Batteries, Volume 4, Issue 4 (December 2018) – 24 articles

Two prelithiation processes (shallow Li-ion insertion, and thrice-repeated deep Li-ion insertion and extraction) were applied to the hard carbon (HC) negative electrode (NE) used in lithium-ion batteries (LIBs). LIB full-cells were assembled using Li(Ni_0.5Co_0.2Mn_0.3)O₂ positive electrodes (PEs) and the prelithiated HC NEs. The assembled full-cells were charged and discharged under a low current density, increasing current densities in a stepwise manner, and then constant under a high current density. The prelithiation process of shallow Li-ion insertion resulted in the high Coulombic efficiency (CE) of the full-cell at the initial charge-discharge cycles as well as in a superior rate capability. The prelithiation process of thrice-repeated Li-ion insertion and extraction attained an even higher CE and a high charge-discharge specific capacity under a low current density. However, both prelithiation processes decreased the capacity retention during charge-discharge cycling under a high current density, ascertaining a trade-off relationship between the increased CE and the cycling performance. Further elimination of the irreversible capacity of the HC NE was responsible for the higher utilization of both the PE and NE, attaining higher initial performances, but allowing the larger capacity to fade throughout charge-discharge cycling. Full article

Attempts have been made to find the best procedure for the detection of premature battery capacity loss (the so called “PCL”) in AGM-VRLA 48 V batteries operating in telecommunication systems. However, recorded changes in internal resistance and potential did not give clear indications of the beginning of the PCL effect. The obtained correlation between internal resistance and potential derived from used batteries does not show the expected trend in measured parameters. It seems that the application of Electrochemical Impedance Spectroscopy (EIS), which is a faster and non-destructive method, may solve this problem. It is demonstrated that the change in internal resistance (which is an indicator of the state of health (SoH)) can be determined from EIS spectra during continuous operation of 12 V monoblocks in a backup power source of a base transceiver station (BTS). Full article

Accurately estimating the state of charge (SOC) of power batteries in electric vehicles is of great significance to the measurement of the endurance mileage of electric vehicles, as well as the safety protection of the power battery. In view of lithium ion batteries’ nonlinear relation between SOC estimation and current, voltage, and temperature, the improved Back Propagation (BP) neural network method is proposed to accurately estimate the SOC of power batteries. To address the inherent limitations of BP neural network, particle swarm algorithm is adopted to modify the relevant weighting coefficients. In this paper, the lithium iron phosphate battery (3.2 V/20 Amper-Hour) was studied. Charge and discharge experiments were conducted under a constant temperature. The training data were used to construct the surrogate model using the improved BP neural network. It is noted that the accuracy of the developed algorithm is increased by 2% as compared to that of conventional BP. Finally, an actual vehicle condition experiment was designed to further verify the accuracy of these two algorithms. The experimental results show that the improved algorithm is more suitable for real vehicle operating conditions than the traditional algorithm, and the estimation accuracy can meet the industry standards to a greater extent. Full article

Self-synthesized rutile iron oxyfluoride (FeOF) was studied as a cathode material for Na-ion batteries. The highly crystalline FeOF provided an initial discharge capacity of 246 mAh g⁻¹ in a voltage range of 1.0–4.0 V, followed by 88% of capacity retention after 20 cycles. This discharge-charge reaction of FeOF between 0.8 and 4.0 V are advanced by the Fe²⁺/Fe³⁺ redox reaction. That is, no conversion reaction was involved in the application of FeOF as a cathode material for Na-ion batteries because of the low potential of Na-insertion. In addition, the structure change of FeOF from rutile to cubic during Na ion insertion, which was similar to that in Li-ion batteries. No remarkable HF release was detected even up to 700 °C, indicating a low toxic risk of the FeOF cathode. The thermal properties of sodiated and desodiated FeOF electrodes in the associated electrolyte were investigated by DSC (Differential scanning calorimetry) up to 500 °C. Sodiated FeOF electrodes showed larger exothermic heat generation than desodiated ones, especially at a temperature higher than 380 °C. Finally, the thermal stability of FeOF cathodes in the associated Li- and Na-ion battery electrolytes was quantitatively compared with variations of the electrode/electrolyte ratio. Full article

