength and density, and further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0040] In some embodiments, 3.5≤X2≤5.4, and the value of X2 can be a value within the range of 3.5, 4.0, 4.2, 4.5, 4.9, 5.4 or any two thereof, so that the oxygen content of the negative electrode material after pressure treatment meets the above range, which is beneficial to further make the surface of the negative electrode material have a coating layer with suitable mechanical strength and density, and further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0041] In some embodiments, the porosity of the negative electrode material layer is K%, 30≤K≤40, preferably 33≤K≤37. The value of K can be 30.0, 33.0, 33.7, 33.9, 34.1, 34.3, 34.9, 35.0, 35.1, 35.3, 37.0, 40.0, or any combination thereof. By ensuring that the porosity of the negative electrode material layer meets the above range, it is beneficial for the negative electrode material to be wetted by the electrolyte, enabling the ether nitrile compound to form a more uniform SEI film on the surface of the negative electrode material, which is beneficial for the conduction of lithium ions between the electrolyte and the negative electrode material. At the same time, it ensures that the negative electrode material layer has suitable strength and a suitable contact area between the negative electrode material particles, and that there is a suitable conductive network within the negative electrode material layer, further improving the rate performance and cycle capacity retention performance of the secondary battery.

[0042] In some embodiments, in the XRD diffraction pattern of the negative electrode, a first characteristic peak exists in the range of 43~44°, and the peak area of ​​the first characteristic peak is A, where 3987≤A≤15013. The value of A can be 3987, 4995, 5011, 5150, 5193, 7253, 8977, 9011, 9054, 9121, 11094, or 15013. A second characteristic peak exists in the range of 50~51°, and the peak area of ​​the second characteristic peak is B, where 1.55≤A / B≤1.75, preferably 1.6≤A / B≤1.7. The value of A / B can be 0.65, 0.70, 0.73, 0.76, 0.80, 0.85, or any combination thereof. The values ​​within the range, where the first characteristic peak is the close-packed surface of the copper foil (111) crystal plane, and the first characteristic peak with a certain peak area reflects the high strength and corrosion resistance of the copper foil. The second characteristic peak is the copper foil (200) crystal plane, and the second characteristic peak with a certain peak area reflects the high ductility of the copper foil. By making the ratio of the peak areas of the first characteristic peak and the second characteristic peak satisfy the above range, this application can make the negative electrode current collector have suitable strength, corrosion resistance and ductility, which is beneficial to reduce the corrosion of the negative electrode current collector by the electrolyte, and at the same time helps to resist the stress generated by the volume expansion of the negative electrode material, thereby increasing the structural stability of the negative electrode sheet and further improving the rate performance and cycle capacity retention performance of the secondary battery.

[0043] In some embodiments, the negative electrode material layer further includes an adhesive, which includes at least one of polyacrylate, polyacrylic acid, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, or potassium hydroxymethyl cellulose.

[0044] In some embodiments, the negative electrode material layer further includes a conductive agent, which includes at least one of conductive carbon black, carbon nanotubes, or sheet graphene, and the carbon nanotubes include at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0045] In some embodiments, the negative electrode material includes silicon-based particles, which include at least one of silicon-carbon particles or silicon-oxygen particles.

[0046] In some embodiments, the negative electrode material includes silicon-based particles, which include silicon-carbon particles. The silicon-carbon particles include porous carbon, silicon particles located at least partially within the pores of the porous carbon, and a carbon layer located on the surface of the silicon-carbon particles.

[0047] In this application, the negative electrode material layer can be formed by coating a negative electrode slurry onto at least one side of the negative electrode current collector and drying it, and calendering can be performed after drying if necessary. The negative electrode slurry includes the aforementioned negative electrode material and a negative electrode binder, and may further include a conductive agent if necessary. In addition, the negative electrode slurry may also contain a solvent. This application does not have any particular limitation on the type of solvent, as long as it can achieve the purpose of this application. For example, the solvent may be an organic solvent such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butenyl carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, formamide, dimethylformamide, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate, trimethoxymethane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolinone, propylene carbonate derivatives, tetrahydrofuran derivatives, methyl propionate, alcohol, or ethyl propionate, or an aqueous solvent such as water, or a mixed solvent composed of two or more of the above solvents.

