Key Takeaways
- Molicel P50B Enhancements: The Molicel P50B offers higher capacity and better thermal management than the P45B, improving performance for demanding applications, though it requires careful handling of silicon-induced degradation.
- Lifetime: Results indicate that while the P50B offers the potential to enhance either performance or lifespan as a direct replacement, achieving both simultaneously may require adjustments to pack-level operations.
- Advanced Modeling for Cell Selection: About:Energy’s 'white-box' models enhance battery pack design by providing detailed degradation insights and simulating various health states, crucial for selecting the optimal cell.
Introduction - The Cell Selection Game
When evaluating battery technologies, the process is both technically and commercially demanding. Beyond engineering metrics like energy density, factors such as supplier reliability and production capacity play a key role in choosing the right cell for your vehicle program. High energy density doesn't always equal better performance; the power-to-energy ratio required for your application may vary, or the battery life could be limiting. What if you could outsource extensive qualification tests and seamlessly integrate precise cell models into your design platform?
At About:Energy, we’ve done the heavy lifting, providing reliable datasets and models that streamline the decision-making process. Let’s dive into Molicel's latest innovation, the P50B, a powerhouse designed for high-performance applications in eVTOLs, superbikes, and hypercars. Is this the cell for today or one to watch for the future? Let's find out.
Data Sheet Comparison
Molicel has partnered with Group14 Technologies to incorporate advanced silicon-based anode materials, specifically Group14's SCC55®, into their high-performance lithium-ion battery cells, likely starting with the P50B. This collaboration could be transformative, showcasing how the combination of cutting-edge materials and innovative battery design can significantly advance energy storage technology.
We recently received a batch of low-volume production run cells, which have undergone a rigorous testing and modeling program. When compared to the Molicel P45B—the previous benchmark in the B-series—the new Molicel P50B demonstrates several key improvements. It offers higher capacity, faster charging, and enhanced discharge capabilities, all while maintaining the same level of resistance (as detailed in Table 1).
Although the P50B is slightly heavier, its increased energy density suggests higher silicon content and concomitant geometric optimisation of the jelly-roll to boost total cell capacity.
Table 1. Comparison between Molicel P45B and P50B using Manufacturer’s Datasheet
Property | Molicel P45B | Molicel P50B | Comment |
Capacity [Ah] | 4.5 | 5.0 | 11% higher |
Mass [g] | 66.0 | 68.8 | 4% higher |
Specific Energy [Wh/kg] | 245 | 260 | 7% higher |
Energy Density [Wh/l] | 643 | 714 | 11% higher |
Peak Current [A] | 13.5 (charge) / 45 (discharge) | 15.0 (charge) / 50 (discharge) | 11% higher |
DCIR at 50% [MΩ] | 15 | 15 | No change |
Battery pack designers have two main options with the Molicel P50B: create a lighter pack or extend range and lifespan. Although it shares the same physical footprint as the P45B, its different internal chemistry introduces new performance characteristics and potential challenges. For instance, the increased silicon in the negative electrode may alter degradation patterns, affecting long-term reliability and complicating battery state estimation due to greater hysteresis. To fully benefit from the P50B, understanding these nuances is essential.
The ‘so what?’ - A Pack Level Comparison
Let’s consider a baseline battery pack using the Molicel P45B in a 240s8p configuration. Assuming a 75% cell-to-pack efficiency, this P45B pack would deliver approximately 186 Wh/kg at the pack level, resulting in a total energy capacity of around 31.5 kWh for a 169 kg pack.
Now, if we switch to the Molicel P50B cells while maintaining the same 169 kg pack, we can achieve the same 31.5 kWh output by cycling only about 90% of the State of Charge (SoC) window, compared to the full 100% SoC required for the P45B. A reduced SOC window of operation would be expected to impact battery life positively. Alternatively, if we utilise the full SoC window with the P50B cells, the pack could deliver nearly 200 Wh/kg and an overall energy capacity of 35 kWh.
Additionally, the P50B's higher capacity would allow for lower operating currents, which would reduce the thermal load on the battery management system. On average, an individual P50B cell would carry 11% less current than an individual P50B cell for the same pack level current demand.
