Hard carbon negative electrode material as well as preparation method therefor and use thereof

Abstract

A hard carbon negative electrode material as well as a preparation method therefor and a use thereof. The hard carbon negative electrode material comprises a hard carbon base material, heteroatoms and metal monoatoms, wherein the metal monoatoms are doped into the hard carbon base material by means of the heteroatoms, the heteroatoms comprise at least one of N, P or S, and the metal monoatoms are metal monoatoms that can undergo an alloying reaction with sodium. The metal monoatoms are doped into the hard carbon base material by means of covalent (chemical bond) interactions with other heteroatoms, so that the doping of single atoms is achieved, thereby improving the overall capacity and rate capability of a sodium ion battery at normal temperature, and ensuring the capacity retention rate of the sodium ion battery under a low temperature condition.

Description

A hard carbon negative electrode material and its preparation method and application Technical Field

[0001] The present invention relates to the technical field related to secondary batteries, and in particular to a hard carbon negative electrode material and a preparation method and application thereof. Background Art

[0002] With the widespread use of lithium-ion batteries in various electronic products, such as electric vehicles, mobile phones, and computers, the demand for lithium is increasing year by year. However, global lithium reserves are extremely limited, unevenly distributed, and costly, severely hindering the development of low-cost, high-performance energy storage devices. Sodium, a member of the same element family, possesses similar electrochemical properties to lithium, is abundant, and is inexpensive, making it the next generation of commercially viable secondary batteries after lithium-ion batteries.

[0003] The mainstream negative electrode material of lithium-ion batteries is graphite. Unlike lithium-ion batteries, the molar mass of sodium ions is three times that of lithium ions and the diameter is 1.3 times that of lithium ions. As a result, sodium ions cannot be reversibly embedded and extracted between graphite layers within the effective potential window. At the same time, the sodium ion-graphite embedded compound is thermodynamically unstable and easily forms NaC 64 Common sodium-ion batteries use hard carbon materials, transition metals and their alloy compounds as negative electrode materials. Among them, transition metals and their alloy compounds have limited commercial prospects due to their complex preparation processes. Hard carbon materials cannot be graphitized and the regularity of carbon layer arrangement is lower than that of soft carbon. More micropores are formed between the layers, which facilitates the insertion and removal of sodium ions. In addition, hard carbon has the advantages of wide availability, low cost and high theoretical reversible specific capacity. It is currently generally considered to be the most suitable negative electrode material for commercial sodium-ion batteries. Technical issues

[0004] However, due to hard carbon's inherent porous structure and numerous active sites, its initial efficiency is low (less than 80%). Furthermore, most existing hard carbon materials suffer from impeded battery ion transport at low temperatures, resulting in low capacity and poor charge-discharge performance. Related technologies attempt to enhance electrochemical properties such as initial efficiency by doping metal atom clusters into the pores of hard carbon. However, since the metal atoms are not fully exposed within the material, the advantages of metal atom clusters in activity and conductivity cannot be fully utilized, resulting in limited improvement in the electrical properties of hard carbon anodes. Technical Solutions

[0005] The present invention aims to address at least one of the technical problems existing in the prior art. To this end, the present invention proposes a hard carbon anode material doped with metal single atoms. The metal single atoms are incorporated into the hard carbon matrix through chemical bonding with heteroatoms, thereby improving the charge-discharge performance and capacity of sodium-ion batteries using the hard carbon anode material.

[0006] The invention also provides a method for preparing the material.

[0007] The present invention also proposes the application of the above materials.

[0008] According to one aspect of the present invention, a hard carbon negative electrode material is proposed, which includes a hard carbon matrix, heteroatoms and metal single atoms, wherein the metal single atoms are doped in the hard carbon matrix through the heteroatoms, the heteroatoms include at least one of N, P or S, and the metal single atoms are metal single atoms that can undergo alloying reaction with sodium.

[0009] According to a preferred embodiment of the present invention, at least the following beneficial effects are achieved: single metal atoms are doped into a hard carbon anode material to form an MXC structure (M is a metal atom, X is a heteroatom). The high loading of MXC fully utilizes active sites, reduces volume change and aggregation, and accelerates the conduction of sodium ions or electrons. Metal atoms are doped into the hard carbon matrix through covalent (chemical bonding) interactions with other heteroatoms, achieving single-atom doping. This improves the overall capacity and rate performance of sodium-ion batteries at room temperature while also ensuring capacity retention at low temperatures. Sodium-ion batteries assembled using the anode material of the present invention can achieve a first coulombic efficiency exceeding 88%, high energy density, excellent cycling stability, and a high safety factor. At low temperatures, they exhibit excellent charge-discharge performance and high capacity. This overcomes the shortcomings of existing sodium-ion hard carbon anode technology and aims to address numerous issues, including low capacity, low first coulombic efficiency, short cycle life, and poor rate performance due to sluggish sodium ion transport kinetics. The anode material of the present invention is widely applicable to large-scale energy storage and other fields, particularly in low-temperature environments.

