CN115991465B - Hard carbon material applied to sodium ion battery and preparation method thereof - Google Patents
Hard carbon material applied to sodium ion battery and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a hard carbon material applied to a sodium ion battery and a preparation method thereof, wherein the hard carbon material is prepared by mixing biomass material and asphalt according to a mass ratio of 10:1-1:10 and then carbonizing the mixture, and the specific surface area of the hard carbon material is 4-6m 2 And/g, wherein the pore size is 6-8nm, and the lattice spacing is 0.385-0.39nm; the mixing method is a mechanical mixing method or a chemical mixing method; the mechanical mixing method is an acoustic resonance mixing method; the chemical mixing method is an acetic acid/methylimidazole composite solvent eutectic method. According to the technical scheme provided by the invention, the hard carbon material produced by mixing the specific biomass material with the asphalt can provide high initial capacity, high first-circle coulomb efficiency and strong capacity stability when being applied to the sodium ion battery.
Description
Technical Field
The invention relates to the technical field of battery materials, in particular to a hard carbon material applied to a sodium ion battery and a preparation method thereof.
Background
The principle of the sodium ion battery is similar to that of a lithium ion battery, and the sodium ion battery belongs to a rocking chair type battery and also comprises a positive electrode, electrolyte, a diaphragm and a negative electrode. The negative electrode material can be divided into an embedding reaction material, a conversion reaction material and an alloy reaction material according to a sodium storage mechanism.
Graphite is a lithium ion battery anode material that has been commercialized, however, the interlayer spacing of graphite is so small relative to the radius of sodium ions that sodium ions are difficult to intercalate between graphite layers, and even after successful intercalation sodium ions migrate between the layers. More seriously, sodium ions react with graphite to form NaC 64 The compound has a reversible capacity of only about 35mAh/g.
Hard carbon is considered to be one of the most potential negative materials for sodium ion batteries. The material does not have the structural characteristic of graphitization, and graphite crystallites are freely oriented, namely structurally short-range ordered and long-range unordered. Meanwhile, the structure contains a large number of defects, which is very favorable for storing sodium ions with larger ion radius, so that the sodium storage capacity is much larger than that of graphite.
When the existing process for producing the hard carbon material is mainly obtained by carbonizing biomass, however, the biomass material has different components due to different plant types, different regions, different climate influences, different soil components and the like, and the biomass material is used as the raw material for preparing the hard carbon material, the biomass material cannot be produced by a uniform process; because of the complicated precursor screening and process selection, a large-scale high-purity hard carbon production mode cannot be formed by simply adopting biomass.
Pitch is a precursor of artificial graphite, and untreated pitch easily forms a graphitized structure in the carbonization process, and is currently used in lithium ion batteries, and cannot be directly used in sodium ion batteries due to too small lattice spacing, but has the advantage of stable raw material supply. Therefore, the asphalt material is subjected to certain process treatment to inhibit graphitization, so that the asphalt material is stably produced into high-quality hard carbon material, and the method is the most popular research direction at present.
Disclosure of Invention
In order to solve the problems, the invention provides a hard carbon material applied to a sodium ion battery and a preparation method thereof.
The invention provides a hard carbon material applied to a sodium ion battery, which is prepared by mixing biomass material and asphalt according to a mass ratio of 10:1-1:10 and then carbonizing, wherein the specific surface area of the hard carbon material is 4-6m 2 And/g, wherein the pore size is 6-8nm, and the lattice spacing is 0.385-0.39nm.
