In my prior articles on battery technology I dived into different battery segments and the intricacies of their cells, their chemistries, and components. It is worth reading those if you have not already (see links below). Investors in the battery sector should appraise themselves of some of the design and engineering constraints currently impacting the EV sector.
In this article I will focus on EVs and also zoom out to examine the battery cell casings/formats and their integration into the vehicle’s bodyworks, since they are the main driver of change in the battery industry these days.
Previous articles can be found here:
- Exploring the four critical user segments of the fast-growing battery sector
- Exploring the world of lithium-ion batteries and their components
Battery cell formats
There are three headline cell formats; Cylindrical, Prismatic and Pouch cells. They all come in different sizes. The primary debate and development focus has been focused on the larger cells because of their manufacturing efficiency, translating into cost reductions.
The second aspect is performance and weight, the quest to combine more Battery Active Materials (BAM) like Anode, Cathode and Electrolyte material in the same space with less packaging like casings, and finally the packaging and integration into the bodywork of the vehicle.
Cylindrical cells have mutated from the decade long format of 18x65mm, which we all know from our electronic devices, into 21x70mm first, and then recently grow into the Tesla Maxwell format of 46x80mm, which again has migrated into 46x100mm and even 46x120mm with other producers.
But with these 46mm diameter cells there have been big design changes and challenges. The energy flow is more directed via the 1 long tab throughout the cell, strangely called “tab-less”, reducing the energy´s travelling distance significantly. I don’t think we have seen the last size here yet, but the current changes do indeed make a lot of sense.
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Prismatic cells exist in multiple sizes and a couple of versions. The most known mutation is BYD´s Blade cell and SVOLTS Short-Blade cells. The direct mounting of BYD´s very long blade cells or CATL Prismatic cells across the full frame and chassis have a clear design and volumetric advantage, which we will investigate below. But of course, squared boxes are easier to align than a cylindrical box and take up more efficient the space within a confined area. It´s just not the only factor that counts!
Pouch cells do not have any standard formats either. Their soft and flexible outer casing/packaging makes them easy to fit into places and this is also their main advantage, in today’s lithium-ion cells. On the other hand, they are more expensive to produce because they don’t scale in the manufacturing process as the hard casing cells does.
The pouch cells are the ones we see today in our mobile phones, and they could become more relevant in automotive design in the future, since they seem to be the better choice for solid-state batteries, since they can flex with the super-dense anodes and cathodes, especially the lithium based “anode-less” anodes, where the lithium-ion in the anode is carried across the cell.
This rethinking of cell size and shapes was started by newcomers like Tesla and Maxwell and have been followed and expanded by others like CATL and BYD, all seeking the same goal: lower weight, costs and complexity, plus higher energy density and safety and charging speed, through different designs and thinking.
The legacy car brands have focussed on next gen cells, solid-state cells sourced from other manufactures. This progress will carry on as long as the safety and charging properties are not undermined.
Battery cell integration into the electric vehicle
The final point to make is around optimal energy density at the lowest possible weight related to the “packaging” of the cells, their cooling and management systems within batteries, and finally inside their ultimate host, the vehicles. This “optimal” Cell to Chassis (CTC) construction has an enormous impact on the modern EV and its effectiveness.
Legacy producers have mastered and refined the self-supporting bodyworks over a century around the engine and a transmission, sometimes in a cardan tunnel, but this construction is not optimal for an EV, and this is where the skateboard comes in; it is not that dissimilar from the older-fashioned chassis constructs in carriages.
Designers seek the least packaging and the highest form of integration, which can advance the effective energy density per kilo by up to 50% by simplifying the packaging and integrating the cells, the cooling and management system properly into the frame of the bodywork.
Source: Tesla
Initially Tesla showed a full frame of 46x80mm cells with a cooling and management system packed with Styrofoam around the cells, making the whole thing a rigid and safe construction inside the carrying frame. BYD went one step further with their Blade cell format, where a single very long prismatic cell crossed the whole frame, and thereby reduced the number of components, cells and connections massively.
This long and slim BYD cell format fitted the iron based (F for Ferro) LFP chemistry extremely well, because it has a very low thermal runaway. This advantage is reduced with nickel-based chemistries.
CATL´s first response to this was their Cell to Pack (CTP) solution Kirin (Qilin) battery pack system where the cells are special because of their prismatic design, but it is the integration of the cooling, and the management system that has made the bigger difference.
Kirin had achieved the highest space utilization of any battery system out there, namely 72%, 2022. Their next step is CATL´s newest solution, their Integrated Intelligent Chassis (CIIC) skateboard platform, which is a Cell to Chassis solution (CTC). The goal around weight reduction and integration is to get to a net effect above 100% through integration and simplification, and that is already visible and being vocalized by none other than Elon Musk.
Weight, security and costs, indifferent of cell chemistry (nearly), are together with dynamics the goals that are sought after by auto designers. Anyone who has driven a sports car knows the weight, the weight distribution, and the centre of gravity of the vehicle is very important, especially when getting around the track fast. EVs on a Skateboard construct have a clear advantage over older constructs, because of the much smaller and lighter engine and the placing of the heavier batteries low in the car.
Final thoughts
The headline goals everyone is seeking are price and performance. Price is relatively simpler to identify, while performance is the result of many factors, within, around and outside the cells. The engineering here in inventions in material science carry us a long way and will also bring progress in many other areas of our future lives dealing with intelligent products.
For electronic vehicle bodyworks, the cells and batteries are all progressing well. The accessible solutions available in 1-3 years will be impressive. Another 3-5 years down that road, once the fog has lifted around a few aspects like solid-state solutions, the landscape might end up looking very different.
In examining the global EV and battery cell landscape, it’s evident that European, Japanese, and North American automotive companies face challenges in leveraging the advantages they have established over many decades. Korean and Chinese companies dominate both manufacturing and the technological fronts in cell production.
The innovative approaches with a central carrying skateboard and Tesla´s ‘un-boxed’ approach to building the whole car could reshape and disrupt the industry once again. Maybe the leapfrogging game plan with a solid-state battery strategy will work for the legacy luxury brands. If not, they might very well face extinction.
The final goal to get as much mileage out of your car, from the least amount of money in the shortest time, is not going to be reached through loading a massive number of cells into the car, but through innovation, elegance and simplicity. Your car does not need cells that can carry it 5-700 miles, but more like 2-400 miles. What is important is that you can charge 80-95% within 8 – 12 minutes. The thoughts of Colin Chapman will once again prevail.
Vision, conviction, guts and execution have been the drivers of the EV industry over the last 10 years, and I believe these qualities will stay the main drivers going forward. In the end, they will decide which brands will still be in the game in 10-15 years, and which will not.
Henrik Mikkelsen is a Strategist, Investment Advisor and Business Developer with Iridis AG, an investment management and corporate advisory firm in Zug, Switzerland. Henrik has more than 30 years of experience from investment banking and commodity trading, running strategies for clients and himself, as well as writing about markets and giving lectures on technical analysis and risk management.
