By Kent Griffith
April 15, 2019 | Twenty-five years ago, the lithium-ion battery changed the world by enabling energy-intensive portable electronics such as cell phones and laptops. The lightweight, high energy density lithium-ion battery now stands poised to empower the electrification of transport. Hundreds of key players met at the 36th annual International Battery Seminar and Exhibit in Fort Lauderdale, Florida in late March. Representatives from battery cell manufacturing, mining and materials, automotive production, power tools, household devices, portable electronics, battery analysis instruments, market strategies and consulting, and university research laboratories came together to share the latest advances and to discuss the future promises and challenges of this critical technology.
Graphite is nearly universal as the anode material in a commercial lithium-ion battery and has thus been thoroughly investigated by hundreds of research groups in university and industry labs. Nevertheless, Mark Verbrugge and co-workers at GM presented evidence for several overlooked features in the capacity–voltage curve of lithium intercalating into graphite. A standard practice in battery research is to determine the number of reactions that occur by analyzing the derivative of the capacity–voltage curve, but noisy or over-smoothed data can hide features. The GM team developed an adaptive-width numerical smoothing method that revealed the additional features in graphite and can be applied to other battery systems.
One problem for researchers that are working to develop next-generation battery materials is understanding the specific requirements of different OEMs. The balance of energy–power–weight–volume–cost can vary considerably between portable technology, electric vehicles, and grid-scale storage. Bob Taenaka from Ford did not mince words when he stated that volumetric performance metrics (Wh×L–1, W×L–1) are key for EVs. Chia-Ying Lee from SharkNinja echoed this sentiment for household electronics such as robotic and handheld vacuum cleaners. Michael McDonald from Motor Coach Industries noted the larger space available in electric buses and suggested their application requires a balance between size and weight, emphasizing that the central priority for motorcoaches is driving range coming from total battery energy. Transit buses, on the other hand, require minimal range and can shift the performance focus to efficiency via regenerative braking, fast charging at bus stops, and battery lifetime.
For decades, lithium cobalt oxide has been the dominant lithium-ion battery cathode material. For the EV sector, we are seeing a shift toward nickel-rich chemistries such as lithium nickel manganese cobalt oxide with 60–80% nickel (known as NMC622, NMC811) from most OEMs and lithium nickel cobalt aluminum oxide with approximately 80% nickel (known as NCA) from Tesla. Cobalt is expensive and geographically concentrated in the Congo so decreasing its content is a good move. However, the simultaneous transition to nickel-rich materials and rapid growth in EV production is putting stress on the nickel supply chain. Several perspectives were offered at the International Battery Seminar on the future raw material supply.
Franz Josef Kruger of Roland Berger underlined the shift toward Ni-rich materials with optimism that the problems with NMC811 were solved and it would be industrialized by 2020. He went on to describe a scenario where nickel supply will not keep pace with increasing demand and will be the driver for increased cost, with shortages being realized as early as 2020 to 2021. From his perspective, it is critical to establish supply chain partnerships to be well-positioned in the high-energy cell market.
An alternative approach to avoiding the issues with nickel (or cobalt) supply is to use cathode materials based on iron or manganese. Didier Marginedes of Blue Solutions – Groupe Bolloré described their Ni-, Co-free lithium metal polymer (LMP) battery being employed for e-buses, stationary modules, and beyond. Vaselin Manev of XALT Energy presented a case for lithium manganese oxide (LMO) cathodes paired with lithium titanium oxide (LTO) anodes that will cycle for well over 10,000 cycles with more than 90% of capacity retention, even under relatively fast charging conditions of tens of minutes.
Tens of thousands of cycles are possible in lower energy density cells but what is the limit for the state-of-the-art high energy density battery? Plenary speaker Jeff Dahn from Dalhousie University conveyed the message that the best artificial graphite anode and NMC cathode can certainly surpass 5,000 cycles with at least 80% capacity retention even when cycled to relatively high voltages to extract the most energy. These figures translate to a future where electric vehicle batteries could last for 500,000 or even 1,000,000 miles! While personal vehicles are not expected to reach these mileages today, car sharing programs and autonomous vehicles will mean that cars spend less time in garages and parking lots and more time on the road, perhaps all on a single battery pack.