Dissolved Metal Ions Research Articles

Boosting the Electrochemical Performance of Li1.2Mn0.54Ni0.13Co0.13O2 by Atomic Layer-Deposited CeO2 Coating

It has been demonstrated that atomic layer deposition (ALD) provides an initially safeguarding, uniform ultrathin film of controllable thickness for lithium-ion battery electrodes. In this work, CeO2 thin films were deposited to modify the surface of lithium-rich Li1.2Mn0.54Ni0.13Co0.13O2 (LRNMC) particles via ALD. The film thicknesses were measured by transmission electron microscopy. For electrochemical performance, ∼2.5 nm CeO2 film, deposited by 50 ALD cycles (50Ce), was found to have the optimal thickness. At a 1 C rate and 55 °C in a voltage range of 2.0−4.8 V, an initial capacity of 199 mAh/g was achieved, which was 8% higher than that of the uncoated (UC) LRNMC particles. Also, 60.2% of the initial capacity was retained after 400 cycles of charge–discharge, compared to 22% capacity retention of UC after only 180 cycles of charge–discharge. A robust kinetic of electrochemical reaction was found on the CeO2-coated samples at 55 °C through electrochemical impedance spectroscopy. The conductivity of 50Ce was observed to be around 3 times higher than that of UC at 60–140 °C. The function of the CeO2 thin-film coating was interpreted as being to increase substrate conductivity and to block the dissolution of metal ions during the charge–discharge process.

Differential Contribution of Constituent Metal Ions to the Cytotoxic Effects of Fast-Dissolving Metal-Oxide Nanoparticles.

The main mechanism of toxicity for fast-dissolving nanoparticles (NPs) is relatively simple as it originates from the intrinsic toxicity of their constituent elements rather than complicated surface reactivity. However, there is little information about the compared toxicity of fast-dissolving NP and its constituent ion, which is essential for understanding the mechanism of NP toxicity and the development of a structure-toxicity relationship (STR) model. Herein, we selected three types of fast-dissolving metal-oxide NPs (CoO, CuO, and ZnO) and constituent metal chlorides (CoCl2, CuCl2, and ZnCl2) to compare dose-response curves between NP and its constituent metal. These materials were treated relevant cell lines for inhalation setting (i.e., differentiated THP-1 cells for macrophages and A549 cells for alveolar epithelial cells) and cytotoxicity as an endpoint was evaluated at 24 h post-incubation. The results showed that CoO and CuO NPs in both cell types showed similar patterns of dose-response curves and cytotoxic potential compared to that of their respective metal chloride. On the other hand, ZnO NPs in both cell types showed a completely different dose-response curve compared to that of ZnCl2: ZnO NPs showed modest slope and much less potential for cytotoxicity compared to that of ZnCl2. These results imply that fast-dissolving metal-oxide NPs are not always have similar dose-response curves and toxic potentials compared to their constituent metal chlorides and this may be due to the differential mechanism of intracellular uptake of these substances and their interaction with intracellular detoxification molecules. Further investigations are needed for the use of toxic potential of metal ions as a predicting factors of fast-dissolving NPs toxicity. In addition, chelating agent specific for dissolved metal ions can be applied for the treatment of these fast-dissolving NPs.

Utilization of chemical stability diagrams for improved understanding of electrochemical systems: evolution of solution chemistry towards equilibrium