This improvement in thermal efficiency would not only enhance the pack’s overall energy and power performance but also potentially extend the pack's lifespan by reducing the stress on individual cells.
In the following sections, we’ll analyse the intricate coupling of electrochemical and thermal characteristics of these two cells and evaluate the real impact of choosing the Molicel P50B.
Comparison using Electrical Models
To begin, we will use electrical models with lumped thermal feedback as our comparison tool to evaluate the differences between the Molicel P45B and P50B. These models have been parameterised and validated using About:Energy’s proprietary cell measurement and modeling approach. For both the P45B and P50B, the models achieved a root-mean-squared error (RMSE) of less than 30 mV in simulated voltage across the cells’ standard operating envelopes. This low error margin enables reliable estimation of key parameters such as available power, state-of-charge (SoC), heat generation rates, and cell temperature rise, which are crucial for optimizing pack design and accelerating development.
To conduct the simulations, we focused on the aerospace sector and developed a custom eVTOL flight profile (Figure 1). This profile includes typical mission phases such as takeoff, landing, transition, and cruise, representing a common use case for an electric vertical take-off and landing (eVTOL) battery system. The simulations were initiated with a State of Charge (SOC) of 100% and a starting temperature of 25°C. We also incorporated a heat sink of 0.5 W per cell to simulate the thermal management system typically used in eVTOLs. It’s worth noting that, in practice, this heat dissipation value could be lower, as many eVTOL manufacturers are moving away from in-flight ‘active’ thermal management systems.
Figure 1. Typical eVTOL Mission Profile
The intricate coupling between electrical and thermal phenomena is illustrated in Figure 2. During the take-off phase of the eVTOL mission profile, the P45B initially exhibits a smaller voltage drop compared to the P50B due to faster heat buildup. However, as the flight progresses, the P50B’s higher capacity comes into play, allowing it to maintain a higher overall voltage. This dynamic highlights how the P50B's improved performance is largely tied to its thermal characteristics, which can have significant implications for pack design and longevity. Furthermore, in practice, at an individual cell level, the P50B would potentially see a lower current demand due to higher pack level capacity than the P45B.
Figure 2. Voltage and Temperature Response for eVTOL Mission Profile simulated using About:Energy Electrical Models with Lumped Thermal Feedback
As detailed in Table 2, these findings led to several noteworthy observations. While the P50B, as expected, outperformed the P45B in terms of final SOC and minimum voltage, it also generated less heat and experienced a lower temperature rise. This improvement is primarily due to the lower operating currents in the P50B, despite similar resistance values and overpotentials between the two cells.
This suggests that one of the most immediate benefits of the P50B over the P45B may be the simplification of thermal management system design.
Table 2. Comparison between Molicel P45B and P50B using About:Energy Electrical Model with Lumped Thermal Feedback: eVTOL Mission Profile Use Case
Metric | Molicel P45B | Molicel P50B |
Final SoC [%] | 35.4 | 42.2 |
Minimum Voltage [V] | 3.185 | 3.242 |
Max Temperature [degC] | 59.8 | 57.7 |
Over the lifespan of the cells, as resistance increases in both the P45B and P50B, the thermal management challenges for the P50B are likely to be easier to address. This could allow for design flexibility, such as reallocating weight budgets to enable a larger pack or offering an extended warranty. The overall benefit of using the P50B, especially in terms of thermal management, is likely to improve cell-to-cell consistency, enhance pack performance, and extend the battery’s lifespan.
Let's consider a more complex scenario: an eVTOL aircraft is unable to land safely and must execute a go-around, extending its flight time and requiring additional power below 50% State of Charge (SOC). The Molicel P50B, with its presumed higher silicon content, is likely to excel in this situation. Silicon anodes boost energy density, providing more usable energy in the lower SOC range. This could ensure the aircraft has sufficient power for additional maneuvers, maintaining stable performance and reducing thermal stress during critical operations. In contrast, the Molicel P45B might face greater challenges, particularly with thermal management, when pushed to its limits in extended flight scenarios. The P50B's enhanced energy density and improved performance at lower SOCs make it a more reliable choice for eVTOL applications, especially in situations requiring unexpected extensions of flight time.
The eVTOL mission profile with go-around appended is shown in Figure 3.
