The lithium-ion batteries that power electric vehicles have so far mostly been based on either lithium iron phosphate or lithium cobalt oxide electrochemistries. A U.K. industry/government RD&E project led by Scottish battery systems supplier Axeon has recently developed a next-generation EV battery pack that incorporates Li-ion cells that use nickel cobalt manganese (NCM) chemistry, a formulation that offers higher energy density and therefore greater range.
Most other Li-ion cells employ cathodes of carbon (graphite); the new NCM lithium-ion cells [Li(NiCoMn)O2] have cathodes composed of nickel, cobalt, and manganese.
In a hypothetical 30-kW·h battery pack, an array of NCM lithium-ion cells could be one-third the mass and half the volume of an array of current lithium-ion phosphate cells in a pack of equivalent power, said Allan Paterson, a senior electrochemical engineer at Dundee-based Axeon, which bills itself as Europe’s largest independent Li-ion battery systems provider. The new technology could enable a 35% improvement in EV range while cutting costs, he added.
The company's lithium NCM batteries offer energy densities from 155 to 190 W·h/kg, or 330 to 365 Wh/L, whereas lithium iron phosphate units generally provide from 90 to 125 W·h/kg, or 130 to 300 Wh/L for electric and plug-in hybrid vehicle applications. Paterson acknowledged, however, that NCM Li-ion batteries feature lower power density (current output-rate capability) than lithium iron phosphate [LiFePO4] types but higher than cobalt oxide [LiCoO2] systems.
The research effort, which included as partners the engineering firm Ricardo and the specialist vehicle supplier Allied Vehicles, was partially funded by the U.K. Technology Strategy Board.
Ricardo contributed its next-generation battery management system (BMS), which monitors the state of a battery and controls key performance parameters to ensure that its multiple cells operate safely and last as long as possible. “The BMS provides optimal functional control, maintains thermal conditions, and can perform dynamic active and passive balancing of the cell array by supplying more energy to the weaker links when needed,” said Paterson. “A large part of our efforts involved fully characterizing the cells and calibrating the control strategy.”
Team engineers packaged the pouch-type NCM-Li cells in modular building blocks that can support various thermal management options (air or liquid cooling) and also enable Axeon to rapidly produce prototypes of the technology for other vehicle types, which would significantly reduce development lead times.
Glasgow-based Allied Vehicles supplied the electric vehicle platform for performance and durability testing as well as validation of the preproduction battery system. When fitted with the lightweight and compact prototype system, the test vehicle demonstrated increased range—rising from about 60 mi (97 km) to more than 100 mi (161 km)—as well as better functionality and performance. Installation of the new power unit, for instance, raised the vehicle’s ground clearance, improved its weight distribution, and endowed it with better driveability.
Several other companies have reportedly developed their own versions of lithium NCM batteries, including Panasonic, International Battery, and Molicel. Both the General Motors' Volt and Nissan's Leaf use dual-composition battery cathodes that combine manganese spinel (a safe though lower-energy-density material) with NCM compounds that boost the former’s performance.
Lithium NCM chemistry is increasingly seen as a preferred solution for battery systems for smaller city-focused EVs, urban delivery EVs, and plug-in hybrid vehicles over the next three to five years, according to Axeon.
The company’s latest cells are among the first of a new “class of lithium-ion chemistries based on mixed metal oxides,” Paterson explained. Other even more capable mixed metal oxide battery formulations, such as nickel cobalt aluminum and layered/layered spinel composite batteries, should arrive during the next several years, he said. The latter type features two chemical oxides in a sandwich structure on the same particle.
Two years ago, the Technology Strategy Board awarded about $1 million to the consortium—bringing the total project funding to $2 million—with the objective of developing an innovative high-energy-density battery system for an EV. A key aim of the project was to confirm that the expected cell-level benefits would pass through to the battery pack level when taking into account overall packaging, cell retention, cooling, and interconnects.
“Our goal was to take the technology nearly up to product readiness,” Paterson said. Axeon and Ricardo are now discussing how to commercialize the new technologies. Prototype NCM-Li cells are already being used by a European vehicle partner in a developmental product as well as on other test vehicle platforms.