As the world decarbonizes the energy systems, energy storage is an important pillar that cannot be ignored. Renewable energy sources are intermittent and non-flexible. Therefore, energy needs to be stored for shorter and longer periods. Since most renewable energy sources provide electricity, chemical battery storage is the most obvious first choice for storage.

And indeed, for short- and medium-term storage, chemical battery storage is economically feasible. However, the current reigning technology, the lithium-ion battery, is far too expensive for world-wide deployment for grid-scale storage. This comes down to material cost, which is connected to resource abundancy. Lithium, nickel, cobalt and other metals are too expensive. One should also not forget that their concentration in only a few places on Earth, makes for a weak supply chain.

New battery chemistries need to be found, that are solely based on abundant and/or renewable materials. Sodium, magnesium, iron, zinc and aluminum are metals that could replace lithium in batteries, while expensive transition metal oxides might be replaced by easily synthesized organic molecules. This thesis explores a few examples of materials that could be used in magnesium batteries.

In chapter 2 perylene diimides are introduced. These versatile and robust molecules have shown promise as battery electrode material. This chapter describes a new and mild synthesis route towards them, the mild imidization. Traditionally perylene diimide synthesis requires harsh conditions, high temperature and corrosive solvents. In this new approach, one only needs the biocompatible solvent DMSO and potassium carbonate at 100 oC. Also, a room temperature variant of the procedure has been developed that uses DBU as a base. The resulting products are also easily obtained through a simple precipitation in water, without the need for purification. The reaction kinetics and substrate scope are also investigated.

Perylene diamic acids, a sister compound to perylene diimides, are described in chapter 3. These are the intermediates in the imide synthesis. When the reaction is done with a secondary amine, the imide cannot be formed, and one is left with a water-soluble salt. The high solubility in water makes this class of molecules stand out in the perylene family. When diamic acids are exposed to acid, the reaction is undone and perylene dianhydride is formed. This compound is very insoluble in water. Chapter 3 shows that very controlled acidification can yield highly colored hydrogels. The gels are characterized by different techniques. The hydrogels might be of interest to material scientists, since they undergo uniform shrinkage over time. In their soluble form, perylene diamic acids are of interest as water-soluble compound in aqueous batteries.

The perylene family is known to be ‘redox tunable’. By changing the side groups of the perylene, one can change the redox potential at which it reacts, which determines the potential at which a battery operates. Chapter 4 looks into a new way to gain more control over the substitution of perylene tetraesters, by making a dibromo-dichloro perylene tetraester. In theory, this gives more control over the substitution pattern compared to tetrachloro and tetrabromo derivatives. This chapter investigates the kinetics of substitution reactions.

Chapter 5 presents a new aqueous polymer electrolyte for magnesium batteries, magnesium alginate. Alginate is a biopolymer that is harvested from algae. It is a polysaccharide of two monomers that both contain carboxylate groups. The difference between the monomers is only the spatial orientation of the carboxylate group. When an alginate solution is mixed with a solution that contains a multivalent cation, it will form a hydrogel. The carboxylate group from crosslinks with the cations, making a covalent-link hydrogel. Magnesium ions, two plus charged, are an exception, judged on the macroscale, they do not form a hydrogel. However, it is known that magnesium makes microscopic instable hydrogels that constantly form and break apart. From this, we can say that although magnesium is mobile in the solution, it is still heavily associated with the alginate backbone, and this is an indication that this electrolyte can act as a ‘water-in-salt’ electrolyte. Chapter 5 shows that magnesium alginate can have good ionic conductivity, even at very low water content. After some cycling, a black layer forms on the magnesium electrodes. This layer enhances the stability of magnesium in water.

Alginate hydrogels can also be used as matrices to encapsulate transition metal cations. Chapter 6 brings a new approach to make a ‘simple’ manganese-iron battery. By encapsulating manganese(II) on one electrode and iron(III) in alginate, we were able to cycle this simple ion pair multiple times. This material might have applications in semi-solid flow battery.

Recent studies emphasise the importance of assessing battery degradation under real operational conditions instead of under laboratory-controlled, often isolated, accelerated ageing conditions. Therefore, this thesis investigates degradation in a grid-scale LFP/graphite battery energy storage system (BESS) subjected to highly dynamic real-world load profiles. Degradation over two years was characterised by a 10% increase in internal resistance and a 9% loss in lithium inventory (LLI), through the first method of data-driven ageing analysis. Key indicators supporting this include internal resistance trends, quasi-constant voltage segments, Tafel-like slopes, and voltage relaxation behaviour.

Currently, BESS owners have to rely on annual warranty checks set by the BESS suppliers and checked by the suppliers through annual self-conducted capacity tests, while system owners often lack insight into internal degradation processes. This highlights the need for independent analysis and improved diagnostic tools.

To quantify degradation, both empirical equivalent circuit models (ECMs) and physics-based models (SPM, SPMe, DFN) were applied. SPMe and DFN show good agreement with measured voltage responses under constant power capacity test simulations. A SEI growth model was fitted to explain calendar ageing, reproducing the observed trends in resistance and LLI, and confirming the assumption of SEI growth as the dominant ageing mechanism. The ageing behaviour showed strong SOC dependence. This work demonstrates how combining data-driven qualitative analysis with empirical and electrochemical modelling enables tracking of cell-level degradation in real-world BESS.

Long-duration energy storage plays a vital role in energy systems with large amounts of renewable power. Its value is highly dependent on the dynamics of the market in which it operates and on its ability to store energy efficiently over time. This thesis investigates how operational flexibility and market volatility influence the performance of an integrated storage system that combines Compressed Air Energy Storage, Thermal Energy Storage, and reversible Solid Oxide Electrolysis Cells. The analysis is based on synthetic day-ahead prices representative of the market behavior of 2020-2024. A numerical framework is developed that links detailed physical models of the three storage assets to a stochastic dynamic programming controller formulated as a Markov Decision Process. The generated price signals vary in one measure of volatility, the chance of a price spike. The operational flexibility of the system is expressed in three ways: the duration of a process, the limits of power transfer between technologies, and the ability to trade multiple types of energy. A factorial study of 32 scenarios explores the effects of process duration, internal power limits, market accessibility, and probability of a price spike.

The results show that annual revenue increases consistently with higher spike probability, demonstrat- ing that the value of long-term energy increases with wider intertemporal spreads. Shorter process durations allow quicker reactions to price changes, increasing both profit and variability. Expanding access to the thermal and hydrogen markets improves revenue across all scenarios by expanding fea- sible dispatch options. Electricity trading remains the dominant operation mode at the assumed thermal and hydrogen price levels. The framework ensures that all energy flows are physically consistent, but does not yet include degradation effects, hydrogen leakage, or partial-load performance. In conclusion, integrated storage of multiple types of energy gains the most from operational agility and broad market access. Furthermore, increasing the transfer of power from and to storage facilities, without increasing the corresponding storage capacities, can decrease the overall performance of such an integrated system. Future research should include component degradation and evaluate the model against both real market data and increase in seasonal volatility of prices.

The use of batteries as an energy carrier has increased enormously in the last decade due to the transition to sustainable energy sources. The rechargeable lithium ion battery with its high energy density is the most commonly used solution for both mobility purposes and stationary energy storage systems. The disadvantages of lithium give reason to look for alternative solutions, such as the Na ion and the Mg ion battery, collectively called metal-ion batteries. These developments require advanced research methods and measurement techniques. In this thesis, two measurement techniques are examined and expanded with new possibilities and insights, expanding the range of measurement techniques for research into metal-ion batteries.

In Chapter 2, new methods and techniques are Investigated to perform advanced measurements on the surface of electrode materials with an Atomic Force Microscope (AFM). The use of scanning probe techniques has been introduced in the last decade in battery research. Until now, Scanning probe microscopy techniques are used to determine surface properties where the moving probe makes full or partial contact with the surface to be examined and the probe as a measuring instrument has as little influence as possible on the surface to be examined during these measurements. However, for electrochemical research it may be desirable for the probe to make an active contribution to the process to be investigated. Therefore, it was examined whether the probe can be provided with a small amount of lithium, so that it becomes part of the electro-chemical process. An Atomic Force Microscope (AFM) is combined with a special designed glovebox system and coupled to a Galvanostat/Potentiostat to allow measurements on electrochemical properties. An open cell design with electrical contacts makes it possible to reach the electrode surface with the cantilever so as to perform measurements during battery operation.

A combined AFM-Scanning Electro-Chemical Microscopy (AFM-SECM) approach makes it possible to simultaneously obtain topological information and electrochemical activity. Several methods have been explored to provide the probe tip with a small amount of lithium. The "wet methods" that use liquid electrolyte appear to have significant drawbacks compared to dry methods, in which no electrolyte is used. Two dry methods were found to be best applicable, with one method applying metallic lithium to the tip and the second method forming an alloy with the silicon of the tip. The amount of lithium applied to the tip was measured by determining the shift of the resonance frequency which makes it possible to follow the lithiation process. A Finite Element Method (FEM)-based probe model has been used to simulate this shift due to mass change.

