Negative electrode material, secondary battery, and electronic device

Abstract

The invention provides a negative electrode material, a secondary battery and an electronic device, the negative electrode material comprises silicon carbon particles, the perimeter of the cross section of each silicon carbon particle is L [mu] m, the contour line of the cross section comprises at least one linear segment feature part, the length of the feature part is X [mu] m, and X / L is greater than or equal to 0.2 and less than or equal to 0.8. The contour line of the section of the silicon-carbon particle in the negative electrode material comprises at least one linear segment characteristic part and meets the condition that X / L is greater than or equal to 0.2 and less than or equal to 0.8, so that the compaction density of the silicon-carbon particle can be improved, and the cycle capacity retention performance and the low-temperature load performance of the secondary battery can be improved at the same time.

Description

Technical Field

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

[0002] Rechargeable batteries, as rechargeable energy storage devices, play a vital role in modern society and are widely used in portable electronic devices, electric vehicles, energy storage systems, and other fields. Their basic principle is to store and release electrical energy through the lithium-ion insertion and extraction process between the positive and negative electrode materials. In rechargeable batteries, the negative electrode material, as the lithium-ion carrier, plays a decisive role in the overall performance of the battery. An ideal negative electrode material should possess excellent energy density and conductivity.

[0003] However, with the continuous development of rechargeable battery technology, improving its cycle performance has become an urgent technical problem to be solved. Cycle performance is related to the rechargeable battery's ability to retain capacity and is crucial for meeting battery life requirements. Therefore, how to improve the cycle performance of rechargeable batteries is a key issue driving the continuous progress and widespread application of rechargeable battery technology. Summary of the Invention

[0004] In view of this, this application provides a negative electrode material, a secondary battery, and an electronic device. By having the outline of the cross-section of silicon-carbon particles in the negative electrode material include a straight segment feature portion and satisfying 0.2≤X / L≤0.8, the compaction density of silicon-carbon particles can be improved, thereby improving both the cycle performance and low-temperature tensile performance of the secondary battery.

[0005] Firstly, this application provides a negative electrode material comprising silicon-carbon particles. The perimeter of the cross-section of the silicon-carbon particles is L μm, and the outline of the cross-section includes at least one straight segment feature portion. The total length of the straight segment feature portion is X μm, and 0.2 ≤ X / L ≤ 0.8. By including the straight segment feature portion in the cross-sectional outline of the silicon-carbon particles in the negative electrode material, this application enables a portion of the surface of the silicon-carbon particles to have planar characteristics. This improves the compaction density of the silicon-carbon particles and increases the contact area between them. This allows for the accommodation of more binder on the contact surface, increasing the stability of the adhesion between the silicon-carbon particles and mitigating the impact of volume changes during lithium insertion / extraction on the negative electrode material. This is beneficial for constructing a stable and efficient conductive network. Furthermore, by ensuring that the silicon-carbon particles satisfy 0.2 ≤ X / L ≤ 0.8, the surface of the silicon-carbon particles includes a suitable area with planar characteristics, which improves the compaction density of the silicon-carbon particles and also improves the cycle performance and low-temperature tensile strength of the secondary battery.

[0006] In some embodiments, the negative electrode material satisfies at least one of the following conditions: (1) 0.3 ≤ X / L ≤ 0.7; (2) 5 ≤ L ≤ 80. By making the negative electrode material satisfy at least one of the above conditions, the compaction density of silicon-carbon particles can be further improved, which also further improves the cycle performance and low-temperature tensile performance of the secondary battery.

[0007] In some embodiments, the average sphericity of the silicon-carbon particles is R, where 0.55 ≤ R ≤ 0.90, preferably 0.64 ≤ R ≤ 0.85. By adjusting the value of R to meet the above range, the compaction density of the silicon-carbon particles can be further improved, thereby further improving the cycle performance and low-temperature tensile strength of the secondary battery.

[0008] In some embodiments, the compacted density of the silicon carbide particles is P g / cm³. 3 0.97≤P≤1.27. By adjusting the value of P within the above range, the compaction density of silicon-carbon particles can be further improved, which in turn further improves the cycle performance and low-temperature tensile performance of the secondary battery.

[0009] In some embodiments, the negative electrode material comprises graphite particles with an average aspect ratio Y of 1.1 ≤ Y ≤ 3.7, preferably 1.3 ≤ Y ≤ 3.2. By adjusting the value of Y within the above range, the compaction density of the silicon-carbon particles can be further improved, thereby further improving the cycle performance and low-temperature tensile strength of the secondary battery.

[0010] In some embodiments, the silicon carbon particles include the test particles, the particle size of which is in the range of 6 μm to 10 μm, and the straightness tolerance of the straight segment feature portion is not greater than 0.2 μm.

[0011] Secondly, this application also provides a secondary battery, including a positive electrode, a negative electrode and an electrolyte, wherein 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, and the negative electrode material layer includes the negative electrode material described in the first aspect above.

