Publications
105 results found
Liu X, Ai W, Naylor Marlow M, et al., 2019, The effect of cell-to-cell variations and thermal gradients on the performance and degradation of lithium-ion battery packs, Applied Energy, Vol: 248, Pages: 489-499, ISSN: 0306-2619
The performance of lithium-ion battery packs are often extrapolated from single cell performance however uneven currents in parallel strings due to cell-to-cell variations, thermal gradients and/or cell interconnects can reduce the overall performance of a large scale lithium-ion battery pack. In this work, we investigate the performance implications caused by these factors by simulating six parallel connected batteries based on a thermally coupled single particle model with the solid electrolyte interphase growth degradation mechanism modelled. Experimentally validated simulations show that cells closest to the load points of a pack experience higher currents than cells further away due to uneven overpotentials caused by the interconnects. When a cell with a four times greater internal impedance was placed in the location with the higher currents this actually helped to equalise the cell-to-cell current distribution, however if this was placed at a location furthest from the load point this would cause a ~6% reduction in accessible energy at 1.5 C. The influence of thermal gradients can further affect this current heterogeneity leading to accelerated aging. Simulations show that in all cases, cells degrade at different rates in a pack due to the uneven currents, with this being amplified by thermal gradients. In the presented work a 5.2% increase in degradation rate, from -7.71 mWh/cycle (isothermal) to - 8.11 mWh/cycle (non-isothermal) can be observed. Therefore, the insights from this paper highlight the highly coupled nature of battery pack performance and can inform designs for higher performance and longer lasting battery packs.
Liu X, Ouyang M, Wang H, et al., 2019, Hierarchical Carbon Nano Fibres for Flexible Zn-Air Batteries, ECS Meeting Abstracts, Vol: MA2019-04, Pages: 228-228
<jats:p> Nanostructured functional materials, specifically carbon nanofibres/nanotubes, are attractive due to their chemical stability and electrochemical properties. Carbon based structures across different length scales have already been used in a range of energy applications including carbon papers for proton exchange membrane fuel cells, carbon nanofibers for supercapacitors and carbon nanotubes as conductive additives in lithium-ion batteries. The development of hierarchical, designed nanomaterials bridging length scales is required for next generation devices because each length scale of interest offers certain advantages, macro-scale fibres offering ease of fabrication and nano-scale tubes offering superior electrochemical performance. Functional carbon nanofibers with hierarchical architectures are essential components in advanced energy applications. Here, we present a simple approach to preparing highly engineered, hierarchical nanofibers and a simple heat treatment. This simple synthesis route has been successfully developed to prepare a 3D structure consisting of large backbone fibres decorated with hierarchical, small carbon nanotubes produced via in-situ growth during carbonisation. The carbon nanofiber with hierarchical structure can significantly enhance the nanoporous 3D carbon network by increasing the specific surface area and number of electron and ion pathways, resulting in a doubled power density when compared to the carbon nanofiber without hierarchical structure. When utilized as an air cathode in the solid-state zinc-air battery, the carbon nanofiber with hierarchical structure showed markedly better electrochemical performance, delivering a long cycle life while remaining highly flexible. </jats:p>
Chen X-L, Wang L-C, Li T, et al., 2019, Sugar accumulation and growth of lettuce exposed to different lighting modes of red and blue LED light., Sci Rep, Vol: 9
The present study evaluated the growth response and sugar accumulation of lettuce exposed to different lighting modes of red and blue LED light based on the same daily light integral (7.49 μmol·m-2). Six lighting treatments were performed, that were monochromatic red light (R), monochromatic blue light (B), simultaneous red and blue light as the control (RB, R:B = 1:1), mixed modes of R, B and RB (R/RB/B, 4 h R to 4 h RB and then 4 h B), and alternating red and blue light with alternating intervals of 4 h and 1 h respectively recorded as R/B(4 h) and R/B(1 h). The Results showed that different irradiation modes led to obvious morphological changes in lettuce. Among all the treatments, the highest fresh and dry weight of lettuce shoot were both detected with R/B(1 h), significantly higher than the other treatments. Compared with plants treated with RB, the contents of fructose, glucose, crude fiber as well as the total sweetness index (TSI) of lettuce were significantly enhanced by R treatment; meanwhile, monochromatic R significantly promoted the activities of sucrose degrading enzymes such as acid invertase (AI) and neutral invertase (NI), while obviously reduced the activity of sucrose synthesizing enzyme (SPS). Additionally. The highest contents of sucrose and starch accompanied with the strongest activity of SPS were detected in plants treated with R/B(1 h). The alternating treatments R/B(4 h) and R/B(1 h) inhibited the activity of SS, while enhanced that of SPS compared with the other treatments, indicating that different light environment might influence sugar compositions via regulating the activities of sucrose metabolism enzymes. On the whole, R/B(1 h) was the optimal lighting strategy in terms of lettuce yield, taste and energy use efficiency in the present study.
