Facile construction of two-dimensional coordination polymers with a well-designed redox-active organic linker for improved lithium ion battery performance

Article abstract of DOI:10.1007/s11426-018-9370-0

A well-designed redox-active organic linker, pyrazine-2,3,5,6-tetracarboxylate (H₄pztc) with brimming active sites for lithium ions storage was utilized to construct coordination polymers (CPs) via a facile hydrothermal reaction. Those two isostructural two-dimensional (2D) CPs, namely [M₂(pztc)(H₂O)₆]_n (M=Co for 1 and Ni for 2), delivered excellent reversible capacities and stable cycling performance as anodes in lithium ion batteries. As demonstrated in electrochemical studies, 1 and 2 can achieve highly reversible capacities of 815 and 536 mA h g^?1 at 200 mA g^?1 for 150 cycles, respectively, best performed for the reported 2D-CP-based anode materials. The electrochemical mechanism studies showed that the remarkable performances can be ascribed to the synergistic Li-storage redox reactions of metal centers and organic moieties. Our work highlights the opportunities of using a well-designed organic ligand to construct low-dimensional CPs as new type of electrode materials for advanced lithium ion batteries.

Full text of DOI:10.1007/s11426-018-9370-0

SCIENCE CHINA
Chemistry
•ARTICLES•
https://doi.org/10.1007/s11426-018-9370-0
SPECIAL ISSUE: Dedicated to the 100th Anniversary of Nankai University
Facile construction of two-dimensional coordination polymers with
a well-designed redox-active organic linker for improved lithium
ion battery performance
Jingwei Liu1, Lin Zhang1, Huanhuan Li1, Peng Zhao1, Peng Ren2, Wei Shi1* & Peng Cheng1,3*
1Department of Chemistry, Key Laboratory of Advanced Energy Materials Chemistry of Ministry of Education, College of Chemistry,
Nankai University, Tianjin 300071, China;
2School of Science, Harbin Institute of Technology (Shenzhen), Shenzhen 518055, China;
3Collaborative Innovation Center of Chemical Science and Engineering (Tianjin), Nankai University, Tianjin 300071, China
Received August 22, 2018; accepted October 16, 2018; published online January 7, 2019
A well-designed redox-active organic linker, pyrazine-2,3,5,6-tetracarboxylate (H4pztc) with brimming active sites for lithium
ions storage was utilized to construct coordination polymers (CPs) via a facile hydrothermal reaction. Those two isostructural
two-dimensional (2D) CPs, namely [M2(pztc)(H2O)6]n (M=Co for 1 and Ni for 2), delivered excellent reversible capacities and
stable cycling performance as anodes in lithium ion batteries. As demonstrated in electrochemical studies, 1 and 2 can achieve
highly reversible capacities of 815 and 536 mA h g−1 at 200 mA g−1 for 150 cycles, respectively, best performed for the reported
2D-CP-based anode materials. The electrochemical mechanism studies showed that the remarkable performances can be
ascribed to the synergistic Li-storage redox reactions of metal centers and organic moieties. Our work highlights the opportu-
nities of using a well-designed organic ligand to construct low-dimensional CPs as new type of electrode materials for advanced
lithium ion batteries.
two-dimensional coordination polymers, anode materials, lithium ion battery
Citation:
Liu J, Zhang L, Li H, Zhao P, Ren P, Shi W, Cheng P. Facile construction of two-dimensional coordination polymers with a well-designed redox-active
organic linker for improved lithium ion battery performance. Sci China Chem, 2018, 61, https://doi.org/10.1007/s11426-018-9370-0
1 Introduction
materials including metal oxides/sulfides, carbon materials,
metallic alloys have been exploited as alternatives to the
traditional graphite anodes for improving electrochemical
performance [6–8]. There is a lot of room to investigate
anode materials with higher capacity, excellent rate cap-
ability and long cycling performance.