Further, the preparation method of the hard carbon material comprises the following steps:
step 1): respectively placing biomass material and asphalt into a ball mill for grinding, wherein the mass ratio of the ball material is 8:1, the ball milling time is 1-6h, and sieving large particles after grinding is finished to obtain particles with the particle size of 10-20 mu m and the specific surface area of 1-5m respectively 2 Biomass powder and pitch powder of (a);
step 2): mixing the biomass powder obtained in the step 1) with asphalt powder to obtain mixture powder, wherein the mixing ratio is 10:1-1:10, and the mixing time is 1-12 h;
step 3): heating the mixture powder obtained in the step 2) to 200-600 ℃ in argon atmosphere, and pre-carbonizing for 1-5h to obtain pre-carbonized powder;
step 4): and 3) carbonizing the pre-carbonized powder obtained in the step 3) at a high temperature in an argon atmosphere, wherein the carbonization temperature is 800-1600 ℃ and the carbonization time is 2-12h, so as to obtain the hard carbon material.
Further, the mixing method in the step 2) is a mechanical mixing method or a chemical mixing method.
Further, the mechanical mixing method in the step 2) is an acoustic resonance mixing method, the acoustic resonance frequency is 50-100HZ, and the resonance time is 1-6h.
Further, the chemical mixing method in the step 2) is an acetic acid/methylimidazole composite solvent co-dissolution method, wherein the acetic acid/methylimidazole composite solvent is a mixed solution of methylimidazole dissolved in acetic acid, and the proportion of methylimidazole is 20-50%; in the co-dissolution method of the acetic acid/methylimidazole composite solvent, the solid-to-liquid ratio of the biomass powder to the asphalt powder to the acetic acid/methylimidazole composite solvent is 1:2, the mixing time is 6 hours, and the mixed emulsion is dried for 6 hours at 80 ℃ to obtain mixture powder.
Further, when the acoustic resonance mixing method is adopted in the step 2), the biomass material adopts a material with high lignin content, including bagasse, wood chips, coconut shells and walnut shells.
Further, when the acetic acid/methylimidazole composite solvent co-dissolution method is adopted in the step 2), the biomass material adopts a material with high cellulose content, including flax and straw.
Further, the biomass material is walnut shell, the mixing ratio of walnut shell powder to asphalt powder is 1:1, and the mixing time is 3 hours.
Further, the biomass material is flax, the mixing ratio of flax powder to asphalt powder is 1:1, and the mixing time is 6 hours.
The beneficial effects of the invention are as follows:
1. at present, raw materials for preparing hard carbon materials comprise biomass materials and asphalt, but the biomass materials have complex components, and various biomass materials are difficult to process by a uniform means, so that the hard carbon is effectively and stably produced; pitch is a stable carbon source, but when carbonized alone at high temperatures, tends to grow graphitized, and is not suitable for the production of hard carbon. According to the technical scheme provided by the invention, the hard carbon material produced by mixing the specific biomass material with the asphalt can provide high initial capacity, high first-circle coulomb efficiency and strong capacity stability when being applied to the sodium ion battery. The invention provides that the mixing ratio of the biomass material and the asphalt is 10:1-1:10.
2. According to the invention, when biomass materials and asphalt are mixed to prepare a hard carbon material, the mixing mode has a great influence on the electrochemical performance of the finally generated hard carbon material, different mixing modes are adopted according to different biomass material properties, and the biomass materials with high lignin content are suitable for being mixed with asphalt by using a mechanical mixing method, the ground and finely divided lignin materials are mixed with the asphalt, so that graphitization of the asphalt can be prevented under high-temperature carbonization, and the mixed decomposition of lignin can reduce the formation of glass carbon and increase the hard carbon yield; the invention also provides a method for effectively liquefying biomass and asphalt by adopting acoustic resonance mixing, so that the two materials can be better mixed. The method is suitable for mixing the biomass material with high cellulose content with asphalt by using a chemical mixing method, the cellulose can be effectively degraded by the chemical mixing method to enter the asphalt structure, and when the mixed material is carbonized at high temperature, the cellulose in the asphalt can become a defect, so that graphitization growth is prevented to generate an amorphous hard carbon material; the invention also provides a method for preparing the high-quality hard carbon material by adopting acetic acid/methylimidazole to effectively degrade cellulose, mutual-soluble asphalt and biomass.
