Tuning the Electron Density of Aromatic Solvent for Stable Solid‐Electrolyte‐Interphase Layer in Carbonate‐Based Lithium Metal Batteries

Abstract

green electric transportation due to its low redox potential (−3.04 V vs standard hydrogen electrode) and unprecedented theoretical capacity (3860 mAh g −1 or 2060 mAh mL −1 ). [1] In spite of these advantages, a substantial gap remains before practical application due to vulnerable dendritic growth during repeated Li deposition and stripping. Dendrite growth causes indiscriminate electrolyte decomposition and dead Li, resulting in inferior charge-discharge reversibility and ultimately severe capacity fading.Li dendrite growth has been described by two models. One is the "space charge" model. This model focuses on ion depletion at the electrode-electrolyte interface; as current density increases, an ion depletion layer on the electrode surface is formed and thickens. [2] In this interfacial evolution, Sand's time, an onset point where an ion depletion layer begins to form, serves as a useful descriptor. Above this point, due to Li ion depletion, Li ions tend to lose their homogeneous distribution in the bulk electrolyte and are rather concentrated toward local spots (so-called surface "tips") with higher electron densities. While this model well explains the behaviors of dendrite growth at different current densities, those at low current densities below Sand's time are described limitedly.The other model focuses on the "uniformity" of the solidelectrolyte-interphase (SEI) layer with respect to morphology and composition, without taking current density into consideration. [3] This model relies on a viewpoint that in the nonuniform SEI layer, Li ion transport becomes uneven over the electrode area, which accelerates dendrite growth and consequently destroys the SEI layer. Therefore, from this model's perspective, success in suppressing dendrite growth depends largely on the uniformity and durability of the SEI layer.Based on the consensus regarding the importance of a uniform SEI layer, numerous approaches have been introduced, including artificial SEI layers, [4] LiNO 3 additives, [5] vinylene carbonate additives, [6,7] fluoroethylene carbonate additives, [8] polymer electrolytes, [9] and high-concentration electrolytes (HCEs). [10][11][12][13] In the case of artificial SEI layers, while their effect is noticeable in the early cycling period, inevitable Lithium metal has been hailed as a key enabler of upcoming rechargeable batteries with high energy densities. Nonetheless, uncontrolled dendritic growth and resulting formation of a nonuniform solid-electrolyte-interphase (SEI) layer constitute an ever-challenging obstacle in long-term cyclability and safety. So far, these drawbacks have been addressed mainly by using noncarbonate electrolytes based on their relatively mild decomposition under reductive environments. Here, toluene as a co-solvent of carbonate-based electrolytes for lithium metal anodes is reported. The electron-donating nature of the methyl group of toluene shifts the reduction of toluene prior to that of commonly used carbonate solvents, resulting in a more uniform and rigid SEI layer. Moreove...

Lithium‐Salt Mediated Synthesis of a Covalent Triazine Framework for Highly Stable Lithium Metal Batteries

“…Numerous approaches have been proposed to address issues associated with Li‐dendrite growth. A variety of electrolyte additives were introduced, including Cs + and Rb + , ionic liquids, co‐solvents, vinylene carbonate, LiNO 3 and polysulfides . These additives were used to promote stable SEI layers by enhancing the mechanical properties and the Li‐ion diffusivity or manipulating electrostatic fields near the Li electrode surface.…”

“…[2] Numerous approaches have been proposed to address issues associated with Li-dendrite growth. Av ariety of electrolyte additives were introduced, including Cs + and Rb + , [3] ionic liquids, [4] co-solvents, [5] vinylene carbonate, [6] LiNO 3 and polysulfides. [7] These additives were used to promote stable SEI layers by enhancing the mechanical properties and the Li-ion diffusivity or manipulating electrostatic fields near the Li electrode surface.T he addition of lithium fluoride (LiF) was found to be particularly beneficial [8] from the perspective of both, mechanical stability and ionic conductivity.I na na ttempt to enhance the mechanical stability of SEI layers and Li-host structures,m ore recently also elastic polymers were incorporated.…”

An ultrastable lithium metal anode enabled by designed metal fluoride spansules

“…The other approach is to stabilize the SEI. Strategies including the exploitation of electrolyte additives (24)(25)(26)(27)(28), artificial protection layers (29)(30)(31)(32), and solid-state electrolytes (4,(33)(34)(35)(36) have been developed to regulate and modify the physicochemical properties of the Li/electrolyte interface (37), leading to uniform Li + ion flux distribution and thus stable Li electroplating. At present, most reported protocols, however, only focused on either inducing uniform Li nucleation or stabilizing the SEI.…”

Lithium Metal Interface Modification for High‐Energy Batteries: Approaches and Characterization

“…In a recent study, Yoo et al suggested aromatic compounds with different functional groups as electrolyte solvents for the formation of a stable SEI layer in carbonatebased Li metal batteries. [203] To form a uniform and rigid SEI layer on the Li metal, the study used the bonding characteristics of benzene rings that do leading to polymeric branch structures in polymerization after initiating itself due to being three double bonds resonance. In addition, three different aromatic compounds, benzene (Ben), toluene (Tol), and trifluorotoluene (Tof), were chosen for the study because the electron density determined by the functional group attached to the benzene group was found to influence the polymerization, as shown in Figure 11a.…”