Sodium Naphthalene-2,6-dicarboxylate: An Anode for Sodium Batteries

Article abstract of DOI:10.1002/cssc.201901626

The conjugated dicarboxylate sodium naphthalene-2,6-dicarboxylate (Na₂NDC) was prepared by a low-energy-consumption reflux method, and its performance as a negative electrode for sodium-ion batteries was evaluated in electrochemical cells. The structure of Na₂NDC was solved for the first time (monoclinic P2₁/c) from powder XRD data and consists of π-stacked naphthalene units separated by sodium–oxygen layers. Through an appropriate choice of binder and conducting carbon additive, Na₂NDC exhibited a reversible two electron sodium insertion at approximately 0.4 V (vs. Na⁺/Na) with remarkably stable capacities of approximately 200 mAh g^?1 at a rate of C/2 and good rate capability (≈133 mAh g^?1 at 5 C). In parallel, the high thermal stability of the material was demonstrated by high-temperature XRD: the framework remained intact to above 500 °C.

Full text of DOI:10.1002/cssc.201901626

Accepted Article
Title: Sodium naphthalene-2,6-dicarboxylate: an Anode for Sodium
Batteries
Authors: Joel M Cabañero, Vanessa Pereira Pimenta, Kieran Cannon,
Russell Morris, and Anthony Robert Armstrong
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: ChemSusChem 10.1002/cssc.201901626
Link to VoR: http://dx.doi.org/10.1002/cssc.201901626
A Journal of
www.chemsuschem.org

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
disadvantage for static applications such as grid storage. In the
case of lithium-ion batteries anode materials operating below
around 0.5 V vs Li+/Li require the use of copper as the current
collector, thereby increasing cost, weight and environmental
impact. One considerable advantage of sodium-ion batteries is
the absence of an alloying reaction with aluminium which means
that it can be used as a current collector regardless of voltage,
providing an additional cost and environmental benefit.
Sodium naphthalene-2,6-
dicarboxylate: an Anode for
Sodium Batteries
Joel M. Cabañero Jr,[a] Vanessa Pimenta,[a] Kieran
C. Cannon,[a] Russell E. Morris[a,b] and A. Robert
Armstrong*[a]
Armand et al. were the first to demonstrate the potential
application of conjugated dicarboxylates as anode materials for
lithium-ion batteries.11 These phases have the advantage that the
raw materials can readily be obtained from green and sustainable
sources such as the recycling of plastic bottles and biomass. By
a
procedure first reported by Kaduk,12 they
Abstract: The conjugated dicarboxylate, sodium naphthalene-
2,6-dicarboxylate (Na2NDC), has been prepared by a low energy
consumption reflux method and its performance as a negative
electrode for sodium-ion batteries evaluated in electrochemical
cells. The structure of Na2NDC was solved for the first time
(monoclinic P21/c) from powder X-ray diffraction data and consists
of π-stacked naphthalene units separated by sodium-oxygen
layers. Through an appropriate choice of binder and conducting
carbon additive Na2NDC exhibits a reversible two electron sodium
insertion at around 0.4 V vs. Na+/Na with remarkably stable
capacities of ca. 200 mA h g-1 at a rate of C/2 and good rate
capability (~133 mA h g-1 at 5C). In parallel the high thermal
stability of the material is demonstrated by HT-X-ray diffraction,
the framework remaining intact to above 500 °C.
developing
synthesized di-lithium terephthalate (Li2C6H4O4) and di-lithium
trans-trans-muconate (Li2C8H4O4). The electrochemical
performance of di-lithium trans-trans-muconate showed an
overall reversible capacity corresponding to approximately 1 Li
per formula unit at a potential of 1.4 V vs Li+/Li, while the
terephthalate salt exhibited
a
highly promising capacity
corresponding to insertion/extraction of 2 Li at the lower voltage
of 0.8 V vs Li+/Li. The latter corresponds to a reversible capacity
of ~ 300 mAhg-1, with 234 mAhg-1 retained after 50 cycles. As a
consequence of this study several other conjugated
dicarboxylates have been described as anodes for lithium-ion
batteries. Ogihara et al. reported excellent performance for lithium
2,6-naphthalenedicarboxylate
(2,6-Naph(COOLi)2).13,14
The
discharge capacity on the first cycle corresponded to 3 Li+ per
molecule with a reversible capacity of 2 Li+ and good capacity
retention. The authors coined the term intercalated metal-organic
framework or iMOF for the material, which had previously been
described as UL-MOF-1.15 The low discharge voltage of 0.8 V vs
Li+/Li, small cell polarization and very low volume change of
0.33% make lithium 2,6-naphthalenedicarboxylate a promising
negative electrode for high-voltage Li-ion batteries. The material
also showed excellent thermal stability; up to 527oC under an Ar
atmosphere.14 Several other conjugated dicarboxylates such as
lithium dihydroxyterephthalate have also shown promising
performance as anode materials for lithium-ion batteries.16,17
One of the primary challenges in the development and
commercial realisation of sodium-ion batteries is to find a suitable
negative electrode. Whilst graphite has proved to be a very
successful anode material for lithium-ion batteries, by contrast
there is negligible sodium intercalation between the graphene
sheets for most electrolyte systems.18,19 A number of other forms
of carbon have been investigated, however, and show promise.
