In 1980, John Goodenough invented the modern lithium-ion battery. Working at Oxford, he and his colleagues invented the rechargeable lithium-ion battery, the bedrock of most of today's electronic devices. With that being said, lithium-ion batteries have become an extremely important energy source for humans, solely because we rely on them for nearly everything from portable devices to cars and even satellites. However, it is hard to improve energy storage and increase battery life while ensuring safe operation.

So, to solve that problem, a Columbia Engineering team, lead by Yuan Yang, assistant professor of materials science and engineering, developed a new method for safely prolonging lithium-ion battery life. They have found that they can insert a nano-coating of boron nitride and in turn, stabilize solid electrolytes in lithium metal batteries. Conventional lithium-ion batteries are widely used in daily life, but they have low energy density and thus shorter battery life. In addition, they contain a highly flammable liquid electrolyte and they have been known to short out and even catch fire.

Previous research has shown that energy density could be improved by using lithium metal to replace the graphite anode, but this method can cause short-circuiting and essentially lower battery safety. However, in the study, the team focused on solid, ceramic electrolytes. The materials show great promise in improving both safety and energy density. This is mainly because most solid electrolytes are ceramic, and therefore non-flammable and in turn, much safer. It is also known that solid ceramic electrolytes have a high mechanical strength that can actually suppress lithium dendrite growth.

The researchers also deposited 5~10 nm boron nitride nano-film as a protective layer to isolate the electrical contact between lithium metal and the ionic conductor-the solid electrolyte. They selected boron nitride as a protective layer, which is only 5~10 nm thick, without lowering the energy density of batteries. The material can work as a barrier to prevent the invasion of lithium metal to solid electrolyte.

The team also has developed a lithium-metal-proof 'vest' for unstable solid electrolytes. It has the ability to achieve a long cycling lifetime in lithium metal batteries.

Currently, the team is extending its method to a broad range of unstable solid electrolytes and plan to further optimize the interface.