Fabrication of Fe nanocomplex pillared few-layered Ti3C2Tx MXene with enhanced rate performance for lithium-ion batteries

Pillaring technologies have been considered as an effective way to improve lithium storage performance of Ti₃C₂T_xMXene.Nevertheless,the pillared hybrids suffer from sluggish Li⁺diffusion kinetics and electronic transportation due to the compact multi-layered MXene structure,thus exhibiting inferior rate performance.Herein,the few-layered Ti₃O₂MXene(f-Ti₃C₂MXene)which is free from restacking can be prepared quickly based on the NH4⁺ions method.Besides,Fe nanocomplex pillared few-layered Ti₃C₂T_x(FPTC)heterostructures are fabricated via the intercalation of Fe ions into the interlayer of f-Ti₃C₂MXene.The f-Ti₃C₂MXene which is immune to restacking can provide a highly conductive substrate for the rapid transport of Li+ions and electrons and possess adequate electrolyte accessible area.Moreover,f-Ti₃C₂MXene can efficiently relieve the aggregation,prevent the pulverization and buffer the large volume change of Fe nanocomplex during lithiation/delithiation process,leading to enhanced charge transfer kinetics and excellent structural stability of FPTC composites.Consequently,the FPTC hybrids exhibit a high capacity of 535 mAh·g^-1after 150 cycles at 0.5 A·g^-1and an enhanced rate performance with 310 mAh·g^-1after 850 cycles at 5 A·g^-1.This strategy is facile,universal and can be extended tofabricate various few-layered MXene-derived hybrids with superior rate capability.     

Facile Synthesis of FePS3 Nanosheets@MXene Composite as a High-Performance Anode Material for Sodium Storage

Searching for advanced anode materials with excellent electrochemical properties in sodium-ion battery is essential and imperative for next-generation energy storage system to solve the energy shortage problem.In this work,two-dimensional(2D)ultrathin FePS3 nanosheets,a typical ternary metal phosphosulfide,are first prepared by ultrasonic exfoliation.The novel 2D/2D heterojunction of FePS3 nanosheets@MXene composite is then successfully synthesized by in situ mixing ultrathin MXene nanosheets with FePS3 nanosheets.The resultant FePS3 nanosheets@MXene hybrids can increase the electronic conductivity and specific surface area,assuring excellent surface and interfacial charge transfer abilities.Furthermore,the unique heterojunction endows FePS3 nanosheets@MXene composite to promote the diffusion of Na^+ and alleviate the drastic change in volume in the cyclic process,enhancing the sodium storage capability.Consequently,the few-layered FePS3 nanosheets uniformly coated by ultrathin MXene provide an exceptional reversible capacity of 676.1 mAh g^−1 at the current of 100 mA g^−1 after 90 cycles,which is equivalent to around 90.6% of the second-cycle capacity(746.4 mAh g^−1).This work provides an original protocol for constructing 2D/2D material and demonstrates the FePS3@MXene composite as a potential anode material with excellent property for sodium-ion batteries.     

Preparation and electrochemical characterization of ultrathin WO<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>/C nanosheets as anode materials in lithium ion batteries

Ultrathin two-dimensional (2D) nanomaterials offer unique advantages compared to their counterparts in other dimensionalities.O-vacancies in such materials allow rapid electron diffusion.Carbon doping often improves the electric conductivity.Considering these merits,the WO3-x/C ultrathin 2D nanomaterial is expected to exhibit excellent electrochemical performance in Li-ion batteries.Here,ultrathin WO3-x/C nanosheets were prepared via an acid-assisted one-pot process.The as-prepared WO3-x/C ultrathin nanosheets showed good electrochemical performance,with an initial discharge capacity of 1,866 mA·h·g-1 at a current density of 200 mA·g-1.After 100 cycles,the discharge and charge capacities were 662 and 661 mA·h·g-1,respectively.The reversible capacity of the WO3-x/C ultrathin nanosheets exceeded those of WO3 and WO3-x nanosheets.The electrochemical testing results demonstrated that WO3-x/C ultrathin nanosheets are promising alternative anode materials for Li-ion batteries.     

