Electrodeposition of Si-O-C Composite Anode Onto Three Dimensional Structures for Lithium Secondary Batteries

Silicon is one of the most promising materials for lithium secondary battery anodes. However, silicon anodes have a critical drawback to their practical application, which is capacity degradation due to pulverization of the active material by the large volume change of silicon during charge–discharge cycles. To solve the problem, some attempts have been proposed such as a formation of thinner film¹, nano-, micro-structure such as nano-wired structure², core-shell structure, porous structure³, alloying with the third metallic elements⁴, and so on. Among them, we have proposed Si-O-C composite anode prepared by electrodeposition process. ^5-8 The Si-O-C composite anode is composed of silicon oxide (SiO_x, 0<x<2) and organic compounds that are derived from decomposed products by the electrochemical co-reduction of Si and the solvent was performed directly on the current collector. ^8,9 The Si-O-C anode showed excellent cycle durability, that is the Si-O-C anode delivered ca. 800 mAh/g-Si even over 7000 cycles. However, the Si-O-C composite anode has room to be improved on specific capacity normalized by electrode area, ca. 50 μAh/cm². To improve the capacity, we applied nanocone-structured substrate as a current collector. Consequently, we succeeded in increasing the thickness of the Si-O-C composite anode, resulting in the capacity of ca. 600 μAh/cm² (800 mAh/g-Si).⁷In the present paper, to improve the specific capacity normalized by electrode area, the Si-O-C composite anode was electrodeposited onto three-dimensional structured material, i.e. carbon paper.

A carbon paper was treated by sulfuric acid and hydrogen peroxide mixture (SPM) to improve the surface of the carbon paper. The Si-O-C composite was electrodeposited on the carbon paper by using an electrolytic solution which contains 0.5 M SiCl₄and 0.5 M tetrabuthylammonium perchlorate / propylene carbonate.

Figure 1 shows whole covering of the Si-O-C composite on the carbon paper which is treated by SPM compared, although the covering of the Si-O-C composite on the carbon paper with no treatment is defective (Figure 2). Thus, the SPM treatment improved the coverage of the Si-O-C composite on the carbon paper. Figure 3 shows the discharge capacity of the Si-O-C composite on the carbon paper treated by SPM. The discharge capacity of the Si-O-C composite anodes on the carbon paper delivered more than 1.5 mAh /cm2 which is more than double compared with the our previous work⁷. Although the half of the capacity was derived from the capacity of the carbon paper, the feasibility of the electrodeposition of Si-O-C composite onto three-dimensional structured materials is demonstrated to be effective to increase the specific capacity normalized by electrode area.

Reference

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Acknowledgement

This work was supported partially by Advanced Low Carbon Technology Research and Development Program (JST-ALCA) Special Priority Research Area "Next-generation Rechargeable Battery".