WO2023039750A1

WO2023039750A1 - Negative electrode composite material and use thereof

Info

Publication number: WO2023039750A1
Application number: PCT/CN2021/118519
Authority: WO
Inventors: 陈志焕
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-09-15
Filing date: 2021-09-15
Publication date: 2023-03-23
Also published as: CN114730883A

Abstract

A negative electrode composite material, which comprises a silicon-solid electrolyte composite material. The silicon-solid electrolyte composite material comprises active silicon particles and a solid electrolyte, and is coated or partially coated with carbon. By means of the negative electrode composite material of the present application, the active silicon particles and the solid electrolyte are compounded, and are then subjected to surface carbon layer coating to obtain a negative electrode composite material for a silicon-containing lithium ion battery, which has rapid ion conduction, a long cycle and low expansion.

Description

A kind of negative electrode composite material and its application

technical field

The present application relates to the technical field of lithium-ion batteries, in particular to a negative electrode composite material and its application.

Background technique

One direction of lithium-ion battery technology innovation is to continuously improve energy density. At present, the actual capacity of the mainstream graphite material is close to the theoretical capacity (372mAh/g), and there is already a bottleneck in increasing the energy density. Silicon-based anode materials have attracted much attention and research because of their abundant reserves, ultra-high theoretical capacity (4200mAh/g), and environmental friendliness. However, the problem of volume expansion (more than 300%) in the cycle process of silicon-based negative electrode materials has seriously affected the process of industrial application of silicon-based negative electrode materials. Aiming at the large volume expansion (120%~300%), poor electrical conductivity (<1S/m) and insufficient dynamic performance caused by by-products during the cycle process of silicon materials, the fast cycle attenuation (400 cycle cycle capacity retention) rate below 80%) and other issues.

At present, the main method to solve the large volume change (120% ~ 300%) and poor conductivity (<1S/m) of silicon materials during the cycle is the nano-silicon material, silicon material and graphite or other materials (metal or non-metal) composite and surface coating etc. However, the specific surface area of nanomaterials is large (the specific surface area of materials smaller than 100nm can be as high as 100m ² /g), which will consume more electrolyte to form SEI film, resulting in low initial Coulombic efficiency. In addition, the preparation of nanomaterials is difficult and the price is high. A series of characteristics limit the further application of nano-silicon materials; in addition, carbon coating is used to improve the conductivity of silicon anode materials (the conductivity of ordinary silicon materials can be increased to 100S/m after carbon coating), but generally CVD hydrocarbon gas coating and Solid-phase asphalt coating, etc. cannot solve the electrical contact failure caused by expansion during cycling. Mixing silicon-based negative electrodes with graphite with good conductivity is also a better way to solve poor conductivity and large expansion, but simple mechanical mixing cannot guarantee the uniformity of mixing. The contact of the base particles also depends on a high-cohesion binder, which will result in a decrease in the rate capability.

Contents of the invention

The purpose of this application is to provide a negative electrode composite material with low expansion, good ion conduction rate and cycle performance.

The first aspect of the present application provides a negative electrode composite material, which includes a silicon-solid electrolyte composite material, the silicon-solid electrolyte composite material includes active silicon particles and a solid electrolyte, and the silicon-solid electrolyte composite material is coated with carbon or partially covered.

In this application, the silicon-solid electrolyte composite material is a mixed state of active silicon particles and solid electrolyte. The solid electrolyte is interspersed between the active silicon particles. The silicon-solid electrolyte composite material forms a core and is surrounded by a shell structure formed by carbon. Coated or partially coated, the shell structure formed by carbon can also be called carbon coating.

The inventors found that in this application, silicon, as the negative electrode active material, has a large capacity; the solid electrolyte can be used as a fast ion-conducting phase to accelerate the diffusion of lithium ions, and improve the ion-conducting performance of the negative electrode composite material. In addition, the solid electrolyte can also be used as a The buffer phase buffers the volume expansion of silicon during the cycle, thereby improving the cell expansion during the cycle; further, the silicon is combined with the solid electrolyte to reduce the area where the silicon directly contacts the electrolyte and reduce the side effects during the cycle. The accumulation of products can improve the cycle performance and fast charging performance during the cycle; coating carbon on the surface of the silicon-solid electrolyte composite material can further improve the conductivity of the composite material, and can also inhibit the volume expansion during the charge and discharge process; this application The negative electrode composite material of the silicon and solid electrolyte is compounded, and then the surface is coated with a carbon layer, and a silicon-containing lithium-ion battery negative electrode material with fast ion conduction, long cycle, and low expansion is obtained.

