Negative electrode materials, electrochemical devices and electronic devices

Abstract

The present application provides a negative electrode material, an electrochemical device and an electronic device, wherein the particles of the negative electrode material include a core and a shell; the number of pores with a pore size in the range of 0.4nm to 5nm within a range of 20nm×20nm of the cross section of the core is 5 to 100, thereby ensuring that the negative electrode material has a higher capacity while ensuring kinetic performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a negative electrode material, an electrochemical device and an electronic device. Background Art

[0002] With the development and progress of electrochemical devices (e.g., lithium-ion batteries), higher and higher requirements are put forward for their capacity and kinetic performance. At present, in order to improve the capacity and kinetic performance of electrochemical devices, although some measures have been taken to achieve some improvements, they are still not satisfactory and further improvements are expected. Summary of the invention

[0003] In the embodiment of the present application, a negative electrode material is provided, wherein the particles of the negative electrode material include a core and a shell; within the range of 20nm×20nm of the cross section of the core, the number of pores with a pore size ranging from 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 pores inside the core and the electrolyte, thereby reducing the consumption of the electrolyte.

[0004] 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 pore size ranging from 2 nm to 5 nm is 5 to 50. 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 pore size ranging from 2 nm to 5 nm is 12 to 50. The negative electrode material is ensured to have a high capacity while ensuring the kinetic performance.

[0005] In some embodiments, the negative electrode material includes a carbon material. In some embodiments, the shell layer is located on the surface of the core. In some embodiments, the shell layer is analyzed using a transmission electron microscope. 2 In the range of 2 nm to 5 nm, the number of pores with a pore size of less than or equal to 5 is less than or equal to 5. It can not only improve the conduction of ions, but also take into account the gram capacity.

[0006] 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 10 nm to 200 nm; (b) the interplanar spacing of the microcrystalline layer of the shell layer is 0.36 nm to 0.4 nm; (c) the shell layer includes amorphous carbon. To ensure ion transport and improve kinetic performance.

[0007] In some embodiments, the negative electrode material satisfies at least one of (d) to (h) as shown below: (d) in the photoelectron spectrum of the negative electrode material, there is at least one peak at 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 spectrum of the negative electrode material, there is a diffraction peak between 18° and 30°, and the half-peak width of the diffraction peak is 4° to 10°; (h) The peak intensity ratio of the G peak and the D peak in the Raman spectrum of the negative electrode material is I G / I D 0.6 to 1.

[0008] In some embodiments, the negative electrode material satisfies at least one of the following (i) to (k): (i) Dv10 of the negative electrode material is 1 μm to 5 μm; (g) 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. In some embodiments, Dv50 of the negative electrode material is 5 μm to 10 μm. Dv10, Dv50 and Dv90 are in a suitable range, which effectively improves the diffusion of ions inside the negative electrode active material layer, improves the rate performance of the negative electrode material and the ability to quickly deintercalate lithium.

[0009] In some embodiments, the negative electrode material includes a carbon material, which can reduce the contact between the pores inside the core and the electrolyte, thereby reducing the consumption of the electrolyte.

[0010] An electrochemical device is also proposed in an embodiment of the present application, including: a positive electrode, a negative electrode, an electrolyte and a separator; the negative electrode includes a negative electrode collector and a negative electrode active material layer located on the negative electrode collector, and the negative electrode active material layer includes any of the above-mentioned negative electrode materials.

[0011] 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, optionally, the resistance of the negative electrode is 20mΩ to 40mΩ. (m) The electrochemical device includes an electrolyte, the electrolyte includes 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 lithium salt concentration is 1mol / L to 2mol / L, and the mass ratio of lithium bis(fluorosulfonyl)imide to 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 react with porous negative electrode materials to effectively improve the cycle and expansion performance of lithium-ion batteries.

[0012] The present application also provides an electronic device, comprising any of the above electrochemical devices.