SnO-SnO2 modified two-dimensional MXene Ti3C2Tx for acetone gas sensor working at room temperature

Acetone,as widely used reagents in industry and laboratories,are extremely harmful to the human.So the detection of acetone gas concentrations and leaks in special environments at room temperature is essential.Herein,the nanocomposite combining SnO-SnO2 (p-n junction) and Ti3C2Tx MXene was successfully synthesized by a one-step hydrothermal method.Because of the existence of a small amount of oxygen during the hydrothermal conditions,part of the p-type SnO was oxidized to n-type SnO2,forming in-situ p-n junctions on the surface of SnO.The hamburger-like SnO-SnO2/Ti3C2Tx sensor exhibited improved acetone gas sensing response of 12.1 (Rg/Ra) at room temperature,which were nearly 11 and 4 times higher than those of pristine Ti3C2Tx and pristine SnO-SnO2,respectively.Moreover,it expressed a short recovery time (9 s) and outstanding reproducibility.Because of the different work functions,the Schottky barrier was formed between the SnO and the Ti3C2Tx nanosheets,acting as a hole accumulation layer (HALs) between Ti3C2Tx and tin oxides.Herein,the sensing mechanism based on the formation of hetero-junctions and high conductivity of the metallic phase of Ti3C2Tx MXene in SnO-SnO2/Ti3C2Tx sensors was discussed in detail.     

PVA-assisted hydrated vanadium pentoxide/reduced graphene oxide films for excellent Li+and Zn2+storage properties

Low-cost,high safety and environment-friendly aqueous energy storage systems(ESSs)are huge poten-tial for grid-level energy storage,but the(de)intercalation of metal ions in the electrode materials(e.g.vanadium oxides)to obtain superior long-term cycling stability is a significant challenge.Herein,we demonstrate that polyvinyl alcohol(PVA)-assisted hydrated vanadium pentoxide/reduced graphene oxide(V2O5·nH2O/rGO/PVA,denoted as the VGP)films enable long cycle stability and high capacity for the Li+and Zn2+storages in both the VGP//LiCl(aq)//VGP and the VGP//ZnSO4(aq)//Zn cells.The binder-free VGP films are synthesized by a one-step hydrothermal method combination with the filtration.The extensive hydrogen bonds are formed among PVA,GO and H2O,and they act as structural pillars and connect the adjacent layers as glue,which contributes to the ultrahigh specific capacitance and ultralong cyclic performance of Li+and Zn2+storage properties.As for Li+storage,the binder-free VGP4 film(4 mg PVA)electrode achieves the highest specific capacitance up to 1381 F g-1 at 1.0 A g-1 in the three-electrode system and 962 F g-1 at 1.0 A g-1 in the symmetric two-electrode system.It also behaves the outstanding cyclic performance with the capacitance retention of 96.5％after 15000 cycles in the three-electrode system and 99.7％after 25000 cycles in the symmetric two-electrode system.As for Zn2+storage,the binder-free VGP4 film electrode exhibits the high specific capacity of 184 mA h g-1 at 0.5 A g-1 in the VGP4//ZnSO4(aq)//Zn cell and the superb cycle performance of 98.5％after 25000 cycles.This work not only provides a new strategy for the construction of vanadium oxides composites and demonstrates the potential application of PVA-assisted binder-free film with excellent electrochemical properties,but also extends to construct other potential electrode materials for metal ion storage cells.     

