We are currently undergoing an energy transition, in which batteries are playing a vital role. Their cost is quickly decreasing and they provide a way of storage for electricity generated by renewable energy sources such as wind and solar power generation. With the increase in demand for battery capacity comes the demand for safer, more energy dense, higher power output and faster charging batteries. To meet these demands researchers are now focusing on solid state batteries. And in these batteries on the anode side on a specif material called silicon (Si). With its abundance in the earth’s crust and a gravimetric energy density of more then 10 times that of graphite, which is currently most used as the anode in lithium ion batteries, this material seems very promising. But the silicon material expands up to 300-400% when fully charged/lithiated. This of course brings challenges for using silicon in solid state batteries, where the expansion could destroy the battery from within. Multiple solutions have been tried to deal with this volume expansion, and one of the solutions is to add nanopores into the silicon material so the material expands into the pores and not outwards. Such a material is provided by a company called E-magy, they have already shown this material to be effective in liquid lithium-ion batteries. But this thesis will focus on how this material performs in solid state batteries by comparing the galvanostatic battery cycling and electrochemical impedance spectroscopy data, to solid state-batteries that use silicon particles of the same size without the nanopores (called Com Si). For the solid electrolyte (SE) in these batteries a Cl rich version of lithium argyrodite is chosen with the chemical formula Li5, 5PS4, 5Cl1, 5. This material combines properties of halides and sulfides resulting in a deformable high ionic conductivity solid electrolyte that can form a stable interface in the battery operating potentials and accommodate the volume expansion of the silicon. Regular lithium argyrodite ( Li6PS5Cl ) and the Cl rich variant where synthesized with respective ionic conductivities of 2,9 and 7,5 mS/cm, to compare there performance in the Si solid state batteries. Si/SE/CNF (Carbon nano fiber to increase the electronic conductivity) composite powder mixture electrodes where made with varying compositions, where the 6/3/1 composition showed the best performance with a initial discharge capacity of 2410 mAh/g with a current density of 0,229 mA/cm2 for Com Si . After the formation cycles this battery showed a capacity retention of 73% going from 1680 mAh/g to 1230 mAh/g at a current density of 0,458 mA/cm over the span of 45 cycles. The CNF was shown to not have a positive and possibly a negative impact on the battery performance and with the results from the Si/SE/CNF batteries there was not a clear difference between the performance of porous and non porous silicon. The switch was made to using Si deposited on Cu electrodes with a PVDF binder instead of the Si/SE/CNF composite electrodes. The best battery performance was achieved with a non porous 1,2 mg Si electrode showcasing a initial discharge capacity of 2700 mAh/g, and a capacity retention of 81,3% after the formation cycles going from 2250 to 1830 mAh/g with the same current densities as before. This test was done with both SE’s showcasing a clear improvement in capacity retention with the Li5, 5PS4, 5Cl1, 5 but still no clear difference between the porous and non porous material. Then, to better preserve the nano porous Si structure, the Si deposited on Cu electrodes where only charged to a capacity of 1000, 1500 and 2000 mAh/g by using time constraints. This showed clear improvements for the nanoporous Si material over the regular Si for capacities of 1000 and 1500 mAh/g over 50 cycles. The 1000 mAh/g E-magy Si battery showed a coulombic efficiency of 99% and a stable minimum negative potential of -0,5 V vs In/LiIn for 50 cycles. Using Li5, 5PS4, 5Cl1, 5 of Li6PS5Cl lead to more stable battery performance and less of an increase in the required potentials to reach the same capacities each cycle. This study provides a insight into how the battery performance of Si solid state batteries is influenced by: Nanopores in the Si material, different Si electrode preparation methods, Si composite electrode composition ratio’s, choice of the olid electrolyte, and the utilized capacity of the Si electrode. And thereby makes a contribution to the large amount of research that is currently being done to allow for Si anodes to successfully be utilized in solid state batteries.

