Calculating Anisotropic Correlated Chemical Expansion of Oxygen and Lithium Vacancies in Li2MnO3 to Determine Vacancy Concentrations

Thursday, 1 June 2017: 10:12
Grand Salon C - Section 13 (Hilton New Orleans Riverside)
C. James (Michigan State University), L. Nation (Brown University), J. Li, N. J. Dudney (Oak Ridge National Laboratory), B. W. Sheldon (Brown University), and Y. Qi (Michigan State University)
Lithium-excess layered cathode materials for lithium-ion batteries of the form Li2MnO3-LiMO2 (M=transition metal(s)) show high capacities (>200 mAhg-1) due to the activation of the Li2MnO3 component.1 This activation process occurs during the first cycle at >4.4V, where it is widely accepted that oxygen is removed from the Li2MnO3 component. Thus, Li2-XMnO3-δ is formed upon cycling, creating a structure with both oxygen vacancies (VO) and lithium vacancies (VLi). It has been shown previously that the VLi and VO interact and that it is energetically favorable for VLi to form near VO.2 VO concentration in the Li2-XMnO3-δ is believed to be dilute, although the exact amount of VO(δ) is unclear.

To estimate the VO concentrations, calculations of the chemical expansion coefficient for vacancies in Li2MnO3 are combined with experimental stress measurements of a lithium-excess layered cathode material. The coupled VO and VLi have previously been shown to exhibit correlated anisotropic chemical expansion in Li2-XMnO3-δ at dilute concentrations.3 Thus, the chemical expansion coefficients for VO and VLi in the system are broken down into a dilute component for coupled VO and VLi and a component to capture the rest of the VLi which are far away from VO  and contribute to the high capacity of these materials. The computational results are used to interpret stress measurements from a multibeam optical stress sensor (MOSS) on Li1.2Mn0.55Ni0.125Co0.125O2.

1. Thackeray, M. M.; et al., Journal of Materials Chemistry 2007, 17(30), 3112-3125.

2. James, C.; et al., Solid State Ionics 2016, 289, 87-94.

3. James, C.; et al., MRS Advances 2016, 1(15), 1037-1042. doi:10.1557/adv.2016.48.