In some embodiments of the present application, the average particle diameter D ₁ of the negative electrode composite material and the average particle diameter D ₂ of the active silicon particles satisfy: 2.5D ₂ ≤ D ₁ ≤ 7D ₂ , the inventors found that when the negative electrode If the ratio of the average particle size of the composite material to the average particle size of the active silicon particles is too large, the number of active silicon particles contained in a single negative electrode composite material particle is too large, which is not conducive to the diffusion of Li ions, and the cycle performance, cell expansion and rate performance deteriorate.

In the present application, the "average particle size" has its well-known meaning, that is, for an actual particle group composed of particles with different sizes and shapes, compared with an imaginary particle group composed of uniform spherical particles, if If both have the same particle diameter and full length, the diameter of the spherical particle is called the average particle diameter of the actual particle group.

In some embodiments of the present application, the average particle diameter D ₁ μm of the negative electrode composite material satisfies: 1≤D ₁ ≤30.

In some embodiments of the present application, the average particle diameter D ₂ μm of the active silicon particles satisfies: 0.3≦D ₂ ≦8. The inventors found that the smaller the particle size of the active silicon particles, it is beneficial to shorten the diffusion path of lithium ions, improve the ion conductivity of the silicon material, and then improve the cycle performance during the cycle; however, the active silicon particles are too small, for example, less than 0.3 μm , will cause the specific surface area of the silicon material to increase, and the by-products generated by the reaction with the electrolyte during the cycle will increase, resulting in deterioration of the cycle performance and expansion; when the particle size of the active silicon particles is too large, the cycle performance, cell expansion and rate performance will all get worse. The inventors found that when the average particle size D ₂ μm of the active silicon particles satisfies the above conditions, it is beneficial to improve both the ion conductivity and cycle performance of the negative electrode composite material.

In some embodiments of the present application, the active silicon particles include at least one of nano-silicon, micro-silicon, silicon carbon, silicon alloy and silicon-oxygen material (SiO _x , where 0.6≤x≤1.5). Wherein, the SiO _x may include SiO and SiO ₂ , and in some embodiments of the present application, the SiO _x may further include nano Si grains, and the size of the nano Si grains is less than 100 nm.

In some embodiments of the present application, based on the total weight of the negative electrode composite material, the content of the active silicon particles is 60% to 97%. The increase in the content of active silicon particles is beneficial to improve the energy density of lithium-ion batteries.

In some embodiments of the present application, the solid electrolyte includes at least one of a polymer solid electrolyte, an oxide solid electrolyte, a sulfide crystalline solid electrolyte, a sulfide glass solid electrolyte, and a glass ceramic solid electrolyte.

In some embodiments of the present application, the solid electrolyte includes lithium phosphate (Li ₃ PO ₄ ), lithium titanium phosphate (Li _x Ti _y (PO ₄ ) ₃ , where 0<x<2 and 0<y<3 ), lithium aluminum titanium phosphate (Li _x Al _y T _z (PO ₄ ) ₃ , where 0<x<2, 0<y<1, and 0<z<3), where 0≤x≤1 and 0≤ Li _1+x+y (Al,Ga) _x (Ti,Ge) _2-x Si _y P _3-y O ₁₂ , lithium lanthanum titanate (Li _x La _y TiO ₃ , where 0<x <2 and 0<y<3), lithium germanium thiophosphate (Li _x Ge _y P _z S _w , where 0<x<4, 0<y<1, 0<z<1, and 0<w< 5), lithium nitride (Li _x N _y , where 0<x<4, 0<y<2), SiS ₂ glass (Li _x Si _y S _z , where 0≤x<3, 0<y<2, and 0<z<4), P ₂ S ₅ glass (Li _x P _y S _z , where 0≤x<3, 0<y<3, and 0<z<7), Li ₂ O, LiF, LiOH, Li ₂ CO ₃ , LiAlO ₂ , Li ₄ SiO ₄ , Li ₂ O-Al ₂ O ₃ -SiO ₂ -P ₂ O ₅ -TiO ₂ -GeO ₂ ceramics and garnet ceramics (Li _3+x La ₃ M ₂ O ₁₂ , wherein 0≤x≤5, and M is at least one of Te, Nb, or Zr).

