A transition metal nitride and amorphous carbon composite material modified with manganese iron phosphate, its preparation method and application

Abstract

This invention discloses a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, its preparation method, and its application, belonging to the field of lithium-ion battery technology. This invention uses vanadium nitride / amorphous carbon to composite-coat lithium manganese iron phosphate material, making the composite cathode material structure more stable. The use of vanadium nitride reduces the amount of carbon coating, avoiding the thickening of the coating layer and the decrease in tap density of the active material caused by high carbon content, which would hinder the lithium iron phosphate process. + The issue of diffusion. Vanadium nitride not only has good electrical conductivity, but also good Li... + Conductive transport properties enable rapid realization of Li + The insertion and extraction of Li not only improves the conductivity of the material, but also further opens up and increases the Li content on the surface of the cathode material. + The diffusion channels reduce the capacity loss of the modified material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating, its preparation method and application. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Since Goodenough et al. first proposed LiMPO4 (M = Mn, Fe, Co, and Ni) lithium-ion battery cathode materials in 1997, lithium manganese phosphate (LMP) has attracted much attention as one of these materials due to its potential high energy density and stable performance. However, it faces a series of challenges in practical applications.

[0004] First, although LMP operates at 4.1V and has a higher energy density than LiFePO4 (LFP), its lower conductivity affects the performance of LiFePO4. + The transport and conduction of electrons are limited, thus restricting its electrochemical performance. Furthermore, due to the Jamin-Taylor effect of Mn, Mn ions readily dissolve from LMP, further affecting the battery's cycle performance.

[0005] To address these issues, researchers have attempted to improve the electrochemical performance of LMPs through methods such as reducing particle size, rapid ion / electron conductor recombination, external conductive carbon coatings, and internal cation substitution. For example, LiMn... 1-x Fe x A solid solution system for lithium manganese iron phosphate (LMFP) (PO4) was proposed, combining the advantages of LFP and LMP to improve electronic conductivity and suppress the Jameer-Taylor effect. However, despite some success, this system remains limited in improving conductivity, lithium diffusion, and high-temperature manganese dissolution. To further improve the conductivity of solid solution materials, carbon coating and nano-sizing have been widely used. For example, patent CN 111900344A discloses a carbon-coated lithium manganese iron phosphate cathode material, which uses conductive carbon coating and ion doping to modify the material. This improves the electronic conductivity, limits particle size growth, and effectively reduces manganese dissolution. 3+ The Jahn-Teller ex-situ effect improves the cycling stability of the material. However, the initial discharge capacity and post-cycle capacity retention of the carbon-coated lithium manganese iron phosphate cathode material prepared by this method are still not ideal and need to be further improved.

[0006] In summary, although lithium manganese iron phosphate (LFP) possesses the potential for high energy density and stability, its performance in practical applications remains limited due to issues such as low conductivity, Mn dissolution, and processing performance. Therefore, further research and improvement of LFP cathode materials remain an important research direction in the battery field. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating, its preparation method, and its application. Lithium manganese iron phosphate serves as the matrix, with an outer layer of transition metal nitride / amorphous carbon composite coating. Based on this material structure, the electrochemical performance of lithium manganese iron phosphate cathode materials can be effectively improved.

[0008] To achieve the above objectives, the technical solution of the present invention is as follows:

[0009] In a first aspect, the present invention provides a method for preparing a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, comprising the following steps:

[0010] Amorphous carbon source and nanoscale transition metal nitrides are added to carbon-coated lithium manganese iron phosphate and mixed to obtain precursor material.

[0011] The precursor material was sintered at high temperature under a protective atmosphere, then cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material with transition metal nitride and amorphous carbon composite coating modification.

[0012] In some embodiments of the present invention, the amorphous carbon source is selected from at least one of sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid;

[0013] The mass of the amorphous carbon source is 0.5-2.0 wt% of the mass of the carbon-coated lithium manganese iron phosphate.

[0014] In some embodiments of the present invention, the transition metal nitride is one or a mixture of several of vanadium nitride, cerium nitride, tungsten nitride, scandium nitride, titanium nitride, chromium nitride, manganese nitride, iron nitride, cobalt nitride, nickel nitride, copper nitride, zinc nitride, yttrium nitride, zirconium nitride, niobium nitride, and molybdenum nitride.

[0015] The mass of the nanoscale transition metal nitride is 0.1-2.0 wt% of the mass of the carbon-coated lithium manganese iron phosphate.

[0016] In some embodiments of the present invention, the carbon-coated lithium manganese iron phosphate is carbon-coated and uniformly dispersed nano-sized lithium manganese iron phosphate.

