High Voltage Conditions Research Articles

Development of Combined Instrument Transformer for Gas-Insulated Switchgears

Accurate measurement of current and voltage information is essential to the safe reliable operation of railway substations. This paper dealt with a combined instrument transformer (CIT) built in a spacer for the purpose of miniaturization and eco-friendliness of a GIS, rated 72.5 kV and 2,000 A. A D-dot sensor and a Rogowski current sensor were applied to voltage and current measurement, respectively, to secure the insulation of the CIT in high-voltage and high-current conditions. As a result of an evaluation based on IEC 60044-7 and IEC 60044-8, the performance of the prototype CIT was found to sufficiently satisfy Class 0.5. When the CIT proposed in this paper was applied to a GIS of rated 72.5 kV, it was possible to reduce the size by 33% in length, 11% in height and 90% in weight per bay of the GIS compared to conventional iron-core transformers. In addition, since the amount of SF6 will be reduced by 15% in terms of volume, it is expected that this method can be used for the digitization, miniaturization and eco-friendliness of railway substations.

Self-Healing Binder for High-Voltage Batteries.

Lithium-ion batteries are core components of flexible electronic devices. However, deformation types, such as impinging, bending, stretching, folding, and twisting, can cause internal cracks and, eventually, damage these batteries. The cracks separate the active particles from the conductive particles and the binder, as well as the electrode from the collector. Self-healing binders can alleviate this mechanical damage and improve the stress response of active material particles during high rates of charging and discharging of these batteries and the operation at a high voltage, thereby enhancing their cycle performance. In the present study, a thermoplastic intrinsic self-healing polymer (TISP) binder is proposed. The TISP is obtained by polymerization of butanediol (2,3-BDO), propylene glycol (1,3-PDO), succinic acid (SuA), sebacic acid (SeA), and iconic acid (IA). The hydroxyl and ester groups in its structure can form diverse bonds including the hydrogen and ion-dipole with active particles and the current collector, thereby producing elevated adhesion. Its properties, including a low glass transition temperature (-60 °C), amorphous structure, and low cross-link density, improve the mobility of polymer chains at 40 °C, and this facilitates structural recovery and the maintenance of strong adhesions. Owing to its higher occupied molecular orbital (HOMO) level than the electrolyte solvent, the TISP is likely oxidized before the main component of the electrolyte during charging. This decomposition produces a chemical passivation interphase on the cathode which reduces side reactions of LiCoO2 and the electrolyte under high-voltage conditions. Tests reveal that a LiCoO2 electrode battery using the TISP as a binder retains 162.4 mAh g-1 after 349 cycles at 4.5 V, and this represents an 86.5% capacity retention. In addition, heating (40 °C, 1 h) of a scratch-damaged electrode can recover a specific capacity of 156.6 mAh g-1 after 349 cycles at 4.5 V. Relative to a battery without any mechanical scratch, this capacity recovery represents approximately 96%, and this demonstrates the importance of the TISP to the high-voltage damaged electrode.

Transformer-Less Soft-Switching High-Gain PWM Boost Converter With Reduced Components and Increased Effective Duty Cycle

A transformer-less soft-switching high-gain pulsewidth-modulation (PWM) converter is proposed in this article. The proposed converter is derived from a single-switch dual-inductor transformer-less boost converter by replacing the complementary diode connected to the switch with a synchronous rectifier switch. Moreover, the peak value of the reverse current of the rear-end inductor in continuous bidirectional conduction mode (CBCM) is regulated to exceed the input inductor valley current. Based on these two measures, the zero-voltage switching (ZVS) for all switches and the natural turn-off for the output diode are realized, and the effective duty cycle is enhanced. Besides, the proposed ZVS converter has the merits of fewer power components count, reduced voltage stress, and lower cost. Furthermore, the ringing issue in the original topology under light load or high input voltage conditions is eliminated. The operation principle, steady-state characteristics, dynamic model, soft-switching operation, and realization conditions are analyzed in detail, and subsequently, the parameter design method is elaborated. The proposed topology demonstrates an enhanced efficiency performance over wide operating operations with a maximum efficiency of 97.1%.

