New porous Li-ion batteries are safer and tougher

Lithium-ion batteries (LIBs) are a huge technological advancement from lead acid batteries which have existed since the late 1850s. Thanks to their low weight, high energy density and slower loss of charge when not in use, these have become the preferred choice for consumer electronics. Lithium-ion cells with cobalt cathodes hold twice the energy of a nickel-based battery and four times that of lead acid. Despite being a superior consumer battery, lithium-ion batteries still have some drawbacks. Current manufacturing technology is reaching the theoretical energy density limit for lithium-ion batteries and overheating leading to thermal runaway ie, 'venting with flame' is a serious concern.

Current lithium-ion battery technology relies on intercalated lithium which functions well, but due to ever-increasing demands from electronic devices to be lighter and more powerful, investigation of novel electrolytes is necessary in order.

Scientists at the Center for Self-assembly and Complexity, Institute for Basic Science (IBS), Department of Chemistry and Division of Advanced Materials Science at Pohang University have developed a high-performance lithium-ion battery from a porous solid which is stable at high temperatures.

The new battery is built from pumpkin-shaped molecules called cucurbit[6]uril (CB[6]), which are organised in a honeycomb-like structure. The molecules have an incredibly thin 1D-channel, only averaging 7.5 Å (a single lithium ion is 0.76 Å, or .76 x 10^-10 m) that runs through them. The physical structure of the porous CB[6] enables the lithium ions to diffuse more freely than in conventional LIBs and exist without the separators found in other batteries.

In tests, the porous CB[6] solid electrolytes showed impressive lithium-ion conductivity. To compare this to existing battery electrolytes, the team used a measurement of the lithium transference number (tLi+), which was recorded at 0.7-0.8 compared to 0.2-0.5 of existing electrolytes. They also subjected the batteries to extreme temperatures of up to 99.85°C, well above the 80°C typical upper temperature window for existing lithium-ion batteries. In the tests, the batteries were cycled at temperatures between 24.85 and 99.85°C for a duration of four days and after each cycle the results showed no thermal runaway and hardly any change in conductivity.

Various conventional liquid electrolytes can incorporate in a porous CB[6] framework and converted to safer solid lithium electrolytes. What makes this new technique most exciting is that it is a new method of preparing a solid lithium electrolyte which starts as a liquid but no post-synthetic modification or chemical treatment is needed.