Room-Temperature Preparation of All-Solid-State Lithium Batteries Using TiO₂ Anodes and Oxide Electrolytes

Abstract

We tried to prepare solid-state batteries consisting of TiO 2 anodes and a Li 3 BO 3 −Li 2 SO 4 −Li 2 CO 3 solid electrolyte only by room-temperature pressing without any sintering process. The solid-state batteries successfully operated at 90 °C and showed reversible capacity in the range of 278−331 mA h g −1 in the first cycles at 0.01C. In addition to this, the rate capability was remarkably improved by the doping of Nb or Ta into TiO 2 : the doped TiO 2 electrodes exhibited a capacity of 140 mA h g −1 at 0.1C, whereas the undoped TiO 2 showed only 10 mA h g −1 . The charge-transfer resistance of TiO 2 was reduced by the doping of Nb or Ta. The improvement in the anode performance was attributed to the improved electronic conductivity and the expanded interlayer distance by doping. These results demonstrated for the first time that the oxide anodes can operate in bulk-type oxide-based solid-state batteries prepared only by room-temperature pressing.

Fe–Nb Co-Doped Rutile TiO2 for Anode Materials of Li-Ion Batteries

“…Impurity-doped rutile TiO 2 has remarkable applicability. Rutile TiO 2 doped with one kind of cation can exhibit good anode performances as Na-ion batteries − and solid-state Li batteries also. Therefore, co-doped rutile TiO 2 is expected to be a promising anode material for these next-generation batteries.…”

“…In contrast, charge−discharge cycling with deeper lithiation up to 1.0 V caused the enhancement in the discharge capacity (Figures S5 and S6) and the irreversible phase change from monoclinic distorted rutile Li x TiO 2 to distorted layered rock-salt Li x TiO 2 . 26,27,30 The Fe−Nb-doped TiO 2 electrode cycled by the standard lithiation up to 1.2 V could show the highest initial discharge capacity of 200 mA h g −1 and the lowest initial Coulombic efficiency of 48% (Figure S7). The irreversible capacity is possibly attributed to (i) irreversible phase change, (ii) amorphization, and (iii) partial pulverization.…”

“…To bring out the potential performance of rutile TiO 2 , the authors have devised their own ideas. − First, by increasing the crystallinity of TiO 2 , it was made possible for Li to be inserted into the inner part of the particle only by diffusing Li through one crystallite. , Next, we significantly improved the low electronic conductivity of TiO 2 by doping impurity elements such as Nb, Ta, and Cu. − , In addition to this, the crystal lattice and Li-ion diffusion path size in TiO 2 were increased because of a substitutional solid solution of Ti with larger-sized ions. The rutile-type TiO 2 with such ingenuity was able to, for the first time, demonstrate excellent performance not only as an anode for LIBs but also for Na-ion batteries. − In response to the impact of our first report, many researchers made great progress in their research on impurity-doped TiO 2 . − …”

Rutile TiO2 Creates Advanced Na-Storage Materials

“…We also confirmed the phase transformation from rutile TiO 2 to distorted layered rock-salt Li x TiO 2 . 54,55 Interestingly, this phase change did not occur in NIBs likely due to the ionic size difference between Li + and Na + . Li + has an ionic radius of 76 pm, similar to that of Ti 3+ (67 pm).…”

“…As a LIB anode material, rutile TiO 2 is considered to have a lower electrochemical activity than anatase TiO 2 and Li 4 Ti 5 O 12 , which are capable of three-dimensional ion diffusion, and has received negligible attention . In contrast, we focused on its anisotropic diffusion characteristics and have developed an original methodology based on materials chemistry concepts, which are effective for maximizing the potential anode properties of rutile TiO 2 . ,,− The Li + diffusion coefficient along the c -axis is extremely high (10 –6 cm 2 s –1 ) . The diffusion path size of approximately 230 pm is larger than the ionic diameters not only of Li + (152 pm) but also of Na + (202 pm).…”