WO2023184125A1 - 电化学装置和电子设备 - Google Patents

电化学装置和电子设备 Download PDF

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WO2023184125A1
WO2023184125A1 PCT/CN2022/083530 CN2022083530W WO2023184125A1 WO 2023184125 A1 WO2023184125 A1 WO 2023184125A1 CN 2022083530 W CN2022083530 W CN 2022083530W WO 2023184125 A1 WO2023184125 A1 WO 2023184125A1
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Prior art keywords
silicon
alloy
negative electrode
carbon
composite material
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PCT/CN2022/083530
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English (en)
French (fr)
Inventor
胡荣涛
苏俊铭
崔航
谢远森
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宁德新能源科技有限公司
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Priority to CN202280051081.0A priority Critical patent/CN117693830A/zh
Priority to PCT/CN2022/083530 priority patent/WO2023184125A1/zh
Publication of WO2023184125A1 publication Critical patent/WO2023184125A1/zh

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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
    • 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
    • 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
    • H01M4/36—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
    • 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

  • This application belongs to the field of electrochemical technology, and specifically relates to an electrochemical device and electronic equipment.
  • Electrochemical devices such as lithium-ion batteries are widely used in all aspects of today's life due to their advantages such as light weight, small size, green environmental protection, and large specific capacity. In recent years, electrochemical devices have developed rapidly in the fields of new energy vehicles and large-scale energy storage. At present, taking lithium-ion batteries as an example, silicon material has the highest theoretical gram capacity (3579mAh/g) and is the most potential anode material to increase the volume energy density of lithium-ion batteries. However, the compacted density of silicon material powder is low and the volume expansion is large, resulting in an insignificant increase in volumetric energy density and rapid capacity fading during its actual application.
  • the purpose of this application is to provide an electrochemical device and electronic equipment, aiming to improve the energy density, capacity and cycle performance of the electrochemical device.
  • a first aspect of the present application provides a silicon-carbon composite material, including: a carbon matrix, and silicon alloy nanoparticles dispersed in the carbon matrix.
  • the mass percentage content ⁇ 1 of the silicon alloy is ⁇ 55%.
  • the silicon-carbon composite material satisfies at least one of conditions (1) to (2):
  • the volume average particle size Dv50 of the silicon-carbon composite material is 4.5 ⁇ m to 6.7 ⁇ m;
  • the volume average particle size Dv10 of the silicon-carbon composite material is 1.6 ⁇ m to 2.5 ⁇ m.
  • the silicon alloy includes silicon barium alloy, silicon calcium alloy, silicon cerium alloy, silicon cobalt alloy, silicon chromium alloy, silicon magnesium alloy, silicon molybdenum alloy, silicon manganese alloy, silicon nickel alloy and silicon At least one of the ferrous alloys.
  • the ferrosilicon alloy satisfies at least one of conditions (3) to (4):
  • the mass percentage of silicon in the ferrosilicon alloy is 30% to 80%;
  • the mass percentage of iron in the ferrosilicon alloy is 18% to 68%.
  • the surface of the silicon alloy nanoparticles includes a carbon layer, and the thickness of the carbon layer is 10 nm to 100 nm.
  • the volume average particle size Dv50 of the silicon-carbon composite material is 4.8 ⁇ m to 6.5 ⁇ m;
  • the volume average particle size Dv10 of the silicon-carbon composite material is 1.8 ⁇ m to 2.3 ⁇ m;
  • the mass percentage of silicon in the ferrosilicon alloy is 35% to 75%
  • the mass percentage of iron in the ferrosilicon alloy is 20% to 65%.
  • the thickness of the carbon layer on the surface of the silicon alloy nanoparticles is 30nm to 70nm.
  • the second aspect of this application provides a method for preparing the silicon carbon composite material described in the first aspect of this application, including:
  • the alloying step includes mechanical alloying treatment of silicon powder and metal powder to obtain silicon alloy nanoparticles;
  • the carbon layer forming step includes chemical vapor deposition processing to obtain silicon alloy nanoparticles whose surfaces include a carbon layer;
  • the carbon matrix composite step includes mixing, ball milling and heat treating the silicon alloy nanoparticles whose surfaces include a carbon layer and the precursor material forming the carbon matrix to obtain the silicon carbon composite material.
  • a third aspect of the present application provides a negative electrode sheet, including: a negative electrode current collector, and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the first aspect of the present application.
  • the fourth aspect of this application is an electrochemical device, including the negative electrode plate described in the third aspect of this application.
  • the negative electrode piece satisfies at least one of conditions (10) to (12):
  • the compacted density of the negative electrode piece is 1.9g/cm 3 to 2.2g/cm 3 ;
  • the single-sided coating weight of the negative electrode piece is 0.02g/1540mm 2 to 0.04g/1540mm 2 ;
  • the porosity of the negative electrode piece is 7% to 14%.
  • the fifth aspect of this application is an electronic device, including the electrochemical device described in the fourth aspect of this application.
  • Figure 1 is an SEM image of an embodiment of the silicon-carbon composite material of the present application.
  • Figure 2 is a lithium-ion battery cycle performance test chart of Example 1 and Comparative Example 1 of the present application.
  • Figure 3 is a TEM image of the surface carbon layer of Example 7 of the present application.
  • Figure 4 is a TEM image of the surface carbon layer of Comparative Example 4 of the present application.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with other lower limits to form an unexpressed range, and likewise any upper limit can be combined with any other upper limit to form an unexpressed range.
  • each individually disclosed point or single value may itself serve as a lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.
  • a term may refer to a variation of less than or equal to ⁇ 10% of the stated numerical value, such as less than or equal to ⁇ 5%, less than or equal to ⁇ 4%, less than or equal to ⁇ 3%, Less than or equal to ⁇ 2%, less than or equal to ⁇ 1%, less than or equal to ⁇ 0.5%, less than or equal to ⁇ 0.1%, or less than or equal to ⁇ 0.05%. Additionally, quantities, ratios, and other numerical values are sometimes presented herein in range format.
  • a list of items connected by the terms “at least one of,” “at least one of,” “at least one of,” or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase “at least one of A and B” means only A; only B; or A and B. In another example, if the items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B and C.
  • Item A may contain a single component or multiple components.
  • Item B may contain a single component or multiple components.
  • Item C may contain a single component or multiple components.
  • silicon material has broad prospects in the application of lithium-ion batteries because of its high theoretical gram capacity (3579mAh/g).
  • the powder compaction density of silicon material is lower than that of graphite.
  • the cold-pressed density of the negative electrode sheet will be further reduced, which is not conducive to the improvement of volume energy density.
  • the volume change of the nano-silicon material during the cycle is small ( ⁇ 300%).
  • the nano-silicon material (particle size > 1 ⁇ m) is not easy to expand after expansion. Crushed and pulverized, it can maintain good structural stability.
  • silicon nanomaterials are difficult to prepare, expensive, and have a large specific surface area, which consumes more electrolyte to form a solid-phase electrolyte interface film, resulting in low first Coulombic efficiency.
  • the good electrical conductivity, ductility and high compaction density of graphite and other materials can be used to improve the electrical conductivity and cold pressing density of the negative electrode, so that it can be used to a certain extent. It can increase the volume energy density of lithium-ion batteries and alleviate the volume expansion of silicon materials during cycling to a limited extent.
  • the inventor found that simple mechanical mixing of silicon materials and graphite is difficult to achieve uniform distribution of materials, and the ohmic contact between graphite particles and silicon powder must rely on a high-adhesion binder, and a large amount of binder Use will cause the capacity of the negative electrode to be reduced.
  • the inventor proposed a silicon-carbon composite material with high conductivity and high capacity through extensive research to improve the energy density and cycle performance of the electrochemical device.
  • the first aspect of the embodiment of the present application provides a silicon-carbon composite material, as shown in Figure 1 , including: a carbon matrix 11, and silicon alloy nanoparticles 12 dispersed in the carbon matrix.
  • a silicon-carbon composite material is formed by embedding silicon alloy nanoparticles into a carbon matrix.
  • the alloyed silicon alloy nanoparticles can enhance the conductivity of silicon; the carbon matrix can buffer the volume expansion of the silicon alloy during the cycle, even if the silicon alloy inevitably pulverizes during the cycle. , and can also maintain good electrical contact with the carbon matrix, which can significantly alleviate capacity fading.
  • silicon alloy nanoparticles have extremely high compaction density, they can significantly increase the volumetric energy density of electrochemical devices, ultimately enabling electrochemical devices to have high energy density, high capacity, and long cycle life.
  • the mass percentage content of the silicon alloy ⁇ 1 is ⁇ 55%.
  • the mass percentage ⁇ 1 of the silicon alloy may be 55% to 60%, 55% to 65%, 55% to 70%, 55% to 75% or 55% to 80%, etc.
  • the mass percentage content of the silicon alloy is within an appropriate range, which can enhance the conductivity of the silicon-carbon composite material and help increase its compaction density, thereby increasing the energy density of the electrochemical device.
  • the mass percentage content of the carbon matrix ⁇ 2 ⁇ 40% based on the total mass of the silicon-carbon composite material.
  • the mass percentage ⁇ 2 of the carbon matrix may be ⁇ 2 ⁇ 35%, ⁇ 2 ⁇ 30%, ⁇ 2 ⁇ 25%, ⁇ 2 ⁇ 20% or ⁇ 2 ⁇ 15%, etc.
  • the carbon matrix has a degree of graphitization of 90% to 95%, which enables the silicon-carbon composite material to have excellent electrical conductivity.
  • the mass percentage of the carbon matrix is within an appropriate range, which can buffer the volume expansion of silicon during the cycle, so that even if the silicon alloy inevitably pulverizes during the cycle, it can maintain good electrical contact with the carbon matrix. Increase the capacity of silicon-carbon composite materials, thereby increasing the capacity and energy density of electrochemical devices.
  • the silicon-carbon composite material meets the condition: the volume average particle diameter Dv50 of the silicon-carbon composite material is 4.5 ⁇ m to 6.7 ⁇ m.
  • the volume average particle diameter Dv50 of the silicon-carbon composite material is 4.5 ⁇ m, 4.8 ⁇ m, 5.1 ⁇ m, 5.4 ⁇ m, 5.7 ⁇ m, 6.0 ⁇ m, 6.3 ⁇ m, 6.6 ⁇ m or within the range of any of the above values.
  • the volume average particle diameter Dv50 of the silicon-carbon composite material is 4.8 ⁇ m to 6.5 ⁇ m.
  • the silicon-carbon composite material meets the condition: the volume average particle diameter Dv10 of the silicon-carbon composite material is 1.6 ⁇ m to 2.5 ⁇ m.
  • the volume average particle diameter Dv10 of the silicon-carbon composite material is 1.6 ⁇ m, 1.8 ⁇ m, 2.0 ⁇ m, 2.2 ⁇ m, 2.4 ⁇ m or within the range of any of the above values.
  • the volume average particle size Dv10 of the silicon-carbon composite material is 1.8 ⁇ m to 2.3 ⁇ m.
  • the volume average particle size Dv50 and Dv10 of the silicon-carbon composite material are within a suitable range, which is conducive to increasing the compaction density of the negative electrode sheet, thereby increasing the energy density of the electrochemical device.
  • the volume average particle diameters Dv50 and Dv10 of the silicon-carbon composite material have well-known meanings in the art, and can be measured using instruments and methods well-known in the art. For example, you can refer to the GB/T 19077-2016 particle size distribution laser diffraction method and use a laser particle size analyzer to conveniently measure it, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Co., Ltd. in the United Kingdom.
  • the silicon alloy nanoparticles include a carbon layer having a thickness of 10 nm to 100 nm.
  • the thickness of the carbon layer is 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm or within the range of any of the above values.
  • the thickness of the carbon layer is 30 nm to 70 nm.
  • the thickness of the carbon layer is within a suitable range, which not only enables the silicon-carbon composite material to have a high capacity, but also allows it to withstand huge volumetric strain during the cycle without rupture, so that during the cycle
  • the gradually pulverized silicon alloy maintains electrical contact with the carbon matrix, enabling electrochemical devices with both high capacity and high cycle stability.
  • the silicon alloy refers to a substance whose main component is an intermetallic compound.
  • the type of the silicon alloy is not particularly limited, as long as there is an intermetallic compound in the binary alloy phase diagram.
  • the silicon alloy includes silicon-barium alloy, silicon-calcium alloy, silicon-cerium alloy, silicon-cobalt alloy, silicon-chromium alloy, silicon-magnesium alloy, silicon-molybdenum alloy, silicon-manganese alloy, silicon-nickel alloy and ferrosilicon alloy.
  • the silicon alloy is ferrosilicon alloy.
  • the ferrosilicon alloy meets the condition: the mass percentage of silicon in the ferrosilicon alloy is 30% to 80%.
  • the mass percentage of silicon in the ferrosilicon alloy is 35% to 75%, 40% to 70%, 45% to 65% or 50% to 60%.
  • the mass percentage of silicon in the ferrosilicon alloy is 35% to 75%.
  • the ferrosilicon alloy meets the condition: the mass percentage of iron in the ferrosilicon alloy is 18% to 68%.
  • the mass percentage of iron in the ferrosilicon alloy is 20% to 65%, 25% to 60%, 30% to 55%, 35% to 50% or 40% to 45%.
  • the mass percentage of iron in the ferrosilicon alloy is 20% to 65%.
  • the mass percentages of silicon and iron in the ferrosilicon alloy are within a suitable range, which can not only increase the capacity of the negative electrode, but also facilitate the presence of a considerable amount of non-electrochemically active or low electrochemically active substances in the ferrosilicon alloy.
  • the non-electrochemically active or low electrochemically active substances can play a role in buffering volume strain during the cycle, which is beneficial to improving cycle performance.
  • the second aspect of the embodiment of the present application provides a method for preparing the silicon-carbon composite material described in the first aspect of the present application, including:
  • the alloying step includes mechanical alloying of silicon powder and metal powder to obtain silicon alloy nanoparticles
  • the carbon layer forming step includes chemical vapor deposition processing to obtain silicon alloy nanoparticles with a carbon layer on the surface;
  • the carbon matrix composite step includes mixing, ball milling and heat treating the silicon alloy nanoparticles whose surface includes a carbon layer and the precursor material forming the carbon matrix to obtain the silicon carbon composite material.
  • the method for preparing silicon-carbon composite materials specifically includes:
  • the average particle size of the silicon alloy nanoparticles is 200 nm to 800 nm.
  • the average particle diameter of the silicon alloy nanoparticles is 250nm to 750nm, 300nm to 700nm, 350nm to 650nm, 400nm to 600nm or 450nm to 550nm.
  • the average particle size of the silicon alloy nanoparticles is 250 nm to 750 nm.
  • the average particle size of silicon alloy nanoparticles has a meaning known in the art and can be measured using instruments and methods known in the art. For example, the following method can be used for measurement: add about 0.02g of powder sample into a 50ml clean beaker, add about 20ml of deionized water, then add a few drops of 1% surfactant to completely disperse the powder in the water, and clean with 120W ultrasonic Ultrasonicate in the machine for 5 minutes, and use MasterSizer 2000 to test the particle size distribution.
  • the type of the metal powder is not particularly limited, as long as it can form an intermetallic compound with silicon after alloying treatment.
  • the metal powder includes barium, calcium, cerium, cobalt, chromium, magnesium, molybdenum, manganese, nickel, iron, etc.
  • the metal powder is iron.
  • step S10 further includes:
  • the mass fraction of other impurities does not exceed 5%. In some embodiments, the mass fraction of other impurities is 5% based on the mass of the ferrosilicon alloy nanoparticles.
  • the mass percentage of silicon powder in the mixed powder is not less than 50%, for example, it can be 55%, 60%, 65%, 70% or any of the above values. range.
  • the mass fraction of iron powder is not higher than 50%, for example, it can be 45%, 40%, 35%, 30%, 25% or within the range of any of the above values.
  • controlling the mass percentage content of silicon powder and iron powder within the above range is beneficial to the mass percentage content of silicon and iron in the final formed ferrosilicon alloy being also within the aforementioned corresponding range, so that the ferrosilicon alloy Considerable amounts of non-electrochemically active or low electrochemically active species are present.
  • the rotation speed of the high-speed ball mill in step S100 is not less than 600 rpm, and the duration is not less than 6 hours.
  • step S100 by alloying silicon in step S100, the conductivity and compaction density of silicon can be improved, which is beneficial to improving the energy density of the silicon-carbon composite material and the cycle performance of the electrochemical device.
  • the carbon layer in the above step S20, as shown in FIG. 3, in the silicon alloy nanoparticles whose surface includes a carbon layer, the carbon layer exhibits a villi-like structure.
  • the villi-like structure is formed by connecting multiple small-sized graphene sheets and has excellent electronic conductivity, which is beneficial to the electrochemical performance of the silicon-carbon composite material.
  • the graphene sheet has high strength and can withstand the huge stress of the silicon alloy during the process of embedding active ions, thereby better maintaining the stability of the silicon-carbon composite material structure.
  • step S20 further includes:
  • the carbon source gas includes at least one of CH 4 , C 2 H 4 , C 7 H 8 , C 2 H 2 , and C 3 H 6 .
  • the carbon source gas is CH 4 .
  • the temperature of the deposition process is 900°C to 1200°C, for example, it can be 900°C, 950°C, 1000°C, 1050°C, 1100°C, 1150°C, 1200°C or above. Any range of values.
  • the temperature of the deposition treatment is 1000°C to 1100°C.
  • the time of the deposition process is 20 min to 40 min, for example, it may be 25 min, 30 min, 25 min, 40 min or within the range of any of the above values.
  • the deposition treatment time is 25 min to 35 min.
  • step S20 specifically includes:
  • the tube furnace stops heating and After natural cooling to room temperature, the argon gas was turned off and the corundum crucible was taken out to obtain ferrosilicon alloy nanoparticles with a carbon layer on the surface.
  • the carbon layer obtained through chemical vapor deposition can exhibit a villi-like structure.
  • the villi-like structure is formed by connecting multiple small-sized graphene sheets. It has excellent electronic conductivity and is beneficial to silicon-carbon composite materials. electrochemical performance.
  • the graphene sheet has high strength and can withstand the huge stress generated by the silicon alloy during the lithium embedding process, thereby better maintaining the stability of the silicon-carbon composite material structure.
  • the precursor material of the carbon matrix is not particularly limited, as long as it can form a carbon matrix after heat treatment.
  • the precursor materials of the carbon matrix include pitch, needle coke, petroleum coke, etc.
  • the carbon matrix has a degree of graphitization of 90% to 95%.
  • the mass ratio of the carbon matrix precursor material to the silicon alloy nanoparticles whose surface includes a carbon layer is 0.30 to 0.70, for example, it can be 0.35, 0.40, 0.45, 0.50 , 0.55, 0.60, 0.65, 0.70 or within the range of any of the above values. Preferably, the mass ratio is 0.35 to 0.65.
  • the mass ratio of the carbon matrix precursor material and the silicon alloy nanoparticles including a carbon layer on the surface within an appropriate range, it is possible to ensure that the silicon-carbon composite material has a high capacity, and at the same time, it is beneficial to the
  • the carbon matrix continuous phase formed by the precursor material can wrap the silicon alloy nanoparticles including a carbon layer on the surface, so that the silicon alloy that is gradually pulverized during the cycle can always maintain electrical contact with the carbon matrix, thereby enabling electrochemical
  • the device combines high capacity with high cycle stability.
  • step S30 specifically includes:
  • the ferrosilicon alloy nanoparticles including a carbon layer on the surface are mixed with needle coke and ball-milled for 3 hours.
  • the corundum crucible containing the ball-milled powder is placed in a sintering furnace.
  • the furnace temperature is raised at a heating rate of 10°C/min in an inert atmosphere. to 1800°C, and the furnace temperature was stabilized at 1800°C for 1 hour. After the furnace temperature was cooled to room temperature, a silicon-carbon composite material in which ferrosilicon alloy was dispersed in a carbon matrix was obtained.
  • the inert atmosphere includes one or more mixtures of argon, nitrogen, helium, etc.
  • the conductivity and compaction density of the silicon material can be improved by alloying silicon; the carbon layer is formed through chemical vapor deposition and then further combined with the carbon matrix grown in situ to obtain the dispersed phase described in this application.
