CN112374552B - Composite modified graphite negative electrode material and preparation method thereof - Google Patents
Composite modified graphite negative electrode material and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a composite modified graphite anode material and a preparation method thereof, wherein the preparation method comprises the following steps: 1) Mixing graphite with an oxidant and an intercalation agent according to a certain mass ratio to obtain a mixed solution; 2) Stirring the mixed solution at constant temperature to react and obtain an intercalation product; 3) Repeatedly washing the intercalation product with deionized water until the pH value of the filtrate is between 5 and 7, drying the washed intercalation product, and heating to a target temperature in an inert atmosphere for a specific time to obtain a target product. The composite modified graphite anode material prepared by the method is manganese oxide loaded sulfur-free micro-expanded graphite, and has nano holes and moderately enlarged graphite lamellar spacing. The method has the advantages of high operability, easy production, low equipment requirement and good repeatability, and the prepared composite modified graphite anode material has higher specific capacity, excellent multiplying power performance and longer cycling stability, and is more easy to be used in the field of commercial lithium ion batteries.
Description
Technical Field
The invention belongs to the technical field of graphite materials, and particularly relates to a composite modified graphite negative electrode material for a lithium ion battery and a preparation method thereof.
Background
Compared with other electrochemical batteries (such as lead-acid batteries, nickel-cadmium batteries and nickel-hydrogen batteries), the lithium ion battery has the characteristics of higher energy density and power density, long cycle life, high working voltage, good safety performance, environmental friendliness and the like, has been widely applied to portable electronic equipment, and is gradually popularized into the fields of new energy automobiles, renewable energy storage, energy conservation, emission reduction and the like. The lithium ion battery can be structurally divided into four parts, namely an anode for providing a lithium source, a cathode capable of inserting lithium, a diaphragm for preventing the anode and the cathode from being shorted and electrolyte for conducting lithium ions, wherein the specific capacity, the multiplying power performance and the cycle performance of the cathode material are one of key factors for determining the comprehensive performance of the lithium ion battery.
At present, the lithium ion battery cathode is the graphite cathode with the most widely applied theoretical specific capacity of 372 mAh/g, so far, the highest reversible specific capacity of the commercial battery-grade graphite cathode is exerted to about 360 mAh/g and is close to the theoretical specific capacity, but the lower specific capacity can not meet the use requirement of the lithium ion battery with high energy density. On the other hand, lithium intercalation compounds (lics) due to graphite 6 ) The size (about 0.37 and nm) of the lithium ion battery is larger than the lamellar spacing (about 0.335 and nm) of the graphite, so that the volume change of the graphite during the charging/discharging process is about 10%, the volume effect causes the stripping and pulverization phenomena of the graphite cathode during the cycling process, the capacity of the lithium ion battery is reduced, and the cycling performance is poor. In addition, the smaller lamellar spacing and the characteristic that lithium ions are difficult to diffuse in the lamellar longitudinal direction seriously reduce the rate capability of the graphite cathode, and prevent the application of the lithium ion battery in the field of high-power output energy storage devices. In order to solve the problems of poor rate performance and poor cycle performance of the graphite negative electrode, a zero-strain lithium titanate negative electrode material with a spinel structure is provided, and the material has the advantages of high coulombic efficiency and high rate, but has lower specific capacity (175 mAh/g) and higher working potential (1.5V vs. Li/Li) + ) The problem of flatulence severely hampers its large sizeScale commercial application. On the other hand, in order to solve the problem of low specific capacity of the graphite negative electrode, materials such as nano silicon negative electrode, carbon coated silicon negative electrode, graphite-silicon negative electrode and the like gradually appear on the market, but are limited by the influence of short cycle life and low power density, and the materials are still difficult to be applied to commercial lithium ion batteries in a large scale in a short time. Therefore, modification (e.g., doping, cladding, etc.) of current commercial graphite anode materials remains a major direction to solve the problems of low specific capacity, low rate, short cycle life, etc. of graphite.
