CN116053425A - Silicon-containing biomass graphite anode material and electrochemical device thereof - Google Patents

Silicon-containing biomass graphite anode material and electrochemical device thereof Download PDF

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CN116053425A
CN116053425A CN202211270947.5A CN202211270947A CN116053425A CN 116053425 A CN116053425 A CN 116053425A CN 202211270947 A CN202211270947 A CN 202211270947A CN 116053425 A CN116053425 A CN 116053425A
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silicon
anode material
biomass graphite
graphite
carbon
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易婷
熊永莲
林圣强
侯全会
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Yancheng Institute of Technology
Yancheng Institute of Technology Technology Transfer Center Co Ltd
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Yancheng Institute of Technology
Yancheng Institute of Technology Technology Transfer Center Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a silicon-containing biomass graphite anode material and an electrochemical device thereof, which comprise porous biomass graphite, a silicon oxide compound and carbon nanotubes, and are characterized in that: one part of the carbon nano tube is positioned on the surfaces of the porous biomass graphite and the silicon oxide compound, the other part of the carbon nano tube penetrates through the porous biomass graphite and the silicon oxide compound, and a carbon coating layer is arranged on the surfaces of the porous biomass graphite and the silicon oxide compound. According to the silicon-containing biomass graphite anode material and the electrochemical device thereof, the porous biomass graphite, the silicon oxide and the carbon nano tube are subjected to co-spheroidization to obtain the composite anode material with low expansion rate, high stability and good lithium ion transmission property, and carbon coating is carried out on the surface of the composite anode material, so that the conductivity of the anode material is further improved. The composite anode material can obviously improve the cycle performance and the expansion performance of the lithium ion battery.

Description

Silicon-containing biomass graphite anode material and electrochemical device thereof
Technical Field
The invention relates to the technical field of electrochemistry, in particular to a silicon-containing biomass graphite anode material and an electrochemical device thereof.
Background
The lithium ion battery is widely applied to the fields of wearable equipment, smart phones, unmanned aerial vehicles, electric vehicles, large-scale energy storage equipment and the like due to the advantages of high energy density, long cycle life, no memory effect and the like, and becomes a novel green chemical power supply with the most development potential at present. Along with the continuous expansion of various application fields, higher requirements are also put on the comprehensive performance of the lithium ion battery.
The traditional graphite raw material belongs to non-renewable resources, the theoretical capacity of graphite is 372mAh/g, the current commercialized graphite can reach 355mAh/g, the bottleneck is reached, and the continuous improvement of the capacity of graphite is difficult.
At present, the optimal scheme for improving the energy density of the lithium ion battery is to improve the capacity of a negative electrode material, and more commercialized applications are to compound graphite with nano silicon to obtain a silicon-carbon composite material (CN 102651476A, CN 114068901A), wherein the composite material has the defects that: 1. the nano silicon is expanded to expand, and the cyclic expansion can lead to poor contact between graphite and silicon, so that the capacity of the lithium ion battery is lost sharply. 2. The silicon-carbon composite material is applied to practice, and the silicon-carbon composite material is mechanically mixed with graphite to obtain matched capacity, so that the uniformity of mixing has a great influence on the performance of the final lithium ion battery, the process steps are increased, and the cost is increased. The existing silicon-carbon composite material is expanded circularly, cannot meet the application requirement, and needs to further reduce expansion.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a silicon-containing biomass graphite anode material and an electrochemical device thereof, and solves the problem that the existing silicon-carbon composite material is expanded circularly and cannot meet the application requirement.
In order to achieve the above purpose, the invention is realized by the following technical scheme: the silicon-containing biomass graphite cathode material comprises porous biomass graphite, a silicon oxide compound and carbon nanotubes, and is characterized in that: and one part of the carbon nano tube is positioned on the surfaces of the porous biomass graphite and the silicon oxide compound, the other part of the carbon nano tube penetrates through the porous biomass graphite and the silicon oxide compound, and a carbon coating layer is arranged on the surfaces of the porous biomass graphite and the silicon oxide compound.
Preferably, the mass of the silica compound is m1, the mass of the porous biomass graphite/silica compound is m, r1=m1/m, the value of r1 is 3% -20%, the mass of the carbon nanotube is m2, the mass of the porous biomass graphite/silica compound is m, r2=m2/m, the value of r2 is 0.05% -1.5%, the mass of the carbon coating layer is m3, the mass of the porous biomass graphite/silica compound is m, r3=m3/m, and the value of r3 is 1% -3%.
