CN108878813B

CN108878813B - Silicon dioxide/lignin porous carbon composite material, preparation method thereof and application thereof in lithium ion battery cathode material

Info

Publication number: CN108878813B
Application number: CN201810617025.4A
Authority: CN
Inventors: 邱学青; 杨东杰; 李常青; 刘伟峰; 楼宏铭; 钱勇; 欧阳新平
Original assignee: South China University of Technology SCUT
Current assignee: South China University of Technology SCUT
Priority date: 2018-06-15
Filing date: 2018-06-15
Publication date: 2020-07-28
Anticipated expiration: 2038-06-15
Also published as: CN108878813A

Abstract

The invention belongs to the technical field of lithium ion battery cathode materials, and discloses a silicon dioxide/lignin porous carbon composite material and a preparation method and application thereof in a lithium ion battery cathode material.

Description

Silicon dioxide/lignin porous carbon composite material, preparation method thereof and application thereof in lithium ion battery cathode material

Technical Field

The invention belongs to the technical field of lithium ion battery cathode materials, and particularly relates to a silicon dioxide/lignin porous carbon composite material, a preparation method thereof and application thereof in a lithium ion battery cathode material.

Background

With the problems of energy shortage and environmental deterioration becoming more prominent, the development of green and environment-friendly new energy is improved to the strategic level in all countries in the world. Therefore, the development of a new energy storage device with green, pollution-free and high power density becomes a hot spot of the current world research. The lithium ion battery has high energy density, long cycle life, environmental protection, safety and other excellent performances, and is widely applied to a plurality of small electronic products, and is developing in the energy storage field of electric automobiles, hybrid electric automobiles and the like, so that the lithium ion battery has important significance for keeping the environment clean and saving energy. The negative electrode material is a platform for carrying out lithium ion intercalation/deintercalation reaction in the battery, and the production cost of the negative electrode material accounts for about 15% of the total cost of the lithium ion battery, so that the negative electrode material has important influence on the performance and the cost of the lithium ion battery.

The lithium ion battery cathode material mainly comprises a silicon-based material, a tin-based material, an alloy material, a carbon material, a transition metal, an oxide thereof and the like. At present, most of commercialized lithium ion battery negative electrode materials adopt micron-sized graphite electrode materials, including artificial graphite, mesocarbon microbeads and the like, and although the graphite negative electrode materials show better cycle performance as the negative electrode materials of the lithium ion battery, the theoretical specific capacity of the graphite negative electrode materials is lower (372mAh/g), and the practical application of the graphite negative electrode materials reaches the theoretical specific capacity basically, so that the application of the graphite negative electrode materials in high-energy-density electrochemistry is greatly limited. Therefore, there is an urgent need to develop a new anode material to replace the graphite anode to improve the storage capacity of the lithium ion battery.

Through research and study on various cathode materials, people begin to turn attention to silicon-based materials. The silicon-based material comprises silicon, silicon-based alloy and silicon oxide, wherein the theoretical lithium intercalation capacity of the silicon is 4200mAh/g, and the silicon is the highest capacity in the currently known negative electrode materials. However, silicon-based anode materials have two major problems: firstly, the volume is extremely easy to expand in the process of lithium ion extraction/insertion, so that the active material is crushed and the electrode structure is damaged, and meanwhile, the active material is difficult to form a stable SEI film due to the huge volume effect, so that the lithium insertion capacity is rapidly reduced and the cycling stability is poor; secondly, the conductivity is poor, and the performance of lithium storage capacity of the active component and the rate capability of the negative electrode material are influenced.

In view of the above problems of the silicon-based materials, on one hand, researchers have made the silicon-based materials into a nano-porous structure to increase the buffer space, and the nano-porous structure has more active sites, such as the surface, pore channels and other regions of the material, so that the nano-material has better electrochemical properties such as specific capacity, rate capability, cycling stability and the like compared with the micron-sized electrode material. In addition, as dimensions are reduced to the nanoscale, some materials may undergo significant changes in their electrochemical properties, even from electrochemically inert to electrochemically active. The mesoporous silicon nano-rod is prepared by taking a multi-wall carbon nano-tube as a template and adopting a TEOS hydrolysis method and a magnesiothermal reduction method by a professor group of Yankee professor of Shandong university (Electrochimica Acta,2014,127(5): 252-. By comparing the porous silicon network structure with the massive silicon, the mesoporous silicon nanorod is found to have better rate performance and cycle performance due to smaller particle size, and the lithium intercalation capacity is as high as 1038 mAh/g. However, the nano silicon material is easy to agglomerate when used alone, and the problem of volume expansion of the nano silicon material is not fundamentally solved when the nano silicon material is prepared into a nano structure.

