Introduction to Graphite Anode Materials for Lithium Batteries

1. Classification and Applications of Graphite Anode Materials

Graphite anode materials are one of the commonly used anode materials in lithium-ion batteries, featuring high energy density and low manufacturing costs. Composed mainly of graphite, they exhibit high electrical conductivity and good chemical stability.

Broadly speaking, graphite is categorized into two types: Natural Graphite (NG) and Artificial Graphite.Natural graphite is mined from rocks and is generally divided into amorphous, flaky (crystalline), massive, or flaky (crystalline) types based on crystallinity, grain size, morphology, and occurrence. Artificial graphite is produced via graphitization processes with a purity of up to 99.9%. Compared to natural graphite, artificial graphite typically has lower density, lower electrical conductivity, and slightly higher porosity. Both natural and artificial graphite are used in batteries, carbon brushes, conductive materials, fuel cells, and lubricants.

Due to their satisfactory electrochemical properties and low manufacturing costs, graphite remains the dominant anode material in commercial lithium-ion batteries.

2. Energy Storage Principle of Graphite Anode Materials

During battery charging and discharging, graphite anode materials store and release electrical energy through the intercalation and deintercalation of lithium ions. When a lithium battery charges, Li⁺ ions from the positive electrode travel through the electrolyte to the negative electrode. The graphite anode, with its layered carbon structure containing micro-pores, allows Li⁺ ions to intercalate into the layered structure and micro-pores. The more Li⁺ ions intercalated, the higher the charging capacity. Anode materials affect key performance indicators of lithium-ion batteries, such as first-cycle efficiency and cycle performance.

The size and morphology of graphite crystals in anode materials significantly impact battery performance. Generally, smaller graphite crystals have a larger specific surface area and higher reaction activity, enabling better electrochemical properties. Additionally, optimizing the structural morphology and physical properties of graphite anode materials can further enhance the energy density and cycle life of lithium-ion batteries.

3. Research Progress of Graphite Anode Materials in Batteries

The theoretical capacity of graphite anode materials is 372 mAh/g. In practical applications, however, their specific capacity typically ranges from 330 to 370 mAh/g. Repeated charging-discharging cycles cause volume expansion and structural changes during Li⁺ intercalation/deintercalation, leading to unstable structures, reduced reversible capacity, and shortened cycle life of graphite anodes.

To address these issues, researchers are exploring novel graphite anode materials, such as composite materials formed by introducing additives to graphite, nanostructured graphite, and graphene-doped graphite. These materials offer higher reversible capacity, more stable structures, and better cycle life, holding promise to become mainstream anode materials in the future.

Case Study 1: Ding's Research

Using natural graphite as the anode and introducing the polymer PGB, Ding improved the electrochemical performance of graphite anodes at different temperatures. Tests showed that the graphite/PGB composite retained a discharge capacity of 230 mAh/g after 1000 cycles at 1.86 A·g⁻¹ (5C) under room temperature. At 60°C, it maintained a high capacity of 345 mAh/g after 200 cycles at 5C.

SEM images revealed that graphite particles in the graphite/PGB electrode were coated with a uniform organic layer, appearing more regular and smooth. This uniform coating promoted the formation of a homogeneous Solid Electrolyte Interface (SEI) layer, contributing to excellent cycle stability across a wide temperature range. XPS analysis showed that the SEI layer of graphite/PGB was richer in inorganic components, which are denser and more stable than organic structures.

Case Study 2: Chen's Research

Using graphene as the carbon matrix, Chen prepared Sb₂O₃/rGO-100 electrodes with outstanding cycle stability and rate performance (397 mAh/g at 2 A·g⁻¹). After 300 cycles, they delivered a high reversible capacity of 513 mAh/g at 0.5 A·g⁻¹.

The anode material features a rich mesoporous structure and high specific surface area, providing a large electrode-electrolyte contact area and more Li⁺ storage sites. Electron microscopy images show uniformly dispersed conductive carbon matrix (rGO) and ultrafine Sb₂O₃ nanoparticles.

Although these studies enhance lithium storage performance and anode stability, their large-scale application is limited by high production costs and complex processes.

4. Characterization of Graphite Anode Materials

The manufacturing processes of graphite-based anode materials, including coating and doping, may introduce trace elements. As battery energy density increases, higher tap density and stricter stability requirements for graphite-based anodes have emerged. Therefore, accurately measuring and removing trace impurity elements in graphite anode materials is crucial to ensure product quality and performance.