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Li et al. Chem Synth 2023;3:30 https://dx.doi.org/10.20517/cs.2023.16 Page 3 of 17

[18]
immobilization .

It is obvious that neither a microporous nor mesoporous structure alone could meet the requirements of a
superior Li-Se battery with a high amount of Se and recycling stability performance at the same time. Other
studies have focused on the bimodal or hierarchically porous carbons to combine the advantages of both
micropores and mesopores, and such works have been reported [19-21] . Park et al. introduced a self-sacrificed
MOF template on polyacrylonitrile to obtain mesopores by direct carbonization and micropores by further
chemical activation. They proved that the obtained porous carbon-containing simultaneously micropores
and mesopores can achieve high cycling stability because the microporous part facilitates polyselenides
trapping and high capacity, while the mesoporous part is beneficial for Se loading and electrolyte
[19]
filtration . Our group also designed various hierarchically porous carbon, such as single ZIF-8 derived
[23]
[22]
[24]
micro-meso-macropores carbon , MWCNTs weaved MOF , 3D hierarchically ordered porous carbon ,
etc. [25,26] All of them achieved good electrochemical performance. This demonstrates again that combining
micropores and mesopores in a carbon host could be a good method to achieve high Se loading and
enhance the adsorption of the polyselenides, leading to high cycle stability with a high energy density Li-Se
battery. Proper pore size distribution of the host materials is critical to achieving good electrochemical
performance of the battery. However, tailoring the ratio of the different size ranges of pores in porous
carbon materials to get good cooperation needs to be deeply researched. It is thus highly valuable to
investigate porous carbon materials with not only the best pores composition but also the optimized pore
sizes ratio to maximize the synergy effects between different size pores.

MOFs have attracted increasing attention in the field of batteries because of their high surface area, uniform
pore size, and chemical structure diversity [27-30] . However, the low electrical conductivity of MOFs resulting
in low capacity impedes their practical application. The pyrolysis of MOFs leads to much improved
conductivity while keeping their defined porosity [31-35] . The widely used MOFs for Li-Se batteries are based
on zinc clusters, such as MOF-5 and ZIF-8. The zinc atoms can be conveniently removed during
pyrolysis [14,36] . However, the low boiling point of zinc tends to break the original order of micropores.
Whereas for Co-MOF, Ni-MOF, and Fe-MOF, the formation of pores by the pyrolysis process will not be
influenced by metal evaporation, and the remaining atoms of Co, Ni, and Fe have been proven to catalyze
the discharge/charge reaction [37-40] . In addition to the advantages same as Co-, Ni-, and Fe-MOF, aluminum-
based MOFs are promising because they can form various MOFs with diverse morphologies with the same
or different ligands in different synthesis conditions.

In this work, three kinds of hierarchically micro-mesoporous carbon materials have been successfully
fabricated by facile aluminum-based MOF carbonization. The three aluminum-based MOFs originally are
composed of the same metal cluster and similar ligands but with fully different pore configurations and
volumes under different synthesis conditions. The obtained hierarchically micro-mesoporous carbon
materials derived from these aluminum-based MOFs with large surface area and pore volume,
interconnected pores, and the different proportions of micropores and mesopores. It is observed that the
different ratios of micropores and mesopores can strongly impact the electrochemical properties of Li-Se
batteries, leading to different charge-discharge capacities, rate capabilities, and recycling stability. By
tailoring the ratio of micropores and mesopores, outstanding properties such as high loading of Se, high
volume variation resistance during the electrochemical reaction, excellent fixing capacity of polyselenides,
fast electrolyte, and electron transportation can be achieved, leading to a capacity as high as 530.1 mA h g
-1
-1
after 200 cycles and excellent rate performance around 307 mA h g at 5 C. This work sheds light on a
generic strategy to boost the electrochemical kinetics and to reduce the shuttle effect by tailoring the ratio of
micropores and mesopores for Se confinement toward the practical implementation of Li-Se battery.