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AAC

Advances in Analytical Chemistry

2163-1557

Scientific Research Publishing

10.12677/aac.2024.142009

AAC-86368

aac2024142_41560393.pdf

化学与材料

K/Co共掺杂的钠离子电池正极材料Na ₃V ₂(PO ₄) ₃的制备和电化学性能研究 Preparation and Electrochemical Properties of K/Co Doping Sodium Ion Battery Cathode Material Na ₃V ₂(PO ₄) ₃

曹

希

² ¹ 翟

建广

² ¹ 李

文尧

² ¹ 王

睿君

² ¹

上海工程技术大学材料科学与工程学院，上海

null

11 05 2024

14 02 70 76

2014

This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

Na₃V₂(PO₄)₃(NVP)材料是一种聚阴离子型磷酸盐类材料，它结构稳定、安全性高、工作电压高并且具有优异的结构。这些优点与其他电极材料相比，更有助于钠离子的快速迁移，这使得它成为一种非常具有发展潜力的钠离子电池正极材料。但由于NVP材料导电性有一定的缺陷，导致它的倍率性能和循环寿命不够优秀。我们对NVP材料采用离子掺杂的改性方法增强其电化学性能。本研究使用K和Co元素共同掺杂的改性思路，使用溶胶凝胶法成功制备出了K_0.1Na_2.95V_1.95Co_0.05(PO₄)₃材料作为钠离子电池正极材料。通过对该材料的表征分析和电化学分析，结果显示在1 C电流密度下，该材料具有107.5 mA·h/g的高比容量，高于NVP的比容量[1 C时99.2 mA·h/g]，并且在循环500圈后仍然保持了70.41%的容量。通过分别掺杂部分K和Co²到Na1和V³位点，使晶胞体积变大来加速Na的转移，用来改善材料的电化学性能。 Na₃V₂(PO₄)₃(NVP) material is a polyanionic phosphate-like material that is structurally stable, safe, has a high operating voltage and has an excellent structure. These advantages contribute to the fast migration of sodium ions compared with other electrode materials, which makes it a very promising anode material for sodium-ion batteries. However, the conductivity of NVP material has some defects, which leads to its multiplicity performance and cycle life not being excellent enough. We used ion doping modification method for NVP material to enhance its electrochemical performance. In this study, using the modification idea of co-doping with K and Co elements, K_0.1Na_2.95V_1.95Co_0.05(PO₄)₃material was successfully prepared as the anode material for sodium-ion batteries using sol-gel method. Characterization and electrochemical analysis of the material showed that the material had a high specific capacity of 107.5 mA-h/g at 1 C current density, which was higher than that of NVP [99.2 mA-h/g at 1 C], and still maintained 70.41% capacity after 500 cycles. By doping some Kand Co²to Na1 and V³sites, respectively, the cell volume was enlarged to accelerate Natransfer to improve the electrochemical performance of the material.

磷酸矾钠，离子掺杂，正极材料，钠离子电池, Na ₃V ₂(PO ₄) ₃ Ionic Doping Cathode Material Sodium-Ion Batteries

摘要

关键词

磷酸矾钠，离子掺杂，正极材料，钠离子电池

Preparation and Electrochemical Properties of K/Co Doping Sodium Ion Battery Cathode Material Na3V2(PO4)3

Xi Cao, Jianguang Zhai^*, Wenyao Li, Ruijun Wang

School of Materials Science and Engineering, Shanghai University of Engineering Science, Shanghai

Received: Apr. 13^th, 2024; accepted: May 3^rd, 2024; published: May 11^th, 2024

ABSTRACT

Na₃V₂(PO₄)₃(NVP) material is a polyanionic phosphate-like material that is structurally stable, safe, has a high operating voltage and has an excellent structure. These advantages contribute to the fast migration of sodium ions compared with other electrode materials, which makes it a very promising anode material for sodium-ion batteries. However, the conductivity of NVP material has some defects, which leads to its multiplicity performance and cycle life not being excellent enough. We used ion doping modification method for NVP material to enhance its electrochemical performance. In this study, using the modification idea of co-doping with K and Co elements, K_0.1Na_2.95V_1.95Co_0.05(PO₄)₃material was successfully prepared as the anode material for sodium-ion batteries using sol-gel method. Characterization and electrochemical analysis of the material showed that the material had a high specific capacity of 107.5 mA-h/g at 1 C current density, which was higher than that of NVP [99.2 mA-h/g at 1 C], and still maintained 70.41% capacity after 500 cycles. By doping some K⁺and Co²⁺to Na1 and V³⁺sites, respectively, the cell volume was enlarged to accelerate Na⁺transfer to improve the electrochemical performance of the material.

