Spinel LiNi0.5Mn1.5O4cathode for rechargeable lithiumion batteries ...

Nano Research 2013, 6(9): 679–687 DOI 10.1007/s12274-013-0343-5

Spinel LiNi0.5Mn1.5O4 cathode for rechargeable lithiumion batteries: Nano vs__ micro, ordered phase (P4332) vs disordered phase (Fd 3m) Jingang Yang, Xiaopeng Han, Xiaolong Zhang, Fangyi Cheng (), and Jun Chen Key Laboratory of Advanced Energy Materials Chemistry (Ministry of Education), College of Chemistry, Nankai University, Tianjin 300071, China

Received: 27 May 2013

ABSTRACT

Received: 20 June 2013

Since the high-voltage spinel LiNi0.5Mn1.5O4 (LNMO) is one of the most attractive cathode materials for lithium-ion batteries, how to improve the cycling and rate performance simultaneously has become a critical question. Nanosizing is a typical strategy to achieve high rate capability due to drastically shortened Liion diffusion distances. However, the high surface area of nanosized particles increases the side reaction with the electrolyte, which leads to poor cycling performance. Spinels with disordered structures could also lead to improved rate capability, but the cyclability is low due to the presence of Mn3+ ions. Herein, we systematically investigated the synergic interaction between particle size and cation ordering. Our results indicated that a microsized disordered phase and a nanosized ordered phase of LNMO materials exhibited the best combination of high rate capability and cycling performance.

Accepted: 24 June 2013 © Tsinghua University Press and Springer-Verlag Berlin Heidelberg 2013

KEYWORDS spinel LiNi0.5Mn1.5O4, nanomaterials, microstructures, crystal phases, lithium-ion batteries

1

Introduction

There is increasing interest in developing new cathode materials with high energy and power density for rechargeable lithium-ion batteries that have potential applications in large-scale energy storage and electric vehicles (EV) [1, 2]. Spinel LiNi0.5Mn1.5O4 (LNMO) is particularly attractive because of its moderate capacity and high-voltage plateau (~4.7 V vs. Li+/Li) offering theoretically 20% higher energy density relative to conventional LiCoO2 cathode materials [3–5]. In Address correspondence to [email protected]

addition, LNMO has advantages including low cost, less environmental impact, and inherent high Li+ diffusivity within the three-dimensional channels of the spinel structure [6]. However, it remains challenging to achieve simultaneously satisfactory capacity, cyclability and rate performance, since the electrochemical properties of LNMO-based materials intimately depend on interrelated physicochemical parameters such as structure, composition, particle shape and size, and surface area [7–17]. LNMO spinels have two types of crystal structure,

680

Nano Res. 2013, 6(9): 679–687

namely the ordered P4332 phase and the disordered — Fd3m phase, depending on the ordering of Ni/Mn in the octahedral sites [8]. In the P4332 space group, Ni and Mn are located in an ordered fashion in the octahedral 4b and 12d sites, respectively, with the Li ions occupying the 8c sites and O ions in 8c and 24e — sites. For the Fd3m phase, Ni and Mn are randomly distributed in the 16d sites, with the Li and O ions occupying the 8a and 32e sites, respectively [9]. Previous investigations indicate that the cycling and rate performances of the disordered LNMO are superior to that of the ordered one due to higher Li+ diffusion coefficients [5, 7], whereas experimental and computational studies have also shown that the ordered spinel exhibits excellent cyclability and high-rate capability [11]. In addition, an order–disorder phase transition of LNMO usually occurs on material annealing, being associated with a loss/gain of oxygen and generation/evanescence of Mn3+ due to charge neutrality constraints [9]. The presence and content of Mn3+ have been demonstrated to intricately affect the electrode performance [5]. On the one hand, the larger ionic radius of Mn3+ relative to Mn4+ results in an expanded lattice, which benefits fast Li+ diffusion [15]. On the other hand, Mn3+ can induce a Jahn–Teller structural distortion and dissolve into the electrolyte via a disproportionation reaction, which has an adverse effect on the capacity retention [18]. Furthermore, particle shapes and sizes of electrode materials are known to play a critical role in determining their electrochemical properties [18–25]. Creating nanostructures is a popular strategy to increase the rate capability due to the drastic reduction of Li+ diffusion lengths [26, 27]. High rate capability and excellent cyclability have been attained for LNMO nanoparticles [16]. However, the occurrence of side reactions with the electrolyte due to the increased surface areas of nanoparticles has attracted increasing attention [28–30]. Therefore, the factors influencing the electrochemical performance should be synergistically taken into consideration for the development of advanced spinel cathodes. With this in mind, we have systematically investigated a series of LNMO materials. Herein, we focus on two dominating factors, the phase (structure and composition) and the particle morphology (size,

