Interfacial Evolution of Lithium Dendrites and Their Solid Electrolyte Interphase Shells of Quasi‐Solid‐State Lithium‐Metal Batteries

Unstable electrode/solid‐state electrolyte interfaces and internal lithium dendrite penetration hamper the applications of solid‐state lithium‐metal batteries (SSLMBs), and the underlying mechanisms are not well understood. Herein, in situ optical microscopy provides insights into the lithium plating/stripping processes in a gel polymer electrolyte and reveals its dynamic evolution. Spherical lithium deposits evolve into moss‐like and branch‐shaped lithium dendrites with increasing current densities. Remarkably, the on‐site‐formed solid electrolyte interphase (SEI) shell on the lithium dendrite is distinctly captured after lithium stripping. Inducing an on‐site‐formed SEI shell with an enhanced modulus to wrap the lithium precipitation densely and uniformly can regulate dendrite‐free behaviors. An in‐depth understanding of lithium dendrite evolution and its functional SEI shell will aid in the optimization of SSLMBs.     

A Sustainable Solid Electrolyte Interphase for High‐Energy‐Density Lithium Metal Batteries Under Practical Conditions

High‐energy‐density Li metal batteries suffer from a short lifespan under practical conditions, such as limited lithium, high loading cathode, and lean electrolytes, owing to the absence of appropriate solid electrolyte interphase (SEI). Herein, a sustainable SEI was designed rationally by combining fluorinated co‐solvents with sustained‐release additives for practical challenges. The intrinsic uniformity of SEI and the constant supplements of building blocks of SEI jointly afford to sustainable SEI. Specific spatial distributions and abundant heterogeneous grain boundaries of LiF, LiN_xO_y, and Li₂O effectively regulate uniformity of Li deposition. In a Li metal battery with an ultrathin Li anode (33 μm), a high‐loading LiNi_0.5Co_0.2Mn_0.3O₂ cathode (4.4 mAh cm^?2), and lean electrolytes (6.1 g Ah^?1), 83 % of initial capacity retains after 150 cycles. A pouch cell (3.5 Ah) demonstrated a specific energy of 340 Wh kg^?1 for 60 cycles with lean electrolytes (2.3 g Ah^?1).     

A Flexible Solid Electrolyte Interphase Layer for Long‐Life Lithium Metal Anodes

Lithium (Li) metal is a promising anode material for high‐energy density batteries. However, the unstable and static solid electrolyte interphase (SEI) can be destroyed by the dynamic Li plating/stripping behavior on the Li anode surface, leading to side reactions and Li dendrites growth. Herein, we design a smart Li polyacrylic acid (LiPAA) SEI layer high elasticity to address the dynamic Li plating/stripping processes by self‐adapting interface regulation, which is demonstrated by in situ AFM. With the high binding ability and excellent stability of the LiPAA polymer, the smart SEI can significantly reduce the side reactions and improve battery safety markedly. Stable cycling of 700 h is achieved in the LiPAA‐Li/LiPAA‐Li symmetrical cell. The innovative strategy of self‐adapting SEI design is broadly applicable, providing opportunities for use in Li metal anodes     

A Diffusion--Reaction Competition Mechanism to Tailor Lithium Deposition for Lithium-Metal Batteries

Lithium metal is recognized as one of the most promising anode materials owing to its ultrahigh theoretical specific capacity and low electrochemical potential. Nonetheless, dendritic Li growth has dramatically hindered the practical applications of Li metal anodes. Realizing spherical Li deposition is an effective approach to avoid Li dendrite growth, but the mechanism of spherical deposition is unknown. Herein, a diffusion-reaction competition mechanism is proposed to reveal the rationale of different Li deposition morphologies. By controlling the rate-determining step (diffusion or reaction) of Li deposition, various Li deposition scenarios are realized, in which the diffusion-controlled process tends to lead to dendritic Li deposition while the reaction-controlled process leads to spherical Li deposition. This study sheds fresh light on the dendrite-free Li metal anode and guides to achieve safe batteries to benefit future wireless and fossil-fuel-free world.     

Highly Stable Lithium Metal Batteries Enabled by Regulating the Solvation of Lithium Ions in Nonaqueous Electrolytes

Safe and rechargeable lithium metal batteries have been difficult to achieve because of the formation of lithium dendrites. Herein an emerging electrolyte based on a simple solvation strategy is proposed for highly stable lithium metal anodes in both coin and pouch cells. Fluoroethylene carbonate (FEC) and lithium nitrate (LiNO₃) were concurrently introduced into an electrolyte, thus altering the solvation sheath of lithium ions, and forming a uniform solid electrolyte interphase (SEI), with an abundance of LiF and LiN_xO_y on a working lithium metal anode with dendrite‐free lithium deposition. Ultrahigh Coulombic efficiency (99.96 %) and long lifespans (1000 cycles) were achieved when the FEC/LiNO₃ electrolyte was applied in working batteries. The solvation chemistry of electrolyte was further explored by molecular dynamics simulations and first‐principles calculations. This work provides insight into understanding the critical role of the solvation of lithium ions in forming the SEI and delivering an effective route to optimize electrolytes for safe lithium metal batteries.     

