Preparation method and application of biomass thick electrode

Abstract

The invention discloses a preparation method and application of a biomass thick electrode, and belongs to the technical field of electrode material preparation. The preparation method of the biomass thick electrode comprises the following steps: mixing biomass carbon with a sulfur source, and carrying out heating reaction in an inert atmosphere to obtain a carbon-sulfur composite material; and mixing the carbon-sulfur composite material, a conductive agent and a binder to prepare slurry, then coating a three-dimensional current collector nickel net with the slurry, drying, and then carrying out picosecond laser processing to obtain the biomass thick electrode. The biomass thick electrode prepared by the invention has lower tortuosity and more surface pore openings, and can play a greater role in inhibiting the shuttle effect of polysulfide of the lithium-sulfur battery, and active substances in the thick electrode can also be immersed into the electrode along with electrolyte to be fully utilized.

Description

Technical Field

[0001] The present invention relates to the technical field of electrode material preparation, and in particular to a preparation method and application of a biomass thick electrode. Background Art

[0002] Among many electrochemical energy storage systems, lithium-sulfur batteries have unique advantages in the design of high specific energy batteries. Their positive active materials are based on a multi-electron reaction mechanism, with a mass energy density as high as 2350 Wh / kg, which is about an order of magnitude higher than that of commercial lithium-ion batteries. However, lithium-sulfur batteries also have some bottlenecks to be overcome. For example, the poor conductivity of elemental sulfur, the easy solubility of intermediate polysulfides in the electrolyte, and the low volume energy density and other factors restrict the performance and commercialization of lithium-sulfur batteries.

[0003] At present, the process for preparing the positive electrode of a lithium-sulfur battery includes coating a slurry composed of active particles, a conductive agent, and a binder on a metal current collector to form a dried electrode particle coating, and then compacting and densifying it. This process is easy to mass-produce roll-shaped battery cores. Assembling the roll-shaped positive and negative electrodes with a separator into a battery core, injecting an electrolyte, and performing charge and discharge activation to finally form square (roll-shaped), cylindrical (roll-shaped), and soft-pack (laminated) battery structure products. The larger the active material loading of the single-layer positive electrode material in the roll-shaped electrode, the greater the volume energy density. In a lithium-sulfur battery, to increase the active material loading and volume energy density, the coating thickness of the positive electrode material needs to be increased. The traditional slurry electrode process needs to be coated on a flat metal foil. During the drying and curing process of a thick coating slurry with a thickness exceeding 50 μm, the unsupported shrinkage stress inside the electrode will generate defects such as cracks and burrs on the surface, resulting in damage and cracking of the electrode material on the surface of the foil and inability to work properly. Therefore, the thickness of the sulfur positive electrode prepared by the traditional process is often only below 50 μm.

[0004] Biomass carbon materials have good conductivity, low price, and are easy to form a porous structure, which can improve the electrochemical performance of lithium-sulfur batteries. Therefore, they are widely used as carrier materials for the active material sulfur in lithium-sulfur batteries. However, biomass carbon materials have a random pore geometry and high tortuosity, resulting in a compacted electrode with a low porosity and fewer charge transport paths. Their ion transport ability is poor, and the electrolyte penetration rate is low, leading to slow sulfur conversion kinetics and low utilization rate of active materials. Therefore, even if a thick sulfur slurry is coated to prepare a battery core, its total capacity still cannot be improved.

[0005] In traditional porous electrode materials, carbon and sulfur particles are in nanosize and are coated on a metal current collector by a slurry to obtain a positive electrode with a thickness below 50 μm. Although traditional current collectors have excellent cycle stability and high specific capacity, most studies are based on a low areal sulfur loading (≤2 mg / cm 2 ), and the areal capacity is lower than that of commercial lithium-ion batteries (4 mAh / cm2 ). Therefore, the areal sulfur loading of the thick sulfur cathode material should be at least greater than 5 mg / cm 2 , so that the areal capacity of the lithium-sulfur battery can exceed that of commercial lithium-ion batteries. To obtain a practical high-energy-density lithium-sulfur battery, the research on high-sulfur-loading cathodes is crucial. However, with the increase in sulfur loading, inherent defects such as the shuttle effect of polysulfides (LiPSs) in lithium-sulfur batteries will be further amplified. To solve this problem, researchers have proposed three-dimensional current collectors with interconnected macropores and thick structures. For example, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are coated on the surface of nickel foam (NF) by chemical vapor deposition, and the unique porous structure is used as the three-dimensional (3D) current collector for lithium-sulfur (Li-S) batteries, providing sufficient space to accommodate the electrode materials inside itself. The thickness of this cathode material can reach 300 μm, but the areal sulfur loading is only 3 mg / cm 2 ; The sulfur-loaded bamboo carbon slurry is coated into copper foam and used as the electrode of the Li-S battery, and its areal sulfur loading can reach 8.6 mg / cm 2 , but the number of cycles at high sulfur loading is only 14 cycles (decreasing from 803 mAh / g to 372 mAh / g). And how to prepare a lithium-sulfur battery cathode material with high areal capacity and good cycle stability has become a technical problem that needs to be solved urgently by those skilled in the art. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method and application of a biomass thick electrode to solve the problems existing in the above-mentioned prior art.

