High-Voltage Pyrophosphate Cathodes

The quest to explore and to discover novel cathode materials is key to sustaining the progress of Li-ion rechargeable batteries. It has encouraged materials chemists to design and develop a variety of polyanionic compounds. This paper reports and summarizes recent progress in the development of alkali metal pyrophosphate based cathode materials for battery applications. It points out that the pyrophosphate-based polyanionic-framework materials offer a rich crystal chemistry, ease of synthesis and robust structure offering good alkali-ion mobility. Thus, they can form a promising class of cathode materials both for lithium- and sodium-ion secondary batteries. In the Perspectives section, it is speculated that keen study of the myriad of pyrophosphate phases, selective screening and design of key pyrophosphate compounds with open frameworks and optimizing those compounds with nanosizing and carbon coating can lead to breakthroughs in the realization of commercially viable high-voltage Li-ion and Na-ion pyrophosphate cathodes.