Argyrodite–Li6PS5cl/Polymer–Based Highly Conductive Composite Electrolyte for All–Solid–State Batteries
Authors: Ahmed Faiz , Li Defu , Liu Gao 
Published: August 2024

The intense focus of research is on all–solid–state lithium–ion batteries (ASSLBs) with solid electrolytes (SEs) owing to their potential qualities such as high energy, high power density, and enhanced safety compared to conventional Lithium Ion batteries (LIBs).1 In spite of the numerous advantages of ASSLBs, a lot of issues still need to be solved before commercialization.2 Typically, SEs demonstrate lower ionic conductivity (σ) compared to liquid electrolytes.1 For instance, lithium phosphorous oxynitride (LiPON), a frequently employed SE, exhibits an σ of ca. 10–6 S/cm. In contrast, a liquid electrolyte like lithium hexafluorophosphate in ethylene carbonate and propylene carbonate demonstrates a higher σ of ca. 10–2 S/cm at room temperature.1

So far, extensive research has been conducted on Argyrodite–Li6PS5Cl (LPSCl) electrolytes, yielding promising results for their applications in Li–ion and Li–S batteries.3However, a significant challenge in using argyrodite LPSCl in ASSLBs applications is the interface instability between the LPSCl and electrodes. During charge-discharge (CD) cycling, LPSCl tends to oxidize, leading to the production of elemental sulfur, polysulfides, phosphates, and lithium chloride at the electrode interface.3These side products ultimately hinder cycling stability and can result in dendrite formation at the interface. Another important drawback of LPSCl is its non–negligible electronic conductivity, which allows for smooth electron transport through the LPSCl electrolyte.4Consequently, Li dendrites can be directly deposited at the grain boundaries of LPSCl particles, leading to a serious self–discharge issue.4

In this study, we have developed a composite electrolyte of LPSCl/polymer to enhance the contact between the electrolyte and electrodes and suppress dendrite formation at the grain boundary of the LPSCl ceramic. The monomer, triethylene glycol dimethacrylate (TEGDMA), is utilized for in–situ polymerization through thermal curing to create the Argyrodite LPSCl/polymer composite electrolyte. Additionally, the ball–milling technique was employed to modify the morphology and particle size of the LPSCl ceramic. The ball–milled LPSCl/polymer composite electrolyte (BLPSCl–P) demonstrates slightly higher ionic conductivity (ca. 2.21 × 10–4 S/cm) compared to the as–received LPSCl/polymer composite electrolyte (ALPSCl–P) (ca. 1.65 × 10–4 S/cm) at 25 °C (Figure 1). Furthermore, both composite electrolytes exhibit excellent compatibility with Li–metal and display cycling stability for up to 1000 hours (375 cycles) (Figure 1), whereas the as–received LPSCl (ALPSCl) and ball–milled LPSCl (BLPSCl) electrolytes maintain stability for up to 600 hours (225 cycles) at a current density of 0.4 mA/cm2. The SSB with the BLPSCl–P delivers high specific discharge capacity (138 mAh/g), Coulombic efficiency (99.97%), and better capacity retention at 0.1C, utilizing the battery configuration of coated NMC811//electrolyte//Li–Indium (In) at 25 °C.

Figure 1

REFERENCES

(1) Li, S.; Zhang, S. Q.; Shen, L.; Liu, Q.; Ma, J. Bin; Lv, W.; He, Y. B.; Yang, Q. H. Progress and Perspective of Ceramic/Polymer Composite Solid Electrolytes for Lithium Batteries. Adv. Sci.
2020, 7 (5).

(2) Lee, S. E.; Sim, H. T.; Lee, Y. J.; Hong, S. B.; Chung, K. Y.; Jung, H. G.; Kim, D. W. Li6PS5Cl–Based Composite Electrolyte Reinforced with High–Strength Polyester Fibers for All–Solid–State Lithium Batteries. J. Power Sources
2022, 542 (6), 231777.

(3) Lee, Y. G.; Fujiki, S.; Jung, C.; Suzuki, N.; Yashiro, N.; Omoda, R.; Ko, D. S.; Shiratsuchi, T.; Sugimoto, T.; Ryu, S.; Ku, J. H.; Watanabe, T.; Park, Y.; Aihara, Y.; Im, D.; Han, I. T. High–Energy Long–Cycling All–Solid-State Lithium Metal Batteries Enabled by Silver–Carbon Composite Anodes. Nat. Energy
2020, 5 (4), 299–308.

(4) Yang, X.; Gao, X.; Jiang, M.; Luo, J.; Yan, J.; Fu, J.; Duan, H.; Zhao, S.; Tang, Y.; Yang, R.; Li, R.; Wang, J.; Huang, H.; Veer Singh, C.; Sun, X. Grain Boundary Electronic Insulation for High–Performance All–Solid–State Lithium Batteries. Angew. Chem. Int. Ed.
2023, 62 (5).

Figure 1