Study finds method to improve lithium-ion battery life

Repeated charging and discharging of a lithium-ion battery causes a significant change in the volume of the anode, which reduces the capacity and life of the battery. Now, researchers from GIST in Korea have developed a method to strengthen the anode, making it more resistant to changes in volume. The anode can be modified regardless of its material or method of manufacture, making the approach universal and opening the doors to long-lasting batteries for smartphones and electric cars.

The advent of electric vehicles has created the demand for high energy density lithium-ion batteries. This led to the development of high charge storage capacity anodes. Unfortunately, this storage capacity tends to degrade over multiple charge/discharge cycles, reducing battery life.

Short battery life results from an irreversible volume change of the anode during cycling, which causes electrical contact degradation and structural collapse. During charging, lithium ions move from the cathode and combine with nanoparticles from the anode. During discharge, the lithium ions return to the cathode. Over time, the anode nanoparticles crack and cluster at the electrode-electrolyte interface. This causes an electrical disconnect, reducing the amount of charge the anode can store or carry.

Above: the chemical process by which battery life can be extended

“As one of the research groups engaged in this area, we wanted to develop an electrode process that would be able to increase energy density in line with the rapid growth of the battery industry,” explains Professor Hyeong-Jin Kim, one of the study’s corresponding authors.

The method developed by the researchers strengthens the anode and makes it more resistant to changes in volume by encapsulating the nanoparticles in an elastic web-like structure.

To demonstrate their approach, the researchers used a conventional anode containing silicon nanoparticles held together by a polymer binder (polyvinylidene fluoride). To accommodate the strip-like structure, they removed the binder by heating the anode using an annealing process. The space between the nanoparticles was then filled with a reduced solution of graphene oxide (rGO), which dried to form a web that held the silicon nanoparticles together and prevented them from cracking. Additionally, the web provided a conductive pathway for electrons, allowing the nanoparticles to bind to lithium.

The researchers used a technique called “spin coating” to coat the surface of the anode with rGO. The rGO coating served as a seed layer for the deposition of a protective layer consisting of zinc oxide to which were added metallic oxides of magnesium and gallium (MGZO). This MGZO layer provided structural stability to the anode.

In testing, the modified anode could retain most of its charge even after multiple charge/discharge cycles. “The structure retained a high storage capacity of 1566 mA hg-1 after 500 cycles and showed a coulombic efficiency of 91%, which is related to battery life. This could pave the way for electric vehicles that will allow us to travel long distances on a single charge,” Professor Kim points out.

While the researchers used a silicon anode, the method developed is applicable to other anode materials, such as Sn, Sb, Al and Mg. Additionally, anodes can be modified regardless of how they are made, making this a universally applicable method of improving battery life.