Ultrahigh rate binder-free Na_3V_2(PO_4)_3/carbon cathode for sodium-ion battery

Sodium ion batteries(SIBs)are very promising for large-scale energy storage in virtue of its high energy density,abundant sodium resources and low environmental impact,etc.However,it is still a big challenge to develop high-performance and durable cathode materials for SIBs.Among different candidate materials,Na_3V_2(PO_4)_3has attracted great attentions due to its high theoretical capacity(117 mAh/g),stable framework structure and excellent ionic conductivity.However,Na_3V_2(PO_4)_3delivers inferior rate capability and cycling stability due to its poor electronic conductivity.In this work,free-standing Na_3V_2(PO_4)_3/carbon nanofiber membranes are synthesized by an electrospinning-sintering route.The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C,which is superior to many state-ofthe-art SIB cathode materials.This can be attributed to the hierarchically distributed Na_3V_2(PO_4)_3crystals in carbon nanofiber network,which possesses outstanding electronic/ionic conductivity and thus leads to an ultrahigh rate capability.     

单斜Li3V2(PO4)3/C复合材料的制备及其电化学性能

以LiOH·H2O、V2O5、H3PO4和蔗糖为原料,采用软化学法制备了锂离子电池正极材料Li3V2(PO4)3/C.通过X射线衍射(XRD)、扫描电镜(SEM)对产物的结构和形貌进行表征,采用恒电流充放电、电化学阻抗考察了产物的电化学性能.结果表明.当煅烧温度达到700℃时,杂质相衍射峰消失,所得的样品为纯相的单斜Li3V2(PO4)3.颗粒粒度为1～2 μm;在3.0～4.5 V电压范围内以0.2C倍率充放电,首次放电比容量达到148.2 mAh·g-1,第50次循环比容量仍为144 mAh·g-1,容量保持率为97%,具有良好的循环性能;另外,样品还具有很好的倍率性能和高温性能.     

磷酸钒锂正极材料的合成与性能研究

本文以LiOH·H2O,NH4VO3,NH4H2PO4和柠檬酸等为原料采用流变相法成功地合成了磷酸钒锂化合物。利用XRD,TEM等手段对目标产物的结构和形貌进行了表征,结果表明:在800℃煅烧的样品具有单一纯相的单斜晶体结构。晶体颗粒分布在200~500nm范围,而且在颗粒表面包覆了一层碳,有利于材料的导电率的改善。对该材料的电化学性质进行了测试,实验发现:800℃煅烧的样品在0.1C和1C倍率电流条件下,首次放电比容量分别高达122.8和107mAh·g-1,经过30次循环后容量衰减很少。交流阻抗谱证实了800℃煅烧的样品具有较高的电导率。本文对800℃煅烧的样品具有较好电化学性能的原因进行了初步讨论。     

Carbon decorated Li_3V_2(PO_4)_3 for high-rate lithium-ion batteries:Electrochemical performance and charge compensation mechanism

Fast charging and high-power delivering batteries are highly demanded in mobile electronics,electric vehicles and grid energy storage,but there are full of challenges.The star-material Li₃V₂(PO₄)₃ is demonstrated as a promising high-rate cathode material meeting the above requirements.Herein,we report the carbon decorated Li₃V₂(PO₄)₃ (LVP/C) cathode prepared via a facile method,which displays a remarkable high-rate capability and long-term cycling performance.Briefly,the prepared LVP/C delivers a high discharge capacity of 122 mAh g^-1(-93% of the theoretical capacity) at a high rate up to 20 C and a superior capacity retention of 87.1% after 1000 cycles.Importantly,by applying a combination of X-ray absorption spectroscopy and full-range mapping of resonant inelastic X-ray scattering,we clearly elucidate the structural and chemical evolutions of LVP upon various potentials and cycle numbers.We show unambiguous spectroscopic evidences that the evolution of the hybridization strength between V and O in LVP/C as a consequence of lithiation/delithiation is highly reversible both in the bulk and on the surface during the discharge-charge processes even over extended cycles,which should be responsible for the remarkable electrochemical performance of LVP/C.Our present study provides not only an effective synthesis strategy but also deeper insights into the surface and bulk electrochemical reaction mechanism of LVP,which should be beneficial for the further design of high-performance LVP electrode materials.     

