Full Length ArticleQuasi-hexagonal Cu 1.5 Mn 1.5 O 4 nanoplates decorated on hollow CuO byKirkendall effect for enhancing lithium storage performancePeng Liu, Xifeng Xia, Wu Lei, Xinyan Jiao, Lei Lu, Yu Ouyang, Qingli Hao ⇑Key Laboratory for Soft Chemistry and Functional Materials, School of Chemical Engineering, Nanjing University of Science and Technology, Nanjing 210094, Chinaa r t i c l e i n f oArticle history:Received 8 January 2018Revised 17 March 2018Accepted 23 March 2018Available online 26 March 2018Keywords:Heterogeneous compositeKirkendall effectNanoplatesVoidsEnhanced performancea b s t r a c tConstructing a hierarchical heterogeneous composite is deemed as an effective way to solve the currentproblems of metal oxides as lithium ion batteries’ anodes. In this work, we simultaneously designed theheterogeneous component and structure of the novel hybrid based on Kirkendall effect. The compositewas composed of quasi-hexagonal Cu 1.5 Mn 1.5 O 4 nanoplates as a shell and CuO with voids as a core.The hybrids were characterized by using XRD, FTIR, TEM and SEM. It was found that the heating rategreatly inf l uences the combination form of Cu 1.5 Mn 1.5 O 4 and CuO. The quasi-hexagonal Cu 1.5 Mn 1.5 O 4nanoplates were assembled into branch-like shell decorated on the CuO surface under the low heatingrate. However, the high heating rate led to a compact Cu 1.5 Mn 1.5 O 4 shell, although the shell was alsoassembled by quasi-hexagonal nanoplates. The reasonable formation mechanism of the unique compo-nent and structure was proposed. Such a hybrid with the branch-like shell exhibited the best lithiumstorage performance. The improved electrochemical performance can be attributed to the unique compo-nent and structure. Typically, the inside voids can alleviate the volume change and the hierarchical shellcan provide much contact and reaction sites. This work not only opens a new view in constructing hetero-geneous hybrid with unique structure by Kirkendall effect, but also can be expanded for many otherstructure-based applications, such as energy storage, sensors, and heterogeneous catalysts.? 2018 Elsevier B.V. All rights reserved.1. IntroductionIn the past two decades, metal oxides have been deemed as thepromising alternative anode material for lithium ion batteriesowing to their high theoretical capacity compared to traditionalanode graphite [1–3]. Many metal oxides, such as CuO [4], CoO[5], Co 3 O 4 [6], Fe 3 O 4 [7], NiO [8], MnO [9], have been studied, buttheir lithium storage performance needs to be improved becausethe intrinsic low electronic conductivity and large volume varia-tion during the lithiation–delithiation process limit their electro-chemical properties. Generally speaking, there are twodominated types of strategies to solve the above problems. Oneis the construction of metal oxides’ structure on size and/or dimen-sion [2,10]. By decreasing the bulk size into nanosize, the transportlength of lithium ions can be shortened and the expansion stresscan be weakened. Besides, a hierarchical structure can make morereaction active sites which enhances the corresponding electro-chemical performance [11]. However, the products with a nanosizealways possess a low density which hinders the improvement ofvolumetric electrochemical performance [12]. The other methodis to form a heterogeneous hybrid composite by integrating onewith other metal oxides or carbonaceous nanomaterial [13,14]. Inthis regard, many heterogeneous metal oxides composites, suchas Fe 2 O 3 @NiCo 2 O 4 [15], SnO 2 ?Fe 2 O 3 [13], CuO@NiO [16],CuO@CuFe 2 O 4 [17], were synthesized which showed the enhancedlithium storage performance compared to single metal oxide. Theenhanced performance benef i ts from the synergetic effect betweenthe heterogeneous components. Besides, the combination form ofthe heterogeneous components also plays an important role inthe electrochemical performance because it determines the nanos-tructure of f i nal composites.The Kirkendall effect is a representative phenomenon ofunequal matter inter-diffusion, which usually accompanies withthe formation of voids when the outside diffusion is faster thanthe inside one [18–20]. This effect is common in metallurgy andnot desirable in alloying and welding if the Kirkendall voids aregenerated [21]. Since Yin et al. [18] reported a conversion frommetal nanoparticles to the hollow oxides and chalcogenidesthrough the Kirkendall effect in nanoscale, many researchers havedesigned hollow structures based on Kirkendall effect for variousapplications, such as lithium ion batteries [22], sodium ion batter-ies [23], catalyst [24]. For instance, Cho and et al. reported a 1-DFe 2 O 3 /Se nanorods composite, which shows an excellent dischargehttps://doi.org/10.1016/j.apsusc.2018.03.1910169-4332/? 2018 Elsevier B.V. All rights reserved.⇑ Corresponding author.E-mail address: qinglihao@njust.edu.cn (Q. Hao).Applied Surface Science 445 (2018) 342–349Contents lists available at ScienceDirectApplied Surface Sciencejournal homepage: www.elsevier.com/locate/apsusc
