CN111056555B - Lithiated silicon-based composite material, and preparation method and application thereof - Google Patents

Lithiated silicon-based composite material, and preparation method and application thereof Download PDF

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CN111056555B
CN111056555B CN201911377839.6A CN201911377839A CN111056555B CN 111056555 B CN111056555 B CN 111056555B CN 201911377839 A CN201911377839 A CN 201911377839A CN 111056555 B CN111056555 B CN 111056555B
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lithium
based composite
nitrogen
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CN111056555A (en
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赵岸光
岳风树
姚钧
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Jiangxi Yijin New Energy Technology Co ltd
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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Abstract

The invention discloses a lithiated silicon-based composite material and a preparation method and application thereof, wherein the silicon-based composite material comprises nano silicon, silicon-based oxide, lithium silicate and a nitrogen-doped carbon coating layer, and the silicate is uniformly distributed in a silicon-based composite to form a homogeneous composite structure; the silicon-based composite material is prepared by soaking carbon-coated silicon-based oxide particles in a solution formed by an ether organic solvent containing a nitrogen-containing conductive polymer and aryl lithium, and then performing the procedures of settling and sintering. The composite material provided by the invention has high first coulombic efficiency and excellent cycle performance when being used as a lithium ion battery cathode material.

Description

Lithiated silicon-based composite material, and preparation method and application thereof
Technical Field
The invention relates to the field of lithium batteries, in particular to a lithiated silicon-based composite material and a preparation method thereof.
Background art:
the modern society solves the problem of increasing shortage of non-renewable energy sources and environmental problems such as pollution caused by combustion and global warming by an integration strategy of clean and efficient energy storage technology, and the most feasible concept at present is chargeable and dischargeable battery technology, wherein the most advanced technology is lithium ion battery technology. Lithium ion batteries have not only dominated the small format battery market for portable electronic products, but have also been successfully introduced for mobile electrical storage and storage system storage. Lithium ion batteries are currently being operated with further improvements in performance, such as specific energy (Wh kg)-1) And volumetric energy density (Wh L)-1) Thereby achieving the purposes of small volume, light weight and long service life. The theoretical specific capacity of the traditional graphite carbon negative electrode material is only 372mAh/g, so that the improvement space of the lithium ion battery on the operation performance is limited, and the silicon negative electrode material with high specific capacity has the theoretical specific capacity up to 4200mAh/g and becomes a hotspot of the current lithium ion battery negative electrode material. However, pure silicon material may cause a volume change of up to 300% during charging and discharging processes, which may result in active materials on the electrode sheetThe electrolyte is broken and pulverized during the circulation process, which aggravates the consumption of the electrolyte and causes a series of side reactions, resulting in a sharp drop in the performance of the battery.
In order to improve the defects of silicon-based materials in lithium ion battery application, in recent years, silicon-based oxide negative electrode material SiOx(0<x<2) Has good cycle performance and lower de-intercalation potential, and is a high-capacity lithium ion battery cathode material with great potential. The problem that the conductivity of the silicon-based oxide is poor and the coulombic efficiency of the first circle is low affects the capacity exertion, generally, in order to improve the cycle performance and the capacity exertion, the chemical vapor deposition method is utilized to carry out carbon coating on the surface of the silicon-based oxide powder, and meanwhile, the cycle performance is improved to a certain extent, but the problem that the coulombic efficiency of the first circle cannot be solved.
For example, after a certain charge-discharge cycle or a certain service life, the content of reversible capacity is reduced significantly, i.e., the active material loss (capacity loss) and the interface internal resistance increase (energy loss), usually by a complex degradation mechanism or an attachment reaction. Due to the existence of oxygen, in the first charge and discharge process of the silicon-based oxide negative electrode material, oxygen and lithium are combined to form lithium silicate and lithium oxide, so that the irreversible capacity is increased, the first coulombic efficiency of the battery is reduced, and the lithium loss is caused. In order to compensate the loss of active lithium and increase the first-turn coulombic efficiency, the nanocomposite containing the Si phase, the lithium silicate phase and amorphous SiO2 is obtained by a method of pre-lithiating the silicon-based oxide negative electrode material, so that the reversible capacity, the energy density and the first-turn coulombic efficiency of the battery are increased.
