Major breakthroughs in battery technologies are needed for electric vehicles that could safely drive longer on a single charge and recharge promptly. At the same time the deployment of wind and solar power for a sustainable economy requires powerful low-cost large-scale batteries with long cycle-life made from sustainable materials resources. It is obvious that the maturing Li-ion battery (LIB) technology relying on costly cathode materials, flammable electrolytes with limited electrochemical stability windows and bulky anodes with limited rate capabilities cannot offer the performance levels required for these key applications. In this talk, current R&D trends in overcoming these challenges will be outlined.

Back to the future - From Li-ion batteries to Li metal batteries: One of the most promising approaches to enhance the energy density and rate capability is to move back from LIBs to batteries that use metallic Li instead as the negative electrode. Replacing conventional graphite or oxide anodes with Li metal opens up a pathway to gravimetric energy densities up to 400 Wh/kg and volumetric energy densities approaching 1000 Wh/L. This approach had been abandoned a few decades ago due to the lack of electrolytes that at that time were known to be stable in contact with metal anodes and high voltage cathodes as well as the hazard of short-circuits by Li dendrites. Recent progress on solid electrolytes raises expectations that these could enable Li-metal batteries by acting as artificial anode protecting solid-electrolyte interfaces and mechanical barriers against dendrite growth.

Quidquid agis ... respice finem – focus on sustainable and scalable designs: For stationary large-scale applications where low cost and volumetric energy density gain importance, analogous strategies are pursued for Na-based batteries, which of course only makes sense if the low-cost high-performance anodes are combined with affordable, scalable cathodes, where high-cost transition metal compounds (e.g. Cobalt) are replaced by earth-abundant cathode materials.

Nihil nisi solidum - From liquid electrolytes to all-solid state batteries: While compatibility with current LIB fabrication may initially favour the replacement of anodes by Li-metal : anode-protecting membrane combinations, it appears natural to get rid of flammable liquid electrolytes altogether in order to enhance safety, (volumetric) energy density as well as reduce the need for enclosure of individual cells and enable longer cycle life systems. While data of individual solid electrolytes imply that this should be within reach, the key challenge remains to be the realisation of electrochemically stable electrolyte:electrode interfaces that ensure smooth charge transfer over a long cycle life despite the volume changes on cycling.

Getting the full picture - From materials design to system design: To overcome performance bottlenecks at system level it is widely recognised that the research focus has to shift from individual materials with record performance to a rational design of devices, which mainly involves the identification and engineering of favourable electrode:electrolyte combinations. Major progress can be expected in this area from combining the emerging experimental in situ and operando characterisation technologies with computational approaches.

Do What You Do Best: Moving from computer-aided to AI design: Analysing the wealth of complex experimental data e.g. from operando experiments or computational characterisations of a vast number of potential materials combinations and matching them to requirement profiles tailored for specific applications with an open mind for novel battery architec¬tures should be a fitting artificial intelligence problem. Thus, the most effective way to accelerate the develop¬ment of high performance energy storage systems may be to set up a dedicated battery design system and feed it with dependable standardised data, leaving the creative design to the AI tool. 

Since the commercialization of lithium-ion battery(LIB) by Sony in 1991, LIB has been the most widely used energy storage device for smart phones, laptop computers, internet of things(IOT), and electric vehicles(EVs). To meet the megatrend of widespread LIB usage, higher capacity and safety must be achieved for long-term operation and stability. Multimodal/multiscale microscopic characterization based on Zeiss light, electron and X-ray microscopy(XRM) systems, combined with atomic force microscopy(AFM), energy-dispersive X-ray spectroscopy(EDS) and Raman systems from the atomic level to the microscale level, is employed to elucidate structural origins and electrical properties of enhanced battery performance and safety.

High resolution imaging and microstructure characterization using Gemini SEM and Crossbeam(FIB): The electrochemical performance of LIB, such as its cyclability and power capability, is highly dependent on electrodes, separator and electrolyte. The high-resolution imaging of main active materials helps to explore what is going on inside the battery with regards to by-products spreading, surface electrolyte interface(SEI) formation, dendrite growth and structural changes. This type of information enables a researcher to understand how the product is operating under the intended service condition and develop the better performance LIB.

