The Li-ion field of battery research has in the latest decades made substantial progress and is seen to be the most promising battery technology due to the high volume and specific energy densities of Li-ion batteries. However, in order to achieve a battery capable of competing with the energy density of a combustion engine, further research into new electrode materials is required. As the cathode materials are the limiting factor in terms of capacity, this is the main area in need of further research. The introduction of 3-D electrodes brought new hope as the ion transportpath is decreased as well as an increased electrode area leading to an increased capacity. This thesis work has focused on the development of aluminium 3-D current collectors in order to improve the electrode area and shorten the Li-ion transportpath. By using a template assisted electrodeposition technique, nanorods of controlled magnitude and order can be synthesized. Furthermore, the electrodeposition brings excellent possibilities of upscaling for future industrial manufacturing of the batterycells. A polycarbonate template material which showed interesting properties,was used in the electrodeposition of aluminium nanorods. As the template pores were nonhomogeneously ordered a number of nonordered nanorods were expected to arise during the deposition. However, a surplus of nanorods in reference to the template pores was acquired. This behavior was investigated and a hypothesis was formed as to the mechanism of the nanorod formation. In order to achieve acomplete cathode electrode, a coating of an ion host material on the nanorods isneeded. Due to its high capacity and voltage, vanadium oxide was selected. Based on previous work with electrodeposition of V2O5 on platinum, a series of experiments were performed to mimic the deposition on an aluminium sample. Unfortunately, the deposition was unsuccessful as the experimental conditions resulted in aluminium corrosion which in turn made deposition of the cathode material impossible. The pH dependence of the deposition was evaluated and the conclusion was drawn, that electrodeposition of vanadium oxide on aluminium is not possible using this approach.

Pressing demands for high power and high energy densities in novel electrical energy storage units have caused reconsiderations regarding both the choice of battery chemistry and design. Practical concerns originating in the conventional use of flammable liquid electrolytes have renewed the interests of using solvent-free polymer electrolytes (SPEs) as solid ionic conductors for safer batteries. In this thesis work, SPEs developed from two polymer host structures, polyethers and polycarbonates, have been investigated for all-solid-state Li- and Li-ion battery applications. In the first part, functional polyether-based polymer electrolytes, such as poly(propylene glycol) triamine based oligomer and poly(propylene oxide)-based acrylates, were investigated for 3D-microbattery applications. The amine end-groups were favorable for forming conformal electrolyte coatings onto 3D electrodes via self-assembly. In-situ polymerization methods such as UV-initiated and electro-initiated polymerization techniques also showed potential to deposit uniform and conformal polymer coatings with thicknesses down to nano-dimensions. Moreover, poly(trimethylene carbonate) (PTMC), an alternative to the commonly investigated polyether host materials, was synthesized for SPE applications and showed promising functionality as battery electrolyte. High-molecular-weight PTMC was first applied in LiFePO4-based batteries. By incorporating an oligomeric PTMC as an interfacial mediator, enhanced surface contacts at the electrode/SPE interfaces and obvious improvements in initial capacities were realized. In addition, room-temperature functionality of PTMC-based SPEs was explored through copolymerization of ε-caprolactone (CL) with TMC. Stable cycling performance at ambient temperatures was confirmed in P(TMC/CL)-based LiFePO4 half cells (e.g., around 80 and 150 mAh g-1 at 22 °C and 40 °C under C/20 rate, respectively). Through functionalization, hydroxyl-capped PTMC demonstrated good surface adhesion to metal oxides and was applied on non-planar electrodes. Ionic transport behavior in polycarbonate-SPEs was examined by both experimental and computational approaches. A coupling of Li ion transport with the polymer chain motions was demonstrated. The final part of this work has been focused on exploring the key characteristics of the electrode/SPE interfacial chemistry using PEO and PTMC host materials, respectively. X-ray photoelectron spectroscopy (XPS) was used to get insights on the compositions of the interphase layers in both graphite and LiFePO4 half cells.

