Jinbao Zhao

Hollow porous nanoparticles with Pt skin on a Ag–Pt alloy structure as a highly active electrocatalyst for the oxygen reduction reaction

Aiming to reduce the dosage of the noble metal Pt and improve the catalytic activity of the catalyst in fuel cells, hollow porous Ag–Pt alloy nanoparticles with Pt coating are prepared via a facile controlled galvanic replacement reaction. Ag is used as the substrate to build a hollow porous structure and alloyed with Pt to minimize the tensile effect of the Ag on the deposited Pt skin which would significantly lower the catalytic performance of the Ag–Pt bimetallic catalyst. This hollow porous Ag/Pt bimetallic catalyst exhibits a long catalytic durability and a mass activity of 0.438 A mgPt−1 at 0.9 V (vs. RHE) towards the oxygen reduction reaction (ORR), which is ca. 3 times higher than that of the commercial Pt/C catalyst. The significant enhancement over the state-of-the-art Pt catalysts can be attributed to (1) the high surface area of the nanoparticles, (2) the more suitable d-band center of the Pt skin deposited on the Ag–Pt alloy substrate, and (3) the high thermal stability of the Ag–Pt alloy. Therefore, this work provides a new strategy for designing high-performance catalysts with low cost. In addition, the synthetic chemistry involved can possibly be extended for fabricating versatile catalysts with a similar structure.

Synthesis of One‐Dimensional Copper Sulfide Nanorods as High‐Performance Anode in Lithium Ion Batteries

Nanorod-like CuS and Cu2 S have been fabricated by a hydrothermal approach without using any surfactant and template. The electrochemical behavior of CuS and Cu2 S nanorod anodes for lithium-ion batteries reveal that they exhibit stable lithium-ion insertion/extraction reversibility and outstanding rate capability. Both of the electrodes exhibit excellent capacity retentions irrespective of the rate used, even at a high current density of 3200 mA g(-1) . More than 370 mAh g(-1) can be retained for the CuS electrode and 260 mAh g(-1) for the Cu2 S electrode at the high current rate. After 100 cycles at 100 mA g(-1) , the obtained CuS and Cu2 S electrodes show discharge capacities of 472 and 313 mAh g(-1) with retentions of 92% and 96%, respectively. Together with the simplicity of fabrication and good electrochemical properties, CuS and Cu2 S nanorods are promising anode materials for practical use the next-generation lithium-ion batteries.

A rational design of separator with substantially enhanced thermal features for lithium-ion batteries by the polydopamine–ceramic composite modification of polyolefin membranes

A separator plays a crucial role in ensuring the safety in lithium-ion batteries (LIBs). However, commercial separators are mainly based on microporous polyolefin membranes, which possess serious safety risks, such as their thermal stabilities. Although many efforts have been made to solve these problems, they cannot yet fully ensure the safety of the batteries, especially in large-scale applications. Herein, we report a rational design of separator with substantially enhanced thermal features. We report how, by a simple dip-coating process, polydopamine (PDA) formed an overall-covered self-supporting film, both on the ceramic layer and on the pristine polyolefin separator, which made the ceramic layer and polyolefin separator appear as a single aspect and furthermore, this layer amended the film-forming properties of the separator. Combining the function of the ceramic and PDA, the developed composite-modified separator displays substantially enhanced thermal and mechanical stability, with no visual thermal shrink and can maintain its mechanical strength up to 230 °C when the polyethylene separator acts as the pristine separator.

Binder-Free Si Nanoparticle Electrode with 3D Porous Structure Prepared by Electrophoretic Deposition for Lithium-Ion Batteries

A binder-free silicon (Si) based electrode for lithium-ion battery was fabricated in an organic solvent through one-step electrophoretic deposition (EPD). The nanosized Si and acetylene black (AB) particles were bonded tightly together to form a homogeneous co-deposited film with 3D porous structure through the EPD process. The 3D porous structure provides buffer spaces to alleviate the mechanical stress due to silicon volume change during the cycling and improves lithium-ion conductivity by shortening ion diffusion length and better ion conducting pathway. The electrode prepared with 5 s deposition duration shows the best cycling performance among electrodes fabricated by EPD method, and thus, it was selected to be compared with the silicon electrode prepared by the conventional method. Our results demonstrate that the Si nanoparticle electrode prepared through EPD exhibits smaller cycling capacity decay rate and better rate capability than the electrode prepared by the conventional method.

