AgP2/C as an anode for high rate performance lithium-ion batteries

Article abstract of DOI:10.1016/j.jallcom.2018.05.244

Red phosphorus attracts significant interest for lithium-ion batteries due to its high theoretical capacity. Nevertheless, its low electronic conductivity and drastic volume change during cycling limit its further applications. In this study, we fabricate a novel AgP₂/C nanocomposite by facile ball milling. The nanocomposite anode delivers a high reversible capacity of 785 mA h g^?1 at 0.5 A g^?1 after 100 cycles and an excellent rate capability with a reversible capacity of 605 mA h g^?1 at10 A g^?1 in half cells. This excellent electrochemical performance is attributed to the uniform dispersion of amorphous carbon and the synergistic effect of intermediate discharge/charge products. In addition, the LiCoO₂‖AgP₂/C full cell exhibits a stable capacity with an operation potential of ～2.8 V, indicating the commercial potential of this material in high rate lithium-ion batteries.

Full text of DOI:10.1016/j.jallcom.2018.05.244

Accepted Manuscript
AgP /C as an anode for high rate performance lithium-ion batteries
2
Miao Zhang, Renzong Hu, Jiangwen Liu, Liuzhang Ouyang, Jun liu, Lichun Yang,
Fang Fang, Min Zhu
PII:
S0925-8388(18)31963-7
10.1016/j.jallcom.2018.05.244
JALCOM 46220
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 1 March 2018
Revised Date: 3 May 2018
Accepted Date: 21 May 2018
Please cite this article as: M. Zhang, R. Hu, J. Liu, L. Ouyang, Jun liu, L. Yang, F. Fang, M. Zhu, AgP /
2
C as an anode for high rate performance lithium-ion batteries, Journal of Alloys and Compounds (2018),
doi: 10.1016/j.jallcom.2018.05.244.
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ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
AgP2/C as an anode for high rate performance lithium-ion
batteries
Miao Zhanga,b, Renzong Hua,b, Jiangwen Liua,b, Liuzhang Ouyanga,b*, Jun liua,b, Lichun Yanga,b,Fang
Fangc,**, Min Zhua
a School of Materials Science and Engineering, Guangdong Provincial Key Laboratory of Advanced
Energy Storage Materials, South China University ofTechnology, Guangzhou, 510641, PR China
b China-Australia Joint Laboratory for Energy & Environmental Materials, Key Laboratory of Fuel
Cell Technology of Guangdong Province, Guangzhou,510641, PR China
c Department of Materials Science, Fudan University, Shanghai, 200433, PR China
*Corresponding author. E-mail: meouyang@scut.edu.cn (L. Z. Ouyang) & f_fang@fudan.edu.cn
Abstract
Red phosphorus attracts significant interest for lithium-ion batteries due to its high theoretical capacity.
Nevertheless, its low electronic conductivity and drastic volume change during cycling limit its further
applications. In this study, we fabricate a novel AgP2/C nanocomposite by facile ball milling. The
nanocomposite anode delivers a high reversible capacity of 785mA h g-1 at 0.5 A g-1 after 100 cycles
and an excellent rate capability with a reversible capacity of 605mA h g-1 at10 A g-1 in half cells. This
excellent electrochemical performance is attributed to the uniform dispersion of amorphous carbon
and the synergistic effect of intermediate discharge/charge products. In addition, the LiCoO2ǁAgP2/C
full cell exhibits a stable capacity with an operation potential of ~2.8 V, indicating the commercial
potential of this material in high rate lithium-ion batteries.
Keywords: silver phosphide, anode material, synergistic effect, lithium ion battery
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1. Introduction
Commercial lithium-ion batteries (LIBs) are typically composed of lithium metal oxide cathodes
and graphite anodes. However, their practical specific energy (~200 Wh kg-1) cannot meet the future
demand for high energy storage systems. To significantly improve the specific energy of LIBs, new
anode materials with high specific capacities are required.[1-3] Therefore, numerous efforts have been
made to explore alternatives to graphite. As one of the possible alternatives, red phosphorus (RP) can
react with three Li to form Li3P and give a high theoretical specific capacity of 2596 mA h g-1.
