Significant Improvement on Electrochemical Performance of LiMn2O4

Subscriber access provided by Kaohsiung Medical University

Article

Significant Improvement on Electrochemical Performance of LiMn2O4 at Elevated Temperature by Atomic Layer Deposition of TiO2 Nanocoating Congcong Zhang, Junming Su, Tao Wang, Kaiping Yuan, Chunguang Chen, Siyang Liu, Tao Huang, Jian-Hua Wu, Hongliang Lu, and Aishui Yu ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b01081 • Publication Date (Web): 01 May 2018 Downloaded from http://pubs.acs.org on May 4, 2018

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 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 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.

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 37 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 Sustainable Chemistry & Engineering

Significant Improvement on Electrochemical Performance of LiMn2O4 at Elevated Temperature by Atomic Layer Deposition of TiO2 Nanocoating Congcong Zhang,† Junming Su,† Tao Wang,‡ Kaiping Yuan,‡ Chunguang Chen,† Siyang Liu,† Tao Huang,† Jianhua Wu,§ Hongliang Lu,*,‡ and Aishui Yu*,† †

Laboratory of Advanced Materials, Department of Chemistry, Shanghai Key Laboratory of

Molecular Catalysis and Innovative Materials, Collaborative Innovation Center of Chemistry for Energy Materials, Institute of New Energy, Fudan University, NO. 2205, Songhu Road, Yangpu District, Shanghai 200438, China ‡

State Key Laboratory of ASIC and System, Shanghai Institute of Intelligent Electronics &

Systems, School of Microelectronics, Fudan University, No. 220, Handan Road, Shanghai 200433, China §

Jiangmen KanHoo Industry Co., Ltd., NO. 22, South Jiaoxing Road, Jianghai District, Jiangmen

City, Guangdong 529040, China

*Corresponding author: Phone: +86-21-51630320. Fax: +86-21-51630320. E-mail: [email protected] Phone: +86-21-65642457. Fax: +86-21-65642457. E-mail: [email protected]

1 ACS Paragon Plus Environment

ACS Sustainable Chemistry & Engineering 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

Abstract: Spinel LiMn2O4 cathode is considered as a promising cathode material for lithium ion batteries. Unfortunately, the poor capacity stability, especially at elevated temperature, hinders its practical utilization. In this study, atomic layer deposition (ALD) technique is employed to deposit TiO2 nanocoating on LiMn2O4 electrode. To maintain electrical conductivity, this amorphous coating layer with high uniformity, conformity and completeness is directly coated on cathode electrodes instead of LiMn2O4 particles. Among all the samples studied, TiO2-coated sample with 15 ALD cycles exhibits the best cyclability at both room temperature of 25 °C and elevated temperature of 55 °C, and has the higher specific capacity of 136.4 mAh g-1 at 0.1 C that is nearly close to theoretical capacity of LiMn2O4. Meanwhile, this sample realizes lower polarization and less self-discharge. The improved electrochemical performance is ascribed to the high conformal and ultrathin TiO2 coating, which enhances the kinetics of Li+ diffusion and stabilizes electrode/ electrolyte interface. Besides, the deconvolution of Ti 2p X-ray photoelectron spectroscopy appears a weaker peak of Ti−O−F after cycling, which indicates that the coexistence of TiO2 and TiOxFy layer can inhibit Mn dissolution and electrolyte decomposition. Keywords: Lithium ion batteries; Spinel LiMn2O4; Atomic layer deposition; TiO2 nanocoating; Improved electrochemical performance Introduction To preserve environment and reduce the global dependence on nonrenewable energy sources, rechargeable lithium-ion batteries (LIBs) with superior energy density and high power density are considered the most attractive energy storage system and have 2 ACS Paragon Plus Environment

Page 2 of 37

Page 3 of 37 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


gained widespread attention from both industry and government funding agencies in recent years.1-3 In addition to energy and power density, thermal stability, safety and cost are also key factors in choosing cathode materials.4,5 As is known, spinel lithium manganese oxide (LiMn2O4) is one of the most promising candidates because of its nonpoisonous character, lower cost, great rate capability and higher thermal stability compared with layered lithium metal oxides (LiMO2, M = Ni, Mn, and Co).6,7 The main obstacle to its commercialization is the capacity fading during cycling, which is well known to be associated with the dissolution of Mn into electrolyte through disproportion reaction (2Mn3+ → Mn2+ ＋ Mn4+), irreversible phase transformation from cubic to tetragonal symmetry by Jahn−Teller effect of Mn3+ ions with high spin, and the decomposition of electrolyte on the electrode surface.7-9 Besides, elevated temperature will exacerbate the capacity decay due to the enhancement of one or more issues mentioned above. Significant efforts have been used to overcome these drawbacks, one of which is surface modification by coating different kinds of materials such as metal oxides,6,10,11 fluorides,12−14 and phosphates.15−17 These coating layers are attempted to serve as an HF scavenger that reduces Mn dissolution or a physical protection barrier that retards side reactions between active materials and electrolyte.18 Conventional coating methods such as wet-chemical process require large amount of solvents and a postheating treatment, resulting in rough coatings that lack of uniformity, conformity, and completeness or core-shell structure coatings that are too thick to impede Li+ diffusion.19,20 Fortunately, these problems can be solved by employing the scalable 3 ACS Paragon Plus Environment


atomic layer deposition (ALD) technique. ALD is a surface-controlled method that relies on two sequential, self-terminating half-reactions. The deposition procedure requires only a minimal amount of precursor and much lower growth temperature.21 One of the distinguishing advantages of ALD is its unique capability to deposit high conformal and uniform coatings on both composite electrodes and particles with controllable nanometer-level thickness.22−24 Therefore, the ultrathin ALD layer cannot block original electrical pathways but rather facilitates Li+ diffusion. More recently, significant effort has been focused on ALD coatings onto cathode, anode, separator and electrolyte to improve performance of LIBs and supercapacitors.25 The coating materials are mainly metal oxides including Al2O3,10 ZrO2,20 and TiO2.26−30 Because TiO2 has great stability and special channels storing Li+, a few of studies have paid attention to TiO2 ALD coating layers, such as LiCoO2,20 LiNi0.8Co0.15Al0.05O2,27 Li1.2Ni0.13Mn0.54Co0.13O2,28 LiMn2O4,29 and carbon nanotubes.30,31 After surface modification, the electrochemical performance of TiO2 ALD coated materials receive great improvements. Up to now, there are two modes of ALD technology, applying an ALD coating to powders of active materials or directly to a fabricated electrode. Considering the practical application, coating on electrode by a rotary reactor is convenient and could achieve maximum production. For powers coating by fluidized bed technology, more efforts are required to raise production capacity. In terms of action mechanism, it is also more effective for electrode coating. When the whole powers are deposit by dense coatings, especially for the insulating layer, ion diffusion and electron transport 4 ACS Paragon Plus Environment

