Solvothermal Synthesis, Development, and Performance of LiFePO 4 Nanostructures Jianxin Zhu, † Joseph Fiore, ‡ Dongsheng Li, § Nichola M. Kinsinger, ‡ Qianqian Wang, ‡ Elaine DiMasi, ⊥ Juchen Guo, †,‡ and David Kisailus* ,†,‡ † Materials Science and Engineering Program, University of CaliforniaRiverside, Riverside, California 92521, United States ‡ Department of Chemical and Environmental Engineering, University of CaliforniaRiverside, Riverside, California 92521, United States § Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States ⊥ Synchrotron Light Source Department, Brookhaven National Laboratory, Upton, New York 11973, United States * S Supporting Information ABSTRACT: We report the synthesis and nanostructural development of polycrystalline and single crystalline LiFePO 4 (LFP) nanostructures using a solvothermal media (i.e., water- tri(ethylene glycol) mixture). Crystal phase and growth behavior were monitored by powder and synchrotron X-ray diffraction, as well as transmission electron microscopy (TEM), while particle morphologies were examined using scanning electron micros- copy (SEM). Initially, thin (100 nm) platelets of Fe 3 (PO 4 ) 2 · 8H 2 O (vivianite, VTE) formed at short reaction times followed by the nucleation of LFP (20 nm particles) on the metastable VTE surfaces. Upon decrease in pH, primary LFP nanocrystals subsequently aggregated into polycrystalline diamond-like particles via an oriented attachment (OA). With increasing reaction time, the solution pH further decreased, leading to a dissolution-recrystallization process (i.e., Ostwald ripening, OR) of the oriented polycrystalline LFP particles to yield evenly sized, single crystalline LiFePO 4 . Samples prepared at short reaction durations demonstrated a larger discharge capacity at higher rates compared with the single crystalline particles. This is due to the small size of the primary crystallites within larger secondary LiFePO 4 particles, which reduced the lithium ion diffusion path while subsequently maintaining a high tap density. Understanding the relationship between solution conditions and nanostructural development as well as performance revealed by this study will help to develop synthetic guidelines to enable efficient lithium ion battery performance. 1. INTRODUCTION As fossil fuel supplies are depleted, efforts to create new and renewable energy sources are being implemented. In addition to the need for renewable energy conversion technologies, there is an urgency for enhanced energy storage for municipal energy storage, electric vehicles, and portable devices. Rechargeable lithium ion batteries offer an effective media to store energy. There has been a marked improvement in Li-ion technologies compared with other alternatives such as the NiCd (nickel-cadmium) or NiMH (nickel-metal hydride) cells. Li-ion cells offer double the specific energy and over three times the energy density versus Ni-H 2 systems (which use pressurized hydrogen), while providing higher energy effi- ciency. 1 Improvement in the material components of Li-ion batteries, specifically the cathode and anode, offers potential to enhance their performance. One such cathode, the olivine-structured lithium iron phosphate (LiFePO 4 , LFP) was invented and reported by Goodenough et al. more than 15 years ago. 2 Because of its low cost, low toxicity, thermal and chemical stability, and good cycle stability, it is an excellent candidate as a cathode in rechargeable lithium batteries used in electric vehicles. 2 However, it is hindered by a low rate capacity due to the poor electronic conductivity and low lithium ion diffusivity, which inhibits expanding its commercial potential. 3,4 In order to overcome this inherent deficiency of LFP, research strategies have focused on utilizing conductive agents (carbon, silver, etc.) 5-7 to increase the electronic conductivity and to improve the mobility of lithium ions via cationic doping. 8,9 A number of different synthesis methods have been developed to produce controlled LFP including solid phase synthesis, 10,11 sol-gel process, 12 solution coprecipitation, 13 and solvothermal treatments. 14 Solvothermal syntheses, which often operate under higher pressures, offer the potential to precisely Received: January 13, 2013 Revised: October 6, 2013 Published: October 9, 2013 Article pubs.acs.org/crystal © 2013 American Chemical Society 4659 dx.doi.org/10.1021/cg4013312 | Cryst. Growth Des. 2013, 13, 4659-4666