Progress and perspective of vanadium‑based cathode materials for lithium ion batteries Tungsten

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Tungsten (2021) 3:279–288

https://doi.org/10.1007/s42864-021-00101-w REVIEW PAPER

Progress and perspective of vanadium‑based cathode materials for lithium ion batteries

Yang‑Yang Zhou¹ · Zi‑Ying Zhang¹ · Hui‑Zhen Zhang² · Yang Li³ · Ying Weng¹

Received: 16 November 2020 / Revised: 16 December 2020 / Accepted: 17 December 2020 / Published online: 11 June 2021

Abstract

With the rapid development of various portable electronic devices, lithium ion battery electrode materials with high energy and power density, long cycle life and low cost were pursued. Vanadium-based oxides/sulfides were considered as the ideal next-generation electrode materials due to their high capacity, abundant reserves and low cost. However, the inherent low conductivity and ion diffusion coefficient limit their practical applications in lithium ion batteries. In recent years, vanadium- based electrode materials have been designed into various nanostructures through a variety of nanofabrication processes to overcome the electrochemical performance bottleneck caused by the above disadvantages due to the new properties of nanomaterials that cannot be achieved at the solid level. However, how to obtain high-performance vanadium-based electrode nanomaterials with controllable morphology and structure through low-cost and environmentally friendly processes is still a huge challenge. In this paper, the basic structure, modified morphologies and synthesis methods of vanadium-based electrode materials for lithium ion batteries were reviewed. In addition, the disadvantages, new challenges and future development direction of vanadium electrode materials were also discussed.

Keywords Vanadium-based materials · Cathode materials · Lithium ion batteries · Energy storage

1 Introduction

With the research of clean energy and renewable energy, more and more attention were paid to efficient energy storage system [1–6]. Lithium ion batteries (LIBs) have domi- nated the market for portable and intelligent electronic devices due to their high energy and power densities, long service life and low environmental pollution [5, 6]. How- ever, LIBs also face the problems of capacity degradation and explosion caused by the volume expansion of electrode materials during charging and discharging. With the rapid development of applications of electric vehicles and portable electronic devices, LIBs are required to have high energy and power density, longer cycle life [7, 8]. Therefore, it is

urgent to develop more advanced next-generation LIB electrode materials to meet these high requirements.

In recent years, vanadium-based cathode materials have attracted much attention due to their high operating volt- ages, theoretical capacities and energy densities [9–20].

Among them, vanadium-based oxides have attracted much attention due to their high specific capacity and good safety [9–12]. However, due to the inherent poor conductivity, the cycle life and rate performance of traditional vanadium- based oxide electrodes cannot meet the practical needs. In general, when electrode materials are reduced to nanometer scale, the transport distance between ions and electrons is greatly shortened. The increase of specific surface area of nano-materials improves the electrochemical performance of electrodes. In addition, the vanadium-based composites with the three-dimensional (3D) nanostructures have also been reported to have better electrochemical performance and stability. Here, the progress in the structure optimization, synthesis and modification of vanadium-based LIB electrode materials were reviewed, and the disadvantages, new challenges and future development trends of vanadium-based LIB electrode materials were discussed.

Tungsten

www.springer.com/42864

* Zi-Ying Zhang zzying@sues.edu.cn

1 School of Materials Engineering, Shanghai University of Engineering Science, Shanghai 201620, China

2 School of Management, University of Shanghai for Science and Technology, Shanghai 200093, China

3 Department of Chemistry, Fudan University, Shanghai 200438, China

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2 Research progress of vanadium‑based electrode materials

Vanadium is a common transition metal element with oxidation states of V²⁺, V³⁺, V⁴⁺ and V⁵⁺. The corresponding oxides are VO, V₂O₃, VO₂ and V₂O₅. In addition to VO, V₂O₃, VO₂ and V₂O₅, vanadium also has some oxides with mixed valence, such as V₆O₁₃, V₄O₉, V₃O₇. In recent years, vanadium oxides, as cathode materials for LIBs, have attracted wide attention [9–12] Their rich valence states impart vanadium oxide electrodes with the characteristics of multi-electron transfer and high theoretical capacity. Table 1 shows the electrochemical properties of typical vanadium oxides [12, 17, 18, 21]. In addition, vanadium sulfides also have the potential to be used as LIB cathode materials due to their layered structure similar to that of the same oxygen group [19, 20].

Vanadates are another important vanadium-based electrode materials due to their high output voltage, stable skeleton and fast ion diffusion coefficient. However, most of these materials have low theoretical specific capacity, which limits their practical applications. In recent years, numerous efforts have been devoted to further improving the theoretical specific capacity and cyclic stability of vanadate electrode materials through structure design and optimization [22–31].

