Ionic Liquid-Nanoporous Polymer Hybrid Electrolyte Membranes for Vehicle Lithium Ion Batteries
The objective of this research project is to develop a new lithium electrolyte that is made from an ionic liquid-filled nanoporous polymer for use in electric vehicle lithium metal batteries. The new electrolyte material will be stable at extreme temperatures, non-flammable (it will be made entirely from non-flammable components), have a high ionic conductivity over a wide temperature range, and be electrochemically stable to ensure a long battery lifetime. Improving safety, without sacrificing performance is the goal of this project. We developed a new lithium ion battery that uses 0% flammable solvents. The electrolyte liquid is an imidazolium ionic liquid. The anode and cathodes were commercial off-the-shelf electrodes produced by NEI Corporation (New Jersey, USA). The ionic liquid itself was stable with the anode in half-cells, but it was not stable in a full cell at 4.2 Volts. However, we were able to solve this problem by adding an artificial SEI layer on the anode and cathode. A nanoporous polymer was pre-formed on the anode surface. This polymer was made by the self-assembly and polymerization of liquid crystal surfactant monomers. The cathode was also protected by an artificial SEI layer made from an ion-conducting polymer. All of the Phase I technical milestones were achieved. These included the production of high high-purity starting materials for our nanoporous polymer electrolyte and ionic liquids, the demonstration of a lithium ion conductivity of 6 mS/cm for our solid polymer material, and the successful formation and cycling of a 200 mAh flat panel lithium-ion cell. The materials we are using as the artificial SEI layers are compatible with both lithium metal and graphite anodes. Lithium metal and lithium-ion coin cells were first demonstrated. After that, 200 mAh lithium-ion cells were demonstrated. Capacity fade associated with the use of the ionic liquid was reduced when the nanoporous polymer SEI was used. Cells were cycled at C5/C2 (charge/discharge) rates after a C10 formation step. Higher discharge rates were used to evaluate the cell resistance, which was approaching the low values needed. The cell resistance was as low as 1.25 Ohm. Although this needs to be reduced to about 0.1 Ohm, we have found that by adding our SEI and optimizing it we were able to reduce this resistance from even higher values (starting from the 10’s of Ohms). We believe that further optimization is still possible to reduce the cell resistance to allow for the high charge/discharge rates needed for electric vehicles. Overall, the new SEI material and the ionic liquid electrolyte offer great promise for developing safer lithium batteries for electric vehicles and other niche applications.
- Research Organization:
- TDA Research, Inc.
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0018756
- OSTI ID:
- 1574021
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- TDA-R-2101-018-F_R; TDA-R-2101-018-F_R
- Country of Publication:
- United States
- Language:
- English
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