1成果簡介

鋰氧電池（LOBs）中的能量-功率權(quán)衡源于多孔正極中氧氣（O?）傳輸遲緩以及過氧化鋰（Li?O?）堵塞孔隙的問題。雖然提高孔隙率能增強(qiáng)電解質(zhì)可及性并提升Li?O?儲存能力，但同時也會增加電解質(zhì)需求，從而削弱電池的整體能量密度。這迫使研究者尋求替代策略，在不犧牲能量密度的前提下提升功率性能。本研究通過O?傳輸理論模擬揭示：相較于孔隙率本身，通過增強(qiáng)孔隙互聯(lián)性降低曲折度對O?傳輸?shù)挠绊懜鼮轱@著。

基于此發(fā)現(xiàn)，本文，日本國立材料科學(xué)研究所Arghya Dutta、Shoichi Matsuda等研究人員在《ADVANCED SCIENCE》期刊發(fā)表名為“Interconnected Hierarchically Porous Graphene-Based Membrane Electrode for High-Power and Long-Cycle Lithium–Oxygen Battery”的論文，研究采用非溶劑誘導(dǎo)相分離法，以聚丙烯腈（PAN）為碳支架、聚乙二醇（PEO）為犧牲孔隙劑，制備出具有高度互聯(lián)巨孔網(wǎng)絡(luò)的自支撐石墨烯基電極。PEO的選擇性分解形成空間互聯(lián)的巨孔結(jié)構(gòu)，有效降低了曲折度。所得電極使鋰氧電池在稀釋電解液條件下，于1.0 mA cm?2電流密度下實現(xiàn)>2500 mAh g?1的能量密度。僅使用3.25 g Ah?1電解液即可在4 mAh cm?2電流密度下保持穩(wěn)定循環(huán)，并在1.5 mA cm?2條件下經(jīng)受90次循環(huán)仍保持高倍率性能。本研究通過合理電極結(jié)構(gòu)設(shè)計，為實用化鋰離子電池同時提升能量密度與功率性能提供了強(qiáng)有力的解決方案。

2圖文導(dǎo)讀

圖1、Variation of the effective diffusion coefficient (Deff) of oxygen (O2) with a) porosity (ε) and b) tortuosity (τ). c–h) Contour plots of normalized O2 concentration across the electrode thickness under different current densities.

圖2、chematic illustration of the structural differences among various carbon electrodes depending on the fabrication approach. The top panel depicts a particle-based porous carbon electrode fabricated using a binder, where pores are primarily confined within individual particles. The middle panel shows a nonideal meso-macroporous carbon membrane in which macropores exist but remain spatially isolated, limiting mass transport. The bottom panel illustrates the ideal architecture, a freestanding carbon membrane featuring a continuous network of interconnected macropores that facilitate efficient electrolyte infiltration and gas diffusion. Small white circles denote mesopores, while large white circles indicate macropore. The micropores and interconnectivity through microporous channels are not shown.

圖3、a) Transmission electron micrograph (TEM) of GMS powder sample. Cross-section scanning electron micrograph (SEM) of b) GMS and c) iGMS membranes. d) Schematic representation of the electrode fabrication processes following NIPS method with and without using PEO. e) Thermogravimetric analysis (TGA) data of PAN and PEO under a helium atmosphere. Pore size distribution curves of GMS and iGMS membranes measured by f) N2 adsorption/desorption and g) Hg porosimetry.

圖4、Galvanostatic discharge profiles of LOB cells with GMS and iGMS electrodes at a) 0.4 mA cm?2 and b) 1.0 mA cm?2 up to 2.0 V versus Li/Li?. c) Average discharge voltages at 1.0 mA cm?2. Cycling profiles of d) GMS and e) iGMS at 0.4 mA cm?2 with 4 mAh cm?2 capacity under EL/C = 6, and f) corresponding cycle lives. Cycling profiles of g) GMS and h) iGMS under EL/C = 4, and i) corresponding cycle lives. High-rate cycling of j) GMS and k) iGMS electrodes. l) Comparison of high-rate cycling stabilities of iGMS electrode with previously reported cells cycled at current densities ≥ 0.8 mA cm?2 and limited capacities.

圖5、Galvanostatic discharge/charge profiles and O2 evolution rates during charging for the a) 1st and b) 5th cycles using KB, GMS, and iGMS electrodes. Comparison of O2 yield in different electrodes for the c) 1st and d) 5th cycles.

3小結(jié)

本研究強(qiáng)調(diào)了在稀薄電解液條件下運行的液態(tài)氧化物電池中，碳電極內(nèi)部互聯(lián)多孔網(wǎng)絡(luò)與優(yōu)化孔隙率的關(guān)鍵作用——其能實現(xiàn)高容量、長循環(huán)壽命，并在高功率運行時保持穩(wěn)定性能。雖然增加電極孔隙率通常與更高容量相關(guān)，但多孔網(wǎng)絡(luò)的合理連接對確保電解液和氧氣的有效擴(kuò)散至關(guān)重要，這是實現(xiàn)高功率性能的基礎(chǔ)。此外，孔隙體積過大且未優(yōu)化的電極往往需要更大電解液容量才能維持穩(wěn)定循環(huán)，反而抵消了比容量優(yōu)勢。反之，當(dāng)電解液容量降低時，高孔隙率電極將面臨嚴(yán)重電解液耗竭，導(dǎo)致顯著的電壓極化及電池過早失效。

開發(fā)具有高度互聯(lián)孔隙網(wǎng)絡(luò)和優(yōu)化孔隙體積的電極，同時最大限度減少非活性孔隙率，為克服鋰離子電池中的能量-功率權(quán)衡提供了有前景的途徑。例如，一種具有優(yōu)化孔隙結(jié)構(gòu)的GMS電極在低電解液負(fù)載比（EL/C=5）下，于1.0 mA cm?2放電速率下展現(xiàn)出2520 mAh g?1的高放電容量。此外，該孔隙優(yōu)化GMS電極在EL/C比值為4時，以4 mAh cm?2的高面積容量實現(xiàn)穩(wěn)定循環(huán)，并在1.5 mA cm?2高倍率下持續(xù)90次循環(huán)，展現(xiàn)卓越的高功率循環(huán)性能。相比之下，在類似稀薄電解液條件下，孔隙體積更大但缺乏合理孔隙連通性的電極，其容量表現(xiàn)欠佳，循環(huán)穩(wěn)定性降低，且倍率性能較弱。這些發(fā)現(xiàn)強(qiáng)調(diào)了精細(xì)調(diào)節(jié)電極孔隙結(jié)構(gòu)的重要性，以在鋰氧電池中平衡容量、循環(huán)穩(wěn)定性、倍率性能和電解液利用率。這些研究還為先進(jìn)碳材料的設(shè)計提供了寶貴見解，為開發(fā)下一代實用鋰氧電池鋪平了道路。

文獻(xiàn)
:https://doi.org/10.1002/advs.202519091

來源：材料分析與應(yīng)用