Difficulties, strategies, and recent research and development of layered sodium transition metal oxide cathode materials for high-energy sodium-ion batteries

Energy-storage systems and their production have attracted significant interest for practical applications.Batteries are the foundation of sustainable energy sources for electric vehicles(EVs),portable electronic devices(PEDs),etc.In recent decades,Lithium-ion batteries(LIBs) have been extensively utilized in largescale energy storage devices owing to their long cycle life and high energy density.However,the high cost and limited availability of Li are the two main obstacles for LIBs.In this regard,sodium-ion batteries(SIBs) are attractive alternatives to LIBs for large-scale energy storage systems because of the abundance and low cost of sodium materials.Cathode is one of the most important components in the battery,which limits cost and performance of a battery.Among the classified cathode structures,layered structure materials have attracted attention because of their high ionic conductivity,fast diffusion rate,and high specific capacity.Here,we present a comprehensive review of the classification of layered structures and the preparation of layered materials.Furthermore,the review article discusses extensively about the issues of the layered materials,namely(1) electrochemical degradation,(2) irreversible structural changes,and(3) structural instability,and also it provides strategies to overcome the issues such as elemental phase composition,a small amount of elemental doping,structural design,and surface alteration for emerging SIBs.In addition,the article discusses about the recent research development on layered unary,binary,ternary,quaternary,quinary,and senary-based O3-and P2-type cathode materials for high-energy SIBs.This review article provides useful information for the development of high-energy layered sodium transition metal oxide P2 and O3-cathode materials for practical SIBs.

ASTUDY OF VALENCE OF YTTRIUM IN Y_2O_3 Mo CATHODE

The valenceofelementyttrium of Y2 O3 Mocathode materialhasbeenstudied by usingther mal weight analysis, X ray diffraction analysis, Scanning electron microscopy and X rayphotoelectronspectrum . It hasbeen provedthatyttrium oxidecan bereduced by molybdenum carbide. Thereaction between powdered Y2 O3 and Mo2 Ccan happen at 1173 , and Y2 O3may bereduced to metallicyttrium . Afterthepowder mixtureof Y2 O3 and Mo2 Cwasheat treated at1873 K, Yttrium existsin two kinds of chemicalstate- yttrium of zero valence and yttrium ofthreevalences.

Chemical States of Lanthanum in Carbonized La_2O_3-Mo Thermionic Cathode Materials

The chemical reaction between lanthanum oxide and molybdenum carbide was studied by thermodynamic calculation, thermal analysis and in situ X ray Photoelectron Spectroscopy. The theoretical results show that at the environment allowing for the evaporation of lanthanum, such as in high vacuum, La 2O 3 in the La 2O 3 Mo materials can be reduced to metallic lanthanum by molybdenum carbide (Mo 2C). To confirm the conclusion, many analysis methods such as XRD, SPS, and TG DTA were taken. The experimental results show that the chemical state of lanthanum changes during heating. It was proved, for the first time, that reacted metallic lanthanum appears at the surface of this kind of material at high temperature.

Chemical stability of La_2O_3 in La_2O_3-Mo cathode materials

Chemical stability of La 2O 3 in carbonized and uncarbonized La 2O 3 Mo cathodes was studied by in situ XPS analysis. Experimental results show that chemical stability of La 2O 3 is not good enough. In vacuum and at high temperature, oxygen can be dissociated from the lattice of La 2O 3 in the uncarbonized La 2O 3 Mo cathode. Binding energy shifts of La?3d5/2 and La?3d3/2 core peaks, and obvious decrease of satellite peak intensity in La?3d doublet with increasing temperature show that metallic La appears at carbonized La 2O 3 Mo cathode surface at high temperature.