Fe-based phosphate nanostructures for supercapacitors

Fe-based phosphates with excellent physical and chemical features are potential electrode materials for supercapacitors.In this work,we successfully synthesized Fe-based phosphates with different dimensions,morphologies,and compositions by one-step hydrothermal method.Influence factors on the chemical composition and morphology of the as-prepared materials were explored and the energy storage performance of the as-prepared samples were tested under the traditional three electrode system.Two-dimensional(2 D) iron metaphosphate(Fe(PO_3)_3) showed the best electrochemical performance.For Fe(PO_3)_3 electrode mate rials,the layered structure can provide a larger specific surface area than the bulk structure,which is conducive to the diffusion and transport of electrolyte ions during charging-discha rging and further improve s the rate perfo rmance and cycle stability of supe rcapacito r.2 D Fe(PO_3)_3 and activated carbon were used as electrode materials to construct a 2 D Fe(PO_3)_3//AC supercapacitor.The supercapacitor showed high energy density,high power density,and excellent cycling stability,which indicates 2 D Fe(PO_3)_3 is a promising electrode material for supercapacitors.     

氧化剂对PAn/PTFE复合导电膜结构和性能影响的研究

分别以过硫酸铵和正钒酸钠作氧化剂,应用膜相渗透原位化学聚合法制备聚苯胺(PAn)/聚四氟乙烯(PTFE)复合导电膜,比较考察了两种氧化剂条件下膜孔中苯胺的聚合生长行为.扫描电镜、孔径分布及电化学测试结果表明:选用两种氧化剂分别制备的复合膜,均具有较小的膜孔径;与过硫酸铵相比,使用正钒酸钠作氧化剂时,复合膜的结构更为致密,且在保持较高表面电导率(2.62S·cm-1)的同时,断面电导率提高了1～2个数量级,电化学活性增强.     

Amorphous Zr(OH)_4 coated LiNi_(0.915)Co_(0.075)Al_(0.01)O_2 cathode material with enhanced electrochemical performance for lithium ion batteries

LiNi_(0.915)Co_(0.075)Al_(0.01)O_2(NCA) with Zr(OH)_4 coating is demonstrated as high performance cathode material for lithium ion batteries(LIBs). The coated materials are synthesized via a simple dry coating method of NCA with Zr(OH)_4 powders, and then characterized with scanning electron microscopy(SEM), transmission electron microscopy(TEM) and X-ray photoelectron spectroscopy(XPS). Experimental results show that amorphous Zr(OH)_4 powders have been successfully coated on the surface of spherical NCA particles, exhibiting improved electrochemical performance. 0.50 wt% Zr(OH)_4 coated NCA delivers a capacity of 197.6 mAh/g at the first cycle and 154.3 mAh/g after 100 cycles with a capacity retention of 78.1% at 1 C rate. In comparison, the pure NCA shows a capacity of 194.6 mAh/g at the first cycle and 142.5 mAh/g after 100 cycles with a capacity retention of 73.2% at 1 C rate. Electrochemical impedance spectroscopy(EIS) results show that the coated material exhibits a lower resistance, indicating that the coating layer can efficiently suppress transition metals dissolution and decrease the side reactions at the surface between the electrode and electrolyte. Therefore, surface coating with amorphous Zr(OH)_4 is a simple and useful method to enhance the electrochemical performance of NCA-based materials for the cathode of LIBs.     

Li_(1.3)Ti_(1.7)Al_(0.3)(PO_4)_3,Na_(1.3)Ti_(1.7)Al_(0.3)(PO_4)_3的离子交换研究

研究了在不同温度下的NaNO3和AgNO3水溶液中Li1.3Ti1.7Al0.3(PO4)3和Na1.3Ti1.7Al0.3(PO4)3离子交换行为.实验表明Li1.3Ti1.7Al0.3(PO4)3和Na1.3Ti1.7Al0.3(PO4)3均显示出了高选择性与Na+和Ag+进行离子交换的特征,且对Ag+的选择性高于Na+.升高温度可显著提高Ag/Li和Ag/Na的交换反应速度.     

