Synthesis, structural characterization and Li ion conductivity of a new vanado-molybdate phase, LiMg3VMo2O12

A new vanado-molybdate LiMg₃VMo₂O₁₂ has been synthesized, the crystal structure determined an ionic conductivity measured. The solid solution Li_2−zMg_2+zV_zMo_3−zO₁₂ was investigated and the structures of the z=0.5 and 1.0 compositions were refined by Rietveld analysis of powder X-ray (XRD) and powder neutron diffraction (ND) data. The structures were refined in the orthorhombic space group Pnma with a∼5.10, b∼10.4 and c∼17.6 Å, and are isostructural with the previously reported double molybdates Li₂M₂(MoO₄)₃ (M=M²⁺, z=0). The structures comprise of two unique (Li/Mg)O₆ octahedra, (Li/Mg)O₆ trigonal prisms and two unique (Mo/V)O₄ tetrahedra. A well-defined 1:3 ratio of Li⁺:Mg²⁺ is observed in octahedral chains for LiMg₃VMo₂O₁₂. Li⁺ preferentially occupies trigonal prisms and Mg²⁺ favours octahedral sheets. Excess V⁵⁺ adjacent to the octahedral sheets may indicate short-range order. Ionic conductivity measured by impedance spectroscopy (IS) and differential scanning calorimetry (DSC) measurements show the presence of a phase transition, at 500-600 °C, depending on x. A decrease in activation energy for Li⁺ ion conductivity occurs at the phase transition and the high temperature structure is a good Li⁺ ion conductor, with σ=1×10⁻³-4×10⁻² S cm⁻¹ and E_a=0.6 to 0.8 eV.     

Cation ordering in the fluorite-like transparent conductors In4+xSn3−2xSbxO12 and In6TeO12

The cation ordering in the fluorite-like transparent conductors In_4+xSn_3−2xSb_xO₁₂ and In₆TeO₁₂, was investigated by Time of Flight Neutron Powder Diffraction and X-ray Powder Diffraction (tellurate). The structural results including atomic positions, cation distributions, metal-oxygen distances and metal-oxygen-metal angles point to a progressive cation ordering on both sites of the Tb₇O₁₂-type structure with a strong preference of the smaller 4d¹⁰ cations (Sn⁴⁺, Sb⁵⁺, Te⁶⁺) for the octahedral sites. The corresponding increase of the overall structure-bonding anisotropy is analyzed in terms of the crystal chemical properties of the OM₄ tetrahedral network of the antistructure. The relationships between the M₇O₁₂ and the M₂O₃ bixbyite-type structures are explored. Within the whole series of compositions In_4+xM_3−xO₁₂ (M=Sn, Sb, Te) there exists an increase of the symmetry gap between the more symmetrical bixbyite structure and the M₇O₁₂ type. This is tentatively correlated with the progressive weakening of thermal stability of these compositions from Sn to Te via Sb.     

PO43-掺杂和AlF3包覆协同增强Li1.2Ni0.13Co0.13Mn0.54O2正极材料电化学性能

本研究采用PO₄^3-掺杂和AlF₃包覆的协同改性策略制备了P-LNCM@AlF₃正极材料(P=PO₄^3- ,LNCM=Li_1.2Ni_0.13Co_0.13Mn_0.54O₂),提高了LNCM的结构稳定性以及抑制了界面副反应。其中,大四面体的PO₄^3-聚阴离子掺杂在晶格中抑制了过渡金属离子的迁移,降低体积变化,从而稳定了晶体结构,而且PO₄^3-掺杂能够扩大锂层间距,促进Li⁺的扩散,从而提升材料的倍率性能。此外,AlF₃包覆层能抑制材料与电解液的副反应从而提升界面稳定性。基于以上优势,P-LNCM@AlF₃正极表现出了优异的电化学性能。在1C电流密度下表现出了179.2 mAh·g^-1的放电比容量,循环200圈后仍有161.5 mAh·g^-1的放电比容量,容量保持率可达90.12%。即使在5C的高电流密度下仍可提供128.8 mAh·g^-1的放电比容量。     

