Manganese Dissolution Research Articles

What Happens to LiMnPO4 upon Chemical Delithiation?

Olivine MnPO4 is the delithiated phase of the lithium-ion-battery cathode (positive electrode) material LiMnPO4, which is formed at the end of charge. This phase is metastable under ambient conditions and can only be produced by delithiation of LiMnPO4. We have revealed the manganese dissolution phenomenon during chemical delithiation of LiMnPO4, which causes amorphization of olivine MnPO4. The properties of crystalline MnPO4 obtained from carbon-coated LiMnPO4 and of the amorphous product resulting from delithiation of pure LiMnPO4 were studied and compared. The phosphorus-rich amorphous phases in the latter are considered to be MnHP2O7 and MnH2P2O7 from NMR, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy analysis. The thermal stability of MnPO4 is significantly higher under high vacuum than at ambient condition, which is shown to be related to surface water removal.

Combined Electron Paramagnetic Resonance and Atomic Absorption Spectroscopy/Inductively Coupled Plasma Analysis As Diagnostics for Soluble Manganese Species from Mn-Based Positive Electrode Materials in Li-ion Cells.

Manganese dissolution from positive electrodes significantly reduces the durability of lithium-ion batteries. Knowledge of dissolution rates and oxidation states of manganese ions is essential for designing effective mitigation measures for this problem. We show that electron paramagnetic resonance (EPR) combined with atomic absorption spectroscopy (AAS) or inductively coupled plasma (ICP) can determine both manganese dissolution rates and relative Mn(3+) amounts, by comparing the correlation between EPR and AAS/ICP data for Mn(2+) standards with that for samples containing manganese cations dissolved from active materials (LiMn2O4 (LMO) and LiNi(0.5)Mn(1.5)O4 (LNMO)) into the same electrolyte solution. We show that Mn(3+), and not Mn(2+), is the dominant species dissolved from LMO, while Mn(2+) is predominant for LNMO. Although the dissolution rate of LMO varies significantly for the two investigated materials, due to particle morphology and the presence of Cr in one of them, the Mn speciation appears independent of such details. Thus, the relative abundance of dissolved manganese ions in various oxidation states depends mainly on the overall chemical identity of the active material (LMO vs LNMO). We demonstrate the relevance of our methodology for practical batteries with data for graphite-LMO cells after high-temperature cycling or stand at 4.2 V.

Kinetic study of the leaching of manganese mine tailings by organic reductant in sulphuric acid solution

A kinetic study of the leaching of manganese mining residue by sulphuric acid and potassium oxalate has been investigated. The effects of the agitation speed, manganese ore particle size, acid concentration, oxalate concentration and temperature on the manganese dissolution rate was determined. The leaching rate is significantly influenced by the reaction temperature, and both concentrations oxalate and acid. The observed effects of the relevant operating variables on the leaching rates are consistent with a kinetic model for chemical control. The apparent activation energy for the leaching of pyrolusite has been calculated using the Arrhenius expression and was found to be (63.7 ± 2.9) kJ mol−1. The experimental results indicate a reaction order of 1.07 for [H2SO4] concentration and 0.96 for [K2C2O4]. It is concluded that the reductive leaching of pyrolusite with potassium oxalate in acid medium is controlled by chemical reaction. The rate expression associated with the dissolution rate of pyrolusite depending on the parameters chosen may be summarised as follows:

