Pinned Electrode/Electrolyte Interphase and Its Formation Origin for Sulfurized Polyacrylonitrile Cathode in Stable Lithium Batteries

Abstract

Sulfurized polyacrylonitrile (SPAN) represents one of the most promising directions for high-energy-density lithium (Li)-sulfur batteries. However, the practical application of Li||SPAN is currently limited by the insufficient chemical/electrochemical stability of electrode/electrolyte interphase (EEI). Here, a pinned EEI layer is designed for stabilizing a SPAN cathode by regulating the EEI formation mechanism in an advanced LiFSI/ether/fluorinated-ether electrolyte. Computational simulations and experimental investigations reveal that, benefiting from the nonsolvating nature, the fluorinated-ether can not only act as a protective shield to prevent the Li polysulfides dissolution but also, more importantly, endow a diffusion-controlled EEI formation process. It promotes the formation of a uniform, protective, and conductive EEI layer pinning into SPAN surface region, enabling the high loading Li||SPAN batteries with superior cycling stability, wide temperature performance, and high-rate capability. This design strategy opens an avenue for exploring advanced electrolytes for Li||SPAN batteries and guides the interface design for broad types of battery systems.

Electrolyte Engineering for Long-Life Li-SPAN Batteries

“…Continued cycling appears to induce further growth of the organic portion of this CEI layer. 43 In dilute ether electrolytes (Figure 3c), ethers are known to be stable toward PS species but are excellent solvents. As a result, lithiation of SPAN results in the formation of soluble long-chain PSs, or -S x -(x > 4), in the liquid phase.…”

“…For example, on the surface of cycled SPAN in LiFSI:DME:TTE (1:1.2:3, mol), the S 2p XPS spectrum shows signals from SO x and SO 2 -F species, while the F 1s XPS spectrum shows signals from LiF and SO x -F (Figure 3j). 43 AIMD simulations support the claim that TTE and LiFSI would decompose to form an inorganic-rich CEI on the SPAN surface, while DME is not a contributor due to its inherent stability. As a result, this electrolyte enables SPAN to show a capacity retention of 86.9% after 400 cycles.…”

“…On the surface of cycled SPAN, the C 1s XPS spectrum (Figure b) shows the presence of ROCO 2 Li and (-CH 2 CH 2 O-) n species due to the nucleophilic reaction between carbonate and Li 2 S 2 , while the salt decomposition results in the formation of Li x P y OF z and LiF, as evidenced by the F 1s signals. Continued cycling appears to induce further growth of the organic portion of this CEI layer …”

“…(Bottom) XPS results for SPAN cathodes after cycling in 1 M LiPF 6 in EC/EMC with VC additives (b), 1 M LiTFSI in DOL/DME (e), 1 M LiTFSI in DOL/DME with LiNO 3 (f), 4 M LiTFSI in DOL/DME, and LiFSI-1.2DME-3TTE (j). Panels b and j reproduced with permission from ref . Copyright 2022 American Chemical Society.…”

“…Since the diluent is highly fluorinated, it does not show solubility toward any lithium salts, including PSs. For example, on the surface of cycled SPAN in LiFSI:DME:TTE (1:1.2:3, mol), the S 2p XPS spectrum shows signals from SO x and SO 2 -F species, while the F 1s XPS spectrum shows signals from LiF and SO x -F (Figure j) . AIMD simulations support the claim that TTE and LiFSI would decompose to form an inorganic-rich CEI on the SPAN surface, while DME is not a contributor due to its inherent stability.…”