Chapter 1 - Fundamental electrochemical energy storage mechanisms

<sec><p indent="0mm">Resource depletion and environmental degradation have driven the development of renewable energy sources, such as solar and wind power, to replace fossil fuels. However, the inherent intermittency of these renewable energy sources poses a significant challenge to the power grid, necessitating the development of large-scale energy storage systems. Recently, rechargeable aqueous Zn batteries using Zn metal as the anode have been revisited as a potential solution for grid energy storage due to the advantages of non-flammability, environmental benignity, low cost, etc. Unlike most metals including Li, Na, K, Mg, Al, etc., Zn metal can be directly applied as the anode for aqueous batteries and also exhibits a high theoretical capacity of 819 mAh g⁻¹, superior volumetric capacity of 5854 mAh cm⁻³ and low redox potential of <sc>−0.762 V</sc> vs. the standard hydrogen electrode. The performance of aqueous Zn-ion batteries, however, remains unsatisfactory for their further commercial application due to uncontrollable dendrite growth and interfacial side reactions. Specifically, the deposition-stripping process of Zn metal is controlled by the Zn anode-electrolyte interface, where the structural evolution of the electric double layer (EDL) is the critical issue for the excellent electrochemical performance of zinc anodes. The EDL is the region where electrochemical reactions occur, and it plays a critical role in electrochemical energy conversion and storage. Previous reports reveal that EDL is crucial to the formation of solid electrolyte interphases and conventional electrochemical double layer capacitors. Generally, the dipolar H₂O molecules exist in the inner Helmholtz layer of the EDL, participating in the interfacial reactions during battery operation. Consequently, uncontrollable electrochemical and chemical corrosion reactions continuously occur, significantly degrading the battery performance. Moreover, the de-solvation process of [Zn(H₂O)₆]²⁺ and the Zn deposition process both occur in the EDL, determining the electrochemical reactions at the surface of the Zn anode and the morphology of Zn deposition. Modifying the EDL structure can greatly influence the efficiency, stability, and overall performance of the battery system. In recent years, researchers have made some achievements in the research of Zn anodes by proposing various modification strategies in Zn anode-electrolyte interface modification. However, due to the limitation of characterization methods, the reaction mechanism of the EDL still remains unclear. </sec><sec> In this work, we systematically investigate the structural evolution mechanism, interfacial reaction mechanisms regulation strategies, electrochemical and <italic>in-situ</italic> spectral characterization methods, and theoretical simulations of the EDL at zinc anode-electrolyte interfaces. Moreover, we introduce novel perspectives for the investigation of the EDL at the Zn anode-electrolyte interface in the future. These include, for example, a multi-scale study on the evolution of the EDL at the zinc anode through the integration of electrochemical, spectroscopic, and theoretical modeling methodologies. Furthermore, we propose to examine the evolution behavior of the EDL at the Zn anode-electrolyte interface under practical application conditions within Ah-scale Zn batteries. These research endeavors will offer references for the practical deployment of aqueous Zn-ion batteries. </sec>

In the early texts on secondary batteries,(1,2) little consideration was given to intercomparison of various systems. These were essentially treatises on the lead-acid battery. This is understandable since the contributions of other secondary systems (e.g., the Edison and Jungner batteries) were then negligible. Since World War II, a number of alkaline electrolyte batteries have been developed and marketed; these have been described in detail.(3) In the past 20 years a host of new secondary battery systems have been investigated and, at present, research in this area is increasing. The impetus for this work is the great variety of new applications for small batteries in the consumer market, and growing interest in electric vehicles, and the possible application of large batteries for utility load leveling. Recently, batteries for electric vehicles(4,5) and utility load leveling(6) have been reviewed. No overall comparison has been made between the several secondary battery systems. The ideal battery using alkali metals and halogens of low atomic weight as the active materials, and meeting the requirements of all applications, has not materialized. As a result, many battery systems are being investigated. The likely outcome is a number of new secondary batteries, each occupying a particular niche in the marketplace because of its unique features.

Due to unreliability of power supply from national grid, high cost of diesel and maintenance of generators being an alternate for national grid, there is need to adopt a renewable energy source for efficient and reliable power supply. Savings associated with conversion of a stand-alone diesel generator powered system to a reliable PV/Diesel hybrid power system with energy storage in batteries for Bayero University Kano Library using HOMER software was presented in this study. The economic parameter of merit used in selecting an optimum energy system from set of configurations was total Net Present Cost (NPC) in billions of naira. Generator + PV + Battery system has a total NPC of (₦ 1.17B) and saves (₦ 0.9B), Generator + PV system has a total NPC of (₦ 1.68B) and saves (₦0.4B), Generator + Battery system has a total NPC of (₦ 2.05B) and saves (₦ 0.03B), PV + Battery system has a total NPC of (₦ 2.28B) and saves (₦ - 0.2B) when all compared with Generator-only system (₦ 2.08B). It can be seen that the best case is the PV + Gen + Battery system. Even though it has the highest capital cost, but it resulted to the least net present cost (NPC); as such, PV + Gen + Battery system is the optimized model to fulfill the load demands. Therefore, this research work shows that the integration of PV with battery storage into the existing diesel stand-alone system in the University library is more reliable at the lowest lifecycle cost.

