Energy storage enabled by cross-linked multilayer films using block copolymer-modified nanocapsules and chitosan biopolymers

The silica nanocapsules were functionalized with poly(methacrylic acid)-block-poly(2-acrylamido-2-methylpropanesulfonic acid) (PMAA-b-PAMPS) and assembled with chitosan (CHI) by layer-by-layer deposition and cross-linking to develop lithium electrolyte nanocomposites in the presence of concentrated alkaline solutions. The inorganic/organic nanocapsules and the assembled CHI chains endowed the multilayer films with well-defined structure, great temperature tolerance, and comparable mechanical properties. The films possessed a high loading capacity of alkaline electrolytes. The entrapment of a concentrated alkaline solution in the film matrix led to high ionic conductivity (~ 0.73 mS cm⁻¹ at 25 °C) and outstanding temperature-tolerated capacity. The films maintained a constant ionic conductivity and physical strength against mechanical deformations. For the first time, the impact of molecular weight of block copolymers on electrochemical properties of electrolyte-loaded multilayer films was investigated. The lithium-ion batteries built by flexible alkaline electrolytes of nanocapsule-based multilayer films demonstrated excellent ionic conductivity and electrochemical sustainability, possessing discharge capacity of 163.5 mA h g⁻¹ and retaining 97.53% of the original capacity after 120 cycles. This work demonstrates the first proof-of-concept platform of polymer/nanocapsule composite-incorporated multilayer films with well-defined internal structure and high loading capacity for energy storage. The multilayer films could be adopted as the reliable electrolyte in lithium-ion batteries and introduce enhanced cycling ability and high rate charge–discharge performance.

Graphical abstract

We describe the structure, surface morphology, and electrochemical properties of multilayer films of block copolymer-functionalized silica nanocapsules and chitosan biopolymers via layer-by-layer deposition and cross-linking. The structure and property of the films could be manipulated by controlling the chain length of the block copolymers. In addition, the films could efficiently entrap alkaline solution, demonstrating excellent ionic conductivity and electrochemical sustainability.