Unfortunately, the low ionic and electronic conductivity within the RP electrode, combined with the
drastic volume change (~300%) during lithiation/delithiation processes, results in a low rate capability
and poor cycle life.[4-6]
To solve these drawbacks, one effective way is to construct nanostructured P/C nanocomposites
with carbon-based materials. The incorporated carbon materials can provide sufficient electrical
conductivity and alleviate the volume change during discharge/charge processes, while the
constructed nanostructure can shorten Li+ diffusion paths and reduce stress from the volume change.
Until now, two main methods have been employed to construct P/C nanocomposites. One is
vaporization-condensation of RP onto various carbon materials and the other is combining RP with
carbon into nanocomposites by high energy mechanical milling (HEMM).[7-10] Although these
methods can effectively improve the electrochemical performance of RP, the vaporization-
condensation process is difficult to control and the electrochemical performance of P/C
nanocomposites prepared by HEMM is less than ideal.
On account of this, metal phosphides have drawn considerable attention. This is because the
intermediate products of metal elements that are formed in situ during the discharge/charge processes
can stabilize P and improve the electrical conductivity of the electrode. A number of metal phosphides
have been explored, such as FeP,[11] CoP,[12] Ni2P,[13] MnP[14] and Cu3P[15]. They react with Li+
via a conversion reaction, 3yLi++3ye-1+MxPy
yLi3P+xM (M=Fe, Co, Ni or Cu). Since these
metals are inactive for Li storage, the theoretical specific capacities of these metal phosphides are
relatively low. Therefore, it is of great interest to explore new metal phosphides with reactive metal
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components for Li storage. Metallic Ag has the highest electrical conductivity of all the metals and
outstanding Li+ diffusivity, which is beneficial for improving the electrochemical performance of
RP.[16] In addition, elemental Ag has a relatively high capacity in a low potential range (0.00–0.25
V).[17]
Herein, we report a metal phosphide AgP2 anode for LIBs with an impressive theoretical
capacity of 1473 mA h g-1 while considering a full lithiation of 3 Ag with 10 Li to form Li10Ag3 and
P with 3 Li to form Li3P. It can be obtained by a simple mechanical-chemical reaction of highly
conductive Ag and high capacity P. When served as an anode material, it delivers an initial discharge
capacity of 1274 mA h g-1, which is higher than the metal phosphides discussed above. By further
compositing AgP2 with carbon black, a new AgP2/C nanocomposite was obtained. As an electrode
material for LIBs, it combines a variety of advantages. First, the in situ formed Li3P serves as a
protective matrix to inhibit Ag grain coarsening during cycling. Second, the Ag nanoparticles and
amorphous carbon can provide sufficient electrical conductivity and mechanical strength to promote
the electrochemical lithiation reaction of P atoms. Third, the nanostructure can reduce the diffusion
length of Li+ and e-. Thus, the AgP2/C nanocomposite shows superior electrochemical performance in
both half and full cells.
2. Experimental
2.1. Preparation of AgP2 and AgP2/C
AgP2 was synthesized by highenergy shake milling (QM-3C, Nanjing, China) of stoichiometric
amounts of Ag (99.9%, 600 mesh, Sinopharm Chemical Reagent Co., Ltd.) and RP (98.5%, Aladdin)
powders at 1200 rpm for 3 h under an Ar atmosphere. For comparison, the pure P sample was
prepared under the same conditions. The AgP2/C nanocomposite was synthesized via high energy
planetary milling (QM-3SP4, Nanjing, China) of the as-prepared AgP2 and carbon black (TIMCAL
Graphite & Carbon) powders in a mass ratio of 8:2 at 200 rpm for 12 h under an Ar atmosphere. The
weight ratio of milling balls to powder was 50:1 for both milling processes.
