CN115332532B - Hard carbon material and preparation method thereof - Google Patents

Hard carbon material and preparation method thereof Download PDF

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CN115332532B
CN115332532B CN202211247384.8A CN202211247384A CN115332532B CN 115332532 B CN115332532 B CN 115332532B CN 202211247384 A CN202211247384 A CN 202211247384A CN 115332532 B CN115332532 B CN 115332532B
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hard carbon
carbon material
capacity
lithium
gram capacity
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CN115332532A (en
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谭福金
易政
郑子桂
谢远森
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Ningde Amperex Technology Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/05—Preparation or purification of carbon not covered by groups C01B32/15, C01B32/20, C01B32/25, C01B32/30
    • 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
    • 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
    • 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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

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  • Inorganic Chemistry (AREA)
  • Organic Chemistry (AREA)
  • Carbon And Carbon Compounds (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The present application provides a hard carbon material comprising carbon formed of a phenolic resin, wherein, when metallic lithium is used as a counter electrode, the ratio of reversible gram capacity between 0 and 0.20V to total reversible gram capacity in lithium removal capacity is 0.80 to 0.86; when metallic sodium is used as a counter electrode, the ratio of reversible gram capacity between 0 and 0.20V to the total reversible gram capacity in the sodium removal capacity is 0.75 to 0.86. The method for preparing the hard carbon material comprises the following steps: (i) Providing phenolic resin, and pyrolyzing the phenolic resin through carbonization to obtain resin pyrolytic carbon; (ii) (ii) mixing the resin pyrolytic carbon from step (i) with hexamethylenetetramine to obtain a blend; (iii) (iii) pyrolytically coating the blend from step (ii) to obtain a hard carbon material.

Description

Hard carbon material and preparation method thereof
Technical Field
The application relates to the field of lithium ion batteries, in particular to a hard carbon material and a preparation method thereof.
Background
Since the commercialization of lithium ion batteries by Sony corporation of japan in 1991, lithium ion batteries have rapidly gained wide applications in the fields of mobile phones, miniature cameras, palm computers, notebook computers, etc. due to their advantages of high energy density, high operating voltage, good load characteristics, fast charging speed, safety, no pollution, etc.
In the composition of lithium ion batteries, a negative electrode material plays an important role. At present, the specific capacity of graphite is close to the theoretical capacity (372 mAh/g), and is difficult to further promote, and meanwhile, the specific capacity cannot meet the requirements of new energy storage equipment, electric automobiles and other large-scale electronic equipment on high-capacity and high-rate discharge. Therefore, the research and preparation of novel high-capacity and high-rate lithium ion battery cathode materials are the key for the continuous development of lithium ion batteries.
The internal structure of the hard carbon material is composed of disordered carbon layers, and a large number of defects and holes exist inside the hard carbon material. The structure different from graphite provides a certain space for the storage of sodium ions and lithium ions, so that the hard carbon material has a long and stable platform region for the sodium storage and lithium storage charging and discharging curves. Among the numerous reported battery negative electrode materials, hard carbon is considered to be one of the most potential battery electrode materials due to its advantages of high reversible specific capacity, good cycling stability, low reaction voltage plateau, low raw material cost, and the like. Most of hard carbon materials in the current research have low first coulombic efficiency, pore utilization rate and energy density and platform capacity caused by the first coulombic efficiency and the pore utilization rate, so that the application of the hard carbon is difficult to further popularize.
Disclosure of Invention
In order to solve the above problems, an object of the present application is to provide a hard carbon material and a method of preparing the hard carbon material.
In a first aspect, the present application provides a hard carbon material, wherein the hard carbon material has a thickness of 0.01 cm 3 G to 0.09 cm 3 A pore volume in the range of/g, and a ratio of reversible gram-volume between 0 and 0.20V to reversible gram-volume of 0 to 2.5V is 0.75 to 0.86. The hard carbon material of the present application has a significantly smaller pore volume than the hard carbon anode materials of the prior art, especially at similar compacted densities, because there are a considerable amount of closed pores in the hard carbon material of the present application, which increase the capacity for lithium and sodium storage while ensuring the energy density of the material.
According to some embodiments of the present application, the hard carbon material has a carbon content in the range of 0.5 to 1.0 g/cm 3 A compacted density in the range of 5 to 70m 2 The specific surface area in the range of/g, the compaction density and the specific surface area are smaller, so that the material can have higher energy density and higher lithium/sodium storage capacity.
According to some embodiments of the present application, the hard carbon material has a reversible gram capacity between 0 and 0.20V of 230 to 570mAh/g.
