A tin-doped sulfided polyacrylonitrile for use as the cathode in aqueous copper-sulfur batteries

Abstract

This invention belongs to the field of electrochemical energy storage technology, specifically relating to a tin-doped sulfurized polyacrylonitrile (SnSPAN) for use as the cathode in aqueous copper-sulfur batteries. The invention prepares a SnSPAN material through processes including raw material blending, sealed reaction, grinding, sieving, and desulfurization. In this SnSPAN, the mass ratio of sulfur, polyacrylonitrile, and tin is 300:100:3~15. Some free Sn diffuses fully, some Sn forms Sn-CN bonds with CN bonds in the polymer, and some N-S-N bonds are replaced by N-Sn-N bonds. When this SnSPAN is used as the cathode in an aqueous copper-sulfur battery, it achieves a specific capacity of over 1500 mAh / g at a current density of 500 mA / g, with a coulombic efficiency consistently above 90%. After 140 cycles, the capacity retention is above 93%, demonstrating high specific capacity and excellent cycle stability.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage technology, specifically relating to a tin-doped sulfided polyacrylonitrile for use as the cathode of an aqueous copper-sulfur battery. Background Technology

[0002] Energy storage power stations require rechargeable batteries with high energy storage capacity and long lifespan. Sulfur can undergo a two-electron redox reaction, possessing a theoretical charge storage capacity of up to 1672 mAh / g, an order of magnitude higher than that of lithium-ion battery (LIB) cathodes. Besides its high specific capacity, sulfur is also inexpensive and readily available. These advantages make sulfur-based batteries one of the hottest topics in energy storage batteries. However, during charge and discharge, long-chain polysulfides diffuse to the negative electrode side, undergoing an irreversible reaction to produce short-chain polysulfides, which then diffuse back to the sulfur cathode for subsequent discharge or charge reactions, resulting in a "shuttle effect." This process not only leads to severe self-discharge and capacity degradation but also corrodes the metal negative electrode, affecting battery cycle life.

[0003] Sulphurized polyacrylonitrile (SPAN) can be synthesized by simply heating polyacrylonitrile (PAN) and sulfur powder under an inert atmosphere, and is a cathode material used to replace sulfur. Compared with sulfur cathode materials, it can suppress the shuttle effect of polysulfides. However, the sulfur content in pure SPAN material is less than 50%, and it is divided into outer active sulfur and inner inactive sulfur. The inner sulfur can hardly participate in the redox reaction, resulting in insufficient electrochemical properties such as capacity and conductivity. Currently, the strategies for modifying SPAN cathodes can be divided into six main methods: adding conductive carbon agents, adding sulfidation promoters, morphology and structure engineering, adding redox promoters, pre-lithiation of SPAN, and heteroatom doping. Among them, heteroatom doping is simple, highly selective, and has a wide range of performance control, making it advantageous among the methods for modifying SPAN. Patent CN 112759874 A discloses a method for preparing Se-doped sulfidized polyacrylonitrile material, which successfully improves the electronic conductivity and ionic conductivity of the material and improves the electrochemical reaction kinetics, but the material's performance at high current densities is insufficient. Patent CN 121583875 A synthesized a high-performance tellurium-doped sulfurized polyacrylonitrile (Te-SPAN) material through tellurium doping. Te-SPAN exhibited excellent rate performance and cycle stability, but its specific capacity was only 546.8 mAh / g, which still needs improvement. The specific capacity of the non-metallic doped SPANs mentioned above is insufficient, while metal doping can directly introduce free electrons to form a conductive network, resulting in superior reaction kinetics. Some metals can even directly participate in the reaction, thereby increasing the specific capacity. For example, patent CN 112382755 A prepared a sulfurized polyacrylonitrile flexible cathode material doped with transition metals (cobalt, manganese, zinc, nickel, copper, and iron), successfully increasing the sulfur content in the SPAN cathode and accelerating the reaction kinetics. The preferred Cox-SPAN-CNT achieved a capacity of 1856 mAh / g at 0.2C, but after 100 cycles, it decreased to 1389 mAh / g, with a capacity retention of less than 80%. Therefore, the capacity and cycling stability of metal-doped sulfurized polyacrylonitrile (SPAN) need further optimization.

