Importantly, the on-demand splitting of the LM composite robots is reversible. To trigger the coalescence process of liquid metal droplets, the system should overcome the energy barrier between two liquid metal droplets that are generated by the surface oxide layer. The oxide layer is in our case removed by the alkaline medium. Afterwards, the coalescence process is a spontaneous process because the liquid metal droplets tend to shrink into spherical shape so as to minimize the surface energy. Upon moving two or more droplets together they merge (coalesce), which is fueled by the high interfacial tension of the liquid metal (and liquid metal oxide), as shown schematically in Figure 4a. Here, the droplets are steered and actuated by a bar magnet located below the acrylic sheet. Upon converging of the two droplets in Figure 4a, the LM-based robots quickly coalesce and the coalescence process is completed in less than 1 second. Moreover, the coalescence of several droplets (see Figure 4b, Movie S3), an array of droplets (see Figure 4c), and a pattern (see Figure 4d) can be done swiftly due to the good precision of the magnetic actuation and the quick coalescence kinetics. This process can be leveraged to remove and recycle the liquid metal-based robots to a high degree.