In addition, another effective method is to compound the silicon-based material and other materials, and utilize the synergistic effect among the components of the composite material to achieve the purpose of complementary advantages. The carbon material has the advantages of stable chemical property, excellent electron transmission capability, low cost, various forms and the like, so the carbon material becomes the first choice for compounding with the silicon-based material. The silicon-based composite material mainly comprises a silicon-carbon composite material and a silicon oxide/carbon composite material. Compared with simple substance silicon, the silicon-carbon composite material can improve the structural stability and the electrical conductivity of the electrode material, thereby improving the cycle stability and the multiplying power of the electrode materialPerformance, and therefore silicon carbon composites are currently the subject of intense research. Tao (Electrochimica Acta,2012,71(71): 194-200) et al for hexagonal mesoporous SiO₂Performing magnesiothermic reduction to form mesoporous silicon, embedding the phenolic resin into the mesoporous silicon, and then carbonizing to obtain the Si @ C composite. The result shows that the interweaving structure of the Si @ C compound can effectively inhibit the expansion of the volume of Si particles and improve the conductivity of the Si particles, the reversible specific capacity reaches 627mAh/g after 220 times of circulation under the current density of 100mA/g, and the specific capacity of pure mesoporous silicon is rapidly attenuated.

Although the silicon-carbon material has a certain breakthrough in the aspects of cycle performance and rate performance, the volume expansion rate of 400% of the silicon-carbon material still causes the lithium insertion capacity of the silicon material and the compound thereof to gradually decrease in the cycle process. The silicon oxide/carbon composite thus begins to come into the line of sight of people. Silicon oxides likewise have a very high theoretical specific capacity, SiO being the most important constituent of the oxides₂Has a theoretical specific capacity of 1960mAh/g, L i irreversibly formed during the lithium deintercalation process₂O and L i₄SiO₄The components are equal, although the first irreversible capacity of the material is increased, the silicon-based composite material can be used as a buffer medium to relieve the volume change of silicon, so that the volume expansion rate is reduced to 100-300%, and the material has better cycle stability. However, crystalline SiO has been found₂Having a strong Si-O bond results in slow intercalation of lithium ions to cause deterioration of electrochemical activity, while amorphous SiO₂The nano material has the advantages of high lithium storage capacity, stable performance, wide source, simple preparation and the like, thereby becoming one of the lithium ion battery cathode materials with important application prospects. The Hui Lei project group (Journal of Power Sources,2013,237(259):291-₂Compounding the gel with cane sugar, ball milling, and carbonizing to obtain SiO₂The specific capacity of the/C-BM nano composite reaches 600mAh/g after 100 cycles under the current density of 100 mA/g.

Currently, the carbon source of the silicon dioxide/carbon composite material mainly adopts saccharides such as monosaccharide, disaccharide and high-glycan and polymer materials such as phenolic resin, epoxy resin and PVDF. In addition, some carbon nanofibers such as carbon nanofibers, carbon nanotubes and graphene are used as carbon sources, but the preparation method is complex and high in cost, so that the method is not suitable for commercial production.

Wang (Inorganic Chemistry Frontiers,2016,3(11): Accepted) et al uses phenolic resin as a precursor of carbon and adopts a one-step template method to prepare SiO₂The nanoparticles are embedded in the shell of the hollow carbon spheres, and SiO is found₂the/C composite material is relative to pure SiO₂Not only the conductivity is greatly improved, but also the specific capacity is improved from 61mAh/g to 624mAh/g under the current density of 100 mA/g.

Liu(Journal of Materials Science&Technology,2016) and the like, a process for producing SiO by hydrolyzing TEOS using PAA as a template₂Coating a layer of cane sugar on the hollow nanospheres, and obtaining SiO after pyrolysis₂@ C composite material. The test result shows that when SiO₂When the mass fraction is 67%, the cycle performance reaches the best, and the discharge specific capacity reaches 653.4mAh/g after 160 cycles under the current density of 0.11 mA/cm.

