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Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Structural and Electrochemical Evaluation of Three- and TwoDimensional Organohalide Perovskites and Their Influence on the Reversibility of Lithium Intercalation Daniel Ramirez,† Yusaku Suto,‡ Nataly Carolina Rosero-Navarro,*,§ Akira Miura,§ Kiyoharu Tadanaga,§ and Franklin Jaramillo*,† †

Centro de Investigación, Innovación y Desarrollo de Materiales − CIDEMAT, Facultad de Ingeniería, Universidad de Antioquia UdeA, Calle 70 No. 52-21, Medellín, Colombia ‡ Graduate School of Chemical Sciences and Engineering and §Division of Applied Chemistry, Faculty of Engineering, Hokkaido University, Sapporo 060-8628, Japan S Supporting Information *

ABSTRACT: Organic−inorganic hybrid perovskite materials have recently been investigated in a variety of applications, including solar cells, light emitting devices (LEDs), and lasers because of their impressive semiconductor properties. Nevertheless, the perovskite structure has the ability to host extrinsic elements, making its application in the battery field possible. During the present study, we fabricated and investigated the electrochemical properties of three-dimensional (3D) methylammonium lead mixed-halide CH3NH3PbI3‑xBrx and two-dimensional (2D) propylammonium-methlylammonium lead bromide (CH3NH3)2(CH3(CH2)2NH3)2Pb3Br10 hybrid perovskite thin films as electrode materials for Li-ion batteries. These electrodes were obtained by solution processing at 100 °C. CH3NH3PbBr3 achieved high discharge/charge capacities of ∼500 mA h g−1 /160 mA h g−1 that could account also for other processes taking place during the Li intercalation. It was also found that bromine plays an important role for lithium intercalation, while the new 2D (CH3NH3)2(CH3(CH2)2NH3)2Pb3Br10 with a layered structure allowed reversibility of the lithium insertion−extraction of 100% with capacities of ∼375 mA h g−1 in the form of a thin film. Results suggest that tuning the composition of these materials can be used to improve intercalation capacities, while modification from 3D to 2D layered structures contributes to improving lithium extraction. The mechanism of the lithium insertion− extraction may consist of an intercalation mechanism in the hybrid material accompanying the alloying−dealloying process of the LixPb intermetallic compounds. This work contributes to revealing the relevance of both composition and structure of potential hybrid perovskite materials as future thin film electrode materials with high capacity and compositional versatility.

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similar way as for inorganic Li3xLa(2/3)−xTiO3 perovskites12 or LiMnO4 spinels.13 The recently calculated diffusion coefficient of lithium ion within the perovskite lattice can exhibit values as high as Dμ ≈ 10−7 cm2 s−1, which implies conductivities within the range of 10−3 Ω−1 cm−1 for highly lithiated electrodes,14 confirming the superionic intrinsic property of hybrid perovskites. On the other hand, it has been found that during Li+ intercalation, conversion reaction of the hybrid perovskite with the electrolyte could take place.15 Additionally, a charge−discharge capacity of around ∼330 mA h g−1 and a stable specific capacity ∼200 mA h g−1 have been reported by fabricating electrodes with CH3NH3PbBr3 (MAPbBr3) powders.10,11 Nevertheless, this is a new field, and therefore the literature is yet to give a good understanding of the working mechanism for the Li+ intercalation, possible

INTRODUCTION In recent years, organic−inorganic hybrid perovskite materials have drawn an intense interest in the scientific community after their first application in solar cells in 2009.1 These threedimensional (3D) hybrid perovskite materials with the general formula AMX3 (A = Cs+, CH3NH3+, or HC(NH2)2+; M = Pb2+; and X = Cl−, Br−, and I−) have presented impressive properties such as high extinction coefficient,2 adequate band gap,3 small exciton binding energy,4 and long exciton and charge diffusion lengths,5 which have allowed achievement of power conversion efficiencies over 22% in this short time. All of these interesting properties have permitted hybrid perovskites to be considered as a family of multifunctional materials with applications not only in solar cells, but also in lasers,6 light emitting diodes (LEDs),7 photodetectors,8 and filed effect transistors (FETs).9 Recent publications10,11 have also suggested that these materials have potential for battery applications, since lithium (Li+) transport can be achieved in a © XXXX American Chemical Society

