Design Parameters for Ionic Liquid–Molecular Solvent Blend Electrolytes to Enable Stable Li Metal Cycling Within Li–O2 Batteries

Effective utilization of Li-metal electrodes is vital for maximizing the specific energy of lithium–oxygen (Li–O₂) batteries. Many conventional electrolytes that support Li–O₂ cathode processes (e.g._, dimethyl sulfoxide, DMSO) are incompatible with Li-metal. Here, a wide range of ternary solutions based on solvent, salt, and ionic liquid (IL) are explored to understand how formulations may be tailored to enhance stability and performance of DMSO at Li-metal electrodes. The optimized formulations therein facilitate stable Li plating/stripping performances, Columbic efficiencies >94%, and improved performance in Li–O₂ full cells. Characterization of Li surfaces reveals the suppression of dendritic deposition and corrosion and the modulation of decomposition reactions at the interface within optimized formulations. These observations are correlated with spectroscopic characterization and simulation of local solvation environments, indicating the persistent importance of DMSO–Li⁺-cation interactions. Therein, stabilization remains dependent on important molar ratios in solution and the 4:1 solvent-salt ratio, corresponding to ideal coordination spheres in these systems, is revealed as critical for these ternary formulations. Importantly, introducing this stable, non-volatile IL has negligible disrupting effects on the critical stabilizing interactions between Li⁺ and DMSO and, thus, may be carefully introduced to tailor other key electrolyte properties for Li–O₂ cells.     

A Multifunctional Catalytic Interlayer for Propelling Solid–Solid Conversion Kinetics of Li2S2 to Li2S in Lithium–Sulfur Batteries

The theoretically high-energy-density lithium–sulfur batteries (LSBs) are seriously limited by the disadvantages including the shuttle effect of soluble lithium polysulfides (LiPSs) and the sluggish sulfur redox kinetics, especially for the most difficult solid–solid conversion of Li₂S₂ to Li₂S. Herein, a multifunctional catalytic interlayer to improve the performance of LSBs is tried to introduce, in which Fe_1–xS/Fe₃C nanoparticles are embedded in the N/S dual-doped carbon network (NSC) composed by nanosheets and nanotubes (the final product is named as FeSC@NSC). The well-designed 3D NSC network endows the interlayer with a satisfactory LiPSs capture-catalytic ability, thus ensuring fast redox reaction kinetics and suppressing LiPSs shuttling. The density functional theory calculations disclose the catalytic mechanisms that FeSC@NSC greatly improves the liquid–solid (LiPSs to Li₂S₂) conversion and unexpectedly the solid–solid (Li₂S₂ to Li₂S) one. As a result, the LSBs based on the FeSC@NSC interlayer can achieve a high specific capacity of 1118 mAh g⁻¹ at a current density of 0.2 C, and a relatively stable capacity of 415 mAh g⁻¹ at a large current density of 2.0 C after 700 cycles as well as superior rate performance.     

Self-Polarized Organic–Inorganic Hybrid Ferroelectric Cathode Coatings Assisted High Performance All-Solid-State Lithium Battery

Ferroelectrics can significantly boost electrochemical performances of all-solid-state batteries by constructing built-in electric field to reduce the space charge layer at cathode/solid-state electrolyte interface. However, the construction mechanism of ferroelectric built-in electric field is poorly understood. Herein, the guanidinium perchlorate (GClO₄) ferroelectrics as the cathode coatings in the LiCoO₂-based all-solid-state lithium battery are reported, which has state-of-the-art specific capacity of 210.6 mAh g⁻¹ (91.6% of the liquid battery). Systematic studies reveal that the flexoelectric effect originating from the lattice mismatch between GClO₄ and LiCoO₂ gives GClO₄ coatings the single-domain state and upward self-polarization. Consequently, a vertically downward built-in electric field is generated relative to the cathode, which transports the lithium ions inside the electrolyte to the three-phase interface to alleviate the space charge layer. These findings highlight that the microstructural characteristics of ferroelectric and electrode materials are the primary concern for building an effective built-in electric field.