A simple mechano-thermal coating process for improved lithium battery cathode materials (original) (raw)
Related papers
Chemistry of Materials, 2015
Both the origin and mechanism of the improvement in the electrochemical performances of post-thermal treated LiCoO 2 as a cathode material for lithium ion batteries are investigated through high-quality characterization. X-ray diffraction and transmission electron microscopy measurements revealed that the high temperature sintering results in Li deficiency and the consequent formation of spinel Li x Co 2 O 4. The slow quenching allows the two phases of LiCoO 2 and Li x Co 2 O 4 to intermix, whereas the post-thermal treatment at 800 °C results in the separation of the spinel phase at the surface of LiCoO 2. The post-thermal treated material exhibits a much better cell performance for the cycling capacity and charge rate capability than the slowly quenched material. From the conductive atomic force microscopy measurement and electrochemical impedance spectroscopy experiment, it is shown that the high electrical conductivity of the effective coating layer of the post-thermal treated LiCoO 2 performs a role in enhancing the charge transfer activity of the active material.
Improvement of electrochemical stability of LiCoO< sub> 2 cathode by a nano-crystalline coating
Journal of power sources, 2004
A nano-crystalline MgO coating was formed on the surface of LiCoO 2 particle via a sol-gel method. MgO coating can improve the cycling stability of LiCoO 2 significantly. After the 40th cycle a discharge capacity of more than 120 mAh/g was remained for 1 mol% MgO-coated LiCoO 2 , while only 13 mAh/g for pristine LiCoO 2 when both charged up to 4.7 V. During heat treatment and charge/discharge process, Mg 2+ in coatings will diffuse into LiO 2 -layers of LiCoO 2 , which does not cause any detectable shift in X-ray diffractometer (XRD) peak positions, but does impact the XRD peak intensity due to the aberrance of (0 0 3) plane. Mg 2+ ions existing in LiO 2 -layers will stabilize the lattice structure of LiCoO 2 , hence improve the cycling performance of LiCoO 2 cathode. More MgO coating on LiCoO 2 is detrimental to the electrochemical properties of LiCoO 2 cathode, probably due to the electrochemical inactivity of MgO particles.
Mechano-thermal nanoparticulate coatings for enhancing the cycle stability of LiCoO2
Journal of Physics and Chemistry of Solids, 2006
A mechano-thermal coating method was adopted for obtaining LiCoO 2 coated particles with pre-formed pseudo-boehmite nanoparticulate, followed by calcination at 723 K for 10 h. From X-ray diffraction (XRD) analysis it was seen that the coated cathode materials did not show any extraneous phase peaks corresponding to the pseudo-boehmite and the crystal structure, a-NaFeO 2 , remained the same as pristine LiCoO 2 . Scanning electron micrograph (SEM) of the coated samples showed that above the 1.0 wt.% coating level, the excess pseudo-boehmite got glued to the coated cathode particles as spherules. TEM images showed that the Al 2 O 3 particles derived from pseudo-boehmite formed $20 nm thickness coating layer on the LiCoO 2 particles. The XPS/ESCA results revealed that the presence of two different O 1s corresponds to the surface coated Al 2 O 3 and the core material. The electrochemical performance of the coated materials by a cycling study suggest that 1.0 wt.% coated Al 2 O 3 derived from pseudo-boehmite on the two commercial LiCoO 2 samples improved cycle stability by a factor of five and 11 times over the pristine LiCoO 2 cathode material. Cyclic voltammetry revealed that the hexagonal-monoclinic-hexagonal phase transformations were retained for the coated cathode materials upon continuous cycling. r
Journal of Power Sources, 2008
Lithium-ion battery a b s t r a c t LiCoO 2 particles were coated with various wt.% of lanthanum aluminum garnets (3LaAlO 3 :Al 2 O 3 ) by an in situ sol-gel process, followed by calcination at 1123 K for 12 h in air. X-ray diffraction (XRD) patterns confirmed the formation of a 3LaAlO 3 :Al 2 O 3 compound and the in situ sol-gel process synthesized 3LaAlO 3 :Al 2 O 3 -coated LiCoO 2 was a single-phase hexagonal ␣-NaFeO 2 -type structure of the core material without any modification. Scanning electron microscope (SEM) images revealed a modification of the surface of the cathode particles. Transmission electron microscope (TEM) images exposed that the surface of the core material was coated with a uniform compact layer of 3LaAlO 3 :Al 2 O 3 , which had an average thickness of 40 nm. Galvanostatic cycling studies demonstrated that the 1.0 wt.% 3LaAlO 3 :Al 2 O 3 -coated LiCoO 2 cathode showed excellent cycle stability of 182 cycles, which was much higher than the 38 cycles sustained by the pristine LiCoO 2 cathode material when it was charged at 4.4 V.
