Porous carbon material and preparation method thereof, silicon carbon material and application

Abstract

The invention discloses a porous carbon material, a preparation method thereof, a silicon-carbon material and application, and belongs to the technical field of battery materials. Wherein the degree of sphericity of the porous carbon material is a, and a is more than or equal to 0.7 and less than or equal to 0.97; the porous carbon material comprises a potassium element; based on the mass of the porous carbon material, the mass ratio of the potassium element is b ppm, and b is greater than or equal to 1 and less than or equal to 2998. According to the present invention, the sphericity degree of the porous carbon material is controlled to be 0.7-0.97, and the mass ratio of the potassium element in the porous carbon is 1-2998 ppm, such that the secondary battery can achieve the high ion conductivity and the expansion buffer performance so as to provide the excellent electrochemical performance;

Description

Technical Field

[0001] The present application belongs to the technical field of battery materials, and specifically relates to a porous carbon material and a preparation method thereof, a silicon-carbon material and applications thereof. Background Art

[0002] Secondary batteries (such as lithium-ion batteries) achieve the conversion of chemical energy into electrical energy through the synergistic effect of positive electrode, negative electrode, electrolyte and separator. The core of its performance depends on the ion conduction rate and structural stability of the electrode material. Among negative electrode materials, silicon is considered an ideal candidate to break through the traditional graphite negative electrode (372mAh / g) due to its high specific capacity of 3579mAh / g. However, its volume expansion (>300%) caused by lithiation / delithiation reaction during charging and discharging can easily lead to electrode pulverization, active material shedding and repeated rupture of solid electrolyte interface (SEI) film, significantly reducing the cycle life.

[0003] To alleviate the above problems, silicon-carbon materials embed silicon materials into carbon matrices and utilize the high conductivity and mechanical buffering properties of the carbon phase to buffer the expansion of silicon materials to a certain extent and improve overall stability. However, the composite structure of existing silicon-carbon materials still faces problems such as insufficient silicon-carbon interface compatibility and obstructed lithium ion diffusion paths, which affect the ion conductivity of secondary batteries. Especially in high compaction density electrodes, the above defects will aggravate electrode polarization and cause rapid capacity decay of secondary batteries. Therefore, how to construct secondary batteries with high ionic conductivity and expansion buffering performance to achieve a synergistic improvement in secondary battery energy density and cycle stability is a key issue to be solved in this field. Summary of the invention

[0004] In view of this, the present application provides a porous carbon material and a preparation method thereof, a silicon-carbon material and an application thereof, which can enable a secondary battery to have both high ion conductivity and expansion buffering performance, thereby enabling it to exhibit excellent electrochemical performance.

[0005] In a first aspect, the present application provides a porous carbon material. The sphericity of the porous carbon material is a, where 0.7 ≤ a ≤ 0.97. The porous carbon material contains potassium element. Based on the mass of the porous carbon material, the mass percentage of the potassium element is b ppm, where 1 ≤ b ≤ 2998. By doping the potassium element into the porous carbon material in the present application, the ionic conductivity of the porous carbon material can be improved, and the initial Coulombic efficiency of the silicon-carbon material can be enhanced. However, the potassium element has a strong etching ability and is prone to damaging the structure of the porous carbon material, causing local structural defects, reducing the elastic modulus of the porous carbon material, and increasing the stress difference inside the silicon-carbon material during the expansion process. In the present application, by controlling the sphericity of the porous carbon material, the isotropy of the sphere can balance the stress during the expansion process, thereby increasing the elastic modulus of the porous carbon material, improving the expansion-inhibiting performance of the silicon-carbon material, and enabling the silicon-carbon material to withstand a greater compaction density, which is beneficial to increasing the energy density and the initial Coulombic efficiency of the secondary battery. Therefore, by optimizing the structure and elemental composition of the porous carbon material, the sphericity characteristics of the porous carbon material and the mass percentage of the potassium element cooperate synergistically, enabling both the improvement of the ionic conductivity of the secondary battery and the expansion-inhibiting performance to be taken into account.

[0006] In some embodiments, the porous carbon material satisfies at least one of the following conditions:

[0007] (1) 50 ≤ a × b ≤ 2800;

[0008] (2) 0.75 ≤ a ≤ 0.95;

[0009] (3) 10 ≤ b ≤ 997.

[0010] Based on the above solution, the ionic conductivity and the expansion-inhibiting performance of the secondary battery can be further improved.

[0011] In some embodiments, in the XRD of the porous carbon material, the full width at half maximum of the diffraction peak of the (002) crystal plane is FWHM°, where 0.4 ≤ FWHM ≤ 1.5. By controlling the full width at half maximum FWMH° of the diffraction peak of the (002) crystal plane in the XRD pattern of the porous carbon material in the present application to satisfy 0.4 ≤ FWMH ≤ 1.5, the porous carbon material of the present application can have an appropriate degree of graphitization. The crystal structure with an orderly arrangement of carbon atoms is beneficial to improving the ionic conductivity of the secondary battery. In combination with the above mass percentage of the potassium element and the sphericity characteristics, the initial Coulombic efficiency of the silicon-carbon material can be further increased, and both the improvement of the ionic conductivity of the secondary battery and the expansion-inhibiting performance can be taken into account.

[0012] In a second aspect, the present application provides a preparation method of the above porous carbon material, including the following steps:

[0013] Step S1, heating the carbon precursor to 600° C. to 1400° C. in an inert gas for carbonization treatment for 2 h to 8 h to obtain a carbonized material; the sphericity of the carbon precursor is 0.7 to 0.97;

[0014] Step S2, mixing the carbonized material and the pore-forming agent in a mass ratio of 1:(1-3) and placing them in a rotary kiln, heating them to T°C in an inert gas for activation treatment, 700≤T≤1000, the activation treatment time is 2h to 20h, and obtaining an activated material; the pore-forming agent includes at least one of potassium hydroxide, potassium carbonate, potassium bicarbonate or potassium chloride;

[0015] Step S3, washing the activated material with water and acid washing in sequence to obtain a porous carbon material; in the acid solution used for acid washing, the molar concentration of hydrogen ions is 0.1 mol / L to 3.0 mol / L.

[0016] The present application can regulate the mass proportion of potassium element in the porous carbon material by simultaneously controlling the type of pore-forming agent, the mass ratio of carbonized material and pore-forming agent, and the molar concentration of hydrogen ions in the acid solution used for pickling, and cooperate with the sphericity characteristics of the carbon precursor to obtain a porous carbon material with a suitable structure and elemental composition, which is beneficial for improving the latter's ion conductivity and inhibiting expansion performance when used in secondary batteries.

