Synthesis and characterization of layered Li1?x(Ni0.5Co0.5)1?yFeyO2(0 ≤ (1 ? x) ≤ 1 and 0 ≤ y ≤ 0.2) cathodes |
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| Institution: | 1. Department of Frontier Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan;2. Department of Materials Science and Chemistry, University of Hyogo, 2167 Shosha, Himeji, Hyogo 671-2280, Japan;3. Department of Electrical and Electronic Information Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan;4. LARMAUR Équipe Verres ERL CNRS 6274, Université de Rennes 1, Campus de Beaulieu, Rennes Cedex 35042, France |
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| Abstract: | Layered Li(Ni0.5Co0.5)1?yFeyO2 cathodes with 0 ≤ y ≤ 0.2 have been synthesized by firing the coprecipitated hydroxides of the transition metals and lithium hydroxide at 700 °C and characterized as cathode materials for lithium ion batteries to various cutoff charge voltages (up to 4.5 V). While the y = 0.05 sample shows an improvement in capacity, cyclability, and rate capability, those with y = 0.1 and 0.2 exhibit a decline in electrochemical performance compared to the y = 0 sample. Structural characterization of the chemically delithiated Li1?x(Ni0.5Co0.5)1?yFeyO2 samples indicates that the initial O3 structure is maintained down to a lithium content (1 ? x) ≈ 0.3. For (1 ? x) < 0.3, while a P3 type phase is formed for the y = 0 sample, an O1 type phase is formed for the y = 0.05, 0.1 and 0.2 samples. Monitoring the average oxidation state of the transition metal ions with lithium contents (1 ? x) reveals that the system is chemically more stable down to a lower lithium content (1 ? x) ≈ 0.3 compared to the Li1?xCoO2 system. The improved structural and chemical stabilities appear to lead to better cyclability to higher cutoff charge voltages compared to that found before with the LiCoO2 system. |
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