H2O-induced self-propagating synthesis of hierarchical porous carbon: A promising lithium storage material with superior rate capability and ultra-long cycling life

Article abstract of DOI:10.1039/c7ta05064j

Hierarchical porous carbon (HPC) has attracted much attention in tackling global environmental and energy problems. For the state-of-the-art routes to synthesize HPC from organic compounds, the emission of carbon dioxide (CO₂) and gaseous pollutants is inevitable during thermal carbonization. Herein, we report an environmentally benign and high-yield route to synthesize HPC from CO₂via H₂O-induced self-propagating reactions. By introducing an initiator of H₂O, CO₂ can react with lithium hydride (LiH) to produce HPC in 13 seconds at low temperatures. The as-synthesized HPC exhibits an interconnected micro-meso-macropore network structure with a high porosity of 83%. The formation mechanism of HPC is discussed on the basis of the conversion reactions from CO₂ to C and the gas blowing effect in producing hierarchical porosity. The HPC evaluated as an anode material for lithium-ion batteries not only delivers a high reversible capacity of ～1150 mA h g^-1 at a current density of 0.2 A g^-1, but also exhibits superior rate capability (～825 mA h g^-1 at 1.0 A g^-1) and excellent cycling properties (up to 2000 cycles). This research opens a new avenue both to synthesize HPC from CO₂ on a large scale and to mitigate greenhouse gas from the atmosphere.

Full text of DOI:10.1039/c7ta05064j

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ISSN 2050-7488
PAPER
Kun Chang, Zhaorong Chang et al.
Bubble-template-assisted synthesis of hollow fullerene-like
MoS2 nanocages as a lithium ion battery anode material
rsc.li/materials-a

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An environmentally benign and high-yield route is developed to synthesize hierarchical porous
carbon for high‒density energy storage.

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H2O-Induced Self-Propagating Synthesis of Hierarchical Porous
Carbon: A Promising Lithium Storage Material with Superior Rate
Capability and Ultralong Cycling Life
Received 00th January 20xx,
Accepted 00th January 20xx
Chu Liang, † Sheng Liang, † Yang Xia, Yun Chen, Hui Huang, * Yongping Gan, Xinyong Tao, Jun
Zhang, and Wenkui Zhang, *
DOI: 10.1039/x0xx00000x
www.rsc.org/
Hierarchical porous carbon (HPC) has attracted much attention in tackling down the global environmental and energy
problems. For the state-of-the-art routes to synthesize HPC from organic compounds, the emission of carbon dioxide (CO2)
and gaseous pollutants is inevitable during thermal carbonization. Herein, we report an environmentally benign and high-
yield route to synthesize HPC from CO2 via H2O-induced self-propagating reactions. By introducing an initiator of H2O, CO2
can react with lithium hydride (LiH) to produce HPC in 13 seconds at low temperatures. As-synthesized HPC exhibits
interconnected micro-meso-macropore network structure with high porosity of 83%. The formation mechanism of HPC is
discussed on the basis of the conversion reactions from CO2 to C and the gas blowing effect in producing hierarchical
porosity. The HPC evaluated as anode materials for lithium ion batteries not only delivers a high reversible capacity of
~1150 mAh g−1 at a current density of 0.2 A g−1, but also exhibits superior rate capability (~825 mAh g−1 at 1.0 A g−1) and
excellent cycling properties (up to 2000 cycles). This research opens a new avenue both to synthesize HPC from CO2 on a
large scale and to mitigate greenhouse gas from the atmosphere.
example, 3D hierarchical porous graphenes prepared by Zuo et
al.10 deliver a reversible lithium storage capacity of 932 and 400
Introduction
Ever-increasing consumption of fossil fuels has led to the global
shortage of fossil fuels and environmental deterioration. The
pursuit of a low-carbon economy has stimulated considerable
effort in the development of efficient conversion and storage of
the renewable energy including solar, wind, water and geothermal
energy.1-4 Lithium-ion batteries, which have come into powering
hybrid electric vehicles and pure electric vehicles, are one of the
most promising energy storage devices in terms of high energy
density and good environmental compatibility. Currently, graphitic
carbons are selected as the leading anode material for commercial
lithium-ion batteries due to their low cost and good cycling
stability. Unfortunately, the low lithium storage capacity
(theoretical capacity of 372 mAh g‒1) and limited rate capability
result in graphitic carbons failing to satisfy the requirements of the
onboard lithium-ion batteries with higher energy density and
power density.5-6 For the large-scale applications of onboard
lithium-ion batteries, therefore, it is of importance to design and
synthesize novel carbon materials with increased lithium storage
capacity and superior rate capability.
