negative muon spin spectroscopy for ion diffusion measurements

2023 Fiscal Year Final Research Report

• Project/Area Number: 20K21149
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 29:Applied condensed matter physics and related fields
• Research Institution: Comprehensive Research Organization for Science and Society
• Principal Investigator: SUGIYAMA Jun 一般財団法人総合科学研究機構, 中性子科学センター, 特任研究員 (40374087)
• Project Period (FY): 2020-07-30 – 2024-03-31
• Keywords: ミュオンスピン回転緩和 / 正ミュオン / 負ミュオン / イオン拡散 / 電池

Outline of Final Research Achievements

In order to study ion diffusion in solids, a positive muon spin rotation and relaxation (muSR) technique has been developed through the observation of the fluctuating internal nuclear magnetic filed caused by ion diffusion. However, positive muons also start to diffuse at high temperatures in any solids, leading to difficulty to extract information on ion diffusion. On the contrary, a negative muon implanted into solids is captured by nuclei so as to form a muonic atom. Such muonic atom is immobile up to the decomposition temperature of the solid, besides the negative muons captured by diffusing ions. Therefore, when both positive and negative muSR provide a dynamic behavior with a similar thermal activation energy, it is evidenced that not muons but ions are diffusing. Using such complementary mu+-SR techniques, we have studied diffusion species in three typical electrode materials for Li-ion battery and found that Li is more mobile than positive muon.

Free Research Field

固体物理、固体化学

Academic Significance and Societal Importance of the Research Achievements

固体中のイオン拡散を測定する手法として提案されたミュオンスピン回転緩和法について、ミュオン自身が拡散している可能性を、負のミュオン素粒子を用いて検証した。典型的なLiイオン電池の正極材料については、Li+が正ミュオンより動的なこと、つまりLi+が拡散していることを示した。これにより、拡散係数を性能指標とした異なる材料間での優劣比較が可能となった。今後開発が進むであろう「全固体電池」においては、固体中のイオン拡散が電池性能を決める。ミュオンスピン回転緩和法が、現行および将来電池の開発に重要なツールとなると期待している。