Emission mechanism of Mo-Y_2O_3 cathode

The valence of element yttrium of Y 2O 3 Mo cathode material was studied by thermal analysis, X ray diffraction analysis, scanning electron microscopy and X ray photoelectron spectra, and the emission mechanism of Mo Y 2O 3 cathode was discussed. It was proved that reaction between powder Y 2O 3 and Mo 2C can happen at 1 173 K, and Y 2O 3 be reduced to metallic yttrium. After the powder mixture of Y 2O 3 and Mo 2C is heat treated at 1 873 K, yttrium exists in two kinds of state—yttrium of zero valence and yttrium of three valences. The formation of monoatomic layer of metallic yttrium at the surface of filament is the cause of emissivity of the cathode. Yttrium at the surface doesn’t provide emission current, but the momoatomic active surface layer has a lower work function than clean molybdenum. [

Amorphous CoSnO_3@rGO nanocomposite as an efficient cathode catalyst for long-life Li-O_2 batteries

An amorphous CoSnO3@rGO nanocomposite fabricated using a surfactant‐assisted assembly method combined with thermal treatment served as a catalyst for non‐aqueous lithium‐oxygen(Li‐O2)batteries.In contrast to the specific surface area of the bare CoSnO3 nanoboxes(104.3 m2 g–1),the specific surface area of the CoSnO3@rGO nanocomposite increased to approximately 195.8 m2 g–1 and the electronic conductivity also improved.The increased specific surface area provided more space for the deposition of Li2O2,while the improved electronic conductivity accelerated the decomposition of Li2O2.Compared to bare CoSnO3,the overpotential reduced by approximately 20 and 60 mV at current densities of 100 and 500 mA g?1 when CoSnO3@rGO was used as the catalyst.A Li‐O2 battery using a CoSnO3@rGO nanocomposite as the cathode catalyst cycled indicated a superior cyclic stability of approximately 130 cycles at a current density of 200 mA g–1 with a limited capacity of 1000 mAh g–1,which is 25 cycles more than that of the bare amorphous CoSnO3 nanoboxes.

掺杂方式对Mo-La_2O_3合金组织和力学性能的影响

分别采用液-固和液-液掺杂方式向钼粉中引入氧化镧,烧结出Mo-La2O3合金,通过扫描电镜和透射电镜观察,研究了不同掺杂方式制备的Mo-La2O3合金中第二相粒子的粒度分布和形貌,分析了第二相粒子在钼基体中的分布规律,检测了钼丝的拉伸性能,通过位错塞积理论讨论了La2O3颗粒形貌和分布对Mo-La2O3拉伸性能的影响机制。结果表明:液-液掺杂方法能够使钼基体中的La2O3粒子均匀分散,细化La2O3粒径;直径0.6mm、液-液掺杂钼丝的拉伸性能优于液-固掺杂钼丝。

Mo-La_2O_3烧结坯的韧化机制研究

通过扫描电镜、定点探针分析、X射线衍射分析及俄歇电子能谱分析研究了Mo La2 O3 烧结坯的韧化机制。结果表明 :La2 O3 的加入提高了烧结钼坯的横向断裂强度和韧性 ;Mo La2 O3 烧结坯的韧化机制源于间隙杂质在La2 O3

Mo-La_2O_3烧结坯间隙杂质的研究

通过扫描电镜 (SEM)、电子探针 (EPMA)、X射线衍射 (XRD)及俄歇电子能谱 (AES)研究了 Mo- La2 O3烧结坯中的间隙杂质。结果表明 :L a2 O3的加入提高了烧结钼坯的抗弯强度和韧性。间隙杂质不仅存在于 Mo中 ,而且在 La2 O3粒子表面吸附 ,使晶界杂质浓度降低。

Surface Carbonization of Mo La_2O_3 Cathode

The carbonized structures of Mo La 2O 3 cathode specimens have been investigated by means of FESEM and XRD, respectively. The substructure of carbonized layer in the Mo La 2O 3 cathode has been found for the first time. The results showed that the carbonized layer with uniform Mo 2C was helpful to emission, while the demixing carbonized layer with a compact MoC outside layer was harmful to emission. The uniform Mo 2C layer consists of coarse particles with lots of grain boundary crevices as well as holes arranging perpendicular to the wire axle and up to surface, which was beneficial to the migration of activated rare earth in activation and operating.