Dissolution Based Analysis of Capacity Fade in Manganese Oxide Spinel Cathode

Due to higher gravimetric and volumetric energy density than other battery technologies, Lithium-ion batteries (LIBs) have assumed an important role as portable energy systems to power electronic devices such as mobiles and laptops. However, implementation of LIBs to power automotive vehicles are limited due to their high cost, low cycle life and capacity loss at high discharge rates. For successful commercialization of electric- (EVs) and hybrid-electric (HEVs) vehicles, battery technology in terms of novel electrode materials, electrolytes and fabrication techniques needs to be further developed so that it is able to deliver better discharge capacity with improved capacity retention and cycle life. LiMn2O4 (LMO) has been used as a promising cathode material in battery systems to power EVs and HEVs due to its abundance, low cost, environmentally benign nature, minimum safety and thermal runaway issues1-3. Along with these exceptional advantages, LMO suffers from poor rate capability and cycling stability due to the imperative manganese (Mn2+) dissolution through disproportionation reaction (2Mn3+=Mn2++Mn4+), structural changes and electrolyte decomposition which act as hindrance to high power applications4-5. Research has been directed towards elucidating novel avenues to improve the cycling performance of LMO cathode for better capacity retention through investigating its electrochemical performance experimentally as well numerically3-7. However, a comprehensive numerical analysis that imitates experimental measurements towards an improved understanding of LMO degradation is missing in the literature. Consequently, galvanostatic charge/discharge, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic intermittent titration technique (GITT) and potentiostatic intermittent titration technique (PITT) has been employed in this work to quantify the performance of LMO half-cell (against Li foil anode). This experimental data has been used as an input to the numerical model to explain the phenomenon of degradation caused by manganese dissolution. Figure 1 (a) shows the experimentally and numerically obtained capacity derived from cycling two 2016 LMO coin cells at 1C rate for the first 100 cycles. The experimental and simulated results are in good agreement which indicates that capacity decreases gradually as cycle number increases. This loss in capacity, which we regard as having been caused by Mn2+ dissolution in electrolyte, induces a reduction in volume fraction of solid matrix of LMO cathode. Figure 1 (b) shows the variation of cell potential with discharge capacity for the 1st and 100th cycles, which also indicates 16.5% loss in discharge capacity due to reduction in volume fraction of solid matrix. Through this study, the rate of dissolution and loss in cyclic lithium with cycling can be quantified, and could be applied to develop novel methods of synthesis of LMO for better cycling performance and capacity retention. References M. Rashid and A. Gupta, “Mathematical model for combined effect of SEI formation and gas evolution in li-ion batteries”, ECS Electrochem. Lett., 3, A95 (2014).M. Rashid, A. Gupta, “Effect of relaxation periods over cycling performance of a li-ion battery”, J. Electrochem. Soc., 162, A3145 (2015).H. Wang, F. Lai, Y. Li, X. Zhang, and Y. Huang, “Excellent stability of spinel LiMn2O4 based cathode materials for lithium-ion batteries”, Electrochim. Acta, 177, 290 (2015).L. Cai, Y. Dai, M. Nicholson, R. E. White, K. Jagannathan, and G. Bhatia, “Life modeling of a lithium ion cell with a spinel-based cathode”, J. Power Sources, 221, 191 (2012).J. Park, J. H. Seo, G. Plett, W. Lu and A. M. Sastry, “Numerical simulation of the effect of the dissolution of LiMn2O4 particles on li-ion battery performance”, Electrochem. Solid State Lett., 14, A14 (2011).C.-H. Lu and S.-W. Lin, “Dissolution kinetics of spinel lithium manganate and its relation to capacity fading in lithium ion batteries”, J. Mat. Res., 17, 1476 (2002).Z. Zhang, T. Zeng, Y. Lai, M. Jia, and J. Li, “A comparative study of different binders and their effects on electrochemical properties of LiMn2O4 cathode in lithium ion batteries”, J. Power Sources, 247, 1 (2014). Figure 1

Chemical Composition and Formation Reactions in the Cathode-Electrolyte Interface Layer of Lithium Manganese Oxide Batteries from Reactive Force Field (ReaxFF) Molecular Dynamics