Plasma transport simulation under different conditions and optimization analysis of dual-stage grid ion thruster

In order to study the extraction and acceleration mechanism of the dual-stage grid, a three-dimensional model based on the Particle-In-Cell/ Monte Carlo Collision (PIC/MCC) method is performed. Dual-stage grid ion thruster is a new type of electrostatic ion thruster, which can break through the limitations of traditional gridded ion thrusters, and greatly improve the specific impulse. The high performance also makes the grid sensitive to operating parameters. In this paper, the influence of grid parameters on xenon ion thruster’s performance in a wide range is systematically simulated, and the optimal operating condition is given. Both the over-focusing of the plume, and the transparency of the screen grid are improved, and the grid corrosion is reduced through simulation optimization. The specific impulse under the given working conditions is 9877.24 s and the thrust is 7.28 mN. Based on the simulation optimization, the limitation of the dual-stage grid is discussed. The grid performs well under high voltage conditions (>3000 V) but not well under low voltage conditions (<2000 V). Finally, since argon is cheaper and more advantageous in future engineering applications, the plasma distribution and grid extraction ability under xenon and argon are analyzed and compared to study the flexibility of the dual-stage grid ion thruster. The simulation results show that a set of optimal parameters is only applicable to the corresponding propellant, which needs to be optimized for different propellant types.

First-Principles Examination of Multiple Criteria of Organic Solvent Oxidative Stability in Batteries

Oxidative instability of the liquid electrolyte at or near battery cathode oxide surfaces has significant detrimental effects on batteries. Organic solvent molecules are often the fuel and precursors of such degradation processes, releasing electrons and protons that react with cathode oxides and electrolyte anions. These reactions contribute to cathode–electrolyte interphase (CEI) film formation, transition-metal ion dissolution, and phase transformation of the surface regions of the cathode. Here we apply density functional theory calculations to examine four criteria of oxidative stability (oxidation potential, hydrogen removal energies, and initial reactivity on two types of oxide facets) using four different solvent/additive molecules (ethylene carbonate, fluoroethylene carbonate, 1,3-dioxolane, and dimethyl ether). The ranking of molecular stability differs with each criterion. Surprisingly, the all-oxygen-terminated basal planes of layered oxides exhibit lower reaction barriers than spinel surface facets with exposed transition-metal cations, especially for ether solvents; the calculations also suggest basal planes contribute to the dissolution of transition-metal ions. The structure–degradation relation complexity underscores the challenge of understanding the function of the CEI but also offers a guide to future degradation-mitigation strategies including facet engineering. Our predictions and models help establish a framework for future studies relevant to high-voltage conditions.

Research on life prediction control of MMC submodule based on fiber sensing

With the rapid development of energy, power electronic equipment plays a crucial role in renewable energy. Modular multilevel converter (MMC) has turned into cutting-edge inverter topology in flexible HVDC and offshore wind power situations. However, under the conditions of high humidity and high voltage, the internal submodules lifetime of MMC might be affected. The system reliability mainly depends on good running of the submodules, so stable performance of the submodules serious threat to the normal operation of the inverter. Therefore, this paper proposes a model based on Peck accelerated life predictable model, and model predictive control (MPC) strategy is improved, at the same time without affecting the external characteristics can better control the submodule voltage fluctuations. What is more, real time monitoring of the working environment of the converter through the optical fiber sensing module. Finally, the experimental and simulative outcomes show that the proposed control strategy can effectively reduce the voltage fluctuations in the small module, and the life parameters of the submodules can be obtained in real time by bringing the results into the proposed life prediction model. By comparing the results, the results can be obtained the proposed control strategy can effectively increase the reliability of the submodule.