shape and surface area). Four representative LNMO samples with similar particulate morphology have been synthesized without treatment such as cation doping or surface coating: a micro-sized P4332 phase — (LNMO-MP), a micro-sized Fd3m phase (LNMO-MF), a nanosized P4332 phase (LNMO-NP), and a nanosized — Fd 3 m phase (LNMO-NF) (Fig. 1). We attempt to identify the parameters that are critical in achieving optimal electrochemical performance including capacity, rate capability, and cyclability.

Figure 1 A schematic illustration of the preparation of LNMONP, LNMO-NF, LNMO-MF, and LNMO-MP.

2 2.1

Experimental Materials synthesis

The LNMO series were synthesized by a polyethylene glycol (PEG)-assisted co-precipitation method as shown in Fig. 1. In a typical synthesis, analytical reagent grade LiCH3COO·2H2O, Ni(CH3COO)2·4H2O, and Mn(CH3COO)2·4H2O in the molar ratio of 1.04:0.5:1.5 and in quantities corresponding to 0.9 g of LNMO were dissolved in 20 mL of water. The solution was heated to 50 °C and then 3 mL of PEG 400 was added. Under constant magnetic stirring, 4.5 g of tartaric acid was added to the solution. Then the solution was heated to 85 °C to afford a green viscous precursor. The precursor was calcined at 700 °C or 900 °C in air for 10 h to obtain the nano-ordered (LMNO-NP) or micro-disordered (LMNO-MF) products, respectively. The as-prepared nano-ordered material was further

| www.editorialmanager.com/nare/default.asp

681

Nano Res. 2013, 6(9): 679–687

annealed at 600 °C for 1 h in Ar to obtain nanodisordered LMNO-NF, whilst the micro-disordered material was annealed at 700 °C for 20 h in air to give the micro-ordered LMNO-MP sample. 2.2

Materials characterization

Structural analysis was carried out by powder X-ray diffraction (XRD, Rigaku MiniFlex-600, X-ray generator operating in transmission mode with a Cu source) and Raman microscopy (DXR, Thermo-Fisher Scientific at 532 nm excitation). The XRD patterns were refined by the Rietveld refinement program RIETAN-2000. The oxidation state of Mn was analyzed by a chemical titration: The samples were dissolved in dilute H2SO4 and H3PO4 solution with an excess of Fe(NH4)2(SO4)2, and titrated with standardized KMnO4 solution. The morphologies were characterized by scanning electron microscopy (SEM, FEI NanoSEM 430) and transmission electron microscopy (TEM, Philips Tecnai F20, 200 kV). The Brunauer–Emmett–Teller (BET) specific surface areas were analyzed by nitrogen adsorption/ desorption measurements at 77 K on a BELSORP-mini instrument. 2.3

Electrochemical investigation

The electrode materials were assembled into 2,032 button cells for electrochemical measurement. The battery assembly experiments were carried out in a glove box (Mikrouna China Universal 2240/750) filled with high-purity argon (99.999%). The cathode was fabricated by blending the as-prepared LNMO samples, acetylene black, and polyvinylidene fluoride (PVDF) (in N-methyl-2-pyrrolidone) with a weight ratio of 80:15:5. The obtained slurry was pasted onto an aluminum foil, and dried at 120 °C for 10 h in vacuum. High-purity lithium was used as the counter electrode and the reference electrode. The electrolyte contained 1.0 mol·L–1 LiPF6 in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC:DMC = 1:1, volume ratio). The charge–discharge tests were performed on a Land battery test system (Land, CT2001A) in the range of 3.5–4.95 V at different rates. The cyclic voltammetry (CV) measurements were carried out at room temperature on an electrochemical workstation (Potentiostat/Galvanostat Model 263A).