Page 4 of 37

Page 5 of 37 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


would be obstructed. Conversely, when ALD is applied to the composite electrode, coating layer is not deposited at contact points between active material particles and current collector, which maintains electric conductivity and enables rapid electron transport.32,33 Therefore, in this paper, we deposit amorphous TiO2 nanocoating with different thickness on LiMn2O4 electrode by ALD technique. By taking advantage of the amorphous phase and atomic-level thickness, we significantly improve the electrochemical properties of LiMn2O4 at both room and elevated temperature, in terms of cycling stability, rate capability, polarization, and self-discharge performance. And the influence of TiO2 ALD coating layer on LiMn2O4 electrode is studied in detail. Experimental Section Preparation of LiMn2O4 electrode. For the preparation of working electrode, 80 wt % LiMn2O4 (LMO; Carus Chemical Company), 10 wt % carbon conductive agents (Super P) and 10 wt % polyvinylidene fluoride (PVDF) as a binder were all dissolved in N-methyl-pyrolline

solvent. The resultant slurry was compressed onto the

aluminum-foil current collector using AFA-automatic film applicator with a thickness of 150 µm and then dried overnight at 80 °C in a vacuum oven. Finally, the dried film was pressed by passing through a rolling mill before depositing the TiO2 layer. TiO2 coating on LiMn2O4 electrode via atomic layer deposition. TiO2 layer was directly deposited on as-prepared LMO electrode using ALD reactor (Beneq TFS-200), with tetrakis (dimethylamino) titanium (TDMAT) and water as precursors, and N2 as the carrier. To avoid decomposition of the PVDF, a low operation 5 ACS Paragon Plus Environment


temperature of 120 °C was used. A typical TiO2 ALD reaction consists of the following steps: (1) pulsing TDMAT for 500 ms, (2) purging the residual precursor and by-products with N2 for 3 s, (3) pulsing deionized water for 500 ms, and (4) purging the residual precursor and by-products with N2 for 3 s. The thickness of the TiO2 films were controlled by varying ALD cycles mentioned above, and 10, 15, 40 and 100 ALD cycles were applied on LMO electrodes, marked as 10-ALD, 15-ALD, 40-ALD and 100-ALD, respectively. Synthesis of TiO2-coated LiMn2O4 particles by sol-gel method. 3 wt% TiO2-coated LiMn2O4 particles were synthesized by sol-gel method as we reported in a previous paper.6 Before electrochemical measurements, particles were made into working electrodes with the same procedure mentioned in section 2.1. Characterization. The crystalline structure and morphology of electrodes were characterized by X-ray diffraction (XRD) on a Bruker D8 Advance X-ray diffractometer equipped with Cu Kα radiation (λ = 1.5406Å), high resolution transmission electron microscopy (HRTEM; JEOL JEM-2100F; Japan) and feild-emission scanning electron microscopy (FE-SEM; Hitachi S-4800; Japan). Energy-dispersive X-ray spectroscopy (EDX, Hitachi S-4800) was used to determine the proportion of Mn, Ti and O, and elemental mapping (EM) was conducted by the same instrument. Inductively coupled plasma-atomic emission spectrometry (ICP-AES; Thermo Scientific E.IRIS Duo; Waltham, MA) was used to measure the content of Mn. The surface chemical compositions of the samples were measured by X-ray photoelectron spectroscopy (XPS; ESCA PHI500C) with Al Kα radiation (hν 6 ACS Paragon Plus Environment

Page 6 of 37

Page 7 of 37 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


=1486.6 eV), and all the spectra were calibrated with C 1s peak at 284.8 eV. Electrochemical measurements. Before evaluating electrochemical performance, TiO2- decorated electrodes were cut into wafers with a diameter of 12 mm, and further dried at 80 °C for 12 h under vacuum. Then, coin cells with CR2016 configuration were assembled in an argon-filled glove box (Mikrouna, Superstar 1220/750/900; China) with the moisture and oxygen being controlled below 0.1 ppm, using Li metal as anode, Celgard 2300 as separator and 1 M LiPF6 dissolved in ethylene carbonate and diethyl carbonate (EC:DEC =1:1 w/w) as electrolyte. The galvanostatic charge-discharge measurements were performed on battery test system (Land CT2001A, Wuhan Jinnuo Electronic Co. Ltd., China) between 3.0 and 4.5 V (vs. Li+/Li) at both 25 and 55 °C. EIS measurements were performed on a Zahner IM6 electrochemical workstation (Zahner-Elektrik GmbH & Co. KG, Kronach, Germany), and an AC voltage of 5 mV amplitude was applied over a frequency range from 100 kHz to 10 mHz at the open circuit potential after various charge-discharge cycles. The EIS results were simulated using ZView software. Results and discussion Figure 1 illustrates the procedure of depositing TiO2 layer on LMO electrode surface via ALD technique, with two self-terminating gas-solid surface reactions as follows:34 TiOH* ＋ Ti[N(CH3)2]4 (g) → Ti−O−Ti[N(CH3)2]3* ＋ HN(CH3)2 (g)

(1)

Ti−O−Ti[N(CH3)2]3* ＋ 2H2O (g) → Ti−TiO2－OH* ＋ 3HN(CH3)2 (g)

(2)

Before the titanium source precursor TDMAT is forced into the reaction chamber, the surface of LMO electrode is hydroxylated by prepulsed water vapor to initiate the 7 ACS Paragon Plus Environment


reaction. The hydroxyl groups then react with TDMAT via chemical adsorption. In this half-reaction, only one Ti−[N(CH3)2]3 monolayer forms on the surface of electrode. Further physisorbed layers and by-products of one alkylamine molecule is purged by a N2 flow before the other reactant is transported. For the second half-reaction, the water molecule, as the oxygen source, reacts with Ti−[N(CH3)2]3 monolayer to produce target TiO2 and new reactive sites. Redundant reactant and by-products are purged out the reactor by a pure N2 flow again. By repeating the sequential half reactions, the ultrathin TiO2 coating layers formed on LMO electrode surface in a layer-by-layer manner. Hence, the thickness can be tuned by varying growth cycles and precisely controlled down to nanometer scale. Because of the hydrophobic selection property of the PVDF binder, TiO2 mainly grows on LMO particles and Super P which have −OH groups to react with the titanium precursor.35

Figure 1. Schematic illustration for TiO2 layer deposited on LMO electrode surface via ALD technique. 8 ACS Paragon Plus Environment

