Development and Characterization of Li(NixMnyCo1-x-y)O2 Layered Cathode Materials for Lithium Ion Batteries
Authors: Piskin Berke , Aydinol Mehmet Kadri 
Published: February 2020

Lithium ion batteries are now widely used especially in mobile applications as a power source. In the case of Li-ion batteries, certain properties such as energy density, cycle life, safety, electrical conductivity and rate capability have great importance. LiCoO2 has been used as a cathode material for Li-ion batteries for many years. However, capacity of the currently used layered LiCoO2 cathodes is limited to perform 50% of its theoretical capacity (140 mAh/g) [1]. In this regard, novel layered Li(Ni1/3Mn1/3Co1/3)O2 cathode materials have been investigated as an alternative cathodes searching for higher capacity, cycle life, rate capability and safety. Li(Ni1/3Mn1/3Co1/3)O2 cathodes exhibit higher capacity that of close to 200 mAh/g with enhanced safety [2]. This high capacity can be associated with the improved chemical stability. However, the rate capability is the most important deficiency which should be improved for new layered Li(Ni1/3Mn1/3Co1/3)O2cathode materials. Moreover, the electrochemical performance of cathode is strongly affected by powder properties such as morphology, surface area and composition. Therefore, spray pyrolysis method was used to obtain spherical fine-sized morphology followed by heat treatment will to obtain better electrochemical activity [3].

The precursor powders were prepared using aquaous solution via spray pyrolysis. Li(NixMnyCo1-x-y)O2 cathode material was produced by using solutions of lithium nitrate (LiNO3), nickel (II) nitrate hexahydrate (N2NiO6.6H2O), manganese (II) nitrate tetrahydrate (Mn (NO3).4H2O and cobalt (II) nitrate hexahydtare (Co(NO3)2.6H2O) with the mole ratio of 1:1/3:1/3:1/3, repectively. The total concentration of the solution is 0.5 M with additives of citric acid and ethylene glycol. Spray pyrolysis was used to obtain spherical fine-sized particles which then heat treated between 800⁰C - 1000⁰C. Different time-temperature combinations were tried and an undefined peak of new layered Li(Ni1/3Mn1/3Co1/3)O2 was observed which heat treated at 1000⁰C. Therefore, temperature range between 800⁰C and 900⁰C was chosen as heat treatment temperature. X-Ray Diffraction (XRD) pattern of obtained layered Li(Ni1/3Mn1/3Co1/3)O2cathode material showed good [006]/[102] and [108]/[110] doublets indicating layered structure and good hexagonal ordering as shown in Figure 1.

Figure 1. XRD spectrum of layered Li(Ni1/3Mn1/3Co1/3)O2cathode materials produced by using spray pyrolysis and then heat treated.

 Precursor concentration, droplet size, gas flow rate and temperature are the main parameters affecting the particle properties. Therefore, these parameters were optimized to obtain particles with spherical fine-sized and narrow size distribution. The morphology of Li(NixMnyCo1-x-y)O2 observed by scanning electron microscopy (SEM) and average particle size was between 0.4 and 0.6 μm, as shown in Figure 2. Li(NixMnyCo1-x-y)O2cathode materials will be investigated focusing on the improvement of capacity, cycle life and especially rate capability via doping elements. With proper cathode composition, experimental parameters, electrode design and doping elements, improved electrochemical properties was achieved. 

Figure 2. SEM images of studied layered Li(Ni1/3Mn1/3Co1/3)O2 cathode materials produced by using spray pyrolysis and then heat treated.

Figure 1