Date Published: January 03, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Mingbo Zheng, Hao Tang, Lulu Li, Qin Hu, Li Zhang, Huaiguo Xue, Huan Pang.
Lithium‐ion batteries (LIBs) have been widely used in the field of portable electric devices because of their high energy density and long cycling life. To further improve the performance of LIBs, it is of great importance to develop new electrode materials. Various transition metal oxides (TMOs) have been extensively investigated as electrode materials for LIBs. According to the reaction mechanism, there are mainly two kinds of TMOs, one is based on conversion reaction and the other is based on intercalation/deintercalation reaction. Recently, hierarchically nanostructured TMOs have become a hot research area in the field of LIBs. Hierarchical architecture can provide numerous accessible electroactive sites for redox reactions, shorten the diffusion distance of Li‐ion during the reaction, and accommodate volume expansion during cycling. With rapid research progress in this field, a timely account of this advanced technology is highly necessary. Here, the research progress on the synthesis methods, morphological characteristics, and electrochemical performances of hierarchically nanostructured TMOs for LIBs is summarized and discussed. Some relevant prospects are also proposed.
The shortage of fossil fuels and increasingly deteriorating environmental pollution have become a threat for humans as the global economy rapidly develops. Thus, green power sources should be developed to replace conventional fossil fuels.1, 2, 3, 4, 5, 6 Solar energy, wind energy, and tidal energy are good alternatives because of their renewability and low pollution. However, these sources are usually restricted by their intermittence and poor storage efficiency.7, 8 Electrochemical energy storage provides a feasible approach to store electric energy from these sources.9, 10, 11, 12, 13, 14, 15, 16 Among various electrochemical energy storage devices, lithium‐ion batteries (LIBs) have drawn more and more attention because of their high energy density, long cycling life, and environmental friendliness.17, 18, 19, 20, 21
Most of TMOs for LIBs are based on conversion reaction or intercalation/deintercalation reaction. There remain a few TMOs, such as ZnO, ZnFe2O4, and ZnCo2O4, which are based on alloying–dealloying reaction or a combination of alloying–dealloying reaction and conversion reaction.
In this review, we make an overview on the recent developments of hierarchically nanostructured TMOs for LIBs. Various TMOs, such as iron oxides, cobalt oxides, nickel oxides, manganese oxides, titanium oxides, niobium oxides, and vanadium oxides, have been investigated as electrodes for LIBs. These TMOs are classified on the basis of two reaction mechanisms, namely, the conversion reaction and the intercalation/deintercalation reaction. Because of their inherent features, the two types of TMOs exhibit different properties when used for LIBs. TMOs based on the conversion reaction usually possess high theoretical specific capacity. For example, iron oxides and manganese oxides can deliver a theoretical specific capacity of up to ≈1000 mA h g−1. However, these kinds of TMO have poor structural integrity caused by the transformation between TMOs and elemental metal during the charge/discharge process. By contrast, TMOs based on the intercalation/deintercalation reaction have relatively low theoretical specific capacity, but maintain the structural integrity and ensure good cycling stability. Hierarchically nanostructured TMOs with various morphologies, such as hierarchical nanowire, nanotube, microbox, and 3D hierarchical microspheres (including 3D hierarchical microflower and hollow spheres), have been discussed systematically. The hierarchical nanostructure can deliver a superior electrochemical performance in comparison with the nonhierarchical structure. A hierarchical nanostructure not only provides more active sites for redox reaction but also shortens the transport distance of Li+. Moreover, the hierarchically nanostructured TMOs can address the problem of serious volume change, which is a disadvantage of TMOs based on the conversion reaction. During electrochemical cycling, the hierarchical structure can accommodate the strains caused by volume expansion.
The authors declare no conflict of interest.