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| Fig. 1: Non-solar energy demand by hour as reported by the California ISO for the date of March 31, 2013 (blue line). [1] The curves out to the year 2020 are extrapolations. If the amount of solar power generated exceeds demand, the "belly" of the duck dips below zero. (Courtesy of the DOE) |
Amid rising demands for electrification in the face of ambitious carbon emission targets, utility companies face a large problem - storing energy produced using renewable sources to meet demand later in time. The duck curve (Fig. 1) illustrates the demand for electricity over the course of a day. [1] Demand is lowest at the same time solar production is highest - midday. When demand peaks in the evening soar production is waning, placing pressure on load serving entities to procure electricity from carbon intensive sources - natural gas peakers, coal plants, etc. A simple solution is to store excess energy during midday solar production in batteries and use these reserves to meet demand in the evening. However, modern lithium-ion batteries are an expensive way to store large amount of electricity to feasibly address grid scale demand. Solid state batteries have arisen as a potential solution to this problem, offering improved energy density compared to their lithium-ion counterparts and lower costs.
Solid state batteries operate using a solid or gel electrolyte as opposed to a liquid electrolyte commonly found in batteries. The use of a solid electrolyte allows for a lithium anode to be utilized instead of the traditional lithium-embedded graphite anode. [2] Whereas graphite has a specific capacity of ~372mAh/g, lithium has one more than 10x higher, ~3800mAh/g. [3] These correspond to a 60% increase in volumetric energy density in solid state batteries compared to liquid electrolyte when using an equivalent ratio capacity (anode/cathode), subsequently driving a 75% reduction in volume and 30% reduction in weight. Many claim solid state batteries are safer than liquid electrolyte, due to the non-volatile nature of the solid electrolyte. Liquid electrolytes are often criticized for being highly flammable and prone to thermal runaway, where the breakdown of the solid electrolyte interphase leads to an uncontrolled interaction between anode and electrolyte, culminating in the high-temperature destruction of the battery. [4]
A commonly cited concern with solid state batteries is a propensity to cracking when subject to many cycles. Solid state batteries are significantly more brittle than liquid electrolyte, making implementation in fields requiring mobility difficult. A solution has been presented in maintaining continual stack pressure on the battery, preventing the formation of dendrites, though this solution requires adding more complexity to the battery. This concern is slightly mitigated when using solid state batteries for grid scale storage due to the batteries not being moved but still presents a concern with regards to performance under long term cycling demands. [4]
Solid state batteries present a promising pathway to driving decarbonization among electric utilities. Their improved energy density and safety address concerns many hold about using liquid electrolyte batteries for grid scale storage. A subsequent benefit of their density is realized in leveled cost of service, where each unit of electricity delivered to consumers comes on the back of lower CAPEX and maintenance costs. It remains to be seen whether they can withstand the immense cycling demands of grid level service and become commonplace among utilities in meeting electrical demand.
© Harnoor Mann. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] P. Denholm et al., "Overgeneration From Solar Energy in California: A Field Guide to the Duck Chart," U.S. National Renewable Energy Laboratory, NREL/TP-6A20-65023, November 2015.
[2] C. M. Costa et al., "An Overview of Solid-State Lithium Metal Batteries: Materials, Properties and Challenges," EnergyChem 7, 100169 (2025).
[3] A. Mukhapadhyay and W. W. Sheldon, "Deformation and Stress in Electrode Materials for Li-Ion Batteries," Prog. Mater. Sci. 63, 58 (2014).
[4] Z. Gao et al., "Promises, Challenges, and Recent Progress of Inorganic Solid-State Electrolytes for All-Solid-State Lithium Batteries," Adv. Mater. 30, 1705702 (2018).