Preferably, the porous biomass graphite is tested for SP by X-ray photoelectron spectroscopy 2 -C (284.8 eV) and SP 3 -C (285.6 eV) area ratio in the range of 2.3-1.5, N 2 The adsorption test pore diameter ranges from 0.3nm to 15nm, and the preferred range is from 3nm to 8nm.
Preferably, the silica compound has a Dv50 of 3 μm to 8 μm and a specific surface area of 1.0m 2 /g-10m 2 /g。
Preferably, the silica compound includes: siOx, wherein 0.5< x <1.6, comprising: at least one of crystalline or amorphous.
Preferably, the carbon nanotube includes: single-walled carbon nanotubes and multi-walled carbon nanotubes.
Preferably, the carbon coating layer is at least one of alkane, alkene and alkyne.
The invention also discloses an electrochemical device of the silicon-containing biomass graphite anode material, which comprises an anode pole piece, a cathode pole piece and a separation film arranged between the anode pole piece and the cathode pole piece, wherein the cathode pole piece comprises a cathode current collector and a cathode active material layer arranged on the cathode current collector, and the cathode active material layer comprises the anode material as claimed in any one of claims 1 to 7.
Preferably, the electrochemical device further includes: and an electrolyte comprising fluoroethylene carbonate in a mass fraction of 4% -30% based on the total mass of the electrolyte.
Advantageous effects
The invention provides a silicon-containing biomass graphite anode material and an electrochemical device thereof. Compared with the prior art, the method has the following beneficial effects:
according to the silicon-containing biomass graphite anode material and the electrochemical device thereof, the porous biomass graphite, the silicon oxide and the carbon nano tube are subjected to co-spheroidization to obtain the composite anode material with low expansion rate, high stability and good lithium ion transmission property, and carbon coating is carried out on the surface of the composite anode material, so that the conductivity of the anode material is further improved. The composite anode material can obviously improve the cycle performance and the expansion performance of the lithium ion battery.
Drawings
FIG. 1 is a model of porous biomass graphite and silica compound of the invention;
FIG. 2 is an XPS spectrum of the porous biomass graphite of the present invention;
fig. 3 is a cycle chart of example 1, example 9 and comparative example 1 of the present invention.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 1-3, the present invention provides 10 embodiments: the silicon-containing biomass graphite anode material has a specific capacity far higher than that of a carbon material, so that more and more electrochemical devices are added with the silicon-based material as the anode material, however, the silicon-based material also has some problems as the anode material, and in the circulation process, the volume change of the silicon-based material is large, so that the silicon-based material is powdered and separated from an anode current collector, and the circulation performance, the rate performance and the like of the electrochemical devices are reduced. The silicon oxide material has silicon dioxide as an expansion buffer phase, and has better cycle stability and expansion performance compared with nano silicon.
The biomass graphite material has porosity, can effectively relieve the lithium intercalation expansion of the silicon oxide, has a renewable resource as a raw material source, is low in price, and can further reduce the cost of the lithium ion battery to a certain extent.
In some embodiments, the cellulose raw material of the biomass graphite is cellulose and hemicellulose, and the cellulose has a similar structure to the hemicellulose and poor thermal stability, so that the biomass graphite is easier to graphitize at a relatively low temperature, and biomass graphite with high graphitization degree and SP of corresponding carbon are obtained 2 The hybridization is higher, the crystallization of the material is regular, the gram capacity is high, and the cycle performance can be better. In some embodiments, the biomass graphite is originally lignin, the lignin has a changeable structure, high thermal stability and high graphitization temperature requirement, so that the graphitization degree of the lignin is lower than that of cellulose under the same temperature condition.
In some embodiments, the graphitization temperature of the cellulose is 1300 ℃ to 1600 ℃, and the higher the temperature is, the higher the graphitization degree of the biomass is, but the higher the graphitization degree is, the poorer the dynamic performance of the material is caused, and the phenomenon of local lithium precipitation is caused in the circulation process, so that the circulation capacity is kept and the expansion rate is slightly poorer.
In some embodiments, D of the silicon-based material v50 From 3 μm to 8 μm. In some embodiments, when the particle size Dv50 of the silica is too large, the particles break more obviously during the circulation process, so that more electrolyte is consumed at the newly exposed material interface, and the expansion becomes large, and the circulation performance becomes poor; when the particle diameter Dv50 of the silica is too small, the specific surface area of the particles increases, and more electrolyte is consumed during the initial cycle, resulting in deterioration of cycle performance; the specific surface area of nano silicon is large, the reactivity is large, and the nano silicon is easier to be combined with electrolyteAnd the reaction causes the cell to expand, so that the cyclic attenuation is accelerated.
