A hard carbon negative electrode composite material, a preparation method thereof, and an application thereof

Abstract

The present invention discloses a hard carbon negative electrode composite material, a preparation method thereof and an application thereof, relating to the technical field of sodium ion batteries. The hard carbon negative electrode composite material includes a core and a shell coated on at least a part of the outer surface of the core; wherein, the material of the core includes graphite, and metal oxides and heteroatoms doped in the graphite; the metal oxides at least include sodium oxide, and the metal oxides can react with sodium to form a sodium alloy material; the material of the shell includes amorphous carbon. The hard carbon negative electrode composite material of the present invention has a high electron conductivity and a first charge-discharge efficiency, and also has good low-temperature performance.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and particularly to a hard carbon negative electrode composite material, a preparation method thereof, and an application thereof. Background Art

[0002] With the increasing requirements of the market for the energy density and power performance of sodium-ion batteries, it is required that the hard carbon negative electrode materials used in sodium-ion batteries have high specific capacity while also improving the fast charging and power performance of the materials. Currently, the commercially available hard carbon materials are mainly prepared by curing and carbonizing biomass or resins. The porous structure for inserting and extracting sodium ions results in a large impedance, reducing their rate performance, and the sodium storage capacity of carbon-based materials is limited, making it difficult to significantly improve the specific capacity of hard carbon. Metal elements form alloy materials with sodium ions and have the characteristic of specific capacity. For example, metals such as tin, cerium, and molybdenum have good power performance, but they have large expansion, so their materials need to be modified and coated to reduce the expansion.

[0003] Although the specific capacity of the negative electrode materials used in the current market has been improved, the power improvement is limited, and the first efficiency has not been improved. Summary of the Invention

[0004] The main object of the present invention is to propose a hard carbon negative electrode composite material, a preparation method thereof, and an application thereof, aiming to solve the problems of poor electronic conductivity, energy density, and first efficiency of hard carbon in the prior art.

[0005] To achieve the above object, the present invention proposes a hard carbon negative electrode composite material, including a core and a shell covering at least a part of the outer surface of the core;

[0006] Wherein, the material of the core includes graphite, as well as metal oxides and heteroatoms doped in the graphite. The metal oxides at least include sodium oxide, and the metal oxides can react with sodium to form a sodium alloy material;

[0007] The material of the shell includes amorphous carbon.

[0008] In an embodiment, in the hard carbon negative electrode composite material, the mass ratio of the material of the core to the material of the shell is (80 - 95):(5 - 20); and / or,

[0009] In the core material, the mass ratio of the metal oxide to the heteroatom particles is (1 - 5):(1 - 5); and / or,

[0010] The metal oxides further include antimony trioxide or antimony pentoxide; and / or,

[0011] The heteroatoms include at least one of nitrogen, phosphorus, and sulfur.

[0012] The present invention also provides a method for preparing a hard carbon negative electrode composite material, comprising the following steps:

[0013] S10. Mix a metal compound, a sodium salt, a carbon source, an ionic liquid and an oxidant, carry out a hydrothermal reaction, and freeze-dry to obtain a first aerogel;

[0014] S20. Mix the first aerogel obtained in step S10 with a heteroatom mixed gas and carry out a carbonization treatment to obtain a second aerogel;

[0015] S30. Cool the second aerogel obtained in step S20, and then mix it with a carbon source gas to deposit amorphous carbon to obtain the hard carbon negative electrode composite material.

[0016] In step S10:

[0017] The mass ratio of the metal compound, the sodium salt, the carbon source and the oxidant is (1-5):(5-15):100:(0.5-2); and / or,

[0018] The metal compound includes at least one of antimony acetate, antimony citrate, antimony lactate, potassium antimony tartrate; and / or,

[0019] The sodium salt includes at least one of sodium 3-aminobenzenesulfonate, sodium m-aminobenzenesulfonate, sodium p-hydroxybenzoate and sodium p-toluenesulfonate; and / or,

[0020] The carbon source includes at least one of glucose, sucrose, maltose and lactose; and / or,

[0021] The oxidant includes one of methyl ethyl ketone peroxide, lauroyl peroxide, cyclohexanone peroxide and benzoyl peroxide.

