A hard carbon material and preparation method thereof

Abstract

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

Description

Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and in particular to a hard carbon material and a preparation method thereof. Background Art

[0002] Since Sony Corporation of Japan commercialized lithium-ion batteries in 1991, lithium-ion batteries have been rapidly used in mobile phones, miniature cameras, PDAs, laptop computers and other fields due to their high energy density, high operating voltage, good load characteristics, fast charging speed, safety and pollution-free.

[0003] Anode materials play a crucial role in lithium-ion battery development. Currently, the specific capacity of graphite is close to its theoretical capacity (372 mAh / g), making further improvement difficult. Furthermore, this specific capacity cannot meet the high-capacity and high-rate discharge requirements of large electronic devices such as new energy storage devices and electric vehicles. Therefore, researching and preparing new high-capacity, high-rate lithium-ion battery anode materials is crucial for the continued development of lithium-ion batteries.

[0004] The internal structure of hard carbon materials is composed of disordered carbon layers with a large number of defects and pores. This structure, unlike graphite, provides a certain amount of space for the storage of sodium and lithium ions, resulting in a long and stable platform region in the sodium and lithium storage charge-discharge curves of hard carbon materials. Among the many battery anode materials reported so far, hard carbon is considered to be one of the most promising battery electrode materials due to its advantages such as high reversible specific capacity, good cycle stability, low reaction voltage platform, and low raw material costs. However, most of the hard carbon materials currently under research have low first coulombic efficiency, pore utilization, and the resulting energy density and platform capacity, making it difficult to further promote the application of hard carbon. Summary of the Invention

[0005] In order to solve the above problems, the purpose of the present application is to provide a hard carbon material and a method for preparing the hard carbon material.

[0006] In a first aspect, the present application provides a hard carbon material, wherein the pore volume of the hard carbon material is 0.01 cm 3 / g to 0.09cm 3 / g, the specific surface area of ​​the hard carbon material is 5m 2 / g to 70m 2 / g, and the reversible gram capacity of the hard carbon material between 0 and 0.20V is 230mAh / g to 570mAh / g. According to some embodiments of the present application, the ratio of the reversible gram capacity of the hard carbon material between 0 and 0.20V to the reversible gram capacity between 0 and 2.5V is 0.75 to 0.86. Compared with the hard carbon negative electrode materials in the prior art, especially at similar compaction density, the hard carbon material of the present application has a significantly smaller pore volume. This is because there are a considerable amount of closed pores in the hard carbon material of the present application. These closed pores increase the lithium and sodium storage capacity while ensuring the energy density of the material.

[0007] According to some embodiments of the present application, the hard carbon material has a relative humidity of 0.5 g / cm 3 to 1.0g / cm 3 The compaction density within the range of 5m 2 / g to 70m 2 The specific surface area is within the range of 100 nm / g, and its compaction density and specific surface area are small, which can ensure that the material has a higher energy density and a higher lithium / sodium storage capacity.

[0008] 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 of the hard carbon material between 0 and 0.20 V to the reversible gram capacity between 0 and 2.5 V is 0.80 to 0.86.

[0009] 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 0.20 V to the reversible gram capacity between 0 and 2.5 V is 0.75 to 0.86.

[0010] 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 0.20 V (vs Li+ / Li) to the reversible gram capacity between 0 and 2.5 V is 0.80 to 0.86, wherein the reversible gram capacity between 0 and 0.20 V (vs Li+ / Li) is 380 mAh / g to 570 mAh / g.

[0011] 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 0.20 V (vs Na+ / Na) to the reversible gram capacity between 0 and 2.5 V is 0.75 to 0.86, wherein the reversible gram capacity between 0 and 0.20 V (vs Na+ / Na) is 230 mAh / g to 370 mAh / g.

[0012] According to some embodiments of the present application, the hard carbon material includes a hard carbon material prepared by using a phenolic resin.

[0013] According to some embodiments of the present application, the hard carbon material further contains a metal compound, which includes one or two of silver nitrate, cobalt nitrate, antimony chloride and tin chloride. The metal elements in these metal compounds are conducive to the deposition of lithium and sodium in the pores, thereby increasing the sodium and lithium storage capacity of the hard carbon material and improving the energy density.

[0014] In a second aspect, the present application provides a method for preparing a hard carbon material, particularly for preparing the hard carbon material according to the first aspect of the present application, wherein the method comprises the following steps:

[0015] (i) providing a phenolic resin, and pyrolyzing the phenolic resin by carbonization to obtain resin pyrolytic carbon;

[0016] (ii) mixing the resin pyrolytic carbon from step (i) with hexamethylenetetramine to obtain a blend;

[0017] (iii) subjecting the blend from step (ii) to pyrolytic coating to obtain a hard carbon material.