Yin C, Liu X, Wei J, et al., 2019, “All-in-Gel” design for supercapacitors towards solid-state energy devices with thermal and mechanical compliance, Journal of Materials Chemistry A, Vol: 7, Pages: 8826-8831, ISSN: 2050-7488
Ionogels are semi-solid, ion conductive and mechanically compliant materials that hold promise for flexible, shape-conformable and all-solid-state energy storage devices. However, identifying facile routes for manufacturing ionogels into devices with highly resilient electrode/electrolyte interfaces remains a challenge. Here we present a novel all-in-gel supercapacitor consisting of an ionogel composite electrolyte and bucky gel electrodes processed using a one-step method. Compared with the mechanical properties and ionic conductivities of pure ionogels, our composite ionogels offer enhanced self-recovery (retaining 78% of mechanical robustness after 300 cycles at 60% strain) and a high ionic conductivity of 8.7 mS cm−1, which is attributed to the robust amorphous polymer phase that enables facile permeation of ionic liquids, facilitating effective diffusion of charge carriers. We show that development of a supercapacitor with these gel electrodes and electrolytes significantly improves the interfacial contact between electrodes and electrolyte, yielding an area specific capacitance of 43 mF cm−2 at a current density of 1.0 mA cm−2. Additionally, through this all-in-gel design a supercapacitor can achieve a capacitance between 22–81 mF cm−2 over a wide operating temperature range of −40 °C to 100 °C at a current density of 0.2 mA cm−2.
Ouyang M, Bertei A, Cooper S, et al., 2019, Design of Fibre Ni/CGO Anode and Model Interpretation, 16th International Symposium on Solid Oxide Fuel Cells (SOFC-XVI)
Liu X, Taiwo O, Yin C, et al., 2019, Aligned ionogel electrolytes for high‐temperature supercapacitors, Advanced Science, Vol: 6, Pages: 1-7, ISSN: 2198-3844
Ionogels are a new class of promising materials for use in all‐solid‐state energy storage devices in which they can function as an integrated separator and electrolyte. However, their performance is limited by the presence of a crosslinking polymer, which is needed to improve the mechanical properties, but compromises their ionic conductivity. Here, directional freezing is used followed by a solvent replacement method to prepare aligned nanocomposite ionogels which exhibit enhanced ionic conductivity, good mechanical strength, and thermal stability simultaneously. The aligned ionogel based supercapacitor achieves a 29% higher specific capacitance (176 F g−1 at 25 °C and 1 A g−1) than an equivalent nonaligned form. Notably, this thermally stable aligned ionogel has a high ionic conductivity of 22.1 mS cm−1 and achieves a high specific capacitance of 167 F g−1 at 10 A g−1 and 200 °C. Furthermore, the diffusion simulations conducted on 3D reconstructed tomography images are employed to explain the improved conductivity in the relevant direction of the aligned structure compared to the nonaligned. This work demonstrates the synthesis, analysis, and use of aligned ionogels as supercapacitor separators and electrolytes, representing a promising direction for the development of wearable electronics coupled with image based process and simulations.
Song W, Liu X, Wu B, et al., 2019, Sn@C evolution from yolk-shell to core-shell in carbon nanofibers with suppressed degradation of lithium storage, Energy Storage Materials, Vol: 18, Pages: 229-237, ISSN: 2405-8297
Metallic Sn has high conductivity and high theoretical capacity for lithium storage but it suffers from severe volume change in lithiation/delithiation leading to capacity fade. Yolk-shell and core-shell Sn@C spheres interconnected by carbon nanofibers were synthesized by thermal vapor and thermal melting of electrospun nanofibers to improve the cycling stability. Sn particles in yolk-shell spheres undergo dynamic structure evolution during thermal melting to form core-shell spheres. The core-shell spheres linked along the carbon nanofibers show outstanding performance and are better than the yolk-shell system for lithium storage, with a high capacity retention of 91.8% after 1000 cycles at 1 A g-1. The superior structure of core-shell spheres interconnected by carbon nanofibers has facile electron conductivity and short lithium ion diffusion pathways through the carbon nanofibers and shells, and re-develops Sn@C structures with Sn clusters embedded into carbon matrix during electrochemical cycling, enabling the high performance.
