Nanoscaled LiMn2O4 for Extended Cycling Stability in the 3 V Plateau

Extending the potential window toward the 3 V plateau below the typically used range could boost the effective capacity of LiMn2O4 spinel cathodes. This usually leads to an "overdischarge" of the cathode, which can cause severe material damage due to manganese dissolution into the electrolyte and a critical volume expansion (induced by Jahn-Teller distortions). As those factors determine the stability and cycling lifetime for all-solid-state batteries, the operational window of LiMn2O4 is usually limited to 3.5-4.5 V versus Li/Li+ in common battery cells. However, it has been reported that nano-shaped particles and thin films can potentially mitigate these detrimental effects. We demonstrate here that porous LiMn2O4 thin-film cathodes with a certain level of off-stoichiometry show improved cycling stability for the extended cycling range of 2.0-4.5 V versus Li/Li+. We argue through operando spectroscopic ellipsometry that the origin of this stability lies in the surprisingly small volume change in the layer during lithiation.

Structural and Electrochemical Properties of the High Ni Content Spinel LiNiMnO4

This work presents a contribution to the study of a new Ni-rich spinel cathode material, LiNiMnO4, for Li-ion batteries operating in the 5-V region. The LiNiMnO4 compound was synthesized by a sol-gel method assisted by ethylene diamine tetra-acetic acid (EDTA) as a chelator. Structural analyses carried out by Rietveld refinements and Raman spectroscopy, selected area electron diffraction (SAED) and X-ray photoelectron (XPS) spectroscopy reveal that the product is a composite (LNM@NMO), including non-stoichiometric LiNiMnO4-δ spinel and a secondary Ni6MnO8 cubic phase. Cyclic voltammetry and galvanostatic charge-discharge profiles show similar features to those of LiNi0.5Mn1.5O4 bare. A comparison of the electrochemical performances of 4-V spinel LiMn2O4 and 5-V spinel LiNi0.5Mn1.5O4 with those of LNM@NMO composite demonstrates the long-term cycling stability of this new Ni-rich spinel cathode. Due to the presence of the secondary phase, the LNM@NMO electrode exhibits an initial specific capacity as low as 57 mAh g−1 but shows an excellent electrochemical stability at 1C rate for 1000 cycles with a capacity decay of 2.7 × 10−3 mAh g−1 per cycle.

Enhancing the durable performance of LiMn2O4 at high-rate and elevated temperature by nickel-magnesium dual doping

Various nickel and magnesium dual-doped LiNi_xMg_0.08Mn_1.92−xO₄ (x ≤ 0.15) were synthesized via a modified solid-state combustion method. All as-prepared samples show typical spinel phase with a well-defined polyhedron morphology. The Ni-Mg dual-doping obviously decreases the lattice parameter that gives rise to the lattice contraction. Owing to the synergistic merits of metal ions co-doping, the optimized LiNi_0.03Mg_0.08Mn_1.89O₄ delivers high initial capacity of 115.9 and 92.9 mAh·g⁻¹, whilst retains 77.1 and 69.7 mAh·g⁻¹ after 1000 cycles at 1 C and high current rate of 20 C, respectively. Even at 10 C and 55 °C, the LiNi_0.03Mg_0.08Mn_1.89O₄ also has a discharge capacity of 92.2 mAh·g⁻¹ and endures 500 cycles long-term life. Such excellent results are contributed to the fast Li⁺ diffusion and robust structure stability. The anatomical analysis of the 1000 long-cycled LiNi_0.03Mg_0.08Mn_1.89O₄ electrode further demonstrates the stable spinel structure via the mitigation of Jahn-Teller effect. Hence, the Ni-Mg co-doping can be a potential strategy to improve the high-rate capability and long cycle properties of cathode materials.

Cryochemically Processed Li1+yMn1.95Ni0.025Co0.025O₄ (y = 0, 0.1) Cathode Materials for Li-Ion Batteries

A new route for the preparation of nickel and cobalt substituted spinel cathode materials (LiMn_1.95Co_0.025Ni_0.025O₄ and Li_1.1Mn_1.95Co_0.025Ni_0.025O₄) by freeze-drying of acetate precursors followed by heat treatment was suggested in the present work. The experimental conditions for the preparation single-phase material with small particle size were optimized. Single-phase spinel was formed by low-temperature annealing at 700 °C. For discharge rate 0.2 C, the reversible capacities 109 and 112 mAh g⁻¹ were obtained for LiMn_1.95Co_0.025Ni_0.025O₄ and Li_1.1Mn_1.95Co_0.025Ni_0.025O₄, respectively. A good cycle performance and capacity retention about 90% after 30 cycles at discharge rate 0.2–4 C were observed for the materials cycled from 3 to 4.6 V vs. Li/Li⁺. Under the same conditions pure LiMn₂O₄ cathode materials represent a reversible capacity 94 mAh g⁻¹ and a capacity retention about 80%. Two independent experimental techniques (cyclic voltammetry at different scan rates and electrochemical impedance spectroscopy) were used in order to investigate the diffusion kinetics of lithium. This study shows that the partial substitution of Mn in LiMn₂O₄ with small amounts of Ni and Co allows the cyclability and the performance of LiMn₂O₄-based cathode materials to be improved.

Stable nickel-substituted spinel cathode material (LiMn1.9Ni0.1O4) for lithium-ion batteries obtained by using a low temperature aqueous reduction technique

Nickel-doping of spinel LiMn₂O₄ cathode material provides physico-chemical properties that allow for enhanced electrochemistry for lithium-ion battery.