Direct Evidence of Concurrent Solid-Solution and Two-Phase Reactions and the Nonequilibrium Structural Evolution of LiFePO4
2012
Sharma, Neeraj | Guo, Xianwei | Du, Guodong | Guo, Zaiping | Wang, Jiazhou | Wang, Zhaoxiang | Peterson, Vanessa K.
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.
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