CN112701270B - Negative electrode material, pole piece containing negative electrode material and electrochemical device - Google Patents
Negative electrode material, pole piece containing negative electrode material and electrochemical device Download PDFInfo
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Abstract
The application provides a negative electrode material, a pole piece containing the negative electrode material and an electrochemical device, wherein the negative electrode material comprises a silicon monoxide particle, the molar ratio A of oxygen to silicon on the surface of the silicon monoxide particle is larger than the molar ratio B of oxygen to silicon in the silicon monoxide particle, so that the molar ratio A of oxygen to silicon on the surface of the silicon monoxide particle and the molar ratio B of oxygen to silicon at any point more than 25nm away from the surface of the silicon monoxide particle satisfy the following conditions: A/B is more than 1.5, so that the volume expansion degree of the electrochemical device in the charge-discharge cycle process is smaller, and the cycle performance is better.
Description
Technical Field
The application relates to the field of electrochemistry, in particular to a negative electrode material, a pole piece containing the negative electrode material and an electrochemical device.
Background
The lithium ion battery has the characteristics of large specific energy, high working voltage, low self-discharge rate, small volume, light weight and the like, and has wide application in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices, people have increasingly high requirements on energy density, cycle performance and the like of lithium ion batteries. The silicon-based negative electrode material has a gram capacity of 1500mAh/g to 2000mAh/g, and is considered as the next generation lithium ion negative electrode material with the most application prospect.
However, the silicon-based negative electrode material has the problems of low conductivity, large volume expansion change in the charging and discharging process and the like, and further application of the silicon-based negative electrode material in the lithium ion battery is hindered. Therefore, a silicon-based negative electrode material capable of further improving the cycle stability of the lithium ion battery and reducing the volume expansion of the lithium ion battery is needed.
Disclosure of Invention
The application aims to provide a negative electrode material, a pole piece comprising the negative electrode material and an electrochemical device, so as to reduce the volume expansion of the electrochemical device and improve the cycle performance of the electrochemical device.
In the following description 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 specific technical scheme is as follows:
a first aspect of the present application provides an anode material comprising a silica particle having a molar ratio a of oxygen to silicon on a surface thereof larger than a molar ratio B of oxygen to silicon inside thereof such that the molar ratio a of oxygen to silicon on the surface of the silica particle and the molar ratio B of oxygen to silicon at any point more than 25nm from the surface of the silica particle satisfy: A/B > 1.5.
In the negative electrode material of the present application, the molar ratio a of oxygen to silicon on the surface of the silicon oxide particles is larger than the molar ratio B of oxygen to silicon inside the silicon oxide particles, and it can be seen that the oxygen element content on the surface of the silicon oxide particles is higher than the oxygen element content inside the silicon oxide particles. The molar ratio A of oxygen to silicon on the surface of the silica particles to the molar ratio B of oxygen to silicon at any point more than 25nm from the surface of the silica particles satisfies: A/B is more than 1.5, so that the negative electrode material has lower lithium intercalation expansion characteristics and enhanced stability. In the present application, the molar ratio of oxygen to silicon in the silica particles decreases gradually from the surface to the inside.
The molar ratio of oxygen to silicon as used herein means the atomic number ratio of the oxygen element to the silicon element in the silicon monoxide particles, i.e., the molar ratio between the oxygen element and the silicon element.
In one embodiment of the present application, the molar ratio B of oxygen to silicon inside the silica particles satisfies: b is more than or equal to 0.5 and less than or equal to 1.5. Without being limited to any theory, when the molar ratio B of oxygen and silicon inside the silica particles satisfies 0.5. ltoreq. B.ltoreq.1.5, it is possible to make the anode material have a lower lithium intercalation expansion characteristic, thereby improving the stability of the anode material. The lower limit value of the molar ratio B of oxygen to silicon inside the silica particles may include: 0.5, 0.7, 0.8, 0.9, or 1.0, and the upper limit value of the molar ratio B of oxygen to silicon inside the silica particles may include: 1.1, 1.2, 1.3, 1.4, or 1.5.
In one embodiment of the present application, a conductive material is further present on the surface of the silica particles to improve the conductive performance of the negative electrode material, and the thickness of the conductive material is 1nm to 50 nm. Without being limited to any theory, when the thickness of the conductive material is too small, for example less than 1nm, it is difficult to effectively improve the conductivity of the negative electrode material; when the thickness of the conductive material is too large, for example, greater than 50nm, the relative content of the active material in the negative electrode plate is reduced, which affects the energy density of the lithium ion battery. The lower limit of the thickness of the conductive material may include one of the following values: 1nm, 5nm, 10nm, 20nm, or 25nm, the upper limit of the thickness of the conductive material may include one of the following values: 30nm, 35nm, 40nm, 45nm, or 50 nm.
The conductive material is not particularly limited as long as the conductive property of the negative electrode material can be further improved. For example, the conductive material may include at least one of amorphous carbon, carbon nanotubes, graphene, or vapor deposited carbon fibers.