Predicting the stability of chemical compounds as a function of solution chemistry is crucial towards understanding the electrochemical characteristics of materials in real-world applications. There are several commonly considered factors that affect the stability of a chemical compound, such as metal ion concentration, mixtures of ion concentrations, pH, buffering agents, complexation agents, and temperature. Chemical stability diagrams graphically describe the relative stabilities of chemical compounds, ions, and complexes of a single element as a function of bulk solution chemistry (pH and metal ion concentration) and also describe how solution chemistry changes upon the thermodynamically driven dissolution of a species into solution as the system progresses towards equilibrium. Herein, we set forth a framework for constructing chemical stability diagrams, as well as their application to Mg-based and Mg–Zn-based protective coatings and lightweight Mg–Li alloys. These systems are analyzed to demonstrate the effects of solution chemistry, alloy composition, and environmental conditions on the stability of chemical compounds pertinent to chemical protection. New expressions and procedures are developed for predicting the final thermodynamic equilibrium between dissolved metal ions, protons, hydroxyl ions and their oxides/hydroxides for metal-based aqueous systems, including those involving more than one element. The effect of initial solution chemistry, buffering agents, complexation agents, and binary alloy composition on the final equilibrium state of a dissolving system are described by mathematical expressions developed here. This work establishes a foundation for developing and using chemical stability diagrams for experimental design, data interpretation, and material development in corroding systems.

Dissolution, migration, and deposition of transition metal ions in Li-ion batteries exemplified by Mn-based cathodes – a critical review

This paper reviews the research activities on the mechanistic understanding and solutions to overcome the TM DMD process, from the earliest discoveries to the latest progress.

Editors' Choice—The Effectiveness of Multifunctional Li-Ion Battery Separators past Their Saturation with Transition Metal Ions

Li-ion batteries (LIBs) for electric vehicles necessitate a 10-year useful life. The dissolution of manganese and other transition metal ions from positive electrodes, and the loss of Li+ ions are two main causes for reduced LIB durability. Multifunctional separators (MFSs) designed to mitigate these degradation modes enable improvements in the electrochemical performance of LIBs at both room and above-ambient temperatures. We report herein on the benefits for the cycle life and rate performance of LixMn2O4||graphite cells by composite MFSs that incorporate a crosslinked styrene-divinylbenzene copolymer functionalized with disodium iminodiacetate groups. Our study shows that: (1) forming effective passivating electrode surface films early in LIB life is essential for good performance and long life; (2) saturation of MFSs with manganese ions does not subsequently lead to an increased capacity loss rate during high-temperature (55°C) cycling; (3) MFSs also improve rate performance. These benefits originate from a diminished crossover of dissolved Mn ions to the negative electrode, reduced losses of electroactive Li+ ions, and smaller interfacial resistances at both positive and negative electrodes.

Communication—Lithium Difluorophosphate as an Electrolyte Additive to Improve the High Voltage Performance of LiNi0.5Co0.2Mn0.3O2/Graphite Cell

Lithium difluorophosphate (LiDFP) is used as an electrolyte additive to improve the electrochemical performances of LiNi0.5Co0.2Mn0.3O2 (NCM523)/graphite cells operating at a high charging cutoff voltage. LiDFP additive generates a more uniform, extremely stable, and lower resistance passivation film on the cathode surface. This passivation film not only suppresses the subsequent decomposition of electrolyte, but also prevents the dissolution of transition metal ions from NCM523 particles, resulting in improved cyclic stability and discharge capability of NCM523/graphite cells. With electrolyte contained 1.0 wt% LiDFP, the 18650 batteries achieves a capacity retention of 88.2% after 300 cycles at 3.0∼4.4 V and 90.0% after 200 cycles at 3.0∼4.45 V, comparing to 77.9% and 66.3% of the batteries without additive.

Multi-omics approaches confirm metal ions mediate the main toxicological pathways of metal-bearing nanoparticles in lung epithelial A549 cells

Our analyses confirm that the dissolution of metal ions mediates the main toxicological pathways of silver and zinc oxide nanoparticles.

