Hongchang Jin; Sen Xin, Chenghao Chuang; Wangda Li; Haiyun Wang; Jian Zhu; Huanyu Xie; Taiming Zhang; Yangyang Wan; Zhikai Qi; Wensheng Yan; Ying-Rui Lu; Ting-Shan Chan; Xiaojun Wu; John B. Goodenough; Hengxing Ji; Xiangfeng Duan SCIENCE 370(6513), p.192-197

Full Article: https://www.science.org/doi/10.1126/science.aav5842

This study employed operando X-ray absorption spectroscopy (XAS) combined with a highly sensitive silicon drift detector (SDD) to precisely monitor the absorption spectrum of phosphorus in real-time under electrochemical charge-discharge conditions. We discovered the formation of a novel lithium-phosphorus (LiP) chemical bond at the interface, which alters the oxidation state of black phosphorus. The XAS spectra corroborated the dynamic changes in the redox states of these new chemical bonds (PLiP, Li2P, Li3P), correlating directly with the instantaneous intercalation and de-intercalation of lithium ions.

The unique synthesis of our material stems from the direct attachment of layered black phosphorus edges to layered graphite edges. An external gelatinous polyaniline then stabilizes the internal structure of the black phosphorus-graphite nanospheres. This gelatinous nanolayer functions as a long-lasting, fast charge-discharge solid-electrolyte interphase. During charging, electrons transfer into the conductive black phosphorus-graphite nanospheres, and lithium ions from the electrolyte pass through the gelatinous layer to bond with the black phosphorus layers. Because the internal black phosphorus and graphite form a robust and stable structure, it not only provides more capacity for charge-discharge but also enables the black phosphorus interface to have lower lithium ion migration energy, leading to ultra-fast charging efficiency.

This paper highlights the novel synthesis of black phosphorus materials, operando synchrotron light source probing, and theoretical interface bonding energies. Its cross-national collaborative achievements represent a significant breakthrough in the battery field. Lithium-ion batteries are currently the most critical core component for the electric vehicle industry, providing energy storage and operation for electric motors. However, current conventional lithium-ion batteries typically offer only 100-300 W/kg performance and require lengthy, safe charging times (e.g., 1-2 hours). To enhance battery charging efficiency and material lifespan, recent years have seen continuous research into the storage capacity and electrochemical stability of anode materials to meet the commercial demand for large capacity and fast charging, such as the condition of fully charging a 350 Wh/kg battery within five minutes. Common anode materials include graphite and silicon alloys; graphite offers fast and stable lithium-ion storage, while silicon alloys provide high lithium-ion storage capacity (4200 mAh/g), though silicon alloy electrodes are only suitable for low-current, long-duration operations.

Recent theoretical proposals suggest black phosphorus materials possess high lithium-ion storage capacity (2596 mAh/g), primarily due to its larger interlayer spacing of approximately 5.2 Å. Furthermore, black phosphorus’s conductivity (300 S/m) is significantly greater than silicon’s (0.067 S/m), and the lithium-ion diffusion barrier in black phosphorus edges (0.08 eV) is much smaller than that in silicon (0.58 eV). Unfortunately, current experimental results still fall short of its theoretical potential. Therefore, we blended black phosphorus with layered graphite to replace single graphite anode sheets, leveraging both high lithium-ion storage capacity and fast, high charge-discharge advantages. Test results show that even under high current conditions (13 A/g), the cyclable energy capacity still reached 350 mAh/g. This means a black phosphorus battery could be fully charged in approximately two minutes. Its energy capacity is about five times higher than that of a Tesla Model 3 series electric vehicle battery (74 mAh/g), which still takes over an hour and twenty minutes to fully charge even with a supercharging station.

A key question arising from this excellent battery performance is: why does the combination of black phosphorus and graphite yield a higher capacity? The performance’s critical point lies in understanding the lithium-ion intercalation and de-intercalation behavior within the black phosphorus composite during charge and discharge. This team leveraged its expertise in operando X-ray analysis, uncovering the secret behind the easy mobility of the new lithium-phosphorus (LiP) chemical bonds, and identifying the reasons for their faster reaction and high stable density. The widespread adoption of all-electric vehicles is now within reach.