[0012] In some embodiments, the adhesion force between the negative electrode material layer and the negative electrode current collector is F1 N / m, where 41 ≤ F1 ≤ 135. By adjusting the value of F1 to meet the above range, the cycle performance and low-temperature tensile performance of the secondary battery can be further improved.

[0013] In some embodiments, the electrolyte includes a type of lithium salt additive, which includes at least one of lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate. The mass percentage of the lithium salt additive is S1% based on the mass of the electrolyte, with a mass ratio of 0.2 ≤ S1 ≤ 5%. By including the lithium salt additive in the electrolyte and adjusting the value of S1 to meet the above range, the cycle performance and low-temperature load-bearing performance of the secondary battery can be further improved.

[0014] In some embodiments, the electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is S2% based on the mass of the electrolyte, with 0.5 ≤ S2 / S1 ≤ 20, preferably 3 ≤ S2 / S1 ≤ 17. By including fluoroethylene carbonate in the electrolyte and adjusting the value of S2 / S1 to be within the above range, the cycle performance and low-temperature load-bearing performance of the secondary battery can be further improved.

[0015] In some embodiments, the electrolyte comprises a nitrile compound, and the mass percentage of the nitrile compound is S3% based on the mass of the electrolyte, with 3.2 ≤ S3 ≤ 9.8, preferably 4.8 ≤ S3 ≤ 8.2. The nitrile compound includes at least one of malononitrile, ethylene glycol bis(propionitrile) ether, butadienenitrile, glutaronitrile, adiponitrile, 1,2,3-propanetricarbonyl, 1,3,5-pentanetricarbonyl, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, and 1,2,3-tris(2-cyanoethoxy)propane. By including a nitrile compound in the electrolyte and adjusting the value of S3 to meet the above range, the cycle performance and low-temperature load-bearing performance of the secondary battery can be further improved.

[0016] 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; (3) the silicon-carbon particles include porous carbon and silicon particles at least partially located in the pores within the porous carbon. By ensuring that the secondary battery satisfies at least one of the above conditions, the cycle performance and low-temperature tensile performance of the secondary battery can be further improved.

[0017] Thirdly, this application also provides an electronic device including the secondary battery described in the second aspect above. Attached Figure Description

[0018] Figure 1 A cross-sectional view of one type of silicon-carbon particle provided in an embodiment of this application; Figure 2 A cross-sectional view of yet another type of silicon-carbon particle provided in an embodiment of this application; Figure 3 A cross-sectional view of another type of silicon-carbon particle provided in an embodiment of this application. Detailed Implementation

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

[0020] To address the problems in the prior art, the inventors of this application provide a negative electrode material comprising silicon-carbon particles. The perimeter of the cross-section of each silicon-carbon particle is L μm, and the outline of the cross-section includes at least one straight segment feature portion. The total length of the straight segment feature portion is X μm, and 0.2 ≤ X / L ≤ 0.8, preferably 0.3 ≤ X / L ≤ 0.7. The value of X / L can be a value within the range of 0.2, 0.3, 0.4, 0.5, 0.7, 0.8, or any two of these values. By including the feature portion in the silicon-carbon particles of the negative electrode material and satisfying 0.2 ≤ X / L ≤ 0.8, this application improves the compaction density of the silicon-carbon particles, thereby improving both the cycle performance and low-temperature tensile strength of the secondary battery.

[0021] Preferring a spherical morphology for silicon-carbon particles in the anode material promotes their close packing and mitigates the impact of volume changes during lithium insertion / extraction on the silicon-carbon particles. However, this approach also presents challenges such as small contact area between silicon-carbon particles, poor conductivity, and excessively high compaction density of the anode material. The applicant has discovered that by including a characteristic portion in the silicon-carbon particles of the anode material and satisfying 0.2 ≤ X / L ≤ 0.8, the compaction density of the silicon-carbon particles can be improved, thereby enhancing both the cycle performance and low-temperature load-bearing capacity of the secondary battery.

[0022] The inventors of this application hypothesize that making the morphology of silicon-carbon particles in the negative electrode material more spherical is beneficial for the close arrangement of silicon-carbon particles, reducing the damage to the mechanical strength of the negative electrode sheet caused by the volume change of silicon-carbon particles during the charging and discharging of the secondary battery, and mitigating the side reactions occurring on the surface of silicon-carbon particles and the electrolyte. However, at the same time, the contact area between silicon-carbon particles is small, which is not conducive to the conduction of electrons between silicon-carbon particles, and the adhesion surface of the binder between silicon-carbon particles is small, resulting in unstable adhesion between silicon-carbon particles. During the lithium insertion and extraction process, the volume change of silicon-carbon particles causes the conductive network between silicon-carbon particles to break, preventing silicon-carbon particles from participating in subsequent electrochemical reactions, increasing the loss of active material and active lithium. In addition, more binder needs to be introduced between silicon-carbon particles to increase the adhesion stability between silicon-carbon particles, further reducing the energy density of the negative electrode material, thereby affecting the cycle performance of the secondary battery. This application improves the compaction density of silicon-carbon particles by including straight segments in the cross-sectional profile of the silicon-carbon particles in the negative electrode material, thus giving some areas of the silicon-carbon particle surface planar characteristics. This improves the compaction density of silicon-carbon particles, alleviates side reactions on the surface of silicon-carbon particles and electrolyte, increases the contact area between silicon-carbon particles, and allows more binder to be accommodated on the contact surface between silicon-carbon particles. This increases the stability of the adhesion between silicon-carbon particles, mitigates the impact of volume changes during lithium insertion / extraction of silicon-carbon particles on the negative electrode material, and is beneficial for building a stable and efficient conductive network. Furthermore, by ensuring that the silicon-carbon particles meet the condition 0.2≤X / L≤0.8, the surface of the silicon-carbon particles has a suitable area of ​​planar characteristics, which improves the compaction density of silicon-carbon particles and also improves the cycle performance and low-temperature tensile performance of the secondary battery.