Based on the problems of the current commercial graphite anode materials, it is becoming important to improve the microstructure thereof to improve the rate capability and cycle performance and to introduce materials with high specific capacity to improve the specific capacity. Chinese patent CN106252662a discloses a low expansion graphite negative electrode, which is obtained by mixing flake graphite with D50 of about 5-10 μm, an easily graphitizable binder and a graphitizing catalyst, then treating at 300-800 ℃ for 10-20 hours under an inert atmosphere, cooling to room temperature, then treating at 2800-3200 ℃ for 24-48 hours under an inert atmosphere, screening to obtain low expansion graphite, and applying to a lithium ion battery negative electrode. The preparation process of the expanded graphite anode material is complex, the required temperature is too high, the equipment requirement is high, the energy consumption is high, and more importantly, the specific capacity of the obtained material is not greatly improved. Chinese patent CN110544766A discloses an expanded graphite nano-silicon composite negative electrode material and a preparation method thereof, and the invention mixes the expanded graphite, nano-silicon suspension and a coated carbon source, and then heats and carbonizes the mixture to obtain the silicon in the expanded graphite nano-silicon composite negative electrode material, so that the specific capacity of the whole negative electrode can be improved, and meanwhile, the volume effect of the silicon in the charging and discharging processes can be relieved by the expanded graphite, and the cycle life can be prolonged. However, the method needs to prepare the expanded graphite in advance, the whole synthesis route is complicated, and the nano-silicon suspension is high in current price and is not suitable for large-scale production. Chinese patent CN109616668A discloses a method for preparing manganese oxide-small-sized micro-diffusion layer natural graphite, which comprises mixing natural crystalline flake graphite with concentrated sulfuric acid, adding potassium permanganate for oxidation intercalation, washing to ph=7 after the reaction, and finally, adding nitrogen gasAnnealing at 500-800 deg.c to obtain target material. The multiplying power performance and the cycle performance of the obtained manganese oxide-small-size micro-diffusion layer natural graphite negative electrode are obviously improved compared with those of natural crystalline flake graphite, but due to the use of concentrated sulfuric acid as an intercalation agent, a part of sulfur element residues exist in the obtained negative electrode material, an intermediate product of sulfur during charging and discharging can be dissolved into electrolyte, the viscosity of the electrolyte is increased, the ion conductivity is reduced, and meanwhile, the combination product Li of the sulfur and lithium ions is obtained 2 S n The cathode has electronic insulation and is insoluble in electrolyte, and the electric conductivity of the whole cathode is reduced by depositing on a conductive framework, so that the performance of the whole cathode is poor, and the cathode is not suitable for being applied to the field of lithium ion batteries at present.
The commercial graphite cathode has low specific capacity, poor multiplying power performance and poor cycle performance, and the existing scheme for modifying graphite has the problems of complex operation, high cost, high equipment requirement, difficulty in expanded production, insignificant product performance improvement, defects of components of products and the like, and seriously hinders the development of high-performance lithium ion batteries. Therefore, the design and development of the lithium ion battery anode material with simple preparation process, low requirement on required equipment, small environmental pollution, high specific capacity of products and excellent rate performance and cycle performance have been unprecedented for further development and application of the lithium ion battery.
Disclosure of Invention
The first object of the invention is to provide a preparation method of a composite modified graphite anode material, the second object of the invention is to provide a composite modified graphite anode material, the third object of the invention is to provide a lithium battery anode material, and the fourth object of the invention is to provide a lithium ion battery.
The first object of the invention is realized in that a preparation method of the composite modified graphite anode material comprises the following steps:
1) Mixing graphite with an oxidant and an intercalation agent according to a certain mass ratio to obtain a mixed solution;
2) Stirring the mixed solution at constant temperature to react and obtain an intercalation product;
3) Repeatedly washing the product with deionized water until the pH value of the filtrate is between 5 and 7, drying the washed intercalation product, calcining in inert atmosphere, heating to the target temperature, and preserving heat for a certain time to obtain the target product.
