Chongyin Yang, Liumin Suo, Oleg Borodin, Fei Wang, Wei Sun, Tao Gao, check out ORCID ProfileXiulin Fan, Singyuk Hou, Zhaohui Ma, Khalil Amine, Kang Xu, and also Chunsheng Wang
bromheads.tv June 13, 2017 114 (24) 6197-6202; very first published might 31, 2017; https://doi.org/10.1073/bromheads.tv.1703937114

Edited by cutting board E. Mallouk, The Pennsylvania State University, university Park, PA, and approved may 9, 2017 (received for testimonial March 8, 2017)


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Significance

Sulfur as an anode coupled through a lithium-ion intercalation cathode in the superconcentrated aqueous electrolyte create a distinct Li-ion/sulfur chemistry, realizing the greatest energy thickness ever accomplished in aqueous batteries, along with high safety and also excellent cycle-life. Mechanism examination finds that the reversible sulfur lithiation/delithiation in together an aqueous electrolyte proceeds with rapid kinetics that substantially differ from the in nonaqueous systems, conversely, polysulfides’ insolubility in such an aqueous electrolyte essentially eliminates the parasitic shuttling. The fantastic performances that Li-ion/sulfur cells no only discover an application of “water-in-salt” electrolyte for beyond Li-ion chemistries, an ext importantly, an different pathway is detailed to fix the “polysulfide shuttling” that has been plaguing the sulfur chemistries in nonaqueous electrolytes.

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Abstract

Leveraging the most recent success in expanding the electrochemical stability home window of aqueous electrolytes, in this work we develop a unique Li-ion/sulfur chemistry that both high energy density and also safety. We show that in the superconcentrated aqueous electrolyte, lithiation that sulfur experiences phase adjust from a high-order polysulfide come low-order polysulfides through solid–liquid two-phase reaction pathway, where the fluid polysulfide step in the sulfide electrode is thermodynamically phase-separated from the superconcentrated aqueous electrolyte. The sulfur with solid–liquid two-phase exhibits a reversible volume of 1,327 mAh/(g of S), along with fast reaction kinetics and negligible polysulfide dissolution. Through coupling a sulfur anode with different Li-ion cathode materials, the aqueous Li-ion/sulfur complete cell it is provided record-high power densities as much as 200 Wh/(kg of complete electrode mass) for >1,000 cycles at ∼100% coulombic efficiency. This performances already approach the of commercial lithium-ion battery (LIBs) utilizing a nonaqueous electrolyte, together with intrinsic safety and security not own by the latter. The great performance of this aqueous battery chemistry significantly promotes the useful possibility that aqueous LIBs in large-format applications.


In the past two decades, rechargeable lithium-ion batteries (LIBs) have actually revolutionized consumer electronics through their high power density and excellent cycle stability, and are the modern candidates for applications ranging from kilowatt hrs for electrical vehicles as much as megawatt hrs for grids (1, 2). The last applications in large-format current much an ext stringent needs for safety, cost, and also environmental friendliness, besides energy density and cycle life. The shortcomings of LIB are mostly due to the flammable and toxic nonaqueous electrolytes and also moderate energy densities (−1) noted by the electrochemical couples currently used (3). Among the assorted “beyond Li-ion” high-energy chemistries (>500 Wh⋅kg−1) explored currently, the nonaqueous lithium/sulfur (Li/S) battery based upon sulfur together a cathode (theoretical volume of 1,675 mAh⋅g−1) and also metallic lithium together an anode seems to it is in the most practical, as shown by the mushrooming literature and far-reaching advances in this system in the previous 5 y (4⇓⇓–7). However, commercialization of this system still encounters challenges because of severe safety and security concerns linked with the dendrite expansion of metallic Li anode in extremely inflammable ether-based electrolytes (8), and also the high self-discharge associated with helminth shuttling the the intermediate polysulfide species. Moreover, the moisture-sensitive nature the the nonaqueous electrolyte would certainly contribute significantly to the cost of the Li/S battery pack because of the stringent moisture-exclusion facilities required during the manufacturing, processing, and packaging that the cells. The indispensable equipment for safety and thermal administration would further drive increase the cost.

