Fast growth of battery market driven by electric vehicle (EV) and stationary energy storage system (ESS) segments has stimulated interest for lithium titanate Li₄Ti₅O₁₂ (LTO) with its low cost, perfect cycleability and excellent safety. Whereas low electric conductivity (10^-8 ÷ 10^–13S/cm) is a weak point of LTO, it can be compensated by the grain size reducing down to sub-micron even nano scales. In spite of modern level of nanotechnology development, the structural characterization is still mainly made by non-local methods. In this work we demonstrate that structural heterogeneity in commercial negative electrode material LTO with sub-micron grain size synthesized using standard solid-state method can be described not only thermodynamically, but also locally in terms of structural characterization of single particles using standard micro-Raman Spectroscopy together with Scanning Electron Microscopy.

Solid state synthesis of Li₄Ti₅O₁₂ was made using chemically pure titanium dioxide TiO₂ (anatase) and chemically pure lithium carbonate Li₂CO₃by the following reaction:

2Li₂CO₃ + 5TiO₂ = Li₄Ti₅O₁₂ + 2CO₂↑                                                                      (1)

Our modification of usual solid-state method, based both on analysis of intermediate reactions and review of the published data, uses three consequent synthesis stages with intermediate grinding which increased influence surface layers on material physical properties. In order to simplify other phases observation we knowingly increased the content of phase diagram nearest compositions TiO₂ и Li₂TO₃by using partial (incomplete) synthesis with skipped third stage.

Raman spectra of single particle (Figure 1) clearly demonstrate heterogeneity of phase transformations during reaction (1) and allow making us some conclusions about the processes peculiarities which can’t be made otherwise.

Figure 1: SEM images and corresponding Raman spectra of single particles of (b) final phase Li₄Ti₅O₁₂ and two nearest phases: (a) Li₂TiO₃ and (c) TiO₂ rutile. SEM images sizes are 0.8×1.0 µm.