Insights into Solid-Electrolyte Interphase Induced Li-Ion Degradation from in Situ Auger Electron Spectroscopy

Abstract

Surface reactions occurring on LiMnO, LiCoO, LiNiO, Li[NiMnCo]O, and LiFePO during charging and overcharging are studied by in situ and ex situ Auger electron spectroscopy. Carbon surface stability at the cathode solid-electrolyte interphase (SEI), associated with carbonate formation, decomposition, and CO/CO evolution, on different electrodes during cycling correlates with their cycle life. To understand how associated CO and CO evolution affects cycle stability, LiMnO is cycled in flowing gas. Flowing Ar enhances cycle life by a factor of 2, while flowing Ar with 1% CO reduces cycle life by a factor of 2. CO is proposed to degrade cycle life by trapping Li and metal ions as carbonate in the anode SEI.

Tensile Fatigue of Poly(Vinyl Alcohol) Hydrogels with Bio‐Friendly Toughening Agents

“…[4,59,60] It is impossible to extract information on a hydrogel's fatigue resistance from single stress amplitude tests, stopped at arbitrary cycle numbers, though many studies have focused on this analysis. [40][41][42][61][62][63][64][65][66] An overarching goal of this work is to understand the tensile fatigue properties of PVA with and without additives. To the author's knowledge, no such study focusing on full-load spectrum cyclic, tensile testing has been published for a high-strength synthetic hydrogel.…”

Flaw‐Insensitive Hydrogels under Static and Cyclic Loads

“…The shear modulus µ was obtained as 1/4 of the initial slope of the stress-stretch curve, under the pure shear setup. [29] As mentioned before, all the samples were 10 mm length and 50 mm width, except for the PAAm-PVA-S hydrogel samples in the transverse direction with λ fix = 1.1, 1.2, and 1.3 (8 mm length and 40 mm width), since the initial sizes of the hydrogels prepared under these conditions were smaller than 50 mm. For the measurement of daily change of stress-stretch curves (Figure 2a,b), an untested sample was used in each measurement.…”

“…Ultimately, all hydrogels suffer fatigue fracture, that is, the gradual extension of crack from an initial flaw under cyclic loads. [28][29][30][31][32][33] The highest threshold for fatigue fracture of a double-network, tough hydrogel reported up-to-date is about 400 J m −2 , still only 1/10 of its bulk fracture toughness. [32] Life has found another way to be tough.…”

“…For the PAAm-PVA-S hydrogel with λ fix = 2.5, the threshold for fatigue fracture in the transverse direction is 44.0 J m −2 ( Figure S7, Supporting Information), comparable to the threshold measured in other hydrogels with a PAAm network. [29][30][31][32][33] In the aligned direction, crack deflection was observed to extend vertically to the ends of the sample (Figure S8, Supporting Information). For the isotropic PAAm-PVA-S hydrogel with λ fix = 1.0, crack deflection also can appear when the hydrogel was loaded under large λ max for many cycles (Figure S9, Supporting Information).…”

“…[23,25] Γ ex can be easily enhanced over thousands of J m −2 through breaking a large amount of weak bonds behind the crack tip, while Γ in is mostly on the order of 10-100 J m −2 , limited by the nature of hydrogel network. [23,25,[28][29][30][31][32][33] At last, the threshold for fatigue fracture only depends on the intrinsic toughness Γ in , but negligibly on Γ ex . [28,31,33,51] Aligning polymer chains to toughen a soft material has been successfully applied in many commercial products such as ultra-stiff, tough, and fatigue-resistant fibers including isotactic polypropylene [53] and polyethylene.…”