A different question from which chemistry ships first
A solid state battery replaces the liquid electrolyte, the material that carries charge inside a cell, with a solid one. This article is not about solid state batteries. It covers 5 chemical families still being tested in the laboratory, fluoride ion, magnesium, lithium air, calcium ion and lithium metal, and states how many cycles a test cell survived before it lost capacity. Some of these designs also use a solid electrolyte, for different reasons than solid state cells do. The spread runs from 5 cycles to at least 1,000.
The lithium air and calcium ion figures are each stated as at least 1,000 cycles or a total of 1,000 tested cycles, not a ceiling where the cell was shown to fail. Lithium metal, a 5th chemistry described in this article, is left out of this chart because its own headline figure is a percentage, coulombic efficiency, not a cycle count comparable to the other 4, and its 2 headline numbers come from 2 different studies rather than 1 cell.
Show the numbers
| Fluoride ion | 5 |
| Magnesium | 200 |
| Lithium air | 1,000 |
| Calcium ion | 1,000 |
The newest design also has the fewest cycles behind it
Researchers at Kyoto University, funded partly by the New Energy and Industrial Technology Development Organization in Japan, built a room temperature battery that carries charge with fluoride ions instead of lithium ions. Their new liquid electrolyte solves a problem that held earlier fluoride ion batteries back, fluoride salts are hard to dissolve and fluoride ions are reactive enough to strip protons from most solvents. A test cell held an electrochemical stability window above 5.4 volts and stable fluoride ion shuttling for up to 100 hours. It discharged 175 milliamp hours of capacity per gram on its first cycle, falling to 158 by the 5th, the only cycle this study tested, a drop of about 9.7%, MAOWCE arithmetic.
5 is the total number of charge and discharge cycles this source tested for this cell, not a point picked from a longer run. The capacity drop between the 1st and 5th cycle is about 9.7%, MAOWCE arithmetic on these 2 source 2 figures.
Show the numbers
| 1st cycle | 175 |
| 5th cycle | 158 |
A magnesium battery that finally works at room temperature
A team at the Institute for Materials Research at Tohoku University, led by Tetsu Ichitsubo, built a magnesium battery that works at room temperature. Its new oxide cathode, the electrode a cell discharges into, lets magnesium ions swap into sites a lithium ion had occupied, opening a path magnesium ions could not otherwise move through fast enough. The finished cell generated more than 2.5 volts, enough to light a blue LED, and discharged usable energy through 200 charge and discharge cycles.
The reason magnesium hasn't been the main material used for batteries is because of a sluggish reaction that prevents room temperature operation.
Tetsu Ichitsubo, researcher at the Institute for Materials Research, Tohoku University. Source 4.
Two designs that already reached 1,000 cycles
Two of the 5 chemistries have already reached 1,000 cycles. Researchers at the Illinois Institute of Technology, Argonne National Laboratory and Northwestern University, described by the United States Department of Energy, built a room temperature lithium air battery with a solid electrolyte that completes a 4 electron reaction, the first design reported to do this at room temperature. The cell was recharged for at least 1,000 cycles. The department says the design could reach an energy density of 1,200 watt hours per kilogram with further development, a target, not a measured figure. Separately, a team at Hong Kong University of Science and Technology, led by Yoonseob Kim, built a calcium ion battery with a quasi solid electrolyte made from a porous material called a covalent organic framework. Their cell kept 74.6% of its capacity after 1,000 cycles.
Dendrites remain the unsolved problem for lithium metal
A 2024 review in the journal Molecules looked at lithium metal anodes, a design that pairs an ordinary liquid electrolyte with a pure lithium electrode instead of the graphite most lithium ion batteries use today. One study it cites reached a coulombic efficiency, the share of lithium recovered intact each time it is plated onto and stripped from the anode, of 99.8%. A separate study it cites built a full cell that ran for over 1,000 cycles using a different material, 2 different studies, not 1 cell achieving both figures at once. The review conclusion states the core problem is still unsolved, dendrites, needle shaped lithium deposits that can grow through a cell during charging and cause a short circuit.