How to improve lithium traction batteries

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Dependence on increasingly troublesome oil supplies and rapid degradation of the environment provide every reason why electric cars, whether hybrid or pure electric, should now be adopted rapidly.

Unfortunately, these cars currently cost 20-100% more than the equivalent models, a penalty only partly dented by newly generous government subsidies and tax breaks. The batteries are the problem and this is despite most traction battery manufacturers selling at a heavy loss to the car manufacturers and the car manufacturers often selling at a loss to the user. The batteries also restrict the electric range of both hybrid and pure electric vehicles to much less than the distance desired by most of the potential purchasers.

Currently Japan rules the roost in electric cars with Toyota being the leading car manufacturer and Panasonic the leading battery manufacturer. Panasonic is even absorbing battery leader Sanyo. The New Energy and Industrial Technology Development Organization (NEDO) was established by the Japanese government to develop new oil-alternative energy technologies and carry out industrial and environmental technology research and development. NEDO has tasked Japanese industry with heroic objectives to get those traction batteries to more nearly resemble what the car industry needs. For both hybrids and pure electric cars, NEDO believes that cost can improve from $1008/kWh in 2010 to $201/kWh in 2020, with equivalent improvement in volumetric energy density. Broadly consistent with this, the US Department of Energy has set a target of $500/kWh for 2012. The planners seek 15 year life to underpin affordability of these new vehicles.

Battery performance targets for hybrids

For hybrids from 2010 to 2020, NEDO sees energy density rising from 70 to 200Wh/kg and - particularly important - output density rising from 2000 to 2500W/kg. The battery in a hybrid protects the conventional engine from changes in speed and torque demanded by the driver. However, we now require it to also have enough  capacity to make plugging in worthwhile. Hybrids are nearly all of the mild hybrid form today - little more than conventional vehicles that pollute less and sometimes use less fuel. In 2020, nearly all hybrids will be plug in PHEVs of much longer electric range permitting users to employ electric fuel most of the time if they wish, in the process saving a great deal of cost. That calls for a different type of battery.

Battery performance targets for pure electric cars
 
In the 2020-2020 timeframe, NEDO targets the energy density oriented batteries needed for pure electric vehicles, where range is the biggest concern, to improve from energy density of 100 to 250Wh/kg and output density from 1000 to 1500W/kg. Given this consensus, analysts assume these figures will be met when they forecast sales of hybrid and pure electric cars. However, there is no assurance that the targets will be met. For example, it is generally agreed that nickel metal hydride batteries are lower cost than the various lithium alternatives and a good match for the needs of mild hybrids. Demand for these will grow strongly over the next few years but it will then peak for two reasons. Firstly, the rapid move to the plug in hybrids that users really want will mean that NiMH, with its poor charge retention and suboptimal energy density is an ever poorer match to what is needed. Secondly, China controls nearly all the lanthanum needed for these batteries and it is already rationing supplies.

Consensus that lithium is the way to go

Because of the fundamental chemistry of lithium, it is the most promising basis of the bulk of traction batteries over the next ten years. Theoretically at least, it should provide nearly all the car traction batteries required in the second half of the next decade because it is more suitable for the good charge retention and high capacity at low weight and volume that will be the primary market demand. All car traction batteries must give longer range at a much lower cost and the world will not be hostage to lanthanum any more than it is going to be hostage to oil. For example, Chile and Australia provide most lithium today but Bolivia has the biggest reserves and China has its own production.

No consensus on the lithium chemistry to use

The devil is in the detail. There are a huge number of potential lithium chemistries for traction batteries. Anodes, cathodes and electrolytes can have a vast number of chemical compositions and the electrodes can have different morphologies, with nanotechnology of increasing interest.