[0013] In an embodiment of the present application, a negative electrode material is proposed, wherein the particles of the negative electrode material include a core and a shell; within the range of 20nm×20nm of the cross section of the core, the number of pores with a pore size ranging from 0.4nm to 5nm is 5 to 100, thereby ensuring that the negative electrode material has a higher capacity while ensuring the kinetic performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a cross-sectional view of a negative electrode material disclosed in the present invention. DETAILED DESCRIPTION

[0015] The following embodiments may enable those skilled in the art to more fully understand the present application, but do not limit the present application in any way.

[0016] Electrochemical devices, such as lithium-ion batteries, are widely used in various fields, and users' requirements for electrochemical devices have also increased accordingly. For the negative electrode materials of electrochemical devices, ion storage capacity, namely capacity and kinetics, are currently the main performance improvement directions. The negative electrode materials currently used 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. The capacity of graphite materials is mainly improved by changing the precursor, granulation, sintering process and other methods, but the bottleneck faced by its capacity improvement is very large, and there is little room for improvement. Graphite materials can also be coated by coating the surface of graphite with materials with high kinetics to improve fast charging and discharging capabilities, but this method often results in the loss of first effect and capacity, and the performance cannot fully achieve better results. The theoretical gram capacity of silicon is 3400mAh / g, which is a high gram capacity material. It has a significant effect on improving energy density. However, silicon materials expand greatly during the charging and discharging process, and the particles break. It is currently difficult to find a very effective way to solve this problem, and it is impossible to meet the requirements for fast charging and fast discharging. These factors limit the application of silicon materials.

[0017] In the embodiments of the present application, a negative electrode material is proposed, wherein the particles of the negative electrode material include a core and a shell; within the range of 20nm×20nm of the cross section of the core, the number of pores with a pore size ranging from 0.4nm to 5nm is 5 to 100. In some embodiments of the present application, a transmission electron microscope (TEM) can be used to photograph the negative electrode material, and a 20nm×20nm area is selected on the photographed microscope photo and the number and pore size of the pores are counted. When counting the pore size of the pores, the maximum diameter of the pores is selected as the pore size. For the negative electrode material, when it has a pore structure with a pore size of not less than 0.4nm, it can have ion storage capacity (the ions are, for example, lithium ions), thereby improving the capacity. When the pore size is too large, the contribution to the ion storage capacity is small, and the volume energy density will be reduced. Therefore, in some embodiments of the present application, the pore size is not greater than 5nm to ensure the volume energy density of the negative electrode material. In addition, when the number of pores is less than 5, the ion storage capacity of the negative electrode material may not be significantly increased. When the number of pores is greater than 100, on the one hand, the volume energy density is reduced, and on the other hand, too many pores lead to a lack of ion diffusion channels. Therefore, in some embodiments of the present application, the number of pores with a pore size in the range of 0.4nm to 5nm in the cross-section of the core body of 20nm×20nm is 5 to 100, thereby ensuring that the negative electrode material has a high capacity while ensuring the kinetic performance.

[0018] In some embodiments of the present application, within the range of 20nm×20nm of the cross section of the core body, the number of pores with a pore size in the range of 2nm to 5nm is 5 to 50. In some embodiments, the pore size in the range of 2nm to 5nm can have both good ion storage capacity and better guarantee 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 pore size in the range of 2nm to 5nm cannot be too low to ensure the capacity of the negative electrode material. The ratio of graphite microcrystal area to 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 lead to a lack of ion diffusion channels. Therefore, within the range of 20nm×20nm of the cross section of the core body, the number of pores with a pore size in the range of 2nm to 5nm is upper limited to 50.

[0019] In some embodiments, the negative electrode material includes a carbon material. In some embodiments, the carbon material may be hard carbon. The negative electrode material may be composed of hard carbon. In some embodiments of the present disclosure, the shell layer 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. 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 and the electrolyte, and reduce the consumption of the electrolyte. In some embodiments of the present application, the shell layer is analyzed by transmission electron microscopy. At any 400nm of the shell layer, 2 In the range of 2 nm to 5 nm, the number of pores with a pore size in the range of 2 nm to 5 nm is less than 5. In some embodiments, the shell material 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 the shell can be hard carbon.

