Effects of nitrogen doping on the electrochemical performance of graphite felts for vanadium redox flow batteries

Vanadium redox flow batteries (VRFB), originally proposed by Skyllas‐Kazacos et al., have been considered as one of the most promising energy storage systems for intermittently renewable energy. However, the poor electrochemical activity and hydrophobicity of graphite felt electrode greatly limit energy storage efficiency of VRFB system. In this paper, two nitrogen‐doped (N‐doped) graphite felts, obtained by heat‐treating in an NH₃ atmosphere at 600 °C and 900 °C, have been investigated as electrodes with high electrochemical performance for vanadium redox flow batteries. In particular, the one obtained at 900 °C exhibits an excellent electrochemical activity for both V²⁺/V³⁺ and VO²⁺/VO₂⁺ redox couples. The cells with different graphite felt electrodes were assembled, and the charge–discharge performance was evaluated. The cell with the N‐doped graphite felts has larger discharge capacity, discharge capacity retention, and energy efficiency, especially with the sample treated at 900 °C. The average energy efficiency of the cell with the 900 °C treated N‐doped graphite felts is 86.47%, 5.44% higher than that of the cell with the pristine graphite felt electrodes. These enhanced electrochemical properties of the N‐doped graphite felt electrodes are attributed to the increased electrical conductivity, more active sites, and better wettability provided by the introduction of the nitrogenous groups on the surface of graphite felts. It indicates that N‐doped graphite felts have promising application prospect in VRFB. Copyright © 2015 John Wiley & Sons, Ltd.     

Commercial and research battery technologies for electrical energy storage applications

Developing green energy solutions has become crucial to society. However, to develop a clean and renewable energy system, significant developments must be made, not only in energy conversion technologies (such as solar panels and wind turbines) but also regarding the feasibility and capabilities of stationary electrical energy storage (EES) systems. Many types of EES systems have been considered such as pumped hydroelectric storage (PHS), compressed air energy storage (CAES), flywheels, and electrochemical storage. Among them, electrochemical storage such as battery has the advantage of being more efficient compared to other candidates, because it is more suitable in terms of the scalability, efficiency, lifetime, discharge time, and weight and/or mobility of the system. Currently, rechargeable lithium ion batteries (LIBs) are the most successful portable electricity storage devices, but their use is limited to small electronic equipment. Using LIBs to store large amounts of electrical energy in stationary applications is limited, not only by performance but also by cost. Thus, a viable battery technology that can store large amounts of electrical energy in stationary applications is needed. In this review, well-developed and recent progress on the chemistry and design of batteries, as well as their effects on the electrochemical performance, is summarized and compared. In addition, the challenges that are yet to be solved and the possibilities for further improvements are explored.     

锂离子电池热管理和安全性研究

温度是影响锂离子电池性能、寿命和安全性的重要因素,电池热管理系统能使电池的工作温度维持在适宜范围,保障电池安全、高效和长寿命使用。因此,电池热管理系统对动力和储能设备在不同工况和环境下的运行至关重要。本文介绍了锂离子电池热模型的发展和应用,对热管理和安全性的研究进行了归纳;总结了本课题组的相关工作进展;在此基础上,指出了锂离子电池热管理和安全性进一步的研究方向。     

Cresyl diphenyl phosphate as flame retardant additive for lithium-ion batteries

To improve the safety of lithium-ion batteries, cresyl diphenyl phosphate (CDP) was used as a flame retardant additive in a LiPF₆ electrolyte solution. The flammability of the electrolytes containing CDP and the electrochemical performances of the cells, LiCoO₂/Li, graphite/Li and the battery LiCoO₂/graphite with these electrolytes, were studied by measuring the self-extinguishing time of the electrolytes, the variation of surface temperature of the battery and the charge/discharge curve of the cells or battery. It is found that the addition of CDP to the electrolyte provides a significant suppression in the flammability of the electrolyte and an improvement in the thermal stability of battery. On the other hand, the electrochemical performances of the cells become slightly worse due to the application of CDP in the electrolyte. This alleviated trade-off between the flammability and thermal stability and cell performances provides a possibility to formulate a nonflammable electrolyte by using CDP.     

