Thermodynamic stability, crystal structure, and cathodic performance of Li x (Mn 1/3Co 1/3Ni 1/3)O 2 depend on the synthetic process and Li content

• Published in: Solid state ionics Vol. 179; no. 17; pp. 625 - 635
• Main Authors: Idemoto, Yasushi, Matsui, Takaaki
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.2008
• Subjects: Cathode; Crystal structure; Li ion battery; Neutron diffraction; Thermodynamic stability; Thermodynamic stability; Li ion battery; Cathode; Neutron diffraction; Crystal structure
• ISSN: 0167-2738; 1872-7689
• DOI: 10.1016/j.ssi.2008.03.024

Li(Mn 1/3Co 1/3Ni 1/3)O 2 were prepared by both solution and solid-state methods and their respective delithiated phases, Li x (Mn 1/3Co 1/3Ni 1/3)O 2 were prepared by chemical delithiation. All samples were determined to be single phase, and we were able to control the composition. A sample of the compound LiMn 1/3Co 1/3Ni 1/3O 2 made by the solution method had a higher discharge capacity and better cycle performance than one obtained by the solid-state synthesis. For these compounds, the enthalpy change per mol of atoms for the formation reaction from simple oxides, Δ H R , increased with decreasing Li content and materials obtained by the solution synthesis were more thermodynamically stable than those obtained by the solid-state method. The Δ H R obtained by each synthetic method is a linear function of the Li content. These results are consistent with the lack of any structural changes in the range 0.4 < x ≤ 1.0 found by the crystal structure analysis. The electron-density images produced by a maximum entropy analysis showed that the 3a site was localized and the covalency of the 3a-6c and 3b-6c bonds decreased with decreasing Li content. The chemical diffusion coefficient of Li + did not vary with the synthetic method, reflecting the stability of the host structure. From these results, we suggest that there is a correlation between the thermodynamic stability, crystal structure and cathode performance.