[0023] The straight line segment feature does not necessarily have to be an ideal straight line. A straight line segment that is not an ideal straight line but is close to an ideal straight line also falls under the definition of the straight line segment feature in this application, and can also improve the cycle performance and low-temperature load performance of the secondary battery. Specifically, the straightness tolerance of the straight line segment feature is no greater than 0.2 μm. The straightness tolerance is the maximum allowable variation of the actual line relative to an ideal straight line. A tolerance of 0.2 μm means that within the region formed by two parallel lines 0.2 μm apart, the fluctuation of the straight line segment perpendicular to the straight line direction does not exceed the distance between the two parallel lines 0.2 μm apart.

[0024] Selecting silicon-carbon particles with a particle size in the range of 6 μm to 10 μm as the test particles makes it easier to measure the straightness tolerance of the straight segment characteristic portion. Therefore, the straightness tolerance test is preferably performed using silicon-carbon particles with a particle size in the range of 6 μm to 10 μm. The profile of the cross-section of the silicon-carbon particle may include a straight segment characteristic portion. For example... Figure 1 As shown, when the outline of the silicon-carbon particle cross section includes only one straight line segment, the length of that straight line segment is the total length X μm of the straight line segment.

[0025] like Figure 2 and Figure 3 As shown, the profile of a silicon-carbon particle cross-section can also include multiple straight line segments. These segments may or may not be adjacent. When multiple segments are adjacent, there are inflection points between them. These segments can also be distributed at intervals via curved surfaces. When the profile of a silicon-carbon particle cross-section includes multiple straight line segments, the total length X μm of each segment is obtained by calculating the length of each individual segment and then summing the results.

[0026] In some embodiments, 5≤L≤80, and the value of L can be a value within the range of 5, 15, 20, 30, 50, 65, 80 or any two of them. By making the perimeter of the silicon-carbon particles meet the above range, the silicon-carbon particles can have a suitable size, which can further improve the compaction density of the silicon-carbon particles, while also taking into account further improving the cycle performance and low-temperature tensile performance of the secondary battery.

[0027] In some embodiments, the average sphericity of the silicon-carbon particles is R, where 0.55 ≤ R ≤ 0.90, preferably 0.64 ≤ R ≤ 0.85. The value of R can be within the range of 0.55, 0.64, 0.67, 0.70, 0.72, 0.76, 0.80, 0.83, 0.85, 0.90, or any two of these values. By ensuring that the average sphericity of the silicon-carbon particles meets the above range, the silicon-carbon particles can have a suitable morphology, fully leveraging the benefits of the synergistic effect of curved and planar regions. This can further improve the compaction density of the silicon-carbon particles, while also mitigating the impact of silicon particle volume changes during lithium insertion / extraction on the silicon-carbon particles, and further improving the cycle performance and low-temperature load-bearing performance of the secondary battery.

[0028] In some embodiments, the compacted density of the silicon carbide particles is P g / cm³. 3 0.97≤P≤1.27, where the value of P can be 0.97, 1.03, 1.04, 1.06, 1.09, 1.10, 1.17, 1.21, 1.22, 1.23, 1.25, 1.27 or any two of these values. By ensuring that the value of P satisfies the above range, it is beneficial to make the silicon-carbon particles have a suitable compaction density, which can further improve the compaction density of silicon-carbon particles, and at the same time further improve the cycle performance and low-temperature tensile performance of the secondary battery.

[0029] In some embodiments, the negative electrode material includes graphite particles with an average aspect ratio Y of 1.1 ≤ Y ≤ 3.7, preferably 1.3 ≤ Y ≤ 3.2. The value of Y can be within the range of 1.1, 1.3, 1.7, 2.0, 2.4, 2.5, 2.8, 3.2, 3.7 or any two of these. By ensuring that the aspect ratio of the graphite particles meets the above range, it is beneficial to give the graphite particles a suitable morphology, increase the contact area between the graphite particles and the silicon-carbon particles, maintain the stability of the adhesion between the silicon-carbon particles and the graphite particles, and build a stable and efficient conductive network between the silicon-carbon particles and the graphite particles. At the same time, it also gives the graphite particles a certain strength, which can alleviate the influence of volume change on the graphite particles during lithium insertion / extraction of silicon-based particles, further improve the compaction density of silicon-carbon particles, and further improve the cycle performance and low-temperature tensile performance of the secondary battery.