[0007] To achieve the above purpose, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention: A preparation method of a biomass thick electrode, comprising the following steps:

[0009] Mix biomass carbon with a sulfur source and heat and react in an inert atmosphere to obtain a carbon-sulfur composite material (BC@S);

[0010] Mix the carbon-sulfur composite material, a conductive agent, and a binder to form a slurry, and then coat the slurry on a three-dimensional current collector nickel mesh and dry to obtain a biomass carbon electrode;

[0011] Perform picosecond laser processing on the biomass carbon electrode to obtain the biomass thick electrode.

[0012] Further, the preparation method of the biomass carbon comprises the following steps:

[0013] Soak the biomass in an alkaline solution (activation process) and then pyrolyze it in an inert atmosphere (carbonization process) to obtain the biomass carbon.

[0014] Further, the biomass includes corncobs; the alkaline solution includes a KOH solution.

[0015] Further, the heating rate of the pyrolysis is 5 - 8 °C / min, the temperature is 800 - 1000 °C, and the heat preservation time is 2 - 3 h.

[0016] The biomass carbon source material is selected as corncobs or other similar carbon sources, which has the characteristics of easy availability of raw materials and simple preparation process. Especially, both the inner and outer surfaces of the pores of corncobs can be impregnated with the alkali solution and provide abundant contact and activation sites. After carbonization, carbon tubes and carbon pore structures with porous or fibrous structures can be formed. Such porous structures can coat the active substances and are ideal porous carbon source materials.

[0017] Further, the mass ratio of the biomass carbon to the sulfur source is 3:7;

[0018] The sulfur source includes elemental sulfur;

[0019] The temperature of the heating reaction is 155 °C and the time is 12 h.

[0020] Further, the loading of the sulfur source on the three-dimensional current collector nickel mesh is 4 - 14 mg / cm 2 ; the thickness of the three-dimensional current collector nickel mesh is 350 μm;

[0021] The laser power of the picosecond laser processing is 5 - 40 W.

[0022] Further, the laser wavelength of the picosecond laser processing (i.e., the picosecond laser processing with ultrashort pulses, and the picosecond laser with ultrashort pulses has characteristics such as ultrashort pulse width and adjustable frequency, and belongs to a laser beam with extremely high pulse energy density) is 1030 nm, the laser speed is 1000 - 2000 m / s, the laser frequency is 20 - 40 kHz, the spacing of the laser processing is 50 μm, the number of laser processing times is 3 - 8 times, the time of each laser processing is 0.2 ms, and the pulse width is 5 - 15 ps.

[0023] The thermal energy effect of the picosecond laser is extremely small and the penetration effect is good, and the porous structure of the biomass carbon can insulate heat, making the heat unable to penetrate deeply. Therefore, obvious cladding characteristics will not be formed on the surface and inside during the laser processing. The pyrolyzed elemental sulfur has a more uniform dispersion (found by EDS elemental analysis), smaller particles, which is beneficial to form a more sufficient sulfur-carbon mixture and improve the conductivity ( Figure 5 the internal resistance of the biomass thick electrode in

[0024] The second technical solution of the present invention: A biomass thick electrode prepared by the above preparation method.

[0025] The third technical solution of the present invention: An application of the above-mentioned biomass thick electrode as a positive electrode of a lithium-sulfur battery.