The AFM-Galvanostat/Potentiostat set-up is used to perform electrochemical measurements. Initial measurements with lithiated probes show that we are able to follow ion currents between tip and sample and perform an electrochemical impedance analysis in absence of an interfering Redox-probe, a so called non-faradaic measurement. The active probe method developed in this way can be extended to techniques in which AFM measurements can be combined with mapping electrochemical processes with a spatial resolution of less than 100 nanometer.

In chapter 3 Positron Annihilation Doppler Broadening Spectroscopy (DBPAS) is presented as a powerful method to analyse the origin and development of defect processes in porous silicon structures. Silicon is a promising negative electrode material due to it's high capacity. The main drawback is the extreme expansion when alloying with lithium. The volume changes cause cracks in the electrode material, resulting in accelerated degradation. Several prepared anodes were lithiated (discharged against Li+/Li) and de-lithiated (charged) with different capacities followed by a distinct treatment procedure and an analysis using the Delft Variable Energy Positron Beam. The results presented here show that we can distinguish two different processes attributed to (1) structural changes in silicon as a result of the alloying process, and (2) the formation of defects that initiate degradation of the material. The limit at which the porous material can be used for at least the first two cycles without the occurrence of damage can thus be accurately determined by using the DBPAS technique.

The long-term performance and degradation of porous silicon anodes under repeated lithiation and delithiation (cycling) was investigated in chapter 4. Employing X-ray diffraction (XRD) and positron annihilation spectroscopy as complementary measurement techniques, 20 samples where cycled between 5 and 76 times and lithiated to capacities of 1000, 1200, and 1500 mAh.g⁻¹, representing 28%, 33.5%, and 42% of silicon's theoretical capacity, respectively. . XRD results show an increase in amorphization upon cycling, evidenced by diminishing normalized silicon peak intensities. This is accompanied by a simultaneously decreasing positron S-parameter, which indicates that amorphization results In a decrease in defects. Higher end capacitances show faster amorphization, which may be related to the plastic deformation around the pores that is exacerbated due to mechanical stress. The study highlights the potential of positron annihilation as an indirect measure of amorphization, although additional techniques are essential to elucidate the complex interactions in silicon cycling.

Fossil-fuel energy is finite and its associated negative environmental impact is fuelling efforts to provide alternative energy sources that are affordable, sustainable and efficient. This energy transition from the dominant fossil fuels to energy sources that have a lower carbon footprint is seen as an urgent call to adopt green and renewable energies. Renewable energy has long been poised as a strong alternative because of its circularity. However, most of the renewable energy sources are intermittent and require storage so as balance out the supply with the demand.

Electrochemical storage using batteries is the most commonly used storage technique due to its versatile nature in meeting varying energy demands. Batteries can be applied in stand-alone systems for large scale storage or in smaller distributed systems with wide spectrum of applications ranging from small portable devices such as mobile phones to EVs. The question now becomes whether the materials used for battery storage meet the threshold for circularity. The most advanced battery systems are based on Li-ion (LiBs) and still Lead-acid (LABs), with Na-ion (NiBs) beginning to gain some ground. Lead is considered toxic to both humans and the environment which has led to the push away from LABs. LiBs have gained popularity due to their high energy density, however, safety concerns and high material costs raise questions about their sustainability. NiBs present a lower cost option compared to the LiBs with acceptable performance. The consensus is that existing battery systems are not capable of meeting future energy storage demands and concerted efforts are underway to explore new battery chemistries that are sustainable, safe and affordable. Some of chemistries that have shown some promise are Zinc-ion and Mg-ion. In this work we focus on multivalent battery systems with a focus on Mg –ion batteries…

The global transition towards renewable energy sources necessitates advancements in energy storage technology to address the intermittency of renewable sources like solar and wind. Redox flow batteries, such as the zinc-air redox flow battery, offer promising solutions with flexible storage capacity and long cycle life. However, identifying a suitable redox mediator for the air side remains a significant challenge. perylene-derivatives, known for their electrochemical activity, recyclability, and redox stability, are potential candidates for this role. This research evaluates various perylene-derivatives for their electrochemical activity as mediators in zinc-air redox flow batteries, focusing on redox potential, solubility, and stability. While the study demonstrated that modifying substitution groups on the perylene core could achieve the desired reduction potential, achieving high solubility remains challenging. Therefor optimization of substitution groups is required to develop perylene-derivatives that meet the necessary criteria. Overall, although more research is required to find effective redox mediators, perylene-derivatives show significant potential for zinc-air redox flow batteries.

