Microwave-assisted synthesis and electrochemical characterization of TiNb2O7 microspheres as anode materials for lithium-ion batteries

TiNb₂O₇ microspheres are prepared via a microwave-assisted solvothermal method. The microwave irradiation lowers the compound formation temperature to 600°C, and highly crystalline TiNb₂O₇ powders are obtained upon calcination at 800°C. Morphological analysis of the sample shows uniformly distributed microspheres with a particle size of around 1 μm. The Li⁺-ion diffusion coefficient calculated from the electrochemical impedance result is around 1.21 × 10⁻¹³ cm² s⁻¹, which is 1.5 times higher than the sample obtained from the conventional solvothermal method. The TiNb₂O₇ sample derived from microwave yields a high discharge capacity of 299 mA h g⁻¹ at 0.1 C, whereas the sample synthesized via the conventional solvothermal process yields only 278 mA h g⁻¹ at 0.1 C. Excellent rate capabilities such as 220 mA h g⁻¹ at 5 C and 180 mA h g⁻¹ at 10 C are also observed for the microwave-assisted solvothermal sample. Moreover, the sample exhibits a large capacity retention of 95.5% after 100 discharge–charge cycles at 5 C. These results reveal the appropriateness of the microwave-assisted solvothermal process to prepare TiNb₂O₇ powders with superior properties for battery applications.     

La2O3-coated Li1.2Mn0.54Ni0.13Co0.13O2 as cathode materials with enhanced specific capacity and cycling stability for lithium-ion batteries

Li-rich layered oxides are the most promising cathode candidate for new generation rechargeable lithium-ion batteries. In this work, La₂O₃-coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were fabricated via a combined method of sol-gel and wet chemical processes. The structural and morphological characterizations of the materials demonstrate that a thin layer of La₂O₃ is uniformly covered on the surface of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ particles, and the coating of La₂O₃ has no obvious effect on the crystal structure of Li-rich oxide. The electrochemical performance of La₂O₃-coated Li-rich cathodes including specific capacity, cycling stability and rate capability has been significantly improved with the coating of La₂O₃. The Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ coated with 2.5 wt% La₂O₃ exhibits the highest discharge capacity, improved cycling stability and reduced charge transfer resistance, delivering a large discharge capacity of 276.9 mAh g⁻¹ in the 1st cycle and a high capacity retention of 71% (201.4 mAh g⁻¹) after 100 cycles. The optimal rate capability of the materials is observed at the coating level of 1.5 wt% La₂O₃ such that the material exhibits the highest discharge capacity of 90.2 mAh g⁻¹ at 5 C. The surface coating of La₂O₃ can effectively facilitate Li⁺ interfacial diffusion, reduce the structural change and secondary reactions between cathode materials and electrolyte during the charge-discharge process, and thus induce the great enhancement in the electrochemical properties of the Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ materials.     

High-rate, high capacity ZrO2 coated Li[Li1/6Mn1/2Co1/6Ni1/6]O2 for lithium secondary batteries

Recently, there have been many reports on efforts to improve the rate capability and discharge capacity of lithium secondary batteries in order to facilitate their use for hybrid electric vehicles and electric power tools. In the present work, we present a ZrO₂-coated Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂. The bare Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ shows a high initial discharge capacity of 224 mAh g⁻¹ at a 0.2 C rate. Owing to the stability of ZrO₂, it was possible to enhance the rate capability and cyclability. After 1 wt% ZrO₂ coating, the ZrO₂-coated Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ showed a high discharge capacity of 115 mAh g⁻¹ after 50 cycles under a 6 C rate, whereas the bare Li[Li_1/6Mn_1/2Co_1/6Ni_1/6]O₂ showed a discharge capacity of only 40 mAh g⁻¹ and very poor cyclability under the same conditions. Based on results of XRD and EIS measurements, it was found that the ZrO₂ suppressed impedance growth at the interface between the electrodes and electrolyte and prevented collapse of the layered hexagonal structure.     

