Fluorinated Poly‐oxalate Electrolytes Stabilizing both Anode and Cathode Interfaces for All‐Solid‐State Li/NMC811 Batteries

Abstract

The relatively narrow electrochemical steady window and low ionic conductivity are two critical challenges for Li+‐conducting solid polymer electrolytes (SPE). Here, a family of poly‐oxalate(POE) structures were prepared as SPE; among them, POEs composed from diols with an odd number of carbons show higher ionic conductivity than those composed from diols with an even number of carbons, and the POE composed from propanediol (C5‐POE) has the highest Li+ conductivity. The HOMO (highest occupied molecular orbital) electrons of POE were found located on the terminal units. When using trifluoroacetate as the terminating unit (POE‐F), not only does the HOMO become more negative, but also the HOMO electrons shift to the middle oxalate units, improving the antioxidative capability. Furthermore, the interfacial compatibility across the Li‐metal/POE‐F is also improved by the generation of a LiF‐based solid‐electrolyte‐interlayer(SEI). With the trifluoroacetate‐terminated C5‐POE (C5‐POE‐F) as the electrolyte and Li+‐conducting binder in the cathode, the all‐solid‐state Li/LiNi0.8Mn0.1Co0.1O2(NMC811) cells showed significantly improved stability than the counterpart with poly‐ether, providing a promising candidate for the forthcoming all‐solid‐state high‐voltage Li‐metal batteries.

Influencing Factors on Li‐ion Conductivity and Interfacial Stability of Solid Polymer Electrolytes, Exampled by Polycarbonates, Polyoxalates and Polymalonates

“…As shown in Figure 2b, the carbonate in PCE, oxalate in POE and malonate in PME coordinate with Li + of LiTFSI, which dissociates the LiTFSI and therefore facilitates the migration of Li + . While, the terminal trifluoroacetyl‐units have been demonstrated benefits to the construction of LiF containing SEI (Figure S3) [14] . For the Li + ‐conductivity of SPEs, a higher molecular asymmetry is beneficial to the suppression of molecular aggregation and so the improvement of Li + ‐migration.…”

A review of all-solid-state electrolytes for lithium batteries: high-voltage cathode materials, solid-state electrolytes and electrode–electrolyte interfaces

“…Therefore, reducing the occurrence of side reactions at the interface between highvoltage electrode materials and solid-state electrolytes is also important for improving the performance of solid-state batteries. 20 Considering the importance of solid-state electrolytes for efficient energy storage and conversion in next-generation batteries, it is necessary to summarize the current development of high-voltage solid-state lithium metal batteries (Fig. 2a).…”

“…Therefore, reducing the occurrence of side reactions at the interface between high-voltage electrode materials and solid-state electrolytes is also important for improving the performance of solid-state batteries. 20…”

Improved Li‐Ion Conduction and (Electro)Chemical Stability at Garnet‐Polymer Interface through Metal‐Nitrogen Bonding

“…As the key component of solid‐state batteries, solid electrolytes with excellent mechanical property potentially allow the use of high specific capacity Li‐metal anode, which can deliver larger energy density than traditional LIBs. [ 6–8 ] Among the reported electrolytes, solid polymer electrolytes (SPEs), such as polyethylene oxide (PEO)‐, polyacrylonitrile (PAN)‐ and poly(vinylidenefluoride) (PVDF)‐based electrolytes with distinct advantages of light, good flexibility, excellent interfacial compatibility, and easy scalability, are most likely to achieve large‐scale application. [ 9–12 ] In particular, PVDF with excellent thermal stability and mechanical strength has been reported a suitable polymer matrix.…”

“…As the key component of solid-state batteries, solid electrolytes with excellent mechanical property potentially allow the use of high specific capacity Li-metal anode, which can deliver larger energy density than traditional LIBs. [6][7][8] Among the reported electrolytes, Organic-inorganic composite solid electrolytes consisting of garnet fillers dispersed in polyvinylidene difluoride (PVDF) frameworks have shown promise to enable high-energy solid-state Li-metal batteries. However, the air-sensitive garnets easily form poorly-conductive residues, which hinders fast Li-ion exchange at the garnet-polymer interface and results in low ionic conductivity.…”