Deshagani S, Liu X, Wu B, et al., 2019, Nickel cobaltite@Poly(3,4-ethylenedioxypyrrole) and carbon nanofiber interlayer based flexible supercapacitor, Nanoscale, Vol: 11, Pages: 2742-2756, ISSN: 2040-3364
Binder free flexible symmetric supercapacitors are developed with nickel cobaltite micro-flowers coated poly(3,4-ethylenedioxypyrrole) (NiCo2O4@PEDOP) hybrid electrodes. Free standing films of carbon nano-fibers (CNF), synthesized by electrospinning, were sandwiched between the NiCo2O4@PEDOP hybrid and the electrolyte coated separators on both sides of the cells. The CNF film conducts both ions and electrons, and confines the charge at the respective electrodes, to result in an improved specific capacitance (SC) and energy density compared to the analogous cell without the CNF interlayers. High SC of 1,775 F g-1 at a low current density of 0.96 A g-1 and a SC of 634 F g-1 achieved at a high current density of 38 A g-1 coupled with a SC retention of ~95% after 5,000 charge-discharge cycles in the NCO@PEDOP/CNF based symmetric supercapacitor, are performance attributes superior to that achieved with NCO and NCO/CNF based symmetric cells. The PEDOP coating serves as a highly conductive matrix for the NCO micro-flowers and also undergoes doping/de-doping during charge-discharge, thus amplifying the overall supercapacitor response, compared to the individual components. The CNF interlayers show reasonably high ion-diffusion coefficients for K+ and OH- propagation implying facile pathways available for movement of ions across the cross-section of the cell, and they also serve as ion reservoirs. The electrode morphologies remain unaffected by cycling, in the presence of the CNF interlayer. LED illumination and a largely unaltered charge storage response was achieved in a mutli-cell configuration, proving the potential for this approach in practical applications.
Yufit V, Tariq F, Biton M, et al., 2019, Operando visualisation and multi-scale tomography studies of dendrite formation and dissolution in zinc batteries, Joule, Vol: 3, Pages: 485-502, ISSN: 2542-4351
Alternative battery technologies are required to meet growing energy demands and address the limitations of present technologies. As such, it is necessary to look beyond lithium-ion batteries. Zinc batteries enable high power density while being sourced from ubiquitous and cost-effective materials. This paper presents, for the first time known to the authors, multi-length scale tomography studies of failure mechanisms in zinc batteries with and without commercial microporous separators. In both cases, dendrites were grown, dissolved, and regrown, critically resulting in different morphology of dendritic layer formed on both the electrode and the separator. The growth of dendrites and their volume-specific areas were quantified using tomography and radiography data in unprecedented resolution. High-resolution ex situ analysis was employed to characterize single dendrites and dendritic deposits inside the separator. The findings provide unique insights into mechanisms of metal-battery failure effected by growing dendrites.
Ouyang M, Bertei A, Cooper SJ, et al., 2019, Design of fibre Ni/CGO anode and model interpretation, ECS Transactions, Vol: 91, Pages: 1721-1739, ISSN: 1938-6737
A new structure of Ni/gadolinium-doped ceria (CGO) is prepared by a highly tuneable and facile combination of electrospinning and tape-casting method. The structure consists of a network made by continuous Ni fibres and filled in with CGO matrices. When used as the anode of solid oxide fuel cell (SOFC), though it has a lower triple phase boundary (TPB) density, it exhibits better performance compared with impregnated and cermet Ni/CGO with higher nickel loading. An algorithm is developed to determine the ceria-pore double phase boundary (DPB) density with different distance from nickel phase. Using the results, the relative electrochemical reaction rate on DPB and TPB of three different electrodes are calculated and proves that fibre-matrices structure has the morphology advantage of efficiently making use of all ceria-pore DPB. The relative contribution of DPB and TPB in anode reaction of SOFC is quantified in the first time and the importance of DPB is further stressed. This work provides new inspirations in material design of SOFC/SOEC and develops a novel strategy to evaluate the performance of electrodes quantitatively.
