Electrochemical Analysis of
Modified Separators for Li-S Batteries
Yu-Chuan Chien, Ruijun Pan, Leif Nyholm, Daniel Brandell, Matthew J. Lacey
Department of Chemistry – Ångström Laboratory, Uppsala University Box 538, SE-751 21 Uppsala, SWEDEN
Motivation
Capacity & C.E.
The lithium-sulfur system is considered a promising energy storage technology due to the high theoretical energy density (2500 Wh kg-1) and abundance of sulfur [1]. However, the problem of the redox shuttle of polysulfides (PS) needs to be solved in order to enhance the cycling
stability for further commercialization [1]. Various concepts for modification of separators have been proposed to address this issue, such as metal oxide coatings [2] or conductive interlayers [3]. Performance improvements have been ascribed to a suppression of polysulfide
transport across the separator, even though this has not always been correlated with the difference in electrochemistry.
Experimental setup
Li S/C Li S/C Li S/C Li S/C
Celgard
®2400 Al
2O
3-coated
PE (ACPE) Nanocellulose CNT-coated
nanocellulose (CCC)
Voltage & resistance
[4]profiles
Rate-capability Self-discharge
cycle number
discharge
charge
Li morphology after the 2
ndcharge
Conclusion
References
[1] S. Urbonaite, et al., Adv. Energy Mater. 5 (2015) [2] Z. Zhang, et al., Electrochim. Acta 129 (2014) [3] H. Yao, et al., Energy Environ. Sci. 7 (2014)
V = 5 kV
WD = 6.7 mm Mag. = 1 kX SE2 detector
100 µm
Celgard ACPE
Cellulose CCC
S-loading: 2~2.5 mg cm-2 | S/C electrode: 65% S, 28% C, 7% PEO:PVP | Electrolyte: 1M LiTFSI 0.25M LiNO3 DME:DOL | Velec. = 6 µL mgS-1
Separator chemistry has considerable influence on S utilization, rate capability and redox shuttle behavior. S utilization is not strongly
correlated with the degree of the redox shuttle. Results indicate restriction of PS mobility in cells with LiNO3 can be counter-productive, as Li passivation may be negatively affected.
Al2O3-coating increases the resistance at the end of the 1st discharge plateau
CNT-interlayer decreases the resistance significantly but increases PS-shuttle
CNT-layer helps at high C-rates CNT-layer does not stop PS- transport at a large time scale
Cellulose-based separators improve Li morphology [5], but the pitting at fully-charged state indicates inferior passivation of Li
Cellulose separators give lower CE
CNT-layer increases capacity but
endless redox shuttle despite LiNO3
*The PS diffusion tests were done in DME:DOL without salts. Pictures were taken after 15 min.
[4] M.J. Lacey, et al., Chem. Commun. 2 (2015)
[5] Z. Wang, et al., ACS Appl. Energy Mater. (2018)
■ Celgard
■ ACPE
■ Cellulose
■ CCC
■ Celgard
■ ACPE
■ Cellulose
■ CCC
■ Celgard
■ ACPE
■ Cellulose
■ CCC
■ Celgard
■ ACPE
■ Cellulose
■ CCC
