WO2024197842A1 - 二次电池及用电装置 - Google Patents

二次电池及用电装置 Download PDF

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Publication number
WO2024197842A1
WO2024197842A1 PCT/CN2023/085564 CN2023085564W WO2024197842A1 WO 2024197842 A1 WO2024197842 A1 WO 2024197842A1 CN 2023085564 W CN2023085564 W CN 2023085564W WO 2024197842 A1 WO2024197842 A1 WO 2024197842A1
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Prior art keywords
silicon
composite material
carbon composite
secondary battery
carbon
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PCT/CN2023/085564
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English (en)
French (fr)
Inventor
刘晶
徐宁波
陈培培
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to PCT/CN2023/085564 priority Critical patent/WO2024197842A1/zh
Priority to CN202380018336.8A priority patent/CN118591903B/zh
Priority to EP23929427.5A priority patent/EP4611061A4/en
Publication of WO2024197842A1 publication Critical patent/WO2024197842A1/zh
Priority to US19/210,885 priority patent/US20250279411A1/en
Anticipated expiration legal-status Critical
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H01M4/386—Silicon or alloys based on silicon
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0048—Molten electrolytes used at high temperature
    • H01M2300/0051—Carbonates
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present application relates to the technical field of secondary batteries, and in particular to a secondary battery and an electrical device.
  • secondary batteries have been widely used in energy storage power systems such as hydropower, thermal, wind and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.
  • Electrode active materials with high gram capacity often have poor cycle performance and kinetic performance. How to improve the battery energy density while taking into account excellent cycle performance and kinetic performance through the mutual coordination of various battery components is a technical problem that needs to be urgently solved in this field.
  • This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery.
  • the volume effect of the active material during the charge and discharge process is suppressed, the interface stability is improved, the internal resistance of the battery is reduced, and the cycle capacity retention rate and rate performance of the battery are improved.
  • a first aspect of the present application provides a secondary battery, comprising: a negative electrode plate and an electrolyte; the negative electrode plate comprises a silicon-carbon composite material having a three-dimensional network cross-linked pore structure, and the electrolyte contains dimethyl carbonate.
  • the silicon-carbon composite material with a three-dimensional network cross-linked pore structure has a stable porous skeleton and good mechanical strength. It can effectively reduce the volume change of silicon before and after charging and discharging while loading a high silicon content.
  • the dimethyl carbonate in the electrolyte can increase the reflux rate of the electrolyte during the charging and discharging process, promote the transmission of ions at the active material/electrolyte interface, and effectively reduce the battery polarization impedance, thereby improving the battery's cycle performance and rate performance.
  • the pore volume per unit mass of the silicon-carbon composite material is Vm, in units of cm 3 /g; based on the total mass of the electrolyte, the mass proportion of dimethyl carbonate in the electrolyte is EL g/g, and the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass proportion EL of dimethyl carbonate in the electrolyte is 0.5 to 20, preferably 2 to 13.
  • the added amount of dimethyl carbonate and the pore volume Vm of the silicon-carbon composite material can cooperate with each other, thereby improving the battery's cycle capacity retention rate and enhancing the battery's rate performance.
  • the pore volume Vm of the silicon-carbon composite material is 0.01 to 0.3, and can be optionally 0.04 to 0.15 cm 3 /g.
  • the pore volume Vm per unit mass of the silicon-carbon composite material is within the above range, small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material and cooperate with it, thereby reducing the internal resistance of the battery and improving the cycle performance of the battery.
  • the mass proportion of the dimethyl carbonate in the electrolyte is EL g/g
  • the mass proportion of the dimethyl carbonate in the electrolyte and the specific surface area of the silicon-carbon composite material are SSA
  • EL:SSA is 0.01 to 0.5
  • dimethyl carbonate can effectively enter the pore structure of the silicon-carbon composite material and fully contact with the silicon-carbon composite material, thereby increasing the migration rate of ions at the electrode/electrolyte interface, reducing the internal resistance of the battery, and improving the cycle performance and high-rate capacity of the battery.
  • the specific surface area SSA of the silicon-carbon composite material is 2 to 10 m 2 /g; optionally 3 to 7 m 2 /g.
  • the specific surface area SSA of the silicon-carbon composite material satisfies the above range, the specific surface area of the silicon-carbon composite material is large, and the secondary battery has good kinetic performance and high rate performance.
  • the mass proportion of dimethyl carbonate in the electrolyte is EL g/g
  • the total pore volume of pores with a pore diameter of less than or equal to 100 nm in the silicon-carbon composite material is V1 cm 3 /g
  • the dimethyl carbonate is The ratio EL:V1 between the mass proportion EL in the electrolyte and the total pore volume V1 of the pores with a pore diameter less than or equal to 100 nm in the silicon-carbon composite material is 10-200, and can be optionally 30-120.
  • Small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material, forming a mutual cooperation with it to further increase the migration rate of ions in the electrode active material, thereby improving the cycle performance and rate performance of the battery.
  • the silicon-carbon composite material includes carbon matrix particles and silicon nanoparticles, the carbon matrix has a three-dimensional network cross-linked pore structure; the silicon nanoparticles are at least partially embedded in the three-dimensional network cross-linked pore structure of the carbon matrix particles.
  • the carbon matrix of the present application has a stable porous skeleton structure, strong supporting capacity, high stress capacity, and excellent mechanical properties and electrical conductivity; the carbon matrix includes a three-dimensional network cross-linked pore structure, which provides more space for embedding silicon-based nanoparticles, and can be used for large-scale silicon storage, effectively increasing the silicon loading capacity in the silicon-carbon composite material.
  • the electrical conductivity of the silicon-carbon composite material can be improved, while the volume effect of silicon in the process of lithium insertion and extraction can be alleviated, and the stress changes of silicon-based nanoparticles can be fully withstood, ensuring the structural stability of the silicon-carbon composite material, and improving the cycle stability and lithium storage capacity of the silicon-carbon composite material. Therefore, when the silicon-carbon composite material is applied to a secondary battery, the cycle performance and energy density of the secondary battery can be improved.
  • the mass ratio of the silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%, and can be optionally 40-60%.
  • the negative electrode material used in the secondary battery of the present application achieves a high loading amount of silicon nanoparticles in the negative electrode material by adopting a carbon-based material having a three-dimensional network cross-linked pore structure, so that the silicon-carbon composite material has a high capacity and can further improve the energy density of the battery.
  • the silicon nanoparticles include one or more of silicon-oxygen compounds, pre-lithium silicon-oxygen compounds, amorphous silicon, crystalline silicon, and silicon-carbon composites.
  • the carbon matrix includes one or more of graphite, soft carbon, and hard carbon.
  • the above-mentioned material is prepared into a porous structure, it is conducive to embedding silicon-based nanoparticles into the pores of the porous structure, and its structural stability is relatively high.
  • the pores in the carbon matrix particles having a pore size greater than 100 nm The total volume is recorded as Vc1 cm 3 /g, and the total volume of pores with a pore diameter of less than or equal to 100 nm in the carbon matrix particles is recorded as Vc2 cm 3 /g. Then the carbon matrix particles satisfy: 1 ⁇ Vc2/Vc1 ⁇ 30; optionally, 3 ⁇ Vc2/Vc1 ⁇ 25.
  • the pore size distribution of the carbon matrix particles can be made moderate, which is beneficial for silicon nanoparticles to enter the pores of the carbon matrix particles, and the specific surface area of the silicon-carbon composite particles can be made moderate, thereby improving their reversible capacity.
  • the ratio of the powder compaction density P11g/ cm3 of the silicon-carbon composite material tested after one powder compaction under a force of 20000N to the compaction density P21g/ cm3 of the silicon-carbon composite material tested after 20 powder compactions under a force of 20000N satisfies: 1.00 ⁇ P21/P11 ⁇ 1.20, optionally, 1.02 ⁇ P21/P11 ⁇ 1.10.
  • the silicon-carbon composite material When the ratio of P21/P11 satisfies the above range, the silicon-carbon composite material has a higher gram capacity and better compression resistance, which improves the structural stability of the negative electrode film layer, so that the secondary battery containing this material has a higher energy density and better cycle performance.
  • the powder compaction density P11 g/cm 3 of the silicon-carbon composite material tested after one powder compaction under a force of 20,000 N satisfies: 1.10 ⁇ P11 ⁇ 1.40, optionally, 1.12 ⁇ P11 ⁇ 1.35.
  • the negative electrode film layer has a higher compaction density, so that the secondary battery has a higher energy density.
  • the conductivity of the electrolyte is 8 to 12 ms/cm, and can be optionally 9 to 11 ms/cm.
  • the conductivity of the electrolyte is within the above range, the migration rate of ions in the electrolyte can be ensured, thereby improving the cycle performance and cycle efficiency of the battery.
  • the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.
  • a second aspect of the present application provides an electrical device, comprising the secondary battery of the first aspect.
  • FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application.
  • FIG2 is an exploded view of the secondary battery of one embodiment of the present application shown in FIG1 ;
  • FIG. 3 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.
  • “Scope” disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range.
  • the scope limited in this way can be including end values or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected.
  • the numerical range "ab” represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers.
  • the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations.