Leaching behavior and ecotoxicological effects of different game shot materials in freshwater

Lead-based game shot used in hunting near waters is considered a main reason for lead-poisoning of waterfowl and aquatic organisms, prompting discussion about alternatives. This study provides a first comparison of the leaching behavior and resulting ecotoxicological impacts of shot exposed to freshwater, comprising lead-based and alternative shots containing bismuth, copper, steel, tungsten, and zinc. Ecotoxicological effect assessment was based on the acuteDaphnia magna48 h toxicity test according to the EN ISO 6341:2012 guideline. Strong leaching of copper (up to 4.22 μmol/L) and zinc (up to 41.12 μmol/L) from three types of alternative game shot caused significantly increased immobilization rates of up to 100%. In contrast, even the highest leaching of lead did not significantly impairDaphniamobility. Highest concentrations of dissolved metal ions only matched the declared main components of the respective shots in 3 out of 9 cases. These results demonstrate that metal release from alternative game shot is an underestimated ecotoxicological risk, particularly since release of copper and zinc from alternative shots was demonstrated to be more hazardous for aquatic biota than conventional lead shot. There is an urgent need of managing the use of shot ammunition near waterbodies based on realistic ecotoxicological risk assessments.

Dissolution of chromite in oxidizing media and sorption of dissolved metal ion onto in situ formed manganese dioxide

Many of the water coolant nuclear reactors are following the zinc ion water chemistry route to mitigate the radioactivity build up in out of core area due to 60Co. Decontamination of these systems with chromium oxide as a passive layer require redox multi cycle process, and permanganate based formulation is used in this regard. The present article highlights the chemical dissolution behaviour of chromites and also sorption behaviour of released metal ion during the permanganate medium treatment. Chromites, MFe x Cr2−x O4 (M = Co, Ni and Zn, x = 0.0, 0.2 and 0.4) were synthesised by combustion process and characterised by XRD and laser Raman spectroscopy and were used for dissolution studies. Cobalt and nickel chromite showed a lower dissolution rate and higher sorption of cobalt on the MnO2 compared to zinc chromite in HMnO4.

Aluminum Oxide Nanoparticles for Highly Efficient Asphaltene Separation from Crude Oil Using Ceramic Membrane Technology

The effects of aluminum oxide nanoparticles on the removal of asphaltenes from an Iranian crude oil (Soroush) using a ceramic membrane with pore size of 0.2 µm were investigated. In order to achieve superior asphaltene separation by ultrafiltration, it is essential to make some changes for destabilizing asphaltene in crude oil. The asphaltene destabilization was done using crude oil contact with an acid containing dissolved metal ions. Metal oxide nanoparticles adsorbed asphaltene molecules and increased their molecular size. The nanoparticle of aluminum oxide was applied to alter precipitation and peptization properties of asphaltenes. Dynamic Light Scattering (DLS) was used to measurement of the asphaltene molecular size dissolved in toluene. Raman spectroscopy and the Tuinstra equation were used to determine the aromatic sheet diameter (La ) via the integrated intensities of the G and D1 modes. This revealed that the asphaltene particles react with nano aluminum oxide and the average molecular size of asphaltene was raised from 512.754 to 2949.557 nm and La from 5.482 to 13.787. The obtained results showed that using nano aluminum oxides, asphaltene separation increased from 60–85 wt% to 90–97 wt% based on the asphaltene content of crude oil.

Artificially-built solid electrolyte interphase via surface-bonded vinylene carbonate derivative on graphite by molecular layer deposition

Vinylene carbonate (VC) is attached in a ring-opened form on a graphite surface by molecular layer deposition (MLD) method, and its role as a solid electrolyte interphase (SEI) former is studied. When VC is added into the electrolyte solution of a graphite/LiNi0.5Mn1.5O4 (LNMO) full-cell, it is reductively decomposed to form an effective SEI on the graphite electrode. However, VC in the electrolyte solution has serious adverse effects due to its poor stability against electrochemical oxidation on the LNMO positive electrode. A excessive acid generation as a result of VC oxidation is observed, causing metal dissolution from the LNMO electrode. The dissolved metal ions are plated on the graphite electrode to destroy the SEI layer, eventually causing serious capacity fading and poor Coulombic efficiency. The VC derivative on the graphite surface also forms an effective SEI layer on the graphite negative electrode via reductive decomposition. The detrimental effects on the LNMO positive electrode, however, can be avoided because the bonded VC derivative on the graphite surface cannot move to the LNMO electrode. Consequently, the graphite/LNMO full-cell fabricated with the VC-attached graphite outperforms the cells without VC or with VC in the electrolyte, in terms of Coulombic efficiency and capacity retention.