Un nanotube de dioxyde de titane autoporteur (TiO2 nts) est exploré en tant qu’électrode négative potentielle pour les microbatteries Li-ion 3D. Différentes modifications chimiques du TiO2 ont été explorées et étudiées, comme le TiO2 allié au Nb, le TiO2 revêtu d'ALD-Al2O3, le titanate de lithium-TiO2 et le TiO2 sulfuré. Le dépôt d'électrolyte polymère à base de PEO (oxyde d'éthylène) (PMMA-PEG) portant le sel de LiTFSI dans du TiO2 a été obtenu par la réaction d'électropolymérisation sur l'anode TiO2 et la cathode Lithum nickel oxyde de manganèse (LNMO). L'objectif principal ici était d'exploiter la surface active des électrodes par électrodéposition et d'améliorer ainsi l'interface électrode-électrolyte. Une telle micro-batterie contenant des électrodes revêtues de polymère révèle que les valeurs de capacité obtenues à différents taux de C sont doublées lorsque les électrodes sont complètement remplies par l'électrolyte polymère par rapport à la micro-batterie à électrodes brutes. Les excellentes performances électrochimiques sont attribuées aux interfaces électrode-électrolyte améliorées dans les deux électrodes / Self-supported titanium dioxide nanotube (TiO2 nts) is explored as a potential negative electrode for 3D Li-ion microbatteries. Different chemical modifications on the TiO2 nts have been explored and studied like Nb-alloyed TiO2 nts, ALD-Al2O3 coated TiO2 nts, Lithium titanate-TiO2 nts and sulphurized TiO2 nts. The deposition of PEO (polyethylene oxide) based polymer electrolyte (PMMA-PEG) carrying LiTFSI salt into TiO2 nts has been achieved by the electropolymerization reaction on the TiO2 nts anode and the Lithum nickel manganese oxide (LNMO) cathode. The main aim here was to exploit the active surface area of the electrodes using electrodeposition and there by enhance the electrode-electrolyte interface. Such a microbattery containing polymer-coated electrodes reveal that the capacity values obtained at different C-rates are doubled when the electrodes are completely filled by the polymer electrolyte compared with the microbattery with the raw electrodes. The excellent electrochemical performance is attributed to the improved electrode-electrolyte interfaces in both the electrodes

Le développement des dispositifs microélectroniques a dopé la recherche dans le domaine des microbatteries tout solide rechargeables. Mais actuellement, les performances de ces microbatteries élaborées par des technologies couche mince (2D) sont limitées et le passage à une géométrie 3D adoptant le concept “Li-ion” ou“rocking chair” est incontournable. Cette dernière condition implique de combiner des matériaux de cathode comme LiCoO2, LiMn2O4 or LiFePO4 avec des anodes pouvant réagir de manière réversible avec les ions lithium. Parmi tous les matériaux pouvant servir potentiellement d'anode, les nanotubes de TiO2 révèlent des propriétés intéressantes pour concevoir des microbatteries Li-ion 3D. Facilement réalisable, la nano-architecture auto-organisée a montré des résultats très prometteurs en termes de capacités à des cinétiques relativement modérées. L'utilisation des nanotubes de TiO2 en tant qu'anode conduit à des cellules présentant de faible autodéchargeet élimine le risque de surcharge grâce au haut potentiel de fonctionnement (1.72 V vs. Li+/Li). Dans ce travail de thèse, nous avons étudié la substitution des ions Ti4+ par Sn4+ et Fe2+ dans les nanotubes de TiO2. Bien que la présence d'ions Fe2+ n'ait pas amélioré les performances électrochimiques des nanotubes, nous avons pu mettre en évidence l'effet bénéfique des ions Sn4+. Nous avons aussi pu montré que la fabrication de matériaux composites à base de nanotubes de TiO2 et d'oxyde de métaux de transition électrodéposés se présentant sous forme de particules (NiO et Co3O4 ) augmentait les capacités d'un facteur 4. / The advent of modern microelectronic devices has necessitated the search for high-performance all-solid-state (rechargeable) microbatteries. So far, only lithium-based systems fulfill the voltage and energy density requirements of microbatteries. Presently, there is a need to move from 2D to 3D configurations, and also a necessity to adopt the “Li-ion” or the “rocking-chair” concept in designing these lithium-based (thin-film) microbatteries. This implies the combination of cathode materials such as LiCoO2, LiMn2O4 or LiFePO4 with the wide range of possible anode materials that can react reversibly with lithium. Among all the potential anode materials, TiO2 nanotubes possess a spectacular characteristic for designing 3D Li-ion microbatteries. Besides the self-organized nano-architecture, TiO2 is non-toxic and inexpensive, and the nanotubes have been demonstrated to exhibit very good capacity retention particularly at moderate kinetic rates. The use of TiO2 as anode provides cells with low self-discharge and eliminates the risk of overcharging due to its higher operating voltage (ca. 1.72 V vs. Li+/Li). Moreover, their overall performance can be improved. Hence, TiO2 nanotubes and their derivatives were synthesized and characterized, and their electrochemical behaviour versus lithium was evaluated in lithium test cells. As a first step towards the fabrication of a 3D microbattery based on TiO2 nanotubes, electrodeposition of polymer electrolytes into the synthesized TiO2 nanotubes was also studied; the inter-phase morphology and the electrochemical behaviour of the resulting material were studied.

