Transition metal nitride and amorphous carbon composite coated and modified lithium manganese iron phosphate composite material as well as preparation method and application thereof

Abstract

The invention discloses a transition metal nitride and amorphous carbon composite coated and modified lithium manganese iron phosphate composite material as well as a preparation method and application thereof, and belongs to the technical field of lithium ion batteries. The vanadium nitride / amorphous carbon is adopted to perform composite coating modification on the lithium manganese iron phosphate material, so that the composite positive electrode material is more stable in structure. The use of vanadium nitride reduces the coating amount of carbon, and avoids the problems of coating layer thickening caused by high carbon content and Li < + > diffusion hindering caused by reduction of tap density of active substances. Vanadium nitride not only has good conductivity, but also has good Li < + > conductivity transmission performance, Li < + > de-intercalation can be rapidly achieved, the conductivity of the material is improved, meanwhile, a Li < + > diffusion channel on the surface of the positive electrode material is further dredged and increased, and the capacity loss of the modified material is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material, and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Since Goodenough et al. first proposed LiMPO4 (M = Mn, Fe, Co and Ni) as a positive electrode material for lithium-ion batteries in 1997, lithium manganese phosphate (LMP) has attracted much attention as one of the 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 has an operating voltage of 4.1V and has a higher energy density than LiFePO4 (LFP), its conductivity is low, which affects the Li + The transport of LMP and the conduction of electrons are affected, thus limiting its electrochemical performance. At the same time, due to the Jan-Taylor effect of the Mn element, Mn ions are easily dissolved from LMP, further affecting the cycle performance of the battery.

[0005] To solve these problems, researchers have tried to improve the electrochemical performance of LMPs by reducing particle size, combining fast ion / electron conductors, external conductive carbon coatings, and internal cation substitution. 1-x Fe x A PO4 (lithium manganese iron phosphate, abbreviated as LMFP) solid solution system was proposed, which combines the advantages of LFP and LMP, aiming to improve electronic conductivity and inhibit the Jan-Taylor effect. However, despite certain effects, the system is still limited in improving electrical conductivity, lithium diffusion and high-temperature manganese dissolution. In order to further improve the conductivity of solid solution materials, carbon coating and nano-sizing are widely used. For example, patent CN 111900344A discloses a carbon-coated lithium manganese iron phosphate positive electrode material, which uses conductive carbon coating and ion doping to modify the material, which can improve the electronic conductivity of the material on the one hand, and limit the growth of particle size on the other hand, while effectively weakening Mn 3+ The Jahn-Teller ex situ effect improves the cycle stability of the material. However, the initial discharge capacity and capacity retention rate after cycling of the carbon-coated lithium manganese iron phosphate positive electrode material prepared by it are still not ideal and need to be further improved.

[0006] In summary, although lithium manganese iron phosphate has potential high energy density and stability, its performance in practical applications is still limited due to its low conductivity, Mn dissolution and processing performance. Therefore, further research and improvement of lithium manganese iron phosphate positive electrode materials remains an important research direction in the battery field. Summary of the invention

[0007] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material and its preparation method and application, wherein lithium manganese iron phosphate is a matrix and the outer layer is a transition metal nitride / amorphous carbon composite coating layer. Based on this material structure, the electrochemical properties of the lithium manganese iron phosphate positive electrode material can be effectively improved.

[0008] In order to achieve the above object, the technical solution of the present invention is:

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

[0010] adding an amorphous carbon source and a nano-scale transition metal nitride into carbon-coated lithium manganese iron phosphate, mixing, and obtaining a precursor material;

[0011] The precursor material is sintered at high temperature in a protective atmosphere, and then ground and sieved after cooling to obtain a lithium manganese iron phosphate composite material coated and modified by a transition metal nitride and amorphous carbon.

[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 nano-scale 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-scale lithium manganese iron phosphate;

[0017] The chemical formula of the nano-scale lithium iron manganese phosphate is LiMnx Fe 1-x-y M y PO4, 0<x<1, 0.001≤y≤0.05; the 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 content of the carbon-coated nano-scale lithium manganese iron phosphate is 0.5-1.0wt%; the carbon is an amorphous carbon source, and the amorphous carbon source is at least one of sucrose, glucose, fructose, starch, cellulose, triglyceride, fatty acid, 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 mixing, the stirring speed is 900-1200 rpm, the mixing time is 40-60 min, and the mixing temperature is 25-45°C.

