Current Response at Grain and Grain Boundaries in LiFePO4 Thin Films By Nano-Scanning Electrochemical Cell Microscopy

Creation of high performance electrodes in rechargeable lithium-ion batteries (LIBs) is one of urgent demand to store unused energy towards low-carbon emission society. To satisfy this demand, a facile characterization technique is required for analyzing electrochemical response related to lithium-ion transport via crystal orientation or crystal boundaries in the electrodes. Recently, we have developed a single-channel nano-scanning electrochemical call microscopy (nanoSECCM).¹ The nanoSECCM can obtain current response related to ion transport only as in-situ measurement with nanometer resolution. In this study, we have applied nanoSECCM to characterize the current repose at grain and grain boundaries on the LiFePO₄ thin film electrode. The film is multi-domain structure with sub-micrometer grains including [010] crystal orientation, confirmed by SEM and XRD analyses. The inhomogeneity of the response at grains was visualized from nanoSECCM mapping. The response at particular grain with higher response presumably indicates that it possesses [010] crystal orientation which is known as higher current response in LiFePO₄.² We show that this analysis is a sensitive and facile measure of the influence for crystal orientation and boundaries in electrodes of LIBs.

[1] Y. Takahashi, A. Kumatani et al., Nat. Communi. 5:5450 (2014).
[2] D. Morgan et al., Electrochem. Solid State Lett. 7, A30 (2004).