Coralline Glassy Lithium Phosphate-Coated LiFePO4 Cathodes withImproved Power Capability for Lithium Ion BatteriesGuoqiang Tan,† Feng Wu,†,‡ Li Li,*,†,‡ Renjie Chen,*,†,‡ and Shi Chen†,‡
†School of Chemical Engineering and Environment, Beijing Key Laboratory of Environmental Science and Engineering, BeijingInstitute of Technology, Beijing 100081, China‡National Development Center of High Technology Green Materials, Beijing 100081, China
ABSTRACT: Novel coralline glassy lithium phosphate-coated LiFe-PO4 cathodes successfully prepared by radio frequency magnetronsputtering have been studied in lithium ion batteries. These coatedLiFePO4 show higher reversible capacity, stable cycle performance, andimproved power capability compared to the bare one. These favorableproperties are considered to be attributed to the good conductivity andstability of the glassy lithium phosphate coating. The amorphousnature of the coating reduces the anisotropy of the surface propertiesof LiFePO4 electrode and enhances the Li+ ionic diffusion into theLiFePO4. The glassy lithium phosphate is an effective Li+ conductor,which increases the ionic and electronic transport on the surface andinto the bulk of LiFePO4 electrode, extends the electroactive zone, andfacilitates the transfer kinetics. It is also a stable Li-excess material,which provides an extra lithium capacity and maintains the electrode structural integrality. Radio frequency sputtering coating ofstable Li+ conductors on the surface of nanosized LiFePO4 is an attractive way to improve its power capability, and these specificLiFePO4 cathodes have great potential for application in high-power lithium ion batteries.
■ INTRODUCTION
Energy and environment are two themes of paramountimportance in the 21st century. Renewable energy technologiesare critical to realize global sustainable development. SinceSONY developed the first commercial Li ion battery in theearly 1990s, lithium ion batteries (LIBs) have been widely usedas advanced electrochemical energy storage and conversionsystems in various electronic devices and environmentallyfriendly vehicles including both hybrid electric vehicles (HEVs)and pure electric vehicles (PEVs).1−4 LIBs with both highenergy and power density are essential to improve EVs.5,6
Currently, lithium iron phosphate (LFP) and lithiummanganese oxide (LMO) are the most promising candidatesfor use as cathode materials in batteries for EVs.7,8 Both LFPand LMO are inexpensive, abundant, safe, and environmentallybenign. LFP shows a higher gravimetric capacity and bettercapacity retention than LMO, but LFP exhibits a poorconductivity, resulting in a low rate performance.9,10 Variousstrategies to overcome the electronic and ionic transportlimitations of LFP have been proposed, including improvingbulk or surface electronic conductivity by doping with foreignatoms or coating with electronically conductive agents,11−13
reducing the path length of electrons and Li+ ions by decreasingthe particle size14−16 or increasing diffusion of Li+ ions acrossthe surface toward the (010) facet by coating stable Li+
conductors on the surface of nanosized LFP.17,18
Herein, radio frequency (RF) magnetron sputtering has beenused to prepare coralline glassy lithium phosphate-coated
LiFePO4 (GLP-coated LFP) cathodes by depositing a thinglassy lithium phosphate coating on the surface of LiFePO4
electrodes. Amorphous lithium phosphate compounds such asLi2O−P2O5, LiPON, and LiBPO are well-known to be stable,facile Li+ conductors and have been used as solid-stateelectrolytes in all-solid-state LIBs.19−21 In this research, ourintention is to introduce a fast, stable Li+ conductor to increaseionic and electronic transport at the surface of LFP andimprove the rate capability of LIBs. The proposed mechanismsfor ionic and electronic transport are shown in Scheme 1. Thethin GLP coating on the surface of LFP electrode increases therate of Li+ ionic transport along the surface as well as Li+ ionicpermeation into the surface of the LFP electrode. Both of theseprocesses promote Li+ ions migration through the electrolyteand cathode into the bulk of LFP crystals through (010)facets.22 The coralline GLP coating acts as cross-linkednetworks to keep LFP particles on the surface layer linkedtogether, reducing the path length of Li+ ions and electronstransfer between LFP particles and creating more conductivepaths for Li+ ions and electrons. The GLPs can be doped withtransition metals to achieve electronic conduction reported inprevious literature,18,23 and these transition metals include Fe,Ti, Co, Ni, Ga, Nb, et al.24 The GLP is believed to be able todissolve partial iron ions during the charge−discharge of LFP
Received: October 1, 2012Revised: February 25, 2013
and increase the electronic conductivity of LFP electrode forrapid mass and charge transfer. All of these factors are beneficialto enhance the power capability of the coralline GLP-coatedLFP cathode. Moreover, the GLP coating with high lithiumcontent may be able to provide extra Li+ ions for theextraction−insertion during the charge−discharge process,increasing the reversible capacity, and it maintains the electrodestructural stability, improving the cycle performance. Herein, itis demonstrated that the nanosized GLP coating cansignificantly improve the electrochemical properties of theLFP cathodes in LIBs. The coralline GLP-coated LFP cathodesexhibit large stable reversible capacities, high rate capabilities,and excellent cycle performance.
