ATOMIC LAYER DEPOSITION OF ALKALI PHOSPHORUS OXYNITRIDE ELECTROLYTES FOR BEYOND-LITHIUM NANOSCALE BATTERIES

Lithium-ion batteries dominate portable energy storage systems today due to their light weight and high performance. However, with the continuing demand for battery capacity projected to outstrip the supply of lithium, alternative energy storage systems based on the more abundant Na and K alkali metals are attractive from both a resource perspective and their similar charge storage mechanism. Beyond limited lithium resources, there remains significant opportunity for innovation to improve battery architecture and thus performance. Nanostructured solid-state batteries (SSBs) are poised to meet the demands of next-generation energy storage technologies, with atomic layer deposition (ALD) being a powerful tool enabling high-performance nanostructured SSBs that offer competitive performance with their liquid-based counterparts. This dissertation has two main objectives: First, the development of the first reported ALD solid-state Na+ and K+ conductors are presented. Second, by leveraging the work on developing new solid- state Na+ ion conductors, a proof-of-principle nanoscale Na-SSB is fabricated and tested.ALD processes are developed for the Na and K based analogues of the well-known solid- state electrolyte (SSE) lithium phosphorus oxynitride (LiPON). In this case; NaPON and KPON. A comprehensive comparison of the structure, electrochemical, and processing parameters between the APON (A = Li, Na, K) family of materials is presented. The structure of NaPON closely resembles that of ALD LiPON, both possessing a N/P of 1, classifying them as alkali polyphosphazenes. Interestingly, KPON exhibits similar ALD process parameters to NaPON and LiPON, but the resulting film composition is quite different, showing little nitrogen incorporation and more closely resembling a phosphate glass. NaPON is determined to be a promising SSE with an ionic conductivity of 1.0 ́ 10-7 S/cm at 25 °C and a wide electrochemical stability window of 0-6.0V vs. Na/Na+. The electrochemical stability and performance of NaPON as a SSE is tested in liquid-based and all solid-state battery configurations comprised of a V2O5 cathode and Na metal anode. Electrochemical analysis suggests intermixing of the NaPON/V2O5 layers during the ALD NaPON deposition, and further reaction during the Na metal evaporation step. The reaction during the ALD NaPON deposition on V2O5 is determined to be two-fold: (1) reduction of V2O5 to VO2 and (2) Na+ insertion into VO2 to form NaxVO2. The Na metal evaporation process is found to exacerbate this reactivity, resulting in the formation of irreversible interphases leading to poor SSB performance. Despite the relatively poor performance, this work represents the first report of a nanoscale Na-SSB and showcases cryo- TEM as a powerful characterization technique to further the understanding of nanoscale SSBs. Looking forward, the intermixing during the ALD NaPON deposition does not impact the cycling of the NaxVO2 electrode in liquid-based cells, with NaPON-coated electrodes outperforming unsodiated V2O5 electrodes. This may be advantageous for the fabrication of SSBs, as the SSE deposition simultaneously could pre-sodiate a stable cathode material, excluding the need for ex-situ sodiation in liquid solutions or depositing a pre-sodiated electrode material. Strategies to pair this NaxVO2/NaPON cathode/electrolyte with a stable anode are discussed, with a focus on the ultimate realization of a high-performance Na-SSB. This work highlights the high reactivity of Na compared to Li based battery chemistries, not only necessitating the need for interfacial coatings in Na SSBs, but also the extreme caution required during fabrication of Na-SSBs or liquid sodium- ion batteries

Unveiling the Stable Nature of the Solid Electrolyte Interphase between Lithium Metal and LiPON via Cryogenic Electron Microscopy

