CN112028065B - SiOx-SiC-C/G silicon-carbon composite material and preparation and application thereof - Google Patents

SiOx-SiC-C/G silicon-carbon composite material and preparation and application thereof Download PDF

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CN112028065B
CN112028065B CN202010863876.4A CN202010863876A CN112028065B CN 112028065 B CN112028065 B CN 112028065B CN 202010863876 A CN202010863876 A CN 202010863876A CN 112028065 B CN112028065 B CN 112028065B
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silicon
sic
sio
composite material
graphite
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CN112028065A (en
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周昊宸
周向清
王鹏
周进辉
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Hunan Chenyu Fuji New Energy Technology Co ltd
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Abstract

The invention belongs to the field of lithium ion battery cells, and particularly discloses SiOxthe-SiC-C/G silicon-carbon composite material comprises a graphite core and SiO coated on the surface of the graphite core layer by layer in situxA layer, a SiC layer, and an amorphous carbon layer; preferably, the particle size of the graphite core is 5-15 μm; coated on SiOxThe total thickness of the layer, the SiC layer and the amorphous carbon layer is 1-5 mu m. The invention also discloses the preparation and application of the material. The invention provides a silicon-carbon composite material with a brand new structure, which takes graphite as a core, and the in-situ of the core is coated with SiOxLayer of SiOxThe layer is coated with a SiC layer in situ, and the surface of the SiC layer is further coated with an amorphous carbon layer in situ. The research of the invention finds that the material with the special structure appearance has better structure stability, capacity and cycling stability.

Description

SiO (silicon dioxide)x-SiC-C/G silicon-carbon composite material and preparation and application thereof
Technical Field
The invention belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a cathode material, in particular to a preparation method using waste carbon residue as a raw material.
Background
Fossil energy mainly comprising coal and petroleum cannot meet the requirement of sustainable development of human beings, so that the energy consumption structure is improved, and the dependence on fossil energy is reduced. Lithium ion batteries have been widely used in the fields of portable electronic devices and electric vehicles as green energy storage devices that are moving forward in science and technology, and these fields also put forward higher and higher demands on the energy density of the energy storage devices. The existing negative electrode material for the lithium ion battery is mainly graphite, and has the defect of low specific capacity, so that the energy density is difficult to further improve. Therefore, it is significant to develop a novel high-capacity anode material. Among the numerous novel anode materials, silicon-based anode materials are widely viewed. Silicon has a theoretical lithium intercalation capacity as high as 3579mAh/g, a lower discharge platform (-0.3 VvsLi/Li +) and a higher earth crust reserve, and is a key point and a hotspot in the research field of novel high-capacity cathode materials for a long time. However, when the silicon negative electrode is applied to a lithium ion battery system, there are the following problems: during the lithium embedding process of the silicon cathode, the volume expansion of up to 300 percent can occur, and during the repeated expansion and contraction processes, the material can crack, pulverize and lose electric contact with a liquid collecting body, and finally the material fails; meanwhile, a Solid Electrolyte Interface (SEI) formed in the process of lithium intercalation for the first time is cracked due to the volume change effect of silicon, a new SEI film is repeatedly formed on the exposed fresh silicon surface, and the continuous thickening and increasing of the SEI film finally cause the structural damage and the performance failure of the silicon material; in addition, the low electronic conductivity and ionic conductivity of silicon itself also limit the capacity exertion of the electrode, and seriously reduce the rate performance.
Silicon oxy compound (SiO)x，x<2) The theoretical specific capacity of the material is lower than that of a pure silicon material, but the volume effect of the material in the charging and discharging process is smaller, the application breakthrough is easier to realize, and the specific capacity of the material is still considerable compared with that of a carbon-based material. Compared with other metal oxides, the dispersive silicon micro-domains formed by SiOx in the charge-discharge process can not generate region fusion, and the formation of large-particle silicon in the cycle process is avoided, so that the SiOx has better cycle stability than other metal oxides. Further, the Si-O bond is stronger than the Si-Si bond, so that SiOxThe structural stability of (a) is superior to that of silicon. But do notFor a silicon oxide-based negative electrode with good cycling stability, the problem of low reaction activity caused by poor conductivity still exists in the charging and discharging processes, and high volume expansion still exists in the electrical cycle, so that the material is in contact with an electrolyte to generate side reaction, the material is fast in failure, and the practical application of the material is severely limited.
Disclosure of Invention
The first purpose of the invention is to provide SiO with excellent structural stability and cycling stability and brand new structural morphologyx-SiC-C/G silicon carbon composite material.
