Transition-Metal-Free Electrodes for Rechargeable Sodium-Ion Batteries: a Path towards Sustainable Energy Storage

Development of sodium-ion batteries (SIBs) is of significant recent interest in energy storage in view of some positive aspects, such as the abundance of sodium over lithium, their fast-charging capability, cobalt-free cathode, safe transportability, etc. although with somewhat lower capacities. With numerous battery applications developing due to the new energy initiatives, SIBs are finding a niche place in this ecosystem. The transition metals (TM)- based electrodes generally suffer from sluggish reaction kinetics, poor structural stability, lattice distortion due to severe Jahn-Teller effects, and inferior oxygen reversibility. Additionally, the heavy utilization of TM resources makes critical concerns about the poor supply along with the carbon footprint related to their processing. This review focuses on developing TM-free electrodes, highlighting their fundamentals, design principles, functionality, and application as both cathode and anode in SIBs. It delves into design and synthesis aspects, challenges to achieve high performance, and strategies to overcome pitfalls to further enhance their applicability. Moreover, it furnishes a comprehensive survey of recent progress and persisting challenges in the domain of batteries containing organic and carbonaceous materials, offering deep insights into future research advancement. We believe that this review will provide pragmatic strategies for the advancements of TM-free electrodes for rechargeable batteries.