Promoted Stability and Reaction Kinetics in Ni-Rich Cathodes via Mechanical Fusing Multifunctional LiZr2(PO4)3 Nanocrystals for High Mass Loading All-Solid-State Lithium Batteries.

Sulfide all-solid-state lithium battery (ASSLB) with nickel-rich layered oxide as the cathode is promising for next-generation energy storage system. However, the Li+ transport dynamic and stability in ASSLB are hindered by the structural mismatches and the instabilities especially at the oxide cathode/sulfide solid electrolyte (SE) interface. In this work, we have demonstrated a simple and highly effective solid-state mechanofusion method (1500 rpm for 10 min) to combine lithium conductive NASICON-type LiZr2(PO4)3 nanocrystals (∼20 nm) uniformly and compactly onto the surface of the single crystallized LiNi0.8Co0.1Mn0.1O2, which can also attractively achieve Zr4+ doping in NCM811 and oxygen vacancies in the LZPO coating without solvent and annealing. Benefiting from the alleviated interface mismatches, sufficient Li+ ion flux through the LZPO coating, promoted structural stabilities for both NCM811 and sulfide SE, strong electronic coupling effect between the LZPO and NCM811, and enlarged (003) d-spacing with enriched Li+ migration channels in NCM811, the obtained LZPO-NCM811 exhibits superior stability (185 mAh/g at 0.1C for 200 cycles) and rate performance (105 mAh/g at 1C for 1300 cycles) with high mass loading of 27 mgNCM/cm2 in sulfide ASSLB. Even with a pronounced 54 mgNCM/cm2, LZPO-NCM811 manifests a high areal capacity of 9.85 mAh/cm2. The convenient and highly effective interface engineering strategy paves the way to large-scale production of various coated cathode materials with synergistic effects for high performance ASSLBs.

Enhancing the electrochemical properties of TiNb2O7 anodes with SP-CNT binary conductive agents for both liquid and solid state lithium ion batteries.

A high performance oxide composite electrode is obtained with a two-step solid state calcined titanium niobium oxide TiNb2O7 (TNO) anode and super P-carbon nanotube (SP-CNT) binary conductive agents. The solid state synthesized TNO-0.2C (the proportion of CNTs in the binary conductive agent is 20% wt) anode exhibits a high reversible discharge capacity of 278.6 mA h g-1 at 0.5C, a competitive rate capability with reported works that employed wet chemical methods at moderate rates (178.1 mA h g-1 at 10C), and an excellent capacity retention of 92.2% after 200 cycles at 1.5C/1.5C. The enhancement in electrochemical properties of the TNO-0.2C anode is mainly attributed to the combination of the short range and long range conductive agents in the SP-CNT binary conductive system, which guarantees an efficient electronic conductive network. The Li|Li1.3Al0.3Ti1.7(PO4)3 composite polymer electrolyte (LATPCPEs)|TNO-0.2C solid state batteries are also assembled, which deliver a high initial reversible discharge capacity of 241.3 mA h g-1 at 1C and a good capacity retention rate of 93% after 50 cycles. This work provides an efficient way to improve the electrochemical properties of TNO anodes in lithium ion batteries, especially for solid state batteries.

Electrocaloric Performance of Multilayer Ceramic Chips: Effect of Geometric Structure Induced Internal Stress.

Driven by an ever-growing demand for environmentally benign cooling systems, the past decade has witnessed the booming development in the field of electrocaloric (EC) cooling technology, which is considered as a promising solid-state cooling approach. Multilayer ceramic chip capacitors (MLCCs) represent the optimum structure for EC cooling elements because of large breakdown strengths, low driving voltages, and high macroscopic volumes of active EC materials. However, fundamental relationships between the geometric parameters of MLCCs and the EC coefficient are less understood. In this study, 0.92Pb(Mg1/3Nb2/3)O3-0.08PbTiO3 (PMN-PT) MLCCs with controlled configurations, such as active/inactive layer thickness, number of layers, and active volume ratio, were fabricated, and their EC performance was evaluated. The electric properties of the MLCCs are confirmed to be closely related to the geometric structure, which influences not only the heat flow but also the internal stress, resulting in the variability of EC performance and reliability/breakdown strength. The internal stress arises due to the residual thermal stress originating from the densification-related shrinkage, thermal expansion mismatch during the sintering, and clamping stress arising from the inactive area due to the large strain from the active area under a high electric field. The geometric structure-based stress distribution and the magnitude of stress on the active layers in MLCCs were determined by finite element modeling (FEM) and correlated with the experimental EC coefficients. The results reveal that a low inactive volume percentage is beneficial toward increasing the breakdown field and enhancement of EC performance because of reduced clamping stress on active EC material.

