Current Battery Systems Research Articles

Unlocking the decomposition limitations of the Li2C2O4 for highly efficient cathode preliathiations

The development of high-energy-density Li-ion batteries is hindered by the irreversible capacity loss during the initial charge-discharge process. Therefore, pre-lithiation technology has emerged in the past few decades as a powerful method to supplement the undesired lithium loss, thereby maximizing the energy utilization of LIBs and extending their cycle life. Lithium oxalate (Li2C2O4), with a high lithium content and excellent air stability, has been considered one of the most promising materials for lithium compensation. However, the sluggish electrochemical decomposition kinetics of the material severely hinders its further commercial application. Here, we introduce a recrystallization strategy combined with atomic Ni catalysts to modulate the mass transport and decomposition reaction kinetics. The decomposition potential of Li2C2O4 is significantly decreased from ∼4.90V to ∼4.30V with a high compatibility with the current battery systems. In compared to the bare NCM//Li cell, the Ni/N-rGO and Li2C2O4 composite (Ni-LCO) modified cell releases an extra capacity of ∼11.7 ​%. Moreover, this ratio can be magnified in the NCM//SiOx full cell, resulting in a 30.4 ​% higher reversible capacity. Overall, this work brings the catalytic paradigm into the pre-lithiation technology, which opens another window for the development of high-energy-density battery systems.

Toward Sustainable Polymer Materials for Rechargeable Batteries: Utilizing Natural Feedstocks and Recycling/Upcycling of Polymer Waste.

The ever-increasing demand for rechargeable battery systems in the era of electric vehicles has spurred extensive research into developing polymeric components for batteries, such as separators, polymer electrolytes, and binders. However, current battery systems rely on expensive and nonrenewable resources, which potentially have a negative environmental impact. Therefore, polymer materials derived from natural resources have gained significant attention, primarily due to their cost-effective and environmentally sustainable features. Moreover, natural feedstocks often possess highly polar functional groups and high molecular weights, offering desirable electro-chemo-mechanical features when applied as battery materials. More recently, various recycling and upcycling strategies for polymeric battery components have also been proposed given the substantial waste generation from end-of-life batteries. Recycling polymeric materials includes an overall process of recovering the components from spent batteries followed by regeneration into new materials. Polymer upcycling into battery materials involves transforming daily-used plastic waste into high-value-added battery components. This review aims to give a state-of-the-art overview of contemporary methods to develop sustainable polymeric materials and recycling/upcycling strategies for various battery applications.

Water Vapor Induced Superionic Conductivity in ZnPS3.

Next-generation batteries based on sustainable multivalent working ions, such as Mg2+, Ca2+, or Zn2+, have the potential to improve the performance, safety, and capacity of current battery systems. Development of such multivalent ion batteries is hindered by a lack of understanding of multivalent ionics in solids, which is crucial for many aspects of battery operation. For instance, multivalent ionic transport was assumed to be correlated with electronic transport; however, we have previously shown that Zn2+ can conduct in electronically insulating ZnPS3 with a low activation energy of 350 meV, albeit with low ionic conductivity. Here, we show that exposure of ZnPS3 to environments with water vapor at different relative humidities results in room-temperature conductivity increases of several orders of magnitude, reaching as high as 1.44 mS cm-1 without decomposition or structural changes. We utilize impedance spectroscopy with ion selective electrodes, ionic transference number measurements, and deposition and stripping of Zn metal, to confirm that both Zn2+ and H+ act as mobile ions. The contribution from Zn2+ to the ionic conductivity in water vapor exposed ZnPS3 is high, representing superionic Zn2+ conduction. The present study demonstrates that it is possible to enhance multivalent ion conduction of electronically insulating solids as a result of water adsorption and highlights the importance of ensuring that increased conductivity in water vapor exposed multivalent ion systems is in fact due to mobile multivalent ions and not solely H+.

