Lithium-ion battery simulation

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At Bold, we take the guesswork out of early-stage projects and rely on low-cost yet highly accurate research to calculate a quotation for your project. Our lengthy experience with custom battery packs has given us the insight needed to devise all the steps to swiftly make a proposal adapted to your project’s specificities. We believe that your custom battery pack should fulfill every requirement without falling short or unnecessarily surpassing the parameters for the application your project sets out to perform.

Lithium-ion batteries

lithium batteries

When compared to standard performance for other chemistries lithium-ion cells are in its own league. Instead, common li-ion cell types are “18650” or “26650” that define its form factor. For instance, 18650 means the cell is 18 mm in diameter and 65 mm in length. The li-ion cell, which is the basic unit of the battery itself, is combined into a pack to create a battery. Huge advances have been made in battery chemistry in the last decade alone. This has allowed several new applications to benefit from the use of batteries, most notably in the emerging electric vehicle industry. Lithium-ion cells are stellar amongst the chemistries that have been developed recently. Although the li-ion cell is the main ingredient that controls the battery pack performance, the arrangement in which cells are combined largely determines the behavior of the pack. Lithium-ion cells are in general more expensive than NiCd and NiMH but are seeing a significant dip in prices as they grow in popularity and have wider-scale production. Prime examples of technology which use this type of chemistry are cell phones, laptops and of course, electric cars. The main reason for opting for li-ion cells is they have the highest energy to weight ratio. The chemical make-up of these batteries should be chosen depending on the parameters on a case-by-case basis. For more, check out our in-depth look at lithium-ion batteries in our post here.

Knowledge before building

Nestled inside the battery pack are cells, all with their own behavior under varying circumstances. Some of the essential information these cells communicate under first scrutiny are SOC (state of charge), temperature, voltage, capacity, amongst others. Bold only needs to study a handful of cells to collect the pertinent information which we later input into our own simulation code. This intelligent script takes physical measured data and works out the behavior of the cell for a given power duty cycle. This cycle is defined to match the real power and energy demands of our customers. Many iterations are done to eventually find a suitable battery pack design based on real data, even before the battery is built. Therefore, the costs are kept down since the crucial real-life testing cells are minimal.

As Bold has done for use in motorsport for an electric series, a high-end battery concept is developed based on a pre-selected cell. Cells are tested to obtain the working parameters for our electrochemical models. We use simple models for initial rough dimensioning of the custom battery pack. Additionally, we use equivalent circuit models to predict behavior of the cells’ systems. We can characterize cells to get data for our models. To compliment this knowledge, we also use data from reliable suppliers or even from tests we had previously carried out.

The difficulties in accurately predicting the thermal behavior and pumping losses in the cooling system are tackled using CFD tools. The main advantage in simulation is the speed at which we can try different ideas and design parameters. On top of that, the post processing tools allow us to understand the behavior of the system to enable our engineers to come up with improvements or discover issues before building prototypes. For instance, when doing the simulations, we might find some issues before meeting the target for pumping losses. However, after looking deeper into the issue along with the help and know-how of the SimScale support team, we fix these problems and start comparing results amongst different designs.

Battery Behavior and Chemistry Testing

There are different approaches for battery simulations. Mainly analytical models using MATLAB / Simulink and CFD (Computational Fluid Dynamics) tools. Bold have these tools available at their skillful fingertips to perform thermal simulations on battery packs from CAD and analytical models. We can develop a set of proprietary numerical tools to treat and simulate the experimental data from the battery cells. Bold purchases battery cells from specialist suppliers that formulate different chemistries. The value we add is in selecting the most appropriate cells for each application. The main factors that drive cell selection are discharge rate and capacity. There are many other factors involved in the selection that are also considered. For example, the quality of the cell also determines the aging performance. Aging of the cells might cause self-discharge, increased impedance and decreased capacity. So now that Bold has collected all the information from the real-life battery cells and have converted that into an intelligent script, we then move on to testing through simulation with MATLAB. Whether your custom battery pack is to be used in electric vehicles, aircraft or industrial applications, it is important to ensure their safe operation, longevity and optimal performance.

The outputs of simulation

The cell data is then tested using MATLAB for both its chemical behavior and overall performance. The cell data is usually gathered for a specific set of working conditions in order to improve accuracy. These tools allow Bold to study the electro-chemical behavior of cells given a power demand cycle. Lithium-ion batteries have relatively long cycle life, from 300 cycles to more than 1000 cycles depending on operating conditions. While there are many chemistry combinations on offer with lithium-ion batteries, that chemistry can be further tweaked to obtain longer life span, higher capacity or high-power rates. With MATLAB, the output can even reveal the ideal cell construction for the whole custom battery pack. Some of those designs to consider for joining all the battery cells could be in a pouch, cylindrical or prismatic packaging. Two more factors disclosed in MATLAB’s output are the cell’s SOC and voltage. Simply put, we will have a clear idea of the lifespan of the battery and the measurements as regards the voltage during the various stages of use, be it lulls, spikes and everything in between. Besides the electronic design of the unit to meet the operational and performance requirements, we can bring the experience in designing cooling systems for correct heat management. This includes liquid cooling with pumps and heat exchangers.

Changes for the better

It is hard to imagine going back to the old way custom battery packs were crafted before the existence of these simulation tools. Also, considering the wide range of battery chemistry available today, it is indispensable to have such testing capabilities on hand for every custom battery pack design. While analytical calculations were still important, it was only achieved through a high degree of simplification and real-world testing. Added to that is the difficulty of rounding up these physical materials with the reality of having to wait on suppliers from across the globe. The advantage to choosing Bold is in knowing we do our own in-house testing and can therefore provide the assurance of swift verification and validation for your custom battery pack. Contact us to learn more so we can get started on your project today!

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