JP7436969B2 - Hard carbon derived from biological materials, anode materials, anodes, and alkaline ion batteries - Google Patents

Description

The present invention relates to hard carbon derived from biological materials, negative electrode materials, negative electrodes, and alkaline ion batteries.

The element sodium is abundant on earth, and sodium ion batteries are being researched as an attractive alternative to lithium ion batteries because they can be expected to be lower in cost. One of the key problems hindering the commercial success of sodium-ion batteries is that suitable negative electrode materials have not yet been found. Graphite-based highly crystalline carbon materials are used as negative electrode materials for sodium ion batteries, but it is difficult to absorb Na into graphite, and they exhibit almost no electrochemical activity. On the other hand, it has been reported that when amorphous carbon is used as a negative electrode material, it has electrochemical activity in the Na system, and hard carbon materials in particular are reported to be promising candidates, but the energy density is Therefore, obtaining high performance has become a challenge. In recent years, Bai et al. have studied the insertion and storage mechanism of sodium into hard carbon (Non-Patent Document 1), and found that the high-potential sloping capacity of hard carbon materials is due to the formation of structural defect sites or heteroatoms in the material. It was revealed that the adsorption of Na+ ions on the nanoparticles is associated with subsequent intercalation between graphene sheets in the plateau region and slight deposition on the pore surface at the plateau edge.

On the other hand, Liu et al. used garlic as a carbon source for a sodium ion negative electrode and found that after carbonizing the garlic at 1300 °C, the obtained negative electrode had a capacity of 100 mAhg ^-1 at 1Ag ^-1 and that its initial It has been reported that the coulombic efficiency reached approximately 50.7% (Non-Patent Document 2).

Chen et al. used sucrose as a precursor and processed it at 500°C to produce carbon microspheres. It has been reported that when these carbon microspheres were used as a negative electrode material, a capacity of 83 mAhg ^-1 was achieved even after 50 cycles at 1Ag ^-1 (Non-Patent Document 3).

It would be useful if a negative electrode material capable of increasing the discharge capacity of an electrode could be manufactured using biological materials.

Advanced Energy Materials, 2018, 1703217 ACS Sustainable Chemistry&Engineering 2019, 7, 12188-12199 Journal of Materials Chemistry A, 2014, 2, 1263-1267

The present invention has been made in view of the above, and provides a hard carbon that can produce a negative electrode material that increases the discharge capacity of an electrode, a negative electrode material made of the hard carbon, a negative electrode made of the negative electrode material, and the negative electrode. The purpose of the present invention is to provide an alkaline ion battery with the following features.

As a result of intensive research to achieve the above object, the present inventors discovered that the above object could be achieved by using an aged biological material as a raw material for the porous carbon material that constitutes the negative electrode material. The invention was completed.

The present invention encompasses the embodiments described below.

Item 1. Roughly spherical porous hard carbon made of aged carbonized biological material.

Item 2. Item 2. The hard carbon according to item 1, which contains approximately spherical hard carbon particles with a particle size of 100 nm to 10 μm.

Item 3. Item 3. The hard carbon according to item 1 or 2, wherein the biological material is a plant.

Item 4. Item 3. A negative electrode material made of hard carbon according to any one of Items 1 to 3.

Item 5. A negative electrode formed by molding the negative electrode material according to item 4.

Item 6. Item 5. An alkaline ion battery comprising the negative electrode according to item 5.

Section 7. A method for producing substantially spherical hard carbon from aged biological material, the method comprising carbonizing the aged biological material.

According to the hard carbon of the present invention, it is possible to produce a negative electrode material that increases the discharge capacity of the electrode. Therefore, the discharge capacity of an alkaline ion battery equipped with a negative electrode made of such a negative electrode material can be increased.

A manufacturing process for a negative electrode according to an embodiment of the present invention. FIG. 2 is a schematic exploded perspective view showing the assembly of a battery. Scanning electron microscope (SEM) photographs of (A) GT-C carbon material and (B) GC-C carbon material. Graph of X-ray diffraction analysis of GT-C carbon material and GC-C carbon material. A graph showing the discharge capacity of a sodium ion battery with respect to the number of cycles when using GT-C carbon material and GC-C carbon material. (A) The electrolyte is NaPF ₆ and (B) the electrolyte is NaOTf. Graph showing the discharge capacity of a lithium ion battery with respect to the number of cycles when GT-C carbon material and GC-C carbon material are used.

(hard carbon)
The hard carbon of one embodiment of the present invention is a substantially spherical porous hard carbon made of a carbide of an aged biological material.

