Synthesis and Electrochemical characterization of LiNi 1-y Co y O 2 powders obtained by complex sol-gel process
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ABSTRACT The layered oxides, among the wide family of intercalation compounds, have received considerable attention as positive electrode materials in high-energy density lithium and lithium ion batteries. Within this frame LiNiO 2 and LiCoO 2 oxides and their solid solutions have been extensively studied as they (and the LiMn 2 0 4 spinels) are the only known materials able to intercalate reversibly lithium at high cell voltage (3.5-4 V). Recently, solid solutions such as LiNi1_xCoxO 2 have attracted the attention as alternative cathodes to the state of art LiCoO 2 in commercial rechargeable Li-ion batteries. Here we have used the Complex Sol-Gel Process (CSGP) to prepare LiNil.-CoO 2 (x= 0, 0.25, 0.5, 0.75, 1). Starting sols were prepared from Li+(1-x)Ni2 +-xCo + acetate aqueous solution in two different routes. According to route-A aqueous ammonia was added to a starting solution containing 0.2M ascorbic acid (ASC) on 1M total Me. According to route B the starting acetate solutions were first alkalized by ammonia and then the ascorbic acid was added. Regular sols were concentrated to 1/3 of their initial volume and dried slowly up to 1701C. Thermal transformation of the gels to solids was studied by XRD and IR. The electrochemical properties of the compound LiNiO. 75Co 0 2502 prepared by the RouteA were evaluated and reported.
1. INTRODUCTION Lithium ion 'rocking-chair' batteries are the only commercially available lithium based batteries which do not suffer of the safety and rechargeability troubles associated with the use of metallic lithium as anode [1]. To overcome the loss in energy density in these systems, where intercalation anodes based on carbonaceous compounds are used, intercalation compounds having high open circuit potentials are usually employed as cathodic materials. To this date LiCoO 2, despite its high cost, is still the preferred material for commercial devices and only recently solid solutions of LiNi×Col.,O 2 have been proposed as an alternative. These materials are relatively easy to prepare and are comparable in performances to LiCoO2 except for a slightly lower discharge potential. The solid state reaction routes commonly utilised to synthesise this kind of materials have the drawback of the necessity of high temperature synthesis (HT). Tarascon [2] et al. and Barboux [3] et al. demonstrated that the HT preparation methods produced larger particles with lower cell capacity and, on the contrary, low temperature (LT) methods, such as the Sol-Gel process, produced finer particles with higher cell capacity. In a previously published work [4] we reported on the preparation and the electrochemical characterisation of the compound LiNi0 5Co 0 502 synthesised by the Sol-Gel Complex Process (SGCP). As a continuation of this work we have extended the study to the entire family of the mixed oxides LiNixCoi.xO 2, in
which x ranges from 1 to 0. In this work we describe the results obtained on the preparation of some members of this family of compounds. Moreover, we report here about some XRD, SEM,
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