Protection of Cobalt-Free LiNiO₂ from Degradation with Localized Saturated Electrolytes in Lithium-Metal Batteries

Abstract

High-nickel layered oxide cathode materials are the most promising candidates for developing lithium-metal batteries (LMBs) because of their high energy density and low cost. Herein, we present a localized saturated electrolyte (LSE) based on readily available, low-cost LiPF6 salt with limited solubility in carbonate solvents for developing LiNiO2 cathodes. Compared to the conventional electrolyte that retains only 55% of the initial capacity after 200 cycles, the LSE retains a record 81% of the initial capacity after 600 deep cycles at 4.4 V (versus Li/Li+). The LSE protects the LiNiO2 surface from degrading into rock-salt and spinel phases during cycling and helps form a robust Li morphology on the Li-metal anode that is covered by an inorganic-rich solid-electrolyte interphase. The drastically enhanced cycling stability with LSE demonstrates the importance of developing robust electrolytes compatible with both high-Ni cathodes and Li-metal anodes.

Uncovering the Solvation Structure of LiPF6‐Based Localized Saturated Electrolytes and Their Effect on LiNiO2‐Based Lithium‐Metal Batteries

“…The reduced rate capability at extremely high C‐rates can be attributed to the relatively lower ionic conductivity of LSEs compared to the LP57 electrolyte. [ 18 ] For example, the ionic conductivities of these five electrolytes are LP57 (8.70 mS cm −1 ) > LSE (TEP) (4.30 mS cm −1 ) > LSE (DME) (3.33 mS cm −1 ) > LSE (FEC/EMC) (2.32 mS cm −1 ) ≈ LSE (EC/EMC) (2.31 mS cm −1 ).…”

“…Therefore, adding FEC as the additive to LSE(EC/EMC) could be a more practical strategy to apply LSEs in lithium batteries. [ 18 ]…”

“…However, at C‐rates of 5C and higher, all four LSEs have lower specific capacities than LP57 (Figure S7, Supporting Information), indicating that the relatively lower ionic conductivity is still a factor for high‐rate performance. [ 18 ]…”

“…More details regarding the LiNiO 2 cathode materials can be found in our recent paper. [18] Electrochemical tests in Figure 2 suggest that selecting an appropriate solvent is crucial to the LSE-LiNiO 2 electrochemical performance interplay. Figure 2a compares the rate capability of LiNiO 2 cathodes tested in different electrolytes with TTE as the diluent for all LSEs.…”

“…However, at C-rates of 5C and higher, all four LSEs have lower specific capacities than LP57 (Figure S7, Supporting Information), indicating that the relatively lower ionic conductivity is still a factor for high-rate performance. [18] Figure 3b compares the cycling stability of LP57 electrolyte and LSE with the four diluents. All four LSEs increase the initial 1C specific discharge capacity from 206 (LP57) to approximately 225 mA h g -1 (LSEs).…”