Lithium ion batteries are set to revolutionise transportation technology as they become the power source for a new generation of electric and hybrid vehicles. But there are a whole range of different lithium ion chemistries with hugely different performance characteristics.
At a workshop this week at the second International Congress of Electric Vehicles in Berlin, Germany, Axeon, Europe’s largest independent lithium-ion battery system supplier, made clear that it is leading the charge on batteries for automotive applications. Currently, Axeon utilises lithium iron phosphate cells, which display an excellent safety profile, as well as good high current discharge performance, excellent cycle life performance and attractive cost-down potential.
However, Axeon has a number of technology development programmes and is undertaking extensive R&D on other cell chemistries, which have the potential to deliver improved energy and power density for its customers, as well as reduced packaged dimensions, making the batteries smaller and lighter.
Axeon is already working with a range of customers across Europe to produce batteries for both volume and prototype applications as diverse as fully electric delivery vehicles, high-performance sports cars, electric buses, hybrid heavy plant vehicles and city cars. Axeon’s technology is fully proven, with vehicles using its batteries having covered more than 300,000 miles on Europe’s roads.
Leading the conference session, George Paterson, Engineering Sales Manager at Axeon, discussed the considerations necessary in selecting the right cells for applications and the construction and management of battery systems.
“Not all customers know exactly what they want a battery to do other than propel a vehicle 100 kilometres,” said Paterson, who has 10 years experience of working with batteries. “The workshop outlined why it is important to specify a battery correctly – not simply to look at what range or top speed it gives the vehicle.”
“When specifying a battery, it is crucial to look at all parameters required, including cell voltage, energy density, power density, useful capacity, charge efficiency, self discharge, cycle life, temperature range and robustness”, Paterson continued. “This enables our engineering team to use its expertise to select the most appropriate cell for that particular application.”
Cells come in a range of shapes and sizes and an understanding of the characteristics of each will enable engineers to choose the right battery for their application. Paterson explained, “Whereas high capacity, larger batteries may be ideal for a commercial vehicle application; a smaller battery with higher energy density may be more suited for applications where space and weight are issues – for example in performance vehicles.”
As well as stressing the importance of battery specification, Paterson also emphasised the importance of managing the supply chain, including auditing suppliers’ facilities and ensuring that the cells have been tested to the correct standards, which are mandatory for bulk shipping.
Often overlooked in battery discussions, given the focus on cell chemistry and packaging, are the Battery Management System (BMS) and system communications. The BMS is essential to the optimal functioning of the battery system, as it monitors the conditions of individual cells and provides information on the state of charge of the cells and battery overall – which is obviously key to working out how much range remains in the electric vehicle. It also balances the cells to maximises the battery life.
Integral to the BMS is the communication architecture of the battery system, which carries information relating to battery status, charge and discharge rates, performance limits, safety and maintenance. The communications system is also used to access information during maintenance and servicing, enabling programming of the battery system and downloading of stored data.
Paterson concluded, “The complexity of cell and battery specifying, design, procurement, manufacturing, transportation and servicing means that understanding cell chemistry, characteristics and performance is essential in creating a quality battery for electric vehicle applications.”