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Constructing a Heterostructural LiNi0.4Mn1.6O4−δ Material from Concentration-Gradient Framework to Significantly Improve Its Cycling Performance Fang Lian,* Fan Zhang, Lin Yang, Leilei Ma, and Yadi Li School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, P.R. China ABSTRACT: A heterostructural LiNi0.35Mn1.65O4−δ-LiNi0.5Mn1.5O4 was achieved via constructing the concentration-gradient material with an average composition of LiNi0.4Mn1.6O4−δ. The as-obtained samples were characterized by cross-sectional scanning electron microscopy and energy dispersive X-ray spectrometry, and it was found that the core material LiNi0.35Mn1.65O4−δ is encapsulated completely by a concentration-gradient shell with the outmost layer of LiNi0.5Mn1.5O4. Demonstrated by high resolution transmission electron microscopy and X-ray photoelectron spectroscopy analysis with a low-energy Ar neutral beam etching method, the structurally stable P4332 phase on the surface coordinates the high conductive Fd3m ̅ phase in the bulk without any detectable interface. At room temperature, the heterostructural samples deliver the initial discharge capacity of 145.1 mAhg−1 at 1 C, close to the theoretical capacity, and the capacity retention after 300 cycles was up to 96.5% of the first discharge capacity. Moreover, it shows excellent rate capability with discharge capacity of 144.3 mAhg−1 at 10 C and significantly improved cycling stability with capacity retention of 85.51% over 50 cycles between 3.0 and 4.95 V at 55 °C. The as-obtained material with coordination of two crystallographic structure domains is a promising cathode to develop high energy, high power, long lifespan, and low cost lithium-ion batteries. KEYWORDS: cathode, lithium-ion batteries, heterostructural, spinel, high energy density
1. INTRODUCTION Sustained efforts have been devoted to improve or explore electrodes with high capacity and power, long calendar life, low cost, and low toxicity for high energy density Li-ion batteries.1−3 Among the reported cathode materials, spinel LiNi0.5Mn1.5O4 with high operating plateau up to 4.7 V has been considered as one of the promising cathode candidates due to its energy density 20% higher than the earliest commercialized LiCoO2.4 Furthermore, LiNi0.5Mn1.5O4 cathode shows a series of advantages, including excellent rate performance, low cost of raw materials, and environmental friendliness.5 However, LiNi0.5Mn1.5O4 suffers from poor cycling performance, particularly at an elevated operating temperature, which limits its practical applications in Li-ion batteries.6 The previous reports demonstrated that the surface coating is an effective approach to protect the substrate material against Mn(II) dissolution and interfacial parasitic reactions with electrolytes.7−9 Specially, Li+ conductor as the coating species has been proposed to dramatically improve cycling stability without compromising the reversible capacity and rate performance of the substrate material.10−13 However, the structural mismatch and residual stress induced by volume change between the substrate material and the cover layer leads to the risk of cracking of the coating and a sudden drop of capacity during repeated lithiation/delithiation.14 In this case, preparation of © XXXX American Chemical Society
particles with concentration gradient shell has been accepted as an improvement strategy to solve the nondurable problem existing in the conventional coating method.15−18 But mere chemical composition gradient is not enough to solve the problems of cycling stability of high-voltage spinel cathode materials.19−21 Moreover, the electrochemical properties of LiNi0.5Mn1.5O4 depend critically on the arrangement of Ni/Mn in the spinel structure.22 Nonstoichiometric LiNi0.5Mn1.5O4−δ with disordered arrangement of Ni/Mn (corresponding space group Fd3̅m) possesses higher electronic conductivity and lithium diffusivity due to the presence of Mn3+ ions. Meanwhile, ordered phase LiNi0.5Mn1.5O4 with space group P4332 has smaller lattice distortion and better electrochemical stability than those of the Fd3̅m disordered phase during a long-term charging/discharging.22,23 It was reported to modulate the ratio of two spinel phases in the material via controlling Mn3+ concentration in the preparation process.24 The coexistence of two crystallographic structures Fd3̅m and P4332 contributes to the superior integrated electrochemical performance.25 However, the disproportion of Mn3+ on the surface accelerates Mn(II) dissolution and capacity fading of the active material. Received: January 24, 2017 Accepted: April 25, 2017 Published: April 25, 2017 A
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces
neutral beam etching method was carried out by using Thermo Fisher ESCALAB 250Xi to acquire the depth-dependent composition. 2.3. Electrochemical Characterization. Electrochemical performances of the samples were characterized using CR 2032 coin cells. The active materials, acetylene black and polyvinylidene fluoride (PVDF) binder, were mixed in the weight ratio of 80:10:10 in Nmethylpyrrolidinone (NMP) to form slurry, which was spread uniformly on an aluminum foil current collector and dried at 110 °C for 12 h under vacuum. The cells were assembled and sealed in an argon-filled glovebox with 1 M LiPF6 dissolved in the mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (3:7 in volume ratio) as electrolyte and metallic lithium and porous polypropylene films as anode and separator, respectively. Charge and discharge tests were all performed galvanostatically between 3.0 and 4.95 V (versus Li+/Li) with a LAND CT2001A battery test system (Jinnuo Wuhan Corp., China) at room temperature and elevated temperature (55 °C).
