Single crystal synthesis technology improves the durability of lithium secondary batteries

The research team recently demonstrated a single-crystal synthesis technique that significantly extends the lifespan of cathode materials for electric vehicles. ACS Materials and InterfacesAn international journal in the field of materials science.

Lithium (Li) secondary batteries, commonly used in electric vehicles, store energy by converting electrical energy into chemical energy through the transfer of Li ions between the cathode and anode, generating electricity, and releasing the chemical energy into electrical energy. Nickel (Ni) cathode materials are mainly used in these secondary batteries due to their high lithium-ion storage capacity. Conventional nickel-based materials have a polycrystalline structure composed of many small crystals, which can cause structural degradation during charging and discharging, significantly shortening their lifespan.

One way to address this issue is to manufacture the cathode material in “single crystal” form. Creating nickel-based cathode material as a single large particle, or “single crystal,” increases its structural and chemical stability and durability. Single crystal materials are synthesized at high temperatures and are known to harden; however, the exact process by which they harden during synthesis and the specific conditions under which this occurs remain unknown.

To improve the durability of nickel cathode materials for electric vehicles, researchers focused on identifying the specific temperature, called the “critical temperature,” at which high-quality single-crystal material is synthesized. The researchers investigated different synthesis temperatures to determine the optimal conditions for forming single crystals in the synthesis of a nickel-based cathode material (N884). The research team systematically observed the effect of temperature on the capacity and long-term performance of the material.

The researchers found that conventional polycrystalline materials synthesized below a certain critical temperature are prone to degradation during long-term use in secondary batteries. However, when synthesized above this critical temperature, high-quality single crystals can be easily produced, resulting in materials with superior life spans. This is due to a process called “densification” that occurs above a certain critical temperature.

During this process, the grain size inside the material increases and the voids within the material are densely filled. The densified single crystal is extremely hard, resistant to degradation over a long period of time, and significantly improves durability. Based on these findings, the research team confirmed that synthesizing single crystals above the critical temperature is a more advantageous material design strategy. They also proposed an effective method for synthesizing high-quality single crystal materials.

The team, in cooperation with POSCO Holdings N.EX.T Hub, in cooperation with POSCO Holdings N.EX.T Hub, in cooperation with POSCO Holdings N.EX.T Hub …

“We have introduced a new synthesis strategy to increase the durability of nickel-based positive electrode materials. We will continue our research to make secondary batteries for electric vehicles cheaper, faster and longer-lasting,” said Professor Park of POSTECH.