Elucidating the Limit of Lithium Difluorophosphate Electrolyte Additive for High-Voltage Li/Mn-Rich Layered Oxide || Graphite Li Ion Batteries

Abstract

Li/Mn-rich layered oxide (LMR) cathode active materials offer remarkably high specific discharge capacity (>250 mAh g⁻¹) from both cationic and anionic redox. The latter necessitates harsh charging conditions to high cathode potentials (>4.5 V vs Li|Li⁺), which is accompanied by lattice oxygen release, phase transformation, voltage fade, and transition metal (TM) dissolution. In cells with graphite anode, TM dissolution is particularly detrimental as it initiates electrode crosstalk. Lithium difluorophosphate (LiDFP) is known for its pivotal role in suppressing electrode crosstalk through TM scavenging. In LMR || graphite cells charged to an upper cutoff voltage (UCV) of 4.5 V, effective TM scavenging effects of LiDFP are observed. In contrast, for an UCV of 4.7 V, the scavenging effects are limited due to more severe TM dissolution compared an UCV of 4.5 V. Given the saturation in solubility of the TM scavenging agents, which are LiDFP decomposition products, e.g., PO₄³⁻ and PO₃F²⁻, higher concentrations of the LiDFP as “precursor” cannot enhance the amount of scavenging species, they rather start to precipitate and damage the anode.