Contemporary social problems, such as energy shortage and environmental pollution, require developing green energy storage technologies in the context of sustainable development. With the application of secondary battery technology becoming widespread, the development of traditional lithium (Li)-ion batteries, which are based on insertion/deinsertion reactions, has hit a bottleneck; instead, conversion-type lithium metal batteries (LMBs) have attracted considerable attention owing to the high theoretical capacity of Li metal anodes. In this review, Li-S, Li-O₂, and Li-SOCl₂ batteries are used as examples to summarize LMBs based on their conversion reactions from the perspectives of cathode material, anode material, electrolyte, separator, and current collector. Key challenges exist regarding the conversion reactions of various batteries. To achieve the optimum performance and improve the application effect, several improvement strategies have been proposed in relation to reasonable designs of next-generation high-performance rechargeable batteries.

The overall energy efficiency of electrochemical systems is severely hindered by the traditional anodic oxygen evolution reaction (OER). Utilizing urea oxidation reaction (UOR) with lower thermodynamic potential to replace OER provides a promising strategy to enhance the energy efficiency. Amorphous and heterojunctions electrocatalysts have been aroused extensive studies owing to their unique physicochemical properties and outperformed activity. Herein, we report a simple method to construct a novel crystalline–amorphous NiO-CrO_x heterojunction grown on Ni foam for UOR electrocatalyst. The NiO-CrO_x electrocatalyst displays excellent UOR performance with an ultralow working potential of 1.32 V at 10 mA·cm⁻² and ultra-long stability about 5 days even at 100 mA·cm⁻². In-situ Raman analysis and temperature-programmed desorption (TPD) measurement verify that the presence of the amorphous CrO_x phase can boost the reconstruction from NiO to active NiOOH species and enhance adsorption ability of urea molecule. Besides, the unique crystalline–amorphous interfaces are also benefit to improving the UOR performance.

Co₃O₄ hollow spheres assembled from nanoparticles have been successfully synthesized by a one-pot hydrothermal carbonization and calcination method. In this method, carbon spheres obtained through hydrothermal carbonization at a low temperature of 140 ℃ are used as sacrificial templates. The carbonization process was monitored by Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. Both the carbon sphere soft templates and the NH₃ released from hexamethylenetetramine play key roles in the formation of these novel hollow structures. The formation of the Co₃O₄ hollow spheres using hydrothermal carbon spheres as templates can be attributed to the synergetic effect of metal ion adsorption and heterogeneous nucleation of Co(OH)₂, which is different from the traditional adsorption theory. The as-obtained Co₃O₄ hollow microspheres exhibit excellent cycling performance and good rate capacity when used as electrode materials in supercapacitors, which can be attributed to the small particle size of Co₃O₄ and the sufficient space available to interact with the electrolytes. This facile strategy may be extended to synthesize other metal oxide hollow spheres, which may find application in sensors and catalysts due to their unique structural features.