The solid electrolyte interphase (SEI) is regarded as the most complex but the least understood constituent in secondary batteries using liquid and solid electrolytes. The nanostructures of SEIs were recently reported to be equally important to the chemistry of SEIs for stabilizing Li metal in liquid electrolyte. However, the dearth of such knowledge in all-solid-state battery (ASSB) has hindered a complete understanding of how certain solid-state electrolytes, such as LiPON, manifest exemplary stability against Li metal. Characterizing such solid-solid interfaces is difficult due to the buried, highly reactive, and beam-sensitive nature of the constituents within. By employing cryogenic electron microscopy (cryo-EM), the interphase between Li metal and LiPON is successfully preserved and probed, revealing a multilayer mosaic SEI structure with concentration gradients of nitrogen and phosphorous, materializing as crystallites within an amorphous matrix. This unique SEI nanostructure is less than 80 nm and is shown stable and free of any organic lithium containing species or lithium fluoride components, in contrast to SEIs often found in state-of-the-art organic liquid electrolytes. Our findings reveal insights on the nanostructures and chemistry of such SEIs as a key component in lithium metal batteries to stabilize Li metal anode

A mini-review on the development of Si-based thin film anodes for Li-ion batteries

This review provides a summary of the progress in research on various Si-based thin films as anode materials for lithium-ion batteries. The lithiation mechanism models, different types of materials from pure monolithic Si thin film to Si-based three-dimensional structured composite thin films, the effect of liquid and solid-state electrolytes on the performance of Si were considered and various available preparation techniques were discussed. A table summarizing important information on such systems including the thin film features, preparation methods and conditions, electrochemical test conditions and obtained results in order to elucidate the approaches used to prepare a stable thin film anode with high capacity and long cycle life is provided. We believe that this review will help the researchers to find some answers and induce some new ideas

ULTRA-THIN ON-CHIP ALD LIPON AS SOLID-STATE ELECTROLYTE FOR HIGH ENERGY AND HIGH FREQUENCY CAPACITOR APPLICATIONS

Liquid electrolytes dominate the supercapacitor market due to their high ionic conductivity leading to high energy and power density metrics. However, with the increase in demand for portable and implantable consumer electronics, all solid-state supercapacitor systems with high safety are an attractive option from both application perspectives and their similar charge storage mechanism. For solid state ionic capacitors, there remains significant room for innovation to increase the ionic conductivity and capacitor architecture to enhance the performance of these devices. Nano-structuring along with advanced manufacturing techniques such as atomic layer deposition (ALD) are powerful tools to augment the performance metrics of these all-solid-state capacitors that can compete with state-of-the-art liquid electrolyte-based supercapacitors. This dissertation has two primary objectives; 1) Study the behavior of polymorphs of ALD LiPON as a capacitor material and 2) Enhance the performance metrics using advanced materials and 3D nanostructuring for improved energy storage and high-frequency applications.In this work, ALD LiPON-based solid state capacitors are fabricated with a gold current collector to study the behavior of the solid electrolyte. LiPON shows a dual energy storage behavior, in low frequency (<10 kHz), LiPON shows an ionic behavior with electric double layer type energy storage, beyond this frequency, LiPON shows an electrostatic behavior with a dielectric constant of 14. The capacitor stack's thin film structure and dual frequency behavior allow for extended frequency operation of these capacitors (100 Hz to 2000 MHz). Next, LiPON's energy storage metrics are enhanced by pseudocapacitive energy storage behavior and increased surface area using ALD oxy-TiN. Finally, new fabrication techniques and ALD recipes are developed and optimized for integration into 3D templates. For fabrication of these capacitors, the material's chemistry is analyzed, and ALD techniques are developed for the deposition of electrode/electrolyte materials and current collectors into the 3D nanostructures. The intermixing during the ALD processes are studied to understand the behavior and reliability of these thin films. This work highlights LiPON characteristics as a capacitor material for high-energy and high-frequency applications. Though incomplete, we discuss progress towards the development of all ALD solid-state 3D supercapacitors that can compete against state-of-the-art capacitors available in the market

ATOMIC LAYER DEPOSITION OF SOLID ELECTROLYTES FOR BEYOND LITHIUM-ION BATTERIES

This thesis outlines methodology and development of an atomic layer deposition (ALD) process for the well-known solid-state electrolyte lithium phosphorous oxynitride (LiPON). I have developed a quaternary ALD LiPON process through a novel stepwise additive development procedure. ALD process kinetics and chemistry were investigated using in-operando¬ spectroscopic ellipsometry and in-situ x-ray photoelectron spectroscopy (XPS). ALD LiPON exhibits a tunable ionic conductivity proportional to N content, with the highest conductivity of 6.5x10-7 S/cm at 16.3% N. Two applications of ALD LiPON are investigated: ALD LiPON films as a protection layer for next-generation lithium metal anodes in the lithium sulfur battery system, and as solid electrolytes in 3D thin film batteries with discussion towards development of an all ALD 3D battery. Lithium metal is considered the “holy grail” of battery anodes for beyond Li-ion technologies, however, the high reactivity of Li metal has until now prevented its commercial use. Here, ALD protection layers are applied directly to the Li anode to prevent chemical breakdown of the liquid electrolytes while allowing ion transport through the protection layer. Protection of lithium metal is investigated with two materials: low ionic conductivity ALD Al2O3, demonstrating a 60% capacity improvement in Li-S batteries by protecting the Li anode from sulfur corrosion during cycling, and high ionic conductivity ALD LiPON, demonstrating a 600% improvement in Li-S battery capacity over unprotected anodes. Interestingly, ALD LiPON also forms a self-healing protection layer on the anode surface preventing deleterious Li dendrite formation during high rate cycling. Solid Li-based inorganic electrolytes offer two profound advantages for energy storage in 3-D solid state batteries: enhanced safety, and high power and energy density. Until now, conventional solid electrolyte deposition techniques have faced hurdles to successfully fabricate devices on challenging high aspect ratio structures, required for improvements in both device energy and power density. In this thesis, I demonstrate fabrication of ALD heterostructures suitable for use in 3D solid batteries, and although this work is incomplete I discuss progress towards future use of ALD LiPON solid electrolytes in all ALD solid-state 3D batteries

Advanced architecture designs towards high-performance 3D microbatteries

Rechargeable microbatteries are important power supplies for microelectronic devices. Two essential targets for rechargeable microbatteries are high output energy and minimal footprint areas. In addition to the development of new high-performance electrode materials, the device configurations of microbatteries also play an important role in enhancing the output energy and miniaturizing the footprint area. To make a clear vision on the design principle of rechargeable microbatteries, we firstly summarize the typical configurations of microbatteries. The advantages of different configurations are thoroughly discussed from the aspects of fabrication technologies and material engineering. Towards the high energy output at a minimal footprint area, a revolutionary design for microbatteries is of great importance. In this perspective, we review the progress of fabricating microbatteries based on the rolled-up nanotechnology, a derivative origami technology. Finally, we discussed the challenges and perspectives in the device design and materials optimization