Conventionally, modification has been performed by inserting lithium into negative electrode active material particles by a redox method. Patent CN105932224A discloses a modified silicon-based negative electrode material embedded with lithium ions, which is prepared by preparing a lithium-containing aromatic hydrocarbon compound solution and subjecting a silicon-based negative electrode substrate to lithium embedding treatment, wherein the aromatic hydrocarbon compound is naphthalene or biphenyl. The patent states that the first efficiency of the silicon-based negative electrode material can be effectively improved, but only drying treatment is carried out, high-temperature treatment is not carried out, the silicon-based oxide after lithium insertion cannot be sufficiently stabilized by heat treatment, and the obtained active material is thermodynamically stableThe qualitative performance is to be verified. Patent CN 108718535a discloses a method for preparing an anode active material containing anode active material particles containing silicon compound particles, which is characterized by preparing an anode active material containing silicon compound (SiO)x: 0.5. ltoreq. x.ltoreq.1.6) and a step of impregnating the silicon compound particles with a liquid phase to insert lithium, and has a negative electrode active material particle containing at least one of a polyphenylene compound and a polycyclic aromatic component. The negative electrode active material used in the above patent is said to contain a carbon layer in its surface layer portion, and to improve conductivity and alleviate expansion stress associated with charging. However, in the above patent, the carbon layer contained in the surface layer of the negative electrode active material is destroyed in the process of liquid-phase impregnation for lithium insertion, and it is not ensured that the finally obtained negative electrode active material particles can improve the conductivity and relieve the expansion stress.
Therefore, the existing lithiated silicon-based composite material still has certain defects, and in order to further improve the performance of the silicon-based negative electrode of the lithium ion battery, particularly the first coulombic efficiency and the conductivity, the lithiation and carbon coating of the silicon-based material still need to be improved.
Disclosure of Invention
The invention aims to solve the problems of low conductivity of a silicon-based oxide material and low coulombic efficiency caused by lithium loss in the preparation process of a negative electrode.
The first object of the invention is to provide a lithiated silicon-based composite material, which comprises nano silicon, silicon oxide, lithium silicate and a nitrogen-doped carbon coating layer, wherein the silicate is uniformly distributed in a silicon-based composite to form a homogeneous composite structure; the silicon-based composite material is prepared by soaking carbon-coated silicon-based oxide particles in a solution formed by an ether organic solvent containing a nitrogen-containing conductive polymer and aryl lithium, and then performing the procedures of settling and sintering to finally obtain the lithiated silicon-based composite material.
In the lithiated silicon-based composite material, lithium accounts for 3-8 wt% of the composite material, and carbon accounts for 3-5 wt% of the composite material.
The aryl lithium is a complex formed by an aryl complexing agent and lithium, the aryl complexing agent is a polycyclic aromatic compound, specifically at least one selected from biphenyl, terphenyl, naphthalene, anthracene, phenanthrene, naphthacene and pentacene, and biphenyl is preferred. The preparation method of the aryl lithium is that the lithium sheet is added into homogeneous solution formed by aryl complexing agent and organic solvent, and stirred under inert atmosphere.
The ether solvent is one or more of 1, 3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether, methyl tert-butyl ether and butyl methyl ether, and is preferably 1, 3-dioxolane, tetrahydrofuran and ethylene glycol dimethyl ether, or a mixed ether solvent. Tetrahydrofuran is most preferred.
The concentration of the nitrogenous conductive polymer in the solution is 1-3mg/mL, preferably 1.5-2 mg/mL.
The concentration of aryl lithium in the solution is 0.5-3mol/L, preferably 1-2 mol/L.
The nitrogen-containing conductive polymer is a high molecular polymer having a nitrogen atom in a molecule, such as at least one of polypyrrole and polyaniline.