The second purpose of the invention is to provide the SiOxA preparation method of-SiC-C/G silicon-carbon composite material; in particular to a method for preparing the SiO by using waste carbon slag (the invention is also called as waste cathode active material and waste graphite)x-SiC-C/G silicon-carbon composite material.
The third purpose of the invention is to provide the SiOxApplication of-SiC-C/G silicon-carbon composite material.
The fourth purpose of the invention is to provide a composition containing the SiOx-SiC-C/G silicon carbon composite material.
SiO (silicon dioxide)xthe-SiC-C/G silicon-carbon composite material comprises a graphite core and SiO coated on the surface of the graphite core layer by layer in situxA layer, a SiC layer, and an amorphous carbon layer.
The invention provides a silicon-carbon composite material with a brand new structure, which takes graphite as a core, and the in-situ of the core is coated with SiOxLayer of SiOxThe layer is coated with a SiC layer in situ, and the surface of the SiC layer is further coated with an amorphous carbon layer in situ. The research of the invention finds that the material with the special structure appearance has better structure stability, capacity and cycling stability.
In the invention, each layer structure is in-situ tightly compounded.
Preferably, the particle size of the graphite core is 5-15 μm; coated on SiOxThe total thickness of the layer, the SiC layer and the amorphous carbon layer is 1-5 mu m.
The invention also provides the SiOx-SiC-C/G silicon carbon composite material comprising the steps of:
step (1):
carrying out first-stage roasting on a graphite material and alkali, and then washing and drying to obtain pretreated graphite;
step (2):
and coating a silicon source and a carbon source on the surface of the pretreated graphite, and then mixing the pretreated graphite with reducing metal for second-stage roasting to obtain the graphite.
The research of the invention finds that the graphite material is subjected to modification pretreatment in advance under alkali, and is innovatively roasted and reduced under reducing metal after the surface of the pretreated carbon material is coated with a silicon source and a carbon source, so that the material with the special morphology structure can be constructed in one step based on a reduction mechanism from inside to outside.
According to the method, the graphite material is pretreated under the assistance of alkali, and then the graphite material is coated with a silicon source and a carbon source and then is subjected to reduction metal-mediated thermal reduction. The graphite material is subjected to an alkali pretreatment process, and the purification of the graphite raw material can be realized; secondly, the graphite material can be subjected to a surface porous structure so as to form more contact area with the added silicon source and carbon source in the subsequent granulation process, and a composite precursor with a stable composite structure is obtained; and thirdly, in the secondary calcination process with metal participation, because of the high specific surface area of the graphite kernel, more channels can be provided for metal permeation, the calcination efficiency is improved, and the contact area of silicon and carbon formed in situ can be improved, so that the silicon carbide is formed in situ. In addition, in the secondary calcining process of metal addition, the local accumulated heat can enable the local temperature of the reaction to be higher than 2000 ℃, so that the restoration and reconstruction of the microstructure of the graphite material, particularly the retired waste graphite material, can be realized under the low-temperature condition.
The method comprises the steps of coating a silicon source and a carbon source on pretreated graphite in advance to form complete secondary particles, and tightly bonding the silicon source on the surface of the pretreated graphite by utilizing the bonding action of the additional carbon source so as to enable the highly conductive pretreated graphite particles to serve as highly conductive inner cores; in a subsequent second calcinationIn the process, the reducing metal reduces the silicon source, and because the surface of the silicon source is wrapped by the carbon source, the silicon formed in situ can rapidly react with the carbon around the silicon source to form a silicon carbide layer, and the silicon oxide (SiO) with incomplete reduction is arranged inside the silicon carbide layerx，x<2) SiO formed therebyxThe core of the-SiC-C/G silicon-carbon composite material is a purified carbon particle, and the periphery of the-SiC-C/G silicon-carbon composite material is a carbon-coated porous silicon oxide/SiC core-shell structure. The problem of volume expansion of the silicon oxide can be solved by the constraint of the porous structure and the outer layer of silicon carbide, and the silicon carbide layer can well prevent the silicon oxide from directly contacting with electrolyte, so that the occurrence of side reaction is avoided, and the coulomb efficiency of the composite material is improved. The problem of poor conductivity of the silica itself can be ensured by the outer carbon layer and the inner core of the purified graphite particles.
In the invention, the graphite material is one of natural graphite, artificial graphite, mesocarbon microbeads, coal-based coke powder, petroleum coke and needle coke; or the graphite material is a waste graphite material. The technical scheme of the invention is particularly suitable for treating waste graphite materials and realizing high-value utilization.
Preferably, the particle size of the graphite material is 8-20 μm;
preferably, the alkali is at least one of hydroxide, carbonate and bicarbonate of alkali metal and/or alkaline earth metal, preferably at least one of sodium hydroxide and potassium hydroxide.
