CN103050668A - Method for preparing Si/C composite cathode material for lithium ion battery - Google Patents

Abstract

The invention discloses a method for preparing a silicon-carbon (Si/C) composite negative electrode material for a lithium-ion battery. Graphite and metal salt additives are uniformly dispersed in concentrated sulfuric acid solution; micro-oxidized graphite is prepared through an oxidation reaction; the obtained Micro-oxidized graphite and silicon source are dispersed in a solution containing carbon source and organic additives, ultrasonically dispersed, stirred and mixed to obtain a suspension, evaporated to dryness, and heat-treated at 600-1000°C to obtain the product; The method is simple and easy to implement, and has a high degree of practicality. The prepared composite material has the advantages of good shape, high tap density, high capacity, good cycle performance and rate performance, and the like.

Description

A kind of preparation method of Si/C composite negative electrode material of lithium ion battery

technical field

The invention belongs to the field of lithium-ion battery materials and preparation methods thereof, and relates to a lithium-ion battery silicon-carbon composite negative electrode material and a preparation method thereof.

Background technique

Lithium-ion batteries are widely used in portable electronic devices and electric vehicles due to their inherent advantages, such as high energy density, high operating voltage, long service life, and portability. Due to its limited capacity (372mAh·g ^-1 ), commercial lithium-ion battery anode material graphite cannot meet the needs of high energy density batteries. Therefore, the development of new anode materials to replace graphite has attracted much attention.

Silicon-based materials are considered to be the best materials for improving the performance of lithium-ion battery anode materials due to their highest specific capacity (4200mAh·g ^-1 ) and low lithium-extraction potential (0.02~0.6V vs. Li ⁺ /Li) one. However, the severe volume expansion and contraction (>300%) of the silicon anode during the process of lithium intercalation and deintercalation results in the destruction of the material structure and mechanical crushing, thus limiting its commercial application. In order to improve these problems, at present, silicon nanometerization, silicon and metal alloying, preparation of silicon thin films, and compounding of silicon with active or inactive substrates are mainly used to improve its performance. Among them, silicon-carbon composite materials have better applications. prospect. In silicon-carbon composite materials, carbon is a mixed conductor of ions and electrons. The "buffer skeleton" composed of carbon materials can compensate the volume expansion of silicon particles, and the volume change is small during charging and discharging, which can maintain the structural stability and good performance of electrode materials. The electrical conductivity of silicon-based materials is improved. In addition, the lithium intercalation potential of carbon materials is similar to that of silicon, and the material capacity loss is relatively small.

Contents of the invention

The purpose of the present invention is to provide a simple and rapid method for preparing a silicon-carbon composite negative electrode material for a lithium-ion battery with good appearance, high tap density, high capacity, good cycleability and rate performance.

The invention provides a method for preparing a Si/C composite negative electrode material for a lithium ion battery. The method is to uniformly disperse graphite and metal salt additives in a concentrated sulfuric acid solution; React at 32~38°C, dilute the reaction solution with deionized water after the reaction is complete, or add an oxidant to react at no more than 2°C, then react at 32~38°C, then dilute the reaction solution with deionized water, and then Continue the reaction at 92~98°C. After the reaction is completed, continue to dilute the reaction solution with deionized water and add hydrogen peroxide; separate the solid and liquid of the final diluted reaction solution, and wash the separated solid with dilute hydrochloric acid and deionized water to pH The value is 3~4, and micro-oxidized graphite is obtained after drying; the obtained micro-oxidized graphite and silicon source are dispersed in a solution containing carbon source and organic additives, ultrasonically dispersed, stirred and mixed to obtain a suspension, and the suspension is evaporated After drying, conduct heat treatment at 600~1000°C to obtain it; wherein the mass ratio of silicon source:graphite:carbon source pyrolysis is x:y:(1-x-y), where 0<x<1 , 0<y<1; the added amount of silicon source accounts for 5~30wt.% of the Si/C composite material, and the added amount of carbon source is calculated as 10~50wt.% of the Si/C composite material based on the pyrolytic carbon obtained after heat treatment .