[0020] In some embodiments of the present application, the thickness of the negative electrode material shell is 10nm to 200nm. In some embodiments, if the thickness of the shell is too small, the protection effect of the core may be reduced. If the thickness of the shell is too large, the conduction of ions may be affected and the gram capacity may be lost.

[0021] In some embodiments of the present application, the interplanar spacing of the microchip layer of the shell layer of the negative electrode material is 0.36nm to 0.4nm. In some embodiments, when 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 detrimental to rate performance. When the interplanar spacing of the microchip layer is too large, it may affect volume 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 photograph the negative electrode material, and the photographed photograph can be analyzed to determine the interplanar spacing of the microchip layer.

[0022] In some embodiments of the present application, the shell layer includes amorphous carbon. In some embodiments, the shell layer may include carbon material. The amorphous carbon structure of the shell layer is conducive to improving ion transport, thereby enhancing the kinetic performance of the negative electrode material.

[0023] In some embodiments of the present disclosure, in the photoelectron spectrum of the negative electrode material, there is at least one peak at 285.4±0.3eV, 287.8±0.3eV and 288.9±0.3eV. In some embodiments, the peak of 285.4±0.3eV is the CO peak, the peak of 287.8±0.3eV is the C=O peak, and the peak of 288.9±0.3eV is the COO peak. In some embodiments, the negative electrode material is prepared by sintering. In order to ensure the kinetic properties of the shell, the sintering temperature should not be too high. Affected by the coating source functional groups, the negative electrode material after sintering has oxygen-containing functional groups on the surface, which can be obtained by photoelectron spectrum testing.

[0024] In some embodiments of the present disclosure, the specific surface area of ​​the negative electrode material is 2 m 2 / g to 10m 2 / g. In some embodiments, affected by 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 that contact the electrolyte, and the side reactions between the negative electrode material and the electrolyte increase, which may lead to a decrease in the initial efficiency 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 more than 7m 2 / g, the first efficiency of the negative electrode material is maintained at a level above 70%. When the specific surface area of ​​the negative electrode material continues to increase, the first efficiency will continue to decrease, which is difficult to meet the application requirements. In some embodiments, the specific surface area of ​​the negative electrode material is tested in the following manner: a sample of 1.5g to 3.5g of the negative electrode material is weighed and loaded into the test sample tube of TriStar II 3020, and the test is performed after degassing at 200°C for 120 minutes. Under 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 monolayer adsorption amount of the sample is obtained based on the Brownauer-Etter-Taylor adsorption theory and its formula, thereby calculating the specific surface area of ​​the negative electrode material.

[0025] 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 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 kinetic performance of the negative electrode material, the powder conductivity of the negative electrode material should not be less than 1×10 -06 μS / cm. In some embodiments, the conductivity of the powder of the negative electrode material is tested in the following manner: the powder of the negative electrode material is placed in a tablet pressing mold, wires are drawn out from both sides of the mold, and the resistance value is measured while applying pressure until the resistance remains unchanged. Then the pressed tablet is taken out and the conductivity of the pressed tablet is tested using a four-probe method or AC impedance.

[0026] In some embodiments of the present application, in the X-ray diffraction spectrum of the negative electrode material, there is a diffraction peak between 18° and 30°, and the half-peak width of the diffraction peak is 4° to 10°. In some embodiments, the presence of 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 of the G peak and the D peak in the Raman spectrum of the negative electrode material is 1 G / I DIn some embodiments, the peak intensity ratio of the G peak to the D peak is G / I D Shows the defect ratio inside the negative electrode material, I G / I D The larger the ratio is, the smaller the proportion of defects in the negative electrode material is, and the higher the crystallinity is. In some embodiments of the present application, the negative electrode material contains a certain number of pores, so I G / I D Should be between 0.6 and 1.

