WO2022205152A1 - 一种负极极片、包含该负极极片的电化学装置和电子装置 - Google Patents

一种负极极片、包含该负极极片的电化学装置和电子装置 Download PDF

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WO2022205152A1
WO2022205152A1 PCT/CN2021/084627 CN2021084627W WO2022205152A1 WO 2022205152 A1 WO2022205152 A1 WO 2022205152A1 CN 2021084627 W CN2021084627 W CN 2021084627W WO 2022205152 A1 WO2022205152 A1 WO 2022205152A1
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silicon
composite material
based composite
negative electrode
pole piece
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PCT/CN2021/084627
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English (en)
French (fr)
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廖群超
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宁德新能源科技有限公司
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Priority to PCT/CN2021/084627 priority Critical patent/WO2022205152A1/zh
Priority to CN202180004450.6A priority patent/CN114127985A/zh
Publication of WO2022205152A1 publication Critical patent/WO2022205152A1/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
    • 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
    • H01M4/36—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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • 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 field of electrochemistry, and in particular, to a negative electrode plate, an electrochemical device and an electronic device comprising the negative electrode plate.
  • Lithium-ion batteries have many advantages, such as large volume and mass energy density, long cycle life, high nominal voltage, low self-discharge rate, small size, and light weight, and are widely used in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices in recent years, people have higher and higher requirements for battery energy density, safety, cycle performance, etc., and look forward to the emergence of new lithium-ion batteries with comprehensive performance improvements.
  • Silicon material has a high specific capacity, and as a negative electrode material for lithium-ion batteries, it can significantly improve the energy density of lithium-ion batteries.
  • the silicon material will produce large volume expansion and volume contraction, consume lithium ions and electrolyte in the lithium ion battery, and even lead to the rupture of the negative electrode material, which seriously affects the energy density and cycle of the lithium ion battery. performance.
  • the size of silicon particles is reduced, but as the size of silicon particles decreases, the specific surface energy of silicon particles increases, especially nano-silicon particles, which are very easy to agglomerate and Affects the energy density and cycling performance of Li-ion batteries.
  • the purpose of this application is to provide a negative pole piece, an electrochemical device and an electronic device comprising the negative pole piece, so as to improve the energy density and cycle performance of the electrochemical device, and reduce the deformation rate of the electrochemical device after multiple cycles.
  • a first aspect of the present application provides a negative pole piece, the negative pole piece comprises a negative electrode material layer, the negative electrode material layer comprises a silicon-based composite material, and the silicon-based composite material comprises a porous carbon matrix and nano-silicon particles in the pores of the carbon matrix,
  • the XRD diffraction pattern of the silicon-based composite material there are diffraction peaks in the range of 2 ⁇ angles from 12° to 38°, the total area of the diffraction peaks is A, and the 2 ⁇ angles in the diffraction peaks are from 12° to the peak of the diffraction peaks.
  • the diffraction peak area within the range is B, and 60% ⁇ B/A ⁇ 70%.
  • the carbon matrix contained in the silicon-based composite material has a porous structure, and the nano-silicon particles are in the pores of the carbon matrix.
  • 60% ⁇ B/A ⁇ 70% is not limited to any theory.
  • nano-silicon particles may refer to silicon particles with an average particle size of nanometers.
  • the particle size of nano-silicon particles is not particularly limited in this application, as long as the purpose of the application can be achieved.
  • the size of nano-silicon particles The average particle size is not more than 500nm.
  • the lower limit value of B/A may be included in the following values: 60%, 61%, 62%, 63% or 64%; the upper limit value of B/A may be included in the following values: 65%, 66% %, 67%, 68%, 69% or 70%.
  • B/A is too small (for example, less than 60%)
  • the carbon atoms in the carbon matrix mainly exist in the form of SP 3 hybridization, and the conductivity of the carbon matrix is low, which deteriorates the rate performance of the electrochemical device
  • B When /A is too large (for example, greater than 70%) the internal part of the pore structure will shrink and collapse. The cycle performance of the device decreases, and the deformation rate of the electrochemical device after cycling increases.
  • a silicon-based composite material with excellent electrical conductivity and uniform distribution of nano-silicon particles can be obtained, which can effectively alleviate the volume expansion of nano-silicon particles in the process of lithium deintercalation and improve the first-time performance of electrochemical devices. Efficiency, cycle performance and rate capability.
  • the porosity of the silicon-based composite material is ⁇ , and based on the total mass of the silicon-based composite material, the mass content of silicon in the silicon-based composite material is C 0 , and 0.2 ⁇ 0.5 ⁇ / (C 0 - ⁇ C 0 ) ⁇ 1.6, preferably 0.4 ⁇ 0.5 ⁇ /(C 0 - ⁇ C 0 ) ⁇ 1.2, this value characterizes the relationship between the mass content of silicon and the porosity in the silicon-based composite material.
  • a lower limit value of 0.5 ⁇ /(C 0 - ⁇ C 0 ) may be included in the following values: 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.8; an upper limit value of 0.5 ⁇ /(C 0 - ⁇ C 0 ) Can be included in the following values: 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.6.
  • the energy density and cycle performance are reduced; when 0.5 ⁇ /(C 0 - ⁇ C 0 ) is too large (for example, greater than 1.6), that is, the porosity ⁇ of the silicon-based composite material is too small or the mass content of silicon in the silicon-based composite material C If 0 is too small, the pores reserved in the silicon-based composite material are too large, which not only deteriorates the mechanical compressive strength of the carbon matrix, but also causes the material to be easily broken during processing, exposing a large number of fresh interfaces, and deteriorating the initial efficiency of the silicon-based composite material. As a result, the energy density of the electrochemical device is reduced and the cycle performance is deteriorated. By controlling 0.5 ⁇ /(C 0 - ⁇ C 0 ) within the above range, the initial efficiency, cycle performance and rate performance of the electrochemical device can be improved.
  • the mass content C 0 of silicon in the silicon-based composite material is 20% to 60%.
  • the lower limit value of the mass content C 0 of silicon in the silicon-based composite material may be included in the following values: 20%, 25%, 30%, 35% or 38%.
  • the upper limit value of the mass content C 0 of silicon in the silicon-based composite material may be included in the following values: 40%, 45%, 50%, 55% or 60%.
  • the silicon-based composite During processing, it is easy to cause the silicon-based composite to crack, exposing a large number of fresh interfaces, which reduces the first efficiency of the electrochemical device ; as the mass content of silicon in the silicon-based composite gradually increases, the first efficiency of the electrochemical device It also increases, but when the mass content C 0 of silicon in the silicon-based composite material is too high (for example, higher than 60%), the space of the pores in the silicon-based composite material cannot satisfy the expansion of the nano-silicon particles during the process of lithium deintercalation. The required space results in a significant decrease in the cycling performance of the electrochemical device. By controlling the mass content C 0 of silicon in the silicon-based composite material to be within the above range, the initial efficiency and cycle performance of the electrochemical device can be improved.
  • the porosity ⁇ of the silicon-based composite material is 10% to 60%, preferably 25% to 50%.
  • the lower limit value of the porosity ⁇ of the silicon-based composite material may include the following values: 10%, 15%, 20%, 25% or 30%; the upper limit value of the porosity ⁇ of the silicon-based composite material may include the following values In value: 35%, 40%, 45%, 50%, 55% or 60%.
  • the porosity ⁇ of the silicon-based composite material is too small (for example, less than 10%), the space required for the expansion of the nano-silicon particles during the lithium-deintercalation process cannot be satisfied, and the carbon matrix is difficult to withstand the huge expansion stress, which may lead to The structure of the silicon-based composite material is destroyed, and even the silicon-based composite material is broken, thereby reducing the cycle performance and energy density of the electrochemical device; when the porosity ⁇ of the silicon-based composite material is too large (for example, greater than 60%), the The mechanical strength of the matrix composite material decreases, and the structure of the silicon matrix composite material is easily damaged in the process of preparing the electrochemical device, and even the silicon matrix composite material is broken, thereby reducing the cycle performance and energy density of the electrochemical device.
  • the porosity ⁇ of the silicon-based composite material refers to the ratio of the volume of pores in the silicon-based composite material to the total volume of the silicon-based composite material.
  • the carbon matrix has pores inside, and the porosity of the carbon matrix is not particularly limited as long as the purpose of the application can be achieved, for example, the pore volume of the carbon matrix is 0.2 g/cc to 0.5 g/cc.
  • the pores of the carbon matrix may include pores with different pore sizes, for example, including micropores with a pore size of less than 2 nm, mesopores with a pore size of 2 nm to 50 nm, and macropores with a pore size of greater than 50 nm.
  • the number of the above-mentioned micropores, mesopores and macropores is not particularly limited, as long as the purpose of the present application can be achieved.
  • the porosity of the carbon matrix refers to the ratio of the volume of pores in the carbon matrix to the total volume of the carbon matrix.
  • the type of the carbon matrix is not particularly limited, as long as the purpose of the present application can be achieved, for example, the carbon matrix can be selected from at least one of hard carbon, soft carbon, and graphite.
  • the above-mentioned hard carbon may include resin carbon, carbon black, organic polymer pyrolytic carbon, and combinations thereof.
  • the soft carbon described above may include carbon fibers, carbon microspheres, and combinations thereof.
  • the Raman spectrum of the silicon-based composite material has a D peak in the range of displacement from 1255 cm -1 to 1355 cm -1 and a G peak in the range of displacement from 1575 cm -1 to 1600 cm -1
  • the peak intensity ratio of D peak to G peak is 0.2 to 2.
  • the lower limit value of the peak intensity ratio of the D peak to the G peak may be included in the following values: 0.2, 0.4, 0.6, 0.8 or 1; the upper limit value may be included in the following values: 1.2, 1.4, 1.6, 1.8 or 2 .
  • the pores in the silicon-based composite can meet the space required for the volume expansion of the nano-silicon particles during lithium deintercalation, which can effectively improve the The expansion deformation of the electrochemical device during the cycle improves the cycle performance of the electrochemical device.
  • the average particle size Dv50 of the silicon-based composite material is not greater than 20 ⁇ m, preferably 1 ⁇ m to 15 ⁇ m.
  • the average particle size of the silicon-based composite material may be in the following data: 1 ⁇ m, 4 ⁇ m, 8 ⁇ m, 12 ⁇ m, 16 ⁇ m or 20 ⁇ m.
  • the average particle size Dv50 of the silicon-based composite material is too large (for example, greater than 20 ⁇ m), the space required for the expansion of the nano-silicon particles during the lithium deintercalation process is also too large, and the carbon-based material needs to bear the stress.
  • the cycle performance of the electrochemical device is reduced.
  • the specific surface area of the silicon-based composite material is not more than 50 m 2 /g, preferably not more than 30 m 2 /g.
  • the specific surface area of the silicon-based composite material may be in the following data: 1 m 2 /g, 10 m 2 /g, 20 m 2 /g, 30 m 2 /g, 40 m 2 /g or 50 m 2 /g.
