Yeqing Chen

Nonlinear thermal expansion in Li 2 NiMn 3 O 8

A lattice thermal expansion study on Li 2 NiMn 3 O 8 , a high-voltage cathode material for lithium-ion batteries, was carried out by high-temperature X-ray diffraction from room temperature to 973 K. Rietveld refinement of a high-quality room-temperature diffraction pattern confirmed that Li 2 NiMn 3 O 8 has the cubic Al 2 MgO 4 spinel type of crystal structure. The analysis of the high-temperature X-ray diffraction patterns showed that the Li 2 NiMn 3 O 8 structure remained stable and no phase transition was detected over the temperature range from 298 to 973 K. As expected, the value of lattice parameter a or unit cell volume V increases with increasing temperature. The increase in a or V is linear only in the low-temperature region and nonlinear over the entire temperature range from 298 to 973 K. Least-squares analysis of the data for a or V showed the thermal expansion of a or V for Li 2 NiMn 3 O 8 can best be fitted by a 3-degree polynomial function of temperature. The linear thermal expansion coefficients for a and V averaged over the entire temperature range from 298 to 973 K were also calculated, and α T a =1.10×10 −5 K −1 ; α T V =3.29×10 −5 K −1 .