CN114631204A - Negative electrode, electrochemical device, and electronic device - Google Patents
Negative electrode, electrochemical device, and electronic device Download PDFInfo
- Publication number
- CN114631204A CN114631204A CN202180005821.2A CN202180005821A CN114631204A CN 114631204 A CN114631204 A CN 114631204A CN 202180005821 A CN202180005821 A CN 202180005821A CN 114631204 A CN114631204 A CN 114631204A
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- Prior art keywords
- active material
- negative electrode
- carbon
- negative
- anode
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- AXCZMVOFGPJBDE-UHFFFAOYSA-L calcium dihydroxide Chemical compound [OH-].[OH-].[Ca+2] AXCZMVOFGPJBDE-UHFFFAOYSA-L 0.000 description 1
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- 239000003990 capacitor Substances 0.000 description 1
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- 238000007872 degassing Methods 0.000 description 1
- 150000004985 diamines Chemical class 0.000 description 1
- QGBSISYHAICWAH-UHFFFAOYSA-N dicyandiamide Chemical compound NC(N)=NC#N QGBSISYHAICWAH-UHFFFAOYSA-N 0.000 description 1
- SBZXBUIDTXKZTM-UHFFFAOYSA-N diglyme Chemical compound COCCOCCOC SBZXBUIDTXKZTM-UHFFFAOYSA-N 0.000 description 1
- QHGJSLXSVXVKHZ-UHFFFAOYSA-N dilithium;dioxido(dioxo)manganese Chemical compound [Li+].[Li+].[O-][Mn]([O-])(=O)=O QHGJSLXSVXVKHZ-UHFFFAOYSA-N 0.000 description 1
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical compound COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 description 1
- SNQXJPARXFUULZ-UHFFFAOYSA-N dioxolane Chemical compound C1COOC1 SNQXJPARXFUULZ-UHFFFAOYSA-N 0.000 description 1
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- 238000012983 electrochemical energy storage Methods 0.000 description 1
- 239000008151 electrolyte solution Substances 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- KLKFAASOGCDTDT-UHFFFAOYSA-N ethoxymethoxyethane Chemical compound CCOCOCC KLKFAASOGCDTDT-UHFFFAOYSA-N 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 239000011245 gel electrolyte Substances 0.000 description 1
- 229910000449 hafnium oxide Inorganic materials 0.000 description 1
- WIHZLLGSGQNAGK-UHFFFAOYSA-N hafnium(4+);oxygen(2-) Chemical compound [O-2].[O-2].[Hf+4] WIHZLLGSGQNAGK-UHFFFAOYSA-N 0.000 description 1
- 229920001903 high density polyethylene Polymers 0.000 description 1
- 239000004700 high-density polyethylene Substances 0.000 description 1
- FAHBNUUHRFUEAI-UHFFFAOYSA-M hydroxidooxidoaluminium Chemical compound O[Al]=O FAHBNUUHRFUEAI-UHFFFAOYSA-M 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000008595 infiltration Effects 0.000 description 1
- 238000001764 infiltration Methods 0.000 description 1
- 239000010954 inorganic particle Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 description 1
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(III) nitrate Inorganic materials [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 239000004973 liquid crystal related substance Substances 0.000 description 1
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 description 1
- DVATZODUVBMYHN-UHFFFAOYSA-K lithium;iron(2+);manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[Fe+2].[O-]P([O-])([O-])=O DVATZODUVBMYHN-UHFFFAOYSA-K 0.000 description 1
- 229920001684 low density polyethylene Polymers 0.000 description 1
- 239000004702 low-density polyethylene Substances 0.000 description 1
- 230000001050 lubricating effect Effects 0.000 description 1
- VTHJTEIRLNZDEV-UHFFFAOYSA-L magnesium dihydroxide Chemical compound [OH-].[OH-].[Mg+2] VTHJTEIRLNZDEV-UHFFFAOYSA-L 0.000 description 1
- 239000000347 magnesium hydroxide Substances 0.000 description 1
- 229910001862 magnesium hydroxide Inorganic materials 0.000 description 1
- MIVBAHRSNUNMPP-UHFFFAOYSA-N manganese(II) nitrate Inorganic materials [Mn+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MIVBAHRSNUNMPP-UHFFFAOYSA-N 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- JDSHMPZPIAZGSV-UHFFFAOYSA-N melamine Chemical compound NC1=NC(N)=NC(N)=N1 JDSHMPZPIAZGSV-UHFFFAOYSA-N 0.000 description 1
- 229940017219 methyl propionate Drugs 0.000 description 1
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- KBJMLQFLOWQJNF-UHFFFAOYSA-N nickel(II) nitrate Inorganic materials [Ni+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O KBJMLQFLOWQJNF-UHFFFAOYSA-N 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 description 1
- GNRSAWUEBMWBQH-UHFFFAOYSA-N oxonickel Chemical compound [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 150000003014 phosphoric acid esters Chemical class 0.000 description 1
- 238000005498 polishing Methods 0.000 description 1
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 1
- 229920002239 polyacrylonitrile Polymers 0.000 description 1
- 229920002647 polyamide Polymers 0.000 description 1
- 229920000139 polyethylene terephthalate Polymers 0.000 description 1
- 239000005020 polyethylene terephthalate Substances 0.000 description 1
- 238000006116 polymerization reaction Methods 0.000 description 1
- 239000004926 polymethyl methacrylate Substances 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920001289 polyvinyl ether Polymers 0.000 description 1
- 239000011148 porous material Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
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- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- HBMJWWWQQXIZIP-UHFFFAOYSA-N silicon carbide Chemical compound [Si+]#[C-] HBMJWWWQQXIZIP-UHFFFAOYSA-N 0.000 description 1
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical compound [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000011734 sodium Substances 0.000 description 1
- AWRQDLAZGAQUNZ-UHFFFAOYSA-K sodium;iron(2+);phosphate Chemical compound [Na+].[Fe+2].[O-]P([O-])([O-])=O AWRQDLAZGAQUNZ-UHFFFAOYSA-K 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 230000006641 stabilisation Effects 0.000 description 1
