A hard carbon negative electrode material / negative electrode for a sodium-ion battery with interface modification, preparation method and application

Abstract

The present invention belongs to the field of sodium-ion batteries, relates to a hard carbon negative electrode, and specifically relates to a sodium-ion battery hard carbon negative electrode material / negative electrode with interface modification, a preparation method and an application. A metal-organic complex film is coated on the surface of a spherical or massive commercial hard carbon material or on the surface of a negative electrode prepared from the hard carbon material, and the film is formed by coordination polymerization of a metal center and an organic molecule on the surface of the carbon material. The method is as follows: after the hard carbon material or the negative electrode prepared from the hard carbon material is successively soaked in an organic molecule solution and a metal ion solution and then dried, a hard carbon negative electrode prepared from the hard carbon material with interface modification or a hard carbon negative electrode with interface modification can be obtained. The present invention innovatively introduces a metal-organic complex film, promotes the interfacial ionic conductivity and stability, significantly improves the sodium storage specific capacity, rate performance and cycle stability of the hard carbon negative electrode, and effectively solves the current dilemmas of the negative electrode of sodium-ion batteries; at the same time, the preparation method is simple, suitable for large-scale operation, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, relates to the preparation of hard carbon anodes, and specifically relates to a sodium-ion battery hard carbon anode material / anode with interfacial modification, a preparation method, and an application thereof. Background Art

[0002] As a medium for energy transmission between renewable energy and large-scale energy storage systems, sodium-ion batteries are regarded as one of the most promising next-generation energy storage systems due to their rich resource reserves and low cost. However, existing sodium-ion battery technologies cannot meet the current social demands in fields such as large-scale energy storage power stations and new energy electric vehicles. Therefore, it has become an urgent need to develop sodium-ion batteries with low cost, high energy density, high power density, and long cycle life.

[0003] Hard carbon has been widely studied due to its low sodium storage voltage (about 0.1V) and high reserves, and is applied to the anode materials of sodium-ion batteries, becoming the main candidate anode material in the commercialization of sodium-ion batteries. However, most hard carbons that can be mass-produced exhibit low specific capacity and poor rate performance. Sodium-ion batteries have price advantages but do not show high electrochemical performance, which brings great troubles to the application of hard carbon materials.

[0004] Research shows that forming a solid electrolyte interface (SEI) on the surface of hard carbon materials will help improve the stability and ionic conductivity of hard carbon materials, and will help improve their sodium storage performance. For example, coating a layer of Al2O3 or NaPO3 on the surface of hard carbon materials can effectively reduce the side reactions between the material and the electrolyte during charge and discharge. However, this preparation method has problems such as long preparation time and high processing cost. Another example is adding additives to the electrolyte to decompose on the surface of the electrode material to optimize the SEI. However, the utilization efficiency of the additives distributed in the electrolyte is low, and it is easy to affect the properties of the electrolyte itself.

[0005] Therefore, in order to achieve further industrial breakthroughs in sodium-ion batteries, there is an urgent need for a cheap and efficient method to stabilize the electrode material / electrolyte interface. Summary of the Invention

[0006] Aiming at the technical problems in the prior art, such as long preparation time, high cost in preparing the hard carbon anode of sodium-ion batteries, and unstable electrolyte interface of sodium-ion batteries, the present invention proposes a sodium-ion battery hard carbon anode material / anode with interfacial modification, a preparation method, and an application thereof. By inducing the formation of a stable and uniform SEI on the surface of the hard carbon anode material or the anode prepared from the hard carbon material, its specific capacity and rate performance are improved. The preparation method is simple, suitable for large-scale operation, and has broad application prospects.

[0007] To achieve the above object, the technical solution of the present invention is implemented as follows:

[0008] A technical solution disclosed by the present invention: a hard carbon negative electrode material for a sodium-ion battery with interface modification, in which a metal-organic complex film formed by coordination of a metal center and an organic molecule is coated on the surface of the hard carbon material, with a thickness of 1 nm - 100 nm, preferably 3 nm - 30 nm.

[0009] The metal center includes any one or several of Cu, Ni, Co, Zn or Fe; the organic molecule includes any one or several of organic molecules containing O / N / S atoms and conjugated large π-bond structures such as benzotriazole, 2-mercaptobenzothiazole, benzothiazole, 3-amino-1,2,4-triazole, quinoline, pyrazole, pyrrole or phenothiazine; the structure of the hard carbon material is spherical or blocky, and its average particle size is 1 - 20 μm.

[0010] A hard carbon negative electrode for a sodium-ion battery with interface modification prepared by using the above hard carbon negative electrode material for a sodium-ion battery with interface modification.

[0011] The preparation method of the hard carbon negative electrode for a sodium-ion battery with interface modification is as follows:

[0012] (1) Immerse the powder of the hard carbon material in the organic molecule solution or drop the organic molecule solution onto the unmodified hard carbon material, dry the hard carbon material after being coated with the organic molecule to obtain hard carbon material a1;

[0013] (2) Then immerse the hard carbon material a1 in the metal salt solution or drop the metal salt solution onto the hard carbon material a1 to obtain hard carbon material b1, immerse and wash the hard carbon material b1 in a solvent, and dry it after the immersion and washing are completed to obtain the hard carbon negative electrode material for a sodium-ion battery with interface modification;

[0014] (3) Mix the hard carbon negative electrode material for a sodium-ion battery with interface modification, a conductive agent and a binder in a solvent to prepare a slurry, coat it on a copper foil, and dry it to obtain the hard carbon negative electrode for a sodium-ion battery with interface modification.

