固态金属锂负极界面研究进展

开发下一代高安全性、高能量密度电池是电动汽车、可穿戴便携电子设备与可再生能源高效利用的关键。固态金属锂电池是极有希望的下一代电池体系。本文首先综述了固态电解质与界面特性,包括固态电解质中的离子传输机理和固态电解质分类,指出金属锂电极与固态电解质之间有限的固-固界面接触是固态金属锂电池实用化的重要挑战,其界面演变特性主导了固态电池的性能表现。界面演变是机械-化学-电化学耦合的过程。其次,文章综述了电池界面失效机制与构筑策略,指出界面失效包括枝晶状沉积引发的电池短路与空穴累积、副反应导致的电化学界面脱触等,使用界面润湿剂、引入界面缓冲层或构造三维多孔骨架结构化电极等是解决界面问题的重要手段。最后,文章总结指出,固态金属锂电池仍有巨大的进步空间,先进的理论研究和表征手段为进一步认识和理解固-固界面提供了新的机遇,通过界面化学、材料科学、系统工程等领域的交叉共融,有望共同推动下一代高安全、高能量密度固态储能技术的发展。     

Stable interfaces constructed by concentrated ether electrolytes to render robust lithium metal batteries

Lithium metal batteries (LMBs) are highly considered as promising candidates for next-generation energy storage systems.However,routine electrolytes cannot tolerate the high potential at cathodes and low potential at anodes simultaneously,leading to severe interfacial reactions.Herein,a highly concentrated electrolyte (HCE) region trapped in porous carbon coating layer is adopted to form a stable and highly conductive solid electrolyte interphase (SEI) on Li metal surface.The protected Li metal anode can poten-tially match the high-voltage cathode in ester electrolytes.Synergistically,this ingenious design promises high-voltage-resistant interfaces at cathodes and stable SEI with abundance of inorganic components at anodes simultaneously in high-voltage LMBs.The feasibility of this interface-regulation strategy is demonstrated in Li | LiFePO4 batteries,realizing a lifespan twice as long as the routine cells,with a huge capacity retention enhancement from 46.4％ to 88.7％ after 100 cycles.This contribution proof-of-concepts the emerging principles on the formation and regulation of stable electrode/electrolyte inter-faces in the cathode and anode simultaneously towards the next-generation high-energy-density batteries.     

锂枝晶的成核、生长与抑制

锂金属电池具有较高的理论比容量和最低的氧化还原电位，被认为是最有前途的电化学储能器件之一。然而，金属锂阳极上的锂枝晶所引起的一些关键问题严重阻碍了其实际应用。首先从离子浓度、电场、应力、温度四方面因素介绍了多形貌锂枝晶成核和生长机理；同时，总结了一些用于表征锂枝晶的先进技术；并归纳了抑制锂枝晶形成的策略，包括控制锂枝晶成核的亲锂表面电极、非均相晶核，控制锂枝晶生长的三维导电基体、物理涂层，以及具有固定阴离子的纳米结构电解质和形成球形锂沉积的盐包水电解质。最后提出了挑战和展望，探讨了锂枝晶的未来研究方向。     

Morphology prediction of lithium plating by finite element modeling and simulations based on non-linear kinetics

Lithium metal has a very high theoretical energy density and is one of the most promising anode materials for a new generation of lithium batteries. It is easy to form dendrites during the deposition of lithium metal, which greatly affects the safety and service life of lithium metal batteries. Mechanism of dendrite propagation in lithium metal batteries (LMB) is still to be fundamentally described. Herein, we studied the effects of electrochemical parameters on the behavior of lithium plating at the electrode/electrolyte interface using a tertiary current model by finite-element methods. The results show that dendrite growth is intrinsically influenced by differences in concentration and potential. A higher diffusion coefficient (D_e) of Li ion in electrolyte is effective to improve uniformity of local concentration and a smaller exchange current density (i⁰) is essential for reducing sensitivity of interface reaction. Activation polarization is beneficial for uniform plating of lithium. Thus, the polarization curve is extremely important to determine whether lithium deposits uniformly or not. This work results in a new understanding of principles for dendrite growth, and is expected to lead to new insights on strategies for dendrite suppression.     

