Enabling Delayed-Full Charging Through Transformer-Based Real-Time-to-Departure Modeling for EV Battery Longevity

Authors: Yonggeon Lee, Jibin Hwang, Alfred Malengo Kondoro, Juhyun Song, Youngtae Noh

Published: December 8, 2025

Electric vehicles (EVs) are key to sustainable mobility, yet their lithium-ion batteries (LIBs) degrade more rapidly under prolonged high states of charge (SOC). This can be mitigated by delaying full charging \ours until just before departure, which requires accurate prediction of user departure times. In this work, we propose Transformer-based real-time-to-event (TTE) model for accurate EV departure prediction. Our approach represents each day as a TTE sequence by discretizing time into grid-based tokens. Unlike previous methods primarily dependent on temporal dependency from historical patterns, our method leverages streaming contextual information to predict departures. Evaluation on a real-world study involving 93 users and passive smartphone data demonstrates that our method effectively captures irregular departure patterns within individual routines, outperforming baseline models. These results highlight the potential for practical deployment of the \ours algorithm and its contribution to sustainable transportation systems.

Bimorph Lithium Niobate Piezoelectric Micromachined Ultrasonic Transducers

Authors: Vakhtang Chulukhadze, Zihuan Liu, Ziqian Yao, Lezli Matto, Tzu-Hsuan Hsu, Nishanth Ravi, Xiaoyu Niu, Michael E. Liao, Mark S. Goorsky, Neal Hall, Ruochen Lu

Published: December 8, 2025

Piezoelectric micromachined ultrasonic transducers (PMUTs) are widely used in applications that demand mechanical resilience, thermal stability, and compact form factors. Lead zirconate titanate (PZT) and aluminum nitride (AlN) active layers are used in PMUTs to enable acoustic actuation, sensing, or bidirectional operation. These platforms rely on bimorph films to maximize electromechanical coupling ($k^2$) through thin-film deposition, which uses intermediate electrode layers to establish opposing electric fields. Consequently, incumbent PMUT platforms are limited in achievable film thickness and feature material interfaces that compromise mechanical integrity and thermal performance. Combined with the intrinsic limitations of PZT and AlN, these factors motivate exploration of alternative PMUT material platforms. Recent efforts have sought to demonstrate that single-crystal lithium niobate (LN) is a promising candidate, offering substantially higher $k^2$ and bidirectional performance. Advances in LN film transfer technology have enabled the formation of periodically poled piezoelectric (P3F) LN, facilitating a bimorph stack without intermediate electrodes. In this work, we showcase bimorph PMUTs incorporating a mechanically robust, 20 micron thick P3F LN active layer. We establish the motivation for LN PMUTs through a material comparison, followed by extensive membrane geometry optimization and subsequent enhancement of the PMUT's $k^2$. We demonstrate a 775 kHz flexural mode device with a quality factor (Q) of 200 and an extracted $k^2$ of 6.4%, yielding a high transmit efficiency of 65 nm/V with a mechanically robust active layer. We leverage the high performance to demonstrate extreme-temperature resilience, showcasing stable device operation up to 600 degrees C and survival up to 900 degrees C, highlighting LN's potential as a resilient PMUT platform.

Interplay of Kekulé bond order and lattice instability in $\mathrm{C}_6\mathrm{Li}$

Authors: Yuanhao Zhang, Zi Yuan, Xiangru Kong, Weijiang Gong, Shaozhi Li

Published: December 8, 2025

Understanding the interplay between charge order and lattice instability in quantum materials remains a central challenge, as their coexistence often obscures causal relationships. This work introduces $\mathrm{C}_6\mathrm{Li}$ as a novel platform to investigate charge order mediated by two distinct mechanisms. We show that the hybridization between carbon $π$ and lithium $s$ orbitals generates an effective long-range hopping within Li-centered hexagons. This hopping drives a Kekulé bond order, whose structure varies with charge density and the sign of the hopping. This bond order induces a Kekulé lattice distortion via electron-phonon coupling. In the limit where lithium atoms are distant from the graphene layer, a Fermi surface nesting-driven Kekulé bond order emerges, stabilized by the electron-phonon interaction. Our results establish $\mathrm{C}_6\mathrm{Li}$ as a tunable platform for elucidating the causal hierarchy between electronic and structural orders in quantum materials.

