Use of a biochar material in lithium-oxygen batteries

Abstract

The application relates to application of a biochar material in a lithium-oxygen battery and belongs to the technical field of lithium-oxygen batteries. The biochar material comprises nitrogen atoms, sulfur atoms and a porous skeleton structure, the nitrogen atoms and the sulfur atoms are doped on the porous skeleton structure, and the material of the porous skeleton structure is a carbon material. The application takes discarded poultry bones as raw materials, utilizes the characteristics of hydroxyapatite decomposition and collagen carbonization in a pyrolysis process, and synthesizes nitrogen and sulfur co-doped biochar materials in one step through a self-template method. In the synthesis process, no activator and additional heteroatom source need to be introduced, the process is simple, the cost is low, and the application is environment-friendly. The biochar material with the skeleton structure prepared by the application shows good oxygen catalytic performance, and a lithium-oxygen battery assembled by using the material shows high energy density.

Description

Technical Field

[0001] This invention relates to the application of biochar material in lithium-oxygen batteries, specifically to a lithium-oxygen battery positive electrode sheet made of biochar material derived from avian bones, belonging to the field of lithium-oxygen battery technology. Background Technology

[0002] With the rapid development of electric vehicles and portable electronic devices, the pursuit of high energy density in battery design has become increasingly prominent. Since its introduction in the 1990s, lithium-ion batteries have become the most widely used rechargeable batteries. Currently, graphite remains the mainstream anode material in commercial lithium-ion batteries, but its relatively low theoretical capacity density (372 mAh / g) limits breakthroughs in energy density. Metal-oxygen batteries, however, utilize lighter gases as reactants and possess very high theoretical energy densities. Among them, lithium-oxygen batteries, using lithium metal as the anode active material and oxygen as the cathode active material, can achieve a theoretical energy density exceeding 3500 Wh / kg, attracting widespread attention.

[0003] In practical applications, lithium-oxygen batteries struggle to realize their theoretical energy density advantage due to the slow kinetics of the electrochemical reduction / oxidation of oxygen at the oxygen cathode. On one hand, the electrode reaction requires overcoming a high potential barrier, resulting in a high overpotential, which hinders rapid reaction. On the other hand, the slow electrode reaction leads to the accumulation of discharge products (lithium peroxide, lithium carbonate, etc.) on the electrode surface, resulting in a vicious cycle of catalytic activity site blockage. Therefore, designing oxygen cathode catalysts with uniform catalytic sites and hierarchical pore structures is crucial for the practical development of lithium-oxygen batteries.

[0004] Extensive research has focused on cathode catalysts including noble metals, metal oxides, and functional carbon materials. An ideal oxygen cathode should possess high conductivity, electrochemical stability, high catalytic activity, low density, and abundant pore structure; therefore, functional carbon materials are increasingly becoming a trend. Differences in the morphology and microstructure of carbon materials exhibit significant differences in their electrochemical oxidation and reduction of oxygen, making them a very promising class of oxygen cathode materials. However, carbon materials themselves have limited catalytic activity for oxygen evolution / reduction. Researchers typically combine carbon materials with metal oxides and noble metals, resulting in complex preparation processes and unavoidable environmental threats.

[0005] Considering material cost and renewability, advanced functionalized carbon materials made from biomass can serve as low-cost, environmentally friendly oxygen cathodes. The defect structure, oxygen-containing groups, and heteroatom doping on the surface of carbon materials have also been shown to have a certain catalytic effect on the oxygen cathode reaction. Therefore, designing the pore structure, surface defect structure, and oxygen-containing group concentration of carbon materials is an important issue in achieving high electrochemical stability of the cathode in lithium-oxygen batteries. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose an application of biochar material in lithium-oxygen batteries. It utilizes inorganic substances such as calcium hydroxyphosphate in poultry bones as natural templates to construct a micro-skeleton structure and uses nitrogen- and sulfur-containing components in bone collagen as nitrogen and sulfur sources to introduce uniform oxygen catalytic sites. This avoids the complex process and environmental risks of introducing additional catalytic species when functional carbon materials are used as catalytic materials in lithium-oxygen batteries.

[0007] The technical solution of this invention is:

[0008] A biochar material comprising nitrogen atoms, sulfur atoms, and a porous structure, wherein nitrogen atoms and sulfur atoms are doped onto the porous structure, and the porous structure is a carbon material.

