Design Current Collector of Different Cell Size Metal Foam for Lithium-ion Batteries

Abstract

Abstract

Design Current Collector of Different cell size Metal Foam Cathode for Lithium-ion Batteries

JIN TAO Department of Materials Science and Engineering The Graduate School Seoul National University

In the last two decades, Lithium-ion batteries could be considered to be the most impressive success story of modern electrochemistry. Among rechargeable batteries, because Lithium-ion batteries have high energy density and high power performance, they are key components of the portable, entertainment, computing and telecommunication equipment. However, the energy density and electrochemical performance are still required to be further improved for more applications. The most important problem is that there are 50-100 ㎛ thick active materials on the foil-type current collector, and to sustain high power performance, the thickness of active materials is only 20-60 ㎛. In this way, to obtain large-scale capacity, the batteries become heavy and large. It is also caused by increased inactive materials, such as separator, current collector and so on. Moreover, one of the big issues for application is high production cost due to the increasing of materials and workload. To solve these problems, three- dimensional structure material – metal foams have been used for Lithium-ion battery electrodes instead of commercial foil-type current collectors in this study. In the condition of same volume, the cathodes using 450 ㎛ cell size metal foam and 3000 ㎛ cell size metal foam are compared in electrochemical performances. According to the charge-discharge test, cyclic voltammetric (CV) analysis, better kinetic performance is obtained for the 450 ㎛ cell size metal foam cathode due to the more triple junctions (junction of active material, metal frame, and electrolyte). But the electrode density of 3000 ㎛ metal foam cathode is higher than 450 ㎛ metal foam cathode, because the weight of active materials of 3000 ㎛ cell size metal foam cathode is more than 450 ㎛ metal foam cathode. It causes 3000 ㎛ metal foam cathode to have high energy density. So it is in need of a cathode which has both high performance of 450 ㎛ metal foam cathode and high capacity of 3000 ㎛ metal foam cathode. Two kinds of metal foam cathode are prepared: one kind of cathodes is sandwiched structure metal foam cathode that is combined with different cell size metal foam cathode as sandwich. The side metal foams(300 ㎛ thickness) which are the same cell size, are different from mid metal foam(1000 ㎛ thickness). And the other kind of cathodes is dual structure metal foam cathode which is combined 450 ㎛ metal foam cathode (600 ㎛ thickness) with 3000 ㎛ metal foam cathode (1000 ㎛ thickness). For the sandwiched structure, mid metal foam cell size is 450 ㎛, the AC Impedance analysis shows that charge transfer resistance is 11.22 Ω, which is less than other cathodes. And the specific currents at positon of peaks of sandwiched structure metal foam cathode whose cell size of mid metal foam is 450 ㎛ shows higher than other cathodes, because there are more triple junction than other cathodes. According to the charge-discharge test, the columbic efficiency of dual structure metal foam cathode is higher than other cathodes. The energy density of dual structure metal foam cathode is higher than sandwiched structure metal foam cathode whose mid metal foam cell size is 450 ㎛, and is equal to the energy density of sandwiched structure metal foam cathode that mid metal foam cell size is 3000 ㎛. And dual structure metal foam cathode exhibited the same proportion of reactiveness of active materials with the 450 ㎛ metal foam cathode in high current density according to the charge-discharge test. Considering the power performance and capacity performance in unit volume, dual structure metal foam cathode is very promising for the high power and high capacity cathode structure for Lithium-ion batteries. It not only almost has the same energy density with 3000 ㎛ cell size metal foam cathode but has superior kinetic performance as 450 ㎛ cell size metal foam cathode as well in unit volume. Based on the study, metal foam cathode which has the dual structure is one of the promising current collectors for high power and high capacity for Lithium-ion batteries.