Tuesday, 11 October 2022
Recently, the quest for lithium-ion batteries (LIBs) with higher energy densities, power densities, and low cost has gained great attention due to the increasing demands of high-power equipment such as electric vehicles. One of the most promising approaches to enhance the energy densities of LIBs is to couple the anode with a high-capacity cathode, since the capacity of LIBs is typically limited by the cathode. Among the high-capacity cathode materials, vanadium pentoxide (V2O5) is receiving attention due to its exceptional theoretical capacity (~294 mAh g-1) [2]. Also, since the V2O5 has no lithium in the chemical, it can increase the specific energy in the cell design of the lithium-metal battery (LMB, ~700 Wh kg-1). Moreover, it needs no first charge enhancing the initial cycling stability of the LMB.
However, it suffers from a poor cycling stability and rate capability due to its structural transformation during cycling and low electrons/lithium-ion conductivities [2]. To overcome this issues, numerous efforts have been focused on shortening the lithium ion (Li+) diffusion length through the development of nanostructured V2O5 such as nanorods, nanobelts, nanosheet, and hollow spheres. Particularly, 1D nanostructured V2O5 along the [010] orientation, which is the fastest growth direction of V2O5 [4], has been suggested in many studies because of its simplicity in synthesis [1]. In nanostructures, however, structural collapse and particles agglomeration could emerge during Li+ ion penetration [3]. Moreover, the [010] direction of V2O5 corresponds to the energy-preferred diffusion pathway of Li+ ion [5]. Accordingly, 1D nanostructured V2O5 provides a long distance for the Li+ ion diffusion along [010] direction. Therefore, it is assumed that to achieve the high kinetics and structural stability, the structure for V2O5 as cathode materials should be re-designed to satisfy the following conditions, favorable to Li-ion accommodation and its pathway : ⅰ) secondary structures consisted of primary nanostructured units to prevent agglomeration. ii) a short [010] length with highly exposed (010) facets to shorten a Li+ ion diffusion pathway and facilitate the Li+ ion intercalation reactions.
In this context, we introduce a facile lithium-treatment method for synthesis of nanoplates-stacked structured V2O5 (Li-treated VO) with highly exposed (010) facets and shorter [010] growth-length (0.7-1.4 um) compared to a V2O5 nanobelt (~20 um) (pristine VO). In lithium-treatment method, Li+ ions from lithium nitrate (LiNO3), which is added to precursor solution, can inhibit the complete crystallization of V2O5 during hydrothermal process, hence evolving xerogel/crystal composite. Afterward, during heat treatment process, the cleavage and oriented attachment mechanism are accompanied, generating Li-treated V2O5 with nanoplates-stacked structure having short [010] length and highly exposed (010) facets (Figure 1). The robust nanoplates-stacked structure can facilitate the fast and efficient transportation of Li+ ion into the [010] channel. In Li//V2O5 half-cell, the Li-treated VO electrodes can achieve a reversible capacity of 252 mAh g-1 at 50 mA g-1 in the voltage range of 2.05–4.0 V (vs. Li/Li+) (Figure 2). Notably, the Li-treated VO electrodes also exhibit a higher rate performance (140 mAh g-1 at 1 A g-1 (Figure 2)) and cycling capability (79 % capacity retention after 100 cycles (Figure 3)) compared to the untreated V2O5 nanobelt (VO) electrodes. In addition, the reversible lithium intercalation reaction and structural stability of Li-treated VO will be discussed in detail.
However, it suffers from a poor cycling stability and rate capability due to its structural transformation during cycling and low electrons/lithium-ion conductivities [2]. To overcome this issues, numerous efforts have been focused on shortening the lithium ion (Li+) diffusion length through the development of nanostructured V2O5 such as nanorods, nanobelts, nanosheet, and hollow spheres. Particularly, 1D nanostructured V2O5 along the [010] orientation, which is the fastest growth direction of V2O5 [4], has been suggested in many studies because of its simplicity in synthesis [1]. In nanostructures, however, structural collapse and particles agglomeration could emerge during Li+ ion penetration [3]. Moreover, the [010] direction of V2O5 corresponds to the energy-preferred diffusion pathway of Li+ ion [5]. Accordingly, 1D nanostructured V2O5 provides a long distance for the Li+ ion diffusion along [010] direction. Therefore, it is assumed that to achieve the high kinetics and structural stability, the structure for V2O5 as cathode materials should be re-designed to satisfy the following conditions, favorable to Li-ion accommodation and its pathway : ⅰ) secondary structures consisted of primary nanostructured units to prevent agglomeration. ii) a short [010] length with highly exposed (010) facets to shorten a Li+ ion diffusion pathway and facilitate the Li+ ion intercalation reactions.
In this context, we introduce a facile lithium-treatment method for synthesis of nanoplates-stacked structured V2O5 (Li-treated VO) with highly exposed (010) facets and shorter [010] growth-length (0.7-1.4 um) compared to a V2O5 nanobelt (~20 um) (pristine VO). In lithium-treatment method, Li+ ions from lithium nitrate (LiNO3), which is added to precursor solution, can inhibit the complete crystallization of V2O5 during hydrothermal process, hence evolving xerogel/crystal composite. Afterward, during heat treatment process, the cleavage and oriented attachment mechanism are accompanied, generating Li-treated V2O5 with nanoplates-stacked structure having short [010] length and highly exposed (010) facets (Figure 1). The robust nanoplates-stacked structure can facilitate the fast and efficient transportation of Li+ ion into the [010] channel. In Li//V2O5 half-cell, the Li-treated VO electrodes can achieve a reversible capacity of 252 mAh g-1 at 50 mA g-1 in the voltage range of 2.05–4.0 V (vs. Li/Li+) (Figure 2). Notably, the Li-treated VO electrodes also exhibit a higher rate performance (140 mAh g-1 at 1 A g-1 (Figure 2)) and cycling capability (79 % capacity retention after 100 cycles (Figure 3)) compared to the untreated V2O5 nanobelt (VO) electrodes. In addition, the reversible lithium intercalation reaction and structural stability of Li-treated VO will be discussed in detail.
References
[1] XU, X., et al. (2020). Materials Today Nano, 10, 100073.
[2] MA, Wenda, et al. (2016). ACS applied materials & interfaces, 8(30), 19542-19549.
[3] DONG, Yujuan, et al. (2015). Journal of Power Sources, 285, 538-542.
[4] CHAN, Candace K., et al. (2007). Nano letters, 7(2), 490-495.
[5] Ma, W. Y., et al. (2013). Journal of Physics D: Applied Physics, 46(10), 105306.