Charged EVs | Tesla battery experts describe million-mile cell in new paper

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At the Tesla Autonomy Event in April, Elon Musk said the Disruptors of Detroit were working on a new battery pack that would last a cool million miles, and said it would be available next year. Now Tesla battery research partner Jeff Dahn and his team have released a paper in which they describe this million-mile battery cell.

The new Li-ion battery cell features a next-generation “single
crystal” NMC cathode and a new type of electrolyte. Dahn’s team has extensively
tested the cells, and believe they could enable a battery pack that lasts over
a million miles in an EV.

The team’s paper, A Wide Range of Testing Results on an Excellent Lithium-Ion Cell Chemistry to be used as Benchmarks for New Battery Technologies, was published in the Journal of The Electrochemical Society. The following brief excerpt (via Electrek) describes the results of testing the new cells:

“Up to three years of testing has been completed for some of the tests. Tests include long-term charge-discharge cycling at 20, 40 and 55° C, long-term storage at 20, 40 and 55° C, and high precision coulometry at 40° C. Several different electrolytes are considered in this LiNi0.5Mn0.3Co0.2O2/graphite chemistry, including those that can promote fast charging. The reasons for cell performance degradation and impedance growth are examined using several methods. We conclude that cells of this type should be able to power an electric vehicle for over 1.6 million kilometers (1 million miles) and last at least two decades in grid energy storage.”

This is a huge advance – the new cells last two to three times longer than Tesla’s current cells – and if the company can bring the new technology into production in a reasonable timeframe, it could radically change the economics of EVs.

The paper notes the importance of long-lasting batteries for
such vehicles as robotaxis, long-haul trucks and transit buses. In these applications,
a battery’s ability to deliver a high number of charge/discharge cycles is
critical, in contrast to the consumer vehicle market, in which maximum range is
the most important feature (at least from a marketing standpoint).

The paper also mentions vehicle-to-grid applications, which
could someday allow EV owners to earn revenue from their cars while they aren’t
being driven (see the upcoming issue of Charged
for a profile of Fermata Energy, a
pioneer in this space).

Meanwhile, job listings on Tesla’s web site seem to confirm rumors that the company plans to start manufacturing its own battery cells (as reported by Electrek).

The possibilities are endless.

Long-term cycling data plotted as percent initial capacity versus equivalent full cycles for NMC/graphite cells as described in the legend. The data from this work for 100% DOD cycling was collected to an upper cutoff potential of 4.3 V. The data from Ecker et al.,2 used 4.2 V as 100% state of charge. The purple and green data (this work) 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.
Capacity remaining versus storage time for NMC/graphite cells as determined by reference performance testing every several months. The data from Ecker et al.2 and Schmitt et al.6 are for Sanyo UR18650E and Sony US18650V3 cells, respectively. The voltages and temperatures at which the cells were stored are given in the legends.
a) Measured properties of the NMC532/graphite 402035 (40 mm x 20 mm x 3.5 mm thick) pouch cells used here. The positive electrode was 94% active material, the loading was 21.1 mg/cm2 (target was 21.3) and the electrode density was 3.5 g/cm3. The negative electrode was 95.4% active material, the loading was 12.2 mg/cm2 (target was 11.8) and the electrode density was 1.55 g/cm3. b) Stack energy density of the NMC532/graphite couple for several electrode thicknesses. b) Stack energy density calculations – gives values for the electrode stack (negative coating/copper/negative coating/separator/positive coating/aluminum/positive coating/separator). Assumptions – copper foil = 8 μm, aluminum foil = 15 μm, separator = 16 μm, N/P capacity ratio = 1.1 at 4.3 V, average cell voltage = 3.75 V. The highlighted row represents the design used in this work.

Source: Journal of The Electrochemical Society via Electrek



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