Polymer Zwitterion-Based Artificial Interphase Layers for Stable Lithium Metal Anodes

Applications of Zwitterions and Zwitterionic Polymers for Li-Ion Batteries

A zwitterion is a neutral compound that has both a cation and an anion in the same molecule. Quaternary ammonium cations are frequently used for zwitterions. Zwitterions with quaternary ammonium cations are also common in biological molecules, such as phospholipids, which are the main components of cell membranes. Chemically, they have broad applicability because they are dielectric, non-volatile, and highly polar compounds with a large dipole moment. In addition, after salt addition, ion exchange does not occur in the presence of zwitterions. Owing to these characteristics, zwitterions have been applied as novel electrolyte materials targeting high ionic conductivity. In this review, application of zwitterions and their polymers for Li-ion batteries is addressed.

Mixed Ion/Electron Conductive Li3N-Mo Interphase Enabling Stable and Ultrahigh-Rate Lithium Metal Anodes

Lithium (Li) metal is a promising anode for high-energy-density batteries; however, its practical viability is hampered by the unstable metal Li-electrolyte interface and Li dendrite growth. Herein, a mixed ion/electron conductive Li₃N-Mo protective interphase with high mechanical stability is designed and demonstrated to stabilize the Li-electrolyte interface for a dendrite-free and ultrahigh-current-density metallic Li anode. The Li₃N-Mo interphase is simultaneously formed and homogeneously distributed on the Li metal surface by the surface reaction between molten Li and MoN nanosheets powder. The highly ion-conductive Li₃N and abundant Li₃N/Mo grain boundaries facilitate fast Li-ion diffusion, while the electrochemically inert metal Mo cluster in the mosaic structure of Li₃N-Mo inhibits the long-range crystallinity and regulates the Li-ion flux, further promoting the rate capability of the Li anode. The Li₃N-Mo/Li electrode has a stable Li-electrolyte interface as manifested by a low Li overpotential of 12 mV and outstanding plating/stripping cyclability for over 3200 h at 1 mA cm^-2. Moreover, the Li₃N-Mo/Li anode inhibits Li dendrite formation and exhibits a long cycling life of 840 h even at 30 mA cm^-2. The full cell assembled with LiFePO₄ cathode exhibits stable cycling performance with 87.9% capacity retention for 200 cycles at 1C (1C = 170 mA g^-1) as well as high rate capability of 83.7 mAh g^-1 at 3C. The concept of constructing a mixed ion/electron conductive interphase to stabilize the Li-electrolyte interface for high-rate and dendrite-free Li metal anodes offers a viable strategy to develop high-performance Li-metal batteries.

Achieving Electronic Engineering of Vanadium Oxide-Based 3D Lithiophilic Sandwiched-Aerogel Framework for Ultrastable Lithium Metal Batteries

Lithium (Li) metal is one of the most promising anode materials for the next-generation batteries, which owns superior specific capacity and energy density. Unfortunately, lithium dendrites that is formed during the charging/discharging process tends to induce capacity degradation and thus short lifespan. In this study, the vanadium oxide (V2O5) and nitrogen-doped vanadium oxide (N-V2O3, N-VO0.9)-modified three-dimensional (3D) reduced graphene oxide ((N)-VOx@rGO) with tunable electronic properties are demonstrated to enable the dendrite-free Li deposition. The soft lithiophilic rGO as the scaffold can provide sufficient void space for Li storage. Meanwhile, the rigid (N)-VOx uniformly anchored on rGO can perfectly maintain the 3D structure, which is crucial for Li to enter the inner space of the 3D framework. Consequently, the (N)-VOx@rGO electrodes achieve dendrite-free electrodeposition under the multifarious deposition capacity and current densities. Compared with the bare lithium electrodes, the asymmetrical cells of (N)-VOx@rGO anode can cycle stably up to 400 h at 2 mA cm-2 current density, together with a low nucleation overpotential of ∼20 mV.

Combining Polymer Zwitterions and Zinc Oxide for High Performance Inverted Organic Solar Cells

Zinc oxide (ZnO) is a widely used cathode interlayer material in inverted organic solar cells (OSCs). However, there are lots of surface or bulk film defects in ZnO layers, which degrades solar cell performance. Here, the typical phosphorylcholine- and sulfobetaine-based polymer zwitterions (PMPC and PDMAPS) were synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization to modify ZnO interlayers for inverted OSCs. The polymer zwitterions can efficiently passivate the defects in ZnO films and thus increase the conductivity of the ZnO interlayers. Both PMPC and PDMAPS modified ZnO interlayers show some general advantages on improving the performance of fullerene-based and non-fullerene-based OSCs. A highest efficiency of 16.69% was achieved by using PMPC modified ZnO interlayers in PM6:Y6 based solar cell devices, which is among the best performance in inverted OSCs. Such an improvement on device performance is attribute to the work function reduction of the polymer zwitterions modified ZnO films, which provides an efficient cathode platform to extract and transport electrons from the active layers, to the benefit of suppressing interfacial charge recombination. As a result, the organic-inorganic hybrid composites (ZnO: polymer zwitterions) show efficient interfacial modification to align energy-levels at the device interface, which have promising application prospects in organic electronics. This article is protected by copyright. All rights reserved.

One-Pot Preparation of Lithium Compensation Layer, Lithiophilic Layer, and Artificial Solid Electrolyte Interphase for Lean-Lithium Metal Anode

Lithium metal is an ideal anode for high-energy-density batteries. However, the low Coulomb efficiency and the generation of dendrites pose a significant limitation to its practical application, while the excess lithium in the battery also generates serious safety concerns. Herein, a layer-by-layer optimized multilayer structure integrating an artificial solid electrolyte interphase (LiF) layer, a lithiophilic (Li_xAu alloy) layer, and a lithium compensation layer is reported for a lean-lithium metal battery, where each layer acts synergistically to stabilize the lithium deposition behaviors and enhances the cycling performance of the battery. The optimized anode could effectively induce homogeneous reversible lithium deposition under the synergistic effect of multilayer films and keep the integrity of the morphological structure unbroken during the deposition. The presence of the lithium compensation layer allows the half-cell to have a high initial CE of 158.9%, and the action of the LiF layer and lithiophilic layer maintains an average CE of 98.8% over 160 cycles, which further demonstrates the stability of the structure. As a result, when combined with LiFePO₄ cathode, an initial capacity of 148 mAh g^-1 and a retention rate of 97.5% over 130 cycles were achieved.

Ternary-Salt Solid Polymer Electrolyte for High-Rate and Long-Life Lithium Metal Batteries

Ternary-salt solid polymer electrolyte (TS-SPE) consisting of LiPF6-LiTFSI-LiFSI salts and poly(1,3-dioxolane) is created by in-situ polymerization. The TS-SPE possesses high ionic conductivity, high Li+ ion transference number, and stable SEI...