[0022] In one embodiment, in step S10, the ionic liquid includes at least one of sodium N-methylimidazole nitrate, sodium N-ethylimidazole nitrate, 1-aminopropyl-3-methylimidazole sodium bromide, 1-aminoethyl-3-methylimidazole sodium bromide and 1-aminopropyl-3-methylimidazole sodium nitrate.

[0023] In one embodiment, in step S20:

[0024] The heteroatom mixed gas includes nitrogen and other gases, the other gases include at least one of ammonia, phosphine and hydrogen sulfide, wherein the volume ratio of the nitrogen to the other gases is (10:1-5), and the inlet flow rate of the heteroatom mixed gas is 100-300 SCCM.

[0025] In one embodiment, in the step of carrying out the carbonization treatment in step S20:

[0026] The temperature of the carbonization treatment is 800 - 1200 °C; and / or,

[0027] The time of the carbonization treatment is 1 - 6 h.

[0028] In one embodiment, in step S30:

[0029] The carbon source gas includes at least one of methane, ethane, ethylene, and acetylene, and the flow rate of the introduced carbon source gas is 100 - 300 SCCM; and / or,

[0030] The deposition temperature for depositing amorphous carbon is 700 - 1000 °C.

[0031] In one embodiment, in step S30, in the step of cooling the second aerogel, it is cooled to 700 - 900 °C.

[0032] The present invention also provides an application, applying the aforementioned hard carbon negative electrode composite material or the hard carbon negative electrode composite material prepared by the preparation method of the aforementioned hard carbon negative electrode composite material to a sodium ion battery.

[0033] In the technical solution of the present invention, the hard carbon negative electrode composite material includes a core and a shell covering at least a part of the outer surface of the core. The core is doped with metal oxides, which serve as active centers to improve the electrochemical performance of the hard carbon material. At the same time, during charge and discharge, the metal oxides can react with sodium in the electrolyte to form a sodium alloy material, having a high specific capacity and improving the specific capacity of the hard carbon negative electrode composite material; the metal oxides at least include sodium oxide, which can improve the insertion and extraction rate of sodium ions during charge and discharge. Doping heteroatoms in the core, the heteroatoms are covalently bonded / embedded into the core to improve the electronic conductivity of the material, and amorphous carbon is coated on the surface of the core, which can reduce the specific surface area, reduce side reactions, and improve the first Coulomb efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the structures shown in these drawings.

[0035] Figure 1 It is the scanning electron microscope image (SEM) of the hard carbon negative electrode composite material in Embodiment 4 provided by the present invention.

[0036] The realization of the object, functional features, and advantages of the present invention will be further described in conjunction with the embodiments with reference to the drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase. In addition, the meaning of "and / or" appearing throughout the text includes three parallel solutions. Taking "A and / or B" as an example, it includes solution A, or solution B, or a solution where both A and B are satisfied simultaneously. In addition, the technical solutions between the various embodiments can be combined with each other, but it must be based on what can be achieved by those of ordinary skill in the art. When the combination of technical solutions results in contradictions or cannot be achieved, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0038] With the increasing requirements of the market for the energy density and power performance of sodium-ion batteries, it is required that the hard carbon negative electrode materials used in sodium-ion batteries have high specific capacity while also improving the fast charging and power performance of the materials. Currently, the commercially available hard carbon materials are mainly prepared by curing and carbonizing biomass or resin. The porous structure for intercalating and deintercalating sodium ions results in a large impedance, reducing its rate performance, and the sodium storage capacity of carbon-based materials is limited, making it difficult to significantly improve the specific capacity of the hard carbon. Metal elements form alloy materials with sodium ions and have the characteristic of specific capacity. For example, metals such as tin, cerium, and molybdenum have good power performance but have large expansion, so their materials need to be modified and coated to reduce the expansion.

