Anion Immobilization Enabled by Cation‐Selective Separators for Dendrite‐Free Lithium Metal Batteries

Abstract

The lithium dendrite issue is a major bottleneck that limits the utilization of lithium metal anodes in high‐energy rechargeable batteries. From the perspective of the dendrite nucleation mechanism, this work develops a new type of cation‐selective (CS) separator with anion immobilization behavior to boost the lithium metal anode. By taking advantage of the poly(vinylidene fluoride) matrix, a strong binding force with anions contributes to an excellent CS property of the separator, which is further confirmed by molecular dynamics simulations. The CS separator developed in this work presents a high lithium‐ion transference number up to 0.81. Considering such a dramatically reduced transference number of anions, it can prolong the nucleation time of lithium dendrite and thus achieve a high‐stable Li plating/stripping cycling for 1000 h at a high applied current density of 3 mA cm−2. The Li metal stabilization function of the CS separator is further studied in detail through both in‐situ and ex‐situ observations of dendrites growth. When integrating into lithium metal batteries (LMBs), the CS separators also contribute to enhanced electrochemical performances including discharge capacity, rate capability, and cycling durability. This work is anticipated to provide considerable insight for the creative design of CS separators toward dendrite‐free LMBs.

Enabling dendrite-free and high-rate lithium anode with a self-standing anionic-MOF separator

“…Specically, AMSs of different thicknesses were prepared by adjusting the proportion of UIO-66-SO 3 Li and PVDF (the MOF mass fractions were 40%, 50%, 60% and 70%, respectively) based on our previous cationic selective separator. 31 The thickness of the AMS was 4.7 mm, 7.9 mm, 8.7 mm and 9.5 mm, respectively (Fig. S2 †).…”

Molecular/Ionic Designs in the Electrolyte and Interphases for Lithium Metal Anode

“…The Zhang Group constructed an ultrathin cationic selective (CS) functional separator, which is very effective in stabilizing Li anode and inhibiting dendrite growth. [22] CS separator (PVDF) has a very high transference number of Li + (0.81). As shown in Figure 11(a), Li + hardly has direct contact with PVDF chains, while the PF 6…”

“…One of the purposes of this method is to fix anions to weaken the space charge field. The Zhang Group constructed an ultrathin cationic selective (CS) functional separator, which is very effective in stabilizing Li anode and inhibiting dendrite growth [22] . CS separator (PVDF) has a very high transference number of Li + (0.81).…”

“…Uneven Li + flux can be also caused by the concentration of the electric field and temperature field on the local protrusion of the Li metal surface (Figure 1c). [21][22][23][24] This is a positive feedback process, which accumulates and leads to the formation of more dendrites. Introducing cationic protective layers on the protrusion can shield the local electric field effectively.…”

Tuning the Metal Ions of Prussian Blue Analogues in Separators to Enable High-Power Lithium Metal Batteries

“…As the reservoir for the electrolyte, the separator is an ideal candidate for regulating the ion transport since both Li + and the anion have to migrate through the separator during charge–discharge. Thereby, extensive efforts have been made to endow the separators with desirable functionalities by modifying the commercial polyolefin-based separators with various functional materials, − such as carbon materials, inorganic ceramics, polymers, and metal/metal oxides. Among these materials, metal–organic frameworks (MOFs) with adjustable pores, high surface area, and periodical crystalline structure provides desirable chances for regulating ion transport, and their applications in separators have come up as a new hotspot. ,,− For instance, Bai et al utilized HKUST-1 to construct a MOF/graphene oxide (GO) composite separator in which the MOF can act as an ionic sieve to allow the transport of Li + while suppressing the migration of polysulfides selectively .…”