3.Department of Physics,Sam Houston State University,Huntsville Texas 77341,USA
Recent research progress of sodium vanadium fluorophosphate as cathode material for sodium-ion batteries
SUN Chang,1, DENG Zerong1, JIANG Ningbo2, ZHANG Lulu,1, FANG Hui3, YANG Xuelin,1
1.College of Electrical Engineering & New Energy, Hubei Provincial Collaborative Innovation Center for New Energy Microgrid, China Three Gorges University, Yichang 443002, Hubei, China
2.College of Materials and Chemical Engineering, China Three Gorges University, Yichang 443002, Hubei, China
3.Department of Physics, Sam Houston State University, Huntsville, Texas 77341, USA
Sodium-ion batteries have substantial potential in large-scale energy storage and low-speed electric vehicles owing to their raw material abundance, low cost, safety, and relatively low environmental impact. Recently, sodium vanadium fluorophosphate [Na3V2(PO4)2F3, NVPF] has become a focus of research into cathode materials for sodium-ion batteries. Key attributes of NVPF are its stable three-dimensional framework structure, high theoretical capacity (128 mA·h/g), and high working voltage (approximately 3.8 V). However, low electronic conductivity and slow ion diffusion rate resulted in both low actual capacity and unsatisfactory rate performance, which had hindered further development. Therefore, researchers have been able to considerably improve electrochemical performance by optimizing the synthesis process, coating, ion doping, and structural design. Together, these improvements have greatly enhanced the potential for application of NVPF in sodium-ion batteries. Based on a review of recent relevant literature, this paper first introduces the cell characteristics of NVPF. Next, it investigates four Na+ extraction/insertion mechanisms (i.e., the solid solution reaction, step-by-step Na+ extraction/insertion, three-step Na+ extraction/insertion, and two-step Na+ extraction/insertion mechanisms). It also briefly summarizes three common synthesis methods (i.e., the high temperature solid-state, hydrothermal, and sol-gel methods) and their advantages and disadvantages. Then, recent progress with enhanced NVPF (modified by coating, ion doping, and optimized structural design) is described in detail. Finally, the practical development of the synthesis and modification of NVPF cathode materials and the NVPF full cell are explored in the context of future real-world applications of NVPF in sodium-ion batteries.
SUN Chang. Recent research progress of sodium vanadium fluorophosphate as cathode material for sodium-ion batteries[J]. Energy Storage Science and Technology, 2022, 11(4): 1184-1200
Fig. 1
(a) Crystal structure of NVPF[33]; (b) ex-situ23Na NMR spectra of NVPF[34]; (c) sodium distribution for different sodium removal phases of NVPF based on Rietveld refinement[35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据。NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应。当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g。NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制。随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程。近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的。例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相。Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下
Fig. 2
(a) SEM images, (b) long cycle performance at 5 C, (c) CV curves, (d) charge-discharge profiles, (e) XRD patterns of NVPF/C synthesized by high temperature solid-state reaction[43]; (f) SEM images, (g) TEM images, (h) CV curves, (i) charge-discharge profiles, (j) XRD patterns of NVPF-H@cPAN prepared by hydrothermal method[45];(k) SEM images, (l) HRTEM images, (m) CV curves, (n) charge-discharge profiles and (o) XRD patterns of NVPF@C synthesized by the sol-gel method[47]
Fig. 3
(a) SEM images, (b) charge-discharge curves at different rate, (c) long cycle performance of full battery at 10 C of NVPF/C synthesized by spray drying assisted solid-state reaction[48], (d) SEM images, (e) TEM images, (f) charge-discharge curves at different rate, (g) long cycle performance of full battery at 1 C of NVPF@C prepared by electrospinning assisted heat treatment technology[49]
