Clarification of underneath capacity loss for O3-type Ni, co free layered cathodes at high voltage for sodium ion batteries

Earth abundant O3-type NaFe_(0.5)Mn_(0.5)O_(2)layered oxide is regarded as one of the most promising cathodes for sodium ion batteries due to its low cost and high energy density.However,its poor structural stability and cycle life strongly impede the practical application.Herein,the dynamic phase evolution as well as charge compensation mechanism of O3-type NaFe_(0.5)Mn_(0.5)O_(2)cathode during sodiation/desodiation are revealed by a systemic study with operando X-ray diffraction and X-ray absorption spectroscopy,high resolution neutron powder diffraction and neutron pair distribution functions.The layered structure experiences a phase transition of O3→P3→OP2→ramsdellite during the desodiation,and a new O3’phase is observed at the end of the discharge state(1.5 V).The density functional theory(DFT)calculations and nPDF results suggest that depletion of Na^(+)ions induces the movement of Fe into Na layer resulting the formation of an inert ramsdellite phase thus causing the loss of capacity and structural integrity.Meanwhile,the operando XAS clarified the voltage regions for active Mn^(3+)/Mn^(4+)and Fe^(3+)/Fe^(4+)redox couples.This work points out the universal underneath problem for Fe-based layered oxide cathodes when cycled at high voltage and highlights the importance to suppress Fe migration regarding the design of high energy O3-type cathodes for sodium ion batteries.

Low cost and low density chloride solid electrolyte for all solid state cathode with high active material ratio

Chloride solid electrolytes(SEs)have attracted widespread attention due to their high room-temperature ionic conductivity and excellent cathode compatibility.However,the conventionally selected central metal elements(e.g.,In,Y and Ta)are usually rare and heavy,inevitably causing the high cost and high density of the obtained chloride SEs.Here,by choosing abundant and light Mg and Al as central metal elements,we develop a cheap and low density Li_(1.2)Mg_(0.95)Al_(0.3)Cl_(4)SE for high active material ratio in all solid state cathode.Partial replacement of Mg^(2+)by Al^(3+)in the framework yields vacancies and lowers the non-lithium metal ions occupancy at Mg/Li co-occupied 16d site,effectively relieving the blocking effects by Mg^(2+)in the pristine spinel Li_(2-2x)Mg_(1+x)Cl_(4).Thus,a significantly improved room-temperature conductivity of 3.08×10^(-4)S·cm^(-1)is achieved,two orders of magnitude higher than that of Li_(1.2)Mg_(1.4)Cl_(4).More attractively,its low density of only 1.98 g·cm-3 enables low SE mass ratio in cathodes(only 16 wt.%)with still effective electrolyte/cathode contact and lithium-ion conduction inside.When charged to potential of 4.30 V,the asfabricated Li_(1.2)Mg_(0.95)Al_(0.3)Cl_(4)-based solid lithium battery with uncoated NCM523 cathode can be cycled for over 100 cycles with a capacity retention of 86.68%at room temperature.

Exploring the structural properties of cathode and anode materials in Li-ion battery via neutron diffraction technique

As a unique microprobe for structure and dynamics of materials,neutron possesses superior ability in penetration as well as sensitivity for light and magnetic elements in comparison with X-ray and electron.As for the research and development of lithium-ion batteries(LIBs),neutron diffraction techniques play an indispensable role in exploring the structural properties of various electrode materials,especially the detailed structural evolution of cathode and anode materials during electrochemical cycling.Moreover,based on thorough analysis of neutron diffraction results,an in-depth and systematic understanding of some fundamental mechanisms,such as the formation mechanism of defects and migration mechanism of lithium ions,could also be established,which is essential for the development of high-performance electrode materials for the next-generation LIBs.Nevertheless,that technique would not seem to be widely applied yet in comparison with the application of X-ray diffraction and more attention should be paid.To demonstrate the advantages of neutron diffraction technique in research of LIBs materials,this work systematically summarizes representative neutron diffraction studies on exploring structural details hidden in electrode materials and on probing structural evolution of electrode materials during charge/discharge processes.Prospects for further applications of neutron diffraction techniques in research of LIBs are also put forward.