The inventors found that the solid electrolyte content is too low, such as less than 2%, which is not conducive to its role in increasing ion conductivity and alleviating expansion; as the solid electrolyte content increases, the cycle performance of lithium-ion batteries improves, and the battery expansion rate increases. When the content of the solid electrolyte is reduced, the rate performance is improved. However, when the content of the solid electrolyte is too high, such as higher than 30%, the rate performance deteriorates. In some embodiments of the present application, based on the total weight of the negative electrode composite material, the content of the solid electrolyte is 2% to 30%.

In some embodiments of the present application, the carbon includes at least one of amorphous carbon, graphene or carbon nanotubes.

The inventors found that increasing the amount of carbon coating is conducive to improving the conductivity of the negative electrode composite material and improving the cycle performance. However, the ion conductivity of the negative electrode composite material deteriorates with the increase of carbon content. When the carbon content is too high, the battery rate performance deteriorates. In some embodiments of the present application, based on the total weight of the negative electrode composite material, the content of the carbon is 0.05% to 10%.

The present application does not limit the preparation method of the negative electrode composite material, for example, it can be prepared by the following method:

1) Put the active silicon particles and the solid electrolyte into a powder mixer for mixing, the stirring speed is 10-100r/min, and the stirring time is 20-120 minutes;

2) Put the mixed powder obtained after mixing into high-temperature and high-pressure sintering equipment for sintering, the sintering temperature is 700-1100°C, and the sintering time is 0.5-6 hours;

3) Mechanically pulverizing the ingot obtained after sintering to obtain a silicon-solid electrolyte composite material;

4) Coating the silicon-solid electrolyte composite material with a carbon layer to obtain the negative electrode composite material.

Wherein, based on the total mass of active silicon particles, solid electrolyte and carbon, the content of the active silicon particles is 60% to 97%, the content of the solid electrolyte is 2% to 30%, and the content of the carbon is 0.05%. to 10%.

Stirring speed and stirring time affect the uniformity of mixing. The inventors found that the uniform dispersion of active silicon particles and solid electrolyte is beneficial to the improvement of cycle performance, cell expansion and rate performance.

The inventors also found that if the sintering temperature is too high or the sintering time is too long, the grains of Si will grow, and the sintering between the solid electrolyte and the silicon particles will be denser, the first effect will be improved, and the rate performance will be improved, but the cycle and expansion will be limited. worsened. When the sintering temperature and sintering time are within the above range, it is beneficial to obtain a negative electrode material with high first efficiency, high cycle performance, high rate and low expansion.

In this application, the ingot obtained after sintering can be mechanically pulverized to obtain the silicon-solid electrolyte composite material with the required particle size. Since the carbon coating layer is usually thin, the particle size of the negative electrode composite material is mainly affected by the silicon-solid electrolyte composite material. Therefore, the particle size of the silicon-solid electrolyte composite material can be equal to the particle size of the negative electrode composite material.

The present application does not limit the method of coating the carbon layer, for example, solid phase method, liquid phase method, CVD method, etc. can be used to realize.

The second aspect of the present application provides a negative electrode sheet, including a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, wherein the negative electrode active material layer includes the negative electrode composite material provided in the first aspect of the present application .

The negative electrode sheet of the present application can be made by arranging the negative electrode active material layer on the negative electrode current collector. Collectors, etc. In the present application, the thickness of the negative electrode current collector and the negative electrode active material layer is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6 μm to 10 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm.

The negative active material layer of the present application may further include a conductive agent and a binder.

In the present application, the type of conductive agent in the negative electrode sheet is not limited, for example, the conductive agent may include at least one of conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black and carbon nanofibers; The addition of the conductive agent can improve the conductivity of the negative electrode. The present application has no special limitation on the content of the conductive agent in the negative electrode active material layer, as long as the purpose of the application can be achieved, for example, the conductive agent accounts for 0% to 1% of the total mass of the negative electrode active material layer.