Atomic Cobalt Covalently Engineered Interlayers for Superior Lithium‐Ion Storage

With the unique‐layered structure, MXenes show potential as electrodes in energy‐storage devices including lithium‐ion (Li⁺) capacitors and batteries. However, the low Li⁺‐storage capacity hinders the application of MXenes in place of commercial carbon materials. Here, the vanadium carbide (V₂C) MXene with engineered interlayer spacing for desirable storage capacity is demonstrated. The interlayer distance of pristine V₂C MXene is controllably tuned to 0.735 nm resulting in improved Li‐ion capacity of 686.7 mA h g^?1 at 0.1 A g^?1, the best MXene‐based Li⁺‐storage capacity reported so far. Further, cobalt ions are stably intercalated into the interlayer of V₂C MXene to form a new interlayer‐expanded structure via strong V–O–Co bonding. The intercalated V₂C MXene electrodes not only exhibit superior capacity up to 1117.3 mA h g^?1 at 0.1 A g^?1, but also deliver a significantly ultralong cycling stability over 15 000 cycles. These results clearly suggest that MXene materials with an engineered interlayer distance will be a rational route for realizing them as superstable and high‐performance Li⁺ capacitor electrodes.     

Surface-Engineered Li4Ti5O12 Nanostructures for High-Power Li-Ion Batteries

Materials with high-power charge–discharge capabilities are of interest to overcome the power limitations of conventional Li-ion batteries.In this study,a unique solvothermal synthesis of Li4Ti5O12 nanoparticles is proposed by using an off-stoichiometric precursor ratio.A Li-deficient off-stoichiometry leads to the coexistence of phaseseparated crystalline nanoparticles of Li4Ti5O12 and TiO2 exhibiting reasonable high-rate performances.However,after the solvothermal process,an extended aging of the hydrolyzed solution leads to the formation of a Li4Ti5O12 nanoplate-like structure with a self-assembled disordered surface layer without crystalline TiO2.The Li4Ti5O12 nanoplates with the disordered surface layer deliver ultrahighrate performances for both charging and discharging in the range of 50–300C and reversible capacities of 156 and 113 mAh g−1 at these two rates,respectively.Furthermore,the electrode exhibits an ultrahigh-charging-rate capability up to 1200C(60 mAh g−1;discharge limited to 100C).Unlike previously reported high-rate half cells,we demonstrate a high-power Li-ion battery by coupling Li4Ti5O12 with a high-rate LiMn2O4 cathode.The full cell exhibits ultrafast charging/discharging for 140 and 12 s while retaining 97 and 66% of the anode theoretical capacity,respectively.Room-(25℃),low-(−10℃),and high-(55℃)temperature cycling data show the wide temperature operation range of the cell at a high rate of 100C.     

碳源对液相法制备Li3V2（PO4）3/C的影响

以4种不同种类的有机物(柠檬酸、水杨酸、聚丙烯酸、蔗糖)为碳源,通过液相反应合成Li3V2(PO4)3/C复合材料。研究了不同碳源对复合材料的晶型结构、形貌及电化学性能的影响。结果表明,碳源对Li3V2(PO4)3/C材料的晶型结构没有影响,但对电化学性能影响较明显,其中采用柠檬酸为碳源制得的Li3V2(PO4)3/C复合材料电化学性能最好。进一步研究了柠檬酸的加入量对复合材料的电化学性能的影响,发现当柠檬酸加入量为钒与碳的物质的量比为1∶4时,样品的平均粒径较小,电化学性能最好,0.1C首次放电比容量为123.59mAhg-1,0.5C首次放电比容量也高达117.27mAhg-1,循环10次后,仍保持在117.19mAhg-1,容量几乎没有衰减,10C时比容量仍有105.43mAhg-1。     

Interface-modulated fabrication of hierarchical yolk–shell Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/C dodecahedrons as stable anodes for lithium and sodium storage

