Electrodes For Lithium Storage Research Articles

Electrochemically Induced Phase Transformation in Nanoscale Olivines Li1−xMPO4 (M = Fe, Mn)

The phase stability and phase transformation kinetics of Li1−xMPO4 olivines are critical to their performance as lithium storage electrodes. In this work, nanoscale (<100 nm primary particle size) Li1−xFePO4 and Li1−xMnPO4 are chosen as model systems for comparison with a coarser-grained LiFePO4 that exhibits a conventional two-phase reaction. The nanoscale materials first exhibit time and state-of-charge dependences of the electrochemical potential and structural parameters which show that stable two-phase coexistence is not reached. The evolution of structural parameters supports the existence of a coherency stress influenced crystal−crystal transformation. However, an additional response, the preferential formation of amorphous phase at nanosize scale, is identified. In Li1−xFePO4, at 34 nm average particle size, at least one amorphous phase of varying Li content coexists with the crystalline phases. In Li1−xMnPO4 of 78 nm particle size, the electrochemically formed delithiated phase is highly disorder...

Li[sub 3]N–Co Nanocomposite: A New Promising Lithium-Ion Storage Material

Li 3 N-Co nanocomposite thin films fabricated by pulsed laser deposition were investigated as lithium storage electrode materials for Li-ion rechargeable batteries for the first time. A considerable capacity of 255 mAh/g could be obtained in the initial charge, indicating that nanosized metal Co could drive the decomposition of Li 3 N at room temperature. Ex situ high-resolution transmission electronic microscopy and selected area electronic diffraction measurements were used to investigate the components and structures of the films after charging and discharging. The ternary compound Li 2.57 Co 0.43 N was revealed to be the lithiated product. A displacement reaction of lithium with a Li 3 N-Co nanocomposite was proposed. Promising results about the Li 3 N-Co nanocomposite used as a new lithium storage material were achieved.

Ionic liquids in electrochromic devices

The ionic liquid (PYR 14TFSI) has proved to be the key material to make a Li-ion conducting element of a complete electrochromic device, when interposed between transparent film electrodes like WO 3 and Li-charged V 2O 5. The key features of this ionic liquid and its mixtures with LiTFSI are the excellent transparency in the visible and NIR optical regions, the good ionic conductivity and the electrochemical compatibility with inorganic Li-intercalation oxide thin film electrodes used in electrochromic devices. The higher optical contrast found during WO 3 colouration with PYR 14TFSI-LiTFSI, compared to that in a conventional non-aqueous electrolyte like PC-LiTFSI, was attributed to the larger inertness of the former one (no decomposition reaction at the lowest electrode potential). This highly conductive ionic liquid has been incorporated into a polymer matrix (P(EO) 10LiTFSI), in order to obtain a transparent solid electrolyte with high Li ion conductivity and good mechanical stability. Finally this solid PYR 14TFSI-P(EO) 10LiTFSI transparent ion conductor was interposed between the same electrodes as above in order to yield a fully solid-state, Li-ion electrochromic device. This new solid electrolyte was able to transfer reversibly a Li ionic charge between 5 mC cm −2 and 10 mC cm −2 from the lithium storage electrode Li x V 2O 5 to the WO 3 electrochromic electrode in less than 100 s at room T, darkening the device from an initial 80% to a final 30% transmittance (at 650 nm). Such a device has been tested first under various constant current conditions, and later under potentiostatic control using ±2 V steps. The latter method allows not only for a faster response of the electrochromic system, but provides also an easier life stability test of the device, which withstood 2000 cycles with little changes in its optical contrast.

Mesoporous Gold Sponge

Mesoporous gold sponge may be prepared by the removal of aluminium from AuAl2 by an alkaline leach. The resulting material has nanoscale pores and channels, with a high specific surface area that can be exploited in electrochemical applications. For example, the material may serve as the basis of a more sensitive capacitive sensor or biosensor, as an electrode material for a high efficiency ultracapacitor, as the semi-transparent current collector in a dye sensitized photovoltaic cell, or as the lithium storage electrode in a lithium ion cell. The properties of the sponge may be controlled by varying its density, pore size, and pore size distribution, factors which are in turn controlled by the microstructure of the precursor compound and the conditions of deposition.

Shape-controlled synthesis and lithium-storage study of metal-organic frameworks Zn 4O(1,3,5-benzenetribenzoate) 2

Polycrystalline metal-organic frameworks Zn 4O(1,3,5-benzenetribenzoate) 2 (named as MOF-177) with different morphologies have been controlled synthesized through a solvothermal route. MOF-177 electrodes for lithium storage exhibit a relatively high irreversible capacity in the first discharge process and a much lower reversible discharge–charge capacity in the following electrochemical cycles. The performance of MOF-177 is found not impressive for application in reversible lithium storage. A preliminary reaction mechanism on the basis of transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) is proposed to understand the chemical behaviors of the electrode.

Electronic Structure and Electrical Conductivity of Undoped LiFePO[sub 4

The electronic structure of LiFePO 4 underpins transport properties important to its use as a lithium storage electrode. Here we have calculated the electronic structure of LiFePO 4 in the ordered olivine structure by a first-principles method to determine (i) the effective mass of carriers and (ii) the nature of the band structure. The electrical conductivity in high purity undoped LiFePO 4 has also been measured experimentally. Spin-polarized calculations show a large electron effective mass and a much smaller but highly anisotropic hole effective mass, suggesting that hole-doped compositions should have the greater electronic conductivity. More surprisingly, the calculations show that this polyanion compound is a half-metal with spin-sensitive band structure, like some other oxides being studied for spintronics applications. This previously unappreciated aspect of the LiFePO 4 electronic structure may play a role in determining transport properties including those relevant to electrochemical applications.

On the electronic conductivity of phospho-olivines as lithium storage electrodes

From our readers: On the electronic conductivity of phospho-olivines as lithium storage electrodes

Electronically conductive phospho-olivines as lithium storage electrodes.

Lithium transition metal phosphates have become of great interest as storage cathodes for rechargeable lithium batteries because of their high energy density, low raw materials cost, environmental friendliness and safety. Their key limitation has been extremely low electronic conductivity, until now believed to be intrinsic to this family of compounds. Here we show that controlled cation non-stoichiometry combined with solid-solution doping by metals supervalent to Li+ increases the electronic conductivity of LiFePO4 by a factor of approximately 10(8). The resulting materials show near-theoretical energy density at low charge/discharge rates, and retain significant capacity with little polarization at rates as high as 6,000 mA x g(-1). In a conventional cell design, they may allow development of lithium batteries with the highest power density yet.

The Carbon-Lithium Negative Electrode for Lithium-Ion Batteries in Polymer Electrolyte

AbstractSeveral types of carbonaceous materials are evaluated as negative electrodes for lithium storage in polymer electrolyte based cells operated at 100ºC. The corresponding faradaic efficiencies of the spherical cycle and the achieved reversible first capacity and rate capacity will be given. A meso carbon yielded a higher capacity than the theoretical 372 mAh/g. This is tentatively explained by the necessary enhancement of the carbon/polymer interfacial properties through the formation of C-Li-O bonding at the carbon surface and by the possible formation of multilayers of lithium on the external a,b planes of disordered carbons. The formation of the passivating layer on the carbon surface will be described.A lithium-ion type battery using coke and LiNiO2 as the negative and positive leads and POE-LiCIO4 was operated at 100ºC and cycled galvanostatically. Good reversible capacity was attained with the LiNiO2 electrode.