Nano-TiO2/MWCNT composite coating with high DC flashover strength and super hydrophobicity

Epoxy resin (EP) materials are frequently used in high voltage power equipment because of their excellent electricity, force, and heat properties. However, under the condition of DC high voltage, the surface of EP insulation material is more likely to accumulate charge, which distorts the nearby electric field and causes flashover along the surface. In this article, a nanocomposite coating was prepared by spraying through the nanoparticles (TiO2 with carbon nanotubes) dispersed in the polydimethylsiloxane (PDMS) elastomers solution. Micro-nano porous structures are introduced in the spraying process, which hinders the development of collision ionization and increases the flashover strength of the coating. At the same time, the change in surface morphology makes the hydrophobic properties of the coating improve and enhances the anti-icing and anti-fouling capacity. Spraying nano filler provides a general method for improving hydrophobicity and flashover strength.

Tailoring solvation chemistry in carbonate electrolytes for all-climate, high-voltage lithium-rich batteries

High-voltage Li-rich layered oxide materials (LLOs) are considered as the promising next-generation cathode materials because of their high energy density and low cost. However, their electrochemical performance continues to deteriorate under high voltages when using traditional lithium hexafluorophosphate (LiPF6)-based carbonate electrolytes, mostly due to the detrimental reactions with free anions, unstable electrode interface and limited Li+ kinetic process. Here, we demonstrate a highly oxidation-resistant carbonate electrolyte by incorporating multifunctional lithium difluoro(oxalato)borate (LiDFOB) and Tris(trimethylsilyl) Phosphite (TMSPi) additives. It is discovered that the introduction of LiDFOB and TMSPi can manipulate the electrolyte solvation structure by reducing the number of coordinated solvent molecules and free PF6−anions at the electrolyte-electrode interface, thus promoting the desolvation process of Li+, suppressing the generation of harmful HF species and conducive to forming a thin and robust cathode electrolyte interphase (CEI) layer. As a result, the Li||LLO cells with dual additives show excellent cycle stability and improved rate capability in a wide temperature ranged from -20 °C to 55 °C, and the retention rate of LLO||graphite pouch cell (2.5 Ah) using EEDB-TMSPi electrolyte is up to 91.1% after 200 cycles. It is anticipated that the work provides a promising strategy for realizing long-cycle stability of layered cathode materials under high-voltage and wide-temperature conditions.

Improvement in U-Shaped Channel SOI Lateral IGBT for Wider Reverse Bias Safe Operating Area

In this article, the inductive turn-off failure mechanism of U-shaped channel silicon-on-insulator lateral insulated-gate bipolar transistor (SOI-LIGBT) under high-voltage and high-current is investigated by experiments and numerical simulations. First, the measured turn-off waveforms before and after failure are compared to infer the cause of the failure. Then, the failure is reproduced by calibrated three-dimensional simulations using Sentaurus TCAD. According to the simulation and measured results, the turn-off failure is resulted from the high impact ionization in the bird’s beak region. To reveal the failure mechanism, the turn-off failure process is divided into two phases. In phase I, the electrons generated by drastic impact ionization in the bird’s beak region act as the base current to keep the operation of parasitic PNP transistor after channel pinching off. In phase II, the parasitic NPN transistor is activated due to the hole current amplified by PNP, and thus, turn-off failure occurs. Based on the revealed turn-off failure mechanism, an improved U-shaped channel SOI-LIGBT with a P-top is proposed. The P-top is arranged in the bird’s beak region to reduce the impact ionization rate. The measured results demonstrate that no failure occurs when the improved device turns off under high-voltage and high-current conditions. Compared with the conventional U-shaped channel SOI-LIGBT, the improved device obtains 275% and 23% improvements in turn-off current at a bus voltage of 450 V and reverse bias safe operation area, respectively.

