Unsaturated coordination modes of Mn/V in manganese vanadate: Inner capture and surface migration of zinc ions for high performance zinc-ion battery

It was synthesized Mn 0·2 V 2 O 5 (H 2 O)·H 2 O (MnVO) porous microflowers and Ti 0·055 V 2 O 5 (H 2 O) 2 ·H 2 O (TiVO) nanosheets. Rietveld refinements and high-angle annular dark-field (HAADF)-scanning transmission election microscope (STEM) reveal they are both constructed by two-dimensional (2D) V-O-V monolayers, lamellar hydrated metal ions and uncoordinated water molecules, in which all the V centers exhibit unsaturated coordination modes. Density functional theory (DFT) calculation proves that the exposed unsaturated V centers on the MnVO (001) surface can boost Zn 2+ migration along the surface with a low barrier of 0.61 eV. Therefore, MnVO shows a dominant surface-controlled capacity. MnVO displays excellent Zn 2+ storage behavior (435 mAh g -1 at 0.1 A g -1 ) with a capacity retention of 96.4 % after 1000 discharge/charge cycles at 5 A g -1 , which is superior to TiVO. And MnVO and TiVO both show higher capacities than the commercial V 2 O 5 . Ex situ characterizations of MnVO discover a conversion of MnVO → Zn m (MnVO) and a partial phase transformation mechanism of MnVO → Zn 3 (OH) 2 V 2 O 7 ·2H 2 O during discharge/charge process. And DFT calculations reveal the intercalation of Zn 2+ into some sites in the inner channel of MnVO is irreversible, leading to the accumulation of Zn 2+ with almost unchanged interlayer spacing. • Mn 0 · 2 V 2 O 5 (H 2 O)·H 2 O (MnVO) exhibits excellent Zn 2+ storage behavior. • Rietveld Refinement reveals MnVO is constructed by V–O–V monolayer and {Mn(H 2 O) 4 } 2+ . • The Mn/V centers in MnVO are both unsaturated coordinated. • The conversion of MnVO .→ Zn m (MnVO) doesn't change the interlayer spacing obviously. • DFT simulation confirms a low Zn 2+ migration barrier on MnVO (001) surface.