Octahedral and Porous Spherical Ordered LiNi0.5Mn1.5O4 Spinel: the

Research Article www.acsami.org

Cite This: ACS Appl. Mater. Interfaces 2018, 10, 31795−31803

Octahedral and Porous Spherical Ordered LiNi0.5Mn1.5O4 Spinel: the Role of Morphology on Phase Transition Behavior and Electrode/ Electrolyte Interfacial Properties Ying Luo,†,‡ Yixiao Zhang,†,‡ Liqin Yan,†,‡ Jingying Xie,*,‡,§ and Taolin Lv†,‡ †

Shanghai Power & Energy Storage Battery System Engineering Tech. Co. Ltd., Shanghai 200241, China Shanghai Engineering Center for Power and Energy Storage Systems, Shanghai 200245, China § Shanghai Institute of Space Power Sources, Shanghai 200245, China Downloaded via KAOHSIUNG MEDICAL UNIV on October 14, 2018 at 05:57:28 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: LiNi0.5Mn1.5O4 compound as positive electrode of the lithium ion battery with high specific energy or high specific power, has a good application prospect in the field of electric vehicles such as PHEV/EVs. The influence of the morphology of ordered LiNi0.5Mn1.5O4 on phase transition behavior and electrode/electrolyte interfacial properties is investigated, including octahedral and porous spherical morphologies. Three phases named LiNi 0.5 Mn 1.5 O 4 (Li1), Li0.5Ni0.5Mn1.5O4 (Li0.5) and Ni0.5Mn1.5O4 (Li0) are detected by in situ X-ray diffraction (XRD) measurement with high time resolution in the octahedral and porous spherical ordered LiNi0.5Mn1.5O4 materials during charge and discharge, and the phase transition kinetics of the two samples at high discharge rate and after charge−discharge cycles are elucidated. It is a clear demonstration that the high-rate capability and cycle life of LiNi0.5Mn1.5O4 material are influenced by crystal morphology. The porous spherical LiNi0.5Mn1.5O4 material exhibits better rate performance, associated with the fast reaction kinetic of Li0.5 phase formation. It is noticed that the coexistence of three cubic phases in the initial discharge stage is observed in the cycled octahedral sample, resulting in a higher capacity fading after 200 cycles at room temperature and 1 C. However, the porous spherical sample exhibits a poor cyclic performance at 55 °C and 1 C. This may be attributed to the fact that the porous spherical sample with high specific surface area leads to an accelerated decomposition of the electrolyte at 55 °C, and the thick interfacial film and high content of LiF on the electrode surface are formed. KEYWORDS: lithium ion battery, LiNi0.5Mn1.5O4 cathodes, morphology, phase transition behavior, electrode/electrolyte interface density and better antiabuse capacity.14−16 Recently, much attention is paid to the research of ordered LiNi0.5Mn1.5O4 cathode. It is reported that three cubic phases named LiNi 0.5 Mn 1.5 O 4 (Li1), Li 0.5 Ni 0.5 Mn 1.5 O 4 (Li0.5) and Ni0.5Mn1.5O4 (Li0) are existence during charge and discharge in the ordered LiNi0.5Mn1.5O4.17,18 Thus, it occurs in two coexistence regions of two-phase in the ordered structure, which involves a lower-voltage platform at around 4.70 V assignable to the coexistence of Li1 and Li0.5, and a highervoltage platform at around 4.74 V assignable to the coexistence of Li0.5 and Li0. In fact, it is noteworthy that the relatively poor rate capability of battery would be speculated, as a result of the occurrence of two-phase transformation in the small voltage range.19 However, understanding the kinetics of phase

1. INTRODUCTION Recently, high voltage cathode materials for lithium-ion batteries have been developed to meet the demand for high specific energy batteries in the field of new energy vehicles. Spinel LiNi0.5Mn1.5O4 is the best candidate among a large number of high voltage cathode materials due to its good rate capability and cyclability.1−4 It is generally known that LiNi0.5Mn1.5O4 cathode has a theoretical specific capacity of 147 mAh g−1 and exhibits a high voltage discharge curves at around 4.7 V. Generally, two kinds of space group structures are found in the LiNi0.5Mn1.5O4 cathodes, such as the ordered P4332 space group and the disordered Fd3̅m space group, according to the amount of oxygen deficiency or the location of Ni atoms.5−9 Most of the research teams have reported that the disordered structure shows a better rate performance and cycle stability because of its higher electronic conductivity and lithium-ion diffusion coefficient, compared with the ordered one.10−13 Nevertheless, the ordered structure still has potential applications for electric vehicles owing to its higher energy © 2018 American Chemical Society

Received: July 5, 2018 Accepted: August 14, 2018 Published: August 14, 2018 31795

DOI: 10.1021/acsami.8b11187 ACS Appl. Mater. Interfaces 2018, 10, 31795−31803

Research Article

ACS Applied Materials & Interfaces

Figure 1. SEM (a, c) and HR-TEM (b, d) images of the octahedral (a, b) and porous spherical (c, d) LiNi0.5Mn1.5O4 cathodes.

a promising way to improve the rate capability and volumetric energy density of LiNi0.5Mn1.5O4 cathode. In this paper, we present the influence of the morphology of ordered LiNi0.5Mn1.5O4 obtained by controlled synthesis processes on phase transition behavior and electrode/electrolyte interfacial properties, including octahedral and porous spherical morphologies. For the first time, the nonequilibrium structure change behaviors of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes are evaluated using in situ timeresolved X-ray diffraction method. The XRD patterns with time are used for analyzing the phase transitions of LiNi0.5Mn1.5O4 at high discharge rate and after charge− discharge cycles.