- 238000011105 stabilization Methods 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- HXJUTPCZVOIRIF-UHFFFAOYSA-N sulfolane Chemical compound O=S1(=O)CCCC1 HXJUTPCZVOIRIF-UHFFFAOYSA-N 0.000 description 1
- 230000008961 swelling Effects 0.000 description 1
- WMOVHXAZOJBABW-UHFFFAOYSA-N tert-butyl acetate Chemical compound CC(=O)OC(C)(C)C WMOVHXAZOJBABW-UHFFFAOYSA-N 0.000 description 1
- ZUHZGEOKBKGPSW-UHFFFAOYSA-N tetraglyme Chemical compound COCCOCCOCCOCCOC ZUHZGEOKBKGPSW-UHFFFAOYSA-N 0.000 description 1
- XOLBLPGZBRYERU-UHFFFAOYSA-N tin dioxide Chemical compound O=[Sn]=O XOLBLPGZBRYERU-UHFFFAOYSA-N 0.000 description 1
- 229910001887 tin oxide Inorganic materials 0.000 description 1
- DQWPFSLDHJDLRL-UHFFFAOYSA-N triethyl phosphate Chemical compound CCOP(=O)(OCC)OCC DQWPFSLDHJDLRL-UHFFFAOYSA-N 0.000 description 1
- WVLBCYQITXONBZ-UHFFFAOYSA-N trimethyl phosphate Chemical compound COP(=O)(OC)OC WVLBCYQITXONBZ-UHFFFAOYSA-N 0.000 description 1
- 229920000785 ultra high molecular weight polyethylene Polymers 0.000 description 1
- LSGOVYNHVSXFFJ-UHFFFAOYSA-N vanadate(3-) Chemical compound [O-][V]([O-])([O-])=O LSGOVYNHVSXFFJ-UHFFFAOYSA-N 0.000 description 1
- 229910001928 zirconium oxide Inorganic materials 0.000 description 1
- PAPBSGBWRJIAAV-UHFFFAOYSA-N ε-Caprolactone Chemical compound O=C1CCCCCO1 PAPBSGBWRJIAAV-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
- H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Inorganic Chemistry (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
Provided are a negative electrode, an electrochemical device, and an electronic device. The negative electrode includes a negative electrode current collector and a negative electrode active material layer, and the cohesive force between the negative electrode active material layer and the negative electrode current collector is greater than or equal to 7N/m. The embodiment of this application has improved the adhesion stress between negative pole active material layer and the negative current collector for the structure of negative pole is more stable, is favorable to promoting electrochemical device's the ability of filling soon.
Description
Technical Field
The present application relates to the field of electrochemical energy storage, in particular to cathodes, electrochemical devices and electronic devices.
Background
As electrochemical devices (e.g., lithium ion batteries) are developed and advanced, higher and higher requirements are placed on their cycle performance and energy density. The negative electrode prepared from graphite has high sheet resistance and poor quick charging performance, and at present, in order to improve the performance of an electrochemical device, some negative electrode materials with high gram capacity (such as silicon-based negative electrode materials, tin-based negative electrode materials, hard carbon materials and the like) are generally adopted to replace the common graphite, however, the negative electrode materials with high gram capacity also bring some new problems, and further improvement is expected.
Disclosure of Invention
Some embodiments of the present application provide a negative electrode including a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer including a negative electrode active material, a cohesive force between the negative electrode active material layer and the negative electrode current collector being greater than or equal to 7N/m.
In some embodiments, the adhesion between the negative active material layer and the negative current collector is greater than or equal to 10N/m.
In some embodiments, the negative active material comprises hard carbon.
In some embodiments, at least one of conditions (a) to (d) is satisfied: (a) a carbon material grows in situ on the surface of the negative active material; (b) the anode active material has Dv50 of 6 to 20 μm; (c) the negative active material further includes a nitrogen element and a transition metal element; (d) the cohesion of the negative electrode active material is 5N/m to 100N/m.
In some embodiments, at least one of conditions (e) through (h) is satisfied: (e) the carbon material includes at least one of a fibrous carbon material, a flaky carbon material, or a particulate carbon material; (f) the mass of the transition metal element in the negative electrode active material is 0.1% to 10%, and the mass of the nitrogen element in the negative electrode active material is 0.1% to 5%; (g) the transition metal element comprises at least one of Co, Fe, Cr, Pt, Cu, Mn, Ag, Ni or Zn; (h) the content by mass of the nitrogen element or the transition metal element in the anode active material particle gradually decreases from the surface of the anode active material particle to the center of the anode active material particle.
In some embodiments, at least one of conditions (i) to (k) is satisfied: (i) the fibrous carbon material has a diameter of 50nm to 500nm and a length of more than 1 μm; (j) the length of the flaky carbon material is more than 1 mu m; (k) the particulate carbon material has an average particle diameter of 50nm to 500 nm.
Some embodiments of the present application provide an electrochemical device including an electrolyte, a separator, a positive electrode, and any of the negative electrodes described above, the separator being disposed between the positive electrode and the negative electrode.
In some embodiments, the electrolyte comprises at least one of fluoroether, fluoroethylene carbonate, or ether nitrile. In some embodiments, the electrolyte comprises a lithium salt comprising lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate, the concentration of the lithium salt being from 1 to 2mol/L, and the molar ratio of lithium bis (fluorosulfonyl) imide to lithium hexafluorophosphate being from 0.05 to 4.
