WO2022266798A1

WO2022266798A1 - Negative electrode material, electrochemical apparatus, and electronic apparatus

Info

Publication number: WO2022266798A1
Application number: PCT/CN2021/101235
Authority: WO
Inventors: 刘茜; 郑席; 杜鹏; 谢远森
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-06-21
Filing date: 2021-06-21
Publication date: 2022-12-29
Also published as: CN114556629A

Abstract

The present application provides a negative electrode material, an electrochemical apparatus, and an electronic apparatus. Particles of the negative electrode material comprise a core and a shell layer; the number of pores with a pore size in the range of 0.4 nm to 5 nm in a 20 nm × 20 nm range of a cross section of the core is 5 to 100, thereby ensuring dynamic performance while ensuring that the negative electrode material has a relatively high capacity.

Description

Anode materials, electrochemical devices and electronic devices

technical field

The present application relates to the field of electrochemical energy storage, in particular to a negative electrode material, an electrochemical device and an electronic device.

Background technique

With the development and progress of electrochemical devices (eg, lithium-ion batteries), higher and higher requirements are placed on their capacity and kinetic performance of electrochemical devices. At present, in order to improve the capacity and kinetic performance of electrochemical devices, although some measures have been taken to obtain some improvements, they are still not satisfactory, and further improvements are expected.

Contents of the invention

In the embodiments of the present application, a negative electrode material is proposed, the particles of the negative electrode material include a core body and a shell layer; within the range of 20nm×20nm of the cross section of the core body, the number of holes with a pore diameter in the range of 0.4nm to 5nm is 5 to 100 . The core-shell structure is conducive to improving the stability of the negative electrode material, and reducing the contact between the internal pores of the core body and the electrolyte, reducing the consumption of the electrolyte.

In some embodiments, within the range of 20 nm×20 nm of the cross-section of the core body, the number of pores with a diameter in the range of 2 nm to 5 nm is 5 to 50. In some embodiments, within the range of 20nm×20nm of the cross-section of the core body, the number of pores with a diameter in the range of 2nm to 5nm is 12 to 50. The kinetic performance is ensured while the negative electrode material has a high capacity.

In some embodiments, the negative electrode material includes carbon material. In some embodiments, the shell is located on the surface of the core. In some embodiments, the shell layer is analyzed by a transmission electron microscope, and the number of pores with a diameter in the range of 2 nm to 5 nm is less than or equal to 5 within any range of 400 nm ² in the shell layer. It can not only improve the conduction of ions, but also take into account the gram capacity.

In some embodiments, the negative electrode material satisfies at least one of the following (a) to (c): (a) the thickness of the shell layer is 10nm to 200nm; (b) the interplanar spacing of the microchip layer of the shell layer is 0.36 nm to 0.4 nm; (c) the shell layer includes amorphous carbon. Guaranteed ion transmission and improved kinetic performance.

In some embodiments, the anode material satisfies at least one of (d) to (h) as shown below: (d) in the photoelectron spectrum of the anode material, at 285.4±0.3eV, 287.8±0.3eV and 288.9±0.3eV There is at least one peak at the position; (e) the specific surface area of the negative electrode material is 2m ² /g to 10m ² /g; (f) the powder conductivity of the negative electrode material is 1×10 ^-06 μS/cm to 9×10 ^{- 08} μS/cm; (g) in the X-ray diffraction pattern of the negative electrode material, there is a diffraction peak between 18° and 30°, and the half-maximum width of the diffraction peak is 4° to 10°; (h) the negative electrode material The peak intensity ratio I _G /ID of the G peak and the _D peak in the Raman spectrum is 0.6 to 1.

In some embodiments, the negative electrode material satisfies at least one of the following (i) to (k): (i) the Dv10 of the negative electrode material is 1 μm to 5 μm; (g) the Dv50 of the negative electrode material is 4 μm to 15 μm; (k) The Dv90 of the negative electrode material is 13 μm to 30 μm. In some embodiments, the Dv50 of the negative electrode material is 5 μm to 10 μm. Dv10, Dv50 and Dv90 are in a suitable range, effectively improving the diffusion of ions in the negative electrode active material layer, improving the rate performance of the negative electrode material and the ability to quickly deintercalate lithium.

In some embodiments, the negative electrode material includes carbon material. The carbon material can reduce the contact between the internal pores of the nucleus and the electrolyte, and reduce the consumption of the electrolyte.

An electrochemical device is also proposed in the embodiment of the present application, including: a positive electrode, a negative electrode, an electrolyte and a separator; the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, and the negative electrode active material layer includes any of the above negative electrode material.