Lignin, a natural renewable aromatic ring-rich high-molecular polymer, is widely present in plant xylem, and has annual output of 1500 hundred million tons throughout the world. The industrial lignin is mainly from alkali lignin in the black liquor of alkaline paper-making pulping, lignosulfonate in the red liquor of acid pulping and enzymolysis lignin in the residue of the biorefinery industry, most of the industrial lignin is treated and discharged as waste liquor, and if the industrial lignin can be recycled, not only can resources be saved, but also the environment can be protected. The lignin is a multi-stage three-dimensional network structure formed by combining three phenylpropane monomers, is partially degraded in the papermaking pulping and biorefinery processes, and generates hydrophilic functional groups such as phenolic hydroxyl, alcoholic hydroxyl, carboxyl and the like in molecules, so that the industrial lignin contains hydrophilic and lipophilic amphiphilic structures in molecules, has certain surface activity, has dispersing performance on inorganic particles, and can be used as a dispersing agent, a surfactant, a binder, a water reducing agent and the like. In addition, the industrial lignin has the characteristics of reproducibility, wide source, low cost and high carbon content (50-80%), so that the industrial lignin is an ideal precursor for preparing the carbon material, but is easy to collapse and agglomerate in the carbonization process, is not beneficial to the transmission of lithium ions and electrons, and needs to be activated to produceAnd (4) a hole. Currently, the activation methods of lignin carbon are divided into chemical activation and physical activation, wherein alkali metal ions (such as K) are passed through⁺，Na⁺) High temperature activated etch pore-forming is a commonly used chemical activation method. However, the method has the defects that the etching of alkali metal ions is uncontrollable and is often over-corroded, so that the carbon material has inconsistent aperture, excessive micropores and low yield, and a large amount of energy and precursors are wasted. The physical activation means that MgO, ZnO and the like are used as templates, or the structural strength of the lignin is enhanced by electrostatic spinning and the like, and the method has mild reaction conditions and better controllability.

In view of the above documents and patents, the reason why the silicon-based composite material is difficult to be applied in a large scale is mainly poor cycle stability. For this reason, Si and SiO₂The volume of the silicon-based composite material is seriously expanded in the charging and discharging processes, and on the other hand, the-OH on the surface of the silicon-based composite material has hydrogen bond action, so that the nano particles are seriously agglomerated, and the silicon-based composite material is difficult to realize uniform dispersion. Because lignin molecules have the dispersing function of the surfactant, Si and SiO can be effectively broken₂The hydrogen bond action among particles, the dispersion of nano silicon and silicon dioxide, the research on the silicon-based material and the lignin carbon compounded as the lithium ion battery cathode material attracts attention, namely Tao (Acs Applied Materials) of the American Kentuki university&Interfaces,2016,8(47):32341), et al, proposed the preparation of a silicon-carbon composite material by dissolving lignin as a carbon source, a dispersant and a binder in DMF, blending with silicon nanoparticles, coating, and carbonizing. However, this material is poor in both cycle stability and adhesion, and is difficult to be commercially used. In addition, the complicated preparation process and high production cost of the silicon-based composite material are obstacles which prevent the silicon-based composite material from advancing to commercial production.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention mainly aims to provide a preparation method of a silica/lignin porous carbon composite material.

Aiming at the problem that the volume expansion of silicon dioxide serving as a lithium ion negative electrode material is serious, the method utilizes nano silicon dioxide as a template and a lithium storage active material, and takes industrial lignin as a carbon source and a dispersing agent to prepare the silicon dioxide/lignin porous carbon composite material, and the silicon dioxide/lignin porous carbon composite material is applied to the lithium ion battery negative electrode active material, so that the energy density, the cycling stability and the rate capability of the lithium ion battery are improved.

The invention also aims to provide the silicon dioxide/lignin porous carbon composite material prepared by the method.

The invention further aims to provide application of the silicon dioxide/lignin porous carbon composite material in a lithium ion battery cathode material.

Aiming at the problem of serious aggregation of silicon dioxide, the method firstly utilizes the hydrogen bond action between hydroxyl in industrial lignin molecules and hydroxyl on the surface of nano silicon dioxide to self-assemble and prepare a silicon dioxide/lignin mixture which is uniformly dispersed in a selective solvent, so that the serious agglomeration among nano silicon dioxide particles is broken; then carrying out hydrothermal reaction to further crosslink the lignin to form a silicon dioxide/lignin compound with a certain compact structure and a three-dimensional network, further enhancing the dispersibility of the silicon dioxide and the structural strength of the lignin, and preventing the re-agglomeration of the silicon dioxide and the structural collapse of the lignin in the carbonization process; and finally, obtaining the silicon dioxide/lignin porous carbon composite material after carbonization activation and acid washing.