mAh g‒1 at the current density of 100 and 1000 mA g‒1
,
respectively, much higher than that of the commercial graphite5.
The hierarchical porous structure and high specific surface area of
hierarchical porous carbons are responsible for the improved
electrochemical lithium storage properties. HPCs with a 1D to 3D
network have been successfully synthesized from various
carbonaceous sources by employing templates,11-12 chemical or
physical activation,13-14 acidic etching,15-16 etc. Generally, the
template synthesis of HPC is time-consuming, energy-intensive
and environment-unfriendly because of the complicated synthesis
procedure, limiting the industrial production. Recently,
tremendous attention has been paid to synthesize HPC on a large
scale via a template-free method.17-19
In order to achieve the environmentally benign synthesis of
HPC, it is critical to select the green synthetic routes and pollution-
free carbonaceous sources. Organic compounds, such as fossil-
based products,20-21 polymers,22-23 biomass,24-25 and metal-organic
frameworks,26-27 are the most important carbon precursor in the
state-of-the-art synthesis of HPC. During the carbonization
process, large amounts of CO2, the most common greenhouse gas,
and gaseous pollutants are released from the organic compounds.
Anthropogenic emissions of CO2 from organic compounds
combustion are regarded as the major contributor to the
continuing global warming.28-29 It was estimated that about 13
billion tonnes of CO2 are produced from the consumption of fossil
HPC has been demonstrated to be the high-capacity and
superior-rate anode material for lithium-ion batteries.7-9 For
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fuels each year.30 Up to now, it is still challenging to reduce the
anthropogenic emission of CO2 into the atmosphere.
filled with gaseous CO2, followed by introducing a small amount of
H2O into the reactor. Fig. 2a shows the time dependence of
sample temperatures and gaseous pressures in the reactor. The
temperature of the LiH–CO2 mixture maintained at RT in the first
stage, whereas it was raised from RT to 315 oC of the highest
reaction temperature in 13 seconds as a small amount of H2O was
simultaneously mixed with LiH and CO2, indicating an exothermic
nature of above synthesis reactions. The time dependence of
gaseous pressures in the reactor is similar to that of the
temperatures. These results imply that CO2 was gradually
consumed in the above exothermic process. The as-obtained solid
residue was washed with hydrochloric acid, and then the post-
washed solid residue (HPC) was collected for energy dispersive X-
ray spectroscopy (EDS) analysis (Fig. S2). Only C and O elements
are identified. The weight ratio of C:O is calculated to be 95.3:4.7
for the HPC. The EDS result demonstrates that CO2 was
successfully converted into carbon in above exothermic reaction
process. The trace amount of O may be resulted from the oxygen
absorbed by carbon.31-32
CO2 has not been used as the carbonaceous source to produce
HPCs because of its thermodynamically and kinetically stable
nature. Herein, we develop a new strategy for the environmentally
benign and efficient synthesis of HPC from CO2 through a self-
propagating reaction between CO2 and LiH. This self-propagating
reaction can be easily initialized at room temperature (RT) by
introducing
a small amount of H2O. The H2O-induced self-
propagating synthesis of HPCs is an energy-saving and
ultraefficient method as CO2 can react with LiH to produce HPC in
13 seconds. Moreover, the as-synthesized HPC exhibits excellent
electrochemical lithium storage properties with a high reversible
capacity of ~830 mAh g‒1 at a current density of 1.0 A g‒1 and
ultralong cycling life (over 2000 cycles). Our green and efficient
strategy (Fig. S1）will open up a new avenue in tackling the long-
term challenges of greenhouse effect, energy crisis and air
pollution.