[0017] In a third aspect, the present application also provides a silicon-carbon material, including a porous carbon material and a silicon material located in the pores of the porous carbon material; the porous carbon material includes any one of the above-mentioned porous carbon materials or a porous carbon material obtained by the above-mentioned preparation method.

[0018] In a fourth aspect, the present application provides a secondary battery comprising a positive electrode, a negative electrode and an electrolyte; the negative electrode comprises a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector; the negative electrode material layer comprises the above-mentioned silicon-carbon material; based on the mass of the negative electrode material layer, the mass proportion of potassium element is C ppm, 1≤C≤100.

[0019] In some embodiments, the electrolyte includes fluoroethylene carbonate and ethylene carbonate; based on the mass of the electrolyte, the mass proportion of fluoroethylene carbonate is D1%, the mass proportion of ethylene carbonate is D2%, and 0.5≤D1 / D2≤2. The electrolyte includes fluoroethylene carbonate (FEC) and ethylene carbonate (EC), which can promote the formation of a flexible solid electrolyte interface film (SEI film). By regulating the mass proportion of the two to conform to the above relationship, the electrolyte can be coordinated with the silicon-carbon material of the present application, thereby further improving the first coulomb efficiency and expansion inhibition performance of the secondary battery.

[0020] In some embodiments, the electrolyte satisfies at least one of the following conditions:

[0021] (1) 0.5 ≤ D1 / D2 ≤ 2;

[0022] (2) 5 ≤ D1 ≤ 20;

[0023] (3) 5 ≤ D2 ≤ 20.

[0024] Based on the above scheme, it can promote the better cooperation of fluoroethylene carbonate and ethylene carbonate, and further improve the initial Coulomb efficiency and inhibit the swelling performance of the secondary battery.

[0025] In some embodiments, the electrolyte includes ethylsulfonyl fluoride; based on the mass of the electrolyte, the mass ratio of ethylsulfonyl fluoride is E%, and 0.1 ≤ E ≤ 2. Ethylsulfonyl fluoride can decompose into fluoride-containing anions. By controlling the mass ratio of ethylsulfonyl fluoride, the electrolyte contains fluoride-containing anions with appropriate concentration, which is beneficial to the combination of fluoride-containing anions with potassium elements in the silicon-carbon material to form a SEI film containing KF, improve the ion transport ability of the SEI film, and also help to improve the flexibility of the SEI film. Cooperating with the mass ratio of potassium elements can improve the structural stability of the silicon-carbon material, reduce the negative electrode swelling rate during the cycle, and thus achieve the improvement of the initial Coulomb efficiency and the inhibition of the swelling performance of the secondary battery.

[0026] In some embodiments, 0.5 ≤ C / E ≤ 100. When the mass ratio of ethylsulfonyl fluoride in the electrolyte and the mass ratio of potassium elements in the negative electrode material layer are regulated to satisfy the above relationship, the synergistic cooperation effect of the two can be improved, and the initial Coulomb efficiency and the inhibition of the swelling performance of the secondary battery can be further improved.

[0027] In the fifth aspect, the present application provides an electronic device including any one of the above secondary batteries. Specific Embodiments

[0028] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0029] During the research process of the silicon-carbon material, the inventors found that: the ionic conductivity of the silicon-carbon material is limited by the porosity of the porous carbon material, the dispersion uniformity of silicon particles, and the interfacial chemical bonding strength, while the swelling inhibition ability is closely related to the mechanical modulus of the porous carbon material and the silicon particle size distribution. In the existing silicon-carbon composite materials, due to the agglomeration of silicon particles and the disorder of the carbon layer structure, the local ionic transport impedance will increase, and at the same time, the anisotropic stress distribution of the porous carbon material is difficult to effectively restrain the silicon phase swelling. On this basis, the present application provides a porous carbon material. By designing the material morphology and composition, the structures of the porous carbon material and the silicon-carbon material are optimized, and a silicon-carbon material with both high ionic conductivity and swelling buffering ability is constructed.

[0030] In this application, the sphericity of the porous carbon material is a, where 0.7 ≤ a ≤ 0.97; the porous carbon material contains potassium element; based on the mass of the porous carbon material, the mass ratio of the potassium element is b ppm, where 1 ≤ b ≤ 2998. Doping the porous carbon material with potassium element in this application can improve the ionic conductivity of the porous carbon material and improve the initial Coulomb efficiency of the silicon-carbon material; however, the potassium element is likely to damage the structure of the porous carbon material, reducing the elastic modulus and compressive strength of the porous carbon material. By controlling the sphericity of the porous carbon material in this application, the isotropic property of the sphere can balance the stress during the expansion process, thereby increasing the elastic modulus of the porous carbon material and improving the expansion-inhibiting performance of the silicon-carbon material, and enabling the silicon-carbon material to withstand a greater compaction density, which is beneficial to improving the energy density and initial Coulomb efficiency of the secondary battery. Therefore, through the synergistic cooperation of the sphericity characteristic of the porous carbon material and the mass ratio of the potassium element, this application can take into account improving the ionic conductivity and expansion-inhibiting performance of the secondary battery.

[0031] In some embodiments, the porous carbon material satisfies: 50 ≤ a × b ≤ 2800; for example, the value of a × b can be 50, 330, 620, 660, 1130, 1480, 1780, 2030, 2420, 2690, 2800 or a value within the range composed of any two of them. When adjusting the mass ratio of the potassium element in the porous carbon material and its sphericity to satisfy the above relationship, the synergistic cooperation effect between the two can be further promoted, and the ionic conductivity and expansion-inhibiting performance of the secondary battery can be further improved.

[0032] In some embodiments, 0.7 ≤ a ≤ 0.97, preferably 0.75 ≤ a ≤ 0.95; exemplarily, a can be 0.7, 0.72, 0.76, 0.79, 0.80, 0.84, 0.87, 0.92, 0.93, 0.97 or a value within the range composed of any two of them. When adjusting the sphericity of the porous carbon material to conform to the above range, the stress generated by the expansion of the silicon material can be reduced, the elastic modulus and structural stability of the porous carbon material can be increased, which is beneficial to further improving the ionic conductivity and expansion-inhibiting performance of the secondary battery.

[0033] In some embodiments, 1 ≤ b ≤ 2998, preferably 10 ≤ b ≤ 997. Exemplarily, b can be 1, 7, 10, 60, 230, 300, 390, 560, 610, 740, 820, 950, 1000, 1170, 1330, 1570, 1870, 1910, 2180, 2410, 2640, 2980, 2998 or a value within the range composed of any two of them. Based on the above solution, the graphitization degree and elastic modulus of the porous carbon material can be balanced, and the ionic conductivity and expansion-inhibiting performance of the secondary battery can be further improved.