The preparation of micro-oxidized graphite in the above preparation method: first add an oxidant to react at no higher than 2°C for 0.3~0.8h, and then react at 32~38°C for 1~3h; or first add an oxidant at a temperature not higher than 2°C React for 0.3~0.8h, then react at 32~38°C for 1~3h, and then continue to react at 92~98°C for 1~3h; choose the way of oxidation reaction according to the degree of oxidation of graphite.

The amount of hydrogen peroxide used is 0.5 to 10 times the mass of graphite; the amount of deionized water used is 1 to 5 times the volume of concentrated sulfuric acid.

The graphite includes: one or more of artificial graphite, natural graphite or graphitized mesocarbon microspheres.

The silicon source includes: one or more of nano-silicon powder, silicon oxide powder, carbon-coated nano-silicon powder, and carbon-coated silicon oxide powder, wherein the silicon oxide powder is SiO _x , where O<x≤2.

The carbon source includes: one or more of graphene, phenolic resin, urea-formaldehyde resin, epoxy resin, polyethylene, perchlorethylene, polyvinyl alcohol, pitch, glucose, citric acid or sucrose.

The oxidant is one or more of hydrogen peroxide, potassium dichromate or potassium permanganate; wherein the amount of hydrogen peroxide is 0.5 to 20 times the mass of graphite, and the amount of potassium dichromate is 1.5 to 2.5 times the mass of graphite. times, the dosage of potassium permanganate is 0.5~4 times of graphite mass.

The heat treatment is performed in an argon or nitrogen environment for 1-6 hours.

The solvent in the solution containing the carbon source and the organic additive is one or more of deionized water, tetrahydrofuran, acetone, pyrrole, ethyl acetate or absolute ethanol.

The solid-liquid separation refers to filtering and centrifuging the diluted solution after standing; the method of evaporating the suspension to dryness includes one or more of evaporative solidification, vacuum drying or spray drying.

The metal salt additive is one or more of sodium nitrate or potassium nitrate.

The organic additives include: polyacrylamide, polyethylene glycol, propylene glycol, polyvinyl acetate, N-N dimethylacetamide, sodium alginate, sodium dodecylbenzenesulfonate, hexadecylamine bromide Or one or more of absolute ethanol.

The evaporation solidification temperature is 70-120°C; the spray drying temperature is 170-200°C; the vacuum drying temperature is 60-90°C.

Technical features of the present invention: use liquid phase treatment to prepare micro-oxidized graphite, which has a good shape, and the obtained micro-oxidized graphite has a porous structure, which establishes a good foundation for the combination with silicon source; on this basis, Si/C negative electrode material is prepared , the prepared Si/C composite material has a good morphology, the silicon source can be better combined with graphite, and a uniform carbon coating layer is formed on the surface; this structure is conducive to the increase of the strength, toughness and vibration of the material. Solid density is improved; at the same time, the method has the advantages of strong adaptability to raw materials, simple operation and the like.

The beneficial effects that the present invention has are:

The micro-oxidized graphite composite silicon-carbon composite negative electrode material of the present invention has the following advantages: through micro-oxidation treatment of graphite, its morphology and surface activity are changed, pores are reserved for the embedding of silicon, and the combination with small particle silicon sources is established. Base. On this basis, part of the silicon source is embedded in the pores of the micro-graphite oxide, and at the same time, it is better combined with the micro-graphite oxide. The carbon source forms a dense and uniform coating layer on the surface of the composite material through pyrolysis. During the pyrolysis process, the carbon source will not be in a pure liquid state, and will not fill all the remaining pores in the composite of silicon and micro-graphite oxide, forming a good "buffer skeleton". Electrical conductivity. Therefore, the prepared composite material can significantly improve the strength and toughness of the Si/C composite material, enhance the structural stability of the material, alleviate the collapse of the electrode structure of the silicon-based negative electrode material during the charge and discharge process to a certain extent, and improve the Si /C composites are electrically conductive, thereby enhancing the cycle stability and rate performance of the material.

The micro-oxidized graphite obtained by liquid phase oxidation has a porous structure, so it provides better composite pores for the composite with silicon. On the basis of carbon source coating, spherical or irregular particles are obtained, which improves the tap density of the material. As a result, the energy density is also improved to a certain extent.