The effective utilization of clean energy and finding alternatives to fossil resources are highly important to ensure the sustainability of human society and are always among the major goals of both chemistry and material science research. Advanced electrochemical devices, such as fuel cells, water electrolysers and metal-air batteries, represent the most promising strategies for clean-energy utilization. In an electrochemical device, the redox reactions are spatially separated by a membrane, allowing direct extraction/transfer of electrons at an electrode-electrolyte interface, which leads to higher intrinsic energy conversion efficiencies, milder process conditions, easy product separation and excellent design features for coupling to renewable energy infrastructure. The performance of such electrochemical processes is fundamentally determined by the physicochemical properties of the electrochemical interfaces, encompassing both the electrocatalyst and the structure of the adjacent electrochemical double layer. Specifically, electrocatalysts play key roles in electrochemical reactions and often limit the performance of entire systems due to their insufficient activity, low durability or high cost. Ideally, the rate, efficiency, and selectivity of the above electrochemical reactions can be substantially improved by developing high-performance electrocatalyst. One of the central tasks for chemists and material scientists is to design and fabricate the high-efficient efficiency but low-cost electrocatalysts systems. The current promising electrochemical reactions mainly focus on the realization of the reversible conversion between chemical and electricity energy, e.g., the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen oxidation reaction (HOR), and hydrogen evolution reaction (HER). Coupling of the above electrochemical reactions provide a solid foundation for various essential electrochemical devices, such as direct hydrogen fuel cells (HOR + ORR); electrolysers (OER + HER); rechargeable zinc (Zn)-air battery (ORR + OER). Therefore, this thesis aims to design and synthesize high-performance electrocatalysts for HER, ORR and OER based on earth-abundant materials with proper hierarchical 2D or 3D nanostructures. Combined with the advanced characterization techniques and density functional theory (DFT) calculations, the relationship between the electrochemical activity and active sites of these earth-abundant electrocatalysts were detailedly explored and confirmed. Furthermore, to emphasize the hierarchical 2D or 3D nanostructures, the actual performance of these electrocatalysts was all evaluated in practical devices including Zn-air battery and proton exchange membrane fuel cell (PEMFC), specifically as follows: (1) The vast majority of the reported HER electrocatalysts performs poorly under alkaline conditions due to the sluggish water dissociation kinetics. In the first work, a hybridization catalyst construction concept is presented to dramatically enhance the alkaline HER activities of catalysts based on 2D transition metal dichalcogenides (TMDs) (MoS2 and WS2). A series of ultrathin 2D-hybrids are synthesized via facile controllable growth of 3d metal (Ni, Co, Fe, Mn) hydroxides on the monolayer 2D-TMD nanosheets. The resultant Ni(OH)2 and Co(OH)2 hybridized ultrathin MoS2 and WS2 nanosheet catalysts exhibit significantly enhanced alkaline HER activity and stability compared to their bare counterparts. The combined theoretical and experimental studies confirm that the formation of the heterostructured boundaries by suitable hybridization of the TMD and 3d metal hydroxides is responsible for the improved alkaline HER activities because of the enhanced water dissociation step and lowers the corresponding kinetic energy barrier by the hybridized 3d metal hydroxides. (2) Nitrogen-coordinated iron atoms on carbon matrix (Fe-N-C) materials are the most active Pt-group-metal-free ORR catalysts but still suffering their low stability and relatively lower activity compared to platinum-based materials. In the second work, Fe and Ni dual sites atomically dispersed in hierarchically ordered macroporous carbon support (Fe-Ni/N-HOMC) was designed and successfully prepared. Isolated atomic Fe- N4 and Ni-N4 active sites were confirmed via various characterizations. The ORR activity and stability of Fe-Ni/N-HOMC in both acid and alkaline electrolyte were much higher than commercial Pt/C and the mono-Fe doping counterpart, which was among the state-of-the-art ORR electrocatalysts. In addition, this 3D ordered interconnected macroporous structure with abundant mesopores and micropores could greatly increase the accessible ORR active site and also enhance the mass transport during the ORR process. When employed as cathodes for PEMFC, we found the excellent ORR activity of Fe-Ni/N-HOMC was completely translated to the cathode in the fuel cell. (3) High-performance bifunctional electrocatalysts with ORR and OER activity is the key to developing efficient rechargeable Zn-air batteries. In the third work, a high-performance bifunctional electrocatalysts for both OER and ORR were synthesized via further hybridizing as-prepared Fe-Ni/N-HOMC with NiFe layer double hydroxides (LDHs). Layered double hydroxides (LDHs) have been reported to be promising OER electrocatalysts with ultrahigh OER performances. The as-synthesized new composites exhibited almost the same ORR activity as Fe-Ni/N-HOMC, revealing that hybridization of NiFe-LDHs would not deteriorate the initial ORR activity. Moreover, the remarkable enhancement of OER activity was observed after the hybridization, which was attributed to the strong coupling of uniformly dispersed small NiFe-LDH nanoparticles with the carbon substrate. The prototype Zn-air battery was assembled using these new composites, which displayed the ultralow voltage gap and long-term stability. (4) Compared with Fe-N-C or Co-N-C based ORR electrocatalysts, the Cu-nitrogen-carbon composites were attracted little attention. However, the natural multicopper oxidases (MCOs) enzymes, such as laccase, can serve as efficient ORR catalyst with almost no overpotential. Inspired by their tris-copper centers in MCO, one novel Cu-nitrogen-carbon composite (Cu SAs/N-CS) with atomic Cu coordination sites were synthesized via the pyrolysis of the Cu-involved metal-organic-framework. The copper contents in Cu SAs/N-CS reaches as high as 3.17 wt.%, and the average distances of adjacent copper sites was around only 3.1 Å. Due to the synergetic effect of abundant single atomic copper active sites with closer distance and ultrathin carbon nanosheet structure, Cu SAs/N-CS exhibited superior ORR activity exceeding commercial Pt/C catalyst, methanol tolerance, and long-term stability in both alkaline and neutral electrolyte. In summary, four kinds of new composites were successfully designed and prepared as high-performance electrocatalysts for HER, ORR and OER. Multi-dimensional heterostructures, atomic metal coordination sites and 3D hierarchically porous structure were designed and observed, which contributed greatly to improve activities of these composites. This thesis suggests several new viewpoints in the design of electrocatalysts based on earth-abundant materials: (i) offering new strategies for the preparation of novel 2D and 3D heterostructures as electrocatalysts; (ii) expanding methods for the synthesis of atomic metal coordination sites and evaluating their activities for ORR; (iii) evaluating the practical performances of achieved electrocatalysts in proton exchange membrane fuel cell and Zn-air battery; (iv) attempting to explain reaction mechanisms of some electrocatalysts by DFT calculation.

