CN105449178B - A kind of preparation method of nano lithium manganese phosphate of lithium/graphene/carbon composite material - Google Patents

Abstract

The invention discloses a method for preparing a nano-lithium manganese phosphate/graphene/carbon composite material. The specific steps are: using ethylene glycol and deionized water as reaction media, first adding glucose to ethylene glycol and keeping it warm at 130-150°C 1‑5h on-line generation of ethylene glycol glucoside surfactant as a grain formation inhibitor, disperse graphene oxide into the above surfactant, use lithium hydroxide, soluble manganese salt and phosphoric acid as raw materials, and use deionized water As a solvent, the boiling point of the reaction solution is controlled at 130-150°C by adjusting the volume ratio of ethylene glycol and water to 3.5:1-1:1.5, and the reflux reaction is 6-24h to prepare the nano-manganese lithium phosphate/graphene composite material, Then compound with organic carbon source to prepare nano-lithium manganese phosphate/graphene/carbon composite material. The target product synthesized by the present invention is not only beneficial to shorten the transmission distance of lithium ions in the solid phase, but also the conductive network formed by the graphene and the amorphous carbon produced by cracking the organic carbon source greatly enhances the electronic conductivity between particles.

Description

A kind of preparation method of nano lithium manganese phosphate/graphene/carbon composite material

technical field

The invention belongs to the technical field of synthesis of positive electrode materials of lithium ion batteries, and in particular relates to a preparation method of nanometer lithium manganese phosphate/graphene/carbon composite material.

Background technique

LiMnPO ₄ has the same olivine structure as LiFePO ₄ , and the theoretical specific capacity is the same, but its working voltage is 4.1V (relative to the electrode potential of Li/Li ⁺ ), which is exactly at the electrode potential of the existing lithium-ion battery electrolyte system. chemical window. Therefore, due to the higher operating voltage, the theoretical specific energy of LiMnPO ₄ can reach nearly 700 Wh/kg, which is about 20% higher than that of LiFePO ₄ . In addition, LiMnPO ₄ has the advantages of abundant raw material resources, low price, environmental friendliness, stable structure, good chemical compatibility and high safety, and is considered to be a promising cathode material for power lithium-ion batteries.

However, the electronic conductivity and ion diffusion coefficient of _LiMnPO4 materials are much smaller than those of _LiFePO4 , resulting in poor reversibility and rate performance of the materials. Yamada et al. calculated the electronic energy level of LiMnPO ₄ from the first principle, and found that the energy gap for electrons to transition in LiMnPO ₄ is 2eV, which is basically an insulator. Therefore, it is very difficult to synthesize LiMnPO ₄ capable of reversible charge and discharge, which is also the main reason why this material has not been industrialized so far.

