GoKawiilA battery technology that’s getting a lot of attention is solid-state batteries, lithium-ion batteries that replace the liquid electrolyte with a solid material. Chinese battery manufacturer CATL alone had more than 1,000 people devoted to solid-state battery research as of 2024, and battery manufacturers like BYD, LG, and Samsung are also working on the technology. US and European startups making solid-state batteries have collectively raised over $4 billion as of 2025.
Solid-state batteries have several potential advantages over the lithium-ion batteries with liquid electrolyte we use now. For one, replacing the liquid electrolyte with a solid should allow for lighter batteries, requiring less mass per unit of energy delivered. And because the liquid electrolyte currently used in batteries is flammable, replacing it with a solid could make batteries safer and less susceptible to fire.
I wanted to better understand why, exactly, solid-state batteries have these advantages compared to conventional lithium-ion batteries, and how they fit into the broader arc of lithium battery improvements.
Battery basics
Batteries supply energy by way of chemical reactions. And chemical reactions, regardless of the chemicals involved, all release or absorb energy using the same mechanism: an electron or electrons move from one potential energy well to another. In a chemical reaction that gives off energy (an exothermic reaction), electrons move from a higher potential well to a lower potential well, giving off energy in the process.
“Potential well” is fairly abstract, so I find it useful to consider an analogy with gravity. Say a ball is in a shallow groove at the top of a tall hill, and there’s another shallow groove at the bottom. The ball is being tugged downward by gravity, which gives it potential energy, a function of how much mass the ball has and how high it is above the bottom of the hill. By itself, the ball at the top of the hill won’t move, but if you give it a little push to nudge it out of its groove, it will roll downhill, releasing its potential energy in the process. This potential energy is converted to kinetic energy (the velocity of the ball), which in turn converts to thermal energy from friction, slowing the ball down until it stops in the lower groove.
Chemical reactions work in a somewhat similar way. But instead of gravity, the potential energy comes from electromagnetism: the positively charged nuclei tugging on the negatively charged electrons. In an exothermic reaction, atoms start in some particular “groove,” their electrons in some particular arrangement. But if you give the atoms a little kick (say, by heating them up so their collisions become more energetic), you can knock them out of their groove, letting them “roll downhill” into a lower-energy configuration, converting their electric potential energy in the process. Some of that potential energy (half, in fact) will go to increasing the electrons’ velocities; the rest will be released as vibration (heat), or as a photon.
So, for instance, say you start with one methane molecule (one carbon and four hydrogens, CH4) and two oxygen molecules (each with two oxygen atoms, O2). These molecules start with their electrons in a particular configuration, the oxygen atoms bonded with each other and the hydrogen atoms bonded with the carbon. At room temperature, O2 and CH4 largely won’t react with each other: each is sitting in its own potential well that takes energy to climb out of. But give them a kick by adding heat, and they can “fall downhill,” going through a series of reactions and ending up in a lower-energy configuration — the hydrogen and carbon atoms each bond with oxygen, forming H2O and CO2. The resulting electron configurations are in lower potential energy wells, with much of the difference being released as heat.
Lithium-ion batteries work by using, unsurprisingly, chemical reactions with lithium. When a lithium-ion battery discharges, lithium ions and their electrons “fall downhill,” moving from one configuration at the anode (inserted between sheets of graphite, known as “intercalation”) into a different, lower-energy configuration at the cathode (intercalated in another material, such as lithium iron phosphate, LiFePO4). The battery is structured to capture energy from this reaction. Lithium ions can pass from the anode into the electrolyte, but electrons can’t: they must go around, through a metallic conductor that connects the anode and the cathode. This flow of electrons is the electrical current that batteries generate. (When a battery is charging, the reverse happens: a voltage placed on the conductor forces electrons back uphill into the anode, with lithium ions flowing back through the electrolyte to keep the charge balanced.)
Lithium ion battery diagram, via link .
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