Hard carbon negative electrode material and preparation method and application thereof

Abstract

The application discloses a kind of hard carbon negative electrode material and its preparation method and application, the hard carbon negative electrode material includes hard carbon matrix, heteroatom and metal monatomic atom, wherein, the metal monatomic atom is doped in the hard carbon matrix by the heteroatom, the heteroatom includes at least one of N, P or S, the metal monatomic atom is the metal monatomic atom capable of alloying reaction with sodium. Metal monatomic atom is doped in hard carbon matrix by the covalent (chemical bond) action with other heteroatoms, realize the doping of single atom, improve the overall capacity of sodium ion battery at room temperature and rate performance, simultaneously, also guarantee its capacity retention rate under low temperature condition.

Description

TECHNICAL FIELD

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

[0002] With the wide application of lithium ion batteries in electric vehicles, mobile phones, computers and other electronic products, the demand for lithium is increasing year by year. However, the global lithium storage is extremely limited, unevenly distributed and high in cost, which seriously limits the development of low-cost and high-performance energy storage devices. Sodium and lithium are homologous elements, which have similar electrochemical properties, abundant reserves and low cost, and are the next generation of market application 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 3 times that of lithium ions, and the diameter is 1.3 times that of lithium ions, which leads to the fact that sodium ions cannot reversibly intercalate and deintercalate in the interlayer of graphite within the effective potential window. At the same time, sodium ion-graphite intercalation compounds are not thermodynamically stable and are prone to form NaC 64 Common sodium ion batteries use hard carbon materials, transition metal and alloy compounds as negative electrode materials. Among them, transition metal and alloy compounds have limited commercial prospects due to complex preparation process, and hard carbon materials cannot be graphitized and have lower carbon layer arrangement regularity than soft carbon. A large number of micropores are formed between the layers, which facilitates the intercalation and deintercalation of sodium ions. Moreover, hard carbon has the advantages of wide source, low cost and high theoretical reversible specific capacity, and is currently considered as the most suitable negative electrode material for commercial sodium ion batteries.

[0004] However, due to the porous structure and a large number of active sites of hard carbon, the first efficiency is low (less than 80%), and the existing hard carbon materials mostly face the problem of ion transport blocked under low temperature conditions, low capacity and poor charge-discharge performance. In related technologies, metal atomic clusters are doped in the pores of hard carbon to improve the first efficiency and other electrochemical properties. However, when metal atomic clusters are doped, the metal atoms are not maximally exposed in the material, so the advantages of activity and electrical conductivity cannot be fully utilized, which limits the improvement of the electrical properties of the hard carbon negative electrode. SUMMARY

[0005] The present application aims to at least solve one of the problems in the prior art. To this end, the present application provides a hard carbon negative electrode material, which is doped with metal monatomic atoms. The metal monatomic atoms are doped in the hard carbon matrix through chemical bonding with heteroatoms, thereby improving the charge-discharge performance and capacity of the sodium ion battery.

[0006] The present application also provides a preparation method of the above-mentioned material.

[0007] The application also provides the material as described above.

[0008] According to an aspect of the application, a hard carbon negative electrode material is provided, which comprises a hard carbon matrix, a heteroatom and a metal monatomic, wherein the metal monatomic is doped in the hard carbon matrix through the heteroatom, the heteroatom comprises at least one of N, P or S, and the metal monatomic is a metal monatomic capable of alloying with sodium.

[0009] According to a preferred embodiment of the application, at least the following beneficial effects are achieved: the metal monatomic is doped in the hard carbon negative electrode material to form a M-X-C structure (M is a metal atom and X is a heteroatom), the high-load M-X-C can fully utilize active sites, reduce volume change and agglomeration, and accelerate the conduction of sodium ions or electrons. The metal monatomic is doped in the hard carbon matrix through covalent (chemical bond) action with other heteroatoms, achieving single-atom doping, improving the overall capacity and rate performance of the sodium ion battery at room temperature, and also ensuring the capacity retention rate of the battery under low temperature conditions. The sodium ion battery assembled by using the negative electrode material of the application has a first coulomb efficiency of more than 88%, high energy density, good cycle stability, high safety factor, good charge-discharge performance and high capacity under low temperature conditions, overcoming the shortcomings of the sodium ion hard carbon negative electrode technology, and aiming to solve the problems of low capacity, low first coulomb efficiency, short cycle life and poor rate performance of the battery due to slow sodium ion transport kinetics of the existing sodium ion battery. The negative electrode material of the application can be widely used in large-scale energy storage and other fields, and is particularly suitable for use in low temperature environments.

