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  • Writer's pictureYashraj Tripathy

Exploring Molicel’s new power cell

About:Energy has tested the latest and greatest batteries on the market. In this Case Study, Yashraj Tripathy, our Head of Product, puts the spotlight on the Molicel P45B and how to think about battery system design, focusing on thermal performance and management. We are not commercially affiliated with or sponsored by Molicel. If you want us to give an honest review of your cell, get in touch!


The latest from Molicel

The 2021 McMurtry Sperling is an exceptional full-electric track car. It made a lot of noise (pun intended!) by shattering the 'Hill Climb' record at the Goodwood Festival of Speed in June 2022. Max Chilton demolished the 1.16-mile course in 39.08 seconds, knocking off 2 seconds from the previous record, a huge margin in races like this. But what fuels its blistering performance?


Image of the McMurty Sperling next to Molicel P45B

Look no further than the best-in-class cell technology provided by Molicel. The Taiwanese manufacturer's cylindrical format 21700 cell design unleashes an unmatched fusion of power optimisation and energy density, standing tall among esteemed Tier 1 cell manufacturers like Samsung and LG Energy Solutions. Molicel is poised to be competitive in energy-focused weight and power-sensitive applications, such as the high-performance automotive sector. With the launch of Molicel’s new generation P45B 21700 cell, we were excited to get this in-house and take a closer look.


Overview of the Molicel P45B

The P45B cell boasts a 10C pulse discharge capability and a 3C charge capability. Despite such high power capability, it still offers a 242 Wh/kg nominal specific energy. Additionally, its low direct current internal resistance (10 s DCIR) of 13.8 mΩ (7.86 mΩ for 0.2 s as measured by About:Energy) bodes well for high C-rate use cases, particularly where the thermal management system is constrained. The P45B battery cell is poised to set a new standard for high-performance applications, delivering exceptional performance, reliability, and efficiency. Molicel is expected to establish itself as a market leader in applications where energy, power, and fast charge capabilities are crucial.

Cell advertisement snapshot for Molicel P45B

Cell advertisement snapshot from Molicel website [Source: INR21700-P45B – Molicel]


Investigation using our coupled electrical & 2D thermal models


Using About:Energy's 'white-box' equivalent circuit models, we simulated the energy density for the advertised 120 W maximum continuous discharge power and simulated conditions in a climate chamber with forced air convection (the conditions under which most companies largely test their cells). We found that the cell became thermally limited before reaching the minimum voltage cut-off. By using models from About:Energy's Voltt platform, battery designers can apply their own thermal boundary conditions to test the performance of the Molicel P45B for their specific battery system designs.


The model parameterisation datasets were collected using our world-leading Peltier element temperature control system which allows for control of the surface temperature to an absolute precision of ± 0.5 °C and a resolution of 0.01 °C. Our proprietary controllers rapidly heat or cool cells to ensure that the cell surfaces remain at the predefined test temperature.


Gravimetric Energy Density and Thermal Energy Wasted with Continuous Discharge C-rate at 25 °C for the Molicel P45B [Simulated for inside Climate Chamber conditions with forced-air convection]


About:Energy also offers tools to visualise how the Molicel P45B would behave under different use cases, such as when testing in a chamber during cell technology validation for battery design, or using bottom cooling during detailed design phases. To demonstrate this, we simulated the Molicel P45B for a 4C continuous discharge under (1) forced-air convection inside a climate chamber, and also for (2) a representative bottom cooling case. Some interesting findings:


We found that the cell cap temperatures were almost 20 °C higher for the bottom cooling case compared to the cell simulated under climate chamber conditions. In fact, in the bottom cooling case, the cell almost reached the manufacturer’s extended operating temperature limit of 80 °C.


In the ‘climate chamber’ case, the temperature gradient across the cell was around 6 °C; in the ‘bottom cooling’ case this increased to almost 15 °C. It is critical that product-focused pack conditions are emulated early on in the product development process to account for this.


Along with an in-cell thermal gradient, pack designers need to account for cell-to-cell thermal gradients, which can be investigated using the Voltt platform along with finite element analysis software. This will not only have an effect on performance during a particular charge/discharge operation but will drastically affect ageing and degradation.


Comparison between Gravimetric Energy Densities for Testing at 25°C for Molicel P45B: Simulation for Climate Chamber (with Forced-Air Convection) versus Only Bottom Cooling (with 80°C Cell Temperature Limit)


How the Molicel P45B stacks up against other cells

One of the main questions is how this compares to the previous champion cell P42A, and more generally, other cells on the market. We also asked which cell is better for certain applications.


In comparison to the P42A, the P45B offers a 7% higher capacity while reducing direct current internal resistance (DCIR) by 22%. Even at a 50% state of charge (SOC), the P45B delivers a remarkable power output of 168 W for 10 seconds, while at 90% SOC, a ridiculous 184 W is potentially accessible from the cell. What is more crucial is that the P45B has a relatively flat resistance value within its operational window, allowing for reliable power delivery even in the lower SOC region, while limiting excessive heat generation and mitigating the risk of the cell. This is important because battery packs generally lose any remaining energy because the weaker cells in the pack become limiting due to higher internal resistance.