Keywords:Na₃V₂(PO₄)₃, Ionic Doping, Cathode Material, Sodium-Ion Batteries

This work is licensed under the Creative Commons Attribution International License (CC BY 4.0).

http://creativecommons.org/licenses/by/4.0/

1. 引言

近年来，随着能源需求的迅速增长，化石燃料的快速消耗和枯竭以及环境污染的加剧已成为人们关注的焦点 [ 1 ] 。锂离子电池因为具有能量密度较高、循环寿命长和环保效益好等特点，被广泛开发和商业化 [ 2 ] 。然而，锂在地壳中的丰富度仅为0.0065%，再加上锂元素在地球上分布非常不均匀，这些问题严重限制了锂电池的大规模发展 [ 3 ] 。钠离子电池和锂离子电池的储能机制相似，钠资源又相当廉价且储量充足，在电动汽车和大规模储能领域比锂离子电池具有更好的发展前景 [ 4 ] [ 5 ] 。在电池里正极材料有着很重要的地位，影响并决定了电池的安全、寿命和性能等方方面面 [ 6 ] 。

截至今日，人们已经研究发现大量可以作为钠离子电池正极的材料，主要分类有过渡金属氧化物 [ 7 ] 、聚阴离子类例如磷酸盐等 [ 8 ] 和普鲁士蓝类等 [ 9 ] 。磷酸盐类聚阴离子型化合物稳定性好，钠含量高和种类丰富等优点被广泛研究 [ 10 ] [ 11 ] 。不过其电压较低，相对没那么稳定，这些缺点也限制了该材料的发展和应用 [ 12 ] 。研究人员采取了各种手段来提升材料性能，例如减小材料尺寸 [ 13 ] 、表面碳包覆 [ 14 ] 和离子掺杂 [ 15 ] 等。离子掺杂可以提高材料的本征电导率，提高材料结构稳定性。目前对磷酸盐类正极材料进行离子掺杂一般是在V位点掺杂Fe [ 16 ] 、Mn [ 17 ] 等元素，以及在Na位点掺杂Li [ 18 ] 、K [ 19 ] 等元素。

本研究使用K和Co元素共同掺杂的改性思路，使用溶胶凝胶法制备出了K_0.1Na_2.95V_1.95Co_0.05(PO₄)₃，下文中简称为(K_0.1Co_0.05-NVP)。该材料中部分K⁺取代了Na1位点的Na⁺，Co²⁺替代了部分V³⁺位，由于K⁺的半径较大，并且使NVP的晶胞体积变大，从而使Na⁺通道变宽，让Na⁺移动的速度更快，也使NVP的NASICON结构更稳定，导电性能更优异。

2. 实验部分 2.1 材料制备

本文通过溶胶凝胶法制备NVP和K_0.1Co_0.05-NVP材料。NVP详细制备过程如下：将一定摩尔量的NH₄VO₃加入烧杯中，将烧杯水浴加热到80℃，加入60 mL去离子水后使用磁力搅拌器搅拌半小时。量取20 mL三倍NH₄VO₃摩尔量的还原剂草酸溶液，加入烧杯中使用磁力搅拌机搅拌均匀的淡蓝色溶液。将一定化学计量的NaH₂PO₄添加到烧杯中持续搅拌约1 h后形成均匀凝胶。随后将所得凝胶放入烘箱中过夜，等待干燥后使用研钵研磨成均匀前驱体粉末。随后进行热处理，将粉末放入管式炉中，在350℃的N₂氛围下预烧3 h后再放置在750℃的N₂氛围下煅烧10 h，煅烧结束后使用研钵研磨均匀后得到NVP粉末样品。

K_0.1Co_0.05-NVP的制备流程图如图1所示，详细制备过程如下：将一定摩尔量的NH₄VO₃和Co(NO₃)₂·6H₂O加入烧杯中，水浴加热到80℃，加入60 mL去离子水后使用磁力搅拌器搅拌半小时。量取20 mL三倍NH₄VO₃摩尔量的还原剂草酸溶液，加入烧杯中使用磁力搅拌机搅拌均匀的淡蓝色溶液。在烧杯中依次加入一定化学计量比的NaH₂PO₄、KH₂PO₄和CH₃COONA·3H₂O，使用磁力搅拌机持续搅拌1 h后形成均匀的凝胶。随后将所得凝胶放入烘箱中过夜，等待干燥后使用研钵研磨成均匀前驱体粉末。随后进行热处理，将粉末放入管式炉中，在350℃的N₂氛围下预烧3 h后再放置在750℃的N₂氛围下煅烧10 h，煅烧结束后使用研钵研磨均匀后得到K_0.1Co_0.05-NVP粉末样品。

2.2. 极片和电池的制作

将导电炭黑(乙炔黑)和正极材料按照1:8的质量比混合，研磨充分后加入粘结剂(5%质量分数的PVDF，用NMP作溶剂)，使用电子搅拌机搅拌约2小时制成均匀浆料，裁剪一块铝箔贴在使用酒精洗净后的玻璃上，将浆料涂在铝箔上，用工型刮刀刮平，放进真空烘箱100℃过夜进行烘干，烘干后用切片机切成14 mm大小的极片作为正极片。使用手套箱，在N₂氛围的手套箱中擀制的钠片作为负极，使用该极片作为正极，隔膜为Whatman GF/A，电解液为1 mol/L的NaCIO₄溶液和EC/DEC (V:V/1:1)溶液和5% FEC溶液，将其依次放入电池壳组装成纽扣电池，从手套箱取出电池后用电池封口机密封。密封完成后室温下静置数小时后方可测试电化学性能。

2.3. 材料的结构形貌表征与电化学性能测试 2.3.1. X射线粉末衍射仪(XRD)

本文采用3KWDMAX2200V PC型号X射线粉末衍射仪来测试样品表面形貌分和测试晶体结构 [ 20 ] 。

2.3.2. 扫描电子显微镜(SEM)

本文采用日立S-3400N型号扫描电子显微镜观察样品的微观形貌，并可以分析粉末材料和颗粒大小的尺寸分布情况。样品为无毒无污染无磁性且干燥的粉末样品，在测试前还要将样品进行喷金处理。

2.3.3. 蓝电电池测试系统(GCD)

图1. K_0.1Co_0.05-NVP的制备流程

使用CT2001型号的蓝电电池测试系统，在室温条件下进行恒流充放电测试测试，测试样品的电化学性能，分析电极材料的循环性能和倍率性能。

3. 结果与讨论 3.1. 晶体结构的变化

图2. NVP与K_0.1Co_0.05-NVP的XRD图谱

图2为K_0.1Co_0.05-NVP及NVP的XRD图，材料的峰形曲线形状平缓，强衍射峰和衍射图谱基本一致，衍射峰都很尖锐，并且没有出现明显的杂峰，这就意味着NVP及含K/Co的K_0.1Co_0.05-NVP都被成功合成且材料结晶性较好，K_0.1Co_0.05-NVP与NASICON型NVP材料的R-3c结构的对应，K和Co元素的掺杂几乎不改变NVP骨架的晶体结构。通过对XRD数据使用相关软件进行精修计算可以得出样品相应的晶格参数。结合晶格参数表(表1)中的a，b，c和V可知，部分K⁺取代了部分Na1位点的Na⁺，部分Co²⁺替代了部分V³⁺位，K/Co掺杂改性的K_0.1Co_0.05-NVP样品的参数值比NVP样品更大，K⁺和Co²⁺都比替换前的Na⁺和V³⁺有更大的离子半径，所以晶胞体积也随之相应扩大，晶胞体积的扩大为Na⁺的移动提供了更宽的通道，从而使K_0.1Co_0.05-NVP样品中的离子传输更快速，也就起到了增加比容量的作用。

Table 1 Lattice parameters of NVP and K0.1Co0.05-NV

样品	A = b/nm	c/nm	v/nm³
NVP	8.726	21.804	143.368
K_0.1Co_0.05-NVP	8.733	21.861	144.796

表1. NVP和K_0.1Co_0.05-NVP的晶格参数

3.2. K0.1Co0.05-NVP表面形貌的改变

图3(a)和图3(b)分别为NVP和K_0.1Co_0.05-NVP的SEM图，通过对比可得，两种样品都是不规则形貌的颗粒，颗粒大小和分布比较均匀，图3(c)和图3(d)显示样品结晶度良好，粒径约在2~3 μm。K_0.1Co_0.05-NVP的颗粒尺寸小于NVP样品，尺寸分布也更均匀。通过减小颗粒尺寸，电极材料和电解液接触面积就会增大，离子和电子的移动距离也会随之减小，电池的充放电速率也就可以更快速地进行。

图3. NVP (a, c)与K_0.1Co_0.05-NVP (b, d)的SEM图

3.3. 电化学性能的变化

图4(a)是NVP和K_0.1Co_0.05-NVP的在0.1 C电流密度下的循环性能。循环次数越多，材料的放电比容量会随着电池循环次数也就随之降低。在0.1 C的电流密度下，NVP的初始比容量为99.2 mA·h/g，50圈充放电循环后比容量降低为86.21 mA·h/g，是初始容量的86.9%；经过500圈充放电循环后比容量仅剩下42.17 A·h/g，仅剩下初始容量的42.51%。经过元素掺杂改性后，K_0.1Co_0.05-NVP正极材料的初始比容量为107.5 mA·h/g，经过50圈充放电循环后容量还有101.85 mA·h/g，是初始容量的94.75%；经过500圈充放电循环后比容量为75.69 A·h/g，是初始比容量的70.41%。经比较发现，K_0.1Co_0.05-NVP的首圈比容量比NVP材料高，容量保持率在循环后也比NVP高。K_0.1Co_0.05-NVP电化学性能提升说明K⁺和Co²⁺双掺给NVP材料带来了协同效应，成功优化了NVP晶体结构，提高了了离子和电子移动传输效率，同时保持了Na⁺可逆脱嵌量没有减少。

图3(b)为NVP和K_0.1Co_0.05-NVP在蓝电电池测试系统下测试得出的倍率性能曲线。经比较可以看出掺杂改性后的材料倍率性能更好，经过元素掺杂改性后材料的倍率性能更优异。在0.1 C到5 C中的不同的电流密度下，NVP的放电比容量分别为94.2、93.3、82.7、74.2、59、40.3 mA·h/g，K_0.1Co_0.05-NVP的放电比容量分别为101.7、99.9、98.5、92.8、82.3、69.6 mA·h/g，并且在之后回到0.1 C电流密度的时候，该材料依然有着92 mA·h/g的放电比容量。在5 C电流密度下NVP的放电比容量是初始数值的40.6%，而K_0.1Co_0.05-NVP是初始数值的64.74%。并且K_0.1Co_0.05-NVP材料在随着电流密度增加，平均极化电压的增幅更小，说明K_0.1Co_0.05-NVP在高倍率下结构更稳定。综上，我们可以得出结论K和Co元素共同掺杂可以增强NVP材料的稳定性，从而增强材料的电化学性能。

图4. NVP和K_0.1Co_0.05-NVP的在0.1 C电流密度下的循环性能(a)和NVP和K_0.1Co_0.05-NVP的倍率性能图(b)

4. 结论

综上所述，我们使用K和Co元素共同掺杂的改性思路获得了改性后的K_0.1Na_2.95V_1.95Co_0.05(PO₄)₃材料作为钠离子电池的正极材料，对NVP材料的导电性能、比容量、可逆性和倍率性能都有提升。K⁺部分取代Na1位点的Na⁺，部分V³⁺位也被Co²⁺替代，扩大晶面间隙和晶胞体积，促进了Na⁺迁移，增加了NVP的电子传导率，增强了NVP在充放电过程中的结构可逆性和离子传导能力，对Na⁺和电子的移动都有促进作用。因此，K/Co共掺对NVP材料的电化学性能有显著的增强作用，是一种改进材料性能的有效方法。

文章引用

曹希,翟建广,李文尧,王睿君. K/Co共掺杂的钠离子电池正极材料Na₃V₂(PO₄)₃的制备和电化学性能研究Preparation and Electrochemical Properties of K/Co Doping Sodium Ion Battery Cathode Material Na₃V₂(PO₄)₃[J]. 分析化学进展, 2024, 14(02): 70-76. https://doi.org/10.12677/aac.2024.142009

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