Electrochemical preparation of free-standing carbon-nanotube/Sn composite paper

•Single-walled carbon nanotube (SWCNT) paper was used as the current collector.•Effect of additives on Sn electrodeposition behavior was studied.•Electrodeposition proceeded only on SWCNT surface at the absence of additive.•The use of formaldehyde and polyethylene glycol led to SWCNT/Sn composite.•Submicron-sized Sn particles were homogeneously distributed in the composite. Toward achieving Li-ion batteries with high energy density, SWCNT/Sn composite paper was electrochemically prepared and the addition effect of formaldehyde (HCHO) and polyethylene glycol (PEG) on Sn electrodeposition morphology was studied. PEG improved the wettability of electroplating bath to enable inhomogeneous Sn embeddedness inside SWCNT paper, and HCHO delivered more nuclear growth. The synergetic effect resulted in a composite paper in which Sn particles with several-hundred nanometer order were distributed. Compared with a commercially-available Cu foil (18 μm-thickness) with 32 mg at 2 cm2 (φ 16 mm), the weight of the SWCNT paper (5 mg) is one sixth of that of the Cu foil. The dramatic reduction of the component greatly contributes to the increase in energy density of batteries.