Studies have shown that nanonization of electrode active material particles and carbon coating on the surface of nanoparticles are effective ways to improve ion diffusion coefficient and electronic conductivity. However, due to the insulating properties of LiMnPO ₄ itself, the requirements for its particle size and dispersion are far more stringent than those of LiFePO ₄ . Compared with the ball milling method and sol-gel method, which are dominated by high-temperature solid-state sintering, the hydrothermal or solvothermal method and the polyol method are more suitable for the preparation and regulation of nanoparticles because they mainly react in the liquid phase. However, most of the LiMnPO ₄ particles synthesized by the hydrothermal method and the polyol method are nanoscale in a certain dimension, and the other dimensions are still micron-scale, such as nanorods and nanosheets. Although the diameter or thickness is about 100 nanometers, the length or width Often up to a few microns. For example, YZDong et al. (Journal of Power Sources 2012, 215:116-121) reported a solvothermal method for preparing LiMnPO ₄ nanosheets under high temperature and pressure. Although the thickness is 50 nm, the width of the nanosheets can reach 2 Micron. The invention patent with the patent application number 201510097239.X discloses a method for preparing LiMnPO ₄ nanorods, using ethylene glycol and an aqueous solution to react at 180°C for 10 hours, but the reaction needs to be carried out in a high-temperature and high-pressure container. The invention patent with the application number of 201410562468.X discloses a preparation method of LiMnPO ₄ nano-microspheres, using ethylene glycol and aqueous solution as solvents in a closed high-pressure vessel to react at 160-240 ° C to form nano-rod agglomerates. Microspheres. The invention patent with the patent application number 201410564186.3 uses the same system and method to synthesize micron flower-shaped LiMnPO ₄ particles with a diameter of 200 nanometers and a length of 2 microns. The invention patent with the application number 201410413701.8 discloses a kind of ethylene glycol solvothermal method under high temperature and high pressure to synthesize nanorods with a long diameter of 0.8-2.8 microns and a short diameter of 0.5-1.8 microns with KOH as a mineralizer. Ellipsoid. These micron-sized particles aggregated by nanorods are difficult to coat the carbon layer on the surface of the inner nanorods in the subsequent carbon coating process, which directly affects the electrical conductivity of the primary particles inside the material. Invention patents with application numbers 201410413620.8, 201410413442.9 and 201410413515.4 disclose a method for synthesizing nanoparticles, but expensive P123 and P127 tri-block copolymers are used as templates in the synthesis, and the reaction is still carried out in a high-pressure closed reactor. High temperature and high pressure are required. The invention patent with application number 201410232083.7 discloses a method for preparing nano-LiMnPO ₄ particles using polyethylene glycol and dimethylformamide as organic solvents and oleic acid as surfactant. conduct. Most of the above-mentioned micro-nano LiMnPO ₄ particles are synthesized by high-temperature and high-pressure solvent method, and the reaction needs to be carried out in a high-pressure and high-temperature container, and the operation is complicated and the cost is high. In recent years, it has been found that graphene has ultra-thin softness and excellent electrical conductivity, and it is used as a conductive agent to compound with LiMnPO ₄ particles to improve the conductivity between particles. For example, the invention patent with application patent number 201410112130.4 discloses a method for preparing sheet-like lithium manganese phosphate/graphene composite material. This method uses a spray-drying-assisted high-temperature sintering method to synthesize micron-sized spherical particles. The invention patent with the application number 201310278122.2 reports a conductive network formed by graphene and amorphous carbon with cracking properties of organic carbon sources to improve the conductivity of LiMnPO ₄ particles. But the method that this method adopts is the hydrothermal reaction of high temperature and high pressure, needs high temperature and pressure.

Contents of the invention

The technical problem that the present invention solves is to provide a kind of preparation method of nano manganese phosphate lithium/graphene/carbon composite material, the glucose in the solution of this method and ethylene glycol can produce the surfactant based on ethylene glycol glucoside It can effectively inhibit the growth of particles. Part of the glucose and ethylene glycol in the solution have a reducing effect, which can reduce graphene oxide to graphene, and compound with the generated nano-LiMnPO ₄ to prepare a particle with a size of no more than 150nm in any dimension. LiMnPO ₄ /graphene composite material, and finally mix the composite material with an organic carbon source and treat at 500-700°C for 1-5h under the protection of an inert gas to obtain the target product. This nano-lithium manganese phosphate/graphene/carbon composite material is used as the positive electrode material of lithium _- ion batteries. The synergistic effect of oxidation and graphene with the amorphous carbon conductive network can greatly improve the electrochemical performance of LiMnPO ₄ materials.