[0026] The fourth technical solution of the present invention: A method for improving the volume energy density of a biomass carbon electrode, comprising the following steps:

[0027] Mix biomass carbon with a sulfur source and heat-react in an inert atmosphere to obtain a carbon-sulfur composite material;

[0028] Mix the carbon-sulfur composite material, a conductive agent, and a binder to form a slurry, then coat the slurry on a three-dimensional current collector nickel mesh, dry to obtain a biomass carbon electrode, and finally perform picosecond laser processing on the biomass carbon electrode.

[0029] The present invention discloses the following technical effects:

[0030] (1) Using a biomass carbon electrode in a battery has disadvantages such as too long transport paths and ion channels, high tortuosity resulting in the inability of the electrolyte to penetrate, and low utilization rate of the loaded activity. The present invention constructs a lattice structure with a spacing of 50-100 μm perpendicular to the surface structure on the surface and inside of the biomass carbon electrode through picosecond laser processing. The straight through-holes of this laser processing can lead to the inside of the biomass thick electrode; this lattice structure enables the prepared biomass thick electrode to have a lower tortuosity and more surface pore openings, which can play a greater inhibitory role on the shuttle effect of polysulfides in the lithium-sulfur battery, and the active substances in the thick electrode can also be fully utilized as the electrolyte infiltrates into the electrode interior.

[0031] (2) The biomass thick electrode prepared by the present invention has a high areal sulfur loading, a high areal capacity, and high stability.

[0032] (3) The picosecond laser processing adopted by the present invention is picosecond laser processing with ultrashort pulses. The average energy of the ultrashort pulse picosecond laser beam is low and the action time is short (in the order of 10 -12 s), with little thermal influence on the sulfur particles attached to the surface of the biomass carbon. It can construct a pore structure with a low tortuosity on the surface of the biomass thick electrode with a high tortuosity, endowing the thick electrode surface with the functional characteristics of being porous and having a low tortuosity, thereby achieving an increase in energy density (the volume energy density of this thick electrode is 708.6 Wh / L, and the volume energy density of the positive electrode of a traditional thin electrode lithium-sulfur battery is between 200-400 Wh / L). Moreover, when irradiating the biomass carbon sulfur nickel foam electrode with a picosecond laser beam, thermal vibration energy will be generated, thereby forming a lattice pore structure with a certain depth on the electrode surface.

[0033] (4) The thickness of the electrode has a direct impact on the volumetric energy density of the lithium-sulfur battery. Generally speaking, the thicker the electrode, the higher the volumetric energy density of the battery. However, the sulfur content in the electrode material is limited. If the electrode is too thick, the sulfur in the battery will be unevenly distributed, resulting in an increase in the tortuosity inside the electrode and a longer ion channel, thereby reducing the utilization rate of the active material. This will lead to a decrease in the diffusion rate of lithium ions in the electrode, thus affecting the volumetric energy density of the battery. Therefore, generally, the electrode thickness is controlled within the range of 10 - 50 μm, and it is impossible to effectively improve the volumetric energy density. In the present invention, by performing picosecond laser processing on the biomass carbon sulfur nickel foam electrode, while increasing the electrode thickness to 350 μm, sulfur can still be evenly distributed, the electrode has a lower tortuosity, the active material in the electrode can be fully utilized, and the volumetric energy density is improved. Description of the Drawings

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0035] Figure 1 Morphologies of the biomass carbon sulfur nickel foam electrodes (BC@S / NF) with different sulfur loadings and the biomass thick electrodes (Laser-BC@S / NF) prepared for Examples 1 - 6, where a) is the micrograph of the BC@S / NF (sulfur loading 4.5 mg / cm 2 ) prepared in Example 2, b) is the micrograph of the BC@S / NF (sulfur loading 7.1 mg / cm 2 ) prepared in Example 3, c) is the micrograph of the BC@S / NF (sulfur loading 10.3 mg / cm 2 ) prepared in Example 4, d) is the micrograph of the BC@S / NF (sulfur loading 13.8 mg / cm 2 ) prepared in Example 1, e) is the micrograph of the Laser-BC@S / NF (5W) prepared in Example 5, f) is the micrograph of the Laser-BC@S / NF (20W) prepared in Example 6, g) is the micrograph of the Laser-BC@S / NF (40W) prepared in Example 1, h) is the cross-sectional SEM image of the Laser-BC@S / NF (sulfur loading 7.1 mg / cm 2 ) prepared in Example 3, i) is the cross-sectional SEM image of the Laser-BC@S / NF (sulfur loading 13.8 mg / cm 2 ) prepared in Example 1;

