Fast and scalable synthesis of durable Na0.44MnO2 cathode material via an oxalate precursor method for Na-ion batteries

Abstract

Na0.44MnO2 has aroused global interest as a promising cathode material for sodium ion batteries due to its unique tunnel structure. Rod-like Na0.44MnO2 is synthesized here via a simple, fast and environment-friendly oxalate precursor-based process, and the electrochemical performances, as well as the structural evolution within the electrode redox process and the chemical mechanism for material synthesis, are systematically investigated. The Na0.44MnO2 material prepared at 900 °C for 3 h (denoted as NMO-9003) possesses the highest reversible capacity of 120 mAh g−1 at 0.2 C and an optimal rate capacity of 106 mAh g−1 at 1 C, while its long-term capacity retention is 86% after 500 cycles at 20 C, indicating superior structural reversibility. In addition, the NMO-9003 sample shows the fastest cationic diffusion rate at approximately 1.2 × 10−13 cm2 s−1. The density functional theory (DFT)-based calculation is adopted to explore the lattice variation of Na0.44MnO2 upon the electrode process, which confirms that the host structure bears a minor volume change approximately 7% from 2.0 to 3.8 V, well demonstrating the origin of excellent reversibility.