Xueping Gao

Multi-electron reaction materials for high energy density batteries

The need for high energy density batteries becomes increasingly important for the development of new and clean energy technologies, such as electric vehicles and electrical storage from wind and solar power. The search for new energetic materials of primary and secondary batteries with higher energy density has been highlighted in recent years. This review surveys recent advances in the research field of high energy density electrode materials with focus on multi-electron reaction chemistry of light-weight elements and compounds. In the first section, we briefly introduce the basic strategies for enhancement of the energy density of primary batteries based on multi-electron reactions. The following sections present overviews of typical electrode materials with multi-electron chemistry and their secondary battery applications in aqueous and non-aqueous electrolytes. Finally, the challenges and ongoing research strategies of these novel electrode materials and battery systems for high density energy storage and conversion are discussed.

A Solar Rechargeable Flow Battery Based on Photoregeneration of Two Soluble Redox Couples

Storable sunshine, reusable rays: A solar rechargeable redox flow battery is proposed based on the photoregeneration of I(3)(-)/I(-) and [Fe(C(10)H(15))(2)](+)/Fe(C(10)H(15))(2) soluble redox couples, which can be regenerated by flowing from a discharged redox flow battery (RFB) into a dye-sensitized solar cell (DSSC) and then stored in tanks for subsequent RFB applications This technology enables effective solar-to-chemical energy conversion.

Alkaline rechargeable Ni/Co batteries: Cobalt hydroxides as negative electrode materials†

It is demonstrated that β-Co(OH)2 has a high discharge capacity and good high-rate discharge ability as a negative electrode material. A new rechargeable battery system with higher energy density, consisting of α-phase nickel hydroxides as the positive electrode material and β-cobalt hydroxides as the negative electrode material, is proposed on the basis of multi-electron reactions.

Protected lithium anode with porous Al2O3 layer for lithium–sulfur battery

The performance of the metallic lithium anode is one of the major factors that affect the cycle stability of a lithium–sulfur battery. The protection of the lithium anode is extremely essential, especially for lithium–sulfur full-cells. Here, a porous Al2O3 layer is fabricated on the surface of a metallic lithium anode by using a spin-coating method as protective layer for a lithium–sulfur battery. The porous Al2O3 protective layer acts as a stable interlayer and suppresses the side reactions between soluble lithium polysulfides and lithium anode by direct contact during the charge–discharge process. In addition, the inhomogeneous dissolution–deposition reaction, and the formation of serious cracks on the protected lithium anode are suppressed to a certain extent, which is beneficial to ensure the good and stable electrochemical activity of the lithium anode. Correspondingly, the sulfur cathode with the protected lithium anode exhibits improved electrochemical performance, accompanied simultaneously with relatively homogeneous lithium deposition on the anode surface due to the even distribution of Li ion flux via the Al2O3 protective layer.

Sn-stabilized Li-rich layered Li(Li0.17Ni0.25Mn0.58)O2 oxide as a cathode for advanced lithium-ion batteries

Li-rich layered oxides have been intensively investigated as cathodes for high energy lithium-ion batteries. However, oxygen loss from the lattice during the initial charge and gradual structural transformation during cycling can lead to capacity degradation and potential decay of the cathode materials. In this work, Sn4+ is used to partially substitute Mn4+ to prepare a series of Li(Li0.17Ni0.25Mn0.58−xSnx)O2 (x = 0, 0.01, 0.03, and 0.05) samples through a spray-drying method. Structural characterization reveals that the Sn4+ substituted samples with a suitable amount show low cation mixing, indicating an enhanced ordered layer structure. Moreover, the metal–oxygen (M–O) covalency is gradually decreased with increasing Sn4+ amount. It is shown from the initial charge–discharge curves that Sn4+ substituted samples present a shorter charging potential plateau at 4.5 V (vs. Li/Li+), implying that oxidation of the O2− ion to O2 is suppressed by Sn4+ substitution and leads to a minor structural change. Among the Sn4+ substituted samples, the Li(Li0.17Ni0.25Mn0.55Sn0.03)O2 sample exhibits a higher capacity retention of 86% after 400 cycles at 0.1C rate and 92% after 200 cycles at 1C rate, showing excellent cycle stability and high-rate capability as compared with the as-prepared sample. The electrochemical performance improvement can be attributed to the influences of Sn such as enlarging the Li ion diffusion channel due to the large ionic radius of Sn4+ substitution with respect to Mn4+, a higher bonding energy of Sn–O than Mn–O, and weakening the M–O covalency. All the influences are favorable for stabilization of the host lattice in Li-rich layered oxides.

