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Potassium-ion batteries (PIBs) have emerged as promising candidates for cost-effective and sustainable energy-storage systems. Nevertheless, limited by the large K+ radius, PIBs have great difficulty in figuring out and designing suitable host materials. Herein, a suitable cathode material K3V2(PO4)2O2F (KVPOF) for PIBs has been carefully prepared. It exhibits a high specific capacity close to the theoretical value, 116.3 mAh/g at 20 mA/g within the voltage window of 2.0–4.5 V vs K+/K, corresponding to a de-/intercalation process of ∼2 mol K+ per formula unit. In addition, it presents an average operating voltage plateau of about 3.5 V, resulting in an energy density of about 410 Wh/kg. The crystal structure and phase transition are revealed by in situ x-ray diffraction, and the structure is found to be fully reversible during the de-/intercalation of K+. Furthermore, the potential of KVPOF cathode for applications at low temperatures was explored, and the full cell matched with graphite anode demonstrated fair electrochemical performance. The experimental results suggest the feasibility of using KVPOF as cathode material for rechargeable PIBs. [ABSTRACT FROM AUTHOR]

The importance of higher-order anharmonic effects on thermal transport has recently been demonstrated in highly symmetrical 2D materials with large acoustic–phonon (A–O) gap. However, the phonon scattering and the thermal transport properties in low-symmetry structures remain ambiguous. In this work, we employed moment tensor potential and Boltzmann transport equation to investigate phonon thermal transport properties of 1T′-ReS2 and 2H-WS2. We show that the mechanism of four-phonon scattering in 1T′-ReS2 is quite different from that in 2H-WS2. In 1T′-ReS2, the four-phonon scattering can reduce the thermal conductivity by up to 40.29%, even in the absence of an acoustic-optical phonon bandgap. The strong four-phonon scattering in 1T′-ReS2 is attributed to A–O phonon scattering mediated by abundant flattening optical phonon modes. However, in 2H-WS2, the strong four-phonon scattering is attributed to the presence of a large A–O phonon bandgap. Our work suggests that considering the four-phonon scattering is essential for calculating the thermal conductivity of 2D materials, even in the absence of an A–O phonon gap. [ABSTRACT FROM AUTHOR]

Photonic computing has the potential to significantly improve energy efficiency and data processing speed beyond that of von Neumann architecture. Although various optical processing techniques have been developed during recent two decades, the photonic manipulation is still a big challenging due to the bosonic nature of photons. Herein, we propose a ferroelectric field-controlled photonic computing based on the heterostructure of ferroelectric/van der Waals semiconductor. The strong and tunable electrostatic coupling of ferroelectric (PMN-PT) with monolayer WS2 results in a multi-level (24 bits) photoluminescence (PL) output. Furthermore, combining device modeling with experiments, we find that the multi-level PL output is because of the regulation of ferroelectric polarization on the net recombination rate of WS2. The ferroelectric field-controlled multi-level PL output enables us to design an optical arithmetic operation in the PMN-PT/WS2 heterostructure, which provides an attractive solution for photonic information computing. [ABSTRACT FROM AUTHOR]

Photonic computing has the potential to significantly improve energy efficiency and data processing speed beyond that of von Neumann architecture. Although various optical processing techniques have been developed during recent two decades, the photonic manipulation is still a big challenging due to the bosonic nature of photons. Herein, we propose a ferroelectric field-controlled photonic computing based on the heterostructure of ferroelectric/van der Waals semiconductor. The strong and tunable electrostatic coupling of ferroelectric (PMN-PT) with monolayer WS2 results in a multi-level (24 bits) photoluminescence (PL) output. Furthermore, combining device modeling with experiments, we find that the multi-level PL output is because of the regulation of ferroelectric polarization on the net recombination rate of WS2. The ferroelectric field-controlled multi-level PL output enables us to design an optical arithmetic operation in the PMN-PT/WS2 heterostructure, which provides an attractive solution for photonic information computing. [ABSTRACT FROM AUTHOR]

In this study, we employ a machine-learning potential approach based on first-principles calculations combined with the Boltzmann transport theory to investigate the impact of lithium-ion de-embedding on the thermal conductivity of LiFePO4, with the aim of enhancing heat dissipation in lithium-ion batteries. The findings reveal a significant decrease in thermal conductivity with increasing lithium-ion concentration due to the decrease in phonon lifetime. Moreover, removal of lithium ions from different sites at a given lithium-ion concentration leads to distinct thermal conductivities, attributed to varying anharmonicity arising from differences in bond lengths and bond strengths of the Fe-O bonds. Our work contributes to a fundamental understanding of the thermal transport properties of lithium iron phosphate batteries, emphasizing the pivotal role of lithium-ion detachment and intercalation in the thermal management of electrochemical energy storage devices. [ABSTRACT FROM AUTHOR]