One thing is agreed. The versions that are not inherently chemically stable against overcharge, overheating and other abuse will not be acceptable much longer. It is one thing to have small lithium cobalt batteries catch fire in laptops and other consumer goods but the ever greater amount of energy stored in car traction battery packs is an altogether greater concern. Water cooling, fuses and electronic protection can make these batteries safe in vehicles but this is at best inelegant and expensive. A better approach is to have all the safety measures, aside from water cooling, with inherently chemically safe lithium batteries. Sensibly then, most of the Obama battery funding in 2009 went to support inherently chemically safe, lithium traction battery development, manufacture and installation.
Certain types of lithium manganese, lithium iron phosphate and lithium polymer battery are claimed to be inherently chemically safe. Some of these are sold with a guaranteed/ 150,000 mile, ten year life today but this is mainly based on disputable accelerated life testing. One company offers 12 year life. No one much agrees on what will be the dominant lithium chemistry in the latter part of the decade as lithium takes over most of the market but the winner may create a $10 billion business because a very similar problem is posed by the 28 million electric bicycles sold yearly, by industrial and commercial electric vehicles and even by the planned super grid. A lot is at stake here, which is why the new IDTechEx report on the subject is called, "Car Traction Batteries- the New Gold Rush 2010-2020".
 
Giants and partnerships

Many giant companies are involved and others are joining the fray. They include BASF, Dow, GE, IBM, Mitsubishi, Sony, Hitachi and LGChem, with East Asia in the lead so far, and alliances the order of the day. In its new report, IDTechEx profiles 39 alliances including 50 battery manufacturers and putative manufacturers plus their many allies in car manufacture. For the car companies, success relies on the battery more than anything else. For investors in small companies and start-ups with key intellectual property in this arena it is something of a one way bet. These companies will either grow to become very large or they will be bought at a handsome price. On the other hand, aware of the saying, "In a gold rush, get there first and sell shovels," companies such as Sumitomo, Mitsubishi and Bollor are seeking to provide that lithium and others are positioning to make everything from specialist production automation to cell integration into battery packs. Then  there is sophisticated  electrical management including thermoelectric, electrodynamic and photovoltaic energy harvesting.

Ten year forecasts

IDTechEx has produced ten year forecasts showing the car traction battery market exceeding $45 billion in 2020. For example, IDTechEx forecasts the value of the market for car traction batteries in 2015 to be divided between those for hybrid and pure electric cars.

Problems being tackled
 
The following illustrates some of the ways that the shortcomings of lithium car traction batteries are being tackled:
 
Cost - The current cost of Li-based batteries is at least a factor of two too high on a kW basis, the problem being both raw materials and materials processing and the cost of cell and module packaging. The US Department of Energy DOE has noted that lithium batteries will not be a cost-effective solution for HEVs unless and until somebody finds a way to slash manufacturing costs by 50%; and they will not be a cost-effective solution for PHEVs unless and until somebody finds a way to slash manufacturing costs by 67% to 80%. IDTechEx notes that promising routes include self assembly, reducing or eliminating cobalt, reduce the amount of materials used and recycling valuable materials but this is a Herculean task.

Performance - The barriers related to battery performance include a loss in discharge power at low temperatures and power fade over time and/or when cycled. High power density is being assisted by use of nanomaterials in the electrodes. To improve gravimetric and volumetric energy density, we can improve intercollation cathodes by trying fluorine based, air oxygen, lithium sulfur and other options. We may replace graphite anodes with metal alloys, silicon or tin and investigate conversion reactions. Improving the charge-discharge speed of lithium traction batteries will greatly expand the addressable market. The speed with which the ions can enter and leave the electrodes governs how fast the battery can be charged or dischargedso, in order to improve this, most eyes are on improving the cathode.


Abuse Tolerance - The US DOE notes that many high-power batteries are not intrinsically tolerant to abusive conditions such as short circuits (including internal short circuits), overcharge, over-discharge, crush, or exposure to fire and/or other high-temperature environment. IDTechEx reports that, in this respect, researchers are focussing on titanium anodes, ionic liquids, polymer or glass electrolytes and polyoxy anion based cathodes for example.
Life - A "supercabattery" construction that is half electrochemical double layer supercapacitor and half battery may improve car traction batteries but it is too early to tell. Improved theoretical understanding and better electrolytes will certainly assist. State-of-the-art liquid electrolytes are composed of a complex mixture of organic solvents and dissolved salts to optimize ionic conductivity over a wide variety of temperatures and voltages.

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