Improved Cycling Performance of P2-Na_0.67Ni_0.33Mn_0.67O₂ Based on Sn Substitution Combined with Polypyrrole Coating

Abstract

P2-Na0.67Ni0.33Mn0.67O2 presents high working voltage with a theoretical capacity of 173 mAh g–1. However, the lattice oxygen on the particle surface participates in the redox reactions when the material is charged over 4.22 V. The resulting oxidized oxygen aggravates the electrolyte decomposition and transition metal dissolution, which cause severe capacity decay. The commonly reported cation substitution methods enhance the cycle stability by suppressing the high voltage plateau but lead to lower average working voltage and reduced capacity. Herein, we stabilized the lattice oxygen by a small amount of Sn substitution based on the strong Sn–O bond without sacrificing the high voltage performance and further protected the particle surface by polypyrrole (PPy) coating. The obtained Na0.67Ni0.33Mn0.63Sn0.04O2@PPy (3.3 wt %) composite showed excellent cycling stability with a reversible capacity of 137.6 (10) and 120.0 mAh g–1 (100 mA g–1) with a capacity retention of 95% (10 mA g–1, 50 cycles) and 82.5% (100 mA g–1, 100 cycles), respectively. The present work indicates that slight Sn substitution combined with PPy coating could be an effective approach to achieving superior cycling stability for high-voltage layered transition metal oxides.

Improving the Na0.67Ni0.33Mn0.67O2 Cathode Material for High-Voltage Cyclability via Ti/Cu Codoping for Sodium-Ion Batteries

“…The materials have good stability and can maintain their crystal structure even in a humid environment. However, when charging and discharging to a voltage at around 4.2 V, the oxygen layer will slip and the P2–O2 type phase transition causes its capacity to rapidly decay and cause the formation of an ordered phase transition superstructure of Na + /vacancies in the material. − In view of the above problems that affect the material’s cycle stability, it can be improved by charging to a lower voltage, − surface coating modification, , and metal ion doping. − However, optimizing the cutoff range of the electrical device reduces its reversible capacity. Material surface coatings, such as an aluminum oxide coating, can effectively reduce interactions between the electrode and electrolyte and reduce electrolyte decomposition, but its rate performance is often not ideal.…”

Cation-Disordered O3-Na0.8Ni0.6Sb0.4O2 Cathode for High-Voltage Sodium-Ion Batteries

“…Rechargeable sodium-ion batteries (SIBs) have been expected as alternatives to lithium-ion batteries (LIBs) for large-scale energy-storage systems. − Among these various cathode materials, layered transitional-metal oxides (Na x TMO 2 , TM = Fe, Co, Ni, Cu, and Mn) have attracted increasing attention since the early 1980s, because of their simple synthesis, environment friendliness, and high electrochemical activity. − Generally, Na x TMO 2 is categorized into O3 and P2 phases based on the Na location (O: octahedral coordination and P: prismatic coordination) . Compared with the P2-type structure, the O3-type structure has a higher initial sodium content, which is advantageous to Na-ion full batteries .…”

Structural degradation mechanisms and modulation technologies of layered oxide cathodes for sodium‐ion batteries

“…Similarly, the Sn 4+ (radius: 0.69 Å) doping in the TM layer increases the working voltage. [95,118,119] In detail, the O3-type Na 0.7 Ni 0.35 Sn 0.65 O 2 material shows an abnormally high potential of 3.7 V (Figure 7a). Sn 4+ ([Kr] 4d 10 ) without single d electrons is unable to interact with O through its d orbitals.…”