Lithium ion batteries have great potential to revolutionize the transportation sector as energy storage media for electric mobility. Among the various lithium metal oxides that have been used, or proposed for use, as cathode active materials, lithium manganese oxide (LiMn2O4) is the primary cathode material presently exploited for automotive applications, on account of its low cost, low toxicity, and simple preparation process. There are, however, well-documented problems with LiMn2O4, the most critical of which is capacity fade due to active material loss. The dissolution of divalent manganese from the surface of the cathode into the electrolyte leads to a progressive decrease in the cathode material available for lithium intercalation. Deposition of dissolved manganese on the anode decreases the lithium content of the anode, further decreasing the overall cell capacity. Experimental observations indicate that the manganese content of the electrolyte increases as the cell ages, suggesting that cathode material loss is the primary reason for reduced cell life in a LiMn2O4 battery. A key to improving the retention of manganese used as cathode material is to understand the reactions that occur at the cathode surface. Although Mn2+ has been experimentally detected in the electrolyte of LiMn2O4 cells, its speciation and reaction mechanisms are not yet well understood. Manganese dissolution is more pronounced in the presence of fluorinated electrolyte salts such as LiPF6, linking fluorine in the electrolyte as a putative trigger for manganese dissolution. Tunneling electron microscopy imaging has shown the presence of a layer of electrolyte decomposition products at the cathode surface, but no experimental composition analysis has been possible due to the thinness and delicate structure of this layer. Fluorinated electrolyte additives such as fluoroethylene carbonate (FEC) are used in commercial cells to enable formation of a more stable anode-electrolyte interface layer, thereby improving battery performance. The impact of this new source of fluorine on manganese dissolution and battery life has not yet been explored. To bridge this knowledge gap, molecular modeling and density functional theory methods were applied to investigate the reactions occurring at the LiMn2O4 cathode surface, the effects of fluorinated electrolyte additives on the cathode-electrolyte interface layer, and the mechanisms of manganese dissolution. Specifically, a reactive force field (ReaxFF) was developed to conduct molecular dynamics (MD) simulations of these electrochemical cells. Reactive force fields can simulate the formation and dissociation of chemical bonds, and thereby help to disclose the dynamic surface reaction chemistry of the cathode. The reactive force field developed for manganese was used to investigate the formation of the cathodeelectrolyte interface layer in electrochemical cells with a LiMn2O4 cathode, ethylene carbonate / dimethyl carbonate electrolyte, LiPF6 salt, and 5% FEC additive. The MD simulations reveal that the electrolyte solvent molecules undergo oxidation by taking up oxygen atoms from the bulk cathode. The cathodeelectrolyte interface layer was found to contain aldehydes, polycarbonates and organic radicals. The oxidation reaction pathways for all the electrolyte solvent molecules reveal the formation of surface hydroxyl species. The removal of oxygen from the cathode lattice exposes manganese atoms to the bulk electrolyte and the hydroxyl molecules are very likely to result in acid formation on the cathode surface, these two processes together result in manganese dissolution from the cathode into the electrolyte. The chemical composition of the cathode surface interface layer with and without the electrolyte additive FEC, and the role of FEC in Mn dissolution were investigated. Simulation results generated by ReaxFF-based MD were found to be in agreement with the experimentally identified cathode-electrolyte interface compounds. Based on the Reax-FF MD simulations, the catalytic properties of manganese oxides lead to oxidative decomposition of electrolyte solvents resulting in consumption of cathode oxygen and dissolution of manganese atoms. Figure 1

Synergetic effects of LiFe0.3Mn0.7PO4–LiMn1.9Al0.1O4 blend electrodes

Composite cathodes are prepared by blending the olivine LiFe0.3Mn0.7PO4 (LFMP) and spinel LiMn1.9Al0.1O4 (LMO) in order to combine the high capacity of LFMP with the rate capability of the spinel. While tap density, capacity and energy density show a linear dependency on the blend ratio, a remarkable synergetic effect between LFMP and LMO improving the electrochemical performance at higher C-rates is demonstrated. Potential curves of blend electrodes at rates of 3C reveal a less pronounced polarization for the Mn2+/3+ plateau than expected from theoretical calculations. This buffer effect is also observed for high current pulses (5C) where blend electrodes resemble the behavior of pure spinel electrodes. In terms of power density at high states of charge (SoC), the performance of the Blend(50LFMP/50LMO cap%) exceeds even that of pure spinel. In addition, the spinel-related manganese dissolution can be drastically reduced by blending spinel with LFMP. This study shows the expected and synergetic effects of LFMP/spinel blends and compares the results with theoretical calculations.

ChemInform Abstract: Research Progress on Design Strategies, Synthesis and Performance of LiMn2O4‐Based Cathodes

AbstractReview: 166 refs.