[0017] The chemical formula of the nanoscale lithium manganese iron phosphate is LiMn.x Fe 1-x-y M y PO4, 0 < x < 1, 0.001 ≤ y ≤ 0.05; M is selected from at least one of Mg, Ca, Al, Zr, Sc, Ti, V, Cr, Co, Ni, Ce, Y, Nb, Mo, Tc, Rh, Pd, Os, La, Ta, Re, and Ir;

[0018] The carbon-coated nano-sized lithium manganese iron phosphate has a carbon content of 0.5-1.0 wt%; the carbon is an amorphous carbon source, which is at least one of sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid.

[0019] In some embodiments of the present invention, 0.005 ≤ y ≤ 0.04.

[0020] In some embodiments of the present invention, the mixing is high-speed stirring, with a stirring speed of 900-1200 rpm, a mixing time of 40-60 min, and a mixing temperature of 25-45℃.

[0021] In some embodiments of the present invention, the high-temperature sintering is carried out at a sintering temperature of 500-700°C, a sintering time of 1-5 hours, and a heating rate of 2-10°C / min.

[0022] In a second aspect, the present invention provides a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, which is prepared by the preparation method described in the first aspect.

[0023] In some embodiments of the present invention, the primary particle size of the transition metal nitride and amorphous carbon composite coated and modified lithium manganese iron phosphate composite material is 50-300 nm, and the average particle size D50 is 0.4-2.0 μm.

[0024] A third aspect of the present invention provides the application of a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating as described in the second aspect in lithium batteries.

[0025] The beneficial effects of this invention are as follows:

[0026] This invention employs nanoscale transition metal nitrides and amorphous carbon to perform composite coating modification on carbon-coated lithium manganese iron phosphate materials. Among these, the nanoscale transition metal nitrides exhibit excellent electron / Li ratio... +It possesses excellent electrical conductivity, resistance to acid and alkali corrosion, thermal conductivity, high melting point, and catalytic activity. Through heat treatment of the substrate with nanoscale transition metal nitrides / amorphous carbon sources at specific temperatures, a composite coating layer of nanoscale transition metal nitrides / amorphous carbon is formed on the surface of lithium manganese iron phosphate. This results in a more stable composite cathode material structure. The strong acid and alkali corrosion resistance of the nanoscale transition metal nitrides effectively inhibits the dissolution of manganese in the coated cathode material, avoiding direct contact corrosion between the lithium manganese iron phosphate electrode surface and the electrolyte, reducing electrolyte side reactions, and improving the material's cycle stability. The good thermal conductivity of the nanoscale transition metal nitrides facilitates the absorption and transfer of heat generated by the battery into the material particles under low-temperature operating conditions, thereby improving the battery's charge and discharge performance at low temperatures. Furthermore, under high-temperature operating conditions, it facilitates the dissipation of internal heat, preventing heat accumulation, lowering battery temperature, reducing electrolyte side reactions, and improving battery safety. Furthermore, the use of vanadium nitride reduces the amount of carbon coating, avoiding the thickening of the coating layer and the decrease in the tap density of the active material caused by high carbon content, which would hinder the Li + The problem of diffusion. Vanadium nitride not only has good electrical conductivity, but also good Li... + Conductive transport properties enable rapid realization of Li + The insertion and extraction of Li not only improves the conductivity of the material, but also further opens up and increases the Li content on the surface of the cathode material. + The diffusion channels are improved, reducing the capacity loss of the modified material. This invention employs transition metal nitrides and carbon coating, with nitrogen atoms filling the interstices of the metal lattice. This helps to improve the water-absorbing properties of lithium manganese iron phosphate and enhances the material's processing performance. Furthermore, the metal nitrides possess certain active sites and catalytic activity, effectively promoting the graphitization of amorphous carbon during high-temperature processing, thereby further increasing the material's conductivity.

[0027] The present invention provides a transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material. The coating matrix is ​​carbon-coated lithium manganese iron phosphate, and the outer layer is a nanoscale transition metal nitride and amorphous carbon composite coating layer. Based on this structure, the material has a uniform particle size distribution and high conductivity. + It exhibits higher diffusion capacity, lower charge transfer resistance, and better crystallinity and stability. When used as a cathode material in lithium-ion batteries, it results in better rate performance, higher initial coulombic efficiency and capacity, lower manganese dissolution rate, and longer cycle life. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0029] Figure 1 The image shows the surface morphology of the lithium manganese iron phosphate composite material obtained in Example 1 of this invention via SEM.

