Battery cells as told by a slide, oranges and a chocolate aero

I would hazard a guess that if challenged in a pub, most automotive engineers would not be able to tell you how an electric battery for an EV?actually?works. They would probably be able to tell you about the battery pack and how it powers the electric motor. They may well describe the battery management system which monitors the health status of the battery cells within the battery pack (though this may not constitute pub appropriate conversation), and I suspect there may even be a few mumbled words about electrons and cobalt whilst they desperately try to recall their GCSE physics.

Until recently, I would count myself within this cohort of automotive professionals. That was until?Karandeep Bhogal joined battery material company?Nexeon, and our dinner time conversations required some sly wikipedia-ing on my part. Nexeon, like?StoreDot?and?Sila?Nanotechnologies are developing silicon based anodes for batteries. I shall attempt to explain why that is significant armed with my new fangled knowledge.

Electro-chemists and material scientists, look away now before I offend you with my terrible (and immensely unscientific) analogy.

Firstly, battery packs are made of battery cells. For an idea of scale, the standard range Tesla Model 3 has 2,976 battery cells arranged in 96 groups of 31. These cells are where the magic happens — i.e. where energy is stored and extracted in order to make the electric vehicle go.

Whether the cells are charging, or discharging to release energy when in use, both states involve moving atoms and electrons from one place to another -in the case of battery cells, from the cathode to the anode. Consider the image below. Here the orange represents an atom of Lithium with the peel representing an electron.

(Introducing the orange, playing the part of Lithium)

When the battery is empty (i.e. has fully discharged), all of the lithium atoms and their electrons are in the cathode — the oranges plus their peel are in the cathode crate.

(Battery cell in its discharged state)

To charge the battery, the atoms must be moved from the cathode to the anode via an electrolyte and external circuit. In this particular analogy the peeled oranges must move up the slide whilst their peel travels via the external circuit. As anyone who has walked up a slide knows, this process uses energy.

(Charging the battery cell)

The orange and peel reunite in the anode where they are stored until the battery needs to extract energy when the vehicle is in use.

(Battery cell in its charged state)

At which point, the peeled oranges flow down the slide and the peel flows in the external circuit, releasing energy and powering the EV motor via this flow of electrons (peel).

(Battery cell discharging and releasing energy)

This flow of oranges and peel can continue as the battery charges and discharges. (I will save battery degradation explained via an orange for another time. But I will use this opportunity to point out that the oranges in our analogy?must?be easy peelers to capture the ease with which Lithium can release electrons. I digress.. )

However, range and charge point availability still remain major barriers to electric vehicle adoption and so we need to increase the capacity of the anode in order to make vehicles go further without just making batteries bigger. Essentially, the anode needs to be able to fit more lithium in it, or our crate needs to carry more oranges.

Battery cells typically use graphite in the anode as it is super stable and its porous nature can hold the lithium in place. Graphite is like filling our crate with aero chocolate such that the oranges can fill the chocolate voids left by the bubbly aero.

(Introducing aero — playing the role of graphite)

The trouble is, you can’t fit that much lithium within the graphite structure — or in our case, can’t fit that many oranges within the aero.

Enter Nexeon.

If the anode were made of silicon, on a ratio basis you can store significantly more lithium for significantly fewer silicon atoms compared to the graphite. i.e more oranges within the same crate = more energy capacity without using a bigger crate.

However, and I admit this is where the analogy gets even shakier, silicon expands up to 300% when combined with lithium. Imagine what would happen if instead of filling the the anode crate with aero, it’s filled with loads of tiny Violet Beauregardes and when she comes into contact with the oranges, she goes full blueberry.

This enormous expansion would clearly damage or break the anode crate. Silicon, or the Violet Beauregardes, need stabilising within the graphite or aero to prevent the swelling whilst still increasing the energy capacity. This is what Nexeon, StoreDot and Silas have been furiously pioneering with techniques and technology that far exceed the limitations of this laboured analogy.

(The limit of the analogy has been reached)

Over the past 5 years electric vehicle uptake has snowballed from the realms of unviable niche to the only responsible future. Battery development has improved exponentially in tandem, with the cost per Kwh standing at 10% of what it was in 2010.

Today this momentum is growing, amplified by the pressing need to decarbonise multiple industries. Batteries are the key to zero emission transportation and large scale renewable energy storage. Battery cells that have more capacity result in battery packs that require less space, fewer raw materials, less time for charging, less investment in infrastructure and less energy. The domino effect up and down the value chain and at every scale is unparalleled.

Whilst I can force my brain to understand the logic, I still find it mind blowing that unprecedented impact is realised by innovating on the nanoscale. Stranger still that the parameters to explore, understand and harness explode into the billions when operating this zoomed in.

I’m excited to watch the progress of the likes of Nexeon, Sila and Storedot who, if battery development to date has been Couch to 5K, they’re taking it from parkrun to the Olympics. In this next phase, material scientists and chemists may just be our latest electrification BNOCs.