The layered solid electrolyte Li2ZrCl6 and Li metal electrodes have a very good contact stability, but the thermal transport properties of Li2ZrCl6 are still unclear. Here, we systematically study the intrinsic lattice thermal conductivity (κp) of Li2ZrCl6 using the machine-learning potential approach based on first-principles calculations combined with the Boltzmann transport theory. The results show that the κp of Li2ZrCl6 at room temperature is 3.94 W/mK along the in-plane (IP) direction and 1.05 W/mK along the out-plane (OP) direction, which means that the κp is significantly anisotropic. In addition, under the compressive stress in the OP direction, the κp evolution along the IP and OP directions exhibits completely different trends, because the stress has a significant regulatory effect on the contribution of optical phonons to κp. With the increase in stress, the κp in the IP direction monotonically decreases, while the κp in the OP direction increases by a factor of 2.2 under a compressive strain of 13%. This is because the contribution of low-frequency optical phonons to κp in the IP direction is as high as 58% when no stress is applied, and this contribution is significantly suppressed with increasing compressive strain. However, the contribution of optical phonons in the OP direction to the κp increases with the increase in stress. Our results reveal the thermal transport properties of Li2ZrCl6 and the effect of the compressive strain on the κp of Li2ZrCl6, thereby providing a reference for the use of Li2ZrCl6 in Li-metal batteries. [ABSTRACT FROM AUTHOR]

Enhanced thermoelectric performance is restricted greatly by the interaction of various transport parameters, and this bottleneck urgently requires a solution. In this paper, first-principles calculations and Boltzmann transport theory are used to study the thermoelectric performance of two-dimensional (PbX) 2 (X = S , Se , Te) monolayers, and it is found that the thermoelectric performance can be enhanced significantly by applying a biaxial tensile strain. The room-temperature ZT values of the p-type (PbS) 2 , (PbSe) 2 , and (PbTe) 2 in zigzag (armchair) directions are boosted as high as 1.97 (1.35), 2.26 (1.31), and 2.45 (1.59), respectively. The results show that it is mainly attributed to the significantly reduced phonon thermal conductivity. Moreover, the sharply reduced phonon thermal conductivity is mainly due to the enhancement of the phonon scattering rate caused by strong phonon anharmonicity. In addition, the excellent ZT value of the p-type (PbX) 2 (X = S , Se , Te) monolayer exhibits their potential application in the thermoelectric field, and the external strain has a good prospect in enhancing the thermoelectric performance. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) metallic transition-metal dichalcogenide (MTMD)/carbon-nanotube (CNT) compounds are competitive electrode materials for solid-state flexible in-plane supercapacitors, resulting from the synergistic effect of the large specific surface area of 2D MTMDs and the excellent mechanical properties of the CNT. In this paper, the high-quality VSe2/CNT electrode material is prepared by the one-step chemical vapor deposition (CVD) method. The CVD method offers a facile and safe way to synthesize a pure VSe2/CNT compound. The VSe2 nanosheets are vertically grown on the surface of the CNT cluster. The vertical configuration of the VSe2 nanosheets on the conductive CNT cluster takes full advantage of the large specific surface area of the VSe2 nanosheets to store charges. The ductile and conductive CNT cluster offers good mechanical and electrical connections to the VSe2 nanosheets. The VSe2/CNT compound is applied as the electrode material of a solid-state flexible in-plane supercapacitor which achieves a specific area capacitance of 1854 μF/cm2 and stable cycling stability, ∼7% degradation after 10 000 times of current cycling. The VSe2/CNT also presents a desirable mechanical stability, and ∼ 90% capacitance is retained after bending up to 40°. This work promotes the application of 2D MTMD compounds in the field of energy storage and wearable devices. [ABSTRACT FROM AUTHOR]

Piezoelectricity has proved itself a promising mechanism for energy conversion and signal sensing by taking advantage of its ability to convert mechanical energy into electricity. Here, we demonstrate that the piezoelectricity in free-standing non-centrosymmetric nanowires can also be triggered directly by heat to produce electricity. The feasibility of the idea is first analyzed by the dynamic theory of crystal lattices and then confirmed by molecular dynamics simulations. The most salient point is that the heat-induced voltage drop across the cross section of the free-standing nanowires alternates periodically with the vibration of the nanowire. Moreover, the electric potential induced by heat here (as large as 0.34 V) is proved to be comparable with the previously reported potentials induced by mechanical energy, and the maximum value can be tuned by controlling the size of the nanowire and the applied heat. [ABSTRACT FROM AUTHOR]

The thermal transport properties of the graphene and boron nitride superlattice (CBNSL) are investigated via nonequilibrium molecular dynamics simulations. The simulation results show that a minimum lattice thermal conductivity can be achieved by changing the period length of the superlattice. Additionally, it is found that the period length at the minimum shifts to lower values at higher temperatures, and that the depth of the minimum increases with decreasing temperature. In particular, at 200 K, the thermal conductivities of CBNSLs with certain specific period lengths are nearly equal to the corresponding values at 300 K. A detailed analysis of the phonon spectra shows that this anomalous thermal conductivity behavior is a result of strong phonon wave interference. These observations indicate a promising strategy for manipulation of thermal transport in superlattices. [ABSTRACT FROM AUTHOR]

In the quest for the origin of the different thermal rectifying behavior of two graded nanowires, we reveal the important role that standing waves play in the thermal transport properties of such graded structures. Evidence for the existence of standing waves is given from two angles, and one possible scenario of the origin of the standing wave is presented. The key point is that the formation of the standing wave, which greatly hinders the propagation of phonon waves, occurs only when the narrow end of the nanowire is at a higher temperature than the wide end, making the heat current flow preferably from the wide end to the narrow end. [ABSTRACT FROM AUTHOR]