Nanostructured LiNi0.5Mn1.5O4 cathode material synthesized by polymer-assisted co-precipitation method with improved rate capability
Highlights
► The polymer-assisted co-precipitation method is successfully developed for preparing nanostructured LiNi0.5Mn1.5O4 cathode materials. ► As-fabricated LiNi0.5Mn1.5O4 showed a nano-scaled particle size with high-uniformity and a porous texture. ► X-ray diffraction revealed high-crystallinity of as-fabricated LiNi0.5Mn1.5O4. ► Nanostructured LiNi0.5Mn1.5O4 performed a superior electrochemical behavior in rate capability for lithium ion battery storage.
Introduction
Recently, the Ni-doped Manganese spinel oxide – LiNi0.5Mn1.5O4 has become the most promising and attracting cathode material for lithium ion battery, due to its good electrochemical properties and high working potential around 5 V [1], [2]. A variety of synthetic methods for preparation of LiNi0.5Mn1.5O4 have been developed, including solid state reaction [3], sol–gel [4], co-precipitation [5], [6], spray pyrolysis [7], [8], electrophoretic deposition [9], pulsed laser deposition [10], molten salt method [11] and emulsion drying [12]. In general, co-precipitation method has been widely used to synthesize LiNi0.5Mn1.5O4 owing to the homogenous mixing of precursors to obtain well-crystallized spinel powders [13], [14], [15], [16]. Besides, the method is relatively low cost. However, particle aggregations and the lack of size uniformity are still observed in the resulting powder due to the undispersed mixture and the high temperature sintering process. In this study, in order to improve the size uniformity of LiNi0.5Mn1.5O4 as well as to reduce particle aggregations, polymer-assisted oxalate co-precipitation method was applied. Polyacrylic acid (PAA) is used as chelating agent to accomplish the nanostructured LiNi0.5Mn1.5O4 with uniformed particle size.
Section snippets
Material synthesis
Chloride-based transition metals (LiCl, NiCl2•6H2O and MnCl2•4H2O) were used as starting precursors with molar ratio of Li : Ni : Mn=1 : 0.5 : 1.5. The co-precipitation process was achieved by mixing metal chlorides with 70% aqueous oxalic acid. The detailed reaction mechanism was described elsewhere [17]. The nanostructured LiNi0.5Mn1.5O4 was achieved by adding 5 wt% aqueous polyacrylic acid (M.W.=1500) into the oxalate precursor route. After thoroughly mixing at 150 °C for 1 h, the mixture was then put
Results and discussion
Fig. 1 shows FE-SEM images of LiNi0.5Mn1.5O4 powders synthesized via different method (a) polymer-assisted method, (b) traditional co-precipitation. Except for the obvious particle size reduction, the uniformity was also successfully improved. Besides, the porous texture of as-synthesized powder was also shown in Fig. 1(c).
The particle size distribution of as-synthesized powders is displayed in Fig. 2(a) and (b). The average particle size in polymer-assisted method is around 70 nm, which
Conclusions
Nanostructured LiNi0.5Mn1.5O4 was successfully synthesized by oxalate co-precipitation method. With assistance of polyacrylic acid as dispersive agents, the particle size was significantly reduced from 300 nm to 70 nm. Besides, the porous texture was also observed in FE-SEM images. The X-ray diffraction showed well-defined diffraction patterns of LiNi0.5Mn1.5O4. The cubic spinel structure was identified without any contains of undesired impurities. Both samples with different particle size
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