In this specification, "approximately spherical" does not have to be a mathematically pure spherical shape in which the particle diameter of one hard carbon particle is the same no matter where it is measured, and it does not have to be a mathematically pure spherical shape in which the particle diameter of one hard carbon particle is the same no matter where it is measured. In this case, it is sufficient if the overall shape can be recognized as spherical.

In this specification, "hard carbon" is also referred to as a non-graphitizable carbon material, and is a carbon material obtained by firing a polymer in which a graphite crystal structure is difficult to develop, and is a carbon material having an amorphous structure. refers to Hard carbon is obtained by carbonizing biological materials that contain carbon.

As used herein, "aging" refers to a period of time, whether artificially or naturally, that occurs after production or harvesting of a biological material so that the organic matter that is a component of the biological material is decomposed or changed by the action of enzymes. It refers to the effect of preserving the food for a period of time, and includes (1) the effect of the enzymatic action of the food itself, and (2) fermentation, which is the ripening of the food by the enzymatic action of microorganisms. Preferably, the biological material is sufficiently matured to have a different flavor than the biological material immediately after production or harvest. The period of time the biological material is retained is not limited, but is usually one week or more.

In one embodiment, "aged biological material" is biological material that has been aged by the enzymatic action of the food itself without the addition of external microorganisms. In another embodiment, the "aged biological material" is a biological material that is fermented by the action of enzymes possessed by microorganisms (yeast, lactic acid bacteria, acetic acid bacteria, natto bacteria, etc.) that are artificially added from the outside. In yet another embodiment, "aged biological material" refers to enzymes contained in microorganisms (yeast, lactic acid bacteria, acetic acid bacteria, natto bacteria, etc.) in the air or in the biological material, without artificially adding microorganisms from the outside. It is a biological material fermented by the action of Furthermore, "aging" is distinguished from spoilage, and "aged biological material" is preferably one that can be eaten by animals including humans. Such aged biological materials may be produced by methods known in the food processing field, or commercially available materials may be used. In one embodiment, the aged biological material has an increased mass ratio of the amount of sugars, i.e. monosaccharides and disaccharides, in the biological material compared to the unaged biological material; The mass ratio is 2 times or more, preferably 5 times or more.

A biological material containing at least one selected from the group consisting of nitrogen (N), phosphorus (P), sulfur (S), and boron (B) is used as a negative electrode material for an alkaline ion battery. It is a carbon resource suitable for hard carbon.

The biological material is preferably a plant. Examples of preferred plants containing a large amount of N and S elements include, but are not limited to, rice straw, wheat straw, rice husk, wood, grass, garlic, persimmon, tea, and soybean. In one embodiment, the aged biological material is fermented biomass such as rice straw, wheat straw, rice husk, wood, grass, garlic, persimmon, tea leaves, soybean, etc.

An example of a hard carbon manufacturing process will be explained. After peeling the biological material as necessary and cutting it into appropriate sizes, it is pre-carbonized using a hydrothermal method. Although the temperature of preliminary carbonization is not limited, it is preferably 120-220°C, more preferably 150-200°C, and most preferably 160-190°C. The pre-carbonization time is not limited, but is preferably 4-48 hours, more preferably 12-40 hours, and most preferably 20-30 hours.

Next, after preliminarily carbonizing the biological material, it is pulverized, and the preliminarily carbonized material is activated if necessary. The activation treatment may be gas activation or chemical activation. The gas activation method is a method of obtaining activated carbon by contacting and reacting with water vapor, carbon dioxide, oxygen, etc. at high temperatures.

The chemical activation method is a method in which activated carbon is obtained by impregnating the raw material after heating carbonization treatment with a known activating chemical and heating it in an inert gas atmosphere such as argon to cause dehydration and oxidation reactions of the activating chemical. be. Examples of the activating chemicals include zinc chloride, sodium hydroxide, potassium hydroxide, and the like.

Next, the activated carbonized material is fired. The firing temperature is not limited, but is preferably 500-1400°C, more preferably 650-900°C, and most preferably 700-850°C. The firing time is preferably 0.5-6 hours, more preferably 1-4 hours, and most preferably 2-3 hours. The resulting material is thoroughly washed with acid solution to remove impurities, followed by distilled water until a neutral pH is reached. The acid in the acid solution is preferably a strong acid, more preferably hydrochloric acid. Finally, the material is washed with absolute ethanol and dried at 100 °C. Here, hard carbon is obtained.

