Lithium Intercalation Process Research Articles

Graphene oxide assisted preparation of V2O5 films for electrochromic and energy storage applications

A V2O5 film is prepared by an electrochemical deposition method with the assistance of graphene oxide (GO). The surface morphology and microstructure of the film are characterized by scanning electron microscope, X-ray diffraction, Raman spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy measurements. The results demonstrate that the prepared film is mainly composed of orthorhombic α-V2O5 with a small amount of tetragonal β-V2O5; the V2O5 film has a wrinkled surface morphology and contains a certain low valance V4+ and a trace amount of graphene oxide residue. The V2O5 film exhibits good lithium storage activity and excellent cycling stability (with a capacity retention rate of 93.6% after 500 cycles at 0.5 mA cm−2). During lithium intercalation and de-intercalation processes, the color of the V2O5 film changes reversibly from yellow to green, and finally blue, with a fast response time (6∼9 s) and high coloration efficiency (19.77 cm2 C−1). In addition, the electrochromic device assembled with the V2O5 film as the electrochromic layer, NiHCF as the ion storage layer, and 1 M LiClO4/propylene carbonate solution as the electrolyte also exhibits excellent cycling stability, suggesting the significant potential of this V2O5 film for electrochromic and energy storage applications.

Application of two-dimensional lamellar lithium titanate in lithium-ion anode batteries

Lithium titanate exhibits effective suppression of lithium metal plating and lithium dendrite formation, attributed to its high lithium ion diffusion coefficient and a relatively high discharge plateau of 1.55 V (vs. Li+/Li). It is considered a zero-strain material, displaying minimal lattice size changes during lithium intercalation and deintercalation processes. The focus of this study was to obtain titanium dioxide through the calcination of selected MXene (Ti2C), and then mix it with lithium carbonate in a specific lithium-titanium ratio to generate lithium titanate. Spinel lithium titanate synthesized via solid-state method retained the sheet-like structure and excellent conductivity characteristics of MXene. Because its sheet structure provides a larger specific surface area for the electrode and enhances ion migration, it shows excellent electrochemical performance. The reaction mechanism was studied by in-situ Raman and variable speed CV. It was found that the reaction mechanism was pseudocapacitance plus lithium ion deintercalation. The obtained structure exhibited excellent electrochemical performance, making it suitable for applications in lithium-ion batteries.

First-principles study on the adsorption and lithium storage capacities of Hf3C2 and Hf3C2T2(T = O, F, S) MXenes

Based on the theoretical framework of the first principle, the adsorption and theoretical lithium storage capacities of Hf3C2 and surface functionalized Hf3C2T2(T = O, F, S) MXenes were studied. The structural stability of the system and the influence of electrical properties on energy storage properties are analyzed when different functional groups are located in different positions. The formation energy results suggest that the three functional Hf3C2T2(T = O, F, S) structures are energetically stable, and the CCP site is the most stable among the possible sites of HCP, TOP and CCP. By calculating the energy bands and density of states, it is proved that F-functionalized Hf3C2F2 is not conducive to adsorption. During the adsorption process, the lithium intercalation process is carried out in the way of surface adsorption of atoms, in which the HCP site of bare Hf3C2 and the CCP site of functionalized Hf3C2T2 are the most favorable adsorption sites. The storage capacities of bare Hf3C2, Hf3C2O2, and Hf3C2S2 are 287.51 mAhg−1, 271.95 mAhg−1 and 258.00 mAhg−1, respectively. The Hf3C2O2 has a higher lithium storage capacity than Hf3C2S2, so both oxygen functionalized Hf3C2O2 and bare Hf3C2 are promising battery materials.

Nano Sn-SnOx embedded in multichannel hollow carbon nanofibers: Microstructure, reversible lithium storage property and mechanism

To ameliorate the lithium storage property of tin-based oxides, nano Sn-SnOx embedded in multichannel hollow carbon nanofibers (Sn-SnOx@MCNF) were identified in this work. Multichannel hollow carbon nanofibers embedded uniformly by amorphous SnOx and proper Sn nanocrystals with various valence states of Sn endowed Sn-SnOx@MCNF quick ion transfer rate, enough catalytic active sites, high structure stability, little agglomeration and superior buffering volume change during alloying/dealloying processes. Accordingly, Sn-SnOx@MCNF-based electrodes possessed predominant reversibility, large capacity and excellent rate capability during the process of lithium intercalation of SnOx to Li2O and LixSn. When applied in practice, the present Sn-SnOx@MCNF-based electrodes expressed a high reversible capacity of 669.2 mAh g−1 even after 600 cycles at 1.0 A g−1 and a high-rate capacity of 525.1 mAh g−1 at 4.0 A g−1. Sn-SnOx@MCNF will be a potential anode material for Li-ion batteries with superior Li-storage performance. The synergistic enhancement mechanism between MCNF and nano Sn-SnOx was proposed in detail.