基于多尺度图像重建的硅负极结构演化定量分析

为了深入了解硅基负极在循环过程中的结构演化,本文首次应用电极和颗粒水平多尺度的三维图像重建技术,对微米硅负极在电循环过程中的结构进行了可视化的定量表征;通过分析电解液中氟代碳酸乙烯酯(FEC)添加剂的影响,生动展示了硅负极的结构/成分演变与电化学性能之间的联系.利用聚焦离子束和扫描电子显微镜(FIB-SEM)技术,对电极中的三种组分(硅活性颗粒,非活性组分和孔隙)的体积和形状变化进行了定量的分析,并统计了循环过程中硅颗粒的平均尺寸.结合电化学分析结果表明,电解液FEC添加剂可以在硅负极的循环早期形成稳定的固态电解质界面(SEI),从而有效抑制硅颗粒的巨大体积膨胀和粉化现象,提高电极的循环稳定性.本文提出的方法为具有类似体积膨胀问题的电极体系提供了新的研究视角.

Alkali and alkaline ions co-substitution of P2 sodium layered oxides for sodium ion batteries

Alkali and alkaline ion substitutions enhance the electrochemical properties of P2 sodium layered oxide,while the effect on electrochemical property enhancement of alkali and alkaline ions co-substitution is still unclear.In this work,the structural and electrochemical properties of the Li alkali and Mg alkaline ions co-substituted P2 layered oxide Na_(0.67)(Li_(0.5)Mg_(0.5))_(0.1)(Ni_(0.33)Mn_(0.67))_(0.9)O_(2)are investigated in detail.Compared to the pristine and single-ion substituted materials,the co-substituted material shows an enhanced cycling performance with a reversible ca-pacity of 127 mAh/g and a capacity retention of 75%over 100 cycles at 0.5C.Galvanostatic intermittent titration technique(GITT)and cyclic voltammetry(CV)results show that the Li and Mg synergistically improve the ion diffusion.Moreover,the structure stability is also improved by the Li and Mg co-substitution that is clarified by operando X-ray diffraction(XRD)measurements.These results explain the origin of the enhanced electrochemical properties of the Li/Mg co-substituted P2 layered oxides for sodium ion batteries.

Application of neutron scattering in organic photovoltaic materials

Over last decades,the development of new organic materials has contributed to the rapid increase of high-power conversion efficiency of photovoltaic cells.At this stage,to understand the structure and the dynamic of materials is of significant importance for designing novel low-cost photovoltaic cells with superior performance.Neutron scattering is a powerful tool to provide unique and non-destructive information for the organic photovoltaic materials with particular advantages of addressing different parts of organic system by deuterium or tritium substitution.In addition,by employing several neutron scattering methods together,it is possible to further access the static structure and dynamic relaxation of the materials.With this perspective review,we introduce three neutron scattering techniques,including neutron reflectivity,small angle neutron scattering,grazing incidence small angle neutron scattering and quasi-elastic neutron scattering,and their applications on the organic photovoltaic materials.

Structural insights into lithium-deficient type Li-rich layered oxide for high-performance cathode

As one of the promising candidate cathode materials for the high-performance lithium-ion batteries,Li-rich layered oxides still suffer from a series of critical drawbacks,such as voltage decay,oxygen release,irrevers-ible migration of transition metal ions,etc.In this work,Li-deficient method has been confirmed as an effective approach to improve the overall electrochemical performances of Li-rich cathode.The optimized lithium-deficient Li-rich layered cathode exhibits splendid discharge capacity of~297 mAh/g at 0.1 C and prominent rate per-formance of-143 mAh/g at 5 C.Subsequently,neutron diffraction in combination with Raman spectroscopy is applied to explore and clarify the underlying mechanism for improved performances.It was found that the lithium-deficient induced nickel migration and oxygen vacancy play an significant role in improving electro-chemical performances,because migration of nickel into Li layer is able to expand the Li layer spacing and reduce the Li/Ni antisite,leading to facilitated diffusion of lithium ions.Moreover,the formation of oxygen vacancy is able to promote anionic redox processes and suppress the gas release,thus leading to higher capacity.The results present valuable structural insights into the influence of lithium deficiency and provide guidance for the devel-opment of Li-rich cathode materials.

Special Issue for Neutron Scattering

Neutrons are uncharged elementary particles that make up the nuclei of atoms.The prominent characteristics of neutrons,such as high penetrability,high sensitivity to light elements,magnetic in nature and nondestructive property,have paved the way for application of neutron scattering techniques in exploring structural properties of advanced materials.By adopting different scattering geometries,different neutron scattering approaches,including neutron diffraction,small angle neutron scattering and neutron reflectometry,can be realized to clarify the crystal and magnetic structures of advanced materials in different length scales ranging from atomic-scale to nano-scale.