57th Annual Report on Research 2012 Under Sponsorship of the ACS Petroleum Research Fund

During the past funding year, we have extended our research to (1) binder-free porous core-shell structured Ni/NiO configuration and porous NiO-Ni nanocomposite anodes; (2) heat treatment effect of current collectors (such as: Ni foam, Stainless Steel, Al, Cu, etc) on electrochemical performance; (3) electrochemically activated carbon micro-electrode arrays; (4) developing mesoporous silicon anodes; (5) nanoporous SiO₂ films fabricated by sol–gel assisted electrostatic spray deposition; (6) porous core-chell Sn@Carbon composite anodes; and (7) novel "self-matrix" NiSnO₃ anode in lithium ion battery application. All these research efforts have significantly enhanced our understanding of fundamental issues regarding intrinsic properties of conversion mechanism and alloying mechanism based porous materials as anodes for Li-ion batteries.

Figure 1 (a) Cyclic voltammograms of NiSnO₃ anode in a voltage window of 0.02~3.0 V at a scan rate of 0.1 mV s^-1, (b) Discharge/charge mechanism of NiSnO₃ anode as "self-matrices" in a lithium ion battery, (c) Schematic mechanism of hollow and nanoporous SiO₂ with tree-like nanostructure on nickel foam synthesized by SG-ESD technique, and (d) Rate capability of Sn@carbon composites heated-treated at 900 °C at different rates: (i) 25, (ii) 100, (iii) 150, (iv) 200, (v) 250, (vi) 300, (vii) 25 mA g^-1, respectively.

We describe some of our research highlights below:

1. A novel nickel tin oxide (NiSnO₃) was proposed and demonstrated to be used as an anode for lithium ion batteries. It was found that NiSnO₃ shows higher cycling performance than the mixture of NiO and SnO₂ with the same elemental composition, and the reversible capacity retention is 57% and 32% after 100 charge/discharge cycles, respectively. The NiSnO₃ anode can be electrochemically decomposed into NiO, Sn and Li₂O in the first discharge process. NiO

and Sn can significantly function as "self-matrices" for each other besides the formed Li₂O matrix. The massive matrices effectively buffer the large volume change and prevent the aggregation of the nanosized particle upon cycling, resulting in the improved cycling

performance without sacrificing the specific energy capacity (Fig 1(a) and (b)).

2. A novel nanoporous tree-like SiO₂ film was synthesized by a sol–gel assisted electrostatic spray deposition (SG-ESD) approach. The sol–gel process employed was better to create SiO₂ with linear cross-link chains for the electrostatic spray deposition. As shown in Fig 1(c), the formation of the nanoporous "tree" structure is related to the preferential landing of droplets on the substrate and the electrostatic repulsion force among landing droplets during the ESD process. The catalytic effect of hydrochloric acid in the sol–gel system contributes to the formation of the hollow and porous structured SiO₂ spheres. The charge-discharge characteristics of the porous SiO₂ as an anode for Li-ion batteries were briefly evaluated and good long-term cycle performance was reached.

3. A three-dimensional porous core-shell Sn-carbon anode on nickel foam substrate was fabricated by electrostatic spray deposition (ESD) technique followed by high temperature treatment. 3D porous structure and carbon shell were designed to buffer volume expansion/shrinkage of Sn lattice upon cycling and increase the electrical conductivity. After 315 charge/discharge cycles Sn-carbon anode exhibited high specific capacity of 638 mAh g^-1 with the low capacity fade of average 0.11 mAh g^-1 per cycle. Sn-carbon based anodes was demonstrated to have promising potential for high performance lithium ion batteries application (Fig 1(d)).

4. Metal current collectors, offering a good connection between the active materials and the external circuit, is an important component in a rechargeable lithium ion battery. Some necessary thermal treatment in the battery fabrication and assembly procedure results in current collectors with some non-negligible reversible energy capacities; however, these energy capacities were negligible in the previous references. We systematically investigated the influence of the thermal treatment of current collectors (such as Ni foam, copper foil and stainless steel disk, etc) on the energy capacity. Our results indicate that different current collector materials have different thermal treatment effect on their electrochemical performance.

List of our journal publications during 2011-2012:

1. Xifei Li and Chunlei Wang, Engineering Nanostructured Anodes via Electrostatic Spray Deposition in High Performance Lithium Ion Battery Application, J. Mater. Chem. A, DOI:10.1039/C2TA00437B

2. Yan Yu, Abirami Dhanabalan, Lin Gu, Chunlei Wang, Hierarchically Macroporous and Mesoporous Sponge-like Fe3O4 Thin Film Electrodes for Application in Li-ion Batteries, Nanoscience and Nanotechnology Letters, in press

3. Xifei Li and Chunlei Wang, Enhanced cycle performance of NiSnO3 anode with "self–matrix" for high–performance lithium ion battery application, RSC Advance, 2012, 2, 6150–6154

4. Xifei Li, Abirami Dhanabalan, Lin Gu, Chunlei Wang*, Three-dimensional Porous Core/shelled Sn-Carbon Composite Anode for High Performance Lithium Ion Batteries Applications, Advanced Energy Materials 2(2012) 238–244

5. Xifei Li, Abirami Dhanabalan, Xiangbo Meng, Lin Gu, Xueliang Sun, Chunlei Wang, Fractal nano–porous SiO2 films fabricated by sol–gel assisted electrostatic spray deposition, Microporous & Mesoporous Materials, Volume 151 (2012) 488–494

6. Xifei Li, Abirami Dhanabalan, Chunlei Wang, Enhanced Electrochemical Performance of Porous NiO-Ni Nanocomposite Anode for Lithium Ion Batteries, J. Power Source, 196 (2011) 9625– 9630

7. Wei Chen, Zhongli Fan, Abirami Dhanabalan, Chunhui Chen, Chunlei Wang, Mesoporous Si Anodes Prepared by Manesiothermic Reduction for Lithium Ion Batteries, Journal of Electrochemical Society. 158 (9) (2011) A1055-A1059

8. Tae Kwon Kim, Wei Chen, Chunlei Wang, Heat treatment effect of the Ni foam current collector in lithium ion batteries, Jounral of Power Source, 196 (2011) 8742-8746

9. Majid Beidaghi, Wei Chen, Chunlei Wang, Electrochemical Activated 3D C-MEMS Based Supercapacitors, J. Power Source, 196 (2011) 2403–2409

10. Tae Kwon Kim, Chunhui Chen, Abirami Dhanabalan and Chunlei Wang, Electrochemical performance of porous NiO films as anode material for lithium ion batteries, ECS transactions, vol 35(34) (2011) 159-165

In addition to our research outcome, this project has big impact on training and education of next generation workforce in energy field. Two postdoctoral researchers, 4 graduate students, 3 undergraduate students, and 3 high school interns were involved in this project. Moreover, ECS student chapter at FIU was actively involved in various educational outreach activities during last funding year, such as: high school visits, open house, poster competitions, etc.