A Korean team led by researchers from the Samsung Advanced Institute of Technology (SAIT) has developed “graphene balls”—graphene-silica 3D assemblies—that can be uniformly coated onto a nickel-rich layered cathode (LiNi0.6Co0.1Mn0.3O2). The graphene-ball coating improves cycle life and fast charging capability by protecting the electrode surface from detrimental side reactions and providing efficient conductive pathways.
The graphene balls can also serve as an anode material with high specific capacity of 716.2 mAh g-1. A full-cell incorporating graphene-balls increases the volumetric energy density by 27.6％ compared to a control cell without graphene-balls, showing the possibility of achieving 800 Wh L-1 in a commercial cell setting, along with a high cyclability of 78.6％ retention of the initial capacity after 500 cycles at 5C and 60 ˚C. An open-access paper on their work is published in Nature Communications.
… as electric vehicles (EVs) have penetrated LIB markets, key electrochemical properties have imposed more challenging standards; while higher energy densities are desired for increased driving mileage, enhanced reaction kinetics are demanded for fast charging and high rate operations. Safety is also definitely a critical factor for EV applications. A formidable challenge lies in overcoming the trade-off relation among these key properties; it is usually nontrivial to improve one property without sacrificing others.
Such a trade-off relation is particularly obvious between energy density and fast charging (or power capability). While the use of nanomaterials as active components and incorporation of carbon nanomaterials as conductive agents have demonstrated improved charging rates by reducing ion diffusion distance and internal resistance, most of those approaches still require further improvement before they can be implemented in current LIB technology. … Furthermore, beside energy density and fast charging, achieving long cycle life, especially at high temperatures (i.e., 60 °C), still remains a challenge for advanced LIBs that incorporate high-capacity electrode materials.
… Here we report a graphene–silica (SiOx) assembly, called a graphene ball (GB), as a coating material for high-capacity Ni-rich layered cathode materials as well as an LIB anode material.—Son et al.
Each GB has a SiOx nanoparticle center with surrounding graphene layers, constituting a three-dimensional (3D) popcorn-like structure. The SiO x nanoparticles serve multiple important functions: avoiding the formation of a silicon carbide (SiC) layer at the SiOx–graphene interface during graphene growth; ensuring uniform coating of GB onto the cathode material, and providing a high specific capacity when GB is used as an anode material.
The uniform coating of GB on the Ni-rich layered cathode enhances the interfacial stability with the electrolyte and the electronic conductivity over the electrode, improving the cyclability and fast charging capability of the cathode substantially.
In a broader perspective, the present mixing approach can be more generally expanded to a variety of graphene-based composites whenever it is desirable to homogeneously integrate graphene with ceramic materials. Other high-strength and heat-radiation applications could immediately benefit from the given approach.—Son et al.
In Hyuk Son, Jong Hwan Park, Seongyong Park, Kwangjin Park, Sangil Han, Jaeho Shin, Seok-Gwang Doo, Yunil Hwang, Hyuk Chang & Jang Wook Choi (2017) “Graphene balls for lithium rechargeable batteries with fast charging and high volumetric energy densities,” Nature Communications 8, Article number: 1561 doi: 10.1038/s41467-017-01823-7