[0010] In some embodiments of the present invention, the metal single atom is at least one of Sn, Sb, Bi, K, Mg, Al, Li, Rb, Cs, Mo, Ru, Rh, Pd, Ag, In, W, Ir or Pb.

[0011] In some embodiments of the present invention, the raw materials for preparing the hard carbon negative electrode material include a hard carbon precursor, a heteroatom precursor and a metal single atom precursor, wherein the heteroatom precursor includes at least one of a nitrogen atom precursor, a sulfur atom precursor or a phosphorus atom precursor.

[0012] In some embodiments of the present invention, the hard carbon precursor includes at least one of a carbohydrate, biomass, or resin. One or more hard carbon sources may be used for calcination, and a hard carbon source containing heteroatoms may also be used for calcination.

[0013] In some embodiments of the present invention, if contained, the carbohydrate substance comprises at least one of sucrose, glucose, fructose, cyclodextrin, starch or cellulose.

[0014] In some embodiments of the present invention, if present, the biomass comprises at least one of lignin, chitosan, bamboo charcoal powder, bamboo fiber powder, coconut shells, nut shells, straw, sugarcane stalks, sawdust, poplar wood, pollen, sawdust, foxtail grass, shells, apple peels, wheat, or dandelion. Using biomass raw materials as hard carbon precursors is green, renewable, economical, and environmentally friendly.

[0015] In some embodiments of the present invention, if present, the resin comprises at least one of phenolic resin, epoxy resin, phenolic epoxy resin, phenol-furfural resin, para-diphenol-formaldehyde resin, polyacrylonitrile, polyaniline, polypyrrole, polystyrene, polyimidazole, polythiophene, polytetrafluoroethylene, and polyvinyl chloride. Having a defined chemical composition allows for qualitative batch production, with different batches of hard carbon having the same properties.

[0016] In some preferred embodiments of the present invention, the hard carbon precursor is bamboo fiber powder.

[0017] In some embodiments of the present invention, if contained, the nitrogen atom precursor includes at least one of urea, glucose ammonium hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acid, protein, aniline, ammonia, nitric acid or nitrous acid.

[0018] In some embodiments of the present invention, if contained, the sulfur atom precursor includes at least one of sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, lipoic acid ester, carbon disulfide, mercaptan, sulfuric acid, magnesium sulfate or hydrogen sulfide.

[0019] In some embodiments of the present invention, if contained, the phosphorus atom precursor includes at least one of phosphoric acid, sodium hypophosphite, calcium hydrogen phosphate, tributyl phosphate, triethyl phosphate, tetraethyl pyrophosphate, and diethyl phosphate.

[0020] Using urea, ammonium glucose hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acids, proteins, ammonia, aniline, nitric acid, nitrous acid and other nitrogen atom precursors; sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, sulfuric acid, magnesium sulfate, carbon disulfide, thiol, hydrogen sulfide, lipoic acid ester and other sulfur atom precursors; phosphoric acid, sodium hypophosphite, tributyl phosphate, triethyl phosphate, calcium hydrogen phosphate, tetraethyl phosphate, diethyl phosphate and other phosphorus atom precursors as other heteroatom precursors, increasing the sodium storage active sites of hard carbon can improve the slope zone capacity of the hard carbon negative electrode. The improved capacity has a fast kinetic response, good rate performance and high reversibility, and can also accelerate the diffusion dynamics of sodium ions.

[0021] In some preferred embodiments of the present invention, the heteroatom precursor is urea.

[0022] In some embodiments of the present invention, the metal single atom precursor includes a metal salt, and the metal salt includes at least one of chlorides, sulfates, sulfites, nitrates, nitrites, oxalates, carbonates, alkyl sulfonates, alkylbenzene sulfonates and hydrates thereof.

[0023] It is understood that the preparation of sodium-ion battery metal single-atom doped hard carbon anode materials uses a variety of hard carbon precursors, other heteroatom precursors, and metal single-atom precursors. Metal single atoms include, but are not limited to, one or more of Sn, Sb, Bi, K, Mg, Al, Li, Rb, Cs, Mo, Ru, Rh, Pd, Ag, In, W, Ir, and Pb. These metal single atoms can undergo alloying reactions with sodium atoms, and this alloying reaction can provide higher capacity. Therefore, the effects of doping with such metal atoms include: 1) regulating the hard carbon structure and increasing the sodium storage capacity of the hard carbon itself; 2) the metal atoms themselves are electrochemically active and can undergo alloying reactions with sodium ions, thereby further improving the capacity of the hard carbon composite material.

[0024] In some embodiments of the present invention, the metal single atom is at least one of Sn, Sb, Bi, K, Mg, Al, Li, Rb, Cs, Mo, Ru, Rh, Pd, Ag, In, W, Ir, or Pb. These metals and their salts are abundant in reserves nationwide, readily available, safe, non-toxic, and relatively low in market price, facilitating industrialization. Furthermore, the doping process of the metal single atom is simple and easy to implement, increasing the interlayer spacing and sodium storage sites in the hard carbon anode material, thereby improving the performance of sodium-ion batteries.