[0018] According to some embodiments of the present application, in step (i), the phenolic resin contains a metal compound, and the metal compound includes one or two of silver nitrate, cobalt nitrate, antimony chloride and tin chloride.

[0019] According to some embodiments of the present application, in step (i), a phenolic resin is provided via the following steps:

[0020] (i.1) adding formaldehyde and glacial acetic acid to deionized water, and then sequentially adding resorcinol, ammonium bicarbonate, and a metal compound, and stirring to obtain a solution;

[0021] (i.2) heating the solution obtained in step (i.1) to obtain a phenolic resin;

[0022] (i.3) Drying the phenolic resin obtained in step (i.2) to obtain a dried phenolic resin.

[0023] By means of the method according to the present application, by using raw materials such as phenolic resin to synthesize a hard carbon material with rich pores and interconnected pores, while ensuring the rapid diffusion of lithium ions or sodium ions inside the pores, the utilization rate of the pores is improved and the closed-pore lithium and sodium storage capacity is increased, thereby improving the energy density of the battery.

[0024] According to some embodiments of the present application, in step (i.1), stirring is performed for about 30 minutes or more to obtain a solution.

[0025] 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 0:1 to 1:1.

[0026] 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 0:100 to 20:100, the molar ratio of ammonium bicarbonate to formaldehyde is approximately 1:83, and the volume ratio of deionized water to formaldehyde solution is in the range of 0:1 to 1:1. By controlling the proportion of water, the size of the pores formed in the material after carbonization can be controlled, and in particular, the pore size and pore volume of the resin pyrolytic carbon can be affected.

[0027] 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 a range of 0:100 to 5:100. The introduction of a small amount of the metal element facilitates the deposition of lithium and sodium within the pores, thereby increasing the sodium and lithium storage capacity of the hard carbon material. However, excessively high levels of the metal element can reduce the energy density of the hard carbon material, while excessively low levels can reduce the effectiveness of lithium and sodium deposition within the pores.

[0028] According to some embodiments of the present application, in step (i.2), the mixture in the solution undergoes a chemical reaction under heating conditions, wherein the reaction is performed in a reactor by heating in an oven, and a solid phenolic resin is obtained after the reaction.

[0029] According to some embodiments of the present application, the heating temperature in step (i.2) is in the range of 60 to 150°C, and the heating time is in the range of 6 to 24 hours, wherein the degree of polymerization and cross-linking of formaldehyde and resorcinol at different hydrothermal reaction temperatures is different. Too long a time will cause the phenolic resin material to agglomerate and cause irregular macrostructure, thereby affecting the overall electrochemical performance. At the same time, too short a reaction time will cause the cross-linking degree of the phenolic resin to be too low, thereby causing the reversible sodium and lithium storage capacity of the hard carbon material after pyrolysis to be low.

[0030] 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 remove all excess water, acid and formaldehyde, thereby obtaining a dry phenolic resin, wherein a large number of open pores can be left in the dry phenolic resin by evaporation of the solvent. In particular, the dry phenolic resin has a 20m 2 / g to 100m 2 / g specific surface area, 10nm to 500nm pore size and 1μm to 200μm particle size.

[0031] According to some embodiments of the present application, the drying process in step (i.3) is firstly kept at 120° C. for 2 to 6 hours, and then raised to a temperature in the range of 150 to 200° C. and kept for 2 to 20 hours.

[0032] According to some embodiments of the present application, in step (i), the carbonization pyrolysis is carried out at a heating rate of 1 to 10°C / min and a target temperature of 800 to 1500°C, wherein the holding time at the target temperature is 2 to 5 hours. Preferably, the carbonization pyrolysis is carried out under an inert gas atmosphere, such as a nitrogen atmosphere.

[0033] According to some embodiments of the present application, in step (i), the product obtained by pyrolysis is washed with ethanol and deionized water in sequence, and then dried and sieved to obtain the resin pyrolytic carbon. Preferably, the resin pyrolytic carbon has a carbon content of 500m 2 / g to 1500m 2 / g specific surface area, 0.6nm to 150nm pore size, 1μm to 200μm particle size, 0.1cm 3 / g to 1.2cm 3 / g pore volume and 20% to 80% porosity. Among them, too high specific surface area and porosity will lead to too low compaction density, and thus lead to low energy density of the material; too small pore size will lead to a decrease in pore volume after coating and the lithium and sodium storage capacity in the pores. Conversely, too large pore size will lead to incomplete coating and the inability to form closed pores, thus failing to achieve the purpose of lithium and sodium storage.