Amorphous hard carbon currently represents the best option for a
working negative electrode, though it shows significant
irreversible capacity on the first cycle.8,20 Several conjugated
dicarboxylates have also been evaluated as anodes for sodium-
ion batteries including sodium terephthalate (sodium benzene-
1,4-dicarboxylate), sodium 4,4’-biphenyldicarboxylate and
sodium dihydroxyterephthalate, all with operating potentials of ~
0.5 V vs Na+/Na.21-25 While these materials show reasonable
capacities and attractive sodium insertion potentials, the rate
performance is typically rather poor. Sodium 4,4’-
biphenyldicarboxylate has demonstrated good rate performance,
Introduction
The increasing demand for energy is one of the major challenges
of the present century and has driven the search for new electrode
materials for rechargeable battery applications. Lithium-ion
batteries have been preferred to their sodium-ion counterparts by
virtue of their higher energy density and operating voltages,
leading to their domination of the portable electronics market and
making them the best candidate for electric vehicles,1 but
concerns about lithium supply have encouraged the development
of more sustainable sodium-ion batteries.2-10 This rising interest in
sodium-ion batteries has been driven by the greater and more
uniform Earth abundance of sodium, compared with lithium, and
resulting lower cost. Sodium-ion batteries could have a significant
role in next-generation low-carbon energy technologies
associated with the growing requirement for large scale batteries
to store the electricity from solar cells, wind turbines and other
renewable sources. The larger mass of sodium, compared with
lithium, leads to a lower specific capacity, but this represents no
[a]
Joel M. Cabañero Jr, Dr Vanessa Pimenta, Kieran C. Cannon, Prof
Russell E. Morris and Dr A. Robert Armstrong*
School of Chemistry
East Chem, University of St Andrews
North Haugh, St Andrews, Fife, KY16 9ST, United Kingdom
E-mail: ara@st-andrews.ac.uk
[b]
Prof Russell E Morris
Department of Physical and Macromolecular Chemistry
Faculty of Sciences, Charles University
Hlavova 8, 128 43 Prague 2, Czech Republic
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
albeit with only 57% active material in the electrode formulation.24
Further new materials have recently been reported including
disodium pyridine-2,5-dicarboxylate and sodium 2,6-naphthalene
dicarboxylate.26-28 Further examples are described in a recent
review by Zhao et al.29
the range 3250 – 2000 cm-1, characteristic of carboxylic acids and
arising from strong hydrogen bonding. This broad peak is absent
from the IR spectrum of Na2NDC which confirms the loss of the -
OH functional group in the product and successful salt formation.
The spectrum for NDCA also shows an intense carbonyl stretch
at 1672 cm-1 and O–H bending vibrations from the carboxylic acid
(COOH) groups at around 900 cm-1. The formation of sodium
Na2NDC has recently been highlighted as anode material by
Deng et al.. The authors describe the synthesis of a graphene-
wrapped nanocomposite displaying 118 mA h g-1 at 5C and 88
mA h g-1 at 10C.27 Such performance is however enhanced by the
synergetic presence of graphene sheets around Na2NDC. More
recently Medabalmi et al. reported that Na2NDC at a rate of C/5,
shows 145 mA h g-1 with 70% retention after 70 cycles and 85 mA
h g-1 at 2.5C.28 These results are already quite promising,
however the electrochemical performance can still be improved
without resorting to the complexity of wrapping with graphene
Herein we report a detailed study of sodium naphthalene-
2,6-dicarboxylate (Na2NDC). The crystal structure was
determined for the first time (ab initio from powder diffraction data)
and the framework robustness was highlighted by HT-XRD. The
electrochemical performance was explored and with the
appropriate choice of carbon additive and binder resulted in a
remarkable electrochemical performance up to rates of 5C
without the need to form a nanocomposite, with the low rate
capacity exceeding 200 mA h g-1 and excellent cycling stability.
naphthalene-2,6-dicarboxylate
(Na2NDC)
via
complete
deprotonation by NaOH leads to a shift in the carbonyl stretching
vibration of the carboxylate groups - a split into two bands at 1557
cm-1 and 1395 cm-1 respectively, which were assigned to
asymmetric and symmetric stretching vibrations, respectively.
