Recent progress in flexible energy storage materials for lithium-ion batteries and electrochemical capacitors: A review

Abstract

With the advent of flexible, wearable and portable electronic products, flexible lithium-ion batteries (LIBs) and electrochemical capacitors (ECs), which are able to withstand repeated deformation or bending, have attracted considerable attention as one type of energy-storage device. However, the fabrication of these flexible electrodes is the main bottleneck in the practical utilization and application of these energy-storage devices. Up to now, enormous efforts have been made in addressing the shortcomings and remarkable improvements have also been achieved. So a systematic review of the status and progresses is highly required. In this review, we first make a short introduction about the challenges faced in the conventional batteries and capacitors. Then, we summarize the recent improvements in flexible and wearable LIBs and ECs with a focus on the flexible active materials and substrates. Finally, we discuss the prospects and challenges towards the practical applications of the flexible electrodes in the future.

Hydrothermal Coating of Patterned Carbon Nanotube Forest for Structured Lithium‐Ion Battery Electrodes

“…Hematite is interesting since it can be synthesized by a variety of well‐documented methods; moreover, it is cost effective and can store 1006 mAh g −1 following a conversion reaction Finally, because hematite nanoparticles are synthesized directly onto the CNT backbones, a binder is only needed locally at the base of the CNT structure to secure it on the Cu current collector foil (see Figure A right), which is advantageous compared to the standard battery electrodes, made from a slurry, which have binder throughout the electrode structure (see Figure A left). This allows to create thick electrodes (here 350 µm) where the top part of the battery is binder free to further enhance transport . Electrochemical measurements show that our proposed electrode architecture allows for over a fourfold improvement in lifetime, combined with a twofold improvement in areal loading and excellent utilization of the active materials (gravimetric capacity of ≈912 mAh g −1 ).…”

From Waste to Wealth: From Kraft Lignin to Free-standing Supercapacitors

“…[26] Non-flexible and bulky devices are the consequence of the state-of-the-art electrodes. [28] Replacing these by free-standing and flexible electrodes gives the opportunity to omit current collectors, insulating binders and conductive additives, as free-standing electrodes constitute both the active material and the current collector. [28] Furthermore, building in flexibility would allow energy storage devices to be molded around electrical vehicles or portable electronics, thus significantly reducing their weight and bulk volume.…”

“…[28] Replacing these by free-standing and flexible electrodes gives the opportunity to omit current collectors, insulating binders and conductive additives, as free-standing electrodes constitute both the active material and the current collector. [28] Furthermore, building in flexibility would allow energy storage devices to be molded around electrical vehicles or portable electronics, thus significantly reducing their weight and bulk volume. Indeed, recently, lignin derived carbon nanofiber (CNF) mats were shown to be well-suited as free-standing and even flexible electrodes in SCs.…”

Integrated Thin Film Battery Design for Flexible Lithium Ion Storage: Optimizing the Compatibility of the Current Collector‐Free Electrodes

“…Although the full device was mechanically robust and flexible, the tedious fabrication method did not conform to the industrial slurry‐casting procedures . All the issues mentioned above need to be properly addressed in the development of mechanical flexible energy storage systems with commercially viable processability …”