3

Results and discussion

The structures of the as-synthesized four LNMO samples were analyzed by powder X-ray diffraction and Raman microscopy. The XRD patterns (see Fig. S1(a) in the Electronic Supplementary Material (ESM)) can be readily indexed to a P4332 spinel phase — (JCPDS card No. 80-2184) and a Fd3m phase (JCPDS card No. 80-2162). Figures 2(c) and 2(d) display the Rietveld refinement patterns of LNMO-MF and LNMO-NP. The observed weak peaks at 2θ angles of 37.5°, 43.7°, and 63.7° (Fig. 2(c)) are assigned to LixNi1–xO [10], which is a common impurity in synthesized LNMO. Small peaks at 15.4° and 57.5° (Fig. 2(d)) indicate a superstructure [8]. The refined lattice parameters are summarized in Table 1, showing an increase in the order LNMO-MP < LNMO-NP < LNMO-MF < LNMO-NF. This order is generally consistent with the content of Mn3+ ions in the samples— the larger lattice parameter of LNMO-NF compared with LNMO-MF may arise from a lattice expansion due to nanosizing, which has been reported in the case of LiCoO2 [22]. Raman spectroscopy is a useful tool to use alongside XRD because it is a sensitive method to distinguish between the P and F phases. Figures 2(e) and 2(f) and Figs. S1(e) and S1(f) (in the ESM) display the Raman mapping spectra of the four LNMO samples. All the mapping images are the result of 100 Raman spectra collected within a selected area of 10 μm × 10 μm. The red, green, and blue colors correspond to the band intensity at 636 cm–1, which is the strongest Raman peak of LNMO [7]. The spectra of P-LNMO (MP and NP) samples exhibit extra peaks at 218, 238, 404 cm–1 and a splitting of peaks around 595 cm–1, which are characteristic of well-separated Ni and Mn sites due to the symmetry lowering in the ordered P4332 phase [7, 10]. In comparison, the spectra of F-LNMO (MF and NF) samples are characteristic of a typical disordered — Fd3m spinel [7, 10]. Thus, the samples can be divided into two categories: P phase (LNMO-MP, LNMO-NP) and F phase (LNMO-MF, LNMO-NF). The morphologies of LNMO-MP, LNMO-MF, LNMO-NP, and LNMO-NF are shown in Fig. 3. The microsized LNMO samples have a uniform particle size of 1 μm (Figs. 3(a), 3(b), 3(d), 3(e)) while the sizes

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano

Research

682

Nano Res. 2013, 6(9): 679–687

Figure 2 Crystal structures of LNMO with (a) Fd 3 m and (b) P4332 space groups. Rietveld refined XRD patterns of the as-prepared LNMOs: (c) LNMO-MF, (d) LNMO-NP with experimental data (red dots), calculated profile (cyan line), allowed Bragg reflections (vertical green bars), and difference curve (blue line). The values of profile R-factor (Rp) weighted Rp (Rwp) are 8.25/12.80 and 5.55/7.47 in (c) and (d), respectively. Raman mapping of (e) LNMO-MF and (f) LNMO-NP within a selected area of 10 μm × 10 μm. The symbols ◆ and * denote LiNixO1–x and P4332-LNMO, respectively. Table 1 Characteristics of the four LNMO spinels obtained under different synthesis conditions % of Mn3+ (%)b

Mn valencec

BET surface area (m2·g–1)

DLi (×10–11 cm2·s–1)d

LNMO-MP 8.159(2)

4.4

3.983

1.0

0.88

LNMO-MF 8.186(4)

9.0

3.934

0.9

10.98

LNMO-NP 8.176(3)

5.3

3.977

5.1

2.03

LNMO-NF 8.190(4)

8.8

3.917

5.3

Samples

a

Lattice parameter a (Å)a

b

9.07 3+

From XRD Rietveld refinement. The relative Mn content is calculated from the discharge capacity between 3.8 and 4.3 V by being divided by the theoretical capacity (147 mA·h·g–1). c From chemical titration. d DLi is the Li+ diffusion coefficient and the details are shown in Figs. S2 and S3 in the ESM.

Figure 3 SEM (a, d, g, j) and TEM (b, e, h, k, c, f, i, l) micrographs of the as-synthesized LNMO-MP (a–c), LNMO-MF (d–f), LNMO-NP (g–i) and LNMO-NF (j–l) samples.


