Control of High Voltage DC Links Between Interconnections for Small Signal Stability.
Abstract not provided.
Pierre, Brian Joseph↗
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Results for “voltage stability”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Broadband THz Modulation via Solid–State Organic Electrochemical Devices
The sub-Terahertz and Terahertz bands play a critical role in next-generation wireless communication and sensing technologies, thanks to the large amount of available bandwidth in this spectral regime. While long-wavelength (microwave to mm-Wave) and short-wavelength (near-infrared to ultraviolet) devices are well-established and studied, the sub-THz to THz regime remains relatively underexplored and underutilized. Traditional approaches used in the aforementioned spectral regions are more difficult to replicate in the THz band, leading to the need for the development of novel devices and structures that can manipulate THz radiation effectively. Herein a novel organic, solid-state electrochemical device is presented, capable of achieving modulation depths of over 90% from ≈500 nm of a conducting polymer that switches conductivity over a large dynamic range upon application of an electronically controllable external bias. The stability of such devices under long-term, repeated voltage switching, as well as continuous biasing at a single voltage, is also explored. Switching stabilities and long-term bias stabilities are achieved over two days for both use cases. Additionally, both depletion mode (always “ON”) and accumulation mode (always “OFF”) operation are demonstrated. These results suggest applications of organic electrochemical THz modulators in large area and flexible implementations.
36 MATERIALS SCIENCE↗
Stabilizing the Solid‐Electrolyte Interphase with Polyacrylamide for High‐Voltage Aqueous Lithium‐Ion Batteries
Abstract The introduction of “water‐in‐salt” electrolyte (WiSE) concept opens a new horizon to aqueous electrochemistry that is benefited from the formation of a solid‐electrolyte interphase (SEI). However, such SEI still faces multiple challenges, including dissolution, mechanical damaging, and incessant reforming, which result in poor cycling stability. Here, we report a polymeric additive, polyacrylamide (PAM) that effectively stabilizes the interphase in WiSE. With the addition of 5 molar % PAM to 21 mol kg −1 LiTFSI electrolyte, a LiMn 2 O 4 ∥L‐TiO 2 full cell exhibits enhanced cycling stability with 86 % capacity retention after 100 cycles at 1 C. The formation mechanism and evolution of PAM‐assisted SEI was investigated using operando small angle neutron scattering and density functional theory (DFT) calculations, which reveal that PAM minimizes the presence of free water molecules at the anode/electrolyte interface, accelerates the TFSI − anion decomposition, and densifies the SEI.
Hou, Xu↗
Stabilizing the Solid‐Electrolyte Interphase with Polyacrylamide for High‐Voltage Aqueous Lithium‐Ion Batteries
Abstract The introduction of “water‐in‐salt” electrolyte (WiSE) concept opens a new horizon to aqueous electrochemistry that is benefited from the formation of a solid‐electrolyte interphase (SEI). However, such SEI still faces multiple challenges, including dissolution, mechanical damaging, and incessant reforming, which result in poor cycling stability. Here, we report a polymeric additive, polyacrylamide (PAM) that effectively stabilizes the interphase in WiSE. With the addition of 5 molar % PAM to 21 mol kg −1 LiTFSI electrolyte, a LiMn 2 O 4 ∥L‐TiO 2 full cell exhibits enhanced cycling stability with 86 % capacity retention after 100 cycles at 1 C. The formation mechanism and evolution of PAM‐assisted SEI was investigated using operando small angle neutron scattering and density functional theory (DFT) calculations, which reveal that PAM minimizes the presence of free water molecules at the anode/electrolyte interface, accelerates the TFSI − anion decomposition, and densifies the SEI.
25 ENERGY STORAGE↗
Acidity-Governed Rules in the Electrochemical Performance of Fluorinated Benzenes for High-Voltage Lithium Metal Batteries
Judicious selection of the optimal fluorobenzene (FB) as a nonsolvating cosolvent for lithium metal batteries (LMBs) is reported. For this work, we found the key correlation between FB structures and cycling stabilities of cells: increased fluorine substitution of FBs results in higher anodic stability but at the expense of reduced reductive stability, and FBs containing three or more fluorine atoms exhibit insufficient anodic stability in the electrolyte system comprised of fluoroethylene carbonate (FEC) and ethyl methyl carbonate (EMC). More importantly, FBs with higher acidity (lower pK a ) due to protons located between two adjacent fluorine atoms tend to be more susceptible to side reactions during cycling. Our results indicate that difluorobenzenes with no “acidic” proton (DFB2 and DFB4) have emerged as the optimal choice with the desired redox stability in high-voltage LMBs. Nuclear magnetic resonance and X-ray photoelectron spectroscopy confirmed these findings, providing guidance for selecting the most suitable FB variants as nonsolvating cosolvents for high-voltage LMBs.