Transition-metal oxides (TMOs) have gradually attracted attention from researchers as anode materials for lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) because of their high theoretical capacity.However,their poor cycling stability and inferior rate capability resulting from the large volume variation during the lithiation/sodiation process and their low intrinsic electronic conductivity limit their applications.To solve the problems of TMOs,carbon-based metal-oxide composites with complex structures derived from metal-organic frameworks (MOFs) have emerged as promising electrode materials for LIBs and SIBs.In this study,we adopted a facile interface-modulated method to synthesize yolk-shell carbon-based Co3O4 dodecahedrons derived from ZIF-67 zeolitic imidazolate frameworks.This strategy is based on the interface separation between the ZIF-67 core and the carbon-based shell during the pyrolysis process.The unique yolk-shell structure effectively accommodates the volume expansion during lithiation or sodiation,and the carbon matrix improves the electrical conductivity of the electrode.As an anode for LIBs,the yolk-shell Co3O4/C dodecahedrons exhibit a high specific capacity and excellent cycling stability (1,100 mAh·g-1 after 120 cycles at 200 mA·g-1).As an anode for SIBs,the composites exhibit an outstanding rate capability (307 mAh·g-1 at 1,000 mA·g-1 and 269 mAh·g-1 at 2,000 mA·g-1).Detailed electrochemical kinetic analysis indicates that the energy storage for Li+ and Na+ in yolk-shell Co3O4/C dodecahedrons shows a dominant capacitive behavior.This work introduces an effective approach for fabricating carbonbased metal-oxide composites by using MOFs as ideal precursors and as electrode materials to enhance the electrochemical performance of LIBs and SIBs.     

Micro-nano structured VNb9O25 anode with superior electronic conductivity for high-rate and long-life lithium storage

The oxygen vacancies and micro-nano structure can optimize the electron/Li+migration kinetics in anode materials for lithium batteries(LIBs).Here,porous micro-nano structured VNb9O25 composites with rich oxygen vacancies were reasonably prepared via a facile solvothermal method combined with annealing treatment at 800℃for 30 h(VNb9 O25-30 h).This micro-nano structure can enhance the contact of active material/electrolyte,and shorten the Li+diffusion distance.The introduction of oxygen vacancies can further boosts the intrinsic conductivity of VNb9O25-30 h for achieving excellent LIB performance.The as-prepared VNb9O25-30 h anode showed advanced rate capability with reversible capacity of 122.2 mA h g-1 at 4 A g-1,and delivered excellent capacity retention of～100％after 2000 cycles.Meanwhile,VNb9O25-30 h provides unexpected long-cycle life(i.e.,reversible capacity of 165.7 mA h g-1 at 1 A g-1 with a high capacity retention of 85.6％even after 8000 cycles).Additionally,coupled with the LiFePO4 cathode,the LiFePO4//VNb9O25-30 h full cell delivers superior LIB properties with high reversible capacities of 91.6 mA h g-1 at 5C for 1000 cycles.Thus,such reasonable construction method can assist in other high-performance niobium-based oxides in LIBs.     

二维纳米材料MXene的研究进展

MXene是一类新型碳/氮化物二维纳米层状材料,一般是利用化学刻蚀的手段通过选择性刻蚀掉前驱体MAX相中的A原子层而得到.其通式可表示为Mn+1XnTx,其中M代表早期过渡族金属,X代表碳和/或氮,Tx代表MXene在刻蚀过程中产生的附着在其表面的官能团(-OH、-F、=O、等).采用一定的手段将多层MXene剥落,可获得类石墨烯形貌的单层MXene.MXene除了具备传统二维材料的性能外,还兼具良好的导电性、亲水性、透光性、柔韧性以及能量储存性能,在复合材料、润滑剂、环境污染治理、电池、电容器、催化、传感器、抗菌等领域具有潜在的应用价值.文章总结了MXene的制备、结构、性能和应用等方面的最新成果,并展望了其今后的研究方向.     

