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 carbon fiber cluster, a binder and silicon-based particles, the carbon fiber cluster is composed of a plurality of carbon fibers, the surface of the negative electrode material layer comprises 36 first to-be-detected areas with the same area, and the first to-be-detected areas are arranged in the binder. The area of the first to-be-detected area is 400 mu m < 2 >, in the first to-be-detected area, the maximum value of ID / IG is A, the minimum value of ID / IG is B, and A-B is larger than or equal to 0.05 and smaller than or equal to 0.5. According to the present invention, the negative electrode material layer satisfies 0.05 < = A-B < = 0.5, such that the distribution of the carbon fiber cluster and the binder in the negative electrode material layer can be improved, the stable conductive network can be easily constructed in the negative electrode material layer, and the cycle performance of the secondary battery can be improved.

Description

Technical Field

[0001] This application belongs to the field of energy storage technology, specifically relating to a secondary battery and electronic device. Background Technology

[0002] Secondary batteries, also known as rechargeable batteries or storage batteries, work on the basis of a reversible chemical reaction. By charging, the active materials are reactivated, thereby achieving the storage and release of electrical energy. They are widely used in electric vehicles, renewable energy storage, and portable electronic devices.

[0003] Adding silicon to the negative electrode can effectively improve the energy capacity of secondary batteries. However, it also presents the problem of silicon expanding in volume during charging and discharging, which can compress the internal structure of the secondary battery. In particular, the stress generated by the expansion of silicon can cause the negative electrode material layer to pulverize and detach, greatly reducing the capacity of the secondary battery and affecting its cycle performance. These problems urgently need to be solved. Summary of the Invention

[0004] In view of this, this application provides a secondary battery and electronic device. By ensuring that the negative electrode material layer satisfies 0.05≤AB≤0.5, the distribution of carbon fiber clusters and binder within the negative electrode material layer can be improved, which is beneficial for constructing a stable conductive network within the negative electrode material layer. This can improve the cycle capacity retention rate of the secondary battery and reduce the thickness expansion rate of the secondary battery.

[0005] In a first aspect, this application provides a secondary battery, including 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 carbon fiber clusters, a binder, and silicon-based particles. The carbon fiber clusters are composed of multiple carbon fibers. The surface of the negative electrode material layer includes 36 first test regions of equal area, each with an area of ​​400 μm. 2 In the first test region, the maximum value of ID / IG is A, the minimum value of ID / IG is B, and 0.05≤AB≤0.5. This application controls the surface of the negative electrode material layer to satisfy 0.05≤AB≤0.5, which helps to make the carbon fiber clusters tend to be uniformly distributed on the surface of the silicon-based particles. The binder, induced by the carbon fibers, also tends to be uniformly distributed on the surface of the silicon-based particles. This reduces the area of ​​the reactive surface between the silicon-based particles and the electrolyte, which helps to reduce side reactions between the silicon-based particles and the electrolyte, thereby improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0006] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) 0.07≤A≤0.58; (2) 0.05≤AB≤0.3. By making the secondary battery satisfy at least one of the above conditions, the cycle capacity retention rate of the secondary battery and the thickness expansion rate of the secondary battery can be further improved.

[0007] In some embodiments, a second test area is included on the surface of the negative electrode material layer, the area of ​​the second test area being 14400 μm. 2 The ID / IG value of the second test area is Z, where 0.03 ≤ Z ≤ 0.51, preferably 0.13 ≤ Z ≤ 0.42. By adjusting the value of Z to meet the above range, the cycle capacity retention rate of the secondary battery and the thickness expansion rate of the secondary battery can be further improved.

[0008] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) the average length of the carbon fibers is L μm, 0.1≤L≤20, preferably 0.8≤L≤15; (2) the average diameter of the carbon fiber clusters is R μm, 0.01≤R≤0.13, preferably 0.03≤R≤0.1. By ensuring that the secondary battery satisfies at least one of the above conditions, the cycle capacity retention rate of the secondary battery and the thickness expansion rate of the secondary battery can be further improved.

[0009] In some embodiments, the resistivity of the negative electrode film is F mΩ·cm, where 1.5 ≤ F ≤ 2.5. By adjusting the value of F to meet the above range, the cycle capacity retention rate of the secondary battery can be further improved and the thickness expansion rate of the secondary battery can be reduced.

[0010] In some embodiments, the average diameter of the silicon-based particles is D μm, where 3.5 ≤ D ≤ 7, and preferably 4.5 ≤ D ≤ 6. By adjusting the value of D to meet the above range, the cycle capacity retention rate of the secondary battery can be further improved and the thickness expansion rate of the secondary battery can be reduced.

