Polycarbonate-Based Solid Polymer Electrolytes for Li-Ion Batteries

Conventional Li-ion batteries containing flammable and volatile liquid electrolytes are challenged to deliver safe and stable performance for practical energy storage applications.  Alternatively, solid polymer electrolytes (SPEs), which intrinsically eliminate the use of organic solvents, display good mechanical stability and flexibility against physical deformation of battery pack and volume retention of electrode materials. The use of SPEs with high thermal and electrochemical stability would contribute to the design and manufacture of safe and cost-effective Li-ion batteries, especially for large-scale applications under elevated temperatures [1].

Host materials for most SPEs have yet been dominated by polyethers with ethylene oxide (EO) and propylene oxide (PO) as repeating units.  As an interesting replacement to the low-molecular-weight cyclic and linear carbonates, a new class of polymer hosts based on polycarbonates has been considered as Li⁺-conducting electrolytes [2]. The incorporation of polar carbonate units in the polymer host could effectively facilitate the separation of ion clusters and allow high salt doping in SPEs.

In this work, we have developed and explored poly(trimethylene carbonate) (PTMC) as a polymer host alternative for all solid-state Li-ion batteries. High-molecular-weight PTMC was synthesized via bulk ring-opening polymerization. Electrochemical and thermal properties of the PTMC/LiTFSI complexes with varied salt concentration were systematically investigated using electrochemical impedance spectroscopy (EIS) and thermal analysis (DSC/TGA). The as-prepared SPEs are amorphous materials and thermally stable up to 200 °C. The best-performing electrolyte could display useful ionic conductivity at elevated temperatures and was also found electrochemically stable towards 5.0 V vs. Li⁺/Li. The cycling performance of Li | SPE | LiFePO₄ half cells has been tested at elevated temperatures and the cells display long-term cycling stability with retained high capacity up to 153 mAh/g. The gradual increase in capacity might be due to improved interfacial contacts during cycling and storage [3]. 

Acknowledgements

This work has been supported by the STandUP for Energy project and KIC InnoEnergy.

References

[1] B. Scrosati, J. Garche, J. Power Sources, 195 (2010) 2419.

[2] a) Smith, M. J. et al. Solid State Ionics, 140 (2001) 345; b) Silva, M. M. et al. J. Power Sources, 111 (2002) 52; c) Silva, M. M. et al. Electrochim. Acta, 49 (2004) 1887; d) Silva, M. M. et al. Solid State Sci., 8 (2006) 1318; e) Barbosa, P. C. et al. Solid State Ionics, 193 (2011) 39.

[3] B. Sun, J. Mindemark, K. Edström, D. Brandell, Solid State Ionics (2013), DOI: 10.1016/j.ssi.2013.08.014.