Hybrid CoMoO3/CoMoO4 nanorods for enhanced lithium-ion battery performance

Abstract

Electrode materials that rely on conversion reactions for lithium-ion batteries (LIBs) possess high energy densities. However, a key issue in their design is bolstering their stability and minimizing volume variations during lithiation and delithiation. Herein, an effective strategy was devised to fulfill the fully reversible conversion reaction for lithium storage in CoMoO4 through the hybridization of CoMoO3. CoMoO3/CoMoO4 with a nanorod structure was synthesized via one-step annealing treatment after a solvothermal process. In such a structure, the CoMoO3/CoMoO4 nanorod can considerably boost mechanical robustness and offer ample space to counteract volume fluctuations throughout successive cycles owing to the cooperative interaction between CoMoO3 and CoMoO4. CoMoO3/CoMoO4 exhibited superior lithium-storage capacity (919.6 mAh/g at 0.1 A/g after 200 cycles) and cycling stability (683.4 mAh/g at 1 A/g after 600 cycles). CoMoO3/CoMoO4 showed a high potential as an anode material for LIBs.

1. Introduction

Transition-metal oxides accumulate lithium through conversion reactions, and they are reduced to metallic nanocrystals within a Li2O matrix during the lithiation phase and re-oxidized to their original form during delithiation [1–5]. In addition, some transitional-metal oxides further accommodate lithium via alloying reactions after the formation of metallic nanocrystals, which provides extra capacity [6–10]. As a result, electrode materials based on metal oxides typically have theoretical specific capacities ranging from 600 to 1000 mAh/g, which surpass those of traditional graphite by a factor of 1.5–3. Moreover, bimetal oxides demonstrate better performance than monometal oxides and are thus well documented as substitutes for anodes with elevated capacities for lithium-ion batteries (LIBs) [11–13].

Among various bimetal oxides, CoMoO4 is a prospective electrode for LIBs, and it is characterized by its theoretical capacity (980 mAh/g) and advantageous properties, including high conductivity and a range of oxidation states from molybdenum [14–19]. However, this material faces challenges, such as its sluggish reaction kinetics and poor cycling stability, which are often attributed to large volume changes and the configuration of a fragile solid–electrolyte interphase (SEI) layer.

The exceptional properties of nanostructure materials include swift migration channels for electrons and lithium ions, a broad interface that enables the interaction of the electrode with the electrolyte, paired with superior pliability and durability to manage the strain resulting from Li+ insertion/extraction. Therefore, the above advantages make nanostructuring a powerful strategy for addressing the aforementioned challenges for CoMoO4. Yu et al. [15] reported a hierarchically porous three-dimensional CoMoO4 electrode that delivers a specific capacity of 894 mAh/g after 100 cycles. Porous CoMoO4 nanorod reported by Wang et al. [20] delivered 603 mAh/g after 300 cycles at 0.4 A/g. They demonstrated exceptional lithium-storage performance after the design and fabrication of CoMoO4 with various nanostructures. The introduction of carbon clamping shell layers is another strategy for preventing severe capacity fading, particularly at high current [21–23]. Furthermore, the large surface area of the modified anode materials can increase the number of ion storage sites and promote the penetration of the electrolyte, which enhances the specific capacity and the rate of ion transport [24]. As evidenced by researches [25–28], the association of CoMoO4 with carbon materials realized improved electrochemical performance over pure CoMoO4. However, carbon coating is often tedious and may lower the tap density or initial Coulombic efficiency [29].

A reported novel strategy introduces highly active nanosized Co-based oxides to stabilize structured electrodes and promote reversible insertion and extraction reactions in an atomically homogeneous manner [30–35]. Thus, seeking suitable Co-based oxide to decorate CoMoO4 should be a powerful strategy to advance lithium-storage capacity, but such a task remains highly challenging. Wang et al. [30] reported a fully reversible MoO3/CoMoO4 was achieved through the introduction of Co-based oxide into CoMoO4. In addition, valence-rich Mo (IV, V) oxides are ...