Counterintuitive Role of Magnesium Salts as Effective Electrolyte Additives for High Voltage Lithium‐Ion Batteries

Abstract

Further development of high voltage lithium‐ion batteries requires electrolyte formulations stable against oxidation or measures to generate a protective cathode/electrolyte interface (CEI) film. In the frame of this work, the actually counterintuitive concept of using metal ions as electrolyte additives to stabilize the CEI has proven to be successful. The addition of 1 wt% magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) as electrolyte additive to a conventional LiPF6/organic carbonate electrolyte suppresses the oxidative decomposition of the bulk electrolyte as displayed in improved capacity retention, increased Coulombic efficiencies, and reduced self‐discharge of LiNi1/3Mn1/3Co1/3O2 (NMC111)/Li half cells charged to the elevated upper cutoff potential of 4.6 V versus Li/Li+ at 20 °C. Moreover, the addition of Mg(TFSI)2 shows no adverse effect on the cycling performance of graphite anodes, as observed by good long‐term cycling results of NMC111/graphite full cells. Ex situ analysis via X‐ray photoelectron spectroscopy, scanning electron microscopy, time‐of‐flight secondary ion mass spectrometry, and electron energy loss spectroscopy of the harvested NMC111 electrodes after cycling indicate that the addition of Mg2+ ions leads to the formation of a CEI layer as a result of an increased hydrolysis reaction of the PF6 – anion.

Learning from Electrochemical Data: Simple Evaluation and Classification of LiMO2‐type‐based Positive Electrodes for Li‐Ion Batteries

“…Increasingt he charge cut-offp otential expectably leads to ahigher specificdischarge energy owing to asimultaneous increase in the specific discharge capacitya sw ell as the total mean discharge potential. [27] However, as exemplarily documentedb yF igure 1, an increase in the charge cut-offp otential is accompanied by an increasei nt he potential polarization and/orh ysteresis as well as an increasei nt he specific capacity loss.T hese effects relativize the goal of maximal discharge potential (ideally equal to charge potential) and maximal specific discharge capacity (ideally equal to specific charge capacity), respectively.…”

“…The specific discharge energies for varied charge cut‐off potentials and LiMO 2 ‐based electrodes are depicted in Figure . Increasing the charge cut‐off potential expectably leads to a higher specific discharge energy owing to a simultaneous increase in the specific discharge capacity as well as the total mean discharge potential …”

Fluorine and Lithium: Ideal Partners for High‐Performance Rechargeable Battery Electrolytes

“…However,m arket demands for higher voltage LIBs force researchers to identify new electrolyte formulations or even solid electrolytes, [13] as current SOTAl iquid electrolytes are oxidatively unstable at potentials > 4.5 Vv ersus Li/Li + and have well-known safety issues because of the presence of flammable organic solvents. [14] Electric car batteries usually contain reactive electrode materials such as high-voltage cathode materials [15] and lithiated graphite. [16] Although these materials hold al ot of energy,they tend to readily consume any other elements they are combined with, thus rendering this combination unusable.…”

New Insights for the Abuse Tolerance Behavior of LiMn2O4 under High Cut‐Off Potential Conditions

“…The C 1s, O 1s and F 1s spectra are shown in Figure . For the cycled electrode, besides peaks around 290.3 eV (in C 1s), 687.9 eV (in F 1s) corresponds to polyvinylidene fluoride (PVDF) binder, the P−F bond of LiPF 6 also can be observed . The other peaks are mainly originated from the electrolyte decomposition.…”