In situ Raman spectroscopy of LiFePO₄: size and morphology dependence during charge and self-discharge

Abstract

Previous studies of the size dependent properties of LiFePO4 have focused on the diffusion rate or phase transformation pathways by bulk analysis techniques such as x-ray diffraction (XRD), neutron diffraction and electrochemistry. In this work, in situ Raman spectroscopy was used to study the surface phase change during charge and self-discharge on a more localized scale for three morphologies of LiFePO4: (1) 25 ± 6 nm width nanorods, (2) 225 ± 6 nm width nanorods and (3) ∼2 μm porous microspheres. Both the large nanorod and microsphere geometries showed incomplete delithiation at the end of charge, which was most likely caused by anti-site defects along the 1D diffusion channels in the bulk of the larger particles. Based on the in situ Raman measurements, all of the morphologies studied exhibited self-discharge with time. Among them, the smallest FePO4 particles self-discharged (lithiated) the fastest. While nanostructuring LiFePO4 can offer advantages in terms of lowering anti-site defects within particles, it also creates new problems due to high surface energies that allow self-discharge. The in situ Raman spectroscopy also showed that carbon coating did not provide significant improvement to the stability of the lithiated particles.

Light-assisted delithiation of lithium iron phosphate nanocrystals towards photo-rechargeable lithium ion batteries

“…Similarly, the dye could not have been reduced considering that its tiny amount (1:1,000) was able to oxidize the whole LFP for at least 15 times as confirmed by Raman analysis (Supplementary Fig. 14) that revealed the presence of N719 (refs 33, 34) in photo-oxidized sample with FePO 4 (refs 35, 36). In addition no new impurities such as Li 2 O, Li 2 CO 3 or LiOH were observed in the analysis of the film as confirmed by EELS analysis (Supplementary Fig.…”

Reaction at the Electrolyte–Electrode Interface in a Li‐Ion Battery Studied by In Situ Raman Spectroscopy

“…The modified coin cell was fabricated using the method described by Wu et al 1 In this study, a 1 mm hole was drilled in the back of a 2032 type coin cell (Wellcos Corporation, Gunpo, Korea), and the cell was used as the cathode can. The modified coin cell was fabricated using the method described by Wu et al 1 In this study, a 1 mm hole was drilled in the back of a 2032 type coin cell (Wellcos Corporation, Gunpo, Korea), and the cell was used as the cathode can.…”

“…[1][2][3][4] Understanding the working mechanism of Liion batteries is very important. 1,2 Therefore, there is demand to improve the capacity, power, durability, and safety of Li-ion batteries.…”

“…[1][2][3][4] Understanding the working mechanism of Liion batteries is very important. [1][2][3][11][12][13] However, the interpretation of the highly overlapped spectra obtained during the charge-discharge process remains difficult because the electrochemical reactions in the batteries are very complicated. Recently, to monitor the cell performance of Li-ion batteries during electrochemical processes, modified cells were fabricated and various analytical tools were applied.…”

In situ methods for Li-ion battery research: A review of recent developments

“…This creates a window for the laser light to go through. In order to reach the electrode, two configurations can be used [61]: The first configuration [62,63] makes use of a top current collector foil perforated near the casing opening, or is based on a current collector grid for which the mesh size is approximately an order of magnitude smaller than the laser beam diameter. The second option comprises of a current collector, a lithium foil and separator, which are all configured with a hole to expose the second electrode at the bottom of the electrochemical cell.…”