Journal of Power Sources 210 (2012) 1–6 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jo ur nal homep age: www.elsevier.com/locate/jpowsour Short communication Restricted growth of LiMnPO 4 nanoparticles evolved from a precursor seed Tae-Hee Kim a , Han-Saem Park a , Myeong-Hee Lee a , Sang-Young Lee b,∗ , Hyun-Kon Song a,∗∗ a i-School of Green Energy, UNIST, Ulsan 689-798, Republic of Korea b Department of Chemical Engineering, Kangwon National University, Chuncheon, Kangwon, Republic of Korea a r t i c l e i n f o Article history: Received 25 January 2012 Received in revised form 14 February 2012 Accepted 15 February 2012 Available online xxx Keywords: Lithium ion batteries Lithium manganese phosphate Cathodes Precipitation Nanostructure a b s t r a c t Herein, we report on a novel precipitation method to enable LiMnPO 4 olivine (LMP) as a cathode material for lithium ion batteries (LIBs) to reach high capacity at high discharge rates. By confining Mn 3 (PO 4 ) 2 precipitation on surface of a precursor seed of Li 3 PO 4 , the size of LMP particles is limited to less than 100 nm for a smaller dimension. The cathode material delivers discharge capacities of 145 mAh g -1 at 0.1 C, 112 mAh g -1 at 1 C to 62 mAh g -1 at 5 C (comparable with top three performances [1–3]). Even if precipitation is one of the versatile strategies to prepare the cathode material, it has not been reported that such a first-tier high performance is obtained from LMP prepared by precipitation methods. When compared with LMP particles synthesized by a conventional co-precipitation method, the performances are recognized to be considerably enhanced. Also, the surface-confined precipitation process described in this work does not involve a ball milling step with a conductive agent such as carbon black [1,2,4–10] so that a low cost synthesis is feasible. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Phospho-olivines (LiMPO 4 where M = Fe, Mn, Co, Ni) have been considered as one of the most potential cathode materials for LIBs, based on a well-defined two phase reaction coupled with one equivalent electron: LiMPO 4 ↔ Li + + MPO 4 + e - [1–10]. The strongest reason for interests in the materials is their relatively high theoretical capacity (∼170 mAh g -1 ) compared with that of more traditional cathode materials such as LiCoO 2 layered structure (140 mAh g -1 within a structurally stable range [11]) and LiMn 2 O 4 spinel (148 mAh g -1 [12]). However, the higher capacity of LiMPO 4 does not always lead to higher energy density because energy den- sity results from the product of its working potential as well as its capacity. LiFePO 4 , the most representative member of the phospho- olivine family, shows its energy density at 585 Wh kg -1 that is the value lower than that of LiMn 2 O 4 spinel (607 Wh kg -1 ). The main cause of the inferior energy density of LiFePO 4 is its low working potential at 3.45 V (versus ∼4.1 V for LiMn 2 O 4 ). By changing the transition metal constituent of LiMPO 4 from Fe to Mn, Co or Ni, its working potential is controlled to be higher values: 4.1 V for M = Mn in LiMPO 4 , [13]: 4.8 V for Co [14]: and 5.2 V for Ni [15]. In the case of M = Fe in phospho-olivines, we demonstrated that a sequential precipitation in which two different intermediate pre- cipitates (Li 3 PO 4 and M 3 (PO 4 ) 2 ) are formed not simultaneously but ∗ Corresponding author. ∗∗ Corresponding author. Tel.: +82 52 217 2512; fax: +82 52 217 2909. E-mail addresses: syleek@kangwon.ac.kr (S.-Y. Lee), philiphobi@hotmail.com (H.-K. Song). consecutively leads to a hollow secondary structure consisting of carbon-coated primary particles [16]. The resultant structure was helpful to overcome demerits of LiFePO 4 such as low electronic and ionic conductivities: ( e = 10 -9 to 10 -8 S cm -1 and D i = 10 -8 to 10 -7 cm 2 s -1 , respectively) [12]. In the other members of the phospho-olivine family, the demerits become even more serious with slower electronic transport ( e ) even if higher energy density is thermodynamically achievable:  e = 10 -11 to 10 -8 , 10 -11 to 10 -9 and 10 -14 to 10 -11 S cm -1 while D i = 10 -9 to 10 -7 , 10 -9 to 10 -5 and 10 -5 cm 2 s -1 for M = Mn, Co and Ni in order [6,17,18]. Therefore, the sequential precipitation method with some modification was applied to LiMnPO 4 system in this work to get the same advantages (Fig. 1). 2. Experimental 2.1. Preparation Olivine LiMnPO 4 was synthesized by precipitating Mn 3 (PO 4 ) 2 on thermally hardened Li 3 PO 4 seeds (Fig. 1). The Li 3 PO 4 seeds were precipitated by introducing 10 mmol H 3 PO 4 to a solution prepared by dissolving 30 mmol LiOH in 12 ml water. The seeds were filtered and then thermally hardened at 300 ◦ C for 3 h. The thermally hard- ened seeds were re-dispersed in 12 ml water and 10 mmol MnSO 4 was added to the re-dispersed solution. The dried mixture of Li 3 PO 4 and Mn 3 (PO 4 ) 2 was calcined at 600 ◦ C for 10 h in an inert atmo- sphere. For coating the resultant LMP, sucrose was mixed with LMP in water at 50 wt.% of the active materials followed by drying and heating at 600 ◦ C for 6 h. As a control, LMP was prepared by 0378-7753/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2012.02.078