Uniform Li Deposition through the Graphene-Based Ion-Flux Regulator for High-Rate Li Metal Batteries.

Lithium (Li) metal is considered an ultimate anode owing to its high specific capacity and energy density. However, uncontrolled Li dendrite growth and low Coulombic efficiency have limited the application of Li metal. Among various strategies introduced to address these limitations, the surface modification of polyolefin separators with functional materials has been widely adopted for improving the mechanical and thermal stabilities of polymer separators and to protect the separator from the penetration of Li dendrites. Herein, we report a new functional polymer separator that is surface-altered with a graphene-based Li-ion flux regulator (GLR) to homogenize the Li-ion flux and suppress the growth of sharp dendritic Li in Li metal batteries. The nanopores distributed through the GLR structure serve as channels for ion transport and junctions for electron transfer, facilitating efficient electrolyte penetration and rapid charge transfer between graphene (Gr) sheets. Owing to these favorable features of porous GLR, a Li-Cu cell with the GLR surface-altered polypropylene separator (GLR-PP) delivers excellent cycle and rate performances compared to a Li-Cu cell with a Gr surface-altered polypropylene separator. In addition, among the tested cells, Li-sulfur cells with GLR-PP exhibit the most stable cycle performance over 500 cycles. These results demonstrate that the concept of tailoring the surface of a polymer separator with porous 2D materials is an effective strategy for improving the long-term cycle stability and electrochemical kinetics of Li metal-based batteries and would trigger further relevant studies.

Considering cell volume in dopant screening for improving Li-ion mobility in an amorphous LiPON solid-state electrolyte: an ab initio study.

Engineering of solid electrolytes of Li-ion batteries is carried out for achieving high levels of ionic conductivity and preserving low levels of electrical conductivity. Doping metallic elements into solid electrolyte materials composed of Li, P, and O is quite challenging due to instances of possible decomposition and secondary phase formation. To accelerate the development of high-performance solid electrolytes, predictions of thermodynamic phase stabilities and conductivities are necessary, as they would avoid the need to carry out exhaustive trial-and-error experiments. In this study, we demonstrated theoretical approach to increase the ionic conductivity of amorphous solid electrolyte by doping: cell volume-ionic conductivity relation. Using density functional theory (DFT) calculations, we examined the validity of the hypothetical principle in predicting improvements in stability and ionic conductivity with 6 candidate doping elements (Si, Ti, Sn, Zr, Ce, Ge) in a quaternary Li-P-O-N solid electrolyte system (LiPON) both in crystalline and amorphous phases. The doping of Si into LiPON (Si-LiPON) was indicated to stabilize the system and enhance ionic conductivity based on our calculated doping formation energy and cell volume change. The proposed doping strategies provide crucial guidelines for the development of solid-state electrolytes with enhanced electrochemical performances.

Size Effect of a Piezoelectric Material as a Separator Coating Layer for Suppressing Dendritic Li Growth in Li Metal Batteries.

Li metal has been intensively investigated as a next-generation rechargeable battery anode. However, its practical application as the anode material is hindered by the deposition of dendritic Li. To suppress dendritic Li growth, introducing a modified separator is considered an effective strategy since it promotes a uniform Li ion flux and strengthens thermal and mechanical stability. Herein, we present a strategy for the surface modification of separator, which involves coating the separator with a piezoelectric material (PM). The PM-coated separator shows higher thermal resistance than the pristine separator, and its modified surface properties enable the homogeneous regulation of the Li-ion flux when the separator is punctured by Li dendrite. Furthermore, PM was synthesized in different solvents via solvothermal method to explore the size effect. This strategy would be helpful to overcome the intrinsic Li metal anode problems.

A Strategic Approach to Use Upcycled Si Nanomaterials for Stable Operation of Lithium-Ion Batteries.

Silicon, as a promising next-generation anode material, has drawn special attention from industries due to its high theoretical capacity (around 3600 mAh g-1) in comparison with conventional electrodes, e.g., graphite. However, the fast capacity fading resulted by a large volume change hinders the pragmatic use of Si anodes for lithium ion batteries. In this work, we propose an efficient strategy to improve the cyclability of upcycled Si nanomaterials through a simple battery operation protocol. When the utilization degree of Si electrodes was decreased, the electrode deformation was significantly alleviated. This directly led to an excellent electrochemical performance over 100 cycles. In addition, the average charge (delithation) voltage was shifted to a lower voltage, when the utilization degree of electrodes was controlled. These results demonstrated that our strategic approach would be an effective way to enhance the electrochemical performance of Si anodes and improve the cost-effectiveness of scaling-up the decent nanostructured Si material.

Surface-Functionalized Separator for Stable and Reliable Lithium Metal Batteries: A Review.

Metallic Li has caught the attention of researchers studying future anodes for next-generation batteries, owing to its attractive properties: high theoretical capacity, highly negative standard potential, and very low density. However, inevitable issues, such as inhomogeneous Li deposition/dissolution and poor Coulombic efficiency, hinder the pragmatic use of Li anodes for commercial rechargeable batteries. As one of viable strategies, the surface functionalization of polymer separators has recently drawn significant attention from industries and academics to tackle the inherent issues of metallic Li anodes. In this article, separator-coating materials are classified into five or six categories to give a general guideline for fabricating functional separators compatible with post-lithium-ion batteries. The overall research trends and outlook for surface-functionalized separators are reviewed.