In situ time-resolved dispersive X-ray absorption fine structure analysis of BaTiO₃–LiCoO₂ composites for lithium ion batteries

Abstract

In this study, in situ time-resolved dispersive X-ray absorption fine structure (DXAFS) analysis of BaTiO 3 LiCoO 2 (BTLC) composites for lithium ion batteries was performed to characterize the cobalt ion valence shift between oxidized and reduced states of driven cells, in an attempt to better understand the contribution of ferroelectric solid electrolyte interfaces (SEIs) to chargedischarge rates. Two types of artificial SEIs, ferroelectric BT and paraelectric Al 2 O 3 , were compared. The magnitude of the shift in the X-ray absorption energy at the peak of the white line, E 1 , during charging and discharging at a 10 C rate, increased in the order of bare LC (0.264 eV) < Al 2 O 3 1 mol % (0.497 eV) < BT 1 mol % (1.15 eV); the corresponding discharge capacities of the laminated cells at 10 C were as follows: bare LC (11.6 mAh/g) < Al 2 O 3 (41.8 mAh/g) < BT (95.1 mAh/g). The increase in E 1 , i.e., the oxidation of Co during charging, intensified under a higher applied potential for the BT-decorated composite compared with that of the Al 2 O 3 -coated specimen. The stronger oxidation of Co for BTLC under application of a large electric field was attributed to the strengthened polarization due to the larger permittivity of BT.

High rate capability of a BaTiO3-decorated LiCoO2 cathode prepared via metal organic decomposition

“…The sharp rise in temperature to the target crystallization temperature of 600 °C, without holding at intermediate temperatures at which LC decomposes in heated octylic acid as mentioned above, yielded a single-phase BT. In our previous study, 22) the XAFS spectra near the Co K edge revealed that the BT-LC composite soaked into the acetic acid followed by sintering at 600 °C for 20 h, corresponding to the same sintering condition of the MOD-3, exhibited slightly broader X-ray absorption peaks than the bare LC. This result indicates that the soaking of the LC into the acid slightly reduces the Co ion from Co 3+ to Co 2+ .…”

“…We have reported the influence of ferroelectric artificial SEIs on the high rate capabilities of LIBs, [19][20][21][22] including decoration of LC with barium titanate (BaTiO 3 ; BT), via a simple liquid phase reaction using Ba acetate and Ti alkoxide as metal precursors. The effect of the BT loading amount on the resulting high rate capability was investigated.…”

“…20) In situ analysis during cell driving was performed to better understand how ferroelectric BT-SEIs contribute to the significant enhancement in high rate capabilities. The results of in situ electrochemical impedance 21) and X-ray absorption fine structure (XAFS) analysis 22) indicated that coating of BTs onto the active materials notably reduces the charge transfer resistance and increase the magnitude of the Co valence shift between Co 3+ and Co 4+ . The polarization of BTs [23][24][25][26] appeared to have an effect on the kinetics of mobile Li ions; however, the exact mechanism has yet to be resolved.…”

Loading effect of a barium titanate artificial interface on high voltage capabilities at high charge and discharge rates

“…The Al 2 O 3 -LC was annealed at 800 °C for 20 h, which are the optimized sintering conditions described elsewhere. 12) Individual cell construction was accomplished by taking the respective synthesized composite powder, acetylene black, and poly(vinylidene fluoride) (PVDF) with a weight ratio of 7 : 2 : 1. These were then mixed into the solvent and integrated into a 2032-type coin cell for evaluation.…”

“…In alignment with this idea, we have been reporting on the markedly enhanced power densities of the LIB cathodes modified with ferroelectric solid electrolyte interfaces (SEIs). [8][9][10][11][12] Amongst these SEIs, the ferroelectric BaTiO 3 (BT) decoration of LiCoO 2 (LC) matrices has shown much promise, exhibiting excellent rate performance. Sol-gelsynthesized 1 mol % BT-LC structures displayed a capacity of 146 mAh=g at a high rate (i.e., 10C).…”