以五氧化二钒干凝胶、碳酸锰、磷酸二氢铵、碳酸锂、乙炔黑为原料,采用固相法在相对较低的温度条件下合成了x Li Mn PO4·y Li3V2(PO4)3锂离子电池复合正极材料。采用X射线衍射(XRD)、扫描电镜(SEM)对其晶体结构和表面形貌进行表征...以五氧化二钒干凝胶、碳酸锰、磷酸二氢铵、碳酸锂、乙炔黑为原料,采用固相法在相对较低的温度条件下合成了x Li Mn PO4·y Li3V2(PO4)3锂离子电池复合正极材料。采用X射线衍射(XRD)、扫描电镜(SEM)对其晶体结构和表面形貌进行表征。结果表明,750℃下烧结15 h合成的3Li Mn PO4·Li3V2(PO4)3为结晶良好的两相结构,颗粒粒径较小且分布比较均匀,其在室温、0.2 C倍率下首次充放电容量分别为144.8 m Ah/g和139.8 m Ah/g,循环50次后容量为130.5 m Ah/g。展开更多
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 chal- lenge...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 chal- lenge to develop high-performance and durable cathode materials for SIBs. Among different candidate materials, Na_3V_2（PO_4）_3 has 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）_3 delivers 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 mute. The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250 cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C, which is superior to many state-of- the-art SIB cathode materials. This can be attributed to the hierarchically distributed Na_3V_2（PO_4）_3 crystals in carbon nanofiber network, which possesses outstanding electronicfionic conductivity and thus leads to an ultrahigh rate capabilitY.展开更多
Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol (PEG) as the dispersing media, micro crystalline phosphors Zn_3(PO_4)_2∶Eu 3+ a...Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol (PEG) as the dispersing media, micro crystalline phosphors Zn_3(PO_4)_2∶Eu 3+ and LaPO_4∶Eu 3+ were synthesized by in-situ co-precipitation method. X-ray diffraction and scanning electronic micrograph were used to characterize the resultant samples, whose particle size are in the range of micrometer. The emission spectra of Zn_3(PO_4)_2∶Eu 3+ (λ_ ex=245 nm) and LaPO_4∶Eu 3+ (λ_ ex=390 nm) shows that the emission for Eu 3+ in Zn_3(PO_4)_2 is dominated by the 5D_0→7F_1 (592 nm) magnetic-dipole transition,While the dominant emission for Eu 3+ in LaPO_4 is the typical hypersensitive transition 5D_0→7F_2 (618 nm).展开更多
Objective To study the structural and anticorrosive property of microcrystalline α-Zn_3(PO_4)_2·4H_2O. Methods Zinc phosphate was prepared from zinc acetate and orthophosphate acid in aqueous solution. Structura...Objective To study the structural and anticorrosive property of microcrystalline α-Zn_3(PO_4)_2·4H_2O. Methods Zinc phosphate was prepared from zinc acetate and orthophosphate acid in aqueous solution. Structural characteristics of products were investigated by XRD, RAMAN, FTIR, TG-DTA, SEM, surface area, particle size distribution, and density measurements. Results The title compound, a highly crystalline, micronized and lamellar α-Zn_3(PO_4)_2·4H_2O, has an orthorhombic monoclinic system, space group a_0=10.597(),b_ 0 =18.308(), c_ 0 =5.0304(), V=975.86 3. Its specific area is 0.701m2/g, density 3.1612g/m3, and average size 4.75μm . Conclusion Comparing with commercial Zinc phosphate, the synthesized lamellar microcrystalline zinc phosphate had excellent anticorrosive property and dispersibility.展开更多
Na_(3)V_(2)(PO_(4))_(3)(NVP)has garnered great attentions as a prospective cathode material for sodium-ion batteries(SIBs)by virtue of its decent theoretical capacity,superior ion conductivity and high structural stab...Na_(3)V_(2)(PO_(4))_(3)(NVP)has garnered great attentions as a prospective cathode material for sodium-ion batteries(SIBs)by virtue of its decent theoretical capacity,superior ion conductivity and high structural stability.However,the inherently poor electronic conductivity and sluggish sodium-ion diffusion kinetics of NVP material give rise to inferior rate performance and unsatisfactory energy density,which strictly confine its further application in SIBs.Thus,it is of significance to boost the sodium storage performance of NVP cathode material.Up to now,many methods have been developed to optimize the electrochemical performance of NVP cathode material.In this review,the latest advances in optimization strategies for improving the electrochemical performance of NVP cathode material are well summarized and discussed,including carbon coating or modification,foreign-ion doping or substitution and nanostructure and morphology design.The foreign-ion doping or substitution is highlighted,involving Na,V,and PO_(4)^(3−)sites,which include single-site doping,multiple-site doping,single-ion doping,multiple-ion doping and so on.Furthermore,the challenges and prospects of high-performance NVP cathode material are also put forward.It is believed that this review can provide a useful reference for designing and developing high-performance NVP cathode material toward the large-scale application in SIBs.展开更多
