Lithium-ion (Li-ion) battery traction packs power most electric vehicles (EVs) on the road today. These batteries enable electric motors to efficiently generate the high torque required for rapid acceleration and consistent speeds.
Although Li-ion batteries offer high energy density and a relatively long lifespan, many automotive companies are actively researching and developing solid-state battery technology. With solid rather than liquid electrolytes, these new batteries promise increased energy storage capacity, faster charging times, and improved safety.
This article reviews the basic components of Li-ion and solid-state batteries, highlighting key advantages and limitations. It also discusses common challenges in solid-state battery development and explores notable innovations from major automotive manufacturers.
Comparing conventional Li-ion and solid-state batteries
Conventional Li-ion batteries are equipped with a cathode typically made of a lithium metal oxide, such as lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt oxide (LiNiMnCoO2), or lithium iron phosphate (LiFePO4).
The cathode stores and releases lithium ions, while the graphite anode intercalates lithium ions during charging and discharging. A separator, usually made of a microporous polymer membrane such as polyethylene or polypropylene, prevents the anode and cathode from contacting each other while allowing ions to flow between them. Liquid electrolytes, composed of lithium salts dissolved in a mixture of carbonates, such as ethylene carbonate or dimethyl carbonate, facilitate the movement of ions between the anode and cathode. Li-ion batteries use current collectors to transfer electrons to and from external circuits.
Figure 1. Comparison of conventional lithium-ion and solid-state batteries, highlighting key differences, including the solid electrolyte that functions as a separator. (Image: muRata)
Most solid-state battery prototypes (Figure 1) consist of a cathode, an anode, and solid electrolytes that also function as separators. Like their conventional Li-ion counterparts, these cathodes are typically made of lithium metal oxides, such as LiCoO2, LiNiMnCoO2, or LiFePO4. In contrast to traditional Li-ion batteries, many solid-state anode designs incorporate lithium metal for its higher energy density potential.
Solid-state batteries often rely on ceramic-based electrolytes, though polymer-based and sulfide-based electrolytes are also used. Enclosed in a protective casing, solid-state batteries use current collectors to transfer electrons to and from external circuits.
Advantages of solid-state battery designs
New solid-state designs (Figure 2) offer many potential advantages over conventional Li-ion batteries. For example, combining lithium metal anodes with solid electrolytes increases energy density, significantly increasing energy storage capacity and extending EV range.
Figure 2. Illustration of a solid-state EV battery, showcasing key components such as the lithium anode, solid electrolytes, and cathode. The image highlights the potential for fast charging, with future solid-state battery packs that could achieve full charge in less than 10 minutes. (Image: American Chemical Society)
Additional potential benefits include:
- Faster charging speeds: Many solid-state battery designs promise fast, safe charging capabilities. Solid electrolytes can reduce the risk of heat-related physical degradation and thermal runaway during rapid charging, improving safety and extending battery lifespan.
- High-temperature stability: Future solid-state batteries may operate more reliably across a broader range of higher external temperatures without significant loss of capacity or discharge limitations.
- Compact footprint: Solid electrolytes eliminate the need for liquid containment, potentially allowing automotive manufacturers to implement more lightweight designs with smaller batteries.
- Improved safety: Solid-state batteries may eventually offer enhanced safety features compared to conventional Li-ion batteries. Non-flammable solid electrolytes, for example, are likely to reduce the risk of fire or explosion in the event of a crash, battery failure, or short circuit.
Limitations and challenges
Automotive companies must overcome significant manufacturing, technical, and economic challenges before solid-state batteries can safely and efficiently power EVs. Without advanced mass production techniques and efficient scaling methods, solid-state batteries will remain more complex and costly to manufacture than conventional Li-ion batteries.
Notably, the sulfide-based solid electrolytes in some solid-state batteries are highly sensitive to moisture and may require dry rooms (Figure 3) during production to prevent degeneration. Moreover, while solid electrolytes can offer advantages such as faster charging, their ionic conductivity at room temperature is generally lower than that of the liquid electrolytes used in Li-ion batteries.
Figure 3. A dry room environment specifically designed for battery manufacturing, implementing controlled humidity levels to prevent moisture from affecting production. (Image: Munters)
The high cost of materials, such as cobalt, nickel, and lithium — especially in their metal form for solid-state anodes — further complicates the widespread adoption of solid-state battery technology. Additionally, the rigid physical characteristics of solid electrolytes, which lack the self-healing properties of liquid electrolytes in conventional Li-ion batteries, increase the susceptibility of solid-state batteries to certain types of degradation. This can lead to dendrite formation, interfacial delamination, lithium creep, and dead lithium, resulting in short circuits, reduced battery capacity, and premature failure.
While some solid-state battery designs are better at resisting physical degradation from high heat, others are more vulnerable to low-temperature extremes. Additionally, they may be less capable of absorbing mechanical stress than the flexible liquid electrolytes used in conventional Li-ion batteries.
Breakthroughs in solid-state battery development
Despite the challenges, many automotive companies are accelerating their development of solid-state batteries. For example, Samsung recently debuted a solid-state EV battery with a 600-mile range and an energy density of 500 watt-hours (Wh) per kilogram (kg), roughly double that of a typical EV battery. Honda is designing a solid-state battery that weighs 50% less than conventional Li-ion batteries, while Nissan plans to launch an EV with solid-state batteries by 2028.
In partnership with Solid Power, BMW expects to have solid-state battery technology ready for prototype vehicle integration by 2025. Similarly, Ford and Solid Power are testing 100 ampere-hours (Ah) solid-state battery cells. Volkswagen is working with QuantumScape through its battery subsidiary Powerco to industrialize and mass-produce EV solid-state batteries. Mercedes-Benz and Hydro-Québec are also jointly developing and testing solid-state batteries.
Lastly, Toyota’s solid-state batteries (Figure 4) are expected to deliver significant improvements over current lithium-ion batteries, such as a 745-mile range (1,200 km), 10-minute fast charging, and reduced production costs.
Figure 4. Toyota’s all-solid-state battery prototype for EVs. (Image: TopSpeed)
Summary
Li-ion battery traction packs with liquid electrolytes power most EVs on the road today, offering high energy density and a relatively long lifespan. New solid-state battery designs, however, promise increased energy storage capacity, faster charging times, and improved safety. Containing solid rather than liquid electrolytes, these new batteries still contend with various limitations and manufacturing challenges, such as high material costs, sensitivity to moisture, and lower ionic conductivity at room temperature.
Nevertheless, many automotive companies, from Nissan and Honda to BMW and Ford, continue accelerating their solid-state battery development.
References
- 6 Ways Solid-State Batteries Are Better Than Lithium-Ion Alternatives in Electric Vehicles, CPI
- What Are Solid-State Batteries?, Murata
- Solid-State Batteries: Benefits and Drawbacks, Econopolis
- Explained: Solid-state Batteries vs Lithium-ion Batteries, TopSpeed
- Navigating the Future: A Guide to Solid State Batteries for Electric Cars, Midtronics
- Electric Vehicle Future Depends On Solid-State Battery Technology, Academy for Technical Training & Career Development
- The Real Story Behind Samsung’s 600-Mile Solid-State Battery, TopSpeed
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