  • It is a silicon-carbon composite material with silicon alloy nanoparticles and a continuous phase of carbon matrix.
  • the silicon-carbon composite material has high compaction density and high capacity, which can improve the energy density and long cycle life of electrochemical devices.
  • a third aspect of the embodiment of the present application provides a negative electrode sheet, including: a negative electrode current collector and a negative electrode active material layer formed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes the negative electrode active material layer of the present application.
  • the negative electrode sheet has a compacted density of 1.9 to 2.2 g/cm 3 .
  • the compacted density of the negative electrode piece is 1.9g/cm 3 , 2.0g/cm 3 , 2.1g/cm 3 , 2.2g/cm 3 or within the range of any of the above values. Controlling the compaction density of the negative electrode piece within an appropriate range can bring the negative active material particles in the negative electrode piece into close contact and increase the negative active material content per unit volume, thereby increasing the energy density of the electrochemical device.
  • the single-sided coating weight of the negative electrode piece is 0.02g/1540mm 2 to 0.04g/1540mm 2 .
  • the single-sided coating weight of the negative electrode piece is 0.025g/1540mm 2 , 0.030g/1540mm 2 , 0.035g/1540mm 2 , 0.040g/1540mm 2 or within the range of any of the above values.
  • the single-sided coating weight of the negative electrode piece is within a suitable range, which enables the electrode piece to have further improved cycle performance and rate performance on the premise of high charge and discharge capacity.
  • the negative electrode sheet has a porosity of 7% to 14%.
  • the porosity of the negative electrode piece is 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% or within the range of any of the above values.
  • the porosity of the negative electrode sheet is within a suitable range, which is beneficial to improving the transmission efficiency of active ions (such as lithium ions), thereby improving the cycle performance of the electrochemical device.
  • each negative electrode piece (such as compaction density) given in this application refer to the parameters of one side of the negative electrode current collector.
  • the negative electrode active material layer is disposed on both sides of the negative electrode current collector, if the parameters on either side meet the requirements of this application, it is deemed to fall within the protection scope of this application.
  • the porosity of the negative electrode sheet has a meaning known in the art, and can be tested using methods known in the art.
  • other negative active materials other than silicon-carbon composite materials are not excluded from the negative active material layer.
  • the specific types of other negative active materials are not subject to specific restrictions and can be selected according to needs.
  • other negative active materials include, but are not limited to, natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO, Li-Sn alloy, Li-Sn -O alloy, Sn, SnO, SnO 2 , spinel structure Li 4 Ti 5 O 12 , and Li-Al alloy.
  • the negative active material layer optionally further includes a binder.
  • the binder may be selected from polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, and polypropylene At least one of nitrile, sodium carboxymethylcellulose, potassium carboxymethylcellulose, sodium carboxymethylcellulose, and potassium carboxymethylcellulose.
  • the negative active material layer optionally further includes a conductive agent.
  • the conductive agent 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 active material layer optionally includes other auxiliaries, such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • auxiliaries such as thickeners (such as sodium carboxymethyl cellulose (CMC-Na)) and the like.
  • the present application is not limited to the above materials.
  • the negative electrode sheet of the present application can also use other well-known materials that can be used as negative active materials, conductive agents, binders and thickeners.
  • the negative electrode current collector has two surfaces opposite in its thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.
  • a metal foil or a porous metal plate can be used as the negative electrode current collector, for example, a foil or a porous plate made of metals such as copper, aluminum, nickel, titanium, iron, or alloys thereof.
  • the negative electrode current collector is copper foil.
  • the negative electrode piece in this application can be prepared according to conventional methods in this field.
  • the silicon-carbon composite material described in the first aspect of this application or the silicon-carbon composite material prepared by the method described in the second aspect of this application, and optional other negative electrode active materials, conductive agents, binders and thickeners The agent is dispersed in a solvent, which can be N-methylpyrrolidone (NMP) or deionized water, to form a uniform negative electrode slurry.
  • NMP N-methylpyrrolidone
  • the negative electrode slurry is coated on the negative electrode current collector, and is obtained by drying, cold pressing and other processes. Negative pole piece.
  • the negative electrode sheet in this application does not exclude other additional functional layers in addition to the negative active material layer.
  • the negative electrode sheet of the present application also includes a conductive undercoat layer (for example, composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode active material layer and disposed on the surface of the negative electrode current collector. composition).
  • the negative electrode sheet of the present application further includes a protective layer covering the surface of the negative active material layer.
  • a fourth aspect of the embodiments of the present application provides an electrochemical device, including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy.
  • an electrochemical device including any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy.
  • it may include but is not limited to: a lithium-ion battery or a sodium-ion battery.
  • the electrochemical device of the present application includes a positive electrode piece, a negative electrode piece, a separator and an electrolyte.
  • the positive electrode piece, the negative electrode piece and the separator film can be made into an electrode assembly through a winding process or a lamination process.
  • the electrochemical device of the present application also includes an outer package for packaging the electrode assembly and the electrolyte.
  • the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or a soft bag, such as a bag-type soft bag.
  • the soft bag may be made of plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • PP polypropylene
  • PBT polybutylene terephthalate
  • PBS polybutylene succinate
  • the negative electrode sheet used in the electrochemical device of the present application is the negative electrode sheet of the third aspect of the embodiment of the present application. [Positive pole piece]
  • the material, composition and manufacturing method of the positive electrode piece used in the electrochemical device of the present application may include any technology known in the prior art.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector and including a positive electrode active material.
  • the positive electrode current collector has two surfaces facing each other in its own thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the cathode active material layer includes a cathode active material.
  • the specific type of the cathode active material is not specifically limited and can be selected according to requirements.
  • the cathode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates with an olivine structure, and their respective modified compounds.
  • the above-mentioned modified compounds of each positive electrode active material may be doping modification, surface coating modification, or doping and surface coating modification of the positive electrode active material.
  • lithium transition metal oxides may include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • the lithium-containing phosphate with an olivine structure may include lithium iron phosphate, a composite of lithium iron phosphate and carbon, a lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, a lithium manganese iron phosphate, a lithium manganese iron phosphate and carbon One or more of the composite materials and their modified compounds. Only one type of these positive electrode active materials may be used alone, or two or more types may be used in combination.
  • the positive active material includes lithium cobalt oxide (LiCoO 2 ).
  • the positive active material layer optionally further includes a conductive agent.
  • the conductive agent may include at least one of superconducting carbon, acetylene black, conductive carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • the positive active material layer optionally further includes a binder.
  • the binder may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene At least one of ethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil can be used as the positive electrode current collector.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may be selected from one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may be selected from polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.
  • the positive electrode piece in this application can be prepared according to conventional methods in this field.
  • the positive electrode active material layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying, and cold pressing.
  • the cathode slurry is usually formed by dispersing the cathode active material, optional conductive agent, optional binder and any other components in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the positive electrode sheet of the present application does not exclude other additional functional layers in addition to the positive active material layer.
  • the positive electrode sheet of the present application also includes a conductive undercoat layer (for example, composed of a conductive agent and a binder) sandwiched between the positive electrode current collector and the positive electrode active material layer and disposed on the surface of the positive electrode current collector. ).
  • the positive electrode sheet of the present application further includes a protective layer covering the surface of the positive electrode active material layer.
  • the electrolyte plays a role in conducting active ions between the positive electrode piece and the negative electrode piece.
  • the electrolyte solution that can be used in the electrochemical device of the present application can be an electrolyte solution known in the art.
  • the electrolyte solution includes an organic solvent, a lithium salt and optional additives.
  • organic solvent a lithium salt and optional additives.
  • the types of the organic solvent, lithium salt and additives are not specifically limited and can be selected according to needs.
  • the lithium salts include, but are not limited to, LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate) , LiFSI (lithium bisfluoromethanesulfonimide), LiTFSI (lithium bistrifluoromethanesulfonimide), LiTFS (lithium triflate), LiDFOB (lithium difluoroxalate borate), LiBOB (lithium dioxalate borate) ), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), and LiTFOP (lithium tetrafluorooxalate phosphate).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • LiClO 4 lithium perchlor
  • the organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), carbonic acid Dimethyl ester (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate Ester (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), Methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS)
  • EC ethylene carbon
  • the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain properties of the battery, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance. wait.
  • the additives include, but are not limited to, fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite Esters (ES), 1,3-propene sultone (PS), 1,3-propene sultone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinonitrile (SN) , at least one of adiponitrile (AND), tris(trimethylsilane)phosphate (TMSP), and tris(trimethylsilane)borate (TMSB).
  • FEC fluoroethylene carbonate
  • VC vinylene carbonate
  • VEC vinyl ethylene carbonate
  • DTD vinyl sulfate
  • ES vinyl sulfite Esters
  • PS 1,3-propene sultone
  • PST 1,3-propene sultone
  • the electrolyte solution can be prepared according to conventional methods in the art.
  • the organic solvent, lithium salt, and optional additives can be mixed evenly to obtain an electrolyte.
  • the additives are added to the organic solvent and mixed evenly to obtain an electrolyte.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents the positive and negative electrodes from short-circuiting and allows active ions to pass through.
  • isolation membrane There is no particular restriction on the type of isolation membrane in this application. Any well-known porous structure isolation membrane with good chemical stability and mechanical stability can be used.
  • the material of the isolation membrane can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride, but is not limited to these.
  • the isolation film can be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer may be the same or different. In some embodiments, a ceramic coating or a metal oxide coating can also be provided on the isolation film.
  • a fifth aspect of the embodiment of the present application provides an electronic device, which includes the electrochemical device of the fourth aspect of the embodiment of the present application, wherein the electrochemical device can be used as a power source in the electronic device.
  • the electronic device of the present application is not particularly limited and may be used in any electronic device known in the art.
  • electronic devices may include, but are not limited to, laptop computers, pen computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headsets, video recorders , LCD TV, portable cleaner, portable CD player, mini CD, transceiver, electronic notepad, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, power-assisted bicycle, bicycle, lighting Appliances, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.