Sodium-ion batteries(SIBs)have rapidly risen to the forefront of energy storage systems as a promising supplementary for Lithium-ion batteries(LIBs).Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)as a common cathode of SIBs,featur...Sodium-ion batteries(SIBs)have rapidly risen to the forefront of energy storage systems as a promising supplementary for Lithium-ion batteries(LIBs).Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)as a common cathode of SIBs,features the merits of high operating voltage,small volume change and favorable specific energy density.However,it suffers from poor cycling stability and rate performance induced by its low intrinsic conductivity.Herein,we propose an ingenious strategy targeting superior SIBs through cross-linked NVPF with multi-dimensional nanocarbon frameworks composed of amorphous carbon and carbon nanotubes(NVPF@C@CNTs).This rational design ensures favorable particle size for shortened sodium ion transmission pathway as well as improved electronic transfer network,thus leading to enhanced charge transfer kinetics and superior cycling stability.Benefited from this unique structure,significantly improved electrochemical properties are obtained,including high specific capacity(126.9 mAh g^(-1)at 1 C,1 C=128 mA g^(-1))and remarkably improved long-term cycling stability with 93.9%capacity retention after 1000 cycles at 20 C.The energy density of 286.8 Wh kg^(-1)can be reached for full cells with hard carbon as anode(NVPF@C@CNTs//HC).Additionally,the electrochemical performance of the full cell at high temperature is also investigated(95.3 mAh g^(-1)after 100 cycles at 1 C at 50℃).Such nanoscale dual-carbon networks engineering and thorough discussion of ion diffusion kinetics might make contributions to accelerating the process of phosphate cathodes in SIBs for large-scale energy storages.展开更多
液态电解质锂离子电池因其潜在的安全性问题,发展新的固态电解质锂离子电池是目前所研究的热点。磷酸铝钛锂(Li_(1.5)Al_(0.5)Ti_(1.5)(PO_(4))_(3),LATP)是一种NASICON型陶瓷材料,由于其空气稳定性和较好的Li^(+)导电性而备受关注。然...液态电解质锂离子电池因其潜在的安全性问题,发展新的固态电解质锂离子电池是目前所研究的热点。磷酸铝钛锂(Li_(1.5)Al_(0.5)Ti_(1.5)(PO_(4))_(3),LATP)是一种NASICON型陶瓷材料,由于其空气稳定性和较好的Li^(+)导电性而备受关注。然而,为了达到良好的离子导电性并降低晶界阻抗,LATP需要950℃以上的高温来实现致密化,这对于大规模应用来说耗时且昂贵。本文使用简单的溶液浇铸法,通过将LATP嵌入共聚物PVDF-HFP(聚偏氟乙烯-六氟丙烯)基体,合成新的复合固态电解质膜。在此基础上,以磷酸铁锂(LiFePO_(4))为正极,使用PVDF-HFP/LATP复合固态电解质膜进行电池组装。在室温下,利用X射线衍射仪(X-ray diffractometer,XRD)、扫描电子显微镜(scanning electron microscope,SEM)对不同质量比的固态电解质膜进行物理特性研究,并进行相关电化学测试。结果表明,PVDF-HFP/LATP质量比为5∶1的复合固态电解质膜,其LATP的NASICON型晶体结构得到了很好的保持;制备的聚合物固态电解质膜具有阻燃性;组装的半电池在常温条件下锂离子迁移数达到0.70。全电池在20次充放电循环下,放电比容量保持率为85%。展开更多
A series of Cr^(3+)-substituted Na_(1+x)Ti_(2−x)Cr_(x)P_(3)O_(12)(x=0.1,0.2,0.3,0.4,0.5,molar fraction)solid electrolytes were prepared by the solid-phase reaction method.The effects of Cr^(3+)ions on the phase compos...A series of Cr^(3+)-substituted Na_(1+x)Ti_(2−x)Cr_(x)P_(3)O_(12)(x=0.1,0.2,0.3,0.4,0.5,molar fraction)solid electrolytes were prepared by the solid-phase reaction method.The effects of Cr^(3+)ions on the phase composition,microstructure,and electrochemical ion conductivity of Na-based conductors were studied using X-ray powder diffraction,field emission scanning electron microscopy,and AC impedance measurement.The results show that the main crystal phase of NaTi_(2)(PO_(4))_(3) is formed in the solid electrolytes.The substitution of Ti4+sites by 15 at.%Cr^(3+)ions contributes to the enhancement of electrical conductivity,which is attributed to the combined effect of suppressing the formation of impurity phases,broadening ion channels,and improving the bonding degree of grains.Na_(1.3)Ti_(1.7)Cr_(0.3)P_(3)O_(12) electrolyte can obtain the best ionic conductivity of 6.13×10^(−6)S/cm at room temperature,which is 8 times that of the undoped NaTi_(2)(PO_(4))_(3) electrolyte.展开更多
Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF) is shown to be an attractive cathode material for sodium storage due to its high theoretical capacity and suitable working voltage.However,its low electronic conductivity and poor cy...Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF) is shown to be an attractive cathode material for sodium storage due to its high theoretical capacity and suitable working voltage.However,its low electronic conductivity and poor cycling stability have to be addressed in order for enhanced high-rate performance and cycle life.Herein,we have prepared a 3D reduced graphene oxide (rGO) host-supported NVPF nanocuboids.We discover that polyvinyl alcohol (PVA) serves as an important structural directing agent that bridges between NVPF and rGO through the hydrogen bonding,and thus regulates the formation of the 3D r GO framework with NVPF nanocuboids embedded inside (NVPF@C@rGO).With such a unique construction,NVPF@C@rGO exhibits excellent cycling stability and rate performance for sodium storage,showing high reversible capacities of 121 m Ah/g and 113 mAh/g at 1C and 10C,respectively,and 103 mAh/g after 700cycles at 50C with 98.3%retention.Even at an extremely high current of 100C,it also delivers a reversible capacity of 64 mAh/g,surpassing the performance of many recently reported NVPF-based electrodes.Cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT) data confirm the much better kinetic properties of NVPF@C@rGO electrode than the control samples of NVPF@rGO and pure NVPF.In-situ XRD results reveal that the 3D rGO housing can effectively suppress the lattice variation of NVPF,with a maximum volume change of only 1.84%during cycling.Moreover,the in-situ temperature sensing reveals the more stable working temperature of NVPF@C@rGO compared to phase-pure NVPF,suggesting a higher temperature safety of the electrode.Using NVPF@C@rGO as the positive electrode and commercial hard carbon as the negative electrode,a sodium-ion full battery has been assembled with about 110 m Ah/g at 1C for 300 cycles,corresponding to an energy density of 291 Wh kg^(-1).The construction of 3D r GO housing as a conductive support offers an effective strategy for high-rate,long cycle life and high safety sodium-ion battery cathodes.展开更多
Ethylene carbonate(EC)is widely used in lithium-ion batteries due to its optimal overall performance with satisfactory conductivity,relatively stable solid electrolyte interphase(SEI),and wide electrochemical window.E...Ethylene carbonate(EC)is widely used in lithium-ion batteries due to its optimal overall performance with satisfactory conductivity,relatively stable solid electrolyte interphase(SEI),and wide electrochemical window.EC is also the most widely used electrolyte solvent in sodium ion batteries.However,compared to lithium metal,sodium metal(Na)shows higher activity and reacts violently with EC-based electrolyte(NaPF_(6)as solute),which leads to the failure of sodium metal batteries(SMBs).Herein,we reveal the electrochemical instability mechanism of EC on sodium metal battery,and find that the com-bination of EC and NaPF_(6) is electrically reduced in sodium metal anode during charging,resulting in the reduction of the first coulombic efficiency,and the continuous consumption of electrolyte leads to the cell failure.To address the above issues,an additive modified linear carbonate-based electrolyte is provided as a substitute for EC based electrolytes.Specifically,ethyl methyl carbonate(EMC)and dimethyl carbon-ate(DMC)as solvents and fluoroethylene carbonate(FEC)as SEI-forming additive have been identified as the optimal solvent for NaFP_(6)based electrolyte and used in Na_(4)Fe_(3)(PO_(4))_(2)(P_(2)O_(7))/Na batteries.The batter-ies exhibit excellent capacity retention rate of about 80%over 1000 cycles at a cut-off voltage of 4.3 V.展开更多
文摘以五氧化二钒干凝胶、碳酸锰、磷酸二氢铵、碳酸锂、乙炔黑为原料,采用固相法在相对较低的温度条件下合成了x Li Mn PO4·y Li3V2(PO4)3锂离子电池复合正极材料。采用X射线衍射(XRD)、扫描电镜(SEM)对其晶体结构和表面形貌进行表征。结果表明,750℃下烧结15 h合成的3Li Mn PO4·Li3V2(PO4)3为结晶良好的两相结构,颗粒粒径较小且分布比较均匀,其在室温、0.2 C倍率下首次充放电容量分别为144.8 m Ah/g和139.8 m Ah/g,循环50次后容量为130.5 m Ah/g。