[0030] The silicon-carbon particles in this application can be prepared using a method including the following steps: S1. A phenolic compound, a stabilizer, and a catalyst are mixed and dissolved in an aldehyde solvent at a mass ratio of 1:(0.5-3.5):(0.5-2.5), and then reacted in an inert atmosphere to obtain a carbon precursor. The phenolic compound includes at least one of phenol, resorcinol, phloroglucinol, and bisphenol A. The stabilizer includes at least one of polyvinyl alcohol, polyethylene glycol, hydroxymethyl cellulose, carboxymethyl cellulose, and polyvinylpyrrolidone. The catalyst includes at least one of hydrochloric acid, sulfuric acid, nitric acid, and oxalic acid. The aldehyde solvent includes at least one of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, and furfural. S2. Add methacrylic acid to the carbon precursor and react at T℃ for t1h. Then add calcium stearate and magnesium oleate and react at T℃ for t2h to obtain the organic precursor. The mass ratio of methacrylic acid to phenolic compounds is V1%, the mass ratio of calcium stearate to phenolic compounds is V2%, and the mass ratio of magnesium oleate to phenolic compounds is V3%. 120≤T≤180, 0.1≤t1≤1.5, 0.1≤t2≤1.5, 5≤V1≤8, 1≤V2≤2.5, 0.3≤V3≤2.5. S3. The organic precursor is cured to obtain a solidified product, and the solidified product is carbonized in an inert gas atmosphere to obtain a carbide. Subsequently, the carbide is activated, silane deposited and carbon coated to obtain silicon-carbon particles.

[0031] Based on the above-described method for preparing silicon-carbon particles, increasing the amount of methacrylic acid, calcium stearate, or magnesium oleate, either individually or simultaneously, can reduce the agglomeration of carbon precursors during the reaction, thereby increasing the area with planar characteristics on the surface of the silicon-carbon particles and thus increasing the X / L value. Alternatively, increasing the reaction time t1 and t2 can also reduce the agglomeration of carbon precursors during the reaction, thereby increasing the area with planar characteristics on the surface of the silicon-carbon particles and thus increasing the X / L value.

[0032] The curing process can be carried out by mixing the organic precursor with ammonia water, reacting it at T2 ℃ for t3h, allowing it to stand, and then sequentially filtering, washing, and drying to obtain the solidified product, wherein 50≤T2≤80 and 2≤t3≤5.

[0033] This application also provides a secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] In this application, the positive electrode material layer includes a positive electrode material. This application does not particularly limit the type of positive electrode material, as long as it achieves the purpose of this application. For example, the positive electrode material may contain lithium nickel cobalt manganese oxide (LiNi). 0.90 Co 0.05 Mn 0.05 O2 (NCM) 955 ), NCM 811 NCM 622 NCM 523 NCM111 The cathode material comprises at least one of the following: lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate. In this application, the cathode material may also contain non-metallic elements, such as at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thickness of the cathode current collector and the cathode material layer, as long as the purpose of this application is achieved.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] The negative electrode material layer of this application includes a negative electrode material.

[0051] In some embodiments, the bonding force between the negative electrode material layer and the negative electrode current collector is F1 N / m, where 41≤F1≤135. For example, the value of F1 can be within the range of 41, 66, 73, 74, 79, 81, 97, 100, 105, 108, 111, 135 or any two of these. By ensuring that the bonding force between the negative electrode material layer and the negative electrode current collector meets the above range, the peeling of the negative electrode material layer from the surface of the negative electrode current collector can be reduced. At the same time, the negative electrode also has suitable elasticity, which can reduce the impact of volume changes during lithium insertion / extraction of silicon-carbon particles on the negative electrode. This is beneficial for maintaining the stability of the negative electrode structure, thereby further improving the cycle performance and low-temperature tensile performance of the secondary battery.

[0052] 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 carboxymethyl cellulose, or potassium carboxymethyl cellulose.

[0053] 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.

[0054] In some embodiments, the silicon-carbon particles comprise porous carbon and silicon particles located at least partially within the voids of the porous carbon.

[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 have any particular limitation on the inorganic particles, which may include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. This application does not have any particular limitation on the binder, which may be at least one of the above-mentioned positive electrode binders or negative electrode binders. The polymer layer contains a polymer. This application does not have any particular limitation on the polymer, which may include at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene). In this application, there is no particular limitation on the thickness of the diaphragm, as long as it can achieve the purpose of this application. For example, the thickness of the diaphragm can be from 5 μm to 500 μm.

[0059] 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.

