Patent Application
20230343946
This application relates to the electrochemical field, and specifically, to a negative electrode material, an electrode plate containing such negative electrode material, and an electrochemical apparatus.
Lithium-ion batteries have been widely used in the field of consumer electronics by virtue of their characteristics such as high specific energy, high working voltage, low self-discharge rate, small size, and light weight. With the rapid development of electric vehicles and mobile electronic devices, people have increasingly high requirements for energy density and cycling performance of lithium-ion batteries. With a gram capacity of up to 1500 mAh/g to 2000 mAh/g, silicon-based negative electrode materials are considered to be the most promising next-generation lithium-ion negative electrode materials.
However, silicon-based negative electrode materials have the problems such as low conductivity and large volume swelling changes during charging and discharging, which hinder further application of the silicon-based negative electrode materials in lithium-ion batteries. Therefore, there is an urgent need for a silicon-based negative electrode material that can further improve cycling stability of lithium-ion batteries and reduce volume swelling of lithium-ion batteries.
This application is intended to provide a negative electrode material, an electrode plate containing such negative electrode material, and an electrochemical apparatus, so as to reduce volume swelling of the electrochemical apparatus and improve cycling performance of the electrochemical apparatus.
It should be noted that in the following content of this application, an example in which a lithium-ion battery is used as an electrochemical apparatus is used to illustrate this application. However, the electrochemical apparatus of this application is not limited to the lithium-ion battery.
Specific technical solutions are as follows:
A first aspect of this application provides a negative electrode material including silicon monoxide particles, where a molar ratio A of oxygen to silicon on a surface of the silicon monoxide particle is greater than a molar ratio B of oxygen to silicon inside the silicon monoxide particle, such that the molar ratio A of oxygen to silicon on the surface of the silicon monoxide particle and a molar ratio B of oxygen to silicon at any point above 25 nm from the surface of the silicon monoxide particle satisfy A/B > 1.5.
In the negative electrode material of this application, the molar ratio A of oxygen to silicon on the surface of the silicon monoxide particle is greater than the molar ratio B of oxygen to silicon inside the silicon monoxide particle, which indicates that the oxygen content on the surface of the silicon monoxide particle is higher than the oxygen content inside the silicon monoxide particle. 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 above 25 nm from the surface of the silicon monoxide particle satisfy A/B > 1.5, so that the negative electrode material of this application has a low lithiation swelling and enhanced stability. In this application, the molar ratio of oxygen to silicon from the surface to the inside of the silicon monoxide particle gradually decreases in a gradient manner.
In this application, the molar ratio of oxygen to silicon is a ratio of the numbers of atoms in oxygen and silicon in the silicon monoxide particle, that is, the molar ratio between elements oxygen and silicon.
In an implementation of this application, the molar ratio B of oxygen to silicon inside the silicon monoxide particle satisfies 0.5 ≤ B ≤ 1.5. Without being limited to any theory, when the molar ratio B of oxygen to silicon inside the silicon monoxide particle satisfies 0.5 ≤ B ≤ 1.5, the negative electrode material can have a smaller lithiation swelling, thereby enhancing the stability of the negative electrode material. A lower limit of the molar ratio B of oxygen to silicon inside the silicon monoxide particle may include 0.5, 0.7, 0.8, 0.9, or 1.0, and an upper limit of the molar ratio B of oxygen to silicon inside the silicon monoxide particle may include 1.1, 1.2, 1.3, 1.4, or 1.5.
In an implementation of this application, a conductive material is further present on the surface of the silicon monoxide particle to improve conductivity of the negative electrode material, where thickness of the conductive material is 1 nm to 50 nm. Without being limited to any theory, when the thickness of the conductive material is excessively small, for example, less than 1 nm, it is difficult to effectively improve the conductivity of the negative electrode material; and when the thickness of the conductive material is excessively large, for example, greater than 50 nm, the relative content of an active material in a negative electrode plate is reduced, affecting energy density of the lithium-ion battery. A lower limit of the thickness of the conductive material may include the following values: 1 nm, 5 nm, 10 nm, 20 nm, or 25 nm, and an upper limit of the thickness of the conductive material may include the following values: 30 nm, 35 nm, 40 nm, 45 nm, or 50 nm.