Neutron powder diffraction study of tetragonal Li7La3Hf2O12 with the garnet-related type structure

We have successfully synthesized a polycrystalline sample of tetragonal garnet-related Li-ion conductor Li₇La₃Hf₂O₁₂ by solid state reaction. The crystal structure is analyzed by the Rietveld method using neutron powder diffraction data. The structure analysis identifies that tetragonal Li₇La₃Hf₂O₁₂ has the garnet-related type structure with a space group of I4₁/acd (no. 142). The lattice constants are a=13.106(2) Å and c=12.630(2) Å with a cell ratio of c/a=0.9637. The crystal structure of tetragonal Li₇La₃Hf₂O₁₂ has the garnet-type framework structure composed of dodecahedral La(1)O₈, La(2)O₈ and octahedral HfO₆. Li atoms occupy three types of crystallographic site in the interstices of this framework structure, where Li(1) atom is located at the tetrahedral 8a site, and Li(2) and Li(3) atoms are located at the distorted octahedral 16f and 32g sites, respectively. These Li sites are filled with the Li atom. The present tetragonal Li₇La₃Hf₂O₁₂ sample exhibits bulk Li-ion conductivity of σ_b=9.85×10⁻⁷ S cm⁻¹ and grain-boundary Li-ion conductivity of σ_gb=4.45×10⁻⁷ S cm⁻¹ at 300 K. The activation energy is estimated to be E_a=0.53 eV in the temperature range of 300-580 K.     

PO43-掺杂和AlF3包覆协同增强Li1.2Ni0.13Co0.13Mn0.54O2正极材料电化学性能

本研究采用PO₄^3-掺杂和AlF₃包覆的协同改性策略制备了P-LNCM@AlF₃正极材料(P=PO₄^3-,LNCM=Li_1.2Ni_0.13Co_0.13Mn_0.54O₂),提高了LNCM的结构稳定性以及抑制了界面副反应。其中,大四面体的PO₄^3-聚阴离子掺杂在晶格中抑制了过渡金属离子的迁移,降低体积变化,从而稳定了晶体结构,而且PO₄^3-掺杂能够扩大锂层间距,促进Li⁺的扩散,从而提升材料的倍率性能。此外,AlF₃包覆层能抑制材料与电解液的副反应从而提升界面稳定性。基于以上优势,P-LNCM@AlF₃正极表现出了优异的电化学性能。在1C电流密度下表现出了179.2 mAh·g^-1     

Double (n=2) and triple (n=3) [M4Bi2n−2O2n] polycationic ribbons in the new Bi∼3Cd∼3.72M∼1.28O5(PO4)3 oxyphosphate (M=Co, Cu, Zn)

The crystal structure of the new Bi_∼3Cd_∼3.72Co_∼1.28O₅(PO₄)₃ has been refined from single crystal XRD data, R₁=5.37%, space group Abmm, a=11.5322(28) Å, b=5.4760(13) Å, c=23.2446(56) Å, Z=4. Compared to Bi_∼1.2M_∼1.2O_1.5(PO₄) and Bi_∼6.2Cu_∼6.2O₈(PO₄)₅, this compound is an additional example of disordered Bi³⁺/M²⁺ oxyphosphate and is well described from the arrangement of double [Bi₄Cd₄O₆]⁸⁺ (=D) and triple [Bi₂Cd_3.44Co_0.56O₄]⁶⁺ (=T) polycationic ribbons formed of edge-sharing O(Bi,M)₄ tetrahedra surrounded by PO₄ groups. According to the nomenclature defined in this work, the sequence is TT/DtDt, where t stands for the tunnels created by PO₄ between two subsequent double ribbons and occupied by Co²⁺. The HREM study allows a clear visualization of the announced sequence by comparison with the refined crystal structure. The Bi³⁺/M²⁺ statistic disorder at the edges of T and D entities is responsible for the PO₄ multi-configuration disorder around a central P atom. Infrared spectroscopy and neutron diffraction of similar compounds (without the highly absorbing Cadmium) even suggests the long range ordering loss for phosphates. Therefore, electron diffraction shows the existence of a modulation vector q^*=1/2a^*+(1/3+ε)b^* which pictures cationic ordering in the (001) plane, at the crystallite scale. This ordering is largely lost at the single crystal scale. The existence of mixed Bi³⁺/M²⁺ positions also enables a partial filling of the tunnels by Co²⁺ and yields a composition range checked by solid state reaction. The title compound can be prepared as a single phase and also the M=Zn²⁺ term can be obtained in a biphasic mixture. For M=Cu²⁺, a monoclinic distortion has been evidenced from XRD and HREM patterns but surprisingly, the orthorhombic ideal form can also be obtained in similar conditions.     

