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Overview of current development in electrical energy storage technologies and the application potential in power system operation

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Recent Advances in Zn-Ion Batteries

Large-scale deployment of intermittent renewable energy (namely wind energy and solar PV) may entail new challenges in power systems and more volatility in power prices in liberalized electricity markets. Energy storage can diminish this imbalance, relieving the grid congestion, and promoting distributed generation. The economic implications of grid-scale electrical energy storage technologies are however obscure for the experts, power grid operators, regulators, and power producers. A meticulous techno-economic or cost-benefit analysis of electricity storage systems requires consistent, updated cost data and a holistic cost analysis framework. To this end, this study critically examines the existing literature in the analysis of life cycle costs of utility-scale electricity storage systems, providing an updated database for the cost elements (capital costs, operational and maintenance costs, and replacement costs). Moreover, life cycle costs and levelized cost of electricity delivered by electrical energy storage is analyzed, employing Monte Carlo method to consider uncertainties. The examined energy storage technologies include pumped hydropower storage, compressed air energy storage (CAES), flywheel, electrochemical batteries (e.g. lead–acid, NaS, Li-ion, and Ni–Cd), flow batteries (e.g. vanadium-redox), superconducting magnetic energy storage, supercapacitors, and hydrogen energy storage (power to gas technologies). The results illustrate the economy of different storage systems for three main applications: bulk energy storage, T&D support services, and frequency regulation.

Electrical energy storage systems: A comparative life cycle cost analysis

Flow batteries, in which the electro-active components are held in fluid form external to the battery itself, are attractive as a potential means for regulating the output of intermittent renewable sources of electricity; an aqueous flow battery based on inexpensive commodity chemicals is now reported that also has the virtue of enabling further improvement of battery performance through organic chemical design. Flow batteries differ from the conventional type in that the electro-active components of flow batteries are held in fluid form external to the battery itself, enabling such systems to store arbitrarily large amounts of energy. Flow batteries are therefore attractive as a potential means for regulating the output of intermittent sources of electricity such as wind or solar power. But an important limitation of most such systems is the abundance and cost of the electro-active materials. To overcome this limitation, Brian Huskinson and colleagues have developed an aqueous flow battery on the basis of inexpensive, non-metallic commodity chemicals, with the added advantage of enabling the tuning of key battery properties through chemical design. As the fraction of electricity generation from intermittent renewable sources—such as solar or wind—grows, the ability to store large amounts of electrical energy is of increasing importance. Solid-electrode batteries maintain discharge at peak power for far too short a time to fully regulate wind or solar power output1,2. In contrast, flow batteries can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all of the electro-active species in fluid form3,4,5. Wide-scale utilization of flow batteries is, however, limited by the abundance and cost of these materials, particularly those using redox-active metals and precious-metal electrocatalysts6,7. Here we describe a class of energy storage materials that exploits the favourable chemical and electrochemical properties of a family of molecules known as quinones. The example we demonstrate is a metal-free flow battery based on the redox chemistry of 9,10-anthraquinone-2,7-disulphonic acid (AQDS). AQDS undergoes extremely rapid and reversible two-electron two-proton reduction on a glassy carbon electrode in sulphuric acid. An aqueous flow battery with inexpensive carbon electrodes, combining the quinone/hydroquinone couple with the Br2/Br− redox couple, yields a peak galvanic power density exceeding 0.6 W cm−2 at 1.3 A cm−2. Cycling of this quinone–bromide flow battery showed >99 per cent storage capacity retention per cycle. The organic anthraquinone species can be synthesized from inexpensive commodity chemicals8. This organic approach permits tuning of important properties such as the reduction potential and solubility by adding functional groups: for example, we demonstrate that the addition of two hydroxy groups to AQDS increases the open circuit potential of the cell by 11% and we describe a pathway for further increases in cell voltage. The use of π-aromatic redox-active organic molecules instead of redox-active metals represents a new and promising direction for realizing massive electrical energy storage at greatly reduced cost.

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A metal-free organic–inorganic aqueous flow battery

Redox flow batteries, which have been developed over the last 40 years, are used to store energy on the medium to large scale, particularly in applications such as load levelling, power quality control and facilitating renewable energy deployment. Various electrode materials and cell chemistries have been proposed; some of the successful systems have been demonstrated on a large-scale in the range of 10 kW–10 MW. Enhanced performance is attributable to the improvements in electrodes, separator materials and an increasing awareness of cell design. This comprehensive review provides a summary of the overall development of redox flow battery technology, including proposed chemistries, cell components and recent applications. Remaining challenges and directions for further research are highlighted.

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Progress in redox flow batteries, remaining challenges and their applications in energy storage

H2O2 is important in large-scale industrial processes and smaller on-site activities. The present industrial route to H2O2 involves hydrogenation of an anthraquinone and O2 oxidation of the resulting dihydroanthraquinone — a costly method and one that is impractical for routine on-site use. Electrosynthesis of H2O2 is cost-effective and applicable on both large and small scales. This Review describes methods to design and assess electrode materials for H2O2 electrosynthesis. H2O2 can be prepared by oxidizing H2O at efficient anodic catalysts such as those based on BiVO4. Alternatively, H2O2 forms by partially reducing O2 at cathodes featuring either noble metal alloys or doped carbon. In addition to the catalyst materials used, one must also consider the form and geometry of the electrodes and the type of reactor in order to strike a balance between properties such as mass transport and electroactive area, both of which substantially affect both the selectivity and rate of reaction. Research into catalyst materials and reactor designs is arguably quite mature, such that the future of H2O2 electrosynthesis will instead depend on the design of complete and efficient electrosynthesis systems, in which the complementary properties of the catalysts and the reactor lead to optimal selectivity and overall yield. Electrosynthesis is a practical and green route to hydrogen peroxide, and could reduce our dependence on less environmentally friendly oxidants. This Review describes catalyst and reactor designs for highly selective hydrogen peroxide electrosynthesis.

Carlos Ponce de León

Papers

Progress in redox flow batteries, remaining challenges and their applications in energy storage

Electrochemical synthesis of hydrogen peroxide from water and oxygen

Graphite felt as a versatile electrode material: Properties, reaction environment, performance and applications

Redox flow batteries for energy storage: their promise, achievements and challenges

Progress in electrochemical flow reactors for laboratory and pilot scale processing