electrosprayed porous fe o /carbon microspheres as anode ... · nano res. 2018, 11(2): 892–904...

Electrosprayed porous Fe3O4/carbon microspheres as anode materials for high-performance lithium-ion batteries

Wenjie Han1,2, Xianying Qin1,3 (), Junxiong Wu3, Qing Li1,2, Ming Liu1,2, Yue Xia1, Hongda Du1,

Baohua Li1 (), and Feiyu Kang1,2

1 Engineering Laboratory for Next Generation Power and Energy Storage Batteries, and Engineering Laboratory for Functionalized

Carbon Materials, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China 2 School of Materials Science and Engineering, Tsinghua University, Beijing 100084, China 3 Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay,

Kowloon, Hong Kong, China

Received: 16 May 2017

Revised: 3 June 2017

Accepted: 6 June 2017

© Tsinghua University Press

and Springer-Verlag GmbH

Germany 2017

KEYWORDS

lithium ion battery,

Fe3O4/carbon microsphere,

hierarchical pores,

electrospray technique,

electrochemical

performance

ABSTRACT

Porous Fe3O4/carbon microspheres (PFCMs) were successfully fabricated via

a facile electrospray method and subsequent heat treatment, using ferrous

acetylacetonate, carbon nanotubes (CNTs), Ketjen black (KB), polyvinylpyrrolidone

(PVP), and polystyrene (PS) as raw materials. The porous carbon sphere framework

decorated with well-dispersed CNTs and KB exhibits excellent electronic

conductivity and acts as a good host to confine the Fe3O4 nanoparticles. The

abundant mesopores in the carbon matrix derived from polymer pyrolysis can

effectively accommodate the volume changes of Fe3O4 during the charge/

discharge process, facilitate electrolyte penetration, and promote fast ion diffusion.

Moreover, a thin amorphous carbon layer on the Fe3O4 nanoparticle formed

during polymer carbonization can further alleviate the mechanical stress associated

with volume changes, and preventing aggregation and exfoliation of Fe3O4

nanoparticles during cycling. Therefore, as anode materials for lithium-ion

batteries, the PFCMs exhibited excellent cycling stability with high specific

capacities, and outstanding rate performances. After 130 cycles at a small current

density of 0.1 A·g–1, the reversible capacity of the PFCM electrode is maintained

at almost 1,317 mAh·g–1. High capacities of 746 and 525 mAh·g–1 were still achieved

after 300 cycles at the larger currents of 1 and 5 A·g–1, respectively. The optimized

structure design and facile fabrication process provide a promising way for the

utilization of energy storage materials, which have high capacities but whose

performance is hindered by large volume changes and poor electrical conductivity

in lithium or sodium ion batteries.

Nano Research 2018, 11(2): 892–904

https://doi.org/10.1007/s12274-017-1700-6

Address correspondence to Xianying Qin, [email protected]; Baohua Li, [email protected]

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

893 Nano Res. 2018, 11(2): 892–904

1 Introduction

In order to address large-scale environmental

deterioration, lithium-ion batteries (LIBs) have arisen

as possible environmentally-friendly alternatives to

fossil fuel-based energy consumption. Their large

voltage-windows, high energy density, and long cycle

life [1, 2] have resulted in their widespread use in

portable electronic products, electric/hybrid vehicles,

and power storage devices. However, it is difficult for

current commercial electrode materials to meet the

performance demands for battery-powered electric

vehicles (EVs), which require higher energy and power

densities, as well as a longer cycle life. Considering

that the theoretical specific capacity of a commercial

graphite anode is low (372 mAh·g–1) [3–5], developing

high-performance anode materials with optimized

structures is an effective way to address the above

issues. In the last decade, new anode materials such

as metal oxides, sulfides, silicon, tin, and carbon

materials [6–18] have been extensively studied to

improve electrochemical performance. Among these

existing anode materials, Fe3O4 is considered as a

promising alternative for energy storage in LIBs. This

is because it is environmentally benign, low-cost, and

has a much higher theoretical capacity (926 mAh·g–1)

than commercial graphite [19, 20]. Nonetheless, the

large volume change (93%) typically observed during

lithiation/delithiation processes, results in the formation

of an unstable solid-electrolyte interphase (SEI), which

further leads to a loss of electrical contact between

the active material and conductive additives, thus,

destroying the electrode integrity and causing significant

capacity fading. Furthermore, the low electrical

conductivity and sluggish ionic diffusion rate greatly

hinder the rate performance of Fe3O4 anodes [21–23].

To solve the problems mentioned above and produce

ideal anode materials with high capacity and stability,

considerable efforts have been devoted to designing

various advanced Fe3O4-based anode materials with

optimized size, structure, and constitution [24]. One

such set of examples is the integration of a Fe3O4-based

active material into various carbonaceous matrices to

form stable hybrid nanostructures with superior

electrical conductivity. In this case, the carbon materials

can not only improve the electron propagation, but

also buffer the volume strain of Fe3O4 during the

charge/discharge process because of their good elasticity

and toughness. Various carbonaceous materials were

used in these studies, such as carbon nanotubes (CNTs)

[25, 26], graphene [27, 28] and amorphous carbon [29].

CNTs are one of the most widely used candidates

in preparing hybrid electrodes because of their high

electrical conductivity and excellent mechanical

tenacity. Recently, Cheng and co-workers have confined

electrochemically prelithiated iron oxide in CNTs by

immersing the carbon-coated anodic aluminum oxide

films into a solution of iron nitrate in ethanol [26].

The prepared nanocomposites exhibited a reversible

specific capacity of 963.7 mAh·g–1 at a current density

of 50 mA·g–1 based on the total mass after 16 cycles.

Chen and co-workers reported a facile method to

synthesize CNTs-Fe3O4@C beaded structures by de-

positing Fe3O4 and carbon layers on CNTs, thus, giving

rise to a recharge capacity retention of 720 mAh·g–1

after 80 cycles at 0.1 A·g–1 [30]. Meanwhile mesoporous

carbon is considered as another ideal framework to

encapsulate electrochemically active particles for LIB

applications [20, 31].

An additional route to improving performance is

the encapsulation of porous Fe3O4 in microstructures.

These porous and secondary structures can effectively

alleviate volume changes in Fe3O4 particles and

provide numerous channels for rapid transportation

of electrolytes as well as lithium ions. Wong and

co-workers fabricated carbon encapsulated hollow

Fe3O4 nanoparticles homogeneously anchored on

graphene nanosheets by a polyol-media solvothermal

method [32]. The hybrid materials delivered a reversible

capacity of 870 mAh·g–1 at 0.1 A·g–1 and excellent rate

performance for lithium storage. The interior voids

of the composites accommodated the large volume

change of Fe3O4 and improved the reaction kinetics.

However, the increase of void fraction can lead to

a structural collapse, and the aggregation of Fe3O4

nanoparticles into larger particles, which pulverize

upon long discharge/charge cycles [33]. In this

case, synthesizing Fe3O4/carbon nanocomposites with

optimized porous structures (porosity and pore size)

is crucial to protect Fe3O4 nanoparticles and obtain

superior electrochemical performances.

