![]() Combined with a suite of state-of-art synchrotron techniques and theoretical approaches, we demonstrate a thermal-healing of lattice defects in single-crystalline cathodes caused by the thermal-induced release of lattice strain and the structured ordering, which contribute to the capacity restoration. Herein, we formulate a mild thermal treatment method (annealing at 150 ☌ for a few hours) to address the afore-discussed challenges in defect and strain modulation for single-crystalline NMC cathodes. These battery materials feature a high degree of complexity in their responses to the temperature 22, 23. At a high temperature, the molten salt reactions have been explored for recycling retired battery cathode materials. At a moderately elevated temperature, detrimental effects, such as oxygen release and Li extrusion, have been reported in charged NMC cathodes 20, 21. For example, to address the sluggish lithium diffusivity at low temperatures, a battery temperature management system is often implemented for preheating the battery before operating it in extreme climates 19. Tuning the battery material properties via controlling the temperature is a viable approach, and has been demonstrated in several different application scenarios. However, the localized stresses that are closely correlated with the microcrack propagation are pervasive in single-crystalline NMC, which entails further efforts to develop a more practical and effective strategy for addressing the origin of the fatigue damage. It has been reported that reducing the crystal size to below a critical threshold at ~3.5 μm could mitigate the catastrophic reactions that damage the integrity of the single crystals 18. Although the intergranular fracturing along grain boundaries is eliminated, the intragranular fracturing caused by the accumulated stresses remains intractable, yet, it still needs to be fine-tuned. This approach eliminates the internal grain boundaries and enables significantly improved cycle performance over the traditional polycrystalline NMC 14, 16, 17. These undesired side reactions are more aggressive in the Ni-rich cathode than in the well-explored NMC compounds with lower Ni contents, e.g., LiNi 1/3Mn 1/3Co 1/3O 2 12, 13, 14, 15.Ī direct and feasible strategy for eliminating the grain-boundary fracturing and for stabilizing the Ni-rich NMC is by using micro-sized single-crystalline particles. These cracks create more solid-liquid interfaces that aggravate unwanted side reactions and further exacerbate structural degradation and performance decay. ![]() The anisotropic lattice breathing during the repeated cycling of the energy devices leads to an accumulation of lattice strain and defects, which could be released via particle cracking, to the detriment of the composite cathode electrode’s multiscale structural integrity. These polycrystalline NMC materials, however, have abundant grain boundaries and, consequently, suffer from the broadly observed structure degradations, e.g., intergranular and intragranular cracks 6, 7, inhomogeneous mechanical strain 8, 9, local phase transformation and segregation 10, 11. For example, the shortened diffusion length is advantageous to lithium transport and the close packing of the primary grains is beneficial to the energy density. There are practical incentives for adopting such a polycrystalline NMC formation. Existing commercial NMC cathodes are predominately in the form of micron-sized secondary particles that are agglomerations of nano-sized primary grains 4, 5. Ni-rich NMC (LiNi xMn 圜o zO 2 x + y + z ≈ 1, x ≥ 0.6) with high capacity (>200 mAh g −1) has demonstrated great potential as a cathode material for high energy density LIBs 1, 2, 3. Sustainable and stable high-energy cathode materials are indispensable for the next-generation lithium-ion batteries (LIBs) for a broad range of applications, such as powering long-range electrical vehicles.
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