Industry works around chemistry constraints to optimize energy storage.
By Brian Fuller
The world has changed dramatically in the 209 years since Alessandro Volta hunched over his table by candlelight and figured out how to capture energy in his voltaic pile, the first electric battery. What has changed little, however, is the battery itself.
Since Volta’s conception, the battery has remained a cell with negative and positive electrodes, an electrolyte, and an ion conductor, all of which turns a chemical reaction into electricity. The chemistry that makes it happen has changed little.
Today the importance of batteries (estimated to be a $15 billion market in North America alone) on scales both large and small is more crucial than ever. System designers struggle with making portable equipment that runs longer on lighter batteries; others are grappling with how to power electric vehicles and maintain storage farms that are envisioned for solar and other renewable energy sources.
But battery improvement, unlike Moore’s Law, is measured in single-digital increments per year, not a doubling of capacity every 18 months. Chemistry, to abuse a phrase, is what it is. “The laws of physics and chemistry dictate what ultimate energy you can get in the battery system,” said Subra Iyer, principal technologist at Quantum Sphere, a Southern California startup using nano-materials to improve battery life and performance.
“There are things that make lithium ion technology almost fundamentally the best [the industry] can do,” said Robin Tichy, technical marketing manager at Micro Power Electronics Inc., Beaverton, Ore. “Look at periodic table of elements. Lithium is the lightest element that gives you highest energy at the lightest weight. There’s not a lot you can do from there. Everything else is going to be incremental.”
Battery research in the past two years has been nothing if not frenetic:
These represent hope, investment and incremental change. But incremental change, according to Tichy, “can enable an awful lot.” The industry today finds itself knee-deep not only in fundamental research, but more important in delivering improvements in and around the battery to squeeze the most out of existing chemistry. These range from nano-scale research in materials development to packaging and metering to power management at the system level, among other approaches.
At Micro-Power, which makes power supplies, battery packs and chargers, engineers are focusing on power-balancing techniques in the hopes that “something seemingly small can make a revolutionary change for a given application,” according to Tichy.
The commercialization of lithium-ion batteries in 1991 brought relatively light weight, cost-effective portability to important markets, including laptops, medical devices and power tools. But lithium ion batteries tend to have a spiky power profile compared with smoother charge-discharge rates of alkaline batteries, and that can be a problem for systems that require accurate battery-capacity measurements.
Micro-Power has implemented fuel gauging for lithium ion batteries that’s 99% correct if used right, Tichy said. The current state of the art, as we know from the IT department, is to drain your laptop battery occasionally to ensure an accurate fuel gauge. But new fuel-gauge technology for laptops self-calibrates opportunistically. This approach can deliver another 15 minutes of run time on a laptop. Assuming a two-hour battery life, that’s an improvement in operation of more than 10%.
The importance of an accurate gauge of battery life is crucial in medical applications. For example, life-support ventilators have had to use lead acid batteries to ensure smooth voltage decline for consistent operation. The design tradeoff is weight and bulk.
More surgical tools, especially in the field, are battery-powered. As Tichy says, anything that’s been mechanical and motorized in the past is entertaining the idea of power by Li-ion battery today, as opposed to heavier nickel-cadmium batteries.
Micro-power helps systems “monitor and understand exactly what the runtime to empty is,” Tichy said. “For life-support medical equipment for obvious reasons, the FDA regulations say you have to have an accurate countdown from 30 minutes.
Quantum Sphere is developing new nano catalysts, electrodes and process chemistries to try to double volumetric capacity over state of the art, according to its CEO, Kevin Maloney. The Santa Ana, Calif.-based company is focusing on two major components of battery performance: energy density and power density.
Quantum is attacking energy density issues as they impact system runtime by using different metals to improve the battery anode. Current Li-ion batteries use graphite for the anode, which limits the battery to 350mAh/gram. Quantum is using different amorphous metal alloys, including tin, magnesium and silicon, to pack more lithium into the anode to improve performance. Nanoscale materials have 2000% greater surface area with just 10% loading in the battery solution. This translates to commensurately higher reactivity, catalysis, energy density and power density.
“Anything that increases more lithium in the anode increases energy density,” Iyer said.
Power density is a way to measure the charge/discharge rate of lithium through the anode, cathode and electrolyte. The faster it gives up the lithium, the more high-power applications the battery can accommodate and the faster it can be recharged.
This is crucial to the development of electric vehicles, especially enabling a quick recharge in a world in which consumers are used to three-minute fill-ups at the gas station.
For example, utilizing QuantumSphere’s nano-integrated gas diffusion electrode, a 320% increase in power density is achieved in metal-air battery systems. This enables enhanced functionality in both consumer and military applications, where higher power and longer lifetime is required.
At NEC, the focus is on making sure the energy stored in those batteries is not being wasted as it powers the system.
“Power management technology is a key enabler,” said Steve Kawamoto, director of marketing for custom SOC solutions at NEC Electronics America in Santa Clara, Calif. For example, work is being done on radio technology to manage the burst-like nature of Internet data activity on a handset. “You’re powering up and down those [power] rails and that’s a very power-hungry aspect of the handset. So you want to power up and down as quickly as possible.”
Power-management techniques have gotten so sophisticated that they can manage power in between texting keystrokes, Kawamoto noted. If the power rails are on in between keystrokes, power is wasted.
“It’s about understanding the system context and what needs to be on in the rest of the system,” he said. “When the user is typing, I can power down other parts of the system, for example the graphics subsystems or other radios.”
Kawamoto notes that applications processor designers are doing “a lot of amazing things” to optimize their end of the battery bargain. “But all this innovation has to be fed back into the power management chip so that there is a device that enables that form factor. It’s important to enable that form factor. “
In a way, the world today is staring at the battery world, saying, in effect, “if only we could find the miracle chemistry” to power cars for 500 miles and enable days of constant use in a range of consumer devices. For now, that’s illusory. And consumers, in the end, are OK with it, whether they realize it consciously or not.
“There’s a threshold that people have,” said Kawamoto. “If they can find value in the device itself, they’ll put up with” battery limitations.
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