2017 Fiscal Year Research-status Report
Design of electrode-electrolyte interface based on hybrid materials for all-solid-state lithium batteries using oxide solid electrolytes
| Project/Area Number |
17K17559
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| Research Institution | Hokkaido University |
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Principal Investigator |
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| Project Period (FY) |
2017-04-01 – 2020-03-31
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| Keywords | Hybrid Material / lithium conductor / interfacial resistance |
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| Outline of Annual Research Achievements |
The first stage of the research was focused in the preparation of hybrid organic-inorganic material doped with lithium.
1.Organic-inorganic hybrid precursor solutions using TEOS (tetraethyl orthosilicate), GPTMS (3-glycidoxypropyltrimethosysilane) and EGDE (ethylene glycol diglycidyl ether) with different LiClO4 content were prepared. Solutions are transparent and stable without the presence of precipitation for long time up to 3-4 weeks. Hybrid crosslinked network was verified by Fourier-transform infrared spectroscopy (FTIR) analysis. The results revealed that the formation of crosslinked structure is achieved after 24 hours of polymerization reaction at 60 Celsius degree and 6 hours of polycondensation reaction at room temperature. The structure has a considerable content of hydroxide groups, which are important for bonding in the interface. The incorporation of lithium ([Li+]/[O]=0.09) source lead to a yellowish transparent solution with an ionic conductivity of 6.6 x 10－5 S cm-1.
2.Membranes were prepared by casting process of hybrid solutions and after a solvent removal at 120 Celsius degree. High homogeneity/flexibility with thickness of ~800 μm were obtained. Li-ion conductivities of 10-6 to 10-7 S/cm at R.T., activation energy of around 0.8 eV and transfer number of 0.4 were obtained. The more rigid structure of membrane limits the mobility of lithium ions through the structure producing a lower ionic conductivity. High conductivity was obtained in a ratio Li/O of 0.09 (the increasing of the content of lithium lead to the drop of the conductivity).
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
The ionic conductivity of the membrane is still low. The target of the proposal is to obtain an ionic conductivity in the order of 10-5 to 10-6 S/cm (solid state) to offer sufficient lithium pathway at the interface between electrode and electrolyte. In this regard, lithium source alternatives are being explored to improve the conductivity of organic-inorganic hybrid material without produce change in its chemical properties (stability). Hybrid structure modification through the incorporation of organic and inorganic precursors is being considered. The meso/micro-structuration of active material is being studied, however, the major effort has been focused in the hybrid material.
In order to prepare an all-solid-state battery using oxide-type solid electrolyte, the surface preparation of solid electrolyte pellet and interface study with lithium anode are also important issues. Surface preparation of solid electrolyte pellet by polishing and electrochemical impedance analysis (AC impedance spectroscopy and DC measurements) of interface formed between lithium anode and solid electrolyte is also being performed. Pre-coating with Au, pellet thickness and thermal treatment for lithium deposition are parameters to be optimized.
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| Strategy for Future Research Activity |
Composite electrode preparation will be studied including the process for its deposition on solid electrolyte for fabrication of all-solid-state battery. In this case, commercial LiCoO2 will be used as reference. Slurry of the composite electrode containing hybrid material, active material and additives will be applied on solid electrolyte pellet. Dispersant and compatible solvents will be used.
Parameters to be optimized: particle size of active material, content of hybrid material in the composite electrode, thickness of composite electrode and thermal treatment. Electrochemical properties will be studied using symmetric cells constructed with solid electrolyte and composite electrode. Reactions at surface (Spring8), morphology, etc. will be also investigated and contrasted with the electrochemical analysis.
The parameters stablished with the commercial LiCoO2 will be extrapolated to prepare the composite electrode combining meso/micro-structured active material and lithium doped hybrid material with high ionic conductivity.
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| Causes of Carryover |
More of the grant was used to buy consumables. The applicant pretended to attend to a national conference, however, it was canceled. Therefore it is expected that this amount can be used during the next fiscal year.
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