One-step electrochemical in-situ Li doping and LiF coating enable ultra-stable cathode for sodium ion batteries

Despite of the higher energy density and inexpensive characteristics,commercialization of layered oxide cathodes for sodium ion batteries(SIBs)is limited due to the lack of structural stability at the high voltage.Herein,the one-step electrochemical in-situ Li doping and LiF coating are successfully achieved to obtain an advanced Na0.79Lix[Li_(0.13)Ni_(0.20)Mn_(0.67)]O_(2)@LiF(NaLi-LNM@LiF)cathode with superlattice structure.The results demonstrate that the Li^(+)doped into the alkali metal layer by electrochemical cycling act as"pillars"in the form of Li-Li dimers to stabilize the layered structure.The supplementation of Li to the superlattice structure inhibits the dissolution of transition metal ions and lattice mismatch.Furthermore,the in-situ LiF coating restrains side reactions,reduces surface cracks,and greatly improves the cycling stability.The electrochemical in-situ modification strategy significantly enhances the electrochemical performance of the half-cell.The NaLi-LNM@LiF exhibits high reversible specific capacity(170.6 m A h g^(-1)at 0.05 C),outstanding capacity retention(92.65%after 200 cycles at 0.5 C)and excellent rate performance(80 mA h g^(-1)at 7 C)in a wide voltage range of 1.5-4.5 V.This novel method of in-situ modification by electrochemical process will provide a guidance for the rational design of cathode materials for SIBs.

Enhancing carrier transport in flexible CZTSSe solar cells via doping Li strategy

The passivation of non-radiative states and inhibition of band tailings are desirable for improving the open-circuit voltage(V_(oc))of CZTSSe thin-film solar cells.Recently,alkali metal doping has been investigated to passivate defects in CZTSSe films.Herein,we investigate Li doping effects by applying Li OH into CZTSSe precursor solutions,and verify that carrier transport is enhanced in the CZTSSe solar cells.Systematic characterizations demonstrate that Li doping can effectively passivate non-radiative recombination centers and reduce band tailings of the CZTSSe films,leading to the decrease in total defect density and the increase in separation distance between donor and acceptor.Fewer free carriers are trapped in the band tail states,which speeds up carrier transport and reduces the probability of deep-level defects capturing carriers.The charge recombination lifetime is about twice as long as that of the undoped CZTSSe device,implying the heterojunction interface recombination is also inhibited.Besides,Li doping can increase carrier concentration and enhance build-in voltage,leading to a better carrier collection.By adjusting the Li/(Li+Cu)ratio to 18%,the solar cell efficiency is increased significantly to 9.68%with the fill factor(FF)of 65.94%,which is the highest FF reported so far for the flexible CZTSSe solar cells.The increased efficiency is mainly attributed to the reduction of V_(oc)deficit and the improved CZTSSe/Cd S junction quality.These results open up a simple route to passivate non-radiative states and reduce the band tailings of the CZTSSe films and improve the efficiency of the flexible CZTSSe solar cells.

Selective Oxidation of PM over Li Doped Potassium Titanate Catalysts

K2Ti2O5 and LixK2-xTi2O5 samples with varying K contents （x=0.125, 0.15, 0.3）, targeted on removal of two main environmental pollutants： PM and NOx, were synthesized by the solid state method using TiO2, KNO3 and LiOH-H2O as starting materials and were characterized by X-ray diffractometry, scanning electron microscopy, and BET. The catalytic activity of titanate catalysts on PM oxidation was evaluated using the temperature programmed oxidation （TPO） method. The test results showed that the perovskite structure of K2Ti205 was still retained after doping a small amount of Li, and the catalytic performance of LixK2-xTi2O5 had been improved significantly compared with that of K2Ti2O5. Li0.15K1.85Ti205 catalyst had the highest catalytic activity with an ignition temperature of 210℃ and a peak temperature of 290℃. The catalytic activity of both K2Ti2O5 and LixK2-xTi2O5 under intimate contact was higher than that under loose contact. When the exhaust gas flow rate was around 100 mL/min, the catalyst samples showed a highest activity. The Li doped K2Ti2O5 could be an excellent candidate for PM oxidation due to its high oxidation activity, water stability, resistance to sulfur poisoning and economical advantages.

Defects Energetics and Electronic Properties of Li Doped ZnO： A Hybrid Hartree-Fock and Density Functional Study

The electronic properties and stability of Li-doped ZnO with various defects have been stud- ied by calculating the electronic structures and defect formation energies via first-principles calculations using hybrid Hartree-Fock and density functional methods. The results from formation energy calculations show that Li pair complexes have the lowest formation energy in most circumstances and they consume most of the Li content in Li doped ZnO, which make the p-type conductance hard to obtain. The formation of Li pair complexes is the main obstacle to realize p-type conductance in Li doped ZnO. However, the formation energy of Lizn decreases as environment changes from Zn-rich to O-rich and becomes more stable than that of Li-pair complexes at highly O-rich environment. Therefore, p-type conductance can be obtained by Li doped ZnO grown or post annealed in oxygen rich atmosphere.

