Given batteries are such an important part of our electric future, it’s not surprising attempts to improve their performance are constant. Some of these attempts are valid, some are the work of charlatans, others are sincere but just wrong.
Battery development tends to move in two broad directions - changes to cell chemistry or changes to battery and cell structure, or perhaps both. The new 4680 cell Tesla provides an example of improved structural engineering, quite apart from any changes to cell chemistry.
One of the most important things about the 4680 cell is that it’s bigger, which gives greater energy density. However, another of the most innovative changes embodied in the 4680 is the so-called ‘tabless’ design of the electrodes. Rather than having current flow through a single concentrated point as with most battery cells, the 4680 features a continuous fringe of tabs folded into one large composite tab as shown in the photograph. This design simultaneously allows the transfer of increased current while reducing the associated heat through a point contact.
The tabless design reduces the cell’s internal resistance. When the electrodes in a cylindrical cell are unrolled, they’re long. In conventional cell designs, current has to pass along the entire length of each electrode to reach the tab. With the 4680, current only has to travel across the electrode (a much shorter distance) to reach the terminal. Also, in many battery designs, the positive and negative cell tabs are connected to the respective busbars by wires. In the 4680 the wires are omitted and the bus bar is welded directly to the metal cap covering the cell tabs.
Finally, the larger diameter of 4680 cells have a reduced surface area compared with smaller cells of the same volume. The outer casing is made of steel so this results in reduced weight. In all, the new cells are said to have five times the energy and six times the power of the smaller cells Tesla has been using, resulting in a range increase of about 16 per cent. So, applying clever engineering to the design of battery packs can yield verifiable service advantages.
Anyone who’s accidentally shorted the terminals of a lead-acid battery with a spanner or the like will forever remember the ensuing fuss. Batteries contain a great deal of stored energy and lithium cells contain the most at the highest voltage. It’s difficult to imagine another chemistry (other than lithium variations) that could perform better in an EV. Importantly, though, lithium cells contain everything needed for a sustained fire that’s almost impossible to extinguish if the electrodes are shorted.
Researchers have devoted a good deal of effort to increase the safety of lithium ion battery packs. Many approaches have involved armouring the packs. Tesla originally fitted a titanium plate to the underside of the Model S to protect against puncture and short circuiting after a number of well publicised fires. However, another company called Enovix has been working on a protective system called BrakeFlow that’s built directly into the cell.
Enovix spokesman TJ Rodgers explains one way to limit thermal runaway between shorted electrodes is to protect the system with a resistor that reduces current. However, a resistor that can do this will probably limit current too much and restrict performance. The BrakeFlow solution employs a number of resistors in parallel. Resistors in parallel reduce overall resistance.
The anode (negative terminal during discharge) of a Li-ion cell contains a carbon matrix that stores lithium ions. However, silicon-based anode material can store many more lithium ions leading to increased energy density. But in such applications silicon expands much more than carbon, which leads to greatly reduced cycle life. Enovix is also active in solving this problem and has developed cells with 100 per cent silicon anodes. How?
Enovix describes its battery technology as 3D, meaning individual strip electrodes are stacked atop each other to form each cell. This construction allows the fitting of stainless steel reinforcing plates that hold the silicon elements tightly in place and prevent expansion. Other battery designs can also do this but require the reinforcing plates to act over a much broader area.
Enovix has been quietly developing its battery technology since about 2010 and has only just released its first batteries in form factors suited to mobile devices. This is because battery capacity in this space commands a price premium compared with EV batteries. The company strategy is to maximise revenue from this market to further fund development of its EV battery technology, which is scheduled for mid-decade availability. A measured approach.
The solid-state battery is another oft-mentioned technology in the discussion of revolutionary battery development. Current Li-ion batteries use a liquid or gel electrolyte with a separator to isolate the electrodes from each other. The liquid electrolyte is a point of vulnerability and is what burns so vigorously (along with other components) during thermal runaway. A solid-state electrolyte alleviates the likelihood of such an event but that’s just part of the story.
Solid-state cells/batteries have a reduced volume compared with conventional lithium ion batteries. This can be seen in the illustration from BMW representing the internal structures of conventional and solid-state cells. The reduced volume means either more charge and longer range for the same sized battery pack, or a smaller, lighter, less expensive battery pack. Solid-state batteries can also be charged much more quickly. Further, the greater efficiency of solid-state batteries means they require less cooling, which also reduces weight.
