Researchers develop new LMR cathode to reduce voltage fade in lithium-ion batteries

Currently, lithium-ion batteries are widely used in equipment such as electric vehicles . According to foreign media reports, a team composed of researchers from City University of Hong Kong, Northwestern University and other institutions in the United States has developed a new cathode that can solve the inherent problems of existing cathodes. Thereby increasing the capacity of lithium battery.

Qi Liu, one of the researchers, said: "This study focuses on a specific type of lithium- and manganese-rich (LMR) layered cathode materials. This material has the potential to store more energy than current commercial cathodes. ”

It is well known that LMR layered cathodes are susceptible to the phenomenon of "voltage decay", causing rapid battery degradation and voltage loss. This greatly limits the performance of lithium batteries. Previously, researchers tried to stabilize the structure by coating cathode materials or adding new elements, but that didn't solve the problem. In recent years, a class of LMR materials with unique O2 stacking structures has attracted attention. These materials exhibit lower voltage losses than conventional O3-type LMRs. In addition, benefiting from the unique O2 stacking, the researchers can also fine-tune the local structure of the inherently unstable honeycomb lattice.

Professor Liu and others tried to construct a new O2-based LMR cathode to stabilize the unique honeycomb structure of LMR materials. Liu said: "Researchers introduce transition metal (TM) ions into the lithium layer above or below the honeycomb structure. The purpose of this is to greatly enhance the stability of the honeycomb structure, effectively alleviate the voltage attenuation problem during cycling, thereby promoting LMR Practical applications of cathode materials in high energy density lithium-ion batteries."

In order to create LMR materials with TM-pinned honeycomb, the researchers used ion exchange technology (i.e., a system that effectively removes or dissolves ions) to combine P2-type Na 0.6 Li 0.2 (Mn 0.6 - x Ni x ) O2 The material is transformed into its desired O2-type LMR cathode. Professor Liu said: "The unique feature of this material is to have TM ions located above or below the honeycomb structure to act as a lid to stabilize the fragile framework. Compared with traditional cathodes, the advantage of this LMR cathode is that During battery use, voltage attenuation can be greatly reduced.”

Initial evaluations show that this lithium-rich cathode performs well, extending the life of lithium-ion batteries and improving their performance. This means electric vehicles may store more energy, extending their range on a single charge. Professor Liu said: "The practical application of LMR cathode materials has long been controversial. This study successfully solved the long-standing voltage attenuation problem in LMR. The results show that adding additional TM to the cathode material can stabilize the honeycomb structure, The voltage attenuation per cycle is only 0.02 mV, which is negligible.”

In the future, this discovery will help improve LMR cathodes or inspire other similar designs. Professor Liu said: "The current work successfully solved the problem of LMR voltage attenuation. The future goal is to solve another key issue - LMR voltage hysteresis. Voltage hysteresis refers to the difference in voltage curves during battery charge and discharge cycles. Previously, people It is generally believed that the voltage hysteresis is caused by the instability of the honeycomb superstructure. However, even with the 'cap' structure proposed in this study, the voltage hysteresis phenomenon is not alleviated."

Next, the researchers plan to further explore the mechanism of LMR cathode voltage hysteresis to improve the cathode design. Professor Liu said: "The next goal is to solve the voltage hysteresis problem and further improve the energy density of cathode materials. The researchers will also look for solutions to scale up the material manufacturing process for large-scale battery production."