Improved Electrochemical Performance of Spinel LiNi0.5Mn1.5O4 Cathode Materials with a Dual Structure Triggered by LiF at Low Calcination Temperature

Improving Fast-Charging Capability of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode under Long-Term Cyclability through Co-Doping Strategy

Co-free spinel LiNi0.5Mn1.5O4 (LNMO) is emerging as a promising contender for designing next generation high-energy-density and fast-charging Li-ion batteries, due to its high operating voltage and good Li+ diffusion rate. However, further improvement of the Li+ diffusion ability and simultaneous resolution of Mn dissolution still pose significant challenges for their practical application. To tackle these challenges, a simple co-doping strategy is proposed. Compared to Pure-LNMO, the extended lattice in resulting LNMO-SbF sample provides wider Li+ migration channels, ensuring both enhanced Li+ transport kinetics, and lower energy barrier. Moreover, Sb creating structural pillar and stronger TM─F bond together provides a stabilized spinel structure, which stems from the suppression of detrimental irreversible phase transformation during cycling related to Mn dissolution. Benefiting from the synergistic effect, the LNMO-SbF material exhibits a superior reversible capacity (111.4 mAh g-1 at 5C, and 70.2 mAh g-1 after 450 cycles at 10C) and excellent long-term cycling stability at high current density (69.4% capacity retention at 5C after 1000 cycles). Furthermore, the LNMO-SbF//graphite full cell delivers an exceptional retention rate of 96.9% after 300 cycles, and provides a high energy density at 3C even with a high loading. This work provides valuable insight into the design of fast-charging cathode materials for future high energy density lithium-ion batteries.

A real time study of the coupled electrochemical and mechanical behaviors of the spinel cathodes in LIBs

Spinel cathode materials have great application prospects in lithium batteries (LIBs) due to their characteristics of abundant raw materials, simple preparation processes, and cobalt-free nature. During the electrochemical cycles, the specific capacity of the electrodes decreases significantly due to the dissolution of excess metal ions and mechanical degradation, which hinder their further application and development. Here, a bending curvature measurement system (BCMS) was designed to simultaneously measure the mechanical properties of the spinel cathodes during the electrochemical reaction. Three types of cathodes were chosen as the working cathode, and the coupled mechanical and electrochemical properties were analyzed to understand their degradation mechanism. During cycling, a hysteresis loop is observed for the curvature, modulus, plain strain, and stress, where LiMn2O4 (LMO) has the largest loop for the mechanical response while the LiNi0.5Mn1.5O4@Al2O3 (LNMO@Al) one has the smallest loop. Besides, the changing trend of LNMO@Al is the smallest in multiple cycles and it shows the more stable mechanical properties. This study shows from in situ mechanical measurements that the mechanical properties can greatly affect the electrochemical performance of the cathodes. These findings could offer new insights into the understanding of the electrochemical performance degradation in the spinel cathodes and can help develop strategies to enhance the performance of LIBs.

Chemical capacitance measurements reveal the impact of oxygen vacancies on the charge curve of LiNi0.5Mn1.5O4-δ thin films

The level of oxygen deficiency δ in high-voltage spinels of the composition LiNi0.5Mn1.5O4-δ (LNMO) significantly influences the thermodynamic and kinetic properties of the material, ultimately affecting the cell performance of the corresponding lithium-ion batteries. This study presents a comprehensive defect chemical analysis of LNMO thin films with oxygen vacancy concentrations of 2.4% and 0.53%, focusing particularly on the oxygen vacancy regime around 4 V versus Li+/Li. A set of electrochemical properties is extracted from impedance measurements as a function of state-of-charge for the full tetrahedral-site regime (3.8 to 4.9 V versus Li+/Li). A defect chemical model (Brouwer diagram) is derived from the data, providing a coherent explanation for all important trends of the electrochemical properties and charge curve. Highly resolved chemical capacitance measurements allow a refining of the defect model for the oxygen vacancy regime, showing that a high level of oxygen deficiency not only impacts the amount of redox active Mn3+/4+, but also promotes the trapping of electrons in proximity to an oxygen vacancy. The resulting stabilisation of Mn3+ thereby mitigates the voltage reduction in the oxygen vacancy regime. These findings offer valuable insights into the complex influence of oxygen deficiency on the performance of lithium-ion batteries based on LNMO.