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Historically long accepted to be the singular root cause of capacity fading, transition metal dissolution has been reported to severely degrade the anode. However, its impact on the cathode behavior remains poorly understood. Here we show the correlation between capacity fading and phase/surface stability of an LiMn2O4 cathode. It is revealed that a combination of structural transformation and transition metal dissolution dominates the cathode capacity fading. LiMn2O4 exhibits irreversible phase transitions driven by manganese(III) disproportionation and Jahn-Teller distortion, which in conjunction with particle cracks results in serious manganese dissolution. Meanwhile, fast manganese dissolution in turn triggers irreversible structural evolution, and as such, forms a detrimental cycle constantly consuming active cathode components. Furthermore, lithium-rich LiMn2O4 with lithium/manganese disorder and surface reconstruction could effectively suppress the irreversible phase transition and manganese dissolution. These findings close the loop of understanding capacity fading mechanisms and allow for development of longer life batteries.

Voltage fade prevents effective use of the excess capacity and represents the most crucial technical challenge faced by Li-and Mn-rich cathode materials (LMR) in modern batteries.Although oxygen release has been arguably considered as an initiator for the failure mechanism, its prerequisite driving force has yet to be fully understood. Herein, relying on the in-situ nanoscale sensitive coherent X-ray diffraction imaging (BCDI) technique, we are able to track the dynamic structure evolution of the LMR cathode. The results, surprisingly, reveal that continuous nanostrain accumulation arose from lattice displacement in nano-domain structures during cell operation is the original driving force for detrimental structure degradations together with oxygen loss that triggers the well-known rapid voltage decay in LMR. By further leveraging primary to multi-particle structure and electrode-level as well as atomic scale observations, we demonstrate that the heterogeneous nature of the LMR cathode inevitably causes pernicious phase displacement which cannot be eliminated by the previous trials. With these fundamental discoveries, we propose the structural design strategy to mitigate the lattice displacement and inhomogeneous electrochemical/structural evolutions, thereby achieving stable voltage and capacity profiles. These findings highlight the significance of lattice displacement in voltage decay mechanism and will inspire a wave of efforts to unlock the potential of the broad-scale commercialization of LMR cathode material.

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