Received: February 12, 2018

A

DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 1. SEM images of the films used as electrode materials for lithium battery applications: (a) MAPbI3, (b) MAPbIBr2, and (c) MAPbBr3. then hand milled. A total of 70 mg of this powder was mixed with 15 mg of acetylene black (AB) and 15 mg of poly(vinylidene fluoride) (PVDF) in 400 μL of N-methyl pyrrolidone (NMP) to form a slurry. The slurry was applied on Cu foil with a gap of 200 μm and heated at 70 °C for 30 min. After the heat treatment, the foil was dried at 120 °C for 12 h under a vacuum to evaporate any residual NMP. The obtained foil was punched into round disks with 0.85 cm in diameter to make working electrodes. Characterization. X-ray diffractograms were collected from 2θ = 5° to 50° in a Bragg−Brentano geometry, from the prepared thin films in a PANalytical diffractometer, using Cu Kα (1.5408 Å) radiation with a step size of 0.04° and a speed of 2° per minute. Thickness of the different layers was obtained using a Bruker DektakXT profilometer. Absorption and reflectance was measured in the 400−850 nm range, using a Cary 100 spectrometer respectively with an integration sphere. Microstructure of the films was characterized by a scanning electron microscopy (JIB-4600F MultiBeam SEM-FIB). Electrochemical measurements were performed in a simple three-electrode cell using the hybrid perovskite film deposited on the indium−tin conductor (ITO) as a working electrode and lithium sheet as both counter and reference electrodes. A mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1:1 volumetric ratio containing 1 M LiPF6 was used as an electrolyte. The assembly of the cells was conducted in a glovebox under an argon atmosphere (H2O ≤ 5 ppm, O2 ≤ 1 ppm). For the thin film electrodes, the constant current charge and discharge profiles were obtained by using a charge−discharge device (Scribner Associates, 580 battery type system). The cycling performance was evaluated at a constant current density of 0.1 mA cm−2 in a voltage range from 0.1 to 1.5 V at room temperature. Schematic illustration of the electrochemical cell used to perform electrochemical characterization is shown in Figure S1. For the powder electrodes, cyclic voltammetry (CV) tests and electrochemical impedance spectroscopy (EIS) analysis were performed using an electrochemical workstation (1260/1287, Solartron Analytical). Charge−discharge performance under constant current density (425 mA g−1) in a voltage range from 0.0 to 1.5 V at 25 °C was investigated. (MA)2(PA)2Pb3Br10 Crystalline Structure. The HighScore Plus software was used to perform Rietveld refinement of the CIF file of the crystalline structure of the already reported (MA)2(BA)2Pb3I10 material.18 Extra carbon atoms were eliminated, and iodine atoms were changed for bromine atoms using the software VESTA. The lattice parameters were modified and fitted to the experimental results. Note that all the peaks were the same for experimental and theoretical spectra; therefore, the main change was in the lower lattice parameters in (MA)2(PA)2Pb3Br10.

improvements for charge capacity, cycling performance, and also exploiting advantages of the low temperature solution processes commonly used to obtain high quality perovskite thin films. This is a very important aspect for the fabrication of microbatteries to be used in microsensors, micromechanics, and microelectronics.16 Most of the thin film electrodes for microbattery applications are also based on high temperature solid-state processes.17 Usually, the sintering process requires temperatures of around 700−900 °C.16 This makes the fabrication process difficult when the purpose is to fabricate solid state batteries where the electrodes are deposited on top of the solid electrolyte. Thus, low-temperature solution methods to obtain thin and functional films can overcome this problem. Herein, we studied the electrochemical properties of 3D hybrid perovskite CH3NH3PbI3‑xBrx (MAPbI3‑xBrx) and a new two-dimensional (2D) hybrid perovskite (CH 3 NH 3 ) 2 (CH3(CH2)2NH3)2Pb3Br10 ((MA)2(PA)2Pb3Br10) with layered structure. To the best of our knowledge, this was the first time for 500 nm hybrid perovskite thin films to have been evaluated as potential electrode materials for Li-ion batteries. In addition, we performed a deeper study on the 2D hybrid perovskite using powder composite electrodes. We also compared the influence of composition and crystalline structure as the two important factors that contribute to high Li+ intercalation and retention capacity.