Electrical property measurement techniques using Hybrid SEM & AFM, Micro-probing system and Electron Beam Absorption Current(EBAC) systems: The performance of LIB is intrinsically linked to the microstructural and electrical properties of its materials. The unit cell consists of many electronics materials such as current collectors, conducting agent, layered graphite and lithium metal oxide particles to utilize electrons during chemical reactions. Electrical properties such as conductivity, electrical potential, and work function on battery materials and cells are the key information to develop higher quality materials and better performance cells along with customized formulations.

Non-destructive, three-dimensional and multiscale measurements using X-ray microscopy(XRM) system: Advances in XRM Versa systems have enabled non-destructive and three-dimensional microstructural characterization to sub-micron resolution in a unique optics and detector design. This invention allows greater flexibility than conventional computed tomography(CT) system, enabling multi-length scale measurement and volumetric change study that range from the observation of cell swelling and deformation to degradation phenomena of electrode microstructures of LIBs.

In this talk I will give a brief overview of the development of focused ion beam (FIB) systems starting with liquid metal ion sources to the current field emission sources. I will start with some of the early developments at Bell Labs where I worked on the development of a liquid metal ion source based focused ion beam systems and finding suitable applications for this technology. I will give examples of a number of material modification where the FIB systems could be of value.

The use of these ion beam systems can be classified largely in to materials modification, lithography and high resolution imaging. I would like to give some examples from the early work done at NUS on our first Helium ion microscope system and speculate on futuristic experiments.

Innovations in microscopy instruments and workflows enable the development of novel materials in various research fields. These new class of materials require advanced imaging and characterization tools to understand the microstructure and related functional properties for subsequent optimization in different applications.

Electron microscopy has become the workhorse technique in the advanced material research with the development made in electron optical components and detector technologies enabling superior resolution and performance even under stringent beam sensitive conditions. Novel technologies incorporating multiple electron beams, up to 91 beams, have revolutionized the scale and speed of analysis over several orders of magnitude. These new developments have enabled high speed inspection and failure analysis of materials and components.

With the addition of focused ion beam columns, the characterization can be extended to 3D volume. Simultaneous imaging and analytical characterization of materials in 3D in a fully automated manner are providing a wealth of information previously inaccessible with other techniques. Furthermore, ZEISS will also provide the fastest solution in the market for the high-resolution analysis of deeply buried structure with our newly developed femtosecond laser option.

Connected microscopy is another key concept in advanced microscopy. Combining the electron microscopy tools with non-destructive 3D characterization using x-ray microscopy has transformed existing workflows and methods of studying materials and devices. Diffraction contrast tomography, in-situ studies and correlative workflows combining the 3D non-destructive X-ray microscopy with high resolution FIB-SEM tomography are key developments that are addressing the multi-scale challenges in studying these materials.

The aberration-corrected scanning transmission electron microscope (STEM) provides real space imaging and spectroscopy with unprecedented sensitivity down to the single atom level. Thoroughly understanding and tailoring structural defects is extremely significant for understanding the structure-property relations of existing high-performance materials, and more importantly, guiding the design of new materials with improved properties. Several representative studies will be presented.

In 2D materials, sub-Ångstrom information transfer can be achieved at only 40 kV, and point defects and their local environments directly identified to correlate with properties. New edge structures in nanoporous MoS2 are found to exhibit excellent catalytic properties [1], and 2D Mo metal membranes can be fabricated from MoSe2 films via beam induced sputtering of Se [2].

In piezoelectrics, the development of lead-free materials with enhanced properties is urgently required. Precise mapping of atomic displacements reveals a hierarchical nanodomain structure as the origin of excellent properties, the coexistence of ferroelectric phases inside nanodomains and gradual polarization rotation between them [3,4]. Similarly, in thermoelectrics, a hierarchical structure ranging from point defects through nanoscale and microscale precipitates results in a high-performance material with lattice thermal conductivity approaching the theoretical minimum [5].

In oxide thin films, interplay of octahedral rotations, charge transfer and interdiffusion has major influence on carrier density and mobility and magnetic properties. Atomic resolution mapping of atomic displacements provides the most fundamental understanding of ferroelectric properties.