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2.2. Material characterization
XRD patterns of the as-prepared powders were recorded by a PANalytical Empyrean with Cu Kα
radiation. Raman spectra were obtained by a HORIBA LabRAM Aramis spectromicroscopy system
with a 633 nm wavelength. XPS data were collected with a Thermo Scientific ESCALAB 250 using
Al Kα source. SEM and TEM images were observed by Carl Zeiss Supra 40 and JEOL JEM-2100,
respectively.
2.3. Electrochemical measurements
The P, AgP2 and AgP2/C nanocomposite electrodes were prepared by pasting the slurry containing
70 wt.% of active materials, 15 wt.% of Super P (TIMCAL Graphite & Carbon) and 15 wt.% of
carboxymethyl cellulose (CMC, Mw=700000)/styrene butadiene rubber (SBR, BM-451B, Zeon) (1:1
m/m) on copper foil. The load density of the active materials was ~1 mg cm-2. For half cells, the
CR2025 coin cells were assembled in an argon-filled glove box with lithium foil as the counter
electrode, polyethylene membranes (Teklon@Gold LP) as the separator and a 1 M LiPF6 solution in
ethylene carbonate/diethyl carbonate/ethyl methyl carbonate (1:1:1 m/m/m) with 10 wt.%
fluoroethylene carbonate as the electrolyte. Galvanostatic charge/discharge experiments were
performed at different current rates on a battery testing system (LAND CT2001A). Cyclic
voltammetry (CV) over the potential range of 0–2 V at 0.1 mV s-1, and impedance spectra at a 5 mV
amplitude signal in a frequency range of 1 MHz to 0.01 Hz, were taken on an electrochemical
workstation (Gamry Interface 1000). For the ex-situ XRD and TEM analyses, we collected the
electrodes by separating the test cells in the argon-filled glove box, washing with DEC several times,
and then vacuum dried in the antechamber of the glove box. Full cells were assembled with
commercial LiCoO2 electrodes as cathodes and AgP2/C nanocomposite electrodes as anodes in an
argon-filled glove box. The LiCoO2 electrodes consisting of 80:10:10 wt. % of active materials, super
P and polyvinylidene fluoride. The CV curves of the full cell were taken between 1.0 and 3.8 V at 0.1
mV s-1. The full cell galvanostatic discharge/charge tests were conducted with a cutoff voltage of 2.0–
3.8 V vs Li/Li+.
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3. Results and discussion
The XRD pattern shown in Fig. 1a indicates the successful generation of AgP2 polycrystalline
powder after 3 h of high energy shake milling.[18] A weak Ag diffraction peak at 38.2º can be
observed in the XRD pattern of AgP2 powder, this could be due to a small amount of Ag powder
adhered to the surface of the ball milling tank, thereby stopping the reaction between Ag and P
powders. The consistency between the XRD patterns of AgP2 and the AgP2/C nanocomposite indicates
no side reactions as a result of high energy planetary milling. The Raman spectrum of the AgP2/C
nanocomposite (insert of Fig. 1a) confirms the existence of carbon, with two peaks at ~1350 and
~1590 cm-1 belonging to the D (disordered) and G (graphite) bands, respectively.[19] The integral area
ratio of the D and G bands is estimated to be 3.29, suggesting the amorphous structure of the carbon in
the AgP2/C nanocomposite. Fig. 1b shows the crystal structural model of monoclinic AgP2. The Ag
atoms are in the form of Ag-Ag covalent bonds and are located in the middle of the layers consisting
of wrinkled P105- rings.
Fig. 1c and d present the XPS P 2p spectra of AgP2 and the AgP2/C nanocomposite. Both of the
materials contain two broad peaks located at ~134.3 and ~129.8 eV. The peak located at ~134.3 eV
3-
can be attributed to PO4 species,[20] resulting from the slight oxidation on the top surface of the
powders in air. The peak located at ~129.8 eV can be ideally separated as P 2p1/2 (~130.5 eV) and 2p3/2
(~129.5eV). These peaks can be ascribed to AgP2 due to the binding energy of these peaks being
slightly lower than that of elemental phosphorus (P 2p1/2 ~130.7 eV and 2p3/2 ~129.8 eV).[21, 22]
Upon further analysis, we find that the PO43- contribution accounts for 36.5% of the AgP2 and 82.4%
for the AgP2/C nanocomposite in the surface area, demonstrating a thicker oxidation layer on the
surface of the AgP2/Cnanocomposite.