Page 8 of 37

Page 9 of 37 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 2(a) shows XRD patterns of the pristine and TiO2-coated LMO electrodes with different ALD cycles. All distinct XRD peaks are sharp after surface modification, indicating that the tested samples are well crystallized. Besides, TiO2-coated samples also reveal a spinel cubic structure with an Fd3m space group (JCPDS: 88−1749) as the pristine LMO, indicating that ALD procedure could not change the crystal structure of the substrate material because of the ultrathin nature of coating layer.36 Meanwhile, no extra peak is observed even when 100 TiO2 ALD layers are formed on LMO electrode, which may be attributed to the amorphous TiO2 phase. Generally, the anatase TiO2 crystalline phase could be formed with deposition temperatures >160 °C, whereas the amorphous phase can be formed at 100−140 °C.30 Due to the lower reaction temperature of 120 °C, the coating layer in this paper is undoubtedly amorphous and will be proved further by TEM images. Furthermore, the enlarged (111) diffraction peak remains in almost the same position, suggesting that the lattice parameter of LMO has no visible change after ALD coating. XPS measurements are further carried out to confirm the presence of TiO2 on the LMO electrode surface. As shown in Figure 2(b), peaks of Li 1s, Mn 2p, O 1s, C 1s, and F 1s stem from LMO particles, conductive agent and PVDF binder, respectively. Noticeably, the spectra of Ti 2p3/2 and Ti 2p1/2 peaks located at 459.2 and 464.9 eV are observed on 15-ALD, which are assigned to Ti−O chemical bond of TiO2 according to the previous report.30 This observation verifies that TiO2 layer is deposited successfully onto the surface of LMO electrode, whereas the Ti element is not detected on the pristine sample. Figure 2(c) shows that the intensity of Ti 2p peaks 9 ACS Paragon Plus Environment


enhances as ALD cycles increase from 10 to 100. Further, Figure S1 and Table S1 shows linear increase between the Ti signal and ALD coating number (from 10 to 40), exhibiting the advantage of precisely controlling thickness of the coating layer by adjusting ALD cycles. Because XPS test mainly gives the surface information within nanometer scale, the rational explanation for the nonlinear increase of 100-ALD is that the thickness of coating layer exceeds the detection limit. Conversely, the peaks of Mn 2p3/2 and 2p1/2 rapidly attenuate in intensity with increasing TiO2 thickness due to the lower weight ratio of Mn element near the outer surface [Figure 2(d)]. The Mn signal of 100-ALD even disappears, which is caused by the detection limit as well. Additionally, the Mn 2p peaks of the coated samples shift to lower binding energies, which may be ascribed to the presence of TiO2 layer that changes the chemical environment of outer surface of spinel particles.37 Taken together, the variation of intensity and binding energy for Ti 2p and Mn 2p peaks clearly proves the presence of TiO2 layer on LMO electrodes with precise thickness controlled by ALD.


Page 10 of 37

Page 11 of 37 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 2. (a) XRD patterns of the pristine and TiO2-coated LMO electrodes with different ALD cycles. The right inset is the enlarged (111) diffraction of (a) and the special symbol◆ is the diffraction signal for Al collector; (b) XPS survey scans for the pristine and 15-ALD; XPS spectra of (c) Ti 2p and (d) Mn 2p peaks for the pristine and TiO2-coated LMO electrodes with different ALD cycles. SEM images of pristine electrode and 100-ALD were collected to study the morphology variation after TiO2 coating. As exhibited in Figure 3(a) and (b), the commercial LMO powders, which consist of a large amount of primary particles with a diameter of 80–100 nm, are mixed with conductive agent to fabricate LMO electrode. Other than becoming a little coarser, the coated electrode preserves the similar morphology and size with pristine sample, implying that the TiO2 ALD layer 11 ACS Paragon Plus Environment


is ultrathin and conformal. Figure S2 shows elemental mapping of three elements for 100-ALD, with Ti element uniformly distributed, demonstrating the high uniformity of TiO2 nanocoating. Compared with the HRTEM image of pristine LMO in Figure 3(c), a conformal and complete layer is covered on the outer surface of 100-ALD [Figure 3(d)], as marked by the blue line. The thickness of this layer is about 6.5 nm, corresponding to a calculated ALD growth rate of 0.065 nm per cycle, which is consistent with previous report of 0.04–0.07 nm per cycle.38 From corresponding Fast Fourier Transform (FFT) images, both the surface and inner region of pristine sample display similar spotted patterns, which are indexed to the planes of (222) and (111), revealing the well-crystallized face-centered cubic spinel structure. In contrast, for TiO2-coated sample, the surface with amorphous phase shows distinctive structure from the bulk region. In general, the amorphous phase with flexible structure has better Li-ion storage properties than crystalline phase and will increase Li-transport kinetics.31,39 Besides, the coating layer can restrain Mn dissolution by preventing direct contact between LMO particles and electrolyte, likely contributing to enhanced electrochemical performance.


Page 12 of 37

Page 13 of 37 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 3. SEM, HRTEM and corresponding FFT images in different region of (a, c) pristine electrode and (b, d) 100-ALD. Electrochemical measurements were performed to evaluate the effect of TiO2 nanocoating on the surface of LMO electrode. Figure 4(a) depicts long-term cycling performance of all samples at 0.2 C (1 C = 120 mA g-1) for the first five cycles and 0.5 C for the subsequent cycles between 3.0 and 4.5 V at room temperature (25 °C). It is evident that all TiO2-coated electrodes exhibit improved cycling stability compared with the pristine sample, with capacity retentions of 89.4 %, 93.9 %, 95.0 % and 99.7 % at 0.5 C after 150 cycles for the pristine, 10-ALD, 15-ALD and 40-ALD, respectively. Obviously, the capacity retention increases with an increasing number of ALD cycles, 13 ACS Paragon Plus Environment


indicating the protective nature of uniform TiO2 layer that effectively reduces side reactions between active materials and electrolyte. Despite 40-ALD has the best cycling stability, however, the value of its specific capacity is far lower than other samples, possibly due to the excess amount of coating layer that increases the resistance for Li+ transportation through the surface. According to literature reports, surface diffusion is the limiting factor for Li+ diffusivity rather than bulk diffusion.40 Thus, the appropriate thickness of coating layer is particularly crucial for electrochemical performance. Considering both specific capacity and cycling stability, TiO2 ALD layer of 15 cycles, with a thickness of 1 nm, is the optimal coating content and will be compared with the pristine sample in the following results. As shown in Figure 4(b), all samples exhibit declining cycling performance at elevated temperature (55 °C). Fortunately, 15-ALD still provides the optimal discharge capacity and cycling stability. The discharge capacity of pristine sample rapidly fades to 59.2 mAh g-1 after 150 cycles with a capacity retention of 56.1 %. At the same condition, however, 15-ALD displays a much-improved capacity retention of 62.4 %. It is obvious that 15-ALD shows the best cycling performance at both 25 and 55 °C and the positive effect of TiO2 coating layer is more remarkable at 55 °C than that at 25 °C. We speculate that higher temperature accelerates the decomposition of LiPF6 and generates more HF acid, thus the improvement in cycling performance by restraining Mn dissolution for 15-ALD is more obvious.11 To compare the extent of Mn dissolution, cathode electrodes of the pristine and 15-ALD after being fully charged to 4.5 V were immersed into electrolyte for two weeks at 55 °C, and the 14 ACS Paragon Plus Environment

