The construction of stable cathode electrolyte interphase (CEI) is the key to improve the NCM811 particle structure and interfacial stability via electrolyte engineering. In He’s work, lithium hexamethyldisilazide (LiHMDS) as the electrolyte additive is proposed to facilitate the generation of stable CEI on NCM811 cathode surface and eliminate H2O and HF in the electrolyte at the same time, which boosts the cycling performance of Li||NCM811 battery up to 1000 or 500 cycles with 4.5 V cut-off voltage at 25 or 60 °C.
The increasing demand for energy storage stimulates the extensive research of high energy density batteries [1,2,3]. Lithium metal battery (LMB) composed by Li anode and LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode is one of the most promising candidates while it is applied at high cut-off voltage (i.e., ≥ 4.5 V vs Li/Li+). However, the poor cycling stability associated with NCM811 cathode breakage is a critical issue which needs to be addressed urgently [4, 5]. The available way is to construct a robust CEI on NCM811 particle surface as well as eliminate trace H2O and HF in electrolyte, which will attack NCM811 particle and Li anode [6, 7]. Thus, finding an effective electrolyte additive to achieve this purpose is highly feasible [8,9,10].
Recently, He’s group reported an efficient electrolyte additive (lithium hexamethyldisilazide, LiHMDS) to enhance the performance of Li||NCM811 battery and also discussed its working mechanism . As shown in Fig. 1a, the Li||NCM811 battery assembled with baseline electrolyte (BE) (1 M LiPF6 in EC, EMC and DMC (1:1:1 by volume), (H2O < 20 ppm)) could only maintain 49.13% capacity retention after 1000 cycles with 4.5 V cut-off voltage at 25 °C. In sharp contrast, the Li||NCM811 battery with 0.6 wt% LiHMDS exhibited superior cycling performance. The capacity retention reached up to 73.92% after 1000 cycles. Moreover, the Li||NCM811 battery with LiHMDS could also obtain outstanding cycling stability at 60 °C. The battery with 0.6 wt% LiHMDS could maintain 66.02% capacity retention with high average coulombic efficiency of 99.11% after 500 cycles, while the battery with BE crashed down after about 450 cycles at 60 °C (Fig. 1b). He and his co-workers considered that the remarkable cycling stability of Li||NCM811 cells with 0.6 wt% LiHMDS was attributed to the scavenging ability of H2O and HF in the electrolyte by LiHMDS. As shown in Fig. 1c, the concentration of H2O in BE is 18.9 ppm, higher than that in the electrolyte with 0.6 wt% LiHMDS (3 ppm). Furthermore, after adding extra 1000 ppm H2O into electrolyte, the H2O concentration can still maintain a low level of 23.3 ppm with the existent of LiHMDS but surge to 969.2 ppm without LiHMDS. Similarly, the concentration of HF reached 17.58 ppm in BE and increased to 776.45 ppm after the addition of extra 1000 ppm H2O (Fig. 1d). However, no HF was detected while the electrolyte contained 0.6 wt% LiHMDS. This confirms the successful elimination of H2O and HF in electrolyte by LiHMDS.
In addition, He’s group also verified a robust and uniform cathode electrolyte interphase (CEI) generated on the surface of NCM811 to enhance its structural stability, which was associated with the preferential oxidization of LiHMDS than electrolyte solvents. With the protection of robust CEI, the NCM811 particles avoided harmful reactions with electrolyte and the reduction of high valence Ni4+. As a result, the phase transition from layered structure to rock-salt phase was restrained (Fig. 1e), ensuring the stability of NCM811 during continual cycling. The function schematic illustration of LiHMDS in Li||NCM811 battery was demonstrated in Fig. 1f. LiHMDS can capture HF and trace H2O in electrolyte to form HMDS and other inorganic products (LiF and LiOH). Besides, LiHMDS can be preferentially oxidized before the electrolyte to build a thin and compact CEI on the surface of NCM811 cathode. Therefore, the superior CEI can inhibit the side reaction of NCM811 with the electrolyte, phase transition from layered structure to rock-salt phase and the dissolution of TM ions from NCM811.