RESULTS AND DISCUSSION
A
broad diffraction peak centered at 25.6° and
a weak
Synthesis and characterization of HPC
diffraction peak centered at 42.7°, which are close to the (002)
Fig. 1 shows the key synthesis procedure of HPC from CO2. Firstly
LiH powder was dispersed at the bottom of a homemade reactor
Fig. 1 Schematic illustration of the synthesis procedure of HPC.
Fig. 2 (a) Time dependence of temperatures and gaseous pressures in the reactor of the HPC synthesis process. (b) Raman spectrum of
HPC.
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and (101) diffraction peaks of hexagonal graphite, respectively,
were observed in the X-ray diffraction (XRD) pattern of HPC (Fig.
S3), indicating that the HPC may not crystallize well. Raman
spectrum was measured to study the degree of graphitization.
Two peaks centered at 1350 and 1580 cm-1 are observed in Fig. 2b,
corresponding to the D band and G band modes of the sp2 C–C
bond, respectively.33 The intensity ratio of the D to G band (ID/IG) is
0.86, implying low graphitization degree of HPC. This result is
consistent with the XRD result. Field emission scanning electron
microscopy (FESEM) and transmission electron microscopy (TEM)
were employed to evaluate the morphology. As shown in Fig. 3a
and b, the as-synthesized carbon exhibits a HPC network
morphology, in which the interconnected pores are randomly
distributed across the carbon sheets. The hierarchical porous
morphology can be observed in TEM and high-resolution TEM
image (Fig. 3c-e) as well. The porosity of HPC was further assessed
by the nitrogen adsorption‒desorption and Hg penetration
measurements. A hysteresis loop (0.45<P/P0<0.98) is observed in
the nitrogen adsorption‒desorption isotherms (Fig. 3f), which is a
typical IV-type curve for mesoporous adsorbents, suggesting that
the interconnected mesoporous channels are presented in HPC.34
The pore diameter distribution of HPC is determined by the
density functional theory (Fig. 3f) and Hg penetration method (Fig.
3g). The HPC exhibits a micro-meso-macropore structure. The
micropores and macropores are centered at 1.45 and 151 nm,
Fig.3 (a, b) SEM images of HPC. (c, d) TEM images of HPC. (e) HRTEM image and SAED pattern of HPC. (f) Nitrogen adsorption–desorption
isotherms and corresponding pore diameter distribution of HPC. (g) Pore diameter distribution of HPC calculated from the Hg penetration
measurement.
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respectively. A continuous pore diameter distribution is found in
the mesopores. From the Hg penetration analysis, the HPC
possesses high porosity of 83% and high total pore volume of 9.51
cm3 g‒1. The specific surface area is calculated to be 334 m2 g‒1 by
the Brunauer Emmett Teller model. The crystalline characteristics
of the HPC was further investigated by high-resolution TEM (Fig.
3e) and selected area electron diffraction (SAED, Fig. 3e), in good
agreement with the results of XRD and Raman spectrum.
indicate that the crystalline Li2O and poor crystalline C are the
major phases in the as-obtained solid residue. As a result, it can be
concluded that the direct chemical reaction between LiH and CO2
may be responsible for the major products of Li2O and C. To
confirm our deduction above, the solid-gas mixture of LiH and CO2
was gradually heated in a sealed reactor. The time dependence of
sample temperatures and gaseous pressures in the reactor are
presented in Fig. 4b. The sample temperature was elevated to 334
oC of the highest reaction temperature in 20 seconds when the
solid-gas mixture of LiH and CO2 was gradually heated to 212 oC.
The mixture of LiH and CO2 exhibits similar changes in the time
dependence of sample temperatures and gaseous pressures with
the mixture of LiH, CO2 and a small amount of H2O as shown in Fig.
2a, suggesting that the small amount of H2O is not a required
reactant for the conversion of CO2 to carbon.
A static weighing method was used to estimate the yield of HPC.