In one embodiment of the present application, the conductive material is present in an amount of 0.5 to 8% by mass, based on the total mass of the negative electrode material. Without being limited to any theory, when the content of the conductive material is too low, for example, less than 0.5%, it is difficult to effectively improve the conductivity of the negative electrode material, and when the content of the conductive material is too high, for example, more than 8%, the relative content of the active material in the negative electrode plate is reduced, which affects the energy density of the lithium ion battery. The lower limit of the content of the conductive material in the present application may include the following values: 0.5%, 1%, 2%, 3%, or 4%, and the upper limit of the content of the conductive material may include one of the following values: 5%, 6%, 7%, or 8%.
In one embodiment of the present application, a polymer is also present on the surface of the silica particles. The silica particles may be at least partially coated with a polymer or may be entirely coated with a polymer. Without being bound to any theory, the polymers themselves generally have good structural stability and can also act as carriers for conductive materials.
In the present application, the mass percentage of the polymer is 1% to 10% based on the total mass of the anode material. Without being limited to any theory, when the content of the polymer is too low, for example, less than 1%, it is difficult to effectively improve the structural stability of the anode material; when the content of the polymer is too high, for example, higher than 10%, the relative content of the active material in the negative electrode sheet is reduced, which affects the energy density of the lithium ion battery. The lower limit of the mass percentage of the polymer may include the following values: 1%, 2%, 3%, or 4%; the upper limit of the mass percentage of the polymer may include the following values: 5%, 6%, 7%, 8%, or 10%.
The polymer is not particularly limited in the present application as long as the object of the invention of the present application is achieved. In one embodiment herein, the polymer may comprise at least one of carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, polyamide, polyacrylate, or derivatives thereof. The above-mentioned polymers may be used singly or in combination of two or more kinds at an arbitrary ratio.
In one embodiment of the present application, the silica particles have a Dv50 of 1 μm to 15 μm. Without being limited to any theory, by controlling the Dv50 of the silica particles within the above range, the stability of the anode material can be further improved. In the volume-based particle size distribution, Dv50 represents the particle size at which 50% of the particles are accumulated in volume from the small particle size side. The lower limit of Dv50 for the silica particles may include one of the following values: 1 μm, 3 μm, 5 μm or 7 μm, the upper limit value of Dv50 of the silica particles may include one of the following values: 9 μm, 10 μm, 12 μm or 15 μm.
In one embodiment of the present application, the anode material may further include amorphous carbon. Specifically, the silica particles may be dispersed in a matrix formed of amorphous carbon to form a silica-amorphous carbon composite material, which can further improve the conductivity of the anode material.
In one embodiment of the present application, the Dv50 of the anode material is 3 μm to 15 μm. Without being bound by any theory, when the Dv50 of the negative electrode material is too small (e.g., less than 3 μm), the specific surface area of the small particles is large, the negative electrode material reacts more easily with the electrolyte, generating more by-products; when the Dv50 of the negative electrode material is too large (for example, larger than 15 μm), the volume change of large particles is large in the circulation process, and the negative electrode material is more likely to be broken, which is not favorable for improving the stability of the negative electrode material.
In one embodiment of the application, the Dv99 of the negative electrode material is 10 μm to 45 μm, which indicates that the particle size distribution of the negative electrode material is uniform, thereby reducing the roughness of the surface of the negative electrode sheet and improving the performance of the negative electrode sheet. Here, Dv99 represents a particle size of 99% of the volume accumulation of the negative electrode material from the small particle size side in the volume-based particle size distribution.
In one embodiment of the present application, the silica particles in the anode material have a Dv50 of 60nm to 500 nm. In the present application, the lower limit value of Dv50 of the silica particles in the anode material may include one of the following values: 60nm, 100nm, 150nm, 200nm, or 250nm, the upper limit value of Dv50 of the silica particles in the anode material may include one of the following values: 300nm, 350nm, 400nm, 450nm or 500 nm.
In one embodiment of the present application, the 2.0V gram capacity of the anode material is 600mAh/g to 1400mAh/g, indicating that the anode material of the present application has a higher gram capacity.
In one embodiment of the present application, the content of the carbon element is 5% to 50% by mass based on the total mass of the anode material. Without being limited to any theory, when the content of the carbon element is too low (for example, less than 5%), the conductivity of the anode material is not improved; when the content of the carbon element is too high (for example, higher than 50%), it is not beneficial to increase the energy density of the lithium ion battery. By controlling the content of the carbon element in the negative electrode material in the range, the negative electrode material has good conductive performance, and the lithium ion battery has high energy density. In the present application, the lower limit of the mass percentage content of the carbon element may include the following values: 5%, 10%, 15%, 20% or 25%, and the upper limit of the mass percentage of the carbon element may include one of the following values: 30%, 35%, 40%, 45% or 50%.