Coordination polymers (CPs) are crystalline materials
composed of one-dimensional (1D), two-dimensional (2D),
or three-dimensional (3D) ordered networks assembled by
joining metal nodes with preferable organic linkers [9].
Metal-organic frameworks (MOFs) are subfamily of CPs,
with the characteristic of porous structure [10]. Due to the
inherent superiority of easy preparation with wide synthesis
procedures, controllable porosities and structures, CPs and
To satisfy the increasingly urgent demands for energy, en-
ormous efforts have been made to exploit renewable and
pollution-free resources [1,2]. Lithium ion batteries (LIBs)
have become one of the most significant devices for elec-
trical energy storage in consumer electronics and electric
vehicles, owing to their high energy capacity, environmental
compatibility, and no memory effect during cycling pro-
cesses. However, the energy and power densities of LIBs can
hardly fulfill the requirements for the large-scale electrical
applications [3–5]. As a result, a wide range of functional
*Corresponding authors (email: shiwei@nankai.edu.cn; pcheng@nankai.edu.cn)
© Science China Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019
chem.scichina.com link.springer.com

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Liu et al. Sci China Chem
MOFs have shown great performance in a variety of appli-
cations, such as gas storage and separation, drug delivery,
chemical sensing and catalysis [11]. Recently, the applica-
tions of pristine MOFs, MOF-composites, and MOF-derived
materials for energy storage and conversion are burgeoning
[12]. In particular, pristine CPs and MOFs have been directly
utilized as electrodes for the improvement of LIBs perfor-
mance [13]. MOF-177 was initially investigated as anode
materials of LIBs in 2006 [14]. Albeit the poor cycling sta-
bility and limited storage capacity, this pioneering work has
boosted the constant discovery of CPs or MOFs as advanced
anode materials for LIBs with superb electrochemical
properties. After that, other MOFs, such as Mn-LCP,
Zn3(HCOO)6, and Fe-MIL-88B have also been reported [15–
17]. According to the previous studies, the electrochemical
reaction mechanisms of lithiation/delithiation in CPs can be
divided into two types. (1) Redox or conversion type: the
redox involvement of metal ions and functional groups or
atoms (carboxyl groups, anime groups and N atoms) of or-
ganic ligands [18]; (2) insertion type: Li-ions stored in the
pores or the conjugated aromatic rings [12,19].
Inspired by the Li-storage mechanism studies, we choose
pyrazine-2,3,5,6-tetracarboxylic acid (H4pztc) as organic
linker to construct CPs for high-performance LIBs. H4pztc is
an ideal ligand material with the features of brimming active
sites for Li-ions storage, easy synthesis, and lower molecular
weight. The functional groups and atoms (carboxyl groups
and N atoms) of H4pztc can reversibly store Li-ions by
means of redox type. Lithium insertion/extraction in the
conjugated aromatic ring can repeatedly occur during elec-
trode reactions through insertion type. As a consequence, the
construction of H4pztc-based coordination polymers is a
sensible strategy for anode materials of LIBs to pull the
pristine MOFs-based anodes out of the current funk. The
ligand was obtained according to the published procedure
(Figure 1(a)) [20].
at 200 mA g−1 over 150 cycles, respectively. In particular, 2
exhibited the most exceptional Li-storage performance
compared with the reported Ni-based MOF anodes [25–28].
Furthermore, the lithiation-delithiation chemistry investiga-
tion of CPs 1 and 2 was intensively studied by ex-situ X-ray
photoelectron spectroscopy (XPS) technology, the results of
which confirm that metal ions and organic moieties sy-
nergistically participate in the redox electrode reactions.
