Energy Storage and Distributed Resources Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, USA.
Nat Commun. 2017 Feb 1;8:14309. doi: 10.1038/ncomms14309.
Understanding the reaction pathway and kinetics of solid-state phase transformation is critical in designing advanced electrode materials with better performance and stability. Despite the first-order phase transition with a large lattice mismatch between the involved phases, spinel LiMnNiO is capable of fast rate even at large particle size, presenting an enigma yet to be understood. The present study uses advanced two-dimensional and three-dimensional nano-tomography on a series of well-formed LiMnNiO (0≤x≤1) crystals to visualize the mesoscale phase distribution, as a function of Li content at the sub-particle level. Inhomogeneity along with the coexistence of Li-rich and Li-poor phases are broadly observed on partially delithiated crystals, providing direct evidence for a concurrent nucleation and growth process instead of a shrinking-core or a particle-by-particle process. Superior kinetics of (100) facets at the vertices of truncated octahedral particles promote preferential delithiation, whereas the observation of strain-induced cracking suggests mechanical degradation in the material.
理解固态相变的反应途径和动力学对于设计具有更好性能和稳定性的先进电极材料至关重要。尽管涉及的相之间存在晶格不匹配的一级相变，但尖晶石 LiMnNiO 能够在大粒径下实现快速倍率，这是一个尚未被理解的谜团。本研究使用一系列成型良好的 LiMnNiO（0≤x≤1）晶体的先进二维和三维纳米断层扫描，在亚颗粒水平上可视化 Li 含量变化时的介观相分布。在部分去锂化晶体上广泛观察到不均匀性以及富锂相和贫锂相的共存，为同时发生的成核和生长过程提供了直接证据，而不是收缩核或逐个颗粒的过程。在截断八面体颗粒顶点处（100）面的优越动力学促进了优先去锂化，而应变诱导开裂的观察表明材料发生了机械降解。
