Lithium–sulfur (Li–S) batteries hold great promise in the field of power and energy storage due to their high theoretical capacity and energy density. However, the “shuttle effect” that originates from the dissolution of intermediate lithium polysulfides (LiPSs) during the charging and discharging process is prone to causing continuous irreversible capacity loss, which restricts the practical development. Beyond the traditional Li–S batteries based on the dissolution-diffusion mechanism, novel Li–S batteries based on solid-phase conversion exhibit superior cycling stability owing to the absolute prevention of polysulfides shuttling. Radically eliminating the formation of polysulfides in cathodes or cutting off their diffusion in electrolytes are the two main ways to achieve solid-phase conversion. Generally, direct transformation of sulfur to final Li₂S without polysulfides participation tends to occur in short-chain sulfur polymers or special molecular forms of sulfur substances, while specific regulations of liquid electrolytes with solvating structure or solid-state electrolytes can effectively suppressing the polysulfides dissolution. In this review, we systematically organized and summarized the structures and approaches to achieve solid-phase conversion, introduce their preparation methods, discuss their advantages and disadvantages, and analyze the factors and effects of different structures on battery performances. Finally, the problems demanding a prompt solution for the practical development of solid-phase conversion-based Li–S batteries, as well as their future development direction, are suggested.

The thermal stability of the polyethylene (PE) separator is of utmost importance for the safety of lithium-ion batteries. Although the surface coating of PE separator with oxide nanoparticles can improve thermal stability, some serious problems still exist, such as micropore blockage, easy detaching, and introduction of excessive inert substances, which negatively affects the power density, energy density, and safety performance of the battery. In this paper, TiO₂ nanorods are used to modify the surface of the PE separator, and multiple analytical techniques (e.g., SEM, DSC, EIS, and LSV) are utilized to investigate the effect of coating amount on the physicochemical properties of the PE separator. The results show that the thermal stability, mechanical properties, and electrochemical properties of the PE separator can be effectively improved via surface coating with TiO₂ nanorods, but the degree of improvement is not directly proportional to the coating amount due to the fact that the forces inhibiting micropore deformation (mechanical stretching or thermal contraction) are derived from the interaction of TiO₂ nanorods directly “bridging” with the microporous skeleton rather than those indirectly “glued” with the microporous skeleton. Conversely, the introduction of excessive inert coating material could reduce the ionic conductivity, increase the interfacial impedance, and lower the energy density of the battery. The experimental results show that the ceramic separator with a coating amount of ~0.6 mg/cm² TiO₂ nanorods has well-balanced performances: its thermal shrinkage rate is 4.5%, the capacity retention assembled with this separator was 57.1% under 7 C/0.2 C and 82.6% after 100 cycles, respectively. This research may provide a novel approach to overcoming the common disadvantages of current surface-coated separators.