[0034] In some embodiments, in the XRD of the porous carbon material, the full width at half maximum of the diffraction peak of the (002) crystal plane is FWHM°, and 0.4 ≤ FWHM ≤ 1.5. In this application, by controlling the full width at half maximum FWMH° of the diffraction peak of the (002) crystal plane in the XRD pattern of the porous carbon material to satisfy 0.4 ≤ FWMH ≤ 1.5, the porous carbon material of this application can have an appropriate degree of graphitization. The crystal structure with ordered arrangement of carbon atoms is beneficial to improving the ionic conductivity of the secondary battery. In combination with the above potassium element mass ratio and sphericity characteristics, it can further improve the first Coulomb efficiency of the silicon-carbon material and take into account improving the ionic conductivity of the secondary battery and suppressing the swelling performance.

[0035] This application also provides a preparation method of the above porous carbon material, including the following steps:

[0036] Step S1: Heat the carbon precursor to 600°C to 1400°C in an inert gas for carbonization treatment for 2h to 8h to obtain a carbonized material; the sphericity of the carbon precursor is 0.7 to 0.97;

[0037] Step S2: Mix the carbonized material and the pore-forming agent in a mass ratio of 1:(1 - 3), put them into a rotary kiln, and heat them to T°C in an inert gas for activation treatment, 700 ≤ T ≤ 1000, and the activation treatment time is 2h to 20h to obtain an activated material; the pore-forming agent includes at least one of potassium hydroxide, potassium carbonate, potassium bicarbonate, or potassium chloride;

[0038] Step S3: Wash and acid-wash the activated material in sequence to obtain a porous carbon material; in the acid solution used for acid-washing, the molar concentration of hydrogen ions is 0.1mol / L to 3.0mol / L.

[0039] By controlling the cooperation of the type of pore-forming agent, the mass ratio of the carbonized material and the pore-forming agent, and the molar concentration of hydrogen ions in the acid solution used for acid-washing in this application, the mass ratio of potassium element in the porous carbon material can be regulated. In combination with the sphericity characteristics of the carbon precursor, a porous carbon material with a suitable sphericity structure and element composition can be obtained, which is beneficial to taking into account improving the ionic conductivity of the latter and suppressing the swelling performance when applied in secondary batteries.

[0040] The porous carbon material obtained by the preparation method of the present application satisfies that the sphericity of the porous carbon material is a, where 0.7 ≤ a ≤ 0.97; the porous carbon material contains potassium element; based on the mass of the porous carbon material, the mass ratio of the potassium element is b ppm, where 1 ≤ b ≤ 2998. Among them, during the activation treatment process, the potassium element has a catalytic graphitization effect on the porous carbon material, which can improve the order degree of the carbon skeleton, reduce the side reaction between silicon element and carbon element, and increase the reversible lithium intercalation amount of the silicon-carbon material. By controlling the mass ratio of the potassium element in the porous carbon material to satisfy 1 ≤ b ≤ 2998, the present application can improve the graphitization degree of the porous carbon material, making the full width at half maximum (FWHM) value of the (002) plane peak smaller and smaller, and the ionic conductivity gradually increasing, which is beneficial to reducing the formation of the surface SEI film, thereby reducing the consumption of the electrolyte, and finally improving the initial Coulomb efficiency of the porous carbon material and the silicon-carbon material. At the same time, by controlling the sphericity of the porous carbon material to satisfy 0.7 ≤ a ≤ 0.97, the present application can evenly disperse the internal stress of the material, improve the elastic modulus of the material, reduce the fragmentation of the silicon-carbon material, and improve the resistance to the expansion of silicon grains; and the above sphericity can balance the contact between the silicon-carbon material and the binder and the conductive agent, improving the initial Coulomb efficiency and the cycle expansion performance of the secondary battery.

[0041] Particularly, when regulating the mass ratio of the potassium element to satisfy 10 ≤ b ≤ 997, it can further reduce the over-porosity of the pore-forming agent to the porous carbon material, increase the thickness and uniformity of the carbon wall of the porous carbon material, improve the elastic modulus of the porous carbon material, and is beneficial to improving the expansion inhibition performance of the secondary battery. On this basis, when the sphericity satisfies 0.75 ≤ a ≤ 0.95, it can further balance the internal stress of the silicon-carbon material and the contact with the conductive agent and the binder, taking into account the improvement of the initial Coulomb efficiency and the cycle expansion performance of the secondary battery.

[0042] In some embodiments, the carbonization treatment includes: putting the carbon precursor into an oven, introducing an inert gas to remove air, then heating to 600 °C to 1400 °C, and holding for 2 h to 8 h to obtain a carbonized material. Then the carbonized material can be cooled to facilitate the subsequent process. The present application has no special requirements for the selection of the carbon precursor, as long as it can meet the requirements of the present application, for example, it can be selected from at least one of biomass precursors, sugar precursors, synthetic resin precursors or asphalt precursors. Among them, the sphericity of the carbon precursor is 0.7 to 0.97, for example, it can be 0.7, 0.72, 0.76, 0.78, 0.83, 0.85, 0.89, 0.91, 0.95, 0.97 or values within the range composed of any two of them. By regulating the sphericity of the carbon precursor, a porous carbon material with a suitable sphericity can be obtained.

[0043] In some embodiments, the activation treatment includes: mixing the carbonized material and the pore-forming agent and then putting them into a rotary furnace, introducing an inert gas, heating up to 700 °C to 1000 °C after removing air, and holding for 2 h to 20 h to obtain an activated material. Then, the activated material can be cooled down for subsequent processes. In this application, the pore-forming agent can be selected from at least one of potassium hydroxide, potassium carbonate, potassium bicarbonate, or potassium chloride, especially at least one of potassium hydroxide, potassium carbonate, or potassium bicarbonate, or a mixture composed of at least one of potassium hydroxide, potassium carbonate, or potassium bicarbonate and potassium chloride. During the activation process, the above-mentioned pore-forming agent can erode the carbonized material to achieve the purpose of pore formation. At the same time, the introduced potassium element can also improve the graphitization degree of the porous carbon material. However, local defects are easily introduced during the activation process, reducing the elastic modulus of the porous carbon material. By regulating the dosage ratio of the carbonized material and the pore-forming agent and cooperating with the sphericity characteristics, it is possible to take into account improving the graphitization degree and elastic modulus of the porous carbon material.

[0044] In some embodiments, the activated material is first washed with water and then washed with an acid solution with a hydrogen ion molar concentration of 0.1 mol / L to 3 mol / L, which can wash away the excess potassium element. Among them, the acid solution can be selected from hydrochloric acid, and the molar ratio of hydrochloric acid to the activator is 1:(1 - 1.3). By removing the excess potassium element and precisely regulating the mass percentage of the remaining potassium element in the porous carbon material, it is possible to promote the better improvement of the structure by the potassium element in the porous carbon material, increase the lithium ion diffusion rate, and reduce the lattice stress of deintercalation.

