Most EV owners tend to buy a vehicle with a battery bigger than their routine needs to eliminate range anxiety. However, they only use up to 30% of the total battery capacity on a daily basis. Long-range EV owners pay a high sunk cost for a battery capacity that is rarely utilised. A swapping solution can potentially solve the range anxiety, inconvenience of high charging time and high cost of ownership of EVs.
However, battery swapping solutions for electric cars present the challenges of large form factors and high Capex requirements. Tesla and Better Place have tried and abandoned the idea in the past.
Today, multiple global players are working on battery swapping solutions for electric cars. e.g. Chinese automaker NIO has built 700 Power Swap Stations in China, and they are scouting for locations in Norway, Denmark, Sweden, Germany, and the Netherlands. By the end of 2022, they expect to have 20 swap stations in Norway. Geely aims to set up 5,000 battery swapping stations globally by 2025. San Francisco- based Ample is partnering with fleet companies in the US, Europe and Japan to set up and provide battery swapping services.
CATL launched its battery swapping solution EVOGO on 18th January 2022. Rahul Bollini discusses CATL’s battery swapping solution for electric cars.
Modular battery blocks
The battery pack in the EVOGO solution is called choco-SEB (Swapping Electric Block), which is a mass-produced battery specially developed for EV battery swapping. This modular battery block boasts of high gravimetric (Wh/Kg) and volumetric (Wh/L) energy density with a small size and minimalist design.
The capacity of each battery block is 26.5 kWh. The block contains a wireless BMS that can communicate with other battery blocks’ BMS wirelessly in case the user uses more than one block. BMS must communicate with each other to maintain a balance in their state of charge (SoC) during discharging.
The traditional approach of a battery pack design contains multiple modules based in battery module frames. Each module has individual cells, slave BMS, thermal management, an electrical box with fuses, switches and other components. This design is preferred because of the high structural rigidity and the ability of each subunit to be protected from external factors such as heat and shocks.
But this approach takes up more space.
Whereas the Cell to pack (CTP) technology integrates the cells directly into a pack without the need to create modules. A cell to pack design would reduce the space usage by more than 30%, but it lacked structural rigidity. BYD’s introduction of Blade cells solved the structural rigidity problem where the cells are long enough to cover the vehicle’s width from one end of the vehicle to the other.
You can read the detailed analysis about BYD’s Blade cells in the November 2021 edition of EVreporter magazine.
In the case of EVOGO blocks, cell to pack technology has been used, which allows for a gravimetric energy density of more than 160Wh/Kg and a volumetric energy density of more than 325Wh/L.
Each battery block is said to have nearly 100 cells connected in series to achieve a high voltage system. Each block is more than 370V.
CATL says that the battery blocks have built-in thermal management equivalent to the fixed batteries that come pre-installed in electric vehicles.
EVOGO swapping station
An EVOGO swapping station takes up a space equivalent to three parking spaces. It can house up to 48 swappable blocks of 26.5kWh each.
The EV enters the swapping station, it is lifted up, an automated system removes the battery, and a fully charged battery is placed by an automated system. The vehicle is brought down, and it is ready to go.
The complete swapping operation only takes one minute to place one block. Each block can deliver up to a 200Km range per swap depending on the motor capacity of an EV. EVs with higher capacity electric motors tend to be less efficient and can have a lower range per swap. An EV can use up to three blocks depending on the space available within the vehicle. The blocks are added in parallel connection with each other. Two blocks will add 53kWh and three blocks will add 79.5kWh.
The modular battery swapping system has internet connectivity and shares the real- time availability of fully charged batteries. The EV user can know their battery’s SoC and search for the nearest available swapping station along with the availability of fully charged blocks on a mobile application.
CATL’s battery swapping system is compatible with Class A00 to Class C model passenger and logistics vehicles, which covers most vehicles plying on the road.
Class A00 vehicles are small length vehicles starting from 2 meters, and Class C vehicles are large length vehicles up to 5 meters, such as an Audi A6. CATL said these blocks are compatible with 80% of the electric cars in the present market and can support electric cars to be launched globally in the coming three years.
About the Author
Rahul Bollini is an independent R&D consultant in the field of Lithium- ion cells and batteries with 7 years of industry experience. The author can be reached at firstname.lastname@example.org or +91 72049 57389
This article was first published in EVReporter March 2022 Magazine that can be accessed here.
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