  • a parameter is expressed as an integer ⁇ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • the method may further include step (c), which means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.
  • the “include” and “comprising” mentioned in this application represent open-ended or closed-ended expressions.
  • the “include” and “comprising” may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.
  • the term "or” is inclusive.
  • the phrase “A or B” means “A, B, or both A and B”. More specifically, any of the following conditions satisfies the condition "A or B”: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).
  • Silicon-based materials have high specific capacity and are suitable for negative electrode materials of high energy density batteries.
  • silicon-based materials have a large volume expansion rate during the charging and discharging process, resulting in poor battery cycle performance, and the solid electrolyte interface film (SEI film) on its surface will be repeatedly regenerated with the expansion of the silicon-based material, increasing the internal resistance of the battery and reducing the dynamic performance.
  • SEI film solid electrolyte interface film
  • the present application proposes a secondary battery, which includes: a negative electrode plate and an electrolyte, the negative electrode plate includes a silicon-carbon composite material with a three-dimensional network cross-linked pore structure; the electrolyte contains dimethyl carbonate.
  • the three-dimensional network cross-linked pore structure generally refers to the presence of two or more pores in the silicon-carbon composite material, especially in the pore structure formed by carbon matrix particles. Structures that are interconnected or interlaced and share pore volume with each other.
  • the pore structure of the silicon-carbon composite material can be tested using equipment and methods known in the art. For example, it can be tested by using a scanning electron microscope (such as ZEISS Sigma 300). As an example, the following steps can be followed: first, the negative electrode sheet containing the silicon-carbon composite material is cut into a sample to be tested of a certain size (for example, 6mm ⁇ 6mm), and the sample to be tested is clamped with two conductive and thermally conductive thin sheets (such as copper foil), and the sample to be tested and the thin sheet are glued and fixed with glue (such as double-sided tape), and a certain mass (such as about 400g) of a flat iron block is pressed for a certain time (such as 1h) to make the gap between the sample to be tested and the copper foil as small as possible, and then the edges are trimmed with scissors, and glued to the sample stage with conductive glue, and the sample slightly protrudes from the edge of the sample stage.
  • a scanning electron microscope such as ZEISS Sigma 300.
  • the sample stage into the sample holder and lock it, turn on the power of the argon ion cross-section polisher (such as IB-19500CP) and draw a vacuum (such as 10Pa-4Pa), set the argon gas flow rate (such as 0.15MPa) and voltage (such as 8KV) and polishing time (such as 2 hours), adjust the sample stage to the rocking mode and start polishing.
  • the argon ion cross-section polisher such as IB-19500CP
  • draw a vacuum such as 10Pa-4Pa
  • the argon gas flow rate such as 0.15MPa
  • voltage such as 8KV
  • polishing time such as 2 hours
  • the silicon-carbon composite material with a three-dimensional network cross-linked pore structure has a stable porous skeleton and good mechanical strength, and can effectively reduce the volume change of silicon before and after charging and discharging while loading a high silicon content.
  • dimethyl carbonate can increase the reflux rate of the electrolyte during the charging and discharging process, promote the transmission of ions at the active material/electrolyte interface, reduce the interface deterioration caused by polarization, and improve the battery's cycle performance and charging and discharging capabilities under high rate conditions.
  • the pore volume of the silicon-carbon composite material is Vm cm 3 /g, and Vm is defined by the following formula: Among them, ⁇ true represents the true density of the silicon-carbon composite material, ⁇ represents the porosity of the silicon-carbon composite material; the mass proportion of dimethyl carbonate in the electrolyte is EL g/g, and the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass proportion EL of dimethyl carbonate in the electrolyte is 0.5-20, preferably 2-13.
  • the ratio EL:Vm between the pore volume Vm of the silicon-carbon composite material and the mass proportion EL of dimethyl carbonate in the electrolyte can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20.
  • True density is a well-known meaning in the art, which refers to the actual mass of a unit volume of solid matter in an absolutely dense state, that is, the density after removing the internal voids of the material or the voids between particles; it can be tested using instruments and methods known in the art.
  • the test method can refer to GB/T 24586-2009, and the test instrument can be a true density tester.
  • the following steps can be followed: place a clean and dry sample cup on a balance, reset it to zero, add a certain amount of powder sample into the sample cup (for example, the sample can occupy 1/2 of the volume of the sample cup), record the mass of the sample, place the sample cup containing the sample in a true density tester for a closed test, introduce helium, detect the pressure of the gas in the sample chamber and the expansion chamber, and then calculate the true volume based on Bohr's law, and then calculate the true density.
  • the pore volume per unit mass of the silicon-carbon composite material is Vm in the range of 0.01 to 0.3, and may be 0.04 to 0.15 cm 3 /g.
  • the pore volume per unit mass of the silicon-carbon composite material is Vm, which can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, or 0.3 cm 3 /g.
  • the pore volume Vm per unit mass of the silicon-carbon composite material is within the above range, small molecular weight dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material and interact with it. Combined, reduce the internal resistance of the battery and improve the battery cycle performance.
  • the ratio EL:SSA between the mass proportion of dimethyl carbonate in the electrolyte and the specific surface area SSA of the silicon-carbon composite material is 0.01 to 0.5, and can be optionally 0.05 to 0.25.
  • the mass proportion of dimethyl carbonate in the electrolyte is EL g/g
  • the specific surface area of the silicon-carbon composite material is SSA
  • EL:SSA can be selected as 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5.
  • the specific surface area SSA has a well-known meaning in the art, and the surface area is usually expressed in units of m2 /g, and can be tested by methods and instruments known in the art. For example, it can be tested by an inert gas (such as nitrogen) adsorption specific surface area analysis test method according to GB/T 19587-2017, and calculated by the BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed by a Tri-Star 3020 specific surface area pore size analysis tester from Micromeritics, USA.
  • an inert gas such as nitrogen
  • BET Brunauer Emmett Teller
  • the specific surface area SSA of the silicon-carbon composite material is 2 to 10 m 2 /g; optionally 3 to 7 m 2 /g.
  • the specific surface area SSA of the silicon-carbon composite material may be 2m2 /g, 3m2 /g, 4m2/g, 5m2 / g, 6m2 /g, 7m2 /g, 8m2 /g, 9m2 /g or 10m2 /g, or a range consisting of any two of the above values.
  • the specific surface area SSA of the silicon-carbon composite material meets the above range, the specific surface area of the silicon-carbon composite material is large, the kinetic properties of the material are good, and it is beneficial to improve the first coulombic efficiency of the battery.
  • the mass proportion of dimethyl carbonate in the electrolyte is EL g/g, and the pore size of the silicon-carbon composite material is small.
  • the total pore volume of pores with a pore size of 100 nm is V1 cm 3 /g, and the ratio EL:V1 between the mass proportion EL of dimethyl carbonate in the electrolyte and the total pore volume V1 of pores with a pore size of less than or equal to 100 nm in the silicon-carbon composite material is 10-200, and can be 30-120.
  • the pore volume test method for pores of different sizes can refer to GB/T 19587-2004, adopt the mesopore pore size distribution test BJH (Barret Joyner Halenda), use the gas adsorption and desorption method to test and select the adsorption branch data under the micro-mesopore model, and measure and count the total pore volume V1 of pores with a pore size less than or equal to 100nm.
  • BJH Barret Joyner Halenda
  • the ratio EL:V1 between the mass proportion EL of dimethyl carbonate in the electrolyte and the total pore volume V1 of pores with a pore size less than or equal to 100 nm in the silicon-carbon composite material can be selected as 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190 or 200.
  • Small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material, forming a mutual cooperation with it to further increase the migration rate of ions in the electrode active material, thereby improving the cycle performance and rate performance of the battery.
  • V1 of the silicon-carbon composite material is ⁇ 0.001 cm 3 /g, and may be 0.005 to 0.01 cm 3 /g.
  • V1 of the silicon-carbon composite material may be 0.005, 0.006, 0.007, 0.008, 0.009 or 0.01 cm 3 /g.
  • V1 of the silicon-carbon composite material is within the above range, small molecule dimethyl carbonate can easily enter the pore structure of the silicon-carbon composite material, forming a mutual cooperation with it to further increase the migration rate of ions in the electrode active material, thereby improving the cycle performance and rate performance of the battery.
  • the silicon-carbon composite material includes carbon matrix particles and silicon nanoparticles, the carbon matrix has a three-dimensional network cross-linked pore structure; the silicon nanoparticles are at least partially embedded in the three-dimensional network cross-linked pore structure of the carbon matrix particles.
  • the carbon matrix of the present application has a stable porous skeleton structure, strong supporting capacity, high stress resistance, and excellent mechanical properties and electrical conductivity; the carbon matrix includes a three-dimensional network cross-linked pore structure, which provides more space for embedding silicon-based nanoparticles and can be used to store a large amount of silicon, effectively increasing the silicon loading capacity in the silicon-carbon composite material.
  • the electrical conductivity of the silicon-carbon composite material can be improved, while relieving
  • the volume effect of silicon in the process of lithium insertion and extraction can fully withstand the stress changes of silicon-based nanoparticles, ensure the structural stability of silicon-carbon composite materials, and improve the cycle stability and lithium storage capacity of silicon-carbon composite materials. Therefore, when silicon-carbon composite materials are used in secondary batteries, the cycle performance and energy density of secondary batteries can be improved.