[0010] In some embodiments of the application, the metal monatomic 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 application, the raw materials for preparing the hard carbon negative electrode material comprise a hard carbon precursor, a heteroatom precursor and a metal monatomic precursor, wherein the heteroatom precursor comprises at least one of a nitrogen atom precursor, a sulfur atom precursor or a phosphorus atom precursor.

[0012] In some embodiments of the application, the hard carbon precursor comprises at least one of a sugar substance, biomass or resin. One or more hard carbon carbon sources can be calcined, or a hard carbon carbon source containing a heteroatom can be selected for calcination.

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

[0014] In some embodiments of the present application, if containing, the biomass includes at least one of lignin, chitosan, bamboo charcoal powder, bamboo fiber powder, coconut shell, nut shell, straw rod, cane rod, wood chip, poplar wood, pollen, wood chip, dog tail grass, shell, apple skin, wheat or dandelion. Using biomass as hard carbon precursor, green and renewable, economic and environmental protection.

[0015] In some embodiments of the present application, if containing, 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, polyvinyl chloride. There is a certain chemical composition, which can realize qualitative batch production, and the performance of hard carbon produced in different batches is the same.

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

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

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

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

[0020] Urea, ammonium gluconate hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acid, protein, ammonia, aniline, nitric acid, nitrous acid and other nitrogen atom precursors; sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, sulfuric acid, magnesium sulfate, carbon disulfide, mercaptan, hydrogen sulfide, thioctic acid ester and other sulfur atom precursors; phosphoric acid, sodium hypophosphite, tributyl phosphate, triethyl phosphate, calcium hydrogen phosphate, tetraethyl pyrophosphate, diethyl phosphate and other phosphorus atom precursors, etc. as other heteroatom precursors, increase the sodium storage active sites of hard carbon, can improve the slope region capacity of hard carbon negative electrode, the capacity of which has fast kinetics response, good rate performance, and high reversibility, and can also accelerate the diffusion kinetics of sodium ions.

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

[0022] In some embodiments of the present application, the metal monatomic precursor comprises a metal salt, which comprises at least one of a chloride salt, a sulfate salt, a sulfite salt, a nitrate salt, a nitrite salt, an oxalate salt, a carbonate salt, an alkyl sulfonate salt, an alkyl benzene sulfonate salt, and a hydrate thereof.

[0023] It can be understood that the hard carbon precursor for preparing the metal monatomic doped hard carbon negative material of the sodium ion battery, other heteroatom precursors, and metal monatomic precursors are various, and the metal monatomic includes but is 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, and the metal monatomic can all be alloyed with sodium atoms, and the alloying reaction can provide higher capacity. Therefore, the effect of doping such metal atoms includes: 1) adjusting the hard carbon structure to improve the sodium storage capacity of the hard carbon itself; and 2) the metal atoms themselves have electrochemical activity and can be alloyed with sodium ions, thereby further improving the capacity of the hard carbon composite material.

[0024] In some embodiments of the present application, the metal monatomic 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 have abundant reserves in the country, are easy to obtain, are safe and non-toxic, have a relatively low market price, are conducive to industrialization, and in addition, the doping process of the metal monatomic is simple and easy to implement, which increases the interlayer spacing and sodium storage sites of the hard carbon negative material and improves the performance of the sodium ion battery.

[0025] In some preferred embodiments of the present application, the metal monatomic precursor is stannous chloride dihydrate.

[0026] It can be understood that the raw materials used in the present application scheme have a wide source and sufficient storage, and the negative material using the present application scheme has high specific capacity and first coulomb efficiency, and 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 reserves of lithium resources, so that its application is not restricted by lithium resources.

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

[0028] In some embodiments of the present application, the mass of the heteroatom precursor is 0.5% to 50% of the mass of the hard carbon precursor. The mass ratio of the two 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%, and the like.

[0029] According to another aspect of the present application, 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 monatomic 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 comprises a reducing gas and a protective gas, and the heteroatom precursor comprises at least one of a nitrogen atom precursor, a sulfur atom precursor, or a phosphorus atom precursor.

