A reliable energy storage ecosystem is imperative for a renewable energy future, and continued research is needed to develop promising rechargeable battery chemistries. To this end, better theoretical and experimental understanding of electrochemical mechanisms and structure-property relationships will allow us to accelerate the development of safer batteries with higher energy densities and longer lifetimes. This Review discusses the interplay between theory and experiment in battery materials research, enabling us to not only uncover hitherto unknown mechanisms but also rationally design more promising electrode and electrolyte materials. We examine specific case studies of theory-guided experimental design in lithium-ion, lithium-metal, sodium-metal, and all-solid-state batteries. We also offer insights into how this framework can be extended to multivalent batteries. To close the loop, we outline recent efforts in coupling machine learning with high-throughput computations and experiments. Last, recommendations for effective collaboration between theorists and experimentalists are provided.

The electrode–electrolyte interface is one of the major components enabling Li‐ion batteries (LIBs) to function reversibly. Often, the solid–electrolyte interphase (SEI) at the anode is regarded as the key interface that determines the cycle life, capacity fade, and overall safety of batteries. There are a plethora of SEI literatures that exist; however, the cathode–electrolyte interphase (CEI) remains relatively unexplored. Unlike in the case of SEI, a detailed understanding of CEI formation and its association with battery performance is not present. This review gives insight into the recent progress in understanding the CEI in LIBs. Though there is a relative dearth of literature, the CEI is generally considered as a heterogeneous multicomponent film formed due to the decomposition of electrolyte at the cathode surface. Besides understanding the thermodynamic properties and relevant kinetic reactions, one of the main challenges lies in developing and stabilizing the CEI layer due to its complex structural composition. Extensive research efforts to engineer a stable CEI are reviewed, including the use of electrolyte additives, artificial engineering, and heteroatom doping of cathode. Furthermore, promising characterization techniques and future outlook in forming a robust CEI for both existing LIB and post‐LIB systems are highlighted.

The electrochemical reversibility of the aluminum–sulfur (Al–S) battery critically depends on the physical and chemical properties of the sulfur cathode.

Post-Li ion battery technologies are gaining importance due to their high theoretical energy density and high specific capacity of the electrode materials.Due to fundamental limitations, the existing Li-ion batteries cannot fulfill rigorous requirements, like cost-effectiveness and high storage capacities. Roomtemperature sodium-sulfur battery (RT-Na/S), in particular, is an emerging candidate with the high theoretical specific capacity of sodium (~1166 mAh/g) and sulfur (~1675 mAh/g) and naturally high abundance of both the electrode materials. Sodium metal, combined with sulfur, is a cheap and energy-dense option to the existing battery technologies. In recent years, this has garnered much interest in the scientific community due to a wide range of possibilities for altering battery performance. With the invention of the high-temperature sodium-sulfur batteries, Na metal-based chemistries remain in oblivion.However, due to increasing concerns over the safety of high-temperature sodium-sulfur batteries, Na metal anode is revived in recent years with the ever-growing demands for high energy density and improved safety. Despite that current Na metal anode still lacks high-reversibility, efficiency, and roomtemperature stability due to limited or no control over the interfacial chemistry of the Na metal anode. The electrochemical reduction of Na + ions is accompanied by the inevitable reduction of organic species, which leads to the growth of the solid-electrolyte interphase (SEI) with Na-deposits. The SEI is inherently unstable due to the localized fluctuations in its chemical and physical properties. A deep understanding of challenges associated with the SEI's localized interfacial chemistry is of prime importance toward developing practical Na metal anodes for RT-Na/S batteries. This minireview highlights critical challenges in developing a stable Na metal anode and further sheds light on its mechanistic aspects. In addition to that, novel approaches to precisely tune the interphase's physicochemical properties are highlighted to pave path for developing a stable and long-life Na-metal anode for RT-Na/S batteries.

Room‐temperature Na metal batteries represent an emerging energy storage technology beyond Li‐ion batteries, owing to the high specific capacity and high natural abundance of Na. However, Na metal anodes are plagued with multiple challenges including unstable solid electrolyte interphase, undesirable dendrite growth, and large volumetric expansion, leading to low Coulombic efficiency during Na plating and stripping. To this end, mechanically stable and sodiophilic hosts with nano‐ or micro‐structured materials have been investigated to accommodate Na in the structured spacing or gaps for enhanced cyclability. In this concept, we will discuss the key concepts and latest developments in guiding uniform Na deposition through host modification, especially carbon, inorganic and polymeric materials. Future prospects and outlook will also be provided, including artificial interphase design, solid‐state electrolytes, and precise nanoscale characterization to improve our fundamental understanding of Na deposition and spur this burgeoning field in Na metal batteries.