| Lithium-ion batteries have been wide spread as electrochemical energy storage technologies due to their high specific energy density, green pollution-free, good operating safety. Generally, the capacity of cathode material is much lower than that of the anode materials in rechargeable lithium batteries, which is a major handicap for enhancing the specific energy of such batteries. Therefore, high specific capacity cathode materials for rechargeable lithium are widely researched in recent years. The development of new metal sulfide cathode material with high specific capacity is one of important direction for high energy density lithium-ion battery research and development.In metal sulfides, different nickel-sulfur compounds can be formed of nickel and sulfur. As a cathode material for lithium-ion batteries NiS showed great potential applications for it’s capacity of lithium, de-intercalation, which theoretical specific capacity is up to590mAh/g. NiS have a hexagonal crystal structure a-NiS and rhombohedral triangular crystal structure β-NiS, their different crystal structure and morphology directly affects the performance of lithium de-intercalation of NiS. Therefore, this paper used a wet chemical method to control the synthesis of nano-NiS powder with different crystal and morphology, and study their performance of lithium de-intercalation. Following are the main results:1. A stable form of nano-laminated flower-like β-NiS was hydrothermally synthesized with nickel acetate and thiourea as the raw material, in the conditions of a molar ratio of1:3, at160℃,24h. The morphology dispersed by the massive body into tiny whiskers and then form nanosheets reunion finally lamellar grow into flower-shaped laminations.The product gradually transformed from NiS2to β-NiS and a-NiS, eventually completely’transformed into β-NiS. The initial discharge capacity reaches573.3mAh/g.2. A microsphere type a-NiS was synthesized by solvothermal method with nickel acetate and thiourea as the raw material, in the conditions of a molar ratio of1:3, at200℃,24h. By adjusting the molar ratio of nickel acetate and thiourea the phase composition of nickel sulfide is controlled. When the molar ratio of nickel acetate and thiourea is morer than1, there is a tendency to produce the phases of P-NiS and Ni3S4. The content of Ni3S4gradually declines with the decreases of molar ratio, and the β-NiS gradually transforms to α-NiS. When the molar ratio of nickel acetate and thiourea is less than1, the product is pure phase α-NiS. The initial discharge capacity reaches420mAh/g.3. The cycling performance of nickel sulfides was improved by Carbon-cladding with glucose. The temperature was reduced to prevent the phase transformation. Comparison of two different crystalline nickel sulfide, P-NiS with a stable form of nano-laminated flower-like have better performance. The first discharge capacity is702.4mAh/g, and after carbon-cladding. After20cycles the discharge capacity remained at120mAh/g. |
