More work reported on approaches to stabilizing lithium metal anodes for high energy rechargeable batteries
Metallic lithium, with a high theoretical capacity of ~3,860 mAh g-1, is one of the most promising materials for anodes in next-generation high energy rechargeable battery systems for long-range electric vehicles. (Earlier post.) Indeed, in a paper in ACS’ Chemical Reviews, Arumugam Manthiram et al. from the University of Texas suggest that “it is reasonable to comment that the success of Li−S batteries requires a reliable lithium metal anode.”
A reliable and stable lithium metal anode is extremely challenging, however; low cycle efficiency and lithium dendrite formation during charge/discharge processes consistently hinder its practical application in addition to raising safety issues. Accordingly, widespread effort is focused on devising solutions to the problem, tackling either the anode material itself, or the electrolyte, or both. The widely reported advance by Stanford researchers (earlier post) is but one of a number of such efforts underway (e.g., earlier post, earlier post, earlier post.)
|University of Michigan spin-off Sakti3, which had its own burst of recent publicity with the announcement that it has produced a battery cell on fully scalable equipment with more than 1100 Watt hours per liter (Wh/l) in volumetric energy density, is taking a different approach by developing a scalable thin-film solid-state system.|
|Although solid-state cells could address some of the issues attendant to using Li metal anodes—especially safety and cycle performance—such solid state cells have been difficult to make, and have not been successfully produced in large scale, Sakti3 noted in one of its patent applications.|
|Sakti3 is developing a thin-film manufacturing process using physical vapor deposition to lay down a cathode barrier, cathode current collector, cathode, electrolyte, anode, anode current collector, and anode barrier over a substrate.|
|As an example outlined in the patent application, Skati3 describes using a lithium vanadium oxide cathode with a Li anode, the latter being overlaid with an anode barrier material of Li3PO4.|
|Our target is to achieve mass production of cells at ~$100/kWh. Our key patents on the technology have been issued, we are up and running on larger tooling, and can now speed up processing. Our first market will be consumer electronics, and after that, we’ll move to other sectors.|
—Dr. Ann Marie Sastry, CEO of Sakti3
Among other recent developments, in the Journal of Power Sources, Miao et al. from Shanghai Jiao Tong University (China) report the use of a new dual-salts electrolyte composed of Li[N(SO2F)2] and Li[N(SO2CF3)2] to simultaneously cope with low cycle efficiency and lithium dendrite formation.
Under the protection of the solid electrolyte interphase (SEI) film formed in this electrolyte solution and the improvement in Li crystal growth pattern, high cycle efficiency of around 99% and dendrite-free Li deposit was achieved.
The excellent cycling performance and favorable lithium morphology can be retained even at high current density of 10 mA cm−2.
Also in the Journal of Power Sources, Osada et al. from the University of Münster (Germany) report developing Li-metal polymer batteries incorporating crosslinked ternary PEO/PYR14TFSI/LiTFSI solid polymer electrolyte (SPE), using V2O5 (vanadium pentoxide) as the active cathode material.
As a result of the optimization of the SPE as well as the cell assembly and cycling conditions, the V2O5 lithium metal polymer batteries reached 796 Wh kg−1 (of V2O5) at C/10 at 40 °C and maintained 663 Wh kg−1 after 200 cycles at 40 °C.
This is higher than the theoretical specific energy of of 609 Wh kg−1 LiCoO2 vs. Li.
Cycling at 80 °C allowed reaching 270 mAh g−1 at C/2 and 210 mAh g−1 at 1 C, while at 20 °C it was still possible to reach a discharge capacity of almost 100 mAh g−1 at low rates.
Imaging post-cycling showed that, after 200 cycles at 40 °C, while the plating of lithium is not fully homogeneous, no sign of dendrite growth nor obvious vanadium dissolution and redeposition on the anode side had occurred.
Chenxi Zu and Arumugam Manthiram (University of Texas) report in the ACS Journal of Physical Chemistry Letters on the use of copper acetate as a surface stabilizer for lithium metal in the polysulfide-rich environment of Li–S batteries.
The lithium surface is protected from parasitic reactions with the organic electrolyte and the migrating polysulfides by an in situ chemical formation of a passivation film consisting of mainly Li2S/Li2S2/CuS/Cu2S and electrolyte decomposition products.