The rapid growing of electronic technologies as well as electric vehicles requires the development of new, higher energy and environmental friendly storage systems. In this scenario ideal candidates are the batteries systems and in particular those based on the electrochemical process of lithium, thanks to long calendar-life and to favorable design. However, although this technology is adequate for the consumer electronics market, it has some serious shortcomings when considering implementation in electric vehicles or in grid energy storage applications. In particular limiting factors are related to the low energy density of LiCoO2 cathodes and graphite anodes. Additionally, the use of Cu as current collector at the anode and also the increasing cost and reducing availability of Co push the research to the development of alternative chemistries exploiting materials environmental friendly, with higher energy density and reduced cost 1-3 . In this contribution, we present new strategies to improve the energy density, increase the safety level and reduce the cost of energy storage systems based on Li process. References (1) B. Scrosati, J. Garche, J. Power Sources. 195, 2419-2430, (2010). (2) Y. Yang, G. Zheng, Y. Cui, Energy Environ. Sci. 6, 1552-1558, (2013). (3) Whittingham, M. Chem. Rev. 104, 4271-4302, (2004).

The field of advanced batteries faces today two main challenges: development of power sources for electro-mobility (i.e., electrochemical propulsion) and development of storage technologies for load-leveling applications (i.e., large scale batteries). Our starting point in this presentation is state-of-the-art Li-ion batteries. Using carbonaceous anodes and lithiated transition metal cathodes with selected combinations of transition metals may offer very suitable batteries for full EVs. Ni rich Li[NiCoMn]O2, Mn and Li rich Li1+x[NiMnCo]1-xO2 cathode materials operating in the right potential windows can provide Li-ion batteries high enough energy density as needed for full electrochemical propulsion. Also, by combining Li-Ti-O anodes with LiMPO4 olivine cathodes it is possible to demonstrate very suitable battery systems for stationary large energy storage applications. We will review briefly the updated frontier of Li-ion battery technology. Despite the high capability of this battery technology, there are so many applications for power sources in modern life, what promote very strongly a search for more new battery systems. The use of sulfur cathodes in Li batteries can increase considerably their gravimetric energy density, however, the volumetric energy density of Li-sulfur battery systems is not advantageous compared to advanced Li ion batteries. The good news are that in recent years, we see a nice progress in developing durable composite sulfur cathodes. It seems that there are 3 main approaches: encapsulating sulfur in activated carbon matrices, the use of substrates to which the LiSn species formed by sulfur reduction adsorb very strongly and the use of composite cathodes with high loading of sulfur and semi-permeable membranes that avoid transport of LiSn species to the negative electrodes. There is intensive work on Li-oxygen systems. We see progress in development of electro-catalysis for these systems. We will demonstrate electro-catalytic electrodes in Li-oxygen cells, which anodic reactions (Li-peroxide oxidation and molecular oxygen evolution) occur at very low over-potential, that does not endanger the stability of the electrolyte solutions. We demonstrate also red-ox mediators in solutions that facilitate both ORR and OER. Despite the frustration from the slow progress made towards practical directions, it is important to continue investing efforts in Li-oxygen systems. The community should understand that a long-term research is still required in order to see practical horizons to Li-air battery systems. A main problem is the reactivity of all kinds of polar-aprotic solvents towards superoxide and peroxide species formed by oxygen reduction, in the presence of the super-electrophilic Li ions. The intensive work on both Li-S and Li-oxygen systems is connected to a renaissance in efforts to develop practical Li metal anodes for rechargeable batteries. However, intensive studies that were carried out during more than 3 decades, concluded more than 15 years ago that there is no way to cycle Li metal anodes in practical rechargeable Li battery systems. Even if dendrites formation is avoided, continuous detrimental reactions between the active metal and any type of relevant electrolyte solution is inevitable. We will examine briefly what are the chances to overcome the intrinsic problems in using Li metal anodes in practical rechargeable batteries. We may be able to suggest practical alternative anodes for non-aqueous batteries based on sulfur or oxygen cathodes. Discussing other options for “beyond Li-ion batteries” usually includes Na-ion and magnesium batteries. In fact, the plethora of relevant Na-ion insertion cathodes available today is a good surprise, especially since many of them demonstrate excellent kinetics. However, there is no way that Na-ion systems can rival Li-ion battery systems in terms of energy density. Hence, Na-ion systems may be relevant for large energy storage applications, that can benefit from the high abundance of Na in earth crust. However for such uses, demonstrating high stability during prolonged cycling is mandatory. Consequently, a major challenge in R&D of Na-ion batteries is to exhibit the durability required for load-leveling applications. Finally, we will mention the status of R&D of rechargeable Mg battery systems: excellent work was done so far on the anode-solutions part. Several families of electrolyte solutions with wide electrochemical windows, in which Mg anodes are fully reversible were demonstrated. We have not seen yet cathodes materials that function well in the solutions in which Mg anodes are fully reversible, except the low voltage/low capacity Chevrel phase cathode materials. Hence, these systems still require long term research work, especially towards high voltage/high capacity cathode materials. A main incentive to develop rechargeable Mg batteries may relate to advantages in safety and high volumetric energy density.

