Electric vehicles (EVs) are a revolutionary technology that is gradually gaining traction worldwide.
The ability of these vehicles to operate without fuel combustion or emissions while potentially providing enough power to sustain a household for days is the culmination of extensive investment and research spanning multiple decades.
However, alongside their increasing prevalence comes a rising concern over EV fires, a topic that lacks sufficient research and public awareness.
Electric Vehicle Fires: An Overview and Analysis seeks to address this educational gap concerning EVs and the associated fire risks.
The origins of EVs trace back nearly two centuries to the invention of the first EV motor in 1828.
Despite initial development efforts in the late 19th century, EVs experienced a decline with the development and popularity of internal combustion engines (ICEs), notably exemplified by the Ford Model T.
A resurgence occurred in the 1970s amidst concerns over oil dependency, yet challenges persisted in terms of performance, range, and affordability.
The pivotal launch of Tesla’s Roadster in 2008 heralded a new era, offering high-performance luxury EVs with extended range capabilities.
Advances in battery technology, particularly lithium-ion batteries (LIBs), further bolstered range and cost-effectiveness, leading to a diverse market of EV options from various manufacturers and a notable shift towards accessible, eco-friendly transportation.
For widespread adoption of EVs, substantial infrastructure development is imperative.
This includes the expansion of charging stations and battery manufacturing facilities, indicating a collective commitment from consumers, manufacturers, and governmental bodies.
When comparing the overall costs of EVs versus ICE vehicles, considerations encompass charging/fueling expenses, maintenance costs, and available incentives.
Research suggests that while EVs typically entail a higher initial investment, the total cost of ownership over the lifetime of the vehicle can be offset with reduced maintenance requirements, ongoing advancements in efficiency-enhancing technologies like regenerative breaking, and potential tax advantages.
The cost dynamics of powering EVs versus refueling ICE vehicles fluctuate depending on electricity and gasoline prices, charging habits, and vehicle usage patterns.
Generally, home charging offers cost savings, though prices may differ based on location.
Although EV fires garner significant media attention, statistically, they occur infrequently.
Although the number of ICE vehicles on the road significantly outnumber those of EV, data from the National Transportation Safety Board indicates that the rate of ICE vehicle fires per 100,000 ICE vehicles far exceeds that of EVs.
Thus, even with the increasing prevalence of EVs, statistical projections suggest a lower frequency of EV fires compared to ICE vehicles based on failure rate data and due to the increased research on LIB safety.
Thermal Runaway (TR) stands as a significant cause of EV battery fires, triggered by various factors such as overcharging or short circuits, and is an additional fire cause outside of those experienced by an ICE vehicle.
Managing EV battery fires poses unique challenges due to the risk of reignition and the complexities involved in suppressing the fire, particularly with stranded energy and suppression agents accessing the battery.
Technological strides like internal battery placement and the development and introduction of solid-state batteries aim to mitigate fire risks while enhancing overall battery performance.
However, ongoing research and development efforts in safety, efficiency, and environmental impact are continuously enhancing EV safety measures.
Numerous safety features are integrated into the design of EVs to help minimize the risk of fire.
Reinforced battery compartments aim to allow for battery use that could prevent punctures that could lead to TR and/or fires.
Active liquid cooling is often used to regulate the battery temperature in avoidance of thermal effects.
Battery management systems are integrated into the EV to monitor and control the health and operating state of the battery cells inside the pack.
There are two primary battery chemistries used in EVs: Lithium Iron Phosphate (LFP) and Lithium Nickel Manganese Cobalt Oxide (NMC).
Cell chemistry heavily impacts the stability, cost, energy density, charge rate, and lifecycle of the battery.
Each chemistry and form factor offers several advantages; however, manufacturers are increasingly utilizing LFP cells over NMC in current/future product vehicles.
LFP batteries have a wide temperature range, are lower cost, and have greater stability, while NMC batteries offer a higher energy capacity and nominal voltage and are overall more electrically powerful.
Safety considerations regarding TR and venting highlight the advantages of thermal stability and slower venting in LFP batteries, though continue to lack in energy compared to NMC batteries.
The ongoing development of battery chemistries will continue to consider factors like safety, range/energy storage and use, environmental impact, and resource availability.
Battery cell form factor selection is critical for maintaining safety, as battery fires can propagate quickly.
There are three main form factors used in EVs: cylindrical, pouch, and prismatic.
Cylindrical cells have high energy density but lower packing efficiency due to unavoidable space between cells.
Prismatic cells have slightly lower energy density, but better packing efficiency.
Cylindrical and prismatic cells can also have integrated vents or other safety features.
Pouch cells are constructed by stacking layers of components into a flexible pouch, offering high energy density and packing efficiency, but lack built-in safety features.
Cylindrical cells have metal casings and limited cell-to cell contact, which can lower propagation rates compared to pouch cells.
Prismatic cells can resist thermal abuse well due to their larger size.
Prismatic and pouch cells are predominantly used in EVs for their electrical strength and flexibility in application.
The original equipment manufacturer of different EVs have different battery connections that may be made in series or parallel to change the electrical characteristics of the battery pack.
Wireless battery connections are just beginning to enter the market and offer potential advantages in reducing complexity and weight of the battery pack, and allow for standardization and easy reconfiguration.
There continues to be a lack of standardized battery specifications, leading manufacturers to choose battery chemistry, form factor, and connections based on specific goals.
Managing battery temperature is also critical in understanding EV fires.
Managing battery temperature can occur through cooling methods like passive radiative fire protection, air, and liquid cooling.
Liquid cooling is the most expensive option, though it is the most effective because it offers high heat conductivity and compactness.
Indirect liquid cooling occurs through the circulation of coolant around the battery pack, and is used in many EVs due to its safety and efficiency.
Comparison studies show indirect liquid cooling outperforms other methods in temperature control, however, it still faces challenges like corrosion and extra weight due to the extra fluid in the battery pack and unpredictable environmental conditions, thus other methods are still frequently used.
EV research advancements focus on safety and efficiency.
Moving the battery inside the vehicle reduces the risk of battery puncture, improves temperature control, and aids firefighting access in the case of a fire.
Research suggests internal battery placement also improves efficiency, range, agility, and manufacturing costs while reducing environmental impact.
Transitioning to solid-state batteries (SSBs) or cobalt-free/nickel-based alternatives aim to mitigate fire risks associated with liquid-electrolyte LIBs, enhancing overall battery safety, but facing challenges in cost, design complexity, and mass production.
Though SSBs require higher temperatures to undergo venting and TR compared to standard LIBs, their venting and TR reactions can be significantly more powerful, hazardous, and difficult to extinguish.
Research on higher voltage batteries targets faster charging, lower heat generation, and longer range, meeting consumer demands while reducing overheating risks.
Battery swapping encounters obstacles in standardization and infrastructure, particularly in diverse markets like the US, though a promising idea.
It is important to fully understand EVs, their history, functionality, materials, cooling mechanisms, safety measures, and societal implications.
The safest and least fire-prone EVs according to this information utilize prismatic LFP batteries with indirect liquid cooling.
Ongoing research will be important in several battery-related areas (i.e. chemistry, form factor, cooling, etc.) to ensure the safety and viability of EVs while highlighting the need for standardized protocols in addressing extinguishing EV fires and their health and environmental repercussions.