[0039] Although the specific capacity of the negative electrode materials used in the current market has been improved, the power improvement is limited, and the first efficiency has not been improved.

[0040] In view of this, to achieve the above objectives, the present invention proposes a hard carbon negative electrode composite material, including a core, and a shell coated on at least a part of the outer surface of the core;

[0041] Wherein, the material of the core includes graphite, as well as metal oxides and heteroatoms doped in the graphite. The metal oxides at least include sodium oxide, and the metal oxides can react with sodium to form a sodium alloy material;

[0042] The material of the shell includes amorphous carbon.

[0043] In the technical solution of the present invention, the hard carbon negative electrode composite material includes a core and a shell covering at least a part of the outer surface of the core. The core is doped with metal oxides, which serve as active centers to improve the electrochemical performance of the hard carbon material. At the same time, the metal oxides can react with sodium in the electrolyte during charge and discharge to form a sodium alloy material, which has a high specific capacity and improves the specific capacity of the hard carbon negative electrode composite material. The metal oxides at least include sodium oxide, which can improve the intercalation and deintercalation rate of sodium ions during charge and discharge. Heteroatoms are doped into the core, and the heteroatoms are covalently bonded / embedded into the core to improve the electronic conductivity of the material. An amorphous carbon is coated on the surface of the core, which can reduce the specific surface area, reduce side reactions, and improve the first Coulomb efficiency.

[0044] In some embodiments of the present invention, in the hard carbon negative electrode composite material, the mass ratio of the material of the core to the material of the shell is (80-95):(5-20). By regulating the mass ratio of the core to the shell materials, the mechanical stability and electrochemical activity of the structures of the two can be optimized.

[0045] In the core material, the mass ratio of the metal oxide to the heteroatom particles is (1-5):(1-5). By reasonably setting the ratio of the metal oxide to the heteroatoms, active sites can be better provided, while ensuring the integrity of the carbon skeleton structure and improving the electronic conductivity.

[0046] In some embodiments of the present invention, the metal oxides further include antimony trioxide or antimony pentoxide. Specifically, in the hydrothermal reaction, organometallic compounds (such as antimony acetate, antimony citrate, etc.) will decompose under high temperature and pressure to release antimony ions (Sb³⁺). These antimony ions interact with other reactants (such as carbon sources and oxidants), and may form antimony oxides (such as Sb2O3, Sb2O5) or form composite materials with carbon.

[0047] In some embodiments of the present invention, the heteroatoms include at least one of nitrogen, phosphorus, and sulfur, which can optimize the electrochemical performance of the hard carbon composite material, enhance the conductivity, improve the sodium storage performance, and optimize the pore structure.

[0048] The present invention also provides a preparation method of a hard carbon negative electrode composite material, including the following steps:

[0049] S10. Mix a metal compound, a sodium salt, a carbon source, an ionic liquid, and an oxidant, carry out a hydrothermal reaction, and freeze-dry to obtain a first aerogel;

[0050] S20. Mix the first aerogel with a heteroatom mixed gas and carry out a carbonization treatment to obtain a second aerogel;

[0051] S30, cooling the second aerogel and mixing it with a carbon source gas to deposit amorphous carbon to obtain the hard carbon negative electrode composite material.

