Negative Muon Spin Rotation and Relaxation Study on Battery Anode Material, Spinel Li4Ti5O12

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To study an intrinsic self-diffusion coefficient of Li + ( D Li J ) in a battery anode material, spinel Li 4 Ti 5 O 12, negative and positive muon spin rotation and relaxation (μ ± SR) spectra were measured using a powder sample in a temperature range of 100–400 K. The implanted μ + in this study locates at an interstitial site near the O 2– ion to form an O–H like bond, whereas the implanted μ – is mainly captured by an oxygen nucleus, resulting in muonic oxygen formation. The μ + at an interstitial site is known to diffuse at high temperatures. Nevertheless, the muonic oxygen is immobile until the spinel decomposition temperature. The field fluctuation rate determined with μ – SR (ν – ) increased with increasing temperature above 200 K with a 0.08(5) eV thermal activation energy. The ν – ( T ) curve agreed well with the ν + ( T ) curve obtained with μ + SR. Thus, the origin of a fluctuation in the internal nuclear magnetic field was unambiguously confirmed as Li + diffusion, i.e., the possibility of μ + diffusion is clearly excluded. From the obtained ν ±, D Li J was estimated to be 8(2) × 10 –12 cm 2 /s at 300 K with E a = 0.08 eV, under the assumption that the Li + ions at the regular tetrahedral site jump to the vacant octahedral site with a random walk process.