ZnNi2S4/C cathode design for biomass-based carbon session and high performance lithium-sulfur batteries

With the rapid increase in the world population, technology has advanced and the demand for energy has increased. With the rapid depletion of fossil fuels on earth, the demand for high performance energy storage technology is increasing. Lithium-ion batteries used commercially for energy storage have been greatly improved. However, the low energy capacity (150-200 Wh/kg) and high cost of these batteries due to the limited capacity of the cathode material limit the lifetime of modern portable electronic devices, especially electric vehicles, and increase their cost. Considering the disadvantages of lithium-ion batteries, many alternative energy storage devices are being developed. Among these is lithium-sulfur battery technology, which has a theoretically high energy capacity (2600 Wh/kg), low cost and non-toxic. Lithium-sulfur batteries have great potential to solve current energy and environmental problems. However, due to the insulating nature of sulfur, the free movement of by-products such as polysulfide between the anode and cathode (PSS effect), and the volume expansion of sulfur (80%) during the cycle, the energy capacity and stability of the battery are much lower than expected. In order to overcome these problems, sulfur-cathode designs are being developed using carbon-based materials, metal oxides, conductive polymers and metal sulfides. Among these, activated carbons, which have high electrical conductivity, large active surface area and the ability to strongly retain the formed polysulfides in their structure, may have the greatest potential for the commercialization of metal sulfides in the lithium-sulfur battery. Activated carbons are a preferred material due to their variable size structure, high conductivity and toughness, large pore volume, specific surface area and low cost. Activated carbon can be obtained from organic wastes. Flax plant is among the most preferred ones. Flax creates a porous structure due to its high lignin content and has a high activated carbon content. When we look at the literature studies, binary metal sulfides (binary) are generally used in sulfur-cathode design. Compared to binary metal sulfides, ternary metal sulfides, which have higher electrical conductivity, active surface area and cation density compared to binary metal sulfides, have only a few studies on sulfur-cathode construction in lithium-sulfur batteries. Therefore, ZnNi2S4 structured thiospinel ternary metal sulfide was synthesized by adding zinc (Zn+2) metal cations separately to nickel-sulfur binary metal sulfide matrix. In this thesis, activated carbons using biomass, synthesis of ZnNi2S4 by microwave method and ZnNi2S4-carbon cathode for high performance lithium-sulfur batteries were studied. In this study, the short-term cycling stability of the S/ZnNi2S4 electrode at 0.24 C was investigated. The first cycle cathode capacity after 0.24 C current density was measured as 617.18 mAhg-1. At the 50th, 100th and 200th cycles, the cathode capacities were 395.91, 343.22 and 288.13 mAhg-1, respectively. At a current density of 0.24 C, the capacity of the S/ZnNi2S4 electrode maintained 44.38% from the first cycle to the 100th cycle and 83.63% from 100 to 200 cycles. The short-term cycling stability of the AK/S/ZnNi2S4 electrode at 0.24 C was tested. The first cycle cathode capacity after 0.24 C current density was 847.44 mAhg-1. At the 50th, 100th and 200th cycles, the cathode capacities were 404.36, 344.66 and 307.49 mAhg-1, respectively. The capacity of the AK/S/ZnNi2S4 electrode maintained 59.3% from the first cycle to the 100th cycle at a current density of 0.24 C, while it maintained 89.2% capacity between 100 and 200 cycles. These findings revealed that the porous structure and high electrical conductivity of activated carbon provided capacity increase in the study.