The second object of the invention is to provide a composite modified graphite negative electrode material, which is prepared by the preparation method of the composite modified graphite negative electrode material, wherein the composite modified graphite negative electrode material is manganese oxide loaded sulfur-free micro-expanded graphite.
The third object of the invention is to provide a lithium battery anode material, which comprises the composite modified graphite anode material.
The fourth object of the invention is to provide a lithium ion battery, which comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the negative electrode comprises the composite modified graphite negative electrode material.
The invention adopts synchronous oxidation intercalation technology, takes graphite material, oxidant (namely potassium permanganate) and intercalation agent (namely proper acid) as raw materials, and utilizes the strong oxidizing property of the potassium permanganate and the intercalation characteristic of the acid to rapidly prepare manganese dioxide (MnO) 2 ) And (3) coating oxidized intercalated graphite, and calcining the obtained intercalated product at high temperature to prepare the manganese monoxide (MnO) -loaded sulfur-free micro-expanded graphite. Compared with the prior art, the method has the following advantages:
1. the preparation method of the modified graphite has the advantages of wide raw material sources, low cost, simple preparation process, high repeatability, low equipment requirement and easy mass production.
2. According to the preparation method, the sulfuric acid without sulfur is used as the intercalation agent, so that the prepared material is free of sulfur, and the defect of poor cycle performance caused by sulfur element when the traditional sulfur-containing expanded graphite is used for a negative electrode of a lithium ion battery can be effectively avoided.
3. The high-temperature calcination temperature in the preparation method is 500-950 ℃, at which the intercalation agent acid molecules and acid radicals in the graphite sheets can be decomposed into gas, and the generated driving force can expand the spacing between the graphite sheets, so that the diffusion resistance of lithium ions in the anode material is reduced, and the multiplying power performance of the whole composite material is improved.
4. Compared with the method of directly placing the expandable graphite at high temperature in the traditional scheme, the preparation method provided by the invention has the advantages that the expansion degree of the obtained material is low and controllable, the compaction density is relatively high when the negative electrode plate is prepared, the improvement of the volume specific capacity of the electrode plate is facilitated, and the preparation method is more feasible in the field of lithium ion batteries.
5. The calcination process in the preparation method adopts inert gas for protection, so that the graphite material can be effectively prevented from being oxidized and combusted at high temperature, ash content in the product is reduced, and side reaction in the use process is avoided.
6. In the preparation method, the manganese dioxide which is a concomitant product in the oxidation intercalation stage can be converted into manganese monoxide (MnO) at high temperature, and the existence of the manganese monoxide with high specific capacity can effectively improve the specific capacity of the composite anode material.
7. In the preparation method, manganese dioxide reacts with graphite in the process of being converted into manganese monoxide, carbon atoms on a graphite sheet layer are consumed, and pore forming is carried out on the graphite sheet layer, so that the obtained nano-pores are beneficial to the diffusion of lithium ions among the graphite sheet layers, the transmission path of the lithium ions in the lithium intercalation-deintercalation process is shortened, and the multiplying power performance of the obtained anode material is further enhanced.
8. In the preparation method, the expansion of graphite and the loading of manganese oxide occur simultaneously and are compounded, and compared with the method of preparing the expanded graphite and then compounding the expanded graphite with the manganese oxide in other schemes, the preparation method is simpler and more convenient.
In conclusion, the method provided by the invention has the advantages of high operability, easiness in production, low equipment requirement and good repeatability, and the prepared material has the characteristics of high specific capacity, excellent rate capability and excellent cycle performance; compared with other graphite modification methods, the graphite modification method has the advantages of wide raw material sources, low price, simple preparation conditions, high repeatability and easiness in large-scale production; compared with modified graphite anode materials prepared by other modification methods, the composite modified graphite anode material with the nano holes and moderately enlarged graphite sheet layer spacing has higher specific capacity, excellent multiplying power performance and longer cycle stability, and is more easy to be used in the field of commercial lithium ion batteries.
