In the March edition of this magazine we looked at various power generation options open to RV designers. In this article we focus on the battery technology that will drive the hybrid solutions for our RV’s. We also consider options for those solutions and the bus technology propelling them. Finally, we reflect on the emerging hydrogen economy, which has the potential to be a complete game changer for our industry.
Words Terry Owen
In an ideal world the perfect battery would be fully rechargeable in minutes and hold a similar amount of power to a tankful of gasoline or diesel. The question is – how far are we from this goal and will we ever get there?
Lithium-sulphur batteries use a sulphur-carbon anode instead of carbon alone and have energy densities of the order of 500 watt-hours per kilogram (W·h/kg). This is significantly better than lithium ion types, which are in the range of 150–250 W·h/kg. The problem, until now at least, has been poor cycle life and self-discharge, with active material being lost from cathode to the anode. Recently, according to The Engineer Magazine, a team of international researchers led by Monash University’s Department of Mechanical and Aerospace Engineering in Melbourne, Australia, have filed a patent for a lithium sulphur battery with a long cycle life that is simple and low-cost to manufacture, using water-based processes. This means a big reduction in hazardous waste. Testing in cars and solar grids is to take place in Australia throughout 2020.
Solid state lithium
All commercial lithium batteries use a liquid or polymer gel electrolyte. This is the medium through which the ions pass between the electrodes when charging and discharging. In a solid-state battery, the liquid or polymer is replaced by a solid compound. The idea is not new but, up to now, poor conductivity of the solid compounds used has restricted development to small, specialist applications such as pacemakers, RFID and wearable devices. However, research is now producing solid state materials with ionic conductivities close to those of liquid electrolytes. The advantages are huge. Firstly, unlike liquid electrolytes, solid-state electrolytes are non-flammable when heated. This makes the technology extremely safe. Another bonus is reduced self-discharge, which means a longer shelf life. Secondly, solid-state electrolytes, can be made to have high capacitances and withstand high voltages. This results in batteries with a higher power-to-weight ratio, making them ideal for RV use. Despite these advances, it is likely to be a few years yet before such batteries have a significant impact on our market.
Batteries from sand
Referred to by some as ‘sand batteries’, lithium-silicon batteries use silicon-carbon composite anodes instead of carbon. Silicon can store a lot more lithium than graphite as the cell discharges. This means that more lithium can be deployed, resulting in more energy density. So – why don’t all lithium batteries use this technology? The problem is that, during the charge/discharge process, silicon expands by more than three times when it reacts with lithium, before shrinking back again. The overall effect is to cause the anode to disintegrate. This problem is being tackled by combining silicon with silicon dioxide (effectively sand) coated with carbon. In 2016 Elon Musk revealed that Tesla’s lithium ion cells are built that way although to date, amounts of silicon have been minimal. Now, Californian company Sila Nanotechnologies Inc., is producing silicon-dominant anode products that can drop into existing battery manufacturing processes, replacing graphite entirely. It promises an increase in energy density of 40% along with a 20-40% improvement in battery life. Initial deployment will be in consumer devices such as smartphones and watches with larger applications coming later. Costs are expected to be similar to exiting with reductions as economies of scale trip in.
Batteries from seawater
With a long history of innovation in material science, IBM Research unveiled a new battery chemistry at the end of 2019. It uses three proprietary materials that have never before been recorded as being combined in a battery. Apparently, these materials are able to be extracted from seawater so eliminating the need for mining or other intrusive sourcing techniques. The bottom line is that the technology could eliminate the need for heavy metals such as cobalt and nickel, so helping to provide long term sustainability in battery production. Currently cobalt is often found in the cathodes of lithium ion batteries where it helps with thermal stability and energy density. Nickel is widely used in battery production, being found in NiCd and NiMh devices. IBM is naturally being somewhat coy about the exact details of its invention but it seems that lithium is used as the anode material and is combined with a safe electrolyte with a high flash point and a cathode that is completely free of cobalt and nickel. Advantages claimed include lower cost, faster charging, high power and energy densities, 90%+ energy efficiency and low flammability. IBM is now working with others to move the technology from exploratory research to commercial development.
Graphene batteries and supercapacitors
As well as the potential to help improve solar panels, mentioned in our previous article, graphene also has the potential to improve battery performance. So far developments have focused on faster charging and discharging without overheating. This is done by covering the anode and cathode with a single layer of graphene rather than redesigning the whole battery. Typically, a cell phone battery can charge fully in just 20 minutes, compared to 90 minutes with conventional technology. Samsung is also working on a version that will enable a 45% increase in capacity. Initially, development was held back by the extremely high cost of graphene, but this has now reduced significantly so, eventually, we can expect to see many more graphene enhanced products (not just batteries). In the meantime, the first products to benefit are likely to be small devices such as smartphones, hearing aids and the portable charger shown here. Graphene also has the potential to make supercapacitors. These store charge directly without the need for a chemical reaction. As a result, they can be charged and discharged extremely quickly. This makes them perfect for applications such as regenerative braking.
Asymmetric temperature modulation (ATM)
One of the problems associated with extreme fast charging of lithium ion batteries is that metallic lithium can become plated on the anode, severely reducing battery life. Researchers from Pennsylvania State University have found that heating a cell to 60°C before charging eliminates the problem. However, the time needs to be limited to about 10 minutes to prevent cell degradation. Discharge is then at a much cooler temperature, hence the term ATM. Heating has been demonstrated using a nickel structure that preheats in less than 30 seconds. The technology is said to be scalable because the cells are based on industrially available components. Using this technology, it should be possible to add a 200-mile range to a battery in just 10 minutes.