An increasing penetration of renewable energy sources in the global energy market necessitates an increasing amount of energy storage. Batteries are an excellent source of short term storage, used in vehicles, home storage and mobile applications. However modern technologies such as Li-ion batteries face resource scarcity and hence introduce geopolitical dependence. To this end Si-air batteries were recently, in 2009, explored in an attempt to devise a battery with high energy density and abundant materials.
The Si-air battery makes use of a silicon anode and an porous carbon cathode, to allow the circulation of air into the battery. Two electrolytes have been looked at in the past, KOH and the Room Temperature Ionic Liquid (RTIL) EMIm(HF)2.3F. The Si-air battery has excellent energy density in theory, with volumetric density being theoretically as high as 1 · 104 Wh/L. However, this theoretical energy density is as of yet far from reached, current research uses electrolytes which have a parasitic corrosion reaction with the silicon anode. This work aims to explore the usage of a new RTIL, BMPyr[NTf2], as the electrolyte in this battery. This RTIL has seen usage in Zn-air batteries, however it is yet untested for Si-air. The objective is to determine the discharge characteristics for a Si-air battery using this RTIL through comparison with KOH, with focus on the conductivity.
To do so first the relationship between conductivity and discharge potential for KOH was determined experimentally. The result found is that the discharge potential using KOH decreases with decreasing conductivity, however, this decrease is much larger than what can be solely attributed to the conductivity. Next the chosen RTIL BMPyr[NTf2], having a conductivity of 2.2 mS/cm at room temperature in a pristine state, was used in the battery discharges, where it was established to have an OCP of 0.7-0.8 V. From measurements no detectable consumption of Si was found after 1 hour of OCP. Further during the discharges it was found that the potential drops rapidly when discharge current is equal or greater to 2.5 μA. In an attempt to decrease the resistance in the battery cell a new design was created where the distance between the two electrodes is
decreased from 2 cm to 0.8 cm, using this second design a maximum OCP of 1.1 V was measured.
Finally by mixing in 1wt% and 3wt% water into the RTIL two mixtures are obtained with conductivity of 2.6 mS/Cm and 3.0 mS/cm at room temperature. Discharging these two mixtures at 20 nA, 100 nA, 500 nA and 2.5 μA it was found that for the 1 wt% the highest potential was found for 20 nA at 0.8 V. Meanwhile for the 3 wt% mixture the 20 nA discharge exhibited significantly lower potential at 0.4 V. For the 100 nA, 500 nA and 2.5 μA increasing conductivity led to increased potential, however similar to the KOH experiment, this difference in potential is larger than what is to be expected from purely conductivity changes. Finally, reproducibility of these experiments is low as a series of discharges with the same materials and current showed different potentials. These results combined lead to the conclusion of this work, thatthe relationship between conductivity and potential for the RTIL BMPyr[NTf2] is inconclusive, there are unknown factors influencing the discharge potential.

District heating networks (DHN) in the Netherlands have the potential to supply sustainable heat but are currently designed to deliver around 80% of the heat from a sustainable source. The peak demand is delivered with a gas boiler because of flexibility and costs. With the share of DHNs increasing in the Netherlands and the goal to be CO₂ neutral by 2050, a replacement for gas boilers in DHNs has to be found. This research evaluates the potential of seasonal thermal energy storage to supply the peak load in small-size DHNs in the Netherlands.

The research consists of three steps. First, the key performance indicators (KPIs) of the implementation of STES in DHNs are determined and the technologies with the most potential per seasonal thermal energy storage (STES) category (sensible heat storage (SHS), latent heat storage (LHS), and thermo-chemical energy storage (TCES)) are determined. Then a Matlab model is developed to determine the volume, storage losses, and total efficiency of the three selected technologies. Multiple scenarios are defined to evaluate the technical and financial potential of STES in different situations and configurations. Lastly, the STES systems are assessed on their potential to be integrated into a DHN to supply peak demand by analyzing investment costs, operating costs, volume, storage losses, and total efficiency. Throughout the research, a gas boiler is used as the reference scenario.

