(585i) Role of Solvents in Solid-State Batteries with Enhanced Thermal Safety

Lithium-ion batteries (LIBs) have proliferated through modern society rapidly through their indisputable advantages in terms of high energy density, excellent cyclability, and dependable performance. Solid-state batteries represent a route to intensifying these advantages by further improvements in the energy density with the use of lithium metal or silicon anodes, as well as conferring intrinsically superior safety through the prevention of chemical cross-talk and the combustion and degradation reactions of conventional liquid electrolytes. As the scale of electrochemical energy storage continues to trend towards larger formats in the form of passenger vehicles and stationary grid-scale applications, the importance of safely sequestering the high energy density of the next generation of LIBs comes into sharper focus. The public relations impact of high-profile mishaps involving LIBs hinders the widespread adoption of the electrochemical energy storage necessary for decarbonization via electrification.

High interfacial impedance, imperfect solid-electrolyte interphase (SEI) formation, and low room-temperature ionic conductivity (σ) present challenges to many current solid-state systems. The role of liquid additives within solid electrolytes has been controversial within the literature, as the inclusion of flammable components into an electrolyte system touted for its safety appears contradictor. Though current work in composite solid electrolyte systems acknowledge the presence of liquid solvent remnants within the system, there exists a substantial knowledge gap into the true impact of such additives on the thermal safety of the overall cell over realistic degradation modes.

The Vilas Pol Energy Research (ViPER) Group has worked extensively to substantiate the claims of excellent thermal safety within solid-state systems with detailed thermal safety studies while engineering high-performance composite polymer electrolyte systems^1,2 and blended electrolytes³. In the referenced works, solid electrolytes are tested with in situ thermal safety studies which confirm that a relatively small heat release (189 J g^-1) is generated during thermal runaway, compared with 812 J g^-1 from a comparable liquid electrolyte cell constructed with conventional electrolytes. This intrinsic safety is confirmed by other studies in creating a blend of polymers which may resist thermal degradation above 200 °C. The retention of solvents within solid electrolytes and their interactions at the electrode interfaces and within the bulk solid electrolyte may be used as a key feature in providing a solution to the ultimate goal of developing LIBs that do not compromise either energy density or safety.

References

1. Zhang, Z. Li, Y. Guo, L. Cai, P. Manikandan, K. Zhao, Y. Li, V. G. Pol, “Room-Temperature, High-Voltage Solid-State Lithium Battery with Composite Solid Polymer Electrolyte with In-situ Thermal Safety Study", Chemical Engineering Journal, 2020, 125996
2. Zhang, Z. Li, L. Cai, Y. Li, V. G. Pol, “Enabling Safer, Ultralong Lifespan All-solid-state Li-organic Batteries”, 2021,416, 129171.
3. A. Jokhakar, D. Puthusseri, P. Manikandan, Z. Li, J. Moon, H-J. Weng, V. G. Pol, “All-solid-state Li-metal Batteries: Role of Blending PTFE with PEO and LiTFSI Salt as a Composite Electrolyte with Enhanced Thermal Stability”, Sustainable Energy & Fuels, 2020, 2229-2235