In some embodiments, the electrochemical device satisfies at least one of the following (l) to (n): (l) the resistance of the negative electrode is 10mΩ to 60mΩ, and optionally, the resistance of the negative electrode is 20mΩ to 40mΩ. (m) The electrochemical device includes an electrolytic solution including at least one of fluoroether, fluoroethylene carbonate or ether nitrile. (n) The electrochemical device includes an electrolyte, the electrolyte includes a lithium salt, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, the concentration of the lithium salt is 1 mol/L to 2 mol/L, and the bis(fluorosulfonyl) ) The mass ratio of lithium imide and lithium hexafluorophosphate is 0.06 to 5. In some embodiments, the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.062 to 4.105. Lithium bis(fluorosulfonyl)imide can interact with porous negative electrode materials, and can effectively improve the cycle and expansion performance of lithium-ion batteries.

The present application also proposes an electronic device, including any one of the above electrochemical devices.

In the embodiments of the present application, a negative electrode material is proposed, the particles of the negative electrode material include a core body and a shell layer; the number of holes with a diameter in the range of 0.4 nm to 5 nm in the cross section of the core body is 5 to 100, Thus, the kinetic performance is guaranteed while the negative electrode material has a high capacity.

Description of drawings

FIG. 1 is a cross-sectional view of an anode material of the present disclosure.

detailed description

The following examples can enable those skilled in the art to understand the present application more comprehensively, but do not limit the present application in any way.

Electrochemical devices, such as lithium-ion batteries, are widely used in various fields, and users' requirements for electrochemical devices are also increasing. For the anode materials of electrochemical devices, the ion storage capacity, that is, capacity and kinetics, is currently the main direction of performance improvement. The currently used negative electrode materials are mainly graphite and silicon materials. The theoretical gram capacity of graphite is 372mAh/g, and the capacity of graphite currently used is close to the limit level. Graphite materials mainly increase the capacity by changing the precursor, granulation, sintering process and other methods, but the bottleneck of capacity improvement is very large, and the room for improvement is small. Graphite materials can also be coated with materials with high kinetics on the surface of graphite to improve the fast charging and fast discharging ability, but this method often leads to the loss of first effect and capacity, and the performance cannot be fully achieved. Effect. The theoretical gram capacity of silicon is 3400mAh/g, which is a high gram capacity material, which can significantly increase the energy density. However, the silicon material expands greatly during the charge and discharge process, and the particles are broken. It is still difficult to find a very effective method for This problem cannot be solved and the requirements for fast charging and fast discharging cannot be met, and these factors limit the application of silicon materials.

In the embodiments of the present application, a negative electrode material is proposed, the particles of the negative electrode material include a core body and a shell layer; within the range of 20nm×20nm of the cross section of the core body, the number of holes with a pore diameter in the range of 0.4nm to 5nm is 5 to 100 . In some embodiments of the present application, a transmission electron microscope (Transmission Electron Microscope, TEM) can be used to take pictures of the negative electrode material, select a 20nm × 20nm area on the taken microscopic picture and count the number and aperture of the holes, and count the holes The largest diameter of the hole is selected as the aperture. For the negative electrode material, when it has a pore structure with a pore size of not less than 0.4nm, it can have the ability to store ions (ions such as lithium ions), thereby increasing the capacity. The energy density decreases, so in some embodiments of the present application, the pore size is not greater than 5 nm, so as to ensure the volume energy density of the negative electrode material. In addition, when the number of pores is less than 5, it may not be possible to significantly increase the ion storage capacity of the negative electrode material. When the number of pores is greater than 100, on the one hand, the volumetric energy density is reduced, and on the other hand, too many pores lead to a lack of ions. diffusion channel. Therefore, for the particles of the negative electrode material in some embodiments of the present application, the number of holes with an aperture in the range of 0.4 nm to 5 nm in the range of 20 nm × 20 nm in the cross section of the core body is 5 to 100, thereby ensuring that the negative electrode material has a higher capacity. At the same time, the dynamic performance is guaranteed.

In some embodiments of the present application, within the range of 20 nm×20 nm of the cross-section of the core body, the number of pores with a pore diameter in the range of 2 nm to 5 nm is 5 to 50. In some embodiments, the pore diameter ranging from 2 nm to 5 nm can not only have better ion storage capacity, but also better ensure ion transmission. In some embodiments, the negative electrode material includes microcrystalline graphite, and the pores are composed of microcrystalline graphite. Within the range of 20nm×20nm of the cross section of the core body, the number of pores with a diameter in the range of 2nm to 5nm cannot be too low to ensure The capacity of the negative electrode material, the ratio of the graphite crystallite area to the pore area is expected to be a minimum of 4:1, and the maximum number of pores is 100, but too large a number of pores will result in a lack of ion diffusion channels, so within the range of 20nm×20nm of the cross section of the core body , the upper limit of the number of pores in the range of 2nm to 5nm is 50.

