Electrolytes

Electrolytes

Organic electrolytes play a critical role to achieve high voltage and a longer lifespan for rechargeable batteries. We develop new electrolytes and additives to meet the challenges of graphite passivation, sulfur chemistry, as well as low temperature environment.

Projects

Liquid Electrolytes and Additives for Lithium-ion Batteries

Liquid Electrolytes and Additives for Lithium-ion Batteries

A series of propylene carbonate (PC) analogue solvents with increasing length of linear alkyl substitutes were synthesized and used as co-solvents with PC for graphite-based lithium-ion half cells. A graphite anode reaches a capacity of around 310 mAh/g in PC and its analogue co-solvents, with CE similar to the values obtained with standard electrolytes.

Electrolyte interaction with the graphite anode and subsequent decomposition determines the graphite anode performance. Solvents with longer alkyl chains are able to prevent graphite exfoliation when used as co-solvents with PC. 

Propylene Carbonate PC
A series of cyclic carbonate derivatives.

 

Graphite Half cell cycled at C/10 rate based on the synthesized PC-cosolvents with 1M LiPF6.
Cycling performances of a graphite half cell in a 1 M LiPF6 solution of (a) EC/DEC=1, (b) HeC/PC=4, (c) OcC/PC=2, and (d) DoC/PC=1 (v/v) at a C/10 rate.

Reference

Zhao, H.;  Park, S. J.;  Shi, F. F.;  Fu, Y. B.;  Battaglia, V.;  Ross, P. N.; Liu, G., Propylene Carbonate (PC)-Based Electrolytes with High Coulombic Efficiency for Lithium-Ion Batteries. J. Electrochem. Soc. 2014, 161 (1), A194-A200.

Fluorinated Electrolyte Additives

Fluorinated Electrolyte Additives

The electrolyte additives and formulations can prevent sulfur dissolution, promote smooth lithium deposition and enhance high voltage stabilities. 

molecular structure of fluorocarbon ethylene oxides
(a) molecular structure of fluorocarbon ethylene oxides with different chain length denotated as F8EO4 and F4EO2 respectively. (b) schematic diagram to show solvation mechanism of LiTFSI with TTE HFE in the electrolyte and formation of micelle complex structure.

  Reference

Zhao, Y. Z.;  Fang, C.;  Zhang, G. Z.;  Hubble, D.;  Nallapaneni, A.;  Zhu, C. H.;  Zhao, Z. W.;  Liu, Z. M.;  Lau, J.;  Fu, Y. B.; Liu, G., A Micelle Electrolyte Enabled by Fluorinated Ether Additives for Polysulfide Suppression and Li Metal Stabilization in Li-S Battery. Front. Chem. 2020, 8, 9.

Electrolytes for Low Temperature Li-ion Batteries

Electrolytes for Low Temperature Li-ion Batteries

Lithium-ion batteries often function poorly at sub-zero temperatures, with corresponding voltage and capacity losses becoming most notable around -20°C. However, many emerging applications require robust energy storage under such conditions; for instance, an electric vehicle must deliver similar driving range in both the winter and summer. Accordingly, the US Department of Energy has set a target of >70% usable energy (compared to room temperature) available at -20°C and C/3 discharge rate for electric vehicle battery packs.We are working to meet this goal through rational engineering of electrolyte composition (additives, solvents, and salts), which has been shown to largely influence lithium-ion behavior at low temperature. By careful study of electrolyte effects on internal resistance via charge transfer, interfacial chemistry, and bulk ion transport, we hope to uncover new insight into low-temperature performance characteristics and develop novel materials strategies to optimize the usable energy of cells.

Graph showing discharge energy density of cells at -20 oC compared to baseline cell at 30 oC.
Discharge energy density of cells at -20 oC compared to baseline cell at 30 oC. Very small percentage of additive enhance the energy at low temperature by 5% without any loss of energy at room temperature.

Reference

Hubble, D.;  Brown, D. E.;  Zhao, Y. Z.;  Fang, C.;  Lau, J.;  McCloskey, B. D.; Liu, G., Liquid electrolyte development for low-temperature lithium-ion batteries. Energy Environ. Sci. 2022, 15 (2), 550-578.

Featured Publications