The local structure evolution of Li_xNi_0.8Co_0.15Al_0.05O₂ (NCA) is linked to its electrochemical response during cycling (and overcharge) by operando Raman spectroscopy with findings supported by complementary techniques, such as online electrochemical mass spectrometry (OEMS) and density functional theory (DFT) phonon calculations. The vibrational motion of lattice oxygens is observed to be highly dependent on the local Li_xMO₂ lattice environment, e.g. M—O bonding strength/length and state of lithiation x. All vibrational modes generally harden upon delithiation due to M—O bond character (ionic → covalent) evolution (disregarding an early bond softening due to Li⁺ vacancy formation) and evidence the important influence of the local structural lattice configuration on the electrochemical response of NCA. Although the intensities of all Raman active bands generally increase upon delithiation, a major inflection point at x = 0.2 marks the onset of a partly irreversible fundamental transition within NCA that is most likely related to electron removal from MO bonding states and partial oxidation of oxygen sublattice, which is also indicated by the observed concomitant O₂ release from the particle surface. Operando Raman spectroscopy with higher time resolution provides unique possibilities for detailed studies of how chemical parameters (Li⁺ vacancy formation, transition metal cation concentration, and lattice doping, etc.) may govern the onset and nature of processes (such as bond character evolution and stability) that define the performance of the Li_xMO₂ class of oxides. The further insights thus gained can be exploited to guide the development of next-generation layered cathodes for Li-ion batteries operating stably at higher voltages and capacities.

中文翻译：

---

用Operando拉曼光谱法阐明Li _x Ni _0.8 Co _0.15 Al _0.05 O ₂氧化还原化学

Li _x Ni _0.8 Co _0.15 Al _0.05 O ₂（NCA）的局部结构演变通过操作拉曼光谱与循环（和过充电）过程中的电化学响应相关联，其发现得到了互补技术的支持，例如在线电化学质谱（OEMS）和密度泛函理论（DFT）声子计算。观察到晶格氧的振动运动高度依赖于本地Li _x MO ₂晶格环境，例如M-O键强度/长度和锂化状态x。所有振动模式通常会因M-O键特性（离子→共价）演变（不考虑由于Li ⁺空位形成而导致的早期键软化）而在脱锂时硬化，并且证明了局部结构晶格构型对NCA电化学响应的重要影响。尽管所有拉曼活性带的强度通常会在脱锂时增加，但x = 0.2处的主要拐点标志着NCA内部发生了部分不可逆的基本跃迁，这很可能与从MO键合态去除电子以及氧亚晶格的部分氧化有关，这也可以通过观察到的伴随的O ₂从颗粒表面的释放来表明。Operando具有更高时间分辨率的拉曼光谱学为详细研究化学参数（Li ⁺空位形成，过渡金属阳离子浓度和晶格掺杂等）如何控制过程的开始和性质（例如键特性演变和稳定性）提供了独特的可能性）定义了Li _x MO ₂类氧化物的性能。由此获得的更多见解可用于指导下一代锂离子电池分层阴极的开发，该阴极可在更高的电压和容量下稳定运行。