Mixed Lithium Salts Electrolyte Improves the High-Temperature Performance of Nickel-Rich Based Lithium-Ion Batteries

Abstract

The long-term cycle performance of NCM811/Li batteries at high temperature was achieved by mixing LiDFOB and LiPF 6 salts into the ethylene carbonate (EC) and ethyl methyl carbonate (EMC) solution (EC/EMC = 3:7 by volume). The differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) tests indicate 0.8 M LiPF 6 /0.2 M LiDFOB electrolyte system could improve thermal stability. The NCM811 cell with the mixed lithium salts electrolyte shows superior high temperature cycling performance, as demonstrated by the high capacity retention (89.00%) after 100 cycles at 0.5 C, which is much better than that of the 1.0 M LiPF 6 electrolyte (51.34%). Inductively coupled plasma (ICP), Scanning electron microscopy (SEM) and other spectroscopic analyses reveal that adding LiDFOB salt could suppress Ni/Co/Mn dissolution into the electrolyte, due to the LiDFOB salt can be decomposed to produce a protective CEI layer on NCM811 surface. These results show that mixed lithium salts (LiDFOB and LiPF 6 ) is an efficient solution to enhance the high temperature performance of nickel-rich based lithium-ion batteries.

Cooperative Shielding of Bi-Electrodes via In Situ Amorphous Electrode–Electrolyte Interphases for Practical High-Energy Lithium-Metal Batteries

“…A “one-step-method” strategy was raised via the conversion of lithium difluoro­(oxalato)­borate (LiDFOB) salt associated with lithium tetrafluoroborate (LiBF 4 ) salt, which generates a dual-interface amorphous CEI/SEI protection (DACP) layer. Controlled by the energy level , and reaction kinetics , of the electrolyte components, LiDFOB is rapidly oxidated at the cathode side to construct CEI via two-step reactions with LiBF 4 generation. LiBF 4 is reduced at the Li anode side to construct the SEI; meanwhile, as a product of LiDFOB oxidation, LiBF 4 blocks the rapid consumption of LiDFOB at the cathode side .…”

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

“…From a theoretical point of view, LiDFOB (−7.57 eV (ref. 45)) possesses a higher highest occupied molecular orbital (HOMO) energy than LiBODFP (−8.41 eV (ref. 46)), indicating that LiDFOB is easier to oxidize to form a CEI film at the cathode/CSE interface.…”

Toward wide‐temperature electrolyte for lithium–ion batteries

“…However, when the upper charge voltage exceeded 4.45 V, the content of Ni, Mn, and Co metal ions in the electrolyte increased, indicating that LiTFSI would aggravate the dissolution of transition metals. Feng 63 investigated the effect of the mixed‐use of LiFSI and LiODFB with different molar ratios on the high‐temperature performance of Li/LiFePO 4 batteries. The blank solvent was EC:EMC (3:7).…”

“…(D) Cycle curves of Li/LiFePO 4 batteries in different electrolytes at 60°C. Reproduced with permission Feng et al 63 Copyright 2020, The Electrochemical Society. DMC, dimethyl carbonate; EC, ethylene carbonate; EMC, ethyl methyl carbonate…”

“…SEM results proved that LiFePO 4 cycled in the blank electrolyte was covered by thick and uneven by-products, while in the mixed salt electrolyte system, a stable and dense SEI film was formed on the electrode surface, which inhibited the interface reaction between the electrode and the electrolyte. XPS revealed that the composition of the SEI film contains LiF, B-O, and B-F bonds, indicating that these two lithium salts 63 Copyright 2020, The Electrochemical Society. DMC, dimethyl carbonate; EC, ethylene carbonate; EMC, ethyl methyl carbonate decomposed and participated in the film formation on the electrode surface, thereby significantly improving the cycling stability and rate capability at high temperatures.…”