Chenhao Zhao

LaPO4-coated Li1.2Mn0.56Ni0.16Co0.08O2 as a cathode material with enhanced coulombic efficiency and rate capability for lithium ion batteries

In this paper, pristine Li-rich layered oxide Li[Li0.2Mn0.56Ni0.16Co0.08]O2 porous microspheres have been successfully synthesized by a urea combustion method, and then coated with 1.0%, 2.0%, and 3.0 wt% LaPO4 via a facile chemical precipitation route. The structures and morphologies of both pristine and LaPO4 coated Li1.2Mn0.54Ni0.16Co0.08O2 were investigated by X-ray diffractometry (XRD), field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HR-TEM). XPS data and FESEM demonstrate that the LaPO4 was successfully coated on the surface of the Li[Li0.2Mn0.56Ni0.16Co0.08]O2 porous microspheres. Especially, the 2 wt% LaPO4 coated-Li[Li0.2Mn0.56Ni0.16Co0.08]O2 demonstrates the best electrochemical performance. As lithium ion battery cathodes, the 2 wt% LaPO4 coated sample, compared with the pristine one, has shown significantly improved electrochemical performances: the initial coulumbic efficiency improves from 78.81% to 84.76% at 0.1C and the rate compatibility increased from 70 mA h g−1 to a high capacity of 112.73 mA h g−1 at a current density of 5C. The analysis of dQ/dV plots and electrochemical impedance spectroscopy (EIS) demonstrate that the enhanced electrochemical performance is mainly attributed to the fact that the LaPO4 coating layer can not only stabilize the cathode structure by reducing the loss of oxygen, but also protect the Li-rich cathodes by decreasing the side reactions of Li[Li0.2Mn0.56Ni0.16Co0.08]O2 with the electrolyte and lower the charge transfer resistance of the sample.

LaF3-coated Li[Li0.2Mn0.56Ni0.16Co0.08]O2 as cathode material with improved electrochemical performance for lithium ion batteries

In this article, the pristine Li-rich layered oxide Li[Li0.2Mn0.56Ni0.16Co0.08]O2 porous microspheres have been successfully synthesized using a urea combustion method and then coated with 1 wt% LaF3 via a facile chemical precipitation route. The structures and morphologies of both pristine and LaF3 coated Li1.2Mn0.54Ni0.16Co0.08O2 were investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HR-TEM). The results reveal that the obtained particles possesses the morphology of porous microspheres and a LaF3 layer with a thickness of 5–8 nm coated on the surface of the Li[Li0.2Mn0.56Ni0.16Co0.08]O2 particles. As lithium ion battery cathodes, the LaF3 coated sample, compared with the pristine one, has shown a significantly improved electrochemical performance; the initial coulombic efficiency improves from 75.36% to 80.01% and the rate compatibility increased from 57.4 mA h g−1 to an extremely high capacity of 153.5 mA h g−1 at 5 C. Decreased electrochemical impedance spectroscopy (EIS) reveals that the enhanced electrochemical performance of the surface coating was attributed to the lower charge transfer resistance of the sample.

Facile synthesis of selenium/potassium tartrate derived porous carbon composite as an advanced Li–Se battery cathode

Porous carbon with a unique 3D structure has been prepared by the immediate carbonization of potassium tartrate. At an optimal carbonization temperature of 700 °C, the carbon mainly composed of micro- and small meso-porous structure has a Brunauer–Emmett–Teller (BET) specific surface area of 816.2 m2 g−1, and the element Se with an amorphous structure is uniformly encapsulated into the porous structure of carbon. The weight ratio of Se in the composite can reach ∼50%. As the Li–Se battery cathode, the composite shows a (2nd) reversible discharge capacity of 550.5 mA h g−1 with an initial coulombic efficiency of 68.2% at 0.24C, and a discharge capacity of 485.3 mA h g−1 can be retained after 80 cycles. Even at a high current density of 1.2C, the cell also delivers a stable discharge capacity of about 452.3 mA h g−1. The good electrochemical performances of the as-prepared composite may be attributed to high specific surface area and small porous size.

Synthesis of Se/chitosan-derived hierarchical porous carbon composite as Li–Se battery cathode

The hierarchical porous carbon with overall macropores and surface micropores has been prepared from carbonization of chitosan/K2CO3 gel-like composite. The specific surface area and pore volume of this carbon can come to 2358.9m2 g−1 and 1.14cm3 g−1, respectively, and the active component Se with amorphous structure is uniformly encapsulated into the microporous structure to form Se/carbon composite. As Li–Se battery cathode, the composite delivers a second discharge capacity of 537.6mAh g−1 at 0.2C, and a discharge capacity of 517.9mA h g−1 can be retained after 100 cycles. Even at a high rate of 5C, the composite still reveals a stable discharge capacity of 325.2mAh g−1. The excellent electrochemical performances of Se/carbon composite may attribute to high specific surface area and hierarchical porous feature.

Synthesis and electrochemical performances of sea-urchin-like Mn2O3 as lithium-ion battery anodes

In this paper, a facile hydrothermal synthesis of precursor MnO2 and subsequent high-temperature calcination has been used to prepare sea-urchin-like Mn2O3.The influences of calcination temperatures on the structures and electrochemical performances of Mn2O3 are clearly studied. The results show that the elevated temperature helps to improve the crystallinity and particle size, the 700°C sample shows an optimal electrochemical performance. Therein, a high discharge capacity of 765.7 mAh g− 1 can be retained after 50 cycles at 200 mA g− 1, and a value of 465.8 mAh g− 1 can be kept at 800 mA g− 1.More importantly, a surprised calcination temperature determines phenomenon that discharges capacity increase upon cycles can be observed, which may be useful for the design and nanostructured of Mn-based oxides as lithium-ion battery anodes.