[0015] Another technical solution disclosed by the present invention: a hard carbon negative electrode for a sodium-ion battery with interface modification, in which a metal-organic complex film formed by coordination of a metal center and an organic molecule is coated on the surface of the hard carbon negative electrode, with a thickness of 1 nm - 100 nm, preferably 3 nm - 30 nm.

[0016] The metal center includes any one or more of Cu, Ni, Co, Zn, or Fe; the organic molecule includes any one or more of organic molecules containing O / N / S atoms and a conjugated large π-bond structure such as benzotriazole, 2-mercaptobenzothiazole, benzothiazole, 3-amino-1,2,4-triazole, quinoline, pyrazole, pyrrole, or phenothiazine.

[0017] The preparation method of the interfacially modified hard carbon negative electrode for a sodium-ion battery is as follows:

[0018] (1) Immerse the hard carbon negative electrode in the organic molecule solution or drop the organic molecule solution onto the hard carbon negative electrode, dry it after the hard carbon negative electrode is coated with the organic molecule to obtain hard carbon negative electrode a2;

[0019] (2) Then immerse hard carbon negative electrode a2 in the metal salt solution or drop the metal salt solution onto hard carbon negative electrode a2 to obtain hard carbon negative electrode b2, soak and wash hard carbon negative electrode b2 in a solvent, and dry it after the soaking and washing are completed to obtain the interfacially modified hard carbon negative electrode for a sodium-ion battery.

[0020] In the preparation method of the interfacially modified hard carbon negative electrode for a sodium-ion battery of the present invention, the solvent of the organic molecule solution includes any one or more of methanol, ethanol, water, dimethyl sulfoxide, N,N-dimethylformamide, or acetonitrile; the concentration of the organic molecule is 0.01 - 10 g / L, the dissolution temperature is 10 - 80 °C; the soaking time is 1 min - 2 h.

[0021] The metal salt includes any one or more of chlorides, sulfates, fluorides, or nitrates of Cu, Ni, Co, Zn, or Fe metal ions.

[0022] The solvent of the metal salt solution includes any one or more of methanol, ethanol, water, dimethyl sulfoxide, N,N-dimethylformamide, or acetonitrile; the concentration of the metal ion is 0.01 - 10 g / L, the dissolution temperature is 10 - 80 °C; the soaking time is 1 min - 2 h.

[0023] The soaking and washing solvent includes any one or more of dimethyl sulfoxide, methanol, water, acetone, ethanol, acetonitrile, or N,N-dimethylformamide; the soaking and washing time is 10 s - 1 h; the drying method after the soaking and washing are completed is air drying or vacuum drying, and the drying temperature is 20 - 100 °C.

[0024] The present invention also discloses a non-aqueous secondary battery, including a negative electrode sheet, a positive electrode sheet, a non-aqueous electrolyte, a separator, and a casing, wherein the negative electrode sheet uses the above-mentioned interfacially modified hard carbon negative electrode for a sodium-ion battery as the negative electrode sheet.

[0025] The positive electrode sheet: contains Nax Materials such as MO2 layered compounds (M includes any one or more of Fe, Mn, Cu, Cr, Ni), polyanionic compounds (phosphates such as sodium iron phosphate, Na fast ion conductors such as sodium vanadium phosphate, pyrophosphates such as sodium iron pyrophosphate, fluorinated phosphates such as sodium vanadium fluorophosphate, sulfates such as sodium iron sulfate, etc.), and Prussian blue compounds.

[0026] The ester-based electrolyte is obtained by dissolving a sodium salt in an organic solvent, with a concentration of 0.3 - 3 mol / L. The sodium salts include any one or several of sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4), sodium trifluoromethanesulfonate (NaSO3CF3), sodium tetrafluoroborate (NaBF4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI); the organic solvents include any one or several of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), trimethyl phosphate (TMP), 1,3-dioxolane (DOL), tetrahydrofuran (THF), ethylene glycol dimethyl ether (DME), fluoroethylene carbonate (FEC), diethylene glycol dimethyl ether (DGM), and triethylene glycol dimethyl ether (TGM).

[0027] The separator includes polypropylene, polyethylene, non-woven fabric separator, glass fiber or cellulose acetate separator, and a coated separator with the above materials as the substrate.

[0028] The outer shell is made of organic plastic, aluminum shell, aluminum-plastic film, stainless steel or their composite materials, and the shape is button-type, columnar or square.

[0029] The non-aqueous secondary battery is applied in fields such as electric vehicles, wind power generation, solar power generation, smart grid or communication base stations.