Les principales évolutions requises pour répondre aux besoins de la microélectronique visent à intégrer une micro-source d’énergie susceptible de fonctionner à plus bas potentiel que les systèmes actuels. Ainsi, en vue de répondre à cette demande, ce travail de recherche s’est focalisé sur l’étude, principalement par spectroscopie photoélectronique à rayonnement X (XPS), de deux matériaux d’électrode positive fonctionnant à 3 V vs Li+/Li : le spinelle LiMn2O4 et le Nasicon Fe2(MoO4)3. Le bismuth, matériau potentiel d’électrode négative susceptible de remplacer le lithium métallique et de subir le procédé de soudure classiquement utilisé en microélectronique (le solder reflow), est également étudié dans le cadre de cette thèse. Avant de caractériser ces matériaux en systèmes tout-solide, la première étape consiste à en étudier les comportements électrochimiques en électrolytes liquides. A cet effet, des couches minces d’une épaisseur d’environ 500 nm sont préparées par pulvérisation cathodique après une étape d’optimisation des paramètres de dépôt (puissance, pression partielle et totale dans l’enceinte de dépôt, température de recuit, …), puis caractérisées sur les plans structural (DRX), morphologique (SEM) et chimique (XPS, RBS, ICP). L’analyse des échantillons par XPS en fin de décharge et de charge a permis de mieux comprendre et d’expliquer les réactions électrochimiques se produisant au sein des matériaux et aux interfaces électrode/électrolyte dans les batteries au lithium. Une étude comparative avec un cyclage face au sodium a également été menée dans le cas du molybdate de fer et du bismuth, ce qui a permis d’identifier des comportements spécifiques lors de l’insertion/désinsertion des deux alcalins. L’homogénéité de la lithiation/sodation des couches minces a également été étudiée à partir de différentes analyses XPS menées après un procédé de décapage permettant de s’affranchir de la couche de passivation formée à l’interface électrode/électrolyte.Cette étude contribue à une meilleure connaissance des matériaux d’électrodes en cyclage pour micro-batteries au lithium et présente des perspectives très intéressantes d’intégration dans des dispositifs « tout solide ». / The main evolutions required for microelectronic applications aim to integrate an energy microsource operating at lower potential than current systems. Thus, in order to meet this demand, this research work has been focused on the study, mainly by X-ray photoelectron spectroscopy (XPS), of two positive electrode materials operating at 3 V vs Li+/Li: the spinel-type material LiMn2O4 and the Nasicon-type one Fe2(MoO4)3. The bismuth, a potential negative electrode material likely to replace the metallic lithium and to undergo the soldering process conventionally used in microelectronics (the solder reflow), has also been studied in this work. Before studying these materials in all-solid-state systems, the first step consists in investigating their electrochemical behaviors in liquid electrolytes. For this purpose, 500 nm-thick thin films are prepared by magnetron sputtering after a step of deposition parameters optimization (power, partial and total pressures in the sputtering chamber, annealing temperature, etc.). Physicochemical proprieties of the deposited thin films are then investigated by XRD, SEM, XPS, RBS and ICP analyses. The analyses of the electrodes by XPS at the end of discharge and charge has allowed better understanding of the electrochemical reactions occurring within the electrode materials and at the electrode/electrolyte interfaces in lithium cells. A comparative study with cycling against sodium has also been carried out in the case of iron molybdate and bismuth materials. This has allowed identifying specific behaviors of the thin films during the insertion/extraction of the two alkalis. The homogeneity of the thin films lithiation/sodiation has also been studied from various XPS analyses realized after etching process which allows eliminating the passivation layer formed at the electrode/electrolyte interface.This study contributes to a better knowledge of three potential electrode materials candidates for lithium micro-batteries and presents very interesting perspectives of materials integration in all solid state systems.

