Energy Density Storage Devices Research Articles

Redox Species-Based Electrolytes for Advanced Rechargeable Lithium Ion Batteries

Seeking high-capacity cathodes has become an intensive effort in lithium ion battery research; however, the low energy density still remains a major issue for sustainable handheld devices and vehicles. Herein, we present a new strategy of integrating a redox species-based electrolyte in batteries to boost their performance. Taking the olivine LiFePO4-based battery as an example, the incorporation of redox species (i.e., polysulfide of Li2S8) in the electrolyte results in much lower polarization and superior stability, where the dissociated Li+/Sx2– can significantly speed up the lithium diffusion. More importantly, the presence of the S82–/S2– redox reaction further contributes extra capacity, making a completely new LiFePO4/Li2Sx hybrid battery with a high energy density of 1124 Wh kgcathode–1 and a capacity of 442 mAh gcathode–1. The marriage of appropriate redox species in an electrolyte for a rechargeable battery is an efficient and scalable approach for obtaining higher energy density storage devices.

Studies of interface characteristics of fine-grain ferroelectric based glass-ceramic composites using impedance spectroscopy

High-quality fine-grained ferroelectric glass-ceramic composites were successfully fabricated by using a modified hybrid processing. The properties of interfaces were investigated by using impedance spectroscopy (IS). In our measured impedance spectra, a polarization with an ideal Debye behavior was observed at intermediate frequency ranging between 1 kHz and 100 kHz. This polarization was attributed to the space charge accumulation at the grain-boundary interfaces, due to the presence of large dielectric constant difference between the fillers and the host. Basing on the IS results, a brick-layer microstructural model was proposed for the ferroelectric glass-ceramic composites. Our studies indicated that the new modified hybrid processing can be used to design composites with desired interfaces that have a homogeneous dielectric constant, so as to achieve high breakdown strength, thus leading to high electrical energy density storage devices.

Graphene based integrated tandem supercapacitors fabricated directly on separators

Integrated supercapacitors with extended operation voltage are important for high energy density storage devices. In this work, we develop a novel direct electrode deposition on separator (DEDS) process to fabricate graphene based integrated tandem supercapacitors for the first time. The DEDS process generates compact graphene‐polyaniline electrodes directly on the separators to form integrated supercapacitors. The integrated graphene‐polyaniline tandem supercapacitors demonstrate ultrahigh volumetric energy density of 52.5WhL−1 at power density of 6037WL−1 and excellent gravimetric energy density of 26.1Whkg−1 at power density of 3002Wkg−1 with outstanding electrochemical stability for over 10,000 cycles. This study show great promises for the future development of integrated energy storage devices.

A novel stand-alone mobile photovoltaic/wind turbine/ultracapacitor/battery bank hybrid power system

This paper presents a new mobile hybrid system using a photovoltaic array, a wind turbine, an ultracapacitor, and a battery bank for grid-independent applications in the city of Cancun, Mexico. A main controller is proposed to manage these different power sources. This controller permits autonomous operation and control over power generation and loading. This proposal used high power and high energy density storage devices, including short- and long-term storage strategies for energy management. An independent load management subsystem was added, given that the mobile application requires the management of critical loads. This subsystem included an ON/OFF pattern for the connection and disconnection of DC and AC power outlets installed inside and outside the mobile unit. In order to verify system performance, each component of the system was modeled and simulated under realistic operating scenarios with a practical load using MATLAB, Simulink, and SimPowerSystems. The results obtained for this simulation showed that, by means of power balancing, this management scheme coordinated the power flow among the different sources and the load. The manager behavior shows that the difference between the power generated and the power demand was 2.08 kW h/day and 4.01 kW h/day in winter and summer, respectively.

Increasing Capacitance of Zeolite-Templated Carbons in Electric Double Layer Capacitors

Enhancement of the specific capacitance in electrochemical double layer capacitors (EDLCs) is of high interest due to the ever increasing demand for high power density energy storage devices. Zeolite templated carbon (ZTC) is a promising EDLC electrode material with large specific surface area and straight, ordered well-defined micropores. In this study, ZTC samples were synthesized using a low pressure chemical vapor deposition (LP CVD) of carbon on sacrificial zeolite Y powder using acetylene gas as a precursor. We demonstrate for the first time how various post-treatments of the produced samples can affect the ZTC microstructure and porosity and how such modifications may significantly improve electrochemical performance characteristics of the ZTC-based EDLC electrodes. The effects of CO2 activation, ball milling and high temperature annealing process were systematically studied. The best performing samples achieved very large capacitance of over 240 Fg−1 at 1 mVs−1 in 1 M solution of tetraethylammonium tetrafluoroborate in acetonitrile and stable performance in symmetric EDLC devices with no noticeable degradation for over 20,000 cycles at a very high current density of 20 Ag−1.

