Ding Zhu

Intermittent operation of the aprotic Li-O2 battery: the mass recovery process upon discharge interval

The intermittent operation of the aprotic Li-O2 battery is systematically studied in this paper. A combined study of the battery charge retention and the electrolyte stability to O2 suggests a low self-discharge rate of the Li-O2 battery, which is a prerequisite to achieve desirable intermittent discharge performance. The battery under intermittent operation exhibits significantly improved discharge performance as compared to the continuously discharged one. It is found that the capacity output is directly associated with the time interval between two discharge steps and with the capacity limit for each discharge step. The open-circuit potential and linear scan voltammetry analyses confirm that a “mass recovery” process, corresponding to the concentration relaxation of the oxygen which is available at the cathode, proceed during the discharge intervals. In the “mass recovery” process, an increased amount of O2 homogeneously redistributes at the electrolyte/carbon interface at both sides of the electrode, which relieves the O2 transport limit, enhances the availability of O2 and the utilization of carbon material for the cathode, and thus significantly improves the discharge performance of the aprotic Li-O2 battery.

Solvent autoxidation, electrolyte decomposition, and performance deterioration of the aprotic Li-O2 battery

The electrolyte decomposition is widely recognized as the greatest challenge to the successful development of the aprotic Li-O2 battery. The decomposition of the organic ethers, which are the commonly used electrolyte solvents in the current studies, can be chemical or electrochemical during discharge or charge. In this paper, the influence of oxygen on the decomposition of the ether-based electrolyte is discussed. Ether solvents are found to be oxidized in contact with oxygen whether the cells operate or not. The solvent autoxidation significantly promotes the electrolyte decomposition during the discharge process of the ether-based Li-O2 battery. As a result, the oxygen exposure time before battery operation significantly affects the electrochemical performance of the ether-based Li-O2 battery. After the prolonged exposure to oxygen, both the discharge capacity and the working potential of the battery decrease to some extent. More importantly, the recharge potential of the battery greatly increases with extending the previous oxygen exposure time.

Composition optimization and electrochemical characteristics of Co-free Fe-containing AB5-type hydrogen storage alloys through uniform design

Abstract In order to reduce the cost of AB 5 -type hydrogen storage alloys, effects of substitution of Ce for La (A side) and Fe, Mn, Al for Ni (B side) on structural and electrochemical properties of (LaCe) 1 (NiFeMnAl) 5 alloys were studied systematically. To make component uniform and operation easy, uniform design (UD) method was introduced into the study of composition optimization of Co-free Fe-containing AB 5 -type alloys for the first time. X-ray diffraction (XRD) results showed that the designed alloys were of single CaCu 5 -type structure phase. The replacement of Fe had a severe effect on electrochemical capacity, and the substitution of Fe and Al had a synergetic action among the unit cell volume, cycling stability and high rate discharge property. Interestingly, it was found that the hydrogen storage alloys with excessively high plateau pressure showed a tilted line in Nyquist plot instead of the semicircle, and the current decayed rapidly to near zero at the beginning of the step in constant potential step (CPS), indicating that electrochemical impedance spectra (EIS) and CPS cannot accurately measure the electrochemical kinetics process of the hydrogen storage alloys with excessively high plateau pressure.

Electrochemical performances of four lanthanum transition-metal complex oxides

As novel negative electrode materials for alkaline batteries, the electrochemical properties of four lanthanum transition-metal (La-TM) complex oxides LaTiO3, LaVO4, LaCrO3 and LaMnO3 were investigated. X-ray diffraction (XRD) and scanning electron microscope (SEM) were employed to characterize their microstructures. All the La-TM oxides were made up of single phases. Electrochemical measurements showed that the maximum discharge capacities of LaTiO3, LaVO4, LaCrO3, and LaMnO3 electrodes at 303 K were 367, 187, 318, and 278 mAh/g, respectively. X-ray photoelectron spectroscopy (XPS) and XRD Rietveld analysis were carried out to discuss the electrochemical reaction mechanism. Electrode kinetics was studied by electrochemical impedance spectrum (EIS). The results showed that the maximum discharge capacity was directly related to the charge-transfer resistance (Rct) of La-TM oxide electrode. The cyclic properties of the four oxides should be further improved and the discharge capacity of LaMnO3 (about 96 mAh/g) was the highest after 10th charge/discharge cycles.

