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Geometrically multifunctional structures inspired by nature can address the challenges in the development of soft robotics. A bioinspired structure based on origami and kirigami can significantly enhance the stretchability and reliability of soft robots. This study proposes a novel structure with individual, overlapping units, similar to snake scales that can be used to construct shape-morphing batteries for untethered soft robots. The structure is created by folding well-defined, two-dimensional patterns with cutouts. The folding lines mimic the hinge structure of snakeskin, enabling stable deformations without mechanical damage to rigid cells. The structure realizes multi-axial deformability and a zero Poisson's ratio without off-axis distortion to the loading axis. Moreover, to maximize areal density, the optimal cell shape is designed as a hexagon. The structure is applied to a stretchable Li-ion battery, constructed to form an arrangement of electrically interconnected, hexagonal pouch cells.

Sodium (Na) organic batteries have attracted great attention because of high abundance of Na, low-production cost, and structure diversity of organic electrode materials. Despite the efforts on organic Na-ion batteries, organic electrodes are still vulnerable to conventional electrolytes, and have a low conductivity which leads to continuous capacity fading and low-rate capability, respectively. In this study, we aimed to reduce solubility in electrolyte and enhance electrical conductivity of organic electrode by anchoring 2,5- dihydroxyterephtalic acid (DHTPA) to carbon black via esterification. Then, the sodiated DHTPA/CB powder was evaluated for an anode in Na-ion battery. The covalent-bonded organic/carbon black electrode retained 90 % of the initial capacity even after 100 cycles, and also showed excellent rate capability up to 1500 mA/g. The result sheds light on the commercialization of organic-based Na-ion batteries, and their large-scale applications to electric vehicles (EVs) and energy storage systems (ESSs) markets.

Binderless, additiveless Si electrode design is developed where a nanoporous ZnO matrix is coated on a Si microparticle electrode to accommodate extreme Si volume expansion and facilitate stable electrochemical cycling. The conversion reaction of nanoporous ZnO forms an ionically and electrically conductive matrix of metallic Zn embedded in Li2O that surrounds the Si microparticles. Upon lithiation, the porous Li2O/Zn matrix expands with Si, preventing extensive pulverization, while Zn serves as active material to form LixZn to further enhance capacity. Electrodes with a Si mass loading of 1.5 mg/cm2 were fabricated, and a high initial capacity of ∼3900 mAh/g was achieved with an excellent reversible capacity of ∼1500 mAh/g (areal capacity ∼1.7 mAh/cm2) beyond 200 cycles. A high first-cycle Coulombic efficiency was obtained owing to the conversion reaction of nanoporous ZnO, which is a notable feature in comparison to conventional Si anodes. Ex situ analyses confirmed that the nanoporous ZnO coating maint...

Here, we studied the effect of thermal annealing on the microstructure and cyclic stability of a (Ti, Fe)-alloyed Si thin-film fabricated by a simple sputtering deposition method for Li-ion battery (LIB) anodes. The anode samples annealed at different temperatures (300–600 °C) were subjected to microstructure analysis and LIB performance test. The (Ti, Fe)-alloyed Si thin-film anode delivered a high capacity of 1563 mA h g−1 for 100 cycles at 0.1 A g−1 with nearly 100% capacity retention. Post-mortem analysis using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) disclosed the microstructural changes of the cycled anodes, revealing that (Ti, Fe) silicides served as a structural buffer against the large volume change of active Si during cycling for enhanced LIB performance.

Next-generation batteries require high-rate energy storage capabilities owing to the advent of fast charging electrical applications. Energy storage materials that can regulate the capacity even at high current densities must be developed. However, this is challenging owing to the limited ion transport kinetics inherent in thick electrodes. The sluggish ion transport can be mitigated by adopting nanomaterials with high specific surface areas or fabricating electrodes with structural alignment. Nevertheless, the rearrangement of materials in electrodes that facilitate fast charging with external forces and additives does not provide a satisfactory ion transport rate. In this study, for realizing a high-rate anode material, facet-controlled three-dimensional holey graphene is fabricated by transferring laser-induced graphene (LIG) to a copper tape in dry condition. This electrode exhibits a consistent capacity of ~114 mAh g−1 at an increased mass loading of 3 mg cm−2 and a high current density of 20 A g−1, implying that 95% capacity can be charged within 3 min. This exceptionally high rate is attributed to the unique structure of the transferred LIG (three dimensionally aligned macro/meso-porous LIG flakes featuring preferential surface facet directions). This fabrication is compatible with the existing manufacturing process for anode materials and can be applied to other energy materials.