According to some embodiments of the present application, when metallic lithium is used as the counter electrode, in the delithiation capacity of the hard carbon material, the ratio of the reversible gram capacity between 0 and 0.20V (vs Li +/Li) to the reversible gram capacity between 0 and 2.5V is 0.80 to 0.86, wherein the reversible gram capacity between 0 and 0.20V (vs Li +/Li) is 380 to 570mAh/g.
According to some embodiments of the present application, when metallic sodium is used as the counter electrode, in the sodium removal capacity of the hard carbon material, the ratio of the reversible gram capacity between 0 and 0.20V (vs Na +/Na) to the reversible gram capacity between 0 and 2.5V is 0.75 to 0.86, wherein the reversible gram capacity between 0 and 0.20V (vs Na +/Na) is 230 to 370 mAh/g.
According to some embodiments of the present application, the hard carbon material comprises a hard carbon material obtained by phenolic resin preparation.
According to some embodiments of the present application, the hard carbon material further comprises a metal compound, the metal compound comprises one or two of silver nitrate, cobalt nitrate, antimony chloride and tin chloride, and metal elements in the metal compound facilitate deposition of lithium and sodium in pores, so that sodium storage and lithium storage capacity of the hard carbon material can be improved, and energy density can be increased.
In a second aspect, the present application provides a method for preparing a hard carbon material, wherein the method comprises the steps of:
(i) Providing phenolic resin, and pyrolyzing the phenolic resin through carbonization to obtain resin pyrolytic carbon;
(ii) (ii) mixing the resin pyrolytic carbon from step (i) with hexamethylenetetramine to obtain a blend;
(iii) (iii) pyrolytically coating the blend from step (ii) to obtain a hard carbon material.
According to some embodiments of the present application, in step (i) the phenolic resin comprises a metal compound comprising one or both of silver nitrate, cobalt nitrate, antimony chloride and tin chloride.
According to some embodiments of the present application, the phenolic resin is provided in step (i) via the steps of:
(i.1) adding formaldehyde and glacial acetic acid into deionized water, then sequentially adding resorcinol, ammonium bicarbonate and a metal compound, and stirring to obtain a solution;
(i.2) heating the solution obtained from step (i.1) to obtain a phenolic resin;
(i.3) drying the phenolic resin obtained from step (i.2) to obtain a dried phenolic resin.
By means of the method, the hard carbon material which is rich in pores and communicated with the pore channels is synthesized by adopting the phenolic resin raw material, so that the utilization rate of the pores is improved, the closed-pore lithium and sodium storage amount is increased while the lithium ions or the sodium ions are rapidly diffused in the pore channels, and the energy density of the battery is improved.
According to some embodiments of the present application, in step (i.1), the stirring is carried out for more than about 30 minutes to obtain a solution.
According to some embodiments of the present application, in step (i.1), the volume ratio of deionized water to formaldehyde is in the range of 0 to 1.
According to some embodiments of the present application, in step (i.1), the mass ratio of glacial acetic acid to formaldehyde is in the range of 0 to 20.
According to some embodiments of the present application, in step (i.1), the metal compound includes one or two of silver nitrate, cobalt nitrate, antimony chloride and tin chloride, wherein the mass ratio of the metal element in the metal compound to resorcinol is in the range of 0 to 5. And a small amount of metal elements are introduced to facilitate the deposition of lithium and sodium in pores, so that the sodium storage capacity and the lithium storage capacity of the hard carbon material are improved. Meanwhile, too high content of metal elements may reduce the energy density of the hard carbon material, and too low content of metal elements may reduce the effect of lithium and sodium deposition in the pores.
According to some embodiments of the present application, in step (i.2), the mixture in the solution is chemically reacted under heating, wherein the reaction is carried out in a reaction kettle by oven heating, and a solid phenolic resin is obtained after the reaction.
According to some embodiments of the present application, the heating temperature in step (i.2) is in a range of 60 to 150 ℃, and the heating time is in a range of 6 to 24 hours, wherein the formaldehyde and the resorcinol are polymerized and crosslinked to different degrees at different hydrothermal reaction temperatures, too long a time can cause agglomeration of the phenolic resin material to cause irregularity of the macrostructure, thereby affecting the overall electrochemical performance, and too short a reaction time can cause too low a degree of crosslinking of the phenolic resin, thereby causing low reversible sodium and lithium storage capacities of the pyrolyzed hard carbon material.
According to some embodiments of the present application, in step (i.3), the solid resin obtained from step (i.2) is crushed and placed in an oven to dry to remove all excess water, acid and formaldehyde, thereby obtaining a dried phenolic resin, wherein a large number of open pores can be left in the dried phenolic resin by means of volatilization of the solvent. In particular, the dry phenolic resin has a thickness of 20m 2 G to 100m 2 Specific surface area/g, pore size of 10nm to 500 nm and particle size of 1 μm to 200. Mu.m.
