Low‐cost electrochemical energy storage systems (EESSs) are urgently needed to promote the application of renewable energy sources such as wind and solar energy. In analogy to lithium‐ion batteries, the cost of EESSs depends mainly on charge‐carrier ions and redox centers in electrodes, and their performance is limited by positive electrodes. In this context, this Minireview evaluates several EESS candidates and summarizes the known mixed polyanionic compounds (MPCs)—a family with robust frameworks and large channels for ion storage and migration. After comprehensive analysis, it is pointed out that a deeper exploration of MPCs may generate numerous novel crystallographically interesting compounds and excellent cathode materials for low‐cost energy storage applications.

Transition-metal oxalates have wide applications in magnetics, photoemission, electrochemistry, etc. Herein, using hydrothermal reactions, five cobalt(II) oxalates, Na, and (NH 4 ) 2 Co 2 (C 2 O 4 )F 4 (V) have been synthesized, and their structures are determined from single-crystal X-ray diffraction or Rietveld refinement of powder X-ray diffraction data. Notably, IV and V are identified for the first time. The structures of these cobalt oxalates are versatile, covering 0D, 1D, 2D, and 3D frameworks, while the coordination environments of Co 2+ centers are uniquely distorted octahedra. As representative examples, I and III are investigated as cathode materials for secondary batteries. Both exhibited electrochemical activity despite large cell polarization. The present study enriches the transition-metal oxalate family and provides new options for energy storage materials.

Kostengünstige elektrochemische Energiespeichersysteme (EESS) sind dringend erforderlich, um die Anwendung erneuerbarer Energiequellen wie Wind, Sonne usw. voranzutreiben. Die Geschichte der Lithium‐Ionen‐Batterien hat gezeigt, dass die Kosten von EESSs hauptsächlich von Ladungsträger‐Ionen und Redoxzentren in den Elektroden abhängen und ihre Leistung durch positive Elektroden begrenzt wird. In diesem Szenario bewertet dieser Kurzaufsatz mehrere EESS‐Kandidaten und fasst die bekannten gemischten polyanionischen Verbindungen (MPVs) zusammen – eine Familie mit robusten Strukturen und großen Kanälen für die Ionenspeicherung und ‐migration. Nach einer umfassenden Analyse wird darauf hingewiesen, dass eine tiefere Erforschung der MPVs zu einer Reihe neuartiger kristallographisch interessanter Verbindungen und ausgezeichneten Kathodenmaterialien für kostengünstige Energiespeicheranwendungen führen kann.