High theoretical capacity and low-cost copper sulfide (CuxS)-based anodes have gained great attention for advanced sodium-ion batteries (SIBs). However, their practical application may be hindered due to their unstable cycling performance and problems with the dissolution of sodium sulfides (NaxS) into electrolyte. Here, we employed metal organic framework (MOF-199) as a sacrificial template to fabricate nanoporous CuxS with a large surface area embedded in the MOF-derived carbon network (CuxS-C) through a two-step process of sulfurization and carbonization via H2S gas-assisted plasma-enhanced chemical vapor deposition (PECVD) processing. Subsequently, we uniformly coated a nanocarbon layer on the Cu1.8S-C through hydrothermal and subsequent annealing processes. The physico-chemical properties of the nanocarbon layer were revealed by the analytical techniques of high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM). We acquired a higher SIB performance (capacity retention (~93%) with a specific capacity of 372 mAh/g over 110 cycles) of the nanoporous Cu1.8S-C/C core/shell anode materials than that of pure Cu1.8S-C. This encouraging SIB performance is attributed to the key roles of a nanocarbon layer coated on the Cu1.8S-C to accommodate the volume variation of the Cu1.8S-C anode structure during cycling, enhance electrical conductivity and prevent the dissolution of NaxS into the electrolyte. With these physico-chemical and electrochemical properties, we ensure that the Cu1.8S-C/C structure will be a promising anode material for large-scale and advanced SIBs.

Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large capacities. However, questions remain regarding the large irreversible loss in capacities for the first charge-discharge cycle due to oxygen removal in lattices related to layered Li2MnO3. Herein we present detailed studies on Li-rich Mn-based layered oxides of 0.4Li2MnO3-0.6LiNi1/3Co1/3Mn1/3O2 (Li-rich NCM) electrochemically activated between 2.5 V and 4.3 or 4.7 V vs. Li+/Li. Electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) revealed unusual manganese reduction after the first charge up to a high voltage of 4.7 V. Moreover, the electronic structure did not fully recover to the original pristine of Mn4+ state after discharge. Interestingly, these phenomena were not limited to a single particle, but were observed across the entire electrode. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and electron dispersive spectra (EDS) also showed a dramatic decline in oxygen content with highly porous morphologies, associated with oxygen vacancy formation following oxidation of O2- ions to O2. Our analysis suggests that an unstable manganese valence state with severe defects due to oxygen vacancies may lead to large irreversible capacity loss during the first charge-discharge cycle of Li-rich layered oxides.

In this study, Li[Ni x Co y Mn z ]O 2 cathode composition library was fabricated using combinatorial methodology and characterized using nanoindentation to create a mechanical properties database as a function of Li[Ni x Co y Mn z ]O 2 composition. A single sputter deposition from LiCoO 2 , LiNiO 2 , and LiMn 2 O 4 compound targets resulted in a composition range of 3–44 at.% Co, 20–80 at.% Ni, and 5–50 at.% Mn. Young’s modulus and hardness values were evaluated before and after charge–discharge cycles, and a strong dependency of the mechanical properties on composition was found; Mn-rich composition showed highest retention of its mechanical properties whereas the properties degraded more significantly for the Ni-rich composition. Electrochemical performance was analyzed and compared to mechanical properties at various Li[Ni x Co y Mn z ]O 2 compositions and a strong correlation between enhanced mechanical properties retention leading to superior discharge capacity retention was found for the Mn-rich compositions. Li[Ni 0.33 Co 0.30 Mn 0.34 ]O 2 composition showed optimized electrochemical and mechanical properties, where it retained 38% and 50% of its Young’s modulus and hardness after cycling while demonstrating 91% discharge capacity retention after 20 cycles at 1 C-rate.