According to the technology, on one hand, the nano silicon dioxide is coated by the lignin carbon, the volume expansion of the silicon dioxide in the process of releasing/inserting lithium ions is inhibited, and the conductivity of the silicon dioxide is enhanced, on the other hand, the pore-forming activation is carried out on the lignin carbon by using part of the nano silicon dioxide as a template to form a uniform mesoporous structure, so that the lithium ions are greatly accelerated to be inserted and released in a composite material, and the energy density, the cycle stability and the rate capability of a lithium ion battery are remarkably improved.

The purpose of the invention is realized by the following scheme:

a preparation method of a silicon dioxide/lignin porous carbon composite material comprises the following steps:

(1) dissolving industrial lignin and an auxiliary agent in ethanol to prepare a solution with the mass concentration of 5-20 g/L, adding nano silicon dioxide, uniformly mixing, adding water to separate out, separating a precipitate, and drying to obtain a silicon dioxide/lignin mixture;

(2) adding the silicon dioxide/lignin mixture obtained in the step (1) into water with the pH value of 2-4, preparing suspension with the concentration of 10-100 g/L, reacting at 120-200 ℃ for 1-3 h, filtering, drying the precipitate, and carbonizing at 500-900 ℃ for 2-5 h in an inert atmosphere to obtain a silicon dioxide/lignin carbon composite material;

(3) soaking the silicon dioxide/lignin carbon composite material prepared in the step (2) in 0.05-2 mol/L hydrofluoric acid, stirring for 1-24 h, washing with water, filtering, and drying to obtain a silicon dioxide/lignin porous carbon composite material;

by weight, industrial lignin: auxiliary agent: the weight ratio of the nano silicon dioxide is respectively 100: (1-10): (25-400);

the industrial lignin is at least one of alkali lignin extracted from the alkaline pulping black liquor, enzymatic hydrolysis lignin extracted from the biorefinery residue and organic solvent lignin obtained by the solvent pulping.

In the step (1), the auxiliary agent is straight-chain alcohol or polyhydric alcohol, and can comprise at least one of n-butanol, n-pentanol, dodecanol, ethylene glycol and glycerol.

In the step (1), the particle size of the nano silicon dioxide is 10-100 nm, and preferably 30 nm.

In the step (1), the volume of the water is 1-10 times of that of the ethanol, and preferably 3 times of that of the ethanol.

The water is preferably added dropwise in the step (1) to separate out, wherein the dropwise adding is performed under a stirring state, and the water adding rate is 5-30 m L/min.

In the step (2), the reaction temperature is preferably 160 ℃, and the reaction time is preferably 1 h.

In the step (1), the step (2) and the step (3), the drying may include one of drying methods such as forced air drying, vacuum drying, infrared drying, spray drying and the like.

The present invention will be described in more detail below.

(1) Uniformly mixing industrial lignin solid powder and an auxiliary agent, dissolving the mixture in absolute ethyl alcohol to prepare a solution with the mass concentration of 5-20 g/L, adding nano silicon dioxide, uniformly mixing, dropwise adding water under a stirring state, centrifugally separating out a precipitate, and drying to obtain a silicon dioxide/lignin mixture;

the step is to utilize the property that industrial lignin is in a stretched state in absolute ethyl alcohol under the action of an auxiliary agent and is in an aggregation state due to pi-pi stacking interaction in water, water is gradually added into an absolute ethyl alcohol dispersion liquid of lignin/silicon dioxide based on the hydrogen bond action between the industrial lignin and the silicon dioxide, and the water is self-assembled in a selective solvent to obtain a silicon dioxide/lignin mixture which is uniformly dispersed.

In this step, since the industrial lignin contains both hydrophilic and lipophilic functional groups, its solubility in absolute ethanol is low, so it needs to be mixed with the auxiliary agent in a certain proportion to increase the solubility of lignin in absolute ethanol. The preferred mass ratio is 100: 1-100: 10, and the dosage is insufficient, so that the effect of increasing the solubility of lignin in absolute ethyl alcohol cannot be achieved; the excessive dosage affects the subsequent dispersion of the nano silicon dioxide.