[0045] In this application, the prepared porous carbon material can be subjected to suction filtration and drying treatments for subsequent applications.

[0046] This application also provides a silicon-carbon material, which includes a porous carbon material and a silicon material located in the pores of the porous carbon material; the porous carbon material includes any one of the above-mentioned porous carbon materials or the porous carbon material obtained by the above-mentioned preparation method.

[0047] The silicon-carbon material of this application can be prepared by a method including the following steps:

[0048] Put the porous carbon material into a rotary furnace, introduce an inert atmosphere and heat up to 450 °C to 600 °C, then introduce a silicon-containing gas for chemical vapor deposition and hold for 2 h to 8 h. Finally, stop introducing the silicon-containing gas to obtain the silicon-carbon material, and then cool it to room temperature.

[0049] In this application, there are no special requirements for the inert gas involved in the preparation, as long as it can meet the purpose of this application. For example, the inert gas can be at least one of nitrogen, argon, or helium.

[0050] This application also provides a secondary battery, which includes a positive electrode, a negative electrode, and an electrolyte.

[0051] Secondary battery

[0052] The secondary battery of the present application is not particularly limited. It can be classified into various categories according to the type of electron transport material. For example, when the electron transport material is lithium (Li, including ions), the secondary battery is a lithium-ion battery; when the electron transport material is sodium (Na, including ions), the secondary battery is a sodium-ion battery. Hereinafter, the present application will be described by taking the secondary battery as an example in combination with the embodiments of the present application. It should be noted that in the specific embodiments of the present application, the secondary battery is used as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the secondary battery.

[0053] According to an embodiment of the present application, the secondary battery may include an electrode assembly and an electrolyte. The electrode assembly may include a packaging material and an electrode assembly disposed inside the packaging material, and the electrolyte may be filled in the internal space formed by the packaging material. The packaging material can protect the electrode assembly from external impacts and prevent the electrolyte from leaking to the outside. According to the shape of the packaging material, the electrode assembly can be divided into a prismatic shape, a cylindrical shape or a soft package type.

[0054] The electrode assembly includes a positive electrode, a negative electrode and a separator, as well as other components known in the art in the secondary battery. The present application does not limit the above other components. Among them, the separator can be interposed between the positive electrode and the negative electrode.

[0055] The present application does not particularly limit the manufacturing method of the secondary battery. For example, it may include the following steps: stacking the positive electrode, the separator and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain the electrode assembly, placing the electrode assembly into the packaging material, injecting the electrolyte into the packaging material and sealing it to obtain the secondary battery.

[0056] Positive electrode

[0057] In the present application, the positive electrode is not particularly limited as long as the purpose of the present 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 above "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 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 positive electrode current collector surface, or can be a partial area of the positive electrode current collector surface. The present application has no particular limitation as long as the purpose of the present application can be achieved.

[0058] There are no particular limitations on the type, size, and shape of the positive electrode current collector in this application, 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, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or a material obtained by surface-treating the surface of aluminum or stainless steel with carbon, nickel, titanium, silver, etc. In this application, the positive electrode current collector can also contain non-metallic elements. For example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon, and sulfur.

[0059] The positive electrode current collector can have an appropriate thickness as needed. Although there are no particular limitations, the positive electrode current collector can have a thickness in the range of 1 μm to 500 μm, or can have a thickness in the range of 1 μm to 300 μm, or can have a thickness in the range of 1 μm to 100 μm, or can have a thickness in the range of 1 μm to 50 μm, or can have a thickness in the range of 1 μm to 20 μm.

[0060] Unless otherwise specifically stated, the terms thickness (or height), width, and length used in this application refer to the average value and can be measured by a measuring instrument that can separately measure the thickness (or height), width, and length and according to the methods in the art.

[0061] The positive electrode current collector can form fine irregularities on its surface, thereby further enhancing the adhesion to the positive electrode material layer. For example, the form of the positive electrode current collector can be one or more selected from a film, sheet, foil, net, porous body, foam, and non-woven fabric.

[0062] In this application, the positive electrode material layer includes a positive electrode active material. There are no particular limitations on the type of the positive electrode active material in this application, as long as the object of this application can be achieved. For example, the positive electrode active material can contain lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2 (NCM 955 ), NCM 811 , NCM 622 , NCM 523 , NCM 111 ), lithium nickel cobalt aluminate, 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 manganate, spinel-type lithium nickel manganate, and lithium titanate. In this application, the positive electrode active material can also contain non-metallic elements. For example, the non-metallic elements include at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In this application, there are no particular limitations on the thicknesses of the positive electrode current collector and the positive electrode material layer, as long as the object of this application can be achieved.

[0063] In some embodiments, the positive electrode material layer may further include a positive electrode binder. The present application does not particularly limit the type of the positive electrode binder, as long as the purpose of the present application can be achieved. 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), polyvinyl ester, polyvinyl alcohol, polyacrylic acid, or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene or polypropylene.

[0064] In some embodiments, the positive electrode material layer may further include a conductive agent. The present application does not particularly limit the type of the conductive agent in the positive electrode material layer, as long as the purpose of the present application can be achieved. In some exemplary embodiments, the conductive agent includes carbon-based materials, such as natural graphite or artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, or carbon fiber; conductive polymers, such as polyphenylene derivatives; conductive metal oxides, such as zinc oxide, titanium oxide, etc.; conductive whiskers, such as potassium titanate, etc.; or a mixture formed by any combination of these substances.

[0065] In the present application, the positive electrode material layer may be formed by coating a positive electrode slurry on at least one surface of a positive electrode current collector and drying, and calendering may be performed after drying as needed. The positive electrode slurry contains the above-mentioned positive electrode active material, positive electrode binder, and conductive agent. In addition, the positive electrode slurry may further contain a solvent. The present application does not particularly limit the type of the solvent, as long as the purpose of the present application can be achieved. For example, N-methyl-2-pyrrolidone may be used as the solvent.

[0066] The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and positive electrode binder in the positive electrode material layer. Those skilled in the art can select according to actual needs as long as the purpose of the present application can be achieved, and these mass ratios can apply known mass ratios.

[0067] Negative electrode

[0068] The present application does not particularly limit the negative electrode, as long as the purpose of the present application can be achieved. For example, the negative electrode includes a negative electrode current collector and a negative electrode material layer provided on at least one surface of the negative electrode current collector. In the present application, the negative electrode material layer may be provided on one surface in the thickness direction of the negative electrode current collector, or may be provided on two surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here may be the entire area of the negative electrode current collector or a partial area of the negative electrode current collector. The present application does not particularly limit it, as long as the purpose of the present application can be achieved.