This thesis presents a microbattery recharging circuit suitable for autonomous microsystems. The battery charger chosen for this design is a constant current battery charger. Two methods of regulating the constant-current are discussed. A published shunt regulator design is analyzed and is presented with enhancements to the design. A series regulator that controls the current to the battery with a switch is designed and fabricated in a 1.5µm CMOS process. The fabricated prototype occupies less than 2.20x2.20mm and is expected to dissipate less than 25µW of power. A discrete model of the integrated circuit is constructed and tested to demonstrate that the series regulator will work using a solar cell as the energy source. The design of the charger is a major step toward the construction of a completely integrated autonomous system.

This dissertation describes the development of a high-power, plastic-based, thick-film lithium-ion microbattery for use in a hybrid micropower system for autonomous microsensors. A composite porous electrode structure and a liquid state electrolyte were implemented in the microbatteries to achieve the high power capability and energy density. The use of single-walled carbon nanotubes (SWNTs) was found to significantly reduce the measured resistance of the cathodes that use LiAl0.14Mn1.86O4 as active materials, increase active material accessibility, and improve the cycling and power performance without the need of compression. Optimized uncompressed macro cathodes were capable of delivering power densities greater than 50 mW/cm2, adequate to meet the peak power needs of the targeted microsystems. The anodes used mesocarbon microbeads (MCMB) with multi-walled carbon nanotubes (MWNTs) and had significantly better power performance than the cathodes. The thick-film microbattery was successfully fabricated using techniques compatible with microelectronic fabrication processes. A Cyclic Olefin Copolymer (COC)-film was used as both the substrate and primary sealing materials, and patterned metal foils were used as the current collectors. A liquid-state electrolyte and Celgard separator films were used in the microbatteries. These microbatteries had electrode areas of c.a. 2 mm x 2 mm, and nominal capacities of 0.025-0.04 mAh/cell (0.63-1.0 mAh/cm2, corresponding to an energy density of ~6.3-10.1 J/cm2). These COC-based batteries were able to deliver constant currents up to 20 mA/cm2 (100% depth of discharge, corresponding to a power density of 56 mW/cm2 at 2.8 V) and pulse currents up to 40 mA/cm2 (corresponding to a power density of 110 mW/cm2). The high power capability, small size, and high energy density of these batteries should make them suitable for the hybrid micropower systems; and the flexible plastic substrate is also likely to afford some unique integration possibilities for autonomous microsystems. The mechanism by which the SWNTs improved the rate performance of composite cathodes was studied both experimentally and theoretically. It was concluded that the use of SWNT improved cathode performance by improving the electronic contacts to active material particles, which consequently improved the accessibility of these particles and improved the rate capability of the composite cathodes.

Microbatteries are being considered as the critical components for portable and smart microelectronics, including remote sensors, micro-electromechanical systems, microrobots, implantable medical devices, and the Internet of Things, owing to their high energy densities, long life span, and facile on-chip integration. To date, tremendous efforts have been devoted to developing new methodologies for building high-performance microbatteries with minimum footprint areas. However, an effective and reliable fabrication procedure that is compatible with the modern microelectronics industry has not yet been reported for microbatteries so far. Two main issues need to be considered for the device design: (1) pursuing satisfying energy and power densities at limited footprint area is highly desired by constructing the 3D microelectrode architecture with high aspect ratio while reducing its footprint; (2) a novel technology is highly demanded to produce the 3D microstructure following an on-chip processing route which is compatible with the manufacturing procedure of microelectronic devices. Rolled-up nanotechnology can transform a large-area planar precursor into a micrometer-sized Swiss-roll by careful strain-engineering and state-of-the-art micro-patterning techniques with a micro-origami self-assembly process, which reduces the device size for monolithic integration. This dissertation demonstrates brand-new 3D Swiss-roll microbatteries with high performance at a sub-square millimeter-scale by employing rolled-up nanotechnology. Two types of micro-batteries with different configurations have been designed and fabricated, including twin Swiss-roll and single Swiss-roll structures. The twin Swiss-roll microbattery is fabricated based on two separated Swiss-roll micro-scaffolds with a parallel structure and controllable distance between them. The tuneable mesostructure benefits the mass loading of electroactive materials, rendering the excellent energy density at a greatly reduced footprint area. The twin Swiss-roll configuration is conducive to compatibility with novel battery chemistries