In some embodiments, the negative electrode material includes carbon material. In some embodiments, the carbon material may be hard carbon, and the negative electrode material may consist of hard carbon. In some embodiments of the present disclosure, the shell is located on the surface of the core. In some embodiments, the particles of the negative electrode material proposed in the present disclosure have a core-shell structure, and the core-shell structure is beneficial to improve the stability of the negative electrode material, reduce the contact between the internal pores of the core body and the electrolyte, and reduce the consumption of the electrolyte. In some embodiments of the present application, the shell layer is analyzed by a transmission electron microscope, and the number of pores with a diameter in the range of 2 nm to 5 nm is less than 5 within any range of 400 nm ² in the shell layer. In some embodiments, the material of the housing is a relatively dense material, which can better protect the core, reduce the penetration of the electrolyte into the core, and reduce the consumption of the electrolyte. In some embodiments, the core and shell may be hard carbon.

In some embodiments of the present application, the thickness of the shell layer of the negative electrode material is 10 nm to 200 nm. In some embodiments, if the thickness of the shell layer is too small, the protection effect on the core body may be reduced; if the thickness of the shell layer is too large, it may affect the conduction of ions and may result in a loss of gram capacity.

In some embodiments of the present application, the interplanar spacing of the microchip layer of the shell layer of the negative electrode material is 0.36 nm to 0.4 nm. In some embodiments, if the interplanar spacing of the microchip layer of the shell layer of the negative electrode material is too small, it may hinder ion transmission, affect kinetic performance, and be unfavorable for rate performance. When the interplanar spacing of the microchip layer is too large, it may It will affect the volumetric energy density. Optionally, the interplanar spacing of the microchip layer is 0.36nm to 0.39nm. In some embodiments, a transmission electron microscope can be used to take pictures of the negative electrode material, and the taken pictures can be analyzed to determine the interplanar spacing of the microchip layer.

In some embodiments of the present application, the shell layer includes amorphous carbon. In some embodiments, the shell may include carbon material. The amorphous carbon structure of the shell is beneficial to improve ion transport, thereby enhancing the kinetic performance of the anode material.

In some embodiments of the present disclosure, in the photoelectron spectrum of the negative electrode material, there is at least one peak at positions of 285.4±0.3eV, 287.8±0.3eV and 288.9±0.3eV. In some embodiments, the peak at 285.4±0.3eV is the C-O peak, the peak at 287.8±0.3eV is the C=O peak, and the peak at 288.9±0.3eV is the COO peak. In some embodiments, the negative electrode material is prepared by sintering. In order to ensure the dynamic performance of the shell layer, the sintering temperature should not be too high. Due to the influence of the coating source functional group, the negative electrode material after sintering has oxygen-containing functional groups on the surface, which can be produced by optoelectronics. Energy spectrum test obtained.

In some embodiments of the present disclosure, the specific surface area of the negative electrode material is 2m ² /g to 10m ² /g. In some embodiments, due to the influence of the negative electrode material itself, the specific surface area is not less than 2m ² /g, and when the specific surface area is too large, there are more sites on the surface of the negative electrode material in contact with the electrolyte, and the side reactions between the negative electrode material and the electrolyte increase, may lead to a decrease in the first effect of the material. In some embodiments, when the specific surface area of the negative electrode material is not less than 2m ² /g and not greater than 7m ² /g, the first efficiency of the negative electrode material is maintained at a level above 70%. When the negative electrode material When the specific surface area continues to increase, it will cause the first effect to continue to decrease, and it is difficult to meet the application requirements. In some embodiments, the specific surface area of the negative electrode material is tested in the following way: Weigh 1.5g to 3.5g of negative electrode material sample into the test sample tube of TriStar II 3020, and perform the test after degassing at 200°C for 120 minutes. At constant temperature and low temperature, after measuring the adsorption amount of gas on the surface of the negative electrode material at different relative pressures, the adsorption amount of the monomolecular layer of the sample is obtained based on the Brownauer-Etter-Taylor adsorption theory and its formula, so as to calculate the negative electrode material. specific surface area.

In some embodiments of the present disclosure, the powder conductivity of the negative electrode material is 1×10 ⁻⁰⁶ μS/cm to 9×10 ⁻⁰⁸ μS/cm. In some embodiments, due to the influence of the properties of the negative electrode material itself, the powder conductivity of the negative electrode material is not higher than 9×10 ^-08 μS/cm. On the other hand, in order to ensure the dynamic performance of the negative electrode material, the powder conductivity of the negative electrode material must be Not less than 1×10 ^-06 μS/cm. In some embodiments, the powder conductivity of the negative electrode material is tested in the following manner: put the powder of the negative electrode material into a tableting mold, lead wires from both sides of the mold, and pressurize while measuring the resistance value until the resistance remains constant. Then take out the pressed sheet, and use the four-probe method or AC impedance to test the conductivity of the pressed sheet.

