Inorganic nickel compound plasma synthesis hard carbon / nickel composite negative electrode material and its preparation method and application

Abstract

The present invention belongs to the technical field of sodium ion batteries, and relates to an inorganic nickel compound plasma synthesized hard carbon / nickel composite negative electrode material, and its preparation method and application. The material is based on biomass carbon as a matrix, an inorganic nickel compound as a plasma source, and a carbonized precursor is prepared by plasma sintering to obtain a hard carbon / nickel composite negative electrode material. The hard carbon / nickel composite negative electrode material prepared by the present invention exhibits high specific capacity, good cycle stability, and excellent rate performance and coulombic efficiency. At the same time, the preparation method provided by the present invention is simple, fast, efficient, and convenient, with mild conditions and easy control, and can effectively introduce sodium storage gain impurities into the hard carbon material, which is helpful to promote the development of hard carbon negative electrode materials for sodium ion batteries.

Description

Technical Field

[0001] The present invention relates to the technical field of hard carbon negative electrode materials for sodium ion batteries, and in particular to a method and material for preparing hard carbon / nickel composite negative electrode materials using inorganic nickel compound plasma technology, and application of the hard carbon / nickel composite negative electrode materials in sodium ion batteries. Background Art

[0002] Hard carbon is the preferred commercial negative electrode material for sodium ion batteries due to its abundant resources, low cost and high theoretical reversible capacity. However, the preparation of hard carbon negative electrodes often requires a high temperature environment, which generates a lot of energy consumption, and hard carbon materials have problems such as low specific capacity, low first coulombic efficiency and poor rate performance. Therefore, it is necessary to find a modification scheme to optimize the first coulombic efficiency of hard carbon negative electrodes as well as the cycle and rate performance.

[0003] At present, the modification methods for hard carbon negative electrode materials mainly include: controlling carbonization temperature, heterogeneous element doping, interface structure modulation, micro-nanostructure optimization design, etc. Among them, controlling the carbonization temperature can improve the graphitization degree of hard carbon materials and optimize the micro-nanostructure, which is beneficial to the sodium ion deintercalation of hard carbon materials. However, the high-temperature pyrolysis carbonization of hard carbon precursors often requires a temperature above 1000 °C, mainly because when the precursor is carbonized at a relatively low temperature (below 1000 °C), its microstructure usually shows a low degree of graphitization, rich defects and a large specific surface area, resulting in a large amount of SEI film formed on the surface of the material during the first cycle, resulting in a decrease in the first coulombic efficiency. Heterogeneous element doping is a more studied and mature method for controlling material defects and interlayer spacing. The introduction of gain heteroatoms can effectively improve the conductivity of hard carbon negative electrode materials, and at the same time, surface interface and bulk defects can be introduced to provide more sodium storage sites, thereby effectively improving the rate performance and specific capacity of hard carbon materials. Cheap transition metal elements (nickel, cobalt, etc.) usually have good electrical conductivity and catalytic function. Introducing transition metal elements into the hard carbon negative electrode has the following advantages: (1) Conductive metals implanted into the hard carbon material can form a three-dimensional conductive network, accelerating the migration rate of electrons and ions; (2) Improving the structural stability of the hard carbon material, effectively inhibiting the volume effect caused by the sodium ion insertion and extraction of the hard carbon material, thereby enhancing the cycle life; (3) Accelerating the activation reaction of the hard carbon material, improving the activation efficiency, and improving the electrochemical performance of the interface and bulk sodium storage; (4) Optimizing the microstructure of the hard carbon material and increasing the sodium storage space and capacity. For example, Professor Zhou Jisheng of Beijing University of Chemical Technology successfully introduced Cu elements into hard carbon nanofibers to produce defect-rich carbon textures without increasing the surface area, effectively improving the reversible capacity of hard carbon materials; Professor Han Fei of Hunan University used a zinc salt template to promote the formation of many closed pores in the hard carbon material during the pyrolysis process, successfully achieving a first-cycle coulomb efficiency of 92.4% and a high specific capacity of more than 340 mAh / g; Professor Li Li of Shanghai University used manganese ion-assisted catalytic carbonization to accurately adjust the degree of graphitization and successfully improved the first charge and discharge efficiency and cycle performance of the material. The introduction of metal elements has been proven to be beneficial to the charge and discharge process of negative electrode materials. However, the doping of nickel elements is usually carried out by ball milling, high-temperature solid-phase synthesis, chemical deposition, spray drying, and sol-gel methods. The doped hard carbon materials prepared by the above methods are usually in the form of surface coating. This combination method has insufficient binding force and stability, which can easily lead to the failure of metal separation or require a high temperature environment of more than 1000 ° C to make the nickel elements and the base material sintered for secondary sintering to form chemical bonds, which is time-consuming and energy-intensive.