Palladium bionanoparticles production from acidic Pd(II) solutions and spent catalyst leachate using acidophilic Fe(III)-reducing bacteria.

The acidophilic, Fe(III)-reducing heterotrophic bacteria Acidocella aromatica PFBCT and Acidiphilium cryptum SJH were utilized to produce palladium (Pd) bionanoparticles via a simple 1-step microbiological reaction. Monosaccharide (or intracellular NADH)-dependent reactions lead to visualization of intra/extra-cellular enzymatic Pd(0) nucleation. Formic acid-dependent reactions proceeded via the first slow Pd(0) nucleation phase and the following autocatalytic Pd(II) reduction phase regardless of the presence or viability of the cells. However, use of active cells (with full enzymatic and membrane protein activities) at low formic acid concentration (5mM) was critical to allow sufficient time for Pd(II) biosorption and the following enzymatic Pd(0) nucleation, which consequently enabled production of fine, dense and well-dispersed Pd(0) bionanoparticles. Differences of the resultant Pd(0) nanoparticles in size, density and localization between the two bacteria under each condition tested suggested different activity and location of enzymes and membrane "Pd(II) trafficking" proteins responsible for Pd(0) nucleation. Despite the inhibitory effect of leaching lixiviant and dissolved metal ions, Pd(0) bionanoparticles were effectively formed by active Ac. aromatica cells from both acidic synthetic Pd(II) solutions and from the actual spent catalyst leachates at equivalent 18-19nm median size with comparable catalytic activity.

Removal of toxic heavy metal ions from aqueous solutions using jute fibers grafted with acrylic acid by gamma irradiation

Jute fibers were grafted with acrylic acid by using the direct gamma irradiation technique, which used as an adsorbent substrate for the toxic heavy metal ions such as Hg2+ and Pb2+ from their aqueous solutions. The structure and crystallinity of the grafted jute fibers were characterized by using Fourier‐transform infrared spectroscopy and X‐ray diffraction, respectively. The effect of pH range of the metal ion solutions, contact time, and the adsorption kinetics of the adsorption process were investigated. The effect of the initial concentration of dissolved metal ions and the adsorption isotherm for both Langmuir and Freundlich adsorption models were also investigated. From the results, it can be concluded that the adsorption process obeys the second‐order kinetic reaction and follows the Langmuir adsorption isotherm model, while, about 86 and 80% of Pb2+ and Hg2+, respectively, were adsorbed at pH 5 and 6 after a contact time of 60 min. J. VINYL ADDIT. TECHNOL., 24:339–346, 2018. © 2017 Society of Plastics Engineers

(Invited) Electrode Crosstalk during Lithium-Ion Battery Aging

Lithium-ion cells containing layered-oxide based positive electrodes and graphite-based negative electrodes are being cycled at high voltages (> 4.30 V) to increase energy density. In this presentation we will detail performance changes in these cells during cycling, with a particular focus on the crosstalk between electrodes. We show that the dissolution of transition metal (TM) ions from the positive electrode, and their migration and incorporation into the solid electrolyte interphase (SEI) of the negative electrode, accelerates markedly as the upper cutoff voltage (UCV) exceeds 4.30 V. At voltages ≥ 4.40 V there is enhanced fracture of the oxide during cycling that creates new surfaces and causes increased solvent oxidation and TM dissolution. Despite this deterioration, cell capacity fade still mainly results from lithium loss in the negative electrode SEI. Among TMs, Mn content in the SEI shows a better correlation with cell capacity loss than Co and Ni contents. We estimate that each Mn ion deposited in the SEI causes trapping of ~100 additional Li+ ions thereby hastening the depletion of cyclable lithium ions. During the presentation we will highlight an electrocatalysis mechanism through which the deposited Mn ions accelerate electrolyte reduction and increase Li trapping in the negative electrode SEI. Methods to mitigate this cross-talk, through the use of coatings and additives, will also be discussed.

