Effect of Doping on the Reuse of Recycled Positive Electrode Materials in Li-Ion Batteries

Summary:

The demand for lithium-ion battery applications in both consumer electronics and electric vehicles is increasing rapidly. This will lead to resource shortages and increases in the prices of several critical metal elements, such as lithium and cobalt, vital for the electrode production. In addition to issues concerning the demands for new applications, the growing market is facing challenges related to the waste management. While recycling processes exist, the field is not properly regulated, and a large part of the used Li-ion batteries end in landfills. This leads to the loss of valuable metals, and exposes the environment to hazardous chemicals, such as fluorine-containing electrolytes. To protect the environment and to answer the high demand for battery chemicals, recycling offers a logical way to introduce the used materials back to the material flow.
In the state-of-art battery recycling processes, Li-ion batteries are generally recycled without separating the different cell parts. The lack of separation at the start of recollection leads to mixing of the electrode materials with e.g. current collector and casing metals. This easily results in the recycled products containing metal impurities. Here, the effect of impurities on the recycling and reuse of materials are discussed. Co and Li are collected from the Li-ion battery waste, and the obtained Co precursor is observed to contain Cu as an impurity. LiCoO2 is synthesized of the obtained precursors and two LiCoO2s with different Cu concentration are obtained. The presence of impurity Cu is observed to decrease the initial capacity of the synthesized LiCoO2s but to improve both the rate capability and cycle life of the materials. Therefore, the role of Cu is concluded to be two-fold, producing both disadvantages and advantages.
To avoid the contamination of active materials by impurity metals, alternative recycling techniques for the state-of-art methods should be developed. To answer this demand, a new method to regenerate spent Li-ion battery positive electrode materials by electrochemical re-lithiation was developed and tested using non-doped reference LiCoO2 and Mg-Ti-doped LiCoO2 electrodes. The performance of the aged re-lithiated electrodes is observed to be similar to the fresh electrodes, the relithiated Mg-Ti-doped LiCoO2 performing notably better than the reference LiCoO2. This indicates that the initial performance of the material has a clear effect on how it behaves after regeneration. The aging mechanisms of the materials are observed to become more prominent during the second cycling, which lowers the cyclability of the regenerated materials slightly. However, the Mg-Ti doped LiCoO2 retains its stacking order better than the reference LiCoO2, which is concluded to explain the difference between the materials in addition to the degradation of the electrode additives. The slightly lowered performance of the re-lithiated electrodes would likely restrict their use in the most demanding applications, but they should be eligible for stationary energy storage in renewable energy production.