The concentration is preferably 5 to 20 g/L, and when the concentration is too low, the yield of the product is low, and when the concentration is too high, the dissolution effect of the industrial lignin is poor.

The dropwise water addition is that the water addition rate is 5-30 m L/min, if the water addition rate is too slow, the yield of the silica/lignin mixture is low, and if the water addition rate is too fast, the nano silica in the mixture is agglomerated.

(2) Adding the silicon dioxide/lignin mixture obtained in the step (1) into water with the pH value of 2-4 to prepare a suspension with the mass concentration of 10-100 g/L, uniformly mixing, reacting at 120-200 ℃ in a hydrothermal reaction kettle for 1-3 h, filtering, drying the precipitate, then placing in a nitrogen atmosphere, and carbonizing at 500-900 ℃ for 2-5 h to obtain a silicon dioxide/lignin carbon composite material;

in the step, hydrothermal reaction enables lignin and nano-silica and lignin molecules to be crosslinked through esterification, so that a silica/lignin compound with a certain compact structure and a uniform three-dimensional network structure is formed, if the step is not adopted, nano-silica is agglomerated again in the carbonization process and the lignin is shrunk to a certain extent in the structure, so that the formation of a uniform mesoporous structure on the lignin carbon is influenced, and the transmission efficiency of lithium ions is reduced.

The mass concentration of the prepared suspension is preferably 10-100 g/L, if the concentration is too low, the yield is too low, the production efficiency is reduced, if the concentration is too high, the dispersion effect and the crosslinking degree are poor, and the carbonization effect is influenced, the hydrothermal reaction temperature is 120-200 ℃, preferably about 160 ℃, the reaction time is preferably 1h, the pH value of water in the reaction is preferably 2-4, and otherwise, the crosslinking effect is poor.

The pH of the water is adjusted using a strong acid. The strong acid is, for example, sulfuric acid, hydrochloric acid or nitric acid. The use of strong acid concentrations is not a critical factor in adjusting the pH, and is typically 10 to 30 wt%.

The carbonization atmosphere in this step is not critical and must be nitrogen, and may be replaced with other inert gases such as argon. The carbonization temperature is required to be within the range of 500-900 ℃, the time is 2-5 h, if the temperature or the time is too low, incomplete carbonization can be caused, and if the temperature or the time is too high, not only can the production cost be increased, but also the carbon structure of lignin is unstable.

(3) Pickling the silicon dioxide/lignin carbon composite material with 0.05-2 mol/L hydrofluoric acid for 1-24 h, washing with deionized water, and drying to obtain the silicon dioxide/lignin porous carbon composite material;

the concentration of hydrofluoric acid is required to be within the range of 0.05-2 mol/L, the pickling time is controlled to be 1-24 h, if the concentration of hydrofluoric acid is too low or the pickling time is too short, on one hand, a material does not have a developed pore channel structure, the cycle performance and the rate capability of the material are greatly reduced, on the other hand, the content of silicon dioxide is too high, so that the volume expansion of the material in the charging and discharging processes cannot be effectively inhibited, and if the concentration of hydrofluoric acid is too high or the pickling time is too long, the silicon dioxide is basically cleaned, the cycle performance is reduced, the cost is improved, the lignin carbon structure is seriously corroded, the pore channel structure is damaged.

The specific surface area range of the silicon dioxide/lignin porous carbon composite material prepared by the method is 100-1500 m²The content range of the silicon dioxide is 10-60 wt%. Can be applied to the cathode material of the lithium ion battery.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the silicon dioxide lignin porous carbon prepared by the method has higher order degree and specific surface area, pore canal size and distribution are uniform, and the nano silicon dioxide in the lignin porous carbon is highly dispersed, so that the volume expansion and the collapse of the lignin porous carbon are effectively inhibited.

(2) In the preparation process of the silicon dioxide/lignin porous carbon, the industrial lignin is used as a carbon source and a dispersing agent, the silicon dioxide is used as a template and an active material, the raw materials are renewable resources with large quantity and wide range, and are cheap and easily available, the preparation process is simple and green, the resource utilization of papermaking black liquor or biorefinery residues can be realized, the resources are saved, and the environment is protected.

