For the first time, the University of Tokyo group has achieved practically stable operation of ultra-5V lithium-ion batteries, which far exceeds the operating upper limit voltage of conventional lithium-ion batteries.
Lithium-ion batteries, which are key devices in a low-carbon and sustainable society, are reaching the theoretical maximum value due to improvements in their capacities, while the maximum operating voltage remains at around 4.3V, further increasing the energy density. It is essential to improve the operating voltage.However, since the electrolytic solution and the positive electrode active material are severely deteriorated during high voltage operation, long-term stable operation at a practical level has not been realized.
Under these circumstances, as a result of conducting a multifaceted analysis of high-voltage lithium-ion batteries, the group has overlooked the insertion of anions (negative ions) in the electrolytic solution into the carbon conductive auxiliary agent added to the positive electrode. It was found to be an important deterioration factor.It is said that the structure is destroyed by the entry of anions (negative ions) between the graphite layers of the carbon conductive auxiliary agent, and the conductivity of the entire positive electrode is lowered, which greatly affects the charge / discharge stability.
Therefore, we adopted a "dense" (high concentration) electrolytic solution that effectively suppresses this side reaction, and also adopted a solvent that forms a protective film that prevents the permeation of anions (negative ions) on the surface of the positive electrode.In this electrolytic solution, anions (minus ions) are strongly bound (coordinated) with lithium ions, so that the insertion of anions (minus ions) into the carbon conductive auxiliary agent is suppressed, and at the same time, the protective film is anions (minus). It is possible to protect the surface of the positive electrode active material from high voltage operation (highly oxidizing atmosphere) while preventing the permeation of ions).
As a result, a practical level of long life (maintenance rate of 5.2% of initial capacity / 93 times charge / discharge) has been achieved for lithium-ion batteries with an upper limit voltage of 1000V.We have shown the possibility of next-generation batteries that will dramatically improve the performance of lithium-ion batteries, which are approaching their theoretical limits.
Paper information:[Joule] An overlooked issue for high-voltage Li-ion Batteries: Suppressing the intercalation of anions into conductive carbon