Chen X, Liu X, Childs P, et al., 2018, Design and fabrication of a low cost desktop electrochemical 3D printer, Pro-AM Conference in 2014, Pages: 395-400, ISSN: 2424-8967
Copyright © 2018 by Nanyang Technological University. Additive manufacturing (AM) (3D printing) is the process of creating 3D objects from digital models through the layer by layer deposition of materials. Electrochemical additive manufacturing (ECAM) is a relatively new technique which can create metallic components based depositing adherent layers of metal ions onto the surface of conductive substrate. In this paper, the design considerations for a meniscus confined ECAM approach is presented which demonstrates superior print speeds to equivalent works. This is achieved through the increase of the meniscus diameter to 400 \im which was achieved through the integration of a porous sponge into the print head to balance the hydraulic head of the electrolyte. Other piston based methods of controlling the electrolyte meniscus are discussed.
Merla Y, Wu B, Yufit V, et al., 2018, An easy-to-parameterise physics-informed battery model and its application towards lithium-ion battery cell design, diagnosis, and degradation, Journal of Power Sources, Vol: 384, Pages: 66-79, ISSN: 0378-7753
Accurate diagnosis of lithium ion battery state-of-health (SOH) is of significant value for many applications, to improve performance, extend life and increase safety. However, in-situ or in-operando diagnosis of SOH often requires robust models. There are many models available however these often require expensive-to-measure ex-situ parameters and/or contain unmeasurable parameters that were fitted/assumed. In this work, we have developed a new empirically parameterised physics-informed equivalent circuit model. Its modular construction and low-cost parametrisation requirements allow end users to parameterise cells quickly and easily. The model is accurate to 19.6 mV for dynamic loads without any global fitting/optimisation, only that of the individual elements. The consequences of various degradation mechanisms are simulated, and the impact of a degraded cell on pack performance is explored, validated by comparison with experiment. Results show that an aged cell in a parallel pack does not have a noticeable effect on the available capacity of other cells in the pack. The model shows that cells perform better when electrodes are more porous towards the separator and have a uniform particle size distribution, validated by comparison with published data. The model is provided with this publication for readers to use.
Liu X, Naylor Marlow M, Cooper S, et al., 2018, Flexible all-fiber electrospun supercapacitor, Journal of Power Sources, Vol: 384, Pages: 264-269, ISSN: 0378-7753
We present an all-fiber flexible supercapacitor with composite nanofiber electrodes made via electrospinning and an electrospun separator. With the addition of manganese acetylacetonate (MnACAC) to polyacrylonitrile (PAN) as a precursor for the electrospinning process and subsequent heat treatment, the performance of pure PAN supercapacitors was improved from 90 F.g-1 to 200 F.g-1 (2.5 mV.s-1) with possible mass loadings of MnACAC demonstrated as high as 40 wt%. X-ray diffraction measurements showed that after thermal treatment, the MnACAC was converted to MnO, meanwile, the thermal decomposition of MnACAC increased the graphitic degree of the carbonised PAN. Scanning electron microscopy and image processing showed that static electrospinning of pure PAN and PAN-Mn resulted in fiber diameters of 460 nm and 480 nm respectively after carbonisation. Further analysis showed that the fiber orientation exhibited a slight bias which was amplified with the addition of MnACAC. Use of focused ion beam scanning electron microscopy tomography also showed that MnO particles were evenly distributed through the fiber at low MnACAC concentrations, while at a 40 wt% loading the MnO particles were also visible on the surface. Comparison of the electrospun separators showed improved performance relative to a commercial Celgard separator (200 F.g-1 vs 141 F.g-1).