The third route for utilizing these materials is the

| www.editorialmanager.com/nare/default.asp

894 Nano Res. 2018, 11(2): 892–904

fabrication of nano-sized Fe3O4-based particles. These

provide short diffusion pathways for lithium ions

and electrons, and therefore eliminate internal stress

on the electrode [34]. Since this route improves

both the reaction kinetics and structural stability, the

electrochemical performance is enhanced [26, 35, 36].

Meng et al. reported the synthesis of Fe3O4/carbon

composite nanofoils with an average thickness of

about 20 nm [37]. The thin nanofoils provided shorter

lithium path lengths compared with the bulk counterpart,

leading to improved rate performances. However,

due to the low conductivity and easy agglomeration of

Fe3O4 nanoparticles during cycling, Fe3O4 nanoparticles

are generally combined with carbonaceous materials

to solve the above issues [26, 33, 38].

Herein, we report an electrospray technique to

fabricate porous Fe3O4/carbon microspheres (PFCMs),

in which Fe3O4 nanoparticles are embedded in a

porous carbon framework consisting of CNTs, Ketjen

black (KB), and amorphous carbon. The resulting

PFCM anodes in LIBs demonstrate a high specific

capacity, excellent cycling stability, and outstanding

rate performance. The reversible capacity of the PFCMs

can reach almost 1,317 mAh·g–1 after 130 cycles at

0.1 A·g–1. Furthermore, high capacities of 746 and

525 mAh·g–1 are still achieved after 300 cycles at 1 and

5 A·g–1, respectively. The superior electrochemical

properties are attributed to the optimized structure

design for PFCMs. The first advantage of our optimized

structure is the intertwining of CNTs and KB particles.

This forms an excellent conductive skeleton and

mechanical scaffold, which greatly promotes the

electron/ion transportation and strengthens the structural

stability. The mesoporous structure provides a second

advantage by efficiently alleviating the large stress

resulting from internal expansion during Fe3O4 lithiation,

thus, ensuring the structural integrity of PFCMs is

maintained during cycling. Lastly, the confined Fe3O4

nanoparticles encapsulated in amorphous carbon

layers can effectively avoid particle agglomeration

and achieve fast reaction kinetics.

2 Experimental

2.1 Chemicals

All the chemicals, including ferrous acetylacetonate

(Fe(acac)2, Sigma Aldrich), polyvinylpyrrolidone (PVP,

MW = 1,300,000, Sigma Aldrich), polystyrene (PS, MW =

192,000, Sigma Aldrich), multi walled CNTs (Chengdu

Organic Chemicals Co. Ltd.), KB (EC-600JD) and

dimethyl formamide (DMF, Fisher), were used directly

without further purification.

2.2 Synthesis of PFCMs

PFCMs were synthesized by electrostatic spraying

followed by heat treatment. In a typical preparation

process, 0.5 g PVP, 0.56 g PS, 0.22 g KB, and 0.1 g CNTs

were added into 20 mL DMF to form a homogeneous

stable suspension under magnetic stirring at 80 °C for

2 h and subsequent ultrasonic dispersion for 2 h. Next,

1 g Fe(acac)2 was added into the above suspension

with magnetic stirring at 80 °C for 2 h and ultrasonic

dispersion for an additional 2 h to form the finial

precursor solution for our electrospray technique.

The spray solution was atomized with a high voltage

of 25 kV and a distance of 15 cm was maintained

between the nozzle and substrate at a flow rate of

1.0 mL·h–1. After electrostatic spraying, the as-prepared

precursor hybrids were stabilized in air at 250 °C for

2 h, and then carbonized in argon at 600 °C for 2 h

with a heating rate of 5 °C·min–1 to obtain the final

PFCMs.

2.3 Material characterization

The morphology and microstructure of PFCMs and

their precursor microspheres were characterized by a

field emission scanning electron microscope (FE-SEM,

HITCH S4800) and a high-resolution transmission

electron microscope (HRTEM, FEI TECNAIG2 F30).

The scanning transmission electron microscope (STEM)

and corresponding energy-dispersive X-ray spectros-

copy (EDX) were performed to investigate the elemental

composition and distribution in the PFCMs. The

phase and crystallographic structure of samples were

identified by X-ray diffraction (XRD, Rigaku D/max

2500/PC using Cu Kα radiation with k = 1.5418 A°).

Thermogravimetric analysis (TGA) was carried out

on a simultaneous thermal analyzer (NETZSCH

STA449F3) with a heating rate of 10 °C·min–1 in an

air atmosphere to characterize the weight content of

Fe3O4 in PFCMs. The porous structure and specific

surface of PFCMs were measured using the Brunauer–


895 Nano Res. 2018, 11(2): 892–904

Emmett–Teller (BET) method based on absorption–

desorption of nitrogen tested on Micrometrics ASAP

2020 surface area and porosity analyzer.

2.4 Electrochemical characterization

Electrochemical performances of PFCMs were tested

with CR2032 coin half-cells assembled in an argon-

filled glove box with moisture and oxygen levels less

than 0.1 and 0.5 ppm. The working electrodes were

prepared by mixing active materials (PFCMs), con-

ductive agent (Super P), and binder (sodium alginate)

with a weight ratio of 8:1:1 in water, followed by

coating the above slurry on a copper foil and drying

in a vacuum oven at 80 °C for 12 h. The copper foil

coated with active materials was punched into circular

discs with a diameter of 12 mm. Metallic lithium foils

were used as both counter and reference electrodes.

Celgard 2250 polypropylene films were used as

separators for cells. The used electrolyte contained

1 M LiPF6 dissolved in a mixture of diethyl carbonate

(DEC), ethylene carbonate (EC), and ethyl methyl

carbonate (EMC) (1:1:1 by volume) with 2 vol% vinylene

carbonate (VC). The cycle life and rate capability of the

cells were tested using Land 2001A battery testing

systems at a voltage range of 0.01–3.00 V (vs. Li+/Li),

and the specific capacity was calculated based on

the total mass loading of PFCMs on electrodes

(0.32 mg·cm–2). Cyclic voltammograms (CVs) were

measured on a VMP3 electrochemical workstation

at a scan rate of 0.1 mV·s–1 within a voltage range of

0.01 to 3 V. Electrochemical impedance spectroscopy

(EIS) was performed on a CHI660C electrochemical

workstation in the frequency range from 100 kHz to

0.01 Hz with a perturbation amplitude of 5 mV.

3 Results and discussion

3.1 Fabrication of PFCMs

Figure 1 shows the detailed synthesis procedure

and structural diagram for PFCMs. In the obtained

precursor solution, the carbon materials (CNTs and

KB particles) and Fe(acac)2 are well dispersed in the

mixed polymer (PVP and PS) solution after intense

stirring dissolution and ultrasonic dispersion. CNTs

and KB were used to construct a conductive framework,

Figure 1 Schematic illustration of the synthesis procedure for the PFCMs nanostructures: (a) homogeneous solution contained CNTs, KB, PVP, PS, and Fe(acac)2; (b) electrospray process; (c) PFCMs precursor microspheres; (d) PFCMs.

