Search Results (3)

Both Co-free and lithium- and manganese-rich layered oxide Li(Li_0.2Mn_xNi_yFe_z)O₂ (MNF) cathodes have recently attracted attention in lithium-ion battery (LIB) research due to their high capacities of over 250 mAhg⁻¹, as well as being more eco-friendly and inexpensive than commercial NMC and LiCoO₂. However, they still suffer from lower experimental capacity as well as capacity decay, voltage fade, poor rate capability, and thermal instability. In this paper, fluorine (F)-doped Li_1.2(Mn_0.5Ni_0.2Fe_0.1)O_2(1−x)F_2x (MNF502010, x = 0, 0.025, 0.05, 0.075, 0.1) cathode materials have been synthesized in the nanoscale via sol–gel and subsequent solid-phase calcination to address some of these problems. The resulting 5% F-doped MNF502010 cathode demonstrates the advantage of fluorine doping, which makes a significant contribution to the formation of a well-ordered layer structure with a minimal LiM₂O₄ spinel phase as an impurity. This composition achieves an initial discharge capacity of 252 mAhg⁻¹ (1C = 250 mAhg⁻¹) and a 156 mAhg⁻¹ discharge capacity at 0.3 C on the 100th discharge, with an average voltage fade of 0.24 V. The optimization of fluorine composition results in an enhancement in the activation of the Li₂MnO₃-type monoclinic phase, as well as an increase in the electronic conductivity compared to the fluorine-free cathode. To understand the structural origin of this improved performance, X-ray absorption spectroscopy (XAS) measurements were carried out on pristine and cycled MNF electrodes. Full article

We present a systematic study of the lithium-ion transport upon the mixed manganese-iron oxide phosphate glasses 3Li₂O-xMn₂O₃-(2-x)Fe₂O₃-3P₂O₅(LM_xF_2−xPO; $0\le x \le 2.0$) proposed for the use in a cathode for lithium secondary batteries. The glasses have been fabricated using a solid reaction process. The electrical characteristics of the glass samples have been characterized by electrical impedance in the frequency range from 100 Hz to 30 MHz and temperature from 30 °C to 240 °C. Differential thermal analysis and X-ray diffraction were used to determine the thermal and structural properties. It has been observed that the dc conductivity decreases, but the activation energies of dc and ac and the glass-forming ability increase with the increasing Mn₂O₃ content in LM_xF_2−xPO glasses. The process of the ionic conduction and the relaxation in LM_xF_2−xPO glasses are determined by using power–law, Cole–Cole, and modulus methods. The Li⁺ ions migrate via the conduction pathway of the non-bridging oxygen formed by the depolymerization of the mixed iron–manganese–phosphate network structure. The mixed iron–manganese content in the LM_xF_2−xPO glasses constructs the sites with different depths of the potential well, leading to low ionic conductivity. Full article

This work continues our systematic study of Li- and Mn- rich cathodes for lithium-ion batteries. We chose Li₂MnO₃ as a model electrode material with the aim of correlating the improved electrochemical characteristics of these cathodes initially activated at 0 °C with the structural evolution of Li₂MnO₃, oxygen loss, formation of per-oxo like species (O₂²⁻) and the surface chemistry. It was established that performing a few initial charge/discharge (activation) cycles of Li₂MnO₃ at 0 °C resulted in increased discharge capacity and higher capacity retention, and decreased and substantially stabilized the voltage hysteresis upon subsequent cycling at 30 °C or at 45 °C. In contrast to the activation of Li₂MnO₃ at these higher temperatures, Li₂MnO₃ underwent step-by-step activation at 0 °C, providing a stepwise traversing of the voltage plateau at >4.5 V during initial cycling. Importantly, these findings agree well with our previous studies on the activation at 0 °C of 0.35Li₂MnO₃·0.65Li[Mn_0.45Ni_0.35Co_0.20]O₂ materials. The stability of the interface developed at 0 °C can be ascribed to the reduced interactions of the per-oxo-like species formed and the oxygen released from Li₂MnO₃ with solvents in ethylene carbonate–methyl-ethyl carbonate/LiPF₆ solutions. Our TEM studies revealed that typically, upon initial cycling both at 0 °C and 30 °C, Li₂MnO₃ underwent partial structural layered-to-spinel (Li₂Mn₂O₄) transition. Full article