Virtual adventures for safe electric vehicle development

This post is created by Puneet Sinha.

What a year 2013 had been for Li-ion batteries and electrification in transport sector! Successful launch of Model S and Tesla posting first quarterly profit that sends its stocks soaring is a welcome sign for electric vehicle industry. Not only Tesla, electric vehicles (plug-in as well as all-electric) from various automakers including, GM, Ford, Nissan, Toyota among others have seen substantial increase in sales. According to International Energy Agency (IEA), more than 77,000 electric vehicle (plug-in and pure electric) have been sold year to date in US alone, approx. 45% increase in sales compared to 2012. Increasing sales numbers, great reviews and recommendation from consumer report and high scores in customer satisfaction all builds on the momentum of vehicle electrification. But then events like 2011 Chevy Volt fire, Boeing 787 fire and most recently Tesla’s Model S catching fire remind that challenges remain in wide spread adoption of this new mode of transportation.

Decision to include a particular Li-ion battery in a product is based on extensive safety testing. So it is intriguing to me to think what can be missing that- despite safety testing in labs- has sometimes led to fire events originated from Li-ion battery pack during on-field operation? EC Power team tried to find an answer. We are lucky that there are so many case studies that one can look at from the successful adoption of ICE engines and automobiles in the last century. My personal favorite case study is vehicle crash worthiness and how it evolved in the last few decades.

Vehicle Crash Worthiness

Till 1990, crash worthiness of vehicles was largely done through brute force vehicle crash testing and today a majority of this work is handled through crash simulations requiring only a few dummy vehicles to be crash tested. 1986 model of Volkswagen Polo and 1990 model of Opel Astra were the first commercial vehicles where simulation tool played a large role in developing crash worthy vehicles. Crash simulations, compared with physical testing, allowed time and cost-effective assessment of vehicle crashworthiness that allowed OEMs to not only meet time pressure of keeping up with increasing safety regulations worldwide but also to open new innovation opportunities. The biggest benefits of using crash simulation tools was that engineers not only could capture the effect similar to that in actual testing but also could evaluate the cause that wasn’t possible through testing-only approach. As these simulation tools became more accurate and faster, they changed the paradigm of vehicle development by allowing engineers to have vehicle safety as a key metric from the beginning of vehicle development process. Fast design iterations early in the vehicle design cycle significantly improved the productivity and thereby saved cost.

Stage is set for Li-ion battery safety simulations

Current process of developing safe Li-ion battery packs and electric vehicles looks very similar to Pre-1990 era for vehicle crashworthiness. It is heavily testing oriented process that allows engineers and scientist to only assess the outcome (i.e. did a battery pass or fail a safety test!) and is very expensive. In addition, it is not always easy to test field-relevant safety scenarios. For instance, testing safety of Li-ion battery against for internal shorting, a key phenomenon that can lead to fire hazards in a Li-ion battery owing to a metal particle of Li dendrite puncturing a cell, is difficult. How to design a battery pack that can contain an event to escalate to the whole pack is one of the many questions that engineers are facing in the pursuit of developing safe battery pack and vehicle. Also, as electric vehicles are growing their global footprint, it can be a challenge to meet different safety standards of different regions. These are some of the catalysts that demand a newer, more efficient approach to safe electric vehicle development. I believe shifting from testing-only to a hybrid approach of hybrid approach that involves testing and Li-ion battery safety simulation is the key going forward.

Li-ion Battery Safety Simulation with AutoLion-3DTM

AutoLion-3DTM is Li-ion battery software developed by EC Power targeted to address on-field relevant safety challenges of Li-ion battery cell and pack. Li-ion battery safety is a strong function of cell energy, cell design, and cell chemistry. Safety simulations, therefore, are very challenging (and interesting) as one has to capture thermal and reaction rates simultaneously. That is what AutoLionTM is set to do.  Users can easily and efficiently evaluate safety of Li-ion battery pack and effectiveness of various mitigation approaches for unsafe events such as internal sort, external shorting and nail penetration. Simulation of mechanical crush of a battery is under development now and should be coming up in our software release very soon. Not only AutLion safety simulations can capture safety testing results pretty well (we have seen good match between our simulations and experimental data), it allows users to explore the limiting mechanisms and how to improve the safety. For more details, visit our case studies.

Few months back, at The Battery Show 2013 I met with Dr. Prabhakar Patil, CEO of LG-Chem Power. During our discussion, he said that Li-ion battery safety is a strong function of cell design and if designed right Li-ion battery should be safe. I couldn’t

AutoLion safety simulations: Temperature (K) evolution in a battery pack during nail penetration

have agreed more. AutoLionTM promises to be a tool to help design a safety-conscious Li-ion battery pack in a time and cost-effective manner. It allows engineers to ask questions that start with “why” and/or “what if”, the questions that have always started innovations. At the beginning of 1980s, engineers as Volkswagen and Opel were asking these questions about vehicle crash. I am hopeful and excited that the same questions when asked and answered for Li-ion battery and electric vehicle safety, it will result is something great.

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