Mitsubishi Electric has been at the forefront of developing specialist automation solutions for automotive battery production for over a decade and has recently appointed Klaus Petersen as Director Lithium Battery Industry EMEA, Mitsubishi Electric Europe BV to help realise the production goals set by European regional government legislation and consumer demand.
Bringing Lithium battery cell production physically closer to established vehicle plants has many operational benefits, especially when the predicted volume increase in battery usage is so high. Of course, the demand for batteries is not just being driven by legislation around personal mobility, but also for increasing grid stability when it comes to renewables. Fortunately, the essential application expertise and automation solutions required are readily available.
“According to the World Economic Forum in 2020 cell production capacities have to increase by 19 times by 2030 to meet climate goals.[i] The European Union is supporting industry players to realize the value chain in Europe. No surprise that the race for cell manufacturing has been unleashed in Europe where several new companies have been founded and others are expected still to come. While the World Economic Forum predicts a need of approximately 3600 GWh per year,iii in March 2021 BloombergNEF was predicting a demand of 2.000 GWh per year where passenger EVs will account for approximately 1.300 GWh per year, representing over 60% of the demand.[ii]
Many European automotive manufacturers have launched pure electric models and many new models have been announced. Traditionally the tier 1 suppliers are located near the assembly factories and the indications seem strong that this sourcing strategy is on the car manufacturers agenda for the batteries too.
There are several battery ‘assembly’ plants already established outside of the US and Asia, however production of individual battery cells themselves is a separate challenge. The techniques used to build a Lithium-ion battery cell (LIB) are well established, the escalating price of raw materials however means that a battery plant must maximize speed and minimize wastage to meet production targets and remain economically viable.
The accepted industry norm for hitting globally competitive economies of scale is a Gigawatt of battery capacity produced annually from a single plant. Quality and consistency requirements within modern lithium-ion battery cell manufacture are critical to efficient production and battery performance where tolerances within the production process require high precision in fast moving applications
Each cell is constructed from layers of metal foil which is coated with a fine layer of active conductive material to form the anode and cathode, which are separated by a protective film in the final battery construction. For maximum power density multiple layers of anode and cathode are required, which are usually being wound or stacked to form a cylindric, prismatic or pouch cell.
The coated foil goes through a complex and precise roll to roll transfer and drying process and is then finally pressed by a calendaring machine in order to achieve optimum battery performance. It is then cut into strips (Slitting) die-cut to size and then stacked or rolled ready to have the positive and negative connections welded before being placed into the battery cell enclosure.[iii] Physically handling the thin foil material at high speed is a critical ‘make or break’ stage of the process and as power density requirements rise, the material becomes thinner and increasingly difficult to handle.
A huge amount of R&D and application experience has been devoted to developing automation systems to control these processes, which is something any new plant would need to adopt to meet a realistic operational timescale for constructing a new production facility. Competition in the EV market is clearly fierce between relatively new manufacturers such as Tesla and the more established brands. This is especially true with the already well documented short timescales achievable for constructing large-scale manufacturing facilities in other parts of the world.[iv]
Managing quality and achieving high OEE is critical to viability
There is another aspect to large-scale Lithium-ion based battery cell production which is not well reported and has been escalated significantly due to recent price hikes in fuel and raw materials. That is process wastage, which can be exceptionally high for a modern manufacturing process. What are considered highly advanced plants can routinely run into double digit percentages and this has a huge knock-on to cost per kwh for the batteries being produced.
Example: Average individual cell cost in 2021 for a battery electric vehicle (BEV) was around $97 per kWh according to BloombergNEF [v], therefore a scrap rate as high as 30% in a gigawatt (1,000,000 kW) factory is already in the tens of millions. Since January 2021, the market price of Lithium carbonate has increased more than 700%[vi] and other lithium-based chemicals have been raising in the same order of magnitude, hence the issue is even more critical.
Mitsubishi Electric has been working closely with the Asian battery manufacturers over the years to develop automation solutions that contribute fundamentally to improve the quality and throughput required to reduce scrap and meet demanding cost targets.
Because the final performance of the battery can only be tested right at the end of the process when the cell is finished, the cell’s quality is defined by the quality of the processes that precede. The slurry needs to be mixed to achieve homogenous state, the coating must be applied very accurately on the substrate so that while calendaring the metal film doesn’t get any waves. The slitting process needs to cut accurately to create symmetric electrodes without short circuits and the winding and stacking process requires accuracy to have perfectly overlapping electrodes. All these steps contribute to maximize the cell’s capacity and ensure maximum mileage for the car manufacturer’s customers.
Therefore, inline testing during the process is required to monitor the quality of the electrode being manufactured. With a highly automated and responsive automation system in place the data provided can be used to change the parameters of the line on-the-fly helping to constantly produce the best cell. When you have a very long line with costly materials coated on a costly metal film you want to be able to predict the quality of your electrode before you test it in the finally assembled battery as you might end up having to scrap the entire electrode already fed into your line. This is key to achieving the required Overall Equipment Effectiveness (OEE).
To the best of our knowledge the materials used such as lithium already contribute 60 to 70% of the overall cost of an individual cell. And with the lithium carbonate price explosion that we have seen from the beginning of 2021 to 2022, a particularly good OEE contributes even further to cost competitiveness in cell manufacturing.
Another good example of technology being applied to improve OEE is the use of line bar scanners that were developed and very successfully used in cash machines being adapted to accurately assess the surface quality and position of the manufactured electrode along the entire process. It’s positioned a few millimetres over the film with integrated lighting ensuring little interferences with other external light sources. On top of other sensors in the line this technology supports early detection of electrode’s quality. Counter measures can then be taken before failures are detected in the testing process of the cell. This solution is already in use and has caught the attention of many other cell manufacturers.
As previously mentioned, accurate control of the tension in the foil rolls is critical. The metal foil being coated to produce the electrode roll and later being cut and wound to produce the cell must be kept under a very exact tension. For smaller lines with lower throughput requirements this can be achieved by using powder breaks and clutches where the powder is activated by a magnetic field to create variable friction in combination with a tension controller and sensors.
To achieve this in machine lines requiring a high throughput however a very dynamic and accurate real-time motion control system is required. We have seen high speed lines failing due to the wrong motion and tension control choice. The metal foil and coating do not respond well to being stretched and need to run at a very accurate speed. Torque and speed control is a key discipline in this process, especially at line speeds of up to 250 m per minute. Our solution employs advanced control algorithms to maintain very accurate tension control and remove harmonic vibration. With a measured frequency response time of 3.5kHz we believe it represents the most dynamic and accurate foil tension control system on the market.
Technology used in the battery cell manufacturing industry has traditionally remained highly confidential. Process knowhow is a key competitive advantage when building new, highly efficient battery cell manufacturing plants. However, with key technology stakeholders such as Mitsubishi Electric bringing knowledge and product solutions into the local market, it will help European companies to achieve their objectives and balance supply with legislation and customer demand.
Klaus Peterson Director Lithium Battery Industry EMEA, Mitsubishi Electric Europe BV