25 ENERGY STORAGE↗
Structural Degradation of High Voltage Lithium Nickel Manganese Cobalt Oxide (NMC) Cathodes in Solid-State Batteries and Implications for Next Generation Energy Storage
In this study, we report the stability of the layered high voltage cathode NMC622 with respect to a standard liquid electrolyte and in an all solid-state configuration. NMC622 cathodes with a (104) orientation were found to suffer from degradation at high voltage (4.5 V vs Li/Li + ) due to electrolyte-promoted degradation of the layered structure in a carbonate electrolyte. The lithium phosphorus oxynitride (LiPON) electrolyte was able to suppress the extent of this decomposition in solid-state cells but not totally prevent it from occurring. In the solid-state cells the capacity decreased from 203 to 93 mAh/g in the first cycle and from 93 to 79 mAh/g over the subsequent 99 cycles, whereas, after 20 cycles, the liquid cell charge capacity was dominated by the irreversible electrolyte degradation. Furthermore, the interfacial resistances of the solid-state cells were stable with cycling, suggesting minimal degradation of the NMC622/LiPON interface and incumbent losses due to structural evolution associated with cathode orientation. This data indicates that accessing stable high voltage capacity in NMCs will not be enabled by simply stabilizing the cathode–electrolyte interface. Optimizing cathode crystallographic orientation may be the key to accessing this high voltage regime.
25 ENERGY STORAGE↗
Revealing the Nature of Binary-Phase on Structural Stability of Sodium Layered Oxide Cathodes
The emergence of layered sodium transition metal oxides featuring a multiphase structure presents a promising approach for cathode materials in sodium-ion batteries, showcasing notably improved energy storage capacity. However, the advancement of cathodes with multiphase structures faces obstacles due to the limited understanding of the integrated structural effects. Herein, the integrated structural effects by an in-depth structure-chemistry analysis in the developed layered cathode system Na x Cu 0.1 Co 0.1 Ni 0.25 Mn 0.4 Ti 0.15 O 2 with purposely designed P2/O3 phase integration, are comprehended. The results affirm that integrated phase ratio plays a pivotal role in electrochemical/structural stability, particularly at high voltage and with the incorporation of anionic redox. In contrast to previous reports advocating solely for the enhanced electrochemical performance in biphasic structures, it is demonstrated that an inappropriate composite structure is more destructive than a single-phase design. The in situ X-ray diffraction results, coupled with density functional theory computations further confirm that the biphasic structure with P2:O3 = 4:6 shows suppressed irreversible phase transition at high desodiated states and thus exhibits optimized electrochemical performance. Finally, these fundamental discoveries provide clues to the design of high-performance layered oxide cathodes for next-generation SIBs.
36 MATERIALS SCIENCE↗
Improved Control Strategy of Grid-Forming Inverters for Fault Ride-Through in a Microgrid System
This paper develops an improved control strategy of grid-forming (GFM) inverters with fault ride-through capabilities to guarantee the stable operation of microgrids under fault conditions, especially islanded microgrids and asymmetrical faults. The proposed control strategy includes the dual control of positive-sequence and negative-sequence control as well as the adaptive virtual impedance (VI) control. Unlike existing works, the proposed strategy applies the VI control for only the d component of the positive-sequence control and leaves the q component of the positive-sequence control and the dq component of the negative-sequence control as zero, thus achieving improved stability and balanced three-phase voltages under asymmetrical faults. The adaptive feature of the VI control guarantees the stability of the GFM inverter under severe faults, which could cause the saturation of the inner current loop and instability if the VI is not adaptive. Simulation results of various unbalanced faults with high- and low-fault impedances show that the proposed control strategy improves the stability of the GFM inverter and achieves stable and balanced output voltages in islanded microgrids. And the algorithm also improves the stability of GFM inverters under balanced faults with high- and low-fault impedances.
