| Abstract | The thermal stability of a high-voltage spinel cathode (LiMn₁.₅Ni₀.₅O₄), synthesized via a sol-gel method, was investigated using Accelerating Rate Calorimetry (ARC) and compared to that of LiMn₂O₄. Both cathode materials crystallize in the Fd¯3¯m space group with nearly identical surface areas (∼0.65 m² g⁻¹), but they show different microstructures and morphologies that affect their reactivity. In the presence of 1 M LiPF¹ in ethylene carbonate (EC): diethyl carbonate (DEC) (1:2 v/v) electrolyte, both materials show an exothermic surface reaction that is dependent on the cathode morphology, at relatively low temperatures (below 200°C). The onset temperature of the self-heating reaction for Li₁₋ₓMn₁.₅Ni₀.₅O₄ sample is found to be as low as 60°C (compared to 140°C for Li₁₋ₓMn₂O₄), significantly affecting the thermal stability of a whole battery containing LiMn₁.₅Ni₀.₅O₄ as the cathode. The decomposition of the spinel material takes place at 195°C for Li₁₋ₓMn₁.₅Ni₀.₅O₄ and at 215°C for Li₁₋ₓMn₂O₄, with significantly higher self-heating rates for Li₁₋ₓMn₁.₅Ni₀.₅O₄ than for LiMn₂O₄. Our results show that, above 200°C, Ni⁴⁺ is reduced to the more stable Ni²⁺ oxidation state and the oxygen released from the cathode during this reaction fuels the combustion of carbonate solvents. |
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