Ceramics International, 2010
Nanometric-sized LiCoO 2 powders were obtained from a novel sol-gel method, in which the gels were synthesized by the polymerization of citric acid and hydroxypropyl cellulose. Molar ratios of citric acid to metal ions were varied, and the resulting effects on the properties of powders were studied using Fourier transfer infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicate that with a molar ratio of citric acid/metal ions = 1, the resin contains a number of bidentate ligand fractions and higher portion of C-C-O structure, which makes it possible to synthesize the low temperature phase of LiCoO 2 at a temperature as low as 300 8C. The powder calcined at 600 8C exhibits a pure high temperature phase of LiCoO 2 (HT-LiCoO 2 ) with a particle size of about 40-60 nm and a specific surface area of 25.24 m 2 /g. The electrode prepared at 600 8C exhibits a better HT-LiCoO 2 structure and demonstrates a higher first run charge/discharge capacities at 186 and 168 mAh/g, respectively.
Synthesis of nanostructured LiCoO2 AS cathode material for lithium-ion batteries
2013
Nanostructured LiCoO2 powders were prepared by Carbon combustion synthesis of oxide method using carbon as starting materials. The thermo-gravimetric analysis was used to identify interaction features in the system LiNO3-Co3O4-Carbon to produce LiCoO2. X-ray diffraction showed that the as-synthesised product were single phase. The crystalline nanoparticles synthesized were nearly spherical, and their average particle diameters ranged from 60 to 200 nm. Cyclic voltammetry and charge-discharge experiments were applied to characterize the electrochemical properties of the powders as cathode materials for lithium-ion batteries. The cyclic voltammogram curves indicated faster diffusion and migration of Li+ cations in the nanostructured LiCoO2 electrode. In the first charge-discharge process, the material showed the capacity of 200 (mAh)/g.
Journal of The Electrochemical Society, 2010
Ultrathin atomic layer deposition ͑ALD͒ coatings enhance the performance of lithium-ion batteries ͑LIBs͒. Previous studies have demonstrated that LiCoO 2 cathode powders coated with metal oxides with thicknesses of ϳ100 to 1000 Å grown using wet chemical techniques improved LIB performance. In this study, LiCoO 2 powders were coated with conformal Al 2 O 3 ALD films with thicknesses of only ϳ3 to 4 Å established using two ALD cycles. The coated LiCoO 2 powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3-4.5 V ͑vs Li/Li + ͒ range. In contrast, the bare LiCoO 2 powders displayed only a 45% capacity retention. Al 2 O 3 ALD films coated directly on the composite electrode also produced improved capacity retention. This dramatic improvement may result from the ultrathin Al 2 O 3 ALD film acting to minimize Co dissolution or reduce surface electrolyte reactions. Similar experiments with ultrathin ZnO ALD films did not display enhanced performance.
