Computational Screening for Design of Optimal Coating Materials to Suppress Gas Evolution in Li-Ion Battery Cathodes

Abstract

Ni-rich layered oxides are attractive materials owing to their potentially high capacity for cathode applications. However, when used as cathodes in Li-ion batteries, they contain a large amount of Li residues, which degrade the electrochemical properties because they are the source of gas generation inside the battery. Here, we propose a computational approach to designing optimal coating materials that prevent gas evolution by removing residual Li from the surface of the battery cathode. To discover promising coating materials, the reactions of 16 metal phosphates (MPs) and 45 metal oxides (MOs) with the Li residues, LiOH, and LiCO are examined within a thermodynamic framework. A materials database is constructed according to density functional theory using a hybrid functional, and the reaction products are obtained according to the phases in thermodynamic equilibrium in the phase diagram. In addition, the gravimetric efficiency is calculated to identify coating materials that can eliminate Li residues with a minimal weight of the coating material. Overall, more MP and MO materials react with LiOH than with LiCO. Specifically, MPs exhibit better reactivity to both Li residues, whereas MOs react more with LiOH. The reaction products, such as Li-containing phosphates or oxides, are also obtained to identify the phases on the surface of a cathode after coating. On the basis of the Pareto-front analysis, PO could be an optimal material for the reaction with both Li residuals. Finally, the reactivity of the coating materials containing 3d/4d transition metal elements is better than that of materials containing other types of elements.

Challenges and Strategies to Advance High‐Energy Nickel‐Rich Layered Lithium Transition Metal Oxide Cathodes for Harsh Operation

“…have proposed a computational approach to design optimal coating materials that can prevent the gas evolution of Ni‐rich cathodes by removing surface residual Li. [ 49 ] They have systematically compared the reactivity of 16 metal phosphates and 45 metal oxides with different Li residues such as Li 2 CO 3 and LiOH, and found that the reactivity of the coating materials containing 3d/4d transition metal elements is better than that of materials containing other types of elements. This study has established a selection rule for future coating materials to suppress gas evolution of Ni‐rich cathodes.…”

Surface/Interface Structure Degradation of Ni‐Rich Layered Oxide Cathodes toward Lithium‐Ion Batteries: Fundamental Mechanisms and Remedying Strategies

“…ii) The dissolution of TM ions and organic electrolyte decomposition starting from the electrode/electrolyte interface are engendered by the highly oxidized Ni 4+ ions during charge–discharge process, which is highly intensified due to the emergence of microcracks resulting from the anisotropic contraction and expansion . iii) The overcharged cathodes are susceptible to thermal decomposition, thus breaking down the TM‐O bonds and releasing oxygen from the host lattice . These detrimental cases preferentially take place at the surface/interface of highly delithiated electrodes.…”

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

“…In this respect, surface coating is one of the most widely used methods in laboratory investigation. Generally, surface coating layers can not only enhance the air-storage stability of Ni-rich cathode materials, but also protect Ni-rich cathode materials from HF corrosion and detrimental side [Min et al, 2017] with permission from American Chemical Society. (B) Schematic diagrams of the working mechanism of CNT& Li 3 PO 4 coating layer and cycling stability of CNT& Li 3 PO 4 coated sample compared to pristine and (C and D) SEM images of the CNT& Li 3 PO 4 coated sample.…”

“…Moreover, the coating layers can be formed in-situ on the surface of Ni-rich cathode materials via chemical reactions between coating media and residual lithium compounds, which could eliminate surface impurities as well as form a functional film on the surface. For example, H 3 PO 4 (Jo et al, 2014a;Min et al, 2017;Yang et al, 2019c), an acidic coating media, can react with the residual lithium compounds, such as LiOH and Li 2 CO 3 to form a Li 3 PO 4 coating layer, which has been verified to effectively enhance the surface stability of Ni-rich cathode materials. Due to the reduced surface insulating impurities and high ionic conductivity of newly generated Li 3 PO 4 , the capacity retention and rate capability of Li 3 PO 4 -coated NCM622 are greatly improved (Jo et al, 2014a).…”

“…Another issue is that due to the intrinsic insulation of surface impurities, the Li + diffusion is seriously restricted, leading to the increased cell polarization and inferior cycling performance (Chen et al, 2019;Wang et al, 2019). Moreover, the electrochemical decomposition of residual lithium compounds will cause cell swelling and localized heating, which are potential safety risks in its practical application (Min et al, 2017;Mao et al, 2019;Renfrew et al, 2019). As a consequence, how to effectively reduce surface residual lithium compounds of Ni-rich cathode materials, has become a current research hotspot.…”