In other embodiments of the present application, an electrochemical device is presented, the electrochemical device comprising: the positive pole piece, negative pole piece and set up the barrier film between positive pole piece and negative pole piece, the negative pole piece includes negative pole current collector and sets up the negative pole active material layer on the negative pole current collector, and negative pole active material layer includes the negative pole material of any one of the above-mentioned items.
In some embodiments, the electrochemical device further comprises: and the electrolyte comprises fluoroethylene carbonate, and the mass fraction of the fluoroethylene carbonate is 3-25% based on the total mass of the electrolyte. In some embodiments of the present application, the FEC can increase the mechanical properties of the SEI film, thereby reducing the cyclic expansion rate of the electrochemical device and improving the cyclic capacity retention rate, and when the amount of FEC is too low, the improvement effect may not be obvious, and when the amount of FEC is too large, the SEI film is continuously generated, the resistance of the electrochemical device is increased, the cyclic capacity retention rate is reduced, and in some embodiments, the cyclic capacity retention rate of the electrochemical device using the silicon-based material can be significantly improved and the cyclic expansion rate is reduced by adding the FEC.
In some embodiments of the present application, the electrolyte includes an organic solvent and a lithium salt; at least one of Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate or ethyl propionate.
In some embodiments, the lithium salt comprises: lithium hexafluorophosphate (LiPF) 6 ) Lithium tetrafluoroborate (LiBF 4 ) Lithium difluorophosphate (LiPO) 2 F 2 ) Lithium bis (trifluoromethanesulfonyl) imide LiN (CF) 3 SO 2 ) 2 (LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO) 2 F) 2 ) (LiLSI), lithium bisoxalato borate LiB (C) 2 O 4 ) 2 (LiBOB), lithium difluorooxalato borate LiBF 2 (C 2 O 4 ) At least one of (LiDFOB).
In some embodiments, the Ethylene Carbonate (EC) comprises 3% to 25% of the volume of the organic solvent; ethylene carbonateThe dielectric constant of the Ester (EC) is high and the main decomposition product is ROCO 2 Li, which can form an effective, dense, stable SEI (solid electrolyte interphase) film on the surface of a negative electrode material, can significantly improve the capacity retention rate and low-temperature performance of an electrochemical device when the volume ratio of EC in an organic solvent is in the range of 4% to 35%. In some embodiments, when the volume ratio of EC in the organic solvent is 25%, the viscosity of the electrolyte increases due to the larger viscosity of EC, and the low-temperature performance is deteriorated.
In some embodiments, the organic solvent comprises fluoroethylene carbonate (FEC), ethylene Carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC), the Ethylene Carbonate (EC) comprising 3% to 25% by volume of the organic solvent; the volume ratio of Ethylene Carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) is (0.1 to 1): 1:1, the mass of fluoroethylene carbonate (FEC) accounts for 15% of the total mass of the electrolyte, and the lithium salt comprises lithium hexafluorophosphate (LiPF) 6 ) Lithium hexafluorophosphate (LiPF) 6 ) The concentration in the electrolyte was 1mol/L. In some embodiments, the mass content of FEC in the electrolyte and the LiPF are controlled by the volume ratio of EC, DMC, and DEC 6 The concentration of (c) in the above range is advantageous in improving the cycle capacity retention rate and rate capability of the electrochemical device and reducing the cycle expansion rate of the electrochemical device.
In some embodiments, a conductive agent may be further included in the anode active material layer. The conductive agent in the anode active material layer may include at least one of carbon black, acetylene black, ketjen black, sheet graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. It should be understood that the above disclosed materials are merely exemplary, and that any other suitable materials may be used for the anode active material layer. In some embodiments, the mass ratio of the anode material, the conductive agent, and the binder in the anode active material layer may be 70 to 99:0.5 to 20:0.5 to 10, it should be understood that this is exemplary only and is not intended to limit the present application.
The positive electrode sheet in the present application is not particularly limited, and any positive electrode sheet known in the art may be employed. For example, a positive electrode sheet containing lithium cobaltate, a positive electrode sheet containing lithium manganate, a positive electrode sheet containing lithium iron phosphate, or a positive electrode sheet containing lithium nickel cobalt manganate or lithium nickel cobalt aluminate.