Moreover, the impurity such as Li1−xNixO or NixO appears inevitably in the synthesis of the disordered material with a certain content of Mn3+, which is detrimental to the reversible capacity.26 Our work attempts to prepare the heterostructural spinel material with disordered phase (Fd3̅m) in the buck and ordered phase (P4332) in the outmost layer, respectively. Herein, the coprecipitation precursor consisting of a core with component of Ni0.175Mn0.825(OH)2 and a shell with component of Ni0.25Mn0.75(OH)2 was employed to prepare the target material. In detail, the ordered LiNi0.5Mn1.5O4 is expected to generate in the outermost shell, which provides the high structural and electrochemical stability of the material during the long-term cycling, while LiNi0.35Mn1.65O4−δ in the core with disordered Fd3m ̅ phase benefits the improvement of capacity and rate capability of the material.27 Moreover, due to the compatibility of ordered P4332 and disordered Fd3̅m spinel structure, it is expected that there is no detectable interface between them. In this paper, the as-prepared samples were evaluated to determine the structural and electrochemical properties via the cross-sectional scanning electron microscopy (SEM), transition electron microscopy (TEM), selected area electron diffraction (SAED), etching X-ray photoelectron spectroscopy (XPS), and galvanostatic charge−discharge test.
3. RESULTS AND DISCUSSION The precursor obtained from coprecipitation method shows spherical agglomerations with a diameter around 6 μm as observed from Figure 1a and the cross-sectional image in Figure 1b. EDS results in Figure 1c indicate that the concentration of Ni and Mn in the core of agglomerated particles was determined to be 18 and 82%, respectively. By contrast, the Ni and Mn contents were determined to be 24
2. EXPERIMENTAL SECTION 2.1. Material Preparation. LiNi0.4Mn1.6O4−δ with a concentration gradient was prepared via the coprecipitation method. To prepare the precursor with component [Ni0.175Mn0.825](OH)2 in the core, the aqueous solution of MnSO4·5H2O and NiSO4·H2O (in a molar ratio of 33:7) with a concentration of 1.0 mol L−1 was pumped into a continuously stirred tank reactor under nitrogen atmosphere. Simultaneously, 2.0 mol L−1 NaOH solution and 0.24 mol L−1 NH4OH solution were fed into the reactor. The preparation parameters, including the pH (10), the temperature (50 °C), and the stirring speed (600r min−1) of the solution were carefully controlled. The reaction to form the [Ni0.175Mn0.825](OH)2 precursor is continued until complete consumption of the mixed solution of Ni/ Mn sulfate. Subsequently, 1.0 mol L−1 aqueous solution of MnSO4· 5H2O and NiSO4·H2O (in a molar ratio of 3:1) was continuously pumped into the reactor to encapsulate [Ni0.175Mn0.825](OH)2 powder to generate core−shell precursor {[Ni0.175Mn0.825](2/3)}core{[Ni0.25Mn0.75](1/3)}shell(OH)2. The precursors were washed with deionized water, filtered, and then dried at 110 °C for 24 h under nitrogen atmosphere. The obtained powder was ground with a stoichiometric amount of LiOH·H2O, and the homogeneous mixture was calcined at 400 °C for 4 h, then heated at 900 °C for 12 h, and finally annealed at 600 °C for 6 h with a heating rate of 3 °C min−1 to prepare LiNi0.4Mn1.6O4−δ with a concentration gradient (denoted as G-LiNi0.4Mn1.6O4−δ). For comparison, homogeneous LiNi0.4Mn1.6O4−δ (denoted as HLiNi0.4 Mn 1.6 O 4−δ ) was also prepared from [Ni0.2 Mn 0.8 ](OH) 2 precursor via the coprecipitation method as mentioned before. 2.2. Material Characterization. The XRD patterns were collected on a D/Max-3C instrument device with Cu Kα radiation from 10° to 80°. The morphology and elemental distribution of the material were observed via field emission scanning electron microscopy (FESEM, SUPRA55), energy dispersive X-ray spectrometry (EDS), and transmission electron microscopy (TEM, JEM2100). Cross sections for SEM and EDS analysis were prepared by embedding the assynthesized particles in an epoxy and polishing them flat on metallographic sand papers. The Fourier transform infrared spectroscopy (FT-IR) was performed on KBr pellets using a NEXUS FTIR670 spectrometer in the frequency range of 400−700 cm−1. The Raman spectroscopy (RS) measurements of the samples were obtained by LabRAM HR Evolution with a 532 nm wavelength. Xray photoelectron spectroscopy (XPS) analysis with low-energy Ar