[0004] To address the issue of poor electrochemical performance of sulfurized polyacrylonitrile (SPAN) as a cathode material in aqueous copper-sulfur batteries, this invention provides a tin-doped sulfurized SPAN for use as a cathode material in aqueous copper-sulfur batteries. Tin (Sn), as a metal element with good metallic conductivity and catalytic activity, has a moderate atomic radius and a low melting point (232℃), which facilitates sufficient diffusion and reaction during SPAN synthesis. The incorporated free Sn diffuses sufficiently, improving the electronic conductivity of the material; another portion of Sn can form Sn-CN bonds with CN bonds in the polymer, stabilizing the binding framework and improving structural stability during cycling; in SnSPAN, some NSN bonds are replaced with N-Sn-N bonds, increasing the reversible sulfur content and improving cycle capacity. The SnSPAN series materials prepared by this invention using an in-situ high-temperature sulfurization method exhibit high specific capacity and excellent cycle stability, good overall electrochemical performance, and low cost, making them a very promising cathode material for aqueous copper-sulfur batteries. Summary of the Invention

[0005] This invention prepares a SnSPAN material through processes including raw material blending, sealed reaction, grinding, sieving, and desulfurization. The mass ratio of sulfur, polyacrylonitrile, and tin in this SnSPAN is 300:100:3~15. Some free Sn diffuses fully, some Sn forms Sn-CN bonds with CN bonds in the polymer, and some NSN bonds are replaced by N-Sn-N bonds. When this SnSPAN is used as the positive electrode in an aqueous copper-sulfur battery, it achieves a specific capacity of over 1500 mAh / g at a current density of 500 mA / g, with a coulombic efficiency consistently above 90%. After 140 cycles, the capacity retention is above 93%, demonstrating high specific capacity and excellent cycle stability.

[0006] The preparation method of the SnSPAN cathode material is as follows:

[0007] (1) Weigh 3 g of sulfur, polyacrylonitrile and tin in a mass ratio of 300:100:3~15, put them into a ball mill jar, add 20 mL of ethanol as a dispersant, and ball mill at 400 r / min for 8 h. The powder after ball milling is dried at 60℃ for 12 h to obtain A.

[0008] (2) Place A into a glass tube and seal it. Place it in a muffle furnace and heat it to 350°C at 5°C / min. Keep it at the temperature for 5 hours and then cool it to room temperature to obtain B.

[0009] (3) Grind B and sieve it to collect powder with a mesh size of less than 1000. Add 5 mL of carbon disulfide to wash it three times and dry it to obtain C.

[0010] (4) Place C in an oven at 60 °C and dry for 12 h, then grind for 0.5 h to obtain the target product SnSPAN powder.

[0011] The beneficial effects of this invention are as follows:

[0012] (1) The SnSPAN powder provided by the present invention has a portion of free Sn that diffuses fully to improve the electronic conductivity of the material; a portion of Sn forms Sn-CN bonds with CN bonds in the polymer to stabilize the binding skeleton and improve the structural stability during cycling; a portion of NSN bonds are replaced by N-Sn-N bonds, and the active reversible sulfur content increases.

[0013] (2) When SnSPAN provided by the present invention is used as a cathode material for aqueous copper-sulfur batteries, it exhibits high specific capacity and excellent cycle stability. Attached Figure Description

[0014] Figure 1 This is the XRD pattern of the SnSPAN prepared according to the present invention.

[0015] Figure 2 This is a SEM image of the SnSPAN prepared according to the present invention.

[0016] Figure 3 These are the first two charge-discharge curves of the SnSPAN prepared in this invention.

[0017] Figure 4 This is a graph showing the cycling performance of the SnSPAN prepared according to the present invention. Specific implementation methods

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments. The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

[0019] Example 1

[0020] Sulfur, polyacrylonitrile, and tin were weighed in a mass ratio of 300:100:9, and placed in a ball mill jar. 20 mL of ethanol was added as a dispersant, and the mixture was ball-milled at 400 r / min for 8 h. The milled powder was then dried at 60 °C for 12 h to obtain A. A was placed in a sealed glass tube and placed in a muffle furnace. The temperature was increased to 350 °C at 5 °C / min and maintained for 5 h. After cooling to room temperature, B was obtained. B was ground and sieved, and powder smaller than 1000 mesh was collected. This powder was washed three times with 5 mL of carbon disulfide and dried to obtain C. C was dried in an oven at 60 °C for 12 h and then ground for 0.5 h to obtain SnSPAN powder with a tin doping content of 3% of the sulfur mass.

[0021] X-ray diffraction analysis was performed on SnSPAN with a tin doping concentration of 3% by mass of sulfur. The results are as follows: Figure 1As shown, it can be seen that none of the samples of this material showed sharp diffraction peaks corresponding to elemental tin, tin sulfides or other crystalline impurities. Only a broad peak appeared in the range of 20° to 30°, showing an amorphous structure.