For a typical synthesis, a total of about 8.000 g LiH was used to
react with CO2. Finally, ca. 2.768 g of HPC was obtained after
washing and drying. The yield of HPC relative to the weight of LiH
is about 34.6%. Even more important, the synthesis reaction of
HPC occurred at a low temperature and a low gaseous pressure
and completed within 13 seconds (Fig. 2a).
The solid product of LiH reacting with gaseous CO2 was
collected for XRD analysis (Fig. 4c). A major phase of Li2O and a
minor phase of Li2CO3 are observed in the XRD pattern. The
Rietveld refinement of XRD pattern exhibits that the weight ratio
of Li2O phase and Li2CO3 phase is ca. 2.53:1, corresponding to ca.
6.25:1 of the molar ratio. After hydrochloric acid washing, the
solid residue is carbon as determined by XRD and EDS analyses
(Fig.
Formation mechanism of HPC
As shown in Fig. 4a, the XRD characteristic peaks of Li2O and Li2CO3
phases were clearly detected in the as-obtained solid residue
derived from the reaction between LiH, CO2 and H2O. The XRD
peaks of C are not observed in Fig. 4a because of its poor
crystallinity. The Rietveld refinement of XRD pattern shows that
the weight ratio of Li2O phase and Li2CO3 phase is 3:2,
corresponding to ca. 3.7:1 of the molar ratio. These results
Fig. 4 (a) Rietveld refinement of the XRD pattern of the as-obtained solid residue of the LiH‒CO2 mixture with 0.09 g H2O. (b) Time
o
dependence of sample temperatures and gaseous pressures in the reactor of the LiH‒CO2 mixture heated from RT to 215 C at a rate of 8
oC min‒1. (c) Rietveld refinement of the XRD pattern of the as-obtained solid residue of the LiH‒CO2 mixture heated from RT to 215 oC at a
rate of 8 oC min‒1. (d) Temperature dependence of pressure difference of CO2 for the Li2O powder heated from RT to 310 oC.
4 | J. Name., 2012, 00, 1-3
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S4 and S5). The same products of C, Li2O and Li2CO3 were
identified in the as-obtained solid products of the LiH‒CO2 mixture
with and without H2O. Moreover, H2 was detected in the gaseous
reaction products of above two samples (Fig. S6). The chemical
reaction between LiH and CO2 can be proposed as follows:
chemical interaction between LiH, H2O and CO2 is the exothermic
reactions. As discussed above, it has been demonstrated that the
reaction of Equation 1 can be initiated by heating the LiH‒CO2
mixture to 212 oC. For the LiH‒CO2 mixture with a small amount of
H2O, the heat released from the exothermic reaction (Equation 3)
occurred at RT initiates the exothermic conversion reaction
between LiH and CO2. The adding H2O acts as an initiator for the
chain reactions between LiH and CO2. According to the standard
enthalpies of formation of reactants and products (Table. S2), the
4LiH + CO2 → C + 2Li2O + 2H2
(1)
According to Equation 1, the theoretical yield of C is about 37.8%,
which is very close to our experimental value of 34.6% relative to
the weight of LiH.
heat released from Equation 1 is calculated to be ‒440.3 kJ mol‒1
,
The minor phase of Li2CO3 may be the product of the newly
developed Li2O reacting with CO2 in the thermal process. The
solid‒gas mixture of Li2O and CO2 was heated from RT to 310 oC at
a rate of 2 oC min−1. The temperature dependence of pressure
differences of CO2 is plotted in Fig. 4d. The pressure differences of
CO2 remarkably decreased as the temperature was elevated to
above 210 oC, implying that CO2 was consumed at the
implying an exothermic nature for the efficient synthesis of HPC
from CO2, which is consistent with the experimental phenomenon
as shown in Fig. 2a. However, the chemical reaction between LiH
o
and CO2 can occur only at the temperature above 212 C (Fig. 4b),
resulting from the high kinetic barrier. The reaction heat released
from the exothermic reactions (Equations 3 and 4) is as high as
177.8 kJ mol‒1. As a consequence, this chemical reaction can be
easily initiated by the reaction heat of the Equations 3 and 4.
o
o
temperature of above 210 C. For the sample heated at 310 C, a
new phase of Li2CO3 was clearly detected in the XRD pattern (Fig.