[0030] Figure 2 The XRD diffraction pattern of the lithium manganese iron phosphate composite material obtained in Example 1 of this invention;

[0031] Figure 3 The graph shows the initial charge-discharge performance of button batteries assembled using the materials obtained in Example 1 and Comparative Example 1 of this invention at 25°C and 0.1C / 0.1C rate.

[0032] Figure 4 The graph shows the charge-discharge cycle performance of button batteries assembled using the materials obtained in Example 1 and Comparative Example 1 of the present invention at 45°C and 1C / 1C rate. Detailed Implementation

[0033] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0034] To address the technical problems of low conductivity in existing lithium manganese iron phosphate cathode materials, resulting in low discharge capacity, poor rate performance, poor cycle retention, and high manganese dissolution rate in lithium-ion batteries, this invention provides a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating, its preparation method, and its application.

[0035] A typical embodiment of the present invention provides a method for preparing a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, comprising the following steps:

[0036] Amorphous carbon source and nanoscale transition metal nitrides are added to carbon-coated lithium manganese iron phosphate and mixed to obtain precursor material.

[0037] The precursor material was sintered at high temperature under a protective atmosphere, then cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material with transition metal nitride and amorphous carbon composite coating modification.

[0038] This invention employs nanoscale transition metal nitrides and amorphous carbon to perform composite coating modification on carbon-coated lithium manganese iron phosphate materials. Among these, the nanoscale transition metal nitrides exhibit excellent electron / Li ratio... +It possesses excellent electrical conductivity, resistance to acid and alkali corrosion, thermal conductivity, high melting point, and catalytic activity. Through heat treatment of the substrate with nanoscale transition metal nitrides / amorphous carbon sources at specific temperatures, a composite coating layer of nanoscale transition metal nitrides / amorphous carbon is formed on the surface of lithium manganese iron phosphate. This results in a more stable composite cathode material structure. The strong acid and alkali corrosion resistance of the nanoscale transition metal nitrides effectively inhibits the dissolution of manganese in the coated cathode material, avoiding direct contact corrosion between the lithium manganese iron phosphate electrode surface and the electrolyte, reducing electrolyte side reactions, and improving the material's cycle stability. The good thermal conductivity of the nanoscale transition metal nitrides facilitates the absorption of heat generated by the battery in low-temperature operating environments, transferring it into the material particles and improving the battery's charge-discharge performance at low temperatures. Furthermore, it facilitates the timely dissipation of heat from the battery's interior under high-temperature operating conditions, preventing heat accumulation, reducing battery temperature, minimizing electrolyte side reactions, and improving battery safety. In addition, the use of nanoscale transition metal nitrides further reduces the amount of carbon coating. When the carbon content is low, a complete and uniform coating layer cannot be formed on the surface of lithium manganese iron phosphate, resulting in insufficient conductivity. As the carbon content increases, the coating layer thickens, reducing the tap density of the active material and hindering the formation of Li. + The diffusion channels. Furthermore, the nanoscale transition metal nitrides in this invention not only possess good electrical conductivity but also good Li₂ diffusion properties. + Conductivity transport properties enable fast Li + The insertion and extraction of Li not only improves the conductivity of the material, but also further opens up and increases the Li content on the surface of the cathode material. + The diffusion channels are improved, reducing the capacity loss of the modified material. In this invention, the metallic nitrides, due to the nitrogen atoms filling the interstices of the metal lattice, possess metallic properties and are less reactive with water, which helps to improve the water-absorbing characteristics of lithium manganese iron phosphate and enhances the material's processing performance. Furthermore, the metallic nitrides possess certain active sites and catalytic activity, effectively promoting the graphitization of amorphous carbon during high-temperature processing, thereby further increasing the material's conductivity.

[0039] Based on this structure, the material has a uniform particle size distribution and high electrical conductivity and Li + It exhibits higher diffusion capacity, lower charge transfer resistance, and better crystallinity and stability. When used as a cathode material in lithium-ion batteries, it results in better rate performance, higher initial coulombic efficiency and capacity, lower manganese dissolution rate, and longer cycle life.

[0040] In some embodiments of this implementation, the amorphous carbon source is selected from at least one of sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid, preferably glucose. Glucose is carbonized by high-temperature sintering to generate amorphous carbon, which, in conjunction with nanoscale transition metal nitrides, further modifies the carbon-coated lithium manganese iron phosphate material.

[0041] In some embodiments of this implementation, the mass of the amorphous carbon source is 0.5-2.0 wt% of the mass of the carbon-coated lithium manganese iron phosphate.