Effect of Nitrate Ions on Repassivation Behavior of Crevice Corrosion on Type 316L Stainless Steel

Once crevice corrosion is initiated on stainless steels in chloride environments, the hydrolysis of dissolved metal ions causes severe acidification inside the crevice, and Cl- ions migrate into the crevice from the bulk solution. This electromigration of Cl- ions promotes subsequent active dissolution inside the crevice. Therefore, neutralization of the pH inside the crevice is expected to be the predominant factor affecting the repassivation of crevice corrosion.To clarify the repassivation behavior of crevice corrosion, in situ observations were performed, and the quantitative relationship between current values and corrosion morphology was analyzed. In addition, to elucidate the effect of the solution composition on the repassivation behavior, an electrochemical flow cell was used. In this study, the effect of NO3 - ions on the repassivation behavior of Type 316L stainless steel was investigated. Type 316L stainless steel was used as specimens. The specimens were heat-treated at 1373 K for 3.6 ks and then water-quenched. A schematic illustration of the electrochemical flow cell is shown in Figure 1. An artificial crevice was formed between a glass plate and the specimen surface. The specimen was polarized at 0.25 V (vs. Ag/AgCl, 3.33 M KCl). Crevice corrosion tests were performed in a flowing 1 M NaCl solution at 298 K. In the case of the solution change experiment, the inlet solution was changed from 1 M NaCl to 1 M NaCl-1 M NaNO3. The solution was changed when the current exceeded 100 μA. The flow rate of the solution was 24 mL h-1 during the crevice corrosion tests. Since the volume of the cell was ca. 24 mL, it took about 1 h to change the solutions completely. During the crevice corrosion tests, the crevice corrosion behavior of the specimen surface inside the crevice was observed using an optical microscope, and the images were taken every 100 s. Figure 2a shows the time variations of the currents in the crevice corrosion test in 1 M NaCl, and Figure 2b shows the results of in situ observations of the specimen surface. From the beginning of the crevice corrosion test to ca. 250 s, the current decreased to ca. 4 μA with time. Around ca. 300 s, the current increased rapidly. This current increase was due to the initiation of crevice corrosion. At this time, two small dark spots were observed inside the crevice (Figure 2b1). These spots were the initiation sites of the crevice corrosion. As shown in Figures 2b1-b3, the crevice corrosion grew toward the crevice mouth. After that, the corroded areas proceeded along the crevice mouth (Figures 2b4-b7). Once the entire crevice mouth was corroded, the crevice corrosion propagated toward the inside of the crevice, and the current increased up to ca. 5 mA at ca. 10 ks. From the results shown in Figure 2, it was confirmed that the crevice corrosion was readily initiated in 1 M NaCl, and no spontaneous repassivation was generated in this solution. Figure 3a shows the time variations of the current in the solution change experiment from 1 M NaCl to 1 M NaCl-1 M NaNO3, and Figure 3b shows the results of in situ observations of the specimen surface. Around 300 s, the current increased rapidly due to the initiation of crevice corrosion. At 406 s, the current exceeded 100 μA, and the inlet solution was then changed to 1 M NaCl-1 M NaNO3. From 406 s to 3.75 ks the current increased to 2.9 mA. In this period, the corroded areas mainly grew along the crevice mouth as shown in Figures 3b2-b5. At 3.75 ks (Figure 3b6), the current started decreasing. Almost at the same time, the growth of the crevice corrosion along the crevice mouth was stopped. From this time, the crevice corrosion propagated toward the inside of the crevice. Afterwards, the current decreased to ca. 150 μA. After 26.1 ks, the current began decreasing again. As shown in Figure 3b8, no propagation of the corroded area was observed after 43.0 ks. This suggested that the surface of the corroded area was completely repassivated. This result indicated that NO3 - bring about the repassivation. Figure 1