[0004] Based on this, the present invention proposes a method for preparing a sodium ion battery hard carbon composite negative electrode material loaded with transition metal nickel having a strong bond with a hard carbon substrate under relatively mild conditions (temperature not higher than 1000°C) and in a relatively short time (less than 1 hour) by using inorganic nickel compound plasma technology, and at the same time regulating the internal microstructure and degree of graphitization of the hard carbon, thereby preparing a high-performance sodium ion battery negative electrode material. Summary of the invention

[0005] The purpose of the present invention is to address a series of problems such as the large amount of energy consumption generated in the preparation process of hard carbon negative electrode materials in the sodium ion battery system, as well as the first coulombic efficiency, specific capacity and rate performance, and provide a method for sintering hard carbon / nickel composite negative electrode materials in an inorganic nickel compound plasma atmosphere, which can effectively prepare high-performance hard carbon / nickel composite negative electrode materials by regulating parameters such as reaction time, reaction temperature, radio frequency power, and vacuum degree. The inorganic nickel compound plasma atmosphere sintering provided by the present invention can prepare hard carbon materials in a short time under a relatively low temperature environment and effectively introduce nickel elements, so that the prepared sodium ion battery hard carbon negative electrode material has high specific capacity, good cycle stability, excellent rate performance and coulombic efficiency, which can effectively promote the commercialization process of hard carbon composite negative electrode materials.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] The present invention provides a preparation method of a hard carbon / nickel composite negative electrode material synthesized by an inorganic nickel compound plasma. The preparation method uses a biomass hard carbon precursor as a hard carbon material matrix, an inorganic nickel compound as a plasma source, utilizes the catalytic effect of the nickel element to accelerate the dehydrogenation, condensation and carbonization of organic matter inside the carbonized precursor, and prepares the hard carbon / nickel composite negative electrode material through plasma sintering.

[0008] Preferably, the preparation method specifically comprises the following steps:

[0009] (1) The biomass hard carbon precursor is pre-carbonized in a protective atmosphere, and then acid-washed and dried to obtain a carbonized precursor;

[0010] (2) placing a mixture of an inorganic nickel compound and a carbonization precursor in a plasma reaction chamber and subjecting the chamber to a vacuum treatment;

[0011] (3) The plasma reaction chamber is heated to a certain temperature, the plasma radio frequency power is adjusted, the inorganic nickel compound plasma is ignited and reacted for a certain period of time, and then sintered to obtain a hard carbon / nickel composite negative electrode material.

[0012] By adopting the above technical solution, biomass carbon is used as the carbon source matrix, which has the great advantages of wide raw material sources and low cost; at the same time, under the action of low-temperature plasma and nickel metal, the dehydrogenation and condensation reaction rates of the carbonization precursor are accelerated, and most of the organic impurities in the raw materials are carbonized or volatilized and removed. The nickel element forms a three-dimensional conductive network inside the hard carbon material, which greatly improves the electronic and ionic conductivity of the material, which is beneficial to Na + Rapid transmission, reaction and storage. In the sintering atmosphere of inorganic nickel compound plasma and under the catalytic action of nickel element, the dehydrogenation and condensation reaction rates of the carbonized precursor during the sintering process are accelerated, most of the organic impurities in the raw materials are carbonized or volatilized, and the nickel element is stably and evenly loaded in the hard carbon matrix, regulating the micro-nano structure and graphitization degree of the hard carbon surface interface and bulk phase, reducing the side reactions caused by excessive contact between the material surface and the electrolyte, and improving the first coulomb efficiency, sodium storage capacity and cycle life; the reducing atmosphere of inorganic nickel compound plasma treatment can introduce more sodium storage space inside the hard carbon material, so that the hard carbon material has more sodium storage sites and capacity. In addition, with the assistance of the new inorganic nickel compound plasma atmosphere sintering technology, nickel-containing hard carbon composite materials can be prepared in a relatively mild environment (temperature not higher than 1000 ° C), reducing reaction energy consumption, reducing costs, and forming a stable chemical bond between the metal element and the hard carbon material, improving material stability, improving the electrochemical properties of the surface interface and bulk of the hard carbon negative electrode material, and further improving the first coulomb efficiency, cycle life and specific capacity of the hard carbon negative electrode material. Compared with conventional nickel metal doping methods such as high-temperature solid phase synthesis and electrochemical deposition, plasma technology can effectively reduce reaction time and temperature, save reaction time and material costs, and improve production efficiency, forming a more uniform and stable nickel element distribution on the material surface.