快离子导体LiTi2(PO4)3在LiNi0.8Co0.1Mn0.1O2正极材料表面的原位反应包覆及其电化学性能

通过原位反应法,利用富镍层状金属氧化物LiNi_0.8Co_0.1Mn_0.1O₂（LNCM811）正极材料表面残余的氢氧化锂和碳酸锂,与C₈H₂₀O₄Ti和（NH₄）H₂PO₄反应,在LNCM811表面原位生成快离子导体LiTi₂（PO₄）₃（LTP）包覆层。这种原位反应的包覆方法有利于移除LNCM811表面有害的残留物氢氧化锂和碳酸锂。而且,获得的LTP均匀包覆层不仅可以有效地抑制LNCM811表面和电解液的直接接触及其副反应,还可以确保充放电循环过程中LNCM811正极材料的快速Li⁺传导。因此,在LTP包覆层的多重作用下,LTP包覆的LNCM811正极材料具有优异的循环稳定性和倍率性能：在0.2C时,首次放电比容量高达200.6 mAh·g^-1,200圈后的可逆容量依然有155.7 mAh·g^-1;在2C和5C的高电流密度下,200圈后的可逆容量仍然有126.4和111.9 mAh·g^-1。     

正极材料Li(Ni0.5Mn0.5)1-xMxO2 (M=Ti，Al；x=0，0.02)电化学行为的比较研究

0IntroductionMany efforts have been made to develop newmaterials as an alternative to LiCoO2due to the rela-tively high cost and toxicity of Co.Much attention hasbeen paid to layered structure cathode materials suchas LiMnO2and LiNiO2due to their lower co…     

Synergistic Engineering of Defects and Heterostructures Enhance Lithium/Sodium Storage Properties of F-SnO2-x-SnS2-x Nanocrystals Supported on N,S-Graphene

Phase engineering of the electrode materials in terms of designing heterostructures, introducing heteroatom and defects, improves great prospects in accelerating the charge storage kinetics during the repeated Li⁺/Na⁺ insertion/deintercalation. Herein, a new design of Li/Na-ion battery anodes through phase regulating is reported consisting of F-doped SnO₂-SnS₂ heterostructure nanocrystals with oxygen/sulfur vacancies (V_O/V_S) anchored on a 2D sulfur/nitrogen-doped reduced graphene oxide matrix (F-SnO_2-x-SnS_2-x@N/S-RGO). Consequently, the F-SnO_2-x-SnS_2-x@N/S-RGO anode demonstrates superb high reversible capacity and long-term cycling stability. Moreover, it exhibits excellent great rate capability with 589 mAh g⁻¹ for Li⁺ and 296 mAh g⁻¹ at 5 A g⁻¹ for Na⁺. The enhanced Li/Na storage properties of the nanocomposites are not only attributed to the increase in conductivity caused by V_O/V_S and F doping (confirmed by DFT calculations) to accelerate their charge-transfer kinetics but also the increased interaction between F-SnO_2-x-SnS_2-x and Li/Na through heterostructure. Meanwhile, the hierarchical F-SnO_2-x-SnS_2-x@N/S-RGO network structure enables fast infiltration of electrolyte and improves electron/ion transportation in the electrode, and the corrosion resistance of F doping contributes to prolonged cycle stability.     