Preferably, the mass ratio of the graphite material to the alkali is 1: 0.05 to 0.25; more preferably 1:0.1 to 0.15.
Preferably, the atmosphere of the first stage firing is a protective atmosphere, and preferably at least one of nitrogen and inert gas.
Preferably, the temperature of the first-stage roasting is 600-1200 ℃; further preferably 750 to 800 ℃.
And (3) washing and drying the product obtained by the first-stage roasting to obtain the pretreated graphite.
In the invention, under the pretreatment of the step (1), the silicon source and the carbon source are matched for double pre-coating, and the metal is combinedThe original means can generate a synergistic effect to obtain the SiO with the morphologyxOn the basis of the-SiC-C/G silicon-carbon composite material, the structural stability of the material can be further improved, and the electrochemical performance is improved.
In the present invention, the surface of the pretreated graphite may be previously coated with a silicon source and a carbon source by a conventional method. For example, the pretreated graphite, the silicon source and the carbon source may be mixed and pelletized, and the surface of the pretreated graphite is coated with the silicon source and the carbon source. The pelletizing method can be realized based on the existing equipment and means.
Preferably, the silicon source is at least one of silicon, silicon oxide, silicate and silicate ester.
Preferably, the silicate is, for example, sodium silicate, potassium silicate, calcium silicate, or the like.
Preferably, the silicate is an ester of silicic acid such as tetramethyl silicate, tetraethyl silicate, tetrapropyl silicate, tetrabutyl silicate, etc., and a monohydric alcohol or polyhydric alcohol having from C1 to C6.
Preferably, the silicon oxide source is at least one of silicon simple substance, silicon dioxide, quartz sand, silica and diatomite; preferably, the particle size of the silicon simple substance or the silicon oxide source is 0.2-2 μm; more preferably, the particle size of the silicon oxide source is 5 to 20% of the particle size of the graphite material. Researches find that the preparation of the structure is facilitated by adopting solid silicon sources such as a silicon simple substance, a silicon oxide source, silicate and the like and further matching the particle size grading, and the electrochemical performance of the material is facilitated.
Preferably, the mass ratio of the pretreated graphite to the silicon source is 1:0.1 to 2; more preferably 1:0.2 to 1.
Preferably, the carbon source is at least one of asphalt, sucrose, glucose, chitosan, sodium alginate, polyacrylonitrile, polypyrrole, polyacrylic acid and carboxymethyl cellulose.
Preferably, the mass ratio of the pretreated graphite to the carbon source is 1: 0.01 to 0.5; more preferably 1:0.1 to 0.4.
Preferably, the reducing metal is at least one of lithium, sodium, magnesium, aluminum, zinc and potassium.
Preferably, the mass ratio of the reducing metal powder to the silicon source is 1: 0.45-2; more preferably 1:1 to 2.
Preferably, the atmosphere of the second stage roasting is protective atmosphere; preferably at least one of nitrogen and inert atmosphere.
Preferably, the treatment temperature of the second-stage roasting is 300-900 ℃; further preferably 500 to 700 ℃.
Preferably, the product of the second stage calcination is washed with an acid solution, preferably a solution of hydrochloric acid and/or sulfuric acid.
The invention also particularly provides a recycling method of waste lithium ion battery carbon powder, which obtains a negative active material of the waste lithium ion battery, uses the negative active material as a graphite material raw material and prepares SiO by using the preparation methodx-SiC-C/G silicon carbon composite material.
For waste cathode active materials, particularly waste graphite materials, the following technical problems need to be solved: the first technical problem is how to realize the high-efficiency purification of the waste carbon slag. The purity of the carbon powder is the most important factor influencing the electrochemical performance of the carbon powder, and how to realize efficient purification is the primary key problem. The second technical problem is how to achieve microstructure restoration of the waste carbon slag. Because the repeated charge-discharge cycle process of the graphite cathode is the repeated insertion and extraction process of lithium ions, the microstructure of the graphite cathode of the retired lithium battery is damaged to a certain extent. Obviously, only the purification of the waste carbon slag cannot guarantee the restoration of the microstructure and the restoration of the electrochemical performance, so the restoration of the microstructure of the purified graphite is the second major key problem. The third technical problem is how to obtain an optimized silicon-carbon composite structure so as to realize that the silicon-carbon composite anode material has high structural stability and high cycle stability. Although the volume expansion rate of silicon oxide is smaller than that of silicon, the expansion problem still exists, the conductivity of the silicon oxide is low, and the structural optimization of the silicon-carbon composite material is the key for improving the cycle capacity and prolonging the service life of the material.
