The negative electrode of a lithium-ion battery is made by uniformly coating both sides of a copper foil with a paste-like adhesive, a mixture of carbon or non-carbon active materials, binders, and additives, followed by drying and rolling. The negative electrode material is the main component of a lithium-ion battery that stores lithium, allowing lithium ions to be inserted and extracted during charging and discharging.
During charging, lithium atoms in the positive electrode ionize into lithium ions and electrons, and the lithium ions move towards the negative electrode to combine with electrons to form lithium atoms. During discharging, lithium atoms ionize from the negative electrode surface within the graphite crystal into lithium ions and electrons, and then combine at the positive electrode to form lithium atoms.
Anode materials primarily affect the initial efficiency and cycle performance of lithium-ion batteries, and their performance directly impacts the overall battery performance. Anode materials account for approximately 5-15% of the total cost of a lithium-ion battery. Types of anode materials include carbon-based and non-carbon-based anodes. From a technological perspective, future lithium-ion battery anode materials will exhibit a diverse range of characteristics.
With technological advancements, current lithium-ion battery anode materials have evolved from a single type of artificial graphite to a situation where natural graphite, mesophase carbon microspheres, and artificial graphite are the main materials, while soft/hard carbon, amorphous carbon, lithium titanate, silicon-carbon alloys, and other anode materials coexist.
Comparison of four anode materials
Graphene, a unique field
Graphene is a two-dimensional crystal composed of carbon atoms, only one atom thick. Its thinness, high hardness, and rapid electron mobility have earned it widespread acclaim from scientists, making it known as the "king of new materials." Despite its excellent chemical properties making it a promising candidate in the new energy market, it remains largely a conceptual work to date.
Using graphene as a lithium-ion battery anode material requires an independent upstream and downstream industrial chain, high prices, and complex processes, which deters many anode material manufacturers. Despite this, some domestic companies are forging ahead, and well-known companies such as Anbao, Dafu Technology, and BTR have already begun to invest in the graphene industry.
However, doubts about using graphene as a negative electrode material are also growing within the industry. Some believe that graphene has very low tap and compaction densities, coupled with its high cost, making its prospects as a battery negative electrode material very bleak. But given that its popularity continues, it's not an exaggeration to call it a dominant force in the market.
Artificial graphite controlling the "home field"
Currently, the main anode materials are natural graphite and artificial graphite, each with its own advantages and disadvantages. Hu Bo, general manager of Huzhou Chuangya, said: "Natural graphite has a higher specific capacity, simpler processing, and lower price, but its liquid absorption and cycle performance are somewhat poor; artificial graphite has a more complex processing and is more expensive, but its cycle and safety performance are better. Through various technological improvements, both types of graphite anode materials can 'maximize their strengths and minimize their weaknesses,' but at present, artificial graphite has a certain advantage in the use of power batteries."
This claim has been confirmed in the market. According to research data from relevant media, China's natural graphite production reached 4,770 tons in the first quarter of this year, a year-on-year increase of 16.3%; while shipments of artificial graphite reached 15,160 tons, a year-on-year increase of 110.5%. These figures show that shipments of artificial graphite far exceed those of natural graphite. A key reason for this phenomenon is the strong market demand for power batteries this year.
Stable mesophase carbon microspheres
Mesophase carbon microspheres possess a highly ordered layered stacking structure, are typical soft carbon, exhibit a high degree of graphitization, structural stability, and excellent electrochemical performance. According to statistics from the China Consulting Network Research Department, China's anode material shipments in 2012 reached 27,650 tons, with natural graphite accounting for 59%, artificial graphite 30%, and graphitized mesophase carbon microspheres 8%. Therefore, mesophase carbon microspheres are the third largest mainstream carbon-based anode material, after natural and artificial graphite.
According to Coating Online, mesophase carbon microspheres outperform natural and artificial graphite in rate performance, offering significant advantages for applications in model aircraft and power tools. Furthermore, their thermal and chemical stability prevents them from undergoing chemical reactions, enhancing safety in lithium batteries. However, their high manufacturing cost, complex processes, and susceptibility to alternatives have kept the production and sales of mesophase carbon microspheres relatively stable, limiting their widespread adoption.
New Continent Silicon-Carbon Composite Material
Recently, an article caught my attention, titled "The Love-Hate Relationship Between Silicon and Graphite!" The article states that silicon anode materials theoretically have a capacity ratio exceeding 4200 mAh/g, far surpassing graphite anodes (372 mAh/g). However, silicon anode materials have an inherent defect: lithium embedding into the silicon cell causes severe expansion of the silicon material, resulting in a rapid decrease in capacity. To overcome these shortcomings, scientists combined silicon anodes with graphite, creating silicon-carbon composite materials, which are hailed as a "new frontier" in lithium-ion battery anode materials.
According to Coating Online, Tesla's Model 3 uses silicon-carbon anodes as a new material for its power batteries. By adding 10% silicon-based materials to artificial graphite, Tesla achieved a battery capacity of over 550 mAh/g and an energy density of 300 Wh/kg. This method of using silicon-carbon composite materials to improve battery energy density is now widely recognized in the industry.
While the four major players in anode materials each have their strengths, the future development of graphene remains uncertain in the current anode material market. Artificial graphite, which has consistently been the top consumer material in recent years, faces challenges from high-performance silicon-carbon composite materials. Tesla, a global leader in the new energy vehicle market, is expected to use silicon-carbon composite materials, which will undoubtedly spark a surge in demand for these materials, potentially reshaping the lithium-ion battery anode material market. Meanwhile, mesophase carbon microspheres, which have maintained a stable position, are not expected to experience significant fluctuations in the future.