[0048] diaphragm The diaphragm in this application refers to a membrane that prevents short circuits between the positive and negative electrodes while allowing electron transport substances to pass through. This application does not impose any particular limitations on the diaphragm, as long as it can achieve the purpose of this application. For example, the material of the diaphragm may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid; the type of diaphragm may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, and spun membrane.

[0049] According to some embodiments of this application, the diaphragm 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.

[0050] 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 mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder. This application does not particularly limit the binder; for example, it may be at least one of the above-mentioned positive electrode binders or negative electrode binders. The polymer layer contains a polymer, and this application does not particularly limit the polymer. For example, the polymer may include at least one of polyamide, polyacrylonitrile, acrylate polymers, 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.

[0051] electrolyte In this application, electrolyte refers to the medium that causes the movement of electron transport substances to facilitate the electrochemical reactions at the positive and negative electrodes.

[0052] In some embodiments, the electrolyte comprises an ether nitrile compound.

[0053] In some embodiments, the ether nitrile compound includes a class of ether nitrile compounds, which includes at least one of the compounds shown in Formulas 1-1 to 1-3: Formula 1-1 Formula 1-2 Equation 1-3; Based on the mass of the electrolyte, the mass percentage of a certain type of ether nitrile compound is E1%, where 0.1 ≤ E1 ≤ 3.5, preferably 0.5 ≤ E1 ≤ 2.4. The value of E1 can be within the range of 0.1, 0.5, 0.8, 1.5, 2.0, 2.4, 3.5, or any two of these ranges. This application, by including a certain type of ether nitrile compound within the above range in the electrolyte, can form a more uniform and elastic SEI film on the surface of the negative electrode material, thereby reducing side reactions between the negative electrode material and the electrolyte, and reducing the negative electrode material's surface surface defects. The volume change during lithium insertion / extraction of the electrode material causes repeated rupture and repair of the SEI film, reducing the consumption of electrolyte and active lithium ions. Furthermore, a class of ether nitrile compounds can decompose in the electrolyte to generate Li3N and introduce it into the SEI film. Li3N is an excellent lithium-ion conductor, which can promote the efficient transfer of lithium ions in the SEI film and give the electrolyte a suitable viscosity, which helps the negative electrode material to be fully wetted by the electrolyte. This can improve the conductivity of lithium ions in the negative electrode material layer and further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0054] In some embodiments, the ether nitrile compound includes a class of ether nitrile compounds, which include at least one of the compounds shown in Formulas 2-1 to 2-3: Formula 2-1 Equation 2-2 Equation 2-3; Based on the mass of the electrolyte, the mass percentage of the second type of ether nitrile compound is E2%, where 0.05 ≤ E2 ≤ 2, preferably 0.1 ≤ E2 ≤ 0.9. The value of E2 can be within the range of 0.05, 0.10, 0.20, 0.25, 0.30, 0.38, 0.40, 0.50, 0.70, 0.90, 2.00, or any two of these ranges. This application, by including the second type of ether nitrile compound within the above range in the electrolyte, facilitates the formation of a SEI film with high mechanical strength on the surface of the negative electrode material. This reduces the repeated rupture and repair of the SEI film caused by volume changes during lithium insertion / extraction of the negative electrode material, and reduces the consumption of electrolyte and active lithium ions. The second type of ether nitrile compound can form a more stable [Li] ether nitrile compound with lithium ions, with a lower desolvation energy barrier. + The triether nitrile structure facilitates faster lithium-ion insertion into the anode material, helps reduce the lithium-ion concentration on the anode material surface, and reduces lithium metal deposition on the anode surface. Furthermore, the Li3N generated by the decomposition of the two types of ether nitrile compounds in the electrolyte can promote the efficient transfer of lithium ions in the SEI film. At the same time, it gives the electrolyte a suitable viscosity, which helps the anode material to be fully wetted by the electrolyte, thereby improving the conductivity of lithium ions in the anode material layer and further improving the rate performance and cycle capacity retention performance of the secondary battery.