On one hand, the complex of lithium and the polycyclic aromatic compound is stable, and can induce lithium to be effectively and uniformly adsorbed on the surface of the silicon-based oxide; on the other hand, the complex compound of the nitrogen-containing conductive polymer wrapped lithium with certain viscosity prevents lithium from losing, and the organic lithium wrapped by the nitrogen-containing conductive polymer can be more uniformly adsorbed on the surface of the silicon-based oxide in a solution impregnation mode.
The lithiated silicon-based composite material contains uniformly distributed silicon, the silicon is generated by disproportionation in silicon oxide, and the crystallite size of nano silicon is more than 3nm and less than 10 nm.
The silicon-based oxide material, which is one of the raw materials for preparing the silicon-based composite material of the present invention, can be represented as SiOxWherein 0 is<x<2, preferably 0.8. ltoreq. x.ltoreq.1.0.
The particle size of the silicon-based oxide material is not particularly limited and can be used in the present invention to prepare the lithiated silicon-based composite material in the range of 0.1 to 100 μm, and the median particle size of the silicon-based oxide material is preferably 1 to 10 μm.
In the lithiated silicon-based composite materialThe material contains uniformly distributed silicon oxide, particularly silicate components, and can generate inert components when lithium is firstly inserted through introducing oxygen, so that the volume change in the lithium inserting and extracting process is relieved. For example, the lithium silicate is Li2SiO3、Li2Si2O5、Li2Si3O7、Li4SiO4、Li2Si3O5、Li6Si2O7、Li8SiO6And Li2Si3O5One or more combinations thereof.
The overall structure of the lithiated silicon-based composite material is a homogeneously distributed composite structure, wherein the median particle size is 3-10 μm, and preferably 4-8 μm.
The silicon-based oxide uniformly coated with the carbon layer is a uniform carbon layer coated with amorphous carbon generated by cracking with a chemical vapor deposition method or a solid phase coating method.
The original uniform carbon coating layer on the surface of the silicon-based composite material is not damaged in the process of forming the composite structure by the lithiated silicon-based composite material. The carbon layer of the silicon-based oxide is coated, so that the conductivity of the silicon-based oxide can be improved, a surface buffer layer is formed, the phenomenon of local enrichment of lithium is inhibited, and the conductivity reduction caused by the insertion of the lithium can be counteracted to a certain extent.
In order to obtain the lithiated silicon-based composite material, the invention provides a preparation method of the lithiated silicon-based composite material, which comprises the following steps:
(1) p-silicon based oxide SiOxCarrying out carbon coating;
(2) uniformly mixing a complexing agent, a nitrogen-containing conductive polymer, metal lithium and an organic solvent, and stirring in an inert atmosphere to obtain a homogeneous solution;
(3) coating the carbon-coated silicon-based oxide SiO of the step (1)xDipping the solution in the homogeneous phase solution obtained in the step (2); centrifuging, standing for solid-liquid separation, and taking the lower silicon-based oxide particles;
(4) and (4) pre-sintering the particles obtained in the step (3) at a low temperature in an inert atmosphere, then performing high-temperature sintering heat treatment, and cooling to obtain the silicon-based composite material.
In a specific embodiment of the invention:
the carbon coating method of step (1) is well known in the art, such as a uniform carbon layer coated with amorphous carbon produced by chemical vapor deposition or solid phase coating cracking. Preferably a hydrocarbon gas, for example, in an acetylene and hydrogen-argon mixed gas atmosphere, the material can be made to have high conductivity by performing uniform carbon coating by decomposing the hydrocarbon gas at 900 ℃ or higher and 1200 ℃ or lower.
Preferably, in the step (2), the complexing agent, the organic solvent and the metal lithium are firstly formed into a homogeneous solution, and then the nitrogenous conductive polymer is added, so that the polymer coats the lithium in the solution, the lithium is prevented from being lost, and the utilization rate is improved.
And (3) soaking the silicon-based oxide in the homogeneous solution at the temperature of 20-30 ℃ for 5-10 h. Under the condition, the active lithium-containing organic solvent can be quickly and uniformly adsorbed on the surface of the silicon-based oxide material, side reaction is not easy to occur to generate lithium compound precipitation, and the proper reaction rate is also favorable for improving the rate of lithium insertion into the silicon-based oxide.
