A longer-lasting smartphone battery has been on the to-do list of tech companies for years. And now Samsung claims to have developed one that could keep your phone humming for 80 percent longer.
But could the new battery really boost battery life by that much? Some scientists are skeptical, saying the study researchers didn't account for energy that's permanently lost after the battery goes through its first charge-recharge cycle.
"I don't see it as a breakthrough technology," John B. Goodenough, a professor of mechanical engineering at the University of Texas, and the man who invented the lithium-ion battery, told Live Science.
Making batteries work harder
Lithium-ion batteries on the market today generate power by using lithium cobalt oxide as the positive terminal (the cathode), with carbon, usually in the form of graphite, as the negative terminal (the anode), and a lithium polymer compound as the electrolyte. When you hook a battery to a current load — a computer or a light bulb — lithium ions move from the anode to the cathode and through the electrolyte, generating power. [Inside Look at How Batteries Work (Infographic)]
However, silicon is denser than graphite, and so can hold more charge in the anode. The problem is silicon expands and contracts as it is charged and discharged in a battery. Such shape-shifting would cause defects in the silicon and reduce its charging capacity. Also, because of this expansion, silicon-based batteries can't be squeezed into slim devices.
What to do? The Samsung team decided to try coating the silicon in graphene. The idea is that the single-atom-thick graphene layers would surround the silicon particles and when they expanded, the layers would slide around each other, allowing the silicon to get bigger without making cracks in the carbon. Graphite, which is made up of thousands and thousands of layers of graphene, wouldn't be able to do that, because it isn't a single-atom layer and wouldn't coat nanoparticles in the same way (it would crack).
"Our approach was to grow something similar to graphite," which is similar to graphite in its chemical structure, said study co-author Jang Wook Choi, of the Korea Advanced Institute of Science and Technology.
At Samsung's Advanced Institute of Technology, Choi and his colleagues used this graphene-coated silicon as the anode; lithium cobalt oxide made up the cathode, while they used a commercial lithium mixture for the electrolyte.
They found that after about 200 cycles of charging and recharging (when a battery's charge is all used up and then gets recharged), the battery lasted between 1.5 and 1.8 times longer than ordinary lithium-ion batteries. Battery capacity is measured in Watt-hours per unit volume, where a 1 Watt-hour battery can power a 1-Watt bulb for an hour. The batteries they built had capacities of 972 Watt-hours per liter on the first charge-discharge cycle and about 700 Watt-hours per liter on the 200th. Most commercial batteries range from about 250 to 620 Watt-hours per liter. (A new iPad battery has about 42.5 Watt-hours of capacity, about 435 Watt-hours per liter).
Energy lost
The method seems to work, but some in the field are skeptical. Goodenough said the Samsung team hasn't really addressed a problem that vexes battery makers: After the first cycle a certain amount of charge capacity is permanently lost. This loss happens in any battery, but especially in lithium-ion batteries, because a partially insulating layer forms at the point where the electrolyte and the anode meet. Absent seeing that data, Goodenough couldn't be sure about this battery.
Choi said the team is looking at just that problem, and that their goal is to get the capacity loss to be more consistent, as well as keep the battery capacity consistent over many cycles – for a typical device 200 cycles would be relatively few. (Think how many times you have to charge your phone in a week.) He is optimistic. "Previously silicon had lots of problems in subsequent cycles," Choi said. "We've increased the numbers quite a bit from previous silicon technology."
The team also plans to try out different electrolyte formulas to work on the charge capacity problem, Choi said. But that has to be done by trial and error. "It's very experience-dependent."
The study is detailed in the June 25 issue of Nature Communications.
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