  • the mass ratio of silicon nanoparticles in the silicon-carbon composite material is greater than or equal to 40%, and can be optionally 40-60%.
  • the mass ratio of silicon nanoparticles in the silicon-carbon composite material may be 40%, 45%, 50%, 55% or 60%.
  • the quality of silicon nanoparticles in silicon-carbon composite materials can be tested by methods and equipment known in the art, for example, it can be measured with reference to EPA 6010D-2014 standard; specifically, ICP-OES (elemental analysis-inductively coupled plasma optical emission spectrometry) testing can be used, and the solid to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into an ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then recovered from the excited state to the ground state; in the above process, energy is released and recorded as different characteristic spectral lines for quantitative analysis of trace elements.
  • ICP-OES electromagnetic analysis-inductively coupled plasma optical emission spectrometry
  • the negative electrode material used in the secondary battery of the present application achieves a high loading amount of silicon nanoparticles in the negative electrode material by adopting a carbon-based material having a three-dimensional network cross-linked pore structure, so that the silicon-carbon composite material has a high capacity and can further improve the energy density of the battery.
  • the silicon nanoparticles include one or more of silicon-oxygen compounds, pre-lithium silicon-oxygen compounds, amorphous silicon, crystalline silicon, and silicon-carbon composites.
  • the carbon matrix includes one or more of graphite, soft carbon, and hard carbon.
  • the above-mentioned material is prepared into a porous structure, it is conducive to embedding silicon-based nanoparticles into the pores of the porous structure, and its structural stability is relatively high.
  • the mass percentage A1 of the carbon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material and the mass percentage B1 of the silicon element of the silicon-carbon composite material relative to the total mass of the silicon-carbon composite material satisfy 0.8 ⁇ B1/A1 ⁇ 2.5, optionally, 1 ⁇ B1/A1 ⁇ 1.5, wherein the peripheral region of the silicon-carbon composite material is a region extending from the outer surface of the silicon-carbon composite material to the interior of the silicon-carbon composite material within a distance of r/2, and r represents the short diameter of the silicon-carbon composite material.
  • the silicon content can be determined by emission spectroscopy (Inductively coupled plasma, ICP) testing as follows: a silicon-carbon composite material is taken as a sample, the sample is digested with aqua regia and hydrofluoric acid HF, the solution digested for 15 minutes and the solution completely digested are taken for ICP testing, and the silicon content in the solution digested for 45 minutes is the silicon content in the "peripheral area of the silicon-carbon composite material".
  • ICP Inductively coupled plasma
  • the carbon content can be analyzed by infrared absorption carbon-sulfur content analysis according to the GB/T20123-2006 test standard, as follows: take the silicon-carbon composite material as a sample, and the carbon content at 20 minutes of testing is the carbon content of the "peripheral area of the silicon-carbon composite material".
  • the mass of silicon nanoparticles attached to the inside of the carbon matrix particles is relatively high, which can significantly improve the capacity of the negative electrode active material, and the voltage of metal ion embedding is low, which is conducive to the embedding of metal ions, thereby further improving the capacity retention rate of the secondary battery during charging and discharging at high rates.
  • the total volume of pores with a pore size greater than 100 nm in the carbon matrix particles is recorded as Vc1 cm 3 /g, and the total volume of pores with a pore size less than or equal to 100 nm in the carbon matrix particles is recorded as Vc2 cm 3 /g.
  • the carbon matrix particles satisfy: 1 ⁇ Vc2/Vc1 ⁇ 30; optionally, 3 ⁇ Vc2/Vc1 ⁇ 25.
  • the pore size distribution of the carbon matrix particles can be made moderate, which is beneficial for silicon nanoparticles to enter the pores of the carbon matrix particles, and the specific surface area of the silicon-carbon composite particles can be made moderate, thereby improving their reversible capacity.
  • the ratio of the powder compaction density P11g/ cm3 of the silicon-carbon composite material tested after one powder compaction under a force of 20000N to the compaction density P21g/ cm3 of the silicon-carbon composite material tested after 20 powder compactions under a force of 20000N satisfies: 1.00 ⁇ P21/P11 ⁇ 1.20, optionally, 1.02 ⁇ P21/P11 ⁇ 1.10.
  • the silicon-carbon composite material When the ratio of P21/P11 satisfies the above range, the silicon-carbon composite material has a higher gram capacity and better compression resistance, which improves the structural stability of the negative electrode film layer, so that the secondary battery containing this material has a higher energy density and better cycle performance.
  • the powder compaction density P11 g/cm 3 of the silicon-carbon composite material tested after one powder compaction under a force of 20000 N satisfies: 1.10 ⁇ P11 ⁇ 1.40, optional Ground, 1.12 ⁇ P11 ⁇ 1.35.
  • the negative electrode film layer has a higher compaction density, so that the secondary battery has a higher energy density.
  • the conductivity of the electrolyte is 8-12 ms/cm, and may be 9-11 ms/cm.
  • the conductivity of the electrolyte is within the above range, the migration rate of ions in the electrolyte can be ensured, thereby improving the cycle performance and cycle efficiency of the battery.
  • a secondary battery includes a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode film layer includes a negative electrode active material.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • a metal foil a copper foil may be used.
  • the composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate.
  • the composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the negative electrode film layer may further include a binder.
  • the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • a conductive agent which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).
  • a thickener eg, sodium carboxymethyl cellulose (CMC-Na)
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil may be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
  • PP polypropylene
  • PET polyethylene terephthalate
  • PBT polybutylene terephthalate
  • PS polystyrene
  • PE polyethylene
  • the positive electrode active material may be a positive electrode active material for a battery known in the art.
  • the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds.
  • the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 , LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1/3 Co 1/3 Mn 1/3 O 2 (also referred to as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also referred to as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2
  • lithium-containing phosphates with an olivine structure may include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO 4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
  • lithium iron phosphate such as LiFePO 4 (also referred to as LFP)
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate
  • LiMnPO 4 lithium manganese phosphate and carbon
  • the positive electrode active material is a nickel-rich material, and the molar ratio of nickel in the transition metal of the positive electrode active material is higher than 85%.
  • the positive electrode film layer may also optionally include a binder.
  • the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer
  • the positive electrode film layer may further include a conductive agent, which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • a conductive agent which may include, for example, at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a solvent such as N-methylpyrrolidone
  • the secondary battery further includes a separator.
  • the present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.
  • the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation.
  • the materials of each layer can be the same or different, without particular limitation.
  • the secondary battery includes at least one of a lithium ion battery, a sodium ion battery, a magnesium ion battery, and a potassium ion battery.
  • an electric device comprising the secondary battery of any embodiment.
  • FIG1 is a secondary battery 1 of a square structure as an example.
  • the outer package may include a shell 11 and a cover plate 13.
  • the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity.
  • the shell 11 has an opening connected to the receiving cavity, and the cover plate 13 can be covered on the opening to close the receiving cavity.
  • the positive electrode sheet, the negative electrode sheet and the isolation film can form an electrode assembly 12 through a winding process or a lamination process.
  • the electrode assembly 12 is encapsulated in the receiving cavity.
  • the electrolyte is infiltrated in the electrode assembly 12.
  • the number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the electrical device includes the secondary battery provided in the present application.
  • the secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device.
  • the electrical device can include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.
  • FIG3 is an example of an electric device.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module may be used.
  • the device may be a mobile phone, a tablet computer, a notebook computer, etc.
  • a device is usually required to be light and thin, and a secondary battery may be used as a power source.
  • a gas containing a silicon precursor is provided to carbon matrix particles having a three-dimensional network cross-linked pore structure; silicon nanoparticles attached to the carbon matrix particles are generated from the silicon precursor by chemical vapor deposition to obtain a silicon-carbon composite material, wherein the silicon precursor is silane and the carbon matrix is hard carbon.
  • the negative electrode active material silicon-carbon composite
  • conductive carbon black thickener sodium carboxymethyl cellulose (CMC)
  • binder styrene-butadiene rubber latex SBR
  • the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811 ), the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were dissolved in a solvent N-methylpyrrolidone (NMP) at a weight ratio of 93:2:5, and the positive electrode slurry was obtained after being fully stirred and mixed; then the positive electrode slurry was evenly coated on the positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet.
  • NMP N-methylpyrrolidone
  • Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol/L, and then 30 wt% of dimethyl carbonate is added and mixed evenly.
  • Polypropylene film is used as the isolation film.
  • the positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is in the positive and negative electrodes.
  • the negative electrode sheets are isolated from each other, and then the bare cells are wound, the tabs are welded to the bare cells, and the bare cells are placed in an aluminum shell, baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery.
  • the uncharged battery is then subjected to the processes of standing, hot and cold pressing, formation, shaping, and capacity testing to obtain the lithium-ion battery product of Example 1.
  • Example 2-5 The preparation method of the battery of Example 2-5 is similar to that of Example 1, but the mass ratio EL of dimethyl carbonate in the electrolyte is adjusted. The specific parameters are shown in Table 1.
  • the preparation method of the battery of Comparative Example 1 is similar to that of Example 1, but dimethyl carbonate is not added to the electrolyte.