  • the specific surface area of the silicon-based composite material when the specific surface area of the silicon-based composite material is too large (for example, greater than 50 m 2 /g), the energy density of the electrochemical device will be reduced; The space required for the expansion of nano-silicon particles during lithium intercalation results in a dramatic decrease in the cycling performance of electrochemical devices.
  • the specific surface area of the silicon-based composite material By controlling the specific surface area of the silicon-based composite material within the above range, the energy density and cycle performance of the electrochemical device can be improved.
  • the silicon-based composite material further includes a protective layer, and the silicon-based composite material may have a protective layer on at least a part of the surface, or may be completely wrapped by the protective layer.
  • the protective layer includes at least one of the elements C, Ti, Al, Zn, S, P, Li, B, and N.
  • the protective layer includes at least one of the elements C, Ti, Al, Zn, S, P, Li, B, N
  • the provision of the protective layer enables the electrochemical device to effectively reduce the side effects during cycling.
  • the product is produced, and has a certain protective effect on the nano-silicon particles in the silicon-based composite material, thereby helping to improve the cycle performance of the electrochemical device.
  • the mass percentage content of the metal element in the protective layer of the silicon-based composite material is 0.1% to 0.9%.
  • the lower limit of the mass percentage content of metal elements in the protective layer may include the following values: 0.1%, 0.2%, 0.3%, 0.4% or 0.47%; the upper limit of the mass percentage content of metal elements in the protective layer Values can be included in the following values: 0.5%, 0.6%, 0.7%, 0.8% or 0.9%.
  • the mass percentage of metal elements in the protective layer is too low (for example, less than 0.1%), it is difficult to play the role of the protective layer, and it has no effect on the performance of the electrochemical device; when the metal elements in the protective layer are When the mass percentage of ZnO is too high (for example, higher than 0.9%), the thickness of the protective layer also increases, resulting in excessive polarization of the electrochemical device, resulting in a significant decrease in the cycle performance of the electrochemical device.
  • the aforementioned metal element may include at least one of Ti, Al, Zn, or Li.
  • the carbon (C) in the protective layer is selected from at least one of amorphous carbon, carbon nanotubes, graphene, and vapor-deposited carbon fibers.
  • the protective layer contains at least one of amorphous carbon, carbon nanotubes, graphene, vapor-deposited carbon fibers, which can increase the electronic conductivity of the silicon-based composite material, while increasing the electrical conductivity with other materials in the electrochemical device.
  • the contact site can effectively reduce the cycle performance degradation caused by contact failure, thereby improving the cycle performance of the electrochemical device.
  • the content of C is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, based on the total mass of the silicon-based composite material, the mass percentage content of C in the protective layer of the silicon-based composite material is 0.1% to 0.5%.
  • the elements contained in the silicon-based composite material are not particularly limited, as long as the purpose of the present application can be achieved.
  • the silicon-based composite material may contain silicon element, carbon element, and oxygen element, and the mass ratio of silicon element, carbon element, and oxygen element is 1:1:1 to 6:3:0.
  • the silicon-based composite material containing silicon element, carbon element, and oxygen element can effectively improve the cycle performance of the electrochemical device.
  • the negative electrode material layer further includes graphite particles and a conductive agent.
  • the mass percentage of the silicon-based composite material is 5 % to 80%, preferably 15% to 60%.
  • the addition of graphite particles can effectively regulate the specific capacity of the negative electrode material layer, and the addition of a conductive agent can effectively regulate the conductivity of the negative electrode material layer.
  • the mass percentage of graphite particles and the mass percentage of conductive agent are not particularly limited, as long as the purpose of the application can be achieved. For example, the mass percentage content of the graphite particles is 20% to 95%, and the mass percentage content of the conductive agent is 0.5% to 5%.
  • a dispersant when the material in the protective layer is a material that is easy to agglomerate, a dispersant can be added at the same time as the material of the protective layer is added, so that the material in the protective layer can be uniformly dispersed.
  • the type and content of the dispersant can be selected according to the specific protective layer material, as long as the purpose of the application can be achieved.
  • the dispersant can be selected from sodium carboxymethyl cellulose, polyvinylpyrrolidone, sodium polyacrylate, polyvinylidene at least one of vinylidene fluoride.
  • the materials used for preparing the protective layer can be appropriately added in excess, as long as the elements in the protective layer (such as C, Ti, Al, Zn, S, P, Li, B
  • the content of at least one of N and N is within the scope of the present application and only needs to meet the purpose of the present application.
  • the preparation process of the silicon-based composite material of the present application is well known to those skilled in the art, and the present application is not particularly limited.
  • carbonization of an organic substance is performed to obtain a carbon matrix, and then the carbon matrix is placed in a gas atmosphere containing silicon, and then heat treatment is performed to obtain a silicon-based composite material.
  • heat treatment is performed to obtain a silicon-based composite material.
  • increasing the carbonization temperature or prolonging the carbonization time can increase the porosity and crystallinity of the carbon matrix, thereby increasing the ratio of B/A; reducing the carbonization temperature or shortening the carbonization time can reduce the porosity of the carbon matrix.
  • the rate and crystallinity can be reduced, so that the crystallinity can be reduced; prolonging the treatment time of the carbon matrix in the silicon-containing gas or increasing the heat treatment temperature can increase the mass content of silicon in the silicon-based composite material; shorten the carbon matrix in the silicon-containing gas.
  • the mass content of silicon in the silicon-based composite material can be reduced by reducing the treatment time in the silicon gas or reducing the temperature of the heat treatment.
  • the present application does not have any special restrictions on the carbonization temperature, carbonization time, treatment time of the carbon matrix in the silicon-containing gas, and heat treatment temperature during the preparation of the silicon-based composite material, as long as the purpose of the present application can be achieved.
  • the carbonization temperature is 400°C to 1600°C
  • the carbonization time is 2h to 12h
  • the carbon substrate is treated in a silicon-containing gas for 2h to 15h
  • the heat treatment temperature is 300°C to 800°C.
  • the carbonization temperature of the carbon matrix in the preparation process is preferably 600°C to 1200°C, preferably 700°C to 1000°C.
  • the carbonization temperature is too high, part of the pore structure inside the carbon matrix will shrink or collapse, making the internal pore distribution uneven, and eventually lead to the uneven distribution of nano-silicon particles in the carbon matrix.
  • the cycle performance of the device is reduced, and the deformation rate after the cycle is increased; when the carbonization temperature is too low, not only will some oxygen-containing functional groups remain on the surface of the carbon matrix, it is easy to have side reactions with the electrolyte in the electrochemical device, and the electrolyte will be consumed.
  • the cycle performance of the electrochemical device is deteriorated; and the conductivity of the carbon matrix is reduced, and the rate performance of the electrochemical device is deteriorated.
  • the preparation process of the negative electrode plate of the present application is well known to those skilled in the art, and the present application is not particularly limited.
  • the silicon-based composite material, graphite particles and conductive agent are mixed to obtain a mixture
  • the mixture, binder and solvent are mixed to obtain a mixed slurry
  • the mixed slurry is coated on the negative electrode current collector and dried, cold-pressed, and slit.
  • a negative electrode sheet containing a negative electrode material layer is obtained.
  • the current collector layer of the negative electrode is not particularly limited as long as it can achieve the purpose of the present application.
  • it may contain copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper or Composite current collectors, etc.
  • the thickness of the current collector layer of the negative electrode is not particularly limited as long as the purpose of the present application can be achieved, for example, the thickness of the current collector layer of the negative electrode is 4 ⁇ m to 12 ⁇ m.
  • the thickness of the negative electrode material layer is not particularly limited as long as the purpose of the present application can be achieved.
  • the thickness of the negative electrode material layer is 30 ⁇ m to 120 ⁇ m.
  • the mass percentage of the binder is not particularly limited, as long as the purpose of the application can be achieved, for example, the mass percentage of the binder The content is 1% to 6%.
  • the conductive agent described above is not particularly limited as long as the purpose of the present application can be achieved.
  • the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, and the like.
  • the carbon nanotubes described above may include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.
  • the above-mentioned carbon fibers may contain at least one of vapor grown carbon fibers (VGCF) and carbon nanofibers.
  • the above-mentioned binder is not particularly limited as long as the object of the present application can be achieved.
  • the binder may contain polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, polyimide, poly At least one of amide-imide, styrene-butadiene rubber, and polyvinylidene fluoride.
  • the above-mentioned solvent is not particularly limited as long as the object of the present application can be achieved.
  • the solvent may include deionized water or N-methylpyrrolidone.
  • the negative pole piece may further comprise a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer.
  • the composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art.
  • the conductive layer includes the above-described conductive agent and the above-described binder.
  • a second aspect of the present application provides an electrochemical device comprising the negative electrode plate described in the embodiments of the present application, and the electrochemical device has good cycle performance and high energy density.
  • the electrochemical device of the present application is not particularly limited, and it may include any device in which an electrochemical reaction occurs.
  • the electrochemical device may include, but is not limited to, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery, and the like.
  • the electrochemical device itself also includes a positive electrode piece, and the positive electrode piece in the present application is not particularly limited, as long as the purpose of the present application can be achieved.
  • a positive electrode sheet typically includes a positive current collector and a layer of positive material.
  • the positive electrode current collector is not particularly limited, as long as the purpose of the present application can be achieved, for example, it may include aluminum foil, aluminum alloy foil, or composite current collector.
  • the positive electrode material layer includes a positive electrode active material, and the positive electrode active material is not particularly limited as long as the purpose of the present application can be achieved.
  • the positive electrode active material may contain at least one of composite oxides of lithium and transition metal elements. The above transition metal element is not particularly limited as long as the purpose of the present application can be achieved.
  • the transition metal element may include at least one of nickel, manganese, cobalt, and iron.
  • the positive electrode active material may include lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganate, iron manganese phosphate At least one of lithium or lithium titanate.
  • the thicknesses of the positive electrode current collector and the positive electrode material layer are not particularly limited as long as the purpose of the present application can be achieved.
  • the thickness of the positive electrode current collector is 8 ⁇ m to 12 ⁇ m
  • the thickness of the positive electrode material layer is 30 ⁇ m to 120 ⁇ m.
  • the positive electrode sheet may further comprise a conductive layer located between the positive electrode current collector and the positive electrode material layer.
  • the composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art.
  • the conductive layer includes a conductive agent and a binder.
  • the conductive agent described above is not particularly limited as long as the purpose of the present application can be achieved.
  • the conductive agent may include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, graphene, and the like.
  • the above-mentioned binder is not particularly limited, and any binder known in the art can be used as long as the purpose of the present application can be achieved.
  • the binder may include polyacryl alcohol, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyimide, polyamideimide, styrene butadiene rubber (SBR), polyvinyl alcohol ( At least one of PVA), polyvinylidene fluoride, polytetrafluoroethylene (PTFE), carboxymethyl cellulose or sodium carboxymethyl cellulose (CMC-Na) and the like.
  • SBR styrene-butadiene rubber
  • SBR styrene-butadiene rubber
  • the electrochemical device itself also includes a separator, and the separator in the present application is not particularly limited, as long as the purpose of the present application can be achieved.
  • the separator in the present application is not particularly limited, as long as the purpose of the present application can be achieved.