The process of preparing the electrochemical device is well known to those skilled in the art, and the present application is not particularly limited. For example, the secondary battery may be manufactured by: the positive electrode and the negative electrode are overlapped through a spacer, are put into a battery container after being wound, folded and the like according to the requirement, and are injected with electrolyte, and are sealed, wherein the negative electrode is the negative electrode plate provided by the application. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the battery container as needed, so that the pressure inside the battery can be prevented from rising and overcharging and discharging.
The application also provides a preparation method of the negative electrode plate, which comprises the following steps: preparation of negative electrode material
Step 1: taking cellulose, hemicellulose, lignin and the like as experimental raw materials, placing the experimental raw materials in a closed box furnace which is filled with inert protective gas (Ar, N2 and the like), carbonizing to remove part of volatile matters, and collecting biomass after the reaction process is that the experimental raw materials are placed in the box furnace, inert gas is filled into the box furnace, the oxygen-containing gas is thoroughly removed by blowing for 1h, then the temperature is increased to 200 ℃ from room temperature at 5 ℃/min, the temperature is kept for 2h, then the temperature is continuously increased to 500 ℃ at 5 ℃/min, the temperature is kept for 8h, and the biomass is collected after the temperature is reduced. The process can partially remove volatile matters in biomass, is easy to crush into required particle size distribution after being prepared into biological coke, and can retain certain porosity after removing part of volatile matters, and the porosity is favorable for loading the catalyst in the third step;
step 2: the biological coke is crushed by a crusher until the particle size is more than or equal to 200 meshes, and the process is favorable for fully converting biomass carbon into a lithium-intercalated carbon material by a catalyst in the catalytic process;
step 3: uniformly stirring and mixing a catalyst containing Fe/Mn/Ni and other mineral substances with crushed biomass carbon, placing the mixture in hydrothermal reaction equipment, reacting at 200 ℃ for 24 hours, cooling, filtering, collecting the biomass carbon loaded by the catalyst, and drying for later use;
step 4: placing the biomass carbon loaded with the catalyst in a box-type furnace, purging with inert gas for 1h to remove oxygen-containing gas, heating to 1300-1600 ℃ from room temperature at a speed of 5 ℃/min, preserving heat for 24h, and cooling to collect a sample;
step 5: a certain amount of the sample prepared in the step 4 is weighed and placed in a beaker filled with HCl solution with the concentration of 6mol/L, and the beaker is placed in a magnetic water bath kettle with the temperature raised to 70 ℃ and magnetically stirred for 12 hours. The above steps are repeated after the HCl solution is removed by suction filtration. Thoroughly removing the catalyst in the sample through the process, and finally, carrying out suction filtration and drying for later use;
step 6: porous biomass graphite and nano SiO prepared in the step 5 are subjected to the process of preparation x The powder, the carbon nano tube solution and a certain amount of binder (the binder comprises asphalt, heavy oil, biomass and the like) are fully mixed and then are placed into a spheroidizing device for spheroidization, and SiO is spheroidized x And the single-wall carbon nano tube is coated in the porous biomass carbon material, and after the sample preparation is finished, the sample is placed in a box furnace for carbonization treatment, and the carbonization flow is as follows: purging with inert gas for 1h to remove oxygen-containing gas, heating to 500 ℃ from room temperature at a speed of 5 ℃/min, preserving heat for 8h, and cooling to collect a sample.
Step 7: graphite/SiO biomass x Placing the powder in a chemical vapor deposition furnace, filling carbon source gas, wherein the carbon source is at least one of alkane, alkene and alkyne, purging the carbon source gas with inert gas for 1h to remove oxygen-containing gas before filling the carbon source gas, heating the powder to 600-1000 ℃ from room temperature at a speed of 5 ℃/min, preserving heat for 4-8 h, cooling and collecting a sample to obtain biomass graphite/SiO with carbon coated on the surface x And (3) a composite anode material.