Fig. 4
(a) Synthesis process and schematic diagram of electronic and ionic transport within the CMK-3 channels; (b) HRTEM images; (c) rate performance; and (d) long cycle performance at 50 C of NVPF@CD nanocomposite[52]
Fig. 5
(a) Synthesis process for NVPF/C-PDPA and its schematic structure; (b) HRTEM images of NVPF/C-PDPA; long cycle performance of samples of NVPF/C-PDPA at 0.5 C (c) and 10 C (d) [55]
Fig. 9
(a) Schematic representation of the modified sol-gel process for preparing nano-Na3V2(PO4)2F3; (b) unit cell of Na3V2(PO4)2F3 and the corresponding lattice spacings; (c) cycle performance of SG at 0.2 C[83]
Fig. 10
(a), (b) Rate performance and long cycle performance at 10 C of the NVPF@C@rGO symmetrical full cell[84]; (c), (d) rate performance and long cycle performance at 10 C of the NVPF@CD||NTP@C full cell[52]; (e), (f), (g) charge-discharge curves, rate performance and long cycle performance at 2 C of NVPF-rGO-650C||NVP full cell[46]; (h), (i), (j) rate performance, energy density at different rates and long cycle performance at 5 C of the NVPF||HC full cell[40]
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... [33];(b) NVPF的非原位 23Na核磁共振波谱[34];(c) 基于Rietveld精修获得的NVPF不同脱钠相的钠分布情况[35];(d) 基于碳热还原法在不同温度下合成NVPF的充放电曲线[39](a) Crystal structure of NVPF[33]; (b) ex-situ23Na NMR spectra of NVPF[34]; (c) sodium distribution for different sodium removal phases of NVPF based on Rietveld refinement[35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
... [33]; (b) ex-situ23Na NMR spectra of NVPF[34]; (c) sodium distribution for different sodium removal phases of NVPF based on Rietveld refinement[35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
(a) Crystal structure of NVPF[33]; (b) ex-situ23Na NMR spectra of NVPF[34]; (c) sodium distribution for different sodium removal phases of NVPF based on Rietveld refinement[35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
... [34]; (c) sodium distribution for different sodium removal phases of NVPF based on Rietveld refinement[35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
... Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
(a) Crystal structure of NVPF[33]; (b) ex-situ23Na NMR spectra of NVPF[34]; (c) sodium distribution for different sodium removal phases of NVPF based on Rietveld refinement[35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
... [35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
... Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
1
... Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
0
1
... Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
(a) Crystal structure of NVPF[33]; (b) ex-situ23Na NMR spectra of NVPF[34]; (c) sodium distribution for different sodium removal phases of NVPF based on Rietveld refinement[35]; (d) charge-discharge curves for NVPF synthesized by carbothermal reduction at different temperatures[39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
... [39]Fig. 1
Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
... Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
4
... Liu等[34]结合理论计算和实验,发现NVPF有两个储钠位点(Na1位和Na2位)[图1(b)],Na1位由两个Na占据,Na2位由1个Na占据.NVPF结构中的三个钠离子中只有两个具有电化学活性,伴随着V3+/V4+的氧化还原过程进行分步脱嵌,而第三个钠离子不参与反应.当NVPF结构中的2个Na+可逆脱嵌时,理论容量高达128 mA·h/g.NVPF作为钠离子电池正极材料被研究初期,其钠离子的嵌入/脱出过程一直被认为是固溶反应,直到Bianchini等[35]通过监测NVPF充电时的结构变化[图1(c)],才发现在形成最终脱钠产物NaV2(PO4)2F3之前还存在Na2.4V2(PO4)2F3、Na2.2V2(PO4)2F3、Na2V2(PO4)2F3和Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)等中间相,其中,只有Na x V2(PO4)2F3(1.8 ≤ x ≤ 1.3)之间经历固溶反应,其他中间相之间均为两相反应,电极的整体结构演变遵循可逆多相变化的分步钠脱嵌机制.随后,人们发现NVPF有三对明显的充放电平台(3.4/3.3 V、3.7/3.6 V和4.2/4.1 V)[36-38],由于Na1位置上的Na比Na2位置上的Na更稳定,所以3.4/3.3 V和3.7/3.6 V的充放电平台对应于Na2位置的Na两步脱嵌过程,而4.2/4.1 V的充放电平台则对应于Na1位置的Na一步脱嵌过程.近期,研究者们又通过大量实验验证发现,3.4/3.3 V的充放电平台实际是由材料中存在的Na3V2(PO4)3杂相引起的.例如,Yang等[39]通过研究不同温度下合成NVPF的电化学性能发现,随着合成温度的升高,材料充放电曲线[图1(d)]中3.4 V的平台越来越长,这是因为更高的温度导致更多氟离子的损失,产生了更多的Na3V2(PO4)3杂相.Deng等[40]通过氨水调节pH值稳定氟源,合成了含有极少杂质的NVPF,该材料只表现出分别对应于钠离子在Na3V2(PO4)2F3/Na2V2(PO4)2F3和Na2V2(PO4)2F3/NaV2(PO4)2F3之间脱嵌的3.7/3.6 V和4.2/4.1 V两对充放电平台,其电化学反应过程如下 ...
(a), (b) Rate performance and long cycle performance at 10 C of the NVPF@C@rGO symmetrical full cell[84]; (c), (d) rate performance and long cycle performance at 10 C of the NVPF@CD||NTP@C full cell[52]; (e), (f), (g) charge-discharge curves, rate performance and long cycle performance at 2 C of NVPF-rGO-650C||NVP full cell[46]; (h), (i), (j) rate performance, energy density at different rates and long cycle performance at 5 C of the NVPF||HC full cell[40]Fig. 10
(a) SEM images, (b) long cycle performance at 5 C, (c) CV curves, (d) charge-discharge profiles, (e) XRD patterns of NVPF/C synthesized by high temperature solid-state reaction[43]; (f) SEM images, (g) TEM images, (h) CV curves, (i) charge-discharge profiles, (j) XRD patterns of NVPF-H@cPAN prepared by hydrothermal method[45];(k) SEM images, (l) HRTEM images, (m) CV curves, (n) charge-discharge profiles and (o) XRD patterns of NVPF@C synthesized by the sol-gel method[47]Fig. 2
... [45];(k) SEM images, (l) HRTEM images, (m) CV curves, (n) charge-discharge profiles and (o) XRD patterns of NVPF@C synthesized by the sol-gel method[47]Fig. 2
... [46];(h), (i), (j) NVPF||HC全电池的倍率性能、不同倍率下的能量密度和5 C下的长循环性能图[40](a), (b) Rate performance and long cycle performance at 10 C of the NVPF@C@rGO symmetrical full cell[84]; (c), (d) rate performance and long cycle performance at 10 C of the NVPF@CD||NTP@C full cell[52]; (e), (f), (g) charge-discharge curves, rate performance and long cycle performance at 2 C of NVPF-rGO-650C||NVP full cell[46]; (h), (i), (j) rate performance, energy density at different rates and long cycle performance at 5 C of the NVPF||HC full cell[40]Fig. 10
(a) SEM images, (b) long cycle performance at 5 C, (c) CV curves, (d) charge-discharge profiles, (e) XRD patterns of NVPF/C synthesized by high temperature solid-state reaction[43]; (f) SEM images, (g) TEM images, (h) CV curves, (i) charge-discharge profiles, (j) XRD patterns of NVPF-H@cPAN prepared by hydrothermal method[45];(k) SEM images, (l) HRTEM images, (m) CV curves, (n) charge-discharge profiles and (o) XRD patterns of NVPF@C synthesized by the sol-gel method[47]Fig. 2
... [48]和静电纺丝辅助热处理技术合成NVPF@C复合材料的(d) 扫描电镜照片、(e) TEM图、(f) 不同倍率下的充放电曲线、(g) 全电池在1 C下的长循环性能图[49](a) SEM images, (b) charge-discharge curves at different rate, (c) long cycle performance of full battery at 10 C of NVPF/C synthesized by spray drying assisted solid-state reaction[48], (d) SEM images, (e) TEM images, (f) charge-discharge curves at different rate, (g) long cycle performance of full battery at 1 C of NVPF@C prepared by electrospinning assisted heat treatment technology[49]Fig. 33 NVPF的改性方法
... [48], (d) SEM images, (e) TEM images, (f) charge-discharge curves at different rate, (g) long cycle performance of full battery at 1 C of NVPF@C prepared by electrospinning assisted heat treatment technology[49]Fig. 33 NVPF的改性方法
... [49](a) SEM images, (b) charge-discharge curves at different rate, (c) long cycle performance of full battery at 10 C of NVPF/C synthesized by spray drying assisted solid-state reaction[48], (d) SEM images, (e) TEM images, (f) charge-discharge curves at different rate, (g) long cycle performance of full battery at 1 C of NVPF@C prepared by electrospinning assisted heat treatment technology[49]Fig. 33 NVPF的改性方法
... [52](a) Synthesis process and schematic diagram of electronic and ionic transport within the CMK-3 channels; (b) HRTEM images; (c) rate performance; and (d) long cycle performance at 50 C of NVPF@CD nanocomposite[52]Fig. 4