Influence of Y^(3+) on Structure and Electrochemical Property of LiMn_2O_4

Li1.02YxMn2-xO4（x = 0, 0. 005, 0.01, 0.02, 0.04, 0. 1） were prepared by solid state reaction method with raw materials Li2CO3, electrolytic MnO2 and Y2O3. Li1.02YxMn2-x O4 with different Y^3＋ contents have good crystal structure, Y^3＋ doping makes the lattice parameter and crystal volume small. Cyclic vohammogram testing result shows that a small quantity of Y^3＋ doping has no influence on the Li^＋ deinsertion-insertion process, but Y^3＋ doping decreases the interacting force among Li^＋ , and then availably avoids the energy level splitting. The electrochemical property testing indicates that the initial discharge ca- pacity at x =0.02 is 117.2 mAh·g^-1 and remains 96.9% with 113.6 mAhg^-1 after 20 cycles, which explains that Y^3＋ doping effectively restricts Jahn-Teller effect and stabilizes the crystal structure. AC analysis shows that conductivity of the samples is clearly improved due to Y^3＋ doping.

Computer Simulation of Adsorption and Separation of CO2/CH4 in Modified COF-102

Covalent organic framework （COF） is a porous material with low density and large BET （Brtmauer-Emmett-Teller） surface area. They have great potential in gas adsorption and separation. In this work, the adsorption of pure CO2 and CO2/CH4 mixture on modified COF-102 was simulated by using GCMC （grand canonical Monte Carlo）. Metal Li was incorporated into COF-102 through three doping methods, including charge exchange, O^--Li6＋ dipolar interaction and O^--Li^＋ chemical bonding. The influence of Li doping on the adsorption of CO2 was studied. The results showed that among the three methods, the dipole doping is the best way to improve CO2 adsorption performance. Further, the ligands of COF-102 were replaced by extended aromatic moieties, such as diphenyl and pyrene. The adsorption capacity of CO2 and CH4, and the selectivity of CO2/CH4 on the ligand-replaced COF-102 were studied. The capacity of CO2 and CH4 on the ligand-replaced COF-102 had obvious changes; hence the selectivity of CO2/CH4 can be adjusted accordingly.

Study of the structural,ferroelectric,dielectric,and pyroelectric properties of the K0.5Na0.5NbO3 system doped with Li+,La3+,and Ti4+

Pure Ko.sNao sNbO3(KNN)and KNN doped with Lit(6%mole),Lat(1.66%,5%,6%mole),and Ti+t(10%mole)were prepared by mixture of oxides using high-energy milling and conventional solid-state reaction.The effects of the dopant on the physical properties of pure KNN have been evaluated based on the structural,ferroelectric,pyroelectric,and dielectric measurements.The XRD measurements show that KNN pure sample contains a mixture of monoclinic and orthorhombic crystalline phases,with a slightly higher concentration of monoclinic phase.In contrast,all doped samples show a higher concentration of the orthorhombic phase,as well as the presence of a secondary phase(K6Nb10.8O3o),also detected by Raman measurements.The samples with a higher concentration of this secondary phase,also present greater dielectric losses and lower values of remnant polarization.The dielectric measurements allowed us to detect temperatures of structural transitions(orthorhombic-tetragonal,O-T)previous to the ferroelectric paraelectric transition(tetragonal-cubic,T-C),and also in this set of samples,a direct correlation was found between the values of remnant polarization and the corresponding pyroelectric signal response.

Enhanced carbon dioxide adsorption performance and kinetic study of K and Al co-doped Li4SiO4

Herein, we report the effects of doped K and Al on the carbon dioxide （CO2） adsorption performance of the Li4SiO4-based adsorbents. The CO2 adsorption capacity of 0.8 wt% K and 1.5 wt% AI doped Li4SiO4 is ～2.2 times and ～1.3 times higher than that of the pristine Li4SiO4 at 500 and 600℃, respectively. The kinetic study further indicated that the reaction rates of the lithium diffusion process is greatly improved by K and AI doping, and the lithium diffusion rate of 0.8 wt% K and 1.5 wt% AI doped Li4SiO4 is ～2 times higher than that of the pristine Li4SiO4 at 575-650 ℃. K and AI doping increases the adsorption capacity of Li4SiO4-based adsorbents, and widens its effective adsorption temperature range

Reorganizing electronic structure of Li3V2(PO4)3 using polyanion(BO3)^3-:towards better electrochemical performances

Doping modification of electrode materials is a sought-after strategy to improve their electrochemical performance in the secondary batteries field. Herein,polyanion（BO3）^3-doped Li3V2（PO4）3 cathode materials were successfully synthesized via a wet coordination method. The effects of（BO3）^3- doping content on crystal structure, morphology and electrochemical performance were explored by X-ray diffraction（XRD）, scanning electron microscopy（SEM）, cyclic voltammetry（CV） and electrochemical impedance spectroscopy（EIS）. All the asprepared samples have the same monoclinic structure;among them, Li3V2（PO4）（2.75）（BO3）（0.15） sample has relatively uniform and optimized particle size. In addition, this sample has the highest discharge capacity and the best cycling stability, with an initial discharge capacity of 120.4mAh·g^-1, and after 30 cycles at a rate of 0.1C, the discharge capacity still remains 119.3 mAh·g^-1. It is confirmed that moderate polyanion（BO3）^3- doping can rearrange the electronic structure of the bulk Li3V2（PO4）3,lower the charge transfer resistance and further improve the electrochemical behaviors.