  • polyethylene PE
  • PP polypropylene
  • PO polyolefin
  • separators based on polytetrafluoroethylene
  • polyester films such as polyethylene terephthalate (PET) films
  • PET polyethylene terephthalate
  • PI Polyimide Membrane
  • PA Polyamide Membrane
  • Spandex or Aramid Membrane Woven Membrane
  • Nonwoven Membrane Non-woven
  • Microporous Membrane Composite Membrane
  • Separator Paper Laminated Membrane, At least one of spun film and the like.
  • the separator of the present application may have a porous structure, and the size of the pore size is not particularly limited as long as the purpose of the present application can be achieved, for example, the size of the pore size is 0.01 ⁇ m to 1 ⁇ m.
  • the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved, for example, the separator has a thickness of 5 ⁇ m to 500 ⁇ m.
  • the release film may include a substrate layer and a surface treatment layer.
  • the substrate layer can be a non-woven fabric, film or composite film with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, etc. kind.
  • polypropylene porous membranes, polyethylene porous membranes, polypropylene non-woven fabrics, polyethylene non-woven fabrics, or polypropylene-polyethylene-polypropylene porous composite membranes may be used.
  • at least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.
  • the inorganic layer includes inorganic particles and a binder
  • the inorganic particles are not particularly limited, and can be selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, for example , at least one of zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate.
  • the binder is not particularly limited, for example, it can be selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyethylene One or a combination of rolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
  • the polymer layer contains a polymer, and the material of the polymer includes polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly( At least one of vinylidene fluoride-hexafluoropropylene) and the like.
  • the electrochemical device of the present application further includes an electrolyte.
  • the electrolyte of the present application may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous solvent.
  • the lithium salt may include LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2. At least one of LiC(SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB or lithium difluoroborate.
  • LiPF 6 may be chosen as the lithium salt because it gives high ionic conductivity and improves cycling characteristics.
  • the non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.
  • the above-mentioned carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
  • Examples of the above-mentioned chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), carbonic acid Methyl ethyl ester (MEC) and combinations thereof.
  • Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), and combinations thereof.
  • Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate Ester, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluorocarbonate -1-methylethylene, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.
  • carboxylate compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, ⁇ -butyrolactone , caprolactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.
  • ether compounds examples include dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethyl ether Oxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.
  • Examples of the above-mentioned other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, Formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.
  • an electrochemical device can be manufactured by the following process: overlapping the positive electrode and the negative electrode through a separator, wrapping them, folding them, etc., and putting them into the casing as needed, injecting the electrolyte into the casing and sealing it, wherein
  • the separator used is the aforementioned separator provided in this application.
  • an overcurrent preventing element, a guide plate, etc. may be placed in the case to prevent pressure rise and overcharge and discharge inside the electrochemical device.
  • a third aspect of the present application provides an electronic device comprising the electrochemical device described in the embodiments of the present application, and the electronic device has good cycle performance and high energy density.
  • the electronic device of the present application is not particularly limited, and it may be used for any electronic device known in the prior art.
  • electronic devices may include, but are not limited to, notebook computers, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders , LCD TV, Portable Cleaner, Portable CD Player, Mini Disc, Transceiver, Electronic Notepad, Calculator, Memory Card, Portable Recorder, Radio, Backup Power, Motor, Automobile, motorcycle, Power-assisted Bicycle, Bicycle, Lighting Appliances, toys, game consoles, clocks, power tools, flashlights, cameras and large household batteries, etc.
  • the present application provides a negative electrode piece, an electrochemical device and an electronic device comprising the negative electrode piece, wherein the negative electrode material layer of the negative electrode piece includes a silicon-based composite material, and the silicon-based composite material includes a porous carbon matrix and carbon matrix pores
  • the negative electrode material layer of the negative electrode piece includes a silicon-based composite material
  • the silicon-based composite material includes a porous carbon matrix and carbon matrix pores
  • the required space can effectively alleviate the phenomenon of material rupture caused by the expansion of nano-silicon particles, and improve the energy density and cycle performance of the electrochemical device.
  • Example 1 is the X-ray diffraction spectrum of the silicon-based composite material in Example 1 of the application;
  • Example 3 is a cycle decay curve diagram of the lithium ion battery in Example 1 and Comparative Example 2 of the present application;
  • Example 4 is a graph showing the expansion of the lithium ion battery in Example 1 and Comparative Example 2 of the present application;
  • FIG. 5 is an X-ray diffraction diagram of the silicon-based composite material in Comparative Example 2 of the present application.
  • the present application is explained by taking a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present application is not limited to a lithium ion battery.
  • the interface of the silicon-based composite was photographed with a scanning transmission electron microscope (STEM), and the obtained STEM image was used to determine the porosity.
  • STEM image is binarized by Image J software, and the size is calibrated according to the scale, and the area of the pores is counted by using Analyze Particles, and the ratio of the area of the pores to the cross-sectional area of the measured silicon matrix composite material That is, the porosity of the silicon-based composite material to be tested; take any 20 or more particles of the silicon-based composite material to carry out the same test, and take the average value as the porosity of the silicon-based composite material.
  • the silicon-based composite material, conductive carbon black and binder polyacrylic acid (PAA) obtained in the examples were mixed according to a mass ratio of 8:1:1, and then deionized water was added to prepare a slurry with a solid content of 70% , use a scraper to coat a coating with a thickness of 100 ⁇ m, and dry it in a vacuum drying oven at 85 ° C for 12 hours. In a dry environment, use a punching machine to cut into 1 cm diameter disks. In the glove box, metal lithium sheets are used as For the counter electrode and separator, polyethylene (PE) film (provided by Celgard Company) was selected, and the electrolyte in Example 1 was added to assemble a button cell. Charge and discharge the battery with the LAND series battery test system, and test its charge and discharge capacity.
  • PE polyethylene
  • the ratio of the first delithiation capacity to the first lithium insertion capacity is the first efficiency of the silicon-based composite material.
  • the test temperature is 25°C or 45°C, charge the lithium-ion battery for the first time, charge the lithium-ion battery to 4.4V with a constant current of 0.7C, charge it with a constant voltage to 0.025C, and discharge it to 0.5C after standing for 5 minutes. 3.0V.
  • the capacity obtained in this step was taken as the initial capacity, and 0.7C charging or 0.5C discharging was carried out for cycle test, and the capacity cycle decay curve was obtained by taking the ratio of the capacity in each step to the initial capacity.
  • the room temperature cycle performance of the lithium-ion battery was recorded as the number of cycles from 25°C to 90% of the capacity retention rate, and the high-temperature cycle performance of the lithium-ion battery was recorded as the number of cycles from 45°C to 80%.
  • the cycle performance of the material is obtained by the number of cycles in this case.
  • the silicon-based composite material, graphite particles and nano-conductive carbon black prepared above are mixed according to a mass ratio of 80:5:15 to obtain a mixed material, and then the mixed material and the binder polyacrylic acid are mixed according to a mass ratio of 1:50. , adding N-methylpyrrolidone (NMP) as a solvent to prepare a slurry with a solid content of 70%, and stirring uniformly.
  • NMP N-methylpyrrolidone
  • the slurry was uniformly coated on one surface of a 10 ⁇ m-thick negative electrode current collector copper foil, and dried at 110° C. to obtain a 150 ⁇ m-thick negative electrode pole piece coated with a negative electrode material layer on one side.
  • the above steps are repeated on the other surface of the negative electrode pole piece to obtain a negative electrode pole piece coated with a negative electrode material layer on both sides. Then, cut the negative pole piece into a size of 74mm ⁇ 867mm for use.
  • the positive active material lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95:2.5:2.5, and NMP is added as a solvent to prepare a slurry with a solid content of 75%, and stir evenly.
  • the slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 ⁇ m, and dried at 90° C. to obtain a positive electrode sheet with a coating thickness of 110 ⁇ m.
  • the single-side coating of the positive electrode sheet is completed.
  • the above steps are repeated on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with positive active material on both sides.
  • the positive pole piece is cut into a size of 74mm ⁇ 867mm, and the tabs are welded for later use.
  • LiPF 6 Lithium salt lithium hexafluorophosphate
  • PE polyethylene
  • the above-prepared positive pole piece, separator and negative pole piece are stacked in sequence, so that the separator is placed between the positive pole and the negative pole to play a role of isolation, and the electrode assembly is obtained by winding.
  • the electrode assembly is placed in an aluminum-plastic film packaging bag, dried and then injected into the electrolyte, and the lithium-ion battery is obtained through the processes of vacuum packaging, standing, chemical formation, degassing, and trimming.
  • Example 2 Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, ⁇ Preparation of silicon-based composite material>, ⁇ Preparation of negative pole piece>,
  • the preparation steps of ⁇ preparation of positive electrode plate>, ⁇ preparation of electrolyte solution>, ⁇ preparation of separator> and ⁇ preparation of lithium ion battery> are the same as those in Example 1, and the changes of relevant parameters are shown in Table 1.
  • Example 10 Example 11, Example 12, Example 13, Example 14, Example 15, ⁇ Preparation of silicon-based composite material>, ⁇ Preparation of negative pole piece>, ⁇ Preparation of positive pole piece>, The preparation steps of ⁇ Preparation of Electrolyte Solution>, ⁇ Preparation of Separator Film> and ⁇ Preparation of Lithium Ion Battery> are the same as those in Example 1, and the changes of relevant parameters are shown in Table 2.
  • the silicon-based composite material and dispersant polyvinylpyrrolidone (PVP) obtained in the preparation step of ⁇ Preparation of silicon-based composite material> were added to absolute ethanol in a mass ratio of 500:11, and stirred for 0.5 h to obtain a uniform suspension , and then add aluminum isopropoxide to the suspension, stir for 0.5h, then dropwise add deionized water to continue the reaction for 4h to obtain a mixed solution, wherein the mass ratio of aluminum isopropoxide and silicon-based composite material is 1:50, isopropoxide
  • the molar ratio of aluminum propoxide to deionized water is 1:3; the mixed solution is spray-dried to obtain powder, and the powder is heated at 500 ° C for 2 hours, cooled to room temperature, and then sieved to obtain a protective layer containing metal elements.
  • Example 2 Silicon based composites.
  • the silicon-based composite material in the preparation step of ⁇ Preparation of Negative Pole Piece> was replaced with a silicon-based composite material containing a metal element protective layer, ⁇ Preparation of Positive Pole Piece>, ⁇ Preparation of Electrolyte>, ⁇ Preparation of separator> and preparation steps of ⁇ Preparation of lithium ion battery> are the same as in Example 2.
  • Example 17 Example 18, Example 19, and Example 20, ⁇ Preparation of silicon-based composite material>, ⁇ Preparation of negative pole piece>, ⁇ Preparation of positive pole piece>, ⁇ Preparation of electrolyte>, ⁇ Preparation of separator> and preparation steps of ⁇ Preparation of lithium ion battery> are the same as in Example 16, and the changes of relevant parameters are shown in Table 3.