Figure 1. SEM images of (a and b) {[Ni0.175Mn0.825](2/3)}core{[Ni0.25Mn0.75](1/3)}shell(OH)2 precursor, EDS spot scan of precursor (c) in the core and (d) shell region, SEM images of (e and f) [Ni0.2Mn0.8](OH)2 precursor, and EDS spot scan of precursor (g) in the core and (h) shell region. B
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
Figure 2. SEM image of (a) G-LiNi0.4Mn1.6O4−δ and (b) H-LiNi0.4Mn1.6O4−δ and EDS for the atomic ratio of transition metals as a function of the distance from the particle center to the surface for (c) G-LiNi0.4Mn1.6O4−δ and (d) H-LiNi0.4Mn1.6O4−δ (cross-sectional image is shown in the inset).
and 76% in the shell of the precursor, as shown in Figure 1d. The initial characterization suggests that the as-prepared precursor presents the core−shell structure {[Ni0.175Mn0.825](2/3)}core{[Ni0.25Mn0.75](1/3)}shell(OH)2. Moreover, SEM results and the cross-sectional image of the homogeneous precursor is presented in Figures 1e and f for comparison; the precursor for H-LiNi0.4Mn1.6O4−δ shows the consistent chemical composition of 19% Ni and 81% Mn, corresponding to stoichiometric [Ni0.2Mn0.8](OH)2. The morphologies of G-LiNi 0.4Mn1.6 O 4−δ and H-LiNi0.4Mn1.6O4−δ are shown in Figure 2, which are wellcrystallized octahedrons with average diameter of 3 μm. Moreover, cross-section of the two samples was characterized by EDS to explore the element distribution. As shown in Figure 2c, Ni/Mn contents gradually change from the center to the surface of particles. In detail, the center domain of the particles is composed of 17.2% Ni and 82.8% Mn in a molar ratio, while the surface of the particles is composed of 22.7% Ni and 77.3% Mn. Whereas, H-LiNi0.4Mn1.6O4−δ demonstrates the homogeneous Ni/Mn distribution with around 20% Ni and 80% Mn content, as shown in Figure 2d. The results suggest that the concentration gradient material with composition LiNi0.35Mn1.65O4−δ in the center and LiNi0.5Mn1.5O4 in the outmost surface has been prepared via a facile approach successfully, which is presented as a flowchart in Figure 3. The XRD patterns of G-LiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ are shown in Figure 4. All of the peaks of the samples can be indexed as the cubic phase (JCPD 80-2162). No diffraction peak of the impurity can be observed in the GLiNi0.4Mn1.6O4−δ pattern. Therefore, constructing the concentration gradient might be a good approach to prepare LiNi0.5−xMn1.5+xO4−δ material in a much lower Ni/Mn ratio without any induced impurity, which is detrimental to the electrochemical properties.28 To determine the degree of cationic ordering, GLiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ were measured by FT-IR spectroscopy and RS, as shown in Figure 5. Both
Figure 3. Preparation process of concentration-gradient framework for the heterostructural LiNi0.4Mn1.6O4−δ material.
Figure 4. XRD patterns of H-LiNi 0.4 Mn 1.6 O 4−δ and G-LiNi0.4Mn1.6O4−δ.
samples present main IR absorption bands at 621, 582, 554, 501, and 466 cm−1, which are the fingerprint of the disordered Fd3̅m phase.29 However, the intensity ratio of the peaks at 582 and 621 cm−1 of G-LiNi0.4Mn1.6O4−δ is higher than that of HLiNi0.4Mn1.6O4−δ, indicating the increasing order degree of Ni/ C
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
Figure 5. (a) FT-IR spectra and (b) Raman spectra of H-LiNi0.4Mn1.6O4−δ and G-LiNi0.4Mn1.6O4−δ.