[0034] According to some embodiments of the present application, in step (ii), hexamethylenetetramine and resin pyrolytic carbon are mixed at a mass ratio of 1:1 to 1:20, in particular, shear crushing mixing.

[0035] According to some embodiments of the present application, in step (iii), the pyrolysis coating is performed at a heating rate of 1 to 10°C / min and a target temperature of 800 to 1200°C, wherein the holding time at the target temperature is 2 to 5 hours.

[0036] According to some embodiments of the present application, in step (iii), the pyrolysis coating is performed under an inert gas atmosphere, such as a nitrogen atmosphere.

[0037] By utilizing the pyrolytic coating method of the present invention, an appropriate coating amount can convert open pores into 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, the specific capacity is reduced. At the same time, excessively thick coating layers can increase the resistance to the diffusion of desolvated ions into the pores and reduce the low-plateau capacity. When the coating ratio is too low, a large number of open pores results, leading to excessive SEI film formation, making it difficult to achieve the purpose of closed-pore lithium and sodium storage.

[0038] In a third aspect of the present application, the present application provides an electrochemical device, in particular a lithium-ion or sodium-ion battery, comprising the hard carbon material according to the first aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 The nitrogen adsorption-desorption curve of the resin pyrolysis carbon according to Example 1 of the present application is schematically shown;

[0040] Figure 2 A schematic diagram schematically shows the pore size distribution of resin pyrolytic carbon according to Example 1 of the present application;

[0041] Figure 3 Schematically shows a cross-sectional SEM image of resin pyrolytic carbon according to Example 1 of the present application;

[0042] Figure 4 A schematic diagram schematically shows the particle size distribution of resin pyrolytic carbon according to Example 1 of the present application;

[0043] Figure 5 Schematically shows a specific capacity curve of a lithium-ion battery according to one embodiment of the present application;

[0044] Figure 6 Schematically shows a specific capacity curve of a sodium ion battery according to one embodiment of the present application;

[0045] Figure 7 The figure schematically shows a specific capacity curve of a sodium ion battery according to one embodiment of the present application. DETAILED DESCRIPTION

[0046] In order 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 in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. The relevant embodiments described herein are illustrative and are used to provide a basic understanding of the present application. The embodiments of the present application should not be interpreted as limiting the present application. Based on the technical solutions and embodiments provided in the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present application.

[0047] For the sake of clarity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0048] In the description herein, unless otherwise specified, “above” and “below” include the number itself.

[0049] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0050] A list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms may mean 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 only A; 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 only A; 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 contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0051] 1. Negative electrode

[0052] The negative electrode includes a current collector and a negative electrode active material layer located on a surface of the current collector, wherein the negative electrode active material layer includes the hard carbon material described in aspect 1. In some embodiments, the current collector includes 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.

[0053] In some embodiments, the negative electrode active material layer further includes a binder, which includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon, etc.

[0054] In some embodiments, the negative electrode active material layer further comprises a conductive agent, which 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 fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0055] The negative electrode of the present application can be prepared using methods known in the art. Typically, a hard carbon material and an optional conductive agent (e.g., carbon black and other carbon materials 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). After stirring, the mixture is evenly coated on the negative electrode current collector, and dried to obtain a negative electrode containing a negative electrode membrane. Materials such as metal foil or porous metal plates can be used as the negative electrode current collector.

[0056] 2. Positive electrode

[0057] The materials, compositions and manufacturing methods of the positive electrode that can be used in the embodiments of the present application include any technology disclosed in the prior art.

[0058] In some embodiments, the positive electrode includes a current collector and a positive electrode active material layer on the current collector.

[0059] In some embodiments, the positive electrode active material includes a positive electrode material capable of absorbing and releasing lithium or sodium. Lithium-releasing positive electrode materials include, but are not limited to, lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium iron phosphate, lithium titanate, and lithium-rich manganese-based materials. Sodium-releasing positive electrode materials may be at least one of transition metal layered oxides, sodium polyanion compounds, Prussian blue, Prussian white, and the like, such as copper-nickel-iron-manganese oxide.

[0060] In some embodiments, the positive electrode active material layer further includes a binder, and optionally a conductive material. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0061] In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0062] 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 fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0063] In some embodiments, the current collector may include, but is not limited to, aluminum.

[0064] The positive electrode can be prepared using methods known in the art. For example, the positive electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition on a current collector. In some embodiments, the solvent may include, but is not limited to, N-methylpyrrolidone. The electrochemical device of the present application has higher energy density and cycle performance, meeting application requirements.

