(124092) Carbon-Coated Current Collectors for High-Power Lithium Ion Secondary Batteries III

The ultimate goal of this project is to develop a viable C-coating process of the current collector in order to improve the overall power performance of the electrode of Li-ion batteries. During this third-year period, the performance of different thickness of carbon coating on Al foil is compared. The result shows that only the samples with sufficient thickness to form conductive channel on the surface would give a positive effect on the performance. Scale up of this coating process is further developed to make 1.5 m long C-coated tape by a contentious process followed with a special batch thermal process called roll-calcination. The same positive effects seen on small samples have been reproduced. Introduction: The basic principle for achieving high-power capability of a battery is minimizing the overall resistance of the electrochemical system. For Li-ion batteries, much research effort has been devoted in the past to minimize the ionic diffusion resistances and electronic resistance associated with the electrode active materials. In the typical electrode configuration, the layer containing the active material is supported on a metallic current collector. The interface between the current collector and active layer imposes additional resistance to charge transfer within the electrode. This resistance source has not received sufficient attention in the past, presumably because it was not considered of significance for the low-power Li-ion electrode materials. However, the advancement in the material synthesis technologies has reduced the ionic and electronic resistances associated with the active materials to certain point that they become competitive to the other resistance sources. Thus, the significance of the electronic resistance at the active layer/current collector (AL/CC) interface is worthy of careful re-examination. The objects of this study is to prepare C-coated Al current collectors by two different coating processes, including high-temperature thermal chemical vapor deposition (HT-CVD) and low-temperature chemical vapor deposition (PA-CVD), and to characterize their electrochemical properties pertain to the power performance and cycling stability of Li-ion batteries. At least two beneficial effects are anticipated to result from the C-coating. For one, the C-coating removes the native surface oxide layer on the metal current collectors. For the other, the C-layer is hydrophobic in nature and hence helps to improve the interfacial bonding. Both effects are expected to reduce the AL/CC interfacial resistance. The ultimate goal is to develop a viable C-coating process of the current collector in order to improve the overall power performance and/or cycle life of the electrode of Li-ion batteries. In last year, we have developed a PA-CVD process for C deposition. The study in this year is to illustrate the effect of film thickness and to scale-up the process to manufacture a tape longer than 1 m.