In some embodiments of the present application, in the X-ray diffraction pattern of the negative electrode material, there is a diffraction peak between 18° and 30°, and the half-maximum width of the diffraction peak is 4° to 10°. In some embodiments, a diffraction peak with a half peak width of 4° to 10° between 18° and 30° indicates that the negative electrode material is not a graphite material, and the negative electrode material may include a hard carbon material. In some embodiments, the peak intensity ratio I _G /ID of the G peak and the _D peak in the Raman spectrum of the negative electrode material is 0.6 to 1. In some embodiments, the peak intensity ratio IG/ID of the _G peak and the _D peak shows the proportion of defects inside the negative electrode material _. The larger the ratio of _IG /ID, the less the proportion of defects inside the negative electrode material. The higher the crystallinity, the negative electrode material in some embodiments of the present application contains a certain number of pores, so I _G / _ID should be 0.6 to 1.

In some embodiments of the present application, the Dv10 of the negative electrode material is 1 μm to 5 μm. In some embodiments, the Dv50 of the negative electrode material is 4 μm to 15 μm. In some embodiments, the Dv90 of the negative electrode material is 13 μm to 30 μm. In some embodiments, if the particle size of the negative electrode material is too small, it may lead to increased electrolyte consumption, which is not conducive to cycle performance. If the particle size of the negative electrode material is too large, it may lead to poor kinetic performance and affect the rate performance. By limiting the particle size of the negative electrode material, the rapid conduction of electrons in the negative electrode material can be ensured. In some embodiments, Dv10, Dv50 and Dv99 are obtained by analyzing the particle size of the sample using a Mastersizer3000 laser particle size distribution tester. Dv10, Dv50, and Dv90 represent the particle diameters that reach 10%, 50%, and 90% of volume accumulation from the small particle diameter side in the volume-based particle size distribution, respectively. During the test, the sampling system is Hydro2000SM wet dispersion, the measuring range is 0.01 μm to 3500 μm, the light source is Red light: Helium neon laser/blue light: Solid state light source, and the detection angle is 0° to 144°. The sample test time is 6s, the background test time is 6s, the number of sample test snaps is 6000 times, the average value is taken for 3 test cycles, the stirring pump speed is 3000rpm, and the analysis mode is set to General purpose.

In some embodiments of the present application, the negative electrode material includes carbon material. In some embodiments, the negative electrode material can be synthesized as follows: sodium carbonate and phenolic materials are mixed in the first solvent to obtain the first mixed material, wherein the phenolic materials can be phenol, resorcinol, hydroquinone Diphenol, catechol, etc., the first solvent is formaldehyde, acetal, furfural, etc.; the copolymer material is dissolved in the mixed solution of ethanol and water to obtain the second compound, wherein the copolymer material can be F127 ( Poloxamer, polyoxyethylene polyoxypropylene ether block copolymer), P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer), SBS (styrene-butanediene ene-styrene block copolymer), etc.; the first mixture is mixed with the second mixture and hydrochloric acid is added to obtain a third mixture. The third mixture is solidified and crushed, and the fourth mixture is added, solidified and sintered and crushed to obtain the above-mentioned negative electrode material, wherein the fourth mixture can be a solution containing phenolic resin, a solution containing epoxy resin, a solution containing sucrose, or a solution containing Glucose solution, etc.

The negative electrode material proposed in some embodiments of the present disclosure is a carbon material with a core-shell structure, as shown in Figure 1, the core body has a porous structure, and the shell layer is a relatively dense amorphous carbon structure, which has a higher capacity , faster ion transport capacity and relatively small specific surface area, with high capacity and high kinetic performance.

An electrochemical device is also proposed in the embodiment of the present application, including: a positive electrode, a negative electrode, an electrolyte and a separator; the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, and the negative electrode active material layer includes any of the above negative electrode material. In some embodiments of the present application, the resistance of the negative electrode is 10mΩ to 60mΩ. In some embodiments, the resistance of the negative electrode is affected by the properties of the material itself, and is not less than 10mΩ. Meanwhile, in order to ensure the dynamic performance of the negative electrode, optionally, the resistance of the negative electrode is 20mΩ to 40mΩ.

In some embodiments of the present application, the electrochemical device includes an electrolyte, and the electrolyte includes at least one of fluoroether, fluoroethylene carbonate, or ether nitrile. In some embodiments, the electrolyte solution includes a lithium salt, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, the concentration of the lithium salt is 1mol/L to 2mol/L, and the bis(fluorosulfonyl) The mass ratio of lithium imide and lithium hexafluorophosphate is 0.06 to 5.

In some embodiments, a conductive agent and a binder may also be included in the negative electrode active material layer. In some embodiments, the conductive agent in the negative electrode active material layer may include at least one of conductive carbon black, Ketjen black, flake graphite, graphene, carbon nanotubes or carbon fibers. In some embodiments, the binder in the negative electrode active material layer may include carboxymethylcellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysilicon At least one of oxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin or polyfluorene. In some embodiments, the mass ratio of the negative electrode material, the conductive agent and the binder in the negative electrode active material layer may be (78 to 98.5):(0.1 to 10):(0.1 to 10). The negative electrode material can be a mixture of silicon-based materials and other materials. It should be understood that the above description is only an example, and any other suitable materials and mass ratios may be used. In some embodiments, the negative electrode current collector may use at least one of copper foil, nickel foil, or carbon-based current collector.

