Latest SIB Anode Hard Carbon Research Update

Why Hard Carbon?

With the intensive production of Sodium-Ion Batteries in the future, the demand for SIB anode will become hot topic for new material selection.

The current commercial graphite anode materials for Lithium-Ion Batteries cannot be directly applied to SIB. The reason is that the radius of sodium ions is larger than that of lithium ions, while the interlayer spacing of graphite anode is narrower. It is impossible to embed enough sodium ions, resulting in extremely low battery capacity.

There are constant disputes in the industry regarding the application and selection o f materials. Finding a suitable sodium storage anode material is crucial.

Amorphous carbon is the mainstream solution for anode materials of sodium ion batteries at this stage. Excellent performance and relatively mature technology, the current mainstream manufacturers are in the technical path of amorphous carbon. The layout is composed of hard carbon anode as the main one and soft carbon anode as the auxiliary one.

Amorphous carbon includes hard carbon and soft carbon. Soft carbon can be converted into artificial graphite through high-temperature graphitization.

Hard carbon is difficult to graphitize. Hard carbon has better energy density and initial performance than soft carbon, while soft carbon has an advantage in terms of cost. In the past, amorphous carbon accounted for about 4% of all anode materials.

For example, the early electric bus market used a lot of soft carbon. As the sodium battery capability increased, amorphous carbon was used in the negative electrode.

Let's take a look at the players in hard carbon field, majority of them are based in Asia, while China and Japan stand out.

About the HC technical routes, it can be roughly divided into three technical routes: resin-based, asphalt-based, and bio-based. Most HC companies are following Kuraray way of Biomass based material, like using Coconut Shell as precursor.

Among them, resin-based hard carbon materials have reliable performance, meet consistency standards, and have relatively few impurities. The material cost is high, and the volatility during the processing leads to low carbon extraction efficiency. Large-scale commercial use requires effective cost control. Currently, the price of resin-based hard carbon negative electrode materials is generally around RMB 100,000 Yuan/ton or more. Famous anode manufacturers such as BYD and Shanshan have already made great progress in the resin-based hard carbon negative electrode path.

Asphalt-based hard carbon raw materials are widely available and inexpensive, with the price per ton dropping to as low as 20,000 Yuan/ton. But the initial performance and energy density of asphalt-based hard carbon is mostly just so so. The preparation process of carbon anode is relatively complicated, and few manufacturers are willing to delve into this path. After process optimization and performance improvement, it is expected to be applied to low-end battery products.

Hard carbon materials based on biomass as precursors have mature technology, superior performance, and high consistency. The precursors can be coconut shells, starch, wine lees and other carbon-containing biological materials. The disadvantage is that the cost is relatively high. The import to China price of Kuraray is 150,000-200,000 Yuan/ton, and the domestic hard carbon price range in 50,000-100,000 Yuan/ton according to the quality. The technology path initially chosen by Japan’s Kuraray, a leading company in the anode industry. The mainstream solutions in the market include both established new energy related companies such as BYD and DFD.

There are fewer paths available for soft carbon precursors, and coal-based materials are low-cost. Anthracite has a high carbon content and is an ideal coal-based hard carbon negative electrode material precursor. Shanghai Hanxing, Hua Na Xin Neng and other companies have reserves on this technical path. The price of Hanxing Technology's anthracite-based soft carbon negative electrode material is as low as 10,000-20,000 Yuan/ton. Although it is slightly inferior in performance, considering that the coal-based negative electrode material process is in its infancy, there is a lot of room for improvement in the future. The focus is on solving the quality control problems of different batches of anthracite and improving product consistency. It can be said that anthracite is also one of the possible development directions of future sodium battery anode precursors, suitable for application scenarios such as energy storage batteries.

One of the most famous soft carbon company in China is Hina, but due to its low consistency performance, Hina is using hard carbon for mass producing sodium cells, with upto 374mAh/g high reversible capacity.

Hard carbon structure compare with graphite is pretty different as "non-graphitizable carbon", which give wide space for the sodium ions to go in and out smoothly.

Some good HC product datasheet for reference.

Compared with lithium-ion graphite, the mechanism of sodium-ion hard carbon is more complicated, the engineering difficulty is greater, and the success rate of trial and error is relatively long.

SIB Anode material cost is currently the most potential one to bring down the full battery cost, we have to find a good precursor that is low cost, good energy and consistency, long term available with big quantity, less carbon footprint, to speed up the SIB commercialization. Let's find out together.

-Jerry Wan