Drawings

FIG. 1 is a graph of rate capability of silica/lignin porous carbon prepared in example 1 of the present invention;

FIG. 2 is a TEM image of silica/lignin porous carbon prepared in example 1 of the present invention;

FIG. 3 is an SEM image of silica/lignin porous carbon prepared according to example 1 of the present invention;

FIG. 4 is a drawing showing nitrogen desorption of silica/lignin porous carbon produced in example 1 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

Example 1

Mixing 1g alkali lignin solid powder with 0.01g dodecanol, adding into 200m L anhydrous ethanol, dissolving, adding 0.25g nanometer silica (particle size 10nm), mixing, adding 200m L water at 5m L/min under stirring, centrifuging to separate precipitate, and drying to obtain silica/lignin mixture.

Placing 1g of silicon dioxide/lignin mixture in a hydrothermal reaction kettle, adding 100m L of water with the pH value of 2, uniformly mixing, heating to 120 ℃, reacting for 1h, filtering and separating to obtain a precipitate, drying, placing in a nitrogen atmosphere, heating to 600 ℃, keeping for 2h to obtain a silicon dioxide/lignin carbon composite material, then placing in 1 mol/L hydrofluoric acid, stirring for 4h, washing with deionized water, filtering, and spray drying to obtain the silicon dioxide/lignin porous carbon composite material.

Example 2

Mixing 0.5g alkali lignin and 0.5g enzymolysis lignin solid powder with 0.1g n-butanol, adding into 50m L anhydrous ethanol for dissolving, adding 1.0g nanometer silicon dioxide (particle size 100nm), mixing, adding 500m L water at 30m L/min under stirring, centrifuging to separate out precipitate, and infrared drying to obtain silicon dioxide/lignin mixture.

Placing 1g of silicon dioxide/lignin mixture in a hydrothermal reaction kettle, adding water with the pH value of 4 of 10m L, uniformly mixing, heating to 200 ℃, reacting for 3h, drying the precipitate after filtering, then placing in a nitrogen atmosphere, heating to 900 ℃, keeping for 2h to prepare the silicon dioxide/lignin carbon composite material, then placing in 0.5 mol/L hydrofluoric acid, stirring for 24h, washing with deionized water, filtering, and drying to obtain the silicon dioxide/lignin porous carbon composite material.

Example 3

Mixing 5g of enzymolysis lignin solid powder with 0.05g of ethylene glycol, adding 250m L of anhydrous ethanol for dissolving, adding 5g of nano silicon dioxide (with the particle size of 30nm), mixing uniformly, adding 750m L of water at the speed of 10m L/min under the stirring state, centrifugally separating out precipitate, and drying to obtain a silicon dioxide/lignin mixture.

Placing 5g of silicon dioxide/lignin mixture in a hydrothermal reaction kettle, adding 50m L of water with the pH value of 3, uniformly mixing, heating to 160 ℃, reacting for 1h, drying the precipitate after filtering, then placing in a nitrogen atmosphere, heating to 700 ℃, keeping for 2h to prepare the silicon dioxide/lignin carbon composite material, then placing in 1 mol/L hydrofluoric acid, stirring for 4h, washing with deionized water, filtering, and drying to obtain the silicon dioxide/lignin porous carbon composite material.

Example 4

Mixing 1g organic solvent lignin solid powder and 0.05g glycerol, adding into 100m L anhydrous ethanol for dissolving, adding 0.5g nanometer silicon dioxide (particle size 100nm), mixing, adding 200m L water at 20m L/min under stirring, centrifuging to separate out precipitate, and infrared drying to obtain silicon dioxide/lignin mixture.

Placing 1g of silicon dioxide/lignin mixture in a hydrothermal reaction kettle, adding 50m L of water with the pH value of 3, uniformly mixing, heating to 160 ℃, reacting for 3h, drying the precipitate after filtering, then placing in a nitrogen atmosphere, heating to 800 ℃, keeping for 2h to prepare the silicon dioxide/lignin carbon composite material, then placing in 1 mol/L hydrofluoric acid, stirring for 4h, washing with deionized water, filtering, and drying to obtain the silicon dioxide/lignin porous carbon composite material.

Example 5

Mixing 3g of enzymolysis lignin and 2g of alkali lignin solid powder with 0.1g of ethylene glycol, adding into 100m L of anhydrous ethanol for dissolving, adding 2.5g of nano silicon dioxide (with the particle size of 50nm), mixing uniformly, adding 400m L of water at the speed of 10m L/min under the stirring state, centrifugally separating out precipitate, and drying to obtain a silicon dioxide/lignin mixture.

