Revisiting Surface Modification of Graphite: Dual-Layer Coating for High-Performance Lithium Battery Anode Materials

Toward Fast-Charging and Dendritic-Free Li Growth on Natural Graphite Through Intercalation/Conversion on MoS2 Nanosheets

During fast-charging, uneven lithium plating on the surface of commercial graphite anode impedes the electrochemical performance of lithium-ion batteries, causing a safety issue. The formation of a passivation layer, the solid-electrolyte interphase (SEI), due to side reactions with the organic electrolyte, correlates with long-term cycling performance under fast-charging conditions, necessitating comprehensive analysis. Herein, it is demonstrated that a molybdenum disulfide (MoS2) coating on natural graphite (NG) modulates the properties of the SEI layer, enabling reduction of the charging time and the enhancement of long-term cycling performance. MoS2 spontaneously transforms into Li2S and Mo nanoclusters through intercalation and conversion with Li+, altering the chemical composition and stability of the SEI layer on the NG, promoting faster Li+ transport, and reducing interfacial resistance. The MoS2-NG anode shows improved fast-charging capability and cycling performance under 3.0 C-charging and 1.0 C-discharging over 300 cycles without compromising energy density. In the full-cell configuration, a charging time of 14.7 min at 80% state of charge is achieved, making it suitable for electric vehicle applications.

Effects of crystal structure and electronic properties on lithium storage performance of artificial graphite

Graphite is nowadays commonly used as the main component of anode materials of lithium-ion batteries (LIBs). It is essential to deeply investigate the fundamentals of artificial graphite to obtain excellent anode, especially crystal structure and electronic properties. In this report, a series of graphite with different crystal structure were synthesized and used for anodes of LIBs. Meanwhile, a concise method is designed to evaluate qualitatively the conductivity of lithium ion (σLi) and a profound mechanism of lithium storage was revealed in terms of solid state theory. The conductivity analysis demonstrates that the graphite with longer crystal plane and lower stacking layers possesses higher conductivity of electron (σe). On the other hand, lower initial charge/discharge voltage indicates the graphite with lower La and higher Lc holds higher conductivity of lithium ion (σLi). According to the solid state theory, graphite is considered to be a semi-conductor with zero activation energy, while the lithium intercalated graphite is like a conductor. The conductivity of graphite mainly depends on the σe, while the conductivity of lithium intercalated graphite can be determined by the summation of σe and σLi. In lower charge/discharge rate, Li+ have enough time to insert into the graphitic layer, making the special capacity of graphite primarily determined by σe. However, with the increase of charge/discharge rate, Li+ insertion/extraction will become more difficult, making σLi become the mainly factor of the graphite special capacity. Therefore, the graphite with longer crystal plane and lower stacking layers owns higher specific capacity under slow charge/discharge rate, the graphite with shorter crystal plane and higher stacking layers shows relatively lower specific capacity under rapid charge/discharge rate. These results provide important insights into the design and improvement of graphite's electrochemical performance.

Carbon materials for ion-intercalation involved rechargeable battery technologies

The development of carbon electrode materials for rechargeable batteries is reviewed from the perspective of structural features, electrochemistry, and devices.