| The theoretical specific energy of Li-S battery is as high as2600Wh/kg, andLi-S battery is considered to be one of the most development potential of the batterysystem. As a cathode material of the highest specific capacity known at present, thetheoretical specific capacity of elemental sulfur is1675mAh/g. Sulfur is abundant innature, low-cost, harmfulless, environmentally friendly. But elemental sulfur is notconductive and the discharge product is soluble in electrolyte in the process ofelectrochemical reaction, this is the fatal shortcomings existing in the application ofthe cathode containing sulfur. It leads to lower the utilization of active material andpoor cycle stability, which seriously restricts the development of Li-S batteries. In thiswork, sulfur was composited with nickel foam substrate possessing high conductivityand high specific surface area. We carried out a series of research about thepreparation and optimization of performance around S-Ni integral cathode. Innovativeresearch results in this work were as follows:(1) Heat treatment process was used to coat sulfur to the porous structure of thenickel foam substrate to prepare the nickel sulfide cathode material. Themicrostructure and composition of the S-Ni integral cathode were characterized bySEM and XRD. The simulation battery was assembled to characterize theelectrochemical performance. The result showed that the three-dimensional netstructure was without any changing, the active material was existed as sulfur-nickelcompounds with homogeneous distribution. The electrochemical reaction was good inthe first20cycles inside the battery, but the active material would strip from thematrix with the progress of the cycle, leading structural damage of the cathode,capacity fading and low coulomb efficiency.(2) In order to stabilize the cathode structure and bring sulfur’s superiority on thetheoretical specific capacity into full play, we used the chemical method to preparethe sulfur-nickel material. Results showed that the active material evenly coated onthe surface nickel foam in the form of elemental sulfur, and there were a few largegranular sulfur attached to the surface. The discharge capacity was higher for the firsttime with the typical charging and discharging voltage platform. The coulombefficiency was close to100%. After100times charging and discharging cycle, thecapacity remained at a rate of75%. However, falling off of large granular sulfur attached to the surface could cause the fluctuation in the process of cycling. This wasbad for the practical application.(3) With a view to eliminate the effect for cycle performance from large granularattached to the surface, sulfur melting processing was proceeded on the nickel sulfidecathode material prepared by the chemical method. The result showed that sulfur asactive material was highly disperseded in the porous structure of matrix, increasingthe micro reaction place in the process of electrochemical reaction, restrainingdissolution of discharge product effectively. The cycle stability was good, theretention rate of capacity was as high as95%after continuous discharge and chargeafter110cycles. And with the progress of the cycle, the electrode interface impedanceand lithium ion diffusion impedance were markedly reduced.In a word, the sulfur-nickel cathode material in this work was prepared based onnickel foam which was used for the current collector traditionally, calling integralcathode. It could be directly used for battery assembly without adding binder,conductive agent and dispersant for pulping and coating. The process was very simple.The cathode integrated prepared by the chemical method has a stable structure withhigh specific surface area, improves the utilization of active material immensely,restrains the dissolution of polysulfide effectively and has well reversibility ofelectrochemical reaction, and it provides experimental basis for the new cathodedesign of Li-S battery. |
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