基金the financial support from the 973 program of China (Grant No. 2014CB932401, 2015CB932500)Beijing Nova Program (Grant No. Z161100004916099)the Tsinghua University Initiative Scientific Research Program (Grant Nos. 20173080001, 20151080367)
文摘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 chal- lenge to develop high-performance and durable cathode materials for SIBs. Among different candidate materials, Na_3V_2（PO_4）_3 has 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）_3 delivers 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 mute. The sample could deliver excellent cycling capability with specific capacity of 112 mAh/g at 1 C after 250 cycles and ultrahigh rate capability with 76.9 mAh/g even at 100 C, which is superior to many state-of- the-art SIB cathode materials. This can be attributed to the hierarchically distributed Na_3V_2（PO_4）_3 crystals in carbon nanofiber network, which possesses outstanding electronicfionic conductivity and thus leads to an ultrahigh rate capabilitY.
文摘Using rare earth and zinc coordination polymers with aromatic carboxylic acids as the precursors, composing with the polyethylene glycol (PEG) as the dispersing media, micro crystalline phosphors Zn_3(PO_4)_2∶Eu 3+ and LaPO_4∶Eu 3+ were synthesized by in-situ co-precipitation method. X-ray diffraction and scanning electronic micrograph were used to characterize the resultant samples, whose particle size are in the range of micrometer. The emission spectra of Zn_3(PO_4)_2∶Eu 3+ (λ_ ex=245 nm) and LaPO_4∶Eu 3+ (λ_ ex=390 nm) shows that the emission for Eu 3+ in Zn_3(PO_4)_2 is dominated by the 5D_0→7F_1 (592 nm) magnetic-dipole transition,While the dominant emission for Eu 3+ in LaPO_4 is the typical hypersensitive transition 5D_0→7F_2 (618 nm).
文摘Objective To study the structural and anticorrosive property of microcrystalline α-Zn_3(PO_4)_2·4H_2O. Methods Zinc phosphate was prepared from zinc acetate and orthophosphate acid in aqueous solution. Structural characteristics of products were investigated by XRD, RAMAN, FTIR, TG-DTA, SEM, surface area, particle size distribution, and density measurements. Results The title compound, a highly crystalline, micronized and lamellar α-Zn_3(PO_4)_2·4H_2O, has an orthorhombic monoclinic system, space group a_0=10.597(),b_ 0 =18.308(), c_ 0 =5.0304(), V=975.86 3. Its specific area is 0.701m2/g, density 3.1612g/m3, and average size 4.75μm . Conclusion Comparing with commercial Zinc phosphate, the synthesized lamellar microcrystalline zinc phosphate had excellent anticorrosive property and dispersibility.
基金partly supported by the National Natural Science Foundation of China(Grant No.52272225).
文摘Na_(3)V_(2)(PO_(4))_(3)(NVP)has garnered great attentions as a prospective cathode material for sodium-ion batteries(SIBs)by virtue of its decent theoretical capacity,superior ion conductivity and high structural stability.However,the inherently poor electronic conductivity and sluggish sodium-ion diffusion kinetics of NVP material give rise to inferior rate performance and unsatisfactory energy density,which strictly confine its further application in SIBs.Thus,it is of significance to boost the sodium storage performance of NVP cathode material.Up to now,many methods have been developed to optimize the electrochemical performance of NVP cathode material.In this review,the latest advances in optimization strategies for improving the electrochemical performance of NVP cathode material are well summarized and discussed,including carbon coating or modification,foreign-ion doping or substitution and nanostructure and morphology design.The foreign-ion doping or substitution is highlighted,involving Na,V,and PO_(4)^(3−)sites,which include single-site doping,multiple-site doping,single-ion doping,multiple-ion doping and so on.Furthermore,the challenges and prospects of high-performance NVP cathode material are also put forward.It is believed that this review can provide a useful reference for designing and developing high-performance NVP cathode material toward the large-scale application in SIBs.
