通过金属辅助化学蚀刻处理多维体积硅阳极的可扩展方法

Commercially available Si powder was immersed in a solution of 5-20 mM silver nitrate  (AgNO₃) and 5 M HF for a controlled time. Immediately after rinsing, the silver deposited  silicon powder was immersed in an etchant consisting of 5 M HF and 1.5% H₂O₂ at 50 ℃  for 1-3 hr to produce silver catalyzed etched Si materials. Depending on the deposition time  of silver nitrate, the size of silver particles was varied (Fig. S1(a-c)). During electroless  deposition of silver, nanopits were also observed by etching in HF solutions. When the  silicon powder having various silver particle sizes was soaked into an etchant, composed of  5 M HF and 1.5% H₂O₂, at 50 o C for 1 hr, nanoporous silicon nanowires, which protrude  out from intact silicon core, were produced with different length and pore size (Fig. S1(d~f)). In addition to size of silver catalyst, the concentration of H₂O₂ that act as an oxidant is  another controllable parameter to tune the Si morphology. As the H₂O₂ concentrations of 1.0, 1.5, and 2.0% were used at a fixed HF concentration (5 M), shallow nanopits, Si  nanowires, and Si macropores were prepared, respectively (Fig. S2). To obtain multidimensional Si powders that nanoporous Si nanowires protrude out from microscale Si  matrix, silver deposited Si samples were etched in a 5 M HF and 1.5% H₂O₂ at 50 o C for 3  hr. As-synthesized Si powders were immersed in 5% HF for 1 min to remove silicon oxide  onto the surface of etched Si, and followed by drying in a vacuum oven at 100 o C for 2 hr  to remove water completely. Subsequently, the etched Si samples were coated by carbon by  thermal decomposition of acetylene gas at 700 o C for 20 min in quartz furnace.

We investigated the effect of carbon coating condition on the electrochemical performance.  The SEM images of mSi carbon-coated at 700, 900, and 1000 o C do not show the distinct  difference (Fig. S3(a-c)). Therefore, Raman and FT-IR spectrum were obtained to  characterized three different samples. Figure S3d shows the Raman spectra of multidimensional Si carbon coated with decomposition of acetylene gas at 700, 900, and 1000 ℃.  From the two peaks appearing at ~1360 (D band) and ~1580 cm^-1 (G band), the  dimensional ratio of the D and G bands of samples carbon coated at 700, 900, and 1000 o C  are 2.5, 2.1, and 3.1, respectively. The FT-IR spectrum of sample prepared at relative low  temperature (700 ℃ shows incomplete decomposition of acetylene molecules appearing at  ~1640    cm^-1, which is associated with the vibration of carbon (vinyl bonds) skeleton of the  sample (Fig. S3(e)). In case of samples coated at 1000 ℃, incomplete decomposition of  acetylene gas was not observed, but lower degree of graphitization was obtained due to  small amount of oxygen remaining carbonization process (Fig. S3(d & e)). All three  samples were prepared with a similar carbon content of ~ 30wt% at three different  temperatures. In order to compare the electrochemical performance of three samples,  galvanostatic discharge/charge experiments were carried out. Figure 6f shows the voltage  profiles of the three c-mSi anodes at 0.1 C rate between 1.2 V and 0.01 V. The first cycle  discharge capacities are 3200, 2440, and 2290 mAh/g for the electrodes of multidimensional Si carbon-coated at 700, 900, and 1000 ℃, respectively, with the  corresponding first charge capacities of 2630, 2150, and 1900 mAh/g. Therefore, the  coulombic efficiencies in the first cycle are 65%, 88%, and 85% for the three different Si  samples carbon-coated at 700, 900, and 1000 o C, respectively. The cycling performance of  samples with high degree of graphitization is superior to that of low degree samples (Fig.  S3(g)). 

Fig1

Effect of carbon-coating temperature on the electrochemical performance. SEM  images showing mSi carbon-coated at (a) 700, (b) 900, and (c) 1000 o C. (d) Raman spectra  of Si anodes coated with carbon at 700, 900, and 1000 o C. (e) The corresponding FT-IR  spectrum of each anode materials. (f) Voltage profiles for the first galvanostatic cycles of  the c-mSi at the 0.1 C rate. All three samples have a similar carbon content of ~28 wt%. (g)  Charge capacity versus cycle number for the carbon-coated Si at the 0.1 C rate. The carbon  coating condition affects the initial capacity and cycling retention. Square, circle, and  triangle symbols represent the carbonization temperature of 700, 900, and 1000 o C,  respectively.