[0027] 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, too small a particle size of the negative electrode material may lead to increased consumption of the electrolyte and is not conducive to the cycle performance. Too large a particle size of the negative electrode material 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 guaranteed. In some embodiments, Dv10, Dv50 and Dv99 are obtained by analyzing the particle size of the sample using a Mastersizer 3000 laser particle size distribution tester. Dv10, Dv50 and Dv90 respectively represent the particle sizes that reach 10%, 50% and 90% of the volume accumulation from the small particle size side in the volume-based particle size distribution. During the test, the injection system was Hydro2000SM wet dispersion, the range was 0.01μm to 3500μm, the light source was Red light: Helium neonlaser / blue light: Solid state light source, and the detection angle was 0° to 144°. The sample test time was 6s, the background test time was 6s, the sample test snap number was 6000 times, the test cycle was averaged 3 times, the stirring pump speed was 3000rpm, and the analysis mode was set to General purpose.

[0028] In some embodiments of the present application, the negative electrode material includes a carbon material. In some embodiments, the negative electrode material can be synthesized by the following method: sodium carbonate is mixed with a phenolic material in a first solvent to obtain a first mixture, wherein the phenol can be phenol, resorcinol, hydroquinone, catechol, etc., and the first solvent is formaldehyde, acetal, furfural, etc.; the copolymer material is dissolved in a mixed solution of ethanol and water to obtain a second mixture, wherein the copolymer material can be F127 (poloxamer, polyoxyethylene polyoxypropylene ether block copolymer), P123 (polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer), SBS (styrene-butadiene-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 a fourth mixture is added, and the solidified 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, a solution containing glucose, etc.

[0029] The negative electrode material proposed in some embodiments of the present disclosure is a carbon material with a core-shell structure, such as Figure 1 As shown, the core has a porous structure, while the shell is a relatively dense amorphous carbon structure, which has a higher capacity, faster ion transport capability and a relatively small specific surface area, and has high capacity and high kinetic performance.

[0030] The present application also proposes an electrochemical device in an embodiment, comprising: a positive electrode, a negative electrode, an electrolyte and a separator; the negative electrode comprises 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 comprises any of the above negative electrode materials. 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 performance of the material itself and is not less than 10mΩ. At the same time, in order to ensure the kinetic performance of the negative electrode, the resistance of the negative electrode is optionally 20mΩ to 40mΩ.

[0031] In some embodiments of the present application, the electrochemical device includes an electrolyte, and the electrolyte includes at least one of a fluoroether, a fluoroethylene carbonate, or an ether nitrile. In some embodiments, the electrolyte includes a lithium salt, and the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, and the concentration of the lithium salt is 1 mol / L to 2 mol / L, and the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.06 to 5.

[0032] In some embodiments, the negative electrode active material layer may further include a conductive agent and a binder. In some embodiments, the conductive agent in the negative electrode active material layer may include at least one of conductive carbon black, Ketjen black, lamellar graphite, graphene, carbon nanotubes or carbon fibers. In some embodiments, the binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinyl pyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, 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 may be a mixture of silicon-based materials and other materials. It should be understood that the above is only an example, and any other suitable material and mass ratio may be used. In some embodiments, the negative electrode current collector may be at least one of copper foil, nickel foil or carbon-based current collector.

[0033] In some embodiments, in some embodiments, the electrochemical device includes a separator disposed between the positive electrode and the negative electrode. The separator 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, they 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 separator is in the range of about 5 μm to 50 μm.

[0034] In some embodiments, the surface of the isolation membrane may further include a porous layer, the porous layer is disposed on at least one surface of the isolation membrane, the porous layer includes inorganic particles and a binder, the inorganic particles are selected from at least one of aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (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 or barium sulfate. 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 at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The porous layer on the surface of the separator can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the separator, and enhance the adhesion between the separator and the pole piece.

[0035] In some embodiments of the present application, the electrochemical device is in a wound, stacked or folded form.

[0036] In some embodiments, the positive electrode and / or negative electrode of the electrochemical device may be a multi-layer structure formed by winding or stacking, or a single-layer structure in which a single-layer positive electrode, a separator, and a single-layer negative electrode are stacked.

[0037] In some embodiments, the electrochemical device includes a lithium ion battery, but the present application is not limited thereto. In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be one or more of a gel electrolyte, a solid electrolyte, and an electrolyte, the electrolyte including a lithium salt and a non-aqueous solvent. 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 or lithium difluoroborate. For example, the lithium salt is selected from LiPF6. 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 may be a chain carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0038] Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC) or combinations thereof. Examples of fluorocarbonate compounds are 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 combinations thereof.

