Probing Anharmonic Lattice Dynamics and Thermal Transport in Layered Perovskite LiYTiO4 Anode

TL;DR

This work analyzes anharmonic lattice dynamics and thermal transport in LiYTiO4 using a NEP-based framework that couples temperature-dependent effective potentials with Wigner thermal transport, alongside Green–Kubo MD and experimental measurements. It reveals dynamical instabilities at 0 K that are stabilized by anharmonic renormalization, and predicts a room-temperature lattice thermal conductivity near 3.8 W m⁻¹ K⁻¹ that agrees with experimental 3.2 ± 0.08 W m⁻¹ K⁻¹; both approaches indicate Li-ion mobility contributes negligibly to κL. The study also decomposes κL into particle-like and wave-like (coherence) channels, showing significant wave-like contributions and strong 4ph scattering effects, particularly at elevated temperatures. Overall, LiYTiO4 exhibits ultralow κL, posing thermal-management challenges for its application as a high-rate, low-potential LIB anode, and the methodology provides a transferable framework for predicting thermal transport in complex battery materials.

Abstract

Layered perovskite lithium yttrium titanate ($\rm LiYTiO_4$) has recently emerged as a promising low-potential, ultrahigh-rate intercalation-type anode material for lithium-ion batteries; however, its lattice dynamics and thermal transport properties remain poorly understood, limiting a complete evaluation of its practical potential. Here, we combine experimental measurements with theoretical modeling to systematically investigate the anharmonic lattice dynamics and heat transport in $\rm LiYTiO_4$. We employ a neural evolution potential (NEP)-based framework that integrates the temperature-dependent effective potential method with the Wigner thermal transport (WTT) formalism, explicitly including both diagonal and off-diagonal terms of the heat-flux operator. Zero-temperature phonon calculations reveal dynamical instabilities associated with $\rm TiO_6$ octahedral rotation, which are stabilized at finite temperatures through anharmonic renormalization. Using the WTT approach with contributions from phonon propagation and coherence contributions, we predict a room-temperature lattice thermal conductivity ($κ_{\rm L}$) of 3.8 $\rm Wm^{-1}K^{-1}$ averaged over all crystal orientations, in close agreement with the measured value of 3.2 \pm 0.08 $\rm Wm^{-1}K^{-1}$ for polycrystalline samples. To further examine the possible influence of ionic motion on high-temperature thermal transport, we compute $κ_{\rm L}$ using a Green-Kubo equilibrium molecular dynamics approach based on the same NEP, which yields consistent results with both experiment and WTT predictions, confirming the negligible role of Li-ion mobility in heat conduction. Our study not only identifies the ultralow thermal conductivity of $\rm LiYTiO_4$ as a key limitation for its practical application but also establishes a reliable computational framework for studying thermal properties in battery materials.

Figures (5)

• Figure 1: Training results showing the convergence of energy, forces, stresses, and error functions. The high consistency of the diagonal correlation plot indicates the strong predictive capability of the NEP.
• Figure 2: (a) The crystal structure of layered perovskite $\rm LiYTiO_4$ (orthorhombic system, space group Pbcm) features each titanium (Ti) atom is surrounded by six oxygen (O) atoms, forming corner-sharing [$TiO_6$] octahedral units. (b) Brillouin zone of $\mathrm{LiYTiO_4}$. (c) Comparison of phonon spectra obtained from NEP at 0 K, 300 K, and 500 K. (d) Comparison of phonon density of states (PDOS) at 0 K, 300 K, and 500 K. (e) Comparison of the potential energy surfaces at (0.5, 0, 0) between the ground state and the TDEP-renormalized at 300 K, dash lines show the potential energy surface decomposed to the second, fourth and sixth orders, respectively. (f) The crystal structure of $\mathrm{LiYTiO_4}$ together with the displacement pattern of the soft phonon mode at the X point.
• Figure 3: (a)Temperature-dependent mean square displacement (MSD) of Li atoms from 300 to 800 K. (b) Comparison of RDF at 300 and 800 K. (c)The heat flux autocorrelation function at 300 K. (d)The running thermal conductivity averaged over three crystallographic directions, computed using EMD method at 300 K.
• Figure 4: (a) Comparison of phonon lifetimes due to three-phonon and four-phonon scattering processes at 300 K. (b) Same as panel (a), but at 800 K. (c) Cumulative thermal conductivity due to three-phonon and four-phonon processes, decomposed into contributions from diffusons and propagating phonons. Top panel: 300 K; bottom panel: 800 K. (d) Cumulative MFP thermal conductivity at room temperature.
• Figure 5: (a) In-plane and out-of-plane thermal conductivity due to three-phonon and four-phonon scattering processes, decomposed into contributions from diffusons and propagating phonons. (b) Comparison of in-plane, out-of-plane, and averaged thermal conductivities with GKEMD simulations and experimental measurements.