[0033] According to the preparation method of a preferred embodiment of the present application, at least the following beneficial effects are achieved: by calcining the hard carbon precursor, the metal monatomic precursor, and the other heteroatom precursor in a protective gas atmosphere containing a reducing gas such as argon or hydrogen, the doping design of the hard carbon can be realized, the metal monatomic doping of the hard carbon matrix is realized by the preparation method of the present application, the sodium storage sites of the hard carbon negative electrode material are increased, the diffusion dynamics of sodium ions is accelerated, thereby improving the reversible specific capacity of the sodium ion battery. At the same time, the electronic conductivity is increased, the rate performance of the battery is improved, and the electrochemical performance of the battery at room temperature and low temperature is improved. The preparation process of the present application is simple, the raw materials are widely available, the types of equipment used are less, the production cost is low, it is suitable for large-scale industrial production, and has good industrial application prospect.

[0034] In some embodiments of the present application, the hard carbon precursor comprises at least one of a sugar substance, biomass, or resin. One or more hard carbon sources can be used for calcination, or a hard carbon source containing a heteroatom can be selected for calcination.

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

[0036] In some embodiments of the present application, if containing, the biomass includes at least one of lignin, chitosan, bamboo charcoal powder, bamboo fiber powder, coconut shell, nut shell, straw rod, cane rod, wood chip, poplar wood, pollen, wood chip, dog tail grass, shell, apple skin, wheat, dandelion. Using biomass as hard carbon precursor, it is green and renewable, and economic and environmental protection.

[0037] In some embodiments of the present application, if containing, 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, polyvinyl chloride. There is a certain chemical composition, which can realize qualitative batch production, and the performance of hard carbon produced in different batches is the same.

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

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

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

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

[0042] Urea, ammonium gluconate hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acid, protein, ammonia, aniline, nitric acid, nitrous acid and other nitrogen atom precursors; sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, sulfuric acid, magnesium sulfate, carbon disulfide, mercaptan, hydrogen sulfide, thioctic acid ester and other sulfur atom precursors; phosphoric acid, sodium hypophosphite, tributyl phosphate, triethyl phosphate, calcium hydrogen phosphate, tetraethyl pyrophosphate, diethyl phosphate and other phosphorus atom precursors, etc. as other heteroatom precursors, increase the sodium storage active sites of hard carbon, can improve the slope region capacity of hard carbon negative electrode, the capacity of which has fast kinetics response, good rate performance, and high reversibility, and can also accelerate the diffusion kinetics of sodium ions.

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

[0044] In some embodiments of the present application, the metal monatomic precursor comprises a metal salt, which comprises at least one of a chloride salt, a sulfate salt, a sulfite salt, a nitrate salt, a nitrite salt, an oxalate salt, a carbonate salt, an alkyl sulfonate salt, an alkyl benzene sulfonate salt, and a hydrate thereof.

[0045] It can be understood that the hard carbon precursor for preparing the sodium-ion battery metal monatomic doped hard carbon negative electrode material, other heteroatom precursors, metal monatomic precursors are various, and the metal monatomic includes but is 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, and the metal monatomic can be alloyed with sodium atoms, and the alloying reaction can provide higher capacity. Therefore, the effect of doping such metal atoms includes: 1) adjusting the hard carbon structure to improve the sodium storage capacity of the hard carbon itself; 2) the metal atoms themselves have electrochemical activity and can be alloyed with sodium ions, thereby further improving the capacity of the hard carbon composite material.

[0046] In some embodiments of the present application, the metal monatomic 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 have abundant reserves in the country, are easy to obtain, are safe and non-toxic, have relatively low market prices, are conducive to industrialization, and in addition, the doping process of the metal monatomic is simple and easy to implement, which increases the interlayer spacing and sodium storage sites of the hard carbon negative electrode material and improves the performance of the sodium-ion battery.

[0047] In some preferred embodiments of the present application, the metal monatomic precursor is stannous chloride dihydrate.

[0048] It can be understood that the raw materials used in the present application are widely available and have sufficient reserves. The negative electrode material prepared by the present application has high specific capacity and first coulombic efficiency, and 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 reserves of lithium resources, so that its application is not restricted by lithium resources. The raw materials used in the sodium-ion battery metal monatomic doped hard carbon negative electrode material of the present application are non-toxic and non-polluting, green and safe, renewable, and low in price, and no toxic and harmful substances are generated during the reaction process. The preparation method is simple, the equipment used is simple, and it is suitable for industrial large-scale production.