In this paper, a network of 37 fiber Bragg grating (FBG) sensors is proposed for real-time, in situ, and operando multipoint monitoring of the surface temperature distribution on a pack of three prismatic lithium polymer batteries (LiPBs). Using the network, a spatial and temporal thermal mapping of all pack interfaces was performed. In each interface, nine strategic locations were monitored by considering a three-by-three matrix, corresponding to the LiPBs top, middle and bottom zones. The batteries were subjected to charge and discharge cycles, where the charge was carried out at 1.0 C, whereas the discharge rates were 0.7 C and 1.4 C. The results show that in general, a thermal gradient is recognized from the top to the bottom, but is less prominent in the end-of-charge steps. The results also indicate the presence of hot spots between two of the three batteries, which were located near the positive tab collector. This occurs due to the higher current density of the lithium ions in this area. The presented FBG sensing network can be used to improve the thermal management of batteries by performing a spatiotemporal thermal mapping, as well as by identifying the zones which are more conducive to the possibility of the existence of hot spots, thereby preventing severe consequences such as thermal runaway and promoting their safety. To our knowledge, this is the first time that a spatial and temporal thermal mapping is reported for this specific application using a network of FBG sensors. Full article

Aqueous binders are highly recommended in battery production for (i) reducing the costs and, (ii) increasing the safety due to the absence of an organic solvent. Unfortunately, the impact of water during the electrode formulation on sodiated phases is still unclear and deserves investigation. In this work, we used carboxymethylcellulose (Na-CMC) binder to prepare electrodes of a high energy density P2-layered oxide material, Na_0.67Mn_0.6Fe_0.25Co_0.15O₂ (NaMFC). We investigated the effects of water-based electrode preparation on the electrochemical performance, by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and neutron diffraction. The water leads to degradation of the material limiting the reversible specific charge at 90 mAh·g⁻¹ instead of 120 mAh·g⁻¹ obtained with N-methyl pyrrolidone (NMP) solvent with polyvinylidene fluoride (PVDF) as binder. The protons exchanged in the structure, occurring during electrode preparation, are assumed to disrupt the Na ions extraction mechanism limiting the specific charge of such a material. Full article

The growing popularity of electric vehicles is one of the main drivers of battery industry transformation. Words like “transport system decarbonization”, “electromobility”, and “environmental-friendly society” are very popular today, but questions remain as to how to measure electric vehicles’ adoption progress and how this transition changes the battery industry. This perspective paper provides a review of the electric cars and buses market, estimates the production volumes of some other electric vehicle types, and discusses the role of traction batteries in the global battery market. A simple estimation of the sales rate allows us to evaluate the prospects of electric vehicle adoption in leading countries. Finally, the application of the main battery chemistries is reviewed and topical issues to the research society are addressed and formulated. Full article

Electrochemical Impedance Spectroscopy (EIS) is a valuable tool for the characterization of electrical, thermal and aging behavior of batteries. In this paper, an EIS measurement technique to acquire impedance spectra with high time resolution is examined, which can be used to gather impedance data during dynamic operating conditions. A theoretical analysis of the used multi-sine excitation signals is performed in detail and a practical measurement system is presented and validated. Afterwards, EIS measurements during the charging process of a lithium-ion battery are performed and discussed. Full article

Despite the appealing features of vanadium redox flow batteries as a promising energy storage solution, the polarization losses, among other factors, prevent widespread applications. The dominant contribution to these polarization losses is the sluggish (even irreversible) electron-transfer towards reactions, leading to large over-potentials (poor rate capability). In particular, the positive half-cell reaction suffers from a complex mechanism since electron- and oxygen-transfer processes are key steps towards efficient kinetics. Thus, the positive reaction calls for electrodes with a large number of active sites, faster electron transfer, and excellent electrical properties. To face this issue, a graphene-wrapped graphite felt (GO-GF) electrode was synthesized by an electrospray process as a cost-effective and straightforward way, leading to a firm control of the GO-deposited layer-by-layer. The voltage value was optimized to produce a homogeneous deposition over a GF electrode after achieving a stable Taylor cone-jet. The GO-GF electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in order to elucidate the electrocatalytic properties. Both analyses reflect this excellent improvement by reducing the over-potentials, improving reversibility, and enhancing collected current density. These findings confirm that the GO-GF is a promising electrode for high-performance VRFB, overcoming the performance-limiting issues in a positive half-reaction. Full article