  • cathode active material LiCoO 2 , conductive carbon black, and binder PVDF according to the weight ratio of 96.7:1.7:1.6, add an appropriate amount of solvent NMP, and use it in a vacuum mixer to obtain a cathode slurry; apply the cathode slurry evenly on the cathode on both surfaces of the current collector aluminum foil; then vacuum dried at 70°C for 12 hours and then punched into circular electrode sheets with a diameter of 10 mm to obtain the positive electrode sheet.
  • ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) at a mass ratio of 1:1:1 to obtain a basic solvent; dissolve LiPF 6 in the above basic solvent, and then Add fluoroethylene carbonate (FEC) and mix evenly to obtain an electrolyte, and then add fluoroethylene carbonate to the electrolyte.
  • EC ethylene carbonate
  • DMC dimethyl carbonate
  • DEC diethyl carbonate
  • FEC fluoroethylene carbonate
  • the mass percentage of LiPF 6 is 12.5%
  • the mass percentage of fluoroethylene carbonate is 10%.
  • PE porous polymeric film is used as the isolation membrane.
  • the bare battery core is placed in the outer packaging, the prepared electrolyte is injected and packaged, and the lithium-ion battery is obtained through processes such as formation, degassing, and trimming.
  • the secondary preparation method is similar to Example 1, except that the amount of needle coke added during the preparation of the silicon-carbon composite material is adjusted.
  • the secondary preparation method is similar to Example 1, except that the mass percentages of silicon and iron in the ferrosilicon alloy are adjusted during the preparation process of the silicon-carbon composite material.
  • the secondary preparation method is similar to Example 7, except that the duration of carbon source gas introduction in the carbon layer formation step during the preparation process of the silicon-carbon composite material is adjusted.
  • the secondary preparation method is similar to Example 1, except that during the preparation process of the silicon-carbon composite material, the ferrosilicon alloy nanoparticles Si 85 Fe 10 @gC whose surface includes a carbon layer are directly physically blended with graphite.
  • the secondary preparation method is similar to Example 1, except that in the preparation process of the silicon-carbon composite material, nano-silica powder is used instead of ferrosilicon alloy nano-particles.
  • the secondary preparation method is similar to Example 7, except that in the preparation process of the silicon-carbon composite material, the step of forming a carbon layer by chemical vapor deposition of ferrosilicon alloy nanoparticles is omitted.
  • the secondary preparation method is similar to Example 7, except that in the preparation process of the silicon-carbon composite material, the resorcinol-formaldehyde resin is coated with a liquid phase and then carbonized at high temperature to form a carbon layer instead of chemical vapor deposition. carbon layer.
  • examples of the process of liquid-phase coating of resorcinol-formaldehyde resin to form a carbon layer are as follows:
  • nano-ferrosilicon alloy Take 30g of nano-ferrosilicon alloy and 92g of cetyltrimethylammonium bromide, add them to a beaker containing 2500mL of deionized water, ultrasonicate in a water bath for 30 minutes, add a magnet for magnetic stirring, and then add 1000mL of ethanol to the system. , 28g resorcinol and 10mL ammonia, stir at room temperature for 30 minutes; then add 40mL formaldehyde dropwise, stir for 6 hours and then let stand for 12 hours, centrifuge, wash and dry the reaction system to obtain resorcinol-formaldehyde resin Coated nano-ferrosilicon alloy.
  • the resorcin-formaldehyde resin-coated nano-ferrosilicon alloy was calcined at 700°C for 3 hours in an inert atmosphere to obtain a nano-ferrosilicon alloy with a carbon layer on the surface.
  • the lithium-ion batteries in the above examples and comparative examples were charged to 4.45V at a constant current of 0.5C, and then discharged to 3.0V at a constant current of 0.5C after standing for 5 minutes. Record the The discharge capacity is the first discharge capacity. Taking the first discharge capacity as the initial capacity, conduct 400 cycle charge and discharge tests according to the above method, and record the discharge capacity each time; and compare the discharge capacity of each subsequent cycle with the initial capacity to obtain the discharge capacity decay curve (see figure 2).
  • Lithium-ion battery capacity retention rate (%) discharge capacity at the 400th cycle/first discharge capacity ⁇ 100%.
  • Energy density (Wh/L) discharge capacity of the 400th cycle ⁇ discharge voltage platform of the 400th time/geometric volume of the lithium-ion battery, where the discharge capacity of the 400th cycle is mAh and the geometric volume of the lithium-ion battery is long (cm) ⁇ width (cm) ⁇ height (cm).
  • lithium-ion batteries of Examples 1 to 5 containing the silicon-carbon composite materials of the present application all showed significantly better performance than those in Comparative Example 1.