Vertically-oriented zinc-doped γ-MnO2 nanowalls as high-rate anode materials for li-ion batteries

Micro lithium-ion batteries (micro-LIBs), featuring small size, lightweight, high capacity, and long cycle life, are considered as promising on-chip micropower sources for a wide variety of miniaturized electronics. Three-dimensional (3D) self-supported anode nanoarchitectures are key to developing high-performance micro-LIBs. Manganese dioxide (MnO2) based rechargeable batteries, with high energy and power density, have received a great deal of attention as a potential alternative to the current battery systems. However, MnO2, with poor electrical conductivity and large volume change, always suffers from insufficient rate capability and inferior cycling stability during Li+ ion insertion/extraction, causing limited commercial applications. Herein, we report a facile one-step electrochemical deposition process for directly growing Zn-doped γ-MnO2 nanowalls (Zn/γ-MnO2 pNW) with inter-networked vertically-oriented 3D porous frameworks onto Ni foam, that results in a superior performance binder-free anode material for micro-LIBs. The 3D porous Zn-doped γ-MnO2 nanowalls exhibit an ultrahigh reversible capacity of ~2579.4 mAh g−1 at 0.1 A g−1. Importantly, the combined advantages of 3D porous nanowall architecture, 1D tunnels in γ-MnO2 crystalline, and zinc doping in MnO2, exhibit tremendous benefits for rate capability, owing to minimization of the electronic and ionic resistance as well as the decrease for ionic diffusion paths, reaching 828.5 mAh g−1 at 20 A g−1. Even at high current density of up to 50 A g−1, the electrode still delivers a capacity of 127.0 mAh g−1 after 5000 cycles. When cycled at 5 A g−1, a reversible capacity of 1545.4 mAh g−1 with a capacity retention of 92.2 % is obtained after 1500 cycles. With a simple synthetic process and desirable electrochemical performance, the Zn/γ-MnO2 pNW may present a promising opportunity for large-scale miniature power sources with high-power properties.

Polymers in Lithium‐Ion and Lithium Metal Batteries

AbstractLithium‐ion batteries play a significant role in modern electronics and electric vehicles. However, current Li‐ion battery chemistries are unable to satisfy the increasingly heightened expectations regarding energy demand and reliability. To boost the overall energy density while ensuring the safety of Li batteries, researchers have focused on alternative battery materials, such as silicon, sulfur, and Li metal. These represent promising avenues, although numerous obstacles (e.g., Si cracking, polysulfide shuttling, Li dendrites, etc.) must be tackled before batteries based on these materials can enter mass production and penetrate the mainstream market. Polymers are a class of materials that are widely used in current battery systems; however, many novel polymer chemistries may offer better performance and reliability than the current ones, and even overcome the issues of the above‐mentioned new battery materials. In this review, selected polymeric materials for solving these issues are categorized into four parts: polymer electrolytes, polymer artificial solid‐electrolyte interphases, binders, and separators. Both the current progress and the characterization methods are included. Potential future directions of energy materials research are pointed out as well.

(Invited) Cation-Disordered Li3VO4-Based Materials As a Pseudocapacitive Negative Electrode