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

[0022] The second aspect of the present invention provides a transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material, 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 modified lithium manganese iron phosphate composite material is 50-300 nm, and the average particle size D50 is 0.4-2.0 μm.

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

[0025] The beneficial effects of the present invention are:

[0026] The present invention uses nano-scale transition metal nitride and amorphous carbon to perform composite coating modification on carbon-coated lithium manganese iron phosphate material. Among them, the nano-scale transition metal nitride has good electron / Li +Electrical conductivity, acid and alkali corrosion resistance, thermal conductivity, high melting point and catalytic activity. Through the heat treatment of nano-scale transition metal nitride / amorphous carbon source and matrix at a specific temperature, the nano-scale transition metal nitride / amorphous carbon forms a composite coating layer on the surface of lithium iron manganese phosphate, so that the structure of the composite positive electrode material is more stable. The strong acid and alkali corrosion resistance of the nano-scale transition metal nitride can also effectively inhibit the dissolution of manganese in the positive electrode material after coating, avoiding the direct contact reaction corrosion between the surface of the lithium iron manganese phosphate electrode and the electrolyte, reducing the side reaction of the electrolyte, and improving the cycle stability of the material. The good thermal conductivity of nano-scale transition metal nitride is beneficial to the battery in a low-temperature working environment. The heat generated by the battery is absorbed and transferred into the material particles, thereby improving the charge and discharge performance of the battery under low-temperature working conditions; on the other hand, when the battery is working in a high-temperature environment and the heat inside the battery is transferred out, the heat is not easy to accumulate, the battery temperature is reduced, the electrolyte side reaction is reduced, and the safety performance of the battery is improved. In addition, the use of vanadium nitride reduces the amount of carbon coating, avoiding the thickening of the coating layer caused by high carbon content and the reduction of the tap density of the active material, which hinders the Li + Diffusion problem. Vanadium nitride not only has good electrical conductivity, but also has good Li + Conductive transport properties enable rapid Li + The deintercalation and insertion of the positive electrode material not only improves the conductivity of the material, but also further dredges and increases the Li + The diffusion channel of the modified material is reduced. The present invention adopts transition metal nitride and carbon coating, and nitrogen atoms are filled in the gaps of the metal lattice, which is conducive to improving the easy water absorption property of lithium manganese iron phosphate and improving the processing performance of the material. In addition, the metal nitride has certain active sites and catalytic activity, which can effectively promote the increase of the graphitization degree of amorphous carbon in high temperature treatment, thereby further increasing the conductivity of the material.

[0027] The transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material provided by the present invention has a coating matrix of carbon-coated lithium manganese iron phosphate and an outer layer of a nano-scale transition metal nitride and amorphous carbon composite coating layer. Based on this structure, the material has a uniform particle size distribution, conductivity, Li + It has higher diffusion capacity, lower charge transfer impedance, better crystallinity and stability. When used as a positive electrode material for lithium-ion batteries, the battery has better rate performance, higher first coulomb efficiency and capacity, lower manganese dissolution rate, and longer cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0029] Figure 1 This is a surface morphology SEM image of the lithium iron manganese phosphate composite material obtained in Example 1 of the present invention;

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

[0031] Figure 3 The first charge and discharge performance diagram of button batteries assembled using the materials obtained in Example 1 of the present invention and Comparative Example 1 at 25° C. and 0.1C / 0.1C rate;

[0032] Figure 4 The following are the charge and discharge cycle performance diagrams of button batteries assembled using the materials obtained in Example 1 of the present invention and Comparative Example 1 at 45° C. and 1C / 1C rate. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] In order to solve the technical problems that the existing lithium iron manganese phosphate positive electrode materials have low conductivity, low discharge capacity, poor rate performance, poor cycle retention rate, and high manganese dissolution rate of lithium-ion batteries, the present invention provides a lithium iron manganese phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating, and a preparation method and application thereof.

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

[0036] adding an amorphous carbon source and a nano-scale transition metal nitride into carbon-coated lithium manganese iron phosphate, mixing, and obtaining a precursor material;

[0037] The precursor material is sintered at high temperature in a protective atmosphere, and then ground and sieved after cooling to obtain a lithium manganese iron phosphate composite material coated and modified by a transition metal nitride and amorphous carbon.

