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...

Expediting redox kinetics of sulfur species by atomic‐scale electrocatalysts in lithium–sulfur batteries

“…However, the insulating end‐redox products (S/Li 2 S) and massive lithium polysulfide migration impose great kinetic challenges to fully realize energy‐dense Li–S batteries . The complex S/Li 2 S deposition and accumulation on the conductive scaffolds render high barriers for both charge and mass transport, especially under high sulfur loading and low electrolyte/sulfur ratio conditions . Therefore, propelling sulfur redox kinetics and mediating Li 2 S precipitation constitute grand challenges to achieve robust Li–S batteries.…”

“…11,12 The complex S/Li 2 S deposition and accumulation on the conductive scaffolds render high barriers for both charge and mass transport, especially under high sulfur loading and low electrolyte/sulfur ratio conditions. [13][14][15][16] Therefore, propelling sulfur redox kinetics and mediating Li 2 S precipitation constitute grand challenges to achieve robust Li-S batteries.…”

A Selection Rule for Hydrofluoroether Electrolyte Cosolvent: Establishing a Linear Free‐Energy Relationship in Lithium–Sulfur Batteries

“…For these new battery systems to be successful, it is critical to develop reliable electrolytes and to understand their working principles . First introduced as an electrolyte cosolvent a decade ago, hydrofluoroethers (HFEs) have rapidly been employed by researchers all over the world to construct functional electrolytes for high‐voltage lithium‐ion, lithium‐metal, lithium–sulfur (Li–S), lithium–air, lithium/selenium–sulfur, and even sodium‐ion batteries . Because of their low solvating ability, HFEs are exceptionally versatile as electrolyte cosolvents.…”

A Selection Rule for Hydrofluoroether Electrolyte Cosolvent: Establishing a Linear Free‐Energy Relationship in Lithium–Sulfur Batteries

“…[4][5][6] Va rious new lithium-battery systems with high theoretical energy density have been proposed. [8,9] First introduced as an electrolyte cosolvent ad ecade ago, [10] hydrofluoroethers (HFEs) have rapidly been employed by researchers all over the world to construct functional electrolytes for high-voltage lithium-ion, [10][11][12] lithium-metal, [13] lithium-sulfur (Li-S), [14] lithium-air, [15,16] lithium/selenium-sulfur, [17] and even sodium-ion batteries. [8,9] First introduced as an electrolyte cosolvent ad ecade ago, [10] hydrofluoroethers (HFEs) have rapidly been employed by researchers all over the world to construct functional electrolytes for high-voltage lithium-ion, [10][11][12] lithium-metal, [13] lithium-sulfur (Li-S), [14] lithium-air, [15,16] lithium/selenium-sulfur, [17] and even sodium-ion batteries.…”

“…[5][6][7] Fort hese new battery systems to be successful, it is critical to develop reliable electrolytes and to understand their working principles. [8,9] First introduced as an electrolyte cosolvent ad ecade ago, [10] hydrofluoroethers (HFEs) have rapidly been employed by researchers all over the world to construct functional electrolytes for high-voltage lithium-ion, [10][11][12] lithium-metal, [13] lithium-sulfur (Li-S), [14] lithium-air, [15,16] lithium/selenium-sulfur, [17] and even sodium-ion batteries. [18,19] Because of their low solvating ability,H FEs are exceptionally versatile as electrolyte cosolvents.T hey offer several important advantages: 1) enhanced oxidative stability of electrolytes, [10][11][12] 2) they serve as excellent thinning reagents for reducing the viscosity of electrolytes, [20][21][22] and 3) they enable the construction of localized concentrated electrolytes,which are highly useful in lithium-metal batteries.…”