eScience

Insights for understanding multiscale degradation of LiFePO₄ cathodes

Wang Li, Qiu Jingyi, Wang Xiaodan, Chen Long, Cao Gaoping, Wang Jianlong, Zhang Hao, He Xiangming

2022, 2(2): 125-137. doi: 10.1016/j.esci.2022.03.006

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Abstract:
Lithium-ion batteries (LIBs) based on olivine LiFePO₄ (LFP) offer long cycle/calendar life and good safety, making them one of the dominant batteries in energy storage stations and electric vehicles, especially in China. Yet scientists have a weak understanding of LFP cathode degradation, which restricts the further development of LFP materials and batteries. Here, we critically review reports on LFP cathode degradation with respect to different electric parameters (including C-rates, storage, and long cycling), mechanical stresses, and thermal fields. The detailed chemical and physical aspects of degradation mechanisms at various scales (i.e., from atomic to devices) and their causes are comprehensively summarized, and discussions of related concerns are provided in each section. We close with a systematic overview of LFP degradation research and mediation strategies, suggesting future directions for developing robust, safe LFP batteries with long cycle life.

Solid-state lithium batteries: Safety and prospects

Guo Yong, Wu Shichao, He Yan-Bing, Kang Feiyu, Chen Liquan, Li Hong, Yang Quan-Hong

2022, 2(2): 138-163. doi: 10.1016/j.esci.2022.02.008

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Abstract:
Solid-state lithium batteries are flourishing due to their excellent potential energy density. Substantial efforts have been made to improve their electrochemical performance by increasing the conductivity of solid-state electrolytes (SEs) and designing a compatible battery configuration. The safety of a solid lithium battery has generally been taken for granted due to the nonflammability and strength of SEs. However, recent results have shown the release of dangerous gases and intense heat due to the formation of lithium dendrites, indicating the safety of solid-state lithium batteries may have been overestimated. In this review, we introduce a safety evaluation methodology, then focus on the garnet Li₇La₃Zr₂O₁₂ (LLZO) and sulfide-based SEs, summarizing their structure, conductivity, compatibility with a lithium metal anode, electrochemical/chemical stability, and mechanical/thermal stability, which correlate closely with battery safety. We also evaluate the safety of all-solid-state lithium batteries, then conclude by discussing future avenues for improving the safety of SE-based batteries.

MXenes: Synthesis strategies and lithium-sulfur battery applications

Zhang Teng, Zhang Long, Hou Yanglong

2022, 2(2): 164-182. doi: 10.1016/j.esci.2022.02.010

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Abstract:
Since their discovery in 2011, the two-dimensional transition-metal carbides, nitrides, and carbonitrides known as MXenes have attracted considerable attention due to their metallic conductivity, mechanical properties, and hydrophilicity, which are closely related to their rich surface terminations. As a result, numerous novel synthesis strategies have been explored and new MXenes have been developed. Some have been applied in the field of energy storage, typically lithium–sulfur batteries (LSBs). This review summarizes recent advances in MXenes for LSBs. We first introduce the structural characterization of these materials, then provide detailed summaries of synthetic methods. Next, we give a comprehensive overview of research progress on MXenes for the cathodes, separators, and anodes in LSBs. Finally, we address challenges and offer perspectives on future directions for research. We hope this review will help researchers gain insight into multifunctional MXenes and their comprehensive applications in LSBs.

Probing thermally-induced structural evolution during the synthesis of layered Li-, Na-, or K-containing 3d transition-metal oxides

Hua Weibo, Yang Xiaoxia, Casati Nicola P.M., Liu Laijun, Wang Suning, Baran Volodymyr, Knapp Michael, Ehrenberg Helmut, Indris Sylvio

2022, 2(2): 183-191. doi: 10.1016/j.esci.2022.02.007

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Abstract:
Layered alkali-containing 3d transition-metal oxides are of the utmost importance in the use of electrode materials for advanced energy storage applications such as Li-, Na-, or K-ion batteries. A significant challenge in the field of materials chemistry is understanding the dynamics of the chemical reactions between alkali-free precursors and alkali species during the synthesis of these compounds. In this study, in situ high-resolution synchrotron-based X-ray diffraction was applied to reveal the Li/Na/K-ion insertion-induced structural transformation mechanism during high-temperature solid-state reaction. The in situ diffraction results demonstrate that the chemical reaction pathway strongly depends on the alkali-free precursor type, which is a structural matrix enabling phase transitions. Quantitative phase analysis identifies for the first time the decomposition of lithium sources as the most critical factor for the formation of metastable intermediates or impurities during the entire process of Li-rich layered Li[Li_0.2Ni_0.2Mn_0.6]O₂ formation. Since the alkali ions have different ionic radii, Na/K ions tend to be located on prismatic sites in the defective layered structure (Na[Ni_0.25Mn_0.75]O₂ or K[Ni_0.25Mn_0.75]O₂) during calcination, whereas the Li ions prefer to be localized on the tetrahedral and/or octahedral sites, forming O-type structures.

