Technical analysis of braided structure for realization of lithium-free lithium-free anode with high lithium loading

【introduction】

Increasingly serious fossil fuel shortages and environmental pollution have caused demand for renewable energy and promoted the rapid development of renewable energy technologies. In secondary battery systems, lithium metal batteries are receiving increasing attention due to their high theoretical specific capacity (3860 mAh g-1) and low redox potential (-3.04V). However, the growth of lithium dendrites in lithium metal batteries may cause "dead lithium" and battery short-circuit, resulting in increased battery risk and reduced capacity.

[Introduction]

Professor Huang Yunhui from Huazhong University of Science and Technology demonstrated that hollow carbon nanofibers with appropriate internal and external radius ratios can selectively deposit lithium ions on the inner surface. Based on this principle, the authors designed a braided structure to realize a dendritic lithium anode with high lithium loading. The lotus-like carbon nanofiber anode and LiNafion are coated as artificial SEI membranes, achieving a capacity of 3600 mAh and improving the coulombic efficiency. The author believes that the understanding of the relationship between lithium ion deposition and matrix geometry will provide a new idea for the rational design of hybrid lithium anodes in lithium battery systems. The results were published on Nano Energy under the title "A Strategy of Selective and Dendrite-Free Lithium Deposition for Lithium Batteries".

[Graphic introduction]

Figure 1 Simulation results of lithium deposition

(A) Simulation of lithium ion deposition in different inner and outer radius hollow carbon nanofibers and experimental results of lithium deposition

(B)(C)(D) Scanning electron microscopy image of 1 mAh lithium deposited at a radius ratio of 8:10, 5:10, 1:10

Note: The insertion graph shows the TEM image of carbon nanofibers deposited at 1mAh in lithium.

Figure 2 LCNF simulation and microscopic images

Schematic representations of (A), (B), (C), (D) SCNF, LCNF, Li-SCNF, Li-LCNF

TEM images of (E), (F), (G), (H) SCNF, LCNF, Li-SCNF, Li-LCNF

SEM images of (I), (J), (K), (L) SCNF, LCNF, Li-SCNF, Li-LCNF

Figure 3 Microtopography

(A), (B) SEM images and TEM images of LCNF@Nafion

(C1) LCNF@Nafion single fiber STEM picture

(C2) Corresponding linear EDX element distribution

(D) LCNF@Nafion slice schematic

(E) LCNF@Nafion slice image, illustration showing LCNF slices without Nafion

(F1) LCNF@Nafion slice TEM image

(F2) Corresponding linear EDX element distribution

(G), (H) SEM, STEM image of Li-LCNF@LNafion after 30 cycles of current density of 1 mA cm-2, 8 mAh cm-2

(I1) STEM image of single fiber LCNF@LNafion

(I2) Corresponding linear EDX element distribution

Figure 4 Coulomb efficiency and specific capacity curve

(A1), (A2) Coulomb efficiency, specific capacity curve of LCNF@LNafion at 1 mA cm-2

(B1), (B2) Coulomb efficiency, specific capacity curve of LCNF@LNafion at 2 mA cm-2

(C1), (C2) Coulomb efficiency, specific capacity curve of LCNF@LNafion at 5 mA cm-2

(D1), (D2) Coulomb efficiency, specific capacity curve of LCNF@LNafion at 8 mA cm-2

Figure 5 Cycle performance chart

(A) LCNF/LNafion (red) and Li/Li (black) batteries with a current density constant current cycle of 1 mA cm-2

(B) Cyclic performance of LCNF/LNafion (red) and SCNF (black) electrodes at current density of 1 mA cm-2

(C) Cycle performance of LiPO4/LI-LCNF@LNation battery

【summary】

In this paper, the growth of Li dendrites is controlled by designing the surface structure of the anode. The results show that hollow carbon nanofibers with appropriate internal and external radius ratio can control lithium dendrites. The authors found that the braided carbon nanofiber matrix allows lithium to preferentially deposit on the inner surface, so a stable carbon shell can block lithium dendrite growth. In addition, the multi-channel structure also gives the LCNF anode high capacity to carry lithium. Due to the presence of the Nafion SEI, the Li-LCNF anode achieved a capacity of 3600 mAh and increased coulombic efficiency (more than 99%). At the same time, lithium iron phosphate and Li-LCNF@LNafion battery also showed excellent electrochemical performance. The author believes that the understanding of lithium ion deposition and matrix geometry will provide a new idea for the rational design of hybrid lithium anode in lithium battery system. .