High entropy materials, a horizon-broadening class of materials with complex stoichiometry, have gained significant interest recently. The ideal regulation and the attractive synergy effect make high entropy materials promising candidates for energy storage devices. In this Perspective, we present a survey of high entropy materials as anodes, cathodes, catalysts, and solid-state electrolytes in rechargeable batteries. The entropy-stabilized rock-salt-type Co0.2Cu0.2Mg0.2Ni0.2Zn0.2O is highlighted due to its multiple functions. Suggestions on future perspectives of HEM as an important role in next-generation batteries are given.

The solid-electrolyte interphase (SEI) is known to dictate the performance of a Li metal anode, where its inorganic compositions are primarily responsible for Li + conduction, electron insulation, and thus a compact Li deposition. In this work, we formulate a nonflammable and highly fluorinated electrolyte recipe for a highly reversible Li metal anode. By concurrently incorporating the F-donating anions and solvent molecules into the primary Li + solvation sheath, an inorganic-rich SEI with high F content is produced. The low solvation energy of the tailored solvation sheath further reduces the barrier for Li + desolvation, contributing to accelerated kinetics under fast charging and subzero conditions. Consequently, dramatic improvements in the Li deposition morphology, Coulombic efficiency (98% over 650 cycles), and Li + desolvation/transfer kinetics are obtained. Full cells pairing with the commercial LiFePO 4 (LFP) and LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) cathodes show stable cyclability at both room-temperature and subzero conditions. Further electrolyte prototypes are showcased to demonstrate the universality of the design principle provided herein.

Sodium metal batteries (SMBs) are promising for large scale energy storage due to the remarkable capacity of sodium metal anode (SMA) and the natural abundance of Na-containing resources. However, multiple challenges exist with regards to the usage of SMBs, including dendritic Na growth, poor cyclability of SMA, and severe safety hazards stemming from the employment of the highly flammable liquid electrolytes. Herein, by introducing two functional fluorinated solvents, 1,1,2,2-tetra-fluoroethyl 2,2,3,3-tetrafluoropropyl ether (HFE) and fluoroethylene carbonate (FEC) into trimethyl phosphate (TMP)-based electrolyte, a SMA-compatible flame-retardant electrolyte is enabled, in which Na/Na symmetrical cells can cycle for 800 h at 1.0 mA cm −2 or 3.0 mAh cm −2 . Specifically, the non-solvating HFE plays a critical role in increasing the local electrolyte concentration and reducing the unfavorable decomposition of TMP molecules. By introducing FEC as the co-solvent simultaneously, its preferential defluorination induces a fluoride-rich solid-electrolyte interphase that prevents Na metal surface against the continuous parasitic reactions. More importantly, the designed electrolyte is endowed with an intrinsic non-flammability, which manifests a prerequisite for the real-life application of SMBs.

Chemical/electrochemical stability at the interfaces greatly affects the performance of solid-state batteries (SSBs). However, the interfacial behavior in SSBs remains elusive due to the subsurface nature of interfaces and the lack of proper characterization methods. Herein, ultrasonic imaging technology is employed to non-destructively investigate the interfacial stability in solid-state pouch cells. Bene ting from the high sensitivity of ultrasound to the gas/vacuum, in-situ ultrasonic imaging can effectively probe the inner gas release and interfacial degradation in pouch cells during long-term cycling. The safety issue of SSBs is highlighted by the ammable gas release detected in ultrasonic images. And the increased interfacial resistance either from contact loss or passivation layer growth is well distinguished.The gradual oxidation and gassing at the cathode interface are tracked by ultrasonic imaging, which leads to the capacity fading of SSBs. The ultrasonic imaging technology is demonstrated to be a powerful tool to evaluate the interfacial stability in SSBs, which can guide the rational design of interfaces and enhance the performance of SSBs.

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