A novel sulfur storage-catalysis integrated lithium-sulfur battery electrode design method

Abstract

The application is a novel sulfur storage-catalysis integrated lithium-sulfur battery electrode design method, and belongs to the technical field of electrochemistry. The method comprises the following steps: loading elemental sulfur by using a porous carbon material; preparing a high-efficiency catalyst with polysulfide catalytic activity; preparing a mixed binder for integrated electrode preparation; respectively beating the catalytic and sulfur storage materials, and preparing a sulfur storage-catalysis integrated lithium-sulfur battery electrode by using a phase transition method.

Description

Technical Field

[0001] A novel electrode design method for lithium-sulfur batteries integrating sulfur storage and catalysis belongs to the field of electrochemistry. Background Technology

[0002] Among novel high-energy-storage battery systems, lithium-sulfur batteries are currently one of the more researched and rapidly developing branches. The biggest advantage of this battery system lies in its very high theoretical capacity; if calculated using elemental sulfur as the cathode, the theoretical capacity of a lithium-sulfur battery can reach 1675 mAh. -1 The theoretical energy density can reach 2600 W h kg -1 Its efficiency is far higher than that of conventional lithium-ion battery systems, second only to the slowly progressing lithium-air batteries. Furthermore, sulfur is inexpensive, abundant, and environmentally friendly; these combined factors make the further commercialization of lithium-sulfur batteries highly promising. Therefore, lithium-sulfur batteries are considered the most anticipated next-generation electrochemical energy storage system.

[0003] Lithium-sulfur batteries still have their own problems. First, the active material sulfur and the discharge product lithium sulfide have extremely low electronic and ionic conductivity, resulting in low utilization of active materials and poor high-current discharge capability. Second, the intermediate product of the electrochemical reaction, lithium polysulfide, is easily soluble in organic electrolytes and migrates back and forth between the positive and negative electrodes under the drive of concentration gradient and electric field, producing a shuttle effect that causes a decrease in battery capacity and cycle performance. Third, during the charge and discharge reaction, due to the density difference between the active material sulfur and the final discharge product lithium sulfide, approximately 80% volume change occurs, causing electrode structure damage, battery instability, and affecting battery electrochemical performance. Finally, using highly active metallic lithium as the counter electrode, volume changes and lithium dendrite growth occur during cycling, which can easily puncture the separator, leading to battery short circuits and posing serious safety hazards.

[0004] Therefore, there is an urgent need for an electrode that can simultaneously transfer sulfur and has catalytic conversion capabilities to solve the problems in lithium-sulfur battery cycling. Summary of the Invention

[0005] To address the problems existing in current preparation technologies, the purpose of this invention is to propose a novel integrated sulfur storage-catalysis lithium-sulfur battery electrode design method. This flexible electrode preparation method is simple and easy to implement.

[0006] This invention provides a novel design method for an integrated sulfur storage-catalysis lithium-sulfur battery electrode, comprising: loading elemental sulfur onto porous carbon materials; preparing a highly efficient catalyst with polysulfide catalytic activity; preparing a mixed binder for the integrated electrode preparation; using the mixed binder in combination with a conductive agent to slurry the sulfur-loaded porous carbon material and the catalyst material respectively; uniformly coating the prepared slurry onto a glass plate in successive layers to a certain thickness; transferring the glass plate coated with the slurry to an aqueous solution of CNTs for an aqueous phase transition; and finally drying the electrode after the phase transition using freeze-drying technology to prepare the integrated sulfur storage-catalysis lithium-sulfur battery electrode.

[0007] Preferably, the porous carbon material is a high specific surface area material prepared through activation, with a specific surface area greater than 2000 m². 2 g -1 The loading of sulfur can include molten, gas-phase, and liquid-phase methods.

[0008] Preferably, the polysulfide catalytic material includes transition metal sulfides / oxides, and composite materials thereof with materials such as CNTs.

[0009] Preferably, the conductive agent material includes highly active conductive materials such as super p, carbon black, KB, CNT, and CNF.

[0010] Preferably, the novel hybrid adhesive is a PAN / TPU, PAN / PVDF, PAN / PEO, or other hybrid adhesives, and the ratio between the hybrid adhesives is 10:0 to 0:10.

[0011] Preferably, the mass ratio of the sulfur-loaded active material and the catalytic material to the conductive agent and the mixed binder is 1:1 to 8:1.