We fabricated a hole transport layer (HTL) using transfer printing to fabricate high efficiency PbS quantum dot solar cell with minimized hysteresis. We applied PbS-EDT(1,2-ethanedithiol) as an HTL and controlled the adhesive properties between the donor substrate and the HTL through the UVO process in order to effectively transfer the HTL to the PbS layer, which enabled multilayer transfer printing as a result. During the transfer printing process, a gradient solid-solution layer was created at the interface with the existing PbS layer to reduce the hysteresis phenomenon, and to improve the power conversion efficiency to about 10% according to the HTL thickness optimization. In addition, the use of the EDT solvent can be remarkably reduced by using the transfer printing when forming the PbS-EDT layer. This can reduce the amount of organic solvent consumed in the process and improve the potential of environmentally friendly processes.

LTO (Li4Ti5O12) has been highlighted as anode material for next-generation lithium ion secondary batteries due to advantages such as a high rate capability, excellent cyclic performance, and safety. However, the generation of gases from undesired reactions between the electrode surface and the electrolyte has restricted the application of LTO as a negative electrode in Li-ion batteries in electric vehicles (EVs) and energy storage systems (ESS). As the generation of gases from LTO tends to be accelerated at high temperatures (40–60 °C), the thermal stability of LTO should be maintained during battery discharge, especially in EVs. To overcome these technical limitations, a thin layer of Al2O3 (~2 nm thickness) was deposited on the LTO electrode surface by atomic layer deposition (ALD), and an electrochemical charge-discharge cycle test was performed at 60 °C. The capacity retention after 500 cycles clearly shows that Al2O3-coated LTO outperforms the uncoated one, with a discharge capacity retention of ~98%. TEM and XPS analyses indicate that the surface reactions of Al2O3-coated LTO are suppressed, while uncoated LTO undergoes the (111) to (222) phase transformation, as previously reported in the literature.

Here, we fabricate poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) by electrospinning for a gel polymer electrolyte (GPE) for use in flexible Li-ion batteries (LIBs). As a solvent, we use N-methyl-2-pyrrolidone (NMP), which helps produce the cross-linked morphology of PVDF-co-HFP separator, owing to its low volatility. The cross-linked PVDF-co-HFP separator shows an uptake rate higher than that of a commercialized polypropylene (PP) separator. Moreover, the PVDF-co-HFP separator shows an ionic conductivity of 2.3 × 10−3 S/cm at room temperature, comparable with previously reported values. An LIB full-cell assembled with the PVDF-co-HFP-based GPE shows capacities higher than its counterpart with the commercialized PP separator, confirming that the cross-linked PVDF-co-HFP separator provides highly efficient ionic conducting pathways. In addition, we integrate a flexible LIB cell using the PVDF-co-HFP GPE with a flexible organic light emitting diode (OLED), demonstrating a fully flexible unit of LIB and OLED.

Carbon-nanotube (CNT)-based textile supercapacitors with MnO2 nanoparticles have excellent power and energy densities, but MnO2 nanoparticles can be delaminated during charge–discharge cycles, which results in significant degradation in capacitance. In this study, polypyrrole conductive polymer was coated on top of MnO2 nanoparticles that are deposited on CNT textile supercapacitor to prevent delamination of MnO2 nanoparticles. An increase of 38% in electrochemical energy capacity to 461 F/g was observed, while cyclic reliability also improved, as 93.8% of energy capacity was retained over 10 000 cycles. Energy density and power density were measured to be 31.1 Wh/kg and 22.1 kW/kg, respectively. An in situ electrochemical–mechanical study revealed that polypyrrole–MnO2-coated CNT textile supercapacitor can retain 98.5% of its initial energy capacity upon application of 21% tensile strain and showed no observable energy storage capacity change upon application of 13% bending strain. After imposing cyclic ...