SmPO4-coated Li1.2Mn0.54Ni0.13Co0.13O2 as a cathode material with enhanced cycling stability for lithium ion batteries

SmPO₄ coated Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode materials were prepared by the precipitation method and calcined at 450 °C. The crystal structures and electrochemical properties of the pristine and coated samples are studied by X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy, electron diffraction spectroscopy, galvanostatic cycling, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). It has been found that the electrochemical performances of the Li-rich cathode material have been substantially improved by SmPO₄ surface coating. Especially, the 2 wt% SmPO₄-coated sample demonstrates the best cycling performance, with capacity retention of 88.4% at 1 C rate after 100 cycles, which is much better than that of 72.3% in the pristine sample. The improved electrochemical properties have been ascribed to the SmPO₄ coating layer, which not only stabilizes the cathode structure by decreasing the loss of oxygen, but also protects the Li-rich cathode material from side reaction with the electrolyte and increases the Li⁺ migration rate at the cathode interface.     

Improved performance of iron-chromium flow batteries using SnO2-coated graphite felt electrodes

Polyacrylonitrile-based graphite felt has the properties of high temperature resistance, corrosion resistance, low thermal conductivity, large surface area and excellent electrical conductivity. It has become the preferred material for flow battery electrodes, but its chemical activity is poor. In order to improve the electrochemical activity of graphite felt electrodes, the electrodes were prepared by SnO₂-coated graphite felt. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to analyze the microscopic morphology of SnO₂-coated graphite felt electrodes. Electrochemical impedance spectroscopy, cyclic voltammetry and charge-discharge tests were performed using an electrochemical workstation to investigate the electrocatalytic activity of SnO₂-coated graphite felt electrodes and their cell performance. The results show that the SnO₂ coating on the graphite felt surface forms a convex and concave microstructure, which further increases the specific surface area of the electrode, and at the same time successfully introduces oxygen-containing functional groups to the electrode surface, increasing the electrochemically active spots on the surface. In addition, the presence of oxygen defects in the SnO₂ crystal structure provides more electrochemically active sites and improves the electrochemical performance of the graphite felt electrode. At a current density of 142 mA cm^?2, the charge-discharge capacity of the battery assembled with the SnO₂-coated graphite felt electrode was significantly improved; when the current density was 250 mAcm^?2, the Coulombic efficiency of the electrode (TGF-2) coated with a concentration of 0.1 M could reach 84%.     

Improved cycling stability of V2O5 modified spinel LiMn2O4 cathode at high cut-off voltage for lithium-ion batteries

Spinel lithium manganese oxide, LiMn₂O₄ coated with V₂O₅ layer (labeled as LMO-VO) has been developed and its electrochemical performances as cathode material for lithium-ion batteries has been evaluated at high cut-off voltage (>4.5 V vs. Li/Li⁺) and compared with pristine LiMn₂O₄ (labeled as LMO). The crystal structure investigations show that LMO-VO has longer Li–O bond length for fast Li-ion diffusion kinetic process. The scanning electron microscopy results indicate that LMO-VO has finer particles and the V₂O₅ layer has been successfully coated on the LMO surface uniformly. The highly conductive V₂O₅ coating layer enhances the ionic conductivity of the LMO cathode, as evidenced by the significant drop of R_ct value from the Nyquist plot. Under high operating voltage, the cell employed with coated LMO shows exceptional cycling performance in capacity retention and potential difference. After 300 cycles, the capacity retention per cycle has been boosted from 99.90% to 99.94% by adopting the V₂O₅ coating layer. In addition, surface coating with V₂O₅ stabilizes the potential difference at very minimal change for a longer period. This convincingly proves that the V₂O₅ coating layer not only protects against hydrofluoric acid (HF) attack and greatly restrains the increase of cell polarization at high voltage.     

Agar-assisted sol-gel synthesis and electrochemical characterization of TiNb2O7 anode materials for lithium-ion batteries

TiNb₂O₇ powders are synthesized via a newly developed agar-assisted sol-gel process for the first time. Phase-pure TiNb₂O₇ powders are obtained upon calcination at 800 °C. On contrast, TiNb₂O₇ powders synthesized via the conventional solid-state method require high calcination temperature at 1100 °C for the complete compound formation. The samples synthesized with agar improve the morphology with submicron-sized particles. The formed porous structure is favorable for enhancing the electrochemical kinetics due to the large contact area between the electrode and the electrolyte. Based on the electrochemical active surface area analysis, the electrical double-layer capacitance of TiNb₂O₇ powders synthesized via both the agar-assisted and the solid-state method is 145 mF cm^?2 and 22 mF cm^?2, respectively. The electrochemical active surface area of the sample prepared via the agar-assisted method is higher than that of the sample prepared via the solid-state method. The TiNb₂O₇ sample synthesized via the agar-assisted process yields 284 mAh g^?1 at 0.1 C, whereas the sample synthesized via the conventional solid-state method yields only 265 mAh g^?1 at 0.1 C. The discharge capacities of the agar-assisted synthesized sample are 205 mAh g^?1 and 174 mAh g^?1 at 5 C and 10 C, respectively. Moreover, the sample exhibits high capacity retention of 91% after 100 discharge-charge cycles at 5 C. Based on the obtained results, the agar-assisted sol-gel process is inferred as one of the facile methods for preparing high performance anode materials for lithium-ion batteries.     