Self-discharge characteristics and performance degradation of Ni-MH batteries for storage applications

The needs for onboard energy storage are practically dependent on the Ni-MH and Li-ion battery packs, because these two power-assisting systems have features of proper energy density, longer cycle lifetime, quick charge acceptance, and proper operating windows for both voltage and temperature. In particular, the Ni-MH power system has a proper tolerance mechanism for overcharge and overdischarge, a lower cost for battery pack maintenance, and a slightly longer cycle lifetime profile. We studied the self-discharge characteristics, state-of-health, state-of-charge, and energy efficiencies at various charge input levels. The end-of-voltages during charge and discharge were evaluated for the Ni-MH storage batteries. The impedance measurements and data analysis have also been conducted for equivalent circuit simulations. The performance deterioration and capacity decay are fundamentally analyzed and discussed in details, including electrode side-reactions, structure degradations, separator weakening, and level changes of electrolyte saturation in the battery. Further battery quality enhancement through cycle duration improvement for onboard energy storage potentially provides more suitable power and energy delivery in order to obtain higher efficiency, save more fuels, and reduce CO₂, SO₂, and NO_x emissions.     

Machine learning approach for solving inconsistency problems of Li-ion batteries during the manufacturing stage

The inconsistency in the mass production of lithium-ion battery (LIB) packs stem from the inconsistency in the capacity, voltage and internal resistance of single batteries that compose packs. The inconsistency issue of these battery packs can greatly reduce the output performance of a large power pack. This paper proposed the machine learning approach based on self-organization mapping (SOM) neural networks for establishing the consistency of LIBs. This method comprehensively compares and analyzes the real-LIB parameters (internal resistance, capacity and voltage) data obtained during charging and discharging to form the clusters of similar performing LIBs. Experimental result validated the clustering analysis and it indicates that the performance of clustered battery pack typically precedes than that of original. The capacity of clustered battery pack increased 1.9% compared with brand-new pack. The temperature distribution of the battery pack assembled after screening is consistent. The peak temperature is 4°-5° lower than the ordinary battery, and the temperature fluctuation is reduced by 2.6°. In addition, the application of cluster analysis is expanded and some key research directions are pointed out.     

The importance of heat evolution during the overcharge process and the protection mechanism of electrolyte additives for prismatic lithium ion batteries

In this work, the rate of heat generation in the overcharge period for 103450 prismatic lithium ion batteries (LIBs) of the LiCoO₂–graphite jellyroll type with a basic electrolyte consisting of 1 M LiPF₆–PC/EC/EMC (1/3/5 in weight ratio) has been found to be more important than the gas evolution which was traditionally considered as the main reason in the overcharge protection mechanism. The cell voltage, charge current, and skin temperature were monitored during the charge process. For a single battery or batteries in parallel, LIBs without any additives is an acceptable design if the cell voltage is not charged above 4.55 V under the common charge program. The rate of heat generation from the polymerization of 3 wt% cyclohexyl benzene (CHB) is high enough to cause the explosion or thermal runaway of a battery, which is not found for an LIB containing 2 wt% CHB + 1 wt% tert-amyl benzene (TAB). In the 12 V overcharge test at 1C, the thermal fuse was broken by the high skin temperature (ca. 80 °C) due to the polymerization of 3 wt% CHB, which was also the case for LIBs containing 2 wt% CHB + 1 wt% TAB. The disconnection of the thermal fuse, however, did not interrupt the thermal runaway of LIBs without any additives because the battery voltage was too high (ca. 4.9 V). The influence of specific surface area of active materials in the anode on the polymerization kinetics of additives has to be carefully considered in order to add correct amount of overcharge protection agents.     

