Structure and Electrochemical Properties of Li4Ti5O12 Prepared via Low-Temperature Precipitation

This work aimed to prepare the spinel phase Li4Ti5O12 by a combination of the low-temperature precipitation technique and assisted calcination step. X-ray diffraction (XRD) revealed that the intermediated phase was Li2TiO3, and the spinel phase could be evidently formed at 700°C for 12 to 20 hours. The morphology of spinel powder, determined by SEM and TEM, exhibited a good distribution at the submicrometric scale that promoted a fast kinetic of Li migration and an excellent performance at the high-rate cycling test. The stable performances were achieved in the charge-discharge test at different current densities: 80 mA/g (165 mAh/g), 320 mA (160 mAh/g), and 1600 mA (145 mAh/g) upon 100 cycles. Moreover, we observe a capacity retention of 48% (corresponding 80 mA/g) at a high rate of 5000 mAh/g. The cyclic voltammetry measurement displayed a reversible system and revealed the lithium diffusion coefficient of 1.15 × 10−11 cm2/s.

Synthesis and Electrochemical Performance of Ni-Doped VO2(B) as a Cathode Material for Lithium Ion Batteries

Ni-doped VO2(B) samples (NixVO2(B)) were fabricated by a facile one-step hydrothermal method. When evaluated as a cathode material for lithium ion batteries (LIBs), these Ni-doped VO2(B) exhibited improved lithium storage performance as compared to the pure VO2(B). In particular, when the doping amount is 3%, NixVO2(B) showed the highest lithium storage capacity, best cycling stability, smallest electrochemical reaction resistance, and largest lithium diffusion coefficient. For example, after 100 cycles at a current density of 32.4 mA/g, NixVO2(B) delivered a high specific discharge capacity of 163.0 mAh/g, much higher than that of the pure VO2(B) sample (95.5 mAh/g). Therefore, Ni doping is an effective strategy for enhancing the lithium storage performance of VO2(B).

Effect of nanostructured carbon coatings on the electrochemical performance of Li1.4Ni0.5Mn0.5O2+ x -based cathode materials

Nanocomposites of Li1.4Ni0.5Mn0.5O2+ x and amorphous carbon were obtained by the pyrolysis of linear and cross-linked poly(vinyl alcohol) (PVA) in presence of Li1.4Ni0.5Mn0.5O2+ x . In the case of linear PVA, the formation of nanostructured carbon coatings on Li1.4Ni0.5Mn0.5O2+ x particles is observed, while for cross-linked PVA islands of mesoporous carbon are located on the boundaries of Li1.4Ni0.5Mn0.5O2+ x particles. The presence of the carbon framework leads to a decrease of the polarization upon cycling and of the charge transfer resistance and to an increase in the apparent Li+ diffusion coefficient from 10−16 cm2·s−1 (pure Li1.4Ni0.5Mn0.5O2+ x ) to 10−13 cm2·s−1. The nanosized carbon coatings also reduce the deep electrochemical degradation of Li1.4Ni0.5Mn0.5O2+ x during electrochemical cycling. The nanocomposite obtained by the pyrolysis of linear PVA demonstrates higher values of the apparent lithium diffusion coefficient, a higher specific capacity and lower values of charge transfer resistance, which can be related to the more uniform carbon coatings and to the significant content of sp2-hybridized carbon detected by XPS and by Raman spectroscopy.