Electrochemically-rechargeable liquids (ERLs) are a relatively low-maturity energy-storage paradigm that offer many compelling attributes over gases (e.g., H2), solid materials (e.g., batteries), or more conventional liquid fuels [1]. ERLs can be comprised of a wide variety of active materials, which may include conventional liquid-organic hydrogen carriers (i.e., LOHCs, such as organics that are liquids at room temperature, like methylcyclohexane), as well as aqueous solutions (e.g., diluted alcohols) or dissolved solids (e.g., redox-flow-battery electrolytes) [2]. ERLs can be used to store both hydrogen and electrical energy using different cell configurations [1], which includes rechargeable liquid fuel cell (RLFC) systems for long-duration energy storage (LDES) applications [3]. Since hydrogen and electricity are expected to be the two major energy carriers of the low-carbon-emissions future, this energy-conversion flexibility makes the ERL concept highly attractive; especially since neither H2 or electricity can be stored as an ambient-temperature liquid, which is the ideal energy-carrier medium. While ERLs are not a new concept, significant improvements are required to make this technology commercially viable. The first part of this invited talk will provide an overview of multiple concepts that can be used to overcome the key technical hurdles to developing competitive ERL-based energy-storage systems. This includes focusing on electrochemical reactions with a relatively low number of electrons per molecule (≤ 4e-), which can still yield attractive energy densities, as shown with some examples in Fig. 1. For example, an ERL with an energy density of 500 Wh/kg can enable a complete energy-storage system that is on par with a state-of-the-art (SOA) Li-ion battery systems, even with modest ERL-conversion cell stack performance (e.g., ½ of a SOA H2/air PEMFC stack) [1].The second part of this invited talk shall focus on using formate/bicarbonate salts (FBS) as an ERL. The FBS cycle has been the subject of growing research since these solutions have an attractive set of key metrics for an ideal energy carrier [4]. Strictly speaking, formate salts are not H2 carriers, they are actually electron-storage compounds, since hydrogenating HCO3 - to HCO2 - does not add hydrogen to the compound, it simply changes the oxidation state of carbon from +4 to +2. Both thermochemical and electrochemical conversions of FBS may be used; however, the electrochemical approach offers significant benefits, since it can directly use or produce electrical energy, operates at milder conditions (i.e., low temperature and pressure), and is not subject to limitations that result from equilibrium reactions since the H2 produced or consumed is separated from the FBS solution by a membrane in the FBS electrolyzer. The key to achieving steady-state conversions of aqueous bicarbonates to formates is to maintain a near-neutral pH to ensure the desired equilibrium of CO2(aq), HCO3 - (aq), and CO3 2- (aq) species, which can be achieved via careful selection of both cell materials and operating conditions [5-7]. References M. L. Perry, “Electrochemically-Rechargeable Liquids in highly Flexible Energy Storage Systems,” ECS Trans., 104, 23 (2021).M. L. Perry and Z. Yang, “Rechargeable-Liquid Fuel Cells with a Novel Recharging Method: Exploratory Results with IPA and VII/VIII Solutions,” J. Electrochem. Soc., 166, A3045 (2019).M. L. Perry, “Rechargeable Liquid Fuel Cell Systems for Long-Duration Energy Storage Applications,” Invited for Symposium A04: Large Scale Energy Storage 16, 247th ECS Meeting, (2025).O. Gutiérrez, T. Autry et.al., “Using earth abundant materials for long duration energy storage: electro-chemical and thermos—chemical cycling of bicarbonate/formate,” Green Chem., 25, 4222 (2023).M. L. Perry, “Rechargeable liquid fuel cell system and method,” U.S. Patent Application 2022/0223895.A. H. Quinn, “Exploring chemical speciation and catalyst behavior for the electrochemical interconversion of formate and bicarbonate,” Electrochem. Soc. Interface, 32 (2023).J. Li, et.al., “A carbon-efficient bicarbonate electrolyzer,” Cell Reports Physical Science, 4 (2023).M. Sadakiyo, S. Hata, X. Cui, and M. Yamauchi, “Electrochemical Production of Glycolic Acid from Oxalic Acid Using a Polymer Electrolyte Alcohol Electrosynthesis Cell Containing a Porous TiO2 Catalyst,” Scientific Reports, 7, 17032 (2017). Figure 1. The cell potential of some electrochemically-rechargeable liquid (ERL) options paired with oxygen multiplied by the number of electrons per molecule (≤ 4e-) vs. practical concentrations of some candidate ERL actives. Some alcohols (squares) and redox couples (diamond) were demonstrated in ERL-conversion cells [2]. The glycolic-/oxalic-acid couple (triangle labeled “GA/OA”) was reported on in 2017 [8]. Two different alkali-metal bicarbonate options are shown, along with potassium formate. Gravimetric energy densities of ≈ 250-700 Wh/kg can be achieved with formate/bicarbonate options, and even higher energy densities are possible if the discharge products (i.e., MHCO3) are stored as two-phase solutions in the tank (i.e., limited by formate, not bicarbonate solubility). Figure 1