[0013] The following is a more preferred technical solution of the present invention:

[0014] Preferably, in step (1), the biomass hard carbon precursor is selected from at least one of bamboo carbon, fir carbon, fruit shell carbon, corn cob carbon and other biomass carbons. The present invention uses biomass carbon as a matrix, and performs surface and bulk modification to load nickel, which has the advantages of low cost and wide source of raw materials.

[0015] Preferably, in step (1), the protective atmosphere is at least one of helium, nitrogen and argon.

[0016] Preferably, in step (1), the pre-carbonization treatment process is: heating rate 5-15 °C / min, temperature 200-600 °C, treatment time 1-3 h, so as to remove moisture from the material, form graphite crystallites and form a stable carbon structure; more preferably, the heating rate is 5 °C / min, the temperature is 300 °C, and the treatment time is 2 h.

[0017] Preferably, in step (1), the pickling solution is at least one of hydrochloric acid, sulfuric acid and phosphoric acid, the pickling concentration is 0.5-2 mol / L, and the pickling time is 1-24 h; more preferably, the pickling solution is hydrochloric acid, the pickling solution concentration is 1 mol / L, and the pickling time is 6 h.

[0018] Preferably, in step (1), the drying temperature ranges from 50 to 100 °C, and the drying time is 2 to 12 h; more preferably, the drying temperature is 60 °C and the drying time is 8 h.

[0019] Preferably, in step (1), the drying is followed by sieving, preferably with a sieve having a mesh size of 300-800 meshes, more preferably 500 meshes.

[0020] Preferably, in step (2), the inorganic nickel compound is selected from at least one of nickel sulfate, nickel carbonate, nickel chloride and nickel oxide, and is used to generate a nickel-containing plasma atmosphere; more preferably, it is one of nickel oxide, nickel chloride and nickel sulfate.

[0021] Preferably, in step (2), the mass proportion of the inorganic nickel compound in the mixture is 2-10 wt.%. If the content of the inorganic nickel compound is too low, the decomposition ability of the organic matter in the precursor carbonization catalyzed by the inorganic nickel compound plasma atmosphere may be reduced, resulting in residual non-carbon impurities in the hard carbon material. On the contrary, if the content is too high, the reversible capacity of the hard carbon material will be reduced and the cost will be too high.

[0022] Preferably, in step (2), the sufficient mixing is to disperse and mix the inorganic nickel compound and the carbonized precursor by ball milling, with a ball-to-material ratio of 10-20:1, a rotation speed of 400-550 r / min, and a ball milling time of 3-12 h; more preferably, the parameters of the ball milling are a ball-to-material ratio of 20:1, a rotation speed of 550 r / min, and a ball milling time of 12 h.

[0023] Preferably, in step (2), the vacuum is evacuated to a vacuum degree of 5-75 Pa.

[0024] Preferably, in step (3), the reaction conditions are: reaction temperature 500-1000°C, RF power maintained at 300-1000 W, system reaction vacuum after inorganic nickel compound plasma excitation is 5-75 Pa, and plasma reaction time is 20-60 min; more preferably, the reaction temperature is 800°C, RF power is 400 W, reaction vacuum is 10 Pa, and reaction time is 30 min. Insufficient reaction time, too low reaction temperature and power will lead to insufficient energy, making it impossible for nickel to be effectively loaded on the surface or inside of the hard carbon material and will lead to incomplete decomposition of organic matter inside the hard carbon precursor. On the contrary, if the reaction time is too long, the plasma may etch the surface of the hard carbon material, causing the internal structure of the material to be destroyed.

[0025] Preferably, in step (3), the nickel loading ratio in the hard carbon / nickel composite negative electrode material formed is 1-5 wt. %; more preferably, the ratio is 2 wt. %. Too low a nickel loading ratio may result in an inability to effectively improve the electron or ion transmission rate of the hard carbon material, while too high a ratio may result in a low reversible capacity of the hard carbon material.