Drawings
FIG. 1 is an XRD pattern of unmodified graphite of comparative example 1;
FIG. 2 is an SEM image of unmodified graphite of comparative example 1;
FIG. 3 is a graph of the rate performance data for the unmodified graphite of comparative example 1;
FIG. 4 is a graph of 1C cycle data for unmodified graphite of comparative example 1;
FIG. 5 is an XRD pattern of the composite modified graphite anode material prepared in example 1;
FIG. 6 is an SEM image of a composite modified graphite anode material prepared in example 1;
FIG. 7 is a graph showing the magnification data of the composite modified graphite anode material prepared in example 1;
FIG. 8 is an XRD pattern of the composite modified graphite anode material prepared in example 2;
FIG. 9 is an SEM image of a composite modified graphite anode material prepared in example 2;
FIG. 10 is a graph of magnification data of the composite modified graphite anode material prepared in example 2;
FIG. 11 is a graph of 1C cycle data for the composite modified graphite negative electrode material prepared in example 2;
FIG. 12 is an XRD pattern of the composite modified graphite anode material prepared in example 3;
FIG. 13 is an SEM image of a composite modified graphite anode material prepared in example 3;
fig. 14 is a graph of magnification data of the composite modified graphite anode material prepared in example 3.
Detailed Description
The invention is further illustrated, but is not limited in any way, by the following examples, and any alterations or substitutions based on the teachings of the invention are within the scope of the invention.
The invention discloses a preparation method of a composite modified graphite anode material, which comprises the following steps:
1) Mixing graphite with an oxidant and an intercalation agent according to a certain mass ratio to obtain a mixed solution;
2) Stirring the mixed solution at constant temperature to react and obtain an intercalation product;
3) Repeatedly washing the intercalation product with deionized water until the pH value of the filtrate is between 5 and 7, drying the washed intercalation product, calcining in inert atmosphere, heating to the target temperature, and preserving heat for a certain time to obtain the target product.
In the step 1, the mass ratio of graphite to oxidant to intercalating agent is 1:1-10:1-10.
The graphite is one or a mixture of more than one of natural graphite, artificial graphite, spherical graphite and graphite intermediate phase, the particle size of the graphite is 1-60 mu m, and the purity is 80-99.9wt%; the oxidant is potassium permanganate, and the purity is 98-99.99%; the intercalation agent is one or a mixture of more of nitric acid, phosphoric acid, perchloric acid, formic acid and acetic acid, and the concentration is 50-98%.
In the step 2, the reaction temperature of the stirring reaction is 10-60 ℃, and the reaction time is 30 min-24 h.
In the step 2, the stirring speed is 100-3000 rpm.
In the step 3, the drying temperature of the washed intercalation product is 30-80 ℃ and the drying time is 6-24 h.
In the step 3, the temperature rising rate in the calcination process is 1-20 ℃/min, the inert atmosphere is one or a mixture of more of nitrogen, argon and helium, the heat preservation temperature in the calcination heat preservation is 500-950 ℃, and the heat preservation time is 30-48 h.
The composite modified graphite negative electrode material is manganese oxide loaded sulfur-free micro-expanded graphite and has nano holes and moderately enlarged graphite lamellar spacing.
The invention relates to a lithium ion battery anode material, which comprises the composite modified graphite anode material.
The invention relates to a lithium ion battery, which comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the negative electrode comprises the composite modified graphite negative electrode material.
The invention is further illustrated by the following examples.
Example 1
An artificial graphite anode material with a particle size of 20 μm and a purity of 99wt% was used with 99.99% potassium permanganate and 50% nitric acid according to 1g: 0.4 g:4mL, stirring at a speed of 1000rpm at 40 ℃ for 12h, washing and filtering the resultant solid by using deionized water at room temperature until the pH of the filtrate is 5, drying the resultant solid at 30 ℃ for 24h, heating to 650 ℃ at 1 ℃/min in a nitrogen atmosphere in a tube furnace for heat preservation for 2h, and calcining to obtain the composite modified graphite negative electrode material, namely the manganese oxide-loaded sulfur-free micro-expanded graphite for the lithium ion battery negative electrode material.