[0049] In some embodiments of the present application, the mass of the metal monatomic precursor is 0.5% to 20% of the mass of the hard carbon precursor. The mass ratio of the two 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 application, the mass of the heteroatom precursor is 0.5% to 50% of the mass of the hard carbon precursor. The ratio of the mass of the two 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%, and the like.

[0051] In some embodiments of the present application, the reducing gas is hydrogen. The reducing gas such as hydrogen is incorporated in the protective gas to avoid the material from being easily oxidized during high-temperature calcination.

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

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

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

[0055] In preferred embodiments of the present application, the volume ratio of the reducing gas in the mixed gas is 5%.

[0056] In some embodiments of the present application, the calcination temperature is 600°C to 1400°C. For example, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, and the like.

[0057] In some embodiments of the present application, the calcination time is 2h to 12h. For example, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, and the like.

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

[0059] In some embodiments of the present application, the step S1 comprises mixing the hard carbon precursor, the heteroatom precursor, and the metal monatomic precursor in a solvent, removing the solvent, and obtaining the mixture.

[0060] In some embodiments of the present application, the solvent comprises water. The use of a solvent such as water allows the raw materials to be mixed more uniformly.

[0061] In some embodiments of the present application, the solvent is removed by freeze-drying or heating drying.

[0062] In some embodiments of the present application, the temperature for the heat drying is 60-100℃. For example, 70℃, 80℃, 90℃.

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

[0064] The temperature and time for the heat drying are not particularly limited, and the heat drying can be performed at 60-100℃ for 6-48 hours.

[0065] According to still another aspect of the present application, a sodium ion battery is provided, which comprises the above negative electrode material.

[0066] The sodium battery according to the preferred embodiment of the present application has at least the following beneficial effects: the negative electrode material of the present application improves the low-temperature ion and electron transport rate and other kinetic problems of the sodium ion battery, improves the low-temperature charge-discharge performance and capacity of the sodium ion battery when hard carbon is used as the negative electrode, and the sodium ion battery using the negative electrode material of the present application has faster kinetics and higher storage capacity, and also has better rate performance and power density.

[0067] Other features and advantages of the present application will be set forth in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or can be learned by practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0068] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the description of the embodiments, taken in conjunction with the following drawings in which:

[0069] Figure 1 is a structural schematic diagram of the hard carbon negative electrode material of the embodiments of the present application;

[0070] Figure 2 is a scanning electron microscope (SEM) image of the hard carbon negative electrode material prepared in Embodiment 1 of the present application;

[0071] Figure 3 is another SEM image and energy dispersive spectroscopy (EDS) image of the hard carbon negative electrode material prepared in Embodiment 1 of the present application;

[0072] Figure 4X-ray powder diffraction pattern (XRD) of the hard carbon negative electrode material prepared in Example 1 of the present application;

[0073] Figure 5 Cycle life curve of the button cell prepared from the hard carbon negative electrode material prepared in Example 1 of the present application;

[0074] Figure 6 Rate performance test results of the button cell prepared from the hard carbon negative electrode material prepared in Example 1 of the present application.

[0075] Label: 1, hard carbon matrix. DETAILED DESCRIPTION

[0076] The concept and the technical effects of the present application will be described in detail below in combination with the embodiments so as to fully understand the objects, features and effects of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments. Based on the embodiments of the present application, other embodiments obtained by those skilled in the art without creative effort fall within the scope of the present application. The test methods used in the embodiments are conventional methods unless otherwise specified. The materials and reagents used in the embodiments are commercially available unless otherwise specified. The same parameters are used in the same way in each embodiment unless otherwise specified. The following described embodiments are exemplary and are used to explain the present application, but cannot be understood as limiting the present application.

[0077] In the description of the present application, the description of the terms “one embodiment”, “some embodiments”, “exemplary embodiment”, “example”, “specific example” or “some examples” means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0078] Example 1

[0079] A hard carbon negative electrode material is prepared in this embodiment, which comprises a hard carbon matrix, heteroatoms and metal monatomic atoms, wherein the metal monatomic atoms are Sn, the heteroatoms are N atoms, and the metal monatomic atoms Sn are doped in the hard carbon matrix through the heteroatoms N atoms.

[0080] The specific preparation process is: 2 g of hard carbon precursor (bamboo fiber powder), 0.4 g of heteroatom precursor (urea) and 0.1 g of metal monatomic 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℃ for 2 hours to obtain a carbonized material; the carbonized material is washed, filtered and dried to obtain a metal monatomic doped hard carbon negative electrode material.