The World's energy consumption has increased drastically over the past several decades, particularly driven by increasing population and economic activities as well as rising living standards with technological advancements. Since the industrial revolution, fossil fuels have been the major source of energy productions, which is today shown as the primary cause of the ongoing climate change and associated environmental challenges in threatening the existence of many living species and human life and comfort. According to the statistics provided by International Energy Agency (IEA),1 the global energy supply was 14 282 Mtoe in 2018 that is 115% higher than that of the value for 1973. Fossil fuels, such as natural gas, coal and oil are still playing a critical role and covering more than 80% of global energy demands. The concerns associated with global warming and depletion of energy sources have been directing the attention to renewable and environmentally-benign energy solutions. However, efficient, affordable, and nature-friendly energy storage systems are the key to using renewable energy sources effectively. In this study, a comprehensive literature search is conducted to study and bibliografically evalute Canada's energy storage research and development activities over the last five decades. The present study intends to present the cumulative picture on energy storage reseach and development efforts and assess how universities, research institutes and funding agencies have contributed to this particular field. The literature search compiles a total of fifty-year data on energy storage-related research and development activities conducted in Canada. The number of conducted studies associated with energy storage regarding research articles, books, research projects, dissertations, and patents is presented in the period from 1971 to 2021. Furthermore, the Canadian institutes are ranked based on their scholarly ouputs and publications to indicate the most productive ones in the field of energy storage based on the data presented in the literature sources. Energy storage is described as the capture of harvested energy for later use to maintain the balance fluctuations between energy demand and supply. As the world moves towards a low-carbon economy, energy storage systems are exepcted to even play a more critical role in extracting more energy from renewable resources.10 The intermittent characteristic of renewable resources, specifically solar and wind, is one of the major challenges ahead of a reliable and steady renewable energy supply. This can be avoided by storing excess energy to re-use when the renewable resources are not sufficient or unavailable. Energy storage systems can be categorized in different ways in regards to the form of converted and stored energy. Figure 1 presents an overview of energy storage system categories which are considered in this study. It is important to note that chemical energy storage allows to storage and transportation of large amounts of energy for long distances with minimal self-discharge rates, which is crucial for the distribution and effective use of renewable energy resources. Figure 2 presents the energy density of various chemical fuels and batteries. Despite possessing high energy density, environmental concerns associated with the production and consumption of fossil-based chemical fuels, e.g. diesel, gasoline or natural gas, should be adrressed. In regards to nature-friendly chemical energy storage, particularly power-to-gas chemical storage, hydrogen is attracting favorable attention nowadays. In this regard, hydrogen appears to be the lightest and most abundant chemical element in the universe, but is not available freely (by itself). However, it occurs naturally within a compound such as water (H2O); therefore, it is an intermediate energy form. Excess electricity from renewables can be utilized in hydrogen production processes, i.e. electrolysis of water, to store energy in chemical form. Power-to-hydrogen chemical energy storage is a unique and clean method, and it can be compatible with electrochemical storage since hydrogen possesses much greater energy content. One of the major challenges with hydrogen is the low calorific value per unit of volume (MJ/m3) due to its low density. This can be avoided by deploying alternative hydrogen carriers, such as ammonia. Liquefaction at atmospheric conditions, high hydrogen atom content and high energy density characteristics make ammonia a favorable medium for storage and transportation of energy. It is further to note that batteries and capacitors are devices allowing electrochemical storage of electricity. The potential energy is stored in chemical form in batteries, while capacitors are expected to store their potential energy in the form of an electric field.14 Batteries are thus most commonly used and matured options that propose high energy densities and voltages. Lithium-ion (Li-ion), sodium-sulphur (NaS), nickel-cadmium (NiCd), lead acid (Pb-acid), lead-carbon batteries, zebra batteries (Na-NiCl2) and flow batteries are the existing battery types used in various applications. Due to their high specific energy (per unit weight) and high specific energy (per unit volume), lithium batteries attract considerable attention in electrical energy storage. Capacitors can be classified as electrostatic capacitors, electrolytic capacitors, and electrochemical capacitors, among which electrochemical, so-called supercapacitors, promote the highest capacitance per unit of volume owing to a porous structure 15. As a mechanical energy storage method, pumped hydro accounts for more than 95% of the global installed energy storage capacity.15 The main advantage of mechanical energy storage is to readily deliver energy. The method is easy to adapt for conversion and storage of energy from various sourcessuch as water current, wave, or tidal. Pumped hydro, compressed air, and flywheel are the commonly practiced mechanical energy storage methods. Pumped hydro and compressed air are bound to specific geographical characteristics, which is the main restriction for the implementation of these energy storage methods. A flywheel stores the energy obtained from a rotor mass spinning at very high speeds as kinetic energy. The stored kinetic energy can be later used to produce electricity by altering the angular velocity of the flywheel through a decelerating torque and using an electric motor in reverse 16. Despite of being non-suitable for long-term energy storage, flywheels offer favorable advantages, that is, long-life spin, high energy densities and low maintenance costs, and fast charging.17 Thermal energy storage (TES) systems are effective systems to store heat in a reservoir for a period of time (defined or undefined) for later use, that is, space heating and cooling, electricity production, hot water. If the reservoir temperature is kept under the atmospheric temperature, the storage process is called cold thermal energy storage.18 Operating temperature range, capacity requirements, charging and discharging requirements are some of important parameters when choosing an appropriate TES system for a desired application. Since the major proportion of produced and consumed energy is heat around the world, TES systems carries a significant weight regarding the development of effective energy systems . Furthermore, energy losses from the systems commonly occur in the form of heat. Decreasing losses via further utilizing from waste energy is one of many way to mitigate environmental impacts, which can be accomplished by implementing TES systems in a cost effective manner. In the current study, an overview of Canada's energy storage related studies from 1971 to 2021 is presented. The scope of this study is to present the contributions of Canadian universities, research institutes and funders to energy storage research and development efforts over the last five decades. The keywords and methodology that are used for the literature search are depicted in Figure 3. The collected and compiled data for the corresponding fields are presented in figures, and results are discussed in the following sections. In this study, an online literature search is conducted on Canada's energy storage related studies over the last five decades. The current section presents collected and compiled data in charts. The findings of the conducted study are discussed in detail. The most productive institutes of Canada regarding conducting or sponsoring energy storage-related studies are presented. The documents associated with energy storage in all subject areas are presented in Figure 4. In this regard, the highest number of energy storage-related studies were conducted in the subject area of engineering in Canada from 1971 to 2021. The fields of energy and chemistry appear as the other two major subject areas in which high number of energy storage research was conducted. While compiling data, attention has been paid to any potential field conflicts concerning the multi attribution of interdisciplinary publications. Therefore, it should be noticed that chemistry may have an impact on the subject areas of biochemistry, genetics, and molecular biology. The same impact of engineering could be seen on the subject area of energy. The data collected and analysed for comparative evaluation reveals that the Canadian institutes have produced 37 386 energy storage-related academic research publications over the last 50-year period. In this regard, Figure 5A presents the breakdown of energy storage-related publications affiliated to Canada in the corresponding material types in accordance with the publication years. Figure 5A shows that studies in this field consistently increases every year. Consequently, the year 2020 appears as the most productive one in this regard as of April 2021. In the light of this trendline, predicting that the year 2021 will be more productive than 2020 would not be wrong. Figure 5B has been prepared as a heat map to show Canada's provinces where energy storage-related studies were conducted over the last 50 years. In this regard, Ontario appears as the most productive province of Canada in terms of scholarly publications. However, one has to keep in mind that Ontario has the highest number of contributing institutes/universities compared to the rest of the provinces in Canada. Figure 6 presents the breakdown of the number of energy storage-related books, book chapters, and editorials in accordance with publication years in Canada. The year 2018 was the most productive year of Canada by producing 200 documents in the corresponding classification. The other important point that should be pinned in the figure is the year 2005. Compared to the previous year, almost five times more energy storage-related books were published in 2005. Compared to 2019, the number of published books decreased almost by half in 2020. The impact of COVID-19 is recognized as one of numerous reasons behind this result. The number of energy storage-related dissertations completed in Canada over the last five decades is primarily searched through and collected from Library and Archives Canada. The search results are, in this regard, presented in Figure 7. It can be noted that the data presented in Figure 7 is based on the number of energy storage-related theses available in the library; and thus, the results are subject to change in accordance with instantaneous new data entry to the library. As of April 2021, there are 626 energy storage-related MSc and PhD theses/dissertations entered in the online system of Library and Archives Canada. The highest number of theses/dissertations was recorded in the year of 2013 with a value of 62. Based on data collected from the website of Canadian Intellectual Property Office, the number of energy storage-related patents of Canada is 11 719 for the last 50 years. The corresponding results are presented Figure 8. According to this, the year of 2018 appeared to be the Canada's most productive year in terms of patents registered under the title of energy storage. Canada is blessed with institutions that have been supporting energy storage-related research and developments by providing funds. Over the evaluated period of 50 years, the Natural Sciences and Engineering Research Council of Canada (NSERC) appears as the major funding agency for Canada's energy storage related research, development, partnership, strategic innovation and commercialization efforts and has supported more than 8500 projects in the field of energy storage. A total number of projects that have been funded by Canadian institutes have become 18021 from 1971 to 2021. It is most likely to observe a major increase in the number of projects by the impact of the recent hydrogen strategic plan of Canada. Being an excellent energy storage medium is one of many advantages of hydrogen. Therefore, there is a significant correlation in between hydrogen and energy storage research efforts. The subject matter report is already named as call-to-action for green hydrogen transition for the energy sector. In the report, the importance of dedicating more domestic resources to green hydrogen efforts to achieve the targets by 2050 is emphasized clearly (Figure 9). The development and implementation efforts of effective, affordable, and nature-friendly energy storage systems are recognized as a key requirement in achieving a green energy transition. In this regard, Canada intends to be the country leading and inspiring many others. Figure 10 shows the a number of Canadian institutes/universities that have produced more than 100 scholarly publications on energy storage under the subject area of energy. According to this, the total number of such scholarly publications has been 9125 over the past five decades. The results clearly show that there are two universities, such as University of Waterloo with 809 publications and Ontario Tech. University (formerly University of Ontario Institute of Technology) with 697 publications, leading in this particular area. University of Waterloo appears as the most productive Canadian university with a total number of 809 publications while Ontario Tech. University, which is one of the Canada's youngest universities, follows with a total number of 697 publications. The specific affiliations in the publications show that the researchers working in the productive environment of Clean Energy Research Laboratory (CERL) at Ontario Tech. have played a major role in this achievement. The data that support the findings of this study are available in Scopus, Library and Archives Canada and Canadian Intellectual Property Office with the reference number of [17], [18], and [19], respectively. These data were derived from the following resources available in the public domain: https://www.scopus.com/search/form.uri?display=basic&zone=header&origin, https://www.bac-lac.gc.ca/eng/services/theses/Pages/search.aspx, https://www.ic.gc.ca/opic-cipo/cpd/eng/search/basic.html?wt_src=cipo-patent-main.