Constructing durable carbon layer on LiMn0.8Fe0.2PO4 with superior long-term cycling performance for lithium-ion battery

LiMn0.8Fe0.2PO4 is becoming one of the most promising cathode materials for lithium ion batteries. However, the capacity suffers from a loss during long-term cycling, which is directly associated with Mn dissolution due to the disproportionation reaction of Mn3+. Here, we report a chemical vapor deposition (CVD) approach to modify LiMn0.8Fe0.2PO4 particles with carbon so as to minimize Mn dissolution from cathode. The deposited carbon layer not only protects LiMn0.8Fe0.2PO4 cathode from electrolyte corrosion, but also enhances the electronic/ionic conductivity owing to its higher graphitize degree. As a consequence, the electrochemical performances have a significant improvement. The capacity retention achieves 96% after 450 cycles at 1C at room temperature (25°C). Even at elevated temperature (55°C), the capacity retention also reaches at 97 % after 50 cycles at 1C rate, which is much higher than that of untreated sample (89%). Hence, the cathode material based on LiMn0.8Fe0.2PO4 encapsulated with durable carbon by CVD method represents a promising strategy for developing its long-term cycling performance through suppressing Manganese dissolution.

Electronic and Bonding Properties of LiMn2O4 Spinel with Different Surface Orientations and Doping Elements and Their Effects on Manganese Dissolution

This paper investigates the effects of surface orientation and doping on the dissolution of Mn ions from LiMn2O4 structures using first principles calculations. Our aim is to understand why certain surface orientations and element dopings produce structures with lower Mn dissolution. By comparing the electronic properties and structures of systems with different surfaces and dopings, Mn dissolution mechanisms and their prevention can be better understood. Based on our calculations, Mn dissolution is strongly correlated with the electronic and bonding properties of the Mn-O bonds. Surface orientations with a larger number of Mn-O bonds and smaller bond length require more energy to break the Mn-O bonds. In addition, doping with certain elements changes the bonding state of Mn, which either prevents or aggravates Mn dissolution.

Phase Stability of Lithium Manganese Oxide Stored at High Temperatures

Capacity degradation of the LiMn2O4 cathode during high-temperature storage was investigated for various lithium contents. The capacity recovery rate was determined after the storage test, and the phases and valence state of manganese ions were investigated by X-ray diffraction and X-ray absorption fine structure. The storage characteristics depend on the state of charge (SOC); a significantly low recovery rate was found for the shallow SOC region of LiMn2O4. The phase changes determined after the deterioration were as follows. (i) The lattice parameters decrease with an increase in manganese valence, caused by the formation of defects at the 16d site due to manganese dissolution. (ii) A new phase forms as a second phase. This phase has higher manganese valence and a larger amount of manganese vacancies. The same type of phase was produced by a high-temperature treatment of the shallow SOC phase at 150°C, which indicates that the phase was stable at high temperatures. (iii) A lower manganese valence state was observed at the spinel surface, which is related to manganese dissolution. Deterioration in the shallow SOC region during high-temperature storage is related to the phase stability of the de-intercalated spinel phases.

The mobility of phosphorus, iron, and manganese through the sediment–water continuum of a shallow eutrophic freshwater lake under stratified and mixed water-column conditions

The management of external nutrient inputs to eutrophic systems can be confounded due to a persistent pool of phosphorus (P) in lake sediments. The behaviors of P and trace metals depend largely on the reductive dissolution of amorphous iron (Fe) and manganese (Mn) (oxy)hydroxides in sediments; however, a holistic understanding of these dynamics in relation to the broader ecological and hydrodynamic conditions of the system remains elusive. We used a high-frequency monitoring approach to develop a comprehensive conceptual model of P, Mn, and Fe dynamics across the sediment water continuum of a shallow bay in Lake Champlain (Missisquoi Bay, USA). The greatest release of sediment P, Mn, and Fe occurred under stable hydrodynamic conditions, particularly during the onset of the cyanobacterial bloom and was associated with low available P and the accumulation of soluble Mn and Fe above the sediment–water interface (SWI). During the warmest part of the season, bloom severity and sediment P release was partially regulated by hydrodynamic drivers, which changed on hourly time scales to affect redox conditions at the SWI and bottom water concentrations of soluble P, Mn, and Fe. A geochemically distinct increase in soluble P and Fe concentrations, but not Mn, marked the influence of riverine inputs during a late season storm disturbance. Despite continued depletion of the reactive sediment P and metals pool into the bloom period, declining temperatures and a well-mixed water column resulted in bloom senescence and the return of P, Mn, and Fe to surface sediments. The closed cycling of P and metals in Missisquoi Bay poses a significant challenge for the long-term removal of P from this system. Multiple time-scale measures of physical and biogeochemical changes provide a basis for understanding P and trace metals behavior across sediments and the water column, which shape seasonally variable cyanobacterial blooms in shallow eutrophic systems.

