Zugeng Lin

Investigations of lithium manganese oxide materials for lithium-ion batteries

Abstract As candidates for cathode materials in lithium-ion batteries, lithium manganese oxides are attractive and competitive. In this work, the feasibility of using a novel manganese oxide with a large-tunnel structure (i.e. todorokite, tunnel size: 3 × 3) as cathode material in lithiumion batteries has been explored. It is found that the initial capacity of todorokite material with Mg2+ in the tunnel is 151 mAh g−1 at a discharge current density of 0.1 mA cm−2. It still has a capacity of 128 mAh g−1 after four charge-discharge cycles. The effects of different cations, such as Co2+, Ni2+, Li+ etc., in the todorokite tunnel structure, on the electrochemical characteristics of the materials are also studied using slow-rate cyclic voltammetry and electrochemical impedance spectroscopy (EIS). Finally, the intercalation process of Li+ in the spinel manganese oxide films has been investigated using the in situ electrochemical quartz crystal microbalance (EQCM) method. It is shown that the intercalation process of Li+ in the films can be divided into at least two stages. The results also implied co-intercalation of solvent with Li+ in the second stage.

Performance and characterization of lithium-manganese-oxide cathode material with large tunnel structure for lithium batteries

Abstract The synthesis, structure characterization and electrochemical performance of novel todorokite electrode materials (tunnel size: 3×3) for lithium batteries have been studied in this paper. It is shown by means of XRD that synthesized materials (e.g., Mg 2+ -containing sample) have todorokite structure. It is also found that the reversibility of the Li + insertion process into the todorokite materials decreased after acid treatment due to removal of Mg 2+ from the tunnel and the breakdown of the tunnel structure during the following intercalation/deintercalation cycles. The electrochemical impedance spectra (EIS) for todorokite electrode materials are measured and simulated. It was measured that the apparent diffusion coefficient ( D Li+ ) of todorokite material is at a level between 10 −7 and 10 −10 cm 2 /s by use of potential-step electrochemical spectroscopy.

Influence of surface pretreatment and charge-discharge mode on cycle performance of metal hydride electrodes

Abstract The influence of surface pretreatment and charge–discharge mode on the cycle performance of metal hydride (MH) electrodes is studied by using stable, AB5-type, hydrogen-storage, alloy particles. The initial electrochemical performance of MH electrodes, which use copper-coated and electroless nickel-plated hydrogen-storage alloy particles, respectively, is improved, but the cycle lives are the same as that of a bare MH electrode. It is considered that the cycle lives of MH electrodes depend primarily on the bulk properties of hydrogen-storage alloy particles. The pulverization of these particles is the main cause of the degradation in electrode life. In addition, it is found that overcharging accelerates the decline in the capacity of the MH electrode. The decreasing charge efficiency of the MH electrode during the course of charge–discharge cycling is due partly to the declining charge–discharge coulombic efficiency of the MH electrode, and its accumulated effect is an important cause of performance degradation of sealed MH/Ni batteries.

Raman spectroscopic study on the surface oxide layer of AB5-type metal hydride electrodes

In conjunction with electrochemical techniques, the microscopic properties and Raman spectra of AB5-type metal hydride (MH) electrodes at different potentials or after different charge‐discharge cycles were characterized by the confocal microprobe Raman method. The experimental results indicate that a composite oxide layer was produced and different Raman spectra were observed for MH electrode at different charge‐discharge stages. It is proposed that nickel plays a main role in the composite surface oxide layer as reactive sites for electrochemical reaction while other components are dispersed evenly to provide a stable corrosion resistance layer to the corrosive electrolyte. Moreover, it was demonstrated that Co, Mn and other alloy components due to their affinity with water, segregated and were enriched progressively in the alloy surface layer, where they subsequently produced oxides, which should be an important cause for the deterioration of MH electrodes.

The effects of surface treatment on metal hydride electrodes using a weak acid solution containing Ni(II)

Abstract A novel surface treatment method using a weak acid solution containing Ni 2+ ions (WANi) for AB 5 -type hydrogen storage alloys is introduced. The properties of treated and untreated metal-hydride (MH) electrodes were investigated using several electrochemical and spectroscopic methods. Ex-situ scanning tunnelling microscopy (STM) and electrochemical results showed that the WANi process modified the alloy surface layer under modest reaction conditions and enhanced the initial electrochemical performances of the electrodes. In-situ confocal microprobe Raman spectroscopic results demonstrated that the formation, growth and properties of alloy surface oxide layers exhibited some differences on the microscopic level. In addition, manganese and cobalt segregated and progressively enriched the alloy surface and were subsequently oxidized/reduced during charge–discharge processes. The changes in the composition and structure of the surface layer of the electrodes are believed to be an important factor causing the deterioration of MH electrodes.

Performance and characterization of metal hydride electrodes in nickel metal hydride batteries

Abstract In this paper, the metal hydride electrodes used in nickel/metal hydride batteries have been investigated, especially the surface properties of the electrodes, using cyclic voltammetry, electrochemical impedance spectrum, in situ laser-scanning photo-electrochemical microscopy (PEM) and ex situ scanning tunnelling microscope (STM). Our results indicate clearly that surface treatment has a great effect on the performance of the electrodes, affecting such as initial discharge capacity and capacity maintenance. Some considerations about design of the surface treatment method are described. In addition, cathodic and anodic photocurrents have been observed in the potential regions of hydride formation and hydride oxidation by using PEM techniques. Ex situ STM results showed that some Ni cluster-like compounds are formed on the electrode surface after treatment with hydrofluoric acid.

In-situ and ex-situ characterization of surface oxide films on AB5-type metal hydride electrodes

Abstract The surface oxide films on AB 5 -type metal hydride electrodes have been investigated by means of in-situ and ex-situ techniques such as in-situ laser scanning photoelectrochemical microscopy (PEM), ex-situ scanning tunneling microscopy (STM) and in-situ confocal Raman spectroscopy. The results indicated that the growth of surface oxide films can be monitored by using in-situ photoelectrochemical methods. Both laser-scanning photoelectrochemical microscopic and confocal Raman microscopic results showed that crack sites on the electrode surface are more feasible to be oxidized than other smooth sites under electrochemical conditions. In addition, the primary surface oxide layer on fresh metal hydride electrode was found to be composite metal oxides with nickel oxide as its main component.

Distribution and laser-induced behavior of lead monooxide on lead electrodes in acid solution

Abstract The distribution and laser-induced behaviour of PbO on lead electrodes have been investigated using photoelectrochemical microscopic (PEM) and cyclic voltammetric techniques. A linear relationship between the potential of the reduction peak for lead monooxide and the pre-oxidation time of the electrodes was obtained at low potential-sweep rates. This result implies that the changes of pH within the inner anodic films could be estimated using the electrochemical method. Some interesting photocurrent characteristics of “laser-induced” oxide “islands” have been observed. In addition, a linear growth mode of PbO has been found at an early stage of growth of the anodic films using a “line-scan” method in the PEM technique.