[0030] The present invention has the following beneficial effects:

[0031] 1. Aiming at the problem that the electrolyte will form an unstable SEI film on the surface of hard carbon anode during cycling, the present invention in-situ generates a metal-organic complex film with a thickness of 1 nm - 100 nm on the surface of the electrode material through a simple interface construction method. After assembling the electrode material into a sodium-ion battery, the metal-organic polymer film introduced on the surface of the electrode material can combine with the SEI film to promote the stability of the SEI film, and finally enable the electrolyte to decompose on the surface of the electrode material to form a uniform, ultra-thin SEI protective film mainly composed of inorganic salts. This SEI protective film can buffer the volume expansion of the electrode material and reduce the dissolution of active materials, and prevent the excessive decomposition of the ester-based electrolyte.

[0032] 2. The hard carbon anode of the sodium-ion battery with interface modification prepared by the method for constructing a stable interface in the present invention can well solve the problems of low cycle stability and rate performance of the existing sodium-ion battery, and the obtained sodium-ion battery has excellent cycle stability. The specific capacity of the sodium-ion battery prepared with the unmodified hard carbon anode is 228 mAh g -1 (0.05 A g -1 ). After 50 cycles, the specific capacity retention rate is about 78.2%. At 0.1 A g -1 , the specific capacity is 41.4% compared with that at 0.02 A g -1 . While the sodium-ion battery prepared in the present invention has good rate performance and specific capacity (4% - 40%) at the same time, and the highest specific capacity is 321.5 mAh g -1 (0.05 A g -1 ). After 50 cycles, the specific capacity retention rate is about 85.7%. At 0.1 A g -1 , the specific capacity is 66.4% compared with that at 0.02 A g -1 .

[0033] 3. The rechargeable sodium-ion battery device prepared in the present invention has a high cycle life and broad market application prospects. 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 drawings in the following description 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 these drawings.

[0035] Figure 1 Scanning electron microscope images of the bulk (A) used in Example 1 and the spherical (B) hard carbon material in Example 6 of the present invention.

[0036] Figure 2 High-resolution transmission electron microscope images of the hard carbon anode modified by 2-mercaptobenzothiazole and Cu ions and the unmodified hard carbon anode prepared in Example 1.

[0037] Figure 3 Charge and discharge curves of the hard carbon anode modified by 2-mercaptobenzothiazole and Cu ions and the pure hard carbon anode prepared in Example 1 of the present invention at 0.05 A g -1 .

[0038] Figure 4 Charge and discharge curves of the hard carbon anode modified by 2-mercaptobenzothiazole and Cu ions and the pure hard carbon anode prepared in Example 1 of the present invention at 0.05 A g-1 Cycling performance graph under

[0039] Figure 5 are the infrared spectra (A) and X-ray photoelectron spectra (B) of the unmodified hard carbon anode and the interfacially modified hard carbon anode prepared in Example 2 of the present invention.

[0040] Figure 6 are the charge-discharge curves of the interfacially modified hard carbon anode and the unmodified hard carbon anode prepared in Example 2 of the present invention at 0.05 A g -1 under.

[0041] Figure 7 are the rate performance graphs of the interfacially modified hard carbon anode and the unmodified hard carbon anode prepared in Example 2 of the present invention at different current densities.

[0042] Figure 8 are the high-resolution transmission electron microscopy images of the SEI formed by discharging the unmodified hard carbon anode (A) and the interfacially modified hard carbon anode (B) prepared in Example 2 of the present invention to 0.01 V in the first cycle.

[0043] Figure 9 is the graph of the soft-pack sodium-ion battery constructed in Example 9 of the present invention. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] The conductive agents and binders used in the embodiments of the present invention are all conventional substances, wherein the conductive agent and the binder are acetylene black and PVDF, and the mass ratio of the hard carbon anode material to the conductive agent and the binder is 8:1:1.

[0046] Example 1

[0047] This example is a preparation method and application of an interfacially modified hard carbon anode for a sodium-ion battery, and the steps are as follows:

[0048] Preparation method of hard carbon anode: Use the commercially available hard carbon purchased as the anode material, which is mainly composed of micron-sized blocky particles (as Figure 1 shown), mix it with a conductive agent and a binder to form a slurry, coat it on a copper foil, and dry it.

[0049] Preparation method of an interfacially modified hard carbon anode: Using methanol as a solvent, prepare a 2-mercaptobenzothiazole (MBT) solution with a concentration of 0.05 g / L. Additionally, using dimethyl sulfoxide as a solvent, prepare a CuCl solution with a concentration of 0.05 g / L. Immerse the unmodified hard carbon anode in the 2-mercaptobenzothiazole solution at 25 °C for 5 min, take it out and dry. Further, place it in the corresponding concentration of CuCl solution, immerse it at 25 °C for 5 min, wash it successively with dimethyl sulfoxide and methanol solvents for 10 min each, and then dry it to obtain the interfacially modified hard carbon anode for a sodium-ion battery.

[0050] Electrochemical performance test: Using a sodium metal sheet as the counter electrode, dissolve NaPF6 salt in an EC:DEC solvent with a volume ratio of 1:1 as the electrolyte (1 mol / L). Using a glass fiber separator and a stainless steel battery case, assemble a coin-type sodium-ion battery with the unmodified hard carbon anode and the interfacially modified hard carbon anode obtained in this example respectively, and test their electrochemical performance.

