A Synthesis of Block Copolymers Based on Dynamic Covalent Bonds and its Application to All-Solid-State Battery Electrolyte

Recently, all-solid-state batteries (ASSB) have been in the spotlight as an alternative to potentially overcome the limitations of the existing liquid electrolyte lithium-ion batteries (LIB). Compared to liquid electrolyte LIB, ASSB has a lower risk of explosion, a higher energy density, and a relatively large electrochemical window. Solid electrolytes are largely classified into three categories: sulfide-based solid electrolytes, oxide-based solid electrolytes, and polymer-based solid electrolytes as key elements of ASSB. The most representative case among them is the lithium lanthanum zirconium oxide (LLZO), which has been extensively studied because it may easily compensate for the shortcomings of the sulfide-based solid electrolyte. Nevertheless, due to the brittleness of the ceramic-based material, it is still difficult to solve a serious interface contact problem between the electrolyte and the electrode. Therefore, many previous studies have attempted to introduce flexible polymer materials as binders to provide better wettability between solid interfaces. Specifically, ceramic-polymer composite solid electrolytes with soft interlayer in LLZO are feasible solutions that improve interfacial contact and inhibit dendrite generation in LIB. However, it is difficult to obtain sufficient ion conductivity and required mechanical properties in the polymer layer at the same time. Therefore, it is necessary to manufacture a flexible polymer membrane that can effectively promote efficient ion transport and control adhesion.<br/>This presentation proposes to synthesize a block copolymer based on a dynamic polymer chain structure and apply the material to an ASSB electrolyte. First, the disulfide (S-S) dynamic bond between the dithiol contained oligomer and PEG chain is synthesized using a disulfide generating agent (pentaerythritol tetrakis (3-mercaptopropionic acid)). The polymer solution for interlayer film is generated by adding bis (trifluoromethanesulfonyl)imide (LiTFSI). Then, a hybrid ceramic-polymer complex is manufactured using a drop casting method that introduces a block copolymer layer on the surface of garnet LLZO. As a result, the dynamic disulfide bond in co-polymer chain improves the adhesion between the solid electrolyte and the cathode as well as the anode, leading to a better contact interface and good dendrite suppression ability. That is, the lithium-ion conductive dynamic network not only lowers the overall impedance and interfacial resistance, but also increases the adhesion of the electrolyte to the electrode material. These modified polymer networks provide adequate ion conductivity and improved wettability to the interface. Through this work, it is possible to effectively develop LLZO-based solid electrolyte that improves surface properties and regulates the ion conduction mechanism.