683

Nano Res. 2013, 6(9): 679–687

of nanosized LNMO samples are around 50 nm (Figs. 3(g), 3(h), 3(j), 3(k)). Note that the particle sizes of LNMO samples are essentially preserved during the transition between ordered and disordered phases. Little variation is also observed in the specific surface areas of the samples having similar particle size, as listed in Table 1. To gain structural information, we performed high-resolution TEM (HRTEM) imaging on the edges of microparticles and isolated nanoparticles (Figs. 3(c), 3(f), 3(i), 3(l)). All the products had high crystallinity with clearly distinguished lattice fringes. Taking LNMO-MP as an example, the measured neighboring interplane distance is consistent with spinel (111) planes, confirming the XRD analysis. The welldefined points in the corresponding fast Fourier transform (FFT) diffraction pattern (inset of Fig. 3(c)) conform to the crystal structure of spinel LNMO. Likewise, the measured interplane distances and FFT patterns of LNMO-MF, LNMO-NP and LNMO-NF well match the neighboring separations and the allow Bragg diffractions of the respective phases. The uniformity of the exposed planes allows us to systematically investigate the effect of phase and particle size on electrochemical properties by excluding the factor of preferential crystal growth. Figure 4(a) displays the typical charge–discharge profiles of four LNMO samples tested in the potential range 3.5–4.95 V and at a current rate of 0.1 C (n C equals to 147n mA·g–1 for LiNi0.5Mn1.5O4). All the spinels exhibit a distinct two-step plateau around 4.7 V, which is attributed to the Ni2+/Ni4+ redox couple. A small plateau in the 4.0 V region (related to the Mn4+/Mn3+ redox couple) is clearly observed in LNMO-MF and LNMO-NF, but is not observed in the profiles of LNMO-MP and LNMO-NP (Fig. 4(b)). The amount of Mn3+ can be estimated from the length of the 4.0 V plateau. On the other hand, we also determined the oxidation state via a chemical titration (Table 1), with the results suggesting a similar trend. The variation in the amount of Mn3+ is mostly in accordance with the variation in lattice parameters and lithium diffusivity DLi determined from cyclic voltamogramm measurements (Figs. S2 and S3 (in the ESM)). This result confirms that the the presence of Mn3+ plays a critical role in determining the electrochemical performance.

Figure 4 (a) Charge–discharge curves and (b) differential capacities versus voltage (dQ/dV) in the 4 V region of the as-prepared LNMO samples.

Figure 5 shows the rate performance of the as-prepared LNMO-MP, LNMO-MF, LNMO-NP and LNMO-NF samples. As shown in Fig. 5(a), the disordered LNMO spinels exhibit higher rate capability than that of ordered spinels with similar size, including lower polarization and higher discharge capacity. This trend is amplified at higher rates (Fig. 5(b)). However, the superiority decreases when the size of the LNMO particles is on the nanometer scale. For the ordered phase, the nanosized sample performs much better than its microsized counterpart. In contrast, the performance of the nanosized and microsized samples of the disordered phase is comparable. Thus, the rate capability increases in the order LNMO-MP < LNMO-NP < LNMO-MF ≈ LNMO-NF, consistent with the variation in DLi, lattice constant and amount of Mn3+ of these samples. These results indicate that the disordered structures afford intrinsically better rate


Research

684

Nano Res. 2013, 6(9): 679–687

Figure 6 (a) Cycling performance at 1 C and (b) the capacity retention at different discharge rates (charge rate: 1 C) after 100 cycles for LNMO-MP, LNMO-MF, LNMO-NP, and LNMO-NF.

Figure 5 Discharge curves (a) and capacities (b) of the synthesized LNMO-MP, LNMO-MF, LNMO-NP, and LNMO-NF samples on cycling sequentially from 1 C to 50 C for every 10 cycles at each discharge rate, with a charge rate of 1 C.