[0011] In some embodiments, the secondary battery satisfies at least one of the following conditions: (1) the carbon fiber includes at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes; (2) the binder 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; (3) the silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles; (4) the silicon-based particles include silicon-carbon particles, wherein the silicon-carbon particles include porous carbon, silicon particles at least partially located in the pores inside the porous carbon, and a carbon layer at least partially located on the surface of the silicon-carbon particles; (5) the negative electrode material layer further includes at least one of graphite particles, hard carbon particles, or soft carbon particles. By making the secondary battery satisfy at least one of the above conditions, the cycle capacity retention rate of the secondary battery and the thickness expansion rate of the secondary battery can be further improved.

[0012] In some embodiments, the electrolyte comprises fluoroethylene carbonate and ethylene carbonate. Based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is P1%, and the mass percentage of ethylene carbonate is P2%, where 5 ≤ P2 ≤ 21, and 0.5 ≤ P2 / P1 ≤ 1.8. Preferably, 0.8 ≤ P2 / P1 ≤ 1.5. By controlling the value of P1 to meet the above range, the cycle capacity retention rate of the secondary battery can be further improved, and the thickness expansion rate of the secondary battery can be reduced.

[0013] In some embodiments, the electrolyte includes a type of lithium salt additive, which includes at least one of lithium difluorophosphate or lithium tetrafluoroborate. Based on the mass of the electrolyte, the mass percentage of the lithium salt additive is S%, where 0.1 ≤ S ≤ 2, preferably 0.3 ≤ S ≤ 1.7. By controlling the value of S to meet the above range, the cycle capacity retention rate of the secondary battery can be further improved and the thickness expansion rate of the secondary battery can be reduced.

[0014] Secondly, this application also provides an electronic device including the secondary battery described in the first aspect above. Detailed Implementation

[0015] 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.

[0016] In a first aspect, this application provides a secondary battery, including 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 carbon fiber clusters, a binder, and silicon-based particles. The carbon fiber clusters are composed of multiple carbon fibers. The surface of the negative electrode material layer includes 36 first test regions of equal area, each with an area of ​​400 μm. 2 In the first test region, the maximum value of ID / IG is A, the minimum value of ID / IG is B, and 0.05≤AB≤0.5, preferably 0.05≤AB≤0.3, where the value of AB can be 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.39, 0.47, 0.50, or any combination thereof. The inventors have discovered that when the negative electrode material layer satisfies 0.05≤AB≤0.5, it is beneficial for the carbon fibers to tend to be uniformly distributed on the surface of the silicon-based particles. The binder, induced by the carbon fibers, also tends to be uniformly distributed on the surface of the silicon-based particles. This helps reduce the impact of the volume expansion of the silicon-based particles during lithium insertion / extraction on the conductive network within the secondary battery. Simultaneously, it can reduce the area of ​​the reactive surface between the silicon-based particles and the electrolyte, which is beneficial for reducing side reactions between the silicon-based particles and the electrolyte. The minimum value of the ID / IG difference AB between the first regions provided in this application is 0.05. When the value of AB is greater than 0.6, the polarity difference between the first regions on the surface of the negative electrode material layer is large. Since carbon fibers tend to be distributed in positions with lower polarity, they tend to be distributed in the gaps between silicon-based particles, increasing the direct contact area between silicon-based particles and electrolyte, and increasing side reactions between silicon-based particles and electrolyte, thereby affecting the cycle performance and rate performance of the secondary battery. In summary, this application improves the distribution of carbon fibers and binders in the negative electrode material layer by controlling the value of 0.05≤AB≤0.5, which is beneficial for building a stable conductive network in the negative electrode material layer, improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0017] This application does not impose any particular restrictions on the method for adjusting the value of AB, as long as it can achieve the purpose of this application. One method for preparing the negative electrode is provided below.

[0018] The preparation method of the negative electrode may include 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. 1≤W≤5, 750≤T1≤1000, 5≤t1≤7. The coating agent includes at least one of asphalt or petroleum coke. The density of the selected asphalt is 1.0-1.1 g / cc and the aromatic hydrocarbon content is 40-60%. The density of the selected petroleum coke is 1.9-2.1 g / cc and the aromatic hydrocarbon content is 70-90%. S2. Hydrocarbon gas is introduced into a silicon-carbon material matrix with a silicon content of S% at T2 ℃ 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%, and the sum of the volume ratios of alkanes and alkenes is V2%. 40≤S≤65, 560≤T2≤700, 3≤t2≤5, 35≤V1≤50, 50≤V2≤65, where the volume ratio of alkanes to alkenes is 1:1. S3. Mix the dispersant, graphite particles and silicon-based particles, and then add carbon fiber, solvent and binder in sequence and at intervals in a stirring environment. After mixing, the negative electrode slurry is obtained. S4. The negative electrode slurry is coated onto the surface of the negative electrode current collector, and then dried, cold-pressed, cut, and welded to the negative electrode tabs in sequence to obtain the negative electrode.