Embodiments of the present application also provide an electronic device including the above electrochemical device.
The embodiment of the application improves the cohesive force between the negative active material layer and the negative current collector, so that the structure of the negative electrode is more stable, the membrane resistance of the negative electrode is favorably reduced, and the performance of the electrochemical device is improved.
Detailed Description
The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.
Some embodiments of the present application provide an anode including an anode current collector and an anode active material layer on the anode current collector. In some embodiments, the negative active material layer may be located on one or both sides of the negative current collector. In some embodiments, the negative active material layer includes a negative active material.
In some embodiments, the negative active material comprises hard carbon. By adopting the hard carbon, on one hand, the gram capacity of the hard carbon is larger than that of the common graphite and can be about twice as large as that of the graphite, so that the energy density of the electrochemical device can be improved. In addition, the negative active material containing hard carbon is adopted, so that the cohesive force between the negative active material layer and the negative current collector is favorably improved, the structural stability of the negative electrode is further improved, and the cycle performance of the electrochemical device prepared by the negative electrode is favorably improved.
In some embodiments, the adhesion between the negative active material layer and the negative current collector is greater than or equal to 7N/m. The embodiment of the application improves the cohesive force between the negative active material layer and the negative current collector, so that the structure of the negative electrode is more stable, and the improvement of the cycle performance of the electrochemical device prepared by the negative electrode is facilitated.
In some embodiments, the adhesion between the negative active material layer and the negative current collector is greater than or equal to 10N/m. By using the negative electrode active material containing hard carbon, it was found that the adhesion between the negative electrode active material layer and the negative electrode current collector can be raised to 10N/m or more, which is much more than 2N/m to 6N/m when graphite is used as the negative electrode active material.
In some embodiments, the surface of the hard carbon in the negative electrode active material is grown in situ with a carbon material. When pure hard carbon is used as the negative electrode active material, in addition to the above advantages, there are some disadvantages, for example, the edge angle of the hard carbon particles is usually sharp, so that the negative electrode current collector may be damaged during the cold pressing process, which is not favorable for the full exertion of the electrochemical performance of the electrochemical device; on the other hand, sharp edges and corners of hard carbon particles are not beneficial to slippage among the particles, so that the conditions of processing brittle fracture and cold pressing strip splitting and strip breaking occur.
One of the strategies to solve the above disadvantages is to coat a layer of material on the surface of the hard carbon particles to coat the edges and corners of the hard carbon particles, but the coating layer is easy to fall off from the surface of the hard carbon particles; hard carbon can also be mixed with graphite to take advantage of the good slip characteristics of graphite, but this can compromise the high gram capacity of hard carbon, affecting the energy density of the electrochemical device; in addition, one-dimensional carbon tubes or two-dimensional graphene can be added, the sharp corner parts of the hard carbon can be wrapped to a great extent, the situation that the hard carbon stabs the isolating film and the copper foil in the processing process is improved, meanwhile, the lubricating effect of the carbon tubes or the graphene can also increase slippage among the hard carbon particles, and the problem of belt breakage of the hard carbon in the processing process is improved.
This application can increase the carbon material that slides at the surperficial normal position growth of hard carbon for solve the sharp-pointed edges and corners condition of hard carbon particle, and increase the slip between the hard carbon particle, solve the difficult slip that hard carbon appears in the course of working simultaneously and harm negative pole mass flow body scheduling problem.
In some embodiments, the Dv50 of the hard carbon is 6 μm to 20 μm. The particle size test method is referred to GB/T19077-2016. The test equipment used was Mastersizer 3000 manufactured by malvern. Particle size measurement is accomplished by measuring the intensity of scattered light as the laser beam passes through the dispersed particle sample during testing. The refractive index of the particles used in the test was 1.8, one sample was tested in triplicate, and the particle size was finally determined as Dv50 by taking the average of the triplicate tests. If the Dv50 of the hard carbon is too small, the hard carbon has a large specific surface area and is likely to undergo side reactions with the electrolyte. If the Dv50 of the hard carbon is too large, the improvement of the rate capability is not favorable.
In some embodiments, the hard carbon-containing anode active material further includes a nitrogen element and a transition metal element. In some embodiments, whether the anode active material containing hard carbon includes a nitrogen element and a transition metal element may be determined by XPS analysis. The carbon material of this application comes by the micromolecule schizolysis, and under the normal condition, the micromolecule can directly volatilize and do not have carbon residue in the pyrolysis process, in order to make the micromolecule carbon can be in the carbon material that hard carbon particle surface pyrolysis increased and slided, can introduce transition metal salt and chooseed for use nitrogenous micromolecule material. The carbon material with a specific structure/morphology is pyrolyzed in situ under the action of transition metal by utilizing the combination of a nitrogen element in a small molecule and a d orbit of a transition metal element, and the fibrous, flaky or granular carbon material can be pyrolyzed on the surface of hard carbon particles according to the difference of the small molecule, so that the problems of poor processing performance of the hard carbon particles and stabbing of an isolating film and a negative current collector are solved.
In some embodiments, the cohesion between the negative active materials is 5N/m to 100N/m. If the cohesion between the anode active materials is too small, the stabilization of the structure of the anode active materials is not facilitated; if the cohesion between the anode active materials is too large, it is not advantageous to improve the rate performance of the electrochemical device.