3. The invention provides the method for preparing the composite material by adopting the mechanical mixing method, wherein when the mechanical mixing method is an acoustic resonance mixing method, the acoustic resonance frequency is 50-100HZ, and the resonance time is 1-6h, the optimal biomass material is walnut shell, the mixing ratio of walnut shell powder to asphalt powder is 1:1, and the mixing time is 3h.
4. The invention provides a co-dissolution method of an acetic acid/methylimidazole composite solvent by adopting a chemical mixing method, wherein the acetic acid/methylimidazole composite solvent is a mixed solution of methylimidazole dissolved in acetic acid, and the proportion of methylimidazole is 20-50%; in the co-dissolution method of the acetic acid/methylimidazole composite solvent, the solid-to-liquid ratio of the biomass powder to the asphalt powder to the acetic acid/methylimidazole composite solvent is 1:2, the mixing time is 6 hours, and the mixed emulsion is dried for 6 hours at 80 ℃ to obtain mixture powder; the optimal biomass material is flax, the mixing ratio of flax powder to asphalt powder is 1:1, and the mixing time is 6 hours.
Drawings
FIG. 1 is an SEM image of a hard carbon material prepared according to example 1;
FIG. 2 is an XRD pattern of the hard carbon material prepared in example 1;
fig. 3 is a graph of the first charge and discharge of the sodium ion battery of example 1;
FIG. 4 is a graph of the cycling performance and coulombic efficiency of sodium ions in example 1;
FIG. 5 is an SEM image of a hard carbon material prepared according to comparative example 1;
FIG. 6 is a graph of the cycling performance and coulombic efficiency of sodium ions in comparative example 1;
FIG. 7 is an SEM image of a hard carbon material prepared according to comparative example 2;
FIG. 8 is a graph of the cycling performance and coulombic efficiency of sodium ions in comparative example 2;
FIG. 9 is an SEM image of a hard carbon material prepared according to example 4;
FIG. 10 is a graph of the cycling performance and coulombic efficiency of sodium ions in example 4;
FIG. 11 is a graph of the cycling performance and coulombic efficiency of sodium ions in comparative example 3;
FIG. 12 is an SEM image of a hard carbon pole piece prepared according to comparative example 4;
FIG. 13 is a graph of the cycling performance and coulombic efficiency of sodium ions in comparative example 4.
Detailed Description
The invention is further illustrated by the following examples.
Example 1: preparation of hard carbon material by mixing walnut shell and petroleum asphalt by acoustic resonance mixing method and application of hard carbon material in sodium ion battery
1. Respectively putting 10g of walnut shell and 10g of petroleum asphalt into a ball mill for crushing, wherein the ball milling time is 2 hours, the ball-to-material ratio is 8:1, and respectively obtaining the particle size of 10-20 mu m and the specific surface area of 10-20m 2 Walnut shell powder and asphalt powder;
2. performing acoustic resonance mixing on the walnut shell powder obtained in the step 1) and the asphalt powder by using a resonance mixer to obtain mixture powder, wherein the mixing ratio of the walnut shell powder to the asphalt powder is 1:1, the mixing time is 3h, and the acoustic resonance frequency is 70Hz;
3. heating the mixture powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ under inert atmosphere for carbonization for 6 hours to obtain a hard carbon material (see fig. 1 and 2); the specific surface area of the hard carbon material is 4m 2 And/g, wherein the pore size is 6nm, and the lattice spacing is 0.385nm;
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
6. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; a conventional electrolyte (100. Mu.L) which is a mixed solvent of EC and DMC (1:1, v/v) was added to each cell; after completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
Experimental results: the specific capacity of the initial discharge can reach 308mAh/g (see figure 3); the initial coulomb efficiency reached 88.1% and the specific capacity remained 86.2% after 60 cycles (see fig. 4).
The results show that the hard carbon material manufactured by the method can provide high initial capacity, high initial coulombic efficiency and strong capacity stability for sodium ion batteries.