[0019] Based on the above embodiments, this application can adjust the difference AB between the maximum ID / IG and the minimum ID / IG values ​​in the first test area on the surface of the negative electrode material layer by adjusting steps S1, S2 and S3, such as: increasing the mass percentage W% of the coating agent to increase the value of AB; increasing the temperature T1 when coating graphite particles to decrease the value of AB; increasing the temperature T2 when coating silicon-based particles to increase the value of AB; increasing the volume percentage V1% of alkynes in hydrocarbon gases to increase the value of AB.

[0020] By adjusting W%, V1%, T1, or T2, the ID / IG values ​​of graphite particles or silicon-based particles can be adjusted to make the ID / IG values ​​of both graphite particles and silicon-based particles smaller, which is beneficial for carbon fibers with lower polarity to be more likely to be distributed on the surface of graphite particles and silicon-based particles.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] This application does not impose any particular restrictions on the type, size, or shape of the negative electrode current collector, as long as it does not cause a chemical change in the battery cell and is conductive. For example, the negative electrode current collector can be made of materials such as stainless steel, copper, nickel, titanium, calcined carbon, or a substance that has been surface-treated with carbon, nickel, titanium, or silver on the surface of copper or stainless steel.

[0037] The negative electrode current collector can have an appropriate thickness as needed. Although there are no particular limitations, the negative electrode current collector can have a thickness in the range of 1 μm to 500 μm, or in the range of 1 μm to 300 μm, or in the range of 1 μm to 100 μm, or in the range of 1 μm to 50 μm, or in the range of 1 μm to 20 μm, or in the range of 5 μm to 10 μm.

[0038] The negative electrode current collector can have fine irregularities formed on its surface, thereby further enhancing its adhesion to the negative electrode material layer. For example, the negative electrode current collector can be selected from one or more of the following: membrane, sheet, foil, mesh, porous body, foam, and nonwoven fabric.

[0039] The negative electrode material layer of this application includes carbon fiber clusters, binder, and silicon-based particles.

[0040] In some embodiments, 0.07≤A≤0.58, and the value of A can be a value within the range of 0.07, 0.14, 0.25, 0.28, 0.31, 0.36, 0.39, 0.42, 0.45, 0.47, 0.54, 0.58 or any two of these. By making the value of A satisfy the above range, it is beneficial to make the negative electrode material have a suitable polarity, which can further improve the distribution of carbon fiber and binder in the negative electrode material layer and further improve the cycle performance of the secondary battery.

[0041] In some embodiments, a second test area is included on the surface of the negative electrode material layer, the area of ​​the second test area being 14400 μm. 2 The ID / IG value of the second test area is Z, 0.03≤Z≤0.51, preferably 0.13≤Z≤0.42, where the value of Z can be a value within the range of 0.03, 0.13, 0.21, 0.23, 0.28, 0.29, 0.30, 0.31, 0.32, 0.42, 0.47, 0.51 or any two of them. By controlling the ID / IG value Z of the second test area to meet the above range, the carbon fiber content is kept within a suitable range, and the silicon-based particles have a lower polarity, which is beneficial for the carbon fiber to be more inclined to be distributed on the surface of the silicon-based particles, further improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0042] Specifically, the second test area may partially overlap with the first test area.

[0043] Specifically, the second test region does not necessarily have to be a continuous single region. The second test region can be a single 120μm × 120μm rectangular region, two 60μm × 120μm rectangular regions, or four 30μm × 120μm rectangular regions. When the second test region comprises multiple regions, the ID / IG value of the second test region is the arithmetic mean of the ID / IG values ​​of the aforementioned multiple regions.

