Optimising organic ionic plastic crystal electrolyte for all solid-state and higher than ambient temperature lithium batteries

Abstract

Organic ionic plastic crystal (OIPC) electrolytes are among the key enabling materials for solid-state and higher than ambient temperature lithium batteries. This work overviews some of the parameter studies on the Li|OIPC interface using lithium symmetrical cells as well as the optimisation and performance of Li|OIPC|LiFePO 4 cells. The effects of temperature and electrolyte thickness on the cycle performance of the lithium symmetrical cell, particularly with respect to the interfacial and bulk resistances, are demonstrated. Whilst temperature change substantially alters both the interfacial and bulk resistance, changing the electrolyte thickness predominantly changes the bulk resistance only. In addition, an upper limit of the current density is demonstrated, above which irreversible processes related to electrolyte decomposition take place. Here, we demonstrate an excellent discharge capacity attained on LiFePO 4 | 10 mol% LiNTf 2 -doped [C 2 mpyr][NTf 2 ]|Li cell, reaching 126 mAh g -1 at 50°C (when the electrolyte is in its solid form) and 153 mAh g -1 at 80°C (when the electrolyte is in its liquid form). Most remarkably, at high temperature operation, the capacity retention at long cycles and high current is excellent with only a slight (3%) drop in discharge capacity upon increasing the current from 0.2 C to 0.5 C. These results highlight the real prospects for developing a lithium battery with high temperature performance that easily surpasses that achievable with even the best contemporary lithium-ion technology.

Ionic transport through a composite structure of N-ethyl-N-methylpyrrolidinium tetrafluoroborate organic ionic plastic crystals reinforced with polymer nanofibres

“…[1][2][3][4][5] OIPCs have these unique properties because they can exist in several distinct solid phases at temperatures below the melting point. [1][2][3][4][5] OIPCs have these unique properties because they can exist in several distinct solid phases at temperatures below the melting point.…”

“…Satisfactory electrochemical performance of the materials was reported when soaked with organic carbonate solvents or ionic liquids as electrolytes. We have chosen to study the OIPC N-ethyl-N-methylpyrrolidinium tetrauoroborate [C 2 mpyr][BF 4 ] due to its broad plastic crystal range, and its composites with PVDF electrospun nanobres, with and without the addition of LiBF 4 . 23 Here we sought to combine the benecial effects of OIPCs as highly conductive solid-state electrolytes with the relatively high mechanical strength and chemical durability of polymer nanobres by bringing them together to make composite electrolyte membranes.…”

Molecular diffusion and dc conductivity perfectly correlated with molecular rotational dynamics in a plastic crystalline electrolyte

“…In fact, plastic-crystalline electrolytes are ideal for portable batteries because their mechanical flexibility reduces the problem of poor electrical contact with the electrodes caused by thermal volume changes of solid electrolytes, while eliminating the leakage problems associated with liquid electrolytes. 11,12 We study here a plastic crystalline electrolyte based on the small, high-symmetry succinonitrile molecule (SN, C 2 H 4 (CN) 2 ). Near room temperature, SN is well-known to exhibit plasticcrystalline characteristics combined with unusually high ion mobility, a feature that has been exploited in the last decade to achieve high-conductivity solid electrolytes.…”

A novel organosilicon-based ionic plastic crystal as solid-state electrolyte for lithium-ion batteries

“…Comparing the impedance spectra of the cell after the first and the third cycles, it was observed that the charge transfer impedance decreased from 800 Ω to 360 Ω after three cycles. The decrease of impedance with increasing cycles might be attributed to the formation of a passivation layer and good contact compatibility between lithium and the solid-state electrolyte interface (Sunarso et al, 2012), which could be the reason for the capacity increase during the first three cycles.…”

“…Shekibi et al (2012) exhibited viable ionic conductivity at the level of 10 −3 S/cm at 100 °C, and the discharge capacity in LiFePO 4 /Li cell was about 100 mA·h/g at 80 °C with current density of C/10. Sunarso et al (2012) Organosilicon-based materials have attracted great attention as electrolytes for electrochemical energy storage devices due to their excellent thermal stability, viable ionic conductivity at low temperatures, low flammability, high electrochemical stability, and environmentally benign characters (Shirota and Castner, 2005;Zhang et al, 2008;Rossi and West, 2009;Weng et al, 2011). We have been dedicated to the design and synthesis of organosiliconbased electrolytes, including liquid electrolytes and ionic liquids, for applications in electrochemical energy storage devices such as lithium-ion batteries and supercapacitors (Zhong et al, 2012;Qin et al, 2013;Yan and Zhang, 2013;Yong et al, 2014).…”