State change of Na clusters in hard carbon electrodes and increased capacity for Na-ion batteries achieved by heteroatom doping
Hideka Ando,
Kenjiro Hashi,
Shinobu Ohki,
Yoshikiyo Hatakeyama,
Yuta Nishina,
Norihiro Kowata,
Takahiro Ohkubo,
Kazuma Gotoh
Affiliations
Hideka Ando
Graduate School of Natural Science & Technology, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan; Center for Nano Materials and Technology (CNMT), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan
Kenjiro Hashi
National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan
Shinobu Ohki
National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan
Yoshikiyo Hatakeyama
Graduate School of Science and Technology, Gunma University, 1-5-1 Tenjincho, Kiryu, Gunma 376-8515, Japan
Yuta Nishina
Graduate School of Natural Science & Technology, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
Norihiro Kowata
Graduate School of Natural Science & Technology, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
Takahiro Ohkubo
Graduate School of Natural Science & Technology, Okayama University, 3-1-1 Tsushima-naka, Okayama 700-8530, Japan
Kazuma Gotoh
Center for Nano Materials and Technology (CNMT), Japan Advanced Institute of Science and Technology (JAIST), 1-1 Asahidai, Nomi, Ishikawa 923-1292, Japan; Corresponding author.
Although heteroatom doping is an effective method to improve the capacity of hard carbon (HC) anodes in Na-ion batteries (NIBs), the complicated structure of HC leads to uncertainty when understanding the effects of heteroatom doping on sodium storage. This study shows the effects of phosphorus and sulfur doping to HC on sodium storage using solid-state NMR to improve the capacity of HC prepared by the carbonization of resorcinol formaldehyde (RF) resin at 1100 °C. Heteroatom doping increased the battery capacity of the HC, especially the plateau capacity, but the interlayer distance of the carbon layers in the HC did not expand considerably. 23Na solid-state NMR revealed that heteroatom doping facilitates the formation of quasi-metallic sodium clusters, thereby contributing to the plateau capacity increase. The metallicity of the sodium clusters in heteroatom-doped HC samples was controlled by the amount of doped-phosphorous. XPS and 31P NMR detected various phosphorus sites such as phosphine and phosphine oxide in the carbon structure.
