The intermetallic Cu6Sn5 is ubiquitous in electronic interconnects where research has focused on controlling the size and distribution of this phase for improved performance. Cu6Sn5 also finds application as an anode material for advanced lithium-ion batteries. Cu6Sn5 anodes can be fabricated via an in-situ growth method involving the reaction between molten Sn and the Cu current collector. This manufacturing route offers some advantages over traditional anode fabrication however the process is slow, limiting its practical application. In this work we show the addition of 6 wt% Ni to the Cu current collector greatly accelerates the growth of (Cu,Ni)6Sn5 in Cu-xNi/Sn solid-melt couples, leading to a growth rate of up to 50x faster, reducing the processing time above 200 °C to less than 10 min. This research studies the dynamics of the formation of (Cu,Ni)6Sn5 between Cu-xNi alloys and liquid Sn through real-time observation using synchrotron X-ray imaging. The (Cu,Ni)6Sn5 growth dynamics are characterised, and the growth kinetics are analysed. Subsequently, the mechanism of the accelerated growth is investigated with electron backscatter diffraction and transmission electron microscopy. The results show the accelerated growth is due to the formation of η-(Cu,Ni)6Sn5 grains with two distinct Ni concentration ranges, leading to finer grains and spalling, which in turn facilitates the diffusion of Sn, enhancing the η-(Cu,Ni)6Sn5 formation kinetics.