Surface Synergistic Protections on Red Phosphorus Anode Material by Poly(3, 4-ethylenedioxythiophene) Coating and Electrolyte Strategy in Sodium Ion Batteries

Red phosphorus has attracted more attention as a promising sodium storage material due to its ultra-high theoretical capacity and suitable sodiation potential. However, the low intrinsic electrical conductivity and large volume change of pristine red phosphorus lead to high polarization and fast capacity fading during cycling. Herein, surface synergistic protections on red phosphorus composite are successfully proposed by conductive poly(3, 4-ethylenedioxythiophene) (PEDOT) coating and electrolyte strategy. Nanoscale red phosphorus is confined in porous carbon skeleton and the outside is packaged by PEDOT coating via in-situ polymerization. Porous carbon provides rich pathways for rapid Na⁺ diffusion and empty spaces accommodate the volume expansion of red phosphorus, PEDOT coating isolates the direct contact between electrolyte and active materials to form a stable solid electrolyte interphase. In addition, the reformulated electrolyte with 3 wt% SbF₃ additives can stabilize the electrode surface and thus enhance the electrochemical performance, especially cycling stability and rate capability (433 mA·h·g^-1 at high current density of 10 A/g).     

Gradient doping of conducting polymer films by means of bipolar electrochemistry

In this paper, we report a novel electrochemical doping method for conducting polymer films based on bipolar electrochemistry. The electrochemical doping of conducting polymers such as poly(3-methylthiophene) (PMT), poly(3,4-ethylenedioxythiophene) (PEDOT), and poly(aniline) (PANI) on a bipolar electrode having a potential gradient on its surface successfully created gradually doped materials. In the case of PEDOT film, the color change at the anodic side was also observed to be gradually transparent. PANI film treated by the bipolar doping gave a multicolored gradation across the film. The results of UV-vis and energy dispersive X-ray analyses for the doped films supported the distribution of dopants in the polymer films reflecting the potential gradient on the bipolar electrode. Furthermore, the reversibility of the bipolar doping of the PMT film was demonstrated by a spectroelectrochemical investigation.     

Synthesis，X－ray Structure and Spectral Propertiesofa Tetra－component Heteropoly Compound

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The design and fabrication of Co_3O_4/Co_3V_2O_8/Ni nanocomposites as high-performance anodes for Li-ion batteries

The Co_3O_4/Co_3V_2O_8/Ni nanocomposites were rationally designed and prepared by a two-step hydrothermal synthesis and subsequent annealing treatment. The one-dimensional(1D) Co_3O_4 nanowire arrays directly grew on Ni foam, whereas the 1D Co_3V_2O_8 nanowires adhered to parts of Co_3O_4 nanowires.Most of the hybrid nanowires were inlayed with each other, forming a 3D hybrid nanowires network.As a result, the discharge capacity of Co_3O_4/Co_3V_2O_8/Ni nanocomposites could reach 1201.8 mAh/g after100 cycles at 100 mA/g. After 600 cycles at 1 A/g, the discharge capacity was maintained at 828.1 mAh/g.Moreover, even though the charge/discharge rates were increased to 10 A/g, it rendered reversible capacity of 491.2 mAh/g. The superior electrochemical properties of nanocomposites were probably ascribed to their unique 3D architecture and the synergistic effects of two active materials. Therefore, such Co_3O_4/Co_3V_2O_8/Ni nanocomposites could potentially be used as anode materials for high-performance Li-ion batteries.     

Enzymeless voltammetric hydrogen peroxide sensor based on the use of PEDOT doped with Prussian Blue nanoparticles

An electrochemical sensor for H₂O₂ was developed based on electrochemically deposited Prussian blue (PB) nanoparticles doped poly(3,4-ethylenedioxythiophene) (PEDOT). The PEDOT/PB composite was composed of PEDOT wrapped PB nanoparticles, where the conducting polymer PEDOT not only protected the PB particles to warrant high stability, but also connected them to enhance the electron transfer. Owing to the excellent conductivity of PEDOT and unique electrocatalytic activity of PB, the PEDOT/PB modified electrode exhibited good catalytic activity toward the electrochemical reduction of H₂O₂, and was used for the detection of H₂O₂ in concentrations ranging from 0.5 to 839 μM, with a detection limit of 0.16 μM. Moreover, the sensor also demonstrated excellent reproducibility, selectivity and long-term stability, showing great promise for the fabrication of electrochemical sensors and H₂O₂ related biosensors.

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Graphical abstract An electrochemical non-enzymatic sensor for hydrogen peroxide with excellent stability was developed. It is based on conducting polymer PEDOT doped with Prussian blue nanoparticles.

