Spherical Agglomeration of Octahedral LiNi0.5Co4xMn1.5–3xO4

Dec 21, 2016 - Spherical Agglomeration of Octahedral LiNi0.5Co4xMn1.5–3xO4 Cathode Material Prepared by a ... College of Mine, Guizhou University, G...
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Spherical Agglomeration of Octahedral LiNi0.5Co4xMn1.5−3xO4 Cathode Material Prepared by a Continuous Coprecipitation Method for 5 V Lithium-Ion Batteries Yue Yang,†,‡ Shuang Li,†,§ Qin Zhang,§ Yun Zhang,† and Shengming Xu*,†,‡ †

Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084, P.R. China Beijing Key Laboratory of Fine Ceramics, Tsinghua University, Beijing 100084, P.R. China § College of Mine, Guizhou University, Guiyang 550025, P.R. China ‡

ABSTRACT: Octahedral LiNi0.5Mn1.5O4 with excellent electrochemical properties prepared by the solvothermal or sol−gel method under harsh conditions is expensive. Therefore, preparing octahedral LiNi0.5Mn1.5O4 with good granularity by a more cost-effective and large-scale method is significant for its industrial applications. In this study, spherical agglomerations of octahedral Co-doped LiNi0.5Co4xMn1.5−3xO4 with micrometer sizes were synthesized by a continuous coprecipitation process. Compared to conventional spherical LiNi0.5Mn1.5O4, the spherical agglomeration of octahedral LiNi0.5Co0.08Mn1.44O4 with a larger specific surface area and pore volume was well crystallized without any impurities and exhibited a high discharge capacity of about 110 mAh·g−1 at a rate of 2C and a high reversible capacity of 99.9% after the rate test (in which rates of 0.1C, 0.5C, 1C, and 2C were tested sequentially for 10 cycles). Remarkably, the discharge capacity of the prepared LiNi0.5Co0.08Mn1.46O4 exhibited a negligible decrement after 100 cycles at 1C, displaying great potential industrial application for 5 V lithium-ion batteries.

1. INTRODUCTION

However, there are still some challenges hampering the widespread application of octahedral LiNi0.5Mn1.5O4 cathode materials in industrial applications. The large-scale production and commercial operation of octahedral LiNi 0.5 Mn 1.5O 4 cathode material is still a difficult task. First, the preparation of the octahedral LiNi0.5Mn1.5O4 cathode material requires harsh conditions such as high temperature and pressure24 and an organic solvent,22,25 making the preparation process complicated and expensive. The present methods (the solvothermal and sol−gel methods) for preparing octahedral LiNi0.5Mn1.5O4 cathode materials still provide a small amount of intermittent production. Second, the high surface energy of nanosized octahedral LiNi0.5Mn1.5O4 particles prepared by the solvothermal or sol−gel method can increase side reactions during the charge−discharge process.26,27 Moreover, the fine octahedral LiNi0.5Mn1.5O4 particles are also hard to handle because these particles easily combine into irregular aggregations with poor granularity in the preparation or drying processes. Finally, the impurity phase LiyNi1−yO is easily formed during the preparation process of LiNi0.5Mn1.5O4 cathode material. Although the reported results have shown that LixNi1−xO exhibits electrochemical properties for lithium-

LiNi0.5Mn1.5O4 cathode material is considered as one of the most promising lithium-ion battery materials for use in hybrid electric vehicles and plug-in hybrid electric vehicles because of their good theoretical capacity (147 mAh·g−1) and high discharge platform (5 V).1−5 Because the electrochemical properties of electrode materials are strongly related to their structures, surface properties, and crystalline anisotropy,6−14 the spinel LiNi0.5Mn1.5O4 cathode material is usually processed into various morphologies (spheres,15 porous peanuts,16 plates,17 nanorods,18 nanowires,9 hollow spheres,19 hollow spherical shells,20 octahedrons,17,21,22 etc.) to obtain an excellent charge−discharge capacity and capacity retention. Among these morphologies, octahedral LiNi0.5Mn1.5O4 cathode materials show impressive comprehensive electrochemical properties.21,23 Aswathy et al.22 prepared octahedral LiNi0.5Mn1.5O4 by the solvothermal method and constructed an aqueous hybrid supercapacitor using the prepared LiNi0.5Mn1.5O4 as the cathode material and nitrogen-doped graphene (NDG) as the anode material. The LiNi0.5Mn1.5O4/ NDG supercapacitor delivered a maximum energy density of 15 Wh·kg−1 at a power density of 110 W·kg−1. Hai et al.17 also prepared octahedral LiNi0.5Mn1.5O4 by the modified molten-salt method. The results showed that the (111)-faceted octahedral crystals delivered a better rate capability and had a much larger chemical diffusion coefficient than the (112)-faceted plates. © XXXX American Chemical Society