[0044] In some embodiments, based on the mass of the negative electrode material layer, the mass of carbon fibers in the negative electrode material layer is C%, 0.5≤C≤1.5, preferably 0.7≤C≤1.3, and the value of C can be a value within the range of 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, or any two of these. By controlling the mass of carbon fibers in the negative electrode material layer to meet the above range, the carbon fiber content can be kept within a suitable range, which is beneficial to further improve the distribution of carbon fibers in the gaps between the negative electrode active particles, thereby further improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0045] In some embodiments, the average length of the carbon fiber is L μm, 0.1≤L≤20, preferably 0.8≤L≤15, where the value of L can be within the range of 0.1, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, 2.0, 5.0, 8.0, 11.0, 14.0, 15.0, 20.0 or any two of these ranges. By ensuring that the average length L of the carbon fiber meets the above range, it is beneficial to control the adhesion degree between the adhesive and the carbon fiber, thereby further improving the distribution of the adhesive, improving the contact area between the negative electrode active material particles and the electrolyte, and at the same time, ensuring that the carbon fiber has a certain length can alleviate the damage to the conductive network between the negative electrode active material particles caused by the volume expansion and contraction of silicon-based particles during lithium insertion and extraction, which is beneficial to improving the connection between adjacent negative electrode active material particles, further improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0046] In some embodiments, the average diameter of the carbon fiber cluster is R μm, 0.01≤R≤0.13, preferably 0.03≤R≤0.1, where the value of R can be within the range of 0.01, 0.03, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13 or any two of these. By ensuring that the average diameter R of the carbon fiber cluster meets the above range, it is beneficial to control the adhesion degree between the adhesive and the carbon fiber, thereby further improving the distribution of the adhesive, improving the contact area between the negative electrode active material particles and the electrolyte, and at the same time enabling the carbon fiber to have a certain strength, reducing the impact of the volume expansion of silicon-based particles during lithium insertion / extraction on the conductive network between the negative electrode active material particles, further improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0047] Specifically, at least some regions of multiple carbon nanotubes are in contact, and the contact areas are arranged in a bundle-like pattern, with at least some regions of the long axes of the multiple carbon nanotubes being parallel to each other. Parallelism includes cases where the angle between the long axes of the carbon nanotubes is less than or equal to 20°. When testing the diameter of the carbon nanotube cluster, the region where multiple carbon nanotubes are in contact and their long axes are parallel is selected for testing.

[0048] In some embodiments, the film resistivity of the negative electrode is F mΩ·cm, 1.5≤F≤2.5, where the value of F can be within the range of 1.50, 1.67, 1.82, 1.95, 1.98, 2.01, 2.04, 2.10, 2.14, 2.17, 2.19, 2.21, 2.23, 2.24, 2.38, 2.39, 2.44, 2.48, 2.50 or any two of these. By controlling F to meet the above range, the negative electrode has a suitable film resistivity, which is beneficial for electron conduction within the negative electrode, further improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0049] In some embodiments, the average diameter of the silicon-based particles is D μm, where 3.5 ≤ D ≤ 7, preferably 4.5 ≤ D ≤ 6. The value of D can be within the range of 3.5, 4.0, 4.5, 4.8, 5.1, 5.4, 5.7, 6.0, 6.5, 7.0, or any two of these values. By controlling D to satisfy the above range, the silicon-based particles have a suitable particle size, which can shorten the diffusion path of lithium ions inside the silicon-based particles. At the same time, the silicon-based particles also have a suitable specific surface area, which helps to alleviate local polarization while reducing side reactions between the silicon-based particles and the electrolyte. This further improves the cycle capacity retention rate of the secondary battery and reduces the thickness expansion rate of the secondary battery.

[0050] In some embodiments, carbon fibers include at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes.

[0051] In some embodiments, the adhesive 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 carboxymethyl cellulose, or potassium carboxymethyl cellulose.

[0052] In some embodiments, silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles.

[0053] In some embodiments, silicon-based particles include silicon-carbon particles, which include porous carbon, silicon particles located at least partially within the pores of the porous carbon, and a carbon layer located at least partially on the surface of the silicon-carbon particles.

[0054] In some embodiments, the negative electrode material layer further includes at least one of graphite particles, hard carbon particles, or soft carbon particles.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] electrolyte In this application, the electrolyte refers to the medium that facilitates the movement of electron transport substances to enable the electrochemical reactions at the positive and negative electrodes. The electrolyte can be a commonly used organic liquid electrolyte, inorganic liquid electrolyte, gel-type polymer electrolyte, molten inorganic electrolyte, etc., but is not limited to these. Solid electrolytes such as gel-type polymer electrolytes can also be used instead of the electrolyte. Batteries using solid electrolytes are generally called solid-state batteries or all-solid-state batteries. Liquid electrolytes (electrolytes) typically contain non-aqueous solvents and lithium salts.