Hybrid Machine Learning-Enabled Potential Energy Model for Atomistic Simulation of Lithium Intercalation into Graphite from Plating to Overlithiation.

Graphite is one of the most widely used negative electrode materials for lithium ion batteries (LIBs). However, because of the rapid growth of demands pursuing higher energy density and charging rates, comprehensive insights into the lithium intercalation and plating processes are critical for further boosting the potential of graphite electrodes. Herein, by utilizing the dihedral-angle-corrected registry-dependent potential (DRIP) (Wen et al., Phys. Rev. B 2018, 98, 235404), the Ziegler-Biersack-Littmark (ZBL) potential (Ziegler and Biersack, Astrophysics, Chemistry, and Condensed Matter; 1985, pp 93-129), and the machine learning-based spectral neighbor analysis (SNAP) potential (Thompson et al., J. Comput, Phys. 2015, 285, 316-330), we have successfully trained a hybrid machine learning-enabled potential energy model capable of simulating a wide spectrum of lithium intercalation scenario from plating to overlithiation. Our extensive atomistic simulations reveal the trapping of intercalated lithium atoms close to the graphite edges due to high hopping barriers, resulting in lithium plating. Furthermore, we report a stable dense graphite intercalation compound (GIC) LiC4 with a theoretical capacity of 558 mAh/g, wherein lithium atoms occupy alternating upper/lower graphene hollow sites with a nearest Li-Li distance of 2.8 Å. Surprisingly, following the same lithium insertion manner would allow the nearest Li-Li distance to be retained until the capacity reaches 845.2 mAh/g, corresponding to a GIC of LiC2.6. Hence, the present study demonstrates that the hybrid machine learning approach could further extend the scope of machine learning energy models, allowing us to investigate the lithium intercalation into graphite over a wide range of intercalation capacity to unveil the underlying mechanisms of lithium plating, diffusion, and discovery of new dense GICs for advanced LIBs with high charging rates and high energy densities.

Diffusion induced thermal effect and stress in layered Li(Ni0.6Mn0.2Co0.2)O2 cathode materials for button lithium-ion battery electrode plates

Abstract This paper develops a coupling model of the relationship between chemical reaction, temperature and stress/strain for Li (Ni0.6Mn0.2Co0.2) O2 cathode materials. With the process of reaction, the concentration of electrolyte salt changes rapidly at the beginning of diffusion and tends to dynamic equilibrium. The concentration of electrolyte LiPF6 in electrode materials diffuses from bottom to top with the process of lithium intercalation. In the process of Li-ion intercalation, the temperature rise of porous electrode materials increases sharply at first, then decreases and then increases slowly. The rate of temperature rise in the cathode material increases with the temperature decreases. The volume of electrode material deformed with the expansion along the X-axis and the radial bending along the Y-axis. And the law of stress variation with time is consistent with the temperature-time curve. By the stress-strain distribution nephogram, it is found that the position where the maximum stress is located at the edge of the upper surface, and which is most vulnerable to failure.

Lithium Intercalation Kinetics and Fast‐Charging Lithium‐Ion Batteries: Rational Design of Graphite Particles Via Spheroidization

Graphite is the state‐of‐the‐art anode active material in lithium‐ion batteries with high specific capacity and long cycling stability. Nevertheless, due to the growing market requirements especially for the automotive sector, many efforts are dedicated to improve the fast‐charging performance of the anode. Therefore, research focuses on different levels of the anode, for example, on material level to improve the kinetics of the lithium intercalation process or by optimization at the electrode level. For anode active material production, the spheroidization of natural and synthetic graphite is a very important step that affects particle characteristics and electrochemical behavior. Herein, natural and synthetic graphite materials are spheroidized by using a lab‐scale spheroidization process. The obtained samples are characterized by means of different analytical techniques to investigate the influence of the spheroidization conditions on selected graphite characteristics that directly influence the charging rate performance. Apart from particle morphology, surface‐related properties induced by the spheroidization process show correlation with the measured lithiation rate performance.

