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Silver-Containing α-MnO2 Nanorods: Electrochemistry in Rechargeable Aqueous Zn-MnO2 Batteries
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Optimization of Hydrogels for non-spillable Zn|MnO2 rechargeable batteries allowing for 2nd electron MnO2 cycling.
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Use of Hydrogel Electrolyte in Zn-MnO2 Rechargeable Batteries: Characterization of Safety, Performance, and Cu2+ Ion Diffusion
Achieving commercially acceptable Zn-MnO2 rechargeable batteries depends on the reversibility of active zinc and manganese materials, and avoiding side reactions during the second electron reaction of MnO2. Typically, liquid electrolytes such as potassium hydroxide (KOH) are used for Zn-MnO2 rechargeable batteries. However, it is known that using liquid electrolytes causes the formation of electrochemically inactive materials, such as precipitation Mn3O4 or ZnMn2O4 resulting from the uncontrollable reaction of Mn3+ dissolved species with zincate ions. In this paper, hydrogel electrolytes are tested for MnO2 electrodes undergoing two-electron cycling. Improved cell safety is achieved because the hydrogel electrolyte is non-spillable, according to standards from the US Department of Transportation (DOT). The cycling of “half cells” with advanced-formulation MnO2 cathodes paired with commercial NiOOH electrodes is tested with hydrogel and a normal electrolyte, to detect changes to the zincate crossover and reaction from anode to cathode. These half cells achieved ≥700 cycles with 99% coulombic efficiency and 63% energy efficiency at C/3 rates based on the second electron capacity of MnO2. Other cycling tests with “full cells” of Zn anodes with the same MnO2 cathodes achieved ~300 cycles until reaching 50% capacity fade, a comparable performance to cells using liquid electrolyte. Electrodes dissected after cycling showed that the liquid electrolyte allowed Cu ions to migrate more than the hydrogel electrolyte. However, measurements of the Cu diffusion coefficient showed no difference between liquid and gel electrolytes; thus, it was hypothesized that the gel electrolytes reduced the occurrence of Cu short circuits by either (a) reducing electrode physical contact to the separator or (b) reducing electro-convective electrolyte transport that may be as important as diffusive transport.
Hydroxyl Conducting Hydrogels Enable Low-Maintenance Commercially Sized Rechargeable Zn–MnO2 Batteries for Use in Solar Microgrids
Zinc (Zn)–manganese dioxide (MnO2) rechargeable batteries have attracted research interest because of high specific theoretical capacity as well as being environmentally friendly, intrinsically safe and low-cost. Liquid electrolytes, such as potassium hydroxide, are historically used in these batteries; however, many failure mechanisms of the Zn–MnO2 battery chemistry result from the use of liquid electrolytes, including the formation of electrochemically inert phases such as hetaerolite (ZnMn2O4) and the promotion of shape change of the Zn electrode. This manuscript reports on the fundamental and commercial results of gel electrolytes for use in rechargeable Zn–MnO2 batteries as an alternative to liquid electrolytes. The manuscript also reports on novel properties of the gelled electrolyte such as limiting the overdischarge of Zn anodes, which is a problem in liquid electrolyte, and finally its use in solar microgrid applications, which is a first in academic literature. Potentiostatic and galvanostatic tests with the optimized gel electrolyte showed higher capacity retention compared to the tests with the liquid electrolyte, suggesting that gel electrolyte helps reduce Mn3+ dissolution and zincate ion migration from the Zn anode, improving reversibility. Cycling tests for commercially sized prismatic cells showed the gel electrolyte had exceptional cycle life, showing 100% capacity retention for >700 cycles at 9.5 Ah and for >300 cycles at 19 Ah, while the 19 Ah prismatic cell with a liquid electrolyte showed discharge capacity degradation at 100th cycle. We also performed overdischarge protection tests, in which a commercialized prismatic cell with the gel electrolyte was discharged to 0 V and achieved stable discharge capacities, while the liquid electrolyte cell showed discharge capacity fade in the first few cycles. Finally, the gel electrolyte batteries were tested under IEC solar off-grid protocol. It was noted that the gelled Zn–MnO2 batteries outperformed the Pb–acid batteries. Additionally, a designed system nameplated at 2 kWh with a 12 V system with 72 prismatic cells was tested with the same protocol, and it has entered its third year of cycling. This suggests that Zn–MnO2 rechargeable batteries with the gel electrolyte will be an ideal candidate for solar microgrid systems and grid storage in general.