Sulfide-based solid-state batteries (SSBs) are emerging as a top contender for next-generation rechargeable batteries with improved safety and outstanding energy densities. SSBs incorporate non-flammable solid-electrolytes (SEs), eliminating safety hazards for batteries in electric vehicles and electronic devices. In addition, the development of SSBs with SEs allows the conventional graphite anode to be replaced by a lithium metal anode, theoretically surpassing the energy densities of lithium-ion batteries (LIBs). However, SSBs with high nickel cathode materials such as LiNi0.8Mn0.1Co0.1O2 (NMC), exhibit several cathode interface-related issues preventing the large-scale adoption of this technology. Specifically, the problems include challenges such as mechanical and chemical instability, which results in particle cracking, contact loss, and decomposition of the solid-electrolyte.
To overcome these challenges, this study used polymeric interlayers at the surface of the NMC to buffer volume changes and passivate chemical side reactions. Herein, the Ni-rich layered oxides polycrystalline NMC811 (PC-NMC) and single-crystal NMC Ni82 (SC-NMC) were coated with PDDA-TFSI, poly(diallyldimethy-lammonium) bis(trifluoro-methanesulfonyl)imide, using a microencapsulation method. Additionally, this study aimed to maximize the utilization of cathode active material with the use of the conductive additive carbon nanofibers (CNFs) and the addition of lithium salt (LiTFSI) in the polymeric coating. Full lab-scale SSBs consisted of a coated NMC-based cathode, a Li-In alloy anode, and Li6PS5Cl solid-electrolyte.
The conductive carbon additive severely increased SSB degradation, which was associated with the formation of decomposition elements sulfates/sulfites (SOx ), polysulfides (P2Sx ), phosphates (POx ), and lithium phosphate phases (P/LixP). The polymeric coating on PC-NMC slightly improved cycle stability. Here, improvements were associated with the significant reduction of contact loss between NMC and Li6PS5Cl particles. The cathode with SC-NMC with a PDDA-(Li)TFSI polymeric coating demonstrated exceptional performance improvements in SSBs, mitigating chemical and mechanical degradation. It showcased improved cycle stability with a capacity retention of 95% observed after 100 cycles at 0.2C, compared to a capacity retention of 84% for SSBs without a cathode interface coating. Furthermore, a significantly improved initial capacity of 155 mAh g−1 at 0.2C was established, compared to an initial
capacity of 144 mAh g−1 for uncoated SSBs. Overall, the results highlight the performance-enhancing effect of a polymeric coating with added lithium salts in Li6PS5Cl-based SSBs.

The objective of this research is to evaluate the effect the air electrode has on the discharge performance of an alkaline silicon-air battery. Experiments are conducted to show that alkaline pre-treatment of the air electrode of up to eight hours leads to an increase in both discharge time and discharge potential of the battery. Furthermore, it is shown that alkaline pre-treatments of sixteen and 24 hours also increase the discharge time and discharge potential of the battery with respect to no pre-treatment. However, the increase in discharge time and discharge potential for these pre-treatments is much smaller than for pre-treatments between three and eight hours. A pre-treatment of 110.75 hours results in a discharge time and discharge potential similar to that of no pre-treatment. In the experiments it is also shown that pre-treating the air electrode with water only, instead of an alkaline solution, has no effect. Finally, the experiments show that discharging the battery at a current higher than 150 μA is not supported. A computer model is then used to evaluate the impact of some qualities of the air electrode on the discharge performance of the silicon-air battery. It is found that the electrical conductivity of the air electrode has very little impact, with a very large increase in electrical conductivity resulting in only a very small increase in discharge potential. The micro-pore surface area in the air electrode has slightly more influence on the discharge performance. Still, a relatively large increase in this parameter only results in an increase of approximately 0.2 V in discharge potential. Both of these parameters are found to have no effect on the discharge time of the battery. To explain the significant increase in both discharge potential and discharge time after alkaline pre-treatment found in the experiments two possible reasons are suggested. Firstly, the adsorption of OH- ions contributing to the oxygen reduction reaction activity of the air electrode material. Secondly, other atmospheric gases besides oxygen might be suffocating the micro-pores of the air electrode. Increased micro-pore area as a result of alkaline pre-treatment could explain the extended time before the air electrode is fully suffocated.

