As we all know, the four main materials of a lithium battery include the positive electrode material, the negative electrode material, the electrolyte, and the separator. So, what is the role of the negative electrode material in lithium battery materials?
Generally speaking, lithium battery anode materials are made by coating both sides of copper foil with a paste-like adhesive composed of active materials, binders, and additives, and then drying and rolling them. Their function is to store and release energy, and they mainly affect the cycle performance and other indicators of lithium batteries.
Anode materials can be divided into two main categories based on the active material used: carbon materials and non-carbon materials.
Carbon-based materials include two routes: graphite materials (natural graphite, artificial graphite, and mesophase carbon spheres) and other carbon-based materials (hard carbon, soft carbon, and graphene).
Non-carbon materials can be further divided into titanium-based materials, silicon-based materials, tin-based materials, nitrides, and metallic lithium, etc.
Unlike cathode materials, although there are many routes for lithium battery anode materials, the final product is very similar, with artificial graphite being the absolute mainstream. Data shows that in 2020, China's shipments of artificial graphite were approximately 307,000 tons, accounting for as much as 84% of the total anode material shipments, a further increase of 5.5% compared to 2019.
Compared to other materials, artificial graphite has good recycling performance, superior safety, mature technology, readily available raw materials, and low cost, making it an ideal choice.
The most critical issue with graphite anodes is that the theoretical upper limit of the energy density of graphite anode materials is 372 mAh/g, while the products of leading companies in the industry can already achieve an energy density of 365 mAh/g, which is close to the theoretical limit. The room for future improvement is extremely limited, and there is an urgent need to find the next generation of alternatives.
Among the new generation of anode materials, silicon-based anodes are popular candidates. They have extremely high energy density, with a theoretical capacity ratio of up to 4200 mAh/g, far exceeding that of graphite materials [14]. However, as an anode material, silicon also has serious defects. Lithium-ion insertion can lead to severe volume expansion, damage the battery structure, and cause a rapid decline in battery capacity.
One of the current common solutions is to use silicon-carbon composite materials. Silicon particles serve as the active material to provide lithium storage capacity, while carbon particles are used to buffer the volume change of the negative electrode during charging and discharging and improve the conductivity of the material, while preventing silicon particles from agglomerating during charge and discharge cycles.
Based on this, silicon-carbon anode materials are considered the most promising technological route and are gradually gaining attention from companies in the industry chain. Tesla's Model 3 has already used artificial graphite anode batteries doped with 10% silicon-based materials, and its energy density has successfully reached 300Wh/kg, significantly outperforming batteries using traditional technological routes.
However, compared to graphite anodes, silicon-carbon anodes face challenges not only from immature processing technology but also from higher costs. Currently, the market price of silicon-carbon anode materials exceeds 150,000 yuan per ton, twice that of high-end artificial graphite anode materials. In the future, once mass production begins, battery manufacturers will face similar cost control issues as they do with cathode materials.