Popcorning Failures in Polymer and MnO2 Tantalum Capacitors
Popcorning is a well-known effect in plastic encapsulated microcircuits (PEM) and it occurs in chip tantalum capacitors. The sensitivity of components to the presence of moisture during soldering is characterized by the moisture sensitivity level (MSL); however, contrary to PEMs, there is no standard procedure for establishing MSL for tantalum capacitors.The effect of absorbed moisture on soldering related degradation and failures in tantalum capacitors have not been studied properly yet, and there is no sufficient information regarding the difference in the sensitivity to soldering between polymer and MnO2 capacitors. In this work, 16 types of polymer and 9 types of MnO2 tantalum capacitors with different moisture content have been tested before and after reflow soldering. The level of moisture release during soldering has been estimated and thermo-mechanical analysis used to assess deformation of capacitorsduring soldering simulations. Results show that moisture uptake in similar parts is approximately two times greater in polymer than in MnO2 capacitors. Cracking of the case and degradation of parameters can occur in both types of parts, but MnO2 capacitors are much more likely to fail catastrophically with a short circuit and possible ignition during the first power-on cycle. This type of failure in MnO2 capacitors is lot-related, can occur even at derated voltages and relatively low levels of moisture sorption that corresponds to room conditions. Baking before soldering is an effective measure to prevent failures even in lots susceptible to popcorning damage.
Effect of Soldering on Polymer and MnO2 Tantalum Capacitors
Soldering might have a strong effect on performance and reliability of most surface mount technology components, including tantalum capacitors. High quality tantalum capacitors are likely the only type of components where soldering simulation is the first step during screening. Nevertheless, post-soldering failures of tantalum capacitors happen and require additional analysis. Popcorning is a well-known effect in plastic encapsulated microcircuits (PEM) and it occurs also in chip tantalum capacitors. The sensitivity of parts to the presence of moisture during soldering is characterized by the moisture sensitivity level (MSL); however, contrary to PEMs, there is no standard procedure for establishing MSL for tantalum capacitors. The effect of absorbed moisture on soldering related degradation and failures in tantalum capacitors have not been studied properly yet, and there is no sufficient information regarding the difference in the sensitivity to soldering between polymer and MnO2 tantalum capacitors. In this work, 16 types of polymer and 9 types of MnO2 cathodes tantalum capacitors with different moisture content have been tested before and after reflow soldering. The level of moisture release after soldering has been estimated and thermo-mechanical analysis used to assess deformation of capacitors during soldering simulations. Results show that moisture uptake in similar parts is approximately two times greater in polymer than in MnO2 capacitors. Cracking of the case and degradation of parameters can occur in both types of parts, but MnO2 capacitors are much more likely to fail catastrophically with a short circuit and possible ignition during the first power-on cycle. This type of failure in MnO2 capacitors is lot-related, can occur even at derated voltages and relatively low levels of moisture sorption corresponding to room conditions. Baking before soldering is an effective measure to prevent failures even in lots susceptible to popcorning damage. Recommendations for baking and testing to establish MSL are suggested.
Mechanistic Investigation of Redox Processes in Zn-MnO2 battery in Mild Aqueous Electrolytes
Zinc-MnO2 based batteries have acquired attention for grid-level applications, due to impressive theoretical performance, cost effectiveness and intrinsic safety. However, there are still many challenges that remain elusive due to the complex and controversial mechanisms of operation that hinders commercialization. In this work, the detailed redox processes that occur at the cathode during Zn-MnO2 battery operation are elucidated. Using a blend of structural and electrochemical techniques, the redox pairs that occur during operation are mechanistically studied while also showcasing the true impact of the electrolyte additive (0.1 M MnSO4) in a 1 M ZnSO4 electrolyte. An electrochemical quartz-crystal microbalance (EQCM) has been leveraged to reveal the effect of zinc hydroxy sulfate salt (Zn4SO4(OH)6·nH2O) and zinc manganese oxide (ZnxMnyOz) dissolution/deposition, which are believed to be major components during discharge and charge conditions. . These results provide insight not currently available, allowing a holistic view of the electrochemical reaction mechanisms during battery operation.