[0069] The present application has no particular limitation on the type, size, and shape of the negative electrode current collector, as long as it does not cause chemical changes in the battery cell and has electrical conductivity. For example, the negative electrode current collector can be made of, for example, stainless steel, copper, nickel, titanium, calcined carbon, or a substance obtained by surface-treating the surface of copper or stainless steel with carbon, nickel, titanium, silver, etc.

[0070] The negative electrode current collector can have an appropriate thickness as needed. Although there is no particular limitation, the negative electrode current collector can have a thickness in the range of 1 μm to 500 μm, or can have a thickness in the range of 1 μm to 300 μm, or can have a thickness in the range of 1 μm to 100 μm, or can have a thickness in the range of 1 μm to 50 μm, or can have a thickness in the range of 1 μm to 20 μm, or can have a thickness in the range of 5 μm to 10 μm.

[0071] The negative electrode current collector can form fine irregularities on its surface, thereby further enhancing the adhesion to the negative electrode material layer. For example, the form of the negative electrode current collector can be one or more selected from films, sheets, foils, meshes, porous bodies, foams, and non-woven fabrics.

[0072] The negative electrode material layer of the present application includes a negative electrode active material, and the negative electrode active material includes the above-mentioned silicon-carbon material. Based on the mass of the negative electrode material layer, the mass ratio of potassium element is C ppm, where 1 ≤ C ≤ 100. For example, C can be 1, 8, 12, 24, 41, 49, 66, 77, 86, 95, 100, or a value within the range formed by any two of them. When the mass ratio of potassium element in the negative electrode material layer is adjusted to meet the above range, the ion conductivity of the secondary battery can be further improved and the swelling performance can be suppressed.

[0073] In some embodiments, the negative electrode active material can further include other materials, such as, but not limited to, carbon materials such as graphite (artificial graphite, natural graphite, or graphitized carbon fiber) or amorphous carbon; metals that can be alloyed with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys, or alloys formed by them and lithium; SiO β (0 < β ≤ 2), SnO, SnO2, vanadium oxides, lithium vanadium oxides, etc., metal oxides that can be doped or de-doped with lithium, or alloys formed by them and lithium; or composites containing the above metals and carbon materials, such as Si-C composites or Sn-C composites; or lithium titanate with a spinel structure, lithiated TiO2-Li4Ti5O 12, and any one of them or a mixture of two or more of them can be used. Specifically, carbon materials such as low-crystalline carbon and high-crystalline carbon can be used. Representative low-crystalline carbon is soft carbon and hard carbon. Examples of high-crystalline carbon can be amorphous, plate-like, flaky, spherical or fibrous natural graphite or artificial graphite, primary graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, carbon microspheres (mesophase carbon microspheres), mesophase pitch, and high-temperature calcined carbon such as petroleum and coal-based coke (coke derived from petroleum or coal tar pitch), etc.

[0074] The negative electrode material layer in this application further includes a negative electrode binder. There is no particular limitation on the type of the negative electrode binder in this application, as long as the purpose of this application can be achieved. For example, the negative electrode binder can include, but is not limited to, at least one selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol, styrene-butadiene rubber (SBR), polyethylene oxide, carboxymethyl cellulose (CMC), hydroxypropyl cellulose, cellulose acetate, diacetyl cellulose, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullulan, polymethyl methacrylate, polybutyl acrylate, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyarylate, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, acrylated styrene-butadiene rubber, epoxy resin or nylon.

[0075] There is no particular limitation on the type of the conductive agent in the negative electrode material layer in this application, as long as the purpose of this application can be achieved. In some exemplary embodiments, the conductive agent includes carbon-based materials such as graphite like natural graphite or artificial graphite, carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, or carbon fiber; 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 a mixture formed by any combination of these substances.

[0076] There is no particular limitation on the mass ratio of the negative electrode active material, the negative electrode conductive agent, and the negative electrode binder in the negative electrode material layer in this application. Those skilled in the art can select according to actual needs as long as the purpose of this application can be achieved, and these mass ratios can apply known mass ratios.

[0077] In the present application, the negative electrode material layer can be formed by coating a negative electrode paste on at least one surface of a negative electrode current collector and drying, and calendering can be performed after drying as needed. The negative electrode paste contains the above-mentioned negative electrode active material and a negative electrode binder, and can further contain a conductive agent as needed. In addition, the negative electrode paste can also contain a solvent. The present application does not particularly limit the type of the solvent, as long as the object of the present application can be achieved. For example, deionized water can be used as the solvent.

[0078] Separator

[0079] The separator of the present application is a film for preventing short circuit between the positive electrode and the negative electrode while allowing electron transport substances to pass through. The present application does not particularly limit the separator, as long as the object of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (such as polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, and aramid; the type of the separator can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film, and a spun film.

[0080] According to some embodiments of the present application, the separator can include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric, a film, or a composite film having a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.

[0081] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer can be a polymer layer, 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. The present application does not particularly limit the inorganic particles. For example, it can include at least one of alumina, silica, magnesia, 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. The present application does not particularly limit the binder. For example, it can be at least one of the above-mentioned positive electrode binder and negative electrode binder. The polymer layer contains a polymer. The present application does not particularly limit the polymer. For example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene). In the present application, the thickness of the separator is not particularly limited, as long as the object of the present application can be achieved. For example, the thickness of the separator can be 5 μm to 500 μm.

[0082] Electrolyte

[0083] In the present application, the electrolyte refers to a medium that causes the movement of electron-transporting substances to smoothly carry out the electrochemical reactions of the positive and negative electrodes. The electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a gel-type polymer electrolyte, a molten inorganic electrolyte, etc. that are commonly used, but is not limited thereto. A solid electrolyte such as a gel-type polymer electrolyte can also be used to replace the electrolyte. A battery using a solid electrolyte is usually called a solid-state battery or an all-solid-state battery. A liquid electrolyte (electrolyte) generally contains a non-aqueous solvent and a lithium salt.

