III-2. Atomic & Solid State Physics (Muon)

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Li-ion diﬀusion in LiFeSix P1−x O4 /C with x = 0 and 0.03
F. Astuti,∗1 D. P. Sari,∗2,∗3 M. Zainuri,∗1 Darminto,∗1 and I. Watanabe∗2
The primary issue in the use of LiFePO4 in battery
applications is its low intrinsic electronic conductivity
and lithium-ion diﬀusion coeﬃcient. Furthermore, there
is an urgent need to improve the cycle life and longterm cyclability of LiFePO4 .1) Several strategies havebeen considered to enhance the electronic/ionic conductivity and cycle life of LiFePO4 , such as carbon coating,
reduction of particle size, and element doping.2)
Powder samples of LiFeSix P1−x O4 /C with x = 0 and0.03 were prepared by a solid-state method. Singlephase samples of LiFePO4 have not been obtained sofar. Our study strongly supports that Si doping signiﬁcantly improves the electrochemical performance ofLiFePO4 as reported in Ref. 3). A sample with x = 0.03
yielded the highest speciﬁc capacity. Further study on
Li-ion diﬀusion is signiﬁcant for increasing the battery
performance. Muon spin relaxation (µSR) is a powerfultool to study Li-ion diﬀusion.
In order to study the Li-ion diﬀusion inLiFeSix P1−x O4 /C further, we measured zero-ﬁeld andlongitudinal-ﬁeld µSR (ZF- and LF-µSR, respectively)
using the ARGUS spectrometer at the RIKEN-RAL
Muon Facility. The ZF-µSR was measured in the temperature range of 5–30 K, and the LF-µSR was measured

Fig. 2. Temperature dependences of ∆ with (a) x = 0 and(b) x = 0.03 and of λ with (c) x = 0 and (d) x = 0.03 forLiFeSix P1−x O4 /C.

at 300 K under low magnetic ﬁelds of 5 G and 10 G.
Figure 1 shows the LF-µSR spectra of LiFeSix P1−x O4 /C with (a) x = 0 and (b) 0.03. The dynamic behavior at
300 K was clearly observed for LiFeSix P1−x O4 /C withx = 0 and 0.03 because there is only a small “decoupling”
eﬀect due to applied LF. The spectra were ﬁtted by an
exponentially relaxing dynamic Kubo-Toyabe function.
Based on Fig. 2, the ﬁeld distribution width (∆)
and ﬁeld ﬂuctuation (λ) were found to be independentof temperature down to 50 K, whereas ∆ and λ increased with temperature decreasing below 50 K for
samples with x = 0 and x = 0.03. There is no abruptchange in ∆ or λ in either sample. Following the results in Ref. 4), we obtained the diﬀusion coeﬃcient as
DLi = (1.598 ± 0.0033) × 10−10 cm2 /s, for x = 0 and
DLi = (1.751 ± 0.0037) × 10−10 cm2 /s for x = 0.03. The
present result demonstrates the slight increase of Li-ion
diﬀusion by silicon substitution, which can improve theperformance of LiFePO4 cathode materials. Additionally, from the ZF-µSR results, the magnetic transition
temperature was detected, starting from the temperature 50 K and close to the estimation of the Neel temperature, TN , LiFePO4 reported in Ref. 5).
Fig. 1. LF-µSR spectra on of LiFeSix P1−x O4 /C with (a) x =0 and (b) x = 0.03.
∗1
∗2
∗3

Department of Physics, Institut Teknologi Sepuluh Nopember
RIKEN Nishina CenterGraduate School of Engineering and Science, Shibaura Institute of Technology

References

1) M. Nishijima et al., Nat. Commun. 5, 4553 (2014).
2) Z. Xu et al., J. Electrochem. Soc. 163, A2600 (2016).
3) M. Zainuri et al., Key Eng. Mater. 860, 75 (2020).
4) M. Månsson et al., J. Phys. Conf. Ser. 551, 012037 (2014).
5) J. Sugiyama et al., Phys. Rev. B 84, 054430 (2011).

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