Polarisation measurements of gamma-ray bursts probe how and where the energy is released in GRBs. Understanding the emission mechanism holds the key to using GRBs as probes of the early universe and of extreme physical processes occurring in the universe, including the newly discovered gravitational waves. SPHiNX is large field-of-view (~120°) Compton scattering polarimeter covering the energy range ~30 - ~600 keV. The polarimeter is proposed for the second Swedish Innosat mission with launch foreseen around 2021. The polarimeter design and expected performance will be discussed.