  • the preparation method of the battery of Comparative Example 2 is similar to that of Example 1, but the pore structure of the carbon matrix particles of Comparative Example 2 is a honeycomb pore structure.
  • the pore structure of the silicon-carbon composite material can be tested using equipment and methods known in the art. For example, it can be tested by using a scanning electron microscope (such as ZEISS Sigma 300). As an example, the following steps can be followed: first, the negative electrode sheet containing the silicon-carbon composite material is cut into a sample to be tested of a certain size (for example, 6mm ⁇ 6mm), and the sample to be tested is clamped with two conductive and heat-conductive thin sheets (such as copper foil), and the sample to be tested and the thin sheet are glued and fixed with glue (such as double-sided tape), and a certain mass (such as about 400g) of a flat iron block is used to press for a certain time (such as 1h) to make the gap between the sample to be tested and the copper foil as small as possible, and then the edges are trimmed with scissors and glued to the sample stage with conductive glue, and the sample slightly protrudes from the edge of the sample stage.
  • a scanning electron microscope such as ZEISS Sigma 300.
  • the sample stage into the sample holder, lock it, turn on the power of the argon ion cross-section polisher (such as IB-19500CP) and evacuate (for example, 10 Pa-4Pa), set the argon flow rate (e.g. 0.15MPa) and voltage (e.g. 8KV) and polishing time (e.g. 2 hours), adjust the sample stage to the swing mode and start polishing.
  • the argon flow rate e.g. 0.15MPa
  • voltage e.g. 8KV
  • polishing time e.g. 2 hours
  • the specific surface area was tested by gas adsorption method according to GB/T19587-2017 test standard, as follows: a silicon-carbon composite material was taken as a sample, the sample tube was immersed in liquid nitrogen at -196°C, and the adsorption amount of nitrogen on the solid surface at different pressures was measured at a relative pressure of 0.05-0.30. The monolayer adsorption amount of the sample was obtained based on the BET multilayer adsorption theory and its formula, thereby calculating the specific surface area of the negative electrode active material.
  • the pore size is tested by the gas adsorption method according to the GB/T19587-2017 & GB/T21650.2-2008 test standards. The details are as follows: take the silicon-carbon composite material as the sample, immerse the sample tube in -196°C liquid nitrogen, and adsorb the nitrogen on the material to be tested at a relative pressure of 0-1.
  • the pore size distribution of the porous material is characterized based on the relationship between the volume of each pore size and the corresponding partial pressure.
  • the test instrument can be a true density tester.
  • the following steps can be followed: take a clean and dry silicon-carbon composite material sample cup and place it on a balance, reset it to zero, add a certain amount of powder sample into the sample cup (for example, the sample can occupy 1/2 of the volume of the sample cup), record the mass of the sample, place the sample cup with the sample in a true density 25-degree tester for airtight testing, pass helium, detect the pressure of the gas in the sample chamber and the expansion chamber, and then calculate the true volume according to Bohr's law, and then calculate the true density.
  • the elemental analysis of ion polished cross section was carried out by energy dispersive spectrometry, and the element distribution of the particle cross section was tested according to the GB-T17359-2012 test standard.
  • the electrolyte was tested at 25°C using a conductivity meter, the model of the conductivity meter being Mettler conductivity meter S230.
  • the secondary batteries prepared in the examples and comparative examples were charged at a constant current of 0.5C to a charge cut-off voltage of 4.25V, then charged at a constant voltage to a current of ⁇ 0.05C, left to stand for 5 minutes, and then discharged at a constant current of 0.33C to a discharge cut-off voltage of 2V, left to stand for 5 minutes. This was a charge and discharge cycle.
  • the battery was subjected to a cyclic charge and discharge test according to this method, and the capacity retention rate of the lithium-ion battery after 800 cycles was calculated.
  • the secondary batteries prepared in the examples and comparative examples were charged at a constant current rate of 0.5C to a charge cut-off voltage of 4.25V, and then charged at a constant voltage to a current of ⁇ 0.05C.
  • the battery was placed in a cyclic charge and discharge test, and the capacity retention rate of the lithium-ion battery after 800 cycles was calculated.