A new concept for high-cycle-life LEO: Rechargeable MnO2-hydrogen
The nickel-hydrogen secondary battery system is now the one of choice for use in GEO satellites. It offers superior energy density to that of nickel-cadmium, with a lifetime that is at least comparable in terms of both cycle life and overall operating life. While the number of deep cycles required for GEO use is small, LEO satellites with long lifetimes (5 to 10 years) will require secondary battery systems allowing 30,000 to 60,000 useful cycles which are characterized by an approximately 2C charge rate and C average discharge rate. Recent work has shown that birnessite MnO2 doped with bismuth oxide can be cycled at very high rates (6C) over a very large number of cycles (thousands) at depths-of-discharge in the 85 to 90 percent range, based on two electrons, which discharge at the same potential in a flat plateau. The potential is about 0.7 V vs. hydrogen, with a cut-off at 0.6 V. At first sight, this low voltage would seem to be a disadvantage, since the theoretical energy density will be low. However, it permits the use of lightweight materials that are immune from corrosion at the positive. The high utilization and low equivalent weight of the active material, together with the use of teflon-bonded graphite for current collection, result in very light positives, especially when these are compared with those in a derated nickel-hydrogen system. In addition, the weight of the pressure vessel falls somewhat, since the dead volume is lower. Calculations show that a total system will have 2.5 times the Ah capacity of a derated nickel-hydrogen LEO battery, so that the energy density, based on 1.2 V for nickel-hydrogen and 0.7 V for MnO2-hydrogen, will be 45 percent higher for comparable cycling performance.
High-rate Li-MnO2 cells for aerospace use
A series of comparative studies were undertaken on representative cells as objectively as possible in order to appreciate the respective advantages of the different systems. After reviewing the first test results our attention was soon focussed on the following four lithium systems: (1) Li-SOCl2; (2) Li-SO2; (3) Li-(CF(sub x))(sub n); and (4) Li-MnO2. This resulted in the decision in 1982 to adopt the Li-MnO2 system for high-rate applications.
Materials Data on MnO2 by Materials Project
MnO2 is Rutile-like structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Mn4+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles are 50°. There are a spread of Mn–O bond distances ranging from 1.92–1.95 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Mn4+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three equivalent Mn4+ atoms.
Materials Data on MnO2 by Materials Project
MnO2 is Rutile-like structured and crystallizes in the tetragonal I4/m space group. The structure is three-dimensional. Mn4+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles are 50°. There are a spread of Mn–O bond distances ranging from 1.92–1.95 Å. There are two inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three equivalent Mn4+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Mn4+ atoms.
Materials Data on MnO2 by Materials Project
MnO2 is Rutile structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. Mn4+ is bonded to six equivalent O2- atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedral tilt angles are 50°. There is four shorter (1.91 Å) and two longer (1.93 Å) Mn–O bond length. O2- is bonded in a distorted trigonal planar geometry to three equivalent Mn4+ atoms.
Materials Data on MnO2 by Materials Project
MnO2 is Rutile-like structured and crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Mn4+ sites. In the first Mn4+ site, Mn4+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedra tilt angles range from 51–52°. There is four shorter (1.93 Å) and two longer (1.94 Å) Mn–O bond length. In the second Mn4+ site, Mn4+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedra tilt angles range from 51–52°. There are a spread of Mn–O bond distances ranging from 1.92–1.95 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal planar geometry to three Mn4+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal planar geometry to three Mn4+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Mn4+ atoms.
Materials Data on MnO2 by Materials Project
MnO2 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are two inequivalent Mn4+ sites. In the first Mn4+ site, Mn4+ is bonded to four O2- atoms to form corner-sharing MnO4 tetrahedra. The corner-sharing octahedra tilt angles range from 57–59°. There are three shorter (1.95 Å) and one longer (2.08 Å) Mn–O bond lengths. In the second Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with three equivalent MnO4 tetrahedra and edges with four equivalent MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.87–2.02 Å. There are four inequivalent O2- sites. In the first O2- site, O2- is bonded in a trigonal planar geometry to three Mn4+ atoms. In the second O2- site, O2- is bonded in a distorted trigonal pyramidal geometry to four Mn4+ atoms. In the third O2- site, O2- is bonded in a distorted T-shaped geometry to three equivalent Mn4+ atoms. In the fourth O2- site, O2- is bonded in a water-like geometry to two equivalent Mn4+ atoms.
