Charging lithium battery electrode mechanical properties cracking

Charging lithium battery electrode mechanical properties cracking

The mechanical stability of the lithium-ion battery pole is also an important factor affecting electrochemical properties, cycle stability, and safety of battery.. There are various cracking phenomena in the electrical performance of the battery, and the common mechanical performance crack is shown in the above view, including: (1) positive, negative electrode material particle crack; (2) internal crystal interior of the active material particles; The positive surface layer is stratified; (4) negative surface SEI rupture; (5) positive electrode active substance phase separation; (6) negative surface of lithium metal.

Crack batteries In actual use, active particles often experience a number of irreversible physical chemistry and mechanical processes, such as local excessive charge and discharge, surface structure collapse, uneven electrode / electrolyte interface, metal dissolution / precipitation, volume expansion / shrinkage , Partial temperature fluctuations, etc.. The interpretation of these side reactions causes the internal mechanical or thermal stress of the active particles, the accumulation of electrochemical stress, and further induces cracks.

. This crack is important in stress concentration and weakness of particles, such as particle surface, SEI film, grain boundary, etc..

Especially like a silicon-based negative electrode, when the lithium inserted and detached in the charging / discharge cycle, the volume change reaches 270%, which causes the mass expansion of the silicon particles to be pulverized, and the coating is separated from the copper set fluid.. In particular, the SEI membrane will continue to break the fracture process, which continuously consumes lithium ions and active substances, causing capacity to continuously attenuate, and the circulatory stability varies.

. The evolution of electrode cracks during charge and discharge process, the cracks in the intraceratures in the particles can cause contact between the particles, the integrity of particles, changes in the electron and ion transmission paths, resulting in a limited diffusion. The results show that electrons and ions increase in the length of the solid phase with the occurrence of cracks.

. This will further affect the electrochemical reaction, which may cause the charge and discharge part of the partition, which causes secondary cracks of particles..

During the surface structure change and phase separation charge and discharge, the electrochemical reaction occurs on the surface of the electrode, and the lithium ions are discharged or embedded from the surface. After multiple cycles, the active particles have a very significant phase change, and the lithium ion may be accompanied by metal. Existed, the layered structure becomes a salt rock phase structure, and this phase structure evolves to expand the internal phase separation to the internal phase separation.

. During the charging of the lithium ion battery, the negative electrode potential is constantly increasing, and the metal lithium can cause a side reaction of the metal lithium in the surface deposition of the negative electrode..

Metal lithium continues to have a negative surface, which will not only affect the capacity of the lithium-ion battery, but also the lithium-delegranes that hazard lithium-ion batteries.. When metal lithium is a negative electrode, the dendritic crystal is more severe, and the negative electrode protection prevents the research hotspots of the lithium delegated crystal to become a metal lithium ion battery.

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