Lithium Stripping Research Articles

A coupled finite element approach to spatially resolved lithium plating and stripping in three-dimensional anode microstructures of lithium-ion cells

In this article, we present a coupled finite element approach to spatially resolved lithium plating and stripping in three-dimensional anode microstructures of lithium-ion cells. The local film thickness of plated lithium at the anode-electrolyte interface is treated as a primary variable in addition to the lithium concentration and the electric potential inside both electrodes as well as the lithium concentration and the electrochemical potential inside the electrolyte. We take the electric resistance of plated lithium into account when evaluating the Butler–Volmer charge transfer kinetics at the anode-electrolyte interface. The overall system of nonlinear equations resulting from discretization in time and space is solved in a monolithic, implicit fashion by the iterative Newton–Raphson method. To ensure stable and fast convergence especially during the final stages of lithium stripping, we introduce a novel regularization technique characterized by a trigonometrical regularization function for the purpose of discontinuity removal, and we show that our regularization is indeed necessary and effective while being superior to an existing one from the literature in several respects. The linear solver is derived from an advanced, physics-oriented preconditioning and solution technique established in one of our previous publications. In a large number of numerical examples, we thoroughly study two different lithium-ion cells involving up to approximately 2.3 million degrees of freedom. We thereby prove that our modeling and simulation approach is straightforwardly applicable to large and complex problem setups, and that it is capable of capturing lithium plating and stripping during continuous cell cycling without any interruptions in the corresponding simulations. Besides validating our implementation and examining various electrochemical properties of lithium plating and stripping, we also demonstrate that our approach is physically plausible and sensitive to overcharging, fast charging, and low-temperature charging as the three major causes of lithium plating. Unlike existing and widely used approaches based on geometric homogenization via morphological model parameters such as the porosity and the tortuosity, our approach offers the opportunity to detect spatial inhomogeneities in the propagation and distribution of plated lithium within anode microstructures. Accurate and in-depth numerical investigations of lithium plating and stripping are thus enabled as a potent alternative to elaborate and often costly experimental studies.

A novel lithium phosphate production method by stripping of lithium from the lithium enolate in kerosene using orthophosphoric acid

A novel orthophosphoric acid stripping (OpaS) system has been developed for the stripping and crystallization of lithium from the synergistically produced organolithium compound consisting of lithium enolate in kerosene. In order to determine regression models and optimum conditions, a D-optimal experimental plan was constituted. Reduced quadratic, cubic and quartic models were selected for lithium and non‑lithium metal stripping responses. Accordingly, the linear terms of A and B (A: Organic/aqueous phase ratio [O/A], B: [H3PO4]) were determined as a major factor for all lithium responses while the only two-factor interaction (2FI) of AB was determined for all responses. In optimization, the non‑lithium responses were minimized while the lithium responses were maximized. The O/A was determined as 8.2 when the upper limit of 1.0 M was targeted for [H3PO4]. The optimum validated lithium stripping yield and mass fraction of lithium crystallized were predicted as 94.1% and 0.77, respectively. Based on the lithium strip McCabe Thiele diagram, two theoretical stages are required with a 1.0 M H3PO4 strip solution at an O/A ratio of 8.2. At the validated optimum equilibrium pH (pH[eq]) of 7.44, the Li3PO4 crystals of 92.2% purity of were obtained. As a result, the OpaS system has been proven to be a novel method for stripping and crystallization of lithium as Li3PO4 from the lithium enolate organic system without any requirement of thermal and extra chemical processes.

Seamless alloying stabilizes solid-electrolyte interphase for highly reversible lithium metal anode

Despite their widespread study, lithium metal anodes still face the bottleneck problem of low average Coulombic efficiency. Herein, we adopt an electroless plating method and introduce additive (vanillin) to develop nanoscale silver hosts. The uniform nanoscale silver layer is conducive to seamless Li/Ag alloying process, thereby enabling flat lithium deposition. Since the Li/Ag alloying process occurs after the formation of solid electrolyte interphase (SEI), the seamless alloying process stabilizes the SEI, which improves the reversibility of the lithium metal anode. On this basis, a 3D-printed copper host-coated dense nanoscale silver layer is constructed, which reduces the effective current density and hence lowers the polarization of lithium deposition or stripping. Moreover, the 3D structure induces the epitaxial growth of lithium and thus alleviates the volume change of lithium metal. As a result, an average Coulombic efficiency of 99.61% is achieved in the Li/3D Ag half-cell.