Finally, recent progress in optical sectioning to reveal the 3D structure of extended defects will be presented.

Reference:
[1] X. Zhao, et al., Nano Lett, 18 (2017) 482–490.
[2] X. Zhao, et al., Adv. Mater. (2018) 1707281.
[3] T. Zheng, et al., Energy Environ. Sci, 10 (2017) 528–537.
[4] B. Wu, et al., J Am Chem Soc, 138 (2016)15459–15464.
[5] Y. Xiao, et al., J Am Chem Soc, 139 (2017) 18732–18738.

The ORION NanoFab is an imaging, nanofabrication and characterization platform based on a high brightness and stable Gas Field Ion Source (GFIS). The GFIS employed exhibits a low energy spread, small virtual source size and a high brightness to produce fine probes of Helium and Neon ion beams. This, in conjunction with the shallow escape depth (<1 nm) of the secondary electrons generated by the incident ions, contribute to the high spatial resolution achievable with this technology. In addition to the high resolution, the integrated electron flood gun enables imaging of insulating samples without any conductive coating without charging artifacts. This has opened the application of this technology to a broad spectrum of multidisciplinary applications from basic materials science and semiconductor applications to the biological sciences.

Furthermore, the appreciable sputter yield from helium and neon ions and the small probe size enable material modification and nanopatterning capabilities at the sub-10 nm dimension. Direct milling and material modification with sub-10 nm features on graphene and other 2D materials, plasmonic devices on metals, nanopores and lithography of resists, direct metal and insulator deposition using gas injection systems have already been demonstrated with this tool.

The sputter process with the primary He or Ne ions results in secondary ions generated from the sample surface like in Secondary Ion Mass Spectroscopy (SIMS). By integrating a custom designed mass spectrometer to this platform, analytical and elemental characterization capabilities have been enabled to add-on to the existing capabilities of the tool. The ability to perform high sensitivity surface analysis and depth profiling with large dynamic range detecting all elements and differentiating isotopes with SIMS complements the surface sensitive imaging observed with this tool. We have demonstrated that our instrument is capable of producing elemental SIMS maps with lateral resolution down to 12 nm. Furthermore, the instruments opens up an in-situ correlative imaging technique combining high resolution SE images and SIMS elemental maps for various applications.

Electronic sensor skins are active area of research for many groups globally due to its potential to enable dramatic changes in how we interact with the digital environment. For example, ‘robots’ can don on sensor active skins to shake human hands with comfortable pressure, measure our health biometrics and possibly aid in wound healing. In my talk, I will discuss the development of electronic sensor skins with some historical context, followed by showcasing of several force sensitive electronic skin technologies with high sensitivity, stretchability and bio-mimetic self-healing abilities [1-5]. More recently, we demonstrated a power-efficient artificial mechano-receptor system inspired by biological mechano-receptors [5]. We further used a channelrhodopsin with fast kinetics and large photocurrents as an optical interface to neuronal systems for next generation opto-tactile prosthetic interfaces.

Reference:
[1] L. Y. Chen*, B. C-K Tee*, et al. Continuous wireless pressure monitoring and mapping with ultra-small passive sensors for health monitoring and critical care. Nature Communications 5, 1–10 (2014). (*equal contribution)
[2] B. C.-K. Tee, et al. An electrically and mechanically self-healing composite with pressure- and flexion-sensitive properties for electronic skin applications. Nature Nanotechnology 7, 1–8 (2012).
[3] S. C. B., Mannsfeld, B. C-K Tee et al. Highly sensitive flexible pressure sensors with microstructured rubber dielectric layers. Nature Materials 9, 859–864 (2010).
[4] Skin-Like Sensors of Pressure and Strain Enabled by Transparent, Elastic Films of Carbon Nanotubes, D.J. Lipomi*, M. Vosgueritchian*, B. C-K. Tee* et al., Nature Nanotechnology, 1–6, (2011)
[5] A skin-inspired organic digital mechanoreceptor, B. C-K. Tee et al., Science, 350, 313–316, (2015)

