While electric vehicles are touted as the transport of tomorrow, significant barriers are preventing their widespread adoption. Limited driving range, hefty and costly batteries, and lengthy charging durations are among the main deterrents for potential buyers. However, numerous corporations claim to possess the technological solution to these challenges.

Toyota, for instance, has hinted at being on the verge of significant innovation. Other car manufacturers are also collaborating with various battery enterprises to explore this emergent technology.

The anticipated innovation is known as the "solid-state battery." The recurring issue with this potential game-changer is that it's perpetually projected to be just a few years away.

"Solid state is the kiss of death for gasoline and diesel" ~ Sandy Munro, leading automotive engineer

What are Solid-State Batteries?

A solid-state battery fundamentally utilizes a solid electrolyte, contrasting with the liquid electrolytes employed in lithium-ion technology.

Structure

The grey central layer serves as the solid-state separator, functioning as both the divider and the electrolyte between the anode and cathode. It facilitates ion movement, exhibits electrical insulation, and provides mechanical separation. This solid, resistant layer enables the elimination of the graphite structure on the anode, ensuring direct accumulation of the lithium metal on the anode.

How Does it Work?

During the charging process, lithium particles traverse from the cathode, through the atomic structure of the separator, and position themselves between the separator and the anode's electrical contact, thereby creating a solid layer of pure lithium. Consequently, the anode solely comprises lithium particles, resulting in a smaller volume than an anode from lithium-ion technology, which incorporates a graphite structure.

Why are we Ditching Liquid Electrolytes?

Better Energy Density

The enhanced inherent safety of solid-state batteries paves the way for a significant leap in energy density. This boost largely stems from the replacement of the graphite anode, which houses migrating ions in lithium-ion batteries. However, in a solid-state battery, the transition leaves behind only the ions, eliminating a dense, weighty component that doesn't actively contribute to energy production.

Recent research suggests that solid-state batteries could possess an energy density that's 2-2.5 times higher than the current lithium-ion technology. This considerable edge could lead to lighter and smaller batteries, a potential game-changer for electric mobility by offering increased range and reduced weight.

Less Dendrite Formation

A significant safety benefit of solid-state batteries is their heightened resilience to dendrites—the jagged lithium accumulations that emerge during ion transition from the cathode to the anode. Lithium's uneven movement often leads to the formation of these needle-like structures which, in severe instances, can puncture the separator. Nonetheless, the robustness of solid separators in these batteries makes them more impervious to dendrite penetration, thereby preventing potential short circuits and progressive cell degradation.

Ultra-Fast Charging Times

Recent research indicates that solid-state batteries could potentially charge at a rate six times that is much faster than existing technologies. While there are prototypes of solid-state batteries that exhibit rapid charging, they may compromise on other crucial performance aspects.

What is known for sure is that liquid electrolytes tend to falter under high temperatures. In contrast, solid electrolytes excel and demonstrate enhanced performance at elevated temperatures, which could bolster their efficiency during quick charging—a process that typically generates significant heat.

Quicker Production

The premise that a solid-state electrolyte, being not in a liquid form, could streamline the production process, thereby consuming less resources and energy, is a popular argument. Although this hypothesis holds merit, it remains untested until this technology is fully scaled up for mass production.

At present, the cell-filling process with the electrolyte is time-consuming: the cell is initially assembled in a hollow state and needs to be punctured to allow the electrolyte to be poured in. Patience is then required for the electrolyte to be fully absorbed, followed by a refill to adjust it to the optimal level before sealing. This stage significantly influences the production process.

With the advent of solid-state technology, there's a potential for substantial enhancements in the production process.

More Safety

Unlike lithium-ion batteries that contain a volatile and potentially flammable liquid electrolyte, solid-state batteries incorporate a solid electrolyte. This key component, which can be a safety concern in lithium-ion batteries, is replaced by a robust separator layer in solid-state batteries. This layer is composed of a heat-resistant material, often ceramic with added substances, enhancing the battery's resilience to high temperatures.