The growing demand for fast charge-discharge electrical energy storage (EES) devices with long cycles lifetimes has led to the need for alternatives to current battery systems, which store energy via slow faradic reactions. Among different EES technologies, electric double layer capacitors (EDLCs) are considered as promising devices due to their high-power, safe and long-lived characteristics. One of the approaches to further enhance the cell voltage and energy density of EDLCs while maintaining their high power is to replace the activated carbon with ultrafast lithium ion battery materials as hybrid supercapacitors.The orthorhombic β-Li3VO4 (β-LVO) has been identified as a promising negative electrode material for hybrid supercapacitors, with theoretical specific capacity of 394 mAh g-1 (2 lithium accommodation)[1]. The electron-donor effect of Li, exactly opposite to the inductive effect of polyanions, lowers the redox potentials of V5+/V4+ and V4+/V3+ to a safe but still low potential range between 1.3 and 0.4 V vs. Li/Li+, compared to the 3.0 V usually observed for V2O5. Recent our studies [1-2] unveiled that both the structure and electrochemical signature change of the β-LVO during the initial cycling, resulting in what we termed as electrochemical activation process. This electrochemical activation process induces the transformation of β-LVO from the pristine cation-ordered structure into an activated LVO, which has a Li+/V5+ cation-disordered structure. Charge discharge curves also change from “battery-like” plateau to “pseudocapacitive” slope via such cation-disordering of LVO, along with its reaction mechanism change from two-phase to solid-solution reaction[2]. Li+ diffusion coefficient (DLi ) evaluation by galvanostatic intermittent titration technique (GITT) reveals that the DLi of cation-disordered LVO is two orders of magnitude higher than the one of pristine β-LVO. Yet, the preparation method of cation-disordered LVO has been a major issue as the electrochemical activation process of β-LVO is impractical from the industrial point of view. Such electrochemical process requires a precycling of β-LVO for 10-20 cycles down to low potential below 0.4 V vs. Li/Li+, which is difficult to control and inevitably produces undesirable irreversible capacity for a full cell assembling.In this talk, we introduce an alternative to the electrochemical process, i.e., the direct synthesis of fully cation-disordered LVO via simple mechanical milling of the pristine β-LVO powder (Fig.1). The mechanochemical process brings about the disordering of LVO cation sublattice and thus enables to obtain thermodynamically metastable cation-disordered LVO phase without any precycling. Comparison of X-ray and neutron powder diffraction patterns confirmed the successful direct synthesis of cation-disordered LVO. The mechanochemically cation-disordered LVO shows superior rate performances to those of β-LVO and even electrochemically cation-disordered LVO. Another strategy to synthesize pseudocapacitive LVO-based material is a partial substitution of V5+ with Si4+ in β-LVO, which results in a transformation into γ-Li3+xV1-xSixO4. The γ-Li3+xV1-xSixO4 , with a partially V5+/Si4+ cation-disordered structure shows similar psuedocapacitive behavior as a fully cation-disordered LVO with enhanced DLi and rate capability compared to the β-LVO, thanks to the randomly distribution of V5+. In the presentation, we introduce those two approaches, “fully” or “partially” cation-disordering, as new paths for transformation of battery into pseudocapacitive materials with improved electrochemical performances by simple cation mixing.

Building Digital Battery System via Energy Digitization for Sustainable 5G Power Feeding

In the upcoming era of 5G, the number of base stations, edge computing nodes and data centers is believed to be three to five times more than that of 4G. Serious challenges on the deployment and operation of 5G networks and services arise, especially on how to build and maintain battery energy storage systems for sustainable 5G power feeding at low cost for all scenarios. Although battery has long been used as a major backup power in various communications systems, current battery systems essentially are dumb devices. In the current battery systems, the charging/discharging energy flow is continuous due to the fixed series-parallel cell topology adopted by existing battery systems. The fixed topology also causes the bucket effect at the system level due to the fact that it is incapable of handling cell difference in a battery system, leading to a series of system-level problems in terms of power density, energy efficiency, cycle life, reliability, and safety. All these will make it very challenging for sustainable 5G power feeding, which will further affect the cost-effective deployment and operation of 5G networks and services. Thanks to the recent breakthrough of power electronics semiconductors, such as power metal-oxide- semiconductor field-effect transistor (MOSFET), silicon carbide (SiC) and gallium nitride (GaN) with their outstanding material properties, it becomes feasible to carry out digital energy processing operations at high switching speed, high voltage, and feverish temperature. By building a new digital grid-to-chip power train using high switching speed power semiconductors, traditional analog battery systems can be transformed into digital battery systems through energy digitization, which will significantly facilitate feasible 5G deployment and operation. In this article, we will propose and describe the basic concept of energy digitization, the design framework of the digital battery system including key components, modeling, and the performance evaluation of the digital battery system. Results of experiments and real-world applications show the effectiveness and efficiency of digital battery system, which offer a promising disruptive approach to sustainable 5G power feeding.

