High Ni LiNixCoyMnzO2 (x+y+z=1) (NMC) have been demonstrated to be the promising cathode materials for high energy lithium ion batteries (LIB). However, Ni rich NMC cathode materials suffer the high surface reactivity issue in the ambient environment with the formation of impurity species like carbonates and hydroxides. The sensitivity of those NMC cathode materials in the CO2 and H2O exposure environment remains as a question. In this work, we combine the technique of transient kinetics and density functional theory (DFT) to study the reaction of CO2 with the NMC cathode materials with different ratios of nickel content (x:y:z =4:3:3(NMC433), x:y:z =5:3:2(NMC532) , x:y:z =6:2:2(NMC622), x:y:z =8:1:1(NMC811)). At room temperature, significant CO2 conversion were observed without any C containing product formation on all NMC materials in a temporal analysis products (TAP) reactor, which implied that the CO2 adsorption is an irreversible process. The amount of CO2 uptake by the surface follows the order of NMC433 &gt; NMC532 &gt; NMC622 &gt; NMC811 in the initial 600 pulses. CO2 uptake at elevated temperatures is more than that at the room temperature. The CO2 binding on different materials is studied theoretically with periodic DFT PBE+U method on a (104) surface. The formation of Li2CO3 is an exothermic process; the two O atoms from CO2 bonded to two surface Li atoms leading to the formation of Li2CO3 are more preferable than that bonded to transition metals. Interestingly, the binding of CO2 on a surface O bound to the metals containing a Mn or a Co is stronger than that on a surface O bound to two Ni atoms. Thus, the studied NMC materials containing more Mn or Co have more active sites with stronger CO2 binding leading to the more CO2 uptake. This is consistent with the experiment in the transient regime under far-from equilibrium conditions. Generally, the more Ni content of NMC materials are believed to be more sensitive to the ambient environment. Our results show that the sensitivity to the ambient is complicated and not only dependent on the CO2 adsorption.

How sensitive are pristine Ni rich NMC cathode materials to CO2?

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.