MULTILAYER COMPOSITE SOLID ELECTROLYTES FOR LITHIUM ION BATTERIES

Lithium ion batteries (LIBs) are becoming the standard energy storage option for an increasingly diverse range of applications from mobile phones to cars. The conventional liquid electrolytes based LIBs are prone to failure in conditions such as high operating temperature, solvent leakage, lithium dendrites formation and thermal runaway, etc. All-solid-state lithium ion batteries (ASSLIBs) provide a promising power strategy to overcome the drawbacks of liquid electrolyte by substituting the highly flammable organic liquid electrolyte with solid electrolytes (SEs). However, up to the present time, the SEs fabrication for practical ASSLIB construction is still a significant challenge. The existing problems include 1) lower ionic conductivity compared to liquid electrolyte, 2) poor solid-solid contact interface between electrode and electrolyte, 3) volume change of the electrode and 4) the unstable interface of lithium metal/polymer electrolytes causes further capacity fading. With the aim of fabricating SEs which possess optimal properties, a novel SE was developed by forming a multilayer structure. The multilayer SE was fabricated using polymeric and ceramic electrolytes, which can integrate the merits from different layers and materials and optimize its overall performance. In order to choose an ideal ceramic material for the multilayer electrolyte fabrication, three different types of ceramic electrolyte material were synthesized, characterized and evaluated, including Li1.3Ti1.7Al0.3(PO4)3 (LATP), Li7La3Zr2O12 (LLZO) and Li0.5La0.5TiO3 (LLT). Their mechanical strength, ionic conductivity, ease of fabrication and synthesis, and economic expenses of synthesis were evaluated experimentally. The influence of sintering temperature, synthesis route, working temperature and pressure to the overall conductivity were evaluated. From experimental observation and analysis, it was concluded that LATP was an ideal candidate for multilayer electrolyte fabrication for its high conductivity, ease of fabrication and synthesis, etc. The electrochemical properties of polymer electrolyte PEO10-LiN(CF3SO2)2, which was fabricated through hot pressing and solvent casting methods respectively, and also gel-polymer electrolyte PVdF-HFP-LiN(CF3SO2)2 were characterized. The lithium ion transference number, ionic conductivity and thermo-stability were evaluated and discussed. Based on the characterized ceramic and polymer electrolytes, the multilayer electrolyte was fabricated through various lamination protocols, which include hot pressing, dip coating and spray coating methods. It was found that negligible interfacial resistance exist at LATP/LLT and SPE material. Also, an enhanced ionic conductivity was found for the bilayer of LATP/solvent casted SPE. This phenomenon was attributed to the formation of a composition region at the polymer/ceramic electrolyte interface. It was suggested that the boundary of polymer body and ceramic grains may induce a pathway for enhanced ionic transportation. The porous LATP was fabricated using PMMA/PVA/PVB as the pore maker. The influencing factors of sintering temperature, material selection of ceramic and pore makers and fabrication methods deserve further investigation. All-solid-state lithium ion coin cell was successfully fabricated and characterized using the as-prepared multilayer electrolyte and lithium metal anode. The coin cell demonstrated satisfactory charge/discharge capability and cyclability at an elevated temperature of 70 °C. The thickness of SE, operating temperature, material types were important factors in the overall resistance of the multilayer solid electrolyte. The unstable lithium/polymer electrolyte interface at high temperature and high potential is the critical problem for developing ASSLIBs with better cyclability in practice. In the end, future work was proposed and discussed based on the existing work, including 1) multilayer fabrication using glass-ceramic material; 2) optimization of porous ceramic electrolyte; 3) multilayer composite electrolyte using ceramic stabilizer at the lithium/electrolyte interface