[0038] The present invention uses nano-scale transition metal nitride and amorphous carbon to perform composite coating modification on carbon-coated lithium manganese iron phosphate material. Among them, the nano-scale transition metal nitride has good electron / Li +Electrical conductivity, acid and alkali corrosion resistance, thermal conductivity, high melting point and catalytic activity. Through the heat treatment of nano-scale transition metal nitride / amorphous carbon source and matrix at a specific temperature, the nano-scale transition metal nitride / amorphous carbon forms a composite coating layer on the surface of lithium iron manganese phosphate, so that the structure of the composite positive electrode material is more stable. The strong acid and alkali corrosion resistance of the nano-scale transition metal nitride can also effectively inhibit the dissolution of manganese elements in the coated positive electrode material, avoiding the direct contact reaction corrosion between the surface of the lithium iron manganese phosphate electrode and the electrolyte, reducing the side reaction of the electrolyte, and improving the cycle stability of the material; the good thermal conductivity of the nano-scale transition metal nitride is beneficial to the battery in a low-temperature working environment. The heat generated by the battery is transferred into the material particles, thereby improving the battery's charge and discharge performance under low-temperature working conditions. On the other hand, it is beneficial for the battery to transfer the heat inside the battery in a timely manner under high-temperature working conditions, so that the heat is not easy to accumulate, reduce the battery temperature, reduce the electrolyte side reactions, and improve the safety performance of the battery; in addition, the use of nano-scale transition metal nitrides further reduces the amount of carbon coating. When the carbon content is low, a complete and uniform coating cannot be formed on the surface of lithium manganese iron phosphate, and sufficient conductivity cannot be obtained. As the carbon content increases, the coating becomes thicker, which reduces the tap density of the active material and also hinders the conductivity of Li + The nanoscale transition metal nitride in the present invention not only has good electrical conductivity, but also has good Li + Conductive transport properties enable fast Li + The deintercalation and insertion of the positive electrode material not only improves the conductivity of the material, but also further dredges and increases the Li + The diffusion channel of the modified material is reduced. The metal nitride in the present invention has metallic properties because nitrogen atoms are filled in the gaps of the metal lattice, which is not easy to react with water, which is beneficial to improve the easy water absorption property of lithium manganese iron phosphate and improve the processing performance of the material. In addition, the metal nitride has certain active sites and catalytic activity, which can effectively promote the increase of the graphitization degree of amorphous carbon in high-temperature treatment, thereby further increasing the conductivity of the material.

[0039] Based on this structure, the material has uniform particle size distribution, conductivity, Li + It has higher diffusion capacity, lower charge transfer impedance, better crystallinity and stability. When used as a positive electrode material for lithium-ion batteries, the battery has better rate performance, higher first coulomb efficiency and capacity, lower manganese dissolution rate, and longer cycle life.

[0040] In some examples of this embodiment, the amorphous carbon source is selected from at least one of sucrose, glucose, fructose, starch, cellulose, triglyceride, fatty acid, and citric acid, preferably glucose. Glucose is sintered and carbonized at high temperature to generate amorphous carbon, which cooperates with nano-scale transition metal nitride to further coat and modify the carbon-coated lithium manganese iron phosphate material.

[0041] In some examples of this embodiment, 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 examples of this embodiment, 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 examples of this embodiment, the mass of the nanoscale transition metal nitride is 0.1-2.0 wt %, preferably 0.5-1.0 wt %, of the mass of the carbon-coated lithium manganese iron phosphate.

[0044] In some examples of this embodiment, the carbon-coated lithium manganese iron phosphate used in the present invention is a commercial product and can be purchased. For example, it can be purchased from Hubei Rongtong New Energy Battery Materials Co., Ltd., which is a carbon-coated and uniformly dispersed nano-scale lithium manganese iron phosphate with a chemical formula of LiMn x Fe 1-x-y M y PO4, wherein 0<x<1, 0.001≤y≤0.03. It is a sintered positive electrode material with an appropriate amount of carbon coating on the surface, and can be used directly without further treatment.

[0045] Wherein, the carbon content in the carbon-coated lithium manganese iron phosphate is 0.5-1.0wt%. During the sintering process of the lithium manganese iron material, a conductive carbon layer is coated on the surface of the material, which is beneficial to inhibit excessive particle growth, reduce particle agglomeration, and reduce conductivity. The carbon content limited by the present invention is sufficient to inhibit particle growth, and the improvement in conductivity is small. Furthermore, the carbon is an amorphous carbon source, and the amorphous carbon source is at least one of sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid, preferably glucose.

