INTERFACE ANALYSIS OF LICL AS PROTECTING LAYER ON LI1.3AL0.3TI1.7(PO4)3 SOLID ELECTROLYTE: FIRST PRINCIPAL STUDY

• Main Author: Sohib, Ahmad
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/62953
• Institution: Institut Teknologi Bandung

The all-solid-state battery (ASSB) is a battery technology innovation that proposes a safety aspect in its application. The main component that differs ASSB from the conventional battery is the solid electrolyte. As an ionic conductor, a solid electrolyte also acts as a separator between cathode and anode. Among various types and structures of solid electrolyte available today, Li1.3Al0.3Ti1.7(PO4)3 (LATP) is a viable option to be applied in a battery. Along with its high ionic conductivity of 10-4 S/cm, LATP has excellent stability against O2 and even moisture in the air, which makes it easier to synthesize. However, inorganic solid electrolytes, such as LATP, still have some issues, especially when in contact with Li anode. Electrons can get through from the anode to the LATP surface and reduce Ti4+ to Ti3+in LATP. The reduction of Ti4+ causes the formation of a layer with lower ionic conductivity and prevents the transfer between LATP and the Li metal. Therefore, several approaches have been utilized to address this problem, including the application of protecting layer in between a solid electrolyte and Li metal. For this purpose, materials with insulating properties are required to prevent electron flow from Li to the LATP surface. However, this protecting layer needs good ionic conductivity to assure facile Li+ conduction. LiCl is a material belonging to lithium binary halides that can be used as a protecting layer in the Li/LATP system for its ability to transfer Li-ions. However, the investigation related to these properties has not been reported, particularly as a protecting layer for LATP. Therefore, we utilize computational modeling to investigate and assess the LiCl potential as a protective barrier between LATP electrolytes and Li metal in this work. The first principle study was carried out via density functional theory (DFT) method to simulate bulk structure and heterostructure. The DFT method is implemented in Vienna Ab-initio Simulation Package (VASP) version 5.4, which is based on the Functional Perdew-Burke-Ernzerhof (PBE) – Generalized Gradient Approximation (GGA) for calculating the total energy convergence. The calculated total energy for the bulk structure indicates that the lattice parameters for the structures Li metal, LiCl, and LATP agree with the experimental results with an error of 0.29%, 1.78% (lattice constant a LATP), and 1.43% (lattice parameters c LATP) respectively. The band gaps for each of these structures are then obtained of 0 eV, 6.25 eV, and 2.30 eV, respectively. Based on the Conduction Band Minimum (CBM), the existance of LiCl on the LATP surface hopefully could restrict electron flows from Li metal to the LATP surface. To analyze the interface between Li metal as negative electrode, LiCl as proecting layer, and LATP solid electrolyte, Li/LiCl and LiCl/LATP heterostructures were constructed using Li (001), LiCl (001)/(111), and LATP (012). The lattice-fit of each material was optimized employing a particle swarm optimization (PSO) algorithm which was implemented within CALYPSO. The lattice-fit of the materials exhibited >99% for Li/LiCl heterotructures, and >94% for LiCl/LATP heterostructure. The optimum distance for the heterostructure-constructing materials is 2.00 ? – 2.25 ? for the Li/LiCl and 2.00 ? - 2.75 ? for the LiCl/LATP. Based on interface analysis of DOS in Li/LiCl heterostructure, it was shown the electron transfer could only occur on the LiCl surface. In the Li/LiCl (001)/(111) heterostructure, the insulating properties began at a thickness of 4.3 ?. From the DOS analysis on the LiCl/LATP heterostructure, a trap state was emerged in LiCl (111) band gap, as a result of the atomic interaction and atomic bonding formed at the interfaces. The existence of the trap state, electron transfer can not migrate to the LATP surface. These results indicate that LiCl (111) is such a potential protecting layer on LATP that the reduction of Ti4+ due to electron migration to the LATP surface can be avoided.