北航《AM》：新里程碑！寒冷条件下推进微米级硅基电池实际应用

摘要：微米级硅 (µSi) 阳极为高能量锂离子电池 (LIB) 带来了巨大的发展前景。然而，μSi 阳极在零摄氏度以下（尤其是零下 20 °C）的可充电循环性仍然具有挑战性，原因是在循环过程中固体电解质相间层（SEI）会发生严重的体积变化和开裂。本文，北京航空航天大

1成果简介

微米级硅 (µSi) 阳极为高能量锂离子电池 (LIB) 带来了巨大的发展前景。然而，μSi 阳极在零摄氏度以下（尤其是零下 20 °C）的可充电循环性仍然具有挑战性，原因是在循环过程中固体电解质相间层（SEI）会发生严重的体积变化和开裂。本文，北京航空航天大学王华教授、中国计量大学Dandan Yu、武汉科技大学高标教授等研究人员在《Adv Mater》期刊发表名为“Cyclable Micron-Sized Silicon-Based Lithium-Ion Batteries at −40 °C Enabled by Temperature-Dependent Solvation Regulation”的论文，研究通过使用具有温度自适应离子-偶极相互作用特征的电解质，实现了 µSi 基LIB的低温循环性。作为弱电子供体的甲基和电负性氟原子的协同作用赋予了二氟乙酸甲酯（MDFA）与锂的弱结合亲和力。

此外，在较低温度下，锂与二氟乙酸甲酯和氟乙烯碳酸酯（FEC）中氧原子之间的亲和力会降低，同时锂离子的配位也会随温度变化而增强。因此，MDFA/FEC 电解质在零下温度时表现出一种以接触离子对为主的特殊溶解结构，有利于锂的脱溶和形成薄而坚固的富无机 SEI。正如预期的那样，μSi 阳极在零下 40 °C、0.1 A g−1 条件下循环 100 次后显示出破纪录的 786 mAh g++++−1 容量，基于μSi 的全电池在零下 40 °C条件下显示出令人印象深刻的可充电性。这项工作为将μSi阳极的应用扩展到极寒条件铺平了道路。

2图文导读

图1、Structures of different solvent molecules, the coordination with Li, and binding energies of Li-solvent complexes (BE represents the abbreviation of binding energy).++

图2、a) The physico-chemical properties of MA, EA, MDFA, and EDFA solvents. b) Temperature-dependent ionic conductivities of MDFA/FEC, EDFA/FEC, MA/FEC, and EA/FEC electrolytes. c) Rate performance of µSi anodes in four electrolytes under current densities ranging from 1 to 10 A g−1 at 25 °C. d) Discharge specific capacities of µSi anodes in four electrolytes at 25 and –40 °C. The error bar represents the standard deviation of the average values of specific capacities. e) Long-term cycling performance of µSi anodes at different temperatures. f) Comparison of specific capacities with representative anodes for lithium-ion batteries at different temperatures.

图3、a) ESP maps of EA, MA, EDFA, and MDFA solvents. b) Raman spectra of four electrolytes, highlighting the characteristic bands of free FSI– (purple, 723 cm−1), CIPs (green, 732 cm−1), and AGGs (blue, 746 cm−1). c) FTIR spectra of different electrolytes and mixed solvents. d) Raman spectra of the MDFA/FEC electrolyte at the temperature ranging from 25 to –40 °C. e) RDF and coordination number of Li-O and Li-N obtained by MD simulations for the MDFA/FEC electrolyte at –40 °C. f) The proportion of SSIPs, CIPs, and AGGs in the MDFA/FEC electrolyte at 25 and −40 °C. g,h) The representative solvation structures of Li in the MDFA/FEC electrolyte at 25 and −40 °C obtained by MD simulations.+

图4、Characterizations of SEI layers formed on µSi anodes in the MDFA/FEC electrolyte at 25 and −40 °C. a) C 1s and Li 1s spectra of SEI layers after different Ar sputtering times. b) Atomic ratios of C, O, Li, F, and Si elements in SEI layers after different Ar etching times. c) Schematic illustration for the impacts of temperature on the composition and structure of SEI layers formed on µSi anodes. d) SEM images (scale bar for 1 µm) and (e) corresponding cross-sectional SEM images (scale bar for 10 µm) of µSi anodes before and after 5 cycles at different temperatures. f) Surface roughness, (g) Young's modulus, and (h) force-displacement curves comparison of SEI layers formed on µSi anodes at 25 and −40 °C.++

图5、Electrochemical performance of µSi-based full cells with the N/P ratio of 1.3. a) Schematic illustration for the working mechanism of full cells consisting of the LVP cathode and µSi anode. b) Cycling profiles of µSi||LVP full cells with the MDFA/FEC-LiNO3 electrolyte at various temperatures. c) Selected charge-discharge curves and (d) cycling performance of µSi||LVP full cells at –20 °C under 0.2 C. e) Cycling performance and (f) the corresponding charge-discharge curves of µSi||LVP full cells at –40 °C under 0.05 C. g) Rate capability and (h) the corresponding charge–discharge curves of µSi||LVP full cells at –40 °C under current densities ranging from 0.05 to 0.2 C.

3小结

总之，我们开发出了一种具有温度自适应离子-偶极相互作用的电解质，成功实现了 µSi 基锂离子电池的低温循环性。MDFA 中 C═O 基团中氧原子的电负性可通过甲基的弱电子供能和吸电子氟原子的加入而显著降低，从而有效削弱了锂-MDFA 的亲和力，并在电解质中诱导出高比例的 CIP 和 AGG。由于在较低温度下锂离子与 MDFA 和 FEC 溶剂中的氧原子之间的亲和力减弱，锂离子与 FSI- 之间的相互作用增强，促进了零下温度下以 CIPs 为主导的溶胶结构的形成，从而实现了高效的锂离子脱溶，并形成了薄而坚固的富含无机物的 SEI，以抵御 µSi 阳极在反复低温循环过程中的体积变化。因此，MDFA/FEC 电解液中的 1.0m LiFSI 使 µSi 阳极在-40 °C、0.1 A g-1 条件下循环 100 次后，容量达到创纪录的 786 mAh g++++-1。组装后的μSi||Li3V2(PO4)3全电池在零下20 °C、0.2 C（1 C = 133 mA g-1）条件下循环200次后，容量保持率达到惊人的约97.8%，即使在零下40 °C的条件下也表现出卓越的可充电性。这项研究标志着在寒冷条件下推进微米级硅基电池实际应用的一个重要里程碑。

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