Enhanced rate performance and specific capacity in Ti-substituted P2-type layered oxide enabled by crystal structure and particle morphology modifications

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2022-11, Vol.448, p.137662, Article 137662
• Main Authors: Vasavan, Hari Narayanan, Badole, Manish, Dwivedi, Sushmita, Kumar, Deepu, Kumar, Pradeep, Kumar, Sunil
• Format: Article
• Language: English
• Subjects: Electrochemical behavior; Layered oxides; Na-ion batteries; Rate performance; Sol-gel process
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2022.137662

Through the modifications in crystal structure and particle morphology introduced by Ti substitution, a faster Na-ion diffusion was achieved in P2-Na0.70Ni0.20Cu0.15Mn0.65O2, which significantly improved specific capacity and rate performance. [Display omitted] •Ti substitution increased the area of Na-ion conduction bottlenecks.•The aspect ratio of particles decreased from ∼8 to ∼1.•Na0.70Ni0.20Cu0.15Mn0.575Ti0.075O2 showed a capacity of 127 mAh/g at 0.1C.•Excellent capacity retention of 97% was achieved after 300 cycles at 1C. In recent years, P2-type layered oxides have received considerable attention as potential cathodes for Na-ion batteries owing to their compositional diversity, good specific capacity, and cyclability. However, poor rate performance and low-capacity retention at high discharge rates have limited their use in commercial battery applications. This study aims to mitigate this issue by synthesizing a series of structurally engineered P2-type cathode materials, through Ti substitution, with high cyclability and improved rate performance. P2-type Na0.70Ni0.20Cu0.15Mn(0.65-x)TixO2 were prepared through a sol–gel route and were characterized for their structural, electrical, and electrochemical properties In the Ti-substituted samples, the Rietveld refinement of XRD data revealed an increased size of the bottleneck area of the Na-O6 prism planes, while the SEM images showed a decrease in the aspect ratio of hexagon-type morphology of particles which facilitates faster Na-ion conduction through the material. These changes in the crystal structure and particle morphology induced by Ti substitution have significantly improved electrical and electrochemical performance compared to the parent material. The sample with x = 7.5% exhibited a specific capacity of 126 mAh/g at a discharge rate of 0.1C in the 2.00–4.25 V window, which was about 25% more than that of the undoped material. At a discharge rate of 1C, the specific capacity of Na0.70Ni0.20Cu0.15Mn0.575Ti0.075O2 was 97 mAh/g compared to 74 mAh/g for Na0.70Ni0.20Cu0.15Mn0.65O2 sample. Na0.70Ni0.20Cu0.15Mn(0.65-x)TixO2 samples also exhibited excellent cyclability, with over 95% of original capacity retained after 300 cycles. Complex impedance measurements corroborated the improved Na-ion conductivity in Ti-doped samples and an associated increase in Na-ion transference number from 0.86 for the sample with x = 0 to 0.97 for the sample with x = 0.075.