Study On Microstructure And Properties Of Nano - Sized Nickel Sulfide By Hydrothermal Synthesis

Development of high energy density rechargeable lithium batteries are demanded duo to the increasing energy consumption of portable and transport applications. 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. Nickel sulfide has been expected to be promising candidates for cathode materials owning to their relatively high theoretical capacity(590mAh/g), energy density as well as functional density.In this dissertation, systematic researches have been carried out on the hydrothermal synthesis of nickel sulfides including their novel morphology and electrochemical properties. The main research works and results are as follows:1. Analytical grade Ni (CH3COOH)2·4H2O and thiourea were chosen as the nickel and sulfur sources for the synthesis of nickel sulfide respectively. A novel morphology of β-NiS with nanowhiskers wrapped spheres, synthesized at140℃for24h, possess better electrochemical and cyclic properties than the other specimens with flaky-type and rodlike morphology. The first discharge specific capacity of this (3-NiS with novel morphology is up to575.4mAh/g. Three carbon cladding methods (carbon nanotube, glucose carbonizing precursor and glucose direct carbon cladding) have been applied to increase the cyclic properties of the specimen prepared on the condition of reaction temperature and time of160℃and24h, respectively. However, the phase was changed to Ni3S2when the glucose carbon cladding temperature was up to600℃. Nanowire was obtained by means of adding citric acid complexing agent, but further experiments the need to be performed to obtain single phase and morphology nickel sulfide.2. γ-NiS has been prepared via hydrothermal synthesis, results indicated that, specimen prepared with reaction temperature180℃, reaction time12h and pH=5displayed better electrochemical properties and the first charge specific capacity was up to589.6mAh/g which was approximate to the theoretical capacity(590mAh/g). Specimens with glucose carbonizing precursor carbon cladding possess better electrochemical properties with specific capacity more than120mAh/g after25cycles than that of carbon nanotube and glucose direct carbon cladding. The emission of by-product H2S has been reduced considerably duo to the addition of acid complexing agent.3. y-NiS used as cathode in rechargeable lithium battery possess better electrochemical properties than the β-NiS.