  • the secondary batteries prepared in the embodiments and comparative examples and the lithium-ion batteries cycled 800 times at 2C rate at 25°C were charged to 4.3V at 1C constant current. Then, they were charged at 4.3V constant voltage until the current was less than 0.05C, and then discharged at 1C for 30 minutes, that is, the battery power was adjusted to 50% SOC. Then, the positive and negative test leads of the TH2523A AC internal resistance tester were respectively contacted with the positive and negative electrodes of the battery, and the internal resistance value of the battery was read by the internal resistance tester, which were recorded as the initial battery internal resistance (m ⁇ ) and the battery internal resistance (m ⁇ ) after 800 cycles.
  • the negative electrode active material of the batteries of Examples 1-9 is a silicon-carbon composite material with a three-dimensional network cross-linked pore structure, and the electrolyte contains dimethyl carbonate.
  • the battery in Comparative Example 2 in which the negative electrode active material is a silicon-carbon composite material with a honeycomb pore structure and the electrolyte contains dimethyl carbonate
  • the battery in Comparative Example 3 in which diethyl carbonate is added
  • the battery in Comparative Example 4 in which ethyl methyl carbonate is added
  • the batteries of Examples 1-9 exhibit lower internal resistance, higher cycle capacity retention, and better high-rate charge and discharge performance.
  • the negative electrode is a silicon-carbon composite material with a honeycomb pore structure. Silicon particles are not easily deposited inside the honeycomb pore structure. Therefore, the mass content of silicon-based particles in the silicon-carbon composite material with a honeycomb pore structure is low, only 7%, and the silicon element is concentrated on the surface of the composite material. The carbon matrix can hardly limit the expansion of the silicon-based particles, and the battery's cycle performance is poor.

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Abstract

本申请提供一种二次电池。该二次电池包括：负极极片和电解液，负极极片包括具有三维网络交联孔结构的硅碳复合材料；电解液包含碳酸二甲酯。通过硅碳复合材料的三维网络交联孔结构与电解液中碳酸二甲酯的配合，抑制活性材料在充放电过程中的体积效应，提高界面稳定性，降低电池内阻，改善电池的循环容量保持率和在高倍率下的充放电性能。

Description

二次电池及用电装置 技术领域
本申请涉及二次电池技术领域，尤其涉及一种二次电池和用电装置。
背景技术
近年来，二次电池广泛应用于水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。
具有高克容量的电极活性材料往往循环性能和动力学性能较差，如何通过电池各组分的相互配合，在提高电池能量密度的同时兼顾优异的循环性能和动力学性能，是本领域亟需解决的技术问题。
发明内容
本申请是鉴于上述课题而进行的，其目的在于提供一种二次电池。通过电解液与负极材料的匹配，抑制活性材料在充放电过程中的体积效应，提高界面稳定性，降低电池内阻，改善电池的循环容量保持率和倍率性能。
本申请的第一方面提供了一种二次电池，包括：负极极片和电解液；所述负极极片包括具有三维网络交联孔结构的硅碳复合材料，所述电解液包含碳酸二甲酯。
具有三维网络交联孔结构的硅碳复合材料具有稳定的多孔骨架、良好的机械强度，能够在负载高的硅含量的同时有效减少硅在充放电前后的体积变化。同时，电解液中搭配的碳酸二甲酯可以提高电解液在充放电过程中的回流速度，促进离子在活性材料/电解质界面的传输，有效地降低电池极化阻抗，从而改善电池的循环性能以及倍率性能。
在任意实施方式中，所述硅碳复合材料单位质量的孔隙体积为Vm，单位为cm3/g；基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，所述硅碳复合材料的孔隙体积Vm与所述碳酸二甲酯在所述电解液中的质量占比EL之间的比值EL：Vm为0.5～20，优选为2～13。
当硅碳复合材料的孔隙体积Vm与碳酸二甲酯在电解液中的质量占比EL之间的比值EL：Vm满足上述范围时，能够使得碳酸二甲酯的添加量与硅碳复合材料的孔隙体积Vm形成相互配合，改善电池的循环容量保持率，提高电池的倍率性能。
在任意实施方式中，所述硅碳复合材料的孔隙体积为Vm为0.01～0.3，可选为0.04～0.15cm3/g。
当硅碳复合材料单位质量的孔隙体积Vm在上述范围内时，小分子的碳酸二甲酯容易进入硅碳复合材料的孔结构中并与其相互配合，降低电池内阻，提高电池的循环性能。
在任意实施方式中，基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，所述碳酸二甲酯在所述电解液中的质量占比与所述硅碳复合材料的比表面积为SSA，EL：SSA为0.01～0.5，可选为0.05～0.25。
当碳酸二甲酯在电解液中的质量占比与硅碳复合材料的比表面积SSA之间的比值EL：SSA满足上述范围时，碳酸二甲酯可以有效地进入硅碳复合材料的孔结构中，与硅碳复合材料充分接触，提高离子在电极/电解质界面处的迁移速率，降低电池内阻，改善电池的循环性能和高倍率容量。
在任意实施方式中，所述硅碳复合材料的比表面积SSA为2～10m2/g；可选为3～7m2/g。
硅碳复合材料的比表面积SSA满足上述范围时，硅碳复合材料的比表面积大，二次电池的动力学性能好、倍率性能高。
在任意实施方式中，基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，所述硅碳复合材料中孔径小于等于100nm的孔的总孔容积为V1cm3/g，所述碳酸二甲酯在 所述电解液中的质量占比EL与所述硅碳复合材料中孔径小于等于100nm的孔的总孔容积V1之间的比值EL：V1为10～200，可选为30～120。
小分子的碳酸二甲酯容易进入硅碳复合材料的孔结构中，与其形成相互配合进一步提高离子在电极活性材料中的迁移速率，改善电池的循环性能和倍率性能。
在任意实施方式中，所述硅碳复合材料包括碳基体颗粒以及硅纳米颗粒，所述碳基体具有三维网络交联的孔结构；所述硅纳米颗粒至少部分地嵌入所述碳基体颗粒的三维网络交联的孔结构中。
本申请的碳基体具有稳定的多孔骨架结构，支撑能力较强，表现为应力能力较高，且具有优异的机械性能和导电性；碳基体包括三维网络交联的孔结构，可供嵌入硅基纳米颗粒的空间较多，可以用于大量储硅，有效提高硅碳复合材料中硅的负载量。在碳基体与硅基纳米颗粒复合后，可以提高硅碳复合材料的导电性，同时缓解硅在脱嵌锂过程中的体积效应，且能够充分承受硅基纳米颗粒的应力变化，保证硅碳复合材料的结构稳定性，提高硅碳复合材料的循环稳定性和储锂能力。因此，在硅碳复合材料应用于二次电池时，能够提高二次电池的循环性能和能量密度。
在任意实施方式中，所述硅纳米颗粒在所述硅碳复合材料中的质量比大于等于40％，可选为40～60％。
本申请二次电池采用的负极材料通过采用包括具有三维网络交联孔结构的碳基材料实现了硅纳米颗粒在负极材料中高的负载量，使得硅碳复合材料具有高的容量，能够进一步提高电池的能量密度。
在任意实施方式中，所述硅纳米颗粒包括硅氧化合物、预锂硅氧化合物、非晶硅、晶体硅和硅碳复合物中的一种或多种。
在任意实施方式中，所述碳基体包括石墨、软碳和硬碳中的一种或多种。
上述材料在制备成多孔结构时，有利于硅基纳米颗粒嵌入多孔结构的孔中，且其结构稳定性相对较高。
在任意实施方式中，所述碳基体颗粒中孔径大于100nm的孔的 总容积记为Vc1 cm3/g，所述碳基体颗粒中孔径小于等于100nm的孔的总容积记为Vc2 cm3/g，则所述碳基体颗粒满足：1＜Vc2/Vc1≤30；可选地，3≤Vc2/Vc1≤25。
通过调控多孔碳基体颗粒中特定尺寸的孔的总孔容积比例，可以使得碳基体颗粒的孔径分布适中，有利于硅纳米颗粒进入碳基体颗粒的孔中，并且可以使得硅碳复合颗粒的比表面积适中，改善其可逆容量。
在任意实施方式中，所述硅碳复合材料在20000N的作用力下经过1次粉压后测试的粉体压实密度P11g/cm3与所述硅碳复合材料在20000N的作用力下经过20次粉压后测试的压实密度记P21g/cm3的比值满足：1.00＜P21/P11≤1.20，可选地，1.02≤P21/P11≤1.10。
当P21/P11的比值满足上述范围时，硅碳复合材料在具有较高克容量的同时还具有较好的抗压性，提高了负极膜层的结构稳定性，从而使得含有该材料的二次电池在具有较高能量密度的同时兼顾较好的循环性能。