In some embodiments, the carbon material grown in situ on the surface of the hard carbon comprises at least one of a fibrous carbon material, a flake carbon material, or a particulate carbon material. In some embodiments, the fibrous carbon material has a diameter of 50nm to 500nm and a length > 1 μm. If the diameter of the fibrous carbon material is too small, the stability of the fibrous carbon material is relatively weak; if the diameter of the fibrous carbon material is too large, the coating flexibility of the fibrous carbon material may be relatively weak. In addition, if the length of the fibrous carbon material is too small, the effect of the carbon material in improving the slip between the hard carbon particles is relatively limited. Diameter and length test of fibrous carbon materials powder of the materials is shot and observed through an SEM (scanning Electron microscope), then, image analysis software is used, 50 fibrous carbon materials are randomly selected from 10 SEM pictures, the respective diameters and lengths of the fibrous carbon materials are measured, and then the average value of the diameters and the lengths of 10 x 50 carbon nanotubes is calculated, namely the diameters and the lengths of the fibrous carbon materials (the lengths and the diameters are similar to the measurement mode of the lengths and the diameters of the carbon nanotubes).
In some embodiments, the length of the sheet-like carbon material is > 1 μm. If the length of the sheet-like carbon material is too small, the effect of the carbon material in improving the slip between the hard carbon particles is relatively limited. The length of the sheet-like carbon material was observed by taking a picture of the material powder using an SEM, 50 sheet-like carbon materials were randomly selected from 10 SEM photographs using image analysis software, the longest length of the sheet-like carbon materials was measured, and the average value of the longest lengths of 10 × 50 sheet-like carbon materials was calculated as the length of the sheet-like carbon material.
In some embodiments, the particulate carbon material has an average particle size of 50nm to 500 nm. If the average particle diameter of the particulate carbon material is too small, sufficient coating of the hard carbon particles is not facilitated; if the average particle diameter of the particulate carbon material is too large, the effect of the particulate carbon material in improving the slip between the hard carbon particles is affected. Average particle diameter test of particulate carbon material powder was photographed and observed by SEM scanning electron microscope, and then soft by image analysisNext, 10 granular carbon materials were randomly selected from the SEM photograph, and the area of each of these material particles was determined, and then, assuming that the material particles were spherical, the particle diameter R (diameter) of each material particle was determined by the following formula: r is 2 × (S/π)1/2(ii) a Wherein S is the area of the material particles; the average particle size of the matrix was determined by performing a process of determining the particle size R of the material particles on 10 SEM images and arithmetically averaging the particle sizes of the 100(10 × 10) material particles obtained.
In some embodiments, the mass of the transition metal element in the anode active material is 0.1% to 10%, and the mass of the nitrogen element in the anode active material is 0.1% to 5%. If the mass percentage of the transition metal element or the nitrogen element is too small, the in-situ growth of the carbon material on the surface of the hard carbon particles is not facilitated; if the mass percentage of the transition metal element or the nitrogen element is too large, the effect of increasing the amount of residual carbon in the in-situ growth process is not significantly increased, and it is not advantageous to increase the energy density of the electrochemical device. In some embodiments, the transition metal element comprises at least one of Co, Fe, Cr, Pt, Cu, Mn, Ag, Ni, or Zn.
In some embodiments, the mass percentage content of the nitrogen element and the transition metal element in the anode active material gradually decreases from the surface of the anode active material to the center of the anode active material. The mass percentage of the nitrogen element and the transition metal element is tested by the linear scanning of the energy spectrum of a scanning electron microscope. When in testing, the pole piece of the negative active material is firstly cut along the section by using an ion polishing or liquid nitrogen brittle fracture mode, the centrally cut negative active material particles are found in a scanning electron microscope, a straight line is drawn from the inside of the particles to the surface, the linear scanning energy spectrum test is carried out along the straight line, and N elements and transition metal elements are selected as test elements.
In some embodiments, if the average length from the volume center to the surface of the anode active material is set to L, the mass of the nitrogen element and the transition metal element on the surface of the anode active material is set to n, the mass percentage content m of the nitrogen element or the transition metal element in the anode active material at any point apart from the surface by the length of L is (n × L)/L, and the following conditions are satisfied: m is more than or equal to 0 and less than or equal to 1. Therefore, gradient distribution of the in-situ grown carbon material can be realized, and the sliding effect of the hard carbon particles can be increased.
Hereinafter, a process of preparing the anode active material is briefly described to better understand the present application, but this is merely exemplary and not intended to limit the present application. In some embodiments, a method of preparing a hard carbon-containing anode active material includes the steps of: dispersing a hard carbon material in a first solvent to prepare a first solution; adding a nitrogen-containing raw material of a carbon material and a transition metal nitrate into the first solution to obtain a uniform second solution; and stirring and evaporating the second solution, and performing heat treatment under inert gas to obtain the negative active material. In some embodiments, the first solvent comprises at least one of distilled water, ethanol, dimethylformamide, or tetrahydrofuran. In some embodiments, the nitrogen-containing starting material of the carbon material comprises at least one of melamine, dicyanodiamine, methylimidazole, bipyridine amine, o-phenylenediamine, bipyridine, dibromobipyridine, bipyridine, phenanthroline, dibromophenanthroline, or imidazopyridine. In some embodiments, the transition metal nitrate comprises Co (NO)3)2、Fe(NO3)3、Cr(NO3)3、H2PtCl6、Mn(NO3)2、AgNO3、Ni(NO3)2Or Zn (NO)3)2At least one of (1). It is to be understood that this method of preparation is exemplary only and that other suitable methods of preparation may also be employed.
In some embodiments, carbon materials of different morphologies can be obtained by adding different small molecule carbon sources. For example, dicyandiamide is used as a carbon source, cobalt nitrate is used as a transition metal salt, a fibrous carbon material can be grown in situ on the surface of hard carbon particles, and the fibrous carbon material is located on the surface of the hard carbon particles, so that the contact problem between the hard carbon particles can be effectively improved, the barrier film and a negative current collector are prevented from being punctured by the hard carbon, the slippage between the hard carbon particles can be effectively increased, and the brittle failure problem can be improved. For example, when o-phenylenediamine is used as a carbon source and cobalt nitrate is used as a transition metal salt, a flaky carbon material can be grown in situ on the surface of the hard carbon particles, and the flaky carbon material is positioned on the surface of the hard carbon particles, so that the contact problem between the hard carbon particles can be effectively improved, the barrier film and the negative electrode current collector are prevented from being punctured by the hard carbon, and the slippage between the hard carbon particles is effectively increased. In addition, the carbon residue rate of the carbon material cracked by the small molecular carbon source is different due to different contents of the transition metal salt. For example, when o-phenylenediamine is used as a carbon source and cobalt nitrate is used as a transition metal salt, the carbon residue rate is 10% when the cobalt nitrate content is 1%, and the carbon residue rate can reach 50% when the cobalt nitrate content is 10%.
In some embodiments, a conductive agent and a binder may also be included in the negative active material layer. In some embodiments, the conductive agent in the negative 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 active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinyl pyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the negative active material, the conductive agent, and the binder in the negative active material layer may be (78 to 98.5): (0.1 to 10): (0.1 to 10). The anode active material may be an anode active material containing hard carbon. It will be appreciated that the above description is merely exemplary and that any other suitable materials and mass ratios may be employed. In some embodiments, the negative electrode current collector may employ at least one of a copper foil, a nickel foil, or a carbon-based current collector.
Embodiments of the present application also provide an electrochemical device including an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. In some embodiments, the negative electrode is any one of the negative electrodes described above.
In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited. 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 electrolytic solution.
In some embodiments, the electrolyte comprises at least one of fluoroether, fluoroethylene carbonate, or ether nitrile. In some embodiments, the electrolyte further comprises a lithium salt comprising lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate, the concentration of the lithium salt being from 1 to 2mol/L, and the molar ratio of lithium bis (fluorosulfonyl) imide to lithium hexafluorophosphate being from 0.05 to 4.
In some embodiments, the electrolyte may further include a non-aqueous solvent. The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.
The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.
Examples of the chain carbonate compound 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 the cyclic carbonate compound are Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), or a combination thereof. Examples of the fluoro carbonate compound are fluoroethylene carbonate (FEC), 1, 2-difluoroethylene carbonate, 1, 2-trifluoroethylene carbonate, 1,2, 2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1, 2-difluoro-1-methylethylene carbonate, 1, 2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or a combination thereof.
Examples of carboxylate compounds are methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ -butyrolactone, decalactone, valerolactone, mevalonic lactone, caprolactone, methyl formate, or combinations thereof.
Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1, 2-dimethoxyethane, 1, 2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.
Examples of other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.
In some embodiments, the positive electrode includes a current collector and a positive active material layer disposed on the current collector, and the positive active material layer may include a positive active material. In some embodiments, the positive active material comprises at least one of lithium cobaltate, lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, lithium vanadium phosphate, sodium vanadium phosphate, lithium vanadyl phosphate, sodium vanadyl phosphate, lithium vanadate, lithium manganate, lithium nickelate, lithium nickel cobalt manganese, a lithium rich manganese based material, or lithium nickel cobalt aluminate. In some embodiments, the positive electrode active material layer may further include a conductive agent. In some embodiments, the conductive agent in the positive 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 positive electrode active material layer may further include a binder, and the binder in the positive electrode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer may be (80 to 99): (0.1 to 10): (0.1 to 10). In some embodiments, the thickness of the positive electrode active material layer may be 10 μm to 500 μm. It should be understood that the above description is merely an example, and any other suitable material, thickness, and mass ratio may be employed for the positive electrode active material layer.
In some embodiments, the current collector of the positive electrode may be an Al foil, but of course, other current collectors commonly used in the art may be used. In some embodiments, the thickness of the current collector of the positive electrode may be 1 μm to 50 μm. In some embodiments, the positive electrode active material layer may be coated only on a partial area of the current collector of the positive electrode.
In some embodiments, the separator comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a 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 separator may further include a porous layer disposed on at least one surface of the separator, the porous layer including inorganic particles selected from alumina (Al) and a binder2O3) Silicon oxide (SiO)2) Magnesium oxide (MgO), titanium oxide (TiO)2) Hafnium oxide (HfO)2) Tin oxide (SnO)2) Cerium oxide (CeO)2) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)2) Yttrium oxide (Y)2O3) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator film have a diameter in the range of about 0.01 μm to 1 μm. The binder of the porous layer is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the pole piece.
In some embodiments of the present application, the electrode assembly of the electrochemical device is a wound electrode assembly, a stacked electrode assembly, or a folded electrode assembly. In some embodiments, the positive electrode and/or the negative electrode of the electrochemical device may be a multilayer structure formed by winding or stacking, or may be a single-layer structure in which a single-layer positive electrode, a single-layer negative electrode, and a separator are stacked.
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 sequentially wound or stacked to form an electrode member, and then the electrode member is placed in, for example, an aluminum plastic film for packaging, and an electrolyte is injected into the electrode member for formation and packaging, so as to form the lithium ion battery. And then, performing performance test on the prepared lithium ion battery.
Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure of the present application.
Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, an unmanned aerial vehicle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.
In the following, some specific examples and comparative examples are listed to better illustrate the present application, wherein a lithium ion battery is taken as an example.
Example 1
Preparation of the positive electrode: mixing a positive electrode active material lithium cobaltate, conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) according to a weight ratio of 97: 1.4: 1.6, adding N-methyl pyrrolidone (NMP) as a solvent, and uniformly stirring. And uniformly coating the slurry (with the solid content of 72 wt%) on an aluminum foil of a current collector of the positive electrode, wherein the coating thickness is 80 mu m, drying at 85 ℃, then carrying out cold pressing, cutting into pieces, slitting, and drying for 4 hours at 85 ℃ under a vacuum condition to obtain the positive electrode.
Preparation of a negative electrode: mixing commercial artificial hard carbon, binder styrene butadiene rubber and sodium carboxymethylcellulose (CMC) according to a weight ratio of 97:2:1 in deionized water to form a negative electrode slurry (40 wt% solids). And (2) adopting copper foil with the thickness of 10 microns as a negative current collector, coating the negative slurry on the current collector of the negative electrode, drying at 85 ℃, then carrying out cold pressing, cutting into pieces, slitting, and drying for 12 hours at 120 ℃ under a vacuum condition to obtain the negative electrode.
Preparing an isolating membrane: the separator was 7 μm thick Polyethylene (PE).
Preparing an electrolyte: in a dry argon atmosphere glove box, Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) are mixed according to the mass ratio of EC to EMC to DEC to 30:50:20, 1.5 wt% of 1, 3-propane sultone and 2 wt% of fluoroethylene carbonate are added, dissolved and fully stirred, and then lithium salt LiPF is added6Mixing uniformly to obtain electrolyte, wherein LiPF6The concentration of (2) is 1 mol/L.
Preparing a lithium ion battery: and sequentially stacking the anode, the isolating membrane and the cathode in sequence to enable the isolating membrane to be positioned between the anode and the cathode to play an isolating role, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an outer packaging aluminum-plastic film, dehydrating at 80 ℃, injecting the electrolyte, packaging, and performing technological processes such as formation, degassing, edge cutting and the like to obtain the lithium ion battery.
In other examples and comparative examples, parameters were changed in addition to the procedure of example 1, and specific changed parameters were as follows.
Example 2 is different from example 1 in that an anode active material containing hard carbon is used, and the anode active material containing hard carbon is prepared by the following method as in example 1:
dispersing 20g of a hard carbon material in 100mL of a solvent to prepare a solution a, wherein the solvent is distilled water; then, 2g of a small molecule material (the small molecule material is dihydrodiamine) and a certain proportion of a transition metal salt (Co (NO)3)2·6H2O) is added into the solution A to obtain a uniform solution B, and the mass ratio of the transition metal in the nitrate to the small molecular material is 20 percent; stirring the solution B at 25 ℃ for 2h, then heating to evaporate the solvent, and obtaining a sample in N2Calcining at 900 ℃ for 2h under the atmosphere. And after cooling, sieving the powder by a 300-standard sieve to obtain the hard carbon-containing negative active material.
Examples 3 to 7 are substantially the same as example 2 except that the mass ratio of the transition metal in the nitrate to the small molecule material is different. The mass ratios of the transition metal to the small molecule material in the nitrates of examples 3 to 7 were 10%, 5%, 2%, 1%, 0%, respectively, and comparative example 1 was the same as example 1 except that the hard carbon in example 1 was replaced with graphite.
The small molecule materials and the mass ratio of the transition metal to the small molecule material in the nitrate in examples 8 to 13 are different from those in example 2, and the other points are the same as those in example 2. The small molecule materials of examples 8 to 13 were replaced with o-phenylenediamine. The mass ratios of the transition metal to the small molecule material in the nitrates of examples 8 to 13 were 20%, 10%, 5%, 2%, 1%, 0%, respectively.
The small molecule materials, the nitrate species, and/or the mass ratio of the transition metal to the small molecule material in the nitrate in examples 14 to 33 are different from example 2, and are otherwise the same as example 2, see the following table specifically.
The small molecule material, the mass ratio of the transition metal in the nitrate to the small molecule material, the Dv50 of the hard carbon particles, and the morphology and size of the carbon material in example 34 were different from those in example 5, and were otherwise the same as in example 5.
The following describes a method of testing various parameters of the present application.
And (3) testing the adhesive force:
the hard carbon negative electrode active material, Styrene Butadiene Rubber (SBR) and sodium carboxymethyl cellulose (CMC) are fully stirred and mixed in a proper amount of deionized water according to the weight ratio of 97:2:1 to form uniform negative electrode slurry, wherein the solid content of the negative electrode slurry is 40 wt%. The slurry was coated on a negative current collector (6 μm copper foil) and double-coated with a coating weight of 5mg/cm2To 8mg/cm2After applicationDrying at 85 ℃, then carrying out cold pressing, cutting into pieces and cutting, and drying for 12 hours at 120 ℃ under vacuum condition to obtain the cathode.
Fixing the obtained negative plate (with the width of 30mm and the length of 100 mm-160 mm) on a steel plate by using double-sided adhesive paper (the model: 3M9448A, the width of 20mm and the length of 90 mm-150 mm), attaching the adhesive paper on the surface of a negative active material layer, connecting one side of the adhesive paper with a paper tape with the same width, adjusting a limiting block of a tensile machine to a proper position, turning over and sliding the paper tape upwards for 40mm at the sliding speed of 50mm/min, and testing the adhesive force between the negative active material layer and a negative current collector under 180 degrees (namely, stretching in the opposite direction).
Measurement of cohesion of negative electrode active material:
the test was carried out using an Instron (model 33652) tester: fixing a negative electrode (with the width of 30mm and the length of 100 mm-160 mm) on a steel plate by using double-sided adhesive paper (the model: 3M9448A, with the width of 20mm and the length of 90 mm-150 mm), attaching the adhesive paper on the surface of a negative electrode active material layer, connecting one side of the adhesive paper with a paper tape with the same width, adjusting a limiting block of a tensile machine to a proper position, turning over and sliding the paper tape upwards for 40mm at the sliding speed of 50mm/min, and testing the polymerization strength between negative electrode active materials in the negative electrode active material layer at 180 degrees (namely, stretching in the opposite direction).