[0039] Examples of the carboxylic acid ester compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0040] Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0041] Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid esters or combinations thereof.

[0042] In some embodiments of the present application, taking a lithium-ion battery as an example, a positive electrode, a separator, and a negative electrode are wound or stacked in sequence to form an electrode component, and then encapsulated in, for example, an aluminum-plastic film, injected with an electrolyte, formed, and encapsulated to form a lithium-ion battery. Then, the prepared lithium-ion battery is subjected to a performance test.

[0043] Those skilled in the art will appreciate that the above-described method for preparing an electrochemical device (eg, a lithium-ion battery) is only an example, and other methods commonly used in the art may be used without departing from the disclosure of the present application.

[0044] Embodiments of the present application also provide an electronic device including the above-mentioned electrochemical device. The electronic device of the embodiment of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a drone, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0045] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein button batteries and lithium-ion batteries are used as examples.

[0046] Assembly of button cell (as shown in Tables 1 to 3):

[0047] The negative electrode material, conductive agent carbon black (Super P), and sodium carboxymethyl cellulose (CMC) were mixed in a certain ratio of 96:0.5:3.5 to make a slurry with a certain solid content (50%), and the slurry was evenly coated on the surface of the copper foil with a scraper, and the pole piece was dried (85℃, 4h), and the pole piece after drying was punched into a small disc with a diameter of 14mm. The obtained small disc, nickel foam, isolation film (7μm, PP polypropylene substrate), lithium sheet (0.066g), steel shell (diameter 24mm), and electrolyte were added to assemble a button battery.

[0048] Preparation of electrolyte: In a dry argon atmosphere glove box, ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC=3:7, and then 2wt% of fluoroethylene carbonate was added to dissolve and stir well, then lithium salt LiPF6 was added and mixed evenly to obtain an electrolyte in which the concentration of LiPF6 was 1 mol / L.

[0049] Lithium ion battery preparation (as shown in Table 4):

[0050] Preparation of positive electrode: Mix the positive electrode active materials lithium cobalt oxide, conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 97:1.4:1.6, add N-methylpyrrolidone (NMP) as a solvent, and stir evenly. The slurry (solid content of 72wt%) is evenly coated on the positive electrode current collector aluminum foil with a coating thickness of 80μm, dried at 85℃, and then cold pressed, cut, and slit, and dried under vacuum conditions at 85℃ for 4 hours to obtain the positive electrode.

[0051] Preparation of 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 at a weight ratio of 97:1.5:1.5 to form a negative electrode slurry (solid content of 40wt%). A 10μm thick copper foil 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 50μm, dried at 85°C, and then cold pressed, cut into pieces, and slit, and then dried under vacuum conditions at 120°C for 12 hours to obtain a negative electrode.

[0052] Preparation of isolation film: The isolation film is 7 μm thick polyethylene (PE).

[0053] Preparation of lithium-ion battery: stack the positive electrode, separator and negative electrode in order, so that the separator is between the positive electrode and the negative electrode to play a role of isolation, and wind them to obtain the electrode assembly. Place the electrode assembly in the outer packaging aluminum plastic film, remove moisture at 80°C, inject the above electrolyte and package, and obtain the lithium-ion battery through the process of formation, degassing, trimming and other processes.

[0054] Lithium-ion battery cycle performance test:

[0055] Five lithium ion batteries prepared in Examples 20 to 23 were taken for each test and the average value was calculated. The lithium ion batteries were repeatedly charged and discharged by the following steps, and the discharge capacity retention rate and thickness expansion of the lithium ion batteries were calculated.

[0056] First, in an environment of 25°C, the first charge and discharge were carried out. Constant current charging was performed at a charging current of 0.7C until the upper limit voltage of 4.48V was reached, and then constant voltage charging was switched. Then, constant current discharge was performed at a discharge current of 1.0C until the final voltage was 3V. The discharge capacity of the first cycle and the thickness of the fully charged lithium-ion battery were recorded. Then, 400 charge and discharge cycles were carried out, and the discharge capacity and the thickness of the fully charged lithium-ion battery were recorded at the 400th cycle.