[0046] Wherein, M is an iron-doping element, which 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, preferably Zr. The present invention limits the iron-doping element to Zr, that is, the coated substrate is a commercial zirconium-containing lithium iron manganese phosphate material (LiMn x Fe 1-x-y Zr y PO4).

[0047] The main innovation of the present invention is to carry out composite coating modification on lithium manganese iron phosphate material. The coating matrix is ​​a lithium manganese iron phosphate positive electrode material doped with Zr and coated with a small amount of carbon. 4+ It will not directly participate in the electrochemical reaction process, but will stabilize the structure of lithium manganese iron phosphate, improve its conductivity and Li + The effect of conductivity will not cause the voltage platform of lithium manganese iron phosphate to decrease, 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 positive electrode materials can be effectively improved.

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

[0049] In some examples of this embodiment, the mixing is high-speed stirring mixing. The present invention can use a high-speed mixer for mixing to obtain 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° C. The high-speed mixer used in the present invention is a conventional commercial product and can be purchased.

[0050] In some examples of this implementation mode, the high temperature sintering has a sintering temperature of 500-700° C., a sintering time of 1-5 hours, and a heating rate of 2-10° C. / min.

[0051] In some embodiments of this embodiment, the precursor material is placed in a tube furnace, heated to 500-700°C at a heating rate of 2-10°C / min under a protective atmosphere, sintered for 1-5 hours, then cooled, ground, and sieved to obtain a transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material (LiMn x Fe 1-x-y M y PO4@nitride conductive coating layer, wherein 0<x<1, 0.001<y≤0.05).

[0052] In some examples of this embodiment, the neutral protective atmosphere can be a combination of one or more of argon, nitrogen or helium.

[0053] In some examples of this embodiment, the preparation method specifically comprises the following steps:

[0054] (1) adding glucose and nano-sized vanadium nitride to carbon-coated lithium manganese iron phosphate, mixing, and obtaining a precursor material;

[0055] The carbon-coated lithium manganese iron phosphate is a commercial carbon-coated nano-scale lithium manganese iron phosphate material, and its chemical formula is 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 the carbon-coated lithium manganese iron phosphate;

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

[0058] (2) The precursor material is heated to 500-700° C. at a rate of 2-10° C. / min under a protective atmosphere, sintered for 1-5 hours, cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material modified by a transition metal nitride and amorphous carbon composite coating.

[0059] The main innovation of the present invention is to coat and modify the lithium manganese iron phosphate material, using commercial titanium-containing lithium manganese iron phosphate as the coating matrix, wherein Zr 4+ It will not directly participate in the electrochemical reaction process, but will stabilize the structure of lithium manganese iron phosphate, improve its conductivity and Li + The effect of conductivity and the fact that the voltage platform of lithium manganese iron phosphate is not reduced ensures the stable electrochemical performance of the matrix material of the present 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 positive electrode material can be effectively improved.

[0060] The present invention adopts vanadium nitride / amorphous carbon to carry out composite coating modification on lithium manganese iron phosphate material, and the vanadium nitride has good electron / Li +Electrical conductivity, acid and alkali corrosion resistance, thermal conductivity, high melting point and catalytic activity. Through heat treatment of vanadium nitride / amorphous carbon source and substrate at a specific temperature, vanadium nitride / amorphous carbon forms a composite coating layer on lithium iron manganese phosphate, so that the structure of the composite positive electrode material is more stable. The strong acid and alkali corrosion resistance of vanadium nitride can also effectively inhibit the dissolution of manganese elements in the positive electrode material after coating, avoiding the direct contact reaction corrosion between the surface of lithium iron manganese phosphate electrode and the electrolyte, reducing the side reaction of the electrolyte, and improving the cycle stability of the material; the good thermal conductivity of vanadium nitride is beneficial to the battery in a low-temperature working environment. The heat generated by the battery is transferred into the material particles, thereby improving the battery's charge and discharge performance under low-temperature working conditions. On the other hand, it is beneficial for the battery to transfer the heat inside the battery in a timely manner under high-temperature working conditions, so that the heat is not easy to accumulate, reduce the battery temperature, reduce the side reaction of the electrolyte, and improve the safety performance of the battery; in addition, the use of vanadium nitride further reduces the amount of carbon coating. When the carbon content is low, a complete and uniform coating cannot be formed on the surface of lithium manganese iron phosphate, and sufficient conductivity cannot be obtained; as the carbon content increases, the coating becomes thicker, which not only reduces the tap density of the active material, but also hinders the conductivity of Li + The vanadium nitride in the present invention not only has good electrical conductivity, but also has good Li + Conductivity and transport properties enable fast Li + The deintercalation and insertion of the positive electrode material not only improves the conductivity of the material, but also further dredges and increases the L i+ The diffusion channel reduces the capacity loss of the modified material; the present invention uses vanadium nitride amorphous carbon for coating. Since nitrogen atoms fill the gaps in the metal lattice, it has metallic properties and is not easy to react with water, which is conducive to improving the easy water absorption of lithium manganese iron phosphate and improving the processing performance of the material. Vanadium nitride has certain active sites and catalytic activity, which can effectively promote the increase of the graphitization degree of amorphous carbon in high-temperature treatment, thereby further increasing the conductivity of the material.