在任意实施方式中，所述硅碳复合材料在20000N的作用力下经过1次粉压后测试的粉体压实密度P11g/cm3满足：1.10≤P11≤1.40，可选地，1.12≤P11≤1.35。
硅碳复合材料在20000N的作用力下经过1次粉压后测试的粉体压实密度P11g/cm3满足上述范围时，负极膜层具有较高的压实密度，从而使得二次电池具有较高的能量密度。
在任意实施方式中，所述电解液的电导率为8～12ms/cm，可选为9～11ms/cm。
电解液的电导率在上述范围内时，可以确保离子在电解液中的迁移速率，改善电池的循环性能和循环效率。
在任意实施方式中，所述二次电池包括锂离子电池、钠离子电池、镁离子电池、钾离子电池中的至少一种。
本申请的第二方面提供了一种用电装置，包括第一方面的二次电池。
附图说明
图1是本申请一实施方式的二次电池的示意图；
图2是图1所示的本申请一实施方式的二次电池的分解图；
图3是本申请一实施方式的二次电池用作电源的用电装置的示意图。
附图标记说明：
1二次电池；11壳体；12电极组件；13盖板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的粘结剂、制备方法、电极、电池及用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
随着二次电池应用范围的推广，对二次电池性能例如能量密度的要求逐步提升。硅基材料克容量高，是适用于高能量密度电池的负极材料。然而，硅基材料在充放电过程中体积膨胀率大，导致电池循环性能差，且其表面的固体电解质界面膜(SEI膜)会随着硅基材料的膨胀不断反复再生，增大电池内阻、降低动力学性能。
基于此，本申请提出了一种二次电池，该二次电池包括：负极极片和电解液，负极极片包括具有三维网络交联孔结构的硅碳复合材料；电解液包含碳酸二甲酯。
在本文中，述三维网络交联的孔结构通常是指在硅碳复合材料中，尤其是碳基体颗粒形成的孔结构中，存在两个或者多个孔相互 联通或交错且相互共用孔容积的结构。
硅碳复合材料的孔结构可以采用本领域已知的设备和方法进行测试。例如，可以通过使用扫描电子显微镜(例如ZEISS Sigma 300)进行测试。作为示例，可以按照如下步骤操作：首先将包含所述硅碳复合材料的负极极片裁成一定尺寸的待测样品(例如6mm×6mm)，用两片导电导热的薄片(如铜箔)将待测样品夹住，将待测样品与薄片之间用胶(如双面胶)粘住固定，用一定质量(如400g左右)平整铁块压一定时间(如1h)，使待测样品与铜箔间缝隙越小越好，然后用剪刀将边缘剪齐，粘在具有导电胶的样品台上，样品略突出样品台边缘即可。然后将样品台装进样品架上锁好固定，打开氩离子截面抛光仪(例如IB-19500CP)电源并抽真空(例如10Pa-4Pa)，设置氩气流量(例如0.15MPa)和电压(例如8KV)以及抛光时间(例如2小时)，调整样品台为摇摆模式开始抛光，抛光结束后，使用扫描电子显微镜(例如ZEISS Sigma 300)得到待测样品的离子抛光断面形貌(CP)图片。
具有三维网络交联孔结构的硅碳复合材料具有稳定的多孔骨架、良好的机械强度，能够在负载高的硅含量的同时有效减少硅在充放电前后的体积变化。同时，碳酸二甲酯可以提高电解液在充放电过程中的回流速度，促进离子在活性材料/电解质界面的传输，降低由于极化带来的界面恶化，改善电池的循环性能以及在高倍率条件下的充电和放电能力。
在一些实施方式中，硅碳复合材料的孔隙体积为Vm cm3/g，且Vm通过下式来定义：其中，ρ真表示所述硅碳复合材料的真密度，α表示所述硅碳复合材料的孔隙率；碳酸二甲酯在所述电解液中的质量占比为EL g/g，硅碳复合材料的孔隙体积Vm与碳酸二甲酯在电解液中的质量占比EL之间的比值EL：Vm为0.5～20，优选为2～13。
在一些实施方式中，硅碳复合材料的孔隙体积Vm与碳酸二甲酯在电解液中的质量占比EL之间的比值EL：Vm可选为0.1、0.2、0.3、0.4、0.5、0.6、0.7、0.8、0.9、1、1.1、1.2、1.3、1.4、1.5、 1.6、1.7、1.8、1.9、2、2.5、3、3.5、4、4.5、5、5.5、6、6.5、7、7.5、8、8.5、9、9.5、10、11、12、13、14、15、16、17、18、19或20。
硅碳复合材料的孔隙体积Vm可以通过以下公式计算得到：其中，ρ真表示硅碳复合材料的真密度，α表示硅碳复合材料的孔隙率。孔隙率是指颗粒内孔体积占据碳基体颗粒总体积的比率。孔隙率可以按照GB/T24586，采用气体置换法测量。孔隙率W＝(L1-L2)/L1*100％，其中L1是样品的表观体积，L2是样品的真实体积。真密度为本领域公知的含义，其是指材料在绝对密实的状态下单位体积的固态物质的实际质量，即去除材料内部空隙或者颗粒间的空隙后的密度；其可以采用本领域已知的仪器及方法进行测试。例如，测试方法可以参考GB/T 24586-2009，测试仪器可以采用真密度测试仪。作为示例，可以按照如下步骤操作：取洁净干燥的样品杯放置在天平，清零，将一定量粉末样品加入到样品杯中(例如，样品可以占样品杯体积的1/2)，记录所取样品的质量，将装有样品的样品杯置于真密度测试仪密闭测试，通入氦气，检测样品室和膨胀室中的气体的压力，再根据玻尔定律来计算真实体积，进而计算真密度。
当硅碳复合材料的孔隙体积Vm与碳酸二甲酯在电解液中的质量占比EL之间的比值EL：Vm满足上述范围时，能够使得碳酸二甲酯的添加量与硅碳复合材料的孔隙体积Vm形成相互配合，改善电池的循环容量保持率，提高电池的倍率性能。
在一些实施方式中，硅碳复合材料单位质量的孔隙体积为Vm为0.01～0.3，可选为0.04～0.15cm3/g。
在一些实施方式中，硅碳复合材料单位质量的孔隙体积为Vm可选为0.01、0.02、0.03、0.04、0.05、0.06、0.07、0.08、0.09、0.1、0.11、0.12、0.13、0.14、0.15、0.16、0.17、0.18、0.19、0.20、0.21、0.22、0.23、0.24、0.25、0.26、0.27、0.28、0.29、0.3cm3/g。
当硅碳复合材料单位质量的孔隙体积Vm在上述范围内时，小分子的碳酸二甲酯容易进入硅碳复合材料的孔结构中并与其相互配 合，降低电池内阻，提高电池的循环性能。
在一些实施方式中，碳酸二甲酯在所述电解液中的质量占比与硅碳复合材料的比表面积SSA之间的比值EL：SSA为0.01～0.5，可选为0.05～0.25。
在一些实施方式中，基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，硅碳复合材料的比表面积为SSA，EL：SSA可选为0.01、0.02、0.03、0.04、0.05、0.06、0.07、0.08、0.09、0.1、0.15、0.2、0.25、0.3、0.35、0.4、0.45或0.5。
在本文中，比表面积SSA为本领域公知的含义，通常表面积以m2/g的单位表示，可采用本领域已知的方法和仪器测试。例如可参照GB/T 19587-2017，采用惰性气体(例如氮气)吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出，其中氮气吸附比表面积分析测试可以通过美国Micromeritics公司的Tri-Star 3020型比表面积孔径分析测试仪进行。
当碳酸二甲酯在电解液中的质量占比与硅碳复合材料的比表面积SSA之间的比值EL：SSA满足上述范围时，碳酸二甲酯可以有效地进入硅碳复合材料的孔结构中，与硅碳复合材料充分接触，提高离子在电极/电解质界面处的迁移速率，降低电池内阻，改善电池的循环性能和高倍率容量。
在一些实施方式中，硅碳复合材料的比表面积SSA为2～10m2/g；可选为3～7m2/g。
硅碳复合材料的比表面积SSA可选为2m2/g、3m2/g、4m2/g、5m2/g、6m2/g、7m2/g、8m2/g、9m2/g或10m2/g，或者是上述任意两个数值组成的范围。
硅碳复合材料的比表面积SSA满足上述范围时，硅碳复合材料的比表面积大，材料的动力学性能较好，有利于提高电池的首次库伦效率。
在一些实施方式中，基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，硅碳复合材料中孔径小 于等于100nm的孔的总孔容积为V1cm3/g，碳酸二甲酯在电解液中的质量占比EL与硅碳复合材料中孔径小于等于100nm的孔的总孔容积V1之间的比值EL：V1为10～200，可选为30～120。
不同大小孔径的孔容积测试方法可以参考GB/T 19587-2004，采用介孔孔径分布测试BJH(Barret joyner Halenda)，在微-介孔模型下采用气体吸脱附方法测试并选取吸附支数据，测定并统计孔径小于等于100nm的孔的孔容积总和V1。
在一些实施方式中，碳酸二甲酯在电解液中的质量占比EL与硅碳复合材料中孔径小于等于100nm的孔的总孔容积V1之间的比值EL：V1可选为10、15、20、25、30、35、40、45、50、55、60、65、70、75、80、85、90、95、100、110、120、130、140、150、160、170、180、190或200。
小分子的碳酸二甲酯容易进入硅碳复合材料的孔结构中，与其形成相互配合进一步提高离子在电极活性材料中的迁移速率，改善电池的循环性能和倍率性能。
在一些实施方式中，硅碳复合材料的V1≥0.001cm3/g，可选为0.005～0.01cm3/g。
在一些实施方式中，硅碳复合材料的V1可选为0.005、0.006、0.007、0.008、0.009或0.01cm3/g。
当硅碳复合材料的V1在上述范围内时，小分子的碳酸二甲酯容易进入硅碳复合材料的孔结构中，与其形成相互配合进一步提高离子在电极活性材料中的迁移速率，改善电池的循环性能和倍率性能。
在一些实施方式中，硅碳复合材料包括碳基体颗粒以及硅纳米颗粒，碳基体具有三维网络交联的孔结构；硅纳米颗粒至少部分地嵌入碳基体颗粒的三维网络交联的孔结构中。
本申请的碳基体具有稳定的多孔骨架结构，支撑能力较强，表现为应力能力较高，且具有优异的机械性能和导电性；碳基体包括三维网络交联的孔结构，可供嵌入硅基纳米颗粒的空间较多，可以用于大量储硅，有效提高硅碳复合材料中硅的负载量。在碳基体与硅基纳米颗粒复合后，可以提高硅碳复合材料的导电性，同时缓解 硅在脱嵌锂过程中的体积效应，且能够充分承受硅基纳米颗粒的应力变化，保证硅碳复合材料的结构稳定性，提高硅碳复合材料的循环稳定性和储锂能力。因此，在硅碳复合材料应用于二次电池时，能够提高二次电池的循环性能和能量密度。
在一些实施方式中，硅纳米颗粒在硅碳复合材料中的质量比大于等于40％，可选为40～60％。
在一些实施方式中，硅纳米颗粒在硅碳复合材料中的质量比可选为40％、45％、50％、55％或60％。
硅纳米颗粒在硅碳复合材料中的质量可以采用本领域已知的方法和设备测试，例如可参考EPA 6010D-2014标准进行测定；具体地，可以采用ICP-OES(元素分析-电感耦合等离子体发射光谱法)测试，先将待测固体用强酸溶解为液体，随后通过雾化的方式将液体引入ICP光源，进一步待测气态原子在强磁场中发生电离和激发后，由激发态恢复到基态；在上述过程中释放能量并被记录为不同的特征谱线，进行痕量元素定量分析。
本申请二次电池采用的负极材料通过采用包括具有三维网络交联孔结构的碳基材料实现了硅纳米颗粒在负极材料中高的负载量，使得硅碳复合材料具有高的容量，能够进一步提高电池的能量密度。
