Chemical delithiation, thermal transformations and electrochemical behaviour of iron- substituted lithium nickelate.
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Chemical delithiation, thermal transformations and electrochemical behaviour of ironsubstituted lithium nickelate. Pedro Lavela, Carlos Pérez-Vicente, and José L. Tirado Laboratorio de Química Inorgánica, Universidad de Córdoba, Campus de Rabanales. Edificio C3, Planta 1. 14071 Cordoba, Spain ABSTRACT Chemical deintercalation in Fe-substituted lithium nickelate and its effects on the thermal stability and electrochemical behaviour are studied. A sample with Fe:Ni ratio of 1:9 was used as the starting material. Chemical deintercalation of the ceramic product was achieved by acid treatment with 0.6 M aqueous hydrochloric acid solutions at room temperature. The atomic Fe:Ni ratio remained unaffected while the Li:(Fe+Ni) ratio decreased significantly down to ca. 0.5 after acid treatment. Infrared spectroscopy was used to discard a proton exchange side reaction. The initial open circuit voltage (OCV) of non-aqueous electrolyte lithium cells using the chemically deintercalated solids was ca. 3.7 V, while 3.0 V were obtained with the pristine oxide. Heat treating the deintercalated solids lead to oxygen evolution at 230ºC with the formation of spinel rock-salt structure solids at 600ºC. The improved thermal stability as compared with iron-free lithium nickelate is an interesting factor for battery safety.
INTRODUCTION The solid state chemistry of layered lithium nickelate is extremely attractive from an academic point of view, but also due to its aptitude towards relevant applications in advanced battery technology. Although its structure and intercalation properties were evaluated more than forty years ago [1, 2], recent works are still devoted to improve its synthesis [3, 4], structural characterization [5, 6] and electrochemical performance [7]. Within the latter objective, partial replacement of nickel by Mn [8], Fe [9], Co [10, 11], Al [12] and/or Mg [10, 11, 13] has allowed the formation of new materials with more or less success in improving the capacity and cycling properties. Recently, the electrochemical behavior of iron-substituted lithium nickelate was studied [13]. 57Fe Mössbauer spectroscopy revealed the simultaneous oxidation of nickel and iron in the electrochemical cell. On the other hand, the possible oxidation of the transition metal together with lithium extraction by chemical procedures was early reported [14, 15]. The chemical delithiation with hydrochloric acid of lithium nickelate takes place by disproportionation of nickel(III), leading to a partial dissolution of the solid with a simultaneous oxidation of nickel in the remaining solid. The chemical deintercalation process was shown to induce several transformations in the solid, including the loss of oxygen with a conversion to the spinel structure at ca. 270ºC and the final conversion to a rock-salt related solid [15]. The aim of this communication is to extend the study of the chemical deintercalation reactions to Fe-substituted lithium nickelate, and to evaluate the effects of this substitution on the thermal stability and electrochemical beha
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