MXenes: An exotic material for hybrid supercapacitors and rechargeable batteries

Fundamentals and key components of sodium-ion batteries: Challenges and future perspectives

Global environmental concerns and the ever increasing need of energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Distributed electricity generation is a suitable option for sustainable development thanks to the load management benefits and the opportunity to provide electricity to remote areas. Solar energy being easy to harness, non-polluting and never ending is one of the best renewable energy sources for electricity generation in present and future time. Due to the random and intermittent nature of solar source, PV plants require the adoption of an energy storage and management system to compensate fluctuations and to meet the energy demand during night hours. This paper presents an efficient, economic and technical model for the design of a MPPT based grid connected PV with battery storage and management system. This system satisfies the energy demand through the PV based battery energy storage system. The aim is to present PV-BES system design and management strategy to maximize the system performance and economic profitability. PV-BES (photovoltaic based battery energy storage) system is operated in different modes to verify the system feasibility. In case of excess energy (mode 1), Li-ion batteries are charged using CC-CV mechanism effectively controlled by fuzzy logic based PID control system whereas during the time of insufficient power from PV system (mode 2), batteries are used as backup to compensate the power shortage at load and likewise other modes for different scenarios. This operational mode change in PV-BES system is implemented by State flow chart technique based on SOC, DC bus voltages and solar Irradiance. Performance of the proposed PV-BES system is verified by some simulations study. Simulation results showed that proposed system can overcome the disturbance of external environmental changes, and controls the energy flow in efficient and economical way.