Mn ions in G-LiNi0.4Mn1.6O4−δ samples.30 Moreover, the additional weak peaks at 651 and 428 cm−1 suggest the presence of ordered P4332 phase in G-LiNi0.4Mn1.6O4−δ and HLiNi0.4Mn1.6O4−δ. Moreover, H-LiNi0.4Mn1.6O4−δ and GLiNi0.4Mn1.6O4−δ shows the similar RS results in Figure 5b. The existence of the weak peaks at 591 and 609 cm−1 indicates the characteristics of ordered P4 3 32 structure in GLiNi0.4Mn1.6O4−δ.31 FT-IR spectra and Raman spectra with a certain penetration depth from the surface (≥0.5 μm) demonstrates a composite structure consisting of a predominant disordered phase (Fd3m ̅ ) and a small amount of ordered phase (P4332) in G-LiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ. G-LiNi0.4Mn1.6O4−δ seems to have ordered characteristics more prominent than those of H-LiNi0.4Mn1.6O4−δ. Therefore, further detailed analysis was performed to detect the structural difference between them. The TEM and HRTEM images and SAED patterns of GLiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ are shown in Figure 6. The G-LiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ particles were observed with octahedral morphology in Figures 6a and e. The HRTEM images in Figures 6b and f present that the particles of the two samples have been crystallized with lattice spacing of 0.47 nm, corresponding to (111) planes of the spinel. For G-LiNi0.4Mn1.6O4−δ, the SAED pattern of the surface (point c) in Figure 6c presents a zone axis of [110] of the extra diffraction spots, which are assigned to cubic symmetry P4332 space group. However, the extra diffraction spots cannot be detected in the bulk region (point d), which is due to the face-centered cubic symmetry Fd3̅m space group, as shown in Figure 6d. By contrast, the SAED patterns on the surface (point g) and in the bulk (point h) of HLiNi0.4Mn1.6O4−δ in Figures 6g and h are ascribed to the dominant disordered Fd3̅m phase. The observations give the evidence that the G-LiNi0.4Mn1.6O4−δ possess the heterostructural character; in detail, P4332 phase with Ni/Mn ordering on the surface and disordered Fd3̅m phase in the bulk.32 Moreover, no interface or interfacial transition region is detected due to the similar d-spacing between P4332 and Fd3̅m symmetry of the spinel. Consecutive surface etching by Ar+ ion in XPS characterization was performed to study the chemical state on the surface as a function of depth. The sample was etched to 30 nm in a direction from surface toward the particle center. Figures 7a and b show the Ni 2p and Mn 2p XPS spectra of GLiNi0.4Mn1.6O4−δ, respectively. The main peak of Ni 2p3/2 is close to 854.8 eV, which corresponds to the binding energy of Ni2+.33 With an increase in etching depth, the peaks location for
Figure 6. (a and e) TEM image, (b and f) HRTEM image, SAED patterns of (c and g) the surface and (d and h) the bulk of GLiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ, respectively.
the Ni 2p3/2 orbital shows undetectable shift. The result implies that Ni remains at the oxidation state of +2 with depth, which is consistent with previous reports for spinel LiNixMn2−xO4,34 while the Mn 2p3/2 main peak for the outmost layer was observed at 642.5 eV, which is ascribed to D
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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Figure 7. Ni 2p and Mn 2p XPS spectra of (a and b) G-LiNi0.4Mn1.6O4−δ and (c and d) H-LiNi0.4Mn1.6O4−δ, respectively.
Figure 8. Coordination of P4332 phase on the surface and dominant Fd3̅m phase in the bulk for the heterostructural LiNi0.4Mn1.6O4−δ material.
the binding energies of Mn4+.35 Moreover, the Mn 2p3/2 peak shifts toward lower binding energy, which indicates the decrease in the oxidation state of Mn with depth. The result suggests that Mn on the surface of G-LiNi0.4Mn1.6O4−δ is in the oxidation state of +4, while Mn3+ appears, and the content of Mn3+ is increasing with etching depth to 30 nm. By comparison, an increasing of etching depth H-LiNi0.4Mn1.6O4−δ in Figures 7c and d keeps a consistent location of the main peaks of Ni 2p3/2 and Mn 2p3/2 at 854.8 and 642.2 eV, respectively. Further analysis from TEM, SAED, and XPS demonstrates that the heterostructural G-LiNi0.4Mn1.6O4−δ has been achieved with disordered phase encapsulated by a concentration-gradient shell with the outmost layer of ordered LiNi0.5Mn1.5O4, as shown in Figure 8.