[0022] Scanning electron microscope (SEM) images of SnSPAN with a tin doping concentration of 3% by mass of sulfur were observed, and the results are as follows: Figure 2 As shown, SnSPAN exhibits micron-sized irregular aggregates without any densification or clumping. The particle surface shows no obvious cracks, demonstrating a good continuous structure.

[0023] The powder, acetylene black, and polyvinylidene fluoride were dispersed in an N-methylpyrrolidone solution at a weight ratio of 7:2:1. The slurry was coated onto conductive carbon cloth using a scraper and dried under vacuum at 80°C for 12 h to obtain the positive electrode sheet. The positive electrode sheet and copper foil were cut into 12 mm diameter discs. Using GF / D glass fiber as the separator and 0.5 M CuSO4 solution as the electrolyte, they were assembled from bottom to top in the following order: negative electrode shell – spring sheet – gasket – copper sheet – separator – positive electrode – positive electrode shell to form a CR2032 aqueous copper-sulfur battery. Charge-discharge and cycle tests were then conducted.

[0024] Charge-discharge tests were performed on SnSPAN with a tin doping concentration of 3% by mass of sulfur, and the charge-discharge curves for the first two cycles were obtained, as shown below. Figure 3 It can be seen that SnSPAN has a high specific capacity, with a discharge specific capacity of up to 2237.35 mAh / g. The charge-discharge platform is stable and the cycle curves have a high degree of overlap.

[0025] Cyclic testing was performed on SnSPAN with a tin doping concentration of 3% by weight of sulfur, and the results are as follows: Figure 4 As shown, the tin-doped SPAN exhibits excellent electrochemical reversibility, effectively preventing irreversible side reactions. The initial discharge specific capacity of SnSPAN is 2315.51 mAh / g, which increases to 2610.51 mAh / g after 150 cycles, demonstrating excellent long-term cycling stability.

[0026] Example 2

[0027] Weigh 3 g of sulfur, polyacrylonitrile, and tin in a mass ratio of 300:100:3, place them in a ball mill jar, add 20 mL of ethanol as a dispersant, and ball mill at 400 r / min for 8 h. Dry the milled powder at 60℃ for 12 h to obtain A. Seal A in a glass tube, place it in a muffle furnace, heat to 350℃ at 5℃ / min, maintain the temperature for 5 h, and cool to room temperature to obtain B. Grind B and sieve it, collecting powder smaller than 1000 mesh. Wash three times with 5 mL of carbon disulfide and dry to obtain C. Dry C in an oven at 60℃ for 12 h, then grind for 0.5 h to obtain SnSPAN powder with a tin doping content of 1% of the sulfur mass.

[0028] Example 3

[0029] Weigh 3 g of sulfur, polyacrylonitrile, and tin in a mass ratio of 300:100:15, place them in a ball mill jar, add 20 mL of ethanol as a dispersant, and ball mill at 400 r / min for 8 h. Dry the milled powder at 60℃ for 12 h to obtain A. Seal A in a glass tube, place it in a muffle furnace, heat to 350℃ at 5℃ / min, maintain the temperature for 5 h, and cool to room temperature to obtain B. Grind B and sieve it, collecting powder smaller than 1000 mesh. Wash three times with 5 mL of carbon disulfide and dry to obtain C. Dry C in an oven at 60℃ for 12 h, then grind for 0.5 h to obtain SnSPAN powder with a tin doping content of 5% of the sulfur mass.

Claims

1. A tin-doped sulfurized polyacrylonitrile (SnPAN) for use as the positive electrode in an aqueous copper-sulfur battery, characterized in that: The mass ratio of sulfur, polyacrylonitrile, and tin in the SnPAN is 300:100:3~15. Some of the free Sn diffuses fully, some Sn forms Sn-CN bonds with CN bonds in the polymer, and some NSN bonds are replaced by N-Sn-N bonds.

2. The tin-doped sulfided polyacrylonitrile for the positive electrode of an aqueous copper-sulfur battery according to claim 1, characterized in that: When SnSPAN is used as the cathode of an aqueous copper-sulfur battery, the specific capacity can reach over 1500 mAh / g at a current density of 500 mA / g, the coulombic efficiency is stable at over 90%, and the capacity retention rate is over 93% after 140 cycles, demonstrating high specific capacity and excellent cycle stability.

3. The tin-doped sulfurized polyacrylonitrile (SnSPAN) for the cathode of an aqueous copper-sulfur battery according to claim 1, wherein the optimal tin doping amount of SnSPAN is 3% of the sulfur mass, the preferred sample has the highest discharge specific capacity of 2237.35 mAh / g, the coulombic efficiency is stable at over 93%, and the capacity reaches 2606.58 mAh / g after 140 cycles, exhibiting the best overall performance.

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