锂/聚合物电解质电化学固/固界面的研究

综述了聚合物锂电池中锂/聚合物电解质电化学固/固界面的研究进展。通过与锂/液体电解质体系进行比较,简要介绍了在锂/聚合物电解质界面上发生的电化学反应、锂钝化层形成及其对界面反应的影响,并侧重讨论了传统电化学方法和谱学方法,特别是现场分析技术在电化学固/固界面研究中的应用。总结了锂/聚合物电解质界面的几种不同改善途径。     

Synergistic Dual-Additive Electrolyte Enables Practical Lithium-Metal Batteries

A rechargeable Li metal anode coupled with a high-voltage cathode is a promising approach to high-energy-density batteries exceeding 300 Wh kg⁻¹. Reported here is an advanced dual-additive electrolyte containing a unique solvation structure and it comprises a tris(pentafluorophenyl)borane additive and LiNO₃ in a carbonate-based electrolyte. This system generates a robust outer Li₂O solid electrolyte interface and F- and B-containing conformal cathode electrolyte interphase. The resulting stable ion transport kinetics enables excellent cycling of Li/LiNi_0.8Mn_0.1Co_0.1O₂ for 140 cycles with 80 % capacity retention under highly challenging conditions (≈295.1 Wh kg⁻¹ at cell-level). The electrolyte also exhibits high cycling stability for a 4.6 V LiCoO₂ (160 cycles with 89.8 % capacity retention) cathode and 4.95 V LiNi_0.5Mn_1.5O₄ cathode.     

Regulation of Cathode‐Electrolyte Interphase via Electrolyte Additives in Lithium Ion Batteries

As the power supply of the prosperous new energy products, advanced lithium ion batteries (LIBs) are widely applied to portable energy equipment and large‐scale energy storage systems. To broaden the applicable range, considerable endeavours have been devoted towards improving the energy and power density of LIBs. However, the side reaction caused by the close contact between the electrode (particularly the cathode) and the electrolyte leads to capacity decay and structural degradation, which is a tricky problem to be solved. In order to overcome this obstacle, the researchers focused their attention on electrolyte additives. By adding additives to the electrolyte, the construction of a stable cathode‐electrolyte interphase (CEI) between the cathode and the electrolyte has been proven to competently elevate the overall electrochemical performance of LIBs. However, how to choose electrolyte additives that match different cathode systems ideally to achieve stable CEI layer construction and high‐performance LIBs is still in the stage of repeated experiments and exploration. This article specifically introduces the working mechanism of diverse electrolyte additives for forming a stable CEI layer and summarizes the latest research progress in the application of electrolyte additives for LIBs with diverse cathode materials. Finally, we tentatively set forth recommendations on the screening and customization of ideal additives required for the construction of robust CEI layer in LIBs. We believe this minireview will have a certain reference value for the design and construction of stable CEI layer to realize desirable performance of LIBs.     

原子力显微镜在锂离子电池界面研究中的应用

近几年,电动汽车市场的飞速发展对锂离子电池的能量密度和安全性提出了更高的要求. 然而,过去近30年,在应用终端市场的大力推动下,锂离子电池的电极材料、电池结构设计和生产工艺都已经发展得比较成熟,容量提升空间已经比较小,想要进一步提高现有锂离子电池的能量密度,需要对锂离子电池的整个系统和工作原理有更深刻和全面的理解. 存在于锂离子电池电极材料和电解液之间的固态电解质中间相（solid electrolyte interphase,SEI）已被证明是一个影响电池性能的重要因素,目前学术界和产业界对其认识还不是很全面,尤其是高分辨、工况下以及多技术联合的界面表征工作较少见到报道. 原子力显微镜（atomic force microscopy,AFM）通过探测针尖与样品之间的相互作用力,能够在原子尺度上原位表征液态电池界面的形貌以及力学特性,对于电极界面的理解和调控非常重要. 本文作者通过总结近几年AFM在锂离子电池SEI研究的中的应用,并结合本课题组在该领域的工作,对AFM技术在锂离子电池SEI研究中的应用做了总结和展望,对加深锂离子电池界面的理解,以及构建稳定锂电池界面的相关研究有参考意义.     

