Li-ion battery material under high pressure: amorphization and enhanced conductivity of Li4Ti5O12

High-pressure Bandgap Engineering and Amorphization in TiNb2O7 Single Crystals

Titanium niobate (TiNb2O7) possesses excellent photocatalytic, dielectric properties, and lithium-insertion capacity. And high-pressure (HP) is a powerful tool for bandgap engineering aiming at widening their applications. Herein, we report the...

Internal resistive heating of non-metallic samples to 3000 K and >60 GPa in the diamond anvil cell

High pressure-temperature experiments provide information on the phase diagrams and physical characteristics of matter at extreme conditions and offer a synthesis pathway for novel materials with useful properties. Experiments recreating the conditions of planetary interiors provide important constraints on the physical properties of constituent phases and are key to developing models of planetary processes and interpreting geophysical observations. The laser-heated diamond anvil cell (DAC) is currently the only technique capable of routinely accessing the Earth's lower-mantle geotherm for experiments on non-metallic samples, but large temperature uncertainties and poor temperature stability limit the accuracy of measured data and prohibits analyses requiring long acquisition times. We have developed a novel internal resistive heating (IRH) technique for the DAC and demonstrate stable heating of non-metallic samples up to 3000 K and 64 GPa, as confirmed by in situ synchrotron x-ray diffraction and simultaneous spectroradiometric temperature measurement. The temperature generated in our IRH-DAC can be precisely controlled and is extremely stable, with less than 20 K variation over several hours without any user intervention, resulting in temperature uncertainties an order of magnitude smaller than those in typical laser-heating experiments. Our IRH-DAC design, with its simple geometry, provides a new and highly accessible tool for investigating materials at extreme conditions. It is well suited for the rapid collection of high-resolution P-V-T data, precise demarcation of phase boundaries, and experiments requiring long acquisition times at high temperature. Our IRH technique is ideally placed to exploit the move toward coherent nano-focused x-ray beams at next-generation synchrotron sources.

Oxygen Vacancy Enhanced Two-Dimensional Lithium Titanate for Ultrafast and Long-Life Bifunctional Lithium Storage

Boosting sufficient Li⁺ ion mobility in Li₄Ti₅O₁₂ (LTO) is crucial for high-rate performance lithium storage. Here, an ultrafast charge storage oxygen vacancy two-dimensional (2D) LTO nanosheet was successfully fabricated through a one-pot hydrothermal method. The selectively doped Al³⁺ into octahedron Li⁺/Ti⁴⁺ 16d sites not only provide bulk oxygen vacancy and appropriate distorted TiO₆ octahedra to facilitate Li⁺ ions diffusion, but also serve as a "pillar" to stabilize the Ti-O framework. The oxygen vacancy lowers Li⁺ ion diffusion energy barrier. Moreover, the 2D structure provides open diffusion channels for fast Li⁺ ion transport. As a result, the sample shows excellent electrochemical performance for bifunctional lithium storage. As a lithium-ion battery anode, the capacity retention reaches 112.8 mA h g^-1 after 5000 cycles at 40 C with a fading rate of 0.288% per 100 cycles. Meanwhile, as a lithium-ion capacitor anode, it exhibits an excellent rate capacity of 120 mA h g^-1 after 5000 cycles at 500 C with nearly 100% Coulombic efficiency. The produced LTO shows much higher rate capacity and longer lifetime than the reported LTO. Density functional theory calculations also demonstrate that oxygen vacancy can facilitate Li⁺ ion diffusion kinetics. The relationship between oxygen vacancy content and Li⁺ ions diffusion energy barrier in LTO is quantified. This work pioneers a defect engineering strategy for synthesized high-performance electrode materials.

Predicted stable Li5P2 and Li4P at ambient pressure: novel high-performance anodes for lithium-ion batteries

Lithium-rich phosphides have recently attracted considerable attention due to their potential application as high-capacity and high-rate anodes for lithium-ion batteries (LIBs). However, there is still short of the promising candidate thus far because of the poor electrical conductivity or huge volume change in the already known Li-P compounds. In this work, we report two novel Li-P states, Li₅P₂ and Li₄P, stabilized under high pressures that are predicted to be quenchable down to ambient conditions by first-principles swarm structure calculations. The predicted P3m1 Li₅P₂ shows interesting features as a p-type semiconductor with an indirect band gap of 0.787 eV, possessing significant anisotropy properties in electrical transport, while R3[combining macron]m Li₄P acts as a typical electride with metallic behavior at pressures of 0-82 GPa. More importantly, our calculations reveal that the theoretical capacities of Li₅P₂ and Li₄P are predicted to reach 2164 and 3462 mA h g^-1, respectively. Combined with the good electrical transport properties, the calculated volume expansion of Li₅P₂ (130%) is found to be much smaller than those of the previously reported Li-P compounds, indicating its potential as a high performance anode material for LIBs.

