Ferroelectric capacitive memories have not achieved the commercial success originally hoped for them in large volume because the area of the capacitors ("footprint") is too large to scale them up to gigabit density devices, [ 1 ] and a restoring pulse is required after a destructive readout. The non-destructive readout of the binary information is possible from the bipolar switching between high-and low-conductance of a ferroelectric diode under two opposite polarizations, as fi rst discovered by Blom et al. in PbTiO 3 perovskite thin fi lms [ 2 ] and later reported by Choi et al. in bulk BiFeO 3 single crystals and Pb(Zr,Ti)O 3 fi lms. [3][4][5] Important properties of such memory are the ultrafast operating speed depending on the polarization fl ipping time (1-2 ps in principle) [ 6 ] and the high ratio of resistance in the forward and reverse directions (3000:1). [ 7 ] However, most ferroelectrics are insulating wide bandgap semiconductors at room temperature, which limits the maximum diode current to the order of ≈ 20 mA cm − 2 . [ 2 , 3 ] Therefore, reaching a suffi cient ferroresistive diode current for the stable detection of memory status using the sense amplifi ers in modern memory circuitry with tiny cell size is a major challenge.In such strongly insulating ferroelectrics, suffi cient diode currents can, in fact, only be observed in ultrathin fi lms, where quantum mechanical tunneling current dominates [ 8 ] and is modulated by varying the tunneling barrier height along with the polarization reversal. Although this effect has been reproducibly demonstrated through local electron transport from an atomic force microscope (AFM) tip into ferroelectric thin fi lms, [9][10][11] the local-probe-based data storage is incompatible with current complementary metal-oxide semiconductor integration processes. Meanwhile, with macroscopic capacitor-type upper and lower electrodes capping the ultrathin ferroelectric layer, an overwhelming leakage current through existing defect-mediated leakage paths could swamp the tunneling current, thereby making the switching signal unreadable. In addition, large lattice-mismatch stresses in ultrathin epitaxial fi lms prevent their use as longtime retention memories due to preferred domain orientations. [ 12 ] One solution to these diffi culties has been to more broadly consider resistive switching effects in (non-ferroelectric) metal oxides. [13][14][15][16][17] However, most of these resistive switching effects are based on a certain type of defect (ionic or electronic) mediated phenomenon, suggesting the inherent diffi culty in precise control of the switching behavior. In contrast, ferroresistive switching behavior is based on the intrinsic switching of ferroelectric domains without invoking of charged defect migration and may, therefore, possess a fundamental merit over defectmediated mechanisms for achieving reliable performance requisite for commercial production once reliable fabrication parameters are established. A critical measure of such success using ferroelectric s...

The lack of high-power and stable cathodes prohibits the development of rechargeable metal (Na, Mg, Al) batteries.Herein, poly(hexaazatrinaphthalene)(PHATN), an environmentally benign, abundant and sustainable polymer, is employed as auniversal cathode material for these batteries. In Na-ion batteries (NIBs), PHATN delivers ar eversible capacity of 220 mAh g À1 at 50 mA g À1 ,c orresponding to the energy density of 440 Wh kg À1 ,and still retains 100 mAh g À1 at 10 Ag À1 after 50 000 cycles,w hich is among the best performances in NIBs.S uch an exceptional performance is also observed in more challenging Mg and Al batteries.P HATN retains reversible capacities of 110 mAh g À1 after 200 cycles in Mg batteries and 92 mAh g À1 after 100 cycles in Al batteries. DFT calculations,X -ray photoelectron spectroscopy, Raman, and FTIR showt hat the electron-deficient pyrazine sites in PHATN are the redoxc enters to reversibly react with metal ions.

The development of lithium metal batteries is hindered by the low Coulombic efficiency and poor cycling stability of the metallic lithium. The introduction of consumptive LiNO3 as an additive can improve the cycling stability, but its low solubility in the carbonate electrolytes makes this strategy impractical for long-term cycling. Herein we propose LiNO3 as a cosalt in the LiPF6–LiNO3 dual-salt electrolyte to enhance the cycling stability of lithium plating/stripping. Competitions among the components and the resultant substitution of NO3 – for PF6 – in the solvation shell facilitate the formation of a Li3N-rich solid electrolyte interphase (SEI) film and suppress the LiPF6 decomposition. The highly Li+ conductive and stable SEI film effectively tailors the lithium nucleation, suppresses the formation of lithium dendrites, and improves the cycling performance. The competitive solvation has profound importance for the design of a complex electrolyte to meet the multiple requirements of secondary lithium batteries.

