摘要
P2-type Mn-based layered oxides are viewed as promising cathode materials for sodium ion battery by virtue of their high theoretical capacity.Considering that pure Na_(2/3)MnO_(2)suffers from poor cycling performances,Cu-substitution strategy is proposed to effectively alleviate this issue.However,the structural evolution mechanism of the Cu-containing samples still remains unclear.Herein,we propose that CuSubstitution P2-type Na_(0.66)Mn_(1-x)Cu_(x)O_(2)with enlarged lattice parameters are conducive to improving the interlayer structure stability through mitigating TMO_(2)slabs distortion.Proved by synchrotron XAS spectra and ex/in situ XRD,the expansion/contraction of MnO_6 octahedron is dramatically reduced with the increased Cu content,showing the facilitated Na ion diffusion.Furthermore,when the ratio of Cu to Mn reaches 1:4,the phase transition from P2 to P'2 type at the end of discharge can be suppressed,resulting in the improved interlayer skeleton stability.The Cu-containing samples with stable interlayer structure exhibit high capacity retention and outstanding rate performances(a capacity of 79.9 m Ah g^(-1)at 5C).This Cu-substitution strategy provides a promising approach to designing highly stable cathodes.
基金
financially supported by the Science and Technology Foundation of Guizhou Province(QKHZC[2020]2Y037)
the Science and Technology Innovation Program of Hunan Province(2020RC4005,2019RS1004)
the Innovation Mover Program of Central South University(2020CX007)。
