A Double Layer of Intrigue: When Liquids Meet Solids. A graphene-capped liquid cell was developed to interrogate liquids, and especially bias-controlled graphene(solid)-liquid interfaces, where the electric double layer resides.  IR imaging and nano-FTIR spectroscopy confirmed liquid cell function and nanoscale resolution of the optical characterization techniques in cases of water and battery-grade nonaqueous organic solvents.  Comparison of ATR-FTIR and nano-FTIR of ionic salt solutions revealed interface specific species associated with the electric double layer and whose relative concentrations were reversibly controllable via electrostatic biasing that altered charge on the graphene electrode.  This pioneering work has inspired others to adopt similar characterization strategies to study living cells, protein assembly, oxide-electrolyte interfaces, and more, and paved a way for future in situ characterizations of a multiplicity of technologically relevant solid-liquid interfaces, including those found in beyond Li-ion batteries.

~~further details can be found in my co-first author publication in Nano Letters

Looking Inside a Battery with Infrared Light. Solid-state batteries based on polymer electrolytes are a promising beyond Li-ion candidate for their low self-discharge rate, compatibility with roll-to-roll large scale manufacturing, and mechanical flexibility that enables solid-state batteries of various shapes.  However, many performance limitations believed to be associated with the electrode-electrolyte interface need to be better understood, and overcome.  In this work we “looked inside” and characterized functional solid-state polymer battery interfaces at various electrochemical states.  Sub-diffraction-limit in situ nano-FTIR spectroscopy measurements of the buried interface revealed that nanoscale structural and stochiometric heterogeneities intrinsically exist in the polymer electrolyte, which gives rise to undesirable heterogeneities in local ionic conductivity and current densities, Li plating amounts, electrolyte decomposition, and SEI formation.  Thus, for metallic Li anode solid-state polymer batteries to be realized, targeted molecular level engineering of the polymer electrolyte surface will likely need to be used to circumvent these intrinsic heterogeneities.

~~further details can be found in my co-first author publication in Nature Communications

Demystifying the Detection and Signal Processing Scheme for nano-FTIR. For decades Fourier transform infrared spectroscopy (FTIR) has arguably been the gold standard for nondestructive chemical fingerprinting.  However, the diffraction limit, which governs the size to which conventional optics can focus light, has limited the spatial resolution of FTIR to roughly the microscale.  Hence, FTIR has no doubt been utilized significantly less than it could have been during the “nano revolution,” had it not been for this physical limit.  Since the introduction of near-field-based IR nano-optics which circumvent the diffraction limit for true infrared nano-FTIR, the characterization method has been garnering significant interest over a breadth of disciplines.  However, the combination of the technique’s complexity and varied practitioner background, lends itself to a sub-optimal understanding of the technique’s implementation, and complicates data interpretation.  I have derived the detection and processing steps involved in producing nano-FTIR spectra.  The largely self-contained work (i) explains how normalized complex-valued nano-FTIR spectra are generated, (ii) rationalizes why the real and imaginary components of spectra relate to dispersion and absorption respectively, (iii) derives a new and generally valid expression for spectra which can be used as a springboard for additional modeling of the scattering processes, and (iv) provides a simple algebraic expression, that is a function of the real and imaginary parts of the nano-FTIR spectra, that approximates the sample’s local extinction coefficient and matches ATR-FTIR data more closely than the nano-FTIR phase, imaginary part, or ratio of reflection coefficients model.

~~further details can be found in my first author publication in Advanced Functional Materials

Reviewing Recent History of Nanoscale Infrared Characterization of Electrochemical Materials and Interfaces. Electrochemical interfaces are central to the function and performance of energy storage devices. Thus, the development of new methods to characterize these interfaces, in conjunction with electrochemical performance, is essential for bridging the existing knowledge gaps and accelerating the development of energy storage technologies.  Of particular need is the ability to characterize surfaces or interfaces in a non-destructive way with adequate resolution to discern individual structural and chemical building blocks. To this end, sub-diffraction-limit low-energy optical probes that exploit near-field interactions, such as pseudoheterodyne imaging, photothermal AFM-IR, and nanoscale Fourier transform infrared spectroscopy, are powerful emerging techniques.  These are capable of surface probing and imaging at nanometer resolution.  This review outlines recent efforts to characterize ex situ and in situ electrode materials and electrochemical interfaces in rechargeable batteries with infrared near-field probes.

~~further details can be found in my first author publication in Curr. Opinion in Electrochem. 