The hard carbon preferably includes approximately spherical hard carbon particles with a particle size of 100 nm to 10 μm. In one embodiment, the hard carbon includes a plurality of generally spherical hard carbon particles, each particle having a particle size of 1000 nm to 9 μm. In another embodiment, the hard carbon includes a plurality of generally spherical hard carbon particles having an average particle size of 3000 nm to 8 μm. The average particle size refers to the average value of the diameters of 20 hard carbon particles measured by SEM. In another embodiment, the hard carbon is an accumulation of a plurality of substantially spherical hard carbon particles each having a particle size of 1 μm to 10 μm, and another hard carbon, the hard carbon It has a part in which a plurality of pores are formed by stacking. In another embodiment, the hard carbon is a part consisting of a plurality of roughly spherical hard carbon particles having an average particle size of 1 μm to 10 μm, and a part where another hard carbon is accumulated, and the hard carbon is It has a portion in which a plurality of pores are formed by stacking. In yet another embodiment, the hard carbon is a part consisting of a plurality of substantially spherical hard carbon particles each having a particle size of 4 μm to 7 μm, and another part where hard carbon is accumulated, It has a portion in which a plurality of pores are formed by stacking carbon. In another embodiment, the hard carbon is a part consisting of a plurality of substantially spherical hard carbon particles having an average particle size of 5 μm to 6 μm, and a part where other hard carbon is accumulated, and the hard carbon is It has a portion in which a plurality of pores are formed by stacking.

Further, the plurality of approximately spherical hard carbon particles preferably have an observation surface occupation ratio of more than 50%, more preferably 60% or more, more preferably 70% or more, and 80% of the entire hard carbon observed. The above is more preferable.

(Negative electrode material)
A negative electrode material according to one embodiment of the present invention is made of the hard carbon described above. In one embodiment, the negative electrode material is formed solely from the hard carbon described above. In another embodiment, the negative electrode material is formed from a composition including the hard carbon described above and an additive different from the hard carbon. Examples of additives include binders and conductive agents. The binder is preferably a polymer formed by polymerizing a plurality of monomer constituent units. For example, it can be one or more of the following binders: water-based binders, such as carboxymethylcellulose (CMC), polyacrylic acid (PAA), styrene-butadiene rubber, SBR), solvent-based binders such as PEO (poly(ethylene oxide)) and PVDF (poly(vinylidene fluoride)). Examples of the conductive agent include carbon black, acetylene black, Ketjenblack, and carbon nanotubes.

(Negative electrode)
A negative electrode, that is, an anode according to one embodiment of the present invention is formed by molding the above negative electrode material.

The negative electrode material is formed into any shape, such as a sheet (plate) or a cylinder, depending on its use, to produce a negative electrode. When the negative electrode material is in the form of a sheet, the outline of the sheet can be made into any shape such as circular, oval, or rectangular.

For example, the hard carbon, binder, conductive agent, etc. mentioned above are dispersed in a solvent (for example, N-methyl-2-pyrrolidone), and the resulting slurry is applied to a current collector (for example, Cu foil) using a film applicator. By drying, a film or sheet-like negative electrode can be formed on the current collector.

(alkaline ion battery)
An alkaline ion battery according to one embodiment of the present invention includes the above negative electrode, positive electrode, that is, a cathode, a separator, and an electrolyte or electrolytic solution. Alkaline ion batteries can be either sodium ion batteries or lithium ion batteries.

The negative electrode is manufactured by laminating, for example, a negative electrode material, which is a composition containing a negative electrode active material, a conductive agent as a conductive auxiliary material, and a binder, on a current collector. Since the hard carbon of the present invention functions as a negative electrode active material, such hard carbon can be used as a negative electrode material.

The positive electrode is manufactured by laminating, for example, a positive electrode material, which is a composition containing a positive electrode active material, a conductive agent as a conductive auxiliary material, and a binder, on a current collector.

In sodium ion batteries, sodium-transition metal composite oxides containing one or more transition metal elements selected from the group consisting of Co, Mn, Cr, V, Ti, and Fe may be used as the positive electrode active material. I can do it. Examples of positive electrode active materials include, but are not limited to, one or more of the following: LiFePO ₄ , LiCoO ₂ , LiNi _x Mn _y Co O ₂ (0.3≦x≦0.95,0.025≦y≦0.4,0.025≦ z≦0.4), LiNi _1-yz Co _y Al _z O ₂ (0.05≦y≦0.15,0<z≦0.05), LiMn ₂ O ₄ , LiMPO ₄ (M=Co,Ni), Li ₂ FePO ₄ F, V ₂ O ₅ , LiXV ₃ O ₈ (1.5<x≦5.5), Li _1-X VOPO ₄ (0.5≦x≦0.92), LiFeMO ₄ (M=Mn,Si), Na ₃ V ₂ (PO ₄ ) ₃ , Na ₂ MnP ₂ O ₇ , NaFePO ₄ , Na ₃ MnZr(PO ₄ ) ₃ .