The conductive material is not particularly limited in this application, provided that the conductivity 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 an implementation of this application, based on a total mass of the negative electrode material, a mass percentage of the conductive material is 0.5% to 8%. Without being limited to any theory, when the percentage of the conductive material is excessively low, for example, lower than 0.5%, it is difficult to effectively improve the conductivity of the negative electrode material; and when the percentage of the conductive material is excessively high, for example, higher than 8%, the relative content of the active material in the negative electrode plate is reduced, affecting the energy density of the lithium-ion battery. In this application, a lower limit of the percentage of the conductive material may include the following values: 0.5%, 1%, 2%, 3%, or 4%, and an upper limit of the percentage of the conductive material may include the following values: 5%, 6%, 7%, or 8%.
In an implementation of this application, a polymer is further present on the surface of the silicon monoxide particle. The silicon monoxide particle may have the polymer on at least part of the surface, or may be entirely encapsulated by the polymer. Without being limited to any theory, the polymer itself generally has a good structural stability and can be used as a carrier for the conductive material.
In this application, based on a total mass of the negative electrode material, a mass percentage of the polymer is 1% to 10%. Without being limited to any theory, when the percentage of the polymer is excessively low, for example, lower than 1%, it is difficult to effectively enhance the structural stability of the negative electrode material; and when the percentage of the polymer is excessively high, for example, higher than 10%, the relative content of the active material in the negative electrode plate is reduced, affecting the energy density of the lithium-ion battery. A lower limit of the mass percentage of the polymer may include the following values: 1%, 2%, 3%, or 4%, and an 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 this application, provided that the invention objectives of this application can be achieved. In an implementation of this application, the polymer may include at least one of carboxymethyl cellulose, polyacrylic acid, polyvinyl alcohol, polyamide, polyacrylic ester, or derivatives of the foregoing substances. One of these polymers may be used alone, or more than two of them may be used in combination at any ratio.
In an implementation of this application, Dv50 of the silicon monoxide particle is 1 µm to 15 µm. Without being limited to any theory, controlling Dv50 of the silicon monoxide particle within the foregoing range can further enhance the stability of the negative electrode material. Dv50 is a particle size where the cumulative distribution by volume reaches 50% as counted from the small particle size side. A lower limit of Dv50 of the silicon monoxide particle may include the following values: 1 µm, 3 µm, 5 µm, or 7 µm, and an upper limit of Dv50 of the silicon monoxide particle may include the following values: 9 µm, 10 µm, 12 µm, or 15 µm.
In an implementation of this application, the negative electrode material may further include amorphous carbon. Specifically, the silicon monoxide particles can be dispersed in a matrix formed by the amorphous carbon to form a silicon monoxide-amorphous carbon composite material, which can further improve the conductivity of the negative electrode material.
In an implementation of this application, Dv50 of the negative electrode material is 3 µm to 15 µm. Without being limited to any theory, when Dv50 of the negative electrode material is excessively small (for example, less than 3 µm), specific surface areas of small particles are large, so the negative electrode material is more likely to react with an electrolyte to generate more by-products; and when Dv50 of the negative electrode material is excessively large (for example, greater than 15 µm), large particles have large volume changes during cycling, so the negative electrode material is more likely to break, which is not conducive to enhancing the stability of the negative electrode material.
In an implementation of this application, Dv99 of the negative electrode material is 10 µm to 45 µm, which indicates that particle size distribution of the negative electrode material is uniform, thereby reducing surface roughness of the negative electrode plate and improving the performance of the negative electrode plate. Dv99 is a particle size of the negative electrode material where the cumulative distribution by volume reaches 99% as counted from the small particle size side.
In an implementation of this application, Dv50 of the silicon monoxide particle in the negative electrode material is 60 nm to 500 nm. In this application, a lower limit of Dv50 of the silicon monoxide particle in the negative electrode material may include the following values: 60 nm, 100 nm, 150 nm, 200 nm, or 250 nm, and an upper limit of Dv50 of the silicon monoxide particle in the negative electrode material may include the following values: 300 nm, 350 nm, 400 nm, 450 nm, or 500 nm.
In an implementation of this application, a gram capacity of the negative electrode material at 2.0 V is 600 mAh/g to 1400 mAh/g, which indicates that the negative electrode material of this application has a high gram capacity.