The present invention adopts following technical scheme for solving the above-mentioned technical problem, a kind of preparation method of nano manganese phosphate lithium/graphene/carbon composite material, it is characterized in that concrete steps are:

(1) Dissolve glucose in ethylene glycol and incubate at 130-150°C for 1-5 hours under the protection of _N2 to obtain light yellow solution A, in which the amount of glucose added is 1-20g of glucose per 100mL of ethylene glycol;

(2) Disperse graphene oxide into solution A to obtain solution A containing graphene oxide, weigh the raw materials respectively according to the ratio of lithium hydroxide, soluble manganese salt and phosphoric acid molar ratio of 3:1:1, and oxidize the hydrogen Dissolving lithium in deionized water to prepare a lithium hydroxide solution, then adding the lithium hydroxide solution to solution A containing graphene oxide to form a uniform solution B, dissolving soluble manganese salts and phosphoric acid in deionized water to prepare solution C, Then add solution C to solution B to form a reaction solution, wherein the boiling point of the reaction solution is controlled at 130-150 by adjusting the volume ratio of deionized water and ethylene glycol used in step (1) to 1:3.5-1.5:1 ℃;

(3) Place the reaction solution obtained in step (2) in a reaction vessel with a reflux device, and conduct a reflux reaction at 130-150°C for 6-24 hours under the protection of _N2 . The obtained precipitate is centrifuged, washed with deionized water and Nano-lithium manganese phosphate/graphene composite material was obtained after vacuum drying;

(4) Mix the nano-lithium manganese phosphate/graphene composite material obtained in step (3) with an organic carbon source, keep it warm at 500-700°C for 2-6 hours under the protection of an inert gas, and pulverize it after cooling to obtain nano-lithium manganese phosphate/graphite Graphene/carbon composite material, wherein the amount of organic carbon source is 10%-20% of the mass of nano-lithium manganese phosphate/graphene composite material, and the inert gas is argon, nitrogen, a mixture of argon and hydrogen or a mixture of nitrogen and hydrogen mixed composition.

It is further defined that the reaction of glucose and ethylene glycol in step (1) produces ethylene glycol glucoside surfactant as a grain growth inhibitor.

Further defined, the soluble manganese salt in step (2) is manganese sulfate, manganese nitrate, manganese chloride or manganese acetate.

Further defined, the vacuum drying condition in step (3) is vacuum drying at 80° C. for 12 hours.

Further defined, the organic carbon source in step (4) is glucose, sucrose, starch, phenolic resin or polyvinyl alcohol.

It is further defined that the volume percentage of hydrogen in the mixed gas of argon and hydrogen or the mixed gas of nitrogen and hydrogen described in step (4) is 1%-10%.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention adopts normal pressure liquid phase synthesis, uses ethylene glycol and water as the reaction medium, and the reaction temperature is lower than 150°C, which avoids the harsh conditions of high temperature and high pressure required by the solvothermal method. The process is simple, the reaction conditions are mild, and the reagents used are Low price, green and environmental protection;

(2) Using online synthesis of ethylene glycol glucoside surfactants as grain growth inhibitors is not only easy to operate and low in cost, but also can effectively control the growth of grains to be less than 150nm in full dimension;

(3) The nanoparticles generated in the liquid phase are adsorbed on the surface of graphene, and the conductive network formed by graphene can connect the nanoparticles to each other to increase their conductivity;

(4) The nano-lithium manganese phosphate/graphene/carbon composite material synthesized by the present invention is not only beneficial to shorten the transmission distance of lithium ions in the solid phase, but also greatly enhances the conductive network formed by graphene and the amorphous carbon produced by the cracking of organic carbon sources The electronic conductivity between the particles can be improved effectively, which can effectively improve the electrochemical performance of lithium manganese phosphate, especially the high-voltage platform performance.

Description of drawings

Fig. 1 is the XRD collection of illustrative plates of the nano-manganese lithium phosphate particle that the embodiment of the present invention 1 makes;

Fig. 2 is the SEM figure of the nano manganese phosphate lithium/graphene/carbon composite material that the embodiment of the present invention 1 makes;

Fig. 3 is the particle size distribution figure of the nano manganese phosphate lithium/graphene/carbon composite material that the embodiment of the present invention 1 makes;

Fig. 4 is the SEM figure of the lithium manganese phosphate/graphene/carbon composite material that comparative example 1 of the present invention makes;

Fig. 5 is the electrochemical charge and discharge curves of the target products prepared in Example 1 and Comparative Example 1 of the present invention.

detailed description

The above-mentioned contents of the present invention are described in further detail below through the embodiments, but this should not be interpreted as the scope of the above-mentioned themes of the present invention being limited to the following embodiments, and all technologies realized based on the above-mentioned contents of the present invention all belong to the scope of the present invention.

