Designing a Lithium-ion Battery for Safety
In an era dominated by technological advancements, lithium-based batteries have become an indispensable part of our daily lives, powering everything from our smartphones to electric vehicles.
Just as petrol/diesel poses risks as a fuel source, lithium batteries carry their own set of potential hazards. Fortunately, these risks can be effectively managed through meticulous design considerations at every stage, from the individual cell to the assembly of the complete battery pack.
In this first ‘brief’ of our Battery Safety series, we consider certain intricacies of battery design at the cell level. Let’s explore the various methods to minimise risks and enhance safety.
The chemistry choice is where it starts, and that means managing trade-offs. There are 20 or more characteristics in choosing cell chemistry, but the main ones are:
Each of these characteristics can be plotted to make a comparison of the different chemistries. To illustrate the point, Lithium Titanate is probably the most inherently stable (therefore safe) chemistry, but the trade-off is that specific energy is low. From a practical standpoint, for a given battery capacity, a Titanate pack would be physically bigger by about a third compared with some of the packs with other chemistries.
The physical construction of the cell can offer additional elements of safety. The cell anode and cathode are separated by a permeable layer (the separator) within the electrolyte which allows the flow of ions from one side to the other.
A short circuit within the cell would cause a build-up of heat potentially melting the separator, therefore escalating the short circuit. This chain reaction can cause ‘catastrophic failure’ (to use an engineering term) of the cell. Some cells employ a ceramic separator which has a higher melting point than other types, therefore preventing the chain reaction.
Another element of cell design for safety is the addition of a vent or valve. One effect of a cell's internal failure is a build-up of pressure. The purpose of the vent is to allow this pressure to ‘vent’ outside of the cell to prevent rupture or explosion of the cell.
Other numerous design elements can be employed for cell safety, such as non-combustible case materials.
Choices made during the battery cell design process play an important role in mitigating potential risks. From carefully selecting cell chemistries with a balanced consideration of specific energy, power, safety, performance, lifespan, and cost, to implementing physical construction features such as ceramic separators and pressure-relief vents, each element contributes to a safer battery design.
Tembo’s team of engineers ensures that all aspects of battery safety are considered to ensure the safety and reliability of its Electric Utility Vehicle (EUV) conversion kit.
Join us in the next edition of our Battery Safety series as we look at the safety measures at the module level of battery design. We will unravel more layers of innovation aimed at ensuring the secure and reliable use of lithium-based batteries.
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