  • the silicon-based composite material obtained in the preparation step of ⁇ Preparation of silicon-based composite material> was added to the single-walled carbon nanotube (SCNT) solution containing the dispersant sodium carboxymethyl cellulose (CMC-Na) and dispersed for 2 hours, until A uniform mixed solution is formed, spray-dried to obtain powder, crushed, and sieved with 400 meshes to obtain a silicon-based composite material containing a protective layer, wherein the mass ratio of silicon-based composite material: SCNT: CMC-Na is 99.75: 0.1: 0.15.
  • SCNT single-walled carbon nanotube
  • Example 13 the silicon-based composite material in the preparation step of ⁇ Preparation of Negative Pole Piece> was replaced with a silicon-based composite material containing a protective layer, ⁇ Preparation of Positive Pole Piece>, ⁇ Preparation of Electrolyte>, ⁇ Separator Film> Preparation> and ⁇ Preparation of lithium ion battery> preparation steps are the same as Example 13.
  • Example 22 Example 23, Example 24, Example 25, Example 26, Example 27, Example 28,
  • Example 29 Example 30, Example 31, Example 32, and Example 33, ⁇ Preparation of silicon-based composite material>, ⁇ Preparation of negative pole piece>, ⁇ Preparation of positive pole piece>, ⁇ Preparation of electrolyte solution
  • the preparation steps of preparation>, ⁇ preparation of separator> and ⁇ preparation of lithium ion battery> are the same as those in Example 21, and the changes of relevant preparation parameters are shown in Table 4.
  • Comparative Example 1 Comparative Example 2, Comparative Example 3, and Comparative Example 4, ⁇ Preparation of silicon-based composite material>, ⁇ Preparation of negative pole piece>, ⁇ Preparation of positive pole piece>, ⁇ Preparation of electrolyte>, ⁇ Preparation of separator> and preparation steps of ⁇ Preparation of lithium ion battery> are the same as in Example 1, and the changes of relevant parameters are shown in Table 1.
  • Example 1 Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 1, Example 2, Example 3, Example 9
  • the preparation parameters and test results of 4 are shown in Table 1; the preparation parameters and test results of Example 10, Example 11, Example 12, Example 13, Example 14, Example 15, Comparative Example 5, Comparative Example 6 As shown in Table 2; the preparation parameters and test results of Example 2, Example 16, Example 17, Example 18, Example 19, Example 20, and Comparative Example 7 are shown in Table 3; Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, Example 28, Comparative Example 12, Example 2, Example 29, Example 30, Example 31
  • Example 32, Example 33, Comparative Example 8, and Comparative Example 9 are shown in Table 4.
  • Example 1 Example 2, Example 3, Example 4, Example 5, Comparative Example 1 and Comparative Example 2
  • the silicon-based composite material with the B/A ratio of the present application can improve the lithium-ion battery
  • the cycle performance, rate performance, and the lithium-ion battery still have a small deformation rate after many cycles.
  • Example 1 Example 2, Example 3, Example 4 and Example 5 that under the condition that the mass content C 0 of silicon in the silicon-based composite material remains unchanged, by increasing the amount of silicon within the scope of the present application
  • the ratio of B/A is large, the initial efficiency of the silicon-based composite material is slightly decreased, and the specific capacity is basically unchanged.
  • the cycle performance of the lithium-ion battery is improved first and then decreased, and the rate performance is improved. , a lithium-ion battery with high cycle performance and rate performance can be obtained.
  • Figure 1 shows the X-ray diffraction pattern of the silicon-based composite material in Example 1. It can be seen from Figure 1 that there are diffraction peaks in the range of 2 ⁇ angle from 12° to 38°, and the B/A ratio is 60 %.
  • FIG. 2 shows the Raman spectrum of the silicon-based composite material in Example 1. It can be seen from FIG. 2 that there is a D peak in the range of displacement of 1255 cm -1 to 1355 cm -1 , and the displacement is 1575 cm -1 A G peak exists in the range to 1600 cm ⁇ 1 , and the peak intensity ratio of the D peak to the G peak is 1.2.
  • Figure 3 shows the cycle decay curves of the lithium ion batteries in Example 1 and Comparative Example 2.
  • FIG. 4 shows the expansion curves of the lithium ion batteries in Example 1 and Comparative Example 2. It can be seen from FIG. 4 that under the condition of the same number of cycles, the deformation rate of the lithium ion batteries provided in Example 1 Significantly smaller than the lithium-ion battery provided by Comparative Example 2.
  • Figure 5 shows the X-ray diffraction pattern of the silicon-based composite material in Comparative Example 2. It can be seen from Figure 5 that although there are diffraction peaks in the range of 2 ⁇ angle from 12° to 38°, the B/A ratio is 73%.
  • Example 3 Example 6, Example 7, Example 8, Example 9, Comparative Example 3 and Comparative Example 4 that the silicon-based composite material with the mass content of silicon of the present application can increase the lithium ion The cycle performance, rate performance of the battery, and the lithium-ion battery still have a small deformation rate after many cycles.
  • Example 3, Example 6, Example 7, Example 8 and Example 9 it can be seen that under the condition that the ratio of B/A remains unchanged, by increasing the silicon-based composite material within the scope of the present application The mass content of silicon in the C 0 , the initial efficiency of the silicon-based composite material increases gradually, and the specific capacity decreases slightly.
  • Example 10 Example 11, Example 12, Example 13, Example 14, Example 15, Comparative Example 5 and Comparative Example 6 that there are 0.5 ⁇ /(C 0 - ⁇ C 0 ) and The mass content C 0 of silicon in the silicon-based composite material is within the scope of the present application, and the obtained lithium-ion battery has both good cycle performance and high energy density.
  • Example 10, Example 11, Example 12, Example 13, Example 14, and Example 15 it can be seen that under the condition that the mass content C 0 of silicon in the silicon-based composite material remains unchanged, with 0.5 ⁇ With the increase of /(C 0 - ⁇ C 0 ), the porosity ⁇ and specific surface area of the silicon-based composite material gradually increased, and the specific capacity did not change significantly.
  • the cycle performance and energy density of the lithium-ion battery first improved and then decreased.
  • the deformation first decreases and then increases. As long as 0.5 ⁇ /(C 0 - ⁇ C 0 ) is within the scope of the present application, a lithium-ion battery with high cycle performance, rate performance and low deformation rate can be obtained.
  • Example 16 From Example 16, Example 17, Example 18, Example 19, Example 20 and Comparative Example 7, it can be seen that the silicon-based composite material with the metal content in the protective layer of the present application can further improve the cycle of lithium ion batteries performance and anti-expansion properties. It can be seen from Example 16, Example 17, and Example 20 that as the metal content in the protective layer gradually increases within the scope of the present application, the specific surface area of the silicon-based composite material gradually increases, and the specific capacity and first-time efficiency increase. A small reduction, but the lithium-ion battery still has a good cycle performance and a small deformation rate.
  • the type and content of carbon materials usually also affect the performance of lithium-ion batteries, from Example 13, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, Example It can be seen from Example 28, Example 29, Example 30, Example 31, Example 32, and Example 33 that as long as the type and content of the carbon material are within the scope of the application, the cycle performance of the lithium-ion battery can be further improved , reducing the deformation rate of lithium-ion batteries after cycling.
  • Example 21 Example 24, Example 25, and Comparative Example 8, it can be seen that when the content of carbon material is too high (for example, Comparative Example 8), lithium-ion batteries cannot be prepared, which may be due to the fact that the carbon material is too high When the slurry cannot be processed.
  • Example 21 Example 22 and Comparative Example 9 that the addition of dispersant can usually improve the agglomeration problem of carbon materials, so that a lithium ion battery with good cycle performance and less deformation rate after cycling can be obtained.

Abstract

本申请提供了一种负极极片、包含该负极极片的电化学装置和电子装置，负极极片包含负极材料层，负极材料层包含硅基复合材料，硅基复合材料包含多孔的碳基体和碳基体孔隙内的纳米硅颗粒，硅基复合材料的XRD衍射图谱中在2θ角为12°至38°范围内存在衍射峰，衍射峰的总面积为A，衍射峰中2θ角为12°至衍射峰的峰值所对应的2θ角范围内的衍射峰面积为B，且60％≤B/A≤70％。具有本申请负极极片的电化学装置具有良好的循环性能、较小的循环变形率、高的能量密度和良好的倍率性能。

Description

一种负极极片、包含该负极极片的电化学装置和电子装置 技术领域
本申请涉及电化学领域，特别是涉及一种负极极片、包含该负极极片的电化学装置和电子装置。
背景技术
锂离子电池具有体积和质量能量密度大、循环寿命长、标称电压高、自放电率低、体积小、重量轻等许多优点，在消费电子领域具有广泛的应用。随着近年来电动汽车和可移动电子设备的高速发展，人们对电池的能量密度、安全性、循环性能等相关需求越来越高，期待着综合性能全面提升的新型锂离子电池的出现。
硅材料具有高的比容量，作为锂离子电池的负极材料能够显著提升锂离子电池的能量密度。但是，在锂离子嵌入负极时，硅材料会产生较大的体积膨胀和体积收缩，消耗锂离子电池中的锂离子和电解液，甚至导致负极材料破裂，严重影响锂离子电池的能量密度和循环性能。另外，为了缓解硅材料体积膨胀和体积收缩的问题，减小硅颗粒的尺寸，但随着硅颗粒尺寸的减小，硅颗粒的比表面能增大，尤其是纳米硅颗粒，极易团聚而影响锂离子电池的能量密度和循环性能。
发明内容
本申请的目的在于提供一种负极极片、包含该负极极片的电化学装置和电子装置，以提高电化学装置的能量密度和循环性能，减小电化学装置多次循环后的变形率。
需要说明的是，在以下内容中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。具体技术方案如下：
本申请的第一方面提供了一种负极极片，负极极片包含负极材料层，负极材料层包含硅基复合材料，硅基复合材料包含多孔的碳基体和碳基体孔隙内的纳米硅颗粒，硅基复合材料的XRD衍射图谱中在2θ角为12°至38°范围内存在衍射峰，衍射峰的总面积为A，衍射峰中2θ角为12°至衍射峰的峰值所对应的2θ角范围内的衍射峰面积为B，且60％≤B/A≤70％。
在本申请中，硅基复合材料所包含的碳基体具有多孔结构，纳米硅颗粒在碳基体的孔隙内。本申请的60％≤B/A≤70％，不限于任何理论，通过调控B/A的比值在上述范围内，可以有效缓解在脱嵌锂过程中纳米硅颗粒的体积膨胀，从而得到的电化学装置同时具有较 高的首次效率、良好的循环性能和倍率性能。
在本申请中，纳米硅颗粒可以是指平均粒径为纳米级的硅颗粒，本申请对纳米硅颗粒的粒径没有特别限制，只要能实现本申请的目的即可，例如，纳米硅颗粒的平均粒径不大于500nm。
在本申请中，B/A的下限值可以包括以下数值中：60％、61％、62％、63％或64％；B/A的上限值可以包括以下数值中：65％、66％、67％、68％、69％或70％。不限于任何理论，当B/A过小时(例如小于60％)，碳基体内部碳原子主要以SP 3杂化形式存在，碳基体的导电率低，使得电化学装置的倍率性能恶化；当B/A过大时(例如大于70％)，会导致内部部分孔结构收缩、坍塌，碳基体中孔隙的均匀度较低，从而使得纳米硅颗粒在碳基体中的分布也不均匀，导致电化学装置的循环性能降低、电化学装置循环后的变形率增大。通过控制B/A的值在上述范围内，能够得到导电性能优异、纳米硅颗粒分布均匀的硅基复合材料，有效缓解在脱嵌锂过程中纳米硅颗粒的体积膨胀，提高电化学装置的首次效率、循环性能和倍率性能。
在本申请的一种实施方案中，硅基复合材料的孔隙率为α，以硅基复合材料的总质量为基准，硅基复合材料中硅的质量含量为C 0，且0.2≤0.5α/(C 0-αC 0)≤1.6，优选为0.4≤0.5α/(C 0-αC 0)≤1.2，该值表征了硅基复合材料中硅的质量含量和孔隙率的关系。例如，0.5α/(C 0-αC 0)的下限值可以包括以下数值中：0.2、0.3、0.4、0.5、0.6、0.7或0.8；0.5α/(C 0-αC 0)的上限值可以包括以下数值中：0.9、1.0、1.1、1.2、1.3、1.4或1.6。不限于任何理论，当0.5α/(C 0-αC 0)过小时(例如小于0.2)，也即硅基复合材料的孔隙率α过大或者硅基复合材料中硅的质量含量C 0过多，硅基复合材料中预留的孔隙难以缓冲纳米硅颗粒的嵌锂体积膨胀，此时碳基体的机械强度难以承受巨大膨胀应力，导致硅基复合材料结构碎裂，恶化其电化学性能，例如能量密度、循环性能降低；当0.5α/(C 0-αC 0)过大时(例如大于1.6)，也即硅基复合材料的孔隙率α过小或者硅基复合材料中硅的质量含量C 0过少，硅基复合材料中预留的孔隙过大，不仅恶化碳基体的机械抗压强度，导致材料在加工时容易碎裂，暴露出大量新鲜界面，恶化硅基复合材料首次效率，会导致电化学装置的能量密度变小、循环性能变差。通过控制0.5α/(C 0-αC 0)在上述范围内，能够提高电化学装置的首次效率、循环性能和倍率性能。
