Solid-state batteries charge quickly and don't catch fire. Why they are still not in smartphones and cars

Solid-state batteries are already outperforming lithium-ion batteries in literally every way: charging speed, twice the power reserve in electric vehicles and stable operation without the risk of thermal overclocking. However, they are not yet widely used commercially.

Advantages of solid-state batteries

In a new extensive review, researchers from University of California, Riverside, analyzes in detail the prospects and drawbacks of solid-state batteries. These batteries operate on a similar principle to Li-ion, moving lithium ions between the cathode and anode during charge-discharge cycles. However, instead of using a liquid electrolyte, solid ceramic, polymeric materials or chemically stable sulfide-based compounds are used to transfer ions. 

This helps to prevent the risk of fire. In addition, the solid materials allow for the use of pure lithium as an ultra-thin anode, which stores more energy per gram than graphite anodes. As a result, batteries can be significantly lighter, have a higher capacity, and have a longer life.

Modern Li-ion batteries typically have a service life of about 1 thousand charge-discharge cycles. Meanwhile, solid-state batteries have been shown to retain more than 90% of their capacity even after 5 thousand cycles. 

This allows solid-state batteries to operate efficiently for 15-20 years, which is twice the average lifespan of modern electric vehicles. The charging speed is also another the advantage of solid-state batteries. The new models are capable of charging up to 80% in just 12 minutes, and in some cases, charging takes up to 3 minutes. У It takes 30 minutes to an hour for Li-ion batteries to do this. 

Each battery limited by the critical current density, which determines how quickly and safely the device can charge. Currently, solid-state batteries have a lower critical current density than Li-ion, due to low ionic conductivity and interfacial resistance. However, recent advances are reducing this gap. 

In particular, solid electrolytes based on sulfides have an ionic conductivity that is close to that of liquid electrolytes and provides faster ion transfer. Compounds such as Li₁₀GeP₂S₁₂ have a conductivity of up to 12 mS/cm, which until recently was considered impossible for solid materials.

In addition, solid-state batteries do not require bulky cooling systems because they operate at lower and more stable temperatures. As a result, they are lighter and smaller, which is important for electric vehicles and the further development of aerospace vehicles. Solid-state batteries can withstand extreme temperatures and radiation and may prove to be promising for powering spacecraft and space bases.

Some solid-state battery designs remain stable even under vacuum conditions and extreme temperatures from -40°C to 120°C. In particular, one of the designs produced by Hitachi Zosen has passed the test for pierced by a nail and did not catch fire, as would be the case with Li-ion. 

What prevents the widespread production and use of solid-state batteries

One of the main obstacles to the development of solid-state batteries is the need to understand what happens inside these batteries during operation. This is where modern diagnostic methods come in handy.

Methods of neutron imaging, X-ray tomography and electron microscopy allow researchers to observe real-time ion flow, structural displacements, and material degradation. The degradation processes include the formation of dendrites — needle-like lithium structures on the anode that can cause short circuit and cause the battery to catch fire. 

Although the occurrence of dendrites is not as common in single-layer batteries, they do occur, especially at grain boundaries in a solid electrolyte. Meanwhile, the mechanisms of their formation are more predictable, which makes it possible to make effective decisions to prevent their formation. 

Some researchers have started to use the processes of sintering to compact the electrolyte grains and reduce the number of dendrites formed. Other scientists are studying the processes of creating materials such as three-dimensional honeycomb anode structures that bend during expansion and contraction, thus avoiding cracking. 

However, the commercial use of solid-state batteries still faces significant challenges. They are still expensive to manufacture and difficult to scale up. The materials must be exceptionally clean and processed under pressure to protect them from moisture and oxygen.

Performance degradation is still observed at the junctions of solid layers. Poor contacts and chemical reactions between electrolyte and electrode can reduce conductivity and shorten battery life.

To solve these problems, scientists use computer modeling and advanced manufacturing technologies. Adding additional protective layers, alloyed materials, and selection of sintering conditions — these are just a few promising strategies.

In addition, there are environmental concerns, as some sulfide-based solid electrolytes emit hazardous gases such as hydrogen sulfide when heated. Although solid-state batteries are more recyclable than Li-ion. For many solid electrolyte formulations, environmentally friendly solutions for recycling and reuse have not yet been developed. 

Large companies such as Toyota, Samsung, QuantumScape, and Solid Power are actively investing in the development of solid-state batteries. Representatives of the Chinese company Qing Tao Energy say, they are already producing solid-state batteries with a capacity of 100 MWh per year and are expanding production to 10 GWh. However, it may take more than a year for them to appear on the market. 

Researchers from University of California, Riverside aims to accelerate the process of bringing solid-state batteries to the commercial market. They have presented an action plan aimed at optimizing the structure of the solid-state electrolyte, improving manufacturing processes, and better understanding material behavior through advanced diagnostics. 

The results of the study are published in the journal Nano Energy

Source: ZME Science