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MATERIALS AND METHODS

Materials and Synthesis. Methylammonium iodide (MAI), methylammonium bromide (MABr), and n-propylammonium iodide bromide (PABr) from Dyesol were used as organic cations. Dimethyl sulfoxide (DMSO, Sigma-Aldrich) and N,N-dimethylformamide (DMF, Alfa Aesar) were used as solvents, and lead iodide (PbI2) (Sigma-Aldrich) and lead bromide (PbBr2) (Alfa Aesar) were used as the lead source. In order to obtain the MAPbI3 precursor solution, 159 mg of MAI, 461 mg of PbI2, and 71.05 μL of DMSO (1:1:1 molar ratio) were dissolved in 560 μL of N,N-dimethylformamide (DMF, Alfa Aesar). For the rest of the compositions, MABr and PbBr2 were used to obtain stoichiometric MAPbI2Br, MAPbIBr2, and MAPbIBr3 by replacing MAI and PbI2, respectively. For the 2D layered perovskite (CH3NH3)2(CH3(CH2)2NH3)2Pb3Br10, PABr, MABr, and PbBr2 (2:2:3 molar ratio) were dissolved with 71.05 μL of DMSO in 560 μL of DMF. Thin Film Electrode Fabrication. Precursor solution was deposited on top of 2.5 cm × 2.5 cm indium tin oxide (ITO) plates by spin coating at 4000 rpm for 25 s. After 10 s of spin coating, 500 μL of diethyl ether was doped in order to quickly remove the DMF. The films were then annealed at 65 °C for 1 min plus 100 °C for 10 min. The average film thickness in all cases was around 500 nm, while the area of the covered ITO was around 2.0 cm × 2.5 cm with 0.5 cm in order to connect the electrode. The mass of the samples (approx. ∼1 mg) was calculated by defining the material volume with the ITO covered area and the thickness, and then by multiplying by the density. Powder Electrode Fabrication. (MA)2(PA)2Pb3Br10 powder was obtained by slow solvent evaporation of the precursor solution and

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RESULTS AND DISCUSSION Three-dimensional hybrid perovskite films combining iodine and bromine as anions were fabricated by directly spin coating of the precursor solution with final annealing temperature of 100 °C. The films deposited on top of conductive ITO presented a different color (Figure S1), changing from dark brown to orange when moving from MAPbI3 to MAPbBr3, indicating the increase of the band gap, as already reported.19 The 500 nm films (∼1 mg) presented a high-quality B

DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 2. Optical and structural characterization of the hybrid perovskite films. (a) Absorption spectra indicating a band gap increasing when iodine is replaced by bromine, (b) calculated band gaps from reflectance spectra using the Kubelka-Munk function, and (c) X-ray diffraction patterns showing the tetragonal to cubic transition from MAPbI3 to MAPbBr3.

Figure 3. (a) First charge−discharge curves for the cells using the hybrid perovskite coatings as a working electrode. A constant current density of 0.1 mA cm−1 was used. A mixture of 1 M LiPF6/ED+DEC was used as electrolyte. (b) Cycling performance for the cells using the hybrid perovskite films as a working electrode. Open circles and open up−down triangles denote the discharge capacities.

from Kubelka-Munk21 fitting of the reflectance measurements. The band gaps shown in Figure 2b are in total agreement with the already reported MAPbI3−xBrx series.19 Band gaps of 1.57 eV, 1.74 eV, 1.92 eV, and 2.28 eV were obtained for MAPbI3, MAPbI2Br, MAPbIBr2, and MAPbBr3, respectively. These single optical band gaps indicate that the films presented adequate mixing of the halogen, and therefore no phase segregation is expected. In order to corroborate this, X-ray diffraction was performed (Figure 2c). As shown in Figure 3a, the extraction reaction of lithium achieved charge capacities of 70−160 mA h g−1 for the first cycle, and a large irreversible capacity was observed. A clear plateau around 0.5− 0.7 V was observed on the first discharge curve, which is attributed to the Li+ insertion concentration