[0061] Based on this structure, the obtained lithium manganese iron phosphate composite material has uniform particle size distribution, conductivity, Li + Higher diffusion capacity, lower charge transfer impedance, better crystallinity and stability.

[0062] When used as a positive electrode material for lithium-ion batteries, the battery has better rate performance, higher first coulomb efficiency and capacity, lower manganese dissolution rate, and longer cycle life.

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

[0064] In some examples of this implementation manner, the primary particle size of the transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material 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 coating modified lithium manganese iron phosphate composite material in lithium batteries. The transition metal nitride and amorphous carbon composite coating modified lithium manganese iron phosphate composite material provided by the present invention has a coating matrix of carbon-coated lithium manganese iron phosphate and an outer layer of a nano-scale transition metal nitride and amorphous carbon composite coating layer. Based on this material structure, the material has a uniform particle size distribution, and the conductivity and Li + It has higher diffusion capacity, lower charge transfer impedance, better crystallinity and stability. When used as a positive electrode material for lithium-ion batteries, the battery has better rate performance, higher first coulomb efficiency and capacity, lower manganese dissolution rate, and longer cycle life.

[0066] In order 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 in conjunction with 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 treatment. The positive electrode substrate A used in the following embodiments of the present invention is a commercial 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 transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material comprises the following steps:

[0069] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6 Fe 0.39 Zr 0.01 PO4, the surface carbon coating content is 0.8wt%.

[0070] 2. Weigh glucose (1.5% of the mass of the positive electrode matrix A) and nano-vanadium nitride (0.7% of the mass of the positive electrode matrix A), add them to the positive electrode matrix A obtained in step 1, and use a high-speed mixer to mix evenly to obtain a 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 ° C.

[0071] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and the temperature is raised to 650°C at a rate of 3°C / min under a nitrogen atmosphere. After being kept warm for 2 hours, the mixture is cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material LiMn modified by a composite coating of transition metal nitride and amorphous carbon. 0.6 Fe 0.39 Zr 0.01 PO4@VN / C.

[0072] Figure 1 The SEM image of the transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material is shown in FIG. Figure 2 Its XRD diffraction pattern shows no obvious impurity phase compared with the standard sample card.

[0073] Example 2

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

[0075] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6 Fe 0.39 Zr 0.01 PO4, the surface carbon coating content is 0.8wt%.

[0076] 2. Weigh glucose (1.5% of the mass of the positive electrode matrix A) and nano-scale yttrium nitride (0.7% of the mass of the positive electrode matrix A), add them to the positive electrode matrix A obtained in step 1, and mix them evenly using a high-speed mixer to obtain a 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°C.

[0077] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and the temperature is raised to 650°C at a rate of 3°C / min under a nitrogen atmosphere. After being kept warm for 2 hours, the mixture is cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material LiMn modified by a composite coating of transition metal nitride and amorphous carbon. 0.6 Fe 0.39 Zr 0.01 PO4@YN / C.

[0078] Example 3

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

[0080] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6Fe 0.39 Zr 0.01 PO4, the surface carbon coating content is 0.8wt%.

[0081] 2. Weigh glucose (1.5% of the mass of the positive electrode matrix A) and nano-grade tantalum nitride (0.7% of the mass of the positive electrode matrix A), add them to the positive electrode matrix A obtained in step 1, and use a high-speed mixer to mix evenly to obtain a 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°C.