基金financially supported by Science and Technology Foundation of Guizhou Province(QKHZC[2020]2Y037)the Science and Technology Innovation Program of Hunan Province(2020RC4005,2019RS1004)+2 种基金Research start-up funding from Central South University(202044019)Innovation Mover Program of Central South University(2020CX007)National Natural Science Foundation of China(U21A20284)
文摘Sodium-ion batteries(SIBs)have rapidly risen to the forefront of energy storage systems as a promising supplementary for Lithium-ion batteries(LIBs).Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF)as a common cathode of SIBs,features the merits of high operating voltage,small volume change and favorable specific energy density.However,it suffers from poor cycling stability and rate performance induced by its low intrinsic conductivity.Herein,we propose an ingenious strategy targeting superior SIBs through cross-linked NVPF with multi-dimensional nanocarbon frameworks composed of amorphous carbon and carbon nanotubes(NVPF@C@CNTs).This rational design ensures favorable particle size for shortened sodium ion transmission pathway as well as improved electronic transfer network,thus leading to enhanced charge transfer kinetics and superior cycling stability.Benefited from this unique structure,significantly improved electrochemical properties are obtained,including high specific capacity(126.9 mAh g^(-1)at 1 C,1 C=128 mA g^(-1))and remarkably improved long-term cycling stability with 93.9%capacity retention after 1000 cycles at 20 C.The energy density of 286.8 Wh kg^(-1)can be reached for full cells with hard carbon as anode(NVPF@C@CNTs//HC).Additionally,the electrochemical performance of the full cell at high temperature is also investigated(95.3 mAh g^(-1)after 100 cycles at 1 C at 50℃).Such nanoscale dual-carbon networks engineering and thorough discussion of ion diffusion kinetics might make contributions to accelerating the process of phosphate cathodes in SIBs for large-scale energy storages.
文摘液态电解质锂离子电池因其潜在的安全性问题,发展新的固态电解质锂离子电池是目前所研究的热点。磷酸铝钛锂(Li_(1.5)Al_(0.5)Ti_(1.5)(PO_(4))_(3),LATP)是一种NASICON型陶瓷材料,由于其空气稳定性和较好的Li^(+)导电性而备受关注。然而,为了达到良好的离子导电性并降低晶界阻抗,LATP需要950℃以上的高温来实现致密化,这对于大规模应用来说耗时且昂贵。本文使用简单的溶液浇铸法,通过将LATP嵌入共聚物PVDF-HFP(聚偏氟乙烯-六氟丙烯)基体,合成新的复合固态电解质膜。在此基础上,以磷酸铁锂(LiFePO_(4))为正极,使用PVDF-HFP/LATP复合固态电解质膜进行电池组装。在室温下,利用X射线衍射仪(X-ray diffractometer,XRD)、扫描电子显微镜(scanning electron microscope,SEM)对不同质量比的固态电解质膜进行物理特性研究,并进行相关电化学测试。结果表明,PVDF-HFP/LATP质量比为5∶1的复合固态电解质膜,其LATP的NASICON型晶体结构得到了很好的保持;制备的聚合物固态电解质膜具有阻燃性;组装的半电池在常温条件下锂离子迁移数达到0.70。全电池在20次充放电循环下,放电比容量保持率为85%。
基金supported by the National Natural Science Foundation of China(No.51972344)the Natural Science Foundation of Hunan Province,China(No.2018JJ3646).
