Electrochimica Acta 50 (2005) 1225–1232 Influence of oxidative stabilization on the electrochemical behaviour of coal tar pitch derived carbons in lithium batteries A. Concheso a , R. Santamar´ ıa a , M. Granda a , R. Men´ endez a , J.M. Jim´ enez-Mateos b , R. Alc´ antara c , P. Lavela c,∗ , J.L. Tirado c a Instituto Nacional del Carb ´ on, CSIC. Apartado 73, 33080 Oviedo, Spain b REPSOL YPF. Ctra. N-V km 18, 28930 M´ ostoles, Madrid, Spain c Laboratorio de Qu´ ımica Inorg´ anica, Universidad de C´ ordoba, Campus de Rabanales,14071 C´ ordoba, Spain Received 27 February 2004; received in revised form 27 April 2004; accepted 31 July 2004 Available online 2 October 2004 Abstract A commercial coal tar pitch was thermally treated at 430 ◦ C for 4 h and then submitted to hot filtration in order to separate the isotropic phase from the mesophase developed during the treatment. Each phase was then oxidatively stabilized in order to preserve its structure during carbonization and then carbonized at temperatures ranging from 700 to 1000 ◦ C. The effect of the microstructure, particle morphology and chemical composition of the carbons and also the influence of their carbonization temperature on the electrochemical behaviour as electrode materials in lithium cells were studied. Galvanostatic cycling of lithium test cells using the carbon materials as positive electrodes showed the improvement of the electrochemical performance in both isotropic and anisotropic phases by stabilization with air previous to carbonization. More subtle differences between isotropic and anisotropic samples were evidenced and interpreted in terms of their textural properties. Moreover, the electrochemical impedance spectroscopy (EIS) has been demonstrated to be an interesting technique to elucidate the changes occurred in the electrode interfaces when these coal tar pitch based carbons are cycled. © 2004 Elsevier B.V. All rights reserved. Keywords: Lithium; Battery; Mesophase; Coal tar pitch; Oxidative stabilization 1. Introduction Since the advent of the lithium-ion concept, the advan- tages of the use of carbonaceous materials as anodes in this type of batteries have been evident [1,2]. Low temperature coal and petroleum cokes have been widely studied because of their economic advantages [3,4]. However, some techni- cal problems remain unsolved due to the occurrence of an initial irreversible capacity caused by partial electrolyte de- composition during the beginning of the first discharge [5]. The irreversible capacity of the negative electrode leads to the misuse of part of the cathode active material, with the conse- quent technical and economical disadvantages. Fortunately, ∗ Corresponding author. Tel.: +34 957218637; fax: +34 957218621. E-mail address: iq1lacap@uco.es (P. Lavela). the deposition of solid products formed by electrolyte de- composition on the carbon particle surface renders basically a passivating layer that inhibits of this phenomenon on further cycling. The reduction of the initial irreversibility is still one of the main challenges for researchers working in this area. In this sense, the contribution to irreversible capacity of factors such as the nature of the carbon, the carbonization temper- ature or the role of chemical modifications are evaluated to optimize the performance of these electrode materials. Carbon materials are often grouped into two categories, soft and hard carbons, attending to their thermal and mi- crostructure properties. Soft carbons present anisotropic tex- ture when observed by optical microscopy and are also called graphitisable carbons, as they can be converted into graphite by high temperature treatment (>2000 ◦ C). On the other hand, hard carbons have an isotropic texture and they cannot be 0013-4686/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.electacta.2004.07.054