LiC₆@Li as a Promising Substitution of Li Metal Counter Electrode for Low‐Temperature Battery Evaluation

Li metal, as a counter electrode, is widely used for electrode materials evaluation in coin type half-cells. However, whether this configuration is suitable for different working conditions has often been neglected. Herein, the large resistance and high cathodic/anodic over-potential of Li metal at low temperature are highlighted, revealing its incompetence as counter electrode on cryogenic condition. In view of this, a novel LiC₆@Li composite electrode is developed as a promising substitution for electrode materials evaluation. In the LiC₆@Li electrode, Li⁺ de-intercalated from LiC₆ preferentially due to the low interface resistance of LiC₆, presenting a cathodic/anodic over-potential of 0.05 V (67 µA cm^-2) at -20 °C, which is ten times lower than that of Li metal. Moreover, the rapid lithium replenishment into LiC₆ from Li metal enables a stable potential of LiC₆@Li. Consequently, the LiC₆@Li-based half-cells enabled more precise evaluation of the Li⁺ storage potential and specific capacities of a series of electrode materials at low temperature. As an extension, KC₈@K is also successfully prepared as a superior counter electrode to K metal. This work proposes a suitable counter electrode for more accurately evaluating electrode materials at subfreezing scenarios, demonstrating the necessity of specialized electrode evaluation systems for particular operating conditions.