Challenges During Lithium-ion Cell Manufacturing Plant Setup – Part 2

April 14, 2023 Lithium-ion batteries 8 min read

PART 2 – Product Meeting Technical Expectations of 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.

It is very common to see articles about a new breakthrough technology that could change the whole market. This could be a cell technology, a major component of the cell or even a sub-component of the cell. While part 1 of this series discussed about clearly defining the target market the Lithium-ion cell manufacturing output would cater to, part 2 discusses the challenges faced during meeting those expectations. I discuss these typical technical parameters below:

Market Trends

New trends are being observed with existing battery technologies in the international market at a Giga scale. Any company entering cell manufacturing must be aware of these to avoid being left out of global competition. Example trends are as follows:

NCA cells max out at 5Ah discharge capacity in 21700 cylindrical form factor presently, which is being upgraded to 5.3Ah by some manufacturers. Hence it can provide a 6% higher discharge capacity in the same volume and has improved gravimetric energy density (Wh/Kg).

LFP cells in 32700 cylindrical form factor max out at 6.5Ah discharge capacity presently. But it is getting updated to 7Ah in the same 32700 form factor, and there is an addition of a 32800 model, which would have 8Ah.

LFP cells have crossed above 400Wh/L for the first time in some models, such as 33140 form factor, providing 15Ah discharge capacity. This is by far the highest volumetric energy density that LFP cells have achieved to date.

Large LFP cells such as pouch cells have improved from 1C max continuous discharge rate to 2C max continuous rate along with improvement in gravimetric energy density from 160Wh/Kg to above 180Wh/Kg. It is a matter of time before it reaches 190Wh/Kg going forward.

Large LFP cell demand is shooting up, especially the 280Ah prismatic cells used in BESS (battery energy storage system). Traditionally they offered cycle life that wouldn’t allow them to operate beyond 10 years at 90% Depth of Discharge (BESS typical operation). Newer cell models have enhanced the cycle life to function beyond 10 years comfortably.

Customer Qualification Plant (CQP)

This is a term being used by new companies setting up a decent size pilot-scale manufacturing facility after they are sure about what they want to produce. The purpose of this plant is to provide regular samples to its potential customers for testing and validating their products. The purpose of this plant is to confirm the kind of setup that exactly needs to be scaled up to a Giga-scale. The main challenge with this plant is optimising the recipe of the cell to the required accuracy in order to achieve the required specification. Most companies face indefinite delays in their QCP, especially those with their own lab-made technology or those collaborating with lab-level technologies. Hence, some companies choose to collaborate with experienced companies who not only have prior experience dealing with such plants but also have experience scaling up to Giga-scale plants and operating them successfully for many years.

Parameters that need to be maintained consistently in QCP are:

Discharge Capacity: It has to be maintained, ranging between minimum capacity and rated capacity at a given C rate of charge and discharge. Consistency in the discharge capacity is very important to battery pack assembly companies, and it is their first step in Quality Control.

Internal Resistance: ACIR (Alternating Current Internal Resistance) and DCIR (Direct Current Internal Resistance) values need to be within the desired range. The higher values categorise the cells under Solar grade (unfit for electric vehicle application).

Self-discharge: During the cell grading process, the self-discharge parameter needs to be within the desired range. The higher values categorise the cells under lower categories such as A- or B grade. It is known as the k value during the grading process, and it refers to the drop in the voltage in a given unit of time (millivolt/day).

Energy Density: The lower gravimetric energy density is a possibility in defined form factors such as 18650 cylindrical cells. The lower volumetric energy density is possible in flexible form factors such as pouch cells. This would mean that the cells are heavier and bulkier than expected, respectively. This can be because of various reasons, such as more dead-weight materials like binder or the use of conductive additives or electrolytes, which can even increase the production cost of the cell.

Temperature Profile: It is a fact that there is a temperature rise in the cells during charge and discharge operations, which varies at various C rates of operation. A consistent cell design incorporated manufacturing process in place ensures that the temperature rise of the cells is uniform. The temperature profile is considered a very important factor while building a battery pack because, based on this, thermal management is designed for the battery pack. A higher temperature rise compared to other similar types of cell manufacturers’ products in the market discourages the buyer.

Efficient Design

Lithium-ion cell manufacturing is not as difficult at a research level; one can hear about it every now and then. However, achieving the required specifications and meeting the overall expectation as per the market standard can be tedious. Starting with the fact that the market grade specification can’t be manufactured in a laboratory, the equipment simply does not support achieving the market standard specification. This is where a gradual increase in discharge capacity is tested out (in the same form factor, without a drastic increase in internal resistance), where laboratory-level technology is taken to a Mega-scale manufacturing, then to a CQP and then to a Giga-scale. The gradual increase in the scale calls for gradual improvement in the cell design and process in order to achieve the set target.

Efficient design also means using the best possible resources to achieve the required cell specification.

NMC 532 cathode with graphite efficiently allows for 2.6Ah discharge capacity in 18650, but achieving the same discharge capacity in NMC 811 would be considered inefficient because NMC 811 cathode is expensive and has the potential to provide higher discharge capacity in 18650, say 2.9Ah. Also, NMC 811 works with an expensive formulated electrolyte, adding more cost.

More will be explained about this aspect in part 5, which discusses about the challenges of process optimisation and skilled manpower.

Part 3 will discuss the challenges faced during securing the raw materials and an outlook of what can be utilised from India.

Upcoming parts of this series:

Part – 3 (Securing Raw Materials)

Part – 4 (Plant Setup Planning)

Part – 5 (Process Optimisation and Skilled Man Power)

Part – 6 (Expansion and Diversification of Portfolio)

Part – 7 (Evolving to Newer Technologies)

Part – 8 (Backward Integration)

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.