[0082] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and the temperature is raised to 650°C at a rate of 3°C / min under a nitrogen atmosphere. After being kept warm for 2 hours, the mixture is cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material LiMn modified by a composite coating of transition metal nitride and amorphous carbon. 0.6 Fe 0.39 Zr 0.01 PO4@TaN / C.

[0083] Example 4

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

[0085] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6 Fe 0.39 Nb 0.01 PO4, the surface carbon coating content is 0.8wt%.

[0086] 2. Weigh glucose (1.5% of the mass of the positive electrode matrix A) and nano-vanadium nitride (0.7% of the mass of the positive electrode matrix A), add them to the positive electrode matrix A obtained in step 1, and use a high-speed mixer to mix evenly to obtain a 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 ° C.

[0087] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and the temperature is raised to 650°C at a rate of 3°C / min under a nitrogen atmosphere. After being kept warm for 2 hours, the mixture is cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material LiMn modified by a composite coating of transition metal nitride and amorphous carbon. 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 comprises the following steps:

[0090] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6 Fe 0.4 PO4, the surface carbon coating content is 0.8wt%.

[0091] 2. Weigh glucose (1.5% of the mass of the 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 a 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°C.

[0092] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and heated to 650°C at a rate of 3°C / min under a nitrogen atmosphere. After being kept warm for 2 hours, the material is cooled, ground, and sieved to obtain an 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 transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material comprises the following steps:

[0095] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6 Fe 0.4 PO4, the surface carbon coating content is 0.8wt%.

[0096] 2. Weigh glucose (1.5% of the mass of the positive electrode matrix A) and nano-vanadium nitride (0.7% of the mass of the positive electrode matrix A), add them to the positive electrode matrix A obtained in step 1, and use a high-speed mixer to mix evenly to obtain a 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 ° C.

[0097] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and the temperature is raised to 650°C at a rate of 3°C / min under a nitrogen atmosphere. After being kept warm for 2 hours, the mixture is cooled, ground, and sieved to obtain a lithium manganese iron phosphate composite material LiMn modified by a composite coating of transition metal nitride and amorphous carbon. 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 comprises the following steps:

[0100] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6 Fe 0.39 Zr 0.01 PO4, the surface carbon coating content is 0.8wt%.

[0101] 2. Weigh glucose (1.5% of the mass of the 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 a 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°C.

[0102] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and heated to 650°C at a rate of 3°C / min under a nitrogen atmosphere. After being kept warm for 2 hours, the material is cooled, ground, and sieved to obtain an 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 comprises the following steps:

[0105] 1. Weigh an appropriate amount of purchased carbon-coated and evenly dispersed nano-scale lithium manganese iron phosphate positive electrode matrix A, whose chemical formula is LiMn 0.6 Fe 0.39 Zr 0.01 PO4, the surface carbon coating content is 0.8wt%.

[0106] 2. Weigh nano-scale vanadium nitride (0.7% of the mass of the 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 a 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°C.

[0107] 3. The mixed precursor material B obtained in step 2 is placed in a tube furnace, and heated to 650°C at a rate of 3°C / min in a nitrogen atmosphere. After being kept warm for 2 hours, the mixture is cooled, ground, and sieved to obtain a 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 battery positive electrode materials to prepare button batteries for electrochemical performance testing.

[0110] The production method is:

[0111] a. The lithium manganese iron phosphate composite material prepared in the embodiment and the comparative example is 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, and the slurry is coated, punched, and vacuum dried; a metal lithium sheet is used as the negative electrode material of the battery, and a polypropylene film with micropores is used as the battery separator; the solvent volume ratio is 1:1 ethylene carbonate (EC) / dimethyl carbonate (DMC), 1 mol / L LiPF6 is used as the electrolyte, and a 2032-type button battery is assembled in a glove box filled with dry high-purity argon and left to stand for 8 hours.

[0112] b. Charge and discharge the button cell at 25°C, 2.5V-4.5V, and 0.1C current rate to test the electrochemical performance of the button cell and calculate its first discharge efficiency, which is the first discharge specific capacity / first charge specific capacity*100%.

