Non-encapsulation approach for high-performance Li–S batteries through controlled nucleation and growth

118

anodes. These new anodes promise an almost 100% increase in practical energy density compared to those of conventional LIB counterparts. [3][4][5][6][7][8][9] While developing cathodes for the next-generation batteries has made a significant progress, relatively fewer research efforts have thus far been devoted to Li metal anodes because of the formation of Li dendrites which is considered a critical drawback instigating devastating safety issues of batteries. [10] Along with recent studies on Li plating behaviors, there have been renewed interests in developing Li metal anodes. [11][12][13] In particular, the dendrite-free Li metal anode was made possible by rationally designing the electrolyte composition and electrode morphologies. [14,15] Nevertheless, the current Li metal anodes are far from being viable because of several reasons. Namely, (1) the dendritic Li emerges when the current density raises above the percolation value; (2) the Coulombic efficiencies (CEs) of Li metal anodes are too low to maintain good cyclic stability of batteries; and (3) the design of Li metal anodes is still inadequate, making it difficult to integrate into the existing LIB configurations, such as pouch and cylindrical cells. [12] Most of the strategies currently exercised for dendrite-free Li metal anodes usually fail to resolve all the above mentioned issues. For example, the all-solid-state Li-metal battery requires certain prestress to reduce the interfacial resistance between the solid-state electrolyte and the electrode, but such a prestress is difficult to apply on pouch cells. [16,17] The feasibility of artificial solid electrolyte interphase (SEI) protection on Li foil remains doubtful because the Li foil alone cannot be used as current collector in practical cells due to its hostless nature and huge volume changes during the repeated cycles. [11,18] Among all potential strategies, the incorporation of conductive substrates to function as both the Li host and current collector is considered an ideal approach for further development of practical Li metal anodes. [19] The growth of Li dendrites at high current densities was mitigated by means of reduced local current densities using conductive substrates. [12] Moreover, the conductive substrates also functioned as the current collector, which is compatible with the existing LIB configurations. While copper has been widely studied as the matrix material for hosting Li metal, carbon is considered a more promising candidate than copper Carbonaceous materials are widely employed to host Li for stable and safe Li metal batteries while relatively little effort is devoted to tailoring the surface properties of carbon to facilitate uniform Li plating. Herein, the correlation between Li plating behavior and the surface characteristics of electrospun porous carbon nanofibers (PCNFs) is systemically elucidated through experiments and theoretical calculations. It is revealed that the neat carbon surface suffers from severe lattice mismatch with Li metal, hindering uniform Li plating....

Section: Plating Behavior In the Presence Of Poressupporting

confidence: 93%

Correlation between Li Plating Behavior and Surface Characteristics of Carbon Matrix toward Stable Li Metal Anodes

Cui

Yao

Ihsan‐Ul‐Haq

et al. 2018

118

“…[1] Electrochemical reduction of solid sulfur (S 8 ) by lithium ions to form lithium sulfide (Li 2 S) yields a gravimetric energy (2600 Wh kg S −1 ) higher than today's Li-ion batteries. [1d,3] The morphology and structure of the solid Li 2 S product are key factors determining the achievable discharge capacity, [4] rate capability, [5] active materials utilization and reversibility of sulfur-based energy storage. [1d,3] The morphology and structure of the solid Li 2 S product are key factors determining the achievable discharge capacity, [4] rate capability, [5] active materials utilization and reversibility of sulfur-based energy storage.…”

Section: Introductionmentioning

confidence: 99%

“…

such as silicene [9a] and ionic compounds [10a] were shown to speed up the Li 2 S lateral passivation rate, leading to lower capacities.

Solvent has a strong impact on Li 2 S deposition. Recently, Pan et al [4] reported that solvents with medium donor number (DN) yield flower-like Li 2 S morphology, low-DN solvents make Li 2 S films, and high-DN solvents give rise small particles. [6a] In addition, the use of discharge mediator was reported to slow down the impingement of insulating Li 2 S islands on carbon and transform the 2D growth to a 3D growth.

…”

mentioning

confidence: 99%

Solvent‐Mediated Li₂S Electrodeposition: A Critical Manipulator in Lithium–Sulfur Batteries