Solid-state battery technology is often described as an EV ‘game changer’ and this would be correct if only such batteries were available for electric vehicles, but they’re not - not yet, anyway. All the big names have solid-state technology in development. Toyota is said to be in front but eventually, when all the production difficulties are solved, the technology will be ubiquitous. Even NASA is working on the technology within its SABERS project with a view to developing a realistic power source for electric aircraft. It uses what’s known as sulphur-selenium technology to reduce material costs because there’s so much sulphur available. It’s a by-product of oil refining. This chemistry also has better energy storage potential than conventional lithium.
Atomic, or nuclear batteries constitute another technology that’s in development. However, these cells are much further behind solid-state batteries in progress towards general availability, despite some over-excited claims. In short, atomic batteries utilise the beta radiation decay of nuclear waste as a source of electrical energy. This is a scientifically valid concept known as betavoltaics and it’s promoted as a useful utilisation of this otherwise waste material. In fact, the long half-life of such nuclear waste is touted as a strong positive if it’s used as the raw material for a battery.
A diamond battery is an atomic battery named after the artificial diamonds upon which the technology will be built. This is to be derived from radioactive graphite currently stored as waste. Atomic batteries are primary types and can’t be recharged like secondary lithium-ion or lead-acid types. However, it’s suggested they could last for thousands of years. NDB (Nano Diamond Batteries) claims they could remain in service for as long as 28,000 years. More moderate claims still suggest a couple of thousand years is possible.
The important thing to remember, though, is that atomic batteries have very low outputs - just a handful of microwatts.
The idea of a radioactive battery in your phone or laptop may seem abhorrent but it’s not as bad as it sounds. Beta radiation is free electrons in motion. These have low penetrating power and pose virtually no risk if they remain outside the body. Further, the NDB system will encase the radioactive diamond in another artificial diamond layer, so the resulting cell will be suitable for use in things like pacemakers. It’s also suggested the technology could be scaled up to run EVs and homes. Despite the hype surrounding atomic, or nuclear batteries, they don’t exist. There have only been lab prototypes produced. That they will ever exist in a form that might support an EV is nothing more than conjecture.
People are clever and there are some unique ideas out there. In fact, some of them can best be described as ‘out there’, like Tanktwo. This is an off-beat attempt to solve the ever present problem of long charging times. In a nutshell, the idea is to vacuum the spent cells out of a car and ‘pump’ replacements in.
Each Tanktwo cell is an ellipsoid covered with six separate conductive panels that can be made individually active, or not. The shape of the cells is such that contact between them is limited. These end up in the tank at random orientations and the various contacts are activated to create the required paths between the cells to conduct the current required. Obviously, the walls of the tank have conductors to draw current from the cells. The company calls this a string battery.
Clearly, the current path through the nest of eggs to the car’s electrical system is going to be complex and different each time the tank is filled. Tanktwo suggests artificial intelligence will be key to calculating such paths. Each cell is to have on-board computing capability needed to control its function within the tank and within the mesh network.
The system would solve a number of EV problems. Charging time is the most obvious but constantly replacing discharged cells for fresh ones would allow low capacity cells to be removed and replaced with others to achieve a balanced battery with matching cells. Also, the tank doesn’t have to be filled. Drivers could load as many cells as needed and be on their way.
Unfortunately, the Tanktwo system doesn’t yet exist. The idea has been in place since 2015 but there doesn’t seem to be a working model. Given the extreme complexity of the system this is not surprising. One of the potential issues we see is limited point contact between the connectors. Also, Tanktwo would still suffer from infrastructure challenges although there might be unique solutions to this. Regardless, the system is yet to materialise and may never. It’s a shame because it’s so innovative.
The EV battery industry is rife with unique ideas that will probably never progress beyond concept and early stage graphics oriented towards attracting investors.
It seems the only true path to implementing innovation is by genuine research and hard work. Enovix seems to have the right approach. The product is real and subjected to on-going testing and validation. Manufacturing processes and operations are well developed and ready for large-scale integration with existing manufacturers. The company has avoided the temptation to trumpet its potential before being ready to support its products in a scalable manufacturing environment. It’s more than just hype.
Solid-state batteries may have been over-hyped but they do exist. It’s a matter of bringing the technology into mass manufacturing mode. Other technologies may claim similar status but do so with nothing more than concept renderings and animations based on theories. The popular press can be as much to blame for this as the companies. It’s a shame scam videos and sites exist because as people get wise and become rightfully cynical, matters will become difficult for those who have genuine announcements.
As featured in Australasian Automotive February 2023.