[0012] Preferably, the step-by-step coating process includes controlling the coating thickness of the sulfur-loaded active material to be 100-500 μm; and continuing to coat the catalytic layer onto the sulfur-loaded layer, controlling the thickness of the catalytic layer to be 20-100 μm.

[0013] Preferably, the phase transition uses an aqueous dispersion of CNTs, wherein the concentration of CNTs is less than 0.001 wt%.

[0014] Preferably, the freeze-drying process must ensure the overall flatness of the electrode sheet, and the phase transformation must be fully carried out before freeze-drying. The cold trap temperature must be less than -50°C.

[0015] The method of this invention is simple and easy to implement. According to the preparation method of this invention, an integrated sulfur storage-catalysis lithium-sulfur battery electrode is prepared, which has the ability to efficiently load sulfur and catalyze the conversion of polysulfides. The electrode is gradually coated and then undergoes a phase transition to realize the construction of the integrated sulfur storage-catalysis structure. The mixed binder crosslinks and polymerizes into a three-dimensional network structure under the action of phase transition. The conductive agent will be composited in the three-dimensional network during the phase transition to form an internal three-dimensional conductive network. The CNTs in the CNT aqueous solution used for phase transition will be dispersed in the middle of the three-dimensional conductive network under the action of surface tension to form an external conductive network. At the same time, the porous structure is conducive to the wetting of the electrolyte and improves the electrode reaction kinetics. Attached Figure Description

[0016] The preferred embodiments of the present invention are described below with reference to the accompanying drawings, in which:

[0017] Figure 1 This is a schematic diagram of the working principle of the integrated sulfur storage-catalysis electrode.

[0018] Figure 2 This is a cross-sectional SEM image of the integrated sulfur storage-catalysis electrode.

[0019] Figure 3 This is a thickness measurement diagram of the integrated sulfur storage-catalysis electrode.

[0020] Figure 4 The graph shows the cycling performance of the integrated sulfur storage-catalysis electrode at a current density of 0.2C. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. It should be understood that the following embodiments and / or drawings are for illustrative purposes only and are not intended to limit the present invention.

[0022] The above-mentioned objective of this invention is preferably achieved through the following technical solutions:

[0023] a) Loading elemental sulfur using porous carbon materials;

[0024] b) Prepare highly efficient catalysts with polysulfide catalytic activity;

[0025] c) Prepare a hybrid binder for integrated electrode fabrication;

[0026] d) Using a mixed binder combined with a conductive agent, the sulfur-loaded porous carbon material and the catalytic material were slurried respectively;

[0027] e) Apply the prepared slurry evenly onto the glass plate in successive layers according to a certain thickness;

[0028] f) The glass plate coated with the slurry was transferred to an aqueous solution of CNTs for an aqueous phase transition;

[0029] g) The electrode after phase transformation is finally dried using freeze-drying technology to prepare an integrated sulfur storage-catalysis lithium-sulfur battery electrode.

[0030] Preferably, the porous carbon material in step a) is a high specific surface area material prepared through activation, with a specific surface area greater than 2000 m². 2 g -1 Sulfur loading can include molten, gas-phase, and liquid-phase methods, with a sulfur loading of 60%-80%.

[0031] Preferably, the polysulfide catalytic material in step b) includes transition metal sulfides / oxides, and composite materials thereof with materials such as CNTs.

[0032] Preferably, the novel mixed adhesive mentioned in step c) is a mixed adhesive such as PAN / TPU, PAN / PVDF, or PAN / PEO, and the ratio between the mixed adhesives is 10:1 to 1:1.

[0033] Preferably, the conductive agent material in step d) includes highly active conductive materials such as super p, carbon black, KB, CNT, and CNF.

[0034] Preferably, in step d), the mass ratio of the sulfur-loaded active material and the catalytic material to the conductive agent and the mixed binder is 1:1 to 8:1.

[0035] Preferably, the sequential coating process described in step e) includes controlling the coating thickness of the sulfur-loaded active material to be 100-500 μm; and continuing to coat the catalytic layer onto the sulfur-loaded layer, controlling the thickness of the catalytic layer to be 20-100 μm.

[0036] Preferably, the phase transition in step f) uses an aqueous dispersion of CNTs, wherein the concentration of CNTs is less than 0.001 wt%.

[0037] Preferably, the freeze-drying process described in step g) must ensure the overall flatness of the electrode, and the phase transformation must be fully carried out before freeze-drying, with the cold trap temperature required to be less than -50°C.