Synthesis and characterizations of two anhydrous metal borophosphates: M2BP3O12 (M=Fe, In)

Two members of M^III₂BP₃O₁₂ borophosphates, namely Fe₂BP₃O₁₂ and In₂BP₃O₁₂, were synthesized by the solid-state method and characterized by the X-ray single crystal diffraction, the powder diffraction and the electron microscopy. They both crystallize in the hexagonal system, space group P6(3)/m (no. 176) and feature 3D architectures, build up of the M₂O₉ units and B(PO₄)₃ groups via sharing the corners; however, they are not isomorphic for the different crystallographically distinct atomic positions. Optical property measurements of both compounds and magnetic susceptibility measurements of Fe₂BP₃O₁₂ also have been performed. Moreover, in order to gain further insights into the relationship between physical properties and band structure of the M^III₂BP₃O₁₂ borophosphates, theoretical calculations based on density functional theory (DFT) were performed using the total-energy code CASTEP.     

XPS study on the STOBA coverage on Li(Ni0.4Co0.2Mn0.4)O2 oxide in pristine electrodes

The additive of self‐terminated oligomers with hyper‐branched architecture (STOBA) in Li(Ni_0.4Co_0.2Mn_0.4)O₂ (LNCM) cathodes of lithium ion batteries improves the battery stability and capacity. In this study, the surface chemistry of pristine LNCM electrodes with and without the STOBA additive was analyzed by means of X‐ray photoelectron spectroscopy and the surface morphology was observed by scanning electron microscopy. It was found that STOBA covers LNCM particles uniformly and the formation of chemical bonding between nitrogen atoms in STOBA and metallic atoms in LNCM was discovered. This bonding may cause the uniform coverage of STOBA on LNCM. The formation of STOBA layer on LNCM improves the coverage of the binder poly(vinylidene fluoride) and inhibits the formation of LiF.     

Defect and dopant properties of the Aurivillius phase Bi4Ti3O12

Computer modelling techniques have been used to investigate the defect and oxygen transport properties of the Aurivillius phase Bi₄Ti₃O₁₂. A range of cation dopant substitutions has been considered including the incorporation of trivalent ions (M³⁺=Al, Ga and In). The substitution of In³⁺ onto the Bi site in the [Bi₂O₂] layer is predicted to be the most favourable. The calculations suggest that lanthanide (Ln³⁺) doping at the dilute limit preferentially occurs in the [Bi₂O₂] layer, with probable distribution over both the [Bi₂O₂] and the perovskite A-site at higher dopant levels. It is predicted that the reduction process involving Ti³⁺ and oxygen vacancy formation is energetically favourable. The energetics of oxide vacancy migration between various oxygen sites in the structure have been investigated.     