Zhou

et al. 2018

293

244

such as silicene [9a] and ionic compounds [10a] were shown to speed up the Li 2 S lateral passivation rate, leading to lower capacities.Solvent has a strong impact on Li 2 S deposition. The kinetics and morphology of Li 2 S deposition in glyme-based polysulfide solutions was studied and a progressive nucleation and a 2D island growth model was proposed. [6a] In addition, the use of discharge mediator was reported to slow down the impingement of insulating Li 2 S islands on carbon and transform the 2D growth to a 3D growth. [11] This is in line with Cuisinier et al. [12] reporting a distinct Li 2 S deposition mechanism in electron pair donor electrolytes compared to glymes due to the partial solvation of Li 2 S and the additional chemical pathways provided by the increased stabilization of polysulfide radicals. Recently, Pan et al. [4] reported that solvents with medium donor number (DN) yield flower-like Li 2 S morphology, low-DN solvents make Li 2 S films, and high-DN solvents give rise small particles. These pioneering studies suggest that the solution mediation process plays a critical role in Li 2 S deposition and highlight the urgent need for developing quantitative and comprehensive correlation between solvent property and Li 2 S nucleation and growth.In this work, we establish structure-property relationship of solvent in controlling solid Li 2 S deposition and develop quantitative solvent-mediated Li 2 S growth models as guides to solvent selection. We investigate three solvent's properties and their roles on Li 2 S deposition: (1) the donicity which governs the stability of the polysulfide anions (i.e., the precursor of Li 2 S deposition) through (Li + ) sol -polysulfide interactions; [12,13] (2) the polarity (dielectric constant) which governs the solvation ability of the final product Li 2 S; [14] (3) the viscosity which strongly affects the diffusivity of polysulfide and dissolved Li 2 S. [15] We show that these solvent-controlled properties are essential factors pertaining to the sulfur utilization, electrode kinetics, and reversibility of electrochemical reduction of elemental sulfur. Finally, we demonstrate the effectiveness of the solvent selection criteria developed in this study in identifying new and more effective electrolytes for Li-S batteries. Results and DiscussionWe study Li 2 S deposition in electrolyte model systems of two major groups: (i) ether-based solvents: 1,2-dimethoxyethane (G1), diethylene glycol dimethyl ether (G2), triethylene glycol Controlling electrochemical deposition of lithium sulfide (Li 2 S) is a major challenge in lithium-sulfur batteries as premature Li 2 S passivation leads to low sulfur utilization and low rate capability. In this work, the solvent's roles in controlling solid Li 2 S deposition are revealed, and quantitative solventmediated Li 2 S growth models as guides to solvent selection are developed. It is shown that Li 2 S electrodeposition is controlled by electrode kinetics, Li 2 S solubility, and the diffusion of polysulfide/Li 2 S, which is dictated...

“…[38] Furthermore, the slow redox reactions can cause the aggregation of solid sulfur species on the electrode surface, resulting in disconnecting of sulfur-species from the conductive networks (deadsulfur). [40] Accelerating the liquid-solid transformation not only enables a more complete reaction (higher SU L ), but also reduces the LiPSs shuttle by consuming the long-chain LiPSs before it migrates to the anode-leading to a superior cycling performance. [40] Accelerating the liquid-solid transformation not only enables a more complete reaction (higher SU L ), but also reduces the LiPSs shuttle by consuming the long-chain LiPSs before it migrates to the anode-leading to a superior cycling performance.…”

mentioning

confidence: 99%

Sandwich‐Like Ultrathin TiS₂ Nanosheets Confined within N, S Codoped Porous Carbon as an Effective Polysulfide Promoter in Lithium‐Sulfur Batteries

Huang

Tang

Luo

et al. 2019

214

112

lithium-sulfur, sodium-, magnesium-, and aluminum-based batteries. [2] Among these competitors, lithium-sulfur battery (LSB) is a promising candidate since the earth-abundant sulfur has a high theoretical capacity of 1675 mAh g −1 and LSB provides a high theoretical energy density of 2600 Wh kg −1 or 2800 Wh l −1 . [3] Nevertheless, the practical application of LSB is still limited by the poor electric/ionic conductivity of sulfur and the "shuttle effect" caused by the dissolution and diffusion of lithium polysulfides (LiPSs), resulting in an uncompetitive capacity, rate performance, and cycling life. [4] To address these issues, intensive studies have been done, such as cathode design, separator modification, electrolyte optimization, and anode protection. [5] LiPSs immobilization and LiPSs ↔ Li 2 S 2 /Li 2 S conversion acceleration are two major considerations for LSB cathode design. [6] The anchoring and catalyzing effect of various candidates (such as metal oxides/sulfide/nitride) have been investigated by first principle calculations [7] or quantitative adsorption experiments. [8] Although some species show strong chemical interactions with LiPSs or effective catalysis on the conversion reaction, battery performances have been largely restrained by the poor electronic/ionic conductivity As the lightest member of transition metal dichalcogenides, 2D titanium disulfide (2D TiS 2 ) nanosheets are attractive for energy storage and conversion. However, reliable and controllable synthesis of single-to few-layered TiS 2 nanosheets is challenging due to the strong tendency of stacking and oxidation of ultrathin TiS 2 nanosheets. This study reports for the first time the successful conversion of Ti 3 C 2 T x MXene to sandwich-like ultrathin TiS 2 nanosheets confined by N, S co-doped porous carbon (TiS 2 @NSC) via an in situ polydopamine-assisted sulfuration process. When used as a sulfur host in lithium-sulfur batteries, TiS 2 @NSC shows both high trapping capability for lithium polysulfides (LiPSs), and remarkable electrocatalytic activity for LiPSs reduction and lithium sulfide oxidation. A freestanding sulfur cathode integrating TiS 2 @NSC with cotton-derived carbon fibers delivers a high areal capacity of 5.9 mAh cm −2 after 100 cycles at 0.1 C with a low electrolyte/sulfur ratio and a high sulfur loading of 7.7 mg cm −2 , placing TiS 2 @NSC one of the best LiPSs adsorbents and sulfur conversion catalysts reported to date. The developed nanospace-confined strategy will shed light on the rational design and structural engineering of metal sulfides based nanoarchitectures for diverse applications.