Near term Improved batteries will enable commercialized flying cars

Technologies are maturing and converging to make small, affordable airplanes feasible says Brian German, an aerospace researcher at Georgia Tech. German argues that lighter and more powerful electric motors, batteries that can store more energy, and more sophisticated aviation software could transform the market for small aircraft.

Each time batteries improve, electric airplanes can be a little lighter and fly a little farther on a single charge.

German says battery technology isn’t quite there yet. He predicts the energy density of batteries will need to approximately double for small electric airplanes to really take off.

Highlights

* analyst indicates energy density of batteries needs to roughly double for small electric planes – flying cars to boom
* solid state batteries could could double energy density of batteries. Progress is being made to commercialize metal solid state batteries with the required energy density

Batteries don’t improve as rapidly as computer chips, so it’s hard to say exactly how quickly batteries will improve. Tesla CEO Elon Musk, who is currently building a giant battery factory, has said that battery density typically improves by 5 to 8 percent per year, which implies that density could double in the next decade — though that could require finding new battery chemistries.

The other key breakthrough is better software. An airplane with 10 propellers is just too complex for a human pilot to manage effectively. But computer software can easily manage 10 propellers at once, supplying power to the propellers where the most thrust is needed.

And German says multi-propeller designs have significant safety advantages. “If you lose one, you still have some left,” he says. “You can design a lot of redundancy.”

The combination of smaller, more powerful electric motors, better batteries, and sophisticated software will open up dramatically new possibilities for aircraft design.

In 2013, the Zee Aero flying car was spotted and it has about ten small electric engines.

Back in October, Uber published a white paper describing its vision of the future small VTOL aircraft could make possible. Uber envisions a network of on-demand aircraft carrying passengers among many landing spots distributed throughout a metropolitan area. For example, right now it takes at least an hour to drive from San Jose, California, to San Francisco — and closer to two hours during rush hour. In contrast, Uber estimates, the same trip could take 15 minutes in a VTOL airplane.

Uber estimates that the trip would initially cost around $129, a cost that would fall to $43 within a few years and could eventually cost as little as $20. That compares favorably to the more than $100 it would cost to take a cab over the same route.

Nature Energy – A solid future for battery development (Sept 2016)

Energy densities of lithium-ion batteries and ionic conductivities of lithium electrolytes.

The vast majority of batteries use organic liquid electrolytes, which are low-cost and easy to prepare.

Higher current densities and quicker charging times are conceivable in solid state batteries (SSB).

Lithium Ion technology is already mature, and the fight for reduced costs (per kWh) and further performance improvement is clearly dominating the market. SSBs will only become a major contender if they can provide a significant performance jump in one or more of the key properties. Usually energy density is considered the top priority, but power density is important when it comes to the need for quick charging. Long-term stability, both long cycle and calendar life (lifetime of batteries in terms of number of discharge/charge cycles and time after production), is another key requirement, as the volume changes of the electrodes during cycling of the SSB cause mechanical strain and stability problems.

Solid electrolytes are often considered ‘enablers’ of high-capacity lithium-metal anodes, as their mechanical strength may prevent dendrite growth. A successful integration of the lithium anode would offer an increase of up to 70% in energy density and serious attempts are surely worth the effort. It is worth noting that lithium-metal electrodes operate well in thin film solid-state batteries with low area-specific capacity, where only about 1 μm of lithium is cycled

In October 2015, SolidEnergy demonstrated the first-ever working prototype of a rechargeable lithium metal smartphone battery with double energy density

In Dec 2016, Researchers are developing game-changing solid-state battery technology, and have made a key advance by inserting a layer of ultra-thin aluminum oxide between lithium electrodes and a solid non-flammable ceramic electrolyte known as garnet. Prior to this advance, there had been little success in developing high-performance, garnet-based solid-state batteries, because the high impedance, more commonly called resistance, between the garnet electrolyte and electrode materials limited the flow of energy or current, dramatically decreasing the battery’s ability to charge and discharge.

The University of Maryland team has solved the problem of high impedance between the garnet electrolyte and electrode materials with the layer of ultrathin aluminum oxide, which decreases the impedance 300 fold. This virtually eliminates the barrier to electricity flow within the battery, allowing for efficient charging and discharging of the stored energy.

“The work by [the University of Maryland research team] effectively solves the lithium metal–solid electrolyte interface resistance problem, which has been a major barrier to the development of a robust solid-state battery technology,” said Bruce Dunn, UCLA materials science and engineering professor. Dunn, a leading expert in energy storage materials, was not involved in this research.

In addition, the high stability of these garnet electrolytes enable the team to use metallic lithium anodes, which contain the greatest possible theoretical energy density and are considered the ‘holy grail’ of batteries. Combined with high-capacity sulfur cathodes, this all solid-state battery technology offers a potentially unmatched energy density that far outperforms any lithium-ion battery currently on the market.

“This technology is on the verge of changing the landscape of energy storage. The broad deployment of batteries is critical to increase the flexibility of how and when energy is used, and these solid-state batteries will both increase the safety and decrease size, weight, and cost of batteries,” said Eric Wachsman, professor and director of the University of Maryland Energy Research Center and the other corresponding author of the paper.

Nature Materials – Negating interfacial impedance in garnet-based solid-state Li metal batteries

Garnet-type solid-state electrolytes have attracted extensive attention due to their high ionic conductivity, approaching 1 mS cm−1, excellent environmental stability, and wide electrochemical stability window, from lithium metal to ~6 V. However, to date, there has been little success in the development of high-performance solid-state batteries using these exceptional materials, the major challenge being the high solid–solid interfacial impedance between the garnet electrolyte and electrode materials. In this work, we effectively address the large interfacial impedance between a lithium metal anode and the garnet electrolyte using ultrathin aluminium oxide (Al2O3) by atomic layer deposition. Li7La2.75Ca0.25Zr1.75Nb0.25O12 (LLCZN) is the garnet composition of choice in this work due to its reduced sintering temperature and increased lithium ion conductivity. A significant decrease of interfacial impedance, from 1,710 Ω cm2 to 1 Ω cm2, was observed at room temperature, effectively negating the lithium metal/garnet interfacial impedance. Experimental and computational results reveal that the oxide coating enables wetting of metallic lithium in contact with the garnet electrolyte surface and the lithiated-alumina interface allows effective lithium ion transport between the lithium metal anode and garnet electrolyte. We also demonstrate a working cell with a lithium metal anode, garnet electrolyte and a high-voltage cathode by applying the newly developed interface chemistry.

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