Challenges during lithium

Jun 22, 2023

Rahul Bollini is writing a series of articles explaining the challenges faced during Lithium-ion cell manufacturing plant setup, which should be relevant to any company entering this field. This article (part 6 of the series) explains the challenges faced by the Lithium-ion cell manufacturing company while planning for expansion and diversification.

Expansion for the same type of cell manufacturing is generally done in a modular way, meaning multiple lines of the same type of equipment are added if the plant is already fully automated. Incase of the plant not being fully automated, automation is deployed to increase the output of the existing equipment.

Less automation allows for more flexibility in the desired output but with some limitations. For example, 15Ah (higher cycle life model) and 16Ah capacity of LFP in 33140 cylindrical form factor scan be produced with the same equipment. Cells with a lower height and similar diameter, such as6Ah of LFP in 32700 cylindrical form factor, can also be produced from the same equipment (some minor changes and tuning required). Additionally, higher and lower gravimetric energy density (Wh)cells can be produced by modifying the inner cell design. LFP cells can reach very close to200Wh/Kg by simply using thinner current collectors and utilising more active material in the cathode and anode slurry composition. But this affects the cycle life, internal resistance, charging speed and will lead to higher temperature rise during operations.

An already well-automated plant running at full capacity utilisation does not have much scope to increase the production capacity. Hence similar size lines are added in more numbers to increase the production capacity. One might ask, what’s the difference in the equipment in the semi-automatic and fully automatic plants? To start with, the mixer capacity would be smaller, and their quantities would be higher in a semi-automatic plant to allow for various formulations and various mixing speeds to produce various types of cells. On the other hand, a fully automatic plant would use a larger capacity to ensure higher homogeneity in the production, and it would focus towards making fewer models of cells.

If the system integrator for the plant expansion is different from the previous one, especially during increasing automation levels, it can pose a challenge in bringing the plant to work as per desired output. There could be certain delays and higher wastage of raw material & production output. With changing styles of automation, there are changes in the production styles, and the workforce needs additional training to handle these changes.

For a cell manufacturing company, producing a diverse range of cells is crucial in order to meet the needs of a wider range of applications. Due to their higher energy density (gravimetric and volumetric), voltage, power and cycle life, Lithium-ion batteries are becoming increasingly popular. As a result, many applications are now transitioning to these batteries. But these applications demand different types of Lithium-ion cells. Consider a Lithium-ion cell used in a cell phone versus the one used in an electric bus. These two applications require different form factors, capacities, and chemistries. It can be challenging for a cell manufacturer to produce for both, but selecting applications that use similar parameters for Lithium-ion cells is a simpler task.

Same form factor, different capacities/power ratings – Ever heard of EV cell and ESS cell? Let’s take an example of a LFP prismatic cell. A manufacturer can produce EV cells that can deliver higher power (C rate) and have higher energy density (gravimetric and volumetric) but lower cycle life. Compare it with ESS cells of the same LFP prismatic type, which would have lower power and lower energy density but provide a higher cycle life. The changes happen in the cell design and in the type of materials (similar but different specifications) used.

This parameter is looked upon as a development plan. Companies plan to enhance the discharge capacity of their products with the same form factor and dimension in order to provide greater gravimetric and volumetric energy density in the future.

Same form factor and different chemistries – This can be explained very well by taking the example of 5Ah capacity cells in 21700 cylindrical form factors. The same cell can be manufactured with NMC 811 + Silicon Graphite and NCA + Silicon Graphite combinations. The choice of cathode materials offers different advantages and disadvantages related to maximum continuous current(charge and discharge), peak discharge current, cycle life and safety.

Same capacity and different form factors– Let’s take the example of 5Ah capacity cells. This capacity can be manufactured in 21700 cylindrical form factor and 26650 cylindrical form factor.21700 uses NMC 811 or NCA cathode + Silicon Graphite while 26650 uses NMC 532/622 +Graphite. The advantages of a 21700 cell, in this case, include higher energy gravimetric and volumetric energy density. The advantages of a 26650 cell, in this case, include higher safety and cycle life and lower cost.

All the diversification plans require the R&D team of a company to make tried and tested products and study them for a good period of time before bringing the product into mass production. There are many tests related to ageing that tell how good the newly developed product will be. These tests can be cycle life at various charge and discharge C rate combinations at various temperatures, end-of-life study, calendar ageing, rise in IR with ageing, thermal profiling with ageing, Wh and Ah efficiency of cell with ageing, etc.

Upcoming parts of this series:

Part – 7 (Evolving to Newer Technologies)

Part – 8 (Backward Integration)

Rahul Bolliniis an R&D expert in Lithium-ion cells with 8 years of experience. Hefounded Bollini Energy to assist in deep understanding of the characteristics ofLithium-ion cells to EV, BESS, BMS and battery data analytics companies acrossthe globe. Rahulcan be reached at +91-7204957389 and [email protected].