固态金属锂电池研究进展：外部压力和内部应力的影响

固态锂金属电池具有理论能量密度高、安全性高等优势,是极有前景的下一代储能系统。然而,固体电极与固体电解质之间有限的固–固接触严重阻碍了界面离子的传输。因此,增加外部压力是增加固–固接触及延长电池循环寿命的重要途径。同时,在充放电过程中,电极体积变化产生的内应力也将影响电池界面特性。通过介绍两种基本物理接触模型,结合硫化物、氧化物、聚合物电解质以及金属锂的物理性质,综述了外压和内部应力对电解质、电极及电池的影响。最后,对外压力与内应力在全固态金属锂电池中的作用进行了总结和展望。     

基于非线性动力学的锂沉积形貌模拟与预测

金属锂具有极高的理论能量密度,是新一代锂电池中最有潜力的负极材料之一。金属锂沉积时容易形成枝晶,极大影响了锂金属电池的安全性与使用寿命。但由于金属锂性质活泼,缺乏锂电极/电解液界面原位表征方法,锂枝晶生长机制尚不明确。通过有限元方法,基于非线性电极过程动力学,以三次电流模型定量研究了电极/电解液界面行为,并分析不同过程参数对表面电流的影响。结果表明,电极/电解质界面的浓度、电场差异是枝晶生长的主要原因,更大的扩散系数有利于提高界面浓度均匀性,更小的交换电流密度有利于减弱界面反应的敏感性。存在电化学极化区间是均匀沉积的必要条件,电化学极化区间越宽,均匀沉积操作窗口越宽。通过极化曲线可以判断体系是否具有均匀沉积的倾向。加深了对锂电极/电解液界面的电沉积过程的理解,对锂负极保护研究具有指导性意义。     

The development and challenges of rechargeable non-aqueous lithium–air batteries

Lithium–air (Li–air) batteries have recently received much attention due to their extremely high theoretical energy densities. The significantly larger theoretical energy density of Li–air batteries is due to the use of a pure lithium metal anode and the fact that the cathode oxidant, oxygen, is stored externally since it can be readily obtained from the surrounding air. However, before Li–air batteries can be realized as high-performance, commercially viable products there are still numerous scientific and technical challenges that must be overcome, from designing the cathode structure, to optimizing the electrolyte compositions and elucidating the complex chemical reactions that occur during charge and discharge. The scientific obstacles that are related to the performance of Li–air batteries open up an exciting opportunity for researchers from many different backgrounds to utilize their unique knowledge and skills to bridge the knowledge gaps that exist in current research projects. This review article is a summary of the most significant developments and challenges of practical Li–air batteries and the current understanding of their chemistry.     

锂离子在三维骨架复合锂金属负极中的沉积规律

锂金属具有极高的理论比容量和极低的氧化还原电极电势,成为了新一代高比能二次电池最理想的负极材料。然而,锂金属负极其走向大规模应用仍存在诸多问题与挑战。三维骨架复合负极可以控制金属锂均匀形核,低电流密度下均匀沉积,有望推动锂金属负极的实用化。为了更高效地指导锂金属负极设计和优化,采用相场理论,对三维骨架锂金属负极中比表面积对金属锂沉积过程的作用机制进行了定量分析和探究,发现了比表面积调控金属锂沉积的两阶段作用机理,并提出了基于比表面积参数的三维骨架负极设计与优化方向,从而最大程度发挥三维骨架在调控稳定金属锂负极上的积极作用。     