Example 1

Dissolve 6g of glucose in 60mL of ethylene glycol and keep it warm at 140°C for ₂ hours under the protection of N2, so that the color of the ethylene glycol solution changes from colorless to light yellow, indicating that there is ethylene glycol glucoside in the ethylene glycol solution Surfactants are generated, and a light yellow solution A is finally obtained. 31.4 mg of graphene oxide was ultrasonically dispersed into solution A to obtain solution A containing graphene oxide. Take 0.06mol lithium hydroxide (LiOH·H ₂ O) and dissolve it in 15mL deionized water, mix it with solution A and stir evenly to obtain solution B. Dissolve 0.02mol manganese sulfate (MnSO ₄ ) and 0.02 mol phosphoric acid (H ₃ PO ₄ ) in 15mL deionized water to obtain solution C, add solution C to solution B to form a reaction solution, and heat the reaction solution under the protection of N ₂ The reflux reaction was carried out for 12 hours, and the reflux reaction temperature was 139°C. The reaction precipitate was centrifuged at 8000 r/min, washed with deionized water and vacuum-dried at 80°C for 12 hours to obtain a nano-lithium manganese phosphate/graphene composite material. The obtained nano-lithium manganese phosphate/graphene composite material was mixed with 20% glucose by mass of the nano-lithium manganese phosphate/graphene composite material, placed in a tube furnace, carbonized at 600°C for 3 hours under the protection of nitrogen, and ball milled after cooling Pulverize to get the target product. XRD analysis proves that the prepared lithium manganese phosphate material has a pure-phase olivine LiMnPO ₄ structure (as shown in Figure 1). Scanning electron microscopy shows that the target product is approximately spherical in shape with a maximum particle size of 150nm (as shown in Figure 2) , the total carbon coverage is 5.0%.

Mix nano-lithium manganese phosphate/graphene/carbon composite material, acetylene black and PVDF in a mass ratio of 85:10:5, add a certain amount of NMP to make a slurry, and spread the slurry evenly on aluminum foil , dried in a vacuum oven at 120°C for 12 hours, and then rolled into a positive electrode sheet, with a lithium metal sheet as the negative electrode, and a polypropylene microporous membrane as the diaphragm, with 1mol/LLiPF ₆ /DEC+DMC+EC (volume ratio 1:1: 1) As the electrolyte, a CR2016 button cell was packed in a glove box filled with argon. Use the LAND battery test system for electrical performance testing, the starting and ending voltage is 3.0-4.5V, the 0.05C discharge capacity is 162.2mAh/g (as shown in Figure 5), and has good high-voltage platform performance, and the discharge capacity above 3.8V reaches 118mAh/g.

