Oxygen Vacancy and Doping Effects on Li+ Ion Migration in Li4Ti5O12

1.Abstract

Li4Ti5O12 is recognized as one of the most promising anode materials for high power Li ion batteries. However, it exhibits low electronic and low ionic conductivities, which do not meet rate performance requirements for use in electric vehicles (EV). Recently, it has been shown that a simple thermal treatment to introduce oxygen vacancy in Li4Ti5O12 could improve the electronic conductivity and cycling performance of Li4Ti5O12. In addition,
various doping such as Mg2+, Al3+, Mo4+, Br-, and Cl- have been shown to promote higher electronic and ionic conductivities and stable cycling performance. However, despite the effectiveness of oxygen vacancy and doping treatments in Li4Ti5O12 that reported in previous experimental studies, there is still a lack of information on how those treatments directly affects or alters Li+ ion migration pathways at atomic level.
The main objectives of this proposed study are to investigate the relationship between the Li4Ti5O12 crystal structure and the ionic conductivity (Li
+ ion migration) in the presence of oxygen vacancies and various cationic/anionic doping in Li4Ti5O12 during Li insertion/extraction process. The first-principle simulations are employed to theoretically study the crystal structure, lattice parameter, band gaps, vibrations of atoms, and Li+
ion diffusion energy barriers. The calculation results would also be complemented with XRD, IR and Raman spectroscopies, and charge-discharge rate measurements of pretreatment LTO samples for insightful analysis and understandings.

2.Keywords
Li4Ti5O12, doping , ionic conductivity, density functional theory.
3.Objective

This proposed research is a part of collaborative research between theoretical and experimental groups in Research Center of Physics, LIPI that meant to assist the ongoing research in synthesizing in-house modified LTO-based anode materials. In general, there are three main tasks that become the objectives of DFT-based simulation, they are:
1) Elucidate the mechanism of oxygen vacancy and metal doping in controlling Li+
ion migration in Li4Ti5O12 to pursue the pathways with the lowest energy
barriers.
2) Draw useful information from available Li4Ti5O12 data measurements using
comparative analysis between DFT and characterization results.
3) Make suggestions to further improve synthesis methods in manipulating atoms
at nanoscale based on DFT predictions.

4.Methodology

The ab initio calculations would be performed under the DFT framework as implemented in the Quantum Espresso package using generalized gradient approximation (GGA) [33] parameterized by Perdew-Burke and Ernzerhof (PBE). The projector augmented wave (PAW) method with a plane wave cut-off of 80 Ry was used. The pseudopotentials approach was adopted where Li (1s2 2s1), Ti(3d2 4s4), and O (2s2 2p 4 ) used as valence states. For finding the equilibrium lattice parameter of perfect Li4Ti5O12, scf calculations on a unit cell Li10Ti14O32 consisting 56 atoms with k-point meshes for Brillouin zone sampling of 4 x 4 x 4 was carried out within the Monkhorst-Pack scheme. The calculation results are summarized in Table 6. As the material is insulator (non-magnetic), spin-polarization scheme will not be included in the calculations. Gaussian smearing was used with a small broadening width of 0.01 Ry. The numerical integration of the Brillouin zone and energy cutoff were reached to produce absolute energy convergence to better than 10-4 Ry/atom, with the forces at each atom converged to within 10-3 Ry/au by the relaxation of internal positions and cell volume.

5.Team

Achmad Subhan, Ferensa Oemry ( Research Center for Physics � LIPI ).

Fadjar Fathurrahman (Department of Engineering Physics � Institut Teknologi Bandung).

6.Computation plan (required processor core hours, data storage, software, etc)

48 processors.
20 GB data storage.
Quantum espresso.

7.Source of funding
Ristek
8.Target/outputs
1 publication per year
9.Date of usage
01/06/2017 - 31/10/2019
10.Gpu usage
-
11.Supporting files
prop_1496028047.pdf
12.Created at
29/05/2017
13.Approval status
approved