Advances in inorganic anode materials and progress in sodium-ion batteries: a comprehensive review

The intermittent nature of renewable energy sources, like solar, wind etc., require efficient and reliable electrical energy storage devices. Currently, the search for a substitute for Lithium-Ion Batteries (LIBs) has been ongoing due to the high-cost, restricted supply, and safety concerns. Since Na is more plentiful, less expensive and safer than Li, Sodium-Ion Batteries (SIBs) have been proposed as a LIB substitute, in applications where weight and size of batteries are less important. Among the components of rechargeable batteries, anode is the most important, which has maximum impact on the performance of the battery. Poor life cycle and lower energy density of SIBs are attributed to heavier and larger Na⁺-ions compared to Li⁺-ions. Numerous attempts have been undertaken to enhance the electrochemical performance of SIBs with various anode materials. In this paper, we present a comprehensive review of inorganic anode materials for SIBs. Based on the mechanism for charge storage, the paper is divided in to i) intercalation, ii) conversion/conversion-intercalation, iii) alloying and iv) adsorption/redox (MOF) based anode materials. These sections are subdivided in subsections on specific anode materials. A mini-section on full cell SIB studies has been included. Finally, a brief summary of the review and future suggestions on research directions consisting of innovations on the existing materials, innovative new materials and advanced characterization techniques as well as theoretical calculations to understand the charge storage and anode degradation on repeated cycling in more detail, are discussed.