■ EXPERIMENTAL SECTION
LFP Cathode Preparation. Commercially available LiFe-PO4 powder (Pulead Technology Industry Co., China) wasused as the cathode material. The cathode electrodes wereprepared by pasting a mixture of 75 wt % LFP, 15 wt %acetylene black, and 10 wt % poly(vinylidene fluoride) (PVDF)onto an aluminum foil current collector using an AFA-IIIautomatic film coater with cover heater (MTI corporation,
South Korea). The thickness of the LFP electrodes wascontrolled at 20 um.
Li3PO4 Target Preparation. Commercially availableLi3PO4 powder (99%, Acros, China) was ball-milled withdehydrated ethanol at a rotating speed of 400 rpm for 5 h usinga planetary ball mill (Fritsch Puluerisette7, Germany) and thendried at 70 °C for 2 days to obtain a fine powder. The finalLi3PO4 target was prepared using a conventional cold-pressmethod. Twenty grams of dried Li3PO4 powder was pressedinto a 60-mm-diameter pellet and then sintered in an electricalfurnace at 600 °C for 5 h in air.
Coralline GLP-Coated LFP Cathode Preparation. Thecoralline GLP-coated LFP cathode was prepared by RFmagnetron sputtering using the Li3PO4 target under a high-purity Ar atmosphere with a specific pattern, as shown inScheme 2. The prepared LFP electrode and Li3PO4 pellet usedas the substrate and target, respectively, were placed in thecorresponding positions in the sputtering chamber. Thedistance between the target and electrode substrate was 6 cm.The chamber was evacuated to a base pressure of 1.0 × 10−5 Pato guarantee a clean sputtering condition. The working pressurewas 1.0 Pa, and the RF power was 100 W. Before deposition,
Scheme 1. Mechanisms for Li+ Ionic and Electronic Transport in the Coralline GLP-Coated LFP Cathode
Scheme 2. Synthetic Route Used To Prepare the Coralline GLP-Coated LFP Electrodes
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the target was presputtered for 15 min. The deposition timewas set in a stepwise manner of 5, 10, 15, 20, 25, and 30 min.Characterization of Properties. The morphologies of the
LFP electrodes were examined by FE-SEM (Zeiss, SUPRA 55)and EDX (Phoenix). XRD was performed on a diffractometer
(Rigaku Ultima IV) using a Cu Kα radiation. FT-IR spectrawere obtained on an infrared spectrometer (Nicolet 6700).Raman spectra were obtained on a Raman spectrometer (JYLabram HR 800). Electrochemical measurements were carriedout by using coin-type cells. The prepared LFP electrode was
Figure 1. FE−SEM images of the (top row) bare LFP cathode and (middle and bottom rows) GLP-coated LFP cathodes after deposition for 10 and20 min, respectively.
Figure 2. (A, B) Top-view and (C, D) cross-sectional FE-SEM images of the GLP-coated LFP cathode after deposition for 20 min.
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used as the cathode and lithium metal as the anode, while theelectrolyte was 1 M LiPF6/EC + DMC (1:1 in volume). Cellswere assembled in an argon-filled glovebox and then aged for24 h before electrochemical testing. Cyclic voltammetry (CV)and electrochemical impedance spectroscopy (EIS) measure-ments were performed using an electrochemical workstation(Chi 604D). Galvanostatic charge−discharge experiments werecarried out between 2.5 and 4.2 V using a battery tester (LandCT2001A). The specific capacity of the coralline GLP-coatedLFP cathode was calculated based on the weight of LFP.