[0065] 3. Isolation Film

[0066] According to some embodiments of the present application, the material and shape of the isolation membrane are not particularly limited, and the isolation membrane can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes a polymer or inorganic material formed of a material that is stable to the electrolyte of the present application.

[0067] The separator may include a substrate layer and a surface treatment layer. The substrate layer is a porous nonwoven fabric, film, or composite film, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene nonwoven fabric, polyethylene nonwoven fabric, or polypropylene-polyethylene-polypropylene porous composite film may be used.

[0068] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0069] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0070] The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0071] 4. Electrolyte

[0072] According to some embodiments of the present application, the present application has no particular restrictions on the composition of the electrolyte, which can be any technology disclosed in the prior art. In some embodiments, the lithium battery electrolyte includes at least one of a fluoroether, a fluoroethylene carbonate, or an ether nitrile. In some embodiments, the electrolyte further includes a lithium salt, the lithium salt including lithium bis(fluorosulfonyl)imide and lithium hexafluorophosphate, the concentration of the lithium salt being 1 mol / L to 2 mol / L, and the molar ratio of lithium bis(fluorosulfonyl)imide to lithium hexafluorophosphate being 0.05 to 4.

[0073] In some embodiments, the sodium ion battery electrolyte includes an organic solvent and a sodium salt, 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.

[0074] In some embodiments, the electrolyte may further include a non-aqueous solvent, which may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof.

[0075] The carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound, or a combination thereof.

[0076] Examples of chain carbonate compounds are diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), or combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, or combinations thereof.

[0077] Examples of the carboxylic acid ester compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0078] Examples of the ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0079] Examples of other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid esters or combinations thereof.

[0080] 5. Electrochemical Device

[0081] The present application provides an electrochemical device, which includes a negative electrode, a positive electrode, an electrolyte, and a separator.

[0082] In some embodiments, the electrochemical device of the present application includes, but is not limited to, all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors.

[0083] In some embodiments, the electrochemical device is a sodium ion battery.

[0084] In some embodiments, the electrochemical device is a lithium secondary battery.

[0085] 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.

[0086] Example

[0087] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein lithium-ion and sodium-ion batteries are used as examples.

[0088] Example 1

[0089] The hard carbon material according to Example 1 was prepared by the following method:

[0090] (i.1) Add 100 mL of formaldehyde and 5 mL of glacial acetic acid to 15 mL of deionized water, then add 78 g of resorcinol and stir. Once the resorcinol has dissolved, add 1.1 g of ammonium bicarbonate and dissolve it. Then, add 2.42 g of cobalt nitrate (mass ratio of cobalt to resorcinol: 1:100) and stir for 30 minutes to obtain a solution.

[0091] (i.2) The solution obtained in step (i.1) was poured into a 500 mL reactor and heated in an oven at 85°C for 24 h to obtain a solid resin;

[0092] (i.3) crushing the solid resin obtained in step (i.2) and drying it in an oven, first at 120°C for 2 hours and then at 150°C for 10 hours to obtain a dry resin;

[0093] (i.4) The dried resin obtained in step (i.3) was placed in a tube furnace for pyrolysis, nitrogen was introduced, and the temperature was increased to 1100°C at a rate of 5°C / min and maintained for 3 hours. The resulting product was rinsed twice with ethanol and three times with deionized water, dried, and sieved through a 300-mesh sieve to obtain resin pyrolytic carbon.

[0094] (ii) Shearing and crushing the resin pyrolytic carbon obtained in step (i.4) and hexamethylenetetramine to obtain a blend, wherein the mass ratio of the resin pyrolytic carbon to the hexamethylenetetramine is 1:5.

[0095] (iii) placing the crushed and mixed resin blend in step (ii) into a tubular furnace for pyrolysis coating, introducing nitrogen, heating to 900° C. at a rate of 5° C. / min and maintaining the temperature for 3 h to obtain coated hard carbon, i.e., hard carbon material.

[0096] The nitrogen adsorption-desorption curve of the resin pyrolysis carbon obtained in step (i) of Example 1 is as follows: Figure 1 As shown in the figure, it can be seen that the resin pyrolytic carbon material has micropores and mesopores, and the resin pyrolytic carbon has a 1112m 2 / g specific surface area.

[0097] The pore size distribution curve of the resin pyrolytic carbon obtained in step (i) of Example 1 is as follows: Figure 2 As shown in the figure, it can be seen that the pore size of the resin pyrolytic carbon is both micropores and mesopores, and these micropores and mesopores have pore diameters of 0.4nm to 6nm and 0.46cm 3 / g pore volume.

