Nickel sulphate: In high-nickel batteries, safety comes into question

electric vehicle

Since May 2020, three cars equipped with the latest NCM811 battery cells, supplied by CATL, have caught fire in China. All three were Aion S model, sedan vehicles manufactured by GAC. Though relatively small in number compared to the overall number of EVs sold in China, the reported car fires have caused a resurgence in safety concerns, particularly regarding the use of lithium-ion batteries with NMC811 cathode material.

Whilst NMC811 cathodes have an energy density advantage over rival NMC and NCA cathode materials, and a lower average cobalt content reducing both raw material price and sustainable sourcing issues, stability of NMC811 cathodes has been questioned continually since its introduction into automotive products.

Roskill View

Roskill’s research shows 20 EV fires have been reported since the beginning of 2020 in China; 85% of these cars were powered by lithium-ion batteries using nickel-based ternary cathode (NCM/NCA). NCM and NCA batteries are playing an important role in faster EV adoption rates, as a result of higher energy density being able to provide longer driving ranges.

However, safety remains an issue as NCM and NCA are prone to thermal runaway, the primary cause for a lithium-ion battery fire. If not contained, thermal runaway can lead to significant dangers. NCM/NCA batteries have lower onset temperature for thermal runaway and higher peak cell temperature during a runaway event, compared with LFP batteries which are regarded as a safer choice for EVs. NCM cells may vent a larger amount of flammable and toxic gas when ignited and can even result in explosion.

Transition temperatures into thermal runaway & maximum temperatures reached by the cell (°C)

The lower thermal runaway threshold for NMC811 cathode materials provides a major concern for EV manufacturers, which are increasingly balancing demands from a competitive EV market against tightening margins and safety limits. Despite the inherent risks to higher-Ni cathode materials, there are several mitigating factors which can reduce the risk of thermal runaway. To improve safety and cycle performance of NCM 811 batteries, advanced surface coatings are fabricated on NCM materials by cathode manufactures, meanwhile, additives are added into the electrolyte by cell makers. Automakers also install advanced battery cooling system and fire suppression systems to guarantee safety for passengers.

Vented gas volume for a single cell reaching a thermal runaway (l)

In addition to this, NCM 811 precursor and cathode materials of uniform quality are difficult to be produced on a large scale as the production requires specific synthesis temperatures and pressures. Despite the lower raw material cost of NMC811 materials because of the lower cobalt content, Roskill has identified that the overall cost for using NCM 811 at EV pack level is considerably higher than other lower-nickel NCM cathodes. This is largely because of the additional battery management and production costs required compared to other Li-ion cathode materials. This is backed-up by comments from major cathode producers such as Umicore, which stated at the AABC Europe 2020 conference that a nickel content of 70% (NCM 712) is the industry’s “sweet spot” when considering all trade-offs on NCM.

Roskill’s Nickel Sulphate: Outlook to 2029, 3rd Edition report was published in May 2020 and includes forecast trends in supply, demand and pricing over the next decade. The report provides detailed profiles for new potential producers and analyses the availability of various feedstock types. Click here for more information.

Roskill’s Nickel: Outlook to 2029, 16th Edition report was published in April 2020 and outlines industry trends and forecasts for the next decade. The report forecasts nickel mine supply used in Class I and Class II production. Click here to download the brochure for the report, or to access further information.

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This article was written by Kevin Shang. Please get in touch below if you wish to discuss further:

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