Battery Technology, September 2019
by David Archibald
2 September 2019
Lithium batteries currently have low recyclability. Lead acid batteries are 90% recyclable on a weight basis. Recycling networks for lithium batteries have not yet been set up. That said, there is a second life for lithium car batteries in micro grids.
Vanadium batteries are slow to charge and discharge, and have low energy density. Economies of scale of vanadium flow batteries have not been reached yet, and may not be if there isn’t sufficient demand.
The easy gains for lithium batteries have been made. Now efficiency is increasing by two to three percent per annum. Energy density continues to rise. The anode hasn’t had the level of research that has gone into the cathode and the electrolyte. Graphite and lithium can intercalate with a lithium atom sitting in the middle of each graphite hexagon.
Current energy density is 370 kWh/kg for Tesla’s batteries. Talga Resources’ battery technology is currently at 420 kWh/kg. Talga expects to eventually get to 600 kWh/kg.
The Tesla battery already incorporates a percentage of Silicon in the anode. Silicon can have a much higher energy density than lithium but brings with it the problem of swelling which, unless it is managed in the micro-architecture, will rupture the battery.
Using a solid state electrolyte is the next big step after silicon. Toyota is developing a battery with a polymer electrolyte; the rest of the world is using ceramics and glass.
High performance can be achieved with a pure lithium metal anode but this is very expensive to make. Graphene-metal hybrid is the most likely anode material.
The target for battery performance is 600 kWh/kg while being much safer than the current technology. A number of the major car makers are aware of the potential negative publicity from battery fires on new models.
The demand for hybrids was driven by range anxiety. Emission standards are now squeezing hybrids. Once cars have 600 km of range on a full charge that is expected to make range anxiety recede as an issue.
Solid state batteries have the promise of charging in three minutes. The cable size for fast charging will be enormous – as thick as your arm. Charging rate is a marketing tool. A higher charge rate decreases battery life.
The energy density of petrol is 13 kWh/kg. The weight of car engines with their transmissions ranges in weight from 150 kg for a small car to 300 kg for a large car. Assuming a weight of 200 kg for an engine and transmission and a 80 litre petrol tank, the combined weight comes to 260 kg of which the petrol constitutes approximately a quarter. Thus to compare like with like, the energy density of the petrol system is a quarter of that of petrol and thus near 3 kWh/kg.
The target for energy density for lithium batteries is 1.2 kWh over the next four to five years.
Li Fe P batteries are safer and slower. This was the Chinese technology. The other major battery chemistry at the time was Ni Co Mn adopted by Japan and Korea. The Chinese went through a phase of setting fire to buses with Ni Co Mn batteries in order to make a case that Li Fe P batteries only should be adopted.
Cobalt makes batteries safer, though recent battery technology has less cobalt. Nickel is good for batteries. Apart from in the battery chemistry, busbars to handle the current from the batteries require high nickel alloys or be nickel-plated. Exposed copper is a corrosion issue; exposed nickel avoids that.
The European market for battery anodes is 300,000 tpa. The raw material is US$1,000/t while anode material is US$11,000/t. The graphite market is 2 mtpa, half natural and half synthetic. Synthetic graphite is made by baking coke pitch for two to three weeks. In refractory carbon bricks, natural graphite is half the market.
Most of the cost of a Tesla is the battery. Generally there are economies of scale in production, so the cost of the batteries is likely to fall. Already the price per kWh has fallen from $750 in 2010 to $150 in 2016. That is an average rate of decrease in cost of 23.6% per year. If that rate of decrease should continue from 2016 to 2022, Li battery cell cost would fall to $30/kWh by 2022. The rate of decrease will likely slow down as physical limits are reached, but even if the rate falls to a 12% decrease in cost, much of this cost is manufacturing techniques, we might reach $60/kWh by 2022.
If battery cost for a Tesla M3 standard plus is currently $150/kWh then battery cost is about $9,000, if battery cost falls to $75/kWh that cost falls by $4,500 and the price of the car falls to $34,500. A more basic car like a Toyota Yaris EV could probably be sold for $25,000.
Farming will likely remain the domain of diesel as the source of power. If the plow attachment for a tractor is 57 feet wide then the optimum horsepower for that is 425 Hp. This setup will do 32 acres per hour at nominal speed, taking 31 hours to plow 1,000 acres. The acres per hour requirement is about completing a large farm (>1000 acres) before planting season expires.
A 21 foot plow will do 12 acres per hour. Tractor power required to get the speed for that number is 310 horsepower. This setup will take 84 hours to do 1,000 acres. The horsepower value is non-linear for speed and therefore labour costs will go up.
At 745 watts per horsepower, the 310 Hp tractor will be 231 Kw of muscle to do that speed. The 84 hours of ploughing will 19,404 kW-hrs. Putting 10 Tesla batteries on it at 100 KW-Hrs/battery, 19 battery recharges are required overnight to fully refill at reasonable 240VAC and amperage levels you can find on a farm. The batteries will weigh close to six tonnes. At 8 hrs to recharge, that’s 152 hours. Nearly twice the time to do the actual work.