[0098] The cross-sectional SEM image of the resin pyrolysis carbon obtained in step (i) of Example 1 is as follows: Figure 3 As shown, due to the influence of instrument resolution, mesopores of 2 to 10 nm cannot be directly observed, so the pore structure cannot be seen in this image, which indicates that there are no mesopores or the number of mesopores is small in the resin pyrolysis carbon obtained in step (i).

[0099] Anode preparation

[0100] The hard carbon material prepared above was thoroughly stirred and mixed with styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) in a weight ratio of 97:2:1 in an appropriate amount of deionized water to form a uniform negative electrode slurry with a solid content of 40wt%. This slurry was then coated onto a negative electrode current collector (copper foil or aluminum foil, copper foil for lithium-ion battery negative electrode collectors and aluminum foil for sodium-ion battery negative electrode collectors), dried at 85°C, cold pressed, cut into pieces, and slit, and then dried under vacuum at 120°C for 12 hours to obtain a negative electrode.

[0101] Cathode preparation

[0102] Lithium iron phosphate (LiFePO4) is used as the positive electrode of lithium-ion batteries, and copper-nickel-iron-manganese oxide (NaCu 1 / 9Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2) as the positive electrode of sodium ion batteries.

[0103] The positive electrode active material (LiFePO4 or NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2), a conductive agent Super P, and a binder polyvinylidene fluoride (PVDF) were thoroughly stirred in an appropriate amount of N-methylpyrrolidone (NMP) solvent in a weight ratio of 97:1.4:1.6 to form a uniform positive electrode slurry with a solid content of 72 wt%. This slurry was coated on an aluminum foil positive electrode current collector and dried at 85°C to obtain a positive electrode.

[0104] Electrolyte preparation

[0105] In a dry argon glove box, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) were mixed in a mass ratio of EC:PC:DEC = 1:1:1. 1.5 wt% of 1,3-propane sultone was added and stirred thoroughly. LiPF6 (for lithium-ion batteries) or NaPF6 (for sodium-ion batteries) was added and mixed thoroughly to form an electrolyte. The concentration of LiPF6 or NaPF6 in the electrolyte was 1 mol / L.

[0106] Isolation film preparation

[0107] A 9 μm thick polyethylene (PE) porous polymer film coated with Al2O3 was used as the isolation membrane.

[0108] Preparation of lithium / sodium ion batteries

[0109] The positive electrode, separator, and negative electrode are stacked in order, so that the separator is between the positive and negative electrodes to play an isolating role, and the electrolyte is added. The positive and negative electrodes are placed in a button-type stainless steel shell to obtain a button-type lithium / sodium ion battery.

[0110] The particle size distribution curve of the resin pyrolysis carbon obtained in step (i) of Example 1 is as follows: Figure 4 As shown, it can be seen that the particle size D of the resin pyrolytic carbon 50 and D 90 27μm and 196μm respectively.

[0111] By the method described in this application, a lithium ion button half-cell was prepared using the hard carbon material obtained in Example 1. After the negative electrode of the lithium ion button half-cell of Example 1 was fixed with lithium at a capacity of 800 mAh / g, no lithium deposition occurred on the surface of the electrode. The charge and discharge curves of the lithium ion button half-cell are shown in FIG. Figure 5 As shown, it can be seen that the negative electrode of the lithium ion button half-cell according to Example 1 has a first coulombic efficiency of 81% and a reversible specific capacity of 648 mAh / g, wherein the low potential platform (0 to 0.20 V) specific capacity is 480 mAh / g.

[0112] The sodium ion button half-cell was prepared using the hard carbon material obtained in Example 1 by the method described in this application. The first cycle charge and discharge curve is as follows: Figure 6 As shown, it can be seen that the negative electrode of the sodium ion button half-cell according to Example 1 has a first coulombic efficiency of 67% and a reversible specific capacity of 330 mAh / g, wherein the specific capacity of the low potential platform (0 to 0.20 V) is 240 mAh / g.

[0113] Example 2

[0114] Example 2 was carried out using substantially the same method as Example 1, except that in step (i.1), the amount of deionized water added was 0 mL, the amount of cobalt nitrate added was 4.84 g (the mass ratio of Co to resorcinol was 2:100), and in step (ii), the mass ratio of resin pyrolysis carbon to hexamethylenetetramine was 1:1.

[0115] Example 3

[0116] 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 4.84 g (the mass ratio of Co to resorcinol was 2:100).