Received: Revised: Accepted: Published: A

September 20, 2016 December 18, 2016 December 21, 2016 December 21, 2016 DOI: 10.1021/acs.iecr.6b03657 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research ion batteries,28 LixNi1−xO usually appears as a secondary phase in the product LiNi0.5Mn1.5O4 cathode material, resulting in an unstable structure and degraded electrochemical properties.29,30 Therefore, it is expected that, for the industrial application of octahedral LiNi0.5Mn1.5O4 cathode materials, it will be necessary to prepare micrometer-sized particles with good granularity by a more cost-effective large-scale continuous production method. Co doping is an effective way to eliminate the LixNi1−xO impurity and provide a more stable spinel structure with enhanced disorder of the cations in the octahedral sites.31−33 It has also been reported that the amount of Co doping can significantly affect the electrochemical performance.31,32,34,35 Co-doped LiNixCoyMnzO4 cathode materials exhibit excellent electrochemical performances when the amount of Co doping is appropriate (y ≈ 0.1).31,34,35 However, the electrochemical performances of Co-doped LiNixCoyMnzO4 are not significantly different from those of LiNi0.5Mn1.5O4 when the amount of Co doping is reduce to a low degree (y ≤ 0.05).34,35 Therefore, in this study, spherical agglomerations of octahedral single-crystalline LiNi0.5Co4xMn1.5−3xO4 cathode materials (x = 0.02 and 0.03) with exposed planes were prepared by hydroxide coprecipitation in an 8-L continuous reaction device (Figure 1)

discharge hole as the feed solutions are continuously injected into the reactor. Compared to the solvothermal or sol−gel process, this continuous precipitation method has some advantages. First, the precipitation method, which can ensure the generation of micrometer-sized particles, has been widely used in synthesizing materials because of its simplicity in operation and availabiliy in industrial applications.38,39 Second, the addition of cobalt can stabilize the structure, eliminate the LixNi1−xO impurity phase, promote the formation of octahedral primary particles, and enhance the electrochemical performances of spinel LiNi0.5Mn1.5O4 cathode materials. Finally, the precursor precipitation, calcination, and postannealing processes are inexpensive and much easier to control than the solvothermal and sol−gel processes.

2. EXPERIMENTAL SECTION 2.1. Synthesis. Conventional spherical LiNi0.5Mn1.5O4 particles and spherical agglomerations of octahedral Codoped LiNi0.5Co4xMn1.5−3xO4 (x = 0.02, 0.03) cathode materials with micrometer-sized particles were prepared by the same facile and low-cost hydroxide coprecipitation method with the help of a homemade continuous reaction device. The spherical hydroxide precursors were first synthesized by a coprecipitation method in a continuous stirred tank reactor. The mother liquor of 1 M NH3·H2O solution was added to the reactor. Then, a 2 M mixed solution of NiSO4, MnSO4, and CoSO4 with the designed cationic ratio was fed into the continuous stirred tank reactor. At the same time, a 4 M mixed alkali solution of NaOH and a 15 wt % NH3·H2O solution were also pumped into the reactor. The reaction temperature was controlled at 60 °C. The pH value of reaction solution was kept at about 10.0−10.5. The whole reaction was conducted under the protection of a N2 atmosphere. The obtained precursors were washed with hot water and dried in a vacuum oven at 80 °C for 12 h. Finally, the obtained precursor particles were mixed with an excess of LiOH·H2O (>5%). The mixture was calcined first in a muffle furnace at 500 °C for 5 h and then in the air at 900 °C for 15 h. To improve the crystallinity and deeply remove any possible impurity phases, annealing experiments were carried out. The obtained materials after calcination at a temperature of 900 °C were annealed for 20 h at 600 °C. 2.2. Characterization and Electrochemical Measurements. The crystal structures of the prepared materials were measured by X-ray diffraction (XRD; Rigaku Ru-200, Cu Kα radiation, 40 kV, 100 mA, λ = 0.154056 nm) at a scan rate of 2°·min−1 in the range of 10−80°. The morphology of obtained materials was observed by scanning electronic microscopy (SEM, MERLIN) and transmission electron microscopy (TEM) (JEOL, JSM 2011). The specific surface area and pore volume were calculated by the Brunauer−Emmett−Teller (BET) method and the Barrett−Joyner−Halenda (BJH) method using a specific surface area and porosity analyzer (Quantachrome, NOVA 3200e). The compositions of the prepared cathode materials were analyzed by energy-dispersive X-ray (EDX) spectroscopy and inductively coupled plasma atomic emission spectrometry (ICP-AES; Varian, VISTAMAPX CCD). To examine the electrochemical performances of the obtained cathode materials, CR2032 coin-type cells were assembled. The cathode electrodes were prepared by uniformly mixing 80 wt % active material with 10 wt % acetylene black and 10 wt % polytetrafluoroethylene (PTFE). A lithium metal

