2015 Fiscal Year Annual Research Report
Metal-Organic Framework-based Cathode Active Materials for Lithium Batteries
| Project/Area Number |
15H06265
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| Research Institution | Nagoya University |
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Principal Investigator |
張 中岳 名古屋大学, 物質科学国際研究センター, 助教 (00755704)
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| Project Period (FY) |
2015-08-28 – 2017-03-31
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| Keywords | Metal-Organic Framework / Energy storage / Battery / Hybrid material |
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| Outline of Annual Research Achievements |
In this fiscal year, we have prepared the nanocrystals of Cu(2,7-AQDC) and Cu(2,6-AQDC) . Their electrochemical performances have been tested. Comparing with the pristine MOF crystals which are ground to ~1um, the nanocrystals with a size distribution of 200-500nm did exhibit a moderately improved battery performance. The capacity fade in first 20 cycles is slightly smaller than the case of original MOF. (130mAh/g vs. 105mAh/g for 20th cycle) But the improvement is not significant and we didn't achieve the 100% capacity retention with the nanoparticles.
On the other hand, we also attempted using functionalized carbon nanotubes to grow the crystal of Cu(2,7-AQDC) MOF. We are expecting the carbon nanotubes to be embedded in the crystals of MOF, but the microscopic data suggested what we obtained is a simple mixture of carbon nanotubes and micro-sized crystals. The cyclic voltammetry indicated an enhanced stability of the hybrid material, and the capacity after 50 cycles was improved by >20%.
Although the battery performance of upper mentioned materials didn't meet our initial expectation, the current result does suggest the nanoscale morphology and the hybridization with carbon material will enhance the electrochemical efficiency. Therefore, further efforts could be invested on the development of hybrid MOF materials, such as MOF/reduced graphene oxides.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We have attempted the proposed material: the nanoparticles of redox active MOFs and the MOF/carbon nanotube hybridization. However we have encountered two issues: first, since the redox active Cu-MOF we used had 2-D structure instead of a 3D architecture, it is difficult to achieve the desired material: a pristine crystal that is penetrated by multiple carbon nanotubes. The microscopic study indicated we obtained nanoparticles of MOF on an amorphous substrate. Second, compared with the pristine MOF, the hybridized material did exhibit an improved battery performance in terms of stability and capacity, while the improvement didn't really meet the initial expectation. We still observed the capacity fade within a small cycle number. Therefore, it is challenging to obtain outstanding properties with this pre-reported hybridization method.
Therefore, we decided to bypass this section and put some effort on the other type of hybridization and modulation method to manipulate the electrochemical properties of MOFs. Also, we employed the equipment to test the Li-S batteries, therefore, we decided to investigate the performance of crystalline porous materials, which are used as a sulfur host in the cathode of Li-S batteries.
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| Strategy for Future Research Activity |
Based on the current result, two directions will be majorly tested in the next fiscal year.The first one is, since the currently obtained MOFs containing electron accepting groups, small molecules with strong electron donating effect will be introduced into the pores of MOFs, forming charge transfer complexes. By this method, we should be able to modulate the electronic conductivity of MOFs with different guests, meanwhile, the battery performance, especially the density of energy storage will be promoted comparing with the pristine material.
The other proposed research topic is to develop novel porous materials with functional groups and unique morphology and use them as hosts of sulfur storage. Li-S batteries is a promising technology in the future market of electrical energy storage devices for the cheap cost and large energy capacity. The main issue of current materials is the fast capacity fade of batteries when they are reused many times. This is caused by the dissolve and escape of sulfur the from cathodes. By introducing binding groups which may form covalent bond with polysulfides, MOFs may act as a strong sulfur binder and host, which could be used as a cathode active material of sulfur batteries. Moreover, with designed morphology such as thin films or hollowspheres, the MOF-based devices may accomodate large amount of sulfur without losing them significantly during the electrochemical process.
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