[0084] In some embodiments, the electrolyte includes fluoroethylene carbonate and ethylene carbonate; based on the mass of the electrolyte, the mass fraction of fluoroethylene carbonate is D1%, and the mass fraction of ethylene carbonate is D2%, and 0.5 ≤ D1 / D2 ≤ 2. In the present application, the electrolyte contains fluoroethylene carbonate (FEC) and ethylene carbonate (EC), and the proportional relationship between the mass fractions of FEC and EC is controlled. By synergistically using the high dielectric constant of EC and with the induction of an appropriate amount of potassium element in the silicon-carbon material, EC can form a solid electrolyte interface film (SEI film) with high ionic conductivity on the surface of the silicon-carbon material. However, a large amount of inorganic components in the SEI film may affect the elasticity of the SEL film, which is not conducive to the SEI film adapting to the volume change of the silicon-carbon material. Making the electrolyte include FEC can further improve the elasticity of the SEL film. By controlling the proportional relationship between the mass fractions of FEC and EC, it helps the electrolyte form an SEI film with both high ionic conductivity and elasticity on the surface of the silicon-carbon material containing an appropriate amount of potassium element, thereby further improving the first Coulombic efficiency and suppressing the swelling performance of the secondary battery.

[0085] In some embodiments, 0.5 ≤ D1 / D2 ≤ 2; preferably 0.75 ≤ D1 / D2 ≤ 1.8; exemplarily, the value of D1 / D2 can be 0.5, 0.7, 0.9, 1.1, 1.3, 1.4, 1.6, 1.8, 1.9, 2 or a value within the range composed of any two of them. When the above relationship is satisfied, it can promote the better cooperation of fluoroethylene carbonate and ethylene carbonate, and further improve the first Coulombic efficiency and suppress the swelling performance of the secondary battery.

[0086] In some embodiments, 5 ≤ D1 ≤ 20; for example, the value of D1 can be 5, 8, 9, 10, 13, 15, 16, 17, 20 or a value within the range composed of any two of them. Adjusting the mass fraction of fluoroethylene carbonate to meet the above range can further improve the first Coulombic efficiency and suppress the swelling performance of the secondary battery.

[0087] In some embodiments, 5 ≤ D2 ≤ 20; for example, the value of D2 can be 5, 8, 9, 10, 13, 15, 16, 17, 20, or a value within the range composed of any two of them. Controlling the mass percentage of ethylene carbonate to meet the above range can further improve the first Coulombic efficiency of the secondary battery and inhibit the swelling performance.

[0088] In some embodiments, the electrolyte includes ethylsulfonyl fluoride; based on the mass of the electrolyte, the mass percentage of ethylsulfonyl fluoride is E%, and 0.1 ≤ E ≤ 2. Exemplarily, E can be 0.1, 0.3, 0.5, 0.6, 0.8, 1.2, 1.3, 1.6, 1.7, 1.8, 2, or a value within the range composed of any two of them. Ethylsulfonyl fluoride (EtSO2F) can decompose to produce fluoride anions. Making the electrolyte contain fluoride anions with appropriate concentration is beneficial for the fluoride anions to combine with potassium elements in the carbon material to form a SEI film containing KF, improving the ion transport ability of the SEI film, and also helping to improve the flexibility of the SEI film. Cooperating with potassium elements can improve the structural stability of the silicon-carbon material, reduce the negative electrode swelling rate during the cycling process, and thus achieve the improvement of the first Coulombic efficiency of the secondary battery and the inhibition of the swelling performance.

[0089] In some embodiments, 0.5 ≤ C / E ≤ 100. Exemplarily, the value of C / E can be 0.5, 1, 4, 9, 20, 29, 42, 55, 67, 75, 84, 95, 100, or a value within the range composed of any two of them. When controlling the mass percentage of ethylsulfonyl fluoride in the electrolyte and the mass percentage of potassium elements in the negative electrode material layer to meet the above relationship, the synergistic cooperation effect of the two can be improved, and the first Coulombic efficiency of the secondary battery and the inhibition of the swelling performance can be further improved.

[0090] According to some embodiments of the present application, the lithium salt can include but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide {LiN(CF3SO2)2, LiTFSI}, lithium bis(fluorosulfonyl)imide {Li(N(SO2F)2), LiFSI}, lithium bis(oxalato)borate {LiB(C2O4)2, LiBOB}, lithium difluoro(oxalato)borate {LiBF2(C2O4), LiDFOB}, LiNO3, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or at least one of lithium difluoroborate. The present application does not limit the content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved.

[0091] The present application has no particular limitation on the non-aqueous solvent. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. The above-mentioned carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. The above-mentioned linear 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 ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonates may include, but are not limited to, at least one of propylene carbonate (PC), butylene carbonate or ethylene ethylene carbonate. The above-mentioned fluorinated carbonate 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 trifluoromethyl ethylene carbonate. The above-mentioned carboxylate 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, decanolide, valerolactone or caprolactone. The above-mentioned ether compounds may include, but are not limited to, at least one of 1,3-dioxolane (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.

[0092] Electronic device

[0093] The present application provides an electronic device including the above-mentioned secondary battery. The electronic device of the present application is not particularly limited and may be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to, laptop computers, pen input computers, mobile computers, e-book players, mobile phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, portable cleaners, portable CD players, minidiscs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium ion capacitors.

[0094] Measurement method

[0095] The physical properties mentioned in this application can be measured by the following methods, and the physical properties in the following examples and comparative examples are measured by the following methods.

[0096] XRD test:

[0097] Use an XRD X-ray powder diffractometer (model: BRUKER D8 Advance), with a Cu target for the test: Take the porous carbon material as the sample to be tested. First, sieve the sample to be tested with a 200-mesh sieve. Then, take the powder under the sieve and put it into the sample cell. Then, flatten the surface and clean the excess powder around. Put the prepared sample to be tested into the XRD X-ray powder diffractometer to test the sample to be tested and collect the XRD pattern; then analyze the collected XRD pattern to obtain the full width at half maximum of the diffraction peak of the (002) crystal plane.

[0098] Ionic conductivity (Dmt) test

[0099] First, use the silicon-carbon material of the example or comparative example as the negative electrode active material to prepare a suspension containing the negative electrode active material, a conductive agent (carbon nanotubes (CNT)), and a binder (poly(methyl acrylate)), where the mass ratio of the negative electrode active material, the conductive agent, and the binder is 8:1:1. Then, coat the suspension on a metal current collector copper foil to form a single-layer particle electrode (SLPE). After coating, dry the electrode by infrared radiation.

[0100] Then, select a 12-μm porous polyethylene film as the separator, assemble the prepared SLPE with a lithium metal counter electrode and the separator into a button cell, and add the electrolyte of Example 1-1 to immerse the SLPE, the lithium metal counter electrode, and the separator in the electrolyte.

[0101] Finally, perform an alternating current impedance spectroscopy (EIS) test on the button cell after injection. Separate the solid diffusion overpotential (ηs) through the intersection of the linear extrapolation and the potential curve, and finally calculate the ionic conductivity (Dmt).

