The impact of oxygen vacancies on lithium vacancy formation and diffusion in Li2-MnO3-

Abstract

High-capacity battery cathode materials containing Li 2 MnO 3 appear to be activated during the first electrochemical cycle through the generation of oxygen vacancies. These oxygen vacancies have been predicted to alter the atomistic scale structure of Li 2 MnO 3 and thus impact the delithiation process. In order to understand the effects of these oxygen vacancies we computationally determine the location of lithium removal in Li 2 MnO 3-δ (δ=0, 0.0625 and 0.125) and study lithium diffusion in Li 2-x MnO 3-δ. This study shows that it is energetically favorable for the lithium vacancies to form in the neighboring positions of the oxygen vacancies, suggesting that there is a strong interaction between the two vacancy types. This interaction also inhibits the diffusion of the lithium-ions, as seen in ab-initio molecular dynamics simulations where less hopping of lithium atoms is observed when oxygen vacancies are present. Additionally, the oxygen vacancy containing structures lead to an increase in the energy barrier for lithium hopping and the calculated diffusion coefficient decreases by ~5 orders of magnitude from the perfect crystal structure.

Unveiling the Role of Oxygen Vacancy in Li2MnO3 upon Delithiation

“…In more detail, for perfect Li 2 MnO 3 , the change of Li-ion extraction energy is rather small in the considered Li content. While, for V O -Li 2 MnO 3 , Li-ion extraction energy gradually increases and then fluctuates in a small range when the number of Li extraction is larger than or equal to 5 which is consistent with the previous work . Bader charge is used to explore the charge distribution in Li 2 MnO 3 and V O -Li 2 MnO 3 during the delithiation.…”

Overview of the Oxygen Behavior in the Degradation of Li2MnO3 Cathode Material

“…Although Li 2 MnO 3 and its composite have a proven large capacity, the capacity fade occurs quickly during the cycling due to degradation, thereby limiting its practical use as a cathode. This degradation has been suggested to originate from complex phenomena such as the oxygen release, − phase transformation, − and Li + /H + exchange reaction, − but the detailed mechanisms governing these degradation behaviors have not been fully understood yet.…”

Temperature-dependent Li vacancy diffusion in Li4Ti5O12 by means of first principles molecular dynamic simulations

“…First, a comparison of the obtained trajectory in a fixed interval with the perfect crystalline structure was performed to determine the positions of the vacancies and extract diffusion pathways. 41 Second, the vacancy position was determined based on the site occupation, assuming that the crystallographic sites are known. Thus, the distance between the ion and the crystallographic site is smaller than twice the vibrational amplitude.…”