Transition Metal Hollow Nanocages as Promising Cathodes for the Long-Term Cyclability of Li–O2 Batteries

Abstract

As a step towards efficient and cost-effective electrocatalytic cathodes for Li–O2 batteries, highly porous hausmannite-type Mn3O4 hollow nanocages (MOHNs) of a large diameter of ~250 nm and a high surface area of 90.65 m2·g−1 were synthesized and their physicochemical and electrochemical properties were studied in addition to their formation mechanism. A facile approach using carbon spheres as the template and MnCl2 as the precursor was adopted to suit the purpose. The MOHNs/Ketjenblack cathode-based Li–O2 battery demonstrated an improved cyclability of 50 discharge–charge cycles at a specific current of 400 mA·g−1 and a specific capacity of 600 mAh·g−1. In contrast, the Ketjenblack cathode-based one can sustain only 15 cycles under the same electrolytic system comprised of 1 M LiTFSI/TEGDME. It is surmised that the unique hollow nanocage morphology of MOHNs is responsible for the high electrochemical performance. The hollow nanocages were a result of the aggregation of crystalline nanoparticles of 25–35 nm size, and the mesoscopic pores between the nanoparticles gave rise to a loosely mesoporous structure for accommodating the volume change in the MOHNs/Ketjenblack cathode during electrocatalytic reactions. The improved cyclic stability is mainly due to the faster mass transport of the O2 through the mesoscopic pores. This work is comparable to the state-of-the-art experimentations on cathodes for Li–O2 batteries that focus on the use of non-precious transition materials.

Oxygen defect regulation, catalytic mechanism, and modification of HfO2 as a novel catalyst for lithium–oxygen batteries

“…Ex situ SEM and first-principles calculation explained the performance and discharge products' morphology difference (nanosheets vs. island-like bulks) between HfO 2 and carbon paper. Ex situ XRD and XPS demonstrated the distinct activation phenomenon of HfO 2 during cycling, which is reported in many carbon, metal oxides, and noble metal catalysts, 32–35 referring to the evolution of oxygen defects in HfO 2 and discharge products (LiO x ). The oxygen defect self-optimization of HfO 2 and its impact on the Li–O reaction path were proposed.…”

Metal–organic framework-derived MnO/CoMn2O4@N–C nanorods with nanoparticle interstitial decoration in core@shell structure as improved bifunctional electrocatalytic cathodes for Li–O2 batteries

“…CPEdl is the constant phase element due to the double layer capacitance. Z w is the Warburg impedance arising due to the resistance against Li + ion diffusion [34,46]. The initial resistance parameters, R s and R ct of MXNC nanorod cathodes before cycles were lower compared to the α-MnO 2 nanorod cathodes (Table S2).…”

“…The full specific discharge capacity of the MXNC nanorods˗650 cathode-based LOB cell is lower due to insufficient graphitization and oxygen vacancies (higher oxygen content than MXNC nanorods) at low carbonization temperature (Figures S3(a), and Table 1). The increasing trend of discharge and charge polarizations with higher specific current density for MXNC nanorod cathode-based LOB cell the increasing specific current density, the gradient of oxygen concentration across the cathodes gets elevated, which builds up a diffusion restriction regime across the gas-cathode interface [46]. Despite that, the MXNC nanorod cathode-based LOB cell could deliver up to 6300 mAh•g -1 specific discharge capacity at 400 mA•g -1 , indicating the kinetic stability of ORR-OER on the MXNC nanorod cathodes [47].…”

LiOH Formation from Lithium Peroxide Clusters and the Role of Iodide Additive

“…Some challenges in the Li-O 2 battery design which demand research to make a practical Li-O 2 battery are the following: ,, The dendrite and low cycling efficiency of lithium metal anodes. Oxygen selective membranes that block the transit of moisture and CO 2 which damage the Li anode. The need of fast oxygen diffusion in the porous air cathode and a catalyst (i.e., oxides of Co, Mn, Ni, and Ru) for the oxygen reduction reaction (ORR) and oxygen evolution (OER) reactions. The accumulation of the Li 2 O 2 discharge product in the porous cathode reduces the electrochemically active surface area and hinders the transport of reactants (oxygen, Li + ) causing early battery death. The electron transport is affected by Li 2 O 2 insulating deposits, thus decreasing the capacity. The sluggish kinetics of the oxygen evolution reaction lead to poor round trip efficiency, a short cycle life, and a large charge overpotential (∼1–1.5 V) . The high overpotential could be due to side reactions involving the electrolyte, poor electron conductivity of the discharge products (Li 2 O 2 , LiO 2 or LiOH), and the nature of the Li 2 O 2 crystal facets involved in the electrochemical decomposition …”