[0025] In some preferred embodiments of the present invention, the metal single atom precursor is stannous chloride dihydrate.

[0026] It can be understood that the various raw materials used in the scheme of the present invention are widely available and have sufficient storage capacity. The negative electrode material using the scheme of the present invention has a high specific capacity and first coulombic efficiency. At the same time, after being assembled into a sodium ion battery, it also has excellent cycle performance and rate performance, which can effectively alleviate the problem of limited lithium resource reserves and enable its application to be unrestricted by lithium resources.

[0027] In some embodiments of the present invention, the mass of the metal single atom precursor is 0.5% to 20% of the mass of the hard carbon precursor. The mass ratio of the metal single atom precursor to the hard carbon precursor can be any ratio between 0.5% and 20%, such as 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, etc.

[0028] In some embodiments of the present invention, the mass of the heteroatom precursor is 0.5% to 50% of the mass of the hard carbon precursor. The mass ratio of the heteroatom precursor to the hard carbon precursor can be any ratio between 0.5% and 50%, such as 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, etc.

[0029] According to another aspect of the present invention, a method for preparing the above-mentioned material is provided, comprising the following steps:

[0030] S1. mixing a hard carbon precursor, a heteroatom precursor, and a metal single atom precursor to obtain a mixture;

[0031] S2, calcining the mixture in a mixed gas to obtain the hard carbon negative electrode material;

[0032] The mixed gas contains reducing gas and protective gas, and the heteroatom precursor includes at least one of a nitrogen atom precursor, a sulfur atom precursor, and a phosphorus atom precursor.

[0033] According to a preferred embodiment of the present invention, the preparation method has at least the following beneficial effects: the doping design of hard carbon can be achieved by calcining a hard carbon precursor, a metal single atom precursor, and other heteroatom precursors in a protective gas atmosphere containing a reducing gas such as argon or hydrogen. The preparation method of the present invention achieves the doping of the hard carbon matrix with metal single atoms, increases the sodium storage sites of the hard carbon negative electrode material, accelerates the diffusion kinetics of sodium ions, and thus improves the reversible specific capacity of the sodium ion battery. At the same time, it increases the electronic conductivity, improves the rate performance of the battery, and improves the electrochemical performance of the battery at room temperature and low temperature. The preparation process of the present invention is simple, the raw materials are widely available, the types of equipment used are relatively few, the production cost is low, it is suitable for industrial large-scale production, and has good industrial application prospects.

[0034] In some embodiments of the present invention, the hard carbon precursor includes at least one of a carbohydrate, biomass, or resin. One or more hard carbon sources may be used for calcination, and a hard carbon source containing heteroatoms may also be used for calcination.

[0035] In some embodiments of the present invention, if contained, the carbohydrate substance comprises at least one of sucrose, glucose, fructose, cyclodextrin, starch or cellulose.

[0036] In some embodiments of the present invention, if present, the biomass comprises at least one of lignin, chitosan, bamboo charcoal powder, bamboo fiber powder, coconut shells, nut shells, straw, sugarcane stalks, sawdust, poplar wood, pollen, sawdust, foxtail grass, shells, apple peels, wheat, and dandelions. Using biomass raw materials as hard carbon precursors is green, renewable, economical, and environmentally friendly.

[0037] In some embodiments of the present invention, if present, the resin comprises at least one of phenolic resin, epoxy resin, phenolic epoxy resin, phenol-furfural resin, para-diphenol-formaldehyde resin, polyacrylonitrile, polyaniline, polypyrrole, polystyrene, polyimidazole, polythiophene, polytetrafluoroethylene, and polyvinyl chloride. Having a defined chemical composition allows for qualitative batch production, with different batches of hard carbon having the same properties.

[0038] In some preferred embodiments of the present invention, the hard carbon precursor is bamboo fiber powder.

[0039] In some embodiments of the present invention, if contained, the nitrogen atom precursor includes at least one of urea, glucose ammonium hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acid, protein, aniline, ammonia, nitric acid or nitrous acid.

[0040] In some embodiments of the present invention, if contained, the sulfur atom precursor includes at least one of sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, lipoic acid ester, carbon disulfide, mercaptan, sulfuric acid, magnesium sulfate or hydrogen sulfide.

[0041] In some embodiments of the present invention, if contained, the phosphorus atom precursor includes at least one of phosphoric acid, sodium hypophosphite, calcium hydrogen phosphate, tributyl phosphate, triethyl phosphate, tetraethyl pyrophosphate, and diethyl phosphate.

[0042] Using urea, ammonium glucose hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acids, proteins, ammonia, aniline, nitric acid, nitrous acid and other nitrogen atom precursors; sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, sulfuric acid, magnesium sulfate, carbon disulfide, thiol, hydrogen sulfide, lipoic acid ester and other sulfur atom precursors; phosphoric acid, sodium hypophosphite, tributyl phosphate, triethyl phosphate, calcium hydrogen phosphate, tetraethyl phosphate, diethyl phosphate and other phosphorus atom precursors as other heteroatom precursors, increasing the sodium storage active sites of hard carbon can improve the slope zone capacity of the hard carbon negative electrode. The improved capacity has a fast kinetic response, good rate performance and high reversibility, and can also accelerate the diffusion dynamics of sodium ions.