Testing the resistance of the diaphragm:
taking the area as 154mm2The test temperature of the negative electrode small wafer is room temperature, the pressure is 0.4T, the pressure intensity is 26MPa, 10 points at different positions are taken in each test, and the average value is taken.
And (3) strip breakage test:
the broken belt refers to the situation that the negative electrode is brittle and broken in the process before the negative electrode passes through the cold pressing roller and is wound. The current collector of the negative electrode is 6 μm copper foil, and the single-side coating weight of the negative electrode is 5mg/cm2To 8mg/cm2(ii) a The cathode material in the cathode is hard carbon material, and the 5 ton powder compaction density is 0.9g/cm3To 1.2g/cm3(ii) a The cold-pressed compacted density of the cathode in the cold-pressing process is between 0.9g/cm3To 1.2g/cm3Sheets of winding-up devices of cold-pressing apparatusThe force is between 3N and 10N.
The belt breakage is divided into serious belt breakage, medium belt breakage and light belt breakage according to the belt breakage degree; in the process of cold pressing the cathode for every 10 meters, the condition that the cathode is subjected to brittle failure for 4 times or more is taken as a serious broken belt, the condition that the cathode is subjected to brittle failure for 2 times to 3 times is taken as a medium broken belt, and the condition that the cathode is subjected to brittle failure for 1 time is taken as a slight broken belt.
Capacity retention rate of lithium ion battery after 400 cycles:
and (3) placing the lithium ion battery in a constant temperature box at 45 ℃, standing for 30 minutes to test the initial thickness of the lithium ion battery after the lithium ion battery reaches a constant temperature. The lithium ion battery reaching a constant temperature was charged at a constant current of 0.5C to a voltage of 4.2V, then charged at a constant voltage of 4.2V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3.0V, which is a charge-discharge cycle. And (3) repeatedly carrying out charge-discharge cycles for 400 circles by taking the capacity of the first discharge as 100%, stopping the test, recording the cycle capacity retention rate, simultaneously measuring the thickness of the battery, and taking the capacity retention rate and the thickness expansion rate as indexes for evaluating the cycle performance of the lithium ion battery.
The cycle capacity retention ratio is the capacity at the time of cycle to 400 cycles/the capacity at the time of first discharge × 100%.
The thickness expansion rate of the lithium ion battery was calculated as follows:
the thickness change of the lithium ion battery after 400 cycles is equal to (the thickness of the battery after 400 cycles-the initial thickness of the battery)/the initial thickness of the battery multiplied by 100%.
The formula for the compaction density described herein is: the compacted density is the mass of the negative electrode material/the stressed area of the negative electrode material/the thickness of the sample; the calculation formula of the cold pressing compaction density is as follows: cold press compacted density is the mass of the negative electrode material/area of negative electrode material forced/thickness of the sample.
Table 1 shows the respective parameters and evaluation results of examples 1 to 13 and comparative example 1.
TABLE 1
And (4) surface note: the mass content of the transition metal element and the mass content of the nitrogen element both refer to the mass ratio of the transition metal element and the nitrogen element in the calcined sample to the whole anode active material. The mass ratio of the transition metal element to the small molecule material in the nitrate refers to the ratio of the weight of the transition metal to the weight of the small molecule material in the entire nitrate, and as in example 3, the weight of the nitrate added is 2g, the weight of the Co element is (2g × 59)/291 ═ 0.4g, and the weight of the small molecule material added is 2g, so the ratio of the transition metal to the small molecule in the nitrate is 0.4g/2g ═ 20% (the calculation in other examples is the same). In the present application, theoretically all diamines are possible (all small carbon-containing molecules with amino groups) since small molecules contain N and can be bound to transition metal elements.
As can be seen by comparing example 1 and comparative example 1, by using hard carbon as the anode active material, the adhesive force between the anode active material layer and the anode current collector was significantly increased. And, compare in graphite material, the diaphragm resistance of hard carbon material is less, does benefit to its promotion of quick charge-discharge performance.
It can be seen from comparison of examples 1,2 and 3 that, by using the negative active material of the modified hard carbon composite particles, compared with using hard carbon, the binding force between the negative active material layer and the negative current collector can be further increased, and examples 2 and 3 have substantially no band breakage, and the content of the transition metal nitrate cannot be too high, and if the content is too high, the content of the transition metal in the composite particles is too high, and the transition metal is agglomerated into small particles, which affects the contact between the carbon material for small molecule conversion and the hard carbon substrate.
The graphite material is soft, so that the belt breakage in processing can not occur, and compared with the hard carbon material, the belt breakage in processing can be avoided due to the fact that the hard carbon material is hard and sharp in edges and corners. The hard carbon of example 1 was hard and sharp in edge angle, and thus was severely broken because of the hard material, which caused no slip and buffer space between particles during processing, and large stress between particles, resulting in brittle fracture. In examples 2 to 6 and 8 to 12, a carbon material that can assist in sliding and buffer the inter-particle stress is grown in situ on the surface of the hard carbon, and wraps the sharp edge of the hard carbon substrate, so that the problem of sharp edge of the hard carbon substrate can be solved, the adhesion between the particles and the current collector is improved, and meanwhile, the condition of processing band breakage is improved, so that the processing performance is improved, and the condition of processing band breakage does not occur. In examples 7 and 13, only small molecules are added, but transition metal salt is not added, so that the small molecules are completely volatilized in the calcining process, and a carbon material cannot grow on the surface of hard carbon, so that the problem of belt breakage in processing is not solved.
Comparative example 1 is graphite which has not been modified with small molecules and nitrates and has a lower binding power than hard carbon, but because graphite is soft and has a layered structure and can slip during cold pressing, ribbon breakage does not occur. However, compared to hard carbon, especially modified hard carbon, graphite has a larger sheet resistance, which is not favorable for outputting fast charge and discharge performance.