Structural and thermal stabilities of layered Li(Ni1/3Co1/3Mn1/3)O2 materials in 18650 high power batteries

The structural and thermal stabilities of the layered Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode materials under high rate cycling and abusive conditions are investigated using the commercial 18650 Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite high power batteries. The Li(Ni_1/3Co_1/3Mn_1/3)O₂ materials maintain their layered structure even when the power batteries are subjected to 200 cycles with 10 C discharge rate at temperatures of 25 and 50 °C, whereas their microstructure undergoes obvious distortion, which leads to the relatively poor cycling performance of power batteries at high charge/discharge rates and working temperature. Under abusive conditions, the increase in the battery temperature during overcharge is attributed to both the reactions of electrolyte solvents with overcharged graphite anode and Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathode and the Joule heat that results from the great increase in the total resistance (R_cell) of batteries. The reactions of fully charged Li(Ni_1/3Co_1/3Mn_1/3)O₂ cathodes and graphite anodes with electrolyte cannot be activated during short current test in the fully charged batteries. However, these reactions occur at around 140 °C in the fully charged batteries during oven test, which is much lower than the temperature of about 240 °C required for the reactions outside batteries.     

Improved potassium ion storage performance of graphite by atomic layer deposition of aluminum oxide coatings

In the context of large scale and low-cost energy storage, the emerging potassium-ion batteries (PIBs) are one potential energy storage system. Graphite, a commercial anode material widely used in lithium-ion batteries (LIBs), can be directly applied to PIBs through forming the stage I graphite intercalation compound (KC₈). However, the dramatic volume expansion during the formation of KC₈ can result in poor cycling performance. In this work, one Al₂O₃ atomic layer coated on the surface of graphite via atomic layer deposition (ALD) process, aiming to construct a stable solid electrode interface and enhance the performance of graphite anode in PIBs. The electrochemical performance analysis shows that the 20 cycles Al₂O₃ deposited graphite have improved cycle stability of 223 mAh g⁻¹ at 50 mA g⁻¹ after 50 cycles compared with the raw graphite anode of 92 mAh g⁻¹.     

Nitrogen-doped mesoporous carbon for energy storage in vanadium redox flow batteries

We demonstrate an excellent performance of nitrogen-doped mesoporous carbon (N-MPC) for energy storage in vanadium redox flow batteries. Mesoporous carbon (MPC) is prepared using a soft-template method and doped with nitrogen by heat-treating MPC in NH₃. N-MPC is characterized with X-ray photoelectron spectroscopy and transmission electron microscopy. The redox reaction of [VO]²⁺/[VO₂]⁺ is characterized with cyclic voltammetry and electrochemical impedance spectroscopy. The electrocatalytic kinetics of the redox couple [VO]²⁺/[VO₂]⁺ is significantly enhanced on N-MPC electrode compared with MPC and graphite electrodes. The reversibility of the redox couple [VO]²⁺/[VO₂]⁺ is greatly improved on N-MPC (0.61 for N-MPC vs. 0.34 for graphite), which is expected to increase the energy storage efficiency of redox flow batteries. Nitrogen doping facilitates the electron transfer on electrode/electrolyte interface for both oxidation and reduction processes. N-MPC is a promising material for redox flow batteries. This also opens up new and wider applications of nitrogen-doped carbon.     

Preparation and characterization of 18650 Li(Ni1/3Co1/3Mn1/3)O2/graphite high power batteries

The commercial 18650 Li(Ni_1/3Co_1/3Mn_1/3)O₂/graphite high power batteries were prepared and their electrochemical performance at temperatures of 25 and 50 °C was extensively investigated. The results showed that the charge-transfer resistance (R_ct) and solid electrolyte interface resistance (R_sei) of the high power batteries at 25 °C decreased as states of charge (SOC) increased from 0 to 60%, whereas R_ct and R_sei increased as SOC increased from 60 to 100%. The discharge plateau voltage of batteries reduced greatly with the increase in discharge rate at both 25 and 50 °C. The high power batteries could be discharged at a very wide current range to deliver most of their capacity and also showed excellent power cycling performance with discharge rate of as high as 10 C at 25 °C. The elevated working temperature did not influence the battery discharge capacity and cycling performance at lower discharge rates (e.g. 0.5, 1, and 5 C), while it resulted in lower discharge capacity at higher discharge rates (e.g. 10 and 15 C) and bad cycling performance at discharge rate of 10 C. The batteries also exhibited excellent cycle performance at charge rate of as high as 8 C and discharge rate of 10 C.     