Preparation of negative electrode plate
Step 1: stirring and mixing the cathode material and the conductive agent to obtain a mixture A, wherein the stirring time is not less than 120min, and the revolution speed of a stirrer is 10-30 r/min;
step 2: adding the binder into the mixture A, stirring uniformly (namely, stirring for the first time), adding deionized water, continuing stirring (namely, stirring for the second time), obtaining mixed slurry, and filtering with a 170-mesh double-layer screen to obtain negative electrode slurry, wherein the first stirring time is not less than 60min, the second stirring time is not less than 120min, the revolution speed of a stirrer is 10-30 r/min, the rotation speed is 1000-1500 r/min, and the stirrer is a vacuum stirrer with the model MSK-SFM-10;
step 3: coating the negative electrode slurry on a copper foil current collector, drying, cold pressing, and compacting the double-sided compact density to 1.3-2.0 g/cm 3 Obtaining a negative electrode plate;
in one embodiment of the present application, the conductive agent may further include at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, or graphene.
In one embodiment of the application, the viscosity of the mixed slurry is 2500-4000mpa.s and the solids content is 35% -55%.
In one embodiment of the application, the mass ratio of the anode material, the conductive agent and the binder is 93.5% -96.5%:1.5% -2.0%:1.5% -2%.
The specific amounts of the above-mentioned negative electrode material, conductive agent, and binder are not particularly limited in this application, as long as the object of the present application can be achieved, and those skilled in the art can reasonably select the amounts of the components according to the ratio ranges of the above-mentioned components. In one embodiment of the present application, two-sided coating may be used, or single-sided coating may be used, each having a thickness of 50-200 μm.
Preparation of positive electrode plate
The active substance NCM613, conductive carbon black and binder are mixed according to the mass ratio of 95 to 98 percent: 1.5% to 5%:1.5 to 5 percent of the aluminum foil is fully stirred and uniformly mixed in an organic solvent system, then is coated on the aluminum foil, dried and cold-pressed to obtain the positive electrode plate, wherein the adhesive is polyvinylidene fluoride, and the organic solvent is N-methyl pyrrolidone.
Preparation of electrolyte
Mixing a solvent EC, DMC, DEC according to a volume ratio of 1:1:1 to obtain a mixed solution, and then adding FEC and LiPF 6 Mixing to obtain electrolyte, wherein the mass concentration of FEC in the electrolyte is 15-30wt%, liPF 6 The molar concentration in the electrolyte is 0.5 to 2mol/L.
Preparation of lithium ion batteries
And taking a Polyethylene (PE) porous polymeric film as an isolating film, sequentially stacking the prepared positive pole piece, the isolating film and the negative pole piece, enabling the isolating film to be positioned in the middle of the positive pole and the negative pole for isolating, and winding to obtain the electrode assembly. And placing the electrode assembly in an outer package, injecting the prepared electrolyte, packaging, and performing technological processes such as formation, degassing, trimming and the like to obtain the lithium ion battery.
Hereinafter, embodiments of the present application will be described in more detail with reference to examples and comparative examples. The various tests and evaluations were carried out according to the following methods. Unless otherwise specified, "parts" and "%" are weight basis.
Example 1
Preparation of porous biomass graphite
Collecting 10kg of cellulose as an experimental raw material, carbonizing the experimental raw material in a closed box furnace filled with inert protective gas (Ar) to remove part of volatile matters, wherein the reaction process comprises the steps of placing the experimental raw material in the box furnace, filling inert gas to purge for 1h to thoroughly remove oxygen-containing gas, heating to 200 ℃ from room temperature at 5 ℃/min, preserving heat for 2h, continuously heating to 500 ℃ at 5 ℃/min, preserving heat for 8h, and cooling to collect biomass carbon.
Crushing biomass carbon to 400 meshes of particle size by a crusher; 50g of FeCl3 catalyst (dissolved in 3L of deionized water to prepare 0.1M solution) and 1kg of crushed biomass carbon are stirred for 8 hours, the mixture is respectively placed in hydrothermal reaction equipment after being uniformly mixed, the reaction temperature is 200 ℃, the reaction time is 24 hours, the biomass carbon loaded by the catalyst is collected through suction filtration after being cooled, and the biomass carbon is dried for 24 hours at 100 ℃ for standby;
placing the biomass carbon loaded with the catalyst in a box-type furnace, purging with inert gas for 1h to remove oxygen-containing gas, heating to 1300 ℃ from room temperature at a speed of 5 ℃/min, preserving heat for 24h, and cooling to collect a sample; the sample was placed in a beaker containing 6mol/L HCl solution, and the beaker was placed in a magnetic water bath with a temperature rise to 70℃and magnetically stirred for 12h. Washing with water, filtering to remove HCl solution, repeating the steps for 3 times, and drying in a 100 ℃ oven for 24 hours for standby.