Table 2 shows the respective parameters and evaluation results of examples 14 to 33 and comparative example 1.
TABLE 2
Table 2 is an extension of the cobalt nitrate in table 1 to other nitrates such as iron nitrate and zinc nitrate. The transition metal element in the transition metal nitrate is expanded from Co to Fe and Zn, the purposes of improving the processing performance and reducing the resistance of the diaphragm can be achieved, and the strip breakage condition of the electrode consisting of the obtained cathode active material is improved. As can be seen from comparison of examples 14 to 18, as the content of the transition metal salt gradually increased, the adhesion and cohesive strength of the electrode sheet composed in the obtained negative active material were improved, and the processing tape breakage was also improved. By comparing examples 14 to 18 with examples 19 to 23, it can be seen that the same rule as in examples 14 to 18 can be obtained by using different types of small molecule materials. Similarly, it is understood from comparative examples 24 to 28 and comparative examples 29 to 33 that the same rules as in examples 14 to 18 can be obtained by using different kinds of transition metal salts.
Table 3 shows the respective parameters and evaluation results of examples 1,3, 9, 34 and comparative example 1.
TABLE 3
It can be seen from table 3 that different morphologies can be grown on the surface of the hard carbon particles by fixing the transition metal nitrate unchanged and changing the types of the small molecular materials, and the purpose of improving the processability can be achieved, the band breakage of the electrode composed of the obtained negative active material is improved, the sheet resistance is reduced, and the comprehensive performance of the battery is better.
Table 4 shows the respective parameters and evaluation results of examples 35 to 37 and example 1.
And (4) surface note: examples 35 to 37 were compared with example 3 except that the electrolyte composition was as shown in Table 4.
As can be seen from Table 4, by comparing example 1 with comparative example 1, LiC was formed after intercalation of lithium into the graphite material6The intercalation compound has certain volume expansion, so the thickness of the lithium ion battery is increased along with the increase of the cycle number of the lithium ion battery, and the thickness is increased by 12 percent after 400 cycles. And hard carbon material due to d002The large surface spacing (about 0.36nm to 0.4nm), the existence of a large number of micropores and the isotropic property of the micropores enable the hard carbon material to have almost no volume change after lithium intercalation, and the thickness change of the electrode after 400 cycles is small and is less than or equal to 5%. Especially after the small molecular carbon material is modified, the buffering among particles is increased and the volume is expandedThe swelling changes less.
On the other hand, examples 35 to 37 show that by changing the concentration and composition of the lithium salt of the electrolyte, the thickness swell is suppressed, and the cycle performance and the thickness swell performance are better.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other combinations of features described above or equivalents thereof. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.
Claims (10)
1. A negative electrode comprising a negative electrode current collector and a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the adhesion between the negative electrode active material layer and the negative electrode current collector being greater than or equal to 7N/m.
2. The negative electrode according to claim 1, wherein a cohesive force between the negative electrode active material layer and the negative electrode current collector is greater than or equal to 10N/m.
3. The anode of claim 1, wherein the anode active material comprises hard carbon.
4. The anode of claim 1, wherein at least one of conditions (a) to (d) is satisfied:
(a) a carbon material grows in situ on the surface of the negative active material;
(b) the anode active material has Dv50 of 6 to 20 μm;
(c) the negative active material further includes a nitrogen element and a transition metal element;
(d) the cohesion of the negative electrode active material is 5N/m to 100N/m.
5. The anode of claim 4, wherein at least one of conditions (e) to (h) is satisfied:
(e) the surface in-situ growth carbon material comprises at least one of fibrous carbon material, flaky carbon material or granular carbon material;
(f) the mass of the transition metal element in the negative electrode active material is 0.1% to 10%, and the mass of the nitrogen element in the negative electrode active material is 0.1% to 5%;
(g) the transition metal element comprises at least one of Co, Fe, Cr, Pt, Cu, Mn, Ag, Ni or Zn;
(h) the content by mass of the nitrogen element or the transition metal element in the anode active material particle gradually decreases from the surface of the anode active material particle to the center of the anode active material particle.
6. The anode of claim 5, wherein at least one of conditions (i) to (k) is satisfied:
(i) the fibrous carbon material has a diameter of 50nm to 500nm and a length of more than 1 μm;
(j) the length of the flaky carbon material is more than 1 mu m;
(k) the particulate carbon material has an average particle diameter of 50nm to 500 nm.
7. An electrochemical device comprising an electrolyte, a separator, a positive electrode, and the negative electrode according to any one of claims 1 to 6, the separator being disposed between the positive electrode and the negative electrode.
8. The electrochemical device of claim 7, wherein the electrolyte comprises at least one of fluoroether, fluoroether carbonate, or ether nitrile.
9. The electrochemical device according to claim 7, wherein the electrolyte includes a lithium salt including lithium bis (fluorosulfonyl) imide and lithium hexafluorophosphate, a concentration of the lithium salt is 1 to 2mol/L, and a molar ratio of the lithium bis (fluorosulfonyl) imide to the lithium hexafluorophosphate is 0.05 to 4.
10. An electronic device comprising the electrochemical device according to any one of claims 7 to 9.
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| CN115036464A (en) * | 2022-08-11 | 2022-09-09 | 宁德新能源科技有限公司 | Electrochemical device and electricity utilization device |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN115036464A (en) * | 2022-08-11 | 2022-09-09 | 宁德新能源科技有限公司 | Electrochemical device and electricity utilization device |
| CN115036464B (en) * | 2022-08-11 | 2022-11-15 | 宁德新能源科技有限公司 | Electrochemical device and power utilization device |
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