Challenges during lithium-ion cell manufacturing plant setup- part 8

Backward integration

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 8 of the series) explains the challenges faced by Lithium-ion cell manufacturing companies while focusing on backward integration, also known as going upstream.

For a growing cell manufacturing company, backward integration provides a price advantage and, most importantly, control over the supply chain for consistency, quality and timely delivery. For example, high-value raw materials in Lithium-ion cells such as Cathode, Electrolyte and Anode can be targeted initially. Below are the raw materials required to manufacture these cell components:

Cathode:

Lithium Carbonate + Iron Phosphate precursor (Phosphoric Acid + Iron Oxide) = LFP cathode active material. There is more than one way to manufacture LFP cathode material. For example, it can also be manufactured using Lithium Phosphate and Iron oxide. Lithium Carbonate can be combined with NMC 532 precursor to produce NMC 532 cathode active material.

Lithium Hydroxide + NMC 811 precursor (Nickel Sulfate + Manganese Sulfate/Electrolytic Manganese Dioxide (EMD) + Cobalt Sulfate) = NMC 811 cathode active material.

Metal Sulfates are processed from their respective metal hydroxides. Generally, metal hydroxides are produced near their respective mines.

Lithium Hydroxide can also be combined with NCA precursor to produce high Nickel NCA cathode active material.

Electrolyte:

Lithium Hydroxide can also be used to manufacture Lithium Hexafluorophosphate (LiPF6) electrolyte salt, which would be combined with Ethylene Carbonate and other organic solvents in various ratios along with different additives at various weight ratios. Generally, the formulation varies for each cell manufacturer as each of the possible combinations has its merits and de-merits, and the trade-off has to be understood very well.

Long-term investment in Lithium mines is beneficial for manufacturing Cathode and Electrolytes. That’s why companies like Tesla do it.

Anode:

Graphite flakes are made into spherical shapes with higher purity to be used as natural graphite. It is a simple process which requires comparatively low capex to set up a plant.

Petroleum coke and coke needles are used together for manufacturing synthetic graphite. Although synthetic graphite has a lower discharge capacity, it is popularly used for its high cycling life. The capital expenditure to set up a plant is higher than the natural graphite setup of the same capacity.

In the next section, we discuss all the other raw materials that can be considered for backward integration.

Aluminium Foil:

Aluminium foil makers for other industries can develop the foil for cells if they use high-tech equipment to maintain a very low tolerance with respect to thickness consistency, as we are talking less than 20-micron thickness here. The market is moving towards 12-micron thickness; some cell manufacturers are even using 8-microns for certain applications.

Copper foil:

Though it looks similar to Aluminium foil, Copper foil is more complex to manufacture because of the following reasons:

• Copper is not a soft metal like aluminium

• Electrodeposition method is required for battery-grade copper foil.

• The cost of plant setup for copper foil is much higher than aluminium foil plant setup.

• The thickness required is lower than aluminium foil, ranging from 4-micron to 10-micron. Some cell manufacturers are even using 3 microns for certain applications.

Lower current collector (aluminium and copper foils) thickness allows a reduction in the weight of the overall cell while holding the same amount of active material and maintaining the same cell capacity, thereby increasing the gravimetric energy density (Wh/Kg) of the cell.

Aluminium and Copper (Nickel-Coated) Tabs:

Rolls can be procured from metal processing companies, and a customised tab-cutting option can be explored at the premises of the Lithium-ion cell manufacturing/raw material storage facility.

NMP Solvent:

NMP solvent is used for making cathode slurry before coating it on the aluminium foil. NMP solvent can be recycled at the plant (for large volumes) and reused. The recovery and recycling rate depends on the sophistication of the equipment used. For the first-time procurement and regular top up volumes (as 100% recovery is not possible), it can be procured from domestic companies that are supplying to the pharmaceutical industry.

Deionised (DI) Water:

It is used as a solvent for making aqueous-based anode slurry before coating it on the copper foil. DI water is made in the cell manufacturing facility using specialised water filters.

Cylindrical Cell Can:

Very few companies manufacture the type of steel that is qualified to be used to produce cylindrical cans. Additionally, aluminium can (because of its low weight) has emerged as a new trend, but it might not replace the steel can market completely. Aluminium cans do not use the crimping method, and hence, for any existing cell manufacturer to shift from steel cans to aluminium cans would require changes in the production equipment.

Prismatic Cell Can:

Generally, it is made up of aluminium. Can’s dimension tolerance must be maintained at a very minimal level to avoid difficulties during battery pack building. Dimension tolerance level is also very critical in cylindrical cells. A prismatic cell cap with an anti-explosive valve has been in use by many companies for EV-grade cells for a decade.

Aluminium Laminated Sheet:

It contains layers of aluminium and polymer-based material to act as an enclosure for pouch cells. Due to its light weight, it helps to increase the gravimetric energy density (Wh/Kg) of the cell. It can be domestically developed, but its strength needs to be tested. Pouch cells might sometimes bulge in the long run, and the strength of the aluminium laminated sheet plays a vital role at that moment.

PVDF:

It is a fluoride-based complex compound used as a binder for Cathode and helps keep the cathode material together on the aluminium foil. It is not the most preferred type of material for backward integration. Even big cell manufacturers in China are procuring PVDF from other companies. When the industry moves to aqueous-based cathode slurry, PVDF will no longer be necessary for Lithium-ion cell manufacturing.

Carbon Additive:

Similar to PVDF, various types of carbon additives (carbon black, acetylene black, CNT, graphene, etc.) are generally imported by big Lithium-ion cell manufacturers in China. They are imported from established manufacturers because it is not easy to achieve the required high conductivity and specific surface area (m^2/g).

CMC and SBR:

They stand for Carboxymethyl Cellulose and Styrene Butadiene Rubber, used as a binder for Anode while preparing aqueous-based Anode slurry. It is a low-value item and is locally available from manufacturers that supply it to other industries.

Generally speaking, the past business background of the Lithium-ion cell manufacturing company plays a major role in deciding which raw material backward integration they should focus on.

With this, my 8-part series of ‘Challenges during the Lithium-ion cell manufacturing plant setup’ comes to an end. I will be back with more technical articles in the coming issues.

Author credit:

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 +917204957389 and bollinienergy@gmail.com.

This article was first published in EVreporter Oct 2023 Magazine

Also Read:

Part 1 Understanding the market

Part 2 Product meeting technical expectation of the market

Part 3 Possibility of localisation, and securing raw materials

Part 4 Plant setup planning

Part 5 Process optimisation and skilled workforce

Part 6 Expansion and diversification of portfolio

Part 7 Evolving to newer technologies