The initial charge−discharge curves and the differential capacity−voltage profiles of G-LiNi0.4Mn1.6O4−δ and HLiNi0.4Mn1.6O4−δ at 0.2 C between 3.0 and 4.95 V at room temperature (25 °C) are shown in Figure 9. HLiNi0.4Mn1.6O4−δ delivers the initial reversible capacity of 143.4 mAhg−1 with the Coulombic efficiency of 96.8%, while, G-LiNi0.4Mn1.6O4−δ shows a slightly improved initial capacity to 146.3 mAhg−1 and significantly increased Coulombic efficiency to 98.2%. Moreover, two pairs of distinct redox peaks near 4.7 V are observed in dQ/dV curves, which are contributed to the coexistent Fd3̅m and P4332 phase of H-LiNi0.4Mn1.6O4−δ and G-LiNi0.4Mn1.6O4−δ. In agreement with the previous report,36 LiNi0.4Mn1.6O4−δ with Ni:Mn ratio of 0.4:1.6 possesses integrated nanodomains of disordered and ordered spinel phases, which is responsible for the higher capacity of both HE
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces
Figure 9. (a) Initial charge−discharge curves and (b and c) differential capacity vs voltage profiles of G-LiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ at 0.2 C between 3.0 and 4.95 V and 25 °C.
Figure 10. (a) Rate performance and (b) the cycling property at 1 C of G-LiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ. (c) Cycling performance of GLiNi0.4Mn1.6O4−δ at 3 and 5 C in voltage range of 3.0−4.95 V at 25 °C.
rates were varied subsequently as 1, 3, 5, 10, and 1 C for every 5 cycles. G-LiNi0.4Mn1.6O4−δ exhibits higher capacity in comparison with that of H-LiNi0.4Mn1.6O4−δ at different current density. Though both samples present slight capacity degradation at the discharge rate of 10 C, G-LiNi0.4Mn1.6O4−δ still delivers higher reversible capacities of 144.3 mAhg−1 than H-LiNi0.4Mn1.6O4−δ. Furthermore, the capacity of both samples is recovered when returning to the 1 C rate, which indicates the
LiNi0.4Mn1.6O4−δ and G-LiNi0.4Mn1.6O4−δ in comparison with stoichiometric LiNi 0.5 Mn 1.5 O 4 . In addition, the G-LiNi0.4Mn1.6O4−δ samples show a charge−discharge overpotential much smaller than that of H-LiNi0.4Mn1.6O4−δ, which is attributed to the prominent ordered characteristics in GLiNi0.4Mn1.6O4−δ.22 The rate performance of G-LiNi0.4Mn1.6O4−δ and HLiNi0.4Mn1.6O4−δ is characterized in Figure 10a. The charge rate was fixed to 1 C (1 C = 147 mAg−1), and the discharge F
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Research Article
ACS Applied Materials & Interfaces excellent structural and electrochemical reversibility of the samples. As known, cycling stability and Coulombic efficiency of high voltage spinel material are critical parameters for industrial applications.37 Their cycling performance at 1 C is compared in Figure 10b. G-LiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ deliver the capacity of 140.2 and 134.4 mAhg−1 over 300 cycles, retaining 96.5 and 93.8% of the initial capacity, respectively. GLiNi0.4Mn1.6O4−δ shows initial Coulombic efficiency of 98.09%, which is much higher than 95.23% for H-LiNi0.4Mn1.6O4−δ. After 8 cycles, the two samples present stable Coulombic efficiency above 99.5%. Moreover, Figure 10c shows the cycling performance of G-LiNi0.4Mn1.6O4−δ at 3 and 5 C, which delivers reversible capacity of 144.8 and 143.7 mAhg−1 with 99.17 and 98.63% retention over 100 cycles, respectively. In contrast to H-LiNi0.4Mn1.6O4−δ with coexistence of ordered and disordered structures as well as the reported concentration-gradient spinel,38 G-LiNi0.4Mn1.6O4−δ has much better rate capability and long-term cycling stability, which is due to the special construction with the high conductive Fd3̅m phase in the bulk and the stable P4332 phase on the surface. Figure 11 shows the cycling performance of the GLiNi0.4Mn1.6O4−δ and H-LiNi0.4Mn1.6O4−δ at 55 °C in voltage
Figure 12. SEM images of G-LiNi 0.4 Mn 1.6 O 4−δ and H-LiNi0.4Mn1.6O4−δ (a and c) before cycling and (b and d) after 50 cycles at 55 °C, respectively.