Reductive leaching of low-grade manganese ore with pre-processed cornstalk

Cornstalk is usually directly used as a reductant in reductive leaching manganese. However, low utilization of cornstalk makes low manganese dissolution ratio. In the research, pretreatment for cornstalk was proposed to improve manganese dissolution ratio. Cornstalk was preprocessed by a heated sulfuric acid solution (1.2 M of sulfuric acid concentration) for 10 min at 80°C. Thereafter, both the pretreated solution and the residue were used as a reductant for manganese leaching. This method not only exhibited superior activity for hydrolyzing cornstalk but also enhanced manganese dissolution. These effects were attributed to an increase in the amount of reductive sugars resulting from lignin hydrolysis. Through acid pretreatment for cornstalk, the manganese dissolution ratio was improved from 50.14% to 83.46%. The present work demonstrates for the first time the effective acid pretreatment of cornstalk to provide a cost-effective reductant for manganese leaching.

Fabrication of densely packed LiNi0.5Mn1.5O4 cathode material with excellent long-term cycleability for high-voltage lithium ion batteries

Densely packed submicron polyhedral LiNi0.5Mn1.5O4 material with disordered Fd3¯m structure was synthesized via a modified sol–gel method. The as-synthesized material has a high tap density of 2.15 g cm−3, guaranteeing a high volumetric energy density for high power batteries. Electrochemical properties were investigated in both a LiNi0.5Mn1.5O4/Li half-cell and a LiNi0.5Mn1.5O4/graphite full-cell. The LiNi0.5Mn1.5O4/Li half-cell exhibits a superior cycle stability and rate capability. Here the LiNi0.5Mn1.5O4 material can deliver capacity retentions of 86% at 25 °C and 75% at 55 °C within 1000 cycles for a charge–discharge rate of 1 C. At a much higher rate of 10 C, a discharge capacity of 95 mAh g−1 can be still obtained. The LiNi0.5Mn1.5O4/graphite full-cell delivers a stable discharge capacity of 130.2 mAh g−1 at 0.2 C, corresponding to a discharge energy density as high as 576.2 Wh kg−1. After 100 cycles, the full cell can maintain a working voltage of 4.55 V and capacity retention of 84.6%. The excellent cycle stability is attributed to the dense structure, large particle size, low specific surface area and less exposed (110) facets, which dramatically reduce irreversible surface chemical reactions and manganese dissolution.

Cycling stability and degradation mechanism of LiMnPO4 based electrodes

Long term stability of LiMnPO4 particles with a crystallite size between ∼20 and 50 nm covered with a dense native carbon coating (14 wt.%) is demonstrated. More than 500 cycles at a rate of C/20, in the potential window of 2.7–4.5 V and a temperature of 55 °C were achieved. During most of the cycling the average capacity decay was less than 0.06% per cycle. After about 500 cycles a sudden capacity drop was observed. Degradation processes in various stages of cycling were thoroughly examined using a range of techniques. Severe surface film formation, manganese dissolution and degradation of LixMnPO4 accompanied by formation of Li4P2O7 were clearly identified. The good long term stability seems to be due to dense, protective carbon coating. Decomposition is most likely initiated at local defects in the microstructure of pyrolytic carbon coating around LiMnPO4 particles. In addition to known degradation mechanisms of LiMnPO4 we observed pronounced gradual amorphization of the olivine crystallites during long-term cycling at 55 °C. Finally, changes in morphology of the carbon black additive after prolonged cycling are reported and commented.

