The LHCb experiment is a single-arm forward particle detector located at the Large Hadron Collider at CERN. After the Upgrade II, it will run at a luminosity of up to $1.5 \cdot 10^{34} cm^{−2}s^{−1}$ to collect 300 fb$^{-1}$ to collect 300 fb$^{-1}$ of data. A major revision of the LHCb Electromagnetic Calorimeter is required due to the increased particle densities and radiation doses. One option for the central part is a sampling spaghetti calorimeter (SPACAL) comprising radiation-hard crystal scintillators and a Tungsten absorber, whereas a SPACAL with plastic scintillators and Lead absorber is candidate for the outer region. A prototype was assembled with fibres of Cerium-doped YAG and GAGG. This contribution presents the development of the SPACAL prototypes, including scintillators and photodetectors studies, the test beam results, and Monte Carlo simulations identifying the materials requirements in a high-rate environment.