We demonstrate the fabrication of flexible micro-supercapacitors based on laser carbonization of polyimide sheets. Localized pulsed laser irradiation rapidly converts the pristine polyimide surface into an electrically conductive porous carbon structure in ambient conditions. Thus, the polyimide sheet acts as both a precursor for the carbonization and a flexible substrate. Effects of various laser parameters are examined to enhance electrical properties and morphology of the carbonized structures. The interdigitated electrode patterns are produced directly on the polyimide sheets by programmed laser scanning. A solid-state polyvinyl alcohol–phosphoric acid gel electrolyte is introduced into the active electrode area to realize a flexible all solid-state microcapacitor assembly. Cyclic voltammetry measurements exhibit the expected electrical double layer behavior. The specific capacitance of the supercapacitors reaches ∼800 μF/cm2 at a voltage scan rate of 10 mV/s with good capacitance retention under mechanical bending. The proposed laser-based approach enables facile fabrication of flexible micro-supercapacitors without tedious photolithographic patterning of porous carbon and metal current collectors.

Silicon anodes for lithium ion batteries (LiBs) have been attracting considerable attention due to a theoretical capacity up to about 10 times higher than that of conventional graphite. However, huge volume expansion during the cycle causes cracks in the silicon, resulting in the degradation of cycling performance and eventual failure. Moreover, low electrical conductivity and an unstable solid electrolyte interface (SEI) layer resulting from repeated changes in volume still block the next step forward for the commercialization of the silicon material. Herein we demonstrate the carbon nanotube (CNT) aerogel/Si nanohybrid structure for anode materials of LiBs via freeze casting followed by an RF magnetron sputtering process, exhibiting improved capacity retention compared to Si only samples during 1000 electrochemical cycles. The CNT aerogels as 3D porous scaffold structures could provide buffer volume for the expansion/shrinkage of Si lattices upon cycling and increase electrical conductivity. In addition, the nanospherical and relatively thin SEI layers of the CNT aerogel/Si nanohybrid structure show better lithium ion diffusion characteristics during cycling. For this reason, the Si@CNT aerogel anode still yielded a high specific capacity of 1439 mA h g−1 after 1000 charge/discharge cycles with low capacity fading. Our approach could be applied to other group IV LiB materials that undergo large volume changes, and also has promising potential for high performance energy applications.

Use of nanoscale architecturing that exhibits superior strength-to-weight ratio has been of recent interest, and here we demonstrate a bulk fabrication of a fully recoverable, ultralight 3D porous composite with high strength composed of Ag nanowire/cellulose nanofiber using a freeze-casting method. A one-step process for highly efficient bulk formation of 3D porous structure via ice crystal formation followed by sublimation was demonstrated that can overcome the cost and scalability associated with lithography methods. 3D porous composite with controlled geometry was fabricated by controlling the nucleation and growth kinetics of ice formation that resulted in highly anisotropic compressive strength and resilience that depends on the wall orientations and composition of composite wall. Strength of the 3D porous composite increased with an increase in the Ag nanowire content as the deformation transitioned from bending dominant toward stretch dominant behavior for the case of vertically aligned walls, and an optimized concentration of Ag nanowires resulted in the compressive strength of 100 kPa at a relative density of 0.96%, which has 1.5 times higher strength when normalized by the material density (2.3 ± 0.2 MPa ⋅ cm3/g) in comparison to that of metal microlattice (1.7 MPa ⋅ cm3/g) fabricated by lithography methods. Horizontally oriented 3D porous structure interestingly showed a fully reversible deformation while also maintaining sufficient conductivity that makes this new material well-suited for a variety of flexible electronics applications.

Binderless, additive-less Si electrode design is developed where a nanoporous ZnO matrix is coated on a Si microparticle electrode to accommodate extreme Si volume expansion and facilitate stable electrochemical cycling. The conversion reaction of nanoporous ZnO forms an ionically and electrically conductive matrix of metallic Zn embedded in Li2O that surrounds the Si microparticles. Upon lithiation, the porous Li2O/Zn matrix expands with Si preventing extensive pulverization while Zn serves as active material to form LixZn to further enhance capacity. Electrodes with Si mass loading of 1.5 mg/cm2 was fabricated and high initial capacity of ~3,900 mAh/g was achieved with excellent reversible capacity of ~1,500 mAh/g (areal capacity ~1.7 mAh/cm2) beyond 200 cycles. A high first cycle coulombic efficiency was obtained owing to the conversion reaction of nanoporous ZnO, which is a notable feature in comparison to conventional Si anodes. Ex situ analyses confirmed that the nanoporous ZnO coating maintained the coalescence of SiMPs throughout extended cycling. Therefore, the Li2O/Zn matrix derived from conversion reacted nanoporous ZnO acted as an effective buffer to lithiation induced stresses from volume expansion and served as a binder-like matrix that contribute to the overall electrode capacity and stability.

