Twin boundary and grain boundary engineering to enhance mechanical strength of nanotwinned Cu

Thin Cu foils have been adopted for current collectors in lithium-ion batteries. Nickel is commonly employed to strengthen Cu because of its low lattice mismatch with Cu. This study delves into the effect of different concentrations of Ni ions (0.0017-0.5 M) on the strength of electroplated nanotwinned (NT) Cu. Results showed that the Ni ions refined the NT-Cu films, and the optimal Ni concentration of 0.05 M was found, which maximally strengthened the mechanical strength of NT-Cu by 33.3% (up to 743 MPa). We also achieved a high international annealed copper standard (IACS) of up to 79%. Microstructure analysis reveals that the twin spacing was decreased from 70.2 nm to 21.1 nm, and the grain size was reduced from 2.67 mu m to 1.31 mu m when adding 0.05 M Ni ions in the electrolyte. Through linear sweep voltammetry (LSV), we found that the presence of Ni ions causes a negative shift in the reduction overpotential of copper, leading to the grain refinement. Confined layer slip model is also proposed to correlate the theoretical values and experimental results.