[0036] Figure 2Micrographs of BC@S / NF (sulfur loading: 13.8 mg / cm 2 ), prepared in Example 1, and Laser-BC@S / NF (sulfur loading: 13.8 mg / cm 2 );

[0037] Figure 3 EDS maps of sulfur for BC@S / NF (sulfur loading: 13.8 mg / cm 2 ), prepared in Example 1, and Laser-BC@S / NF (sulfur loading: 13.8 mg / cm 2 );

[0038] Figure 4 EDS maps of carbon for BC@S / NF (sulfur loading: 13.8 mg / cm 2 ), prepared in Example 1, and Laser-BC@S / NF (sulfur loading: 13.8 mg / cm 2 );

[0039] Figure 5 Internal resistance change graphs of BC@S / NF (sulfur loading: 13.8 mg / cm 2 ), prepared in Example 1, and Laser-BC@S / NF (sulfur loading: 13.8 mg / cm 2 );

[0040] Figure 6 Cycling stability test results of Laser-BC@S / NF (sulfur loading: 13.8 mg / cm 2 ), prepared in Example 1;

[0041] Figure 7 Specific capacities of BC@S / NF, Laser-BC@S / NF (40 W), prepared in Example 1, and Laser-BC@S / NF (5 W), prepared in Example 5 Detailed Description of the Invention

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be construed as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terms used in the present invention are merely for describing particular embodiments and are not intended to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0045] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the specification of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the specification of this invention are obvious to those skilled in the art. The specification and examples of this application are merely exemplary.

[0046] Regarding "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0047] It should be noted that those aspects not described in detail in this invention are all conventional operating means in the art and are not the focus of this invention.

[0048] In a first aspect of this invention, a method for preparing a biomass thick electrode is provided, comprising the following steps:

[0049] (1) After the corncob is alternately ultrasonically washed several times with water and absolute ethanol, it is dried in an oven at 55 °C for 12 h, then soaked in a 10 wt.% KOH solution for 8 h and dried overnight to obtain a pretreated biomass precursor;

[0050] (2) The pretreated biomass precursor is pyrolyzed under a N 2 atmosphere (the heating rate of pyrolysis is 5 - 8 °C / min, the temperature is 800 - 1000 °C, and the holding time is 2 - 3 h). After naturally cooling to room temperature, it is pulverized to reach a uniform state, then the product is washed with a 1 M dilute hydrochloric acid (HCl) solution and thoroughly washed with water until the pH value reaches neutral (pH = 7), and after drying, biomass carbon (BC) is obtained;

[0051] (3) Biomass carbon (BC) and a sulfur source are mixed at a mass ratio of 3:7 and ground in a ball mill at a speed of 300 rpm for 50 min, with a ball-to-powder ratio of 15:1; subsequently, the sample is transferred to a Teflon-lined autoclave (25 mL), filled with N 2 and heated in a vacuum drying oven at 155 °C for 12 h, and after natural cooling, a carbon-sulfur composite material (BC@S) is obtained;

[0052] (4) The carbon-sulfur composite material (BC@S), conductive agent, binder, and solvent are mixed evenly at a ratio of 8 g:1 g:1 g:100 mL to obtain the slurry for preparing the thick electrode; the slurry is evenly coated on a three-dimensional current collector nickel mesh with a thickness of 350 μm (the volume ratio of the slurry to the area of the three-dimensional current collector nickel mesh is 5 mL:1 cm 2 ), and vacuum dried at 60 °C for 12 h to obtain a biomass carbon-sulfur nickel foam electrode (BC@S / NF) with a thickness of 350 μm;

[0053] The mass ratio of the carbon-sulfur composite material (BC@S), conductive agent, and binder (PVDF) is controlled at 8:1:1. Reducing the proportion of the carbon-sulfur composite material (BC@S) will result in insufficient sulfur loading and a decrease in areal capacity.

[0054] (5) The biomass carbon-sulfur nickel foam electrode (BC@S / NF) is processed (etched) by picosecond laser to obtain a biomass thick electrode (Laser-BC@S / NF);

[0055] Among them, the parameters of picosecond laser processing include: the spacing of laser processing is 50 μm, the laser speed is 1000 - 2000 m / s, the time of each laser processing is 0.2 ms, the number of laser processing times is 3 - 8 times, the laser frequency is 20 - 40 kHz, the focused spot diameter is 40 μm, the laser wavelength is 1030 nm, the laser power is 5 - 40 W, and the pulse width is 5 - 15 ps.

