In the last ten years, the focus of scientific and industrial development in lithium-ion batteries has been on increasing energy density while reducing costs. With the increasing success of electromobility and the mass production of batteries, the end-of-life discussion (recycling) is now also becoming a priority. This discussion is driven by legal regulations that require a recycling rate of up to 80% for the scrapping of (electric) cars, depending on the respective region or country. The development of recycling technologiest that recovers raw materials in used batteries as completely as possible can lead decisively to a sustainable supply of raw materials and significantly reduce the material and energy requirements for new cells.
The materials used in the lithium-ion battery are far too valuable not to be recycled. Although they do not contain any precious metals. It is the sheer amount of non-ferrous metals (copper, nickel and cobalt), aluminum and lithium in batteries that makes recycling lucrative: for example, one ton of nickel-containing rock from a nickel mine contains only about 20 kg of nickel. In contrast, the battery in a Tesla Model 3 contains 60 kg of nickel. With a total battery weight of 500 kg, this is five times the enrichment of that metal compared to the mine. For lithium, this factor is even higher: 6 kg of lithium in a battery means that successful recycling saves the processing of several thousand cubic metres of salt solution containing lithium.
At present, the few lithium-ion batteries that are recycled are sent to existing plants to recover their non-ferrous metals. During this process, a large portion of the non-ferrous metals such as cobalt, nickel or copper can be recovered, while the lithium is lost in the slag. Since the situation is not satisfactory and the lithium especially needs to be recycled, alternative scenarios have been devised and a number of processes have been pre-developed in recent years. The now most intensively researched process is as follows: the batteries are collected decentrally, deep discharged and then semi-automatically dismantled into modules and cells. Housing components and cables can already be collected separately. The cells are then mechanically crushed in a nitrogen atmosphere and the separator, copper and aluminium foils are separated using an air separation processes. What remains is a so-called “black powder”, that is a mixture of cathode and anode material as well as electrolyte. The electrolyte can be removed by vacuum treatment at a higher temperature. The dry black powder is then processed further using a wet chemical process. It is first dissolved in sulphuric acid and then the metals are individually fractionated. Recycling rates of > 85% can already be achieved for nickel and cobalt, while this value is currently closer to 70% for lithium. One problem is that traces of fluorine enter the cell via the lithium-containing conducting salt and various binders during battery construction. Fluorine and fluorine-containing compounds are difficult to eliminate during the recycling process and remain through all process stages, affecting the purity of the metals being recovered. In the RecycleBatt project, funded by the Baden-Württemberg Ministry of Economic Affairs, ZSW is trying to evaluate a different recycling route whereby the anode and cathode materials are recovered directly from the black powder to then be directly reused in less demanding batteries such as those used for stationary electricity storage.