In lithium batteries, the positive electrode active material is a composite oxide of lithium and fiber metal containing one or more transition metal elements selected from the group consisting of Co, Ni, and Mn, or a phosphoric acid such as _LiFePO4 . Iron etc. can be used.

Carbon black, Ketjenblack, acetylene black, carbon whiskers, carbon fibers, natural graphite, artificial graphite, carbon nanoparticles, carbon nanotubes, titanium oxide, ruthenium oxide, aluminum, nickel, and mixtures thereof as conductive agents for negative and positive electrodes. One or more conductive agents selected from the group consisting of:

As a binder for the negative electrode and positive electrode, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, fluororubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoroethylene Propylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoro Ethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE) , one or more selected from the group consisting of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, and ethylene-acrylic acid copolymer binder can be used.

The separator can be manufactured using a known separator material for batteries, or a commercially available product can be used. Examples of separator materials include, but are not limited to, one or more of the following: glass fiber (GF), polyolefin (polyolefin), (e.g. polypropylene (PP), polyethylene (PE)). , polyethylene terephthalate (PET), polyamide (PA, polyamide) (e.g. poly(m-phenyleneisophthalamide) (PMIA, poly(m-phenyleneisophthalamide)), polyimide (PI, polyimide), polybenzoxazole (PBO, polybenzoxazole), Cellulose or composite materials thereof.

The electrolyte may be any known electrolyte for alkaline ion batteries, including, but not limited to, one or more of the following: solid electrolytes, gel electrolytes, liquid electrolytes, and lithium salts dissolved in polar solvents. or sodium salts) (e.g. LiPF ₆ or NaPF ₆ added to ethylene carbonate (EC) and diethyl carbonate (DEC)), sodium trifluoromethylsulfonate (NaOTf, Sodium trifluoromethylsulfonate) dissolved in diethylene glycol dimethylether (DGDE, diethylene glycoldimethylether) , 1,3-dioxolane (DOL,1,3-dioxolane) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dissolved in 1,2-dimethoxyethane (DME, i.e. LiTFSI _in DOL:DME) etc.

(Hard carbon, negative electrode and battery manufacturing method)
FIG. 1 shows a schematic diagram of the manufacturing process of hard carbon (14) and negative electrode (18) according to one embodiment of the present invention.

As the raw material biomass (10), those listed above as examples of biological materials can be used. Examples of preferred biomass are plants, and more preferably plants containing a large amount of N and S elements, such as garlic, persimmon, tea, and soybean.

Prepare the aged biomass (12). Aged biomass (12) contains a large amount of sugar and is easier to convert into char compared to unripened biomass (10). Carbonize the aged biomass (12) to obtain hard carbon (14). As a material to be carbonized, the raw material biomass (10) may or may not be added to the aged biomass (12). The details of the obtained hard carbon (14) are as explained in the (hard carbon) section.

The carbide may be further treated with acid or alkali for activation. Furthermore, when a metal sulfide, oxide, or the like is doped onto the carbide obtained after the carbonization step, the electrochemical properties can be further improved.

The obtained hard carbon (14) may be used as a negative electrode material as it is, or may be used as a negative electrode material by adding an additive (16).

As described above, examples of the additive (16) include binders, conductive agents, and the like. The negative electrode material is formed into any shape such as spherical or sheet-like (plate-like) depending on its use, and when it is made into a sheet, the outline is shaped into a circle, oval, rectangle, etc., and the negative electrode (18) is produced. do.

FIG. 2 shows the assembly of an alkaline ion battery using the negative electrode (18) of FIG. 1.

Details of the negative electrode (18), positive electrode (20), separator (22), and electrolyte (24) are as explained in the (alkaline ion battery) section.

An alkaline ion battery is constructed by moistening the separator (22) with the electrolyte (24) and assembling the negative electrode (18), the positive electrode (20), and the separator (22) between them. Methods of assembling batteries with negative electrodes, positive electrodes, separators, and electrolytes are well known in the art.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto.

