|Illustration of the carbon-coated SnO2 hollow nanospheres in solvothermal synthesis with different thicknesses of SnO2 shell. Credit: ACS, Lin et al. Click to enlarge.|
Researchers at National Tsing Hua University in Taiwan have synthesized tin oxide (SnO2) hollow nanospheres covered with a carbon layer for anode material in lithium-ion batteries.
Hollow nanospheres with 15 nm in SnO2 thickness exhibited a reversible capacity of 500 mAh g-1 at 5 C. In a paper published in the ACS Journal of Physical Chemistry C, the team said that the “extraordinary performance” should be associated with the ultrathin SnO2 shell and the carbon layer, which could accommodate the volume changes and prevent the agglomeration of Sn particles during cycling.
Electrochemical performance of the material was significantly improved by the hollow structure and strongly affected by the shell thickness of SnO2.
Tin is one of the promising elements nuder consideration as a higher-capacity anode material, due to its higher theoretical capacity, higher lithium packing density, and operating voltage. However, tin experiences severe volume expansion and contraction during cycling, eventually pulverizing the Sn metal particles and limiting the cycle life of the anode.
Among the solutions considered to address this problem have been preparation of tin oxide materials and the design of hollow structure materials. Hollow structures offer three main benefits, the researchers noted:
- local empty space can partially accommodate the large volume change during cycling, delaying capacity fading;
- cavities in the hollow structure may provide extra space for the storage of lithium ions, being beneficial for enhancing specific capacity; and
- lithium could go through a surface path, facilitating lithium diffusion.
Earlier work led by Lynden Archer at Cornell showed that coaxial SnO2@carbon hollow nanospheres offer highly reversible lithium storage. The team in Taiwan developed an alternative approach to fabricate carbon-coated SnO2 hollow spheres with various thicknesses of SnO2 shell.
SnO2 nanospheres were synthesized from glucose and SnCl2 solution under hydrothermal environment and calcinations. The carbon layer was then deposited as a buffer layer via hydrothermally treated glucose solution. The thickness of the SnO2 shell in the hollow structures could be adjusted by changing the concentration of the SnCl2 coating solution. The thickness of SnO2 under 0.1 and 1 M SnCl2 coating solution was 15 and 60 nm, respectively.
Carbon-coated SnO2 nanospheres with different SnO2 shell thickness were successfully fabricated through simple hydrothermal process and calcinations. The elastic hollow structure powder with ultrathin SnO2 shell manifests superior cycling performance, namely, a stable capacity of about 500 mAh g-1 at 5 C. This structure incorporates simultaneously two advantages for high-power anode materials, such as hollow interior space and carbon nanopainting. Hollow structure creates a rapid lithium transportation path and facilitates the C-rate capability. The hollow structural materials with ultrathin SnO2 shell exhibits a highly reversible capacity, due to the reoxidation of Sn clusters.
Moreover, a ductile carbon matrix relieves the stress induced by volume change upon cycling and eliminates pure metallic Sn from agglomeration. As a result, the carbon-coated hollow nanospheres might be a promising material as high-performance anodes for the next-generation lithium-ion batteries.
—Lin et al.
Yu-Sheng Lin, Jenq-Gong Duh and Min-Hsiu Hung (2010) Shell-by-Shell Synthesis and Applications of Carbon-Coated SnO2 Hollow Nanospheres in Lithium-Ion Battery. J. Phys. Chem. C 114 (30), pp 13136–13141 doi: 10.1021/jp1042624
Lou, X. W.; Li, C. M.; Archer, L. A. (2009) Designed Synthesis of Coaxial SnO2@carbon Hollow Nanospheres for Highly Reversible Lithium Storage. Adv. Mater. 21, 2536 doi: 10.1002/adma.200803439