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cu foams possess high porosity, good conductivity and a low coefficient of friction, and are used as current collectors in Li-ion batteries. Their intrinsic structural integrity and void spaces also allow them to buffer stress generated by large volume changes in high-capacity anode materials during cycling. However, the combination of these desirable properties is not easily achieved in a three-dimensional porous structure. In this article, a novel anode design concept is introduced by combining directional freeze-casting and sol-gel coating processes to fabricate a 3D macroporous cu foam electrode with dual pore-size distribution. The 3D microstructure provides continuous metallic struts that serve as effective electron pathways and local void spaces to alleviate stress. The result is an electrode with excellent reversible capacity, superior rate capability and stable cycle retention.
The X-ray diffraction patterns of the as-prepared cu foams showed that they are composed of pure copper material, indicating no contamination by other metal oxides. The etched cu foams and the cu foams modified by n-EE, n-HDE, and n-ODE had different surface morphologies, as shown in Figure 1. In order to evaluate their stability, the cu foam samples were immersed in 0.1 M HCl, 0.1 M NaOH, and 3.5% NaCl solutions for 5 min, 10 min, and 10 h respectively. After that, the samples were washed with deionized water and dried by nitrogen.
The X-ray diffraction pattern of the SnO2/cu foam shows the characteristic peaks of tetragonal rutile-structure SnO2 and that of copper (JCPDS 41-1445) without other peaks. The reversible oxidation behavior is confirmed by the integrated charge in differential curves at higher voltages (Supplementary Fig. S12c). The area corresponding to the reversible oxidation decreases sharply for both SnO2/cu foam and SnO2 NPs after 30 cycles.