Study on Electrochemical Properties of Carbon Submicron Fibers Loaded with Cobalt-Ferro Alloy and Compounds

In this work, carbon submicron fiber composites loaded with a cobalt-ferric alloy and cobalt-ferric binary metal compounds were prepared by electrospinning and high temperature annealing using cobalt-ferric acetone and ferric acetone as precursors and polyacrylonitrile as a carbon source. The phase transformation mechanism of the carbon submicron fiber-supported Co-Fe bimetallic compound during high temperature annealing was investigated. The electrochemical properties of the carbon submicron fiber-supported Co-Fe alloy and Co-Fe oxide self-supported electrode materials were investigated. The results show that at 138 °C, the heterogeneous submicron fibers of cobalt acetylacetonate and acetylacetone iron began to decompose and at 200 °C, CoFe2O4 was generated in the fiber. As the annealing temperature increases further, some metal compounds in the carbon fiber are reduced to CoFe2O4 alloy, and two phases of CoFe2O4 and CoFe-Fe-alloy exist in the fiber. After 200 cycles, the specific capacity of CF-P500 is 500 mAh g−1. The specific capacity of the composite carbon submicron fiber electrode material can be significantly improved by the introduction of CoFe2O4. When the binary metal oxides are used as electrode materials for lithium-ion batteries, alloy dealloying and conversion reactions can occur at the same time in the reverse process of lithium intercalation, the two reactions form a synergistic effect, and the cobalt-iron alloy in the material increases the electrical conductivity. Therefore, the carbon submicron fiber loaded with CoFe2O4/CoFe has an excellent electrochemical performance.

Advanced performance of S and N co-doped Sb@CNFs with a 3D conductive network as superior lithium-ion battery anodes

Antimony-based anodes possessing advantages of stable operating voltage and high theoretical capacity can replace graphene as alloy-based electrodes material in LIBs applications. However, the problems of capacity decaying and poor stability of Sb-based materials due to volume expansion and structural crushing during the long-term cycling remain to be solved. Therefore, we propose a strategy of using S and N co-doped carbon nanofibers encapsulated with Sb nanoparticles to overcome the above problems. The proposed material exhibits an excellent lithium storage performance with a high reversible specific capacity of 734 mAh g−1 at 0.1 A g−1 after 50 cycles (474.8 mAh g−1 at 1 A g−1 after 800 cycles, 394.5 mAh g−1 at 2 A g−1 after 2000 cycles). Importantly, a specific capacity of 288.5 mAh g−1 remains after more than 5000 cycles. The superior electrochemical performance of the S and N co-doped electrode is attributed to the proven structure and stability of the carbon matrix alleviating the volume changes of Sb during the process of lithium intercalation and extraction. The alloying/de-alloying reactions of the S@Sb@N-CNFs composite in the first charging/discharging process were systematically investigated by ex-situ XRD. This strategy of S and N co-doped carbon matrix could establish Sb-based materials as potential high-performance anodes for LIBs.

Preparation of Hollow Core-Shell Fe3O4/Nitrogen-Doped Carbon Nanocomposites for Lithium-Ion Batteries.

Iron oxides are potential electrode materials for lithium-ion batteries because of their high theoretical capacities, low cost, rich resources, and their non-polluting properties. However, iron oxides demonstrate large volume expansion during the lithium intercalation process, resulting in the electrode material being crushed, which always results in poor cycle performance. In this paper, to solve the above problem, iron oxide/carbon nanocomposites with a hollow core–shell structure were designed. Firstly, an Fe2O3@polydopamine nanocomposite was prepared using an Fe2O3 nanocube and dopamine hydrochloride as precursors. Secondly, an Fe3O4@N-doped C composite was obtained by means of further carbonization treatment. Finally, Fe3O4@void@N-Doped C-x composites with core–shell structures with different void sizes were obtained by means of Fe3O4 etching. The effect of the etching time on the void size was studied. The electrochemical properties of the composites when used as lithium-ion battery materials were studied in more detail. The results showed that the sample that was obtained via etching for 5 h using 2 mol L−1 HCl solution at 30 °C demonstrated better electrochemical performance. The discharge capacity of the Fe3O4@void@N-Doped C-5 was able to reach up to 1222 mA g h−1 under 200 mA g−1 after 100 cycles.