To solve the above problemsThe invention innovatively utilizes the silicon-carbon material preparation method, takes the waste negative electrode active material as the graphite material raw material, and can recycle the waste negative electrode material and construct the SiO with the brand-new shape and structure by the primary pretreatment under the condition of the step (1) and the secondary treatment of pre-coating metal by matching with the carbon source and the silicon source in the step (2)x-SiC-C/G silicon carbon composite material. Researches show that the waste carbon slag can be recycled by implementing the process, and the prepared silicon-carbon negative electrode material has high structural stability and long cycle life.
In the method, through the first stage of roasting pretreatment in the step (1), valuable metals such as aluminum, copper, lithium and the like in the waste graphite material can be leached, and microscopic physical and chemical structures can be repaired and reconstructed, and moreover, the treatment process in the step (1) and the process in the step (2) have a synergistic effect, so that the leaching of valuable metals such as iron, calcium, cobalt, nickel, manganese and the like in the waste carbon slag (waste graphite, also called as a waste cathode active material) can be further realized, the secondary purification of the waste carbon slag is realized, the layer-by-layer coating structure can be constructed, and the microscopic physical and chemical structures can be reconstructed, so that the high-efficiency purification and co-production of waste graphite powder of the waste lithium ion battery can be realized, and the material with high electrochemical performance can be obtained.
The preferred recovery processing method of the waste lithium ion battery carbon powder (waste negative electrode active material and waste carbon residue) comprises the following steps:
firstly, uniformly mixing waste carbon slag and sodium hydroxide, and carrying out first-stage roasting;
washing and drying the primary calcined material to obtain pretreated graphite;
uniformly mixing the pretreated graphite, the silicon source and the carbon source, and granulating to obtain secondary particles (the pretreated graphite is coated with the silicon source and the carbon source);
fourthly, the secondary particles and the reduced metal powder are evenly mixed and then are roasted for the second period;
fifthly, acid washing, water washing, filtering and drying are carried out on the secondary calcined material.
The waste graphite slag (waste carbon slag) is carbon slag obtained by primary separation after the disassembly of waste lithium ion batteries, and mainly comprises graphite, an organic binder, a conductive agent and metal impurities (lithium, nickel, cobalt, manganese, copper, aluminum and the like).
The mass ratio of the waste carbon residue to the sodium hydroxide is 1: 0.05 to 0.25.
The primary calcination is heat treatment under protective atmosphere, the protective atmosphere is one or a mixture of several inert gases such as argon, helium, nitrogen and the like, and the treatment temperature range of the heat treatment is 600-1200 ℃.
The silicon source is at least one of silicon dioxide, quartz sand, silica, diatomite, sodium silicate and ethyl orthosilicate, and the mass ratio of the pretreated graphite to the silicon source is 1:0.1 to 2.
The carbon source is one or more of carbon-containing organic matters or inorganic matters such as asphalt, sucrose, glucose, chitosan, sodium alginate, polyacrylonitrile, polypyrrole, polyacrylic acid, carboxymethyl cellulose and the like, and the mass ratio of the pretreated graphite to the carbon source is 1: 0.01 to 0.5.
The reductive metal powder is one or more of reductive alkaline metals such as lithium, sodium, magnesium, aluminum, zinc, potassium and the like, and the mass ratio of the metal powder to the silicon source in the step III is 1: 0.45 to 2.
The secondary calcination is heat treatment in protective atmosphere, the protective atmosphere is one or a mixture of several inert gases such as argon, helium, nitrogen and the like, and the treatment temperature range of the heat treatment is 300-900 ℃.
And fifthly, the acid cleaning is to adopt hydrochloric acid with the volume fraction of 2-20% to carry out secondary treatment on the materials.
The invention also provides the SiOxApplication of the-SiC-C/G silicon-carbon composite material to a negative active material of a lithium ion battery.
The invention also provides a lithium ion battery comprising the SiOx-SiC-C/G silicon carbon composite material.
Preferably, the lithium ion battery comprisesWith the SiO compounded withx-SiC-C/G silicon-carbon composite material.
More preferably, the SiO-containing composite material containsx-a negative plate of SiC-C/G silicon-carbon composite material.
The lithium ion battery, the anode material, the diaphragm, the battery structure and the battery can be components and structures known in the prior art, and the SiO of the invention is utilizedxthe-SiC-C/G silicon-carbon composite material belongs to the protection scope of the invention.