Electrochromic devices have been widely adopted in energy saving applications by taking advantage of the electrode coloration, but it is critical to develop a new electrochromic device that can undergo smart coloration and can have a wide spectrum in transmittance in response to input light intensity while also functioning as a rechargeable energy storage system. In this study, a photoresponsive electrochromic supercapacitor based on cellulose-nanofiber/Ag-nanowire/reduced-graphene-oxide/WO3 -composite electrode that is capable of undergoing "smart" reversible coloration while simultaneously functioning as a reliable energy-storage device is developed. The fabricated device exhibits a high coloration efficiency of 64.8 cm2 C-1 and electrochemical performance with specific capacitance of 406.0 F g-1 , energy/power densities of 40.6-47.8 Wh kg-1 and 6.8-16.9 kW kg-1 . The electrochromic supercapacitor exhibits excellent cycle reliability, where 75.0% and 94.1% of its coloration efficiency and electrochemical performance is retained, respectively, beyond 10 000 charge-discharge cycles. Cyclic fatigue tests show that the developed device is mechanically durable and suitable for wearable electronics applications. The smart electrochromic supercapacitor system is then integrated with a solar sensor to enable photoresponsive coloration where the transmittance changes in response to varying light intensity.

LTO (Li4Ti5O12) has been highlighted as anode material for next-generation lithium ion secondary batteries due to advantages such as a high rate capability, excellent cyclic performance, and safety. However, the generation of gases from undesired reactions between the electrode surface and the electrolyte has restricted the application of LTO as a negative electrode in Li-ion batteries in electric vehicles (EVs) and energy storage systems (ESS). As the generation of gases from LTO tends to be accelerated at high temperatures (40–60 °C), the thermal stability of LTO should be maintained during battery discharge, especially in EVs. To overcome these technical limitations, a thin layer of Al2O3 (~2 nm thickness) was deposited on the LTO electrode surface by atomic layer deposition (ALD), and an electrochemical charge-discharge cycle test was performed at 60 °C. The capacity retention after 500 cycles clearly shows that Al2O3-coated LTO outperforms the uncoated one, with a discharge capacity retention of ~98%. TEM and XPS analyses indicate that the surface reactions of Al2O3-coated LTO are suppressed, while uncoated LTO undergoes the (111) to (222) phase transformation, as previously reported in the literature.

In this study, we fabricate a three-dimensional (3D) crystalline Si (c-Si)/carbon nanotube (CNT) nanocomposite anode by sputtering Si on 3D CNTs followed by laser annealing for Si crystallization — a simple, cost-effective route — for advanced Li-ion battery (LIB) applications. We use scanning electron microscopy, X-ray diffraction spectroscopy, and Raman spectroscopy to analyze the samples annealed at different laser energy densities. As a result, we confirm that laser annealing enables Si crystallization without damaging the CNTs. We assemble half-type coin cells for the battery performance test: the 3D c-Si/CNT anode sample demonstrates a specific capacity superior to that of its control counterpart; the cyclic stability is also enhanced significantly.

This paper investigates the effects of the Sb content (х) on (Bi1−xSbx–2Te3 thermoelectric films with х changing widely from 0 (Sb2Te3) to 1 (Bi2 Te3). First, the XRD analysis discloses that with the Sb content (x) increasing, the phase changed gradually from Bi2Te3 to Sb2Te3 as Sb atoms replaced substitutionally Bi atoms. Further microstructure analysis reveals that an extensive grain growth occurred during post-annealing for the samples with high Sb contents. According to the measurement of electrical and thermoelectric properties, the polarity of the charge carrier and Seebeck coefficient switched n-type to p-type in the range of x = 0.45∼0.63. For the n-type samples, the power factor is highest when x = 0.18 around 46.01 μW/K2 whereas Sb2Te3, for the p-type samples, shows the highest value, 62.48 μW/K2cm.

