Lithium nickel cobalt manganese oxide synthesized using alkali chloride flux: morphology and performance as a cathode material for lithium ion batteries
Yongseon Kim1,2*
1
SAMSUNG SDI CO., LTD, Yongin-si, Gyeonggi-do, 446-577, Korea
2
Department of Materials Science and Engineering, Seoul National University, Seoul, 151-742,
Korea
S.1. Determination of face indices: Particle morphology which frequently appeared in literatures or in our experiment is presented in the figure below. The relevant crystallographic facets were selected by simulating various possible layered structure growth morphologies using the Morphology tool embedded in the Material Studio simulation package (Accelys Software Inc.). The minimum surface energies for various LiNiO2 and LiCoO2 facet planes are presented together. The energy was smallest for the (0 0 3) facets, and it increased in the order of the (1 0 4), (1 -1 -1), (0 1 2) facets. This indicated that the surface which consists mainly of (0 0 3), (1 0 4), (1 -1 -1) facets and their equivalent planes under 3� m point
symmetry is the most stable for layer-structured LiTMO2. For each surface, various type of configurations such as Li-terminated, transition metal-terminated, O-terminated, or non-polar mixed layers are included in the calculation, and the minimum energy was selected as the surface energy.
S.2. Morphology and XRD of solid-state reaction products (without flux): Primary particle size of NCM811 could be increased with simple solid-state reaction by applying higher firing temperatures. However, the growth was not as dramatic as flux-growth, and severe agglomeration appeared. This requires additional pulverization process, which causes problems such as generation of unstable fracture surface or fine particles.
(NCM811 fired at 900oC without flux before and after pulverization)
For simple solid state reaction that does not use flux, the (0 0 3)/(1 0 4) ratio decreased and (0 1 8) and (1 1 0) peaks merged with increase of synthesis temperature. This is similar behavior to fluxgrowth as discussed in the Results and Discussion section of the manuscript.
(XRD patterns of NCM811synthesized without chloride flux at 800oC (a), 850oC (b), and 900oC (c))
S.3. Effect of primary particle size and surface coating on gas evolution during high temperature storage of charged NCM 523 electrodes: Increase of primary particle size reduced the amount of gas evolution. We added ~5% of excess Li2CO3 or increased heating temperature for growth of primary particles. Regardless of the methods, the gas amount turned out to be strongly related to the primary particle size. Surface coating with Al2O3 was also effective reducing gas. All these results support our interpretation that interfacial area between cathode material and electrolyte is a major factor for gas generation.
((a) NCM523 fired at 900oC, (b) fired at 950oC, (c) fired at 900oC with excess Li, and (d) NCM523 coated with Al2O3)
S.4. Charging/Discharging profile of commercial Si-SiO2 composite anode materials: The efficiency of commercial Si-SiO2 composite (usually called SiOx) is around 70%, far lower than conventional carbon based ones. Thus, this large irreversibility of Si-based anode should be compensated by large charging capacity of the cathode designing lithium ion batteries with efficient performance.
(Charging/discharging profile of commercial SiOx anode from different makers (0.05C rate).)
S.5. SEM image of commercial NCM: The secondary particles have spherical shape, which originates from spherical shape of the hydroxide precursors. The primary particles have isotropic shape and facet planes are not developed clearly.