Fe(acac)2 was used to form Fe3O4 nanoparticles, PS

and KB were employed to form the microsphere

morphology, and PVP was used to act as surfactant

in order to facilitate the dispersion of CNTs and KB

particles in the mixed solution. During the electrospray

process, the precursor solution was atomized into

microdroplets under a high voltage (Fig. 1(c)). After

solvent evaporation, as-sprayed microdroplets were

solidified into precursor microspheres of PFCMs

(Fig. 1(c) and Fig. S1 in the Electronic Supplementary

Material (ESM)). All components (CNTs, KB, Fe(acac)2,

PVP and PS) are tightly integrated.

The desired PFCMs (Figs. 1(d) and 2) were obtained

after final carbonization treatment. In the typical

structure, CNTs and KB combine to form a scaffold-

like carbon skeleton with good mechanical strength.

The formed Fe3O4 nanoparticles were confined in the

carbon framework, while the skeleton and Fe3O4 were

further integrated with the interconnection effect of

amorphous carbon derived from organic polymers.

In order to further explore the formation mechanism

of precursor microspheres of PFCMs and the functions

of different components in the electrospray process,

reference experiments were carried out by controlling

solution compositions for electrostatic spraying. The

detailed information of the precursor solution com-

positions is shown in the caption of Fig. S2 in the

ESM. After electrospraying under optimal conditions,

the as-sprayed products were obtained and their SEM


896 Nano Res. 2018, 11(2): 892–904

images are shown in Fig. S2 in the ESM. For the

products without PS component (Figs. S2(a) and S2(b)

in the ESM), it is clearly noted that the microsphere

structure does not successfully form during electrostatic

spraying, suggesting that PS plays a vital role as a

template for forming the spherical morphology. It is

well-known that the carbon yield of PS is very low

due to its severe thermal degradation during heat

treatment [18]. Therefore, KB particles and CNTs

act both as a template and a conductive skeleton

to maintain the microsphere structure after PS

pyrolyzation. PVP, on the other hand, is used as a

surfactant to disperse the nano-carbon components

(KB and CNT) and promote the formation of

microspheres with uniform morphology. As shown

in Figs. S2(c) and S2(d) in the ESM, the sphericity and

uniformity of the as-sprayed precursors are considerably

different when the experiment is done without PVP.

In this case, a fibrous structure is formed together

with the spheres. Figures S2(e) and S2(f) in the ESM

show images of the as-sprayed precursor spheres

without CNTs. There is a large variation in the size

distribution of the precursor without CNTs, and the

resulting PFCM microspheres are fragile due to the

mechanical stacking of KB particles. This therefore

shows that CNTs play an important role in maintaining

the structural stability of composite microspheres.

Another important effect of CNTs on PFCMs is

the improvement of the electronic conductivity and

electrochemical properties, which will be discussed

in further detail in the subsequent section. The results

from all the control experiments further illustrate

the rationality of our procedure for optimizing the

composite structure design.

3.2 Characteristics of PFCMs

SEM and TEM images, as shown in Fig. 2, were used

to analyze the morphology and microstructure of

PFCMs. Figure 2(a) notes that the PFCM diameters are

1–2 μm after annealing the precursor microspheres

(Fig. S1 in the ESM). Figure 2(b) shows that CNTs, KB,

and amorphous carbon intertwine to form a porous

hybrid microsphere. In order to observe the size and

distribution of Fe3O4 nanoparticles in the porous

carbon framework, the microstructures of PFCMs are

further investigated by TEM imaging (Figs. 2(c) and

2(d)) and the corresponding EDX elemental maps

(Figs. 2(f)–2(i)). As shown in Fig. 2(c), CNTs penetrate

through the entire bulk structure, acting as a conductive

and structural skeleton to truss all parts together. The

Fe3O4 nanoparticles, which have diameters of ~ 20 nm,

are uniformly dispersed in the carbon matrix. Based

on the HRTEM image (Fig. 2(d)), the lattice fringes

are defined to be 0.45 nm, fitting well with the (111)

planes of a cubic Fe3O4 structure, which can be further

confirmed by subsequent XRD analysis. Furthermore,

it is also noted from Fig. 2(d) that Fe3O4 nanoparticles

are coated with a thin amorphous carbon layer,

which not only improves electron transfer, but also

buffers the volume changes of Fe3O4 during lithiation/

delithiation. This benefits device performance by

enabling the formation of stable SEI films and

preventing the loss of electrical contact. Moreover, the

EDX elemental mapping images (Figs. 2(f)–2(i)) reveals

bright spots from iron are homogeneously dispersed

in the carbon background, therefore indicating a

uniform distribution of Fe3O4 nanoparticles in PFCMs.

We can also distinctly observe that numerous voids

are distributed in the matrix uniformly, which are

formed by decomposition of the polymers and

accumulation of the CNTs and KB particles.

Figure 2 (a) and (b) SEM, (c) TEM and (d) HRTEM images of PFCMs; (e) STEM image of PFCMs and (f)–(h) EDX elemental mappings of (f) iron, (g) oxygen and (h) carbon.


897 Nano Res. 2018, 11(2): 892–904

The crystal structure of as-prepared PFCMs was

investigated by XRD. As shown in Fig. 3(a), all the

diffraction peaks of PFCMs agree well with the standard

XRD data of cubic-phase Fe3O4 (JCPDS card, file no.

89-4319) with the exception of a broad peak at around

26°, which corresponds to the (002) reflection of the

carbon matrix. The XRD results indicate that a pure

Fe3O4 component is formed in the carbon matrix by

decomposing Fe(acac)2 under the selective annealing

conditions.

Nitrogen adsorption/desorption isotherm measure-

ments were carried out to characterize the porous

structure of PFCMs (Fig. 3(b)). The BET specific surface

area and the pore volume of PFCMs are calculated

to be 190 m2·g–1 and 0.61 cm3·g–1, respectively. The

relative pore size distribution based on Barrett–Joyner–

Halenda (BJH) desorption is also shown in the inset

of Fig. 3(b). We note that the nanopores deliver a

hierarchical size distribution, mainly ranging from 2

to 10 nm and centering around 3.5 nm. The hierarchical

pore structure can not only shorten the lithium ion

pathway by facilitating electrolyte infiltration, but also

can accommodate the volume changes Fe3O4 undergoes

during cycling.

TGA was performed from 30 to 1,000 °C with a

heating rate of 10 °C·min–1 in an air atmosphere to

verify the actual Fe3O4 content of PFCMs. The weight

loss curve of PFCMs is shown in Fig. 3. The initial

weight-loss of PFCMs below 200 °C is small and

attributed to moisture volatilization. For temperature

increases from 200 to 800 °C, the Fe3O4 component was

entirely oxidized to Fe2O3, while the carbon matrix

was completely pyrolyzed to CO2/CO gases. This

results in a drastic weight loss for the PFCMs. According

to the TGA curve, the contents of Fe3O4 and carbon

can be calculated to be 36.7 wt.% and 63.3 wt.%, res-

pectively (further details are provided in the ESM).