due to its separated parallel Swiss-roll structure. In order to further decrease the overall footprint area, a single Swiss-roll configuration is designed for a fully integrated Swiss-roll microbattery. Micro-anode and micro-cathode are integrated into a single Swiss-roll configuration with an extremely small footprint area, which benefits the integration and miniaturization of microelectronics. Finally, an integrated device composed of a single Swiss-roll microbattery and UV photodetector is successfully fabricated within 1 mm2. The concept presented here enables the high-performance microbattery that can break through the limitation on microbattery’s footprint area, which opens up the new vision for the future on-chip microelectronics.:Table of contents Chapter 1. Introduction 1 1.1. Background and motivation of this work 1 1.2. Dissertation structure 2 Chapter 2. Overview of 3D microbatteries 5 2.1. Electrochemical energy storage 5 2.2. Rechargeable zinc batteries 6 2.2.1. Alkaline rechargeable zinc batteries 7 2.2.2. Aqueous zinc ion batteries 8 2.2.3. Dual-ion hybrid zinc batteries 9 2.3. Configurations for 3D microbatteries 10 2.3.1. 3D sandwiched architecture 12 2.3.2. 3D interdigital architecture 13 2.3.3. Rolled-up microtubular architecture 15 2.4. Conclusion 17 Chapter 3. Overview of rolled-up technology 21 3.1. Self-rolled-up inorganic layers 21 3.2. Self-rolled-up polymeric shapeable platform 24 3.3. Applications of rolled-up nanomembranes for energy storage devices 26 3.3.1. Rolled-up active materials for LIBs 26 3.3.2. Rolled-up micro-platform for in-situ investigation 27 3.3.3. Rolled-up integratable 3D micro-capacitors/supercapacitors 29 Chapter 4. Experimental methods 35 4.1. Fabrication technologies 35 4.1.1. Photolithography 36 4.1.2. Electron beam evaporation 37 4.1.3. Magnetron sputtering deposition 38 4.1.4. Electrochemical deposition 39 4.2. Characterization methods 40 4.2.1. Scanning electron microscopy, focused ion beam milling, and energy dispersive spectrometry 40 4.2.2. X-ray diffraction 41 4.2.3. Raman spectroscopy 41 4.2.4. Electrochemical characterization 42 4.2.5. Finite element method simulations 43 Chapter 5. A twin Swiss-roll microbattery 45 5.1. Introduction 45 5.2. Fabrication and characterization of twin Swiss-roll microbattery 46 5.2.1. Reshape a 2D precursor to a 3D mesostructured Swiss-roll 46 5.2.2. The construction of Swiss-roll microelectrodes 48 5.3. Results and discussion 51 5.3.1. The encapsulation of twin Swiss-roll microbattery 51 5.3.2. Electrochemical performance of twin Swiss-roll microbattery 52 5.3.3. Practical applications of twin Swiss-roll microbattery 55 5.4. Conclusion 57 Chapter 6. A single Swiss-roll microbattery 59 6.1. Introduction 59 6.2. Fabrication of Swiss-roll Zn-Ag microbattery 60 6.2.1. Fabrication of micro-origami layer stack 61 6.2.2. Fabrication of battery components 63 6.2.3. Self-roll-up of single Swiss-roll microbattery 63 6.3. Results and discussion 65 6.3.1. Materials characterization 65 6.3.2. Electrolyte optimization 65 6.3.3. Electrochemical performance of single Swiss-roll microbattery 70 6.4. Conclusion 73 Chapter 7. Summary and outlook 75 7.1. Summary 75 7.2. Outlook 77 Bibliography 79 List of figures 87 List of tables 91 Versicherung 93 Acknowledgment 95 Publications and presentations 97 Curriculum vita 99

Dans le développement des technologies microélectroniques, l’analyse de défaillance permet par l’étude des mécanismes de défaillance potentiels de définir des solutions correctives. La mise en œuvre des techniques de localisation et d’observation des défauts requiert une méthodologie, dont l’étape clé est la préparation d’échantillons. Celle-ci doit continuellement évoluer pour s’adapter aux innovations technologiques qui introduisent de nouveaux matériaux, et augmentent la complexité des composants assemblés. Cette thèse s’est intéressée à la méthodologie de préparation d’échantillons pour l’analyse de défaillance de deux familles de produits : les produits discrets et IPAD, et les micro-batteries. Pour les produits discrets et IPAD, une optimisation de la méthodologie existante a été réalisée en intégrant de nouvelles approches, développées pour résoudre des cas jusqu’alors en échec. Pour les micro-batteries, les matériaux utilisés et leur architecture ont nécessité une remise en question complète de la méthodologie de préparation d’échantillon. / In the development of microelectronic technologies, the failure analysis makes it possible to define corrective actions thanks to the understanding of the failure mechanism. In order to define the most adequate localization and observation techniques to use, a failure analysis flow is required. The sample preparation is a key step of this flow. This flow must continuously evolve to take into account the technological innovations that introduce new materials, and increase the complexity of assembled components. This work concerned the sample preparation flow for the failure analysis of two product families : the discrete products and IPAD, and the micro-batteries. Concerning the discrete products and the IPAD, an optimization of the current flow was performed with the integration of new approaches developed to solve failed cases. For the micro-batteries, the used materials and their architecture required an entire reappraisal of the sample preparation flow.