Moreover, the characteristic O–H bending vibrations for the
carboxylic acid groups, located around 900 cm-1, disappeared.
These values are in excellent agreement with those reported
previously.27 The chemical structure was confirmed using 1H and
13C DEPTQ NMR spectroscopy with D2O as the solvent. The
solvent exchanges readily with the protons of the carboxylic acid
group; hence the NMR spectra of the acids and the salts were
indistinguishable. Thus NMR alone was not a definitive tool for
determining the structure and purity of the product since the
presence of the excess ligand and/or monosodium compounds
cannot be excluded. However, when NMR results are combined
with FTIR and elemental analysis data, the structure could be
elucidated (fig. S1). Elemental analysis results revealed high
purity of the product with values of 55.29 % C, 2.29% H;
compared to theoretical values of 55.40% C, 2.33% H.
Results and Discussion
Structural characterization
Sodium
naphthalene-2,6-dicarboxylate
(Na2NDC)
was
synthesised as described in the experimental section. The acid–
base reaction of naphthalene-2,6-dicarboxylic acid (NDCA) with
sodium hydroxide was verified by Fourier transform infrared (FT-
IR) spectroscopy. As shown in Figure 1 the spectrum of
naphthalene-2,6-dicarboxylic acid (NDCA) shows a broad peak in
Figure 2. Fitted synchrotron X-ray diffraction pattern for Na2NDC; the red dots
represent the observed data and the solid line the calculated pattern; the lower
line is the difference/esd. Tick marks represent the allowed reflections.
Figure 1. Infra-red spectra for sodium naphthalene-2,6-dicarboxylate (red line)
and naphthalene-2,6-dicarboxylic acid (black line).
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
Figure 3. Schematic representation of the crystal structure of Na2NDC: bc plan showing the sodium layers (a); stacking of the inorganic layers with deprotonated
naphthalene rings along the [010] direction (b); 3D framework with small 1D cavities (c).
A powder X-ray diffraction pattern for Na2NDC is shown in fig. S2.
aromatic bridging units. The sodium ions show a rather irregular
The pattern could be indexed on the basis of a monoclinic unit cell, coordination environment, being penta-coordinated with Na-O
space group P21/c, with approximate cell parameters a = 12.1, b
= 3.6, c = 11.36 Å, β = 103.8°. A profile fit to the synchrotron X-
ray diffraction data is shown in Figure 2 and refined structural
parameters are presented in Table S1. The π-stacking of the
aromatic rings together with the rigid naphthalene structural unit
enabled the crystal structure to be solved ab initio from powder
diffraction data. This was achieved by analogy with the previously
reported structure of potassium terephthalate.12 Potassium
terephthalate exhibits a generally similar set of unit cell
parameters with analogous π-stacking of the aromatic rings
(Fig.S3). In the case of Na2NDC the additional limitations of the
rigid molecular structure meant that the C-C bond at the junction
of the fused benzene rings could be placed at the inversion centre
of the unit cell. The structure was then refined using Topas
Academic applying constraints to both bond lengths and
angles.30,31 Numerous other naphthalene derivatives crystallise in
the monoclinic space group P21/c, in particular alkali based
Li2NDC, alkaline earth Ca2(OH)2NDC32 or even 3d metal based
frameworks such as Zn2(OH)2NDC33 and (VIVO)2(OH)2NDC
(P21/n).34 Interestingly, sodium biphenyldicarboxylate (Na2BPDC)
also adopts the same type of structure.24 The framework of
Na2NDC is built up from successive sodium layers separated by
bonds with a range of bond lengths from 1.78 – 3.08 Å. Sodium
atoms occupy one independent crystallographic position and are
associated in Na2O8 dimers through a sharing edge. Each dimer
is connected to the adjacent also by two shared edges, forming
[Na2O7] chains. The chains alternate in opposite direction along
b and are connected by four sharing corners (Figure 3 a). The
layered inorganic sub-units are stacked with deprotonated
naphthalene rings along the [010] direction (Figure 3 b) and the
naphthalene rings are separated by 3.62 Å. The framework is
three-dimensional with small cavities (Figure 3 c). In order to
investigate the porosity of the network, N2 and CO2 adsorption
measurements were performed, however Na2NDC did not show
significant adsorption properties (Fig. S4).