[0043] In some preferred embodiments of the present invention, the heteroatom precursor is urea.

[0044] In some embodiments of the present invention, the metal single atom precursor includes a metal salt, and the metal salt includes at least one of chlorides, sulfates, sulfites, nitrates, nitrites, oxalates, carbonates, alkyl sulfonates, alkylbenzene sulfonates and hydrates thereof.

[0045] It is understood that the preparation of sodium-ion battery metal single-atom doped hard carbon anode materials uses a variety of hard carbon precursors, other heteroatom precursors, and metal single-atom precursors. Metal single atoms include, but are not limited to, one or more of Sn, Sb, Bi, K, Mg, Al, Li, Rb, Cs, Mo, Ru, Rh, Pd, Ag, In, W, Ir, and Pb. These metal single atoms can undergo alloying reactions with sodium atoms, and this alloying reaction can provide higher capacity. Therefore, the effects of doping with such metal atoms include: 1) regulating the hard carbon structure and increasing the sodium storage capacity of the hard carbon itself; 2) the metal atoms themselves are electrochemically active and can undergo alloying reactions with sodium ions, thereby further improving the capacity of the hard carbon composite material.

[0046] In some embodiments of the present invention, the metal single atom is at least one of Sn, Sb, Bi, K, Mg, Al, Li, Rb, Cs, Mo, Ru, Rh, Pd, Ag, In, W, Ir, or Pb. These metals and their salts are abundant in reserves nationwide, readily available, safe, non-toxic, and relatively low in market price, facilitating industrialization. Furthermore, the doping process of the metal single atom is simple and easy to implement, increasing the interlayer spacing and sodium storage sites in the hard carbon anode material, thereby improving the performance of sodium-ion batteries.

[0047] In some preferred embodiments of the present invention, the metal single atom precursor is stannous chloride dihydrate.

[0048] It is understandable that the various raw materials used in the scheme of the present invention are widely available and have sufficient storage capacity. The negative electrode material using the scheme of the present invention has a high specific capacity and first coulombic efficiency. At the same time, after being assembled into a sodium ion battery, it also has excellent cycle performance and rate performance, which can effectively alleviate the problem of limited lithium resource reserves and make its application unrestricted by lithium resources. The raw materials used in the sodium ion battery metal single atom doped hard carbon negative electrode material of the present invention are non-toxic and pollution-free, green and safe, renewable, and inexpensive. No toxic or harmful substances are produced during the reaction process. The preparation method is simple and the equipment used is single, which is suitable for industrial large-scale production.

[0049] In some embodiments of the present invention, the mass of the metal single atom precursor is 0.5% to 20% of the mass of the hard carbon precursor. The mass ratio of the metal single atom precursor to the hard carbon precursor can be any ratio between 0.5% and 20%, such as 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, etc.

[0050] In some embodiments of the present invention, the mass of the heteroatom precursor is 0.5% to 50% of the mass of the hard carbon precursor. The mass ratio of the heteroatom precursor to the hard carbon precursor can be any ratio between 0.5% and 50%, such as 1%, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, etc.

[0051] In some embodiments of the present invention, the reducing gas is hydrogen. Hydrogen or other reducing gases are added to the protective gas to prevent the material from being easily oxidized during the high-temperature calcination process.

[0052] In some embodiments of the present invention, the protective gas is at least one of an inert gas or nitrogen.

[0053] In some preferred embodiments of the present invention, the inert gas is argon.

[0054] In some embodiments of the present invention, the volume proportion of the reducing gas in the mixed gas is 1-10%. The inclusion of a certain proportion of reducing gas can ensure that the material is not easily oxidized during the high-temperature calcination process.

[0055] In a preferred embodiment of the present invention, the volume proportion of the reducing gas in the mixed gas is 5%.

[0056] In some embodiments of the present invention, the calcination temperature is 600°C to 1400°C, such as 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, etc.

[0057] In some embodiments of the present invention, the calcination time is 2 hours to 12 hours, such as 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, etc.

[0058] The temperature and time of high-temperature calcination and carbonization are not particularly limited, and the calcination may be performed at 600-1400° C. for 2-12 hours.

[0059] In some embodiments of the present invention, the step S1 includes mixing a hard carbon precursor, a heteroatom precursor, and a metal single atom precursor in a solvent, and removing the solvent to obtain the mixture.

[0060] In some embodiments of the present invention, the solvent includes water. Water and other solvents can be used to mix the raw materials more evenly.

[0061] In some embodiments of the present invention, the solvent is removed by freeze drying or heat drying.

[0062] In some embodiments of the present invention, the heating and drying temperature is 60°C to 100°C, such as 70°C, 80°C, or 90°C.