The standing time in the step (3) is 2-5 h; the time of centrifugal separation is 5-20 min.
And (4) the inert atmosphere is at least one of nitrogen, helium and argon.
The low-temperature presintering temperature is 70-100 ℃, and the presintering time is 3-8 h. Within the temperature and time ranges, the excessive solvent can be removed, the crystal growth of silicon in the silicon-based oxide can be inhibited, the adhesion of the nitrogen-containing conductive polymer on the particle surface is enhanced, and the cycle stability is improved.
The high-temperature sintering temperature is 650-850 ℃, and the heat preservation time is 1-3 h. In the temperature range and within the time, the crystal growth of silicon in the silicon-based oxide can be inhibited, so that better circulation stability is maintained, the silicon-based oxide after the nitrogenous conductive polymer is wrapped with organic lithium and inserted is subjected to heat treatment stabilization, a nitrogenous carbon-like layer is formed under the atmosphere of high-temperature inert gas, NH is converted into high-electron active nitrogen, and the high-electron active nitrogen is conjugated and conducted in carbon atoms, so that the active material which is wrapped with the nitrogenous carbon-like layer and is thermodynamically stable is obtained, and the self conductivity, the reversible charge-discharge capacity and the first-turn efficiency are improved.
The inventors have found that, in the heat treatment process of the present invention, when low-temperature calcination is performed and then high-temperature calcination is performed, not only is the growth of silicon crystals in the silicon-based oxide particles rapidly suppressed, but also the amount of crystalline silicon in the silicon-based oxide particles generated during the production process can be suppressed by preheating, and the nitrogen-containing conductive polymer is carbonized on the surface layer to tightly coat the particles, thereby reducing the volume expansion of silicon during the charge and discharge processes, and effectively suppressing the decrease in cycle stability.
The third purpose of the invention is the application of the silicon-based composite material or the lithiated silicon-based composite material prepared by the preparation method in a lithium ion battery. The lithiated silicon-based composite material prepared by the preparation method has good conductivity, high reversible capacity, large energy density and high coulombic efficiency in the first circle and is applied as a negative electrode material of a lithium ion secondary battery.
Compared with the prior art, the lithiated silicon-based composite material and the preparation method thereof provided by the invention have the following advantages:
(1) the invention discloses a lithiated silicon-based composite negative electrode material for a lithium ion secondary battery, which has the following structure: the nano silicon is dispersed in the organic solution of the organic lithium wrapped by the nitrogenous conductive polymer, and the organic lithium is fully and uniformly contacted without mutual agglomeration, so that the cracking and crushing of silicon in the charging and discharging process can be relieved, the problem of volume expansion is relieved, and the cycle performance of the composite material is effectively improved; the silicon monoxide is used as a substrate to form the composite particles, and the carbon layer is uniformly coated on the whole particle surface and has a stable structure.
(2) The composite structure containing amorphous Si, silicon oxide and silicate can consume lithium pre-consumed by inactive components of lithium ions, and the first coulombic efficiency of the composite material is effectively improved; on the other hand, the lithium silicate irreversible phase is formed by utilizing the in-situ lithiation, the consumption of active lithium is compensated, the irreversible lithium loss in the first charge-discharge process is reduced, and the first coulombic efficiency is improved.
(3) The pre-lithiated silicon-based composite negative electrode material coated with the nitrogen-containing carbon layer is prepared by soaking a silicon-based oxide material uniformly coated with the carbon layer in an organic solvent in which a nitrogen-containing conductive polymer and metal lithium are dissolved, uniformly adsorbing organic lithium coated with the nitrogen-containing conductive polymer on the surface of silicon-based oxide particles through solid-liquid mixing, pre-sintering at a low temperature under a specific program, and then performing heat treatment through high-temperature sintering. The method of the present invention has the lithium source in an ionic state, can uniformly and sufficiently lithiate the silicon-based oxide material, and is easy to obtain a stable lithium silicate material in an aqueous binder slurry.