A key feature of organic dicarboxylate anode materials is their
unusually high thermal stability. In order to examine the thermal
stability of Na2NDC, thermogravimetric analysis (TGA) and
temperature dependent X-ray diffraction were carried out (HT-
XRD). As shown in Figure 4 a, no significant weight loss is
observed in the thermogram until around 500 oC, indicating
retention of the framework. This excellent thermal stability is due
to the efficient π-stacking interaction between adjacent
naphthalene rings, as previously observed for the lithium
Figure 4. TGA trace for Na2NDC under flowing argon at a heating rate of 2 oC per minute (a); HT-XRD of Na2NDC from RT to 500 oC under flowing helium at a
heating rate of 2 oC per minute (b).
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
analogue.14 Figure 4 b shows the evolution of the X-ray pattern
upon heating. The HT-XRD studies confirm the stability of the
framework. Upon heating, a shift of the Bragg peaks at 2θ = 30.5o
and 34.8o towards lower angles indicates an evolution of the cell
parameters. All patterns were refined using Le Bail fitting method,
showing that upon heating the network becomes distorted, with a
simultaneous increase of b parameter and unit cell volume, while
β decreases and a and b stay more-or-less constant (Fig. S5).
The distortion of the framework is fully reversible and all Bragg
peaks shift to their initial position once the sample is cooled to
room temperature. The X-ray powder diffractograms are shown in
Fig. S6.
Equation 1. Proposed reaction scheme for sodium insertion and extraction in
sodium naphthalene-2,6-dicarboxylate.
numerous organic and inorganic species make up the SEI. In
SIBs both classes of compound are also present, however the
presence of inorganic compounds is greater than the organic
derivatives (both produced by the electrolyte and binder
decomposition)36,37 and the organic species are mainly distributed
near the surface while the interior of the SEI is mainly composed
of inorganic species.38
After taking the capacity contribution of the conductive carbon into
account, the second discharge capacity is equivalent to
approximately 2 Na+, which corresponds to the theoretical
capacity of Na2NDC, according to the proposed reaction scheme
shown in Equation 1.
On succeeding cycles the capacity remains at this value,
providing confirmation that the discharge and charge processes
of Na2NDC involve a one-step two-electron reversible redox
process as shown in Equation 1. The first discharge potential of
0.22 V vs. Na+/Na is markedly lower than the second and
subsequent discharges (0.38 V vs. Na+/Na), whilst the charging
potential remains at around 0.50 V. Similar, albeit less
pronounced, behaviour was observed for the lithium analogue
where a difference of 40 mV was observed between first and
subsequent discharges. The raising of the voltage plateau from
the first discharge process to the subsequent discharge
processes of Li2NDC is associated with the decrease in IV
resistance after the initial Li intercalation.13
Electrochemical characterisation
The electrochemical performance of Na2NDC was evaluated
using coin cells with sodium metal as the negative electrode.
Initial studies were performed using Super P carbon as the
conducting additive with Kynar 2801 (a co-polymer based on
PVDF) as the binder. Figure S7 shows the voltage profile of the
first five cycles of the material at a rate of 0.1C (C rate defined as
200 mA g-1), while Figure 5 shows a cyclic voltammogram for the
first 5 cycles at a sweep rate of 0.1 mV s-1.
In order to investigate the phenomenon electrochemical
impedance spectroscopy (EIS) was carried out at various states
of charge.
Figure 6a shows the EIS Nyquist plots of the cell as-prepared (at
OCV), at the end of the first discharge and after first and second
charge. Bode plots can be found in fig. S7. As the measurements
were performed in a two electrode half-cell, the EIS spectra
includes the overall cell resistance. However, it can be assumed
that the anode contribution remains constant since the ohmic
resistance is similar in all cycles. For the as-prepared cell, the
impedance is very high, the spectrum showing a complex shape
with the overlapping of several features. Upon cycling the system
becomes more conductive as evident from the decreased
impedance (Figure 6b). After the first discharge, the high
frequency (HF) semicircle corresponding to the SEI appears at
~25 kHz, which is more pronounced for the charged samples
(Figure 6c,d), which explains the initial capacity loss due to the
SEI formation. Furthermore, the mid-frequency semicircle (at ~60
Hz) corresponding to the charge transfer process at the
SEI/electrode interface can be distinguished, along with the low-
frequency Warburg tail39, corresponding to the sodium diffusion in
Figure 5. Cyclic voltammograms at a scan rate of 0.1 mV s-1 for Na2NDC.
In common with similar sodium materials a large irreversible
capacity is observed on the first cycle. This arises from two
sources - the formation of solid electrolyte interphase (SEI) layer35
and irreversible capacity from the conductive carbon additive.