2 Experimental
2.1 Materials and method
All the reagents and solvents were of analytical grade
without any purification, except for H4pztc, which was
synthesized following the published procedure [20]. Powder
X-ray diffraction (PXRD) measurements were recorded on a
Rigaku Ultima IV instrument (Japan) in the 2θ range of 5°–
50° at the scanning rate of 0.2° s−1. Elemental analyses (EA)
of C, H and N were collected on a Vario EL cube elemental
analyzer (Elementar, Germany). The thermal gravimetric
analysis (TGA) experiments were carried out using a Labsys
NETZSCH TG 209 Setaram apparatus (Germany) at the
heating rate of 10 °C min−1 under nitrogen atmosphere. The
Fourier transform infrared (FT-IR) spectra were obtained in
the wavenumber range of 400–4000 cm−1 on a Bruker AL-
PHA-T infrared spectrophotometer (Germany). Scanning
electron microscopy (SEM) images were measured by a
ZEISS MERLIN compact (field emission) scanning electron
microscope (Germany) operating at 5 kV, 100 μA. X-ray
photoelectron spectroscopy (XPS) was recorded on a Kratos
AXIS Ultra DLD spectrometer (UK) with an Al Kα X-ray
source.
2.2 Synthesis of H4pztc
A
mixture of 2,3,5,6-tetramethylpyrazine (22.1 mmol,
At present, numerous CPs as anode materials of LIBs have
been extensively studied [13]. However, the framework
structures of 3D CPs usually decompose accompanied by the
reduction of metal ions during discharging, and the structures
cannot recover after the recharge process. It has been pro-
posed that reducing the dimensions and judicious selection
of organic ligands are effective ways to develop advanced
conversion-type and insertion-type CPs as anode materials of
LIBs [21]. Inspired by the successful application of 2D
materials (i.e., graphene, transition metal oxides, transition
metal dichalcogenides) in the energy storage and conversion
field because of their atomically thin structures and great
diversities [22–24], we introduced two isostructural CPs
[M2(pztc)(H2O)6]n (M=Co for 1, Ni for 2) with 2D layered
structures achieved by a simple hydrothermal reaction as
anode materials for LIBs. As expected, CPs 1 and 2 showed
highly reversible specific capacities of 815 and 536 mA h g−1
3.00 g), potassium hydroxide (52.8 mmol, 2.96 g) was dis-
solved in water (250 mL). KMnO4 powder was added to the
mixture in batches, which was stirred for 6 h at 60 °C to
complete the oxidization. After that, adequate amount of
ethanol was dropped to the mixture and the filtrate was
concentrated and acidified to acquire the white power. Then
the oxidation products were recrystallized from 25 mL of
20% aq. HCl, yield 55%. 13C NMR (400 MHz, D2O): δ
167.53, 145.57.
2.3 Synthesis of CPs 1 and 2
A mixture of Co(NO3)2•6H2O (58 mg, 0.2 mmol), H4pztc
(25.8 mg, 0.1 mmol), H2O (5 mL) was sealed in a 10 mL vial
and heated at 80 °C for 48 h, and then slowly cooled to room
temperature. Light yellow crystals of 1 were obtained as a
pure phase and rinsed with water and ethanol three times,

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Liu et al. Sci China Chem
followed by vacuum desiccation at room temperature over-
night. 2 was synthesized in the same way as 1 by changing
Co(NO3)2•6H2O to Ni(NO3)2•6H2O (58 mg, 0.2 mmol).
Elemental analysis calcd (%) for C4H6CoNO7: C 20.10, H
2.53, N 5.86; found: C 19.96, H 2.47, N 6.01. Elemental
analysis calcd (%) for C4H6NiNO7: C 20.12, H 2.53; found:
C 19.78, H 2.86, N 6.12. In FT-IR spectra (Figure S1, Sup-
porting Information online), the positions and strength of the
peaks are basically the same for the two isostructural metal-
organic materials.
