Redox flow batteries (RFBs) are secondary battery systems suitable for large-scale, stationary energy storage applications, and are capable of storing large quantities of energy (MWh) and power (MW). 1 One principle advantage of flow batteries is the ability to decouple energy and power density, and scale both independently. The all-vanadium RFB represents the current state-of-the-art in flow battery technology, but uses expensive ion exchange membranes including Nafion®, and the relatively high cost of vanadium leads to expensive electrolytes. 2 The development of manganese-based anolytes as a suitable alternative to vanadium anolytes for redox flow batteries is attractive for various reasons, including a higher reversible potential for Mn 2+ /Mn 3+ than VO 2+ /VO 2 + , higher natural abundance, and lower cost than vanadium. Flow battery anolytes based on the Mn 2+ /Mn 3+ redox couple have been reported in the literature, and the high standard electrode potential of Mn 2+ /Mn 3+ (1.51 V) has been utilized in manganese anolyte (Mn 2+ /Mn 3+ )/vanadium catholyte (V 2+ /V 3+ ) redox flow batteries, featuring a theoretical open circuit voltage of 1.77 V. 2,3 The usage of manganese anolytes can lead to a higher cell voltage, yet the disproportionation reaction of Mn 3+ is a technical hurdle that needs to be resolved in order for manganese-based anolytes to find widespread utility in redox flow batteries. 2,4 This presentation will disclose investigations on the development of manganese-anolyte based redox flow batteries, and will show results from two different systems, including Ti/Mn, and V/Mn. Half–cell and full cell performance metrics, including cycle life testing, will be presented for each system. References 1) Wang, W. et al. J. Power Sources. 2012 , 216 , 99. 2) Xue, F.-Q. et al. Electrochimica Acta. 2008 , 53 , 6636. 3) Hong, T.; Xue, F. “Investigation on manganese (Mn 2+ /Mn 3+ )-vanadium (V 2+ /V 3+ ) redox flow battery.” 2009 Asia-Pacific Power and Energy Engineering Conference (APPEEC). 4) Swartz, C. R.; Lipka, S. M.; Rogers, F. III; Chen, R.; Kodenkandath, T. “Aqueous Manganese-Based Electrolytes for Redox Flow Batteries.” ECS abstract MA2014-02, 616.

Redox flow batteries (RFBs) are an emerging technology suitable for large-scale, stationary energy storage applications, including grid storage. Redox flow batteries are capable of storing high amounts of both energy (MWh) and power (MW).1 One principle advantage of flow batteries is the ability to decouple the energy density and power density of the system, and scale both independently. The all-vanadium RFB represents the current state-of-the-art in flow battery technology, and features several advantages, including rapid response times, high depth of discharge, long cycle life, and good cell performance metrics (i.e. efficiencies). Anolyte and catholyte cross-contamination is eliminated through the use of the same active metal cation in both compartments of the cell. Issues associated with the vanadium RFB include a low cell voltage (1.26 V), the use of expensive membranes including Nafion®, and the relatively high cost of vanadium, leading to expensive electrolytes.2 The development of anolytes with higher reversible potentials than VO2+/VO2 +, along with electroactive species featuring higher natural abundance and lower cost than vanadium, represents an attractive alternative to vanadium-based anolytes. Flow battery anolytes based on the Mn2+/Mn3+ redox couple have been reported in the literature, and the high standard electrode potential of Mn2+/Mn3+ (1.51 V) has been utilized in manganese anolyte (Mn2+/Mn3+)/vanadium catholyte (V2+/V3+) redox flow batteries, featuring a theoretical open circuit voltage of 1.77 V.2,3 The usage of manganese anolytes can lead to higher cell voltages (Figure 1) and cheaper anolytes, but the disproportionation reaction of Mn3+ to Mn2+ and MnO2 is a technical issue that needs to be resolved in order for manganese-based anolytes to find widespread utility in redox flow batteries.2 This presentation will disclose our investigations on the development of manganese-based anolytes for redox flow batteries. The effect of various additives on electrolyte stability and electrochemical kinetics for the Mn2+/Mn3+ redox couple will be quantified using cyclic voltammetry, RDE measurements, electrochemical impedance spectroscopy, overpotential measurements, and full-cell testing (constant current charge/discharge) of Mn/V redox flow batteries (Figure 2). References 1) Wang, W. et al. J. Power Sources. 2012, 216, 99. 2) Xue, F.-Q. et al. Electrochimica Acta. 2008, 53, 6636. 3) Hong, T.; Xue, F. “Investigation on manganese (Mn2+/Mn3+)-vanadium (V2+/V3+) redox flow battery.” 2009 Asia-Pacific Power and Energy Engineering Conference (APPEEC).

The structural changes and magnetoresistance (MR) properties of as-grown and post-annealed La0.7Ca0.3MnO3 films were investigated by transmission electron microscopy (TEM) and x-ray diffraction (XRD). The data for the films were compared to that for bulk La0.7Ca0.3MnO3 post-annealed under the same conditions. The main structure of the as-grown films was face-centered pseudo-cubic with a doubled perovskite unit cell, of size ∼2ap × ∼2ap × 2ap, where ap is the single perovskite parameter. The phase showed a cube-on-cube epitaxy with the underlying LaAlO3 substrate. Upon annealing to a saturation point, a minor primitive pseudo-tetragonal structure evolved, of cell parameters. A total of four possible orientations of the two structures was observed by TEM, comprised of one orientation of the ∼ 2ap × ∼ 2ap × ∼ 2ap cell, i.e., the cube-on-cube epitaxy, giving rise to (00l) peaks in x-ray, and three orientations of the cell, giving rise to a single (00l)/(hk0) peak in x-ray. The bulk La0.7Ca0.3MnO3 sample also contains the × structure. The difference between the bulk and the film and the effects of annealing on films can be ascribed to the influence of strain between the film and substate, induced by lattice mismatch.