Page 14 of 37

Page 15 of 37 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


amount of Mn ion was determined by ICP-AES. The weight percentages of Mn dissolution from the pristine electrode and 15-ALD were 40.8 % and 27.1 % respectively. This result convincingly confirms that uniform TiO2 nanocoating effectively inhibits Mn dissolution, and thus contributing to improved cycling performance. Charge-discharge curves of pristine electrode and 15-ALD during the 6th, 30th, 60th, and 100th cycles at 0.5 C after first five cycles of 0.2 C between 3.0 and 4.5 V at both 25 and 55 °C are shown in Figure 4(c) and (d). Both samples have similar charge-discharge shapes and display two plateaus at approximately 4.0 and 4.1 V at 25 °C, which agrees well with the two pairs of redox peaks from corresponding differential capacity plots shown in Figure 4(e). This demonstrates that amorphous TiO2 coating layer would not change the typical charge-discharge characteristic of spinel LMO during the process of Li+ insertion and extraction. On the contrary, capacity fading has been refrained by this coating layer. As exhibited in Figure 4(c), discharge capacities of pristine electrode are 118.2, 115.7, 113.2 and 110.4 mAh g-1 at the 6th, 30th, 60th and 100th cycles, whereas the discharge capacities of 15-ALD are 127.7, 126.5, 124.9, and 123.3 mAh g-1 respectively. It has been reported that the capacity fading of LMO at room temperature occurred only in higher voltage region and primarily was attributed to the unstable two-phase structure coexisting in this region.41 In this case, the charge curve of pristine LMO in higher voltage region during cycling changes from L-shape to S-shape, implying that the two-phase structure transformed into one-phase structure. In contrast, the charge curves of 15 ACS Paragon Plus Environment


15-ALD remain L-shape because that TiO2 ALD layer stabilized the structure of spinel LMO. In addition, Figure 4(c) shows that 15-ALD not only has lower oxidization potential and higher reduction potential but also possesses smaller voltage drop than pristine electrode during long-term cycling. Figure 4(d) and 4(f) show charge-discharge curves and corresponding differential capacity plots at 55 °C. It can be observed from Figure 4(d) that both samples reveal severer capacity fading and voltage decay at 55 °C compared to that at 25 °C, which is related to the accelerated Mn dissolution at elevated temperature. Another possibility for inferior electrochemical performance stems from the decomposition of electrolyte at high temperature.9 Mn3+ in LMO can be oxidized to Mn4+ at the end of charge process, and then the strong oxidization ability of Mn4+ will bring about the decomposition of electrolyte.19 As shown in Figure 4(f), an obvious peak located at 4.30 V is observed from the 100th cycle of pristine electrode. Thus, we speculate that the procedure mentioned above leads to the formation of peak at 4.30 V. This peak is absent at room temperature, however, as shown in Figure 4(e). The difference may be attributed to the fact that higher temperature can facilitate the decomposition of electrolyte, which is negligible at room temperature. Furthermore, the presence of TiO2 layer makes the potential of the peak extend to 4.43 V and the intensity weaken sharply. Hence, it is reasonable to conclude that TiO2 nanocoating reduces the decomposition of electrolyte. Meanwhile, 15-ALD performs smaller hysteresis between oxidization and reduction potential at both 6th and 100th cycles, suggesting that TiO2 nanocoating can alleviate the polarization of LMO materials. 16 ACS Paragon Plus Environment

Page 16 of 37

Page 17 of 37 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. Cycling performance of the pristine and TiO2-coated LMO electrodes with different ALD cycles at (a) 25 °C and (b) 55 °C; charge-discharge curves of the pristine electrode and 15-ALD from different electrochemical cycles at 0.5 C after first five cycles of 0.2 C at (c) 25 °C and (d) 55 °C; corresponding differential capacity plots of the pristine electrode and 15-ALD during the 6th and 100th cycles at (e) 25 °C and (f) 55 °C. To further emphasize the advantage of TiO2 nanocoating layer, rate capabilities of 17 ACS Paragon Plus Environment


pristine electrode and 15-ALD were tested from 0.1 C to 5 C between 3.0 and 4.5 V at room temperature and then back to 0.1 C, sustaining each rate for five cycles. A statistical error value was calculated from the standard deviation between these three cells. As shown in Figure 5(a), both samples reveal the capacity-fading tendency with increasing discharge rates. 15-ALD shows the higher discharge capacity under each current densities than pristine sample, especially at 0.1 C, 2 C and 5 C which are 135.9, 109.1 and 96.5 mAh g-1 respectively. Meanwhile, 15-ALD also displays excellent reversibility when the current density is reverted to 0.1 C, displaying a high specific capacity of 134.4 mAh g−1. The higher specific capacity, nearly close to the theoretical capacity, endows the LiMn2O4 cathode material with more extensive applied space, which may stem from the following three aspects: (1) TiO2 is a semiconductor, which could increase its electrical conductivity, (2) the compact and ultrathin coating layer on the electrode surface results in a more uniform current density,42 and (3) this coating layer inhibits electrolyte decomposition, which suppresses the influence of solid electrolyte interface (SEI) on kinetics.29 Figure 5(b) exhibits the first discharge curves at various rates and the corresponding voltage drop is marked inset. Because the capacity fading of LMO at room temperature is attributed mainly to the higher voltage region, discharge plateau at 4.10 V is used as the standard to calculate voltage fade. It is distinct that the value of voltage decay for 15-ALD is smaller than that of pristine sample. This remarkable outcome originates from the TiO2 nanocoating that decreases electrochemical polarization and charge transfer resistance, which will be further confirmed by EIS test. 18 ACS Paragon Plus Environment

Page 18 of 37

Page 19 of 37 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. (a) Rate capability at various rates from 0.1 C to 5 C and (b) the first discharge curves for the pristine (based on cell 1) and 15-ALD (based on cell 1) at corresponding rate between 3.0 to 4.5 V at room temperature. TiO2 ALD nanocoating not only improves the cycling performance and rate capability of spinel LMO, but also influences self-discharge of half cell. The phenomenon of self-discharge refers to the loss of battery capacity at the open circuit potential, and the extent is attributed to cathode and cell preparation, nature and purity of the electrolytes, temperature and time of storage.43 It is important to explore the self-discharge phenomenon in the storage process because it is related to the lifetime of battery. From the electrochemical performance discussed earlier, the TiO2 layer demonstrates outstanding improvement in electrochemical performance of LMO at elevated temperature. Therefore, the electrodes being tested are kept at 55 °C for different length of time after charging to 4.5 V. As shown in Figure 6, the discharge capacities of both samples reduce as the storage time extends. In addition, pristine electrode loses much more capacity and exhibits a faster rate of voltage decay than 15-ALD. The more severe self-discharge behavior results from two steps.44 First, the electrolyte oxidizes at the electrode surface and releases electrons according to the 19 ACS Paragon Plus Environment


Page 20 of 37

following reaction: Electrolyte → oxidation products ＋ ye−

(3)

Second, the oxidized LixMn2O4 intercalates lithium using the released electrons by the following reaction: LixMn2O4 ＋yLi+ ＋ ye- → Lix+yMn2O4

(4)

As noted, the protective TiO2 nanocoating at electrode/ electrolyte interface can effectively reduce electrolyte decomposition. In other words, the reaction (3) has been inhibited, resulting in weaker self-discharge phenomenon of 15-ALD.