morphology as observed in the SEM images in Figure 1a−c, and high surface coverage was also observed in the lower magnification SEM images (Figure S2). For the case of MAPbI3, highly compact films with grains of an average size of around 200 nm were observed. The introduction of bromine in the MAPbIBr2 material decreased the grain size, while the MAPbBr3 presented a very smooth morphology with grain boundaries almost indiscernible. The UV−visible absorption spectra of the obtained films are shown in Figure 2a. As expected, the absorption onset shifted to shorter wavelengths when the iodine anion was replaced by bromine, since the band gap is mainly determined by the hybridization of the metal Pb2+ and halogen X− molecular orbital hybridization.20 The optical band gaps were obtained C

DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry approaching y = 1 (LiyMAPbX3).11 The calculated number of Li+ ions per mole of electrode material were 9.7, 6.6, and 8.7 for MAPbI3, MAPbIBr2, and MAPbBr3, respectively. Improved charge and discharge capacity was found when iodine (MAPbI3) was completely substituted for bromine (MAPbBr3). Hybrid perovskite with a partial substitution of bromine (MAPbIBr2) led to the lower charge−discharge capacity, indicating that there is a competition between crystalline structure and bromine content, as when moving from tetragonal MAPbI3 to cubic MAPbBr3, the lattice parameter is reduced, and therefore a lower amount of lithium is expected to be intercalated. Nevertheless, the higher capacity of MAPbBr3 suggests that the halogen also plays an important role. It should be noted that the theoretical discharge capacity for these materials is close to 50 mA g−1 when there is 1 vacant site per mol available in the pristine hybrid materials for an intercalation mechanism. Our high values are an indication that there must be other processes taking place, such as changes in the perovskite structure or the called conversion reaction process.15 Cycling behaviors of the cells using the hybrid perovskite films were also examined up to 10 cycles. Figure 3b displays the cycle performance for the charge and discharge capacities. Open circles and open up−down triangles denote the discharge capacities. All cells showed a high capacity fade during the first 3−5 cycles, and then the specific capacity achieves ∼50 mA h g−1 with a relative capacity retention of around 87% after 10 cycles, which could plausibly be improved by the use of a binder22 or a more compact layer. Note that this value is close to the already mentioned theoretical value for 1 Li+ ion per mole of electrode material. The capacity reported in this work is comparable to that reported by the composite cathode prepared by doctor blade method containing hybrid perovskite powder (MAPbBr3), binder and carbon additives, which reports a capacity of 330 mA h g−1 (200 mA g−1)10 − 550 mA h g−1 (200 mA g−1)11 and specific capacity of around 150−200 mA h g−1 after 10 cycles. The capacity fade observed in the first cycles is associated with the reactions in the interface between the active material (hybrid perovskite coating) and electrolyte, leading to the formation of a solid electrolyte interface layer (SEI). It is very well-known that this SEI passivating layer consists of a complicated mixture of inorganic and organic components including compounds such as Li2O, LiF, Li2CO3, LiCO2-R, alkoxides, and nonconducting polymers.23,24 This reaction can be mitigated using a protective inorganic coating on the active material.24 The absence of binder or conductor materials can also contribute to the capacity fade and the loss of the capacity retention. We examined the thin film electrode after electrolyte immersion (SEM/EDS results for MAPbBr3 in Figure S3) and after battery cycling. MAPbBr3 was still present as indicated by compositional EDS analysis (Table 1), and also according to other reports demonstrating that the perovskite electrode is still present after battery cycling.11 Nevertheless, there was a change

