Mechanistic Investigation of Polymer‐Based All‐Solid‐State Lithium/Sulfur Battery

Abstract

Although employing solid polymer electrolyte (SPE) in all-solid-state lithium/ sulfur (ASSLS) batteries is a promising approach to obtain a power source with both high energy density and safety, the actual performance of SPE-ASSLS batteries still lag behind conventional lithium/sulfur batteries with liquid ether electrolyte. In this work, combining characterization methods of X-ray photoelectron spectroscopy, in situ optical microscopy, and three-electrode measurement, a direct comparison between these two battery systems is made to reveal the mechanism behind their performance differences. In addition to polysulfides, it is found that the initial elemental sulfur can also dissolve into and diffuse through the SPE to reach the anode. Different from the shuttle effect that causes uniform corrosion on the anode in a liquid electrolyte, dissolved sulfur species in SPE unevenly passivate the anode surface and lead to the inhomogeneous Li + plating/stripping at the anode/SPE solid-solid interface. Such inhomogeneity eventually causes void formation at the interface, which leads to the failure of SPE-ASSLS batteries. Based on this understanding, a protection interlayer is designed to inhibit the shuttling of sulfur species, and the modified SPE-ASSLS batteries show much-improved performance in cycle life.

Perspective of polymer-based solid-state Li-S batteries

“…Generally, ASSPEs composed of lithium salts, polymer matrices and/or solid additives have been considered as some of the most appealing candidates to replace LEs due to their high safety, excellent flexibility and processability, and superior physical contact with the electrodes, in contrast to inorganic-based solid electrolytes [20] . Among all the different polymer matrices, poly(ethylene oxide) (PEO) is the most prevailing choice for developing ASSPE-based Li-S batteries, owing to its superior solvation ability, excellent mechanical properties, low cost and facile processability [21][22][23][24][25] . In PEO-based ASSPEs, lithium salts are dissociated and solvated by Lewis-base ether units (i.e., ethylene oxide) and the transportation of lithium cations is associated with the segmental motion of PEO chains by intrachain and/or interchain hopping [26] .…”

High-Efficiency Hybrid Sulfur Cathode Based on Electroactive Niobium Tungsten Oxide and Conductive Carbon Nanotubes for All-Solid-State Lithium–Sulfur Batteries

“…ASSLSBs have a different discharge/charge mechanism from traditional liquid Li–S batteries. − Usually, a single discharge/charge voltage platform can be observed in ASSLSBs, corresponding to the direct conversion from sulfur into lithium disulfide. , Therefore, LiPS could not be produced in ASSLSBs, ensuring high cycling stability . Furthermore, ASSLSBs have good safety and high energy density at the same time. , In order to exert excellent performance of ASSLSBs, the development of suitable solid-state electrolytes and high-efficiency cathode materials are particularly important. Among all the solid-state electrolytes, sulfide electrolytes not only have high ionic conductivity but also excellent ductility, which can be well used in ASSLSBs. − However, the utilization of sulfur and electrochemical capacity of the cathode are not satisfactory.…”

“…40 Furthermore, ASSLSBs have good safety and high energy density at the same time. 41,42 In order to exert excellent performance of ASSLSBs, the development of suitable solid-state electrolytes and high-efficiency cathode materials are particularly important. Among all the solid-state electrolytes, sulfide electrolytes not only have high ionic conductivity but also excellent ductility, which can be well used in ASSLSBs.…”

Fluoride-Rich Solid Electrolyte Membrane in Solid-State Li–S Batteries: Improvement of Lithium Cycle Stability and Shuttle Effects

“…The side reactions at the interface deteriorated the performance of Li–S batteries . A large interfacial impedance was then generated and led to irreversible degradation of the battery capacity. , What is worse, the other side reactions generated by the reductive nature of lithium reduced the stability of the electrode interface, which deteriorated the battery life through a complex mechanism. − The failure mechanism of the SPE solid-state Li–S batteries (SSLSBs) was more complex than in liquid Li–S batteries . The key point lies in the anode–SPE interface, including the parasitic reactions between LiPSs and Li, uneven Li + plating/stripping, and nonideal contact of the solid–solid interface.…”