Unlocking the Potential of Solid-State Batteries with Carbon Nanotubes

Solid-state batteries have become a prominent field of research in the quest for more efficient, safer, and longer-lasting storage solutions. While these batteries offer promising advantages such as high energy density and safety, they have been plagued by a significant challenge: the insufficient interfacial contact between the solid electrolytes and the sulfur-active material.

 

Solid-state battery technology. Image used courtesy of Adobe Stock

 

Recently, Chinese Academy of Sciences (CAS) researchers introduced a novel approach that addresses these challenges, significantly enhancing the performance and lifespan of solid-state batteries. 

 

Solid-State Battery Challenges

The primary challenge hindering the widespread adoption of all-solid-state lithium-sulfur batteries (ASSLSBs) lies in the insufficient interfacial contact between the solid electrolytes (SEs) and the sulfur, which serves as the active material.

In conventional liquid electrolyte batteries, the liquid facilitates easy ion transport between the cathode and anode. However, in ASSLSBs, the solid-state nature of the electrolyte complicates this ion transport. The lack of adequate contact between the SEs and sulfur results in poor electronic and ionic conduction pathways. This is particularly problematic because efficient ion and electron transport are crucial for high charge and discharge rates, essential for electric vehicles and grid storage applications.

The inadequate conduction pathways lead to an increase in interfacial resistance. This is a significant issue because higher resistance means more energy is lost as heat during the charge and discharge cycles, reducing the overall efficiency of the battery. Over time, this increased resistance contributes to a phenomenon known as capacity decay. Capacity decay is the gradual loss of the battery's ability to hold a charge, which is a critical factor in determining the lifespan and usability of energy storage devices.

Moreover, the issue of insufficient interfacial contact and the resulting capacity decay become even more pronounced under extreme conditions, such as low temperatures. Under such conditions, the already limited mobility of ions is further restricted, exacerbating the problems associated with interfacial resistance.

 

Carbon Nanotube Breakthroughs 

CAS researchers proposed a new solution to address the issues surrounding solid-state batteries.

 

The researchers introduce P-CNTs to improve ASSLSB performance. Image used courtesy of Wang et al.

Specifically, the researchers utilized porous carbon nanotubes (P-CNTs) as a sulfur-bearing matrix, forming composite cathodes known as S@P-CNTs for ASSLSBs. The P-CNTs possess a larger specific surface area and more oxygen-containing groups than conventional carbon nanotubes (CNTs). These attributes enhance the interfacial contact between the sulfur and the solid electrolyte, improving electronic and ionic conduction. The P-CNTs also form a three-dimensional conductive network within the composite cathodes. This facilitates the efficient migration of electrons and the diffusion of ions, which are critical for the battery's electrochemical performance.

Another innovative aspect is the use of defect engineering. By designing defects and increasing active sites on the surface of P-CNTs, the researchers could uniformly encapsulate sulfur on both the inner and outer surfaces of the activated P-CNTs. This uniform encapsulation optimizes the ion and electron transport networks, substantially improving the reaction activity and stability of the sulfur cathode in the ASSLSB.

 

Research Results

The researchers found that the S@P-CNTs-based ASSLSBs displayed a capacity of 1,099.2 mAh/g  at a current density of 1.34 mA/cm^2 and maintained 70.4% of the initial capacity over 1,400 cycles. Additionally, the solid-state electrolyte developed by the team showed excellent performance even under extreme conditions like -40°C, solving a significant problem plaguing sulfide-based ASSLSBs.

According to the team, this research addresses and effectively solves the critical challenges limiting the performance and lifespan of ASSLSBs. Their work will open up new avenues for developing high-performance, long-lasting energy storage systems, making ASSLSBs more viable for applications requiring high energy density and safety.