adaptive virtual impedance control↗
Improved Control Strategy of Grid-Forming Inverters for Fault Ride-Through in a Microgrid System
This paper develops an improved control strategy of grid-forming (GFM) inverters with fault ride-through (FRT) capabilities to guarantee the stable operation of microgrids under fault conditions, especially islanded microgrids and asymmetrical faults. The proposed control strategy includes the dual control of positive-sequence and negative-sequence control as well as the adaptive virtual impedance (VI) control. Unlike existing works, the proposed strategy applies the VI control for only the d component of the positive-sequence control and leaves the q component of the positive-sequence control and the dq component of the negative-sequence control as zero, thus achieving improved stability and balanced three-phase voltages under asymmetrical faults. The adaptive feature of the VI control guarantees the stability of the GFM inverter under severe faults, which could cause the saturation of the inner current loop, and the instability if the VI is not adaptive. Simulation results of various unbalanced faults with high and low fault impedances show that the proposed control strategy improves the stability of the GFM inverter and achieves stable and balanced output voltages in islanded microgrids. And the algorithm also improves the stability of GFM inverters under balanced faults with high and low fault impedances.
adaptive virtual impedance control↗
Stabilizing lattice oxygen redox in layered sodium transition metal oxide through spin singlet state
Abstract Reversible lattice oxygen redox reactions offer the potential to enhance energy density and lower battery cathode costs. However, their widespread adoption faces obstacles like substantial voltage hysteresis and poor stability. The current research addresses these challenges by achieving a non-hysteresis, long-term stable oxygen redox reaction in the P3-type Na 2/3 Cu 1/3 Mn 2/3 O 2 . Here we show this is accomplished by forming spin singlet states during charge and discharge. Detailed analysis, including in-situ X-ray diffraction, shows highly reversible structural changes during cycling. In addition, local CuO 6 Jahn-Teller distortions persist throughout, with dynamic Cu-O bond length variations. In-situ hard X-ray absorption and ex-situ soft X-ray absorption study, along with density function theory calculations, reveal two distinct charge compensation mechanisms at approximately 3.66 V and 3.99 V plateaus. Notably, we observe a Zhang-Rice-like singlet state during 3.99 V charging, offering an alternative charge compensation mechanism to stabilize the active oxygen redox reaction.
25 ENERGY STORAGE↗
High-Voltage and High-Safety Practical Lithium Batteries with Ethylene Carbonate-Free Electrolyte
Serious safety issues are impeding the widespread adoption of high-energy lithium-ion batteries for transportation electrification and large-scale grid storage. Herein, a triple-salt ethylene carbonate (EC) free electrolyte for high-safety and high-energy pouch-type LiNi 0.8 Mn 0.1 Co 0.1 O 2 |graphite (NMC811|Gr) cells is reported. This EC-free electrolyte can effectively stabilize the NMC811 surface under high potential (up to 4.5 V), as well as generate a stable interphase to achieve a superior compatibility with the Gr anode. The electrolyte strategy enables significantly enhanced intrinsic safety (trigger temperature of thermal runaway (TR) increased by 67.0 °C), excellent electrochemical properties (4.2V, ≈100% after 200 cycles), and superior high voltage stability (4.5 V, 82.1% after 200 cycles). Furthermore, the work opens up a new avenue for developing novel electrolyte systems to build safer high-energy batteries for practical applications.
25 ENERGY STORAGE↗
Delineating the Factors Impacting the Electrochemical Behavior of Single-Crystal High-Nickel Layered Oxide Cathodes
High-nickel (Ni) (≥80%) single-crystal LiNi 1-x-y Mn x Co y O 2 (NMCs) have garnered recent interest as cathodes in lithium (Li)-ion batteries (LIBs). However, capacity fade at high voltages, particularly after the onset of the H2–H3 phase transition, hampers their viability. In this study, single-crystal LiNi 0.8 Mn x Co 0.2-x O 2 (x = 0.2, 0.1, 0) are synthesized and tested in LiPF 6 in ethyl methyl carbonate-based electrolytes, with and without monofluoroethylene carbonate and LiF 2 PO 2 additives, to clarify the effects of Co/Mn ratio and surface stabilization on high-voltage cycling degradation. By imposing a kinetic barrier to the accessible H2–H3 capacity, surface reconstruction is identified as the primary driver of high-voltage capacity loss, being greater in the Co-free cathode and in the absence of fluorinated electrolyte components. This is attributed to a synergy between increased mechanical stress due to worsened bulk and interfacial H2–H3 kinetics and decreased interfacial stability due to the poor passivating capability of the electrolyte. Here, the findings highlight the importance of limiting cathode impedance growth during high-voltage cycling, which can be achieved by tuning bulk dopants and electrolyte chemistry.