fonso in 2001 [32]. Single-crystal X-ray diffraction analysis
of 1 reveals that the two CPs are isostructurally crystallized
in the triclinic space group Pī. CPs 1 and 2 are also char-
acterized by FT-IR and PXRD measurements (Figures S1
and S2). The crystal structure of 1 is described as an ex-
ample. There are two crystallographically independent Co2+
ions located in two types of distorted octahedral environ-
ments (Figure 1(b)). Co1 is connected with four H2O mo-
lecules and two carboxyl oxygen atoms from two pztc4−
anions. The coordination environment of Co2 is completed
by two carboxyl oxygen atoms and two nitrogen atoms from
two pztc4− anions, in addition to two oxygen atoms from two
H2O molecules (Figure 1(c)). The Co–O bond lengths vary
from 2.056(6) to 2.116(8) Å, and the Co–N bond distance is
2.176(7) Å (Table S2). Each pztc4− anion serves as a linker
and connected with four CoII ions via N and O atoms to
afford a 2D network structure (Figure 1(d)). The adjacent 2D
layers are connected by hydrogen bonds of O6–H6A···O2,
O7–H7A···O6 and O7–H7B···O1 (Table S3) from co-
ordinated water molecules and carboxyl groups of pztc4−
2.4 X-ray crystallography
The crystal structure of 1 was acquired by an Agilent
Technologies Supernova single-crystal X-ray diffractometer
(USA) using graphite-monochromatic Mo Kα radiation (λ=
0.71073 Å) at 120 K. The structure was solved with direct
methods using SHELXS program and refined with full-ma-
trix least-squares techniques on F2 using SHELXL in the
Olex2 software packages [29]. All the hydrogen atoms on the
organic ligands were calculated geometrically and refined by
riding model [30,31]. The crystallographic data and structure
refinement parameters are summarized in the Table S1
(Supporting Information online).
anions to form
(Figure 1(e)).
a
3D supramolecular framework
For the application of CPs as electrode materials for LIBs,
high chemical stability of CPs in the electrolyte is crucial.
Fortunately, the formation of the 2D planes linked by hy-
drogen bonds can increase the chemical and structural dur-
ability of both CPs in the electrolyte. These active materials
maintain crystallinity after soaked in the electrolyte of LIBs
for 7 d (Figure S3), which is confirmed by PXRD and FT-IR
measurements (Figures S2 and S4). PXRD patterns of the
obtained CPs 1 and 2 are in agreement with the simulated
patterns based on the single-crystal data, confirming a pure
solid-state phase (Figure S2). The TGA of CPs 1 and 2 were
2.5 Lithium ion battery fabrication
Standard CR2032 coin-type half-cells were assembled in an
argon-filled glovebox to investigate the lithiation/delithia-
tion behaviors of the prepared anodes. A homogenous slurry
was acquired by mixing the electrode-active materials with
Ketjen black and polyvinylidene fluoride (70:20:10 in
weight) in N-methyl-2-pyrrolidone. The obtained slurry was
cast on a copper foil and dried at 60 °C under a vacuum for
24 h in succession. The mass loading of a work electrode is
about 1.2–1.6 mg cm−2. For lithium ion battery fabrication,
Li metal served as the counter/reference electrode. The
composition of the electrolyte was 1 M LiPF6 dissolved in
ethylene carbonate (EC)/diethylcarbonate (DEC) (1:1, v/v).
The separators of the cells were polypropylene film. The
batteries were aged overnight before electrochemical tests.
Galvanostatic charge-discharge tests were performed on a
LAND battery tester in a temperature-controlled thermotank
with the potential range of 0.01–3.0 V (vs. Li/Li+) based on
the weight of the active materials. Cyclic voltammetry (CV)
and electrochemical impedance spectroscopy (EIS) mea-
surements were performed on a CHI 660E electrochemical
workstation (ChenHua Instruments Co., China).
Figure 1 (a) Synthesis of H4pztc; (b) coordination geometries of CoII ions
in 1; (c) the coordination environments in 1 (hydrogen atoms were omitted
for clarity); (d) wavy layers along the b axis; (e) the 3D supramolecular
structure of 1 along the a axis. Atom colors: Co (purple), C (gray), N (blue),
and O (red) (color online).
3 Results and discussion
The crystal structure of 2 has been initially reported by Al-

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Liu et al. Sci China Chem
measured in the temperature range of 40–800 °C (Figure S5).
1 shows a weight loss of 22.36% from 80 to 305 °C and that
of 2 is 22.38% from 95 to 312 °C, corresponding to the
release of six coordinated water molecules (calcd 22.59% for
1 and 22.61% for 2). Further heating generated rapid weight
losses, indicating the collapse of the frameworks. The results
indicate that the CPs display good crystalline phases and
relatively high thermal stabilities.
To evaluate the redox activities of H4pztc and H4pztc based
metal-organic materials, the energy levels of the lowest un-
occupied molecular orbital (LUMO) and the highest occu-
pied molecular orbital (HOMO) were calculated using
density functional theory (DFT) [33,34]. The deeper LUMO
is, the higher electron affinity (EA) and oxidizability ex-
hibits. As shown in Figure 2, the LUMO of 1 (−5.52 eV) and
2 (−4.16 eV) are lower than that of H4pztc (−3.15 eV). Be-
sides, the energy gaps (ΔΕ) between the LUMO and HOMO
levels are relevant to the intrinsic electrochemical activities,
and a lower gap represents better activity [35,36]. On ac-
count of the coordination interaction between H4pztc and the
metal ions, the energy gaps of 1 (0.81 eV) and 2 (0.32 eV)
are much lower than that of H4pztc (4.75 eV), indicating that
the intrinsic electrochemical activities in CPs 1 and 2 are
higher than that for H4pztc.
The electrochemical performances of the two isostructural
CPs as LIBs anode materials were evaluated in a voltage
window of 0.01–3.0 V (vs. Li/Li+). Figure 3(a, b) shows the
charge-discharge profiles of selected individual cycles at a
representative current density of 200 mA g−1. The electrode
with 1 presents a meaningfully lower discharge plateau in
comparison to that of 2, indicating a more advantageous
anodic characteristic. For 1, the initial discharge and charge
Figure 2 Calculation of the relative energies and spatial distributions of
HOMO and LUMO energy levels for H4pztc, 1, and 2. The left axis re-
presents the relative energy voltage (vs. Li/Li+,
) and the right axis
+
ELi /Li
represents the relative energy level in vacuum (Evac) (color online).
capacity are 2165 and 1107 mA h g−1, respectively, with an
initial Coulombic efficiency (ICE) of 51.1%. The initial ir-
reversible capacity loss is attributed to the irreversible pro-
cesses, including the decomposition of the electrolyte to
form solid electrolyte interphase (SEI) layers and interfacial
lithium storage [37,38]. Besides, the formation of Li2O in-
side the interlayers or on the surface caused by the reaction
between coordinated water molecules in 1 and lithium leads
to the reversible capacities decay from the second cycle to
the 10th cycle [39,40]. The ICE of 2 is only 47.3%, and then
the CE maintains steady at nearly 100% in the following
cycles, indicating that the SEI layers are stable.
Figure 3 Electrochemical performances of two CPs as LIBs anodes: charge-discharge profiles at 200 mA g−1 of the 1 (a) and the 2 (b); cycling perfor-
mances of 1 (c) and 2 (d) at 200 mA g−1 over 150 cycles; rate performance of 1 (e) and 2 (f) at different current densities (color online).

