Cycle Discharge Capacity Research Articles

Synthesis of non-stoichiometric lithium nickel cobalt oxides and their structural and electrochemical characterization

Non-stoichiometric phases of lithium nickel cobalt oxides were synthesized by a sol–gel method using oxalic acid as a chelating agent. The structural properties have been examined using X-ray diffraction techniques. Electrochemical coin cell studies showed materials with excess lithium stoichiometry had interesting properties of improved capacity and cyclability. Of all the compositions with excess lithium stoichiometry, Li 1.1Ni 0.8Co 0.2O 2, showed better electrochemical characteristics with a first cycle discharge capacity of 182 mAh/g and a 10th cycle of 172 mAh/g than the ideal stoichiometry LiNi 0.8Co 0.2O 2. The structural and electrochemical properties of Li x Ni 0.8Co 0.2O 2 with x=1.00, 1.05, 1.10 and 1.15 are discussed in detail.

Study on C xN and C xS with disordered carbon structure as the anode materials for secondary lithium batteries

C x N ( x = 12.5 and 7.3) and C x S ( x = 31.8 and 28.0) with disordered carbon structure was synthesized by chemical vapor deposition (CVD) from pyridine and thiophene, respectively, at 800 °C in the absence or presence of chlorine. Lithium was reversibly inserted into these materials. In addition, C x N and C x S had larger capacities than pyrolytic carbon synthesized by CVD from benzene at 800 °C. The capacities of C x N and C x S increased with increase in nitrogen or sulfur content. In particular, C 7.3N had a first cycle discharge capacity of 507 mAh/g in the potential range of 0–3 V versus Li/Li +, which exceeds the theoretical capacity of graphite (372 mAh/g). C 28.0S had a large first cycle discharge capacity of 551 mAh/g. The average interlayer spacing of C 7.3N increased during charging and decreased during discharging like that of pyrolytic carbon. On the other hand, the average interlayer spacing of C 28.0S hardly changed during charging and discharging.

Thiospinels as cathode for lithium secondary battery

The defect thiospinel Cu x M 2S 4 (MTi, Cr) has been studied as a cathode material for the lithium secondary battery. Cu 0.18Ti 2S 4 showed a good reversibility with smooth lithium intercalation and deintercalation. When it was cycled at the current density of 1 mA cm −2, the discharge capacity of the first cycle was about 170 mA h g −1, which corresponds to Li 1.5Cu 0.18Ti 2S 4. The defect Li x Cu 1− y Cr 2S 4 was prepared by the reaction of CuCr 2S 4 and n-butyllithium. The reduced copper metal was deposited on the surface of the compound. This material did not show the reversible electrode reaction. The X-ray diffraction measurements indicated that the copper metal returned to the 8a sites of the spinel framework in the charge process. This copper atom blocks the lithium diffusion via 16c and 8a sites.