With the advent of the sustainable energy transition, the deployment of renewable energy sources is rapidly growing. One of the main problems for sustainable systems like wind and polar power is the fluctuating and intermittent behaviour of these sources. In order to make these systems more reliable energy storage is needed to compliment these systems. A multitude of different systems are now in development at different institutions and companies in order to fulfill this need, one of which being the Greenbattery under development at AquaBattery. The Greenbattery is an Acid Base Flow Battery (AB-FB), which is a further iteration of their original Concentration Gradient Flow Battery (CGFB or Bluebattery). The AB-FB shows promising market potential due to its low impact on the environment, relatively low cost and being easily scalable. Currently the AB-FB is on par in energy densities with systems such as Pumped Hydro Storage and Compressed Air Storage, while not being dependent on geological features or scale of size. However, the AB-FB still needs improvement as co-ion transportation degrades its potential energy density over time. In order to make this technology more viable parameters must be found in order to limit the co-ion transportation. During this thesis research is performed to identify any other potential losses, as well as testing the operational limits and behaviour of the membranes. After this the battery is subjugated to conditions simulating real life operation. During these tests the charge/discharge density, as well as depth of charge, is incrementally changed. By doing this insight is gained in the amount of co-ion transportation that is occurring and whether or not this improves the battery lifetime. The results show the battery can last up to twice as long before falling below 80 % of its original energy density. This is done by reducing the upper and lower limits of the state of charge. However, as a trade off, there is reduction in the energy density of the battery. Following this, research has been performed into the viability of resetting the system, which led to promising results. With this knowledge the operator gains insight whether he wants to put priority in higher energy density or longer lifetime, as well as when he should reset the system to keep it at maximum potential energy density. This gives flexibility to the AB-FB and hopefully help AquaBattery sell its product in the coming years.

The ongoing worldwide energy transition has prompted significant scientific interest in energy storage. Rechargeable lithium-ion batteries have become a standard for energy storage in mobile devices and electric vehicles for their mass-energy density. While industry standard lithium-ion cells are currently based on liquid electrolytes, solid electrolytes promise to bring the next step towards safety, energy density and sustainability. However, there are critical challenges, notably improving the lithium conduction of solid electrolytes. Furthermore, as a relatively new research field it is important to target high recyclability and sustainability for materials early on. Battery modelling facilitates performance comparisons of for example battery materials and geometric properties, and subsequent optimisation. The report treats battery modelling with a specific focus on solid electrolytes. Two solid electrolyte models, based on weak electrolyte theory and a lattice gas model by Landstorfer et al., were implemented in the Multiphase Porous Electrode Theory software (Smith,2017). The former is relevant for glass type electrolytes, while the latter models crystalline materials. The models showed comparable performance, with a constant voltage offset but good mutual agreement in term of behaviour. It is important to verify the results experimentally. The numerical methods used in porous electrode theory were treated with the creation of a standalone porous electrode model, with separate domains for the electrolyte and active cathode particles. This model is stable and functional with the two domains in isolation, while a fault remains in the coupling between the domains. Lastly, a proposal is made for the addition of interface regions in the MPET software. With these domains situated between the bulk electrolyte and active cathode particles, porous electrode models could include a variety of phenomena that are currently impossible to implement. For solid electrolytes in particular, modelling dynamic stress effects and lithium conduction across particle boundaries would be valuable additions.

Solid state Li ion batteries have garnered attention due to their high safety and increased energy density. A key challenge towards commercialization is reduction of the high interface resistance affecting the charge transfer and in turn performance. In this thesis the aim is to analyze lithium phosphorous oxynitride (LiPON) properties. By variation of layer thicknesses and electrode conguration, LiPON bulk and interfacial properties were determined using electrochemical impedance spectroscopy. The results show a high degree of consideration with respect to surface morphology and deposition conditions is required for the reduction of interface resistance in solid state 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.

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.