Strained Relations can Turn Parasitic in Batteries too. It is well known that Si possess an impressively large specific energy density - almost an order of magnitude more than graphite (3579 mAh/g vs. 372 mAh/g).  Equally well known are a handful of challenges that need to be overcome for commericialization of Si anodes.  Most orriginate from the large and dynamic volume changes that Si undergoes during cycling and associated mechanical degradation mechanisms.  Encouragingly, many of these challenges have been addressed through various nanotechnologies, which have enabled Si-anode Li-ion batteries with much imporoved cycle life.  However, Si-anode Li-ion batteries still suffer from subpar calendar life.  In this work two custom cells were designed, for a comparative study: one allowed, and one suppressed,  static strain on the SEI.  We found that parasictic currentls in statically strained cases where as much as 25% greater than their unstrained counterparts.  Spectroscopies of the interfaces revealed that static mechanical deformation of the SEI on Si reduces pasivation stability (and therefore calendar life) by allowing EMC to selectively penetrate the SEI, and increase parasitic reacations.  This research provided helpful insights into how strategic steps can be taken to increase the passivation stability/calendar life of Si-andode Li-ion batteries. 

~~further details can be found in my co-first author publication in ACS Nano 

Li Dynamics within Stressed Solid-State Oxide Electrolytes.  Pascalammetry is a characterization approach I invented which draws inspiration from voltammetry.  In pascalammetry, a stress waveform is applied to a diffusion-limited solid-state battery at a fixed cell voltage, and induced currents are measured and analyzed.  By accessing this rarely studied thermodynamic phase space, pascalammetry has proven invaluable in elucidating how ions transport through stressed and degrading solid state electrolytes.  If the time dependence of induced current transients deviates from Cottrell’s famous prediction in a certain way, this indicates high levels of stress within the electrolyte and the onset of stress-assisted diffusion.  I demonstrated this both empirically, and theoretically, by deriving and solving a modified "diffusion-activation equation" which allows for the activation of latent ionic species within the electrolyte to diffuse as a result of increased stress.  Representative data for stress-step pascalammetry measurements are displayed on the right-hand side of the Figure.

~~further details can be found in my first author publication in Science Advances

Nanoscale Li Manipulation & Kinetics on Model Si Electrodes. Scanning Li-nanopipette and probe microscopy is based on an open-ended multi-walled carbon nanotube affixed to the apex of a conductive atomic force microscope cantilever and serves as both probe-tip and working electrode (top left of Figure).  In this way, quantities of  attograms of Li (hundreds to hundreds-of-thousands of atoms) can be electrochemically transferred with local nm-scale precision (top right of figure).  Subsequent, in situ topographic characterization over time (bottom of figure), in conjunction with a 2D diffusion modeling scheme I also developed, can yield surface transport properties of Li on battery electrode surfaces. 

~~further details can be found in my first author publication in Small

Solid-State Electrochemistry at the Nanoscale. Nanobattery(Microbattery) Probes are metallic scanning tunneling microscope tips clad with nano(micro)-thick layers of active battery materials.  When mechanical contact is made with a counter or working electrode surface of choice, a localnanobattery (microbattery) full-cell is created (left side of Figure).  Since the lion’s share of electrochemical energy storage experiments are performed in layered devices, like coin or pouch cells, all measurement results using such devices are implicitly insensitive to any form of planar heterogeneity in performance because results are averaged over the entire interfacial area.  Nanobattery (Microbattery) probes enable precision-based local lithiation at the nanoscale (microscale), in order to study how local (and non-local) electrochemistry is influenced by local properties such as topography, Li-content, stress, degradation, and more.  The right-hand side of the Figure shows a representative example of a CV collected in this manner; note the current scale is in pA.

~~further details can be found in my Ph.D. dissertation

Electronic Phase Transitions in Battery Materials. Inverted scanning tunneling spectroscopy inverts the paradigm of scanning tunneling spectroscopy by bringing a tip clad with a semiconducting battery material close to a metallic surface in order to perform IV tunneling measurements to determine the electronic band gap of the battery material at the tip’s end (left side of Figure). The tip-end in this case mimics the apex of an individual, large aspect ratio, nanoscale structure within a mesoscale architecture of nanostructures – like the end of a nanotube in a forest of nanotubes.  This technique enables the electrical characterization of nano-thin material coatings at the apex of high aspect ratio nanostructures, in stochiometric and sub-stochiometric states (right side of Figure).

~~further details will be found in my first author work to be published soon