Preparation Method and Application of a Biomass Thick Electrode

Abstract

The present invention discloses a preparation method and application of a biomass thick electrode, belonging to the technical field of preparation of electrode materials. The preparation method of the biomass thick electrode of the present invention comprises the following steps: mixing biomass carbon with a sulfur source, heating and reacting under an inert atmosphere to obtain a carbon-sulfur composite material; mixing the carbon-sulfur composite material, a conductive agent and a binder to form a slurry, then coating the slurry on a three-dimensional current collector nickel mesh, and performing picosecond laser processing after drying to obtain a biomass thick electrode. The biomass thick electrode prepared by the present invention has a lower tortuosity and more surface pore openings, can play a greater inhibitory effect on the shuttle effect of polysulfides in lithium-sulfur batteries, and the active substances in the thick electrode can also be fully utilized as the electrolyte infiltrates into the electrode interior.

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 various electrochemical energy storage systems, lithium-sulfur batteries offer unique advantages in high-energy-density battery design. Their cathode active materials, based on a multi-electron reaction mechanism, boast a mass energy density of 2350 Wh / kg, approximately an order of magnitude higher than commercial lithium-ion batteries. However, lithium-sulfur batteries also face several bottlenecks, such as the poor conductivity of elemental sulfur, the solubility of intermediate lithium polysulfide in the electrolyte, and low volumetric energy density, which hinder their development and commercialization.

[0003] The current process for preparing lithium-sulfur battery cathodes involves coating a metal current collector with a slurry consisting of active particles, a conductive agent, and a binder to form a dry electrode particle coating, which is then compacted and densified. This process is suitable for large-scale production of jellyroll-shaped battery cells. The jellyroll-shaped positive and negative electrodes are assembled with a separator into a battery cell, injected with electrolyte, and activated by charge and discharge. This results in prismatic (jellyroll), cylindrical (jellyroll), and pouch (layered) battery structures. A higher active material loading in a single layer of the positive electrode material in a jellyroll electrode results in a higher volumetric energy density. To increase the active material loading and volumetric energy density in lithium-sulfur batteries, the thickness of the cathode material coating must be increased. Traditional slurry electrode processes require coating onto flat metal foil. During the drying and curing process of thick slurry coatings exceeding 50μm, the unsupported shrinkage stress within the electrode can cause surface defects such as cracks and burrs, leading to damage and cracking of the electrode material on the foil surface and impaired operation. Therefore, sulfur cathodes produced using traditional processes are often less than 50μm thick.

[0004] Biomass carbon materials have good electrical conductivity, are inexpensive, and can be easily made into porous structures, which can improve the electrochemical performance of lithium-sulfur batteries. Therefore, they are widely used as carrier materials for the active sulfur in lithium-sulfur batteries. However, biomass carbon materials have random pore geometries and high tortuosity, resulting in low porosity and fewer charge transfer pathways in compacted electrodes. This leads to poor ion transport and low electrolyte permeability, resulting in slow sulfur conversion kinetics and low active material utilization. Therefore, even when thick sulfur slurry is applied to prepare battery cells, the total capacity cannot be improved.

[0005] In traditional porous electrode materials, carbon and sulfur particles are nanosized and coated on metal current collectors using slurry to obtain positive electrodes with a thickness of less than 50 μm. Although traditional current collectors have excellent cycle stability and high specific capacity, most studies are based on low areal sulfur loading (≤2 mg / cm 2 ), the area capacity is lower than that of commercial lithium-ion batteries (4mAh / 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 polysulfide (LiPSs) shuttle effect 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 object 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 object, 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 biomass in an alkaline solution (activation process) and then pyrolyze (carbonization process) in an inert atmosphere 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 alkaline 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., picosecond laser processing with ultrashort pulses. 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. Moreover, the porous structure of the biomass carbon can insulate heat, preventing the heat from penetrating deeply. Therefore, obvious cladding features will not be formed on the surface and inside during 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 volumetric energy density of a biomass carbon electrode, comprising the following steps:

[0027] Mix biomass carbon with a sulfur source and heat and 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 a transport path and ion channels, high tortuosity resulting in inability of the electrolyte to penetrate, and low utilization rate of the loaded activity. The present invention constructs a dot matrix 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 dot matrix structure enables the prepared biomass thick electrode to have a lower tortuosity and more surface pore openings, which can play a greater inhibitory role in 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), and the thermal influence on the sulfur particles attached to the surface of the biomass carbon is small. 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 realizing the improvement of the energy density (the volumetric energy density of this thick electrode is 708.6 Wh / L, and the volumetric energy density of the positive electrode of a traditional thin electrode lithium-sulfur battery is between 200 and 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 dot matrix 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, through picosecond laser processing of 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. BRIEF 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. Among them, 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 (5W) prepared in Example 5, f) is the micrograph of Laser-BC@S / NF (20W) prepared in Example 6, g) is the micrograph of Laser-BC@S / NF (40W) 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, i) is the cross-sectional SEM image of 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 ), and Laser-BC@S / NF (sulfur loading: 13.8 mg / cm 2 ) prepared in Example 1;

[0037] Figure 3 EDS maps of sulfur element 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;

[0038] Figure 4 EDS maps of carbon element 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;

[0039] Figure 5 Internal resistance change diagrams 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;

[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

[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 only for describing specific 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 implementation 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 said 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 description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this application are merely exemplary.