  • the cycle stability of lithium-ion batteries is attributed to the fact that the ferrosilicon alloy is wrapped by a carbon matrix as a dispersed phase. The contact between the ferrosilicon alloy and the carbon matrix is surface contact, which is better than point contact in direct physical mixing.
  • in-situ grown pyrolytic graphite has closer contact with ferrosilicon alloys, is more resistant to stress changes, and can maintain good electrical contact and structural stability. Therefore, lithium-ion batteries are both It can achieve high capacity, high cycle stability, and high energy density.
  • Non-electrochemically active or low electrochemically active substances such as FeSi2 can also play a certain role in buffering volume strain, which can further improve the capacity, energy density and cycle capacity retention rate of lithium-ion batteries, and improve their cycle performance.
  • the villi-like structure is It is formed by connecting countless small-sized graphene sheets, which has better electronic conductivity and is more conducive to the electrochemical performance of active materials.
  • the graphene sheets are strong and can withstand the generation of ferrosilicon alloys during the lithium insertion process. stress to better maintain the structural stability of active materials and increase the capacity of silicon-carbon composite materials.
  • the negative electrode sheet has a greater compaction density of the electrode sheet and smaller pores. Rate. Because the ferrosilicon alloy as a dispersed phase is randomly distributed in the continuous phase of the carbon matrix, the contact mode between the ferrosilicon alloy and the carbon matrix is surface contact, which is better than the point contact in the direct physical mixing method; the ferrosilicon alloy as a dispersed phase is separated by the continuous phase.
  • the carbon matrix coating can form larger-sized particles.
  • the silicon-carbon composite material in which the ferrosilicon alloy is dispersed in the carbon matrix has a larger negative electrode.
  • the compacted density of the sheet and the smaller porosity of the electrode sheet can improve the capacity, energy density and cycle capacity retention rate of the lithium-ion battery, and improve its long cycle life.

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Abstract

本申请提供一种电化学装置和电子装置。所述电化学装置包括负极极片，所述负极极片包括负极集流体和负极活性物质层，所述负极活性物质层包括硅碳复合材料，其中，所述硅碳复合材料包括碳基质和分散在所述碳基质中的硅合金纳米微粒。本申请提供的电化学装置同时具备高容量、高的能量密度和长循环寿命。

Description

电化学装置和电子设备 技术领域
本申请属于电化学技术领域，具体涉及一种电化学装置和电子设备。
背景技术
电化学装置例如锂离子电池因质量轻、体积小、绿色环保、比容量大等优点，广泛应用在如今生活的各个方面。近年来，电化学装置更是在新能源汽车和大规模储能领域得到了迅猛发展。目前，以锂离子电池为例，硅材料因具有极高的理论克容量(3579mAh/g)，是提升锂离子电池体积能量密度最具潜力的负极材料。但是，硅材料粉末压实密度低、体积膨胀大，导致其实际应用时体积能量密度提升不明显、容量衰减快。
发明内容
本申请的目的在于提供一种电化学装置和电子设备，旨在提升电化学装置的能量密度、容量和循环性能。
本申请第一方面提供一种硅碳复合材料，包括：碳基质，和分散在所述碳基质中的硅合金纳米微粒。
在本申请任意实施方式中，基于所述硅碳复合材料的总质量，所述硅合金的质量百分含量ω 1≥55％。
在本申请任意实施方式中，所述硅碳复合材料满足条件(1)至(2)中的至少一者：
(1)所述硅碳复合材料的体积平均粒径Dv50为4.5μm至6.7μm；
(2)所述硅碳复合材料的体积平均粒径Dv10为1.6μm至2.5μm。
在本申请任意实施方式中，所述硅合金包括硅钡合金、硅钙合金、硅铈合金、硅钴合金、硅铬合金、硅镁合金、硅钼合金、硅锰合金、硅镍合金及硅铁合金中的至少一种。
在本申请任意实施方式中，所述硅铁合金满足条件(3)至(4)中的至少一者：
(3)所述硅铁合金中硅的质量百分含量为30％至80％；
(4)所述硅铁合金中铁的质量百分含量为18％至68％。
在本申请任意实施方式中，所述硅合金纳米微粒表面包括碳层，所述碳层的厚度为10nm至100nm。
在本申请任意实施方式中，满足条件(5)至(9)中的至少一者：
(5)所述硅碳复合材料的体积平均粒径Dv50为4.8μm至6.5μm；
(6)所述硅碳复合材料的体积平均粒径Dv10为1.8μm至2.3μm；
(7)所述硅铁合金中硅的质量百分含量为35％至75％；
(8)所述硅铁合金中铁的质量百分含量为20％至65％。
(9)所述硅合金纳米微粒表面碳层的厚度为30nm至70nm。
本申请第二方面提供一种用于制备本申请第一方面所述的硅碳复合材料的方法，包括：
合金化步骤，包括对硅粉和金属粉末进行机械合金化处理，以得到硅合金纳米微粒；
碳层形成步骤，包括通过化学气相沉积处理，以得到表面包括碳层的硅合金纳米微粒；
碳基质复合步骤，包括对所述表面包括碳层的硅合金纳米微粒与形成碳基质的前驱体材料进行混合球磨及热处理，以得到所述硅碳复合材料。
本申请第三方面提供一种负极极片，包括：负极集流体，和形成于所述负极集流体至少一个表面上的负极活性物质层，其中，所述负极活性物质层包含本申请第一方面所述的硅碳复合材料或通过本申请第二方面所述方法制得的硅碳复合材料。
本申请第四方面一种电化学装置，包括本申请第三方面所述的负极极片。
在本申请任意实施方式中，所述负极极片满足条件(10)至(12)中的至少一者：
(10)所述负极极片的压实密度为1.9g/cm 3至2.2g/cm 3；
(11)所述负极极片的单面涂布重量为0.02g/1540mm 2至0.04g/1540mm 2；
(12)所述负极极片的孔隙率为7％至14％。
本申请第五方面一种电子设备，包括本申请第四方面所述的电化学装置。
附图说明
图1是本申请的硅碳复合材料的一实施例的SEM图。
图2是本申请的实施例1与对比例1的锂离子电池循环性能测试图。
图3是本申请的实施例7的表面碳层的TEM图。
图4是本申请的对比例4的表面碳层的TEM图。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合实施例对本申请的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。在此所描述的有关实施例为说明性质的且用于提供对本申请的基本理解。本申请的实施例不应该被解释为对本申请的限制。
为了简明，本文仅具体地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围， 同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，除非另有说明，“以上”、“以下”包含本数。
除非另有说明，本申请中使用的术语具有本领域技术人员通常所理解的公知含义。除非另有说明，本申请中提到的各参数的数值可以用本领域常用的各种测量方法进行测量(例如，可以按照在本申请的实施例中给出的方法进行测试)。
术语“约”用以描述及说明小的变化。当与事件或情形结合使用时，所述术语可指代其中事件或情形精确发生的例子以及其中事件或情形极近似地发生的例子。举例来说，当结合数值使用时，术语可指代小于或等于所述数值的±10％的变化范围，例如小于或等于±5％、小于或等于±4％、小于或等于±3％、小于或等于±2％、小于或等于±1％、小于或等于±0.5％、小于或等于±0.1％、或小于或等于±0.05％。另外，有时在本文中以范围格式呈现量、比率和其它数值。应理解，此类范围格式是用于便利及简洁起见，且应灵活地理解，不仅包含明确地指定为范围限制的数值，而且包含涵盖于所述范围内的所有个别数值或子范围，如同明确地指定每一数值及子范围一般。
术语“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B及C的全部。项目A可包含单个组分或多个组分。项目B可包含单个组分或多个组分。项目C可包含单个组分或多个组分。
目前，在锂离子电池的负极材料中，硅材料因具有高的理论克容量(3579mAh/g)，因而在锂离子电池的应用中有着广阔的前景。但是，硅材料的粉末压实密度与石墨相比较低，特别是在硅含量逐渐增加的应用上，会进一步降低负极极片的冷压密度，这不利于体积能量密度的提升。
另外，发明人发现，随着活性离子如锂离子的嵌入和脱出，硅材料在充放电循环过程中会发生巨大的体积变化，这将导致硅材料连续粉化，一方面导致固相电解质界面膜不断被破坏并暴露出活性界面，持续消耗电解液重构固相电解质膜；另一方面，粉化的硅碎片脱离了集流体，无法参与后续的嵌锂/脱锂过程，导致锂离子电池的容量快速衰减。
为了提升硅材料粉末的压实密度以及缓解循环过程中的体积膨胀，目前常规的解决方法包括硅材料纳米化，将硅材料与石墨或其他材料(金属或非金属)混合，以及硅材料表面惰性层包覆等。
硅材料纳米化后，纳米硅材料在循环过程中的体积变化较小(＜300％)，与非纳米硅材料相比(粒径＞1μm)，纳米硅材料(粒径＜150nm)膨胀后不易破碎粉化，能够保持良好的结构稳定性。但是硅纳米材料制备困难、价格较高，而且比表面积大，这会消耗更多的电解液形成固相电解质界面膜，导致首次库伦效率偏低，这些缺点限制了硅纳米材料的进一步应用。