One‐pot synthesis of composite NiO/graphitic carbon flakes with contact glow discharge electrolysis for electrochemical supercapacitors

Thanks to their high power density and degree of reversibility, supercapacitors are electrochemical devices that narrow the gap between secondary batteries and traditional dielectric capacitors in the traditional Ragone plot. However, their use is still hindered by their capability to achieve higher energy density. In this work, we present a one‐pot synthesis procedure of composite graphitic carbon flake‐supported NiO for electrochemical energy storage application. We used cathodic contact glow discharge electrolysis by applying 120 Vdc terminal voltage between a thin Pt wire, slightly submerged in an aqueous solution of NiSO₄(H₂O)₆ + Na₂SO₄, and a large surface area carbon graphite anode. Strong active species generated within the micro‐plasma volume locally reduce the nickel precursors to form NiO materials, while at the anodically polarized graphite rod, the forces holding the graphene layers together are weakened by ion/solvent intercalation producing micrometer‐sized graphitic carbon flakes. The morphological characterization is carried out by electron microscopy, energy dispersive X‐ray spectroscopy, powder X‐ray diffraction, and micro‐Raman spectroscopy. Cyclic voltammetry, constant‐current charge/discharge, and electrochemical impedance spectroscopy in 5 mol l^?1 KOH solution are carried out to evaluate the electrochemical energy storage performance of the material. We show that carbon flake‐supported NiO exhibits the dual combination of electric double‐layer capacitance with faradic behavior, giving 495 F g^?1 specific capacitance at 2 A g^?1 current density. Copyright © 2015 John Wiley & Sons, Ltd.     

A novel experimental study on discharge characteristics of an aluminum‐air battery

In order to explore the discharge characteristics of aluminum‐air battery and find out the best discharge performance of aluminum‐air battery under the optimum working conditions, this paper studies discharge performances of an aluminum‐air battery under various ambient temperature and battery discharge conditions. The relationship between the temperature rise of the battery electrolyte and the discharge current density was studied by an experimental method. Effects of the electrolyte concentration and the ambient temperature on the battery discharge voltage were investigated. In addition, a novel method for calculating the efficiency of the aluminum‐air battery was proposed. Results show that the temperature of the aluminum‐air battery electrolyte gradually increases as its discharge current density increases and the electrolyte temperature rise could reach as high as 10°C after 60 minutes with a constant 35 mA cm^?2 discharge current density. The specific energy and the specific capacity of the aluminum‐air battery first increase and then decrease as the current density increases. When the current density is 25 mA cm^?2, the specific energy has a peak of 3105 Wh kg^?1 for the condition of the chamber temperature 40°C and the electrolyte concentration 2 mol L^?1 (2 M), while the specific capacity has a peak of 2207 Ah kg^?1; furthermore, its efficiencies under various conditions increase first with the current density, reach a peak range of 19.6% to approximately 36% at 25 mA cm^?2, and then decrease. These experimental results could be used as a technical guidance for the optimization in thermal management designs of the aluminum‐air battery under various operating conditions.     