Drawings
FIG. 1 is an X-ray diffraction pattern of a lithiated silicon-based composite material prepared in example 1 of the present invention.
FIG. 2 is a scanning electron micrograph of a lithiated silicon-based composite material prepared in example 1 of the present invention.
FIG. 3 is a TEM micrograph (500nm) of a lithiated Si-based composite material obtained in example 1 of the present invention.
FIG. 4 is a TEM micrograph (10nm) of a lithiated Si-based composite material obtained in example 1 of the present invention.
Fig. 5 is a charge-discharge curve of the lithiated silicon-based composite material prepared in example 1 of the present invention as a negative electrode of a lithium ion secondary battery.
Detailed Description
The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.
The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.
Example 1
(1) Carbon-coated silicon-based oxide powder: for use in the present invention, the silicon-based oxide powder is a commercial silica material, i.e., SiOxWherein x is 1. Pulverizing the silica material into particles with particle diameter of 1-10 μm by gas flow, placing in CVD vapor deposition furnace, and performingAnd introducing acetylene gas, carrying out thermal decomposition and deposition at 750 ℃ for 3h, maintaining the material in an inert gas protection atmosphere, heating to 900 ℃ at a heating rate of 5 ℃/min, and keeping the temperature for 1h to obtain the silicon oxide material uniformly coated with the carbon layer.
(2) A dissolving process: dissolving biphenyl in an ultra-dry tetrahydrofuran solvent, stirring and dissolving, adding 350mg of lithium sheets into 50mL of solution under an inert atmosphere, magnetically stirring for 30 minutes to obtain a homogeneous solution containing lithium and a biphenyl complex, wherein the concentration of aryl lithium is 1mol/L, and adding 75mg of polypyrrole for full dissolution to obtain the homogeneous solution.
(3) A mixing procedure: adding the silicon-based oxide powder uniformly coated with the carbon layer into the homogeneous solution at 25 ℃ and at room temperature, and soaking for 1 hour at room temperature; wherein lithium accounts for 5 wt% of the silicon-based oxide material, i.e. 6.65g of the silicon-based oxide material coated with the carbon layer is added.
(4) A settling procedure: centrifuging at 12000r/min for 5min to remove the upper solution and leave silicon-based oxidized particles with the nitrogen-containing conductive polymer coating the organic lithium. And continuously adding a small amount of tetrahydrofuran solvent into the material to completely remove the surface active byproducts of the silicon-based oxide particles, and centrifuging again to finally leave the silicon-based oxide particles uniformly inserted with lithium.
(5) A firing process: and (3) placing the obtained material under the protection of an argon environment, heating to 70 ℃ at the heating rate of 5 ℃/min, preserving heat for 6 hours, carrying out low-temperature pretreatment, heating to 750 ℃ at the heating rate of 5 ℃/min, preserving heat for 2 hours, carrying out high-temperature sintering heat treatment, naturally cooling to obtain a lithiated silicon-based composite material, and fully grinding the material by using an agate mortar to obtain the negative electrode material.
FIG. 1 is an XRD diffraction pattern of the lithiated silicon-based composite material prepared in example 1, in which significant silicon and Li are present2SiO3And Li2Si2O5The diffraction peak of (1).
FIG. 2 is an SEM image of the lithiated silicon-based composite material prepared in example 1, and it can be seen from the SEM image that the composite material is massive, has a compact surface and uniform particle size, has a particle size range of 1-10 μm, has uniform particle distribution, and has a median particle size of 5.1 μm.
Fig. 3 and 4 are TEM images of lithiated silicon-based composites made in example 1. As can be seen from FIG. 3, the composite material has nano-silicon inside, the particle size ranges from 5nm to 15nm, the surface is coated with a compact carbon layer, the thickness range of the coating layer is 15nm to 25nm, and the coating is uniform. As can be seen from fig. 4, the silicon-based composite material prepared in example 1 has a distinct layered structure, which is lithiated silicon-based oxide, a carbon coating layer, and a nitrogen-doped carbon coating layer, respectively, from the inside to the outside.
