A method for carbon coating Wadsley-Roth phase materials in a whole process solid phase and its application

Abstract

The present invention belongs to the technical field of lithium ion batteries, and discloses a method and application thereof for carbon coating of Wadsley-Roth phase materials by solid phase in the whole process, which is solvent-free in the whole process and comprises the following steps: (1) dispersing the Wadsley-Roth phase material, reducing particle agglomeration, and making the material reach a primary particle state; (2) crushing the solid carbon source, reducing the particle size and making the carbon source in a fully dispersed state; (3) mixing the two, dispersing them again, and obtaining a powder mixture precursor; (4) performing gradient temperature heat treatment, and obtaining the carbon-coated Wadsley-Roth phase material after cooling; wherein the gradient temperature heat treatment comprises two heat preservation stages, the first heat preservation stage corresponds to the glass transition of the carbon source, and the second heat preservation stage corresponds to the carbonization of the carbon source. The carbon-coated Wadsley-Roth phase material prepared by the present invention has a uniform and complete carbon coating layer thickness, which can effectively improve the electronic conductivity of the material, so the material has high specific capacity, rate performance and cycle performance as a negative electrode material for lithium ion batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and more specifically, relates to a method for carbon coating a Wadsley-Roth phase material in a full-process solid phase and an application thereof. Background Art

[0002] Since their commercialization, lithium-ion batteries (LIBs) have been widely used in consumer electronics, electric vehicles (EVs), hybrid electric vehicles (HEVs), grid energy storage and other fields. However, the slow lithium ion migration rate in the graphite anode makes the rate and low-temperature performance of most commercial lithium-ion batteries poor. At the same time, the low working voltage of the graphite anode (-0.1V vs. Li+ / Li) makes it prone to lithium dendrite precipitation, and the poor thermal stability of lithiated graphite can easily lead to safety accidents. In order to meet the needs of special application scenarios, it is urgent to develop safe lithium-ion battery anode materials. Spinel structure lithium titanate (Li4Ti5O 12 ) anode material has a high working potential of ~1.5V (vs.Li+ / Li), which can avoid the formation of lithium dendrites during battery cycling. Therefore, it can meet the application requirements of low temperature and fast charging scenarios and is considered to be a highly safe lithium-ion battery anode material. However, the low theoretical specific capacity of lithium titanate (175mAh g -1 ), which severely limits its practical application.

[0003] Wadsley-Roth phase materials have a stable crystal structure, small volume change during lithium ion deintercalation, and can perform highly reversible lithium ion deintercalation; the working potential is similar to that of lithium titanate (~1.5V vs.Li+ / Li), making them very suitable as negative electrode materials for high-safety lithium-ion batteries. At the same time, the theoretical specific capacity of Wadsley-Roth phase negative electrode materials is comparable to that of commercial graphite negative electrode materials (372mAh g -1) is similar to that of lithium titanate; and the density of the material is large, which can achieve a compaction density far greater than that of graphite, so that the battery can simultaneously obtain a higher mass and volume specific energy. However, the inherent low electronic conductivity and ion diffusion rate of Wadsley-Roth phase materials seriously restrict their actual electrochemical lithium storage capacity, cycle life and rate performance, so further material modification is needed to improve their electrochemical performance. At present, in order to improve the electronic conductivity and ion diffusion rate of Wadsley-Roth phase materials, nano-sizing, porous structure, surface modification and other designs and carbon coating based on these designs are usually adopted to improve the electrochemical performance of the materials. These modification methods usually use liquids such as water, ethanol, propylene glycol as dispersants to mix Wadsley-Roth phase materials with carbon sources, and then completely dry the dispersant and perform heat treatment to obtain carbon-coated Wadsley-Roth phase materials. However, the drying process of the solvent will not only increase the production cost but also produce a large amount of waste to pollute the environment, and the volatilization of flammable solvents will greatly increase the safety hazards in the production process. At the same time, these preparation methods are often not suitable for actual production due to complex processes, high costs, uncontrollable waste liquid, and difficulty in large-scale production. Therefore, it is of great significance and value to develop carbon-coated Wadsley-Roth phase materials with simple preparation processes, low costs, environmental friendliness, easy large-scale production, and excellent electrochemical lithium storage performance. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the purpose of the present invention is to provide a method for carbon coating Wadsley-Roth phase materials in a solid phase throughout the whole process and its application. By designing and improving the process flow, wherein step (1) is for dispersing the Wadsley-Roth phase material, step (2) is for pulverizing the solid carbon source, and step (3) is for dispersing the mixture of the two, the effects of reducing material agglomeration, reducing the particle size of the carbon source, and fully dispersing and uniformly mixing can be respectively played. The method can be carried out in a machine such as a blender, a pulverizer, an air mill, etc. that can shear and impact disperse the powder material at high speed. No solvent is used in the whole process. The method can effectively solve the problems of complex process, high cost, and difficulty in large-scale production brought about by the nano-sizing, porous structure design and surface modification methods used in traditional Wadsley-Roth phase materials to improve their electronic conductivity. The carbon-coated Wadsley-Roth phase material obtained by the method of the present invention has a uniform thickness of the carbon coating layer (for example, the thickness can be 2-20 nm) and is complete, which can effectively improve the electronic conductivity of the material. Therefore, the material has high specific capacity, rate performance and cycle performance as a negative electrode material for lithium-ion batteries. In addition, the method of the present invention does not involve any solvent, so no waste liquid is generated during the preparation process.

