Researchers in China have developed a safe and relatively inexpensive synthesis of a sandwiched LiMn2O4@rGO nanocomposite that uses a one-pot solvothermal method. They have successfully tested the performance of this nanocomposite as a cathode material for the next generation n of high-performance lithium-ion batteries. [Chen, Y. et al., Mater. Today Adv. (2019)]
Lithium ion batteries have become ubiquitous energy storage systems for a wide range of portable electronic devices, such as mobile phones, laptops, video cameras, and household appliances. They arose as a need for cadmium-free batteries became apparent but there are, with all rechargeable batteries issues surrounding their lifespan with repeated charging and discharging. The main problem is just how reversible is the intercalation/deintercalation of those lithium ions that generate the current. Cathode materials are considered a significant target for improving lithium-ion batteries and much research effort is currently being expended in improving these materials to boost energy and power density of the batteries overall but also to improve safety and critically lifespan of such batteries.
The layered rock salt structure has been commonly used for cathode materials, but there is much interest in the spinel structure too. Specifically, spinel lithium oxido(oxo)manganese nanoparticles have attracted attention as alternative lithium materials for rechargeable batteries. Now, they can be loaded on to reduced graphene oxide using a facile one-pot solvothermal method, according to Huaqiang Cao of Tsinghua University in Beijing, China, and colleagues. The team has used transmission electron microscopy and Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetry analysis to characterize the materials. They found that their nanocomposite materials display better performances as cathode materials for lithium-ion batteries when compared with pure LiMn2O4 or that material simply mixed with reduced graphene oxide.
"The LiMn2O4-reduced graphene oxide nanocomposite retains about 110 millamp-hours per gram at 0.5 Celsius even after 150 charging cycles," the team reports. This, they say, indicates a better cycling stability than pure LiMn2O4 electrode. The graphene material provides a protective "fishnet" structure that also greatly shortens the electron transfer path. The nanostructuring of the cathode material also improves lithium ion movement. In addition, the graphene nanosheets preclude to some degree the undesirable migration of manganese ions into the electrolyte.