A high efficiency electrolyte enables robust inorganic-organic solid electrolyte interfaces for fast Li metal anode

Operando insights into ammonium-mediated lithium metal stabilization: surface morphology modulation and enhanced SEI development

Lithium-ion batteries (LiBs) with graphite as an anode and lithiated transition metal oxide as a cathode are approaching their specific energy and power theoretical values. To overcome the limitations of LiBs, lithium metal anode with high specific capacity and low negative redox potential is necessary. However, practical application in rechargeable cells is hindered by uncontrolled lithium deposition manifesting, for instance, as Li dendrite growth which can cause formation of dead Li, short circuits and cell failure. The electrochemical behaviour of a protic additive (NH4PF6) in a carbonate-based electrolyte has been investigated by operando confocal Raman spectroscopy, in situ optical microscopy, and X-ray photoelectron spectroscopy, elucidating its functional mechanism. The ammonium cation promotes a chemical modification of the lithium metal anode-electrolyte interphase by producing an N-rich solid electrolyte interphase and chemically modifying the lithium surface morphology by electrochemical pitting. This novel method results in stable lithium deposition and stripping by a decreasing the local current density on the electrode, thus limiting dendritic deposition.

High concentration in situ polymer gel electrolyte for high performance lithium metal batteries

A high concentration gel polymer electrolyte (GPE) was prepared by simply using LiFSI-LiNO3 dissolved in 1,3-dioxolane. The Li‖Li cell achieves stable battery cycling for over 3200 h. Furthermore, the Li‖Cu cell demonstrates a high CE of 99.2%. Even at a high current density of 8 mA cm-2, a high CE of 98.5% was still achieved. Notably, in a Li‖LiFePO4 cell, this electrolyte enables high capacity retention of 94.5% and an average CE of 99.8% over 500 cycles, showing promising prospects for high-performance lithium metal batteries.

Hybrid-Electrolytes System Established by Dual Super-lyophobic Membrane Enabling High-Voltage Aqueous Lithium Metal Batteries

Aqueous electrolytes and related aqueous rechargeable batteries own unique advantage on safety and environmental friendliness, but coupling high energy density Li-metal batteries with aqueous electrolyte still represent challenging and not yet reported. Here, this work makes a breakthrough in "high-voltage aqueous Li-metal batteries" (HVALMBs) by adopting a brilliant hybrid-electrolytes strategy. Concentrated ternary-salts ether-based electrolyte (CTE) acts as the anolyte to ensure the stability and reversibility of Li-metal plating/stripping. Eco-friendly water-in-salt (WiS) electrolyte acts as catholyte to support the healthy operation of high-voltage cathodes. Most importantly, the aqueous catholyte and non-aqueous anolyte are isolated in each independent chamber without any crosstalk. Aqueous catholyte permeation toward Li anode can be completely prohibited without proton-induced corrosion, which is enabled by the introduction of under-liquid dual super-lyophobic membrane-based separator, which can realize the segregation of the most effective immiscible electrolytes with a surface tension difference as small as 6 mJ m-2. As a result, the aqueous electrolyte can be successfully coupled with Li-metal anode and achieve the fabrication of HVALMBs (hybrid-electrolytes system), which presents long-term cycle stability with a capacity retention of 81.0% after 300 cycles (LiNi0.8Mn0.1Co0.1O2 || Li (limited) cell) and high energy density (682 Wh kg-1).

In Situ Polymerization Derived from PAN-Based Porous Membrane Realizing Double-Stabilized Interface and High Ionic Conductivity for Lithium-Metal Batteries

Polymer polyacrylonitrile (PAN), with exceptional mechanical strength and ionic conductivity, is considered a potential electrolyte. However, the huge interfacial impedance of PAN-derived C≡N polar nitrile groups and Li anode limited its application. In this study, a double-stabilized interface was integrated by in situ polymerization of DOL between electrodes and a three-dimensional (3D) porous PAN polymer matrix containing SN plasticizer and LLZTO ceramic fillers to optimize the challenge of interfacial instability. The fabricated PDOL-PAN(SN/LLZTO)-PDOL composite solid electrolyte (CSE) exhibited the maximum ionic conductivities of 1.9 × 10-3 S cm-1 at room temperature and 2.5 × 10-3 S cm-1 at 60 °C, an electrochemical stability window (ESW) of 4.9 V, and a high Li+ transference number (tLi+) of 0.65. In addition, the side reactions of the PAN/Li metal were effectively prevented by inserting PDOL between the 3D porous membrane and Li electrode. Benefiting from the superior interface compatibility and ion conductivity, the Li symmetric battery showed more than 2000 h of cyclability. The solid Li/LiFePO4 full battery delivered excellent cycling performance, showing an original specific capacity of 136.2 mAh g-1 with a capacity retention of 90.1% after 350 cycles at 1C and 60 °C. Furthermore, the cycling of solid-state Li/NCM622 batteries also proved their application potential. This work presents an effective approach to solving interface problems of the PAN electrolyte for solid lithium-metal batteries (LMBs).