Cho JIS, Neville T, Trogadas P, et al., 2018, Nature-inspired flow-fields and water management for PEM fuel cells, Pages: 74-75
Flow-field design is crucial to polymer electrolyte membrane fuel cell (PEMFC) performance, since non-uniform transport of species to and from the membrane electrode assembly (MEA) results in significant power losses[1]. The long channels of conventional serpentine flow-fields cause large pressure drops between inlets and outlets, thus large parasitic energy losses and low fuel cell performance[2]. Here, a lung-inspired approach is used to design flow fields guided by the structure of a lung. The fractal geometry of the human lung has been shown to ensure uniform distribution of air from a single outlet (trachea) to multiple outlets (alveoli). Furthermore, the human lung transitions between two flow regimes: 14-16 upper generations of branches dominated by convection, and 7-9 lower generations of space-filling acini dominated by diffusion[3,4]. The upper generations of branches are designed to slow down the gas flow to a rate compatible with the rate in the diffusional regime (Pé ~ 1)[5], resulting in uniform distribution of entropy production in both regimes[3,4]. By employing a three-dimensional (3D) fractal structure as flow field inlet channel, we aim to yield similar benefits from replicating these characteristics of the human lung. The fractal pattern consists of repeating “H” shapes where daughter “H's” are located at the four tips of the parent “H”. The fractal geometry obeys Murray's law, much like the human lung, hereby leading to minimal mechanical energy losses. Furthermore, the three-dimensional branching structure provide uniform local conditions on the surface of the catalyst layer as only the outlets of the fractal inlet channel are exposed to the MEA. Numerical simulations were conducted to determine the number of generations required to achieve uniform reactant distribution and minimal entropy production. The results reveal that the ideal number of generations for minimum entropy production lies between N
Trogadas P, Cho JIS, Neville TP, et al., 2017, A lung-inspired approach to scalable and robust fuel cell design, Energy and Environmental Science, Vol: 11, Pages: 136-143, ISSN: 1754-5692
A lung-inspired approach is employed to overcome reactant homogeneity issues in polymer electrolyte fuel cells. The fractal geometry of the lung is used as the model to design flow-fields of different branching generations, resulting in uniform reactant distribution across the electrodes and minimum entropy production of the whole system. 3D printed, lung-inspired flow field based PEFCs with N = 4 generations outperform the conventional serpentine flow field designs at 50% and 75% RH, exhibiting a 20% and 30% increase in performance (at current densities higher than 0.8 A cm2) and maximum power density, respectively. In terms of pressure drop, fractal flow-fields with N = 3 and 4 generations demonstrate 75% and 50% lower values than conventional serpentine flow-field design for all RH tested, reducing the power requirements for pressurization and recirculation of the reactants. The positive effect of uniform reactant distribution is pronounced under extended current-hold measurements, where lung-inspired flow field based PEFCs with N = 4 generations exhibit the lowest voltage decay (B5 mV h1). The enhanced fuel cell performance and low pressure drop values of fractal flow field design are preserved at large scale(25 cm2), in which the excessive pressure drop of a large-scale serpentine flow field renders its use prohibitive.
Wu B, Myant C, Weider SZ, 2017, The value of additive manufacturing: future opportunities, Briefing paper, 2
The global additive manufacturing (AM) – 3D printing – industr y was valued at $6 billion for 2016, and is predicted to grow to more than $26 billion by 20221. This rapid growth has arisen mainly because of the evolution of AM from primarily a prototyping tool to a useful end-product fabrication method in some high-value manufacturing applications (e.g., in the aerospace, medical device and automotive industries).• AM has the potential to offer many economic, technical and environmental advantages over traditional manufacturing approaches, including decreased production costs and times, the possibility of flexible and bespoke production, as well as a reduction in energy usage and waste. To realise these benefits, however, several barriers – across the entire AM process chain – need to be overcome. For example, improved design software, faster printing technology, increased automation and better industry standards are required.• To realise a more-efficient and more-profitable industr y, ‘game-changing’ AM research breakthroughs are thus required. Involving more researchers – from a wide array of scientific and engineering backgrounds – will be beneficial, as will a closer working relationship between academia and industr y.• The concept of molecular science and engineering2 – melding a deep understanding of molecular science with an engineering mind-set – provides an excellent framework for the ‘cross pollination’ of research ideas. In the pursuit of solving some of the biggest needs in AM, scientists and engineers – from a range of disciplines – can be brought together to communicate and collaborate at all stages of the AM research-to-final-product chain. In this way, costly late-stage changes can be avoided and the route to final, functional end-use products can be rapidly optimised. In addition, a new generation of scientists and engineers can be trained in a transdi
Chen X, Liu X, Childs P, et al., 2017, A low cost desktop electrochemical metal 3D printer, Advanced Materials Technologies, Vol: 2, ISSN: 2365-709X
Additive manufacturing (AM), or 3D printing as it is more commonly known, is the process of creating 3D objects from digital models through the sequential deposition of material in layers. Electrochemical 3D printing is a relatively new form of AM that creates metallic structures through electrochemical reduction of metal ions from solutions onto conductive substrates. The advantage of this process is that a wide range of materials and alloys can be deposited under ambient conditions without thermal damage and more importantly at low cost, as this does not require expensive laser optics or inert gas environments. Other advantages include the fact that this process can be both additive and subtractive through reversal of potential allowing for recycling of components through electrochemical dissolution. However, one main limitation of this technology is speed. Here, a novel electrochemical 3D printer design is proposed using a meniscus confinement approach which demonstrates deposition rates three orders of magnitude higher than equivalent systems due to improved mass transport characteristics afforded through a mechanical electrolyte entrainment mechanism. Printed copper structures exhibit a polycrystalline nature, with decreasing the grain size as the potential is increased resulting in a higher Vickers hardness and electronic resistivity.