transitions only through electrochemical reactions is very difficult. Some investigator has indicated that the capacity fading of LiNi0.5Mn1.5O4 cathode has been attributed to the side reactions on the cathode-electrolyte interface at high voltage and forming a cathode-electrolyte interface (CEI) layer.20−24 Moreover, particle morphology is also thought to affect the electrochemical performance of LiNi0.5Mn1.5O4 cathode.25−28 It is helpful to inhibit the side reactions on the electrode/ electrolyte interface and to improve the interfacial stability through controlling the specific morphology of LiNi0.5Mn1.5O4 cathode. In previous researches, the lowest surface energy and the best stability were found in the (111) crystal plane of LiNi0.5Mn1.5O4, compared with the (100) and (110) crystal planes.29−33 Manthiram et al. reported that octahedron-shaped LiNi0.5Mn1.5O4 showed a better electrochemical performance, due to the formation of the stable CEI on the (111) plane.34 Chen et al. contrasted the chemical diffusion coefficients of the octahedron-shaped particles with (111) crystal planes and the plate-shaped particles with (112) crystal planes.35 The calculation indicated that (111) crystal plane had a higher Li ion diffusion coefficient, which was in accordance with the octahedron-shaped sample with the better electrochemical property. Furthermore, particle size is one key factor which influences the rate performance of LiNi0.5Mn1.5O4.36−38 Generally, the small particle size would lead to a short lithium ion diffusion distance, resulting in an excellent rate capability. However, the use of nanoparticle has some disadvantages. For example, the nanoparticles with large surface area would accelerate the decomposition of electrolyte on the electrode/electrolyte interface, especially operating at high voltage. Amarilla et al. reported that the spinel material with ϕ > 500 nm showed a better cyclic performance at room temperature or at elevated temperature (55 °C), compared with that with ϕ < 500 nm.39 Meanwhile, nanoscaled LiNi0.5Mn1.5O4 cathode with low tap density leads to a low volumetric energy density, which hinders its industrial application on electric vehicles.40 Thus, nanosized particles are aggregated to form a micrometer particle, which is

2. EXPERIMENTAL SECTION 2.1. Materials Synthesis. The hydroxides and carbonates of Mn and Ni were prepared by a coprecipitation method, respectively, as the precursors for the octahedral and porous spherical LiNi0.5Mn1.5O4 samples. In a typical process, stoichiometric amounts of NiSO4·6H2O and MnSO4·H2O were dissolved in distilled water to obtain an aqueous solution (2 mol L−1, 0.5 L), and then pumped into a continuously stirred tank reactor. Next, NaOH (2 mol L−1, 1 L) or Na2CO3 (2 mol L−1, 0.5 L) as a precipitation agent and ammonium hydroxide as a complexing agent was mixed to form a homogeneous solution, and then pumped into the reactor with pH controlled at 11 and 8.5 under continuous stirring, respectively. The resulting precursors were dried overnight in air at 120 °C, and ground with a stoichiometric amount of Li2CO3. Then the obtained mixtures were sintered under oxygen atmosphere at 400 °C for 6 h and then at 900 °C for 20 h. Finally, the ordered samples with the octahedral and porous spherical morphologies were obtained through annealed again at 700 °C for 15 h. 2.2. Characterization methods. The phase transition behaviors of the above-mentioned samples were studied in a pouch-type cell, as shown in Supporting Information (SI) Figure S1. First, the cathode materials (80 wt %), conductive carbon black (super P) (10 wt %) and polyvinylidene fluoride (PVDF) (10 wt %) were mixed in the Nmethyl-2-pyrrolidone (NMP) solvent to obtain the cathode slurry. And then the electrodes were prepared by drying at 80 °C for 24 h under vacuum after casting the slurry on the carbon-coated Al foil. The composite electrode loading was 3 mg·cm−2. Finally, the pouchtype cell with a size of 2 × 3 cm2 was fabricated with a LiNi0.5Mn1.5O4 31796


Research Article


Figure 2. In-situ XRD patterns (a, c) and charge curves (b, d) of the fresh octahedral (a, b) and porous spherical (c, d) LiNi0.5Mn1.5O4 electrodes in the pouch-type cells during charge at 1 C.

regular micron-sized particles with a size of ∼3 μm and a small number of small irregular particles. In contrast, the micronsized porous spherical sample is formed by agglomeration of nanoscale polyhedron of ∼100 nm in size, as seen in Figure 1c. The morphologies and particle sizes of the two samples are affected by the microstructures of the precursors. As displayed in SI Figure S2, the morphologies of the hydroxide precursor and carbonate precursor for the octahedral and porous spherical samples are characterized by SEM. This result illustrates the significant differences in the morphology and particle size for two precursors. The loose small irregular agglomerations are presented in the hydroxide precursor, while the carbonate precursor is composed of dense large spheres. Upon heating at 900 °C, it is convenient to transform into the micron-sized regular octahedral morphology from loose small irregular agglomerations for the hydroxide precursor. Nevertheless, the formation of the small irregular particles is unavoidable due to the different growth kinetics of the loose agglomeration. Figure 1b and d shows the HR-TEM images of the samples. It was reported from the literature that the major (111) crystal planes on the surface facets can be observed in the octahedron.34 This result reveals that the octahedral sample has an interplanar spacing of 4.73 Å, which indicates it is comprised of (111) crystal planes on the surface, as seen in Figure 1b. Examination of the porous spherical sample demonstrates that the sample consists of (111) crystal planes, as shown in Figure 1d. However, there should be other various crystal planes on the surface of the porous spherical sample