25 ENERGY STORAGE↗
Different interfacial reactivity of lithium metal chloride electrolytes with high voltage cathodes determines solid-state battery performance
A deep understanding of the interaction of the surface of cathode materials with solid electrolytes is crucial to design advanced solid-state batteries (SSBs). This is especially true for the new class of lithium metal chloride (Li-M-Cl) solid electrolytes which are receiving rapidly growing attention due to their very high oxidative stability (>4 V) in combination with good ionic conductivity that can enable long cell cycle life. While Li-M-Cl electrolytes typically contain resource-limited metals (M) such as indium or rare earths, work has focused on substituting M with more abundant elements such as zirconium. Via operando resistance measurements using intermittent current interruption we explore the dynamic evolution of the interphase at the surface of Ni-rich NCM85 or NCM111 cathode particles inside a working SSB with three different Li-(M 1 ,M 2 )-Cl catholytes (Li 3 InCl 6 , Li 2 Sc 1/3 In 1/3 Cl 4 and Li 5/2 Y 1/2 Zr 1/2 Cl 6 ) to reveal the impact of the cationic metal substitution on the interfacial chemistry. We show that the metal plays a critical role in determining high voltage stability, contrary to prior assumptions. Using a combination of cyclic voltammetry and ultraviolet photoelectron spectroscopy measurements of the electronic band structure to assess oxidative stability; coupled with DFT calculations and ToF-SIMS to evaluate products formed at the interface at different upper cutoff potentials and degrees of delithiation, we are able to differentiate between electrochemical and chemical degradation. We find that Li 2 Sc 1/3 In 1/3 Cl 4 yields the highest (and Li 3 InCl 6 the lowest) stability against electrochemical oxidation, while Li 5/2 Y 1/2 Zr 1/2 Cl 6 undergoes a detrimental chemical reaction with oxygen released from Ni-rich NCM85 at high potentials, resulting in fast capacity fading. Altogether, our work establishes a platform for the metrics and an approach that can be utilized to efficiently evaluate the stability of new halide SEs in SSB cells.
25 ENERGY STORAGE↗
Spatial Heterogenous Redox Couples Degradation in Sodium-Ion Battery Cathode Materials and the Mitigation of Voltage Fade by Blocking Oxygen Release
The use of anionic redox has become a new paradigm for improving the energy density of rechargeable batteries, which is essential for improving the market competitiveness of sodium-ion batteries. However, issues such as voltage attenuation and cycling stability degradation persist in layered oxide anion redox cathode materials. Here, in this study, we systematically investigate the classic Na-ion cathode material Na 0.6 Li 0.2 Mn 0.8 O 2 , and the primary causes of voltage decay are identified as the activation of cations and the reduction in anion redox activity. In addition, the activation of cations is closely associated with anion reactions. Through the application of sophisticated multiscale synchrotron absorption spectroscopy and imaging techniques, we have identified a pronounced pattern of spatially dependent degradation in the evolution of redox couples, which is more evident from the material’s surface to its core. With this understanding, we introduced a surface fluorination approach that modulates the local chemical coordination environment. This strategy increases the formation energy of surface oxygen vacancies and locks transition metals oxide state. Consequently, it enables more reversible anionic redox reactions, which block the spatial progression of degradation and mitigates voltage decay.