[0042] In some embodiments of this implementation, the transition metal nitride is one or a mixture of several of vanadium nitride, cerium nitride, tungsten nitride, scandium nitride, titanium nitride, chromium nitride, manganese nitride, iron nitride, cobalt nitride, nickel nitride, copper nitride, zinc nitride, yttrium nitride, zirconium nitride, niobium nitride, and molybdenum nitride, preferably vanadium nitride.

[0043] In some embodiments of this implementation, the mass of the nanoscale transition metal nitride is 0.1-2.0 wt% of the mass of the carbon-coated lithium manganese iron phosphate, preferably 0.5-1.0 wt%.

[0044] In some embodiments of this implementation, the carbon-coated lithium manganese iron phosphate used in this invention is a commercially available product that can be purchased. For example, it can be purchased from Hubei Rongtong New Energy Battery Materials Co., Ltd., and is a carbon-coated and uniformly dispersed nano-sized lithium manganese iron phosphate with the chemical formula LiMn. x Fe 1-x-y M y PO4, where 0 < x < 1, 0.001 ≤ y ≤ 0.03. It is a sintered cathode material with a suitable amount of carbon coating on its surface, which can be used directly without further processing.

[0045] In the carbon-coated lithium manganese iron phosphate, the carbon content is 0.5-1.0 wt%. During the sintering process, coating the surface of the lithium manganese iron phosphate material with a conductive carbon layer helps to inhibit excessive particle growth, reduce inter-particle agglomeration, and lower conductivity. The carbon content specified in this invention is only sufficient to inhibit particle growth, resulting in a relatively small improvement in conductivity. Furthermore, the carbon is an amorphous carbon source, preferably at least one selected from sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid, with glucose being the most preferred.

[0046] Wherein, M is an iron-doping element, selected from at least one of Mg, Ca, Al, Zr, Sc, Ti, V, Cr, Co, Ni, Ce, Y, Nb, Mo, Tc, Rh, Pd, Os, La, Ta, Re, and Ir, preferably Zr. This invention specifies that the iron-doping element is Zr, meaning the coating matrix is ​​a commercially available zirconium-containing lithium manganese iron phosphate material (LiMn). x Fe 1-x-y Zr y PO4).

[0047] The main innovation of this invention is the composite coating modification of lithium manganese iron phosphate materials. The coating matrix is ​​a Zr-doped lithium manganese iron phosphate cathode material with a small amount of carbon coating. 4+ It does not directly participate in the electrochemical reaction process, but plays a role in stabilizing the structure of lithium manganese iron phosphate, improving its conductivity, and Li + The conductivity is utilized without causing a decrease in the voltage plateau of lithium manganese iron phosphate, ensuring the stable electrochemical performance of the matrix material. The outer layer is a transition metal nitride / amorphous carbon composite coating layer. Based on this material structure, the electrochemical performance of lithium manganese iron phosphate cathode material can be effectively improved.

[0048] The molar ratio of the iron-doped element to the carbon-coated and uniformly dispersed nano-sized lithium manganese iron phosphate is 0.001:1 to 0.04:1, preferably 0.005:1 to 0.04:1, i.e., 005≤y≤0.04.

[0049] In some embodiments of this implementation, the mixing is high-speed stirring. The present invention can use a high-speed mixer to perform the mixing, thereby obtaining the precursor material. Specifically, the stirring speed of the high-speed mixer is 900-1200 rpm, the mixing time is 40-60 min, and the mixing temperature is 25-45℃. The high-speed mixer used in this invention is a commercially available product.

[0050] In some embodiments of this implementation, the high-temperature sintering is carried out at a sintering temperature of 500-700℃, a sintering time of 1-5h, and a heating rate of 2-10℃ / min.

[0051] In some embodiments of this implementation, the precursor material is placed in a tube furnace and heated to 500-700°C at a heating rate of 2-10°C / min under a protective atmosphere. It is then sintered at this temperature for 1-5 hours, followed by cooling, grinding, and sieving to obtain a lithium manganese iron phosphate composite material (LiMn) with transition metal nitride and amorphous carbon composite coating modification. x Fe 1-x-y M y PO4@nitride conductive coating, where 0 < x < 1, 0.001 < y ≤ 0.05).

[0052] In some embodiments of this implementation, the protective atmosphere may be one or more of argon, nitrogen, or helium.

