Demonstrating Apparently Inconspicuous but Sensitive Impacts on the Rollover Failure of Lithium-Ion Batteries at a High Voltage

Layered oxides, such as Li[Ni0.5Co0.2Mn0.3]O-2 (NCM523), are promising cathode materials for operation at a high voltage, i.e., high-energy lithium-ion batteries. The instability-reasoned transition metal dissolution remains a major challenge, which initiates electrode cross-talk, alteration of the solid electrolyte interphase, and enhanced Li-metal dendrite formation at the graphite anode, consequently leading to rollover failure. In this work, relevant impacts on this failure mechanism are highlighted. For example, a conventional coating of NCM523 with aluminum oxide as a typical high-voltage modification improves kinetic aspects but can only postpone the rollover failure to later charge/discharge cycles. Interestingly, a similar effect on the rollover failure is observed merely after modification of the cell formation protocol, i.e., the first cycles. Further influences of specific test protocols are highlighted and show that the rollover failure even disappears at C-rates above 2C, which can be attributed to a more homogeneous distribution of Li-metal dendrite formation. It is worth noting that a variation of anode porosity can reveal similar effects, as, e.g., variations in anode processing also impact Li dendrite distribution and the appearance of rollover failure. Overall, the rollover failure is a valid but complex phenomenon, which sensitively depends on apparently inconspicuous parameters and should not be disregarded.

Automated summary

Layered oxides like Li[Ni0.5Co0.2Mn0.3]O-2 (NCM523) are promising cathode materials for high-energy lithium-ion batteries, but face challenges of transition metal dissolution leading to electrode cross-talk and rollover failure. Various modifications, including coating with aluminum oxide and altering cell formation protocols, can postpone or reduce rollover failure. Specific test protocols influence the appearance of rollover failure but it can disappear at higher C-rates due to more homogeneous distribution of Li-metal dendrite formation. Overall, rollover failure is a complex phenomenon dependent on subtle parameters.