[0060] In some embodiments, the electrolyte includes a type of lithium salt additive, which includes at least one of lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate. The mass percentage of the lithium salt additive is S1% based on the mass of the electrolyte, with a mass ratio of 0.2 ≤ S1 ≤ 5. Exemplarily, the value of S1 can be within the range of 0.2, 0.3, 0.4, 0.6, 0.7, 0.8, 1.0, 1.4, 1.6, 2.5, 3.2, 5, or any two of these values. By including the lithium salt additive within the above range in the electrolyte, an SEI film with a suitable LiF content can be formed on the surface of the silicon-carbon particles, thereby improving the mechanical strength of the SEI film. Stability helps to constrain the volume change of silicon-carbon particles during lithium insertion / extraction, reduces the stress generated during lithium insertion / extraction at the interface between the first and second regions on the surface of silicon-carbon particles, reduces the impact of volume change on silicon-carbon particles during lithium insertion / extraction, reduces the risk of SEI breakage and increased side reactions caused by volume change during lithium insertion / extraction, reduces the side reactions between silicon-carbon particles and electrolyte due to increased contact area between silicon-carbon particles, and inhibits electrolyte decomposition and gas generation. At the same time, it gives the electrolyte good wettability and good ionic conductivity, which can further improve the cycle performance and low-temperature load performance of secondary batteries.

[0061] In some embodiments, the electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate is S2% based on the mass of the electrolyte, with 0.5 ≤ S2 / S1 ≤ 20; preferably, 3 ≤ S2 / S1 ≤ 17. For example, the value of S2 / S1 can be within the range of 0.5, 3, 8, 13, 17, 20, or any two of these values, so that the electrolyte includes fluoroethylene carbonate within the above range. This allows the formation of an SEI film with a suitable organic polymer content on the surface of silicon-carbon particles. This film can synergize with a type of lithium salt, improving the flexibility and ductility of the SEI film formed on the surface of silicon-carbon particles. This helps to restrain the volume change of silicon-carbon particles during lithium insertion / extraction, reduces the stress generated during lithium insertion / extraction at the junction of the first and second regions on the surface of silicon-carbon particles, reduces the impact of volume change on silicon-carbon particles during lithium insertion / extraction, reduces the increased side reactions between silicon-carbon particles and the electrolyte due to the increased contact area of ​​silicon-carbon particles, and simultaneously ensures that the electrolyte has suitable wettability and suitable lithium-ion migration efficiency. This further improves the cycle performance and low-temperature load performance of the secondary battery.

[0062] In some embodiments, the electrolyte comprises a nitrile compound, and the mass percentage of the nitrile compound is S3% based on the mass of the electrolyte, 3.2≤S3≤9.8, preferably 4.8≤S3≤8.2, and the value of S3 can be 3.2, 4.0, 4.2, 4.6, 4.8, 5.2, 6.4, 8.2, or 9.8; the nitrile compound includes at least one of malononitrile, ethylene glycol bis(propionitrile) ether, butadienenitrile, glutaronitrile, adiponitrile, 1,2,3-propanetricarbonyl, 1,3,5-pentanetricarbonyl, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane, and 1,2,3-tris(2-cyanoethoxy)propane. By including nitrile compounds in the electrolyte and ensuring that the S3 value meets the above-mentioned range, it is beneficial to form a stable and dense SEI film on the surface of silicon-carbon particles. This helps to confine the volume change of silicon-carbon particles during lithium insertion / extraction, reduces the stress generated during lithium insertion / extraction at the interface between the first and second regions on the surface of silicon-carbon particles, reduces the impact of volume change on silicon-carbon particles during lithium insertion / extraction, and reduces the side reactions between silicon-carbon particles and the electrolyte due to the increased contact area between silicon-carbon particles. At the same time, by ensuring that the electrolyte has a suitable viscosity, the lithium-ion conductivity of the electrolyte can be improved, which can further improve the cycle performance and low-temperature load performance of the secondary battery.

[0063] 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(oxalato)borate {LiB(C2O4)2, LiBOB}, lithium difluorooxalatoborate {LiBF2(C2O4), LiDFOB}, LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, or lithium difluoroborate. This application does not limit the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0064] 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 ethylene carbonate (EC), 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.

[0065] 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.

[0066] Measurement methods The physical properties mentioned in this application can be measured using the following methods, and the physical properties in the following embodiments and comparative examples are measured using the following methods.

[0067] <Methods for measuring the cross-sectional perimeter and total length of the characteristic portion of a straight line segment of silicon-carbon particles> The negative electrode sheet was sliced ​​using an ion polisher. Then, silicon-carbon particles were randomly selected using a ZEISS SEM (Sigma-02-33) (0.1-30KV) in backscatter mode at 1000K magnification. The perimeter of the cross-section of the silicon-carbon particles (the two-dimensional image of the silicon-carbon particles under the scanning electron microscope is used as the cross-section of the silicon-carbon particles) was measured to be L μm, and the total length of the straight segment feature part was X μm.

[0068] Measurement of the average sphericity of silicon carbide particles The negative electrode cross-section was observed in backscatter mode of a scanning electron microscope. One hundred silicon-based particles were randomly selected, and the area S' of the circumcircle of the selected silicon-based particle cross-section was calculated. Circularity was calculated as S / S'. The arithmetic mean of the sphericity of the 100 silicon-based particles was calculated as the average circularity R of the silicon-based particles.

