Enhancing Proton Co-Intercalation in Iron Ion Batteries Cathodes for Increased Capacity.

Recently, aqueous iron ion batteries (AIIBs) using iron metal anodes have gained traction in the battery community as low-cost and sustainable solutions for green energy storage. However, the development of AIIBs is significantly hindered by the limited capacity of existing cathode materials and the poor intercalation kinetic of Fe2+. Herein, we propose a H+ and Fe2+ co-intercalation electrochemistry in AIIBs to boost the capacity and rate capability of cathode materials such as iron hexacyanoferrate (FeHCF) and Na4Fe3(PO4)2(P2O7) (NFPP). This is achieved through an electrochemical activation step during which a FeOOH nanowire layer is formed in situ on the cathode. This layer facilitates H+ co-intercalation in AIIBs, resulting in a high specific capacity of 151 mAh g-1 and 93% capacity retention over 500 cycles for activated FeHCF cathodes. We found that this activation process can also be applied to other cathode chemistries, such as NFPP, where we found that the cathode capacity is doubled as a result of this process. Overall, the proposed H+/Fe2+ co-insertion electrochemistry expands the range of applications for AIBBs, in particular as a sustainable solution for storing renewable energy.

Origins and Importance of Intragranular Cracking in Layered Lithium Transition Metal Oxide Cathodes.

Li-ion batteries have a pivotal role in the transition toward electric transportation. Ni-rich layered transition metal oxide (LTMO) cathode materials promise high specific capacity and lower cost but exhibit faster degradation compared with lower Ni alternatives. Here, we employ high-resolution electron microscopy and spectroscopy techniques to investigate the nanoscale origins and impact on performance of intragranular cracking (within primary crystals) in Ni-rich LTMOs. We find that intragranular cracking is widespread in charged specimens early in cycle life but uncommon in discharged samples even after cycling. The distribution of intragranular cracking is highly inhomogeneous. We conclude that intragranular cracking is caused by local stresses that can have several independent sources: neighboring particle anisotropic expansion/contraction, Li- and TM-inhomogeneities at the primary and secondary particle levels, and interfacing of electrochemically active and inactive phases. Our results suggest that intragranular cracks can manifest at different points of life of the cathode and can potentially lead to capacity fade and impedance rise of LTMO cathodes through plane gliding and particle detachment that lead to exposure of additional surfaces to the electrolyte and loss of electrical contact.

Surface reduction in lithium- and manganese-rich layered cathodes for lithium ion batteries drives voltage decay.

Li- and Mn-rich layered oxides (Li1.2Ni0.2Mn0.6O2) are actively pursued as high energy and sustainable alternatives to the current Li-ion battery cathodes that contain Co. However, the severe decay in discharge voltage observed in these cathodes needs to be addressed before they can find commercial applications. A few mechanisms differing in origin have been proposed to explain the voltage fade, which may be caused by differences in material composition, morphology and electrochemical testing protocols. Here, these challenges are addressed by synthesising Li1.2Ni0.2Mn0.6O2 using three different hydrothermal and solid-state approaches and studying their degradation using the same cell design and cycling protocols. The voltage fade is found to be similar under the same electrochemical testing protocols, regardless of the synthesis method. X-ray absorption near edge, extended X-ray absorption fine structure spectroscopies, and energy loss spectroscopy in a scanning transmission electron microscope indicate only minor changes in the bulk Mn oxidation state but reveal a much more reduced particle surface upon extended cycling. No spinel phase is seen via the bulk structural characterisation methods of synchrotron X-ray diffraction, 7Li magic angle spinning solid state nuclear magnetic resonance and Raman spectroscopy. Thus, the voltage fade is believed to largely result from a heavily reduced particle surface. This hypothesis is further confirmed by galvanostatic intermittent titration technique analysis, which indicates that only very small shifts in equilibrium potential take place, in contrast to the overpotential which builds up after cycling. This suggests that a major source of the voltage decay is kinetic in origin, resulting from a heavily reduced particle surface with slow Li transport.

Onset Potential for Electrolyte Oxidation and Ni-Rich Cathode Degradation in Lithium-Ion Batteries.

