Energy Storage Research Group, Department of Materials Science and Engineering, Rutgers University , North Brunswick, New Jersey 08902, United States.
Department of Materials Science and Engineering, Rutgers University , Piscataway, New Jersey 08854, United States.
Langmuir. 2017 Sep 19;33(37):9333-9353. doi: 10.1021/acs.langmuir.7b00863. Epub 2017 Jun 22.
Enabling practical utilization of layered R3̅m positive electrodes near full delithiation requires an enhanced understanding of the complex electrode-electrolyte interactions that often induce failure. Using Li[NiCoAl]O (NCA) as a model layered compound, the chemical and structural stability in a strenuous thermal and electrochemical environment was explored. Operando microcalorimetry and electrochemical impedance spectroscopy identified a fingerprint for a structural decomposition and transition-metal dissolution reaction that occurs on the positive electrode at full delithiation. Surface-sensitive characterization techniques, including X-ray absorption spectroscopy and high-resolution transmission electron microscopy, measured a structural and morphological transformation of the surface and subsurface regions of NCA. Despite the bulk structural integrity being maintained, NCA surface degradation at a high state of charge induces excessive transition-metal dissolution and significant positive electrode impedance development, resulting in a rapid decrease in electrochemical performance. Additionally, the impact of electrolyte salt, positive electrode surface area, and surface LiCO content on the magnitude and character of the dissolution reaction was studied.
实现层状 R3̅m 正极在近乎完全脱锂状态下的实际应用，需要深入了解复杂的电极-电解质相互作用，这些相互作用往往会导致失效。本研究选用 Li[NiCoAl]O（NCA）作为模型层状化合物，在苛刻的热和电化学环境中探索其化学和结构稳定性。原位微热量法和电化学阻抗谱确定了正极在完全脱锂状态下发生结构分解和过渡金属溶解反应的特征指纹。表面敏感的表征技术，包括 X 射线吸收光谱和高分辨率透射电子显微镜，测量了 NCA 表面和次表面区域的结构和形态转变。尽管保持了体相结构的完整性，但在高荷电状态下 NCA 表面降解会导致过渡金属的过度溶解和显著的正极阻抗增加，从而导致电化学性能的快速下降。此外，还研究了电解质盐、正极表面积和表面 LiCO 含量对溶解反应幅度和特征的影响。