Jute sticks derived novel graphitic porous carbon nanosheets as Li-ion battery anode material with superior electrochemical properties

Graphitic porous carbon sheets (GPCS), which were synthesized at a low temperature of 900°C by KOH chemical activation technique, possess a specific surface area of 1246 m² g^-1 with high pore volume. The size of the pores varied in micro-mesopore regions and exhibited three-dimensional sheet-like morphology composed of multilayered graphene sheets with an inter planar distance of 0.360 nm. The GPCS material was tested as anode for Li-ion battery (LIB) application in half cell mode (vs Li⁺/Li). The fabricated GPCS electrode shows excellent electrochemical properties in comparison with commercial graphite such as a high discharge specific capacity of 1022 mA h g^-1 after 10 cycles at 100 mA g^-1 and excellent specific capacity retention of 170 mA h g^-1 at a very high current rate of 8000 mA g^-1 and also retains a high capacity of 541 mA h g^-1 after 250 cycles at 500 mA g^-1, which suggests that GPCS material can be a promising electrode for LIB application. A brief comparison with commercial graphite and various carbonaceous materials from literature demonstrated that the GPCS electrode was potential material for high rate LIBs.     

Effect of americium‐241 source activity on total conversion efficiency of diamond alpha‐voltaic battery

High‐quality diamond intrinsic layer was epitaxially grown on a IIb‐type boron‐doped diamond substrate. The quality of the epitaxy layer was evaluated by Raman spectroscopy and cross‐polarizer images and compared with other samples. The dark current of the diode was analyzed, revealing a rectification ratio as high as 2 × 10⁹ at ±7 V. Current‐voltage characteristics of the converter under the irradiation of different americium‐241 activity sources were investigated. A maximum total conversion efficiency (η_total) of 1.41%, short‐circuit current (I_sc) of 6.68 nA/cm², and open‐circuit voltage (V_oc) of 1.06 V from the diamond alpha‐voltaic battery were obtained under the irradiation of an americium‐241 source with a source activity of 8.85 μCi/cm². The trend for the battery parameters with the increase in the activity of the americium‐241 source was clarified. Parameters I_sc and V_oc increase with the increase in the radioactive source activity. The η_total increases with the increase in the source activity but fluctuates in a certain activity interval with an increase in the fill factor, and then decreases with the increase in radioactive source activity. The research results are significant for the design of nuclear batteries.     

Research progress on capacitive lithium-ion battery

锂离子电池具有高的能量密度,而超级电容器则以高功率密度和长循环寿命为突出优势。电容型锂离子电池是在锂离子电池的正极中加入部分电容炭材料,在不显著降低能量密度的情况下,大幅度改善锂离子电池的功率特性和循环寿命,从而实现电容与电池技术的融合。本文综述了国内外近年来在电容型锂离子电池领域的最新研究进展,介绍了主要的电容型锂离子电池体系及其性能特点,并对其未来发展方向进行了展望。     

Heterostructural composite of few-layered MoS2/hexagonal MoO2 particles/graphene as anode material for highly reversible lithium/sodium storage

The heterostructural construction of metal disulfide/oxide is essential in the electrochemical performance as anode material for lithium- and sodium-ion batteries (LIBs and SIBs). In this work, an integrated composite of molybdenum disulfide (MoS₂) and hexagonal molybdenum dioxide (MoO₂) together enwrapped in reduced graphene oxide (rGO) is synthesized under hydrothermal condition. In the pelletizing MoS₂-MoO₂/rGO composite, rGO as substrate effectively prevents the restacking and pulverization of MoS₂-MoO₂ during a long cycling process. Meanwhile, the synergistic effect among the MoS₂, MoO₂, and rGO components are responsible for abundant active sites and shorten ionic transport channels. When evaluating as anode material for LIB, MoS₂-MoO₂/rGO sample presents excellent cyclic performance and still delivers a high capacity of 1062.3 mA h g⁻¹ after 120 cycles at 0.2 A g⁻¹; evaluating in a SIB at 0.04 A g⁻¹, it presents excellent cyclic performance and delivers 430 mA h g⁻¹ at the 80th cycle. The heterostructural composite MoS₂-MoO₂/rGO is one of the candidate anode materials for high-performance LIB and SIB.     