Dendrite‐Free Lithium Deposition and Stripping Regulated by Aligned Microchannels for Stable Lithium Metal Batteries

AbstractLi metal is the ultimate choice for the anode in next‐generation high energy density rechargeable batteries. However, undesired dendrite growth, dead Li formation, and a large volume change of the lithium metal anode lead to severe safety hazards such as short‐circuiting, fire, or even explosion. Graphene oxide (GO) in large areas has been prepared as the Li metal host via a continuous centrifugal casting method. Aligned microchannels are then fabricated in it by a simple punching method using 3D printed templates. The GO matrix effectively regulates the lithium plating/stripping behavior while the aligned channels uniformly distributes the Li‐ion flux and provides short Li‐ion diffusion paths. The Li/ holey GO composite is flexible with a controllable thickness from 50 to 150 µm, which corresponds to capacities from 9.881 to 27.601 mAh cm−2. As a result, the anode has a low overpotential of 30 mV after 100 h, a high capacity of ≈3538 mAh g−1 (91.4% of the theoretical capacity), and a superior rate ability of up to 50 C with a LiFePO4 cathode. The holey GO/Li electrode is also paired with other cathodes and used in pouch cells, indicating its suitability for various high‐energy battery systems.

Controlled Lithium Deposition

Lithium metal is a promising anode material for its low redox potential and high theoretical specific capacity. However, the commercial application of the lithium metal anode is hindered with safety concerns arising from the uncontrolled growth of the lithium dendrites and significant volume variation during the lithium plating and stripping processes. Modification to the current collector is effective in tailoring the morphology of the deposited lithium and improving the cycling performance of the lithium metal batteries This review summarizes at first the global research advances in the structural design and the selection of the current collectors and their textures. It then presents some of our efforts in realizing controlled lithium deposition by designing current collectors in three aspects, lithium deposition induced by the micro-to-nano structures, lithiophilic alloys and iron carbides. Finally, conclusions and prospects are made for the further research of the current collectors.

A flexible artificial solid-electrolyte interlayer supported by compactness-tailored carbon nanotube network for dendrite-free lithium metal anode

A dendrite-free lithium metal anode requires a stable interface designed for efficient and reversible lithium plating and stripping. In this work, we have devised a mechanically flexible artificial Li3N solid-electrolyte interlayer supported by a dual-layer compactness-tailored carbon nanotube fiber network. The more compact side of the network ensures a full coverage of Li3N, which prevents the reaction between electrolyte and lithium. The other side, with sparsely distributed nanotube fibers, provides mechanical flexibility for the film, and induces three-dimensional lithium deposition along its structure without any dendrite formation. The resulting full cell with NCM811 cathode has a high capacity retention of 95.1% for 160 cycles compared with less than 80% for the control.

Elastomeric electrolytes for high-energy solid-state lithium batteries.

The use of lithium metal anodes in solid-state batteries has emerged as one of the most promising technologies for replacing conventional lithium-ion batteries1,2. Solid-state electrolytes are a key enabling technology for the safe operation of lithium metal batteries as they suppress the uncontrolled growth of lithium dendrites. However, the mechanical properties and electrochemical performance of current solid-state electrolytes do not meet the requirements for practical applications of lithium metal batteries. Here we report a class of elastomeric solid-state electrolytes with a three-dimensional interconnected plastic crystal phase. The elastomeric electrolytes show a combination of mechanical robustness, high ionic conductivity, low interfacial resistance and high lithium-ion transference number. The in situ-formed elastomer electrolyte on copper foils accommodates volume changes for prolonged lithium plating and stripping processes with a Coulombic efficiency of 100.0percent. Moreover, the elastomer electrolytes enable stable operation of the full cells under constrained conditions of a limited lithium source, a thin electrolyte and a high-loading LiNi0.83Mn0.06Co0.11O2 cathode at a high voltage of 4.5volts at ambient temperature, delivering a high specific energy exceeding 410watt-hours per kilogram of electrodepluselectrolyte. The elastomeric electrolyte system presents a powerful strategy for enabling stable operation of high-energy, solid-state lithium batteries.

Dead lithium formation in lithium metal batteries: A phase field model

Lithium metal batteries are the most promising choices for next-generation high-energy–density batteries. However, there is little mechanism understanding on lithium dendrite growth during lithium plating and the dead lithium (the main component of inactive lithium) formation during lithium stripping. This work proposed a phase field model to describe the lithium stripping process with dead lithium formation. The coupling of galvanostatic conditions enables the phase field method to accurately match experimental results. The factors influencing the dead lithium formation on the increasing discharge polarization are revealed. Besides, the simulation of the battery polarization curve, the capacity loss peak, and the Coulomb efficiency is realized. This contribution affords an insightful understanding on dead lithium formation with phase field methods, which can contribute general principles on rational design of lithium metal batteries.

Selective separation of lithium from the high magnesium brine by the extraction system containing phosphate-based ionic liquids

The new extraction system containing phosphate-based ionic liquid ([N 1888 ][P 507 ] + TBP+FeCl 3 ) could significantly reduce the striping acidity from 6–9 mol·L −1 to 1~1.5 mol·L –1 . At the same time, the Li + extraction efficiency and separation factor were 63.8% and 190.7, respectively. • For the new system, Li + could be effectively stripped by HCl (1~1.5 mol·L −1 ). • The optimal results of E (Li) and β (Li/Mg) were 63.8% and 190.7, respectively. • The E (Li) remained above 70% by six extraction-stripping-extraction cycles. The high acidity of stripping is one of the major problems that hinder the industrialization of the tributyl phosphate (TBP) + FeCl 3 system for lithium extraction from the salt lake brines with high Mg/Li ratio. In this study, a novel solvent extraction system, trialkylmethylammonium di(2-ethylhexyl)orthophosphinate ([N 1888 ][P 507 ]) + TBP + FeCl 3 , was developed to significantly reduce the difficulty of stripping and simplify the extraction process. The conditions of extraction and stripping were systematically studied in the present work. The results showed that Li + extraction efficiency could reach 61% under the optimal extraction parameters and Li + stripping ratio was 90% with a relative mild conditions of O/A = 10:1, [HCl] aq = 1.5 mol·L –1 . Also, combined with experimental results, FT-IR analysis, and UV analysis, the possible mechanisms of lithium extraction and stripping were put forward. Li + was extracted from the aqueous phase through the formation of [Li·2TBP][FeCl 4 ] adduct, meanwhile [N 1888 ][P 507 ] was just slightly involved in the extraction step. In the stripping procedure, the interaction between [FeCl 4 ] − and [Li·2TBP] + might be destroyed, and new possible complexes, [Li·2TBP] + , and [FeCl 4 ·TBP·P 507 ] 2− /[FeCl 4 ·P 507 ] 2− were formed in the organic phase. Additionally, the extraction efficiency of Li + remained above 70% while the organic phase was reused for six cycles. Compared with the traditional system, the addition of [N 1888 ][P 507 ] resulted in a slight decrease of Li + extraction efficiency (about 5%), the stripping acidity significantly reduced from 6 mol·L –1 HCl to 1.5 mol·L –1 HCl. This new extraction system showed a promising performance in selective extracting and easy stripping in lithium separation from the salt lake brines with high Mg/Li ratio.

High-Rate Lithium Metal Plating and Stripping on Solid Electrolytes Using a Porous Current Collector with a High Aperture Ratio

Dendritic Li metal growth and low Coulombic efficiency hinder the Li metal negative electrode’s applications. Solid electrolytes (SEs) have the potential to inhibit the growth of dendritic Li metal due to their high mechanical strength and number of transmissions; however, the extrusion of the Li metal into voids and cracks in the SEs due to the increased mechanical stress of the Li metal during the plating reaction makes it difficult to prevent internal short circuits. Here, this obstacle was uniquely solved using a porous current collector (PCC) with a high aperture ratio. Li metal plating in many pores of the PCC prevented the increase of mechanical stress of the Li metal. Moreover, the combination with the SE, which also has a high tolerance to the dendritic Li metal growth, showed a synergic effect. Additionally, the Au coating on the PCC’s surface extended the Li plating/stripping performance. As a result, a record-high value of critical current density (the maximum plating/stripping current density without internal short circuits) over 6 mA cm–2 was recognized by the galvanostatic Li metal plating/stripping tests. Notably, the excellent cycle performance with a high average Coulombic efficiency of 98.7% for 300 cycles was also achieved in the Li electrode-free system. Our works exhibit the potential for attaining Li metal all-solid-state cells.

Visualizing Heterogeneous Lithium Plating and Stripping during Fast Charging

Lithium plating is an obstacle for the development of fast-charge batteries and enabling of widescale electric vehicle adoption. Synchrotron high-energy X-ray diffraction was used to directly identify and track lithium plating in a full LiNi0.5Mn0.3Co0.2O2 / graphite pouch cell operated with a 6C charge rate for greater than 1200 cycles. The magnitude and spatial distribution of lithium plating, lithium stripping, and the effect of plating on lithium intercalation into graphite were quantified. For discharged cell maps, irreversible and fully lithiated graphite (LiC6) was closely correlated with lithium plating and can be considered a highly reliable indicator of lithium plating in cases where plated lithium is below the detection sensitivity. Isolated regions of slight plating initially stripped to below the detection limit, but over time the coverage and amount of plated lithium increased while the stripping efficiency decreased. Long term monitoring of lithium formation in a fast-charge battery provides important information for a better understanding of lithium plating and stripping mechanisms in practical cells.

Effect of Electrochemical and Mechanical Properties of SEI on Dendritic Growth during Lithium Deposition on Lithium Metal Electrode

In the past three decades, lithium-ion batteries experienced a long series of successful improvements, which nowadays make them a widespread technology. Intercalation electrodes, like graphite in the negative electrode, drove large part of this success. On the other hand, they constitute a limit in terms of energy density, which makes them unlikely to match the increasing demands set by renewable energies and especially electric mobility. Thus, it becomes fundamental to investigate new materials that overcome these limits. Lithium metal represents the optimal candidate for the negative electrode, due to its high theoretical capacity (3860 mAh.g-1) and low potential (-3.04 V SHE). On the other hand, the major drawback of this technology is the formation of dendrites, which are lithium structures that form during its deposition. They can cause thermal runaway and internal short-circuits, potentially leading to explosion. Moreover, during lithium stripping, some parts of the lithium electrode tend to be isolated in the electrolyte. This phenomenon causes a reduction of the electroactive lithium quantity thus a limited lifetime of the cell. Therefore, a deeper comprehension of the interfacial phenomena involved during lithium deposition and stripping is necessary to make lithium metal a viable and competitive option as a negative electrode, fostering the transition towards the next generations of batteries.The proposed model starts from the stability analysis of the electrode interface proposed by Newman and Monroe [1] that considers the effect of the mechanical properties on the lithium deposition. Different from it, the presented model studies a time-dependent variation of the surface and it includes a pseudo-2D representation of the Solid Electrolyte Interface (SEI) component. The approach to model the SEI is based on the work of Liu and Lu [2]; and it includes both SEI creation, due to deposition side reactions, and SEI thickness deformation due to the change in geometry of the underlying electrode. In addition, the model considers the effect of the mechanical properties of the SEI on the surface evolution of the electrode. Therefore, starting from the initial surface geometry and the electrochemical and mechanical properties of the components, the model is able to predict the conditions that favors dendritic growth. The figure shows lithium electrodeposition, starting from the same surface defect, on the lithium metal electrode in a liquid electrolyte. After the same quantity of lithium is deposited, it is possible to distinguish different patterns of surface evolution, due to the difference in magnitude of the current density applied: a quasi-uniform growth at low current density (left), a mossy behavior at medium current density (center) and a branching pattern at high current density (right). The difference in dendritic regime is strictly connected to the local change in the SEI thickness, as shown in the figure, which confirms the importance of this component, often neglected in the literature of dendrites models.Since SEI has a major impact on dendritic growth, a consistent set of experiments has been designed to provide its parameters to the model. Electrochemical Impedance Spectroscopy (EIS) was applied to find the electrochemical parameters of the SEI (e.g. SEI diffusion coefficient, SEI resistivity), while Atomic Force Microscopy (AFM) was conducted to find its mechanical properties (e.g. SEI Young’s modulus). The proposed model has the goal of guiding the experiments in finding ways to avoid or curtail dendrites formation, being able to simulate the effects on dendrites growth of operative conditions, SEI and electrolyte compositions, electrode surface defects and coatings. Starting from the model, innovative ways to increase the lifetime of the lithium metal anodes will be analyzed during the presentation; including coatings, surface morphology modification and pulse charging.[1] C. Monroe, J. Newman, Journal of the Electrochemical Society 151(6), A880-A886 (2004)[2] G. Liu, W. Lu, Journal of the Electrochemical Society 164(9), A1826-A1833 (2017) Figure 1

(Invited) Enabling Reversible Plating and Stripping of Lithium Metal in Lithium Metal Batteries

Lithium metal batteries with lithium metal anodes have the potential to almost double the energy density of today's lithium-ion batteries. However, non-uniform lithium plating and stripping causes poor cycling stability, low Coulombic efficiency, potential safety issues, and has hindered the commercialization of lithium metal batteries at scale. We discuss several promising strategies to achieve stable lithium plating and stripping.We report a nanocomposite coating for the protection of lithium metal anodes, which consists of nano-sized LiF particles embedded into a PEO polymer matrix [1]. The composite offers a large LiF/PEO interface area throughout the coating, promoting exceptionally high lithium-ion conductivity of 0.97 mS cm–1 and high lithium-ion transference number of 0.77 at room temperature in contact with a carbonate-based liquid electrolyte. Both properties are key to realize uniform lithium plating and stripping and prevent lithium dendrite formation. Lithium metal electrodes coated with this protective coating enable stable lithium plating and stripping at 1 mA cm–2 for over 1000 h at room temperature. A full cell with the coated lithium metal anode and a NMC622 cathode with an areal capacity of 1 mAh cm–2 shows much improved specific capacity and cycling stability at high current density. The cell exhibits a high initial capacity of 135 mAh g–1 and 83% capacity retention after 500 cycles at 1 mA cm–2. Even at a high current density of 3 mA cm–2, the full cell shows an initial capacity of 125 mAh g–1 and 74% capacity retention after 300 cycles.We will also discuss challenges and opportunities to stabilize plating and stripping of lithium metal in all-solid-state batteries [2-4].[1] C. Fu and C. Battaglia, ACS Appl. Mater. Interf. 2020, 12, 41620[2] M. Bay, M. Wang, R. Grissa, M. V. F. Heinz, J. Sakamoto, and C. Battaglia, Adv. Energy Mater. 2019, 1902899[3] R. Grissa, S. Payandeh, M. Heinz, and C. Battaglia, ACS Appl. Mater. Interf. 2021, 13, 14700[4] F. Pagani, C. Fu, and C. Battaglia, in preparation

All-Solid-State Battery Using Interface Engineering of Garnet-Type Solid Electrolytes

Currently, the demand for lithium-ion batteries is high due to its application in portable electronics, electric vehicles, and grid energy storage.1-2 The safety threat imposed by the liquid organic electrolyte can be eliminated by employing solid-state electrolytes (SSEs) that would also potentially enable the use of lithium metal anode (highest theoretical capacity, 3861 mAh g-1).3 Among several SSEs, garnet-type SSEs are comparatively stable with metallic lithium and they possess a wide electrochemical stability window.4 However, there are several unaddressed issues like the high interfacial resistance, instability of garnets in moisture containing atmosphere, propagation of lithium dendrites, etc. that hinders their practical application.3 Our investigation focuses on the removal of the detrimental lithium carbonate and lithium hydroxide layers from the surface of the garnets using two methods, namely argon-ion sputtering and ultra-high vacuum annealing. Precise control of the surface contaminant removal was achieved using in-situ X-ray photoelectron spectroscopy (XPS).5 The pristine garnet surface was found to be extremely atmosphere sensitive through XPS measurements. To overcome the sensitivity issue, atomic layer deposition (ALD) of 3 nm of h-BN was carried out using tris(dimethylamino)borane and ammonia precursors at 450 oC. The initial layers close to the garnet were present in an oxidized form (BNxOy) due to the oxygen-rich composition of garnet and the h-BN was capped over these layers, which were confirmed using angle-resolved XPS. The interfacial resistance drastically reduced from 1145 to 18 Ω cm2 through these processes. The inherent insulating nature of h-BN blocked the leakage of electrons across the solid-electrolyte and prevented the propagation of lithium dendrites. This enabled the plating and stripping of lithium in a symmetrical cell at a current density of 0.5 mA cm-2 with uniform polarization for over 200 hours. All-solid-state battery assembled using LiFePO4 cathode and Li anode exhibited stable cycling with a capacity of 130 mAh g-1 with minimum capacity fade.

Thin Lithium Metal Foil Technology for Advanced Battery Manufacturing

Lithium metal anode is regarded as the holy grail for the next generation battery materials due to its high theoretical specific capacity which is 10 times higher than that of graphite1. Currently, the most advanced lithium-ion battery cells have energy density of ~300 Wh/kg. Whereas, lithium metal batteries with liquid or semi solid electrolyte from Solidenergy2 and Sion Power3 have demonstrated record specific energy density of over 400 Wh/kg. Solid-state batteries use non-flammable solid electrolytes instead of liquid and, therefore, offer improved safety. The 20 Ah multi-layer all solid-state cells made by Solid Power have achieved 330 Wh/kg.4 However, solid state batteries can exceed the energy density of today's lithium-ion batteries only when the thin lithium metal foil (<20 um thickness) is used as anode enabling a pathway to beyond 400Wh/kg.Industrial scale thin Lithium metal foil is produced by hydraulic extrusion followed by a rolling process. This process usually requires a delicate balance between the pressure and tension created by both extruder and winder, so that the resulting foil is not torn or stretched, retaining all the dimensional characteristics required. This process can be extremely challenging when making lithium metal films with thickness less 20 µm due to the poor mechanical properties of lithium metal.5 Moreover, the cost of making these foils dramatically increases as the thickness decreases. Livent has recently developed Printable Lithium Technology (PLT), which incorporates stabilized lithium metal powder (SLMP®) into a stable printable formulation. This presentation will cover thin lithium foil manufacturing processes and highlight advantages and disadvantages of our approach. The electrochemical performance results will be presented.Figure 1A compares the 50 μm commercially available lithium foil (left) and 20 μm printed lithium foil (right) laminated to copper current collector. Figure 1A shows that a uniform film made from printable lithium formulation is consistent across the application area. Figure 1B and figure 1C are the optical microscope images of 50 μm commercially available lithium foil and 20 μm printed lithium foil, respectively. Figure 1B shows commercial foil made with conventional extrusion and rolling process has rough and scratched surface. Figure 1C shows that printed lithium foil preserves the shape of precursor particles and boundaries are formed creating higher surface area that potentially can mitigate dendrite growth by distributing current over a wider area. Figure 1D and 1E show the SEM and EDS images of the printed Lithium foil after lamination. Figure 1D and 1E show the clear presence of oxygen at the boundaries. Figure 1F shows the microscope image of printed lithium foil before calendering which is a monolayer. Figure 1G compares lithium plating and stripping properties of testing conducted in a symmetric pouch cell format with a current collector coated with 20 um printed lithium foil vs. 50 um commercially available lithium foil. Figure 1G shows that the cell containing the printed lithium foil, with lower thickness, has exceptional cycling stability with negligible potential increases during the first 70 cycles, indicating that the growth of dendritic lithium has been significantly mitigated.Figure Captions: Figure 1A. Image of 50 μm commercially available lithium foil (left) and 20 μm printed lithium foil (right) on a copper current collector. Figure 1B. Microscope (200x) image of the Printed Lithium Foil before lamination. Figure 1C. SEM Image (500x) of the Printed Lithium Foil after lamination. Figure 1D Microscope image of 50 μm commercially available lithium foil. Figure 1E. Microscope image of 20 μm printed lithium foil. Figure 1F. EDS surface mapping of oxygen for the printed foil. FIG. 1G. Lithium plating and stripping properties tested in a pouch cell with a copper current collector coated with 20 μm printable lithium formulation compared to 50 μm commercially available lithium foil. Cycling voltage is between -0.5V and 0.5 V and a current density is 0.5 C for 1h. References D. Lin, Y. Liu, and Y. Cui, Nature Nanotechnology, 12, 194–206 (2017) http://dx.doi.org/10.1038/nnano.2017.16.Q, Hu, Y. Matulevich and Y, Tang, Solidenergy Systems, US Patent No. 16/308,023, June 08th, 2016https://sionpower.com/2021/sion-power-announces-licerion-ev-targeting-electric-vehicles-with-a-large-format-17-ah-400-wh-kg-cell/https://www.greencarcongress.com/2020/12/20201216-solidpower.htmlO. Mashtalir, M. Nguyen, E. Bodoin, L. Swonger, and S. P. O’Brien, ACS Omega, 3, 181–187 (2018).Shu-Hua Wang et al., Nat. Commun.2019,10,4930 Figure 1

Asymmetric Li-Ion Diffusion Profiles during Lithium Plating and Stripping in Ionic Liquid Electrolytes

The electrochemical behavior of lithium metal in ionic-liquid based Li-electrolytes is typically characterized by an anodic peak due to the formation of an inhibition layer. In symmetric Li-Li cells, this shows up as a symmetric set of peaks in the current-cell voltage curves (Figure left), as here the current is limited by the slowest process, in this case the anodic dissolution side. Indeed, for 3-electrode measurements with a Li reference electrode and a lithium counter electrode with much larger surface area as the lithium working electrode, an asymmetric cathodic and anodic current-potential behavior is found (Figure right). Peculiar is that this behavior is reversible and thus not due to a single formation of an irreversible electrolyte decomposition layer, often referred to as a solid-electrolyte interphase or SEI layer even though the dense electronically isolating character and even ionic conductance of these decomposition layers are often doubtful. Our group has reported previously on the peculiar electrochemical behavior of ionic-liquid based electrolytes against lithium metal [1],[2]. We attributed the asymmetric behavior in the 3 electrode measurements to the formation of a temporary passivation layer on top of the usual SEI layer (dead lithium) which diffuses away when stopping the lithium dissolution, i.e., explaining the reversible behavior. As the focus of these papers was on the electrolyte material and cell performance, respectively, we did not go into more detail on the mechanism. In this paper, we will discuss the changes at the interface explaining the time dependent change in kinetics.[1] “Silica gel solid nanocomposite electrolytes with interfacial conductivity promotion exceeding the bulk Li-ion conductivity of the ionic liquid electrolyte filler” Xubin Chen, Brecht Put, Akihiko Sagara, Knut Gandrud, Mitsuhiro Murata, Julian A. Steele, Hiroki Yabe, Thomas Hantschel, Maarten Roeffaers, Morio Tomiyama, Hidekazu Arase, Yukihiro Kaneko, Mikinari Shimada, Maarten Mees and Philippe M. Vereecken, Science Advances, 6, 2, eaav3400 (2020). [2] “ High-Rate Performance Solid-State Lithium Batteries with Silica-Gel Solid Nanocomposite Electrolytes using Bis (fluorosulfonyl) imide-Based Ionic Liquid” Akihiko Sagara, Xubin Chen, Knut B Gandrud, Mitsuhiro Murata, Maarten Mees, Yukihiro Kaneko, Hidekazu Arase, Philippe M Vereecken, Journal Electrochemical Society 167 (7), 070549 (2020). Figure 1

Lithium Metal Deposition and Stripping in Porous Hosts Coupled with Viscous Polymer Electrolytes

High energy density rechargeable batteries are desired to meet global goals of increased use of renewable energy and vehicle electrification. Higher energy densities can be achieved by replacing graphite anodes with metal anodes. Among metal anode materials, lithium metal anodes are promising due to their high theoretical capacity and low reduction potential. However, obstacles such as dendrite growth and continuous electrolyte decomposition need to be addressed for successful commercialization of rechargeable batteries with lithium metal anodes. It is widely reported that porous 3D lithium metal hosts can mitigate dendrite growth by accommodating lithium deposition uniformly within the hosts during cycling. Continuous electrolyte decomposition can also be mitigated by replacing liquid electrolytes with solvent-free electrolytes. We incorporate both strategies in this work to address the critical issues described above by demonstrating lithium deposition/stripping cycling on 3D electrode hosts with viscous polymer electrolytes. First, lithium metal deposition/stripping cycling within non-conductive and conductive hosts were compared, where zinc oxide (ZnO) coated polyacrylonitrile (PAN) nanofibers was used as the non-conductive lithium metal host and ZnO coated copper nanowires were prepared as the conductive lithium metal host. The non-conductive host showed successful cycling of 5 mAh/cm2(25 µm thickness) of lithium metal without short circuiting. Further, deposition/stripping cycling with viscous star polymers (polystyrene-co-poly(polyethylene glycol) methyl ether acrylate (PS-co-PPEGMA)) and a linear oligomer polyethylene glycol dimethyl ether (PEGDME) were compared. The effects of the physical and electrochemical properties of the polymer electrolytes on lithium deposition and interfacial impedance will be discussed.

Interphase Control for Electrodeposition of Thin Lithium Films for Lithium Metal Batteries

Rechargeable lithium metal batteries including Li-S batteries, need a thin lithium anode with high purity for high energy density and long cycle life. Today, lithium metal is typically produced from Li2CO3. In contrast to the price of Li2CO3, which is often used for benchmarking, pure lithium metal is actually a costly component. In addition, it has quite some CO2 footprint as it needs significant amounts of energy to produce. Lithium foils of few hundred micron thick are produced by lithium extrusion and cold rolling. To limit cost and to increase energy density, maximum only a few tens of microns is. However, due to the soft nature of lithium, foils of few tens of micrometers are very difficult to manufacture at large volumes and too expensive for cost competitive high energy density Li-metal based cells. Hence, the production of thin lithium foils is currently a bottleneck.The electrodeposition of thin lithium films directly on copper current collector foils could be a cost effective and elegant method, where it not for the high reactivity of lithium with the electrolyte solution and the poor control of lithium morphology. Recently, several approaches have been pursued on lithium electrodeposition by stabilizing the lithium metal-electrolyte interface with the use of solid electrolytes and polymer coatings on electrode [1], however a poor quality of solid electrolyte interphase (SEI) and lithium metal deposition remain as a challenge.Among the various solid-state electrolytes, nitrogen doped lithium phosphate glass or LiPON has been evaluated as solid-electrolyte coatings on electrode particles as buffer layer between active material and the bulk electrolyte [2]. Previously, we investigated the stability of 100 nm down to 10 nm LiPON thin-films as artificial solid-electrolyte interphase for lithium plating and stripping on copper current collectors. We demonstrated the reversible plating/stripping of 150 nm lithium layer for over 100 cycles, indicating formation of a uniform lithium metal layer in-between substrate and LiPON layer [3].In the present work, we further investigated the effect of artificial solid electrolyte interphase, such as LiPON and poly(ethylene) glycol (PEG) coatings, on the deposition behavior of lithium to fabricate micro-meter thick lithium layer which is desirable for negative electrode in next-generation battery application. With a thin LiPON (<150 nm) layer, lithium layer uniformly grew up to 1 μm between substrate and LiPON without breaking of LiPON layer. However, the breakage of the thin LiPON layer was observed with further growth of lithium layer leading to dendrite growth. On the other hand, with a thick PEG coating (> 1 μm) dendrite growth was mitigated by increasing the molar mass of PEG from 8000 to 600,000 g/mol. Furthermore, addition of PEG into the carbonate-based electrolyte resulted in a denser lithium film with a thickness of 2-5 μm without dendrites. In the presentation, effect of molar mass, concentration of PEG on growth behavior of lithium will be further discussed.

Dynamics of Lithium Stripping on Graphite Electrodes

As fast charging of lithium-ion batteries becomes a critical barrier to the widespread adoption of electric vehicles, development of facile methods of detection and quantification of lithium plating is a top priority. The voltage plateau observed during the rest or discharge phase ensuing a charge in which plating has occurred is a popular in-operando signature of lithium plating. Recent works have shown that the length of the stripping plateau is not a reliable metric for plating quantification, as was previously thought. An improved analytical method for relative quantification of lithium plating is presented herein. Furthermore, an in-situ method is developed for direct visualization of lithium stripping and graphite phase redistribution during the open circuit rest phase after charge. The dependence of lithium stripping dynamics on temperature and charge rate are comprehensively investigated. These techniques help in understanding the mechanistic underpinnings of the stripping processes occurring in the graphite electrode during relaxation after fast charging and enhance the capability to study lithium plating in a non-destructive manner.

Regulating Lithium Plating and Stripping by Using Vertically Aligned Graphene/CNT Channels Decorated with ZnO Particles.

Lithium (Li) metal is regarded as the ultimate anode material for use in Li batteries due to its high theoretical capacity (3860 mA h g-1 ). However, the Li dendrites that are generated during iterative Li plating/stripping cycles cause poor cycling stability and even present safety risks, and thus severely handicap the commercial utility of Li metal anodes. Herein, we describe a graphene and carbon nanotube (CNT)-based Li host material that features vertically aligned channels with attached ZnO particles (designated ZnO@G-CNT-C) and show that the material effectively regulates Li plating and stripping. ZnO@G-CNT-C is prepared from an aqueous suspension of Zn(OAc)2 , CNTs, and graphene oxide by using ice to template channel growth. ZnO@G-CNT-C was found to be mechanically robust and capable of guiding Li deposition on the inner walls of the channels without the formation of Li dendrites. When used as an electrode, the material exhibits relatively low polarization for Li plating, fast Li-ion diffusion, and high Coulombic efficiency, even over hundreds of Li plating/stripping cycles. Moreover, full cells prepared with ZnO@G-CNT-C as Li host and LiFePO4 as cathode exhibit outstanding performance in terms of specific capacity (155.9 mA h g-1 at 0.5 C), rate performance (91.8 mA h g-1 at 4 C), cycling stability (109.4 mA h g-1 at 0.5 C after 800 cycles). The methodology described can be readily adapted to enable the use of carbon-based electrodes with well-defined channels in a wide range of contemporary applications that pertain to energy storage and delivery.