在一些实施方式中，硅纳米颗粒包括硅氧化合物、预锂硅氧化合物、非晶硅、晶体硅和硅碳复合物中的一种或多种。
在一些实施方式中，碳基体包括石墨、软碳和硬碳中的一种或多种。
上述材料在制备成多孔结构时，有利于硅基纳米颗粒嵌入多孔结构的孔中，且其结构稳定性相对较高。
在一些实施方式中，在硅碳复合材料的外周区域中，硅碳复合材料的碳元素相对于硅碳复合材料总质量的质量百分含量A1与硅碳复合材料的硅元素相对于硅碳复合材料总质量的质量百分含量B1满足0.8≤B1/A1≤2.5，可选地，1≤B1/A1≤1.5，其中，硅碳复合材料的外周区域为从硅碳复合材料的外表面向硅碳复合材料内部延伸距离在r/2以内的区域，r表示所述硅碳复合材料的短径。
硅元素含量可以通过发射光谱测试(Inductively coupled plasma，ICP)测定硅元素含量，具体如下：取硅碳复合材料作为样品，用王水和氢氟酸HF对样品进行消解，取15min消解的溶液和完全消解的溶液进行ICP测试，45min消解的溶液中硅含量为“硅碳复合材料的外周区域”硅含量。
碳元素含量可以通过红外吸收法碳-硫含量分析，依据GB/T20123-2006测试标准测试，具体如下：取硅碳复合材料作为样品，测试20min时的碳含量为“硅碳复合材料的外周区域”碳含量。
A1和B1满足上述范围时，附着于碳基体颗粒内部的硅纳米颗粒的质量相对较高，能够显著提高负极活性材料的容量，并且金属离子嵌入的电压较低，有利于金属离子的嵌入，从而进一步提高二次电池在高倍率下充放电时的容量保持率。
在一些实施方式中，碳基体颗粒中孔径大于100nm的孔的总容积记为Vc1cm3/g，碳基体颗粒中孔径小于等于100nm的孔的总容积记为Vc2cm3/g，则碳基体颗粒满足：1＜Vc2/Vc1≤30；可选地，3≤Vc2/Vc1≤25。
通过调控多孔碳基体颗粒中特定尺寸的孔的总孔容积比例，可以使得碳基体颗粒的孔径分布适中，有利于硅纳米颗粒进入碳基体颗粒的孔中，并且可以使得硅碳复合颗粒的比表面积适中，改善其可逆容量。
在一些实施方式中，硅碳复合材料在20000N的作用力下经过1次粉压后测试的粉体压实密度P11g/cm3与硅碳复合材料在20000N的作用力下经过20次粉压后测试的压实密度记P21g/cm3的比值满足：1.00＜P21/P11≤1.20，可选地，1.02≤P21/P11≤1.10。
当P21/P11的比值满足上述范围时，硅碳复合材料在具有较高克容量的同时还具有较好的抗压性，提高了负极膜层的结构稳定性，从而使得含有该材料的二次电池在具有较高能量密度的同时兼顾较好的循环性能。
在一些实施方式中，硅碳复合材料在20000N的作用力下经过1次粉压后测试的粉体压实密度P11g/cm3满足：1.10≤P11≤1.40，可选 地，1.12≤P11≤1.35。
硅碳复合材料在20000N的作用力下经过1次粉压后测试的粉体压实密度P11g/cm3满足上述范围时，负极膜层具有较高的压实密度，从而使得二次电池具有较高的能量密度。
在一些实施方式中，电解液的电导率为8～12ms/cm，可选为9～11ms/cm。
在一些实施方式中，电解液的电导率可选为8、9、10、11或12ms/cm。
电解液的电导率在上述范围内时，可以确保离子在电解液中的迁移速率，改善电池的循环性能和循环效率。
在一些实施方式中，二次电池包括负极极片，负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极膜层，所述负极膜层包括负极活性材料。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极膜层设置在负极集流体相对的两个表面中的任意一者或两者上。
在一些实施方式中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(铜、铜合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，负极膜层还可选地包括粘结剂。所述粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的至少一种。
在一些实施方式中，负极膜层还可选地包括导电剂。导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，负极膜层还可选地包括其他助剂，例如增稠剂(如羧甲基纤维素钠(CMC-Na))等。
在一些实施方式中，可以通过以下方式制备负极极片：将上述用于制备负极极片的组分，例如负极活性材料、导电剂、粘结剂和任意其他组分分散于溶剂(例如去离子水)中，形成负极浆料；将负极浆料涂覆在负极集流体上，经烘干、冷压等工序后，即可得到负极极片。
在一些实施方式中，二次电池包括正极极片，正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极膜层，所述正极膜层包括本申请第一方面的正极活性材料。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极膜层设置在正极集流体相对的两个表面的其中任意一者或两者上。
在一些实施方式中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
在一些实施方式中，正极活性材料可采用本领域公知的用于电池的正极活性材料。作为示例，正极活性材料可包括以下材料中的至少一种：橄榄石结构的含锂磷酸盐、锂过渡金属氧化物及其各自的改性化合物。但本申请并不限定于这些材料，还可以使用其他可被用作电池正极活性材料的传统材料。这些正极活性材料可以仅单独使用一种，也可以将两种以上组合使用。其中，锂过渡金属氧化物的示例可包括但不限于锂钴氧化物(如LiCoO2)、锂镍氧化物(如LiNiO2)、锂锰氧化物(如LiMnO2、LiMn2O4)、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物(如LiNi1/3Co1/3Mn1/3O2(也可以简称为NCM333)、LiNi0.5Co0.2Mn0.3O2 (也可以简称为NCM523)、LiNi0.5Co0.25Mn0.25O2(也可以简称为NCM211)、LiNi0.6Co0.2Mn0.2O2(也可以简称为NCM622)、LiNi0.8Co0.1Mn0.1O2(也可以简称为NCM811)、锂镍钴铝氧化物(如LiNi0.85Co0.15Al0.05O2)及其改性化合物等中的至少一种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂(如LiFePO4(也可以简称为LFP))、磷酸铁锂与碳的复合材料、磷酸锰锂(如LiMnPO4)、磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料中的至少一种。
在一些实施方式中，正极活性材料为富镍材料，镍元素在正极活性材料过渡金属中的摩尔比例高于85％。
在一些实施方式中，正极膜层还可选地包括粘结剂。作为示例，所述粘结剂可以包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物及含氟丙烯酸酯树脂中的至少一种。
在一些实施方式中，正极膜层还可选地包括导电剂。作为示例，所述导电剂可以包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的至少一种。
在一些实施方式中，可以通过以下方式制备正极极片：将上述用于制备正极极片的组分，例如正极活性材料、导电剂、粘结剂和任意其他的组分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可得到正极极片。
在一些实施方式中，二次电池中还包括隔离膜。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。
在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、聚乙烯、聚丙烯及聚偏二氟乙烯中的至少一种。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，二次电池包括锂离子电池、钠离子电池、镁离子电池、钾离子电池中的至少一种。
本申请的一个实施方式中，提供一种用电装置，包括任意实施方式的二次电池。
本申请对二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的二次电池1。
在一些实施方式中，参照图2，外包装可包括壳体11和盖板13。其中，壳体11可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体11具有与容纳腔连通的开口，盖板13能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件12。电极组件12封装于所述容纳腔内。电解液浸润于电极组件12中。二次电池1所含电极组件12的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
用电装置包括本申请提供的二次电池。二次电池可以用作用电装置的电源，也可以用作用电装置的能量存储单元。用电装置可以包括移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等，但不限于此。
图3是作为一个示例的用电装置。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注 明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
一、二次电池
实施例1
(1)、硅碳复合材料的制备
提供包含硅前驱体的气体至具有三维网络交联孔结构的碳基体颗粒；通过化学气相沉积，由所述硅前驱体生成附着于所述碳基体颗粒上的硅纳米颗粒，得到硅碳复合材料。其中，硅前驱体为硅烷，碳基体为硬碳。
(2)、负极极片的制备
将负极活性材料(硅碳复合体)、导电炭黑、增稠剂羧甲基纤维素钠(CMC)、粘结剂丁苯橡胶乳液(SBR)按96.5：1.0：1.0：1.5重量比在适量的去离子水中充分搅拌混合，使其形成均匀的负极浆料；将负极浆料涂覆于负极集流体上，经烘干等工序后，得到负极极片。
(3)、正极极片的制备
采用厚度为8μm的铝箔作为正极集流体。将正极活性材料LiNi0.8Co0.1Mn0.1O2(NCM811)，导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按重量比为93:2:5溶于溶剂N-甲基吡咯烷酮(NMP)中，充分搅拌混合均匀后得到正极浆料；之后将正极浆料均匀涂覆于正极集流体上，再经过烘干、冷压、分切，得到正极极片。
(4)、电解液的制备
将碳酸乙烯酯(EC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)按照按体积比1:1:1进行混合得到有机溶剂，接着将充分干燥的锂盐LiPF6溶解于混合后的有机溶剂中，配制成浓度为1mol/L的电解液，再加入30wt％的碳酸二甲酯混合均匀。
(5)、隔离膜
以聚丙烯膜作为隔离膜。
(6)、电池的制备