cathode, a metallic lithium foil anode and a celgard separator. One M LiPF6 in ethylene carbonate and ethylmethyl carbonate (EC: EMC, 3:7 v %) solution was used as the electrolyte. The cyclic performance at room temperature and rate capability of the pouch-type cell were tested at 3.5−4.9 V (vs Li+/Li) on a battery test instrument (LAND CT 2001A, Land). The phase transition behaviors of the pouch-type cell discharged at different rate and charged or discharged before and after cycled at room temperature and 1 C were discussed through the results of in situ time-resolved X-ray diffraction measurement, using the BL14B1 beamline at Shanghai Synchrotron Radiation Facility with a λ of 0.6884 Å, China. To study the phase transition in real time, an image plate detector was used to collect the XRD data which can be detected continuously in 8 s with the interval of 2 s in transmission mode.41 Rietveld refinements of XRD data were carried out using the X’pert HighScore Plus software. The cyclic performances at 55 °C and 1 C of the octahedral and porous spherical LiNi0.5Mn1.5O4 samples were tested using CR 2032 coin cell. Its compositions were the same as that of pouch-type cell. The LiNi0.5Mn1.5O4 electrodes after 200 cycles in the coin cells at 55 °C and 1 C were collected in an argon-filled glovebox. To analyze the morphology and composition of the surface films on the cycled LiNi0.5Mn1.5O4 electrodes, the scanning electron microscopy (SEM, HITACHI S-4800), high resolution transmission electron microscopy (HR-TEM, JEOL JEM-2100F) and X-ray photoelectron spectroscopy (XPS, ESCALAB 250 Xi) were carried out, after cleaning the cycled electrodes with pure dimethyl carbonate (DMC).

3. RESULTS AND DISCUSSION The morphologies of the octahedral and porous spherical LiNi0.5Mn1.5O4 cathodes were examined by SEM. As seen in Figure 1a, the octahedral sample consists of a large number of 31797


Research Article


Figure 3. Evolution of lattice parameters with lithium content during charge (a, b) and discharge (c, d) of the octahedral (a, c) and porous spherical (b, d) LiNi0.5Mn1.5O4 electrodes in the pouch-type cells at 1 C.

phase (Li0) starts to grow at the expense of the second cubic phase (Li0.5). Two successive two-phase reactions are identified during charge for two samples, corresponding to the oxidation of Ni2+/Ni3+ and Ni3+/Ni4+, respectively. It is found to be reversible during discharge, as shown in SI Figure S4. As reported from the literature, the less ordered phase is, the lower initial capacity is.46 Thus, due to its lower ordering degree, a slight lower initial charge−discharge capacity of the porous spherical sample is observed. To adjust the oxidation states of Ni ion and Mn ion, X-ray absorption nearedge structure (XANES) of the Ni and Mn K-edges for the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes at pristine state and charged state (4.9 V) are shown in SI Figure S5. This result indicates that the oxidation state of Ni changes from Ni (II) to Ni (IV) while the oxidation state of Mn has no obvious change during charge. Furthermore, compared with the octahedral sample, the K-edge energy of the porous spherical sample at charged state (4.9 V) is slightly lower, suggesting that the Ni average valence of the charged porous spherical sample is lower, and it agrees well with the sequence of the charge capacity. The lattice parameters for different phases during charge and discharge are determined by fitting and plotted against Li+ deintercalation depth, as shown in Figure 3. The phase fraction changes during charge and discharge at 1 C can be seen in SI Figure S6. It is gradually decreasing in lattice parameter of each phase during charge. Obviously, the expected increasing in lattice parameter of each phase is observed during discharge. The estimated cubic lattice parameters in the octahedral sample are 8.1717, 8.0942, and 8.0124 Å, respectively, while they are slightly larger in the porous spherical sample, which are correspond to 8.1743, 8.0961, and 8.0139 Å. It is worth noting that the second cubic phase is not clearly detected at

because the primary particle is comprised of nanoscale polyhedron. From the results of Raman spectra, as shown in SI Figure S3, some bands at 218 and 240 cm−1 are detected and the bands at 608 and 591 cm−1 from the splited acromion associated with the symmetric Mn4+-O stretching vibration F2g(1) are observed, suggesting that the space groups of the octahedral and porous spherical LiNi0.5Mn1.5O4 are in accordance with an ordered P4332 structure. Furthermore, it can be noticed that the peak intensity of the porous spherical sample is general decrease. As reported from Y. J. Wei, the higher the electronic conductivity of material is, the shallower the optical skin depth of the incident laser beam is, and the lower the peak intensity of Raman spectra is.42 This means that there are some trace disordered Fd3m structure with high electronic conductivity in the porous spherical sample, except for a large number of ordered P43 32 structure. Nonetheless, the content of disordered structure is so low that there is no obvious change in the vibration modes of Raman spectra. In fact, some groups have reported the case of a combination of two space group structure (ordered and disordered).43−45 Figure 2 shows the in situ XRD patterns and charge curves of the fresh octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the pouch-type cells measured during charge at 1 C. It can be clearly seen the significant shifts in the (311), (331), (511), and (531) diffraction peaks, when the cell is charged. Three cubic spinel phases of Li1, Li0.5, and Li0 are sequentially formed in the octahedral and porous spherical LiNi0.5Mn1.5O4 cathodes, which are consistent with the literature.17 A second cubic phase (Li0.5) appears rapidly after charge and grows at the expense of the first cubic phase (Li1) through a biphasic transition for two samples. Then, the first cubic phase disappears and instead we see the third cubic 31798


Research Article


Figure 4. Rate performances (a, b) and in situ XRD patterns (c, d) during discharge at 8 C of the octahedral (a, c) and porous spherical (b, d) LiNi0.5Mn1.5O4 electrodes in the pouch-type cells.

