Spray pyrolysis synthesis of nanostructured LiFexMn2−xO4 cathode materials for lithium-ion batteries

A series of partially Fe-substituted lithium manganese oxides LiFe_xMn_2−xO₄ (0 ≦ x ≦ 0.3) was successfully synthesized by an ultrasonic spray pyrolysis technique. The resulting powders were spherical nanostructured particles which comprised the primary particles with a few tens of nanometer in size, while the morphology changed from spherical and porous to spherical and dense with increasing Fe substitution. The densification of particles progressed with the amount of Fe substitution. All the samples exhibited a pure cubic spinel structure without any impurities in the XRD patterns.The as-prepared powders were then sintered at 750 °C for 4 h in air. However, the particles morphology and pure spinel phase of LiFe_xMn_2−xO₄ powders did not change after sintering. The as-sintered powders were used as cathode active materials for lithium-ion batteries, and cycle performance of the materials was investigated using half-cells Li/LiFe_xMn_2−xO₄. The first discharge capacity of Li/LiFe_xMn_2−xO₄ cell in a voltage 3.5-4.4 V decreased as the value x increased, however these cells exhibited stable cycling performance at wide ranges of charge-discharge rates.     

SYNTHESIS OF NANOSTRUCTURED LiM0.15Mn1.85O4 (M = Mn,Co, Al,AND Fe) PARTICLES BY SPRAY PYROLYSIS IN A FLUIDIZED BED REACTOR

A novel technique has been developed to directly produce fine ceramic powders from liquid solution via spray pyrolysis in a fluidized bed reactor (SPFBR). Using this technique the preparation of LiM_0.15Mn_1.85O₄ (M = Mn, Co, Al, and Fe), which are the most promising cathode materials for lithium-ion batteries, has been carried out at a superficial velocity U₀ of 0.71 m/s, a reactor temperature T of 800°C, and a static bed height L_s of 100 mm. The as-prepared powders were spherical nanostructured particles that comprised primary particles of a few tens of nanometers in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. The chemical composition of as-prepared samples showed good agreement with the theoretical values that proved stoichiometric formulae of the compounds. The specific surface area of as-prepared LiM_0.15Mn_1.85O₄ (M = Mn, Co, Al, and Fe) powders decreases with increasing the static bed height in each doping metal, while the crystallite size increases with the static bed height. As a result, the as-prepared powders showed larger crystallite size and smaller specific surface area than those prepared by conventional spray pyrolysis.     

All‐Purpose Electrode Design of Flexible Conductive Scaffold toward High‐Performance Li–S Batteries

The main obstacles that hinder the development of efficient lithium sulfur (Li–S) batteries are the polysulfide shuttling effect in sulfur cathode and the uncontrollable growth of dendritic Li in the anode. An all‐purpose flexible electrode that can be used both in sulfur cathode and Li metal anode is reported, and its application in wearable and portable storage electronic devices is demonstrated. The flexible electrode consists of a bimetallic CoNi nanoparticle‐embedded porous conductive scaffold with multiple Co/Ni‐N active sites (CoNi@PNCFs). Both experimental and theoretical analysis show that, when used as the cathode, the CoNi and Co/Ni‐N active sites implanted on the porous CoNi@PNCFs significantly promote chemical immobilization toward soluble lithium polysulfides and their rapid conversion into insoluble Li₂S, and therefore effectively mitigates the polysulfide shuttling effect. Additionally, a 3D matrix constructed with porous carbonous skeleton and multiple active centers successfully induces homogenous Li growth, realizing a dendrite‐free Li metal anode. A Li–S battery assembled with S/CoNi@PNCFs cathode and Li/CoNi@PNCFs anode exhibits a high reversible specific capacity of 785 mAh g^?1 and long cycle performance at 5 C (capacity fading rate of 0.016% over 1500 cycles).     

Nickel embedded porous macrocellular carbon derived from popcorn as sulfur host for high-performance lithium-sulfur batteries

Due to the demands for high performance and ecological and economical alternatives to conventional lithium-ion batteries (LiBs),the development of lithium-sulfur (Li-S) batteries with remarkably higher theoretical capacity (1675 mA h g-1) has become one of the extensive research focus directions world-wide.However,poor conductivity of sulfur,critical cyclability problems due to shuttle of polysulfides as intermediate products of the cathodic reaction,and large volume variation of the sulfur composite cathode upon operation are the major bottlenecks impeding the implementation of the next-generation Li-S batteries.In this work,a unique three-dimensional (3D) interconnected macrocellular porous carbon (PC) architecture decorated with metal Ni nanopatticles was synthesized by a simple and facile strategy.The as-fabricated Ni/PC composite combines the merits of conducting carbon skeleton and highly adsorptive abilities of Ni,which resulted in efficient trapping of lithium polysulfides (LiPSs) and their fast conversion in the electrochemical process.Owing to these synergistic advantageous features,the composite exhibited good cycling stability (512.3 mA h g-1 after 1000 cycles at 1 C with an extremely low capacity fading rate 0.03 ％ per cycle),and superior rate capability (747.5 mAh g-1 at 2 C).Accordingly,such Ni nanoparticles embedded in a renewable puffed corn-derived carbon prepared via a simple and effective route represent a promising active type of sulfur host matrix to fabricate high-performance Li-S batteries.     

