Abstract
Electrochemically driven functioning of a battery inevitably induces thermal and mechanical effects, which in turn couple with the electrochemical effect and collectively govern the performance of the battery. However, such a coupling effect, whether favorable or detrimental, has never been explicitly elucidated. Here we use in situ transmission electron microscopy to demonstrate such a coupling effect. We discover that thermally perturbating delithiated LiNi0.6Mn0.2Co0.2O2 will trigger explosive nucleation and propagation of intragranular cracks in the lattice, providing us a unique opportunity to directly visualize the cracking mechanism and dynamics. We reveal that thermal stress associated with electrochemically induced phase inhomogeneity and internal pressure resulting from oxygen release are the primary driving forces for intragranular cracking that resembles a “popcorn” fracture mechanism. The present work reveals that, for battery performance, the intricate coupling of electrochemical, thermal, and mechanical effects will surpass the superposition of individual effects.
Highlights
Driven functioning of a battery inevitably induces thermal and mechanical effects, which in turn couple with the electrochemical effect and collectively govern the performance of the battery
Since rechargeable lithium-ion batteries (LIB) were first commercialized in the 1990s, continuous efforts have focused on developing high-energy-density LIBs, which can be accomplished by simultaneously increasing the energy densities of both the cathode and the anode[1,2,3]
The electrochemical process often can trigger thermal and mechanical processes, and in turn, the thermo-mechanical effects can mediate the electrochemical process. These three processes are intimately coupled in ways that result in mutual reinforcement; that is, together they often result in an aggravate effect on battery performance
Summary
Driven functioning of a battery inevitably induces thermal and mechanical effects, which in turn couple with the electrochemical effect and collectively govern the performance of the battery. It has been observed that high voltage cycling can lead to rapid performance decay, which may be attributed to aggravating redox reactions at the cathode–electrolyte interface[12], cathode surface-phase transformation[13], active material dissolution into the electrolyte[14], electrolyte decomposition[12], cathode passivation layer formation[15], intergranular cracking[16,17,18], and intragranular cracking[19,20]. The origins of these detrimental factors has been correlated to electrochemical, thermal, and mechanical effects[21]. Incubation cracks work demonstrates that intimate coupling of the electrochemical, thermal, and mechanical processes leads to much more severe cathode degradation
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