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Liu et al. Sci China Chem
The cycling performances of the two CP-based anodes
were investigated at 200 mA g−1. As shown in Figure 3(c, d),
the two CPs exhibited remarkable cycling stability with high
reversible capacity. After 150 cycles, the discharge capa-
cities of CPs 1 and 2 still retain at 815 and 536 mA h g−1 with
relatively high capacity retention, which are higher than the
theoretical capacity of commonly used graphite
(372 mA h g−1). After the specific capacities decrease for the
first 10 cycles caused by the formation of Li2O, the capacities
of electrodes increase from the 10th to the 80th cycle and
then maintain stable up to 150 cycles. This phenomenon of
the capacities increasing should be related to the gradually
electrochemical activation of the SEI film accompanied by
better Li-diffusion kinetics during cycling [41], which was
also observed in other CPs or MOFs [17,27,42]. When per-
formed at 500 mA g−1, the reversible capacities of CPs 1 and
2 are 615 and 410 mA h g−1 after 400 cycles, respectively
(Figure S6(a, b)). The rate performances of the electrodes are
illustrated in Figure 3(e, f). When the rates are gradually
changed from 100 to 200, 300, 500, 1000 and 2000 mA g−1,
the corresponding discharge capacities are 845, 743, 698,
656, 558 mA h g−1 for 1 and 668, 483, 420, 365, 273,
211 mA h g−1 for 2, respectively. When the current rate is
reduced back to 100 mA g−1, the reversible capacities swiftly
recover to the initial stage without apparent decay, demon-
strating the excellent cycling stability to tolerate the current
change. In comparison with the organic ligand H4pztc (Fig-
ure S7) and other pristine CPs as anode materials (Table S4),
the two isostructural CPs in this work possess high reversible
capacity and excellent electrochemical cycling stability and
outperform all the reported 2D-CP-based anode materials.
To investigate the electrochemical redox reaction me-
chanism, cyclic voltammetry (CV) measurement was per-
formed first. As shown in Figure S8, in the first cycle, the CV
curves are different from the subsequent cycles, which can be
related to the formation of SEI layers in both CPs 1 and 2. In
the subsequent scans, two apparent catholic peaks at 0.68 and
1.30 V, as well as two anodic peaks at 1.49 and 1.92 V are
observed for 1 (Figure 4(a)), coinciding well with the gal-
vanostatic charge-discharge profiles. The former pair of re-
dox peaks can be clearly attributed to the redox process
between Co2+ and Co0, while the latter redox peaks result
from lithiation and delithiation of the carboxylate groups
[43]. For 2, a reversible delithiation potential was remained
at 1.47 V (Figure 4(b)). Lithiation process took place at 0.61
and 1.28 V, indicating that similar two-step redox reactions
as that in 1 are happening during the discharging process.
The results of CV and galvanostatic charge-discharge
measurements have demonstrated the two-step lithiation/
delithiation redox processes in the metal centres and carbo-
nyl groups. To further confirm the electrochemical reaction
mechanism, we tracked the change of valence and chemical
bonding state of electrode materials during discharging/
charging processes by ex-situ XPS experiments. The two
typical characteristic peaks at 781.3 and 797.2 eV corre-
spond to Co 2p1/2 and Co 2p3/2 in Co2+; the two main peaks at
856.4 and 873.6 eV can be assigned to Ni 2p1/2 and Ni 2p3/2 in
Ni2+ (Figure 4(c, d)). The signals at 785.1, 801.7 eV, for Co
2p, and 860.9 and 879.5 eV for Ni 2p are satellite peaks.
After being fully discharged, the characteristic Co 2p peaks
shift toward 778.3 and 793.0 eV and the characteristic Ni 2p
peaks shift toward 852.2 and 870.1 eV, confirming the ex-
istence of Co0 and Ni0 (Figure 4(e, f)) [44]. The C 1s and O
1s spectra were also investigated to study the redox in-
volvement of the organic ligand during lithiation-delithiation
processes (Figures S9 and S10). The C 1s and O 1s spectra
peak shifts and conversions of CPs 1 and 2 are analogous on
account of the identical organic moieties. The C1s spectra
after Li-ions insertion process can be divided into three peaks
at (Figure S9(c, d)), i.e., 284.6 eV for the C=C bond of the
pyrazine ring, 285.9 eV for carboxyl groups, and 289.8 eV
for C–C bond of the enol structures, respectively [45]. The
results indicate that the carboxyl groups of pztc4− trans-
formed into the enol structures after discharging process. In
the O 1s spectra of the discharged electrodes (Figure S10(c,
d)), the peaks at 529.6 (or 529.4) and 531.1 eV are attributed
to the lattice oxygen and the Li–O bond [46]. In addition,
theoretical studies and electron paramagnetic resonance
(EPR) measurements have concluded that the N atoms on the
aromatic ring can participate in the electrochemical redox
reaction during cycling [18,19], as observed in the Zn-ODCP
electrode [47], N-COFs [48] and NNU-11 [49] electrodes.
