Abstract
Hard carbon is the leading candidate anode for commercialization of Na-ion batteries. Hard carbon has a unique local atomic structure, which is composed of nanodomains of layered rumpled sheets that have short-range local order resembling graphene within each layer, but complete disorder along the c-axis between layers. A primary challenge holding back the development of Na-ion batteries is that a complete understanding of the structure–capacity correlations of Na-ion storage in hard carbon has remained elusive. This article presents two key discoveries: first, the characteristics of hard carbons structure can be modified systematically by heteroatom doping, and second, that these structural changes greatly affect Na-ion storage properties, which reveals the mechanisms for Na storage in hard carbon. Specifically, via P or S doping, the interlayer spacing is dilated, which extends the low-voltage plateau capacity, while increasing the defect concentrations with P or B doping leads to higher sloping sodiation capacity. The combined experimental studies and first principles calculations reveal that it is the Na-ion-defect binding that corresponds to the sloping capacity, while the Na intercalation between graphenic layers causes the low-potential plateau capacity. The understanding suggests a new design principle of hard carbon anode: more reversibly binding defects and dilated turbostratic domains, given that the specific surface area is maintained low.
Original language | English |
---|---|
Journal | Advanced Energy Materials |
Volume | 7 |
Issue number | 18 |
DOIs | |
State | Published - Sep 20 2017 |
Funding
Z.L. and C.B. contributed equally to this work. X.J., P.A.G., and M.D. thank the financial supports from the National Science Foundation of the United States, Award No. 1507391. The authors are thankful to Prof. Chih-Hung Chang and Mr. Changqing Pan for Raman analysis. The authors thank the help of Mr. Andy Ungerer and Mr. Jesse Muratli on ICP-OES measurements and ICP sample preparation. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by Oak Ridge National Laboratory. This is based upon work supported by the U.S. Department of Energy, Office of Science, under Contract No. DE-AC05-00OR22725.
Funders | Funder number |
---|---|
National Science Foundation | 1507391 |
U.S. Department of Energy | |
Office of Science | DE-AC05-00OR22725 |
Oak Ridge National Laboratory |
Keywords
- Na-ion batteries
- hard carbon anodes
- heteroatom doping
- local structures
- mechanisms