Promoting the reversibility of lithium ion/lithium metal hybrid graphite anode by regulating solid electrolyte interface

Recent research revealed graphite anode can not only be used to intercalate lithium ions but also plate lithium metal on them, leading to the development of graphite-based lithium ion/metal hybrid anode with capacity more than twice that of the lithium ion battery system. Currently, there is limited understanding on this system, consequently suitable strategies to further enhance and stabilize the capacity are still lacked. In this work, the influence of electrolytes, i.e. lithium bis(fluorosulfonyl)imide (LiFSI) and lithium hexafluorophosphate (LiPF6) in the carbonate solvents, on the evolution of solid electrolyte interface (SEI) and electrochemical performance were studied via in situ electrochemical atomic force microscopy (EC-AFM). An ideal SEI with high reversibility and mechanical/chemical stability was finally achieved by regulating structural uniformity in the LiFSI-based electrolyte. The graphite anode with the as-designed SEI exhibited a high initial capacity of 1531 mAh g−1 and columbic efficiency higher than 90% after 120 cycles, much higher than the reported graphite-based lithium ion or metal anode. The capacity degradation mainly originates from the irreversible lithium (de)intercalation processes. In addition, the full cells of graphite anode pre-deposited with limited Li capacity coupling with LiFePO4 cathode achieved stable cycling performance. This work highlights the reversible capacity of the hybrid graphite anode can be greatly improved via suitable electrolyte design and the corresponding SEI structural regulation.

LiCl Photodissociation on Graphene: A Photochemical Approach to Lithium Intercalation.

The interest in the research of the structural and electronic properties between graphene and lithium has bloomed since it has been proven that the use of graphene as an anode material in lithium-ion batteries ameliorates their performance and stability. Here, we investigate an alternative route to intercalate lithium underneath epitaxially grown graphene on iridium by means of photon irradiation. We grow thin films of LiCl on top of graphene on Ir(111) and irradiate the system with soft X-ray photons, which leads to a cascade of physicochemical reactions. Upon LiCl photodissociation, we find fast chlorine desorption and a complex sequence of lithium intercalation processes. First, it intercalates, forming a disordered structure between graphene and iridium. On increasing the irradiation time, an ordered Li(1 × 1) surface structure forms, which evolves upon extensive photon irradiation. For sufficiently long exposure times, lithium diffusion within the metal substrate is observed. Thermal annealing allows for efficient lithium desorption and full recovery of the pristine G/Ir(111) system. We follow in detail the photochemical processes using a multitechnique approach, which allows us to correlate the structural, chemical, and electronic properties for every step of the intercalation process of lithium underneath graphene.

Investigating lithium intercalation and diffusion in Nb-doped TiO2 by first principles calculations

1) BackgroundRecent research has shown growing interest in developing titanium dioxide (TiO2) based anode for lithium ion batteries due to its high theoretical specific capacity, safety, chemical stability, and abundance. Niobium-doped (Nb-doped) TiO2 anode was proposed for lithium ion batteries and demonstrated to improve cycling stability and cycling performance. 2) MethodsIn this study, first principles calculation based on density functional theory (DFT) was used to reveal and understand the mechanism of Nb-doped TiO2 outperforming pristine TiO2 as the anode material of lithium ion batteries. The lithium intercalation energy, lithium diffusion energy barrier, electron density difference mapping, and electronic structure of Nb-doped TiO2 at dilute lithium concentration were computed and compared to those of pristine TiO2. 3) Significant FindingsFor all three investigated polymorphs: anatase, rutile, and TiO2(B), Nb-doping enhances the lithium intercalation process by lowering the intercalation energy, but slightly increasing the energy barrier of lithium diffusion due to stronger interaction between the intercalated lithium and polaron induced by Nb dopant in TiO2. From the analysis of electronic structure, new energy states are formed, induced by doping with Nb. These new states narrow the band gap and shift Fermi levels towards the conduction band, thus facilitating improvement of electronic conductivity for all three phases studied.

