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Improve Li-ion battery performance using hydrogen

Posted: 10 Nov 2015 ?? ?Print Version ?Bookmark and Share

Keywords:Lawrence Livermore National Laboratory? lithium ion? battery? electrode? electric vehicle?

There is an increasing demand for energy storage that underlines the urgent need for higher-performance batteries. In particular are lithium ion batteries, which are a class of rechargeable battery types where lithium ions move from the negative electrode to the positive electrode during discharge and back when charging.

Several key characteristics of lithium ion battery performance (capacity, voltage and energy density) are ultimately determined by the binding between lithium ions and the electrode material. Subtle changes in the structure, chemistry and shape of an electrode can significantly affect how strongly lithium ions bond to it.

Through experiments and calculations, the Lawrence Livermore National Laboratory team discovered that hydrogen-treated graphene nanofoam electrodes in the LIBs show higher capacity and faster transport.

"These findings provide qualitative insights in helping the design of graphene-based materials for high-power electrodes," said Morris Wang, an LLNL materials scientist and co-author of a paper appearing in Nature Scientific Reports.

Jianchao Ye works on a lithium ion battery, while Morris Wang looks on

From left, LLNL postdoc Jianchao Ye works on a lithium ion battery, while Morris Wang looks on. The two are part of a team studying the use of hydrogen for longer-lasting batteries. Photos by Julie Russell.

Lithium ion batteries are growing in popularity for electric vehicle and aerospace applications. For example, lithium ion batteries are becoming a common replacement for the lead acid batteries that have been used historically for golf carts and utility vehicles. Instead of heavy lead plates and acid electrolytes, the trend is to use lightweight lithium ion battery packs that can provide the same voltage as lead-acid batteries without requiring modification of the vehicle's drive system.

Commercial applications of graphene materials for energy storage devices, including lithium ion batteries and supercapacitors, hinge critically on the ability to produce these materials in large quantities and at low cost. However, the chemical synthesis methods frequently used leave behind significant amounts of atomic hydrogen, whose effect on the electrochemical performance of graphene derivatives is difficult to determine.

Yet Livermore scientists did just that. Their experiments and multiscale calculations reveal that deliberate low-temperature treatment of defect-rich graphene with hydrogen can actually improve rate capacity. Hydrogen interacts with the defects in the graphene and opens small gaps to facilitate easier lithium penetration, which improves the transport. Additional reversible capacity is provided by enhanced lithium binding near edges, where hydrogen is most likely to bind.

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