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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.

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.

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.

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.

Recently developed textile and paper based supercapacitors are well-suited for wearable energy storage devices due to their mechanical flexibility and stretchability. In this study, the effects of mechanical straining on carbon nanotube coated textiles are studied, and we demonstrate the pre-straining of the textile can result in an enhanced specific capacitance as well as power and energy densities. In-situ resistance measurement during mechanical straining of the textile capacitors show a decrease in resistance with tensile straining, which contributed directly to the enhancement of electrochemical performance. Two different carbon nanotube textiles based on polyester and cotton with different mechanical behaviors are examined, where the polyester textile show an increase in specific capacitance from 53.6 F g � 1 to 85.7 F g � 1 after the textile is pre-strained to 30% permanent elongation prior to electrochemical testing, constituting a 37% enhancement. Similarly, the cotton textile shows an enhancement in specific capacitance from 122.1 F g � 1 to 142.0 F g � 1 after 30% permanent elongation, which is a 22% enhancement. Specific capacitance, energy density, and power density are increased further by electroplating of MnO2 nanoparticles on the carbon nanotube coated cotton textile and then imposing a permanent elongation of 30%. Our results indicate that the simple mechanical pre-straining of the textile fibers contribute to significant enhancements in the electrochemical performance of the supercapacitors.

This paper reports the results of a study on the microstructure evolution of sputtered BiSb–Te thermoelectric films during post-annealing and its effects on their electronic transport and thermoelectric properties. Combining X-ray diffraction, transmission electron microscopy, and Raman spectroscopy, we illuminate the fundamental aspects of the microstructure evolution: the as-deposited film was Bi0.5Sb1.5Te3 compound in the Bi2Te3-type phase with a nano-crystalline microstructure and the post-annealing prompted a drastic grain growth. The electrical and thermoelectric properties also closely changed following the trend of the grain growth. The Seebeck coefficient, electron mobility, and thermal conductivity increase while the carrier concentration remains flat. The ZT value escalates systematically with the annealing time increasing, reaching around 0.94 after 12 h annealing.

This study examined the sensitive effects of composition on the microstructure evolution and thermoelectric properties of sputtered Bi-Te films. Bi-Te films of various Te compositions (49 at.% to 60 at.%) were grown by cosputtering deposition and annealed at 200°C for different durations. We examined the microstructure of the films using x-ray diffraction (XRD) and transmission electron microscopy (TEM), and measured the electronic transport and thermoelectric properties. As the Te composition of the films changed from 49 at.% to 60 at.%, the phase of the as-sputtered film changed from the rhombohedral BiTe-type phase to the metastable rock-salt phase, which eventually transformed to the Bi2Te3-type phase upon annealing, instigating microstructure evolution. This phase transformation profoundly influenced the electrical and thermoelectric properties of the films.

FeRh/FePt bilayers on MgO (100) substrates were fabricated by rf-magnetron sputtering, and the magnetic properties and microstructures of the bilayers were studied in terms of Ta addition to the storage layer. Compared to undoped FeRh/FePt bilayers, FeRh/FePt-Ta bilayer films showed improved magnetic properties and lower degree of interdiffusion. The FeRh/FePt-Ta bilayers clearly demonstrated the AFM-FM transition. Reduced interdiffusion by Ta segregation along grain boundaries was speculated to be a possible cause for the observed improvement in magnetic properties when fabricated at high temperature.

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.

Quantitative analysis of the interfacial adhesion energy of Cu-Cu thermocompression bonds was performed using the four-point bending method with various wet pretreatment conditions. The evaluated interfacial adhesion energies for 1-μm-thick Cu bonding layers were 0.29 J/m2, 1.28 J/m2, 1.64 J/m2, 1.17 J/m2, and 0.43 J/m2 for different acetic acid pretreatment times of 0 min, 1 min, 5 min, 10 min, and 15 min, respectively. There exists an optimum wet etch time for maximum adhesion strength. The change of surface properties with increasing wet etch time was believed to result in the variation of the interfacial adhesion energy. The decrease in interfacial adhesion energy after 5 min seems to result from a decrease in the plastic dissipation energy during interfacial crack propagation with thinner Cu film thickness caused by overetching.