In some embodiments, the electrochemical device includes a separator disposed between the positive electrode and the negative electrode. The isolation film includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Especially polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through the shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 5 μm to 50 μm.

In some embodiments, the surface of the isolation membrane may also include a porous layer, the porous layer is arranged on at least one surface of the isolation membrane, the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from alumina (Al 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), oxide Zinc (ZnO), calcium oxide (CaO), zirconia (ZrO ₂ ), yttrium oxide (Y ₂ O ₃ ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or sulfuric acid at least one of barium. In some embodiments, the pores of the isolation membrane have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is selected from polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, poly At least one of vinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The porous layer on the surface of the separator can improve the heat resistance, oxidation resistance and electrolyte wettability of the separator, and enhance the adhesion between the separator and the pole piece.

In some embodiments of the present application, the electrochemical device is wound, stacked or folded. In some embodiments, the positive electrode and/or negative electrode of the electrochemical device may be a wound or stacked multi-layer structure, or a single-layer structure in which a single-layer positive electrode, a separator, and a single-layer negative electrode are stacked.

In some embodiments, the electrochemical device includes a lithium-ion battery, although the present application is not limited thereto. In some embodiments, the electrochemical device may also include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte and an electrolytic solution, and the electrolytic solution includes a lithium salt and a non-aqueous solvent. 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 , LiBOB or one or more of lithium difluoroborate. For example, LiPF ₆ is selected as the lithium salt. The non-aqueous solvent may be a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof. The carbonate compound can be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound or a combination thereof.

Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl carbonate Ethyl Ester (MEC) and combinations thereof. Examples of the cyclic carbonate compound are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), or combinations thereof. Examples of the fluorocarbonate compound are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, Fluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-carbonic acid - Difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.

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

Examples of ether compounds are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxy ethyl ethane, 2-methyltetrahydrofuran, tetrahydrofuran or a combination thereof.

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

In some embodiments of the present application, taking a lithium-ion battery as an example, the positive electrode, separator, and negative electrode are sequentially wound or stacked into an electrode part, and then packed into an aluminum-plastic film for packaging, injected with an electrolyte, formed, Encapsulation, that is, made of lithium-ion batteries. Then, performance tests were performed on the prepared lithium-ion batteries.

It will be appreciated by those skilled in the art that the above-described fabrication methods of electrochemical devices (eg, lithium-ion batteries) are examples only. Other methods commonly used in the art can be adopted without departing from the content disclosed in the present application.

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

Some specific embodiments and comparative examples are enumerated below to better illustrate the present application, wherein a button battery and a lithium ion battery are used as examples.

Assembly of button cells (as shown in Table 1 to Table 3):

Prepare negative electrode material, conductive agent carbon black (Super P), and sodium carboxymethylcellulose (CMC) in a certain ratio of 96:0.5:3.5 to make a slurry with a certain solid content (50%), and use a scraper to evenly mix the slurry Coating on the surface of copper foil, drying the pole piece (85°C, 4h), punching the dried pole piece into a small disc with a diameter of 14mm. The obtained small disc, nickel foam, separator (7 μm, PP polypropylene substrate), lithium sheet (0.066 g), steel shell (diameter 24 mm), and electrolyte were added to assemble a button battery.

Preparation of electrolyte: In a dry argon atmosphere glove box, mix ethylene carbonate (EC) and diethyl carbonate (DEC) according to the mass ratio of EC:PC:DEC=3:7, then add 2wt% The fluoroethylene carbonate was dissolved and fully stirred, then lithium salt LiPF ₆ was added, and the electrolyte was obtained after mixing uniformly, wherein the concentration of LiPF ₆ was 1mol/L.

Lithium-ion battery preparation (as shown in Table 4):

Preparation of the positive electrode: mix the positive active material lithium cobaltate, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 97:1.4:1.6, and add N-methylpyrrolidone (NMP) as a solvent , stir well. The slurry (solid content is 72wt%) is uniformly coated on the aluminum foil of the positive electrode current collector with a coating thickness of 80 μm, dried at 85°C, and then cold-pressed, cut into pieces, and slit, and vacuum-coated at 85°C Dry under the same conditions for 4 hours to obtain a positive electrode.

