Highly reversible capacity nanocomposite anode for secondary lithium-ion batteries Alok Kumar Rai a , Jinsub Lim a , Vinod Mathew a , Jihyeon Gim a , Jungwon Kang a , Baboo Joseph Paul a , Donghan Kim a , Seungho Ahn b , Saheum Kim b , Kyunyoung Ahn b , Jaekook Kim a, ⁎ a Department of Materials Science and Engineering, Chonnam National University, 300 Yongbong-dong, Bukgu, Gwangju 500-757, Republic of Korea b Hyundai Motor, 231, Yangjae-dong, Seocho-gu, Republic of Korea abstract article info Article history: Received 16 February 2012 Received in revised form 27 February 2012 Accepted 27 February 2012 Available online 6 March 2012 Keywords: Lithium ion batteries TiP 2 O 7 Li 2.6 Co 0.4 N Irreversibility compensation Blending A TiP 2 O 7 /Li 2.6 Co 0.4 N composite anode electrode is prepared to reduce the initial high irreversible capacity of TiP 2 O 7 and Li 2.6 Co 0.4 N, which hinders their potential application in lithium-ion batteries. The new composite electrode not only eliminates the initial irreversibility, but also provides reversible capacities. Moreover, this new composite electrode presents initial discharge and charge capacities of 652.57 mAh/g and 647.54 mAh/g, respectively, with a capacity retention of 98% after 20 cycles. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Finding anode materials with high capacities for lithium intercala- tion and improved cyclability is an important research subject for Li- ion batteries. To replace the conventional graphite anode that suffers from severe limitations, such as its low capacity, a series of anode ma- terials have been proposed. In this context, polyanionic compounds comprising a 3-D structural frame-work of phosphates appear to offer an exciting prospect for Li-ion mobility at lower potentials. In particular, transition metal phosphates such as titanium pyrophos- phate, with a low Ti 4+ /Ti 3+ redox potential (~ 1.5 V) versus Li/Li + represents an attractive anode for Li-ion batteries. Initially, TiP 2 O 7 was investigated as a cathode material and displayed a fair plateau around 2.6 V vs. Li/Li + upon discharging [1]. However, recently, a re- port demonstrated that this pyrophosphate exhibited fairly reason- able capacities at low potentials of 0–1.5 V when used as an anode in a Li-ion battery with an aqueous electrolyte [2]. Unfortunately, a serious disadvantage hindering the practical use of this material is its high irreversible capacity in the first cycle attributed to the forma- tion of irreversible lithium compounds. On the other hand, lithium cobalt nitride Li 2.6 Co 0.4 N (LCN), as anode displaying capacities greater than 700 mAh/g with impressive cycle abilities (0.7 V versus Li on average), has been studied [3,4]. However, a major barrier to the use of lithium transition metal nitride anodes are their Li-rich structure and resulting irreversible charge capacity in the initial cycle [5,6]. Therefore, in the case where LCN is combined with high-potential cathodes, the lithium ion should be extracted first in either a chemical or electrochemical way [7]. However, by mixing Li 2.6 Co 0.4 N with lithium storage metals or oxides, it is expected that the active lithium within it can compensate for the first irreversible capacity. In this study, we developed a novel hybrid nanocomposite anode composed of Li 2.6 Co 0.4 N and TiP 2 O 7 which is free not only from the ini- tial irreversible discharge/charge capacity observed in the individual materials but also with balanced and higher electrochemical stabilities. 2. Experimental 2.1. Preparation of TiP 2 O 7 , Li 2.6 Co 0.4 N and TiP 2 O 7 /Li 2.6 Co 0.4 N composite Nanocrystalline titanium pyrophosphate TiP 2 O 7 was prepared by the co-precipitation method. The typical procedure used for the syn- thesis is as follows: appropriate molar concentrations of Li-acetate (CH 3 COOLi 99% Junsei Chemicals, Japan), titanium tetraisopropoxide (TTIP, 98% Junsei Chemicals, Japan) and H 3 PO 4 (85%) were dissolved in distilled water, while the pH of the solution was controlled by am- monium hydroxide. The solution was stirred at mild temperatures ranging from 60 to 80 °C for several hours to facilitate the evapora- tion of water and subsequently the precipitate was dried at 120 °C for 12 h in an oven. The final powder was obtained after annealing the as-prepared samples at 600 °C for 3 h in air and is hereafter denoted as TPO. The preparation of lithium cobalt nitride, Li 2.6 Co 0.4 N was achieved using the starting materials Li 3 N (99.5%, Aldrich) and cobalt (Co) Electrochemistry Communications 19 (2012) 9–12 ⁎ Corresponding author. Tel.: + 82 62 530 1703; fax: + 82 62 530 1699. E-mail address: jaekook@chonnam.ac.kr (J. Kim). 1388-2481/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.elecom.2012.02.036 Contents lists available at SciVerse ScienceDirect Electrochemistry Communications journal homepage: www.elsevier.com/locate/elecom