3.3 Electrochemical properties of PFCMs

The electrochemical characteristics of the discharge–

charge, CV, and EIS curves for PFCM anodes are

shown in Fig. 4. The discharge–charge profiles of

PCFMs are shown in Fig. 4(a) for the voltage range of

0.01–3.0 V at different current densities (from 0.1 to

Figure 3 (a) XRD pattern, (b) nitrogen adsorption/desorption isotherm and pore size distribution, and (c) TGA curve of PFCMs.


898 Nano Res. 2018, 11(2): 892–904

5 A·g–1). The various cycles at 0.1 A·g–1 are shown

in Fig. 4(b). All the discharge–charge profiles present

obvious voltage plateaus, which is essential for the

industrial application of electrode materials. This

therefore indicates that Fe3O4 active materials are well

supported in the PFCM hybrids. As shown in Fig. 4(b),

the PFCM anode exhibits an initial charge capacity

of 999 mAh·g–1 and an initial discharge capacity of

1,795 mAh·g–1, the latter of which is considerably higher

than the theoretical specific capacity of Fe3O4. The

ultrahigh initial discharge capacity may mainly result

from irreversible processes such as the reaction of

lithium with oxygen-containing functional groups, the

inevitable decomposition of the electrolyte to form an

SEI layer, and irreversible Li+ trapping in the matrix

[24, 39]. Thus, the irreversible capacity loss of the first

discharge–charge process could be attributed to the

formation of a SEI layer via electrolyte decomposition

and trapped Li+ inserted in the abundant inner holes

of PFCMs [40, 41]. These processes are ubiquitous for

the redox reactions of most anode materials in LIBs.

Figure 4(c) shows the CV profiles of the PFCM

electrode for the initial 10 cycles. These were recorded

in the potential window of 0.01–3.0 V at a scan rate of

0.1 mV·s–1. There are two obvious peaks in the initial

discharge process. The strong peak at 0.76 V reveals

the reduction reaction Fe3O4 + Li+ → Fe0 + Li2O, and the

small peak at 0.93 V may be ascribed to the irreversible

reactions of the electrolyte to form the SEI layer [42,

43]. For the charge process, two oxidation peaks occur

at around 1.58 and 1.85 V and can be attributed to the

oxidation of Fe0 to Fe2+ and Fe3+ during the delithiation

reactions [44–46]. During the subsequent cycles, the

reduction and oxidation peaks are relatively unaltered,

therefore indicating the presence of a stable SEI film

on the PFCM surface and an excellent reversibility

for the lithiation/delithiation process.

EIS measurements were conducted in the frequency

range of 0.1 Hz to 100 kHz to further reveal the

electrochemical characteristics of the PFCM electrode.

The impedance spectra of PFCMs in the initial state,

as well as the fully charged states (after the 3rd and

100th cycles at 1 A·g–1) are both shown in Fig. 4(d).

The depressed semicircle in the high-medium frequency

region indicates a charge transfer process, while the

inclined line in the low frequency region suggests the

diffusion of lithium ions into the electrode materials.

It is noted that the semicircle radius after three cycles

Figure 4 Discharge–charge profiles of PFCM anode at (a) different current densities and (b) a current density of 0.1 A·g–1 for different cycles; (c) CV curves of PFCM electrode at a scan rate of 0.1 mV·s–1; (d) impedance spectra of PFCM electrode before and after cycling.


899 Nano Res. 2018, 11(2): 892–904

is slightly smaller than in the initial state due to the

activation reaction. The slight increase of resistance

after the 100th cycle may be related to the stable SEI

film formed on the outside surface of PFCMs during

cycling [26, 47].

To better understand the aforementioned phenomena,

we further investigate the electrochemical capacities

and rate performances of PFCM anodes in detail. The

cycle performance of PFCMs in a voltage range of

0.01–3.0 V vs. Li/Li+ at 0.1 A·g–1 is shown in Fig. 5(a).

After activating for a few cycles, the PFCMs have a

stable Coulombic efficiency (above 97%) and the

reversible capacity is maintained at ~ 1,000 mAh·g–1.

Notably, the specific capacity of PFCMs keeps increasing

through almost the entire discharge/charge processes,

rising to 1,317 mAh·g–1 at the 130th cycle. Such a high

and stable capacity at a low current density (0.1 A·g–1)

resulted from the optimized and stabilized micros-

tructures of PFCMs. CNTs, KB, and amorphous carbon

are intertwined together to construct an electrically

conductive skeleton, which greatly promotes the

electron/ion transportation. Additionally, coating the

confined Fe3O4 nanoparticles with carbon layers can

efficiently avoid particle agglomeration and achieve

fast reaction kinetics. Furthermore, abundant mesopores

can buffer the volume changes of Fe3O4 during

lithiation/delithiation processes. As a result, a stable

and thin SEI layer can be generated on the surface of

Fe3O4/carbon composite. Meanwhile, consumption of

electrolyte is effectively suppressed [44, 48–50].

It is worth noting that the capacity of the PFCM

electrode clearly increased under the current density

of 0.1 A·g–1. The gradual increase of capacity might

be attributed to the formation of stable organic

polymeric/gel-like layers resulting from kinetically

activated electrolyte degradation [35]. These organic

polymeric/gel-like layers can repeatly absorb and

release lithium ions, resulting in a slight increase

of capacity during cycling. This effect is especially

pronounced under low current densities [24, 26, 33,

38, 45, 51–53]. For instance, Lou and co-authors

fabricated carbon coated α-Fe2O3 hollow nanohorns

on CNT backbones. As an anode in LIBs, the capacity

of the α-Fe2O3/carbon composite shows a gradual

increase from 660 to 820 mAh·g–1 after 100 cycles at a

current density of 500 mA·g–1 [24]. Lu et al. prepared

carbon-coated Fe3O4 nanotubes, which delivered a

capacity increase up to 1,155 mAh·g–1 during the initial

90 cycles under 0.2 A·g–1 [34]. Furthermore, while using

in-situ TEM to study the structural evolution of lithium

insertion/extraction in electrochemically prelithiated

Fe2O3 nanoparticles confined in CNTs, Cheng’s group

also observed this phenomenon [26]. Most of these

researchers ascribed this phenomenon to the reversible

growth of a polymeric gel-like film resulting from

kinetically activated electrolyte degradation [54–56].

Due to the high electrochemical activity of the nano-

sized Fe3O4 particles protected by a carbon matrix,

the thin organic polymeric/gel-like layer does not

have a serious effect on the transmission of ions and

electrons [24, 38] This effect, however, can be altered

if the layers are significantly thicker. The capacity

increase in iron oxide and other metal oxide anodes

has already been investigated both experimentally

and theoretically [57–60].

As shown in Fig. 5(b), the PFCM electrodes also

possess excellent rate performances at different current

densities. The initial discharge capacity is as high as

1,796 mAh·g–1 with a Coulombic efficiency of 56.2%.