Example 2
An artificial graphite negative electrode material with the grain diameter of 20 mu m and the purity of 89wt percent is used, and the mixture of 99 percent of potassium permanganate and 70 percent of concentrated nitric acid is used according to the following ratio of 1g:1.46g:4mL, stirring at a speed of 1000rpm at 40 ℃ for 12h, washing and filtering the resultant solid by using deionized water at room temperature until the pH value of the filtrate is 6, drying the resultant solid at 60 ℃ for 12h, heating to 650 ℃ at 10 ℃/min in a tubular furnace under argon atmosphere, and preserving heat for 12h for calcination, thus obtaining the composite modified graphite anode material.
Example 3
An artificial graphite negative electrode material with the grain diameter of 20 mu m and the purity of 80wt percent is used, and 98 percent of potassium permanganate and 98 percent of concentrated nitric acid are used according to the following ratio of 1g: 3.067 g:4mL, stirring at 1000rpm for 12h at 40 ℃, washing and filtering the resultant solid by using deionized water at room temperature until the pH value of the filtrate is 7, drying the resultant solid at 80 ℃ for 6 hours, heating to 650 ℃ at 20 ℃/min in a helium atmosphere in a tube furnace, and preserving heat for 12h for calcination to obtain the composite modified graphite anode material.
Example 4
The natural graphite anode material with the grain diameter of 1 mu m and the purity of 90wt percent is used for preparing the anode material, and 99.99 percent of potassium permanganate and 90 percent of formic acid are used for preparing the anode material according to the following formula 1g: 6.357 g: mixing 8mL, stirring at 2000rpm for 24h at 10 ℃, washing and filtering the resultant solid by using deionized water at room temperature until the pH of the filtrate is 5, drying the resultant solid at 30 ℃ for 24h, heating to 950 ℃ at 5 ℃/min in a tubular furnace under argon atmosphere, and preserving heat for 30min for calcination to obtain the composite modified graphite anode material.
Example 5
A spherical graphite anode material with a particle size of 20 μm and a purity of 95wt% was used together with 99.99% potassium permanganate and 90% acetic acid according to 1g: 7.471g:10 mixing the materials in the ratio of mL, stirring the materials at 100rpm for 18h at 50 ℃, washing and filtering the resultant solid by using deionized water at room temperature until the pH value of the filtrate is 6, drying the resultant solid at 40 ℃ for 18h, heating the resultant solid to 850 ℃ at 5 ℃/min in a tubular furnace under argon atmosphere, and preserving heat for 1.5 h to calcine the resultant solid to obtain the composite modified graphite anode material.
Example 6
Graphite intermediate phase negative electrode material with the purity of 85wt% and the particle size of 60 mu m is used together with 99% potassium permanganate and 90% phosphoric acid according to the following ratio of 1g: 7.471g:10 mixing the materials in the ratio of mL, stirring at 600rpm for 30min at 60 ℃, washing and filtering the resultant solid by using deionized water at room temperature until the pH value of the filtrate is 7, drying the resultant solid at 50 ℃ for 15h, heating to 500 ℃ at 15 ℃/min in a helium atmosphere in a tube furnace, and preserving heat for 48 and h to calcine to obtain the composite modified graphite anode material.
Example 7
Spherical graphite anode material with the particle size of 30 mu m and the purity of 90wt percent is used together with 99.99 percent of potassium permanganate and 98 percent of perchloric acid according to the following weight percentage of 1g: 1.312g: mixing 3mL, stirring at a speed of 3000rpm for 8 hours at 55 ℃, washing and filtering the resultant solid by using deionized water at room temperature until the pH value of the filtrate is 7, drying the resultant solid at 60 ℃ for 12 hours, heating to 750 ℃ at 12 ℃/min in a helium atmosphere in a tube furnace, and preserving heat for 2h for calcination to obtain the composite modified graphite anode material.