Compared to the already reported Li2NDC compound13, Na2NDC
shows a more significant irreversible capacity on the first cycle
since the SEI formation mechanism in Na-ion batteries differs
from that of Li systems. The SEI thickness in both LIBs and SIBs
ranges from 10 to 100 nm.36 However the main difference remains
in the composition of the solid electrolyte interphase. In LIBs
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
Figure 6. Impedance spectra for Na2NDC at various states of charge (black – as-prepared electrode; red – after first discharge; blue – after one cycle; green – after
two cycles)(a). High frequency regions of the spectra (b,c,d).
the electrode material. In subsequent cycling the RSEI and Rct
remain in the same range, slightly increasing at the 1st charge but
decreasing again after the 2nd full change (Table S2). As charge
transfer resistance provides information about the kinetics of the
Na insertion/disinsertion process, it can be said that in Na
insertion step the low RCT reveals an enhanced electron transfer,
while in the Na disinsertion step the RCT increases again, meaning
a process with lower kinetics. After two cycles RCT decreases
again, suggesting that after the SEI formation the kinetics of the
Na insertion is faster than at the 1st cycle. Although ex-situ powder
X-ray diffraction patterns were recorded at different states of
charge (fig. S8), it was not possible to refine the parameters and
shed light to the sodium insertion mechanism. Nevertheless, it is
clear from the patterns that the structure remains stable and
reveal a highly reversible sodium insertion process with only small
structural changes at the end of discharge. Compared to the Li
compound, where a mixed electronic and ionic conductivity
mechanism is highlighted40, one cannot clearly indicate if the
nature of the sodium intercalation mechanism is comparable.
Further investigations in a three electrode cell, as well as pellet
measurements at different temperatures will help to unravel the
Na insertion mechanism and the activation energy. It is
nonetheless possible to consider that among the three electron
conduction hopping path demonstrated for the Li compound40,
Na2NDC would show at least two similar hopping paths, since the
π- stacking of the aromatic cycles is oriented in a similar way to
Li2NDC and the basal packing of sodium layers is ensured.
Whilst electrodes prepared with Super P carbon and PVDF-based
binders showed high initial capacities (fig. S9), the long-term
cycling stability was unsatisfactory (fig. S10). As a result, changes
were made to both the conducting carbon additive and the binder.
Use of carboxymethyl cellulose (CMC) as binder was found to
result in enhanced cycling stability and improved rate capability,
perhaps as a result of solubility of the electrode material in the
deionized water used to prepare the slurry ensuring intimate
mixing of the constituents. The use of CMC as a binder instead of
PVDF has also been reported for the lithium equivalent.41 The
enhancement of the cycling performance can be explained by the
amphiphilic character of CMC chains, where the carboxylate
groups on the outside of the polymer chain have a hydrophilic
character and the main chain has rather a hydrophobic character.
Due to this amphiphilic character, the outside carboxylic groups
interact with Na2NDC particles while the hydrophobic part with
the conductive carbon additive. The Na2NDC slurry had a dark
black colour, meaning a homogeneous dispersion and a full
coating of the white Na2NDC particles as described for the
Li2NDC.41 This full coating will therefore improve the electronic
conductivity of the electrode. Cycling performance enhancement
related to the use of CMC binder has also been reported in Na-
ion batteries.42 Compared to PVDF, the SEI formed when CMC is
used has a smoother and more homogeneous surface, showing
how binder degradation (PVDF fluorine content can contribute to
the formation of insulating NaF) can also play a key role in SEI
formation and consequently a long-term cycling stability.37
Cycling performance for electrodes containing 60% active
material: 30% Super P carbon: 10% CMC at a variety of rates
from 0.1C up to 1C is shown in fig. S11. This represents a
performance enhancement compared with the results reported by
Medabalmi et al. using PVDF as binder.28
In order to reduce the overall carbon content of the electrodes,
partial replacement of Super P carbon with the higher surface
area Ketjenblack carbon was investigated. This resulted in a
further enhancement in the performance, especially at higher
cycling rates.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
The cycling performance of Na2NDC with an electrode
composition consisting of 65% active material: 10% Super P: 15%
Ketjenblack: 10% CMC at rates of 100 mA g-1 (C/2) and 400 mA
g-1 (2C) is shown in Figure 7.
Figure 8. Rate performance for Na2NDC obtained between 0.05 and 2.0 V vs.
Na+/Na at various rates and at room temperature. The data were recorded for a
single cell, and the applied current was varied every 10 cycles. Rates are
indicated on top of each set of data.
Figure 7. Cycling data for Na2NDC obtained between 0.05 and 2.0 V vs. Na+/Na
progressively increasing rates from C/2 (100 mA g-1) up to 5C
(1000 mA g-1) before returning to C/2, as shown in Figure 8. High
capacities are maintained up to a rate of 5C and on reducing the
cycling rate to C/2 the capacity recovers to around 200 mA h g-1.
at 100 mA g-1 (C/2, red circles) and 400 mA g-1 (2C), blue squares).