S7). These results prove our deduction that the newly developed
Li2O further reacted with CO2 to produce the minor phase of
Li2CO3 as shown in Fig. 4c.
As for the formation mechanism of HPC, the gas blowing effect
plays a key role in producing hierarchical porosity.14,36 A series of
simultaneous/consecutive reactions including Equations 1‒4
occurred in the synthesis process of HPC. A lot of H2 is released
from these chemical reactions. The gas blowing effect of H2 is
responsible for the generation of interconnected macropores in
HPC as the macroporous structure can be clearly observed in the
as-obtained solid residue (Fig. 5a). Moreover, the C and O
elements are shown to be homogeneously distributed within the
as-obtained solid residue (Fig. 5b and c), indicating that the
byproducts of Li2O, Li2CO3 and LiOH are homogeneously dispersed
into HPC. So, it can be concluded that the mesopores and
micropores are probably produced during the removal of the
byproducts (Li2O, Li2CO3 and LiOH) and/or by the
chemical/physical activation of LiOH and residual CO2.37-38
Li2O + CO2 → Li2CO3
(2)
Combined with the Rietveld refinement results (Fig. 4a and c), it
can be known that the content of Li2CO3 is not equal for the as-
obtained solid residues derived from the LiH‒CO2 mixture with
and without H2O. This result suggests that the content of Li2CO3
may relate to the amount of H2O. For the LiH‒CO2 mixture
reacting with various amounts of H2O, the XRD patterns of as-
obtained solid residues were analyzed with the Rietveld
refinement (Fig. 4a, 4c and Fig. S8‒S11). The abundance of major
phases of Li2CO3 and Li2O are listed in Table. S1. It is obvious that
the content of Li2CO3 phase increases with the amount of H2O,
implying that the Li2CO3 can also be produced by the chemical
reaction between LiH, H2O and CO2.
It is well known that LiH can react with H2O to produce LiOH and
give off H2 at RT.35 Gaseous CO2 can be quickly absorbed by LiOH
at RT (Fig. S12). Hence, the Li2CO3 derived from the LiH, H2O and
CO2 mixture can be described by the following chemical reactions.
LiH + H2O → LiOH + H2
(3)
(4)
2LiOH + CO2 → Li2CO3 + H2O
The newly produced H2O will exist in gas state because of the
reactor temperature above its boiling point, preventing from the
reaction between newly produced H2O and LiH. On the basis of
Equation 3 and 4, the theoretical content of Li2CO3 is 20.6 wt.%,
which is less than the experimental value of 40.0 wt%, for the as-
obtained solid residue as shown in Fig. 4a. It can be concluded,
therefore, that the chemical reactions (Equations 2, 3 and 4) are
together responsible for the Li2CO3 formation from the LiH‒CO2
mixture with a small amount of H2O.
Fig. 5 (a) SEM image of the as-obtained solid residue from the LiH‒
CO2 mixture with a small amount of H2O. (b, c) the corresponding
elemental mappings of C and O.
The reaction heat of Equation 3 and 4 is calculated to be ‒111.2
and ‒133.2 kJ mol‒1 (Table. S2), respectively, suggesting that the
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Fig. 6 (a) Cyclic voltammograms of HPC at a scan rate of 0.1 mV s−1. (b) Galvanostatic charge and discharge curves of HPC at a current
density of 0.2 A g −1. (c) Cycling properties and Coulombic efficiency of HPC and commercial graphite at a current density of 0.2 A g−1. (d)
Galvanostatic charge and discharge curves of HPC at 0.2, 0.5, 1, 2 and 4 A g −1. (e) Ultralong cycling life and rate performance of HPC and
the cycling properties of commercial graphite cycled at 1 A g −1
.