1. Introduction Conventional Li rechargeable battery system contains transition metal based electrodes. These conventional transition metal based electrodes have severe problems such as scarcity of resources, potentially high cost, and toxicity. With respect to the high sustainability for the next-generation energy storage system, another candidate of electrode materials is needed. Due to high sustainability and chemical tunability, organic battery system holds a great potential in next generation energy storage system. In order to develop these new battery system, understanding factors affecting a performance should have priority than others. It is well-known that the LUMO level of organic compounds has a linear correlation with redox voltage in rechargeable batteries (Figure 2). 6 However, it has been recently reported additional factors affecting redox voltage of organic electrode materials. 4,5 This research is focusing on categorization of factors affecting a voltage, especially, on cation-substituents interaction. With many references and our experiment results, it is convinced that voltage of organic materials is determined by several factors. Additional substituent effect and cation species effect should be considered for predicting an exact voltage behavior with molecular tuning. 2. Results and Discussion The target species based on terephthalate are shown in Figure 3. Terephthalate is one of the simplest form in organic electrode materials. Therefore, another effect can be reduced to study cation-substituent effect. The plot of LUMO level vs. discharge voltage of target species is shown in Figure 4. Four types of cathode materials have same redox center based on terephthalate already reported by J.-M. Tarascon group.7 Tendency of almost species follows conventional rules which of correlation between LUMO level and discharge voltage, but some species having special substituent shows different behavior. Table 1. LUMO level vs. Experimental voltage Species Na2H2TP Na2TP Na2DMTP Na2MeO2TP Li cell (vs. Li/Li+) 0.93 0.84 0.81 0.9 Na cell (vs. Na/Na+) 0.55 0.59 0.54 0.38 LUMO (eV) -1.58 -1.41 -1.4 -1.34 3. Concluding remarks Firstly, some special substituent gives a big effect to determine a voltage. Methoxy group (-OCH3) is an electron-donating substituent. With LUMO level, voltage should be lower than others. But, in Li cell system, it does not follow. Interaction between lithium and oxygen from methoxy group make a stable discharge form. On the other hand, in Na cell system, sodium ion has a bigger size than lithium ion. So, interaction between oxygen cannot be occurred because of steric strain. Secondly, with LUMO level, voltage of Na2H­2TP should be higher than Na2TP. But, in Na cell system, it is not. Steric strain affect to the voltage of Na2H2TP. In our conclusion, lithium ion size is negligible affecting to the voltage but sodium ion size starts to affect the lowering of voltage in Na2H2TP electrode material. It is expected that competition between factors affecting a voltage of organic electrode materials. In summary, cation-substituent interaction should be considered to predict an exact voltage. It is important for tuning an organic electrode material to make an appropriate voltage in our use. More additional factors may exist and it is needed to categorize them. The more understanding of factors affecting to a voltage gathered, then more accurate prediction and molecular tuning can be possible. 4.

Batteries are commonly used for energy storage in renewable energy systems. A microgrid is a small, independent or grid-connected energy system that enables the coupling and management of energy sources (photovoltaic, wind, grid), energy storage systems (batteries, supercapacitors) and different loads (water heating, electric car, etc.). Lithium-ion technology is today the most widely distributed battery technology for stationary energy storage. Unfortunately, the lifetime of state-of-the-art battery systems is considered still too low to make energy storage commercially viable. Aging on the cell level is a complex process depending strongly on operating conditions [1]. On the battery level, additional aging drivers can result from unbalanced cells or cells with different capacity. In the present study we investigate the aging behavior of a stationary storage system consisting of two lithium-ion battery systems embedded in a microgrid consisting of renewable energy sources (photovoltaic panels and wind turbine), real electrical loads (electric car, offices) and load simulators [2]. 28 commercial 180 Ah high-energy LFP/graphite prismatic cells were assembled into two 8 kWh stacks with different architectures, that is, serial and parallel connection of the cells. The individual cells were characterized under laboratory conditions before system assembly, and selection of the cells was carried out, providing cells of similar capacity to the serial configuration and cells with a large capacity spread to the parallel system. Thus, the influence of the stack architecture both on performance and on aging could be investigated. The stacks were operated in the microgrid, providing both stacks strictly with the same power demand. In regular intervals the individual cells were disassembled from the system to perform laboratory checkups that consisted of capacity, internal resistance and electrochemical impedance measurements. The capacity loss of individual cells and stacks was quantified by laboratory checkups and microgrid operation data, respectively. In parallel, two nominally identical cells were aged under laboratory conditions by continuous full cycling (100 % DOD) for a total of 1,200 cycles. These cells were investigated by the same checkups as the microgrid cells, performed at the beginning of life and at certain cycle times. By combining the laboratory and microgrid operation data, this study allows the comparison of stack-level aging as function of stack architecture and the comparison of cell-level aging under laboratory cyclic aging. Acknowledgements: The authors acknowledge the Federal Ministry of Education and Research (BMBF) for funding this work as part of the STABIL project (13FH004PX5). Reference s : [1] B. Weißhar and W. G. Bessler, “Model-based lifetime prediction of an LFP/graphite lithium-ion battery in a stationary photovoltaic battery system”, J. Energy Storage 14, 179-191 (2017). [2] D. Dongol, T. Feldmann, and E. Bollin, “An overview to the concept of smart coupling and battery management for grid connected photovoltaic system”, J. Electronic Science and Technology 13, 367-372 (2015). Figure 1

