Abstract
Sub-micron sized LiNi0.8Co0.15Al0.05O2 cathode materials with improved electrochemical performance caused by the reduced cationic disordering in Li slab were synthesized through a solid state reaction routine. In a typical process, spherical precursor powder was prepared by spray drying of a uniform suspension obtained from the ball-milling of the mixture of the starting raw materials. Then the precursor powders were pressed into tablets under different pressures and crushed into powder. The pressing treated powders were finally calcinated under oxygen atmosphere to obtain the target cathode materials. XRD investigation revealed a hexagonal layered structure without impurity phase for all samples and significant increase in the diffraction intensity ratio of I(003)/I(104) was observed. Rietveld refinement further confirmed the reduced cationic disordering in Li slab by such pressing treatment, and the smallest disordering was observed for sample S4 with only 1.3% Ni ions on Li lattice position. The electrochemical testing showed an improvement in electrochemical behavior for those pressing treated samples. The calculation of diffusion coefficients using EIS data showed improved Li diffusion coefficient after pressing treatment. The sample S4 presented a diffusion coefficient of 4.36 × 10−11 cm2·s−1, which is almost 3.5 times the value of untreated sample.
Highlights
In the commercial synthesis process, since it is very difficult to oxidize Ni2+ into Ni3+, cationic disordering is observed for such layered cathode materials, leading to the formation of a lithium deficient cathode material (Li1−xNi2x+)(Ni2x+Ni13−+2x)O26–8. ing, which leads to the collapse
It was reported by the other groups that the intensity ratio can be regarded as an indicator of the ion mixing within the Li Slab, and a higher ratio of I(003)/I(104) represents a better degree of ordering in Li slab[6, 21]
A simple synthesis routine was presented to prepared submicron sized NCA cathode materials with improved electrochemical performance
Summary
In the commercial synthesis process, since it is very difficult to oxidize Ni2+ into Ni3+, cationic disordering is observed for such layered cathode materials, leading to the formation of a lithium deficient cathode material (Li1−xNi2x+)(Ni2x+Ni13−+2x)O26–8. ing, which leads to the collapse. In the commercial synthesis process, since it is very difficult to oxidize Ni2+ into Ni3+, cationic disordering is observed for such layered cathode materials, leading to the formation of a lithium deficient cathode material (Li1−xNi2x+)(Ni2x+Ni13−+2x)O26–8. The Ni2+ in the Li site will be oxidized to Ni3+ during of layered structure around Ni3+ ions since the radius the electrochemical chargof Ni3+ is smaller than that of Li+, further results in a huge polarization loss in the specific capacity. It is reported that the use of surface modification methods (LiCo29, 10, Al2O311, LiMnPO43, ZnO12, FeF313, TiO214,) can effectively solve the above-mentioned problems. There are few ways to solve above problems at the same time by optimizing the synthesis method. H19 et al reported a synthesis method with 5-sulfosalicylic acid as a chelating agent to solve the ion pollution. There are still some inherent shortcomings of such improved co-precipitation method, such as the complex synthesis process and the large amounts of waste water produced by the rinsing procedure
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