将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、 负极片之间起到隔离的作用，然后卷绕得到裸电芯，给裸电芯焊接极耳，并将裸电芯装入铝壳中，并在80℃下烘烤除水，随即注入电解液并封口，得到不带电的电池。不带电的电池再依次经过静置、热冷压、化成、整形、容量测试等工序，获得实施例1的锂离子电池产品。
实施例2-5
实施例2-5的电池的制备方法与实施例1相似，但是调整了碳酸二甲酯在电解液中的质量占比EL。具体参数如表1所示。
实施例6-9
实施例6-9的电池的制备方法与实施例1相似，但是同时调整了碳酸二甲酯在电解液中的质量占比EL与硅碳复合材料的相关参数。
对比例1
对比例1的电池的制备方法与实施例1相似，但是不在电解液中加入碳酸二甲酯。
对比例2
对比例2的电池的制备方法与实施例1相似，但是对比例2的碳基体颗粒的孔结构为蜂窝状孔结构。
二、测试方法
1、硅碳复合材料
1)硅碳复合材料的结构表征
硅碳复合材料的孔结构可以采用本领域已知的设备和方法进行测试。例如，可以通过使用扫描电子显微镜(例如ZEISS Sigma 300)进行测试。作为示例，可以按照如下步骤操作：首先将包含所述硅碳复合材料的负极极片裁成一定尺寸的待测样品(例如6mm×6mm)，用两片导电导热的薄片(如铜箔)将待测样品夹住，将待测样品与薄片之间用胶(如双面胶)粘住固定，用一定质量(如400g左右)平整铁块压一定时间(如1h)，使待测样品与铜箔间缝隙越小越好，然后用剪刀将边缘剪齐，粘在具有导电胶的样品台上，样品略突出样品台边缘即可。然后将样品台装进样品架上锁好固定，打开氩离子截面抛光仪(例如IB-19500CP)电源并抽真空(例如10 Pa-4Pa)，设置氩气流量(例如0.15MPa)和电压(例如8KV)以及抛光时间(例如2小时)，调整样品台为摇摆模式开始抛光，抛光结束后，使用扫描电子显微镜(例如ZEISS Sigma 300)得到待测样品的离子抛光断面形貌(CP)图片。
2)硅碳复合材料的孔隙率
将电池拆解后取负极膜层，将负极膜层在xxx高温烧蚀后去除粘结剂获得硅碳复合材料粉末，按照GB/T24586，采用气体置换法测量。孔隙率P＝(V1-V2)/V1*100％，其中V1是样品的表观体积，V2是样品的真实体积。
3)硅碳复合材料的比表面积SSA
依据GB/T19587-2017测试标准采用气体吸附法测试比表面积，具体如下：取硅碳复合材料作为样品，样品管浸没在-196℃液氮中，在0.05-0.30相对压力下测定不同压力下氮气在固体表面的吸附量，基于BET多层吸附理论及其公式求得试样单分子层吸附量，从而计算出负极活性材料的比表面积。
BET的计算公式如下：
式中，na—被吸附气体的量，单位mol/g；p/p0—相对压力；nm—单分子层吸附量；C表示修订参数，其用于限制吸附剂表面上的吸附层的数量。
4)硅碳复合材料的孔径
气体吸附法测试孔径，依据GB/T19587-2017&GB/T21650.2-2008测试标准测试，具体如下：取硅碳复合材料作为样品，将样品管浸没在-196℃液氮中，氮气在0-1的相对压力下吸附在待测材料上，基于各级孔径的体积与相应分压下的关系图来表征多孔材料的孔径分布。
5)粉体压实密度
参照GB/T 24533-2009，使用电子压力试验机(如UTM7305) 测试：将一定质量G的待测粉末样品放于压实专用模具上(底面积S)，设置不同压力(本申请中可采用20000N或50000N)，保压20s，卸除压力，等待10s，在设备上读出该压力下粉末压5实后的厚度H，计算可得该压力下的压实密度，材料在该压力下的压实密度＝G/(H*S)。
6)硅碳复合材料的真密度
参考GB/T 24586-2009，测试仪器可以采用真密度测试仪。作为示例，可以按照如下步骤操作：取洁净干燥的硅碳复合材料样品杯放置在天平，清零，将一定量粉末样品加入到样品杯中(例如，样品可以占样品杯体积的1/2)，记录所取样品的质量，将装有样品的样品杯置于真密25度测试仪密闭测试，通入氦气，检测样品室和膨胀室中的气体的压力，再根据玻尔定律来计算真实体积，进而计算真密度。
7)硅碳复合材料中硅、碳元素分布表征
采用能谱法离子抛光断面元素分析，依据GB-T17359-2012测试标准，测试颗粒断面的元素分布。
2、电解液
1)电解液的电导率测试
使用电导率仪对电解液在25℃下进行测试，电导率仪的型号为梅特勒电导率仪S230。
3、电池性能
1)循环容量保持率
在25℃下，将各实施例和对比例制备得到的二次电池以0.5C倍率恒流充电至充电截止电压4.25V，之后恒压充电至电流≤0.05C，静置5min，再以0.33C倍率恒流放电至放电截止电压2V，静置5min，此为一个充放电循环。按照此方法对电池进行循环充放电测试，计算锂离子电池循环800次后的容量保持率。
2)高倍率下的循环容量保持率
在25℃下，将各实施例和对比例制备得到的二次电池以0.5C倍率恒流充电至充电截止电压4.25V，之后恒压充电至电流≤0.05C，静 置5min，再以0.33C倍率恒流放电至放电截止电压2V，静置5min，此为一个充放电循环。然后以2C倍率恒流充电至充电截止电压4.25V，再以0.33C倍率恒流放电至放电截止电压2V，按照此方法对电池进行循环充放电测试，计算锂离子电池循环800次后的容量保持率。
3)、电池内阻测试
在25℃下，将各实施例和对比例制备得到的二次电池和25℃以2C倍率循环800次的锂离子电池以1C恒流充电至4.3V。然后，以4.3V恒压充电至电流小于0.05C，然后再以1C放电30min，即将电池的电量调整到50％SOC。然后，将TH2523A交流内阻测试仪的正负表笔分别接触电池的正负极，通过内阻测试仪读取电池的内阻值，分别记为初始电池内阻(mΩ)和800次后电池内阻(mΩ)。
三、各实施例、对比例测试结果分析
按照上述方法分别制备各实施例和对比例的二次电池，并测量各项参数，结果见下表1。
表1
根据表1的结果可知，实施例1-9的电池的负极活性材料为三维网络交联孔结构的硅碳复合材料，并且电解液包含碳酸二甲酯，相比于对比例1中负极活性材料为三维网络交联孔结构的硅碳复合材料且电解液不包含碳酸二甲酯的电池、对比例2中负极活性材料为蜂窝状孔结构的硅碳复合材料且电解液包含碳酸二甲酯的电池、对比例3中加入碳酸二乙酯的电池、对比例4中加入碳酸甲乙酯的电池，实施例1-9的电池表现出更低的内阻，更高的循环容量保持率，更优异的高倍率充放电性能。
对比例中负极为蜂窝状孔结构的硅碳复合材料，硅颗粒不容易沉积在蜂窝状孔结构的内部，因此，蜂窝孔状结构的硅碳复合材料中硅基颗粒的质量含量低，仅为7％，且硅元素集中于复合材料的表面分布，碳基体难以起到限制硅基颗粒膨胀的作用，电池的循环性能差。
从实施例2-3与实施例4-5的对比可见，控制硅碳复合材料的孔隙体积Vm与碳酸二甲酯在电解液中的质量占比EL之间的比值EL：Vm在0.5～20的范围内，能够在提高电池循环容量保持率的同时显著的提高电池的倍率性能。
从实施例6-9可见，控制EL：SSA为0.05～0.25或EL：V1为30～120，可以进一步提高电池的循环性能和倍率性能。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。

Claims (17)

  1. 一种二次电池，其特征在于，包括
    负极极片，所述负极极片包括具有三维网络交联孔结构的硅碳复合材料；和
    电解液，所述电解液包含碳酸二甲酯。
  2. 根据权利要求1所述的二次电池，其特征在于，
    所述硅碳复合材料单位质量的孔隙体积为Vm，单位为cm3/g；
    基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，
    所述硅碳复合材料的孔隙体积Vm与所述碳酸二甲酯在所述电解液中的质量占比EL之间的比值EL：Vm为0.5～20，可选为2～13。
  3. 根据权利要求2所述的二次电池，其特征在于，所述硅碳复合材料单位质量的孔隙体积为Vm为0.01～0.3cm3/g，可选为0.04～0.15cm3/g。
  4. 根据权利要求1至3中任一项所述的二次电池，其特征在于，基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，所述硅碳复合材料的比表面积为SSA，EL：SSA为0.01～0.5，可选为0.05～0.25。
  5. 根据权利要求1至4中任一项所述的二次电池，其特征在于，所述硅碳复合材料的比表面积SSA为2～10m2/g；可选为3～7m2/g。
  6. 根据权利要求1至5中任一项所述的二次电池，其特征在于，基于所述电解液的总质量计，所述碳酸二甲酯在所述电解液中的质量占比为EL g/g，所述硅碳复合材料中孔径小于等于100nm的孔的总孔容积为V1cm3/g，所述碳酸二甲酯在所述电解液中的质量占比 EL与所述硅碳复合材料中孔径小于等于100nm的孔的总孔容积V1之间的比值EL：V1为10～200，可选为30～120。
  7. 根据权利要求1至6中任一项所述的二次电池，其特征在于，所述硅碳复合材料的V1≥0.001cm3/g，可选为0.005～0.01cm3/g。
  8. 根据权利要求1至7中任一项所述的二次电池，其特征在于，所述硅碳复合材料包括：碳基体颗粒，所述碳基体颗粒具有三维网络交联的孔结构；以及硅纳米颗粒，所述硅纳米颗粒至少部分地嵌入所述碳基体颗粒的三维网络交联的孔结构中。
  9. 根据权利要求8所述的二次电池，其特征在于，所述硅纳米颗粒在所述硅碳复合材料中的质量比大于等于40％，可选为40～60％。
  10. 根据权利要求8或9所述的二次电池，其特征在于，所述硅纳米颗粒包括硅氧化合物、非晶硅、晶体硅和硅碳复合物中的一种或多种。
  11. 根据权利要求8至10中任一项所述的二次电池，其特征在于，所述碳基体包括石墨、软碳和硬碳中的一种或多种。
  12. 根据权利要求8至11中任一项所述的二次电池，其特征在于，所述碳基体颗粒中孔径大于100nm的孔的总容积记为Vc1cm3/g，所述碳基体颗粒中孔径小于等于100nm的孔的总容积记为Vc2cm3/g，则所述碳基体颗粒满足：1＜Vc2/Vc1≤30；可选地，3≤Vc2/Vc1≤25。
  13. 根据权利要求1至12中任一项所述的二次电池，其特征在于，所述硅碳复合材料在20000N的作用力下经过1次粉压后测试的 粉体压实密度P11g/cm3与所述硅碳复合材料在20000N的作用力下经过20次粉压后测试的压实密度记P21g/cm3的比值满足：1.00＜P21/P11≤1.20，可选地，1.02≤P21/P11≤1.10。
  14. 根据权利要求1至12中任一项所述的二次电池，其特征在于，所述硅碳复合材料在20000N的作用力下经过1次粉压后测试的粉体压实密度P11g/cm3满足：1.10≤P11≤1.40，可选地，1.12≤P11≤1.35。
  15. 根据权利要求1至14中任一项所述的二次电池，其特征在于，所述电解液的电导率为8～12ms/cm，可选为9～11ms/cm。
  16. 根据权利要求1至15中任一项所述的二次电池，其特征在于，所述二次电池包括锂离子电池、钠离子电池、镁离子电池、钾离子电池中的至少一种。
  17. 一种用电装置，其特征在于，包括权利要求1至16中任一项所述的二次电池。
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