Leaching of base metals from spent Ni–metal hydride batteries with emphasis on kinetics and characterization

Nickel–metal hydride (Ni–MH) batteries which generally contain nearly 55–60% Ni and 4–6% Co along with a few other metals may be considered an important resource for recycling and supply of these metals. In this study, leaching kinetics of nickel and cobalt, and other base metals from the spent Ni–MH batteries in sulfuric acid solutions have been investigated with an emphasis on the process characterization at different stages of the treatment. The maximum dissolution of nickel, cobalt, iron, manganese and zinc was found to be 91.6, 97.8, 65.5, 93.5 and 99.2%, respectively in a single stage under the optimum conditions comprising of 2M H2SO4, 100g/L pulp density and 348K temperature after 120min of leaching. Kinetic data for the dissolution of all the metals including the rare earths (as a group) showed the best fit to the chemical control shrinking core model. The activation energy of 8.7, 6.8, 7.12, 6.7 and 7.9kJ/mol was determined for the leaching of base metals viz., nickel, cobalt, iron, manganese and zinc, respectively in the temperature range 305–348K. With the help of the XRD phase analysis and the change in morphological features along with the elemental mapping in the leach residues with time and the untreated electrode material by SEM-EDS, the leaching mechanism was established. The process characterization corroborated the kinetic model for the leaching of metals which progressed through the chemical reaction of the lixiviant on the surface of the spherical particles of electrode powder. The XRD analysis of the residue showed the presence of metallic nickel which required stringent conditions for improved recovery of this metal.

Li+ adsorption/desorption properties of lithium ion-sieves in aqueous solution and recovery of lithium from borogypsum

This study presents the recovery of lithium from borogypsum by lithium ion-sieves known as selective adsorbents. In the study two types of ion-sieves were used. One was λ-MnO2 which was obtained by the treatment of LiMn2O4 with acid and the other was prepared via the acid treatment of LiNi0.5Mn1.5O4 which occurred by the substitution some of manganese with nickel. Besides the lithium adsorption and desorption capacities, manganese and nickel dissolution ratios from the spinel powders were also studied. Optimum adsorption and desorption conditions were determined in the LiOH and HCl solutions. XRD and SEM analyses showed that substitution of manganese with nickel and treatment of spinel powders with acid did not destroy the spinel structure and morphology. Because of the cell-contraction, nickel-substituted spinel did not show any satisfying Li+ extraction and adsorption properties.

High Cycling Stability and Extreme Rate Performance in Nanoscaled LiMn2O4 Thin Films.

Ultrathin LiMn2O4 electrode layers with average crystal size of ∼15 nm were fabricated by means of radio frequency sputtering. Cycling behavior and rate performance was evaluated by galvanostatic charge and discharge measurements. The thinnest films show the highest volumetric capacity and best cycling stability, retaining the initial capacity over 70 (dis)charging cycles when manganese dissolution is prevented. The increased stability for film thicknesses below 50 nm allows cycling in both the 4 and 3 V potential regions, resulting in a high volumetric capacity of 1.2 Ah/cm3. It is shown that the thinnest films can be charged to 75% of their full capacity within 18 s (200 C), the best rate performance reported for LiMn2O4. This is explained by the short diffusion lengths inherent to thin films and the absence of phase transformation.

Manganese dissolution from LiMn2O4 cathodes at elevated temperature: methylene methanedisulfonate as electrolyte additive

Diethyl carbonate (DEC) electrolyte decomposition reactions resulting from PF5 attacked produce HF by several side reaction steps. The resulting HF can dissolve the Mn from spinel-type lithium manganese oxide (LiMn2O4). To verify that methylene methanedisulfonate (MMDS) suppress Mn3+ dissolution mechanism of lithium manganese oxide spinel cathode using methylene methanedisulfonate as electrolyte additive at elevated temperature, a DEC-based electrolyte using MMDS as electrolyte additive is developed in this work. The linear sweep voltammetry (LSV) indicates the start oxidation potential of the electrolyte with 0.5 wt% MMDS is around 3.83 V (vs. Li/Li+), which is lower than the control (4.12 V). Self-discharge and inductively coupled plasma-atomic emission spectrometry (ICP-AES) reveal that Mn3+ dissolution from the spinel cathode is hindered. The results of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) demonstrate that MMDS would help to form the stable passivation film, which would effectively suppress to oxidize the control electrolyte solvents and HF generation is suppressed, and result in less Mn3+ dissolution from the spinel cathode.