2.1 Basic properties and research progress of V₂O₅ As a typical layered crystal structure, V₂O₅ is one of the most concerned electrode materials [32–36]. Its layer framework is composed of V–O polyhedron with common points and common edges, and the layer spacing is 0.44 nm. Therefore, the excellent interlayer structure of V₂O₅ provides an open two-dimensional (2D) transport path for the free diffusion of lithium ions. As a kind of cathode material for LIBs, V₂O₅ has excellent electrochemical performance, and its theoretical specific capacity can reach 280 mAh·g⁻¹. The researchers successfully synthesized a variety of low-dimensional V₂O₅ nano-materials by different methods. Pan et al. [21] synthesized a novel V₂O₅ with well-aligned rodlike nanoparticles by thermal decomposition of vanadyl oxalate in air by increasing

the molar ratio of oxalic acid in the starting reagents. After thermal decomposition treatment, the particle size of these well-aligned V₂O₅ nanorods was much smaller than that of the commercial V₂O₅ products due to the release of CO and CO₂ generated by the decomposition of the precursor during roasting, ensuring more voids between the particles.

This locally disoriented nanorod structure and void space between particles facilitate the penetration of the electrolyte, and the crystal separation is beneficial to phase transition and reduces the energy barrier of lithium ion diffusion. As shown in Fig. 1a, Zhai et al. [35] synthesized a high-quality single-crystalline centimeter-long V₂O₅ nanowires by using an environmentally friendly hydrothermal approach with- out dangerous reagents, harmful solvents, and surfactants.

Figure 1b shows the V₂O₅ nanowires not only had good electron transport properties, but also exhibited a very large discharge specific capacity. However, those V₂O₅ materials also suffered from very serious capacity degradation due to the self-agglomeration of the low-dimensional nano-materials. After 20 cycles, the capacity of V₂O₅ nanowires was reduced to 175 mAh·g⁻¹ with a capacity retention rate of only 50%. To improve the cycling performance of V₂O₅ nanomaterials, Mai et al. [37] synthesized cucumber-like V₂O₅/ Pedot&MnO₂ nanowires by combining the in situ chemical oxidative polymerization with facile soaking process (Fig. 1c–j). Compared with the pure V₂O₅ nanowires, these cucumber-like nanowires had better cycling performance due to their more stable structure, higher active surface area, and shorter ion diffusion path (Fig. 1k, l). Their discharge capacity can be maintained at 166 mAh·g⁻¹ with a current density of 50 mA·g⁻¹ after 40 cycles. It was worth noting that although the cycling performance of V₂O₅/Pedot&MnO₂ nanowires was improved in comparison with the pure V₂O₅ nanowires, their capacity was still significantly reduced during cycling, especially under large current density. In order to further improve the electrochemical performance of V₂O₅, various 3D V₂O₅nanostructures have been synthesized in recent years. Su et al. [38] synthesized single-crystal double- layer vanadium oxide nanobelts by a simple solvothermal method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization revealed that the prepared single-crystal double-layer vanadium oxide nanobelts had large layer spacing (Fig. 1m, n), which is conducive to the insertion and extraction of lithium ions. As shown in Fig. 1o, p, single-crystal double-layer vanadium oxide nanobelts had good cycling performance. Ng et al. [39] prepared a kind of V₂O₅ nanoparticles with good electrochemical performance by a one-step and scalable flame spray pyrolysis (FSP) process. V₂O₅ nanoparticles were interlinked by sinter- ing to form a chain-like agglomerate. This structure improves the specific surface area and stress resistance stability of the nanomaterials and enables the materials to obtain good specific capacity and cycling performance (Fig. 2a). In order

Table 1 Electrochemical properties of typical vanadium oxides Materials Highest revers-

ible capacity (mAh·g⁻¹)

Average discharge voltage (V)

Energy den-

sity (Wh·kg⁻¹) References

VO 265 ~ 2.8 740 [12]

V₂O₃ 356 ~ 1.0 420 [12]

VO₂ 290 ~ 2.6 750 [12]

V₂O₅ 294 ~ 3.0 700 [21]

V₆O₁₃ 364 ~ 2.4 860 [17]

V₃O₇ 280 ~ 2.2 695 [18]

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Fig. 1 a, b V₂O₅ nanowires. Reproduced with permission from Ref.

Electrostatic spraying. Reproduced with permission from Ref. [40].

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to improve cycle stability V₂O₅ nanomaterials, Wang et al.