[0060] In some embodiments, the electrolyte comprises fluoroethylene carbonate and ethylene carbonate. Based on the mass of the electrolyte, the mass percentage of fluoroethylene carbonate is P1%, and the mass percentage of ethylene carbonate is P2%, where 5 ≤ P2 ≤ 21. The value of P2 can be a value within the range of 5, 7, 9, 11, 14, 15, 17, 18, 21, or any two of these values. 0.5 ≤ P2 / P1 ≤ 1.8, preferably 0.8 ≤ P2 / P1 ≤ 1.5, where the value of P1 / P2 can be a value within the range of 0.5, 0.8, 1.3, 1.5, 1.8, or any two of these values. By controlling P1 / P2 to satisfy the above range, This application includes fluoroethylene carbonate and ethylene carbonate in the electrolyte, which is beneficial for forming a dense SEI film on the surface of silicon-based particles. This reduces the impact of volume expansion of silicon-based particles during lithium insertion / extraction on the SEI film, reduces the pulverization and shedding of the negative electrode material layer, and reduces side reactions between silicon-based particles and electrolyte. At the same time, the decomposition of fluoroethylene carbonate allows the SEI film to contain more LiF, which can further improve the stability of the SEI film and the lithium-ion conductivity. This is beneficial for the migration of lithium ions between the silicon-based particles with carbon fibers and binders on the surface and the electrolyte, further improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0061] In some embodiments, the electrolyte includes a type of lithium salt additive, which includes at least one of lithium difluorophosphate or lithium tetrafluoroborate. Based on the mass of the electrolyte, the mass percentage of the lithium salt additive is S%, 0.1≤S≤2, preferably 0.3≤S≤1.7, where the value of S can be a value within the range of 0.1, 0.3, 0.6, 1.0, 1.3, 1.7, 2.0, or any two thereof. By controlling S to satisfy the above range, this application, by including a type of lithium salt additive within the above range in the electrolyte, facilitates the formation of [a specific type of lithium salt additive] on the surface of silicon-based particles. Forming a dense and stable solid electrolyte (SEI) film can reduce the impact of volume changes during lithium insertion / extraction of silicon-based particles on the negative electrode, thereby reducing the continuous consumption of active lithium and electrolyte. It can also more effectively suppress the continuous decomposition of electrolyte on the surface of silicon-based particles, while giving the electrolyte suitable wettability, allowing the electrolyte to fully wet the silicon-based particles with carbon fibers and binders distributed on the surface. This is conducive to the further formation of a uniform and dense SEI film on the surface of silicon-based particles, improving the lithium-ion conductivity of the electrolyte, further improving the cycle capacity retention rate of the secondary battery and reducing the thickness expansion rate of the secondary battery.

[0062] According to some embodiments of this application, the lithium salt may include, but is 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, Li2SiF6, or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). This application does not limit the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0063] 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, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, or methyl ethyl carbonate (EMC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of propylene carbonate (PC), butylene carbonate, or vinyl ethylene carbonate. The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of 1,3-dioxapentane (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, 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; nitrile solvents such as R-CN (where R is a straight-chain, branched, or cyclic hydrocarbon group with 2 to 20 carbon atoms, and may include double bonds, aromatic rings, or ether bonds) (e.g., acetonitrile); 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 solvents such as trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. In the above text, the hydrocarbon group may be selected from one or more of alkyl, alkenyl, or alkynyl groups.

[0064] 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.

[0065] Measurement methods <Raman Spectroscopy Test> The secondary battery was discharged to 2.5V at a rate of 0.05C, and then left to stand for 5 minutes. This process was repeated three times. The negative electrode was then removed from the secondary battery, soaked in dimethyl carbonate solution, and dried. The negative electrode was then cut into 2cm × 2cm rectangular samples using ceramic scissors. These samples were placed on the Raman testing stage, and the 50x objective lens was focused until the test area was clear. Two 14400μm areas were then selected using the selection tool. 2 The rectangular region was divided into 36 small squares of equal area, forming the first test region, and the other region had an area of ​​14400 μm. 2 The rectangular area is the second test area, using a 532nm light source, with the Raman wavenumber range set to 400~3000cm⁻¹. -1 ; Raman spectra 1300~1400cm -1 The maximum strength is ID, 1500~1700cm -1 The maximum intensity is IG. A Raman spectrum is recorded for the second test region and each of the first test regions, and the ID / IG value of that region is calculated. The maximum value of the ID / IG value among the 36 first test regions is denoted as A, the minimum value as B, and the ID / IG value of the second test region is denoted as Z.