capability. Nanosizing is effective in achieving high rate capability, which is particularly important for an ordered LMNO spinel. The cycling performances of the LNMO samples at different discharge rates are compared in Fig. 6(a) and Fig. S4 (in the ESM). The discharge capacity retentions over 100 cycles are plotted in Fig. 6(b). At a relatively low rate of 1 C, the capacity retentions of LNMO-MP, LNMO-MF, LNMO-NP, and LNMO-NF are 93.7%, 98.4%, 95.7%, and 92.4%, respectively. LNMO-NF shows the fastest capacity degradation. LNMO-MP, with the features of an ordered phase and microsize beneficial for cycling performance, fails to

achieve the best cycling capability. This is due to its poorest DLi value, which makes Li+ ions easily pile-up on the surfaces of particles, which has an adverse effect on the cycling performance. The capacity decay is more evident as the discharge rate increases (Fig. S4 in the ESM). The LNMO-MF displayed the best capacity retention at 1 C rate because of the synergistic effect of micro-size (small specific surface area reduces the contact with the electrolyte) and disordered phase (which ensures fast Li diffusion for Li+ extraction and insertion). However, at higher rates, LNMO-NP shows the highest capacity retention. Moreover, the LNMO-NP presents the smallest change of capacity retention with discharge rate. Therefore, our results strongly suggest that the optimized combination of phase and size (disordered-micro, ordered-nano) is necessary in order to improve the cycling performance. To further evaluate the cycling stability, we cycled LNMO-MF and LNMO-NP for an extended 300 cycles (Fig. 7). After an initial activation process with relatively


685

Nano Res. 2013, 6(9): 679–687

Figure 7 Cycling performance of LNMO-MF and LNMO-NP at 5 C discharge rate and 1 C charge rate.

lower coulombic efficiency, the highest capacities were achieved at about the 10th cycle. After 300 cycles, the capacities of LNMO-MF and LNMO-NP were 110 and 115 mA·h·g–1, with capacity retention of 90.4% and 91.3%, respectively. Such performance is comparable to the best results reported previously [4, 10], suggesting the efficacy of controlling the phase and particle size of LNMO cathode materials. The above results clearly indicate that nanosize particles and a disordered structure are the critical factors in giving rate capability, while microsize particles and an ordered phase are beneficial factors for cyclability. Figure 8 schematically compares the electrochemical behavior of ordered and disordered LNMO. On the one hand, the intrinsic Li+ diffusion is slower in ordered LNMO than in disordered LNMO due to the smaller lattice parameter resulting from the absence of Mn3+. As a result of low Li+ diffusivity, Li+ ions may not access the particle core and will accumulate on the surface or outer layer of the electrode particles, especially at high discharge rates. This results in local excessive discharge, reducing Mn4+ to Mn3+, and thus leading to poorer cycling performance [31]. Reducing the size of the ordered LNMO particles is an effective solution to this problem as decreased Li+ diffusion length L can greatly shorten the characteristic diffusion time t (t = L 2/2DLi [27]). Figures 8(c) and 8(d) illustrate the different cycle performances of ordered and disordered spinels. On the other hand, although the presence of Mn3+ increases both the electrical conductivity and DLi, the Jahn– Teller structural distortion and, more importantly, the

Figure 8 A schematic diagram showing the effects of orderedLNMO (a, c) and disordered-LNMO (b, d) on the rate and cycling performance.

Mn dissolution associated with the presence of Mn3+ induces the structural collapse and active mass loss of the cathode, which results in fast capacity degradation during cycling. In this regard, the use of microsized particles could mitigate side reactions with the electrolyte due to the lower specific surface area. Moreover, the stability of the electrolyte at high voltage is also important for cycling performance. The formation of a passivating solid-electrolyte interphase (SEI) layer on the electrode surface is of great importance in preventing electrolyte decomposition; however, the SEI layer is usually broken up by particle dissolution and volume change upon cycling [32]. The presence of a ordered phase and nanosized particles is beneficial in terms of maintaining the stability of the SEI due to the absence of Mn3+ and the minimal particle deformation. Thus, a synergic effect between the crystal phase and particle size should be taken into account in order to attain both high rate capability and cyclability for LNMO spinel electrodes.

4

Conclusions

We have prepared LNMO cathode materials with different particle sizes and crystal phases. Electrochemical measurements indicate that spinel LNMO phases with disordered cation distributions favor high rate capability while the presence of an ordered phase


Research

686

Nano Res. 2013, 6(9): 679–687

benefits cyclability. Meanwhile, forming nanosized spinel particles greatly improves the high rate performance but worsens the cycling performance. The phase- and size-dependent behaviors can be understood in terms of ionic and electronic diffusion, structural variation, and side reactions associated with Mn3+. By synergistically considering phase and size effects, we achieved excellent electrode performance with LNMO-MF (microsized and disordered phase) and LNMO-NP (nanosized and ordered phase) spinels, which delivered 5 C discharge capacities near 130 mA·h·g–1 and sustained capacity retention exceeding 90% after 300 cycles. This study highlights the importance of both phase and particle size control in developing superior 5 V-spinel cathode materials for advanced rechargeable lithium-ion batteries.