[40] fabricated porous V₂O₅ thin films by electrostatic spray deposition followed by annealing at 350 °C in air. As shown in Fig. 2b, the evolution process from 2D layered structure to 3D porous multi-cage structure could be clearly observed.

This porous structure had excellent electrolyte permeability and lithium ion diffusion rate, resulting in a high capacity and excellent cycling performance. Figure 3a shows that, owing to the decomposition of the polyvinylpyrrolidone (PVP) polymer template, the morphologies of V₂O₅ thin films evolved from nanofibers into porous nanotubes when the vanadium (IV) precursor annealed at 400 °C [41]. When the annealing temperature was raised to 450 °C, although the porous V₂O₅ nanotubes were retained, the nanograin spacing was simultaneously formed due to the nearby material con- sumption (Fig. 3b), which indicates that at higher annealing temperature, the continuous grain growth eventually formed the nanograin spacing. Further increasing the annealing temperature to 500 °C, the continuous grain growth resulted in the loss of the nanograin spacings, and the porous nanotubes were replaced by hierarchical nanofibers attached to the V₂O₅ nanobelts (Fig. 3c). In order to fully release the potential of V₂O₅ and solve some inherent defects of V₂O₅ in macro- crystal, Li et al. [42] proposed a facile and environmental- friendly method to prepare 3D porous V₂O₅ nanorods in large scale. In the synthesis process, oxalic acid played a dual role:

it reduced vanadium ions and released carbon dioxide during annealing, forming a porous structure. The 3D porous structure provides continuous mass transfer, reduces the diffusion barrier and the interconnected Li⁺ transport network, thus improving storage performance of lithium ions. The electrochemical measurements demonstrated that the 3D porous V₂O₅ architectures exhibited good charge transfer kinetics and lithium ion diffusion rate. After 50 cycles at 0.5 C, their discharge capacity was 248 mAh·g⁻¹, and their capacity retention was 93%. Different from the traditional cationic adsorption mechanism, Wang et al. [32] proposed a concept

of competitive anion adsorption by CMS templates followed by a Trojan catalytic combustion process to prepared metal oxide multilayer hollow microspheres with a well-controlled shell number, thickness, porosity and crystallinity (Fig. 4).

Their approach overcomes the previous limitation and greatly enriches the variety of metal oxide hollow microspheres.

Those multilayer V₂O₅ hollow microspheres showed excellent electrochemical performance. Even at a high current density of 1000 mA·g⁻¹, their capacity retention rate was up to 90% after 100 cycles. It could be seen that the 3D micro-nano structure not only effectively avoided the self-agglomeration of low-dimensional nano-materials, but also had excellent structural stability. In addition, these nanostructures had more electrochemical reaction sites and shorter ion transport path, which greatly improved the cycling performance and capacity of the V₂O₅ electrodes.

2.2 Basic properties and research progress of VO₂ As a typical metal–insulator transition material, VO₂ can be reversibly transformed between rutile VO₂(M) and rutile VO₂(R) at 68 °C. As shown in Fig. 5, the V–V chain of VO₂(R) is linear along the c_R axis with a lattice spacing of 0.288 nm, while the V–V chain of VO₂(M) is serrated with spacings of 0.313 and 0.266 nm, respectively [43]. Com- pared with VO₂(R), VO₂(M) is favorable for lithium intercalation due to its layered structure. Its theoretical specific capacity is 161 mAh·g⁻¹. Usually, the VO₂(M) nanoparticles with a particle size of 100 nm can be obtained by reducing V₂O₅ powder with borohydride. In addition, 1D VO₂(M) nanostructure was also reported to have good lithium storage performance. However, the rate performance of these con- ventional nanostructures is far from satisfactory [44]. There- fore, it is necessary to further improve the electronic conductivity of VO₂(R). Rui et al. [45] synthesized VO₂(R)@C nanosheets by hydrothermal method. The sucrose-derived amorphous carbon grew in situ and adhered to the surface

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of VO₂(R) with a thickness of about 4.3 nm (Fig. 6a–d).

By adjusting the concentration of sucrose, VO₂(R)@C with different thickness carbon layers were obtained. The electrochemical test results revealed that these products with different thickness of carbon layers had similar electrochemical

performance (Fig. 6e–g). To further improve the electrochemical performance of VO₂(R), Mai et al. [46] synthesized VO₂ (R), a hybrid nanostructure composed of nanoscrolls, nanobelts and nanowires, by hydrothermal driving splitting and self-rolled method. The hybrid nanostructure

Fig. 4 Schematic illustration of V₂O₅ hollow microspheres induced by anion. Reproduced with permission from Ref. [32].