Protecting Li-metal in O2 atmosphere by a sacrificial polymer additive in Li-O2 batteries

Li-O2 batteries (LOBs) with Li-metal as the anode are characterized by their high theoretical energy density of 3500 W h kg-1 and are thus considered next-generation batteries with an unlimited potential. However, upon cycling in a harsh O2 atmosphere, the poor-quality solid electrolyte interphase (SEI) film formed on the surface of the Li-metal anode cannot effectively suppress the shuttle effect from O2, superoxide species, protons, and soluble side products. These issues lead to aggravated Li-metal corrosion and hinder the practical development of LOBs. In this work, a polyacrylamide-co-polymethyl acrylate (PAMMA) copolymer was innovatively introduced in an ether-based electrolyte as a sacrificial additive. PAMMA was found to preferentially decompose and promote the formation of a dense and Li3N-rich SEI film on the Li-metal surface, which could effectively prohibit the shuttle effect from a series of detrimental species in the Li-O2 cell during the discharge/charge process. Using PAMMA, well-protected Li-metal in a harsh O2 atmosphere and significantly enhanced cycling performance of the Li-O2 cell could be achieved. Thus, the use of a sacrificial polymer additive provides a promising strategy for the effective protection of Li-metal in Li-O2 cells in a severe O2 atmosphere during practical applications.

An artificial interfacial layer with biomimetic ionic channels towards highly stable Li metal anodes

Lithium (Li) metal with low electrochemical potential and high theoretical capacity is a promising anode material for next-generation batteries. However, the low reversibility and safety problems caused by the notorious dendrite growth significantly impede the development of high-energy-density lithium metal batteries (LMBs). Here, to enable a dendrite-free and highly reversible Li metal anode (LMA), we develop a cytomembrane-inspired artificial layer (CAL) with biomimetic ionic channels using a scalable spread coating method. The negatively charged CAL with uniform intraparticle and interparticle ionic channels facilitates the Li-ion transport and redistributes the Li-ion flux, contributing to stable and homogeneous Li stripping and plating. Furthermore, a robust underneath transition layer with abundant lithiophilic inorganic components is in-situ formed through the transformation of CAL during cycling, which promotes Li-ion diffusion and suppresses the continuous side reactions with the electrolyte. Additionally, the resulting cytomembrane-inspired artificial Janus layer (CAJL) displays an ultrahigh Young's modulus (≥10.7 GPa) to inhibit the dendrite growth. Consequently, the CAJL-protected LMA (Li@CAJL) is stably cycled with a high areal capacity of 10 mAh cm^-2 at a high current density of 10 mA cm^-2. More importantly, the effective CAJL modification realizes the stable operation of a practical 429.2 Wh kg^-1 lithium-sulfur (Li-S) pouch cell using a low electrolyte/sulfur (E/S) ratio of 3 μL mg^-1. The facile yet effective protection strategy of LMAs can promote the practical application of LMBs.

Covalent Organic Frameworks and Their Derivatives for Better Metal Anodes in Rechargeable Batteries

Metal anodes based on a plating/stripping electrochemistry such as metallic Li, Na, K, Zn, Ca, Mg, Fe, and Al are recognized as promising anode materials for constructing next-generation high-energy-density rechargeable metal batteries owing to their low electrochemical potential, high theoretical specific capacity, superior electronic conductivity, etc. However, inherent issues such as high chemical reactivity, severe growth of dendrites, huge volume changes, and unstable interface largely impede their practical application. Covalent organic frameworks (COFs) and their derivatives as emerging multifunctional materials have already well addressed the inherent issues of metal anodes in the past several years due to their abundant metallophilic functional groups, special inner channels, and controllable structures. COFs and their derivatives can solve the issues of metal anodes by interfacial modification, homogenizing ion flux, acting as nucleation seeds, reducing the corrosion of metal anodes, and so on. Nevertheless, related reviews are still absent. Here we present a detailed review of multifunctional COFs and their derivatives in metal anodes for rechargeable metal batteries. Meanwhile, some outlooks and opinions are put forward. We believe the review can catch the eyes of relevant researchers and supply some inspiration for future research.