Comparative example 1: preparation of hard carbon material from walnut shell and application of hard carbon material in sodium ion battery
1. 10g of walnut shell is put into a ball mill for crushing, the ball milling time is 2 hours, the ball-material ratio is 8:1, the particle size is 10-20 mu m, and the specific surface area is 10-20m 2 Is prepared from walnut shell powder;
2. heating the walnut shell powder obtained in the step 1) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
3. heating the pre-carbonized powder in the step 2) to 1500 ℃ under inert atmosphere for carbonization for 6 hours to obtain a hard carbon material (see figure 5); the specific surface area of the hard carbon material is 6m 2 And/g, wherein the pore size is 8nm, and the lattice spacing is 0.39nm;
4. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
5. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; a conventional electrolyte (100. Mu.L) which is a mixed solvent of EC and DMC (1:1, v/v) was added to each cell; after completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
Experimental results: the specific capacity of the initial discharge can reach 228mAh/g; the initial coulomb efficiency reached 58.1% and the specific capacity remained at 46.2% after 60 cycles (see fig. 6).
Example 2: screening the optimal mixing proportion and mixing time of walnut shell and petroleum asphalt when using acoustic resonance mixing method
1. Respectively pulverizing walnut shell and petroleum asphalt in ball mill to obtain powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 Walnut shell powder, pitch powder; ball milling time is 2h, and ball-material ratio is 8:1;
2. performing acoustic resonance mixing on the walnut shell powder obtained in the step 1) and the asphalt powder by using a resonance mixer to obtain mixture powder, wherein the mixing ratio of the walnut shell powder to the asphalt powder is 10:1-1:10, and the mixing time is 1-6h;
3. heating the mixture powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ in an inert atmosphere for carbonization for 6 hours to obtain a hard carbon material;
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
6. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; to each cell was added a conventional electrolyte (100. Mu.L) which was a mixed solvent of EC and DMC (1:1, V/V), and after standing at 25℃for 8 hours after completion of assembly, charge-discharge cycles were performed at a rate of 0.1C between 0.01V and 2.5V.
The mixing ratio and mixing time of the walnut shells and the petroleum asphalt of different test groups are shown in table 1:
table 1 comparative data table of hard carbon materials prepared by mixing walnut shells and petroleum pitch with acoustic resonance mixing method at different mixing ratios and mixing times and applied to sodium ion battery
The comparison experiment shows that:
(1) As the acoustic resonance time is longer, the particle size of the obtained mixture is smaller;
(2) Because the walnut shell contains more lignin, when the proportion of the lignin is larger, more mixing time is needed to achieve smaller particle size and better mixing effect;
(3) The mixed powder with too small particle size obtained after too long mixing time is not suitable for being prepared into hard carbon materials due to too large specific surface area, and has poor performance when being applied to sodium ion batteries; preferably the mixing time is 3 hours;
(4) The ratio of the walnut shell to the asphalt is preferably 1:1; this is due to the fact that when the walnut shell ratio is large (> 1:1), the hard carbon yield is reduced, and the sodium ion battery coulomb efficiency is reduced due to too many defects; when the walnut shell ratio is small (< 1:1), the defects are small, and graphite carbon generation by asphalt cannot be inhibited, so that the generated hard carbon material has low specific capacity when being applied to sodium ion batteries.
