Ultrahigh Performance All Solid-State Lithium Sulfur Batteries: Salt Anion’s Chemistry-Induced Anomalous Synergistic Effect

Abstract

With a remarkably higher theoretical energy density compared to lithium-ion batteries (LIBs) and abundance of elemental sulfur, lithium sulfur (Li-S) batteries have emerged as one of the most promising alternatives among all the post LIB technologies. In particular, the coupling of solid polymer electrolytes (SPEs) with the cell chemistry of Li-S batteries enables a safe and high-capacity electrochemical energy storage system, due to the better processability and less flammability of SPEs compared to liquid electrolytes. However, the practical deployment of all solid-state Li-S batteries (ASSLSBs) containing SPEs is largely hindered by the low accessibility of active materials and side reactions of soluble polysulfide species, resulting in a poor specific capacity and cyclability. In the present work, an ultrahigh performance of ASSLSBs is obtained via an anomalous synergistic effect between (fluorosulfonyl)(trifluoromethanesulfonyl)imide anions inherited from the design of lithium salts in SPEs and the polysulfide species formed during the cycling. The corresponding Li-S cells deliver high specific/areal capacity (1394 mAh g, 1.2 mAh cm), good Coulombic efficiency, and superior rate capability (∼800 mAh g after 60 cycles). These results imply the importance of the molecular structure of lithium salts in ASSLSBs and pave a way for future development of safe and cost-effective Li-S batteries.

Plating/Stripping Behavior of Actual Lithium Metal Anode

“…

density. [6] Various methods have been proposed, such as nonaqueous electrolyte optimization (solvent, [7] Li salt, [8] anion, [9] and additives [10] ), ex situ interfacial modifications, [11] highly concentrated electrolyte, [12] solid-state electrolyte, [13] Li metal hosts, [14,15] and 3D current collectors. [4] However, dendrite growth on Li metal anode along with its unstable interface against electrolytes result in safety concerns, low utilization, and a short lifespan of Li metal anode, severely impeding the implementation of Li metal batteries (LMBs).

…”

“…[4] However, dendrite growth on Li metal anode along with its unstable interface against electrolytes result in safety concerns, low utilization, and a short lifespan of Li metal anode, severely impeding the implementation of Li metal batteries (LMBs). [6] Various methods have been proposed, such as nonaqueous electrolyte optimization (solvent, [7] Li salt, [8] anion, [9] and additives [10] ), ex situ interfacial modifications, [11] highly concentrated electrolyte, [12] solid-state electrolyte, [13] Li metal hosts, [14,15] and 3D current collectors. [6] Various methods have been proposed, such as nonaqueous electrolyte optimization (solvent, [7] Li salt, [8] anion, [9] and additives [10] ), ex situ interfacial modifications, [11] highly concentrated electrolyte, [12] solid-state electrolyte, [13] Li metal hosts, [14,15] and 3D current collectors.…”

“…The detailed stripping process of Li dendrites can be observed form Figure S4 in the Supporting Information, where active Li is gradually dissolved, leaving dead Li wrapped by corrugated solid electrolyte Adv. 2019, 9,1902254 interphase (SEI, Figure S4d, Supporting Information). 2019, 9,1902254 interphase (SEI, Figure S4d, Supporting Information).…”

“…A three-electrode test is conducted with S-Li, P-Li, and a Li wire as the working, counter, and reference electrode, respectively. 2019, 9,1902254 first cycle leads to a much larger initial stripping voltage. In the first cycle of S-Li, the initial stripping voltage is ≈300 mV ( Figure S6a, Supporting Information), which is much higher compared to that of the following cycles (<50 mV).…”

“…2019,9, 1902254 The Li stripping preferentially starts from the deposited Li dendrites(Figure 1d 1 ,d 2andFigure S3c, Supporting Information), while bulk Li participates at the end of stripping to compensate the Adv.…”