Three-Dimension Hierarchical Al2O3 Nanosheets ... - ACS Publications

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Three-Dimension Hierarchical Al2O3 Nanosheets Wrapped LiMn2O4 with Enhanced Cycling Stability as Cathode Material for Lithium Ion Batteries Feiyan Lai, Xiaohui Zhang, Hongqiang Wang, Sijiang Hu, Xian Ming Wu, Qiang Wu, Youguo Huang, Zeqiang He, and Qingyu Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05640 • Publication Date (Web): 04 Aug 2016 Downloaded from http://pubs.acs.org on August 5, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

Three-Dimension Hierarchical Al2O3 Nanosheets Wrapped LiMn2O4 with Enhanced Cycling Stability as Cathode Material for Lithium Ion Batteries Feiyan Lai,† Xiaohui Zhang,† Hongqiang Wang,†,‡ Sijiang Hu*,‡ Xianming Wu,§ Qiang Wu, † Youguo Huang,† Zeqiang He,§ and Qingyu Li*,† † Guangxi Key Laboratory of Low Carbon Energy Materials, School of Chemistry and Pharmaceutical Sciences, Guangxi Normal University, Guilin, China. ‡ Hubei Key Laboratory for Processing and Application of Catalytic Materials, College of Chemical Engineering, Huanggang Normal University, Huanggang, China §

The Collaborative Innovation Center of Manganese-Zinc-Vanadium Industrial Technology, Jishou University, Jishou, China * Corresponding author: [email protected] (Q. Li), Tel: +86-773-5856104; [email protected] (S. Hu), Tel: +86-713-8833119 ABSTRACT Three dimension (3D) Al2O3 coating layer was synthesized by a facile approach including stripping and in situ self-assembly of γ-AlOOH. The uniform flower-like Al2O3 nanosheets

with high specific area largely sequesters acidic species produced by side reaction between electrode and electrolyte. The inner coating layer wrapping spinel LiMn2O4 effectively inhibits the dissolution of Mn by suppressing directive contact with electrolyte to enhance cycling stability. The rate performance is improved because of the better electrolyte storage of the assembled hierarchical architecture of the 3D coating layer affording unimpeded Li+ diffusion from electrode to electrolyte. The electrochemical results reveal the as-prepared coated LiMn2O4 sample with the amount of Al2O3 at 1 wt% exhibits superior cycle stability under room temperature even at elevated temperature. The initial specific discharge capacity is 128.5 mAh g-1 at 0.1 C and retains 89.8% of the initial capacity after 800 cycles at 1 C rate. When cycling at 55 °C, the composite shows 93.6% capacity retention after 500 cycles. This 1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

facile surface modification and effective structure of coating layer can be adopted to enhance the cycling performance and thermal stability of other electrode materials for which Al2O3 plays its role. KEYWORDS: Lithium ion batteries, LiMn2O4, surface modification, Al2O3 coating, hierarchical architecture

1. INTRODUCTION With high safety, abundant resource, environmentally friendly, non-toxic and low cost, LiMn2O4 is considered one of the most promising and practical cathode materials for lithium ion batteries (LIBs) applied in energy storage systems, hybrid electric vehicle (HEV) and electric vehicles (EV).1-3 However, the critical problems to LiMn2O4 is poor stability with electrolyte and capacity degradation upon extend electrochemical cycling at elevated temperature which limits its further practical applications.4,5 The fast capacity fading is mainly ascribed to manganese dissolution on electrode surface by the Jahn-Teller effect and impurity HF from the thermal decomposition of LiPF6-based carbonate electrolytes in the presence of trace water. 6 Among various targeted measures proposed, partial substitution and surface coatings of metal oxides have been demonstrated as the efficient approaches to solve the issues and improve the electrochemical performances. Introducing a heterogeneous atom into the host structure of LiMn2O4 can improve structure stability,7 but the degree of doping cannot be increased more than a certain extent weighed by doping level and specific capacity. A coating layer can not only reduce the contact area of electrode/electrolyte interface and partly suppress the dissolution of Mn2+ but also effectively inhibit the generation of HF.8,9 Surface 2


Page 2 of 28

Page 3 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


modifications by coating with stable electrochemical properties onto the surface of LiMn2O4 have been employed to yield better improvement of capacity retention. As protective coatings, the metal oxides (such as Al2O3, ZrO2, SnO2 and MgO) sequester acidic species in the electrolyte,6,10-12 inhibit Mn dissolution and thus improve capacity retention. In addition, Kannan et al suggest surface coatings structurally reinforce the underlying spinel to prevent microstrain upon cycling at elevated temperatures.13 Although various types of coatings and thin film deposition procedures of metal oxides have been explored to improve the electrochemical stability of LiMn2O4 cathode materials in recent years,14-17 few of the studies published have reported the effect of morphology and architectural pattern of the thin layer on the properties. Moreover, the increasing of the coating amount to cover fully the active materials results in reduction in capacity and increase in ionic resistance. Therefore, the structure of the coating layer is also the key parameter determining coating function. For example, it has been proved that high surface area coatings provide superior protection compared to dense coatings.18-20 The study by Walz et al has demonstrates that nanoporous ZrO2 and TiO2 coating has stabilizing effect on LiMn2O4 electrodes, resulting from predominantly neutralization of HF the LiMn2O4 electrode and a more uniform current distribution provided by the nanoporous coating at the LiMn2O4 particle surface.21 Kim et al found the porosity and high-surface area of ZrO2 particles remove both HF and H2O effectively from the electrolyte, thereby minimizing the solubility of the spinel electrode.22 However, the reported high surface coating usually consists of agglomerated nanoparticles, this comes at the expense of specific capacity in general. Although the ultrathin dense coating by the new technique of atomic layer deposition (ALD) used very recently also show 3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

