The increasing demand for high energy density batteries urges the community to seek novel chemistries. Among them, Li/S and Li-O2 have received the most attentions due to their great potential and the community's extensive experience in Li chemistry. In contrast, multivalent chemistries (Mg and Al) attract less attention despite of their unique and remarkable advantages. Although their higher reduction potentials (Mg=-2.36V vs SHE; Al=-1.3V vs SHE) compromises battery voltages, their less reactive nature has enabled a better (elec)chemical compatibility at the metal/electrolyte interface, which eliminates any surface layer and leads to a high coulombic efficiency (100%) for metal deposition/striping. This is crucial for a rechargeable battery chemistry based on metal anode, because the formation of surface layer would cause continuous consumption of electrolyte during repeated cycling. Furthermore, the deposition of multivalent metal (Mg and Al) shows uniform morphology with no whiskers (‘dendrite’) below Sand’s time, which eliminates the possibility of whiskers penetrating through separators and internal short circuit of the battery. This feature allows multivalent metal batteries to function in a much safer manner than Li metal batteries.
The success of multivalent battery chemistry relies on development of proper electrolytes and cathode materials. While great progress has been made regarding the former, few advance was seen in the latter. In this presentation, we will introduce our latest achievement in tackling the cathode challenges. Our study has focused on metal/sulfur chemistries, because 1) they provide close or even higher volumetric energy density than Li/S chemistry; 2) the potentially fast reaction kinetics of the non-topotactic reaction compared with intercalation reaction.