In addition to Li Batts’ much higher upfront cost, many of their disadvantages are rooted in the same characteristics as their advantages.
For assistive technology applications, Li Batts – both Li-NMC and LiFePO4 – are typically two-three times more expensive than traditional batteries.
Compared to traditional batteries, for optimal performance, greater care and precision must be applied to charging Li Batts. Li-NMC Batts can become dangerously unstable at the end of their useful life, if charged improperly, or if their battery management system (BMS) fails; LiFePO4 Batts are significantly less prone to these modes of failure.
In Li Batts, lithium metal (cathode) and lithium salts (electrolyte) are highly flammable, and if Li Batts are compromised, the resulting electrochemical process can lead to “thermal runaway” where the battery’s internal temperature accelerates, releasing more energy, further increasing temperature, releasing more energy, etc. in a self-perpetuating uncontrolled cycle – which can lead to very intense, hard-to-extinguish fires and/or explosions. Research and experience generally show that LiFePO4 Batts are significantly less prone to these risks.
Since they can store and deliver so much energy for their weight, when the medium-to-high-capacity Li Batts used in assistive technology applications (especially Li-NMC Batts) malfunction or fail, they have a much higher potential to do so catastrophically and dangerously compared to traditional batteries.
Currently, facilities are few for recycling Li Batts at the end of their useful lives back into constituent parts than can be used to make new Li Batts as part of a circular economy sustainability and social value plan. Specialist electrical waste management companies have to gather economically viable quantities of Li Batts and transport them to the nearest recycler – but assembling large quantities of end-of-life and/or damaged Li Batts has to be done very carefully to manage fire and explosion risks, adding significant expense and complexity to Li Batts.
Li Batts present many advantages for assistive technology, especially mobility scooters and powered wheelchairs.
Typically, Li-NMC Batts are around 1/3 the weight of traditional batteries – and LiFePO4 Batts only 20 percent heavier than Li-NMC Batts – which makes them easier for users and carers to move and reduces the overall weight of the device being powered.
Cared for properly, Li Batts may last significantly longer than traditional batteries – Li-NMC Batts up to two times longer and LiFePO4 Batts up to five-seven times longer – due in part to their higher cycle life (the number of charging and discharging cycles a battery can undergo without compromising its performance).
Whereas traditional batteries’ voltage drops significantly throughout the charge-life (experienced as weakening power output as the charge dissipates), Li Batts’ voltage remains steady throughout the charge-life, weakening only when nearly fully discharged.
Compared to traditional batteries, Li Batts are capable of storing much larger amounts of energy.
Again, compared to traditional batteries, Li Batts are capable of delivering much larger amounts of energy relative to their weight.
DoD is the maximum capacity of a fully charged battery that can be used prior to recharging without negatively affecting the battery’s overall lifecycle; traditional batteries have a c. 50 percent DoD whereas Li Batts have a c. 80-90 percent DoD – meaning, effectively, Li Batts can be used for longer without recharging.
Li Batts for assistive technology applications are typically 2-3 times more expensive than traditional batteries – however, due to longer life, Li Batts (especially LiFePO4 Batts) can, if maintained properly, reduce overall cost.