According to some embodiments of the present application, the drying process in step (i.3) is first incubation at 120 ℃ for 2 to 6 hours, followed by warming to a temperature in the range of 150 to 200 ℃ for 2 to 20 hours.
According to some embodiments of the present application, the carbonization pyrolysis is performed in step (i) at a ramp rate of 1 to 10 ℃/min and a target temperature of 800 to 1500 ℃, wherein the holding time at the target temperature is 2 to 5 hours, preferably the carbonization pyrolysis is performed under an inert gas atmosphere, such as a nitrogen atmosphere.
According to some embodiments of the present application, in step (i), the resin pyrolytic carbon is obtained after washing the product obtained by pyrolysis with ethanol and deionized water in sequence, followed by drying and sieving, preferably, the resin pyrolytic carbon has 500 to 1500 m 2 Specific surface area/g, pore size from 0.6 to 150 nm, particle size from 1 to 200 μm, pore volume from 0.1 to 1.2 cm, and porosity from 20% to 80%. Wherein too high a specific surface area and porosity results in too low a compacted density and thus a low energy density of the material; too small a pore size will result in a decrease in the pore volume after coating and the sodium storage capacity for lithium and sodium in the pores, whereas too large a pore size will result in a coatingThe coating is incomplete and closed pores cannot be formed, so that the purposes of lithium storage and sodium storage cannot be achieved.
According to some embodiments of the present application, in step (ii), hexamethylenetetramine is mixed, in particular shear-break mixing, with the resin pyrolytic carbon in a mass ratio of 1.
According to some embodiments of the present application, the pyrolytic coating is performed in step (iii) at a ramp rate of 1 to 10 ℃/min and a target temperature of 800 to 1200 ℃, wherein the incubation time at the target temperature is 2 to 5 hours.
According to some embodiments of the present application, in step (iii), the pyrolysis coating is carried out under an inert gas atmosphere, such as a nitrogen atmosphere.
With the pyrolytic coating according to the present application, a suitable amount of coating can change the open pores to closed pores, thereby reducing the specific surface area and pore volume of the hard carbon material, thereby increasing the low plateau capacity. When the coating ratio is too high, a decrease in specific capacity may result, while too thick a coating layer may result in increased resistance to diffusion of desolvated ions into the pores and a decrease in low plateau capacity. When the coating proportion is too low, the number of open pores is large, the SEI film is excessively formed, and the purposes of closing pores and storing lithium and sodium are difficult to achieve.
In a third aspect of the present application, there is provided an electrochemical device, in particular a lithium-ion or sodium-ion battery, comprising a hard carbon material according to the first aspect of the present application.
Drawings
Fig. 1 schematically shows a nitrogen adsorption-desorption graph of a resin pyrolytic carbon according to example 1 of the present application;
FIG. 2 is a schematic view showing the pore size distribution of a resin pyrolytic carbon according to example 1 of the present application;
FIG. 3 schematically shows a cross-sectional SEM image of a resin pyrolytic carbon according to example 1 of the present application;
FIG. 4 is a schematic view showing a particle size distribution of a resin pyrolytic carbon according to example 1 of the present application;
fig. 5 schematically illustrates a specific capacity plot of a lithium ion battery according to an embodiment of the present application;
fig. 6 schematically illustrates a specific capacity profile of a sodium ion battery according to an embodiment of the present application;
fig. 7 schematically shows a specific capacity profile of a sodium ion battery according to an embodiment of the present application.
Detailed Description
To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below with reference to the embodiments, and it is obvious that the described embodiments are a part of the embodiments of the present application, and not all of the embodiments. The embodiments described herein are illustrative and are provided to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application. All other embodiments obtained by those skilled in the art without any creative effort based on the technical solutions and the given embodiments provided in the present application belong to the protection scope of the present application.
For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Further, each separately disclosed point or individual value may itself, as a lower limit or upper limit, be combined with any other point or individual value or with other lower limit or upper limit to form a range not explicitly recited.
In the description herein, "above" and "below" include the present numbers unless otherwise specified.
Unless otherwise indicated, terms used in the present application have well-known meanings that are commonly understood by those skilled in the art. Unless otherwise indicated, the numerical values of the parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, the test can be performed according to the methods given in the examples of the present application).
A list of items to which the term "at least one of," "at least one of," or other similar term is connected may imply any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items a, B, and C are listed, the phrase "at least one of a, B, and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or all of A, B and C. Item A may comprise a single component or multiple components. Item B can comprise a single component or multiple components. Item C may comprise a single component or multiple components.
1. Negative electrode
The negative electrode includes a current collector and a negative electrode active material layer on a surface of the current collector, the negative electrode active material layer including the hard carbon material according to the first aspect. In some embodiments, the current collector comprises: copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.
