**4. Conclusions**

In conclusion, we fabricated novel 1D–PSiNW anodes with the high specific area of 323.47 <sup>m</sup>2·g<sup>−</sup><sup>1</sup> by a one-step silver-assisted chemical etching method. The TEM image demonstrated that the nanowires were several μm length and 60–500 nm in diameter with highly uniform porosity at the surface, with both pore diameter and wall thickness around 7 nm. This small pore size of the silicon nanoporous structure offered sufficient void space to accommodate the large volume change. Our designed 1D–PSiNWs as anodes for LIBs show a reversible specific capacity of 2061.1 mAh·g<sup>−</sup><sup>1</sup> after 1000 cycles under a fast charge–discharge condition at 1.5 <sup>A</sup>·g<sup>−</sup>1. Even after 5000 cycles, a reversible capacity of 586.7 mAh·g<sup>−</sup><sup>1</sup> was retained at the ultrafast charge–discharge current density of 16.0 <sup>A</sup>·g<sup>−</sup>1. The small feature size acted as a short Li+/electron conductive path during the lithiation/delithation processes. The superior electrochemical performance and excellent cycling life of the nanoporous 1D–PSiNW anodes were attributed to the 1D structure with uniform interconnected nanoporous channels existing inside the silicon nanowires.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-4991/8/5/285/s1. Figure S1: Energy-band diagrams of N-type silicon in aqueous HF/AgNO3 solution. Figure S2: (a) SEM and EDX of dendritic Ag-coated 1D–PSiNWs after etching, (b) SEM cross-section of 1D–PSiNWs, and (c) top view SEM image of 1D–PSiNWs. Figure S3: XPS survey spectra of 1D–PSiNWs. Figure S4: Cyclic voltammetry curves of 1D–PSiNW anodes of 200th, 201st, 202nd cycles in the voltage window from 0.01 V to 2.0 V at rate of 0.1 mV·s<sup>−</sup>1. Figure S5: The results of cycling performance of 1D–PSiNW anodes tested at a current density of 8.0 <sup>A</sup>·g<sup>−</sup>1.

**Author Contributions:** Xu Chen designed the experiments and wrote the paper. Qinsong Bi and Muhammad Sajjad prepared and characterized the samples. Xu Wang and Yang Ren provided useful discussion. Xiaowei Zhou contributed analysis experimental data. Wen Xu and Zhu Liu conceived the study and provided critical advice for each designed experiment.

**Acknowledgments:** We gratefully acknowledge the financial support from the Natural Science Foundation of China (grant nos. 61664009 and 51771169) and the Youth Project of Applied Basic Research of the Yunnan Science and Technology Department (grant no. 2015FD001). This work is also funded in part by the High-End Scientific and Technological Talents Introduction Project of Yunnan Province (grant No. 2013HA019). Moreover, the authors wish to acknowledge Kuiqing Peng for his help in useful discussions about reaction principle. Gang Cao provided useful discussion. Long Li and Ying Huang designed the experiments and battery assembly test.

**Conflicts of Interest:** The authors declare no conflicts of interest.