Huang M, Finlayson E, Liu H, et al., 2017, The current and future prospects for vanadium flow batteries in China, International Flow Battery Forum
Wu B, Offer G, 2017, Environmental impact of hybrid and electric vehicles, Environmental Impacts of Road Vehicles : Past, Present and Future, Editors: Harrison, Hester, Publisher: Royal Society of Chemistry
Hybrid and electric vehicles play a critical role in reducing global greenhouse gas emissions, with transport estimated to contribute to 14% of the 49 GtCO2eq produced annually. Analysis of only the conversion efficiency of powertrain technologies can be misleading, with pure battery electric and hybrid vehicles reporting average efficiencies of 92% and 35% in comparison with 21% for internal combustion engine vehicles. A fairer comparison would be to consider the well-to-wheel efficiency, which reduces the numbers to 21–67%, 25% and 12%, respectively. The large variation in well-to-wheel efficiency of pure battery electric vehicles highlights the importance of renewable energy generation in order to achieve true environmental benefits. When calculating the energy return on investment of the various technologies based on the current energy generation mix, hybrid vehicles show the greatest environmental benefits, although this would change if electricity was made with high amounts of renewables. In an extreme scenario with heavy coal generation, the CO2eq return on investment can actually be negative for pure electric vehicles, highlighting the importance of renewable energy generation further. The energy impact of production is generally small (∼6% of lifetime energy) and, similarly, recycling is of a comparable magnitude, but it is less well studied.
Gupta G, Wu B, Mylius S, et al., 2016, A systematic study on the use of short circuiting for the improvement of proton exchange membrane fuel cell performance, International Journal of Hydrogen Energy, Vol: 42, Pages: 4320-4327, ISSN: 1879-3487
Proton exchange membrane fuel cells suffer from reversible performance loss during operation caused by the oxidation of the Pt catalyst which in turn reduces the electrochemically active surface area. Many fuel cell manufacturers recommend using short circuiting during the operation of the fuel cell to improve the performance of the cells over time. However, there is lack of understanding on how it improves the performance as wellas on how to optimise the short circuiting strategy for different fuel cell systems. We present a simple procedure to develop an optimised short circuiting strategy by maximising the cumulative average power density gain and minimising the time required to recover the energy loss during short circuiting. We obtained average voltage improvement from 10 to 12% at different current densities for a commercial H-100 system and our short circuiting strategy showed ~2% voltage improvement in comparison to a commercial strategy. We also demonstrated that the minimum short circuiting time is a function of double layer capacitance by the use of electrochemical impedance spectroscopy.