Interaction in Binary Mixtures of Gemini Surfactant G12-6-12 and CTAB by NMR

The interaction between N, N′-bis（dimethyldodecyl）-1,6-hexanediammoniumdibromide （G12-6-12） and cetyltrimethylammonium bromide （CTAB） in D20 aqueous medium has been investigated by NMR at 298 K. The G12-6-12 and CTAB are about 0.773 and measured critical micelle concentration （cmc） of 0.668 mmol/L, respectively. The cmc^＊ （cmc of mixture） values are less than CMC^＊ （cmc of ideally mixed solution） in the mixed system, and the interaction parameter βM〈0 at different molar fractions α of G12-6-12 in the mixed systems, but just when α≤0.3, cmc^＊ values are much smaller than CMC^＊, and βM satisfies the relation of ｜βM｜〉｜ln（cmc1/cmc2）｜ （cmcl： cmc of pure G12-6-12 and cmc2： cmc Of pure CTAB）. The results indicate that there exists synergism between G12-6-12 and CTAB, and they can form mixed micelles, which is further proven by 2D NOESY and self-diffusion coefficient D experiments. There are intermolecular cross peaks between G12-6-12 and CTAB in 2D NOESY, and the radius of micelles in mixed solution is bigger than that in G12-6-12 pure solution in D experiments, indicating there are mixed micelles. However, when α〉0.3, we find that cmc^＊≈CMC^＊, βM≈0, obviously, the two surfactants are almost ideal mixing fitting the pseudo-phase separation model and regular solution theory.     

ZrO2包覆的层状富锂正极材料0.6Li[Li1/3Mn2/3]O2·0.4LiNi5/12Mn5/12Co1/6O2的电化学性能

采用喷雾干燥法合成了富锂层状氧化物正极材料0.6Li[Li_1/3Mn_2/3]O₂·0.4LiNi_5/12Mn_5/12Co_1/6O₂(简称LNMCO),并使用Zr (CH₃COO)₄进行ZrO₂的包覆改性。TEM测试结果显示纳米级的ZrO₂颗粒附着在LNMCO的表面。包覆质量分数为1.5%的ZrO₂包覆样品的首圈库伦效率和放电比容量有着显著提升,在室温下其首圈库伦效率和放电比容量(电流密度：20 mA·g^-1,电压：2.0~4.8 V)分别为87.2%,279.3 mAh·g^-1,而原样则为75.1%,224.1 mAh·g^-1,循环100圈之后,1.5% ZrO₂包覆样品的放电比容量为248.3 mAh·g^-1,容量保持率为88.9%,高于原样的195.9 mAh·g^-1和87.4%。     

Theoretical analysis of vibronic coupling in the lowest T1[3A'2(ππ*)] state of triphenylene-h12 and-d12

The recently observed T₁ ← S_O excitation spectra of triphenylene-h₁₂ and -d₁₂ are analysed in terms of interstate pseudo-Jahn-Teller and intrastate Jahn-Teller coupling of the two lowest triplet states, T₁ [³A'₂(ππ¹)] and T₂[³E'(ππ^*)], via an e' mode.     

Lithium-Ion conducting oxides: Synthesis,structure, and electroconducting properties

The properties of perovskite type ABO₃ lithium-ion conducting oxides based on lanthanum lithium titanate (La,Li)TiO₃, lanthanum lithium niobate and tantalate, and Li₅La₃M₂O₁₂ (M = Nb, Ta) garnets were considered. Approaches to modification of the properties of these oxides, as well as the charge-compensation mechanisms associated with nonisovalent doping were discussed. Special consideration was given to phase formation and crystal structure in relation to the composition and preparation conditions of the oxides.     

ZrO_2包覆的层状富锂正极材料0.6Li[Li_(1/3)Mn_(2/3)]O_2·0.4LiNi_(5/12)Mn_(5/12)Co_(1/6)O_2的电化学性能

采用喷雾干燥法合成了富锂层状氧化物正极材料0.6Li[Li_(1/3)Mn_(2/3)]O2·0.4LiNi_(5/12)Mn_(5/12)Co_(1/6)O_2(简称LNMCO),并使用Zr(CH3COO)4进行ZrO_2的包覆改性。TEM测试结果显示纳米级的ZrO_2颗粒附着在LNMCO的表面。包覆质量分数为1.5%的ZrO_2包覆样品的首圈库伦效率和放电比容量有着显著提升,在室温下其首圈库伦效率和放电比容量(电流密度:20 m A·g-1,电压:2.0~4.8 V)分别为87.2%,279.3 m Ah·g-1,而原样则为75.1%,224.1 m Ah·g-1,循环100圈之后,1.5%ZrO_2包覆样品的放电比容量为248.3 m Ah·g-1,容量保持率为88.9%,高于原样的195.9 m Ah·g-1和87.4%。     