锂电池中的凝胶聚合物电解质

锂电池目前在人们生活中已经得到广泛应用,但是传统的液体电解质沸点低且易泄漏,容易引起锂枝晶生长和安全问题。凝胶聚合物电解质(GPEs)的状态介于液态电解质和固态电解质之间,不仅可以作为电解质,还可以作为隔膜,这样可以减少液体电解质的泄漏以及改善固体电解质的界面电阻。本文综述了锂电池中制备不同类型的GPEs的方法,如溶液浇铸法、相转化法、原位聚合法、UV(紫外)固化法和静电纺丝法等,重点总结了不同纤维基的GPEs(聚(偏二氟乙烯)(PVDF)、聚(偏二氟乙烯-共六氟丙烯)(PVDF- HFP)、聚甲基丙烯酸甲酯(PMMA)、聚丙烯腈(PAN)和聚间亚苯基间苯二甲酰胺(PMIA))在锂电池中的运用,并通过对不同基质的改性来改善电解质的离子电导率,阻碍锂枝晶的生长。最后,本文对锂电池中GPEs的未来发展前景进行了展望,讨论和提出的策略将为今后高性能锂电池的实际应用提供更多的途径。     

Deep-Eutectic-Solvent-Based Self-Healing Polymer Electrolyte for Safe and Long-Life Lithium-Metal Batteries

The deployment of high-energy-density lithium-metal batteries has been greatly impeded by Li dendrite growth and safety concerns originating from flammable liquid electrolytes. Herein, we report a stable quasi-solid-state Li metal battery with a deep eutectic solvent (DES)-based self-healing polymer (DSP) electrolyte. This electrolyte was fabricated in a facile manner by in situ copolymerization of 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (UPyMA) and pentaerythritol tetraacrylate (PETEA) monomers in a DES-based electrolyte containing fluoroethylene carbonate (FEC) as an additive. The well-designed DSP electrolyte simultaneously possesses non-flammability, high ionic conductivity and electrochemical stability, and dendrite-free Li plating. When applied in Li metal batteries with a LiMn₂O₄ cathode, the DSP electrolyte effectively suppressed manganese dissolution from the cathode and enabled high-capacity and a long lifespan at room and elevated temperatures.     

锂离子电池中固体电解质界面膜(SEI)研究进展

本文综述了锂离子电池中固体电解质界面膜(SEI膜)的研究进展.在总结SEI膜的形成机理及模型的基础上,讨论了对SEI膜可能的影响因素及其改性方法,以及各种表征技术、特别是原位分析技术在SEI膜研究中的实际应用.指出在今后的研究中,正极表面与电解液间的界面膜,以及引入水溶性粘合剂体系后正负极表面与电解液间的相互作用将成为人们关注的热点。     

锂离子塑性晶体常温固体电解质

固体塑性晶体是制备常温固体锂离子导电电解质的优良材料,其常温离子导电率可达到10^-3S cm^-1的实用水平。本文综述了塑性晶体材料作为锂离子常温固体电解质的最新研究进展。     

N-Doped Graphdiyne Coating for Dendrite-Free Lithium Metal Batteries

Nonuniform nucleation is one of the major reasons for the dendric growth of metallic lithium, which leads to intractable problems in the efficiency, reversibility, and safety in Li-based batteries. To improve the deposition of metallic Li on Cu substrates, herein, a freestanding current collector (NGDY@CuNW) is formed by coating pyridinic nitrogen-doped graphdiyne (NGDY) nanofilms on 3D Cu nanowires (CuNWs). Theoretical predictions reveal that the introduction of nitrogen atoms in the 2D GDY can enhance the binding energy between the Li atom and GDY, therefore improving the lithiophilicity on the surface for uniform lithium nucleation and deposition. Accordingly, the deposited metallic Li on the NGDY@CuNW electrode exhibits a dendrite-free morphology, resulting in significant improvements in terms of the reversibility with a high coulombic efficiency (CE) and a long lifespan at high current density. Our research provides an efficient method to control the surface property of Cu, which also will be instructive for other metal batteries.     

锂离子电池LiBOB电解质盐研究进展

本文介绍了可用于锂离子电池的新型锂盐--双乙二酸硼酸锂（LiBOB）的基本性质,包括结构组成、合成方法、物理化学性能及其与结构的关系。综述了近年来在LiBOB新型电解质锂盐研究与探索方面的新成果,重点评价了BOB-阴离子对于石墨负极和金属氧化物正极材料表面的电化学性能。讨论了这种盐在锂离子系中杂质和安全性等问题,归纳了其优缺点,指出今后电解质锂盐的研究发展方向。     

高浓度锂盐电解液

基于1 mol ·dm^-3 LiPF₆/EC的传统非水型电解液已在锂离子电池中应用了20年。高功率、高比能锂离子电池以及锂金属电池（如Li-O₂和Li-S）的发展,对电解液提出了更高的要求,使得电解液的研究与开发到了一个革新换代的阶段。研究者们已经在离子液体、聚合物电解质和无机固态电解质等新型体系研究方面取得一定的研究成果,但是这些新体系存在的本征问题使其商业化应用面临一定的困难。研究者们也开始重新审视已优化的常规液态电解液体系,高浓度锂盐电解液（>3 mol ·dm^-3）再次引起广泛关注。本文综述了高浓度锂盐电解液的发展历程、溶液结构特征、分类标准及其特殊的物理化学性能、锂离子传输性质和电解液/电极相容性;对高浓度锂盐电解液存在的主要问题进行了简要分析,提出了相应的改进措施,展望了高浓度锂盐电解液未来的发展方向,为新型电解液的开发提供了一条新思路。