Analysis of several common hard carbon biomass precursors

· 1. Coconut shells
   Agricultural wastes are mainly supplied from South Asia and Southeast Asia, or are dependent on imports Coconut shell is the endocarp of the coconut with a hard texture, which is generally used in the production of utensils, crafts and activated charcoal. Coir-based hard carbon has a well-developed pore structure, low ash content and H/C to O/C ratio, which is an ideal anode material, and the industrialization progress is early and the performance is good.

As a kind of biomass waste, the yield of coconut shell is limited by the production of coconut. The main producing areas of coconut are Sri Lanka, Malaysia, India and the Philippines, and a small amount of planting in Hainan, Taiwan and other regions in China, of which the planting area of Hainan Province accounts for more than 99% in China. The domestic coconut shell production is difficult to meet the demand for hard carbon industrialization, and the coconut shell route will be dependent on raw material imports in the future. It is generally believed that the yield of hard carbon produced by coconut shell is 20%-25%, and the demand for hard carbon anode for 1GWh battery is about 1500 tons, so the annual production potential of domestic coconut shell can meet the use of about 6GWh batteries at most. In addition, compared with the Philippines, Indonesia and other coconut producing areas, China's Hainan Province has a higher latitude, weaker sunshine time and intensity, and the coconut shell produced is thinner and has low hardness, which is not the best material for the manufacture of coconut shell carbonization material, and the coconut shell produced in Southeast Asia is generally the first choice for enterprises.

· 2. Starch

Industrial products, high purity, can ensure product consistency 

Starch is one of the most abundant renewable biomaterials and is widely found in a variety of plants. As a typical polysaccharide, starch has simple composition, high carbon content, low price, and compared with other biomass precursors, starch exhibits a natural spherical shape that makes it a highly competitive precursor material for the preparation of hard carbon. Starch and sucrose are selected as precursors for the mass production route of Baisige, and the product has excellent indicators such as gram capacity and first effect, and its performance ranks among the top in the industry. As an industrial product, starch has sufficient domestic supply and high purity. China's annual starch output is large, with a domestic starch output of 33.89 million tons in 2020, and a large number of manufacturers, sufficient and stable market supply, and no single supplier risk. Starch is an organic high-molecular carbohydrate with high purity. When organic polymer compounds are used as hard carbon sources, hard carbon materials with special morphology can be obtained by combining specific synthesis methods, and the synthesis process is often complex, but it can avoid impurities and ensure the consistency of structure.·

3. Moso bamboo

Renewable resources with a short growth cycle, activated carbon manufacturers have entered, and the moso bamboo route is worth looking forward to Moso bamboo is a plant of the genus Bamboo, with a thick rod type, fast growth, and stable after 5-8 years of growth, and is the bamboo species with the highest economic value in the bamboo category, which is widely used in the construction industry, paper industry and other fields.

China is rich in bamboo forest resources. China is the hometown of moso bamboo and the most abundant yield, the results of the ninth national forest resources inventory show that the bamboo forest area in China is 6.4116 million hectares, of which moso bamboo forest accounts for 72.96%. Moso bamboo is mainly distributed in the Qinling Hanshui Basin and the south of the Yangtze River Basin in China, among which Fujian Province ranked first with 957 million bamboo production in 2020, accounting for 29.51%.

Activated carbon and hard carbon raw materials, preparation process is similar, sodium electricity industry space is broad, activated carbon leading enterprises (Yuanli) entered. The hard carbon preparation process is usually divided into three parts: precursor pretreatment, carbonization and post-treatment, among which the process route of using hard carbon precursor as raw material (coconut shell charcoal, bamboo charcoal, biochar, etc.) is similar to that of artificial graphite, but no graphitization process is required. The activated carbon preparation process usually includes raw material processing, activation, carbonization and other processes, which has a high degree of overlap with the pre-process of hard carbon preparation, but does not require the activation process of pore-making. Generally, the preparation process of biomass-based hard carbon such as bamboo does not include post-treatment processes, and the preparation process of activated carbon is similar to that of hard carbon. Yuanli Co., Ltd., a leading domestic activated carbon company, announced that it has conquered the hard carbon route of moso bamboo, and the company's future hard carbon production will be dominated by moso bamboo.

