Solid-State vs. Lithium-Ion Batteries: Which Is Best?

The electric vehicle (EV) space is in its early stages but carries substantial environmental and financial consequences. As such, it’s home to much debate and competing technologies. One of the most significant is the emerging choice between solid-state vs. lithium-ion batteries.

Solid-State vs. Lithium-Ion: The Differences

In order to safely prioritize one battery technology over the other, decision-makers must first understand the differences between them. In that spirit, here’s a closer look at lithium-ion and solid-state batteries.

Lithium-Ion Batteries

Lithium-ion cells are the most common battery materials in the world today, not just in EVs. These are the standard for rechargeable batteries across all electronics segments, from cell phones to laptops to electric construction machinery.

These batteries transmit lithium ions between the anode and cathode through a liquid electrolyte. At its core, this process is largely the same as most other rechargeable battery types, including the lead-acid batteries in most combustion engines. However, lithium-ion cells’ unique materials offer several advantages.

Compared to older alternatives, lithium-ion batteries are lighter, more energy-dense, resistant to self-discharging and charge faster. Those benefits have led them to become ubiquitous across the consumer electronics market and a natural choice for EVs, though EV batteries are much larger than conventional lithium-ion batteries.

Solid-State Batteries

Solid-state batteries are similar to lithium-ion alternatives but have one primary difference. Instead of using a liquid electrolyte, these cells pass lithium ions through a solid electrolyte — hence the term “solid state.” They also use a lithium anode, whereas conventional lithium-ion battery anodes are often graphite or carbon.

Most solid-state batteries are also lithium-ion batteries, but not all are. Some organizations are researching zinc-ion solid-state batteries as a low-cost energy storage solution, for example. However, lithium is still the most common ion under this umbrella, especially in the EV market.

It’s possible to make solid electrolytes out of a wide range of materials. Ceramics are among the most common, but other batteries use polymers, metals or a hybrid of multiple resources. Varying these materials can give the resulting battery different qualities.

Pros and Cons of Lithium-Ion Batteries

The differences between solid-state vs. lithium-ion batteries are more pronounced in their real-world effects. Conventional lithium-ion batteries’ biggest advantage is their availability. These are the only market-viable EV batteries today, making others hard to justify on a large scale.

Much of that availability stems from the fact that lithium-ion batteries are relatively inexpensive — at least, compared to solid-state alternatives. That’s important from both a business and an environmental standpoint. Cheaper options are obviously preferable to reduce manufacturing costs, but they also promote a faster transition from fossil fuels. Consumers will be more willing to buy a less expensive EV.

Despite these advantages, conventional lithium-ion batteries have some significant drawbacks. One of the most prominent is that liquid electrolytes take up a lot of space and weigh a lot. Average EV battery packs weigh around 1,000 pounds, putting excess pressure on aging roads and car tires.

Many broader EV concerns stem from these batteries, including limited ranges and slow charging times. Liquid electrolytes can also pose safety risks in some situations, as they’re often highly flammable.

Pros and Cons of Solid-State Batteries

Solid-state batteries, by contrast, are perfectly safe, as they eliminate the flammable components from EV battery design. They’re also more energy-dense than those using liquid electrolytes. That energy density translates into longer driving distances, addressing the issue of range anxiety.

Similarly, solid-state batteries can charge in less time. One design from researchers at Harvard can recharge in just 10 minutes — certainly more than refueling a gas car but far less than conventional EV charging. That same design also boasts a longer life span than other lithium-ion batteries, retaining 80% of its capacity after 6,000 charging cycles.

Another advantage of solid-state batteries is their size. Because solids are naturally denser than liquids, a solid-state battery requires less physical space than a liquid-electrolyte alternative of the same size. Consequently, EVs can reduce their weight or include more batteries for longer ranges without being bigger.

Of course, solid-state batteries have downsides of their own. The most prominent is their cost. Experts predict solid-state prices to fall between $80 and $90 per kilowatt-hour (kWh) by 2030, while conventional lithium-ion batteries could reach $60 per kWh by the same time. Producing these more complex components at scale may also prove challenging.

Solid-State vs. Lithium-Ion: Which Holds the Future for EVs?

Given these advantages and disadvantages, solid-state batteries hold more long-term potential for EVs than conventional lithium-ion alternatives. However, it may take a while for the industry to switch.

The cost and complexity of manufacturing solid-state batteries at scale stop them from becoming market-viable for now. Until that shift happens, EV manufacturers will likely focus on liquid-filled lithium-ion batteries. The sooner the industry makes the switch, though, the better it will be for the environment.

Embracing solid-state batteries will make EVs more practical in terms of their range, charging time, longevity, safety and weight. Those benefits will make them a more attractive option to drivers, encouraging a broader move away from fossil fuels. At the same time, they must be cheaper to appeal to the wider market.

Other EV Battery Technologies

It’s important to note that the debate between solid-state vs. lithium-ion doesn’t cover the full scope of EV battery technology. Other alternatives have emerged in recent years that could provide even more benefits.

Many manufacturers pledged to move away from cobalt in their batteries, as this material is scarce and environmentally harmful to mine. While some cobalt-free batteries still use lithium ions, others use lithium-iron phosphate,  bis-tetraaminobenzoquinone (TAQ), sodium ions or lithium-sulfur molecules.

It’s likely that no single battery technology will become dominant and define the green transport transition. Rather, manufacturers will likely choose varying options based on what fits their specific goals the best. This varied approach will create a more diverse EV market, making clean alternatives to gas-powered vehicles more accessible.

The Future of EV Batteries Is Still Uncertain

The solid-state vs. lithium-ion debate isn’t as black and white as it may seem at first. EV batteries are complicated, and it’s still unclear which technologies will provide the break this market needs. 

While lithium-ion is the most straightforward option for automakers today, solid-state alternatives show significant promise. Other battery technologies offer similar improvements, too. Learning more about these options is the first step to a safe green transition in transportation.