Hierarchical 3D ZnCo 2 O 4 Nanowire Arrays/Carbon Cloth Anodes for A Novel Class of High-Performance Flexible Lithium-ion Batteries

Transcription

1 Supporting Information Hierarchical 3D ZnCo 2 O 4 Nanowire Arrays/Carbon Cloth Anodes for A Novel Class of High-Performance Flexible Lithium-ion Batteries Bin Liu, Jun Zhang, Xianfu Wang, Gui Chen, Di Chen, * Chongwu Zhou, * and Guozhen Shen, * Wuhan National Laboratory for Optoelectronics and College of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan , China Department of Electric Engineering, University of Southern California, Los Angeles, CA 90089, United States Address correspondence to (G.Z.S.) gzshen@mail.hust.edu.cn; (C.W.Z.) chongwuz@usc.edu; (D. C) dichen@mail.hust.edu.cn

2 Materials and Methods Preparation of carbon cloth substrate. Using carbon cloth as templates, hierarchical ZnCo 2 O 4 nanowire arrays/carbon cloth anodes were fabricated by hydrothermal treatments. Before the fabrication of ZnCo 2 O 4 samples, the carbon cloth substrates were cleaned by sonication sequentially in acetone, deionized (DI) water, and ethanol for 30 min each. After dried, the well-cleaned carbon cloth were transferred into Teflon-lined stainless autoclave. Sample preparation. Hierarchial ZnCo 2 O 4 nanowire arrays/carbon cloth was synthesized via a two-step process. In a typical process, 1 mmol zinc nitrate (Zn(NO 3 ) 2 6H 2 O), 2 mmol cobalt nitrate (Co(NO 3 ) 2 6H 2 O), 2 mmol ammonium fluoride (NH 4 F), and 5 mmol urea (CO(NH 2 ) 2 ) were added to a given amount (35 ml) of distilled water and the mixture was dispersed to form a homogeneous solution by constant intense stirring. After putting a piece of cleaned carbon cloth (2 cm 4 cm), the solution was then transferred into a Teflon-lined stainless autoclave. The autoclave was sealed and maintained at 120 C for 5 h. After the autoclave cooled down to room temperature, the product was collected, washed, vacuum dried and then thermal treated at 400 C for 2 h. Fabrication and Electrochemical Measurement of Lithium-ion Batteries. Carbon cloth with samples covered was first cut into many smaller round pieces with the diameter of 13 mm. Both the carbon cloth with loading samples and bar carbon cloth were weighed in a high-precision analytical balance (Sartorius, max weight 5100 mg, d=0.001 mg). The reading difference was the exact mass for the coated

3 samples on carbon cloth. The loading density of the ZnCo 2 O 4 active materials is calculated as 0.3 ~ 0.6 mg/cm 2. The electrochemical performance of the as-synthesized ZnCo 2 O 4 product was investigated by using it as a binder-free anode in lithium-ion batteries in coin-type half-cells, which were laboratory-assembled by a CR2032 press in an argon-filled glove box. A lithium foil was used as the counter electrode and reference electrodes. A piece of the hierarchical ZnCo 2 O 4 nanowire arrays/carbon cloth was used directly as the working electrode without any polymeric binder or carbon black conductive additives involved and Celgard 2400 polymer separators were employed. As the electrolyte, 1 M LiPF 6 in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 by volume) was used. Coin-type half-cells were cycled at various C-rate (1C corresponding to about 900 mah g -1 with respect the anode mass) and with voltage range of V (vs Li + /Li) at room temperature, using a Land Battery Measurement System. Highly flexible full battery was assembled by using the as-fabricated ZnCo 2 O 4 /carbon cloth as the anode, commercial LiCoO 2 as a cathode (Shanghai ND Energy Technology Co. Ltd, China), LiPF 6 electrolyte, and polymer separator. Using a similar method, the mass of the sample is calculated to be around 15.4~17.7 mg, and the loading density of the ZnCo 2 O 4 active materials is calculated as 1.0~1.2 mg/cm 2. The injection of the electrolyte was conducted in an argon filled glove box after the negative electrode, positive electrode, and separator were rolled together to make the battery core. The electrochemical tests were performed between V for complete anode-limited flexible cells at a constant current density of 200 ma/g with

4 respect to the anode mass on a Land Battery Measurement System. Materials Characterization. Products were characterized with X-ray diffractometer (XRD; X Pert PRO, PANalytical B.V., the Netherlands) with radiation from a Cu target (Kα, λ = nm), field emission scanning electron microscopy (FESEM; JEOL JSM-6700F, 5 kv), and transmission electron microscopy (HRTEM; JEOL, JEM-2010 HT). Battery Assembly. The electrochemical performance of the as-synthesized ZnCo 2 O 4 product was investigated by using it as a binder-free anode in lithium-ion batteries in coin-type half-cells, which were laboratory-assembled by a CR2032 press in an argon-filled glove box with oxygen and water contents below 1 and 0.1 ppm, respectively. A lithium foil was used as the counter electrode. A piece of the hierarchical ZnCo 2 O 4 nanowire arrays/carbon cloth was used directly as the working electrode without any polymeric binder or carbon black conductive additives involved and Celgard 2400 polymer separators were employed. As the electrolyte, 1 M LiPF 6 in ethylene carbonate (EC) and diethyl carbonate (DEC) (1:1 by volume) was used. To make a full battery, aluminum and nickel strip as the current collectors were jointed to the side of cathode and anode electrodes, respectively. An aqueous solution of 1.05 mol/l LiPF 6 in a mixture of ethylene carbonate (EC) and diethyl carbonate (DMC) (v/v = 1:1) served as the electrolyte and a Celgard 2400 membrane was used as the separator. The whole assembly was packaged with flexible plastic bag by edge

5 bonding machine. Figure S1. The FESEM image of the carbon cloth. Figure S2. The SEM of as-fabricated ZnCo 2 O 4 nanowire arrays growing on carbon cloth.

6 Figure S3. Charge-discharge cycling test of carbon cloth at the current density of 200 mah g -1 from 0.01 to 3.0 V. Figure S4. TEM of the nanostructured electrode after charge-discharge cycles at 25 C. (a) after 50th discharge. (b) after 50th charge.

7 Figure S5. XRD pattern of the discharged electrode at 0.02 V after 30 cycles at 25 C. The calculated d-spacings are in good agreement with the standard values of Li 2 O, Zn, Co, and LiF from JCPDS files (Li 2 O: ; Zn: ; Co: ; LiF: ). Figure S6. (a-c) Digital images of flexible batteries based on ZnCo 2 O 4 /liquid electrolyte/licoo 2 in the practical applications. The flexible battery could be used to repeatedly light up a commercial green LED and a LCD mobile display in the dark.