Pillared-Layer Metal–Organic Frameworks for Improved Lithium-Ion Storage Performance

Abstract

Recently, more and more metal-organic frameworks (MOFs) have been directly used as anodic materials in lithium-ion batteries, but judicious design or choice of MOFs is still challenging for lack of structural-property knowledge. In this article we propose a pillared-layer strategy to achieve improved Li-storage performance. Four Mn(II) and Co(II) MOFs with mixed azide and carboxylate ligands were studied to illustrate the strategy. In these 3D MOFs, layers (1, 3, and 4) or chains (2) with short bridges are linked by long organic spacers. All the MOFs show very high lithiation capacity (1170-1400 mA h g at 100 mA g) in the first cycle owing to the rich insertion sites arising from the azide ion and the aromatic ligands. After the formation cycles, the reversible capacities of the anodes from 1, 3, and 4 are kept at a high level (580-595 mA h g) with good rate and cycling performance, while the anode from 2 undergoes a dramatic drop in capacity. All the MOFs lose the crystallinity after the first cycle. While the amorphization of the chain-based framework of 2 leads to major irreversible deposit of Li ions, the amorphous phases derived from the pillared-layer frameworks of 1, 3, and 4 still retain rich accessible space for reversible insertion and diffusion of active Li ions. Consistent with the analysis, electrochemical impedance spectra revealed that the pillared-layer MOFs led to significantly smaller charge-transfer resistances than 2. Soft X-ray absorption spectroscopy suggested that no metal conversion is involved in the lithiation process, consistent with the fact that the isomorphous Co(II) (3) and Mn(II) (4) MOFs are quite similar in anodic performance.

Solvent‐Driven Reversible Phase Transition of a Pillared Metal–Organic Framework

“…Powder X‐ray diffraction (PXRD) was performed by using a TTRIII X‐30 ray diffractometer (Rigaku, Japan) with Cu Kα radiation at 40 kV and 200 mA. Scanning electron microscopy (SEM) imaging was performed with a QUANTA200 scanning electron microscope (FEI, USA) operated at 30 kV, and transmission electron microscopy (TEM) imaging was performed with a JEM 2100 (TEM, JEOL, Japan) . UV/Vis absorption spectroscopy was performed by using a UV‐240IPC UV/Vis spectrometer (Shimadzu, Japan).…”

“…Scanning electron microscopy (SEM) imaging was performed with aQ UANTA200 scanning electron microscope (FEI, USA) operated at 30 kV,a nd transmission electron microscopy (TEM) imaging was performed with aJ EM 2100 (TEM, JEOL, Japan). [35] UV/Vis absorption spectroscopy was performed by using aU V-240IPC UV/Vis spectrometer (Shimadzu, Japan). FTIR spectra were recorded in the range 4000-400 cm À1 using aT hermo Nicolet spectrometer with KBr pellets.…”

“…[25,26] By contrast, 3D MOFs can also be exfoliated into nanoplatelets of 2D structures by meanso fm echanical treatment, such as sonication, ball milling, and heating. [27][28][29][30] Althoughm any MOFs possessalayered structure (typically pillared MOFs), [31][32][33][34][35] the reversible structuralt ransformation between 3D architectures and 2D morphologies of MOFs remains al argely unexplored area,p robablya saresult of the low stability of 2D MOFs, which are prone to degradation under strongm echanical forces. This meanso vercoming the interlayer interactions during the exfoliationp rocess.…”

Bimetallic zeolite imidazolate framework for enhanced lithium storage boosted by the redox participation of nitrogen atoms

“…Recently, conjugated carboxylates based MOFs, such as Co-BDC [7,8], Mn-BDC [9], Fe-BDC [10,11], Mn-BTC [12], CoBTC [13], Cu-BTC [14] and Fe-BTC [15], are being employed in LIBs and have attracted tremendous attention for their high performances. Further researches indicate that lithium is inserted into organic moiety in these MOFs and it is deduced that the electron withdrawing effect of the conjugated carboxylates should be the main impetus in storing lithium-ions [12][13][14][15][16][17][18][19]. However, MOFs-based electrodes with other kinds of organic linkers are seldom employed in LIBs for the lack of highly-active lithiation sites.…”

Metal-Organic Frameworks for Batteries

“…36,100 Morphology, particle size, surface area, and coordinated solvents of MOFs can influence their electrochemical behavior in LIBs. Various morphologies, such as hollow microspherical, 29 lamellar, 34 shell-like, 33 and pillar-layer 101 morphologies, have been reported, showing porous structures with abundant inner voids, which is beneficial to electrolyte penetration, lithium-ion transportation, and volume-variation accommodation during the charge/discharge processes. The particle size and homogeneity can influence the surface area of MOFs, which has two opposite impacts on the electrochemical behavior.…”