Characterization of negative electrodes prepared from fabric-shaped current collector

Abstract

Negative electrode of lithium-ion batteries are composed of active material, binder, conducting agent and current collector. In this work, the materially and structurally distinguishable current collectors are utilized to make advanced negative electrodes. First, carbon fabric is used as a current collector to make the high specific capacity negative electrode. Secondly, stainless steel (SUS) fabric is utilized as a current collector to fabricate the flexible and high rate capable negative electrode. Cu6Sn5-deposited carbon fiber paper (carbon fabric) is prepared successfully to develop high capacity negative electrode. Graphite is well-known to be highly electric conductive material, and it has a potential to be used as a current collector. When using graphite as a current collector, it is not only acting as a conventional current collector but reacting with lithium ion. In this study, carbon fabric is chosen as a current collector to increase overall electrode capacity. In the case of Cu6Sn5, it is prepared as active material, and there is no observation engaged with severe material detachment from carbon fabric during cycling. As a result, negative electrode which shows specific capacity about 300 mA h g-1 stably could be made. When comparing with conventional negative electrode which uses Cu foil as a current collector, the specific capacity considering the weight of current collector is almost 70 % larger. The other beneficial feature offered by the carbon fabric current collector is negligible electrode swelling, which is possible because the void spaces in the carbon fabric can accommodate the volume expansion of Cu6Sn5 component. The simple method for loading active material is invented to generalize the utility of carbon fabric. The conventional slurry spreading method is modified and applied to carbon fabric system. The viscosity of prepared slurry was decreased, and the slurry was soaked into carbon fabric by home-made suction equipment. The solid content of prepared slurry was 30 wt. %, and the suction process was conducted during 3 mins. As a result, the weight of loaded slurry was about 1.8 times heavier than that of carbon fabric. From the thickness information, it is checked that the loaded slurry was almost penetrated into carbon fabric. The fabricated electrode shows a good electrochemical properties, and especially, it delivers the high volumetric capacity because of the loaded slurry, which fills the void spaces of carbon fabric. TiO2-deposited SUS fabric is prepared successfully to develop the flexible negative electrode. SUS fabric characterized by 3-dimensional structure is used as a current collector for negative electrode of lithium-ion battery. TiO2 which plays the role of active material is deposited onto SUS fabric by liquid-phase deposition in the microstructure of core (SUS fabric, current collector)/shell (TiO2, active material). The flexibility of TiO2-deposited SUS fabric is tested under the extreme condition, called folding test, and there is no detachment of active material. When using TiO2-deposited SUS fabric as negative electrode and executing folding test during electrochemical cycling, there is no change in voltage profile and the cycle performance compared with non-folded one. The reason for granted flexibility of TiO2-deposited SUS fabric is summarized as follows. First, imposed stress occurred during flexible test is effectively dissipated by 3-dimensional structure of SUS fabric utilized as a current collector. Second, the stress experienced by active material is overcome with strong adhesion strength obtained via covalent bond between TiO2 and SUS fabric generated during liquid-phase deposition. Third, the selection of active material, which undergoes less volume change during cycling, helps initial adhesion strength remain even after electrochemical cycling. SUS fabric, which provides a 3-dimensionally well-constructed electric path and large contact area between active material and electrolyte, is utilized as a current collector for the high rate capable negative electrode. When comparing with the conventionally prepared negative electrode, which uses Cu foil as a current collector, they have a big difference in the structure of current collector. As a result, the electrode composed by SUS fabric shows a better rate capability than the conventional electrode, although they use same kind of active material. In this research, properties of negative electrode are improved by using unique current collector, although there is no modification in active material. There has been no sufficient research on current collector. However, the importance of current collector is now obvious, and it is expected for lots of following researches.