[0052] In the technical solution of the present application, step S10 includes: mixing a metal compound, a sodium salt, a carbon source, an ionic liquid and an oxidant. Under hydrothermal conditions, the carbon source forms a cross-linked carbon network through polymerization reaction and dehydration condensation reaction, and a porous structure is initially constructed. The sodium salt promotes the decomposition of the carbon source through catalysis or complexation, thereby improving the formation efficiency of the carbon network. At the same time, the metal compound undergoes a redox reaction with the oxidant to generate a metal oxide or a metal hydroxide, which is partially dispersed in the cross-linked carbon network. In addition, the oxygen free radicals released by the oxidant can further promote the cross-linking of the carbon network to form a first aerogel with a three-dimensional porous structure. The metal oxide or metal hydroxide not only acts as an active center to improve the electrochemical properties of the hard carbon material, but also releases gas through subsequent heat treatment to further generate pores, providing more active sites for the embedding of sodium ions or sodium ions. At the same time, freeze drying is used to avoid the pore collapse caused by capillary forces in the traditional drying process, and the three-dimensional porous structure of the first aerogel is retained to the maximum extent.

[0053] In step S20, the first aerogel is treated with a heteroatom mixed gas for carbonization. Under high temperature conditions, the organic matter in the first aerogel decomposes, and the skeleton is converted into a carbon skeleton to form a more stable porous structure. At the same time, the heteroatoms are doped into the carbon skeleton by covalent bonding, embedding or surface modification at high temperature to form a second aerogel. The doping of heteroatoms significantly improves the conductivity of the carbon skeleton, while increasing the active sites for the embedding of lithium / sodium ions, further improving the specific capacity and cycle stability of the electrode material.

[0054] In step S30, the second aerogel of step S20 is cooled to avoid destroying the structure of the heteroatoms and the first aerogel, while also avoiding excessive decomposition of the carbon source. It is then mixed and decomposed with the carbon source gas at high temperature to deposit amorphous carbon on its surface, so that the amorphous carbon layer fills the pores of the second aerogel, thereby increasing the mass density of the hard carbon negative electrode composite material and enhancing the cyclic stability of the material. It also provides more lithium / sodium insertion sites and improves the sodium / lithium storage capacity.

[0055] In step S10: the mass ratio of the metal compound, the sodium salt, the carbon source and the oxidant is (1-5): (5-15): 100: (0.5-2). Within this mass range, the formation of aerogel is favorable, and the porosity and dispersibility of the first aerogel can be improved.

[0056] The metal compound includes at least one of antimony acetate, antimony citrate, antimony lactate and potassium antimony tartrate. The metal compound has good water solubility and dispersibility and is evenly distributed in the reaction system.

[0057] The sodium salts include at least one of sodium 3-aminobenzenesulfonate, sodium m-aminobenzenesulfonate, sodium p-hydroxybenzoate, and sodium p-toluenesulfonate. The sodium ions of the provided sodium salts can participate in the polymerization reaction and dehydration condensation reaction of the carbon source, promote the cross-linking formation of the carbon network, and the presence of the sodium salts makes the generated carbon aerogel have more pore structures, reduce the defects in the material core, reduce the irreversible capacity, and the sufficient sodium ions improve the diffusion rate and insertion / extraction rate of sodium ions during the charge-discharge process, and improve the rate performance.

[0058] The carbon source includes at least one of glucose, sucrose, maltose, and lactose. The above carbon sources are easily carbonizable polyhydroxy compounds, which can form a continuous three-dimensional cross-linked carbon network structure after carbonization, and gas is released during the carbonization process, which is beneficial to the formation of a porous structure, improve the specific surface area and sodium ion storage capacity.

[0059] The oxidant includes one of methyl ethyl ketone peroxide, lauroyl peroxide, cyclohexanone peroxide, and benzoyl peroxide. The above oxidant participates in the hydrothermal reaction, increases the reaction rate of the carbon source and the metal compound, obtains metal oxides or metal hydroxides, combines with the carbon skeleton, and some oxidants will decompose to generate gas, improving the specific surface area of the material.

[0060] In some embodiments of the present invention, in step S10, the ionic liquid includes at least one of sodium N-methylimidazole nitrate, sodium N-ethylimidazole nitrate, 1-aminopropyl-3-methylimidazole sodium bromide, 1-aminoethyl-3-methylimidazole sodium bromide, and 1-aminopropyl-3-methylimidazole sodium nitrate.