Design and Performance of High Voltage Chip-Level Series-Connected SiC MOSFET Module

In medium voltage (MV) and high voltage (HV) applications, HV SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> with a single chip competes with series-connected low voltage (LV) SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> . The cost of the former is high due to immature process, and the parasitic inductance of the latter is large due to series-connected devices. In this article, a novel chip-level series-connected SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> module based on planar packaging is proposed to compromise cost and parasitic inductance. Several LV chips are connected in series through metal layers, and then packaged as a whole. Compared with HV module with a single chip, the proposed module has significant advantages in cost. Considering the effects of the buffer layer and direct bonded copper on the parasitic inductance, junction temperature, thermal stress, and electric field, electro-thermo-mechanical simulation is conducted to optimize the structure. Compared with existing series-connected structures, the parasitic inductance of the proposed module is reduced by at least 50.15%. Finally, 6.5 kV chip-level series-connected module with six 1.2 kV SiC <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> is fabricated and tested. The results show the performance of the proposed module is comparable with that of HV module with a single chip, which means that the application of the proposed module in MV and HV conditions is promising.

Wavelength and Polarization Sensitive Synaptic Phototransistor Based on Organic n-type Semiconductor/Supramolecular J-Aggregate Heterostructure.

Human retina- and brain-inspired optoelectronic synapses, which integrate light detection and signal memory functions for data processing, have significant interest because of their potential applications for artificial vision technology. In nature, many animals such as mantis shrimp use polarized light information as well as scalar information including wavelength and intensity; however, a spectropolarimetric organic optoelectronic synapse has been seldom investigated. Herein, we report an organic synaptic phototransistor, consisting of a charge trapping liquid-crystalline perylene bisimide J-aggregate and a charge transporting crystalline dichlorinated naphthalene diimide, that can detect both wavelength and polarization information. The device shows persistent positive and negative photocurrents under low and high voltage conditions, respectively. Furthermore, the aligned organic heterostructure in the thin-film enables linearly polarized light to be absorbed with a dichroic ratio of 1.4 and 3.7 under transverse polarized blue and red light illumination, respectively. These features allow polarized light sensitive postsynaptic functions in the device. Consequently, a simple polarization imaging sensor array is successfully demonstrated using photonic synapses, which suggests that a supramolecular material is an important candidate for the development of spectropolarimetric neuromorphic vision systems.

Microstructure and surface engineering through indium modification on Ni-rich layered cathode materials for enhanced electrochemical performance of lithium-ion batteries

Ni-rich layered lithium transition metal oxides have been considered as one of the most promising cathodes for next-generation lithium-ion batteries (LIBs) because of their high capacities and affordable costs. However, they still suffer bulk and surface structural instability, leading to rapid performance decay and subsequent cathode failure. In this context, Ni-rich layered cathodes with indium modified crystal and surface structures are developed by a simple one-pot calcination approach. Battery tests manifest that the indium modified LiNi0.8Co0.1Mn0.1O2 electrodes exhibit remarkably enhanced rate capability and cycling stability compared to the pristine one, including under high operating voltage condition. Further studies evidence a simultaneous mitigation of intra/inter-granular mechanical cracks and resistive surface films growth, which directly embodied in a dramatically suppressed ohmic loss after long-term cycling. The improved microstructural and surface stability are attributed by the synergistic functions of indium modification. On the one hand, trace amount of In3+ occupy crystalline Li+-site, which not only dissipate the intrinsic lattice strain during cycling, but also reduce Li+/Ni2+ antisite to avoid the undesired layer to rock-salt phase transformation. On the other hand, the rest of indium deplete lithium residues, and form conductive LiInO2 adherent coatings to protect the cathode from side reactions with electrolyte. The present work demonstrates that microstructure and surface engineering through indium modification offers a promising design strategy for further improvements of Ni-rich layered cathodes.

A Fluorine-Based Linear Carbonate Electrolyte Additive for Enhanced High-Voltage Cycle Performance of Li-Metal Secondary Batteries