[0117] Example 4

[0118] Example 4 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 4.84 g (the mass ratio of Co to resorcinol was 2:100), and in step (ii), the mass ratio of resin pyrolysis carbon to hexamethylenetetramine was 1:7.

[0119] Example 5

[0120] 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 2.42 g (the mass ratio of Co to resorcinol was 1:100), and in step (ii), the mass ratio of resin pyrolysis carbon to hexamethylenetetramine was 1:10.

[0121] Example 6

[0122] 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 1:10.

[0123] Example 7

[0124] Example 7 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 1:15.

[0125] Example 8

[0126] Example 8 was carried out using a method substantially identical to Example 1, except that in step (i.1), the amount of deionized water added was 60 mL, the amount of glacial acetic acid added was 10 mL, and the amount of cobalt nitrate added was 0 g; in step (i.4), the carbonization pyrolysis temperature was 900° C.; and in step (ii), the mass ratio of resin pyrolysis carbon to hexamethylenetetramine was 1:10.

[0127] Example 9

[0128] Example 9 was carried out using substantially the same method as Example 1, except that in step (i.1), the amount of deionized water added was 60 mL, the amount of glacial acetic acid added was 10 mL, the amount of cobalt nitrate added was 0 g, and in step (ii), the mass ratio of resin pyrolytic carbon to hexamethylenetetramine was 1:10.

[0129] Example 10

[0130] Example 10 was carried out using substantially the same method as Example 1, except that in step (i.1), the amount of deionized water added was 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 1:15.

[0131] Example 11

[0132] Example 11 was carried out using substantially the same method as Example 1, except that in step (i.1), the amount of deionized water added was 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 1:15.

[0133] Comparative Example 1

[0134] Comparative Example 1 was carried out using substantially the same method as Example 1, except that in step (i.1), the amount of cobalt nitrate added was 36.3 g (the mass ratio of Co to resorcinol was 15:100).

[0135] Comparative Example 2

[0136] Comparative Example 2 was carried out using substantially the same method as Example 10, except that, in step (i.1), the amount of deionized water added was 200 mL.

[0137] Comparative Example 3

[0138] Comparative Example 3 was carried out using substantially the same method as Example 7, except that, in step (ii), the mass ratio of the resin pyrolytic carbon to the hexamethylenetetramine was 1:30.

[0139] Test Method

[0140] 1. Powder porosity test

[0141] Weigh 3 g of the sample, accurate to 0.0002 g, and place it in a clean density bottle. Inject bubble-free n-butanol to 2 / 3 of the bottle and boil for 3 minutes. Do not allow the sample to splash out at this time. After removing the bottle, inject bubble-free n-butanol slightly above the scale line. Place it together with another dropping bottle injected with only n-butanol in a constant temperature water bath and keep it at 25℃±0.2℃ for more than 30 minutes. Use a dropping bottle to adjust the liquid level to the scale line and wipe the inner wall above the liquid level. After taking it out, carefully wipe the outside of the bottle with a clean towel and quickly weigh it.

[0142] The porosity of the powder is calculated as:

[0143] D=m1 / (V-(m2-m0-m1) / ρ)

[0144] T=(D-D1) / D1

[0145] Where m0 is the mass of the density bottle (g), m1 is the mass of the sample (g), m2 is the mass of the sample and n-butanol (g), and V is the volume of the density bottle (mL). ρ is the density of n-butanol at 25°C (0.81 g / cm 3 ), unit is g / cm3. D1 is the true density of ideal graphite (2.26g / cm 3 ).

[0146] 2.SEM testing

[0147] The negative electrode ion milling (Cross-section) sample preparation process: the electrode is cut into 0.5cm×1cm size, and the cut negative electrode is adhered to a 1cm×1.5cm silicon wafer carrier using conductive glue. Then, one end of the negative electrode is processed with the help of argon ion polishing (parameters: 8KV acceleration voltage, 4h per sample). This argon ion polishing technology uses a high-voltage electric field to ionize argon gas to produce an ion state. The generated argon ions bombard the negative electrode surface at high speed under the action of the acceleration voltage, and the negative electrode is eroded layer by layer to achieve the polishing effect.

[0148] Scanning electron microscopy (SEM) uses the interaction of an electron beam with a sample to image the sample's morphology using secondary electron signals. In this application, a JEOL JSM-6360LV SEM and its accompanying X-ray energy dispersive spectrometer were used to analyze the sample's cross-sectional morphology and elemental distribution, and to observe pore size distribution.