Reagents, equipment and experimental conditions
NaOTf, _NaPF6 , and diethylene glycol dimethyl ether (DGDE) were purchased from Sigma-Aldrich Corp., Japan. Carbon black (Super-P) was obtained from Alfa Aesar Co., Ltd. England. Poly(vinylidene fluoride) (PVDF) binder was purchased from MTI Corp., Japan. 1M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,3-dioxolane (DOL):dimethoxyethane (DME) (1:1vol.%) (60μl) was purchased from China XiamenTob New Energy Technology Co., Ltd. Purchased from. The battery test system was LAND Battery Test System CT2001A (manufactured by Wuhan Land Electronics Co., Ltd.). The film applicator is manufactured by BEVS Industrial Co., Ltd. Japan. The glove box (Miwa Seisakusho, Japan) was an Ar gas environment in which the amount of H ₂ O and O ₂ was below the 0.1 ppm level.

Example 1 Preparation of negative electrode material First, microbially aged garlic (black garlic from Aomori Prefecture) was purchased from a local market (Aomori, Japan), peeled and cut into small pieces, and then processed using a hydrothermal method. Garlic was pre-carbonized at 180°C for 24 hours. Thereafter, the pulverized and pre-carbonized material: KOH was uniformly mixed in a 1:2 weight % ratio, and then calcined at 800° C. for 2 hours under an argon atmosphere. The resulting material was thoroughly washed with 1.0 M HCl to remove impurities, followed by distilled water until a neutral pH was reached. Finally, the material was washed with absolute ethanol and dried at 100 °C. Here, the obtained carbon material is referred to as GT-C carbon material.

The morphology of the GT-C carbon material was characterized using a scanning electron microscope (SEM, Hitachi SU8010). Its crystal structure was determined by an X-ray diffractometer (XRD, RigakuSmart Lab X-ray diffractometer) using a Cu-Kα (λ = 1.5405 Å) radiation source in the 2θ range of 10-90°.

Next, the GT-C carbon material, carbon black (Super-P), and poly(vinylidene fluoride) (PVDF) binder (weight ratio 80:10:10) were completely dispersed in N-methyl-2-pyrrolidone solvent. The resulting slurry was applied to Cu foil using a film applicator and dried at 100°C for 24 hours to produce a GT-C negative electrode film.

Example 2 Assembly and electrochemical measurement of Na-C half cell using GT-C carbon material as negative electrode
A half cell consisting of a GT-C negative electrode (12 mm diameter), a glass fiber separator (16 mm diameter) moistened with liquid electrolyte, and a Na metal positive electrode (12 mm diameter) was assembled. At this time, a 1M NaPF ₆ DGDE solution (60 μl) was used as the liquid electrolyte. The electrochemical performance of the half cell was tested in a LAND battery test system at 30°C under a cutoff voltage range of 0-3V.

Example 3 Assembly and electrochemical measurement of Li-C half cell using GT-C carbon material as negative electrode
A half cell was assembled consisting of a GT-C negative electrode (12 mm diameter), a glass fiber separator moistened with liquid electrolyte (16 mm diameter), and a Li metal positive electrode (12 mm diameter). At this time, a DOL solution of 1M LiTFSI: DME (1:1 vol.%) (60 μl) was used as the liquid electrolyte. Similar to Example 2, the electrochemical performance was tested in a LAND battery test system at 30°C under a cutoff voltage range of 0-3V.

Comparative Example 1 Preparation of Negative Electrode Material First, ordinary garlic was purchased from a local market (Aomori, Japan). As in Example 1, the garlic was peeled, cut into small pieces, and then pre-carbonized using a hydrothermal method at 180° C. for 24 hours. Thereafter, the pulverized and pre-carbonized material: KOH was uniformly mixed in a 1:2 weight % ratio, and then calcined at 800° C. for 2 hours under an argon atmosphere. The resulting material was thoroughly washed with 1.0 M HCl to remove impurities, followed by distilled water until a neutral pH was reached. Finally, the material was washed with absolute ethanol and dried at 100 °C. Here, the obtained carbon material is referred to as GC-C carbon material.

The morphology of the GC-C carbon material was characterized using a scanning electron microscope (SEM, Hitachi SU8010). Its crystal structure was determined by an X-ray diffractometer (XRD, RigakuSmart Lab X-ray diffractometer) using a Cu-Kα (λ = 1.5405 Å) radiation source in the 2θ range of 10-90°.