Specifically, the composite anode exhibits high rever-

sible specific capacities of 1,084, 883, 809, 738, 648,

and 545 mAh·g–1 at current densities of 0.1, 0.2, 0.3, 0.5,

1, and 2 A·g–1, respectively. Even after cycling at a

large current density (5 A·g–1), the reversible capacity

is still maintained at 410 mAh·g–1 after total 70 cycles

under different current densities. Clearly, the co-existence

of CNTs and KB leads to a closely combined structure

with a high conductivity, which contributes to the

excellent rate capability. When the current rate returns

to its initial value of 0.1 A·g–1, the charge capacity can

recover to 1,052 mAh·g–1 at the 71st cycle and increase

slowly with further cycling. After the subsequent

80 cycles at 0.1 A·g–1, the specific capacity further

improves and increases up to 1,234 mAh·g–1, which

was higher than both the theoretical capacity of Fe3O4

(926 mAh·g–1) and the capacity during the initial

ten cycles. This phenomenon of capacity increase is

frequent in the field of various nanostructured iron

oxide electrodes [26, 33, 61]. For example, Zhang et al.

prepared hierarchically porous Fe3O4/C nanocomposite

microspheres by a hydrothermal process. After testing

as anode materials in LIBs, these porous Fe3O4/C


900 Nano Res. 2018, 11(2): 892–904

microspheres show a high reversible capacity of

1,231 mAh·g–1 at 0.5 A·g–1 after 100 cycles [2]. Fan et al.

coated uniform Fe3O4 sheaths of 5–7 nm onto CNT

scaffolds by magnetron sputtering to fabricate a Fe3O4/

CNT electrode, which delivered a high specific capacity

of 1,670 mAh·g−1 and exhibited significant capacity

increases during cycling [61]. Recently, Cheng’s group

tried to study the structural evolution of electro-

chemically prelithiated Fe2O3 nanoparticles confined

in CNTs during lithium insertion/extraction by in situ

TEM. They observed a high reversible capacity of

2,071 mAh·g−1 for the encapsulated Fe2O3 nanoparticles

in CNTs [9]. It was also demonstrated that the capacity

increase might relate to the following factors: extra

lithium storage from the two-phase capacitive behavior

of the Li2O/Fe interface confined in the pores of the

carbon matrix, which allows for the storage of Li+ on

the Li2O compound side and electrons on the Fe side

[62, 63]; and a reversible conversion reaction of LiOH to

form LiH and Li2O on the organic polymeric/gel-like

layers [2, 26, 64].

It is well-known that, compared to gravimetric

capacity, the volumetric capacity for porous materials

is a more appropriate index for determining the

practicality of using these materials for industrial

applications. Based on the BET and TGA results, as

well as the specific capacities shown in Figs. 5(a) and

5(b), the reversible volumetric capacities of PFCM

anodes are more than 1,000 mAh·cm–1 at 0.1 A·g–1,

which is higher than that of graphite anodes (about

760 mAh·cm–3). The detailed calculation process is

provided in the ESM.

Remarkably, the PFCM electrode exhibits long

lifespans of over 300 cycles at the high current densities

of 1 and 5 A·g–1 (Fig. 5(c)). Its initial charge capacities

are 766 and 616 mAh·g–1 at 1 and 5 A·g–1, respectively.

After 300 cycles, the discharge capacities still remained

at 746 and 525 mAh·g–1 under the current densities of

Figure 5 (a) Cycling performance and Coulombic efficiency of PFCMs anode at a current density of 0.1 A·g–1; (b) rate capability and Coulombic efficiency of PFCMs anode under different current densities; (c) cycling performances and Coulombic efficiency at high current densities of 1 and 5 A·g–1.


901 Nano Res. 2018, 11(2): 892–904

1 and 5 A·g–1, respectively. These display the corres-

ponding capacity retentions of 97% and 85%. The

superior rate performance and cycling stability of

PFCMs are fairly competitive compared to other

Fe3O4-based anodes reported in recent literatures

(Table S1 in the ESM). The excellent electrochemical

performances of PFCMs should therefore be attributed

to: (1) the well-dispersed and encapsulated Fe3O4

nanoparticles; (2) the support, protection, and high

electronic conductivity provided by the porous carbon

matrix; and (3) the high mechanical strength, abundant

pore volume, and hierarchical pore distribution.

Cycling performances of the carbon matrix anode

without Fe3O4 and the PFCM anode with a lower

concentration of CNTs (adding 0.05 g CNTs into

precursor solution, while the masses of the other

components are unchanged) is shown in Fig. S3 in

the ESM. These studies were conducted in order to

investigate the roles of both the entire carbon matrix

and CNTs in the electrochemical performances of

PFCMs. Figure S3(a) in the ESM shows the cycle

performance of the porous carbon matrix anode obtained

by etching Fe3O4 in PFCMs with hydrochloric acid. It

can be seen that the carbon matrix exhibits capacities

of 419 and 370 mAh·g–1 at 0.1 and 1 A·g–1 after 200 cycles

without significant capacity decay from the 50th to the

200th cycle. This therefore indicates that the stable

carbon matrix plays a crucial role in the electrochemical

performance of our PFCM composite anode. As shown

in Fig. S3(b) in the ESM, the reversible specific capacities

of PFCMs with lower CNT content start to clearly

decrease after 70 cycles at current densities of both

0.1 and 1 A·g–1, which further confirms the skeleton

support and conductive effects of CNTs on the whole

composite material.

The morphology and inner microstructure of the

PFCM electrode after 100 cycles at 1 A·g–1 are shown

in Fig. S5 in the ESM. The spherical structure of the

cycled PFCMs (Figs. S5(a) and S5(c) in the ESM) is

maintained and indicates a good structural stability

of the PFCM anode materials during electrochemical

cycling. Furthermore, the STEM image (Fig. S5(d)

in the ESM) and EDX elemental mapping images

(Figs. S5(e)–S5(g) in the ESM) show that the Fe3O4

nanoparticles are still homogeneously dispersed in

the carbon matrix without obvious agglomeration. The

superior structural stability of the PFCM electrode

can be ascribed to the robust support and protection

of the porous carbon matrix composed of CNTs, KB,

and amorphous carbon, which can effectively prevent

the aggregation of Fe3O4 nanoparticles, accommodate

their volumetric change, and maintain their structural

integrity during cycling, thus, leading to the excellent

electrochemical performances of the PFCM anode of

LIBs.

4 Conclusion

PFCMs with superior electrical conductivity and

mechanical strength were successfully fabricated based

on a facile electrospray synthesis. The PFCMs show

excellent electrochemical performances as the anode

of LIBs. The composite features with homogeneously

dispersed Fe3O4 nanoparticles were confined in the

highly conductive carbon matrix composed of CNTs,

KB, and amorphous carbon. The porous structure

provides enough space to accommodate the volume

change of Fe3O4 nanoparticles. Also, the interlaced

networks of interconnecting pores and carbon

framework provide perfect channels and pathways

for electrolyte penetration and electron conduction.