Placing 5g of silicon dioxide/lignin mixture in a hydrothermal reaction kettle, adding 100m L of water with the pH value of 3, uniformly mixing, heating to 160 ℃, reacting for 1h, drying the precipitate after filtering, then placing in a nitrogen atmosphere, heating to 900 ℃, keeping for 3h to prepare the silicon dioxide/lignin carbon composite material, then placing in 1 mol/L hydrofluoric acid, stirring for 6h, washing with deionized water, filtering, and drying to obtain the silicon dioxide/lignin porous carbon composite material.

Example 6

Mixing 1g organic solvent lignin solid powder and 0.02g dodecanol, adding into 100m L anhydrous ethanol for dissolving, adding 0.5g nanometer silica (particle size of 30nm), mixing, adding 300m L water at 20m L/min under stirring, centrifuging to separate precipitate, and drying to obtain silica/lignin mixture.

Placing 1g of silicon dioxide/lignin mixture in a hydrothermal reaction kettle, adding water with the pH value of 3 of 20m L, uniformly mixing, heating to 180 ℃, reacting for 3 hours, drying the precipitate after filtering, then placing in a nitrogen atmosphere, heating to 800 ℃, keeping for 2 hours to prepare a silicon dioxide/lignin carbon composite material, then placing in 0.05 mol/L hydrofluoric acid, stirring for 24 hours, washing with deionized water, filtering, and drying to obtain the silicon dioxide/lignin porous carbon composite material.

The prepared silicon dioxide/lignin porous carbon composite material is applied to a lithium ion battery cathode material and subjected to electrochemical test and material characterization, and the results are shown in table 1 and figures 1-4.

The morphology and size of the samples of the present invention were tested by field emission scanning electron microscopy (SEM, Hitachi S-550) and high resolution field emission transmission electron microscopy (HRTEM, JEO L JEM-2100F,200kV) equipped with an energy spectrometer (ThermoFisher Scientific, NORAN System 7.) the testing of sample specific surface area and pore structure was performed using a fully automated specific surface and porosity analyzer (Micromeritics ASAP2020 instrument).

The battery assembly adopts a half battery assembly, the model is CR2032, the positive electrode material comprises 80 wt% of active substance, 10 wt% of carbon black and 10 wt% of polyvinylidene fluoride (PVDF), N-methyl-2-pyrrolidone (NMP) is adopted as a solvent for coating, wherein the active substance is the prepared silicon dioxide/lignin porous carbon composite material, the lithium sheet is used as a counter electrode, and the electrolyte is 1 mol/L L iPF₆As solute, the volume ratio is 1: 1: 1 Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and dimethyl carbonate (DMC) as solvent. The whole installation process of the lithium ion half cell is carried out under argonAnd finishing the operation in the protective glove box. The constant current charging/discharging performance test of the battery is carried out under the current density of 100mA/g and 5A/g in the voltage range of 0.01V-3.0V by using a Neware battery performance test system, and the multiplying power performance test is completed under the current density of 50mA/g, 100mA/g, 200mA/g, 500mA/g and 1000 mA/g.

Table 1 compares the cycle performance of the silica/lignin porous carbon composite prepared in the above examples with pure nanosilica (particle size 10nm) and lignin porous carbon.

In order to further study whether the silicon dioxide really has a certain lithium intercalation capacity in the lignin porous carbon, the lignin porous carbon material (table 1) is prepared by washing off all the silicon dioxide and used as a comparison sample, and the preparation process is as follows:

Putting 1g of silicon dioxide/lignin mixture into a hydrothermal reaction kettle, adding 100m L of water with the pH value of 2, uniformly mixing, heating to 120 ℃, reacting for 1h, filtering and separating to obtain a precipitate, drying, putting into a nitrogen atmosphere, heating to 600 ℃, keeping for 2h to obtain a silicon dioxide/lignin carbon composite material, then putting into 2 mol/L hydrofluoric acid, stirring for 24h, completely washing off silicon dioxide, washing with deionized water, filtering, and spray-drying to obtain the lignin porous carbon material.

TABLE 1 Cyclic Properties of silica/Lignin porous carbon composites

Table 1 illustrates: the specific discharge capacity of the silica/lignin porous carbon composite material prepared in the embodiment 1 after 100 cycles under the low current density of 100mA/g and the high current density of 5A/g is 820mAh/g and 232mAh/g respectively, and the cycle stability is good and is obviously superior to that of similar materials.