The models developed in the research are validated and can be used in specific case studies to determine the necessary volume of the STES, temperature profile throughout the year in the STES, mass flows and temperature of the supply HTF to the DHN, and the total losses of the STES, using the heat demand of the DHN, the HTF, the PCM, the reactant, the shape of the tank, the insulation thickness and material, and the heat supply of the source. With the outputs of the developed models, the costs can be calculated. The output of the model and the costs can be used to select the optimal STES to be implemented in the DHN of that specific case study.

This research shows that SHS is most feasible to be integrated into a small-size district heating network to deliver winter peak load in the existing built environment regarding volume, CO₂ emissions, and costs. A buried tank with water as the storage medium and heat transfer fluid (HTF) is selected as the technology with the most potential within SHS. For LHS, paraffin is selected as phase change material (PCM) and water as HTF. For TCES, potassium carbonate is selected as the reactant.

 A climate change mitigation strategy seen in the maritime sector is the electrification of berths through implementing shore power installations. The incorporation of grid-connected battery energy storage systems (BESS) into shore power installations, thereby creating hybrid installations, potentially accelerates the implementation of shore power. According to a gap in literature, this research evaluates the potential of various BESS to enhance the economic viability of shore power projects in the portal area in Rotterdam by prioritising consumer energy arbitrage and also trading on the day-ahead market, which is referred to as wholesale energy arbitrage.

This research consists of a techno-economic approach of assessing hybrid installations’ economic viability. First, a literature analysis provided insights in the most suitable BESS types for hybrid installations. Then, evaluation of various shore power projects in the port of Rotterdam resulted in the decision to focus on two impacting berths, namely on the Stena Line (SL) and the Cruise Port (CP) terminal. To assess the economic viability of hybrid installations, two models were designed, namely a BESS costs model and an energy management strategy algorithm. Eventually, the economic viability is evaluated by the net present value, the energy efficiency and effectiveness of the various hybrid installations.

This study reveals that none of the hybrid installations are economically feasible in the way they are examined. Nevertheless, it is indicated that lithium iron phosphate batteries are most suitable to enhance the economic viability of hybrid installations due to a high round-trip efficiency and low system costs. The energy demand of the SL terminal is smaller and more frequent compared to the CP terminal, thereby enhancing the potential of the BESS to cycle more often and to create more revenue. The research includes certain assumptions and uncertainties of which the individual impact on the outcome of the research is analysed. Also, potential scenarios ensuring economic viability are presented.

This research aims to analyse the non-ohmic resistance of multiple ion-exchange membranes (IEM) in series, for a better understanding of membrane resistances. These membranes can be found in series in energy storage systems such as acid-base flow batteries (ABFB).
The effect of different current densities on the ohmic and non-ohmic resistance of bipolar membranes (BPM), under forward and reverse bias were studied using electrochemical impedance spectroscopy (EIS). Hereafter, an anion exchange membrane (AEM), cation exchange membrane (CEM) and BPM were examined individually and in series using EIS, to compose a simplified equivalent circuit for a whole ABFB triplet.
For the effect of different current densities on the BPM, an exponential decline of the non-ohmic resistance of the diffusion boundary layer (DBL) was found as a function of the current density. Under forward bias, the DBL resistance becomes significant. The resistance of the water dissociation reaction (WDR) was minimal under all current densities. Flow experiments validate a depletion and enrichment of the DBL during water association and dissociation, respectively.
To compose a simplified equivalent circuit for an AEM, BPM and CEM in series, it was found that the specific resistances of all membranes can be summed at their respective frequencies. This made it possible to construct a simplified equivalent circuit for a whole triplet containing an AEM, BPM and CEM.

Batteries gained a lot of attention due to a raising demand for energy storage, as required for renewable energy generation systems, portable electronics and transport applications. For the development of new battery materials understanding of fundamental processes is essential, which often relies on the development of new characterisation techniques and tools that enable to study the underlying electrochemical processes at the relevant length scales, i.e. from an atomistic to a macroscopic level. Future batteries should be able to store more energy (per unit mass and or volume) and should be safer. Battery material solutions to achieve this are in principle known, where this thesis focusses on: (1) Si being one of the most promising negative electrode based on its large Li storage capacity (ten times higher than current graphite) and (2) solid electrolytes, replacing liquid electrolytes, which would practically annihilate safety concerns of Li batteries. However, for these new battery materials the challenge is to achieve a long cycle life by slowing down, or even preventing degradation reactions at the interfaces between the electrode and the electrolyte. This is the binding theme, and the topic of the main research questions of this thesis are thus: What are these degradation mechanisms and what is the impact of strategies to prevent it and achieve a long cycle life. The focus in this thesis is on Si negative electrodes in combination with liquid electrolytes in general, and for solid electrolytes in particular

In this thesis several aspects of PEM fuel cells are discussed. From an atomic scale, e.g. crystal and electronic structure of a non-noble metal material, e.g. (H)zLiMn2O4 (protonated spinel lithium manganese oxide) for electrocatalysis and its dynamics, to meso-macro scale effects such as those concerning transport resistances at the membrane/electrode interface.