Example 2

Dissolve 8g of glucose in 40mL of ethylene glycol and keep it warm at 130°C for 5 hours under the protection of _N2 , so that the color of the ethylene glycol solution changes from colorless to light yellow, which indicates that there is ethylene glycol glucoside in the ethylene glycol solution Surfactants are generated, and a light yellow solution A is finally obtained. 15.7 mg of graphene oxide was ultrasonically dispersed in solution A to obtain solution A containing graphene oxide. Take 0.06mol lithium hydroxide (LiOH·H ₂ O) and dissolve it in 30mL deionized water, mix it with solution A and stir evenly to obtain solution B. Dissolve 0.02mol of manganese chloride (MnCl ₂ ) and 0.02mol of phosphoric acid (H ₃ PO ₄ ) in 30mL of deionized water to obtain solution C, add solution C to solution B to form a reaction solution, and dissolve the reaction solution under the protection of N ₂ Heat to reflux for 24 hours, and the reflux reaction temperature is 130°C. The reaction precipitate was centrifuged at 8000 r/min, washed with deionized water and vacuum-dried at 80° C. for 12 hours to obtain a nano-lithium manganese phosphate/graphene composite material. The obtained nano-lithium manganese phosphate/graphene composite material was mixed with 15% sucrose by mass of the nano-lithium manganese phosphate/graphene composite material, placed in a tube furnace, and carbonized at 600°C for 2 hours under the protection of an inert gas. It is a mixed gas of nitrogen and hydrogen, the volume fraction of hydrogen is 5%, and the target product is obtained after cooling, grinding and crushing. The XRD analysis proves that the obtained lithium manganese phosphate material has a pure-phase olivine LiMnPO ₄ structure. The scanning electron microscope shows that the target product is approximately spherical in shape, with a maximum particle size of 140nm, a carbon coating thickness of 3.5nm, and a carbon content of 3.5%. . After electrochemical test, the 0.05C discharge capacity is 159.2mAh/g, the high-voltage discharge platform is excellent, and the discharge capacity above 3.8V reaches 116mAh/g.

Example 3

Dissolve 0.7g of glucose in 70mL of ethylene glycol and incubate at 150°C for 1 hour under the protection of _N2 , so that the color of the ethylene glycol solution changes from colorless to light yellow, indicating that there is ethylene glycol glucose in the ethylene glycol solution Glycoside surfactants were formed, and a pale yellow solution A was finally obtained. 31.4 mg of graphene oxide was ultrasonically dispersed in solution A to obtain solution A containing graphene oxide. Take 0.03mol lithium hydroxide (LiOH·H ₂ O) and dissolve it in 10mL deionized water, mix it with solution A and stir evenly to obtain solution B. Dissolve 0.01mol manganese nitrate (Mn(NO ₃ ) ₂ ) and 0.01mol phosphoric acid (H ₃ PO ₄ ) in 10mL deionized water to obtain solution C, add solution C to solution B to form a reaction solution, under the protection of N ₂ The reaction solution was heated to reflux for 6 hours, and the reflux reaction temperature was 150°C. The reaction precipitate was centrifuged at 8000 r/min, washed with deionized water and vacuum-dried at 80° C. for 12 hours to obtain a nano-lithium manganese phosphate/graphene composite material. Mix the obtained nano-lithium manganese phosphate/graphene composite with 10% sucrose by mass of the nano-lithium manganese phosphate/graphene composite, place it in a tube furnace, and carbonize it at 500°C for 6 hours under the protection of an inert gas. It is a mixed gas of nitrogen and hydrogen, the volume percentage of hydrogen is 5%, and the target product is obtained after cooling, grinding and crushing. XRD analysis proved that the prepared lithium manganese phosphate material had a pure-phase olivine LiMnPO ₄ structure. Scanning electron microscopy showed that the target product was approximately spherical in shape, with a maximum particle size of 145nm and a carbon content of 2.5%. According to the electrochemical test, the 0.05C discharge capacity is 158.2mAh/g, and the high-voltage discharge platform has excellent performance, and the discharge capacity above 3.8V reaches 115mAh/g.