Enhanced electrochemical properties of SnO2 anode by AlPO4 coating

A SnO₂ anode material undergoes severe capacity loss, which is mainly associated with cracking/crumbling of the material by the large volume change between the Li_xSn and Sn phases, and the intensive reactions with the electrolyte solution. However, AlPO₄ nanoparticle coating showed drastically improved electrochemical properties with decreased surface cracks. The AlPO₄-coated SnO₂ exhibited a capacity of 781 mAh/g, approaching its theoretical capacity at the first cycle, with 44% capacity retention after 15 cycles between 2.5 and 0 V at a relatively high C rate of 105 mA/g. In contrast, the bare SnO₂ showed an initial capacity of 680 mAh/g, with only 8% capacity retention after 15 cycles.     

Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.     

Synthesis of TiNb6O17/C composite with enhanced rate capability for lithium ion batteries

TiNb₆O₁₇/C composites were obtained via a facile solid-state reaction with TiO₂, Nb₂O₅ and glucose as the starting materials. The lattice structure and morphology of the composite were investigated by X-ray diffraction, scanning electronic microscopy and transmission electron microscopy. The electrochemical properties were characterized by rate charge/discharge measurements and cyclic voltammetry. Electrochemical measurements demonstrate that the TiNb₆O₁₇/C composite exhibits electrochemical properties superior to those of pure TiNb₆O₁₇, especially at high current rates. The initial discharge capacities of TiNb₆O₁₇/C are 239, 225.1 and 199.8 mAh g⁻¹ at 1, 5 and 10 C, respectively. Even after 500 cycles at 10 C, the capacity still remains 165.1 mAh g⁻¹, while the capacity of TiNb₆O₁₇ is only 74.8 mAh g⁻¹. The excellent electrochemical performance of TiNb₆O₁₇/C is attributed to the improvement of the electrical conductivity resulting from carbon coating.     

Modification of LiNi0.5Co0.2Mn0.3O2 with a NaAlO2 coating produces a cathode with increased long-term cycling performance at a high voltage cutoff

A long-lived cycling property is an important factor for the extensive use of the lithium-ion batteries. In this study, a NaAlO₂ layer was initially coated on the LiNi_0.5Co_0.2Mn_0.3O₂ surface. Electrochemical tests indicate that the coated surface achieves better cycling stability and a higher capacity at 25 °C. In addition, the 1 wt % NaAlO₂-coated sample exhibits the best performance, and it also exhibits a discharge specific capacity of 189.6 mAh∙g⁻¹ at 0.1C in the first cycle. After 800 cycles at 1C, the capacity retention of the 1 wt % NaAlO₂-coated sample is approximately 73.31%, a value that is 21.26% higher than the pristine sample. The electrochemical impedance spectroscopy (EIS) analysis reveals a decrease in the LiNi_0.5Co_0.2Mn_0.3O₂ charge transfer impedance and a significant increase in lithium ion diffusion after the application of the NaAlO₂ coating. The high ion diffusion coefficient and low charge transfer impedance are conducive to the better rate performance of NaAlO₂-coated LiNi_0.5Co_0.2Mn_0.3O₂.     

Preparation and evaluation of α-Al2O3 supported lithium ion sieve membranes for Li+ extraction