The battolyser concept is based on an old fashioned nickel iron battery, consisting of a positive nickel(oxy) hydroxide electrode and negative iron (hydroxide) electrode. Research has been performed on the structural changes of the nickel and iron electrode upon charge and discharge. A lot of research can be found for the nickel electrode, but crystal structure studies are few. Much less research is performed on the iron electrode. Therefore the structural changes of the nickel(oxy) hydroxide and iron (hydroxide) electrodes during operation are further researched. Ni(OH)2 exists in the form of an α- or β-modification and NiOOH in a β- or γ-modification. The structure of the nickel(oxy)hydroxide phases has layers of edge-sharing NiO2 octahedra, where in between guest atoms can situate. Conventional nickel electrodes operate mainly between β-Ni(OH)2 and β-NiOOH, so most research focussed on this area. Upon overcharge the γ-NiOOH is formed and when discharging a direct reduction of β-NiOOH and γ-NiOOH into β-Ni(OH)2 occurs. The research on the nickel electrode published in this thesis is compared with a previous discharge study performed by Morishita et al. In their Rietveld refinement of the β-phases an ideal and fault phase model are assumed and the weight fraction of all phases present in the samples at 0, 50, 100 and 150% of state of charge (SOC) are determined. For the iron electrode four phases can be distinguished. The pure Fe in the electrode upon discharge becomes Fe(OH)2, under deep discharge this transforms even further towards FeOOH. For the deactivation process the reaction moves towards magnetite (Fe3O4). First the battery electrodes from the shelf are analysed by SEM-edx , X-ray diffraction and neutron diffraction. Then neutron powder and X-ray diffraction analysis have been performed to study the structural changes of the electrodes during charge and discharge. The nickel electrodes are measured at various states of charge from 0 to 100% and iron electrodes 0 to 90%. Preliminary experiments for the in-situ neutron diffraction test setup are performed. Different thicknesses of quartz glass, several sizes of nickel foam current collectors are tested for the amount of their background noise. In the nickel electrode are next to the carbon, 3 phases present. In the comparison with Morishita et al. significant differences are found. The transition towards β-NiOOH and subsequently γ-NiOOH occurs faster. Already at 50% of SOC the weight fraction of β-NiOOH is 58 wt% and at 100% of SOC the γ-NiOOH is 57 wt%. The c-parameter of γ-NiOOH is in agreement with Morishita et al. with a lattice distance of 20.8 Å. Morishita et al. did not specify how they determined the state of charge, so maybe they calculated the SOC in a different way. In the iron electrode three phases are identified, namely iron (Fe), goethite (FeOOH) and magnetite (Fe3O4). This is a strange result, because where Fe(OH)2 is expected, FeOOH is found. Probably discharged too far, moving the reaction into the second discharge plateau. The weight fraction of Fe increases and FeOOH decreases with increasing state of charge. The hydrogen content is decreasing with increasing SOC proportional to the background function for both the nickel and iron electrode.

Lithium ion batteries are currently the most attractive choice for mobile energy storage and power sources [4] in terms of energy density. However, it is unlikely that current battery chemistries will reach the energy density desired for future applications [8]. Li-metal, which has the highest reduction potential of all metals and the highest achievable capacity per weight unit, could significantly increase the energy density when used as an Anode. Unfortunately, the dendritic growth of Li-metal is a safety hazard, and the low electrochemical potential of Li-metal
is outside the stability window of many electrolytes leading to capacity degradation.
It has been suggested that safe Li-metal Anodes may be possible in combination with solid electrolytes, as the higher shear modulo of solid over liquid electrolytes may be able to suppress dendrite formation [21].
To study the stability of the interface between Li-metal and the solid electrolyte Li6PS5Cl, electrochemical measurements of the cells, ex-situ x-ray diffraction, and solid state Nuclear Magnetic Resonance measurements were made. It was not possible to confirm the decomposition products that were proposed in literature by density functional theory calculations and in-situ XPS. The XRD-pattern of the cycled electrolyte did not show additional phases. The NMR spectra developed broader peaks and one additional phosphorous environment upon cycling. As a tool to study dendritic growth through Li-ion concentration profiles, a cell for in-situ neutron depth profiling (NDP) was developed. The electrochemical performance is comparable to regular cells, except for a voltage drop due to contact problems during the break after Li-metal stripping. A thin layer of Li-metal between the window and the electrolyte pellet, as well as a collimator plate to put some pressure on the window, could be the solution
to go towards operando measurements.
The current standard data analysis method was implemented and its sensitivity towards gaussian broadening, due to energy straggling (from small angle scattering in the material and the stochastic nature of energy loss), was
investigated. It is shown that the standard deviation of energy straggling is larger than that of energy broadening due to the detector resolution, and that the error on the depth scale is in the order of micrometers.

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.

In the search for renewable energy storage materials, lithium metal has been considered the ideal electrode material for decades, due to its high specific capacity. However, dendrite formation leading to poor cycling behaviour has seemed an insurmountable problem ever since. In recent years, advancements in observational- and nanotechnologies have allowed for the identification of many of the factors that influence dendrite formation, as well as many suggestions to overcome them.
Obtaining further understanding of the fundamental processes at play in dendrite formation is crucial in developing the next generation lithium batteries.
In order to investigate dendrite formation at the nanoscale, in operando synchrotron X-ray diffraction experiments were conducted. A pouch cell with a Li-Li symmetric cell using a LiPF6 1:1 EC:DMC electrolyte was used to perform the experiments.
The growth rate of individual crystallites was determined, as well as the consumption of lithium crystallites by the electrolyte to form solid-electrolyte interphase (SEI).
By determining the volume of individual crystallites over time, their formation and decay rate could be determined. Three categories were put forward to classify the types of behavior of individual crystallites during plating and relaxation. It was found that a significant part of dendrites show behaviour that is independent of the macroscopic current density.