Studies Shed Light on Advances in Solid-state Battery Tech

All-solid-state lithium-ion batteries (ASSLBs) are receiving considerable attention due to their potential to improve energy density, safety, and lifetime compared to traditional liquid electrolyte batteries. These batteries use a solid-state electrolyte instead of a liquid electrolyte, which eliminates the risk of leakage, improves thermal stability, and allows using metallic lithium as an anode. Solid-state electrolytes also allow for thinner, lighter, and more flexible batteries, making them a promising technology for electric vehicles, portable electronics, and energy storage applications.

 

Battery Challenges

However, despite their advantages, all-solid-state batteries still face several challenges. One of the main issues is the high interfacial resistance between the solid-state electrolyte and the electrode, which limits the ionic conductivity and, in turn, the battery's power and rate capability. The solid-state electrolyte also tends to be less conductive than the liquid electrolyte, which can reduce the battery's energy density and cycling stability. Additionally, the manufacturing processes for all-solid-state batteries are more complex and costly than liquid batteries, which can hinder their commercialization.

Two recent studies on ASSLBs focus on the challenges, as mentioned earlier, associated with them and provide insights into creating better solid-state batteries.

 

Effective Transport Mechanism for Fast Ion Transport in Solid-state Batteries

A research team led by Professor Jiajun Wang from the Harbin Institute of Technology (HIT) reveals that the inferior performance of solid-state batteries originates from the imbalance of ion transport and electrode reaction. In addition, they proposed a tortuosity-gradient thick electrode strategy to enable fast charge transport and enhance performance and lifecycle. 

First, the team investigated the effects of electrode thickness on ion transport. Lithium ions tend to move slowly across the solid-solid interfaces in ASSLBs. And when the transport path within the solid-state electrode increases, electrons cannot smoothly migrate between the solid-state electrolyte and the current collector, resulting in concentration gradients of lithium ions along the path. 

 

Illustration and data depicting poor electrochemical properties of thickened solid-state batteries. Image used courtesy of HIT

 

The team created a tortuosity-gradient solid-state electrode that modifies the lithium-ion transport path and balances the ion transport and reaction rates. The electrode includes a fast transport layer (FTL) with an ionic percolation network and a reaction equilibrium layer (REL) with large-sized particles. 

Thanks to low tortuosity (a parameter to determine the transport properties of porous materials) provided by small particles in the FTL, it has a short path length and ensures lithium ions transport rapidly. The balance between lithium-ion transport and charge delithiation is maintained by the REL layer as it has a small specific surface area, requiring only a few lithium ions to achieve a certain delithiation level.

 

Boosting Ionic Conductivity With a New Approach

A team from Lawrence Berkeley National Laboratory and Florida State University has proposed a new design for solid-state batteries that is less dependent on the specific type of materials that are expensive and unavailable in large quantities, making the manufacturing process affordable.

The researchers synthesized and tested multiple lithium-ion and sodium-ion materials with multiple mixed metals and found that these multi-metal materials perform better. They observed that the materials exhibit ionic conductivity orders of magnitude faster than the single-metal materials. The researchers suggest that each material with unusual distortions provides a new ion transport pathway in its crystal structure. 

 

Microscope images showing elemental distribution in a solid electrolyte. Image used courtesy of Berkeley Lab and Florida State University

 

The researchers plan to apply this new approach to explore new solid electrolyte materials that can further improve battery performance.