Molecular/Ionic Designs in the Electrolyte and Interphases for Lithium Metal Anode

Abstract

The undesirable interactions between the charge carriers (Li + ) and various objects in the special microenvironment of batteries would cause uneven lithium (Li) metal deposition behavior, which severely impedes the application of Li metal batteries (LMBs). In recent years, many works focus on optimizing these interactions by functional molecules/ions modification. Nevertheless, related reviews are still absent. Here, this review introduces the regulation methods of Li metal deposition from molecular/ionic designs, which is a new perspective including Li + flux homogenization, the de-solvation process regulation, optimizing the solid electrolyte interphase (SEI) in conventional solvation structure and anion-rich solvation structure. Also, the general design principles are studied in each mechanism and some suggestions are proposed in the prospective future directions, aiming to guide the development of molecular/ionic designs and the actual application of LMBs with high energy densities.

Position‐Responsive SEI Layer in Bicomponent‐Bidirectional Gradient Current Collector Induces Homogenized Ion Flux for Highly Reversible Li Metal Anode

“…To study the reasons for the great differences in CE between different current collectors, the Li metal deposition behavior was investigated and different amounts of Li metal were electrodeposited into Cu, TCC, GCC, and BGCC at 1 mA cm −2 . For the Cu foil, uneven and porous deposition was observed, stemming from the poor lithophilicity and tip effect of Cu foil ( Figure a,b) [ 3 ] This results in low CE values and poor cycling stability of the bare Cu foil. TCC showed a more uniform deposition behavior of Li metal due to the ability to reduce the local current density.…”

“…Metallic Li has recently regained interest with its alluring properties of ultra-high theoretical specific capacity (3860 mAh g −1 ) and extremely low redox potential (−3.04 V vs standard hydrogen electrodes) in rechargeable batteries. [1][2][3][4] Especially, when matched with high-voltage cathodes and carbonate-based electrolytes, the higher-energy-density Li metal batteries (LMBs) will be made possible. [5,6] However, the poor reversibility and safety hazards are still the main obstacles limiting the commercial application of LMBs.…”

Recent advances in robust and ultra‐thin Li metal anode

“…However, the naturally formed SEI layer in the carbonate electrolyte is generally composed of Li 2 O, Li 2 CO 3 , and LiF with low ionic conductivity, where the desolvated Li + is hard to migrate through the SEI layer, leading to large polarization as well as rapid Li + depletion at the interface with the formation of needle-like Li dendrite. [40][41][42] According to the diffusion-reaction competition model proposed by Zhang's group, [43] Li deposition with a highly ion-conductive SEI exhibits a reaction-controlled behavior with uniform local current density and spherical morphology, while harder diffusion of Li + across the slow SEI is a diffusion dominated step, inducing dendrite nucleation and growth around the dendrite tips (Figure 4b). This mechanism can be further quantitatively evaluated by using the second Damköhler (D a ) number…”

Solid Electrolyte Interphase on Lithium Metal Anodes

“…Moreover, the presence of LiBr effectively reduces the diffusion barrier for Li + within the SEI film. As a result, the LiFePO 4 |Li battery is able to operate stably for over 1200 cycles at 1 C. Additionally, an increase in the concentration of lithium salt leads to a majority of large solvent molecules and anions coordinating with Li + , forming contact ion pairs and aggregate clusters, effectively facilitating their reduction at the anode [121] …”