In Si/C composite materials, the mass ratio of silicon source:graphite:pyrolytic carbon=x:y:(1-xy), in which the capacity of silicon source is higher (such as nano silicon powder is 4200mAh·g ^-1 ), is the decision The key active material of the capacity of the composite material, therefore, the high-capacity Si/C composite negative electrode material can be obtained by adjusting the silicon source component and its proportion in the composite material.

Description of drawings

[Figure 1] is the SEM image of natural graphite before and after liquid phase micro-oxidation, a is the SEM image of natural graphite, and b is the SEM image of micro-oxidized natural graphite.

[Fig. 2] is the SEM figure of Example 2 of the present invention: a is the SEM figure of nano-silicon powder in Example 2, b is the SEM figure of nano-silicon powder after carbon coating in Example 2; c is the SEM figure of Example 2 The SEM image of the prepared Si/C composite anode material.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. The following implementation examples are intended to illustrate the present invention rather than to further limit the present invention.

Example 1

Measure _120mL of concentrated _H2SO4 solution, add an appropriate amount of potassium nitrate and 10g of natural graphite to the solution, place it in an ice bath at 0°C, and stir it magnetically for 0.5h; weigh a certain amount of 5~20g of potassium permanganate and slowly Add it to the above-mentioned feed liquid, react at a medium temperature of 38°C for 1.5h, slowly add a large amount of deionized water to dilute to about 1L, and control the temperature of the feed liquid below 100°C; filter after standing, and use a large amount of absolute ethanol and Wash with deionized water until the pH value is 3~4, and dry for later use. The morphology of graphite before and after oxidation is shown in Figure 1. Weigh 1g of nano-silica powder, 2g of micro-oxidized graphite, and 5g of glucose according to the design capacity of the composite material, dissolve them in an appropriate amount of deionized water, use 0.15g of hexadecyl ammonium bromide as a dispersant, ultrasonicate for 1h, stir evenly, and then carry out vacuum drying , the obtained solid is transferred to a temperature-programmed furnace and subjected to a high-temperature treatment at 800° C. for 1 to 6 hours in a nitrogen or argon atmosphere to obtain a Si/C composite negative electrode material.

Example 2

Measure 200mL of concentrated H ₂ SO ₄ solution, add appropriate amount of potassium nitrate and 5g of natural graphite powder to the solution, place it in an ice bath at 0°C, and stir magnetically for 0.5h; weigh 5~20g of potassium permanganate and slowly add Into the above feed liquid, control the reaction temperature below 2°C, react at a medium temperature at 35°C for 2 hours, slowly add a large amount of deionized water to dilute to about 0.6L, and control the temperature of the feed liquid below 100°C; then at 95°C After high-temperature reaction for 2 hours, add appropriate amount of hydrogen peroxide and 400-800 mL of deionized water, centrifuge, wash with a large amount of absolute ethanol and deionized water until the pH value is 3-4, freeze-dry and set aside. 10% glucose pyrolytic carbon was coated on the surface of nano-silicon, and the morphology before and after coating was shown in Figure 2(a) and Figure 2(b). Weighed 1g nano-silicon powder, 2g micro-graphite oxide, And 1.67g of glucose was dissolved in an appropriate amount of deionized water, 0.15g of sodium dodecylbenzenesulfonate was used as a dispersant, ultrasonicated for 1h, stirred evenly, and then spray-dried, and the obtained solid was transferred to a temperature-programmed furnace in a nitrogen or argon atmosphere The Si/C composite anode material was obtained after a high temperature treatment at 800 °C for 1~6 h, as shown in Figure 2(c).

Example 3

Measure the concentrated H ₂ SO ₄ solution, add appropriate amount of sodium nitrate and 10g of natural graphite powder to the solution, place it in an ice bath at 0°C, and stir it magnetically for 0.5h; weigh 15~25g of potassium dichromate and slowly add it to In the above feed solution, react at a medium temperature of 38°C for 1.5h, slowly add a large amount of deionized water to dilute to about 1L, and control the temperature of the feed liquid below 100°C; filter after standing, and wash with a large amount of absolute ethanol and deionized water until the pH value is 3~4, dry for later use. Weigh nano-silica powder, micro-graphite oxide, and phenolic resin according to the design capacity of the composite material, dissolve them in an appropriate amount of absolute ethanol, ultrasonicate for 1 hour, stir for 2 hours, and then evaporate to dryness at 80°C. The Si/C composite negative electrode material is obtained after a high temperature treatment at 800° C. for 1 to 6 hours in a nitrogen or argon atmosphere.