Preparation of the negative electrode: the negative electrode material used in Example 3, the binder styrene-butadiene rubber and sodium carboxymethyl cellulose (CMC) were dissolved in deionized water in a ratio of 97:1.5:1.5 by weight to form the negative electrode slurry ( Solid content is 40wt%). Copper foil with a thickness of 10 μm was used as the negative electrode current collector, and the negative electrode slurry was coated on the negative electrode current collector with a coating thickness of 50 μm, dried at 85 ° C, and then cold-pressed, cut into pieces, and cut at 120 °C under vacuum conditions for 12 hours to obtain a negative electrode.

Preparation of the isolation membrane: the isolation membrane is polyethylene (PE) with a thickness of 7 μm.

Preparation of lithium-ion battery: stack the positive electrode, separator, and negative electrode in order, so that the separator is in the middle of the positive electrode and the negative electrode to play the role of isolation, and wind up to obtain the electrode assembly. The electrode assembly is placed in the outer packaging aluminum-plastic film, after dehydration at 80°C, the above electrolyte is injected and packaged, and the lithium-ion battery is obtained through chemical formation, degassing, trimming and other processes.

Lithium-ion battery cycle performance test:

Take 5 lithium-ion batteries prepared in Examples 20 to 23, and take the average value. Lithium-ion batteries were charged and discharged repeatedly through the following steps, and the discharge capacity retention and thickness expansion of the lithium-ion batteries were calculated.

First, charge and discharge for the first time in an environment of 25°C, carry out constant current charging at a charging current of 0.7C until the upper limit voltage of 4.48V is reached, then switch to constant voltage charging, and then charge at a discharging current of 1.0C Carry out constant current discharge until the final voltage is 3V, record the discharge capacity of the first cycle and the thickness of the fully charged lithium-ion battery; then perform 400 charge and discharge cycles, record the discharge capacity of the 400th cycle and the thickness of the fully charged lithium-ion battery .

Cycle capacity retention = (discharge capacity of the 400th cycle/discharge capacity of the first cycle) × 100%;

Cycle thickness expansion=(thickness of fully charged lithium-ion battery at the 400th cycle/thickness of fully charged lithium-ion battery at the first cycle)×100%.

Test for the number of holes in the material

1) Sample preparation

Method 1: Fully grind the material, use a mortar to grind the sample as much as possible so that the size of the sample is between 50nm and 70nm, then dissolve the powder sample in absolute ethanol, and disperse the sample as much as possible by ultrasonic dispersion , and then use the support net to pick up the sample and prepare the sample.

Method 2: The material is embedded and cured with epoxy resin, and then the material is cut into a size of 50nm to 70nm by using the ultra-thin section method, and the sample is prepared.

2) Test steps

1. Select a micro-area in the image field, the magnification (projector mirror excitation current) should not be too large (about 2000×), and find an area with good light transmission. 2. Adjust the intensity of the converged beam to concentrate the converged electron beam at the center. 3. Press the diffraction button to go to the diffraction field. If the focus is not good at this time, and the electron beams cannot be gathered, adjust the focus button to focus. 4. Adjust the objective lens grating to the 4th gear (from the original neutral gear), that is, just select a spot in the center to let the transmitted beam pass through. 5. Press the diffraction button to switch back to the image field. 6. Find a grain to observe in the image field, the darker the color of the area, the better. 7. Adjust the intensity button of the electron beam to converge the electron beam at the center. 8. Press the diffraction button to return to the diffraction field. 9. In the diffraction field, you can see the Kikuchi belt and the Kikuchi pole, and then adjust the center point to the Kikuchi point. 10. Press diffraction to return to the image field, and press intensity to zoom in. If the sample stage is double-tilted, adjust the alpha and beta values, pay attention to the image, and ensure that the center is still in the grain. 11. Adjust the intensity button of the electron converging beam, converge the electron beam at the center, press the diffraction button, return to the diffraction field, and check whether it is adjusted to the pole of Kikuchi. 12. Repeat 10 to 11 until you reach Kikuchi. 13. Press diffraction to return to the image field, open the selected area grating, the second file, select the area, press diffraction to return to the diffraction field, and you can see the electron diffraction spot pattern.

3) Judgment of holes

In the range of 20×20nm or 400nm ² , the sample is observed, and the hole is judged as: within the limited range of 2nm to 5nm, there is no microchip layer, and the range is blank, surrounded by microchip layers.

Test method for gram capacity of materials

Let the obtained button battery stand for 4 hours and test according to the following procedure to obtain the material capacity: 0.05C discharge to 0V, 50μA discharge to 0V, 20μA discharge to 0V, let stand for 5min, 0.01C charge to 2.5V, charge the gram The capacity is reported as the gram capacity of the material.

First effect: test method for the first effect of materials

After the obtained button battery was left to stand for 4 hours, it was tested according to the following procedures to obtain the material capacity: discharge at 0.05C to 0V, discharge to 0V at 50μA, discharge to 0V at 20μA, let stand for 5min, charge at 0.1C to 2.5V, charge gram The ratio of capacity to discharge gram capacity is the first effect of the material.