High-capacity Ni-rich layered metal oxide cathodes are highly desirable to increase the energy density of lithium-ion batteries. However, these materials suffer from poor cycling performance, which is exacerbated by increased cell voltage. We demonstrate here the detrimental effect of ethylene carbonate (EC), a core component in conventional electrolytes, when NMC811 (LiNi0.8Mn0.1Co0.1O2) is charged above 4.4 V vs Li/Li+-the onset potential for lattice oxygen release. Oxygen loss is enhanced by EC-containing electrolytes-compared to EC-free-and correlates with more electrolyte oxidation/breakdown and cathode surface degradation, which increase concurrently above 4.4 V. In contrast, NMC111 (LiNi0.33Mn0.33Co0.33O2), which does not release oxygen up to 4.6 V, shows a similar extent of degradation irrespective of the electrolyte. This work highlights the incompatibility between conventional EC-based electrolytes and Ni-rich cathodes (more generally, cathodes that release lattice oxygen such as Li-/Mn-rich and disordered rocksalt cathodes) and motivates further work on wider classes of electrolytes and additives.

Structurally Colored Radiative Cooling Cellulosic Films.

Daytime radiative cooling (DRC) materials offer a sustainable approach to thermal management by exploiting net positive heat transfer to deep space. While such materials typically have a white or mirror-like appearance to maximize solar reflection, extending the palette of available colors is required to promote their real-world utilization. However, the incorporation of conventional absorption-based colorants inevitably leads to solar heating, which counteracts any radiative cooling effect. In this work, efficient sub-ambient DRC (Day: -4 °C, Night: -11 °C) from a vibrant, structurally colored film prepared from naturally derived cellulose nanocrystals (CNCs), is instead demonstrated. Arising from the underlying photonic nanostructure, the film selectively reflects visible light resulting in intense, fade-resistant coloration, while maintaining a low solar absorption (≈3%). Additionally, a high emission within the mid-infrared atmospheric window (>90%) allows for significant radiative heat loss. By coating such CNC films onto a highly scattering, porous ethylcellulose (EC) base layer, any sunlight that penetrates the CNC layer is backscattered by the EC layer below, achieving broadband solar reflection and vibrant structural color simultaneously. Finally, scalable manufacturing using a commercially relevant roll-to-roll process validates the potential to produce such colored radiative cooling materials at a large scale from a low-cost and sustainable feedstock.

Cycle-Induced Interfacial Degradation and Transition-Metal Cross-Over in LiNi0.8Mn0.1Co0.1O2-Graphite Cells.

Ni-rich lithium nickel manganese cobalt (NMC) oxide cathode materials promise Li-ion batteries with increased energy density and lower cost. However, higher Ni content is accompanied by accelerated degradation and thus poor cycle lifetime, with the underlying mechanisms and their relative contributions still poorly understood. Here, we combine electrochemical analysis with surface-sensitive X-ray photoelectron and absorption spectroscopies to observe the interfacial degradation occurring in LiNi0.8Mn0.1Co0.1O2-graphite full cells over hundreds of cycles between fixed cell voltages (2.5-4.2 V). Capacity losses during the first ∼200 cycles are primarily attributable to a loss of active lithium through electrolyte reduction on the graphite anode, seen as thickening of the solid-electrolyte interphase (SEI). As a result, the cathode reaches ever-higher potentials at the end of charge, and with further cycling, a regime is entered where losses in accessible NMC capacity begin to limit cycle life. This is accompanied by accelerated transition-metal reduction at the NMC surface, thickening of the cathode electrolyte interphase, decomposition of residual lithium carbonate, and increased cell impedance. Transition-metal dissolution is also detected through increased incorporation into and thickening of the SEI, with Mn found to be initially most prevalent, while the proportion of Ni increases with cycling. The observed evolution of anode and cathode surface layers improves our understanding of the interconnected nature of the degradation occurring at each electrode and the impact on capacity retention, informing efforts to achieve a longer cycle lifetime in Ni-rich NMCs.

Hollow-core optical fibre sensors for operando Raman spectroscopy investigation of Li-ion battery liquid electrolytes.