Decimal Solvent-Based High-Entropy Electrolyte Enabling the Extended Survival Temperature of Lithium-Ion Batteries to −130 °C

Freezing and crystallization of commercial ethylene carbonate-based binary electrolytes, leading to irreversible damage to lithium-ion batteries (LIBs), remain a significant challenge for the survi...

Estimating revenues from offshore wind-storage systems: The importance of advanced battery models

We investigate six different lithium-ion battery modeling approaches to highlight the importance of accurately representing batteries in decision tools. Advanced mixed-integer-linear battery models account for efficiencies as a function of the discharge power, power-limits as a function of the state-of-charge, along with degradation, which are usually not accounted for in power systems models. The revenue potential from offshore wind paired with battery systems is then examined using the more advanced representation where degradation is the sum of the capacity fades resulting from calendar- and cycle-aging. The impacts of variability of offshore wind output along with energy- and capacity-market prices are evaluated using publicly available data from 2010 to 2013 using NYISO as a test case. For 2013, results highlight that without accurate battery representations, models can overestimate battery revenues by up to 35%, resulting primarily from degradation-tied costs. Advanced dispatch algorithms that account for calendar- and cycle-aging of the battery can help operate the battery more efficiently. Locating the battery onshore yields higher revenues and with wider useable SOC windows, it is possible to monetize higher arbitrage opportunities, which can compensate for any additional degradation-tied costs. The added value of a MWh of energy storage varies from $2 to $4.5 per MWh of wind energy, which leads to a breakeven cost range of $50–115 per kWh for the battery systems. As such, energy- and capacity-market revenues were found to be insufficient in recovering the investment costs of current battery systems for the applications considered in this analysis.

(Invited) Design and Application of Advanced Materials in Electrochemical Energy Storage Systems

Green, efficient energy storage and conversion systems are an important means of addressing global environmental and energy crisis. The current battery systems have been difficult to meet the increasing market demand due to their relatively low energy densities, therefore it is urgent to develop new energy storage technologies with high energy density and low cost. To this end, Professor Zhongwei Chen and his research group adhere to a bottom-up “material-electrode-battery-system” strategy to develop a variety of advanced energy storage technologies, including lithium-ion batteries, zinc-air batteries, fuel cells, for a wide range of energy storage applications. Through the rational material design and engineering, various high-performance electrodes with hierarchical micro- and nanostructures have been developed. Moreover, the electrode structures are controlled and optimized toward high recharge efficiency and energy density. Together, these innovate materials and electrode architectures practically allow industrial assembly and production of more efficient, affordable, and safer battery systems for clean and sustainable energy storage.

Self-Diffusion of Electrolyte Species in Composite Battery Electrodes Using PFG-SE MAS NMR for Better Understanding of Their Electrochemical Performance