[0005] To achieve the above object, according to one aspect of the present invention, a method for carbon coating a Wadsley-Roth phase material in a full-process solid phase is provided, characterized in that it comprises the following steps:

[0006] (1) dispersing the prepared Wadsley-Roth phase material under solvent-free conditions to reduce particle agglomeration and make the material reach a primary particle state;

[0007] (2) crushing the solid carbon source required for carbon coating under solvent-free conditions to reduce the particle size and make the carbon source in a fully dispersed state;

[0008] (3) In the absence of solvent, the Wadsley-Roth phase material obtained in step (1) and the carbon source obtained in step (2) are mixed at a mass ratio of the Wadsley-Roth phase material to the carbon source of 6:1-9.5:1, and then dispersed again to fully disperse and mix the two to obtain a powder mixture precursor;

[0009] (4) subjecting the powder mixture precursor obtained in step (3) to a gradient temperature heat treatment under protective gas conditions, and then cooling to obtain a carbon-coated Wadsley-Roth phase material;

[0010] Among them, the gradient temperature heat treatment includes two insulation stages, wherein the target insulation temperature of the first insulation stage corresponds to the glass transition temperature range of the carbon source, the temperature range is 150-400°C, the insulation time is 1-5 hours, and the heating rate is 0.5-10°C per minute; the target insulation temperature of the second insulation stage corresponds to the carbonization temperature range of the carbon source, the temperature range is 500-900°C, the insulation time is 1-10 hours, and the heating rate is 0.5-10°C per minute.

[0011] As a further preferred embodiment of the present invention, in step (1), the Wadsley-Roth phase material is a Wadsley-Roth phase material containing niobium oxide, preferably TiNb2O7, Ti2Nb 10 O 29 、TiNb 24 O 62 or Nb 16 W5W 55 .

[0012] As a further preferred embodiment of the present invention, the carbon source obtained in step (2) has a particle size of 50 nm-50 μm;

[0013] The carbon source includes one or more of sucrose, glucose, citric acid, melamine, asphalt, polyvinyl alcohol, vitamin C, polyethylene glycol, and anthracene.

[0014] As a further preferred embodiment of the present invention, in step (3), the Wadsley-Roth phase material obtained in step (1) is mixed with the carbon source obtained in step (2), specifically, the Wadsley-Roth phase material and the carbon source are mixed in a mass ratio of 6:1-9.5:1.

[0015] As a further preference of the present invention, the gradient temperature heat treatment in step (4) is preferably carried out in a multi-temperature zone tiltable atmosphere protection rotary tube furnace, a split atmosphere protection rotary tube furnace, an atmosphere rotary furnace, an atmosphere tube furnace or an atmosphere box furnace.

[0016] As a further preference of the present invention, in step (4), the protective gas is a non-oxidizing gas; preferably a mixed gas of one or more of argon, nitrogen, ammonia and helium.

