Spongy zinc battery may beat lithium-ion on safety, price, recycling
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If nearly 500,000 deposits of $1,000 each on the new Tesla Model 3 indicate bridled demand, the electric cars have a sure future.
Tesla plans to start delivery of the $35,000 vehicles on July 28, when it will release the first 30. Palo Alto-based Tesla aims to crank out about three cars a day in August, boost output to 1,500 in September and build to a rate of 20,000 a month by the end of 2017.
Tesla electric cars rely on lithium-ion batteries. The company is building a gargantuan battery factory in Nevada — some 5.8 million square feet — slated for completion in 2020. The enormous production capacity could drive down battery costs by about 30 percent, Tesla said, from batteries now produced by Panasonic in Japan.
But a Marin-based aerospace engineer sees problems with lithium-ion technology: potential for explosions as occurred in Samsung phones in 2016; high cost; and poor recyclability. He suggests zinc, the metal used to stop corrosion in galvanized steel, as an alternative.
In June, the U.S. Naval Research Laboratory entered a commercial licensing agreement with EnZinc, co-founded by San Anselmo-based Michael Burz, the company’s president, who worked previously on design of the Tomahawk cruise missile as well as for Nissan. The agreement gives the company exclusive rights to a nickel-zinc battery for use in electric road vehicles, hybrids based on the battery and microgrids up to 60 megawatts.
Burz expects his zinc-based battery technology to be ready for market in about two years, with another year to gear up production.
The next step is to put the zinc battery into a case then heat, freeze and overcharge it, simulating real-world stresses that can derail technology. Then EnZinc will test the battery in electric bicycles and cars.
Battery failure can derail a business. Samsung’s Galaxy Note 7 lithium-ion batteries caused fires and explosions last year and cost the company some $5 billion as it recalled nearly 3 million smartphones. Some of the 3,500-milliamp-hour batteries were too big for the smartphones, causing shorts, according to reports from the company, or insulation tape was missing.
Samsung aims to rebound from the fiasco with release of a Galaxy Note 8 expected by September. They still have lithium-ion batteries.
Huge market for batteries
Energy storage is a gigantic marketplace. Two battery designs dominate the field: lead-acid batteries commonly used to start gas and diesel cars, and lithium-ion batteries used in smartphones and electric cars.
Transparency Market Research estimated the global lithium-ion-battery market at $30 billion in 2015, rising to more than $75 billion by 2024.
Competition among scientists and engineers is intense in the field. Scientists tried using various materials to boost battery efficiency, with modest results, for decades. Lithium-ion batteries may use other materials including magnesium, cadmium, manganese or cobalt oxide. The batteries contain a flammable electrolyte, raising risks beyond those of lead-acid batteries.
EnZinc batteries incorporate less-volatile metals — zinc and nickel — in an unusual spongy architecture that addresses a problem with zinc in batteries. During charge-recharge cycles, zinc is susceptible to dendrite deposits that result from zinc oxide formation. Deposits create hot spots and short out the batteries in barely 20 cycles. Lithium-ion batteries also get dendrites, especially when charged fast, as microscopic fibers of lithium build up on the surface of the lithium electrode, eventually shorting the battery or causing a fire.
Scientists explored a couple of ways to get around zinc’s weakness for dendrites. One is to create a flow battery; a slurry keeps moving to replace the zinc. Such batteries are big because they require pumps, tanks and valves. For energy storage in shipping-container proportions, the technology works.
Another strategy is to slow dendrite deposits with costly additives in the electrolyte to bring the functional charge-discharge cycle number to about 500.
The U.S. Naval Research Laboratory discovered that making a sponge structure out of zinc brought advantages. “It looks like the sponge on your sink,” Burz said, “but on a micro-scale — nanometers. Zinc oxide forms on the outside skin of the sponge, but the inside walls of the sponge are clean. They carry current (in) a continuously wired structure. There’s always a path” for electricity to travel.
In 2015, EnZinc finished a $500,000 project under an Advanced Research Projects Agency-Energy award, part of the Dept. of Energy, designed to develop technology with commercial potential. The project goal was to reach 100 cycles in the zinc batteries without dendrites.
The zinc sponge has about 30 percent porosity. Burz is experimenting with decreasing porosity to pack more zinc into the structure, boosting lifespan. “For the first time, zinc can be used in a high-performance, totally safe, totally recyclable battery,” he said.
Repeatedly discharging the battery to 80 percent reduces cycle life. Dropping discharge to 40 percent before recharging increased battery life to a level comparable to lithium-ion cells. The Navy is experimenting with higher-density zinc sponges that allow discharge to 60 percent.
Batteries are measured by energy density or “specific energy”— how much energy (watt-hours) is stored in a given unit of volume (liters) or weight (kilograms). Lead-acid batteries have effective specific energy around 40, too low for use in electric cars. “We’re at around 120,” with zinc-sponge batteries a third the weight of lead-acid for equivalent energy storage. Lithium-ion cells are at around 160 “for the kind used by the Nissan Leaf,” Burz said, “to 260 or 280 for the kind used by Tesla.”
Lithium goes rogue
If lithium is packed too densely, danger results. “You have to control it so it doesn’t go rogue like it did on the Samsung phone,” Burz said. With a large lithium-ion battery, “going rogue” translates to becoming a bomb in a “thermal runaway.”
A Tesla car contains nearly 140 pounds of lithium, almost 7,000 times the third of an ounce of lithium in a smartphone. A full battery pack weighs about 1,000 pounds in a Tesla car.
Battery manufacturing for lithium-ion batteries is guided by Underwriters Laboratories standard 1642, established in 2012. “These requirements are intended to reduce the risk of fire or explosion when lithium batteries are used in a product,” according to UL.
Tesla installed systems to manage the high energy and boost the car’s range, including a computer that carefully manages charge-discharge to avoid overheating battery modules, an active cooling system with pumped glycol, and armor on the bottom so that if the compartment is punctured, volatile electrolyte won’t ignite and “melt the car,” Burz said. The Tesla Model S required such armor, “to keep objects on the road from punching through the battery. If that happens, the battery can ignite.”
Extra equipment drops effective specific energy from 260 to about 140, slightly better than zinc-based specific energy at 120.
EnZinc’s batteries don’t need extra monitors, cooling system or armor. “You can puncture a zinc battery and all you get is loss of voltage,” he said. “Zinc is inherently safer. It’s harmless.”
Zinc costs much less than lithium and is more readily available. For an electric car, a zinc-sponge battery would hold roughly 60 kilowatt-hours, weigh about 500 pounds and provide range of some 200 miles. The lithium-ion battery for a Tesla Model 3 will cost about $15,000, Burz said. “Ours will be about $10,000.”