4c and d show the in situ XRD patterns of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the pouch-type cells during discharge at 8 C. Obviously, the XRD peaks intensities of the two samples are similarly decreased. It is of much interest that the XRD peaks indicated Li0.5 phase is not significantly observed and it seems that there is only one twophase reaction from Li0 phase to Li1 phase in the octahedral sample during discharge at 8 C, which is different from the behavior during discharge at 1 C. It thus implies that the slow crystal growth from Li0 phase to Li0.5 phase leads to the transformation of Li0.5 phase to Li1 phase before the component content of the Li0.5 phase reaches the detection limit of XRD during discharge at 8 C. However, all three cubic phases through two-phase reactions are clearly observed in the porous spherical sample during discharge at 8 C, suggesting that the reaction kinetics of Li0.5 phase is fast. Additionally, the in situ XRD patterns at 3 and 5 C are represented in SI Figure S7 and Figure S8. At 3 C, though all three cubic phases are detected in two samples, the intensities of XRD peaks associated with the Li0.5 phase in the octahedral sample are remarkable lower than that in the porous spherical sample. Even at 5 C, they have not been detected obviously in the octahedral sample. As reported from Li Hong,49 the formation of the Li0.5 phase as a buffer is favor to process the large cell parameter difference between Li0 phase and Li1 phase during charge and discharge. Thus, the rate performance can be improved when the reaction kinetics of the Li0.5 phase formation is fast, which may be one reason for the better rate performance of the porous spherical sample. Furthermore, the Li+ diffusion coefficients (DLi) of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the pouch-type cells were calculated through a series of CV curves under different scan rate. The k values represent the slope of the peak current (ip) versus the square root of the scan

the beginning of charge, although the two-phase reaction has been started. This is because the newly formed phase can only be detected when the component content reaches the detection limit of XRD and the component is crystalline phase with structurally ordered domains. Remarkably, the appearance of Li0.5 phase in the porous sample during the initial stage of charge and discharge is slightly later than that in the octahedral sample. It can be explained by its lower ordering degree and smaller primary nanoscale particle, leading to a small solid solution-type reaction first, followed by a two-phase reaction in this sample.47,48 In addition, during discharge the Li0.5 phase disappears completely at around x = 0.81 in the octahedral sample, while the Li0 phase disappears at around x = 0.59 and the Li1 phase appears at around x = 0.71. Thus, a wide coexistence region of the Li0.5 and Li0 phases is observed, as seen in SI Figure S6. Comparing with the octahedral sample, both the Li0.5 phase (at around x = 0.64) and the Li0 phase (at around x = 0.40) disappear early in the porous spherical sample, as well as the appearance of the Li1 phase (at around x = 0.51). It is an evidence to indicate that the porous spherical sample exhibits the fast crystal growths from Li0 phase to Li0.5 phase and Li0.5 phase to Li1 phase, corresponding to the fast reaction kinetics of phase transition. The high rate capability of LiNi0.5Mn1.5O4 is scientifically interesting and practically important, considering its stable three-dimensional lithium ion channel. The rate performances of the octahedral and porous spherical LiNi 0.5 Mn 1.5 O 4 electrodes in the pouch-type cells are illustrated in Figure 4a and b. Higher discharge capacity and higher discharge voltage platform are observed at high rate in the porous spherical sample. Furthermore, the phase transition behaviors of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes are examined through the shifts of XRD peaks and two-phase coexistence region during discharge under various rates. Figure 31799


Research Article

ACS Applied Materials & Interfaces rate (v1/2), as plotted in SI Figure S9. According to the Randles-Sevcik equation,50 the diffusion coefficients of the two samples are calculated and listed in SI Table S1. This result reveals that the porous spherical sample presents much larger diffusion coefficient. It indicates the faster lithium ion intercalation kinetics in the porous spherical sample, which is also benefited to improve its high rate performance. The cyclic performances at room temperature of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the pouch-type cells are investigated, as shown in SI Figure S10. Although the porous spherical sample exhibits a low discharge capacity at 1 C, the capacity retention is increased to 94% after 200 cycles, implying the improved cyclic performance. To further understand the phase transitions of the cycled octahedral and porous spherical samples, in situ XRD patterns of the cycled samples during discharge at 1 C are illustrated in Figure 5. After cycled, two impurity peaks associated with

cycled octahedral sample, which increase the battery polarization, resulting in a lower discharge capacity. The EIS spectra of the cycled octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the pouch cells and the fitting results are shown in SI Figure S11 and Table S2. A slight higher RSEI resistance of the cycled octahedral sample is observed. Figure 6 shows the cyclic performance and discharge curves of the octahedral and porous spherical LiNi0.5 Mn1.5 O 4

Figure 6. Cyclic performance (a) and discharge curves (b) of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the coin cells at 55 °C and 1 C.

electrodes in the coin cells at 55 °C and 1 C. After cycled, both the discharge capacity and voltage platform are significantly decayed, especially that of the porous spherical sample, suggesting a great polarization is formed during cycled at 55 °C and 1 C. To investigate the influence of morphology on electrode/electrolyte interfacial chemistry, the SEM and TEM images of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the coin cells after 200 cycles at 55 °C and 1 C are shown in Figure 7. Both of the electrodes are covered with surface layers after 200 cycles, which can be ascribed to the decomposition of electrolyte. Meanwhile, it is important to note that there are a large number of nanosized particles and a surface film of about 10 nm thick on the octahedral electrode surface, while a paste-like and rough surface film of above 20 nm is observed on the porous spherical electrode surface. Moreover, a high RSEI resistance of the porous spherical sample is indicated through the result of EIS (seen in SI Figure S12 and Table S3), leading to a large electrochemical polarization. The components of the electrode/electrolyte interfacial layers of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes in the coin cells after 200 cycles at 55 °C and 1 C were discussed by XPS analysis, as shown in Figure 8. Although the similar component species of the two samples are observed, their component contents are significant different.

