Understanding the Role of Imide‐Based Salts and Borate‐Based Additives for Safe and High‐Performance Glyoxal‐Based Electrolytes in Ni‐Rich NMC$_{811}$ Cathodes for Li‐Ion Batteries

Herein, the design of novel and safe electrolyte formulations for high-
voltage Ni-rich cathodes is reported. The solvent mixture comprising
1,1,2,2-tetraethoxyethane and propylene carbonate not only displays
good transport properties, but also greatly enhances the overall safety
of the cell thanks to its low flammability. The influence of the conducting
salts, that is, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium
bis(fluorosulfonyl)imide (LiFSI), and of the additives lithium bis(oxalato)borate
(LiBOB) and lithium difluoro(oxalato)borate (LiDFOB) is examined. Molecular
dynamics simulations are carried out to gain insights into the local structure
of the different electrolytes and the lithium-ion coordination. Furthermore,
special emphasis is placed on the film-forming abilities of the salts to suppress
the anodic dissolution of the aluminum current collector and to create
a stable cathode electrolyte interphase (CEI). In this regard, the borate-based
additives significantly alleviate the intrinsic challenges associated
with the use of LiTFSI and LiFSI salts. It is worth remarking that a superior
cathode performance is achieved by using the LiFSI/LiDFOB electrolyte,
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displaying a high specific capacity of 164 mAh g−1 at 6 C and ca. 95% capacity
retention after 100 cycles at 1 C. This is attributed to the rich chemistry of the
generated CEI layer, as confirmed by ex situ X-ray photoelectron spectroscopy.