[0061] It can be understood that the ionic liquid has excellent solubility and structure-directing effects, can regulate the micropore size and framework strength of the carbon skeleton, and using the above ionic solution can ensure the uniformity of the formed aerogel structure.

[0062] In some embodiments of the present invention, in step S20:

[0063] The heteroatom mixed gas includes nitrogen and other gases. The other gases include at least one of ammonia, phosphine, and hydrogen sulfide. Among them, the volume ratio of the nitrogen and the other gases is (10:1 to 5), and the inlet flow rate of the heteroatom mixed gas is 100-300 SCCM. The heteroatom gas can provide activity, and controlling the inlet flow rate can control the reaction rate, which can ensure the doping uniformity and the stability of the aerogel structure.

[0064] In some embodiments of the present invention, in step S20, in the step of carbonization treatment:

[0065] The carbonization temperature is 800 - 1200 °C. Within this temperature range, it can ensure the complete carbonization of the aerogel and avoid the structural collapse caused by too high temperature. The carbonization time is 1 - 6 h, which can ensure the full progress of the reaction and control the energy consumption.

[0066] In some embodiments of the present invention, in step S30:

[0067] The carbon source gas includes one of methane, ethane, ethylene, and acetylene. The flow rate of the carbon source gas introduced is 100 - 300 SCCM. By controlling the introduced flow rate, the outer shell of the amorphous carbon generated is made more uniform.

[0068] The deposition temperature for depositing amorphous carbon is 700 - 1000 °C. The addition of the above carbon source gas can decompose at 700 - 1000 °C to generate amorphous carbon to coat the inner core.

[0069] Further, in some embodiments of the present invention, in step S30, in the step of cooling the second aerogel, it is cooled to 700 - 900 °C. Within this temperature range, it can avoid the graphitization of amorphous carbon due to too high temperature and can also deposit amorphous carbon uniformly.

[0070] The present invention also provides an application, applying the foregoing hard carbon negative electrode composite material or the hard carbon negative electrode composite material prepared by the foregoing preparation method of the hard carbon negative electrode composite material to a sodium ion battery. The hard carbon negative electrode composite material has all the above beneficial effects and will not be elaborated herein one by one.

[0071] The technical solutions of the present invention will be further described in detail below in conjunction with specific embodiments and drawings. It should be understood that the following embodiments are only used to explain the present invention and are not used to limit the present invention.

[0072] Example 1

[0073] A hard carbon negative electrode composite material includes an inner core and a shell covering at least a part of the outer surface of the inner core. The material of the inner core includes graphite, metal oxides, and heteroatoms doped in the graphite.

[0074] Among them, the metal oxide includes antimony oxide; the heteroatom includes p. The mass ratio of the hard carbon to the amorphous carbon is 90:10, and the mass ratio of the metal oxide to the heteroatom is 1:1.

[0075] Example 2

[0076] Example 2 is similar to Example 1, the difference being that:

[0077] The metal oxide includes antimony oxide; the heteroatom includes S, the mass ratio of the hard carbon to the amorphous carbon is 95:5, and the mass ratio of the metal oxide to the heteroatom is 1:5.

[0078] Example 3

[0079] Example 3 is similar to Example 1, except that:

[0080] The metal oxide includes antimony oxide; the heteroatom includes S, the mass ratio of the graphite to the amorphous carbon is 80:20, and the mass ratio of the metal oxide to the heteroatom is 5:1.

