Introduction To Hard Carbon Materials

Hard carbon: It is a type of carbon that is difficult to graphitize even at temperatures above 2500 ℃, named after its high mechanical hardness. The form of hard carbon can be spherical, linear, or porous. Hard carbon precursors are generally thermosetting materials, so they are usually able to maintain the morphology of the precursor during the material synthesis process. After high-temperature carbonization, short graphene sheets (also known as graphite domains or pseudo graphite) in hard carbon are arranged in a short-range ordered manner, forming a finite stack of 2 to 6 layers, with a length of up to 40 Å.
Several hard carbon biomass precursors
1. Coconut shell
Coconut shell is the inner skin of coconut, with a hard texture, and is generally used in the production of vessels, handicrafts, and activated carbon. Coconut shell based hard carbon has a well-developed pore structure, low ash content, and H/C to O/C ratio, making it an ideal negative electrode material. Currently, its industrialization progress is early and its performance is good. The main production areas of coconuts are Sri Lanka, Malaysia, India, and the Philippines. There are a small number of plantations in regions such as Hainan and Taiwan in China, with Hainan Province accounting for over 99% of the domestic planting area. In addition, compared to coconut producing areas such as the Philippines and Indonesia, Hainan Province in China has a higher latitude, weaker sunshine time and intensity, thinner coconut shells, lower hardness, and is not a material for manufacturing coconut shell carbonization materials. Coconut shells in Southeast Asia are generally produced by enterprises.
2. Starch
Starch is one of the abundant renewable biomaterials, widely present in various plants. As a typical polysaccharide, starch has a simple composition, high carbon content, and low price. At the same time, compared to other biomass precursors, starch exhibits a natural spherical shape, making it a highly competitive precursor material for preparing hard carbon. Starch, as an industrial product, has sufficient domestic supply and high purity. Starch is an organic high molecular carbohydrate with high purity. When organic polymer compounds are used as hard carbon sources, they can be combined with specific synthesis methods to obtain hard carbon materials with special morphologies. The synthesis process is often complex, but it can avoid impurities and ensure structural consistency.
3. Moso bamboo
Moso bamboo is a plant of the Poaceae family, belonging to the genus Corydalis. It has a thick and fast rod shape, and can grow stably after 5-8 years. It is an economically valuable bamboo species and is widely used in the construction industry, paper making industry, and other fields. China has abundant bamboo forest resources. China is the hometown of bamboo and has abundant production. The results of the ninth national forest resource inventory show that the bamboo forest area in China is 6.4116 million hectares, of which bamboo forest accounts for 72.96%. Moso bamboo is mainly distributed in the Qinling Han River Basin and the southern region of the Yangtze River Basin in China.
4. Straw
Straw, as agricultural waste, is abundant in resources. China is a major agricultural country, and high-yield crops such as wheat, corn, and rice provide a huge amount of biomass straw resources every year. In 2020, the domestic production of crop straw was 792 million tons, of which 667 million tons could be collected as resources. Straw, as agricultural waste, has long been mainly used for heating energy, livestock feed, and organic fertilizers. Among them, fertilizer utilization accounted for 51.2% in 2020.