Carbon-nanotube (CNT)-based textile supercapacitors with MnO2 nanoparticles have excellent power and energy densities, but MnO2 nanoparticles can be delaminated during charge-discharge cycles, which results in significant degradation in capacitance. In this study, polypyrrole conductive polymer was coated on top of MnO2 nanoparticles that are deposited on CNT textile supercapacitor to prevent delamination of MnO2 nanoparticles. An increase of 38% in electrochemical energy capacity to 461 F/g was observed, while cyclic reliability also improved, as 93.8% of energy capacity was retained over 10 000 cycles. Energy density and power density were measured to be 31.1 Wh/kg and 22.1 kW/kg, respectively. An in situ electrochemical-mechanical study revealed that polypyrrole-MnO2-coated CNT textile supercapacitor can retain 98.5% of its initial energy capacity upon application of 21% tensile strain and showed no observable energy storage capacity change upon application of 13% bending strain. After imposing cyclic bending of 750 000 cycles, the capacitance was retained to 96.3%. Therefore, the results from this study confirmed for the first time that the polypyrrole-MnO2-coated CNT textile can reliably operate with high energy and power densities with in situ application of both tensile and bending strains.

Correction for ‘The role of thermal annealing on the microstructures of (Ti, Fe)-alloyed Si thin-film anodes for high-performance Li-ion batteries’ by Minsub Oh et al., RSC Adv., 2018, 8, 9168–9174.

Developing a commercially viable silicon anode as a replacement for graphite has been the topic of intense research and discussion. Numerous attempts have been made including the use of nanoscale structures smaller than silicon’s critical fracture size (e.g. nanoparticles, nanowires, nanotubes, etc.). However, nanoscale structures, while sufficiently effective in lab scale, are difficult and expensive to scale up. To address this issue, applying a thin coat of polymer with self-healing chemistries has been reported as an effective remedy to enhance the cycle life of the silicon microparticle anode. The self-healing chemistry enabled mechanical fractures generated during the cycling process to self-heal. As a result, excellent cycle life was obtained compared to conventional microscale anodes. However, there still is room to improve the mechanical and electrochemical performances of the anode, most notably areal capacity and flexibility, while using large scale processes. In this study, a free standing silicon microparticle and self-healing polymer (SiSHP) composite is fabricated demonstrating long cycle life while still retaining high capacity (up to ~2,800mAhg-1 and ~3.5mAhcm-2) without a metal foil current collector. SiSHP composite is prepared by simple, inexpensive, and scalable approach. The SiSHP composite consists of silicon microparticles embedded within a self-healing polymeric matrix providing sufficient space for volume expansion during lithiation. The self-healing chemistry reduces irreversible loss of electric contact due to mechanical degradation prevalent in conventional slurry cast silicon electrode design. In addition, because the SiSHP composite eliminates the need for a metal current collector, adhesion issues between the electrode and current collector that arise with repeated bending are eliminated, thereby ensuring minimal loss in mechanical and electrochemical properties even after undergoing repeated bending. We found that a 1:1 Si/SHP weight ratio with 10 wt. % carbon conductive additive exhibits the optimal balance between high capacity and providing sufficient polymer matrix for stable cycling behavior. The fabricated SiSHP composite is moldable into the required shape and dimension ranging from millimeter to tens of centimeter-scale. The freestanding feature of the SiSHP composite anode eliminates the need for a metal foil current collector thereby reducing the non-active mass, which is beneficial to enhancing capacity and energy density of Lithium-ion cells.

This paper introduces oxygen-deficient black TiO2 with hierarchically ordered porous structure fabricated by a simple hydrogen reduction as a carbon- and binder-free cathode, demonstrating superior energy density and stability. With the high electrical conductivity derived from oxygen vacancies or Ti3+ ions, this unique electrode features micrometer-sized voids with mesoporous walls for the effective accommodation of Li2O2 toroid and for the rapid transport of reaction molecules without the electrode being clogged. In the highly ordered architecture, toroidal Li2O2 particles are guided to form with a regular size and separation, which induces the most of Li2O2 external surface to be directly exposed to the electrolyte. Therefore, large Li2O2 toroids (≈300 nm) grown from solution can be effectively charged by incorporating a soluble catalyst, resulting in a very small polarization (≈0.37 V). Furthermore, disordered nanoshell in black TiO2 is suggested to protect the oxygen-deficient crystalline core, by which oxidation of Ti3+ is kinetically impeded during battery operation, leading to the enhanced electrode stability even in a highly oxidizing environment under high voltage (≈4 V).

