Innovation
Package options: Most current Li-ion batteries are cylinders (centre) but “pouch” batteries (left) may be an option for automotive configurations (right) ➾
driving the search for differentmaterials for all applications, and the automotive industry has pressures of its own, related in themain part to size and configuration. The difficulty, says Paterson, is that no
one electrochemistry has so far emerged to fit all the applications. “The driver in the main applications so far, such asmobile phones and laptops, has been energy density, the ability to storemore charge for a given volume ormass, with cost reduction also important.” With automotive applications, these
factors are still important, but there are other factors coming forward into play too. In particular, the cycle life – the number of times the battery can be charged and discharged – is now a big issue. Car owners want not just to be able to drive 100miles or so without running out of power, but they also don’t want to have to change the battery pack every few weeks,months or even years. Ideally, the battery would last as long as the vehicle: up to 10 years in standard use. Michael Sinkula, head of business
development and one of Envia’s co- founders, says: “The challenge with batteries in cars ismatching a typical car warranty which ismuch longer than the usage period of amobile phone or laptop, the traditionalmarket for lithium batteries.” The upshot of these various pressures is
the development of a range of new Li-ion chemistries now coming on to themarket: lithiumiron phosphate (LFP), which is more stable, less toxic andmore susceptible to safety regulations than the cobalt-based materials, and lithiummanganese compounds, not just lithiummanganese oxide but alsomore complex chemistries involving nickel and cobalt, though these seemless likely. The first large-scale production vehicles
that have declared their hands, the Volt and the Nissan Leaf, have both opted for lithiummanganese oxide. This is, says Paterson, the “middle of the road” option, offering lower power density than the cobalt units but better performance in
36 ◆ Environmental Engineering ◆ February 2011
terms of cycle life, safety and toxicity. “There are still some unanswered questions, though,” he says, “and people are still verymuch looking at the chemistry.” Michael Sinkula at Envia agrees that
battery options seemoften to involve a degree of trade-off between different desirable characteristics. “The greatest strength of ourHCMR is energy density,” he says. “As a trade-off, ourmaterial has slightly less power. But it does not compromise life, safety or performance at different temperatures.” But it’s not just the chemistry, Paterson
says. One of the advantages ofmanganese is low cost, and the effect of that is, perversely, to increase the importance of other factors in the battery package. So testing routines in the electrochemistry laboratories, in the companies such as Axeon which are putting cells together to make full-scale batteries and in the OEMs in automotive and other industries, are geared up to answer other questions. These are about packaging and form
factors, resistance to damage and accident, the batterymanagement systemincluding areas such as the constant charging from technologies such as regenerative braking
Beyond lithium
Lithium-ion batteries are likely to be the short- to medium-termpower source for hybrid electric vehicles. For the longer termothermaterials are being investigated, including silicon-based materials for the anode andmetal-air combinations. But, says Allan Paterson of battery systems developer Axeon, which is working with funding fromthe UK’s Technology Strategy Board to identify likely
directions, some concepts are a long way fromrealisation, with problems such as large- scale expansion in high temperatures and increased complexity. There are as-yet no signs of a “Eureka”moment and newer technologies, like current and older ones, still offer an advantage/disadvantage trade-off thatmay vary depending onmarket sector and economic factors.
systems, andmanufacturability and quality issues. When battery packs for vehicles consist
of several thousand small cells, a quality assurance systemthatmeasures failures in parts permillion is a starting point rather than an end-goal. Putting cells into larger formatsmay help, says Paterson; putting theminto different formats, such as the pouch cell idea where there isminimal packaging,may not be practical if durability is a key criterion. Testing of new battery types and
chemistries is still heavily dependent on empirical test, with factors such as cycle life subject to accelerated tests through raised temperature. Increasingly, says Paterson, the technology to simulate batteries is being developed, but some of the chemistry in areas such as performance degradation over time as charge/discharge cycles take their toll is still very difficult to simulate. This is the stage that the Envia high-
capacitymanganese-rich batteries are now in the throes of undergoing. “Our testing is initially done at the cell level,” says Sinkula. “Materials on their own are not typically tested outside of a battery. In a cell, other components are held constant and the new material is introduced so you have an apples to apples comparison on the previous cell’smaterial. These cells are tested for power, energy, cycle life, calendar life, temperature tests and safety. The tests are then repeated at a pack level and then at a vehicle level.” But it is not just cars that are driving
battery development. Envia’smaterialmay have received the boost of investment by GM, but Sinkula says it is also being developed for consumer electronics markets. “We are focused on the automotivemarket initially because our competitive advantages in thismarket versus what is currently being used are very significant, and we believe that the growth potential of thismarket is greater than the growth of the consumer electronics market.” Like the batterymarket as a whole, there seems to be no shortage of work still to do. ■
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52