Lithium‐Rich Layered Oxide Li1.18Ni0.15Co0.15Mn0.52O2 as the Cathode Material for Hybrid Sodium‐Ion Batteries

Li‐rich layered oxide Li_1.18Ni_0.15Co_0.15Mn_0.52O₂ (LNCM) is, for the first time, examined as the positive electrode for hybrid sodium‐ion battery and its Na⁺ storage properties are comprehensively studied in terms of galvanostatic charge–discharge curves, cyclic voltammetry and rate capability. LNCM in the proposed sodium‐ion battery demonstrates good rate capability whose discharge capacity reaches about 90 mA h g^?1 at 10 C rate and excellent cycle stability with specific capacity of about 105 mA h g^?1 for 200 cycles at 5 C rate. Moreover, ex situ ICP‐OES suggests interesting mixed‐ions migration processes: In the initial two cycles, only Li⁺ can intercalate into the LNCM cathode, whereas both Li⁺ and Na⁺ work together as the electrochemical cycles increase. Also the structural evolution of LNCM is examined in terms of ex situ XRD pattern at the end of various charge–discharge scans. The strong insight obtained from this study could be beneficial to the design of new layered cathode materials for future rechargeable sodium‐ion batteries.     

The crystal chemistry of the M+VO3 (M+ = Li,Na, K,NH4, Tl,Rb, and Cs) pyroxenes

The crystal structures of M⁺VO₃(M⁺ = K, NH₄, and Cs) have been refined using three-dimensional counter-diffractometer X-ray data and full-matrix least-squares methods. The structure of these compounds is characterized by a (V⁵⁺O^2?₃)^?_∞ chain extending along the c-axis (Pbcm orientation), with adjacent chains linked by the alkali metal cation. The structure may be considered as a variant of the pyroxene structure, and standard atom nomenclature is proposed in order to facilitate comparison with silicate pyroxenes. Structural variation across this series is discussed in detail and is compared with the analogous M⁺M³⁺Si₂O₆ (M⁺ = Li, Na; M³⁺ = Al, Cr, Fe, Sc, In) series.     

The synergic effects of Ca and Sm co-doping on the crystal structure and electrochemical performances of Li4-xCaxTi5-xSmxO12 anode material

Li₄Ti₅O₁₂ as the well-known “zero strain” anode material for lithium ion batteries (LIBs) suffers from low intrinsic ionic and electronic conductivity. The strategy of lattice doping has been widely taken to relieve the intrinsic issues. But the roles of the dopants are poorly understood. Herein, we propose to modulate the crystal structure and improve the electrochemical performance of Li₄Ti₅O₁₂ by substituting Li and Ti with Ca and Sm, respectively. The roles of Ca and Sm on the crystal structure and electrochemical performances have been comprehensively investigated by means of X-ray diffraction (XRD), neutron diffraction (ND) and electrochemical analysis. The Rietveld refinement of ND data indicate that Ca and Sm prefer to take 8a site (tetrahedral site) and 16d site (octahedral site), respectively. Li_3.98Ca_0.02Ti_4.98Sm_0.02O₁₂ has the longer Li1-O bond and shorter Ti-O bond length which reduces Li⁺ migration barrier as well as enhances the structure stability. Ca-Sm co-doping also alleviates the electrode polarization and enhances the reversibility of oxidation and reduction. In compared to bare Li₄Ti₅O₁₂ and Li_3.95Ca_0.05Ti_4.95Sm_0.05O₁₂, Li_3.98Ca_0.02Ti_4.98Sm_0.02O₁₂ electrode shows the lower charge transfer resistance, higher Li⁺ diffusion coefficient, better rate capability and cycling performance. The proposed insights on the roles of dopants are also instructive to design high performance electrode materials by lattice doping.