Strategies to Avert Electrochemical Shock and Their Demonstration in Spinels

Abstract

We demonstrate that extensive electrochemical shock–electrochemical cycling induced fracture–occurs due to coherency stresses arising from first order cubic-to-cubic phase transformations in the spinels LiMn[subscript 2]O[subscript 4] and LiMn[subscript 1.5]Ni[subscript 0.5]O[subscript 4]. Electrochemical shock occurs despite the isotropy of the shape changes in these materials. This electrochemical shock mechanism is strongly sensitive to particle size; for LiMn[subscript 2]O[subscript 4] and LiMn[subscript 1.5]Ni[subscript 0.5]O[subscript 4], fracture can be averted with particle sizes smaller than ~1 μm. As a further critical test of the proposed mechanism, iron-doping was used to induce continuous solid solubility of lithium in LiMn[subscript 1.5]Ni[subscript 0.5]O[subscript 4], and shown to virtually avert electrochemical shock, while having minimal impact on the electrode potential and capacity.