Improving the Na_0.67Ni_0.33Mn_0.67O₂ Cathode Material for High-Voltage Cyclability via Ti/Cu Codoping for Sodium-Ion Batteries

Abstract

P2-type Na0.67Ni0.33Mn0.67O2 cathode materials that show high discharge voltage and theoretical specific capacity have attracted extensive research, although the problem of rapid capacity decay under high voltage needs to be overcome. Here, a series of Na0.67Ni0.33–x Cu x Mn0.67–y Ti y O2 cathode materials were synthesized that had good cyclic stability and rate performance at a high voltage of 4.5 V. The combined analyses of Rietveld refinement X-ray diffractometer (XRD), X-ray photoelectron spectroscope (XPS), Raman, and transmission electron microscope (TEM) showed that Ti4+ and Cu2+ had been successfully incorporated into the material crystal lattice. The Ti/Cu dual-doping materials operated at a high mid-voltage of ∼3.2 V vs Na/Na+ and exhibited a reversible capacity of 93 mA·h·g–1 at 5C. The voltage step of Ti4+/Cu2+-doped materials at ∼4.2 V was clearly suppressed with increased Cu content, and NNMT-0.14Cu materials exhibited an initial discharge capacity of 153.2 mA·h·g–1 owing to Cu contributing to reversible capacity based on Cu2+/Cu3+. Galvanostatic intermittent titration technology measurements showed that’ the Na+ mobility of NNMT-0.14Cu materials was improved.

Cathode material stability enhancement for layered manganese-based sodium-ion batteries by doping titanium

“…26 Therefore, Na + can be more advantageously embedded and removed during the charging and discharging process of the batteries. 27 No significant shift in the peak of Ni2p (shown in Fig. 5c) was observed.…”

Excellent Structural Stability-Driven Cyclability in P2-Type Ti-Based Cathode for Na-Ion Batteries

“…The curve portrays a broad peak at 3.7 V, which can be attributed to the Ni 2+/4+ and Cu 2+/3+ redox couples. 58,67 On the other hand, the NNCT and NNCMT samples showed two distinct peaks for Ni 2+/4+ and Cu 2+/3+ reactions between 3.3 and 4.0 V, along with some vacancy ordering peaks, particularly in NNCM. This could be due to a comparatively higher disordering in the NNCT structure that inhibits Na-vacancy ordering.…”

Recent Advances on High‐Capacity Sodium Manganese‐Based Oxide Cathodes for Sodium‐ion Batteries

“…) [26‐28] and/or electrochemically inactive elements (Mg 2+ , Ca 2+ , Ti 4+ , Cu 2+ , etc. ) [29‐32] have been extensively developed. Among these materials, the Mn−Fe based Na 2/3 [Mn x Fe 1‐x ]O 2 materials have the advantages of sufficient raw materials, low price and environmental friendliness, thus greater application potential.…”

“…Pei et al. prepared Ti/Cu co‐doped Na 0.67 Ni 0.33 Mn 0.67 O 2 cathode material, which possesses excellent rate performance and cycle stability [31] . Since Mn 4+ (0.53 Å) and Ti 4+ (0.66 Å) have similar ionic radii and valence, Ti 4+ ions can be homogeneously doped into the manganese layer without damaging the P2‐type layered structure, therefore restraining phase transformation and oxygen loss.…”