Characteristics and properties of nano-LiCoO2 synthesized by pre-organized single source precursors: Li-ion diffusivity, electrochemistry and biological assessment

Background: LiCoO2 is one of the most used cathode materials in Li-ion batteries. Its conventional synthesis requires high temperature (>800 degrees C) and long heating time (>24 h) to obtain the micronscale rhombohedral layered high-temperature phase of LiCoO2 ( HT-LCO). Nanoscale HT-LCO is of interest to improve the battery performance as the lithium (Li+) ion pathway is expected to be shorter in nanoparticles as compared to micron sized ones. Since batteries typically get recycled, the exposure to nanoparticles during this process needs to be evaluated. Results: Several new single source precursors containing lithium (Li+) and cobalt (Co2+) ions, based on alkoxides and aryloxides have been structurally characterized and were thermally transformed into nanoscale HT-LCO at 450 degrees C within few hours. The size of the nanoparticles depends on the precursor, determining the electrochemical performance. The Li-ion diffusion coefficients of our - LiCoO2 nanoparticles improved at least by a factor of 10 compared to commercial one, while showing good reversibility upon charging and discharging. The hazard of occupational exposure to nanoparticles during battery recycling was investigated with an in vitro multicellular lung model. Conclusions: Our heterobimetallic single source precursors allow to dramatically reduce the production temperature and time for HT-LCO. The obtained nanoparticles of LiCoO2 have faster kinetics for Li+ insertion/extraction compared to microparticles. Overall, nano-sized - LiCoO2 particles indicate a lower cytotoxic and (pro-)inflammogenic potential in vitro compared to their micron-sized counterparts. However, nanoparticles aggregate in air and behave partially like microparticles

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Additional file1: Text 1. Synthesis of bimetallic compounds. Table S1. Crystal data. Text 2. Single crystal structure descriptions. Text 3. Argentometric titration. Table S2. Idealistic oxidation reactions of two types of compounds, precursors 1, 5 with 2:1 and precursors 8, 9 with 1:1 stoichiometric ratio between Li+ and Co2+. Table S3. Results of the argentometric titration of chloride and ICP-measurements for lithium. Table S4. ICP analysis for Li+ and Co3+ of LiCoO2 obtained from different precursors. Figure S6. XRD study of commercial LCO, and nano-LCO obtained from LiOtBu before annealing and after annealing at 600°C and 700°C. Figure S7. XRD of LiCoO2 from 9-LiOPh calcined at 450°C before washing. The red line corresponds to HT-LCO and the blue lines are Li2CO3. Table S5. The combustion temperature and the thermal measurement conditions of the compounds 1, 8-12. Table S6. TGA weight loss in percentage [%] with associated steps of compounds 1, 8-12. Equation S1-S5. Determination of the particle and crystallite sizes. Figure S8. Morphologies of LiCoO2 prepared with different precursors at 450°C. Figure S9. (a) Cyclic voltammograms of the 15 nm LCO prepared from the compound 12 at different sweep rates. (b) The maximum anodic and cathodic current peaks of LiCoO2 electrode versus the square root of sweep rate. Table S7. Li+ diffusion coefficients determined for HT-LCO obtained from different precursors. Figure S10. Nyquist plot for LiCoO2 electrodes from LiOtBu with fit: filled markers – experimental points, open markers – fit points with error bars a) and corresponding equivalent circuit model b) with fitting report c). Figure S11. Nyquist plot obtained for LiCoO2 electrodes from LiOPh with fit: filled markers – experimental points, open markers – fit points with error bars a) and corresponding equivalent circuit model b) with fitting report c)