In one embodiment of the present application, the elemental silicon is present in an amount of 15 to 38% by mass, based on the total mass of the anode material. Without being bound by any theory, when the content of silicon element is too low (for example, less than 15%), it is not beneficial to increase the energy density of the lithium ion battery; when the content of the silicon element is too high (for example, higher than 38%), it is not favorable for improving the stability of the anode material. By controlling the content of the silicon element in the negative electrode material in the range, the negative electrode material has good stability, and the lithium ion battery has high energy density. In the present application, the lower limit of the percentage by mass of the silicon element may include the following values: 15%, 20%, 23% or 25%, and the upper limit of the percentage by mass of the silicon element may include one of the following values: 27%, 30%, 35% or 38%.
The method for producing the negative electrode material of the present application is not particularly limited, and a production method known to those skilled in the art may be employed, and for example, the following production method may be employed:
mixing silicon dioxide and metal silicon powder in a molar ratio of 1:5 to 5:1 to obtain a mixed material; at 10 -4 kPa to 10 -1 Heating the mixed material at 1200-1450 deg.C for 0.5-24 h under kPa to obtain gas; the obtained gas is condensed to obtain a solid, and then the obtained solid is crushed and sieved to obtain the silica particles with different particle size distributions.
And (3) placing the prepared silicon monoxide particles in an inert atmosphere with the oxygen content of less than 5% by volume, and carrying out heat treatment at the temperature of 250-700 ℃ for 0.5-12 h to obtain the cathode material.
Or, the prepared silica particles are put into a sand mill containing an organic solvent (such as absolute ethyl alcohol) and a dispersing agent (such as asphalt) for ball milling for 2 to 48 hours, and an oxide layer on the surface of the silica particles is oxidized in the organic solvent or naturally oxidized in the air.
The surface of the silica particles may also be provided with a conductive material to form a conductive layer, which may be formed by:
the silicon monoxide particles are placed in a Chemical Vapor Deposition (CVD) furnace, and deposition is carried out at 600 ℃ to 900 ℃ by utilizing gas of hydrocarbon such as methane, acetylene, ethylene and the like. The products may be post-treated after deposition, such as grading, demagnetising, etc.
Alternatively, the silica particles, the conductive material and the dispersant are sufficiently dispersed and stirred in an organic solvent, and the organic solvent is removed to obtain solid powder, that is, the conductive layer is formed on the surface of the silica particles. The solid powder can also be subjected to post-treatment such as crushing, sieving, demagnetizing, sintering and the like.
In the present application, the organic solvent is not particularly limited, and may be, for example, absolute ethyl alcohol, as long as the surface of the silica particles is oxidized to form an oxide layer. The amount of the organic solvent to be added is not particularly limited, and for example, the mass ratio of the organic solvent to the silica particles is 1: 20 to 1: 30.
The addition amount of the dispersing agent is not particularly limited, and for example, the mass ratio of the dispersing agent to the silica particles is 0.5 to 3: 97 to 99.5, as long as the silica particles are sufficiently dispersed in the organic solvent.
The inert atmosphere is not particularly limited, such as argon or helium.
A second aspect of the present application provides a negative electrode tab comprising a negative electrode material as described in any of the embodiments above.
The positive electrode sheet in the present application is not particularly limited as long as the object of the present application can be achieved. For example, the positive electrode tab generally includes a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is not particularly limited, and may be any positive electrode current collector known in the art, such as an aluminum foil, an aluminum alloy foil, or a composite current collector. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is not particularly limited, and any positive electrode active material known in the art may be used, and for example, may include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, a lithium rich manganese-based material, lithium cobalt oxide, lithium manganese iron phosphate, or lithium titanate.
The separator of the present application includes, but is not limited to, at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one component selected from the group consisting of high density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of lithium ion batteries by means of a shutdown effect.
The surface of the separation film may further include a porous layer disposed on at least one surface of the separation film, the porous layer including inorganic particles selected from alumina (Al) and a binder, and the inorganic particles 2 O 3 ) Silicon oxide (SiO) 2 ) Magnesium oxide (MgO), titanium oxide (TiO) 2 ) Hafnium oxide (HfO) 2 ) Tin oxide (SnO) 2 ) Cerium oxide (CeO) 2 ) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO) 2 ) Yttrium oxide (Y) 2 O 3 ) Silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The adhesive is selected from one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
The porous layer can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the bonding performance between the isolating membrane and the anode or the cathode.
The lithium ion battery of the present application further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte including a lithium salt and a non-aqueous solvent.
In some embodiments herein, the lithium salt is selected from 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 、LiC(SO 2 CF 3 ) 3 、LiSiF 6 One or more of LiBOB and lithium difluoroborate. For example, the lithium salt may be LiPF 6 Since it can give high ionic conductivity and improve cycle characteristics.
The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.
Examples of the above chain carbonate compound are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Methyl Ethyl Carbonate (MEC), and combinations thereof. Examples of the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), and combinations thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, and combinations thereof.
Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, and combinations thereof.
Examples of the above ether compounds are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.
Examples of such other organic solvents are dimethylsulfoxide, 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.
In a third aspect of the present application, there is provided an electrochemical device comprising the negative electrode sheet of the second aspect.
A fourth aspect of the present application provides an electronic device including the electrochemical device according to the third aspect described above.
The electronic device of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.
The process for preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, the electrochemical device may be manufactured by the following process: the positive electrode and the negative electrode are overlapped through a separation film, and are placed into a shell after being wound, folded and the like according to needs, electrolyte is injected into the shell and the shell is sealed, wherein the separation film is the separation film provided by the application. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the case as necessary to prevent a pressure rise and overcharge/discharge inside the electrochemical device.
The application provides a negative electrode material, a pole piece containing the negative electrode material and an electrochemical device, wherein the negative electrode material comprises silicon oxide particles, the molar ratio A of oxygen to silicon on the surfaces of the silicon oxide particles is larger than the molar ratio B of oxygen to silicon in the silicon oxide particles, and the stability of the surfaces of the negative electrode material is enhanced. The molar ratio A of oxygen to silicon on the surface of the silica particles and the molar ratio B of oxygen to silicon at any point more than 25nm away from the surface of the silica particles satisfy: A/B is more than 1.5, the stability of the surface of the negative electrode material is further improved, and the ion transmission capability of the negative electrode material can be improved, so that the electrochemical device containing the negative electrode material has smaller volume expansion degree and better cycle performance in the charge-discharge cycle process.
Drawings
In order to illustrate the technical solutions of the present application and the prior art more clearly, the following briefly introduces examples and figures that need to be used in the prior art, it being obvious that the figures in the following description are only some examples of the present application.
FIG. 1 is a FIB-TEM line scan elemental distribution map of example 7 of the present application;
FIG. 2 is a FIB-TEM line scan elemental distribution diagram of comparative example 1 of the present application.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is further described in detail below with reference to the accompanying drawings and examples. It is to be understood that the embodiments described are only a few embodiments of the present application and not all embodiments. All other technical solutions obtained by a person of ordinary skill in the art based on the embodiments in the present application belong to the scope of protection of the present application.
In the embodiments 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.
Examples
Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. Various tests and evaluations were carried out by the following methods. Unless otherwise specified, "part" and "%" are based on mass.
The test method and the test equipment are as follows:
testing of powder properties of the anode material:
and (3) observing the microscopic morphology of the powder particles of the negative electrode material: and (3) observing the powder microscopic morphology of the cathode material by using a scanning electron microscope, wherein the selected test instrument is as follows: OxFORD EDS (X-max-20 mm) 2 ) And the accelerating voltage is 10KV, the focal length is adjusted, the observation multiple is high-power observation from 50K, and the agglomeration condition of the anode material particles is mainly observed under the low power of 500-2000.
Testing the specific surface area of the anode material:
after the adsorption amount of the gas on the solid surface at different relative pressures is measured at constant temperature and low temperature, the adsorption amount of the monomolecular layer of the sample is obtained based on the Bronuore-Eltt-Taylor adsorption theory and the formula (BET formula) thereof, so that the specific surface area of the negative electrode material is calculated.
The BET formula is:
wherein W represents the mass of gas adsorbed by a solid sample under relative pressure; wm represents the saturated adsorption capacity of gas spread over a monolayer; (c-1)/(WmC) represents the slope; 1/WmC represents the intercept. The total surface area St is: st ═ w × N × Acs/M, specific surface area S is: st/m, where m denotes the sample mass and Acs denotes each N 2 The average area occupied by the molecules was 16.2A 2 。
In the test, 1.5g to 3.5g of the negative electrode material powder sample was weighed into a test sample tube of a specific surface area and porosity analyzer (model TriStar II 3020), and the test was performed after degassing at 200 ℃ for 120 min.
And testing the granularity of the anode material:
adding 0.02g of negative electrode material powder sample into a 50ml clean beaker, adding 20ml of deionized water, then dropwise adding 3-5 drops of surfactant with the mass concentration of 1% to completely disperse the powder sample into water, then carrying out ultrasonic oscillation for 5 minutes in an ultrasonic cleaning machine with the power of 120W, and testing the particle size distribution by using a laser particle size analyzer (model MasterSizer 2000).
And testing the tap density of the negative electrode material:
the national standard GB/T5162-2006 determination of tap density of metal powder is adopted.
Testing the carbon content of the anode material:
the cathode material sample is heated and combusted at high temperature by a high-frequency furnace under the condition of oxygen enrichment to oxidize carbon into carbon dioxide, the gas enters a corresponding absorption cell after being processed, corresponding infrared radiation is absorbed, and then the infrared radiation is converted into corresponding signals by a detector. The signal is sampled by a computer, is converted into a numerical value in direct proportion to the concentration of the carbon dioxide after linear correction, then the value of the whole analysis process is accumulated, after the analysis is finished, the accumulated value is divided by a weight value in the computer, and then multiplied by a correction coefficient, and blanks are deducted, so that the carbon percentage content in the sample can be obtained. The sample was tested using a high frequency infrared carbon sulfur analyzer (model number shanghai decek HCS-140).