Due to growing demand for electric vehicles (EVs) and energy storage systems (ESS), it is essential to meet the requirement for high energy density of Li secondary batteries. In this sense, an electrode chemistry matching high-Ni cathode materials and thin Li metal anode has been investigated most actively under high voltage operation. As a result, there are a variety of degradation issues on both electrodes like high-resistance cathode electrolyte interphase (CEI) as well as solid electrolyte interphase (SEI) on the anode, electrolyte depletion, or Li dendritic growth. Thus, advanced electrolytes containing functional additives are extensively being developed to mitigate those stresses occurred in the high-energy-density Li-metal secondary batteries (LMSBs). Especially, to minimize the amount of expensive additives, many research groups have made much effort in discovering new or multi-functional additives for LMSBs.In this work, we report a bis(2-fluoroethyl) carbonate (B-FEC) as a new fluorine-based linear carbonate electrolyte additive to stabilize the SEI even in the high voltage conditions (4.5 V cut-off). To confirm the role of B-FEC on electrochemical properties, we evaluated its electrochemical properties with Li/Li symmetric cells as well as LiNi0.6Co0.2Mn0.2O2 (NCM 622)/Li cells with or without B-FEC. Also, various analysis data were also gathered to check the morphological and compositional changes caused by B-FEC through SEM, XPS, etc.

Study on Aluminum Corrosion in Lithium Perchlorate-Based Super-Concentrated Electrolyte Solution

For realizing sustainable world, Lithium-ion batteries are required to have higher energy density. Aluminum metal have been dominantly used as a current collector of positive electrode. A mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1 mol dm-3 Lithium hexafluorophosphate (LiPF6) has been used as an electrolyte solution, however, aluminum corrosion may occur due to this electrolyte solution under high voltage condition. On the other hand, super-concentrated electrolyte solution (SCES), which consists of only two or three times as much solvent as lithium salt, has been attracting attention as a new electrolyte solution of Lithium-ion battery. Motsumoto et al. proposed that aluminum corrosion was remarkably suppressed in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based SCES. However, the electrolyte solution containing fluorine has the problem which is the dissolution of the active material due to the decomposition product of the electrolyte solution．In the present work, we investigated aluminum corrosion in the lithium perchlorate (LiClO4)-based SCES as a fluorine-free solution.The LiClO4 based SCES was prepared by dissolving LiClO4 into DMC as the molar ratio of 1 : 2. For comparison, DMC solution containing 1 mol dm-3 LiClO4 was also prepared. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were measured. X-ray photospectroscopy (XPS) was performed to evaluate the decomposition product on the aluminum electrode. Anodic current of the dilute electrolyte solution is observed at 3.9 V vs. Li/Li+. By contrast, in the LiClO4 based SCES, the anodic current is less than 100 µA cm-2 when polarized to 6 V vs. Li/Li+. In the dilute electrolyte solution, the ClO4 - anion is decomposed to form Cl-, which promotes aluminum corrosion. By contrast, the SCES has high oxidative stability, suggesting that the liquid structure of the SCES differ from that of the dilute electrolyte solution. two intense peaks appear at 196 and 198 eV in in XPS spectra of Cl 2p for the aluminum surface after LSV measurement in the dilute electrolyte solution. On the other hand, a weak peak is observed at approximately 199 eV in XPS spectra of Cl 2p for the aluminum surface after LSV measurement in the SCES. This result suggests that the ClO4 - anion is not decomposed in the SCES.

Characterization of Low Cobalt Cathode Degradation Using Distribution of Relaxation Times Analysis