[0055] In some embodiments, the ether nitrile compound includes a first-class ether nitrile compound and a second-class ether nitrile compound. Based on the mass of the electrolyte, the mass percentage of the first-class ether nitrile compound is E1%, and the mass percentage of the second-class ether nitrile compound is E2%. 1.3 ≤ E1 / E2 ≤ 8, preferably 2 ≤ E1 / E2 ≤ 6. The value of E1 / E2 can be a value within the range of 1.3, 2.0, 2.9, 3.0, 6.0, 8.0, or any two of these. This application ensures that the value of E1 / E2 meets the above range, which is beneficial for the surface of the negative electrode material to include an SEI film with suitable mechanical strength and suitable elasticity, further enhancing the synergistic effect between the first-class and second-class ether nitrile compounds, and further improving the rate performance and cycle capacity retention performance of the secondary battery.

[0056] In some embodiments, the electrolyte further includes a primary ester and a secondary ester. The primary ester includes at least one of methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate, or methyl acetate. The secondary ester includes at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate, propylene carbonate, or ethylene carbonate. Based on the mass of the electrolyte, the primary ester accounts for Z% of the mass, and the secondary ester accounts for Y%. 5 ≤ Y ≤ 27, and the value of Y can be 5, 8, 11, 13, 16, 18, 19, 20, 27, or any two of these values. 2 ≤ Z / Y ≤ 6, preferably 2.5 ≤ Z / Y ≤ 4, and the value of Z / Y can be 2.0, 2.5, 2.8, 3.1, 3.4, 3.6, or 4. Values ​​within the range of 0, 6, or any two thereof, in this application include a type I ester and a type II ester in the electrolyte. Type II esters facilitate the formation of a dense and stable SEI film on the surface of the negative electrode material layer, reducing the volume expansion during lithium insertion / extraction of the negative electrode material, which leads to repeated breakage and repair of the SEI film, reducing the consumption of electrolyte and lithium ions, and restraining the volume expansion during lithium insertion of the negative electrode material. At the same time, type I esters can reduce the viscosity of the electrolyte and reduce the impact of high-viscosity type I esters, allowing the negative electrode material to be fully wetted by the electrolyte and improving the migration efficiency of lithium ions between the electrolyte and the negative electrode material. In addition, type I esters can reach and repair the damaged SEI film in a timely manner with the electrolyte, further improving the rate performance and cycle capacity retention performance of the secondary battery.

[0057] In some embodiments, the diesters include fluorinated diesters and non-fluorinated diesters. The fluorinated diesters include at least one of fluoroethylene carbonate, difluoroethylene carbonate, or trifluoromethylethylene carbonate, and the non-fluorinated diesters include at least one of propylene carbonate or ethylene carbonate. Based on the mass of the electrolyte, the mass percentage of fluorinated diesters is Y1%, and the mass percentage of non-fluorinated diesters is Y2%. The value of Y2 / Y1 is 0.6 ≤ Y2 / Y1 ≤ 2.6, preferably 0.8 ≤ Y2 / Y1 ≤ 2. The value of Y2 / Y1 can be within the range of 0.6, 0.8, 1.0, 1.2, 1.4, 1.5, 1.7, 2.0, 2.6 or any two of these. This application includes fluorinated and non-fluorinated diesters in the electrolyte within the above range. Fluorinated diesters are beneficial for forming a more stable SEI film with higher mechanical strength on the surface of the negative electrode material. This helps to reduce the repeated rupture and repair of the SEI film caused by volume changes during lithium insertion / extraction of the negative electrode material, reduce the consumption of electrolyte and active lithium ions, and can restrain the volume changes generated during lithium insertion / extraction of the negative electrode material. At the same time, non-fluorinated diesters can improve the wetting performance of the electrolyte, which is beneficial for improving the conductivity of lithium ions and can further improve the rate performance and cycle capacity retention performance of the secondary battery.