文摘A series of Cr^(3+)-substituted Na_(1+x)Ti_(2−x)Cr_(x)P_(3)O_(12)(x=0.1,0.2,0.3,0.4,0.5,molar fraction)solid electrolytes were prepared by the solid-phase reaction method.The effects of Cr^(3+)ions on the phase composition,microstructure,and electrochemical ion conductivity of Na-based conductors were studied using X-ray powder diffraction,field emission scanning electron microscopy,and AC impedance measurement.The results show that the main crystal phase of NaTi_(2)(PO_(4))_(3) is formed in the solid electrolytes.The substitution of Ti4+sites by 15 at.%Cr^(3+)ions contributes to the enhancement of electrical conductivity,which is attributed to the combined effect of suppressing the formation of impurity phases,broadening ion channels,and improving the bonding degree of grains.Na_(1.3)Ti_(1.7)Cr_(0.3)P_(3)O_(12) electrolyte can obtain the best ionic conductivity of 6.13×10^(−6)S/cm at room temperature,which is 8 times that of the undoped NaTi_(2)(PO_(4))_(3) electrolyte.
基金financially supported by the National Natural Science Foundation of China (No. 52372176)Guangdong Basic and Applied Basic Research Foundation (No. 2024A1515011517)。
文摘Na_(3)V_(2)(PO_(4))_(2)F_(3)(NVPF) is shown to be an attractive cathode material for sodium storage due to its high theoretical capacity and suitable working voltage.However,its low electronic conductivity and poor cycling stability have to be addressed in order for enhanced high-rate performance and cycle life.Herein,we have prepared a 3D reduced graphene oxide (rGO) host-supported NVPF nanocuboids.We discover that polyvinyl alcohol (PVA) serves as an important structural directing agent that bridges between NVPF and rGO through the hydrogen bonding,and thus regulates the formation of the 3D r GO framework with NVPF nanocuboids embedded inside (NVPF@C@rGO).With such a unique construction,NVPF@C@rGO exhibits excellent cycling stability and rate performance for sodium storage,showing high reversible capacities of 121 m Ah/g and 113 mAh/g at 1C and 10C,respectively,and 103 mAh/g after 700cycles at 50C with 98.3%retention.Even at an extremely high current of 100C,it also delivers a reversible capacity of 64 mAh/g,surpassing the performance of many recently reported NVPF-based electrodes.Cyclic voltammetry (CV) and galvanostatic intermittent titration technique (GITT) data confirm the much better kinetic properties of NVPF@C@rGO electrode than the control samples of NVPF@rGO and pure NVPF.In-situ XRD results reveal that the 3D rGO housing can effectively suppress the lattice variation of NVPF,with a maximum volume change of only 1.84%during cycling.Moreover,the in-situ temperature sensing reveals the more stable working temperature of NVPF@C@rGO compared to phase-pure NVPF,suggesting a higher temperature safety of the electrode.Using NVPF@C@rGO as the positive electrode and commercial hard carbon as the negative electrode,a sodium-ion full battery has been assembled with about 110 m Ah/g at 1C for 300 cycles,corresponding to an energy density of 291 Wh kg^(-1).The construction of 3D r GO housing as a conductive support offers an effective strategy for high-rate,long cycle life and high safety sodium-ion battery cathodes.
基金supported by the National Natural Science Foundation of China(52172201,51732005,51902118,and 52102249)the China Postdoctoral Science Foundation(2019M662609and 2020T130217)for financial support。
文摘Ethylene carbonate(EC)is widely used in lithium-ion batteries due to its optimal overall performance with satisfactory conductivity,relatively stable solid electrolyte interphase(SEI),and wide electrochemical window.EC is also the most widely used electrolyte solvent in sodium ion batteries.However,compared to lithium metal,sodium metal(Na)shows higher activity and reacts violently with EC-based electrolyte(NaPF_(6)as solute),which leads to the failure of sodium metal batteries(SMBs).Herein,we reveal the electrochemical instability mechanism of EC on sodium metal battery,and find that the com-bination of EC and NaPF_(6) is electrically reduced in sodium metal anode during charging,resulting in the reduction of the first coulombic efficiency,and the continuous consumption of electrolyte leads to the cell failure.To address the above issues,an additive modified linear carbonate-based electrolyte is provided as a substitute for EC based electrolytes.Specifically,ethyl methyl carbonate(EMC)and dimethyl carbon-ate(DMC)as solvents and fluoroethylene carbonate(FEC)as SEI-forming additive have been identified as the optimal solvent for NaFP_(6)based electrolyte and used in Na_(4)Fe_(3)(PO_(4))_(2)(P_(2)O_(7))/Na batteries.The batter-ies exhibit excellent capacity retention rate of about 80%over 1000 cycles at a cut-off voltage of 4.3 V.