[0051] Figure 2 These are high-resolution transmission electron microscope images of the hard carbon anode interfacially modified with 2-mercaptobenzothiazole and Cu ions prepared in this example and the unmodified one. The thickness of the metal-organic complex film coated on the surface of the hard carbon anode is about 6 nm.

[0052] Figure 3 These are the charge-discharge curves of the hard carbon anode interfacially modified with 2-mercaptobenzothiazole and Cu ions prepared in this example and the unmodified hard carbon anode at 0.05 A g -1 . In the voltage range of 0.01 - 2.0 V, when the current density is 0.05 A g -1 the specific capacity of the hard carbon anode prepared in this example is 303 mAh g -1 . Compared with the specific capacity of the unmodified hard carbon anode (228 mAh g -1 ), it is increased by 32.9%.

[0053] Figure 4 These are the cycling performance graphs of the hard carbon anode interfacially modified with 2-mercaptobenzothiazole and Cu ions prepared in this example and the unmodified hard carbon anode at 0.05 A g -1 . The specific capacity retention rate of the unmodified hard carbon anode after 50 cycles is 78.2%, and that of the interfacially modified hard carbon anode after 50 cycles is 85.7%.

[0054] Example 2

[0055] This example is about the preparation method and application of an interfacially modified hard carbon anode for a sodium-ion battery, and the steps are as follows:

[0056] Preparation method of hard carbon anode: The commercially available hard carbon purchased is used as the anode material, which is mainly composed of micron-sized blocky particles. It is mixed with a conductive agent and a binder to form a slurry, coated on a copper foil, and dried.

[0057] Preparation method of interface-modified hard carbon anode: Using methanol as the solvent, a 2-mercaptobenzothiazole solution with a concentration of 0.1 g / L is prepared. Additionally, a CuCl solution with a concentration of 0.1 g / L is prepared using dimethyl sulfoxide as the solvent. The uninterface-modified hard carbon anode is immersed in the 2-mercaptobenzothiazole solution at 30 °C for 1.5 h, taken out and dried. Further, it is put into the corresponding concentration of CuCl solution and immersed at 30 °C for 1.5 h, washed successively with dimethyl sulfoxide and methanol solvents for 5 min each, and dried to obtain the interface-modified hard carbon anode for sodium-ion batteries, with the thickness of the metal-organic complex film being about 15 nm.

[0058] Electrochemical performance test: Using a sodium metal sheet as the counter electrode, 1 mol / L NaPF6 salt dissolved in a 1:1 volume ratio of EC:DEC solvent as the electrolyte, and using a glass fiber separator and a stainless steel battery case to assemble a coin-type sodium-ion battery and test its electrochemical performance. Figure 5 The infrared spectrum (A) and X-ray photoelectron spectroscopy (B) of the uninterface-modified hard carbon anode and the interface-modified hard carbon anode prepared in this example. Among them, compared with the uninterface-modified hard carbon anode, C-N bonds and Cu-N / Cu-S chemical bonds exist in the interface-modified hard carbon anode, proving the formation of the interface metal-organic coordination structure.

[0059] Figure 6 The charge-discharge curves of the interface-modified hard carbon anode and the uninterface-modified hard carbon anode prepared in this example at 0.05 A g -1 . In the voltage range of 0.01 - 2.0 V, when the current density is 0.05 A g -1 the specific capacity of the hard carbon anode prepared in this example is 310 mAh g -1 . Compared with the specific capacity of the uninterface-modified hard carbon anode (228 mAh g -1 ), it is increased by 35.9%.

[0060] Figure 7 The rate performance diagrams of the interface-modified hard carbon anode and the uninterface-modified hard carbon anode prepared in this example at different current densities. At 0.02 A g -1 , 0.05 A g -1 and 0.1 A g -1At a current density of [current density value], the hard carbon negative electrode prepared in this example has a specific capacity retention rate of about 66.4% after cycling 5 times, while the specific capacity retention rate of the unmodified hard carbon negative electrode is about 41.4%. Compared with the unmodified hard carbon negative electrode, the rate performance is improved by 60%, and there is a significant improvement in the rate performance.

[0061] Figure 8 This is a high-resolution transmission electron microscope image of the SEI formed when the unmodified hard carbon negative electrode (A) and the interface-modified hard carbon negative electrode (B) prepared in this example are discharged to 0.01 V in the first cycle. The SEI on the surface of the unmodified hard carbon negative electrode is rich in organic phase, easy to dissolve in the electrolyte and has an unstable structure. While the SEI of the interface-modified hard carbon negative electrode has rich and clear lattice fringes, indicating that this SEI is mainly composed of inorganic substances and has higher stability, which can promote the structural stability of the electrode material.

[0062] Example 3

[0063] This example is a preparation method and application of an interface-modified hard carbon negative electrode for a sodium-ion battery, and the steps are as follows:

[0064] Preparation method of hard carbon negative electrode: Use commercially available hard carbon purchased as the negative electrode material, which is mainly composed of micron-sized blocky particles. Mix it with a conductive agent and a binder to form a slurry, coat it on a copper foil, and dry it.