In an implementation of this application, based on a total mass of the negative electrode material, a mass percentage of carbon is 5% to 50%. Without being limited to any theory, when the percentage of carbon is excessively low (for example, lower than 5%), it is not conducive to improving the conductivity of the negative electrode material; and when the percentage of carbon is excessively high (for example, higher than 50%), it is not conducive to improving the energy density of the lithium-ion battery. Controlling the percentage of carbon in the negative electrode material of this application within the foregoing range allows the negative electrode material to have a good conductivity and the lithium-ion battery to have a high energy density. In this application, a lower limit of the mass percentage of carbon may include the following values: 5%, 10%, 15%, 20%, or 25%, and an upper limit of the mass percentage of carbon may include the following values: 30%, 35%, 40%, 45%, or 50%.
In an implementation of this application, based on the total mass of the negative electrode material, a mass percentage of silicon is 15% to 38%. Without being limited to any theory, when the percentage of silicon is excessively low (for example, lower than 15%), it is not conducive to improving the energy density of the lithium-ion battery; and when the percentage of silicon is excessively high (for example, higher than 38%), it is not conducive to enhancing the stability of the negative electrode material. Controlling the percentage of silicon in the negative electrode material of this application within the foregoing range allows the negative electrode material to have a good stability and the lithium-ion battery to have a high energy density. In this application, a lower limit of the mass percentage of silicon may include the following values: 15%, 20%, 23%, or 25%, and an upper limit of the mass percentage of silicon may include the following values: 27%, 30%, 35%, or 38%.
A preparation method of the negative electrode material is not particularly limited in this application and can be a preparation method well known to persons skilled in the art. For example, the following preparation methods can be used.
Silicon dioxide and metal silicon powder are mixed at a molar ratio of 1:5 to 5:1 to obtain a mixed material. The mixed material is heated at 1200° C. to 1450° C. for 0.5 h to 24 h at 10-4 kPa to 10-1 kPa to obtain gas. The obtained gas is condensed to obtain a solid, and then the obtained solid is crushed and sieved to obtain silicon monoxide particles with different particle size distributions.
The obtained silicon monoxide particles are placed in an inert atmosphere with an oxygen content of less than 5% by volume fraction, and subjected to heat treatment at 250° C. to 700° C. for 0.5 h to 12 h to obtain a negative electrode material.
Alternatively, the obtained silicon monoxide particles are placed in a sand mill containing an organic solvent (for example, absolute ethanol) and a dispersant (for example, asphalt) for ball milling for 2 h to 48 h, and the oxide layer on the surface of the silicon monoxide particles is oxidized in the organic solvent or naturally oxidized in the air.
The conductive material may also be present on the surface of the silicon monoxide particle so that a conductive layer is formed. The conductive layer may be formed in the following methods.
The silicon monoxide particles are placed in a chemical vapor deposition (CVD) furnace and deposited at 600° C. to 900° C. using hydrocarbon gases such as methane, acetylene, and ethylene. The resulting product can be subjected to post-treatments such as grading and demagnetization after deposition.
Alternatively, the silicon monoxide particles, the conductive material, and the dispersant are fully dispersed and stirred in the organic solvent, and then the organic solvent is removed to obtain solid powder, that is, to form a conductive layer on the surface of the silicon monoxide particles. The solid powder can also be subjected to post-treatments such as crushing, sieving, demagnetization, and sintering.
The organic solvent is not particularly limited in this application, for example, the organic solvent may be absolute ethanol, provided that the surface of the silicon monoxide particles can be oxidized to form an oxide layer. An amount of the organic solvent added is not particularly limited, for example, a mass ratio of the organic solvent to the silicon monoxide particles is 1:20 to 1:30.
An amount of the dispersant added is not particularly limited, for example, a mass ratio of the dispersant to the silicon monoxide particles is (0.5 to 3):(97 to 99.5), provided that the silicon monoxide particles can be fully dispersed in the organic solvent.
The inert atmosphere is not particularly limited, for example, the inert atmosphere may be argon or helium.
A second aspect of this application provides a negative electrode plate including the negative electrode material according to any one of the foregoing implementations.
The positive electrode plate of this application is not particularly limited, provided that the objectives of this application can be achieved. For example, the positive electrode plate generally includes a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is not particularly limited and can be any positive electrode current collector well known in the art, for example, aluminum foil, aluminum alloy foil, or 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 can be any positive electrode active material well known in the art, for example, the positive electrode active material may include at least one of lithium nickel cobalt manganate (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganate oxide, lithium manganese iron phosphate, or lithium titanate.
