Long-Range and Short-Range Transport Dynamics of Li Ions in LiMn₂O₄

Abstract

Investigation of lithium ion transport between different crystallographic sites in different phase structures has been regarded as a challenging diffraction issue. In this work, isothermal dielectric spectroscopy and the electric modulus of LiMn 2 O 4 (LMO) were adopted to reveal Li-ion transport behavior. Dielectric and electric modulus spectra show three thermally activated processes: (i) enhanced mid-frequency dielectric permittivity above 133 K contributed by the short-range migration of Li ions, (ii) high-frequency dielectric relaxation associated with hopping of small polarons, and (iii) low-frequency giant dielectric loss (dc conductivity) caused by the long-range migration of Li ions at high temperature. In addition, an obvious change of dielectric permittivity around 280 K happens at structural transition from cubic to tetragonal of LMO. Furthermore, it was found that the short-range mobility of Li ions and hopping of small polarons lead to the variation of β in the Kohlrausch−Williams−Watts (KWW) function of the electric modulus. Thus, our work provides a revealing insight into the electrical transport mechanism and migration dynamics of Li ions in LMO.

Understanding the Effect of Al Doping on the Electrochemical Performance Improvement of the LiMn2O4 Cathode Material

“…3 Nevertheless, when the batteries worked at higher C-rates or at elevated temperatures (over 55 °C), significant capacity fading and structural instability of the LiMn 2 O 4 electrode would occur. 4 The fast capacity decay of LiMn 2 O 4 may result from the following: (1) the coordinated Jahn−Teller effect of high-spin Mn 3+ ions, 5 (2) lattice mismatch between Li + -rich and Li + -deficient domains due to the volume change between the charged and discharge states in the electrode, 6 (3) decomposition of the electrolyte due to the high charge/discharge voltage, 7 and (4) loss of crystallinity during cycling. 8 To solve the above problems, partial replacement of Mn 3+ through chemical doping was used to increase the average oxidation state of Mn (higher than 3.5), which will well restrain the structural deformation caused by Jahn−Teller distortion and hence improve the cyclic performance of LiMn 2 O 4 .…”

“…Nevertheless, when the batteries worked at higher C-rates or at elevated temperatures (over 55 °C), significant capacity fading and structural instability of the LiMn 2 O 4 electrode would occur . The fast capacity decay of LiMn 2 O 4 may result from the following: (1) the coordinated Jahn–Teller effect of high-spin Mn 3+ ions, (2) lattice mismatch between Li + -rich and Li + -deficient domains due to the volume change between the charged and discharge states in the electrode, (3) decomposition of the electrolyte due to the high charge/discharge voltage, and (4) loss of crystallinity during cycling …”

Crystal structure, optical characterization, conduction and relaxation mechanisms of a new hybrid compound (C6H9N2)2[Sb2Cl8]

“…When the frequency is low ( ω → 0), the electron hops from one site to another throughout the whole lattice, producing long-range dynamics, whereas short-range dynamics are produced when the hopping motion of the electron is restricted to isolated sites at high frequencies. 64 Electron hopping may be thought of as the mobility of electron in an endless lattice of identical potential wells at low frequencies, whereas at high frequencies, the hopping of electron is constrained in a double well with infinite potential barriers via forward-backward hopping. 65 …”

High Ionic Conduction and Polarity-Induced Piezoresponse in Layered Bimetallic Rb4Ag2BiBr9 Single Crystals

“…As per this theory, in the LF region, the ions exhibit a successful jump from one lattice site to another and can be treated as hopping ionic motion throughout an infinite lattice of the identical potential well. , This results in the long-range mobility of the ions, giving rise to frequency-independent DC conductivity in the LF region. On the other hand, in the HF region, the hopping motion of ions can be impeded by being confined in the double-potential well with barriers, sometimes resulting in an unsuccessful jump (forward–backward–forward hopping) , and hence the frequency-dependent, dispersive HF region. The frequency-independent DC conductivity region is observed to cross over to the frequency-dependent dispersive region at the hopping frequency, ω = ω H where the transition from long-range to short-range ionic transport takes place.…”