And (3) testing the surface atomic ratio of the anode material:
spraying a negative electrode material on a copper foil containing a conductive adhesive, polishing a cut section by using a plasma polisher (Leica EM TIC 3X-Ion Beam slit Cutter), then putting the polished section into a Scanning Electron Microscope (SEM) to find a cut silicon monoxide particle, cutting the silicon monoxide particle along the vertical direction of the section by using a Focused Ion Beam (FIB) to obtain a slice (about 50nm) containing the section of the silicon monoxide particle, measuring by using a Transmission Electron Microscope (TEM), and performing EDS analysis on a point A 'randomly taken from 1 to 2nm away from the outer surface, namely the atomic ratio of Si to O on the outer surface of the silicon monoxide particle is A, and the point A' extends from the outer surface to the inside of the silicon monoxide particle in a direction perpendicular to the outer surface and the atomic ratio of Si to O on the point B 'more than 25nm away from the outer surface of the point A' is B.
Testing the primary efficiency of the button cell:
mixing the negative electrode materials prepared in the embodiments and the comparative examples with conductive carbon black and a polymer according to a ratio of 80: 10, adding deionized water, stirring to form slurry, coating a coating with the thickness of 100 microns on the surface of a current collector by using a scraper, drying in a vacuum drying oven for 12 hours at 85 ℃, cutting into a wafer with the diameter of 1cm in a drying environment by using a punching machine, taking a metal lithium sheet as a counter electrode in a glove box, selecting a ceglard composite membrane as an isolating membrane, adding an electrolyte to assemble a button cell, and performing charge-discharge test on the cell by using a blue (LAND) series cell test, wherein the first efficiency calculation mode is as follows: the discharge cutoff voltage was 2.0V for the capacity/charge voltage to 0.005V for the capacity.
Gram capacity calculation mode of button cell:
the button cell discharges to a gram capacity corresponding to a voltage of 2.0V.
And (3) testing the performance of the full battery:
and (3) testing the cycle performance:
the test temperature was 25 ℃ or 45 ℃, and the voltage was charged to 4.4V at a constant current of 0.7C, to 0.025C at a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes. And taking the capacity obtained in the step as the initial capacity, performing a cycle test by adopting 0.7C charging/0.5C discharging, and taking the ratio of the capacity of each step to the initial capacity to obtain a capacity fading curve. The cycle number of the battery with the capacity retention rate of 90% in the 25 ℃ cycle is taken as the room-temperature cycle performance of the battery, the cycle number of the battery with the capacity retention rate of 80% in the 45 ℃ cycle is taken as the high-temperature cycle performance of the battery, and the cycle number of the battery is compared with the cycle number of the battery under the two conditions.
And (3) testing the full charge expansion rate of the lithium ion battery:
and testing the half-charge thickness of the lithium ion battery by using a spiral micrometer, namely the thickness of the lithium ion battery in a 50% state of charge (SOC), and when the lithium ion battery is in a full-charge state, namely in a 100% SOC state, testing the thickness of the lithium ion battery by using the spiral micrometer when the lithium ion battery is circulated to 400 circles, and comparing the thickness with the thickness of the lithium ion battery in the initial half-charge state to obtain the expansion rate of the lithium ion battery in the full-charge state.
Examples
Example 1
< preparation of negative electrode Material >
Mixing silicon dioxide and metal silicon powder in a molar ratio of 1:1 to obtain a mixed material; at 10 -4 Heating the mixed material for 10 hours under the temperature conditions of kPa and 1400 ℃ to obtain gas; condensing the obtained gas to obtain a solid, and then pulverizing and sieving the obtained solid to obtain Silica (SiO) particles having a Dv50 of 5.2 μm;
and (3) placing the silicon monoxide particles in argon with the oxygen content of less than 5% by volume fraction, and carrying out heat treatment at 400 ℃ for 10h to obtain the anode material with the oxide layer thickness of 22 nm.
< preparation of button cell >
Mixing the prepared negative electrode material with conductive carbon black and a binding agent polypropylene glycol (PAA) according to a ratio of 80: 10, adding deionized water, stirring to form slurry with the solid content of 40%, coating a coating with the thickness of 100 mu m on the surface of a current collector by using a scraper, drying in a vacuum drying oven for 12 hours at 85 ℃, cutting into a wafer with the diameter of 1cm in a drying environment by using a punching machine, taking a metal lithium sheet as a counter electrode in a glove box, selecting a ceglard composite membrane as an isolating membrane, and adding an electrolyte to assemble the button cell.
