Identifying Element-Modulated Reactivity and Stability of the High-Voltage Spinel Cathode Materials via In Situ Time-Resolved X-Ray Diffraction.

Designing and identifying a dopant-involved material is quite significant, especially for battery science. LiNi0.5Mn1.5O4, being one of the most appealing candidates for high-potential lithium-ion batteries, has attracted immense attention and been investigated with Al or F dopants for its undesirable inherent structural challenges. Although the excellent performance of Al- or F-doped LiNi0.5Mn1.5O4 has been reported previously, the relationship between dopants, structural variation, and electrochemistry has not been fully identified. Hence, synchronous time-resolved XRD techniques are applied for identifying a guideline of the phase variations in cathodic (Al3+)- and anodic (F-)-substituted LiNi0.5Mn1.5O4, which revealed a three-phase evolution as a function of structural stability. Also, the Al-substituted materials exhibit excellent reactivity and stability, which can be clearly identified via the stable buffer phase existing in high power density or after long cycling due to the improvement in reaction kinetics of phase transition and the lithium-ion diffusion coefficient, just opposite to F doping. This provides a good guideline for identifying an element-modulated mechanism of reactivity or stability of materials science.