In some embodiments, the negative active material layer further includes a binder including, but not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, or the like.
In some embodiments, the negative electrode active material layer further includes a conductive agent including, but not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.
The negative electrode of the present application may be prepared using a method known in the art. Generally, a hard carbon material, an optional conductive agent (e.g., carbon materials such as carbon black and metal particles), a binder (e.g., SBR), and other optional additives (e.g., PTC thermistor materials) are mixed together and dispersed in a solvent (e.g., deionized water), uniformly stirred and then uniformly coated on a negative current collector, and dried to obtain a negative electrode containing a negative membrane. As the negative electrode current collector, a material such as a metal foil or a porous metal plate may be used.
2. Positive electrode
Materials, compositions, and methods of making the positive electrode useful in embodiments of the present application include any of the techniques disclosed in the prior art.
In some embodiments, the positive electrode includes a current collector and a positive active material layer on the current collector.
In some embodiments, the positive active material includes a positive material capable of absorbing and releasing lithium or sodium. Lithium-releasing cathode materials include, but are not limited to, lithium cobaltate, lithium nickel cobalt manganese, lithium nickel cobalt aluminate, lithium manganate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials. The positive electrode material for releasing sodium may be at least one of transition metal layered oxide, sodium polyanion compound, prussian blue, prussian white, etc., such as cupronickel manganese oxide.
In some embodiments, the positive active material layer further includes a binder, and optionally a conductive material. The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector.
In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy, nylon, or the like.
In some embodiments, the conductive material includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fibers, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.
In some embodiments, the current collector may include, but is not limited to: aluminum.
The positive electrode may be prepared by a preparation method known in the art. For example, the positive electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include, but is not limited to: n-methylpyrrolidone. The electrochemical device has higher energy density and cycle performance, and can meet the application requirements.
3. Isolation film
According to some embodiments of the present application, the present application does not particularly limit the material and shape of the separation film, which may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.
The release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used.
At least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.
The inorganic layer includes inorganic particles selected from at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate, and a binder. The binder is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.
The polymer layer comprises a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride and poly (vinylidene fluoride-hexafluoropropylene).
4. Electrolyte solution
According to some embodiments of the present application, the composition of the electrolyte is not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the lithium electrolyte includes 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 1 to 2mol/L, and the molar ratio of lithium bis (fluorosulfonyl) imide to lithium hexafluorophosphate being 0.05 to 4.
In some embodiments, the sodium ion battery electrolyte comprises an organic solvent and a sodium salt, etc., wherein the organic solvent may be at least one of EC, PC, DMC, DEC, EMC, EA, FEC, VC, etc.; the sodium salt may be at least one of NaClO4, naPF6, naBF4, naFSI, naTFSI, etc.
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-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, gamma-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.
5. Electrochemical device
An electrochemical device includes a negative electrode, a positive electrode, an electrolyte, and a separator.
In some embodiments, the electrochemical devices of the present application include, but are not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors.
In some embodiments, the electrochemical device is a sodium ion battery.
In some embodiments, the electrochemical device is a lithium secondary battery.
In some embodiments, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.
Examples
In the following, some specific examples and comparative examples are listed to better illustrate the application, wherein lithium-ion and sodium-ion batteries are taken as examples.
Example 1
A hard carbon material according to example 1 was prepared by the following method:
(i.1) 100mL of formaldehyde and 5mL of glacial acetic acid were added to 15 mL of deionized water, followed by 78g of resorcinol and stirring. After resorcinol is dissolved, adding 1.1 g of ammonium bicarbonate to dissolve, continuously adding 2.42g of cobalt nitrate (the mass ratio of cobalt to resorcinol is 1;
(i.2) pouring the solution obtained from the step (i.1) into a 500mL reaction kettle, and heating and reacting for 24 hours in an oven at 85 ℃ to obtain a solid resin;
(i.3) crushing the solid resin obtained in the step (i.2), placing the crushed solid resin in an oven for drying, preserving heat at 120 ℃ for 2 hours, and then preserving heat at 150 ℃ for 10 hours to obtain dried resin;
(i.4) putting the dried resin obtained in the step (i.3) into a tube furnace for pyrolysis, introducing nitrogen, heating to 1100 ℃ at the speed of 5 ℃/min, and keeping the temperature for 3 hours. Washing the obtained product with ethanol twice, washing the product with deionized water three times, drying the product, and sieving the dried product with a 300-mesh sieve to obtain resin pyrolytic carbon;
(ii) (ii) subjecting the resin pyrolytic carbon obtained from the step (i.4) and hexamethylenetetramine to shear crushing and mixing to obtain a blend, wherein the mass ratio of the resin pyrolytic carbon to the hexamethylenetetramine is 1.
