Lithium-ion batteries, used in various devices ranging from smartphones to electric cars, store energy through ion intercalation, where lithium ions slip between graphite layers in the anode during charging.
The more lithium ions a battery can absorb and release, the more energy it stores. Though this process is well-known, its microscopic details were unclear.
A team from the University of Manchester has shed new light on this phenomenon by studying bilayer graphene, the thinnest possible battery anode composed of just two carbon layers.
Surprising process in lithium intercalation for energy storage
The research by the Manchester scientists, published in Nature Communications, reveals an unexpected ‘in-plane staging’ process during lithium intercalation in bilayer graphene, potentially leading to advancements in energy storage technology.
Graphite has long been used as an anode material in Li-ion batteries due to its chemical stability, reversible intercalation, good cyclability, and low cost. In their experiments, the researchers swapped the usual graphite anode for bilayer graphene and observed how lithium ions behaved during intercalation.
Surprisingly, they discovered that lithium ions don’t enter the two layers simultaneously or randomly. Instead, the process occurs in four distinct stages, with the ions arranging themselves in organized, progressively denser hexagonal lattices at each stage.
According to Professor Irina Grigorieva, who led the research team, the discovery of in-plane staging was unexpected. It showed a much higher level of interaction between the lithium-ion lattice and the graphene crystal lattice than previously believed.
“This understanding of the intercalation process at the atomic level opens up new avenues for optimising lithium-ion batteries and possibly exploring new materials for enhanced energy storage,” Grigorieva explains.
Bilayer graphene offers insights but falls short on lithium storage capacity
The study also found that bilayer graphene has a lower lithium storage capacity compared to traditional graphite. This is because it provides less effective screening of interactions between positively charged lithium ions, resulting in stronger repulsion and forcing the ions to stay farther apart.
Although bilayer graphene may not provide higher storage capacity than bulk graphite, its unique intercalation process represents a significant advance. This discovery suggests that using atomically thin metals could enhance the screening effect and potentially improve storage capacity in the future.
The research also advances the understanding of lithium-ion intercalation and provides a foundation for developing more efficient and sustainable energy storage solutions. As demand for improved batteries rises, these findings could influence the development of future energy storage technologies.