Direct Exfoliation of Conductive MoS2 Using Peroxide for Solid State Sensor and Catalytic Applications

Two-dimensional (2D) materials have attracted much attention over the last decade due to their high performance in nanoelectronic devices. The discovery of graphene opened up many opportunities to investigate and explore other 2D materials. There has been a drive to expand the toolbox of 2D materials to also include insulators and semiconductors with a variety of bandgaps. As a result, a wide range of materials have been discovered or predicted, with molybdenum disulfide (MoS2) being particularly popular. Using the semiconducting phase of MoS2 (2H-MoS2) requires a relatively high voltage to get sufficient conductivity due to the presence of a band gap. However, for applications in batteries, supercapacitors, electrocatalysts and solar cells, a substantially increased conductivity is required in order to achieve reasonable currents.1 The most common source of conductive MoS2 is metallic MoS2 (1T-MoS2) that has been prepared via the lithium intercalation process, which requires inert atmosphere processing and safety procedures.2 Hence, there is a desire to develop a safer and more efficient process to yield conductive MoS2. Defects play a very important role in modulating the electrical properties of MoS2. Sonication of MoS2 in an appropriate solvent results in many disordered structural defects. The most common defects on MoS2 are sulfur defects. These defects increase the energy level of the gap state and eventually deteriorate the device performance. Thiol based molecules are commonly used to reduce the number of sulfur defects on MoS2. Other molecules such as oxygen or organic super acids like bis(trifluoromethane) sulfonamide (TFSI) have also been reported to passivate the surface defect.3 Past research has mainly focused on the theoretical study of defective MoS2 and how to utilize those defects for improving photoluminescent efficiency. However, those defects can also be utilized to improve the conductivity of MoS2 as a safer alternative for applications in batteries, supercapacitors, solar cells, electrocatalyst and sensors.Conductive MoS2 (c-MoS2) can be used as active material for low-cost solid-state chemiresistive pH sensors.4 In chemiresistive sensors, conductivity changes are observed based on direct interactions between the active material and the analyte.5 Even though chemiresistive pH sensors based on exfoliated graphene, carbon nanotubes, or graphitic materials are available, their sensing response is limited to less than 20%.6 On the other hand, MoS2 has attracted great attention as a promising electrocatalyst for the hydrogen evaluation reaction (HER) because of abundant active sites at edge sites and on the basal plane for facilitating hydrogen production. Water splitting is the simplest and most convenient method to generate hydrogen. In industrial applications, an electrocatalyst is commonly used to accelerate the HER and reduce the overpotential. Even though 2H-MoS2 has good catalytic activity at the edge sites, its low electrical conductivity limits the achievable current density, resulting in a high Tafel value and making it unsuitable for practical application in HER.In this work, we show a simple and effective way to prepare few layer c-MoS2 under ambient conditions using 0.06 vol% aqueous hydrogen peroxide. We have demonstrated that the bulk conductivity of the conductive MoS2 that we prepared is up to seven orders of magnitude higher than that of the semiconducting phase of MoS2. The samples were also characterized with Hall measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy which showed that hydrogen molybdenum bronze (HxMoO3) and substoichiometric MoO3−y help tune the conductivity of the nanometer-scale thin films without impacting the sulfur-to-molybdenum ratio. C-MoS2 was further functionalized with thiols to determine the number of residual reactive sites. An important goal of our work is to control the conductivity of the MoS2 thin films in safe and facile ways that enable their application in low-cost chemiresistive sensors in liquid environments. We fabricated chemiresistive pH sensors with centimeter channel lengths while maintaining low measurement voltages. We further measured the catalytic activity of c-MoS2 films in 0.5 M H2SO4 electrolyte solution with three electrode systems using linear sweep voltammetry (LSV) which showed a lower Tafel value at 10 mA/cm2 current density. The lower Tafel value demonstrated that c-MoS2 has potential to use as catalyst for HER. Our study furthers the understanding of conductive forms of MoS2, and also opens up a new pathway for next generation electronic and energy conversion devices.