in the morphology of the electrode with some small detached zones, which has been already proposed by theoretical calculations to correspond to PbX6 octahedra being pulled apart by the inclusion of Li.15 After the experiments were run, it was noticed that the film presented a morphological change, probably due to formation of the SEI, as depicted in Figure 4. The formation of compounds such as LiF and Li2CO3 was corroborated from X-ray diffraction (Figure S4). The presence of metallic Pb and/ or different LixPb metallic alloy was also observed. This indicated that the processes taking place during lithium intercalation were more complex and that some kind of electrode degradation was occurring. A small (200) XRD peak indicated the presence of MAPbI3, but it was not possible to observe other diffraction peaks for this and for the other materials due to their low thickness compared to the SEI layer, which caused the signal to be screened. Our results based on 3D hybrid perovskite shown above indicate the potential application of these class of materials, demonstrating that extrinsic Li+ ions can achieve good intercalation into a 3D perovskite material with poor Li+ extraction capacity. Nevertheless, it has been demonstrated that 2D materials are more suitable for battery applications, since they can allow more intercalation into the free space between layers.25 Therefore, we synthesized 2D hybrid perovskites by including the larger organic cation propylammonium (PA), which has been demonstrated to isolate the 3D structure into layers separated by this large cation, resulting in an increased free volume in the crystalline structure. The new 2D (MA)2(PA)2Pb3Br10 layers presented a yellow color with a slightly large band gap of 2.34 eV (Figure S5) compared to its 3D counterpart MAPbBr3. Figure 5a,b shows the X-ray diffractogram and the schematized crystalline structure, respectively. This tetragonal structure with an interplanar distance along the (020) plane of 20.7 Å is expected to host more Li+ ions. As shown in Figure 5c, the 2D thin film also presented a smooth morphology with small grains due to spatial confinement introduced by the PA molecule. Figure 5d displays the first charge−discharge curves for the cell using a cutoff voltage 0.1−1.2 V and a constant current density of 0.1 mA cm−2 (corresponding to ∼425 mA g−1 normalized by mass of hybrid perovskite thin film). The first discharge curve achieves ∼375 mA h g−1, being lower than that of the 3D hybrid perovskite films and equivalent to 22.3 Li+ ions per mole of material, which is surprisingly high. To clarify the electrochemical performance of the 2D hybrid perovskite films, a composite electrode was prepared by the doctor blade method, mixing 2D (MA)2(PA)2Pb3Br10 powder, carbon, and PVD binder (gap of 200 μm). The composite electrode is named from here as 2D hybrid perovskite powder. Figure 6a shows the cyclic voltammetry (CV) of the 2D hybrid perovskite powder performed at 0.1 mv s−1. The redox behavior is in good agreement with the recent results published by Tathavadekar et al.26 In the first discharge cycle, peaks at 1.1, 0.6, 0.5, and 0.4 V were clearly identified. In agreement with previous XRD results, the large reduction peak at or near 1.1 V corresponds to the Pb(II) → Pb(0) reduction process, and the peaks between 0.4−0.6 V are associated with the formation of different LixPb intermetallic compounds.27 Li−Pb compounds such as LiPb, Li2.6Pb, Li3Pb, Li3.5Pb, and Li4.4Pb have been also identified in the same voltage range using lead-based anode materials.28 In the first charge cycle between 0.2−0.8 V, the

Table 1. Change in Composition of the MAPbBr3 Electrode during Electrochemical Characterizationa sample

atomic ratio before immersion

atomic ratio after electrolyte immersion

atomic ratio after battery cycling

MAPbBr3

Pb:Br = 26:74

Pb:Br:F = 13:69:18

Pb:Br:F = 4:8:88

a Note the increase in fluorine concentration due to the formation of the SEI layer.

D

DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 4. SEM images of the 3D hybrid perovskite films after battery 10th cycling (a) MAPbI3, (b) MAPbIBr2, and (c) MAPbBr3.

Figure 5. (a) X-ray diffractogram, (b) crystalline structure, and (c) SEM image of 2D (MA)2(PA)2Pb3Br10 layered perovskite. Note that in the crystalline structure image, small brown dots correspond to nitrogen atoms, blue dots to carbon atoms, pink dots to hydrogen atoms, yellow dots to bromine, and large gray dots to lead atoms, respectively. (d) First charge−discharge curves. Inset corresponds to the cycling performance.