Example 4

Dissolve 10g of glucose in 50mL of ethylene glycol and keep it warm at 134°C for 4 hours under the protection of _N2 , so that the color of the ethylene glycol solution changes from colorless to light yellow, indicating that there is ethylene glycol glucoside in the ethylene glycol solution Surfactants are generated, and a light yellow solution A is finally obtained. 188.4 mg of graphene oxide was ultrasonically dispersed in solution A to obtain solution A containing graphene oxide. Take 0.12mol lithium hydroxide (LiOH·H ₂ O) and dissolve it in 25mL deionized water, mix it with solution A and stir evenly to obtain solution B. Dissolve 0.04mol manganese acetate (Mn( _{CH 3} COO) ₂ ) and 0.04mol phosphoric acid (H ₃ PO ₄ ) in 25mL deionized water to obtain solution C, add solution C to solution B to form a reaction solution, and protect The reaction solution was heated under reflux for 12 hours, and the reflux reaction temperature was 134°C. The reaction precipitate was centrifuged at 8000 r/min, washed with deionized water and vacuum-dried at 80° C. for 12 hours to obtain a nano-lithium manganese phosphate/graphene composite material. Mix the obtained nano-lithium manganese phosphate/graphene composite material with 15% phenolic resin by mass of the nano-lithium manganese phosphate/graphene composite material, place in a tube furnace, carbonize at 700°C for 2 hours under the protection of nitrogen, cool, grind and pulverize to obtain the target product. XRD analysis proved that the prepared lithium manganese phosphate material had a pure-phase olivine LiMnPO ₄ structure. Scanning electron microscopy showed that the target product was approximately spherical in shape, with a maximum particle size of 135nm and a carbon content of 3.0%. After electrochemical test, the discharge capacity at 0.05C is 160.1mAh/g, and the high-voltage platform performance is excellent, and the discharge capacity above 3.8V reaches 116mAh/g.

Example 5

Dissolve 6g of glucose in 60mL of ethylene glycol and keep it warm at 140°C for ₂ hours under the protection of N2, so that the color of the ethylene glycol solution changes from colorless to light yellow, indicating that there is ethylene glycol glucoside in the ethylene glycol solution Surfactants are generated, and a light yellow solution A is finally obtained. 156.7 mg of graphene oxide was ultrasonically dispersed in solution A to obtain solution A containing graphene oxide. Take 0.06mol lithium hydroxide (LiOH·H ₂ O) and dissolve it in 15mL deionized water, mix it with solution A and stir evenly to obtain solution B. Dissolve 0.02mol manganese sulfate (MnSO ₄ ) and 0.02mol phosphoric acid (H ₃ PO ₄ ) in 15mL deionized water to obtain solution C, add solution C to solution B to form a reaction solution, and heat the reaction solution under the protection of N ₂ The reflux reaction was carried out for 12 hours, and the reflux reaction temperature was 139°C. The reaction precipitate was centrifuged at 8000 r/min, washed with deionized water and vacuum-dried at 80° C. for 12 hours to obtain a nano-lithium manganese phosphate/graphene composite material. Mix the nano-lithium manganese phosphate/graphene composite material with 20% glucose by mass of the nano-lithium manganese phosphate/graphene composite material, place it in a tube furnace, carbonize it at 600°C for 3 hours under the protection of nitrogen, and pulverize it by ball milling after cooling. target product. XRD analysis proves that the prepared lithium manganese phosphate material has a pure-phase olivine LiMnPO ₄ structure. Scanning electron microscopy shows that the target product is approximately spherical in shape, with a maximum particle size of 150nm and a total carbon coverage of 5.2%. After electrochemical test, the 0.05C discharge capacity is 156.1mAh/g, and the high-voltage platform performance is excellent, and the discharge capacity above 3.8V reaches 110mAh/g.

Comparative example 1

Take 0.06 mol of lithium hydroxide (LiOH·H ₂ O) and dissolve it in 15 mL of deionized water, and directly mix it with 60 mL of ethylene glycol containing 31.4 mg of graphene oxide to form solution B. Dissolve 0.02mol manganese sulfate (MnSO ₄ ) and 0.02mol phosphoric acid (H ₃ PO ₄ ) in 15mL deionized water to obtain solution C, add solution C to solution B to form a reaction solution, and the rest of the steps are the same as in Example 1. Mix the obtained lithium manganese phosphate/graphene composite material with 20% glucose by mass of the lithium manganese phosphate/graphene composite material, place in a tube furnace, carbonize at 600°C for 3 hours under the protection of nitrogen gas, cool and pulverize by ball milling to obtain the target product. The XRD analysis proved that the prepared lithium manganese phosphate material contained a small amount of impurities, and the scanning electron microscope showed that the target product was a micron-sized aggregate (as shown in Figure 4), with a total carbon coverage of 4.6%. According to the electrochemical test, the 0.05C discharge capacity is 153.2mAh/g, but the high-voltage platform performance is poor, and the discharge capacity above 3.8V is 73mAh/g.