[0081] Example 4

[0082] A preparation method of a high-capacity and high-power hard carbon negative electrode composite material includes the following steps:

[0083] Step S10: Add 3 g of antimony acetate and 10 g of 3-aminobenzenesulfonic acid sodium salt to 1000 g of a 10 wt% glucose N-methylimidazole sodium nitrate solution, then add 1 g of methyl ethyl ketone peroxide, and through hydrothermal reaction, react at a temperature of 100 °C and a pressure of 3 Mpa for 3 h. The obtained material is freeze-dried at -40 °C for 24 h to obtain a metal-doped carbon aerogel, that is, the first aerogel;

[0084] Step S20: Transfer the metal-doped aerogel to a tube furnace, first introduce argon inert gas to discharge the air in the tube, and then introduce ammonia mixed gas (volume ratio, ammonia: nitrogen = 3:10), at a flow rate of 200 SCCM, carbonize at a high temperature of 1000 °C for 3 h to obtain an intermediate material, that is, the second aerogel;

[0085] Step S30: Then stop introducing the ammonia mixed gas, cool down to 800 °C, introduce ethylene gas, and introduce it at a flow rate of 200 SCCM for 150 min to deposit amorphous carbon on the surface of the intermediate to obtain a hard carbon negative electrode composite material.

[0086] Example 5

[0087] A preparation method of a high-capacity and high-power hard carbon negative electrode composite material includes the following steps:

[0088] Step S10: Add 1 g of antimony citrate and 5 g of m-aminobenzenesulfonic acid sodium salt to 1000 g of a 10 wt% sucrose N-ethylimidazole sodium nitrate solution, then add 0.5 g of lauroyl peroxide, and through hydrothermal reaction, react at a temperature of 80 °C and a pressure of 5 Mpa for 6 h. The obtained material is freeze-dried at -40 °C for 24 h to obtain a metal-doped carbon aerogel, that is, the first aerogel;

[0089] Step S20: Transfer the metal-doped aerogel to a tubular furnace. First, introduce argon inert gas to expel the air in the tube, and then introduce a phosphine mixed gas (volume ratio, phosphine:argon = 1:10). At a high temperature of 800 °C, carbonize it for 6 h at a flow rate of 100 SCCM to obtain an intermediate material, that is, the second aerogel;

[0090] Step S30: Then stop introducing the phosphine mixed gas, cool down to 700 °C, introduce acetylene gas, and introduce it at a flow rate of 100 SCCM for 300 min to deposit amorphous carbon on the surface of the intermediate to obtain a hard carbon negative electrode composite material.

[0091] Example 6

[0092] A preparation method of a high-capacity and high-power hard carbon negative electrode composite material includes the following steps:

[0093] Step S10: Add 5 g of antimony lactate and 15 g of sodium p-hydroxybenzoate to 1000 g of a 1-aminopropyl-3-methylimidazolium bromide solution of 10 wt% maltose. Then add 2 g of cyclohexanone peroxide, and through a hydrothermal reaction, react at a temperature of 150 °C and a pressure of 1 Mpa for 6 h. The obtained material is freeze-dried at -40 °C for 24 h to obtain a metal-doped carbon aerogel, that is, the first aerogel;

[0094] Step S20: Transfer the metal-doped aerogel to a tubular furnace. First, introduce argon inert gas to expel the air in the tube, and then introduce a hydrogen sulfide mixed gas (volume ratio, hydrogen sulfide:argon = 5:10). At a high temperature of 1200 °C, carbonize it for 1 h at a flow rate of 300 SCCM to obtain an intermediate material, that is, the second aerogel;

[0095] Step S30: Then stop introducing the hydrogen sulfide mixed gas, cool down to 900 °C, introduce methane gas, and introduce it at a flow rate of 300 SCCM for 30 min to deposit amorphous carbon on the surface of the intermediate to obtain a hard carbon negative electrode composite material.

[0096] Comparative Example 1

[0097] The difference from Example 4 is that antimony acetate and 3-aminobenzenesulfonic acid sodium are not added, that is, the metal oxide is removed, and the others are the same as Example 4.

[0098] Comparative Example 2

[0099] The difference from Example 4 is that in Step S20, the ammonia mixed gas is not introduced, that is, no heteroatoms are doped, and the others are the same as Example 4.

