The science behind battery development and use in F1

To many people, a battery is a battery. They may differentiate between the lead acid batteries found in most road cars and the lithium batteries found in battery electric vehicles and also in Formula 1 cars, but few realise there are many different types of lithium ion batteries – each with different characteristics and costs.

The history of lithium batteries is a relatively recent one and the result of cumulative work done in the USA, UK and Japan. This was recognised in 2019 with the award of the Nobel prize to Stanley Whittingham, John Goodenough and Akira Yoshino from those countries respectively.

Before talking of the different types of battery it’s worth a quick look at how a battery works since this will indicate why different types of battery have been developed. Essentially a battery consists of an anode, which is the negative electrode, and a cathode which is the positive electrode. In between is an electrolyte which is normally liquid. During charging, the positively charged ions flow from the cathode through the electrolyte to the anode. They are stored there and when no more can be stored the battery is fully charged. Negative charge electrons flow from the negative electrode to the positive through the charging circuit. During discharge the opposite happens with the electrons flowing through the device which needs power – the electric motor in our case. When all the ions have moved back through the electrolyte to the cathode, the battery is fully discharged.

In a lead acid battery the cathode is made of lead dioxide and the anode is metallic lead. The electrolyte is sulphuric acid. In a lithium ion battery the anode is generally graphite and the electrolyte generally a lithium salt, but the cathodes can be quite different in different batteries. The two most common cathode types are LFP and NMC, although many others are vying for popularity since this is where much development to improve performance is taking place.

Of the two electrodes the anode is largely responsible for charging times and the cathode has more to do with range, but it also has a very strong influence on costs. It’s the cathode, therefore, which has been the focus of development and hence the fact most batteries in use at the moment are either LFP or NMC. LFP is an acronym for lithium iron phosphate.

While lithium prices have increased considerably over the past two years, it’s a material over which there are no long-term concerns over supply. Hence even with the increased raw material costs an LFP battery is considerably cheaper than an NMC, and is found in some of the cheaper battery electric vehicles from MG, Hyundai and base variants from Tesla.

NMC stands for nickel, manganese, cobalt and, not surprisingly, these are the elements that make up the cathode in this type of battery. Cobalt is termed a strategic material because 50% of the planet’s reserves of it are found in the Democratic Republic of the Congo, where 20% is extracted in artisanal mines with dubious safety and human rights standards. Much of the processing of the ore is done in China, which accounts for nearly half of the world’s production.

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Photo by: Giorgio Piola

The NMC cathodes are significantly more expensive than LFP, with the material costs amounting to 62% of the cost of the cell, but they do give significantly better performance. Because of this the exact proportions of NMC are varied. An NMC 532 cell contains 50% nickel, 30% manganese and 20% cobalt. The trend now is to use NMC 811 which has 80% nickel and only 10% of manganese and cobalt. Others, like Volkswagen, are pursuing high-manganese chemistries which are believed to give the performance of NMC 532 at the cost of LFP cells.

While development focus is on cathodes, anodes are also being experimented upon and the addition of silicon to the graphite material looking promising. Focus is also turning to other chemistries such as sodium-ion. Sodium is abundant and starting to challenge the efficiency of LFP cells.

So much for the chemistry, but what makes up a battery? The first level is the cell itself. These are most commonly cylindrical, resembling a slightly overgrown version of the AA battery everyone is familiar with. Some manufacturers prefer pouch cells which resemble a small envelope and have the highest power and energy densities at cell level. The final type is prismatic cells, these are rectangular block-shaped cells but aren’t common in automotive use.

A battery that overheats is not only inefficient but could be prone to thermal runaway and subsequent fire

The cells, whatever geometry they may be, are connected in groups called modules and these modules are connected together and housed in what we would term a battery. The Tesla Model S has 16 modules, each containing 444 cells. The modules are connected in series, thus a battery contains 7104 cells giving a capacity of just under 90 kilowatt hours (KWh). In different batteries, different configurations of series and parallel connections can determine voltage and capacity.

The last parts that make up a battery are extremely important. One is the cooling system which must maintain the battery at optimum temperature for use. In road cars this is usually a water and glycol mix, but high-performance batteries may use immersion in a dielectric oil for weight reduction. A battery that overheats is not only inefficient but could be prone to thermal runaway and subsequent fire.

Finally we have the battery management system or BMS. This is a piece of sophisticated electronics and software that gathers data from each cell and ensures the cells are balanced in terms of voltage, charge and temperature. It will also monitor safety-critical aspects. The software will then pass information on the state of charge and of health to the energy distribution system, which determines the electrical conduction path through the battery.

So while in essence the lithium ion battery in your torch is a close cousin of the one in an F1 car, it’s a simple example of what can grow into an extremely sophisticated energy storage device.

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