■ RESULTS AND DISCUSSIONMorphology and Structure. The surface morphologies of
the bare and coated LFP electrodes are shown in Figure 1.Generally, the bare LFP electrode exhibited a relatively roughsurface that might easily cause active materials to dissolve in theelectrolyte in LIBs. The morphologies of coated LFP electrodeswere influenced by the thickness of the GLP film, which wascontrolled by varying the deposition time. As the depositiontime was increased, the thickness of the GLP film graduallyincreased, and the electrode surface became smoother anddenser. From a microscopic point of view, the GLP-coatednanosized LFP particles on the surface layer of the electrodeconnected with each other to form a network as the depositiontime increased. The FE−SEM images also showed the chargesin the pore structure of the LFP electrodes as a function of thedeposition time. As the time was increased, the pore size of theLFP electrode gradually decreased. After sputtering for 20 min,the LFP electrode possessed a coralline surface morphologywith sufficient porosity. The cross-linked networks could createmore conductive paths for Li+ ions and electrons, and theuniform porous structure guaranteed the infiltration of theelectrolyte. Figure 2 revealed that the GLP coating generated bythe RF sputtering method become a thin and condensed filmand was stacked well on the surface of the LFP electrode, with ahomogeneous and glassy texture. The thickness of the GLP filmmeasured by FE−SEM was about 200 nm after deposition for20 min.The GLP film exhibited amorphous glassy behavior, as
confirmed by XRD, FT−IR, and Raman measurements asshown in Figure 3. In Figure 3A, the XRD pattern of the bareLFP electrode possessed clear diffraction peaks that wereconsistent with the orthorhombic olivine phase of LiFePO4(space group: Pnma).25 No obvious diffraction peakscorresponding to graphite were present; this indicated thecarbon in the electrode was not well crystallized. The XRDpattern of the GLP-coated LFP electrode showed somediffraction peaks consistent with Li3PO4.
11,18 The weakintensity of these peaks indicated that the layer of Li3PO4 onthe surface of the LFP electrode possessed a glassy structure. InFigure 3B, the FT-IR spectrum of the bare LFP electrode wascomplex with a large number of bands. In the range of 800−1200 cm−1, bands were related to the stretching modes of the(PO4)
3− anion; the first two bands at 876 and 934 cm−1
corresponded to symmetric stretching modes, and those at1034, 1098, and 1136 cm−1 corresponded to the antisymmetricstretching modes of the P−O bonds.26 Bands in the range of420−570 cm−1 were related to the bending modes of the(PO4)
3− anion.27 In the FT-IR spectra of the GLP-coated LFPelectrode, the obvious changes were the appearance of two newbands at 900 and 1258 cm−1; the former was caused by thesuperposition of bands of crystalline LFP and glassy Li3PO4,and the latter was attributed to the stretching vibrations of
terminal PO3 units of glassy Li3PO4.28,29 In Figure 3C, the
Raman spectrum of the bare LFP electrode exhibited twointense bands at 1355 and 1593 cm−1 that were attributed tothe D-band (disorder-induced phonon mode) and G-band(graphite band) of highly disordered carbon, respectively.10
Other bands in the range of 100−500 and 500−1100 cm−1
corresponded to the Raman vibrations of Fe−O and (PO4)3− in
LFP, respectively. The intramolecular vibrational bands of the(PO4)
3− anion were observed at 582, 985, and 1030 cm−1.26,27
These were consistent with the presence of well-crystallizedLFP. The Raman spectrum of the GLP-coated LFP electrodecould almost be superposed on that of the bare LFP electrodeexcept for a new weak band at 636 cm−1, and the intensity ofthe bands at 445 and 985 cm−1 were increased. These changeswere attributed to the glassy Li3PO4 film, the band at 636 cm
−1,and the increased band at 445 cm−1 corresponding to thebending modes of the (PO4)
3− anion; the other increased bandat 985 cm−1 was attributed to the stretching modes of the(PO4)
3− anion in glassy Li3PO4.29,30
Figure 3. (A) XRD patterns, (B) FT-IR spectra, and (C) Ramanspectra of the (a) bare LFP and (b) GLP-coated LFP (20 min)cathodes.
