The Formation, Detriment and Solution of Residual Lithium Compounds on Ni-Rich Layered Oxides in Lithium-Ion Batteries

Abstract

Ni-rich layered transition-metal oxides with high specific capacity and energy density are regarded as one of the most promising cathode materials for next generation lithium-ion batteries. However, the notorious surface impurities and high air sensitivity of Ni-rich layered oxides remain great challenges for its large-scale application. In this respect, surface impurities are mainly derived from excessive Li addition to reduce the Li/Ni mixing degree and to compensate for the Li volatilization during sintering. Owing to the high sensitivity to moisture and CO2 in ambient air, the Ni-rich layered oxides are prone to form residual lithium compounds (e.g. LiOH and Li2CO3) on the surface, subsequently engendering the detrimental subsurface phase transformation. Consequently, Ni-rich layered oxides often have inferior storage and processing performance. More seriously, the residual lithium compounds increase the cell polarization, as well as aggravate battery swelling during long-term cycling. This review focuses on the origin and evolution of residual lithium compounds. Moreover, the negative effects of residual lithium compounds on storage performance, processing performance and electrochemical performance are discussed in detail. Finally, the feasible solutions and future prospects on how to reduce or even eliminate residual lithium compounds are proposed.

On the role of surface carbonate species in determining the cycling performance of all-solid-state batteries

“…To achieve high energy densities (>250 Wh kg −1 ) on a cell level, layered Ni-rich oxide cathode active materials (CAMs), such as LiNi 1−x−y Co x Mn y O 2 (referred to as NCM or NMC in the battery community), are commonly employed and currently represent a hot topic in cathode R&D [1,2]. However, it has been recognized both in academia and industry that surface residuals, primarily carbonate and hydroxide species, remaining from the synthesis (use of excess reagents) or formed during storage and handling, play a critical role on their processability and cyclability [3][4][5][6][7]. Especially the carbonate contaminants have been thoroughly studied in the past and shown to contribute to gas evolution via chemical (equation ( 1)) and/or electrochemical decomposition (equation ( 2)), which can lead to problems with battery performance and safety [4,[8][9][10]:…”

Oxygen Loss in Layered Oxide Cathodes for Li-Ion Batteries: Mechanisms, Effects, and Mitigation

“…Regardless of the accelerating effect of the high cutoff voltage on its formation, Li 2 O has been observed across NMC, LiCoO 2 , and LMR cathodes under various electrochemical conditions, including simple immersion of the layered oxide in electrolyte without cycling. The maximum Li 2 O is generated at the activation of the cathode and progressively transforms to Li 2 CO 3 , LiOH, or LiF compounds as the electrochemical cycling proceeds. , …”

Air/Water Stability Problems and Solutions for Lithium Batteries

“…This result suggests that Li 2 CO 3 tends to grow on the surface of Ni-rich cathodes (Figure 7(b)). Chemically active Ni 3+ tends to convert to Ni 2+ because this alleviates the local lattice distortion of the Ni-O octahedra, while also releasing some of the residual stress and reducing the system energy [81]. In addition, the highly reactive oxygen species will be accelerated with the reduction reaction of Ni 3+ [82].…”