A separator of this application includes but is not limited to at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one composition selected from high-density polyethylene, low-density polyethylene, and ultra-high-molecular-weight polyethylene. Particularly, polyethylene and polypropylene can well prevent short circuit, and can enhance stability of the lithium-ion battery through a shutdown effect.
A surface of the separator may further include a porous layer. The porous layer is disposed on at least one surface of the separator and includes inorganic particles and a binder. The inorganic particles are selected from a combination of one or more of aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), ceria oxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from a combination of one or more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate ester, polyacrylic acid, polyacrylate salt, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.
The porous layer can improve heat resistance, oxidation resistance, and electrolyte infiltration performance of the separator, and enhance bonding between the separator and the positive electrode or the negative electrode.
The lithium-ion battery of this application further includes an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte solution. The electrolyte solution includes a lithium salt and a non-aqueous solvent.
In some implementations of this application, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. For example, LiPF6 may be selected as the lithium salt because it can provide high ionic conductivity and improve cycling characteristics.
The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, another organic solvent, or a combination thereof.
The carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.
An example of the linear carbonate compound is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), or a combination thereof. An example of the cyclic carbonate compound is ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or a combination thereof. An example of the fluorocarbonate compound is fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.
An example of the carboxylate compound is methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, or a combination thereof.
An example of the ether compound is dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxy ethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.
An example of the another organic solvent is dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, phosphate ester, or a combination thereof.
A third aspect of this application provides an electrochemical apparatus including the negative electrode plate according to the second aspect.
A fourth aspect of this application provides an electronic apparatus including the electrochemical apparatus according to the third aspect.
The electronic apparatus of this application is not particularly limited and can be any known electronic apparatus used in the prior art. In some embodiments, the electronic apparatus may include but is not limited to a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable fax machine, a portable copier, a portable printer, a stereo headset, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a storage card, a portable recorder, a radio, a standby power source, a motor, an automobile, a motorcycle, a motor bicycle, a bicycle, a lighting appliance, a toy, a game console, a clock, an electric tool, a flash lamp, a camera, a large household battery, or a lithium-ion capacitor.
A preparation process of the electrochemical apparatus is well known to persons skilled in the art, and is not particularly limited in this application. For example, the electrochemical apparatus may be manufactured in the following process: a positive electrode and a negative electrode are stacked with a separator therebetween, and are put into a housing after operations such as winding and folding as needed. An electrolyte is injected into the housing and then the housing is sealed. The separator used is the separator provided in this application. In addition, an overcurrent prevention element, a guide plate, and the like may also be placed into the housing as needed, so as to prevent pressure increase, overcharge, and overdischarge inside the electrochemical apparatus.
This application provides a negative electrode material, an electrode plate containing such negative electrode material, and an electrochemical apparatus. The negative electrode material includes silicon monoxide particles, and a molar ratio A of oxygen to silicon on a surface of the silicon monoxide particle is greater than a molar ratio B of oxygen to silicon inside the silicon monoxide particle, enhancing stability of the surface of the negative electrode material. The molar ratio A of oxygen to silicon on the surface of the silicon monoxide particle and a molar ratio B of oxygen to silicon at any point above 25 nm from the surface of the silicon monoxide particle satisfy A/B > 1.5, which can improve ion transmission capability of the negative electrode material while further enhancing the stability of the surface of the negative electrode material, so that the electrochemical apparatus containing such negative electrode material has a smaller volume swelling and better cycling performance during charge and discharge cycles.
To describe the technical solutions in this application and the prior art more clearly, the following briefly describes the accompanying drawings required for describing embodiments and the prior art. Apparently, the accompanying drawings in the following description show merely some embodiments of this application.
To make the objectives, technical solutions, and advantages of this application more comprehensible, the following further describes this application in detail with reference to accompanying drawings and embodiments. Apparently, the described embodiments are merely some rather than all of the embodiments of this application. All other technical solutions obtained by persons of ordinary skill in the art based on some embodiments of this application shall fall within the protection scope of this application.
It should be noted that in specific embodiments of this application, an example in which a lithium-ion battery is used as an electrochemical apparatus is used to illustrate this application. However, the electrochemical apparatus of this application is not limited to the lithium-ion battery.
The following describes some embodiments of this application more specifically by using examples and comparative examples. Various tests and evaluations are performed according to the following methods. In addition, unless otherwise specified, “part” and “%” are based on weight.