We describe a method for forming a nanoparticle dispersion in YBa2Cu3O7 superconducting films grown by metal-organic deposition on RABiTS substrates. Two separate precursor modifications have been shown by transmission electron microscopy to give nanoparticles of (Y,Dy)2O3 and BaZrO3 with size distributions of 10–50nm and 10–25nm, respectively and that are well dispersed in the film. These particles are effective flux pinning centers and enhance the transport critical current by up to 100% at 77K for a magnetic field of 1.5T applied perpendicular to the tape. The processing required to grow these films is not greatly altered from that of unmodified YBCO and can be readily transferred to continuous processing of long-length wires.

High critical current densities ( J c ) in thick films of the Y 1 Ba 2 Cu 3 O 7–δ (YBCO, T c ≈ 92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application‐dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect‐free conductor in which the grain‐to‐grain connectivity maintains levels of inter‐grain J c that are comparable to the intra‐grain J c . That is, high critical current ( I c ) YBCO coated conductors must contain engineered inhomogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high‐performance YBCO coated‐conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano‐engineer the microstructure for tuneable superconducting wires. Multi‐scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher I c wires for large‐scale, commercial application are discussed within the context of these recent advances.

We have formed BaZrO3 nanoparticles in YBa2Cu3O7−δ second-generation HTS wires through modification of the chemical solution precursor for metal-organic deposition. Transmission-electron microscopy shows the particles to be 10–25nm in diameter, approximately spherical, and well dispersed through the film. The in-field critical current density is enhanced over a wide angular range compared to undoped wires.

Significant enhancements in flux-pinning were obtained for Dy-doped, YBCO films via a metalorganic deposition (MOD) process on rolling-assisted biaxially textured substrates (RABiTS). It has been reported previously that incorporation of excess rare-earth ions during the MOD process, results in improvement of J(c) for H//c, however, a decrease in J(c) for H//ab is observed. We report here that by altering the processing conditions the reduction in the magnitude of the current peak for H//ab can be minimized while significantly enhancing the random pinning at all field orientations. The result is a YBCO film with significantly reduced anisotropy compared to the typical YBCO films prepared by the MOD process. This is accomplished by incorporating both a high density of stacking faults and (Dy, Y)(2) O-3 nanoparticles which result in the strong pinning for H//ab and a broad pinning peak for H//c respectively.

American Superconductor has successfully scaled up its low-cost, high volume second generation (2G) HTS wire process into pre-pilot scale production, with performance approaching first generation (1G) HTS wire. AMSC’s manufacturing approach is based on RABiTSTM/MOD wide strip technology, with metal organic deposition (MOD) process for the YBCO layer and the Rolling Assisted Biaxially Textured Substrate (RABiTS) process for the template. In this paper, we review the status of the 2G manufacturing scale up at AMSC and describe the properties and architecture of the 2G wire being manufactured and developed for various applications.

The metal organic deposition (MOD) of buffer layers on RABiTS substrates is considered a potential, low-cost approach to manufacturing high performance Second Generation (2G) high temperature superconducting (HTS) wires. The typical architecture used by American Superconductor in their 2G HTS wire consists of a Ni-W (5 at.%) substrate with a reactively sputtered Y2O3 seed layer, YSZ barrier layer and a CeO2 cap layer. This architecture supports critical currents of over 300 A/cm-width (77 K, self-field) with 0.8 mum YBCO films deposited by the TFA-MOD process. The main challenge in the development of the MOD buffers is to match or exceed the performance of the standard vacuum deposited buffer architecture. We have recently shown that the texture and properties of MOD - La2Zr2Ogamma (LZO) barrier layers can be improved by inserting a thin sputtered Y2O3 seed layer and prepared MOD deposited LZO layers followed by MOD or RF sputtered CeO2 cap layers that support MOD-YBCO films with Ic's of 200 and 255 A/cm-width, respectively. Detailed X-ray and microstructural characterizations indicated that MOD - CeO2 cap reacted completely with MOD YBCO to form BaCeOs. However, sputtered CeO2 cap/MOD YBCO interface remains clean. By further optimizing the coating conditions and reducing the heat-treatment temperatures, we have demonstrated an Ic of 336 A/cm with improved LZO layers and sputtered CeO2 cap and exceeded the performance of that of standard vacuum deposited buffers.

The improvement of critical current densities of superconducting wires is essential for commercial applications. Many approaches have been demonstrated to enhance flux pinning of YBa2Cu3O7−δ (YBCO) second-generation (2G) superconducting wires and therefore to increase critical current densities of the materials. In this work, we study the microstructures which lead to enhanced critical current density through flux pinning by nanoparticles in metal-organic deposited (MOD) YBCO films with Dy or Zr additions. Transmission electron microscopy (TEM) observation revealed that large densities of nanoparticles can be formed in YBCO films through altering the precursor stoichiometry and cation additions. Most of these nanoparticles are in the range of 10–50nm, and are well dispersed, making them ideal for flux pinning in YBCO 2G wires. The effects on critical current of these nanoparticles acting as flux pinning centers are investigated.

Two different types of defect structures have been identified to be responsible for the enhanced pinning in Metal Organic Deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible for the large current enhancement when the magnetic field is oriented in the ab-plane. TEM studies showed that the intergrowths emanate from cuprous; containing secondary phase particles, whose density is partially controlled by the rare earth doping level. Critical process parameters have been identified to control this phase formation, and therefore, control the 124 intergrowth formation. This work has shown that through process control and proper conductor design, either by adjusting the composition or by multiple coatings of different functional layers, the desired angular dependence can be achieved.