Based on the above observations and discussions, the re-
markable LIBs performances of two CPs are achieved by the
synergistic Li-storage reactions of metal ions and organic
linkers (Figure S11).
But obviously, the electrochemical performance of 1 is
much better than that of 2, which could be ascribed to the
coordination affinity difference to organic ligands as well as
the electrochemical property of the metal ions [50]. The
performance inferiority of 2 over 1 could result from the
following reasons: (1) Ni2+ has a larger ion radius than Co2+,
leading to stronger steric hindrance in 2 toward Li-ions; (2)
the Li-ions migration kinetics of 2 after 150 discharge-charge
cycles is lower than that of 1 (Figures S12 and S13); (3) the
calculated b-values of the anodic and cathodic peaks for 2
(0.56, 0.61) indicate a relatively weak surface-controlled
capacitive contribution to total capacity when compared with
1 (Figure S14).
Structural stability is a significant characteristic of CPs or
MOFs as electrode materials during the electrochemical re-
actions. SEM, PXRD and FT-IR measurements were con-
ducted to analyse the chemical and structural durability of
the active materials after the cycling test. From the SEM
images, PXRD patterns and FT-IR spectra, the active mate-
rials after 10 cycles can maintain chemical and structural

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Liu et al. Sci China Chem
Figure 4 Cyclic voltammetry (CV) curves for the 2–4 cycles of 1 (a) and 2 (b) at a scan rate of 0.1 mV s−1 in the voltage window of 0.01–3.0 V vs. Li/Li+.
XPS spectra of 1 and 2 from the assembled electrodes before (c and d) and after (e and f) the electrochemical discharge processes (color online).
stabilities compared to that of the pristine CPs (Figures S15–
S17). Besides, the morphologies of the assembled electrode
materials can be well retained after 100 cycles at 500 mA g−1
(Figure S18). The results indicate that the 2D layer-based
supramolecular structures can effectively tolerate the volume
effects during charge and discharge processes, thereby, in
favour of their long cycling performance.
ions and organic moieties. In comparison with 3D CPs, the
2D layered CPs can effectively tolerate the volume effects
during electrode reactions and facilitate Li-ions diffusion as
well as electron transfer, which could further contribute to
the improved LIBs performance. The present study may
open a new avenue for the design and construction of low-
dimensional (1D, 2D) CPs with a delicate designed organic
ligand of multi-electron redox property for energy storage
and conversion.
4 Conclusions
Acknowledgements This work was supported by the National Natural
Science Foundation of China (21622105, 21501071, 21421001), Shenzhen
Fundamental Research Project (JCYJ20160525164227350), the Ministry of
Education of China (B12015), and the Natural Science Foundation of
Tianjin (18JCJQJC47200).
In summary, we proposed a strategy of utilizing a well-de-
signed redox-active organic ligand to construct 2D CPs for
Li-storage for the first time. Two isostructural H4pztc-based
2D layered CPs were obtained by a simple hydrothermal
reaction. Both CPs exhibited highly reversible capacities and
excellent rate performance, higher than any of the reported
2D-CP-based anode materials, to the best of our knowledge.
The remarkable electrochemical properties are mainly as-
cribed to the synergistic Li-storage redox reactions of metal
Conflict of interest The authors declare that they have no conflict of
interest.
Supporting information The supporting information is available online at
http://chem.scichina.com and http://link.springer.com/journal/11426. The
supporting materials are published as submitted, without typesetting or

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Liu et al. Sci China Chem
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