Investigation of Rechargeable Calcium Metal-Selenium Batteries Enabled by Borate-Based Electrolytes

Calcium-ion batteries (CIBs) are a promising next-generation energy storage system given the low redox potential of calcium metal and high abundance of calcium compounds. For continued CIB development, the discovery of high energy density calcium ion cathodes is needed to achieve practical energy density values. Here, we report on the use of elemental Se as a promising candidate for a high-capacity cathode material for CIBs that operates via a conversion mechanism in a Ca metal battery at room temperature. The Se electrodes demonstrate a reversible specific capacity of 180 mA h g-1 with a discharge plateau near 2.0 V (vs Ca2+/Ca) at 100 mA g-1 using an electrolyte based on the salt calcium tetrakis(hexafluoroisopropyloxy)borate (Ca(B(hfip)4)2) in 1,2-dimethoxyethane (DME) and Ca metal. The reversible electrochemical reaction between calcium and selenium is investigated using operando synchrotron-based techniques and the possible reaction mechanism discussed.

Automated summary

Calcium-ion batteries (CIBs) have potential for next-generation energy storage due to the low redox potential and abundance of calcium compounds. This study reports the use of elemental Se as a high-capacity cathode material for CIBs operating via a conversion mechanism in a Ca metal battery at room temperature. The Se electrodes exhibit reversible specific capacity and a discharge plateau near 2.0 V (vs Ca2+/Ca). The electrochemical reaction between calcium and selenium is investigated using operando synchrotron-based techniques and discussed.