[0102] Potassium element mass fraction test

[0103] Test for the mass fraction of potassium element in the porous carbon material:

[0104] Take 1.25 g of porous carbon material or negative electrode material powder and add it to 50 ml of deionized water. Stir at 80 °C for 4 h and then filter to obtain the filtrate. Use a PXBJ-287L portable ion meter for the test. Put the calibrated potassium ion electrode into the filtrate and read the molar concentration reading of potassium ions in the filtrate to calculate the mass fraction of potassium element relative to the porous carbon material or the negative electrode material layer.

[0105] First Coulombic Efficiency Test

[0106] Electrode Preparation: The silicon-carbon material of the example or comparative example was used as the negative electrode active material. The negative electrode active material, conductive agent (carbon nanotubes (CNT)), binder (polymethyl acrylate), and thickener (sodium carboxymethyl cellulose (CMC)) were thoroughly stirred and mixed in deionized water as the solvent according to a weight ratio of 95.7:1.5:1.8:1 to form a uniform negative electrode slurry. The negative electrode slurry was evenly coated on the negative electrode current collector copper foil, dried, and cold-pressed to form a negative electrode active material layer. After cutting and welding the tab, the negative electrode plate was obtained.

[0107] Button Cell Assembly: Using metallic lithium as the counter electrode, a metallic lithium sheet with a diameter of 18 mm and a thickness of 0.6 mm, a separator (a 12-μm porous polyethylene film), and the negative electrode plates in each example and comparative example (after being cut into a diameter of 18 mm) were assembled and stacked in sequence, and the corresponding electrolyte of the example or comparative example was added. Then, they were placed in a positive and negative button stainless steel shell for encapsulation to obtain a button cell.

[0108] At 25 °C, after the button cell was left standing for 4 h, it was discharged at a constant current of 0.02C to 5 mV, left standing for 5 min, and then charged at a constant current of 0.02C to 2.0 V; the charging capacity and discharging capacity of the first cycle were recorded. The first-cycle Coulombic efficiency = charging capacity of the first cycle / discharging capacity of the first cycle.

[0109] Sphericity Test

[0110] The particle samples of the negative electrode active material were observed using a ZEISS-SEM (sigma-02-33) scanning electron microscope. Twenty particles of the porous carbon material were randomly selected, and their perimeter equivalent diameter and area equivalent diameter were calculated. The sphericity of each porous carbon material = perimeter equivalent diameter / area equivalent diameter. The arithmetic mean of the sphericities of the 20 porous carbon materials was calculated as the sphericity of the porous carbon material.

[0111] Cyclic Swelling Performance Test

[0112] The lithium-ion battery was left standing in a constant temperature oven at 25 °C ± 1 °C for 30 minutes, charged at a constant current of 0.5C to 4.35 V, then charged at a constant voltage of 4.35 V to 0.025C, left standing for 5 minutes, and then discharged at 0.5C to 3.0 V. This was one charge-discharge cycle process. The initial thickness H0 of the lithium-ion battery was recorded. After that, it was cycled 600 times according to the above cycle process. The thickness H1 after the 600th cycle was recorded.

[0113] Cyclic Swelling Rate = (H1 - H0) / H0 × 100%.

[0114] Taking a lithium-ion battery as an example, the solution of the present application will be described in conjunction with the following specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments are all from ordinary commercially available products, and the devices or equipment used are all purchased from conventional market sales channels.

[0115] Example 1-1

[0116] Preparation method of silicon-carbon material:

[0117] Step S1: Heat the carbon precursor resin with a sphericity of 0.95 to 1100 °C in argon for carbonization treatment for 5 h to obtain a carbonized material.

[0118] Step S2: Mix the carbonized material with the pore-forming agent potassium carbonate in a mass ratio of 1:0.4, put it into a rotary kiln, heat it to 850 °C in argon for activation treatment for 6 h to obtain an activated material.

[0119] Step S3: Wash the activated material with water and then pickle it with hydrochloric acid to obtain a porous carbon material; the molar concentration of hydrogen ions in the hydrochloric acid is 0.5 mol / L, and the molar ratio of hydrochloric acid to potassium carbonate is 1:1.

[0120] Step S4: Put the porous carbon material into a rotary kiln, introduce argon and heat it to 550 °C, then introduce a silicon-containing gas for chemical vapor deposition, keep it warm for 4 h, and finally stop introducing the silicon-containing gas to obtain a silicon-carbon material, and then cool it to room temperature.

[0121] Preparation of the negative electrode:

[0122] Mix the silicon-carbon material and artificial graphite in a mass ratio of 10:90 to obtain the negative electrode active material. Mix the negative electrode active material (95 wt%), conductive carbon black (0.5 wt%), polymethyl acrylate (3.5%), and carboxymethyl cellulose (1%), then add deionized water and stir evenly to prepare a negative electrode slurry. Coat the negative electrode slurry evenly on one surface of the copper foil, and repeat the above steps on the other surface of the copper foil after drying to obtain a negative electrode plate with a double-sided coated negative electrode material layer. Cut the coated copper foil into a specified size after drying and pressing, and weld the tab to obtain the negative electrode.

[0123] Preparation of the positive electrode:

[0124] Mix lithium cobaltate (97 wt%), conductive carbon black (1.5 wt%), and polyvinylidene fluoride (1.5 wt%) in N-methylpyrrolidone to prepare a positive electrode slurry. Coat the positive electrode slurry evenly on one surface of the aluminum foil, and repeat the coating step on the other surface of the aluminum foil after drying to obtain a positive electrode plate with a double-sided coated positive electrode material layer. Cut the coated aluminum foil into a specified size after drying and pressing, and weld the tab to obtain the positive electrode.

[0125] Preparation of separator: A polyethylene (PE) microporous membrane with a thickness of 7 μm was selected as the separator.

[0126] Preparation of electrolyte:

[0127] In a glove box under an argon atmosphere with a water content of less than 10 ppm, ethyl propionate (EP) and propyl propionate (PP) (mass ratio 3:1) were mixed to obtain a basic solvent. Then, ethylene carbonate, fluoroethylene carbonate, 1,3 - propane sultone, and lithium hexafluorophosphate were added to the above - mentioned basic solvent and mixed evenly to obtain the electrolyte. Based on the mass of the electrolyte, the mass fraction of lithium hexafluorophosphate was 12.5%, the mass fraction of ethylene carbonate was 12%, the mass fraction of fluoroethylene carbonate was 9%, and the mass fraction of 1,3 - propane sultone was 2%. The balance was the basic solvent.

[0128] Battery fabrication:

[0129] The positive electrode, separator, and negative electrode were stacked in sequence, with the separator placed between the positive electrode and the negative electrode to play an insulating role, and then wound to obtain an electrode assembly. The electrode assembly was placed in an outer packaging aluminum - plastic film, baked, and then the above - mentioned electrolyte was injected. After processes such as vacuum packaging, standing, formation, shaping, and capacity testing, a lithium - ion battery was obtained.

