Dendrite-Suppressing Polymer Materials for Safe Rechargeable Metal Battery Applications: From the Electro-Chemo-Mechanical Viewpoint of Macromolecular Design

Covalent Organic Frameworks for Separator Modification of Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are regarded as one of the promising energy storage systems. However, rapid capacity attenuation caused by shuttle effect of soluble polysulfides is major challenge in practical application. The separator modification is regarded as one countermeasure besides the construction of sulfur host materials. Covalent organic frameworks (COFs) are one type of outstanding candidates for suppressing shuttle effect of polysulfides. Herein, recent advances of COFs in the application as commercial separator modifiers are summarized. COFs serve as ionic sieves, the importance of porous size and surface environments in inhibiting soluble polysulfides shuttling and promoting lithium ions conduction is highlighted. The superiority of charge-neutral COFs, ionic COFs, and the composites of COFs with conductive materials for improving reversible capacity and cycling stability is demonstrated. Some new strategies for the design of COF-based separator modifiers are proposed to achieving high energy density. The review provides new perspectives for future development of high-performance Li-S batteries.

Regulating Na Electrodeposition by Sodiophilic Grafting onto Porosity-Gradient Gel Polymer Electrolytes for Dendrite-Free Sodium Metal Batteries

Sodium metal batteries have been emerging as promising candidates for post-Li battery systems owing to the natural abundance, low costs, and high energy density of Na metal. However, exploiting an Na metal anode is accompanied by uncontrolled Na electrodeposition, particularly concerning dendrite growth, hampering practical Na metal battery applications. Herein, we propose sodiophilic gel polymer electrolytes with a porosity-gradient Janus structure to alleviate Na dendrite growth. Tethering only 1.1 mol % sodiophilic poly(ethylene glycol) to poly(vinylidene fluoride-co-hexafluoropropylene) suppresses Na dendrites by regulating homogeneous Na⁺ distribution, which relies on molecular-level coordination between Na⁺ and the sodiophilic functional groups. By exploiting the porosity-gradient Janus structure, we have demonstrated that regular porosity and well-defined morphology of polymer electrolytes, particularly at the Na/electrolyte interface, significantly impact dendrite growth. This study provides new insights into the rational design of Na dendrite-suppressing polymer electrolytes, primarily focusing on the ion-regulating ability achieved by surface engineering.

Hydrogels Enable Future Smart Batteries

The growing trend of intelligent devices ranging from wearables and soft robots to artificial intelligence has set a high demand for smart batteries. Hydrogels provide opportunities for smart batteries to self-adjust their functions according to the operation conditions. Despite the progress in hydrogel-based smart batteries, a gap remains between the designable functions of diverse hydrogels and the expected performance of batteries. In this Perspective, we first briefly introduce the fundamentals of hydrogels, including formation, structure, and characteristics of the internal water and ions. Batteries that operate under unusual mechanical and temperature conditions enabled by hydrogels are highlighted. Challenges and opportunities for further development of hydrogels are outlined to propose future research in smart batteries toward all-climate power sources and intelligent wearables.

Photo-Crosslinked Single-Ion Conducting Polymer Electrolyte for Lithium-Metal Batteries

Polymer electrolytes are considered potential key enablers for lithium-metal batteries due to their compatibility with the lithium-metal negative electrode. Herein, crosslinked selfstanding single-ion conducting polymer electrolytes were obtained via a facile UVinitiated radical polymerization using pentaerythritol tetraacrylate as the crosslinker and lithium (3methacryloyloxypropylsulfonyl)-(trifluoromethylsulfonyl)imide as ionic functional group. Incorporating propylene carbonate as charge-transport supporting additive allowed for achieving single-ion conductivities of 0.21 mS cm^-1 at 20°C and 0.40 mS cm^-1 at 40°C, while maintaining a suitable electrochemical stability window for 4V-class positive electrodes (cathodes). As a result, this single-ion polymer electrolyte featured good cycling stability and rate capability in Li||LiFePO₄ and Li||LiNi_0.6 Mn_0.2 Co_0.2 O₂ cells. These results render this polymer electrolyte as potential alternative to liquid electrolytes for high-energy lithium-metal batteries. This article is protected by copyright. All rights reserved.

Development and Progression of Polymer Electrolytes for Batteries: Influence of Structure and Chemistry

Polymer electrolytes continue to offer the opportunity for safer, high-performing next-generation battery technology. The benefits of a polymeric electrolyte system lie in its ease of processing and flexibility, while ion transport and mechanical strength have been highlighted for improvement. This report discusses how factors, specifically the chemistry and structure of the polymers, have driven the progression of these materials from the early days of PEO. The introduction of ionic polymers has led to advances in ionic conductivity while the use of block copolymers has also increased the mechanical properties and provided more flexibility in solid polymer electrolyte development. The combination of these two, ionic block copolymer materials, are still in their early stages but offer exciting possibilities for the future of this field.