Zhaolin Liu

Synthesis and characterization of LiNi1−x−yCoxMnyO2 as the cathode materials of secondary lithium batteries

Abstract LiNi1−x−yCoxMnyO2 (0≤x≤0.5, 0≤y≤0.3) were prepared by heating Ni1−x−yCoxMny(OH)2 and LiNO3 in flowing oxygen for 10 h at 550°C, followed by another heating at 750°C. The XRD patterns of LiNi1−x−yCoxMnyO2 (0≤x≤0.5, 0≤y≤0.3) samples with different x and y values show a pure phase of layered hexagonal structure. The lattice parameters a, c and the unit cell volume are found to decrease with increasing x in LiNi1−xCoxO2. The partial substitution of Ni by Co and Mn as in LiNi1−xCoxO2 and LiNi1−yCo0.2MnyO2 has a positive effect on lithium stoichiometry. However, lithium deficiency is still found after a prolonged thermal treatments (24 h). Among the doped materials synthesized, LiNi0.8Co0.2O2 and LiNi0.7Co0.2Mn0.1O2 have shown the best characteristics in terms of initial capacity and cycle life.

Electroless preparation and tribological properties of Ni-P-Carbon nanotube composite coatings under lubricated condition

Ni-P-Carbon nanotube (CNT) composite coatings as well as Ni-P-SiC and Ni-P-graphite coatings were prepared by electroless plating. The tribological properties of these composite coatings were investigated using a ring-on-block test rig under lubricated condition. The Ni-P-CNT composite coatings exhibited not only high wear resistance but also low friction coefficient compared with the Ni-P-SiC and Ni-P-graphite composite coatings. The favorable effects of CNTs on the tribological properties of the electroless coatings are attributed to improved mechanical properties and unique topological structure of the hollow nanotubes. In addition to preventing the rough contact between the two mating metal surfaces, the shorter CNTs can easily slide or roll within the surfaces of friction pairs. Therefore, the wear rate and friction coefficient of Ni-P-CNT composite coatings can be substantially reduced.

Cycle life improvement of LiMn2O4 cathode in rechargeable lithium batteries

Abstract Spinel LiMn 2 O 4 and LiCo 0.1 Mn 1.9 O 4 were synthesized by solid state reactions and were used as the positive electrode in liquid cells with Li as the negative electrode. Through extensive ball milling of the spinel with carbon black during the preparation of the cathodic mix, significant decrease in contact resistance between the oxide phase and carbon particles was achieved. The spinel LiCo 0.1 Mn 1.9 O 4 cathode so prepared showed good cyclability and rate capability.

Electrochemical lithiation and de-lithiation of carbon nanotube-Sn2Sb nanocomposites

Nanocomposites of carbon nanotubes (CNTs) with Sn2Sb alloy nanoparticles were prepared by KBH4 reduction of SnCl2 and SbCl3 precursors in the presence of CNTs. SEM and TEM examinations showed that most of the Sn–Sb alloy nanoparticles were present in high dispersion in the CNT web, while others were deposited directly on the outside surface of the carbon nanotubes. Constant current charge and discharge tests using the nanocomposites as Li+ storage compounds showed higher specific capacities than pristine CNTs and better cyclability than unsupported Sn2Sb particles. The first cycle de-lithiation capacity of 580 mAh/g from a CNT–56 wt%Sn2Sb nanocomposite was nevertheless reduced to 372 mAh/g after 80 deep charge and discharge cycles. The uniform dispersion of Sn2Sb alloy in the CNT web and on the surface of CNTs have substantially improved the usability of the Sn2Sb particles to the extent that the nanocomposites of CNTs and Sn2Sb may be considered as a candidate anode material for Li-ion batteries.

A new method for preparing lithiated vanadium oxides and their electrochemical performance in secondary lithium batteries

Abstract This paper describes a new method for preparing lithiated vanadium oxides which are suitable as the cathode material for secondary lithium batteries. Characterization by powder X-ray diffraction (XRD), infrared spectroscopy (IR), scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) shows that these oxides are somewhat structurally different from LiV 3 O 8 prepared by the solid-state reaction route, although the starting materials are identical in both cases. The discharge capacity of the oxide is much higher than that of crystalline LiV 3 O 8 , and can attain 250 mAh g −1 at the current density of 0.2 mA cm −2 . The specific capacity and the cycling behaviour of these lithiated vanadium oxides are closely related to post-synthesis heat treatment. This suggests that the amount of water bound to the structure determines electrochemical performance of the oxide in secondary lithium batteries.

Amorphous Sn2P2O7, Sn2B2O5 and Sn2BPO6 anodes for lithium ion batteries

Abstract BPO 4 was used as an intimate mixture of B 2 O 3 and P 2 O 5 to react with SnO to form amorphous Sn 2 BPO 6 , and to alleviate the need for ternary reactions between SnO and the volatile oxides P 2 O 5 and B 2 O 3 . The BPO 4 -synthesised amorphous Sn 2 BPO 6 performed better than previous attempts, and amorphous Sn 2 P 2 O 7 and Sn 2 B 2 O 5 prepared similarly for comparison; even under conditions of high current density (150 mA/g) and high discharge potential limit (1.4 V). In Sn 2 B 2 O 5 the clustering of Sn was evident by X-ray diffraction after charging and discharging. The good performance of Sn 2 BPO 6 is perhaps due to the robustness of the BPO 6 4− framework in repeated cycling. The reversibility in charge and discharge reactions from the second cycle onwards can be rationalised by the usual alloying mechanism. Both the initial decomposition reactions of the glasses and the passivation of the anode surface by electrolyte solution components are believed to contribute to the observed first cycle irreversibility.

Preparation of sodium molybdenum oxides by a solution technique and their electrochemical performance in lithium intercalation

Abstract Several sodium molybdenum oxides with different structures were prepared by acidification of Na 2 MoO 4 solutions with 1–3.5 N of strong acids (HCl, HNO 3 ) at 100°C followed by heat treatment. Structural and compositional analyses of the oxides show that their structures were determined by preparation conditions such as acid type and concentration, and heat-treatment temperature. The electrochemical intercalation of lithium into these oxides was attempted using them as the positive electrode materials for secondary lithium batteries. The results show reversible lithium intercalation and electrochemical performance that greatly depends on the oxide structure and composition.

Modifications of synthetic graphite for secondary lithium-ion battery applications

Abstract Experimentally, three types of synthetic graphite from TimRex (SFG44, SFG15 and KS6) were plated with copper electrolessly. The specific capacities of untreated TimRex samples are typically in the range of 140–280 mA h/g, with low coulombic efficiencies in the first few cycles of charge and discharge. Electroless copper plating on these graphites could substantially improve the material performance in discharge capacity and coulombic efficiency. Some improvement in high rate dischargeability was also observed.