2.1 Pristine MOFs
Pristine MOFs are often described as such—that is,
they refer to the initial frameworks before any post-
synthetic treatments or functionalization. High purity
in pristine MOFs is essential for maintaining MOFs'
intrinsic properties: high surface areas, tunable
porosity, and diverse chemical functionality in
different applications, such as gas storage, separation,
catalysis, and sensing (Li et al, 2020). Pristine MOFs
have some properties that are very attractive to energy
storage researchers for use as electrode materials in
batteries. Most conventional battery materials suffer
from some problems, which include low capacity,
poor cycling stability, and slow kinetics. Pristine
MOFs, with their high surface areas and tunable pore
structures, offer promise for addressing these
challenges by providing more active sites for
electrochemical reactions and assisting in ionic
transport. Applications have been made with MOF in
LIB using their electrode materials.
MOFs can serve as both cathode and anode
materials. For instance, the high porosity of MOFs
can accommodate large volumes of lithium ions,
enhancing the battery's capacity. Additionally, the
structural flexibility of MOFs can mitigate the
volume changes during lithiation and DE-lithiation
processes, thus improving the cycling stability (Li et
al, 2019). Pristine MOFs such as MIL-101(Cr) and
MOF-177 have been explored for their excellent
capacity retention and rate performance as cathode
materials in LIBs (Liu et al, 2019).
A significant shortcoming of pristine MOFs as
electrodes in lithium-ion batteries is their relatively
low electrical conductivity. Generally, MOFs consist
of metal ions or clusters coordinated to organic
ligands with a high porosity configuration. This high
porosity is beneficial for ion transport. However,
bringing about an inner limitation in electron
transport due to the organic nature of the ligands and
significant possible separation between the metal
centers (Rao et al, 2021).
Above all, directly choosing pristine MOFs
materials to produce LIBs electrodes is not an
efficient method to enhance traditional LIBs
performance.
2.2 MOFs in Cathode Materials
One of the primary advantages of MOFs as cathode
materials is their high specific surface area, which
contributes to rapid lithium-ion diffusion and
improves the overall capacity and cycling
performance of the battery. The structure of MOFs,
consisting of metal nodes connected by organic
linkers, creates a highly porous network that can store
and release lithium ions efficiently. This
characteristic is particularly advantageous for
enhancing the energy density and power performance
of lithium-ion batteries.
Zhou et al., (2020) had studied on demonstrating
the effectiveness of a nickel-based MOF (Ni-MOF)
as a cathode material. The Ni-MOF showed a high
initial discharge capacity of 182 𝑚𝐴ℎ/𝑔 at 0.1 𝐶 ,
which remained at 155 𝑚𝐴ℎ/𝑔 after 100 cycles,
indicating excellent capacity retention. The high
capacity and good cycling stability were attributed to
the large surface area and uniform pore structure of
the Ni-MOF, which was helpful to efficient lithium-
ion transport and minimized structural degradation
during cycling. The specific surface area of the Ni-
MOF used in this researching was measured at
1320 𝑚²/𝑔 , significantly higher than that of
conventional cathode materials like LiCoO2, which
typically have surface areas below 50 m²/g (Sun et al,
2020).
Going through other literatures, it is found that a
cobalt-based MOF (Co-MOF) was employed as a
cathode material and showed promising results. The
Co-MOF delivered an initial capacity of 160 𝑚𝐴ℎ/𝑔
at 0.1 𝐶, maintaining 140 𝑚𝐴ℎ/𝑔 after 200 cycles.
This performance is attributed to the robust
framework of the Co-MOF, which helps maintain
structural integrity during the lithium-ion
intercalation/deintercalation process. The Co-MOF
used in this study also exhibited a high surface area
of 1250 𝑚²/𝑔 , which contributed to its superior
electrochemical performance (Tarascon & Armand,
2001).
MOFs can also act as conductive additives in
cathode composites. Traditional cathode materials
like LiCoO2 suffer from poor electrical conductivity,
which limits their rate capabilities. Incorporating
MOFs can address this issue by providing a
conductive matrix that enhances electron transport
within the electrode. For example, a study by Chen et
al. (2018) incorporated a conductive MOF into a
LiCoO2 cathode, resulting in a composite with
significantly enhanced conductivity. The
LiCoO2/MOF composite exhibited a discharge
capacity of 190 𝑚𝐴ℎ/𝑔 at 0.1 𝐶 , compared to
150 𝑚𝐴ℎ/𝑔 for pure LiCoO2. Moreover, the
composite retained 92% of its initial capacity after
500 cycles, compared to 80% for the pure LiCoO2.