Replacement the the nonaqueous electrolyte by its aqueous counterpart is constantly tantalizing, because it would essentially remove safety, toxicity, and also at least part of the cost pertains to (9⇓–11). In particular, broad electrochemical stability windows (>3.0 V) similar to those that nonaqueous electrolytes have been freshly demonstrated by water-in-salt (WiS) and also water-in-bisalt (WiBS) electrolytes. V water molecule still far outnumbering the of Li salts, this course of totally nonflammable WiS and also WiBS electrolytes realized a dramatic innovation in safety, when placing numerous Li-ion and even past Li-ion chemistries in ~ the with of aqueous electrolytes (12, 13). Historically, it has been very complicated to use elemental sulfur together the cathode material in aqueous electrolytes, primarily due to the fact that of the high solubility that short-chain lithium polysulfide (Li2Sx, x 2S in aqueous media, and also the strong parasitic shuttling reaction emerging thereafter (14). A compromise method used aqueous equipment of lithium polysulfide as the liquid energetic cathode (catholyte), yet only 61% that the theoretical capacity was accessed in the Li2S4/Li2S redox pair (15⇓–17). The hydrogen evolution in this aqueous system and the side reaction in between the Li2S4/Li2S and H2O have to be suppressed to attain high coulombic efficiency. A Li steel anode deserve to be used, yet only after a thick Li-ion-conducting ceramic great is engineered on the Li surface ar to prevent Li dendrite formation and also prevent the reaction the Li anode indigenous aqueous catholyte (17).

However, the report electrochemical stability windows the the superconcentrated aqueous electrolytes (WiS, WiBS) to be >3.0 V, with cathodic and also anodic boundaries located in the vicinity of ∼1.9 V and also ∼4.9 V vs. Li, respectively. This home window would comfortably envelop the lithiation/delithiation reactions of high-capacity sulfur materials at the anode next and change metal oxide products at the cathode side. The electrochemical coupling that a sulfur anode and an intercalation cathode would certainly thus create a new cell chemistry there is no Li metal, i m sorry is based upon Li+ intercalation/deintercalation in ~ the cathode, and also conversion reaction of sulfur varieties at anode. This Li-ion/sulfur chemistry (Li+/S) can supply theoretic energy densities up to 260 Wh·kg−1, and also combines the high capacities of a cheap sulfur anode and mature LIB cathode, and also the intrinsic safety and security of an aqueous electrolyte. Added benefits include substantial cost palliation at the battery module or load level, via removed of moisture-free facilities for processing and fabrication, and the feasible simplification the the safety and security management.

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In this work, we show this highly reversible aqueous Li+/S chemistry using a simple sulfur/carbon composite together the anode and LiMO (LiMn2O4 and LiCoO2) together the cathodes. With in situ and also ex situ spectroscopic way during electrochemical reactions, the distinctive lithiation/delithiation device of sulfur in WiBS electrolyte to be revealed to proceed reversibly in a solid liquid phase. A total of 80% (1,327 mAh⋅g−1) of sulfur theoretical volume (1,675 mAh⋅g−1) was accessed with excellent reversibility, as confirmed by volume retention of 86% for 1,000 cycles. This superior performance is attributed come the step separation of S/polysulfide solid–liquid step from high-concentration aqueous electrolytes, wherein the liquid WiBS electrolyte functions in a comparable manner together solid electrolyte in isolating the polysulfide varieties generated in ~ anode native LiMO cathodes, hence eliminating the helminth shuttlings that have actually been plaguing the nonaqueous Li/sulfur chemistry. When the sulfur anode to be paired with common LIB cathode products like LiMn2O4 or high-voltage LiCoO2, energy densities that 135∼200 Wh⋅kg−1 were ceded at complete cell level. These findings imply that safety, cost, environmental considerations, and energy thickness requirements can be simultaneously completed by the aqueous Li+/S battery for large-scale applications, such together smart-grid warehouse or automotive power systems.