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A High‐Performance Primary Nanosheet Heterojunction Cathode Composed of Na 0.44 MnO 2 Tunnels and Layered Na 2 Mn 3 O 7 for Na‐Ion Batteries
Author(s) -
Zheng Peng,
Su Jiaxin,
Wang Yibing,
Zhou Wei,
Song Jiajia,
Su Qinmei,
ReevesMcLaren Nik,
Guo Shouwu
Publication year - 2020
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.201903543
Subject(s) - faraday efficiency , nanosheet , heterojunction , oxygen evolution , materials science , cathode , analytical chemistry (journal) , electrochemistry , nanotechnology , chemical engineering , electrode , chemistry , optoelectronics , chromatography , engineering
Owing to its large capacity and high average potential, the structure and reversible O‐redox compensation mechanism of Na 2 Mn 3 O 7 have recently been analyzed. However, capacity fade and low coulombic efficiency over multiple cycles have also been found to be a problem, which result from oxygen evolution at high charge voltages. Herein, a Na 0.44 MnO 2 ⋅ Na 2 Mn 3 O 7 heterojunction of primary nanosheets was prepared by a sol‐gel‐assisted high‐temperature sintering method. In the nanodomain regions, the close contact of Na 0.44 MnO 2 not only supplies multidimensional channels to improve the rate performance of the composite, but also plays the role of pillars for enhancing the cycling stability and coulombic efficiency; this is accomplished by suppressing oxygen evolution, which is confirmed by high‐resolution (HR)TEM, cyclic voltammetry, and charge/discharge curves. As the cathode of a Na‐ion battery, at 200 mA g −1 after 100 cycles, the Na 0.44 MnO 2 ⋅ Na 2 Mn 3 O 7 heterojunction retains an 88 % capacity and the coulombic efficiency approaches 100 % during the cycles. At 1000 mA g −1 , the Na 0.44 MnO 2 ⋅ Na 2 Mn 3 O 7 heterojunction has a discharge capacity of 72 mAh g −1 . In addition, the average potential is as high as 2.7 V in the range 1.5–4.6 V. The above good performances indicate that heterojunctions are an effective strategy for addressing oxygen evolution by disturbing the long‐range order distribution of manganese vacancies in the Mn‐O layer.