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Electrochemical Properties. The electrochemical proper-ties of the bare and GLP-coated LFP cathodes were evaluatedby cyclic voltammetry (CV), electrochemical impedancespectroscopy (EIS), and galvanostatic charge−discharge testing.Figure 4 shows the charge−discharge profiles and cycle
performance of the LFP cathodes at a constant current densityof 16 mA g−1 (0.1 C). In Figure 4A, the capacity of the GLP-coated LFP cathode was obviously increased, and its potentialplateau was slightly decreased compared to that of the bare LFPcathode. As our consideration, these were attributed to the GLPcoating, which improved the kinetics of the LFP electrode andalso provided partial additional capacity for the LFP electrode.In Figure 4B, the bare LFP cathode delivered an initialdischarge capacity of 156.4 mAh g−1, with capacity retention of95.5% after 51 cycles. Comparatively, the GLP-coated LFPcathode exhibited a higher initial discharge capacity of 167.3mAh g−1 and capacity retention of 98.6% after 51 cycles,demonstrating its ultrahigh cyclability at the low rate.The electrochemical kinetic performance of the LFP
cathodes was analyzed by the EIS measurement. Figure 4B(inset) shows the impedance spectra of the bare LFP and GLP-coated LFP electrodes discharged to 2.5 V after selected cycles,and Figure 5 shows the corresponding test circuits andequivalent circuits used to explain the impedance spectra.Generally, for the bare LFP electrode, the impedance spectra ofthe Li/LFP cell is composed of a semicircle at high frequencyand a straight sloping line at low frequency. An intercept at theZ′real axis at high frequency corresponds to the cell electrolyteresistance (Rs). The semicircle indicates the charge transfer
resistance (Rct) and double-layer capacitance (Cdl). The slopingline represents the Warburg impedance (Zw) related to theeffect of the diffusion of lithium ions at the electrode/electrolyte interface. Rs is also referred to as the “ohmicimpedance”, and the combination of Rct and Zw is called the“faradaic impedance”, which reflects the kinetics of the cellreactions.31,32 The Rct values of the bare LFP and GLP-coatedLFP cathodes after 2 cycles were 158.6 and 50.4 Ω,respectively. The smaller Rct of the GLP-coated LFP cathodesuggested that the transfer of Li+ ions and electrons was morefeasible on this electrode, indicating that the GLP coatingimproved the electrochemical activity of the LFP electrode.When after 51 cycles, the Rct of the bare LFP and GLP-coatedLFP cathodes became 520.6 and 240.4 Ω, respectively. Theslow increase in Rct with increased cycles confirmed the goodcycle performance of the LFP cathodes at the low rate.Interestingly, the impedance spectra of the GLP-coated LFPcathode after 51 cycles exhibited two partially overlappingsemicircles and a straight sloping line. As our consideration, theappearance of the first depressed semicircle at high frequencywas attributed to the GLP coating, and the subsequentsemicircle represented the charge transfer process on the LFPparticles. The parameters Rct1 and Cdl1 were responsible for theresistance and capacitance of the GLP coating, respectively,whereas Rct2 and Cdl2 represented the charge transfer resistanceand double-layer capacitance for the LFP, respectively. In thecells, the GLP coating acted as a transition layer between theelectrolyte and LFP electrode. The GLP film was very thin andpossessed a fast Li+ ionic conductibility; it could reduce theresistance of Li+ ions transfer from the electrolyte into the LFPelectrode. It was also proposed that the disorder nature of thecoating modified the surface potential of lithium to facilitate theLi+ ionic adsorption from the electrolyte by providing differentlithium sites with a wide range of energies that can be matchedto the energy of lithium in the electrolyte.18 All of theseprocesses resulted in a decreased charge transfer resistance.Meanwhile, the GLP might be able to dissolve partial iron ionsduring the charge−discharge to increase its electronicconductivity, facilitating the mass and charge transfer.The rate performance of the LFP cathodes was also
investigated at different test conditions. Figure 6A shows thecycle performance of the LFP cathodes discharged at a rate of 1C. The cells were first discharged at a rate of 0.1 C for 10 cyclesto activate them and then discharged at a rate of 1 C for 90cycles. The initial discharge capacities of the bare LFP andGLP-coated LFP at 1 C became 152.6 and 165.8 mAh g−1,respectively. After 90 cycles, the bare LFP exhibited a relativelylow capacity of 135.7 mAh g−1 with average Coulombicefficiency of 99.1% for 100 cycles. However, the correspondingvalues for the GLP-coated LFP were 159.1 mAh g−1 and 99.7%,respectively. These results indicated that the cycle performanceof the GLP-coated LFP was much better than that of the bareLFP at 1 C rate. The improved cycle performance of the GLP-coated LFP was primarily ascribed to its structural stability. Thestable GLP coating prevented the dissolution of active materialsfrom the electrode into the electrolyte. Figure 6B shows theimpedance spectra of the GLP-coated LFP cathode dischargedto 2.5 V during cycles. After 2 cycles, the impedance spectrashowed no obvious resistance characteristic of the GLP layer,with a low Rct of 48.4 Ω. But after 51 cycles, two partiallyoverlapping semicircles were observed, and the total Rct became282.6 Ω. Figure 6C shows the CV curves of the LFP cathodesobtained at different scan rates. In contrast to the bare LFP
Figure 4. (A) Initial charge−discharge profiles and (B) cycleperformance of the bare and GLP-coated LFP (20 min) cathodesdischarged at a rate of 0.1 C; inset: EIS of the Li/LFP cells dischargedto 2.5 V after selected cycles.
