Illustration of a SnO2−carbon hybrid cellular nanosheet and its features that contribute to the electrochemical performance. Credit: ACS, Yu et al. Click to enlarge.

The development of next-generation energy-storage devices is of primary importance to meet the challenges in the electronics and automobile industries in the near future. In particular, there has been increasing interest in the development of new multicomponent nanomaterials that can overcome a number of intrinsic limitations of single-component electrode materials for lithium-ion batteries (LIBs). The considerable volume changes of the active materials from lithiation and delithiation lead to the mechanical deformation, causing the high internal resistance and low cycle stability. This is especially pronounced for the high-capacity anode materials such as Si, Ge, Sn, SnO₂, and Fe₂O₃ because they have a very large volume change during cycling. Also, the side reactions at the interface between the electrolyte and the active material can decrease in the Coulombic efficiency and cause safety problems.

Since the early 2000s, multicomponent nanostructures that consist of hollow carbon shell encapsulating active materials have attracted strong interest because they can provide very effective solutions to these limitations of anode materials. In this structure, the carbon shell confines the active material within a closed volume so that the loss of capacity due to pulverization and agglomeration can be minimized and good electric contact with the active material can be ensured during cycling. Furthermore, the assembled structure of carbon shells can reduce the contact area between the electrolyte and the active materials inside of the shell, reducing the formation of the solid–electrolyte interphase (SEI). Also, the extended carbon network of the assembled structure can facilitate the electron transport.

Thus far, various carbon-based multicomponent hybrid nanostructures for LIB anodes have been reported to exhibit high electrochemical performance in either long stability, high capacity, or high rate capability. … an ideal hybrid nanostructure that combines key aspects of the electrode materials including cycling stability, specific capacity, and rate performance is highly anticipated. Herein, we report a new synthetic method of carbon-based hybrid nanosheets that exhibit outstanding performance in many key aspects of the LIB anode.

—Yu et al.

The as-prepared nanosheets have close-packed uniform cubic empty “cells” of ∼12 nm side length that are enclosed by 3.5 nm thick carbon walls. Inorganic anode materials are incorporated into the empty cells by simple vapor deposition. The cubic cells enclosed by the carbon walls provide enough space for the volume change of the inorganic active material inside and retain the mechanical integrity during lithiation and delithiation, the team said.

Further, the cubic shape ensures the maximum packing density and the larger contact area with the active material compared to a spherical shape with the same volume. The nanosheet structure also provides a short diffusion length of Li ions in the thickness direction—enabling a high rate capability—and facile electron transport through its carbon network which is as large as hundreds of square micrometers.

The team compared the electrochemical performance of SnO₂−carbon hybrid cellular nanosheets with that of a carbon cellular nanosheets and an SnO₂ nanosheet and found that their hybrid materials significantly outperformed the others.

Cycling performance of three kinds of nanosheets: SnO2−carbon, carbon, and SnO2 nanosheets. Credit: ACS, Yu et al. Click to enlarge.

… we show that very effective hybrid nano-structured electrode material can be prepared via a relatively simple procedure. Because many different kinds of materials can be immobilized in the carbon cellular nanosheets, the resulting hybrid cellular nanosheets can be applied to various areas including electrochemical devices and catalysis.

—Yu et al.

Resources

• Seung-Ho Yu, Dong Jun Lee, Mihyun Park, Soon Gu Kwon, Hyeon Seok Lee, Aihua Jin, Kug-Seung Lee, Ji Eun Lee, Myoung Hwan Oh, Kisuk Kang, Yung-Eun Sung and Taeghwan Hyeon (2015) “Hybrid Cellular Nanosheets for High-Performance Lithium-Ion Battery Anodes” Journal of the American Chemical Society doi: 10.1021/jacs.5b03673