As a result, the PFCM electrodes exhibit high specific

capacities of 1,317 mAh·g–1 at 0.1 A·g–1 after 130 cycles,

and 746 mAh·g–1 at 1 A·g–1 and 525 mAh·g–1 at 5 A·g–1

after 300 cycles. This work has provided a facile

method to fabricate metal oxide electrodes with a

well-designed structure for high-performance energy

storage.

Acknowledgements

This work was supported by the National Basic

Research Program of China (No. 2014CB932400), Joint

Fund of the National Natural Science Foundation

of China and the China Academy of Engineering

Physics (Nos. U1330123 and U1401243), the National

Natural Science Foundation of China (No. 51232005),

and Shenzhen Technical Plan Project (No. JCYJ

20150529164918735).

Electronic Supplementary Material: Supplementary

material (calculation methods of Fe3O4 content and


902 Nano Res. 2018, 11(2): 892–904

volumetric capacity; SEM images of various as-sprayed

precursor microspheres before annealing; electro-

chemical performances of carbon matrix and PFCM

with less CNTs; SEM, TEM and EDX elemental

mapping images of the PFCM anode after cycling;

and a comparison of electrochemical performances of

Fe3O4-based anodes for LIBs) is available in the online

version of this article at https://doi.org/10.1007/

s12274-017-1700-6.

References

[1] Dunn, B.; Kamath, H.; Tarascon, J.-M. Electrical energy

storage for the grid: A battery of choices. Science 2011, 334,

928–935.

[2] Ding, C.; Zeng, Y. W.; Cao, L. L.; Zhao, L. F.; Zhang, Y.

Hierarchically porous Fe3O4/C nanocomposite microspheres

via a CO2 bubble-templated hydrothermal approach as

high-rate and high-capacity anode materials for lithium-ion

batteries. J. Mater. Chem. A 2016, 4, 5898–5908.

[3] Zhang, G. Q.; Wu, H. B.; Hoster, H. E.; Lou, X. W. Strongly

coupled carbon nanofiber–metal oxide coaxial nanocables

with enhanced lithium storage properties. Energy Environ.

Sci. 2014, 7, 302–305.

[4] Choi, N. S.; Chen, Z. H.; Freunberger, S. A.; Ji, X. L.; Sun,

Y. K.; Amine, K.; Yushin, G.; Nazar, L. F.; Cho, J.; Bruce,

P. G. Challenges facing lithium batteries and electrical

double-layer capacitors. Angew. Chem., Int. Ed. 2012, 51,

9994–10024.

[5] Armstrong, M. J.; O’Dwyer, C.; Macklin, W. J.; Holmes, J.

D. Evaluating the performance of nanostructured materials

as lithium-ion battery electrodes. Nano Res. 2014, 7, 1–62.

[6] Yu, H. J.; Guo, G. N.; Ji, L.; Li, H. W.; Yang, D.; Hu, J. H.;

Dong, A. G. Designed synthesis of ordered mesoporous

graphene spheres from colloidal nanocrystals and their

application as a platform for high-performance lithium-ion

battery composite electrodes. Nano Res. 2016, 9, 3757–3771.

[7] Duan, B.; Gao, X.; Yao, X.; Fang, Y.; Huang, L.; Zhou, J.;

Zhang, L. N. Unique elastic N-doped carbon nanofibrous

microspheres with hierarchical porosity derived from

renewable chitin for high rate supercapacitors. Nano Energy

2016, 27, 482–491.

[8] Jiang, B. B.; Han, C. P.; Li, B.; He, Y. J.; Lin, Z. Q. In-situ

crafting of ZnFe2O4 nanoparticles impregnated within

continuous carbon network as advanced anode materials.

ACS Nano 2016, 10, 2728–2735.

[9] Xin, S.; Chang, Z. W.; Zhang, X. B.; Guo, Y.-G. Progress

of rechargeable lithium metal batteries based on conversion

reactions. Natl. Sci. Rev. 2017, 4, 54–70.

[10] Deng, J. J.; Yu, X. L.; He, Y. B.; Li, B. H.; Yang, Q.-H.;

Kang, F. Y. A sliced orange-shaped ZnCo2O4 material as

anode for high-performance lithium ion battery. Energy

Storage Mater. 2017, 6, 61–69.

[11] Wu, S. P.; Xu, R.; Lu, M. J.; Ge, R. Y.; Iocozzia, J.; Han, C. P.;

Jiang, B. B.; Lin, Z. Q. Graphene-containing nanomaterials

for lithium-ion batteries. Adv. Energy Mater. 2015, 5,

1500400.

[12] Xing, Z.; Ju, Z. C.; Yang, J.; Xu, H. Y.; Qian, Y. T.

One-step hydrothermal synthesis of ZnFe2O4 nano-octahedrons

as a high capacity anode material for Li-ion batteries. Nano

Res. 2012, 5, 477–485.

[13] Shan, T. T.; Xin, S.; You, Y.; Cong, H. P.; Yu, S. H.;

Manthiram, A. Combining nitrogen-doped graphene sheets

and MoS2: A unique film–foam–film structure for enhanced

lithium storage. Angew. Chem., Int. Ed. 2016, 128, 12975–

12980.

[14] Wu, J. X.; Qin, X. Y.; Zhang, H. R.; He, Y.-B.; Li, B. H.;

Ke, L.; Lv, W.; Du, H. D.; Yang, Q.-H.; Kang, F. Y.

Multilayered silicon embedded porous carbon/graphene

hybrid film as a high performance anode. Carbon 2015, 84,

434–443.

[15] Wu, S. P.; Han, C. P.; Iocozzia, J.; Lu, M. J.; Ge, R. Y.;

Xu, R.; Lin, Z. Q. Germanium‐based nanomaterials for

rechargeable batteries. Angew. Chem., Int. Ed. 2016, 55,

7898–7922.

[16] Yu, W. J.; Zhang, L. L.; Hou, P. X.; Li, F.; Liu, C.; Cheng, H.

M. High reversible lithium storage capacity and structural

changes of Fe2O3 nanoparticles confined inside carbon

nanotubes. Adv. Energy Mater. 2016, 6, 1501755.

[17] Han, C. P.; Yang, D.; Yang, Y. K.; Jiang, B. B.; He, Y. J.;

Wang, M. Y.; Song, A.-Y.; He, Y.-B.; Li, B. H.; Lin, Z. Q.

Hollow titanium dioxide spheres as anode material for

lithium ion battery with largely improved rate stability and

cycle performance by suppressing the formation of solid

electrolyte interface layer. J. Mater. Chem. A 2015, 3,

13340–13349.

[18] Zhou, F.; Xin, S.; Liang, H.-W.; Song, L.-T.; Yu, S.-H.

Carbon nanofibers decorated with molybdenum disulfide

nanosheets: Synergistic lithium storage and enhanced electro-

chemical performance. Angew. Chem., Int. Ed. 2014, 53,

11552–11556.

[19] Li, X. F.; Wang, C. L. Engineering nanostructured anodes

via electrostatic spray deposition for high performance lithium

ion battery application. J. Mater. Chem. A 2013, 1, 165–182.

