Revealing the Relationships between Washing/Recalcination Processes and Structure Performance of Ni-Rich Layered Cathode Materials

Abstract

Ni-rich layered oxides are the most promising cathode materials for Li-ion batteries due to their high specific capacity and reasonable cost. Unfortunately, undesired residual Li compounds (RLCs) tend to form on the surface of Ni-rich materials, causing severe limitations to their commercialization. In this work, water washing and subsequent recalcination strategies were adopted to eliminate surface RLCs as well as guarantee the cycling stability of LiNi 0.83 Co 0.11 Mn 0.06 O 2 materials. The washing/recalcination processes not only induced the migration of Li + and the redox of Ni 2+ /Ni 3+ but also contributed to the variation of the specific surface area. Combined with the electrochemical properties, we found that these structure evolutions showed different impacts on the performance as the recalcination temperatures changed. Taking capacity and cycling stability into account, the optimal recalcination condition was selected. More importantly, the relationships between washing/recalcination processes and structure performance were established. This work reinforces the understanding of modified Ni-rich materials and motivates the development of advanced cathodes for batteries.

Microstructures of layered Ni-rich cathodes for lithium-ion batteries

“…Process optimization is necessary to achieve good cycle stability. 124–127 For example, prolonged exposure of NCA particles to water dissolves Al species besides the dissolution of Li residuals, which changes the surface structure and exacerbates their electrochemical performance. 128 While for an NCM particle, the surface Li + ions can exchange with protons in water via 122 Li + | NCM + H 2 O → H + | NCM + Li + + OH − Thus, the water pH gradually increases during the washing process.…”

Gradient and multilevel surface modification of Ni-rich layered cathodes by gas penetration for enhanced electrochemical performance

“…To offset the volatilization of lithium, excessive lithium salts were added during the high-temperature calcination process, resulting in extra lithium oxides (Li-O) on the surface of the Ni-rich material. 29 The Li-O tended to react with H 2 O and CO 2 in ambient air to form residual Li compounds (RLCs) composed of Li 2 CO 3 / LiOH. 30 In the subsequent phosphorization process, gaseous PH 3 which was generated from the decomposition of the upstream NaH 2 PO 2 reagent would downstream migrate with carrier N 2 gas and react with the NCM materials, and the surface RLCs gradually transferred to the Li 3 PO 4 coating.…”

Investigating Surface Reactivity of a Ni-Rich Cathode Material toward CO2, H2O, and O2 Using Ambient Pressure X-ray Photoelectron Spectroscopy

“…Investigating the surface chemistry and its reactivity is a crucial step, not only for understanding the mechanism of the degradation layer formation 12 but also for gaining insights into the subsequent development of water-based Ni-rich electrode processing. 13 In this work, we show how ultrahigh vacuum (UHV) storage can be used to remove the native carbonate species from the pristine NMC 811 surface. Furthermore, the interactions between NMC 811 and single gases CO 2 , H 2 O, and O 2 , as well as gas mixtures of CO 2 /O 2 and CO 2 /H 2 O/O 2 were followed by using ambient pressure photoelectron spectroscopy (APPES) to determine the surface reactions.…”

“…The chemical species present in the degradation layer are still not fully determined, and the reaction mechanisms leading to these products during exposure to CO 2 /H 2 O/O 2 have not been investigated with in situ measurements. Investigating the surface chemistry and its reactivity is a crucial step, not only for understanding the mechanism of the degradation layer formation but also for gaining insights into the subsequent development of water-based Ni-rich electrode processing …”