Introduction Rechargeable battery systems with different transporting ions are an alternative choice to Li batteries that can expand and diversify the existing energy storage market. Magnesium batteries are the most promising technology to achieve substantially greater energy density than Li-ion batteries, due to their divalent nature (two electron redox couple). Furthermore, because of its “green” character Mg is environmentally friendly, with high natural abundance in the Earth’s crust (13.9% as compared to 0.0007 % for Li), and atmospheric stability.The current quest for new cathode materials for rechargeable Mg batteries is focused on intercalation compounds exhibiting high working potential and capacity1. When transporting ions have much larger diameter or charge than the host metal ion, segregation of transporting and host metal ions in the crystalline structure is forseable. In this case deintercalation will lead to the collapse of the crystalline structure and breaking of electric conductance. Therefore, our approach to achieving magnesium intercalation is to use nanoscale material that have adjustable d spacing and two-dimensional layered structure that can to control polarizability of Mg2+ions and accommodate large charge/volume changes.Nanostructured electrode materials represent one of the most attractive strategies to dramatically enhance battery performance. Short diffusion length associated with the nanosized dimensions effectively reduces the distance that ions and electrons must travel during cycling. Their large surface area increases the contact area between electrode and electrolyte and hence the number of active sites for electrode reactions, which in turn reduces electrode polarization loss and improves power density, energy efficiency, and usable energy.Nanostructured bilayered V2O5 is highly efficient 3 V cathode material for ambient temperature sodium ion batteries2. It shows superb performance: theoretical reversible capacity for Na2V2O5 stochiometry of 250 mAh/g, excellent rate capability and cycle life, as well as high energy and power densities. Preliminary results show that it is possible to extend the reversible ion-insertion chemistry of nanostructured layered V2O5 beyond lithium and larger in size Na+ ions to those with higher charge: Mg2+ions. Results and Discussion As–prepared nanostructured bilayered V2O5 cathode is synthesized in the charged state. To provide source enrichment, prior to assembling into full Mg-ion cell, it was necessary to pre-condition V2O5 cathode (intercalate with Mg2+ ions). Half-cells were discharged galvanostatically at 20mA down to and 0.01 V versus Mg/ Mg2+, respectively, using an automated Maccor battery tester at ambient temperature. As shown in Figure 1., upon electrochemical pre-condition (Mg-ion half cell) the X-ray edge energy for vanadium is shifted toward the lower energy as a consequence of a vanadium reduction due to Mg intercalation. Pre-edge peak is proportional to the octahedral symmetry of the vanadium sites and its decrease upon transporting ion intercalation is due to modification of vanadium local environment into more ordered, symmetric structure. Based on the main-edge peak position and comparison with Na-ion half cell we estimate 1 Mg is incorporated in the V2O5 structure (V5+ is reduced to V4+). It was previously shown that the V5+ was reduced to V4+ when discharged to 1.5V versus Na/ Na+ (Na-ion half cell)2. As a result of this electrochemical pre-condition we created Mg-rich V2O5 cathodes that were able to provide source of Mg-ions in full-cell. Furthermore, we employed HRTEM, X-Ray fluorescence (XRF) imaging and classical molecular dynamics simulations to understand the role of environment in the intercalation processes of Mg-ions into V2O5cathode. Conclusions We have developed high-voltage nanostructured V2O5 cathode for Mg-ion rechargeable batteries that can operate in commercial electrolytes. Our results emphasize the importance of tailoring nanoarchitecture of electrode materials and open up new opportunities for rechargeable Mg batteries. In the near future, we plan using the combined experimental and theoretical approach to guide our efforts to increase the Mg enrichment to reach the ultimate goal of inserting 2 Mg-ions/V2O5. Acknowledgement. This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by DOE, Office of Science, Basic Energy Science (BES). Use of the Center for Nanoscale Materials was supported by the U. S. Department of Energy, Office of Science, and Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. References (1) On the Way to Rechargeable Mg Batteries: The Challenge of New Cathode Materials, E. Levi, Y. Gofer, and D. Aurbach, Chem. Mater. 2010, 22, 860–868.(2) Vanadium Oxide Electrodes for Rechargeable Sodium-Ion Batteries, Sanja Tepavcevic, Hui Xiong, Vojislav R. Stamenkovic, Xiaobing Zuo, Mahalingam Balasubramanian, Vitali B. Prakapenka, Christopher S. Johnson, and Tijana Rajh, Nanostructured Bilayered ACS Nano, 2012, 6 (1), 530–538.

Renewable distributed power sources such as wind power and photovoltaic power generation are connected to the power grid, which will bring problems such as increased network loss and reduced power quality. In this paper, a two-layer optimization model for energy storage systems is proposed under large-scale new energy access, and the coupling effects of energy storage planning and operation are considered comprehensively. In the upper layer model, energy storage planning is considered, with the location and capacity of energy storage configuration being the decision variables and the planning cost of the energy storage system being the objective function. The lower layer considers the economy and stability of the grid when the energy storage system is operating, with the output of the energy storage system at each moment as the decision variable and the grid vulnerability, active network loss, and power purchase cost as the objective function. The improved IEEE33 node system has been selected for simulation verification. The results show that the proposed model calculates the optimal capacity configurations of wind power combined energy storage as 0.919 and 0.820 MWh, respectively, and the model can obtain a reasonable energy storage configuration scheme and, in comparing the economic indicators under different scenarios, can obtain the dual storage configuration as the best scheme for the simulation system.