Tuning and Balancing the Donor Number of Lithium Salts and Solvents for High-Performance Li Metal Anode

Abstract

The low reversibility of Li deposition/stripping in conventional carbonate electrolytes hinders the development of lithium metal batteries. Herein, we proposed a combination of solvents with a moderate donor number (DN) and LiNO 3 as the sole salt, which has rarely been attempted due to its low solubility or dissociation degree in common solvents. It is found that the DN value of solvents is highly correlated to the reversibility of Li deposition behavior when LiNO 3 is applied as the sole salt. The combination of LiNO 3 and solvents with moderate DN behaves like a quasi-concentrated electrolyte even at a common or moderate concentration, while neither the solvents with poor solubility and low dissociation for LiNO 3 (which usually corresponds to a low DN) nor the solvents with high dissociation for LiNO 3 (which usually corresponds to an overly high DN) can achieve a high reversibility for low conductivity or excessive solvent decomposition. As a result, a Coulombic efficiency as high as 99.6% for Li deposition/stripping is achieved with the optimized combination. We believe this work will give a better understanding of the role of anions and solvents in the regulation of the solvation structure, and DN can be utilized as an important guideline to sieve suitable solvents for LiNO 3 as the main salt to exhibit intriguing properties beyond traditional cognition.

Rational Molecular Engineering via Electron Reconfiguration toward Robust Dual-Electrode/Electrolyte Interphases for High-Performance Lithium Metal Batteries

“…With further understanding at the molecular level, it can be seen that the issues of current additives are related to electron structure. The insolubility of LiNO 3 stems from the strong bonding between nitrate and lithium ions, coexisting with the lack of electron-donating capacity of the electrolyte system. , The low reducibility of NO 3 – is associated with the high resonance electron cloud structure, containing large π bonds with four centers and six electrons. , In addition, the narrow oxidation window of ether implicates the removal of lone pair electrons from the ether-oxygen functional group, accompanied by H-abstraction and radical intermediates. , …”

“…In comparison, the SEI formed in BCE-SN displays a uniform and thin morphology (12 nm), containing large amounts of crystalline inorganic nanoparticles with the coexistence of Li 2 O and Li 3 N (Figure b–d). Li 3 N possesses superior ionic conductivity and mechanical property, and Li 2 O plays a vital role in promoting the robustness and stability of electrode interphases. ,,− These high-quality SEI components and abundant grain boundaries can provide fast Li transport and uniform Li-ion flux for chunky lithium deposition.…”

Constructing an inorganic-rich solid electrolyte interphase by adjusting electrolyte additives for stable Li metal anodes

“…28 As a type of inorganic Li compound, Li 3 N with excellent Li + conductivity (10 −3 S cm −1 ) can promote Li + transport in SEI to facilitate diffusion kinetics and regulate the uniform deposition of Li + . [29][30][31] Nevertheless, Li 3 N alone on SEI cannot effectively suppress Li dendrites due to the low interface energy of Li 3 N against Li. 32 So, balancing the synergistic effect between the different components will maximize the creation of an ideal SEI and improve the electrochemical performance of the battery.…”

Enhancing the Stability of Metallic Li Anodes for Aprotic Li–O2 Batteries with Dual-Anion Electrolytes

“…Nonetheless, the polarization exhibited by the LiNO 3 electrolyte markedly surpasses that in LiFPFSI-related electrolytes, indicating a larger interfacial resistance. This can likely be attributed to the intrinsic inferior ionic conductivity, as a result of the increased dissociation energy within low dielectric media. − Conversely, as confirmed by the smaller voltage gap, Li + migration is preferential in LiFPFSI-based cells, likely due to higher dissociation levels . However, the decreased CE reflects the continuous Li exhaustion owing to deficient SEI.…”