Advantageous effects
1. The invention provides SiO with a brand new structurexThe SiC-C/G silicon-carbon composite material has the advantage that the material with the brand new structure has better electrochemical performance. SiO of the inventionxIn the-SiC-C/G silicon-carbon composite material, the structural stability of silicon oxide is doubly guaranteed by the porous structure of the silicon oxide and the high-mechanical-strength silicon carbide layer on the outer layer, and the electrical conductivity of the silicon oxide is doubly guaranteed by pyrolytic carbon on the outer layer and graphite particles on the inner layer. The silicon carbide layer not only can play a role in protecting the stability of the silicon oxide core structure, but also can form a layer of shielding on the surface of the silicon oxide, so that the phenomenon that the coulomb efficiency is influenced because the silicon oxide is in direct contact with electrolyte is avoided; the pyrolytic carbon layer can tightly adhere silicon oxide coated with silicon carbide to the surface of the graphite inner core, so that the electron transmission of secondary particles is effectively ensured, and the pyrolytic carbon layer can also improve the isotropy of the composite lithium intercalation reaction, and effectively improve the rate capability of the material. SiO of the inventionxthe-SiC-C/G silicon-carbon composite material not only can be used as a cathode independently, but also can be mixed with other carbon materials in batches to obtain the silicon-carbon composite material meeting different use requirements.
2. The invention innovatively utilizes the graphite material to be roasted and pretreated under alkali in advance, then coats the carbon source and the silicon source and reduces the carbon source and the silicon source under the existence of reducing metal, thus the SiO with the special structure can be obtained by one-step constructionxSiC-C/G material, and the material is found to have better structural stability and electrochemical performance.
3. Preparation described in the inventionThe method is particularly suitable for the treatment of waste graphite materials and the co-production of highly-obtained SiOx-SiC-C/G silicon carbon composite:
the purification effect can be effectively improved by primary alkali purification and secondary acid purification of the waste cathode slag. In the process of secondary acid purification, further purification of waste carbon powder and the porous structure of silicon oxide can be realized simultaneously, a certain reserved space is promoted for the charge-discharge process of the waste carbon powder, and the damage to the application of the waste carbon powder to the outer-layer silicon carbide layer is reduced.
Secondly, the pretreatment of graphite, a silicon source and a carbon source are compounded through a granulation process, so that the silicon source wrapped by the carbon source can be effectively and tightly coated on the surface of the primary purified carbon particles. When the secondary particles are calcined for the second time, the metal powder is reduced, the reduction reaction is carried out from outside to inside, the high-reactivity silicon formed on the periphery can react with carbon in situ to form a silicon carbide layer, and the silicon carbide layer can effectively prevent heat from diffusing to a silicon oxide core, so that the heat generated by the exothermic reaction is used for repairing the microstructure of graphite, the silicon oxide in the core is prevented from being heated to be fused, the agglomeration is reduced, and an important support is formed for forming a reserved hole structure after acid washing.
The acid washing process has multiple functions, not only the waste carbon powder is further purified, but also the removal of soluble metal salt after the metal thermal reduction reaction is realized, and a porous structure is formed in the silicon oxide.
The nano silicon with long preparation flow, high preparation cost and extremely high surface energy is not needed to be used as a raw material to obtain the silicon-carbon composite material, but the porous silicon oxide is prepared by metallothermic reduction under the low-temperature condition, so that the material synthesis cost can be effectively reduced, the volume expansion rate of the silicon oxide is smaller than that of silicon, the circulation stability is better than that of silicon, and the prepared silicon-carbon composite material is more favorable for obtaining high circulation stability and long circulation life;
the graphite adopted is a negative electrode material of the waste lithium ion battery, the microstructure of the waste carbon slag is recovered without being carried out under the traditional high-temperature graphitization condition, but the heat generated in the metal thermal reduction process with the exothermic property is utilized to realize the graphitization of the waste stone ink powder under the low-temperature reaction condition, thereby being beneficial to reducing the energy consumption;
in the process of metal thermal reduction, the graphitization of the waste carbon slag can improve the crystallinity of the waste carbon slag, is more beneficial to removing impurities among layers of the waste carbon slag, and the impurities are more fully dissolved out by acid washing after the thermal reduction, thereby greatly improving the purity of the composite material;
in conclusion, by using the method provided by the invention, the waste carbon slag can be effectively recycled, and the high-value utilization of the silicon-carbon composite anode material can be realized by preparing the silicon-carbon composite anode material.
Drawings
FIG. 1 is a schematic flow diagram;
FIG. 2 is an XRD pattern of the waste graphite slag of example 1;
FIG. 3 is an XRD pattern of a silicon carbon material obtained in example 1;
FIG. 4 is an SEM photograph of a silicon carbon material obtained in example 2;
as can be seen from the attached figure 2, the raw material also contains characteristic peaks of impurities besides the obvious characteristic peaks of graphite; as can be seen from the attached figure 3, XRD of the obtained composite material has characteristic peaks of graphite and silicon carbide, and silicon oxide exists in an amorphous state; it can be seen from FIG. 4 that the composite material is in the form of particles having a particle size of 10-20 μm.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but the present invention is not limited to the following examples.