Free-standing TiO2 nanowire-embedded graphene hybrid membrane for advanced Li/dissolved polysulfide batteries

The increasing demand for electric vehicles and large-scale smart grids has aroused great interest in developing high energy density storage devices. Lithium–sulfur (Li–S) battery has attracted much attention owing to its high theoretical energy density and abundance, but many challenges such as rapid capacity fade and low sulfur loading and utilization have impeded its practical use. Here, we present a free-standing TiO2 nanowire/graphene hybrid membrane for Li/dissolved polysulfide batteries with high capacity and long cycling life. Graphene membrane with high electrical conductivity is used as a current collector to effectively reduce the internal resistance in the sulfur cathode and physically immobilize the dissolved lithium polysulfides. The TiO2 nanowires introduced into the graphene membrane offer a hierarchical composite structure, in which the TiO2 nanowires not only have strong chemical binding with the lithium polysulfides, but also show a strong catalytic effect for polysulfide reduction and oxidation, promoting a fast redox reaction kinetics with high capacity and low voltage polarization. This hybrid electrode delivers a high specific capacity of 1327mAhg−1 at 0.2C rate, a Coulombic efficiency approaching 100%, high-rate performance of 850mAhg−1 at 2C rate, and long cyclic stability with a capacity of 1053mAhg−1 at 0.2C rate over 200 cycles, demonstrating great prospect for application in high energy Li–S batteries.

A graphene foam electrode with high sulfur loading for flexible and high energy Li-S batteries

Lithium-sulfur (Li-S) batteries have attracted great attention as next-generation high specific energy density storage devices. However, the low sulfur loading in the cathode for Li-S battery greatly offsets its advantage in high energy density and limits the practical applications of such battery concepts. Flexible energy storage devices are also becoming increasingly important for future applications but are limited by the lack of suitable lightweight electrode materials with robust electrochemical performance under cyclic mechanical strain. Here, we proposed an effective strategy to obtain flexible Li-S battery electrodes with high energy density, high power density, and long cyclic life by adopting graphene foam-based electrodes. Graphene foam can provide a highly electrically conductive network, robust mechanical support and sufficient space for a high sulfur loading. The sulfur loading in graphene foam-based electrodes can be tuned from 3.3 to 10.1mgcm−2. The electrode with 10.1mgcm−2 sulfur loading could deliver an extremely high areal capacity of 13.4mAhcm−2, much higher than the commonly reported Li-S electrodes and commercially used lithium cobalt oxide cathode with a value of ~3–4mAhcm−2. Meanwhile, the high sulfur-loaded electrodes retain a high rate performance with reversible capacities higher than 450mAhg−1 under a large current density of 6Ag−1 and preserve stable cycling performance with ~0.07% capacity decay per cycle over 1000 cycles. These impressive results indicate that such electrodes could enable high performance, fast-charging, and flexible Li-S batteries that show stable performance over extended charge/discharge cycling.

Enhanced dielectric and ferroelectric characteristics in Ca-modified BaTiO3 ceramics

Synergic modification of BaTiO3 ceramics was investigated by Ca-substitution, and the superior dielectric and ferroelectric properties were determined together with the structure evolution. X-ray diffraction (XRD) analysis demonstrated a large solubility limit above x = 0.25 in Ba1−xCaxTiO3 solid solution where the fine grain structure was observed with increasing x. Room temperature dielectric constant as high as 1655 was achieved in the present ceramics together with the significantly reduced dielectric loss of 0.013 (x = 0.20 at 100 kHz), where the Curie temperature kept almost a constant while other two transition temperatures decreased continuously with increasing x. More importantly, the remanent polarization Pr and dielectric strength Eb were significantly enhanced by Ca-substitution, and the best Pr (11.34 μC/cm2) and the highest dielectric strength Eb (75 kV/cm) were acquired at x = 0.25. The present ceramics should be very desirable for the applications such as high density energy storage devices.

Update on Na-based battery materials. A growing research path

This work presents an up-to-date information on Na-based battery materials. On the one hand, it explores the feasibility of two novel energy storage systems: Na-aqueous batteries and Na–O2 technology. On the other hand, it summarises new advances on non-aqueous Na-ion systems. Although all of them can be placed under the umbrella of Na-based systems, aqueous and oxygen-based batteries are arising technologies with increasing significance in energy storage research, while non-aqueous sodium-ion technology has become one of the most important research lines in this field. These systems meet different requirements of energy storage: Na-aqueous batteries will have a determining role as a low cost and safer technology; Na–O2 systems can be the key technology to overcome the need for high energy density storage devices; and non-aqueous Na-ion batteries have application in the field of stationary energy storage.