Although the LiMn2O4 cathode can provide high nominal cell voltage, high thermal stability, low toxicity, and good safety in Li-ion batteries, it still suffers from capacity fading caused by the combination of structural transformation and transition metal dissolution. Herein, a carbon-coated LiMn2O4 cathode with core@shell structure (LMO@C) was therefore produced using a mechanofusion method. The LMO@C exhibits higher cycling stability as compared to the pristine LiMn2O4 (P-LMO) due to its high conductivity reducing impedance growth and phase transition. The carbon shell can reduce direct contact between the electrolyte and the cathode reducing side reactions and Mn dissolution. Thus, the cylindrical cell of LMO@C//graphite provides higher capacity retention after 900 cycles at 1 C. The amount of dissoluted Mn for the LMO@C is almost 2 times lower than that of the P-LMO after 200 cycles. Moreover, the LMO@C shows smaller change in lattice parameter or phase transition than P-LMO, indicating to the suppression of λ-MnO2 phase from the mixed phase of Li1-δMn2O4 + λ-MnO2 when Li-delithiation at highly charged state leading to an improved cycling reversibility. This work provides both fundamental understanding and manufacturing scale demonstration for practical 18650 Li-ion batteries.
Scalable aqueous-based supercapacitors are ideal as future energy storage technologies due to their great safety, low cost, and environmental friendliness. However, the corrosion of metal current collectors e.g., aluminium (Al) foil in aqueous solutions limits their practical applications. In this work, we demonstrate a low-cost, scalable, and simple method to prepare an anti-corrosion current collector using a concept of hydrophobicity by coating the hydrophobic graphite passivation layer on the Al foil via a roll-to-roll coating technology at the semi-automation scale of production pilot plant of 18,650 cylindrical supercapacitor cells. All qualities of materials, electrodes, and production process are therefore in the quality control as the same level of commercial supercapacitors. In addition, the effects of the graphite coating layer have been fundamentally evaluated. We have found that the graphite-coated layer can improve the interfacial contact without air void space between the activated carbon active material layer and the Al foil current collector. Importantly, it can suppress the corrosion and the formation of resistive oxide film resulting in better rate capability and excellent cycling stability without capacitance loss after long cycling. The scalable supercapacitor prototypes here in this work may pave the way to practical 18,650 supercapacitors for sustainable energy storage systems in the future.
Rechargeable aqueous Zn-MnO2 batteries have been considered as one of the promising alternative energy technologies, due to their high abundance, environmental friendliness, and safety for both Zn-metal anode and manganese...
Insight into the influence of hydration energy of structural cations within birnessite-type layered MnO 2 on charge storage mechanisms via redox reaction and intercalation/deintercalation processes with the ion-exchange process is demonstrated. The redox activity and Mn utilization observed from ex situ X-ray absorption spectroscopy are Li−MnO x > Ca−MnO x > Sr−MnO x > Ba−MnO x . Although Li−MnO x shows higher redox activity than Ca−MnO x , the Ca− MnO x exhibits higher specific capacitance due to its higher hydration energy of Ca 2+ (−500 kcal mol −1 ) as compared to −465 and −436 kcal mol −1 of Sr−MnO x and Ba−MnO x , respectively, which dominates the ion-exchange affinity within the birnessite structure. Therefore, the charge storage mechanism of the birnessite depends strongly on the hydration energy of structural cations which can further be probed by inductively coupled plasma-optical emission spectrometry technique. Additionally, Ca−MnO x with the smallest number of the remaining structural Ca 2+ as compared with other cations demonstrates the highest specific capacitance followed by Sr−MnO x , Li−MnO x , and Ba−MnO x . Furthermore, all the as-prepared samples demonstrate the excellent cycling stability (above 96%) after 11 000 cycles at a current density of 5 A g −1 . This finding may be useful for further development of practical manganese oxide supercapacitors.
This work demonstrates the effect of trimetallic and bimetallic electrocatalysts of spinel‐type metal oxides towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). The trimetallic spinel‐type Co0.5Ni0.5Mn2O4 shows higher bifunctional electrocatalytic activity towards ORR and OER than bimetallic oxides such as CoMn2O4 and NiMn2O4. The in situ X‐ray absorption spectroscopy was applied to observe the change in the oxidation number of Mn, Ni, and Co during the reactions to demonstrate the active metals on the ORR and OER. The Co plays a more important role in the ORR process than the Ni and Mn, while the three metals exhibit an equivalent contribution on the OER activity as observed from the oxidation state shift. Additionally, the practicality of Zn‐air batteries using the trimetallic spinel catalyst is demonstrated to power light‐emitting diode and spinning motor with a nominal voltage of 3 V. Bifunctional trimetallic electrocatalysts in this work may be useful for other metal‐air batteries.
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