In the present application, the type of binder in the negative electrode sheet is not limited. For example, the binder may include polyvinylidene fluoride, a copolymer of vinylidene fluoride-fluorinated olefin, polyvinylpyrrolidone, polypropylene At least one of nitrile, polymethylacrylate, polytetrafluoroethylene, styrene-butadiene rubber, polyurethane, fluorinated rubber and polyvinyl alcohol; the addition of binder can improve the viscosity of the negative active material layer and reduce the negative active material layer The possibility of falling off of the negative electrode active material and conductive agent in the battery can also reduce the possibility of the negative electrode active material layer falling off from the current collector. The present application has no special limitation on the content of the binder in the negative electrode active material layer, as long as the purpose of the application can be achieved, for example, the binder accounts for 0.5% to 10% of the total mass of the negative electrode active material layer.

The third aspect of the present application provides an electrochemical device, and the electrochemical device obtained by including the negative electrode sheet provided by the second aspect of the present application has good kinetic performance and cycle performance.

In the electrochemical device provided by this application, the negative electrode sheet provided by this application is used as the negative electrode sheet; while other components, including the positive electrode sheet, separator and electrolyte, are not particularly limited.

For example, a positive electrode sheet generally includes a positive electrode current collector and a positive electrode active material layer. Wherein, the positive electrode current collector is not particularly limited, and may be a positive electrode current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, composite current collector, and the like. The positive electrode active material layer includes a positive electrode active material, the positive electrode active material is not particularly limited, and can be a positive electrode active material known in the art, for example, including nickel cobalt lithium manganate (811, 622, 523, 111), nickel cobalt lithium aluminate, At least one of lithium iron phosphate, lithium-rich manganese-based materials, lithium cobaltate, lithium manganate, lithium iron manganese phosphate or lithium titanate. In the present application, the thicknesses of the positive electrode current collector and the positive electrode active material layer are not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 8 μm to 12 μm, and the thickness of the positive electrode active material layer is 25 μm to 100 μm.

Optionally, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited, and may be a commonly used conductive layer in the field. The conductive layer includes a conductive agent and a binder. The conductive agent is not particularly limited, and may be any conductive agent known to those skilled in the art or a combination thereof, for example, at least one of a zero-dimensional conductive agent, a one-dimensional conductive agent and a two-dimensional conductive agent may be used. Preferably, the conductive agent may include at least one of carbon black, conductive graphite, carbon fiber, carbon nanotube, VGCF (Vapor Grown Carbon Fiber) or graphene. The amount of the conductive agent is not particularly limited, and can be selected according to common knowledge in the art. One of the above-mentioned conductive agents may be used alone, or two or more of them may be used in combination in an arbitrary ratio.

The binder in the conductive layer is not particularly limited, and may be any binder known to those skilled in the art or a combination thereof, such as polyacrylate, polyimide, polyamide, polyamideimide, polyamideimide, At least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, and the like. These binders may be used alone or in combination of two or more in any ratio.

The lithium ion battery of the present application also includes a separator, which is used to separate the positive pole piece and the negative pole piece, prevent the internal short circuit of the lithium ion battery, allow electrolyte ions to pass freely, and complete the electrochemical charge and discharge process. In the present application, the separator is not particularly limited, as long as the purpose of the present application can be achieved.

For example, polyethylene (PE), polypropylene (PP)-based polyolefin (PO)-based release film, polyester film (such as polyethylene terephthalate (PET) film), cellulose film, polyamide Imine film (PI), polyamide film (PA), spandex or aramid film, woven film, non-woven film (non-woven fabric), microporous film, composite film, separator paper, rolled film, spun film, etc. at least one of the

For example, a separator may include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide, etc. kind. Optionally, polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane can be used. Optionally, at least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.

For example, the inorganic layer includes inorganic particles and a binder, the inorganic particles are not particularly limited, for example, can be selected from aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide, At least one of zinc oxide, calcium oxide, zirconia, 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, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidine One or a combination of ketone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer comprises a polymer, and the polymer material 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 lithium ion battery of the present application also includes an electrolyte, which can be one or more of gel electrolyte, solid electrolyte and electrolyte, and the electrolyte includes lithium salt and non-aqueous solvent.

In some embodiments of the first aspect of the present application, the lithium salt is selected from lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), Lithium tetraphenylborate (LiB(C ₆ H ₅ ) ₄ ), lithium methanesulfonate (LiCH ₃ SO ₃ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethanesulfonylimide ( One of LiN(SO ₂ CF ₃ ) ₂ ), LiC(SO ₂ CF ₃ ) ₃ , lithium hexafluorosilicate (LiSiF ₆ ), lithium bisoxalate borate (LiBOB) and lithium difluoroborate (LiF ₂ OB) or more. For example, LiPF ₆ may be selected as a lithium salt because of its high ion conductivity and improved cycle characteristics.

The non-aqueous solvent can be carbonate compound, carboxylate compound, ether compound, other organic solvent or their combination.

The above-mentioned carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound or a combination thereof.

Examples of the aforementioned chain carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), carbonic acid Ethyl methyl ester (EMC) 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 Ethyl carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-dicarbonate Fluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.

Examples of the above carboxylate compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone , decanolactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.

Examples of the aforementioned ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethyl Oxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

Examples of the aforementioned other organic solvents are dimethylsulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, Formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters, and combinations thereof.

The preparation process of an electrochemical device is well known to those skilled in the art, and there is no particular limitation in this application. For example, an electrochemical device can be manufactured through the following process: overlap the positive pole piece and the negative pole piece through the separator, and put it into the case after winding, folding, etc. as required, inject the electrolyte into the case and seal it. In addition, anti-overcurrent elements, guide plates, etc. can also be placed in the casing as needed, so as to prevent pressure rise and overcharge and discharge inside the electrochemical device.

The fourth aspect of the present application provides an electronic device, including the electrochemical device provided in the third aspect of the present application.

The electronic device of the present application is not particularly limited, and it may be used in any electronic device known in the prior art. In some embodiments, electronic devices may include, but are not limited to, notebook computers, pen-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, video recorders , LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting Appliances, toys, game consoles, clocks, electric tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.

The negative electrode composite material of the present application obtains a silicon-containing lithium ion battery negative electrode composite material with fast ion conduction, long cycle and low expansion by compounding active silicon particles and solid electrolyte, and then coating the surface with a carbon layer.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application and the prior art, the following briefly introduces the accompanying drawings required in the embodiments and the prior art. Obviously, the accompanying drawings in the following description are only the present invention. For some embodiments of the application, those skilled in the art can also obtain other drawings based on these drawings without creative work.

FIG. 1 is a schematic structural view of the negative electrode composite material of Example 3.

FIG. 2A is a photomicrograph of the negative electrode composite material of Example 3. FIG.

FIG. 2B is an element distribution diagram of the negative electrode composite material of Example 3. FIG.

Detailed ways

In order to make the purpose, technical solution, and advantages of the present application clearer, the present application will be further described in detail below with reference to the accompanying drawings and examples. Apparently, the described embodiments are only some of the embodiments of this application, not all of them. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in this application belong to the protection scope of this application.

It should be noted that, in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to the lithium-ion battery.

In the following examples and comparative examples, the reagents, materials and instruments used are commercially available unless otherwise specified.

Test Methods:

Average particle size test of negative electrode composite materials:

Add 0.02g of negative electrode composite material powder samples prepared in Examples 1-30 and Comparative Examples 1 and 2 to a 50ml clean beaker, add 20ml of deionized water, and then add a few drops of 1% surfactant to completely disperse the powder in water , Ultrasonic in a 120W ultrasonic cleaning machine for 5 minutes, use MasterSizer 2000 to test the particle size distribution and obtain the average particle size of the sample.

Determination of gram capacity of negative electrode composite material:

The negative electrode composite materials prepared in each embodiment and comparative example were prepared into slurry, coated on copper foil, dried in a vacuum oven at 85°C for 12 hours, and cut into diameters of 1.4 cm with a punching machine in a dry environment. Weigh the disc and weigh it. The mass of the negative electrode composite material is calculated as m; in the glove box, a metal lithium sheet is used as the counter electrode, the separator is a ceglard composite film, and the electrolyte is added to assemble a button battery. Use the LAND series of battery tests to conduct charge and discharge tests on the battery to test its charge and discharge performance. The obtained capacity is set as C1 (mAh), and the negative electrode composite material gram capacity (mAh/g)=C1/m.

Full battery performance test:

First efficiency test:

During the first charge and discharge process of the full battery, it is charged to 4.45V with a constant current of 0.5C, and then charged to 0.025C with a constant voltage of 4.45V, (the obtained capacity is C0), and after standing for 5 minutes, it is discharged to 3.0V at 0.5C (obtained Discharge capacity D0). Full battery first efficiency = D0/C0.

High temperature cycle test:

The test temperature is 45°C, charge to 4.45V at a constant current of 0.7C, charge to 0.025C at a constant voltage, and discharge to 3.0V at 0.5C after standing for 5 minutes. The capacity obtained in this step is taken as the initial capacity, and 0.7C charging/0.5C discharging is carried out for cycle test, and the capacity at each step is compared with the initial capacity to obtain the capacity decay curve, and the cycle number results when the capacity decays to 80% are shown in Table 1.

Battery full-charge expansion rate test: Use a screw micrometer to test the thickness of the lithium-ion battery when it is initially half-charged. At 45°C, when the charge-discharge cycle reaches 400 times, the lithium-ion battery is fully charged, and then use a screw micrometer to test the thickness of the lithium-ion battery at this time, and compare it with the thickness of the lithium-ion battery at the initial half-charge. Expansion rate of Li-ion battery when fully charged.

Discharge rate test:

At 25°C, discharge at 0.2C to 3.0V, let stand for 5 minutes, charge at 0.5C to 4.4V, charge at constant voltage to 0.05C and let stand for 5 minutes, adjust the discharge rate, respectively at 0.2C, 0.5C, 1C, 1.5C, 2.0C for discharge test to obtain the discharge capacity respectively, compare the capacity obtained at each rate with the capacity obtained at 0.2C to obtain a ratio, and compare the rate performance by comparing the ratio.

Full battery preparation:

Positive pole piece preparation:

Dissolve the positive electrode active material lithium cobaltate, conductive carbon black, and binder polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP) solution at a weight ratio of 96.7︰1.7︰1.6, and prepare a solid A positive electrode slurry with a content of 75%; using a 10 μm thick aluminum foil as the positive electrode current collector, coating the positive electrode slurry on the positive electrode current collector with a coating thickness of 50 μm, and drying to obtain a positive electrode sheet coated on one side; after that , repeating the above steps on the other surface of the positive electrode sheet to obtain a positive electrode sheet coated with positive active materials on both sides.

Negative pole piece preparation:

The negative electrode composite material prepared in each example and comparative example, the conductive agent acetylene black, and the acrylic resin emulsion PAA were fully stirred and mixed in the deionized water solvent system according to the weight ratio of 95:1.2:3.8, and then prepared to have a solid content of 50%. The negative electrode slurry is coated on one surface of a copper foil current collector with a thickness of 10 μm, and the coating thickness is 50 μm, and dried to obtain a negative electrode sheet coated on one side; after that, on the other surface of the negative electrode sheet Repeat the above steps above to obtain a negative electrode sheet coated with negative active materials on both sides.

Electrolyte preparation:

In an environment with a water content of less than 10ppm, lithium hexafluorophosphate (LiPF ₆ ) and non-aqueous organic solvents are mixed according to the following formula: ethylene carbonate (EC): propylene carbonate (PC): propyl propionate (PP): diethyl carbonate (DEC )=1:1:1:1 weight ratio to prepare the electrolyte solution, wherein the concentration of LiPF ₆ is 1.15mol/L.

Full battery assembly:

The positive electrode sheet, separator, and negative electrode sheet are stacked in order, and the PE porous polymer film is used as the separator, so that the separator is placed in the middle of the positive and negative electrodes to play the role of isolation, and the electrode assembly is obtained by winding. The electrode assembly is placed in the outer packaging aluminum-plastic film, and after dehydration at 80°C, the above-mentioned electrolyte is injected and packaged, and the lithium-ion battery is obtained through processes such as formation, degassing, and edge trimming.

Negative electrode composite material preparation:

Example 1

1) Put 100g of silicon-oxygen material (SiO _x , where 0.6≤x≤1.5, average particle size D=1.5μm) and 1g of solid electrolyte lithium germanium thiophosphate into a powder mixer for mixing at a stirring speed of 60r /min, the stirring time is 60 minutes.

2) Put the mixed powder obtained after mixing into high temperature and high pressure sintering equipment for sintering, the sintering temperature is 900°C, and the sintering time is 4h.

3) The ingot obtained after sintering is mechanically pulverized to obtain a silicon-solid electrolyte composite material with a particle size of about 4-5 μm.

4) Coating 3g of amorphous carbon on the surface of the silicon-solid electrolyte composite material by CVD method to obtain negative electrode composite material.

In Example 2 to Example 5, except that the corresponding preparation parameters and/or substances are adjusted according to Table 1, the rest are the same as Example 1.

Example 6

Except that the average particle size of the silicon-oxygen material is adjusted to 0.5 μm, and the particle size of the silicon-solid electrolyte composite material is about 1-2 μm, the rest is the same as that of Example 3.

Example 7

Except that the average particle size of the silicon-oxygen material is adjusted to 4 μm, and the particle size of the silicon-solid electrolyte composite material is about 10-15 μm, the rest is the same as that of Example 3.

Example 8

Except that the average particle size of the silicon-oxygen material is adjusted to 10 μm, and the particle size of the silicon-solid electrolyte composite material is about 25-30 μm, the rest is the same as that of Example 3.

In Example 9 to Example 20, except that the corresponding preparation parameters and/or substances are adjusted according to Table 1, the rest are the same as Example 3.

Example 21

Except that the particle size of the silicon-solid electrolyte composite material is adjusted to be about 3-4 μm, the rest is the same as that of Example 3.

Example 22

Except that the particle size of the silicon-solid electrolyte composite material is adjusted to be about 8-9 μm, the rest is the same as that of Example 3.

In Example 23 to Example 30, except that the corresponding preparation parameters and/or substances are adjusted according to Table 1, the rest are the same as Example 3.

Comparative example 1

Except that no solid electrolyte is added, the rest is the same as in Example 3.

Comparative example 2

Except that the obtained silicon-solid electrolyte composite material is not coated with carbon, the rest is the same as that of Example 3.

The material parameters and preparation parameters of each example are shown in Table 1, and the physical parameters and full battery performance of the full battery prepared with the negative electrode materials prepared in each example are shown in Table 2.

The structure diagram of the negative electrode composite material prepared in Example 3 is shown in FIG. 1 , which includes a carbon coating layer 1 , active silicon particles 2 and a solid electrolyte 3 . The scanning electron microscope photo of the negative electrode composite material prepared in Example 3 is shown in Figure 2A, and the element distribution in the negative electrode composite material prepared in Example 3 is measured by X-ray energy spectrometer, and the results are shown in Figure 2B. From the element distribution results It can also be seen from the figure that in the negative electrode composite material of the present application, the solid electrolyte is inserted between the active silicon particles, and the carbon is coated on the surface of the negative electrode active material.

Table 1

Table 2

From the comparison of Examples 1-5 and Comparative Example 1, it can be seen that with the increase of the solid electrolyte content, the gram capacity of the silicon composite material decreases, the initial efficiency does not change much, the expansion rate of lithium-ion batteries gradually decreases, and the cycle performance and The rate performance is improved, but when the solid electrolyte content reaches 30%, the rate performance deteriorates. Therefore, in some preferred embodiments of the present application, based on the total weight of the negative electrode composite material, the content of the solid electrolyte is 2% to 30%.

It can be seen from Examples 3 and 6-8 that as the particle size of the active silicon particles increases, the cycle performance of the battery first increases and then decreases, the battery expansion first decreases and then increases, and the rate performance increases with the particle size of the active silicon particles To some extent, in some preferred embodiments of the present application, the average particle diameter D ₂ μm of the active silicon particles satisfies: 0.3≦D _{2 ≦} 8.

Examples 3, 9-12 show that appropriately prolonging the stirring time or increasing the stirring speed is conducive to the uniform dispersion of active silicon particles and solid electrolyte, and the cycle performance, expansion rate and rate performance of the battery are all improved.

Examples 3, 13-16 illustrate that the sintering temperature increases or the sintering time is prolonged, the first effect of the battery is improved, and the rate performance is improved, but the cycle and expansion are deteriorated, not limited to any theory, the inventor believes that this may be due to Si The crystal grains gradually grow up with the increase of sintering temperature or the extension of sintering time, which makes the sintering between solid electrolyte and silicon particles more dense.