An initial capacity of around 230 mA h g-1 was observed at the
lower cycling rate and, after dropping over the first few cycles, this
stabilizes at around 200 mA h g-1. The initial capacity exceeds the
theoretical value corresponding to the insertion of two sodium ions
(208 mA h g-1) as a result of a small contribution from the
conducting carbon additive. In order to quantify this contribution,
cells were fabricated with electrodes having the composition 36%
Super P: 54% Ketjenblack: 10% CMC. These were then cycled
under the same conditions. Load curves for these carbon
electrodes from the 20th cycle, the point at which the capacity
stabilizes, are shown in fig. S12 and reveal a contribution to the
overall capacity corresponding to approximately 15 mA h g-1. This
value was higher for the first few cycles.
Conclusions
Sodium naphthalene-2,6-dicarboxylate (Na2NDC) has been
prepared by a straightforward low-cost route, characterized using
a range of techniques including PXRD, IR and TGA. The structure,
determined ab initio from synchrotron powder X-ray diffraction
data, consists of π-stacked naphthalene units which form layers
along the [010] direction. This confers high thermal stability to
above 500 °C.
The behaviour of Na2NDC as an anode material in sodium-ion
batteries has been studied. With appropriate choice of binder and
conducting carbon additive Na2NDC exhibits a reversible two
electron sodium insertion at around 0.4 V vs. Na+/Na and delivers
stable high capacities of ca. 200 mA h g-1 at a rate of C/2 and
good rate capability (~133 mA h g-1 at 5C).
Very stable cycling was obtained for Na2NDC even at the higher
rate of 2C, with excellent capacity retention (99.92% per cycle) up
to 200 charge-discharge cycles. Further evaluation of the rate
performance was carried out by cycling for 10 cycles at
Experimental Section
Synthesis of sodium naphthalene dicarboxylate (Na2NDC): The
synthesis of Na2NDC was modified from that employed by Ogihara et al.13
for the preparation of lithium naphthalene-2,6-dicarboxylate (Li2NDC).
Sodium hydroxide (0.5291g, 13.23 mmol) (as pre-dissolved in 100 ml
methanol and naphthalene-2,6-dicarboxylic acid (NDCA) (1.0 g, 4.63
mmol) was rapidly added to the solution at room temperature while stirring.
Formation of a white precipitate was observed within 20 minutes. The
resulting suspension was then stirred under reflux conditions at 353 K for
24 h. The hot solution was vacuum filtered, washed twice with methanol
and dried under vacuum at 413 K for 12 h.
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
Structural characterisation. In this study, the diffraction measurements
were carried out on capillary samples (0.5mm) using a Stoe STADI/P
diffractometer in Debye-Scherrer mode, using Cu Kα1 radiation (λ =
1.54056 Å) and a position sensitive detector. Synchrotron X-ray diffraction
data were obtained on capillaries using the I11 diffractometer at the
Diamond Light Source, UK (λ = 0.825848(10) Å). Ex-situ powder XRD was
performed in order to confirm the structural stability upon cycling. Pristine
Na2NDC was hand ground with Super C65 carbon and powders were
collected after the 1st discharge and after one complete cycle. The cells
were disassembled in an Ar-filled glovebox, and the powders washed with
propylene carbonate and dried under vacuum overnight. The obtained
powder was then transferred to capillaries for diffraction measurements.
High-temperature X-ray thermodiffraction was carried out under helium
flow from RT to 500°C in an Anton Paar XRK 900 high temperature furnace
using a Panalytical X’Pert Pro diffractometer (Co Kα radiation).
Infrared spectroscopy was used as a tool for differentiating the starting
material from the product. A Shimadzu IR affinity-1 Fourier Transform
infrared spectrophotometer in attenuated total reflectance (ATR) mode
was employed in this study and the samples were scanned in the range
600 - 3800 cm-1.
Solution-phase 1H and 13C NMR were used to elucidate the chemical
structure of the synthesized compounds. 13C NMR spectra editing was
performed with DEPTQ (Distortionless Enhancement by Polarisation
Transfer with retention of Quaternaries) in order to facilitate easier
structure elucidation as the non-protonated carbons in the sample appear
as a peak with a sign similar to that of CH2 groups. All the samples were
first dissolved in a deuterated solvent containing trimethylsilane (TMS) as
an internal reference and were then measured on a 400 MHz Bruker
Avance III spectrometer. 1H NMR was performed at 400 MHz while 13C
NMR was performed at 100 MHz.
