The thermochemical decomposition of sunflower oil cake (SuOC) with ZnCl2 and AlCl3 additives was studied by thermogravimetric (TG) analysis at a heating rate of 5 °C/min under a controlled nitrogen atmosphere with flow value of (20 mL/min). The present study focused on the development of evaluation criteria of the thermal decomposition of SuOC with additives. Evaluation criteria were suggested based on a comparison of kinetic data of an actual mixture with that of a corresponding reference mechanical mixture (RMM). Assessment of the additives influences on the thermal behaviour of SuOC showed that AlCl3 provided up to a 70% enhancement of devolatilization in comparison with the RMM and a 7.5–10% decrease of activation energy at the low pyrolysis temperature of 242 °C by providing a biomass conversion degree of α = 60–70%. In contrast, the ZnCl2 provided the same value of biomass conversion degree, but only in the temperature range of 450–550 °C.