< full cell preparation >
< preparation of negative electrode sheet >
Mixing graphite, the prepared negative electrode material, a conductive agent (conductive carbon black) and a binder (PAA) according to a mass ratio of 70: 15: 5: 10, adding deionized water as a solvent to prepare slurry with the solid content of 60%, adding a proper amount of deionized water, and adjusting the viscosity of the slurry to be 5000 Pa.s to prepare the negative electrode slurry. And coating the prepared negative electrode slurry on one surface of a copper foil with the thickness of 8 mu m, drying at 110 ℃, and cold pressing to obtain a negative electrode plate with the coating thickness of 100 mu m. And then repeating the coating steps on the other surface of the negative pole piece to obtain the negative pole piece with the negative active material layer coated on the two surfaces. Cutting the negative pole piece into a size of 74mm multiplied by 867mm, and welding a pole lug for later use.
< preparation of Positive electrode sheet >
Mixing the positive active material lithium cobaltate, the conductive carbon black and the polyvinylidene fluoride (PVDF) according to the mass ratio of 95: 2.5, adding N-methyl pyrrolidone (NMP) as a solvent, preparing slurry with the solid content of 75%, and uniformly stirring. And uniformly coating the slurry on one surface of an aluminum foil with the thickness of 12 mu m, drying at 90 ℃, cold-pressing to obtain a positive pole piece with the thickness of a positive active material layer of 110 mu m, and repeating the steps on the other surface of the positive pole piece to obtain the positive pole piece with the positive active material layer coated on the two surfaces. Cutting the positive pole piece into the specification of 76mm × 851mm, and welding the pole lugs for later use.
< preparation of separator >
A Polyethylene (PE) porous polymer film having a thickness of 15 μm was used as a separator.
< preparation of electrolyte solution >
Under the environment that the water content is less than 10ppm, the non-aqueous organic solvent propylene carbonate (P)C) Ethylene Carbonate (EC), diethyl carbonate (DEC) were mixed in a mass ratio of 1:1, and then lithium hexafluorophosphate (LiPF) was added to the non-aqueous organic solvent 6 ) Dissolving and mixing uniformly, and adding fluoroethylene carbonate (FEC) to obtain the electrolyte. Wherein, LiPF 6 The molar concentration in the electrolyte was 1.15mol/L, and the mass concentration of FEC in the electrolyte was 12.5%.
< preparation of lithium ion Battery >
And (3) stacking the prepared positive pole piece, the prepared isolating film and the prepared negative pole piece in sequence, so that the isolating film is positioned between the positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) putting the electrode assembly into an aluminum-plastic film packaging bag, dehydrating at 80 ℃, injecting the prepared electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.
Example 2
The procedure was repeated as in example 1, except that the heat treatment time was adjusted to 5 hours in < preparation of anode material >.
Example 3
The procedure was repeated as in example 1, except that the heat treatment time was adjusted to 0.5h in < preparation of anode material >.
Example 4
The procedure was repeated as in example 2 except that in < preparation of anode material >, Dv50 of silica was 1.3 μm.
Example 5
The procedure was repeated as in example 2 except that in < preparation of anode material >, Dv50 of silica was 14.6 μm.
Example 6
The same as example 1 except that < preparation of anode material > was different.
< preparation of negative electrode Material >
The silica particles prepared in example 1 were placed in a sand mill containing anhydrous ethanol and dispersant pitch for ball milling for 24 hours, Dv50 of the silica particles was 110nm, the surface of the silica particles was oxidized in the solution to form an oxide layer with a thickness of 23nm, and the obtained mixture was dried to obtain a negative electrode material. Wherein the mass ratio of the asphalt to the silica particles is 1: 99, and the mass ratio of the absolute ethyl alcohol to the silica particles is 1: 5.
Example 7
The procedure of example 6 was repeated, except that in < preparation of anode material >, Dv50 of the silica particles was adjusted to 190nm, and the ball milling time was adjusted to 12 hours.
Example 8
The procedure of example 6 was repeated, except that in < preparation of anode material >, Dv50 of the silica particles was adjusted to 520nm, and the ball milling time was adjusted to 8 hours.
Example 9
The procedure of example 6 was repeated, except that in < preparation of anode material >, the Dv50 of the silica particles was adjusted to 80nm, and the ball milling time was adjusted to 48 hours.
Example 10
The same as example 2 except that < preparation of anode material > was different.
< preparation of negative electrode Material >
The negative electrode material obtained in example 2 was used as a base material, the conductive material amorphous carbon, and the dispersant carboxymethyl cellulose were dispersed in absolute ethyl alcohol at a mass ratio of 96: 3.2: 0.8, and the mixture was stirred at room temperature, and then the absolute ethyl alcohol was removed to obtain a solid, and the obtained solid was pulverized and sieved to obtain a negative electrode material.
Example 11
The same procedure as in example 10 was repeated, except that in the preparation of the negative electrode material, the conductive material was carbon nanotubes, and the mass ratio of the base material, the conductive material and the dispersant was 96.1: 3.1: 0.8. Wherein the aspect ratio of the carbon nanotube is 3000.