Example 2
A negative electrode active material was prepared in the same manner as in example 1, except that the ether solvent was changed to 1, 3-dioxolane as a solvent system in the dissolving step.
Example 3
A negative electrode active material was prepared in the same manner as in example 1, except that the ether solvent was changed to ethylene glycol dimethyl ether as a solvent system in the dissolving step.
Comparative example 1
A negative electrode active material was prepared in the same manner as in example 1, except that the solvent was changed to dimethyl carbonate (DMC) in the dissolving step.
Example 4
A negative electrode active material was prepared in the same manner as in example 1, except that the concentration of aryl lithium in the homogeneous solution of lithium and biphenyl complexes in the dissolution step was 2 mol/L.
Example 5
A negative electrode active material was prepared in the same manner as in example 1, except that the impregnation time of the silicon-based oxide material in the homogeneous solution was set to 10 hours in the mixing step.
Example 6
A negative electrode active material was prepared in the same manner as in example 1, except that the heat treatment temperature for high-temperature firing in the firing step was 600 ℃.
Example 7
A negative electrode active material was prepared in the same manner as in example 1, except that the heat treatment temperature for high-temperature firing in the firing step was 900 ℃.
Example 8
A negative electrode active material was prepared in the same manner as in example 1, except that the heat treatment time for the high-temperature firing in the firing step was set to 1 hour.
Example 9
A negative electrode active material was prepared in the same manner as in example 1, except that the impregnation time of the silicon-based oxide material in the homogeneous solution was set to 3 hours in the mixing step.
Example 10
In the dissolving process, polypyrrole was replaced with polyaniline, and the rest was the same as in example 1, and a negative electrode active material was prepared.
Example 11
In the dissolving step, the amount of polypyrrole was changed to 50mg, and the rest was the same as in example 1, and a negative electrode active material was prepared.
Example 12
In the dissolving step, the amount of polypyrrole was changed to 100mg, and a negative electrode active material was prepared in the same manner as in example 1.
Example 13
In the dissolving step, the amount of polypyrrole was changed to 150mg, and a negative electrode active material was prepared in the same manner as in example 1.
Example 14
In the dissolving procedure, biphenyl, an ultra-dry tetrahydrofuran solvent, a lithium sheet and polypyrrole are magnetically stirred for 30 minutes in an inert atmosphere environment to obtain a homogeneous solution containing lithium and a biphenyl complex, wherein the concentration of aryl lithium is 1mol/L, and the concentration of polypyrrole is 1.5 mg/mL.
Comparative example 2
A negative electrode active material was prepared in the same manner as in example 1, except that only the low-temperature pretreatment of holding 70 ℃ for 6 hours was performed in the firing step, and the subsequent high-temperature firing heat treatment step was not performed.
Comparative example 3
A negative electrode active material was prepared in the same manner as in example 1, except that the temperature was maintained at 750 ℃ at a temperature increase rate of 5 ℃/min for 2 hours in the firing step, and the low-temperature pre-firing treatment was not performed.
Application example
The electrochemical properties of the silicon-based composite materials prepared in the examples and comparative examples were measured according to the following methods: the lithiated silicon-based composite material is used as a negative active material of a lithium ion secondary battery, carbon black, carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR) composite binder are mixed to prepare slurry (wherein the mass ratio of the CMC to the SBR is 2:3) according to the mass ratio of 8:1:1, the slurry is uniformly coated on a copper foil current collector, and a working electrode is prepared after vacuum drying for 12 hours; lithium foil as counter electrode (available from Tianjin lithium-energy industry), glass fibre membrane (available from Whatman, UK) as separator, 1mol/L LiPF6(the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with the volume ratio of 1: 1) is used as electrolyte, VC with the volume fraction of 1% and FEC with the volume fraction of 5% are added into the electrolyte, and the button cell is assembled in a German Braun inert gas glove box in an argon atmosphere.
And (3) carrying out charge and discharge tests on the assembled battery on a LAND charge and discharge tester.