4. CONCLUSIONS In this work, heterostructural high voltage spinel cathode material was prepared with an average composition of LiNi0.4Mn1.6O4−δ. The detail characterization confirms that the functionally gradient material was achieved, consisting of LiNi0.35Mn1.65O4−δ in the core and concentration-gradient shell with the utmost layer of LiNi0.5Mn1.5O4. Through construction of the concentration gradient framework, it is realized that the disordered Fd3̅m domain in the bulk coordinates the ordered P4332 LiNi0.5Mn1.5O4 on the surface, which contributes to the high discharge capacity of 145.1 mAhg−1 at 1 C rate, capacity retention of 96.5% after 300 cycles, excellent rate capacity even at 10 C, and significantly improved cycling stability at 55 °C. The heterostructural construction is believed to be an effective approach, making full use of advantages of each structure in the electrode material to satisfy the requirement for the excellent integrated properties of high energy density lithium-ion batteries.
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Figure 11. Cycling performance of G-LiNi0.4Mn1.6O4−δ and HLiNi0.4Mn1.6O4−δ in voltage range of 3.0−4.95 V at 1 C and 55 °C.
AUTHOR INFORMATION
Corresponding Author
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[email protected]; Tel.: +86 10 82377985; Fax: +86 10 82377985. ORCID
Fang Lian: 0000-0002-6446-4432
range of 3.0−4.95 V. At the elevated temperature, HLiNi0.4Mn1.6O4−δ presents drastically reduced capacity to 66.8 mAh g−1 at 1 C with about 48.4% retention after 50 cycles. By contrast, G-LiNi0.4Mn1.6O4−δ remains at a discharge capacity of 124.5 mAhg−1 with much higher capacity retention of 85.51% at 55 °C. Furthermore, the morphology of electrodes before cycling and after 50 cycles at 55 °C was measured for comparison. As shown in Figure 12, the particles of GLiNi0.4Mn1.6O4−δ still have the original octahedral morphology, while some primary particles of H-LiNi0.4Mn1.6O4−δ show abnormal growth and a corroded surface. The result indicates that the significantly improved cycling stability is achieved for G-LiNi0.4Mn1.6O4−δ, in which the stable ordered LiNi0.5Mn1.5O4 at the outmost layer prevents the serious dissolution of active material and the attack of electrolyte at the elevated temperature.39
Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was financially supported by the Beijing Municipal Science and Technology Project (D151100003115002) and National 863 Program of China (2013AA050901).
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REFERENCES
(1) Winter, M.; Brodd, R. J. What are Batteries, Fuel cells, and Supercapacitors? Chem. Rev. 2004, 104, 4245−4270. (2) Scrosati, B.; Garche, J. Lithium Batteries: Status, Prospects and Future. J. Power Sources 2010, 195, 2419−2430. (3) Goodenough, J. B.; Kim, Y. Challenges for Rechargeable Li Batteries. Chem. Mater. 2010, 22, 587−603. (4) Kang, B.; Ceder, G. Battery Materials for Ultrafast Charging and Discharging. Nature 2009, 458, 190−193. G
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
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ACS Applied Materials & Interfaces
