title: N-substituted phenothiazine derivatives: how the stability of the neutral and radical cation forms affects overcharge performance in lithium-ion batteries.
abstract: Phenothiazine and five N-substituted derivatives were evaluated as electrolyte additives for overcharge protection in LiFePO4 /synthetic graphite lithium-ion batteries. We report on the stability and reactivity of both the neutral and radical-cation forms of these six compounds. While three of the compounds show extensive overcharge protection, the remaining three last for only one to a few cycles. UV/Vis studies of redox shuttle stability in the radical cation form are consistent with the overcharge performance: redox shuttles with spectra that show little change over time exhibit extensive overcharge performance, whereas those with changing spectra have limited overcharge protection. In one case, we determined that a C-N bond cleaves upon oxidation, forming the phenothiazine radical cation and leading to premature overcharge protection failure; in another case, poor solubility appears to limit protection.
authors.affiliation: Department of Chemistry, University of Kentucky, Lexington, KY, 40506-0055 (USA).
authors.forename: Kishore Anand
authors.initials: KA
authors.lastname: Narayana
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Casselman
authors.forename: Corrine F
authors.initials: CF
authors.lastname: Elliott
authors.forename: Selin
authors.initials: S
authors.lastname: Ergun
authors.forename: Sean R
authors.initials: SR
authors.lastname: Parkin
authors.forename: Chad
authors.initials: C
authors.lastname: Risko
authors.forename: Susan A
authors.initials: SA
authors.lastname: Odom
keywords: overcharge protection; phenothiazine; radical cations; redox shuttles; substituent effects