Mesoporous multi-valence manganese oxides composite nanotubes boosting long-life lithium-ion batteries

Multi-component nano-oxide composite materials may present special synergistic effects as anode materials for lithium-ion batteries. Mesoporous β-MnO₂/Mn₃O₄ composite nanotubes are built here via controlling the deoxidation process of carbon-coating to induce a partial phase transition of high valence manganese dioxides. Compared to single β-MnO₂ nanotubes or Mn₃O₄@C nanotubes, the mesoporous β-MnO₂/Mn₃O₄@C composite nanotubes exhibit superior electrochemical properties. 679 mA h g^-1 of reversible specific capacity and 86% of capacity retention after 1000 cycles at 1 A g^-1 current density are obtained. The excellent performance is attributed to the unique multiple phase transitions regulation phenomena of manganese oxide occurring in the β-MnO₂/Mn₃O₄ composite material during the electrochemical processes, which significantly extends the cycle life of the β-MnO₂/Mn₃O₄ composite material.

Advanced Matrixes for Binder-Free Nanostructured Electrodes in Lithium-Ion Batteries

Commercial lithium-ion batteries (LIBs), limited by their insufficient reversible capacity, short cyclability, and high cost, are facing ever-growing requirements for further increases in power capability, energy density, lifespan, and flexibility. The presence of insulating and electrochemically inactive binders in commercial LIB electrodes causes uneven active material distribution and poor contact of these materials with substrates, reducing battery performance. Thus, nanostructured electrodes with binder-free designs are developed and have numerous advantages including large surface area, robust adhesion to substrates, high areal/specific capacity, fast electron/ion transfer, and free space for alleviating volume expansion, leading to superior battery performance. Herein, recent progress on different kinds of supporting matrixes including metals, carbonaceous materials, and polymers as well as other substrates for binder-free nanostructured electrodes in LIBs are summarized systematically. Furthermore, the potential applications of these binder-free nanostructured electrodes in practical full-cell-configuration LIBs, in particular fully flexible/stretchable LIBs, are outlined in detail. Finally, the future opportunities and challenges for such full-cell LIBs based on binder-free nanostructured electrodes are discussed.

Flexible Graphene-Wrapped Carbon Nanotube/Graphene@MnO2 3D Multilevel Porous Film for High-Performance Lithium-Ion Batteries

The ingenious design of a freestanding flexible electrode brings the possibility for power sources in emerging wearable electronic devices. Here, reduced graphene oxide (rGO) wraps carbon nanotubes (CNTs) and rGO tightly surrounded by MnO₂ nanosheets, forming a 3D multilevel porous conductive structure via vacuum freeze-drying. The sandwich-like architecture possesses multiple functions as a flexible anode for lithium-ion batteries. Micrometer-sized pores among the continuously waved rGO layers could extraordinarily improve ion diffusion. Nano-sized pores among the MnO₂ nanosheets and CNT/rGO@MnO₂ particles could provide vast accessible active sites and alleviate volume change. The tight connection between MnO₂ and carbon skeleton could facilitate electron transportation and enhance structural stability. Due to the special structure, the rGO-wrapped CNT/rGO@MnO₂ porous film as an anode shows a high capacity, excellent rate performance, and superior cycling stability (1344.2 mAh g^-1 over 630 cycles at 2 A g^-1 , 608.5 mAh g^-1 over 1000 cycles at 7.5 A g^-1 ). Furthermore, the evolutions of microstructure and chemical valence occurring inside the electrode after cycling are investigated to illuminate the structural superiority for energy storage. The excellent electrochemical performance of this freestanding flexible electrode makes it an attractive candidate for practical application in flexible energy storage.