[0149] 3. Particle size test of hard carbon material particles

[0150] The particle size of the hard carbon material particles was tested using a Malvern particle size tester: the hard carbon material was dispersed in an ethanol dispersant and ultrasonicated for 30 minutes. The sample was then added to the Malvern particle size tester to test the particle size of the hard carbon material particles. 50 and D 90 .

[0151] 4. Pore size distribution test of hard carbon materials

[0152] The test instrument, an ASAP2460 physical adsorption analyzer, placed the dried and degassed sample in liquid nitrogen. The nitrogen adsorption was measured at different test pressures, and adsorption and desorption isotherms were plotted. The pore shape was determined based on the hysteresis loop, and the pore distribution and pore volume were calculated using different pore models. The BJH model was used to fit the pore size distribution curves for mesopores and macropores, while the DFT model was used to fit the pore size distribution curve for micropores.

[0153] 5. Reversible gram capacity test of hard carbon materials

[0154] The hard carbon prepared above was thoroughly mixed with styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) in a weight ratio of 97:2:1 in an appropriate amount of deionized water to form a uniform negative electrode slurry with a solid content of 40wt%. This slurry was then coated onto the negative electrode current collector (copper foil), dried at 85°C, and then cold-pressed, cut, and slit, and then dried under vacuum at 120°C for 12 hours to obtain the negative electrode. When used as the negative electrode for a sodium-ion battery, the current collector can be replaced with aluminum foil. A button-type half-cell uses metallic lithium or metallic sodium as the counter electrode. A lithium / sodium sheet with a diameter of 18mm and a thickness of 0.6mm is assembled and stacked with a separator and a hard carbon electrode in sequence. Electrolyte is added and the battery is encapsulated in a button-type stainless steel case with positive and negative electrodes to obtain a lithium / sodium ion button-type half-cell.

[0155] Sodium ion button cell half-cell test: The button cell is discharged at 0.05C to 5.0mV, discharged at 50μA to 0mV, discharged at 20μA to 0mV, and charged at 0.05C to 2.0V. The capacity of the button cell at this time is recorded and recorded as the reversible gram capacity. 0.05C refers to the current value at 0.05 times the designed reversible gram capacity, and 0.1C refers to the current value at 0.1 times the designed reversible gram capacity.

[0156] Lithium-ion button cell half-cell test: Discharge the button cell at 0.05C to 800 or 700 mAh / g, then charge it at 0.05C to 2.0V. Record the capacity at this point, which is referred to as the reversible gram capacity. 0.05C refers to the current value at 0.05 times the designed reversible gram capacity, and 0.1C refers to the current value at 0.1 times the designed reversible gram capacity.

[0157] 6. Lithium / sodium ion battery cycle performance test:

[0158] Five lithium-ion and sodium-ion batteries prepared from all comparative examples and examples were taken, and the average value was calculated. The lithium-ion and sodium-ion batteries were repeatedly charged and discharged using the following steps, and the discharge capacity retention rates of the lithium-ion and sodium-ion batteries were calculated.

[0159] Lithium-ion battery cycle performance test

[0160] First, in an environment of 25°C, the first charge and discharge were performed. Constant current charging was performed at a charging current of 1C (0.5C) until the upper limit voltage of 3.8V was reached, and then constant voltage charging was switched to. Then, constant current discharge was performed at a discharge current of 1C (0.5C) until the final voltage was 1.2V. The data of the first cycle and the 200th cycle were recorded.

[0161] Cycle capacity retention rate = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100%;

[0162] Sodium ion battery cycle performance test:

[0163] First, in an environment of 25°C, the first charge and discharge were performed. Constant current charging was performed at a charging current of 1C (0.5C) until the upper limit voltage of 3.95V was reached, and then constant voltage charging was switched to. Then, constant current discharge was performed at a discharge current of 1C (0.5C) until the final voltage was 2V. The data of the first cycle and the 200th cycle were recorded.

[0164] Cycle capacity retention rate = (discharge capacity at the 200th cycle / discharge capacity at the first cycle) × 100%;

[0165] result

[0166] The compositions of the hard carbon materials according to Examples 1-11 and Comparative Examples 1-3 are shown in Table 1; the physical characterizations of the resin pyrolytic carbons according to Examples 1-11 and Comparative Examples 1-3 are shown in Table 2; and the electrochemical properties of the batteries according to Examples 1-11 and Comparative Examples 1-3 are shown in Table 3.

[0167] It can be seen from Table 1 and Table 2 that by controlling the content of deionized water, pores with different pore sizes (<10 nm) and pore volumes (0.2 to 1.02 cm 3 The catalyst (glacial acetic acid) and pyrolysis temperature also affect the pore size and pore volume, but the degree of influence is smaller than that of the solvent deionized water.