In the embodiment and the comparative example of the invention, the first coulombic efficiency, the first reversible capacity and the capacity retention rate are determined by assembling the obtained material with a smear and a button cell.
The graphite used in the examples is a finished graphite product of star cheng graphite or natural graphite powder from alatin; the nano-silicon (average particle size of 100nm) used is from the silicon industry of Zhongning.
In the following cases, the particle sizes referred to refer to the D50 particle sizes unless otherwise stated.
In the invention, the waste graphite residues are negative electrode materials obtained by separating waste lithium ion batteries. The material is obtained by adopting a common method for recovery, for example, the negative plate is soaked in deionized water, ultrasonically stripped and then screened.
Example 1:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 0.5g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 750 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 0.5g of quartz sand (the particle size of D50 is 5-20% of that of the pretreated graphite) and 2.5g of asphalt, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained particles is 12-18 mu m;
adding 1g of metal magnesium powder, mixing uniformly, placing the mixture into a reaction container, heating to 650 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the temperature for 2 hours, and naturally cooling to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution.
The electrochemical performance test method of the obtained material is as follows: the resulting material was mixed with conductive carbon, PAA in 8: 1:1, mixing materials, adding water for pulping, coating the mixture on the surface of copper foil, drying at 80 ℃, and assembling the lithium button half cell. The test voltage range is 0.005-2V, and the test current is 0.2C. (the following examples and comparative examples, the manner of testing the electrochemical properties of the resulting materials, as in this case)
Example 2:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 1.5g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 800 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 1g of silicon dioxide (the particle size of D50 is 5-20% of that of the pretreated graphite) and 0.5g of glucose, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained granules is 12-18 mu m;
adding 0.8g of aluminum powder, mixing uniformly, placing the mixture into a reaction container, heating the mixture to 550 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the heat for 2 hours, and naturally cooling the mixture to room temperature;
fifthly, taking out the materials, dissolving the materials in a hydrochloric acid solution with the volume fraction of 5%, stirring the materials for 6 hours at normal temperature, filtering, washing and drying the materials. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Example 3:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 1.5g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 800 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 5g of silicon dioxide (the particle size of D50 is 5-20% of that of the pretreated graphite) and 2g of cane sugar, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained granules is 12-18 mu m;
adding 4g of magnesium powder, mixing uniformly, placing the mixture into a reaction container, heating the mixture to 700 ℃ at a speed of 5 ℃/min in an argon atmosphere furnace, preserving the heat for 2 hours, and naturally cooling the mixture to room temperature;
fifthly, taking out the materials, dissolving the materials in a hydrochloric acid solution with the volume fraction of 20%, stirring the materials for 2 hours at normal temperature, filtering, washing and drying the materials. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Example 4:
compared with the embodiment 2, the difference is mainly that the silicon source is different, specifically:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 1.5g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 800 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 1g of ethyl orthosilicate and 0.5g of glucose, uniformly mixing the materials, and placing the materials in a granulator for secondary granulation, wherein the particle size of the obtained granules is 12-18 mu m;
adding 0.5g of aluminum powder, mixing uniformly, placing the mixture into a reaction container, heating the mixture to 550 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the heat for 2 hours, and naturally cooling the mixture to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Example 5:
compared with the embodiment 3, the difference is mainly that the types of graphite and metal are different, specifically:
uniformly mixing 10g of artificial graphite (with the particle size of 12-15 microns) and 1.5g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 800 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 5g of silicon dioxide (the particle size of D50 is 5-20% of that of the pretreated graphite) and 2g of cane sugar, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained granules is 14-18 mu m;
adding 4g of zinc powder, mixing uniformly, placing the mixture into a reaction container, heating the mixture to 700 ℃ at a speed of 5 ℃/min in an argon atmosphere furnace, preserving the heat for 2 hours, and naturally cooling the mixture to room temperature;
fifthly, taking out the materials, dissolving the materials in a hydrochloric acid solution with the volume fraction of 20%, stirring the materials for 2 hours at normal temperature, filtering, washing and drying the materials. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Example 6:
compared with the embodiment 3, the difference is mainly that graphite, a silicon source, a carbon source and the like are different, and specifically:
uniformly mixing 10g of natural graphite (with the particle size of 12-15 microns) and 1.5g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 800 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 1g of diatomite (the particle size of D50 is 5-20% of that of the pretreated graphite) and 0.5g of polyacrylonitrile, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained particles is 14-18 mu m;
adding 0.5g of aluminum powder, mixing uniformly, placing the mixture into a reaction container, heating the mixture to 550 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the heat for 2 hours, and naturally cooling the mixture to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Experimental example 7:
compared with the embodiment 1, the difference is mainly that the silicon source has different types, specifically:
uniformly mixing 10g of waste graphite slag and 1g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 750 ℃ at a speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 2g of nano silicon powder (the particle size of D50 is 5-20% of that of the pretreated graphite) and 0.5g of asphalt, uniformly mixing, and placing in a granulator for secondary granulation;
adding 2g of metal magnesium powder, mixing uniformly, placing the mixture into a reaction container, heating to 650 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the temperature for 2h, and naturally cooling to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Comparative example 1:
compared with the example 1, the difference is that no silicon source is added, specifically:
uniformly mixing 10g of waste graphite slag (with the particle size of 12-15 microns) and 1g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 750 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite and 0.5g of asphalt, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained particles is 12-18 mu m;
adding 2g of metal magnesium powder, mixing uniformly, placing the mixture into a reaction container, heating to 650 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the temperature for 2h, and naturally cooling to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Comparative example 2:
compared with the example 1, the difference is that no carbon source silicon source is added, specifically:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 1g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 750 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite and 2g of quartz sand, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained particles is 12-18 mu m;
adding 2g of metal magnesium powder, mixing uniformly, placing the mixture into a reaction container, heating to 650 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the temperature for 2h, and naturally cooling to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Comparative example 3:
compared with the example 1, the difference is that no metal salt is added, specifically:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 1g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 750 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 2g of quartz sand and 0.5g of asphalt, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained granules is 12-18 mu m;
placing the secondary particles in an argon atmosphere furnace, heating to 650 ℃ at the speed of 5 ℃/min, preserving the heat for 2h, and naturally cooling to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Comparative example 4: without adding silicon source and carbon source
Compared with the example 1, the difference is that no carbon source and no silicon source are added, specifically:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 1g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 750 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
thirdly, weighing 5g of pretreated graphite, adding 2g of metal magnesium powder, mixing uniformly, placing the mixture into a reaction container, heating the mixture to 650 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the heat for 2h, and naturally cooling the mixture to room temperature;
and fourthly, taking out the materials, dissolving the materials into hydrochloric acid solution with the volume fraction of 10%, stirring the materials for 4 hours at normal temperature, filtering, washing and drying the materials. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Comparative example 5:
compared with the embodiment 1, the difference is that no silicon source, carbon source and reducing metal powder are added, specifically:
uniformly mixing 10g of waste graphite slag (with the particle size of 10-15 microns) and 1g of sodium hydroxide, placing the mixture in an atmosphere furnace, heating to 750 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2 hours, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
thirdly, placing the pretreated graphite in a reaction container, heating to 650 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving heat for 2h, and naturally cooling to room temperature;
and fourthly, taking out the materials, dissolving the materials into hydrochloric acid solution with the volume fraction of 10%, stirring the materials for 4 hours at normal temperature, filtering, washing and drying the materials. The electrochemical performance of the alloy was tested in the same manner as in example 1.
Comparative example 6: without adding sodium hydroxide
Compared with example 1, the difference is only that sodium hydroxide is not added, specifically:
putting 10g of waste graphite slag (with the particle size of 10-15 mu m) into an atmosphere furnace, heating to 750 ℃ at the speed of 5 ℃/min under the protection of argon atmosphere, preserving heat for 2h, and naturally cooling to room temperature;
dissolving the cooled material in 500ml of deionized water, stirring, performing suction filtration and washing, and drying in a drying oven at 100 ℃; obtaining pretreated graphite;
weighing 5g of pretreated graphite, 2g of quartz sand and 0.5g of asphalt, uniformly mixing, and placing in a granulator for secondary granulation, wherein the particle size of the obtained granules is 12-18 mu m;
adding 2g of metal magnesium powder, mixing uniformly, placing the mixture into a reaction container, heating to 650 ℃ at the speed of 5 ℃/min in an argon atmosphere furnace, preserving the temperature for 2h, and naturally cooling to room temperature;
fifthly, taking out the materials, dissolving the materials in 10 volume percent hydrochloric acid solution, stirring the solution for 4 hours at normal temperature, filtering, washing and drying the solution. The electrochemical performance of the alloy was tested in the same manner as in example 1.
The following table shows the electrochemical performance data of the waste carbon slag and the samples obtained in the examples and the comparative examples:
Figure BDA0002649081880000151
the waste graphite slag in Table 1 refers to non-waste graphite slag used in the examples of this case. The nano silicon is the nano silicon of the embodiment 7. The artificial graphite was the graphite material used in example 8.
