Design strategy and thermal stability characterization of high-strength nanotwinned Cu-Ni foils

• Systematic control of Ni ion concentration during DC electroplating enables precise tuning of NT-Cu microstructures. • An optimal Ni content (0.05 M) yields NT-Cu foils with tensile strengths exceeding 850 MPa and good ductility. • Different Ni concentrations effectively regulate twin spacing, grain size, and dislocation density. • Thermal stability is maintained after annealing at 300–400 °C, retaining a strength of over 500 MPa and high conductivity. • Comprehensive microstructural analysis by EBSD, KAM, GND, and FIB guides high-performance battery foils. In this study, the microstructure and high-temperature thermal stability of electroplated copper-nickel (Cu-Ni) foils are explored by tuning Ni ion concentrations. The maximum strength of 850.8 MPa was achieved using 0.05 M Ni ions. With 0.1 M, the strength remained above 530 MPa with good ductility after the annealing at 400°C. However, excessive impurities at Ni concentrations over 0.25 M increased void formation during electroplating and potential brittle fractures at high temperatures. Cross-section electron backscattered diffraction (EBSD) was employed to analyze grain size distribution, Kernel average misorientation (KAM), and geometrically necessary dislocation density (ρGND). We comprehensively analyzed Nanotwinned Cu-Ni (NT-Cu-Ni) foils with varying Ni concentrations and provide a detailed examination of the high-temperature mechanical properties associated with each Ni level. This research aims to contribute a new material for lithium batteries.