Furthermore, the microstructure of AgP2 and the AgP2/C nanocomposite was investigated by
electron microscopy. Fig. 2a and b show the SEM images of AgP2 and the AgP2/C nanocomposite,
with untreated commercial Ag and P powders for comparison. The AgP2 is constituted of dense
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particles with sizes from hundreds of nanometers to a few microns. The morphology of the raw
materials, including aggregated Ag particles and the bulk size of P particles, disappeared after
continuous fracture and welding processes during high energy shake milling.[23] After high energy
planetary milling, the AgP2/C nanocomposite is an aggregation of many sub-micron particles.
Fig. 2c and d exhibit the HRTEM images of AgP2 and the AgP2/C nanocomposite. Both images
__
__
reveal the clear lattice fringes corresponding to the (112) and (113) planes of AgP2. Compared with
AgP2, the AgP2/C nanocomposite has a much smaller crystalline grain size and more amorphous
interfacial regions. Further observations reveal that the AgP2 particles are surrounded by amorphous
carbon in the AgP2/C nanocomposite. In addition, consistent with the XRD results, both samples show
__
__
clear polycrystalline rings corresponding to the (112), (113) and (300)/ (202) planes of AgP2 in
selected area electron diffraction (SAED) patterns. Elemental mapping under scanning transmission
electron microscopy (STEM), as shown in Fig. 2e-h, displays the homogeneous distribution of Ag, P
and C in the sample, indicating the uniform coating of the carbon layer.
Fig. 3a shows the initial discharge/charge curves of P, AgP2 and the AgP2/C nanocomposite at a
current density of 0.1 A g-1. It can be seen that the P electrode shows the highest discharge capacity of
2535 mA h g-1, but with a poor Coulombic efficiency of 4.18%. In comparison, the initial discharge
capacity of the AgP2 electrode is decreased to 1274 mA h g-1, although a higher initial Coulombic
efficiency of 72.6% is achieved. The significantly improved initial Coulombic efficiency may be
attributed to the enhancement of electrical conductivity of the AgP2 electrode. Compare to the AgP2
electrode, due to the existence of amorphous carbon in the AgP2/C nanocomposite, the initial
discharge capacity of the AgP2/C nanocomposite electrode is decreased ~200 mA h g-1, but with a
relative higher initial Coulombic efficiency of 78.3% achieved. The increased Coulombic efficiency
of the AgP2/C nanocomposite electrode can be attributed to the amorphous carbon network, which not
only improves the conductivity of the electrode but also reduces the direct conduct between AgP2
particles and the electrolyte.
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The electrochemistry impedance spectra measurements were performed after the first cycle at 2 V
to compare the conductivity of the three electrodes. As presented in Fig. 3b, the semicircle in the
medium-to-low frequency region corresponds to charge-transfer resistance (Rct) and the inclined line
in the low-frequency region can be attributed to Li+ diffusion in the electrode.[24] The value of the
Rct was obtained by fitting the EIS using an equivalent circuit. It has been found that the Rct values of
the P, AgP2 and AgP2/C nanocomposite electrodes are 245.8, 61.7 and 35.7 ꢀ, respectively, indicating
the highest e- transfer rate in the AgP2/C nanocomposite electrode.
Fig. 3c compares the cycling performance of the AgP2 and AgP2/C nanocomposite electrodes. The
capacity of the AgP2 electrode decreased to 541 mA h g-1 after 100 cycles. In contrast, in the AgP2/C
nanocomposite electrode, the uniform carbon layer not only enhances the electrical conductivity of the
electrode, but also alleviates the volume change of active materials during cycling. Furthermore, the
small particle size after planetary milling can alleviate the absolute volume change and reduce the Li+
diffusion length, this results in a relatively higher capacity of 785 mA h g-1 for the AgP2/C
nanocomposite after 100 cycles.
