Engineered Electronic Contacts for Composite Electrodes in Li Batteries Using Thiophene-Based Molecular Junctions (original) (raw)
Related papers
Bulletin of Materials Science, 2016
The P3HT grafted on CNTs to form the P3HT-g-CNTs nanocomposites was synthesized and their morphologies, structure have been characterized via the sedimentation test, scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results showed that the P3HT-g-CNTs has a better thermal stability than that of the P3HT/CNTs blend. The nanocomposite based on P3HT-g-CNTs and doped spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) have been fabricated via mixing process. The structure and morphologies of LNMO/P3HT-g-CNTs nanocomposites have also been performed by SEM, XRD and TEM. The electrochemical performance of LNMO/P3HT-g-CNTs nanocomposites as cathode materials of lithium-ion batteries were investigated by cyclic voltammetry and electrochemical impedance spectroscopy and exhibited the high diffusion of lithium ions in the charge-discharge process.
Electrochimica Acta, 2015
Triple carbon coated LiFePO 4 composite is prepared by spray drying-carbothermal reduction (SD-CTR) method. The triple carbon sources (viz. graphene oxide, thermoplastic phenolic resin and water-solubility starch) play different roles in constructing the hierarchical conductive architecture. The structure, component and morphology of the as-obtained LiFePO 4 composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy. The results indicate that, compared with double carbon coated LiFePO 4 counterparts, the triple carbon coated LiFePO 4 composite possesses smaller crystallite and high-efficiency of carbon coating such as more complete coating, lower I D /I G ratio, and better conductive architecture. Benefited from the above mentioned superiority, the triple carbon coated LiFePO 4 composite exhibits outstanding electrochemical performance, especially for high-rate capability, which reaches up to 120 mA h g −1 at 10 C.
2009
The amphiphilic Ru-bipyridine complex, Z-907Na acts as a surfactant for solubilization of single walled carbon nanotubes (SWNTs) in acetonitrile+t-butanol. The supramolecular assembly Z-907Na/SWNT was characterized by optical and Raman spectro/electrochemistry. Its redox potential of 3.5 V vs. Li/Li + is matching almost exactly the formal potential of LiFePO4/FePO4 couple. The Z907Na/SWNT assembly is adsorbed on the surface of LiFePO4 (olivine) via the free carboxylic groups at the bipyridine ligand. This provides a composite material with roughly monolayer coverage by Z-907Na. Electrodes fabricated from Z-907Na/SWNT/LiFePO4 composite exhibited greatly enhanced activity for electrochemical Li + extraction/insertion compared to the performance of electrodes made from pure LiFePO4. Ke ywords: olivine cathode, Li-ion battery, carbon nanotubes, Ru-bipyridine complexes
In the present study, we have developed a simple and cost-effective approach for the synthesis of carbon coated LiFePO 4 wherein different carbon precursors were used to find out the suitable precursor for carbon coating. Initially, the appropriate amount of Li, Fe, and P precursors and carbon source (glucose/sucrose/fructose) were dissolved in ethanol solution followed by hydrothermal treatment at 180 C to obtain carbon coated LiFePO 4. The structure and morphological analysis of in-situ carbon coated LiFePO 4 revealed the formation of thin and homogeneous carbon layer on crystalline single-phase LiFePO 4 particles with fructose used as carbon precursor. Raman analysis confirms the presence of more ordered graphitic carbon and the I D /I G ratio is 1.01, 0.69 and 0.87 for C-LFP-S, C-LFP-F and C-LFP-G respectively, indicating that fructose assisted in-situ carbon coating leads to the formation of more ordered carbon coating on LiFePO 4 with high graphitization degree in comparison with carbon coating by glucose and sucrose. HR-TEM results revealed the presence of uniform carbon distribution, which encapsulates the crystalline LiFePO 4 particles forming a core-shell structure in the presence of fructose as carbon precursor. C-LFP-S delivered a capacity of 125 mAh/g at 0.1 C rate but then due to non-uniform carbon layer distribution, the capacity faded out completely when tested at higher Crates. Whereas C-LFP-F delivered a discharge capacity of 98 mAh/g at 0.1 C and 48 mAh/g at 1 C, which is promising compared to the LiFePO 4 carbon coated using sucrose and glucose. It is concluded that LiFePO 4 carbon coated using monosacrides as carbon precursors showed better electro-chemical performance in terms of capacity and cyclic stability when compared to LiFePO 4 carbon coated using dissacrides, attributing that uniform, thin layer, and highly ordered graphitic carbon coverage on nano sized LiFePO 4 particles greatly reduces the polarization resistance and hence improving the electrochemical performance of C-LFP-F.