Long charging times and low power to mass output of current battery systems limit their widespread use for automotive applications. The maximum charging rate is believed to be ultimately limited by diffusion of the lithium ion in the pores of the electrode. The interplay between electrode microstructure, electrochemical performance and lithium ion diffusion must be further studied to improve battery engineering. Electrochemical modelling combined with complementary experimental measurements will enable the development of a tool that will allow battery engineers to tailor battery architectures and in turn increase their performance. Herein, the electrochemical performance of NMC532-based positive electrodes designed for EV application were analyzed with the penetration depth model. A very simple relation was postulated by Gallagher et.al. [1] relating the depth of penetration of the lithium salt in the electrode pore matrix with the ratio of the capacity of the battery at high C-rates (typically C or higher) against its capacity at low rates (typically C/100 or lower). DoD = (Qhigh C-rate/Qlow C-rate) = Ld/L = [(ε⋅D0⋅C0⋅F)/(TL(1-t+)I)] Where Ld is the salt penetration distance, L is the thickness of the electrode, ϵ is the porosity, T is the tortuosity, D0 is the salt self-diffusion coefficient in the electrolyte, C0 is the electrolyte concentration, F is the Faraday’s constant, I is the applied current density and t+ is the cation transference number. The penetration depth model was then used to reproduce experimental electrochemical data of the NMC532-based electrodes. Half-cells made with NMC532 positive electrodes and Li metal negative electrodes were assembled. The NMC532 electrodes were designed with varying degrees of loading, mass percentages of electrode components and calendaring to evaluate electrode microstructure effects against electrode performance. LP30 was chosen as electrolyte and the cells were cycled thru a power test. Three formation cycles of C/10 followed by a power series that includes charge and discharge steps ranging between C/10 and 10C. The temperature was also varied from 0°C to 40°C to evaluate its influence on the electrochemical performance. Electrochemical data shows that denser (less porous) electrodes exhibited less gravimetric capacity than more porous electrodes at higher C-rates whereas the opposite is observed at low C-rates. It was also observed that electrodes having increased active material content and decreased carbon additive content have increased gravimetric capacity than their counterparts. Results from these electrochemical tests were then compared to the fits obtained from the penetration depth model and the resulting fits were in good accordance with each other. The fitted self-diffusion coefficient D0 (which probes the ability of the lithium salt to diffuse into the electrode pores) was retrieved at various temperatures, displaying a trend parallel to the one measured for D(Li+) obtained from PFG-SE NMR for comparison, indicating similar activation energies. However, the effective D0 is smaller compared to the bulk electrolyte, even after accounting for tortuosity and porosity, highlighting other additional effects. Pulsed Field Gradient Spin - Echo NMR (PFG-SE NMR) probes the self-diffusion of spin-bearing species in liquids. Although the technique has been applied to measure self-diffusion coefficients of the electrolyte species when confined into separators and/or membranes, it has never been applied to battery electrodes.[2,3] Paramagnetic electrode materials prevent the measurement of PFG-SE signals, however, composite model electrodes with alumina can be studied by PFG-SE NMR if Magic Angle Spinning is applied to increase resolution. Therefore, the role of binder materials on lithium diffusion was probed by PFG-SE NMR with binder films wetted with LP30 electrolyte, or with alumina/binder/carbon black composites, shedding a new light on these complex systems. Acknowledgments Financial funding from the ANR program no. ANR-15-CE05-0001-01 is acknowledged.

Membrane-Less Hydrogen Iron Redox Flow Battery

In this study, a new type of redox flow battery (RFB) named “membrane-less hydrogen-iron RFB” was investigated for the first time. The membrane is a cell component dominating the cost of RFB, and iron is an abundant, inexpensive, and benign material, and thus, this iron RFB without the membrane is expected to provide a solution to the challenging issues of current battery systems such as high cost and safety concerns. The research focus in this study was placed on defining key design parameters to make this new system promising as an RFB. Crossing rate of reactants over carbon porous electrode (CPE) was controlled by modifying its pore structure with Teflon impregnation, and the effects of the Teflon on crossover, kinetic, Ohmic, and mass transfer was investigated by cell-based test and one-dimensional computational model. It was found that the cell performance (i.e., charge and discharge polarization) of the new membrane-less system was equivalent to that of the conventional membrane-system (i.e., RFB having a membrane). Especially, the Ohmic properties of the new system were constant and stable, while in the conventional membrane system, they were significantly varied and deteriorated as cell tests were continued, indicating that degradation or contamination of membrane affecting Ohmic properties could be mitigated effectively in the membrane-less system, which was found first in this research. The modeling analysis provided insight into the system, showing that the effect of reactant crossover on performance decay was not significant, and Teflon impregnation in the CPE caused significant kinetic and Ohmic losses by impeding ion transport and reactant access to reaction sites. From this study, it was found that the membrane-less H2-iron system is feasible and promising in resolving the challenge issues of the conventional systems. And the results of this study are expected to provide guidelines for research and development of flow battery systems without having a membrane.

