Solid-State Redox Reactions of LiNi1 / 2Co1 / 2 O 2 ( R 3¯m ) for 4 Volt Secondary Lithium Cells
Abstract
LiNi(1/2)Co(1/2)O2 (R3 bar m; a = 2.84 angstroms, c = 14.1 angstroms in hexagonal setting) whose parent structure was a solid solution of LiNiO2 and LiCoO2 was prepared and examined in a nonaqueous lithium cell. The oxidation of LiNi(1/2)Co(1/2)O2 and reduction of d'Alembertian Ni(1/2)Co(1/2)O2 proceeded reversibly in the voltage range above 3.5 V. X-ray diffractional examinations indicated the reaction proceeded in a topotactic manner. During the oxidation of LiNi(1/2)Co(1/2)O2, the c-axis dimension elongated from 14.1 to 14.5 angstroms and the a-axis shortened from 2.84 to 2.80 angstroms almost linearly as a function of x in Li(1-x)Ni(1/2)Co(1/2)O2 until x reached about 0.5. Consequently, the lattice volume remained almost invariable at 98.5 angstroms(exp 3). Further oxidation resulted in the shrinkage of the c-axis dimension and the elongation of the a-axis. Detained open-circuit voltage measurements also were carried out. The open-circuit voltages varied as a function of x in Li(1-x)Ni(1/2)Co(1/2)O2 following a hyperbolic tangent curve, not an S-shaped Nernstian curve. The composition-dependent open-circuit voltage curve together with the XRD observations indicated that the reaction proceeded in a homogeneous phase. Differences and similarities of the solid-state redox reactions among LiNiO2, LiNi(1/2)Co(1/2)O2, and LiCoO2 were discussed.
- Publication:
-
Journal of the Electrochemical Society
- Pub Date:
- August 1994
- DOI:
- 10.1149/1.2055051
- Bibcode:
- 1994JElS..141.2010U
- Keywords:
-
- Electrochemistry;
- Electrodes;
- Lithium Oxides;
- Oxidation-Reduction Reactions;
- Solid Solutions;
- Storage Batteries;
- Cobalt Oxides;
- Crystal Lattices;
- Electrical Measurement;
- Nickel Oxides;
- X Ray Analysis;
- Electronics and Electrical Engineering