[0065] Preparation method of interface-modified hard carbon negative electrode: Use methanol as a solvent to prepare a benzotriazole (BTA) solution with a concentration of 0.2 g / L. In addition, use dimethyl sulfoxide as a solvent to prepare a CuCl solution with a concentration of 0.2 g / L; Immerse the unmodified hard carbon negative electrode in the benzotriazole solution at 30 °C for 2 h, take it out and dry it; Further put it into the corresponding concentration of CuCl solution, soak it at 30 °C for 2 h, wash it with dimethyl sulfoxide and methanol solvents for 5 min in turn, and dry it to obtain an interface-modified hard carbon negative electrode for a sodium-ion battery. The thickness of the obtained metal-organic complex film is about 20 nm.

[0066] Electrochemical performance test: Use a sodium metal sheet as the counter electrode, 1 mol / L NaPF6 salt dissolved in a solvent with a volume ratio of 1:1 of EC:DEC as the electrolyte, and use a glass fiber separator and a stainless steel battery case to assemble a button-type sodium-ion battery to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, when the current density is 0.05 A g -1 the specific capacity is 267 mAh g -1 . Compared with the specific capacity of the unmodified hard carbon negative electrode (228 mAh g -1 ), it is increased by 17.1%.

[0067] Example 4

[0068] This example is about the preparation method and application of a sodium-ion battery hard carbon anode with interface modification, and the steps are as follows:

[0069] Preparation method of the hard carbon anode: Use the commercially purchased hard carbon as the anode material, which is mainly composed of micron-sized blocky particles. Mix it with a conductive agent and a binder to form a slurry, coat it on a copper foil, and dry it.

[0070] Preparation method of the interface-modified hard carbon anode: Use methanol as the solvent to prepare a benzotriazole (BTA) solution with a concentration of 0.02 g / L. Additionally, use dimethyl sulfoxide as the solvent to prepare a CuCl solution with a concentration of 0.1 g / L. Immerse the unmodified hard carbon anode in the benzotriazole solution at 20 °C for 1 h, take it out and dry it. Further, put it into the corresponding concentration of CuCl solution, immerse it at 20 °C for 1 h, wash it with dimethyl sulfoxide and methanol solvents for 10 min each in turn, and dry it to obtain the interface-modified sodium-ion battery hard carbon anode. The thickness of the obtained metal-organic complex film is about 30 nm.

[0071] Electrochemical performance test: Use a sodium metal sheet as the counter electrode, dissolve NaPF6 salt in an EC:DEC solvent with a volume ratio of 1:1 as the electrolyte (1 mol / L), and use a glass fiber separator and a stainless steel battery case to assemble a coin-type sodium-ion battery to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, when the current density is 0.05 A g -1 the specific capacity is 238 mAh g -1 . Compared with the unmodified hard carbon anode with a specific capacity of 228 mAh g -1 , it is increased by 4.4%.

[0072] Example 5

[0073] This example is about the preparation method and application of a sodium-ion battery hard carbon anode with interface modification, and the steps are as follows:

[0074] Preparation method of the hard carbon anode: Use the commercially purchased hard carbon as the anode material, which is mainly composed of micron-sized blocky particles. Mix it with a conductive agent and a binder to form a slurry, coat it on a copper foil, and dry it.

[0075] Preparation method of the interface-modified hard carbon anode: Use methanol as the solvent to prepare a 2-mercaptobenzothiazole (MBT) solution with a concentration of 0.1 g / L. Additionally, use dimethyl sulfoxide as the solvent to prepare a CuCl solution with a concentration of 0.1 g / L. Drop 2-mercaptobenzothiazole onto the surface of the unmodified hard carbon electrode, take it out and dry it. Further, drop the CuCl solution onto the obtained hard carbon anode, wash it with methanol solvent for 10 min, and dry it to obtain the interface-modified sodium-ion battery hard carbon anode. The thickness of the obtained metal-organic complex film is about 25 nm.

[0076] Electrochemical performance test: Using a sodium metal sheet as the counter electrode, NaPF6 salt dissolved in an EC:DEC solvent with a volume ratio of 1:1 as the electrolyte (1 mol / L), a button-type sodium-ion battery was assembled using a glass fiber separator and a stainless steel battery case to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, when the current density is 0.05 A g -1 the specific capacity is 272 mAh g -1 . Compared with the specific capacity of the unmodified hard carbon negative electrode (228 mAh g -1 ), it is increased by 19.3%.

[0077] Example 6

[0078] This example is about the preparation method and application of an interfacially modified hard carbon negative electrode for a sodium-ion battery, and the steps are as follows:

[0079] Preparation method of the hard carbon negative electrode: Using commercially available hard carbon purchased as the negative electrode material, which is mainly composed of spherical particles (as shown Figure 1 ), it is mixed with a conductive agent and a binder to form a slurry, coated on a copper foil, and dried.

