Nanoplates-Stacked Vanadium Oxide Cathode Employing Higher Kinetics and Stability in a Lithium-Ion Battery
Authors: Sim Kiyeon , Eom Kwang Sup 
Published: July 2022

In recent years, the popularity of high-power equipment such as electric vehicles demands a higher the energy density, higher the power density, and low cost in lithium-ion batteries (LIBs). The capacity of LIBs is typically limited by the cathode. For example, in LIBs based on LiCoO2//graphite system, which have achieved great success in commercialization, the reversible capacity of LiCoO2 (~137 mAh g-1) is lower than that of graphite (~370 mAh g-1) [1]. Hence, it is necessary to improve the capacity of the cathode in order to improve the performance of LIBs. Among the cathode materials, Vanadium pentoxide (V2O5) is considered as one of the ideal next-generation electrode materials due to its high theoretical capacities (294 mAh g-1), high energy densities, good safety and low cost [2]. Nevertheless, its cycle performance and poor rate-capability caused by severe structural changes during the repeated lithiation/de-lithiation, slow diffusion of lithium ion (Li+), and low electrical conductivity hinders its commercialization [2]. Various attempts to fabricate the nanostructured V2O5 such as nanorods, nanobelts, nanosheet, and hollow spheres have been pursued to remedy the issues. The nanostructures are used to overcome their kinetic limitation by reduction of Li+ ion diffusion distance and increase in the electrode/electrolyte contact area. In nanostructures, however, structural collapse and particles agglomeration could emerge during Li+ ion penetration procedure [3]. In particular, many studies have focused on the 1D nanostructured V2O5 in length along [010], the fastest growth direction of V2O5, because of its simplicity in synthesis [4]. However, 1D-nanostructured V2O5 has long Li+ ion diffusion distance along [010] direction, which is corresponding to the energy preferred Li+ ion diffusion path [5]. 1D diffusion along the short [010] direction in V2O5 can be the fast Li+ ion diffusion path for cathode in LIBs. Therefore, to design an optimal structure for V2O5 as cathode materials, the following conditions should be satisfied: ⅰ) structures consisted of primary nanostructured units to prevent agglomeration. ii) a short [010] length with high percentage of exposed (010) facets to shorten a Li+ ion diffusion path and facilitate the Li+ ion intercalation reactions.

In this context, we fabricated nanoplates–stacked V2O5 (Li-treated VO) through Li-treatment method in hydrothermal synthesis followed by heat treatment. Li+ ions from lithium nitrate (LiNO3), which is added to precursor solution, can inhibit the completely phase transition from xerogel to crystal during hydrothermal process, leading to formation of xerogel/crystal composite. During following heat treatment process, the cleavage and oriented attachment mechanism are accompanied, evolving nanoplates–stacked V2O5 with short [010] length and highly exposed (010) facets (Figure 1). The Li-treated VO electrodes could facilitate the fast and efficient transportation of Li+ ion into the [010] channel. In particular, 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 untreated V2O5 nanobelt (VO) electrodes. In addtion, the reversible lithium intercalation reaction and structure stability of Li-treated VO are confirmed by further analyses.

Figure 1