Cathode discovery ‘opens up new pathways’ for calcium-ion storage

With growing concerns over the availability and supply chains of various materials that are essential to lithium-ion batteries today, on top of the need for higher storage capacities, longer lifetimes and faster, safer performance, scientists are hard at work investigating new materials for use in batteries.

And they aren’t short of options, with sodium, aluminum, oxygen and many more all showing strong potential for development in storage solutions. Calcium has attracted some recent attention among these, ticking all the boxes in terms of performance potential, safety, abundance and low-cost production. However, calcium-ion storage remains in the earlier stages of research, and there are still plenty of challenges in the way of demonstrating a viable calcium-ion battery.

Among these challenges are short cycle life and low capacity, as well as a tendency for big changes in volume as the battery cycles, leading to structural damage. A group of scientists led by Seoul National University in South Korea applied knowledge gained from its research into sodium batteries to these problems, fabricating a calcium-ion battery with a cathode made from NVPF, a material that has proven successful in sodium-ion batteries. “A large calcium ion intercalation in the host is supposed to cause an extended volume change of the host, which triggers a premature degradation of the cathode structure,” the researchers explain. “The discovery of a reliable calcium cathode material or strategy that can mitigate these issues would expedite the development of the CIBs, and thus has long been awaited.”

The battery is described in full in the paper A new high-voltage calcium intercalation host for ultra-stable and high-power calcium rechargeable batteries, published in Nature Communications. Knowing that NVPF showed very low volume change during cycling in a sodium battery, the group saw that it had strong potential in calcium as well. The battery demonstrated reversible intercalation of calcium ions at 3.2 volts, and a capacity fade rate of 0.02% per cycle, among the best recorded for a calcium-ion battery.

Analysis of the cathode at work revealed that it relies on a new type of intercalation, which helps to unlock more of calcium’s storage potential. The group hopes that its discovery will clear the way for more improvements in CIB technology, enabling the realization of “stable and high power cathodes in CIBs.”