DFT Electronic Properties and Synthesis Thermodynamics of Li _x La_1−x TiO₃ Electrolytes for Li-Ion Batteries

Abstract

Lithium lanthanum titanate perovskites Li x La1−x TiO3 (LLTO) are promising solid-electrolytes for Li-ion batteries. We studied, in the Density-Functional-Theory framework, the thermodynamic stability and the electronic and magnetic properties of LLTO, as bulk materials and as thin slabs with (001) exposed surfaces. Results show that LaTiO3 (LTO) exhibits semiconductor behavior and G-type antiferromagnetic order (AFMG), whereas the TiO2-terminated LTO slab is a semiconductor with ferromagnetic (FM) order. Contrasting, the LTO slab exposing a LaO-terminated surface is a conductor with AFMG ordered Ti cations' magnetic moments (MMs), but at the surface there are some FM ordered MMs (La atoms). LLTO bulk electrolyte is a semiconductor (x = 0.25) or insulator (x = 0.50). The LLTO slab is a FM (non-magnetic) conductor (TiO2 (LiO)-terminated surface) or a FM semiconductor (LaO-terminated). Besides, the stability of the LLTO bulk and slabs structures was analyzed, as well as the slabs’ preferences for LiO, LaO or TiO2 ends.

Effects of High Hydrostatic Pressure on the Structural, Electronic, and Elastic Properties, and Li-Ion Diffusion Barrier of Lithium Lanthanum Titanate Electrolytes: A DFT Study

“…1a), as in previous reports. 16,50,51 In this work, only Li concentration x = 0.50 was considered, for two reasons: (i) to maintain the charge neutrality in the LLTO unit cell through the oxidation states presented by the Li + , La 3+ , Ti 4+ , and O 2− , taking care that the oxygen anions have completed their octet (i.e., eight electrons surround each O atom) and, consequently, their oxidation state 2-(this guarantees the energetic stability of LLTO perovskite); (ii) although the first requirement is met with x = 0.25 (for charge neutrality, the Ti cations have a mixed oxidation state of 3+ and 4+, as described in previous work, 16 where using the formal charges, the unit stoichiometric formula is Li + 0.25 La 3+ 0.75 Ti 3+ 0.5 Ti 4+ 0.5 O 2-3 or Li + La 3+ 3 Ti 3+ 2 Ti 4+ 2 O 2-12 by unit cell), the results showed that this LLTO compound is mechanically unstable. At zero GPa, the LLTO electrolyte presents a low-symmetry structure (triclinic) with 21 independent elastic stiffness coefficients after the geometric optimization process.…”

“…Using these requests, three LLTO configurations with nonequivalent structural, electronic, and elastic properties are found. 16 These LLTO structures are labeled as layered, columnar, and rocksalt bulk phases (LLTO-L, -C, and -RS, respectively). 53 In the LLTO-L, -C, and -RS structures, La 3+ are replaced by Li + at the sites (1, 2), (1,4), and (2, 4), respectively (Figs.…”

“…This could reduce the energy gap and promote the electrons associated with the Ti 3+ to the conduction band, which is not desired in an SSE. [16][17][18] Likewise, the surface area contact between the electrode and the SSE is not optimal as in the case of liquid electrolytes. 12 Nevertheless, these problems could be solved if, for example, the anode were replaced by another material that has high specific and volumetric capacity and a low electrical potential as Si, 19 which is more abundant and cheaper than Li, as well as incorporating methods of synthesis that ensure surface contact between the electrode and the electrolyte, such as growing Si semiconductors with a diamond-like structure on an LLTO substrate with a perovskite-like structure.…”

Stable Li|LAGP Interface Enabled by Confining Solvate Ionic Liquid in a Hyperbranched Polyanionic Copolymer for NASICON-Based Solid-State Batteries

“…1−7 Therefore, safety is one of the most critical issues to be solved in developing large-scale applications for secondary lithium batteries with long cycling life. 7−12 Compared with the organic liquid electrolytes, ceramic electrolytes, such as NASICON, 13 perovskites, 14 garnet, 15 and sulfide-type ceramic/glass, 16 have the advantages of non-flammability, a high shear modulus (10−100 GPa) 17 against Li dendrite growth, and a high Li-ion transference number (t Li+ ≈ 1) at room temperature (R.T.). 18−21 Thus, all-solid-state lithium−metal batteries are recognized as the best candidate for next-generation energy storage by replacing the liquid electrolyte with a solid electrolyte (SE).…”

“…Traditional commercial lithium-ion batteries usually use toxic, flammable, and corrosive liquid (organic) electrolytes, thereby bringing potential safety hazards, such as battery explosion and short circuits caused by thermal runaway behavior and uncontrolled growth of lithium dendrites. − Therefore, safety is one of the most critical issues to be solved in developing large-scale applications for secondary lithium batteries with long cycling life. − Compared with the organic liquid electrolytes, ceramic electrolytes, such as NASICON, perovskites, garnet, and sulfide-type ceramic/glass, have the advantages of non-flammability, a high shear modulus (10–100 GPa) against Li dendrite growth, and a high Li-ion transference number ( t Li+ ≈ 1) at room temperature (R.T.). − Thus, all-solid-state lithium–metal batteries are recognized as the best candidate for next-generation energy storage by replacing the liquid electrolyte with a solid electrolyte (SE). − Unfortunately, these SEs suffer from physicochemical stability issues, including high impedance at solid/solid interfaces and poor chemical stability in contact with Li metal, which hinder the application of solid-state batteries.…”