Garnet-Poly(ε-caprolactone-co-trimethylene carbonate) Polymer-in-Ceramic Composite Electrolyte for All-Solid-State Lithium-Ion Batteries

Funeka P Nkosi,Nurul A Dzulkurnain,Sabina Abbrent,Libor Kobera,Kristina Edström,Jonas Mindemark,Guiomar Hernández,Jiri Brus,Andrii Mahun,Mario Valvo

doi:10.1021/acsaem.0c03098

Abstract

A composite electrolyte based on a garnet electrolyte (LLZO) and polyester-based co-polymer (80:20 ε-caprolactone (CL)-trimethylene carbonate, PCL-PTMC with LiTFSI salt) is prepared. Integrating the merits of both ceramic and co-polymer electrolytes is expected to address the poor ionic conductivity and high interfacial resistance in solid-state lithium-ion batteries. The composite electrolyte with 80 wt % LLZO and 20 wt % polymer (PCL-PTMC and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at 72:28 wt %) exhibited a Li-ion conductivity of 1.31 × 10–4 S/cm and a transference number (tLi+) of 0.84 at 60 °C, notably higher than those of the pristine PCL-PTMC electrolyte. The prepared composite electrolyte also exhibited an electrochemical stability of up to 5.4 V vs Li+/Li. The interface between the composite electrolyte and a LiFePO4 (LFP) cathode was also improved by direct incorporation of the polymer electrolyte as a binder in the cathode coating. A Li/composite electrolyte/LFP solid-state cell provided a discharge capacity of ca. 140 mAh/g and suitable cycling stability at 55 °C after 40 cycles. This study clearly suggests that this type of amorphous polyester-based polymers can be applied in polymer-in-ceramic composite electrolytes for the realization of advanced all-solid-state lithium-ion batteries.

Highlights

Commercial lithium-ion batteries (LIBs) based on organic liquid electrolytes pose some safety concerns due to the flammability of their solvents, unrestrained electrochemical side reactions, lithium dendrite formation, and internal short circuits.[1]
The cubic structure of the LLZO was stabilized by aluminum doping and the X-ray diffraction (XRD) pattern was indexed to the space group Ia3̅d with minor impurities.[34−36] The XRD pattern of the composite displays strong peaks that are characteristic of LLZO, suggesting that there is no significant structural change when incorporating the LLZO particles in the polymer matrix
This may account for the reduced cycling performance observed upon repeated cycling. These results indicate promising electrochemical performance for this composite electrolyte when used in an all-solid-state lithium-ion battery

Summary

INTRODUCTION

Commercial lithium-ion batteries (LIBs) based on organic liquid electrolytes pose some safety concerns due to the flammability of their solvents, unrestrained electrochemical side reactions, lithium dendrite formation, and internal short circuits.[1]. High ionic conductivity and transference number, together with good mechanical strength, electrochemical stability, and thermal stability, are necessary to achieve improved composite electrolytes, which are essential for highly performing all-solidstate batteries. This requires composite electrolytes with high ceramic loadings, known as polymer-in-ceramic composites. Cubic LLZO ceramic was used here because of its chemical stability against lithium metal anodes, high ionic conductivity (σ ≈ 10−3−10−5 S/cm at 25 °C), and a wide potential window for reliable electrochemical operation (>5 V vs Li/Li+).[31,32] A synergy between these different polymeric and ceramic electrolyte components has been observed, making this type of composite electrolytes attractive for advancing all-solidstate Li-ion batteries

EXPERIMENTAL SECTION

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES