Ion Conductive High Li⁺ Transference Number Polymer Composites for Solid-State Batteries

Solid-state electrolytes are a promising field of study to improve the safety and energy density of lithium-based batteries. Composite solid electrolytes seek to leverage both the desirable mechanical properties of polymers and the high conductivity of active ceramic fillers; however, Li + transport through the composite, and especially the extent of Li + through the ceramic phase, remains an open question. 1, 2 Simulations suggest that decreasing interfacial resistance between polymer and ceramic would promote transport through ceramic particles. 1 Our work seeks to improve Li + transport in the ceramic phase by engineering both polymer and ceramic materials that minimize the interfacial resistance between the two. Traditional polymer electrolytes have a low transference number (~0.15) compared to ceramics (~1), and when combined in composites this mismatch has been suggested as a major contributor to interfacial impedance. 3 We explore the effect of the transference number mismatch by using a single-ion conducting polymer poly((trifluoromethane)sulfonamide lithium methacrylate) (PMTFSILi). The Li + transport in a composite electrolyte with high transference number PMTFSILi is compared with that of a system utilizing a lithium salt. Contaminants on ceramic surface can also contribute to interfacial resistance. We consider how lithium carbonate (Li 2 CO 3 ) content on the surface of LLZTO (Li 6.4 La 3 Zr 2 Ta 0.6 O 12 ) affects Li + transport. Accompanying this study is a detailed description of washing procedures used to clean the LLZTO surface. Titration Mass Spectrometry (TiMS) is used to quantify Li 2 CO 3 content in our ceramic particles and assess the effectiveness of our cleaning procedures. Inductively-coupled plasma mass spectrometry (ICP-MS) data also assists in measuring the impact (Li + exchange and transition metal dissolution) of various washing procedures (basic, acidic) on the LLZTO particles. Solid-state NMR has proven to be a useful tool in deconvoluting Li + transport in different phases of composite electrolytes 2 and is the primary technique we use to quantify transport in our system. These findings will provide a deeper understanding into the relationship between interfacial resistance and Li + transport in composite electrolyte systems and shed light on how material choices can better utilize the highly conductive ceramic phase for Li + transport. Kim, HK., Barai, P., Chavan, K. et al. Transport and mechanical behavior in PEO-LLZO composite electrolytes. J Solid State Electrochem 26 , 2059–2075 (2022). https://doi.org/10.1007/s10008-022-05231-w Zheng J., Hu, Y. New Insights into the Compositional Dependence of Li-Ion transport in polymer-ceramic composite electrolytes. ACS Appl. Mater. Interfaces , 10 , 4, 4113–4120 (2018). https://doi.org/10.1021/acsami.7b17301 Mehrotra A. et al. Quantifying Polarization Losses in an Organic Liquid Electrolyte/Single Ion Conductor Interface. Electrochem. Soc. 161 A1681 (2014). https://doi.org /10.1149/2.0721410jes