Pressure-Induced Modulation of Electronic and Optical Properties of Surface O-Functionalized Ti2C MXene

Functionalized MXenes have gained increasing interest in the fields of thermoelectric materials, hydrogen storage, and so forth. In this work, pressure-induced band modulation and optical properties of the Ti2CO2 monolayer are investigated by using density functional theory with the hybrid (HSE06) functional. The calculation reveals that Ti2CO2 MXenes under pressure are stable because of the positive E coh. Ti2CO2 undergoes a semiconductor-to-metal phase transition at about 7 GPa. The metallization of Ti2CO2 mainly results from the Ti-d state. Research indicates that there exist strong interactions between Ti-d and C-p, and Ti-d and O-p states, which are further confirmed by the charge analysis. In addition, the absorption is enhanced in the visible region with increasing pressure. We also observed some new absorption peaks in the visible region.

Reduced Energy Barrier for Li+ Transport Across Grain Boundaries with Amorphous Domains in LLZO Thin Films

The high-resistive grain boundaries are the bottleneck for Li+ transport in Li7La3Zr2O12 (LLZO) solid electrolytes. Herein, high-conductive LLZO thin films with cubic phase and amorphous domains between crystalline grains are prepared, via annealing the repetitive LLZO/Li2CO3/Ga2O3 multi-nanolayers at 600 °C for 2 h. The amorphous domains may provide additional vacant sites for Li+, and thus relax the accumulation of Li+ at grain boundaries. The significantly improved ionic conductivity across grain boundaries demonstrates that the high energy barrier for Li+ migration caused by space charge layer is effectively reduced. Benefiting from the Li+ transport paths with low energy barriers, the presented LLZO thin film exhibits a cutting-edge value of ionic conductivity as high as 6.36 × 10-4 S/cm, which is promising for applications in thin film lithium batteries.

Anisotropic alignments of hierarchical Li2SiO3/TiO2 @nano-C anode//LiMnPO4@nano-C cathode architectures for full-cell lithium-ion battery

We report on low-cost fabrication and high-energy density of full-cell lithium-ion battery (LIB) models. Super-hierarchical electrode architectures of Li2SiO3/TiO2@nano-carbon anode (LSO.TO@nano-C) and high-voltage olivine LiMnPO4@nano-carbon cathode (LMPO@nano-C) are designed for half- and full-system LIB-CR2032 coin cell models. On the basis of primary architecture-power-driven LIB geometrics, the structure keys including three-dimensional (3D) modeling superhierarchy, multiscale micro/nano architectures and anisotropic surface heterogeneity affect the buildup design of anode/cathode LIB electrodes. Such hierarchical electrode surface topologies enable continuous in-/out-flow rates and fast transport pathways of Li+-ions during charge/discharge cycles. The stacked layer configurations of pouch LIB-types lead to excellent charge/discharge rate, and energy density of 237.6 Wh kg-1. As the most promising LIB-configurations, the high specific energy density of hierarchical pouch battery systems may improve energy storage for long-driving range of electric vehicles. Indeed, the anisotropic alignments of hierarchical electrode architectures in the large-scale LIBs provide proof of excellent capacity storage and outstanding durability and cyclability. The full-system LIB-CR2032 coin cell models maintain high specific capacity of ∼89.8% within a long-term life period of 2000 cycles, and average Coulombic efficiency of 99.8% at 1C rate for future configuration of LIB manufacturing and commercialization challenges.

LiCrO2 Under Pressure: In-Situ Structural and Vibrational Studies

The high-pressure behaviour of LiCrO2, a compound isostructural to the battery compound LiCoO2, has been investigated by synchrotron-based angle-dispersive X-ray powder diffraction, Raman spectroscopy, and resistance measurements up to 41, 30, and 10 Gpa, respectively. The stability of the layered structured compound on a triangular lattice with R-3m space group is confirmed in all three measurements up to the highest pressure reached. The dependence of lattice parameters and unit-cell volume with pressure has been determined from the structural refinements of X-ray diffraction patterns that are used to extract the axial compressibilities and bulk modulus by means of Birch–Murnaghan equation-of-state fits. The pressure coefficients for the two Raman-active modes, A1g and Eg, and their mode-Grüneisen parameters are reported. The electrical resistance measurements indicate that pressure has little influence in the resistivity up to 10 GPa. The obtained results for the vibrational and structural properties of LiCrO2 under pressure are in line with the published results of the similar studies on the related compounds. Research work reported in this article contributes significantly to enhance the understanding on the structural and mechanical properties of LiCrO2 and related lithium compounds.