Physical and electrochemical properties of LiMnPO4/C composite cathode prepared with different conductive carbons

The olivine structured LiMnPO₄/C composites were prepared by a combination of spray pyrolysis and wet ballmilling using different conductive carbons: acetylene black and two types of ketjen black. The ketjen black with a larger specific surface area and dibutyl phthalate absorption number was found to be more preferable compared with other conductive carbons studied in this work. The LiMnPO₄/C composite cathode with ketjen black, which has the largest specific surface area, exhibited the largest discharge capacity compared with other LiMnPO₄/C composites. The largest discharge capacity delivered by this composite cathode was 166 mAh g⁻¹ at 0.05 C, which is about 97% of the theoretical value for LiMnPO₄. The performance improvement by using this conductive carbon was attributed to its extremely large specific surface area and high ability to absorb the electrolyte, which provide enhanced charge transfer and lithium ion transport in the composite cathode structure.     

Preparation of carbon coated LiMnPO4 powders by a combination of spray pyrolysis with dry ball-milling followed by heat treatment

Nanostructured LiMnPO₄ particles could be successfully synthesized by an ultrasonic spray pyrolysis method from the precursor solution; LiNO₃, Mn(NO₃)₂·6H₂O and H₃PO₄ were stoichiometrically dissolved into distilled water. The X-ray diffraction analysis showed that the as-prepared powders which had the desired olivine structure without any impurity phase could be obtained in the reactor temperatures ranging from 500 to 800 °C. Carbon coated LiMnPO₄ could be prepared from the as-prepared powders by a dry ball-milling followed by heat treatment for 4 h in a N₂ + 3% H₂ atmosphere. Transmission Electron Microscopy observation confirmed that a carbon layer was formed on the surface of LiMnPO₄ particles, which aimed to enhance the electronic conductivity of the material as well as inhibit the agglomeration during annealing. The carbon coated LiMnPO₄ was used as cathode active materials for lithium-ion batteries, and electrochemical performance was investigated using the Li|1 M LiClO₄ in EC:DEC = 1:1|LiMnPO₄ cells at room temperature and 55 °C. At a charge/discharge rate of 0.05 C, the cell exhibited first discharge capacities of 70 mAh g^?1 at room temperature and 140 mAh g^?1 at 55 °C. Moreover, it showed excellent cycleability even at elevated temperature and a high charge/discharge rate of 2 C.     

Enhancing purity and ionic conductivity of NASICON-typed Li1.3Al0.3Ti1.7(PO4)3 solid electrolyte

Increasing demand for safe energy storage and portable power sources has led to intensive investigation for all-solid state Li-ion batteries and particularly to solid electrolytes for such rechargeable batteries. One of the most promising types of solid electrolytes is NASICON-structured Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) due to its relatively high ionic conductivity and stability towards air and moisture. Here, the work is aimed on implementing the steps to hinder formation of impurity phases reported for various synthesis routes. Consequently, the applied modifications in the preparation strategies alter a crystal shape and size of prepared material. These two parameters have an enormous impact on properties of LATP. Fabrication of larger particles with a cubic shape significantly improves its ionic conductivity. As a result, LATP preparation methods such as a solution chemistry and molten flux resulted in the highest ionic conductivity samples with the value of ~10^?4 S cm^?1 at room temperature. Other LATPs obtained by solid-state reaction, sol-gel and spray drying methods depicted the ionic conductivity of ~10^?5 S cm^?1. The activation energy of lithium ion transfer in LATP varied in a range of 0.25–0.4 eV, which is in well agreement with the previously reported data.     

Dealloying-derived nanoporous deficient titanium oxide as high-performance bifunctional sulfur host-catalysis material in lithium-sulfur battery

In this work,we report a facile dealloying strategy to tailor the surface state of nanoporous TiO2 towards high-efficiency sulfur host material for lithium-sulfur(Li-S)batteries.When used as a sulfur cathode material,the oxygen-deficient TiO2-x exhibits enhanced lithium polysulfides(LiPS)adsorption and con-version kinetics that effectively tackle the shuttle effect in lithium-sulfur batteries.The excellent ability of the oxygen vacancy sites on TiO2-x surface to trap LiPS is proved by experimental observations and density functional theory(DFT)calculations.Meanwhile,it also promotes conversion kinetics of lithium polysul-fides,as verified by the asymmetric cell experiment.Accordingly,compared with the S/TiO2 cathode,the oxygen-deficient S/TiO2-x electrode exhibits preeminent rate and cycling performance in lithium-sulfur batteries:it delivers an ultra-low capacity decay of0.039％per cycle after 1000 cycles at 1 C.Tunning the surface state of metal oxides by dealloying method offers a new facile strategy to design efficient sulfur cathode materials for lithium-sulfur batteries.     

Synthesis of spherical LiMnPO4/C composite microparticles

Spherical LiMnPO₄/C composite microparticles were prepared by a combination of spray pyrolysis and spray drying followed by heat treatment and examined as a cathode material for lithium batteries. The structure, morphology and electrochemical performance of the resulting spherical LiMnPO₄/C microparticles were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electronic microscopy and standard electrochemical techniques. The final sample was identified as a single phase orthorhombic structure of LiMnPO₄ and spherical powders with a geometric mean diameter of 3.65 μm and a geometric standard deviation of 1.34. The electrochemical cells contained the spherical LiMnPO₄/C microparticles exhibited first discharge capacities of 112 and 130 mAh g⁻¹ at 0.05 C at room temperature and 55 °C, respectively. These also showed a good rate capability up to 5 C at room temperature and 55 °C.