From the comparison of Example 3, Examples 17-20 and Comparative Example 2, it can be seen that when the amount of carbon coating is too small, the gram capacity of the negative electrode composite material is low, and the initial efficiency is low. Not limited to any theory, the inventor believes that , it may only be due to the fact that the amount of carbon coating is too small, the conductivity of the negative electrode composite material is poor, and it is difficult to achieve the complete intercalation and extraction of lithium; as the amount of carbon coating increases, the gram capacity of the negative electrode composite material increases, and the battery The first-time efficiency, cycle performance, and rate performance are all improved, and the battery expansion rate is reduced; however, when the carbon coating amount is too large, the battery rate performance deteriorates, so in some preferred embodiments of the present application, based on the negative electrode composite The total weight of the material, the carbon content is 0.05% to 10%.

It can be seen from Examples 3, 21, and 22 that as the ratio of the average particle size of the negative electrode composite material to the average particle size of the silicon particle increases, the battery cycle performance, battery expansion rate, and rate performance deteriorate thereupon, not limited to any theory, the inventor It is considered that this may be due to the excessive amount of silicon particles contained in a single negative electrode composite material, which is not conducive to the diffusion of Li ions.

Examples 23-30 use different active silicon particles, solid electrolytes and carbon, all of which can achieve improvements in cycle performance and expansion rate.

The above is only a preferred embodiment of the application, and is not intended to limit the application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the application should be included in the application. within the scope of protection.

Claims

A negative electrode composite material, which includes a silicon-solid electrolyte composite material, the silicon-solid electrolyte composite material includes active silicon particles and a solid electrolyte, and the silicon-solid electrolyte composite material is coated or partially coated with carbon.
The negative electrode composite material according to claim 1, wherein the average particle diameter D 1 of the negative electrode composite material and the average particle diameter D 2 of the active silicon particles satisfy: 2.5D 2 ≤ D 1 ≤ 7D 2 .
The negative electrode composite material according to claim 1, wherein the average particle diameter D 1 μm of the negative electrode composite material satisfies 1≤D 1 ≤30.
The negative electrode composite material according to claim 1, wherein the average particle diameter D 2 μm of the active silicon particles satisfies 0.3≦D 2 ≦8.
The negative electrode composite material according to claim 1, wherein the active silicon particles include at least one of nano-silicon, micro-silicon, silicon carbon, silicon alloy and SiOx , 0.6≤x≤1.5.
The negative electrode composite material according to claim 5, wherein the SiO x contains nano-Si grains, and the size of the nano-Si grains is less than 100 nm.
The negative electrode composite material according to claim 1, wherein, based on the total weight of the negative electrode composite material, the content of the active silicon particles is 60% to 97%.
The negative electrode composite material according to claim 1, wherein the solid electrolyte comprises at least one of a polymer solid electrolyte, an oxide solid electrolyte, a sulfide crystalline solid electrolyte, a sulfide glass solid electrolyte, and a glass ceramic solid electrolyte.
The negative electrode composite material according to claim 1, wherein the solid electrolyte comprises lithium phosphate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium lanthanum titanate, lithium germanium thiophosphate, lithium nitride, SiS 2 glass, P 2 S 5 glass, Li 2 O, LiF, LiOH, Li 2 CO 3 , LiAlO 2 , Li 4 SiO 4 , Li 2 O-Al 2 O 3 -SiO 2 -P 2 O 5 -TiO 2 - At least one of GeO2 ceramics and garnet ceramics.
The negative electrode composite material according to claim 1, wherein, based on the total weight of the negative electrode composite material, the content of the solid electrolyte is 2% to 30%.
The negative electrode composite material according to claim 1, wherein the carbon comprises at least one of amorphous carbon, graphene or carbon nanotubes.
The negative electrode composite material according to claim 1, wherein, based on the total weight of the negative electrode composite material, the content of the carbon is 0.05% to 10%.
A negative electrode sheet, comprising a current collector and a negative electrode active material layer disposed on at least one surface of the current collector, wherein the negative electrode active material layer comprises the negative electrode composite material according to any one of claims 1-12.
An electrochemical device comprising the negative electrode sheet according to claim 13.
An electronic device comprising the electrochemical device according to claim 14.