One of the possible ways to obtain a safe and high-energy-density anode (negative electrode) for a rechargeable lithium battery is the replacement of lithium by carbon materials. Rechargeable lithium-ion batteries (LIB) using two kinds of carbon as the anode material have been accepted in the marketplace. One is graphite with a theoretical capacity 372 mAh/g (C 6 Li). Another is hard carbon with very low H/C atomic ratios (smaller than 0.1), which can store more lithium, with discharge capacities surpassing the theoretical capacity of graphite.On the other hand, there is another kind of interesting carbonaceous material that has not been used in the LIB industry. Carbon materials with high H/C atomic ratios in the range of 0.2 to 0.4 can store much more lithium, with discharge capacities surpassing those of hard carbons with low H/C atomic ratios. We reported that polyacenic semiconductor (PAS) material with an H/C of 0.25 obtained by pyrolyzing phenolic resins showed a reversible capacity of 850 mAh/g. 1 Dahn et al. 2 reported that polyvinyl chloride (PVC)-based disordered carbon with an H/C of 0.36 had a reversible capacity of 940 mAh/g. 2 Takami showed that perylene-based disordered carbon with an H/C of 0.26 had a reversible capacity of 804 mAh/g. 3 Although these materials have high capacities, they show low efficiency (65-75%) during the first charge and discharge. In particular, Li charged into the carbon electrode cannot be discharged from these electrodes. It is well known that the lithium supply in the LIB arises from the cathode when the cell is manufactured. In order to compensate for the loss of lithium that is irreversibly consumed, an excess of cathode material must be used. As a result, the energy density of the cell decreases and the cost of the cell increases. In order to make practical use of this kind of material, not only a large capacity is important, but also a high efficiency is necessary.In this study, we report the devleopment of a new carbonaceous material with a discharge capacity of 1017 mAh/g and efficiency of 81.5% for LIB using isotropic pitch as the raw material. According to our solid-state 13 C-nuclear magnetic resonance (NMR) results, a crystallite of the carbonaceous materials consists of graphene sheets with a disk-like shape. Therefore, we call these materials polycyclic aromatic hydrocarbons (PAHs) in this study. ExperimentalPreparation of PAHs.-The PAHs were produced in a tube furnace for general experiments. Generally, 30 g of isotropic pitch was placed in a ceramic boat and introduced into the tube furnace. Air in the furnace was replaced by N 2 for at least 20 min. The raw material was heated at a rate of 10ЊC /min to 650ЊC under a nitrogen atmosphere, which was maintained for 4 h. The obtained carbonaceous material was cooled to room temperature under a nitrogen atmosphere. As a reference material, PAS using phenolic resin as the raw material was also prepared under the same conditions.Structural characteristics of the carbonaceous material.-13 C NMR measurements were ...

Herein, the impact of wet O 2 annealing on the phase transition of ZrO 2 thin films was investigated and compared with the impact on phase transition of HfO 2 thin films. The results showed that wet O 2 annealing to crystallized ZrO 2 and HfO 2 dramatically promoted the phase transition from tetragonal (t) to orthorhombic (o) to monoclinic (m) compared with dry O 2 annealing. In addition, the ferroelectric phase of approximately 17nm thick ZrO 2 films was formed without m-phase formation by wet O 2 annealing, and the ferroelectricity of ZrO 2 was found to be independent of wet O 2 annealing temperature. The switchable polarization (P SW ) and the coercive field (E C ) were approximately 6 μC cm −2 and 1.5 MV cm −1 , respectively. Furthermore, larger P SW was obtained for thinner ZrO 2 films. Finally, we discussed the possible approaches to further promote the t→o-phase transition for ZrO 2 thin films by wet O 2 annealing.

Wet annealing of the ZrO2 thin film can promote martensitic phase transition, leading to the formation of the ferroelectric orthorhombic (o-) phase. However, the present remanent polarization does not achieve the corresponding material potential of ferroelectric ZrO2. In this study, to enhance the ferroelectricity of ZrO2 thin films, the o-phase formation mechanism by wet annealing was presented considering the thermodynamics by systematically investigating the impact of wet annealing on the HfO2–ZrO2 solid solution for promoting phase transition. The structural analysis results indicated that wet annealing at low and high temperatures can promote the martensitic transition of Zr-rich Hf1–x Zr x O2 and Hf-rich Hf1–x Zr x O2, respectively. In addition, the Zr content exhibiting strong ferroelectricity increased from 0% (HfO2) to 66%. We performed a quantitative estimation of the phase deconvolution through polarization-electric field simulations, incorporating the depolarization field model. According to the change in the phase fraction by wet annealing, all results can be qualitatively and clearly understood based on the phase diagram of the HfO2–ZrO2 system. The impact of wet annealing pertains to the film-thinning effect, which tends to increase the thermodynamic driving force. Finally, we discuss possible solutions to suppress the film-thinning effect by introducing OH ions and improving ZrO2 ferroelectricity.

No abstract