Honeycomb carbon fibers strengthened composite phase change materials for superior thermal energy storage

•Thermal conductive property of paraffin was enhanced by honeycomb carbon fibers.•Honeycomb carbon fiber bundles were prepared from biomass sisal.•The composite PCM presented a high thermal conductivity of 1.77 W m−1 k−1.•The composite PCM showed an anisotropic and high thermal conductivity along the fiber direction.•The composite exhibit good form-stability and high thermal capacity.