Spinel lithium manganese oxide ion-sieves have been considered the most promising adsorbents to extract Li⁺ from brines and sea water. Here, we report a lithium ion-sieve which was successfully loaded onto tubular α-Al₂O₃ ceramic substrates by dipping crystallization and post-calcination method. The lithium manganese oxide Li₄Mn₅O₁₂ was first synthesized onto tubular α-Al₂O₃ ceramic substrates as the ion-sieve precursor (i.e. L-AA), and the corresponding lithium ion-sieve (i.e. H-AA) was obtained after acid pickling. The chemical and morphological properties of the ion-sieve were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Both L-AA and H-AA showed characteristic peaks of α-Al₂O₃ and cubic phase Li₄Mn₅O₁₂, and the peaks representing cubic phase could still exist after pickling. The lithium manganese oxide Li₄Mn₅O₁₂ could be uniformly loaded not only on the surface of α-Al₂O₃ substrates but also inside the pores. Moreover, we found that the equilibrium adsorption capacity of H-AA was 22.9 mg·g⁻¹. After 12 h adsorption, the adsorption balance was reached. After 5 cycles of adsorption, the adsorption capacity of H-AA was 60.88% of the initial adsorption capacity. The process of H-AA adsorption for Li⁺ correlated with pseudo-second order kinetic model and Langmuir model. Adsorption thermodynamic parameters regarding enthalpy (∆ H), Gibbs free energy (∆ G) and entropy (∆ S) were calculated. For the dynamic adsorption–desorption process of H-AA, the H-AA exhibited excellent adsorption performance to Li⁺ with the Li⁺ dynamic adsorption capacity of 9.74 mg·g⁻¹ and the Mn²⁺ dissolution loss rate of 0.99%. After 3 dynamic adsorption–desorption cycles, 80% of the initial dynamic adsorption capacity was still kept.     

Highly enhanced electrochemical performances of LiNi0.815Co0.15Al0.035O2 by coating via conductively LiTiO2 for lithium-ion batteries

LiTiO₂ film-coated layered LiNi_0.815Co_0.15Al_0.035O₂ (NCA) material was successfully synthesised through in situ hydrolysis–lithiation to improve electrochemical properties. Herein, NCA was synthesised using solid state reaction, coated by hydrolysis of tetrabutyl titanate and subjected to lithiation process. The optimal molar ratio (LiTiO₂: NCA) was found to be 1.0 mol%, and the thickness of LiTiO₂ film coated on the surface of NCA of 18 nm was observed through HRTEM images. Compared with pristine NCA, 1.0 mol% LiTiO₂-coated NCA demonstrated better electrochemical performance with larger capacity of 20 mAh g⁻¹ under 1 C after 100 cycles. Its related capacity retention was 90.8%. The 1.0 mol% LiTiO₂-coated sample exhibited high discharge capacity of 157.6 mAh g⁻¹ at a current rate of 10 C, whereas the pristine sample only presented 145.3 mAh g⁻¹. The considerably improvement of the rate and cycling properties of the NCA cathode material is achieved using LiTiO₂ as a Li⁺-conductive coating layer. These new findings contribute towards the design of a stable-structured Ni-rich material for lithium-ion batteries.     

Effect of SiC whiskers on the anti-oxidation properties of Yb2Si2O7/mullite/SiC tri-layer environmental barrier coating for CMCs

The mullite and ytterbium disilicate (β-Yb₂Si₂O₇) powders as starting materials for the Yb₂Si₂O₇/mullite/SiC tri-layer coating are synthesized by a sol–gel method. The effect of SiC whiskers on the anti-oxidation properties of Yb₂Si₂O₇/mullite/SiC tri-layer coating for C/SiC composites in the air environment is deeply studied. Results show that the formation temperature and complete transition temperature of mullite were 800–1000 and 1300°C, respectively. Yb₂SiO₅, α-Yb₂Si₂O₇, and β-Yb₂Si₂O₇ were gradually formed between 800 and 1000°C, and Yb₂SiO₅ and α-Yb₂Si₂O₇ were completely transformed into β-Yb₂Si₂O₇ at a temperature above 1200°C. The weight loss of Yb₂Si₂O₇/(SiC_w–mullite)/SiC tri-layer coating coated specimens was 0.15 × 10⁻³ g cm⁻² after 200 h oxidation at 1400°C, which is lower than that of Yb₂Si₂O₇/mullite/SiC tri-layer coating (2.84 × 10⁻³ g cm⁻²). The SiC whiskers in mullite middle coating can not only alleviate the coefficient of thermal expansion difference between mullite middle coating and β-Yb₂Si₂O₇ outer coating, but also improve the self-healing performance of the mullite middle coating owing to the self-healing aluminosilicate glass phase formed by the reaction between SiO₂ (oxidation of SiC whiskers) and mullite particles.     

