A Ni-coated 3D steel sheet, at a quarter of the cost of conventional Ni foam, was designed as a substrate for the positive electrode of a nickel/metal hydride battery. A new thin positive electrode was developed using this substrate, and the electrochemical properties were investigated. The thin positive electrode using the Ni-coated 3D sheet and polystyrene acrylic acid ester (PSA) as a binder maintained a discharge capacity of more than 80% of initial capacity even after 1000 cycles in cycle test under 25 degrees C, which was comparable to the Ni foam electrode. However, the electrode showed capacity fade after 180 cycles in cycle test under 45 degrees C, because of the decomposition of PSA. The results of Fourier transform IR analysis indicated that styrene-maleic acid resin (SMA) had high stability in alkaline solution at high temperatures and was more suitable as a binder than PSA. A new battery for hybrid electric vehicles (HEVs) was developed using the thin positive electrode with the Ni-coated 3D sheet and SMA. The power density of the new battery achieved 1055 W/kg, compared with 480 W/kg for the conventional one. In the HEV mode cycle test, both the capacity and the power output of the cell remained at more than 80% of the initial value even after 25,000 cycles. (c) 2005 The Electrochemical Society.