significant effect,23,24 as reported the Al2O3 coating layer with less than one nanometer in thickness provided significant improvement in capacity retention, this technique is mostly used in basic research due to high cost and low production. Herein, it is of most practical importance to prepare an effective coating with low mass percentage by a facile method for large-scale production using low-cost starting material. In light of the previous studies, a novel agglomerated coating layer of Al2O3 nanosheets is prepared by a facile technique consisted of stripping and self-assembly of layered boehmite γ-AlOOH in this work. In the designed 3D hierarchical structure, the flower-like outer layer with high surface area is assembled from low-cost γ-AlOOH as precursor which is one kind of industrial raw material applied largely in the fields of catalyst support, catalyst and adsorbent. The exceptive coating layer can scavenge HF impurity effectively and prevents undesirable reactions at the interface. The porous architecture offers large storage space for electrolyte storage for Li+ diffusion from electrode to electrolyte. More important, low cost of raw source and facile procedure make it practical to large scale modification of the relevant electrode materials attacked by electrolyte when charged to high potentials and similarly could benefit from surface stabilization.25,26 2. EXPPERIMENTAL SECTION 2.1 Synthesis of Al2O3-coated LiMn2O4 materials AlOOH·xH2O (Aluminum corporation of China), selected as the starting material, was added into deionized water. The suspension was stirred for 1 h at 85 ℃. Then LiMn2O4 (CITIC Dameng Mining Industries Ltd. Guangxi) was added into the mixture. The mixture was stirred with a magnetic stirrer for 4 h at 85 ℃. NH3·H2O was added as a gelling agent 4


Page 4 of 28

Page 5 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


into the mixture and stirred sequentially for 1 h then dry gel was obtained at 85 ℃ for 8 h in vacuum. Finally, the obtained dry gel powders were heated in a tube furnace at 500 ℃ for 4 h in oxygen atmosphere. The samples with the coating amount of Al2O3 (0.5, 1 and 2 wt%) were marked as 0.5A-LMO, 1A-LMO and 2A-LMO respectively, while the pristine LiMn2O4 sample under the same procedure without adding AlOOH was marked as LMO. 2.2 Materials characterizations The crystalline phases and morphologies of the samples were characterized by X-ray diffraction (XRD, D/Max-2500/PC, Rigaku, Japan) using Cu Kα radiation (k=0.15406 nm) and field emission scanning electron microscopy (FE-SEM, Q-200, Hillsboro, USA) equipped with an energy dispersive spectrometer (EDS) for elemental analysis. The microregion structure of the coating layer was observed by a transmission electron microscope (TEM, JEOL 2100F, Tokyo, Japan). The component ratio of the coated samples and the Mn dissolution in electrolyte after 800 cycles was measured. Inductively coupled plasma (Nexlon 300x ICP-MS) was employed to measure the amount of the dissolution. 2.3 Electrochemical testing Electrochemical test was performed in R2025 coin type cells with lithium foil as the negative electrode. The positive electrode was fabricated by blending the cathode material, super P (SP) and polyvinylidene fluoride (PVDF) (weight ratio of 85:10:5) in N-methyl-2-pyrrolidone (NMP). The slurry was coated onto the aluminum foil current collector and dried under vacuum at 100 ℃ for 12 h. The coated foil was cut into circular discs 12 mm in diameter. The electrolyte solution was 1.0 M LiPF6 in ethylene carbonate (EC) and dimethyl carbonate (DMC) mixture (v/v=1:1), which was from Shandong Hirong Power 5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Supply Material Co., LTD. A thin porous polypropylene film was used as the separator (Celgard 2400, 16 µm). All cells were assembled in an argon-filled gloved box. The galvanostatic charge and discharge cycles tests were carried out at 25 and 55 ℃ between 3.0 V and 4.3 V using a battery tester (LAND CT2001A, China). The cyclic voltammogram (CV) test was carried out at a scan rate of 100 µV·s-1 between 3.0 and 4.3 V and the electrochemical impedance spectroscopy (EIS) was examined by applying an AC voltage of 5 mV over the frequency range of 0.01 Hz to 100 kHz using a Zahner IM6 electrochemical workstation (Zahner-Elektrik GmbH & Co.KG, Germany). 3. RESULTS AND DISCUSSION

Figure 1. XRD patterns of γ-AlOOH precursor, γ-Al2O3 and the 1A-LMO samples prepared at 500 ℃ for 4 h (A) and the diffraction peaks of the pristine LMO and coated samples with different Al2O3 coating amounts (B).

Figure 1A shows the powder XRD patterns of AlOOH precursor, Al2O3 and 1wt% Al2O3-coated LiMn2O4 (1A-LMO) samples. All the sharp reflection peaks can be readily indexed as orthorhombic γ-AlOOH (JCPDS 21-1307) with high purity and crystallinity. The powder prepared by calcinations of the γ-AlOOH material at 500 ℃ for 4 h are identified as cubic γ-Al2O3 (JCPDS 29-0063), suggesting the coating material can be obtained from the selected precursor of boehmite by calcination. The diffraction peaks of the coated LiMn2O4 6