Figure 6. Discharge curves of the pristine and 15-ALD after being charged to 4.5 V and subsequently kept at 55 °C for 2 or 7 days. To evaluate its application value, ALD technique is compared with sol-gel method, by which 3 wt% TiO2 layer is directly coated on the surface of LMO particles. Figure S3 shows that the coating layer is also amorphous and the thickness is about 5 nm, 20 ACS Paragon Plus Environment

Page 21 of 37 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


more than five times thickness of 15-ALD. From the perspective of practical application, energy density is extremely important which is determined by capacity and voltage. Therefore, we investigate the cycling performance and evolution of average discharge voltages between 3.0 and 4.5 V at 25 °C, as shown in Figure S4. The detailed values are displayed in Table S2. It is obvious that the pristine LMO behaves serious capacity decay, corresponding to the capacity retention of 83.3 %, while the TiO2-coated LMO samples synthesized by ALD or sol-gel method are 93.5 % and 93.1 % from the 1st cycle to 150th cycles. More striking, 15-ALD displays much higher discharge capacity than sol-gel method, demonstrating that uniform TiO2 layer on the fabricated electrode prepared by ALD is good for discharge capacity to the maximum. As performed in Figure S4(b), the pristine LMO exhibits a rapid voltage decay of 0.043 V, which is considerably higher than the voltage fade of 15-ALD (0.0093 V) and TiO2-coated LMO particles by sol-gel method (0.0019 V). Apparently, TiO2-coated LMO samples, no matter synthesized by ALD technique or sol-gel method, show more stable voltage than pristine sample and have the similar voltage fade, indicating the superior structural stability after surface modification. Meanwhile, both of samples show smaller electrochemical polarization than the pristine LMO, as shown in Figure S5. In consideration of discharge capacity and voltage, TiO2 ALD-coated LMO electrode exhibits higher energy density than TiO2-coated LMO particles prepared by sol-gel method. ALD technique not only produces high-quality layer but also realizes deposition on electrode, which is incomparable for sol-gel method. Therefore, ALD technique has a promising application. 21 ACS Paragon Plus Environment


To intensively explore the positive effect of TiO2 nanocoating on the electrode surface and the factors for improved electrochemical performance, EIS test was conducted with a frequency range from 100 kHz to 10 mHz. Figure 7(a) depicts the Nyquist plots of pristine and TiO2-coated electrodes after first charge-discharge cycle and the inset picture shows the plots at an enlarged scale. All samples perform similar profile composed of three parts: an intercept of Z＇real axis, one semicircle and a sloping line. In principle, the intercept in the high-frequency region corresponds to the solution resistance (Rs). The semicircle in the high- to medium-frequency region represents a combination of charge transfer resistance (Rct) in the electrode/ electrolyte interface and a constant phase element (CPE), while the sloping line in the low-frequency region refers to Warburg resistance (Zw, Li+ diffusion in the bulk materials).10,45 As shown in Figure 6(a), the Rct value of 40-ALD is nearly twice as high as that of pristine electrode because superfluous amount of TiO2 coating amount impedes the charge transfer. In addition, the Rct values of 10-ALD and 15-ALD are reduced compared with that of pristine sample. In particular, 15-ALD has the lowest Rct value. These results are consistent with the cycling performance and specific capacity shown in Figure 4. Figure 7(b) and 7(c) exhibit Nyquist plots of pristine sample and 15-ALD after 30, 60, and 100 cycles, and the inset equivalent circuits are used to obtain quantitative values of resistance. The fitted results listed in Table 1 show similar Rs values between 15-ALD and pristine electrode, indicating that ultrathin TiO2 layer has almost no influence on solution resistance. Furthermore, the Rct values of both samples increase as a function of cycle number; however, the 22 ACS Paragon Plus Environment

Page 22 of 37

Page 23 of 37 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


values of Rct for 15-ALD are much smaller than those for pristine sample. After 30 cycles, it is only about 58.9 Ω, about half of the pristine electrode. The relatively lower Rct values of 15-ALD could be explained as follows: the protective TiO2 nanocoating at the interface between active materials and electrolyte suppresses harmful side reactions and reduces electrochemical polarization. These EIS results again confirm the positive effect of TiO2 ALD nanocoating on the electrode surface and explain the reason for enhanced rate capability shown in Figure 5. The Li+ diffusion coefficient (DLi+) can be calculated from corresponding EIS plots in the low frequency region according to eq. (5):46 R2 T 2

DLi+ 2A2 n4 F4C2σ2

(5)

Where R is the gas constant (8.314 J mol-1 K-1), T is the temperature (298.15 K), A is the surface area of the electrode, n is the number of electrons per molecule involved in transfer reaction (n = 1), F is the Faraday constant (96500 C mol-1), C is the molar concentration of Li+ in the electrode (0.024 mol cm-3, C = ρ/M)47 and σ is the Warburg coefficient, which can be calculated form eq. (6):

+ +

(6)

From the linear relationship of Z＇against ω-1/2 (ω is the angular frequency) shown in Figure 7(d), the value of σ can be obtained from the slope of the fitted line in the Warburg region. By combining of eqs. (5) and (6), DLi+ can be calculated (listed in Table 1). The DLi+ values of 15-ALD are nearly one order of magnitude higher than that of pristine sample, likely due to the formation of lithium easy diffusion path. It has been reported that ALD nanocoating directly coated on cathode particles may 23 ACS Paragon Plus Environment


obstruct Li+ diffusion and electron transfer.10 To eliminate this drawback, the TiO2 ALD layer was directly deposited on the electrode surface in this work. By avoiding deposition at contact points among active materials, conductive agent, and the current collector, rates of Li+ diffusion and electron transfer can be accelerated greatly.32,33 As noted, the thickness of coating layer also plays a vital role. A thicker coating can effectively inhibit Mn dissolution; however, it brings terrible discharge capacity and the capacity retention is also ideal for the thinner layer. Therefore, only the appropriate thickness of 15 ALD cycles with smaller electron transfer resistance and larger Li+ diffusivity can enhance the entire electrochemical performance to an optimal extent.