... [52];(e), (f), (g) NVPF-rGO-650C||NVP全电池的充放电曲线、倍率性能和2 C下的长循环性能图[46];(h), (i), (j) NVPF||HC全电池的倍率性能、不同倍率下的能量密度和5 C下的长循环性能图[40](a), (b) Rate performance and long cycle performance at 10 C of the NVPF@C@rGO symmetrical full cell[84]; (c), (d) rate performance and long cycle performance at 10 C of the NVPF@CD||NTP@C full cell[52]; (e), (f), (g) charge-discharge curves, rate performance and long cycle performance at 2 C of NVPF-rGO-650C||NVP full cell[46]; (h), (i), (j) rate performance, energy density at different rates and long cycle performance at 5 C of the NVPF||HC full cell[40]Fig. 10
... [52]; (e), (f), (g) charge-discharge curves, rate performance and long cycle performance at 2 C of NVPF-rGO-650C||NVP full cell[46]; (h), (i), (j) rate performance, energy density at different rates and long cycle performance at 5 C of the NVPF||HC full cell[40]Fig. 10
... [55](a) Synthesis process for NVPF/C-PDPA and its schematic structure; (b) HRTEM images of NVPF/C-PDPA; long cycle performance of samples of NVPF/C-PDPA at 0.5 C (c) and 10 C (d) [55]Fig. 5
... 目前研究者们一致认为,NVPF在充放电过程中只能脱嵌两个钠离子.然而,Yan等[82]却发现,通过形成四方对称的无序Na x V2(PO4)2F3相在1~4.8 V的电压范围内可以激活NVPF中的第三个钠离子,当与碳负极组装成全电池时能量密度提高了14%,该研究突破了人们对NVPF材料容量极限的认识,也为提高NVPF电池的能量密度提供了一个新的思路.此外,Peng等[83]还发现,在合成NVPF的过程中加入过量柠檬酸,利用柠檬酸热解释放的气体可使材料产生一定的晶格畸变和缺陷,得到Na3V2(PO4)2F3纳米材料(SG)[图9(a)].随着NVPF层间距的扩大[图9(b)],钠离子间的静电斥力减弱,NVPF中可以嵌入额外的钠离子,形成Na4V2(PO4)2F3,使NVPF在0.2 C时的首次放电比容量高达250 mA·h/g,远高于固相法合成的Na3V2(PO4)2F3(SS);但是额外钠离子的脱嵌容易造成材料结构的不可逆破坏,使材料的循环性能变差,所以该材料循环20圈后的容量保持率只有72%[图9(c)].所以,当对NVPF进行结构设计使额外的钠离子脱嵌时,如何稳定充放电过程中材料的结构也将是NVPF未来发展的一个研究热点. ...
3
... 目前研究者们一致认为,NVPF在充放电过程中只能脱嵌两个钠离子.然而,Yan等[82]却发现,通过形成四方对称的无序Na x V2(PO4)2F3相在1~4.8 V的电压范围内可以激活NVPF中的第三个钠离子,当与碳负极组装成全电池时能量密度提高了14%,该研究突破了人们对NVPF材料容量极限的认识,也为提高NVPF电池的能量密度提供了一个新的思路.此外,Peng等[83]还发现,在合成NVPF的过程中加入过量柠檬酸,利用柠檬酸热解释放的气体可使材料产生一定的晶格畸变和缺陷,得到Na3V2(PO4)2F3纳米材料(SG)[图9(a)].随着NVPF层间距的扩大[图9(b)],钠离子间的静电斥力减弱,NVPF中可以嵌入额外的钠离子,形成Na4V2(PO4)2F3,使NVPF在0.2 C时的首次放电比容量高达250 mA·h/g,远高于固相法合成的Na3V2(PO4)2F3(SS);但是额外钠离子的脱嵌容易造成材料结构的不可逆破坏,使材料的循环性能变差,所以该材料循环20圈后的容量保持率只有72%[图9(c)].所以,当对NVPF进行结构设计使额外的钠离子脱嵌时,如何稳定充放电过程中材料的结构也将是NVPF未来发展的一个研究热点. ...
... [83](a) Schematic representation of the modified sol-gel process for preparing nano-Na3V2(PO4)2F3; (b) unit cell of Na3V2(PO4)2F3 and the corresponding lattice spacings; (c) cycle performance of SG at 0.2 C[83]Fig. 94 NVPF全电池
... [84];(c), (d) NVPF@CD||NTP@C全电池的倍率性能和10 C下的长循环性能图[52];(e), (f), (g) NVPF-rGO-650C||NVP全电池的充放电曲线、倍率性能和2 C下的长循环性能图[46];(h), (i), (j) NVPF||HC全电池的倍率性能、不同倍率下的能量密度和5 C下的长循环性能图[40](a), (b) Rate performance and long cycle performance at 10 C of the NVPF@C@rGO symmetrical full cell[84]; (c), (d) rate performance and long cycle performance at 10 C of the NVPF@CD||NTP@C full cell[52]; (e), (f), (g) charge-discharge curves, rate performance and long cycle performance at 2 C of NVPF-rGO-650C||NVP full cell[46]; (h), (i), (j) rate performance, energy density at different rates and long cycle performance at 5 C of the NVPF||HC full cell[40]Fig. 10
... [84]; (c), (d) rate performance and long cycle performance at 10 C of the NVPF@CD||NTP@C full cell[52]; (e), (f), (g) charge-discharge curves, rate performance and long cycle performance at 2 C of NVPF-rGO-650C||NVP full cell[46]; (h), (i), (j) rate performance, energy density at different rates and long cycle performance at 5 C of the NVPF||HC full cell[40]Fig. 10