The researchers have developed novel oxide cathode materials of 4 V class for potassium-ion batteries as the next generation of storage batteries, in collaboration with Nanjing University of Posts and Telecommunications and Ritsumeikan University.

A model diagram showing the crystalline structure and potassium ion diffusion pathways of the developed layered K2/3M2/3Te1/3O2

Potassium-ion batteries have taken center stage in research and development of the next-generation storage batteries, following the success of lithium ion batteries. Due to its abundance in the earth's crust, potassium is expected to be low cost, and thus offers a real possibility for catering for our ever-increasing energy storage capacity needs and their associated costs as we venture towards a future seeking clean energy solutions. In addition to cost, potassium-ion batteries have a high energy density and thus represent a novel class of 4 V materials.

Before this press release was announced, the working voltage of positive electrode (cathode) materials for such batteries has been 4 V only for Prussian blue materials, and limited to only about 3 V for oxide materials despite the oxide materials exhibiting better thermal stability and other more desirable characteristics.

The researchers selected candidate compounds using crystal structure analysis and theoretical calculations, and developed a complex oxide group with a working potential of approximately 4 V, the same level as working potential of the layered oxide-based materials used as the positive electrode materials for lithium-ion batteries. In particular, the developed oxide group has a theoretical specific capacity of 130 to 140 mA h g^–1, an average working potential of 3.6 to 4.3 V (vs. K⁺/K), and an energy density based on the positive electrode material reaches 470 to 600 W h kg^–1. Thus its performance vastly exceeds prior oxide materials and holds enormous promise for battery applications. Moreover, this development is an example of successful selection of candidate compounds in advance using computational science, demonstrating the utility of this new path for material development. This development of oxide cathode materials for 4 V class potassium-ion batteries represents a crucial advancement in large-cation battery technology.

Despite this progress, research on potassium-ion batteries is still in its infancy, and thus requires additional research and development for the materials to be put to practical use. Nonetheless, the developed materials serve as major contribution towards building a potassium-ion battery that is poised to surpass the success of the lithium-ion battery^*, and thus usher in a new era of potassium-ion batteries. Among other things, this requires researchers to use this achievement to improve the performance of positive electrode materials while particularly developing viable negative electrodes, electrolytic solutions, and solid electrolytes suitable for the improved positive electrode materials.

^*This success of lithium-ion battery culminated in the 2019 Nobel Prize in Chemistry.