Preparation and optimization of ZrO2 modified P2-type Na2/3Ni1/6Co1/6Mn2/3O2 with enhanced electrochemical performance as cathode for sodium ion batteries

Surface stabilization is necessary for cathode materials to gain a long-term cycling stability because of unfavorable side reactions and exfoliation caused by corrosive environment. To improve the cyclic stability of P2-type ternary cathode Na_2/3Ni_1/6Co_1/6Mn_2/3O₂ for sodium ion batteries, we prepare a ZrO₂-coated Na_2/3Ni_1/6Co_1/6Mn_2/3O₂ through a simple wet chemical method. The coating layer is distributed homogeneously on the surface, and the fraction of ZrO₂ (1 wt-%, 2 wt-%, 3 wt-%, 4 wt-%, 5 wt-%) helps control the thickness of the coating layer. It turns out that all the materials exhibit pure P2 structure without any impurities. The material with a 2 wt-% ZrO₂ coating exhibits the best electrochemical performance in rate capability and long-term cyclic stability. It delivers a superior initial discharge capacity of 140 mA h·g⁻¹ between 2 and 4.5 V at 20 mA g⁻¹. Even cycles at high current density (100 mA g⁻¹), it shows 106 mA h·g⁻¹ reversible discharge capacity with 88% capacity retention after 300 cycles. The improvement in electrochemical performance is attributed to the segregation of cathode materials from the corrosive electrolyte by the nano-sized ZrO₂ layer. The EIS results confirm that a thin ZrO₂ coating layer can effectively protect the electrode from dissolution and stabilize the SEI film. This study can be used to develop the electrochemical performance of cathode materials for sodium ion batteries by surface modification via ZrO₂.     

Electrochemical properties and microstructures of LiMn2O4 cathodes coated with aluminum zirconium coupling agents

In this study, we developed a novel and facile modification method to improve the performance of LiMn₂O₄ (LMO) electrodes for lithium ion batteries. We used an aluminum-zirconium coupling agent (AZCA) to treat LMO cathodes via a simple pyrolysis method at 450 °C. The microstructures and properties of the cathodes were examined by carrying out X-ray diffraction, scanning electron microscopy, X-ray photoelectron microscopy, transmission electron microscopy, and electrochemical analyses. The results showed that an amorphous Al₂O₃/ZrO₂ composite layer was uniformly coated on the surface of the positive material, and the thickness of the coating was about 6 nm. The coating did not affect the particle morphology and crystal structure of the samples. However, it could enhance the surface stability and result in reducing the polarization, improving the rate properties and cycle reversibility of LMO especially at high temperatures. The optimum AZCA amount for the deposition of the composite coating was found to be 3 wt%. After coating, the discharge capacity of LMO at 3C increased by 14.37% and 74.95% at 25 and 55 °C, respectively. Noteworthy, after 100 cycles at 55 °C and 1C rate, the capacity retention of LMO increased from 61.3% to 88.1%. The improvement in the properties of the AZCA-treated LMO cathodes can be attributed to the synergy between Al₂O₃ and ZrO₂, which improved the chemical stability of the cathode surface, suppressed the side reaction between the cathode and the electrolyte and enhanced the reversible deinsertion/insertion ability of Li⁺. In addition, the composite coating can greatly stabilize the crystal structure of LMO during charging-discharging cycling.     

LiNi0.8Co0.15Al0.05O2 cathode materials prepared by TiO2 nanoparticle coatings on Ni0.8Co0.15Al0.05(OH)2 precursors

Synthesis, electrochemical, and structural properties of LiNi_0.8Co_0.15Al_0.05O₂ cathodes prepared by TiO₂ nanoparticles coating on a Ni_0.8Co_0.15Al_0.05(OH)₂ precursor have been investigated by the variation of coating concentration and annealing temperature. TiO₂-coated cathodes showed that Ti elements were distributed throughout the particles. Among the coated cathodes, the 0.6 wt% TiO₂-coated cathode prepared by annealing at 750 °C for 20 h exhibited the highest reversible capacity of 176 mAh g⁻¹ and capacity retention of 92% after 40 cycles at a rate of 1C (=190 mA g⁻¹). On the other hand, an uncoated cathode showed a reversible first discharge capacity of 186 mAh g⁻¹ and the same capacity retention value to the TiO₂-coated sample at a 1C rate. However, under a 1C rate cycling at 60 °C for 30 cycles, the uncoated sample showed a reversible capacity of 40 mAh g⁻¹, while a TiO₂-coated one showed 71 mAh g⁻¹. This significant improvement of the coated sample was due to the formation of a possible solid solution between TiO₂ and LiNi_0.8Co_0.15Al_0.05O₂. This effect was more evident upon annealing the charged sample while increasing the annealing temperature, and at 400 °C, the coated one showed a more suppressed formation of the NiO phase from the spinel LiNi₂O₄ phase than the uncoated sample.     