Microscopic morphology observation of negative electrode material powder particles: A scanning electron microscope was used for the microscopic morphology observation of negative electrode material powder. The selected test instrument was OXFORD EDS (X-max-20 mm2), with an acceleration voltage of 10 kV. The focus was adjusted, observation magnification was increased from 50K for high magnification observation, and agglomeration of the negative electrode material particles was mainly observed at low magnification of 500 to 2000.
At a constant low temperature, the amounts of gas adsorbed by the surface of a solid under different relative pressures were determined, and then an adsorption amount of a monomolecular layer of the sample was found based on the Brunauer-Emmett-Teller adsorption theory and its equation (BET equation), to calculate a specific surface area of the negative electrode material.
The BET equation is:
W indicates the mass of gas adsorbed by the solid sample at a relative pressure; Wm indicates the amount of gas adsorbed for full monomolecular layer coverage; (c – 1) /(WmC) indicates the slope; and 1/WmC indicates the intercept. Total specific surface area St is: St = (Wm*N*Acs/M), and specific surface area S is: S = St/m, where m indicates the sample mass, and Acs indicates that the average area occupied by each N2 molecule is 16.2 A2.
During testing, 1.5 g to 3.5 g of the negative electrode material powder sample was weighed and put into a test sample tube of a specific surface area and porosity analyzer (model TriStar II 3020), and was degassed at 200° C. for 120 min before testing.
0.02 g of the negative electrode material powder sample was added into a 50 ml clean beaker, and 20 ml of deionized water was added, with 3 to 5 drops of surfactant with a mass concentration of 1% added to make the powder sample fully dispersed in the water. Then, the sample was subjected to ultrasonic oscillation for 5 minutes in a 120 W ultrasonic cleaning machine, and particle size distribution was tested with a laser particle size analyzer (model MasterSizer 2000).
Refer to the national standard GB/T 5162-2006 Metallic Powders -Determination of Tap Density.
The negative electrode material sample was heated and burned at high temperature in a high-frequency furnace under an oxygen-rich condition to oxidize carbon to carbon dioxide, and the gas was treated, entered a corresponding absorption cell to absorb corresponding infrared radiation, and then was converted into a corresponding signal by a detector. The signal was sampled by using a computer and converted into a value in direct proportional to a concentration of carbon dioxide after linear correction, and then values in an entire analysis procedure were added. After the analysis, a sum was divided by mass and then multiplied by a correction coefficient in the computer; and a blank was deducted to obtain the percentage of carbon in the sample. A high-frequency infrared carbon and sulfur analyzer (model Shanghai Dekai HCS-140) was used for sample testing.
On copper foil containing the negative electrode material sprinkled on a conductive adhesive, the cut section was polished using a plasma polisher (Leica EM TIC 3X-Ion Beam Slope Cutter) and then placed into a scanning electron microscope (SEM) to find the cut silicon monoxide particle. A focused ion beam (FIB) was used to cut the foregoing silicon monoxide particle along a direction perpendicular to the section to obtain a slice (about 50 nm) containing the section of the silicon monoxide particle, then a transmission electron microscopy (TEM) was used for measurement, and a random point A′ at a distance of 1 nm to 2 nm from the outer surface was taken for an EDS analysis. To be specific, the Si:O atomic ratio on the outer surface of the silicon monoxide particle was A, and extending from the point A′ into the silicon monoxide particle along a direction perpendicular to the outer surface, the Si:O atomic ratio at B′ at a distance of greater than 25 nm from the outer surface of the point A′ was B.
The negative electrode material prepared in each example and comparative example was mixed with conductive carbon black and polymer at a ratio of 80:10:10, deionized water was added, and then the mixture was stirred to form a slurry. A 100 µm thick coating was applied on the surface of the current collector using a scraper, dried in a vacuum drying oven at 85° C. for 12 hours, and then cut into wafers with a diameter of 1 cm in a dry environment using a punching machine. In a glove box, a button cell was assembled with a lithium metal plate as a counter electrode, a Ceglard composite membrane as a separator, and electrolyte added. A LAND (LAND) series battery tester was used to conduct a charge and discharge test on the button cell. The first-cycle efficiency was calculated as follows: capacity at discharge cut-off voltage of 2.0 V/capacity at charge cut-off voltage of 0.005 V.
Gram capacity of button cell at discharge cut-off voltage of 2.0 V.
