Improving the High Temperature Performance of Li-Ion Batteries with Transition Metal Ion Trapping Separators - a Brief Review

Abstract

One of the main performance degradation mechanisms in Li-ion batteries is initiated by the dissolution of transition metal (particularly manganese) cations from positive electrode active materials. These ions will electro-migrate to and deposit on the negative electrode surface. The deposited manganese species induce the catalytic decomposition of solvent molecules and the concurrent depletion of electrochemically active lithium, leading surface film growth, gassing, exfoliation of graphite particles, and an overall degradation of battery performance (increased cell resistance, reduced power capability, and a shortened battery life). Several measures for mitigating manganese dissolution or its consequences have been reported over the years in the literature,1,2 including elemental substitutions (doping) in the bulk of the positive electrode active material,3 surface coatings4 and the application an inorganic barrier coatings onto electrodes by atomic layer deposition,5 passivating additives in the electrolyte solution,6and the reduction of the state-of-charge swing during battery operation. Unfortunately, no single mitigation measure has proven completely successfully so far, i.e., without negatively affecting other properties of the LIB such as energy density and internal resistance. A different - and complementary - approach, that of using a separator containing manganese ion chelating agents, may avoid the previously described drawbacks.7-9 Such a separator captures the manganese ions in the inter-electrode space by means of a polymeric chelating agents with cyclic or open structures, thus preventing the migration of manganese ions to, and subsequent contamination of, the negative electrode. We will review the present status of the chelating agents approach for mitigating the consequences of Mn dissolution for battery performance and will discuss some remaining challenges.