Improved analytical tools are urgently required to identify degradation and failure mechanisms in Li-ion batteries. However, understanding and ultimately avoiding these detrimental mechanisms requires continuous tracking of complex electrochemical processes in different battery components. Here, we report an operando spectroscopy method that enables monitoring the chemistry of a carbonate-based liquid electrolyte during electrochemical cycling in Li-ion batteries with a graphite anode and a LiNi0.8Mn0.1Co0.1O2 cathode. By embedding a hollow-core optical fibre probe inside a lab-scale pouch cell, we demonstrate the effective evolution of the liquid electrolyte species by background-free Raman spectroscopy. The analysis of the spectroscopy measurements reveals changes in the ratio of carbonate solvents and electrolyte additives as a function of the cell voltage and show the potential to track the lithium-ion solvation dynamics. The proposed operando methodology contributes to understanding better the current Li-ion battery limitations and paves the way for studies of the degradation mechanisms in different electrochemical energy storage systems.

Electrolyte Reactivity at the Charged Ni-Rich Cathode Interface and Degradation in Li-Ion Batteries.

The chemical and electrochemical reactions at the positive electrode-electrolyte interface in Li-ion batteries are hugely influential on cycle life and safety. Ni-rich layered transition metal oxides exhibit higher interfacial reactivity than their lower Ni-content analogues, reacting via mechanisms that are poorly understood. Here, we study the pivotal role of the electrolyte solvent, specifically cyclic ethylene carbonate (EC) and linear ethyl methyl carbonate (EMC), in determining the interfacial reactivity at charged LiNi0.33Mn0.33Co0.33O2 (NMC111) and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathodes by using both single-solvent model electrolytes and the mixed solvents used in commercial cells. While NMC111 exhibits similar parasitic currents with EC-containing and EC-free electrolytes during high voltage holds in NMC/Li4Ti5O12 (LTO) cells, this is not the case for NMC811. Online gas analysis reveals that the solvent-dependent reactivity for Ni-rich cathodes is related to the extent of lattice oxygen release and accompanying electrolyte decomposition, which is higher for EC-containing than EC-free electrolytes. Combined findings from electrochemical impedance spectroscopy (EIS), TEM, solution NMR, ICP, and XPS reveal that the electrolyte solvent has a profound impact on the degradation of the Ni-rich cathode and the electrolyte. Higher lattice oxygen release with EC-containing electrolytes is coupled with higher cathode interfacial impedance, a thicker oxygen-deficient rock-salt surface reconstruction layer, more electrolyte solvent and salt breakdown, and higher amounts of transition metal dissolution. These processes are suppressed in the EC-free electrolyte, highlighting the incompatibility between Ni-rich cathodes and conventional electrolyte solvents. Finally, new mechanistic insights into the chemical oxidation pathways of electrolyte solvents and, critically, the knock-on chemical and electrochemical reactions that further degrade the electrolyte and electrodes curtailing battery lifetime are provided.

Large-scale fabrication of structurally coloured cellulose nanocrystal films and effect pigments.

Cellulose nanocrystals are renewable plant-based colloidal particles capable of forming photonic films by solvent-evaporation-driven self-assembly. So far, the cellulose nanocrystal self-assembly process has been studied only at a small scale, neglecting the limitations and challenges posed by the continuous deposition processes that are required to exploit this sustainable material in an industrial context. Here, we addressed these limitations by using roll-to-roll deposition to produce large-area photonic films, which required optimization of the formulation of the cellulose nanocrystal suspension and the deposition and drying conditions. Furthermore, we showed how metre-long structurally coloured films can be processed into effect pigments and glitters that are dispersible, even in water-based formulations. These promising effect pigments are an industrially relevant cellulose-based alternative to current products that are either micro-polluting (for example, non-biodegradable microplastic glitters) or based on carcinogenic, unsustainable or unethically sourced compounds (for example, titania or mica).

The influence of electrochemical cycling protocols on capacity loss in nickel-rich lithium-ion batteries.

The transition towards electric vehicles and more sustainable transportation is dependent on lithium-ion battery (LIB) performance. Ni-rich layered transition metal oxides, such as NMC811 (LiNi0.8Mn0.1Co0.1O2), are promising cathode candidates for LIBs due to their higher specific capacity and lower cost compared with lower Ni content materials. However, complex degradation mechanisms inhibit their use. In this work, tailored aging protocols are employed to decouple the effect of electrochemical stimuli on the degradation mechanisms in graphite/NMC811 full cells. Using these protocols, impedance measurements, and differential voltage analysis, the primary drivers for capacity fade and impedance rise are shown to be large state of charge changes combined with high upper cut-off voltage. Focused ion beam-scanning electron microscopy highlights that extensive microscale NMC particle cracking, caused by electrode manufacturing and calendering, is present prior to aging and not immediately detrimental to the gravimetric capacity and impedance. Scanning transmission electron microscopy electron energy loss spectroscopy reveals a correlation between impedance rise and the level of transition metal reduction at the surfaces of aged NMC811. The present study provides insight into the leading causes for LIB performance fading, and highlights the defining role played by the evolving properties of the cathode particle surface layer.