[0063] In some embodiments of the present invention, the heating and drying time is 6 hours to 48 hours, such as 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, 30 hours, 31 hours, 32 hours, 33 hours, 34 hours, 35 hours, 36 hours, 37 hours, 38 hours, 39 hours, 40 hours, 41 hours, 42 hours, 43 hours, 44 hours, 45 hours, 46 hours, 47 hours, 48 ​​hours, etc.

[0064] The temperature and time of heat drying are not particularly limited, and heat drying can be performed at 60 to 100° C. for 6 to 48 hours.

[0065] According to yet another aspect of the present invention, a sodium ion battery is provided, comprising the above-mentioned negative electrode material.

[0066] According to a preferred embodiment of the present invention, a sodium battery has at least the following beneficial effects: the negative electrode material of the present invention improves the kinetic problems of sodium ion batteries such as low ion and electron transfer rates at low temperatures, and improves the charge and discharge performance and capacity of sodium ions under low temperature conditions when hard carbon is used as the negative electrode. The sodium ion battery using the negative electrode material of the present invention has faster kinetics and higher storage capacity, and at the same time, also has better rate performance and power density. Beneficial effects

[0067] The sodium ion battery negative electrode material prepared by the present invention contains highly dispersed metal single atoms, which are doped in the hard carbon matrix through covalent interactions with heteroatoms. These metal atoms, as high-capacity active centers, can undergo alloying reactions with sodium, and enhance the charge and discharge process of the negative electrode through the "adsorption-intercalation-pore filling" of sodium ions on hard carbon and reversible alloying reactions with metal atoms. At the same time, the strong bonding between these metal single atoms and the carbon matrix on the interface not only stabilizes the dispersion of single metal atoms, but also regulates the electronic structure of hard carbon, promotes electron transfer, and minimizes the possibility of metal single atom clustering during the chemical reaction. High-load MXC can make full use of active sites, reduce volume changes and agglomeration, and accelerate the conduction of sodium ions or electrons. The sodium ion battery metal single atom doped hard carbon negative electrode material of the present invention simultaneously realizes heteroatom doping and metal single atom doping design, which can improve the rapid kinetic slope zone capacity and low potential platform zone capacity of the sodium ion battery. Due to the increase in sodium storage sites, the assembled sodium ion battery has high capacity, good cycle performance, and high safety factor, and can achieve high capacity retention rate and ion transfer rate of the sodium ion battery at low temperature, solving the problem of limited electrochemical performance of the sodium ion battery under low temperature conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0069] FIG1 is a schematic structural diagram of a hard carbon negative electrode material according to an embodiment of the present invention;

[0070] FIG2 is a scanning electron microscope image (SEM) of the hard carbon negative electrode material prepared in Example 1 of the present invention;

[0071] FIG3 is another SEM image and energy dispersive spectrum (EDS) analysis of the hard carbon negative electrode material prepared in Example 1 of the present invention;

[0072] FIG4 is an X-ray powder diffraction pattern (XRD) of the hard carbon negative electrode material prepared in Example 1 of the present invention;

[0073] FIG5 is a cycle life curve of a button cell made from the hard carbon negative electrode material prepared in Example 1 of the present invention;

[0074] FIG6 shows the rate performance test results of a button cell made from the hard carbon negative electrode material prepared in Example 1 of the present invention.

[0075] Reference numerals: 1. Hard carbon matrix. Modes for Carrying Out the Invention

[0076] The following will clearly and completely describe the concept of the present invention and the technical effects produced in conjunction with the embodiments, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention. Unless otherwise specified, the test methods used in the embodiments are all conventional methods; the materials, reagents, etc. used, unless otherwise specified, are reagents and materials obtained from commercial channels. Unless otherwise specified, the same parameter in each embodiment has the same value. The embodiments described below are exemplary and are only used to explain the present invention, and are not to be understood as limitations of the present invention.

[0077] In the description of the present invention, reference to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the exemplary expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0078] Example 1

[0079] This embodiment prepares a hard carbon negative electrode material, including a hard carbon matrix, heteroatoms and metal single atoms, wherein the metal single atom is Sn, the heteroatom is N atom, and the metal single atom Sn is doped in the hard carbon matrix through the heteroatom N atom.

[0080] The specific preparation process is as follows: 2g of hard carbon precursor (bamboo fiber powder), 0.4g of heteroatom precursor (urea) and 0.1g of metal single atom precursor (stannous chloride dihydrate) are dissolved in deionized water; the mixture is placed in a freeze dryer for freeze drying; the mixture is placed in a tube furnace and calcined at 1000°C for 2 hours to obtain a carbonized material; the carbonized material is washed, filtered and dried to obtain a metal single atom-doped hard carbon negative electrode material.

[0081] Example 2-23

[0082] This embodiment prepares a hard carbon negative electrode material. The difference between this embodiment and embodiment 1 is that a different type of hard carbon precursor is used. For specific hard carbon precursors, refer to Table 1.