(Invited) Mixed Conducting Layered Oxides for Energy Storage: Challenges and Their Mitigation

Lithium-ion batteries have aided the revolution in portable electronic devices, and they are now being intensively pursued for electric vehicles and grid storage. Cost, safety, cycle life, energy, power, and environmental impact are the major factors for adopting a specific battery chemistry for a specific application, and often tradeoffs among the factors are needed in the selection. Although the layered LiMO2 (M = Ni and Co) oxides with mixed lithium-ion and electronic conductivity were first demonstrated more than 30 years ago as a lithium-insertion host, they still remain to be the dominant candidate for lithium-ion technology due to several appealing features displayed by them. With an aim to increase the charge-storage capacity and energy density, layered oxides with a high Ni content (> 50%) are now at the forefront in the battery industry around the world. However, compositions with high Ni content are hampered by high surface reactivity with the organic liquid electrolyte and the consequent impedance rise and fast capacity fade during cycling. Furthermore, they also suffer from high surface reactivity with ambient air, forming lithium hydroxide and lithium carbonate on the particle surface and thereby hampering the electrode fabrication process. A firm fundamental understanding of the origin of the fast capacity fade with advanced characterization methodologies and design and development of nickel-rich cathode compositions with robustness in contact with the liquid electrolyte and ambient air are critically needed to make the technology practically move forward. Accordingly, this presentation will focus on the characterization of nickel-rich layered oxides with advanced surface techniques and development of less reactive compositions with robust surface structures. To develop a fundamental understanding of the degradation mechanisms, the nickel-rich layered oxide cathodes are investigated before and after long-term cycling in full cells with X-ray photoelectron spectroscopy (XPS), time-of-flight – secondary ion mass spectroscopy (TOF-SIMS), and high-resolution transmission electron microscopy. In-depth surface characterization as a function of sputtering time and cross-sectional analyses reveal that surface active mass dissolution caused by the acidic species in the electrolyte during cell operation and migration of dissolved metal ions from the cathode to the graphite anode cause impedance rise at the graphite anode, lithium dendrite growth, and capacity fade. Utilizing the in-depth understanding gained, stabilized full cells are designed and the degradation is being mitigated. Promise of cathode compositions with Ni contents as high as 94% and capacities as high as ~ 220 mAh/g with high power capability will be presented. The progress paves the way to design and develop high-power lithium-ion cells with high volumetric and gravimetric energy densities for portable, vehicle, and grid storage applications.

Enhanced electrochemical performance of Li-rich layered cathode materials via chemical activation of Li2MnO3 component and formation of spinel/carbon coating layer

Li-rich layered oxides are promising cathode materials for advanced Li-ion batteries because of their high specific capacity and operating potential. In this work, the Li-rich layered oxide Li1·2Mn0·54Ni0·13Co0·13O2 (LMNC), is modified via a carbonization-reduction process (yielding the corresponding reduced compound denoted LMNC-R). Compared to the pristine oxide, LMNC-R delivers significantly enhanced initial discharge capacity/columbic efficiency, remarkably improved rate performance with an accelerated Li+ diffusion rate, and significantly increased capacity/voltage retention. The specific energy density and energy retention after 100 cycles increase from 378.2 Wh kg−1 and 47.7% for LMNC to 572.0 Wh kg−1 and 71.3%, respectively, for LMNC-R. The enhancement in the electrochemical performance of LMNC-R can be attributed to the synchronous formation of the oxygen non-stoichiometric Li2MnO3-δ component and to the carbon/spinel double coating layer in the material that resulted from the post-treatment process. Thus, the carbonization-reduction modification process can be used to tailor the structural evolution procedure and to suppress the metal ion dissolution of the Li-rich layered oxide during cycling.