Surface segregation of La_2O_3 molecules in Mo La_2O_3 cathode materials

The surface segregation of La 2O 3 in Mo La 2O 3 cathode was carried out by Auger electron spectroscopy. Lanthanum and oxygen ions (La 3+ and O 2- ) diffuse from the grain boundaries to the surface respectively, and these ions recombine into La 2O 3 molecules on the surface. The results were analyzed by kinetics of grain boundary diffusion. In the temperature range of 1 123～1 423 K, the diffusion coefficients of La 3+ and O 2- ions were found to fit with the following equations: D La =3.670 3×10 -16 exp(-1.016 39×10 5/ RT ) D O=1.512 2×10 -16 exp(-8.130 66×10 4/ RT ). [

Direct Synthesis of Al_2O_3-modified Li(Ni_(0.5)Co_(0.2)Mn_(0.3))O_2 Cathode Materials for Lithium Ion Batteries

To improve the cyclic stability at high temperature and thermal stability, the spherical Al2O3-modified Li（Ni0.5Co0.2Mn0.3）O2 was synthesized by a modified co-precipitation method, and the physical and electrochemical properties were studied. The TEM images showed that Li（Ni0.5Co0.2Mn0.3）O2 was modified successfully with nano-Al2O3. The discharge capacity retention of Al2O3-modified Li（Ni0.5Co0.2Mn0.3）O2 maintained about 99% after 200 cycles at high temperature（55 ℃）, while that of the bare one was only 86%. Also, unlike bare Li（Ni0.5Co0.2Mn0.3）O2, the Al2O3-modified material cathode exhibited good thermal stability.

Synthesis and Characterization of Mg_3(PO_4)_2-coated Li_(1.05)Ni_(1/3)Mn_(1/3)Co_(1/3)O_2 Cathode Material for Li-ion Battery

Mg3（PO4）2-coated Li1.05Ni1/3Mn1/33Co1/3O2 cathode materials were synthesized via co-precipitation method. The morphology, structure, electrochemical performance and thermal stability were characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, cyclic voltammetry（CV）, electrochemical impedance spectroscopy（EIS）, charge/discharge cycling and differential scanning calorimeter （DSC）. SEM analysis shows that Mg3（PO4）2-coating changes the morphologies of their particles and increases the grains size. XRD and CV results show that Mg3（PO4）2-coating powder is homogeneous and has better layered structure than the bare one. Mg3（PO4）2-coating improved high rate discharge capacity and cycle-life performance. The reason why the cycling performance of Mg3（PO4）2-coated sample at 55 ℃ was better than that of room temperature was the increasing of lithium-ion diffusion rate and charge transfer rate with temperature rising. Mg3（PO4）2-coating improved the cathode thermal stability, and the result was consistent with thermal abuse tests using Li-ion cells： the Mg3（PO4）2 coated Li1.05Ni1/3Mn1/3Co1/3O2 cathode did not exhibit thermal runaway with smoke and explosion, in contrast to the cells containing the bare Li1.05Ni1/3Mn1/3Co1/3O2.

不同退火温度对Mo-La_2O_3板材微观组织及力学性能的影响

本文研究了不同退火温度对Mo-La2O3板材微观组织及力学性能的影响。通过金相显微镜、扫描电镜观察了钼合金显微组织及断口形貌,利用透射电镜研究了La2O3对位错分布的影响规律。结果表明,随着退火温度的升高,钼合金晶粒长大,拉伸性能、断裂韧性及显微硬度显著降低。对于退火后的试样,当La2O3粒径较大时,这种颗粒位于晶界处,在颗粒及晶界处形成位错塞积;在退火后的钼合金中,La2O3粒径较小时,绝大多数颗粒位于晶粒内部,位错越过这些颗粒,在晶界或亚晶界上形成位错塞积。

碳化Mo-La_2O_3阴极丝高温光电子能谱分析

本文报道了Ｘ射线光电子能谱（ＸＰＳ）对新型热电子发射材料Ｍｏ－Ｌａ２Ｏ３（简称Ｍｏ－Ｌａ）阴极丝材高温状态下表面物质的分析过程。实验结果表明：随温度升高，Ｍｏ－Ｌａ阴极丝材表面Ｌａ２Ｏ３明显增多，半定量计算１３５０～１４５０℃时，表面Ｌａ２Ｏ３约为室温时的４倍；温度再升高，表面含量又减少，说明了Ｍｏ－Ｌａ阴极的激活和过激活过程，与实际装管试验结果相符。对不同温度下样品的Ｌａ３ｄ峰峰位和半高宽计算分析以及纯Ｌａ样品的谱峰分析结果显示，高温状态下Ｍｏ－Ｌａ阴极表面有可能分离出少的超额Ｌａ原子，对Ｍｏ－Ｌａ阴极发射机理研究具有直接指导意义。