Figure 7. Nyquist and fitting plots of (a) pristine and TiO2-coated electrodes after first cycle at 0.2 C between 3.0 to 4.5 V at room temperature, (b) the pristine and (c) 24 ACS Paragon Plus Environment

Page 24 of 37

Page 25 of 37 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


15-ALD after 30, 60, and 100 cycles with the equivalent circuit in the inset; (d) the corresponding linear relationship of Z' and ω-1/2 at low frequency for pristine and 15-ALD Table 1. The impedance parameters of equipment circuits and calculated Li+ diffusion coefficient Samples

Pristine

15-ALD

Rs/Ω

Rct/Ω

DLi+/cm2 s-1

Rs/Ω

Rct/Ω

DLi+/cm2 s-1

30th

4.3

119.5

7.80×10-15

3.6

58.9

2.52×10-14

60th

4.4

122.5

5.31×10-15

3.6

96.2

1.27×10-14

100th

4.9

156.9

3.04×10-15

4.8

131.4

9.96×10-15

The chemical valence state and their variations in charge-discharge process are particularly significant to understand the mechanism of electrochemical degradation. XPS signals of Mn 2p orbital for pristine and 15-ALD and Ti 2p orbital for 15-ALD before and after 150 charge-discharge cycles are performed in Figure 8. All spectra of Mn 2p and Ti 2p are separated in half because of the spin-orbital splitting.48 To confirm the exact peak positions and relative areas of subpeaks, peak fitting is performed. Both Mn 2p and Ti 2p orbits are fitted using one doublet (Mn 2p3/2 - Mn 2p1/2, Ti 2p3/2 - Ti 2p1/2) with a fixed area ratio of 2:1. The doublet separation for Mn 2p is 11.5 eV, whereas the Ti 2p is 5.7 eV. As shown in Figure 8(a), the Mn 2p3/2 subpeak located at 642.1 and 643.7 eV before cycling is assigned to the binding energy of Mn3+ and Mn4+, which is in accordance with the previous report.49 Furthermore, the proportion of Mn3+ (57.8 %) from 15-ALD (shown in Figure 8(b)) is 25 ACS Paragon Plus Environment


reduced compared with that of pristine electrode (58.2 %). It is well known that the HF acid generated from the reaction between LiPF6 and water in electrolyte can induce a disproportion reaction, bringing about detrimental Mn dissolution.8 Accordingly, it is reasonable to consider that 15-ALD with smaller amount of Mn3+ could inhibit disproportion reaction and exhibit perfect electrochemical performance among all samples. After long-term cycling, the amount of Mn4+ enlarges from 41.8 % to 42.8 % after cycling, with the increment of 1%, supporting the formation of defective spinel phases with higher fraction of Mn4+.15 The excess Mn4+ that stems from the solid product (λ-MnO2) of disproportion reaction further confirm the phenomenon of Mn dissolution during charge-discharge process. Additionally, the Mn 2p3/2 subpeaks of pristine sample shift toward lower binding energy and the value of shift is about 1 eV, which may be due to the increase of oxidation state for Mn. In addition, the product of electrolyte decomposition could change the chemical and bonding environment of outer surface on spinel particle, bringing about nonnegligible peak shift of Mn.37 For 15-ALD, however, their binding energies nearly remain unchanged after cycling and the ratio of Mn4+ adds from 42.2 % to 42.4 %. This result proves that the TiO2 nanocoating suppresses the disproportion of Mn3+ and subsequent formation of Mn4+ through shielding the direct contact between LMO particles and electrolyte, thus resulting in improved electrochemical performance.50 Other than Mn 2p peak, the XPS spectra of Ti 2p from 15-ALD are also collected to study the influence of coating layer on LMO electrode, shown in Figure 8(c). After 26 ACS Paragon Plus Environment

Page 26 of 37

Page 27 of 37 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


cycling, the Ti 2p peaks appear a degree of asymmetry and the deconvolution of the peaks lead to additional weaker peaks located at 459.7 eV (Ti 2p3/2) and 465.4 eV (Ti 2p1/2). Accordingly, the original peaks assigned to Ti−O bonding shift to higher binding energies of 458.9 eV (Ti 2p3/2) and 464.6 eV (Ti 2p1/2). Based on the standard values of TiF4 (461.1 and 466.9 eV) in National Institute of Standards and Technology XPS Database, it is obvious that the binding energies of new peaks are between Ti−O bonding and Ti−F bonding. Therefore, we speculate that the new peaks may refer to the Ti−O−F bonding. On the basis of XPS analysis and time-of-flight secondary-ion mass spectrometry (ToF-SIMS), Charlton et al. identified the existence of TiOxFy on TiO2 surface,51 which is consistent with our deduction. So far, we think that part of TiO2 nanocoating reacts with both of HF and H2O molecules to produce the TiOxFy, which is inert for acidic HF and can also scavenge HF. Thus, the coexistence of TiO2 and TiOxFy stabilizes the electrode/ electrolyte interface. In addition, higher intensity of Ti−O bonding after cycling indicates that the TiO2 layer has not reacted entirely with HF and transformed into TiOxFy, which supports the viewpoints that the TiO2 nanocoating is stable enough to endure long-term electrochemical cycling and results in great electrochemical performance.



Figure 8. XPS spectra of Mn 2p for (a) pristine electrode and (b) 15-ALD before cycling and after 150 charge-discharge cycles, and (c) Ti 2p for 15-ALD before cycling and after 150 charge-discharge cycles. Conclusions 28 ACS Paragon Plus Environment

Page 28 of 37

Page 29 of 37 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


We successfully deposited amorphous TiO2 nanocoating on LiMn2O4 electrode surface by ALD technique. The thickness of the coating layer could be precisely controlled and has great effect on the electrochemical performance at both room temperature of 25 °C and elevated temperature of 55 °C. The sample of 15-ALD exhibits the best cycling stability and discharge capacity, nearly close to theoretical capacity. Besides, greater rate capability, lower polarization and self-discharge phenomenon of 15-ALD also have been observed. Directly coating TiO2 ALD layer on cathode electrodes instead of LiMn2O4 particles can maintain the electrical conductivity of the materials and thus reduces the electron transfer resistance. Furthermore, the presence of Ti−O−F peak from Ti 2p peaks after cycling reveals that partial TiO2 layer transforms into inert TiOxFy, meaning that the joint effect of TiO2 and TiOxFy layer can scavenge HF and thus retards Mn dissolution and electrolyte decomposition. Our study demonstrates that ALD technique is facile to control the coating thickness by varying growth cycles and thus enhances the entire electrochemical performance to the optimal extent, which presents a wide range of possibilities for the further development of high-quality electrodes for lithium ion batteries. Associated Content Supporting Information The variation of peak areas of Ti 2p, SEM image of 100-ALD and corresponding EDX mapping images, HRTEM image of 3 wt% TiO2-coated LiMn2O4 particles by sol-gel method, and charge-discharge curves, cycling performance and evolution of 29 ACS Paragon Plus Environment