[0066] Measurement of carbon fiber length and carbon fiber cluster diameter The negative electrode material powder was placed in ethanol and ultrasonically dispersed to obtain a dispersion. The dispersion was then dropped onto a silicon wafer. Using SEM, 20 carbon fiber clusters were randomly selected, and the diameter of each individual cluster was measured. The arithmetic mean of the diameters of the 20 clusters was calculated to obtain the average diameter of the carbon fiber clusters. Similarly, 50 carbon fibers were randomly selected, and the length of each individual fiber was measured. The arithmetic mean of the lengths of the 50 fibers was calculated to obtain the average length of the carbon fibers.

[0067] <Measurement of resistivity of the negative electrode> The negative electrode was cut into small 10cm × 10cm pieces. Four electrodes were applied to four locations on the surface of the sample. Current was then applied through two electrodes, while voltage was measured through the other two. The resistivity of the sample could be calculated based on the measured current and voltage data.

[0068] <Measurement of the average diameter of silicon-based particles> The cross-section of the negative electrode was observed using a scanning electron microscope in backscatter mode, and 100 silicon-carbon particles were randomly selected. The cross-sectional area S of the silicon-carbon particles was measured, and the result was obtained using S=πr². 2 The diameter r is calculated, and 2r is taken as the diameter of a single silicon-carbon particle. The arithmetic mean of the diameters of the selected 100 silicon-carbon particles is used to obtain the average diameter of the silicon-carbon particles.

[0069] <Cyclic Performance Testing> At a test temperature of 25℃, the lithium-ion battery under test was left to stand for 5 minutes, and the thickness M0 of the lithium-ion battery at 50% SOC was recorded. Then, the lithium-ion battery was charged to 4.45V at a constant current of 0.7C, and then charged to 0.05C at a constant voltage of 4.45V; left to stand for 5 minutes, and then discharged to 3.0V at a constant current of 1C, and the discharge capacity C1 before the cycle was recorded; then left to stand for 5 minutes, and the above charge and discharge cycle process was repeated 1000 times, and the discharge capacity C2 of the last constant current discharge to 3.0V at 1C and the thickness M1 of the lithium-ion battery at full charge after the cycle were recorded.

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

[0071] Thickness expansion rate (%) = (M1-M0) / M0×100%.

[0072] 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.

[0073] Example 1 Preparation of the negative electrode: S1. Graphite particles and petroleum coke are mixed and stirred for 6 minutes at a mass ratio of 98:2 to obtain a mixture. Then, the mixture is heated to 900℃ at a heating rate of 10℃ / min under an inert gas protective atmosphere and kept at that temperature for 5 hours to obtain carbon-coated graphite particles. The density of the petroleum coke is 2.0 g / cc and the aromatic hydrocarbon content is 80%. S2. Hydrocarbon gas is introduced into a silicon-carbon material matrix with a silicon content of 50% and the reaction is maintained at 600°C for 3 hours to obtain silicon-based particles with a carbon coating on the surface. The hydrocarbon gas includes alkynes, alkanes, and alkenes. Based on the volume of the hydrocarbon gas, the volume percentage of alkynes is 40%, the volume percentage of alkanes is 30%, and the volume percentage of alkenes is 30%. S3. Graphite particles and silicon-based particles are mixed at a ratio of 85:15 to obtain the negative electrode active material. Carboxymethyl cellulose and the negative electrode active material are placed in a mixing tank at a mass ratio of 1:93 and stirred at a revolution speed of 30 rpm and a rotation speed of 500 rpm for 10 min. Then, carbon nanotube slurry is added and stirring is continued for 10 min, wherein the mass ratio of carbon nanotube slurry to negative electrode active material is 100:93. Then, deionized water is added and stirred at a revolution speed of 18 rpm for 90 min, wherein the mass ratio of deionized water to negative electrode active material is 2.279:2. Then, polyacrylic acid is added and stirred at a revolution speed of 30 rpm and a rotation speed of 1500 rpm for 150 min to obtain the negative electrode slurry, wherein the mass ratio of polyacrylic acid to negative electrode active material is 3.5:93. The carbon nanotube slurry is composed of single-walled carbon nanotubes, carboxymethyl cellulose and deionized water at a mass ratio of 1.5:1:97.5. S4. The negative electrode slurry is uniformly coated onto one surface of the copper foil. After drying, the above steps are 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 is dried, cold-pressed, cut, and then welded with tabs to obtain the negative electrode.