[0083] Examples 24-50

[0084] This embodiment prepares a hard carbon negative electrode material, which differs from Example 1 in that different heteroatom precursors are used. For specific heteroatom precursors, refer to Table 1.

[0085] Examples 51-78

[0086] This embodiment prepares a hard carbon negative electrode material, which differs from Example 1 in that different metal single atom precursors are used. For specific metal single atom precursors, refer to Table 1.

[0087] Examples 79-107

[0088] This embodiment prepares a hard carbon negative electrode material, which differs from embodiment 1 in that different calcination temperatures and / or times are used. For specific temperatures and times, refer to Table 2.

[0089] Examples 108-161

[0090] This embodiment prepares a hard carbon negative electrode material, which differs from embodiment 1 in that different metal single atom doping amounts are used. For specific doping amounts, refer to Table 3.

[0091] Structural characterization

[0092] The structural schematic of the hard carbon negative electrode material of the present invention is shown in Figure 1. Metal single atoms are doped into the hard carbon matrix 1 via heteroatoms. The micromorphology of the hard carbon negative electrode materials prepared in each example was examined by scanning electron microscopy and energy spectrum analysis was performed. The SEM and EDS images of the hard carbon negative electrode material prepared in Example 1 are shown in Figures 2 and 3. As can be seen in Figures 2 and 3, no single metal particles are observed, indicating that the metal is dispersed in the hard carbon in the form of single atoms.

[0093] In addition, X-ray powder diffraction analysis was performed on the hard carbon negative electrode materials prepared in each example, and the results are shown in Figure 4. As can be seen from Figure 4, the hard carbon negative electrode material prepared in Example 1 has a typical hard carbon peak. In addition, only the Sn diffraction peak (PDF#86-2265) is present, further indicating that the metal elements in the hard carbon negative electrode material prepared in Example 1 of the present invention are doped in the hard carbon matrix in the form of metal single atoms.

[0094] Application effect examples

[0095] The above-mentioned negative electrode materials were used in the preparation of sodium batteries. The prepared hard carbon negative electrode material was mixed with Super P and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 8:1:1. N-methylpyrrolidone (NMP) was added and ground into a slurry. The slurry was evenly coated on aluminum foil, dried in an 80°C vacuum oven for 12 hours, and cut into circular electrode pieces. A sodium metal sheet was used as the counter electrode, a Whatman glass fiber separator (GF / D) was used as the separator, and 1M NaPF6 and 80μL of EC / DMC / EMC were added as the electrolyte to assemble a button half-cell.

[0096] The performance of the sodium battery prepared from the above negative electrode materials at room temperature and low temperature was tested in the voltage range of 0.01V-2.0V. The specific test process is as follows:

[0097] At room temperature (25°C) and a current density of 0.2C (1C=300mA / g), the performance of the metal single-atom doped hard carbon negative electrode was tested, including specific capacity, first coulombic efficiency, and the number of cycles at which the capacity decayed to 80%. The voltage range of the test was 0.01-2.0V. In addition, the rate performance was tested at room temperature (25°C) in the range of 0.01-2.0V. The gram-specific capacities of 0.1C\0.2C\0.5C\1C\0.5C\0.2C\0.1C were tested in sequence, and each rate was tested for 10 weeks.

[0098] At low temperature (-40°C) and a current density of 0.2C, the performance of the metal single-atom doped hard carbon anode was tested, including specific capacity and the number of cycles until the capacity decayed to 80%. The test voltage range was 0.01-2.0V.

[0099] The test results are shown in Tables 1 to 3. The specific capacity, initial coulombic efficiency, and the number of cycles until the capacity decays to 80% of the negative electrode materials prepared with different raw materials are compared in Table 1:

[0100] Table 1 Performance comparison of negative electrode materials prepared from different raw materials

[0101]

[0102]

[0103]

[0104]

[0105] As can be seen from Table 1, the hard carbon negative electrode materials prepared from different hard carbon precursors, heteroatom precursors and / or metal single atom precursors in the embodiments of the present invention have good overall specific capacity, first coulomb efficiency and cycle performance. Even in ultra-low temperature environments, they have high specific capacity and cycle performance, indicating that the raw materials applicable to the present invention are widely available and only require a simple preparation process to produce hard carbon negative electrode materials with extremely good performance. Different raw materials have a certain influence on the electrical properties of the prepared negative electrode materials. Among the different hard carbon precursors used in the embodiments, bamboo fiber powder has the best comprehensive performance; among the negative electrode materials prepared from different heteroatoms, the negative electrode material prepared from N atoms has the best comprehensive performance. Among them, when urea is used as the heteroatom precursor, the comprehensive performance is better than that of other heteroatom precursors; when stannous chloride dihydrate is used as the precursor of the metal single atom precursor, the comprehensive performance of the doped negative electrode material is the best.