[0100] Performance Test

[0101] (1) SEM Test

[0102] The hard carbon negative electrode composite material prepared in Example 4 was subjected to SEM testing, and the test results are as follows Figure 1 shown. It can be seen from Figure 1 that the composite material presents a spherical-like structure, and its particle size D 50 is about 5 μm, and the size distribution is uniform.

[0103] (2) Physicochemical properties and coin cell testing

[0104] The hard carbon negative electrode composite materials prepared in Examples 4-6 and Comparative Examples 1-2 were tested for interlayer spacing (D002), specific surface area, and tapped density. The testing method was carried out according to the method of the national standard GB / T 43114-2023 "Hard Carbon"; the powder resistance was tested using a four-probe tester, and the grain size was tested and calculated using XRD. The test results are shown in Table 1.

[0105] The hard carbon negative electrode composite materials in Examples 4-6 and Comparative Examples 1-2 were assembled into coin cells as the negative electrode materials of sodium ion batteries. The specific preparation method of the negative electrode materials was as follows: mixed according to the mass ratio of hard carbon negative electrode composite material: CMC: SBR: SP: H2O = 93:3:2:2:150 to obtain a negative electrode sheet; a sodium sheet was used as the counter electrode; the electrolyte used NaPF6 (the solvent was EC: DEC: PC: polypropylene glycol polyoxypropylene ether = 1:2:1:0.05, concentration 1.3 mol / L) as the electrolyte; the separator used a composite film of polyethylene PE, polypropylene PP, and polyethylene-propylene PEP. The coin cell assembly was carried out in a glove box filled with argon. The electrochemical performance was tested on a Wuhan Blue Electric CT2001A battery tester. The charge-discharge voltage range was 0.00V to 2.0V, and the charge-discharge rate was 0.1C. The first discharge capacity and first efficiency of the coin cell were tested, and the rate performance (1C / 0.1C) of the coin cell was also tested. The test results are shown in Table 1.

[0106] Table 1

[0107] It can be seen from Table 1 that the hard carbon negative electrode composite materials prepared in Examples 4-6 are superior to Comparative Examples 1-2 in terms of powder conductivity, specific capacity, La, etc. The reason is that the material is doped with antimony oxide metal compounds to form sodium alloy materials during the charge-discharge process, improving the specific capacity of the material, and by doping metal oxides, reducing its irreversible capacity, improving the first efficiency and the diffusion rate of sodium ions, and improving the rate performance.

[0108] (3) Soft pack battery testing:

[0109] The hard carbon negative electrode composite materials in Examples 4-6 and Comparative Examples 1-2 were slurried and coated to prepare negative electrode sheets, and a layered oxide (NaFe 1 / 3 Mn 1 / 3Ni 1 / 3 O2) is used as the positive electrode, and NaPF6 (the solvent is PC:EC:FEC = 1:1:0.05, concentration 1.1 mol / L) is used as the electrolyte to prepare a 5 Ah soft-pack battery.

[0110] Test the cycle performance: charge and discharge current 1.0C / 1.0C, voltage range 1 - 4.0V, cycle number 500 times.

[0111] Test the rate performance: the constant current ratio under the condition of 2C charging = 2C constant current capacity / (2C constant current capacity + 0.1C constant voltage capacity).

[0112] The test results are shown in Table 2.

[0113] Table 2

[0114]

[0115] It can be seen from Table 2 that compared with the comparative examples, the cycle performance in Examples 4 - 6 is significantly better than that in Comparative Examples 1 - 2. The reason for the analysis is that: compared with Comparative Examples 1 - 2, the metal oxides and heteroatoms doped in the materials of the examples, and the heteroatoms can increase the lattice defects of the original hard carbon material or form new crystal phases, which will lead to an increase in the distance between carbon layers. At the same time, the presence of metal oxides can prevent the close packing of carbon layers, thereby obtaining a large interlayer spacing, reducing expansion, and improving the cycle performance; the introduction of heteroatoms and metal oxides in the materials of the examples can disrupt the ordered arrangement in the carbon matrix, prevent the stacking and growth of carbon layers, and help maintain a small grain size and low powder resistivity, thereby improving the constant current ratio of the hard carbon negative composite material.