Electrochemistry Communications, 2009
The poor electronic conductivity of LiFePO 4 has been one of the major issues impeding it from achieving high power and energy density lithium-ion batteries. In this communication, a novel polymer-wiring concept was proposed to improve the conduction of the insulating electrode material. By using a polymer with tethered ''swing" redox active molecules (S) attached on a polymer chain, as the standard redox potential of S matches closely the Fermi level of LiFePO 4 , electronic communication between the redox molecule and LiFePO 4 is established. Upon charging, S is oxidized at the current collector to S + , which then delivers the charge (holes) to the LiFePO 4 particles by intermolecular hopping assisted by a ''swing" -type motion of the shuttle molecule. And Li + is extracted. Upon discharging, the above process is just reversed. Preliminary studies with redox polymer consisting of poly (4-vinylpyridine) and phenoxazine moiety tethered with a C 12 alkyl chain have shown promising result with carbon-free LiFePO 4 , where effective electron exchange between the shuttle molecule and LiFePO 4 has been observed. In addition, as the redox polymer itself could act as binder, we anticipate that the polymer-wiring concept would provide a viable approach to conducting-additive and binder free electrode for high energy density batteries.
Improvement of electrochemical performances of LiFePO4 cathode materials by coating of polythiophene
Journal of Alloys and Compounds, 2010
A series LiFePO 4 /polythiophene (LiFePO 4 /PTh) composites were synthesized by in situ polymerizing thiophene monomers on the surface of LiFePO 4 particles. Electrochemical impedance spectra (EIS) measurements show that the coating of polythiophene significantly decreases the charge transfer resistance of LiFePO 4 electrodes. Transmission electron microscopy (TEM) tests show that LiFePO 4 could be completely coated by addition of proper amount of polythiophene. The electrochemical performance of polythiophene and LiFePO 4 /PTh for lithium insertion and extraction was examined by charge/discharge testing. The composites demonstrated an increased reversible capacity and better cycling ability compared to the bare LiFePO 4 .
A new process is developed for preparation of conductive carbon coated LiFePO 4. Excess lithium significantly improved the electrochemical performance of LiFePO 4. M€ ossbauer spectroscopy identifies the presence of new impurity phases. LiFePO 4 with excess lithium made in presence of surfactant is a promising cathode. a b s t r a c t We have synthesized carbon coated LiFePO 4 (C-LiFePO 4) and C-Li 1.05 FePO 4 with 5 mol% excess Li via sol egel method using oleic acid as a source of carbon for enhancing electronic conductivity and reducing the average particle size. Although the phase purity of the crystalline samples was confirmed by x-ray diffraction (XRD), the 57 Fe M€ ossbauer spectroscopy analyses show the presence of ferric impurity phases in both stoichiometric and non-stoichiometric C-LiFePO 4 samples. Transmission electron microscopy measurements show nanosized C-LiFePO 4 particles uniformly covered with carbon, with average particle size reduced from ~100 nm to ~50 nm when excess lithium is used. Electrochemical measurements indicate a lower charge transfer resistance and better electrochemical performance for C-Li 1.05 FePO 4 compared to that of C-LiFePO 4. The aim of this work is to systematically analyze the nature of impurities formed during synthesis of LiFePO 4 cathode material, and their impact on electrochemical performance. The correlation between the morphology, charge transfer resistance, diffusion coefficient and electro-chemical performance of C-LiFePO 4 and C-Li 1.05 FePO 4 cathode materials are discussed.
Carbon nanotube-modified LiFePO4 for high rate lithium ion batteries
A hybrid cathode material for high rate lithium ion batteries was prepared by ball-milling and spray-drying a slurry containing LiFePO4 nanoparticles, glucose and carbon nanotubes (CNTs) in water, followed by pyrolysis at 600 oC for 6h under a gas mixture of 5% H2 in Ar. CNTs with a large aspect ratio form a continuous conductive network connecting the LiFePO4 nanoparticles and amorphous carbon, which significantly reduces the electrical resistance of the cathode. The hybrid material can deliver a specific capacity of 99 mAh/g at a 50 C charge/discharge rate. An excellent cycling performance was also demonstrated, with a capacity loss of less than 10% after 450 cycles at a 10 C rate.