Construction of a flexible, integrated rechargeable Li battery based on a coaxial anode with a carbon fiber core encapsulated in FeNiMnO₄ and a nitrogen-doped carbon sheath

A coaxial anode with a carbon fiber core encapsulated in nanocrystalline FeNiMnO₄ with a nitrogen-doped carbon sheath was prepared using carbon fiber cloth as the core, FeNiMnO₄ nanocrystallite arrays as the first coating layer and nitrogen-doped carbon derived from F127 (a kind of triblock copolymer)-resorcinol-melamine gel as the outer layer. After annealing at 600 °C it was used as the anode material of an all solid flexible lithium ion battery using LiFePO₄ as the cathode material and boron nitride modified polyethylene oxide as the electrolyte. The battery had a large areal capacity of ～1.40 mAh cm⁻² and satisfactory cycling stability under different bending and strain states. Annealing below 600 °C leads to incomplete carbonization of the nitrogen-doped carbon and thus a low electrical conductivity while above 600 °C aggregation of FeNiMnO₄ nanocrystallites and their detachment during cycling are observed under bending and strain.