[0009] A method for preparing biochar material, the method comprising the following steps:

[0010] (1) Boil poultry bones in boiling water for 1-1.5 hours, remove the poultry bones and remove impurities from the bone sticks, then air dry at room temperature and pulverize to obtain bone powder;

[0011] (2) Place the bone powder obtained in step (1) into a tube furnace and calcine it at 700-900℃ for 1-2 hours under a nitrogen or inert gas protective atmosphere with a heating rate of 5-10℃ / min to obtain carbonized products.

[0012] (3) Soak the carbonized product obtained in step (2) in dilute nitric acid for 2-3 hours to remove inorganic components, filter it to obtain filter cake A, wash filter cake A with deionized water until neutral to obtain filter cake B.

[0013] (4) The filter cake B obtained in step (3) is soaked in ascorbic acid solution to regulate the heteroatoms and functional groups on the surface of filter cake B. After filtration, filter cake C is obtained. Filter cake C is washed with deionized water until neutral and dried to obtain biochar material derived from poultry bones.

[0014] In step (3), the concentration of dilute nitric acid is 1-2M;

[0015] In step (4), the concentration of the ascorbic acid solution is 5-20 g / L.

[0016] The application of a biochar material in a lithium-oxygen battery, wherein the biochar material is used as an oxygen cathode material;

[0017] The oxygen cathode is prepared by mixing the obtained biochar material, conductive agent and binder evenly, adding N-methylpyrrolidone to make a slurry, coating the prepared slurry on carbon paper, drying it and cutting it into round pieces.

[0018] The conductive agent is acetylene black, the binder is polyvinylidene fluoride, the mass ratio of biochar material, conductive agent and binder is 6-8:1-3:1, and the diameter of the disc is 11-16 mm.

[0019] The assembly method of the lithium-oxygen battery is as follows: using the aforementioned oxygen positive electrode as the positive electrode, lithium sheet as the negative electrode, Whatman glass fiber membrane as the separator, and 1M lithium bis(trifluoromethanesulfonyl)imide in tetraethylene glycol dimethyl ether solution as the electrolyte, a Swagelok mold battery is assembled in an argon atmosphere glove box; then the assembled mold battery is transferred to a sealed container, and oxygen is introduced into the container for 12 hours to fully impregnate and dissolve it; finally, a constant current charge-discharge test is performed on the mold battery in the sealed container, with a test current of 0.02-0.2 mA / cm². 2 The cutoff voltage is 2-4.5V.

[0020] Beneficial effects

[0021] (1) This invention uses waste poultry bones as raw material and takes advantage of the decomposition of calcium hydroxyphosphate and carbonization of collagen during pyrolysis to synthesize nitrogen- and sulfur-doped biochar materials in one step via a self-template method. The synthesis process does not require the introduction of activators or additional heteroatom sources, is simple, low-cost, and environmentally friendly.

[0022] (2) The biochar material with a framework structure prepared in this invention exhibits a porous structure, which can promote mass transfer of reactants in the electrode, provide more three-phase reaction interfaces, and accommodate more discharge products, thereby achieving a higher discharge capacity (at 0.02 mA / cm²). 2 At this point, the discharge capacity is 1.45 mAh / cm³. 2 ).

[0023] (3) The uniform nitrogen and sulfur atom doping introduced by collagen in this invention has a certain catalytic effect on oxygen reduction / oxygen evolution reaction, and can reduce the reaction overpotential (at 0.02 mA / cm). 2 The charging platform is 3.57V and 4.24V, and the discharging platform is 2.74V, thereby improving the cycle performance of the lithium-oxygen battery. Attached Figure Description

[0024] Figure 1The image shows a scanning electron microscope (SEM) image of the biochar material prepared in Example 1.

[0025] Figure 2 The image shows the X-ray photoelectron spectroscopy (XPS) results of the biochar material prepared in Example 1; where a is the full spectrum scan image, and the inset in image a is a magnified view of a part; b is the C1s high-resolution scan image, c is the N1s high-resolution scan image, and d is the S2p high-resolution scan image.

[0026] Figure 3 The lithium-oxygen battery assembled in Example 1 operates at 0.02 mA / cm². 2 Performance at full discharge point during the first cycle under current density;

[0027] Figure 4 The lithium-oxygen battery assembled in Example 1 operates at 0.2 mA / cm. 2 Performance at full discharge point during the first cycle under current density;

[0028] Figure 5 The lithium-oxygen battery assembled in Example 1 operates at 0.02 mA / cm². 2 Current density, 0.1 mAh / cm³ 2 Cyclic performance diagram under cutoff capacity;

[0029] Figure 6 The image shows a scanning electron microscope (SEM) image of the biochar material prepared in Example 2.