average discharge voltages of the pristine and TiO2-coated LMO samples by ALD technique and sol-gel method. Author Information Corresponding author *E-mail: [email protected]. Phone: +86-21-51630320. Fax: +86-21-51630320. *E-mail: [email protected]. Phone: +86-021-6564245. Fax: +86-21-51630320. Notes The authors declare no competing financial interest. Acknowledgements The authors acknowledge funding supports from the 973 Program (No. 2013CB934103) and Science & Technology Commission of Shanghai Municipality (No. 08DZ2270500), China. References (1) Armand, M.; Tarascon, J. M. Building Better Batteries. Nature 2008, 451, 652−657. (2) Nitta, N.; Wu, F.; Lee, J. T.; Yushin, G. Li-Ion Battery Materials: Present and Future. Mate. Today 2015, 18, 252-264. (3) 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. (4) Choi, J. W.; Aurbach, D. Promise and Reality of Post-Lithium-Ion Batteries with 30 ACS Paragon Plus Environment

Page 30 of 37

Page 31 of 37 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


High Energy Densities. Nat. Rev. Mater. 2016, 1, 16013. (5) Grey, C. P.; Tarascon, J. M. Sustainability and in Situ Monitoring in Battery Development. Nat. Mater. 2016, 16, 45-56. (6) Zhang, C.; Liu, X.; Su, Q.; Wu, J.; Huang, T.; Yu, A. Enhancing Electrochemical Performance of LiMn2O4 Cathode Material at Elevated Temperature by Uniform Nanosized TiO2 Coating. ACS Sustainable Chem. Eng. 2017, 5, 640-647. (7) Park, O. K.; Cho, Y.; Lee, S.; Yoo, H. C.; Song, H. K.; Cho, J. Who Will Drive Electric Vehicles, Olivine or Spinel?. Energy Environ. Sci. 2011, 4, 1621-1633. (8) Gummow, R. J.；Kock, A. de.；Thackeray, M. M. Improved Capacity Retention in Rechargeable 4 V Lithium/Lithium-Manganese Oxide (Spinel) Cells. Solid State

Ion. 1994, 69, 59-67. (9) Xia, Y.; Zhou, Y.; Yoshio, M. Capacity Fading on Cycling of 4 V Li/LiMn2O4 Cells. J. Electrochem. Soc. 1997, 144, 2593-2600. (10) 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. (11) 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. (12) Tron, A.; Park, Y. D.; Mun, J. AlF3-Coated LiMn2O4 as Cathode Material for 31 ACS Paragon Plus Environment


Aqueous Rechargeable Lithium Battery with Improved Cycling Stability. J. Power

Sources 2016, 325, 360-364. (13) Zhao, S.; Bai, Y.; Chang, Q.; Yang, Y.; Zhang, W. Surface Modification of Spinel LiMn2O4 with FeF3 for Lithium Ion Batteries. Electrochim. Acta 2013, 108, 727-735. (14) Chen, Q.; Wang, Y.; Zhang, T.; Yin, W.; Yang, J.; Wang, X. Electrochemical Performance of LaF3-Coated LiMn2O4 Cathode Materials for Lithium Ion Batteries.

Electrochim. Acta 2012, 83, 65-72. (15) Lee, S.; Jeong, M.; Cho, J. Optimized 4-V Spinel Cathode Material with High Energy Density for Li-Ion Cells Operating at 60 °C. Adv. Energy Mater. 2013, 3, 1623-1629. (16) Shang, Y.; Liu, J.; Huang, T.; Yu, A. Effect of Heat Treatment on the Structure and Electrochemical Performance of FePO4 Coated Spinel LiMn2O4. Electrochim.

Acta 2013, 113, 248-255. (17) Feng, X.; Zhang, J.; Yin, L. Enhanced Cycling Stability of Co3(PO4)2-Coated LiMn2O4 Cathode Materials for Lithium Ion Batteries. Powder Technol. 2016, 287, 77-81. (18) Chen, Z.; Qin, Y.; Amine, K.; Sun, Y. K. Role of Surface Coating on Cathode Materials for Lithium-Ion Batteries. J. Mater. Chem. 2010, 20, 7606-7612. (19) Zhao, J.; Wang, Y. Ultrathin Surface Coatings for Improved Electrochemical Performance of Lithium Ion Battery Electrodes at Elevated Temperature. J. Phys.

Chem. C 2012, 116, 11867-11876. (20) Li, X.; Liu, J.; Meng, X.; Tang, Y.; Banis, M. N.; Yang, J.; Hu, Y.; Li, R.; Cai, M.; 32 ACS Paragon Plus Environment

Page 32 of 37

Page 33 of 37 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


Sun, X. Significant Impact on Cathode Performance of Lithium-Ion Batteries by Precisely Controlled Metal Oxide Nanocoatings Via Atomic Layer Deposition. J.

Power Sources 2014, 247, 57-69. (21) Meng, X. B.; Yang, X. Q.; Sun, X. L. Emerging applications of atomic layer deposition for lithium-ion battery studies. Adv. Mater. 2012, 24, 3589−3615. (22) Ma, L.; Nuwayhid, R. B.; Wu, T. P.; Lei, Amine, K.; Lu, J. Atomic layer deposition for lithium-based batteries. Adv. Mater. Interfaces 2016, 3, 1600564. (23) George, S. M. Atomic layer deposition: an overview. Chem. Rev. 2009, 110, 111-131. (24) Marichy, C.; Bechelany, M.; Pinna, N. Atomic layer deposition of nanostructured materials for energy and environmental applications. Adv. Mater. 2012, 24, 1017-1032. (25) Ahmed, B.; Xia, C.; Alshareef, H. N. Electrode surface engineering by atomic layer deposition: a promising pathway toward better energy storage. Nano Today 2016, 11, 250-271. (26) 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. (27) Dai, G.; Du, H.; Wang, S.; Cao, J.; Yu, M.; Chen, Y.; Tang, Y.; Li, A.; Chen, Y. Improved Electrochemical Performance of LiNi0.8Co0.15Al0.05O2with Ultrathin and Thickness-Controlled TiO2 shell Via Atomic Layer Deposition Technology. RSC Adv. 2016, 6, 100841-100848. 33 ACS Paragon Plus Environment


(28) Zhang, X. F.; Belharouak, I.; Li, L.; Lei, Y.; Elam, J. W.; Nie, A. M.; Chen, X. Q.; Yassar, R. S.; Axelbaum, R. L. Structural and Electrochemical Study of Al2O3 and TiO2 Coated Li1.2Ni0.13Mn0.54Co0.13O2 Cathode Material Using ALD. Adv. Energy

