Biochar from renewable wood as an ion-conducting protective layer on stable magnesium metal anodes

Rechargeable Mg-metal batteries (RMBs) are expected to be a potential competitor for lithium (Li) counterparts. However, the Mg metal anode readily passivates with conventional organic electrolytes, leading to the formation of an ion-blocking interphase layer. Here, we propose that bamboo charcoals (BCs) used as a Mg²⁺-conducting protective layer on the surface of Mg metal. In this process, it has been demonstrated that compared to apple-wood charcoals (ACs), BCs, distinguished by their plentiful functional groups, high degree of disorder, and large layer spacing, exhibit outstanding Mg²⁺ conductivity. Furthermore, we have proposed a facile and processable method to fabricate BCs/Mg composite, with a focus on circumventing the generation of by-products at the interface. The resultant system of three-dimensional (3D) BCs protective layer effectively increases the number of ion transport channels, thereby boosting ion transport efficiency while concurrently mitigating electrolyte decomposition. The Mg-Mg symmetrical cell with BCs/Mg anode demonstrates lower overpotential (∼0.27 V) and interfacial impedance than bare Mg and ACs/Mg electrode using a common electrolyte of Mg(TFSI)₂ in acetonitrile. The cycling stability, Coulombic efficiency (CE), and voltage hysteresis of the BCs/Mg||V₂O₅ full cell are greatly improved compared to the other two electrodes in both oxidation-resistant electrolyte and its water-containing electrolyte. We expect that this study will provide experimental substantiation by developing passivation-free anode materials tailored for alkali metal battery systems that require interface protection.