纳滤和反渗透组合回收盐湖提锂尾液中锂的研究

盐湖提锂后的尾液中仍含有大量的锂,直接外排至盐田会造成锂资源的浪费,并且会对盐湖系统造成破坏,而降低提锂尾液中的镁锂比是回收提锂尾液中锂的关键。采用纳滤和反渗透组合工艺成功地回收了提锂尾液中的锂。考察了7种型号的纳滤膜对提锂尾液中镁锂分离的效果,结果表明1号纳滤膜的分离效果最好。以1号纳滤膜为纳滤元件,考察了纳滤膜在不同的过滤压力、实验温度和提锂尾液稀释倍数条件下对提锂尾液中镁锂分离的效果,得到较优操作条件：过滤压力为4 MPa、提锂尾液稀释倍数为6倍、实验温度为35 ℃。以1号纳滤膜为纳滤元件,在较优操作条件下采用二级纳滤对提锂尾液进行镁锂分离,再通过反渗透对富锂液相进行浓缩,得到镁锂质量比为13.8、锂离子质量浓度为0.39 g/L的富锂液相。富锂液相经过浓缩除杂,然后与纯碱反应,可制备电池级碳酸锂。纳滤截留的镁离子含量较高的液相则外排至尾液池,经蒸发浓缩排入盐田再回收利用。     

Hybrid Poly(Ethylene Oxide)-Based composite polymer electrolyte for high-performance all-solid-state lithium batteries

Composite solid-state electrolytes (CSSEs) using solid-state lithium metal batteries (SSLMBs) are widely used as one among the primary technological paths aimed towards chemically necessary safety with acceptable energy density. Nevertheless, the unchecked growth of lithium dendrites and the sluggish transport of lithium ions impede the development of SSLMBs based on CSSEs. Herein, the simultaneous introduction of multilayer g-C₃N₄ and exceptionally thermally stable boron nitride (BN) into the PVDF/PEO system is presented. Benefitting from the unique trait and synergistic effect of g-C₃N₄ and BN in the synthesized CSSEs (g-C₃N₄/BN/PVDF/PEO-LiTFSI), the prepared CSSEs yield excellent Li⁺ transfer number (0.75), surprising thermal stability (shrinkage of only 14.13% after heated at 130 °C for 4 h), and high electrochemical stability window over 4.73 V vs. Li/Li⁺, which are much higher than those reported in the current literature PEO-based CSSEs. Moreover, the Li||CSSEs||LiFePO₄ cell applying the CSSEs attained outstanding cycling stability (capacity retention rate of 85% after 350 cycles) and excellent rate performance (58.6 mAh g⁻¹ at 5C). This study offers a simple, promising application, robust, and scalable manufacturing strategy to develop a dual role for stable and safe polymer-based all-solid-state lithium batteries.     

原位构建富氟SEI的凝胶电解质用于金属锂二次电池

以六氟磷酸锂（LiPF₆）为四氢呋喃的聚合引发剂制备凝胶电解质,同时作为氟源在金属锂负极表面原位构建富含LiF的固态电解质界面层（solid electrolyte interface,SEI）来抑制锂枝晶的生长以及金属锂/电解液之间的副反应。所制备的凝胶电解质具有较高的室温离子电导率（1.33 mS·cm^-1）和较宽的电化学稳定窗口（4.5 V）。原位聚合方式组装金属锂对称电池循环后,锂负极表面没有明显的锂枝晶和被损毁的形貌出现;XPS结果表明锂负极表面生成了富含LiF的SEI。组装的LiFePO₄全电池在1 C的电流密度下,稳定循环400周后仍保持118.7 mAh·g^-1的放电比容量。得益于四氢呋喃在开环聚合反应过程中,促进了LiPF₆分解反应平衡的正向移动,在锂负极表面形成稳定的富含LiF的SEI,能够抑制锂枝晶的生长并防止其被持续性的腐蚀破坏。     

