ABSTRACT
The uncontrollable formation of polymorphous Li deposits, e.g., whiskers, mosses, or dendrites resulting from nonuniform interfacial current distribution and internal stress release in the upward direction on the conventional current collector (e.g., Cu foil) of Li metal rechargeable batteries with a lithium-metal-free negatrode (LMFRBs), leads to rapid performance degradation or serious safety problems. The 3D carbon nanotubes (CNTs) skeleton has been proven to effectively reduce the current density and eliminate the internal accumulated stress. However, remarkable electrolyte decomposition, inherent Li source consumption due to repeated SEI formation, and Li+ intercalation in CNTs limit the application of 3D CNTs skeleton. Thus, it is necessary to avoid the side effects of the 3D CNTs skeleton and retain uniform interfacial current distribution and stress mitigation. In this work, we integrate the CNTs network with a soft functional polymer polyvinylidene fluoride (PVDF) to form a relatively dense coating layer on Cu foil, which can shield the contact between the internal surface of the 3D CNTs framework and the electrolyte. Simultaneously, the Li-F-rich SEI resulting from the partial reduction of PVDF with deposited Li and the soft nature of the coating layer release the accumulation of internal stress in the horizontal direction, resulting in mosses/whisker-free Li deposition. Thus, improved Li deposition/dissolution and stable cycling performance of the LMFRBs can be achieved.
ABSTRACT
In this work, five vanadium oxide materials with a series of pre-intercalated cations A (AmV2O5), including Zn2+, Mg2+, NH4+, Li+, and Ag+, have been successfully prepared by a two-step method. All of them possess binary monoclinic and orthorhombic V2O5 phases with an open layered structure that allows the ionic storage and diffusion of hydrated cations. The interlayer space for the monoclinic V2O5 phase is strongly dependent on the radii of hydrated cations A, while the one for the orthorhombic V2O5 phase remains the same regardless of the radii of cations A. Among them, AmV2O5 with pre-intercalated Zn2+ (ZVO) has the best storage ability of Zn2+ with a reversible capacity close to 400 mAh g-1, and AmV2O5 with pre-intercalated Ag+ shows the highest rate capacity with a nearly 40% capacity retention at a current of 20 A g-1 (≈25 C). Kinetic studies have clearly shown that pseudocapacitive behavior dominates the electrochemical reaction on ZVO. During the Zn2+ (de)intercalation reaction, a highly reversible transformation of binary monoclinic or orthorhombic V2O5 phases into a single triclinic ZnxV2O5·nH2O phase is demonstrated on ZVO. Vanadium atoms are identified as the redox centers that undergo the mutual transition among the chemical states of V3+, V4+, and V5+. They together with oxygen atoms constitute reasonable V-O coordination polyhedra to generate a layered structure with a suitable interlayer space for the insertion or removal of zinc ions. Actually, the intrinsic coordination chemistry changes between VO5 square pyramids and VO6 octahedra account for the phase transformation during the Zn2+-(de)intercalation reaction.
ABSTRACT
Lithium metal batteries (LMBs) are a promising candidate for next-generation energy storage devices. However, the high irreversibility and dead Li accumulation of the lithium metal anode caused by its fragile original solid electrolyte interface (SEI) seriously hinder the practical application of LMBs. Herein, a facile slurry-coating and one-step thermal fluorination reaction method is proposed to construct the 3D structural LiF-protected Li/G composite anode. The existence of a 3D LiF protection layer is convincingly confirmed and the function of the Li/G skeleton is discussed in detail. The 3D structural LiF protection layer results in superior electrochemical performance by improving the utilization of Li and suppressing the accumulation of dead Li in symmetric and full coin cells. Moreover, a 0.85 Ah pouch cell strictly following the parameters of the practical battery industry can work stably for 140 cycles with a gradual internal resistance increase. This novel Li/G composite anode indicates a promising strategy in lithium/carbon composite anodes for LMBs, and the facile thermal fluorination reaction method presented in this paper offers a new method for the construction of a 3D structural protection layer for lithium metal anodes.
