New Insights into the Mechanism of LiDFBOP for Improving the Low-Temperature Performance via the Rational Design of an Interphase on a Graphite Anode

Abstract

The high impedance of the solid electrolyte interphase (SEI) is one of the important factors that deteriorate the charge behavior of lithium-ion batteries (LIBs) at low temperatures, which hinders their practical application in portable electronic products and electric vehicles under extreme conditions. Based on this consideration, a LiF-rich SEI film with low impedance, using lithium difluorobis(oxalato)phosphate (LiDFBOP) as an electrolyte additive and a blank electrolyte without commercial additives, is constructed on a graphite surface. The decomposition mechanism of LiDFBOP is further deduced by density functional theory calculations. This additive inhibits the decomposition of the electrolyte and then forms a thin SEI film with more LiF. LiF, possessing high Young's modulus, makes the SEI film dense and stable. At the same time, more LiF/Li 2 CO 3 interfaces are formed to increase the ionic conductivity. Benefiting from the components and the structure of the SEI, the graphite/Li cells exhibit excellent cycling stability (ca. 85.5% initial capacity retention for 200 cycles at 1 C) and an impressive low-temperature performance (ca. 200% capacity for electrolytes without LiDFBOP at −20 °C). This work presents an effective strategy for developing a functional electrolyte to meet the requirement of LIBs with enhanced low-temperature performance.

Optimized functional additive enabled stable cathode and anode interfaces for high-voltage all-solid-state lithium batteries with significantly improved cycling performance

“…These enhanced stabilities against the Li anode may be attributed to the film-forming abilities of LiBODFP and LiDFOB additives, which have been proven effective to form a stable SEI film on the surface of the Li anode in LLIBs. 42–44…”

“…These enhanced stabilities against the Li anode may be attributed to the lm-forming abilities of LiBODFP and LiDFOB additives, which have been proven effective to form a stable SEI lm on the surface of the Li anode in LLIBs. [42][43][44] Polycrystalline LiNi 0.6 Co 0.2 Mn 0.2 O 2 (PC622)/CSE/Li coin cells are assembled to further investigate the effects of different types of additives in practical cells. Fig.…”

A novel cyclopentyl methyl ether electrolyte solvent with a unique solvation structure for subzero (−40 °C) lithium-ion batteries

“…The F 1s spectra can be divided into 3 different peaks representing C–F (687.7 eV), PO x F y (687.1 eV), and LiF (684.6 eV). 12,26,27 a The intensity of the PO x F y -based porous organic species is higher than that of the LiF peak in the CE resulting from a continuous reduction of LiPF 6 over cycling. In contrast, the 1 M CPME has a higher content of LiF.…”

“…This may be due to the formation of an unstable and porous SEI composed of dominant Li 2 CO 3 and small LiF over cycling. 12 This SEI has an electron donating nature and creates a favourable situation for continuous reduction of electrolytes causing capacity degradation. In contrast, 1 M CPME forms a robust thin SEI made of LiF-rich content and a small amount of Li 2 C 2 O 4 even at a 1C rate.…”

“…To address these issues, several approaches such as making multiple solvent mixtures with suitable properties to extend the liquid temperature range 10,11 or by using functional additives 12 to modify the SEI have been reported. This could improve the low-temperature operation to a certain extent.…”