We thank the EPSRC (EP/K025112/1) and the Leverhulme Trust
(RPG-2016-323) for funding and Diamond Light Source for rapid
access to synchrotron radiation facilities. We thank Dr. Paul A.
Connor (School of Chemistry, University of St. Andrews) for
assistance with EIS measurements, Sujoy Saha (Collège de
France) for the EIS fitting and Dr. Philip Landon for the HT-XRD
measurements.
Keywords: Batteries • Na-ion • organic redox • anodes • MOFs
[1]
[2]
D. Larcher, J-M. Tarascon, Nature Chem., 2015, 1, 19.
S-W. Kim, D-H. Seo, X. Ma, G. Ceder and K. Kang, Adv. Energy Mater.,
2012, 2, 710.
[3]
[4]
[5]
B. L. Ellis, L. F. Nazar, Current Opinion in Solid State and Materials
Science, 2012, 16, 168.
V. Palomares, P. Serras, I. Villaluenga, K. B. Hueso, J. C. González, T.
Rojo, T. Energy Environ. Sci., 2012, 5, 5884.
V. Palomares, M. C. Cabanas, E. C. Martínez, M. H. Han, T. Rojo,
Energy Environ. Sci., 2013, 6, 2312.
[6]
[7]
H. Pan, Y.-S. Hu, L. Chen, Energy Environ. Sci., 2013, 6, 2338.
M. D. Slater, D. Kim, E. Lee, C. S. Johnson, Adv. Funct. Mater., 2013,
23, 947.
[8]
A. Ponrouch, E. Marchante, M. Courty, J.-M. Tarascon, M. R. Palacin,
Energy Environ. Sci., 2012, 5, 8572.
[9]
K. Kubota, S. Komaba, J. Electrochem. Soc., 2015, 162, A2538.
[10] J.-Y. Hwang, S.-T. Myung, Y.-K. Sun, Chem.Soc. Rev., 2017, 46, 3529.
[11] M. Armand, S. Grugeon, H. Vezin, S. Laruelle, P. Ribière, P. Poizot, J.-
M. Tarascon, Nature Mater., 2009, 8, 120.
[12] J. A. Kaduk, Acta Crystallogr.B, 2000, 56, 474.
[13] N. Ogihara, T. Yasuda, Y. Kishida, T. Ohsuna, K. Miyamoto, N. Ohba,
Angew. Chem. Int. Ed. 2014, 53, 11467.
In this study, the elemental (CHN) analysis results were obtained using the
service of London Metropolitan University, United Kingdom (S. Boyer). In
order to probe the thermal stability of the material thermogravimetric
analysis (TGA) was performed on a TA Instruments NETZSCH TG 209
instrument with simultaneous TGA/DTA furnace. Samples were heated
from 30 °C at a rate of 2 °C/minto a maximum temperature of 750 °C under
flowing argon.
[14] T. Yasuda, N. Ogihara, Chem. Commun. 2014, 50, 11565.
[15] D. Banerjee, S. J. Kim, J. B. Parise, Crystal Growth & Design 2009, 9,
2500.
[16] S. Wang, L. Wang, K. Zhang, Z. Zhu, Z. Tao, J. Chen, Nano Lett., 2013,
13, 4404.
[17] B. Häupler, A. Wild, U. S. Schubert, Adv. Energy Mater. 2015, 5, 140234.
[18] P. Ge, M. Fouletier, Solid State Ionics, 1988, 28, 1172.
[19] D. A. Stevens, J. R. Dahn, J. Electrochem. Soc., 2001, 148, A803.
[20] D. A. Stevens, J. R. Dahn, J. Electrochem. Soc., 2000, 147, 1271.
[21] L. Zhao, J. Zhao, Y-S. Hu, H. Li, Z. Zhou, M. Armand, L. D. Chen, Adv.
Energy Mater. 2012, 2, 962.
Electrochemical characterisation: In the initial studies the working
electrodes were made by mixing the active material (Na2NDC), conductive
carbon (Super P) and Kynar 2801 (a co-polymer based on PVDF) as
binder in N-methyl-2-pyrrolidone. The slurry was then cast on aluminium
foil using a doctor blade and dried overnight. Subsequent studies used
carboxymethyl cellulose (CMC) as the binder and the slurry was mixed in
deionized water. Ketjenblack was used as an alternative carbon source to
Super P. Several active material/conductive carbon/CMC mass ratios
were investigated including 60: 30 (Super P): 10 and 65: 10 (Super P): 15
(Ketjenblack): 10. The approximate active mass loading per disc was 2.5
mg cm-2. Electrodes were incorporated into coin cells (CR2325 type, NRC
Canada) with a sodium metal counter electrode, and with an electrolyte
solution composed of 1M NaClO4 in propylene carbonate (PC) containing
3% (wt) of fluoroethylene carbonate (FEC) additive. The cells were
assembled in an argon-filled glove box (MBraun) with moisture content and
oxygen level below 1 ppm. Electrochemical measurements were carried
out at room temperature using a Biologic MacPile II system.
