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Highlights A critical assessment of electrolytes’ limiting factors, which affect the low-temperature performance of Li-metal batteries. Summary of emerging strategies to improve low-temperature performance from the aspects of electrolyte design and electrolyte/electrode interphase engineering. Perspectives and challenges on how to develop creative solutions in electrolytes and correlative materials for low-temperature operation.

Abstract The thermal stability window of current commercial carbonate-based electrolytes is no longer sufficient to meet the ever-increasing cathode working voltage requirements of high energy density lithium-ion batteries. It is crucial to construct a robust cathode–electrolyte interphase (CEI) for high-voltage cathode electrodes to separate the electrolytes from the active cathode materials and thereby suppress the side reactions. Herein, this review presents a brief historic evolution of the mechanism of CEI formation and compositions, the state-of-art characterizations and modeling associated with CEI, and how to construct robust CEI from a practical electrolyte design perspective. The focus on electrolyte design is categorized into three parts: CEI-forming additives, anti-oxidation solvents, and lithium salts. Moreover, practical considerations for electrolyte design applications are proposed. This review will shed light on the future electrolyte design which enables aggressive high-voltage cathodes.

Carbon dots (CDs), as a new zero-dimensional carbon-based nanomaterial with desirable optical properties, exhibit great potential for many application fields. However, the preparation technique of multiple emission CDs with high yield is difficult and complex. Therefore, exploring the large-scale and straightforward synthesis of multicolor CDs from a simple carbon source is necessary. In this work, the solvent-free method prepares a series of multicolor emission CDs from dihydroxybenzoic acid (DHBA). The maximum emission wavelengths are 408, 445, 553, 580, and 610 nm, respectively, covering the visible light region. The 2,4- and 2,6-CDs possess the longer emission wavelength caused by the 2,4-, and 2,6-DHBA easily undergo decarboxylation to form the larger sp2 domain graphitized structure. These CDs incorporated with g-C3N4 can significantly improve the photocatalytic water-splitting hydrogen production rate by extending the visible light absorption and enhancing the charge separation efficiency. The long-wavelength emission CDs can further enhance photocatalytic activity primarily by improving visible light absorption efficiency.

Entropy, once overlooked, is an essential aspect of electrolytes. Recently emerged high-entropy electrolytes with multiple components provide vast compositional space and interfacial chemistry possibilities for electrolyte design. It is noteworthy that high-entropy electrolytes exhibit extraordinarily high ionic conductivity at low temperatures, thereby creating a new direction for batteries to operate at ultra-low temperatures. This commentary discusses the underlying mechanism, challenges encountered, and potential solutions of high-entropy electrolyte design in the hope of sparking future research in this subject.

High voltage aqueous Li-ion batteries have the potential for sustainable large-scale energy storage due to their intrinsic advantages of safety, low cost, as well as environmental friendliness. "Water-in-salt" electrolytes have significantly enhanced the energy density of aqueous Li-ion batteries by extending the aqueous electrolyte stability window to 3.0 V. However, the cathodic limit and salt concentration need to be reduced, enabling to operate low cost LiMn2O4/Li4Ti5O12 cells. In addition, gravimetric energy density of LiMn2O4/Li4Ti5O12, self-discharge rate, and operation temperature range remain rarely studied. This perspective aims to briefly summarize the opportunity and challenges of aqueous batteries for practical applications. [ABSTRACT FROM AUTHOR]