ORIGINAL PAPER An efficient process to fabricate spherical hierarchical LiFePO 4 /C cathode composites with controllable coating thickness Yinglin Yan 1 & Qiaole Li 1 & Bing Ren 1 & Rong Yang 1 & Yunhua Xu 1,2 & Lisheng Zhong 1 & Hong Wu 2 Received: 18 December 2016 /Revised: 7 July 2017 /Accepted: 18 July 2017 # Springer-Verlag GmbH Germany 2017 Abstract Hierarchical lithium iron phosphate/carbon (LiFePO 4 /C) microspheres were fabricated successfully using a facile spray drying-assisted coprecipitation method. A rela- tively short calcination time and a relatively low calcination temperature were adopted to prepare the hierarchical LiFePO 4 /C microspheres. The hierarchical microspheres consisted of nanoparticles with a uniform coating of amor- phous carbon. The thickness of the carbon layer was con- trolled by the addition of glucose. The hierarchical LiFePO 4 / C microspheres exhibited a high tap density and a large spe- cific surface area. The electrochemical properties of the sam- ple were investigated. The sample exhibited a better rate ca- pability and a better cyclability than the coral-like LiFePO 4 /C cathode material, and these were ascribed to the highly uni- form carbon coating and the self-assembled nanoparticles. Keywords Lithium iron phosphate . Hierarchical microstructure . Carbon coating . Spray drying method Introduction Over the last couple of decades, rechargeable lithium ion bat- teries (LIBs) have attracted significant attention as a promising energy storage system for applications in electron- ics, electric vehicles, and hybrid electric vehicles [1–5]. Since olivine structured LiFePO 4 was proposed in 1997 by Goodenough et al. [6], it has been regarded as one of the most promising cathode materials for LIBs because of its high spe- cific mass capacity and outstanding cyclability. LiFePO 4 has also been considered as a promising candidate in large-scale applications because of its low material cost, excellent chem- ical stability, environmentally benign nature, and safety [7, 8]. However, LiFePO 4 suffers from an intrinsically poor electron- ic conductivity and sluggish lithium ion motion ability, which largely inhibit its industrialization and wide application in transportation systems [9, 10]. Up to now, significant en- deavors have been devoted to overcoming these drawbacks. For instance, a conductive carbon coating layer on the surface has been used to focus on improving the electrical conductiv- ity [11, 12]. However, a thick carbon layer may block lithium ion diffusion through the cathode/electrolyte interface, so a uniform and controllable carbon layer is necessary [8]. It has also been reported that the downsizing strategy is effective for shortening the diffusion distance of lithium ions [13]. However, this adversely affects the tap density and volumetric energy density [14]. In addition, doping metals have been an effective way to enhance the kinetics of LiFePO 4 . However, the drawbacks of LiFePO 4 have not been solved while the processing cost has grown continuously [15]. Recently, electrode materials with self-assembled nano/ microhierarchical structures have been one of the most desir- able structures of choice for improving lithium storage prop- erties because these structures combine the advantages of high specific capacity, enhanced kinetics of nanometer-sized build- ing blocks, and high tap density of micrometer-sized assem- blies [16–19]. Most of these structures were coated with a uniform conductive carbon layer on the surface of the primary particles. However, in the reported references, the fabrication * Yinglin Yan yyl3550@xaut.edu.cn 1 Institute of Chemical Power Sources, School of Materials Science and Engineering, Xi’an University of Technology, 5 South Jinhua Road, Xi’an 710048, People’ s Republic of China 2 Shaanxi Key Laboratory of Nano-materials and Technology, Xi’an University of Architecture and Technology, Xi’an 710055, People’ s Republic of China Ionics DOI 10.1007/s11581-017-2232-5