[6]

[7]

[8]

[9]

Acknowledgements This work was supported by programs of the National Basic Research Program (973 Program) of China (No. 2011CB935900), the National Natural Science Foundation of China (Nos. 21231005 and 21076108), and the Discipline Innovative Intelligence Plan (111 Project, No. B12015). Electronic Supplementary Material: Supplementary material (XRD measurements, Raman spectroscopy measurements and CV data) is available in the online version of this article at http://dx.doi.org/10.1007/ s12274-013-0343-5.

[10]

[11] [12]

[13]

References [1] Tarascon, J.-M.; Armand, M. Issues and challenges facing rechargeable lithium batteries. Nature 2001, 414, 359–367. [2] Cheng, F. Y.; Liang, J.; Tao, Z. L.; Chen, J. Functional materials for rechargeable batteries. Adv. Mater. 2011, 23, 1695–1715. [3] Xiao, X. L.; Liu, X. F.; Wang, L.; Zhao, H.; Hu, Z. B.; He, X. M.; Li, Y. D. LiCoO2 nanoplates with exposed (001) planes and high rate capability for lithium-ion batteries. Nano Res. 2012, 5, 395–401. [4] Zhou, L.; Zhao, D. Y.; Lou, X. W. LiNi0.5Mn1.5O4 hollow structures as high-performance cathodes for lithium ion batteries. Angew. Chem. Int. Ed. 2012, 51, 239–241. [5] Xiao, J.; Chen, X. L.; Sushko, P. V.; Sushko, M. L.; Kovarik,

[14]

[15]

[16]

L.; Feng, J. J.; Deng, Z. Q.; Zheng, J. M.; Graff, G. L.; Nie, Z. M.; et al. High-performance LiNi0.5Mn1.5O4 spinel controlled by Mn3+ concentration and site disorder. Adv. Mater. 2012, 24, 2109–2116. Arrebola, J. C.; Caballero, A.; Cruz, M.; Hernán, L.; Morales, J.; Castellón, E. R. Crystallinity control of a nanostructured LiNi0.5Mn1.5O4 spinel via polymer-assisted synthesis: A method for improving its rate capability and performance in 5 V lithium batteries. Adv. Funct. Mater. 2006, 16, 1904–1912. Wang, L. P.; Li, H.; Huang, X. J.; Baudrin, E. A comparative study of Fd 3 m and P4332 “LiNi0.5Mn1.5O4”. Solid State Ionics 2011, 193, 32–38. 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: Fd 3 m and P4332. Chem. Mater. 2004, 16, 906–914. Cabana, J.; Cabans-cabanas, M.; Omenya, F. O.; Chernova, N. A.; Zeng, D. L.; Whittingham, M. S.; Grey, C. P. Composition–structure relationships in the Li-ion battery electrode material LiNi0.5Mn1.5O4. Chem. Mater. 2012, 24, 2952–2964. Song, J.; Shin, D. W.; Lu, Y. H.; 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. Ma, X. H.; Kang, B.; Ceder, G. High rate micron-sized ordered LiNi0.5Mn1.5O4. J. Electrochem. Soc. 2010, 157, A925–A931. 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. Zheng, J. M.; Xiao, J.; Yu, X. Q.; Kovarik, L.; Gu, M.; Omenya, F.; Chen, X. L.; Yang, X.-Q.; Liu, J.; Graff, G. L.; et al. Enhanced Li+ ion transport in LiNi0.5Mn1.5O4 through control of site disorder. Phys. Chem. Chem. Phys. 2012, 14, 13515–13521. Chen, Z. X.; Qiu, S.; Cao, Y. L.; Ai, X. P.; Xie, K.; Hong, X. B.; Yang, H. X. Surface-oriented and nanoflake-stacked LiNi0.5Mn1.5O4 spinel for high-rate and long-cycle-life lithium ion batteries. J. Mater. Chem. 2012, 22, 17768–17772. Wang, H. L.; Tan, T. A.; Yang, P.; Lai, M. O.; Lu, L. Highrate performances of the Ru-doped spinel LiNi0.5Mn1.5O4: Effects of doping and particle size. J. Phys. Chem. C 2011, 115, 6102–6110. Shaju, K. M.; Bruce, P. G. Nano-LiNi0.5Mn1.5O4 spinel: A high power electrode for Li-ion batteries. Dalton Trans. 2008, 5471–5475.


687

Nano Res. 2013, 6(9): 679–687

[17] 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. [18] Cheng, F. Y.; Wang, H. B.; Zhu, Z. Q.; Wang, Y.; Zhang, T. R.; Tao, Z. L.; Chen, J. Porous LiMn2O4 nanorods with durable high-rate capability for rechargeable Li-ion batteries. Energy Environ. Sci. 2011, 4, 3668–3675. [19] Li, C. S.; Zhang, S. Y.; Cheng, F. Y.; Ji, W. Q.; Chen, J. Porous LiFePO4/NiP composite nanospheres as the cathode materials in rechargeable lithium ion batteries. Nano Res. 2008, 1, 242–248. [20] Lee, H.-W.; Muralidharan, P.; Ruffo, R.; Mari, C. M.; Cui, Y.; Kim, D. K. Ultrathin spinel LiMn2O4 nanowires as high power cathode materials for Li-ion batteries. Nano Lett. 2010, 10, 3852–3856. [21] Li, T.; Ai, X. P.; Yang, H. X. Reversible electrochemical conversion reaction of Li2O/CuO nanocomposites and their application as high-capacity cathode material for Li-ion batteries. J. Phys. Chem. C 2011, 115, 6167–6174. [22] Okubo, M.; Hosono, E.; Kim, J.; Enomoto, M.; Kojima, N.; Kudo, T.; Zhou, H. S.; Honma, I. Nanosize effect on high-rate Li-ion intercalation in LiCoO2 electrode. J. Am. Chem. Soc. 2007, 129, 7444–7452. [23] Xiao, X. L.; Lu, J.; Li, Y. D. LiMn2O4 microspheres: Synthesis, characterization and use as a cathode in lithium ion batteries. Nano Res. 2010, 3, 733–737. [24] Jiang, Y.; Yang, Z.; Luo, W.; Hu, X. L.; Huang, Y. H. Hollow 0.3Li2MnO3·0.7LiNi0.5Mn0.5O2 microspheres as a high-performance cathode material for lithium-ion batteries. Phys. Chem. Chem. Phys. 2013, 15, 2954–2960.

[25] Liu, J. L.; Chen, L.; Hou, M. Y.; Wang, F.; Che, R. C.; Xia, Y. Y. General synthesis of xLi2MnO3· (1–x)LiMn1/3Ni1/3Co1/3O2 nanomaterials by a molten-salt method: Towards a high capacity and high power cathode for rechargeable lithium batteries. J. Mater. Chem. 2012, 22, 25380–25387. [26] Lee, K. T.; Cho, J. Roles of nanosize in lithium reactive nanomaterials for lithium ion batteries. Nano Today, 2011, 6, 28–41. [27] Guo, Y. G.; Hu, J. S.; Wan, L. J. Nanostructured materials for electrochemical energy conversion and storage devices. Adv. Mater. 2008, 20, 2878–2887. [28] 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. [29] Arrebola, J. C.; Caballero, A.; Hernán, L.; Morales, J. Expanding the rate capabilities of the LiNi0.5Mn1.5O4 spinel by exploiting the synergistic effect between nano and microparticles. Electrochem. Solid-State Lett. 2005, 8, A641–A645. [30] Aricò, A. S.; Bruce, P.; Scrosati, B.; Tarascon, J. M.; Schalkwijk, W. V. Nanostructured materials for advanced energy conversion and storage devices. Nat. Mater. 2005, 4, 366–377. [31] Liu, J.; Manthiram, A. Understanding the improved electrochemical performances of Fe-substituted 5 V spinel cathode LiMn1.5Ni0.5O4. J. Phys. Chem. C 2009, 113, 15073–15079. [32] Zhang, X. L.; Cheng, F. Y.; Yang, J. G.; Chen, J. LiNi0.5Mn1.5O4 porous nanorods as high-rate and long-life cathodes for Li-ion batteries. Nano Lett. 2013, 13, 2822–2825.


Research