[0058] According to some embodiments of this application, lithium salts may include, but are not limited to, at least one of: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide {LiN(CF3SO2)2, LiTFSI)}, lithium bis(fluorosulfonyl)imide {Li(N(SO2F)2), LiFSI}, lithium bis(oxalateborate)borate {LiB(C2O4)2, LiBOB}, lithium difluorooxalateborate {LiBF2(C2O4), LiDFOB}, LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or lithium difluoroborate. This application does not limit the content of lithium salts in the electrolyte, as long as the purpose of this application is achieved.

[0059] This application does not impose any particular limitation on non-aqueous solvents, as long as they can serve as a medium for the movement of ions participating in the electrochemical reactions of the battery cell. For example, non-aqueous solvents may include, but are not limited to, ketone solvents such as 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, and cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; alcohol solvents such as ethanol and isopropanol; amide solvents such as dimethylformamide; dioxolane solvents such as 1,2-dioxolane and 1,3-dioxolane; or sulfone solvents such as dimethyl sulfoxide, sulfolane, and methyl sulfolane; or phosphate ester solvents such as trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. In the above description, the hydrocarbon group may be selected from one or more of alkyl, alkenyl, or alkynyl groups.

[0060] Electronic devices This application provides an electronic device including the aforementioned secondary battery. The electronic device 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-based 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.

[0061] Measurement methods <Oxygen Content Test of Negative Electrode Materials> Weigh 0.025 g of the anode material powder, and use an oxygen, nitrogen, and hydrogen analyzer to measure the oxygen content of the anode material powder. Repeat the measurement 3 times and take the average value, denoted as X1. Subsequently, weigh 1 g of the anode material powder and pour it into a cylindrical hollow mold with a diameter of 13 mm. Place the mold in the exact center of the pressure plate, set the pressure to 127.39 MPa, and the pressing time to 60 s to press the anode material powder in the mold. After the pressing is completed, remove the mold, take out the pressed powder, scatter it with a sample spoon, and collect it into a 10 mL vial. After leaving it open for 6 hours, take 0.025 g of the pressed powder as a sample and use an oxygen, nitrogen, and hydrogen analyzer to measure the oxygen content. Repeat the measurement 3 times and take the average value, denoted as X2.

[0062] <Porosity Test of Anode Material Layer> Remove the anode from the lithium-ion battery, soak it in a dimethyl carbonate solution and then perform a drying treatment in sequence. Cut the dried anode plate into round specimens, and measure the area, thickness of the specimens, and the volume of the anode material layer. Refer to the standard of GB / T 24586-2009 Determination of Apparent Density, True Density and Porosity of Iron Ore to test the porosity K of the anode material layer.

[0063] <XRD Diffraction Pattern Test> Discharge the secondary battery at a rate of 0.05C to 2.5V, then let it stand for 5 min. After repeating the above operation three times, remove the anode from the secondary battery, soak the anode in a dimethyl carbonate solution and dry it. Subsequently, use a ceramic scissors to cut the anode into a rectangular sample of 2 cm × 2 cm, fix it on a glass slide with transparent tape, and perform the test using an X-ray diffractometer in accordance with JJSK0131-1996 General Rules for X-ray Diffraction Analysis Method. Use Cu Kα ray as the X-ray source, set the test voltage to 40 kV, the current to 30 mA, the scanning angle range to 20° to 60°, and the scanning speed to 4° / min to obtain the XRD diffraction pattern of the electrode plate.

[0064] Calculation of peak area A:

[0065] I is the intensity corresponding to each angle in the XRD spectrum corresponding.

[0066] Calculation of peak area B:

[0067] I is the intensity corresponding to each angle in the XRD spectrum corresponding.

[0068] <Rate Performance Test> The lithium-ion batteries used in the examples / comparative examples to be tested were placed at a test temperature of 25°C and allowed to stand for 5 minutes. Then, they were charged at a constant current of 0.7C to 4.53V, followed by constant voltage charging at 4.53V to 0.05C. After standing for 5 minutes, they were discharged at a constant current of 0.2C to 3.0V, and the 0.2C discharge capacity was recorded. This process was repeated for another 5 minutes, followed by constant current discharge at 2C, and the 2C discharge capacity was recorded. The ratio of the 2C discharge capacity to the 0.2C discharge capacity was used as the evaluation index for rate performance; a higher ratio indicates better rate performance.