[0030] Figure 7 The image shows the X-ray photoelectron spectroscopy (XPS) results of the biochar material prepared in Example 2.

[0031] Figure 8 The lithium-oxygen battery assembled in Example 2 operates at 0.02 mA / cm². 2 Performance at full discharge point during the first cycle under current density;

[0032] Figure 9 The image shows the X-ray photoelectron spectroscopy (XPS) results of the biochar material prepared in Example 2.

[0033] Figure 10 The lithium-oxygen battery assembled in Example 3 operates at 0.02 mA / cm². 2 Performance at full discharge point during the first cycle under current density;

[0034] Figure 11 The lithium-oxygen battery assembled in Example 3 operates at 0.02 mA / cm². 2 Current density, 0.06 mAh / cm² 2 Cyclic performance diagram under cutoff capacity. Detailed Implementation

[0035] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0036] Example 1

[0037] Boil chicken leg bones in boiling water for 1 hour to remove impurities from the bones, then air dry them at room temperature and crush them.

[0038] The bone powder was placed in a corundum ceramic boat and heated to 800°C in a tube furnace at a heating rate of 10°C / min under a nitrogen atmosphere, and held at that temperature for 1.5 hours.

[0039] The obtained product was acid-washed with 1M dilute hydrochloric acid, washed with deionized water until neutral, and then soaked in 10g / L ascorbic acid solution for 12h. After drying, poultry bone porous biochar material was obtained.

[0040] Biochar powder, acetylene black, and PVDF are then mixed evenly in a mass ratio of 8:1:1 to obtain a slurry. The slurry is then coated onto carbon paper and dried in a vacuum drying oven at 80°C. After rolling and cutting, the positive electrode sheet for lithium-oxygen batteries is obtained.

[0041] Figure 1 The image shows a SEM image of the biochar material prepared in Example 1. It can be seen that the prepared biochar material has an irregular porous structure and a rough surface texture. The porous structure and rough surface texture facilitate mass transfer of oxygen and reaction intermediates in the electrode, providing numerous reaction sites for the electrode reaction. Simultaneously, the numerous pores provide ample storage space for discharge products, promoting rapid and reversible electrode reactions, thereby increasing the capacity of the lithium-oxygen battery.

[0042] Figure 2 This is an XPS test result image of the biochar material prepared in Example 1. Figure 2 XPS full-spectrum scans of sample a revealed the presence of C, N, O, and S, with atomic contents of 82.07%, 5.54%, 11.93%, and 0.46%, respectively. This indicates that N and S were successfully doped into the prepared biochar material, and ascorbic acid, through its strong reducing properties, resulted in a high carbon-to-oxygen ratio. In N1s (e.g.) Figure 8 The high-resolution scan image (as shown) indicates that N mainly exists in the form of pyridine nitrogen, pyrrole nitrogen, and quaternary ammonium nitrogen; in S2p (such as... Figure 8 The high-resolution scanning image (shown) shows that S mainly exists in the form of carbon-sulfur bonds and sulfate ions. The doping of heteroatoms and the generation of carbon defects provide catalytic sites for the reaction of oxygen at the cathode.

[0043] The above positive electrode sheets were assembled into a Swagelok structure battery, and electrochemical tests were performed.

[0044] The assembled lithium-oxygen battery operates at 0.02 mA / cm². 2 The discharge capacity at the current density is 1.45 mAh / cm³. 2 ,like Figure 3 As shown; at 0.2 mA / cm 2 The discharge capacity at the current density is 0.92 mAh / cm³. 2 ,like Figure 4 As shown in the figure. The results confirm the beneficial effects of heteroatom doping and porous structure in the prepared biochar material on improving the capacity of lithium-oxygen batteries.

[0045] Figure 3 The results show that the prepared biochar cathode exhibited a discharge plateau of 2.74V and two charging plateaus at 3.57V and 4.34V during the first week of full charge-discharge testing. These results indicate that the synthesized biochar material promoted the oxygen reduction / oxygen evolution reaction and reduced the reaction overpotential. Figure 5 The cycle performance test results show that the battery can cycle stably for 65 cycles with a small overpotential.

[0046] Example 2

[0047] Same as Example 1, except that it was soaked in 5g / L ascorbic acid solution for 12h.

[0048] Figure 6 The image shows an SEM image of the biochar material prepared in Example 2. It can be seen that the prepared biochar material has a smaller particle size and a more open pore structure compared to Example 1, indicating that the material has a lower degree of aggregation under low concentration ascorbic acid treatment.