FullyPrinted Flexible Plasmonic Metafilms with Directional Color Dynamics.

Plasmonic metafilms have been widely utilized to generate vivid colors, but making them both active and flexible simultaneously remains a great challenge. Here flexible active plasmonic metafilms constructed by printing electrochromic nanoparticles onto ultrathin metal films (<15 nm) are presented, offering low-power electricallydriven color switching. In conjunction with commercially available printing techniques, such flexible devices can be patterned using lithography-free approaches, opening up potential for fullyprinted electrochromic devices. Directional optical effects and dynamics show perceived upward and downward colorations can differ, arising from the dissimilar plasmonic mode excitation between nanoparticles and ultrathin metal films.

Corrigendum: 3D Hybrid Scaffolds Based on PEDOT:PSS/MWCNT Composites.

[This corrects the article DOI: 10.3389/fchem.2019.00363.].

3D Hybrid Scaffolds Based on PEDOT:PSS/MWCNT Composites.

Conducting polymer scaffolds combine the soft-porous structures of scaffolds with the electrical properties of conducting polymers. In most cases, such functional systems are developed by combining an insulating scaffold matrix with electrically conducting materials in a 3D hybrid network. However, issues arising from the poor electronic properties of such hybrid systems, hinder their application in many areas. This work reports on the design of a 3D electroactive scaffold, which is free of an insulating matrix. These 3D polymer constructs comprise of a water soluble conducting polymer (PEDOT:PSS) and multi-walled carbon nanotubes (MWCNTs). The insertion of the MWCNTs in the 3D polymer matrix directly contributes to the electron transport efficiency, resulting in a 7-fold decrease in resistivity values. The distribution of CNTs, as characterized by SEM and Raman spectroscopy, further define the micro- and nano-structural topography while providing active sites for protein attachment, thereby rendering the system suitable for biological/sensing applications. The resulting scaffolds, combine high porosity, mechanical stability and excellent conducting properties, thus can be suitable for a variety of applications ranging from tissue engineering and biomedical devices to (bio-) energy storage.

Scalable electrochromic nanopixels using plasmonics.

Plasmonic metasurfaces are a promising route for flat panel display applications due to their full color gamut and high spatial resolution. However, this plasmonic coloration cannot be readily tuned and requires expensive lithographic techniques. Here, we present scalable electrically driven color-changing metasurfaces constructed using a bottom-up solution process that controls the crucial plasmonic gaps and fills them with an active medium. Electrochromic nanoparticles are coated onto a metallic mirror, providing the smallest-area active plasmonic pixels to date. These nanopixels show strong scattering colors and are electrically tunable across >100-nm wavelength ranges. Their bistable behavior (with persistence times exceeding hundreds of seconds) and ultralow energy consumption (9 fJ per pixel) offer vivid, uniform, nonfading color that can be tuned at high refresh rates (>50 Hz) and optical contrast (>50%). These dynamics scale from the single nanoparticle level to multicentimeter scale films in subwavelength thickness devices, which are a hundredfold thinner than current displays.

Strongly coloured thiocyanate frameworks with perovskite-analogue structures.

We report the first examples of thiocyanate-based analogues of the cyanide Prussian blue compounds, MIII[Bi(SCN)6], M = Fe, Cr, Sc. These compounds adopt the primitive cubic pcu topology and show strict cation order. Optical absorption measurements show these compounds have band gaps within the visible and near IR region, suggesting that they may be useful for applications where light harvesting is key, such as photocatalysis. We also show that Cr[Bi(SCN)6] can reversibly uptake water into its framework structure pointing towards the possibility of using these frameworks for host/guest chemistry.

Roll-to-roll fabrication of touch-responsive cellulose photonic laminates.