在本申请的一种实施方案中，硅基复合材料中硅的质量含量C 0为20％至60％。例如，硅基复合材料中硅的质量含量C 0的下限值可以包括以下数值中：20％、25％、30％、35％ 或38％。硅基复合材料中硅的质量含量C 0的上限值可以包括以下数值中：40％、45％、50％、55％或60％。不限于任何理论，当硅基复合材料中硅的质量含量C 0过低时(例如低于20％)，硅基复合材料中的碳基体的孔隙大部分未被占据，在对碳基复合材料加工时，容易导致硅基复合材料破裂，暴露出大量的新鲜界面，使得电化学装置的首次效率下降；随着硅基复合材料中硅的质量含量C 0逐渐增大，电化学装置的首次效率也随之提升，但当硅基复合材料中硅的质量含量C 0过高时(例如高于60％)，硅基复合材料中的孔隙的空间不能满足在脱嵌锂过程中纳米硅颗粒膨胀所需的空间，导致电化学装置的循环性能明显下降。通过控制硅基复合材料中硅的质量含量C 0在上述范围内，能够提高电化学装置的首次效率和循环性能。
在本申请的一种实施方案中，硅基复合材料的孔隙率α为10％至60％，优选为25％至50％。例如，硅基复合材料的孔隙率α的下限值可以包括以下数值中：10％、15％、20％、25％或30％；硅基复合材料的孔隙率α的上限值可以包括以下数值中：35％、40％、45％、50％、55％或60％。不限于任何理论，当硅基复合材料的孔隙率α过小时(例如小于10％)，不能满足在脱嵌锂过程中纳米硅颗粒膨胀所需的空间，碳基体难以承受巨大的膨胀应力可能导致硅基复合材料的结构被破坏，甚至使硅基复合材料破裂，从而降低电化学装的循环性能和能量密度；当硅基复合材料的孔隙率α过大时(例如大于60％)，导致硅基复合材料的机械强度下降，在制备电化学装置的过程中硅基复合材料的结构容易被破坏，甚至使硅基复合材料破裂，从而使得电化学装置的循环性能降低和能量密度降低。通过控制硅基复合材料的孔隙率在上述范围内，能够提高电化学装置的循环性能和能量密度。其中，硅基复合材料的孔隙率α是指，硅基复合材料中孔隙的体积与硅基复合材料总体积的比值。
在本申请中，碳基体的内部具有孔隙，碳基体的孔隙率没有特别限制，只要能实现本申请的目的即可，例如碳基体的孔体积为0.2g/cc至0.5g/cc。可以理解的是，碳基体的孔隙可以包含不同孔径的孔隙，例如，包含孔径小于2nm的微孔、孔径为2nm至50nm的介孔和大于50nm的大孔。在本申请中，对上述微孔、介孔和大孔的数量没有特别限定，只要能够实现本申请目的即可。其中，碳基体的孔隙率是指，碳基体中孔隙的体积与碳基体总体积的比值。在本申请中，碳基体的种类没有特别限制，只要能实现本申请的目的即可，例如碳基体可以选自硬碳、软碳、石墨中的至少一种。示例性地，上述硬碳可以包括树脂碳、碳黑、有机聚合物热解碳及其组合。上述软碳可以包括碳纤维、碳微球及其组合。
在本申请的一种实施方案中，硅基复合材料的拉曼光谱图中在位移为1255cm -1至 1355cm -1范围内存在D峰，在位移为1575cm -1至1600cm -1范围内存在G峰，D峰与G峰的峰强度比值为0.2至2。例如，D峰与G峰的峰强度比值的下限值可以包括以下数值中：0.2、0.4、0.6、0.8或1；的上限值可以包括以下数值中：1.2、1.4、1.6、1.8或2。不限于任何理论，将D峰与G峰的峰强度比值控制在0.2至2范围内，硅基复合材料内的孔隙能够满足脱嵌锂时纳米硅颗粒体积膨胀所需的空间，从而能够有效改善电化学装置在循环过程中的膨胀变形，提高电化学装置的循环性能。
在本申请的一种实施方案中，硅基复合材料的平均粒径Dv50不大于20μm，优选为1μm至15μm。例如，硅基复合材料的平均粒径可以为以下数据中：1μm、4μm、8μm、12μm、16μm或20μm。不限于任何理论，当硅基复合材料的平均粒径Dv50过大时(例如大于20μm)，在脱嵌锂过程中纳米硅颗粒膨胀所需的空间也过大，碳基材料所需承受的应力也过大，得到的硅基复合材料稳定性较低，使得电化学装置的循环性能降低；当硅基复合材料的平均粒径Dv50过小时(例如小于1μm)，硅基复合材料的容易团聚，使得电化学装置的循环性能降低。通过控制硅基复合材料的平均粒径在上述范围内，能够提高电化学装置的循环性能。
在本申请的一种实施方案中，硅基复合材料的比表面积不大于50m 2/g，优选为不大于30m 2/g。例如，硅基复合材料的比表面积可以为以下数据中：1m 2/g、10m 2/g、20m 2/g、30m 2/g、40m 2/g或50m 2/g。不限于任何理论，当硅基复合材料的比表面积过大时(例如大于50m 2/g)，会导致电化学装置的能量密度降低；当硅基复合材料的比表面积过小时，不能满足在脱嵌锂过程中纳米硅颗粒膨胀所需的空间，使得电化学装置的循环性能急剧下降。通过控制硅基复合材料的比表面积在上述范围内，能够提高电化学装置的能量密度和循环性能。
在本申请的一种实施方案中，硅基复合材料还包括保护层，硅基复合材料可以至少部分表面存在保护层，也可以是全部被保护层包裹。保护层包括元素C、Ti、Al、Zn、S、P、Li、B、N中的至少一种。不限于任何理论，当保护层包括元素C、Ti、Al、Zn、S、P、Li、B、N中的至少一种时，保护层的设置使得电化学装置在循环过程中能有效减少副产物的产生，且对硅基复合材料中的纳米硅颗粒具有一定的保护作用，从而有利于提高电化学装置的循环性能。
在本申请的一种实施方案中，以硅基复合材料的总质量为基准，硅基复合材料保护层中金属元素的质量百分含量为0.1％至0.9％。例如，保护层中金属元素的质量百分含量的 下限值可以包括以下数值中：0.1％、0.2％、0.3％、0.4％或0.47％；保护层中金属元素的质量百分含量的上限值可以包括以下数值中：0.5％、0.6％、0.7％、0.8％或0.9％。不限于任何理论，当保护层中金属元素的质量百分含量过低时(例如低于0.1％)，难以发挥保护层的作用，对电化学装置的性能基本无影响；当保护层中金属元素的质量百分含量过高时(例如高于0.9％)，保护层的厚度也随之增大，导致电化学装置的极化过大，使得电化学装置的循环性能明显下降。通过控制保护层中金属元素的质量百分含量在上述范围内，能够进一步提高电化学装置的循环性能。前述的金属元素可以包括Ti、Al、Zn或Li中的至少一种。
在本申请的一种实施方案中，保护层中的碳(C)选自无定形碳、碳纳米管、石墨烯、气相沉积碳纤维中的至少一种。不限于任何理论，保护层中包含无定形碳、碳纳米管、石墨烯、气相沉积碳纤维中的至少一种，能够增加硅基复合材料的电子导电率，同时增加与电化学装置中其它材料的接触位点，有效减少因为接触失效导致的循环性能衰减，从而提高电化学装置的循环性能。本申请对C的含量没有特别限制，只要能实现本申请的目的即可。例如，以硅基复合材料的总质量为基准，硅基复合材料保护层中C的质量百分含量为0.1％至0.5％。
在本申请的硅基复合材料中，硅基复合材料中包含的元素没有特别限制，只要能实现本申请的目的即可。例如，硅基复合材料可以包含硅元素、碳元素、氧元素，且硅元素、碳元素、氧元素的质量比为1︰1︰1至6︰3︰0。不限于任何理论，硅基复合材料包含硅元素、碳元素、氧元素能够有效提高电化学装置的循环性能。
在本申请的一种实施方案中，负极材料层中还包括石墨颗粒和导电剂，以硅基复合材料、石墨颗粒和导电剂的总质量为基准，硅基复合材料的质量百分含量为5％至80％，优选为15％至60％。不限于任何理论，石墨颗粒的加入能够有效调控负极材料层的比容量，导电剂的接入能够有效调控负极材料层的导电性。在本申请中，以硅基复合材料、石墨颗粒和导电剂的总质量为基准，石墨颗粒的质量百分含量和导电剂的质量百分含量没有特别限制，只要能实现本申请的目的即可，例如，石墨颗粒的质量百分含量为20％至95％，导电剂的质量百分含量为0.5％至5％。
在本申请中，当保护层中的材料为易团聚的材料时，可以在加入保护层材料的同时加入分散剂，以使保护层中的材料分散均匀。分散剂的种类和含量可以根据具体的保护层材料进行选择，只要能实现本申请的目的即可，例如，分散剂可以选自羧甲基纤维素钠、聚 乙烯吡咯烷酮、聚丙烯酸钠、聚偏二氟乙烯中的至少一种。在制备保护层时，考虑到制备过程中材料的损耗，可以适当过量加入制备保护层所用的材料，只要使得保护层中的元素(例如C、Ti、Al、Zn、S、P、Li、B、N中的至少一种)含量在本申请的范围内、满足本申请的目的即可。
本申请的硅基复合材料的制备过程为本领域技术人员所熟知的，本申请没有特别限制。例如，将有机物进行碳化，得到碳基体，再使碳基体处于含硅的气体氛围中，然后进行热处理，得到硅基复合材料。可以理解的是，升高碳化温度或延长碳化时间，可以提高碳基体的孔隙率和结晶度，从而可以使B/A的比值增大；降低碳化温度或缩短碳化时间，可以降低碳基体的孔隙率和结晶度，从而可以使结晶度减小；延长碳基体在含硅气体中的处理时间或升高热处理的温度，可以使硅基复合材料的中硅的质量含量提高；缩短碳基体在含硅气体中的处理时间或降低热处理的温度，可以使硅基复合材料的中硅的质量含量降低。本申请对制备硅基复合材料过程中的碳化温度、碳化时间、碳基体在含硅气体中处理时间、热处理温度没有特别限制，只要能实现本申请的目的即可。例如，碳化温度为400℃至1600℃、碳化时间为2h至12h、碳基体在含硅气体中处理时间2h至15h和热处理温度300℃至800℃。
在本申请中，碳基体在制备过程中的碳化温度优选为600℃至1200℃，优选为700℃至1000℃。不限于任何理论，当碳化温度过高时，会导致碳基体内部部分孔结构收缩或坍塌，使其内部孔隙分布不均匀，最终导致纳米硅颗粒在碳基体中的分布也不均匀，使电化学装置的循环性能降低、循环后的变形率增大；当碳化温度过低时，不仅会使碳基体表面残留部分含氧官能团，容易与电化学装置中的电解液产生副反应，消耗电解液，使电化学装置的循环性能变差；而且使碳基体导电率降低，恶化电化学装置的倍率性能。
本申请的负极极片的制备过程为本领域技术人员所熟知的，本申请没有特别限制。例如，将硅基复合材料、石墨颗粒和导电剂混合得到混合物，将混合物、粘结剂和溶剂混合得到混合浆料，将混合浆料涂敷于负极集流体上经过干燥、冷压、分条后得到含有负极材料层的负极极片。在本申请中，对负极的集流体层没有特别限制，只要能够实现本申请目的即可，例如，可以包含铜箔、铜合金箔、镍箔、不锈钢箔、钛箔、泡沫镍、泡沫铜或复合集流体等。在本申请中，对负极的集流体层的厚度没有特别限制，只要能够实现本申请目的即可，例如，负极的集流体层的厚度为4μm至12μm。在本申请中，负极材料层的厚度没有特别限制，只要能实现本申请的目的即可。例如，负极材料层的厚度为30μm至 120μm。在本申请中，以混合物、粘结剂和溶剂的总质量为基准，粘结剂的质量百分含量没有特别限制，只要能实现本申请的目的即可，例如，粘结剂的质量百分含量为1％至6％。
上述所述导电剂没有特别限制，只要能够实现本申请目的即可。例如，导电剂可以包括导电炭黑(Super P)、碳纳米管(CNTs)、碳纤维、鳞片石墨、科琴黑或石墨烯等中的至少一种。上述碳纳米管可以包含单壁碳纳米管和多壁碳纳米管中的至少一种。上述碳纤维可以包含气相生长碳纤维(VGCF)、纳米碳纤维中的至少一种。
上述粘结剂没有特别限制，只要能够实现本申请目的即可。例如，粘结剂可以包含聚丙烯酸、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚乙烯醇、羧甲基纤维素、羧甲基纤维素钠、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶、聚偏氟乙烯中的至少一种。上述溶剂没有特别限制，只要能够实现本申请目的即可。例如，溶剂可以包括去离子水或N-甲基吡咯烷酮。
任选地，负极极片还可以包含导电层，所述导电层位于负极集流体和负极材料层之间。所述导电层的组成没有特别限制，可以是本领域常用的导电层。所述导电层包括上述导电剂和上述粘结剂。
本申请的第二方面提供了一种电化学装置，包含本申请实施方案中所述的负极极片，该电化学装置具有良好的循环性能和较高的能量密度。本申请的电化学装置没有特别限定，其可以包括发生电化学反应的任何装置。在一些实施例中，电化学装置可以包括但不限于：锂离子二次电池(锂离子电池)、锂聚合物二次电池或锂离子聚合物二次电池等。
本身请的电化学装置还包括正极极片，本申请中的正极极片没有特别限制，只要能够实现本申请目的即可。例如，正极极片通常包含正极集流体和正极材料层。其中，正极集流体没有特别限制，只要能够实现本申请目的即可，例如，可以包含铝箔、铝合金箔或复合集流体等。正极材料层包括正极活性材料，正极活性材料没有特别限制，只要能够实现本申请目的即可，例如，正极活性材料可以包含锂和过渡金属元素的复合氧化物中的至少一种。上述过渡金属元素没有特别限制，只要能实现本申请的目的即可，例如，过渡金属元素可以包含镍、锰、钴、铁中的至少一种。具体的，正极活性材料可以包含镍钴锰酸锂(811、622、523、111)、镍钴铝酸锂、磷酸铁锂、富锂锰基材料、钴酸锂、锰酸锂、磷酸锰铁锂或钛酸锂中的至少一种。在本申请中，正极集流体和正极材料层的厚度没有特别限制，只要能够实现本申请目的即可。例如，正极集流体的厚度为8μm至12μm，正极材料层的厚度为30μm至120μm。
任选地，正极极片还可以包含导电层，所述导电层位于正极集流体和正极材料层之间。所述导电层的组成没有特别限制，可以是本领域常用的导电层。所述导电层包括导电剂和粘结剂。