[0080] Preparation method of the interfacially modified hard carbon negative electrode: Using methanol as the solvent, a benzotriazole (BTA) solution with a concentration of 0.2 g / L is prepared. In addition, a CuCl solution with a concentration of 0.2 g / L is prepared using dimethyl sulfoxide as the solvent; the unmodified hard carbon negative electrode is immersed in the benzotriazole solution at 35 °C for 2 h, taken out and dried; further, it is put into the corresponding concentration of CuCl solution, immersed at 35 °C for 2 h, washed with methanol solvent for 20 min, and dried to obtain the interfacially modified hard carbon negative electrode for a sodium-ion battery. The thickness of the obtained metal-organic complex film is about 25 nm.

[0081] Electrochemical performance test: Using a sodium metal sheet as the counter electrode, NaPF6 salt dissolved in an EC:DEC solvent with a volume ratio of 1:1 as the electrolyte (1 mol / L), a button-type sodium-ion battery was assembled using a cellulose acetate separator and a stainless steel battery case to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, when the current density is 0.05 A g -1 the specific capacity is 265 mAh g -1 . Compared with the specific capacity of the unmodified hard carbon negative electrode (228 mAh g -1 ), it is increased by 16.23%.

[0082] Example 7

[0083] This example is about the preparation method and application of an interfacially modified hard carbon negative electrode for a sodium-ion battery, and the steps are as follows:

[0084] Preparation method of hard carbon anode: The commercially available hard carbon purchased is used as the anode material, which mainly consists of micron-sized blocky particles. It is mixed with a conductive agent and a binder to form a slurry, which is coated on a copper foil and dried.

[0085] Preparation method of interface-modified hard carbon anode: Using methanol as the solvent, a 2-mercaptobenzothiazole (MBT) solution with a concentration of 0.1 g / L is prepared. Additionally, a CuCl solution with a concentration of 0.1 g / L is prepared using dimethyl sulfoxide as the solvent. The unmodified hard carbon anode is immersed in the 2-mercaptobenzothiazole solution at 30 °C for 30 min, taken out and dried. Further, it is placed in the corresponding concentration of CuCl solution and immersed at 30 °C for 30 min, washed with methanol solvent for 20 min, and dried to obtain the interface-modified hard carbon anode for sodium-ion batteries. The thickness of the obtained metal-organic complex film is about 27 nm.

[0086] Electrochemical performance test: Using a sodium metal sheet as the counter electrode, NaSO3CF3 salt is dissolved in DGM solvent as the electrolyte (1 mol / L). A button-type sodium-ion battery is assembled using a glass fiber separator and a stainless steel battery case to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, when the current density is 0.2 A g -1 the specific capacity is 282 mAh g -1 . Compared with the unmodified hard carbon anode with a specific capacity of 228 mAh g -1 , it is increased by 23.68%.

[0087] Example 8

[0088] This example is about the preparation method and application of the interface-modified hard carbon anode for sodium-ion batteries, and the steps are as follows:

[0089] Preparation method of hard carbon anode: The commercially available hard carbon purchased is used as the anode material, which mainly consists of micron-sized blocky particles. It is mixed with a conductive agent and a binder to form a slurry, which is coated on a copper foil and dried.

[0090] Preparation method of interface-modified hard carbon anode: Using methanol as the solvent, a 2-mercaptobenzothiazole (MBT) solution with a concentration of 0.1 g / L is prepared. Additionally, a FeSO4 solution with a concentration of 0.1 g / L is prepared using dimethyl sulfoxide as the solvent. The unmodified hard carbon anode is immersed in the 2-mercaptobenzothiazole solution at 40 °C for 2 h, taken out and dried. Further, it is immersed in the 0.1 g / L FeSO4 solution at 40 °C for 2 h, washed with methanol solvent for 20 min, and dried to obtain the interface-modified hard carbon anode for sodium-ion batteries. The thickness of the obtained metal-organic complex film is about 15 nm.

[0091] Electrochemical performance test: A sodium metal sheet was used as the counter electrode, and NaPF6 salt was dissolved in an EC:DEC solvent with a volume ratio of 1:1 as the electrolyte (1 mol / L). Using a glass fiber separator and a stainless steel battery case, a button-type sodium-ion battery was assembled to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, when the current density was 0.2 A g -1 the specific capacity was 243 mAh g -1 . Compared with the specific capacity of the unmodified hard carbon negative electrode (228 mAh g -1 ), it was increased by 6.58%.

[0092] Example 9

[0093] This example is about the preparation method and application of an interface-modified hard carbon negative electrode for a sodium-ion battery, and the steps are as follows:

[0094] Preparation method of the hard carbon negative electrode: The commercially purchased hard carbon was used as the negative electrode material, which was mainly composed of micron-sized blocky particles. It was mixed with a conductive agent and a binder to form a slurry and coated on a copper foil, and then dried.