Figure 1. Schematic diagrams of the continuous reaction device: (a) cutaway view of reaction device, (b) structural drawing of the reactor cover, (c) top view of the tank.

using a combinational postannealing method. The electrochemical performances of conventional spherical LiNi0.5Mn1.5O4 particles and spherical agglomerations of octahedral Co-doped LiNi0.5Co4xMn1.5−3xO4 cathode materials prepared by the same method were compared. As can be seen in Figure 1, the feed solutions were injected into the reaction device through a feeding hole. Because the spherical agglomeration process involves the interplay of events of particle-to-particle adhesion, apparently, the baffle could provide a higher frequency of collision,36 which, in turn, assisted nucleation contact between the solid and liquid phases, resulting in the generation of micrometer-scale spherical particles.37 The mature spherical particles can flow from the B

DOI: 10.1021/acs.iecr.6b03657 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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but much smaller than that of Ni2+ (0.69 Å),43 a variation of the lattice parameter can occur in LiNi0.5Co4xMn1.5−3xO4. SEM images of the prepared LiNi0.5Co4xMn1.5−3xO4 (x = 0, 0.02, and 0.03) cathode materials are shown in Figure 3. It can

sheet was used as the anode electrode. The electrolyte was composed of 1 M LiPF6 mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1:1. A Celgard 2400 polypropylene microporous membrane was performed as separator. The assembly of the cells was carried out in an argon-filled glovebox. Galvanostatic charge−discharge tests were measured in the voltage range from 3.5 to 4.95 V with a Land-CT2001A instrument. Electrochemical impedance spectroscopy (EIS) data were collected at an ac amplitude of 5 mV in the frequency range between 0.1 MHz and 0.01 Hz, and cyclic voltammetry (CV) curves were performed at scan rate of 0.1 mV·s−1 in the voltage range from 3.0 to 4.9 V on a PARSTAT2273 electrochemical workstation.

3. RESULTS AND DISCUSSION The XRD patterns of the prepared LiNi0.5Co4xMn1.5−3xO4 (x = 0, 0.02, and 0.03) cathode materials are shown in Figure 2. All

Figure 3. SEM images of LiNi0.5Co4xMn1.5−3xO4 for x = (a,b) 0, (c,d) 0.02, and (e,f) 0.03.

be seen that the pristine LiNi0.5Mn1.5O4 (Figure 3a,b) forms spherical agglomerations (7−9 μm). The particle sizes of the spherical agglomerations (3−6 μm) of Co-doped LiNi0.5Co4xMn1.5−3xO4 cathode materials (x = 0.02, Figure 3c,d; x = 0.03, Figure 3e,f) were smaller than hose of the pristine LiNi0.5Mn1.5O4, which can shorten the charge-transfer pathway.44,45 It can also be seen that the well-dispersed spherical agglomerations of Co-doped cathode materials were composed of regular octahedral primary particles. The clear boundaries existing on the surfaces of the primary particles (x = 0.02) mean that the Co-doped cathode materials formed with better crystal growth. To further investigate the crystallization of the obtained LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) cathode material, the TEM image, SAED pattern, and high-resolution transmission electron microscopy (HRTEM) image of LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) were obtained. The TEM image in Figure 4a shows a primary particle of LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) cathode material. Meanwhile, the selected-area electron diffraction (SAED) pattern is shown in Figure 4b. The clear regular diffraction spots in the SAED