[0069] <Testing the compaction density of negative electrode materials> Place the silicon carbide powder into the powder density tester mold (test mold (CARVER#3619 (13mm)); the testing equipment is a Sansi Zongheng UTM7305. Place the mold in the middle of the upper and lower pressure plates of the equipment. Click the run button on the equipment. The equipment will first pressurize to 5T according to the set parameters and then depressurize. Record the height after depressurization as the compacted height H. The set parameters include a pressurization rate of 10mm / min, a pressurization holding time of 30s, a depressurization rate of 30mm / min, and a depressurization holding time of 10s. The compacted density of the powder can be calculated using the following formula: P = m / V = m / (S × H), In the formula: P ----- compacted density of powder, g / cm³ 3 ; m ----- The mass of the material weighed, in grams; S----- Mold base area, cm² 2 ; H-----Height after compaction, in cm.

[0070] Measurement of the average aspect ratio of graphite particles Using a ZEISS SEM (Sigma-02-33) (0.1-30KV) at an accelerating voltage of 5 kV and a magnification of 1000K, the longest and shortest diameters of 100 randomly selected graphite particles were measured using image analysis software. Then, the aspect ratio of all observed graphite particles within the field of view was calculated according to the formula: aspect ratio = longest diameter / shortest diameter. The average aspect ratio of the graphite particles was then obtained by taking the average value.

[0071] <Adhesion test between negative electrode material layer and negative electrode current collector> The instrument used for testing the adhesion between the negative electrode material layer and the negative electrode current collector was an Instron instrument, model 33652. A negative electrode (30mm wide × 150mm long) was fixed to a steel plate with double-sided adhesive tape (model: 3M9448A, 20mm wide × 120mm long). A paper strip of the same width as the negative electrode was fixed to one side of the negative electrode with adhesive tape. The limit block of the tensile testing machine was adjusted to a suitable position, and the paper strip was folded upward and slid 40mm at a sliding speed of 50mm / min. The adhesion between the negative electrode active layer and the negative electrode current collector was tested at 180° (i.e., reverse stretching).

[0072] <Cyclic Performance Testing Methods> The test temperature was 25℃. The prepared secondary battery was charged at a constant current of 0.7C to 4.5V, then charged at a constant voltage of 0.025C, and after resting for 5 minutes, discharged at 0.5C to 3.0V. The capacity obtained in this step was used as the initial capacity, and cyclic testing was performed using 0.7C charge / 0.5C discharge. The capacity decay curve was obtained by comparing the capacity at each step with the initial capacity. The number of cycles at 25℃ until 90% capacity retention was achieved was recorded as the room temperature cycle performance of the battery. The cycle performance of the materials was compared by comparing the number of cycles.

[0073] <Low Temperature Tension Test> At 25℃, the prepared secondary battery was discharged to 2.8V at 0.2C, allowed to stand for 5 minutes, charged to 4.5V at 0.5C, charged at a constant voltage to 0.05C, allowed to stand for 5 minutes, discharged to 2.8V at 0.2C, allowed to stand for 5 minutes, charged to 4.5V at 0.5C, charged at a constant voltage to 0.05C, allowed to stand for 5 minutes, discharged at 0.1C for 8 hours, allowed to stand for 5 minutes, the ambient temperature was adjusted to -20℃, allowed to stand for 30 minutes, and then the four-step discharge process was repeated 10 times in sequence at 1CDCto100ms, 0.4CDCto10s, 1.2CDCto100ms, and 0.4CDCto02s. The voltage at this time was then measured and recorded as the low-temperature load voltage.

[0074] 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.

[0075] Example 1 Preparation of silicon-carbon particles: S1. Phenol, polyvinyl alcohol and hydrochloric acid were added to a three-necked flask in a mass ratio of 1:1.7:2. After mixing evenly, formaldehyde was added and the mass ratio of phenol to formaldehyde was controlled at 1:1.8. The mixture was reacted at 100°C for 2.0 h under an inert atmosphere. Then the temperature was raised to 140°C and kept at that temperature for 2.0 h to obtain the carbon precursor. S2. Add 5% (by mass of phenol) of methacrylic acid to the carbon precursor and keep it at 140°C for 0.1 h. Then add 1% (by mass of phenol) of calcium stearate and 0.3% (by mass of phenol) of magnesium oleate and keep it at 140°C for another 0.1 h. After the reaction is complete, filter and wash to obtain the organic precursor. S3. The organic precursor and ammonia water with a mass concentration of 2% were mixed at a mass ratio of 1:10 and reacted at 60°C for 2 hours. After standing for 1 hour, the mixture was filtered, washed and dried to obtain a solidified product. The solidified product was heated to 600°C at a heating rate of 5°C / min under a nitrogen atmosphere and kept at that temperature for 2 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain a carbide. S4. The carbide, potassium hydroxide and sodium carbonate are mixed in a mass ratio of 1:1:0.5 and reacted at 750℃ for 1 hour. After the reaction is completed, the mixture is cooled to room temperature and then washed and dried to obtain porous carbon material. S5. At a temperature of 600℃, porous carbon material is deposited using a silane inert gas mixture with a silane concentration of 25%. After 15 hours of deposition, the ambient temperature is lowered to 580℃, and a mixture of acetylene and nitrogen with a volume ratio of 1:1 is introduced for 9 hours. Other gas components are inert gases, resulting in silicon carbon particles.

