The rock-salt phase (RSP) formed on the surface of Ni-rich layered cathodes in liquid-electrolyte lithium-ion batteries is conceived to be electrochemically "dead". Here we show massive RSP forms in the interior of LiNi_xMn_yCo_(1−x-y)O₂ (NMC) crystals in sulfide based all solid state batteries (ASSBs), but the RSP remains electrochemically active even after long cycles. The RSP and the layered structure constitute a two-phase mixture, a material architecture that is distinctly different from the RSP in liquid electrolytes. The tensioned layered phase affords an effective percolation channel into which lithium is squeezed out of the RSPs by compressive stress, rendering the RSPs electrochemically active. Consequently, the ASSBs with predominant RSP in the NMC cathode deliver remarkable long cycle life of 4000 cycles at high areal capacity of 4.3 mAh/cm². Our study unveils distinct mechano-electrochemistry of RSPs in ASSBs that can be harnessed to enable high energy density and durable ASSBs.

Persulfates ((peroxymonosulfate (PMS) and peroxydisulfate (PDS)) can disintegrate waste activated sludge (WAS), but their influence on volatile fatty acid (VFA) production during anaerobic fermentation is largely unclear. Particularly, it is unknown whether persulfates can improve fermentation without any preactivation. This study investigated how the direct addition of PMS and PDS into the fermenter influences VFA production from WAS, and uncovered possible mechanisms of improved VFA production. At the PMS dosage of 1.0 mM/gVS, maximum VFA yield (1025 ± 55 mg COD/L) was observed in 5 days of fermentation, which was 24% higher than that with an equimolar addition of PDS and 132% higher than that without persulfate addition. However, the cost-effectiveness of PMS in enhancing VFA production is lower than that of PDS. The in situ generated hydroxyl and sulfate radicals from persulfates in the fermenter enhanced not only WAS disintegration and solubilization but also the formation of biodegradable substances for acidification. Moreover, the direct addition of persulfates into the fermenter shifted the microbial community toward hydrolysis-acidification such as Clostridium_sensu_stricto_10 and Fonticella. Results of this study also suggest that preactivation is not necessary when persulfates are applied to improve WAS fermentation.