Figure 5. In-situ XRD patterns of the cycled octahedral (a) and porous spherical (b) LiNi0.5Mn1.5O4 electrodes in the pouch-type cells during discharge at room temperature and 1 C.

NiMn2O4 spinel at 16° and 22.5° can be observed in two samples. The phase fractions of NiMn2O4 spinels in the cycled octahedral and porous spherical samples are 15.3% and 6.9% by refining the XRD patterns, respectively. It suggests that the partly active material shows an irreversible lithium intercalation and deintercalation reaction during charge and discharge, thus forming a nonelectrically active phase and leading to a capacity fading. Three cubic phases present at the same time during discharge in two samples, indicating that the kinetics of phase transition is decreased after cycled. However, three cubic phases obviously coexist in the early stage of discharge in the 31800


Research Article


Figure 7. SEM (a, c) and TEM (b, d) images of the octahedral (a, b) and porous spherical (c, d) LiNi0.5Mn1.5O4 electrodes in the coin cells after 200 cycles at 55 °C and 1 C.

Figure 8. XPS patterns of the octahedral (a) and porous spherical (b) LiNi0.5Mn1.5O4 electrodes in the coin cells after 200 cycles at 55 °C and 1 C.

in SI Figure S13. However, the decomposition of the electrolyte in the LiNi0.5Mn1.5O4 cell is increased significantly at the elevated temperature, leading to the weak interfacial stability of electrode/electrolyte and forming the thick and high-impedance surface film, which becomes the main reason for the performance degradation of LiNi0.5Mn1.5O4 cell at the elevated temperature. Moreover, by comparing the specific surface area of the octahedral and porous spherical samples, a higher specific surface area in the porous spherical sample is observed, as seen in SI Table S4. Thus, all the results suggest that the decomposition of the electrolyte can be accelerated due to the enlarged contact area between the cathode and electrolyte, which may explain why a poor cyclic performance at 55 °C and 1 C of the porous spherical sample can be obtained.

Especially, a higher relative atomic ratio of LiF in the porous spherical sample suggests that a large number of LiPF6 are decomposed and deposited on the electrode surface, leading to a significant increase in the impedance of the sample. Furthermore, a thicker interfacial film on the porous spherical sample can be indicated by the lower relative atomic ratio of metal oxide in the O 1s spectrum. The interfacial stability of electrode/electrolyte is the important factor to influence the electrochemical performance of LiNi0.5Mn1.5O4, except for its structure and morphology. The decomposition of the electrolyte is related to the working temperature. Only a small number of decomposition products are precipitated on the surface of the cycled electrode at room temperature, suggesting a low decomposition of electrolyte, indicated from the SEM image of the cycled octahedral LiNi0.5Mn1.5O4 electrode at room temperature, as represented 31801


Research Article


4. CONCLUSIONS LiNi0.5Mn1.5O4 materials with octahedral and porous spherical morphology were synthesized by using hydroxide or carbonate as precursor. The in situ XRD analysis clearly indicates that both of the octahedral and porous spherical LiNi0.5Mn1.5O4 electrodes exhibit two two-phase coexistence regions under charge and discharge at 1 C, including the two-phase region of Li1 and Li0.5 in the lower voltage platform and that of Li0.5 and Li0 in the upper voltage platform. The fast reaction kinetic of Li0.5 phase in the porous spherical sample is demonstrated, leading to the improved rate performance. It is found that the impurity spinel NiMn2O4 phase is formed in the cycled octahedral and porous spherical samples at room temperature. Meanwhile, the kinetics of phase transition is decreased, resulting in the coexistence of three cubic phases during discharge. The elevated temperature cyclic performance is greatly influenced by the morphology. The porous spherical sample with high specific surface area is believed to accelerate the decomposition of the electrolyte and form a thick and highimpedance interfacial film on the electrode surface, exhibiting a poor cyclic performance at 55 °C and 1 C, compared with the octahedral sample. Thus, it is necessary to optimize the morphology of LiNi0.5Mn1.5O4 material and its operating conditions to obtain desirable performances.

■

at the beamlines BL14B1 and BL14W1 were supported by Shanghai Synchrotron Radiation Facility. We thank staff working at the beamline for their help during experiments.