[0069] <Cyclic Performance Testing> At a test temperature of 25℃, the lithium-ion battery was charged to 4.5V with a constant current of 0.7C, and then charged to 0.05C with a constant voltage of 4.5V. After resting for 5 minutes, it was discharged to 3.0V with a constant current of 1C. The discharge capacity C1 before the cycle was recorded. After resting for 5 minutes, the above charge and discharge cycle process was repeated 1000 times. The discharge capacity C2 of the last discharge to 3.0V with a constant current of 1C was recorded.

[0070] Cyclic capacity retention rate (%) = C2 / C1 × 100%.

[0071] The following uses a lithium-ion battery as an example to illustrate the solution of this application with reference to the 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.

[0072] Example 1 Preparation of the negative electrode: Graphite particles and petroleum coke were mixed at a mass ratio of 98:2 and stirred for 6 minutes to obtain a mixture. The mixture was then heated to 900℃ at a heating rate of 10℃ / min and held for 5 hours under an inert gas atmosphere to obtain graphite particles. The density of the petroleum coke was 2.0 g / cc and the aromatic hydrocarbon content was 80%. Hydrocarbon gases were introduced into a silicon-carbon matrix with a silicon element content of 51% at 650℃ and held for 5 hours to obtain silicon-based particles. The hydrocarbon gases included alkynes, alkanes, and alkenes. Based on the volume of the hydrocarbon gases, the volume ratio of alkynes was 50%, and the sum of the volume ratios of alkanes and alkenes was 50%, with a volume ratio of 1:1 between alkenes and alkanes. Graphite particles and silicon-based particles were mixed at a mass ratio of 85:15 to obtain the negative electrode material.

[0073] A negative electrode material, single carbon nanotubes, polyacrylic acid, and carboxymethyl cellulose were mixed in a mass ratio of 95:0.5:3.5:1. Deionized water was then added and the mixture was stirred until homogeneous to form a negative electrode slurry. This negative electrode slurry was uniformly coated onto one surface of a copper foil. After drying, the above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. The coated copper foil was dried, pressure-treated, cut to the specified size, and electrode tabs were welded on to fabricate the negative electrode.

[0074] Preparation of the positive electrode: Lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride were dissolved in N-methylpyrrolidone at a mass ratio of 97:1.5:1.5 to prepare a positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of an aluminum foil. After drying, the coating process was repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. The coated aluminum foil was dried, pressure-treated, cut to the specified size, and electrode tabs were welded on to fabricate the positive electrode.

[0075] Preparation of the diaphragm: A 12 μm thick polyethylene (PE) microporous membrane was selected as the diaphragm.

[0076] Electrolyte preparation: In an argon-atmospheric glove box with a water content of less than 10 ppm, diethyl carbonate was used as the base solvent. Lithium hexafluorophosphate, the compound shown in Formula 1-1, the compound shown in Formula 2-1, EP, PP, FEC, EC, and PC were then added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass percentages were: lithium hexafluorophosphate 12.5%, the compound shown in Formula 1-1 0.5%, the compound shown in Formula 2-1 0.38%, EP 7%, PP 30%, FEC 5%, EC 3%, and PC 3%. The remainder was the base solvent.

[0077] Battery making: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to form an electrode assembly. The electrode assembly is placed in an outer aluminum-plastic film, baked, and then injected with the electrolyte. After vacuum sealing, settling, formation, shaping, and capacity testing, a lithium-ion battery is obtained.

[0078] The only difference between Examples 2 to 12, Comparative Examples 1 to 2 and Example 1 is that the parameters were adjusted according to Table 1. For details of the parameter adjustments and test results, please refer to Table 1.

