Solvothermal Synthesis, Development, and Performance of LiFePO4 Nanostructures

• Published in: Crystal growth & design 2013-11, Vol.13 (11), p.4659-4666
• Main Authors: Zhu, Jianxin, Fiore, Joseph, Li, Dongsheng, Kinsinger, Nichola M, Wang, Qianqian, DiMasi, Elaine, Guo, Juchen, Kisailus, David
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Diffusion in solids; Equations of state, phase equilibria, and phase transitions; Exact sciences and technology; General studies of phase transitions; Growth from solutions; MATERIALS SCIENCE; Methods of crystal growth; physics of crystal growth; Nanoscale materials and structures: fabrication and characterization; Nucleation; Other topics in nanoscale materials and structures; Physics; Transport properties of condensed matter (nonelectronic)
• ISSN: 1528-7483; 1528-7505
• DOI: 10.1021/cg4013312

We report the synthesis and nanostructural development of polycrystalline and single crystalline LiFePO4 (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 microscopy (SEM). Initially, thin (100 nm) platelets of Fe3(PO4)2·8H2O (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 LiFePO4. 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 LiFePO4 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.