The passivation film also suppresses lithium dendrite formation by controlling the lithium deposition sites, leading to a stabilized lithium surface characterized by a dendrite-free morphology and improved surface chemistry.
In the Journal of the American Chemical Society, Khurana et al. from Cornell report a cross-linked polyethylene/poly(ethylene oxide) solid polymer electrolyte (SPE_ with both high ionic conductivity (>1.0 × 10–4 S/cm at 25 °C) and excellent resistance to dendrite growth from the lithium anode.
Other groups had proposed that SPEs with shear moduli of the same order of magnitude as lithium could be used to suppress dendrite growth; however, in contrast to these theoretical predictions, the low-modulus (G′ ≈ 1.0 × 105 Pa at 90 °C) cross-linked SPEs of Khurana et al. showed “remarkable” dendrite growth resistance. These results suggest that a high-modulus SPE is not a requirement for the control of dendrite proliferation, the team concluded.
As a final example of recent work, Lu et al. (another team from Cornell, also led by Prof. Lynden Archer) report in Angewandte Chemie on their investigations of ionic liquid and ionic-liquid–nanoparticle hybrid electrolytes based on 1-methy-3-propylimidazolium (IM) and 1-methy-3-propylpiperidinium (PP).
They found that PP-based electrolytes were more conductive and substantially more efficient in suppressing dendrite formation on cycled lithium anodes; as little as 11 wt% PP-IL in a PC-LiTFSI host produces more than a ten-fold increase in cell lifetime.
They also found that both PP- and IM-based nanoparticle hybrid electrolytes provide up to 10,000-fold improvements in cell lifetime than anticipated based on their mechanical modulus alone.
Galvanostatic cycling measurements in Li/Li4Ti5O12 half cells using IL–nanoparticle hybrid electrolytes revealed more than 500 cycles of trouble-free operation and enhanced rate capability.
Arumugam Manthiram, Yongzhu Fu, Sheng-Heng Chung, Chenxi Zu, and Yu-Sheng Su (2014) “Rechargeable Lithium–Sulfur Batteries” Chem. Rev., doi: 10.1021/cr500062v
Sakti3 patent application US 20120058380 A1 Monolithically integrated thin-film solid state lithium battery device having multiple layers of lithium electrochemical cells
Rongrong Miao, Jun Yang, Xuejiao Feng, Hao Jia, Jiulin Wang, Yanna Nuli (2014) “Novel dual-salts electrolyte solution for dendrite-free lithium-metal based rechargeable batteries with high cycle reversibility” Journal of Power Sources Volume 271, Pages 291–297 doi: 10.1016/j.jpowsour.2014.08.011
Irene Osada, Jan von Zamory, Elie Paillard, and Stefano Passerini (2014) “Improved lithium-metal/vanadium pentoxide polymer battery incorporating crosslinked ternary polymer electrolyte with N-butyl-N-methylpyrrolidinium bis(perfluoromethanesulfonyl)imide” Journal of Power Sources Volume 271, Pages 334–341 doi: 10.1016/j.jpowsour.2014.08.019
Chenxi Zu and Arumugam Manthiram (2014) “Stabilized Lithium–Metal Surface in a Polysulfide-Rich Environment of Lithium–Sulfur Batteries” J. Phys. Chem. Lett., 5 (15), pp 2522–2527 doi: 10.1021/jz501352e
Rachna Khurana, Jennifer L. Schaefer, Lynden A. Archer and Geoffrey W. Coates (2014) “Suppression of Lithium Dendrite Growth Using Cross-Linked Polyethylene/Poly(ethylene oxide) Electrolytes: A New Approach for Practical Lithium-Metal Polymer Batteries” J. Am. Chem. Soc., 136 (20), pp 7395–7402 doi: 10.1021/ja502133j
Lu, Y., Korf, K., Kambe, Y., Tu, Z. and Archer, L. A. (2014), “Ionic-Liquid–Nanoparticle Hybrid Electrolytes: Applications in Lithium Metal Batteries,” Angew. Chem., 126: 498–502. doi: 10.1002/ange.201307137