We evaluate the efficiency and capacity of electrochemically reversible insertion electrodes for use in targeted ion removal applications in aqueous solutions. The relative attributes of insertion material chemistry are evaluated by comparing the performance of two different sodium insertion materials, NaTi2(PO4)3 and Na4Mn9O18, in different electrolyte environments. We performed experiments over a range of solution compositions containing both sodium and other non-inserting ions, and we then developed mechanistic insight into the effects of solution concentration and composition on overpotential losses and round trip Coulombic efficiency. In dilute aqueous streams, performance was limited by the rate of ion transport from the bulk electrolyte region to the electrode interface. This leads to slow rates of ion removal, large overpotentials for ion insertion, parasitic charge loss due to water electrolysis, and lower round trip Coulombic efficiencies. This effect is particularly large for insertion electrodes with redox potentials exceeding the water stability window. In solutions with high background concentrations of non-inserting ions, the accumulation of non-inserting ions at the electrode interface limits inserting ion flux and leads to low ion removal capacity and round trip Coulombic efficiency.

•No published manufacturing models compare cylindrical to prismatic li-ion cell cost.•We present a process based cost model for specified cylindrical cell dimensions.•Economies of scale already reached in cylindrical cell manufacturing.•Larger cells or cells with thicker electrodes offer a lower cost per kWh.•Prismatic cells, which can be larger, offer more opportunity for cost reduction.The relative size and age of the US electric vehicle market means that a few vehicles are able to drive market-wide trends in the battery chemistries and cell formats on the road today. Three lithium-ion chemistries account for nearly all of the storage capacity, and half of the cells are cylindrical. However, no specific model exists to examine the costs of manufacturing these cylindrical cells. Here we present a process-based cost model tailored to the cylindrical lithium-ion cells currently used in the EV market. We examine the costs for varied cell dimensions, electrode thicknesses, chemistries, and production volumes. Although cost savings are possible from increasing cell dimensions and electrode thicknesses, economies of scale have already been reached, and future cost reductions from increased production volumes are minimal. Prismatic cells, which are able to further capitalize on the cost reduction from larger formats, can offer further reductions than those possible for cylindrical cells.

The inherent chemical stability of NaTi2(PO4)3 in aqueous solutions with higher pH values, and resulting implications for using this material as an anode are explored. Scanning electron microscopy, x-ray powder diffraction, and Fourier transform infrared spectroscopy were used to investigate morphological, structural, and chemical changes for samples exposed to varying basic pHs at 25° C and 70° C. Significant structural degradation and precipitation of a secondary phase were observed in all samples prepared at 70 °C along with 25° C samples exposed to more extreme pH solutions. Infrared spectroscopy results indicated a loss of phosphate from the precipitated material, while x-ray diffraction shows that the secondary phases were from the layered sodium titanate family. Cyclic voltammetry of the samples indicated some degree of capacity loss for all of the samples, while some showing features related to the observed secondary phase that has some electrochemical functionality. The implications of these results on the stability of NaTi2(PO4)3 in various electrolyte environments is discussed.

While energy storage technologies have existed for decades, fast-ramping grid-level storage is still an immature industry and is experiencing relatively rapid improvements in performance and cost across a variety of technologies. In this innovation cycle, it is important to determine which properties of emerging energy storage technologies are most valuable. Decreased capital cost, increased power capability, and increased efficiency all would improve the value of an energy storage technology and each has cost implications that vary by application, but there has not yet been an investigation of the marginal rate of technical substitution between storage properties. We use engineering-economic models of four emerging fast-ramping energy storage technologies and examine their cost-effectiveness for four realistic current applications. We determine which properties have the greatest effect on cost-of-service by performing an extended sensitivity analysis on the storage properties for combinations of application and storage type. We find that capital cost of storage is consistently important, and identify applications for which power/energy limitations are important. Each combination is different and blanket statements are not always appropriate.Highlights► The sensitivity of cost-of-service to different storage properties is calculated. ► Storage technologies: NaS batteries, Li-ion batteries, flywheels, and supercapacitors. ► Applications: frequency regulation, peak shaving, and wind integration. ► Reduction in capital cost of storage is consistently valuable. ► Power/energy limitations of energy storage can be important, depending on application.

An approach to making large format economical energy storage devices based on a sodium-interactive set of electrodes in a neutral pH aqueous electrolyte is described. The economics of materials and manufacturing are examined, followed by a description of an asymmetric/hybrid device that has λ-MnO2 positive electrode material and low cost activated carbon as the negative electrode material. Data presented include materials characterization of the active materials, cyclic voltammetry, galvanostatic charge/discharge cycling, and application-specific performance of an 80 V, 2.4 kW h pack. The results indicate that this set of electrochemical couples is stable, low cost, requires minimal battery management control electronics, and therefore has potential for use in stationary applications where device energy density is not a concern.Highlights► Overview of a new class of large format energy storage devices we are developing. ► New approach: carbon anode and cubic spinel MnO2 cathode with Na as functional ion. ► Very large format (∼30 W h) asymmetric energy storage devices demonstrated. ► Many cell units perform well when connected in series. ► We show the performance of a 60 V, 2.4 kW h battery pack made from these units.

