Lithium-ion battery appears to be one of the most preferred power sources applied in portable devices such as laptops, smart phones, smart grid, and electric vehicles. With the ever rising demand for high capacity power sources, advanced lithium-ion batteries need to have higher energy density, higher stability and higher power density. To realize this, most researchers have focused on the development of new anode materials in view of the fact that the type of anode active materials used for lithium storage in the course of charge and discharge greatly affects the performance of the battery.
Graphite has been used as the most popular anode active material, but exhibits insufficient theoretical capacity. Therefore, graphite is not suitable for high capacity and high power battery applications. Tin appears to be the next advanced anode material exhibiting twice as much theoretical capacity than graphite. However, tin undergoes volumetric expansion during insertion and extraction of lithium ions. This means that over repeated discharge and recharge cycles, this volumetric change may lead to pulverization and insufficient electrical contact at the electrode.
Using active materials at nanometer dimension such as nanowires and nanosheets appears to be a better solution to the volumetric expansion problem. To be more precise, the scaffold of a 3-D porous current collector made from copper or nickel then thinly coated with active material can be a better solution. Therefore, Ms. Hyeji Park and her colleagues at Kookmin University in Republic of Korea prepared a 3D tin-copper architecture as an anode material for application in a lithium-ion battery. They used micro-lamellar-structured 3D copper foam as the anode current collector. Their research work is now published in Applied Surface Science.
The authors used copper oxide with 40-80 nm particle size as the starting material. The copper oxide powder was mixed with water and binder, and the slurry was then poured into a Teflon mold on a copper rod. The cupric oxide was reduced to copper and sintered. The resulting three-dimensional porous copper foam was elongated and aligned pores formed. The copper scaffold was cut into thick coins, which were used as anode current collector.
The research team subsequently applied electroless tin plating onto the resulting three-dimensional copper scaffold forming tin-coated copper anode. After plating and subsequent washing, the tin-coated copper foam anode specimens were heat-treated at elevated temperature.
The electroless plating process onto the copper foam enabled the authors to fabricate a 3D tin-coated copper foam integrated with a current collector as well as an active material that was free of a binder and a conducting material. The 3D scaffold architecture exhibited excellent cyclic stability and superior capacity when compared to the electrochemical performance of the typical copper foil current collector coated with tin.
This high electrochemical performance is attributed to the short lithium-ion diffusion path as well as regular void spaces, which accommodated the volume expansion in the tin-copper scaffold. The formation of Cu10Sn3 phase could enhance the cyclic stability of the 3D tin-copper foam after heat-treatment at 500 °C by alleviating the volume expansion of the tin oxide when tin oxide conversion reaction was initiated.
The outcomes of this study show that the tin-copper scaffold synthesized by applying freeze-casting, electroless plating, and heat treatment possesses application potential as a self-supporting advanced anode architecture for application in high capacity lithium-ion batteries.
Hyeji Park, Ji Hyun Um, Hyelim Choi, Won-Sub Yoon, Yung-Eun Sung, Heeman Choe. Hierarchical micro-lamella-structured 3D porous copper current collector coated with tin for advanced lithium-ion batteries. Applied Surface Science, volume 399 (2017), pages 132–138.Go To Applied Surface Science