Materials Data on MnO2 by Materials Project
MnO2 crystallizes in the orthorhombic Pbcm space group. The structure is three-dimensional. Mn4+ is bonded to six O2- atoms to form a mixture of edge and corner-sharing MnO6 octahedra. The corner-sharing octahedra tilt angles range from 0–50°. There are a spread of Mn–O bond distances ranging from 1.84–2.06 Å. There are three inequivalent O2- sites. In the first O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three equivalent Mn4+ atoms. In the second O2- site, O2- is bonded in a square co-planar geometry to four equivalent Mn4+ atoms. In the third O2- site, O2- is bonded in a bent 120 degrees geometry to two equivalent Mn4+ atoms.
Materials Data on MnO2 by Materials Project
MnO2 crystallizes in the triclinic P1 space group. The structure is three-dimensional. there are twelve inequivalent Mn4+ sites. In the first Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share a cornercorner with one MnO4 tetrahedra and edges with five MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.86–2.02 Å. In the second Mn4+ site, Mn4+ is bonded to six O2- atoms to form edge-sharing MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.93–1.95 Å. In the third Mn4+ site, Mn4+ is bonded to six O2- atoms to form edge-sharing MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.91–1.96 Å. In the fourth Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share a cornercorner with one MnO4 tetrahedra and edges with five MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.84–2.01 Å. In the fifth Mn4+ site, Mn4+ is bonded to six O2- atoms to form edge-sharing MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.93–1.95 Å. In the sixth Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share a cornercorner with one MnO4 tetrahedra and edges with five MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.87–2.02 Å. In the seventh Mn4+ site, Mn4+ is bonded to six O2- atoms to form edge-sharing MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.92–1.95 Å. In the eighth Mn4+ site, Mn4+ is bonded to six O2- atoms to form edge-sharing MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.93–1.95 Å. In the ninth Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent MnO4 tetrahedra and edges with five MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.92–1.95 Å. In the tenth Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent MnO4 tetrahedra and edges with five MnO6 octahedra. There is three shorter (1.93 Å) and three longer (1.94 Å) Mn–O bond length. In the eleventh Mn4+ site, Mn4+ is bonded to six O2- atoms to form MnO6 octahedra that share corners with two equivalent MnO4 tetrahedra and edges with five MnO6 octahedra. There are a spread of Mn–O bond distances ranging from 1.92–1.95 Å. In the twelfth Mn4+ site, Mn4+ is bonded to four O2- atoms to form corner-sharing MnO4 tetrahedra. The corner-sharing octahedra tilt angles range from 55–59°. There are a spread of Mn–O bond distances ranging from 1.91–2.00 Å. There are twenty-four inequivalent O2- sites. In the first O2- site, O2- is bonded in a water-like geometry to two Mn4+ atoms. In the second O2- site, O2- is bonded in a water-like geometry to two Mn4+ atoms. In the third O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the fourth O2- site, O2- is bonded in a water-like geometry to two Mn4+ atoms. In the fifth O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the sixth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Mn4+ atoms. In the seventh O2- site, O2- is bonded in a distorted trigonal pyramidal geometry to four Mn4+ atoms. In the eighth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Mn4+ atoms. In the ninth O2- site, O2- is bonded in a 3-coordinate geometry to three Mn4+ atoms. In the tenth O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the eleventh O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the twelfth O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Mn4+ atoms. In the thirteenth O2- site, O2- is bonded in a 3-coordinate geometry to three Mn4+ atoms. In the fourteenth O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the fifteenth O2- site, O2- is bonded in a 3-coordinate geometry to three Mn4+ atoms. In the sixteenth O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the seventeenth O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the eighteenth O2- site, O2- is bonded in a 3-coordinate geometry to three Mn4+ atoms. In the nineteenth O2- site, O2- is bonded in a 3-coordinate geometry to three Mn4+ atoms. In the twentieth O2- site, O2- is bonded in a distorted T-shaped geometry to three Mn4+ atoms. In the twenty-first O2- site, O2- is bonded in a trigonal planar geometry to three Mn4+ atoms. In the twenty-second O2- site, O2- is bonded in a trigonal planar geometry to three Mn4+ atoms. In the twenty-third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to three Mn4+ atoms. In the twenty-fourth O2- site, O2- is bonded in a trigonal planar geometry to three Mn4+ atoms.