[0095] Preparation method of the interface-modified hard carbon negative electrode: Using methanol as the solvent, a 2-mercaptobenzothiazole solution with a concentration of 0.1 g / L was prepared. In addition, a CuCl solution with a concentration of 0.1 g / L was prepared using dimethyl sulfoxide as the solvent; the unmodified hard carbon negative electrode was soaked in the 2-mercaptobenzothiazole solution at 50 °C for 2 h, taken out and dried; further, it was soaked in a 0.1 g / L FeSO4 solution and soaked at 50 °C for 2 h, washed with methanol solvent for 20 min, and dried to obtain the interface-modified hard carbon negative electrode for a sodium-ion battery. The thickness of the obtained metal-organic complex film was about 20 nm.

[0096] Electrochemical performance test: A positive electrode plate was obtained by coating a NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 active material, a conductive agent and a binder. NaPF6 salt was dissolved in an EC:DEC solvent with a volume ratio of 1:1 as the electrolyte (1 mol / L), and glass fiber was used as the separator. The capacity ratio of the negative electrode and the positive electrode materials was adjusted to 1:1.2, and an aluminum-plastic film was used as the outer shell (as Figure 9 shown) to assemble a soft-pack sodium-ion battery to test its electrochemical performance. In the voltage range of 1.0 - 3.5 V, when the current density was 0.02 A g -1 the specific capacity was 235 mAhg -1 . Compared with the specific capacity of the unmodified hard carbon negative electrode (210 mAh g -1 ), it was increased by 11.9%.

[0097] Example 10

[0098] The preparation method and application of a hard carbon negative electrode prepared from interface-modified hard carbon powder are as follows:

[0099] Preparation method of interface-modified hard carbon powder: 0.5 g of benzotriazole (BTA) and 0.25 g of hard carbon powder (composed of micron-sized blocky particles) are mixed and dispersed in 100 mL of methanol solution and stirred continuously for 1 h, and then centrifuged and dried; in addition, 1.277 g of CuSO4 is dissolved in 150 mL of dimethyl sulfoxide, and then the hard carbon powder obtained in the previous step is added, and it is stirred vigorously for 2 min, centrifuged, washed three times, and dried to obtain the interface-modified hard carbon powder. The thickness of the obtained metal-organic complex film is about 20 nm.

[0100] Electrochemical performance test: The interface-modified hard carbon powder, conductive agent, and binder are mixed in N,N-dimethylpyrrolidone solvent to prepare a slurry, which is coated on a copper foil and dried. A sodium metal sheet is used as the counter electrode, NaPF6 salt is dissolved in an EC:DEC solvent with a volume ratio of 1:1 as the electrolyte (1 mol / L), and glass fiber is used as the separator to assemble a button-type sodium-ion battery to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, when the current density is 0.05 Ag -1 the specific capacity of the hard carbon negative electrode prepared from the interface-modified hard carbon powder is 247 mAh g -1 which is 8.33% higher than that of the hard carbon negative electrode without interface modification (228 mAh g -1 ).

[0101] Example 11

[0102] The preparation method and application of an interface-modified sodium-ion battery hard carbon negative electrode are as follows:

[0103] Preparation method of hard carbon negative electrode: The commercially available hard carbon purchased is used as the negative electrode material, which is mainly composed of spherical particles. It is mixed with a conductive agent and a binder to form a slurry, coated on a copper foil, and dried.

[0104] Preparation method of interface-modified hard carbon negative electrode: Using ethanol as the solvent, a benzothiazole (BT) solution with a concentration of 5 g / L is prepared. In addition, using acetonitrile as the solvent, a ZnCl2 solution with a concentration of 5 g / L is prepared; the unmodified hard carbon negative electrode is soaked in the benzothiazole solution at 80 °C for 1 min, taken out and dried; further, it is put into the corresponding concentration of ZnCl2 solution and soaked at 80 °C for 1 min, washed with ethanol and acetonitrile solvents for 10 s and 20 s respectively, and dried at 20 °C to obtain the interface-modified sodium-ion battery hard carbon negative electrode. The thickness of the obtained metal-organic complex film is about 25 nm.

[0105] Electrochemical performance test: Sodium iron phosphate was used as the positive electrode sheet, 0.3 mol / L NaBF4 salt dissolved in a solvent of EMC:DMC with a volume ratio of 1:1 was used as the electrolyte, cellulose acetate membrane was used as the separator, and stainless steel was used as the casing to assemble a button-type sodium-ion battery to test its electrochemical performance. In the voltage range of 0.01 - 2.0 V, the specific capacity was 237 mAh g -1 at a current density of 0.05 A g -1 . Compared with the specific capacity of the unmodified hard carbon negative electrode (228 mAh g -1 ), it increased by 4.0%.

[0106] Example 12

[0107] This example is about the preparation method and application of an interface-modified hard carbon negative electrode for a sodium-ion battery, and the steps are as follows:

[0108] Preparation method of hard carbon negative electrode: The commercially purchased hard carbon was used as the negative electrode material, mainly composed of spherical particles. It was mixed with a conductive agent and a binder into a slurry and coated on a copper foil, and then dried.