Merla Y, Wu B, Yufit V, et al., 2016, Extending battery life: a low-cost practical diagnostic technique for lithium-ion batteries, Journal of Power Sources, Vol: 331, Pages: 224-231, ISSN: 0378-7753
Modern applications of lithium-ion batteries such as smartphones, hybrid & electric vehicles and grid scale electricity storage demand long lifetime and high performance which typically makes them the limiting factor in a system. Understanding the state-of-health during operation is important in order to optimise for long term durability and performance. However, this requires accurate in-operando diagnostic techniques that are cost effective and practical. We present a novel diagnosis method based upon differential thermal voltammetry demonstrated on a battery pack made from commercial lithium-ion cells where one cell was deliberately aged prior to experiment. The cells were in parallel whilst being thermally managed with forced air convection. We show for the first time, a diagnosis method capable of quantitatively determining the state-of-health of four cells simultaneously by only using temperature and voltage readings for both charge and discharge. Measurements are achieved using low-cost thermocouples and a single voltage measurement at a frequency of 1 Hz, demonstrating the feasibility of implementing this approach on real world battery management systems. The technique could be particularly useful under charge when constant current or constant power is common, this therefore should be of significant interest to all lithium-ion battery users.
Liu X, Jervis R, Maher RC, et al., 2016, 3D-Printed Structural Pseudocapacitors, Advanced Materials Technologies, Vol: 1, ISSN: 2365-709X
Direct metal laser sintering is used to create 3D hierarchical porous metallic scaffolds which are then functionalized with a co-electrodeposition of MnO2, Mn2O3, and doped conducting polymer. This approach of functionalizing metal 3D printed scaffolds thus opens new possibilities for structural energy storage devices with enhanced performance and lifetime characteristics.
Liu X, Rhodri Jervis, Robert C Maher, et al., 2016, 3D Printed Structural Pseudocapacitors - a Multi-Scale X-Ray Tomography Study, ECS
Li J, wu BILLY, Myant CONNOR, 2016, The Current Landscape for Additive Manufacturing Research
Liu X, Wu B, Brandon NP, et al., 2016, Tough ionogel-in-mask hybrid gel electrolytes in supercapacitors with durable pressure and thermal tolerances, Energy Technology, Vol: 5, Pages: 220-224, ISSN: 2194-4288
A primary challenge of gel electrolytes in development of flexible and wearable devices is their weak mechanical performances, including their compressive stress, tensile strength, and puncture resistance. Here we prepare an ionogel-mask hybrid gel electrolyte, which successfully achieves synergic advantages of the high mechanical strength of the mask substance and the superior electrochemical and thermal characteristics of the ionogel. The fabricated supercapacitor can maintain a relatively stable capacitive performance even under a high pressure of 3236 kPa. Meanwhile, with the good thermal stability of the composite gel electrolyte, the solid-state supercapacitor can be operated at high temperatures ranging from 25 °C to 200 °C. The ionogel-mask hybrid gel can be superior tough gel electrolyte for solid-state flexible supercapacitors with durable advantages in both high temperatures and pressures.
Wu B, Parkes MP, de Benedetti L, et al., 2016, Real-time monitoring of proton exchange membrane fuel cell stack failure, Journal of Applied Electrochemistry, Vol: 46, Pages: 1157-1162, ISSN: 1572-8838
Uneven pressure drops in a 75-cell 9.5-kWe protonexchange membrane fuel cell stack with a U-shaped flowconfiguration have been shown to cause localised flooding.Condensed water then leads to localised cell heating, resultingin reduced membrane durability. Upon purging of the anodemanifold, the resulting mechanical strain on the membranecan lead to the formation of a pin-hole/membrane crack and arapid decrease in open circuit voltage due to gas crossover.This failure has the potential to cascade to neighbouring cellsdue to the bipolar plate coupling and the current densityheterogeneities arising from the pin-hole/membrane crack.Reintroduction of hydrogen after failure results in cell voltageloss propagating from the pin-hole/membrane crack locationdue to reactant crossover from the anode to the cathode, giventhat the anode pressure is higher than the cathode pressure.Through these observations, it is recommended that purging isavoided when the onset of flooding is observed to preventirreparable damage to the stack.