[0056] When the laser power is less than 5 W, the depth of the straight through-hole will be insufficient; when the laser power is greater than 40 W, the material will be burned through by the laser.

[0057] The laser speed of 1000 - 2000 m / s can make the contact time between the material and the laser very short during the processing, and the laser thermal effect is very small. When processing materials rich in carbon and sulfur elements, it can avoid problems such as oxidation, decreased conductivity, and reduced active substances during the thermal processing. At the same time, after laser processing, the microcracks on the surface of the electrode material are significantly reduced, and the surface impedance will decrease, thereby improving the specific capacity of the active substance.

[0058] The power of the picosecond laser itself is not high enough to melt the surface of the material. Using it to process the surface of the inorganic amorphous material (biomass carbon-sulfur nickel foam electrode) can obtain a unique dot matrix structure, thereby better inhibiting the shuttle effect of polysulfide lithium and improving the stability of the cathode material.

[0059] In the specific embodiment of the present invention, the sulfur source includes elemental sulfur.

[0060] In a specific embodiment of the present invention, the conductive agent includes Super P conductive agent; the binder includes polyvinylidene fluoride (PVDF, weight average molecular weight is 534000); the solvent includes N-methyl-2-pyrrolidone (NMP).

[0061] In the second aspect of the present invention, there is provided a biomass thick electrode prepared by the above preparation method.

[0062] In the third aspect of the present invention, there is provided an application of the above biomass thick electrode as a positive electrode of a lithium-sulfur battery.

[0063] In the fourth aspect of the present invention: a method for improving the volume energy density of a biomass carbon electrode, and the specific method is the same as the preparation method of the biomass thick electrode.

[0064] The raw materials used in the specific embodiment of the present invention are as follows:

[0065] Absolute ethanol, KOH solution, dilute hydrochloric acid (HCl), N-methyl-2-pyrrolidone (NMP), polyvinyl alcohol difluoroethylene, and elemental sulfur were purchased from Changrui Biotechnology Co., Ltd.; the three-dimensional current collector nickel mesh was purchased from Sanhe New Materials Technology Co., Ltd.; Super P conductive agent was purchased from Kelude Company.

[0066] Example 1

[0067] A method for preparing a biomass thick electrode:

[0068] (1) Preparation of biomass carbon:

[0069] A. The corn cob was ultrasonically washed several times with pure water and absolute ethanol alternately, dried in an oven at 55 °C for 12 h, then soaked in a 10 wt.% KOH solution for 8 h and dried overnight to obtain a pretreated biomass precursor.

[0070] B. The pretreated biomass precursor was pyrolyzed under N 2 atmosphere (the heating rate of pyrolysis was 5 °C / min, the temperature was 800 °C, and the holding time was 2 h), naturally cooled to room temperature and then pulverized to make it in a uniform state, and then the product was washed with 1 M dilute hydrochloric acid (HCl) solution and thoroughly washed with pure water until the pH value reached neutral (pH = 7), and biomass carbon (BC) was obtained after drying.

[0071] (2) Preparation of biomass carbon sulfur nickel foam electrode (BC@S / NF):

[0072] A. Biomass carbon (BC) and elemental sulfur were mixed at a mass ratio of 3:7 and ground in a ball mill at a speed of 300 rpm for 50 min, and the ball-to-powder ratio was 15:1; then the sample was transferred to a Teflon-lined autoclave (25 mL) and filled with N2 Subsequently, it was heated in a vacuum drying oven at 155 °C for 12 h and then naturally cooled to obtain a carbon-sulfur composite material (BC@S);

[0073] B. The carbon-sulfur composite material (BC@S), conductive agent (super p conductive agent), binder (polyvinylidene fluoride, weight average molecular weight of 534000), and solvent (N-methyl-2-pyrrolidone) were mixed uniformly at a ratio of 8 g:1 g:1 g:100 mL to obtain a slurry for preparing a thick electrode; the slurry was evenly coated on a three-dimensional current collector nickel mesh with a thickness of 350 μm using a coater (the volume ratio of the slurry to the area of the three-dimensional current collector nickel mesh was 0.5 mL:1 cm 2 ), and vacuum dried at 60 °C for 12 h to obtain a biomass carbon-sulfur nickel foam electrode (BC@S / NF) with a sulfur loading of 13.8 mg / cm 2 (calculated based on weight change) and a thickness of 350 μm;