Electrolyte formulations in standard lithium ion and lithium metal batteries are complex mixtures of various components. In this article, we review molecular key principles of ion complexes in multicomponent electrolyte solutions in regards of their influence on charge transport mechanisms. We outline basic concepts for the description of ion–solvent and ion–ion interactions, which can be used to rationalize recent experimental and numerical findings concerning modern electrolyte formulations. Furthermore, we discuss benefits and drawbacks of empirical concepts in comparison to molecular theories of solution for a more refined understanding of ion behavior in organic solvents. The outcomes of our discussion provide a rational for beneficial properties of ions, solvent, co-solvent and additive molecules, and highlight possible routes for further improvement of novel electrolyte solutions. Full article

The possibilities of manufacturing batteries with Nafion 117 membranes in the Na⁺-form intercalated by mixtures of non-aqueous organic solvents used both as an electrolyte, separator, and binder were investigated. Electrochemical stability of various organic solvent mixtures based on N,N-dimethylacetamide, ethylene carbonate, propylene carbonate, and tetrahydrofuran were characterized. It was shown that a sodium battery based on a Nafion-Na membrane intercalated by mixture of ethylene carbonate and propylene carbonate with a Na₃V_1.9Fe_0.1(PO₄)₃/C positive electrode is characterized by a discharge capacity of ≈110 mAh·g⁻¹ (current density of 10 mA·g⁻¹) at room temperature and shows the ability to cycle without degradation during 20 cycles. Batteries with Nafion membrane electrolytes, containing N,N-dimethylacetamide, were characterized using capacity fading during cycling, which is due to the interaction of N,N-dimethylacetamide and a negative sodium electrode. Full article

In this study, we have proposed a novel concept of hybrid flow batteries consisting of a molten Na-Cs anode and an aqueous NaI catholyte separated by a NaSICON membrane. A number of carbonaceous electrodes are studied using cyclic voltammetry (CV) for their potentials as the positive electrode of the aqueous NaI catholyte. The charge transfer impedance, interfacial impedance and NaSICON membrane impedance of the Na-Cs ‖ NaI hybrid flow battery are analyzed using electrochemical impedance spectroscopy. The performance of the Na-Cs ‖ NaI hybrid flow battery is evaluated through galvanostatic charge/discharge cycles. This study demonstrates, for the first time, the feasibility of the Na-Cs ‖ NaI hybrid flow battery and shows that the Na-Cs ‖ NaI hybrid flow battery has the potential to achieve the following properties simultaneously: (i) An aqueous NaI catholyte with good cycle stability, (ii) a durable and low impedance NaSICON membrane for a large number of cycles, (iii) stable interfaces at both anode/membrane and cathode/membrane interfaces, (iv) a molten Na-Cs anode capable of repeated Na plating and stripping, and (v) a flow battery with high Coulombic efficiency, high voltaic efficiency, and high energy efficiency. Full article

To understand better the thermal behaviour of lithium-ion batteries under different working conditions, various experiments were applied to a 13 Ah Altairnano lithium titanate oxide battery cell by means of isothermal battery calorimeter. Several parameters were measured such as the battery surface temperature, voltage, current, power, heat flux, maximum temperature and power area. In addition, the efficiency was calculated. Isothermal battery calorimeter was selected as the most appropriate method for heat loss measurements. Temperatures on the surface of the battery were measured by employing four contact thermocouples (type K). In order to determine the heat loss of the battery, constant current charge and discharge pulses at sixteen different C-rates were applied to the battery. It was seen that the charge and discharge C-rates has a considerable influence on the thermal behaviours of lithium-ion batteries. In this research paper, the C-rate was linked to the peak temperature, efficiency and heat loss and it was concluded that they are linear dependent on the C-rate. In addition, the outcomes of this investigation can be used for battery thermal modelling and design of thermal management systems. Full article