液-液掺杂Mo-La_2O_3板材的室温力学性能

采用液-液掺杂、粉末冶金的方法制备出Mo-La2O3板坯并轧制成板材,经不同温度退火后进行室温拉伸测试,并利用SEM和EDS等检测手段对其断口形貌、氧化镧含量及分布进行了分析。结果表明:Mo-La2O3板材的延伸率始终高于纯钼板;随着氧化镧含量的增加,Mo-La2O3板材的室温抗拉强度显著提高;而随退火温度的升高,Mo-La2O3板材的断口形貌由韧窝形转变为解理形;氧化镧均匀分布于晶内和晶界,大大降低了晶界上杂质的浓度,抑制了显微空穴和微孔的长大,从而提高了钼板的强度和韧性。

掺杂方式对Mo-La_2O_3合金断裂韧性及掺杂粒子显微结构的影响

分别采用液-固和液-液掺杂方式向钼粉中加入氧化镧,用粉末冶金方法烧结出Mo合金。通过透射电镜和扫描电镜研究了不同掺杂方式制备的Mo-La2O3材料中第二相颗粒的粒度分布、形貌,以及钼合金的断口形貌。试验结果表明,液-液掺杂方法有利于细化、分散La2O3;液液掺杂试样的断裂韧性优于液固掺杂试样。并通过位错塞积理论讨论了La2O3的粒度分布对钼合金性能的影响。

锻造镦粗Mo-La_2O_3的横向塑性和组织

利用锻造镦粗工艺制备了高横向塑性Mo-La2O3棒材,并检测了其在退火过程中横向弯曲性能,观察了其组织结构,利用SEM进行了断口形貌分析。结果表明:Mo-La2O3棒经锻造镦粗变形85%后横向具有较好的塑性,延伸率达到了2%,在退火过程中横向塑性逐渐升高,在1200℃时延伸率达到10%以上,经1570℃退火1 h后,合金发生了再结晶,此时延伸率为1.5%;Mo-La2O3棒中形成了大量的位错胞亚结构,胞内有大量的位错缠结在一起,这些位错还被La2O3钉扎;Mo-La2O3棒经1200℃退火后,断口有"分层"现象,且断口上具有明显的河流状花样和解理台阶,断裂面上伴有大量塑性变形的韧带和撕裂岭。

Mo-La_2O_3阴极碳化机理

研究了碳化温度、碳化时间、碳化时苯的压强对Mo La2 O3 阴极碳化度大小和碳化层组织的影响。结果表明 :在 172 3K ,苯的压强为 1.5× 10 -2 Pa,碳化 6min后Mo La2 O3 阴极碳化度达到 19.7%,碳化层为疏松多孔的Mo2 C组织 ,有利于阴极热电子发射。应用扫描电镜 (SEM)、X射线衍射仪 (XRD)等手段对Mo La2 O3 阴极碳化层的显微组织和微观结构、物相等进行了观察与分析。并从热力学与动力学两方面对Mo La2 O3 阴极碳化机理进行了探讨。

Mo-La_2O_3复合材料微观结构与力学性能的研究

采用X射线衍射仪(XRD),扫描电子显微镜(SEM),维氏硬度计,电子万能材料试验机,动态热模拟机研究了稀土钼复合材料的结构、形貌、硬度、断裂韧性、高温屈服强度、强韧化机理等。结果表明:在钼中添加适量的La2O3,可起到室温强韧化和高温强化作用。随着La2O3含量的增加,样品的硬度、断裂韧性呈先增后减的规律,其最大值分别为l0.85 GPa7,.25 MPa.m1/2。该材料的强化机制为细晶优化和晶界强化;韧化机制为细晶韧化,裂纹偏转、微桥接和弯曲韧化。