DEVELOPMENT OF VAPOR-PHASE DEPOSITED THREE DIMENSIONAL ALL-SOLID-STATE BATTERIES

Thin film solid state batteries (SSBs) are an attractive energy storage technology due to their intrinsic safety, stability, and tailorable form factor. However, as thin film SSBs are typically fabricated only on planar substrates by line-of-sight deposition techniques (e.g. RF sputtering or evaporation), their areal energy storage capacity (< 1 mWh/cm2) and application space is highly limited. Moving to three dimensional architectures provides fundamentally new opportunities in power/energy areal density scaling, but requires a new fabrication process. In this thesis, we describe the development of the first solid state battery chemistry which is grown entirely by atomic layer deposition (ALD), a conformal, vapor-phase deposition technique. We first show the importance of full self-alignment of the active battery layers by measuring and modelling the effects of nonuniform architectures (i.e. does not reduce to a one-dimensional system) on the internal reaction current distribution. By fabricating electrochemical test structures for which generated electrochemical gradients are parallel to the surface, we directly quantify the insertion of lithium into a model cathode material (V2O5) using spatially-resolved x-ray photoelectron spectroscopy (XPS). Using this new technique, we show that poorly electrically contacted high aspect ratio structures show highly nonuniform reaction current distributions, which we describe using an analytical mathematical model incorporating nonlinear Tafel kinetics. A finite-element model incorporating the effects of Li-doping on the local electrical conductivity of V2O5, which was found to be important in describing the observed distributions, is also described. Next, we describe the development of a novel solid state electrolyte, lithium polyphosphazene (LPZ), grown by ALD. We explore the thermal ALD reaction between lithium tert-butoxide and diethyl phosphoramidate, which exhibits self-limiting half-reactions and a growth rate of 0.09 nm/cycle at 300C. The resulting films are primarily characterized by in-situ XPS, AFM, cyclic voltammetry, and impedance spectroscopy. The ALD reaction forms the amorphous product Li2PO2N along with residual hydrocarbon contamination, which is determined to be a promising solid electrolyte with an ionic conductivity of 6.5 × 10-7 S/cm at 35C and wide electrochemical stability window of 0-5.3 V vs. Li/Li+ . The ALD LPZ is integrated into a variety of solid state batteries to test its compatibility with common electrode materials, including LiCoO2 and LiV2O5, as well as flexible substrates. We demonstrate solid state batteries with extraordinarily thin solid state electrolytes, mitigating the moderate ionic conductivity (< 40 nm). Finally, we describe the successful integration of the ALD LPZ into the first all-ALD solid state battery stack, which is conformally deposited onto 3D micromachined silicon substrates and is fabricated entirely at or below 250C. The battery includes ALD current collectors (Ru and TiN), an electrochemically formed LiV2O5 cathode, and a novel ALD tin nitride conversion-type anode. The full cell exhibits a reversible capacity of ~35 μAh cm-2 μmLVO -1 with an average discharge voltage of ~2V. We also describe a novel fabrication process for forming all-ALD battery cells, which is challenging due to ALD’s incompatibility with conventional lithography. By growing the batteries into 3D arrays of varying aspect ratios, we demonstrate upscaling the areal capacity of the battery by approximately one order of magnitude while simultaneously improving the rate performance and round-trip efficiency

ELECTROCHEMICAL PROTECTION OF LITHIUM METAL ANODE IN LITHIUM-SULFUR BATTERIES AND BEYOND

With the growing demand of advanced energy storage devices that have high energy density and high power density to power electric vehicles and electrical grid, scientists and engineers are exploring technologies beyond conventional Li-ion batteries which have transformed the industry in the past thirty years. Li-S batteries have much higher energy density than Li-ion batteries and are gaining momentum. However, the intrinsic issues of Li-S batteries require a comprehensive systematic study of the protection of Li metal anodes to put them into practical applications. In the first study of this dissertation, we investigated using conventional electrolyte of Li-S batteries that includes 1,3-dioxolane to electrochemically pretreat Li metal anodes. We concluded that the electrochemical pretreatment of Li metal anodes generated an organic-inorganic artificial solid electrolyte interface (ASEI) layer that greatly enhanced the battery performance of the Li-S batteries. The properties of this ASEI can be tuned by manipulating the current density and cycle number of the electrochemical pretreatment. In the second study, we studied the comprehensive development and surface protection of Li10GeP2S12 (LGPS) material as solid-state electrolyte, which has ionic conductivity comparable to liquid electrolytes, potentially for solid-state Li-S batteries. Lithium phosphorus oxynitride (LiPON) was coated onto LGPS pellets by atomic layer deposition (ALD). It demonstrated great compatibility with LGPS and extends the electrochemical stability window. The third study explored the potential of transferring this electrochemical pretreatment method to the protection of other metal anodes, particularly Mg. The study discovered the surprising catalytic capability of Mg2+ in the polymerization of solvent 1,3-dioxolane (DOL). A layer with poly-DOL component was also found to grow on the surface of Mg metal anodes as a result of the electrochemical pretreatment, and the overpotential of Mg-Mg symmetric cells cycling dropped with the growth of the layer. Future studies are required to test the effectiveness of this method in Mg batteries. Overall, these studies can help to understand the surface chemistry of the electrochemically pretreated Li metal anodes, provide guidelines on the improvement of Li-S batteries and contribute to the development of solid-state Li-S batteries and multivalent metal anode batteries