[0026] The present invention provides a method for preparing a hard carbon / nickel composite negative electrode material synthesized by an inorganic nickel compound plasma. So far, there has been no report in the field on the application of inorganic nickel compound plasma in the preparation of hard carbon negative electrode materials for sodium ion batteries. In the present invention, with the assistance of plasma technology, a hard carbon negative electrode material with excellent synthesis performance is successfully prepared in a relatively low temperature environment (not higher than 1000 ° C) and metal nickel is uniformly and firmly implanted in the structure of the hard carbon material. Nickel, as a transition metal, has a catalytic effect. During the plasma treatment process, it can accelerate the dehydrogenation, condensation, and carbonization of organic impurities in the carbonization precursor, increase the degree of graphitization of the material, and reduce the side reactions occurring when the surface of the material contacts the electrolyte. At the same time, the presence of nickel can increase the transmission rate of ions and electrons in the material and reduce the polarization degree of the electrochemical reaction of the material. Therefore, the hard carbon / nickel composite negative electrode material prepared by sintering in an inorganic nickel compound plasma atmosphere exhibits higher capacity, more superior rate performance and coulombic efficiency, providing new commercial application possibilities for sodium ion batteries.

[0027] The present invention also provides an inorganic nickel compound plasma synthesized hard carbon / nickel composite negative electrode material prepared by any of the above preparation methods.

[0028] The present invention also provides an application of an inorganic nickel compound plasma synthesized hard carbon / nickel composite negative electrode material prepared by any of the above preparation methods in the field of sodium ion batteries.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The hard carbon / nickel composite negative electrode material described in the present invention is prepared by sintering reaction of inorganic nickel compound solid source plasma and hard carbon negative electrode material. Under plasma treatment, hard carbon material is successfully synthesized under relatively low temperature environment and the introduction of nickel element forms a three-dimensional conductive network inside the hard carbon material, which significantly improves the conductivity of the material. At the same time, nickel, as a transition metal element, has the function of catalytic activation, which is beneficial to accelerate the decomposition of organic impurities inside the carbonization precursor, improve the degree of graphitization of hard carbon and increase the sodium storage sites of the material, and reduce the side reactions occurring when the surface of the hard carbon material contacts the electrolyte. Therefore, the hard carbon negative electrode material exhibits good cycle stability, rate performance and coulombic efficiency. The preparation method of the hard carbon / nickel composite negative electrode material described in the present invention is simple, fast, efficient and convenient, with mild conditions and easy control. It can effectively introduce sodium storage gain impurity elements into the hard carbon material, which is helpful to promote the commercial development of hard carbon negative electrode of sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a schematic diagram of an inorganic nickel compound plasma reaction device of the present invention;

[0032] Figure 2 The SEM morphology comparison diagram of the materials of Comparative Example 1 (left) and Example 1 (right);

[0033] Figure 3 This is the EDS element distribution diagram of the hard carbon / nickel composite negative electrode material of Example 1;

[0034] Figure 4 This is a transmission electron microscope TEM image of the hard carbon / nickel composite negative electrode material of Example 1;

[0035] Figure 5 The Raman spectra of the materials of comparative example 1 and example 1 are compared;

[0036] Figure 6 This is a comparison chart of the cycle test performance of the materials of Comparative Example 1, Comparative Example 2 and Example 1 at a current density of 100 mA / g. DETAILED DESCRIPTION

[0037] For ease of understanding, the technical solutions and implementation methods of the present invention are further described clearly, completely and in detail through specific examples and in combination with the accompanying drawings. It should be noted that the embodiments described in the present invention are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operating processes are given, but they are only part of the embodiments of the present invention, not all of the embodiments. The specific implementation methods described are limited to explaining and interpreting the present invention, and do not limit the present invention. Based on the embodiments in the present invention, all other implementation methods obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0038] The experimental methods and conditions used in the following examples are conventional methods and conventional conditions unless otherwise specified. The materials, reagents or instruments, devices, etc. used in the examples are conventional substances or equipment known to those skilled in the art and can be obtained from commercial sources unless otherwise specified. The reaction conditions embodied in the content of the invention of the present invention can achieve the reaction and obtain the product of the expected effect. Due to space limitations, only some embodiments are listed below to further illustrate the advantages of the technical solution of the present invention. Example 1