At a test temperature of 25° C. or 45° C., the battery was charged to 4.4 V at a constant current of 0.7 C, charged to 0.025 C at a constant voltage, left standing for 5 minutes, and then discharged to 3.0 V at 0.5 C. A capacity obtained in this step was the initial capacity. Then, a 0.7 C charge and 0.5 C discharge cycling test was performed. A ratio of the capacity of each step to the initial capacity was calculated to obtain a capacity degradation curve. The number of cycles to a capacity retention rate of 90% at 25° C. was recorded as cycling performance of a battery under room temperature; and the number of cycles to a capacity retention rate of 80% at 45° C. was recorded as cycling performance of the battery under high temperature. The numbers of cycles in the above two cases were compared to compare cycling performance of the material.
Thickness of the lithium-ion battery at half charge, that is, in 50% state of charge (SOC), was measured by a spiral micrometer. After 400 cycles, the lithium-ion battery was at full charge, that is, in 100% SOC state, and then thickness of the lithium-ion battery at that time was measured again by the spiral micrometer, and compared with the initial thicknesses of the lithium-ion battery at half charge to obtain a swelling rate of the lithium-ion battery at full charge at that time.
Silicon dioxide and metal silicon powder were mixed at a molar ratio of 1:1 to obtain a mixed material. The mixed material was heated at 1400° C. for 10 h at 10-4 kPa to obtain gas. The obtained gas was condensed to obtain a solid, and then the obtained solid was crushed and sieved to obtain silicon monoxide (SiO) particles with Dv50 of 5.2 µm.
The silicon monoxide particles were placed in argon with an oxygen content of less than 5% by volume fraction, and subjected to heat treatment at 400° C. for 10 h to obtain a negative electrode material with a 22 nm thick oxide layer.
The prepared negative electrode material was mixed with conductive carbon black and a binder polyallyl alcohol (PAA) at a ratio of 80:10:10, deionized water was added, and then the mixture was stirred to form a slurry with a solid content of 40%. A 100 µm thick coating was applied on the surface of the current collector using a scraper, dried in a vacuum drying oven at 85° C. for 12 hours, and then cut into wafers with a diameter of 1 cm in a dry environment using a punching machine. In a glove box, a button cell was assembled with a lithium metal plate as a counter electrode, a Ceglard composite membrane as a separator, and electrolyte added.
Graphite, the prepared negative electrode material, a conductive agent (conductive carbon black), and a binder (PAA) were mixed at a mass ratio of 70:15:5:10, and then deionized water was added as a solvent to obtain a slurry with a solid content of 60%. Then, an appropriate amount of deionized water was added to adjust viscosity of the slurry to 5000 Pa·s to obtain a negative electrode slurry. The prepared negative electrode slurry was applied on one surface of an 8 µm thick copper foil, dried at 110° C., and cold pressed, to obtain a negative electrode plate with a 100 µm thick coating. Then, the foregoing coating step was repeated on the other surface of the negative electrode plate to obtain the negative electrode plate coated with a negative electrode active substance layer on both surfaces. The negative electrode plate was cut into a size of 74 mm × 867 mm and then welded with tabs for use.
A positive electrode active substance lithium cobalt oxide, conductive carbon black, and polyvinylidene fluoride (PVDF) were mixed at a mass ratio of 95:2.5:2.5, then N-methylpyrrolidone (NMP) was added as a solvent to obtain a slurry with a solid content of 75%, and the slurry was stirred to uniformity. The slurry was uniformly applied on one surface of a 12 µm thick aluminum foil, dried at 90° C., and cold pressed, to obtain a positive electrode plate with a 110 µm thick positive electrode active substance layer. Then, the foregoing step was repeated on the other surface of the positive electrode plate to obtain the positive electrode plate coated with a positive electrode active substance layer on both surfaces. The positive electrode plate was cut into a size of 76 mm × 851 mm and then welded with tabs for use.
A 15 µm thick polyethylene (PE) porous polymer film was used as a separator.
In an environment with a water content less than 10 ppm, a non-aqueous organic solvent propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed at a mass ratio of 1:1:1, lithium hexafluorophosphate (LiPF6) was added into the non-aqueous organic solvent for dissolving and mixing to uniformity, and then fluoroethylene carbonate (FEC) was added, to obtain an electrolyte. A molar concentration of LiPF6 in the electrolyte was 1.15 mol/L, and a mass concentration of FEC in the electrolyte was 12.5%.
