Two Birds with One Stone: Interfacial Engineering of Multifunctional Janus Separator for Lithium–Sulfur Batteries

Abstract

Li‐dendrite growth and unsatisfactory sulfur cathode performance are two core problems that restrict the practical applications of lithium–sulfur batteries (LSBs). Here, an all‐in‐one design concept for a Janus separator, enabled by the interfacial engineering strategy, is proposed to improve the performance of LSBs. At the interface of the anode/separator, the thin functionalized composite layer contains high‐elastic‐modulus and high‐thermal‐conductivity boron nitride nanosheets and oxygen‐group‐grafted cellulose nanofibers (BNNs@CNFs), by which the formation of “hot spots” can be effectively avoid, the Li‐ion flux homogenized, and dendrite growth suppressed. Meanwhile, at the interface between the separator and the cathode, the homogenously exposed single‐atom Ru on the surface of reduced graphene oxide (rGO@Ru SAs) can “trap” polysulfides and reduce the activation energy to boost their conversion kinetics. Consequently, the LSBs show a high capacity of 460 mAh g–1 at 5C and ultrastable cycling performance with an ultralow capacity decay rate of 0.046% per cycle over 800 cycles. To further demonstrate the practical prospect of the Janus separator, a lithium–sulfur pouch cell using the Janus separator delivers a cell‐level energy density of 310.2 Wh kg–1. This study provides a promising strategy to simultaneously tackle the challenges facing the Li anode and the sulfur cathode in LSBs.

Novel Concept of Separator Design: Efficient Ions Transport Modulator Enabled by Dual‐Interface Engineering Toward Ultra‐Stable Zn Metal Anodes

“…Moreover, Figure 4g shows that the exchange current density of cell based on DIE separator (6.76 mA cm −2 ) obtained from the Tafel plots is also much larger than that of the GF separator-based cell (2.12 mA cm −2 ), further demonstrating the modified cell a reduced space charge and surface barrier and thus accelerating Zn 2+ transport kinetics on the electrode surface. [46,47] On the other hand, considering the hydrophilicity of separator also plays an important role in influencing the electrolyte penetration during energy storage process. [48] The contact angle test of separator before and after DIE modification was also conducted, as shown in Figure S23, Supporting Information.…”

Pushing Lithium–Sulfur Batteries towards Practical Working Conditions through a Cathode–Electrolyte Synergy

“…However, since the parasitic reaction in a practical pouch cell is much more severe than that of a small‐scale coin cell, it remains challenging to achieve a stable cycling performance in a Li−S pouch cell. And most of the reported Li−S pouch cells utilized the Li‐metal anode with the thickness >100 μm (Supporting Information Table S3) [49–51] . As a result, we applied thin Li metal foil (40 μm) as the anode and controlled the E/S ratio to 7 μL mg −1 of the Li−Se/S pouch cell to validate the effectiveness of our concept in limiting the parasitic reaction and thus enhance the stability of the Li−Se/S pouch cell.…”

“…And most of the reported LiÀ S pouch cells utilized the Li-metal anode with the thickness > 100 μm (Supporting Information Table S3). [49][50][51] As a result, we applied thin Li metal foil (40 μm) as the anode and controlled the E/S ratio to 7 μL mg À 1 of the LiÀ Se/S pouch cell to validate the effectiveness of our concept in limiting the parasitic reaction and thus enhance the stability of the LiÀ Se/S pouch cell. As shown in Figures 5f and g, the as-assembled LiÀ Se/S pouch cell can deliver an initial specific capacity of 931.12 mAh g À 1 at 200 mA g À 1 .…”

Interfacial Engineering of Binder‐Free Janus Separator with Ultra‐Thin Multifunctional Layer for Simultaneous Enhancement of Both Metallic Li Anode and Sulfur Cathode

“…It is considered to be a facile and effective approach to functionalizing separators to confine LiPSs and synchronously regulate the Li dissolution/deposition in LSBs. [18][19][20] The commercial polyolefin separator with a low melting point and nonpolar characteristics results in poor electrolyte affinity and difficulty in modification. [21,22] In addition, most of the functionalization strategies have not paid attention to the thickness and weight, which would apparently reduce the energy density of LSBs.What's worse, the stripping of the coated layer from the separator extensively exists in traditional separator modification methods, which would significantly diminish practical performance and even raise serious safety concerns about Li-metal batteries.…”

“…It is considered to be a facile and effective approach to functionalizing separators to confine LiPSs and synchronously regulate the Li dissolution/deposition in LSBs. [18][19][20] The commercial polyolefin separator with a low melting point and nonpolar characteristics results in poor electrolyte affinity and difficulty in modification. [21,22] In addition, most of the functionalization strategies have not paid attention to the thickness and weight, which would apparently reduce the energy density of LSBs.…”