Example 12
The procedure of example 10 was repeated, except that graphene was used as the conductive material, and the mass ratio of the base material, the conductive material, and the dispersant was 95.2: 4.0: 0.8.
Example 13
The procedure of example 10 was repeated, except that vapor deposited carbon fibers were used as the conductive material, and the mass ratio of the base material, the conductive material and the dispersant was 91.2: 8.0: 0.8.
Example 14
The procedure of example 10 was repeated, except that the mass ratio of the base material, the conductive material and the dispersant was 98.7: 0.5: 0.8 in < preparation of anode material >.
Example 15
The same as example 6 was repeated except that < preparation of anode material > was different.
< preparation of negative electrode Material >
The negative electrode material obtained in example 6 was used as a base material, the base material and amorphous carbon were dispersed in absolute ethyl alcohol at a mass ratio of 88: 12, and the mixture was stirred at room temperature, and then absolute ethyl alcohol was removed to obtain a solid, and the obtained solid was pulverized and sieved to obtain a negative electrode material.
Example 16
The procedure was carried out in the same manner as in example 15 except that the mass ratio of the base material to the amorphous carbon was 82: 18 in < preparation of anode material >.
Example 17
The procedure was carried out in the same manner as in example 15 except that the mass ratio of the base material to the amorphous carbon was 70: 30 in < preparation of anode material >.
Example 18
The procedure was carried out in the same manner as in example 15 except that the mass ratio of the base material to the amorphous carbon was 55: 45 in < preparation of anode material >.
Example 19
The same as example 1 except that < preparation of anode material > was different.
Taking the negative electrode material obtained in example 1 as a base material, dispersing the base material and polymer carboxymethyl cellulose in absolute ethyl alcohol according to a mass ratio of 99: 1, stirring uniformly at room temperature, removing the absolute ethyl alcohol to obtain a solid, crushing the obtained solid, and sieving to obtain the negative electrode material.
Example 20
The procedure of example 19 was repeated, except that polyacrylic acid was used as the polymer, and the mass ratio of the matrix material to the polymer was 95: 5.
Example 21
The procedure of example 19 was repeated, except that in < preparation of negative electrode material >, polyamide was used as the polymer, and the mass ratio of the matrix material to the polymer was 90: 10.
Comparative example 1
The same as example 1 except that in < preparation of anode material >, SiO was not subjected to heat treatment in argon gas having an oxygen content of less than 5% by volume fraction.
Comparative example 2
The same procedure as in example 1 was repeated, except that in < preparation of anode material >, the treatment temperature and the treatment time were adjusted so that a/B was 1.33.
Comparative example 3
Except that in < preparation of anode material >, SiO was not subjected to heat treatment in argon gas having an oxygen content of less than 5% by volume fraction, the same was as in example 6.
Comparative example 4
The same as in comparative example 1 except that < preparation of anode material > was different.
Taking the negative electrode material obtained in the comparative example 1 as a base material, dispersing the base material, amorphous carbon and carboxymethyl cellulose serving as a dispersing agent in absolute ethyl alcohol according to the mass ratio of 96: 3.2: 0.8, uniformly stirring at room temperature, removing the absolute ethyl alcohol to obtain a solid, and crushing and sieving the obtained solid to obtain the negative electrode material.
The preparation parameters and test data for the examples and comparative examples are shown in tables 1-1, 1-2, 2-1, 2-2, 3-1, 3-2, 4-1, 4-2, 5-1 and 5-2.
It can be seen from examples 1,2, and 3 and comparative examples 1 and 2 that when the silicon monoxide particles are in the micron order, the cycle performance of the lithium ion battery gradually becomes better and the expansion of the lithium ion battery gradually decreases with the increase of the oxygen content on the surface of the negative electrode material, which indicates that the cycle performance and the expansion resistance of the lithium ion battery with the negative electrode material of the present application are improved.
As can be seen from examples 4 and 5, the Dv50 of silica affects the cycle performance and the expansion rate of the lithium ion battery, and if the Dv50 of silica is within the range of the present application, the cycle performance and the expansion resistance of the lithium ion battery can be improved.
It can be seen from examples 6, 7, 8, 9 and comparative example 3 that when the silicon monoxide particles are all in the nanometer level, the cycle performance and the anti-expansion performance of the lithium ion battery with the negative electrode material are improved at 25 ℃, and the anti-expansion performance is improved at 45 ℃; from examples 6 and 9 and comparative example 3, it can be seen that the cycle performance of the lithium ion battery with the negative electrode material of the present application is improved under the condition of 45 ℃.
As can be seen from examples 10, 11, 12, 13, and 14 and comparative example 4, when the negative electrode materials all contain the conductive material, the cycle performance and the anti-swelling performance of the lithium ion battery with the negative electrode material of the present application are further improved.