The prepared positive electrode plate, separator, and negative electrode plate were stacked in sequence, so that the separator was sandwiched between the positive electrode plate and the negative electrode plate for separation. Then the resulting stack was wound to obtain an electrode assembly. The electrode assembly was placed into an aluminum-plastic packaging bag and dehydrated at 80° C., and the prepared electrolyte was injected, followed by processes such as vacuum sealing, standing, formation, and shaping, to obtain a lithium-ion battery.
Example 2 was the same as Example 1 except that in <Preparation of negative electrode material>, the heat treatment time was adjusted to 5 h.
Example 3 was the same as Example 1 except that in <Preparation of negative electrode material>, the heat treatment time was adjusted to 0.5 h.
Example 4 was the same as Example 2 except that in <Preparation of negative electrode material>, Dv50 of silicon monoxide was 1.3 µm.
Example 5 was the same as Example 2 except that in <Preparation of negative electrode material>, Dv50 of silicon monoxide was 14.6 µm.
Example 6 was the same as Example 1 except <Preparation of negative electrode material>.
The silicon monoxide particles obtained in Example 1 were placed in a sand mill containing absolute ethanol and a dispersant asphalt for ball milling for 24 h. Dv50 of the silicon monoxide particles was 110 nm, and the surface of the silicon monoxide particles was oxidized in the solution to form a 23 nm thick oxide layer. The obtained mixture was dried to obtain a negative electrode material. A mass ratio of asphalt to the silicon monoxide particles was 1:99, and a mass ratio of absolute ethanol to the silicon monoxide particles was 1:5.
Example 7 was the same as Example 6 except that in <Preparation of negative electrode material>, Dv50 of the silicon monoxide particles was adjusted to 190 nm and the ball milling time was adjusted to 12 h.
Example 8 was the same as Example 6 except that in <Preparation of negative electrode material>, Dv50 of the silicon monoxide particles was adjusted to 520 nm and the ball milling time was adjusted to 8 h.
Example 9 was the same as Example 6 except that in <Preparation of negative electrode material>, Dv50 of the silicon monoxide particles was adjusted to 80 nm and the ball milling time was adjusted to 48 h.
Example 10 was the same as Example 2 except <Preparation of negative electrode material>.
The negative electrode material obtained in Example 2 was used as a matrix material, and the matrix material, a conductive material amorphous carbon, and a dispersant carboxymethyl cellulose were dispersed in absolute ethanol at a mass ratio of 96:3.2:0.8. The mixture was stirred to uniformity at room temperature, and then absolute ethanol was removed to obtain a solid. The obtained solid was crushed and sieved to obtain a negative electrode material.
Example 11 was the same as Example 10 except that in <Preparation of negative electrode material>, the conductive material was carbon nanotubes and the mass ratio of the matrix material, the conductive material, and the dispersant was 96.1:3.1:0.8. A length-diameter ratio of the carbon nanotubes was 3000.
Example 12 was the same as Example 10 except that in <Preparation of negative electrode material>, the conductive material was graphene and the mass ratio of the matrix material, the conductive material, and the dispersant was 95.2:4.0:0.8.
Example 13 was the same as Example 10 except that in <Preparation of negative electrode material>, the conductive material was vapor-deposited carbon fibers and the mass ratio of the matrix material, the conductive material, and the dispersant was 91.2:8.0:0.8.
Example 14 was the same as Example 10 except that in <Preparation of negative electrode material>, the mass ratio of the matrix material, the conductive material, and the dispersant was 98.7:0.5:0.8.
Example 15 was the same as Example 6 except <Preparation of negative electrode material>.
The negative electrode material obtained in Example 6 was used as a matrix material, and the matrix material and amorphous carbon were dispersed in absolute ethanol at a mass ratio of 88:12. The mixture was stirred to uniformity at room temperature, and then absolute ethanol was removed to obtain a solid. The obtained solid was crushed and sieved to obtain a negative electrode material.
Example 16 was the same as Example 15 except that in <Preparation of negative electrode material>, the mass ratio of the matrix material and amorphous carbon was 82:18.
Example 17 was the same as Example 15 except that in <Preparation of negative electrode material>, the mass ratio of the matrix material and amorphous carbon was 70:30.
Example 18 was the same as Example 15 except that in <Preparation of negative electrode material>, the mass ratio of the matrix material and amorphous carbon was 55:45.
