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Increased generation of spent lithium-ion batteries (LIBs) has driven the exploration of new methods for reusing and/or recycling LiCoO2 cathode materials. Herein, an electrochemical relithiation method was proposed to directly regenerate LiCoO2 cathode materials using the waste Li x CoO2 electrode as a base. It was shown that Li+ was successfully inserted into the waste Li x CoO2 electrode, and this relithiation process became faster with either a higher Li2SO4 concentration or a higher cathodic current density. The XRD analysis confirmed that the peak positions of the relithiation products were consistently close to those of a standard LiCoO2 material. The crystal structure of the relithiation products was restored with a post-annealing process. The activation energy for electrochemical relithiation (E a) was estimated at 22 kJ mol–1, and the constant of equilibrium constant k 0 was determined as 1.35 × 10–6 cm s–1. The relithiation process was controlled by the charge transfer process when the Li2SO4 concentration was high (e.g., 1, 0.8, and 0.5M), and a lower concentration at 0.01–0.3 M led to a diffusion control pattern. The electrode made of the regenerated LiCoO2 materials had a charge capacity of 136 mAh g–1, close to that of the commercial LiCoO2 electrode (140 mAh g–1). A potential mechanism of electrochemical relithiation was proposed involving lithium defects, relithiation, and crystal regeneration.

Many countries have gained benefits through the solar cells industry due to its high efficiency and nonpolluting power generation associated with solar energy. Accordingly, the market of solar cell modules is expanding rapidly in recent decade. However, how to environmentally friendly and effectively recycle waste solar cell modules is seldom concerned. Based on nitrogen pyrolysis and vacuum decomposition, this work can successfully recycle useful organic components, glass, and gallium from solar cell modules. The results were summarized as follows: (i) nitrogen pyrolysis process can effectively decompose plastic. Organic conversion rate approached 100% in the condition of 773 K, 30 min, and 0.5 L/min N2 flow rate. But, it should be noted that pyrolysis temperature should not exceed 773 K, and harmful products would be increased with the increasing of temperature, such as benzene and its derivatives by GC-MS measurement; (ii) separation principle, products analysis, and optimization of vacuum decomposition were discussed. Gallium can be well recycled under temperature of 1123 K, system pressure of 1 Pa and reaction time of 40 min. This technology is quite significant in accordance with the "Reduce, Reuse, and Recycle Principle" for solid waste, and provides an opportunity for sustainable development of photovoltaic industry.