[0074] (3) Preparation of the biomass thick electrode (Laser-BC@S / NF):

[0075] The biomass carbon-sulfur nickel foam electrode (BC@S / NF) was processed by a picosecond fiber pulsed laser (model YLPP-25-3-50-R, IPG Corporation) to obtain a biomass thick electrode (Laser-BC@S / NF);

[0076] Among them, the spacing of the laser processing was 50 μm, the laser speed was 1000 m / s, the time of each laser processing was 0.2 ms, the number of laser processing times was 3 times, the laser frequency was 20 kHz, the diameter of the focused light spot was 40 μm, the laser wavelength was 1030 nm, the laser power was 40 W, and the pulse width was 10 ps.

[0077] Example 2

[0078] Same as Example 1, the only difference was that the volume ratio of the slurry to the area of the three-dimensional current collector nickel mesh was 0.15 mL:1 cm 2 ; the sulfur loading calculated based on weight change was 4.5 mg / cm 2 .

[0079] Example 3

[0080] Same as Example 1, the volume ratio of the slurry to the area of the three-dimensional current collector nickel mesh was 0.2 mL:1 cm 2 ; the sulfur loading calculated based on weight change was 7.1 mg / cm 2 .

[0081] Example 4

[0082] Same as Example 1, except that the volume ratio of the slurry to the area of the three-dimensional current collector nickel mesh is 0.3 mL: 1 cm 2 ; The sulfur loading calculated based on the weight change is 10.3 mg / cm 2 .

[0083] Example 5

[0084] Same as Example 1, except that the laser power of picosecond laser processing is 5 W.

[0085] Example 6

[0086] Same as Example 1, except that the laser power of picosecond laser processing is 20 W.

[0087] Effect Example 1

[0088] The morphologies of the biomass carbon sulfur foam nickel electrodes (BC@S / NF) with different sulfur loadings and the biomass thick electrodes (Laser-BC@S / NF) prepared in Examples 1-6 are shown in Figure 1 , Figure 1 , where a) is the micrograph of BC@S / NF (sulfur loading 4.5 mg / cm 2 ) prepared in Example 2, b) is the micrograph of BC@S / NF (sulfur loading 7.1 mg / cm 2 ) prepared in Example 3, c) is the micrograph of BC@S / NF (sulfur loading 10.3 mg / cm 2 ) prepared in Example 4, d) is the micrograph of BC@S / NF (sulfur loading 13.8 mg / cm 2 ) prepared in Example 1, e) is the micrograph of Laser-BC@S / NF (5 W) prepared in Example 5, f) is the micrograph of Laser-BC@S / NF (20 W) prepared in Example 6, g) is the micrograph of Laser-BC@S / NF (40 W) prepared in Example 1, h) is the cross-sectional SEM image of Laser-BC@S / NF (sulfur loading 7.1 mg / cm 2 ) prepared in Example 3, and i) is the cross-sectional SEM image of Laser-BC@S / NF (sulfur loading 13.8 mg / cm 2 ) prepared in Example 1.

[0089] From Figure 1 Figures h)-i), it can be seen that the thickness of the biomass thick electrode (Laser-BC@S / NF) reaches 350 μm.

[0090] Effect Example 2

[0091] The BC@S / NF (sulfur loading 13.8 mg / cm 2), and the micrographs of Laser-BC@S / NF (sulfur loading 13.8 mg / cm 2 ) are shown in Figure 2 .

[0092] The sulfur element EDS maps of BC@S / NF (sulfur loading 13.8 mg / cm 2 ) and Laser-BC@S / NF (sulfur loading 13.8 mg / cm 2 ) prepared in Example 1 are shown in Figure 3 .

[0093] The carbon element EDS maps of BC@S / NF (sulfur loading 13.8 mg / cm 2 ) and Laser-BC@S / NF (sulfur loading 13.8 mg / cm 2 ) prepared in Example 1 are shown in Figure 4 .

[0094] It can be seen from Figure 2 that after laser processing, the microcracks on the surface of the electrode material are significantly reduced, and the surface impedance will decrease, thereby improving the specific capacity of the active material.