[0113] c. At 45°C, the button battery was tested for cycle performance at 2.5V-4.5V with 1C charge / 1C discharge, and its capacity retention rate after 100 cycles was calculated. The formula is as follows: Capacity retention rate = 100th discharge specific capacity / first discharge specific capacity*100%.

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

[0115] Table 1 Performance test data of button batteries

[0116]

[0117] It can be seen from Table 1 that, compared with Comparative Example 1, the electrical properties (first efficiency and discharge specific capacity) and cycle performance of the composite modified positive electrode materials prepared in each embodiment of the present invention are significantly improved. Figure 3 From the charge and discharge curves in Figure 2, it can be found that the polarization of the sample in Comparative Example 1 is larger, and the charge and discharge capacity, first discharge efficiency and cycle retention rate are all lower. Example 1 also exhibits good cycle performance at 45°C and 1C rate, which also shows that its rate performance and manganese dissolution phenomenon are improved.

[0118] The reasons for the effects achieved in the above embodiments are as follows: the present invention uses vanadium nitride / amorphous carbon to perform composite coating modification on lithium manganese iron phosphate material, and the vanadium nitride has good electron / Li+ It has the characteristics of electrical conductivity, acid and alkali corrosion resistance, thermal conductivity, high melting point and catalytic activity. By heat treating the vanadium nitride / amorphous carbon source and the matrix at a specific temperature, the vanadium nitride / amorphous carbon forms a composite coating layer on the lithium iron manganese phosphate, thereby making the structure of the composite positive electrode material more stable. The strong acid and alkali corrosion resistance of vanadium nitride can also effectively inhibit the dissolution of manganese elements in the coated positive electrode material, avoiding the direct contact reaction corrosion between the surface of the lithium iron manganese phosphate electrode and the electrolyte, reducing the side reactions of the electrolyte, and improving the cycle stability of the material. Vanadium nitride not only has good electrical conductivity, but also has good Li + Conductive transmission performance, can quickly achieve L i+ The deintercalation and insertion of the positive electrode material can improve the conductivity of the material and further dredge and increase the Li + The diffusion channel can reduce the capacity loss of the modified material. Transition metal nitrides have certain active sites and catalytic activity, which can effectively promote the increase of graphitization degree of amorphous carbon in high temperature treatment, thereby further increasing the conductivity of the material.

[0119] In the present invention, the LMFP composite positive electrode material is prepared by a solid phase method and a composite coating modification of vanadium nitride and amorphous carbon, which has a simple process, controllable conditions, high crystallinity, less crystal impurities, and a relatively uniform product particle size. At the same time, it is also cost-effective, environmentally friendly, and easy to commercially expand.

[0120] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material, characterized in that: The steps include: adding an amorphous carbon source and a nano-scale transition metal nitride into carbon-coated lithium manganese iron phosphate, mixing, and obtaining a precursor material; The precursor material is sintered at high temperature in a protective atmosphere, and then ground and sieved after cooling to obtain a lithium manganese iron phosphate composite material coated and modified by a transition metal nitride and amorphous carbon.

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

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

4. The preparation method according to claim 1, characterized in that: The carbon-coated lithium manganese iron phosphate is carbon-coated and uniformly dispersed nano-scale lithium manganese iron phosphate; The chemical formula of the nano-scale lithium iron manganese phosphate is LiMn x Fe 1-x-y M y PO4, 0<x<1, 0.001≤y≤0.05; the 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; The carbon content of the carbon-coated nano-scale lithium manganese iron phosphate is 0.5-1.0wt%; the carbon is an amorphous carbon source, and the amorphous carbon source is at least one of sucrose, glucose, fructose, starch, cellulose, triglycerides, fatty acids, and citric acid.

5. The preparation method according to claim 4, characterized in that: 0.005≤y≤0.04。 6. The preparation method according to claim 1, characterized in that: The mixing is high-speed stirring mixing, the stirring speed is 900-1200 rpm, the mixing time is 40-60 min, and the mixing temperature is 25-45°C.

7. The preparation method according to claim 1, characterized in that: The high temperature sintering has a sintering temperature of 500-700° C., a sintering time of 1-5 hours, and a heating rate of 2-10° C. / min.

8. A transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material, characterized in that: The compound is prepared by the preparation method described in any one of claims 1 to 7.

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

10. Use of the transition metal nitride and amorphous carbon composite-coated modified lithium manganese iron phosphate composite material according to claim 8 or 9 in a lithium battery.

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