Reversible Capacity Loss of LiCoO₂ Thin Film Electrodes

Abstract

Capacity loss mechanisms of lithium-ion batteries (LIBs) are intensively studied. In this study, planar LiCoO2 (LCO) thin film electrodes are successfully prepared by pulsed laser deposition and used to explore a diffusion-controlled reversible capacity loss mechanism of layered oxide cathodes. It is found that the reversible capacity loss of LCO originates from asymmetric lithium chemical diffusion kinetics during (de)­lithiation, which is eventually rooted in the intrinsic lithium vacancy dependent diffusivity in the layered structure of LCO. The understanding of the reversible capacity loss may be highly beneficial for the development of LIBs and other systems based on intercalation compounds.

Lithium‐Diffusion Induced Capacity Losses in Lithium‐Based Batteries

“…Slow Li‐ion diffusion during the end stages of lithiation has been linked to first cycle capacity losses for layered metal oxide positive electrodes. [ 46,79,80,83–85 ] This is in agreement with the observed behavior for negative electrode materials such as Si. [ 20,86 ]…”

“…Slow Li-ion diffusion during the end stages of lithiation has been linked to first cycle capacity losses for layered metal oxide positive electrodes. [46,79,80,[83][84][85] This is in agreement with the observed behavior for negative electrode materials such as Si. [20,86] It was recently shown that Ni-based cathodes that are typically low-stress materials can crack during high SOC cycling leading to a capacity decay as intraparticle fragments become ionically disconnected from the electrolyte.…”

“…Early indications of diffusion-controlled Li-trapping can often be found by comparing the electrochemical performance during galvanostatic cycling with results obtained with techniques such as CV and electrochemical impedance spectroscopy. Li-trapping in negative electrode materials can then be detected via shifts in the lithiation (but not the delithiation) potential [20,29,36,46] toward more negative values as this indicates an increase in the Li concentration in the electrode. Cycling protocols with different lithiation and delithiation rates can also be used as an increase in the duration of the delithitation step should decrease the influence of the diffusion-controlled trapping effect.…”

“…Many of these results were obtained as a result of the use of new electrode characterization procedures facilitating the detection of trapped lithium and lithium concentration gradients in cycled electrodes. Incomplete delithiation has, for example, been identified in studies involving comparisons of pristine and delithiated cycled electrodes composed of, for example, Si, [20,21,[27][28][29][30] Sn, [28,31] Al, [32][33][34][35] TiO 2 , [36] LiFePO 4 (LFP), [37][38][39] LiNi 1/3 Co 1/3 Mn 1/3 O 2 (NCM) , [40] V 2 O 5 , [41][42][43][44] MoO 3 , [45] LiCoO 2 (LCO) , [46] as well as ordered [47,48] and disordered carbon. [49][50][51][52][53][54] A large amount of diffusion-controlled trapped elemental lithium (i.e., 3.3 mol Li per mol Si) was, for example, found in optimized nano-silicon composite electrodes after 650 cycles of capacity limited (i.e., 1200 mAh g −1 ) cycling.…”

A Dry‐Processed Al2O3/LiAlO2 Coating for Stabilizing the Cathode/Electrolyte Interface in High‐Ni NCM‐Based All‐Solid‐State Batteries

“…This step is necessary to ensure comparability between P‐NCM and Alu‐NCM600 as the impedance of layered oxide cathode materials depends on the lithium content (state of charge) of the electrode. [ 58 ] Comparing the impedance spectra after the 1 st and 100 th cycle, displayed in Figure a, a distinct increase of the impedance is observed for the pristine sample indicating a strong degradation reaction at the SSE/CAM interface due to the oxidation of the solid electrolyte. [ 16,21 ] The total impedance of the coated NCM cell is significantly lower after the 1 st and 100 th cycle, corroborating the protection function of the Al 2 O 3 /LiAlO 2 coating.…”