Porous biomass graphite/SiO x Preparation of composite materials
Porous typeBiomass graphite (475 g), siO x Powder (50 g), carbon nanotubes (5 g) and binder pitch (15 g) N in a ball mill 2 Mixing for 4h at 500r/min (SiO) x ，0.5＜x＜1.6，D v50 4 μm; specific surface area of 3.5m 2 /g). The mixed powder is spheroidized by air flow classification equipment to obtain carbon nano tube penetrating and adhering to porous biomass graphite/SiO x Spherical composite material of surface. After the sample preparation is finished, the sample is placed in a box-type furnace for carbonization treatment, and the carbonization flow is as follows: purging with inert gas (Ar) for 1h to remove oxygen-containing gas, heating to 500 ℃ from room temperature at a speed of 5 ℃/min, preserving heat for 8h, and cooling to collect a sample.
Carbon coated biomass graphite/SiO x Preparation of composite materials
Placing the spherical composite material in a chemical vapor deposition (Chemical Vapor Deposition, CVD) furnace, and charging carbon source gas (CH) 4 ) And (3) purging with inert gas (Ar) for 1h to remove oxygen-containing gas before introducing carbon source gas, heating to 950 ℃ from room temperature at a speed of 5 ℃/min, preserving heat for 4h, and cooling to collect a sample. Obtaining carbon-coated CNT-modified biomass graphite/SiO x And (3) a composite anode material.
Lithium ion battery preparation
And stirring and mixing the composite anode material and the conductive agent to obtain a mixture A. Wherein the stirring time is 120min, and the revolution speed of the stirrer is 15r/min.
Adding the binder into the mixture A, stirring uniformly (namely, stirring for the first time), adding deionized water, stirring continuously (namely, stirring for the second time) to obtain mixed slurry, and filtering with a 170-mesh double-layer screen to obtain negative electrode slurry; wherein, the first stirring time is 60min, the second stirring time is 120min, the revolution speed of the stirrer is 15r/min, the rotation speed is 1200r/min, and the stirrer is a vacuum stirrer with the model MSK-SFM-10.
Coating the negative electrode slurry on a copper foil current collector, drying, cold pressing, and compacting the double surfaces to a density of 1.8g/cm 3 And obtaining the negative electrode plate.
The conductive agent is conductive carbon black, the final viscosity of the mixed slurry is 3000 Pa.S, and the solid content is 40%.
The mass ratio of the anode material, the conductive agent and the binder is 96.5 percent: 1.5%:2%.
The negative electrode plate is coated on two sides, and the thickness of each side of the coating is 95 mu m.
Preparation of positive electrode plate
The active substance NCM613, conductive carbon black and binder are mixed according to the mass ratio of 97 percent: 1.5%: and (3) fully stirring and uniformly mixing 1.5% of the mixture in an organic solvent system, coating the mixture on an Al foil, drying and cold pressing the mixture to obtain a positive electrode plate, wherein the binder is polyvinylidene fluoride, and the organic solvent is N-methyl pyrrolidone.
Preparation of electrolyte
Mixing a solvent EC, DMC, DEC according to a volume ratio of 1:1:1 to obtain a mixed solution, and then adding FEC and LiPF 6 Mixing to obtain electrolyte, wherein the mass concentration of FEC in the electrolyte is 15wt%, liPF 6 The molar concentration in the electrolyte was 0.5mol/L.
Preparation of lithium ion batteries
And taking a Polyethylene (PE) porous polymeric film as an isolating film, sequentially stacking the prepared positive pole piece, the isolating film and the negative pole piece, enabling the isolating film to be positioned in the middle of the positive pole and the negative pole for isolating, and winding to obtain the electrode assembly. And placing the electrode assembly in an outer package, injecting the prepared electrolyte, packaging, and performing technological processes such as formation, degassing, trimming and the like to obtain the lithium ion battery.
Example 2
The conditions were the same as in example 1 except that hemicellulose was used as the biomass material. (lower charring ratio, less difference in properties)
Example 3
The conditions were the same as in example 1 except for lignin used as a biomass raw material. (graphitization degree is low, and temperature is required to be high)
Example 4
The conditions were the same as in example 1 except that the temperature of the first step of cellulose catalyzed graphitization was 1400 ℃.
Example 5
The conditions were the same as in example 1 except that the temperature for the first step of cellulose catalyzed graphitization was 1600 ℃.