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electrode, the GLP-coated LFP showed sharper redox peaks
with reduced separation. Even at a high rate of 5 mV s−1, the
sharp redox peaks were still maintained. This suggested that the
reversibility and kinetics than the bare one. This was believed
to be attributed to the increased ionic and electronic
conductibility. Figure 6D illustrates the discharge profiles of
the GLP-coated LFP electrode at various rates. At a rate of 0.1
Figure 5. Nyquest plots, equivalent circuits, and test circuits for the bare LFP and GLP-coated LFP (20 min) cathodes.
Figure 6. (A) Cycle performance of the LFP cathodes discharged at a rate of 1 C; (B) EIS of the Li/LFP cell discharged at a rate of 1 C to 2.5 V afterselected cycles; (C) cyclic voltammograms of the Li/LFP cells at different scan rates; (D) initial discharge curves and specific capacity versus cyclenumber (inset) for the GLP-coated LFP cathode at different discharge rates. All cells were charged at a rate of 0.1 C at room temperature, and theGLP-coated LFP cathode in this figure was deposited for 20 min.
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C, the initial discharge capacity of the GLP-coated LFPelectrode was 168 mAh g−1, which was very close to thetheoretical capacity of LFP. Although the capacity decreasedwith increasing rate, the GLP-coated LFP electrode exhibitedexcellent rate capability. A high capacity of 158 mAh g−1 wasachieved at a rate of 2 C; even at the highest rate of 10 C, acapacity of 138 mAh g−1 was still obtained. Its dischargecapacity remained stable upon cycling at each rate, as confirmedby the cycle performance shown in the inset of Figure 6D. Thecapacity recovered to its original value when the initial currentrate of cycling was restored. This also suggested that the GLP-coated LFP electrode showed excellent kinetics and structuralintegrity. The rate performance of the LFP cathodes at variouscharge and discharge rates was also investigated. In Figure 7A,
the bare LFP cathode showed an acceptable rate capability withdischarge capacities of 155 (0.1 C), 148 (0.2 C), 139 (0.5 C),122 (1 C), and 82 mAh g−1 (2 C). In contrast, in Figure 7B, theGLP-coated LFP cathode exhibited an improved rate capabilitywith discharge capacities of 168 (0.1 C), 165 (0.2 C), 156 (0.5C), 143 (1 C), and 125 mAh g−1 (2 C). The charge anddischarge capacity maintained stable upon cycling for eachcurrent rate. This indicated that the GLP coating was tolerantto the various current rates, and the integrity of the GLP-coatedLFP electrode was well maintained. In order to investigate theinterface information between the LFP electrode and electro-lyte, the surface morphology of the LFP electrodes after therate test was analyzed by SEM, as shown in Figure 8. The bareLFP cathode after the rate test showed a badly destructivesurface morphology. The LFP particles on the electrode surfacewere obviously cracked after the high rate test. However, thesurface morphology of the GLP-coated LFP after the rate testillustrated its structural integrity. The electrode was well
protected, and active material particles were mutuallyconnected through a GLP layer, forming a stable networkstructure. The GLP had a good oxidation resistivity because(PO4)3− anion formed a strong covalent bond between P andO, and it was not easily oxidized.33 The EDX spectra of theGLP-coated LFP electrode also showed a decreased C contentin contrast to that of the bare LFP electrode. Therefore, it couldpreserve electrode structural integrity at a high current rate withfast lithium ion conduction at the interface between theelectrode and electrolyte. These results confirmed that theGLP-coated LFP cathode maintained a good structural stabilityand exhibited an excellent rate performance.The rate performance versus cycle performance of all LFP
electrode samples with different deposition times was alsoobtained, as shown in Figure 9. We could see that the reversiblecapacity and cycle performance were gradually improved as thedeposition time increased until 20 min. However, thecorresponding performance was no more increased butdecreased when the deposition time was sequentially increasedto 25 and 30 min. This suggested an optimization amount ofthe GLP coating on the LFP electrode. The longer depositiontime introduced a thicker GLP coating, which reduced the porestructure on the LFP electrode to retard the infiltration of theelectrolyte, resulting in the decreased charge transfer efficiency.As expected, improved electrochemical properties including