(iii) And (3) putting the crushed and mixed resin blend in the step (ii) into a tube furnace for pyrolysis coating, introducing nitrogen, heating to 900 ℃ at the speed of 5 ℃/min, and preserving heat for 3 h to obtain coated hard carbon, namely the hard carbon material.
The nitrogen adsorption/desorption curve of the resinous pyrolytic carbon obtained in step (i) of example 1 is shown in FIG. 1, and it can be seen that the resinous pyrolytic carbon material has micropores and mesopores, and the resinous pyrolytic carbon has 1112 m 2 Specific surface area in g.
The pore size distribution curve of the resinous pyrolytic carbon obtained in step (i) of example 1 is shown in FIG. 2, and it can be seen that the pore size of the resinous pyrolytic carbon has both micropores and mesopores having a pore size of 0.4nm to 6 nm and 0.46 cm 3 Pore volume per gram.
As shown in fig. 3, the SEM image of the cross section of the resin pyrolytic carbon obtained in step (i) of example 1 shows that mesopores of 2 to 10nm are not directly observed due to the influence of the resolution of the instrument, and thus the pore structure is not seen in the image, which indicates that there is no mesopore or the number of mesopores is small in the resin pyrolytic carbon obtained in step (i).
Preparation of negative electrode
And (2) fully stirring and mixing the hard carbon material prepared in the above step with Styrene Butadiene Rubber (SBR) and sodium carboxymethyl cellulose (CMC) in a proper amount of deionized water according to a weight ratio of 97. The slurry is coated on a negative current collector (copper foil or aluminum foil, copper foil optional for a lithium ion battery negative current collector and aluminum foil optional for a sodium ion battery negative current collector), dried at 85 ℃, and then dried for 12 hours under the vacuum condition of 120 ℃ after cold pressing, cutting and slitting, so as to obtain the negative electrode.
Preparation of positive electrode
Using lithium iron phosphate (LiFePO) 4 ) As the positive electrode of the lithium ion battery, copper nickel iron manganese oxide (NaCu) was used 1/ 9 Ni 2/9 Fe 1/3 Mn 1/3 O 2 ) As the positive electrode of the sodium ion battery.
Mixing the positive electrode active material (LiFePO) 4 Or NaCu 1/9 Ni 2/9 Fe 1/3 Mn 1/3 O 2 ) Conductive agent Super P and adhesive polyvinylidene fluorideEthylene (PVDF) was fully stirred and mixed in a suitable amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97.4. And coating the slurry on an aluminum foil of a positive current collector, and drying at 85 ℃ to obtain the positive electrode.
Preparation of electrolyte
In a dry argon atmosphere glove box, ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC) were mixed in a mass ratio of EC: PC: DEC =1:1:1, mixing; 1.5wt% of 1, 3-propane sultone is added, the mixture is fully stirred, and lithium salt LiPF is added 6 (in lithium ion batteries) or NaPF 6 (in a sodium ion battery), and mixing uniformly to obtain the electrolyte. In the electrolyte, liPF 6 Or NaPF 6 The concentration of (2) is 1mol/L.
Preparation of isolating film
Coated with Al on the surface 2 O 3 A Polyethylene (PE) porous polymer film having a thickness of 9 μm as a separator.
Preparation of lithium/sodium ion battery
Stacking the anode, the isolating membrane and the cathode in sequence to ensure that the isolating membrane is positioned between the anode and the cathode to play an isolating role, adding electrolyte, and packaging in a button stainless steel shell of the anode and the cathode to obtain the button lithium/sodium ion battery
The particle size distribution curve of the resinous pyrolytic carbon obtained in step (i) of example 1 is shown in FIG. 4, and it can be seen that the particle size D of the resinous pyrolytic carbon 50 And D 90 27 μm and 196 μm, respectively.
By the method introduced in the application, the hard carbon material obtained in example 1 is used to prepare the lithium ion button half cell, and no lithium precipitation occurs on the surface of the pole piece after the negative electrode of the lithium ion button half cell in example 1 is embedded with 800 mAh/g in constant volume. The charge and discharge curves of the lithium ion button half cell are shown in fig. 5, and it can be seen that the negative electrode of the lithium ion button half cell according to example 1 has 81% of first coulombic efficiency and 648 mAh/g of reversible specific capacity, wherein the low potential platform (0 to 0.20V) specific capacity is 480 mAh/g.
By the method described in this application, a sodium ion button half cell was prepared using the hard carbon material obtained in example 1, the first loop charge and discharge curve of which is shown in fig. 6, and it can be seen that the negative electrode of the sodium ion button half cell according to example 1 had a first coulombic efficiency of 67% and a reversible specific capacity of 330 mAh/g, wherein the low potential plateau (0 to 0.20V) specific capacity was 240 mAh/g.