through Control of Site Disorder. Phys. Chem. Chem. Phys. 2012, 14, 13515−13521. (24) Xiao, J.; Chen, X.; Sushko, P. V.; Sushko, M. L.; Kovarik, L.; Feng, J.; Choi, D. High-performance LiNi0.5Mn1.5O4 Spinel Controlled by Mn3+ Concentration and Site Disorder. Adv. Mater. 2012, 24, 2109−2116. (25) Xu, G.; Liu, Z.; Zhang, C.; Cui, G.; Chen, L. Strategies for improving the cyclability and thermo-stability of LiMn2O4-based batteries at elevated temperatures. J. Mater. Chem. A 2015, 3, 4092− 4123. (26) Wang, L.; Liu, G.; Wu, W.; Chen, D.; Liang, G. Synthesis of Porous Peanut-like LiNi0.5Mn1.5O4Cathode Materials through an Ethylene Glycol-assisted Hydrothermal Method using Urea as a Precipitant. J. Mater. Chem. A 2015, 3, 19497−19506. (27) Kunduraci, M.; Al-Sharab, J. F.; Amatucci, G. G. High-Power Nanostructured LiMn2-xNixO4 High-Voltage Lithium-Ion Battery Electrode Materials: Electrochemical Impact of Electronic Conductivity and Morphology. Chem. Mater. 2006, 18, 3585−3592. (28) Liu, H.; Wang, J.; Zhang, X.; Zhou, D.; Qi, X.; Qiu, B.; 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. (29) Chen, Z.; Zhao, R.; Li, A.; Hu, H.; Liang, G.; Lan, W.; Chen, H. Polyhedral Ordered LiNi0.5Mn1.5O4Spinel with Excellent Electrochemical Properties in Extreme Conditions. J. Power Sources 2015, 274, 265−273. (30) 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. (31) Kunduraci, M.; Amatucci, G. G. Synthesis and Characterization of Nanostructured 4.7 V LixMn1.5Ni0.5O4 Spinels for High-Power Lithium-Ion Batteries. J. Electrochem. Soc. 2006, 153, A1345−A1352. (32) Kim, J. H.; Huq, A.; Chi, M.; Pieczonka, N. P.; Lee, E.; Bridges, C. 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 (15), 4377−4386. (33) Lee, J. H.; Kim, K. J. Structural and Electrochemical Evolution with Post-annealing Temperature of Solution-based LiNi0.5Mn1.5O4 Thin-film Cathodes for Microbatteries with Cyclic Stability. Electrochim. Acta 2014, 137, 169−174. (34) Wei, Y.; Kim, K. B.; Chen, G. Evolution of the Local Structure and Electrochemical Properties of Spinel LiNixMn2−xO4(0 ≤ x ≤ 0.5). Electrochim. Acta 2006, 51, 3365−3373. (35) Treuil, N.; Labrugère, C.; Menetrier, M.; Portier, J.; Campet, G.; Deshayes, A.; Choy, J. H. Relationship between Chemical Bonding Nature and Electrochemical Property of LiMn2O4 Spinel Oxides with Various Particle Sizes:“Electrochemical Grafting” Concept. J. Phys. Chem. B 1999, 103, 2100−2106. (36) Wan, L.; Deng, Y.; Yang, C.; Xu, H.; Qin, X.; Chen, G. Ni/Mn Ratio and Morphology-dependent Crystallographic Facet Structure and Electrochemical Properties of the High-voltage Spinel LiNi0.5Mn1.5O4 Cathode Material. RSC Adv. 2015, 5, 25988−25997. (37) Mao, J.; Dai, K.; Xuan, M.; Shao, G.; Qiao, R.; Yang, W.; Liu, G. Effect of Chromium and Niobium Doping on the Morphology and Electrochemical Performance of High-Voltage Spinel LiNi0.5Mn1.5O4 Cathode Material. ACS Appl. Mater. Interfaces 2016, 8, 9116−9124. (38) Liu, Y. Z.; Zhang, M. H.; Xia, Y. G.; Qiu, B.; Liu, Z. P.; Li, X. One-step Hydrothermal Method Synthesis of Core−shell LiNi0.5Mn1.5O4 Spinel Cathodes for Li-ion Batteries. J. Power Sources 2014, 256, 66−71. (39) Song, J.; Shin, D. W.; Lu, Y.; Amos, C. D.; Manthiram, A.; Goodenough, J. B. Role of Oxygen Vacancies on the Performance of Li[Ni0.5‑xMn1.5+x]O4 (x= 0, 0.05, and 0.08) Spinel Cathodes for Lithium-Ion Batteries. Chem. Mater. 2012, 24, 3101−3109.
