Gas Generation in Lithium Cells with High-Nickel Cathodes and Localized High-Concentration Electrolytes

Abstract

High-nickel layered-oxide cathodes (LiNi x Mn y Co 1-x-y O 2 , x ≥ 0.8) exhibit high capacities but also experience rapid capacity fade during cycling, and are susceptible to heat generation and gas release. Advanced electrolytes, such as localized high-concentration electrolytes (LHCEs), substantially stabilize the cathode during cycling and have lower flammability than conventional electrolytes, but gas generation with these electrolytes is yet to be assessed. We demonstrate here that gas generation from a high-nickel cathode in an LHCE is half as much as in a conventional electrolyte at 4.4 V. The gas generation in the LHCE is further reduced at 4.3 V, but the LHCE generates a similar amount of gas as the conventional electrolyte at 4.6 V. Neither electrolyte can prevent gas generation after cycling; cathodes after 200 cycles generate similar amounts of gas as pristine cathodes during high-voltage hold. It is shown that, in both electrolytes, oxygen from the cathode lattice plays a critical role in gas generation.

Solvent versus Anion Chemistry: Unveiling the Structure-Dependent Reactivity in Tailoring Electrochemical Interphases for Lithium-Metal Batteries

“…Severe gas evolution (CO 2 , O 2 , CO, etc.) at 4.6 V was reported in 1,2-dimethoxyethane (DME)-based LHCEs due to solvent oxidation . Under high-rate charging conditions, the uneven Li deposition tends to induce dendrite growth and increase polarization, accelerating active Li consumption and even short-circuiting .…”

“…at 4.6 V was reported in 1,2-dimethoxyethane (DME)-based LHCEs due to solvent oxidation. 25 Under high-rate charging conditions, the uneven Li deposition tends to induce dendrite growth and increase polarization, accelerating active Li consumption and even short-circuiting. 26 These results point out that the interphase composition and structure established by the anion chemistry have shown inadequacy for protecting ultrahigh-voltage cathodes and reactive Li-metal anodes.…”

Strongly Solvating Ether Electrolytes for High-Voltage Lithium Metal Batteries

“…Due to the shielding effect of diluent molecules, the Li + –anion interactions could be intensified in the inner solvation sheath, which further improves the cycling stability of high-voltage LMBs. In addition, weakly solvating ether solvents with steric groups or electron-withdrawing groups were proposed to further increase the enrichment of anions in the solvation complex and promote the anion-related interfacial reactions. − However, the reliance on anion-related interfacial reactions for cathode protection has fallen short of further expanding the anodic stability of ether-based electrolytes beyond 4.5 V . Because of the ever-increasing need for ultrahigh-voltage cathodes, it is critical to seek effective design strategies to further improve the oxidation stability of ether-based electrolytes for LMB applications.…”

Unveiling the Critical Role of Ion Coordination Configuration of Ether Electrolytes for High Voltage Lithium Metal Batteries

“…Moreover, recent developments of localized high concentration electrolytes with non-solvating diluents (e.g., hydrofluoroethers) not only improve the physical properties of the electrolytes (e.g., viscosity, ionic conductivity, wettability, etc.) but also enhance the electrochemical stability of ether electrolytes [18][19][20][21][22][23] . However, recent studies have found the instability of DME-based electrolytes under higher voltages over 4.5 V 18 .…”

“…but also enhance the electrochemical stability of ether electrolytes [18][19][20][21][22][23] . However, recent studies have found the instability of DME-based electrolytes under higher voltages over 4.5 V 18 . For future applications of ether electrolytes, it is urgent to further improve the electrolyte oxidation stability on Ni-rich cathodes with reactive Ni 3+ /Ni 4+ surface sites.…”