Figure 6. (a) Cyclic voltammetry (CV) of 2D hybrid perovskite powder performed at 0.1 mV s−1. (b) Charge−discharge profiles of 2D hybrid perovskite powder performed at the constant current of 0.1 mA cm−2.

dealloying reaction of LixPb intermetallic compounds takes place, confirming that these reactions are reversible. At higher oxidation voltages, >0.8 V, oxidation peaks were not observed. This result suggests the formation of irreversible reactions at the hybrid perovskite material during the first lithium insertion process. In the subsequent cycles, the alloying−dealloying

process of the LixPb intermetallic compounds observed at 0.2− 0.8 V shows very stable and reversible reactions. Figure 6b displays the charge−discharge profiles of 2D hybrid perovskite powder performed at the constant current of 425 mA g−1. The first discharge capacity achieves 375 mA h g−1, which coincides with the value obtained from the 2D hybrid perovskite film E

DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX

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After the first charge, the resistances associated with the liquid electrolyte and the 2D hybrid perovskite material remained almost in the same value of 15 and 20 Ω, while the semicircle associated with the interfacial reaction was not observed in the frequency range. Figure 7c shows Nyquist plot of 2D hybrid perovskite after the fifth charge−discharge measurement. The results reveal a similar tendency as those described above for the first charge− discharge measurement. The EIS comparison between first and fifth charge−discharge measurements reveal a reversible mechanism of lithium insertion−extraction behavior without significant modification of the 2D perovskite hybrid material. After the first discharge, the resistance of the 2D perovskite hybrid material became stable, around 25−35 Ω, corresponding to a stable formation of 2D perovskite hybrid material and SEI. The reversible reaction verified by the semicircle at middle-frequency, observed after discharge (0.15 Hz) and its absence during charge, was associated with the formation of a reversible reaction of Li−Pb compounds. The mechanism of the lithium insertion− extraction may consist of intercalation mechanism in the hybrid material accompanied by the alloying−dealloying process of the LixPb intermetallic compounds. Taking into account the CV and charge−discharge profile measurements, we can infer that the initial irreversible reaction observed during first discharge, Pb(II) → Pb(0) reduction process, does not produce a substantial contribution in the EIS profile. This result advised that the reaction produced in the lithium insertion lead to the formation of a stable SEI, which could prevent the degradation of the 2D hybrid perovskite material in the subsequent cycles. In fact, after the first discharge measure, the battery shows a good electrochemical performance with a capacity efficiency of 90% after the fifth cycle. The irreversible reaction was also observed in the first discharge curves of 3D hybrid perovskite films (Figure 3a), which can be associated with the larger calculated number of Li+ ions per mole of electrode material. The formation of insoluble products on the lithium surface electrode was observed after electrochemical performance (Figure S8). The dissolution of the 2D hybrid perovskite materials was observed during the electrochemical performance of the films, but no visible depositions on the lithium electrode were observed. Either in the capacity obtained from 2D hybrid perovskite film or powder, an underestimation of the total capacity is supposed. The layer formed on the lithium electrode could be responsible for the clear difference of the first charge capacity of the 2D hybrid perovskite obtained from the film and powder, showing that the lower capacity is a result of the difficult intercalation from the perovskite to the lithium surface. As shown in Figure S9 and Table S2 for the images of the 2D hybrid perovskite powder electrode and the atomic composition, respectively; there were some changes on the electrode, but there was still Pb and Br in the composition, after discharge, charge, and CV characterization showing that the powder electrode is more stable than the film electrode. According to XRD of the 2D perovskite composite electrode (Figure S10), similar peaks as those found in the 3D perovskites were observed, indicating the formation of LixPb alloys and intermediate products. After the fifth charge−discharge cycle there was still some 2D perovskite present. As mentioned previously, the use of a binder to mitigate the reactivity of the perovskite with the electrolyte helped, but new alternatives should be explored for the practical use of the hybrid perovskite

(Figure 5d). The discharge profile, lithium insertion, shows different plateaus (voltage slope) that match well with the CV discussed above. The plateaus around 1.2 V and 0.2−0.6 V correspond to the Pb(II) → Pb(0) reduction process and the formation of LixPb intermetallic compounds, respectively. The first charge capacity attains 80 mA h g−1, which is ca. 20% of the capacity efficiency. The successive discharge−charge curves show a considerable improvement of the capacity efficiency of 90%, retaining a reversible capacity of ∼80 mA h g−1. Impedance measurements were carried out to understand the charge−discharge behavior of 2D hybrid perovskite powder. The impedance measurements were performed in the asprepared cell and after charge−discharge process at first and fifth cycles. Figure 7a shows Nyquist plot of 2D hybrid