Figure 3. Typical eVTOL Mission Profile with Go-Around
As shown in Table 3, the P45B could not complete the go-around mission profile. This failure wasn't due to the cell reaching the 2.5 V cut-off voltage (top), but rather because it hit the maximum temperature limit of 60°C (bottom). This thermal limit was breached within just 2-3 seconds of additional flight time, a seemingly brief period that may have catastrophic implications in an eVTOL context. In contrast, the Molicel P50B successfully completed the go-around mission due to its superior thermal management. These improvements are modest at best, but they are enough to demonstrate that the additional capacity in the P50B has not resulted in any resistance-related trade-offs, whether in power capability or thermal performance.
Table 3. Comparison between Molicel P45B and P50B using About:Energy Electrical Model with Lumped Thermal Feedback: eVTOL Mission Profile Use Case with Go-Around
Metric | Molicel P45B | Molicel P50B |
Final SoC [%] | 22.0 | 29.7 |
Minimum Voltage [V] | 3.005 | 3.038 |
Max Temperature [degC] | 60.0 | 58.8 |
Fast Charge Performance
We examined the charging performance of cells. In this study, we also included a typical 5 Ah 21700 cell with an NMC positive electrode, similar to the Molicel P45B. The cells were charged from 5% SOC using a constant 50 W power. If any cell hit 4.2 V, it switched to constant voltage (CV) mode. The aim was to either maintain a 50 W charge for 10 minutes or measure the charge capacity before reaching 60°C. All tests started at 25°C with no active cooling, and results are based on simulations using electrical equivalent circuit models (ECMs) with thermal feedback. As shown in Figure 4, both the Molicel P45B and P50B cells far outperformed the generic 21700 cell. The generic cell couldn’t complete the 10-minute charge cycle, reaching 60°C and 4.2 V in around five minutes, leading to premature termination due to excessive heat.
In contrast, the Molicel cells managed heat effectively and maintained better charging efficiency, making them more suitable for fast-charging applications.
Figure 4. Comparison between Molicel P45B / P50B and Generic NMC-based 5 Ah 21700 Cell for Fast Charge Performance: (1st graph) Cell Voltage, (2nd graph) Charge Throughput, (3rd graph) Temperature, and (4th graph) Internal Cell Heat Generation
The Molicel 21700 technology enhances charging performance by featuring lower internal resistance, which reduces heat generation during the charging process. This not only improves charging efficiency but could also help avoid negative potentials that can harm battery performance and lifespan. Lower internal resistance contributes to more stable operation and less thermal stress, which can significantly extend battery life and enhance safety. For a deeper dive into how such advancements can optimize fast-charge profiles for electric vehicles, you can refer to About:Energy’s technical article in partnership with MathWorks: Generating Safe Fast-Charge Profiles for EV Batteries - MATLAB & Simulink.
Comparison using 2D Thermal Models
We employed About:Energy’s 2D thermal model to investigate the temperature distribution across both the P45B and the P50B. To ensure that both cells had a fair comparison, we generated a representative eVTOL heat generation profile, and we initialised both the P45B and P50B thermal models as per below (note: these settings are available on the user interface for the models by default):
Initial cell temperature: 25°C
Heat transfer approach:
Base heat transfer coefficient = 100 W/m^2/K
Surface heat transfer coefficient = 10 W/m^2/K
Cap heat transfer coefficient = 0 W^2/K
Coolant temperature = 15°C
Note, these results differ from those of the electrical model due to the different ways thermal phenomena are represented: the electrical model integrates thermal behavior with electrical performance, while the 2D thermal model uses a common heat generation profile. An example result for the Molicel P50B is given in Figure 5. As expected due to base-cooling the cap temperatures are much higher than the temperature at the base of the cell, which would be closer to the coolant temperature. This is crucial to optimise, as while a greater cooling magnitude may drop the bulk temperature of the cell, parts of the cell would see a much higher temperature leading to premature degradation and safety issues.
Figure 5. Temperature Distribution for eVTOL Mission Profile employing Base Cooling simulated using About:Energy 2D Thermal Model - Molicel P50B
Table 4 shows that if a 2D thermal model for the Molicel P45B is considered, the cell would not be able able safely complete the desired mission profile. The P45B reaches 60°C before mission completion, and again during landing, potentially causing premature mission termination or operation beyond safe limits. This significant temperature gradient could lead to uneven cell degradation and an earlier end-of-life for the battery pack.