In addition, the AgP2/C nanocomposite electrode also presents excellent rate capability. As shown
in Fig. 3d, the reversible capacities are 843,745, 677, 651, 620 and 605 mAh g-1 at 0.1, 1, 3, 5, 8 and
10 A g-1, respectively. When the current density returns to 0.1 A g-1, a reversible capacity of 777 mAh
g-1 can be recovered, indicating the good reversibility of the AgP2/C nanocomposite. Fig. 3e indicates
that the AgP2/C nanocomposite has higher superior rate capability than other reported metal
phosphides.[13, 25-32] Furthermore, the AgP2/C nanocomposite electrode exhibits good cycling
performance even at high current densities. As presented in Fig. 3f, all electrodes were tested at 0.1 A
g-1 for the initial three cycles and then different current densities for the following cycles. When
cycling at a current density of 1 A g-1, the AgP2/C nanocomposite slowly decreases from 834 to 731
mA h g-1. Further increases the current density to 3 A g-1, although it shows relacively lower reversible
capacities, a good capacity retention still can be achieved, for it just decline ~100 mAh/g during 97
cycles and obtain a discharge capacity of 611 mA h g-1 at the end of 100 cycles. While at a current
density of 5 A g-1, it shows the lowest reversibe capacities, however, the discharge capacity can still
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remain as high as 572 mA h g-1 after 100 cycles with 82.5% retention of the initial discharge capacity
at 5 A g-1 (693 mA h g-1), indicating high rate capabiity for the AgP2/C nanocomposite electrode.
In order to gain more information regarding the electrochemical reaction processes of the AgP2/C
nanocomposite, we performed CV, ex-situ XRD, ex-situ HRTEM and SAED analyses on the
discharge/charge electrode. As shown in Fig. 4a, during the initial cathodic scan, the broad peak from
0.4 to 0.8 V can be ascribed to the conversion reaction between Li and AgP2 to form Ag and LiP3.
Then, the potential below 0.2 V is believed to be the alloy reaction between Li and elemental Ag.[16]
After first cycle, three peaks located from 0.4 to 1.2 V are consistent with the cathodic peaks of
elemental P.[4, 5] In the reverse sweeps, two small oxidation peaks located at 0.1 and 0.3 V can be
ascribed to the dealloying reaction of Ag with Li,[33] while the anodic peaks from 1.0 to 1.5 V
correspond to stepwise Li extraction from Li3P.[8] In addition, no obvious shifts are observed from the
second cycle, indicating the good cycling stability of the AgP2/C nanocomposite.
To confirm this mechanism, we performed ex-situ XRD measurements of the AgP2/C
nanocomposite electrodes at seven different discharge/charge states during the first cycle. As shown
in Fig. 4b and c, the characteristic peaks of the AgP2 phase disappeared after discharge to 0.3 V, while
the Ag signals increased their intensities and the XRD peaks of Li3P are observed. As the potential
lowered further to 0.1 V, the metallic Ag alloyed with Li to form LiAg (cubic), LiAg (tetragonal) and
Li9Ag4 phases. When the electrode fully discharged to a terminate voltage of 0.01 V, the XRD pattern
shows the presence of Li3P and Li10Ag3. Upon reversed charging to 0.8 V, the Li-Ag alloy phases
completely convert to elemental Ag. After further charging to 1.2 V, the Li3P phase is partially
delithiated to form a new LiP7 phase. When the electrode is fully charged, only the Ag phase peaks are
detected, this result illustrates that AgP2 cannot be regenerated after initial discharge/charge processes.