[0053] In some embodiments of this implementation, the preparation method specifically includes the following steps:

[0054] (1) Add glucose and nano-sized vanadium nitride to carbon-coated lithium manganese iron phosphate and mix to obtain a precursor material;

[0055] The carbon-coated lithium manganese iron phosphate is a commercially available carbon-coated nanoscale lithium manganese iron phosphate material with the chemical formula LiMn. x Fe 1-x-y Zr y PO4, where 0 < x < 1, 0.005 ≤ y ≤ 0.04;

[0056] The amount of glucose used is 0.5-2.0% of the mass of carbon-coated lithium manganese iron phosphate;

[0057] The amount of nano-sized vanadium nitride used is 0.5-1.0% of the mass of carbon-coated lithium manganese iron phosphate;

[0058] (2) The precursor material is heated to 500-700℃ at a rate of 2-10℃ / min under a protective atmosphere, held for sintering for 1-5h, cooled and ground, and sieved to obtain a lithium manganese iron phosphate composite material with transition metal nitride and amorphous carbon composite coating modification.

[0059] The main innovation of this invention is the coating modification of lithium manganese iron phosphate materials, using commercially available titanium-containing lithium manganese iron phosphate as the coating matrix, wherein Zr 4+ It does not directly participate in the electrochemical reaction process, but plays a role in stabilizing the structure of lithium manganese iron phosphate, improving its conductivity, and Li + The conductivity, without causing a decrease in the voltage plateau of lithium manganese iron phosphate, ensures the stable electrochemical performance of the matrix material of this invention. The outer layer is a transition metal vanadium nitride / amorphous carbon composite coating layer. Based on this material structure, the electrochemical performance of the lithium manganese iron phosphate cathode material can be effectively improved.

[0060] This invention employs vanadium nitride / amorphous carbon to composite-coat lithium manganese iron phosphate materials, and the vanadium nitride exhibits good electron / Li ratio. +It possesses excellent electrical conductivity, resistance to acid and alkali corrosion, thermal conductivity, high melting point, and catalytic activity. By heat-treating vanadium nitride / amorphous carbon source and matrix at specific temperatures, a composite coating layer of vanadium nitride / amorphous carbon is formed on lithium manganese iron phosphate, resulting in a more stable composite cathode material structure. The strong acid and alkali corrosion resistance of vanadium nitride effectively inhibits the dissolution of manganese in the coated cathode material, avoiding direct contact corrosion between the lithium manganese iron phosphate electrode surface and the electrolyte, reducing electrolyte side reactions, and improving the material's cycle stability. The good thermal conductivity of vanadium nitride facilitates the absorption and transfer of heat generated by the battery into the material particles under low-temperature operating conditions, thereby improving the battery's charge-discharge performance at low temperatures. On the other hand, it helps the battery dissipate heat quickly under high-temperature operating conditions, preventing heat accumulation, reducing battery temperature, minimizing electrolyte side reactions, and improving battery safety. Furthermore, the use of vanadium nitride further reduces the amount of carbon coating. When the carbon content is low, a complete and uniform coating layer cannot be formed on the surface of lithium manganese iron phosphate, resulting in insufficient conductivity. As the carbon content increases, the coating layer thickens, which not only reduces the tap density of the active material but also hinders the Li-Phase Ionization process. + The diffusion channels. In this invention, vanadium nitride not only has good electrical conductivity, but also good Li... + Conductivity and transport properties enable rapid Li + The insertion and extraction processes not only improve the conductivity of the material but also further open up and increase the L-type surface area of ​​the positive electrode material. i+ The diffusion channels are improved, reducing the capacity loss of the modified material. This invention uses vanadium nitride amorphous carbon for coating. Because nitrogen atoms fill the interstices of the metal lattice, it possesses metallic properties and is less reactive with water, which helps to improve the water-absorbing properties of lithium manganese iron phosphate and enhances the material's processing performance. Furthermore, vanadium nitride possesses certain active sites and catalytic activity, which can effectively promote the graphitization of amorphous carbon during high-temperature processing, thereby further increasing the material's conductivity.

[0061] Based on this structure, the resulting lithium manganese iron phosphate composite material exhibits uniform particle size distribution and high conductivity, as well as high Li... + It has higher diffusion capacity, lower charge transfer impedance, and better crystallinity and stability.

[0062] When used as a cathode material for lithium-ion batteries, it results in better rate performance, higher initial coulombic efficiency and capacity, lower manganese leaching rate, and longer cycle life.

[0063] Another typical embodiment of the present invention provides a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, which is prepared by the above-described preparation method.

[0064] In some embodiments of this implementation, the primary particle size of the transition metal nitride and amorphous carbon composite coated and modified lithium manganese iron phosphate is 50-300 nm, and the average particle size D50 is 0.4-2.0 μm.