Molicel P45B 10s DC Resistance Spread with Capacity Discharged

Molicel P45B 10s DC Resistance Spread with Capacity Discharged [Source: INR21700-P45B – Molicel]


There are other cells which offer either higher energy density, such as the LG M50LT (285 Wh/kg versus the P45B’s 242 Wh/kg), or higher power density, such Molicel’s own P28A which has marginally higher peak power capability. There is really no other cell which offers the unique power-to-energy ratio that the Molicel P45B does. For example, the LG M50LT has a P/E ratio of 3.6, whereas the P45B has a P/E ratio of 8.1, which means that the P45B is ideal for power-focused energy-sensitive applications, whereas for the other cells one would be either limited by energy or power. The only other cell which comes close is perhaps the Samsung 50S.



Molicel P45B Compared to Other Cylindrical Cells - Investigating Power & Energy



Simulating these cells in planes

The P45B is ideal for high-power applications such as the high-performance automotive sector and in the emerging electric aviation market. Recent partnership announcements from Archer and Vertical Aerospace highlight Molicel's commitment to optimising power and fast-charging capabilities. In the eVTOL sector, where charging times and power availability for landing are critical components of the business case, this technology strategy becomes paramount. Ultimately, the number of safe flights per day is what will make or break the industry in terms of profitability.


What makes the P45B compelling is its excellent life performance, and ability to limit capacity and power fade even under fast charging, offering >80% performance after 500 cycles. This attribute holds tremendous significance as it diminishes the need for battery oversizing, leading to cost savings and improvements to the weight budget available.


To assess the Molicel P45B for eVTOL applications, we generated a custom eVTOL profile scaled to a typical 21700 cylindrical cell level and simulated it using our very own 2D electrical and thermal coupled equivalent circuit model for the P45B which includes a spatially resolved thermal parameterisation of the cell, discerning cap from jelly-roll and axial from radial conductance.


It was interesting to see that the temperature where it would be normally measured for the cell (the side surface of the cell, halfway from either end) was always below 60 °C while the temperature of the cell cap was around 67 °C. This is higher than the normal operating temperature limit of the cell. While not a thermal runaway risk yet, it could lead to rapid cell degradation, leading to limited battery life. This is a tough sell for the eVTOL industry as extreme thermal gradients through the cell could have implications on the number of flights per day. This in turn could negatively impact the business case for such aircraft and the rest of the electric aviation industry.


Generic Aerospace eVTOL Mission -  (a) Power, (b) Voltage, (c) Current and (d) Heat Generation
Generic Aerospace eVTOL Mission - (a) Power, (b) Voltage, (c) Current and (d) Heat Generation

Generic Aerospace eVTOL Mission - Comparing Temperatures Axially for Bottom-Cooled Molicel P45B (Using Simscape 2D Thermal Model coupled with Electrical ECM)


Using About:Energy’s 2D thermal modelling capabilities, battery designers can investigate axial and radial thermal gradients for diverse use cases to quantify the optimal use conditions for their cells. Empowered with this data, engineers are able to make data-informed decisions around system design and battery usage. We also compared the accuracy of our 2D thermal model for the P45B with temperature profiles generated from our P45B COMSOL Multiphysics 3D thermal model (as shown below), the simulated temperature compares favourably - results differ by 1-2 °C, particularly around the high power demand phase towards the end of the mission profile. This demonstrates the suitability of the 2D thermal network model.

Generic Aerospace eVTOL Mission - Comparing Temperatures Axially for Bottom-Cooled Molicel P45B (Using COMSOL Multiphysics)
Generic Aerospace eVTOL Mission - Comparing Temperatures Axially for Bottom-Cooled Molicel P45B (Using COMSOL Multiphysics)


Access Molicel and the latest power cells

We’re excited to work with battery solutions providers. If you're keen to access the Molicel P42A, P45B, and many other high performance cells to unlock the potential of your next battery product, sign up for the Voltt.


Alternatively, don't hesitate to reach out to us directly at sales@aboutenergy.co.uk, we'll be in touch soon.


Biography

About:Energy is a leading battery software company headquartered in London. The company was founded in 2021 by Gavin White and Kieran O’Regan, two researchers from Imperial College London and the University of Birmingham respectively. About:Energy has focused on building a portfolio of battery measurement and modelling capabilities to provide a software solution for battery design.


About:Energy provides organisations with the tools to streamline their R&D, reducing time-to-market and enhancing battery system performance. About:Energy’s data informs better decision-making across the value chain, from mine to end-of-life. These activities include battery system design, lifetime prediction, and cell optimisation. Customers include organisations across the automotive, manufacturing and aerospace industries.

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