Figure 2. X-ray diffraction patterns of LiNi0.5Co4xMn1.5−3xO4 for x = (a) 0, (b) 0.02, and (c) 0.03.

prepared pristine and Co-doped LiNi0.5Mn1.5O4 cathode materials belonging to typical diffraction patterns of a cubic spinel (Fd3m space group) are well-crystallized. Meanwhile, the XRD pattern of pristine LiNi0.5Mn1.5O4 at about 37° indicates an impurity phase of LixNi1−xO.40,41 In sharp contrast, no impurity phases are observed in the Co-doped samples. The lattice parameters (length of the crystal axis c in the cubic spinel of the Fd3m space group) of LiNi0.5Co4xMn1.5−3xO4 (x = 0, 0.02, and 0.03) cathode materials obtained by the refinement were a = 8.169, 8.173, and 8.182 Å (Table 1), whose values are similar to the reported results.42 Because the ionic radius of Co3+ (0.545 Å) is slightly larger than that of Mn4+ (0.53 Å)38,42 Table 1. Refined Lattice Parameters of the LiNi0.5Co4xMn1.5−3xO4 (x = 0, 0.02, and 0.03) Cathode Materials sample

lattice parameter (a) (Å)

x=0 x = 0.02 x = 0.03

8.169 8.173 8.182

Figure 4. (a) TEM image, (b) SAED pattern, and (c) HRTEM image of LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) cathode materials. C

DOI: 10.1021/acs.iecr.6b03657 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 5. EDX spectra of the prepared LiNi0.5Co4xMn1.5−3xO4 materials.

pattern indicate that the primary particles of octahedral LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) are single crystals. Figure 4c shows an HRTEM image of a typical truncated octahedral particle (from the selected area in Figure 4a). As can be seen in Figure 4c, clear lattice fringes appeared. The interplanar spacing of these lattice fringes was 0.475 nm indexed to the [111] plane of cubic spinel structure. These results show that the prepared LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) cathode material was wellcrystallized, which can result in better electrochemical performances. To confirm the successful incorporation of cobalt, the materials were analyzed by EDX spectroscopy and ICP-AES. Figure 5 shows the EDX spectra of the obtained cathode materials. It is apparent that the pristine LiNi0.5Mn1.5O4 cathodes materials were composed of Ni and Mn; no other chemical elements were detected. However, the presence of Co can be clearly seen in the Co-doped LiNi0.5Co4xMn1.5−3xO4 cathode materials (x = 0.02 and 0.03). The compositions of the prepared materials analyzed by ICP-AES are reported in Table 2, which shows that the compositions of the obtained samples were in good agreement with the required compositions. Table 2. Compositions of the Obtained LiNi0.5Co4xMn1.5−3xO4 Materials Ni/Co/Mn atomic ratio sample

ICP-AES analysis

required value

x=0 x = 0.02 x = 0.03

0.5:0:1.52 0.49:0.08:1.50 0.47:0.12:1.46

0.5:0:1.5 0.5:0.08:1.44 0.5:0.12:1.41

Figure 6. (a) N2 adsorption isotherms of the prepared cathode materials and (b) corresponding BJH pore-size distributions.