Example 6
The conditions were the same as in example 3 except that the temperature of the first step lignin catalytic graphitization was 1600 deg.c
Example 7
Removing SiOx, D v50 7 μm; specific surface area of 3.0m 2 Per g, other conditions are the same as in example 1
Example 8
SiO removal x Dv50 is 3 μm; specific surface area of 4.8m 2 Per g, other conditions are the same as in example 1
Example 9
The conditions were the same as in example 1 except that the final source of the coating was ethylene (C2H 4).
Example 10
Except that the final coating gas source was acetylene (C 2 H 2 ) Other conditions were the same as in example 1.
Comparative example 1
The biomass graphite is replaced by graphite and compounded with silicon oxide, and other conditions are the same as the examples.
Comparative example 2
The nano silicon (150 nm) was used instead of the silicon oxide, and the other conditions were the same as in example 1.
Comparative example 3
Dv50 for silica was 2 μm; specific surface area of 6.3m 2 The other conditions were the same as in example 1.
Comparative example 4
With D for silica v50 Is 10 mu m; specific surface area of 1.8m 2 The other conditions were the same as in example 1.
Comparative example 5
1kg spherical composite material and N in 100g asphalt ball mill 2 Mixing for 4 hours at 500r/min, placing the uniformly mixed sample in a tube furnace, introducing inert gas (Ar), purging for 1 hour to remove oxygen-containing gas, heating to 800 ℃ from room temperature at a speed of 5 ℃/min, preserving heat for 4 hours, and cooling to collect the sample. Obtaining CNT-modified biomass graphite/S with surface coated carboniO x And (3) a composite anode material. Other conditions were the same as in example 1.
Performance testing
The negative electrode materials, negative electrode tabs, and lithium ion batteries prepared in each example and each comparative example were tested using the following methods:
graphitization degree test: measured by using a Bruker D8 advanced type X-ray diffractometer. Test conditions are Cu K alpha ray source, tube voltage 40kV, tube current 10mA, scanning rate: 0.25 DEG/min, and scanning range 2θ=24 DEG-30 DEG to obtain C 002 Then according to Bragg formula 2d 002 Sinθ 002 =λ, G (degree of graphitization) = (0.344-d 002 ) 100% of the total weight of the catalyst was used to obtain graphitization degree data (0.344-0.3354).
Testing of X-ray photoelectron spectroscopy: the Thermo ESCALAB 250 instrument was used (single color alkα excitation, hν= 1486.6 eV). The binding energies of all the measurement elements were calibrated with a peak position of the binding energy of 284.6eV carbon.
And (3) cyclic test: the lithium ion battery containing the negative electrode material is subjected to cycle test, the test temperature is 25 ℃, the constant current charging is carried out at 0.5C to 4.45V, the constant voltage charging is carried out at 0.025C, the constant voltage charging is carried out for 5 minutes, the discharging is carried out at 0.5C to 3.0V, the capacity obtained in the step is taken as the initial capacity, the cycle test is carried out by charging at 0.5C/discharging at 0.5C, the ratio of the capacity of each step to the initial capacity is taken, and the capacity attenuation curve is obtained after the cycle is carried out for 400 times.
Cell expansion rate test: and testing the thickness of the lithium ion battery in a half-charge state (namely 50% state of charge (SOC)) by using a spiral micrometer, and when the battery circulates to 400 times, testing the thickness of the battery at the moment by using the spiral micrometer, and comparing the thickness of the battery with the thickness of the battery in an initial half-charge state (50% SOC) to obtain the expansion rate of the battery in the full-charge state (100% SOC).
The preparation parameters and test results of each example and comparative example are shown in table 1 below.
TABLE 1
Figure BDA0003893009650000131
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Figure BDA0003893009650000141
As is clear from comparative examples 1, 2, 3 and 6, the graphitization degree of biomass graphite using cellulose and hemicellulose as raw materials is higher than that of biomass graphite using lignin as raw material under the same conditions. The higher the graphitization degree, the corresponding SP of carbon 2 The hybridization is higher, the crystallization of the material is regular, the gram capacity is high, and the cycle performance can be better. Cellulose is highly similar in structure to hemicellulose, so properties are substantially consistent, but hemicellulose yields are lower. The lignin has a changeable structure, higher thermal stability and higher graphitization temperature requirement, so that the graphitization degree of the lignin is lower than that of cellulose under the same temperature condition.