A hybrid process of biofiltration of secondary effluent followed by ozonation and short soil aquifer treatment for water reuse

The Shafdan reclamation project facility (Tel Aviv, Israel) practices soil aquifer treatment (SAT) of secondary effluent with hydraulic retention times (HRTs) of a few months to a year for unrestricted agricultural irrigation. During the SAT, the high oxygen demand (>40 mg L−1) of the infiltrated effluent causes anoxic conditions and mobilization of dissolved manganese from the soil. An additional emerging problem is the occurrence of persistent trace organic compounds (TrOCs) in reclaimed water that should be removed prior to reuse. An innovative hybrid process based on biofiltration, ozonation and short SAT with ∼22 d HRT is proposed for treatment of the Shafdan secondary effluent to overcome limitations of the existing system and to reduce the SAT's physical footprint. Besides efficient removal of particulate matter to minimize clogging, coagulation/flocculation and filtration (5–6 m h−1) operated with the addition of hydrogen peroxide as an oxygen source efficiently removed dissolved organic carbon (DOC, to 17–22%), ammonium and nitrite. This resulted in reduced effluent oxygen demand during infiltration and oxidant (ozone) demand during ozonation by 23 mg L−1 and 1.5 mg L−1, respectively. Ozonation (1.0–1.2 mg O3 mg DOC−1) efficiently reduced concentrations of persistent TrOCs and supplied sufficient dissolved oxygen (>30 mg L−1) for fully oxic operation of the short SAT with negligible Mn2+ mobilization (<50 μg L−1). Overall, the examined hybrid process provided DOC reduction of 88% to a value of 1.2 mg L−1, similar to conventional SAT, while improving the removal of TrOCs and efficiently preventing manganese dissolution.

In Situ Study of the Gassing Behavior in LiNi0.5Mn1.5O4 Based Full-Cells By Dems and Neutron Imaging

Lithium ion batteries are generally considered to be the technology of choice for hybrid electric and full electric vehicles. However, further enhancement in the energy and power densities of lithium ion batteries is necessary to fulfill the requirements imposed by automotive applications [1, 2]. High voltage LiNi0.5Mn1.5O4 spinel (LNMO) appears to be a very promising cathode-active material in combination with state-of-the-art graphite anodes. This is due, in part, to its low cost, high theoretical specific capacity (147 mAh g–1) and high nominal operating voltage (4.7 V vs. Li/Li+). However, there are severe performance limitations that need to be overcome before commercialization can be contemplated. LNMO/Li half-cells typically show high cycling stability, even at elevated temperatures [3]. Full-cells made of LNMO cathode and graphite anode suffer from capacity fading upon cycling. In recent years, several degradation mechanisms have been identified and correlated with the overall performance. Major issues arise from electrolyte decomposition [4, 5] accompanied by formation of gaseous species [6] and manganese dissolution [7]. In this study, we focus on the in situ gas analysis of LNMO based full-cells during charge and discharge. Two different cell systems, LNMO/graphite and LNMO/LiFePO4, are investigated. In the LNMO/graphite system both electrodes contribute to the gassing processes. By using delithiated LiFePO4 as anode, gas evolution on LNMO can be studied separately, because no gaseous byproducts are formed on LiFePO4. The evolving gases were studied using an analysis setup allowing for in situ investigation by means of mass spectrometry (DEMS: differential electrochemical mass spectrometry). A visualization of forming gas bubbles and a quantitative estimation of the formed gas volume in the cell was achieved by in operando neutron imaging. Mechanistic insights into the decomposition processes were gained by correlating the cell potential to the pattern of the evolving gases. The influence of other electrochemical parameters, like constant voltage steps, charge/discharge current rate and formation processes (i.e., pre-aging of the electrodes at different temperatures), on the gassing behavior and gas composition was also investigated. These effects and their impact on the cycling stability are discussed.