Surface Chemical Analysis of Solid-Electrolyte Interphase Layer on Germanium Thin Films and the Effect of Vinylene Carbonate Electrolyte Additive

Germanium thin-film anodes for Li-ion battery applications are the focus of the present work. As part of this chapter, we shall briefly review the use of germanium thin films in Li-ion batteries, and subsequently, new results pertaining to the effect of vinylene carbonate (VC) as electrolyte additive on the electrochemical performance are presented. We have used cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy to investigate the performance. Thin-film electrode performance with 0 wt. %, 5 wt. %, and 10 wt.% VC as electrolyte additive was compared to understand the role of additive’s concentration. The cell with 5 wt.% VC as electrolyte additive exhibited best performance with high specific capacity of 975 mAh/g, with a retention of 94 and 99% Coulombic efficiency at the end of 100 cycles. Ex situ surface chemical analysis of the solid-electrolyte interphase (SEI) layer has been studied in detail using X-ray photoelectron spectroscopy and correlated with the electrochemical performance

High-Performance Zr-Doped P3-Type Na_0.67Ni_0.33Mn_0.67O₂ Cathode for Na-Ion Battery Applications

Sodium-ion battery (SIB) technology started to bloom along with lithium-ion batteries (LIBs) as a supportive energy source to alleviate the cost of lithium sources for the development of energy storage devices and electric vehicles. Layered cathode materials are considered potential candidates to produce high-energy-density batteries. Among the layered cathode materials, P3-type cathodes are the least investigated in spite of their capacities, which are comparable to those of P2-type cathodes. P3-type cathodes show high polarization, leading to a poor cycle life, which impedes their extensive use in practical applications. In this work, we report on zirconium doping as an effective strategy to improve cycling stability and reduce voltage fading, another serious issue of layered cathode materials. It is found that an optimum composition of the P3-type cathode with Zr doping at the Mn site, leading to a composition of Na0.67Ni0.33Mn0.64Zr0.033O2, shows good electrochemical performance in terms of retention (89% after 100 cycles) when compared to Na0.67Ni0.33Mn0.60Zr0.067O2 (85% after 100 cycles) and an undoped sample (83% after 100 cycles). Also, remarkable performance is delivered by the Na0.67Ni0.33Mn0.64Zr0.033O2 sample, with a retention rate of 72% after 450 cycles. This result is also supported by an analysis of the amount of polarization for undoped and doped samples, which found that doping helps in improving the diffusion of ions, and the least polarization is obtained for the Na0.67Ni0.33Mn0.64Zr0.033O2 sample

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing.

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope

Ultralong (10K) Cycle-Life and High-Power Li-Ion Storage in Li₄Ti₅O₁₂ Films Developed via Sustainable Electrophoretic Deposition Process

A critical challenge for Li-ion battery electrodes is to provide high energy density, power density, and excellent cycle-life combined with safety and sustainability. Increasing conductive additive concentration in composite electrodes enables relatively higher power density but compromises energy density. The energy density increment can be attained by fabricating additive-free electrodes, maximizing active mass, while improving the charge transport to maintain high power density is significantly important especially for materials that have inherent conductivity issues (such as Li₄Ti₅O₁₂). Herein, we demonstrate a nanostructured spinel lithium titanate (LTO) anode which is inherently safe and benign, deposited without additives through a green and scalable electrophoretic deposition (EPD) technique. The electrode is capable of rendering high capacity (160 mA h/g), high rate capability (72C), and excellent cycle-life (10 000 cycles). The outstanding performance in terms of cycle-life, energy, and power is attributed to the formation of electrically interconnected LTO nanoparticle films with porosity enabling better electrolyte percolation and rapid charge transfer. The porous nature of the film is visualized utilizing confocal fluorescence microscopy imaging which confirms the dye impregnation into the bulk of the films as well. The benefit of EPD is due to its potential for sustainability, scalability, rapid deposition rate, simple apparatus, and formation of porous film

Sustainable Chemical Synthesis for Phosphorus-Doping of TiO₂ Nanoparticles by Upcycling Human Urine and Impact of Doping on Energy Applications

Recently, there has been significant research interest toward sustainable chemical synthesis and processing of nanomaterials. Human urine, a pollutant, requires energy intensive processing steps prior to releasing into rivers and oceans. Upcyling urine has been proposed and practiced as a sustainable process in the past. Doping is one of the foremost processes to elevate the functionality of nanomaterials depending on the applications it is sought for. Phosphorus doping in to TiO₂ nanomaterials has been of research interest over a decade now, that has been chiefly done using acidic precursors. Here we demonstrate, upcycling urine, a sustainable process for phosphorus doping into TiO₂ lattice. Upon doping the changes in morphology, surface chemistry and band gap is studied in detail and compared with undoped TiO₂ that is prepared using deionized water instead of urine. X-ray photoelectron spectroscopy confirmed that the P was replacing Ti in the lattice and exists in P⁵⁺ state with a quantified concentration of 2.5–3 at %. P-doped nanoparticles were almost 50% smaller in size with a lower concentration of surface −OH groups and a band gap increase of 0.3 eV. Finally, impact of these changes on energy devices such as dye-sensitized solar cells and li-ion batteries has been investigated. It is confirmed that P-doping induced surface chemical and band gap changes in TiO₂ affected the solar cell characteristics negatively, while the smaller particle size and possibly wider surface channels improved Li-ion battery performance

