1成果簡介

高壓陰極的氧氣穿透是開發(fā)高能量密度鋰離子電池面臨的關(guān)鍵挑戰(zhàn)，因為它會在石墨陽極引發(fā)寄生反應(yīng)，并破壞固體電解質(zhì)界面（SEI）的穩(wěn)定性。本文，北京科技大學(xué)詹純 教授、中國科學(xué)院物理研究所 王雪鋒、華北電力大學(xué) 劉桂成 教授等在《Green Chem》期刊發(fā)表名為“Graphene shields enabling oxygen-durable graphite anode in high-energy lithium-ion batteries”的論文，研究通過在石墨負(fù)極上設(shè)計石墨烯屏蔽層來解決這一關(guān)鍵問題，該屏蔽層可阻隔氧氣滲透，并在形成周期中強制排出氧氣，這一效果已通過差分電化學(xué)質(zhì)譜法（DEMS）得到驗證。

低溫透射電子顯微鏡（cryo-TEM）與原子力顯微鏡（AFM）揭示，石墨烯屏蔽層促進了富無機物的SEI形成，顯著提升了其化學(xué)與機械強度（楊氏模量：17.63 GPa vs. 6.69 GPa基線值）。電化學(xué)評估表明，屏蔽陽極在4.8V全電池循環(huán)中實現(xiàn)了更優(yōu)的初始庫侖效率、更低的不可逆容量損耗及更強的容量保持能力。尤其值得注意的是，該氧氣屏蔽方案在4.8V條件下經(jīng)100次循環(huán)后，容量保持率達(dá)到原始石墨陽極的1.6倍。展望未來，該方法通過與陰極穩(wěn)定化及電解液工程的協(xié)同整合，有望為高性能鋰離子電池的商業(yè)化開辟可行路徑：在實現(xiàn)突破性能量密度（超過400 Wh kg?1）的同時，通過系統(tǒng)性界面工程優(yōu)化顯著延長循環(huán)壽命耐久性。

2圖文導(dǎo)讀

圖1、Schematic illustration of SEI formation in Gr anode using rGO shields to modulate oxygen crossover.

圖2、(a–d) SEM images of the pristine Gr and shielded Gr@xrGO (x = 1, 3, 5) samples. (e–h) TEM images and corresponding high-resolution magnified views of both the pristine sample and the graphene-modified sample. (i and g) TEM images of the wrinkled graphene film and its corresponding SAED pattern. (k) XRD patterns of rGO-shielded and the pristine samples. (l) Raman spectra of all the as-prepared samples.

圖3、(a and b) Initial charge/discharge profiles of the assembled full cells and statistical chart of charging capacity contribution per battery. (c and d) Schematic diagram using two half-cells in reverse series to exclude the effect of oxygen crossover and the corresponding initial charge/discharge profiles. (e) Initial charge/discharge curves of LFP||Gr with different rGO content shields. XPS spectra of C 1s (f) and F 1s (g) from Gr and Gr@3rGO after formation stage. (h) The relative atomic ratio ofC–C, C–O, C=O, and ROCO2Li based on C 1s spectra and Li–F, and P–F based on F 1s spectra.

圖4、(a) Cycling performance of the pristine and rGO-shielded full cells. Cryo-TEM images and Fourier transform patterns of SEI layers of Gr (b–d) and Gr@3rGO (e–g) after 100 cycles.

圖5、 (a and b) Top-down SEM images of Gr (a) and Gr@3rGO (b). (c–f) Cross-sectional SEM images of Gr and Gr@3rGO after 100 and 200 cycles. (g and h) Relative atomic ratios of C–C, C–O,C=O,and ROCO2Li based on C 1s spectra as well as Li–F and P–F based on F 1s spectra.

圖6、 (a and b) Nyquist plots of Gr||Ref (Li) in each system with three electrode set-up. (c) The RSEI value of Gr||Ref (Li) in each system with three electrode set-up. (d) Normalized current density vs. time curves of Gr||Li, measured by potentiostatic test for 110 h at 0.2 V. (e) Normalized capacity density vs. time curves Gr/Li, converted from the curves in d. (f) The growth rates of capacity loss of each half cell.

圖7、AFM height images and Young's modulus mappings of Gr (a and b) and Gr@3rGO (c and d) anodes. (e) Force-displacement approaching curves for Gr and Gr@3rGO anodes.

3小結(jié)

綜上所述，我們開發(fā)了一種基于rGO的理性設(shè)計氧氣阻隔屏障，將其應(yīng)用于石墨負(fù)極，有效緩解了LRMO全電池中氧氣穿透引起的性能衰減。該rGO屏蔽層展現(xiàn)出三重功能：(1) 通過立體位阻實現(xiàn)選擇性氧氣阻隔（層間距：0.32–0.34 nm）；(2) 通過邊緣缺陷維持鋰離子滲透性；(3) 通過抑制寄生氧-電解質(zhì)反應(yīng)增強界面穩(wěn)定性。與未涂覆陽極相比，rGO改性系統(tǒng)使氧氣排出量提高30%，從而減少表面氧氣積累。因此，采用rGO屏蔽陽極的全電池在1/3C循環(huán)100次后，容量保持率提升1.6倍，首充放電容量超過270 mAh g?1，初始庫侖效率達(dá)74.48%。此外，相較于原始樣品，rGO屏蔽樣品的RSEI值顯著降低。這表明rGO屏蔽層能抑制氧氣穿透引發(fā)的副反應(yīng)，優(yōu)化SEI層結(jié)構(gòu)并增強界面穩(wěn)定性。冷凍透射電子顯微鏡、X射線光電子能譜與原子力顯微鏡聯(lián)合驗證：屏蔽陽極形成富含LiF的薄層（約12納米）SEI，其楊氏模量高達(dá)17.63GPa，顯著區(qū)別于未涂覆樣品中厚層有機主導(dǎo)的SEI。本研究強調(diào)了陽極側(cè)界面工程在調(diào)控高電壓正極系統(tǒng)氧行為中的關(guān)鍵作用。基于物理篩分與界面穩(wěn)定化的rGO屏蔽概念，可廣泛推廣至其他產(chǎn)氧正極材料（如富鋰錳氧化物、富鎳層狀氧化物）。展望未來，該方法若能與陰極穩(wěn)定化及電解液工程協(xié)同整合，有望為實現(xiàn)能量密度突破400 Wh kg?1且循環(huán)壽命更長的實用鋰離子電池鋪平道路。

文獻：

• DOI
• https://doi.org/10.1039/D5GC04826E
• DOI
• https://doi.org/10.1039/D5GC04826

來源：材料分析與應(yīng)用