Not long ago, big powertrain news involved the launch of new engine plants like JLR’s Engine Manufacturing Centre. Now the attention has switched to battery manufacturing and the best way to produce lithium ion batteries for EVs.
Some, like Tesla, keep schtum about the precise details, but lithium ion EV batteries all have the same basic components. Individual cells are arranged into modules that are connected together via a high-voltage connector (busbar) and encased to form a single battery pack. Two other main components are the battery management system, which controls and monitors every aspect of the battery’s performance and behaviour, and the liquid cooling system.
Individual cells work in much the same way, with an anode and cathode separated by a thin polymer layer and surrounded by electrolyte, but those components can be rolled to make cylindrical cells, assembled as a pouch (a bit like cat food) or formed into a prism shape. The chemistries within can be very different, each with pros and cons, and they continue to evolve.
The first-gen Nissan Leaf had a 24kWh lithium manganese oxide battery (LMO). All lithium ion batteries rely on electronics to prevent uncontrolled overheating, known as thermal runaway, during charge or discharge, but LMO has the benefit of being intrinsically safe at the cost of other factors such as energy density. But the technology has evolved. The BMW i3 and 2019 62kWh Leaf have lithium nickel manganese cobalt oxide (NMC) batteries. These are a favourite choice for anything from power tools to EVs and give the best of most worlds. The Leaf battery is also structured differently, with cells joined by laser welding so Nissan can ring the changes with the configuration of the battery for greater flexibility.
The Volkswagen’s ID 3’s battery pack is a straightforward layout of up to six modules containing 24 cells each, making a 408V pack. Like the Leaf, the VW cells are NMC, but that doesn’t mean they are identical because manufacturers work with cell suppliers to fine-tune the quantities of the main ingredients, playing to the strength of each. Nickel is good for high power density but has poor stability on its own. Manganese is the stable partner and the two are a great combination. Nickel is predominant over cobalt because it’s cheaper. Small amounts of silicon at the anode play a role in boosting energy density.