reversible capacity, power capability, and cycle performancewere obtained for the GLP-coated LFP electrode, which wereascribed to the presence of the GLP coating. On the one hand,the amorphous nature of the GLP removed the anisotropy ofthe surface properties of the LFP electrode and enhanced thedelivery of Li+ to the LFP. It acted as a fast ionic conductingsurface, providing rapid Li+ ionic transport along the surfaceand permeation into the bulk of LFP. It also acted as a porousLi+ absorbing agent and modified the surface potential oflithium to facilitate the Li+ ionic adsorption from theelectrolyte. Increased Li+ ionic diffusion across the surfacewas known to facilitate Li insertion into the bulk of the LFPcrystal in the (010) direction. All of these mechanisms wereimportant for the LFP cathode because it could exchange Li+
ions with the electrolyte over its whole surface. On the otherhand, the GLP acted as cross-linked networks that reduced theLi+ ionic and electronic transfer path length between LFPparticles and created more conductive paths for the Li+ ionsand electrons, significantly increasing the size of the electro-active zone. The GLP was also believed to be able to dissolvepartial iron ions during the charge−discharge of the LFPelectrode, forming a new Fe-doped phosphate compound,which could increase the electronic conductivity of the LFPelectrode, further improving the kinetics of the LFP electrode.All of these factors improved electrochemical properties of theLFP electrode, especially its rate capability. Moreover, the GLPhad a good oxidation resistivity, so it could well protect thestructural integrity of LFP electrode to ensure an excellent cycleperformance. In a word, the coralline LFP cathodes exhibitedimproved electrochemical properties, and these were mainlyattributed to the increased ionic and electronic conductivitiesand stable network structure.
■ CONCLUSIONIn conclusion, a kind of GLP-coated LFP cathode was preparedby RF magnetron sputtering. The GLP coating was a thin,homogeneous, glassy film and was stacked well on the LFPcathode. The GLP-coated LFP cathodes possessed coralline
Figure 7. Rate performances of the (A) bare LFP and (B) GLP-coatedLFP (20 min) cathodes at various current densities (the charge currentis the same as the discharge current at each current density).
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surface morphology with uniform microporous structure afteran optimization deposition time. The nanosized GLP coating,as a fast and stable ionic conductor, improved the electronicand ionic transport in the LFP cathode, facilitating the massand charge transfer and enhancing the reversible capacity andpower capability of the LFP cathode. It also acted as a stableprotective layer to maintain the structural stability of the LFPcathode, improving the cycle performance. This coralline GLP-coated LFP cathode possessing excellent properties is apromising candidate cathode for high-power lithium ionbatteries.
NotesThe authors declare no competing financial interest.
■ ACKNOWLEDGMENTS
This study was supported by the National Key Program forBasic Research of China (No. 2009CB220100), the Interna-tional S&T Cooperation Program of China (2010DFB63370),the National 863 Program (2011AA11A256), New CenturyEducational Talents Plan of Chinese Education Ministry(NCET-10-0038), and Beijing Novel Program (2010B018).
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Figure 8. SEM images and corresponding EDX spectra of the (A, a) bare LFP and (B, b) GLP-coated LFP (20 min) cathodes after discharged at arate test for 51 cycles to 2.5 V. The discharge procedure was shown in Figure 6D.
Figure 9. Rate performances of all GLP-coated LFP cathodes withdifferent deposition times at different discharge current densities. Allcells were charged at a rate of 0.1 C at room temperature.
The Journal of Physical Chemistry C Article
dx.doi.org/10.1021/jp309724q | J. Phys. Chem. C XXXX, XXX, XXX−XXXH
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The Journal of Physical Chemistry C Article
dx.doi.org/10.1021/jp309724q | J. Phys. Chem. C XXXX, XXX, XXX−XXXI
