Effectiveness of salification against shuttle effect in p-type organic batteries: Case studies of triflimide and iodide salts of N,N’-dimethylphenazine

The triflimide and iodide salts of N,N’-dimethylphenazinium were employed as case studies in implementing the salification strategy for improving the performance of p-type organic battery compounds. Successful implementation hinges on maintaining the cation–anion interactions through all states-of-charge, and compatibility between all cell components and battery operation parameters. [Display omitted] •Salification can improve the battery performance of p-type organic electrodes.•[DMPZ][TFSI] proved that introducing an anion can decrease the final capacity.•[DMPZ][I] showed that the anion with An–/(n+1)– is optimal for salification.•The criteria of anions for salification look significant for organic batteries. Salification is one solubility reduction strategy for limiting the deleterious shuttle effect in organic batteries, although its applicability for oxidizable (p-type) cationic compounds is less established. Using as case studies the salts N,N’-dimethylphenazinium iodide,[DMPZ][I], and triflimide, [DMPZ][TFSI], we demonstrate that solubility reduction by the anion does not necessarily translate into improved battery performance. As exemplified by the formation of the well-known I–/I2 shuttle in [DMPZ][I] cathode, intermolecular interactions that reduce solubility can be lost as state-of-charge changes during redox reaction (i.e. charge/discharge). Another point of consideration is the compatibility in terms of (electro)chemical stability of the electrode components and the charge/discharge parameters when placed together within a cell, even if they are individually stable. Here, the iodide salt underwent decomposition within the literature-optimized electrolyte to form a cathode-electrolyte interface, encapsulating the redox-active compound and changing the charge storage mechanism to one of pseudo-capacitance, thus deteriorating capacity retention. Considering the multitude of requirements as listed here, salification appears challenging to implement for improving battery performance for p-type molecular compounds.