[0039] Combination Figure 1 Bamboo powder was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min under an argon atmosphere for 2 h, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500 mesh screen to obtain a carbonized precursor. The carbonized precursor and nickel oxide were fully mixed and dispersed with a ball-to-material ratio of 20:1 and ball milled at 550 r / min for 12 h to obtain a mixture, and the nickel oxide content in the mixture was 5 wt.%. 5 g of the mixture was placed in a rotating plasma reaction chamber, and then copper rings were connected to the two ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 °C. Turn on the radio frequency power switch, adjust the radio frequency power, adjust the radio frequency power of the nickel oxide plasma to 400 W for the ignition reaction, and adjust the reaction vacuum to 10 Pa. In the plasma reaction chamber, nickel oxide is excited into a plasma state and a nickel-containing plasma atmosphere is constructed, catalyzing the dehydrogenation, condensation, and carbonization of organic impurities inside the carbonization precursor and forming chemical bonds with hard carbon. The hard carbon material matrix is ​​successfully prepared by plasma sintering and nickel particles are implanted. After reacting for 30 minutes, the RF power supply is turned off to obtain a hard carbon / nickel composite negative electrode material with a nickel content of 2 wt.%.

[0040] Example 2-17

[0041] On the basis of Example 1, the conditions such as the type of biomass hard carbon precursor and pre-carbonization temperature, the type and content of the inorganic nickel compound, the reaction temperature, the plasma reaction power, the reaction vacuum degree, the reaction time, etc. were changed. The reaction conditions are shown in Table 1 below:

[0042] Table 1 Summary of reaction conditions of various examples

[0043] Comparative Example 1

[0044] The bamboo powder was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min for 2 h in an argon atmosphere, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500-mesh screen to obtain a carbonized precursor. The carbonized precursor was then sintered to 1200 °C at a heating rate of 5 °C / min for 2 h in an argon atmosphere to form a hard carbon material. Comparative Example 2

[0045] Nickel oxide and the hard carbon material prepared in Comparative Example 1 were placed in a ball mill, where the mass proportion of nickel oxide was 2.5 wt. %, the ball-to-material ratio was 20:1, the rotation speed was 550 r / min, and the ball milling was performed for 12 h to disperse and obtain a hard carbon / nickel composite negative electrode material with a nickel content of 2 wt. %. Comparative Example 3

[0046] The hard carbon material and nickel oxide prepared in Comparative Example 1 were dispersed by ball milling, with a ball-to-material ratio of 20:1 and a rotation speed of 550r / min for 12 h to be fully mixed and placed in a rotating plasma reaction chamber, wherein the nickel oxide content was 5 wt.%. Copper rings were then connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 ° C. Turn on the radio frequency power switch, adjust the radio frequency power, adjust the radio frequency power of the nickel oxide plasma to 400 W for the ignition reaction, and the reaction vacuum was 10 Pa. After reacting for 30 min, the radio frequency power was turned off to obtain a hard carbon / nickel composite negative electrode material with a nickel content of 1 wt.%. Comparative Example 4

[0047] Bamboo powder was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min for 2 h in an argon atmosphere, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500 mesh to obtain a carbonized precursor. The carbonized precursor and nickel sulfite were fully mixed and dispersed at a ball-to-material ratio of 20:1 and ball milled at 550 r / min for 12 h to obtain a mixture, and the nickel sulfite content in the compound was 5 wt.%. 5 g of the mixture was taken and placed in a rotating plasma reaction chamber, copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 °C. Turn on the RF power switch, adjust the RF power, adjust the RF power of nickel sulfite plasma to 400 W for ignition reaction, adjust the reaction vacuum to 10 Pa, react for 30 min, turn off the RF power, and obtain a hard carbon / nickel composite negative electrode material with a nickel content of 2 wt.%. Comparative Example 5

[0048] Bamboo powder was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min for 2 h in an argon atmosphere, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500 mesh to obtain a carbonized precursor. The carbonized precursor was fully mixed and dispersed with nickelocene (organic nickel compound) at a ball-to-material ratio of 20:1 and ball milled at 550 r / min for 12 h to obtain a mixture, in which the nickelocene content in the compound was 5 wt.%. 5 g of the mixture was taken and placed in a rotating plasma reaction chamber, copper rings were connected to both ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 °C. Turn on the RF power switch, adjust the RF power, adjust the RF power of the nickelocene plasma to 400 W for the ignition reaction, adjust the reaction vacuum to 10 Pa, and after reacting for 30 min, turn off the RF power to obtain a hard carbon / nickel composite negative electrode material with a nickel content of 2.5 wt.%. Comparative Example 6