The state-of-the-art functionality test of classic redox-flow-stacks measures the current–voltage characteristic with the technical electrolyte. This research paper aims to simplify the validation of redox flow batteries’ functionality by conducting electrochemical impedance spectroscopy (EIS) on redox flow stacks. Since the electrolyte used in the batteries is usually toxic and aggressive, it would be a significant simplification to verify the functionality with an alternative, non-toxic fluid. EIS measurements on batteries with larger sized electrodes, multiple cells, and different fluids were performed. It was demonstrated that all impedances are repeatable, thereby validating this procedure as a qualification method for full-size and complex batteries with an alternative fluid. EIS measurements were able to detect deliberately manipulated cells. This research uses three different analysis methods for the acquired data to identify errors. The respective approaches are, firstly, (1) a comparison of the Nyquist plots; secondly, (2) a comparison of the Bode plots; and thirdly, (3) a comparison of the calculated characteristic values of the equivalent circuits. The analysis found that all methods are suitable to detect errors in the batteries. Nevertheless, the bode-plot comparison method proves to be especially advantageous, because it enables a quantitative statement. Full article

In the near future, a large volume of electric vehicle (EV) batteries will reach their end-of-life in EVs. However, they may still retain capacity that could be used in a second life, e.g., for a second use in an EV, or for home electricity storage, thus becoming part of the circular economy instead of becoming waste. The aim of this paper is to explore second life of EV batteries to provide an understanding of how the battery value chain and related business models can become more circular. We apply qualitative research methods and draw on data from interviews and workshops with stakeholders, to identify barriers to and opportunities for second use of EV batteries. New business models are conceptualized, in which increased economic viability of second life and recycling and increased business opportunities for stakeholders may lead to reduced resource consumption. The results show that although several stakeholders see potential in second life, there are several barriers, many of which are of an organizational and cognitive nature. The paper concludes that actors along the battery value chain should set up new collaborations with other actors to be able to benefit from creating new business opportunities and developing new business models together. Full article

This study presents the application of pyrolyzed spent coffee beans as a potential electrode material to replace commercial bipolar graphite plate in vanadium redox flow batteries (VRB). The results indicate that the biochar obtained from spent coffee beans shows relatively good electrochemical charge transfer kinetics of vanadium redox reactions as well as generates higher energy and voltage efficiency in a static cell test when compared to TF6 bipolar graphite plate. Additionally, the biochar was activated via steam at various activation times to increase its surface area, and their effect on the kinetics of the electrochemical reactions was investigated. The activated carbon did not exhibit any improvement neither in electron transfer kinetics nor in the battery efficiency, despite their increased surface area. The performed studies demonstrate that the biochar obtained from spent coffee beans can be a low-cost electrode material for VRB with improved performance characteristics. Full article

Systematic steady-state measurements were performed in order to investigate the effect of operating temperature on the individual half-cell reactions in all vanadium redox flow cells. Results confirm that the kinetic losses are dominated by the negative half-cell reaction. Steady-state polarization and AC impedance measurements allowed for extraction of kinetic parameters (exchange current densities, activation energy) of the corresponding half-cell reaction. Full article

The incessant growth in energy demand has resulted in the deployment of renewable energy generators to reduce the impact of fossil fuel dependence. However, these generators often suffer from intermittency and require energy storage when there is over-generation and the subsequent release of this stored energy at high demand. One such energy storage technology that could provide a solution to improving energy management, as well as offering spinning reserve and grid stability, is the redox flow battery (RFB). One such system is the 200 kW/400 kWh vanadium RFB installed in the energy station at Martigny, Switzerland. This RFB utilises the excess energy from renewable generation to support the energy security of the local community, charge electric vehicle batteries, or to provide the power required to an alkaline electrolyser to produce hydrogen as a fuel for use in fuel cell vehicles. In this article, this vanadium RFB is fully characterised in terms of the system and electrochemical energy efficiency, with the focus being placed on areas of internal energy consumption from the regulatory systems and energy losses from self-discharge/side reactions. Full article

Vanadium redox flow batteries (VRFBs) offer great promise as a safe, cost effective means of storing electrical energy on a large scale and will certainly have a part to play in the global transition to renewable energy. To unlock the full potential of VRFB systems, however, it is necessary to improve their power density. Unconventional stack design shows encouraging possibilities as a means to that end. Presented here is the novel concept of variable porous electrode compression, which simulations have shown to deliver a one third increase in minimum limiting current density together with a lower pressure drop when compared to standard uniform compression cell designs. Full article

