Development and Challenges of Functional Electrolytes for High‐Performance Lithium–Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries, as one of the most important candidates of next-generation batteries, are famous for high energy density, low cost, and environmental friendly benignity. However, issues originating from polysulfide shuttle of common liquid electrolytes (e.g., capacity fade, poor cycle life, and safe issue) have hindered the applications of Li-S batteries in various occasions. This review summarizes the main efforts in the electrolytes of Li-S batteries, including liquid, solid state, and hybrid electrolyte systems. The development of functional electrolytes for Li-S batteries is hopeful to alleviate the problems Li-S batteries faced today. The liquid electrolytes circumvent the polysulfide shuttle and the resultant problems by utilizing different functional solvents, lithium salts, and additives. Solid-state electrolytes as promising electrolytes are optimized to enhance the ionic conductivity at room temperature and decrease the interfacial resistance. Hybrid electrolytes that consist of two or more single electrolytes may be considered as unique categories because they have the potential advantages than the single electrolyte systems. Challenges and perspectives of Li-S electrolytes are also proposed based on the requirement for high-performance Li-S batteries.be reduced to short-chain ones, which subsequently migrate back to cathode and are reoxidized to long-chain lithium polysulfide intermediates. This endless movement and shuttle of polysulfides between cathode and anode is generally called as polysulfide shuttle. During cycling, the shuttle effect of polysulfides continuously occurs and results in lower Coulombic efficiency and anode corrosion. [3a,4,5] c) Safety issues: the electrolyte solvents may be not stable when the high reactivity of lithium metal and the soluble polysulfides are present, which results in the gradual depletion of solvents and the gas expansion of batteries. [6] High flammable organic solvents increase safety hazard, when used under high-temperature conditions. [7] Moreover, the growth of lithium dendrites can potentially penetrate the separator, which leads to internal short circuits of batteries and serious safety issues. [8] In order to overcome the issues mentioned above and improve battery performance, some strategies have been examined, including the design of sulfur cathodes, [4,9] the protection of lithium anode, [10] and the optimization of electrolytes. [11] The electrolyte between cathode and anode is a crucial component as it affects the lithium-ion transport during the cycling process, which in part determines the batteries performance. [12] Electrolyte development is time consuming because it requires high-throughput experiment but is indispensable. Some works have therefore focused on the development of functional electrolyte in the last several years. Different roads lead to the same thing that usable electrolytes should possess many characters, such as high ionic transport, low viscosity, good chemical and electrochemical stability, nonflammab...

The Synergistic Catalytic Effect of 2D Ultrathin Fe 2 O 3 ‐Fe 3 O 4 Heterointerface on Lithium Polysulfides

“…The S 2p XPS spectrum revealed a significant increase in the intensity of sulfate‐related peaks. This result provided related evidence for the catalytic generation of sulfates and sulfides during the LiPS conversion, confirming their positive role in promoting redox mediation processes at the catalyst interface [23].…”

Realizing an Applicable “Solid → Solid” Cathode Process via a Transplantable Solid Electrolyte Interface for Lithium–Sulfur Batteries

“…CMK-3 has uniform mesopores with the size of 2.5–4.3 nm (Figure S1a) and large pore volume of 1.36 cm 3 g –1 (Figure S1b), ensuring a high S loading capability. In the previous reports, the CMK-3/S cathode can only work in the ether-based electrolyte because of the side reactions between the carbonate solvent and the nucleophilic PS. − In our case, CMK-3 can unify the particle size of the insulative S to afford a decent electrochemical accessibility. Meanwhile, a high-concentration dual-salt electrolyte with carbonate solvent is chosen to form the SEI on the cathode.…”

Dissolution–Crystallization Transition within a Polymer Hydrogel for a Processable Ultratough Electrolyte

“…It is clear that the ionic conductivities of the composite gels decrease with increasing NaAc mass ratio. However, as shown in Figure e, the lowest ionic conductivity 0.1 S m −1 of A 15 D 0 –NaAc 1.6 is still higher than that of most nonliquid electrolytes . The hydration layer around NaAc crystals due to precipitation–dissolution equilibrium in Figure S9 in the Supporting Information provides an aligned ion migration channel along the needle‐like crystals, similar to the aligned pores structure within hydrogel electrolyte .…”