[0049] Figure 7 The figure shows the XPS test results of the biochar material prepared in Example 2. The figure shows that the sample contains C, N, O and S, with atomic contents of 70.66%, 5.82%, 22.77% and 0.75%, respectively. The forms of N and S are similar to those in Example 1, but the content of O atoms is relatively higher. Although this provides more defect sites for carbon materials, it inevitably leads to more side reactions.

[0050] The assembled lithium-oxygen battery operates at 0.02 mA / cm². 2 The discharge capacity at the current density is 0.88 mAh / cm³. 2 ,like Figure 8 As shown in the figure. The results confirm that even at a low carbon-to-oxygen ratio, the material still exhibits a high areal capacity when used as a cathode material for lithium-oxygen batteries due to its porous structure and heteroatom doping.

[0051] Example 3

[0052] Same as Example 1, except that it was soaked in 20g / L ascorbic acid solution for 12h.

[0053] Figure 9 The figure shows the XPS test results of the porous biochar material prepared in Example 3. The figure shows that the sample contains C, N, O and S, with atomic contents of 80.94%, 7%, 11.66% and 0.4%, respectively. The forms of N and S are similar to those in Example 1. Under the reduction of high concentration of ascorbic acid, the content of O atoms is relatively low.

[0054] The assembled lithium-oxygen battery operates at 0.02 mA / cm². 2 The discharge capacity at the current density is 0.79 mAh / cm³. 2 ,like Figure 10 As shown; at 0.02mA / cm 2 The current density is 0.06 mAh / cm³. 2 At the cutoff capacity, it can be cycled stably for 15 cycles with a low overpotential, such as Figure 11 As shown.

[0055] In summary, the above are merely preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a biochar material in a lithium-oxygen battery, characterized in that: When applied, this biochar material is used as an oxygen cathode material; The oxygen cathode is prepared by mixing biochar material, conductive agent and binder evenly, adding N-methylpyrrolidone to make a slurry, coating the prepared slurry on carbon paper, drying it and cutting it into round pieces. In the lithium-oxygen battery, the obtained biochar material discs are used as the positive electrode, lithium sheets are used as the negative electrode, Whatman glass fiber membranes are used as the separators, and 1 M lithium bis(trifluoromethanesulfonylimide) in tetraethylene glycol dimethyl ether solution is used as the electrolyte. The biochar material includes nitrogen atoms, sulfur atoms, and a porous structure, with nitrogen atoms and sulfur atoms doped onto the porous structure, and the porous structure is a carbon material. The method for preparing the biochar material includes the following steps: (1) Boil poultry bones in boiling water for 1-1.5 hours, remove the poultry bones and remove impurities from the bone sticks, then air dry at room temperature and pulverize to obtain bone powder; (2) Place the bone powder obtained in step (1) into a tube furnace and calcine it at 700-900 ℃ for 1-2 h at a heating rate of 5-10 ℃ / min under an inert gas protective atmosphere to obtain carbonized products. (3) Soak the carbonized product obtained in step (2) in dilute nitric acid for 2-3 h to remove inorganic components, filter it to obtain filter cake A, wash filter cake A with deionized water until neutral to obtain filter cake B. (4) The filter cake B obtained in step (3) is soaked in ascorbic acid solution to regulate the heteroatoms and functional groups on the surface of filter cake B. After filtration, filter cake C is obtained. Filter cake C is washed with deionized water until neutral and dried to obtain biochar material derived from poultry bones.

2. The application of a biochar material according to claim 1 in a lithium-oxygen battery, characterized in that: The conductive agent is acetylene black, the binder is polyvinylidene fluoride, the mass ratio of biochar material, conductive agent and binder is 6-8:1-3:1, and the diameter of the disc is 11-16 mm.

3. The application of a biochar material according to claim 1 in a lithium-oxygen battery, characterized in that: In step (3), the concentration of dilute nitric acid is 1-2M; In step (4), the concentration of ascorbic acid solution is 5-20 g / L.

4. The application of a biochar material according to claim 1 in a lithium-oxygen battery, characterized in that: A Swagelok mold battery was assembled in an argon atmosphere glove box using biochar as the positive electrode, lithium sheet as the negative electrode, Whatman glass fiber membrane as the separator, and 1 M lithium bis(trifluoromethanesulfonyl)imide in tetraethylene glycol dimethyl ether solution as the electrolyte.

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