Example 3: screening of optimal biomass materials for mixing with petroleum asphalt using acoustic resonance mixing
1. Respectively pulverizing different biomass materials and petroleum asphalt in ball mill to obtain powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 Biomass powder and pitch powder of (a); ball milling time is 2h, and ball-material ratio is 8:1;2. carrying out acoustic resonance mixing-mechanical mixing method on the biomass powder obtained in the step 1) and the asphalt powder by using a resonance mixer to obtain mixture powder, wherein the mixing ratio of the biomass powder to the asphalt powder is 1:1, and the mixing time is 3 hours;
3. heating the mixture powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ in an inert atmosphere for carbonization for 6 hours to obtain a hard carbon material;
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
6. and (3) taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode. A conventional electrolyte (100 μl) was added to each cell. The conventional electrolyte is a mixed solvent of EC and DMC (1:1, v/v). After completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V. The different biomass used for the different test groups are shown in table 2:
table 2 comparative experiments in which the acoustic resonance mixing method was applied to the preparation of hard carbon materials by mixing different biomass and petroleum pitch and application to sodium ion batteries
The comparison experiment shows that:
(1) The biomass material with higher lignin content has higher hard carbon yield after being mixed by an acoustic resonance method, because the biomass material with high lignin content is better mixed with petroleum asphalt by the acoustic resonance method, and glass carbon generated by lignin sintering is reduced;
(2) When biomass with low lignin content such as flax is subjected to acoustic resonance mixing, a good mixing effect cannot be achieved, and the generated carbon material has a large number of defects, so that the first-circle coulomb efficiency is low.
Comparative example 2: the walnut shell and petroleum asphalt are mixed to prepare hard carbon material by a conventional mechanical stirring mixing method and are applied to sodium ion batteries
1. Walnut shell,Pulverizing petroleum asphalt in ball mill to obtain powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 Walnut shell powder, pitch powder; ball milling time is 2h, and ball-material ratio is 8:1;
2. mixing the walnut shell powder obtained in the step 1) with asphalt powder by using a stirring tank to obtain mixture powder, wherein the mixing ratio of the walnut shell powder to the asphalt powder is 1:1, and the mixing time is 1h;
3. heating the mixture powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ under inert atmosphere for carbonization for 6 hours to obtain a hard carbon material (see figure 7);
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
6. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; a conventional electrolyte (100 μl) was added to each cell; the traditional electrolyte is a mixed solvent of EC and DMC (1:1, v/v); after completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
Test results: the specific capacity of the first discharge is 258mAh/g; the first cycle coulombic efficiency reached 78.2% and the specific capacity remained at 66.3% after 60 cycles (see fig. 8).
As can be seen from the above examples and comparative examples, the yield of hard carbon materials prepared by using different mechanical mixing methods, mixing different biomass materials with petroleum pitch, and the performance impact of assembled sodium ion batteries showed the following laws:
(1) The acoustic resonance mixing method is suitable for mixing asphalt and biomass materials with high lignin content, and can be used for liquefying the biomass materials due to the high lignin content, and completely mixing and coating the biomass materials with asphalt, so that graphitization of the asphalt can be prevented, and glass carbon generated by lignin can be reduced;
(2) The acoustic resonance mixing method is not suitable for mixing materials with high cellulose content and starch polysaccharides;
(3) The acoustic resonance mixing method is superior to the conventional mechanical stirring mixing method, because the simple mechanical stirring mixing method cannot grind biomass materials with high lignin content well, and the combination with asphalt is poor, so that the prepared hard carbon material has poor effect when applied to sodium ion batteries.
Example 4: mixing flax and petroleum asphalt to prepare hard carbon material by acetic acid/methylimidazole solvent co-dissolution method and application thereof in sodium ion battery
1. Respectively pulverizing 10g of flax and 10g of petroleum asphalt in ball mill to obtain powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 The milling time is 2 hours, and the ball-to-material ratio is 8:1;
2. the flax powder and the asphalt powder obtained in the step 1) are co-dissolved by a chemical mixing method, namely an acetic acid/methylimidazole composite solvent, so as to obtain a mixed emulsion, wherein the mixing ratio of the flax powder and the asphalt powder in the mixed solution is 1:1, the mixing time is 6h, and the methylimidazole content is 40%; then the obtained mixed emulsion is pretreated, dried at the temperature of 80 ℃ for 6 hours to obtain mixed powder;
3. heating the mixed powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ under inert atmosphere for carbonization for 6 hours to obtain a hard carbon material (see figure 9); the specific surface area of the hard carbon material is 5m 2 And/g, wherein the pore size is 7nm, and the lattice spacing is 0.385nm;
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
6. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; a conventional electrolyte (100 μl) was added to each cell; the traditional electrolyte is a mixed solvent of EC and DMC (1:1, v/v); after completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
Test results: the initial discharge specific capacity can reach 296mAh/g, the initial coulomb efficiency reaches 87.6%, and the specific capacity is kept at 85.4% after 60 circles (see figure 10); the results show that the hard carbon material prepared by using flax and petroleum asphalt can provide high initial capacity, high first-circle coulomb efficiency and strong capacity stability for sodium ion batteries.