■

(1) Julien, C. M.; Mauger, A. Review of 5-V Electrodes for Li-Ion Batteries: Status and Trends. Ionics 2013, 19, 951−988. (2) Hu, M.; Pang, X.; Zhou, Z. Recent Progress in High-Voltage Lithium Ion Batteries. J. Power Sources 2013, 237, 229−242. (3) Kim, J. H.; Pieczonka, N. P.; Yang, L. Challenges and Approaches for High-Voltage Spinel Lithium-Ion Batteries. ChemPhysChem 2014, 15, 1940−1954. (4) Santhanam, R.; Rambabu, B. Research Progress in High Voltage Spinel LiNi0.5Mn1.5O4 Material. J. Power Sources 2010, 195, 5442− 5451. (5) Zheng, J.; Xiao, J.; Yu, X.; Kovarik, L.; Gu, M.; Omenya, F.; Chen, X.; Yang, X. Q.; Liu, J.; Graff, G. L.; Whittingham, M. S.; Zhang, J. G. Enhanced Li+ Ion Transport in LiNi0.5Mn1.5O4 through Control of Site Disorder. Phys. Chem. Chem. Phys. 2012, 14, 13515− 13521. (6) Kim, J. H.; Myung, S. T.; Yoon, C. S.; Kang, S. G.; Sun, Y. K. Comparative Study of LiNi0.5Mn1.5O4‑δ and LiNi0.5Mn1.5O4 Cathodes Having Two Crystallographic Structures: Fd3m and P4332. Chem. Mater. 2004, 16, 906−914. (7) Kuppan, S.; Xu, Y.; Liu, Y.; Chen, G. Phase Transformation Mechanism in Lithium Manganese Nickel Oxide Revealed by SingleCrystal Hard X-Ray Microscopy. Nat. Commun. 2017, 8, 14309− 14318. (8) Samarasingha, P. B.; Andersen, N. H.; Sørby, M. H.; Kumar, S.; Nilsen, O.; Fjellvåg, H. Neutron Diffraction and Raman Analysis of LiMn1.5Ni0.5O4 Spinel Type Oxides for Use as Lithium Ion Battery Cathode and Their Capacity Enhancements. Solid State Ionics 2016, 284, 28−36. (9) Duncan, H.; Hai, B.; Leskes, M.; Grey, C. P.; Chen, G. Relationships between Mn3+ Content, Structural Ordering, Phase Transformation, and Kinetic Properties in LiNixMn2−xO4 Cathode Materials. Chem. Mater. 2014, 26, 5374−5382. (10) Wu, H. M.; Tu, J. P.; Yuan, Y. F.; Li, Y.; Zhao, X. B.; Cao, G. S. Electrochemical and ex Situ XRD Studies of a LiMn1.5Ni0.5O4 HighVoltage Cathode Material. Electrochim. Acta 2005, 50, 4104−4108. (11) Lin, M.; Ben, L.; Sun, Y.; Wang, H.; Yang, Z.; Gu, L.; Yu, X.; Yang, X.-Q.; Zhao, H.; Yu, R.; Armand, M.; Huang, X. Insight into the Atomic Structure of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material in the First Cycle. Chem. Mater. 2015, 27, 292−303. (12) Luo, Y.; Li, H.; Lu, T.; Zhang, Y.; Mao, S. S.; Liu, Z.; Wen, W.; Xie, J.; Yan, L. Fluorine Gradient-doped LiNi0.5Mn1.5O4 Spinel with Improved High Voltage Stability for Li-Ion Batteries. Electrochim. Acta 2017, 238, 237−245. (13) Yi, T.-F.; Mei, J.; Zhu, Y.-R. Key Strategies for Enhancing the Cycling Stability and Rate Capacity of LiNi0.5Mn1.5O4 as HighVoltage Cathode Materials for High Power Lithium-Ion Batteries. J. Power Sources 2016, 316, 85−105. (14) Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Chem. Mater. 2010, 22, 587−603. (15) Shin, D. W.; Bridges, C. A.; Huq, A.; Paranthaman, M. P.; Manthiram, A. Role of Cation Ordering and Surface Segregation in High-Voltage Spinel LiMn1.5Ni0.5−xMxO4 (M = Cr, Fe, and Ga) Cathodes for Lithium-Ion Batteries. Chem. Mater. 2012, 24, 3720− 3731. (16) Ma, X.; Kang, B.; Ceder, G. High Rate Micron-Sized Ordered LiNi0.5Mn1.5O4. J. Electrochem. Soc. 2010, 157, A925−A931. (17) Arai, H.; Sato, K.; Orikasa, Y.; Murayama, H.; Takahashi, I.; Koyama, Y.; Uchimoto, Y.; Ogumi, Z. Phase Transition Kinetics of LiNi0.5Mn1.5O4 Electrodes Studied by in Situ X-Ray Absorption NearEdge Structure and X-Ray Diffraction Analysis. J. Mater. Chem. A 2013, 1, 10442−10449. (18) Shimoda, K.; Murakami, M.; Komatsu, H.; Arai, H.; Uchimoto, Y.; Ogumi, Z. Delithiation/Lithiation Behavior of LiNi0.5Mn1.5O4

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b11187. Appearance of the pouch-type cell for in situ XRD test, SEM images of the hydroxide precursor and carbonate precursor, Raman spectra and BET, XANES of the Ni and Mn K-edges for the two samples at pristine state and at charged state (4.9 V), in situ XRD patterns and discharge curves of the two samples in the pouch-type cells at 1 C, phase fractions of Li1, Li0.5 and Li0 for the two samples in the pouch-type cells during charge and discharge at 1 C, in situ XRD patterns of the two samples in the pouch-type cells during discharge at 3 or 5 C, CV curves and lithium diffusion coefficients of the two samples in the pouch-type cells, the cyclic performances of the two samples in the pouch-type cells at room temperature, EIS spectra and fitting results of the two samples in the pouch-type cells after cycled at room temperature or in the coin cells after cycled at 55 °C, and SEM images of the octahedral sample after cycled at room temperature (PDF)

■

REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Jingying Xie: 0000-0002-3877-8745 Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work was supported by shanghai science and technology engineering research center program (No. 15DZ2282000), national key research and development plan of China (No. 2017YFB0102204). The in situ XRD and XANES experiments 31802