Electrochemical analysis tests were performed on the lithiated silicon-based composite material obtained in example 1 to form an electrode, and assembled to a 2032 type coin cell, and the results are shown in fig. 4. The charging and discharging interval is 0-1.5V, the material capacity can reach 1380mAh/g when the charging and discharging are carried out under the current density of 675mAh/g (0.5C), the first-turn coulombic efficiency is 94.3 percent (as shown in figure 4), and the capacity retention rate is over 86 percent after 100 cycles of circulation, so that the lithiated silicon-based composite material has excellent first-time charging and discharging efficiency and higher reversible capacity.
Electrochemical test results of button cells assembled by the above-described method for negative electrodes obtained in examples of the present invention and comparative examples are shown in table 1.
TABLE 1
Figure BDA0002341471840000081
Figure BDA0002341471840000091
As can be seen from the data in table 1, the lithiated silicon-based negative electrode material prepared according to the present invention exhibits satisfactory telephone performance. The performance of the cathode material can be influenced to a certain extent by regulating and controlling the preferable process parameters such as the raw material proportion, the dipping time and the like.
In the mixing procedure, the silicon-based oxide powder with the uniform carbon coating layer is dipped in the solution to obtain the silicon-based oxide material coated with the nitrogen-containing conductive polymer and coated with the organic active lithium. In this step, the solvent used for the lithium-containing solution is an ether solvent, and in the examples of the present invention, biphenyl is used as a solute of the polycyclic aromatic compound in different ether solvents, and among them, tetrahydrofuran is most preferably used because lithium and biphenyl can rapidly form a highly active and stable complex in tetrahydrofuran, and organic lithium encapsulated in the nitrogen-containing conductive polymer can be rapidly adsorbed on the silicon-based oxide and can be continuously adsorbed. Further, in comparative example 1, an ether solvent is not used, but an ester solvent commonly used in a battery is used, so that the performance of the battery is degraded, and a complex formed by lithium and biphenyl in the ether solvent stably exists compared with other solvents, thereby facilitating the rapid and continuous adsorption of lithium on the surface of the silicon-based oxide.
In the firing process, high-temperature firing inhibits the crystal growth of silicon in the silicon-based oxide, so that better cycle stability is maintained, and side reactions are not easy to generate, so that the first efficiency of the lithiated silicon-based oxide material after heat treatment is improved. The first coulombic efficiency of example 6 was slightly decreased because the thermal stability to lithium intercalation into silicon-based oxide was not high and insufficient at lower temperature, and the nitrogen-containing conductive polymer was not carbonized sufficiently and the conductivity was poor. The example 7, in which lithium has been inserted into the silicon-based oxide and stabilized at 900 ℃, the nitrogen-containing conductive polymer is sufficiently carbonized to give a thermodynamically stable material, but the capacity is somewhat decreased.
In addition, the proper sintering heat preservation time can fully inhibit the crystal growth of silicon in the silicon-based oxide, fully carbonize the nitrogen-containing conductive polymer, and improve the thermal stability of the lithium-inserted silicon-based oxide material. The sintering time of example 8 was short, the nitrogen-containing conductive polymer was not sufficiently carbonized, and the stability of lithium insertion into the silicon-based oxide was slightly poor, resulting in slightly low conductivity and first efficiency. Comparative example 3 does not go through the high temperature sintering process, after preheating at low temperature and completely removing the solvent, the active organic lithium compound coated with the nitrogen-containing conductive polymer generated during lithium insertion is stabilized in structure, but the nitrogen-containing conductive polymer cannot be carbonized and the lithium insertion silicon-based oxide is poor in sufficiency and thermal stability, resulting in low conductivity and low first-pass efficiency.
In summary, it can be seen from the examples and comparative examples that the lithiated silicon-based composite negative electrode material obtained by the preparation method of the present invention has a stable structure, and the lithium ion secondary battery prepared by using the lithiated silicon-based composite material of the present invention has high conductivity and first coulombic efficiency, the first coulombic efficiency is above 88%, the capacity retention rate of 100 cycles at 0.5C is above 84%, and the electrochemical performance is obviously superior to that of the conventional carbon-coated silicon oxide negative electrode material.