[0017] As a further preferred embodiment of the present invention, the principle on which the dispersion treatment in step (1) is based is to perform high-speed shearing on the material and the collision between the materials to achieve uniform dispersion and reduce the particle size, and is preferably carried out in a mixer, a pulverizer, an air mill, or an air flow pulverizer; wherein, when a mixer, a pulverizer or an air mill is used, the rotation speed is 500-20000 rpm, and the dispersion treatment time is 30 seconds-2 hours; when an air flow pulverizer is used, the pulverization flux is 0.5-100 Kg / h, and the air flow pressure is 0.2-50 Mpa;

[0018] The pulverization treatment in step (2) is preferably carried out in a blender, a pulverizer, an air mill, or an air flow pulverizer. The principle is to perform high-speed shearing on the carbon source and collision between materials to achieve uniform dispersion and reduce the particle size. When a blender, a pulverizer, or an air mill is used, the rotation speed is 500-20000 rpm and the treatment time is 30 seconds to 2 hours. When an air flow pulverizer is used, the pulverization flux is 0.5-100 Kg / h and the air flow pressure is 0.2-50 Mpa.

[0019] The dispersion treatment in step (3) is preferably carried out in a blender, a pulverizer, an air mill or an air flow pulverizer. The principle is to perform high-speed shearing on the material and the collision between the materials to achieve uniform dispersion and reduce the particle size. When a blender, a pulverizer or an air mill is used, the rotation speed is 500-20000 rpm and the treatment time is 30 seconds-2 hours. When an air flow pulverizer is used, the pulverization flux is 0.5-100 Kg / h and the air flow pressure is 0.2-50 Mpa.

[0020] According to another aspect of the present invention, the present invention provides a carbon-coated Wadsley-Roth phase material obtained by the above method.

[0021] According to another aspect of the present invention, the present invention provides the use of the above carbon-coated Wadsley-Roth phase material as a negative electrode material for a lithium-ion battery.

[0022] According to another aspect of the present invention, the present invention provides a lithium-ion battery, characterized in that its negative electrode plate adopts the above-mentioned carbon-coated Wadsley-Roth phase material as an active material.

[0023] Compared with the prior art, the above technical solution conceived by the present invention can achieve the following beneficial effects:

[0024] 1. This method is used to carbon-coat Wadsley-Roth phase materials. The whole process is solvent-free, so there is no waste liquid, which is extremely green and environmentally friendly. In addition, the whole process of material mixing is solvent-free, so there is no need for an additional solvent drying process after the materials are mixed, which can greatly save the electricity cost in the production process; it can also avoid the safety hazards and additional waste disposal costs caused by the use of organic solvents as dispersants in other preparation methods; and effectively avoid the stratification of Wadsley-Roth phase materials and carbon sources during the solvent drying process when organic solvents are used as dispersants in other preparation methods, and avoid uneven material mixing.

[0025] 2. Generally, the Wadsley-Roth phase material prepared by high-temperature sintering aggregates the primary particles to form soft agglomerated secondary large particles due to the action of molecular thermal motion, which is not conducive to the uniform carbon coating of the material. When the Wadsley-Roth material is dispersed by conventional ball milling, the integrity and structure of the primary particles of the Wadsley-Roth phase material will be destroyed due to the long-term high-energy collision between the ball milling beads and the material, which is not conducive to the electrochemical performance of the material. If the ball milling time is too short, the effect of dispersing the material cannot be achieved. At the same time, ball milling can usually be carried out with the assistance of solvents, and ball milling without solvent participation cannot disperse the material well. The principle of dispersing the material in the present invention is to perform short-term high-speed shearing on the material under solvent-free conditions, and the collision between the materials makes the material uniformly dispersed to the size of the primary particles without destroying the particle integrity and structure of the material. For example, a mixer, a pulverizer, or an air mill can be used, the rotation speed can be controlled to 500-20000rpm, and the dispersion treatment time can be 30 seconds-2 hours (of course, the faster the rotation speed and the higher the intensity, the treatment time can be appropriately shortened). In addition, air flow mills are also applicable. During processing, the air flow mill pulverizing flux can be controlled to 0.5-100Kg / h, and the air flow pressure can be controlled to 0.2-50Mpa. Similarly, when using ball milling to disperse the carbon source, it usually needs to be carried out with the assistance of a solvent. If there is no solvent involved, the ball mill beads will impact the carbon source onto the wall of the ball mill under the action of centrifugal force. Not only can it not play the role of dispersing the carbon source, but it will aggravate the agglomeration of the carbon source. The principle of dispersing the carbon source of the present invention is to perform short-term high-speed shearing on the material under solvent-free conditions, and the carbon sources collide with each other so that the carbon source can be evenly dispersed and the particles can be reduced. In the subsequent process, the method of the present invention is used to mix the two fully dispersed powders together, which is conducive to the carbon source being effectively and evenly coated on the surface of the Wadsley-Roth phase material during subsequent heat treatment and carbonized into a conductive layer. In addition, this high-speed shearing can usually make the material reach a uniform mixing state in a short time, effectively shortening the production time of the material.

