Professor Chang Zhi and Professor Pan Anqiang Small: Lithium metal batteries with lithium metal batteries induced by the directional lithium deposition direction induced by lithium metal substrates
Article information
Lithophilic magnetic carbon substrates induce directional deposition toward applicable lithium metal batteries
First author: Zhou Shuang
Corresponding authors: Chang Zhi*, Pan Anqiang*
Unit: Central South University
Research background
With the rapid development of the electric vehicle energy storage market, people have put forward higher requirements for the energy density of batteries. The high specific capacity of lithium metal (3860 mAh g-1) and low electrochemical potential (-3.04 V compared to standard hydrogen electrodes) provide higher energy density for batteries than other anode materials. However, the efficient and stable cycle of lithium metal faces problems such as large volume changes, many side reactions and safety hazards caused by dendrites. The construction of three-dimensional lithium metal anode can reduce the local current density, uniform ion flow, and resist the volume change of the electrode during the cycle process, which is a very effective modification strategy.
Introduction to the article
Based on this, the team of Professor Chang Zhi & Professor Pan Anqiang of Central South University designed a carbon nanofiber backbone (Co3O4-CCNFs) anchored with magnetic Co3O4 nanocrystals on the fiber surface to stabilize the lithium metal anode. This modified skeleton has superior performance, and magnetic Co3O4 as a nucleation site can induce the formation of micromagnetic fields on the electrode surface, thereby inducing the directional uniform nucleation and deposition of lithium metal on the fiber, and inhibiting the growth of dendrites. In addition, the interconnected self-supporting carbon nanofiber frame has a large specific surface area and excellent mechanical properties, which can uniformly distribute the current and lithium ion flux, reduce the effective current density in the electrode and reduce the volume expansion generated by lithium metal during cycling, and prolong the life of the electrode. The assembled symmetrical battery can be stable for 1600 hours (2 mAcm−2, 1 mAh cm−2) under limited lithium conditions of only 10 mAh cm-2. LiFePO4|| The cycle stability of the whole battery assembled by Co3O4-CCNFs@Li was still significantly improved under the practical condition of limited negative/positive capacity ratio (2.3:1) (86.6% capacity retention in 440 cycles).
Figure 1. Preparation of the as-prepared Co3O4-CCNFs and schematic diagrams of different Li deposition process on a) CNF and b) Co3O4-CCNFs. The blue dotted arrow represents the direction of the magnetic field.
Point 1.Exploring the influence of magnetic fields on the deposition process of lithium metal
In order to explore the influence of magnetic fields on the lithium metal deposition process, zinc is used instead of lithium to simulate the metal deposition process on a three-dimensional substrate during battery cycling. As shown in Figure 3a, no zinc deposition was found at the bottom of the carbon cloth after 120s plating under the action of electric field alone. When the plating time is extended to 300 s and 450 s, the zinc deposition at the bottom of the carbon cloth remains slight and uneven. However, when using a combination of electric and magnetic fields, after 120s of Zn deposition, the bottom of the carbon cloth is covered with gray plating products and becomes more compact and uniform over time (Figure 3b). A similar phenomenon has been observed on copper foam substrates. Further, using methylene blue as an indicator, the migration process of metal ions in the electrolyte can be observed. The results of Figure 3c-e show that under the action of only a magnetic field, the ions move slowly in the electrolyte; Under the action of only the electric field, the ions will slowly diffuse and migrate in the direction of the electric field; Under the simultaneous action of electric and magnetic fields, ions will rotate and migrate at a very fast speed to obtain a more uniform and dense lithium deposition morphology.
Figure 3. Digital photos of carbon cloth (the bottom-side) after electroplating Zn a) with electric field and b) with both electric field and magnetic field. Zn ions under c) magnetic field, d) electric field, e) both electric field and magnetic field.
Point 2. Study on the directional regulation of lithium deposition behavior by Co3O4-CCNFs
The morphology of lithium metal with different loads deposited on CNFs and Co3O4-CCNFs was characterized by SEM. When lithium is deposited into CNFs, lithium metal accumulates on the substrate surface of CNFs (Figure 4a), which is due to the top deposition due to the strength of the electric field near the diaphragm end, and because CNFs are not lipophilic, the inhomogeneous deposition is more serious. In contrast, when depositing lithium metal on Co3O4-CCNFs, due to the uniform distribution of fine Co3O4 nanocrystals and diffuse carbon nanotubes on the fibers, the active lithium metal will react with the Co3O4 nanocrystals to generate Co/LiO, which will induce uniform deposition of Li around the Co3O4-CCNFs fiber (Figure 4b).
In order to further explore the deposition behavior of lithium on different substrates, COMSOL simulation was performed by nonlinear concentration field and electrode situation based on Butler-Volmer electrochemical reaction kinetics. It can be seen from Figure 5 that the concentration of lithium ions on the surface of Co3O4-CCNFs fibers is much higher than that on the surface of CNFs fibers at the same time of deposition, indicating that the lithium philicity of Co3O4-CCNFs is better than that of CNFs. In addition, the distribution of lithium ions on the surface of Co3O4-CCNFs fibers is also more uniform than that on the surface of CNFs fibers, because the introduction of Co3O4 nanocrystals adds more nucleation sites to the substrate and homogenizes the lithium ion flow on the surface.