Table 4. Comparison between P45B and P50B showing difference between using lumped thermal model and 2D thermal model.
Parameter | P45B with lumped thermal | P45B with 2D thermal | P50B with lumped thermal | P50B with 2D thermal |
Time [s] | 910 | 868.5 | 910 | 910 |
Mission Completion [%] | 100 | 95.4 | 100 | 100 |
Effective thermal management is crucial for extending battery life and ensuring safe operation. Even small variations in temperature within a battery cell can lead to accelerated degradation and reduced performance over time. Advanced thermal modeling techniques are essential as they offer precise predictions of temperature behavior and degradation patterns. These insights enable the development of improved design and management strategies for battery systems, enhancing their reliability and efficiency. A 2D thermal model, in particular, provides detailed temperature distribution data, whether used to refine initial estimates from electrical models or in combination with them. About:Energy’s suite of models facilitates this process, offering seamless integration for optimal battery management.
Life and Degradation: Spotlight on P50B
When selecting a battery cell, lifetime performance is a critical factor. Although manufacturer data and basic estimates offer initial insights, detailed design decisions require advanced degradation testing. As demonstrated in Figure 6, we conducted tests on both the Molicel P45B and P50B using our advanced Peltier-controlled test fixtures. These tests involved aggressive charge and discharge cycles (constant power) at a typical operating temperature relevant for high-power, energy-dense, and weight-sensitive cells.
Assuming the End-of-Life (EoL) capacity for both the P45B and P50B is defined as 80% of the P45B’s Beginning-of-Life (BoL) capacity, i.e., 3.6 Ah, our findings indicate that the Molicel P50B lasts up to 50% longer in terms of cycle life compared to the P45B before reaching this 3.6 Ah threshold.
This conclusion is based on 0.1C discharge capacity checks conducted every 50 cycles. Additionally, DCIR testing at 50% state of charge (SoC), conducted every 50 cycles, revealed that the P50B’s relative resistance increased at a slower rate compared to the P45B. This is significant not only in terms of the available energy from the cells but also for potential differences in thermal management requirements at the pack level.
Figure 6. Comparison between Molicel P45B and P50B for Accelerated Cycle Life Degradation Under Aggressive Charge & Discharge Combinations Operated at Elevated Temperatures
These results indicate that while the P50B offers the potential to enhance either performance or lifespan as a direct replacement, achieving both simultaneously may require adjustments to pack-level operations. For example, operating the P50B within a narrower state of charge (SOC) window could help mitigate the silicon-related degradation that becomes more pronounced at lower SOCs.
Overall, the Molicel P50B represents a significant advancement over the P45B in both lifespan and performance, paving the way for greater techno-economic benefits for customers of the Taiwanese cell manufacturer.
Access Molicel and the latest power cells
Interested in a Molicel P50B model? Book a demo here: https://calendly.com/tim-aboutenergy/molicel-p50b-sales-enquiry
We’re excited to work with battery solutions providers. If you're keen to access the Molicel P50B, P45B, and many other high-performance cells to unlock the potential of your next battery product, sign up for the Voltt. There you can access our suite of electrical, thermal and electrochemical models (physics-based), and arrays of degradation data and analytics on your favourite cells.
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 with its headquarters in London. Founded in 2022 by Gavin White and Kieran O’Regan—researchers from Imperial College London and the University of Birmingham, respectively—the company has concentrated on developing a comprehensive portfolio of battery measurement and modelling capabilities. These advancements are aimed at providing a sophisticated software solution for battery design and use.
The company equips organisations with cutting-edge tools to streamline their R&D processes, significantly reducing time-to-market and improving the performance of battery systems. About:Energy’s data plays a crucial role in enhancing decision-making throughout the value chain, from mining to end-of-life management. The Voltt, their flagship product, supplies critical data for widely used batteries across various industries, including automotive, motorsports, and aviation. This data supports a wide range of activities, such as cell selection, battery pack design, lifetime prediction, and cell optimisation.
Comments