Synthesis Of LiNi_0.8Co_0.1Mn_0.1O₂ And LiFePO₄ Lithium Ion Cathode Material From Laterite

The development of laterite metallurgy, Li-ion batteries and cathode materials are reviewed in detail. The thesis presents new synthesis routes of LiFePO4 and LiNi0.8Co0.1Mn0.1O2 from laterite, and studies of impact of metal substitutions on LiFePO4 and LiNi0.8Co0.1Mn0.1O2.Fe, The major impurity element of laterite, was successfully removed as metal substitution FePO4·xH2O precursors, via H3PO4 co-precipitation from laterite lixivium. Experimental results show that no Fe exist in filtrate, and the recovery rate of Ni, Co and Mn in filtrate is 88.83%,92.66% and 93.48%, respectively, the dopant contents in FePO4·xH2O are close to 2 mol%. The Ni, Co and Mn in filtrate were further extracted by NaS co-precipitation. The Ni, Co and Mn contents in precipitate, under optimal conditions, is 33.79%,0.95% and 5.28%, respectively, which is about 34,15 and 21 times than that of raw ore, and the total recovery rate of Ni, Co and Mn in precipitate is 80.27%,45.6% and 54.5%, respectively.LiFePO4 samples were directly synthesized from the FePO4·xH2O precursors, which were attained from laterite lixiviums with different HCl/ore rates. ICP analysis confirms that all samples own Al, Mg, Cr and Ni dopant, and with the HCl/ore rate increase, the dopant contents increase. LiFePO4 particles are wrapped by carbon, the distribution of all elements is homogeneous, but Cr prefers existing on the surface of particle. Rietveld refinement results show that, with the dopant contents increase, Li+ vacancies increase. Electrochemical studies confirm that the LiFePO4 samples prepared from laterite are better than the pristine LiFePO4, which exhibits 139.6 mAh·g-1 initial discharge capacity at 1C rate, and retains almost 100% cycle efficiency after 100 cycles.Ni0.8Co0.1Mn0.1(OH)2 precursors are successfully synthesized by fast co-precipitation method. TEM, Electron Diffraction and XRD results show that sample synthesized with 1 min is nanocrystalline materials, which owns well particle distribution, and 70 nm size. LiNi0.8Co0.1Mn0.1O2materials are attained from the precursors and lithium salts, which exhibits 192.4 mAh g-1 initial discharge capacity at 0.1 C rate, and retains 91.56% cycle efficiency after 40 cycles. CV results show that the reversibility of Li+ insertion/desertion process is good.The impacts of laterite impurities, Cr, Mg, Al, Ca and Fe substitutions, and Cr-Mg co-substitution on LiNio.8Co0.1Mn0.1O2 material have been systematically studied. The results show that Fe, Ca and Al could destroy material structure. Mg substitution could inhibit the Li/Ni mixing degree, improve initial coulombic efficiency, but Mg substitution could also lead to capacity loss.Cr substitution is beneficial to LiNi0.8Co0.1Mn0.1O2. Electrochemical studies confirm that with Cr contents increase, the discharge capacity increase at first, and slow down later. It is noted that the sample with 0.01 Cr content owns the best electrochemical performance, which exhibits 152.8 mAh·g-1 at IOC.XRD, Rietveld refine, XPS and Thermo Avantage fitting results revealed the mechanisms of Cr substitution:First of all, Cr tends to occupy metal layer, and suitable Cr substitution could decrease the Li/Ni mixing degree; secondly, Cr owns electrochemical activity; thirdly, due to Cr prefers existing in the surface of particle, Cr substitution could decrease the Ni3+ contents in surface, and inhibits the erosion by electrolyte, besides, Cr substitution could also increase the Mn3+ contents, which is harmful to material structure, therefore, Cr substitution cannot be excessive. CV analyses show that the sample with 0.01 Cr content owns the most stable structure and best reaction reversibility. EIS results show that after 50 cycles, the reaction impedance of Cr substitution sample is smaller than that of pristine sample, which means its particle surface suffer less erosion by electrolyte.The impact of Cr-Mg co-substitution on LiNi0.8Co0.1Mn0.1O2 material has also been studied. Experimental results reveal that, Cr-Mg co-substitution owns a kind of synergistic reaction, and inherits the advantage of both Cr substitutiton and Mg substitution, which could decrease the Li/Ni mixing degree, and improve electrochemical performance.LiNi0.8Co0.1Mn0.1O2 material was synthesized from laterite ore concentrate. First, lixivium was attained from laterite ore concentrate by atmospheric HCl acid leaching. Second, H3PO4 was added to the attained laterite lixivium to remove Fe, and filtrate was attained. Third, NaF was added to the filtrate to remove Ca, Mg and partial Cr, and laterite clean fluid was attained. Fourth, LiNi0.7756Co0.101Mn0.1M0.023402 (M is Cr, Mg, Al and Ca), which is called as ore sample, was synthesized from the attained laterite clean fluid, via fast co-preicpitation. TEM and EDS results show that the dopants M are totally incorporated into LiNi0.8Co0.1Mn0.102 crystal, and Cr is enriched in the surface layer of particles. Rietveld refine show that the Li/Ni mixing of ore sample is smaller, Mg occupy 3a site, and Cr occupy 3b site. XPS results find that the ionic valence state of ore sample is similar to that of LiNio.79Co0.1Mn0.1Cr0.01O2, which is conducive to inhibit the erosion by electrolyte. Electrochemical studies confirm that, although the initial discharge capacity of ore sample is 186.9 mAh·g-1, less than that of the pristine sample 192.4 mAh·g-1, ore sample exhibits better initial coulombic efficiency, rate performance and cycle ability.