[0168] By mixing with hexamethylenetetramine and coating and pyrolysis, the specific surface area and pore volume of the resin pyrolytic carbon pores were significantly reduced, indicating that the open pores of the resin pyrolytic carbon became closed pores after coating, preventing nitrogen from entering the pores, thereby achieving the purpose of storing lithium and sodium in the pores.

[0169] In addition, by introducing metal elements into hard carbon materials, the lithium and sodium storage capacities can be further increased. However, when too many metal elements are introduced, the pore volume can be reduced and the reversible capacity can be affected, while the energy density can be reduced.

[0170] The present application synthesizes hard carbon materials with different pore sizes and pore volumes by controlling the content of deionized water, and at the same time makes more effective use of the pores by coating and introducing metal elements, thereby improving the capacity of the hard carbon materials (450-650 mAh / g of reversible lithium storage capacity and 300-450 mAh / g of reversible sodium storage capacity at 0.05C, and the capacity retention rates of lithium-ion button batteries and sodium-ion button batteries at 1C are higher than 80% and 85%, respectively), rate performance and cycle performance.

[0171] Table 1

[0172]

[0173]

[0174] Table 2

[0175]

[0176] Table 3

[0177]

[0178]

Claims

1. A method for preparing a hard carbon material, characterized in that: The preparation method comprises the following steps: (i) providing a phenolic resin and obtaining resin pyrolytic carbon by carbonizing and pyrolyzing the phenolic resin, wherein the phenolic resin contains a metal compound, and the metal compound includes one or two of silver nitrate, cobalt nitrate, antimony chloride and tin chloride; (ii) mixing the resin pyrolytic carbon from step (i) with hexamethylenetetramine to obtain a blend; (iii) subjecting the blend from step (ii) to pyrolysis coating to obtain a hard carbon material; Wherein, the pore volume of the hard carbon material is 0.01cm 3 / g to 0.09cm 3 / g, the specific surface area of ​​the hard carbon material is 5m 2 / g to 70m 2 / g, when metallic lithium is used as a counter electrode, and / or when metallic sodium is used as a counter electrode, the reversible gram capacity of the hard carbon material between 0 and 0.20 V is 230 mAh / g to 570 mAh / g; The compacted density of the hard carbon material is 0.5 g / cm 3 to 1.0g / cm 3 .

2. The method for preparing a hard carbon material according to claim 1, wherein: The ratio of the reversible specific capacity of the hard carbon material between 0 and 0.20 V to the reversible specific capacity between 0 and 2.5 V is 0.75 to 0.

86.

3. The method for preparing a hard carbon material according to claim 1, wherein: When metallic lithium is used as a counter electrode, in the delithiation capacity of the hard carbon material, a ratio of the reversible specific capacity between 0 and 0.20 V to the reversible specific capacity between 0 and 2.5 V of the hard carbon material is 0.80 to 0.

86.

4. The method for preparing a hard carbon material according to claim 1, wherein: When metallic sodium is used as a counter electrode, in the sodium removal capacity of the hard carbon material, a ratio of the reversible specific capacity between 0 and 0.20 V to the reversible specific capacity between 0 and 2.5 V is 0.75 to 0.

86.

5. The method for preparing a hard carbon material according to claim 1, wherein: 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 0.20 V to the reversible gram capacity between 0 and 2.5 V is 0.80 to 0.86, wherein the reversible gram capacity between 0 and 0.20 V is 380 mAh / g to 570 mAh / g, and / or when metallic sodium is used as the counter electrode, in the desodiumization capacity of the hard carbon material, the ratio of the reversible gram capacity between 0 and 0.20 V to the reversible gram capacity between 0 and 2.5 V is 0.75 to 0.86, wherein the reversible gram capacity between 0 and 0.20 V is 230 mAh / g to 370 mAh / g.

6. The method for preparing a hard carbon material according to claim 1, wherein: The specific surface area of ​​the resin pyrolysis carbon obtained by pyrolysis in step (i) is 500m 2 / g to 1500m 2 / g, pore size ranges from 0.6nm to 150nm, particle size ranges from 1μm to 200μm, and pore volume ranges from 0.1cm 3 / g to 1.2cm 3 / g, and the porosity is 20% to 80%.

7. A secondary battery, characterized in that: The secondary battery includes a negative electrode, the negative electrode includes a hard carbon material, and the hard carbon material is prepared according to the method for preparing a hard carbon material according to any one of claims 1 to 6.

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