In the search for new large-scale battery technologies that are cheap, safe and durable, in this research it is found that the state of the art semi-solid redox flow battery (“SSRFB”) technology shows perspective. Therefore, a novel, cheap and safe aqueous SSRFB design is introduced based on iron- and manganese hydroxide materials. This design was subsequently tested in the lab through which it was concluded that it is not possible to effectively make a SSRFB based on FeOOH and Mn(OH)2 semi-solid electrode (“SSE”) suspensions. Systematic proof is provided on how this can be attributed to the specific combination of the active materials in the highly alkaline environment, but that in itself, both the tested SSRFB configuration and SSE suspensions are functional. On the one hand, a complex chemical system of the active species consisting of multiple thermodynamic equilibria had the consequence that the open circuit voltage (“OCV”) had a very low value of 0.2 V instead of the expected 0.63 V. On the other hand, it was shown that both the FeOOH and the Mn(OH)2 SSE suspension could be separately cycled versus respectively a solid zinc and copper electrode and that a cheap microfiltration membrane suffices in the design of a SSRFB (on the condition that ionic active species are not apparent in the system). In sum, this research demonstrates that the SSRFB by its very nature is a suitable battery technology in which cheap and safe materials can be used for large-scale energy storage. However, that the combination and optimization of the right active materials in the right environment proves to be fundamental for proper operation and is in fact a complex balance between electric and ionic conductivity, colloidal stability, viscosity and (electro)chemical stability.

Renewable energy sources (RES) such as Solar and Wind energy rely on the availability of natural resources like sunlight in the case of Solar and wind speed in the case of Wind energy generation which is variable in nature. There are periods where there is excess energy production than needed and periods of energy shortage where not enough energy is produced to meet the demand. To mitigate this mismatch, a short term solution is to use batteries in order to store energy at times where energy production is more than the energy demand. This stored energy would be later used at times where energy production is low and meet the energy demand. However, the current battery technology is still novel for this application making it uneconomical when compared to current energy infrastructure of using power plants. The current battery market is held by Li-ion batteries which uses lithium as a raw material which is a rare earth material. In 2009, a battery cell utilizing Si as its anode and air as its cathode was discovered. As this system relies on two of the most abundant elements in the earth's crust which is silicon and oxygen and has much higher theoretical energy density than Li-ion batteries, it has become a growing area of research and development. Battery models are created to simulate battery operations based on empirical formulas and electrochemical reactions taking place in the battery. Development of these models are very critical as they provide results and optimum condition evaluations much faster than physical testing with minimal resources. A battery model for the alkaline Si-air battery which utilizes KOH as the cell electrolyte is developed in Simscape (MATLAB) as part of this thesis. The modelling parameters are also subjected various physical conditions such as varying electrolyte concentration and change in electrode materials and the variation is investigated for model validation to study whether changing physical conditions of the Si-air cell has an effect on the modelling cell parameters. It is supported with experimental results obtained from discharging a fabricated Si-air cell. It was concluded that there are cell parameters which are dependent only on the state of charge (SOC) of the cell and one cell parameter that is a function of both the SOC as well as the discharge profile of the cell. The fabricated Si-air cell gives higher open-circuit potential (OCP) values than what was reported constant 1.4 V in literature which is speculated to be due to the usage of a 99% Aluminum and 1% Silicon (Al:Si) back contact layer. Average OCPs ranging from 1.5 V to 1.45 V which varies due to change in electrolyte (KOH) concentration is achieved. The MATLAB battery block is calibrated to be integrated with energy system models as a Si-air battery.

