Anti-fluorite Li6CoO4 as an alternative lithium source for lithium ion capacitors: an experimental and first principles study

Abstract

As a promising hybrid energy storage system, lithium ion capacitors (LICs) have been intensively investigated regarding their practical use in various applications, ranging from portable electronics to grid support. The asymmetric LIC offers high-energy and high-power densities compared with conventional energy storage systems such as electrochemical double-layer capacitors (EDLCs) and lithium ion batteries (LIBs). To enable suitable operation of the LIC, the negative electrode should be pre-lithiated prior to cell operation, which is regarded as a key technology for developing self-sustainable LICs. In this work, we have demonstrated the potential use of Li₆CoO₄ as an alternative lithium source to metallic lithium. A large amount of Li⁺ can be electrochemically extracted from the structure incorporated into the positive electrode via a highly irreversible process. Most of the extracted Li⁺ is available for pre-lithiation of the negative electrode during the first charge. This intriguing electrochemical behaviour of Li₆CoO₄ is suitable for providing sufficient Li⁺ to the negative electrode. To obtain a fundamental understanding of this system, the electrochemical behaviour and structural stability of Li₆CoO₄ is thoroughly investigated by means of electrochemical experiments and theoretical validation based on first principles calculations.