[0057] Cycle capacity retention rate = (discharge capacity of the 400th cycle / discharge capacity of the first cycle) × 100%;

[0058] Cycle thickness expansion = (thickness of the fully charged lithium-ion battery at the 400th cycle / thickness of the fully charged lithium-ion battery at the first cycle) × 100%.

[0059] Test of the number of holes in the material

[0060] 1) Sample preparation

[0061] Method 1: Grind the material thoroughly, 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 anhydrous ethanol, use ultrasonic dispersion to disperse the sample as much as possible, then use a support net to scoop up the sample, and prepare the sample.

[0062] Method 2: The material is embedded and cured with epoxy resin, and then the material is cut into sizes of 50nm to 70nm using ultrathin sectioning to prepare the sample.

[0063] 2) Test steps

[0064] 1. Select a micro area in the image field. The magnification (projection mirror excitation current) should not be too large (about 2000×). Find an area with good light transmittance. 2. Adjust the intensity (intensity) of the converging light beam to focus the converging electron beam at the center. 3. Press the diffraction button to switch to the diffraction field. If the focus is not good at this time and the electron beam cannot be converged, adjust the focus button to focus. 4. Modulate the objective lens grating to the 4th gear (from the original neutral gear), that is, just select a spot in the center to allow the transmitted beam to pass. 5. Press the diffraction button to switch back to the image field. 6. Find a grain to be observed in the image field. The darker the color of the area, the better. 7. Adjust the intensity button of the electron converging beam to converge the electron beam at the center. 8. Press the diffraction button to return to the diffraction field. 9. The Kikuchi band and Kikuchi pole can be seen in the diffraction field. Next, adjust the center point to the Kikuchi point. 10. Press diffraction to return to the image field, press intensity to zoom in, if the sample stage is double-tilted, adjust the alpha and beta values, pay attention to the image, and make sure the center is still in the grain. 11. Adjust the intensity button of the electron beam to converge the electron beam at the center, press the diffraction button, return to the diffraction field, and see if it is adjusted to the Kikuchi pole. 12. Repeat 10 to 11 until it is adjusted to the Kikuchi pole. 13. Press diffraction to return to the image field, turn on the selection grating, gear 2, select the area, press diffraction to return to the diffraction field, and you can see the electron diffraction spot pattern.

[0065] 3) Hole determination

[0066] At 20×20nm or 400nm 2 The sample is observed within the range, and the hole is judged as follows: there is no microchip layer in the limited area of ​​2nm to 5nm, and the area is blank and surrounded by microchip layers.

[0067] Test method for gram capacity of materials

[0068] The obtained button battery was left to stand for 4 hours and tested according to the following process to obtain the material capacity: discharge to 0V at 0.05C, discharge to 0V at 50μA, discharge to 0V at 20μA, stand for 5min, charge to 2.5V at 0.01C, and record the charged gram capacity as the gram capacity of the material.

[0069] First effect: Test method for first effect of materials

[0070] After the obtained button battery was left standing for 4 hours, it was tested according to the following process to obtain the material capacity: discharge to 0V at 0.05C, discharge to 0V at 50μA, discharge to 0V at 20μA, stand for 5min, charge to 2.5V at 0.1C, and the ratio of the charged gram capacity to the discharged gram capacity is the first efficiency of the material.

[0071] Test methods for material rate performance

[0072] Rapid lithium insertion performance:

[0073] After the obtained button battery was left to stand for 4 hours, it was tested according to the following process to obtain the fast charging performance of the material: discharge to 0V at 0.05C, then discharge to 0.005C at constant voltage, let stand for 5 minutes, charge to 2.5V at 0.01C, and the discharge capacity in grams was recorded as D; discharge to 0V at 0.01C, 0.02C, 0.05C, 0.1C, 0.2C, 0.5C, and 1C, discharge to 0V at constant voltage to 0.005C, let stand for 5 minutes, and charge to 2.5V at 0.01C. The discharge capacities were recorded as D1, D2, D3, D4, D5, D6, and D7 respectively.

