• 
  Liangtao, Y.; Yanan, S.; Adelhelm, P.: Electrochemical Properties of Layered Na_xNi_x/2Mn_1-x/2O₂ (0.5 ≤ x ≤ 1.1) with P3 Structure as Cathode for Sodium-Ion Batteries. Energy Technology 10 (2022), p. 2101121/1-7

10.1002/ente.202101121
Open Access Version

Abstract:
The Na properties of Ni and Mn containing layered oxides of the type Na x Ni x/2Mn1−x/2O2 are explored between Na contents of 0.5≤x≤1.1. Charge balance is maintained by adjusting the Ni/Mn ratio. X-ray diffraction and scanning electron microscopy are used to characterize the structure and morphology. The primary phase for all as-synthesized materials is P3, especially at Na contents below x ≤ 0.8. Samples with a Na content of x ≥ 0.9 lead to the formation of Na and Ni secondary phases. The Na storage properties are studied in half cells with two different voltage windows between 1.5–4.0 V and 2.2–4.5 V (vs Na+/Na). Ni and Mn redox are active between 1.5 and 4.0 V accompanying three voltage plateaus at 3.7, 3.0, and 2.1 V, respectively. An additional high-voltage plateau (>4.0 V) is observed when increasing the cutoff voltage to 4.5 V. The initial Na content has a strong influence on the discharge capacity which ranges from 90 mAh g−1 (x = 1.1) to 210 mAh g−1 (x = 0.6). C-rate tests up to 2C and cycle life over 150 cycles are discussed. Overall, the composition Na0.6Ni0.3Mn0.7O2 shows the most favorable properties with respect to capacity retention, rate capability, and initial Coulomb efficiency.