将硅材料与石墨或其他材料(金属或非金属)混合后，可利用石墨等材料良好的导电性、延展性和高压实密度，提升负极的导电性和冷压密度，从而可在一定程度上提升锂离子电池的体积能量密度，并有限程度上缓解循环过程中硅材料的体积膨胀。但是，发明人发现，将硅材料与石墨等进行简单的机械混合，难以实现物料的均匀分布，而石墨颗粒与硅粉末的欧姆接触必须依赖高粘结力的粘结剂，粘结剂的大量使用会造成负极极片可发挥容量的降低。
为了解决上述问题，发明人通过大量研究提出了一种具备高导电性以及高容量的硅碳复合材料，以提升电化学装置的能量密度和循环性能。
硅碳复合材料
本申请实施方式的第一方面提供了一种硅碳复合材料，如图1所示，包括：碳基质11，和分散在所述碳基质中的硅合金纳米微粒12。
本申请中，通过将硅合金纳米微粒嵌入到碳基质中，形成硅碳复合材料。在所述硅碳复合材料中，合金化的硅合金纳米微粒能够增强硅的导电性；碳基质能够缓冲硅合金在循环过程中的体积膨胀，即使硅合金在循环过程中发生不可避免的粉化，也能与碳基质保持良好的电接触，由此可以大幅缓解容量衰减。此外，由于硅合金纳米微粒具有极高的压实密度，因此可以显著提升电化学装置的体积能量密度，最终使电化学装置具备高能量密度、高容量以及长循环寿命。
在一些实施方式中，基于所述硅碳复合材料的总质量，所述硅合金的质量百分含量ω 1≥55％。例如，所述硅合金的质量百分含量ω 1可为55％至60％，55％至65％，55％至70％，55％至75％或55％至80％等。硅合金的质量百分含量在合适范围内，能够增强硅碳复合材料的导电性，并有利于提升其压实密度，从而提升电化学装置的能量密度。
在一些实施方式中，基于所述硅碳复合材料的总质量，所述碳基质的质量百分含量ω 2≤40％。例如，所述碳基质的质量百分含量ω 2可为ω 2≤35％，ω 2≤30％，ω 2≤25％，ω 2≤20％或ω 2≤15％等。在一些实施方式中，所述碳基质的石墨化度为90％至95％，可使硅碳复合材料具有优异的导电性。碳基质的质量百分含量在合适范围内，能够缓冲硅在循环过程中产生的体积膨胀，使得硅合金在循环过程中即使发生不可避免的粉化，也能与碳基质保持良好的电接触，提升硅碳复合材料的容量，进而提升电化学装置的容量和能量密度。
在一些实施方式中，所述硅碳复合材料满足条件：所述硅碳复合材料的体积平均粒径Dv50为4.5μm至6.7μm。例如，所述硅碳复合材料的体积平均粒径Dv50为4.5μm， 4.8μm，5.1μm，5.4μm，5.7μm，6.0μm，6.3μm，6.6μm或处于以上任何数值所组成的范围内。优选的，所述硅碳复合材料的体积平均粒径Dv50为4.8μm至6.5μm。
在一些实施方式中，所述硅碳复合材料满足条件：所述硅碳复合材料的体积平均粒径Dv10为1.6μm至2.5μm。例如，所述硅碳复合材料的体积平均粒径Dv10为1.6μm，1.8μm，2.0μm，2.2μm，2.4μm或处于以上任何数值所组成的范围内。优选的，所述硅碳复合材料的体积平均粒径Dv10为1.8μm至2.3μm。
本申请中，硅碳复合材料的体积平均粒径Dv50和Dv10在合适范围内，有利于提升负极极片的压实密度，进而提升电化学装置的能量密度。
硅碳复合材料的体积平均粒径Dv50和Dv10为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如可以参照GB/T 19077-2016粒度分布激光衍射法，采用激光粒度分析仪方便地测定，如英国马尔文仪器有限公司的Mastersizer 2000E型激光粒度分析仪。
在一些实施方式中，所述硅合金纳米微粒包括碳层，所述碳层的厚度为10nm至100nm。例如，所述碳层的厚度为10nm，20nm，30nm，40nm，50nm，60nm，70nm，80nm，90nm，100nm或处于以上任何数值所组成的范围内。优选的，所述碳层的厚度为30nm至70nm。
本申请中，碳层的厚度在合适范围内，在使得硅碳复合材料具备较高容量的同时，还能使其在循环过程中耐受巨大的体积应变而不发生破裂，使得在循环过程中逐渐粉化的硅合金能够始终保持与碳基质的电接触，从而使电化学装置兼具高容量和高的循环稳定性。
在一些实施方式中，所述硅合金指的是主要成分为金属间化合物的物质，所述硅合金的种类没有特别的限制，只要二元合金相图中存在金属间化合物的硅合金都可以。例如，所述硅合金包括硅钡合金、硅钙合金、硅铈合金、硅钴合金、硅铬合金、硅镁合金、硅钼合金、硅锰合金、硅镍合金及硅铁合金等。优选的，所述硅合金为硅铁合金。
在一些实施方式中，所述硅铁合金满足条件：所述硅铁合金中硅的质量百分含量为30％至80％。例如，所述硅铁合金中硅的质量百分含量为35％至75％，40％至70％，45％至65％或50％至60％。优选的，所述硅铁合金中硅的质量百分含量为35％至75％。
在一些实施方式中，所述硅铁合金满足条件：所述硅铁合金中铁的质量百分含量为18％至68％。例如，所述硅铁合金中铁的质量百分含量为20％至65％，25％至60％，30％至55％，35％至50％或40％至45％。优选的，所述硅铁合金中铁的质量百分含量为20％至65％。
本申请中，所述硅铁合金中硅与铁的质量百分含量在合适范围内，既能够提升负极的容量，又有利于使硅铁合金中存在数量可观的非电化学活性或低电化学活性物质，例如Fe 2Si、FeSi 3、FeSi 2等，所述非电化学活性或低电化学活性物质在循环过程中能够起到缓冲体积应变的作用，进而有利于提升循环性能。
本申请实施方式的第二方面提供了一种用于制备本申请第一方面所述的硅碳复合材料的方法，包括：
S10、合金化步骤，包括对硅粉和金属粉末进行机械合金化处理，以得到硅合金纳米微粒；
S20、碳层形成步骤，包括通过化学气相沉积处理，以得到表面包括碳层的硅合金纳米微粒；
S30、碳基质复合步骤，包括对所述表面包括碳层的硅合金纳米微粒与形成碳基质的前驱体材料进行混合球磨及热处理，以得到所述硅碳复合材料。
在一些实施方式中，所述用于制备硅碳复合材料的方法具体包括：
将硅粉与金属粉进行高速球磨，得到硅铁合金，通过破碎分级处理得到特定粒径的硅合金纳米微粒；再对硅合金纳米微粒进行化学气相沉积，得到表面包括碳层的硅合金纳米微粒；接着将形成碳基质的前驱体材料与表面包括碳层的硅合金纳米微粒按一定比例混合球磨，然后在惰性气氛中进行热处理，冷却后得到硅合金分散在连续的碳基质中的硅碳复合材料。
在一些实施方式中，上述步骤S10中，所述硅合金纳米微粒的平均粒径为200nm至800nm。例如，所述硅合金纳米微粒的平均粒径为250nm至750nm，300nm至700nm，350nm至650nm，400nm至600nm或450nm至550nm。优选的，所述硅合金纳米微粒的平均粒径为250nm至750nm。
本申请中，通过将硅合金纳米微粒的平均粒径控制在合适范围内，有利于后续保证负极极片具有较高的压实密度。
硅合金纳米微粒的平均粒径为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。例如，可以采用如下方法进行测量：在50ml洁净烧杯中加入约0.02g粉末样品，加入约20ml去离子水，再滴加几滴1％的表面活性剂，使粉末完全分散于水中，120W超声清洗机中超声5分钟，利用MasterSizer 2000测试粒度分布。
在一些实施方式中，上述步骤S10中，所述金属粉末的种类没有特别的限制，只要在合金化处理后能够与硅形成金属间化合物即可。例如，所述金属粉末包括钡、钙、铈、钴、铬、镁、钼、锰、镍及铁等。优选的，所述金属粉末为铁。
在一些实施方式中，以金属粉末为铁粉作为示例，上述步骤S10进一步包括：
S100、将硅粉和铁粉组成的混合粉体置于球磨罐中，进行高速球磨，然后通过破碎分级处理得到硅铁合金纳米微粒SixFey。
在一些实施方式中，所述硅铁合金纳米微粒Si xFe y中，基于所述硅铁合金纳米微粒的质量，硅的质量分数为x，铁的质量分数为y，其中，x≥50％，y≤50％，x+y≥95％，其它杂质的质量分数不超过5％。在一些实施方式中，基于所述硅铁合金纳米微粒的质量，其他杂质的质量分数为5％。
在一些实施方式中，步骤S100中，所述混合粉体中硅粉的质量百分含量不低于 50％，例如，可以为55％，60％，65％，70％或上述任何数值所组成的范围。铁粉的质量分数不高于50％，例如，可以为45％，40％，35％，30％，25％或处于以上任何数值所组成的范围内等。混合粉体中，将硅粉与铁粉的质量百分含量控制在上述范围内，有利于最终形成的硅铁合金中硅与铁的质量百分含量也在前述相应的范围内，使硅铁合金中存在数量可观的非电化学活性或低电化学活性物质。
在一些实施方式中，步骤S100中高速球磨的转速不低于600rpm，持续时间不低于6h。
本申请中，通过步骤S100中将硅进行合金化，能够提高硅的导电性和压实密度，进而有利于提升硅碳复合材料的能量密度和电化学装置的循环性能。
在一些实施方式中，上述步骤S20中，如图3所示，所述表面包括碳层的硅合金纳米微粒中，所述碳层呈现绒毛状结构。所述绒毛状结构是多个小尺寸的石墨烯片层连接形成，具有优异的电子导电性，有利于硅碳复合材料电化学性能的发挥。而且石墨烯片层强度大，能够耐受硅合金在嵌活性离子过程中的巨大应力，由此能够更好地维持硅碳复合材料结构的稳定性。
在一些实施方式中，上述步骤S20进一步包括：
S200、在900℃至1200℃、优选为1000℃至1100℃的温度下，使碳源气体与所述硅合金纳米微粒接触并进行20min至40min、优选为25min至35min的沉积处理。
在一些实施方式中，所述碳源气体包括CH 4、C 2H 4、C 7H 8、C 2H 2、C 3H 6中的至少一种。优选的，所述碳源气体为CH 4。
在一些实施方式中，步骤S200中，所述沉积处理的温度为900℃至1200℃，例如，可以为900℃，950℃，1000℃，1050℃，1100℃，1150℃，1200℃或处于以上任何数值所组成的范围内。优选的，所述沉积处理的温度为1000℃至1100℃。
在一些实施方式中，步骤S200中，所述沉积处理的时间为20min至40min，例如，可以为25min，30min，25min，40min或处于以上任何数值所组成的范围内。优选的，所述沉积处理的时间为25min至35min。
在一些实施方式中，以硅合金纳米微粒为硅铁合金作为示例，上述步骤S20具体包括：
将装有硅铁合金纳米微粒的刚玉坩埚置于化学气相沉积管式炉中，炉管抽真空后缓慢通入氩气持续30分钟，再以10℃/min的升温速率将炉温升至1000℃，炉温稳定在1000℃持续30分钟后断氩气、通入碳源气体(如纯度为99.95％的甲烷)，持续一段时间后断碳源气体、通入氩气，管式炉停止加热并自然冷却至室温后，断氩气取出刚玉坩埚得到表面包括碳层的硅铁合金纳米微粒。
本申请中，通过化学气相沉积处理获得的碳层能够呈出绒毛状结构，该绒毛状结构是多个小尺寸的石墨烯片层连接形成，具有优异的电子导电性，有利于硅碳复合材料电化学性能的发挥。而且石墨烯片层强度大，能够耐受硅合金在嵌锂过程中产生的巨大 应力，由此能够更好地维持硅碳复合材料结构的稳定性。
在一些实施方式中，上述步骤S30中，所述碳基质的前驱体材料没有特别的限制，只要经过热处理能够形成碳基质即可。例如，所述碳基质的前驱体材料包括沥青、针状焦及石油焦等。
在一些实施方式中，所述碳基质的石墨化度为90％至95％。可通过粉末X射线衍射法测试碳基质的石墨化度：对碳基质进行粉末X射线衍射分析，计算X射线衍射图谱中(002)峰的面间距d(002)＝λ/(2sinθ)，其中，λ为入射X射线的波长，θ为(002)峰对应的衍射角度值，按照公式石墨化度＝(0.344-d(002))/(0.344-0.3354)×100％计算所述碳基质的石墨化度。
在一些实施方式中，上述步骤S30中，所述碳基质的前驱体材料与所述表面包括碳层的硅合金纳米微粒的质量比为0.30至0.70，例如，可以为0.35，0.40，0.45，0.50，0.55，0.60，0.65，0.70或处于以上任何数值所组成的范围内。优选的，所述质量比为0.35至0.65。
本申请中，通过将碳基质的前驱体材料与表面包括碳层的硅合金纳米微粒的质量比控制在合适范围内，能够保证硅碳复合材料具备高的容量，同时有利于在热处理之后，所述前驱体材料形成的碳基质连续相能够将表面包括碳层的硅合金纳米微粒包裹其中，从而使循环过程中逐渐粉化的硅合金始终能够保持与碳基质的电接触，由此使电化学装置兼具高容量和高的循环稳定性。