[0074] Preparation of the positive electrode: Lithium cobalt oxide (97 wt%), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) were dissolved in N-methylpyrrolidone to prepare a positive electrode slurry. The lithium cobalt oxide used included Al, Mg, and Ti elements, with Al accounting for 0.5% of the mass, Mg for 0.4%, and Ti for 0.2% of the mass, based on the mass of the lithium cobalt oxide. 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, pressurized, cut to the specified size, and then welded with tabs 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-atmosphere glove box with a water content of less than 10 ppm, propyl propionate, ethyl propionate, and propylene carbonate (mass ratio 3:2:1) were mixed to obtain a base solvent. Then, lithium hexafluorophosphate, fluoroethylene carbonate (FEC), ethylene carbonate (EC), lithium tetrafluoroborate, adiponitrile, succinitrile, and 1,3,6-hexanetrionitrile were added to the base solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the mass content of lithium hexafluorophosphate was 12.5%, adiponitrile, succinitrile, and 1,3,6-hexanetrionitrile were each 1%, the mass content of fluoroethylene carbonate (FEC) was 11%, the mass content of ethylene carbonate (EC) was 5%, and the mass content of lithium tetrafluoroborate was 1%. 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 4, Examples 9 to 20, and Comparative Example 1 and Example 1 is that the differences between the maximum and minimum values ​​of ID / IG in the first test area on the surface of the negative electrode material layer AB, the ID / IG value Z in the second test area, the average length L of the carbon fiber, the average diameter R of the carbon fiber, the resistivity F of the film resistor, and the average diameter D of the silicon-based particles are adjusted according to Table 1. The specific adjustment parameters and performance test results are shown in Table 1 below.

[0079] The only difference between Examples 5 to 8 and Example 1 is the mass percentage of carbon fiber in the negative electrode material layer. Specifically, the mass percentage of carbon fiber in Example 5 is 1.5%, in Example 6 it is 1.3%, in Example 7 it is 0.7%, and in Example 8 it is 0.5%.

[0080] The value of AB can be increased by increasing the mass percentage (W%) of the coating agent, which in turn increases the value of Z. Alternatively, Z can be decreased by increasing the carbon fiber content in the negative electrode material layer.

[0081] Table 1

[0082] As shown in Table 1 above, when the first test region and the second test region satisfy 0.05≤AB≤0.5, the secondary battery exhibits excellent cycle performance. In particular, when 0.05≤AB≤0.3 is satisfied, the cycle performance of the secondary battery can be further improved.

[0083] Specifically, when the third test region on the surface of the negative electrode material layer satisfies 0.03≤Z≤0.51, the cycle performance of the secondary battery can be further improved. In particular, when it satisfies 0.13≤Z≤0.42, the cycle performance of the secondary battery can be further improved.

[0084] In particular, when the average length of the carbon fiber satisfies 0.1≤L≤20, the cycle performance of the secondary battery can be further improved. Especially, when 0.8≤L≤15, the cycle performance of the secondary battery can be further improved.

[0085] In particular, when the average diameter of the carbon fiber satisfies 0.01≤R≤0.13, the cycle performance of the secondary battery can be further improved. Especially, when it satisfies 0.03≤R≤0.1, the cycle performance of the secondary battery can be further improved.

[0086] In particular, when the average diameter of the silicon-based particles satisfies 3.5 ≤ D ≤ 7, the cycle performance of the secondary battery can be further improved. Especially, when it satisfies 4.5 ≤ D ≤ 6, the cycle performance of the secondary battery can be further improved.

[0087] The only difference between Examples 2-1 to 2-11 and Example 2 is that the parameters are adjusted according to Table 2. The specific parameter adjustments and performance test results can be found in Table 2 below.

[0088] When adjusting the components in the electrolyte, the amount of base solvent is adjusted adaptively to ensure that the sum of the proportions of each component in the electrolyte is 100%, while maintaining the mass ratio between each component in the base solvent.

[0089] Table 2

[0090] In particular, when the electrolyte ratio satisfies 0.5 ≤ P2 / P1 ≤ 1.8, the cycle performance of the secondary battery can be further improved. Especially when the ratio satisfies 0.8 ≤ P2 / P1 ≤ 1.5, the cycle performance of the secondary battery can be further improved.

[0091] In particular, when the electrolyte meets the condition of 0.1≤S≤2, the cycle performance of the secondary battery can be further improved. Especially when the condition of 0.3≤S≤1.7 is met, the cycle performance of the secondary battery can be further improved.

[0092] Example 21 Except for the steps specifically described below, the procedure is the same as in Example 1.

[0093] Preparation of the negative electrode: After fabricating the negative electrode using the same method as in Example 1, laser grooving was performed on the negative electrode material layers on both sides of the negative electrode. The depth of the grooves was 30 μm, and the vertical distance between the grooves was 1.5 mm.

