Direct Electrodeposition Li-V-Mn-Ni-O Composite Films on Al Foils Toward Li Ion Battery Cathode Materials
Authors: Inoue Takato , Kure-Chu Song-Zhu Shochiku , Moriguchi Yukihisa , Miyazaki Reona , Hihara Takehiko , Yashiro Hitoshi 
Published: February 2020

Nowadays, Lithium-ion secondary batteries (LIBs) are considered as indispensable power sources in our daily life, because they are widely used in various mobile electronic products such as smart phones, portable computers, and recently, extended to electric vehicles (EVs). Commercial LIB comprises LiCoO2 cathode with maximum capacity of 140 mAh g−1. V2O5 has been widely investigated because of its high theoretical capacity of 294 m Ah g−1, low cost and abundant sources on the earth crust. However, problems, such as severe capacity fading and poor rate capability, prevent its use in commercial LIBs. So far, much effort has been done to improve the cycling stability of V2O5 by doping Ag, Cu, Zn, and Mn through sol-gel process, beam evaporation, hydrothermal reaction, etc.

In this study, we proposed a novel hybrid electrodeposition to fabricate Li-V-Mn-Ni-O composite films directly on Al foils in ethanol-water bath containing V5+、Ni2+, Mn2+ ions as sulfate or chloride, with and without adding Li+ ions. Before electrodeposition, an electro-etching pretreatment was used to enhance the adhesion between the Al substrate and the electrodeposits. The microstructures, chemical composition, and crystalline structure of the anodized specimens before and after annealed were investigated FE-SEM (EDS), TEM (FIB), XRD, XPS, and GD-OES. Moreover, the cyclic voltammetric behaviors, electrochemical impedance, and charge-discharge performances of various nanostructured composite films on Al foils were investigated as binder-free cathode materials for Li ion secondary batteries.

Figs. 1a-b show the representative surface FE-SEM images of as-deposited Li-V-Mn-Ni-O composite films on Al foils. The composite films coated uniformly on electro-etched Al foils irrespectively of the rough surface, composing of nano-flakes (Fig.1a) and nanoparticles (Fig.1b). According to EDS analysis, the compositions of V, Mn, and Ni components except for O were 69 at%–23 at%–8 at% and 45 at%–21 at%–34 at% for the nano-flake and nanoparticle regions respectively. The XPS analysis confirmed that the vanadium existed mainly as mixed V4+ and Mn5+ oxides, manganese as mixed Mn2+ and Mn4+ oxides, and nickel as metallic Ni and Ni2O3 for the composite films before and after heated at different temperatures. Moreover, it was found from GD-OES measurements that Li also included in the V-Mn-Ni-O composite films through a co-deposition process and/or a Li+ insertion/dis-insertion process.

Fig. 1c shows the cyclic voltammograms (CVs) of Li-V-Mn-Ni-O composite films after being heated at 723 and 923 K for 2 h, as cathodes with Li-metal as the counter and reference electrodes, in the potential range 2.0–4.5 V vs. Li/Li+, at a slow scan rate of 0.1 mV s-1. Two main anodic peaks (Li-extraction) at around 3 and 4 V are noted for both specimens heated at 723 and 923 K, which can be ascribed to the Li extraction reactions from vanadium oxides and V-Mn-Ni-O compounds. Especially, the current density of 4-V peak increased with heating temperature, indicating the transformation and crystallization of V-Mn-Ni-O compounds from vanadium oxides. Furthermore, the composite films after being heated at different temperatures worked well as binder-free and conductor-free cathode materials for LIBs in galvanostatic charge/discharge tests, and the results will be reported on the meeting.

Figure 1