From examples 15, 16, 17 and 18 and comparative examples 1 and 2, it can be seen that when the negative electrode material is a silica-amorphous carbon composite material, the cycle performance and the expansion resistance of the lithium ion battery are further improved at 25 ℃; the cycle performance at 45 ℃ is improved. And the cycle performance and the anti-expansion performance of the lithium ion battery tend to increase along with the increase of the carbon content.
As can be seen from examples 19, 20 and 21 and comparative examples 1 and 2, when the negative electrode materials all contain polymers, the cycle performance and the expansion resistance of the lithium ion battery with the negative electrode material are further improved at 25 ℃; the cycle performance at 45 ℃ is improved.
Fig. 1 is a schematic view (FIB-TEM line scan elemental distribution diagram) of the molar ratio of oxygen to silicon of the anode material according to example 7 of the present application as a function of the extension distance, specifically, a schematic view of the molar ratio of oxygen to silicon as a function of the extension distance when the anode material extends outward from an inner point at 25nm from the surface of the anode material. As can be seen from FIG. 1, the molar ratio of oxygen to silicon in the silica particles gradually increases from the inside to the surface.
Fig. 2 is a schematic view (i.e., FIB-TEM line scan elemental distribution diagram) of the molar ratio of oxygen to silicon of the anode material of comparative example 1 as a function of extension distance, specifically, as a schematic view of the molar ratio of oxygen to silicon as measured as a function of extension distance as the anode material extends outward from a point inside the anode material at 25nm from the surface thereof. As can be seen from fig. 2, the molar ratio distribution of oxygen and silicon from the inside to the surface of the silica particles is irregular.
In conclusion, the lithium ion battery with the cathode material has improved cycle performance and expansion resistance.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (9)
1. An anode material comprising a silica particle having a molar ratio A of oxygen to silicon on a surface thereof larger than a molar ratio B of oxygen to silicon inside thereof such that the molar ratio A of oxygen to silicon on the surface of the silica particle and the molar ratio B of oxygen to silicon at any point more than 25nm from the surface of the silica particle satisfy: A/B >1.5, the molar ratio B of oxygen to silicon inside the silica particles satisfying: b is more than or equal to 0.5 and less than or equal to 1.5.
2. The anode material according to claim 1, wherein a conductive material is further present on the surface of the silica particles, and the thickness of the conductive material is 1nm to 50 nm; the conductive material comprises at least one of amorphous carbon, carbon nanotubes, graphene or vapor deposited carbon fibers; the conductive material is contained in an amount of 0.5 to 8% by mass based on the total mass of the negative electrode material.
3. The negative electrode material according to claim 1, wherein a polymer is further present on the surface of the silica particles, and the polymer is contained in an amount of 1 to 10% by mass based on the total mass of the negative electrode material; the polymer comprises at least one of carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, polyamide, polyacrylate or derivatives thereof.
4. The anode material according to claim 1, wherein the silica particles have a Dv50 of 1 to 15 μ ι η.
5. The anode material according to claim 1, further comprising amorphous carbon.
6. The anode material according to claim 1, wherein the anode material satisfies at least one of the following characteristics:
(a) the Dv50 of the negative electrode material is 3 μm to 15 μm;
(b) the Dv99 of the negative electrode material is 10 to 45 μm;
(c) the Dv50 of the silica particles in the negative electrode material is 60nm to 500 nm;
(d) the 2.0V gram capacity of the negative electrode material is 600mAh/g to 1400 mAh/g;
(e) the mass percentage content of the carbon element is 5-50% based on the total mass of the cathode material;
(f) based on the total mass of the cathode material, the mass percentage content of the silicon element is 15-38%.
7. A negative electrode tab comprising the negative electrode material of any one of claims 1-6.
8. An electrochemical device comprising the negative electrode tab of claim 7.
9. An electronic device comprising the electrochemical device of claim 8.
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| CN107046125B (en) * | 2017-02-22 | 2020-08-04 | 深圳市金润能源材料有限公司 | Composite negative electrode, preparation method thereof and lithium ion battery |
| CN108946744A (en) * | 2018-07-23 | 2018-12-07 | 江苏载驰科技股份有限公司 | A kind of lithium ion battery preparation method for aoxidizing sub- silicium cathode material |
| CN109449406B (en) * | 2018-10-30 | 2021-08-10 | 中科廊坊过程工程研究院 | SiO with multi-layer structurexNegative electrode material and preparation method and application thereof |
| CN109888246B (en) * | 2019-03-25 | 2022-03-11 | 合肥国轩高科动力能源有限公司 | Silicon monoxide composite negative electrode material with gradient structure and preparation method and application thereof |
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| CN110911635B (en) * | 2019-11-14 | 2021-01-01 | 宁德新能源科技有限公司 | Negative electrode material, and electrochemical device and electronic device comprising same |
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| CN110911636A (en) * | 2019-11-14 | 2020-03-24 | 宁德新能源科技有限公司 | Negative electrode material, and electrochemical device and electronic device comprising same |
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