Claims (10)

1. A preparation method of Si/C composite negative electrode material for lithium ion battery, characterized in that graphite and metal salt additives are uniformly dispersed in the concentrated sulfuric acid solution; first add oxidizing agent to react at no higher than 2°C, and then React at 32~38°C, dilute the reaction solution with deionized water after the reaction is complete, or add an oxidant to react at no more than 2°C, then react at 32~38°C, then dilute the reaction solution with deionized water, and then in Continue the reaction at 92~98°C. After the reaction is completed, continue to dilute the reaction solution with deionized water and add hydrogen peroxide; separate the solid and liquid of the final diluted reaction solution, and wash the separated solid with dilute hydrochloric acid and deionized water to the pH value 3~4, micro-graphite is obtained after drying; the obtained micro-graphite and silicon source are dispersed in a solution containing carbon source and organic additives, ultrasonically dispersed, stirred and mixed to obtain a suspension, and the suspension is evaporated to dryness Afterwards, heat treatment at 600~1000°C to obtain it; wherein the mass ratio of silicon source:graphite:carbon source pyrolysis pyrolysis carbon is x:y:(1-x-y), where 0<x<1, 0<y<1; the added amount of silicon source accounts for 5~30wt.% of the Si/C composite material, and the added amount of carbon source is calculated as 10~50wt.% of the Si/C composite material based on the pyrolytic carbon obtained after heat treatment. 2. The preparation method according to claim 1, characterized in that the oxidizing agent is added to react at no higher than 2°C for 0.3~0.8h, and then reacted at 32~38°C for 1~3h; Add an oxidant to react at 2°C for 0.3~0.8h, then react at 32~38°C for 1~3h, and then continue to react at 92~98°C for 1~3h. 3. the preparation method according to claim 1, is characterized in that, described hydrogen peroxide consumption is 0.5～10 times of graphite quality; Deionized water consumption is 1～5 times of the vitriol oil volume. 4. The preparation method according to claim 1, wherein the graphite comprises: one or more of artificial graphite, natural graphite or graphitized mesocarbon microspheres. 5. The preparation method according to claim 1, wherein the silicon source comprises: one or more of nano-silicon powder, silicon oxide powder, carbon-coated nano-silicon powder, and carbon-coated silicon oxide powder. species, wherein the silica powder is SiO _x , 0<x≤2; the carbon source includes: graphene, phenolic resin, urea-formaldehyde resin, epoxy resin, polyethylene, perchlorethylene, polyvinyl alcohol, asphalt, glucose , one or more of citric acid or sucrose. 6. The preparation method according to claim 1, wherein the oxidant is one or more of hydrogen peroxide, potassium dichromate or potassium permanganate. 7. The preparation method according to claim 1, wherein the heat treatment is performed in an argon or nitrogen environment for 1-6 hours. 8. preparation method according to claim 1, is characterized in that, the solvent in the solution that is dissolved with carbon source and organic additive is deionized water, tetrahydrofuran (THF), acetone, pyrrole, ethyl acetate or dehydrated alcohol. one or several. 9. The preparation method according to claim 1, characterized in that, the solid-liquid separation is filtering or centrifuging after the diluted solution is allowed to stand; the method of evaporating the suspension to dryness includes evaporative solidification, vacuum drying or spraying One or more of the dry. 10. The preparation method according to claim 1, characterized in that, the metal salt additive is one or more of sodium nitrate or potassium nitrate; the organic additive comprises: polyacrylamide, polyethylene glycol One or more of alcohol, propylene glycol, polyvinyl acetate, N-N dimethylacetamide, sodium alginate, sodium dodecylbenzenesulfonate, cetyl ammonium bromide or absolute ethanol.

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