The electrochemical alkali ion exchange is a powerful technique to synthesize novel active materials for secondary batteries or to study Li/Na/K analogous intercalation compounds. Herein, we report for the first time the electrochemically conducted exchange of Li-ions by Na-ions within the host lattice of LiCoO₂. Li-Na substitution in a potential range of 2.0 – 4.0 V vs Na/Na⁺ leads to the formation of a Li-Na-mixed intercalation compound. Operando XRD measurements and ex-situ EDS-mappings indicate that the different ionic radii and the corresponding CoO₂-layer distances forbid Li-Na mixing in the lattice, resulting in the emergence of Na- and Li-rich domains during Na-ion insertion. Charging and discharging of the resulting Li-Na-mixed intercalation compound is dominated by Na-insertion and extraction, while Li-ions remain in the lattice until it is completely depleted of Na-ions. These novel insights concerning competitive kinetics, thermodynamics and phase evolution behavior can be highly useful to understand similarities and differences of Na- and Li-insertion chemistries to develop materials for future Na-ion batteries based on the comprehensive scientific knowledge in Li-ion technology.

电化学碱离子交换是一种强大的技术，可以合成用于二次电池的新型活性材料或研究Li / Na / K相似的嵌入化合物。在本文中，我们首次报道了LiCoO ₂的主晶格内Na离子对Li离子的电化学交换。与Na / Na ^+相比， Li-Na的电位范围为2.0 – 4.0 V，导致形成Li-Na混合插层化合物。Operando XRD测量和易位EDS映射表明不同的离子半径和相应的CoO ₂层距离禁止Li-Na混合在晶格中，导致在Na离子插入过程中出现富含Na和Li的畴。插入的锂和萃取主要控制混合的锂-钠混合插层化合物的充放电，而锂离子则保留在晶格中，直到完全耗尽钠离子为止。这些有关竞争动力学，热力学和相演化行为的新颖见解对于理解锂离子和锂离子插入化学的异同对于基于锂离子技术的综合科学知识开发未来的钠离子电池材料非常有用。