A STUDY OF HEAT GENERATION AND CYCLING PERFORMANCE OF SODIUM-ION CELLS

Abstract

This thesis reveals heat generation and impedance characteristics of different 18650-sized sodium-ion cells with monoclinic Na₂Fe₂(CN)₆·2H₂O (MPB), rhombohedral Na₂Fe₂(CN)₆ (RPB), pristine Na₃V₂(PO₄)₃ (P-NVP), and modified Na_3.2V_1.8Zn_0.2(PO₄)₃ (M-NVP) as cathodes and hard carbon (HC) as anode, filled with non-flammable electrolyte: 1 M NaBF₄ in tetraglyme. Comparison of calorimetric studies performed on 18650 cells reveals lower heat generation in MNVP <i>vs.</i> HC among all the tested cells. Internal resistance, which is the major contributor to heat generation, is assessed by analysing the impedance spectra of the cells. Furthermore, variation in subcomponents of internal resistance across different depths of discharge is determined by equivalent circuit fitting and distribution of relaxation times (DRT) analysis. Moreover, a long-term cycling study is conducted on M-NVP <i>vs.</i> HC coin cells filled with 1 M NaBF₄ in tetraglyme to evaluate the effect of different operating conditions on cycle life and to determine capacity degradation mechanisms in sodium-ion cells.