Researchers at Dalhousie University, led by Professor Jeff Dahn, have developed an excellent moderate-energy-density lithium-ion pouch cell chemistry that they say should be able to power an electric vehicle for more than 1.6 million kilometers (1 million miles) and last at least two decades in grid energy storage. An open-access paper in the Journal of Electrochemistry JES details the new cell and the testing to which the team subjected it to create a benchmark for further research.

Professor Dahn and his research group is Tesla’s battery research partner, following an agreement signed in 2015. (Earlier post.)

In this paper, testing results on LiNi_0.5Mn_0.3Co_0.2O₂/artificial graphite (NMC532/AG) cells are presented. The NMC532 used in these cells is “single crystal” NMC532 as described in the papers by Jing Li et al. and Lin Ma et al. The artificial graphite (AG) used in these cells is provided by Kaijin (China) and is grade AML-400. Over the last 10 years the Dalhousie research group has tested a wide variety of Li-ion cells with various positive electrodes, negative electrodes and electrolytes. Of all the cells tested, the ones with the longest lifetime are the single crystal NMC532/AG cells with optimized electrolytes reported here. Therefore, we believe it is valuable to present a comprehensive summary of this test data for others to benchmark against.

—Harlow et al.

Long-term cycling data plotted as percent initial capacity versus equivalent full cycles for NMC/graphite cells. The data from Harlow et al. for 100% DOD cycling was collected to an upper cutoff potential of 4.3 V. The data from Ecker et al. used 4.2 V as 100% state of charge. The purple and green data (Dahn’s results) should be compared to the black data (Ecker et al.). Data for restricted range cycling (i.e. 25 - 75% SOC and 40 -60% SOC) for the cells in this work is not available but is expected to be far better than the data shown for 0 – 100% DOD cycling by analogy with the cells tested by Ecker et al. Credit: JEC, Harlow et al.

Single crystal NMC532/graphite cells with exceptional lifetime have been developed. Storage and cycle testing up to 3 years in duration has been presented at 20, 40 and 55°C. The lifetime of these cells far exceeds that of other NMC/graphite cells reported in the literature and which have been used for lifetime modelling. It is suggested that lifetime models for NMC532/graphite cells consider the data presented here.

Full details of these cells including electrode compositions, electrode loadings, electrolyte compositions, additives used, etc. have been provided in contrast to literature reports using commercial cells. This has been done so that others can re-create these cells and use them as benchmarks for their own R+D efforts be they in the spaces of Li-ion cells or “beyond Li-ion cells”.

The cells described here have two dominant failure mechanisms at 20, 40 and 55°C. These are Li inventory loss and impedance growth. We find virtually no evidence for loss of active material in these cells during cycle testing under the conditions used here.

—Harlow et al.

Dahn’s research team is delivering a series of lectures including information on new battery technology at the upcoming 236^th ECS Meeting in Atlanta, Georgia (13-17 October).

The work was supported by NSERC and Tesla Canada under the auspices of the Industrial Chairs program.

Resources

• Jessie E. Harlow, Xiaowei Ma, Jing Li, Eric Logan, Yulong Liu, Ning Zhang, Lin Ma, Stephen L. Glazier, Marc M. E. Cormier, Matthew Genovese, Samuel Buteau, Andrew Cameron, Jamie E. Stark, and J. R. Dahn (2019) “A Wide Range of Testing Results on an Excellent Lithium-Ion Cell Chemistry to be used as Benchmarks for New Battery Technologies” J. Electrochem. Soc. 166(13): A3031-A3044; doi: 10.1149/2.0981913jes