[0074] Rapid lithium removal performance:

[0075] After the obtained button battery was left to stand for 4 hours, it was tested according to the following process to obtain the fast charging performance of the material: discharge to 0V at 0.05C, discharge to 0V at 50μA, discharge to 0V at 20μA, stand for 5 minutes, charge to 2.5V at 0.01C, and the charged capacity in grams was recorded as C, discharge to 0V at 0.05C, discharge to 0V at 50μA, discharge to 0V at 20μA, stand for 5 minutes, and charge to 2.5V at 0.01C, 0.02C, 0.05C, 0.1C, 0.2C, 0.5C, and 1C respectively, and the discharge capacities were recorded as C1, C2, C3, C4, C5, C6, and C7 respectively.

[0076] The number of core holes in Table 1 is controlled by adjusting the amount of template F127 (polyoxyethylene polyoxypropylene ether block copolymer) in the experiment. After a certain adjustment, the effect in Table 1 can be achieved. In order to adjust the number of holes, the ratio of F127: phenol: aldehyde is mainly changed during the synthesis of the core layer material, and the ratio range is (0.3 to 0.6): (0.8 to 1.2): (0.8 to 1.2).

[0077] Table 1 shows the parameters and evaluation results of each negative electrode material of Examples 1 to 10.

[0078]

[0079] Note: The core-pore number is the number of pores with a pore size range of 2nm to 5nm within the 20nm×20nm range of the core cross section. The shell-pore number is the 400nm range of the shell. 2 In the range of pore diameter, the number of pores is in the range of 2 nm to 5 nm.

[0080] Please refer to Table 1. Examples 1 to 6 show the effect of the number of pores of 2nm to 5nm in the cross section of the core of the negative electrode material in the range of 20nm×20nm on the performance. As can be seen from Table 1, when the core-pore number is greater than 100 (Comparative Example 2), the values ​​of C7 / C1 and D7 / D1 are small, which indicates that the performance of rapid lithium insertion and rapid lithium removal of the negative electrode material is poor at this time. When the core-pore number is less than 5 (Comparative Example 1), the gram capacity of the negative electrode material is quite different from that of the embodiment. Although C7 / C1 and D7 / D1 are not much different, the comprehensive electrochemical performance is low. Therefore, when the core-pore number is 5 to 100, the performance is better.

[0081] Since the pores in the core body have the function of storing lithium, the gram capacity of the negative electrode material when the core body has 5 pores is lower than the gram capacity when the core body has 50 pores. This reflects the effect of the number of pores in the core body of the negative electrode material on the gram capacity of the negative electrode material, that is, the more pores there are, the higher the gram capacity is. Examples 5 and 6 show that the continued increase in the number of pores is beneficial to the capacity.

[0082] Comparative Example 1 shows that the core has fewer pores and the material capacity is low. In Comparative Example 2, the core has too many pores, which forms a supercapacitor-like negative electrode structure to a certain extent. This structure reduces the overall first efficiency of the material and has a high lithium de-lithiation voltage platform, which is not conducive to application. And the performance of the multiple ratio decreases when there are too many pores.

[0083] Table 2 shows the parameters and evaluation results of each negative electrode material of Examples 7 to 10.

[0084]

[0085] As shown in Examples 7 to 10 in Table 2, the first effect decreases with the increase in the number of shell-holes. As the number of shell-holes increases, the specific surface area of ​​the shell of the negative electrode material increases, and the electrolyte easily enters the core body and reacts with the core body, increasing the side reaction between the negative electrode material and the electrolyte, affecting the first effect and gram capacity. The control of the number of shells is mainly controlled by controlling the temperature rise program, thereby controlling the volatilization process of the components during the combustion process of the material, and obtaining different numbers of shell holes in the material.

[0086] In Table 3, the shell layer variation is obtained by adjusting the concentration of the fourth mixed material. The higher the concentration, the thicker the shell layer. The concentration range is controlled within a range of 0.1 mol / L to 20 mol / L.

[0087] Table 3 shows the parameters and evaluation results of each negative electrode material of Examples 11 to 20.