The results for the lignin porous carbon in table 1 show: after 100 cycles at 100mA/g, the lithium intercalation capacity is only 507mAh/g, the volume expansion of pure nano-silica (with the particle size of 10nm) which is not treated is not effectively inhibited, and the specific discharge capacity at 100mA/g is only 31mAh/g, so that compared with pure silica and lignin porous carbon, the silica/lignin porous carbon composite material prepared by the invention has a more excellent energy storage effect.

FIG. 1 is a graph of rate capability of a silica/lignin porous carbon composite material prepared in example 1 of the present invention. As can be seen from the figure, the silicon dioxide/lignin porous carbon composite material also has larger specific capacity under high multiplying power, and the specific capacity is 50 mA.g^-1，100mA·g^-1，200mA·g^-1，500mA·g^-1And 1A. g^-1The specific capacity under the current density is 979 mAh.g^-1，766mAh·g^-1，626mAh·g^-1，432mAh·g^-1And 331mAh · g^-1. In addition, the reversible performance of the composite material is better, and when the current density is reduced to 50mA · g again^-1When the specific capacity is increased to 954 mAh.g^-1。

FIG. 2 is a TEM image of a silica/lignin porous carbon composite prepared in example 1 of the present invention. The figure shows that the lignin carbon material on the outer layer has a developed pore channel structure uniformly distributed, and the nano silicon dioxide is mainly dispersed in the lignin porous carbon in a granular form, so that the volume expansion generated in the charge and discharge process of the lignin porous carbon material is remarkably inhibited, and the lithium intercalation capacity and rate capability of the lignin porous carbon material are improved.

FIG. 3 is an SEM image of a silica/lignin porous carbon composite prepared in example 1 of the present invention. It can be seen from the figure that the lignin carbon on the surface is crosslinked, the structure is compact, and the pore canals are not uniform in shape but are distributed and uniform in size.

FIG. 4 is a drawing showing nitrogen desorption of the silica/lignin porous carbon composite material prepared in example 1 of the present invention. The figure shows that the silicon dioxide/lignin porous carbon composite material belongs to IV-type desorption, has a developed mesoporous structure and a specific surfaceThe volume and the pore volume respectively reach 1069cm²G and 3.04cm³The particle size of the nano-silica particles is not greatly different from that of the nano-silica particles (10nm), which indirectly shows that the nano-silica particles are distributed in the lignin carbon quite uniformly.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A preparation method of a silicon dioxide/lignin porous carbon composite material is characterized by comprising the following steps:

the industrial lignin comprises: auxiliary agent: the weight ratio of the nano silicon dioxide is respectively 100: (1-10): (25-400);

the auxiliary agent is straight-chain alcohol or polyhydric alcohol.

2. The method for preparing a silica/lignin porous carbon composite according to claim 1, characterized in that: the auxiliary agent is at least one of n-butyl alcohol, n-amyl alcohol, dodecanol, ethylene glycol and glycerol.

3. The method for preparing a silica/lignin porous carbon composite according to claim 1, characterized in that: the industrial lignin is at least one of alkali lignin extracted from the alkaline pulping black liquor, enzymatic hydrolysis lignin extracted from the biorefinery residue and organic solvent lignin obtained by the solvent pulping.

4. The method for preparing a silica/lignin porous carbon composite according to claim 1, characterized in that: the particle size of the nano silicon dioxide is 10-100 nm.

5. The method for preparing a silica/lignin porous carbon composite according to claim 1, characterized in that: in the step (1), the volume of the water is 1-10 times of that of the ethanol.

6. The preparation method of the silica/lignin porous carbon composite material according to claim 1, wherein the step (1) of adding water is characterized in that water is added dropwise under a stirring state, and the dropwise adding of water is performed at a water adding rate of 5-30 m L/min.

7. The method for preparing a silica/lignin porous carbon composite according to claim 1, characterized in that: in the step (2), the reaction temperature is 160 ℃, and the reaction time is 1 h.

8. A silica/lignin porous carbon composite material characterized by being obtained by the preparation method according to any one of claims 1 to 7.

9. The use of the silica/lignin porous carbon composite of claim 8 in a lithium ion battery negative electrode material.