Janus Graphene Could 10X the Energy Capacity of Sodium-ion Batteries

Sodium batteries could become much cheaper than lithium-ion batteries but sodium-ion batteries capacity has been too low.

“We have added a molecule spacer on one side of the graphene layer. When the layers are stacked together, the molecule creates larger space between graphene sheets and provides an interaction point, which leads to a significantly higher capacity,” says researcher Jinhua Sun at the Department of Industrial and Materials Science at Chalmers and first author of the scientific paper, published in Science Advances.

Ten times the energy capacity of standard graphite

Typically, the capacity of sodium intercalation in standard graphite is about 35 milliampere hours per gram (mA h g-1). This is less than one tenth of the capacity for lithium-ion intercalation in graphite. With the novel graphene the specific capacity for sodium ions is 332 milliampere hours per gram. the energy capacity boost gets sodium batteries near the capacity of lithium in graphite. The results also showed full reversibility and high cycling stability.

Science Advances, “Real-time imaging of Na+ reversible intercalation in “Janus” graphene stacks for battery applications” written by Jinhua Sun, Matthew Sadd, Philip Edenborg, Henrik Grönbeck, Peter H. Thiesen, Zhenyuan Xia, Vanesa Quintano, Ren Qiu, Aleksandar Matic and Vincenzo Palermo.

Abstract
Sodium, in contrast to other metals, cannot intercalate in graphite, hindering the use of this cheap, abundant element in rechargeable batteries. Here, we report a nanometric graphite-like anode for Na+ storage, formed by stacked graphene sheets functionalized only on one side, termed Janus graphene. The asymmetric functionalization allows reversible intercalation of Na+, as monitored by operando Raman spectroelectrochemistry and visualized by imaging ellipsometry. Our Janus graphene has uniform pore size, controllable functionalization density, and few edges; it can store Na+ differently from graphite and stacked graphene. Density functional theory calculations demonstrate that Na+ preferably rests close to -NH2 group forming synergic ionic bonds to graphene, making the interaction process energetically favorable. The estimated sodium storage up to C6.9Na is comparable to graphite for standard lithium ion batteries. Given such encouraging Na+ reversible intercalation behavior, our approach provides a way to design carbon-based materials for sodium ion batteries.

SOURCES- Science Advances, Chalmers
Written By Brian Wang, Nextbigfuture.com