The above embodiments have described the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What are described in the above embodiments and description are only to illustrate the principles of the present invention. Without departing from the scope of the principle of the present invention, there will be various changes and improvements in the present invention, and these changes and improvements all fall within the protection scope of the present invention.

Claims (6)

1. a kind of preparation method of nano lithium manganese phosphate of lithium/graphene/carbon composite material, it is characterised in that concretely comprise the following steps：

（1）Glucose is dissolved in ethylene glycol and in N₂1-5h is incubated in 130-150 DEG C yellow solution A is made under protection, wherein The addition of glucose is per 100mL ethylene glycol correspondence glucose 1-20g；

（2）Graphene oxide is distributed to the solution A containing graphene oxide is obtained in solution A, wherein graphene oxide with it is molten The charge ratio of ethylene glycol is 31.4mg in liquid A:60mL、15.7mg:40mL、31.4mg:70mL、188.4mg:50mL or 156.7mg:60mL, the mol ratio by lithium hydroxide, soluble manganese salt and phosphoric acid is 3:1:1 ratio weighs raw material respectively, will Lithium hydroxide, which is dissolved in deionized water, prepares lithium hydroxide solution, then lithium hydroxide solution is added to containing graphene oxide Uniform solution B is formed in solution A, soluble manganese salt and phosphoric acid are dissolved in deionized water and prepare solution C, then solution C is added Enter and reaction solution is formed into solution B, wherein using deionized water and step by adjusting（1）It is using the volume ratio of ethylene glycol 1:3.5-1.5:1 causes the boiling point control of reaction solution at 130-150 DEG C；

（3）By step（2）Obtained reaction solution is placed in the reaction vessel with reflux, in N₂In 130-150 under protection DEG C back flow reaction 6-24h, gained sediment through centrifugation, deionized water wash and vacuum drying after nano lithium manganese phosphate of lithium/stone is made Black alkene composite；

（4）By step（3）Obtained nano lithium manganese phosphate of lithium/graphene composite material is protected after being mixed with organic carbon source in inert gas 2-6h is incubated in 500-700 DEG C under shield, is crushed after cooling and obtains nano lithium manganese phosphate of lithium/graphene/carbon composite material, wherein organic The consumption of carbon source is the 10%-20% of nano lithium manganese phosphate of lithium/graphene composite material quality, and inert gas is argon gas, nitrogen, argon gas With the mixed gas or nitrogen and the mixed gas of hydrogen of hydrogen.

2. the preparation method of nano lithium manganese phosphate of lithium/graphene/carbon composite material according to claim 1, it is characterised in that： Step（1）Described in glucose and glycol reaction generation glycol polyglucoside class surfactant be used as crystal grain to suppress to give birth to Long agent.

3. the preparation method of nano lithium manganese phosphate of lithium/graphene/carbon composite material according to claim 1, it is characterised in that： Step（2）Described in soluble manganese salt be manganese sulfate, manganese nitrate, manganese chloride or manganese acetate.

4. the preparation method of nano lithium manganese phosphate of lithium/graphene/carbon composite material according to claim 1, it is characterised in that： Step（3）Described in vacuum drying condition for 80 DEG C vacuum drying 12h.

5. the preparation method of nano lithium manganese phosphate of lithium/graphene/carbon composite material according to claim 1, it is characterised in that： Step（4）Described in organic carbon source be glucose, sucrose, starch, phenolic resin or polyvinyl alcohol.

6. the preparation method of nano lithium manganese phosphate of lithium/graphene/carbon composite material according to claim 1, it is characterised in that： Step（4）Described in inert gas argon gas and the mixed gas or nitrogen of hydrogen and the mixed gas of hydrogen in hydrogen volume Percentage composition is 1%-10%.