Unique aqueous Li-ion/sulfur chemistry with high energy density and reversibility

Abstract

Leveraging the most recent success in expanding the electrochemical stability window of aqueous electrolytes, in this work we create a unique Li-ion/sulfur chemistry of both high energy density and safety. We show that in the superconcentrated aqueous electrolyte, lithiation of sulfur experiences phase change from a highorder polysulfide to low-order polysulfides through solid-liquid two-phase reaction pathway, where the liquid polysulfide phase in the sulfide electrode is thermodynamically phase-separated from the superconcentrated aqueous electrolyte. The sulfur with solid-liquid two-phase exhibits a reversible capacity of 1,327 mAh/(g of S), along with fast reaction kinetics and negligible polysulfide dissolution. By coupling a sulfur anode with different Li-ion cathode materials, the aqueous Li-ion/sulfur full cell delivers record-high energy densities up to 200 Wh/(kg of total electrode mass) for >1,000 cycles at ∼100% coulombic efficiency. These performances already approach that of commercial lithium-ion batteries (LIBs) using a nonaqueous electrolyte, along with intrinsic safety not possessed by the latter. The excellent performance of this aqueous battery chemistry significantly promotes the practical possibility of aqueous LIBs in large-format applications.water-in-salt | rechargeable aqueous battery | aqueous sulfur battery | gel polymer electrolyte | phase separation I n the past two decades, rechargeable lithium-ion batteries (LIBs) have revolutionized consumer electronics with their high energy density and excellent cycling stability, and are the state-of-the-art candidates for applications ranging from kilowatt hours for electric vehicles up to megawatt hours for grids (1, 2). The latter applications in large-format present much more stringent requirements for safety, cost, and environmental friendliness, besides energy density and cycle life. The shortcomings of LIB are mostly due to the flammable and toxic nonaqueous electrolytes and moderate energy densities (<400 Wh·kg −1 ) provided by the electrochemical couples currently used (3). Among the various "beyond Li-ion" high-energy chemistries (>500 Wh·kg −1 ) explored currently, the nonaqueous lithium/sulfur (Li/S) battery based on sulfur as a cathode (theoretical capacity of 1,675 mAh·g −1 ) and metallic lithium as an anode seems to be the most practical, as evidenced by the mushrooming literature and significant advances in this system in the past 5 y (4-7). However, commercialization of this system still faces challenges because of severe safety concerns associated with the dendrite growth of metallic Li anode in highly inflammable ether-based electrolytes (8), and the high self-discharge associated with parasitic shuttling of the intermediate polysulfide species. Moreover, the moisture-sensitive nature of the nonaqueous electrolyte would contribute significantly to the cost of the Li/S battery pack due to the stringent moisture-exclusion infrastructure required during the manufacturing, processing, and packaging of the cells. The indispensabl...

Flexible Aqueous Li‐Ion Battery with High Energy and Power Densities

“…The mass loading of electrode materials was ≈5 mg cm −2 . The aqueous gel electrolytes were prepared by dissolving 25 m (mol‐salt in kg‐solvent) LiTFSI (>98%, TCI Co., Ltd.) and 10 wt% PVA (Sigma‐Aldrich) in water (HPLC grade), which was similarly described in previous work . A homogeneous aqueous gel electrolyte formed at 95 °C for 5 h under vigorous stirring.…”

Materials and Device Constructions for Aqueous Lithium–Sulfur Batteries

“…(2) Since elementary sulfur have disadvantages of low electronic and ionic conductivity, a large activation polarization is required for utilization of active materials . The utilization of the discharged product of Li 2 S or short‐chain polysulfide is also very low due to the electronically and ionically insulating natures . That is, the conversion of insoluble short‐chain Li 2 S 2 and Li 2 S into soluble long‐chain polysulfides is very challenging in organic electrolytes during charging because of the energy required for nucleation of the solid‐state phase and the sluggish solid‐state diffusion in the bulk.…”

“…Although the critical technical problems of two aqueous batteries are different, narrow potential window of the aqueous electrolytes is common in both. In a similar manner to the chemical strategy of 4 V ARLIB, water‐in‐salt electrolyte was used to enlarge the potential window of aqueous Li–S batteries . The energy efficiency of Li–S batteries can be improved mitigating voltage hysteresis through fast kinetic reaction and high ionic conductivity of aqueous systems .…”

Advances in Flexible and Wearable Energy‐Storage Textiles

“…Electrodes can be either active materials attaching to current collectors or freestanding active materials, and the capability of storing energy majorly depends on the properties of active materials. Electrolytes are usually solutions with desired ionic conductivity, while recently more and more researchers are focusing on hydrogel electrolytes (quasi‐solid‐state) and solid‐state electrolytes, as the elimination of liquid may help to address the safety issues caused by toxic and flammable solutions, raise the cycle stability, avoid electrolyte leakage, and erase the necessity of separators . Separators are used to separate two electrodes; otherwise, contact of the electrodes will lead to short circuit.…”