In recent years, technological innovations have revolutionized many aspects of daily life, leading to the widespread use of electric devices and vehicles. These innovations not only offer convenience but also serve as a cleaner, more environmentally friendly alternative to fuel-driven machines. One of the driving forces behind this transition to cleaner technology is the battery. As the core power source for a wide range of products, from smartphones to electric vehicles (EVs), batteries, specifically lithium-ion batteries (LIBs), have become indispensable in the modern world. However, as demand for these technologies continues to rise, safety concerns surrounding their performance, particularly in high-demand applications like electric vehicles, have become more pronounced.
LIBs are the standard power source for most modern electric devices and vehicles due to their high energy density and long cycle life. These batteries typically consist of an organic electrolyte solution, which is crucial for their energy efficiency. Despite their popularity, the use of these electrolytes raises safety concerns, as they are flammable and can cause severe risks in the event of overheating or physical damage. This is particularly critical as the market for electric vehicles and portable power sources expands rapidly, pushing the limits of battery performance.
To address these concerns, researchers have turned their attention to the development of solid-state batteries, which promise enhanced safety by eliminating the flammable liquid electrolytes. However, the development of solid-state batteries is not without its own set of challenges. Specifically, the interface between the solid electrodes and the electrolyte presents significant hurdles in terms of ion transfer, which can hinder performance. Additionally, the expansion and contraction of solid electrodes during charge and discharge cycles can disrupt the interface, leading to poor performance and safety risks.
In response to these challenges, a team of researchers from Japan has made significant strides in developing a safer and more efficient battery technology. Their work focuses on a non-flammable quasi-solid-state lithium-ion battery (LIB) that combines the best of both solid-state and liquid-based technologies. This novel approach addresses many of the limitations of conventional lithium-ion batteries and has the potential to improve the safety and performance of next-generation energy storage systems.
The Development of the Quasi-Solid-State LIB
The research, led by Ryosuke Kido from Doshisha University and TDK Corporation, along with Professors Minoru Inaba and Takayuki Doi from Doshisha University and Atsushi Sano from TDK Corporation, was published in the Journal of Energy Storage. Their study presents a quasi-solid-state LIB that overcomes the limitations of traditional liquid-based and solid-state batteries. According to Mr. Kido, the main author of the paper, increasing the capacity of the positive and negative electrode active materials to achieve higher energy density typically comes at the cost of cycle performance and safety. The new flame-retardant quasi-solid-state battery developed by the researchers, which combines both liquid and solid electrolytes, provides a safer and more durable alternative to all-solid-state batteries while maintaining high energy density.
The design of the new battery features a silicon (Si) negative electrode and a LiNi0.8Co0.1Mn0.1O2 (NCM811) positive electrode, both considered next-generation materials for lithium-ion batteries. The Si electrode, in particular, is of great interest due to its high theoretical capacity compared to traditional graphite anodes. The two electrodes are separated by a solid lithium-ion conducting glass ceramic sheet (LICGC), developed by OHARA, which serves as a separator and enhances the ion conductivity between the electrodes.
One of the key innovations of this quasi-solid-state battery is the electrolyte system. The researchers designed a non-flammable, nearly saturated electrolyte solution that is tailored to the specific properties of each electrode. The solution combines tris(2,2,2-trifluoroethyl) phosphate and methyl 2,2,2-trifluoroethyl carbonate, which are both highly compatible with the electrodes and the solid electrolyte interface. This design significantly enhances the thermal stability, ionic conductivity, and electrochemical performance of the battery.
Performance Evaluation and Findings
The team conducted extensive testing to assess the performance of the quasi-solid-state LIB. Using techniques like electrochemical impedance spectroscopy (EIS), charge-discharge cycling tests, and accelerating rate calorimetry (ARC), they measured the battery’s electrochemical performance, thermal stability, and safety characteristics.
The results were promising. The quasi-solid-state pouch cells demonstrated excellent ionic conductivity, which is essential for efficient energy storage and rapid charge/discharge cycles. Additionally, the battery exhibited strong thermal stability, with minimal changes in internal resistance during cycling. This is important because an increase in internal resistance can lead to overheating, reduced performance, and safety risks in conventional lithium-ion batteries.
Perhaps the most significant finding came from the ARC tests, which revealed that the Si-LICGC-NCM811 structure with the specially designed electrolyte solutions showed improved thermal stability. The heat generated by side reactions was found to be very low, even at high temperatures around 150°C. This is a critical factor for improving the safety of lithium-ion batteries, as excessive heat generation can lead to battery failure, fires, or explosions.
The battery also demonstrated high charge/discharge capacity and excellent cycle performance. Over multiple cycles, there was very little degradation in performance, and the internal resistance remained stable, further supporting the battery’s long-term durability.
Implications for Electric Vehicles and Consumer Electronics
The quasi-solid-state LIB developed by the research team holds significant promise for a wide range of applications, from electric vehicles to consumer electronics. With electric vehicles (EVs gaining traction worldwide as an environmentally friendly alternative to gasoline-powered vehicles, ensuring the safety, efficiency, and longevity of their batteries is paramount. The new battery design has the potential to significantly enhance the development of safer and more durable batteries for EVs. By addressing the critical safety challenges associated with flammable liquid electrolytes and improving energy density, the quasi-solid-state LIB could play a crucial role in advancing the EV market.
In addition to EVs, the new battery technology could also be applied to other cordless devices, such as drones, power tools, and portable electronics. As the demand for these devices continues to grow, the need for batteries that offer both high performance and safety becomes increasingly important. The flame-retardant properties of the new quasi-solid-state battery make it an ideal candidate for use in high-demand applications, where safety and performance are paramount.
A Step Toward Sustainable Energy Storage
The development of the quasi-solid-state lithium-ion battery represents a significant step toward achieving the broader goal of sustainable energy storage solutions. As the world moves toward carbon neutrality, renewable energy sources such as solar and wind power are expected to play a more prominent role in the global energy mix. However, these sources are intermittent, meaning that efficient and reliable energy storage systems will be necessary to store energy for use when generation is low.
Electric vehicles, as well as grid-scale energy storage systems, will be key to meeting this demand. By improving the energy density and safety of lithium-ion batteries, researchers like Mr. Kido and his team are contributing to the development of energy storage solutions that will help facilitate the transition to a cleaner, more sustainable energy future.
Mr. Kido concludes with a look at the long-term implications of their work: “As the world moves toward carbon neutrality, electric vehicles have been gaining significant attention in recent years. It is vital to develop highly safe automotive batteries with extended lifespans. The quasi-solid-state battery from our study has the potential to improve the longevity of liquid-based LIBs and enhance energy density while maintaining the safety of all-solid-state batteries.”
Conclusion
The study conducted by the Japanese research team highlights the potential of quasi-solid-state lithium-ion batteries to improve the safety, performance, and efficiency of energy storage systems. By combining liquid and solid electrolyte technologies, the new battery design addresses many of the shortcomings of traditional lithium-ion batteries, including safety concerns and performance limitations. With its high energy density, improved thermal stability, and long cycle life, this innovative battery has the potential to play a significant role in the future of electric vehicles, consumer electronics, and other high-demand applications. As the demand for cleaner, more efficient energy storage solutions grows, the development of such batteries will be crucial in helping to drive the transition to a more sustainable, low-carbon future.
Reference: Ryosuke Kido et al, Highly safe quasi-solid-state lithium ion batteries with two kinds of nearly saturated and non-flammable electrolyte solutions, Journal of Energy Storage (2024). DOI: 10.1016/j.est.2024.114115