Off-grid solar energy storage system with hybrid lithium iron phosphate (LFP) and lead-acid batteries in high mountains: a case report of Jiujiu Cabins in Taiwan

Authors: Hsien-Ching Chung

Published: December 8, 2025

Mountain huts are buildings located at high altitude, offering a place for hikers and providing shelter. Energy supply on mountain huts is still an open issue. Using renewable energies could be an appropriate solution. Jiujiu Cabins, a famous mountain hut in Shei-Pa National Park, Taiwan, has operated an off-grid solar energy storage system (ESS) with lead-acid batteries. In 2021, a serious system failures took place, leading to no electricity. After an detailed on-site survey, a reorganization and repair project implemented, the energy system came back to operate normally. Meanwhile, a eco-friendly lithium iron phosphate battery (LFP battery) ESS replaces part of the lead-acid battery ESS, forming a hybrid ESS, making a better and green off-grid solar ESS. In this case report, the energy architecture, detailed descriptions, and historical status of the system are provided. An on-site survey of the failed energy system, a system improvement project, and future plan are listed.

Heterogeneous back-end-of-line integration of thin-film lithium niobate on active silicon photonics for single-chip optical transceivers

Authors: Lingfeng Wu, Zhonghao Zhou, Weilong Ma, Haohua Wang, Ziliang Ruan, Changjian Guo, Shiqing Gao, Zhishan Huang, Lu Qi, Jie Liu, Jing Feng, Dapeng Liu, Kaixuan Chen, Liu Liu

Published: December 8, 2025

The explosive growth of artificial intelligence, cloud computing, and large-scale machine learning is driving an urgent demand for short-reach optical interconnects featuring large bandwidth, low power consumption, high integration density, and low cost preferably adopting complementary metal-oxide-semiconductor (CMOS) processes. Heterogeneous integration of silicon photonics and thin-film lithium niobate (TFLN) combines the advantages of both platforms, and enables co-integration of high-performance modulators, photodetectors, and passive photonic components, offering an ideal route to meet these requirements. However, process incompatibilities have constrained the direct integration of TFLN with only passive silicon photonics. Here, we demonstrate the first heterogeneous back-end-of-line integration of TFLN with a full-functional and active silicon photonics platform via trench-based die-to-wafer bonding. This technology introduces TFLN after completing the full CMOS compatible processes for silicon photonics. Si/SiN passive components including low-loss fiber interfaces, 56-GHz Ge photodetectors, 100-GHz TFLN modulators, and multilayer metallization are integrated on a single silicon chip with efficient inter-layer and inter-material optical coupling. The integrated on-chip optical links exhibit greater than 60 GHz electrical-to-electrical bandwidth and support 128-GBaud OOK and 100-GBaud PAM4 transmission below forward error-correction thresholds, establishing a scalable platform for energy-efficient, high-capacity photonic systems.

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

Authors: Lin Zhang, Wen Liu, Mingquan He, Jun Huang

Published: December 7, 2025

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.

Morphology-engineered nanostructured silver- and antimony-telluride films for flexible thermoelectric generators

Authors: Ankit Kashyap, Conner Wallace, Geetu Sharma, Collin Rowe, Mahima Sasikumar, Niraj Kumar Singh, Per Eklund, Theodorian Borca-Tasciucc, Ganpati Ramanath, Ajay Soni

Published: December 7, 2025

Harvesting low-grade heat to electricity is attractive for powering wearable electronic devices. Here, we demonstrate nW-scale thermoelectric power generation in devices from thin film assemblies of microwave-synthesized p-Sb2Te3 nanoplates and n-Ag2Te nanowires on polyvinylidene fluoride membranes. While microwave cycling is crucial for Ag2Te nanocrystal shaping, Sb2Te3 formation is sensitive to precursors and surfactant concentrations. Introducing S doping in Sb2Te3 in the 1 - 1.5 atomic percent range via thioglycolic acid during synthesis yields an up to eightfold higher power-factor, due to a fivefold increase in electrical conductivity and 25% increase in Seebeck coefficient. Our microfilm devices generate up to 33.6 mV from 5 deg C to 50 deg C thermal gradients, with 120 nW maximum power output at Delta T 30 deg C, which is sixtyfold higher than Sb2Te3 paper devices. Mechanical bending can increase device resistance by up to 125% due to diminished inter-nanostructure electronic transport. These findings provide insights for integrating synthesis, morphology engineering and device design for next-generation wearable thermoelectric systems.