[0065] Another typical embodiment of the present invention provides an application of the above-mentioned transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material in lithium batteries. The transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material provided by the present invention has a carbon-coated lithium manganese iron phosphate matrix and an outer layer of nanoscale transition metal nitride and amorphous carbon composite coating. Based on this material structure, the material has a uniform particle size distribution and high conductivity. + It exhibits higher diffusion capacity, lower charge transfer resistance, and better crystallinity and stability. When used as a cathode material in lithium-ion batteries, it results in better rate performance, higher initial coulombic efficiency and capacity, lower manganese dissolution rate, and longer cycle life.

[0066] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments. The chemical reagents (AR grade) used in the following embodiments of the present invention are all commercially available products, purchased from Sinopharm Chemical Reagents, and can be used directly without further processing. The positive electrode substrate A used in the following embodiments of the present invention is a commercially available carbon-coated nano-scale lithium manganese iron phosphate substrate material, purchased from Hubei Rongtong New Energy Battery Materials Co., Ltd.

[0067] Example 1

[0068] A method for preparing a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating includes the following steps:

[0069] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6 Fe 0.39 Zr 0.01 PO4, with a surface carbon coating content of 0.8 wt%.

[0070] 2. Weigh glucose (1.5% of the mass of cathode matrix A) and nano-sized vanadium nitride (0.7% of the mass of cathode matrix A), add them to the cathode matrix A obtained in step 1, and mix them evenly using a high-speed mixer to obtain mixed precursor material B. The high-speed mixer speed is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0071] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the LiMn composite material of lithium manganese iron phosphate with transition metal nitride and amorphous carbon composite coating modification. 0.6 Fe 0.39 Zr 0.01 PO4@VN / C.

[0072] Figure 1 The image shows a SEM image of the resulting lithium manganese iron phosphate composite material with transition metal nitride and amorphous carbon coating. Figure 2 The XRD diffraction pattern of the sample was compared with that of the standard sample card, and no obvious impurities were observed.

[0073] Example 2

[0074] A method for preparing a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating includes the following steps:

[0075] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6 Fe 0.39 Zr 0.01 PO4, with a surface carbon coating content of 0.8 wt%.

[0076] 2. Weigh out glucose (1.5% of the mass of cathode matrix A) and nano-sized yttrium nitride (0.7% of the mass of cathode matrix A), add them to the cathode matrix A obtained in step 1, and mix them evenly using a high-speed mixer to obtain mixed precursor material B. The high-speed mixer speed is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0077] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the LiMn composite material of lithium manganese iron phosphate with transition metal nitride and amorphous carbon composite coating modification. 0.6 Fe 0.39 Zr 0.01 PO4@YN / C.

[0078] Example 3

[0079] A method for preparing a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating includes the following steps:

[0080] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6Fe 0.39 Zr 0.01 PO4, with a surface carbon coating content of 0.8 wt%.

[0081] 2. Weigh out glucose (1.5% of the mass of positive electrode substrate A) and nano-sized tantalum nitride (0.7% of the mass of positive electrode substrate A), add them to the positive electrode substrate A obtained in step 1, and mix them evenly using a high-speed mixer to obtain mixed precursor material B. The speed of the high-speed mixer is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0082] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the LiMn composite material of lithium manganese iron phosphate with transition metal nitride and amorphous carbon composite coating modification. 0.6 Fe 0.39 Zr 0.01 PO4@TaN / C.

[0083] Example 4

[0084] A method for preparing a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating includes the following steps:

[0085] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6 Fe 0.39 Nb 0.01 PO4, with a surface carbon coating content of 0.8 wt%.

[0086] 2. Weigh glucose (1.5% of the mass of cathode matrix A) and nano-sized vanadium nitride (0.7% of the mass of cathode matrix A), add them to the cathode matrix A obtained in step 1, and mix them evenly using a high-speed mixer to obtain mixed precursor material B. The high-speed mixer speed is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0087] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the LiMn composite material of lithium manganese iron phosphate with transition metal nitride and amorphous carbon composite coating modification. 0.6 Fe 0.39 Nb 0.01 O4@NV / C.

[0088] Comparative Example 1

[0089] A method for preparing an amorphous carbon-coated modified lithium manganese iron phosphate composite material includes the following steps:

[0090] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6 Fe 0.4 PO4, with a surface carbon coating content of 0.8 wt%.

