Investigating the Limit of Lithium Difluorophosphate Electrolyte
Additive for High-Voltage Li/Mn-Rich Layered Oxide ||
Graphite Cells
Abstract
Li/Mn-rich layered oxide (LMR) cathode active materials offer remarkably
high specific discharge capacity (>250 mAh g-1) stemming 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
cut-off voltage (UCV) of 4.5 V, effective TM scavenging effects of LiDFP
is observed. In contrast, in cells with an UCV of 4.7 V, the scavenging
effects is limited due to more severe TM dissolution compared an UCV of
4.5 V. Worth noting, the low solubility limit of the TM scavenging
agents, e.g., PO43- and PO3F2-, which are the decomposition products of
LiDFP, cannot scavenge additional TMs, even when higher LiDFP
concentration are added to the electrolyte and can even worsen the
performance.