Electroactive polymeric nanofibrous composite to drive in situ construction of lithiophilic SEI for stable lithium metal anodes

Chen Ai-Long, Shang Nan, Ouyang Yue, Mo Lulu, Zhou Chunyang, Tjiu Weng Weei, Lai Feili, Miao Yue-E, Liu Tianxi

2022, 2(2): 192-200. doi: 10.1016/j.esci.2022.02.003

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Abstract:
Uncontrolled lithium dendrite growth hinders the practical application of lithium metal batteries (LMBs). Herein, we report a novel Li⁺ flux distributor achieved by placing an electroactive polyvinylidene fluoride/polymethyl methacrylate (PVDF/PMMA) composite nanofiber interlayer on a current collector, inducing uniform lithium deposition to mitigate the dendrite problem. Specifically, the released PMMA reacts with Li⁺ to form abundant C–O–Li bonds and generate in situ a stable lithiophilic PMMA-Li solid electrolyte interphase layer. Theoretical calculations reveal that polar C–F groups in the PVDF framework and lithiophilic PMMA-Li provide homo-dispersed Li⁺ migration pathways with low energy barriers. Consequently, uniform Li nucleation is achieved at the molecular level, resulting in ultrahigh cycling stability with dendrite-free Li deposition at 5 mA cm⁻² and 5 mAh cm⁻² for over 500 h. The PVDF/PMMA ∼ Li || LiFePO₄ (LFP) full cell presents an increased rate capacity of 110 mAh g⁻¹ at 10 C. In addition, a soft-package battery demonstrates a high energy density of 289 Wh kg⁻¹. This work provides a facile design for stable lithium metal anodes to promote the practical use of LMBs and other alkali metal batteries.

A polymer electrolyte with a thermally induced interfacial ion-blocking function enables safety-enhanced lithium metal batteries

Zhang Huanrui, Huang Lang, Xu Hantao, Zhang Xiaohu, Chen Zhou, Gao Chenhui, Lu Chenglong, Liu Zhi, Jiang Meifang, Cui Guanglei

2022, 2(2): 201-208. doi: 10.1016/j.esci.2022.03.001

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Abstract:
Lithium metal batteries (LMBs) have recently been revitalized as one of the most promising electrochemical energy storage systems, owing to the ultrahigh specific capacity (3860 mAh g⁻¹) and ultralow potential (−3.04 V vs. standard hydrogen electrode) of lithium metal anodes. However, safety hazards originating from lithium dendrite growth and pulverization during cycling and thermal stimulation present significant challenges to the practical application of LMBs. To address this issue, we have developed an in situ polymer electrolyte with thermally induced interfacial ion-blocking ability. We demonstrate that the repolymerization and deposition of residual vinylene carbonate in the as-prepared electrolyte under thermal abuse predominantly results in thermally induced ion blocking at the solid electrolyte interface, thus achieving superior LMB safety. The developed polymer electrolyte also yields superior cyclability in LMBs. This design philosophy provides a good paradigm for improving the safety of LMBs.

Simultaneous regulation of cations and anions in an electrolyte for high-capacity, high-stability aqueous zinc–vanadium batteries

Wang Ziqing, Zhou Miao, Qin Liping, Chen Minghui, Chen Zixian, Guo Shan, Wang Liangbing, Fang Guozhao, Liang Shuquan