     

Nitrogen-doped Carbon Coated Na3V2(PO4)3 with Superior Sodium Storage Capability

Cathodes with high cycling stability and rate capability are required for ambient temperature sodium ion batteries in renewable energy storage application. Na₃V₂(PO₄)₃ is an attractive cathode material with excellent electrochemical stability and fast ion diffusion coefficient within the 3D NASICON structure. Nevertheless, the practical application of Na₃V₂(PO₄)₃ is seriously hindered by its intrinsically poor electronic conductivity. Herein, solvent evaporation method is presented to obtain the nitrogen-doped carbon coated Na₃V₂(PO₄)₃ cathode material, delivering enhanced electrochemical performances. N-Doped carbon layer coating serves as a highly conducting pathway, and creates numerous extrinsic defects and active sites, which can facilitate the storage and diffusion of Na⁺. Moreover, the N-doped carbon layer can provide a stable framework to accommodate the agglomeration of the electrode upon electrode cycling. N-Doped carbon coated Na₃V₂(PO₄)₃(NC-NVP) exhibits excellent long cycling life and superior rate performances than bare Na₃V₂(PO₄)₃ without carbon coating. NC-NVP delivers a stable capacity of 95.9 mA·h/g after 500 cycles at 1 C rate, which corresponds to high capacity retention(94.6%) with respect to the initial capacity(101.4 mA·h/g). Over 91.3% of the initial capacity is retained after 500 cycles at 5 C, and the capacity can reach 85 mA·h/g at 30 C rate.     

纳米Al2O3包覆富锂锰基正极材料Li1.2Ni0.13Co0.13Mn0.54O2的性能研究

采用纳米三氧化二铝(Al₂O₃)对富锂锰基正极材料Li_1.2Ni_0.13Co_0.13Mn_0.54O₂进行表面均匀包覆, 并考察了最优纳米Al₂O₃包覆量下材料的电化学性能. 扫描电子显微镜(SEM)和透射电子显微镜(TEM)显示了纳米Al₂O₃对富锂锰基正极材料表面均匀包覆, X射线衍射分析(XRD)结果表明包覆后富锂材料依然具有良好的层状结构. 恒流充/放电循环测试发现, 包覆后的Li_1.2Ni_0.13Co_0.13Mn_0.54O₂材料的首次放电比容量为249.7 mA·h/g, 循环100次后的容量保持率为89.5%, 与未包覆的Li_1.2Ni_0.13Co_0.13Mn_0.54O₂材料相比, 容量保持率提升约13%. 循环伏安(CV)和电化学阻抗(EIS)测试结果表明, 纳米Al₂O₃包覆可有效抑制材料极化, 降低界面阻抗和电荷转移阻抗, 进而提升富锂锰基正极材料的电化学性能.     

Ni3S2@碳纳米管复合材料的制备及其储钠性能

采用一步固相煅烧工艺制备了碳纳米管原位封装Ni₃S₂纳米颗粒（Ni₃S₂@CNT）,并研究了其作为钠离子电池（SIBs）负极材料的电化学性能. 通过X射线衍射（XRD）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）、循环伏安测试、恒流充放电以及交流阻抗等研究了Ni₃S₂@CNT的物相结构、形貌特征以及电化学性能. 电化学测试表明,材料在100 mA·g ^-1电流密度下,放电容量可以达到541.6 mAh·g ^-1,甚至在2000 mA·g ^-1的大电流密度下其放电比容量也可以维持在274.5 mAh·g ^-1. 另外,材料在100 mA·g ^-1电流密度下,经过120周充放电循环后其放电和充电比容量仍然可以保持在374.5 mAh·g ^-1和359.3 mAh·g ^-1,说明其具有良好倍率性能和循环稳定性能. 良好的电化学性能归因于这种独特的碳纳米管原位封装Ni₃S₂纳米颗粒结构. 碳纳米管不但可以提高复合材料的导电性,也可以缓冲Ni₃S₂纳米颗粒在反复充放电过程中产生的体积膨胀效应,明显改善了Ni₃S₂@CNT负极复合材料的电化学性能.     