[20] Yang, S. L.; Cao, C. Y.; Li, G.; Sun, Y. B.; Huang, P. P.;

Wei, F. F.; Song, W. G. Improving the electrochemical

performance of Fe3O4 nanoparticles via a double protection

strategy through carbon nanotube decoration and graphene

networks. Nano Res. 2015, 8, 1339–1347.


903 Nano Res. 2018, 11(2): 892–904

[21] Qin, X. Y.; Zhang, H. R.; Wu, J. X.; Chu, X. D.; He, Y.-B.;

Han, C. P.; Miao, C.; Wang, S.; Li, B. H.; Kang, F. Y. Fe3O4

nanoparticles encapsulated in electrospun porous carbon

fibers with a compact shell as high-performance anode for

lithium ion batteries. Carbon 2015, 87, 347–356.

[22] Cheng, Y.-T.; Verbrugge, M. W. The influence of surface

mechanics on diffusion induced stresses within spherical

nanoparticles. J. Appl. Phys. 2008, 104, 083521.

[23] Fei, H. L.; Peng, Z. W.; Li, L.; Yang, Y.; Lu, W.; Samuel, E.

L. G.; Fan, X. J.; Tour, J. M. Preparation of carbon-coated

iron oxide nanoparticles dispersed on graphene sheets and

applications as advanced anode materials for lithium-ion

batteries. Nano Res. 2014, 7, 502–510.

[24] Wang, Z. Y.; Luan, D. Y.; Madhavi, S.; Hu, Y.; Lou, X. W.

Assembling carbon-coated α-Fe2O3 hollow nanohorns on

the CNT backbone for superior lithium storage capability.

Energy Environ. Sci. 2012, 5, 5252–5256.

[25] He, Y.; Huang, L.; Cai, J.-S.; Zheng, X.-M.; Sun, S.-G.

Structure and electrochemical performance of nanostructured

Fe3O4/carbon nanotube composites as anodes for lithium

ion batteries. Electrochim. Acta 2010, 55, 1140–1144.

[26] Yu, W.-J.; Zhang, L. L.; Hou, P.-X.; Li, F.; Liu, C.; Cheng,

H.-M. High reversible lithium storage capacity and structural

changes of Fe2O3 nanoparticles confined inside carbon

nanotubes. Adv. Energy Mater. 2016, 6, 1501755.

[27] Chen, X. H.; Lai, X.; Hu, J. H.; Wan, L. An easy and novel

approach to prepare Fe3O4–reduced graphene oxide composite

and its application for high-performance lithium-ion batteries.

RSC Adv. 2015, 5, 62913–62920.

[28] Chen, Y.; Xia, H.; Lu, L.; Xue, J. M. Synthesis of porous

hollow Fe3O4 beads and their applications in lithium ion

batteries. J. Mater. Chem. 2012, 22, 5006–5012.

[29] Qu, Q. T.; Chen, J. M.; Li, X. X.; Gao, T.; Shao, J.; Zheng,

H. H. Strongly coupled 1D sandwich-like C@Fe3O4@C

coaxial nanotubes with ultrastable and high capacity for

lithium-ion batteries. J. Mater. Chem. A 2015, 3, 18289–18295.

[30] Xu, Y.; Feng, J. D.; Chen, X. C.; Kierzek, K.; Liu, W. B.;

Tang, T.; Mijowska, E. Beaded structured CNTs-Fe3O4@C

with low Fe3O4 content as anode materials with extra enhanced

performances in lithium ion batteries. RSC Adv. 2015, 5,

28864–28869.

[31] Lee, S. H.; Yu, S. H.; Lee, J. E.; Jin, A. H.; Lee, D. J.;

Lee, N.; Jo, H.; Shin, K.; Ahn, T. Y.; Kim, Y. W. et al.

Self-assembled Fe3O4 nanoparticle clusters as high-performance

anodes for lithium ion batteries via geometric confinement.

Nano Lett. 2013, 13, 4249–4256.

[32] Zuo, Y. T.; Wang, G.; Peng, J.; Li, G.; Ma, Y. Q.; Yu, F.;

Dai, B.; Guo, X. H.; Wong, C.-P. Hybridization of graphene

nanosheets and carbon-coated hollow Fe3O4 nanoparticles

as a high-performance anode material for lithium-ion batteries.

J. Mater. Chem. A 2016, 4, 2453–2460.

[33] Liu, J. L.; Qian, D.; Feng, H. B.; Li, J. H.; Jiang, J. B.; Peng,

S. J.; Liu, Y. C. Designed synthesis of TiO2-modified iron

oxides on/among carbon nanotubes as a superior lithium-ion

storage material. J. Mater. Chem. A 2014, 2, 11372–11381.

[34] Cabana, J.; Monconduit, L.; Larcher, D.; Palacín, M. R.

Beyond intercalation-based Li-ion batteries: The state of the

art and challenges of electrode materials reacting through

conversion reactions. Adv. Mater. 2010, 22, E170–E192.

[35] Li, X. W.; Qiao, L.; Li, D.; Wang, X. H.; Xie, W. H.; He, D.

Y. Three-dimensional network structured α-Fe2O3 made from

a stainless steel plate as a high-performance electrode for

lithium ion batteries. J. Mater. Chem. A 2013, 1, 6400–6406.

[36] Aurbach, D. Review of selected electrode–solution interactions

which determine the performance of Li and Li ion batteries.

J. Power Sources 2000, 89, 206–218.

[37] Ding, C.; Zeng, Y. W.; Cao, L. L.; Zhao, L. F.; Meng, Q. Y.

Porous Fe3O4-NCs-in-carbon nanofoils as high-rate and

high-capacity anode materials for lithium-ion batteries

from Na-citrate-mediated growth of super-thin Fe-ethylene

glycolate nanosheets. ACS Appl. Mater. Interfaces 2016, 8,

7977–7990.

[38] Han, F.; Ma, L. J.; Sun, Q.; Lei, C.; Lu, A. H. Rationally

designed carbon-coated Fe3O4 coaxial nanotubes with

hierarchical porosity as high-rate anodes for lithium ion

batteries. Nano Res. 2014, 7, 1706–1717.

[39] Meunier, V.; Kephart, J.; Roland, C.; Bernholc, J. Ab Initio

investigations of lithium diffusion in carbon nanotube

systems. Phys. Rev. Lett. 2002, 88, 075506.

[40] Guo, C.; Wang, L. L.; Zhu, Y. C.; Wang, D. F.; Yang, Q. Q.;

Qian, Y. T. Fe3O4 nanoflakes in an N-doped carbon matrix

as high-performance anodes for lithium ion batteries.

Nanoscale 2015, 7, 10123–10129.

[41] Mao, J. W.; Hou, X. H.; Wang, X. Y.; He, G. N.; Shao, Z. P.;

Hu, S. J. Corncob-shaped ZnFe2O4/C nanostructures for

improved anode rate and cycle performance in lithium-ion

batteries. RSC Adv. 2015, 5, 31807–31814.