Encapsulating sulfur into a hybrid porous carbon/CNT substrate as a cathode for lithium–sulfur batteries

A hybrid carbon substrate as a sulfur immobilizer is obtained via simple processes to fabricate cathode materials for lithium–sulfur batteries. The microstructure and morphology of the sulfur/carbon composites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is demonstrated that commercial carbon black and multi-walled carbon nanotubes (CNTs) in the hybrid substrate cooperate well with each other in an appropriate mass ratio. In particular, a large sulfur content of 81.7 wt% can be loaded into the hybrid carbon substrate forming the sulfur/carbon composite. When the mass ratio of carbon black and CNTs is 1u2006:u20061, the composite delivers a high initial capacity of 837.3 and 685.9 mA h g−1(composite) at the current densities of 80 and 160 mA g−1(composite) when used as a cathode-active material. The discharge capacity remains at 554.4 mA h g−1(composite) at a current density of 160 mA g−1(composite) after 150 cycles, indicating a low capacity fading of about 0.12% per cycle. Besides, the composite offers a high Coulombic efficiency of about 100%. The significant improvements in the electrochemical performance are associated with the desirable combination of carbon black and CNTs in the hybrid carbon substrate. Therefore, this work proposes a low-cost and effortless approach to prepare sulfur/carbon composites with high performance as cathodes for lithium–sulfur batteries.

Lanthanum Nitrate As Electrolyte Additive To Stabilize the Surface Morphology of Lithium Anode for Lithium–Sulfur Battery

Lithium-sulfur (Li-S) battery is regarded as one of the most promising candidates beyond conventional lithium ion batteries. However, the instability of the metallic lithium anode during lithium electrochemical dissolution/deposition is still a major barrier for the practical application of Li-S battery. In this work, lanthanum nitrate, as electrolyte additive, is introduced into Li-S battery to stabilize the surface of lithium anode. By introducing lanthanum nitrate into electrolyte, a composite passivation film of lanthanum/lithium sulfides can be formed on metallic lithium anode, which is beneficial to decrease the reducibility of metallic lithium and slow down the electrochemical dissolution/deposition reaction on lithium anode for stabilizing the surface morphology of metallic Li anode in lithium-sulfur battery. Meanwhile, the cycle stability of the fabricated Li-S cell is improved by introducing lanthanum nitrate into electrolyte. Apparently, lanthanum nitrate is an effective additive for the protection of lithium anode and the cycling stability of Li-S battery.

Hydrogen adsorption of metal nickel and hydrogen storage alloy electrodes

Abstract An improvement in the electrocatalytic activity of the hydrogen storage alloy electrodes is essential to ensure a high rate capability of an Ni–MH battery. Previous experimental results showed that there was a hydrogen adsorption phenomenon on the alloy surface and the activation energy barrier of the electrochemical reaction process should be reduced by hydrogen adsorption. Therefore, the hydrogen adsorption is of benefit in improving the electrocatalytic activity of the alloy electrode. In this work, the hydrogen adsorption performance on the surfaces of Zr(V0.2Mn0.2Ni0.6)2.4, MmNi3.6Mn0.4Co0.75Al0.25 alloy electrodes and carbonyl nickel electrode was measured by means of cyclic voltammetry. In addition, the hydrogen adsorption performance of the metal nickel ribbon was performed by electrochemical impedance spectra. The results showed that the Ni sites on the surface of the metal hydride electrodes play an important role in the hydrogen adsorption.

The surface decoration and electrochemical hydrogen storage of carbon nanofibers

Abstract The tube-like CNFs with cone-shaped structure were synthesized by catalytic pyrolysis of methane. The outer surface of purified CNFs was decorated with Ni–P alloy particles having polycrystalline or nanocrystalline structure instead of amorphous structure. The low Ni–P content appeared to be more efficient to cover the outer surface of CNFs. The electrochemical discharge capacity increased with increasing the Ni–P content on the outer surface of CNFs owing to the synergistic effect between metal and carbon in the electrochemical reaction. The heat treatment contributed to the higher crystallization of surface alloy and improvement of the electrochemical capacity of the composite.

Electrochemical properties of MmNi3.6Co0.7Al0.3Mn0.4 alloy containing carbon nanotubes

Abstract MmNi3.6Co0.7Al0.3Mn0.4 alloys containing carbon nanotubes were prepared by an arc-melting method. It was confirmed by SEM images that a few carbon nanotubes coated or uncoated with AB5 alloy stuck out of the surface of the alloy. The effects of the addition of carbon nanotubes on the structure and the electrochemical characteristics of AB5-type alloy were investigated by XRD and electrochemical measurements. Discharge plateau curves of sigmoid shape were clearly observed for AB5-CNT electrodes during the initial activation, which was different from the original AB5 electrode. In addition, the results indicate that, with the addition of carbon nanotubes, the unit cell volume decreased resulting in a decrease of the stability of the metal hydride and an increase in the discharge plateau potential. The discharge capacity for the alloys decreased with decreasing stability of the metal hydride due to the decrease of maximum amount of the absorbed hydrogen, but the high-rate dischargeability was improved due to the increase in the rate of hydrogen diffusion in the alloys. The capacity retaining ability of the alloys did not remarkably decrease with the addition of carbon nanotubes.