[0038] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific types of sulfur-loading materials, catalytic materials, conductive agents, mixed binders, solid content of the slurry, coating thickness, and solutions used for phase transitions in the following examples are merely examples within a suitable range. That is, those skilled in the art can select from the suitable range described herein, and are not intended to be limited to the specific values ​​in the examples below.

[0039] Example 1

[0040] 1) Using PAN / TPU as the mixed adhesive, with a ratio of PAN:TPU = 8:2 and DMF as the solvent, the mixture was magnetically stirred at room temperature for 12 hours to obtain 10 wt% P8T2 adhesive.

[0041] 2) Microporous carbon was prepared using silk as a carbon source and ZnCl2 as a pore-forming activator.

[0042] 3) Mix porous carbon and elemental sulfur in a ratio of 3:7 and transfer the mixture into a polytetrafluoroethylene liner, then heat it at 155°C for 16 hours.

[0043] 4) A one-dimensional MoS2 / CNT composite material was prepared using a hydrothermal method and used as a polysulfide catalytic material.

[0044] 5) Mix the sulfur-storage carbon-sulfur composite material and catalytic material with P8T2 binder, KB, and CNF in a ratio of 70:20:5:5 and slurry them, and label them as slurry A and slurry B.

[0045] 6) Apply slurry A onto the glass plate one after another using a 400μm doctor blade, and apply slurry B onto slurry A using a 500μm doctor blade.

[0046] 7) Place the glass plate coated with the active material into the CNT dispersion to undergo phase transition until solvent exchange is complete.

[0047] 8) Remove the electrode after phase transition, freeze it from bottom to top with liquid nitrogen, and then freeze-dry it under vacuum.

[0048] The obtained electrode film was cut into 10mm diameter circular pieces. Using the cut electrode pieces as the positive electrode, a lithium metal sheet as the negative electrode, a polypropylene microporous membrane (Celgard 2400) as the separator, and an ether-based electrolyte, with the catalyst layer in contact with the separator, a coin cell was assembled. Its electrochemical performance was tested, and the charge-discharge cycle performance was as follows: Figure 4 At 0.2C (1C = 1670 mAg) -1At the current density, the initial reversible specific capacity is 1280 mAh g. -1 After 200 cycles, the discharge specific capacity is 676, demonstrating good cycle stability. The integrated electrode principle is as follows: Figure 1 As shown, the electrode images are as follows Figure 2 and 3 As shown.

[0049] Example 2

[0050] 1) Using PAN / TPU as the mixed adhesive, with a ratio of PAN:TPU = 8:2 and DMF as the solvent, the mixture was magnetically stirred at room temperature for 12 hours to obtain 10 wt% P8T2 adhesive.

[0051] 2) Commercially available high specific surface area porous carbon is used as a carbon source.

[0052] 3) Mix porous carbon and elemental sulfur in a ratio of 3:7 and transfer the mixture into a polytetrafluoroethylene liner, then heat it at 155°C for 16 hours.

[0053] 4) A one-dimensional MoS2 / CNT composite material was prepared using a hydrothermal method and used as a polysulfide catalytic material.

[0054] 5) Mix the sulfur-storage carbon-sulfur composite material and catalytic material with P8T2 binder, KB, and CNF in a ratio of 70:20:5:5 and slurry them, and label them as slurry A and slurry B.

[0055] 6) Apply slurry A onto the glass plate one after another using a 400μm doctor blade, and apply slurry B onto slurry A using a 500μm doctor blade.

[0056] 7) Place the glass plate coated with the active material into the CNT dispersion to undergo phase transition until solvent exchange is complete.

[0057] 8) Remove the electrode after phase transition, freeze it from bottom to top with liquid nitrogen, and then freeze-dry it under vacuum.

[0058] The obtained electrode film was cut into circular pieces with a diameter of 10 mm. The cut electrode pieces were used as positive electrodes, lithium metal sheets as negative electrodes, polypropylene microporous membranes (Celgard 2400) as separators, and ether electrolytes were used. The catalyst layer was in contact with the separator to assemble a coin cell and test its electrochemical performance.

[0059] Example 3

[0060] 1) Using PAN / TPU as the mixed adhesive, with a ratio of PAN:TPU = 8:2 and DMF as the solvent, the mixture was magnetically stirred at room temperature for 12 hours to obtain 10 wt% P8T2 adhesive.