[0076] Preparation of the negative electrode: The silicon-carbon particles obtained above were mixed with artificial graphite at a mass ratio of 10:90 to obtain the negative electrode active material. The negative electrode active material (95 wt%), single-walled carbon nanotubes (0.5 wt%), polyacrylic acid (3.5%), and carboxymethyl cellulose (1%) were mixed, then deionized water was added and stirred until homogeneous to prepare a negative electrode slurry. This negative electrode slurry was uniformly coated onto one surface of a copper foil, dried, and then 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.

[0077] Preparation of the positive electrode: A positive electrode slurry was prepared by dissolving lithium cobalt oxide (97 wt%), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) in N-methylpyrrolidone. The lithium cobalt oxide used was Al and Mg co-doped. Based on the mass of lithium cobalt oxide, the mass percentage of Al was 0.3%, and the mass percentage of Mg was 0.4%. 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 double-sided coating of positive electrode material. The coated aluminum foil was dried, pressurized, cut to the specified size, and electrode tabs were welded to fabricate the positive electrode.

[0078] Preparation of the diaphragm: A 12μm thick polyethylene (PE) microporous membrane was selected as the diaphragm.

[0079] Electrolyte preparation: In an argon atmosphere glove box with a water content of less than 10 ppm, propyl propionate, ethyl propionate, propylene carbonate, and ethylene carbonate (mass ratio 3:1:1:1) are mixed to obtain a base solvent. Then, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, fluoroethylene carbonate, adiponitrile, succinic acid, 1,3,6-hexanetrionitrile, ethylene sulfate, vinylene carbonate, and 1,3-propanesulfonate lactone are added to the base solvent and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, lithium hexafluorophosphate accounts for 12.5%, lithium tetrafluoroborate accounts for 1%, lithium bis(trifluoromethanesulfonyl)imide accounts for 4%, fluoroethylene carbonate accounts for 2.5%, adiponitrile accounts for 2%, succinitrile accounts for 2%, 1,3,6-hexanetrionitrile accounts for 2.4%, vinyl sulfate accounts for 0.5%, vinylene carbonate accounts for 0.5%, 1,3-propanesulfonate lactone accounts for 3%, and the remainder is the base solvent.

[0080] 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.

[0081] Comparative Example 1 In the preparation of silicon-carbon particles, calcium stearate and magnesium oleate are not added in step S2. The rest is the same as in Example 1.

[0082] The only difference between Examples 2 to 12 and Comparative Example 1 and Example 1 is that the perimeter L μm of the cross section of the silicon-carbon particles, the length X μm of the characteristic part of the silicon-carbon particles, the average roundness R of the silicon-carbon particles, and the average aspect ratio Y of the graphite particles were adjusted according to Table 1. The specific adjustment parameters and performance test results are shown in Table 1 below.

[0083] The cross-section of the silicon-carbon particles in Comparative Example 1 was measured. The outline of the cross-section of the silicon-carbon particles in Comparative Example 1 does not include the straight line segment feature.

[0084] The X / L value can be increased by adding more methacrylic acid, calcium stearate, or magnesium oleate during the preparation of silicon carbide particles.

[0085] Table 1

[0086] As shown in Table 1 above, this application enables the silicon-carbon particles to include characteristic portions and satisfy 0.2≤X / L≤0.8, thereby giving the silicon-carbon particles excellent compaction density and enabling the secondary battery to have excellent cycle performance. In particular, satisfying 0.3≤X / L≤0.7 further improves the compaction density of the silicon-carbon particles and further improves the cycle performance of the secondary battery.

[0087] Specifically, achieving an average sphericity of 0.55 ≤ R ≤ 0.90 for silicon-carbon particles further improves the compaction density of the silicon-carbon particles and the cycle performance of the secondary battery. In particular, achieving a compaction density of 0.64 ≤ R ≤ 0.85 further improves the compaction density of the silicon-carbon particles and the cycle performance of the secondary battery.

[0088] Specifically, when the average aspect ratio of graphite particles satisfies 1.1≤Y≤3.7, the compaction density of silicon-carbon particles can be further improved, and the cycle performance of the secondary battery can be further improved. In particular, when the aspect ratio satisfies 1.3≤Y≤3.2, the compaction density of silicon-carbon particles can be further improved, and the cycle performance of the secondary battery can be further improved.