[0081] Examples 2-23

[0082] In this embodiment, a hard carbon negative electrode material is prepared, which is different from example 1 in that different types of hard carbon precursors are used, and the specific hard carbon precursors are referred to table 1.

[0083] Examples 24-50

[0084] In this embodiment, a hard carbon negative electrode material is prepared, which is different from example 1 in that different heteroatom precursors are used, and the specific heteroatom precursors are referred to table 1.

[0085] Examples 51-78

[0086] In this embodiment, a hard carbon negative electrode material is prepared, which is different from example 1 in that different metal monatomic precursors are used, and the specific metal monatomic precursors are referred to table 1.

[0087] Examples 79-107

[0088] In this embodiment, a hard carbon negative electrode material is prepared, which is different from example 1 in that different calcination temperatures and / or times are used, and the specific temperatures and times are referred to table 2.

[0089] Examples 108-161

[0090] In this embodiment, a hard carbon negative electrode material is prepared, which is different from example 1 in that different metal monatomic doping amounts are used, and the specific doping amounts are referred to table 3.

[0091] Structural characterization

[0092] The structural schematic diagram of the hard carbon negative electrode material of the present application is shown in Figure 1 The metal monatomic atom is doped in the hard carbon matrix 1 through the heteroatom. The microstructure of the hard carbon negative electrode material prepared in each example is tested by scanning electron microscopy, and the energy spectrum analysis of the prepared hard carbon negative electrode material is carried out, wherein the SEM and EDS of the hard carbon negative electrode material prepared in example 1 are shown in Figure 2 and 3. As can be seen from Figure 2 and 3 In the figure, no metal monomer particles are observed, indicating that the metal is dispersed in the hard carbon in the form of monatomic atoms.

[0093] In addition, the hard carbon negative electrode material prepared in each embodiment is subjected to X-ray powder diffraction analysis, and the results are shown in FIG. 2. Figure 4 As can be seen from FIG. 2, the hard carbon negative electrode material prepared in Example 1 has typical hard carbon peaks, and in addition, only Sn diffraction peaks (PDF #86-2265) exist, further indicating that the metal element in the hard carbon negative electrode material prepared by the scheme of Example 1 of the present application is in the form of metal single atom doped in the hard carbon matrix. Figure 4

[0094] Application effect example

[0095] The above negative electrode material is used for sodium battery preparation. The hard carbon negative electrode material prepared is mixed with Super P and a binder polyvinylidene fluoride (PVDF) at a mass ratio of 8:1:1, and N-methyl pyrrolidone (NMP) is added to grind into a slurry. The slurry is uniformly coated on an aluminum foil and dried in a vacuum drying oven at 80°C for 12 hours, and then cut into a circular electrode. A metal sodium sheet is used as a counter electrode, Whatman glass fiber separator (GF / D) is used as a separator, 1M NaPF6 and EC / DMC / EMC 80μL are added as electrolyte, and a button half battery is assembled.

[0096] The performance of the above negative electrode material at room temperature and low temperature when prepared into a sodium battery is tested in the voltage range of 0.01V-2.0V, and the specific test process is as follows:

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

[0098] At low temperature (-40°C), the performance of the metal single atom doped hard carbon negative electrode is tested at a current density of 0.2C, including specific capacity and cycle number at which the capacity decays to 80%. The voltage range for testing is 0.01-2.0V.

[0099] The test results are shown in Tables 1-3, wherein the specific capacity, first coulombic efficiency, and cycle number at which the capacity decays to 80% of the negative electrode materials prepared from different raw materials are compared as shown in Table 1:

[0100] Table 1 Comparison table of performance of negative electrode materials prepared from different raw materials

[0101] ​

[0102]

[0103]

[0104]

[0105] As can be seen from Table 1, the overall specific capacity, the first coulombic efficiency and the cycle performance of the hard carbon negative electrode material prepared from different hard carbon precursors, heteroatom precursors and / or metal monatomic precursors in the embodiment of the application are good, and even in an ultra-low temperature environment, the specific capacity and the cycle performance are high, indicating that the raw materials suitable for the application scheme are widely available and only a simple preparation process is required, and an excellent hard carbon negative electrode material can be prepared. Different preparation raw materials have certain influence on the electrical properties of the prepared negative electrode material. Among the different hard carbon precursors used in the embodiment, the comprehensive performance of bamboo fiber powder is the best; among the negative electrode materials prepared from different heteroatoms, the comprehensive performance of the negative electrode material prepared from N atoms is the best, and when urea is used as the heteroatom precursor, the comprehensive performance is better than that of other heteroatom precursors; among the metal monatomic precursors, when stannous chloride dihydrate is used as the precursor, the comprehensive performance of the doped negative electrode material is the best.

