Influence of NCM Particle Cracking on Kinetics of Lithium-Ion Batteries with Liquid or Solid Electrolyte

Abstract

In liquid electrolyte-type lithium-ion batteries, Nickel-rich NCM (Li1+x (Ni1−y−z Co y Mnz)1−x O2) as cathode active material allows for high discharge capacities and good material utilization, while solid-state batteries perform worse despite the past efforts in improving solid electrolyte conductivity and stability. In this work, we identify major reasons for this discrepancy by investigating the lithium transport kinetics in NCM-811 as typical Ni-rich material. During the first charge of battery half-cells, cracks form and are filled by the liquid electrolyte distributing inside the secondary particles of NCM. This drastically improves both the lithium chemical diffusion and charge transfer kinetics by increasing the electrochemically active surface area and reducing the effective particle size. Solid-state batteries are not affected by these cracks because of the mechanical rigidity of solid electrolytes. Hence, secondary particle cracking improves the initial charge and discharge kinetics of NCM in liquid electrolytes, while it degrades the corresponding kinetics in solid electrolytes. Accounting for these kinetic limitations by combining galvanostatic and potentiostatic discharge, we show that Coulombic efficiencies of about 89% at discharge capacities of about 173 mAh gNCM −1 can be reached in solid-state battery half-cells with LiNi0.8Co0.1Mn0.1O2 as cathode active material and Li6PS5Cl as solid electrolyte.

Polycrystalline and Single Crystalline NCM Cathode Materials—Quantifying Particle Cracking, Active Surface Area, and Lithium Diffusion

“…This procedure allows the assumption of semi‐infinite conditions where c 0 , the initial concentration of lithium in the bulk of the material, is unchanged by the polarization step. [ 21,34 ] To extract the lithium diffusion coefficient assuming semi‐infinite boundary condition, the voltage relaxation measurements were interpreted using the same method as in our previous study. [ 21 ] Briefly, the open circuit potential V OC was assumed to evolve with time according to the following equation …”

“…In fact, experiments that were carried out using cathode morphologies that are not significantly affected by cracking, such as Li x Ni 0.8 Co 0.2 O 2 thin films (1 × 10 –11 cm 2 s −1 ), Li x Ni 0.8 Co 0.1 Mn 0.1 O 2 single crystals (7 × 10 –11 cm 2 s −1 ), or Li x Ni 0.8 Co 0.1 Mn 0.1 O 2 in contact with LiPS 5 Cl solid electrolyte (6 × 10 –12 cm 2 s −1 ) determine to be in the same range as for the present data on SC NCM (2 × 10 –11 cm 2 s −1 ) at comparable degree of lithiation ( x = 0.4, ≈3.9 V vs Li + /Li). [ 21,46,47 ]…”

“…In a previous study, we addressed how liquid infiltration inside the microcracks formed during the first charge leads to a higher apparent lithium diffusion coefficient and shorter pathways for lithium diffusion, consistent with an increase of the electrochemically active surface area and reduction of effective particle size in the cathode materials. [ 21 ] This was not observed with mechanically rigid solid electrolytes that could not fill the newly created space in the secondary particles. Therefore, crack‐free single crystalline CAM is expected to incur similar kinetic limitations even when a liquid electrolyte is employed.…”

Probing the charged state of layered positive electrodes in sodium-ion batteries: reaction pathways, stability and opportunities

“…Similar observations of particle cracking have been observed in several lithium-ion battery systems, where performance degradation has also been attributed to the exposure of new surfaces to the electrolyte causing electrode surface decomposition and electrolyte consumption. [285][286][287][288] A number of in situ electron microscopy studies have also been used to study the dynamic processes occurring in working batteries which have been summarised in some informative review articles. 289,290 4.7.2 Scanning transmission electron microscopy/electron energy loss spectroscopy.…”

Thin Film NCM Cathodes as Model Systems to Assess the Influence of Coating Layers on the Electrochemical Performance of Lithium Ion Batteries

“…The thin films exhibit a smooth surface and a randomly distributed orientation of the crystallites making them an ideal model system, which allows not only to determine the intrinsic properties of cathode materials, such as the lithium diffusion coefficient, but also enables a detailed study of the electrode–electrolyte interface properties before and after cycling using surface sensitive techniques. [ 42 ] To assess the suitability of the thin films to serve as model electrodes, the influence of a protective coating on their electrochemical performance was investigated. For this purpose, some thin films were coated with an ultra‐thin Al 2 O 3 protective layer using atomic layer deposition (ALD).…”