Wu B, Ibrahim KA, Brandon NP, 2016, Electrical conductivity and porosity in stainless steel 316L scaffolds for electrochemical devices fabricated using selective laser sintering, Materials and Design, Vol: 109, Pages: 51-59, ISSN: 1873-4197
Battery electrode microstructures must be porous, to provide a large active surface area to facilitate fast charge transfer kinetics. In this work, we describe how a novel porous electrode scaffold, made from stainless steel 316L powder can be fabricated using selective laser sintering by proper selection of process parameters. Porosity, electrical conductivity and optical microscopy measurements were used to investigate the properties of fabricated samples. Our results show that a laser energy density between 1.50–2.00 J/mm2 leads to a partial laser sintering mechanism where the powder particles are partially fused together, resulting in the fabrication of electrode scaffolds with 10% or higher porosity. The sample fabricated using 2.00 J/mm2 energy density (60 W–1200 mm/s) exhibited a good electrical conductivity of 1.80 × 106 S/m with 15.61% of porosity. Moreover, we have observed the porosity changes across height for the sample fabricated at 60 W and 600 mm/s, 5.70% from base and increasing to 7.12% and 9.89% for each 2.5 mm height towards the top surface offering graded properties ideal for electrochemical devices, due to the changing thermal boundary conditions. These highly porous electrode scaffolds can be used as an electrode in electrochemical devices, potentially improving energy density and life cycle.
Patsios C, Wu B, Chatzinikolaou E, et al., 2016, An integrated approach for the analysis and control of grid connected energy storage systems, Journal of Energy Storage, Vol: 5, Pages: 48-61, ISSN: 2352-152X
This paper presents an integrated modelling methodology which includes reduced-order models of a lithium ion battery and a power electronic converter, connected to a 35-bus distribution network model. The literature contains many examples of isolated modelling of individual energy storage mediums, power electronic interfaces and control algorithms for energy storage. However, when assessing the performance of a complete energy storage system, the interaction between components gives rise to a range of phenomena that are difficult to quantify if studied in isolation. This paper proposes an integrated electro–thermo–chemical modelling methodology that seeks to address this problem directly by integrating reduced-order models of battery cell chemistry, power electronic circuits and grid operation into a computationally efficient framework. The framework is capable of simulation speeds over 100 times faster than real-time and captures phenomena typically not observed in simpler battery and power converter models or non-integrated frameworks. All simulations are performed using real system load profiles recorded in the United Kingdom. To illustrate the advantages inherent in such a modelling approach, two specific interconnected effects are investigated: the effect of the choice of battery float state-of-charge on overall system efficiency and the rate of battery degradation (capacity/power fade). Higher state-of-charge operation offers improved efficiency due to lower polarisation losses of the battery and lower losses in the converter, however, an increase in the rate of battery degradation is observed due to the accelerated growth of the solid-electrolyte interphase layer. We demonstrate that grid control objectives can be met in several different ways, but that the choices made can result in a substantial improvement in system roundtrip efficiency, with up to a 43% reduction in losses, or reduction in battery degradation by a factor of two, depending on b
Wu B, Merla Y, Yufit V, et al., 2016, Novel application of differential thermal voltammetry as an in-depth state-of-health diagnosis method for lithium-ion batteries, Journal of Power Sources, Vol: 307, Pages: 308-319, ISSN: 1873-2755
Understanding and tracking battery degradation mechanisms and adapting its operation have become a necessity in order to enhance battery durability. A novel use of differential thermal voltammetry (DTV) is presented as an in-situ state-of-health (SOH) estimator for lithium-ion batteries.Accelerated ageing experiments were carried on 5Ah commercial lithium-ion polymer cells operated and stored at different temperature and loading conditions. The cells were analysed regularly with various existing in-situ diagnosis methods and the novel DTV technique to determine their SOH. The diagnosis results were used collectively to elaborate the degradation mechanisms inside the cells. The DTV spectra were decoupled into individual peaks, which each represent particular phases in the negative and positive electrode combined. The peak parameters were used to quantitatively analyse the battery SOH.A different cell of the same chemistry with unknown degradation history was then analysed to explore how the cell degraded. The DTV technique was able to diagnose the cell degradation without relying on supporting results from other methods nor previous cycling data.
Parkes MA, Chen T, Wu B, et al., 2015, “can” you really make a battery out of that?, Journal of Chemical Education, Vol: 93, Pages: 681-686, ISSN: 1938-1328
This classroom activity introduces students to battery electrochemistry through the construction of a simple battery made from household products. Students will use a set of simple design rules to improve the performance of the battery, and power a light emitting diode. The electrochemical performance of the batteries is characterized using potentiostatic cyclic voltammetry and chronoampometry, and suggestions for implementing this activity into a high school teaching environment are presented. Designed for United Kingdom secondary schools and exam boards, the supplementary teaching package contains problem sheets and activities appropriate for students age 14 and up.
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