Batteries ideal for RE applications

Saft Sunica has announced more details on its rechargeable nickel-cadmium battery range. The company highlights that they are designed to provide optimum energy storage solutions for renewable energy applications such as photovoltaic and windpower systems offering a number of important advantages compared with standard batteries including high efficiency, reliability, long service life and the potential for both shallow and deep cycling. The batteries are ideally suited for a wide variety of remote installations including navigational aids, telecommunications, rail signalling, oil and gas platforms and electric utilities. The manufacturers claim that the Saft Sunica batteries are designed specifically to offer a number of key advantages for renewables, namely: constant charging efficiency over time; continuous operation at any state of charge; minimal self-discharge rates; a high available performance even at very low states of charge; sustained efficiency even at high or low temperatures; and long cycle life even when the charge/discharge cycle involves 100 percent depth of dischargeThis is a short news story only. Visit www.re-focus.net for the latest renewable energy industry news.     

An investigation of optimum PV and wind energy system capacities for alternate short and long‐term energy storage sizing methodologies

The goal of this study is to find the optimal sizes of renewable energy systems (RES) based on photovoltaic (PV) and/or wind systems for three energy storage system (ESS) scenarios in a micro‐grid; (1) with pumped hydro storage (PHS) as a long‐term ESS, (2) with batteries as a short‐term ESS, and (3) without ESS. The PV and wind sizes are optimally determined to accomplish the maximum annual RES fraction (F_RES ) with electricity cost lower than or equal to the utility tariff. Furthermore, the effect of the use of battery and PHS on the electricity cost and F_RES are studied. A university campus on a Mediterranean island is selected as a case study. The results show that PV‐wind hybrid system of 8 MW wind and 4.2 MW PV with 89.5 MWh PHS has the highest F_RES of 88.0%, and the highest demand supply fraction as 42.6%. Moreover, the results indicate that the economic and technical parameters of RESs are affected significantly by the use of ESSs depending on the type and the capacity of both the RES and the ESS.     

Development of the all‐vanadium redox flow battery for energy storage: a review of technological,financial and policy aspects

The commercial development and current economic incentives associated with energy storage using redox flow batteries (RFBs) are summarised. The analysis is focused on the all‐vanadium system, which is the most studied and widely commercialised RFB. The recent expiry of key patents relating to the electrochemistry of this battery has contributed to significant levels of commercialisation in, for example, Austria, China and Thailand, as well as pilot‐scale developments in many countries. The potential benefits of increasing battery‐based energy storage for electricity grid load levelling and MW‐scale wind/solar photovoltaic‐based power generation are now being realised at an increasing level. Commercial systems are being applied to distributed systems utilising kW‐scale renewable energy flows. Factors limiting the uptake of all‐vanadium (and other) redox flow batteries include a comparatively high overall internal costs of $217 kW^?1 h^?1 and the high cost of stored electricity of ≈ The commercial development and current economic incentives associated with energy storage using redox flow batteries (RFBs) are summarised. The analysis is focused on the all‐vanadium system, which is the most studied and widely commercialised RFB. The recent expiry of key patents relating to the electrochemistry of this battery has contributed to significant levels of commercialisation in, for example, Austria, China and Thailand, as well as pilot‐scale developments in many countries. The potential benefits of increasing battery‐based energy storage for electricity grid load levelling and MW‐scale wind/solar photovoltaic‐based power generation are now being realised at an increasing level. Commercial systems are being applied to distributed systems utilising kW‐scale renewable energy flows. Factors limiting the uptake of all‐vanadium (and other) redox flow batteries include a comparatively high overall internal costs of $217 kW^?1 h^?1 and the high cost of stored electricity of ≈ $0.10 kW^?1 h^?1. There is also a low‐level utility scale acceptance of energy storage solutions and a general lack of battery‐specific policy‐led incentives, even though the environmental impact of RFBs coupled to renewable energy sources is favourable, especially in comparison to natural gas‐ and diesel‐fuelled spinning reserves. Together with the technological and policy aspects associated with flow batteries, recent attempts to model redox flow batteries are considered. The issues that have been addressed using modelling together with the current and future requirements of modelling are outlined. Copyright © 2011 John Wiley & Sons, Ltd.