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with buffered cross section provided facile strain relaxation during lithiation/delithiation, resulting in excellent structural stability and cyclability. Their internal and interconnecting voids of nanoscrolls shortened the ion diffusion pathway and greatly enhanced the rate performance. At the current

density of 100 mA·g⁻¹, these 3D microstructures maintained a capacity of 139 mAh·g⁻¹ after 100 cycles. They then prepared VO₂(R) hollow spheres assembled from long nanowires (Fig. 7) to further improve the specific surface area of the VO₂(R) hollow microspheres [47].

Fig.6 a–c FESEM images of VO₂(B)@C nanobelts. d HRTEM image of VO₂(B)@C nanobelts. e Initial galvanostatic charge–discharge voltage profiles of VO₂(B)@C nanobelts at a current density of 100 mA·g⁻¹. f Discharge capacities of VO₂(B)@C electrodes at

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2.3 Basic properties and research progress of vanadium sulfides

The properties of transition metal sulfides are similar to those of transition metal oxides. Their theoretical specific capacities are very high. In addition, the conductivity of transition metal sulfides is higher than that of oxides, which is beneficial to improve the rate performance of electrodes [48, 49].

Although vanadium sulfide electrode materials have many advantages, the large size of vanadium sulfides prepared by traditional methods inhibits their excellent electrochemical performance. Therefore, it is of great significance to develop the preparation method of nano-vanadium sulfide electrode materials. Fang et al. [50] synthesized VS₂ nanosheets and graphene composites by one-step hydrothermal method.

The special interaction between VS₂ and GNS allowed for rapid electron transfer between graphene and VS₂ and easy diffusion of lithium ions in the electrodes. In addition, as a topological template for nucleation and growth of 2D VS₂ nanosheets and a buffer substrate, GNS could alleviate volume expansion/contraction of VS₂ during electrochemical charging and discharging, and promote the improvement of cyclic stability. Their initial discharge capacity was 185.4

mAh·g⁻¹, and the capacity remained at 160.9 mAh·g⁻¹ after 200 cycles. Ou et al. [51] synthesized nanostructured V₅S₈/ graphite composites by a simple method combining solid- state vulcanization and liquid stripping. Their study indicates that the reduced stacking of the V₅S₈ layers and the conductive graphite material cladding relaxed the strain and lowered the barrier for Li⁺ insertion and extraction, resulting in excellent cycle performance and superior rate capability.

Even at the current density of 1A·g⁻¹, the specific capacity of the composites remained 846 mAh·g⁻¹ after 700 cycles.

Similarly, Rout et al. [52] successfully synthesized VS₄ and graphene oxide composites, and Britto et al. [53] conducted further studies on the lithium storage mechanism of VS₄. To improve the conductivity and stability of VS₄, more attention has been paid to the composite of VS₄ with other conductive materials [54–57]. After the surface of multi-walled carbon nanotubes (MWCNTs) was treated with acid and coated with glucose, Zhou et al. [58] synthesized VS₄@MWCNTs composites by solvothermal method. Figure 8 shows that some MWCNTs were embedded in VS₄ nanoparticles, which promoted the internal charge transfer of VS₄ particles. The un-embedded parts were connected to each other to form a conductive network, which enhanced the charge transfer

Fig. 8 a, b SEM images of VS₄–MWCNTs composites. c, d TEM images of VS₄–MWCNTs composites. Reproduced with permission from Ref.

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between adjacent particles. The electrochemical test results revealed that the reversible capacity of the VS₄@MWCNTs composites was 922 mAh·g⁻¹ after 100 cycles at a current density of 500 mA·g⁻¹. The reversible capacity of 576 and 401 mAh·g⁻¹ could be, respectively, achieved even after 1000 cycles at a current density of 2 and 5 A·g⁻¹. Although vanadium sulfides as cathode materials for LIBs have not been widely studied, they still show good research potential due to their excellent cyclic stability.

2.4 Basic properties and research progress of vanadates

As a kind of important vanadium oxides, vanadates can be used as electrode material for lithium and niobium [22–28].

