Energy storage is increasingly important for a diversity of applications. Batteries can be used to store solar or wind energy providing power when the Sun is not shining or wind speed is insufficient to meet power demands. For large scale energy storage, solutions that are both economically and environmentally friendly are limited. Flow batteries are a type of battery technology which is not as well-known as the types of batteries used for consumer electronics, but they provide potential opportunities for large scale energy storage. These batteries have electrochemical recharging capabilities without emissions as is the case for other rechargeable battery technologies; however, with flow batteries, the power and energy are decoupled which is more similar to the operation of fuel cells. This decoupling provides the flexibility of independently designing the power output unit and energy storage unit, which can provide cost and time advantages and simplify future upgrades to the battery systems. One major challenge of the existing commercial flow battery technologies is their limited energy density due to the solubility limits of the electroactive species. Improvements to the energy density of flow batteries would reduce their installed footprint, transportation costs, and installation costs and may open up new applications. This review will discuss the background, current progress, and future directions of one unique class of flow batteries that attempt to improve on the energy density of flow batteries by switching to solid electroactive materials, rather than dissolved redox compounds, to provide the electrochemical energy storage.

A new type of non-aqueous redox couple without carbon additives for flow batteries is proposed and the target anolyte chemistry is demonstrated. The socalled "Solid Dispersion Redox Couple" incorporates solid electroactive materials dispersed in organic lithium-ion battery electrolyte as its flowing suspension. In this work, a unique and systematic characterization approach has been used to study the flow battery redox couple in half cell demonstrations relative to a lithium electrode. An electrolyte laden with Li 4 Ti 5 O 12 (LTO) has been characterized in multiple specially designed lithium half cell configurations. The flow battery redox couple described in this report has relatively low viscosity, especially in comparison to other flow batteries with solid active materials. The lack of carbon additive allows characterization of the electrochemical properties of the electroactive material in flow without the complication of conductive additives and unambiguous observation of the electrorheological coupling in these dispersed particle systems. 2 3 4 5 6 7 8

One attribute that has limited performance for some lithiumion battery active material systems is large particle size. While many methods have been reported in the literature for producing high-performance sub-micrometer sized battery particles, often these procedures are difficult to adapt to large battery electrode powder production and/or the processing is relatively expensive compared to traditional methods. We report a highly scalable process to produce high performance sub-micrometer battery active material using an initial demonstration cathode chemistry, LiCoO 2 (LCO). We adopted a template-based process which took advantage of a cobalt oxalate precursor material with a rod morphology. Lithiation of the precursor via calcination produced loosely connected sub-micrometer sized LCO particles which were easily dispersed into individual particles through a low energy mechanical method. The sub-micrometer sized LCO particulates exhibited excellent electrochemical performance as lithium-ion battery cathode active materials, including high discharge capacity, rate capability, and coulombic efficiency.

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A variety of physical and electrochemical properties are used to characterize lithium-ion battery active materials, both in the academic literature to understand the fundamental structure-property relationships of materials and in a manufacturing setting to provide quality control during battery material production. One important metric of battery performance is the ability to retain capacity at increasing rates of discharge, or rate capability; however, it can be influenced by a number of factors related to different electrode components and preparations and also requires time consuming cell fabrication and testing. Herein, we describe a relatively fast test that relies on electrochemical evaluation of battery active material particles in a suspension undergoing collisions with a current collector. While this technique does not provide a full rate capability characterization for a material, these results will demonstrate that the measured resistance provides the relative rate capability of the active materials without the potential interference of other composite electrode components. High performance battery active materials are a key enabler in the development and improvement of plug-in hybrid and battery electric vehicles, and lithium-ion (Li-ion) battery chemistry is the predominant battery technology within these applications.1,2 Among many physical and electrochemical evaluations conducted on Li-ion electrode active materials as part of material characterization and validation protocols, rate capability is an important metric in applications that require fast charge and/or high power output.3,4 Rate capability is the ability of active materials to retain electrochemical capacity at high cycling rates, i.e. high currents. 5,6 It is highly dependent on the overpotential while discharging the cell, which is especially large at high rates of charge/discharge. 5,[7][8][9] This overpotential is dependent on many factors at the cell level that are not specific to the active material, including electrode contact to the current collector, pressure applied to the electrode and/or calendaring, connectivity of cell components, homogeneity of electrode slurry, conductive carbon loading, binder integrity, and other factors. 10 For the active material itself, rate capability can be dependent on additional attributes including material stoichiometry, crystal structure, particle size, and crystallinity; 3,5,6,8,9,11 therefore, there is value in evaluating the electrochemical properties of active materials independent of the influences of other cell components or fabrication practices. Obtaining such material properties is important both from a research perspective to compare the electrochemical properties between candidate materials and from a quality control perspective of validating batch to batch variability between battery active materials in a manufacturing process.Electrochemical evaluation of active materials is frequently reported in the literature by casting the material into thin film composite electrodes from s...

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A variety of properties are used to characterize lithium-ion battery active materials when synthesizing a new material in the lab or controlling the quality in a manufacturing product line. Rate capability is one of these measured properties and is important because many applications need good high rate performance, for example plug-in hybrid electric vehicles. Rate capability tests are time and material intensive because they require electrode fabrication, cell fabrication, and cell cycling, and this entire process can take up to a couple of weeks. In addition, properties derived from coin cell cycling are not just dependent on the active material properties but also can be dependent on other electrode components and the electrode microstructure. In this talk, we will describe recent efforts to characterize suspensions of lithium-ion battery active materials. The electrochemical evaluation is relatively fast, under 30 minutes, and characterizes the active material particles in the electrolyte without the complicating factors of conductive additives, binders, and resulting electrode microstructures. The particles colliding with a current collector result in a single measured resistance, and in this talk we will demonstrate proof-of-concept that this resistance can correlate to the relative rate capability between active materials. Current limitations of the technique will also be described.