PHOTO CAPTION: Better Place battery exchange station in Israel.

Battery Exchange Networks Key to Electric Car 'Holy Grail'

Better Place business analyst Ben Cebon sees slow but steady improvement in battery cost and energy density.

Published: 27-Aug-2012

In discussions about when – or whether – electric cars will dominate our roads, there’s one concept that always gets people excited: the bigger, better battery.

Some see it as the ‘holy grail’ that will trigger mass adoption. After all, if your car has a battery that can take you 500km or more, suddenly it’s in the same league as petrol… right? And if Moore’s Law applies to computer chips, why can’t battery technology improve exponentially too?

While it’s true that battery technology has been steadily improving, lithium ion batteries face very real physical constraints which limit the rate of development. Let’s get technical for a minute to understand why this is the case.

The technology inside batteries

An automotive battery pack is filled with hundreds of individual batteries, or “cells”. Within each cell, positively charged lithium ions flow from the negative to the positive electrode, and to balance the charge, electrons do the same through wires outside the cell. To recharge it, you simply use electricity to push the whole system backwards. The amount of energy (electricity) you can squeeze into a cell is directly related to the number of lithium ions you can move back and forth between the electrodes.

What happens at the electrodes is crucial. Lithium ions can’t just cluster together when they get there – they need to be accommodated in honeycomb-like structures. Most improvements in battery technology come from tweaking the design of these structures, but every tweak creates trade-offs. It’s a bit like a sheet that’s too small for the bed: each time you pull it to cover one corner, you uncover the other three.

The result is a range of lithium ion chemistries that with different strengths and weaknesses. Some exhibit fantastic energy capacity for their size and weight, like laptop or phone batteries, but at the expense of longevity. Others trade energy density for charge rate, or cost for safety, and so on. Unlike computer chips, the rate of improvement tends to be slow and steady, and looks set to continue this way.

Battery technology outlook

Since lithium ion batteries were first invented in the 1970s, the world’s largest electronics and chemical companies have poured money into R&D. Most of these efforts have focused on improving energy density while maintaining current high standards of longevity, safety, and resilience.

A recent McKinsey analysis predicted that battery capacity should roughly double in the coming decade, pointing to new materials and manufacturing techniques in development. That’s around a 7 per cent (compound) improvement in energy density per year. This figure, however, relies on the success of a range of developing technologies, and most of the mooted improvements still face significant hurdles. Lithium ion technology will indeed continue to improve, but not in giant leaps and bounds.

What other battery possibilities exist beyond lithium ion?

Lithium will always remain king, since – beyond putting a nuclear reactor in your car – no other metal can pack the energy-for-weight punch that lithium provides.

But could it be possible to remove the bulky electrode structures and produce a battery with only lithium and air? Such a battery already exists, and it provides much more energy per cell.

Its unique weakness however, is that it utilises such an energetic process that it’s almost impossible to recharge. It reacts slowly with oxygen from the air, effectively burning the lithium – and recharging the cell means reversing that process. ‘Unburning’ the lithium is the electrochemical equivalent of unscrambling an egg. Even the most optimistic estimates place lithium air batteries 20 years away from making it into cars.

Battery cost outlook

Over time, battery costs are expected to fall significantly. McKinsey expect prices to drop to around $200 per kilowatt-hour by 2020, a prediction that almost perfectly matches that made by the US Department of Energy in 2010, who forecast that a typical battery pack should cost around $5000 by 2020. As EVs become cheaper (and petrol becomes more expensive) they will gain serious market share, and start to make a real dent in our transportation emissions.

But battery technology will continue to improve slowly and steadily, rather than in leaps and bounds. The prospect of seeing a good, cheap, long-lasting 500km battery is still a very faint one, and even if such a battery did eventually exist, charging it would severely stretch either your schedule or your nearest substation. That is why Better Place believes that infrastructure is crucial to the success of the electric vehicle market – we want EV drivers to be able to drive wherever they want, whenever they want, just as they currently do in a petrol car.

Ben Cebon holds a PhD in chemistry, and is a business analyst at Better Place.

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