Lithium metal is an ideal anode material due to its high specific capacity and low redox potential. However, issues such as dendritic growth and low Coulombic efficiency prevent its application in secondary lithium batteries. The use of three-dimensional (3D) porous current collector is an effective strategy to solve these problems. Herein, commercial carbon nanotube (CNT) sponge is used as a 3D current collector for dendrite-free lithium metal deposition to improve the Coulombic efficiency and the cycle stability of the lithium metal batteries. The high specific surface area of the CNT increases the density of the lithium nucleation sites and ensures the uniform lithium deposition while the "pre-lithiation" behavior of the porous CNT enhances its affinity with the deposited lithium. Meanwhile, the lithium plating/stripping on the sponge maintains high Coulombic efficiency and high cycling stability due to the robust structure of graphitic-amorphous carbon composite in the ether-based electrolyte. Our findings exhibit the feasibility of using CNT sponge as a 3D porous current collector for lithium deposition. They shed light on designing and developing advanced current collectors for the lithium metal electrode and will promote the commercialization of the secondary lithium batteries.

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Enhancing the stability of the interface between the electrode and electrolyte at high voltages is crucial concerning the development of Li-ion batteries with high energy densities. Application of some additives in the electrolyte is not only the simplest but also the most effective way to form a protection layer against the electrolyte decomposition and the electrolyte corrosion to the electrode. Herein, we introduce trimethyl borate (TMB) as an additive of the commercial electrolyte to ameliorate the performance of a LiCoO2 cell charged to 4.5 V because its addition lowers the oxidation potential of the baseline electrolyte (3.75 V vs 4.25 V). By being oxidized preferentially and thus forming a compact protection layer of about 25 nm thick on the cathode surface, the additive suppresses the electrolyte decomposition and protects the LiCoO2 cathode against the structural degradation. The capacity retention of the cell after 100 cycles between 2.5 and 4.5 V at 0.1 C increases from 64 to 81% when 2.0 wt % TMB is added into the baseline electrolyte. The X-ray photoelectron spectroscopic results demonstrate the oxidation of TMB on the cathode and therefore the suppressed decomposition of the electrolyte. The results of the X-ray diffraction and Raman spectroscopy show the better structural maintenance of the LiCoO2 material in the TMB-containing electrolyte. The protection mechanism of the TMB additive was comprehensively studied.

The strong electrostatic interaction between Al3+ and close-packed crystalline structures, and the single-electron transfer ability of traditional cationic redox cathodes, pose challenged for the development of high-performance rechargeable aluminum batteries. Here, to break the confinement of fixed lattice spacing on the diffusion and storage of Al-ion, we developed a previously unexplored family of amorphous anion-rich titanium polysulfides (a-TiSx, x = 2, 3, and 4) (AATPs) with a high concentration of defects and a large number of anionic redox centers. The AATP cathodes, especially a-TiS4, achieved a high reversible capacity of 206 mAh/g with a long duration of 1000 cycles. Further, the spectroscopy and molecular dynamics simulations revealed that sulfur anions in the AATP cathodes act as the main redox centers to reach local electroneutrality. Simultaneously, titanium cations serve as the supporting frameworks, undergoing the evolution of coordination numbers in the local structure.

The lithium and sodium storage behavior of porous carbon remains controversial, though it shows excellent cycling stability and rate performances. This Letter discloses the insertion, adsorption, and filling properties of porous carbon. 7 Li nuclear magnetic resonance (NMR) spectroscopy recognized inserted and adsorbed lithium in this porous carbon but did not observe any other forms of lithium above 0.0 V vs. Li + /Li. In addition, although lithium insertion mainly takes place at low potentials, adsorption was found to be the main form of lithium storage throughout the investigated potential range. Such a storage feature is responsible for the excellent rate performance and high specific capacity of porous carbon. Raman spectroscopy further demonstrated the structural reversibility of the carbon in different potential ranges, verifying the necessity to optimize the potential range for a better cycling performance. These findings provide insights for the design and application of porous carbon.