One dimensional lead-free (K,Na)NbO3 nanostructures for a flexible self-powered sensor.

Lead-free (K,Na)NbO3 (KNN) nanorods (NRs), which have a relatively high piezoelectric response and good environmental compatibility, are expected to be used in the application fields of sensors, actuators, etc. In the present study, flexible composite devices with piezoelectric KNN nanostructures were successfully fabricated as a flexible and cost-effective strain sensor. The composition-controlled KNN nanorods (NRs) were synthesized via the molten salt reaction, while piezoresponse force microscopy (PFM) was utilized to characterize the three-dimensional (3-D) morphology as well as the piezoelectric properties of single crystalline KNN nanorods. Then, the KNN NR-polydimethylsiloxane (PDMS) films were fabricated through the tape casting process, and assembled into the self-powered sensor with Cu-coated polyethylene terephthalate (PET) substrates. The as-fabricated KNN-PDMS sensor was affected by the pressing and releasing activities of the human body, and the output voltage was measured concurrently. As a result, the strain sensor obtains an output signal of ∼0.5 V with KNN NR fillers of 0.5 vol% in PDMS, which implies that KNN NRs are promising in the application of lead-free flexible sensor devices.

Significantly improved piezoelectric performance of PZT-PMnN ceramics prepared by spark plasma sintering.

A high-performance piezoelectric material, 0.95Pb(Zr0.52Ti0.48)O3-0.05Pb(Mn1/3Nb2/3)O3 (PZT-PMnN) ceramic, was prepared by using a spark plasma sintering (SPS) method. By systematically comparing the electrical properties, the spark-plasma-sintered sample was demonstrated to be superior to a conventionally sintered sample. With respect to conventionally sintered ceramic, the d 33 of spark-plasma-sintered ceramic increases from 323 pC/N to 412 pC/N, and the increases from 318 pm V-1 to 553 pm V-1. More importantly, the mechanical quality factor (Q m) reaches 583, which is three times higher than the conventionally sintered sample (Q m ∼ 182). Furthermore, the SPS method was found to be capable of promoting other electrical properties simultaneously. Therefore, the SPS method is proposed to be an effective processing method to fabricate PZT-PMnN ceramics of higher performance.

Thickness-dependent phase boundary in Sm-doped BiFeO3 piezoelectric thin films on Pt/Ti/SiO2/Si substrates.

Sm-doped BiFeO3 thin films were fabricated on platinized silicon substrates via a sol-gel method. Sm contents and thicknesses were varied in a wide range to investigate their effects on the phase structure and piezoelectricity. X-ray diffraction and Raman spectroscopy experiments revealed a rhombohedral to orthorhombic phase transition and the co-existence of both phases in a certain compositional vicinity. It is found that the proportion of a rhombohedral phase increased with film thickness at the compositions corresponding to the phase transition boundary, indicating the influence of the film thickness on the phase structure. The phase transition phenomenon and film thickness effect on the boundary were also studied by piezoresponse force microscopy. Based on the structure analysis and piezoelectric characterization results, a phase diagram of thickness versus composition was proposed, in which the morphotropic phase boundary was located at 9% to 11% in thinner Sm-doped films and shifted towards the Sm-rich side with increasing thickness.

Synthesis of highly piezoelectric lead-free (K, Na)NbO3 one-dimensional perovskite nanostructures.

High-aspect-ratio single-crystalline KNN nanorods (length ~10-20 µm and diameter ~400 nm) are synthesized using a facile method based on a molten-salt reaction, whose formation mechanism has been revealed. The lead-free piezoelectric nanorods showing high piezoelectric coefficient d*33 up to ~230 pm V(-1) may be used in bio-sensing and energy-harvesting micro-devices.