Example 2
Example 2 was carried out using substantially the same method as example 1 except that in step (i.1), deionized water was added in an amount of 0mL, cobalt nitrate was added in an amount of 4.84g (mass ratio of Co to resorcinol was 2 to 100), and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Example 3
Example 3 was carried out using substantially the same method as example 1 except that in step (i.1), the amount of cobalt nitrate added was 4.84g (mass ratio of Co to resorcinol was 2.
Example 4
Example 4 was carried out using substantially the same method as example 1 except that in step (i.1), deionized water was added in an amount of 30 mL, cobalt nitrate was added in an amount of 4.84g (mass ratio of Co to resorcinol was 2 to 100), and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Example 5
Example 5 was carried out using substantially the same method as example 1, except that in step (i.1), the amount of deionized water added was 30 mL, the amount of cobalt nitrate added was 2.42g (mass ratio of Co to resorcinol was 1 to 100), and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Example 6
Example 6 was carried out using substantially the same method as example 1, except that in step (i.1), the amount of deionized water added was 30 mL, the amount of cobalt nitrate added was 0 g, and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Example 7
Example 7 was carried out using essentially the same procedure as example 1, except that in step (i.1), deionized water was added in an amount of 30 mL. The amount of cobalt nitrate added was 0 g, and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Example 8
Example 8 was carried out using essentially the same procedure as example 1, except that in step (i.1), deionized water was added in an amount of 60 mL. The amount of glacial acetic acid added was 10 mL, the amount of cobalt nitrate added was 0 g, the carbonization pyrolysis temperature in step (i.4) was 900 ℃, and the mass ratio of resin pyrolysis carbon to hexamethylenetetramine in step (ii) was 1.
Example 9
Example 9 was carried out using essentially the same procedure as example 1, except that in step (i.1), deionized water was added in an amount of 60 mL. Glacial acetic acid was added in an amount of 10 mL, cobalt nitrate was added in an amount of 0 g, and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Example 10
Example 10 was carried out using essentially the same procedure as example 1, except that in step (i.1), deionized water was added in an amount of 100 mL. The amount of cobalt nitrate added was 0 g, and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Example 11
Example 11 was carried out using essentially the same procedure as example 1, except that in step (i.1) deionized water was added in an amount of 100 mL. The amount of glacial acetic acid added was 15 mL. The amount of cobalt nitrate added was 0 g, and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Comparative example 1
Comparative example 1 was carried out using substantially the same method as in example 1 except that in step (i.1), the amount of cobalt nitrate added was 36.3 g (mass ratio of Co to resorcinol was 15.
Comparative example 2
Comparative example 2 was conducted using substantially the same method as in example 10 except that, in step (i.1), the amount of deionized water added was 200 mL.
Comparative example 3
Comparative example 3 was conducted using substantially the same method as in example 7 except that in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1.
Test method
1. Powder porosity test
Weighing 3g of sample, weighing to 0.0002 g, placing in a clean density bottle, injecting bubble-free n-butyl alcohol to 2/3 of the bottle, boiling for 3 min, not allowing the sample to splash, taking off the bottle, injecting the bubble-free n-butyl alcohol to a position slightly higher than a scribed line, placing another drop bottle only injected with the n-butyl alcohol into a constant temperature water bath, keeping the temperature at 25 +/-0.2 ℃ for more than 30 min, adjusting the liquid level to the scribed line by using the drop bottle, wiping the inner wall above the liquid level, taking out, carefully wiping the outside of the bottle by using a clean towel, and quickly weighing the quality.
The method for calculating the porosity of the powder comprises the following steps:
D=m1/(V-(m 2 -m 0 -m 1 )/ ρ)
T=(D-D 1 )/D 1
wherein m is 0 Mass (g) of density bottle, m 1 Is the mass (g) of the sample, m 2 The mass (g) of the sample and n-butanol was taken as the charge, and V was the volume (mL) of the density bottle. Rho is the density of n-butanol at 25 ℃ (0.81 g/cm) 3 ) The unit is g/cm3.D 1 The true density of the ideal graphite (2.26 g/cm) 3 )。
2. SEM test
Preparation process of negative electrode ion grinding (Cross-section) sample: the pole piece is cut to be 0.5 cm multiplied by 1cm, the cut negative pole is adhered to a silicon wafer carrier with the size of 1cm multiplied by 1.5cm by using conductive adhesive, then one end of the negative pole is processed by means of argon ion polishing (the parameter is the acceleration voltage of 8KV, each sample is 4 hours), the argon ion polishing technology utilizes a high-voltage electric field to ionize argon gas to generate an ionic state, the generated argon ions bombard the surface of the negative pole at high speed under the action of the acceleration voltage, and the negative pole is denuded layer by layer to achieve the polishing effect.