[42] Ma, F. X.; Hu, H.; Wu, H. B.; Xu, C. Y.; Xu, Z. C.; Zhen, L.;

Lou, X. W. Formation of uniform Fe3O4 hollow spheres

organized by ultrathin nanosheets and their excellent lithium

storage properties. Adv. Mater. 2015, 27, 4097–4101.

[43] Xia, T.; Xu, X. L.; Wang, J. P.; Xu, C. B.; Meng, F. C.; Shi, Z.;

Lian, J.; Bassat, J.-M. Facile complex-coprecipitation synthesis

of mesoporous Fe3O4 nanocages and their high lithium

storage capacity as anode material for lithium-ion batteries.

Electrochim. Acta 2015, 160, 114–122.

[44] He, C. N.; Wu, S.; Zhao, N. Q.; Shi, C. S.; Liu, E. Z.; Li, J.

J. Carbon-encapsulated Fe3O4 nanoparticles as a high-rate


904 Nano Res. 2018, 11(2): 892–904

lithium ion battery anode material. ACS Nano 2013, 7,

4459–4469.

[45] Meng, X. F.; Xu, Y. L.; Sun, X. F.; Wang, J.; Xiong, L. L.;

Du, X. F.; Mao, S. C. Graphene oxide sheets-induced growth

of nanostructured Fe3O4 for a high-performance anode

material of lithium ion batteries. J. Mater. Chem. A 2015, 3,

12938–12946.

[46] Ma, F. X.; Wu, H. B.; Xu, C. Y.; Zhen, L.; Lou, X. W.

Self-organized sheaf-like Fe3O4/C hierarchical microrods

with superior lithium storage properties. Nanoscale 2015, 7,

4411–4414.

[47] Jiao, J. Q.; Qiu, W. D.; Tang, J. G.; Chen, L. P.; Jing, L. Y.

Synthesis of well-defined Fe3Os nanorods/N-doped graphene

for lithium-ion batteries. Nano Res. 2016, 9, 1256–1266.

[48] Zhang, W.-M.; Wu, X.-L.; Hu, J.-S.; Guo, Y.-G.; Wan, L.-J.

Carbon coated Fe3O4 nanospindles as a superior anode

material for lithium-ion batteries. Adv.Funct. Mater. 2008,

18, 3941–3946.

[49] Lee, J. E.; Yu, S.-H.; Lee, D. J.; Lee, D.-C.; Han, S. I.; Sung,

Y.-E.; Hyeon, T. Facile and economical synthesis of

hierarchical carbon-coated magnetite nanocomposite particles

and their applications in lithium ion battery anodes. Energy

Environ. Sci. 2012, 5, 9528–9533.

[50] Zhu, T.; Chen, J. S.; Lou, X. W. Glucose-assisted one-pot

synthesis of FeOOH nanorods and their transformation to

Fe3O4@carbon nanorods for application in lithium ion

batteries. J. Phys. Chem. C 2011, 115, 9814–9820.

[51] Hu, Y. Y.; Liu, Z. G.; Nam, K. W.; Borkiewicz, O. J.;

Cheng, J.; Hua, X.; Dunstan, M. T.; Yu, X. Q.; Wiaderek,

K. M.; Du, L. S. et al. Origin of additional capacities in metal

oxide lithium-ion battery electrodes. Nat. Mater. 2013, 12,

1130–1136.

[52] Wei, W.; Yang, S. B.; Zhou, H. X.; Lieberwirth, I.; Feng,

X. L.; Müllen, K. 3D graphene foams cross-linked with pre-

encapsulated Fe3O4 nanospheres for enhanced lithium

storage. Adv. Mater. 2013, 25, 2909–2914.

[53] Luo, J. S.; Liu, J. L.; Zeng, Z. Y.; Ng, C. F.; Ma, L. J.;

Zhang, H.; Lin, J. Y.; Shen, Z. X.; Fan, H. J. Three-

dimensional graphene foam supported Fe3O4 lithium battery

anodes with long cycle life and high rate capability. Nano

Lett. 2013, 13, 6136–6143.

[54] Grugeon, S.; Laruelle, S.; Dupont, L.; Tarascon, J. M. An

update on the reactivity of nanoparticles Co-based compounds

towards Li. Solid State Sci. 2003, 5, 895–904.

[55] Do, J.-S.; Weng, C.-H. Preparation and characterization of

CoO used as anodic material of lithium battery. J. Power

Sources 2005, 146, 482–486.

[56] Zhou, G. M.; Wang, D.-W.; Li, F.; Zhang, L. L.; Li, N.;

Wu, Z.-S.; Wen, L.; Lu, G. Q.; Cheng, H.-M. Graphene-

wrapped Fe3O4 anode material with improved reversible

capacity and cyclic stability for lithium ion batteries. Chem.

Mater. 2010, 22, 5306–5313.

[57] Zhu, K.; Wang, Q.; Kim, J.-H.; Pesaran, A. A.; Frank, A. J.

Pseudocapacitive lithium-ion storage in oriented anatase TiO2

nanotube arrays. J. Phys. Chem. C 2012, 116, 11895–11899.

[58] Adelhelm, P.; Hu, Y.-S.; Antonietti, M.; Maier, J.; Smarsly,

B. M. Hollow Fe-containing carbon fibers with tubular tertiary

structure: Preparation and Li-storage properties. J. Mater.

Chem. 2009, 19, 1616–1620.

[59] Wang, L.; Yu, Y.; Chen, P. C.; Zhang, D. W.; Chen, C. H.

Electrospinning synthesis of C/Fe3O4 composite nanofibers

and their application for high performance lithium-ion batteries.

J. Power Sources 2008, 183, 717–723.

[60] Zhou, J. S.; Song, H. H.; Ma, L. L.; Chen, X. H. Magnetite/

graphene nanosheet composites: Interfacial interaction and

its impact on the durable high-rate performance in lithium-

ion batteries. RSC Adv. 2011, 1, 782–791.

[61] Wu, Y.; Wei, Y.; Wang, J. P.; Jiang, K. L.; Fan, S. S.

Conformal Fe3O4 sheath on aligned carbon nanotube scaffolds

as high-performance anodes for lithium ion batteries. Nano

Lett. 2013, 13, 818–823.

[62] Balaya, P.; Li, H.; Kienle, L.; Maier, J. Fully reversible

homogeneous and heterogeneous Li storage in RuO2 with

high capacity. Adv. Funct. Mater. 2003, 13, 621–625.

[63] Zhukovskii, Y. F.; Balaya, P.; Kotomin, E. A.; Maier, J.

Evidence for interfacial-storage anomaly in nanocomposites

for lithium batteries from first-principles simulations. Phys.

Rev. Lett. 2006, 96, 058302.

[64] Laruelle, S.; Grugeon, S.; Poizot, P.; Dollé, M.; Dupont, L.;

Tarascon, J. M. On the origin of the extra electrochemical

capacity displayed by MO/Li cells at low potential. J.

Electrochem. Soc. 2002, 149, A627–A634.

electrosprayed porous fe o /carbon microspheres as anode ... · nano res. 2018, 11(2): 892–904...

Documents