[0091] 2. Weigh out glucose (1.5% of the mass of positive electrode matrix A), add it to the positive electrode matrix A obtained in step 1, and mix it evenly using a high-speed mixer to obtain mixed precursor material B. The speed of the high-speed mixer is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0092] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the amorphous carbon composite-coated modified lithium manganese iron phosphate composite material LiMn. 0.6 Fe 0.4 PO4@C.

[0093] Comparative Example 2

[0094] A method for preparing a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating includes the following steps:

[0095] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6 Fe 0.4 PO4, with a surface carbon coating content of 0.8 wt%.

[0096] 2. Weigh glucose (1.5% of the mass of cathode matrix A) and nano-sized vanadium nitride (0.7% of the mass of cathode matrix A), add them to the cathode matrix A obtained in step 1, and mix them evenly using a high-speed mixer to obtain mixed precursor material B. The high-speed mixer speed is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0097] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the LiMn composite material of lithium manganese iron phosphate with transition metal nitride and amorphous carbon composite coating modification. 0.6 Fe 0.4 O4@NV / C.

[0098] Comparative Example 3

[0099] A method for preparing an amorphous carbon-coated modified lithium manganese iron phosphate composite material includes the following steps:

[0100] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6 Fe 0.39 Zr 0.01 PO4, with a surface carbon coating content of 0.8 wt%.

[0101] 2. Weigh out glucose (1.5% of the mass of positive electrode matrix A), add it to the positive electrode matrix A obtained in step 1, and mix it evenly using a high-speed mixer to obtain mixed precursor material B. The speed of the high-speed mixer is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0102] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the amorphous carbon composite-coated modified lithium manganese iron phosphate composite material LiMn. 0.6 Fe 0.39 Zr 0.01 PO4@C.

[0103] Comparative Example 4

[0104] A method for preparing a transition metal nitride-coated modified lithium manganese iron phosphate composite material includes the following steps:

[0105] 1. Weigh an appropriate amount of commercially available nano-sized lithium manganese iron phosphate cathode substrate A, which is carbon-coated and uniformly dispersed. Its chemical formula is LiMn. 0.6 Fe 0.39 Zr 0.01 PO4, with a surface carbon coating content of 0.8 wt%.

[0106] 2. Weigh out nano-sized vanadium nitride (0.7% of the mass of cathode substrate A), add it to cathode substrate A obtained in step 1, and mix it evenly using a high-speed mixer to obtain mixed precursor material B. The high-speed mixer speed is 1000 rpm, the mixing time is 60 min, and the mixing temperature is 25-45℃.

[0107] 3. Place the mixed precursor material B obtained in step 2 into a tube furnace, heat it to 650℃ at a rate of 3℃ / min under a nitrogen atmosphere, hold it at that temperature for 2 hours, then cool it down, grind it, and sieve it to obtain the transition metal nitride-coated modified lithium manganese iron phosphate composite material LiMn. 0.6 Fe 0.39 Zr 0.01 PO4@NV / C.

[0108] Performance verification:

[0109] The lithium manganese iron phosphate composite materials obtained in Examples 1-4 and Comparative Examples 1-4 were used as positive electrode materials to prepare coin cells for electrochemical performance testing.

[0110] The production method is as follows:

[0111] a. The lithium manganese iron phosphate composite materials prepared in the examples and comparative examples were stirred in a ratio of positive electrode material powder: conductive agent (SP): adhesive (PVDF) = 90:5:5 to form a uniformly dispersed positive electrode slurry. The slurry was then coated, punched, and vacuum dried. Lithium metal sheets were used as the negative electrode material for the battery, and a polypropylene film with micropores was used as the battery separator. Ethylene carbonate (EC) / dimethyl carbonate (DMC) with a solvent volume ratio of 1:1 and 1 mol / L LiPF6 were used as the electrolyte. The batteries were assembled into 2032 button batteries in a glove box filled with dry high-purity argon gas and left to stand for 8 hours.

[0112] b. After the button battery has been left to stand, charge and discharge it at an ambient temperature of 25°C, at a current rate of 0.1C, at a voltage of 2.5V-4.5V. Test the electrochemical performance of the button battery and calculate its first discharge efficiency. First discharge efficiency = first discharge specific capacity / first charge specific capacity * 100%.

[0113] c. At 45℃, the button cell was charged and discharged at 1C at 2.5V-4.5V. The capacity retention rate after 100 cycles was calculated using the following formula: Capacity retention rate = Specific capacity after 100 discharges / Specific capacity after first discharge * 100%.

[0114] Please refer to Table 1 for specific test data.