Figure 4. Morphology study and the related simulations of Li plating on a) CNFs and b) Co3O4-CCNFs. Surface SEM image of anodes with i) 2 mAh cm−2 and ii,iii) 6 mAh cm−2 deposited Li. The Li+ concentration field simulation for different electrode (CNFs and Co3O4-CCNFs) after iv) 0 s, v) 1s, and vi) 5 s during Li deposition.
Point 3. Electrochemical performance of Co3O4-CCNFs in symmetrical and half-cell cells
In order to evaluate the electrochemical performance of different substrate materials, the nucleation and deposition overpotential of lithium metal of different substrates were tested by half-cell. As shown in Figure 5a, among the four substrate materials, lithium has the easiest nucleation and the most stable deposition on Co3O4-CCNFs, indicating that the Co3O4-CCNFs substrate has the best lithiphilicity. As one of the important indicators to measure the long-term stable cycle of lithium metal batteries, coulomb efficiency (CE) has always been the focus of attention.
To study the CE value of several substrate materials, Li|| was assembled Cu、Li|| CNFs、Li|| CCNFs and Li|| Co3O4-CCNFs half-cells were tested. As shown in Figure 5b, under the conditions of 1 mA cm-2 and 1 mAh cm-2, Cu foil electrodes can only cycle stably for 30 cycles at an average CE of 95.1%, and the life of CNFs is slightly longer than that of Cu foils, the analysis is that the CNFs electrodes are three-dimensional frames with large specific surface area, corresponding to small local current densities. Both CCFs and Co3O4-CCNFs outperform CNFs, stabilizing cycles of 240 and 250 cycles with an average CE of 98%, respectively. Co3O4-CCNFs have the best performance, and can cycle stably for 400 cycles with a high average CE of 99.1%, keeping the surface capacity unchanged and increasing the current density, and Co3O4-CCNFs can still perform excellent CE (Figure 5 c-e).
In order to measure the cycle stability of lithium metal batteries, pre-deposited 10 mAh cm-2 lithium composed of Co3O4-CCNFs@Li symmetrical batteries, as shown in Figure 5f, Co3O4-CCNFs@Li symmetrical batteries have good performance and can maintain stable cycles for 1600 hours without obvious voltage increase. SEM was used to further characterize the morphology of different composite electrodes after cycling, and the results were shown in Figure 5 g-i, and it can be seen that the electrode surface of the bare lithium anode is covered with a large amount of mossy lithium and dead lithium after 146 cycles. CNFs@Li composite anode situation is similar, which is consistent with battery performance. However, even after 1600 cycles, the Co3O4-CCNFs@Li composite anode does not have any lithium dendrites and dead lithium on its surface.
Figure 5. Cycling performances of Li|| Cu half-cells and Li|| Li symmetric cells based on different substrates. a) Li deposition curves of Li|| Cu half-cells based on Cu, CNFs, and Co3O4-CCNFs electrode at 1 mA cm−2 (nucleation overpotentials of electrodes were marked. b) CE of the Li|| Cu, Li|| CNFs, Li|| CCNFs, and Li|| Co3O4-CCNFs at 1 mA cm−2, 1 mAh cm−2. CE of the Li|| Cu and Li|| Co3O4-CCNFs at c) 3 mA cm−2, 1 mAh cm−2; d) 1 mA cm−2, 2 mAh cm−2; and e) 1 mA cm−2, 10 mAh cm−2. f) Electrochemical performance of symmetric cells (Cu@Li, bare Li, CCNFs@Li Co3O4-CCNFs@Li) at 2 mA cm−2 for 1 mAh cm−2. The surface SEM image of g) Cu@Li anode after 145 cycles, h) CCNFs@Li anode after 880 cycles, and i) Co3O4-CCNFs@Li anode after 1600 cycles in symmetric cell at 2 mA cm−2 for 1 mA h cm−2.
Point 4. Performance evaluation of Co3O4-CCNFs in lithium metal whole battery
The Co3O4-CCNFs@Li composite anode was further matched with the lithium iron phosphate (LFP) cathode and assembled into a lithium metal battery for performance evaluation. As shown in Figure 6a, at 0.2 C, 0.5 C, 1 C, 2 C, LFP|| Co3O4-CCNFs@Li full battery ratio LFP|| Cu@Li exhibits significantly enhanced electrochemical performance (Figure 6b). Charge-discharge voltage hysteresis is an important parameter for the internal polarization and electrode stability of the reaction battery. Summarizing the voltage hysteresis values at different rates of the two batteries into Figure 6 c, you can see LFP|| The voltage hysteresis value of Co3O4-CCNFs@Li is much less than Cu@Li|| LFP。 Further explanation of LFP|| Co3O4-CCNFs@Li has small internal polarization, few side reactions, and good electrode interface stability.