Next, the GC-C carbon material, carbon black (Super-P), and poly(vinylidene fluoride) (PVDF) binder (weight ratio 80:10:10) were completely dispersed in N-methyl-2-pyrrolidone solvent. The resulting slurry was applied to Cu foil using a film applicator and dried at 100°C for 24 hours to produce a GC-C negative electrode film.

Comparative Example 2 Assembly and electrochemical measurement of Na-C half cell using GC-C carbon material as negative electrode
A half cell consisting of a GC-C negative electrode (12 mm diameter), a glass fiber separator moistened with liquid electrolyte (16 mm diameter), and a Na metal positive electrode (12 mm diameter) was assembled. At this time, a 1M NaPF ₆ DGDE solution (60 μl) was used as the liquid electrolyte. The electrochemical performance was tested in a LAND battery test system at 30°C under a cut-off voltage range of 0-3V.

Comparative Example 3 Assembly and electrochemical measurement of Li-C half cell using GC-C carbon material as negative electrode
A half cell consisting of a GC-C negative electrode, a glass fiber separator (16 mm diameter) moistened with liquid electrolyte, and a Li metal positive electrode (12 mm diameter) was assembled. At this time, a DOL solution of 1M LiTFSI: DME (1:1 vol.%) (60 μl) was used as the liquid electrolyte. Similar to Comparative Example 2, the electrochemical performance was tested in a LAND battery test system at 30°C under a cutoff voltage range of 0-3V.

Results As shown in Fig. 3, scanning electron microscope (SEM) images of the GT-C carbon material (Fig. 3A) and the GC-C carbon material (Fig. 3B) showed different morphologies. In the case of GT-C carbon material, many carbon spheres were observed.

Figure 4 shows the results of X-ray diffraction analysis of GT-C carbon material and GC-C carbon material. Two broad peaks centered around 24° and 43° are clearly present in all XRD profiles, corresponding to the (002) and (100) crystal planes of graphite. In particular, the GT-C material showed a broader and lower intensity peak, suggesting that the amount of amorphous hard carbon produced was greater than the GC-C material and less than the graphitized carbon content. Additionally, the (002) peak shifted to a higher diffraction angle in the GT-C carbon material than in the GC-C carbon material, suggesting an improvement in the structural order of the material.

FIG. 5 is a graph showing the discharge capacity of a sodium ion battery versus the number of cycles when GT-C carbon material and GC-C carbon material are used. Compared with GC-C negative electrode, GT-C negative electrode|Na metal cell with _NaPF6 electrolyte has higher discharge capacity (115.3mAhg ^-1 after 100 cycles at high current density 1Ag ^- 1) and initial Coulombic efficiency. showed a remarkable improvement of approximately 55.42% (Fig. 5A). Furthermore, the discharge capacity was also improved when a NaOTf type electrolyte was used (Figure 5B).

According to the results in Figure 3 and the electrochemical measurement results in Figure 5, the increase in discharge capacity of the aged garlic-derived GT-C negative electrode is due to the appropriate surface area of carbon spheres and the pores formed by stacking secondary particles. Due, at least in part, to its unique structure with a uniform distribution of As shown in Fig. 6, compared with the case using GC-C anode, the GT-C anode|Li metal cell with commercial liquid electrolyte showed higher discharge capacity (200 mAcm ^-2 After a number of cycles, 157.9mAhg ^-1 ). Therefore, the negative electrode made of GT-C carbon material with abundant hard carbon spheres and pores is also more suitable for lithium-ion batteries.

Claims (6)

A negative electrode material made of substantially spherical porous hard carbon made of fermented carbonized plant material (excluding magnetic activated carbon containing iron oxide nanoparticles having a diameter larger than the size of pores in the carbonized biomass), A negative electrode material, wherein the plant is garlic, persimmon, tea, or soybean . The negative electrode material according to claim 1 , wherein the hard carbon includes approximately spherical hard carbon particles with a particle size of 100 nm to 10 μm. A negative electrode formed by molding the negative electrode material according to claim 1 or 2 . An alkaline ion battery comprising the negative electrode according to claim 3 . Pre-carbonization of plants fermented with microorganisms at 120-220°C (hydrothermal treatment of aqueous solutions containing biomass at autogenous pressures at temperatures between 180-250°C under acidic conditions and in the presence of iron ions) ), and a method for producing substantially spherical hard carbon from a fermented plant, the method comprising: firing the pre-carbonized plant at 500 to 1400°C. 6. The manufacturing method according to claim 5, further comprising, after the step of pre-carbonizing, activating the pre-carbonized plant with potassium hydroxide.