Electrochemical lithium storage properties of HPC
electrolyte and the formation of the solid electrolyte interphase
(SEI) layer in the carbon electrode. Another weak cathodic peak
centered at ~1.50 V may originate from the irreversible reaction of
lithium ions with functional groups on the surface of the carbon
electrode.39-41 These irreversible reactions are further confirmed
The electrochemical lithium storage properties of HPC were
evaluated using CR2032 coin-type half cells. Fig. 6a illustrates its
cyclic voltammetry (CV) curves measured at a scanning rate of 0.1
mV s‒1. The electrochemical behaviors of the sample at the first
cycle, particularly for the cathodic scan, are different from those
at the subsequent cycles. In the first cathodic scan, two weak
reduction peaks centered at ~0.65 V and 1.50 V, which were only
detected in the initial lithiation process, are observed. The peak
around 0.65 V can be attributed to the decomposition of the
by the galvanostatic discharge/charge result that
a large
irreversible capacity of 647 mAh g−1 is found at the first cycle (Fig.
6b). The dominant peak at 0‒0.5 V corresponds to the reversible
lithium storage of HPC. From the second to third cycle, the CV
curves have no obvious changes in voltages vs. Li/Li+ and peak
current densities, demonstrating good reversibility of HPC for
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lithium storage. The redox peaks at 0.9/1.2 V can be clearly seen in
the second and third cycles CV curves, which are associated with
reversible lithium storage in the defects and pores of the
HPC.18,42,43 The electrochemical behaviors of HPC are found to be
similar to those of the non-graphitic carbon.
mesopores and macropores) and surfaces/interfaces, which acts
as reservoirs for electrochemical lithium storage.44 Meanwhile, the
hierarchical porous structure can buffer the large volumetric
effect (about 10% for lithium storage in the graphite50) during
repeated intercalation and deintercalation of lithium ions in the
HPC, contributing to excellent cycling stability. Of course, a large
As shown in Fig. 6c, the HPC delivers a discharge capacity of
1160 mAh g−1 and a charge capacity of 513 mAh g−1 at a current
density of 0.2 A g−1 during first cycle, corresponding to an initial
Coulombic efficiency of 44%. The low initial Coulombic efficiency
can be attributes to form SEI layers on the large surface and
interface areas of HPC and/or the irreversible lithium storage
reaction of Li+ with functional groups on the surfaces.18,44 After
several cycles, the HPC reaches a stable discharge capacity of ~
470 mAh g−1 and high Coulombic efficiencies of ~99%. The capacity
of HPC decreases at first several cycles may be mainly resulted
from the gradual formation of the SEI layers on HPC electrode. It
should be noted that the discharge capacity increases gradually
with the cycle number in the continued cycling (Fig. 6c). The
discharge capacity increases from 470 mAh g−1 to 558 mAh g−1 at
the 100th cycle. This phenomenon has been also observed in other
irreversible
capacity
is
inevitable
during
first-cycle
discharge/charge as shown in Fig. 6c because of the high
surface/interface area of the HPC. For understanding the superior
rate capability of HPC, the electrochemical impedance spectra (Fig.
S15) were measured. The HPC has lower diffusion impedance and
interfacial and charge transfer resistance than graphite at both
open-circuit voltage and after forming stable SEI layers. It can be
concluded that the interconnected porous nanostructure with
high porosity of 83% not only promotes the continuous and rapid
transport of electrons but also supplies fast transport channels for
lithium ions. The synergistic effects of macropores, mesopores and
micropores result in the superior rate capability of HPC.
Conclusions
In summary, we have developed an environmentally benign,
efficient and high-yield route to synthesis HPC from greenhouse
gas through H2O-induced self-propagating reactions between CO2
and LiH. The as-synthesized HPC exhibited the interconnected
micro-meso-macropore network structure with high porosity of
83%. The formation mechanism of HPC was investigated with XRD,
EDS, SEM, TEM, MS analyses and time dependence of sample
temperature and gaseous pressure measurements. Owing to the
unique hierarchical porous structure and high porosity, the HPC
showed excellent electrochemical lithium storage properties with
a reversible capacity of ~1150 mAh g‒1 at a current density of 0.2 A
g-1 and ~ 555 mAh g−1 up to 2000 cycles even at a high current
density of 2.0 A g-1. Our results may provide a new avenue in
tackling down the long-term challenges of greenhouse effect,
energy crisis and air pollution.