Research Article

ACS Applied Materials & Interfaces Studied by In Situ and Ex Situ 6,7Li NMR Spectroscopy. J. Phys. Chem. C 2015, 119, 13472−13480. (19) Boulet-Roblin, L.; Borel, P.; Sheptyakov, D.; Tessier, C.; Novák, P.; Villevieille, C. Operando Neutron Powder Diffraction Using Cylindrical Cell Design: The Case of LiNi0.5Mn1.5O4 vs Graphite. J. Phys. Chem. C 2016, 120, 17268−17273. (20) Ma, J.; Hu, P.; Cui, G.; Chen, L. Surface and Interface Issues in Spinel LiNi0.5Mn1.5O4: Insights into a Potential Cathode Material for High Energy Density Lithium Ion Batteries. Chem. Mater. 2016, 28, 3578−3606. (21) Luo, Y.; Lu, T.; Zhang, Y.; Yan, L.; Xie, J.; Mao, S. S. Enhanced Electrochemical Performance of LiNi0.5Mn1.5O4 Cathode using an Electrolyte with 3-(1,1,2,2-tetrafluoroethoxy)-1,1,2,2-tetrafluoropropane. J. Power Sources 2016, 323, 134−141. (22) Luo, Y.; Lu, T.; Zhang, Y.; Yan, L.; Mao, S. S.; Xie, J. Surfacesegregated, High-voltage Spinel Lithium-Ion Battery Cathode Material LiNi0.5Mn1.5O4 Cathodes by Aluminium Doping with Improved High-Rate Cyclability. J. Alloys Compd. 2017, 703, 289−297. (23) Bouayad, H.; Wang, Z.; Dupré, N.; Dedryvère, R.; Foix, D.; Franger, S.; Martin, J. F.; Boutafa, L.; Patoux, S.; Gonbeau, D.; Guyomard, D. Improvement of Electrode/Electrolyte Interfaces in High-Voltage Spinel Lithium-Ion Batteries by Using Glutaric Anhydride as Electrolyte Additive. J. Phys. Chem. C 2014, 118, 4634−4648. (24) Bae, S.-Y.; Shin, W.-K.; Kim, D.-W. Protective Organic Additives for High Voltage LiNi0.5Mn1.5O4 Cathode Materials. Electrochim. Acta 2014, 125, 497−502. (25) Chemelewski, K. R.; Lee, E.-S.; Li, W.; Manthiram, A. Factors Influencing the Electrochemical Properties of High-Voltage Spinel Cathodes: Relative Impact of Morphology and Cation Ordering. Chem. Mater. 2013, 25, 2890−2897. (26) Manthiram, A.; Chemelewski, K.; Lee, E.-S. A Perspective on the High-Voltage LiMn1.5Ni0.5O4 Spinel Cathode for Lithium-Ion Batteries. Energy Environ. Sci. 2014, 7, 1339−1350. (27) Li, H.; Luo, Y.; Xie, J.; Zhang, Q.; Yan, L. Effect of Lithium and Fluorine Doping on the Electrochemical and Thermal Stability of LiNi0.5Mn1.5O4 Spinel Cathode Material. J. Alloys Compd. 2015, 639, 346−351. (28) Lin, H. B.; Zhang, Y. M.; Rong, H. B.; Mai, S. W.; Hu, J. N.; Liao, Y. H.; Xing, L. D.; Xu, M. Q.; Li, X. P.; Li, W. S. Crystallographic Facet- and Size-Controllable Synthesis of Spinel LiNi0.5Mn1.5O4 with Excellent Cyclic Stability as Cathode of High Voltage Lithium Ion Battery. J. Mater. Chem. A 2014, 2, 11987− 11995. (29) Maiyalagan, T.; Chemelewski, K. R.; Manthiram, A. Role of the Morphology and Surface Planes on the Catalytic Activity of Spinel LiMn1.5Ni0.5O4 for Oxygen Evolution Reaction. ACS Catal. 2014, 4, 421−425. (30) Hai, B.; Shukla, A. K.; Duncan, H.; Chen, G. The Effect of Particle Surface Facets on the Kinetic Properties of LiMn1.5Ni0.5O4 Cathode Materials. J. Mater. Chem. A 2013, 1, 759−769. (31) Chemelewski, K. R.; Li, W.; Gutierrez, A.; Manthiram, A. HighVoltage Spinel Cathodes for Lithium-Ion Batteries: Controlling the Growth of Preferred Crystallographic Planes through Cation Doping. J. Mater. Chem. A 2013, 1, 15334−15341. (32) Liu, H.; Wang, J.; Zhang, X.; Zhou, D.; Qi, X.; Qiu, B.; Fang, J.; Kloepsch, R.; Schumacher, G.; Liu, Z.; Li, J. Morphological Evolution of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Materials for Lithium-Ion Batteries: The Critical Effects of Surface Orientations and Particle Size. ACS Appl. Mater. Interfaces 2016, 8, 4661−4675. (33) Chen, Z.; Zhao, R.; Du, P.; Hu, H.; Wang, T.; Zhu, L.; Chen, H. Polyhedral LiNi0.5Mn1.5O4 with Excellent Electrochemical Properties for Lithium-Ion Batteries. J. Mater. Chem. A 2014, 2, 12835− 12848. (34) Chemelewski, K. R.; Shin, D. W.; Li, W.; Manthiram, A. Octahedral and Truncated High-Voltage Spinel Cathodes: The Role of Morphology and Surface Planes in Electrochemical Properties. J. Mater. Chem. A 2013, 1, 3347−3354.