Mater. 2013, 3, 1299-1307. (29) Mattelaer, F.; Vereecken, P.; Dendooven, J.; Detavernier, C. The Influence of Ultrathin Amorphous ALD Alumina and Titania on the Rate Capability of Anatase TiO2 and LiMn2O4 Lithium Ion Battery Electrodes. Adv. Mater. Interfaces. 2017, 4, 1601237. (30) Xie, M.; Sun, X.; Zhou, C.; Cavanagh, A. S.; Sun, H.; Hu, T.; Wang, G.; Lian, J.; George, S. M. Amorphous Ultrathin TiO2 Atomic Layer Deposition Films on Carbon Nanotubes as Anodes for Lithium Ion Batteries. J. Electrochem. Soc. 2015, 162, A974-A981. (31) Wang, H.; Jia, G.; Guo, Y.; Zhang, Y.; Geng, H.; Xu, J.; Mai, W.; Yan, Q.; Fan, H. J. Atomic Layer Deposition of Amorphous TiO2 on Carbon Nanotube Networks and Their Superior Li and Na Ion Storage Properties. Adv. Mater. Interfaces 2016, 3, 1600375. (32) Jung, Y.; Cavanagh, A.; Riley, L.; Kang, S.; Dillon, A.; Groner, M.; George, S.; Lee, S. Ultrathin Direct Atomic Layer Deposition on Composite Electrodes for Highly Durable and Safe Li–Ion Batteries. Adv. Mater. 2010, 22, 2172-2176. (33) Li, X.; Liu, J.; Banis, M.; 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. 34 ACS Paragon Plus Environment

Page 34 of 37

Page 35 of 37 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


Sci. 2014, 7, 768-778. (34) Xie, Q.; Jiang, Y.; Detavernier, C.; Deduytsche, D.; Ru, G.; Li, B.; Qu, X.; Atomic Layer Deposition of from Tetrakis-Dimethyl-Amido Titanium or Ti Isopropoxide Precursors and H2O. J. Appl. Phys. 2007, 102, 083521. (35) Lee, J.; Wang, F.; Cheng, C.; Li, C.; Lin, C. Low-Temperature Atomic Layer Deposited Al2 O3 Thin Film on Layer Structure Cathode for Enhanced Cycleability in Lithium-Ion Batteries. Electrochim. Acta 2010, 55, 4002-4006. (36) Xiao, B.; Liu, J.; Sun, Q.; Wang, B.; Banis, M. N.; Zhao, D.; Wang, Z.; Li, R.; Cui, X.; Sham, T.-K.; Sun, X. Unravelling the Role of Electrochemically Active FePO4 coating by Atomic Layer Deposition for Increased High-Voltage Stability of LiNi0.5Mn1.5O4 cathode Material. Adv. Sci. 2015, 2, 1500022. (37) Zhao, J.; Wang, Y. Surface Modifications of Li-Ion Battery Electrodes with Various Ultrathin Amphoteric Oxide Coatings for Enhanced Cycleability. J. Solid

State Electrochem. 2013, 17, 1049-1058. (38) Lee, M.-L.; Su, C.-Y.; Lin, Y.-H.; Liao, S.-C.; Chen, J.-M.; Perng, T.-P.; Yeh, J.-W.; Shih, H. C. Atomic Layer Deposition of TiO2 on Negative Electrode for Lithium Ion Batteries. J. Power Sources 2013, 244, 410-416. (39) Song, H.; Kim, J. Y.; Kim, K. T.; Park, Y. J. Enhanced Electrochemical Properties of Li(Ni0.4Co0.3Mn0.3)O2 Cathode by Surface Modification Using Li3PO4-Based Materials, J. Power Sources 2013, 196, 6847-6855. (40) Park, M. H.; Noh, M.; Lee, S.; Ko, M.; Chae, S.; Sim, S.; Choi, S.; Kim, H.; Nam, H.; Park, S.; Cho, J. Flexible High-Energy Li-Ion Batteries with Fast-Charging 35 ACS Paragon Plus Environment


Capability. Nano Lett 2014, 14, 4083-4089. (41) Xia, Y.; Yoshio, M. An Investigation of Lithium Ion Insertion into Spinel Structure Li−Mn−O Compounds. J. Electrochem. Soc. 1996, 143, 825-833. (42) Walz, K.; Johnson, C.; Genthe, J.; Stoiber, L.; Zeltner, W.; Anderson, M.; Thackeray, M. Elevated Temperature Cycling Stability and Electrochemical Impedance of LiMn2O4 Cathodes with Nanoporous ZrO2 and TiO2 Coatings. J. Power

Sources 2010, 195, 4943-4951. (43) Pistoia, G.; Antonini, A.; Rosati, R.; Zane, D. Storage Characteristics of Cathodes for Li-Ion Batteries. Electrochim. Acta 1996, 41, 2683-2689. (44) Guyomarda, D.; Tarascon, J. M. The Carbon/Lil+xMn2O4 System. Solid State Ion. 1994, 69, 222-237. (45) 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. (46) Chen, B.; Liu, E.; Cao, T.; He, F.; Shi, C.; He, C.; Ma, L.; Li, Q.; Li, J.; Zhao, N. Controllable Graphene Incorporation and Defect Engineering in MoS2 -TiO2 Based Composites: Towards High-Performance Lithium-Ion Batteries Anode Materials.

Nano Energy 2017, 33, 247-256. (47) Zhang, Q.; Xie, X.; Fan, W.; Wang, X. Lithium Polyacrylate-Coated LiMn2O4 Cathode Materials with Excellent Performance for Lithium Ion Batteries. Ionics 2016,

22, 2273-2280. (48) Wang, H. Q.; Lai, F. Y.; Li, Y.; Zhang, X. H.; Huang, Y. G.; Hu, S. J.; Li, Q. Y. 36 ACS Paragon Plus Environment

Page 36 of 37

Page 37 of 37 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


Excellent Stability of Spinel LiMn2O4-Based Cathode Materials for Lithium-Ion Batteries. Electrochim. Acta 2015, 177, 290-297. (49) 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. (50) Kang, B. J.; Joo, J. B.; Lee, J. K.; Choi, W. Surface Modification of Cathodes with Nanosized Amorphous MnO2 Coating for High-Power Application in Lithium-Ion Batteries. J. Electroanal. Chemistry 2014, 728, 34-40. (51) Charlton, M. R.; Dylla, A. G.; Stevenson, K. J. Direct Evidence of a Chemical Conversion Mechanism of Atomic-Layer-Deposited TiO2 anodes During Lithiation Using LiPF6 salt. J. Phys. Chem. C 2015, 119, 28285-28291.

TOC

Synopsis: This work provide information of LIBs and ALD and stimulate insightful studies of using ALD for development of next-generation LIBs. 37 ACS Paragon Plus Environment

Significant Improvement on Electrochemical Performance of LiMn2O4

Recommend Documents