[0049] Bamboo powder was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min for 2 h in an argon atmosphere, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500 mesh screen to obtain a carbonized precursor. The carbonized precursor and nickel oxide were fully mixed and dispersed with a ball-to-material ratio of 20:1 and ball milled at 550 r / min for 12 h to obtain a mixture, and the nickel oxide content in the compound was 15 wt.%. 5 g of the mixture was taken and placed in a rotating plasma reaction chamber, and then copper rings were connected to the two ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 °C. Turn on the RF power switch, adjust the RF power, adjust the RF power of nickel oxide plasma to 400 W for ignition reaction, adjust the reaction vacuum to 10 Pa, react for 30 min, turn off the RF power, and obtain a hard carbon / nickel composite negative electrode material with a nickel content of 10 wt.%. Comparative Example 7

[0050] Bamboo powder was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min for 2 h in an argon atmosphere, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500 mesh screen to obtain a carbonized precursor. The carbonized precursor and nickel oxide were fully mixed and dispersed with a ball-to-material ratio of 20:1 and ball milled at 550 r / min for 12 h to obtain a mixture, and the nickel oxide content in the compound was 0.5 wt.%. 5 g of the mixture was taken and placed in a rotating plasma reaction chamber, and then copper rings were connected to the two ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 °C. Turn on the RF power switch, adjust the RF power, adjust the RF power of nickel oxide plasma to 400 W for ignition reaction, adjust the reaction vacuum to 10 Pa, react for 30 min, turn off the RF power, and obtain a hard carbon / nickel composite negative electrode material with a nickel content of 0.2 wt.%. Comparative Example 8

[0051] The epoxy resin was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min under an argon atmosphere for 2 h, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500 mesh to obtain a carbonized precursor. The carbonized precursor and nickel oxide were fully mixed and dispersed at a ball-to-material ratio of 20:1 and ball milled at 550 r / min for 12 h to obtain a mixture, and the nickel oxide content in the compound was 5 wt.%. 5 g of the mixture was taken and placed in a rotating plasma reaction chamber, and then copper rings were connected to the two ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 °C. Turn on the RF power switch, adjust the RF power, adjust the RF power of nickel oxide plasma to 400 W for ignition reaction, adjust the reaction vacuum to 10 Pa, react for 30 min, turn off the RF power, and obtain a hard carbon / nickel composite negative electrode material with a nickel content of 2 wt.%. Comparative Example 9

[0052] The asphalt was pre-carbonized by heating to 300 °C at a heating rate of 5 °C / min under an argon atmosphere for 2 h, then pickled with 1 mol / L hydrochloric acid for 6 h, dried at 60 °C for 8 h, and sieved through a 500 mesh screen to obtain a carbonized precursor. The carbonized precursor and nickel oxide were fully mixed and dispersed with a ball-to-material ratio of 20:1 and ball milled at 550 r / min for 12 h to obtain a mixture, and the nickel oxide content in the compound was 5 wt.%. 5 g of the mixture was taken and placed in a rotating plasma reaction chamber, and then copper rings were connected to the two ends of the plasma device, and the copper rings were connected to the generator of the radio frequency power supply with a wire, and the rest of the devices were connected. The plasma device was then evacuated to 5 Pa, and the plasma reaction chamber was heated to 800 °C. Turn on the RF power switch, adjust the RF power, adjust the RF power of nickel oxide plasma to 400 W for ignition reaction, adjust the reaction vacuum to 10 Pa, react for 30 min, turn off the RF power, and obtain a hard carbon / nickel composite negative electrode material with a nickel content of 2 wt.%.

[0053] Performance Testing

[0054] The materials prepared in the above Examples 1-17 and Comparative Examples 1-9 were assembled into button-type half-cells for electrochemical testing. The electrolyte was 1 mol / L NaPF 6 in DME=100 vol% (DME: ethylene glycol dimethyl ether), the diaphragm is a glass fiber diaphragm. The battery is assembled in the order of positive electrode shell, hard carbon / nickel negative electrode sheet, electrolyte, diaphragm, sodium sheet, and negative electrode shell and sealed with a packaging machine. The hard carbon / nickel negative electrode sheet is composed of hard carbon / nickel composite negative electrode material, conductive carbon black, and sodium carboxymethyl cellulose in a mass ratio of 8:1:1. An appropriate amount of deionized water is added and stirred with a homogenizer for 30 minutes to form a slurry. The slurry is then evenly coated on a bright aluminum foil and vacuum dried at 80 °C for 12 h. Finally, the electrode sheet is cut into circular electrodes with a diameter of 12 mm. For each electrode, the loading amount of active material is 0.9 - 1.5 mg. After the battery was allowed to stand for 24 hours, electrochemical tests were carried out using the Xinwei test system and Chenhua electrochemical workstation. The electrochemical tests were all carried out at 30 o The constant current charge and discharge test is carried out under the constant temperature condition of 100000C, mainly for constant current charge and discharge test. In the constant current charge and discharge test, the main indicators include reversible capacity, cycle life, coulomb efficiency and so on. The long cycle performance of the battery is tested at a current density of 100 mA / g. The process of constant current charge and discharge test is: standby for 5 min-constant current discharge-standby for 5 min-constant current charge, and the cycle is 500 times.