Acid activation of upper Eocene Ca-bentonite for soybean oil clarification

In central Tunisia, many upper Eocene outcrops supply smectitic claystone which are characterized by several analytical techniques (calcimetry, XRD, SediGraph, chemical analysis, surface area, etc.). Beidellite is the main mineral detected by the XRD method. Representative raw samples M1, taken from Henchir Souar (Zaghouan, Tunisia), were acid activated in order to improve their physicochemical properties. This study consists in optimizing the activation conditions with HCl 3N by varying the following parameters: time (2, 4, and 6h) and temperature (25, 50, 75, and 90°C). The characterization by XRD and chemical analysis was carried out on the samples (M1, activated for 2 and 6h at 75°C), showing a structural modification of the clay by reduction of intensity reflection 001 order of smectite and dissolution of metal ions (Al3+, Fe3+, and Mg2+) from clay structure. Optimum condition for soybean oil clarification is obtained using a variety of amount raw clays (0.5, 0.75, and 1%). Thus, the best clarification yield is given at 0.75% of clay, showing a capacity of about 55%. Various forms of activated materials were used with a 75% proportion to leach soybean oil. Results were compared with commercial bentonite (Tonsil) having surface area (378m2/g). The activated sample M1 during 4h at 75°C possesses a decolorizing capacity of about 85% greater than the oil treated by Tonsil in laboratory (58%).

Trimethylsilylcyclopentadiene as a novel electrolyte additive for high temperature application of lithium nickel manganese oxide cathode

Electrolyte additives are necessary for the application of high potential cathode in high energy density lithium ion batteries, especially at elevated temperature. However, the electrolyte additives that can effectively suppress the dissolution of transition metal ions from cathode have seldom been developed up to date. In this work, we propose a novel electrolyte additive, trimethylsilylcyclopentadiene (SE), for high temperature application of a representative high potential cathode, lithium nickel manganese oxide (LiNi0.5Mn1.5O4). It is found that the dissolution of Mn and Ni from LiNi0.5Mn1.5O4 can be effectively suppressed by applying SE. With applying 0.25% SE, the dissolved amount of Mn and Ni is decreased by 97.4% and 98%, respectively, after 100 cycles at 55 °C. Correspondingly, the cyclic performance of LiNi0.5Mn1.5O4 is significantly improved. Physical characterizations and electrochemical measurements show that SE can be preferentially oxidized and generate a protective film on LiNi0.5Mn1.5O4. The resulting film inhibits the electrolyte decomposition and the transition metal ion dissolution.

Structural insights into the light-driven auto-assembly process of the water-oxidizing Mn4CaO5-cluster in photosystem II.

In plants, algae and cyanobacteria, Photosystem II (PSII) catalyzes the light-driven splitting of water at a protein-bound Mn4CaO5-cluster, the water-oxidizing complex (WOC). In the photosynthetic organisms, the light-driven formation of the WOC from dissolved metal ions is a key process because it is essential in both initial activation and continuous repair of PSII. Structural information is required for understanding of this chaperone-free metal-cluster assembly. For the first time, we obtained a structure of PSII from Thermosynechococcus elongatus without the Mn4CaO5-cluster. Surprisingly, cluster-removal leaves the positions of all coordinating amino acid residues and most nearby water molecules largely unaffected, resulting in a pre-organized ligand shell for kinetically competent and error-free photo-assembly of the Mn4CaO5-cluster. First experiments initiating (i) partial disassembly and (ii) partial re-assembly after complete depletion of the Mn4CaO5-cluster agree with a specific bi-manganese cluster, likely a di-µ-oxo bridged pair of Mn(III) ions, as an assembly intermediate.