The applicant states that the present invention is illustrated by the above examples to describe the detailed preparation method of the present invention, but the present invention is not limited to the above detailed preparation method, i.e. it does not mean that the present invention must rely on the above detailed preparation method to be carried out. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (12)

1. A lithiated silicon-based composite material comprises nano silicon, silicon-based oxide, lithium silicate and a nitrogen-doped carbon coating layer, wherein the silicate is uniformly distributed in the silicon-based composite material to form a homogeneous composite structure; the silicon-based composite material is prepared by the steps of dipping carbon-coated silicon-based oxide particles into a solution formed by an ether organic solvent containing a nitrogen-containing conductive polymer and aryl lithium, and then performing the procedures of settling and sintering to obtain a lithiated silicon-based composite material;
the nitrogen-containing conductive polymer is at least one of polypyrrole and polyaniline;
the firing procedure is to pre-fire at low temperature and then fire at high temperature; the low-temperature presintering temperature is 70-100 ℃, and the presintering time is 3-8 h; the high-temperature sintering temperature is 650-850 ℃, and the heat preservation time is 1-3 h.
2. The silicon-based composite material of claim 1, wherein the lithium comprises 3 to 8 wt% of the composite material and the carbon comprises 3 to 5 wt% of the composite material.
3. The silicon-based composite material according to claim 1, wherein the aryl lithium is a complex formed by an aryl complexing agent and lithium, and the aryl complexing agent is a polycyclic aromatic compound.
4. The silicon-based composite material according to claim 1, wherein the ether solvent is one or more of 1, 3-dioxolane, tetrahydrofuran, ethylene glycol dimethyl ether, methyl tert-butyl ether, and butyl methyl ether.
5. The silicon-based composite material according to claim 4, wherein the ether solvent is a single or mixed ether solvent of 1, 3-dioxolane, tetrahydrofuran, and ethylene glycol dimethyl ether.
6. The silicon-based composite material according to claim 1, wherein the concentration of the nitrogen-containing conductive polymer in the solution is 1-3 mg/mL; and/or the concentration of aryl lithium in the solution is 0.5-3 mol/L.
7. The silicon-based composite material according to claim 6, wherein the concentration of the nitrogen-containing conductive polymer in the solution is 1.5 to 2mg/mL, and/or the concentration of the aryl lithium in the solution is 1 to 2 mol/L.
8. The silicon-based composite material according to claim 1, wherein the lithiated silicon-based composite material comprises a uniform distribution of nano-silicon, the silicon being formed by disproportionation of silicon oxide, wherein the crystallite size of the nano-silicon is greater than or equal to 3nm and greater than or equal to 10nmThe following; and/or the silicon-based oxide material may be represented as SiOxWherein 0 is<x<2。
9. Silicon-based composite material according to claim 8, characterized in that SiOxIn the formula, x is more than or equal to 0.8 and less than or equal to 1.0.
10. A process for the preparation of a silicon-based composite material according to any one of claims 1 to 9, comprising the following steps:
(1) p-silicon based oxide SiOxCarrying out carbon coating;
(2) uniformly mixing a complexing agent, a nitrogen-containing conductive polymer, metal lithium and an organic solvent, and stirring in an inert atmosphere to obtain a homogeneous solution;
(3) coating the carbon-coated silicon-based oxide SiO of the step (1)xDipping the solution in the homogeneous phase solution obtained in the step (2); centrifuging, standing for solid-liquid separation, and taking the lower silicon-based oxide particles;
(4) and (4) pre-sintering the particles obtained in the step (3) at a low temperature in an inert atmosphere, then performing high-temperature sintering heat treatment, and cooling to obtain the silicon-based composite material.
11. The method of claim 10, wherein step (2) comprises adding the nitrogen-containing conductive polymer after the complexing agent, the organic solvent and the lithium metal form a homogeneous solution.
12. The method of claim 10, wherein the silicon-based oxide of step (3) is immersed in the homogeneous solution at a temperature of 20 ℃ to 30 ℃ for a period of 5 hours to 10 hours.
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