Among them, LiV₃O₈ is an excellent cathode material for LIBs, which can transmit 269 mAh·g⁻¹ specific capacity at a current density of 300 mA·g⁻¹ [59]. Compared with the graphite cathode, Li₃VO₄ also has attracted great attention due to its safe discharge platform (0.75 V). Its specific capacity (323 mAh·g⁻¹) is larger than that of Li₄Ti₅O₁₂. In recent years, vanadium phosphates have become the development direction of LIBs electrode materials due to the advantages of high output voltage, stable skeleton and fast ion diffusion coefficient. However, their actual capacity and rate capability need to be improved due to their low conductivity. Zeng et al. [29] improved the capacity of lithium vanadium phosphate by the co-substitution of Mg²⁺ and Cl⁻ and the addition of carbon coating. Mean- while, the modified lithium vanadium phosphate had high average discharge voltage (3.8 V, vs. Li⁺/Li). Sui et al. [30]

synthesized spherical LiVPO₄F/C by spray drying–roasting method. Their study showed that LiVPO₄F/C composites with good spherical shape and uniform size were obtained at the calcination temperature of 750 °C. After 50 cycles, the spherical LiVPO₄F/C composites delivered a discharge capacity of 137.9 mAh·g⁻¹ at a rate of 0.1 C in the range of 3.0–4.5 V, with the capacity retention remaining 91.4%.

Recently, monoclinic Li₃V₂(PO₄)₃ also attracts much attention because of its high energy density, high theoretical capacity and operating voltage, relatively good Li⁺ mobil- ity, excellent thermal and cyclic stability, and high safety performance [31]. However, their intrinsic low electri- cal conductivity and sluggish kinetics hinder its potential application in high rate performance. By using acetylene black as the template and polyethylene glycol-4000 (PEG- 4000) as the surface modification reactant, Mai et al. [60]

synthesized 3D porous Li₃V₂(PO₄)₃/C composite spheres.

When no PEG was added, the products agglomerated and their granularity was large. By adding an appropriate amount of PEG, 3D porous Li₃V₂(PO₄)₃/C composite spheres with uniform morphology and appropriate carbon layer thickness were obtained. The as-prepared Li₃V₂(PO₄)₃ composite

spheres delivered good rate performance and cycling stability supported by the continuous carbon network and carbon coating. After 1000 cycles at a rate of 5 C, those porous Li₃V₂(PO₄)₃/C composite spheres maintained 83% of their initial capacity. Through further structural regulation and reasonable doping, vanadate/vanadium phosphate electrode materials with high energy density and long cycling life are expected to be further developed.

3 Conclusion and outlook

In summary, this paper highlighted the progress and perspective of vanadium-based cathode materials for LIBs.

Vanadium-based cathode materials have been widely proved to have good application prospects due to their large theoretical capacity, high working voltage and good cycle performance. In the past few years, a large number of nano- vanadium-based electrode materials have been developed.

3D composite nanostructures can effectively improve the conductivity and cycling performance of vanadium-based electrode materials due to their reduced volume expansion effect and good lithium ion transport characteristics. Consid- ering the large-scale application of energy storage devices, although vanadium-based LIB electrode materials have a promising prospect, there is still a large space for development in the following aspects:

1. The multi-dimensional vanadium-based nanocomposites with good conductivity and thermal conductivity should be further developed to reduce accidents caused by volume and temperature changes and lithium metal precipitation.

2. Although progress has been made in the charging and discharging capacity of vanadium-based LIB electrodes through various nanometer manufacturing processes, cycling performance remains an important issue for these electrodes. With the insertion of lithium ions, the conductivity of vanadium-based electrode nanomaterials decreases due to the change of structure, which leads to the decrease of capacity. Therefore, it is of great significance to further design nano-electrode materials with high cycling performance.

3. The structures and properties of vanadium oxides/

sulfides prepared by different methods are different. It is necessary to develop a novel, simple, environmentally friendly and low-cost method for synthesizing vanadium-based materials.

4. Vanadium-based electrodes help LIBs work under more complex conditions, such as high pressure and low temperature. In order to meet the complex working conditions of vanadium-based LIBs, it is necessary to develop supporting electrolytes.

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5. Vanadium-based sulfides should be further developed due to their high conductivity and theoretical specific capacity.

Acknowledgements This work was supported by Shanghai Natural Science Foundation (Grant No.14ZR1418700), and Shanghai Univer- sity of Engineering Science Innovation Fund (Grant No. 18KY0504).

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Dr. Zi‑Ying Zhang is an associate professor in School of Materials Engineering at Shanghai Univer- sity of Engineering Science. He began his research career in 2007 and received his doctoral degree in Materials Science from Fudan University in 2013. He has par- ticipated in more than ten aca- demic research projects as prin- cipal investigator/director or key participant and is a special expert on development in the northern Jiangsu province of China. His recent research inter- ests focus on the corrosion and protection of metallic materials, the theoretical research and computa- tional simulation of the structure and properties of IOL materials and battery electrochemistry.