Synthesis,structure and electronic calculation of alkali metals borate Li2Na[B5O8(OH)2]

A new alkali metals borate complex, Li₂Na[B₅O₈(OH)₂], has been successfully synthesized by a facile hydrothermal method. Single-crystal X-ray diffraction analysis reveals that it crystallizes in orthorhombic space group Pbcn with a = 8.919(3) Å, b = 9.181(3) Å, c = 8.416(2) Å, Z = 4. The crystal structure is constructed of two dimensional (2D) [(B₅O₈)(OH)₂]_∞ layers, while stacking along b axis and then connected by Li⁺ and Na⁺ cations to extend to 3D framework Li₂Na[B₅O₈(OH)₂]. UV-vis-NIR spectrum shows that Li₂Na[B₅O₈(OH)₂] possesses a wide range of transparency and a UV cut-off edge below 190 nm which indicates that it may be applied in the deep ultraviolet region. The calculated band structures and the density of states indicate that Li₂Na[B₅O₈(OH)₂] is a direct band gap compound with a band gap of 5.68 eV. In addition, IR spectroscopy, thermal stability and theoretical calculations of Li₂Na[B₅O₈(OH)₂] are also reported in this work.     

Stable composite electrolytes of PVDF modified by inorganic particles for solid-state lithium batteries

Polymer electrolytes have been attracting much attention because of their flexibility and easy follow-up processing, but their Li⁺ conductivity in lithium-metal batteries (LIBs) is unsatisfactory. Stable composite electrolytes of poly (vinylidene fluoride) (PVDF) polymer with high lithium-ion conductivity have been prepared by a trigger structural modification of Li_6.5La₃Zr_1.5Nb_0.25Ta_0.25O₁₂ (LLZNTO) garnet ceramic and TiO₂ oxide. The influences of various amounts of TiO₂ and LLZNTO on electrochemical performance were systematically examined. These composite electrolytes exhibited maximal Li⁺ conductivity of 2.89 × 10⁻⁴ S cm⁻¹, which is consistent with the value of pure ceramic electrolytes. Furthermore, it possessed the stable long-term Li cycling and the wide electrochemical window, involving repeated Li plating/stripping at 0.2 mA cm⁻² over 280 h without failure. The discharge specific capacity and Coulomb efficiency for all-solid-state LIBs assembled with these membranes delivered outstanding cycling stability with high discharge capacities (117.9 mA h g⁻¹) at 0.1 C rate and Coulomb efficiency reached 99.9% after 25 cycles. The high Li⁺ conduction capability can be ascribed function of introducing TiO₂ and LLZNTO to restrain tremendously the crystalline behavior of the polymer. Furthermore, the LLZNTO can be complex with PVDF for dehydrofluorination, and it can also offer a burst transportation route for lithium ions. This system might serve as an attractive use for polymer solid electrolytes and open up new possibilities for safe all-solid-state LIBs.     

Engineering an ultrathin amorphous TiO2 layer for boosting the weatherability of TiO2 pigment with high lightening power

TiO₂ pigments are typically coated with inert layers to suppress the photocatalytic activity and improve the weatherability. However, the traditional inert layers have a lower refractive index compared to TiO₂, and therefore reduce the lightening power of TiO₂. In the present work, a uniform, amorphous, 2.9-nm-thick TiO₂ protective layer was deposited onto the surface of anatase TiO₂ pigments according to pulsed chemical vapor deposition at room temperature, with TiCl₄ as titanium precursor. Amorphous TiO₂ coating layers exhibited poor photocatalytic activity, leading to a boosted weatherability. Similarly, this coating method is also effective for TiO₂ coating with amorphous SiO₂ and SnO₂ layers. However, the lightening power of amorphous TiO₂ layer is higher than those of amorphous SiO₂ and SnO₂ layers. According to the measurements of photoluminescence lifetime, surface photocurrent density, charge-transfer resistance, and electron spin resonance spectroscopy, it is revealed that the amorphous layer can prevent the migration of photogenerated electrons and holes onto the surface, decreasing the densities of surface electron and hole, and thereby suppress the photocatalytic activity.