在一些实施方式中，以碳基质的前驱体材料为针状焦作为示例，上述步骤S30具体包括：
将表面包括碳层的硅铁合金纳米微粒与针状焦混合后球磨3h，将装有球磨后粉料的刚玉坩埚置于烧结炉中，惰性气氛中以10℃/min的升温速率将炉温升至1800℃，炉温稳定在1800℃持续1h，炉温冷却至室温后得到硅铁合金分散在碳基质中的硅碳复合材料。
在一些实施方式中，所述惰性气氛包括氩气、氮气、氦气等中的一种或多种的混合气。
本申请中，通过将硅合金化能够提高硅材料的导电性和压实密度；通过化学气相沉积形成碳层后再进一步与原位生长的碳基质进行复合，能够得到本申请所述的分散相为硅合金纳米微粒、连续相为碳基质的硅碳复合材料，所述硅碳复合材料具有高压实密度和高容量，可提升电化学装置的能量密度和长循环寿命。
负极极片
本申请实施方式的第三方面提供一种负极极片，包括：负极集流体和形成于所述负极集流体至少一个表面上的负极活性物质层，其中，所述负极活性物质层包含本申请第一方面所述的硅碳复合材料或通过本申请第二方面所述方法制得的硅碳复合材料。
在一些实施方式中，所述负极极片的压实密度为1.9g/cm 3至2.2g/cm 3。例如，所述负极极片的压实密度为1.9g/cm 3，2.0g/cm 3，2.1g/cm 3，2.2g/cm 3或处于以上任何数值所 组成的范围内。负极极片的压实密度控制在合适的范围内，能使负极极片中的负极活性物质颗粒紧密接触，提高单位体积内的负极活性物质含量，由此提升电化学装置的能量密度。
在一些实施方式中，所述负极极片的单面涂布重量为0.02g/1540mm 2至0.04g/1540mm 2。例如，所述负极极片的单面涂布重量为0.025g/1540mm 2，0.030g/1540mm 2，0.035g/1540mm 2，0.040g/1540mm 2或处于以上任何数值所组成的范围内。负极极片的单面涂布重量在合适范围内，能使极片在具备高充放电容量的前提下，还具有进一步提升的循环性能和倍率性能。
在一些实施方式中，所述负极极片的孔隙率为7％至14％。例如，所述负极极片的孔隙率为7％，8％，9％，10％，11％，12％，13％，14％或处于以上任何数值所组成的范围内。负极极片的孔隙率在合适范围内，有利于提升活性离子(例如锂离子)的传输效率，从而提高电化学装置的循环性能。
需要说明的是，本申请所给的各负极极片参数(例如压实密度)均指负极集流体单侧的参数。当负极活性物质层设置在负极集流体的两侧时，其中任意一侧的参数满足本申请，即认为落入本申请的保护范围内。
本申请中，负极极片的压实密度为本领域公知的含义，可采用本领域已知的方法测试。例如，负极极片冷压后，用冲片机分别冲出面积为S的完全涂布有浆料的圆片和未涂布有浆料的圆片若干，分别进行称重得到平均质量W 2、W 1，分别进行测厚得到平均厚度T 2、T 1，负极极片的压实密度＝(W 2-W 1)/(T 2-T 1)/S。
本申请中，负极极片的单面涂布重量为本领域公知的含义，可采用本领域已知的方法测试。例如，取单面涂布且经冷压后的负极极片(若是双面涂布的负极极片，可先擦拭掉其中一面的负极活性物质层)，冲切成面积为S1的小圆片，称其重量，记录为M 1；然后将上述称重后的负极极片的负极活性物质层擦拭掉，称量负极集流体的重量，记录为M 0；负极膜层的单面涂布重量＝负极极片的重量M 1-负极集流体的重量M 0。
本申请中，负极极片的孔隙率为本领域公知的含义，可采用本领域已知的方法测试。例如，可采用真密度测试仪(AccuPyc II 1340)进行测量。将负极极片冲成直径大小为10mm或14mm的圆片，选取30至40片相对平整无缺的极片，记录面积平均值S，用螺旋千分尺记录厚度平均值H，并记录装样的极片数量(样品量以装满样品杯为准)，把样品杯放入样品仓中开始测试，测试完成后记录测试结果的平均值，记录该极片的平均真实体积V，负极极片的孔隙率＝(S*H-V)/S*H*100％。
在一些实施方式中，所述负极活性物质层中并不排除除了硅碳复合材料的其他负极活性材料。其他负极活性材料的具体种类不受到具体的限制，可根据需求进行选择。作为示例，其他负极活性材料包括但不限于天然石墨、人造石墨、中间相微碳球(MCMB)、硬碳，软碳、硅、硅-碳复合物、SiO、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的Li 4Ti 5O 12、Li-Al合金中的至少一种。
在一些实施方式中，负极活性物质层还可选地包括粘结剂。所述粘结剂可选自聚丙烯酸酯、聚酰亚胺、聚酰胺、聚酰胺酰亚胺、聚偏氟乙烯、丁苯橡胶、海藻酸钠、聚乙烯醇、聚四氟乙烯、聚丙烯腈、羧甲基纤维素钠、羧甲基纤维素钾、羟甲基纤维素钠、羟甲基纤维素钾中的至少一种。
在一些实施方式中，负极活性物质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，负极活性物质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。
但本申请并不限定于上述材料，本申请的负极极片还可以使用可被用作负极活性材料、导电剂、粘结剂和增稠剂的其它公知材料。
在一些实施方式中，所述负极集流体具有在自身厚度方向相对的两个表面，负极活性物质层设置于负极集流体所述两个相对表面中的任意一者或两者上。
负极集流体可以使用金属箔材或多孔金属板，例如使用铜、铝、镍、钛、铁等金属或它们的合金的箔材或多孔板。作为示例，负极集流体为铜箔。
本申请中负极极片可以按照本领域常规方法制备。例如将本申请第一方面所述的硅碳复合材料或通过本申请第二方面所述方法制得的硅碳复合材料，及可选的其他负极活性材料，导电剂，粘结剂和增稠剂分散于溶剂中，溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，形成均匀的负极浆料，将负极浆料涂覆在负极集流体上，经烘干、冷压等工序得到负极极片。
本申请中的负极极片并不排除除了负极活性物质层之外的其他附加功能层。例如，在某些实施方式中，本申请的负极极片还包括夹在负极集流体和负极活性物质层之间、设置于负极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请的负极极片还包括覆盖在负极活性物质层表面的保护层。
电化学装置
本申请实施方式的第四方面提供一种电化学装置，包括其中发生电化学反应以将化学能与电能互相转化的任何装置，例如可以包括但不限于：锂离子电池或钠离子电池。
在一些实施方式中，本申请的电化学装置包括正极极片、负极极片、隔离膜和电解液。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
本申请的电化学装置还包括外包装，用于封装电极组件及电解液。在一些实施方式中，外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等，也可以是软包，例如袋式软包。软包的材质可以是塑料，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)中的至少一种。
[负极极片]
本申请的电化学装置中使用的负极极片为本申请实施方式第三方面的负极极片。[正极极片]
本申请的电化学装置中使用的正极极片的材料、构成和其制造方法可包括任何现有技术中公知的技术。
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上且包括正极活性材料的正极活性物质层。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，正极活性物质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，正极活性物质层包括正极活性材料，正极活性材料的具体种类不受到具体的限制，可根据需求进行选择。例如，正极活性材料可以包括锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。在本申请的电化学装置中，上述各正极活性材料的改性化合物可以是对正极活性材料进行掺杂改性、表面包覆改性、或掺杂同时表面包覆改性。
作为示例，锂过渡金属氧化物可以包括锂钴氧化物、锂镍氧化物、锂锰氧化物、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、锂镍钴铝氧化物及其改性化合物中的一种或几种。作为示例，橄榄石结构的含锂磷酸盐可以包括磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、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及其改性化合物中的一种或几种。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。
在一些实施方式中，正极活性材料包括钴酸锂(LiCoO 2)。
在一些实施方式中，正极活性物质层还可选的包括导电剂。作为示例，所述导电剂可以包括超导碳、乙炔黑、导电炭黑、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，正极活性物质层还可选的包括粘结剂。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，正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，正极集流体可采用铝箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，金属材料可选自铝、铝合金、镍、镍合金、钛、钛合金、银、银合金中的一种或几种。作为示例，高分子材料基层可选自聚丙烯、聚对苯二甲酸乙二醇酯、聚对苯二甲酸丁二醇酯、聚苯乙烯、聚乙烯等。
本申请中正极极片可以按照本领域常规方法制备。例如，正极活性物质层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)，但不限于此。
本申请的正极极片并不排除除了正极活性物质层之外的其他附加功能层。例如，在一些实施方式中，本申请的正极极片还包括夹在正极集流体和正极活性物质层之间、设置于正极集流体表面的导电底涂层(例如由导电剂和粘结剂组成)。在另外一些实施方式中，本申请的正极极片还包括覆盖在正极活性物质层表面的保护层。
[电解液]
电解液在正极极片和负极极片之间起到传导活性离子的作用。可用于本申请电化学装置的电解液可以为现有技术已知的电解液。
在一些实施方式中，所述电解液包括有机溶剂、锂盐和可选的添加剂，有机溶剂、锂盐和添加剂的种类均不受到具体的限制，可根据需求进行选择。
在一些实施方式中，作为示例，所述锂盐包括但不限于LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(二草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中的至少一种。上述锂盐可以单独使用一种，也可以同时使用两种或两种以上。
在一些实施方式中，作为示例，所述有机溶剂包括但不限于碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1，4-丁内酯(GBL)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的至少一种。上述有机溶剂可以单独使用一种，也可以同时使用两种或两种以上。可选地，上述有机溶剂同时使用两种或两种以上。
在一些实施方式中，所述添加剂可以包括负极成膜添加剂、正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温或低温性能的添加剂等。
作为示例，所述添加剂包括但不限于氟代碳酸乙烯酯(FEC)、碳酸亚乙烯酯(VC)、乙烯基碳酸乙烯酯(VEC)、硫酸乙烯酯(DTD)、硫酸丙烯酯、亚硫酸乙烯酯(ES)、1，3-丙磺酸内酯(PS)、1，3-丙烯磺酸内酯(PST)、磺酸酯环状季铵盐、丁二酸酐、丁二腈(SN)、己二腈(AND)、三(三甲基硅烷)磷酸酯(TMSP)、三(三甲基硅烷)硼酸酯(TMSB)中的至少一种。