[0061] 2) Commercially available high specific surface area porous carbon is used as a carbon source.

[0062] 3) Mix porous carbon and elemental sulfur in a ratio of 3:7 and transfer the mixture into a polytetrafluoroethylene liner, then heat it at 155°C for 16 hours.

[0063] 4) Commercially available MoS2 was used as the catalyst.

[0064] 5) Mix the sulfur-storage carbon-sulfur composite material and catalytic material with P8T2 binder, KB, and CNF in a ratio of 70:20:5:5 and slurry them, and label them as slurry A and slurry B.

[0065] 6) Apply slurry A onto the glass plate one after another using a 400μm doctor blade, and apply slurry B onto slurry A using a 500μm doctor blade.

[0066] 7) Place the glass plate coated with the active material into the CNT dispersion to undergo phase transition until solvent exchange is complete.

[0067] 8) Remove the electrode after phase transition, freeze it from bottom to top with liquid nitrogen, and then freeze-dry it under vacuum.

[0068] The obtained electrode film was cut into circular pieces with a diameter of 10 mm. The cut electrode pieces were used as positive electrodes, lithium metal sheets as negative electrodes, polypropylene microporous membranes (Celgard 2400) as separators, and ether electrolytes were used. The catalyst layer was in contact with the separator to assemble a coin cell and test its electrochemical performance.

[0069] Finally, it should be noted that the above embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A novel integrated sulfur storage-catalysis lithium-sulfur battery electrode design method, characterized in that, include: Elemental sulfur is loaded using porous carbon materials; Prepare highly efficient catalysts with polysulfide catalytic activity; Preparation of hybrid binders for integrated electrode fabrication; A mixed binder combined with a conductive agent was used to slurry the sulfur-loaded porous carbon material and the catalytic material, respectively. The prepared slurry is applied evenly to the glass plate in successive layers according to a certain thickness. The glass plate coated with the slurry was transferred to an aqueous solution of CNT to undergo an aqueous phase transition; Electrodes prepared by phase transition method are finally dried using freeze-drying technology to prepare sulfur storage-catalysis integrated lithium-sulfur battery electrodes; The sulfur loading includes molten, gas-phase, and liquid-phase methods; The catalyst is any catalyst with polysulfide catalytic function; The mixed adhesive is any one of PAN / TPU, PAN / PVDF, and PAN / PEO, and the ratio of PAN to the other adhesive in the mixed adhesive is 10:0-0:

10. The pulping process includes mixing a mixed binder with a conductive agent and a sulfur-loaded porous carbon material in a certain proportion and pulping to prepare a sulfur-loaded active material slurry; and mixing a mixed binder with a conductive agent and a catalytic material in a certain proportion and pulping to prepare a catalytic material slurry. The coating process involves first coating the active material slurry onto a glass plate, and then using different thicknesses of doctor blades to coat the catalytic material slurry onto the previous slurry. The aqueous solution of CNT is a CNT dispersion that is uniformly dispersed in a certain proportion. Before drying, the phase transformation must be fully carried out, and the cold trap temperature must be less than -50°C.

2. The design method according to claim 1, characterized in that, The sulfur loading content is 60% - 90%.

3. The design method according to claim 1, characterized in that, The catalytic material includes transition metal sulfides / oxides.

4. The design method according to claim 1, characterized in that, The conductive agent includes one or more of the highly active conductive materials selected from super p, KB, CNT, and CNF.

5. The design method according to claim 1, characterized in that, The conductive agent includes carbon black.

6. The design method according to claim 1, characterized in that, The hybrid binder comprises various hard segment polymers with supporting structures and polymers with flexible segment structures, in a ratio of 10:0 to 0:

10.

7. The design method according to claim 1, characterized in that, The mass ratio of the sulfur-loaded active material and the catalytic material to the conductive agent and the mixed binder is 1:1 to 8:

1.

8. The design method according to claim 1, characterized in that, The coating process includes controlling the coating thickness of the sulfur-loaded active material to be 100-500 μm; and continuing to coat the catalytic layer onto the sulfur-loaded layer, controlling the thickness of the catalytic layer to be 20-100 μm.

9. The design method according to claim 1, characterized in that, The phase transition uses an aqueous dispersion of CNTs in a solution, wherein the concentration of CNTs is less than 0.001 wt%.

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