In this study, we fabricate an electrode structure, in which a carbon nanotube (CNT) film is coated on the composite of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS). Electromechanical tests disclose that incorporation of a high density of well-dispersed CNTs (with the aid of UV/O3 treatment) in the PDMS substrate offers an alternative current path when the CNT film cracked, helping demonstrate much improved electromechanical characteristics. Further analysis using scanning electron microscopy (SEM) combined with the data from the electromechanical tests illuminates some interesting electromechanical features and the failure mechanism of the material.

Silicon anode for lithium ion battery (LiB) has been attracted considerable attention due to providing theoretical capacity up to about 10 times higher than that of conventional graphite. However, huge volume expansion during the cycle cause crack in the silicon, resulting in degradation of cycling performance and eventual failure. Moreover, low electrical conductivity and unstable solid electrolyte interface (SEI) layer aroused from repeated changes in volume still block the next step forward to commercialization of silicon material. Herein we demonstrate Si-carbon nanotube (CNT) aerogel core-shell nanostructure for LiB via freeze casting followed by RF magnetron sputtering process, exhibiting improved capacity retention as compared to Si only samples while 1,000 times of electrochemical cycle. The freeze casted CNT aerogel as 3D porous scaffold structures could provide buffer volume expansion/shrinkage of Si lattice upon cycling and increase electrical conductivity. In addition, the CNT aerogel could maintain the conducting network between pulverized Si materials during cycling. For this reason, after 1,000 charge/discharge cycles with high current densities (4.0 A g-1), Si@CNT aerogel anode yielded a high specific capacity of 1439 mAh g-1 with low capacity fade. Our approach could be applied to other LiB materials that go through large volume changes, and also affords promising potential for high performance energy applications.

Although carbon is ubiquitously used as the basis of the cathode, its use in Li-O2 battery is still problematic in that carbon decomposes on charge above 3 V vs. Li/Li+, and leads to electrolyte decomposition on both discharge and charge, rendering it unsuitable for aprotic Li-O2 cells. Meanwhile, a pioneering work from Bruce et al., [1] suggested that carbon be replaced with TiC which promoted reversible formation of Li2O2. By the way, it is open to debate that the stability of TiC originates from the TiO2 at the surface, and TiO2 itself can be an air cathode, provided that the electrical conductivity is guaranteed. For this reason, porous TiO2 [2] with some deliberate oxygen vacancies [3] was synthesized so that the electrode exhibited large surface area with moderate electronic and ionic conductivity. The porous black electrode showed a stable cycle-life performance, and the polarization during the decomposition of Li2O2 is greatly improved. Therefore, it is expected that the electronic conductivity- and porosity-tuned TiO2 can be a suitable substrate for Li-O2 chemistry. Finally, the origin of high stability of this porous black TiO2 as an air cathode is also investigated. [1] M. M. Ottakam Thotiyl, S. A. Freunberger, Z. Peng, Y. Chen, Z. Liu, and P.G.Bruce, Nat. Mater. 12, 1050 (2013). [2] J.-H. Shin, J.-H. Kang, W.-M. Jin, J. H. Park, Y.-S. Cho, and J. H. Moon, Langmuir, 27, 85 (2011). [3] X. Chen, L. Liu, and F. Huang, Chem. Soc. Rev. 44, 1861 (2015).