Example 8
The invention provides a lithium ion battery, which adopts the composite modified graphite anode material in the embodiment 1.
A lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the positive electrode is composed of one or a mixture of more of lithium cobaltate, lithium manganate, lithium nickel manganate, lithium iron phosphate, ternary positive electrode materials and lithium-rich manganese-based positive electrode materials, the negative electrode is prepared from the composite modified graphite negative electrode material in the embodiment 1, the diaphragm is one of a polyethylene film, a polypropylene film and a polypropylene/polyethylene/polypropylene composite film, and the electrolyte is lithium hexafluorophosphate (LiPF 6 ) Is an electrolyte of a main lithium salt.
Comparative example 1:
this comparative example is an artificial graphite negative electrode material of 20 μm which is unmodified graphite used in example 1.
Performance test of composite modified graphite negative electrode Material in examples 1-3 and unmodified graphite of comparative example 1
1. The detection method comprises the following steps:
1. XRD, SEM test: XRD and SEM characterization are respectively carried out on the composite modified graphite anode materials in the examples 1-3 and the unmodified graphite in the comparative example 1, wherein the scanning range of XRD is 5-90 degrees; .
2. Electrochemical testing: the composite modified graphite anode materials of examples 1-3 and the unmodified graphite of comparative example 1 were tested for rate performance and cycle performance by the following specific methods: assembled in a glove box (water/oxygen content less than 0.3 ppm) using a button half cell test (i.e., lithium sheet as reference electrode/counter electrode), using a conventional electrolyte (i.e., 1M LiPF) 6 EC/DMC/EMC (1:1:1)), the assembled CR2025 coin cell was tested after standing at room temperature for 12h, with a charge-discharge voltage ranging from 0.005 to 3V. The multiplying power test sequentially carries out constant current charge and discharge at 0.1, 0.2, 0.5, 1, 3, 5 and 0.1 and C current, and the cycle performance test carries out constant current charge and discharge at 1C current. Here, 1C current is defined as 372 mA/g.
2. Detection results and analysis:
1. the XRD pattern (fig. 1) of the unmodified graphite of comparative example 1 reflects its good graphite structure and no other impurity phases are present; SEM images of unmodified graphite (fig. 2) reflect that the graphite sheets are tightly bound together and that the surfaces of the graphite sheets are smooth and void-free.
The rate capability data for unmodified graphite (FIG. 3) shows that the reversible specific capacity of graphite at 0.1C is about 360 mAh/g and at 1C is about 80 mAh/g (retention of about 22%). The 1C cycle performance data of fig. 4 shows that the specific capacity of the unmodified graphite after 50 cycles is only 33.2 mAh/g, and the capacity retention is about 35.8%.
2. The XRD pattern (fig. 5) of the composite modified graphite negative electrode material prepared in example 1 confirmed that the resultant material contained only graphite and MnO, and the SEM pattern (fig. 6) of the composite modified graphite negative electrode material prepared in example 1 showed that the tightly bound lamellar structure of graphite in the resultant material was modified into an organ-like structure, the lamellar spacing was enlarged, mnO was attached to the surface of the micro-expanded graphite, and significant nano-scale etching holes were formed in the graphite lamellar around the MnO particles.
The ratio performance data (figure 7) of the composite modified graphite negative electrode material prepared in the example 1 shows that the reversible specific capacity of the composite modified graphite negative electrode material is about 375 mAh/g at 0.1C, which shows that the specific capacity of the obtained composite modified graphite negative electrode material is improved compared with that of the unmodified graphite negative electrode material; the reversible specific capacity at 1C is about 220 mAh/g (the retention rate is about 58.6%), which shows that the obtained composite modified graphite negative electrode material has improved rate capability compared with the unmodified graphite negative electrode material.