It is worth looking forward to the consistency problem solved by enterprises in resource-rich areas with the ability of raw materials and channels. Yuanli shares are located in Nanping, Fujian, surrounded by hairy bamboo production areas (Jian'ou, Shunchang, Youxi, etc.). The abundant supply of moso bamboo in a similar geographical environment can effectively alleviate the consistency problem of hard carbon precursor raw materials.

· 4. Straw
Agricultural waste is abundant in resources, and the "bio-solvent method" is expected to solve the consistency problem
As an agricultural waste, straw is rich in resources. China is a large agricultural country, and high-yielding crops such as wheat, corn and rice provide huge amounts of biomass straw resources every year. In 2020, the domestic crop straw production was 792 million tons, of which 667 million tons of resources could be collected. As an agricultural waste, straw has long been mainly used in heating energy, livestock feed and organic fertilizer, among which fertilizer utilization accounts for the highest proportion, accounting for 51.2% in 2020.

The biosolvent method is expected to solve the problem of consistency of straw raw materials. Shengquan Group uses the "Shengquan Biological Solvent Method" biomass refining technology to selectively transfer lignin, some hemicellulose and cellulose components with high carbon content and easy charcoal formation in straw into biological solvents, and intermolecular and intramolecular rearrangements occur in the biological solvents, in which the migrating molecules or groups are completely free and separated from the original system, and then rearranged and connected with the new system. Through molecular design methods such as rearrangement, bio-based resin is formed according to process requirements, which is further processed into biochar as a hard carbon precursor. The resynthesized bio-based resin has uniform molecular weight composition, stable physical and chemical properties, and the structure and composition of the biomass hard carbon formed are consistent.

· 5. There is no significant difference in the performance of biomass precursor products in each route
The hard carbon material products prepared from four biomass precursors, coconut shell, starch, bamboo and straw, have excellent performance. At present, narrowing the energy density gap between sodium battery cells and lithium iron phosphate cells is the top priority of the industry, and high gram capacity, high first efficiency, and high compaction are the development goals of hard carbon materials. From the perspective of product performance, the gram capacity of hard carbon materials prepared from coconut shell, starch, bamboo and straw is generally higher than 300 mAh/g, and the first effect is higher than 85%. Through the surface treatment of CVD method, Kuraray coir-based hard carbon products have good performance in terms of first effect, compaction density, and charge-discharge rate. Through the uniform doping of elements, the gram capacity of starch was significantly improved.
The comprehensive cost of biomass precursors was in the middle, and there was no significant difference in the cost of preparing hard carbon from coconut shell, starch, straw and bamboo. Manufacturing cost & direct labor cost end, precursor pretreatment and carbonization process manufacturing cost is low, because all kinds of precursors (except anthracite) have special processes, assuming that the manufacturing cost labor cost is 25,000 yuan, the CVD method for surface treatment cost is higher, assuming that the manufacturing cost is increased by an additional 50,000 yuan. On the raw material cost side, except for phenolic resin and anthracite, the difference in raw material cost of other routes is limited.
· 6. The stable and consistent supply of raw materials constitutes a bottleneck in the mass production of biomass-based hard carbon
The industrialization of biomass precursors needs to solve the problems of supply stability and consistency, and ensuring the consistency of material structure is the basis for ensuring the cycle life and safety of battery systems. The structure of hard carbon materials depends on the state of the precursor and the carbonization process, and only by ensuring that the precursor has a high degree of consistency and uniform heating during the carbonization process can the consistency of the final hard carbon material product be guaranteed. In addition, unlike lithium battery anode, biomass-based part of the raw materials are non-industrial products, and the raw material supply channel may constitute an industry barrier. Enterprises need to be close to resource areas to ensure reasonable procurement costs; At the same time, it is necessary to establish a stable supplier and raw material supply system in the long-term procurement accumulation.