High Pressure Effect on Structural and Electrochemical Properties of Anionic Redox-Based Lithium Transition Metal Oxides

Summary The richness of anionic redox chemistry in the solid state offers new opportunities and a possible paradigm shift in energy storage. The excess capacity that goes beyond conventional theoretical values is attributed to the anionic redox in Li-rich transition metal oxide cathodes for Li-ion batteries. Their electrochemical behavior is thermodynamically determined by structural evolution. To better understand the electrochemical dependence on structural factors, we have induced structural modifications in pristine and electrochemically activated Li1.144Ni0.136Co0.136Mn0.544O2 through high-pressure treatment. A unique cyclical change of structural reordering is observed in the anionic redox-activated material during operando pressure sweep, characterized by a periodic evolution of superlattice peak intensity in synchrotron X-ray diffraction patterns. During the structural reordering period, the bulk compressibility of the material decreases, even becoming negative. These insights elucidate the structural flexibility and metastability of anionic redox-based materials, which can undergo large compressions and structural modifications while delivering good electrochemical properties.

Hierarchical porous carbon doped with high content of nitrogen as sulfur host for high performance lithium–sulfur batteries

The applications of Li S batteries are restricted by the issues of the imperfect conductivity and severe volumetric change of active materials together with shuttle effect of lithium polysulfides, which requires a kind of material with appropriately multifunctional structure as sulfur host. Herein, an N–doped hierarchical porous carbon composite is synthesized via a high temperature carbonization method. The N–doped hierarchical porous carbon with a large number of micropores, mesopores and macropores provides the abundant interconnected network matrixes and high specific surface area, thus guaranteeing a high sulfur loading, and adapting the volumetric expansion during the lithium intercalation process. The macropore channels and conductive interconnected networks can accelerate the diffusion of electrons/ions among the cathode. Moreover, the mesopores and micropores besides the high amount N–doping accommodate high–level sulfur loading and immobilize lithium polysulfides via physical absorption and chemical confinement. The as–prepared N–doped hierarchical porous carbon compounded with sulfur as a cathode delivers a satisfactory initial capacity of 1285 mAh g −1 at 0.2 A g −1 and a reversible capacity of 517 mAh g −1 at 0.5 A g −1 over 1000 cycles, illustrating the improved electrochemical performances of the cathode. The high temperature carbonization method provides a new way to construct the hierarchical porous structured carbon with chemical doping. • N-doped hierarchical porous carbon was developed. • It has a large number of micropores, mesopores and macropores. • N-doped hierarchical porous carbon exhibit high capacity and rate performance. • High performance is ascribed to the porous hierarchical structure and N doping.

Tuning the Conductivity of Molybdenum Disulfide (MoS2) Thin Films through Defect Engineering

Two-dimensional (2D) materials have attracted much attention over the last decade due to their high performance in nanoelectronic devices. The discovery of graphene opened up many opportunities to investigate and explore other 2D materials. There has been a drive to expand the toolbox of 2D materials to also include insulators and semiconductors with a variety of bandgaps. As a result, a wide range of materials have been discovered or predicted,1 with molybdenum disulfide (MoS2) being particularly popular. The semiconducting phase of MoS2 (2H-MoS2) is one of the most commonly studied among the transition metal dichalcogenides.2 It has a thickness dependent band gap which has drawn attention for field-effect transistors (FET) where a high on/off current ratio is desired.3-5 However, for applications in batteries,6supercapacitors,7 and solar cells,8 a substantially increased conductivity is required in order to achieve reasonable currents. Using 2H-MoS2 requires a relatively high voltage to get sufficient conductivity due to the presence of a band gap. The most common source of conductive MoS2 is metallic MoS2 (1T-MoS2) that has been prepared via the lithium intercalation process, which requires inert atmosphere processing and safety procedures.9 Hence, there is a desire to develop a safer and more efficient process to yield conductive MoS2. Defects plays a very important role in modulating the electrical properties of MoS2. Sonication of MoS2 in an appropriate solvent results in many disordered structural defects. The most common defects on MoS2 are sulfur defects.10 These defects increase the energy level of the gap state and eventually deteriorate the device performance. Thiol based molecules are commonly used to reduce the number of sulfur defects on MoS2.11 Other molecules such as oxygen or organic super acids like bis(trifluoromethane) sulfonamide (TFSI) have also been reported to passivate the surface defect.12,13 Past research has mainly focused on the theoretical study of defective MoS2 and how to utilize those defects for improving photoluminescent efficiency. However, those defects can also be utilized to improve the conductivity of MoS2 as a safer alternative for applications in batteries, supercapacitors, solar cells and sensors.In this work, we show a simple and effective way to prepare few layer conductive MoS2 under ambient conditions. We have demonstrated that the sheet resistance of the conductive MoS2 that we prepared is up to five orders of magnitude higher than that of the semiconducting phase of MoS2, depending on the dopant concentration. The samples were also characterized with Hall measurements, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. An important goal of our work is to control the conductivity of the MoS2 thin films in safe and facile ways that enable their application in low-cost chemiresistive sensors in liquid environments. We fabricated chemiresistive pH sensors with centimeter channel lengths while maintaining low measurement voltages. Our study furthers the understanding of conductive forms of MoS2, and also opens a new pathway for next generation electronic devices.