Measuring the buried interphase between solid electrolytes and lithium metal using neutrons

Authors: Andrew S. Westover, Katie L. Browning, Antonino Cannavo, Ralph Gilles, Jiri Vacik, James F. Browning, Neelima Paul, Giovanni Ceccio, Vasyl Lavrentiev

Published: December 6, 2025

Interfaces are the key to next generation high energy batteries including solid state Li metal batteries. In solid state batteries, the buried nature of solid solid electrolyte electrode interfaces makes studying them difficult. Neutrons have significant potential to non destructively probe these buried solid solid interfaces. This work presents a comparative study using both neutron depth profiling (NDP) and neutron reflectometry (NR) to study a model lithium metal-lithium phosphorus oxynitride (LiPON) solid electrolyte system. In the NDP data, no distinct interphase is observed at the interface. NR shows a difference between electrodeposited, and vapor deposited LiPON -Li interfaces but finds both are gradient interphases that are less than 30 nm thick. Additional simulations of the LiPON-Li2O-Li system demonstrate that NDP has an excellent resolution in the 50 nm-1 mm regime while NR has an ideal resolution from 0.1 - 200 nm with different sample requirements. Together NDP and NR can provide a complementary understanding of interfaces between Li metal and solid electrolytes across relevant length scales.

Frequency modulated enhancement of microwave resonator sensing

Authors: Pranaya Kishore Rath, James D. Philips, Taekwan Yoon, Kent R. Shirer, Arash Fereidouni, Johannes Pollanen

Published: December 6, 2025

We use the Pound-Drever-Hall (PDH) technique to characterize the frequency stability of a microwave-frequency surface acoustic wave (SAW) resonator-based sensor. The multi-mode acoustic resonator is integrated in a notch geometry with a transmission line, all fabricated on Y-cut lithium niobate. We measure the amplitude and phase of the resonator transfer function and the PDH signal across the resonator full spectral range. We use these measurements to emphasize the differences between the PDH measurement and a standard Phase-Locked Loop (PLL) technique. As compared to a PLL, we demonstrate that PDH is insensitive to phase error and exhibits a reduced Allan deviation of the center frequency measurement, in each case by up to an order of magnitude. The method rejects spurious effects and background frequency drift, demonstrating the enhancements possible with PDH-based measurements, which can be realized in a wide range of microwave-frequency resonator-based sensors and devices.

The tube transducer as a novel source for power ultrasound: A case study in delamination of graphite coating from lithium-ion battery anode

Authors: Shida Li, Paul Daly, Ben Jacobson, Joshua Cooke, Chunhong Lei, Andrew P. Abbott, Andrew Feeney, Paul Prentice

Published: December 5, 2025

Developing high throughput applications of sonochemistry and sonoprocessing is an outstanding ultrasonic engineering challenge that continues to limit widespread industrial adoption. Conventional mass-produced Langevin-based technologies, such as the sonotrode or cleaning bath transducers, are not particularly well suited to treating large liquid volumes or flow-based systems, with a compromise between cavitation intensity and distribution through liquid bulk typically required. We report on the development of a tube transducer from a single element radially poled tubular piezoceramic, excited to generate an axially focused field. High-speed imaging and sonochemiluminescence are used to characterise the cavitation generated, which is also compared to the well-known activity at the tip of a sonotrode. Tube transducer and sonotrode sonications are then assessed for the material recycling application of graphite coating delamination from lithium-ion battery anode, both for intact and flaked anode sheets. The findings show that the tube transducer generates cavitation at sonotrode-like intensities or higher but distributed throughout the bore of the tube, with peak activity at the central axis. Prospects for developing tube transducer technology for high throughput flow-based applications are discussed.