[0026] 3. When the Wadsley-Roth phase material is carbon-coated according to this method, a gradient temperature heat treatment is used. The first stage insulation temperature is the glass transition temperature range of the carbon source. In this temperature range, the carbon source will transform from a glassy solid phase to a viscous liquid phase, so that the carbon source flows and infiltrates on the surface of the Wadsley-Roth phase material particles to further make them uniformly compounded; the second stage is the carbonization temperature range of the carbon source. In this temperature range, the liquid viscous carbon source uniformly coated on the surface of the Wadsley-Roth phase material will be further carbonized, so that the carbon layer is uniformly and completely coated on the surface of the Wadsley-Roth phase material to increase the conductivity of the material; the thickness is thin and no carbon accumulation is formed, so the carbon coating will not reduce the lithium ion mobility of the material.

[0027] 4. The carbon coating layer of the carbon-coated Wadsley-Roth phase material prepared by this method is uniform, complete and does not form carbon accumulation, which can effectively improve the electronic conductivity of the material and does not hinder the rapid diffusion of lithium ions in the bulk phase, does not increase the diffusion distance of lithium ions, and can effectively improve the various electrochemical properties of the material. At the same time, the complete and uniform carbon coating layer can effectively alleviate the generation of side reactions such as electrolyte decomposition, thereby improving the cycle life of the material.

[0028] 5. The carbon-coated Wadsley-Roth phase material prepared by this method has a small surface area and a high tap density because the carbon layer is uniformly coated on the surface of the Wadsley-Roth phase material and no carbon accumulation is formed. It is very suitable as a negative electrode material for lithium-ion batteries. When it is used to prepare electrode sheets, a high compaction density and volume energy density can be obtained.

[0029] 6. The carbon-coated Wadsley-Roth phase material prepared by this method has a very simple process, low cost, and excellent material performance.

[0030] In summary, the advantages of the present invention are as follows: (1) The present invention adopts a simple material preparation route, has a simple process, is easy to operate, is easy to industrialize, and has a low production cost; (2) The carbon-coated Wadsley-Roth phase material prepared by the present method does not involve any solvent in the entire preparation process, and no waste liquid is generated; (3) The carbon coating layer of the carbon-coated Wadsley-Roth phase material prepared by the present invention is uniform and complete, and there is no excess carbon accumulation while effectively coating the material, so the carbon content of the material can be reduced to the greatest extent; (4) The carbon-coated Wadsley-Roth phase material prepared by the present invention has the characteristics of high specific capacity, high rate and long cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is an X-ray diffraction (XRD) diagram of carbon-coated TiNb2O7 prepared in the preferred embodiment 1 constructed according to the present invention.

[0032] Figure 2 This is a 10,000-fold scanning electron microscope (SEM) image of the carbon-coated TiNb2O7 prepared in the preferred embodiment 1 constructed according to the present invention.

[0033] Figure 3 This is a 50,000-fold scanning electron microscope (SEM) image of the carbon-coated TiNb2O7 prepared in the preferred embodiment 1 constructed according to the present invention.

[0034] Figure 4 It is a transmission electron microscope (TEM) image of carbon-coated TiNb2O7 prepared in the preferred embodiment 1 constructed according to the present invention.

[0035] Figure 5 This is a performance diagram of the first charge and discharge capacity of a half-cell of a carbon-coated TiNb2O7 electrode sheet prepared in the preferred embodiment 1 constructed according to the present invention at a rate of 0.2C.

[0036] Figure 6 It is a rate performance diagram of a half-cell of a carbon-coated TiNb2O7 electrode sheet prepared in the preferred embodiment 1 constructed according to the present invention.

[0037] Figure 7 It is a cycle performance diagram of carbon-coated TiNb2O7 prepared in the preferred embodiment 1 constructed according to the present invention.

[0038] Figure 8 This is a 50,000-fold scanning electron microscope (SEM) image of the carbon-coated TiNb2O7 prepared in Comparative Example 1.