[0055] The performance test results are shown in Table 2 below:

[0056] Table 2 Summary of performance test results of various embodiments and comparative examples

[0057]

[0058] From the performance test results of each embodiment and comparative example in Table 2, it can be found that the hard carbon / nickel composite negative electrode material prepared by plasma sintering of inorganic nickel compounds in Examples 1-17 has excellent electrochemical performance at a current density of 100 mA / g, and the first cycle specific capacity, first cycle coulomb efficiency and 500 cycle capacity retention rate are not less than 360 mAh / g, 80% and 70% respectively. On the contrary, the hard carbon negative electrode material in Comparative Examples 1-9 has poor electrochemical performance at a current density of 100 mA / g, and cannot maintain the first cycle specific capacity, first cycle coulomb efficiency and capacity retention rate at a high level, which shows that the preparation of hard carbon / nickel composite negative electrode materials by plasma sintering of inorganic nickel compounds can effectively improve the sodium storage capacity of the material, and improve the first coulomb efficiency and cycle stability of the material.

[0059] Figure 1 The schematic diagram of the inorganic nickel compound plasma reaction device of the present invention is shown in FIG. 1 ; the device is composed of a radio frequency plasma excitation device, a tubular furnace, a rotary transmission device, a special-shaped tube, and a copper ring. Figure 1 The equipment in the middle is a tubular furnace. Nickel oxide and other inorganic nickel compounds are ball-milled and compounded with carbonized precursors and placed in the middle of a special-shaped tube, located in the plasma reaction temperature chamber. Copper rings for plasma excitation are set at both ends of the special-shaped tube, such as Figure 1 It can be seen that the glow of nickel oxide plasma after excitation is white. Located at the two ends of the device is a rotating transmission device, which can keep the hard carbon material undergoing plasma reaction sintering in a state of motion, ensure uniform excitation of the solid source and avoid incomplete local carbonization of the material.

[0060] Figure 2 The SEM morphology comparison diagram of the unmodified hard carbon material in Comparative Example 1 and the hard carbon / nickel composite negative electrode material prepared by pretreatment, ball milling and sintering in a nickel oxide plasma atmosphere in Example 1; Figure 2 The SEM image shows that the surface of the hard carbon that has not been treated with nickel oxide plasma is relatively clean and flat, while the surface of the hard carbon prepared by sintering in a nickel oxide plasma atmosphere to load nickel appears rougher, with many small particles attached, indicating that nickel oxide reacts strongly with the hard carbon material under the excitation of the plasma equipment, resulting in significant differences in the material morphology.

[0061] Figure 3 The EDS element distribution diagram of the hard carbon / nickel composite negative electrode material prepared by pretreatment, ball milling and sintering in a nickel oxide plasma atmosphere in Example 1; Figure 3 It can be found from the EDS element distribution diagram of the hard carbon / nickel composite negative electrode material that the presence of nickel element can be detected in the hard carbon / nickel composite negative electrode material in the EDS test and the distribution is relatively uniform.

[0062] Figure 4 This is a transmission electron microscope (TEM) image of the hard carbon / nickel composite negative electrode material prepared by pretreatment, ball milling, and sintering in a nickel oxide plasma atmosphere in Example 1; Figure 4 The TEM image shows that nickel was successfully loaded into the hard carbon material structure with the assistance of plasma technology.

[0063] Figure 5 This is a Raman spectrum comparison diagram of the unmodified hard carbon material in Comparative Example 1 and the hard carbon / nickel composite negative electrode material prepared by pretreatment, ball milling, and sintering in a nickel oxide plasma atmosphere in Example 1; Figure 5 The Raman spectrum shows that the intensity ratio of the D peak to the G peak of the hard carbon / nickel material prepared by sintering with nickel oxide plasma technology is lower than that of the unmodified hard carbon material, which proves that the organic matter inside the pre-carbonized hard carbon precursor has been completely carbonized and the degree of graphitization is higher after nickel oxide plasma treatment.

