Development of High-Capacity Black Phosphorus Carbon Composite Anode Material with Suppressed Dendrite Generation and Its Lithium-Ion Batteries
Authors: Inui Naoki , Nasara Ralph Nicolai , Hashiwaki Hiroki , Inokuchi Daisuke , Yamada Izumi , Lee Changhee , Miyahara Yuto , Miyazaki Kohei , Abe Takeshi 
Published: December 2024

1, Introduction
For further implementation of electric vehicles in society, it is essential to further improve the capacity and the fast-charging performance of battery, which are largely dependent on active materials. To improve the energy density and rate characteristics of lithium-ion batteries, it is inevitable to develop new anode materials. As new materials to replace the current graphite anode, alloy-based anode materials such as silicon and metallic lithium have been studied for many years, and some of them are actually used. Although silicon-based materials exhibit high theoretical capacity, there is a trade-off between long life and capacity. Increasing the silicon content improves the energy density, but there is an upper limit to the amount of silicon in the negative electrode because it causes cycle degradation. On the other hand, industrial use of metallic lithium as the ultimate high-capacity negative electrode has been researched and developed for many years, but lithium dendrites remain a major problem, in addition to the large volume change of expansion and contraction during the charge/discharge process.
In contrast, phosphorus-based materials have high theoretical capacity (2596mAh/g) and high lithium insertion potential (0.7V vs. Li/Li+), so they are expected to be a high-capacity negative electrode with dendrite suppression. Among them, black phosphorus-carbon composites have been studied in various ways because of their high capacity and high electronic conductivity.[1][2] Although the chemical bonding between phosphorus and carbon is said to be important for high capacity,[3] no material has yet been found that simultaneously satisfies capacity, rate characteristics, and cycle life. Therefore, for the purpose of achieving both of these goals in this study, cup-stacked nanotubes (CSCNTs), which contain many edge structures calculated to be highly reactive with phosphorus,[4] were used for the first time as a model material to prove the hypothesis, and CSCNTs were complexed with black phosphorus to investigate their analytical and electrochemical properties. [5]

2, Experiment
Black phosphorus (Rasa Industries) and cup-stacked nanotubes (CSCNT, GSI Creos) were mixed and ball milled under inert atmosphere for 12 hours to synthesize black phosphorus carbon composite negative electrode material A. The obtained materials were analyzed by HR-STEM, EELS, XRD, XPS, Raman, TG-DTA, and BET specific surface area. A 2023-type coin cell using lithium metal as the counter electrode was also prepared, and charge/discharge tests were conducted.
3, Result and discussion
The synthesized black phosphorus carbon composite anode material A showed a high specific capacity (0.18A/g) of 1642mAh/g (based on the whole anode composite) and a high ICE of 89.3% (Fig.). The rate characteristics of this material A was 1455mAh/g at 9.0A/g and as the cycle performance of it, 90% capacity retention after 200cycles of charge/discharge at 25°C(0.001-2.5V, 3.6A/g) was confirmed.
While The BET specific surface area of the raw material CSCNT was >75 m2/g (black phosphorus: <11 m2/g), the composite anode material A was <13 m2/g, showing a significant reduction compared to the initial CSCNT. XRD measurement of material A showed that both black phosphorus and CSCNT peaks disappeared completely and changed to amorphous state, HR-STEM analysis showed that it has a partially layered structure different from the black phosphorus interlayer distance (0.54 nm), and EELS mapping confirmed that the carbon and phosphorus are homogeneously dispersed on the nm order homogeneous dispersion of carbon and phosphorus. As for the bonding state of phosphorus and carbon, peaks suggesting P-O-C bonding were observed in XPS, but XPS and Raman did not convincingly and certainly show if P-C bond exists or not. It is assumed that the high energy density, high rate, and long life are achieved by the nano-dispersion of phosphorus, which contributes to high capacity, through the bonding with carbon which has electronic conductivity.
4, Conclusion
The black phosphorus carbon composite anode material using the cup-stacked carbon nanotube (CSCNT) exhibited a high specific capacity of 1642mAh/g (0.18A/g) and an ICE of 89.3%. The rate characteristic of this material was 1455mAh/g at 9.0A/g, and the cycle test at 25°C (0.001-2.5V, 3.6A/g) showed 90% capacity retention. As for the bonding between phosphorus and carbon, a peak suggesting P-O-C bonding was observed by XPS. It is assumed that the phosphorus, which contributes to high capacity, is nano-dispersed by bonding with electron conductive carbon, resulting in high capacity, high rate, and long life.
5, Reference
[1] H. Jin et al., Science 370,192-197 (2020).
[2] R. Amine et al., Nano Energy 74, 1048-49 (2020).
[3] J. Sun, et al., Nano Lett. 14, 8, 4573-4850 (2014).
[4] S. Zhang et al., ACS Nano 15, 3365-3375 (2021).
[5] Y. Ju et al., Electrochemistry 90, 027007 (2022).

Figure 1