Because surface properties are among the most important factors affecting the electrochemical performances of materials, the specific surface areas and pore size distributions of the prepared cathode materials were analyzed by the Brunauer− Emmett−Teller (BET) method and the Barrett−Joyner− Halenda (BJH) method, respectively (Figure 6). As can be seen in Figure 6a, the specific surface areas of LiNi0.5Co4xMn1.5−3xO4 (x = 0, 0.02, and 0.03) cathode materials were 2.09, 4.31, and 5.35 m2·g−1, respectively. This indicates that larger specific surface areas could be obtained with more exposed planes on the surface of the crystals through doping with cobalt. Meanwhile, as determined by the Barrett−Joyner− Halenda (BJH) method (Figure 6b), the average pore sizes of the prepared LiNi0.5Co4xMn1.5−3xO4 (x = 0, 0.02, and 0.03) cathode materials were 1.91, 2.73, and 3.15 nm, respectively. The larger specific surface areas and better pore properties of the prepared LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) cathode

materials are beneficial for making contact with electrolytes, forming solid electrolyte interphase (SEI) films, and supporting material contact with the electrolyte and Li+ diffusion, resulting in excellent electrochemical performances.46 The initial charge−discharge curves of the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials are shown in Figure 7. The charge and discharge tests were carried out at 0.1C in the voltage range from 3.5 to 4.95 V at 25 °C. It can be seen that the obtained LiNi0.5Co4xMn1.5−3xO4 cathode materials with different contents of Co had similar voltage profiles at about 4.7 V because of the Ni2+/Ni4+ redox couple.47 The Co-doped LiNi0.5Mn1.5O4 cathode materials exhibited a smaller plateau about at 4.0 V, which can be attributed to the Mn3+/Mn4+ redox couple.42,48 The redox peak in the 4 V region can be seen more clearly in the cyclic voltammetry (CV) curves of the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials in the D

DOI: 10.1021/acs.iecr.6b03657 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 9. Rate performances of the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials in the voltage range from 3.5 to 4.95 V at 25 °C.

Figure 7. Initial charge−discharge curves of LiNi0.5Co4xMn1.5−3xO4 cathode materials at 0.1C in the voltage range from 3.5 to 4.95 V at 25 °C for x = (a) 0, (b) 0.02, and (c) 0.03.

after 50 cycles, the discharge capacities returned to the initial levels for all samples. Hence, the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials also illustrate advanced capacity retention. Figure 10 shows the cycling performances of the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials cycled between 3.5

voltage range from 3.5 to 4.95 V (Figure 8). The redox peaks in the range of approximately 4.0 V increased with increasing Co

Figure 8. Cyclic voltammetry (CV) curves of the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials in the voltage range from 3.5 to 4.95 V at 25 °C. Figure 10. Cycle performances of the prepared LiNi0.5Mn1.5O4 cathode materials at 1C in the voltage range from 3.5 to 4.95 V at 25 °C.

content. of the trivalent Co element was located in the sites of tetravalent Mn, oxygen deficiencies occur easily upon Co introduction, which should result in an increase in the Mn3+ content to compensate for the increase in oxygen deficiencies.34,42 The discharge curves at various rates of the obtained LiNi0.5Co4xMn1.5−3xO4 cathode materials are presented in Figure 9. The cathode materials were discharged at 0.1C, 0.5C, 1C, and 2C in the voltage range from 3.5 to 4.95 V at 25 °C. As shown in Figure 9, the discharge capacities of the obtained LiNi0.5Co4xMn1.5−3xO4 cathode materials decreased with increasing discharge current rate. The discharge capacity of the LiNi0.5Co4xMn1.5−3xO4 (x = 0.02) cathode material was about 110 mAh·g−1 at a high current density (2C) after 40 cycles, which is about 84.5% of its capacity at 0.1C, whereas samples of LiNi0.5Co4xMn1.5−3xO4 (x = 0 and 0.03) delivered 103 and 102 mAh·g−1, respectively, at the rate of 2C, which are only about 79.2% and 78.9%, respectively, of their discharge capacities at 0.1C. When the rate was changed back to 0.1C

and 4.95 V at a rate of 1C and a temperature of 25 °C. As can be seen in Figure 10, the discharge capacities of the LiNi0.5Co4xMn1.5−3xO4 cathode materials (x = 0, 0.02, and 0.03) remained at 90.5, 106.7, and 103 mAh·g−1, respectively, after 100 cycles. The capacity retention of the Co-doped materials was higher than that of pristine LiNi0.5Mn1.5O4, and the highest capacity retention (92.8% of the initial capacity) of the LiNi0.5Co4xMn1.5−3xO4 cathode materials after 100 cycles at 1C was obtained for x = 0.02. Figure 11 shows the electrochemical impedance spectroscopy (EIS) of the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials after 100 cycles at 1C. It can be seen that pristine cycled LiNi0.5Mn1.5O4 exhibited a semicircle at high frequency and a straight sloping line at low frequency, whereas the plots of Codoped cathode materials are composed of two semicircles and a E

