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成果報告書詳細
管理番号20190000000573
タイトル*2018年度中間年報 革新型蓄電池実用化促進基盤技術開発(国立大学法人東京農工大学)
公開日2019/6/11
報告書年度2018 - 2018
委託先名国立大学法人東京農工大学
プロジェクト番号P16001
部署名次世代電池・水素部
和文要約
英文要約Title: Research and Development Initiative for Scientific Innovation of New Generation Batteries 2 (RISING2) (FY2016-FY2020) FY2018 Annual Report, Tokyo University of Agriculture & Technology

To realize innovative batteries using conversion-type metal fluorides and insertion- type metal sulfides as positive electrodes with high specific capacities, stabilized Si negative electrodes (NEs) was mainly improved by the optimization of Li pre-doping condition including the behavior analysis.
From dQ/dV analysis of the charge/discharge curves for Li pre-doped Si NEs, the capacity fading was found to be attributed to the electronic contact loss between Si nanoparticles by large volume change, which causes to destroy the stabilized Si interphase. At first, we tried to keep the electronic conductivity by the following three methods; i) use of CCCV mode for charging, ii) the cut off potential lowering at discharge in the range of 1.5 to 0.7 V, and iii) pressure loading by laminated cell. The CCCV mode enabled to achieve 2573 and 2377 mAh g-1 (discharge capacity retention: 83 and 77%) at 50th and 100th cycle, respectively. The cut off potential lowering suppressed an increase in the overpotential upon the cycles by keeping the electronic conductivity. Pressure loading by laminated cell successfully reduced the electronic contact loss and kept the stabilized Si interphase.
For the application to innovative batteries, the relationship between the loading amount of Si on current collector and Li pre-doping behavior was investigated by using 4 kinds of Si NEs with different loading amounts, i.e. 0.47, 0.65, 1.23, and 1.78 mg cm-2. The Li content and homogeneity was found to be lowered with increasing the loading amount of Si by CV and Raman spectroscopy especially for the highest loading in the depth direction of NEs. For the problem, Li-naphthalene (NTL) complex solution method was applied to the high loading Si NEs. The XRD and Raman spectroscopy clarified improvement of the Li pre-doping homogeneity. However, Li content became lower than that for the direct pre-doping with Li metal foil. Last year, we suggested that a NTL derivative was effective to increase the Li content. In this year, we newly found a THF derivative as good solvent for deeper Li pre-doping (initial discharge capacity: > 3000 mAh g-1), indicating the effect of electron-donating functional group.
Although 80% utilization rate of Si for 50 cycles was successfully achieved, the Si nanoparticle used in this research found to be difficult to attain 3000 mAh g-1 by the capacity limitation and to keep the stabilized Si interphase. Therefore, we are now also synthesizing a new chestnut-shaped Si microparticle and exploring the proper synthesis condition for mass production. In the next year, we will challenge to continue and establish the mass production methodology together with the particle size control, and produce newly stabilized Li-Si alloy NEs by applying the developed Li pre-doping methods.
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