NOVEMBER 26, 2020tags: Electric Cars
By Paul Homewood
Fast-charging of electric batteries can ruin their capacity after just 25 charges, researchers have said, after they ran experiments on batteries used in some popular electric cars.
High temperatures and resistance from fast charging at commercial stations can cause cracks and leaks, said the engineers from the University of California, Riverside.
The team charged one set of discharged lithium-ion batteries using the same industry fast-charging method found at motorway stations.
The researchers also charged a set using a new fast-charging algorithm based on the battery’s internal resistance, which interferes with the flow of electrons. The internal resistance of a battery fluctuates according to temperature, charge state, battery age and other factors. High internal resistance can cause problems during charging.
The algorithmic charging method – known as internal resistance charging – is adaptive, learning from the battery by checking its internal resistance during charging. It rests when internal resistance kicks in, to prevent loss of charge capacity.
For the first 13 charging cycles, the battery storage capacities for both charging techniques reportedly remained similar. After that, however, the industry fast-charging technique caused capacity to fade much faster – after 40 charges the batteries only had 60% of their storage capacity.
At 80% capacity, rechargeable lithium-ion batteries have reached the end of ‘use life’ for most purposes. Batteries charged using the industry method reached this point after 25 charging cycles, while batteries charged with internal resistance charging were good for 36 cycles.
“Industrial fast-charging affects the lifespan of lithium-ion batteries adversely because of the increase in the internal resistance of the batteries, which in turn results in heat generation,” said doctoral student and co-author Tanner Zerrin.
Even worse effects came after 60 charging cycles using fast industry charging. Electrodes and electrolytes were exposed to the air, increasing the risk of fire or explosion. High temperatures of 60ºC accelerated the damage and the risk.
“Capacity loss, internal chemical and mechanical damage, and the high heat for each battery are major safety concerns,” said researcher Mihri Ozkan.
Internal resistance charging reportedly resulted in much lower temperatures and no damage.
“Our alternative, adaptive, fast-charging algorithm reduced capacity fade and eliminated fractures and changes in composition in the commercial battery cells,” said researcher Cengiz Ozkan.
The technique could be used to improve safety and lifespan of car batteries.
The researchers have applied for a patent on the algorithm, which could be licensed by battery and car manufacturers. In the meantime, the team recommended minimising the use of commercial fast chargers, recharging before the battery is completely drained, and preventing overcharging.
The research was published in Energy Storage.
The paper is here.
It is not clear how fast the “fast chargers” are which the study tested. They talk of motorway service station standards, which in the UK tend to be 50KW. I don’t know if the US is much different.
However, their trials suggest two hour charging, which would imply 50KW as well.
If so, this will be a huge blow for anybody who needs to use public chargers regularly. You may be able to get away with the occasional rapid charge when you go on a long trip. But for those unable to charge at home, or who travel long distances regularly, anything slower than 50KW is a non starter.
Below is the chart from the study, showing how rapidly the battery capacity deteriorates. Even algorithmic charging method (IR) loses capacity quickly as well, dipping well below the 80% benchmark after about 40 cycles.
This whole saga highlights how electric cars are being pushed forward with no thought about the consequential problems.
In the normal world, technologies only take off once the obstacles have been resolved.