In conclusion, the work from He’s group has given a systematic and comprehensive explanation of LiHMDS as the electrolyte additive, which can bring a remarkable improvement of Li||NCM811 cells performance between 3 and 4.5 V, 25 and 60 ℃. This work provides a novel strategy to preferentially construct a robust CEI on nickel-rich NCM cathodes and eliminate the HF and H2O in electrolyte simultaneously for long cycling stability of high-voltage batteries at elevated temperature. It also proves the feasibility of electrolyte additives and guides the further research for high-voltage LMB.
D. Wu, J. He, J. Liu, M. Wu, S. Qi et al., Li2CO3/LiF-rich heterostructured solid electrolyte interphase with superior lithiophilic and Li+-transferred characteristics via adjusting electrolyte additives. Adv. Energy. Mater. 12(18), 2200337 (2022). https://doi.org/10.1002/aenm.202200337
S. Qi, H. Wang, J. He, J. Liu, C. Cui et al., Electrolytes enriched by potassium perfluorinated sulfonates for lithium metal batteries. Sci. Bull. 66(7), 685–693 (2021). https://doi.org/10.1016/j.scib.2020.09.018
Z. Yu, P.E. Rudnicki, Z. Zhang, Z. Huang, H. Celik et al., Rational solvent molecule tuning for high-performance lithium metal battery electrolytes. Nat. Energy 7(1), 94–106 (2022). https://doi.org/10.1038/s41560-021-00962-y
J. Huang, J. Liu, J. He, M. Wu, S. Qi et al., Optimizing electrode/electrolyte interphases and Li-ion flux/solvation for lithium-metal batteries with qua-functional heptafluorobutyric anhydride. Angew. Chem. Int. Ed. 60(38), 20717–20722 (2021). https://doi.org/10.1002/anie.202107957
W. Xue, M. Huang, Y. Li, Y.G. Zhu, R. Gao et al., Ultra-high-voltage Ni-rich layered cathodes in practical Li metal batteries enabled by a sulfonamide-based electrolyte. Nat. Energy 6(5), 495–505 (2021). https://doi.org/10.1038/s41560-021-00792-y
P. Xiao, Y. Zhao, Z. Piao, B. Li, G. Zhou et al., A nonflammable electrolyte for ultrahigh-voltage (4.8 V-class) Li||NCM811 cells with a wide temperature range of 100 °C. EnergY Environ. Sci. 15(6), 2435–2444 (2022)
F. Li, J. Liu, J. He, Y. Hou, H. Wang et al., Additive-assisted hydrophobic Li+-solvated structure for stabilizing dual electrode electrolyte interphases through suppressing LiPF6 hydrolysis. Angew. Chem. Int. Ed. 61(27), e202205091 (2022). https://doi.org/10.1002/anie.202205091
X. Fan, C. Wang, High-voltage liquid electrolytes for Li batteries: progress and perspectives. Chem. Soc. Rev. 50(18), 10486–10566 (2021). https://doi.org/10.1039/D1CS00450F
T. Liu, J. Liu, L. Li, L. Yu, J. Diao et al., Origin of structural degradation in Li-rich layered oxide cathode. Nature 606(7913), 305–312 (2022). https://doi.org/10.1038/s41586-022-04689-y
X. Li, J. Liu, J. He, S. Qi, M. Wu et al., Separator-wetted, acid- and water-scavenged electrolyte with optimized Li-ion solvation to form dual efficient electrode electrolyte interphases via hexa-functional additive. Adv. Sci. 9(20), 2201297 (2022). https://doi.org/10.1002/advs.202201297
D. Zhang, M. Liu, J. Ma, K. Yang, Z. Chen et al., Lithium hexamethyldisilazide as electrolyte additive for efficient cycling of high-voltage non-aqueous lithium metal batteries. Nat. Commun. 13(1), 6966 (2022). https://doi.org/10.1038/s41467-022-34717-4
We thank the support from the National Natural Science Foundation of China (Grant No.51971090 and U21A20311).
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Huang, J., Yang, Y., Liu, Y. et al. Lithium Hexamethyldisilazide Endows Li||NCM811 Battery with Superior Performance. Nano-Micro Lett. 15, 33 (2023). https://doi.org/10.1007/s40820-022-00998-z
- Lithium metal battery
- Electrolyte additive
- Cathode electrolyte interphase
- Lithium hexamethyldisilazide
- Cycling performance