LiCoO₂-Based Fiber Cathodes for Electrospun Full Cell Li-ion Batteries

Particle/polymer electrospinning was used to prepare fiber mat cathodes containing LiCoO₂ nanoparticles, carbon powder, and poly(vinylidene fluoride) for Li-ion batteries. The fibers had a high LiCoO₂ particle content (70 wt%) which allowed for a high gravimetric capacity of 90 mAh g⁻¹ (corresponding to 128 mAhg_LiCoO2⁻¹) at 0.1C (1C = 274 mAhg_LiCoO2⁻¹). Cathode performance was stable in a half cell with 78% capacity retention over 200 cycles at 0.5C. Unlike previous work on electrospun LiCoO₂ nanofibers prepared using sol-gel chemistry and high temperature processing, the particle/polymer fiber mat cathodes reported here were made thick with a high fiber volume fraction for high areal and volumetric capacities at fast charge/discharge rates (e.g., 0.81 mAh cm⁻² and 62 mAh cm⁻³ at 2C) which were much greater than that of a slurry cast cathode of the same composition (0.004 mAh cm⁻² and 0.30 mAh cm⁻³ at 2C). Full cells containing a LiCoO₂/C/PVDF fiber mat cathode and C/PVDF fiber mat anode were also prepared and characterized. These electrospun batteries exhibited a high energy density of 144 Wh kg⁻¹ at 0.1C and an areal capacity of 1.03 mAh cm⁻² at 1C. The excellent performance of the electrospun particle/polymer cathodes and anodes is attributed to electrolyte penetration throughout the 3D fiber electrode mats, a large electrode/electrolyte interfacial area, and short Li⁺ transport pathways between the electrolyte and active material nanoparticles in the radial fiber direction.