High-capacity cathode materials with reduced or eliminated cobalt usage are being pursued for lithium-ion batteries (LIB) due to environmental and humanitarian issues in the cobalt supply chain. Consequently, increased nickel content and reduced cobalt content results in faster cell degradation. A connection between morphological and chemical changes within the cathode microstructure, charge cut-off voltage, and operating temperature has been developed through a combination of cycling conditions, X-ray Diffraction (XRD), and Distribution of Relaxation Times (DRT) analysis.Low cobalt half-cell batteries were fabricated with Li(Ni0.8Mn0.1Co0.1)O2 (NMC811) active material and tested under high cut-off voltage (4.3V), low cut-off voltage (4.0V), high temperature (60°C), and ambient temperature (25°C). XRD analysis of high cut-off voltage samples show a presence of NiOx crystalline structure, a low diffusivity rock-salt phase. To further understand the electrochemical changes due to the appearance of the rock-salt phase, DRT analysis was conducted on the electrochemical impedance spectra taken after formation of the solid electrolyte interphase (SEI) and after cycling. DRT analysis is becoming a preferred method of analysis due to the fact that electrochemical processes, like solid-state diffusion, cathode electrolyte interphase (CEI), and SEI formation, show up at characteristic frequencies, allowing for interpretation of changes that are often not visible within typical impedance plots. Prior to cycling, the primary contribution was initially found to be from the CEI and SEI. At low cut-off voltage cycling conditions, ambient temperature cycling showed that the contribution shifted from the CEI to diffusion resistance, but changes within the SEI and CEI were still detected. High temperature cycling conditions within the low cut-off voltage samples showed that the diffusion resistance again increased and the contributions from the CEI and SEI decreased. At high cut-off voltage cycling conditions, ambient temperature cycling showed that diffusion was becoming the main contribution but changes due to the CEI were still evident. High temperature cycling conditions in the high cut-off voltage samples showed that the mechanism was completely taken over by diffusion, due to the lithium transport being limited by the rock-salt phase or electrolyte degradation.XRD patterns confirmed that the rock-salt phase was beginning to form within the low cut-off voltage high temperature cycling condition, but in much lower intensity than that of the high cut-off voltage condition. This observation clearly shows that the diffusion mechanism, which hinders intercalation and deintercalation, is driven by the formation of the non-conductive rock-salt phase. While primarily influenced by cut-off voltage, elevated temperature may also contribute to this degradation mechanism. The combination of different electrochemical and microstructural characterization techniques supports this observation and demonstrate that DRT analysis is an effective method to better understand the driving mechanisms behind battery degradation.

The effect of magnet core size on the performance of a cylindrical Hall thruster with the near-anode cusp magnetic field

Effect of magnet core size on the performance of a cylindrical Hall thruster with the near-anode magnetic field has been investigated. Experiments found that extending magnetic core and rising discharge voltage show similar effects on the ionization process. When the magnetic core ends flush with the anode and discharge voltage is fixed at 240 V, the upstream ionization related with the electron E × B drift is hardly established under an approximately axial magnetic field and the ionization region is located at the near-axial magnetic mirror field, the thruster manifests the highest propellant utilization efficiency (as high as 1.43), the lowest current utilization efficiency (0.54) and beam divergence efficiency (0.52). When the magnet core extends towards the thruster exhaust, the enhancement of upstream ionization results in significant enhancements in the current utilization efficiency (by 14.6%) and the beam divergence efficiency (by 27.1%). However, the reduction of magnetic mirror ionization also led to a reduction of propellant utilization efficiency (by 32.1%). Therefore, the anode efficiency varies non-monotonically (climbing up and then declining) and has an optimal solution: shorter magnet core performs higher anode efficiency in low voltage condition and longer magnet core performs higher anode efficiency in high voltage condition.

Extraction of Dynamic Threshold Voltage in Resistive Load Hard Switching Operation of Schottky-Type p-GaN Gate HEMT

Threshold voltage (VTh) drift of Schottky-type p-GaN gate high-electron mobility transistor (HEMT) was analyzed under high-voltage and hard switching conditions with a resistive load (R-Load). To overcome the distortion in the drain current (ID) – gate voltage (VG) curve caused by the internal drain capacitance (IDisp) charging current during the switching transients, a method is presented to accurately measure dynamic VTh through appropriate correction of IDisp. The dynamic variation of VTh was tracked with a gate-drive rise/fall times of 200 ns. During the switching operation, VTh increases rapidly at the beginning and then saturates at a stable value. This is attributed to the gate forward current during turn-on that increases the hole depletion of the p-GaN gate through the AlGaN barrier. The dynamic VTh increases linearly at a rate of 40% with the increase of gate turn-on voltage. VTh is independent of duty cycle but minorly increases with frequency at high voltages, suggesting that channel hot electrons be injected into the AlGaN barrier and p-GaN.