The cutting-edge sensing technology is evolving from silicon based microsensors to the nano-antennas based optical sensors and wearable self-powered flexible sensors. Looking into the new market of internet of the things (IoT), we introduce two kinds of promising sensing technologies in this talk. Firstly, “hybrid metamaterial” absorber platform is presented by integrating the nano-antennas based metamaterial with a gas-selective-trapping polymer for highly selective and miniaturized optical sensing of CO2 gas in the 5–8μm mid-IR spectral window. This optical sensor offers a minimum of 40 ppm detection limit at ambient temperature on a small footprint (20 μm by 20 μm), fast response time (≈2 min), and low hysteresis. Secondly, triboelectric nanogenerator (TENG) based self-powered flexible sensors have been investigated as a sensing platform for various applications including 1) amenity sensor for smart home under IoT concept; 2) implantable flexible volume sensor to detect the fullness of the bladder, where we have also demonstrated a self-controlled system for neurogenic underactive bladder by integrating microactuator and flexible volume sensor; 3) a self-powered 3D controller made of liquid-metal and polydimethylsiloxane (PDMS) mixture that deforms and contacts with different sensing electrodes under different applied force. By employing vector properties of force and signal analysis from the eight sensing electrodes, detection of six-axis directions in 3D space is achieved by analyzing triboelectric sensor outputs for the first time. It is capable of generating a triggering signal to drive a small vehicle in the real world and controlling the attitude (both the position and rotation) of an object in 3D virtual space; 4) a flexible conductive textile sensor to detect the finger motion in terms of self-powered sensory information from textile as a novel human-machine interface towards virtual reality (VR) and Augmented Reality (AR) control applications.

Electron Microscopy is a powerful imaging tool for analysis of composition, ultrastructure and function of biological samples and materials. From tissues and cells to subcellular structures and macromolecular complexes, Transmission and Scanning electron microscopy provides 2D and 3D morphological analysis. Studying and analysing structures in minute detail means we can learn more about how they function, leading to new insights into health and disease.

The presentation will describe several key examples from case studies to illustrate the use of Electron Microscopy. In microorganisms, morphological characterization provided valuable insights into Chikungunya virus of epidemic potential, Enterovirus 71 infection of the brain in Hand, foot and Mouth disease, the role of pili in streptococci, the localization of UL44 protein in HCMV infection. Working with cells, we can observe how Drosophilia cells use tunneling nanotubes for transport, how Shigella survives in Hela cells, Listeria monocytogenes in zebrafish and Chikungunya virus in Mosquitoes.
All are great examples of interactions between microorganisms and host cells and tissues.

Electron microscopy imaging has been used as a valuable research tool in the Life Sciences for many years. From research of single cell organisms, viruses or eukaryotic cells to identification of synaptic contacts between neurons, the ability to image biological samples in nanometer resolution has proven to be extremely valuable for many areas of biological research. The majority of these examples has been studied using the well-established Transmission Electron Microscopy (TEM) technique which requires thin sample preparations and limits the third dimension in scale and resolution.

Recent developments in Scanning Electron Microscopy (SEM) opens the spectrum of high resolution and high-volume imaging of biological tissue. Based on sample block-face scanning in combination with milling (e.g. Focused Ion Beam (FIB)) or block-face cutting techniques, SEM enables dramatic resolution improvements in the third dimension above what is possible with TEM. Furthermore, SEM offers large field of view imaging and opens up applications that have previously been unachievable in the lab.

In addition to the high volume and high-resolution imaging of SEM, FIB 3D SEM offers three-dimensional imaging of unstained cryo-frozen biological tissue opening the field for novel correlative studies using confocal microscopy. These include 3D colocalization of genetic markers and increase of context information for electron microscopy data.

Further correlative applications utilize X-Ray Microscopy (XRM) to non-destructively assess sample structure prior to subsequent analysis using electron microscopy. The correlation of datasets across length scale and imaging modality (light microscopy to XRM to electron microscopy) extends the portfolio of applications for research that has previously been unachievable in the lab. In addition, pre-scanning assessment of biological samples prior to 3D electron microscope techniques such as serial sectioning SEM or Focused Ion Beam SEM reduces experiment failure rate and experiment duration.

This talk will introduce some of the latest work in Life Science using 3D SEM techniques and discuss the future possibilities that imaging with this technology could provide.