Estimation of a lithium battery electrical impedance can provide relevant information regarding its characteristics. Currently, electrochemical impedance spectroscopy (EIS) constitutes the most recognized and accepted method. Although highly precise and robust, EIS is usually performed during laboratory testing and is not suitable for any on-board application, such as in battery electric vehicles (BEVs) because it is an instrumentally and computationally heavy method. To address this issue and on-line system applications, this manuscript describes, as a main contribution, a passive method for battery impedance estimation in the time domain that involves the voltage and current profile induced by the battery through its ordinary operation without injecting a small excitation signal. This method has been tested on the same battery with different passive voltage and current profile and has been validated by achieving similar results. Compared to the original idea presented in the published conference paper, this manuscript explains, in detail, the previously developed method of transforming the battery impedance from the frequency domain to time domain. Moreover, this impedance measurement is used to estimate more robustly the battery state of charge (SoC) through Kalman filters. In the original published conference paper, only an extended Kalman filter (EKF) was applied. However, in this manuscript, an EKF and an unscented Kalman filter (UKF) are used and their performances are compared. Full article

Leaching of metals from waste button cell batteries was explored in this study. Aspergillus niger spent medium was used for metal leaching to avoid toxicity of metals toward microbial cells. Process parameters including time, temperature, shaking speed, and volume of the spent medium were optimized. We obtained 100% leaching of zinc and silver in six hours at 60 °C and 100 rpm using 15 mL spent medium. The use of spent medium supported the indirect leaching process. The organic acid produced by fungi acts as a lixiviant, aiding the metal leaching in this process. Full article

Carbon plays a critical role in improving the electronic conductivity of cathodes in lithium ion batteries. Particularly, the characteristics of carbon and its composite with electrode material strongly affect battery properties, governed by electron as well as Li⁺ ion transport. We have reviewed here various types of carbon materials and organic carbon sources in the production of conductive composites of nano-LiMnPO₄ and LiCoO₂. Various processes of making these composites with carbon or organic carbon sources and their characterization have been reviewed. Finally, the type and amount of carbon and the preparation methods of composites are summarized along with their battery performances and cathode materials. Among the different processes of making a composite, ball milling provided the benefit of dense and homogeneous nanostructured composites, leading to higher tap-density and thus increasing the volumetric energy densities of cathodes. Full article

Industrial and academic communities have embarked on investigating the sustainability of vehicles that contain embedded electrochemical energy storage systems. Circular economy strategies for electric vehicle (EV) or hybrid electric vehicle (HEV) battery systems are underpinned by implicit assumptions about the state of health (SOH) of the battery. The internal resistance of battery systems is the essential property for determining available power, energy efficiency, and heat generation. Consequently, precise measurement is crucial to estimate the SOH; however, the international standards and best practice guides that exist to define the measurements include long preconditioning and rest times that make the test duration prohibitive. The aim of this research is to critically evaluate whether test duration times for internal resistance measurements can be reduced to values that may facilitate further end-of-life (EOL) options. Results reveal a newly developed technique using pulse-multisines is two to four times faster to perform when compared to the standard protocol whilst maintaining accuracy for battery electric vehicle (BEV) and HEV cells, respectively. This novel method allows different stakeholders to rank the relative importance of test accuracy verses experimental test time when categorising used Li-ion cells for different EOL applications. Full article

The vanadium redox flow battery (VRFB) is one of the most mature and commercially available electrochemical technologies for large-scale energy storage applications. The VRFB has unique advantages, such as separation of power and energy capacity, long lifetime (>20 years), stable performance under deep discharge cycling, few safety issues and easy recyclability. Despite these benefits, practical VRFB operation suffers from electrolyte imbalance, which is primarily due to the transfer of water and vanadium ions through the ion-exchange membranes. This can cause a cumulative capacity loss if the electrolytes are not rebalanced. In commercial systems, periodic complete or partial remixing of electrolyte is performed using a by-pass line. However, frequent mixing impacts the usable energy and requires extra hardware. To address this problem, research has focused on developing new membranes with higher selectivity and minimal crossover. In contrast, this study presents two alternative concepts to minimize capacity fade that would be of great practical benefit and are easy to implement: (1) introducing a hydraulic shunt between the electrolyte tanks and (2) having stacks containing both anion and cation exchange membranes. It will be shown that the hydraulic shunt is effective in passively resolving the continuous capacity loss without detrimentally influencing the energy efficiency. Similarly, the combination of anion and cation exchange membranes reduced the net electrolyte flux, reducing capacity loss. Both approaches work efficiently and passively to reduce capacity fade during operation of a flow battery system. Full article