According to the above analysis, the reaction mechanism of AgP2 can be described as follows:
During the initial lithiation process:
AgP2
Ag + Li3P
Li10Ag3 + Li3P
During subsequent delithiation and lithiation processes:
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Li10Ag3
Li3P
Ag
P
To gain more information into the phasecomposition and distribution of the AgP2/C nanocomposite
during cycling, the reaction products of fully lithiated AgP2/C to 0.01 V and fully delithiated AgP2/C
at 2 V were investigated by HRTEM and SEAD. Fig. 4d shows the ex-situ HRTEM and SAED
images of the lithiated (discharged) AgP2/C nanocomposite. The HRTEM image clearly shows the
coexistence of the (411) plane of Li3Ag10 and the (011) plane of Li3P with the lattice fringes of ~0.235
and ~0.333 nm, respectively. The two phases are uniformly distributed in the amorphous carbon
matrix. The corresponding SAED pattern further confirms the existence of Li3Ag10 and Li3P
nanocrystals. After charging to 2 V, the HRTEM image (Fig. 4e) exhibits ultrafine Ag nanoparticles
that are highly dispersed in the amorphous P/C host matrix. Furthermore, in agreement with the ex-situ
XRD results, the SAED pattern only shows the multiple rings of the Ag phase. In the following 10th,
30th, 50th and 100th cycles, the Ag phasesdo not tend to coarsen to form large grains, which is reflected
by their lack of significantly changed diffraction peaks in Fig. 4f.
On basis of the above analysis, a schematic illustration is given to summarize the electrochemical
reaction processes. As illustrated in Fig. 4g, the intermediate discharge/charge products of the AgP2/C
nanocompositeare combined to give a synergistic effect during cycling. The in-situ formed Li3P phase
serves as a shielding matrix to prevent the Ag grains coarsening during cycling, while the highly
dispersed Ag nanoparticles and amorphous carbon network act as electronic pathways and buffer the
matrix to promote reversible Li storage reaction of the P component.
As a result of its good electrochemical performance in half cells, the AgP2/C nanocomposite was
further tested in full cells with LiCoO2 as the cathode. Fig. 5a shows that the pouch-type
LiCoO2ǁAgP2/C full cell is able to drive a SCUT icon fan.We then conducted CV and galvanostatic
discharge/charge measurements with coin-type cells. Fig. 5b shows the CV curves of the
LiCoO2ǁAgP2/C full cell at a scanning rate of 0.1 mV s-1 between 1.0 and 3.8V. During the initial
charging process, the main peaks from 2.8 to 3.5 V can be attributed to the Li+ extraction of LiCoO2
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and reaction with AgP2. In subsequent cycles, these peaks are shifted to a lower potential due to the
reduced electrode polarization after initial activation of theAgP2/C electrode. In the reverse scan, the
dominant peaks between 2.3 and 3.0 V can be ascribed to the delithiation ofLi3P and lithiation of Li1-
xCoO2.
According to the CV results, we chose 2.0–3.8 V as the cutoff voltage to conduct galvanostatic
discharge/charge tests. Fig.5c and d show the voltage profiles and cycling performance of the
LiCoO2ǁAgP2/C full cells at a current density of 0.1 A g-1 for the initial three cycles and 0.5 A/g for
the subsequent cycles. The operation potential of this cell is ~2.8 V, which is higher than
LiTi5O12/LiFePO4 (2.0 V). However, the initial charge capacity (723 mA h g-1 vs. anode) and
Coulombic efficiency (64% vs. anode) in the full cells are much less than in the half cells. Despite all
this, the anode electrode still shows high capacity (431 mA h g-1) after 100 cycles. The lower initial
Coulombic efficiency and capacities may be caused by many factors, such as the limited cut-off
voltages of the cell and unmatched capacity ratio of the two electrodes. We will do in-depth research
into these points and give results in future work.
4. Conclusions
In summary, we have successfully synthesized a new AgP2/C nanocomposite anode via a simple
mechanochemical reaction of metallic Ag, elemental P and carbon black. The as-prepared AgP2/C
nanocomposite anode exhibits high reversible capacities, excellent rate capability and superior cycling
stability in half cells. These excellent electrochemical performances are attributed to the uniformly
distributed carbon matrix and synergistic Li-storage reactions of Ag and P components, where the in-
situ formed Li3P phase serve as a shielding matrix to prevent the aggregation and alleviate the volume
change of Ag nanoparticles during cycling, while the highly dispersed Ag nanoparticles act as
electronic pathways and buffer matrix to promote the reversible Li storage reaction of P component.