[0106] The specific capacity, the first coulombic efficiency and the cycle number of the negative electrode material prepared at different calcination temperatures and times are compared as shown in Table 2:

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

[0108]

[0109]

[0110] As can be seen from Table 2, the overall specific capacity, the first coulombic efficiency and the cycle performance of the hard carbon negative electrode material prepared at different calcination temperatures and times are good, and even in an ultra-low temperature environment, the specific capacity and the cycle performance are high. There are certain differences in the electrical properties of the prepared negative electrode material due to different calcination conditions, and the effect is the best when calcined at 1000°C for two hours.

[0111] The specific capacity, the first coulombic efficiency and the cycle number of the negative electrode material prepared at different metal monatomic doping amounts are compared as shown in Table 3:

[0112] Table 3 Performance comparison table of negative electrode materials prepared at different metal monatomic doping amounts

[0113]

[0114]

[0115]

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

[0117] Wherein, 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] From Table 3, it can be seen that the overall specific capacity, the first coulombic efficiency and the cycle performance of the hard carbon negative electrode material prepared by different metal single atom doping ratios are good, and even in the environment of ultra-low temperature, the hard carbon negative electrode material also has high specific capacity and cycle performance. Due to different calcination conditions, the electrical properties of the prepared negative electrode material are different, and the effect is best when the tin element is doped at a ratio of 4wt%.

[0119] The cycle life curve of the button cell prepared by the hard carbon negative electrode material prepared by the embodiment 1 of the present application is shown in FIG. 1. Figure 5 As can be seen from the figure, the hard carbon negative electrode material prepared by the embodiment of the present application has good cycle performance when prepared into a sodium battery. The rate performance test results of the button cell prepared by the hard carbon negative electrode material prepared by the embodiment 1 of the present application are shown in FIG. 2. Figure 6 As can be seen from the figure, the hard carbon negative electrode material prepared by the embodiment of the present application has good rate performance when prepared into a sodium battery. The effects of other embodiments are similar, and to avoid redundancy, they are not shown one by one.

[0120] The prepared sodium ion battery contains nitrogen metal monatomic doped hard carbon negative material, which can be 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 rod, walnut shell, nut shell, sugarcane rod, sawdust, poplar wood, pollen, sawdust, dogtail grass, shell, apple skin, wheat, dandelion and other hard carbon precursors; urea, glucose ammonium hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, amino acid, protein, ammonia, aniline, nitric acid, nitrous acid and other nitrogen atom precursors; sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, sulfuric acid, magnesium sulfate, carbon disulfide, mercaptan, hydrogen sulfide, thioctic 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 chloride, sulfate, sulfite, nitrate, nitrite, oxalate, carbonate, alkyl sulfonate, alkyl benzene sulfonate and its hydrate as metal monatomic precursor; The raw material cost is low, there is no pollution, the specific capacity, cycle performance and initial coulomb efficiency of the obtained negative material are improved, and it can be used for high-performance sodium ion battery negative electrode and low-temperature sodium ion battery negative electrode. The emergence of sodium ion battery not only alleviates the problem of limited lithium ion resources and high cost, but also the positive and negative electrode materials are simple, cheap and easy to obtain. The sodium ion battery prepared by the hard carbon negative material of the present application is a kind of sodium ion battery with high specific capacity, high cycle performance and high safety.

