Building Next-Generation Li-ion Capacitors with High Energy: An Approach beyond Intercalation

Hybridization of two prominent electrochemical energy storage systems, such as high-energy Li-ion batteries and high-power supercapacitors into a single system, tends to deliver high-energy and high-power capabilities; such systems are often called Li-ion capacitors (LICs). The utilization of battery-type electrodes, which undergo a traditional intercalation process, in LICs provides the necessary energy; however, their limited reversible capacities and higher redox potentials (except graphite and hard carbon) hinder achieving high values. Using materials that can undergo either alloying or conversion or both together with Li, rather than intercalation, is an attractive approach to achieve high energy without compromising both power capability and cyclability. This Perspective discusses the possibility of using high-capacity, exhibiting relatively lower redox potential than transition metal-based intercalation hosts, low-cost materials in conversion and alloying reactions with Li, along with prelithiation strategies (Aravindan, V.; Lee, Y.-S.; Madhavi, S. Best Practices for Mitigating Irreversible Capacity Loss of Negative Electrodes in Li-Ion Batteries. Adv. Energy Mater. 2017, 7, 1602607). Future prospects on working with alloying and conversion-type materials are discussed in detail.