Page 6 of 28

Page 7 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


samples in the pattern are indexed to the cubic spinel of Fd-3m space group (JCPDS No. 35-0782). There is no impurity phase appearing, as can be seen from Figure 1B, indicating the surface coating process does not change the spinel structure of LiMn2O4 active material. Al2O3 is not detected may owing to the low mass concentration. Calculated from the result of the elements concentration obtained from ICP (listed in Table S1), the mass percent of Al2O3 in the 0.5A-LMO, 1A-LMO and 2A-LMO samples are 0.57, 1.13 and 2.03 % repetitively, which are close to the theoretical value. The morphology of the pristine LiMn2O4 is shown in Figure 2A. The discrete grains with smooth surface are in a large size range less than 1 µm. After being coated by Al2O3, the surface becomes rough and loses the smooth contours. A porous hierarchical layer is built up on the surface of the LiMn2O4 bulks, the thin sheets in petal shape grow out. The wrinkled two-dimension (2D) nanosheets are connected and interwoven into 3D network. The thickness of the Al2O3 nanosheets is in a range from several to dozens of nanometers. The hierarchical network of nanosheets increases the specific area of the coating layer and is beneficial to scavenge HF impurity. Moreover, the porous structure provides rich storage space for electrolyte and reduces internal resistance which is of importance to transferring of lithium ions. At higher magnification, it is evident that the Al2O3 walls are not isolated. The interconnected structure separate electrode from electrolyte, prevent undesirable reactions at the interface and partly suppress the dissolution of Mn. By composition of the samples with different Al2O3 contents, it can be seen that the coating layer remains 3D porous hierarchical structure, and the stacking density increases with the increasing contents. As shown in Figure 2E, the EDS results present the peaks of Mn, O and Al elements. The mapping images of the 7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1A-LMO sample shows the homogeneous distribution of O and Mn elements in the particles. It is evident that Al elements are evenly distributed on the surface, indicating the LiMn2O4 bulks are uniformly coated with Al2O3 layer.

Figure 2. SEM images of the bare LMO (A), 0.5A-LMO (B), 1A-LMO (C) and 2A-LMO (D) samples prepared at 500 ℃ for 4 h. EDS spectroscopy and electron probe micro analysis images for Al, Mn and O elements of the 1A-LMO sample (E). Compared with the clean contours of the bear LiMn2O4, the surface of the particles coated with Al2O3 present rough layer comprised of many cross-linked nanoflakes (Figure 3A). High magnification TEM image shows that the nanosheets on the particle surface banked up and forms a porous coating layer. As shown in Figure 3D of high-resolution TEM (HRTEM), the 8


Page 8 of 28

Page 9 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


lattice fringe of two sample is clear. The measured separation between the fringe patterns of the coating is 0.478 nm, which corresponds to the interplanar distance of the [111] plane of the LiMn2O4.27 The outer edge of LiMn2O4 grain is covered more intensely with a broad inter-layer of amorphous Al2O3 phase suppressing direct contract with electrolyte. The compaction degree is an important index for the commercial electrode materials for actual application in batteries. For the surface modified cathode materials, the coating layer with three-dimension hierarchical structure will has a negative influence on the compaction degree. After detection, the index of the 1A-LMO sample and the LMO sample without modification are 2.91 and 2.97 g cm-3 respectively. The tiny reduction of degree for the coated sample suggests this coating has almost no effect on the compaction degree of the composite material.

Figure 3. SEM (A) and TEM (B and C) images of the 1A-LMO sample, HRTEM image of the LiMn2O4 grain and Al2O3 coating layer of the 1A-LMO sample (D).

Based on the results obtained and the research findings reported previously, the synthesis mode of the 3D hierarchical Al2O3 coating layer is proposed as shown in Figure 4. The 9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 28

aphanitic γ-AlOOH is block shape. In the layered crystal structure along with [010] orientation, octahedrons [Al (O, OH) 6] connect in a axis to form waved octahedral layer, and anion O2- is located at octahedral layers while OH- is on the top and bottom.

The layers

connect with each other are bound together by hydrogen bond.28,29 When the AlOOH particles are added into water, it becomes gelatinous status in situ coating on LiMn2O4 bulks by the adhesive property. In heating treatment, hydrogen bond linking the layers is destroyed along with the increasing temperature. The hydrogel aggregate is stripped to form nanosheets with suspended hydroxyls on the surface. As the temperature further increases, the AlOOH nanosheets lost hydroxyls to form Al2O3 on the surface. According to the rolling-up mechanism,30 the outer layers roll up due to high surface energy. As a result, the 3D hierarchical Al2O3 nanosheets are in situ self-assembled as a coating layer on LiMn2O4 bulks. Figure S1 further illustrates the change in which the granular AlOOH raw material was stripped into nanosheets through the sol-gel produce and heating treatment without LiMn2O4 grains' participation. As shown in Figure S1A, the AlOOH raw material shows spherical particles with a broad size distribution. After the sol-gel produce and heating treatment, the product present secondary particles assembled by the stripped Al2O3 nanosheets (see Figure S1B). From the TEM image of Figure S1C, the curling sheets irregularly piled in together driven by high surface energy and the absence of LMO bulks as matrix to attach.

10


Page 11 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. Scheme illustration of the synthesis of the Al2O3-coated LiMn2O4 sample.

The electrochemical properties of the bare LMO and Al2O3-coated LiMn2O4 samples were examined through galvanostatic charging-discharging cycling, CV and EIS tests using coin cells. Figure 5A presents the voltage profiles during the first charge/discharge cycle at a constant rate of 0.1 C with the voltage ranging from 3.0 to 4.3 V at 25 °C. The initial specific capacity for all the samples is similar. The three coated electrodes deliver slightly lower capacity than the uncoated LiMn2O4, because the mass of the inactive Al2O3 layer is also taken in count, not appropriate for improving the capacity. Rate measurement is conducted at the currents gradually increasing to 10 C and finally returning back to 0.1 C, as shown in Figure 5B. At the low rates tested less than 1 C, a large decrease in capacity is observed for the bare LMO sample even at room temperature attributed to the Jahn-Teller distortion occurring at the surface under nonequilibrium conditions.31 In the contrast, the coated samples do not show a commensurate fall in their capacity, and the 1A-LMO electrode with the coated amount of Al2O3 at 1 wt% exhibits the highest capacity while the 2 wt% coated Al2O3 electrode exhibits the highest relative rate capability. The superior retention capability is contributed to the coating improving the homogeneity of near-surface current density on the coated electrodes and the porous structure for the transfer of lithium ions between electrode and electrolyte. Moreover, when the current return back to 0.1 C, the capacity is reduced to 120.6 mAh g-1 and the fading is more than 10% for the LiMn2O4 without coating, due to the attack from the electrolyte. By contrast, the coated electrodes recover their capacity nearly equivalent to the initial value. For example the capacity of the 1A-LMO sample retains 97%. The effect of coating on capacity retention is apparent according to the result obtained from 11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

the cycling test at room and elevated temperatures. Suggested by Figure 5C of extended cycling up to 800 times at room temperature, a drastic reduction in specific capacity at 1 C is observed for the pristine LMO sample. The severe reduction is attributed to the dissolution of transition metals by HF attack and electrolyte decomposition may cause a rapid increase of the interfacial resistance thereby accelerates the capacity loss as cycling progresses. The 0.5A-LMO sample shows similar reduction to the pristine LMO sample, demonstrating the invisible effect of the low content of coating material. However, when the amount of the coating layer increases to 1 wt%, a straight line of capacity-cycling number suggests excellent capacity retention ratio. The capacity retains 89.8% after the 800th cycle at 1 C rate between 3.0 and 4.3 V, while the bare LMO and 2A-LMO samples suffered 45.0% and 35.6% capacity loss, respectively. It can be seen when the mass concentration of Al2O3 further increases to more than 1wt%, the capacity loss also undergoes a serious fading. According to the previous research conclusion, the reaction between HF acid and Al2O3 produces more water further exacerbating capacity fade. So the excessive Al2O3 nanosheet with large surface area boosts the negative side reaction. Moreover, high amount of Al2O3 tends to form thick coating layer on the surface of the bulk, negative to lithium ions transferring between electrode and electrolyte. However, for the 1A-LMO sample with a proper coating amount, the hierarchical nanosheets of metal oxide can sequester HF in electrolyte containing LiPF6, the rich pores improve the ionic conductivity of the coating layer and Al2O3 thin film close to the bulk does not strongly inhibit the electronic conductivity.32,33 The cyclic performance of all the materials was tested at a higher temperature (55℃) accelerating electrolyte decomposition and Mn dissolution process, which is crucial for large-scale applications in power batteries.34-36 From 12


Page 12 of 28

Page 13 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


the Figure 5D, it is noted that all the samples present more severe capacity damping, compared to the test at room temperature. It shows less than 70 mAh g-1 for the bare LMO just after the 300th cycle. Moreover, the smallest retention of 66.4% is delivered by the 0.5A-LMO sample with 0.5wt% Al2O3 coating material. Under a higher temperature, as the side reaction aggravated, the protective layer suffers stronger destroys. But the 1A-LMO sample shows better cycle stability and the retention retains more than 80% after 500 cycles. The proper coating amount can also suppresses the formation of the passive film of solid state electrolyte acting as a highly effective lithium ion conductor, which consequently helps enhance the rate capability at the elevated temperature.

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 5. Initial charge-discharge curve (a), rate (B) and cycling performances at 25℃ (C) and 55℃ (D) of the as-prepared 0.5A-LMO, 1A-LMO and 2A-LMO samples with different Al2O3 coating amounts. Figure 6A displays the CV curves conducted in the potential range of 3.3~4.3 V at a sweep rate of 0.1 mV s-1. As is shown, all samples present two pairs of separated cathodic/anodic peaks which content with regular LiMn2O4/Li profile, suggesting the Al2O3 coating does not change the insertion/extraction mechanism of lithium ions in spinel structure.37 The peaks at about 3.9/4.05 V are attributed to the insertion/extraction of Li+ from/into one half of the tetrahedral sites with Li-Li interaction and the peaks at about 4.1/4.2 V are attributed to the insertion/extraction of Li+ from/into the other half of the tetrahedral sites, without Li-Li interaction.38,39 The sample with the coating ratio 0.5wt% of Al2O3 is similar to the pristine LMO, while the samples of 1A-LMO and 2A-LMO with more Al2O3 coating exhibit higher peak current and sharper area. This demonstrates that the superior reversibility of ions and good diffusion through the interface between the electrolyte and electrodes, because of the rich diffusion channels for Li-ion supplied by the hierarchical and porous coating layer. On the other hand, the normalized sweeping area of 2A-LMO electrode is smaller than that of 1A-LMO sample. The reason is that the thicker Al2O3 layer blocks the Li-ion diffusion, leading to reduced utilization of the active material in cell operation.40 14


Page 14 of 28

Page 15 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. Cyclic voltammogram of the as-prepared 0.5A-LMO, 1A-LMO and 2A-LMO samples with different Al2O3 coating amount prepared at 500 ℃ for 4 h (A), EIS spectra of LMO, 0.5A-LMO, 1A-LMO and 2A-LMO samples (B), and 1A-LMO electrode (C) after the 1st, 3nd and 100th cycles, and the concentration comparison of Mn dissolved in 1 M LiPF6/(EC : DEC) from the LMO and 1A-LMO electrodes (D). EIS analysis is conducted on the cells to understand the beneficial effect of coating architecture on the electrochemical performance of LiMn2O4 materials. Figure 6B presents the Nyquist plots of the four electrodes after the first cycle of discharge at 0.1 C and fitting results is listed in Table S1. In general, the impedance spectra present two semicircles and a line inclined at constant angle to the real axis. The semi-circle at high frequency region is fit with a circuit model consisting of a resistor and capacitor expressed as Rsf and C1, representing the impedance owing to SEI film on the surface of the electrodes. The depressed semi-circle at the intermediate frequency is fitted with a resistor and constant-phase element 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

in parallel model expressed as Rct and CPE1. The Rct represents the charge transfer resistance in the interface of electrode and electrolyte. The slope in the low frequency region is due to lithium ion diffusion in the bulk material. Moreover, X-axis offset treated as Rs represents the impedance of electrolyte and the contact resistance at electrode/current-collector. As shown in the figure, the coating materials has nearly no influence on Rs. When the mass percent of Al2O3 is 0.5%, the protective layer does not coated the surface perfectly, the Rp (polarization resistance) is more than the value of the uncoated sample, which may be distributed to the low coating amount of Al2O3 just acting as an insulator. The 1A-sample shows the lowest Rp value, the porous structure is produced on the surface as the amount of the hierarchical sheets increases to 1 wt%, and the numerous pores formed offers large space for the storage of electrolyte, which is benefit to the transfer of charge and a more uniform current distribution provided by the nanoporous coating at the LiMn2O4 particle surface.21 However, the resistance increases for the 2A-LMO, which can be due to the increased coating layer. Figure 6C compares the Nyquist plots of the 1A-LMO sample after 1st, 3rd and 100th cycle at room temperature. The cycling times for the coated LiMn2O4 with 1wt% Al2O3 coating content also do not change the solution resistance. It is can be observed that the Rp has a large drop along with the increased cycling number. As known, the formation of the solid-state interface layer during cycling raises the impendence. In this regard, the coating is effective in restraining the process.41 Moreover, it is perhaps due to the removal of the unidentified phase in the pre-cycled electrode or due to the influence of a native passivation layer on the electrodes.42 The impendence reduction demonstrates an enhancement in the kinetics of the lithium-ion diffusion through the surface layer, and a consequent increases in rate capability. 16


Page 16 of 28

Page 17 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. FT-IR spectra of the LMO, 0.5A-LMO, 1A-LMO and 2A-LMO samples before (A) and after (B) cycling test.

FT-IR spectra are performed to explore the inter-action between Al2O3 layer and LiMn2O4 bulk and further prove that the protective effect of the coating layer on the electrode materials. Two distinct and broad absorption bands, caused by the Mn-O stretching vibration of MnO6 octahedron are observed in FT-IR spectra for all samples,43 as shown in Figure 7A. The bands of the four samples at 612 and 512 cm-1 assign to the asymmetrical stretching vibration of Mn(Ⅳ)-O and Mn(Ⅲ)-O respectively. The peak shapes of the Al2O3-coated LiMn2O4 become more subdued as the concentration of coating material increases, suggesting the Al2O3 coating effectively on the surface of the active material. Moreover, the IR bands for the Al2O3-coated LiMn2O4 samples prepared with various concentration of coating layer shift slightly toward a higher wave number than the pure LiMn2O4. This blue shift may be contributed to the reason that a little amount of aluminum ions penetrate into the spinel structure on the surface, which decreases the average bond length of Mn-O and strengthens the surface stability of structure.44 In contrast to the curves of the samples before cycling, a dramatic change happens to the ones after cycling. As shown Figure 7B, the curve of LMO turns to be more gentle due to the inconspicuous peaks of asymmetrical stretching vibrations 17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

for Mn(Ⅳ)-O and Mn(Ⅲ)-O. To the contrary, the coated samples show more sharp shape of the two peaks than the ones before cycling, suggesting the crystal structure of the surface is preserved well by the protective layer. The result of ICP-AES test reveals the solution amount of Mn ions are 69.4 and 4.44 ppm from the cathodes of LMO and 1A-LMO respectively, after 500 cycles at elevated temperature (see Figure 6D). Both the changes of the FT-IR curves and the ICP result reveal that the electrolyte has a significant damage to the structure on the surface while the coating plays an important role in protecting the structure stability. Figure 8 shows more intuitive observation of the protective effect of the coating on the LiMn2O4 after long-term cycle. As shown in Figure 8A, the pristine LMO grains are glued together, the smooth surface become very rough, and the sharp edge disappear. All of the morphology changes reveal a serious destroy of the LiMn2O4 by electrolyte. It is interesting that the sample with 0.5 wt% coating amount becomes smooth and the edge appears clear, but the coating layer disappears as shown in Figure 8B. For the samples with more coating materials of Al2O3, a residual coating layer with similar morphology to the initial appearance is left. There is a thin film wrapping on the surface and the wrapping film is encrusted with some incomplete fragments of the 1A-LMO sample, while a compact layer covers the secondary particles of the 2A-LMO sample (Figure 8C and D). Combined with the morphologies shown by the SEM images before cycling, it can be deduced that the nanosheets of the outer coating layer is consumed in the reaction with electrolyte, and some new phases are formed at the inner film.

18


Page 18 of 28

Page 19 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. SEM images of the LMO (A), 0.5A-LMO (B), 1A-LMO (C) and 2A-LMO (D) samples after 800 cycles at 1 C.

Figure 9. Al 2p XPS peak comparing the Al2O3-coated samples of 1A-LMO before (A) and after (B) cycling.

Further investigation to the phase in the thin film on the surface was determined by X-ray photoelectron spectroscopy (XPS). Figure 9 shows the Al 2p photoelectron peaks of the Al2O3-coated samples of 1A-LMO before and after cycling. A single well defined peak of the binding energy at ~73.2 eV is identified in the Al 2p region before electrochemical cycling (Figure 9A). Then the peak shifts to higher binding energy of 74.6 eV after 800 cycles, as 19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

shown in Figure 9B. It suggests that there may be a chemical binding change after long electrochemical cycling. The spectra present two Al 2p major peaks: the one at 74.7 eV is assigned to Al-F, Al-O is responsible for the other one at 73.4 eV. It is supported by observing the relative intensity of the assumed Al-F and Al-O peaks that some compounds of fluorine oxygen are formed, which further proves protective coating material can gobble up HF effectively. In addition, the products may react with the inner Al2O3 to yield some fluorine oxygen compound which stops the vicious cycling reaction of Al2O3 with HF, so the reaction cannot produce more H2O.45 Sun et al observed another weak peak assigned to LiAlO2 in synchrotron based XPS spectra for sulfur electrode after cycling coated by ALD deposited Al2O3. It has been reported that the formed fluorine oxygen and Li-Al-O compounds are favorable to the ionic conductivity and enhance the Li ion diffusion.3, 46, 47 This conclusion also illustrates the improved rate performance of the coated electrodes.

4. CONCLUSION A novel and effective Al2O3 coating was realized by a facile stripping and heat-treatment route for large-scale production. In preparation of coating, the stripped ultrathin Al2O3 nanosheets from boehmite (AlOOH) particles forms 3D hierarchical coating structure by in-situ self-assembled approach. The uniform flower-like Al2O3 coating layer with high specific area largely sequesters acidic species produced by side reaction and reduces the attack of the acid to the active material. The protective layer closely wraps the spinel LiMn2O4 bulk with the bonding effect of AlOOH precursor and thus effectively inhibits the dissolution of Mn by suppressing directive contact with electrolyte to enhance cycling stability. In addition, the capacity and rate performance are further improved because of the 20


Page 20 of 28

Page 21 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


better electrolyte storage within the rich pores left by the assembled hierarchical architecture, as well as the produced formed fluorine oxygen and Li-Al-O compounds. The electrochemical results reveal the as-prepared sample exhibits supervisor cycle stability under room temperature even at elevated temperature. The initial specific discharge capacity is 128.5 mAh g-1 at 0.1 C and remains 89.8% of the initial capacity after 800 cycles at 1 C rate. When cycling at 55 °C, the composite shows 93.6% capacity retention after 500 cycles. This facile surface modification with low-cost starting material and effective structure of coating layer can be adopted to enhance the cycling performance and thermal stability of other electrode materials, for which Al2O3 plays its role. AUTHOR INFORMATION Corresponding Author [email protected] (Q. Li), Tel: +86-773-5856104; [email protected] (S. Hu), Tel: +86-713-8833119. Notes The authors declare no competing financial interest. ACKNOWLEDGEMENTS F. Y. Lai and X. H. Zhang contributed equally to this work. This research was supported by the National Natural Science Foundation of China (U1401246, 21473042, 51474110 and 51474077) and the Provincial Natural Science Foundation of Guangxi (2013GXNSFDA019027). REFERENCES (1) Evarts E.C. Lithium Batteries: To the Limits of Lithium Nature 2015, 526, S93-S95. 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(2) Ren, J.; Zhang, Y.; Bai, W.; Chen, X.; Zhang, Z.; Fang, X.; Weng, W.; Wang, Y.; Peng, H. Elastic and Wearable Wire-Shaped Lithium-Ion Battery with High Electrochemical Performance Angew. Chem. Int. Edit. 2014, 53, 7864-7869. (3) Xiao, X.; Lu, P.; Ahn, D. Ultrathin Multifunctional Oxide Coatings for Lithium Ion Batteries Adv. Mater. 2011, 23, 3911-3915. (4) Sun, W.; Liu, H.; Liu, Y.; Bai, G.; Liu, W.; Guo, S.; Zhao, X. Z. A General Strategy to Construct Uniform Carbon-Coated Spinel LiMn2O4 Nanowires for Ultrafast Rechargeable Lithium-Ion Batteries with A Long Cycle Life Nanoscale 2015, 7, 13173-13180. (5) Tang, D.; Sun, Y.; Yang, Z.; Ben, L.; Gu, L.; Huang, X. Surface Structure Evolution of LiMn2O4 Cathode Material upon Charge/Discharge Chem. Mater. 2014, 26, 3535-3543. (6) Zhao, J.; Wang, Y. Atomic Layer Deposition of Epitaxial ZrO2 Coating on LiMn2O4 Nanoparticles for High-Rate Lithium Ion Batteries at Elevated Temperature Nano Energy 2013, 2, 882-889. (7) Wen, W.; Ju, B.; Wang, X.; Wu, C.; Shu, H.; Yang, X. Effects of Magnesium and Fluorine Co-Doping on the Structural and Electrochemical Performance of the Spinel LiMn2O4 Cathode Materials. Electrochim. Acta 2014, 147, 271-278. (8) Kim, K.C.; Jegal, J.-P.; Bak, S.-M.; Roh, K.C.; Kim, K.-B. Improved High-Voltage Performance of FePO4-Coated LiCoO2 by Microwave-Assisted Hydrothermal Method Electrochem. Comm. 2014, 43, 113-116. (9) Tang, W.; Liu, L.; Zhu, Y.; Sun, H.; Wu, Y.; Zhu, K. An Aqueous Rechargeable Lithium Battery of Excellent Rate Capability Based on a Nanocomposite of MoO3 Coated with PPy and LiMn2O4 Energy Environ. Sci. 2012, 5, 6909-6913. (10) Kitta, M.; Akita, T.; Kohyama, M. Preparation of A Spinel LiMn2O4 Single Crystal Film from A MnO 22


Page 22 of 28

Page 23 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Wafer. J. Power Sources 2013, 232, 7-11. (11) Jing, H.-K.; Kong, L.-L.; Liu, S.; Li, G.-R.; Gao, X.-P. Protected Lithium Anode with Porous Al2O3 Layer for Lithium-Sulfur Battery. J. Mater. Chem. 2015, 3, 12213-12219. (12) Zhao, J.; Wang, Y. Surface Modifications of Li-Ion Battery Electrodes with Various Ultrathin Amphoteric Oxide Coatings for Enhanced Cycleability J. Solid State Electrochem. 2012, 17, 1049-1058. (13) Kannan, A.M.; Manthiram, A. Surface/Chemically Modified LiMn2O4 Cathodes for Lithium-Ion Batteries. Electrochem. ST. 2002, 5, A167-A169. (14) Wang, Y.; Cao, G. Developments in Nanostructured Cathode Materials for High-Performance Lithium-Ion Batteries Adv. Mater. 2008, 20, 2251-2269. (15) Guan, D.; Jeevarajan, J. A.; Wang, Y. Enhanced Cycleability of LiMn2O4 Cathodes by Atomic Layer Deposition of Nanosized-Thin Al2O3 Coatings Nanoscale 2011, 3, 1465-1469. (16) Sun, Y.K.; Lee, M.J.; Yoon, C.S.; Hassoun, J.; Amine, K.; Scrosati, B. The Role of AlF3 Coatings in Improving Electrochemical Cycling of Li-Enriched Nickel-Manganese Oxide Electrodes for Li-ion Batteries Adv. Mater. 2012, 24, 1192-1196. (17) Shi, T.; Dong, Y.; Wang, C.-M.; Tao, F.; Chen, L. Enhanced Cycle Stability at High Rate and Excellent High Rate Capability of La0.7Sr0.3Mn0.7Co0.3O3-Coated LiMn2O4 J. Power Sources 2015, 273, 959-965. (18) Lee, K.-S.; Myung, S.-T.; Bang, H.; Amine, K.; Kim, D.-W.; Sun, Y.-K. Effect of Protecting Metal Oxide (Co3O4) Layer on Electrochemical Properties of Spinel Li1.1Mn1.9O4 as A Cathode Material for Lithium Battery Applications J. Power Sources 2009, 189, 494-498. (19) Yan, D.-J.; Zhu, X.-D.; Wang, K.-X.; Gao, X.-T.; Feng, Y.-J.; Sun, K.-N.; Liu, Y.-T. Facile and Elegant Self-Organization of Ag Nanoparticles and TiO2 Nanorods on V2O5 Nanosheets as A Superior Cathode Material for Lithium-Ion Batteries J. Mater Chem. A 2016, 4, 4900-4907. 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 28

(20) Kim, K. J.; Kwon, H. K.; Park, M. S.; Yim, T.; Yu, J. S.; Kim, Y. J. Ceramic Composite Separators Coated with Moisturized ZrO2 Nanoparticles for Improving the Electrochemical Performance and Thermal Stability of Lithium Ion Batteries Phys. Chem. Chem. phys. 2014, 16, 9337-9343. (21) Walz, K.A.; Johnson, C.S.; Genthe, J.; Stoiber, L.C.; Zeltner, W.A.; Anderson, M.A.; Thackeray, M.M. Elevated Temperature Cycling Stability and Electrochemical Impedance of LiMn2O4 Cathodes with Nanoporous ZrO2 and TiO2 Coatings J. Power Sources 2010, 195, 4943-4951. (22) Kim, J. S.; Johnson, C. S.; Vaughey, J. T.; Hackney, S. A.; Walz, K. A.; Zeltner, W. A.; Anderson, M. A.; Thackeray, M. M. The Electrochemical Stability of Spinel Electrodes Coated with ZrO2, Al2O3, and SiO2 from Colloidal Suspensions. J. Electrochem. Soc 2004, 151, A1755-A1761. (23) Li, X.; Liu, J.; Banis, M. N.; Lushington, A.; Li, R.; Cai, M.; Sun, X. Atomic Layer Deposition of Solid-State Electrolyte Coated Cathode Materials with Superior High-.Voltage Cycling Behavior for Lithium Ion Battery Application Energy Environ. Sci. 2014, 7, 768-778. (24) Han, X.; Liu, Y.; Jia, Z.; Chen, Y.C.; Wan, J.; Weadock, N.; Gaskell, K.J.; Li, T.; Hu, L. Atomic-Layer-Deposition Oxide Nanoglue for Sodium Ion Batteries Nano lett. 2014, 14, 139-147. (25) Thackeray, M.M.; Kang, S.-H.; Johnson, C.S.; Vaughey, J.T.; Benedek, R.; Hackney, S.A. Li2MnO3-Stabilized LiMO2 (M = Mn, Ni, Co) Electrodes for Lithium-Ion Batteries J. Mater Chem. 2007, 17, 3112-3115. (26) Kang,

S.-H.;

Thackeray,

M.

M.

Enhancing

the

Rate

Capability

of

High

Capacity

xLi2MnO3·(1−x)LiMO2 (M=Mn, Ni, Co) Electrodes by Li–Ni–PO4 Treatment 2009, 11, 748-751. (27) 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. 24


Page 25 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(28) Vogels, R.J.M.J.; Kloprogge, J.T.; Buining, P.A.; Seykens, D.; Jansen, J.B.H.; Geus J.W. The Tridecameric Aluminum Complex as An Appropriate Precursor for Fibrous Boehmite A27Al NMR Study on the Partial Hydrolysis of Aluminum Sec-Butoxide J of Non-Cryst. Solids 1995, 191, 38-44. (29) Bi, S.; Wang, C.; Cao, Q.; Zhang, C. Studies on the Mechanism of Hydrolysis and Polymerization of Aluminum Salts in Aqueous Solution: Correlations Between the “Core-Links” Model and “Cage-Like” Keggin-Al13 Model Coordination Chem. Rev. 2004, 248, 441-455. (30) Zhu, W.; Zhu, S.; Xiang, L. Successive Effect of Rolling Up, Oriented Attachment and Ostwald Ripening on the Hydrothermal Formation of Szaibelyite MgBO2(OH) Nanowhiskers CrystEngComm 2009, 11, 1910-1919. (31) Thackeray, M.M.; Shao-Horn, Y.; Kahaian, A.J.; Kepler, K.D.; Skinner, E.; Vaughey, J.T.; Hackney, S.A. Structural Fatigue in Spinel Electrodes in Hihg Voltage (4V) Li/LixMn2O4 Cells Electrochem. Solid ST. 1998, 1, 7-9. (32) Jung, S.C.; Han, Y.-K. How Do Li Atoms Pass Through the Al2O3 Coating Layer During Lithiation in Li-Ion Batteries? J. Phys. Chem. Lett. 2013, 4, 2681-2685. (33) Morales, J.; Trócoli, R.; Franger, S.; Santos-Peña, J. Cycling-Induced Stress in Lithium Ion Negative Electrodes: LiAl/LiFePO4 and Li4Ti5O12/LiFePO4 Cells. Electrochim. Acta 2010, 55, 3075-3082. (34) Zhang, W.; Chi, Z.X.; Mao, W.X.; Lv, R.W.; Cao, A.M.; Wan, L.J. One-Nanometer-Precision Control of Al2O3 Nanoshells Through A Solution-Based Synthesis Route Angew. Chem. Int. Edit. 2014, 53, 12776-12780. (35) Qiu, B.; Wang, J.; Xia, Y.; Wei, Z.; Han, S.; Liu Z. Enhanced Electrochemical Performance with Surface Coating by Reactive Magnetron Sputtering on Lithium-Rich Layered Oxide Electrodes ACS Appl. Mater. Inte. 2014, 6, 9185-9193. 25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(36) Scott, I.D.; Jung, Y.S.; Cavanagh, A.S.; Yan, Y.; Dillon, A.C.; George, S.M.; Lee, S.H. Ultrathin Coatings on Nano-LiCoO2 for Li-Ion Vehicular Applications Nano Lett. 2011, 11, 414-418. (37) Cho, J.; Kim, Y. J.; Kim, T.-J.; Park, B. Zero-Strain Intercalation Cathode for Rechargeable Li-Ion Cell Angew. Chem. Int. Edit. 2001, 40, 3367-3369. (38) Wang, R.; Li, X.; Wang, Z.; Guo, H. Manganese Dissolution from LiMn2O4 Cathodes at Elevated Temperature: Methylene Methanedisulfonate as Electrolyte Additive J. Solid State Electrochem. 2015, 20, 19-28. (39) Zhu, C.; Saito, G.; Akiyama, T. A New CaCO3-Template Method to Synthesize Nanoporous Manganese Oxide Hollow Structures and Their Transformation to High-Performance LiMn2O4 Cathodes for Lithium-Ion Batteries J. Mater. Chem. A 2013, 1, 7077-7082. (40) Hu, D.-H.; Zhao, S.-X.; Deng, Y.-F.; Nan, C.-W. Synthesis and Electrochemical Performance of Rod-Like Spinel LiMn2O4 Coated by Li–Al–Si–O Solid Electrolyte J. Mater. Chem. A 2013, 1, 14729-14735. (41) Lin, H. B.; Hu, J. N.; Rong, H. B.; Zhang, Y. M.; Mai, S. W.; Xing, L. D.; Xu, M. Q.; Li, X. P.; Li, W. S Porous LiMn2O4 Cubes Architectured with Single-Crystalline Nanoparticles and Exhibiting Excellent Cyclic Stability and Rate Capability as the Cathode of A Lithium Ion Battery J. Mater. Chem. A 2014, 2, 9272-9279. (42) Li, X.; Liu, J.; Wang, B.; Banis, M. N.; Xiao, B.; Li, R.; Sham, T.-K.; Sun, X. Nanoscale Stabilization of Li–Sulfur Batteries by Atomic Layer Deposited Al2O3. RSC Adv. 2014, 4, 27126. (43) Kim, W.-K.; Han, D.-W.; Ryu, W.-H.; Lim, S.-J.; Kwon, H.-S. Al2O3 Coating on LiMn2O4 by Electrostatic Attraction Forces and Its Effects on the High Temperature Cyclic Performance. Electrochim. Acta 2012, 71, 17-21. 26


Page 26 of 28

Page 27 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(44) Waller, G.H.; Brooke, P.D.; Rainwater, B.H.; Lai, S.Y.; Hu, R.; Ding, Y.; Alamgir, F.M.; Sandhage, K.H.; Liu, M.L. Structure and Surface Chemistry of Al2O3 Coated LiMn2O4 Nanostructured Electrodes with Improved Lifetime J. Power Sources 2016, 306, 162-170. (45) Ammundsen, B.; Burns, G. R.; Islam, M. S.; Kanoh, H.; Roziere, J. Lattice Dynamics and Vibrational Spectra of Lithium Manganese Oxides: A Computer Simulation and Spectroscopic Study. J. Phys. Chem. B 1999, 103, 5157-5180. (46) Li, X.; Xu, Y.; Wang, C. Suppression of Jahn–Teller Distortion of Spinel LiMn2O4 Cathode J Alloy Compd 2009, 479, 310-313. (47) Xiong, L.; Xu, Y.; Tao, T.; Du, X.; Li, J. Double Roles of Aluminium Ion on Surface-Modified Spinel LiMn1.97Ti0.03O4 J Mater. Chem. 2011, 21, 4937-4944.

27



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Graphical Abstract


Page 28 of 28

Three-Dimension Hierarchical Al2O3 Nanosheets ... - ACS Publications

Recommend Documents