The mechanical behavior of Pt and Pt–Ru solid solution alloy thin films was evaluated using wafer curvature and nanoindentation techniques. Films approximately 200 nm thick with nominal compositions of 0, 1, 2, 5, 10, and 20 wt% Ru were prepared by co-sputtering on oxidized Si wafers. For temperatures below approximately 500 °C, at which dislocation motion dominates behavior, the elastic modulus, flow stress, and hardness all increase with increasing Ru content. These experimental results were compared to flow stress calculations that are based on existing models for dislocation motion. This analysis indicates that the solid solution strengthening mechanism is a major contributor to the film strengthening. The critical temperature above which diffusion-controlled plasticity dominates is not significantly affected by solute content. Above this temperature, the degree of stress relaxation was dependent on Ru content, which could be attributed to a limit on diffusional relaxation.

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.

The surface of water provides an excellent environment for gliding movement, in both nature and modern technology, from surface living animals such as the water strider, to Langmuir–Blodgett films. The high surface tension of water keeps the contacting objects afloat, and its low viscosity enables almost frictionless sliding on the surface. Here we utilize the water surface as a nearly ideal underlying support for free-standing ultra-thin films and develop a novel tensile testing method for the precise measurement of mechanical properties of the films. In this method, namely, the pseudo free-standing tensile test, all specimen preparation and testing procedures are performed on the water surface, resulting in easy handling and almost frictionless sliding without specimen damage or substrate effects. We further utilize van der Waals adhesion for the damage-free gripping of an ultra-thin film specimen. Our approach can potentially be used to explore the mechanical properties of emerging two-dimensional materials. The mechanical testing of thin films is non-trivial, due to their very fine dimensions. Kim et al. use the inherent surface tension of water as a platform for the frictionless tensile testing of gold films, with a thickness as fine as 55 nm.

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).

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.

Cu2O has been investigated as a candidate of the promising anode materials for Lithium ion batteries (LIB) due to its several advantages such as reversible mechanism with Li ion, relatively low-cost, non-toxicity, and higher theoretical capacity than graphite. However, the Li ion charge and discharge (C-D) processes accompany huge volume expansion and shrinkage, by which mechanical stresses are induced and lead to poor C-D cycle life due to the failure of the contacts between anode material and current collector. In order to avoid the drawbacks of large volume change in anode material, several efforts have been taken to use Cu2O nanopowders as an anode. However, the usage of nanopowders requires additional conductive carbon sources or binders which are disadvantageous in simplifying fabrication process and lowering cost. In this talk, we present a template-free and surfactant-free electrochemical nanosynthesis of single crystalline Cu2O nanostructures. The electrochemical growth of Cu2O nanostructures originated from filamentary effect related to the electric field enhancement on the pyramidal Cu2O grains in an ultra-dilute CuSO4 aqueous electrolyte. The synthesized Cu2O nanorods showed much more excellent electrochemical properties as an anode material for LIBs than Cu2O films; the electrochemical capacities exceptionally increased from 340 to 1249 mAh/g during 500 cycles exceeding the theoretical capacity of Cu2O. The capacity enhancement was due to the phase transformation from Cu2O to CuO, nanostructuring from nanorods to fragmented nanoparticles, and progressive generation of electroactive polymeric gel-like layer on the surface of the nanoparticles. The present nanostructuring of Cu2O is expected to contribute to the development of higher capacity LIBs in near future.

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m-thick copper films deposited on silicon wafers were successfully bonded at 415 C/25 kN for 40 minutes in a thermo-compression bonding method that did not involve a pre-cleaning or pre-annealing process. The original copper bonding interface disappeared and showed a homogeneous microstructure with few voids at the original bonding interface. Quantitative interfacial adhesion energies were greater than 10.4 J/m as measured via a four-point bending test. Post-bonding annealing at a temperature that was less than 300 C had only a slight effect on the bonding energy, whereas an oxygen environment significantly deteriorated the bonding energy over 400 C. This was most likely due to the fast growth of brittle interfacial oxides. Therefore, the annealing environment and temperature conditions greatly affect the interfacial bonding energy and reliability in Cu-Cu bonded wafer stacks. Key word Adhesion, 3-D Integration, 4-point bending test, Cu-Cu bonding, post annealing