Des nanotubes de dioxyde de titane (TiO2nts) sont étudiés comme électrodes négatives potentielles pour des microbatteries Li-ion 3D. Ces TiO2nts lisses et hautement auto-organisés sont élaborés par anodisation du Ti dans des électrolytes organiques à base de glycérol ou d'éthylène glycol contenant des ions fluor et de l'eau en faible quantité. Les structures présentant un diamètre de 100 nm et une longueur variant de 1,5 à 14 µm sont particulièrement appropriés pour l'application visée. Les TiO2nts ont été tapissés de manière conforme par un électrolyte polymère (PMA-PEG) comportant un sel de lithium (LiTFSI) grâce à la technique d'électropolymérisation. Les études morphologiques menées par SEM et TEM ont montré que les nanotubes sont entièrement recouverts d'un film mince polymère de 10 nm d'épaisseur, ce qui permet de préserver la structure 3D de l'électrode. Les tests électrochimiques portant sur les nanotubes seuls ainsi que sur les TiO2nts tapissés d'électrolyte polymère ont été effectués en demi-cellule et en cellule complète en utilisant un électrolyte polymère à base de MA-PEG contenant du LiTFSI. En demi-cellule, les TiO2nts de 1,5 µm de long delivrent une capacité surfacique de 22 µAh cm-2 relativement stable sur 100 cycles. La performance de la demi-cellule est améliorée de 45% à une cinétique de 1C lorsque les TiO2nts sont tapissés de manière conforme par un electrolyte polymère (PMA-PEG). Cet effet résulte d'un meilleur transport de charges lié à l'augmentation de la surface de contact entre l'électrode et l'électrolyte. / Titania nanotubes (TiO2nts) as potential negative electrode for 3D lithium-ion microbatteries have been reported. Smooth and highly-organized TiO2nts are fabricated by electrochemical anodization of Ti foil in glycerol or ethylene glycol electrolyte containing fluoride ions and small amount of water. As-formed TiO2nts shows the open tube diameter of 100 nm and the length from 1.5 to 14 µm which are suitable for the fabrication of the 3D microcbatteries. The deposition of PMA-PEG polymer electrolyte carrying LiTFSI salt into TiO2nts has been achieved by the electropolymerization reaction. The morphology studies by SEM and TEM reveal that the nanotubes are conformally coated with 10 nm of the polymer layer at the inner and outer walls from the bottom to the top without closing the tube opening. 1H NMR and SEC show that the electropolymerization leads to PMA-PEG that mainly consists of trimers. XPS confirms the presence of LiTFSI salt in the oligomers.The electrochemical studies of the as-formed TiO2nts and polymer-coated TiO2nts have been performed in the half-cells and full cells using MA-PEG gel electrolyte containing LiTFSI in Whatman paper as separator. The half-cell of TiO2nts (1.5 µm long) delivers a stable capacity of 22 µAh cm-2 over 100 cycles. The performance of the half-cell is improved by 45% at 1C when TiO2nts are conformally coated with the polymer electrolyte. The better performance results from the increased contact area between electrode and electrolyte, thereby improving the charge transport.