[0079] The value of X2-X1 is reduced by increasing the volume ratio of alkynes V1; the value of A / B is increased by selecting copper materials with a higher proportion of (111) crystal planes.

[0080] Table 1

[0081] As can be seen from Table 1 above, this application enables the secondary battery to have excellent initial coulombic efficiency and cycle capacity retention performance by controlling the negative electrode material to meet 1.5≤X2-X1≤3 and simultaneously making the electrolyte include fluorinated esters. In particular, when it meets 1.7≤X2-X1≤2.5, the initial coulombic efficiency and cycle capacity retention performance of the secondary battery can be further improved.

[0082] Specifically, ensuring the porosity of the negative electrode material layer meets the requirement of 30 ≤ K ≤ 40 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery. In particular, when the requirement of 33 ≤ K ≤ 37 is met, the initial coulombic efficiency and cycle capacity retention performance of the secondary battery can be further improved.

[0083] Specifically, ensuring that the ratio of the peak areas of the first characteristic peak to the second characteristic peak in the XRD diffraction pattern of the negative electrode satisfies 1.55 ≤ A / B ≤ 1.75 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery. In particular, when 1.6 ≤ A / B ≤ 1.7 is satisfied, the initial coulombic efficiency and cycle capacity retention performance of the secondary battery can be further improved.

[0084] The only difference between Examples 2-1 to 2-26 and Example 2 is that the parameters are adjusted according to Table 2. Specific parameter adjustments and performance tests can be found in Table 2. Example 2 and Example 2-10 are the same example, differing only in their example numbers.

[0085] When adjusting the component content in the electrolyte, the amount of base solvent used should be adjusted accordingly.

[0086] Table 2

[0087] As shown in Table 2 above, including a class of ether nitrile compounds in the electrolyte and satisfying 0.1≤E1≤3.5 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery. In particular, when 0.5≤E1≤2.4 is satisfied, the initial coulombic efficiency and cycle capacity retention performance of the secondary battery can be further improved.

[0088] Specifically, including a class II ether nitrile compound in the electrolyte and satisfying 0.05 ≤ E2 ≤ 2 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery. In particular, when 0.1 ≤ E2 ≤ 0.9 is satisfied, the initial coulombic efficiency and cycle capacity retention performance of the secondary battery can be further improved.

[0089] Specifically, including both a class I and a class II ether nitrile compounds in the electrolyte and satisfying 1.3 ≤ E1 / E2 ≤ 8 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery. In particular, when 2 ≤ E1 / E2 ≤ 6 is satisfied, the initial coulombic efficiency and cycle capacity retention performance of the secondary battery can be further improved.

[0090] Specifically, including both type I and type II esters in the electrolyte and satisfying 2 ≤ Z / Y ≤ 6 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery. In particular, satisfying 2.5 ≤ Z / Y ≤ 4 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery.

[0091] Specifically, including fluorinated and non-fluorinated diesters in the electrolyte and satisfying 0.6 ≤ Y2 / Y1 ≤ 2.6 can further improve the initial coulombic efficiency and cycle capacity retention performance of the secondary battery. In particular, when 0.8 ≤ Y2 / Y1 ≤ 2 is satisfied, the initial coulombic efficiency and cycle capacity retention performance of the secondary battery can be further improved.

[0092] 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. A secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, the negative electrode comprising a negative electrode current collector and a negative electrode material layer on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode material, the negative electrode current collector being a copper foil, characterized in that, The content of oxygen element in the negative material is X1%, the content of oxygen element in the negative material after the pressure treatment is X2%, 0.5≤X2-X1≤1.4, the pressure applied to the negative material in the pressure treatment is 127Mpa, and the pressure holding time is 60 seconds. The electrolyte comprises an ether nitrile compound.

2. The secondary battery according to claim 1, characterized by The secondary battery satisfies at least one of the following conditions: （1）3.0≤X1≤4.0； （2）3.5≤X2≤5.4； (3) 0.7≤X2-X1≤1.

1.

3. The secondary battery according to claim 1, characterized by The porosity of the negative material layer is K%, 30≤K≤40, preferably 33≤K≤37.