[0039] Fig. 9 This is a 50,000-fold scanning electron microscope (SEM) image of the carbon-coated TiNb2O7 prepared in Comparative Example 2. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] In general, the method of the present invention comprises the following steps: (1) dispersing the prepared Wadsley-Roth phase material under solvent-free conditions to reduce particle agglomeration; (2) crushing the carbon source required for carbon coating under solvent-free conditions to reduce the particle size and make the carbon source in a fully dispersed state; (3) fully mixing the prepared Wadsley-Roth phase material and the carbon source under solvent-free conditions to obtain a precursor; (4) placing the obtained precursor powder in an inert atmosphere furnace for gradient temperature heat treatment.

[0042] In the following examples and comparative examples, the crystal phase structure of the prepared electrode materials was characterized by an X-ray diffractometer and analyzed to determine the molecular formula of the materials. In addition, the microstructure of the samples was observed by a scanning electron microscope. The crystal structure of the samples was observed by a transmission electron microscope.

[0043] Example 1

[0044] Weigh 950g TiNb2O7 and place it in a jet mill with a crushing flux of 1.2Kg / h and a gas flow pressure of 0.6Mpa to obtain uniformly dispersed TiNb2O7 powder for use. The powder particle size is reduced from 10-20 micron soft agglomerated secondary particles to ~1 micron primary particles.

[0045] Weigh 50 g of sucrose and place it in a jet mill with a grinding flux of 1.2 Kg / h and an air flow pressure of 0.6 MPa to obtain sucrose powder with a particle size of 0.5-10 μm and uniform dispersion for use.

[0046] The obtained uniformly dispersed TiNb2O7 and the uniformly dispersed sucrose powder with a particle size of 0.5-10 microns are placed in an air flow mill with a crushing flux of 1.2 Kg / h and an air flow pressure of 0.6 MPa to obtain a uniformly mixed TiNb2O7 and sucrose mixture powder for use.

[0047] The obtained mixed powder was placed in a rotary furnace (furnace tube rotation speed was 5 rpm), and the temperature was raised to 200°C at 5°C / min and kept for 2 hours under pure argon atmosphere. Subsequently, the temperature was raised to 700°C at 5°C / min and kept for 3 hours, and then naturally cooled to room temperature to obtain carbon-coated TiNb2O7 material.

[0048] In addition, in addition to the above-mentioned condition parameter settings, the pulverizing flux of the air flow mill can also be 0.5-10Kg / h, and the air flow pressure can also be 0.2-5Mpa.

[0049] The carbon-coated TiNb2O7 material was subjected to XRD testing, and the results were as follows: Figure 1 As shown in the figure, it can be seen that the characteristic diffraction peaks appearing in the sample are all diffraction peaks of TiNb2O7, and there is no obvious carbon diffraction peak, which means that the carbon-coated TiNb2O7 has a single crystal phase and no impurities. At the same time, there are no defects in the crystal and the crystal structure is complete.

[0050] The carbon-coated TiNb2O7 material was subjected to SEM examination at a magnification of 10,000 times. Figure 2 As shown in the figure, it can be seen that TiNb2O7 is interconnected under the action of the carbon layer to form large particles with a porous structure of tens of microns. The carbon coating layer plays the role of a conductive network in the large particles. The porous structure can effectively conduct lithium ions. At the same time, the large particle size can effectively increase the tap density of the material, thereby improving the compaction density and volume energy density of the material when used as an active material to prepare electrode sheets.

[0051] The SEM results at a magnification of 50,000 times are as follows Figure 3As shown in the figure, it can be seen that the sample particle size ranges from 0.8 to 3 microns, indicating that the material is a micron / submicron structure. At the same time, we can see from the figure that there is no obvious carbon layer on the surface of TiNb2O7, indicating that the carbon coating layer of the carbon-coated TiNb2O7 material prepared by this method is thin and completely and evenly coated on the surface of TiNb2O7.

[0052] The carbon-coated TiNb2O7 material was further tested by TEM. Figure 4 As shown, we can see that the surface of TiNb2O7 is covered with a carbon layer with a thickness of ~3nm, and the carbon layer is uniform and complete; at the same time, the interface between the carbon layer and TiNb2O7 is crystallographically complete, which is consistent with the XRD analysis results.

