Direct recovery of degraded LiCoO2 cathode material from spent lithium-ion batteries: Efficient impurity removal toward practical applications.

Regenerating cathode material from spent lithium-ion batteries (LIBs) permits an effective approach to resolve resource shortage and environmental pollution in the increasing battery industry. Directly renovating the spent cathode materials is a promising way, but it is still challenging to efficiently remove all of the complex impurities (such as binder, carbon black, graphite and current collectors) without destroying the material structure in the electrode. Herein, a facile strategy to directly remove these impurities and simultaneously repair the degraded LiCoO2 by a target healing method is reported. Specifically, by using an optimized molten salt system of LiOH-KOH (molar ratio of 3:7) where LiNO3 and O2 both serve as oxidants, the impurities can be completely removed, while the structure, composition and morphology of degraded LiCoO2 can be successfully repaired to commercial level based on a two-stage heating process (300 °C for 8 h and 500 °C for 16 h, respectively), resulting in a high recovery rate of approximately 100% for cathode material. More importantly, the regenerated LiCoO2 exhibits a high reversible capacity, good cycling stability and excellent rate capability, which are comparable with commercial LiCoO2. This work demonstrates an efficient approach to recycle and reuse advanced energy materials.

Identification of fouling mechanisms in MBRs at constant flowrate: model applications and SEM-EDX characterizations.

A fundamental understanding of fouling mechanisms is critical to improving filtration operations. The performance of four parallel membrane bioreactors (MBRs) with different sludge retention times (SRTs) was monitored during long-term constant flowrate filtration. The characteristics of the membrane and transmembrane pressure (TMP) profiles obtained were studied to demonstrate fouling mechanisms. Both classical blocking models and their combined models were evaluated. The intermediate model provided very good agreement with all the TMP data. However, the combined cake-intermediate and intermediate-standard models were more effective in the description of the experimental data. Contributions analysis indicated that the cake, intermediate and standard blocking models were the dominant fouling mechanisms. Scanning electron microscopy and energy dispersive X-ray (SEM-EDX) imaging showed that cake blocking by organic matter and standard blocking by inorganic matter made the main contributions to membrane fouling. The combined cake-intermediate and intermediate-standard models may be applicable to systems where these two models are consistent with the experimentally observed fouling mechanisms in an MBR.