Micro/Nanostructured Li-rich Cathode Materials with. Enhanced Electrochemical Properties for Li-ion. Batteries

Transcription

1 Supporting information Layered/spinel Heterostructured and Hierarchical Micro/Nanostructured Li-rich Cathode Materials with Enhanced Electrochemical Properties for Li-ion Batteries Ya-Ping Deng, Zu-Wei Yin, Zhen-Guo Wu,, Shao-Jian Zhang, Fang Fu, Tao Zhang, Jun-Tao Li*,, Ling Huang and Shi-Gang Sun*,, College of Energy, Xiamen University, Xiamen, , China State Key Lab of Physical Chemistry of Solid Surface, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen, , China School of Chemical Engineering, Sichuan University, Chengdu, , China Corresponding Author * address: (S. Sun) * address: (J. Li) S-1

2 Experimental details Materials synthesis A one-step solvothermal strategy was developed to synthesis Li-rich materials of Li1.16Mn0.6Ni0.12Co0.12O2. In a typical synthesis route, a stoichiometric proportion of metal acetates, Mn(CH3OO)2 H 2O (0.02 mol), Ni(CH3OO)2 H 2O (0.004 mol), Co(CH3OO)2 H 2O (0.004 mol) of analytical grade, were dissolved to form 100 ml of ethanol solution. Before mol of LiCH3OO H2O with 5% excess was added as lithium source with stirring vigorously, 50 ml ethanol solution of mol H2C2O4 was introduced dropwise as a precipitant agent. Afterwards, the mixed solution was transferred and pretreated in a Teflon-lined autoclave at 180 C for 12h. With continuous stirring, white solvothermal precursor was collected by evaporation of mixed solution. The obtained precursor was precalcined at 450 C for 6 h, and then calcined respectively at 650 C for 24 h or 900 C for 12 h in air. According to their different structural features, samples were named as LS (Layered/Spinel heterostructure, 650 C for 24 h) and PL (Pure-Layered structure, 900 C for 12 h). Materials characterizations The composition, structure and morphology of as-prepared materials were systematically characterized by an inductively coupled plasma optical emission spectrometer (ICP-OES, Thermo Electron IRIS Intrepid II XSP), X-ray diffraction (XRD, Philips X Pert Pro Super X-ray diffractometer with Cu Kα radiation), XRD refinement of Rietveld method (PDXL program, Rigaku Corporation, PDXL 2.1), Raman spectra (XploRA, HORIBA), X-ray absorption fine structure (XAFS, Beamline BL14W1 at the Shanghai Synchrotron Radiation Facility), scanning electron microscopy (SEM, Hitachi S-4800 SEM) and transmission electron microscopy (TEM, JEOL JEM-2100 microscopy). Electrochemical tests Electrodes were prepared by drying the slurry of 80 wt% active materials, 10% acetylene black and 10% PVDF binder onto Al foil current collectors. Such prepared electrodes were dried in vacuum at S-2

3 110 C for 12 h. The loading density of the active materials was approximately 3-4 mg cm -2. The thickness of electrode is about 150 µm. Electrochemical tests were conducted using CR2025 coin cells with lithium foil as anode and Celgard 2400 membranes (Celgard Corporation, USA) as a separator on a Land battery tester (LAND-V2001A, Land Electronic Co. Ltd., Wuhan, China). The electrolyte was 1 M LiPF6 dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) (1:1 in v/v, Guangzhou Tianci High-tech Materials CO. Ltd, China). The galvanostatically charge-discharge measurements were carried out at 30 C with a voltage range of V (vs. Li/Li + ). In our definition, a 1 C rate represents 200 ma g -1. The potentiostatic intermittent titration technique (PITT) experiments have been conducted during the initial discharge process on a CHI660D electrochemical working station. The potential difference of E is -50 mv for each step and the time span is 3600 s. Electrochemical Impedance Spectroscopy (EIS) was conducted over the frequency range of 0.01 Hz to 100 khz on CHI660D workstation. S-3