Hollow multi-nanochannel carbon nanofiber/MoS2 nanoflower composites as binder-free lithium-ion battery anodes with high capacity and ultralong-cycle life at large current density

The electrode materials with high pseudocapacitance can enhance the rate capability and cycling stabil-ity of lithium-ion storage devices.Herein,we fabricated MoS2 nanoflowers with ultra-large interlayer spacing on N-doped hollow multi-nanochannel carbon nanofibers(F2-MoS2/NHMCFs)as freestanding binder-free anodes for lithium-ion batteries(LIBs).The ultra-large interlayer spacing(0.78～1.11 nm)of MoS2 nanoflowers can not only reduce the internal resistance,but also increase accessible active sur-face area,which ensures the fast Li+intercalation and deintercalation.The NHMCFs with hollow and multi-nanochannel structure can accommodate the large internal strain and volume change during lithi-ation/delithiation process,it is beneficial to improving the cycling stability of LIBs.Benefiting from the above combined structure merits,the F2-MoS2/NHMCFs electrodes deliver a high rate capability 832 mA h g-1 at 10 A g-1 and ultralong cycling stability with 99.29 and 91.60％capacity retention at 10 A g-1 after 1000 and 2000 cycles,respectively.It is one of the largest capacities and best cycling stability at 10 A g-1 ever reported to date,indicating the freestanding F2-MoS2/NHMCFs electrodes have potential applications in high power density LIBs.     

Layered Li0.88[Li0.18Co0.33Mn0.49]O2 nanowires for fast and high capacity Li-Ion storage material

Layered Li0.88[Li0.18Co0.33Mn0.49]O2 nanowires are prepared using Co0.4Mn0.6O2 nanowires and lithium nitrate as precursors at 200 degrees C via a hydrothermal method for fast and high capacity Li-ion storage material. The obtained nanowires exhibit a reversible capacity of 230 mAh/g between 2 and 4.8 V, even at the high current rate of 3600 mA/g.     

层状LiMnO_2的水热合成

采用X射线衍射的方法系统研究了由Mn2O3和LiOH作为反应物时,正交层状LiMnO2的水热合成条件.结果表明,在200℃温度下,Mn3+与Li+的摩尔比小于等于1∶10,反应2 h以上可获得纯的产物.Rietveld分析表明,产物为正交层状结构,空间群为Pmnm,晶胞参数为a=566(3),b=5.751(2),c=2.808(1);晶体结构中,在2a位置有2%~3%的Li+、Mn3+占位无序.对200℃温度下,Mn3+与Li+的摩尔比为1∶10,反应2 h合成的正交层状LiMnO2的电化学性能测试表明,在0.1C的电流下,循环3次后放电容量可达175 mAh.g-1.     

Si/C particles on graphene sheet as stable anode for lithium-ion batteries

Silicon is considered as one of the most promising anodes for Li-ion batteries (LIBs),but it is limited for commercial applications by the critical issue of large volume expansion during the lithiation.In this work,the structure of silicon/carbon (Si/C) particles on graphene sheets (Si/C-G) was obtained to solve the issue by using the void space of Si/C particles and graphene.Si/C-G material was from Si/PDA-GO that silicon particles was coated by polydopamine (PDA) and reacted with oxide graphene (GO).The Si/C-G material have good cycling performance as the stability of the structure during the lithiation/dislithiation.The Si/C-G anode materials exhibited high reversible capacity of 1910.5 mA h g-1 and 1196.1 mA h g-1 after 700 cycles at 357.9 mA g-1,and have good rate property of 507.2 mA h g-1 at high current density,showing significantly improved commercial viability of silicon electrodes in high-energy-density LIBs.     

雾化贮氢合金的电化学活化性能

用铝盐水溶液对雾化贮氢合金的表面进行化学处理,以改善其电化学活性,结果表明,处理后的雾化合金第一周期放电容量即达到231mA.h.g^-1,未处理合金的第五周期放电容量只有185mA.h.g^-1,AES和XPS分析表明,表面氧化层的性质是影响雾化合金在碱溶液中活化的重要因素。     