(5) Santhanam, R.; Rambabu, B. Research Progress in High Voltage Spinel LiNi0.5Mn1.5O4 Material. J. Power Sources 2010, 195, 5442− 5451. (6) Li, B.; Xing, L.; Xu, M.; Lin, H.; Li, W. New Solution to Instability of Spinel LiNi0.5Mn1.5O4 as Cathode for Lithium Ion Battery at Elevated Temperature. Electrochem. Commun. 2013, 34, 48−51. (7) Sun, Y. K.; Lee, Y. S.; Yoshio, M.; Amine, K. Synthesis and Electrochemical Properties of ZnO-Coated LiNi0.5Mn1.5O4 Spinel as 5 V Cathode Material for Lithium Secondary Batteries. Electrochem. Solid-State Lett. 2002, 5, A99−A102. (8) Wu, H. M.; Belharouak, I.; Abouimrane, A.; Sun, Y. K.; Amine, K. Surface Modification of LiNi0.5Mn1.5O4 by ZrP2O7 and ZrO2 for Lithium-ion Bbatteries. J. Power Sources 2010, 195, 2909−2913. (9) Li, J.; Zhang, Y.; Li, J.; Wang, L.; He, X.; Gao, J. AlF3 Coating of LiNi0.5Mn1.5O4 for High-performance Li-ion Batteries. Ionics 2011, 17, 671−675. (10) Kobayashi, Y.; Miyashiro, H.; Takei, K.; Shigemura, H.; Tabuchi, M.; Kageyama, H.; Iwahori, T. 5 V Class All-solid-state Composite Lithium Battery with Li3PO4 Coated LiNi0.5Mn1.5O4. J. Electrochem. Soc. 2003, 150, A1577−A1582. (11) Lee, M. J.; Lee, S.; Oh, P.; Kim, Y.; Cho, J. High Performance LiMn2O4 Cathode Materials Grown with Epitaxial Layered Nanostructure for Li-ion batteries. Nano Lett. 2014, 14, 993−999. (12) Qiu, T.; Wang, J.; Lu, Y.; Yang, W. Improved Elevated Temperature Performance of Commercial LiMn2O4 Coated with LiNi0.5Mn1.5O4. Electrochim. Acta 2014, 147, 626−635. (13) Sun, Y. K.; Myung, S. T.; Kim, M. H.; Prakash, J.; Amine, K. Synthesis and Characterization of Li[(Ni0.8Co0.1Mn0.1)0.8(Ni0.5Mn0.5)0.2]O2 with the Microscale Core-shell Structure as the Positive Electrode Material for Lithium Batteries. J. Am. Chem. Soc. 2005, 127, 13411−13418. (14) Sun, Y. K.; Chen, Z.; Noh, H. J.; Lee, D. J.; Jung, H. G.; Ren, Y.; Amine, K. Nanostructured High-energy Cathode Materials for Advanced Lithium Batteries. Nat. Mater. 2012, 11, 942−947. (15) Sun, Y. K.; Kim, D. H.; Yoon, C. S.; Myung, S. T.; Prakash, J.; Amine, K. A Novel Cathode Material with a Concentration-gradient for High-energy and Safe Lithium-ion Batteries. Adv. Funct. Mater. 2010, 20, 485−491. (16) Sun, Y. K.; Kim, D. H.; Jung, H. G.; Myung, S. T.; Amine, K. High-voltage Performance of Concentration-gradient Li[Ni0.67Co0.15Mn0.18]O2 Cathode Material for Lithium-ion Batteries. Electrochim. Acta 2010, 55, 8621−8627. (17) Sun, Y. K.; Myung, S. T.; Kim, M. H.; Prakash, J.; Amine, K. Synthesis and Characterization of Li[(Ni0.8Co0.1Mn0.1)0.8(Ni0.5Mn0.5)0.2]O2 with the Microscale Core-shell Structure as the Positive Electrode Material for Lithium Batteries. J. Am. Chem. Soc. 2005, 127, 13411−13418. (18) Sun, Y. K.; Lee, B. R.; Noh, H. J.; Wu, H.; Myung, S. T.; Amine, K. A Novel Concentration-gradient Li[Ni0.83Co0.07Mn0.10]O2 Cathode Material for High-energy Lithium-ion Batteries. J. Mater. Chem. 2011, 21, 10108−10112. (19) Wei, Q.; Wang, X.; Yang, X.; Ju, B.; Hu, B.; Shu, H.; Hu, H. Spherical Concentration-gradient LiMn1.87Ni0.13O4 Spinel as a High Performance Cathode for Lithium Ion Batteries. J. Mater. Chem. A 2013, 1, 4010−4016. (20) Wen, W.; Wang, X.; Chen, S.; Shu, H.; Yang, X. Design and Preparation of Spherical High Voltage LiNi0.5Mn1.5O4 with a Novel Concentration-gradient shell for lithium ion batteries. J. Power Sources 2015, 281, 85−93. (21) Wang, J.; Yu, Y. Y.; Wu, B. H.; Lin, W. Q.; Li, J. Y.; Zhao, J. B. A Homogeneous Intergrown Material of LiMn2O4 and LiNi0.5Mn1.5O4 as a Cathode Material for Lithium-ion Batteries. J. Mater. Chem. A 2015, 3, 2353−2360. (22) Kim, J. H.; Myung, S. T.; Yoon, C. S.; Kang, S. G.; Sun, Y. K. Comparative Study of LiNi0.5Mn1.5O4−δ andLiNi0.5Mn1.5O4 Cathodes Having Two Crystallographic Structures: Fd3m and P4332. Chem. Mater. 2004, 16, 906−914. (23) Zheng, J.; Xiao, J.; Yu, X.; Kovarik, L.; Gu, M.; Omenya, F.; Whittingham, M. S. Enhanced Li+ Ion Transport in LiNi0.5Mn1.5O4 H
DOI: 10.1021/acsami.7b01235 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
