Elucidating the Electrochemical Behavior of a P3-type High-Na-Content Cathode
Samriddhi Saxena, Manish Badole, Hari Narayanan Vasavan, Velaga Srihari, Asish Kumar Das, Pratiksha Gami, Neha Dagar, Sonia Deswal, Pradeep Kumar, H. K. Poswal, Sunil Kumar
Abstract
Layered oxide materials are often regarded as prospective positive electrodes for Na-ion batteries owing to their superior electrochemical properties and facile synthesis. In this work, a high-Na-content P3-type cathode (NaMn 0.6 Ni 0.3 Cu 0.1 O 2; P3-NMNC) was prepared by the sol–gel technique. These materials exhibited excellent rate performance and specific capacity (discharge specific capacity at 3C being 77% of that at 0.1C). Even at 10C, the cells retained ∼45 mAh g –1 . The P3-NMNC half-cells were cycled between two voltage ranges, 2.0–4.0 V and 2.0–4.2 V, among which the former exhibited an 83% capacity retention after 200 cycles, which was vastly superior to the latter, where the degradation in the capacity dropped below 80% in just 75 cycles. The dQ/dV vs V plots revealed an irreversible peak above 4.0 V during the first desodiation process, which is attributed to an irreversible anionic redox leading to poor cyclability. Operando synchrotron X-ray diffraction studies revealed a reversible P3 ↔ P3′ ↔ O3 transformation in NMNC during sodiation–desodiation. The repeated P3′ ↔ O3 transformations resulted in strain due to changes in lattice parameters causing capacity degradation. The D N a + was determined using the galvanostatic intermittent titration technique in the order of 10 –12 to 10 –10 cm 2 s –1 . These results underscore the importance of the scarcely explored high-Na-content P3-type layered oxide cathodes toward the advancement of Na-ion batteries.