3. The XRD pattern (fig. 8) of the composite modified graphite negative electrode material prepared in example 2 confirmed that the resultant material contained only graphite and MnO, while the SEM pattern (fig. 9) of the composite modified graphite negative electrode material prepared in example 2 showed that the tightly bound lamellar structure of graphite in the resultant material was modified into an accordion-like structure, the lamellar spacing was enlarged, the MnO adhering to the surface of the micro-expanded graphite lamellar layer was significantly increased and particles were enlarged as compared with the material prepared in example 1, and another part of MnO particles was in the middle of the interlayer of the graphite lamellar layer.
The ratio performance data (figure 10) of the composite modified graphite negative electrode material prepared in the example 2 shows that the reversible specific capacity of the composite modified graphite negative electrode material is about 413 mAh/g in 0.1C, which shows that the specific capacity of the obtained composite modified graphite negative electrode material is improved compared with that of the non-composite modified graphite negative electrode material; the reversible specific capacity at 1C is about 280 mAh/g (the retention rate is about 67.8%), which shows that the obtained composite modified graphite negative electrode material has improved rate capability compared with the unmodified graphite negative electrode material. The specific capacity of the composite modified graphite negative electrode material prepared in example 2 (fig. 11) after 50 circles of 1C circulation is 203.3 mAh/g, and the capacity retention rate is about 68.1%, which indicates that the cycle performance of the obtained composite modified graphite negative electrode material is improved compared with that of the unmodified graphite negative electrode material.
4. XRD patterns in the composite modified graphite anode material prepared in example 3 (fig. 12) confirm that only graphite and MnO are contained in the resultant material, and SEM patterns (fig. 13) of the composite modified graphite anode material prepared in example 3 indicate that MnO in the resultant material forms a network-like structure and encapsulates a part of micro-expanded graphite.
The data (fig. 14) of the rate performance of the composite modified graphite negative electrode material prepared in example 3 shows that the reversible specific capacity of the composite modified graphite negative electrode material is about 424 mAh/g at 0.1C, which indicates that the specific capacity of the obtained composite modified graphite negative electrode material is improved compared with that of the unmodified graphite negative electrode material; the reversible specific capacity at 1C is about 241 mAh/g (the retention rate is about 57.0%), which indicates that the obtained composite modified graphite negative electrode material has improved rate capability compared with the unmodified graphite negative electrode material.
Taken together, XRD, SEM tests indicate that: compared with a control group, namely unmodified graphite, the interlayer spacing of the composite modified graphite anode material prepared by the method is obviously increased, and obvious nano-scale etching holes are formed in a graphite sheet layer and manganese oxide is loaded; electrochemical tests showed that: the electrochemical performance, such as reversible specific capacity, multiplying power performance and cycle performance, of the composite modified graphite negative electrode material prepared by the method is obviously superior to that of the unmodified graphite serving as a control group, that is, the preparation method of the modified graphite negative electrode material provided by the invention can obviously improve the electrochemical performance of graphite.
Claims (3)
1. A preparation method of a composite modified graphite negative electrode material is characterized in that an artificial graphite negative electrode material with the grain diameter of 20 mu m and the purity of 89wt percent is mixed with 99 percent of potassium permanganate and 70 percent of concentrated nitric acid according to the proportion of 1g to 1.46g to 4mL, then the mixture is stirred for 12 hours at the speed of 1000rpm at the temperature of 40 ℃, then deionized water is used for cleaning and filtering the resultant solid at room temperature until the pH value of the filtrate is 6, the resultant solid is dried for 12 hours at the temperature of 60 ℃, and then the temperature is raised to 650 ℃ at the speed of 10 ℃/min in a tubular furnace for heat preservation for 12 hours for calcination, thus obtaining the composite modified graphite negative electrode material.
2. The composite modified graphite negative electrode material obtained by the preparation method according to claim 1, which is characterized in that the composite modified graphite negative electrode material is manganese oxide loaded sulfur-free micro-expanded graphite and has nano holes and moderately enlarged graphite lamellar spacing.
3. A lithium ion battery prepared from the composite modified graphite negative electrode material according to claim 2, comprising a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the negative electrode comprises the composite modified graphite negative electrode material.
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