As is clear from comparative examples 1, 4 and 5, the higher the temperature, the higher the graphitization degree of the biomass, but the higher the graphitization degree, the poorer the dynamic properties of the material, and the phenomenon of local lithium precipitation during the cycle, so that the cycle capacity retention and the expansion rate are slightly degraded.
As is clear from comparison of examples 1, 7 and 8 with comparative examples 2, 3 and 4, when the particle diameter Dv50 of the silicon oxide is more than 8 mu m, the phenomenon that particles are broken in the circulation process is more obvious, so that more electrolyte is consumed at the newly exposed material interface, the expansion is increased, and the circulation performance is poor; when the particle diameter Dv50 of the silica is less than 3 μm, the specific surface area of the particles increases, and more electrolyte is consumed during initial circulation, resulting in deterioration of the circulation performance; the nano silicon has large specific surface area and large reactivity, is easier to react with electrolyte, and causes the expansion of the battery core, thereby accelerating the cycle attenuation.
As can be seen from the comparison between example 1 and comparative example 1, the composite cycle stability of the biomass graphite and the silica is better and less expansion than that of the conventional graphite and the silica. The biomass graphite has a porous structure, so that the lithium intercalation expansion of the silicon oxide can be effectively relieved, and meanwhile, the biomass graphite has stronger reproducibility than natural graphite and artificial graphite, and the green sustainable development concept is compounded.
As can be seen from comparison of examples 1, 9 and 10 with comparative example 5, the gas phase coating has better cycle performance and expansion performance than the liquid phase coating, and the main reason is that the uniformity of the gas phase coating is better, the liquid asphalt coating can have more residual impurity groups, such as-OH, etc., and is more prone to side reaction with electrolyte, consuming electrolyte, and resulting in poor cycle performance; the CH4 in the coating air source has the best coating performance, and the alkane can form a carbon layer with a flocculent structure in the carbonization process, thereby being beneficial to the direct conductive contact of materials and ensuring the stability of circulation.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (9)

1. The silicon-containing biomass graphite anode material comprises porous biomass graphite, a silicon oxide compound and carbon nanotubes, and is characterized in that: and one part of the carbon nano tube is positioned on the surfaces of the porous biomass graphite and the silicon oxide compound, the other part of the carbon nano tube penetrates through the porous biomass graphite and the silicon oxide compound, and a carbon coating layer is arranged on the surfaces of the porous biomass graphite and the silicon oxide compound.
2. The silicon-containing biomass graphite anode material according to claim 1, wherein: the mass of the silica compound is m1, the mass of the porous biomass graphite/silica compound is m, r1=m1/m, the value of r1 is 3% -20%, the mass of the carbon nano tube is m2, the mass of the porous biomass graphite/silica compound is m, r2=m2/m, the value of r2 is 0.05% -1.5%, the mass of the carbon coating layer is m3, the mass of the porous biomass graphite/silica compound is m, r3=m3/m, and the value of r3 is 1% -3%.
3. According to claim 1The silicon-containing biomass graphite anode material is characterized in that: x-ray photoelectron spectroscopy test SP of porous biomass graphite 2 -C (284.8 eV) and SP 3 -C (285.6 eV) area ratio in the range of 2.3-1.5, N 2 The adsorption test pore diameter ranges from 0.3nm to 15nm, and the preferred range is from 3nm to 8nm.
4. The silicon-containing biomass graphite anode material according to claim 1, wherein: the Dv50 of the silica compound is 3-8 μm, and the specific surface area of the silica compound is 1.0m 2 /g-10m 2 /g。
5. The silicon-containing biomass graphite anode material according to claim 1, wherein: the silica compound includes: siOx, wherein 0.5< x <1.6, comprising: at least one of crystalline or amorphous.
6. The silicon-containing biomass graphite anode material according to claim 1, wherein: the carbon nanotube includes: single-walled carbon nanotubes and multi-walled carbon nanotubes.
7. The silicon-containing biomass graphite anode material according to claim 1, wherein: the carbon coating layer is at least one of alkane, alkene and alkyne.
8. An electrochemical device of a siliceous biomass graphite anode material is characterized in that: comprising a positive electrode sheet, a negative electrode sheet and a separator provided between the positive electrode sheet and the negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, the negative electrode active material layer comprising the negative electrode material according to any one of claims 1 to 7.
9. The electrochemical device of claim 8, wherein the silicon-containing biomass graphite anode material comprises: the electrochemical device further includes: and an electrolyte comprising fluoroethylene carbonate in a mass fraction of 4% -30% based on the total mass of the electrolyte.
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