Infrared Spectroscopy Signatures of Aluminum Segregation and Partial Oxygen Substitution by Sulfur in LiNi_0.8Co_0.15Al_0.05O₂

Substitution of aluminum in nickel-rich layered oxides plays a vital role in structural and thermal stability. Hence comprehension of aluminum distribution in nickel-rich layered oxides such as LiNi_0.8Co_0.15Al_0.05O₂ (LNCA) is crucial. However, investigation of aluminum distribution in LNCA is extremely challenging, and sophisticated techniques such as ²⁷Al and ⁷Li MAS NMR, individual atom probe tomography, X-ray and neutron diffraction, and SQUID magnetic susceptibility measurements are recently employed. We demonstrate the use of a combination of versatile techniques such as X-ray diffraction, energy dispersive X-ray analysis mapping, and vacuum Fourier transform infrared spectroscopy to identify the distribution of aluminum and anion substitution at the oxygen site in LNCA synthesized by the coprecipitation-assisted solid-state reaction. The influence of metal salts used for the coprecipitation of α/β interstratified Ni_{1–<i>x</i>–<i>y</i>}Co_<i>x</i>Al_<i>y</i>(OH)₂ (<i>x</i> = 0.15, <i>y</i> = 0/0.05) on anion substitution at the oxygen site in LNCA was investigated. While no anion substitution is observed in LNCA synthesized using nitrate metal salts, sulfur is substituted at the oxygen site when sulfate metal precursors are used. The distribution of Al in LNCA is uniform when Al­(OH)₃, NiCo­(OH)₂ are used as Al and Ni, Co precursors, respectively, during the solid-state reaction with LiOH. Segregation of Al is observed in LNCA when α/β interstratified Ni_0.8Co_0.15Al_0.05(OH)₂ is used as Ni, Co, and Al precursor. Electrochemical properties of LNCA are strongly influenced by Al distribution and sulfur substitution. While uniform Al distribution reduces the voltage fading due to lower Ni²⁺ concentration in Li⁺ site, sulfur substitution increases the cyclic stability

Dual Stabilization and Sacrificial Effect of Na₂CO₃ for Increasing Capacities of Na-Ion Cells Based on P2-Na_<i>x</i>MO₂ Electrodes

Sodium ion battery technology is gradually advancing and can be viewed as a viable alternative to lithium ion batteries in niche applications. One of the promising positive electrode candidates is P2 type layered sodium transition metal oxide, which offers attractive sodium ion conductivity. However, the reversible capacity of P2 phases is limited by the inability to directly synthesize stoichiometric compounds with a sodium to transition metal ratio equal to 1. To alleviate this issue, we report herein the <i>in situ</i> synthesis of P2-Na_<i>x</i>MO₂ (<i>x</i> ≤ 0.7, M = transition metal ions)-Na₂CO₃ composites. We find that sodium carbonate acts as a sacrificial salt, providing Na⁺ ion to increase the reversible capacity of the P2 phase in sodium ion full cells, and also as a useful additive that stabilizes the formation of P2 over competing P3 phases. We offer a new phase diagram for tuning the synthesis of the P2 phase under various experimental conditions and demonstrate, by <i>in situ</i> XRD analysis, the role of Na₂CO₃ as a sodium reservoir in full sodium ion cells. These results provide insights into the practical use of P2 layered materials and can be extended to a variety of other layered phases