Dear Colleagues,

Batteries have been a game-changing development in the way we consider electrical energy storage. The development of lithium-ion batteries for nomadic electronics, to electric automobiles and grid storage is accelerating exponentially further. With the intrinsic limitation of LIBs getting closer, there is intensive research on next-generation storage.

Polymers are ubiquitous in today’s batteries. The housing of pouch cells is made of metal–plastic laminates that provide flexibility and imperviousness to air and humidity while avoiding the evaporation of solvents. The electrolyte, a mixture of organic carbonates + LiPF₆ is soaked into a separator, a sophisticated microporous membrane with the use of both PP and PE to offer the function of shutdown. Electrode materials are used as composite materials with carbon addition to allow electron exchange, and the mixture is held together as a coating with a binder, either a water-soluble ionomer (CMC) at the negative side or highly oxidation-resistant PVDF at the positive.

However, an increasing fraction of the research goes toward polymer electrolytes, i.e., a replacement of the liquid-based salt solution and the separator by a macromolecular membrane to which the addition of a salt (Li, Na) confers ionic conductivity. The first identification of a suitable polymer host came in the late 1970s, with poly(ethylene oxide) (PEO) for which a set of metal salts were later identified (LiTFSI, LiFSI) in replacement of hazardous LiClO₄. Due to the crystallinity of PEO and the sluggishness of chain reorientation at T_g, for the required conductivity (10^‑4 Scm^‑1), it is necessary to warm the system to 70°C. The great advantage of PEO-based electrolytes is the possible harnessing of the lithium metal electrode. In fact, the company Blue Solutions has been equipping cars and now buses (Daimler) with all solid-state batteries with the Li°//LiFePO₄ electrode pair. The safety of the system is above criticism, and the life reaches 3000 cycles.

In the last ten years, new polymer hosts have been identified, mostly polyesters and poly(carbonates). The immediate advantage is the high stability at positive potentials (≥ 4.3V), a weak point of PEO-based systems that oxidize at ≥ 3.9 V, i.e., below the potential of operation of layered oxides. Polyesters and poly(carbonates), however, are not stable vs. Li metal, and double layer electrolytes have to be used. 

This Special Issue welcomes original research and reviews based on synthesis characterization or implementation of polymers or copolymers, composite polymers for electrodes; composite solid polymers electrolytes; and gel polymer electrolytes for next-generation energy storage.

Prof. Dr. Peter G. Bruce
Prof. Dr. Loïc Dupont
Prof. Dr. Michel Armand
Guest Editors

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• lithium-ion batteries
• electrode
• polymer electrolyte
• composite solid polymers
• electrolyte
• copolymers
• gel electrolyte
• conductive polymers
• separator