Hanemann, T.

Hofmann, A.

Schulz, M.

Tosoni, M.

English

KITopen

KIT – University of the State of Baden-Wuerttemberg and National Research Center of the Helmholtz Association Effect of Conducting Salts in Ionic Liquid based Electrolytes for Li-Ion-Batteries Andreas Hofmann*, Martin Tosoni*, Michael Schulz*, Thomas Hanemann*,** Institut für Angewandte Materialien Werkstoffprozesstechnik *   Karlsruher Institut für Technologie, Institut für Angewandte Materialien - Werkstoffprozesstechnik, Karlsruhe, Germany    Andreas Hofmann, e-mail: andreas.hofmann2@kit.edu, Tel. +49 (0)721-608-25920 ** Universität Freiburg, Professur für Werkstoffprozesstechnik, Institut für Mikrosystemtechnik (IMTEK), Freiburg, Germany  Summary           Motivation      Li-Ion Cell                        Composition, conductivity and viscosity of selected salt mixtures               Enhancement of the temperature stability of Li-Ion battery electrolytes  Influence of conducting salts on ionic liquid based electrolytes  Improvement of the lithium ion mobility   Study of the solid electrolyte interface (SEI)   Study of conducting salts in ionic liquid – propylene carbonate liquid electrolytes  Interaction of ionic liquid based electrolytes with graphite and NMC electrodes  Li+ conductivity, safety, cycle stability Mixtures in Li|NMC and Li|C cells                     NMC|C - cell performance                        Conclusions           Acknowledgements  Strong dependence of the cell performance of the applied conducting salts in the following order: LiTFSA > LiPF6 > LiClO4 > LiOTf > LiBF4  Best performance in case of lithium bis(trifluoromethylsulfonyl)azanide as conducting salt  Successful cycling of the NMC|C cells up to current rates of C/5  (specific capacity > 100 mAh/g) is possible   Different performing of the electrolytes in Li|NMC and Li|C cells (especially for LiBF4)   LiTFSA and LiPF6 exhibit the best results in Li|NMC as well as Li|C cells  SEI formation is already finished after the first cycle (Li|C cells)  Lithium intercalation in graphite is observed for every electrolyte mixture  Current rates up to C/4 (Li|NMC) as well as C/6 (Li|C) are realizable at room temperature* graphite       separator +       NMC (negative)     electrolyte     (positive)   discharging Batterietag NRW & Kraftwerk Batterie - No. PB08  Functionality of Li-ion batteries   Negative graphite electrode  Positive NMC electrode   (NMC = LiNi1/3Co1/3Mn1/3O2)  Electrolyte based on DMMA-TFSA and propylene carbonate  Cell design:   Swagelok type cells and coin cells (CR 2032)  Separator: Whatman glass fiber, thickness: 450 mm  Conducting salts:  - LiBF4 :  lithium tetrafluoroborate  - LiPF6 :  lithium hexafluorophosphate  - LiClO4 :  lithium perchlorate  - LiOTf :  lithium triflate  - LiTFSA :   lithium bis(trifluoromethylsulfonyl)azanide   (= lithium bis(trifluoromethylsulfonyl)imide)  - DMMA (as cation):   N,N-diethyl-N-methyl-N-(2-methoxy-ethyl)ammonium We acknowledge IoLiTec Ionic Liquids Technologies GmbH for kindly providing ionic liquids.  sample conducting salt  (1 mol/kg) solvent (1:1 wt%) conductivity [mS/cm] (20 °C) viscosity [mPa·s] (20 °C) density  [g/cm3] L-0 - PC – DMMA-TFSA  9.8  0.9 7.9 ± 0.2 1.29  0.20 L-1 LiBF4 PC – DMMA-TFSA  3.1 ± 0.2 39.6 ± 0.6 1.35 ± 0.02 L-2 LiOTf PC – DMMA-TFSA  2.3 ± 0.2 55.1 ± 0.5 1.39 ± 0.03 L-3 LiClO4 PC – DMMA-TFSA  2.2 ± 0.1 69.7 ± 1.8 1.37 ± 0.02 L-4 LiPF6 PC – DMMA-TFSA  1.9 ± 0.1 78.9 ± 4.1 1.38 ± 0.03 L-5 LiTFSA PC – DMMA-TFSA  1.6 ± 0.1 70.7 ± 2.2 1.44 ± 0.04  High conductivity, independent of the conducting salt  Measurements reveal a suitability for Li-Ion-Cells   LiBF4, LiOTf, and LiClO4 exhibit a poor cell performance in NMC|C cells  LiTFSA exhibits the best results in C|NMC cells in performance testing as well as in cells at constant current rates of C/20*  Specific capacities of >150 mAh/g are received in a potential range of    3 – 4.2 V for the LiTFSA electrolyte reversibly  Current rates up to C/2.5 are realizable at 40 °C  Discharge Capacity of 80% after 400 cycles * C/n: current rate when the cell is charged or discharged completely in n h L-1 = LiBF4  L-2 = LiOTf L-3 = LiClO4 L-4 = LiPF6 L-5 = LiTFSA L-1 = LiBF4  L-2 = LiOTf L-3 = LiClO4 L-4 = LiPF6 L-5 = LiTFSA Cell cycling tests of Li|NMC (left) and Li|C  cells (middle) at room temperature with different current rates in a potential range of 3 – 4.2 V vs. Li/Li+ (left) and 0 – 2.0 V vs. Li/Li+ (middle). On the right side there are depicted the first two cycles of C|Li cell with electrolyte L-5. (t’: the time scale is normalized at the beginning of the cycle) Cycling tests of C|NMC cells (left) at room temperature with different current rates in a potential range of 3 – 4.2 V vs. Li/Li+ (left). In the middle a coin cell is shown which is running for 120 cycles with mixture L5 (3 – 4.2 V, C-rate up to 0.5 C). On the right side the temperature dependence of the C|NMC cell with mixture L-5 at 0.4 C is depicted.  

Effect of conducting salts in ionic liquid based electrolytes for Li-ion-batteries

https://publikationen.bibliothek.kit.edu/220094249/3816440

Effect of conducting salts in ionic liquid based electrolytes for Li-ion-batteries

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