Self-Standing Hydrogels Composed of Conducting Polymers for All-Hydrogel-State Supercapacitors

Conducting polymer hydrogels that are capable of contacting with electrolytes at the molecular level, represent an important electrode material. However, the fabrication of self-standing hydrogels merely composed of conducting polymers is still challenging owing to the absence of reliable methods. Herein, a novel and facile macromolecular interaction assisted route is reported to fabricate self-standing hydrogels consisting of polyaniline (PANi: providing high electrochemical activity) and poly(3,4-ethylenedioxythiophene) (PEDOT: enabling high electronic conductivity). Owing to the synergistic effect between them, the self-standing hydrogels possess good mechanical properties and electronic/electrochemical performances, making them an excellent potential electrode for solid-state energy storage devices. A proof-of-concept all-hydrogel-state supercapacitor is fabricated, which exhibits a high areal capacitance of 808.2 mF cm⁻², and a high energy density of 0.63 mWh cm⁻³ at high power density of 28.42 mW cm⁻³, superior to many recently reported conducting polymer hydrogels based supercapacitors. This study demonstrates a novel promising strategy to fabricate self-standing conducting polymer hydrogels.     

The effect of phosphate additive on the positive electrolyte stability of vanadium redox flow battery

The electrolyte is one of the most important components of vanadium redox flow battery(VRFB),and its stability and solubility determines the energy density of a VRFB.The performance of current positive electrolyte is limited by the low stability of VO_2~+at a higher temperature.Phosphate is proved to be a very effective additive to improve the stability of VO_2~+.Even though,the stabilizing mechanism is still not clear,which hinders the further development of VRFBs.In this paper,to clarify the effect of phosphate additive on the positive electrolyte stability,the hydration structures of VO_2~+cations and the reaction mechanisms of precipitation with or without phosphate in the supporting electrolyte of H_2SO_4solutions were investigated in detail based on calculations of electronic structure.The stable configurations of complexes were optimized at the B3LYP/6-311+G(d,p)level of theory.The zero-point energies and Gibbs free energies for these complexes were further evaluated at the B3LYP/aug-cc-pVTZ level of theory.It shows that a structure of[VO_2(H_2O)_2]~+ surrounded by water molecules in H_2SO_4solution can be formed at the room temperature.With the temperature rises,[VO_2(H_2O)_2]~+ will lose a proton and form the intermediate of VO(OH)_3,and the further dehydration among VO(OH)_3molecules will create the precipitate of V_2O_5.When H_3PO_4was added into electrolytes,the V-O-P bond-containing neutral compound could be formed through interaction between VO(OH)_3and H_3PO_4,and the activation energy of forming the V-O-P bond-containing neutral compound is about 7 kcal mol~(-1) lower than that of the VO(OH)_3dehydration,which could avoid the precipitation of V_2O_5and improve the electrolyte stability.     

C-LiFePO4/聚三苯胺复合锂离子电池正极材料的制备与性能

通过低温溶剂热法和高温热处理技术合成了橄榄石结构的LiFePO₄/carbon (C-LiFePO₄)纳米材料. 在此基础上,通过溶液共混法制备了一种新型的聚三苯胺(PTPAn)修饰包覆的C-LiFePO₄复合锂离子电池正极材料(C-LiFePO₄/PTPAn). 利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、电化学阻抗谱(EIS)以及恒电流充放电等测试方法,考察PTPAn 包覆量对C-LiFePO₄/PTPAn 复合正极材料性能的影响. 结果表明：通过溶液共混法PTPAn能够致密地包覆在C-LiFePO₄表面,形成一个有效的电子/离子传输通道从而有效提高CLiFePO₄基复合材料的电化学活性. 所有样品中C-LiFePO₄/10% (w) PTPAn作为正极材料呈现出最佳的电化学性能,在0.1C倍率恒流充放电下材料首次放电比容量为154.5 mAh·g^-1,在10C高倍率恒流充放电下材料的放电比容量达到114.2 mAh·g^-1. 当C-LiFePO₄/PTPAn 复合材料表面包覆的PTPAn 含量进一步增加,复合材料的电化学性能出现下降的趋势. 电化学阻抗测试表明PTPAn包覆层明显减小了C-LiFePO₄电极的电荷转移电阻.     

Site-controlled application of electric potential on a conducting polymer "canvas"

A novel patterning method for conducting polymer films was successfully demonstrated using the concept of bipolar electrochemistry. The local application of an anodic potential to poly(3-methylthiophene) (PMT) and poly(3,4-ethylenedioxythiophene) (PEDOT) on a bipolar electrode (BPE) realized local electrochemical doping and reaction depending on the supporting salt used. The potential applied on the BPE was measured and corresponded well to the patterns. The array-type driving electrode system was able to draw complex patterns in a site-controlled manner.