4. The secondary battery according to claim 1, characterized by In the XRD diffraction spectrum of the negative electrode, a first characteristic peak exists in the range of 43-44°, the peak area of the first characteristic peak is A, 3987≤A≤15013, a second characteristic peak exists in the range of 50-51°, the peak area of the second characteristic peak is B, 1.55≤A / B≤1.75, preferably 1.6≤A / B≤1.

7.

5. The secondary battery according to any one of claims 1 to 4, characterized by The ether nitrile compound comprises a first type of ether nitrile compound, the first type of ether nitrile compound comprises at least one of the compounds shown in formula 1-1 to formula 1-3: Formula 1-1, Formula 1-2, Formula 1-3; The mass percentage of the first type of ether nitrile compound is E1% based on the mass of the electrolyte, 0.1≤E1≤3.5, preferably 0.5≤E1≤2.

4.

6. The secondary battery according to any one of claims 1 to 4, characterized by The ether nitrile compound comprises a second type of ether nitrile compound, the second type of ether nitrile compound comprises at least one of the compounds shown in formula 2-1 to formula 2-3: Formula 2-1, Formula 2-2, Equation 2-3; The mass percentage of the second type of ether nitrile compound is E2% based on the mass of the electrolyte, 0.05≤E2≤2, preferably 0.1≤E2≤0.

9.

7. The secondary battery according to any one of claims 1 to 4, characterized by The ether nitrile compound comprises a first type of ether nitrile compound and a second type of ether nitrile compound, the mass percentage of the first type of ether nitrile compound is E1% based on the mass of the electrolyte, the mass percentage of the second type of ether nitrile compound is E2%, 1.3≤E1 / E2≤8, preferably 2≤E1 / E2≤6.

8. The secondary battery according to any one of claims 1 to 4, characterized by The electrolyte comprises a first type of ester and a second type of ester, the first type of ester comprises at least one of methyl propionate, methyl butyrate, ethyl acetate, ethyl propionate, propyl propionate, ethyl butyrate or methyl acetate; The second type of ester comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethyl ethylene carbonate, propylene carbonate or ethylene carbonate; The mass percentage of the first type of ester is Z% based on the mass of the electrolyte, the mass percentage of the second type of ester is Y% based on the mass of the electrolyte, 5≤Y≤27, 2≤Z / Y≤6, preferably 2.5≤Z / Y≤4.

9. The secondary battery according to claim 8, characterized by The second type of ester comprises a fluorinated second type of ester and a non-fluorinated second type of ester, the fluorinated second type of ester comprises at least one of fluoroethylene carbonate, difluoroethylene carbonate or trifluoromethyl ethylene carbonate, the non-fluorinated second type of ester comprises at least one of propylene carbonate or ethylene carbonate; The mass percentage of the fluorinated second type of ester is Y1% based on the mass of the electrolyte, the mass percentage of the non-fluorinated second type of ester is Y2%, 0.6≤Y2 / Y1≤2.6, preferably 0.8≤Y2 / Y1≤2.

10. The secondary battery according to claim 1, characterized by The secondary battery satisfies at least one of the following conditions: (1) the negative material layer further comprises a binder, the binder comprises at least one of polyacrylate, polyacrylic acid, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, butadiene-styrene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose; (2) the negative material layer further comprises a conductive agent, the conductive agent comprises at least one of conductive carbon black, carbon nanotube or flaky graphene, the carbon nanotube comprises at least one of single-walled carbon nanotube or multi-walled carbon nanotube; (3) the negative material comprises silicon-based particles, the silicon-based particles comprise at least one of silicon-carbon particles or silicon-oxygen particles; (4) the negative material comprises silicon-based particles, the silicon-based particles comprise silicon-carbon particles, the silicon-carbon particles comprise porous carbon, silicon particles at least partially located in internal pores of the porous carbon and a carbon layer located at a surface layer of the silicon-carbon particles.

11. An electronic device, comprising: A secondary battery comprising the negative material according to any one of claims 1 to 10.

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