[0115] Table 1 Performance test data of button batteries

[0116]

[0117] As shown in Table 1, compared with Comparative Example 1, the electrical performance (first-time efficiency and discharge specific capacity) and cycle performance of the composite modified cathode materials prepared in the various embodiments of the present invention are significantly improved. Figure 3 The charge-discharge curves show that the polarization of Comparative Example 1 is relatively large, and its charge-discharge capacity, initial discharge efficiency, and cycle retention are all low. Example 1 also exhibits good cycle performance at 45°C and 1C rate, indicating that its rate performance and manganese dissolution phenomenon have been improved.

[0118] The reasons for the effects achieved in the above embodiments are as follows: This invention uses vanadium nitride / amorphous carbon to composite-coat and modify lithium manganese iron phosphate materials, and its vanadium nitride has good electron / Li ratio.+ It possesses excellent electrical conductivity, resistance to acid and alkali corrosion, thermal conductivity, high melting point, and catalytic activity. By heat-treating vanadium nitride / amorphous carbon source and matrix at specific temperatures, a composite coating layer of vanadium nitride / amorphous carbon is formed on lithium manganese iron phosphate, thereby making the composite cathode material structure more stable. The strong acid and alkali corrosion resistance of vanadium nitride effectively inhibits the dissolution of manganese in the coated cathode material, avoiding direct contact corrosion between the lithium manganese iron phosphate electrode surface and the electrolyte, reducing side reactions in the electrolyte, and improving the cycle stability of the material. Vanadium nitride not only has good electrical conductivity but also good Li-... + Conductive transport properties enable rapid realization of L i+ The insertion and extraction of Li not only improves the conductivity of the material, but also further opens up and increases the Li content on the surface of the cathode material. + The diffusion channels are improved, reducing capacity loss in the modified material. Transition metal nitrides possess certain active sites and catalytic activity, and can effectively promote the graphitization of amorphous carbon during high-temperature treatment, thereby further increasing the conductivity of the material.

[0119] In this invention, an LMFP composite cathode material was prepared by a solid-state method using vanadium nitride and amorphous carbon composite coating modification. The process is simple, the conditions are controllable, the crystallinity is high, there are few crystalline impurities, and the product has a relatively uniform particle size. Furthermore, it is cost-effective, environmentally friendly, and easily commercially scalable.

[0120] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, characterized in that, Includes the following steps: Amorphous carbon source and nanoscale transition metal nitrides are added to carbon-coated lithium manganese iron phosphate and mixed to obtain precursor material. The precursor material was sintered at high temperature under a protective atmosphere, then cooled and ground and sieved to obtain a lithium manganese iron phosphate composite material with transition metal nitride and amorphous carbon composite coating modification. The transition metal nitride is vanadium nitride; The carbon-coated lithium manganese iron phosphate is a uniformly dispersed, carbon-coated nano-sized lithium manganese iron phosphate; the chemical formula of the nano-sized lithium manganese iron phosphate is LiMnxFe. 1-x-y M y PO4, 0 < x < 1, 0.001 ≤ y ≤ 0.05; M is selected from Zr or Nb; The high-temperature sintering is carried out at a temperature of 500-700℃, a sintering time of 1-5h, and a heating rate of 2-10℃ / min.

2. The preparation method according to claim 1, characterized in that, The amorphous carbon source is selected from at least one of sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid.

3. The preparation method according to claim 1, characterized in that, The mass of the amorphous carbon source is 0.5-2.0 wt% of the mass of the carbon-coated lithium manganese iron phosphate.

4. The preparation method according to claim 1, characterized in that, The mass of the nanoscale transition metal nitride is 0.1-2.0 wt% of the mass of the carbon-coated lithium manganese iron phosphate.

5. The preparation method according to claim 1, characterized in that, The carbon-coated nano-sized lithium manganese iron phosphate has a carbon content of 0.5-1.0 wt%; the carbon source in the carbon coating is at least one of sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid.

6. The preparation method according to claim 1, characterized in that, 0.005≤y≤0.04。 7. The preparation method according to claim 1, characterized in that, The mixing is a high-speed stirring mixture with a stirring speed of 900-1200 rpm, a mixing time of 40-60 min, and a mixing temperature of 25-45℃.

8. A lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, characterized in that, It is prepared by any one of the preparation methods described in claims 1-7.

9. The lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating as described in claim 8, characterized in that, The primary particle size of the lithium manganese iron phosphate composite material modified by the transition metal nitride and amorphous carbon composite coating is 50-300 nm, and the average particle size D50 is 0.4-2.0 μm.

10. The application of a lithium manganese iron phosphate composite material modified by transition metal nitride and amorphous carbon composite coating as described in claim 8 or 9 in lithium batteries.

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