The microstructure of LiNi0.8Co0.1Mn0.1O2 cathode materials was controlled by the addition of lithium silicate, and the influence on the cycle performance and the rate capability was investigated. Si was not included within the lattice, but localized at the grain boundaries of the primary particles and the pores inside the secondary particles. The addition of the lithium silicate greatly decreased the density of the pores between the primary particles and improved the density of the secondary particles. The capacity retention was successfully improved for lithium silicate-added LiNi0.8Co0.1Mn0.1O2. When lithium silicate-free LiNi0.8Co0.1Mn0.1O2 was charged to 4.3 V, many cracks were formed along the grain boundaries even in the first cycle, while crack formation was remarkably inhibited for lithium silicate-added LiNi0.8Co0.1Mn0.1O2. Moreover, lithium silicate-added LiNi0.8Co0.1Mn0.1O2 particles were almost free from visible microcracks even after 100 cycles at the discharged state. These results suggest that the lithium silicate reinforces the grain-adhesion at the grain boundaries, inhibiting crack formation and electrolyte decomposition inside the cracks.

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LiNi0.5Co0.2Mn0.3O2 (NCM) particles coated with lithium boron oxide were prepared by an antisolvent precipitation method. In the antisolvent precipitation method, ethanol was used to strip off the hydrated water coordinated with lithium ions and borate ions. By the antisolvent precipitation method, the NCM particles were coated with a uniform layer of LiBO2. The capacity fading on cycling was successfully suppressed for the lithium boron oxide‐coated samples. In addition, the rate capability was also improved by the coating. The lithium boron oxide coating effectively suppressed the increase of the electrode impedance associated with the electrolyte decomposition. Crack formation in the secondary particles after charge‐discharge cycling was greatly inhibited for lithium boron oxide‐coated NCM. It was demonstrated that the lithium boron oxide coating layer suppressed the side reactions not only on the particle surface, but also in the intergranular cracks by inhibiting the penetration of the electrolyte solution.

Lithium silicate was incorporated within Ni0.5Co0.2Mn0.3(OH)2 precursor particles via an anti-solvent precipitation method to prepare lithium silicate-added LiNi0.5Co0.2Mn0.3O2 (NCM) particles. Lithium silicate was found at the grain boundaries in the NCM secondary particles, which significantly improved the capacity retention in high voltage operation (3.0–4.6 V). Cross-sectional SEM images revealed that cracks were seriously formed inside the lithium silicate-free NCM particles after cycling, while crack formation was remarkably inhibited for lithium silicate-added NCM. These results suggested that lithium silicate at the grain boundaries strengthened the interfacial-adhesion between primary particles, resulting in the improved cycling stability.

It is known that the deterioration of LiNi 0.5 Co 0.2 Mn 0.3 O 2 is suppressed by inhibiting direct contact between the cathodes and the electrolyte by surface coating. In order to evaluate the influence of the electrode/electrolyte interface degradation, it is necessary to eliminate the influence of particle cracking. In this study, LiNi 0.5 Co 0.2-Mn 0.3 O 2 particles with a small size (500 nm to 1 µm) without crack formation after charge-discharge cycling were synthesized by a spray pyrolysis method. Hard X-ray photoelectron spectroscopy was used to investigate the structural changes of the cathode. It was revealed that the cathode coated with lithium boron oxide (LBO) by an antisolvent precipitation method had high durability against the surface structure changes by the reduction of transition metal ions. The formation and dissolution of NiO occurred in the uncoated sample during cycling, but the formation of NiO was suppressed in the LBO-coated sample. It was considered that the structural changes of the active material surface during cycling led to an increase in surface resistance of the uncoated sample, which is the main reason for the capacity fading of the spray pyrolyzed LiNi 0.5 Co 0.2 Mn 0.3 O 2 cathode particles.