Enhanced electrochemical performance of Li–O2 battery based on modifying the solid-state air cathode with Pd catalyst

Pd nanoparticles were deposited onto carbon nanotubes (CNTs) via a simple wet chemical method and were employed to fabricate a highly efficient cathode for a Li–O2 battery using a solid-state air cathode. The results demonstrate that the introduced Pd catalyst showed promising catalytic activity, making the battery exhibit improved rate ability and excellent cycling performance. The fabricated CNTs@Pd electrode tended to induce the poorly crystalline Li2O2 to form preferentially in the solid-state air cathode, which could be decomposed at a lower potential in comparison to the Pd-free electrode. The Li–O2 battery using a solid-state CNTs@Pd electrode exhibited a long cycle life up to 50 cycles without capacity fading (capacity limit of 500 mA h g−1). The unique architecture of the CNTs@Pd electrode minimised the side reactions relating to carbon and the discharge product. Our results provide a snapshot toward developing a high performance solid-state Li–O2 battery.

Effects of Co Substitution for Ni on Microstructures and Electrochemical Properties of LaNi3.8 Hydrogen Storage Alloys

The effects of Co partial substitution for Ni on the microstructures and the electrochemical properties of the LaNi3.8-type phase LaNi3.8-xCox (x=0.0, 0.2, 0.4, 0.6) alloys were systematically studied. All the alloys mainly consist of LaNi5-type phase, rhombohedral Ce5Co19-type phase and hexagonal Pr5Co19-type phase. With increasing Co content, the relative abundance of each phase changes while the cell volume increases monotonously, which lower the hydrogen desorption pressure down to the desirable range (0.01~0.1 MPa) for hydride electrode of Ni/MH battery. All the Co-containing alloys display an enhanced cycle ability compared to LaNi3.8 alloy. The LaNi3.4Co0.4 alloy has the biggest discharge capacity, which is consistence with the solid hydrogen desorption capacity of the alloy. The LaNi3.6Co0.2 alloy exhibits the best rate performance corresponding to its maximum exchange current density (Io) and minimum charge transfer resistance (Rct).

Nanoscale tungsten nitride/nitrogen-doped carbon as an efficient non-noble metal catalyst for hydrogen and oxygen recombination at room temperature in nickel–iron batteries

A nanoscale tungsten nitride/nitrogen-doped carbon (WN/NC) catalyst was synthesized through a facile route, and it exhibited efficient catalytic performance for hydrogen and oxygen recombination at room temperature with an average catalytic velocity of 140 μmol h−1 gcat−1 and long catalytic life of 954 660 s without decay in the catalytic performance. With the WN/NC catalyst, a nickel–iron battery could be sealed and maintenance-free, and it also exhibited low cost; thus, the nickel–iron battery can be used for large-scale energy storage systems in rural/remote areas.

Hydroxylated carbon black as improved deposition support for discharge products in lithium air(oxygen)batteries

To date, compared with that of lithium oxygen batteries, the operation of lithium air batteries is still a great challenge due to the highly deteriorated cathode performances in air, including worse discharge capacities and OER/ORR dynamics. Herein, we propose hydroxylated carbon black as an improved deposition support, which not only functions as a conductive agent, but also improves the morphology of the discharge products. These improvements can significantly enhance the discharge properties and chargeability of the gas cathode, particularly in simulated air or ambient air. For example, the hydroxylated carbon black doubles the energy output of the air cathode in ambient air. It is believed that increased defects and hydroxyls on the hydroxylated carbon surface might play an important role. By the first principle calculation, it is revealed that a strong affinity between the hydroxyls and Li2O2 occurs, and this facilitates the nucleation of Li2O2. It is believed that the promoted nucleation can restrain the growth of the discharge products due to the competitive relationship between nucleation and growth of new phase in chemical reactions. Finally, smaller Li2O2 nanosheets formed on the hydroxylated carbon cathode instead of the dense discharge product layer, avoid the block of the porous cathode, thus benefiting the electrochemical performances. These results show that besides developing better catalysts, hydroxylation of carbon matrix is also an effective strategy to enhance the electrochemical performances of the lithium air battery.

Improved charging performances of Li 2 O 2 cathodes in non-aqueous electrolyte lithium-air batteries at high test temperatures

Charging overpotential, which is still relatively too high for non-aqueous electrolyte lithium-air batteries, can be extremely low at high test temperatures. The charging overpotential decreases with the increase of test temperature from 303 K to 343 K. Charging voltage plateau is about 3.1 V and 3.6 V under the current density of 100 mA g-1 and 500 mA g-1, respectively, at the test temperature of 343 K. X-ray diffraction is carried out to prove the oxidative decompositions of Li2O2 during the charging process. The results of electrochemical impedance spectroscopy indicate the influence of test temperature on the charge-transfer resistance. This discovery could lead to new development orientation of lithium-air battery.