Comparative example 3: hard carbon material prepared from flax and application of hard carbon material in sodium ion battery
1. Pulverizing 10g of flax in ball mill to obtain flax powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 The milling time is 2 hours, and the ball-to-material ratio is 8:1;
2. heating the flax powder obtained in the step 1) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
3. heating the pre-carbonized powder in the step 2) to 1500 ℃ in an inert atmosphere for carbonization for 6 hours to obtain a hard carbon material;
4. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
5. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; a conventional electrolyte (100 μl) was added to each cell; the traditional electrolyte is a mixed solvent of EC and DMC (1:1, v/v); after completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
Test results: the initial discharge specific capacity can reach 216mAh/g, the initial coulomb efficiency reaches 47.7%, and the specific capacity is kept at 35.6% after 60 circles (see figure 11).
Example 5: screening optimal mixing proportion and methylimidazole content of flax and petroleum asphalt during mixing by using acetic acid/methylimidazole solvent co-dissolution method
1. Pulverizing flax and petroleum asphalt in ball mill to obtain powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 The milling time is 2 hours, and the ball-to-material ratio is 8:1;
2. the flax powder and the asphalt powder obtained in the step 1) are co-dissolved by a chemical mixing method-acetic acid/methylimidazole composite solvent to obtain mixed emulsion, wherein the mixing ratio of the flax powder and the asphalt powder in the mixed solution is 1:10-10:1, the mixing time is 6h, and the methylimidazole content is 20-50%; then the obtained mixed emulsion is pretreated, dried at the temperature of 80 ℃ for 6 hours to obtain mixed powder;
3. heating the mixed powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ in an inert atmosphere for carbonization for 6 hours to obtain a hard carbon material;
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
6. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; a conventional electrolyte (100 μl) was added to each cell; the traditional electrolyte is a mixed solvent of EC and DMC (1:1, v/v); after completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
The mixing ratio and methylimidazole content of flax and petroleum asphalt mixtures of different test groups are shown in Table 3:
TABLE 3 preparation of hard carbon by mixing flax and Petroleum asphalt with acetic acid/methylimidazole solvent Co-dissolution method at different mixing ratios and methylimidazole content and application to sodium ion batteries
The following conclusions can be drawn from the above experiments:
(1) When the acetic acid/methylimidazole solvent co-dissolution method is adopted, the content of methylimidazole influences the dissolution of biomass, and when the content of methylimidazole is increased, the dissolution rate of biomass materials is high, and the mixture of the biomass materials and asphalt is better;
(2) When the biomass ratio is low (< 1:1), the asphalt graphitization cannot be prevented because the leaching amount of the biomass is low, and the generated hard carbon material cannot effectively embed sodium ions, so that the sodium ion battery capacity is low;
(3) When the biomass proportion is high (> 1:1), the biomass is dissolved out to be excessively embedded into asphalt, and the carbon material has excessive defects under high-temperature carbonization, so that the sodium ion battery has high capacity but low coulombic efficiency;
(4) The optimized proportion is flax to petroleum asphalt=1:1, and in the state, the asphalt graphitization can be prevented, the enough high specific capacity can be ensured, and the biomass material can be sufficiently dissolved when the content of methylimidazole is 40%. Example 6: the method of co-dissolving acetic acid/methylimidazole solvent is applied to the preparation of hard carbon by mixing different biomass and petroleum asphalt and the application of the hard carbon on sodium ion batteries
