Lithium–sulfur batteries (LSBs) represent a promising next-generation energy storage system, with advantages such as high specific capacity (1675 mAh g−1), abundant resources, low price, and ecological friendliness. During the application of liquid electrolytes, the flammability of organic electrolytes, and the dissolution/shuttle of polysulfide seriously damage the safety and the cycle life of lithium–sulfur batteries. Replacing a liquid electrolyte with a solid one is a good solution, while the higher mechanical strength of solid-state electrolytes (SSEs) has an inhibitory effect on the growth of lithium dendrites. However, the lower ionic conductivity, poor interfacial contact, and relatively narrow electrochemical window of solid-state electrolytes limit the commercialization of solid-state lithium–sulfur batteries (SSLSBs). This review describes the research progress in LSBs and the challenges faced by SSEs, which are classified as polymer electrolytes, inorganic solid electrolytes, and composite electrolytes. The advantages, as well as the disadvantages of various types of electrolytes, the common coping strategies to improve performance, and future development trends, are systematically described.

Li−CO 2 batteries with high theoretical energy densities are recognized as next-generation energy storage devices for addressing the range anxiety and environmental issues encountered in the field of electric transportation. However, cathode catalysts with unsatisfactory activity toward CO 2 absorption and reduction/evolution reactions hinder the development of Li−CO 2 batteries with desired specific capacities and sufficient cycle numbers. In this work, a multifunctional nanofibrous cathode catalyst that integrates N-rich carbon shells embedded with molybdenum carbide nanoparticles and multiwalled carbon nanotube cores was designed and prepared. The N-rich carbon shell could strengthen the absorption capacity of CO 2 and Li 2 CO 3 . The molybdenum carbide nanoparticles would improve the catalytic activity of both CO 2 reduction and evolution reactions. The carbon nanotube cores would provide an efficient network for electron transportation. The synergistic effect of the cathode catalysts enhances the electrochemical performance of Li−CO 2 batteries. A high cycling stability of more than 150 cycles at a current density of 250 mA g −1 with a cutoff capacity of 1000 mAh g −1 and a charge/discharge overpotential of less than 1.5 V is achieved. This work provides a feasible strategy for the design of a high-performance cathode catalyst for lithium−air batteries.

Traditional lithium–air batteries (LABs) have been seriously affected by cycle performance and safety issues due to many problems such as the volatility and leakage of liquid organic electrolyte, the generation of interface byproducts, and short circuits caused by the penetration of anode lithium dendrite, which has hindered its commercial application and development. In recent years, the emergence of solid-state electrolytes (SSEs) for LABs well alleviated the above problems. SSEs can prevent moisture, oxygen, and other contaminants from reaching the lithium metal anode, and their inherent performance can solve the generation of lithium dendrites, making them potential candidates for the development of high energy density and safety LABs. This paper mainly reviews the research progress of SSEs for LABs, the challenges and opportunities for synthesis and characterization, and future strategies are addressed.

Metal–air batteries are considered the research, development, and application direction of electrochemical devices in the future because of their high theoretical energy density. Among them, lithium–carbon dioxide (Li–CO2) batteries can capture, fix, and transform the greenhouse gas carbon dioxide while storing energy efficiently, which is an effective technique to achieve “carbon neutrality”. However, the current research on this battery system is still in the initial stage, the selection of key materials such as electrodes and electrolytes still need to be optimized, and the actual reaction path needs to be studied. Carbon tube-based composites have been widely used in this energy storage system due to their excellent electrical conductivity and ability to construct unique spatial structures containing various catalyst loads. In this review, the basic principle of Li–CO2 batteries and the research progress of carbon tube-based composite cathode materials were introduced, the preparation and evaluation strategies together with the existing problems were described, and the future development direction of carbon tube-based materials in Li–CO2 batteries was proposed.

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