Dual anchoring effect on the surface/bulk structure of Co-free Mn-based layered oxides via titanium doping
Cobalt-free manganese-based layered oxides such as LiNi 0.5 Mn 0.5 O 2 are promising cathodes for next-generation high-energy-density lithium-ion batteries owing to their high theoretical capacity. However, their structural instability in highly delithiated states leads to considerable degradation of both the surface and bulk phases during cycling, limiting their applicability. To address this structural instability, a “pinning” and “pillaring” strategy via titanium doping is proposed herein. Titanium ions act as “pillars” in highly delithiated states in the bulk structure, enhancing phase transition reversibility during cycling. In situ and ex situ X-ray diffraction analyses confirm that Titanium doping stabilizes the bulk structure within 3.0–4.8 V at room temperature. X-ray photoelectron spectroscopy reveals that Titanium ions form a “cationic barrier” at the surface, anchoring lattice oxygen and suppressing undesired phase transformations. This dual mechanism endows the 3 % Titanium-doped material with excellent cycling stability. It exhibits an initial discharge capacity of 157.7 mA h g −1 at C/2 and retains 83.45 % of this capacity after 120 cycles. This represents a 24.17 % increase in initial capacity and a 41.30 % improvement in capacity retention compared to those of undoped LiNi 0.5 Mn 0.5 O 2 . The voltage decay rate of the doped material also reduces to 1.64 mV per cycle, indicating a 90.24 % improvement. The proposed approach is a viable strategy for advancing Cobalt-free manganese-based layered oxides for use in high-energy-density lithium-ion batteries.
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