1. Respectively pulverizing different biomass materials and petroleum asphalt in ball mill to obtain powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 Biomass powder of (2), pitch powder; ball milling time is 2h, and ball-material ratio is 8:1;
2. mixing the biomass powder obtained in the step 1) with asphalt powder by using an acetic acid/methylimidazole composite solvent co-dissolution method to obtain a mixed emulsion, wherein the mixing ratio of the biomass powder to the asphalt powder in the mixed solution is 1:1, the mixing time is 6h, and the methylimidazole content is 40%; then the obtained mixed emulsion is pretreated, dried at the temperature of 80 ℃ for 6 hours to obtain mixed powder;
3. heating the mixed powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ in an inert atmosphere for carbonization for 6 hours to obtain a hard carbon material;
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece;
6. taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode; a conventional electrolyte (100 μl) was added to each cell; the traditional electrolyte is a mixed solvent of EC and DMC (1:1, v/v); after completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
The different biomass used for the different test groups are shown in table 4:
TABLE 4 comparative experiments on the application of the chemical mixture-acetic acid/methylimidazole composite solvent co-dissolution method to the preparation of hard carbon by mixing different biomass and petroleum asphalt and the application on sodium ion batteries
The comparison experiment shows that:
(1) Under the condition of high cellulose content, the hard carbon yield can be improved by using a chemical mixing-acetic acid/methylimidazole composite solvent co-dissolution method;
(2) The chemical mixing-acetic acid/methylimidazole composite solvent co-dissolution method is used for mixing the biomass with high cellulose content, so that the first-circle specific capacity and stability of the obtained hard carbon material can be obviously increased.
Comparative example 4: hard carbon prepared by mixing flax with petroleum asphalt by deionized water and application of hard carbon to sodium ion battery
1. Pulverizing flax and petroleum asphalt in ball mill to obtain powder with particle diameter of 10-20 μm and specific surface area of 1-5m 2 Biomass powder of (2), pitch powder; ball milling time is 2h, and ball-material ratio is 8:1;
2. mixing the flax powder obtained in the step 1) and the asphalt powder by deionized water to obtain mixed slurry, wherein the mixing ratio of the flax powder to the asphalt powder in the mixed slurry is 1:1, and the mixing time is 6 hours; then the obtained mixed slurry is pretreated, dried at the temperature of 80 ℃ for 6 hours to obtain mixed powder;
3. heating the mixed powder obtained in the step 2) to 600 ℃ in an argon atmosphere, and pre-carbonizing for 3 hours to obtain pre-carbonized powder;
4. heating the pre-carbonized powder in the step 3) to 1500 ℃ in an inert atmosphere for carbonization for 6 hours to obtain a hard carbon material;
5. preparing slurry from carbonized hard carbon material according to the ratio of hard carbon to carbon black to CMC to SBR=94:1.5:1.5:3, and coating the slurry on copper foil to obtain a hard carbon pole piece (see figure 12);
6. and (3) taking the hard carbon pole piece as a negative electrode of the sodium ion battery, and assembling the battery in a glove box filled with argon, wherein the hard carbon pole piece, the glass fiber and the sodium piece are respectively used as a working electrode, a diaphragm and a counter electrode. A conventional electrolyte (100 μl) was added to each cell. The conventional electrolyte is a mixed solvent of EC and DMC (1:1, v/v). After completion of the assembly, the battery was allowed to stand at 25℃for 8 hours, and then charge and discharge cycles were carried out at a rate of 0.1℃between 0.01V and 2.5V.
Test results: the first discharge specific capacity is 288mAh/g; the first cycle coulombic efficiency was 71.3% and the specific capacity after 60 cycles was maintained at 66.3% (see fig. 13).
