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PO 4 / C as a Cathode Material for Lithium Ion Battery
| Content Provider | Semantic Scholar |
|---|---|
| Author | Xiong, Jun-Wei Wang, Yuan-Zhong Wang, Ying-Ying Jian-Xin Zhang |
| Copyright Year | 2016 |
| Abstract | Olivine plate-like structure LiMn0.8Fe0.2PO4/C has been successfully synthesized under mild conditions using H2O/DMSO as solvent and CTAB as surfactant. DMSO and CTAB promote the formation of plate-like structure. The prepared plate-like structure LiMn0.8Fe0.2PO4/C delivers a reversible capacity of 141mAh·g at 0.1C-rate, with 80.2% capacity retention at 7C-rate. Meanwhile, the plate-like structure LiMn0.8Fe0.2PO4/C exhibits excellent cycling stability at room temperature with 98.8% capacity retention after 60 cycles at 1C-rate. The plate-like structure LiMn0.8Fe0.2PO4/C cathode materials may have a promising potential application in li-ion batteries. Introduction The olivine-structured lithium transition metal (LiMPO4, M=Mn, Fe, Ni, Co) as a cathode materials for lithium ion batteries has been attracted increasing attention because of its high theoretical capacity, low cost, potential electrochemical property, thermal stability and environmental friendliness [1]. These LiMPO4 materials have the ability to restrict the internal short circuit in lithium ion battery, because the open phosphate structure of LiMPO4 can promote the motion of lithium ions and the strong covalent P-O bond energy contributes to avoid the oxygen loss and enhance the structure stability [2,3]. The LiMn1-xFexPO4 solid solution cathode materials with high potential(~4.1V) and improved ionic and electronic conductivities are becoming present research focuses. Up to now, considerable studies have been conducted on LiMn1-xFexPO4, with an emphasis on the synthetic methods to control the morphology and improve the electrochemical performance. Various morphologies such as nanoparticles [4-7], nanorods [8], nanoplates [9,10], microspheres [1,11,12] and hollow spheres [13,14] have been synthesized for the LiMn1-xFexPO4. The structure superiorities of different morphologies have been used to improve lithium ion storage properties compared with the bulk counterparts. However, all these synthetic methods for various morphologies demonstrate their deficiencies, such as complicated synthetic process, high cost for large-scale production and high time-energy consumption. Exploring a simple, reliable and less chemical intensive techniques still face large challenges. To use porous material owning high electrode-electrolyte effective contact area, short diffusion path for Li transport and good volume strain accommodate as the cathode of lithium-ion batteries is one possible strategy to enhance the rate performance and cycling life of electrode materials. Herein, we synthesized plate-like structure LiMn0.8Fe0.2PO4/C using a facile and energy-saving oil bath method under relative low temperature(130°C) and normal pressure followed with further annealing process. The dimethylsulfoxide (DMSO) was used to raise the boiling point of hybrid reactants and reduce the Gibbs Free Energy for the reaction. Cetyl Trimethyl Ammonium Bromide (CTAB) serves as surfactant. The synergy of DMSO and CTAB promoted the formation of 2nd Annual International Conference on Advanced Material Engineering (AME 2016) © 2016. The authors Published by Atlantis Press 527 plate-like structure. Moreover, plate-like structure LiMn0.8Fe0.2PO4/C, as electrodes, show excellent rate capability and cycle stability. Experimental Section Materials Synthesis Plate-like structure LiMn0.8Fe0.2PO4/C was synthesized with oil bath method using H2O/DMSO as solvent and CTAB as surfactant. Firstly, according to the stoichiometry, a certain amount of MnSO4·H2O, FeSO4·7H2O and (NH4)H2PO4 were dissolved in a certain volume of distilled water in sequence to form 0.8M MnSO4·H2O, 0.2M FeSO4·7H2O and 1M (NH4)H2PO4 aqueous solutions. Secondly, the same volume of DMSO was added to the solution. 0.5g CTAB was added into the above mixture with magnetically stirring for about 1h. Afterward, 3M LiOH·H2O was added into the above solution slowly with continuous stirring for about 2h. A spot of ammonium hydroxide was added dropwise into the mixture to adjust the pH of 10. The mixture was heated in an oil bath at 130°C for 6 h under argon atmosphere. After the solution was cooled to room temperature, the solid precipitate was washed for several times with deionized water and absolute ethanol, and finally dried in a vacuum drying oven at 80°C for 10h, then sieved to obtain LiMn0.8Fe0.2PO4 sample. For comparison, LiMn0.8Fe0.2PO4 sample without CTAB was also synthesized via the same procedures. In order to obtain a uniform carbon coating on the surfaces of the LiMn0.8Fe0.2PO4 products, they were mixed with sucrose in a weight ratio of 10:1. The mixture was pre-sintered at 250°C for 2h and subsequently calcined at 600°C for 10h under dynamic argon atmosphere with a heating rate of 10°C·min. After cooling down to room temperature, the LiMn0.8Fe0.2PO4/C materials were obtained. Material Characterization The crystal phases of as-prepared samples were characterized by X-Ray Diffraction (XRD) using a Rigaku Dmax-rc diffractometer with Cu Kα radiation (λ=0.154nm), and the morphologies were observed by field emission scanning electron microscopy (FESEM, Hitachi SU-70, Japan) and high resolution transmission electron microscopy (HRTEM, JEM-2100, 200 kV, Japan). The Brunauer-Emmett-Teller (BET) surface area and pore size distribution were performed by ASAP 2020 V3.01 G system. Electrochemical Performance Tests Electrochemical measurements were carried out using CR2025 coin-type cells with lithium foil as the counter and reference electrodes. The working electrodes was mixed by dispersing the sample powders, acetylene black and polyvinylidene fluoride(PVDF) in a weight of 8:1:1 in N-methyl-2-pyrrolidone (NMP). The mixture was magnetic stirred for 24h. Then the acquired slurry was coated uniformly on aluminum foil and dried under a vacuum at 120°C overnight. The electrode was cut into a circle shape with diameter of 14mm for a cell. The cells were assembled in an Ar-filled glove box (SG2400/750TS, Vigor). The electrolyte solution was 1 mol·L LiPF6 dissolved in ethylene carbonate (EC) and dimethyl carbonate (DMC) and diethyl carbonate (DEC) with the volume ratio of 3:1:1. The electrochemical performances of the samples were measured by galvanostatic cycling between 2.5V and 4.5V on a multi-channel battery testing instrument (LAND CT2001A) at various current densities (1C=170mA·g). For the as-prepared materials, the electrochemical impedance spectroscopy (EIS) within 10-100KHz was performed by Advanced Electrochemical System (Ametek PARSTAT 2273). |
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| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