(35) Kuppan, S.; Duncan, H.; Chen, G. Controlling Side Reactions and Self-discharge in High-Voltage Spinel Cathodes: The Critical Role of Surface Crystallographic Facets. Phys. Chem. Chem. Phys. 2015, 17, 26471−26481. (36) Talyosef, Y.; Markovsky, B.; Lavi, R.; Salitra, G.; Aurbach, D.; Kovacheva, D.; Gorova, M.; Zhecheva, E.; Stoyanova, R. Comparing the Behavior of Nano- and Microsized Particles of LiMn1.5Ni0.5O4 Spinel as Cathode Materials for Li-Ion Batteries. J. Electrochem. Soc. 2007, 154, A682−A691. (37) Xue, Y.; Wang, Z.-B.; Zheng, L.-L.; Yu, F.-D.; Liu, B.-S.; Zhang, Y.; Zhou, Y.-X. Synthesis and Performance of Hollow LiNi0.5Mn1.5O4 with Different Particle Sizes for Lithium-Ion Batteries. RSC Adv. 2015, 5, 100730−100735. (38) Kunduraci, M.; Amatucci, G. G. The Effect of Particle Size and Morphology on the Rate Capability of 4.7 V LiMn1.5+δNi0.5−δO4 Spinel Lithium-Ion Battery Cathodes. Electrochim. Acta 2008, 53, 4193−4199. (39) Aklalouch, M.; Rojas, R. M.; Rojo, J. M.; Saadoune, I.; Amarilla, J. M. The Role of Particle Size on the Electrochemical Properties at 25 and at 55°C of the LiCr0.2Ni0.4Mn1.4O4 Spinel as 5V-Cathode Materials for Lithium-Ion Batteries. Electrochim. Acta 2009, 54, 7542− 7550. (40) Ariyoshi, K.; Maeda, Y.; Kawai, T.; Ohzuku, T. Effect of Primary Particle Size upon Polarization and Cycling Stability of 5-V Lithium Insertion Material of LiNi1/2Mn3/2O4. J. Electrochem. Soc. 2011, 158, A281−A284. (41) Yang, T.; Wen, W.; Yin, G.; Li, X.; Gao, M.; Gu, Y.; Li, L.; Liu, Y.; Lin, H.; Zhang, X.; Zhao, B.; Liu, T.; Yang, Y.; Li, Z.; Zhou, X.; Gao, X. Introduction of the X-ray Diffraction Beamline of SSRF. Nucl. Sci. Technol. 2015, 26, 020101. (42) Wei, Y. J.; Yan, L. Y.; Wang, C. Z.; Xu, X. G.; Wu, F.; Chen, G. Effects of Ni Doping on [MnO6] Octahedron in LiMn2O4. J. Phys. Chem. B 2004, 108, 18547−18551. (43) Patoux, S.; Daniel, L.; Bourbon, C.; Lignier, H.; Pagano, C.; Le Cras, F.; Jouanneau, S.; Martinet, S. High Voltage Spinel Oxides for Li- Ion Batteries: From the Material Research to the Application. J. Power Sources 2009, 189, 344−352. (44) Xiao, J.; Chen, X.; Sushko, P. V.; Sushko, M. L.; Kovarik, L.; Feng, J.; Deng, Z.; Zheng, J.; Graff, G. L.; Nie, Z.; Choi, D.; Liu, J.; Zhang, J.-G.; Whittingham, M. S. High-Performance LiNi0.5Mn1.5O4 Spinel Controlled by Mn3+ Concentration and Site Disorder. Adv. Mater. 2012, 24, 2109−2116. (45) Kim, J.-H.; Huq, A.; Chi, M.; Pieczonka, N. P. W.; Lee, E.; Bridges, C. A.; Tessema, M. M.; Manthiram, A.; Persson, K. A.; Powell, B. R. Integrated Nano-Domains of Disordered and Ordered Spinel Phases in LiNi0.5Mn1.5O4 for Li-Ion Batteries. Chem. Mater. 2014, 26, 4377−4386. (46) Yoon, J.; Kim, D.; Um, J. H.; Jeong, M.; Oh, W.; Yoon, W.-S. Effect of Local Structural Changes on Rate Capability of LiNi0.5Mn1.5O4‑δ Cathode Material for Lithium Ion Batteries. J. Alloys Compd. 2016, 686, 593−600. (47) Kunduraciz, M.; Amatucci, G. G. Synthesis and Characterization of Nanostructured 4.7 V LixMn1.5Ni0.5O4 Spinels for HighPower Lithium-Ion Batteries. J. Electrochem. Soc. 2006, 153, A1345− A1352. (48) Sudant, G.; Baudrin, E.; Larcher, D.; Tarascon, J.-M. Electrochemical Lithium Reactivity with Nanotextured AnataseType TiO2. J. Mater. Chem. 2005, 15, 1263−1269. (49) Wang, L.; Li, H.; Huang, X.; Baudrin, E. A Comparative Study of Fd-3m and P4332 “LiNi0.5Mn1.5O4. Solid State Ionics 2011, 193, 32−38. (50) Zhang, Y. X.; Luo, Y.; Chen, Y.; Lu, T. L.; Yan, L. Q.; Cui, X. L.; Xie, J. Y. Enhanced Rate Capability and Low-Temperature Performance of Li4Ti5O12 Anode Material by Facile Surface Fluorination. ACS Appl. Mater. Interfaces 2017, 9, 17145−17154.

31803


Octahedral and Porous Spherical Ordered LiNi0.5Mn1.5O4 Spinel: the

Recommend Documents