[0053] Furthermore, the carbon-coated TiNb2O7 material is used to make a carbon-coated TiNb2O7 electrode sheet, in which the mass ratio of active material is 90%, the mass ratio of conductive agent is 7%, the mass ratio of binder is 3%, and the surface loading of the electrode sheet is 8.5 mg / cm 2 , compacted density is 2.6g / cm 3 Then, the carbon-coated TiNb2O7 electrode sheet was used to make a half-cell, which consisted of a working electrode TiNb2O7 electrode sheet, a counter-motor lithium metal, and a PP separator. The half-cell was tested, and its first charge and discharge capacity performance at a rate of 0.2C was as follows: Figure 5 As shown in the figure, it can be seen that the first discharge capacity of carbon-coated TiNb2O7 at 0.2C current density in the voltage range of 1.0-3.0 is as high as 310mAh / g, the first coulombic efficiency is as high as 95.8%, and the discharge platform is about 1.53V, indicating that the carbon-coated TiNb2O7 constructed according to the present invention can effectively exert its electrochemical performance, with small electrode polarization and high energy efficiency.

[0054] The half-cell was tested for rate performance, and the results were as follows: Figure 6 As shown in the figure. It can be seen from the figure that when the battery is charged and discharged at 0.5C, its discharge capacity can reach 296mAh / g. Even when the battery is charged and discharged at a high current density of 50C, its discharge capacity is still as high as 170mAh / g, the capacity retention rate can reach 57.4%, and the coulombic efficiency is close to 100%, indicating that the prepared carbon-coated TiNb2O7 material has good rate performance.

[0055] The half-battery was tested for cycle performance, and the results were as follows: Figure 7 As shown in the figure, when the battery is charged and discharged at a current density of 5C, its discharge capacity can reach a discharge capacity of 210mAh / g after 100 cycles, indicating that the prepared carbon-coated TiNb2O7 material has good cycle performance.

[0056] Example 2

[0057] Weigh 700g Ti2Nb 10 O 29 Place in a high-speed mixer and stir at high speed for 5 minutes at a stirring speed of 10000 rpm to obtain uniformly dispersed Ti2Nb 10 O 29 The powder is ready for use. The powder particle size is reduced from 10-20 micron soft agglomerated secondary particles to ~0.8 micron primary particles.

[0058] Weigh 300 g of glucose and place it in a high-speed blender. Stir at high speed for 30 seconds at a stirring speed of 10,000 rpm to obtain glucose powder with a particle size of 0.5-10 microns and uniform dispersion for later use.

[0059] The uniformly dispersed Ti2Nb 10 O 29 The uniformly dispersed glucose powder with a particle size of 0.5-10 microns was placed in a high-speed mixer and stirred at a high speed of 10000 rpm for 5 minutes to obtain a uniformly mixed Ti2Nb 10 O 29 and glucose mixture powder for later use.

[0060] The obtained mixed powder was placed in a tube furnace, and heated to 150°C at 0.5°C / min and kept at this temperature for 1 hour under a pure nitrogen atmosphere. Subsequently, the temperature was raised to 500°C at 0.5°C / min and kept at this temperature for 1 hour, and then naturally cooled to room temperature to obtain carbon-coated Ti2Nb 10 O 29 Material.

[0061] Example 3

[0062] Weigh 900g TiNb 24 O 62 Place in a crushing and grinding machine and stir at high speed for 1 min at a stirring speed of 20000 rpm to obtain uniformly dispersed TiNb 24 O 62 The powder is ready for use. The powder particle size is reduced from 10-20 micron soft agglomerated secondary particles to ~500 nanometer primary particles.

[0063] Weigh 100 g of citric acid and place it in a high-speed mixer. Stir it at high speed for 1 min at a stirring speed of 20,000 rpm to obtain citric acid powder with a particle size of 3-10 microns and uniform dispersion for use.

[0064] The uniformly dispersed TiNb 24 O 62The citric acid powder with a particle size of 3-10 microns and uniform dispersion was placed in a high-speed mixer and stirred at high speed for 2 minutes at a stirring speed of 20000 rpm to obtain a uniformly mixed TiNb 24 O 62 and citric acid mixture powder for later use.

[0065] The obtained mixed powder was placed in an atmosphere box furnace, and the temperature was raised to 400°C at 10°C / min and kept at this temperature for 5 hours under a pure nitrogen atmosphere. Subsequently, the temperature was raised to 900°C at 10°C / min and kept at this temperature for 10 hours, and then naturally cooled to room temperature to obtain carbon-coated TiNb 24 O 62 Material.

[0066] Example 4

[0067] Weigh 800g Nb 16 W5W 55 Place it in an air mill and grind it at high speed for 2 hours at a speed of 500 rpm to obtain uniformly dispersed Nb 16 W5W 55 The powder is ready for use. The powder particle size is reduced from 10-20 micron soft agglomerated secondary particles to ~3 micron primary particles.

[0068] Weigh 200 g of melamine and place it in an air mill. Grind it at high speed for 2 hours at a speed of 500 rpm to obtain melamine powder with a particle size of 3-10 microns and uniform dispersion for later use.

[0069] The uniformly dispersed Nb 16 W5W 55 The melamine powder with a particle size of 3-10 microns and uniform dispersion was placed in an air mill and subjected to high-speed air grinding for 2 hours at a speed of 500 rpm to obtain a uniformly mixed Nb 16 W5W 55 and melamine mixture powder for later use.

[0070] The obtained mixed powder was placed in an atmosphere box furnace, and the temperature was raised to 300°C at 5°C / min and kept at this temperature for 5 hours under a pure nitrogen atmosphere. Subsequently, the temperature was raised to 800°C at 5°C / min and kept at this temperature for 7 hours, and then naturally cooled to room temperature to obtain carbon-coated Nb 16 W5W 55 Material.

[0071] Comparative Example 1

[0072] Weigh 400g TiNb2O7 and place it in anhydrous ethanol, high-energy ball mill for 10 hours at a speed of 500rpm; then weigh 100g sucrose and place it in deionized water and magnetically stir it for 2 hours at a speed of 300rpm; then, mix the two solutions together and magnetically stir them for 5 hours at a speed of 300rpm, and place them in a forced air drying oven to dry for 24 hours to obtain the precursor powder. The obtained powder is placed in a muffle furnace, heated to 800℃ at 5℃ / min under argon atmosphere for 6 hours, and then cooled naturally to room temperature to obtain carbon-coated TiNb2O7.

[0073] Comparative Example 2

[0074] Weigh 400g TiNb2O7 and high-energy ball mill for 10 hours at a speed of 500rpm; then weigh 100g sucrose and high-energy ball mill for 2 hours at a speed of 300rpm; then, mix the two solid powders together and high-energy ball mill for 2 hours at a speed of 300rpm to obtain the precursor powder. The obtained powder is placed in a muffle furnace, heated to 700℃ at 5℃ / min under argon atmosphere for 3 hours, and then cooled naturally to room temperature to obtain carbon-coated TiNb2O7.

[0075] The carbon-coated TiNb2O7 materials obtained in Comparative Example 1 and Comparative Example 2 were subjected to SEM examination (50,000 times), and the results are as follows: Figure 8 and Fig. 9 As shown, it can be seen from the white frame lines in the figure that the carbon-coated materials prepared according to the methods of Comparative Example 1 and Comparative Example 2 have obvious carbon agglomerates on the surface of TiNb2O7, and the formed carbon coating layer is incomplete and uneven.

[0076] The incomplete carbon coating makes the conductive network in the material structure incomplete, reducing the electronic conductivity of the material; at the same time, carbon accumulation will block the effective migration of lithium ions and reduce the tap density of the material, thereby reducing the compaction density and volume energy density of the material when used as an active material to prepare electrode sheets.

[0077] The above embodiments are only examples. For example, when carbon-coated TiNb2O7 material is used to make electrode sheets, the mass ratio of active materials in the electrode sheets can be 80-95%, the mass ratio of conductive agents can be 3-10%, the mass ratio of binders can be 2-10%, and the surface loading of the electrode sheets can be 4-15 mg / cm 2 , correspondingly, the compacted density is 2.4-3.1g / cm 3 .

[0078] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for carbon coating a Wadsley-Roth phase material in a whole solid phase process, characterized in that: The steps include: (1) dispersing the prepared Wadsley-Roth phase material under solvent-free conditions to reduce particle agglomeration and make the material reach a primary particle state; (2) crushing the solid carbon source required for carbon coating under solvent-free conditions to reduce the particle size and make the carbon source in a fully dispersed state; (3) In the absence of solvent, the Wadsley-Roth phase material obtained in step (1) and the carbon source obtained in step (2) are mixed at a mass ratio of the Wadsley-Roth phase material to the carbon source of 6:1-9.5:1, and then dispersed again to fully disperse and mix the two to obtain a powder mixture precursor; (4) subjecting the powder mixture precursor obtained in step (3) to a gradient temperature heat treatment under protective gas conditions, and then cooling to obtain a carbon-coated Wadsley-Roth phase material; Among them, the gradient temperature heat treatment includes two insulation stages, wherein the target insulation temperature of the first insulation stage corresponds to the glass transition temperature range of the carbon source, the temperature range is 150-400°C, the insulation time is 1-5 hours, and the heating rate is 0.5-10°C per minute; the target insulation temperature of the second insulation stage corresponds to the carbonization temperature range of the carbon source, the temperature range is 500-900°C, the insulation time is 1-10 hours, and the heating rate is 0.5-10°C per minute.

2. The method according to claim 1, characterized in that: In the step (1), the Wadsley-Roth phase material is a Wadsley-Roth phase material containing niobium oxide.

3. The method according to claim 2, characterized in that: In the step (1), the Wadsley-Roth phase material is TiNb2O7, Ti2Nb 10 O 29 、TiNb 24 O 62 or Nb 16 W5W 55 .

4. The method according to claim 1, characterized in that: The carbon source obtained in step (2) has a particle size of 50 nm-50 μm; The carbon source includes one or more of sucrose, glucose, citric acid, melamine, asphalt, polyvinyl alcohol, vitamin C, polyethylene glycol, and anthracene.

5. The method according to claim 1, characterized in that: In the step (3), the Wadsley-Roth phase material obtained in the step (1) is mixed with the carbon source obtained in the step (2), specifically, the Wadsley-Roth phase material and the carbon source are mixed in a mass ratio of 6:1-9.5:

1.

6. The method according to claim 1, characterized in that: The gradient temperature heat treatment in step (4) is carried out in a multi-temperature zone tiltable atmosphere protection rotary tube furnace, a split atmosphere protection rotary tube furnace, an atmosphere rotary furnace, an atmosphere tube furnace or an atmosphere box furnace.

7. The method according to claim 1, characterized in that: In the step (4), the protective gas is a non-oxidizing gas.

8. The method according to claim 7, characterized in that: In the step (4), the protective gas is a mixed gas of one or more of argon, nitrogen, ammonia and helium.

9. The method according to claim 1, characterized in that: The principle of the dispersion treatment in step (1) is to perform high-speed shearing on the materials and the collision between the materials to achieve uniform dispersion and reduce the particle size. The dispersion treatment is carried out in a mixer, a pulverizer, an air mill, or an air flow pulverizer. When a mixer, a pulverizer, or an air flow pulverizer is used, the rotation speed is 500-20000 rpm and the dispersion treatment time is 30 seconds to 2 hours. When an air flow pulverizer is used, the pulverization flux is 0.5-100 Kg / h and the air flow pressure is 0.2-50 Mpa. The pulverization process in step (2) is carried out in a mixer, a pulverizer, an air mill, or an air flow pulverizer. The principle is to perform high-speed shearing on the carbon source and the collision between the materials to achieve uniform dispersion and reduce the particle size. When a mixer, a pulverizer, or an air mill is used, the rotation speed is 500-20000 rpm and the processing time is 30 seconds to 2 hours. When an air flow pulverizer is used, the pulverization flux is 0.5-100 Kg / h and the air flow pressure is 0.2-50 Mpa. The dispersion treatment in step (3) is carried out in a mixer, a pulverizer, an air mill, or an air flow pulverizer. The principle is to perform high-speed shearing on the material and the collision between the materials to achieve uniform dispersion and reduce the particle size. When a mixer, a pulverizer, or an air mill is used, the rotation speed is 500-20000 rpm and the treatment time is 30 seconds to 2 hours. When an air flow pulverizer is used, the pulverization flux is 0.5-100 Kg / h and the air flow pressure is 0.2-50 Mpa.

10. A carbon-coated Wadsley-Roth phase material obtained by the method according to any one of claims 1 to 9.

11. Use of the carbon-coated Wadsley-Roth phase material as claimed in claim 10 as a negative electrode material for lithium-ion batteries.

12. A lithium ion battery, characterized in that: The negative electrode plate adopts the carbon-coated Wadsley-Roth phase material as claimed in claim 10 as the active material.

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