The Importance of Surface Oxygen for Lithiation and Morphology Evolution during Calcination of High‐Nickel NMC Cathodes

Abstract

both thermally and electrochemically. [2][3][4] Cathodes with high nickel content (y > 0.8) are also more difficult to synthesize, requiring oxygenrich calcination conditions, and are more prone to lithium/transition-metal siteexchange. [5][6][7][8][9] Thermal parameters play a critical role in the morphology of the final cathode, which strongly affects its rate performance and cyclability. Advanced understanding of the underlying chemistry during synthesis is necessary to enable Ni-rich cathodes to operate closer to their theoretical performance limits.Preparation of Ni-rich LiNi y Mn z Co 1−y−z O 2 cathode material is a two-stage process, first involving the co-precipitation of a Ni 0.8 Mn 0.1 Co 0.1 (OH) 2 species followed by calcination of the resultant precursor with a lithium salt, typically LiOH•H 2 O. Calcination, which requires prolonged times at temperatures up to 750-900 °C in pure oxygen condition for Ni-rich cathodes, is the most energy intensive step. [10] During this process, water is lost from Ni y Mn z Co 1−y−z (OH) 2 , and lithium and oxygen enter the structure forming the final LiNi y Mn z Co 1−y−z O 2 cathode. The details of this transformation are not fully understood. While both the hydroxide precursor and final LiNi y Mn z Co 1−y−z O 2 cathode share a layered structure, prior research has implicated an intermediate cubic structure resembling rock salt, [11] recently confirmed using in situ powder X-ray diffraction (XRD). [12,13] These phases share an oxygen sub-lattice, and so the mechanism has been ascribed to a topotactic transformation involving extensive cation ordering. [14,15] In addition, several competing processes occur at high temperatures, where cation mixing and particle growth have been shown to depend on calcination temperature and hold time. [16] The final cathode performance is closely tied to the morphology of the constituent particles. [17] LiNi 0.8 Mn 0.1 Co 0.1 O 2 often has a hierarchical structure consisting of large (≈10 μm) agglomerates of small (≈100 nm) single crystal primary particles. Secondary particle size is largely controlled by coprecipitation conditions, whereas primary particles are affected by thermal parameters during calcination.Smaller particles (<100 nm) result in higher rate capability, [18][19][20][21] attributed to increased surface area and shorter Nanoscale morphology has a direct impact on the performance of materials for electrochemical energy storage. Despite this importance, little is known about the evolution of primary particle morphology nor its effect on chemical pathways during synthesis. In this study, operando characterization is combined with atomic-scale and continuum simulations to clarify the relationship between morphology of cathode primary particles and their lithiation during calcination of LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC-811). This combined approach reveals a key role for surface oxygen adsorption in facilitating the lithiation reaction by promoting metal diffusion and oxidation, and simultaneously providing surface sites for ...

Designer Particle Morphology to Eliminate Local Strain Accumulation in High-Nickel Layered Cathode Materials

“…Regardless of the processing conditions, the secondary particles of all NCM90 cathode materials exhibit a spherical morphology with an average secondary particle size of ∼10 μm. The morphological changes in the DX-NCM90 cathode materials observed here agree with the recent literature, which suggests that increased oxygen surface coverage, such as high oxygen pressure here, leads to small primary particles due to slowed particle growth, and the details are shown in Supporting Information . As shown in Table S1, for the same equipment and temperature, the mole of oxygen is directly proportional to the pressure; e.g., the amount of oxygen at 5 MPa is almost 50 times that at an ambient oxygen atmosphere of ∼0.1 MPa.…”

“…DX-NCM90 (X ≥ 5) cathode materials, without doping or coating, show excellent electrochemical cycling performance, signifying the vital role of primary particle size and size distribution. Furthermore, compared to using doping or coating to modify the morphology of high-nickel layered cathode materials, which introduce an inevitable loss of capacity due to the introduction of electrochemically inactive materials, the DX-NCM90 (X ≥ 5) cathode materials engineered under high oxygen pressure show an excellent high and reversible capacity. ,− This study also provides a method based on deep learning for obtaining intercomparable information about primary particles (e.g., number per area, size, and standard deviation). In addition, improving the electrochemical performance of high-Ni cathodes without the need for foreign ions is particularly interesting amid the ever-increasing price of globally unevenly distributed or depleted dopant resources.…”

“…Interestingly, there is a limited investigation of oxygen involvement in the precursor’s lithiation, despite its critical role in developing the final lithiated high-nickel layered cathode materials. Recent XRD analysis and computational works revealed that high surface oxygen leads to smaller primary particles due to reduced particle growth energy . Despite the importance of the morphology to the electrochemical cycling performance, ,, the size information on the primary particles of high-nickel layered cathode materials is typically studied via scanning electron microscopy (SEM) or transmission electron microscopy (TEM).…”

Stability Enhancement and Microstructural Modification of Ni-Rich Cathodes via Halide Doping

“…A notable difference in the curves can be observed between 150 and 300 °C. PR and 5F display firm endothermic peaks at ∼260 °C, which can be attributed to the decomposition of transition-metal hydroxides to oxides and the subsequent generation of H 2 O vapor. , This conversion typically precedes lithiation, which occurs at or after the melting point of the lithium source (460 °C for pure LiOH), although some reports suggested that a solid-state lithiation of the oxide can occur at temperatures below the melting point . In the case of 5Br and 5Cl samples, the endothermic peak intensity is mostly suppressed, which suggests that simultaneous exothermic reaction(s) occur within this temperature range.…”

Targeted Adaptive Design

“…In real-world manufacturing applications the highly simplified model represented by the mapping X → Y from control space to design space can be clouded. For example, a product's desired design properties might require so-called ex situ measurements at facilities external to the manufacturing facilities [26], and this requirement can in- troduce long time latencies in the measurement of the experimental response function that vitiate the practical application of a direct TAD-based methodology. In such cases one can still envision a place for the TAD algorithm in the design workflow.…”