[0064] Figure 6 The performance comparison chart of the cycle test at a current density of 100 mA / g is shown for the unmodified hard carbon material in Comparative Example 1, the hard carbon / nickel composite negative electrode material prepared by ball milling in Comparative Example 2, and the hard carbon / nickel composite negative electrode material prepared by pretreatment, ball milling, and sintering in a nickel oxide plasma atmosphere in Example 1. The implantation of nickel helps to form a three-dimensional conductive network, improve the conductivity of the material and the stability of the material structure. Figure 6 The cycle performance diagram shows that the hard carbon / nickel composite negative electrode material exhibits excellent cycle performance. At a current density of 100 mA / g, the initial discharge capacity is 382 mAh / g, the first cycle coulomb efficiency is 91.8%, and after 500 cycles, the capacity retention rate is 80.8%. The unmodified hard carbon material and the hard carbon / nickel composite negative electrode material prepared by ball milling of nickel oxide and hard carbon have low discharge capacity and decay rapidly. The initial discharge capacity is only 346 and 356 mAh / g, and the first cycle coulomb efficiency is less than 80%. After 500 cycles, the capacity is only 29.2% and 32.8%, respectively. This shows that the use of inorganic nickel compounds in plasma atmosphere sintering to prepare hard carbon materials can effectively improve the material's sodium storage reversible capacity and cycle stability.

[0065] The sodium ion battery hard carbon negative electrode material loaded with nickel by plasma technology has more sodium storage sites. The hard carbon negative electrode prepared by the material has lower impedance and excellent cycle performance and rate performance. It has broad application prospects in small mobile electronic devices, electric vehicles, solar power generation, aerospace and other fields.

[0066] The above-described embodiments are only preferred solutions of the present invention and are not intended to limit the present invention in any form. Other variations and modifications are possible without exceeding the technical solutions described in the claims.

Claims

1. A method for preparing a hard carbon / nickel composite negative electrode material by plasma synthesis of an inorganic nickel compound, characterized in that: The preparation method is to use a biomass hard carbon precursor as a hard carbon material matrix, an inorganic nickel compound as a plasma source, and prepare a hard carbon / nickel composite negative electrode material by plasma sintering, comprising the following steps: (1) Pre-carbonizing the biomass hard carbon precursor in a protective atmosphere, followed by acid washing and drying to obtain a carbonized precursor; (2) placing a mixture of an inorganic nickel compound and a carbonization precursor in a plasma reaction chamber and subjecting the chamber to a vacuum treatment; (3) heating the plasma reaction chamber to a certain temperature, adjusting the plasma radio frequency power, and allowing the inorganic nickel compound plasma to react for a certain period of time after ignition to obtain a hard carbon / nickel composite negative electrode material; Wherein, in step (2), the inorganic nickel compound is selected from at least one of nickel sulfate, nickel carbonate, nickel chloride and nickel oxide; In step (3), the reaction conditions are: reaction temperature 500-1000°C, RF power 300-1000 W, reaction vacuum degree 5-75 Pa, and reaction time 20-60 min.

2. The method for preparing a hard carbon / nickel composite negative electrode material synthesized by plasma synthesis of an inorganic nickel compound according to claim 1, characterized in that: In step (1), the biomass hard carbon precursor is selected from at least one of bamboo charcoal, fir charcoal, fruit shell charcoal, and corn cob charcoal.

3. The method for preparing a hard carbon / nickel composite negative electrode material synthesized by plasma synthesis of an inorganic nickel compound according to claim 1, characterized in that: In step (1), the pre-carbonization treatment conditions are: heating rate 5-15 °C / min, temperature 200-600 °C, and treatment time 1-3 h.

4. The method for preparing a hard carbon / nickel composite negative electrode material by plasma synthesis of an inorganic nickel compound according to claim 1, characterized in that: In step (2), the inorganic nickel compound is one of nickel oxide, nickel chloride and nickel sulfate.

5. The method for preparing a hard carbon / nickel composite negative electrode material synthesized by plasma synthesis of an inorganic nickel compound according to claim 1, characterized in that: In step (2), the mass percentage of the inorganic nickel compound in the mixture is 2-10%.

6. The method for preparing a hard carbon / nickel composite negative electrode material by plasma synthesis of an inorganic nickel compound according to claim 1, characterized in that: The nickel content in the hard carbon / nickel composite negative electrode material is 1-5 wt. %.

7. An inorganic nickel compound plasma synthesized hard carbon / nickel composite negative electrode material prepared according to the preparation method according to any one of claims 1 to 6.

8. Use of the inorganic nickel compound plasma synthesized hard carbon / nickel composite negative electrode material according to claim 7 in the field of sodium ion batteries.

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