The Impact Of Al, Mg Or Mn-Mg Substitutions On The Structure, Electrochemistry And Thermal Stability Of LiCoO₂ And LiNi_1/3Mn_1/3Co_1/3O₂

Lithium-ion batteries (LIB) have been widely used in portable appliances such as cell phones, digital cameras and laptop, because they have high specific energy and long charge-discharge cycle life. Lithium-ion batteries are beginning to be used as power sources for electrified vehicles and for storing energy from renewable sources (e.g. wind and solar). Recent incidents involving battery-related computer or phone fires have focused attention on the safety of lithium ion batteries. The safety of lithium-ion batteries is central to their continued success in the market place and is one obstacle to their use in large-scale applications.LiCoO2-based Li-ion batteries are dominant in cell-phone and computer applications where the thermal instability of delithiated LiCoO2 in electrolyte can be managed due to the small size of the cells. Larger cells often incorporate less expensive and less reactive materials such as LiFePO4 or LiMn2O4 positive electrode materials. However these have smaller volumetric energy density than LiCoO2 and other common layered positive electrode materials. There has recently been research focusing on improving the thermal stability of layered positive electrode materials so they are more benign than LiMn2O4 at only a small penalty in energy density. Layered LiNi1/3Co1/3Mn1/3O2 (NMC) is iso-structural to LiCoO2 and it integrates the attractive features of LiCoO2 (good charge-discharge cycle life, high energy density), while being less expensive and much more thermally stable. Therefore NMC has attracted worldwide attention as an alternative to LiCoO2.The thesis presents studies of the impact of Al, Mg or Mn-Mg substitutions on the structure, electrochemistry and thermal stability of LiCoO2 and LiNi1/3Mn1/3Co1/3O2.Hydroxide precursors of Li[Co1-zAlz]O2 and Li[Co1-zMgz]O2 were synthesized by the co-precipitation method. No layered double hydroxide (LDH) phases were formed in the hydroxide precursor of Li[Co1-zMgz]O2, Co1-zMgz(OH)2, when divalent metal cations, Mg2+ were substituted for Co2+. By contrast an LDH phase appeared when trivalent metal cations, Al3+ partially substituted for Co2+ in the brucite-like layers of the hydroxide phase. The impact of Al substitution on structure of Co-Al hydroxides was studied in detail.Li[Co1-zAlz]O2 samples were prepared by co-precipitation and solid state methods. The samples prepared by co-precipitation were single phase over a wider range of Al content. The solid state method may not produce materials with a uniform cation distribution when the aluminum content is large.Thirty stoichiometric, lithium deficient and lithium excess (Lii-z)xMgz[Co1-zMgz]O2and Lix[Co1-zMgz]O2 samples with 0.9