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

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

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

[0049] (1) After washing corncobs with water and absolute ethanol alternately by ultrasonic for several times, drying them in an oven at 55 °C for 12 h, and then soaking them in a 10 wt.% KOH solution for 8 h and drying overnight, a pretreated biomass precursor is obtained;

[0050] (2) Pyrolyzing the pretreated biomass precursor under a N2 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), naturally cooling it to room temperature and then pulverizing it to make it in a uniform state, then washing the product with 1 M dilute hydrochloric acid (HCl) solution and thoroughly washing it with water until the pH value reaches neutral (pH = 7), and drying to obtain biomass carbon (BC);

[0051] (3) Mixing biomass carbon (BC) and a sulfur source in a mass ratio of 3:7, grinding them with a ball mill at a speed of 300 rpm for 50 min, with a ball-to-powder ratio of 15:1; then transferring the sample to a Teflon-lined autoclave (25 mL), filling it with N2 and heating it in a vacuum drying oven at 155 °C for 12 h, and naturally cooling to obtain a carbon-sulfur composite material (BC@S);

[0052] (4) Mix the carbon-sulfur composite material (BC@S), conductive agent, binder, and solvent evenly at a ratio of 8 g: 1 g: 1 g: 100 mL to obtain the slurry for preparing the thick electrode; coat the slurry evenly 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 dry it 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) Perform picosecond laser processing (etching) on the biomass carbon-sulfur nickel foam electrode (BC@S / NF) 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 diameter of the focused spot 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 using it to process materials rich in carbon and sulfur elements, problems such as oxidation, decreased conductivity, and reduced active substances during the thermal processing can be avoided. 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 substances.

[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 suppressing the shuttle effect of polysulfide lithium and improving the stability of the positive electrode 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 volumetric 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 corncobs were 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 a N2 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 a 1 M dilute hydrochloric acid (HCl) solution and then 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. Mix biomass carbon (BC) and elemental sulfur in a mass ratio of 3:7, grind them in a ball mill at a speed of 300 rpm for 50 min, with a ball-to-powder ratio of 15:1; then transfer the sample to a Teflon-lined autoclave (25 mL), fill it with N2, and heat it in a vacuum drying oven at 155 °C for 12 h. After natural cooling, a carbon-sulfur composite material (BC@S) is obtained;

[0073] B. Mix 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) in a ratio of 8 g:1 g:1 g:100 mL to obtain a slurry for preparing a thick electrode; use a coater to evenly coat the slurry 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 0.5 mL:1 cm 2 ), and dry it in a vacuum 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] Use a picosecond fiber pulse laser (model YLPP-25-3-50-R, IPG Corporation) to perform picosecond laser processing on the biomass carbon-sulfur nickel foam electrode (BC@S / NF) to obtain a biomass thick electrode (Laser-BC@S / NF);

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

[0077] Example 2

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

[0079] Example 3

[0080] The same as Example 1, the volume ratio of the slurry to the area of the three-dimensional current collector nickel mesh is 0.2 mL:1 cm 2 ; the sulfur loading calculated based on weight change is 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 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, 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 micrographs of BC@S / NF prepared in Example 1 (sulfur loading of 13.8 mg / cm 2 ), and Laser-BC@S / NF (sulfur loading of 13.8 mg / cm 2 ) are shown in Figure 2 .

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

[0093] The EDS maps of carbon in BC@S / NF prepared in Example 1 (sulfur loading of 13.8 mg / cm 2 ), and Laser-BC@S / NF (sulfur loading of 13.8 mg / cm 2 ) 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 decreases, thus 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, a Celgard separator, and an electrolyte of 1 mol / L 1,3-dioxolane (DOL)-ethylene glycol dimethyl ether (DME)-based lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte, denoted as LiTFSI / DOL-DME (volume ratio 1:1), and add 0.1 mol / L LiNO3 to assemble button cells. Then test the battery performance, and 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 a high active material utilization rate 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 0.1 C, the discharge capacity in the first cycle reached 856 mAh / g and could be stably cycled more than 80 times; at a rate of 0.05 C, the discharge capacity in the first cycle could reach 1151 mAh / g.

[0099] It was found by comparison that when the laser power was 40 W, 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: It includes the following steps: Mix biomass carbon with a sulfur source, heat and react under an inert atmosphere to obtain a carbon-sulfur composite material; 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, and perform picosecond laser processing after drying to obtain the biomass thick electrode; The preparation method of the biomass carbon includes the following steps: Soak biomass in an alkaline solution and pyrolyze it under an inert atmosphere to obtain the biomass carbon; The loading amount of the sulfur source on the three-dimensional current collector nickel mesh is 4 to 14 mg / cm 2 ; the thickness of the three-dimensional current collector nickel mesh is 350 μm; The laser power of the picosecond laser processing is 5 - 40 W; The laser wavelength of the picosecond laser processing 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, and the time of each laser processing is 0.2 ms.

2. The preparation method according to claim 1, characterized in that, The biomass includes corncobs; the alkaline solution includes KOH solution.

3. The preparation method according to claim 1, characterized in that 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.

4. 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 includes elemental sulfur; And / or, the temperature of the heating reaction is 155 °C and the time is 12 h.

5. A biomass thick electrode prepared by the preparation method according to any one of claims 1 - 4.

6. An application of the biomass thick electrode according to claim 5 as a positive electrode of a lithium-sulfur battery.

Images