Uncovering the degradation mechanism induced by ion-diffusion kinetics in large-format lithium-ion pouch cells

Battery electrochemistry in an actual cell is a complicated behavior influenced by the current density,uniformity,and ion-diffusion distance,etc.The anisotropism of the lithiation/delithiation degree is usually inevitable,and even worse,due to a trend of big-size cell design,typically such as 4680 and blade cells,which accelerated a battery failure during repeat lithiation and delithiation of cathodes.Inspire by that,two big-size pouch cells with big sizes,herein,are selected to reveal the ion-diffusion dependency of the cathodes at different locations.Interestingly,we find that the LiCoO_(2) pouch cell exhibits ~5 A h loss after 120 charge-discharge cycles,but a 15 A h loss is verified in a LiNixMnyCO_(1-x)-yO_(2)(NCM) cell.Synchrotron-based imaging analysis indicates that higher ion-diffusion rates in the LiCoO_(2)than that in the LiNixMnyCO_(1-x)-yO_(2)is the determined factor for the anisotropic cathode fading,which is responsible for a severe mechanical issue of particle damage,such as cracks and even pulverization,in the cathode materials.Meanwhile,we verify the different locations at the near-tab and bottom of the electrode make it worse due to the ion-diffusion kinetics and temperature,inducing a spatially uneven electrochemistry in the big-size pouch cell.The findings give an in-depth insight into pouch cell failure and make a guideline for high-energy cell design and development.

Open-cell mullite ceramic foams derived from porous geopolymer precursors with tailored porosity

Porous geopolymer precursors were firstly prepared by the direct foaming method using bauxite,fly ash(FA),and metakaolin(MK)as raw materials,and porous mullite ceramics were prepared after ammonium ion exchange and then high-temperature sintering.The effects of chemical foaming agent concentration,ion-exchange time,and sintering temperature on porous geopolymerderived mullite ceramics were studied,and the optimal preparation parameters were found.Studies have shown that the concentration of blowing agent had great influence on open porosity(q)and porosity and cell size distributions of geopolymer samples,which in turn affected their compressive strength(σ).Duration of the ion exchange had no obvious effect on the sintered samples,and the amount of mullite phase increased with the increase in the sintering temperature.Mullite foams,possessing an open-celled porous structure,closely resembling that of the starting porous geopolymers produced by directly foaming,were obtained by firing at high temperatures.Stable mullite(3Al_(2)O_(3)·2SiO_(2))ceramic foams with total porosity(ε)of 83.52 vol%,high open porosity of 83.23 vol%,and compressive strength of 1.72 MPa were produced after sintering at 1400 for 2 h in℃ air without adding any sintering additives using commercial MK,bauxite,and FA as raw materials.