Solid‐State Sodium Batteries

AbstractRechargeable Na‐ion batteries (NIBs) are attractive large‐scale energy storage systems compared to Li‐ion batteries due to the substantial reserve and low cost of sodium resources. The recent rapid development of NIBs will no doubt accelerate the commercialization process. As one of the indispensable components in current battery systems, organic liquid electrolytes are widely used for their high ionic conductivity and good wettability, but the low thermal stability, especially the easy flammability and leakage make them at risk of safety issues. The booming solid‐state batteries with solid‐state electrolytes (SSEs) show promise as alternatives to organic liquid systems due to their improved safety and higher energy density. However, several challenges including low ionic conductivity, poor wettability, low stability/incompatibility between electrodes and electrolytes, etc., may degrade performance, hindering the development of practical applications. In this review, an overview of Na‐ion SSEs is first outlined according to the classification of solid polymer electrolytes, composite polymer electrolytes, inorganic solid electrolytes, etc. Furthermore, the current challenges and critical perspectives for the potential development of solid‐state sodium batteries are discussed in detail.

Developments of Lithium Solid Electrolytes and their Application to All Solid-State Batteries

Lithium solid electrolytes promise the potential to replace organic liquid electrolytes and thereby improve safety of the next-generation batteries. Among the electrolytes proposed, the sulphide system is a candidate for practical batteries because of their high ionic conductivity; the Li10GeP2S12 (LGPS) phase exhibits high ionic conductivity of over 10-2 S cm-1 at room temperature and is promising for applications requiring batteries with high powers and energy densities. The present study focuses on several topics of the all solid-state system using the inorganic electrolytes. (i) Material varieties of the LGPS system may provide suitable combinations of the electrodes and the electrolyte. To improve the materials variety, the substitution systems with the LGPS type structure were examined, and their phase diagram, structure and ionic conduction were studied. (ii) The combination with high-voltage electrode or high-capacity electrode may provide high capacity systems. The all solid-state batteries using various electrode materials were examined. (iii) The reaction at the electrolyte/electrode interface is the important issue to improve the stability and rate capabilities. High resistance at the interface of the solid-state system might prevent their usage for high current battery systems. Reactions at the interface were also examined. Based on these experimental results, the battery characteristics of the all solid-state system using LGPS electrolytes will be discussed.

Revealing Lithium Dendrite Morphologies Via in Situ Optical Microscopy and X-Ray Nano-CT

Introduction Lithium ion (Li-ion) batteries have been revolutionary in the advancement of portable electronic devices due to their unparalleled energy density. However, even with the energy densities afforded by existing lithium-ion battery technologies, requirements of sustained and long-range operation of electrified vehicles and devices have prompted research on new materials and strategies for improving performance and safety of current battery systems. One of the most tantalizing strategies for improving energy density is to use lithium metal as the anode. Lithium’s low redox potential, high gravimetric/volumetric specific capacities, and fast reaction kinetics all contribute towards both high energy and high power density. However, the implementation of lithium metal as the anode has largely been prevented due to safety concerns resulting from lithium dendrite growth – causing short-circuits, leading to thermal runaway reactions, and fires/explosions [1]. Many models have been proposed to describe dendrite morphologies during initiation and propagation, with conflicting theories as to the preferential location of Li electro-deposition at the early stages of dendrite formation [2-5]. Admittedly, the complexity of dendrite morphology is exacerbated by numerous factors influencing the initiation and propagation including, but not limited to, temperature, electrolyte composition, current density and over-potentials [6]. Herein, we employ in situ optical microscopy and x-ray nano-CT (computed tomography) to establish relationships between electrochemical parameters and the resultant dendrite morphologies during initiation (early stage) and propagation (late stage) of Li electro-deposits on copper wires. X-ray nano-CT is employed as a unique, non-destructive technique capable of 3-dimensional imaging of the surface and internal structures of opaque materials, with ~50 nm resolution. This allows for 3D morphological characterization during the early stages of Li dendrite initiation. The subsequent propagation morphologies will be characterized and tracked via in situ optical microscopy. Results and discussions Single projection, large field-of-view, phase contrast mosaic radiographs of lithium electro-deposited onto 80 micron diameter copper (Cu) wire are shown in Figure 1. The dark contrasts within the radiographs reflect highly x-ray attenuating elements (i.e. Cu) and the lighter contrast features are due to the electro-deposited lithium. At low current densities, lithium deposits uniformly along the surface of the Cu wire as seen in Figure 1a. At high current densities, non-homogeneous (~10 – 50 mm) features are evident in Figure 1b. These non-homogeneous features appear to exhibit complex architectures with regions containing both continuous and isolated porous networks, depicted with the 3-dimensional reconstructed rendering in Figure 1c.

