Phthalocyanine as catalyst for rechargeable lithium-oxygen batteries

Tetrabutylammonium lithium phthalocyanine (TBA-LiPc) can function as a soluble catalyst in low-donor-number (DN) solvents such as tetraethylene glycol dimethyl ether (TEGDME) for rechargeable lithium-oxygen cells. Molecular oxygen forms a complex with the lithium phthalocyanine anion thereby keeping oxygen and the reaction intermediates in solution. Density functional theory (DFT) calculations show the mechanism for complex formation and cyclic voltammetry results show reaction intermediates are soluble in solution during oxygen reduction and oxygen evolution reactions. Tetrabutylammonium lithium phthalocyanine (TBA-LiPc) can function as a soluble catalyst in low-donor-number (DN) solvents such as tetraethylene glycol dimethyl ether (TEGDME) (DN=16.6) for rechargeable lithium-oxygen cells. It is able to do so given that molecular oxygen forms a complex with the lithium phthalocyanine anion thereby keeping oxygen and the reaction intermediates in solution. Density functional theory (DFT) calculations show the mechanism for complex formation and cyclic voltammetry results support the notion of reaction intermediates that are soluble in solution during oxygen reduction and oxygen evolution reactions. Deep discharge of a lithium-oxygen cell with TBA-LiPc had a capacity that was 3.6 times greater (5.28 mAh) than a similar cell with no TBA-LiPc (1.47 mAh). Long-term cycling of a lithium-oxygen cell with TBA-LiPc at a fixed capacity of 0.55 mAh did not fail after 100 cycles. A similar cell without TBA-LiPc failed after 37 cycles. Long-term cycling of a lithium-oxygen cell with TBA-LiPc and using natural air in low humidity as the source of oxygen cycled 151 times before cell failure.