[0106] The specific capacity, first coulombic efficiency and the number of cycles for the capacity to decay to 80% of the negative electrode materials prepared at different calcination temperatures and times are shown in Table 2:

[0107] Table 2 Performance comparison of negative electrode materials prepared at different calcination temperatures and times

[0108]

[0109]

[0110] As shown in Table 2, the hard carbon anode materials produced at different calcination temperatures and times exhibit excellent overall specific capacity, initial coulombic efficiency, and cycling performance, even at ultra-low temperatures. The electrical properties of the resulting anode materials vary depending on the specific calcination conditions, with calcination at 1000°C for two hours achieving the best results.

[0111] The specific capacity, first coulombic efficiency and the number of cycles for capacity decay to 80% of the negative electrode materials prepared with different metal single atom doping amounts are shown in Table 3:

[0112] Table 3 Performance comparison of negative electrode materials prepared with different metal single atom doping amounts

[0113]

[0114]

[0115]

[0116] Note: The metal single atom doping mass ratio is calculated based on the mass ratio of the metal single atom precursor to the hard carbon precursor.

[0117] Among them, the precursor of bismuth is bismuth nitrate pentahydrate, the precursor of antimony is antimony nitrate trihydrate, the precursor of rubidium is rubidium carbonate, and the precursor of cesium is cesium nitrate.

[0118] As shown in Table 3, the hard carbon anode materials prepared with different metal single-atom doping ratios exhibit excellent overall specific capacity, initial coulombic efficiency, and cycling performance, even at ultra-low temperatures. The electrical properties of the resulting anode materials vary depending on the specific calcination conditions, with the best performance achieved when tin was doped at 4wt%.

[0119] The cycle life curve of a button-type battery made from the hard carbon negative electrode material prepared in Example 1 of the present invention is shown in Figure 5. As can be seen from the figure, the hard carbon negative electrode material prepared using this embodiment of the present invention exhibits excellent cycle performance when fabricated into a sodium battery. The rate performance test results of a button-type battery made from the hard carbon negative electrode material prepared in Example 1 of the present invention are shown in Figure 6. As can be seen from the figure, the hard carbon negative electrode material prepared using this embodiment of the present invention exhibits excellent rate performance when fabricated into a sodium battery. The results of the other examples are similar and are not shown individually to avoid redundancy.

[0120] The sodium ion battery nitrogen-containing metal single atom doped hard carbon negative electrode material prepared by the present invention can be made of hard carbon precursors such as sucrose, glucose, fructose, chitosan, starch, cyclodextrin, cellulose, lignin, phenolic resin, epoxy resin, phenolic epoxy resin, polyacrylonitrile, polyaniline, polypyrrole, polystyrene, polyimidazole, polythiophene, polytetrafluoroethylene, polyvinyl chloride, phenol-furfural resin, p-diphenol-formaldehyde resin, bamboo charcoal powder, bamboo fiber powder, coconut shell, straw, walnut shell, nut shell, sugarcane stalk, sawdust, poplar, pollen, sawdust, foxtail grass, shell, apple peel, wheat, dandelion, etc.; nitrogen atom precursors such as urea, glucose ammonium hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acids, proteins, ammonia, aniline, nitric acid, nitrous acid, etc.; sodium toluenesulfonate. , sodium ethylbenzenesulfonate, sulfuric acid, magnesium sulfate, carbon disulfide, thiol, hydrogen sulfide, lipoic acid ester and other sulfur atom precursors; phosphoric acid, sodium hypophosphite, tributyl phosphate, triethyl phosphate, calcium hydrogen phosphate, tetraethyl phosphate, diethyl phosphate and other phosphorus atom precursors; Sn, Sb, Bi, K, Mg, Al, Li, Rb, Cs, Mo, Ru, Rh, Pd, Ag, In, W, Ir, Pb chlorides, sulfates, sulfites, nitrates, nitrites, oxalates, carbonates, alkyl sulfonates, alkylbenzenesulfonates and their hydrates are used as metal single atom precursors; the raw materials are low in cost and pollution-free, and the specific capacity, cycle performance and first coulombic efficiency of the obtained negative electrode materials are improved, which can be used for high-performance sodium ion battery negative electrodes and sodium ion battery negative electrodes at low temperatures. The emergence of sodium-ion batteries not only alleviates the problems of limited lithium-ion resources and high costs, but also the positive and negative electrode materials are simple, cheap and easy to obtain. The sodium-ion battery prepared using the hard carbon negative electrode material of the present invention is a sodium-ion battery with high specific capacity, high cycle performance and high safety.

[0121] In summary, the sodium ion battery negative electrode material prepared by the present invention contains highly dispersed metal single atoms, which are doped in the hard carbon matrix through covalent interactions with heteroatoms. These metal atoms, as high-capacity active centers, can undergo alloying reactions with sodium, and enhance the charge and discharge process of the negative electrode through the "adsorption-intercalation-pore filling" of sodium ions on hard carbon and reversible alloying reactions with metal atoms. At the same time, the strong bonding between these metal single atoms and the carbon matrix on the interface not only stabilizes the dispersion of single metal atoms, but also regulates the electronic structure of hard carbon, promotes electron transfer, and minimizes the possibility of metal single atom clustering during the chemical reaction. High-load MXC can make full use of active sites, reduce volume changes and agglomeration, and accelerate the conduction of sodium ions or electrons. The sodium ion battery metal single atom doped hard carbon negative electrode material of the present invention simultaneously realizes heteroatom doping and metal single atom doping design, which can improve the rapid kinetic slope zone capacity and low potential platform zone capacity of the sodium ion battery. Due to the increase in sodium storage sites, the assembled sodium ion battery has high capacity, good cycle performance, and high safety factor, and can achieve high capacity retention rate and ion transfer rate of the sodium ion battery at low temperature, solving the problem of limited electrochemical performance of the sodium ion battery under low temperature conditions.