4 Figure S1 XRD pattern (a) and the initial charge/discharge curves (b) at 1 C between V of spinel Li4Mn5O12. The spinel Li4Mn5O12 was also prepared via the solvothermal route with a stoichiometric ratio of Mn(CH3OO)2, LiCH3OO and H2C2O4 as raw materials. And the preparation condition was as same as that of LS. All main diffraction peaks of XRD in Figure S1a are attributed to Fd3 m structure. As for its electrochemical properties (Figure S1b), as-prepared Li4Mn5O12 presents an obvious long reduction plateau at about 2.7 V in the initial discharge and corresponding oxidation plateau at about 3.0 V in the 2nd charge. Such redox plateaus are derived from Mn 3+ /Mn 4+ of spinel Li4Mn5O12. Due to large capacities offered by the discharge plateau, the initial coulombic efficiency of spinel Li4Mn5O12 at 1 C between 2.0 and 4.8 V was calculated as high as 249%. S-4

5 Figure S2 XRD Rietveld refinement results of PL (a) and LS (b). S-5

6 Table S1 Compositions and XRD Rietveld refinement Results for PL and LS. PL LS ICP-OES results Li1.06Mn0.6Ni0.11Co0.12O2 Li1.11Mn0.6Ni0.11Co0.12O2 Lattice parameter (Å) ahex chex acub I003/I Ni 2+ % (Ni 2+ 3b/Ni 2+ total) Spinel (wt%) 18 Rwp (%) Rp (%) S-6

7 Figure S3 XPS spectra of survey spectra (a), Mn 2p (b), Ni 2p (c) and Co 2p (d) for PL and LS. As shown in the comparative spectra, no shift of peak sites has been found between PL and LS. The dominant peaks of 2p3/2 at binding energies of 641.8, and ev reflect Mn 4+, Ni 2+ and Co 3+ in both PL and LS, respectively. S-7

8 Figure S4 The dq/dv plots of PL (a) and LS (b). S-8

9 Table S2 The comparative data of 1 st cycle electrochemical performance at different rates of PL and LS. Rates PL LS 1 st Charge Capacity (mah g -1 ) 1 st Discharge Capacity (mah g -1 ) Initial Efficiency (%) 1 st Charge Capacity (mah g -1 ) 1 st Discharge Capacity (mah g -1 ) Initial Efficiency (%) 0.2 C C C C S-9

10 Table S3. The comparative data of initial coulombic efficiency and rate performance at V of Li-rich materials from different literatures. Initial Efficiency Rate Capacity / mah g -1 1 C 2 C 5 C [1] 71% ~220 ~200 ~160 [2] 78% (0.1 C) [3] ~67% (1 C) [4] 76% (0.2 C) (3 C) [5] 65.8% (0.5 C) [6] 90% (0.1 C) 140 ~100 ~60 [7] 74% (0.05 C) ~ Unknown [8] 74% (0.5 C) This work 94% (0.2 C) S-10

11 Figure S5 Normalized discharge curves at 1.0 C for PL (a) and LS (b). S-11

12 Figure S6 Plots of chronoamperometry and the relationship of ln I versus t for PL (a, b) and LS (c, d) at first discharge process. The DLi obtained from PITT experiments was calculated based on the solution of a partial differential equation of Fick s second law with mathematical manipulation: D Li = d ln I d t (2L π )2. I (A) is the step current, L (mm) represents the diffusion distance, which is approximately the cathode thickness commonly, and t (s) refers to the step time. S-12

13 Figure S7 Electrochemical impedance spectroscopy (EIS) Nyquist plots of PL and LS at open circle voltage. S-13

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15 8. Zhang, T.; Li, J.-T.; Liu, J.; Deng, Y.-P.; Wu, Z.-G.; Yin, Z.-W.; Guo, D.; Huang, L.; Sun, S.-G., Suppressing the Voltage-Fading of Layered Lithium-Rich Cathode Materials via an Aqueous Binder for Li-ion Batteries. Chem. Commun. 2016, 52, S-15