Overcharge‐Induced Phase Heterogeneity and Resultant Twin‐Like Layer Deformation in Lithium Cobalt Oxide Cathode for Lithium‐Ion Batteries

Abstract

Overcharging is expected to be one of the solutions to overcome the current energy density limitation of lithium‐ion battery cathodes, which will support the rapid growth of the battery market. However, high‐voltage charging often poses a major safety threat including fatal incendiary incidents, limiting further application. Numerous researches are dedicated to the disadvantages of the overcharging process; nonetheless, the urgent demand for addressing failure mechanisms is still unfulfilled. Herein, it is revealed that overcharging induces phase heterogeneity into layered and cobalt oxide phases, and consequent “twin‐like deformation” in lithium cobalt oxide. The interplay between the uncommon cobalt(III) oxide and the deformation is investigated by revealing the atomistic formation mechanism. Most importantly, abnormal cracking is discovered in the vicinity of the cobalt oxide where structural instability induces substantial contraction. In addition, surface degradation is widely observed in the crack boundary inside the particle. As unintentional overcharging can occur due to local imbalance in state‐of‐charge in severe operating conditions such as fast charging, the issues on overcharging should be emphasized to large extent and this study provides fundamental knowledge of overcharge by elucidating the crack development mechanism of layered cathodes, which is expected to broaden the horizon into high voltage operation.

Challenges and Opportunities for Fast-Charging Batteries

“…Overcharge is another important limiting factor for fast charging. For LCO, it can induce phase heterogeneity, thus posing a major safety threat. , In addition, mechanical pulverization of various electrode materials often occurs under fast-charging conditions resulting from the gradient distribution of Li concentration, causing the loss of active material. The cracks of the cathode particle are mainly due to heterogeneous stress distribution along the grain boundary in the agglomerated particles.…”

In-Situ-Polymerized 1,3-Dioxolane Solid-State Electrolyte with Space-Confined Plasticizers for High-Voltage and Robust Li/LiCoO2 Batteries

“…In addition to characterization of the lithium surface, we also conducted SEM characterization of the LiCoO 2 cathodes after cycled in the three electrolytes, as illustrated in Figure 4d−f. Some visible cracks are found in LiCoO 2 particles of the PDOL sample (Figure 4d), which originated from mechanical stress accumulation caused by lithium-ion extraction/insertion during charge−discharge cycles, 45 indicating that there was no CEI layer formed on the surface or low-quality CEI with poor mechanical strength formed on the LiCoO 2 surface, which could not prevent the cracking of layered transition metal oxides under long-term circulation. By contrast, LiCoO 2 cathodes cycled in PDOL-F (Figure 4e) and PDOL-F/S (Figure 4f) both have relatively smooth surfaces without obvious cracks, implying that CEI with high mechanical strength formed on LiCoO 2 to hinder particle cracking, which may originate from the reactions between FEC and cathodes.…”

Unraveling the Dynamic Correlations between Transition Metal Migrations and the Oxygen Dimer Formation in the Layered LiCoO2 Cathode

“…[10][11][12][13][14] Extensive previous studies show that the structural degradation is caused by the transition metal (TM) cation migrations from the TM layer to the Li layer when Li ions are gradually extracted. [15][16][17][18][19][20][21][22] Migrations of the TM cation lead to the blocking effect on the Li ion diffusion and thus the loss of the irreversible capacity, which is detrimental to the battery performance. On the other hand, once the migrations of the TM cation occur, it will inevitably be accompanied by the precipitation of the oxygen owing to the formation of TM vacancies, which could lead to potential safety problems for the battery.…”