Scanning Electron Microscopy (SEM) is the process of obtaining the morphology of a sample by the interaction of an electron beam with the sample and imaging with secondary electron signals. In the application, a JSM-6360LV type scanning electron microscope of JEOL company and a matched X-ray energy spectrometer are used for analyzing the cross-sectional morphology structure and element distribution of a sample, and the distribution of pore diameters is observed.
3. Particle size testing of hard carbon particles
Testing the particle size of the hard carbon material particles by using a Malvern particle size tester: dispersing the hard carbon material in an ethanol dispersant, carrying out ultrasonic treatment for 30 minutes, adding a sample into a Malvern particle size tester, and testing D of hard carbon material particles 50 And D 90 。
4. Pore size distribution test for hard carbon material
The testing instrument is an ASAP 2460-physical adsorption analyzer, the dried and degassed sample is placed in liquid nitrogen, different test pressures are adjusted, the adsorption capacity to nitrogen is respectively measured, and adsorption and desorption isotherms are drawn. Determining the shape of the holes according to the shape of the hysteresis loop, calculating the hole distribution and the hole volume according to different hole models, fitting the pore size distribution curves of mesopores and macropores by using a BJH model, and fitting the pore size distribution curves of micropores by using a DFT model.
5. Reversible gram capacity test for hard carbon materials
And (3) fully stirring and mixing the hard carbon prepared in the previous step, styrene Butadiene Rubber (SBR) and sodium carboxymethyl cellulose (CMC) in a proper amount of deionized water according to a weight ratio of 97. Coating the slurry on a negative current collector (copper foil), drying at 85 ℃, then carrying out cold pressing, cutting and slitting, and drying for 12 hours at 120 ℃ under a vacuum condition to obtain a negative electrode; when the current collector is used as the negative electrode of the sodium ion battery, the current collector can be replaced by an aluminum foil. The button half cell uses metal lithium or metal sodium as a counter electrode, a lithium/sodium sheet with the diameter of 18mm and the thickness of 0.6mm, a separation membrane and a hard carbon electrode are sequentially assembled together, electrolyte is added, and the lithium/sodium ion button half cell is packaged in a positive and negative button stainless steel shell to obtain the lithium/sodium ion button half cell.
Sodium ion button half cell test: the button cells were discharged to 5.0mV at 0.05C, to 0mV at 50 μ A, to 0mV at 20 μ A, and to 2.0V at 0.05C, and the capacity of the button cells at this time was recorded and reported as the reversible gram capacity. 0.05C means a current value at 0.05 times the design reversible gram capacity, and 0.1C means a current value at 0.1 times the design reversible gram capacity.
Lithium ion button half cell test: the button cells were discharged at 0.05C to 800 or 700 mAh/g and charged at 0.05C to 2.0V, and the capacity of the button cells at this time was recorded as reversible gram capacity. 0.05C means a current value at 0.05 times the design reversible gram capacity, and 0.1C means a current value at 0.1 times the design reversible gram capacity.
6. And (3) testing the cycle performance of the lithium/sodium ion battery:
the lithium ion and sodium ion batteries prepared using all comparative examples and examples were averaged, 5 each. The lithium ion and sodium ion batteries were repeatedly charged and discharged through the following steps, and the discharge capacity retention rates of the lithium ion and sodium ion batteries were calculated.
Lithium ion battery cycle performance test
First, in an environment of 25 ℃, first charging and discharging are carried out, constant current charging is carried out under a charging current of 1C (0.5C), the charging is changed into constant voltage charging until an upper limit voltage is reached to be 3.8V, then constant current discharging is carried out under a discharging current of 1C (0.5C) until a final voltage is 1.2V, and data of the first cycle and the 200 th cycle are recorded.
Cycle capacity retention ratio = (discharge capacity at 200 th cycle/discharge capacity at first cycle) × 100%;
and (3) testing the cycle performance of the sodium-ion battery:
first, in an environment of 25 ℃, first charging and discharging are carried out, constant current charging is carried out under a charging current of 1C (0.5C), the charging is changed into constant voltage charging until an upper limit voltage of 3.95V is reached, then constant current discharging is carried out under a discharging current of 1C (0.5C) until a final voltage is 2V, and data of the first cycle and the 200 th cycle are recorded.
Cycle capacity retention rate = (discharge capacity at 200 th cycle/discharge capacity at first cycle) × 100%;
results
The compositions of the hard carbon materials according to examples 1 to 11 and comparative examples 1 to 3 are shown in table 1; physical characterization of the resin pyrolytic carbons according to examples 1-11 and comparative examples 1-3 is shown in table 2; and electrochemical properties of the batteries according to examples 1 to 11 and comparative examples 1 to 3 are shown in table 3.