滴加速率对TiO2/RGO复合材料结构和储钠性能的影响

以钛酸丁酯为前驱物,无水乙醇为溶剂,采用溶胶-凝胶法和热处理法制备了钠离子电池TiO_2/还原氧化石墨烯复合负极材料(TiO_2/RGO),研究了溶胶-凝胶法过程中反应物钛酸丁酯滴加速率对TiO_2/RGO复合材料形貌结构及储钠性能的影响。结果表明,TiO_2/RGO复合材料由锐钛矿相TiO_2和还原氧化石墨烯组成,TiO_2富集在RGO片层边缘。电化学测试结果表明,随着滴加速率的增大,首次放电比容量和库伦效率呈现先增大后减小的趋势;当滴加速率为1.0mL/min时,TiO_2/RGO复合材料具有良好的储钠性能,在1C(1C=20mA·g~(-1))倍率下首次放电比容量和库伦效率分别为140.14mAh·g~(-1)和27.92%,具有良好的循环和倍率性能。     

NaFeTiO4 nanorod/multi-walled carbon nanotubes composite as an anode material for sodium-ion batteries with high performances in both half and full cells

NaFeTiO4 nanorods of high yields (with diameters in the range of 30-50 nm and lengths of up to 1-5 μm) were synthesized by a facile sol-gel method and were utilized as an anode material for sodium-ion batteries for the first time.The obtained NaFeTiO4 nanorods exhibit a high initial discharge capacity of 294 mA·h·g-1 at 0.2 C (1 C =177 mA·g-1),and remain at 115 mA·h·g-1 after 50 cycles.Furthermore,multi-walled carbon nanotubes (MWCNTs) were mechanically milled with the pristine material to obtain NaFeTiO4/MWCNTs.The NaFeTiO4/MWCNTs electrode exhibits a significantly improved electrochemical performance with a stable discharge capacity of 150 mA·h·g-1 at 0.2 C after 50 cycles,and remains at 125 mA·h·g-1 at 0.5 C after 420 cycles.The NaFeTiO4/MWCNTs//Na3V2(PO4)3/C full cell was assembled for the first time;it displays a discharge capacity of 70 mA·h·g-1 after 50 cycles at 0.05 C,indicating its excellent performances.X-ray photoelectron spectroscopy,ex situ X-ray diffraction,and Raman measurements were performed to investigate the initial electrochemical mechanisms of the obtained NaFeTiO4/MWCNTs.     

高能球磨法制备PTFE/科琴黑-C柔性复合材料及其电化学应用

对荷叶进行多阶温度炭化得到前驱炭材料,将材料与科琴黑（KB）、聚四氟乙烯（PTFE）按照2:2:3的质量比球磨混合后真空抽滤制备一种锂硫电池中间层柔性材料,PTFE/KB-C复合材料的多孔结构能为高阶硫化物Li₂S_n（4≤n≤8）的进一步还原提供较多的三相反应位点,并利用PTFE/KB-C复合材料良好的多层多孔化学吸附作用来抑制可溶性多硫化物的穿梭。该中间层在以纯硫材料为正极的锂硫电池电性能测试表征中,1.0 C（电流密度1 675 mA·g-1）倍率下首次放电比容量达1 350 mAh·g-1,没有硝酸锂添加剂条件下经过100次充放电循环后比容量依旧保持在960 mAh·g-1,库伦效率基本在95%以上,保持了良好的循环稳定性。      

二维晶体材料MXene的电化学应用研究进展

MXene是一种类石墨烯结构的新型二维过渡金属碳化物或碳氮化物,通过氟盐和盐酸或氢氟酸刻蚀前驱体MAX相中的活泼金属元素得到,其化学通式为Mn+1XnT(n=1,2,3…),T表示表面所附着的官能团(-H、-F或-OH)。得益于其表面的官能团,MXene在储能方面应用较为广泛。通过表面改性、离子插层,增加MXene晶面间距,提高离子传输效率,以优化MXene在电化学方面的应用。综述了以Ti3C2为代表的MXene的制备方法、理论研究以及在锂离子电池、锂硫电池、超级电容器等方面的应用研究进展,展望了MXene在电化学领域的应用前景和未来的研究方向。