Lithium intercalation drives mechanical properties deterioration in bulk and single-layered black phosphorus: a first-principles study

It is of critical importance to understand the mechanical properties change of electrode materials during lithium intercalation in the mechanical design of Li-ion batteries (LIBs), for the purpose of the high reliability and safety in their applications. Here, we investigated the mechanical properties of both bulk and single-layered black phosphorus (BP) during the lithium intercalation process by using the first-principles calculations. Our results show that the Young’s modulus of bulk and single-layered phosphorus strongly depends on the lithium intercalation. The mechanical bearing capacities, such as critical strain and stress, are significantly reduced by several times after lithium intercalation in both bulk and single-layered BP, which may reduce the reliability of LIBs. Our findings suggest that this notable mechanical properties deterioration during lithium intercalation should be considered carefully in the mechanical design of LIBs, in order to keep the work reliable and safe in the charge-discharge process.

4D imaging of lithium-batteries using correlative neutron and X-ray tomography with a virtual unrolling technique

The temporally and spatially resolved tracking of lithium intercalation and electrode degradation processes are crucial for detecting and understanding performance losses during the operation of lithium-batteries. Here, high-throughput X-ray computed tomography has enabled the identification of mechanical degradation processes in a commercial Li/MnO2 primary battery and the indirect tracking of lithium diffusion; furthermore, complementary neutron computed tomography has identified the direct lithium diffusion process and the electrode wetting by the electrolyte. Virtual electrode unrolling techniques provide a deeper view inside the electrode layers and are used to detect minor fluctuations which are difficult to observe using conventional three dimensional rendering tools. Moreover, the ‘unrolling’ provides a platform for correlating multi-modal image data which is expected to find wider application in battery science and engineering to study diverse effects e.g. electrode degradation or lithium diffusion blocking during battery cycling.

Optimizing Anode Performance Using Silicon Nanoparticle to Li<sub>4</sub>Ti<sub>5</sub>O<sub>12</sub> as Prepared by Hydrothermal Mechanochemical Process with Li<sub>2</sub>CO<sub>3</sub> as Lithium Ion Source

Lithium titanat Lithium titanate (Li4Ti5O12)/LTO is one of more favourable materials to be used as anode electrode to replace graphite in Li-ion battery application. The LTO has a crystal structure that is more stable than graphite, and undergoes less strain during lithium intercalation process. However, along with the increasing demand for batteries with high performance, the capacity of LTO also needs to be increased, among others by combining with a high capacity material, i.e: silicon, which theoretical capacity can reach 4200 mAh/g, but with volumetric strain of 300%. To minimize volume expansion effect, nanoscale silicon particle is used to form the LTO/Si nanocomposite. This research is carried out to synthesize the spinel LTO prepared by hydrothermal and mechanochemical process from xerogel TiO2. During preparation of slurry mixture of active material to make anode sheet, the LTO is mixed with silicon nanoparticle at 5%, 10% and 15% by weight. The coin cell type battery is assembled with lithium metal as the counter electrode. The material characterization instruments used are X-Ray diffraction (XRD) and Transmission Electron Microscope (TEM) with Energy Dispersive Spectrometer (EDS) showing the elements mapping. The battery performance is tested using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and charge discharge (CD). From EIS testing, the conductivity values of the samples decrease along with the increasing weight of Si nanoparticles. The CV test shows that the highest capacity of 197.09 mAh/g is achieved on the sample with 5wt% Si-nano. The CD test shows that this LTO/Si nanocomposite is capable to withstand at high charge/discharge rate at until 12 C exceeding the electric car battery requirement at 10 C.