Evolving to newer technologies
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 7 of the series) explains the challenges faced by Lithium-ion cell manufacturing companies while understanding and planning to be in tune with evolving and newer technologies.
New technology does not necessarily mean shifting to a new cell chemistry. It can mean any of the following:
New cathode material: This is the most talked about type of innovation in cell manufacturing space. For example, when it is said that LMFP (Lithium Manganese Iron Phosphate) cell is an emerging trend, it simply refers to a new type of cathode material. The rest of the raw materials for LMFP cell are very similar to LFP. It makes a lot of sense for companies manufacturing LFP cells to consider innovating to LMFP because of its ability to improve the cell voltage, energy density (gravimetric and volumetric) and lower cost of manufacturing with similar type of stability (cycle life, fast charging and safety).
New anode material: This can be best explained by taking an example of NMC cell with graphite anode and NMC cell with silicon graphite (SiGr) anode. Variable Silicon content is possible in Silicon Graphite anode, which can decide the final capacity of the cell. For example, the following capacities are possible in 18650 cylindrical cells:
- NMC 811 Cathode + Graphite Anode = 2900mAh capacity
- NMC 811 Cathode + Silicon Graphite Anode (lower Silicon content) = 3200mAh capacity
- NMC 811 Cathode + Silicon Graphite Anode (higher Silicon content) = 3350mAh capacity
Changes in multiple components: A lot of permutation and combinations are possible when trying out different cell components. For example, the same Silicon Graphite Anode (higher Silicon content) mentioned previously when paired with high nickel NCA cathode material, can reach 3500mAh capacity. It is the best mass production capacity available for 18650 cylindrical cells.
New type of other components: Let us discuss this with some examples –
- Using different molar ratio of electrolyte salt with varying types and combinations of solvents and additives can greatly enhance the cell’s stability and increase cycle life.
- Using a different process separator along with multiple materials coating can greatly increase the mechanical strength and high-temperature performance of the separator, thereby ensuring high safety during harsh conditions of operations.
- Using a different type of additive, such as carbon nanotubes (CNT) along with LFP cathode to enhance the power delivery of the cell. This has become a new industry norm for LFP cells meant for the EV market.
- Using solid-state electrolyte in NMC/Graphite cell instead of traditional Lithium based salt in organic solvent along with additives. This ensures that thermal runaway issue of the NMC cell is taken care of.
New type of cell design with higher capacity for the same application: With maturing technology, a newer design for the same cell capacity can ensure lower internal resistance and deliver higher power. For example, when 5000mAh capacity cells were produced in 21700 cylindrical format initially, they were high energy type. Once the technology matured, there was a change in the cell’s category from high energy (HE) or low power to medium energy (ME) or medium power. It means it can now deliver more power. Earlier, 5000mAh capacity was the maximum; now, 5300mAh has been launched, and soon, 5800mAh is expected to be launched in 21700 cylindrical formats.
New type of cell design for a different application: A company making cells for EV applications could consider catering to a different market segment, such as drones (lower energy density but higher power density) or ESS (lower energy density but higher cycle life).
New type of cell design for higher performance: An example would be a 5000mAh cell evolving from high energy to medium energy type. Another example prismatic cells using Z stack method instead of the traditional winding method. This allows for better heat dissipation and mechanical strength and therefore a longer cycle life.
New type of cell altogether: This covers cells such as Sodium-ion, Lithium Sulfur, etc. Every component used in these types of cells is different compared to traditional Lithium-ion cell chemistries. For example, Sodium-ion cells would use Sodium based cathode, hard carbon and Sodium based electrolyte salt when compared to Lithium based cathode, graphite (natural, synthetic or silicon graphite) based anode and Lithium based electrolyte salt in Lithium-ion cells. These new types of cells need validation to understand their characteristics:
- Cycle life at various temperatures at various C rates of charge and discharge
- Calendar ageing profile at various temperature storage conditions, self-discharge profile
- Safety aspect of the cell with aging at different operating temperatures
- DCIR values at various SoC at different temperatures after various number of cycles
- Cell charge-discharge efficiency after various number of cycles
- OCV-SoC (corresponding voltage of the cell at a particular SoC) relation of the cell during charging and discharging at various temperatures. The consistency of this data for various test samples will ensure that the cell is matured
- Derating of the cell by high pulse power characterisation test. It concerns the ability of the cell to provide maximum power of charge or discharge at various SoC and temperature
If the results are satisfactory, the product is ready for customer qualification and mass manufacturing. Some test characteristics can be interpreted with certain logical and scientific predictions.
Upcoming part of this series:
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 firstname.lastname@example.org.
This article was first published in EVreporter Sep 2023 magazine.
Part 1 Understanding the market
Part 4 Plant set up planning
Subscribe today for free and stay on top of latest developments in EV domain.