In order to get closer to the practical application and ensure the energy density of the lithium metal full battery, the charge and discharge test of the constant current is carried out with a full battery with a larger LFP surface load and lower N/P (Figure 6d), LFP|| Co3O4-CCNFs@Li has excellent cycling performance, with a capacity retention rate of 88.6% after 440 stable cycles. In addition, electrochemical impedance spectroscopy (EIS) was used to characterize the battery interface before and after cycling, and LFP|| can be seen The contact impedance of Co3O4-CCNFs@Li increases only slightly after 70 cycles (Figure 6 e,f), indicating that there are fewer side reactions in the battery, and the SEM results show LFP|| Co3O4-CCNFs@Li the surface by-product of the internal electrode piece of the battery is more than LFP|| Cu@Li the battery is significantly reduced (Figure 6 g, h), further illustrating the LFP|| The cycle stability of Co3O4-CCNFs@Li composite anode is good.
Co3O4-CCNFs are self-supporting substrates with good flexibility and are expected to be applied to flexible lithium metal batteries. As a concept test, the Co3O4-CCNFs@Li negative electrode and the flexible CNF100@LFP positive electrode are matched into a flexible pouch battery, as shown in Figure 6i, and the flexibility test of the assembled pouch metal lithium battery is carried out, whether it is bent, folded many times, or repeatedly knocked after folding, the pouch battery can smoothly supply power to the blue strip light.
Figure 6. Electrochemical performance of LFP|| Li full-cells and the anode morphology after cycling. a) The rate performance of the LFP|| Cu@Li and LFP|| Co3O4-CCNFs@Li full-cells. Comparison of b) specific capacity and c) charge–discharge voltage hysteresis in Cu@Li|| LFP and Co3O4-CCNFs@Li|| LFP full-cells at different rates. d) The cycling performance of the Cu@Li|| LFP and LFP|| Co3O4-CCNFs@Li full-cells at 1 C (1 C = 150 mAh g−1). Impedance spectroscopy of the e) LFP|| Cu@Li and f) LFP|| Co3O4-CCNFs@Li full-cells before and after 70 cycles at 1 C. The surface SEM image of g) Cu@Li anode and h) Co3O4-CCNFs@Li anode after 150 cycles. i) Schematic and flexibility test of a flexible LMB (CNF1000@LFP|| Co3O4-CCNFs@Li) pouch-cell to light a series of LEDs up under different states.
Article link
Lithiophilic Magnetic Host Facilitates Target-Deposited Lithium for Practical Lithium-Metal Batteries
https://doi.org/10.1002/smll.202207764
About the corresponding author
Professor Chang Zhi Profile: Professor of School of Materials Science and Engineering, Central South University, doctoral student/master supervisor, selected into the National Overseas High-level Young Talents Program (Overseas Excellent Youth) in 2022. Ph.D. and postdoctoral fellows studied under the tutelage of Professor Haoshen Zhou, an internationally renowned electrochemistry expert (University of Tsukuba & Japan Institute of Advanced Industrial Science and Technology - AIST). Mainly engaged in the research of high specific energy lithium-ion battery/lithium metal battery electrolyte, functional separator, solid electrolyte, metal anode protection and other directions.
In the past five years, he has published more than 60 SCI papers, including the first author (including co-authors)/co-corresponding authors in Joule, Nat. Commun. (x 2)，Angew. Chem. Int. Ed. (x 3)，Adv. Mater.，Energy Environ. Sci. (x 2)，Adv. Funct. Mater. (x2)，Energy Storage Mater. (x 2)，Small，J. Mater. Chem. A (x 4) and other journals published 26 papers, he cited more than 3600 times, H factor 31, applied for 6 national invention patents. He is a guest editor of the SCI journal Materials, a young editor of eScience and a member of the Nat. Commun.，Adv. Mater.，Angew. Chem. Int. Ed.，Energy Environ. Sci.，J. Am. Chem. Soc.，Adv. Funct. Reviewer of Mater., Adv. Energy Mater., Energy Storage Mater. and other prestigious international journals.
Professor Pan Anqiang Profile: Professor of School of Materials Science and Engineering, Central South University, Head of Department of Materials Physics. He has been selected as a New Century Outstanding Talent of the Ministry of Education, a young talent of Huxiang, a young scholar of the "Furong Scholar Award Program" of Hunan Province, a young scholar of the "Yangtze River Scholar Award Program" of the Ministry of Education, and a leading talent of science and technology innovation in Hunan Province. His main research areas are secondary power and energy storage batteries. So far in Nat. Commun., Angew. Chem. Int. Ed., Adv. Mater., Adv. Energy Mater., Adv. Funct. Mater., Energy Environ. He has published more than 150 papers in international journals such as Sci., Nano Energy., Energy Storage Mater., including more than 40 papers in 10 IF> papers, and more than 10,000 citations. He has applied for more than 20 invention patents, participated in domestic and foreign conferences and made invited reports more than 20 times, and cited more than 7,000 papers.