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Lithium-ionbatteries are undergoing rapid development to meetthe energy demands of the transportation and renewable energy-generationsectors. The capacity of a lithium-ion battery is dependent on theamount of lithium that can be reversibly incorporated into the cathode.This work directly quantifies the time- and current-dependent lithiumtransfer within a cathode functioning under conventional charge–dischargecycling. We examine Li1+yMn2O4under real working conditions using in situ neutronpowder diffraction and link the atomic-scale structure to the batteryperformance. The lithium location and content, oxygen positional parameter,and lattice parameter of the cathode are measured and linked to thebattery’s charge/discharge characteristics. Lithium insertion(discharge) differs from extraction (charge), a feature that may explainthe relative ease of discharge (compared with charge) of this material.An atomic-scale understanding of cathode functionality, such as revealedhere, will direct improvements in battery performance at both thepractical and the fundamental level. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries power many portable devices and in the future are likely to play a significant role in sustainable-energy systems for transportation and the electrical grid. LiFePO4 is a candidate cathode material for second-generation lithium-ion batteries, bringing a high rate capability to this technology. LiFePO4 functions as a cathode where delithiation occurs via either a solid-solution or a two-phase mechanism, the pathway taken being influenced by sample preparation and electrochemical conditions. The details of the delithiation pathway and the relationship between the two-phase and solid-solution reactions remain controversial. Here we report, using real-time in situ neutron powder diffraction, the simultaneous occurrence of solid-solution and two-phase reactions after deep discharge in nonequilibrium conditions. This work is an example of the experimental investigation of nonequilibrium states in a commercially available LiFePO4 cathode and reveals the concurrent occurrence of and transition between the solid-solution and two-phase reactions. [ABSTRACT FROM AUTHOR]