[0089] The only difference between Examples 2-1 to 2-16 and Example 2 is that the types of lithium salt additives, the mass percentage of lithium salt additives S1%, the mass percentage of fluoroethylene carbonate S2%, the types of nitrile compounds, and the mass percentage of nitrile compounds S3% were adjusted according to Table 2. The specific adjustment parameters and performance test results are shown in Table 2 below.

[0090] When adjusting the components in the electrolyte, the amount of base solvent should be adjusted accordingly, while maintaining the mass ratio of each component in the base solvent.

[0091] Table 2

[0092] As shown in Table 2 above, when the electrolyte includes a type of lithium salt additive and fluoroethylene carbonate, and satisfies 0.5 ≤ S2 / S1 ≤ 20, the cycle performance of the secondary battery can be further improved. In particular, when 3 ≤ S2 / S1 ≤ 17, the cycle performance of the secondary battery can be further improved.

[0093] In particular, when the electrolyte includes nitrile compounds and satisfies 3.2 ≤ S3 ≤ 9.8, the cycle performance of the secondary battery can be further improved. Especially, when 4.8 ≤ S3 ≤ 8.2 is satisfied, the cycle performance of the secondary battery can be further improved.

[0094] Example 13 Except for the steps specifically described below, the procedure is the same as in Example 1.

[0095] 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.

[0096] 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 0.7% of the mass, Mg accounts for 0.3% of the mass, and Ti, Zr, La, Y, Ce and W each account for 0.1% of the mass.

[0097] After the positive electrode is manufactured in the same manner as in Example 1, the positive electrode sheet is embossed using an embossing roller. The surface of the embossed positive electrode sheet has convex and concave portions, with the convex portions having an area of ​​3 mm. 2 The area of ​​the concave part is 3 mm. 2 The height of the convex part is 25 μm, and the depth of the concave part is 28 μm.

[0098] 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 75% alumina by mass, while the coating facing the negative electrode contained 45% alumina by mass.

[0099] 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 the table below. The mass percentages of each component shown in the table are based on the mass of the electrolyte.

[0100]

[0101] In Example 13, the number of cycles at 25°C to 90% was 1598, and the voltage after 10 load cycles at -20°C to 2.8V was 2.70V.

[0102] 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 negative electrode material, characterized in that, The negative electrode material includes silicon-carbon particles, the perimeter of the cross-section of the silicon-carbon particles is L μm, the outline of the cross-section includes at least one straight line segment feature portion, the total length of the straight line segment feature portion is X μm, and 0.2≤X / L≤0.

8.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions: (1) 0.3 ≤ X / L ≤ 0.7; （2）5≤L≤80。 3. The negative electrode material according to claim 1, characterized in that, The average sphericity of the silicon-carbon particles is R, where 0.55 ≤ R ≤ 0.90, preferably 0.64 ≤ R ≤ 0.

85.

4. The negative electrode material according to claim 1, characterized in that, The compacted density of the silicon-carbon particles is P g / cm³. 3 , 0.97≤P≤1.

27.

5. The negative electrode material according to claim 1, characterized in that, The negative electrode material includes graphite particles, the average aspect ratio of which is Y, 1.1≤Y≤3.7, preferably 1.3≤Y≤3.

2.

6. The negative electrode material according to any one of claims 1 to 5, characterized in that, The silicon-carbon particles include the test particles, the particle size of which is in the range of 6 μm to 10 μm, and the straightness tolerance of the straight segment feature portion is no greater than 0.2 μm.

7. A secondary battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein 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, characterized in that, The negative electrode material layer comprises the negative electrode material according to any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized in that, The bonding force between the negative electrode material layer and the negative electrode current collector is F1 N / m, where 41≤F1≤135.

9. The secondary battery according to claim 7, characterized in that, The electrolyte includes a type of lithium salt additive, which includes at least one of lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, or lithium difluorophosphate. Based on the mass of the electrolyte, the mass percentage of the type of lithium salt additive is S1%, where 0.2 ≤ S1 ≤ 5.

10. The secondary battery according to claim 9, characterized in that, The electrolyte includes fluoroethylene carbonate, and based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is S2%, 0.5≤S2 / S1≤20, preferably 3≤S2 / S1≤17.

11. The secondary battery according to claim 7, characterized in that, The electrolyte includes nitrile compounds, and based on the mass of the electrolyte, the mass percentage of the nitrile compounds is S3%, where 3.2 ≤ S3 ≤ 9.8, and preferably, 4.8 ≤ S3 ≤ 8.

2. The nitrile compounds include at least one of malononitrile, ethylene glycol bis(propionitrile) ether, butadiene, glutaronitrile, adiponitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoethoxy)propane and 1,2,3-tris(2-cyanoethoxy)propane.

12. The secondary battery according to claim 7, characterized in that, The secondary battery satisfies at least one of the following conditions: (1) 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. (2) The negative electrode material layer further includes a conductive agent, which includes at least one of conductive carbon black, carbon nanotubes or sheet graphene; (3) The silicon-carbon particles include porous carbon and silicon particles located at least partially in the voids inside the porous carbon.

13. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 7 to 12.

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