Overview of Aging Mechanisms in Sige Hbts

This paper reviews the recent studies in hot carrier degradation mechanisms of SiGe HBTs under saturation mode and off-state operation. Reliability of these devices gets increased scrutiny as technological scaling drives down device dimensions. Even as the performance of these devices increases, the hot carrier generation and reaction kinetics concepts driving degradation in sensitive regions of the device remain the same. The new mechanisms discussed here can be broadly categorized using the physics of high-voltage or high-current electrical stress conditions that have been well-studied. Measurements and TCAD simulations suggest that voltage-limited mechanisms consistently see worse degradation at lower temperatures while current-limited mechanisms respond to both higher temperature and higher current density. These limitations must be carefully evaluated during the development of new technologies and circuits.

Aluminium corrosion in power semiconductor devices

In this study, insulated gate bipolar transistor (IGBT) power modules were exposed to high voltage, high humidity, high temperature and reverse bias (HV-H3TRB) conditions until end-of-life (EoL). The limited lifetime of power semiconductor devices when used in demanding applications involving high relative humidity during operation is commonly reported to be associated with the design of the edge termination in power transistor or diode chips. A physics-of-failure (PoF) oriented methodology was adopted in failure analysis, including using lock-in thermography (LiT) for failure localisation and using an advanced microwave-induced plasma (MIP) decapsulation technique for the selective etching of the edge termination polyimide passivation film. A focused ion beam (FIB) was utilised to create a cross-section of the samples for both scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) analysis. The evidence gathered using the physics-of-failure methodology were compared with the results from advanced statistical analysis of the failure distributions in Weibull plots, including comparison of α and β parameters. This analysis revealed correlation with the Weibull distributions and the results from the physics-of-failure. Aluminium corrosion products were systematically observed on guard rings (GR) and field plates (FP) showing that the migration of these corrosion products forming an electrical path between the guard rings that seems to be a major failure mechanism in high humidity environments when reverse bias voltage is applied.

Novel polyimide binder for achieving high-rate capability and long-term cycling stability of LiNi0.8Co0.1Mn0.1O2 cathode via constructing polar and micro-branched crosslinking network structure

LiNi0.8Co0.1Mn0.1O2 (NCM811) material, as the promising cathode candidate for next-generation high-energy lithium-ion batteries, has gained considerable attention for extremely high theoretical capacity and low cost. Nevertheless, the intrinsic drawbacks of NCM811 such as unstable structure and inevitable interface side reaction result in severe capacity decay and thermal runaway. Herein, a novel polyimide (denoted as PI-OmDT) constructed with the highly polar and micro-branched crosslinking network is reported as a binder material for NCM811 cathode. The micro-branched crosslinking network is achieved by using 1,3,5-Tris(4-aminophenoxy) benzene (TAPOB) as a crosslinker via condensation reaction, which endows excellent mechanical properties and large free volume. Meanwhile, the massive polar carboxyl (−COOH) groups provide strong adhesion sites to active NCM811 particles. These functions of PI-OmDT binder collaboratively benefit to forming the mechanically robust and homogeneous coating layer with rapid Li+ diffusion on the surface of NCM811, significantly stabilizing the cathode structure, suppressing the detrimental interface side reaction and guaranteeing the shorter ion-diffusion and electron-transfer paths, consequently enhancing electrochemical performance. As compared to the NCM811 with PVDF binder, the NCM811 using PI-OmDT binder delivers a superior high-rate capacity (121.07 vs. 145.38 mAh g−1) at 5 C rate and maintains a higher capacity retention (80.38% vs. 91.6%) after 100 cycles at 2.5–4.3 V. Particularly, at the high-voltage conditions up to 4.5 and 4.7 V, the NCM811 with PI-OmDT binder still maintains the remarkable capacity retention of 88.86% and 72.5% after 100 cycles, respectively, paving the way for addressing the high-voltage operating stability of the NCM811 cathode. Moreover, the full-charged NCM811 cathode with PI-OmDT binder exhibits a significantly enhanced thermal stability, improving the safety performance of batteries. This work opens a new avenue for developing high-energy NCM811 based lithium-ion batteries with long cycle-life and superior safety performance using a novel and effective binder.