Please cite this article in press as: Wen, L., et al. Open-pore LiFePO 4 /C microspheres with high volumetric energy density for lithium ion batteries. Particuology (2014), http://dx.doi.org/10.1016/j.partic.2014.11.002 ARTICLE IN PRESS G Model PARTIC-750; No. of Pages 6 Particuology xxx (2014) xxx–xxx Contents lists available at ScienceDirect Particuology jo ur nal home page: www.elsevier.com/locate/partic Invited paper Open-pore LiFePO 4 /C microspheres with high volumetric energy density for lithium ion batteries Lei Wen a , Xiaodong Hu b , Hongze Luo c , Feng Li a,∗ , Huiming Cheng a a Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China b Shenzhen Kingrunning Energy Materials Co., Ltd., Shenzhen 518000, China c Council for Scientific and Industrial Research, Pretoria 0001, South Africa a r t i c l e i n f o Article history: Received 1 September 2014 Received in revised form 15 November 2014 Accepted 24 November 2014 Keywords: Lithium iron phosphate Lithium ion batteries Volumetric energy density Open-pore structure a b s t r a c t LiFePO 4 /C microspheres with different surface morphologies and porosities were prepared from different carbon sources. The effects of the surface morphology and pore structure of the microspheres on their electrochemical properties and electrode density were investigated. The electrochemical performance and electrode density depended on the morphology and pore structure of the LiFePO 4 /C microspheres. Open-pore LiFePO 4 /C microspheres with rough surfaces exhibited good adhesion with current collectors and a high electrode density (2.6 g/cm 3 ). They also exhibited high performance in a half cell and full battery with a high volumetric energy density. © 2014 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved. Introduction Olivine lithium iron phosphate (LiFePO 4 ) has a high lithium intercalation voltage of 3.4 V versus lithium, and a high theoret- ical capacity of 170 mA h/g. It also has a high thermal stability, high safety, and excellent cycling life. Since its discovery (Padhi, Nanjundaswamy, & Goodenough, 1997), LiFePO 4 has been investi- gated as a cathode material for electric vehicles (EVs) and in renew- able energy storage plants, because of its low cost, abundance, and environment friendliness (Sun, Oh, Park, & Scrosati, 2011b). LiFePO 4 suffers from a poor rate capability, due to its low lithium ion diffusion coefficient and poor electrical conductivity (Amin, Balaya, & Maier, 2007; Prosini, Lisi, Zane, & Pasquali, 2002). Poor rate performance issues can be overcome by fabricating nm- sized particles (Arnold et al., 2003; Delacourt, Poizot, Levasseur, & Masquelier, 2006; Gibot et al., 2008; Kim & Kim, 2006; Kim et al., 2007; Saravanan et al., 2009), and coatings of thin conductive car- bon layers (Belharouak, Johnson, & Amine, 2005; Joachin, Kaun, Zaghib, & Prakash, 2009; Konarova & Taniguchi, 2009; Lu, Fey, & Kao, 2009; Shin, Cho, & Jang, 2006; Zaghib, Mauger, Gendron, & Julien, 2008). Such nano-LiFePO 4 /C has exhibited a gravimetric capacity close to the theoretical maximum, improved rate capa- bility, and a very low tap density. Cathode materials with low ∗ Corresponding author. Tel.: +86 024 83970065; fax: +86 24 23891320. E-mail address: fli@imr.ac.cn (F. Li). tap densities usually result in low volumetric energy densities for lithium ion batteries (LIBs). Therefore, nano-LiFePO 4 /C cathodes are unsuitable for LIBs for plug-in hybrid vehicles (PHEVs) or EVs. Nano-LiFePO 4 /C also suffers from low thermodynamic stability, surface side-reactions, and high cost (Liu, Li, Ma, & Cheng, 2010). Fabricating micron-sized LiFePO 4 with a high tap density has received much interest. Ying et al. (2006) prepared micro spher- ical Li 0.97 Cr 0.01 FePO 4 /C particles with a powder tap density of 1.8 g/cm 3 . Sun, Rajasekhara, Goodenough, and Zhou (2011a) pre- pared LiFePO 4 /C microspheres with an open three-dimensional porous microstructure, by a solvothermal approach and high- temperature calcination. Oh et al. (2009) prepared spherical m-sized LiFePO 4 /C particles with a tap density of 1.5 g/cm 3 . Such LiFePO 4 /C microspheres have high tap densities and excellent rate capabilities. Many studies have used the tap density to estimate the volu- metric energy density of LIBs (Oh et al., 2009; Ying et al., 2006). During manufacture, electrode materials are usually mixed with a polymer binder (e.g., polyvinylidene fluoride (PVDF)) and conduct- ing materials (e.g., carbon black). This mixture is then coated onto a metal current collector (e.g., aluminum or copper foil), then dried and calendered to form the electrodes. Scheme 1 shows the difference between the tap density and electrode density for LIBs. The tap density is the apparent den- sity of a volume of powder obtained when its container is tapped or vibrated. The electrode density of a calendered electrode is the mass of the active material membrane per cm 3 on the metal current http://dx.doi.org/10.1016/j.partic.2014.11.002 1674-2001/© 2014 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.