Preparation of SPEEK based electrolytes using lithium slats

Advancements in energy storage technologies need to keep pace with the accelerating transition to renewable energy sources. Li metal anodes and high voltage cathode materials are widely considered to be the path into next generation Li-ion batteries, while the scare amounts of lithium in the earth's crust has prompted research into other battery materials. Of these, Sodium-ion batteries are extremely interesting due to the abundance of Na, similar insertion chemistry to Li as well as the possibility of using aqueous electrolytes due to higher redox potential. Next generation Li-ion batteries are currently held back due to issues like - dendrite formation at the metal anode which may lead to internal short circuiting and thermal runaway of the organic electrolyte. Similarly, Na-ion systems have issues with organic electrolytes due to the limited solubility of Na electrolyte salts. Solid state electrolytes (SSEs) have rapidly garnered interest as a potential alternative. SSEs vastly improve battery safety due to their superior thermal stability and mechanical strength. However, there are still limitations for SSEs in both these systems that need to be resolved prior to implementing these electrolytes in commercial batteries.In this study, alginate salts, which are natural polysaccarides extracted from brown algae, have been examined as a solution to the problems in these systems. Initially, sodium and lithium salts (NaAlg and LiAlg) of alginic acid were synthesized followed by their physical characterization. Conductivity for sodium and lithium alginate (with 0% water) were both promising at 0.2 mS/cm. Additionally, both LiAlg and NaAlg exhibit excellent performance as binders in anode systems compared to PVdF (polyvinylidene difluoride) binders.For utilizing the LiAlg in Li solid-state batteries, NaSICON-based LAGP electrolyte was synthesized and characterized for this study. The degradation of LAGP on Li contact has already been well researched. To combat the issue, we try to utilize a layer of LiAlg as protective layer at the LAGP surface. The coated LAGP remains stable against Li without undergoing degradation. The Li cyclability and electrochemical performance of LiAlg was further analysed by coating it on a various electrodes and studying their rate capabilities against Li. LiAlg displayed excellent performance as a secondary polymer electrolyte on the surface and in the bulk of the electrodes. These tests show exceptional cycling performances and establish a proof of concept for LiAlg as a polymer electrolyte.NaAlg which was chosen as the electrolyte in Na-ion batteries, displays better gelation properties. The effects of water content and operating temperature on Na conductivity were investigated. For a fixed water content, increasing the temperature results in improved conductivity - though this effect is more prominent at higher water concentrations and within the margin of error at lower water concentrations. At a fixed temperature, the conductivity shows linear improvement in at low (<25%) and high (>90%) water concentrations, while remaining constant between 25% and 90%. Additionally, the performance of NaAlg electrolytes (2w% NaAlg aq. solution) and GPE (20w% NaAlg Gel Polymer Electrolyte) was compared with the conventional Na2SO4 electrolyte. During these tests, the electrolyte underwent degradation possibly caused due to cross-linking induced by the dissolution of Mn2+ from the cathode on de-sodiation. Nevertheless, as a proof of concept, the NaAlg showed promise as an electrolyte (aq. and GPE) but further system optimization needs to be done to fully establish its scope as electrolytes for Na batteries.

Metal anode based batteries, considered the ideal upgrade to Lithium ion batteries in terms of energy density, are currently held back by the non-homogeneous deposition phenomenon that leads to the formation of dendrites that short circuit the cell. The solution to this problem is twofold: while it is important to come up with solutions that mitigate/resist dendrite formation, it is more important to fully understand the deposition phenomena in metal anodes through experiments and theoretical analyses. This study aimed to first understand the deposition mechanism in Zinc and Lithium metal anodes, and then study the feasibility of polymer coatings based on Sulfonated Poly Ether Ether Ketone (SPEEK) as a solution to mitigating the dendrites.
The electrochemical performance of Zinc in ZnSO4 electrolyte systems was studied
for a wide range of current densities and for different operating conditions with the help of operando microscopy and ex-situ SEM. Further, the mechanism of initial Zinc deposition was visualized with the help of in-situ TEM. The origins of the different types of morphology observed at these conditions were explained on the basis of competition between the mass transfer and the kinetics for control over the overall process. Further, a proof of concept was established for the use of SPEEK based coatings on Zinc metal, and the electrochemical performance of polymer coated Zinc electrodes was analyzed.
In the case of Lithium, the deposition in carbonate based electrolytes was first studied with the help of operando microscopy for Bare Lithium. Operando microscopy was also carried out to study the influence of the SEI, the separator and a standard polymer coating (PVDF) on Lithium deposition. Further, Lithiated SPEEK was used as a polymer coating on Lithium, and itwas observed that a more even Lithium deposition takes place with the Li-SPEEK coating on Lithium. Slight improvements were observed in the Li+ conductivity of the coating with the addition of TiO2 nanofiller to the polymer. However, performance issues were observed with long term cycling, possibly due to the instability of the polymer coating in carbonate electrolytes over long periods.