DOI: 10.1021/acs.iecr.6b03657 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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4. CONCLUSIONS Spherical agglomerations of LiNi0.5Co4xMn1.5−3xO4 cathode materials with micrometer-sized particles (3−6 μm) were successfully prepared by a facile and low-cost hydroxide coprecipitation method with the help of a homemade continuous reaction device. The XRD results showed that the prepared samples belong to the Fd3m space group and that cobalt doping can completely eliminate the LixNi1−xO impurity phase. Compared to the conventional spherical LiNi0.5Mn1.5O4 particles prepared by the same method, the Co-doped LiNi0.5Co4xMn1.5−3xO4 cathode materials (x = 0.02) with larger specific surface areas and pore volumes were better crystallized, resulting in an impressive rate capability (99.9% of the initial discharge capacity when the rate is restored to 0.1C after 50 cycles at different rates such as 0.1C, 0.5C, 1C, 2C, and 0.1C) and excellent capacity retention (92.8% of the initial discharge capacity after 100 cycles at 1C). In addition, the Co-doped LiNi0.5Co4xMn1.5−3xO4 cathode materials (x = 0.02 and 0.03) prepared by this method exhibited regular spherical agglomerations composed of octahedral primary particles, rendering manipulation in the subsequent battery preparation process easy and enhancing the durability in long-term charge− discharge processes. Basically, the octahedral Co-doped LiNi0.5Co4xMn1.5−3xO4 spherical agglomerates prepared by this facile and low-cost method can significantly improve the electrochemical performances of spinel LiNi0.5Mn1.5O4 cathode materials and have great potential industrial applications for 5 V lithium-ion batteries.

Figure 11. Electrochemical impedance spectra of the prepared LiNi0.5Co4xMn1.5−3xO4 cathode materials after 100 cycles at 1C.

low-frequency slopping line. It has been reported that the semicircle at high frequency corresponds to the transport of Li+ ions through the SEI film.49,50 The midfrequency semicircle reflects the charge-transfer resistance at the electrode/electrolyte interface.49 The straight line at low frequency is caused by solid-phase diffusion in the electrode materials.51 The resistance values of Co-doped cathode materials are lower than that of pristine LiNi0.5Mn1.5O4 after 100 cycles at 1C. Meanwhile, the appearance of the two more distinct semicircles in the plot of Co-doped cathode material for x = 0.02 indicates the formation of a stable SEI film. The SEI film formed by full contact between the exposed planes and the electrolyte might enhance the cyclability of cathode materials dramatically. Remarkably, Figure 12 shows an SEM image of the LiNi0.5Co4xMn1.5−3xO4 cathode material (x = 0.02) after 100 cycles at 1C. It can be seen from Figure 12 that the cathode material maintained an octahedral shape, which displays attractive morphological stability. Therefore, the improved electrochemical performance can be attributed to the Co doping and special morphology as follows: (1) Co doping can eliminate the adverse effects of the impurity phase. (2) The more exposed octahedral planes promote contact between the doped materials and the electrolyte, as well as formation of a stable SEI film. (3) Stability of the morphological is a benefit to the cyclability of cathode materials.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-10-62773585. Fax: +86-10-62773585. E-mail: [email protected]. ORCID

Shengming Xu: 0000-0002-6765-9251 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Commission-Yunnan joint fund project of China (No. U1402274), funding from the State Key Laboratory of Advanced Technologies for Comprehensive Utilization of Platinum Metals (No. SKL-SPM-201211), and the Program for Changjiang Scholars and Innovative Research Team in University of China (IRT13026).

Figure 12. SEM image of the LiNi0.5Co4xMn1.5−3xO4 cathode material (x = 0.02) after 100 cycles at 1C. F

DOI: 10.1021/acs.iecr.6b03657 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.iecr.6b03657 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX