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Accurate Determination of Coulombic Efficiency for Lithium Metal Anodes and Lithium Metal Batteries
Lithium (Li) metal is an ideal anode material for high energy density batteries. However, its low Coulombic efficiency (CE) and formation of dendrites during the plating and stripping processes has hindered its applications in rechargeable Li metal batteries. The accurate measurement of Li CE is a critical factor to predict the cycle life of Li metal batteries, but the measurement of Li CE is affected by various factors that often leads to conflicting values reported in the literature. Here, we investigate various factors that affect the measurement of Li CE and propose a more accurate method of determining Li CE. It was also found that the capacity used for cycling greatly affects the stabilization cycles and the average CE. A higher cycling capacity leads to a shorter number of stabilization cycles and higher average CE. With a proper high-concentration ether-based electrolyte, Li metal can be cycled with a high average CE of 99.5 % for over 100 cycles at a high capacity of 6 mAh cm-2 suitable for practical applications.
Lithium Difluorophosphate as a Dendrite-Suppressing Additive for Lithium Metal Batteries
The growth of lithium (Li) dendrite and the low Coulombic efficiency (CE) of Li anode during repeated Li plating/stripping processes are the two major obstacles to the development of rechargeable Li metal batteries (LMBs). Introducing a dendrite-suppressing additive into the nonaqueous electrolyte is one of the facile and effective solutions to promote the commercialization of LMBs. Herein, Li difluorophosphate (LiPO2F2, LiDFP) is used as an electrolyte additive to suppress the growth of Li dendrites by forming a vigorous and stable solid electrolyte interphase layer on the Li metal surface. Moreover, the Li CE can be largely improved from 84.6% for the conventional LiPF6-based electrolyte to 95.2% by the addition of an optimal concentration of LiDFP at 0.15 M. The optimal LiDFP-containing electrolyte can allow the Li||Li symmetric cells to cycle stably for more than 500 and 200 h at 0.5 and 1.0 mA cm-2, respectively, much longer than the control electrolyte without LiDFP additive. Meanwhile, this LiDFP-containing electrolyte can also greatly enhance the cycle life of the Li||LiNi1/3Co1/3Mn1/3O2 cells with a moderately high mass loading of 9.7 mg cm-2. These results demonstrate that LiDFP has extensive application prospects as a dendrite-suppressing additive in advanced LMBs.
Effect of Propagating Dopant Reactivity on Lattice Oxygen Loss in LLZO Solid Electrolyte Contacted with Lithium Metal
Lithium lanthanum zirconium oxide (LLZO) is widely known as the most stable solid electrolyte against lithium metal electrodes. This thermodynamic stability can be lost by the presence of dopants which are required to stabilize the cubic phase of LLZO and can be reduced by lithium metal. However, the role of oxygen in such reactions is taken for granted. In this work, the reduction of Nb-substituted LLZO (Nb-LLZO) is explored by Li metal and shows that interfacial reactions propagate and lead to the decomposition with substantial Nb 5+ reduction deep into the bulk electrolyte. Scanning Transmission Electron Microscopy with Energy Dispersive X-ray Spectroscopy and thermogravimetric analyses show much of the reduction is due to oxygen vacancies formed, leading to increased electronic conductivity mapped with conductive Atomic Force Microscopy. Density functional theory calculations indicate oxygen release is favored by increased excess lithiation of Nb-LLZO. Electrochemical impedance of polycrystalline Nb-LLZO shows the continuous evolution of ionically resistive interphases near the lithium metal interface with Nb-LLZO while single crystals show little reactivity at room temperature and self-limiting reduction at 60°C. This work underlines the role of grain boundaries in propagating destructive solid electrolyte reactions and highlights previously unseen mechanisms involving lattice oxygen in LLZO.
Nanoscale Nucleation and Growth of Electrodeposited Lithium Metal
Lithium metal has re-emerged as an exciting anode for high energy lithium-ion batteries due to its high specific capacity of 3860 mAh g -1 and lowest electrochemical potential of all known materials. However, lithium has been plagued by the issues of dendrite formation, high chemical reactivity with electrolyte, and infinite relative volume expansion during plating and stripping, which present safety hazards and low cycling efficiency in batteries with lithium metal electrodes. There have been a lot of recent studies on Li metal although little work has focused on the initial nucleation and growth behavior of Li metal, neglecting a critical fundamental scientific foundation of Li plating. Here, we study experimentally the morphology of lithium in the early stages of nucleation and growth on planar copper electrodes in liquid organic electrolyte. We elucidate the dependence of lithium nuclei size, shape, and areal density on current rate, consistent with classical nucleation and growth theory. We found that the nuclei size is proportional to the inverse of overpotential and the number density of nuclei is proportional to the cubic power of overpotential. Finally, based on this understanding, we propose a strategy to increase the uniformity of electrodeposited lithium on the electrode surface.
Interface Modifications of Lithium Metal Anode for Lithium Metal Batteries
Lithium metal batteries (LMBs) enable much higher energy density than lithium–ion batteries (LIBs) and thus hold great promise for future transportation electrification. However, the adoption of lithium metal (Li) as an anode poses serious concerns about cell safety and performance, which has been hindering LMBs from commercialization. To this end, extensive effort has been invested in understanding the underlying mechanisms theoretically and experimentally and developing technical solutions. In this review, we devote to providing a comprehensive review of the challenges, characterizations, and interfacial engineering of Li anodes in both liquid and solid LMBs. Finally, we expect that this work will stimulate new efforts and help peer researchers find new solutions for the commercialization of LMBs.
An Artificial Protective Coating toward Dendrite-Free Lithium-Metal Anodes for Lithium–Sulfur Batteries
Not provided.
Simultaneous Stabilization of LiNi 0.76 Mn 0.14 Co 0.10 O 2 Cathode and Lithium Metal Anode by Lithium Bis(oxalato)borate as Additive
Abstract The long‐term cycling performance, rate capability, and voltage stability of lithium (Li) metal batteries with LiNi 0.76 Mn 0.14 Co 0.10 O 2 (NMC76) cathodes is greatly enhanced by lithium bis(oxalato)borate (LiBOB) additive in the LiPF 6 ‐based electrolyte. With 2 % LiBOB in the electrolyte, a Li∥NMC76 cell is able to achieve a high capacity retention of 96.8 % after 200 cycles at C/3 rate (1 C=200 mA g −1 ), which is the best result reported for a Ni‐rich NMC cathode coupled with Li metal anode. The significantly enhanced electrochemical performance can be ascribed to the stabilization of both the NMC76 cathode/electrolyte and Li‐metal‐anode/electrolyte interfaces. The LiBOB‐containing electrolyte not only facilitates the formation of a more compact solid–electrolyte interphase on the Li metal surface, it also forms a enhanced cathode electrolyte interface layer, which efficiently prevents the corrosion of the cathode interface and mitigates the formation of the disordered rock‐salt phase after cycling. The fundamental findings of this work highlight the importance of recognizing the dual effects of electrolyte additives in simultaneously stabilizing both cathode and anode interfaces, so as to enhance the long‐term cycle life of high‐energy‐density battery systems.
Behavior of Lithium Metal Anodes under Various Capacity Utilization and High Current Density in Lithium Metal Batteries
Not Available
Application of non-self-adjoint operators for description of electronic excitations in metallic lithium
Metallic lithium is used to demonstrate the possibilities of applying non-self-adjoint operators for quantitative description of orbital excitations of electrons in crystals. It is shown that, the nonequilibrium distribution function can be calculated when solving the spectral problem; therefore, the kinetic properties of a material can also be described with the unified band theory.
Lithicone‐Protected Lithium Metal Anodes for Lithium Metal Batteries with Nickel‐Rich Cathode Materials
The high energy density advantage of lithium (Li) metal batteries (LMBs) makes them increasingly desirable; however, problems such as strong reactivity and dendrite growth of Li metal anode limit their practical uses. In this work, a novel Li‐containing glycerol (LiGL) or lithicone protection layer on a 50 μm thick Li metal anode is employed for improving the performance of LMBs. This LiGL layer was accurately deposited via a molecular layer deposition (MLD) process at 150 °C, using lithium tert‐butoxide and glycerol as precursors. The as‐formed LiGL coating layer is highly tunable in its thickness by simply adjusting MLD cycles and shows a good stability and outstanding ionic transport properties. The LiGL layer is found to effectively mitigate side reactions and enhance cycling stability in both symmetric cells and full cells. Specifically, the LMBs with LiGL@Li anode of 400 MLD cycles and LiNi 0.6 Mn 0.2 Co 0.2 O 2 cathode enable a capacity retention of ≈87%, much higher than ≈35% of the cells with bare Li after 200 cycles at a charge/discharge current density of 2.1 mA cm −2 . This work paves a feasible way for practical LMBs with improved capacity and stability through applying an innovative protection layer on Li metal anodes.