上述所述导电剂没有特别限制，只要能够实现本申请目的即可。例如，导电剂可以包括导电炭黑(Super P)、碳纳米管(CNTs)、碳纤维、鳞片石墨、科琴黑或石墨烯等中的至少一种。上述所述粘结剂没有特别限制，可以使用本领域公知的任何粘结剂，只要能够实现本申请目的即可。例如，粘结剂可以包括聚丙烯醇、聚丙烯酸钠、聚丙烯酸钾、聚丙烯酸锂、聚酰亚胺、聚酰亚胺、聚酰胺酰亚胺、丁苯橡胶(SBR)、聚乙烯醇(PVA)、聚偏氟乙烯、聚四氟乙烯(PTFE)、羧甲基纤维素或羧甲基纤维素钠(CMC-Na)等中的至少一种。例如，粘结剂可选用丁苯橡胶(SBR)。
本身请的电化学装置还包括隔离膜，在本申请的隔离膜没有特别限制，只要能够实现本申请目的即可。例如，聚乙烯(PE)、聚丙烯(PP)、聚四氟乙烯为主的聚烯烃(PO)类隔膜，聚酯膜(例如聚对苯二甲酸二乙酯(PET)膜)、纤维素膜、聚酰亚胺膜(PI)、聚酰胺膜(PA)，氨纶或芳纶膜、织造膜、非织造膜(无纺布)、微孔膜、复合膜、隔膜纸、碾压膜、纺丝膜等中的至少一种。本申请的隔离膜可以具有多孔结构，孔径的尺寸没有特别限制，只要能实现本申请的目的即可，例如，孔径的尺寸为0.01μm至1μm。在本申请中，隔离膜的厚度没有特别限制，只要能实现本申请的目的即可，例如，隔离膜的厚度为5μm至500μm。
例如，隔离膜可以包括基材层和表面处理层。基材层可以为具有多孔结构的无纺布、膜或复合膜，基材层的材料可以包括聚乙烯、聚丙烯、聚对苯二甲酸乙二醇酯和聚酰亚胺等中的至少一种。任选地，可以使用聚丙烯多孔膜、聚乙烯多孔膜、聚丙烯无纺布、聚乙烯无纺布或聚丙烯-聚乙烯-聚丙烯多孔复合膜。任选地，基材层的至少一个表面上设置有表面处理层，表面处理层可以是聚合物层或无机物层，也可以是混合聚合物与无机物所形成的层。
例如，无机物层包括无机颗粒和粘结剂，所述无机颗粒没有特别限制，例如可以选自氧化铝、氧化硅、氧化镁、氧化钛、二氧化铪、氧化锡、二氧化铈、氧化镍、氧化锌、氧化钙、氧化锆、氧化钇、碳化硅、勃姆石、氢氧化铝、氢氧化镁、氢氧化钙和硫酸钡等中的至少一种。所述粘结剂没有特别限制，例如可以选自聚偏氟乙烯、偏氟乙烯-六氟丙烯的共聚物、聚酰胺、聚丙烯腈、聚丙烯酸酯、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚 乙烯醚、聚甲基丙烯酸甲酯、聚四氟乙烯和聚六氟丙烯中的一种或几种的组合。聚合物层中包含聚合物，聚合物的材料包括聚酰胺、聚丙烯腈、丙烯酸酯聚合物、聚丙烯酸、聚丙烯酸盐、聚乙烯呲咯烷酮、聚乙烯醚、聚偏氟乙烯或聚(偏氟乙烯-六氟丙烯)等中的至少一种。
本申请的电化学装置还包括电解质，本申请的电解质可以是凝胶电解质、固态电解质和电解液中的一种或多种，电解液包括锂盐和非水溶剂。在本申请一些实施方案中，锂盐可以包括LiPF 6、LiBF 4、LiAsF 6、LiClO 4、LiB(C 6H 5) 4、LiCH 3SO 3、LiCF 3SO 3、LiN(SO 2CF 3) 2、LiC(SO 2CF 3) 3、LiSiF 6、LiBOB或二氟硼酸锂中的至少一种。举例来说，锂盐可以选用LiPF 6，因为它可以给出高的离子导电率并改善循环特性。
非水溶剂可为碳酸酯化合物、羧酸酯化合物、醚化合物、其它有机溶剂或它们的组合。上述碳酸酯化合物可为链状碳酸酯化合物、环状碳酸酯化合物、氟代碳酸酯化合物或其组合。上述链状碳酸酯化合物的实例为碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸甲乙酯(MEC)及其组合。环状碳酸酯化合物的实例为碳酸乙烯酯(EC)、碳酸亚丙酯(PC)、碳酸亚丁酯(BC)、碳酸乙烯基亚乙酯(VEC)及其组合。氟代碳酸酯化合物的实例为氟代碳酸乙烯酯(FEC)、碳酸1,2-二氟亚乙酯、碳酸1,1-二氟亚乙酯、碳酸1,1,2-三氟亚乙酯、碳酸1,1,2,2-四氟亚乙酯、碳酸1-氟-2-甲基亚乙酯、碳酸1-氟-1-甲基亚乙酯、碳酸1,2-二氟-1-甲基亚乙酯、碳酸1,1,2-三氟-2-甲基亚乙酯、碳酸三氟甲基亚乙酯及其组合。上述羧酸酯化合物的实例为甲酸甲酯、乙酸甲酯、乙酸乙酯、乙酸正丙酯、乙酸叔丁酯、丙酸甲酯、丙酸乙酯、丙酸丙酯、γ-丁内酯、癸内酯、戊内酯、甲瓦龙酸内酯、己内酯及其组合。上述醚化合物的实例为二丁醚、四甘醇二甲醚、二甘醇二甲醚、1,2-二甲氧基乙烷、1,2-二乙氧基乙烷、乙氧基甲氧基乙烷、2-甲基四氢呋喃、四氢呋喃及其组合。上述其它有机溶剂的实例为二甲亚砜、1,2-二氧戊环、环丁砜、甲基环丁砜、1,3-二甲基-2-咪唑烷酮、N-甲基-2-吡咯烷酮、甲酰胺、二甲基甲酰胺、乙腈、磷酸三甲酯、磷酸三乙酯、磷酸三辛酯和磷酸酯及其组合。
电化学装置的制备过程为本领域技术人员所熟知的，本申请没有特别的限制。例如电化学装置可以通过以下过程制造：将正极极片和负极极片经由隔离膜重叠，并根据需要将其卷绕、折叠等操作后放入壳体内，将电解液注入壳体并封口，其中所用的隔离膜为本申请提供的上述隔离膜。此外，也可以根据需要将防过电流元件、导板等置于壳体中，从而防止电化学装置内部的压力上升、过充放电。
本申请的第三方面提供了一种电子装置，包含本申请实施方案中所述的电化学装置，该电子装置具有良好的循环性能和和较高的能量密度。
本申请的电子装置没有特别限制，其可以是用于现有技术中已知的任何电子装置。在一些实施例中，电子装置可以包括但不限于，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、照相机和家庭用大型蓄电池等。
本申请提供的一种负极极片、包含该负极极片的电化学装置和电子装置，负极极片的负极材料层中包含硅基复合材料，硅基复合材料包含多孔的碳基体和碳基体孔隙内的纳米硅颗粒，本申请中，硅基复合材料的XRD衍射图谱中在2θ角为12°至38°范围内存在衍射峰，衍射峰的总面积为A，衍射峰中2θ角为12°至衍射峰的峰值所对应的2θ角范围内的衍射峰面积为B，通过控制60％≤B/A≤70％，使得在电化学装置充电和放电的过程中，可以满足纳米硅颗粒膨胀时所需的空间，从而有效缓解由于纳米硅颗粒膨胀引起的材料破裂等现象，提高电化学装置的能量密度和循环性能。
附图说明
为了更清楚地说明本申请实施例和现有技术的技术方案，下面对实施例和现有技术中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本申请的一些实施例。
图1为本申请实施例1中的硅基复合材料的X射线衍射谱图；
图2为本申请实施例1中的硅基复合材料的的拉曼光谱图；
图3为本申请实施例1和对比例2中的的锂离子电池的循环衰减曲线图；
图4为本申请实施例1和对比例2中的锂离子电池的膨胀曲线图；
图5为本申请对比例2中的硅基复合材料的X射线衍射谱图。
具体实施方式
为使本申请的目的、技术方案、及优点更加清楚明白，以下参照附图并举实施例，对本申请进一步详细说明。显然，所描述的实施例仅仅是本申请一部分实施例，而不是全部的实施例。基于本申请中的实施例，本领域普通技术人员所获得的所有其他实施例，都属 于本申请保护的范围。
需要说明的是，本申请的具体实施方式中，以锂离子电池作为电化学装置的例子来解释本申请，但是本申请的电化学装置并不仅限于锂离子电池。
实施例
以下，举出实施例及对比例来对本申请的实施方式进行更具体地说明。各种的试验及评价按照下述的方法进行。另外，只要无特别说明，“份”、“％”为质量基准。
测试方法和设备：
硅基复合材料比表面积测试：
在恒温低温(-199℃至-193℃)下，测定不同相对压力时的气体在固体表面的吸附量后，基于布朗诺尔-埃特-泰勒吸附理论及其公式(BET公式)求得试样单分子层吸附量，从而计算出固体的比表面积。
BET公式：
Figure PCTCN2021084627-appb-000001
其中：W---相对压力(P/P0)下固体样品所吸附的气体的质量，单位cm 3/g；Wm---铺满一单分子层的气体饱和吸附量，单位cm 3/g；C---与第一层吸附热和凝聚热有关的常数；斜率：(c-1)/(WmC)，截距：1/WmC，总比表面积：(Wm×N×Acs/M)；比表面积：S＝St/m，其中m为样品质量，Acs：每个N 2分子的所占据的平均面积16.2A 2。
称取1.5g至3.5g粉末样品装入TriStar II 3020的测试测试样品管中，200℃脱气120min后进行测试。
硅基复合材料孔隙率测试：
采用扫描透射电镜(STEM)拍摄硅基复合材料的界面，并使用所得到的STEM图像来测定孔隙率。具体的：将STEM图像采用Image J软件对图像做二值化处理，根据比例尺标定尺寸后，利用分析粒子(Analyze Particles)统计孔隙的面积，孔隙的面积与所测硅基复合材料截面面积的比值即为被测硅基复合材料的孔隙率；取任意20个以上硅基复合材料的颗粒进行相同的测试，取平均值为硅基复合材料的孔隙率。
硅基复合材料粒度测试：
在50mL洁净烧杯中加入0.02g硅基复合材料，再加入20mL去离子水，再滴加3至5滴质量浓度为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，利用激光粒度仪(MasterSizer 2000)测试粒度分布。Dv50为颗粒采用激光散射粒度仪测试得到的体积基准分布中累计50％的直径。
硅基复合材料首次效率测试：
将实施例中得到的硅基复合材料、导电炭黑与粘结剂聚丙烯酸(PAA)按照质量比为8︰1︰1进行混合，然后加去离子水调配成为固含量为70％的浆料，利用刮刀涂覆厚度为100μm的涂层，在85℃经过12小时真空干燥箱烘干后，在干燥环境中用冲压机切成直径为1cm的圆片，在手套箱中以金属锂片作为对电极，隔离膜选择聚乙烯(PE)薄膜(Celgard公司提供)，加入实施例1中的电解液组装成扣式电池。用蓝电(LAND)系列电池测试系统对电池进行充放电测试，并测试其充放电容量。
首先采用0.05C放电至0.005V，静止5分钟后，用50μA放电至0.005V，再静止5分钟后，用10μA放电至0.005V，得到材料的首次嵌锂容量；然后用0.1C充电至2V，得到首次脱锂容量。最终，用首次脱锂容量比上首次嵌锂容量即为硅基复合材料的首次效率。
循环性能测试：
测试温度为25℃或45℃，对锂离子电池进行第一次充电，将锂离子电池以0.7C恒流充电到4.4V，恒压充电到0.025C，静置5分钟后以0.5C放电到3.0V。以此步得到的容量为初始容量，进行0.7C充电或0.5C放电进行循环测试，以每一步的容量与初始容量做比值，得到容量循环衰减曲线。以25℃循环截至到容量保持率为90％的圈数记为锂离子电池的室温循环性能，以45℃循环截至到80％的圈数记为锂离子电池的高温循环性能，通过比较上述两种情况下的循环圈数而得到材料的循环性能。
放电倍率测试：
在25℃下，将锂离子电池以0.2C放电到3.0V，静置5分钟后，以0.5C充电到4.45V，恒压充电到0.05C后静置5分钟，调整放电倍率，分别以0.2C、0.5C、1C、1.5C、2.0C进行放电测试，分别得到放电容量，以每个倍率下得到的容量与0.2C得到的容量对比，通过比较2C与0.2C下的比值比较倍率性能。
锂离子电池满充膨胀率测试：
用螺旋千分尺测试半充时新鲜锂离子电池的厚度L1，循环至400圈(cls)时，锂离子电池处于满充状态下，再用螺旋千分尺测试此时锂离子电池的厚度L2，则满充锂离子电池膨胀率为(L2-L1)L1×100％。
能量密度计算：
将锂离子电池在25℃下充电至4.45V后，采用0.2C放电至3V，得到锂离子电池放电容量(C)和平均电压平台(U)，再用激光测厚仪测试锂离子电池的长、宽、高，得到锂离子电池的体积(V)，其体积能量密度(ED)可通过如下公式计算得到：ED＝C×U/V。
实施例1
<硅基复合材料的制备>
将110g的间二苯酚和150g的40wt％甲醛水溶液加入到烧瓶中得到第一混合液，加热至40℃后，加入40mL的摩尔浓度为50mmol/L的Na 2CO 3溶液，持续搅拌5h，得到第二混合液，再将第二混合液在75℃下密封老化120h后去除溶剂，并于80℃下进行干燥，得到碳质块体；将上述碳质块体破碎至粒径Dv50为7.5μm的粉末后进行碳化处理，碳化温度T1为800℃，碳化时长t1为6h，最终得到碳基体；将碳基体置于管式炉中，向管式炉中通入硅烷和H 2的混合气体(硅烷和的H 2体积比为5︰95)，管式炉中的温度T2为500℃，通入气体的时长t2为12h，降温后即得到上述的硅基复合材料。
<负极极片的制备>
将上述制得的硅基复合材料、石墨颗粒和纳米导电炭黑按照质量比80︰5︰15进行混合得到混合材料，再将混合材料和粘结剂聚丙烯酸按照质量比1︰50进行混合后，加入N-甲基吡咯烷酮(NMP)作为溶剂，调配成为固含量为70％的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为10μm的负极集流体铜箔的一个表面上，110℃条件下烘干，得到涂层厚度为150μm的单面涂覆有负极材料层的负极极片。在该负极极片的另一个表面上重复以上步骤，得到双面涂覆有负极材料层的负极极片。然后，将负极极片裁切成74mm×867mm的规格待用。
