Intrinsic Origins of Crack Generation in Ni-rich LiNi0.8Co0.1Mn0.1O2 Layered Oxide Cathode Material

Abstract

Ni-rich LiNi0.8Co0.1Mn0.1O2 layered oxide cathodes have been highlighted for large-scale energy applications due to their high energy density. Although its specific capacity is enhanced at higher voltages as Ni ratio increases, its structural degradation due to phase transformations and lattice distortions during cycling becomes severe. For these reasons, we focused on the origins of crack generation from phase transformations and structural distortions in Ni-rich LiNi0.8Co0.1Mn0.1O2 using multiscale approaches, from first-principles to meso-scale phase-field model. Atomic-scale structure analysis demonstrated that opposite changes in the lattice parameters are observed until the inverse Li content x = 0.75; then, structure collapses due to complete extraction of Li from between transition metal layers. Combined-phase investigations represent the highest phase barrier and steepest chemical potential after x = 0.75, leading to phase transformations to highly Li-deficient phases with an inactive character. Abrupt phase transformations with heterogeneous structural collapse after x = 0.81 (~220 mAh g−1) were identified in the nanodomain. Further, meso-scale strain distributions show around 5% of anisotropic contraction with lower critical energy release rates, which cause not only micro-crack generations of secondary particles on the interfaces between the contracted primary particles, but also mechanical instability of primary particles from heterogeneous strain changes.

Enhanced Electrochemical Properties of Zr4+-doped Li1.20[Mn0.52Ni0.20Co0.08]O2 Cathode Material for Lithium-ion Battery at Elevated Temperature

“…All samples have demonstrated the similar charge curve for the two typical charge steps. The first step of charging process exists in the potential region from 2.0 V to 4.5 V, corresponding to the Li + -extraction from layer LiNi 0.50 Co 0.20 Mn 0.30 O 2 component and the oxidation of Ni 2+ to Ni 4+ and Co 3+ to Co 4+  31,32 . For the second step, all samples exhibit a long voltage plateau at about 4.5 V, where the irreversible Li + extract and oxygen release from the Li 2 MnO 3 phase 33,34 .…”

Degradation Mechanisms and Mitigation Strategies of Nickel-Rich NMC-Based Lithium-Ion Batteries

“…Here, studies based on microscopy [21], crystallography [22], mass spectroscopy [23], gas measurements [24] and calorimetry [8] have revealed that parasitic reactions [7], cation mixing (leading to restructured surface regions) [25], active material dissolution [26] and oxygen release [23,25] are primary factors responsible for cathode degradation at the atomic scale. In addition, scanning electron microscopy (SEM) [13] together with computational studies [27] has revealed that intergranular cracking can weaken connections between primary particles. Despite these findings, the majority of recently published studies are insufficient and only partially cover the processes through which degradation occurs.…”

Coupling of electrochemically triggered thermal and mechanical effects to aggravate failure in a layered cathode

“…However, excessive extraction of lithium from layered cathodes could cause structural instability, along with other parasitic degradation pathways in LIB cells. It has been observed that high voltage cycling can lead to rapid performance decay, which may be attributed to aggravating redox reactions at the cathode–electrolyte interface 12 , cathode surface-phase transformation 13 , active material dissolution into the electrolyte 14 , electrolyte decomposition 12 , cathode passivation layer formation 15 , intergranular cracking 16–18 , and intragranular cracking 19,20 . The origins of these detrimental factors has been correlated to electrochemical, thermal, and mechanical effects 21 .…”