[0095] Effect Example 3

[0096] Assemble 2032 button cells: Cut the BC@S / NF, Laser-BC@S / NF (40 W) prepared in Example 1, and Laser-BC@S / NF (5 W) prepared in Example 5. Use a lithium sheet as the negative electrode, adopt a Celgard separator, and select a 1,3-dioxolane (DOL)-ethylene glycol dimethyl ether (DME)-based lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte with a concentration of 1 mol / L as the electrolyte, denoted as LiTFSI / DOL-DME (volume ratio 1:1), and add 0.1 mol / L of LiNO 3 , assemble into button cells, and then test the battery performance. The results are shown in Figure 5 , Figure 6 and Figure 7 . Figure 5 is the internal resistance of BC@S / NF and Laser-BC@S / NF prepared in Example 1, Figure 6 is the cycle stability of Laser-BC@S / NF (40 W) prepared in Example 1, Figure 7 is the specific capacity of BC@S / NF, Laser-BC@S / NF (40 W) prepared in Example 1, and Laser-BC@S / NF (5 W) prepared in Example 5.

[0097] It can be seen from Figure 5It can be seen that the Laser-BC@S / NF cathode material prepared in Example 1 has a smaller internal resistance and a higher electron-ion transport efficiency inside the electrode.

[0098] From Figure 6 and Figure 7 It can be seen that the Laser-BC@S / NF cathode material prepared in Example 1 achieved high active material utilization and high areal capacity (11.81 mAh / cm 2 ) under the harsh conditions of high mass loading (13.8 mg / cm 2 ) and high thickness of 350 μm, as well as stable cycling stability. The specific capacity and cycling performance were improved. At a rate of 0.1C, the discharge capacity in the first cycle reached 856 mAh / g and could stably cycle more than 80 times; at a rate of 0.05C, the discharge capacity in the first cycle could reach 1151 mAh / g.

[0099] It was found by comparison that when the laser power was 40W, it had the highest specific capacity and volume energy density (708.6 Wh / L), showing potential commercial value.

[0100] The above-described embodiments are only descriptions of the preferred embodiments of the present invention and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for preparing a biomass thick electrode, characterized in that: The following steps are involved: The biomass carbon is mixed with a sulfur source, and heated to react under an inert atmosphere to obtain a carbon-sulfur composite material; The carbon-sulfur composite material, the conductive agent and the binder are mixed to form a slurry, and then the slurry is coated on a three-dimensional current collector nickel mesh, and after drying, picosecond laser processing is performed to obtain the biomass thick electrode.

2. The preparation method according to claim 1, characterized in that: The method for preparing biomass carbon comprises the following steps: The biomass carbon is obtained by pyrolyzing the biomass in an inert atmosphere after the biomass is soaked in an alkaline solution.

3. The preparation method according to claim 2, characterized in that: The biomass includes corn cobs; and the alkaline solution includes KOH solution.

4. The preparation method according to claim 2, characterized in that: The heating rate of the pyrolysis is 5-8°C / min, the temperature is 800-1000°C, and the insulation time is 2-3h.

5. The preparation method according to claim 1, characterized in that: The mass ratio of the biomass carbon to the sulfur source is 3:7; and / or, the sulfur source comprises elemental sulfur; And / or, the heating reaction temperature is 155° C. and the time is 12 hours.

6. The preparation method according to claim 1, characterized in that: The sulfur source is loaded on the three-dimensional current collector nickel mesh in an amount of 4 to 14 mg / cm 2 ; The thickness of the three-dimensional current collector nickel mesh is 350 μm; And / or, the laser power of the picosecond laser processing is 5~40W.

7. The preparation method according to claim 1, characterized in that: The laser wavelength of the picosecond laser processing is 1030nm, the laser speed is 1000-2000m / s, the laser frequency is 20-40khz, the laser processing interval is 50μm, the number of laser processing is 3-8 times, and the time of each laser processing is 0.2ms.

8. A biomass thick electrode prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the biomass thick electrode according to claim 8 as a positive electrode of a lithium-sulfur battery.

10. A method for improving the volume energy density of a biomass carbon electrode, characterized in that: The following steps are involved: The biomass carbon is mixed with a sulfur source, and heated to react under an inert atmosphere to obtain a carbon-sulfur composite material; The carbon-sulfur composite material, the conductive agent and the binder are mixed to form a slurry, and then the slurry is coated on a three-dimensional current collector nickel mesh, and after drying, a biomass carbon electrode is obtained, and finally the biomass carbon electrode is processed by picosecond laser.

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