[0109] Preparation method of interface-modified hard carbon negative electrode: Using water as the solvent, a pyrazole (Pyro) solution with a concentration of 10 g / L was prepared. In addition, a NiSO4 solution with a concentration of 10 g / L was prepared using N,N-dimethylformamide as the solvent; the unmodified hard carbon negative electrode was soaked in the pyrazole solution at 20 °C for 2 h, taken out and dried; then it was further put into the corresponding concentration of NiSO4 solution and soaked at 10 °C for 2 h, washed with N,N-dimethylformamide and water solvents for 1 h in sequence, and dried at 70 °C to obtain the interface-modified hard carbon negative electrode for a sodium-ion battery. The thickness of the obtained metal-organic complex film was about 30 nm.

[0110] Electrochemical performance test: Sodium vanadium fluorophosphate compound was used as the positive electrode sheet, 1.0 mol / L NaClO4 salt dissolved in a solvent of EC:PC with a volume ratio of 1:1 and 5% FEC as an additive was used as the electrolyte. The capacity ratio of the negative electrode and the positive electrode materials was adjusted to 1:1.2, polyvinylidene fluoride was used as the separator, and a composite material of an aluminum shell and an aluminum-plastic film was used as the casing to assemble a button-type sodium-ion battery to test its electrochemical performance. In the voltage range of 1.0 - 4.0 V, the specific capacity was 240 mAh g -1 at a current density of 0.02 A g -1 . Compared with the specific capacity of the unmodified hard carbon negative electrode (220 mAh g -1 ), it increased by 9.09%.

[0111] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. An interface-modified hard carbon anode material for sodium-ion batteries, characterized in that: Coat a hard carbon material surface with a metal-organic complex thin film formed by coordination of a metal center and an organic molecule, with a thickness of 3 nm - 30 nm; The metal center is Cu; the organic molecule is 2-mercaptobenzothiazole; The preparation method is as follows: (1) Immerse the powder of the hard carbon material in the organic molecule solution or drop the organic molecule solution onto the unmodified hard carbon material at the interface. The concentration of the organic molecule solution is 0.05 - 0.1 g / L. After the hard carbon material is coated with the organic molecule and dried, hard carbon material a1 is obtained; (2) Then immerse hard carbon material a1 in the metal salt solution or drop the metal salt solution onto hard carbon material a1. The concentration of the metal salt solution is 0.05 - 0.1 g / L to obtain hard carbon material b1. Immerse and wash hard carbon material b1 in a solvent at an immersion temperature of 25 - 30 °C for an immersion time of 1 min - 2 h. After the immersion and washing are completed, dry it to obtain the interfacially modified hard carbon negative electrode material for a sodium-ion battery.

2. An interface-modified hard carbon anode for sodium-ion batteries, characterized in that: Prepared using the interfacially modified hard carbon negative electrode material for a sodium-ion battery described in claim 1.

3. An interface-modified hard carbon anode for sodium-ion batteries, characterized in that: Coat a hard carbon negative electrode surface with a metal-organic complex thin film formed by coordination of a metal center and an organic molecule, with a thickness of 3 nm - 30 nm; the metal center is Cu; the organic molecule is 2-mercaptobenzothiazole; The preparation method is as follows: (1) Immerse the hard carbon negative electrode in the organic molecule solution or drop the organic molecule solution onto the hard carbon negative electrode. The concentration of the organic molecule is 0.05 - 0.1 g / L. After the hard carbon negative electrode is coated with the organic molecule and dried, hard carbon negative electrode a2 is obtained; (2) Then immerse hard carbon negative electrode a2 in the metal salt solution or drop the metal salt solution onto hard carbon negative electrode a2 to obtain hard carbon negative electrode b2. Immerse and wash hard carbon negative electrode b2 in a solvent. The concentration of the metal salt solution is 0.05 - 0.1 g / L, the immersion temperature is 25 - 30 °C, and the immersion time is 1 min - 2 h. After the immersion and washing are completed, dry it to obtain the interfacially modified hard carbon negative electrode for a sodium-ion battery.

4. The interface-modified hard carbon anode for sodium-ion batteries according to claim 3, characterized in that: The solvent of the organic molecule solution includes any one or more of methanol, ethanol, water, dimethyl sulfoxide, N,N-dimethylformamide, or acetonitrile.

5. The interface-modified hard carbon anode for sodium-ion batteries according to claim 3, characterized in that: The metal salt is any one or more of the chloride, sulfate, fluoride, or nitrate salts of Cu metal ions.

6. The interface-modified hard carbon anode for sodium-ion batteries according to claim 3, characterized in that: The solvent of the metal salt solution includes any one or more of methanol, ethanol, water, dimethyl sulfoxide, N,N-dimethylformamide, or acetonitrile.

7. The interface-modified hard carbon anode for sodium-ion batteries according to claim 3, characterized in that: The immersion and washing solvent includes any one or several of dimethyl sulfoxide, methanol, water, acetone, ethanol, acetonitrile, or N,N-dimethylformamide; the drying method after the immersion and washing are completed is air drying or vacuum drying, and the drying temperature is 20 - 100 °C.

8. A non-aqueous secondary battery, comprising a negative electrode sheet, a positive electrode sheet, a non-aqueous electrolyte, a separator and a casing, characterized in that: The negative electrode plate uses the interfacially modified hard carbon negative electrode for a sodium-ion battery described in claim 2 or 3 as the negative electrode plate.

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