Portable electronics are very convenient except for one thing: Their battery life is horrible. No matter what the capacity of their battery is, they all require frequent recharging throughout the day and have a limited lifespan that lasts between 400 to 1200 cycles. Eventually, these batteries all die and need to be replaced with new (and often expensive) versions that will also meet the same fate. Still, these types of batteries are the best available and have also become a popular choice for electric vehicles, aerospace applications and even military projects.
These batteries are called lithium-ion (li-ion) and became the industry standard for consumer electronics in the early 1990s. For 25 years we have used them to power our cell phones, laptops and most gadgets that need to function without being plugged in all the time. But future applications in portable electricity will soon demand higher energy storage density and something will have to replace traditional li-ion batteries because they simply won’t be powerful enough.
Advantage of Li-ion Batteries
- High energy density with potential for higher capacities
- Don’t require prolonged priming when new
- Relatively low self-discharge rate
- Low maintenance
- Specialty cells can provide high current to many different types of applications
Disadvantage of Li-ion Batteries
- Require protection circuit to maintain voltage
- Subject to aging, even when not in use
- Must be stored in a cool place to reduce aging effect
- Transportation restrictions
- Expensive to manufacture
Many scientists have focused their research efforts on high-capacity electrode materials that use silicon and tin as anodes, and sulfur and oxygen as cathodes. But pure lithium metal is still the optimum choice because it has the highest capacity (3,860 mAh g–1) of them all. Unfortunately, it’s is also very dangerous.
“Lithium has major challenges that have made its use in anodes difficult. Many engineers had given up the search, but we found a way to protect the lithium from the problems that have plagued it for so long.”
–Guangyuan Zheng, Doctoral Candidate at the Stanford School of Material Science and Engineering
Zheng is part of a team of Stanford engineers led by Professor Yi Cui who claim to have overcome three major problems posed by lithium: dendrite buildup that causes short circuits, chemical reactions that reduce battery life, and overheating that leads to explosions. Their solution is to build a protective honeycomb layer of interconnected carbon domes on top of the lithium anode that is projected to improve battery life by about four times what we’re accustomed to today.
The honeycomb design – called a nanosphere by the researchers – is only 20 nanometers thick but is chemically stable and mechanically strong enough to deter chemical reactions and withstand expansion during charging. The end result is a pure lithium battery that is smaller and more powerful than anything we’ve ever seen.
Charging you smartphone once a month or driving your electric vehicle over 300 miles on a single charge are just two things that will be possible if pure lithium batteries ever replace li-ion technology. But while the nanosphere does seem promising, there’s still more work to be done before we can safely replace our batteries.
To be considered feasible, batteries must have a coulombic efficiency of 99.9 percent or higher. This percentage is a ratio of the amount of lithium that can be extracted from the anode when the battery is in use compared to when it’s charging. Previously, lithium metal achieved 96 percent efficiency which dropped to 50 percent in only 100 cycles. The nanosphere improves these numbers to 99 percent efficiency at 150 cycles but is still not good enough to be regarded as being commercially viable.
“The difference between 99 percent and 96 percent, in battery terms, is huge. So, while we’re not quite to that 99.9 percent threshold, where we need to be, we’re close and this is a significant improvement over any previous design. With some additional engineering and new electrolytes, we believe we can realize a practical and stable lithium metal anode that could power the next generation of rechargeable batteries.”
–Yi Cui, Professor at the Stanford School of Material Science and Engineering
Cui is calling the pure lithium battery the “holy grail” of mobile technology and for good reason: it seems too good to be true. Not only will it reduce the number of times we have to recharge our devices, but it will also result in smaller batteries because they will be much lighter. Lithium batteries will transform the way we use our devices along with the way they are designed. All the extra hardware that could be used to replace the space li-ion batteries are taking up in our phones, laptops and cars could be used to make the devices even more powerful than we ever imagined.
The only question is: what are we going to do with all the extra power?