The first circle of coulomb efficiency is the most important in electrochemical performance of the hard carbon material used as the sodium ion battery, and the sodium ion battery finished by the hard carbon material prepared by the acetic acid/methylimidazole solvent co-dissolution method of the invention also takes flax and petroleum asphalt as raw materials, wherein the first circle of coulomb efficiency is 87.6 percent (example 4), which is improved by 23 percent compared with the sodium ion battery finished by the hard carbon material prepared by the deionized water mixing method of comparative example 4, the difference can be said to be two orders of magnitude in the sodium ion battery, the first circle of coulomb efficiency is 87.6 percent, and the first circle of coulomb efficiency is 71.3 percent, which is difficult to commercialize.
As can be seen from the above examples and comparative examples, the yield of hard carbon materials prepared by mixing different biomass materials with petroleum asphalt and the performance impact of assembled sodium ion batteries by adopting an acetic acid/methylimidazole solvent co-dissolution method show the following rules:
the acetic acid/methylimidazole solvent co-dissolution method is suitable for biomass materials with high cellulose content, because the acetic acid/methylimidazole can effectively degrade cellulose and dissolve the cellulose so that the cellulose and the petroleum asphalt are mixed in a mutual dissolution way, the two materials can be effectively compounded, the defect can be manufactured, the graphitization transformation of the asphalt during high-temperature carbonization can be restrained, and the hard carbon yield of the fiber biomass material can be effectively improved.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.
Furthermore, it should be understood that although the present disclosure describes embodiments, not every embodiment is provided with a separate embodiment, and that this description is provided for clarity only, and that the disclosure is not limited to the embodiments described in detail below, and that the embodiments described in the examples may be combined as appropriate to form other embodiments that will be apparent to those skilled in the art.
Claims (2)
1. A hard carbon material applied to a sodium ion battery is characterized in that the specific surface area of the hard carbon material is 4-6m 2 And/g, wherein the pore size is 6-8nm, the lattice spacing is 0.385-0.39nm, and the preparation method of the hard carbon material comprises the following steps:
step 1): respectively putting biomass material and asphalt into a ball millThe ball material mass ratio is 8:1, the ball milling time is 1-6h, and after the grinding is finished, large particles are sieved out, and the particle size is 10-20 mu m and the specific surface area is 1-5m respectively 2 Biomass powder/g, pitch powder;
step 2): mixing the biomass powder obtained in the step 1) with asphalt powder to obtain mixture powder, wherein the mixing ratio is 1:1, and the mixing time is 1-12 h;
step 3): heating the mixture powder obtained in the step 2) to 200-600 ℃ in argon atmosphere, and pre-carbonizing for 1-5h to obtain pre-carbonized powder;
step 4): carbonizing the pre-carbonized powder obtained in the step 3) at a high temperature in an argon atmosphere, wherein the carbonization temperature is 800-1600 ℃ and the carbonization time is 2-12h, so as to obtain the hard carbon material;
the mixing method of the step 2) is an acetic acid/methylimidazole composite solvent co-dissolution method, wherein the acetic acid/methylimidazole composite solvent is a mixed solution of methylimidazole dissolved in acetic acid, and the proportion of methylimidazole is 20-50%; in the co-dissolution method of the acetic acid/methylimidazole composite solvent, the solid-to-liquid ratio of the biomass powder to the asphalt powder to the acetic acid/methylimidazole composite solvent is 1:2, the mixing time is 6 hours, and the mixed emulsion is dried for 6 hours at 80 ℃ to obtain mixture powder;
when the step 2) adopts an acetic acid/methylimidazole composite solvent co-dissolution method, the biomass material adopts a material with high cellulose content, including flax and straw.
2. The hard carbon material for sodium ion battery according to claim 1, wherein the biomass material is flax, and the mixing ratio of flax powder to asphalt powder is 1:1, and the mixing time is 6h.
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