[0122] The embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge scope of ordinary technicians in the relevant technical field without departing from the scope of the present invention.

Claims

1. A hard carbon negative electrode material, characterized in that: The hard carbon negative electrode material includes a hard carbon matrix, heteroatoms and metal single atoms, wherein the metal single atoms are doped in the hard carbon matrix through the heteroatoms, the heteroatoms include at least one of N, P or S, and the metal single atoms are metal single atoms that can undergo an alloying reaction with sodium.

2. The hard carbon negative electrode material according to claim 1, characterized in that: The metal single atom is at least one of Sn, Sb, Bi, K, Mg, Al, Li, Rb, Cs, Mo, Ru, Rh, Pd, Ag, In, W, Ir or Pb.

3. The hard carbon negative electrode material according to claim 1, characterized in that: The raw materials for preparing the hard carbon negative electrode material include a hard carbon precursor, a heteroatom precursor and a metal single atom precursor, wherein the heteroatom precursor includes at least one of a nitrogen atom precursor, a sulfur atom precursor or a phosphorus atom precursor.

4. The hard carbon negative electrode material according to claim 3, characterized in that: The hard carbon precursor includes at least one of a sugar substance, a biomass or a resin; and / or, If contained, the nitrogen atom precursor includes at least one of urea, ammonium glucose hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acid, protein, aniline, ammonia, nitric acid or nitrous acid; and / or, If contained, the sulfur atom precursor includes at least one of sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, lipoic acid ester, carbon disulfide, mercaptan, sulfuric acid, magnesium sulfate or hydrogen sulfide; and / or, If contained, the phosphorus atom precursor includes at least one of phosphoric acid, sodium hypophosphite, calcium hydrogen phosphate, tributyl phosphate, triethyl phosphate, tetraethyl pyrophosphate, and diethyl phosphate; And / or, the metal single atom precursor includes a metal salt, and the metal salt includes at least one of chlorides, sulfates, sulfites, nitrates, nitrites, oxalates, carbonates, alkyl sulfonates, alkylbenzene sulfonates and hydrates thereof.

5. The hard carbon negative electrode material according to claim 4, characterized in that: If contained, the sugar substance includes at least one of sucrose, glucose, fructose, cyclodextrin, starch or cellulose; and / or, If contained, the biomass comprises at least one of lignin, chitosan, bamboo charcoal powder, bamboo fiber powder, coconut shell, nut shell, straw, sugarcane stalk, sawdust, poplar, pollen, sawdust, foxtail grass, shell, apple peel, wheat or dandelion; and / or, If contained, the resin includes at least one of phenolic resin, epoxy resin, phenolic epoxy resin, phenol-furfural resin, p-diphenol-formaldehyde resin, polyacrylonitrile, polyaniline, polypyrrole, polystyrene, polyimidazole, polythiophene, polytetrafluoroethylene, and polyvinyl chloride.

6. The hard carbon negative electrode material according to claim 3, 4 or 5, characterized in that: The mass of the metal single atom precursor is 0.5% to 20% of the mass of the hard carbon precursor; and / or the mass of the heteroatom precursor is 0.5% to 50% of the mass of the hard carbon precursor.

7. A method for preparing a hard carbon negative electrode material according to any one of claims 1 to 6, characterized in that: The steps include: S1, mixing a hard carbon precursor, a heteroatom precursor and a metal single atom precursor to obtain a mixture; S2, calcining the mixture in a mixed gas to obtain the hard carbon negative electrode material; The mixed gas contains reducing gas and protective gas, and the heteroatom precursor includes at least one of a nitrogen atom precursor, a sulfur atom precursor or a phosphorus atom precursor.

8. The preparation method according to claim 7, characterized in that: The reducing gas is hydrogen; and / or, The protective gas is at least one of an inert gas or nitrogen; The volume proportion of reducing gas in the mixed gas is 1-10%.

9. The preparation method according to claim 7, characterized in that: The calcination temperature is 600° C. to 1400° C.; and / or the calcination time is 2 h to 12 h.

10. The preparation method according to claim 7, characterized in that: The step S1 comprises mixing a hard carbon precursor, a heteroatom precursor and a metal single atom precursor in a solvent, and removing the solvent by freeze drying or heat drying to obtain the mixture.

11. A sodium ion battery, characterized in that: The sodium ion battery comprises the hard carbon negative electrode material according to any one of claims 1 to 6.

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