Porous LiNi0.5Mn1.5O4 sphere as 5 V cathode material for lithium ion batteries

A new type of microsized porous spherical LiNi0.5Mn1.5O4 (LNMO-Air) cathode material for a lithium ion secondary battery has been synthesized by an impregnation method using highly reactive nanocupule MnO2 spheres as the manganese source. These LNMO-Air spheres are aggregates of nanosized polyhedron particles with well-defined cubic spinel structure. They showed excellent rate capability and cycle stability, compared with other microspheres of LNMO. We also investigated the effect of the trace amounts of Mn3+ in the crystal structure on its specific capacity and cycle stability. Compared with the sample (LNMO-O2) calcined in an oxygen atmosphere, which is considered to be Mn3+ free, LNMO-Air exhibits superior specific capacity, cycling ability and rate capability. Because of the presence of trace amounts of Mn3+, the LNMO-Air sample presents a discharge specific capacity of 108 mA h g−1 at 5 C rate at 55 °C after 80 cycles without significant reduction. These improvements can be explained by better ion conductivity as the metal oxide layer spacing is enlarged to facilitate faster ion transfer and significantly improved electrical conductivity; both are attributed to the presence of Mn3+.

Flexible inorganic membranes used as a high thermal safety separator for the lithium-ion battery

A flexible SiO2 porous fiber membrane (SF) is prepared by electrospinning followed by calcination in this work. Compared with an organic substrate separator, the SF used as a separator will be an absolute guarantee of the battery thermal safety. The porosity of the SF is 88.6%, which is more than twice that of a regular PP separator. Hydrophilic SF shows better electrolyte wetting ability and its high porosity enables the SF to absorb 633% liquid electrolyte on average, while the lithium-ion conductivity reaches 1.53 mS cm−1. The linear sweep voltammogram testing of PP and SF suggested that SF, with great electrochemical stability, can meet the requirements of lithium-ion batteries. The cyclic and rate performances of batteries prepared with SF are improved significantly. Such advantages of the SF, together with its potential in mass production, make the SF a promising membrane for practical applications in secondary lithium-ion batteries.

A facile spray drying route for mesoporous Li3VO4/C hollow spheres as an anode for long life lithium ion batteries

Mesoporous Li3VO4/C hollow spheres have been prepared by a facile drying method and subsequent heat treatment process. The unique structure of the composite offers a synergistic effect to facilitate the transport of Li+ ions and electrons and afford an anode with superior rate capability and cyclic stability.

A homogeneous intergrown material of LiMn2O4 and LiNi0.5Mn1.5O4 as a cathode material for lithium-ion batteries

Micro-/nano-structured spherical intergrown LiMn2O4–LiNi0.5Mn1.5O4 (LMO–LNMO I, LiNi0.25Mn1.75O4) particles as a cathode material have been synthesized by an impregnation method with highly reactive chestnut-like MnO2 nano-spheres as a manganese source and structural template. The LMO–LNMO I consisted of aggregates of nano-sized particles with a well-defined cubic spinel structure. The electrochemical performance and thermostability of LMO–LNMO I are better than those of a simple mechanical mixture of LiMn2O4 and LiNi0.5Mn1.5O4 (LMO–LNMO M), and much better than those of individual LiMn2O4 and LiNi0.5Mn1.5O4 monomers. Within this special structure, LNMO acts as a skeleton to stabilize the structure of LMO and enables more lithium ions in LMO to participate in the charge–discharge process along with those in LNMO, leading to high specific discharge capacities. In addition, this material exhibits excellent cycle stabilities at room temperature (25 °C) as well as at elevated temperature. It presented a discharge capacity of 130 mA h g−1, with 96.2% capacity retention after 100 cycles at 25 °C at 1 C. When the temperature and rate are increased to 55 °C and 5 C, it still delivers a discharge capacity of 131 mA h g−1, with a capacity retention of 95% after 100 cycles. Being synthesized by a special impregnation method, LMO–LNMO I shows a more homogeneous ion mixing of Ni and Mn in the structure at the atomic level with a more enhanced thermostability due to its high Mn content compared to LNMO. The structural stability and high electrical conductivity of LMO–LNMO I are responsible for the excellent electrochemical performance and outstanding thermal stability.

High sulfur loading lithium–sulfur batteries based on a upper current collector electrode with lithium-ion conductive polymers

We report an effective double current collector electrode. In this study, we achieve a high areal loading double current collector electrode with high areal capacity density and long cycle life. We also adjust the charging condition (constant capacity charging) which leads to long cycle life with almost no capacity fading.

Prussian Blue: A Potential Material to Improve the Electrochemical Performance of Lithium–Sulfur Batteries

The Prussian blue, as a potential adsorbent of polysulfides to suppress the dissolution and shuttle of polysulfides for lithium-sulfur batteries, has been studied in this work. Our results show that Prussian blue improves the electrochemical reaction kinetics during discharge/charge processes. More importantly, the cathode with Prussian blue exhibits better cycling stability and higher discharge capacity retention (722 mAh g-1 at 0.2 A g-1 after 100 cycles) than the one without Prussian blue (151 mAh g-1). These improvements of electrochemical performances are ascribed to the fact that Prussian blue is very effective in suppressing the dissolution of polysulfides into liquid electrolyte by chemical adsorption.