[0088]

[0089] Please refer to Table 3. As shown in Examples 11 to 15, when the shell thickness of the negative electrode material is different, the first efficiency of the negative electrode material is affected. When the shell layer of the negative electrode material is thin, it may be because the shell layer is difficult to coat evenly, part of the core layer pore structure is exposed, the specific surface area of ​​the negative electrode material increases, and the first efficiency of the negative electrode material is low. As the shell thickness of the negative electrode material increases, the specific surface area decreases, and the first efficiency of the negative electrode material is improved. However, 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 consider the gram capacity and first efficiency comprehensively, and the shell thickness needs to be within an appropriate range.

[0090] 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, affecting the overall initial efficiency of the negative electrode material, while when the particle size of the negative electrode material is too large, the specific surface area decreases, the lithium insertion channels decrease, and the excessively large particle size affects the diffusion of ions inside 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 insert and release lithium.

[0091] Table 4 shows various evaluation results of the lithium ion battery electrolyte components of Examples 20 to 23.

[0092]

[0093] Note: The molar mass of LiFSI is 187.07 g / mol, and the molar mass of LiPF6 is 151.91 g / mol.

[0094] 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 (lithium bis(fluorosulfonyl)imide) to the electrolyte, it can react with the porous negative electrode material in the present invention, and can effectively improve the cycle and expansion performance of the lithium ion battery.

[0095] The above description is only a preferred embodiment of the present application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of disclosure involved in the present application is not limited to the technical solution formed by a specific combination of the above technical features, but should also cover other technical solutions formed by any combination of the above technical features or their equivalent features. For example, the above features are replaced with the technical features with similar functions disclosed in the present application.

Claims

1. A negative electrode material, characterized in that: The particles of the negative electrode material include a core and a shell; In the 20 nm×20 nm area of ​​the cross section of the core body, the number of pores with a pore diameter ranging from 0.4 nm to 5 nm is 5 to 100; The shell layer is located on the surface of the core body. The shell layer is analyzed by transmission electron microscopy. 2 Within the area, the number of pores with a pore diameter ranging from 2 nm to 5 nm is less than 5; The specific surface area of ​​the negative electrode material is 2m 2 / g to 10m 2 / g.

2. The negative electrode material according to claim 1, characterized in that The number of pores having a pore diameter ranging from 2 nm to 5 nm is 5 to 50 within a 20 nm×20 nm range of the cross section of the core body.

3. The negative electrode material according to claim 1, characterized in that The negative electrode material includes a carbon material.

4. The negative electrode material according to claim 1, characterized in that Satisfies at least one of the following (a) to (c): (a) the thickness of the shell layer is 10 nm to 200 nm; (b) the interplanar spacing of the microcrystalline layer of the shell layer is 0.36 nm to 0.4 nm; (c) The shell layer comprises amorphous carbon.

5. The negative electrode material according to claim 1, characterized in that Satisfies at least one of the following (d) to (h): (d) in the photoelectron spectrum of the negative electrode material, there is at least one peak at 285.4±0.3 eV, 287.8±0.3 eV and 288.9±0.3 eV; (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-peak width of the diffraction peak is 4° to 10°; (h) The peak intensity ratio I of the G peak and the D peak in the Raman spectrum of the negative electrode material G / I D 0.6 to 1.

6. The negative electrode material according to claim 1, characterized in that 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.

7. An electrochemical device, characterized in that: include: Positive electrode, negative electrode, electrolyte and separator; The negative electrode comprises 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 comprises the negative electrode material according to any one of claims 1 to 6.

8. The electrochemical device according to claim 7, characterized in that Satisfies at least one of the following (l) to (n): (l) the resistance of the negative electrode is 10 mΩ to 60 mΩ; (m) the electrolyte comprises at least one of a fluoroether, a fluoroethylene carbonate or an ether nitrile; (n) The electrolyte includes a lithium salt, wherein the lithium salt includes lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, the lithium salt concentration is 1 mol / L to 2 mol / L, and the mass ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate is 0.06 to 5.

9. An electronic device, characterized in that: Comprising the electrochemical device as claimed in claim 7 or 8.

Images