Reciprocal Salt Flux Growth of LiFePO₄ Single Crystals with Controlled Defect Concentrations

Improved methods for the flux growth of single crystals of the important battery material LiFePO₄ have been developed, allowing the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. The structural characterization of these samples by both powder X-ray diffraction and single crystal diffraction (X-ray and neutron) indicates that the samples are typically stoichiometric with a very low concentration of Fe defects on the Li site, though crystals with larger concentrations of defects can be specifically grown using Fe-rich fluxes. These defects occur through the formation of a Fe-rich (Li_{1–2<i>x</i>}Fe_<i>x</i>)­FePO₄ partial solid solution, in contrast to the antisite defects more commonly discussed in the literature which would preserve the ideal LiFePO₄ stoichiometry. The LiFePO₄ defects are shown to be sarcopside-like (2 Li⁺ → Fe²⁺ + vacancy) based on compositions refined from single crystal diffraction data, the observed dependence of unit cell parameters on defect concentration, and their observed phase behavior (defects only appear in growths from fluxes which are Fe-rich relative to stoichiometric LiFePO₄). The distribution of defects has been studied by aberration corrected scanning transmission electron microscopy and was found to be highly inhomogenous, suggesting that defect-containing crystals may consist of endotaxial intergrowths of olivine LiFePO₄ and sarcopside Fe₃(PO₄)₂ in a manner that minimizes the detrimental influence of Fe_Li defects on the rate of Li-ion transport within crystallites

Reciprocal Salt Flux Growth of LiFePO₄ Single Crystals with Controlled Defect Concentrations

Improved methods for the flux growth of single crystals of the important battery material LiFePO₄ have been developed, allowing the facile preparation of single crystals up to 1 cm across with well-developed facets at relatively low temperatures. The structural characterization of these samples by both powder X-ray diffraction and single crystal diffraction (X-ray and neutron) indicates that the samples are typically stoichiometric with a very low concentration of Fe defects on the Li site, though crystals with larger concentrations of defects can be specifically grown using Fe-rich fluxes. These defects occur through the formation of a Fe-rich (Li_{1–2<i>x</i>}Fe_<i>x</i>)­FePO₄ partial solid solution, in contrast to the antisite defects more commonly discussed in the literature which would preserve the ideal LiFePO₄ stoichiometry. The LiFePO₄ defects are shown to be sarcopside-like (2 Li⁺ → Fe²⁺ + vacancy) based on compositions refined from single crystal diffraction data, the observed dependence of unit cell parameters on defect concentration, and their observed phase behavior (defects only appear in growths from fluxes which are Fe-rich relative to stoichiometric LiFePO₄). The distribution of defects has been studied by aberration corrected scanning transmission electron microscopy and was found to be highly inhomogenous, suggesting that defect-containing crystals may consist of endotaxial intergrowths of olivine LiFePO₄ and sarcopside Fe₃(PO₄)₂ in a manner that minimizes the detrimental influence of Fe_Li defects on the rate of Li-ion transport within crystallites

In Situ STEM-EELS Observation of Nanoscale Interfacial Phenomena in All-Solid-State Batteries

Behaviors of functional interfaces are crucial factors in the performance and safety of energy storage and conversion devices. Indeed, solid electrode–solid electrolyte interfacial impedance is now considered the main limiting factor in all-solid-state batteries rather than low ionic conductivity of the solid electrolyte. Here, we present a new approach to conducting in situ scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) in order to uncover the unique interfacial phenomena related to lithium ion transport and its corresponding charge transfer. Our approach allowed quantitative spectroscopic characterization of a galvanostatically biased electrochemical system under in situ conditions. Using a LiCoO₂/LiPON/Si thin film battery, an unexpected structurally disordered interfacial layer between LiCoO₂ cathode and LiPON electrolyte was discovered to be inherent to this interface without cycling. During in situ charging, spectroscopic characterization revealed that this interfacial layer evolved to form highly oxidized Co ions species along with lithium oxide and lithium peroxide species. These findings suggest that the mechanism of interfacial impedance at the LiCoO₂/LiPON interface is caused by chemical changes rather than space charge effects. Insights gained from this technique will shed light on important challenges of interfaces in all-solid-state energy storage and conversion systems and facilitate improved engineering of devices operated far from equilibrium