Electrochimica Acta, 2015
Lithium titanates are introduced as coating materials on the surface of Mg-doped LiCoO 2 in which the residual Li 2 CO 3 after synthesis of the active materials is used as a lithium source. It is revealed that two completely different lithium titanate phases (monoclinic Li 2 TiO 3 and spinel Li 4 Ti 5 O 12) can be obtained as the coating materials depending on the concentration of a titanium source. Characterization of the coating materials is performed with various experimental techniques including XRD, nano SIMS, TEM, EELS and current measurement using nano probe. The Li 4 Ti 5 O 12 coating layer from the high concentration of titanium source secures better electrochemical performances than the Li 2 TiO 3 one from the low concentration of titanium source due to its "zero-strain" characteristic. In addition, it is shown that the doped ions (Mg 2+) from the active materials move to the coating layer and strongly enhance the conductivity of Li 4 Ti 5 O 12. Consequently, synergistic effects on the cell performances of cyclability and rate capability from coating and doping for the LiCoO 2 cathode materials are rigorously investigated.
Enhanced electrochemical performance and thermal stability of La 2O 3-coated LiCoO 2
Electrochimica Acta, 2006
An enhanced electrochemical performance LiCoO 2 cathode was synthesized by coating with various wt.% of La 2 O 3 to the LiCoO 2 particle surfaces by a polymeric method, followed by calcination at 923 K for 4 h in air. The surface-coated materials were characterized by XRD, TGA, SEM, TEM, BET and XPS/ESCA techniques. XRD patterns of La 2 O 3 -coated LiCoO 2 revealed that the coating did not affect the crystal structure, ␣-NaFeO 2 , of the cathode material compared to pristine LiCoO 2 . TEM images showed a compact coating layer on the surface of the core material that had an average thickness of about ∼15 nm. XPS data illustrated that the presence of two different environmental O 1s ions corresponds to the surface-coated La 2 O 3 and core material. The electrochemical performance of the coated materials by galvanostatic cycling studies suggest that 2.0 wt.% coated La 2 O 3 on LiCoO 2 improved cycle stability (284 cycles) by a factor of ∼7 times over the pristine LiCoO 2 cathode material and also demonstrated excellent cell cycle stability when charged at high voltages (4.4, 4.5 and 4.6 V). Impedance spectroscopy demonstrated that the enhanced performance of the coated materials is attributed to slower impedance growth during the charge-discharge processes. The DSC curve revealed that the exothermic peak corresponding to the release of oxygen at ∼464 K was significantly smaller for the La 2 O 3 -coated cathode material and recognized its high thermal stability.
LiCoO 2 thin film cathodes grown by sol–gel method
Journal of Electroceramics, 2009
Lithiated layered transitional metal oxide materials of the LiMO2 type and especially LiCoO2 presents interesting specific properties as high energy density, long cycle life and constant discharging properties in a wide range of working conditions as well as a good safety. These properties made these materials excellent candidates as active compounds for high capacity cathode materials for rechargeable lithium batteries. LiCoO2 is the most common lithium storage material for lithium rechargeable batteries, used widely to power portable electronic devices. Operation of lithium rechargeable batteries is dependent on reversible lithium insertion and extraction processes into and from the host materials of lithium storage. In this study, LiCoO2 thin films were prepared by the sol–gel spin coating technique using metal acetate and citric acid as starting materials. Citric acid acts as a chelating agent, which promotes the preliminary reaction between lithium and cobalt and suppresses the precipitation of acetates. The sol–gel method is well known as one of promising thin-film preparation methods, which has good advantages such as low fabrication cost, relatively easy stoichiometry control, high deposition rate and also known as a low-temperature synthesis method for various ceramics. In addition, the crystal phases involved in the thin film can also be controlled by changing the chemical compositions of the sol. The crystallinity, microstructure and electrochemical properties of final films are also studied by XRD, SEM, AFM and galvanostatic charge/discharge cycling test. Films heat-treated under appropriate conditions exhibit high capacity and good crystallinity so those films are considered to be candidates as cathodes for thin-film micro batteries.