<正极极片的制备>
将正极活性材料钴酸锂、导电炭黑、聚偏二氟乙烯(PVDF)按质量比95︰2.5︰2.5混合，加入NMP作为溶剂，调配成为固含量为75％的浆料，并搅拌均匀。将浆料均匀涂覆在厚度为10μm的正极集流体铝箔的一个表面上，90℃条件下烘干，得到涂层厚度为110μm的正极极片。以上步骤完成后，即完成正极极片的单面涂布。之后，在该正极极片的另一个表面上重复以上步骤，即得到双面涂布正极活性材料的正极极片。涂布完成后，将正极极片裁切成74mm×867mm的规格并焊接极耳后待用。
<电解液的制备>
在干燥氩气气氛中，将有机溶剂碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)和碳酸二乙酯(DEC)以质量比EC︰EMC︰DEC＝30︰50︰20混合，然后向有机溶剂中加入锂盐六氟磷酸锂(LiPF 6)溶解并混合均匀，得到锂盐的浓度为1.15mol/L的电解液。
<隔离膜的制备>
采用厚度为15μm的聚乙烯(PE)薄膜(Celgard公司提供)。
<锂离子电池的制备>
将上述制备得到的正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正极和负极中间已起到隔离的作用，卷绕得到电极组件。将电极组件置于铝塑膜包装袋中，干燥后注入电解液，经过真空封装、静置、化成、脱气、切边等工序得到锂离子电池。
实施例2、实施例3、实施例4、实施例5、实施例6、实施例7、实施例8、实施例9中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例1相同，相关参数的变化如表1中所示。
实施例10、实施例11、实施例12、实施例13、实施例14、实施例15中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例1相同，相关参数的变化如表2中所示。
实施例16
将<硅基复合材料的制备>制备步骤中得到的硅基复合材料和分散剂聚乙烯吡咯烷酮(PVP)按质量比为500︰11加入到无水乙醇中，搅拌0.5h，得到均匀的悬浮液，再向悬浮液中加入异丙醇铝，搅拌0.5h后，再滴加去离子水继续反应4h得到混合溶液，其中，异丙醇铝与硅基复合材料的质量比为1︰50，异丙醇铝与去离子水的摩尔比为1︰3；将混合溶液通过喷雾干燥的方式得到粉末，将粉末在500℃下加热2h，冷却至室温后过筛处理，得到含有金属元素保护层的硅基复合材料。并将实施例2中<负极极片的制备>制备步骤中的硅基复合材料替换成含有金属元素保护层的硅基复合材料，<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例2相同。
实施例17、实施例18、实施例19、实施例20中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例16相同，相关参数的变化如表3中所示。
实施例21
将<硅基复合材料的制备>制备步骤中得到的硅基复合材料加入到含有分散剂羧甲基纤维素钠(CMC-Na)的单壁碳纳米管(SCNT)溶液中分散2小时，直至形成均匀的混合溶液，喷雾干燥得到粉末，破碎，400目过筛得到含有保护层的硅基复合材料，其中，硅基复合材料：SCNT︰CMC-Na的质量比为99.75︰0.1︰0.15。并将实施例13中<负极极片的制备>制备步骤中的硅基复合材料替换成含有保护层的硅基复合材料，<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例13相同。
实施例22、实施例23、实施例24、实施例25、实施例26、实施例27、实施例28、
实施例29、实施例30、实施例31、实施例32、实施例33中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例21相同，相关制备参数的变化如表4中所示。
对比例1、对比例2、对比例3、对比例4中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例1相同，相关参数的变化如表1中所示。
对比例5、对比例6中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例1相同，相关参数的变化如表2中所示。
对比例7中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例16相同，相关制备参数的变化如表3中所示。
对比例8、对比例9中，<硅基复合材料的制备>、<负极极片的制备>、<正极极片的制备>、<电解液的制备>、<隔离膜的制备>及<锂离子电池的制备>的制备步骤均与实施例21相同，相关制备参数的变化如表4中所示。
实施例1、实施例2、实施例3、实施例4、实施例5、实施例6、实施例7、实施例8、实施例9、对比例1、对比例2、对比例3、对比例4的制备参数和测试结果如表1所示；实施例10、实施例11、实施例12、实施例13、实施例14、实施例15、对比例5、对比例6的制备参数和测试结果如表2所示；实施例2、实施例16、实施例17、实施例18、实施例19、实施例20、对比例7的制备参数和测试结果如表3所示；实施例13、实施例21、 实施例22、实施例23、实施例24、实施例25、实施例26、实施例27、实施例28、对比例12、实施例2、实施例29、实施例30、实施例31、实施例32、实施例33、对比例8、对比例9的制备参数和测试结果如表4所示。
表1
Figure PCTCN2021084627-appb-000002
表2
Figure PCTCN2021084627-appb-000003
表3
Figure PCTCN2021084627-appb-000004
Figure PCTCN2021084627-appb-000005
注：表3中的“/”表示不存在该对应制备参数。
表4
Figure PCTCN2021084627-appb-000006
Figure PCTCN2021084627-appb-000007
注：表4中的“/”表示不存在该对应制备参数，SCNT为单壁碳纳米管，MCNT为多壁碳纳米管，P为聚丙烯酸钠。
从实施例1、实施例2、实施例3、实施例4、实施例5、对比例1和对比例2可以看出，具有本申请B/A比值的硅基复合材料，能够提高锂离子电池的循环性能、倍率性能，以及使锂离子电池在多次循环后仍具有较小的变形率。从实施例1、实施例2、实施例3、实施例4和实施例5可以看出，在硅基复合材料中硅的质量含量C 0不变的情况下，通过在本申请的范围内增大B/A的比值，硅基复合材料的首次效率稍有下降、比容量基本无变化，锂离子电池的循环性能先提升再降低、倍率性能提高，可见只要使得B/A在本申请范围内，就能够得到高循环性能和倍率性能的锂离子电池。
图1示出了实施例1中的硅基复合材料的X射线衍射谱图，从图1中可以看出在2θ角为12°至38°范围内存在衍射峰，且B/A比值为60％。图2示出了实施例1中的硅基复合材料的的拉曼光谱图，从图2中可以看出在位移为1255cm -1至1355cm -1范围内存在D峰，在位移为1575cm -1至1600cm -1范围内存在G峰，且D峰与G峰的峰强度比值为1.2。图3示出了实施例1和对比例2中的锂离子电池的循环衰减曲线图，从图3中可以看出，在容量保持率相同的情况下，实施例1制备的锂离子电池的循环圈数明显大于对比例2提供的锂离子电池。图4示出了实施例1和对比例2中的锂离子电池的膨胀曲线图，从图4中可以看出，在相同循环圈数的情况下，实施例1提供的锂离子电池的变形率明显小于对比例2提供的锂离子电池。图5示出了对比例2中的硅基复合材料的X射线衍射谱图，从图5中可以看出在2θ角为12°至38°范围内虽然存在衍射峰，但B/A比值为73％。
从实施例3、实施例6、实施例7、从实施例8、实施例9、对比例3和对比例4可以看出，具有本申请硅的质量含量的硅基复合材料，能够提高锂离子电池的循环性能、倍率性能，以及使锂离子电池在多次循环后仍具有较小的变形率。从实施例3、实施例6、实施例7、从实施例8和实施例9可以看出，在B/A的比值不变的情况下，通过在本申请的范围内增大硅基复合材料中硅的质量含量C 0，硅基复合材料的首次效率逐渐增大、比容量稍有减小，锂离子电池的循环性能虽有小幅度的下降，但循环后的变形率仍然较小，倍率性能提高，只要使得C 0在本申请范围内，就能够得到高循环性能、倍率性能、低变形率的锂离子电池。
从实施例10、实施例11、实施例12、实施例13、实施例14、实施例15、对比例5和对比例6可以看出，具有本申请0.5α/(C 0-αC 0)和硅基复合材料中硅的质量含量C 0在本申请的范围内，得到的锂离子电池同时具有良好的循环性能和高的能量密度。从实施例10、实施例11、实施例12、实施例13、实施例14、实施例15可以看出，在硅基复合材料中硅 的质量含量C 0不变的情况下，随着0.5α/(C 0-αC 0)的增大，硅基复合材料的孔隙率α和比表面积逐渐增大、比容量无明显改变，锂离子电池的循环性能和能量密度先提升后降低、循环后的变形率先减小再增大，只要使得0.5α/(C 0-αC 0)在本申请范围内，就能够得到高循环性能、倍率性能、低变形率的锂离子电池。
从实施例16、实施例17、实施例18、实施例19、实施例20和对比例7可以看出，具有本申请保护层中金属含量的硅基复合材料，能够进一步提高锂离子电池的循环性能及抗膨胀性能。从实施例16、实施例17、实施例20可以看出，随着保护层中金属含量在本申请的范围内逐渐增大，硅基复合材料的比表面积逐渐增大、比容量和首次效率有小幅度的减小，但锂离子电池仍具有良好的循环性能和较小的变形率。
碳材料的种类和含量通常也会影响锂离子电池的性能，从实施例13、实施例21、实施例22、实施例23、实施例24、实施例25、实施例26、实施例27、实施例28、实施例29、实施例30、实施例31、实施例32、实施例33可以看出，只要使得碳材料的种类和含量在本申请范围内，就能够进一步提高锂离子电池的循环性能，降低锂离子电池循环后的变形率。
从实施例21、实施例24、实施例25、对比例8可以看出，当碳材料的含量过高时(例如对比例8)，则无法制备锂离子电池，这可能是由于碳材料过高时将导致浆料无法加工。
从实施例21、实施例22和对比例9可以看出，分散剂的加入通常能够改善碳材料的团聚问题，从而能够得到具有良好的循环性能和循环后变形率较小的锂离子电池。
以上所述仅为本申请的较佳实施例，并不用以限制本申请，凡在本申请的精神和原则之内，所做的任何修改、等同替换、改进等，均应包含在本申请保护的范围之内。

Claims (10)

  1. 一种负极极片，所述负极极片包含负极材料层，所述负极材料层包含硅基复合材料，所述硅基复合材料包含多孔的碳基体和所述碳基体孔隙内的纳米硅颗粒，所述硅基复合材料的XRD衍射图谱中在2θ角为12°至38°范围内存在衍射峰，所述衍射峰的总面积为A，所述衍射峰中2θ角为12°至所述衍射峰的峰值所对应的2θ角范围内的衍射峰面积为B，且60％≤B/A≤70％。
  2. 根据权利要求1所述的负极极片，其中，所述硅基复合材料的孔隙率为α，所述硅基复合材料中硅的质量含量为C 0，且0.2≤0.5α/(C 0-αC 0)≤1.6。
  3. 根据权利要求1所述的负极极片，其中，所述负极极片满足以下特征中的至少一者：
    (a)所述硅基复合材料中的硅质量含量C 0为20％至60％；
    (b)所述硅基复合材料的孔隙率α为10％至60％；
    (c)所述硅基复合材料的平均粒径Dv50不大于20μm；
    (d)所述硅基复合材料的比表面积不大于50m 2/g。
  4. 根据权利要求1所述的负极极片，其中，所述硅基复合材料的拉曼光谱图中在位移为1255cm -1至1355cm -1范围内存在D峰，在位移为1575cm -1至1600cm -1范围内存在G峰，D峰与G峰的峰强度比值为0.2至2。
  5. 根据权利要求1所述的负极极片，其中，所述硅基复合材料还包括保护层，所述保护层包括元素C、Ti、Al、Zn、S、P、Li、B、N中的至少一种。
  6. 根据权利要求5所述的负极极片，其中，以所述硅基复合材料的总质量为基准，所述保护层中金属元素的质量百分含量为0.1％至0.9％。
  7. 根据权利要求5所述的负极极片，其中，所述保护层中的C选自无定形碳、碳纳米管、石墨烯、气相沉积碳纤维中的至少一种。
  8. 根据权利要求1所述的负极极片，其中，所述负极材料层中还包括石墨颗粒和导电剂，以所述硅基复合材料、石墨颗粒和导电剂的总质量为基准，所述硅基复合材料的质量百分含量为5％至80％。
  9. 一种电化学装置，其包括权利要求1至8中任一项所述的负极极片。
  10. 一种电子装置，其包括权利要求10所述的电化学装置。
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