2022, 2(2): 209-218. doi: 10.1016/j.esci.2022.03.002

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Abstract:
Safe, inexpensive aqueous zinc-ion batteries (AZIBs) are regarded as promising energy storage devices. However, they still face issues, including dissolution and collapse of the cathode as well as H₂ evolution and the growth of Zn dendrites on the Zn anode. Herein, we simultaneously regulate the cations and anions in the electrolyte for high-capacity, high-stability aqueous zinc–vanadium (Zn–V) batteries based on a bimetallic cation-doped Na_0.33K_0.1V₂O₅nH₂O cathode. We demonstrate that Na⁺ cations suppress cathode dissolution and restrain Zn dendrite growth on the anode via an electrostatic shield effect. We also illustrate that ClO₄⁻ anions participate in energy storage at the cathode and are reduced to Cl⁻, generating a protective layer on the Zn anode surface and providing a stable interface to decrease Zn dendrites and H₂ evolution during long-term cycling. When Na⁺ and ClO₄⁻ are introduced into an aqueous ZnSO₄ electrolyte, a Zn/Zn symmetric cell shows durable and reversible Zn stripping/plating for 1500 h at a current density of 1 mA cm⁻² and with an area capacity of 1 mAh cm⁻². Zn/Na_0.33K_0.1V₂O₅nH₂O full batteries exhibit a high capacity of 600 mAh g⁻¹ at 0.1 A g⁻¹ and long-term cycling performance for 5000 cycles, with a capacity of 200 mAh g⁻¹ at 20 A g⁻¹.

A first-principles study on the electrochemical reaction activity of 3d transition metal single-atom catalysts in nitrogen-doped graphene: Trends and hints

Zheng Caiyan, Zhang Xu, Zhou Zhen, Hu Zhenpeng

2022, 2(2): 219-226. doi: 10.1016/j.esci.2022.02.009

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Abstract:
Electrochemical reactions are essential in the processes of energy storage and conversion, and performance is tightly dependent on the electrocatalysts. Herein, we systematically investigate the activity of 3d transition metal embedded nitrogen-doped graphene (MN_x-G) for single-atom catalysts (SACs) in the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER). The calculated volcano curves reveal the optimal SAC configuration for each reaction to be CoN₃-G for the ORR, CoN₄-G for the OER, and Ni/CuN₃-G for the HER. Analysis based on the machine learning method suggests that high catalytic performance is dominated by the number of valence electrons occupying the d orbitals, the covalent radius, the electronegativity, the ratio of nearest-neighbor N and C atoms for the metal atoms, and the bond length between metal atoms and adsorbates. This work may shed some light on further studies of the ORR, OER, and HER with non-precious metal SACs.

Large-scale synthesis of N-doped carbon capsules supporting atomically dispersed iron for efficient oxygen reduction reaction electrocatalysis

Yang Hui, Liu Yanfang, Liu Xiaolu, Wang Xiangke, Tian He, Waterhouse Geoffrey I.N., Kruger Paul E., Telfer Shane G., Ma Shengqian

2022, 2(2): 227-234. doi: 10.1016/j.esci.2022.02.005

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Abstract:
The large-scale synthesis of platinum-free electrocatalysts for the oxygen reduction reaction (ORR) remains a grand challenge. We report the large-scale production of stable and active ORR electrocatalysts based on iron, an earth-abundant element. A core–shell zeolitic imidazolate framework–tannic acid coordination polymer composite (ZIF-8@K-TA) was utilized as the catalyst precursor, which was transformed into iron atoms dispersed in hollow porous nitrogen-doped carbon capsules (H-Fe-N_x-C) through ion exchange and pyrolysis. H-Fe-N_x-C features site-isolated single-atom iron centers coordinated to nitrogen in graphitic layers, high levels of nitrogen doping, and high permeability to incoming gases. Benefiting from these characteristics, H-Fe-N_x-C demonstrated efficient electrocatalytic activity (E_1/2 = 0.92 V, vs. RHE) and stability towards the ORR in both alkaline and acidic media. In ORR performance, it surpassed the majority of recently reported Fe-N-C catalysts and the standard Pt/C catalyst. In addition, H-Fe-N_x-C showed outstanding tolerance to methanol.

Modelling of photovoltaic production and electrochemical storage in an autonomous solar drone

Cosson Mickael, David Benjamin, Arzel Ludovic, Poizot Philippe, Rhallabi Ahmed

2022, 2(2): 235-241. doi: 10.1016/j.esci.2022.02.004

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Abstract:
A simple, efficient simulator has been developed to predict the generation of photovoltaic energy and its storage in Li-ion batteries, for an autonomous drone with four wings covered by solar panels based on thin-film gallium arsenide photovoltaic cells (III–V). This simulator allows prediction of the effective photovoltaic power produced by the solar panels as well as the battery pack voltage when the drone is flying. Flight parameters such as irradiance, sun inclination angles, and drone Euler angles are considered as input parameters. The measured photovoltaic power and battery pack voltage are in good agreement with the simulated values, making practical use by the XSun company possible. This parametric study shows the effects of climatic and geographic conditions on drone autonomy. In optimal weather conditions on a sunny day, drone flight can last 12 h.

2022 Vol. 2, No. 2