According to Dr Alex Holland, Principal Technology Analyst at IDTechEx, the next generation of silicon anode materials are inching closer to commercialisation as energy density and rate capability improves.

There are contenders for the crown currently held by graphite, which has good overall performance and which is low in cost. While graphite is predicted to maintain its dominance in the Li-ion industry, there is also lithium metal and anode-free materials to consider. Other options, such as niobium oxides, have also garnered some interest for fast-charging batteries.  

Graphite has been used in Li-ion anodes for the last 30 years and is expected to remain the most widely used anode material for the medium term. Li-ion graphite anodes will continue to grow and exceed 2m tonnes by 2029

The graphite used for Li-ion anodes are either natural or synthetic. Each has its own advantages and disadvantages, says Holland.

Natural graphite is generally a lower-cost option than synthetic. It can also offer a slightly higher initial capacity and also tends to have a lower cycle life, C-rate capability and initial coulombic efficiency. Synthetic graphite is more expensive due to the higher energy requirements for graphitisation, as well as being more difficult to mill into spherical particles. It also tends to offer longer cycle life and marginally higher initial coulombic efficiency.

There can be an overlap in the performance and cost of these two types of graphite, and the differences between them have also been closing, concedes Holland. Beyond just the type of graphite, various cell design factors such as cathode choice, electrolyte additives, coatings, particle size and distribution, electrode balance, as well as the specification and quality of the graphite product will have a significant impact on eventual cell performance, cost, and cycle life.

IDTechEx estimate that there is a roughly even split, by kt sales, between synthetic graphite and natural graphite but there has been a slight shift toward natural graphite over the past few years due to cost pressures and high energy prices.

The output of natural graphite has proven challenging. The US DoE and the European Commission have included natural graphite in their latest critical raw materials/minerals lists due in part to Li-ion batteries' important role in transport electrification and stationary storage applications. China's dominance of graphite anode production also presents a supply risk, though Li-ion graphite anode production outside of China is starting to develop from players such as Syrah Resources, Northern Graphite, and Nouveau Monde in North America, or Talga Resources, SGL Carbon and Vianode (synthetic) in Europe, amongst others.

In addition to diversifying material supply, improved sustainability and ESG metrics will be important factors for new graphite production. Lower energy consumption and embedded emissions will become increasingly important metric, particularly in Europe, with the European Battery Regulation set to implement carbon footprint labels and declarations for Li-ion batteries above 2 kWh in size. This may favour natural graphite and its lower energy consumption, though particulate emissions and acid waste streams from the purification process also need to be carefully managed. Lower cost and low carbon energy from renewable sources could help improve the competitiveness of synthetic graphite, though it will still be reliant on fossil feedstock.