[0116] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A hard carbon negative electrode composite material, characterized in that: comprising a core, and a shell covering at least a portion of the outer surface of the core; Wherein, the material of the inner core includes graphite, and metal oxides and heteroatoms doped in the graphite, the metal oxides include at least sodium oxide, and the metal oxides can react with sodium to form a sodium alloy material; The material of the shell includes amorphous carbon; The preparation of the hard carbon negative electrode composite material comprises the following steps: S10, mixing the metal compound, the sodium salt, the carbon source, the ionic liquid and the oxidant, performing a hydrothermal reaction, and freeze-drying to obtain a first aerogel; S20, mixing the first aerogel of step S10 with a heteroatom mixed gas, and performing a carbonization treatment to obtain a second aerogel; S30, cooling the second aerogel in step S20, and then mixing it with a carbon source gas to deposit amorphous carbon, thereby obtaining the hard carbon negative electrode composite material.

2. The hard carbon negative electrode composite material according to claim 1, characterized in that: In the hard carbon negative electrode composite material, the mass ratio of the material of the core to the material of the shell is (80-95): (5-20); and / or, In the core material, the mass ratio of the metal oxide to the heteroatom is (1-5): (1-5); and / or, The metal oxide further comprises antimony trioxide or antimony pentoxide; and / or, The heteroatom includes at least one of nitrogen, phosphorus and sulfur.

3. The method for preparing the hard carbon negative electrode composite material according to claim 1, characterized in that: In step S10: The mass ratio of the metal compound, the sodium salt, the carbon source and the oxidant is (1-5): (5-15): 100: (0.5-2); and / or, The metal compound comprises at least one of antimony acetate, antimony citrate, antimony lactate and potassium antimony tartrate; and / or, The sodium salt comprises at least one of sodium 3-aminobenzenesulfonate, sodium m-aminobenzenesulfonate, sodium p-hydroxybenzoate and sodium p-toluenesulfonate; and / or, The carbon source comprises at least one of glucose, sucrose, maltose and lactose; and / or, The oxidant includes one of methyl ethyl ketone peroxide, lauroyl peroxide, cyclohexanone peroxide and benzoyl peroxide.

4. The method for preparing the hard carbon negative electrode composite material according to claim 1, characterized in that: In step S10, the ionic liquid includes at least one of N-methylimidazole sodium nitrate, N-ethylimidazole sodium nitrate, 1-aminopropyl-3-methylimidazole sodium bromide, 1-aminoethyl-3-methylimidazole sodium bromide and 1-aminopropyl-3-methylimidazole sodium nitrate.

5. The method for preparing the hard carbon negative electrode composite material according to claim 1, characterized in that: In step S20: The heteroatom mixed gas includes nitrogen and other gases, and the other gases include at least one of ammonia, phosphine and hydrogen sulfide, wherein the volume ratio of the nitrogen to the other gases is 10: (1-5), and the inlet flow rate of the heteroatom mixed gas includes 100-300 SCCM.

6. The method for preparing the hard carbon negative electrode composite material according to claim 1, characterized in that: In step S20, in the step of carbonization treatment: The temperature of the carbonization treatment is 800-1200°C; and / or, The carbonization treatment time is 1-6h.

7. The method for preparing the hard carbon negative electrode composite material according to claim 1, characterized in that: In step S30: The carbon source gas includes at least one of methane, ethane, ethylene and acetylene, and the flow rate of the carbon source gas includes 100-300 SCCM; and / or, The deposition temperature of the deposited amorphous carbon is 700-1000°C.

8. The method for preparing the hard carbon negative electrode composite material according to claim 1, characterized in that: In step S30, the second aerogel is cooled to 700-900°C.

9. An application, characterized in that, The hard carbon negative electrode composite material as claimed in claim 1 or 2 is applied to a sodium ion battery.

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