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Three-dimensionally ordered macro-porous Sn-C composites were prepared by using polystyrene microsphere as a template. The Sn-C composites were composed of well-interconnected pore with circular shape and wall structure with wall thickness of a few tens of nano-meters. This porous three-dimensional structure is readily and uniformly accessible to the electrolyte, which facilitates lithium ion diffusion during charge-discharge reactions. The wall thickness of the composites was increased as the increase of Sn content of the composite. From EDS analysis, it is confirmed that the Sn was dispersed uniformly in Sn-C composites. The capacity was increased as the Sn content increased, which is due to Sn anode with high capacity. The Sn-C composites with high Sn content showed superior cyclic performances. Such enhancement is ascribed to the thick wall thickness and small pore size of the sample with high Sn content. The Sn-C composite with Sn 30 wt% showed relatively high capacity and stable cycle life, however, the stability of the 3-dimensional structure should be enhanced by further work.

Surface modification by coating is one of the most effective methods for improving the electrochemical property of the cathodes of lithium-ion batteries. In previous studies, the surface of the cathode powder has been coated with stable oxides, 1-6 phosphates, 7-10 and fluorides [11][12][13] to obtain enhanced cyclic performance, rate capability, and thermal stability. However the coating effect is highly dependent upon the control of interface reaction.14-16 Thus, careful characterization of the interface reaction among the cathode, coating layer, and electrolyte is essential to obtain an optimum surface coating. However, it has been difficult to characterize the interface reaction directly, because of the small particle size of the pristine powder, very low thickness of coating layer, and rough surface of positive electrode. To solve this problem, the thin film electrode was successfully introduced as a pristine cathode to investigate the interface reaction among the electrolyte, coating layer, and pristine cathode in detail.17 The surface of a thin film cathode is much wider and smoother than that of a bulk-type electrode, which may offer a good chance for a careful observation of the interface reaction of coating layer. In this work, the surface damage of a pristine and ZrO 2 -coated LiCoO 2 thin film during storage was focused to confirm the coating effect. Specially, the damaged surface was directly observed by SEM and depth profile of elements was measured by SIMS before and after storage.The ZrO 2 coating layer was confirmed in the previous work.17 The coating thickness was controlled through the concentration of the coating solution. The ZrO 2 -coated LiCoO 2 films were prepared using 0.1 and 0.2 mol % coating solutions. The two coated samples obtained in this manner are hereafter called sample 1 (the sample fabricated using 0.1 mol % coating solution) and sample 2 (the sample fabricated using 0.2 mol % coating solution). Considering the concentration of the coating solution, sample 2 will have a thicker coating layer than sample 1. The pristine and coated samples showed similar discharge capacities and cyclic performances at 30 °C with a current density of 0.2 mA·cm −2 . 17 To characterize the electrochemical properties of the samples under more chemically unstable conditions, the current density and measuring temperature were increased to 0.4 mA·cm −2 and 45 °C, respectively. Under these measurement conditions, the effect of coating on the electrochemical property of the samples was clearly observed. As shown in Figure 1, the initial discharge capacities of the pristine and sample 2 (with a relatively thick coating layer) were similar. However, the discharge capacity of sample 1 was significantly higher (~250 mAh·cm ). Moreover, the cyclic performance of cathodes was noticeably enhanced after surface coating. The discharge capacity of the pristine film rapidly dropped during cycling at 45°C. However, the coated sample still maintained a stable cyclic performance under the same measurement conditions. ...