The risk of fire electric lithium batteries are widely known. These fires occur most often in cases when the batteries overheat or run down quickly because of the high speed of the machine.
And given that every year electric cars on the roads becomes all the more necessary at the level of technology to eliminate this danger. Researchers at the Chicago College of engineering University of Illinois published in the journal Advanced Functional Materials, the results of their work, which can solve the problem.
The batteries are heated to fire temperatures due to high-speed driving, when the battery is very heavily discharged, or ultra-fast charging stations when the battery is intensively charged, the newspaper notes Science Daily.
Under these conditions, the cathode inside the battery, which in most lithium batteries made of lithium-containing oxide (usually lithium cobalt oxide), begins to break down and releases oxygen. If oxygen is combined with other flammable products released during the decomposition of the electrolyte at a high enough temperature, it may cause spontaneous combustion.
“We thought that if there was a way to prevent the cathode of oxygen and its mixing with other flammable products in the battery, we can reduce the risk of fire,” says Reza Shahbazian-Yassar, associate Professor of the Department of mechanics.
The perfect solution to the problem provided the material with which scientists are familiar is graphene, an ultra thin layer of carbon atoms with unique properties. Shahbazian-Yassar and his colleagues have used graphene to help modulate the accumulation of lithium at electrode in lithium metal batteries.
The researcher and his colleagues knew that graphene sheets are impermeable to oxygen atoms. Graphene is also durable, flexible and it can be made electrically conductive. Shahbazian-Yassar and Soros of Sharifi-ASL, Ph. D. candidate mechanical engineering and industrial engineering and lead author, suggested that if lithium-cobalt-oxide cathode will be “wrapped” with a layer of graphene, it will prevent the release of oxygen.
As a result, by placing a graphene coating on the cathode and after a series of tests, the researchers found that the evolution of oxygen at high temperatures significantly decreased. Then they made a working cathode with a sheath and placed it in a lithium-ion battery. And even after 200 cycles of rapid charge-discharge in the battery was almost no free oxygen.
“Graphene is an ideal material to block the release of oxygen in the electrolyte, says Shahbazian-Yassar. – It is impermeable to oxygen, conductive, flexible and strong enough. Its thickness is only several nanometers, so the battery weight will not change.”
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