Hydroxypropyl-cellulose (HPC), a derivative of naturally abundant cellulose, can self-assemble into helical nanostructures that lead to striking colouration from Bragg reflections. The helical periodicity is very sensitive to pressure, rendering HPC a responsive photonic material. Recent advances in elucidating these HPC mechano-chromic properties have so-far delivered few real-world applications, which require both up-scaling fabrication and digital translation of their colour changes. Here we present roll-to-roll manufactured metre-scale HPC laminates using continuous coating and encapsulation. We quantify the pressure response of the encapsulated HPC using optical analyses of the pressure-induced hue change as perceived by the human eye and digital imaging. Finally, we show the ability to capture real-time pressure distributions and temporal evolution of a human foot-print on our HPC laminates. This is the first demonstration of a large area and cost-effective method for fabricating HPC stimuli-responsive photonic films, which can generate pressure maps that can be read out with standard cameras.

Nonenzymatic gluconeogenesis-like formation of fructose 1,6-bisphosphate in ice.

The evolutionary origins of metabolism, in particular the emergence of the sugar phosphates that constitute glycolysis, the pentose phosphate pathway, and the RNA and DNA backbone, are largely unknown. In cells, a major source of glucose and the large sugar phosphates is gluconeogenesis. This ancient anabolic pathway (re-)builds carbon bonds as cleaved in glycolysis in an aldol condensation of the unstable catabolites glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, forming the much more stable fructose 1,6-bisphosphate. We here report the discovery of a nonenzymatic counterpart to this reaction. The in-ice nonenzymatic aldol addition leads to the continuous accumulation of fructose 1,6-bisphosphate in a permanently frozen solution as followed over months. Moreover, the in-ice reaction is accelerated by simple amino acids, in particular glycine and lysine. Revealing that gluconeogenesis may be of nonenzymatic origin, our results shed light on how glucose anabolism could have emerged in early life forms. Furthermore, the amino acid acceleration of a key cellular anabolic reaction may indicate a link between prebiotic chemistry and the nature of the first metabolic enzymes.

Blue-Green Color Tunable Solution Processable Organolead Chloride-Bromide Mixed Halide Perovskites for Optoelectronic Applications.

Solution-processed organo-lead halide perovskites are produced with sharp, color-pure electroluminescence that can be tuned from blue to green region of visible spectrum (425-570 nm). This was accomplished by controlling the halide composition of CH3NH3Pb(BrxCl1-x)3 [0 ≤ x ≤ 1] perovskites. The bandgap and lattice parameters change monotonically with composition. The films possess remarkably sharp band edges and a clean bandgap, with a single optically active phase. These chloride-bromide perovskites can potentially be used in optoelectronic devices like solar cells and light emitting diodes (LEDs). Here we demonstrate high color-purity, tunable LEDs with narrow emission full width at half maxima (FWHM) and low turn on voltages using thin-films of these perovskite materials, including a blue CH3NH3PbCl3 perovskite LED with a narrow emission FWHM of 5 nm.

Absorptive carbon nanotube electrodes: consequences of optical interference loss in thin film solar cells.

A current bottleneck in the thin film photovoltaic field is the fabrication of low cost electrodes. We demonstrate ultrasonically spray coated multiwalled carbon nanotube (CNT) layers as opaque and absorptive metal-free electrodes deposited at low temperatures and free of post-deposition treatment. The electrodes show sheet resistance as low as 3.4 Ω â–¡(-1), comparable to evaporated metallic contacts deposited in vacuum. Organic photovoltaic devices were optically simulated, showing comparable photocurrent generation between reflective metal and absorptive CNT electrodes for photoactive layer thickness larger than 600 nm when using archetypal poly(3-hexylthiophene) (P3HT) : (6,6)-phenyl C61-butyric acid methyl ester (PCBM) cells. Fabricated devices clearly show that the absorptive CNT electrodes display comparable performance to solution processed and spray coated Ag nanoparticle devices. Additionally, other candidate absorber materials for thin film photovoltaics were simulated with absorptive contacts, elucidating device design in the absence of optical interference and reflection.

Carbon nanotubes: present and future commercial applications.

Worldwide commercial interest in carbon nanotubes (CNTs) is reflected in a production capacity that presently exceeds several thousand tons per year. Currently, bulk CNT powders are incorporated in diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and water filters. Advances in CNT synthesis, purification, and chemical modification are enabling integration of CNTs in thin-film electronics and large-area coatings. Although not yet providing compelling mechanical strength or electrical or thermal conductivities for many applications, CNT yarns and sheets already have promising performance for applications including supercapacitors, actuators, and lightweight electromagnetic shields.