Test method for material rate performance

Fast lithium intercalation performance:

After the obtained button battery was left to stand for 4 hours, the fast charging performance of the material was tested according to the following procedure: 0.05C discharge to 0V, then constant voltage discharge to 0.005C, standing for 5min, 0.01C charge to 2.5V, discharge gram The capacity is recorded as D; respectively, 0.01C, 0.02C, 0.05C, 0.1C, 0.2C, 0.5C, 1C discharge to 0V, constant voltage discharge to 0.005C, stand for 5min, 0.01C charge to 2.5V, discharge capacity They are respectively recorded as D1, D2, D3, D4, D5, D6, and D7.

Fast delithiation performance:

After the obtained button battery was left to stand for 4 hours, the fast charging performance of the material was tested according to the following procedure: discharge at 0.05C to 0V, discharge to 0V at 50μA, discharge to 0V at 20μA, stand for 5min, charge at 0.01C to 2.5V, The charging gram capacity is recorded as C, 0.05C discharge to 0V, 50μA discharge to 0V, 20μA discharge to 0V, stand for 5min, and charge to 0.01C, 0.02C, 0.05C, 0.1C, 0.2C, 0.5C, 1C respectively 2.5V, the discharge capacity is recorded as C1, C2, C3, C4, C5, C6, C7 respectively.

The number of nucleosome pores in Table 1 was controlled by adjusting the amount of template F127 (polyoxyethylene polyoxypropylene ether block copolymer) in the experiment, and after a certain adjustment, the effects in Table 1 can be achieved. In order to adjust the number of pores, the ratio of F127:phenols:aldehydes was mainly changed during the synthesis of the core layer material, and the ratio ranged from (0.3 to 0.6):(0.8 to 1.2):(0.8 to 1.2).

Table 1 shows the parameters and evaluation results of the respective negative electrode materials of Examples 1 to 10.

Note: The number of nucleus-holes is the number of pores within the range of 20nm×20nm of the cross-section of the nucleus, and the pore diameter is in the range of 2nm to 5nm. Shell - pore count is the number of pores in the range of ^400nm2 of the shell with a pore diameter in the range of 2nm to 5nm.

Please refer to Table 1, Examples 1 to 6 show the influence of the number of pores of 2nm to 5nm in the cross section of the core body of the negative electrode material in the range of 20nm×20nm on the performance. It can be seen from Table 1 that when the number of nuclei-pores is greater than 100 (comparative example 2), the values of C7/C1 and D7/D1 are small, which indicates that the negative electrode material has fast lithium insertion and fast delithiation performance at this time. Poor, when the nucleosome-hole number is less than 5 (comparative example 1), the gram capacity of negative electrode material is compared with embodiment difference is bigger, although C7/C1 and D7/D1 differ little, comprehensive electrochemical performance is lower, Therefore, when the nucleosome-pore number is 5 to 100, the performance is better.

Since the pores in the core body have the function of storing lithium, the gram capacity of the negative electrode material in the case of a core body-pore number of 5 holes is lower than that in the case of a core body-pore number of 50. It reflects the influence of the number of pores in the negative electrode material nucleus on the gram capacity of the negative electrode material, that is, the more the number of pores, the higher the gram capacity. Examples 5 and 6 show that the number of pores continues to increase, which is beneficial to the capacity.

Comparative example 1 shows the case of less pore structure in the nucleus, and the material capacity is low. Comparative example 2 has too many pores in the nucleus to form a supercapacitor-like negative electrode structure to a certain extent. This structure makes the overall first effect of the material The overall reduction, and the delithiation voltage platform is relatively high, which is not conducive to application. And the multi-hole multiplier performance is reduced.

Table 2 shows the parameters and evaluation results of the respective negative electrode materials of Examples 7 to 10.

As shown in Examples 7 to 10 in table 2, the first effect decreases with the increase of the number of shell-holes, and the increase of the number of shell-holes increases the specific surface area of the shell of the negative electrode material, and the electrolyte easily enters the core. The reaction with the nucleosome in the body increases the side reaction between the negative electrode material and the electrolyte, which affects the first effect and the gram capacity. The control of the number of shells is mainly controlled by controlling the temperature rise program, so as to control the volatilization process of the components in the combustion process of the material, and obtain the number of shell pores of different materials.

In Table 3, the change of the shell layer is obtained by adjusting the concentration of the fourth mixture, the higher the concentration, the thicker the shell layer, and the range of the concentration is controlled at 0.1mol/L to 20mol/L.

Table 3 shows the parameters and evaluation results of the respective negative electrode materials of Examples 11 to 20.

