Single-crystal LiNi1–x–y Co x Mn y O2 cathode materials can effectively suppress intergranular cracks that usually is seen in commercial polycrystal LiNi1–x–y Co x Mn y O2 cathode materials. However, the surface structure degradation for single-crystal LiNi1–x–y Co x Mn y O2 cathode materials is still aggravated at a higher cutoff voltage (over 4.5 V). In this work, we prepare single-crystal LiNi0.6Co0.2Mn0.2O2 cathode materials via a solid-state method and then coat an ultrathin Li–Si–O layer on their surface by a wet coating method. The results show that the single-crystal LiNi0.6Co0.2Mn0.2O2 cathode materials with a Li–Si–O coating layer deliver excellent cycling performance even at a higher cutoff voltage of 4.5 V. The optimized Li–Si–O-modified sample displays a capacity retention of 90.6% after 100 cycles, whereas only 68.0% for unmodified single-crystal LiNi0.6Co0.2Mn0.2O2. Further analysis of the cycled electrodes reveals that the surface structure degradation is the main reason for the decrease of electrochemical performance of single-crystal LiNi0.6Co0.2Mn0.2O2 at a high voltage (4.5 V). In contrast, with Li–Si–O coating, this phenomenon can be suppressed effectively to maintain interfacial stability and prolong the cycling life.

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Ni-rich ternary layered oxide materials have become the preferred cathode materials for lithium-ion batteries due to their high specific discharge capacity and low price. However, the hierarchical structure of the...

Herein, the physical properties (structure, morphology, lattice strain, specific surface area, particle size, and compaction density) of polycrystal LiNi 0.6 Co 0.2 Mn 0.2 O 2 (PC622) and single-crystal LiNi 0.6 Co 0.2 Mn 0.2 O 2 (SC622) materials have been comparatively investigated. We have also investigated the electrochemical performance of PC622 and SC622 electrodes with different compaction densities. The results show that secondary particle collapse is widely observed in highly compacted PC622 electrodes. Moreover, the improvement in compaction density is beneficial for specific capacity and initial Coulombic efficiency. SC622 exhibits good cycling performance at room temperature (25 °C) and an elevated temperature (55 °C) even when the density increases to 3.52 g cm −3 . The capacity retention values of SC622 are 86.0% (150 cycles, 1C, 25 °C) and 94.1% (100 cycles, 1C, 55 °C), which are significantly higher than PC622 (78.7 and 75.7%, respectively). Further studies via TEM on these electrodes with high compaction densities show that a thinner rock-salt phase region is found on the surface of the SC622 particles. Hence, SC622 maintains crystallite integration, excellent cycling performance, and thermal stability and can easily be manufactured into high compaction density electrodes. KEYWORDS: polycrystal LiNi 0.6 Co 0.2 Mn 0.2 O 2 , single-crystal LiNi 0.6 Co 0.2 Mn 0.2 O 2 , micro/lattice strains, high compacted density, structural stability, particle crack/cleave

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The development of single-crystal nickel-rich layered LiNi x Co y Mn 1−x−y O 2 materials (S-NCMs) represents the most significant progress for the electrification applications of nickel-rich ternary materials. There has been prior research on the important role of transition metal elements in agglomerated materials, supplemented by surface and internal lattice optimization to drive the performance improvements. However, studies on S-NCMs, especially on the role of transition metals (TM, i.e., Co and Mn), have not been reported. In this study, we synthesized four kinds of S-NCMs with different Co/Mn contents and studied their structural, electrochemical, kinetic, and thermodynamic properties with different Co/Mn contents. The results were as follows: (1) Electrochemically, Co was more effective than Mn at 25 °C at enhancing the intercalation/deintercalation kinetics, which resulted in an increased discharge capacity, an improved rate capability, and a reduced energy loss. (2) Thermodynamically, Mn was more effective at maintaining a higher thermal stability than Co, especially at a low cutoff voltage, but at a high cutoff voltage, the difference between the action of Co and Mn decreased. The main finding of this work was the enhanced structural stability provided by Co, which could be attributed to the following: (i) the absence of the H2/H3 phase transformation when Co exceeded 15%, which inhibited the irreversible phase transformation and reduced the volume strain, and (ii) the lower degrees of decrease in the cell parameters a and c with higher contents of Co, which contributed to a low cracking degree along the (003) crystal plane. The current work provides an important reference for the single-crystallization strategy of nickel-rich materials.

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