Lithium Metal Polymer Battery Interfaces Studied By Hard X-Ray Microtomography
Solid block copolymer electrolytes are a class of SPEs that contains a mechanical reinforced block and an ion conducting block doped with a Li salt.4 The block immiscibility induces microphase separation, producing ordered morphologies on the nanometer scale.5 The seminal work done by K.J. Harry et al.6 on solid polystyrene-b-poly(ethylene oxide) (SEO) block copolymer electrolyte led to a better understanding of Li dendrite formation and growth. Using Li symmetric cells dendrite evolution was observed and imaged by a non-destructive tool, hard X-ray microtomography.
To go toward the application, batteries were imaged by hard X-ray microtomography. The batteries are made of a Li metal anode, a SEO electrolyte layer and a composite cathode. The cathode deposited onto on Aluminum (Al) foil, contains LiFePO4 as active material, SEO electrolyte as binder, and carbon black. Hard X-ray microtomography enables to visualize the microstructural changes at the Li/SEO and SEO/cathode interfaces to get insight on the battery failure mechanisms.
The batteries were cycled at 90°C at a C/20 charge rate and a C/8 discharge rate (Figure 1a). Prior and after battery cycling, the electrode-electrolyte interfaces were imaged by hard X-ray microtomography as shown in figure 1b and 1c, respectively. We found that the supposed intimate Li/SEO interface undergoes a strong delamination phenomenon that leads to the formation of voids (Figure 1b). Using a rendering image software, the void fraction can be measured all along the Li/SEO interfaces, and its effect on the battery capacity fading be estimated.
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