Please refer to Table 3, as shown in Examples 11 to 15, under the condition that the thickness of the shell layer of the negative electrode material is different, the first effect of the negative electrode material is affected. The coating of the layer is difficult to cover uniformly, part of the core layer pore structure is exposed, the specific surface area of the negative electrode material increases, and the first effect of the negative electrode material is low. With the increase of the shell thickness of the negative electrode material, the specific surface area decreases. The first effect of the negative electrode material is improved, but the thickness of the shell layer of the negative electrode material increases, which reduces the lithium storage space of the core layer and has a certain weakening effect on the capacity. Therefore, it is necessary to combine the gram capacity and the first effect, and the thickness of the shell layer needs to be in an appropriate range.

It can be seen from Examples 15 to 19 that when the particle size Dv50 of the negative electrode material is small, the specific surface area increases, which affects the overall first effect of the negative electrode material, while the particle size of the negative electrode material is too large, the specific surface area decreases, and the lithium intercalation channel decreases. Moreover, excessive particle size affects the diffusion of ions in the negative electrode active material layer to a certain extent, reduces the rate performance of the negative electrode material, and affects the ability to quickly deintercalate lithium.

Table 4 shows the results of different evaluations of the electrolyte components of the lithium ion batteries of Examples 20 to 23.

Note: The molar mass of LiFSI is 187.07 g/mol, and the molar mass of LiPF ₆ is 151.91 g/mol.

In Table 4, the negative electrode materials used in Examples 20 to 23 are the negative electrode materials used in Example 3. By comparing Example 20 with Examples 21 to 23, it can be seen that by adding LiFSI (bis(fluorosulfonyl)imide lithium) to the electrolyte, it can work with the porous negative electrode material of the present invention, and can effectively improve the lithium ion concentration. The cycle and expansion performance of the battery.

The above description is only a preferred embodiment of the present application and an illustration of the applied technical principles. Those skilled in the art should understand that the scope of disclosure involved in this application is not limited to technical solutions formed by a specific combination of the above technical features, but also covers other technical solutions formed by any combination of the above technical features or their equivalent features. Technical solutions. For example, a technical solution formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application.

Claims

A negative electrode material, characterized in that,

The particles of the negative electrode material include a core body and a shell;

Within the range of 20nm×20nm of the cross-section of the core body, the number of pores with a diameter in the range of 0.4nm to 5nm is 5 to 100.
The negative electrode material according to claim 1, characterized in that, within the range of 20nm×20nm of the cross-section of the core body, the number of pores with a diameter in the range of 2nm to 5nm is 5 to 50.
The negative electrode material according to claim 1, wherein the negative electrode material comprises carbon material.
The negative electrode material according to claim 1 , wherein the shell is located on the surface of the core body, and the shell is analyzed by a transmission electron microscope, and within the area of 400nm of the shell, The number of pores having a pore diameter in the range of 2nm to 5nm is less than 5.
The negative electrode material according to claim 1, wherein at least one of the following (a) to (c) is satisfied:

(a) the thickness of the shell is 10nm to 200nm;

(b) the interplanar spacing of the microchip layer of the shell is 0.36nm to 0.4nm;

(c) The shell layer includes amorphous carbon.
Negative electrode material according to claim 1, is characterized in that, satisfies at least one of (d) to (h) shown below:

(d) in the photoelectron spectrum of the negative electrode material, there is at least one peak at the positions of 285.4±0.3eV, 287.8±0.3eV and 288.9±0.3eV;

(e) the specific surface area of the negative electrode material is 2m 2 /g to 10m 2 /g;

(f) the powder conductivity of the negative electrode material is 1×10 -06 μS/cm to 9×10 -08 μS/cm;

(g) In the X-ray diffraction pattern of the negative electrode material, there is a diffraction peak between 18° and 30°, and the half-maximum width of the diffraction peak is 4° to 10°;

(h) The peak intensity ratio I G /ID of the G peak and the D peak in the Raman spectrum of the negative electrode material is 0.6 to 1.
Negative electrode material according to claim 1, is characterized in that, satisfies at least one of following (i) to (k):

(i) the Dv10 of the negative electrode material is 1 μm to 5 μm;

(g) the Dv50 of the negative electrode material is 4 μm to 15 μm;

(k) Dv90 of the negative electrode material is 13 μm to 30 μm.
An electrochemical device, characterized in that, comprising:

Positive electrode, negative electrode, electrolyte and separator;

The negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, and the negative electrode active material layer includes the negative electrode material according to any one of claims 1 to 7.
The electrochemical device according to claim 8, wherein at least one of the following (1) to (n) is satisfied:

(l) the resistance of the negative electrode is 10mΩ to 60mΩ;

(m) the electrolyte includes at least one of fluoroether, fluoroethylene carbonate or ether nitrile;

(n) The electrolytic solution includes a lithium salt, the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, the concentration of the lithium salt is 1mol/L to 2mol/L, and the bis(fluorosulfonyl) The mass ratio of lithium imide and lithium hexafluorophosphate is 0.06 to 5.
An electronic device, characterized by comprising the electrochemical device described in claim 8 or 9.