Appl Phys A DOI 10.1007/s00339-013-7768-2 Effects of high-energy milling on the solid-state synthesis of pure nano-sized Li 4 Ti 5 O 12 for high power lithium battery applications Seung-Woo Han · Joayoung Jeong · Dang-Hyok Yoon Received: 12 March 2013 / Accepted: 8 May 2013 © Springer-Verlag Berlin Heidelberg 2013 Abstract Li 4 Ti 5 O 12 was synthesized from Li 2 CO 3 and anatase TiO 2 using different degree of milling to test the hy- pothesis that finer starting materials can result in a smaller Li 4 Ti 5 O 12 particle size and better high-rate discharging ca- pacities. The degree of milling was controlled using three different ZrO 2 media sizes for 3 hours of high-energy milling, whereas 5 mm balls were used for 24 hours ball milling. High-energy milling produced significantly finer starting materials and Li 4 Ti 5 O 12 particles compared to those produced by ball milling. Among the three different balls used in high-energy milling, the 0.10 mm media showed the most favorable results. Pure Li 4 Ti 5 O 12 with a mean particle size of 146 and 175 nm were synthesized by an economic solid-state reaction combined with high-energy milling us- ing 0.05 and 0.10 mm beads, respectively. These pure nano- sized Li 4 Ti 5 O 12 exhibited a much higher specific capacity and superior rate capability than those of coarse rutile TiO 2 - contained Li 4 Ti 5 O 12 particles. 1 Introduction Spinel-type lithium titanate (Li 4 Ti 5 O 12 ) is a promising anode material for high power lithium-ion batteries ow- ing to its high structural stability and capability for rapid charging [1, 2]. Based on previous reports, the overall S.-W. Han · D.-H. Yoon ( ) School of Materials Science and Engineering, Yeungnam University, Gyeongsan 712-749, Korea e-mail: dhyoon@ynu.ac.kr Fax: +82-53-8104628 J. Jeong Cell Precedence Development Group, Samsung SDI, Yongin 446-577, Korea variation of the Li 4 Ti 5 O 12 lattice parameter during the lithiation/delithiation process is ∼0.07 %, changing from 8.3538 to 8.3596 Å, which is almost negligible [3–5]. Li 4 Ti 5 O 12 has been also suggested to confer a faster charg- ing/discharging rate due to its 3-dimensional Li + diffusion path than the current 2-dimensional graphite anode. In addi- tion, the possible safety problems originating from the de- position of highly reactive lithium metal in a graphite anode can be avoided because of the high Li insertion potential (1.55 V vs. Li/Li + ) of Li 4 Ti 5 O 12 [6]. Li 4 Ti 5 O 12 is generally synthesized by an economic solid- state reaction using TiO 2 and Li 2 CO 3 followed by heat treatment at 800–900 ◦ C. Nevertheless, two main barriers, i.e., the coarse particle size and low purity of Li 4 Ti 5 O 12 , have arisen with this powder for high power applications. A coarse particle hinders rapid Li + intercalation and de- intercalation owing to its long diffusion path and reduced electrode–electrolyte contact area. For this reason, wet chemical methods have been used to synthesize fine par- ticles despite their high cost [7, 8]. On the other hand, the presence of rutile TiO 2 transformed from anatase TiO 2 in the final product, which is very difficult to eliminate even by a calcination at 900 ◦ C for 15 hours, is an important issue as- sociated with the solid-state synthesis of Li 4 Ti 5 O 12 [9]. Al- though the theoretical capacity of TiO 2 for Li + insertion is 335 mAh/g, bulk rutile TiO 2 can insert/extract only negligi- ble amounts of Li + with a capacity of ≈50 mAh/g [10–12], which decreases the capacity and rate property. Therefore, the synthesis of pure Li 4 Ti 5 O 12 is very important for en- hancing the electrochemical properties. Recently, a breakthrough has been made in the produc- tion of fine particles using a solid-state reaction due to the introduction of high-energy milling, which enables efficient reduction of the starting materials. Compared to ball milling, high-energy milling has significantly higher milling effi-