Abstract
In recent years, Lithium metal batteries (LMBs) have gained great interests thanks to their high capacity that can respond to the continuous increasing need for energy storage and device. The design and development of new solid-state electrolytes e.g. polymer based ones (SPEs) then became crucial towards intrinsically safer LMBs. A successful electrolyte candidate needs to fulfill several requirements such as high transference number (tLi+) and a compromise between two antagonist properties: conductivity and mechanical properties. Most researches focused on the synthesis of single-ion conducting electrolytes as a strategy to overcome these difficulties1,2. However, these materials often require complicated and delicate chemistry and their conductivity often remains low (σ < 10-5 S/cm at 60°C). An alternative promising route that received much less attention is the development of bulky Lithium salts with macroanion. The bulky anion reduces ion paring and salts aggregation and present negligible mobility compared to Lithium cation resulting in higher transference number3.
In this work, we present a new macroanion based on Polyhedral Oligomeric Silsesquioxane (POSS) grafted with either polyethylene oxide oligomers (PEG) and/or Lithium sulfonyl (trifluoromethanesulfonyl) imide (LiTFSI) denoted as POSS-LiTFSI-PEG or POSS-LiTFSI respectively. Thus, SPE has been prepared with a reference high molecular weight polyethylene oxide at different OE/Li ratio from 10 to 25. This new concept of bulky multi-anion based on TFSI moieties allows a complete salt dissociation, an enhancement of the mechanical properties thanks to the presence of the inorganic POSS multi anions that play the role of nano fillers, and finally, a strong increase of the Li+ transference number (tLi+>0,55), which opens many perspectives. The cycling performance obtained in both Lithium symmetric cells and LMBs prototypes will be also presented.
References
(1) Bouchet, R.; Maria, S.; Meziane, R.; Aboulaich, A.; Lienafa, L.; Bonnet, J.-P. P.; Phan, T. N. T.; Bertin, D.; Gigmes, D.; Devaux, D.; et al. Single-Ion BAB Triblock Copolymers as Highly Efficient Electrolytes for Lithium-Metal Batteries. Nat. Mater. 2013, 12 (5), 452–457.
(2) Zhang, H.; Li, C.; Piszcz, M.; Coya, E.; Rojo, T.; Rodriguez-Martinez, L. M.; Armand, M.; Zhou, Z. Single Lithium-Ion Conducting Solid Polymer Electrolytes: Advances and Perspectives. Chem. Soc. Rev. 2017, 46 (3), 797–815.
(3) Chinnam, P. R.; Wunder, S. L. Polyoctahedral Silsesquioxane-Nanoparticle Electrolytes for Lithium Batteries: POSS-Lithium Salts and POSS-PEGs. Chem. Mater. 2011, 23 (23), 5111–5121.
Figure 1