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Challenges during Lithium-ion cell manufacturing plant setup

PART 1 – Understanding the Market

Rahul Bollini is writing a series of articles over the next few months explaining the challenges faced during Lithium-ion cell manufacturing plant setup, which should be relevant to any company entering this field.

The first thing to do while setting up a Lithium-ion cell manufacturing plant is to clearly define the target market to which the Lithium-ion cell manufacturing output would cater. The target market has to be further defined to a sub-category level. For example, identifying the target market as EVs (electric vehicles) is not enough. It has to be further narrowed down to which type of EVs, such as two-wheeler, three-wheeler, four-wheeler or bus. The type of EVs has to be further narrowed down to if the two-wheeler is a low-speed or a high-speed vehicle, if the three-wheeler is an L3 (passenger e-rickshaw or e-cargo loader) or an L5 (passenger auto or heavy duty cargo loader) vehicle or if the four-wheeler is an LCV (light commercial vehicle) or an electric car and so on.

After narrowing down the exact application, the following parameters come into play:

  • Space/Volume: It is a critical factor (Wh/L of the cells/battery pack) in narrowing down the suitable cell chemistry in terms of the space available for the battery in the application.
  • Weight: Although weight (Wh/kg of the cells/battery pack) is a less important factor compared to battery space availability in the target application, weight does play a vital role in designing the centre of gravity of the application, which is taken seriously in EVs.
  • Battery Pack Capacity: The battery pack capacity (in terms of kWh) is considered based on the expected range per charge with respect to a realistic driving pattern. A higher range increases the battery capacity requirement and drives up the price of the EV, making them difficult to compete with ICE vehicle prices.
  • Form Factor: Based on the dimensions of the available space to accommodate the battery pack, the form factor is chosen. For example, a low-floor sedan incorporating battery at a chassis level would either consider cylindrical cells or blade-type pouch or prismatic cells. Regular prismatic cells would not be ideal since it is recommended to use them in a vertical position, which would make their height exceed the height of the available battery dimensions in a low-floor sedan. Available form factors are cylindrical (popular models in production are 18650, 21700, 26650, 26700, 32700, 32135, 33140, 4680, 66160), pouch (regular model with both tabs on the same side and blade type model with tabs on opposite sides) and prismatic (regular type, VDA module type, blade type).
  • Cell Capacity: Based on the form factor suitable and the available dimensions inside the battery pack, a suitable capacity of the cell is decided. A lower number of cells in parallel connection is considered better, but having very big-sized cells is also considered unsafe, especially when those are NMC and NCA cells.
  • Cycle Life: Suitable cell chemistry is selected based on the life required for the application. In long-range vehicles where space is a constraint, a compromise is made in the cycle life to achieve a higher range using cells that have high volumetric energy density (Wh/L). This compromise leads to lower cycle life and lower safety due to the simple fact that when the battery gets smaller and lighter, its safety and life reduces. The long-range of the vehicle does make up for the lower cycle life to be able to provide service life as per the expectation from the application. For example, electric car companies provide 8 years of battery warranty in India.
  • Power Density: It is the ability of the battery to take and give power (during charging and discharging). It is essential to check the compatibility of the cell form factor and chemistry to perform at the required C rates to be able to deliver power for the required EV application. This relates to fast charging capability, maximum continuous discharge current capability, peak pulse discharge current, the amount of time peak pulse current can be delivered and the ability to handle regeneration current coming from the braking of the vehicle. The cell engineering structure has to be designed internally to be able to deliver such power to bring down the internal resistance of the cell. I’ll talk more about this in the next part of this article next month.

There can be more than one possible solution for each application, and the ideal way would be to figure out the combination suitable for the highest number of target applications. Since Indian cell manufacturing plants have not yet taken off in a big way yet, below are the type of cells (imported) popularly used in India for catering to EV applications.

  • 2.6Ah NMC cell in Cylindrical 18650
  • 2.9Ah NMC cell in Cylindrical 18650
  • 5Ah NMC cell in Cylindrical 26650
  • 5Ah NCA cell in Cylindrical 21700
  • 6Ah LFP cell in Cylindrical 32700
  • 15Ah LFP cell in Cylindrical 33140
  • 30Ah LFP cell in Pouch (tabs on the same side)
  • 100Ah LFP cell in Prismatic (winding type)

Upcoming parts of this series:

Rahul Bollini is an R&D expert in Lithium-ion cells with 8 years of experience. He founded Bollini Energy to assist in deep understanding of the characteristics of Lithium-ion cells to EV, BESS, BMS and battery data analytics companies across the globe. Rahul can be reached at +91-7204957389 and bollinienergy@gmail.com.

This article was originally published in EVReporter March 2023 Magazine that can be accessed here.

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