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Effect of crystallinity of transition metal oxides on lithium insertion/extraction
| Title: | Effect of crystallinity of transition metal oxides on lithium insertion/extraction |
| Other Titles: | リチウム挿入/脱離反応に対する遷移金属酸化物の結晶性の効果 |
| Authors: | Tsumura, Tomoki1 Browse this author |
| Authors(alt): | 津村, 朋樹1 |
| Issue Date: | 25-Mar-1997 |
| Publisher: | Hokkaido University |
| Abstract: | Recently, demand for high energy density batteries has increased with the spread of portable electronic equiptnent and for the develo pment of electric vehicle. Lithium ion battery is one of the candidates, and some battery systems for portable phones and video cameras, such as LiCoO2/C and LiMn2O4C, have already been developed and put on the market. In the lithium ion batteries, lithium insertion/extraction with redox reaction of host is made use of as both cathode and anode reactions. Some transition metal oxides show reversible lithium insertion/extraction and have been studied for electrode materials. Because it is possible for these oxides to have a diiiferent crystal structure and to have a wide range of crystallmity, distinct electrochemical performances of these oxides have been reported. The purpose of the present thesis is to study the effect of the crystallinity of transition metal oxides on lithium insertion/extraction. Five transition metal oxides, spinel type LiMn204, ordered rock-salt type LiCo0.5sNi0.5O2, anatase type TiO2 crystalline V2O5, and crystalline ct-MoO3, were selected as cathode materials. In the first two lithium containing oxides, lithium ions situated in lattice sites (8a sites in LiMn2O4 and 3b sites in LiCo0.5Ni0.5O2) are extracted and inserted. For the rest of three samples, interstitial sites are used as diffusion pass and accommodation sites for lithium ions. LiMn204 and TiO2 have three dimensional channels, LiCo0.5Ni0.5O2, and α-MoO3, have two dimensional gaps, V2O5 has one dimensional channels for the diffusion of lithium ions. In order to investigate electrochemical properties of these oxides, lithium cells using each oxide as cathode were fabricated and the potential change with time during chargedischarge was recorded. Sample powders were characterized by means of X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-VIS absorption spectroscopy. In order to get sample powders with different crystallinity, LiMn2O4 and LiCo0.5Ni0.5O2 were prepared via dicarboxylate. For LiMn2O4, structure and thermal decomposition of the precursor, lithium-manganese-dicarboxylate, were investigated. In oxalate and succinate systems, the precursor was suggested to have a chain-like structure, in which lithium and manganese ions were liked by dicarboxylate ions. For malonate and tartrate systems, mixtures of complex and mangancse salt seemed to be formed. In the complex salt, manganese ion was connected with two dicarboxylate ions as bidentate to be complex anion. Charge balance of the anion was achieved with lithium ion and proton. In all the four precursor systems, mixing on atomic scale of lithium and manganese ions was achieved, and these precursors decomposed at around 300℃ and changed to LiMn2O4 phase without any by-product. For LiMn204 samples, crystallinity of the sample was characterized by lattice parameter, a03 and lattice strain, ε, which were determined by XRD measurements. Lattice parameter increases and lattice strain decreases with the increase in heating temperature and these changes seemed to be due to improvement of cation distnbution in spinel structure and the decrease of mean oxidation state of manganese ion. The first discharge capacity above 3.5 V was found to increase linearly with the decrease of lattice strain and the increase of lattice parameter. Crystallinity of LiCo0.5Ni0.5O2 samples was evaluated by haif width of XRD lincs. The half widths of 003 and 104 lines, which corresponded to development of stacking thickness and extension of the layers, respectively, seemed to increase with the increase of distributio n, or the increase of disorder rock-salt type cubic LiCo0.5O2 domains. The first discharge capacity above 3.O V increascs with the improvement of crystallinity, or the decrease of disordered rock-salt type cubic LiCo0.5Ni0.5O2 domains. For lithium contaming transition metal oxides, the decrease of crystallinity causes not only the decrease of the crystallite size but also imperfection of cation distnbution. Thus the decrease of the crystallinity leads to change in the structural skeleton of host and the structural change seemed to be concerned with the decrease of the capacity. On the other three transition metal oxides, Tio2, v2o5, and MoO3, the first discharge capacity was independent from the crystallinity of the host. For MoO3 powders, any effect of the crystallinity on electrochemical performance was not observed. At the beginning of the first discharge (at the plateau around 2.8 V), the spacing of the van der Waals gap in starting MoO3 structure was widened irreversibly from O.69 to 1.2 nm and the inner structure of the Mo-O octahedron layers was also changed by lithiation. So the effect of crystallinity of pristine MoO3 did not affect to the electrochemical performance. TiO2 powders prepared by hydrothermal treatment of amorphous TiO2 powders were proved to be comprised from amorphous and crystalline anatase parts, though they were reported to be a single phase of anatase type structure. The crystallinity of anatase parts decreased and the amount of amorphous part increased with the decrease in heating temperature. The first discharge curve of TiO2 powders prepared under hydrothermal conditions showed gradual decrease of potential from 3.O to 1.75 V and a plateau at 1.75 V, which are corresponding to lithium insertion into amorphous and crystalline parts respectively. The capacity down to 1.6 V, or capacity of the gradual potential decrease plus that of plateau region, was almost the same among the samples used. For V205 samples, the first discharge potential change up to 400 mA・h・g-1 was strongly affected by host morphology, extension of VO5 layer, but the total capacity down to O.5 V was almost the samples with different crystallinity. The difference in discharge potential was due to slow diffusion of lithium ion in the V205 structure. Electrochemical performance of the cathode of the five transition metal oxides is classified into two groups on the basis that whether the crystallinity of these oxides affects to the capacity or dose not. One shows a pronounce effect of crystallinity on the capacity of lithium insertion/extraction and the other shows no effect of the crystallinity on the capacity. LiMn204 and LiCo0.5Ni0.5O2 belong to the former group and TiO2, V2O5, and MoO3 belong to the latter. In the latter group, potential change during discharge was affected by structure type. This classfiication is able to be extended to other electrode materials; graphite, LiCoO2 and LiNiO2 appertain to the former and almost all other electrode materials to the latter. |
| Conffering University: | 北海道大学 |
| Degree Report Number: | 甲第4141号 |
| Degree Level: | 博士 |
| Degree Discipline: | 工学 |
| Type: | theses (doctoral) |
| URI: | http://hdl.handle.net/2115/51421 |
| Appears in Collections: | 学位論文 (Theses) > 博士 （工学）
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Submitter: 津村 朋樹
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