A new water-based battery part could be the key to safe, powerful batteries that don’t risk catching on fire. Though they don’t last as long as the batteries already in our phones, researchers hope it’s an important next step toward solving the scourge of exploding electronics.
The most common batteries are lithium-ion batteries, which have electrical conductors, or electrodes, on the two sides. These charge and discharge when ions move from one electrode to the other. Electrolytes in the middle help the ions move. Most of the time, electrolytes are made of organic chemicals that easily burst into flame. Fireproof, water-based electrolytes exist, too, but because water isn’t very reactive, these safer batteries usually aren’t very powerful, says Chunsheng Wang, an engineer at the University of Maryland and co-author of the new study. Now, scientists have developed lithium-ion batteries with a water-based electrolyte that won’t explode and can reach four volts — the same voltage as more common, organic electrolytes. The results were published today in the journal Joule.
Two years ago, Wang’s team (working with chemist Kang Xu at the US Army Research Laboratory) created a water-based electrolyte that reached three volts. But though the electrolyte was safe, it degraded one of the electrodes, so it couldn’t hold a lot of energy. In today’s paper, they developed a water-based electrolyte with a special feature that only organic electrolytes usually have: a solid coating that protects the electrodes from degrading.
In lithium-ion batteries with organic electrolytes, some of the chemicals decompose into a solid, protective layer on the surface of the electrode during the first charge. This layer is called the “solid electrolyte interphase” (SEI). Water-based electrolytes usually don’t have an SEI, because decomposing water doesn’t form any of the chemicals to make the solid layer.
But the team created a water-based electrolyte with a very high concentration of salt, and this electrolyte was then able to create an SEI. So, you still get the safety of water, along with a solid layer protects the electrodes from breaking down, allowing it to hold more energy.
These batteries are already better than other water-based ones. But there’s one big limitation: they only work for about 70 cycles, and battery companies want batteries that last for at least 500. “The next step is to make a longer cycle,” says co-author Chongyin Yang, also an engineer at UMD. “We really want to push the technology to a real application and move forward to market.”