电解液可以按照本领域常规的方法制备。例如，可以将有机溶剂、锂盐、可选的添加剂混合均匀，得到电解液。各物料的添加顺序并没有特别的限制，例如，将锂盐、可选的添加剂加入到有机溶剂中混合均匀，得到电解液；或者，先将锂盐加入有机溶剂中，然后再将可选的添加剂加入有机溶剂中混合均匀，得到电解液。
[隔离膜]
隔离膜设置在正极极片和负极极片之间，主要起到防止正负极短路的作用，同时可以使活性离子通过。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，隔离膜的材质可以选自玻璃纤维、无纺布、聚乙烯、聚丙烯、聚偏氟乙烯中的一种或几种，但不仅限于这些。隔离膜可以是单层薄膜，也可以是多层复合薄膜。隔离膜为多层复合薄膜时，各层的材料相同或不同。在一些实施方式中，隔离膜上还可以设置陶瓷涂层、金属氧化物涂层。
电子设备
本申请实施方式的第五方面提供了一种电子设备，其包括本申请实施方式第四方面的电化学装置，其中，所述电化学装置可在所述电子设备中作为电源使用。
本申请的电子设备没有特别限定，其可以是用于现有技术中已知的任何电子设备。在一些实施方式中，电子设备可以包括但不限于，笔记本电脑、笔输入型计算机、移动电脑、电子书播放器、便携式电话、便携式传真机、便携式复印机、便携式打印机、头戴式立体声耳机、录像机、液晶电视、手提式清洁器、便携CD机、迷你光盘、收发机、电子记事本、计算器、存储卡、便携式录音机、收音机、备用电源、电机、汽车、摩托车、助力自行车、自行车、照明器具、玩具、游戏机、钟表、电动工具、闪光灯、照相机、家庭用大型蓄电池和锂离子电容器等。
实施例
下述实施例以锂离子电池为例更具体地描述本发明公开的内容，这些实施例仅仅用于阐述性说明，因为在本发明公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比、和比值都是基于质量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1
硅碳复合材料的制备
(1)将硅粉、铁粉组成的混合粉体至于球磨罐中，进行时转速不低于600rpm的高速球磨，持续时间不低于6小时，最后通过破碎分级处理得到硅铁合金纳米微粒Si 85Fe 10；其中，混合粉体中硅的质量分数为85％，铁的质量分数为10％。
(2)将装有30g硅铁合金纳米微粒Si 85Fe 10的刚玉坩埚置于化学气相沉积管式炉中，炉管抽真空后缓慢通入氩气持续30分钟，再以10℃/min的升温速率将炉温升至1000℃，炉温稳定在1000℃持续30分钟后断氩气、通入碳源气体(如纯度为99.95％的甲烷)，持续3小时后断碳源气体、通入氩气，管式炉停止加热并自然冷却至室温后，断氩气取出刚玉坩埚得到表面包括碳层的硅铁合金纳米微粒Si 85Fe 10@g-C。
(3)将该表面包括碳层的硅铁合金纳米微粒Si 85Fe 10@g-C与15g针状焦混合后球磨3小时，将装有球磨后粉料的刚玉坩埚置于烧结炉中，惰性气氛中以10℃/min的升温速率将炉温升至1800℃，炉温稳定在1800℃持续1小时，炉温冷却至室温后得到硅铁合金分散在碳基质中的硅碳复合材料Si 85Fe 10@g-C/Graphite。
负极极片的制备
将上述制备得到的硅碳复合材料、导电剂乙炔黑、粘结剂海藻酸钠按照重量比100∶7∶19进行混合，加入适量的溶剂去离子水，在真空搅拌机作用下获得负极浆料；将负极浆料均匀涂覆在负极集流体铜箔的两个表面上；然后经过70℃真空干燥12h后冲成直径为10mm的圆形电极片，得到负极极片。
正极极片的制备
将正极活性材料LiCoO 2、导电炭黑、粘结剂PVDF按照重量比96.7∶1.7∶1.6进行混合，加入适量的溶剂NMP，在真空搅拌机作用获得正极浆料；将正极浆料均匀涂覆在正极集流体铝箔的两个表面上；然后经过70℃真空干燥12h后后冲成直径为10mm的圆形电极片，得到正极极片。
电解液的制备
将碳酸乙烯酯(EC)、碳酸二甲酯(DMC)及碳酸二乙酯(DEC)按照质量比为1∶1∶1进行混合，得到基础溶剂；将LiPF 6溶解在上述基础溶剂中，再加入氟代碳酸乙烯酯(FEC)混合均匀，得到电解液，再向电解液中加入氟代碳酸乙烯酯。其中，基于电解液的质量，LiPF 6的质量百分含量为12.5％，氟代碳酸乙烯酯的质量百分含量为10％。
隔离膜的制备
采用PE多孔聚合薄膜作为隔离膜。
锂离子电池的制备
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中间，并卷绕得到裸电芯。将裸电芯置于外包装中，注入配好的电解液并封装，经过化成、脱气，切边等工艺流程得到锂离子电池。
实施例2至5
二次的制备方法与实施例1类似，不同之处在于：调整了硅碳复合材料制备过程中针状焦的添加量。
实施例6至10
二次的制备方法与实施例1类似，不同之处在于：调整了硅碳复合材料制备过程中，硅铁合金中硅与铁的质量百分含量。
实施例11至14
二次的制备方法与实施例7类似，不同之处在于：调整了硅碳复合材料制备过程中，碳层形成步骤中碳源气体通入的持续时间。
对比例1
二次的制备方法与实施例1类似，不同之处在于：在硅碳复合材料的制备过程中，将表面包括碳层的硅铁合金纳米微粒Si 85Fe 10@g-C与石墨直接进行物理共混。
对比例2
二次的制备方法与实施例1类似，不同之处在于：在硅碳复合材料的制备过程中，用纳米硅粉替代硅铁合金纳米微粒。
对比例3
二次的制备方法与实施例7类似，不同之处在于：在硅碳复合材料的制备过程中，去掉硅铁合金纳米微粒的化学气相沉积形成碳层的步骤。
对比例4
二次的制备方法与实施例7类似，不同之处在于：在硅碳复合材料的制备过程中，用液相包覆间苯二酚-甲醛树脂后高温碳化形成碳层替代利用化学气相沉积形成碳层。其中，液相包覆间苯二酚-甲醛树脂形成碳层的过程示例如下：
取30g纳米硅铁合金、92g十六烷基三甲基溴化铵，加入盛有2500mL去离子水的烧杯中，水浴超声30分钟后加入磁子进行磁力搅拌，再向该体系中依次加入1000mL乙醇、28g间苯二酚和10mL氨水，室温搅拌30分钟；然后逐滴加入40mL甲醛，搅拌持续6小时后静置12小时，对此反应体系进行离心、洗涤、干燥得到间苯二酚-甲醛树脂包覆的纳米硅铁合金。最后，将该间苯二酚-甲醛树脂包覆的纳米硅铁合金在惰性气氛中700℃煅烧3小时，得到表面包括碳层的纳米硅铁合金。
上述实施例1至14及对比例1至4的相关参数和测试结果详见表1至表4。
测试部分
锂离子电池性能测试
在45℃、常压环境下，将上述实施例及对比例中的锂离子电池以0.5C恒流充电到4.45V，静置5分钟后以0.5C恒流放电到3.0V，记录此时的放电容量为首次放电容量。以首次放电容量为初始容量，按照上述方法进行400次循环充放电测试，记录每次的放电容量；并以后续每一循环的放电容量与初始容量做比值，得到放电容量衰减曲线(可参见图2)。
负极极片容量值(mAh/g)＝首次放电容量/负极极片重量。
锂离子电池容量保持率(％)＝第400次循环的放电容量/首次放电容量×100％。
能量密度(Wh/L)＝第400次循环的放电容量×第400次的放电电压平台/锂离子电池的几何体积，其中第400次循环的放电容量为mAh，锂离子电池的几何体积为长(cm)×宽(cm)×高(cm)。
表1
Figure PCTCN2022083530-appb-000001
Figure PCTCN2022083530-appb-000002
表2
Figure PCTCN2022083530-appb-000003
表3
Figure PCTCN2022083530-appb-000004
表4
Figure PCTCN2022083530-appb-000005
由表1可以看出，与对比例1中硅铁合金直接与石墨物理掺混相比，含有本申请的硅碳复合材料的实施例1至5的锂离子电池均表现出显著优于对比例1中锂离子电池的循环稳定性，这要归因于硅铁合金作为分散相被碳基质所包裹，硅铁合金与碳基质的接触方式为面接触，优于在直接物理混合方式中的点接触。相比于直接与石墨物理掺混，原位生长的热解石墨与硅铁合金的接触更为紧密，更能耐受应力变化，更能保持良好的 电接触与结构稳定性，因此锂离子电池既能实现高容量又可具有高的循环稳定性，同时具有较高的能量密度。
由表2可看出，当硅铁合金中硅的质量百分含量为30％至80％以及铁的质量百分含量为18％至68％时，适宜的铁含量使硅铁合金中存在数量可观的非电化学活性或低电化学活性物质如FeSi2，同时可以起到一定的缓冲体积应变的作用，可进一步提高锂离子电池的容量、能量密度和循环容量保持率，提升其循环性能。
分析表3可知，当硅铁合金微粒表面的碳层厚度为10nm至100nm时，适宜的碳层厚度可以耐受硅基合金颗粒的体积应变而不发生破裂，在循环中逐渐粉化的硅铁合金始终能保持电接触，进一步提高锂离子电池的容量和提升其循环性能。采取化学气相沉积法在硅铁合金表面形成碳层要优于液相法在硅铁表面形成碳层，因气相沉积形成的碳层呈现出绒毛状结构，如图3所示，该绒毛状结构是由无数个小尺寸石墨烯片层连接形成，具有更好的电子导电性，更有利于活性物质电化学性能的发挥，且石墨烯片层强度大，能够耐受硅铁合金在嵌锂过程中产生的应力，更好地维持活性物质的结构稳定性，提升硅碳复合材料的容量。
由表4可以看出，采用本申请提出的由碳基质和分散在碳基质中的硅合金纳米微粒组成的硅碳复合材料时，负极片具有更大的极片压实密度和更小的孔隙率。因为硅铁合金作为分散相无序分布于碳基质的连续相中，硅铁合金与碳基质的接触方式为面接触，优于在直接物理混合方式中的点接触；硅铁合金作为分散相被连续相的碳基质包裹能组成尺寸更大的颗粒，因此相比于硅铁合金掺混在石墨中形成的负极材料，本申请中所述的硅铁合金分散在碳基质中的硅碳复合材料具有更大的负极极片压实密度以及更小的极片孔隙率，由此能够提高锂离子电池的容量、能量密度及循环容量保持率，提高其长循环寿命。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (10)

  1. 一种电化学装置，包括负极极片，所述负极极片包括负极集流体和负极活性物质层，所述负极活性物质层包括硅碳复合材料，其中，所述硅碳复合材料包括碳基质和分散在所述碳基质中的硅合金纳米微粒。
  2. 根据权利要求1所述的电化学装置，其中，基于所述硅碳复合材料的总质量，所述硅合金的质量百分含量ω 1≥55％。
  3. 根据权利要求1所述的电化学装置，其中，所述硅碳复合材料满足条件(1)至(2)中的至少一者：
    (1)所述硅碳复合材料的体积平均粒径Dv50为4.5μm至6.7μm；
    (2)所述硅碳复合材料的体积平均粒径Dv10为1.6μm至2.5μm。
  4. 根据权利要求1所述的电化学装置，其中，所述硅合金纳米微粒表面包括碳层，所述碳层的厚度为10nm至100nm。
  5. 根据权利要求1所述的电化学装置，其中，所述硅合金包括硅钡合金、硅钙合金、硅铈合金、硅钴合金、硅铬合金、硅镁合金、硅钼合金、硅锰合金、硅镍合金及硅铁合金中的至少一种。
  6. 根据权利要求5所述的电化学装置，其中，所述硅铁合金满足条件(3)至(4)中的至少一者：
    (3)所述硅铁合金中硅的质量百分含量为30％至80％；
    (4)所述硅铁合金中铁的质量百分含量为18％至68％。
  7. 根据权利要求1至6中任一项所述的电化学装置，满足条件(5)至(9)中的至少一者：
    (5)所述硅碳复合材料的体积平均粒径Dv50为4.8μm至6.5μm；
    (6)所述硅碳复合材料的体积平均粒径Dv10为1.8μm至2.3μm；
    (7)所述硅铁合金中硅的质量百分含量为35％至75％；
    (8)所述硅铁合金中铁的质量百分含量为20％至65％；
    (9)所述硅合金纳米微粒表面碳层的厚度为30nm至70nm。
  8. 根据权利要求1所述的电化学装置，其中，所述负极极片满足条件(10)至(12)中的至少一者：
    (10)所述负极极片的压实密度为1.9g/cm 3至2.2g/cm 3；
    (11)所述负极极片的单面涂布重量为0.02g/1540mm 2至0.04g/1540m；
    (12)所述负极极片的孔隙率为7％至14％。
  9. 根据权利要求1所述的电化学装置，其中，所述碳基质的石墨化度为90％至95％。
  10. 一种电子装置，包括权利要求1至9中任一项所述的电化学装置。
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