Magnesium ion batteries (MIB) have attracted much attention from battery researchers around the globe. Magnesium is divalent in nature and offer a higher theoretical capacity than that of lithium. However, the magnesium research is still in the niche stage and the search continues for better electrolyte systems and for high voltage cathode materials. Currently, extensive research is being done in employing organic materials for battery cathode materials. Organic materials are made from naturally occurring compounds and are easy to dispose since they have no metals. Perylene diimide is an organic material gaining importance as cathode material in metal ion batteries.

The goal of the project is to determine the voltage window of perylene in lithium and magnesium battery systems. Cyclic Voltammetry (CV) is employed to measure the electrochemical activity of the cell. The output of the CV is a scan of the current versus the voltage. During the operation of the cell, duck shaped peaks are observed which correspond to the reduction/oxidation activity of the cathode and the anode respectively. The current corresponding to the peaks is used to determine the cathodic and anodic current of the cell. Once the voltage and the current are known, the area under the peaks is calculated to determine the
charge/discharge capacity of the cell.

Since no prior research was done on magnesium, the most common cathode material (inorganic), chevrel phase molybdenum sulphide is synthesized and tested. Research with the perylene as cathode material is started with lithium because lithium is being studied extensively in the research group. Tests with both the monomer and the polymer has been conducted against lithium and magnesium battery systems. The lithium cell employing perylene is optimized as much as possible and is shown to be electrochemically active. The lithium cell shows a redox voltage of 2.5V vs Li/Li+. In the magnesium system, perylene is active as small peaks are observed at 1.5V and 1.7V vs Mg/Mg2+. However, the cell fails to operate after the first charge. This is most likely due to the electrolyte forming a passive film on the surface of the anode. It is recommended to disassemble the magnesium cell after the first discharge cycle to observe the magnesiation on the cathode and the passive film formation on the anode.

Li-ion batteries have major disadvantages. One of which is the growth of dendrites (in case Li metal based batteries), a major safety issue. In addition to that, Li-ion batteries also use elements such as Co, and Li, which are regionally scarce. Mg-ion batteries are one of the alternatives for Li-ion batteries. However, the electrolyte and cathode materials for Mg-ion batteries, are still in developmental stages.
In this study, the use of a sulphur-based spinel (also known as thiospinel) material as a cathode is explored. After literature review, MgMn2S4 and MgTi2S4 were identified as suitable cathode materials. Following which, the MgMn2S4 spinel is doped with Ti in the place of Mn at different doping ratios and the resulting combinations are evaluated for their stability, average intercalation voltage, volume change, spinel inversion and migration barriers. Two combinations MgMnTiS4 and MgMn0.75Ti1.25S4 are found to be stable with respect to the end members i.e. MgMn2S4 and MgTi2S4. Average voltages of 1.702 and 1.527 V (vs. Mg/Mg2+) are observed for MgMnTiS4 and MgMn0.75Ti1.25S4. However, spinel inversion is observed in MgMnTiS4. A volume change of 21.2, and 20% is observed in MgMnTiS4 and MgMn0.75Ti1.25S4, respectively.

Large scale stationary energy storage is becoming the need of the hour as the world transitions to a renewable economy. For this, there is a necessity of higher energy density batteries that can cope well both in storing excess energy and minimizing fluctuations on the grid. Solid polymer electrolyte batteries can be extremely safe and reduce packaging while also preventing dendrite formation in Lithium-ion batteries.

Sodium ion movement is seen from one oxygen atom to another for an arbitrary Na+ ion. This thesis shows that MD simulations can be a promising method to study the mechanisms involved in alginate polymer electrolytes. Further work is necessary to enable rigorous analysis by incorporating both mannuronates and guluronates. Neutron Magnetic Resonance (NMR) can be carried out to validate the results obtained through MD simulations.

MD simulations on sodium alginate (primarily of guluronate) as a solid polymer electrolyte appear to indicate the interaction of Na+ ion with O2 atom of the polyguluronate residue is in preference to interaction of Na+ ion with carboxylate oxygen atoms. Diffusion constant of Na+ ion is seen to drop in MD simulations with increase in Ca2+ ion concentrations both at temperatures 300 K and 373 K.