[22] A. Abouimrane, W. Weng, H. Eltayeb, Y. Cui, J. Niklas, O. Poluektov, K.
Amine, Energy Environ. Sci. 2012, 5, 9632.
[23] Y. Park, D. S. Shin, S. H. Woo, N. S. Choi, K. H. Shin, S. M. Oh, K. T.
Lee, S. Y. Hong, Adv. Mater. 2012, 24, 3562.
[24] A. Choi, Y. K. Kim, T. K. Kim, M.-S. Kwon, K. T. Lee, H. R. Moon, J.
Mater. Chem. A, 2014, 2, 14986.
[25] S. Wang, L. Wang, Z. Zhu, Z. Hu, Q. Zhao, J. Chen, Angew. Chem. Int.
Ed. 2014, 53, 5892.
[26] H. Padhy, Y. Chen, J. Lüder, S.R. Gajella, S. Manzhos, P. Balaya, Adv.
Energy Mater. 2018, 8, 1701572.
[27] W. Deng, J. Qian, Y. Cao, X. Ai, H. Yang, Small 2016, 12, 583.
[28] V. Medabalmi, N. Kuanr, K. Ramanujam, J. Electrochem. Soc. 2018, 165,
A175.
Electrochemical impedance spectroscopy (EIS) measurements were
conducted on coin cells. Data were collected using a Solartron 1255
frequency response analyser coupled with Solartron 1287 electrochemical
interface. A perturbation voltage of 10 mV, together with a frequency range
of 0.1 Hz to 0.1 MHz, was employed. EIS was measured for the pristine
sample, after the 1st discharge, 1st charge and two complete cycles.
[29] Q. Zhao, Y. Lu, J. Chen, Adv. Energy Mater. 2017, 7, 1601792.
[30] A. A. Coelho, J. Appl. Crystallogr, 2000, 33, 899.
[31] A. A. Coelho, J.S.O. Evans, I.R. Evans, A. Kern, S. Parsons, Powder
Diffraction 2011, 26, S22.
[32] C.Volkringer, J.Marrot, G.Ferey, T.Loiseau, Cryst.Growth Des. 2008, 8,
685.
[33] K.O.Kongshaug, H.Fjellvag, J.Solid State Chem. 2004, 177, 1852.
Acknowledgements
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
[34] S. Cevik, Z. A. Alkaya, H. Dal, Musa Sari, Synth.React.Inorg.,Met.-
Org.,Nano-Met.Chem. 2016, 46, 1426.
[39] K. Li, J. Zhang, D. Lin, D.-W. Wang, B. Li, W. Lv, S. Sun, Y.-B. He, F.
Kang, Q.-H. Yang, L. Zhou and T. Y. Zhang, Nature Comm. 2019, 10,
[35] M. Winter, J. O. Besenhard, M. E. Spahr, P. Novak, Adv. Mater. 1998,
10, 725.
725
[40] N. Ogihara, N. Ohba, Y. Kishida, Sci. Adv. 2017, 8, 1603103.
[36] E. Peled, S. Menkin, J. Electrochem. Soc. 2017, 164, A1703.
[37] C. Bommier, X. Ji, Small 2018, 14, 1703576.
[38] B. Philippe, M. Valvo, F. Lindgren, H. Rensmo, K. Edström, Chem. Mater.
2014, 261, 75028.
[41] N. Ogihara, Y. Ozawa, O. Hiruta, J. Mater. Chem. A 2016, 4, 3398.
[42]
This article is protected by copyright. All rights reserved.

10.1002/cssc.201901626
ChemSusChem
FULL PAPER
Entry for the Table of Contents (Please choose one layout)
Layout 1:
FULL PAPER
Text for Table of Contents
Joel M. Cabañero Jr, Vanessa Pimenta, Kieran C. Cannon,
Russell E. Morris and A. Robert Armstrong*
Page No. – Page No.
Sodium naphthalene-2,6-dicarboxylate: an Anode for Sodium
Batteries
Layout 2:
FULL PAPER
Author(s), Corresponding Author(s)*
((Insert TOC Graphic here; max. width: 11.5 cm; max. height: 2.5 cm))
Page No. – Page No.
Title
Text for Table of Contents
This article is protected by copyright. All rights reserved.