Incorporation of solid state electrolytes (SSEs) leads to significant improvements in energy and power density of next generation lithium ion batteries (LIBs)[1]. SSEs also demonstrate better thermal stability than liquid electrolytes, which eventually enable enhancement in safety. However, dendrite growth in metal anodes during lithium deposition, and large resistance at anode/SSE interface, are major issues presently experienced by SSEs[2]. Similarly, at the positive electrode, volume change of the cathode particles during lithiation and delithiation can result in evolution of stress at the cathode/SSE interface, which may cause delamination, and subsequently impedance rise along with capacity fade[3]. All these issues at both anode/SSE and cathode/SSE interfaces prevent the implementation of SSEs in commercial LIBs. In the present research, the extent of mechanical degradation at the interface of cathode and ceramic SSE, and its impact on performance, will be investigated through computational techniques.

Lithium ion cells with SSEs are fabricated with cathodes in a lithiated state, which corresponds to a discharged condition. During the first charge process, the cathodes experience delithiation, and shrink in size, which induces stress at the cathode/SSE interface. The amount of volume change in cathode, and subsequent stress generation, depends on the partial molar volume of lithium within the cathode material[4, 5]. Depending on the adhesion strength between the cathode and SSE, interfacial detachment may occur at the cathode/SSE interface[3]. Such loss of contact would lead to decrease in electro-chemically active surface area, and effectively increase the interfacial resistance. A computational model has been developed to capture the volume change in cathode and evolution of stress at cathode/SSE interface. This technique has also been extended to investigate the propensity of interfacial delamination and subsequent deterioration in cell performance. The impact of rate of operation, depth of discharge, and number of cycles, on the cathode/SSE interfacial delamination induced performance decay, will be elucidated in the present research.

References

1. Kato, Y., et al., High-power all-solid-state batteries using sulfide superionic conductors.Nature Energy, 2016. 1.

2. Cheng, E.J., A. Sharafi, and J. Sakamoto, Intergranular Li metal propagation through polycrystalline Li6.25Al0.25La3Zr2O12 ceramic electrolyte.Electrochimica Acta, 2017. 223: p. 85-91.

3. Koerver, R., et al., Capacity Fade in Solid-State Batteries: Interphase Formation and Chemomechanical Processes in Nickel-Rich Layered Oxide Cathodes and Lithium Thiophosphate Solid Electrolytes.Chemistry of Materials, 2017. 29(13): p. 5574-5582.

4. Bucci, G., et al., Mechanical instability of electrode-electrolyte interfaces in solid-state batteries.Physical Review Materials, 2018. 2(10).

5. Hao, F. and P.P. Mukherjee, Mesoscale Analysis of the Electrolyte-Electrode Interface in All-Solid-State Li-Ion Batteries.Journal of the Electrochemical Society, 2018. 165(9): p. A1857-A1864.