[0130] Examples 1 - 2 to Examples 1 - 10, Comparative Examples 1 - 1 to Comparative Examples 1 - 3

[0131] The difference from Example 1 - 1 was only that, according to Table 1, the sphericity, mass fraction of potassium element, and full - width at half - maximum of the (002) crystal plane diffraction peak of the porous carbon material were adjusted. The specific adjustment parameters and performance test results are shown in Table 1 below. Among them, for each example or comparative example in Table 1, the sphericity of the porous carbon material was increased by selecting a carbon precursor with a higher sphericity, and the mass fraction of potassium element in the porous carbon material was increased by reducing the mass ratio of the carbonized material to the pore - forming agent, thereby reducing the full - width at half - maximum of the (002) crystal plane diffraction peak. Potassium carbonate was not added in Comparative Example 1 - 2 in step S2.

[0132] Table 1

[0133]

[0134]

[0135] As can be seen from Table 1, in this application, the mass content of potassium element is controlled to satisfy 1 ≤ b ≤ 2998, and the sphericity of the porous carbon material is satisfied with 0.7 ≤ a ≤ 0.97, which can improve the ionic conductivity of the porous carbon material and take into account the improvement of the first Coulomb efficiency and cycle expansion performance of the secondary battery. In particular, when the relationship of 50 ≤ a × b ≤ 2800 is satisfied, the first Coulomb efficiency and cycle expansion performance of the secondary battery can be further improved. Especially, when the sphericity is controlled to 0.75 ≤ a ≤ 0.95 in this application, the stress and contact degree inside the anode material can be balanced, and the first Coulomb efficiency and cycle expansion performance of the secondary battery can be taken into account. Preferably, controlling the mass ratio of potassium element to satisfy 10 ≤ b ≤ 997 can further improve the ionic conductivity of the porous carbon material, as well as the first Coulomb efficiency and cycle expansion performance of the secondary battery.

[0136] Examples 2-1 to 2-9

[0137] The difference compared with Example 1-1 is only that the mass ratio of potassium element and the mass ratios of fluoroethylene carbonate (FEC), ethylene carbonate (EC) and ethylsulfonyl fluoride in the electrolyte are adjusted according to Table 2. The specific adjustment parameters and performance test results are shown in Table 2 below. At the same time, the content of the base solvent is adjusted adaptively, where the mass ratio of EP and PP remains unchanged.

[0138] Table 2

[0139]

[0140]

[0141] As can be seen from Table 2, in this application, the electrolyte is controlled to include fluoroethylene carbonate and ethylene carbonate, and the mass ratio of the two satisfies 0.5 ≤ D1 / D2 ≤ 2, which can make the electrolyte cooperate with the silicon-carbon material of this application to further improve the first Coulomb efficiency and swelling inhibition performance of the secondary battery.

[0142] In particular, when the regulated electrolyte includes ethylsulfonyl fluoride and its mass ratio E% satisfies 0.1 ≤ E ≤ 2, the first Coulomb efficiency and swelling inhibition performance of the secondary battery can be further improved. Especially, when the mass ratio with potassium element C% satisfies 0.5 ≤ C / E ≤ 100, the first Coulomb efficiency and swelling inhibition performance of the secondary battery can be further improved.

[0143] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, improvements, etc. made within the principle of this application shall be included in the protection scope of this application.

Claims

1. A porous carbon material, characterized in that: The sphericity of the porous carbon material is a, 0.7≤a≤0.97; The porous carbon material includes potassium element; based on the mass of the porous carbon material, the mass proportion of the potassium element is bppm, 1≤b≤2998.

2. The porous carbon material according to claim 1, characterized in that The porous carbon material satisfies at least one of the following conditions: (1)50≤a×b≤2800; (2)0.75≤a≤0.95； (3)10≤b≤997。 3. The porous carbon material according to claim 1 or 2, characterized in that: In the XRD of the porous carbon material, the half maximum width of the (002) crystal plane diffraction peak is FWHM°, and 0.4≤FWHM≤1.

5.

4. A method for preparing a porous carbon material according to any one of claims 1 to 3, characterized in that: The following steps are involved: Step S1, heating the carbon precursor to 600° C. to 1400° C. in an inert gas for carbonization treatment, wherein the carbonization treatment time is 2 h to 8 h, to obtain a carbonized material; the sphericity of the carbon precursor is 0.7 to 0.97; Step S2, mixing the carbonized material and the pore-forming agent in a mass ratio of 1:(1-3) and placing them in a rotary kiln, heating them to T°C in an inert gas for activation treatment, 700≤T≤1000, the activation treatment time is 2h to 20h, and obtaining an activated material; the pore-forming agent includes at least one of potassium hydroxide, potassium carbonate, potassium bicarbonate or potassium chloride; Step S3, washing the activated material with water and acid washing in sequence to obtain the porous carbon material; the molar concentration of hydrogen ions in the acid solution used for acid washing is 0.1 mol / L to 3.0 mol / L.

5. A silicon-carbon material, characterized in that: It comprises a porous carbon material and a silicon material located in the pores of the porous carbon material; the porous carbon material comprises the porous carbon material according to any one of claims 1 to 3 or the porous carbon material obtained by the preparation method according to claim 4.

6. A secondary battery, characterized in that: It 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 disposed on at least one surface of the negative electrode current collector; the negative electrode material layer comprises the silicon-carbon material according to claim 5; Based on the mass of the negative electrode material layer, the mass proportion of the potassium element is C ppm, 1≤C≤100.

7. The secondary battery according to claim 6, characterized in that: The electrolyte includes fluoroethylene carbonate and ethylene carbonate; Based on the mass of the electrolyte, the mass proportion of the fluoroethylene carbonate is D1%, the mass proportion of the ethylene carbonate is D2%, and 0.5≤D1 / D2≤2.

8. The secondary battery according to claim 7, characterized in that: The electrolyte satisfies at least one of the following conditions: (1) 0.75 ≤ D1 / D2 ≤ 1.8; (2)5≤D1≤20； (3)5≤D2≤20。 9. The secondary battery according to any one of claims 6 to 8, characterized in that: The electrolyte includes ethylsulfonyl fluoride; Based on the mass of the electrolyte, the mass proportion of the ethylsulfonyl fluoride is E%, and 0.1≤E≤2.

10. The secondary battery according to claim 9, characterized in that: 0.5≤C / E≤100.

11. An electronic device, characterized in that: A secondary battery comprising the secondary battery according to any one of claims 6 to 10.

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