In this study, we explore various electrode materials (Au, Ti, and Sb) for use as contact materials on Bi2Te3 and Sb2Te3 thermoelectric films. Using the transmission line method (TLM), we measured the specific resistivity of the contacts, which showed that Au has the lowest contact resistivity for both the thermoelectric films (after annealing): 2.7 × 10−10 Ω m2 for Bi2Te3 and 2.9 × 10−11 Ω m2 for Sb2Te3. The specific contact resistivity data suggest that the dominant factor for the contact properties is interface states. After annealing, the contact resistivity does not change much for the Bi2Te3 contacts while it drops greatly for the Sb2Te3 ones. Analysis of the carrier transport mechanism across the contacts discloses that changes in the carrier concentration in the thermoelectric films after annealing are responsible for the different behaviors.

Lithium-ion battery cathode material has been the subject of much research in both academia and industry in order to improve its electrochemical properties and cyclability. A prime candidate for replacing the relatively expensive and unstable LiCoO2, is the Lil[NiCoMn]O2 cathode material. Being a ternary material, the Li[NiCoMn]O2 has ample room for composition optimization. As such, extended investigations have been conducted to optimize the electrochemical properties of Li[NiCoMn]O2. However, there arose a need for the evaluation of the mechanical properties of Li[NiCoMn]O2 in order to remedy the deterioration of cathode cycle life due to stress development during repeated charge/discharge cycles. In this study, an efficient and high throughput combinatorial methodology is developed using sputter deposition technique and applied to the characterization of mechanical properties degradation of Li[NiCoMn]O2 as a result of repeated charge/discharge cycling. Co-sputter deposition of LiCoO2, LiNiO2, and LiMn2O4 compound targets was carried out in order to create the necessary concentration gradient to efficiently fabricate a Li[NiCoMn]O2 composition library. EDS analysis confirmed that the fabricated composition library encompassed a broad composition range of 20~80 at. % Ni content, 3~44 at. % Co content, and 5~50 at. % Mn content. XRD analysis confirmed a layered α -NaFeO2 (R3-m) structure for all compositions. Mechanical properties characterization by nanoindentation was carried out pre and post five charge/discharge cycles conducted via voltammetry sweep cycles between 2.5V and 4.5V at a scan rate of 1mV/s. Elastic modulus and hardness values pre and post charge/discharge cycles were found to both exhibit a strong composition dependency; Ni-rich compositions exhibited highest hardness values of 12GPa and Mn-rich compositions exhibited highest modulus values of 170GPa pre charge/discharge cycling. However, post charge/discharge cycling nanoindentation results indicated that Mn-rich compositions were characterized to have highest retention of its mechanical properties whereas the properties degraded more significantly for Ni-rich and Co-rich compositions. Electrochemical performance was analyzed at Ni-rich Li[Ni0.80Co0.10Mn0.10]O2, Co-rich Li[Ni0.40Co0.50Mn0.10]O2, and Mn-rich Li[Ni0.60Co0.03Mn0.37]O2, Li[Ni0.45Co0.10Mn0.45]O2­, and Li[Ni0.33Co0.30Mn0.37]O2 compositions. Overall, a strong correlation for enhanced mechanical properties retention leading to superior discharge capacity retention was found with high Mn compositions demonstrating both superior mechanical properties retention and discharge capacity retention. Li[Ni0.33Co0.30Mn0.37]O2 composition, which retained 50% and 38% of its hardness and elastic modulus after cycling, demonstrated 90.61% discharge capacity retention after 20 cycles at 1C rate. Our results, obtained via the developed high throughput and efficient combinatorial analysis, indicate that the manganese rich compositions, which were characterized to have superior mechanical properties, demonstrate the best discharge capacity retention capability even after multiple charge/discharge cycles.

The results of employing (Ti, Fe)-alloyed Si thin-film anode for Li-ion batteries are reported. The material demonstrates an impressive cyclic stability with stable operation for more than 500 cycles at a capacity higher than 1400 mAh g−1. Materials characterization using scanning electron microscopy and transmission electron microscopy illuminates an intriguing materials process behind the performance: ripple-like pattern formation via electrochemically driven segregation of the inactive elements (Ti and Fe). The ripple structure plays a buffer role by suppressing loss of the active material upon further cycling, allowing the anode to gradually transform into an array of microbumps. The morphological evolution helps the anode endure long cycles (even up to 1000 cycles) without catastrophic failure as the bumps shrank slowly and steadily, consistent with the electrochemical data.