[0121] In summary, the prepared sodium ion battery negative electrode material contains highly dispersed metal monomers, and the metal monomers are doped in the hard carbon matrix through covalent action with heteroatoms. These metal atoms act as high-capacity active centers and can alloy with sodium. Through the "adsorption-intercalation-pore filling" of sodium ions on hard carbon and the reversible alloying reaction with metal atoms, the charge-discharge process of the negative electrode is improved. At the same time, the strong bonding between the metal monomers and the carbon matrix on the interface not only stabilizes the dispersion of the single metal atoms, but also adjusts the electronic structure of the hard carbon, promotes the transfer of electrons, and minimizes the possibility of metal monomer clusters during the chemical reaction. High-load M-X-C can fully utilize active sites, reduce volume change and agglomeration, and accelerate the conduction of sodium ions or electrons. The sodium ion battery metal monomer doped hard carbon negative electrode material of the application simultaneously realizes heteroatom doping and metal monomer doping design, which can improve the slope region capacity and low potential platform region capacity of the fast kinetics of the sodium ion battery. Due to the increase of sodium storage sites, the assembled sodium ion battery has high capacity, good cycle performance, high safety factor, and can realize high capacity retention rate and ion transmission 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 above describes the embodiments of the application in detail, but the application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the purpose of the application.

Claims

1. A hard carbon negative electrode material, characterized by: The hard carbon negative electrode material comprises a hard carbon matrix, a heteroatom, and a metal monatomic atom, wherein the metal monatomic atom is doped in the hard carbon matrix through chemical bonding with the heteroatom, the heteroatom comprises at least one of N, P, or S, and the metal monatomic atom is a metal monatomic atom capable of alloying with sodium; The preparation method of the hard carbon negative electrode material comprises the following steps: S1, mixing a hard carbon precursor, a heteroatom precursor, and a metal monatomic 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 comprises a reducing gas and a protective gas, and the heteroatom precursor comprises at least one of a nitrogen atom precursor, a sulfur atom precursor, or a phosphorus atom precursor. 2.The hard carbon negative electrode material of claim 1, characterized in that: The metal monatomic 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 anode material according to claim 1, characterized in that: The hard carbon precursor comprises at least one of a sugar substance, biomass, or resin; and / or, The nitrogen atom precursor comprises at least one of urea, glucosamine hydrochloride, pyrrole, imidazole, melamine, dicyandiamide, thiourea, an amino acid, a protein, aniline, ammonia, nitric acid, or nitrous acid; and / or, The sulfur atom precursor comprises at least one of sodium methylbenzenesulfonate, sodium ethylbenzenesulfonate, thioctic acid ester, carbon disulfide, a mercaptan, sulfuric acid, magnesium sulfate, or hydrogen sulfide; and / or, The phosphorus atom precursor comprises at least one of phosphoric acid, sodium hypophosphite, calcium hydrogen phosphate, tributyl phosphate, triethyl phosphate, tetraethyl pyrophosphate, diethyl phosphate; And / or, the metal monatomic atom precursor comprises a metal salt, and the metal salt comprises at least one of a chloride salt, a sulfate salt, a sulfite salt, a nitrate salt, a nitrite salt, an oxalate salt, a carbonate salt, an alkyl sulfonate salt, an alkyl benzene sulfonate salt, and a hydrate thereof. 4.The hard carbon negative electrode material of claim 3, characterized in that: The sugar substance comprises at least one of sucrose, glucose, fructose, cyclodextrin, starch, or cellulose; and / or, The biomass comprises at least one of lignin, chitosan, bamboo charcoal powder, bamboo fiber powder, coconut shell, nut shell, rice straw, sugarcane pole, wood chip, poplar wood, pollen, dogtail grass, shell, apple skin, wheat, or dandelion; and / or, The resin comprises 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.

5. The hard carbon negative electrode material of claim 3 or 4, wherein: The mass of the metal monatomic 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.

6. A method for preparing the hard carbon negative electrode material according to any one of claims 1 to 5, characterized in that: The preparation method comprises the following steps: S1, mixing a hard carbon precursor, a heteroatom precursor, and a metal monatomic 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 comprises a reducing gas and a protective gas, and the heteroatom precursor comprises at least one of a nitrogen atom precursor, a sulfur atom precursor or a phosphorus atom precursor.

7. The method of claim 6, wherein: The reducing gas is hydrogen; and / or, The protective gas is at least one of an inert gas or nitrogen; The volume ratio of the reducing gas in the mixed gas is 1-10%.

8. The method of claim 6, wherein: The calcination temperature is 600-1400 DEG C; and / or, the calcination time is 2-12 hours.

9. The method of claim 6, wherein: The step S1 comprises mixing the hard carbon precursor, the heteroatom precursor and the metal monatomic precursor in a solvent, removing the solvent by freeze drying or heating drying to obtain the mixture.

10. A sodium-ion battery, characterized by: The sodium ion battery comprises the hard carbon negative electrode material according to any one of claims 1-5.

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