原位构建富氟SEI的凝胶电解质用于金属锂二次电池

以六氟磷酸锂（LiPF₆）为四氢呋喃的聚合引发剂制备凝胶电解质,同时作为氟源在金属锂负极表面原位构建富含LiF的固态电解质界面层（solid electrolyte interface,SEI）来抑制锂枝晶的生长以及金属锂/电解液之间的副反应。所制备的凝胶电解质具有较高的室温离子电导率（1.33 mS·cm^-1）和较宽的电化学稳定窗口（4.5 V）。原位聚合方式组装金属锂对称电池循环后,锂负极表面没有明显的锂枝晶和被损毁的形貌出现;XPS结果表明锂负极表面生成了富含LiF的SEI。组装的LiFePO₄全电池在1 C的电流密度下,稳定循环400周后仍保持118.7 mAh·g^-1的放电比容量。得益于四氢呋喃在开环聚合反应过程中,促进了LiPF₆分解反应平衡的正向移动,在锂负极表面形成稳定的富含LiF的SEI,能够抑制锂枝晶的生长并防止其被持续性的腐蚀破坏。     

从浓缩盐湖卤水中萃取分离锂的实验研究

采用溶剂萃取法,对中国青海某盐湖浓缩后的高镁锂比老卤中的锂进行分离提取,系统考察了萃取剂浓度、萃取相比、卤水酸度等因素对锂萃取率的影响。对富锂有机相进行反萃取,考察了反萃取相比、反萃剂盐酸浓度等条件对锂负载有机相反萃取的影响。萃取工艺对从高镁锂比盐湖卤水中分离锂具有较好的应用前景。     

Synthesis and structural properties of lithium titanium oxide powder

Recently, lithium titanium oxide material has gained renewed interest in electrodes for lithium ion rechargeable batteries. We investigated the influence of excess Li on the structural characteristics of lithium titanium oxide synthesized by the conventional powder calcination method, considering the potential for mass production. The lithium excess ratio is controlled by using different weight of Li₂CO₃ powder during calcination. X-ray diffraction (XRD) measurement for the synthesized powder showed that the lithium titanium oxide material with excess lithium content had a spinel crystal structure as well as a different crystal one. In addition, high resolution transmission electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM) measurement revealed that the lithium titanium oxide powders with a lithium excess ratio of 5–20% exhibited a two phase formation. Inductively coupled plasma — atomic emission spectrometer (ICP-AES) and energy dispersive x-ray spectroscopy (EDX) measurements were used to analyze composition of the lithium titanium oxide powder. These results suggested that the conventional calcination method, considering the potential for mass production, formed two phases according to the Li excess amount in initial raw materials.     

Safety evaluation of rechargeable cells with lithium metal anodes and amorphous V2O5 cathodes

Rechargeable cells with lithium metal anodes have a very large theoretical energy density and are a promising cell system. However, rechargeable lithium metal cells are not yet currently commercially available. One of the biggest problems with the cells is the poor safety aspect resulting from the high chemical reactivity of lithium. We have been studying a cell system consisting of an amorphous (a-)V2O5P2O5 (95:5 in molar ratio) cathode, a lithium (Li) metal anode and an organic electrolyte in fabricating an AA-size prototype. In this paper, we report recent progress on our rechargeable lithium metal cell focusing on its safety.     

Growth of carbon dendrites on cathode above liquid ethanol using surface plasma

The newly developed method presented in this paper allows growth of carbon dendrites, which exhibit glassy carbon- and pyrocarbon-like structures, using surface plasma on the cathode surface above dehydrated ethanol. The process is based on the polarization of polar organic molecules under the influence of external high electric field strength. Ethanol molecules have a dipole moment, they were aligned in the direction of the electric field, and the process of electronic/dipole-relaxation polarization started to occur in liquid ethanol. The dipole density was maximized in the cathode region located at 7–10 mm above the liquid ethanol owing to the non-uniform electric field. The electronic breakdown started in the region experiencing the maximum electric field strength. The decomposition of ethanol molecules changed the condition of the gas phase in the breakdown region a resultant current started to flow in the circuit. The growth of carbon dendrites on the Pt cathode, possible under the stability of surface plasma discharges, was characterized by formation of carbon nuclei on the cathode surface. Another advantage of the plasma surface process is that it enables growth of carbon dendrite on dielectric surfaces without increasing of plasma power generation.     