Example 19 was the same as Example 1 except <Preparation of negative electrode material>.
The negative electrode material obtained in Example 1 was used as a matrix material, and the matrix material and a polymer carboxymethyl cellulose were dispersed in absolute ethanol at a mass ratio of 99:1. The mixture was stirred to uniformity at room temperature, and then absolute ethanol was removed to obtain a solid. The obtained solid was crushed and sieved to obtain a negative electrode material.
Example 20 was the same as Example 19 except that in <Preparation of negative electrode material>, the polymer was polyacrylic acid and the mass ratio of the matrix material and the polymer was 95:5.
Example 21 was the same as Example 19 except that in <Preparation of negative electrode material>, the polymer was polyamide and the mass ratio of the matrix material and the polymer was 90:10.
Comparative Example 1 was the same as Example 1 except that in <Preparation of negative electrode material>, SiO was not placed in argon with an oxygen content of less than 5% by volume fraction for heat treatment.
Comparative Example 2 was the same as Example 1 except that in <Preparation of negative electrode material>, the treatment temperature and the treatment time were adjusted so that A/B was 1.33.
Comparative Example 3 was the same as Example 6 except that in <Preparation of negative electrode material>, SiO was not placed in argon with an oxygen content of less than 5% by volume fraction for heat treatment.
Comparative Example 4 was the same as Comparative Example 1 except <Preparation of negative electrode material>.
The negative electrode material obtained in Comparative Example 1 was used as a matrix material, and the matrix material, amorphous carbon, and a dispersant carboxymethyl cellulose were dispersed in absolute ethanol at a mass ratio of 96:3.2:0.8. The mixture was stirred to uniformity at room temperature, and then absolute ethanol was removed to obtain a solid. The obtained solid was crushed and sieved to obtain a negative electrode material.
For the preparation parameters and test data of the examples and comparative examples, refer to 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 all the silicon monoxide particles are micronscale, as the oxygen content on the surface of the negative electrode material increases, the cycling performance of the lithium-ion battery gradually becomes better and the swelling of the lithium-ion battery gradually decreases. This indicates that the cycling performance and anti-swelling performance of the lithium-ion battery with the negative electrode material of this application are improved.
It can be seen from Examples 4 and 5 that Dv50 of silicon monoxide affects the cycling performance and swelling rate of the lithium-ion battery. Provided that Dv50 of silicon monoxide is within the range of this application, the cycling performance and anti-swelling performance of the lithium-ion battery can be improved.
It can be seen from Examples 6, 7, 8, and 9 and Comparative Example 3 that when all the silicon monoxide particles are nanoscale, the lithium-ion battery with the negative electrode material of this application has improved cycling performance and anti-swelling performance at 25° C. and improved anti-swelling performance at 45° C. It can be seen from Examples 6 and 9 and Comparative Example 3 that the lithium-ion battery with the negative electrode material of this application has improved cycling performance at 45° C.
It can be seen from Examples 10, 11, 12, 13, and 14 and Comparative Example 4 that when the negative electrode materials all contain the conductive material, the lithium-ion battery with the negative electrode material of this application has further improved cycling performance and anti-swelling performance.
It can be seen from Examples 15, 16, 17, and 18 and Comparative Examples 1 and 2 that when the negative electrode material is a silicon monoxide-amorphous carbon composite material, the lithium-ion battery of this application has further improved cycling performance and anti-swelling performance at 25° C. and improved cycling performance at 45° C. In addition, as the carbon content increases, the cycling performance and anti-swelling performance of the lithium-ion battery tend to increase.
It can be seen from Examples 19, 20, and 21 and Comparative Examples 1 and 2 that when the negative electrode materials all contain the polymer, the lithium-ion battery with the negative electrode material of this application has further improved cycling performance and anti-swelling performance at 25° C. and improved cycling performance at 45° C.
In conclusion, the lithium-ion battery with the negative electrode material of this application has improved cycling performance and anti-swelling performance.
The foregoing descriptions are merely preferable embodiments of this application, but are not intended to limit this application. Any modification, equivalent replacement, or improvement made without departing from the spirit and principle of this application shall fall within the protection scope of this application.
This application is a continuation application of PCT/CN2020/140342, filed on December 28th, 2020, the disclosure of which is hereby incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CN2020/140342 | Dec 2020 | WO |
| Child | 18342044 | US |