[0094] Preparation of the positive electrode: The lithium cobalt oxide used contains Al, Mg, Ti, Zr, La, Y, Ce and W elements. Based on the mass of lithium cobalt oxide, Al accounts for 0.5% of the mass, Mg accounts for 0.5% of the mass, and the mass percentages of Ti, Zr, La, Y, Ce and W elements are each 0.12% of the mass.

[0095] After the positive electrode is manufactured in the same manner as in Example 1, it is embossed using an embossing roller. The embossed positive electrode has convex and concave portions on its surface, each with an area of ​​3 mm. 2 The height of the protrusion is 30 μm.

[0096] Preparation of the diaphragm: A coating containing alumina and polyvinylidene fluoride was formed on both sides of a 12 μm thick polyethylene (PE) microporous membrane. The coating facing the positive electrode contained 70% alumina by mass, while the coating facing the negative electrode contained 30% alumina by mass.

[0097] Electrolyte preparation: The electrolyte was prepared in an argon atmosphere glove box with a water content of less than 10 ppm, resulting in the electrolyte with the components and contents shown in Table 3 below. The mass percentages of each component shown in the table are based on the mass of the electrolyte.

[0098] Table 3

[0099] The cycle capacity retention rate of Example 21 was 88.35%, and the thickness expansion rate was 7.8%.

[0100] 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.

[0101] 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 carbon fiber clusters, a binder, and silicon-based particles, the carbon fiber clusters consisting of a plurality of carbon fibers, characterized in that, The surface of the negative material layer includes 36 first to-be-measured regions with equal areas, the area of the first to-be-measured region is 400 μm 2 In the first to-be-measured region, the maximum value of ID / IG is A, the minimum value of ID / IG is B, and 0.05≤A-B≤0.

5.

2. The secondary battery according to claim 1, characterized by The secondary battery satisfies at least one of the following conditions: （1）0.07≤A≤0.58； (2) 0.05 ≤ A - B ≤ 0.

3.

3. The secondary battery according to claim 1, characterized by The second measurement area is included on the surface of the negative electrode material layer, and has an area of 14400 μm 2 The value of ID / IG of the second measurement area is Z, 0.03 ≤ Z ≤ 0.51, preferably 0.13 ≤ Z ≤ 0.

42.

4. The secondary battery according to claim 1, characterized by The secondary battery satisfies at least one of the following conditions: (1) the average length of the carbon fibers is L μm, 0.1 ≤ L ≤ 20, preferably, 0.8 ≤ L ≤ 15; (2) the average diameter of the carbon fiber clusters is R μm, 0.01 ≤ R ≤ 0.13, preferably, 0.03 ≤ R ≤ 0.

1.

5. The secondary battery according to claim 1, characterized by The sheet resistance of the negative electrode is F mΩ·cm, 1.5 ≤ F ≤ 2.

5.

6. The secondary battery according to claim 1, characterized by The average diameter of the silicon-based particles is D μm, 3.5 ≤ D ≤ 7, preferably, 4.5 ≤ D ≤ 6.

7. The secondary battery according to claim 1, characterized by The secondary battery satisfies at least one of the following conditions: (1) the carbon fibers include at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes; (2) the binder 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; (3) the silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles; (4) the silicon-based particles include silicon-carbon particles, the silicon-carbon particles including porous carbon, silicon particles at least partially located in internal pores of the porous carbon, and a carbon layer at least partially located at a surface layer of the silicon-carbon particles; (5) the negative electrode material layer further includes at least one of graphite particles, hard carbon particles, or soft carbon particles.

8. The secondary battery according to any one of claims 1 to 7, characterized by The electrolyte includes fluoroethylene carbonate and ethylene carbonate, the mass percentage of the fluoroethylene carbonate is P1%, the mass percentage of the ethylene carbonate is P2%, 5 ≤ P2 ≤ 21, 0.5 ≤ P2 / P1 ≤ 1.8, preferably, 0.8 ≤ P2 / P1 ≤ 1.5, based on the mass of the electrolyte.

9. The secondary battery according to any one of claims 1 to 7, characterized by The electrolyte includes a first lithium salt additive, the first lithium salt additive includes at least one of lithium difluorophosphate or lithium tetrafluoroborate, the mass percentage of the first lithium salt additive is S%, 0.1 ≤ S ≤ 2, preferably, 0.3 ≤ S ≤ 1.7, based on the mass of the electrolyte.

10. An electronic device, comprising: The secondary battery includes any one of claims 1 to 9.

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