Joining electrode material and solid electrolyte by flash-sintering crystallization for solid-state batteries

• Grant number: 24/08265-8
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: August 01, 2025
• End date: July 31, 2027
• Field of knowledge: Engineering - Materials and Metallurgical Engineering - Nonmetallic Materials
• Principal Investigator: Ana Candida Martins Rodrigues
• Grantee: Joseph Nzabahimana
• Host Institution: Centro de Ciências Exatas e de Tecnologia (CCET). Universidade Federal de São Carlos (UFSCAR). São Carlos , SP, Brazil
• Associated research grant: 13/07793-6 - CEPIV - Center for Teaching, Research and Innovation in Glass, AP.CEPID

Abstract

Materials with a NaSICON structure (short for "Na superionic conductor") have shown significant promise for serving as electrolytes in the next generation of all-solid-state batteries (ASSBs). These solid-state electrolytes (SSEs) enable the utilization of high-voltage cathodes and metallic anodes, leading to batteries with heightened energy density and enhanced safety compared to those employing currently prevalent liquid electrolytes, which are prone to flammability.Despite the acknowledged advantages of ASSBs, several challenges still need to be addressed before their widespread adoption. Among these challenges, one prominent issue is the elevated interface resistance between the electrolyte and the electrodes. This heightened resistance may arise due to various factors such as insufficient interfacial contact, interfacial degradation stemming from mutual diffusion, and mechanical deficiencies in the contacts, such as cracks or pore formation. These interfacial degradation processes can be categorized by their origin as either chemical or mechanical.Regarding mechanical interfacial problems, these can be mitigated through the implementation of improved surface joining methods. For instance, an assembly comprising an anode || electrolyte || cathode (NVP-NZSP-Csp || NZSP || NVP-NZSP-Csp, respectively) was successfully sintered at once using the Spark-Plasma Sintering (SPS) technique, resulting in an optimized interface between the battery components.In this context, the investigation of the Flash-Joining technique presents an intriguing avenue. This technique shows promise in bonding ceramics and metals by reducing micro shear and bending stresses, which prevents crack and defect formation at the interface due to differences in thermal expansion coefficients and sintering rates within multilayer systems. Flash-Joining essentially involves applying Flash-Sintering to a multilayer material. Flash Sintering involves applying an electric field during the heating of an NTC (negative thermal coefficient) type ceramic material. At specific combinations of electric field and temperature, a flash event occurs-a moment when the electric current passing through the material abruptly increases, leading to a corresponding rise in temperature. Once the electric current reaches a predetermined value, the source transitions to current control mode, maintaining it constant. This establishes a thermal equilibrium between Joule heating and heat dissipation to the environment, known as a steady-state regime.Recently, our research group has developed the Flash Sinter Crystallization technique for concurrently sintering and crystallizing glass powder compacts, as well as Flash Crystallization for solely crystallizing monolithic glasses. Through Flash Sinter-Crystallization, we achieved a remarkable reduction in furnace temperature and sinter-crystallization time for two glass systems: Li1.5Al0.5Ge1.5(PO4)3 (LAGP) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), down to 480 and 460 °C, and accomplished complete crystallization in just 20 seconds! Traditionally, the concurrent sintering and crystallization of these materials necessitate furnaces operating at 850 and 950 °C, respectively, and require at least 2 hours to achieve complete crystallization. Moreover, aside from the evident reductions in processing time and energy consumption, this technique yielded materials with superior ionic conductivity compared to conventionally produced ones.Thus, there exists an exciting opportunity to leverage Flash Sinter Crystallization and Flash Crystallization to optimize the ionic conductivity of materials featuring NaSICON structure combined with the Flash-Joining technique to optimize the interface between the cathode material and the NaSICON-structured electrolyte material, for potential application in ASSB's.