We examine the potential economic implications of using vehicle batteries to store grid electricity generated at off-peak hours for off-vehicle use during peak hours. Ancillary services such as frequency regulation are not considered here because only a small number of vehicles will saturate that market. Hourly electricity prices in three U.S. cities were used to arrive at daily profit values, while the economic losses associated with battery degradation were calculated based on data collected from A123 Systems LiFePO4/Graphite cells tested under combined driving and off-vehicle electricity utilization. For a 16 kWh (57.6 MJ) vehicle battery pack, the maximum annual profit with perfect market information and no battery degradation cost ranged from ∼US$140 to $250 in the three cities. If the measured battery degradation is applied, however, the maximum annual profit (if battery pack replacement costs fall to $5000 for a 16 kWh battery) decreases to ∼$10–120. It appears unlikely that these profits alone will provide sufficient incentive to the vehicle owner to use the battery pack for electricity storage and later off-vehicle use. We also estimate grid net social welfare benefits from avoiding the construction and use of peaking generators that may accrue to the owner, finding that these are similar in magnitude to the energy arbitrage profit.

The effects of combined driving and vehicle-to-grid (V2G) usage on the lifetime performance of relevant commercial Li-ion cells were studied. We derived a nominal realistic driving schedule based on aggregating driving survey data and the Urban Dynamometer Driving Schedule, and used a vehicle physics model to create a daily battery duty cycle. Different degrees of continuous discharge were imposed on the cells to mimic afternoon V2G use to displace grid electricity. The loss of battery capacity was quantified as a function of driving days as well as a function of integrated capacity and energy processed by the cells. The cells tested showed promising capacity fade performance: more than 95% of the original cell capacity remains after thousands of driving days worth of use. Statistical analyses indicate that rapid vehicle motive cycling degraded the cells more than slower, V2G galvanostatic cycling. These data are intended to inform an economic model.

Here we demonstrate Na4Mn9O18 as a sodium intercalation positive electrode material for an aqueous electrolyte energy storage device. A simple solid-state synthesis route was used to produce this material, which was then tested electrochemically in a 1 M Na2SO4 electrolyte against an activated carbon counter electrode using cyclic voltammetry and galvanostatic cycling. Optimized Na4Mn9O18 was documented as having a specific capacity of 45 mAh/g through a voltage range of 0.5 V, or an equivalent specific capacitance of over 300 F/g. With the proper negative:positive electrode mass ratio, energy storage cells capable of being charged to at least 1.7 V without significant water electrolysis are documented. Cycling data and rate studies indicate promising performance for this unexplored low-cost positive electrode material.

The only viable PEM-based fuel cell catalyst systems documented to date contain significant fractions of noble metals. Approaches to lowering the necessary content of these costly materials consist of at least some combination of (1) developing novel catalyst materials that contain alternative materials, and (2) creating ultra high surface area catalyst structures that allow for efficient use of the functional catalyst surfaces. In addressing the latter, we disclose here a fully novel methodology for augmenting the functional surface area of a membrane surface: ultrafast/femtosecond laser modification. This type of photon/solid interaction can result in unexpected morphologies as a result of the exceptionally high energy and short duration photon packets that are exploited. Results include morphological analyses as well as electrochemical testing which are combined to conclusively indicate that this approach is viable.

The efficacy of composite Li-ion battery cathodes made by mixing active materials that possessed either high-rate capability or high specific energy was examined. The cathode structures studied contained carbon-coated LiFePO4 and either Li[Li0.17Mn0.58Ni0.25]O2 or LiCoO2. These active materials were arranged using three different electrode geometries: fully intermixed, fully separated, or layered. Discharge rate studies, cycle-life evaluation, and electrochemical impedance spectroscopy studies were conducted using coin cell test structures containing Li-metal anodes. Results indicated that electrode configuration was correlated to rate capability and degree of polarization if there was a large differential between the rate capabilities of the two active material species.

The effects of adding Zr to PtNi oxygen reduction reaction (ORR) electrocatalyst alloys were examined in a study aimed at probing the possibility of creating catalysts with enhanced resistance to corrosion in a PEM fuel cell environment. Samples consisting of pure Pt or PtNiZr alloys with a range of compositions (not exceeding 11 at.% Zr) were fabricated using co-sputter deposition. A high-throughput fabrication approach was used wherein 18 distinct thin film catalyst alloy samples with varying compositions were deposited onto a large-area substrate with individual Au current collector structures. A multi-channel pseudo-potentiostat allowed for the simultaneous quantitative study of catalytic activity for all 18 electrodes in a single test bath, a first for the study of ORR electrocatalysts. A properly stirred oxygenated 1 M H2SO4 electrolyte solution was used to provide each electrode with a steady-state flow of reactants during electrochemical evaluation. The onset potentials, absolute current density values, and Tafel analysis data obtained using this technique were compared with literature reports. The analyses showed that most PtNiZr alloys tested offered improvements over pure Pt, however those surfaces with a high mole fraction (>4 at.%) of Zr exhibited reduced activity that was roughly inversely correlated to the amount of Zr present. Film composition, morphology, and crystallographic properties were examined using X-ray energy dispersive spectroscopy (XEDS), X-ray photoelectron spectroscopy (XPS), SEM, and synchrotron X-ray diffraction. These data were then correlated with electrochemical data to elucidate the relationships between composition, structure, and relative performance for this ternary system.