New Horizons for Conventional Lithium Ion Battery Technology.

Secondary lithium ion battery technology has made deliberate, incremental improvements over the past four decades, providing sufficient energy densities to sustain a significant mobile electronic device industry. Because current battery systems provide ∼100-150 km of driving distance per charge, ∼5-fold improvements are required to fully compete with internal combustion engines that provide >500 km range per tank. Despite expected improvements, the authors believe that lithium ion batteries are unlikely to replace combustion engines in fully electric vehicles. However, high fidelity and safe Li ion batteries can be used in full EVs plus range extenders (e.g., metal air batteries, generators with ICE or gas turbines). This perspective article describes advanced materials and directions that can take this technology further in terms of energy density, and aims at delineating realistic horizons for the next generations of Li ion batteries. This article concentrates on Li intercalation and Li alloying electrodes, relevant to the term Li ion batteries.

A low cost, all-organic Na-ion Battery Based on Polymeric Cathode and Anode

Current battery systems have severe cost and resource restrictions, difficultly to meet the large scale electric storage applications. Herein, we report an all-organic Na-ion battery using p-dopable polytriphenylamine as cathode and n-type redox-active poly(anthraquinonyl sulphide) as anode, excluding the use of transition-metals as in conventional electrochemical batteries. Such a Na-ion battery can work well with a voltage output of 1.8 V and realize a considerable specific energy of 92 Wh kg−1. Due to the structural flexibility and stability of the redox-active polymers, this battery has a superior rate capability with 60% capacity released at a very high rate of 16 C (3200 mA g−1) and also exhibit an excellent cycling stability with 85% capacity retention after 500 cycles at 8 C rate. Most significantly, this type of all-organic batteries could be made from renewable and earth-abundant materials, thus offering a new possibility for widespread energy storage applications.

Design and Characterization of a Liquid-Fueled Microcombustor

As part of an effort to develop a microscale gas turbine engine, this paper presents the design and experimental characterization of a microcombustor that catalytically burns JP8 fuel. Due to the high energy densities of hydrocarbon fuels, microscale heat engines based on them may enable compact power sources with specific energies higher than those of current battery systems. In addition, utilizing a commonly available logistics fuel would provide advantages for military applications. Thus, a microscale engine burning JP8 fuel is attractive as a portable power source. A liquid-fueled microcombustor with a combustion chamber volume of 1.4 cm3 and an overall die size of 36.4×36.4×6.5 mm3 was designed, microfabricated, and experimentally characterized. Two configurations were tested and compared, one with the combustion chamber entirely filled with a catalyst and the other with the combustion chamber partially filled with a catalyst. In the configuration filled with a catalyst, JP8 combustion was sustained at mass flow rates up to 0.1 g/s and an exit gas temperature of 780 K; an overall combustor efficiency of 19% and a power density of 43 MW/m3 were achieved. The primary limitation on increasing the mass flow rates and temperature further was the structural failure of the device due to thermal stresses. With the partially filled configuration, a mass flow rate of 0.2 g/s and a corresponding power density of 54 MW/m3 were obtained. The exit gas temperature for the partially filled configuration was as high as 720 K, and the maximum overall efficiency was over 22%. Although the reduced amount of catalyst led to incomplete combustion, smaller thermal losses resulted in an increase in the overall combustor efficiency and power density. A nondimensional operating map was constructed based on the experiment, and it suggests that improving the thermal efficiency would be necessary to achieve higher efficiencies in the device.