In April 2024, an announcement from the Chinese electric battery manufacturer CATL shakes the automotive world. It promises a battery that would provide 1,000 km of autonomy to vehicles and recharge by 60% in ten minutes!
The Shenxing Plus, that’s its name, promises unprecedented performance for a lithium-ion battery. Is this really possible? To answer this question, you must first understand how this type of accumulator works. A lithium-ion battery relies on moving lithium ions through a liquid electrolyte. During discharge, ions go from the negative electrode, the anode, to the positive electrode, the cathode, and vice versa for charging. The faster the ion transfer, the shorter the battery charge time. The particularity of these batteries lies in the intercalation of lithium in the electrode materials, that is to say their capacity to retain charged ions: “It’s as if these materials were sponges; their crystalline structures welcome or release lithium ions” explains Patrice Simon, professor at Toulouse III-Paul Sabatier University. The energy capacity of the battery, and therefore the autonomy, is linked to the quantity of lithium stored in the electrode materials.
For the anodes, lithium ions are intercalated between sheets of carbon (often graphite). For the cathode, the choice is wider. In the first batteries, cobalt oxide was used, but the financial and environmental cost of extracting this metal is pushing manufacturers to reduce its presence. It is therefore replaced, in a certain proportion, by nickel and aluminum, which gives the Li-NCA battery (nickel, cobalt, aluminum). Advantage, it is less expensive and has a high energy density; disadvantage, it presents thermal instability. At the same time, manufacturers are developing the Li-NMC (nickel, manganese, cobalt) battery which today equips Tesla and Stellantis automobiles (PSA, Fiat, Chrysler Automobiles). Manufacturers are actively researching combinations of materials for these cathodes to the extent that they represent around 40% of the price of the battery, and still pose environmental problems.
Sometimes the best soups are made in old pots. “In 1997”, says Michel Armand (CNRS), pioneer in the research of Li-ion batteries, “I received by e-mail the presentation planned by John Goodenough* for the next conference of the Electro-mical Society. This is a lithium, iron, phosphate (LFP) cathode. According to him, its conductivity is too poor to equip Li-ion batteries, but its crystalline structure offers never before equaled storage stability, and above all there is no nickel or cobalt! When I read that, my blood boiled and I took the first flight to meet him. ” Michel Armand is working on increasing the diffusion of electrons by depositing a thin layer of carbon on the elementary grains of the electrodes. By combining his research with the structure imagined by John Goodenough, the LFP cathode was created. Its stable structure increases safety while reducing manufacturing costs. “Less efficient initially than the NCA and NMC cathodes, manufacturers did not bet on it… except the Chinese”, adds Michel Armand.
However, it is precisely the LFP cathode which today equips the Shenxing Plus battery.
CATL announces that it has succeeded in optimizing lithium storage thanks to a technology called “granular gradation technology” and by developing a “3D honeycomb” anode. For Michel Armand, it is perhaps a strategic error on the part of European and American manufacturers not to have invested in the LFP. But the tide is turning: Renault management has just announced that certain cars, such as the Renault 5, will be equipped with Li-LFP. As for the announcement on the Shenxing Plus, no one in the industry is commenting, suggesting that the sector remains doubtful about the announced performance.
The lithium-ion battery will definitely dominate the 21st century and beyond
Liquid or solid electrolyte?
For Patrice Simon, “Lithium-ion batteries in conventional technologies are reaching an apex; if we push all the sliders – materials and energy management – we can hope to reach 600 km or 700 km of autonomy, but it is difficult to imagine going beyond that”. Or, “it would be necessary to change the liquid electrolyte into a solid. We can thus use a metallic lithium anode and increase the energy density of the batteries by ten: this is the all-solid-state battery” explains Professor Trang Phan of Aix-Marseille University. This chemist is developing a solid electrolyte composed of two polymers. “There are other avenues, such as the use of ceramic electrolytes, but for me, the polymer avenue is the most successful,” she adds.
Global research into all-solids is booming. China launched the Casip (China All-Solid State Battery Collaborative Innovation Platform) program, with a budget of $828 million. At the European level, “each country wants to play its own card, but it is difficult to win if we do not work together with real government will and involved industrialists”says Jean-Marie Tarascon, CNRS gold medalist researcher, creator of the network on electrochemical energy storage (RS2E).
In the all-solid state, there is also the sodium-ion battery. Sodium, like lithium, easily donates an electron, which makes it a good candidate and it is more virtuous than lithium. “Sodium-ion batteries will not be able to match the energy capacity of lithium batteries, but they are perfect for autonomous or shared cars in urban centers,” says Jean-Marie Tarascon.
These batteries fitted Autolib [des voitures partagées développées par Blue Solutions, NDLR]. However, to work, the polymer electrolyte had to be heated to 70°C. The ideal would therefore be to develop an electrolyte operating at room temperature. This is the objective of the start-up Tiamat, resulting from CNRS research; a gigafactory should open in France in 2025. This sodium-ion battery, combining power and eco-compatibility, has a bright future, but Jean-Marie Tarascon knows it: “ It will position itself as a complement to the lithium-ion battery, which will definitely dominate the 21st century and even beyond.”
* American physicist, Nobel Prize in Chemistry in 2019 with the British Stanley Whittingham and the Japanese Akira Yoshino for their contributions to the lithium-ion battery.