Safety evaluation of rechargeable cells with lithium metal anodes and amorphous V2O5 cathodes

Rechargeable cells with lithium metal anodes have a very large theoretical energy density and are a promising cell system. However, rechargeable lithium metal cells are not yet currently commercially available. One of the biggest problems with the cells is the poor safety aspect resulting from the high chemical reactivity of lithium. We have been studying a cell system consisting of an amorphous (a-)V2O5P2O5 (95:5 in molar ratio) cathode, a lithium (Li) metal anode and an organic electrolyte in fabricating an AA-size prototype. In this paper, we report recent progress on our rechargeable lithium metal cell focusing on its safety.     

High-voltage all-solid-state lithium metal batteries prepared by aerosol deposition

High-energy-density and safe rechargeable batteries are key components to realizing a low-carbon society. All-solid-state Li-metal batteries have the potential to achieve both high safety and high energy densities. However, the large interfacial resistance between solid electrolytes and cathodes is the major challenge for developing all-solid-state Li-metal batteries. Here we deposited a Li-rich layered metal oxide Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNC) thin film (6 µm thick) on an Al-doped Li₇La₃Zr₂O₁₂ (LLZO) substrate at room temperature by aerosol deposition. The LMNC particles were coated with Li₃BO₃ (LBO), which acted as a binder to hold LMNC and LLZO together at heating. As a result, good interfacial contact was achieved between LMNC and LLZO. Yet reactions between LMNC and LBO would occur at heat treatment temperatures above 600 °C. The highest discharge capacity of the all-solid-state Li/LLZO/LBO-LMNC cell at 0.1 C and 60 °C was 223 mAh g^-1. The main reason for the cell capacity decay was the cracking of the LBO-LMNC cathode layer during cycling. Searching for a more suitable binder material with a high fracture toughness is crucial for further developing the aerosol-deposited LLZO-based all-solid-state Li metal batteries.     

高镁锂比盐湖镁锂分离与锂提取技术研究进展

随着锂离子电池在电动汽车、便携式电子设备、电动工具及电网储能中的用量持续增加,锂资源需求量快速增长。我国盐湖集中分布在青藏高原地区,青海盐湖普遍具有高镁锂比、低锂含量的特征。高镁锂比盐湖提锂是世界性难题。本文综述了高镁锂比盐湖卤水镁锂分离与锂提取技术的最新研究进展,包括萃取法、吸附法、反应/分离耦合技术、膜法和电化学法。从各技术原理、特点、性能等方面分析了各方法特征和适用性。在现有技术中,吸附法更适合高镁锂比卤水;萃取法可用于锂浓度较低的卤水;新发展的反应/分离耦合技术能实现高效提锂与镁锂资源综合利用;以纳滤、电渗析、双极膜为代表的膜法具有能耗较低和模块化的优点;电化学法具有装置简单的优势,但仍需进一步优化系统。我国盐湖锂资源提取需提高总收率,提升提锂后资源综合利用程度,发展锂产品高值化、多元化利用途径,加强盐湖提锂的工程化技术研究,突破并掌握核心技术与装备,实现盐湖资源高效、综合、可持续利用的目标。     

Ab initio study on the Li deintercalation in ternary lithium nitridocuprate Li2.5Cu0.5N

Using the first-principles method within the density functional theory and the generalized gradient approximation, the properties of lithium deintercalation were studied in the ternary lithium transition metal nitride Li_2.5Cu_0.5N. The lithium deintercalation formation energies per lithium atom were found to be between −2.72 and −4.08 eV for various amounts of Li extraction. The changes in the crystal volume, the electronic structures and the changes in charge densities of the Li_xCu_0.5N due to Li extractions are also presented. This study demonstrates that the extraction of lithium ions from the [Li₂N] layer is easier than that from the [Li_0.5Cu_0.5] layer. The change in unit cell volume was less than 5% for extractions of less than 30% of the Li ions in the unit cell. However, for a higher percentage of Li extractions, the system could shrink much more remarkably. The sequence of Li deintercalation, which was based on the calculated formation energies and the ratio of volume change, also gave some insight into the amorphization phenomenon after the first charge.