Engineering topics
Peng, Yong
Publications and source records attributed to Peng, Yong.
A Li-rich layered oxide cathode with negligible voltage decay
With high capacity at low cost, Li- and Mn-rich (LMR) layered oxides are a promising class of cathodes for next generation Li-ion batteries. However, substantial voltage decay during cycling, due to the unstable Li 2 MnO 3 honeycomb structure, is still an obstacle for their practical deployment. Here we report a Co-free LMR Li-ion battery cathode without voltage decay. The material has a composite structure consisting of layered LiTMO 2 and various stacked Li 2 MnO 3 components, where transition metal (TM) ions partially reside in the Li layers of Li 2 MnO 3 , serving as a “cap” to strengthen the stability of the honeycomb structure. This unique capped-honeycomb structure is persistent after high-voltage cycling and prevents TM migration and oxygen loss, as shown by experimental and computational results. Furthermore, this work demonstrates that the long-standing voltage decay problem in LMRs can be effectively eliminated by internally pinning the honeycomb structure, which opens an avenue to developing nextgeneration high-energy cathode materials.
Twin suppression effect of dihydroxy-benzene isomers during the secondary growth of b -oriented zeolite MFI nanosheet films
In this study, the presence of MFI twin crystals on b-axis oriented zeolite MFI nanosheet films was suppressed by adding dihydroxy-benzene isomers in the synthesis mixture. The resulting nanosheet films exhibit good intergrowth and a small grain thickness of 30–45 nm within a relatively short synthesis time (hours). The possible twin suppression mechanisms for the three isomers are discussed.
Role of cobalt phthalocyanine on the formation of high-valent cobalt species revealed by in situ Raman spectroscopy
In situ Raman spectroscopy reveals that CoPc facilitates the formation of disordered-CoOOH and high-valence-CoO 2 , endowing Co-MOF-74@CoPc with outstanding OER performance.
High-Voltage and High-Safety Practical Lithium Batteries with Ethylene Carbonate-Free Electrolyte
Serious safety issues are impeding the widespread adoption of high-energy lithium-ion batteries for transportation electrification and large-scale grid storage. Herein, a triple-salt ethylene carbonate (EC) free electrolyte for high-safety and high-energy pouch-type LiNi 0.8 Mn 0.1 Co 0.1 O 2 |graphite (NMC811|Gr) cells is reported. This EC-free electrolyte can effectively stabilize the NMC811 surface under high potential (up to 4.5 V), as well as generate a stable interphase to achieve a superior compatibility with the Gr anode. The electrolyte strategy enables significantly enhanced intrinsic safety (trigger temperature of thermal runaway (TR) increased by 67.0 °C), excellent electrochemical properties (4.2V, ≈100% after 200 cycles), and superior high voltage stability (4.5 V, 82.1% after 200 cycles). Furthermore, the work opens up a new avenue for developing novel electrolyte systems to build safer high-energy batteries for practical applications.
Possible Topological Hall Effect above Room Temperature in Layered Cr 1.2 Te 2 Ferromagnet
Topological Hall effect (THE) has been used as a powerful tool to unlock spin chirality in novel magnetic materials. Recent focus has been widely paid to THE and possible chiral spin textures in two-dimensional (2D) layered magnetic materials. However, the room-temperature THE has been barely reported in 2D materials, which hinders its practical applications in 2D spintronics. In this paper, we report a possible THE signal featuring antisymmetric peaks in a wide temperature window up to 320 K in Cr 1.2 Te 2 , a new quasi-2D ferromagnetic material. The temperature, thickness, and magnetic field dependences of the THE lead to potential spin chirality origin that is associated with the spin canting under external magnetic fields. Furthermore, our work holds promise for practical applications in future chiral spin-based vdW spintronic devices.
Deformation of Néel-type skyrmions revealed by Lorentz transmission electron microscopy
Néel-type magnetic skyrmions in multilayers are promising candidates for ultra-low power spintronic devices. To image the Néel-type skyrmions using Lorentz transmission electron microscopy (L-TEM), the samples must be tilted. Thus, the external magnetic field consists of both in-plane and out-of-plane components. To date, it is still not well known on the effect of the in-plane magnetic field on the L-TEM images, leading to ambiguities in retrieving the structure of Néel-type skyrmions. Here, Néel-type skyrmions in three [Pt/Co/Ta]$_{20}$ multilayer samples, with the easy magnetization axis being tuned from the out-of-plane to the in-plane direction by increasing the Co thickness from 1.8 to 2.2 nm, are imaged. When using a smaller defocus value (-2 mm) and a higher magnification (×9100) of L-TEM, a surprising dark-bright-dark-bright double contrasted pattern, instead of the previously reported dark-bright contrasted pattern, is observed. The additional dark-bright contrasted pattern becomes more evident for thicker Co layer samples in which the magnetization axis tilts more toward the in-plane direction. Further analysis, via a combination of magnetic force microscopy experiments, micromagnetic simulations, and micromagnetic analysis to Lorentz TEM simulation, shows that the additional dark-bright features originate from the deformation of the Néel-type skyrmions within an in-plane magnetic field.
Softening Behavior of Electron Beam Welded 22SiMn2TiB Steel
Softening behavior occurs in heat-affected zone of many types of high strength steels causing the deterioration of mechanical properties. In this study, the softening behavior of 22SiMn2TiB joint was revealed by experimental and numerical analysis. The microstructure and hardness of the joint were tested and analyzed. The numerical simulations of the temperature field were carried out to obtain the thermal cycle. Based on the continuous cooling transformation diagram, the phase transformation was investigated. The results indicated that the microhardness in the HAZ was significantly decreased, and its minimum value was 273 HV which was 63.5% of base metal. The softening behavior occurs in intermediate critical heat-affected zone and the subcritical heat-affected zone, and its peak temperature is between 853.7 °C (Ac{sub 3}) and 450 °C. When 22SiMn2TiB steel was heated above 732.3 °C (Ac{sub 1}), martensite begins to transform into austenite. With different cooling rates, austenite may transform into martensite, bainite and ferrite, and the volume fraction of soft phases could increase resulting in the softening. When the peak temperature is between 732.3 and 450 °C, the recovery phenomenon and the decomposition of martensite caused softening with the decrease in the dislocation density and martensite.