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Battery technology

Time : 2020.12.24

The modern standard for electric vehicle batteries is lithium-ion, often with an iron phosphate or manganese cathode chemistry.It offers three times the energy density of technologies such as nickel-metal hydride, similar to nickel cadmium, which is used in hybrids, and is generally cheaper, safer and easier to make.

Lithium-ion batteries are also made of non-toxic elements which makes them easier to recycle and dispose of. They also maintain their charge when parked up rather than gradually cannibalising their own energy for temperature control.

Energy density is the key to battery development, translating into greater range for electric vehicle (EV) drivers. Range currently averages from 80 miles up to 100 miles.

Range, payload weight and battery size are inextricably linked; the further you want to go or the more you want to carry without recharging, the larger or more energy-intensive the battery must be.

Battery is highest cost in an EV

This is the major factor which makes EVs so expensive upfront; effectively the user is paying a huge proportion of fuel costs on purchase. Allan Paterson, electrochemical engineer at Axeon, says: “The battery is the biggest cost in an EV. 60% of that cost is the cells; and 60% of cell cost is the materials needed for the cathode.”

This means that although battery technology has halved in the past three years as cheaper elements have been utilised, even high volume production will not completely mitigate the price of the chemicals needed.

“We will see cell costs halve in the next five to 10 years, but the price will struggle to come down further,” says Paterson.

“Currently costs run to $600/kWh and the target is to bring them down to $300. But that will be a struggle.”

Manufacturers are not just beleaguered by a lack of volume production, but face heavy costs in R&D, patents and establishing plant infrastructure, all of which they will be recouping over the next couple of generations of product.

Lithium-ion batteries have no memory effects – so they can be part charged without degrading capacity.

However, the same cannot always be said for fast or rapid charging. The faster energy is poured into and out of the battery, the hotter it gets and the less stable its environment; this will affect performance.

Rapid charging – using DC current – is extremely fast; for instance, APT Technologies’ DC charger can charge a vehicle to 80% capacity in 15 minutes, but business development manager Justin Meyer admits: “In reality DC charging, and thereby over-heating, will probably degrade 20% of the capacity.”

Although the rapid charging debate continues, it is highly likely that many motorists, and particularly fleet managers keen to sweat the asset, will see gradual battery degradation as an acceptable cost against higher productivity and a faster return on investment.

Little demand for DC charging

Azure Dynamic, which produces the batteries for the Ford Transit Connect Electric, doesn’t believe there is yet a significant market demand for DC charging.

All charge and discharge cycles affect battery charge capacity over time. Valence, which supplies batteries for Smith Electric Vehicles, predicts 3% to 4% degradation for every 600 cycles (ie two years of daily use). Battery capacity fades gradually.

Ian Goodman, chief executive at LifeBatt, which produces batteries for Ashwoods hybrid vehicles, says customers should understand battery life in terms of their individual needs. Smith, for instance, says its batteries should retain 80% charge after eight to 10 years.

“That’s just quoting battery specs however. It makes more sense to say that a battery should handle 100,000 miles, for instance, at 100 miles per day; after that it may handle 80 miles a day.

In fact, if the user never does 80 miles in a day, they won’t notice the difference. Manufacturers should explain this stuff to the public better.”

Goodman says current batteries could be engineered in mileage increments to fit in the same package but it isn’t cost-effective for manufacturers to do so.

“NCAP testing in particular is very expensive for EV batteries, because there is insufficient experience in the industry yet to know appropriate ways of testing for guaranteed results. We are working towards industry standards, but the industry has yet to decide what size plug to put on a vehicle – goodness knows how long it will take to agree passenger safety standards.”

The rigours of testing and volume production mean new battery technologies will be slow to market. Lithium ion will probably dominate the field for the next five years but there are technologies in labs now with huge potential.

“There are new electrolytes which will open up performance,” says Paterson. “Annode technologies such as silicon alloy could increase energy density and be cheaper. On the cathode side, traditional chemistry will only take us so far.

“There are blue sky projects such as lithium sulphur which will offer 300-400kWh a kilo or Lithium Air which could offer five times the energy density.”

Huge potential of Lithium Air

Currently Lithium Air doesn’t exist outside the lab, but it has huge potential. “We are 15-20 years away,” says Paterson.

LifeBatt thinks metal air technologies could deliver faster than this.

“None of the existing vehicles use current cutting edge technologies,” says Goodman. “We think Lithium Air will come in in the next five to 10 years.”

One of the areas of contention over EVs in fleets is residual value. CV operators such as TNT have written their EVs down aggressively, expecting them to run on for two or three years further, and for the battery itself to have a residual value at the end of the vehicle’s life.

The used market remains unconvinced of the residual value of EVs, however, based largely on concerns about battery life.

Axeon is involved with various projects to investigate the second life for batteries and cost-analysis around recycling or disposal.

Paterson says: “We have not been running them long enough to fully understand the economics of degradation. However, it may be more sensible to recycle them than to put them into a second life as capacitors.” nd the challenges

 

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