carbon
materials.43,45-47
The
remarkable
increase
in
discharge/charge capacity can be ascribed to the cycle-activating
process of the carbon electrode during Li insertion/extraction.44,48
The HPC exhibits excellent cycling properties and superior rate
capability. The long cycling properties were evaluated at the
current density of 1.0 A g-1 and the corresponding results are
presented in Fig. 6e. It delivers a high reversible capacity of ~830
mAh g‒1 after 1000 cycles, which is about 8 times and 10 times
higher than that of the commercial graphite (Fig. 6e) and the
amorphous activated carbon (Fig. S13), respectively. After the
initial 1000 cycles discharged/ charged at the current density of
1.0 A g-1, the HPC was cycled at various current densities (Fig. 6d‒
e). Its reversible capacity reaches as high as ~1150 mAh g−1 at the
current density of 0.2 A g−1. It is obvious that the reversible
capacity of the HPC decreases with the increasing
discharge/charge current density. The discharge capacities are
~1000, 825, 655 and 470 mAh g−1, respectively, for the HPC cycled
at the current densities of 0.5, 1.0, 2.0 and 4.0 A g−1. When the
current density is returned to 1.0 A g−1 after 100 cycles, the
reversible capacity is recovered to ~815 mAh g−1 without
remarkable capacity fading after 100 cycles. To examine the longer
cycling stability, the HPC was further cycled at the current density
of 2.0 A g−1. The reversible capacity of ~555 mAh g−1 is maintained
up to 2000 cycles (Fig. 6e), corresponding to a high capacity
retention of 85%.
Experimental Section
Chemical reagents
LiH (97%, Aladdin), CO2 (>99.995%, Jingong), anhydrous ethanol
(99.5%, Aladdin), Li2O (97%, Aladdin) and hydrochloric acid (AR,
Sinopharm) were used as received without further purification. To
prevent air and moisture contamination of LiH and Li2O, these
reagents were handled in a MBRAUN glovebox filled with purified
argon (>99.995%, Jingong).
Materials synthesis
Compared with commercial graphite and other carbonaceous
The synthesis of HPC was performed in a homemade reactor
equipped with 2 gas valves and a thermocouple. The sample
temperatures and gaseous pressures in the reactor were
monitored by the thermocouple and pressure transducer. The
reactor was sealed with copper gasket. For a typical experiment,
post-milled LiH powder (about 0.8 g) was loaded into a reactor in a
glovebox (MBRAUN) filled with purified argon. About 6.5 bar CO2
was introduced into the reactor to mix with LiH powder. The
chemical reaction between LiH and CO2 could be initialized by
adding water and heating, respectively. In one case, a small
amount of deionized water (e.g. 0.09, 0.18, 0.27, 0.36 and 0.45 g)
7,10,18,41,45-47,48,49
materials reported,
the HPC exhibits a higher
reversible capacity during the discharge/charge cycling and
ultralong cycle life (Table. S3). The rate capability of the HPC is also
superior to that of the commercial graphite and other carbon
nanomaterials10,11,18,45-47 as depicted in Fig. S14. These superior
electrochemical properties are assigned to the unique
nanostructure of the HPC. It has been known that the reversible
lithium storage capacity of the HPC is much greater than that of
graphite (Fig. S14). The excess capacity may result from a high
amount of extra lithium storage in the pores (including micropores,
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was mixed with the solid‒gas mixture LiH‒CO2 through a gas valve.
In the other case, the solid‒gas mixture LiH‒CO2 was heated from
RT to 215 oC at a rate of 8 oC min‒1. At the end of the reaction, the
reactor was gradually cooled to RT, followed by washing the solid
product with excess hydrochloric acid (6 M). The suspension of
solid products was filtered from the above solution by microfilter.
Subsequently, the as-obtained solid products were washed by
deionized water and absolute ethanol. This procedure was
repeated several times. Finally, the solid products were dried at 80
oC in a vacuum oven.
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This work was supported by the National Natural Science
Foundation of China (Nos. 51677170, 51572240 and 21403196)
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