In conclusion, based on the preparation method provided by the invention, a material with a special morphology structure can be obtained, and the material has better electrochemical performance.

Claims (29)

1. SiO (silicon dioxide)xthe-SiC-C/G silicon-carbon composite material is characterized by comprising a graphite core and SiO coated on the surface of the graphite core layer by layer in situxA layer, a SiC layer, and an amorphous carbon layer; wherein x is less than 2.
2. SiO as claimed in claim 1xthe-SiC-C/G silicon-carbon composite material is characterized in that the particle size of the graphite core is 5-15 mu m; coated on SiOxThe total thickness of the layer, the SiC layer and the amorphous carbon layer is 1-5 mu m.
3. SiO as claimed in claim 1xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized by comprising the following steps of:
step (1):
carrying out first-stage roasting on a graphite material and alkali, and then washing and drying to obtain pretreated graphite; the temperature of the first stage roasting is 600-1200 ℃;
step (2):
coating a silicon source and a carbon source on the surface of the pretreated graphite, and then mixing the pretreated graphite with reducing metal for second-stage roasting to obtain the graphite; the second stage roasting treatment temperature is 300-900 ℃.
4. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the graphite material is one of natural graphite, artificial graphite, mesocarbon microbeads, coal-based coke powder, petroleum coke and needle coke; or the graphite material is a waste graphite material.
5. SiO as claimed in claim 4xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the particle size of the graphite material is 8-20 microns.
6. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the alkali is at least one of hydroxide, carbonate and bicarbonate of alkali metal and/or alkaline earth metal.
7. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the mass ratio of the graphite material to the alkali is 1: 0.05 to 0.25.
8. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the atmosphere of the first-stage roasting is protective atmosphere.
9. SiO as claimed in claim 8xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the atmosphere of the first-stage roasting is at least one of nitrogen and inert gas.
10. SiO as claimed in claim 8xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the temperature of the first-stage roasting is 750-800 ℃.
11. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the pretreated graphite, the silicon source and the carbon source are mixed for pelletizing, and the silicon source and the carbon source are coated on the surface of the pretreated graphite.
12. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the silicon source is at least one of silicon simple substance, silicon oxide source, silicate and silicate ester.
13. SiO as claimed in claim 12xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the silicon oxide source is at least one of silicon dioxide, quartz sand, silica and diatomite.
14. SiO as claimed in claim 12xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the particle size of the silicon oxide source is 0.2-2 mu m.
15. SiO as claimed in claim 14xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the particle size of the silicon oxide source is 5-20% of that of the graphite material.
16. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the mass ratio of the pretreated graphite to the silicon source is 1:0.1 to 2.
17. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the carbon source is at least one of asphalt, sucrose, glucose, chitosan, sodium alginate, polyacrylonitrile, polypyrrole, polyacrylic acid and carboxymethyl cellulose.
18. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the mass ratio of the pretreated graphite to the carbon source is 1: 0.01 to 0.5.
19. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the reducing metal is at least one of lithium, sodium, magnesium, aluminum, zinc and potassium.
20. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the mass ratio of the reducing metal to the silicon source is 1: 0.45 to 2.
21. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the atmosphere of the second-stage roasting is protective atmosphere.
22. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the processing temperature of the second-stage roasting is 500-700 ℃.
23. SiO as claimed in claim 3xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the product of the second-stage roasting is washed by acid liquor.
24. SiO as claimed in claim 23xThe preparation method of the-SiC-C/G silicon-carbon composite material is characterized in that the acid solution is hydrochloric acidAnd/or a solution of sulfuric acid.
25. A method for recycling waste lithium ion battery carbon powder is characterized in that a negative active material of a waste lithium ion battery is obtained and is used as a graphite material raw material, and SiO is prepared by the preparation method of claim 3x-SiC-C/G silicon carbon composite material.
26. An SiO as claimed in claim 1 or 2x-SiC-C/G silicon carbon composite material, SiO prepared by the method of any one of claims 3 to 24xApplication of the-SiC-C/G silicon-carbon composite material is characterized in that the SiC-C/G silicon-carbon composite material is used as a negative active material of a lithium ion battery.
27. A lithium ion battery comprising the SiO of claim 1 or 2x-SiC-C/G silicon carbon composite material and SiO prepared by the preparation method of any one of claims 3 to 24x-SiC-C/G silicon carbon composite material.
28. The lithium ion battery of claim 27, comprising said SiO compounded thereinx-SiC-C/G silicon-carbon composite material.
29. The lithium ion battery of claim 28, comprising said SiO compounded thereinx-a negative plate of SiC-C/G silicon-carbon composite material.
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