Tuning Rate-Limiting Factors to Achieve Ultrahigh-Rate Solid-State Sodium-Ion Batteries

High-performance all-solid-state electrolyte for sodium batteries enabled by the interaction between the anion in salt and Na3SbS4

All-solid-state sodium batteries with poly(ethylene oxide) (PEO)-based electrolytes have shown great promise for large-scale energy storage applications. However, the reported PEO-based electrolytes still suffer from a low Na⁺ transference number and poor ionic conductivity, which mainly result from the simultaneous migration of Na⁺ and anions, the high crystallinity of PEO, and the low concentration of free Na⁺. Here, we report a high-performance PEO-based all-solid-state electrolyte for sodium batteries by introducing Na₃SbS₄ to interact with the TFSI⁻ anion in the salt and decrease the crystallinity of PEO. The optimal PEO/NaTFSI/Na₃SbS₄ electrolyte exhibits a remarkably enhanced Na⁺ transference number (0.49) and a high ionic conductivity of 1.33 × 10⁻⁴ S cm⁻¹ at 45 °C. Moreover, we found that the electrolyte can largely alleviate Na⁺ depletion near the electrode surface in symmetric cells and, thus, contributes to stable and dendrite-free Na plating/stripping for 500 h. Furthermore, all-solid-state Na batteries with a 3,4,9,10-perylenetetracarboxylic dianhydride cathode exhibit a high capacity retention of 84% after 200 cycles and superior rate performance (up to 10C). Our work develops an effective way to realize a high-performance all-solid-state electrolyte for sodium batteries.

A high-performance all-solid-state PEO/NaTFSI/Na₃SbS₄ electrolyte for sodium batteries is realized owing to the electrostatic interaction between TFSI⁻ in the salt and Na₃SbS₄, which immobilizes TFSI⁻ anions and promotes the dissociation of NaTFSI.

Progress in Solid Polymer Electrolytes for Lithium-Ion Batteries and Beyond

Solid-state polymer electrolytes (SPEs) for high electrochemical performance lithium-ion batteries have received considerable attention due to their unique characteristics; they are not prone to leakage, and they exhibit low flammability, excellent processability, good flexibility, high safety levels, and superior thermal stability. However, current SPEs are far from commercialization, mainly due to the low ionic conductivity, low Li⁺ transference number (t_Li+ ), poor electrode/electrolyte interface contact, narrow electrochemical oxidation window, and poor long-term stability of Li metal. Recent work on improving electrochemical performance and these aspects of SPEs are summarized systematically here with a particular focus on the underlying mechanisms, and the improvement strategies are also proposed. This review could lead to a deeper consideration of the issues and solutions affecting the application of SPEs and pave a new pathway to safe, high-performance lithium-ion batteries.

Synergistic Dissociation-and-Trapping Effect to Promote Li-Ion Conduction in Polymer Electrolytes via Oxygen Vacancies

Despite their promised safety and mechanical flexibility, solvent-free polymer electrolytes suffer from low Li-ion conductivities due to poor dissociation of conducting salts and low Li⁺ -transference numbers due to Li⁺ -trapping by ether-linkages. In this work, the authors found that oxygen vacancies carried by nanosized Al₂ O₃ fillers preferentially promotes Li⁺ -conduction in poly(ethylene oxide) (PEO). These vacancies and free electrons therein, whose concentration can be tuned, effectively break up the ion pairs by weakening the Coulombic attraction within them, while simultaneously interacting with the anions, thus preferentially constraining the movement of anions. This synergistic dissociation-and-trapping effect leads to the significant and selective improvement in Li-ion conductivity. Solid state batteries built on such PEO-based electrolytes exhibits superior performance at high current density. This discovery reveals a molecular-level rationale for the long-observed phenomenon that certain inorganic nano-fillers improve ion conduction in PEO, and provides a universal approach to tailor superior polymer-based electrolytes for the next generation solid-state batteries.