As can be seen from tables 1 and 2, different pore sizes can be obtained by controlling the content of deionized water: (<10 nm) and pore volume (0.2 to 1.02 cm) 3 /g) of resin pyrolytic carbon. Catalyst (glacial acetic acid) and pyrolysis temperature also have an effect on pore size and pore volume, but to a lesser extent than the solvent deionized water.
The specific surface area and the pore volume of pores of the resin pyrolytic carbon are obviously reduced by mixing with hexamethylenetetramine and coating pyrolysis, which shows that open pores of the resin pyrolytic carbon become closed pores after coating, so that nitrogen can not enter the pores, and the purposes of storing lithium and sodium in the pores are achieved.
In addition, the lithium storage amount and the sodium storage amount can be further increased by introducing a metal element into the hard carbon material, but when too much metal element is introduced, the pore volume can be reduced and the reversible capacity is affected, while the energy density is reduced.
According to the method, the hard carbon materials with different pore diameters and pore volumes are synthesized by controlling the content of deionized water, and the pores are more fully utilized by coating and introducing metal elements, so that the capacity of the hard carbon material (the reversible lithium storage capacity of 450-650 mAh/g and the reversible sodium storage capacity of 300-450 mAh/g under 0.05 ℃, and the capacity retention rates of the lithium-ion button battery and the sodium-ion button battery under 1 ℃ are respectively higher than 80% and 85%), the multiplying power performance and the cycle performance are improved.
Figure 136456DEST_PATH_IMAGE001
Figure 381492DEST_PATH_IMAGE002
Figure 738393DEST_PATH_IMAGE003

Claims (9)

1. A hard carbon material characterized in that the hard carbon material has a pore volume of 0.01 cm 3 G to 0.09 cm 3 Wherein, when metal lithium is used as a counter electrode, the ratio of reversible gram capacity between 0 and 0.20V to reversible gram capacity between 0 and 2.5V in the lithium removal capacity of the hard carbon material is 0.80 to 0.86, and/or when metal sodium is used as a counter electrode, the ratio of reversible gram capacity between 0 and 0.20V to reversible gram capacity between 0 and 2.5V in the sodium removal capacity of the hard carbon material is 0.75 to 0.86.
2. The hard carbon material according to claim 1, characterized in that the reversible gram capacity of the hard carbon material between 0 and 0.20V is 230 to 570mAh/g.
3. The hard carbon material as claimed in claim 1, wherein the hard carbon material has a compacted density of 0.5 to 1.0 g/cm 3 The specific surface area of the hard carbon material is 5 to 70m 2 /g。
4. The hard carbon material according to claim 1, wherein a ratio of a reversible gram capacity between 0 and 0.20V to a reversible gram capacity between 0 and 2.5V in the delithiation capacity of the hard carbon material is between 0.80 and 0.86, wherein the reversible gram capacity between 0 and 0.20V is between 380 and 570mAh/g, when metallic lithium is used as a counter electrode, and/or a ratio of a reversible gram capacity between 0 and 0.20V to a reversible gram capacity between 0 and 2.5V in the delithiation capacity of the hard carbon material is between 0.75 and 0.86, wherein the reversible gram capacity between 0 and 0.20V is between 230 and 370 mAh/g, when metallic sodium is used as a counter electrode.
5. The hard carbon material according to claim 1, further comprising a metal compound including at least one of silver nitrate, cobalt nitrate, antimony chloride, and tin chloride.
6. A method for preparing a hard carbon material according to any one of claims 1 to 4, characterized in that it comprises the following steps:
(i) Providing phenolic resin, and pyrolyzing the phenolic resin through carbonization to obtain resin pyrolytic carbon;
(ii) (ii) mixing the resin pyrolytic carbon from step (i) with hexamethylenetetramine to obtain a blend;
(iii) (iii) pyrolytically coating the blend from step (ii) to obtain a hard carbon material.
7. The method of claim 6, wherein in step (i) the phenolic resin comprises a metal compound comprising one or both of silver nitrate, cobalt nitrate, antimony chloride and tin chloride.
8. The method according to claim 6, wherein the resin pyrolytic carbon obtained by pyrolysis in step (i) has a specific surface area of 500m 2 G to 1500 m 2 (vii)/g, pore size 0.6 nm to 150 nm, particle size 1 μm to 200 μm, pore volume 0.1 cm to 1.2 cm both when thin and long, porosity 20% to 80%.
9. A secondary battery characterized by comprising an anode comprising the hard carbon material according to any one of claims 1 to 5.
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