上海大学《AFM》：分层多孔硅/碳复合材料，用于高能锂离子电池

摘要：锂离子电池（LIB）硅阳极的电化学性能主要受应力应变和传输动力学的影响。然而，传统的硅/碳复合材料往往不能很好地平衡这两个因素。本文，上海大学张海娇研究员、武汉理工大学苏宝连教授等在《ADVANCED FUNCTIONAL MATERIALS》期刊发表名

1成果简介

锂离子电池（LIB）硅阳极的电化学性能主要受应力应变和传输动力学的影响。然而，传统的硅/碳复合材料往往不能很好地平衡这两个因素。本文，上海大学张海娇研究员、武汉理工大学苏宝连教授等在《ADVANCED FUNCTIONAL MATERIALS》期刊发表名为“A Stress-Buffering Hierarchically Porous Silicon/Carbon Composite for High-Energy Lithium-Ion Batteries”的论文，研究在有限元分析的指导下，以多孔硅（pSi）和掺氮介孔碳（NMC）分别作为卵黄和外壳，开发了一种具有高锂存储容量的分层多孔硅/碳复合材料（pSi@void@NMC）。

内部和外部的培养设计使 pSi@void@NMC 复合材料具有快速的转移动力学、有效的应力缓冲、低体积膨胀和优异的机械稳定性。与核壳 pSi@NMC 和裸 pSi 电极相比，所制备的 pSi@void@NMC 阳极在 0.2Ag-1 的条件下循环 300 次后显示出 1769.8 mAh g-1 的高可逆容量，而且循环稳定性极佳，每个循环的容量衰减率仅为 0.016%。原位和非原位表征结果进一步证实，得益于富含无机 LiF 的 SEI 薄膜的形成，锂在电化学反应过程中的插入/析出具有很高的可逆性。此外，所开发的 pSi@void@NMC 复合材料还显示出良好的全电池应用潜力。这些发现提供了一种简便的设计理念和研究策略，可用于解决硅基负极材料应力断裂和传输动力学不足的问题，从而实现高性能锂电池。

2图文导读

图1、Advantages/disadvantages and stress–strain evolution of three different structures. a) 2D schematic diagrams of three structural evolution before and after cycling, b) Finite element simulation models of pSi@void@NMC, pSi@NMC, and pSi stress–strain in after full lithiation, and c) simulation curves of stress variation in different electrode materials during the process of lithium insertion.

图2、Synthesis and structural characterization of pSi@void@NMC. a) Synthetic diagram, b,c) SEM images, d,e) TEM images, f,g) HRTEM images, h) STEM image and corresponding EDX mappings of Si, O, C, and N elements, respectively.

图3、a) XRD patterns, b) Raman spectra. c) FT-IR spectra of pSi@void@NMC, pSi@NMC, and pSi samples. d) TGA curves of pSi@void@NMC and pSi@NMC. e,f) High-resolution XPS spectra of Si 2p and N 1s of pSi@void@NMC. g–i) N2 adsorption-desorption isotherms of pSi@void@NMC, pSi@NMC, and pSi samples.

图4、Electrochemical performances of pSi@void@NMC, pSi@NMC, and pSi electrodes. a) CV curves at 0.2 mV s−1, b) Voltage profiles for different cycles, c) Galvanostatic charge/discharge curves of the pSi@void@NMC electrode at different current densities. d) Cycling stabilities at a current density of 0.2 A g−1, the current density for the first three cycles is 0.1 A g⁻¹. e) Rate performance. f) Comparison of cycle performances between the pSi@void@NMC electrode and other Si/C anodes for LIBs. g) Surface contact angles at 0 and 2s of pSi@void@NMC, pSi@NMC, and pSi electrodes. h) GITT voltage profiles, and i) Li diffusion coefficient. j) The b-value of anodic (0.51 V) and cathodic (0.17 V) peaks derived from cyclic voltammetry (CV) experiments at various sweep rates.+

图5、a–d) In situ EIS spectra of the pSi@void@NMC electrode collected during initial and second lithiation/delithiation processes (0.01–1.3 V), and e–h) The DRT transformation of EIS spectra in a–d. i,j) In situ Raman spectra of the pSi@void@NMC electrode during the lithiation/delithiation process, and k) corresponding variation trends of ID/IG ratios during the discharge/charge processes.

图6、a) Cross-sectional SEM images of the pSi@void@NMC, pSi@NMC, and pSi electrodes (fresh and after 100 cycles), and b) Comparison of electrode thickness before and after cycling, along with expansion rate. c) Hierarchical pore network models encompass a range of scales, spanning from individual pores to interconnected meso-micropore structures, and d) ion transport paths in three different porous network models: individual mesopore, micro/mesopore, and micro/meso-mesopore. e) Structural changes and lithium storage advantages of the pSi@void@NMC, pSi@NMC, and pSi electrodes after many cycles.

图7、XPS depth etching spectra of pSi@void@NMC and pSi@NMC electrodes after 100 cycles at 1.0 A g−1: a) C1s, and b) F1s. c) Evolution of the peak area ratios of C, F, and Si signals at different etching depths, and d) Evolution of the peak area ratios of the C─C, C─O, ROCO2Li, Li2CO3, CFx, organic-F, and LiF signals at different etching depths. Schematic SEI components of e) pSi@void@NMC, and f) pSi@NMC electrodes.

图8、a) Schematic illustration of the pSi@void@NMC//LFP full-cell, b,c) galvanostatic charge/discharge profiles, d,e) Cycling performance and rate capacity of the pSi@void@NMC//LFP full-cell (inset is lighting a digital photo of the LED device with the “SHU” pattern).

3小结

总之，我们采用微孔 ZSM-5 沸石作为独特的硅前驱体，并将其与镁热还原法和共聚物定向组装策略相结合，制造出分层多孔硅/碳复合材料。这种简便的设计实现了体积膨胀产生的应力应变与能量传输动态之间的微妙平衡。从理论模拟到细致对比，卵壳结构与核壳 pSi@NMC 和裸 pSi 电极相比具有综合性能优势，实现了材料设计中 “内外兼修 ”的目标。外部 "指的是圆柱形介孔碳壳和空隙，它们能增强电子/离子传输，同时确保结构和界面的稳定性。内部 "方面则涉及微/介孔硅核，它可以缓解体积膨胀，同时通过介孔加强锂离子传输，并通过微孔增加活性位点。凭借这些优点，用于 LIB 的 pSi@void@NMC 阳极在 0.2 A g-1 条件下可实现 1769.8 mAh g+-1 的高放电容量，并具有较长的循环稳定性。同时，pSi@void@NMC//LFP 全电池在 0.5 摄氏度条件下循环 100 次后，也显示出 142 mAh g-1 的高可逆容量。

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