TG-FTIR-GC/MSを用いた使用済リチウムイオン電池正極の熱分解特性の評価

Pyrolysis characteristics of cathode from spent lithium-ion batteries using advanced TG-FTIR-GC/MS analysis.

• Shaoqi Yu
• Jingjing Xiong
• Daidai Wu
• Xiaoshu Lü
• Zhitong Yao
• Shaodan Xu
• Junhong Tang

抄録

使用済みリチウムイオン電池(LIB)のリサイクル時におけるAl箔と正極材の分離には、熱処理が有効である。本研究では、使用済みリチウムイオン二次電池の正極の熱分解挙動を、ガスクロマトグラフ質量分析計(TG-FTIR-GC/MS)を用いた熱重量分析法を用いて調べた。また、使用済電池に含まれるフッ素の挙動についても調べた。TG分析の結果、正極の分解は3段階のプロセスを経ていることがわかった。最大質量減少率の温度はそれぞれ470℃及び599℃であった。FTIR分析の結果、195℃から928℃までの温度上昇に伴ってCOの放出が増加した。しかし、599℃以上になるとHOの放出は減少傾向を示した。また、フッ化物誘導体の放出も減少傾向を示し、470℃以上になると検出されなくなった。GC-MS分析の結果、HOとCOの放出は同様の傾向を示し、最初の2段階で放出強度が大きくなることがわかった。また、1,4-ジフルオロベンゼンと1,3,5-トリフルオロベンゼンも同様の傾向を示し、最初の2段階で放出強度が大きくなった。しかし、COの放出は異なる傾向を示し、1,2,4-トリフルオロベンゼンの放出と同様に第3段階で最大の放出強度を示し、主に300-400℃の温度で放出が集中した。1,2,4-トリフルオロベンゼンと1,3,5-トリフルオロベンゼンの放出強度は、1,4-ジフルオロベンゼンの放出強度よりは小さいものの、同程度であった。本研究は、使用済LIBの大規模リサイクルに向けた実用的な支援となる。

Thermal treatment offers an alternative method for the separation of Al foil and cathode materials during spent lithium-ion batteries (LIBs) recycling. In this work, the pyrolysis behavior of cathode from spent LIBs was investigated using advanced thermogravimetric Fourier transformed infrared spectroscopy coupled with gas chromatography-mass spectrometer (TG-FTIR-GC/MS) method. The fate of fluorine present in spent batteries was probed as well. TG analysis showed that the cathode decomposition displayed a three-stage process. The temperatures of maximum mass loss rate were located at 470 °C and 599 °C, respectively. FTIR analysis revealed that the release of CO increased as the temperature rose from 195 to 928 °C. However, the evolution of HO showed a decreasing trend when the temperature increased to above 599 °C. The release of fluoride derivatives also exhibited a decreasing trend, and they were not detected after temperatures increasing to above 470 °C. GC-MS analysis indicated that the release of HO and CO displayed a similar trend, with larger releasing intensity at the first two stages. The evolution of 1,4-difluorobenzene and 1,3,5-trifluorobenzene also displayed a similar trend-larger releasing intensity at the first two stages. However, the release of CO showed a different trend, with the largest release intensity at the third stage, as did the release of 1,2,4-trifluorobenzene, with the release mainly focused at the temperature of 300-400 °C. The release intensities of 1,2,4-trifluorobenzene and 1,3,5-trifluorobenzene were comparable, although smaller than that of 1,4-difluorobenzene. This study will offer practical support for the large-scale recycling of spent LIBs.