In addition, the anode electrode shows higher capacity than graphite in a LiCoO2ǁAgP2/C full cell,
indicating the commercial potential of this material.
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Acknowledgements
This work was supported by the International Science & TechnologyCooperation Program of China
(2015DFA51750) andFoundation for Innovative Research Groups of the National Natural Science
Foundation of China (No. NSFC51621001), the National Natural Science Foundation of China
Projects (No. 51431001and 51771075) and by the Natural Science Foundation of Guangdong
Province of China (Nos. 2016A030312011). We also acknowledge the support of the Guangdong
Province Universities and Colleges Pearl River Scholar Funded Scheme (2014).
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Figure caption
Fig. 1 (a) XRD patterns of the AgP2 and AgP2/C nanocomposite (insert shows Raman spectrum of the
AgP2/C nanocomposite), (b) structural demonstration of the monoclinic AgP2, (c) XPS P 2p spectrum
of the AgP2 and (d) XPS P 2p spectrum of the AgP2/C nanocomposite.
Fig. 2 SEM images of (a) the AgP2 and (b) AgP2/C nanocomposite (the insets of Fig. 2a are SEM
images of Ag and P powers), TEM images of (c) the AgP2 and (d) AgP2/C nanocomposite (the insets
are corresponding SEAD patterns), (e) STEM image and (f-h) element mapping images of the AgP2/C
nanocomposite.
Fig. 3 Galvanostalic discharge/charge profiles of (a) the AgP2 and AgP2/C nanocomposite at a current
density of 0.1 A/g, (b) Nyquist plots of the AgP2 and AgP2/C nanocomposite at fully charged state
after the first cycle (the inset is corresponding to equivalent circuit), (c) cycling performance of the
AgP2 and AgP2/C nanocomposite electrodes, all electrodes were tested at a current density of 0.1 A g-1
for the initial three cycles and then 0.5 A/g for the following cycles, (d) rate capability of the AgP2/C
nanocomposite, (e) comparison of rate capability of AgP2/C composites with other reported metal
phosphides and (f) capacity vs. cycle number of the AgP2/C nanocomposite at different current rates
(0.1 A g-1 for the initial three cycles).
Fig. 4 (a) CV curves of the AgP2/C nanocomposite electrode at a scanning rate of 0.1 mV s-1, (b)
initial potential vs. capacity curve of the AgP2/C nanocompositewith seven electrochemical reaction
states for ex-situ XRD measurements, namely open cell potential (OCP), discharge to 0.3, 0.1 and 0.01
V, recharged to 0.8, 1.2 and 2.0 V, (c) ex-situ XRD patterns of the AgP2/C nanocompositeelectrodeat
seven different states for the first cycle, ex-situ HRTEM and SEAD images of the AgP2/C
nanocomposite electrodes after (d) discharge to 0.01 V and (e) charge to 2 V, (f) comparison ex-situ
XRD patterns of the AgP2/C nanocomposite electrodes at fully charged state for different cycles (1st,
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10th, 30th, 50th and 100th) and (g) a schematic illustrationof the electrochemical reaction processes of
the AgP2/C nanocomposite electrode.
Fig. 5 (a) Optical imagesof a SCUT icon fan driven by the pouch-type LiCoO2ǁAgP2/C full cell, (b)
CV curves of the LiCoO2ǁAgP2/C full cell and LiCoO2 electrode with a scanning rate of 0.1 mV s-1, (c)
galvanostatic discharge/charge profiles and (d) cycling performance of the LiCoO2ǁAgP2/C full cells
in the voltage window of 2.0-3.8 V. The above cells were tested at a current density of 0.1 A g-1 for
the first three cycles and 0.5 A/g for the subsequent cycles.
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Highlights
• We have successfully synthesized AgP2 and AgP2/C composite powders for lithium ion
batteries.
• The AgP2/C composite has not been reported in use of lithium-ion batteries.
• The AgP2/C composite demonstrates excellent electrochemical performance for both
half and full cells.
• The method is high yield, low-cost and environmentally friendly.