Quantifying inactive lithium in lithium metal batteries
Lithium metal anodes offer high theoretical capacities (3,860 milliampere-hours per gram)1, but rechargeable batteries built with such anodes suffer from dendrite growth and low Coulombic efficiency (the ratio of charge output to charge input), preventing their commercial adoption. The formation of inactive (‘dead’) lithium— which consists of both (electro)chemically formed Li + compounds in the solid electrolyte interphase and electrically isolated unreacted metallic Li 0 —causes capacity loss and safety hazards. Quantitatively distinguishing between Li + in components of the solid electrolyte interphase and unreacted metallic Li 0 has not been possible, owing to the lack of effective diagnostic tools. Optical microscopy, in situ environmental transmission electron microscopy, X-ray microtomography and magnetic resonance imaging provide a morphological perspective with little chemical information. Nuclear magnetic resonance, X-ray photoelectron spectroscopy and cryogenic transmission electron microscopy can distinguish between Li + in the solid electrolyte interphase and metallic Li 0 , but their detection ranges are limited to surfaces or local regions. Here we establish the analytical method of titration gas chromatography to quantify the contribution of unreacted metallic Li 0 to the total amount of inactive lithium. We identify the unreacted metallic Li 0 , not the (electro)chemically formed Li + in the solid electrolyte interphase, as the dominant source of inactive lithium and capacity loss. By coupling the unreacted metallic Li 0 content to observations of its local microstructure and nanostructure by cryogenic electron microscopy (both scanning and transmission), we also establish the formation mechanism of inactive lithium in different types of electrolytes and determine the underlying cause of low Coulombic efficiency in plating and stripping (the charge and discharge processes, respectively, in a full cell) of lithium metal anodes. Here we propose strategies for making lithium plating and stripping more efficient so that lithium metal anodes can be used for next-generation high-energy batteries.
Aligning lithium metal battery research and development across academia and industry
Successful integration of metallic lithium anodes into secondary batteries could enhance energy density and enable new forms of electrified transportation. However, the outlook for widespread lithium metal adoption in energy storage devices remains mixed. This comes in part from existing gaps in our understanding of the relationships connecting the initial state of lithium, its evolution with cycling, and end-of-life state. It remains important to develop standardized protocols for material and cell characterization, cycling performance, safety, and recycling procedures for lithium metal-based batteries. In February 2023 a cohort of scientists and engineers from academia, national laboratories, and industry gathered to converge on a list of critical challenges and action items to provide better understanding of lithium metal evolution and to enhance academic, governmental, and industrial partnerships to address these challenges. Here, we highlight the major discussion topics revolving around the manufacturing of lithium metal, its related metrology and integration into battery form factors, and best practices testing its electrochemical performance relevant to automotive applications. We introduce a power-controlled discharge testing protocol for research and development cells, in alignment between major automotive stakeholders, that may reveal lithium metal battery dynamics closer to practical driving behavior.
Sorption of atmospheric gases by bulk lithium metal
Lithium conditioning of plasma facing components has enhanced the performance of several fusion devices. Elemental lithium will react with air during maintenance activities and with residual gases (H 2 O, CO, CO 2 ) in the vacuum vessel during operations. We have used a mass balance (microgram sensitivity) to measure the mass gain of lithium samples during exposure of a ~1 cm 2 surface to ambient and dry synthetic air. For ambient air, we found an initial mass gain of several mg/h declining to less than 1 mg/h after an hour and decreasing by an order of magnitude after 24 h. A 9 mg sample achieved a final mass gain corresponding to complete conversion to Li 2 CO 3 after 5 days. Exposure to dry air resulted in a 30 times lower initial rate of mass gain. The results have implications for the chemical state of lithium plasma facing surfaces and for safe handling of lithium coated components.
Hybrid Lithium-Sulfur Batteries with an Advanced Gel Cathode and Stabilized Lithium-Metal Anode
The insulating nature of sulfur, polysulfide shuttle effect, and lithium metal deterioration cause a decrease in practical energy density and fast capacity fade in lithium-sulfur batteries. Here, we present an integrated strategy for the development of hybrid Li-S batteries based on a gel sulfur cathode, a solid electrolyte, and a protective anolyte composed of highly-concentrated salt electrolyte containing mixed additives. The dense solid electrolyte completely blocks polysulfide diffusion, and also makes it possible to investigate the cathode and anode independently. This gel cathode effectively traps the polysulfide active material while maintaining a low electrolyte to sulfur ratio (E/S) of 5.2 mL/g. The anolyte effectively protects the Li metal and suppresses the consumption of liquid electrolyte, enabling stable long-term cycling for over 700 hours in Li symmetric cells. This advanced design can simultaneously suppress the polysulfide shuttle, protect Li metal, and reduce the liquid electrolyte usage. The assembled hybrid batteries exhibit remarkably stable cycling performance over 300 cycles with high capacity. Finally, surface-sensitive techniques were carried out to directly visualize and to probe the interphase formed on the surface of the LAGP pellet, which may help stabilize the solid-liquid interface.