The solid separator layer ensures a dependable barrier between the anode and cathode, reducing the risk of short circuits. This feature remains effective even under conditions of misuse or wear and tear, thereby elevating the inherent safety of the battery cells.

What Recent Studies Shows Promise?

Metal Alloy Electrolytes

(Credit: Jenny Nuss/Berkeley Lab)

A team from Lawrence Berkeley National Laboratory (Berkeley Lab) and Florida State University researched electrolytes that are less dependent on a single chemical element [1]

The novel multi-metal compositions (as shown on the right) exhibit superior performance, with ionic conductivity rates significantly surpassing those of single-metal counterparts. Scientists suggest that the amalgamation of diverse metals engenders additional routes, facilitating rapid transit of lithium ions through the electrolyte.

Absent these routes, the lithium ions' progression through the electrolyte from one terminal of the battery to the other would be sluggish and restricted (as shown on the left)

3D Printed Polymers

In another trial, engineers from UNSW Sydney developed a process to print solid-state polymer electrolytes into any shape desired for use in energy storage. [2]

The current state of solid-state electrolytes presents a trade-off: enhancing the material's mechanical resilience results in a significant drop in conductivity. Conversely, if you aim for higher conductivity, the material becomes considerably less durable.

The high-performance solid polymer electrolyte crafted by the UNSW team can be produced cost-effectively using readily accessible 3D printers, negating the need for advanced engineering machinery.

Another advantage of this SPE in energy storage systems is its ability to enhance cycling stability, which refers to the number of charge and discharge cycles a device can undergo before its capacity diminishes to a specified level.

3D printing minimizes waste and cuts costs by enabling the production of variously shaped materials using a single machine, according to the researchers.

Looking ahead, product designers could potentially leverage this SPE to develop items boasting significantly enhanced energy storage density.

How Far Away Are We?

Undoubtedly, there are some questions before SSBs take over the market.

Stability

In the charging-discharging cycle, a solid-state cell's lithium-metal anode expands and contracts, much like breathing, which can cause degradation over time. The key challenge is maintaining the cells stable and compressed.

Securing the cell within a structure isn't enough as it needs to "breathe". In small prototypes, springs, and plates maintain compression, but this isn't suitable for mass production.

It's impossible to prevent a solid-state cell from expanding, but research can focus on reducing pressure requirements or exploring materials that allow expansion while keeping the cell compressed and stable.

Costs

The current pricing for solid-state batteries is steep due to their cutting-edge nature, which necessitates higher costs for both materials and manufacturing processes compared to mass-produced batteries. The ultimate pricing of this technology remains uncertain. However, the significant investments by major vehicle manufacturers suggest a strong belief that these costs can be tailored to accommodate large-scale production.

Limited Temperature Range

Existing high-performing separators function optimally at elevated temperatures, as solid electrodes primarily exhibit superior conductivity above 50 degrees. This temperature constraint restricts the practical application of solid-state technology in actual vehicles, given that it's unrealistic to maintain constant high battery temperatures. The performance of solid-state batteries tends to depreciate significantly when not heated. Therefore, it is crucial to enhance the solid electrolyte's efficiency at progressively lower temperatures.

What Does a Future With SSBs Look Like?

The Automotive Industry

In the automotive industry, SSBs could make electric cars more competitive with their gasoline counterparts, overcoming the current limitations of lithium-ion batteries. This could accelerate the transition towards electric mobility, reducing carbon emissions and dependence on fossil fuels.

Consolidation

In terms of market dynamics, the SSB industry could witness consolidation, with larger corporations taking the lead in research and production. This could result in standardization of technology and economies of scale, driving down costs and fostering innovation.

References

1. Yan Zeng et al., High-entropy mechanism to boost ionic conductivity.Science378,1320-1324(2022).DOI:10.1126/science.abq1346

2. K. Lee, Y. Shang, V. A. Bobrin, R. Kuchel, D. Kundu, N. Corrigan, C. Boyer, 3D Printing Nanostructured Solid Polymer Electrolytes with High Modulus and Conductivity. Adv. Mater. 2022, 34, 2204816. https://doi.org/10.1002/adma.202204816