Figure 7. Nyquist plot of 2D hybrid perovskite: (a) before, (b) first, and (c) fifth charge−discharge measurements.

perovskite before charge−discharge measurements; three resistance components were observed at 1 MHz, 200 and 1 Hz. The EIS data were quantitatively analyzed using the equivalent circuit model shown in Figure S7a. The resistance in the high-frequency at 1 MHz of ∼15 Ω is attributed to the resistance of liquid electrolyte, which can be observed in the intersection point at the Z′ axis with the middle-frequency semicircles. The other two resistances at middle-frequency of 25 Ω and 23 Ω could indicate the resistance derived from the 2D hybrid perovskite material and interfacial reaction, respectively.29,30 The interfacial reaction resistance could be attributed to a SEI produced by a simultaneous reaction between 2D hybrid perovskite material and liquid electrolyte. Figure 7b shows the Nyquist plot of 2D hybrid perovskite after first charge−discharge measurement. Three resistance components were observed after lithium insertion at 1 MHz, 50 and 0.15 Hz. The EIS data were quantitatively analyzed using the equivalent circuit model shown in Figure S7a-b. After the first discharge, the resistance associated with the liquid electrolyte was not modified; however, the resistances associated with the 2D hybrid perovskite material and interfacial reaction became higher, achieving 35 Ω and 97 Ω. F

DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX

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as an active material in batteries including the compatibility with adequate lithium electrolyte and the preparation of composites electrodes.

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partially supported by the Colombian “Departamento Nacional de Planeación”, SGR Collaborative Project 2013000100184 between Empresas Públicas de Medellin, Andercol S.A., Sumicol S.A.S., and Universidad de Antioquia. SEM analysis was carried out with JIB-4600F at the “Joint-use Facilities: Laboratory of Nano-Micro Material Analysis”, Hokkaido University, supported by the “Material Analysis and Structure Analysis Open Unit (MASAOU)”.

CONCLUSIONS In summary, we have successfully fabricated thin film electrodes of 3D and 2D organic−inorganic hybrid perovskites for battery/microbattery applications. We investigated the effect of composition and crystalline structure on the charge/ discharge capacities. Charge capacity improved when moving from MAPbI3 to MAPbBr3 in the 3D MAPbI3‑xBrx family. The fabricated cells with these 3D hybrid perovskites exhibited large discharge capacities of 350−500 mA h g−1, while charge capacities were 70−160 mA h g−1 in the first cycle that may account for other processes taking place during the Li intercalation. The identification of bromine as improving capacity element allowed us to investigate (MA)2(PA)2Pb3Br10 as a new 2D material for battery applications, leading to the reversibility of the lithium insertion−extraction of 100% in the first cycle. The combination of the low temperature solution processing and high capacities obtained in this work highlight the potentiality of these new materials for battery and microbattery applications. We also found that the mechanism of the lithium insertion−extraction may consist of an intercalation mechanism in the hybrid material accompanied by alloying−dealloying process of the LixPb intermetallic compounds. Finally, further investigation to improve the electrode stability, as well as optimal electrolyte and battery configuration is required, since it has been demonstrated that these class of materials are also able to host Na+ ions,31 which will motivate future investigations.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00397. Scheme of the battery electrochemical characterization and hybrid perovskite thin film images, lower magnification SEM images, SEM/EDS analysis for MAPbBr3 after electrolyte immersion, XRD after battery cycling and SEM of the 2D film and powder composite electrode, photographs of the composite electrode and equivalent circuit models of the EIS data (PDF) Accession Codes

CCDC 1828504 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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REFERENCES

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AUTHOR INFORMATION

Corresponding Authors

*(F.J.) E-mail: [email protected]. *(NC.R.N.) E-mail: [email protected]. ORCID

Nataly Carolina Rosero-Navarro: 0000-0001-6838-2875 Akira Miura: 0000-0003-0388-9696 Franklin Jaramillo: 0000-0003-1722-5487 G

DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.inorgchem.8b00397 Inorg. Chem. XXXX, XXX, XXX−XXX