25 ENERGY STORAGE↗
Materials design of sodium chloride solid electrolytes Na3MCl6 for all-solid-state sodium-ion batteries
All-solid-state sodium-ion batteries have attracted increasing attention owing to the low cost of sodium and the enhanced safety compared to conventional Li-ion batteries. Recently, halides have been considered as promising solid electrolytes (SEs) due to their favorable combination of high ionic conductivity and chemical stability against high-voltage cathode materials. Although a wide variety of lithium chloride SEs, Li 3 MCl 6 , have been developed for high-voltage all-solid-state batteries, only a limited number of sodium chloride SEs have been reported. This study aims to offer a material design insight for the development of sodium chloride SEs through systematic assessment of the phase stability, electrochemical stability, and transport properties of novel Na 3 MCl 6 SEs. Structural calculations indicate that Na 3 MCl 6 exhibits trigonal $P\bar{3}$1c, monoclinic P2 1 /n, and trigonal $R\bar{3}$ phases, and the stable phase of Na 3 MCl 6 is dependent on the type and ionic radius of M. Na 3 MCl 6 typically exhibits a high oxidation potential, demonstrating good electrochemical stability against cathodes. The bond-valence site energy and ab initio molecular dynamics calculations revealed that Na 3 MCl 6 with P2 1 /n and $R\bar{3}$ phases showed low ionic conductivity, while the $P\bar{3}$1c phase slightly improved the ionic conductivity of Na 3 MCl 6 . The formation of Na vacancies by aliovalent substitution considerably increased the ionic conductivity up to four orders of magnitude for pristine Na 3 MCl 6 , exhibiting ~10 –5 S cm –1 for trigonal $P\bar{3}$1c and $R\bar{3}$ phases. The formation of defects could further enhance the ionic conductivity of Na 3 MCl 6 , and the optimization of defect type and ratio can be helpful in developing superionic Na chloride SEs. The material design of Na 3 MCl 6 in this study will provide fundamental guidelines for the development of novel sodium halide SEs for all-solid-state sodium-ion batteries.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Hydrogen bonds enhanced composite polymer electrolyte for high-voltage cathode of solid-state lithium battery
Polymer electrolyte is one of the important components for developing advanced solid-state lithium batteries (SSLBs). However, the narrow electrochemical stability window restricts the practical application with high-voltage cathodes. In this study, a series of composite solid electrolytes (CSEs), possessing both wide electrochemical stability window (up to 5.0 V vs. Li + /Li) and high ionic conductivity (over 1.35×10 -3 S/cm at 25 °C), were reported by integrating SiO 2 nanoparticles into poly(vinyl ethylene carbonate) polymer electrolyte. The enhanced anti-oxidation performances are mainly caused and confirmed by the local intermolecular interactions of hydrogen bonds in CSE. Based on this CSE, the SSLBs with LiCoO 2 cathode present good cycle stability at high voltage, and the capacity retention with 4.5 V cut-off voltage is about 94% after 200 cycles. This work not only proves the importance of intermolecular interactions in CSE, but also provides an effective method for achieving high-energy SSLBs with enhanced interface compatibility between polymer electrolyte and highvoltage cathodes
25 ENERGY STORAGE↗
Systems-level investigation of aqueous batteries for understanding the benefit of water-in-salt electrolyte by synchrotron nanoimaging
Water-in-salt (WIS) electrolytes provide a promising path toward aqueous battery systems with enlarged operating voltage windows for better safety and environmental sustainability. In this work, a new electrode couple, LiV 3 O 8 -LiMn 2 O 4 , for aqueous Li-ion batteries is investigated to understand the mechanism by which the WIS electrolyte improves the cycling stability at an extended voltage window. Operando synchrotron transmission x-ray microscopy on the LiMn 2 O 4 cathode reveals that the WIS electrolyte suppresses the mechanical damage to the electrode network and dissolution of the electrode particles, in addition to delaying the water decomposition process. Because the viscosity of WIS is notably higher, the reaction heterogeneity of the electrodes is quantified with x-ray absorption spectroscopic imaging, visualizing the kinetic limitations of the WIS electrolyte. This work furthers the mechanistic understanding of electrode–WIS electrolyte interactions and paves the way to explore the strategy to mitigate their possible kinetic limitations in three-dimensional architectures.
36 MATERIALS SCIENCE↗
Additive engineering for robust interphases to stabilize high-Ni layered structures at ultra-high voltage of 4.8 V
Nickel-rich layered cathode materials promise high energy density for next-generation batteries when coupled with lithium metal anodes. However, the practical capacities accessible are far less than the theoretical values due to their structural instability during cycling, especially when charged at high voltages. Here we demonstrate that stable cycling with an ultra-high cut-off voltage of 4.8 V can be realized by using an appropriate amount of lithium difluorophosphate in a common commercial electrolyte. The Li||LiNi 0.76 Mn 0.14 Co 0.10 O 2 cell retains 97% of the initial capacity (235 mAh g -1 ) after 200 cycles. The cycling stability is ascribed to the robust interphase on the cathode. It is formed by lithium difluorophosphate decomposition, which is facilitated by the catalytic effect of transition metals. The decomposition products (Li 3 PO 4 and LiF) form a protective interphase. This suppresses transition metal dissolution and cathode surface reconstruction. It also facilitates uniform Li distribution within the cathode, effectively mitigating the strain and crack formation.
25 ENERGY STORAGE↗