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Lithium morphology after charge-discharge rate test. (a), Lithium morphology generated in a cell cycled with a symmetric charge-discharge protocol of C/5 D/5. (b)–(c), Morphology from an asymmetric faster charge protocol of C/2 D/5 (b) and C/4 D/10 (c). (d)–(f), Morphology from an asymmetric slower charge protocol of C/2.5 D/1 (d), C/5 D/2 (e) and C/10 D/4 (e). Cells were cycled 20 times between 3.6–4.5 V at 40 °C under low pressure (170 kPa). The electrolyte used was 0.6 M LiDFOB 0.6 M LiBF4 FEC:DEC (1:2).
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Optimizing the performance of the lithium metal anode is required to enable the next generation of high energy density batteries. Anode-free lithium metal cells are particularly attractive as they facilitate the highest energy density cell architecture. In this work, we investigate the performance of anode-free cells cycled under different protocol...
Citations
... 16 Such uneven anode surfaces and/or cracks in the solid electrolyte interface (SEI) act as pathways for electrolyte to penetrate through to the underlying Li metal anode. 17 Continuous reaction of electrolyte with Li metal causes unmitigated electrolyte consumption and the formation of a porous SEI that continues to grow in thickness. This continued SEI growth leads to impedance rise, which in turn facilitates further non-uniform Li metal deposition. ...
... As the cells cycle, the Li anode expands and becomes porous due to non-uniform plating, which lowers the volumetric energy density and increases resistance. 17 Optimal levels of compression forces on the electrode stack can allow for uniform and dense plating onto the anode during charging, and better stripping performance during discharging. ...
... As pointed out by Dr. Dahn's recent publications, charging current density can significantly impact the total service time of LMB: 17 with C/10 charging rate, the LMB can survive >1200 h till capacity retention reaches 70%, which is twice as of C/5 (∼600 h) and 6 times of C/2 (∼200 h) charging rates. 17 The morphology of the deposited Li metal is also a function of current density. Jiao et al. showed that at current densities below 1 mA cm −2 , nearly 20 μm of Li was used and the surface morphology was relatively unchanged. ...
Lithium metal battery (LMB) technology is very attractive as it has the potential to offer energy densities greater than 1000 Wh L⁻¹. A thorough investigation of cell performance against various vehicle operational requirements is required for the successful deployment of this technology in practical electric vehicle applications. For instance, there have been several reports on the high reactivity of Li metal with electrolyte leading to continuous electrolyte consumption in LMB. Due to these parasitic reactions, electrolyte dries out and Li metal morphological changes occur leading to reduced cycle life of lithium metal batteries. In contrast, there are also claims of stable and long cycle life of LMB in several publications, although most of the results were obtained in coin cells. In this report we will take a closer look at the LMB cell to understand its performance and manufacturability. Our goal is to investigate and provide a thorough report on advances and challenges starting from the cell level down to component design of LMB.
... Formation and cycling parameters ranging from electrochemical protocols to temperature and pressure have long been shown as ways to benefit cell lifetime (Qian et al., 2016). More recently, Louli et al. (2021) demonstrated that an asymmetry in charge and discharge rates proves to be more important than the absolute current densities Specifically, discharging at faster rates generates a concentration gradient at the lithium surface which thereby results in preferential stripping of lithium protrusions at the anode, leaving behind a uniform surface at the end of discharge. This strategy is employed throughout the experiments in this work such that the discharge rate ranges from 1 to 2× the charge rate. ...
... Cell performance would likely continue to improve with ΔT cold at an increased ratio between discharge and charge rate (Qian et al., 2016;Louli et al., 2021). Optimization of xC|yD rate is required to find the cycling conditions, which benefit most from the ΔT cold strategy in the pouch cell form factor. ...
Zero excess lithium metal batteries (LMBs) have traditionally suffered from short cycle life due to nonuniform processes that result in parasitic side reactions and a subsequent loss of lithium inventory and electrolyte. The experiments herein demonstrate that zero excess LMB cells cycled with a low thermal average and thermal gradient outperform cells cycled under isothermal conditions during early cycles. Specifically, a low thermal average of ∼6.4°C and thermal gradient of <1°C across the cell is shown to increase the overpotential for lithium deposition at the anode current collector, likely resulting in smaller and higher density nucleates, providing film like morphologies observed with microscopy. Improved performance from this approach is demonstrated at high cycling rates (>4C) and mismatched charge/discharge rates. Optimal cycling behavior was observed with 2C charging (30 min) and 3C discharging (20 min). These advantages were translated to the system relevant form factor-pouch cell (20X capacity). Based on the performance enhancement observed with extended application of a thermal gradient, we demonstrate the use of the environment as a formation strategy, to perpetuate improved plating in stripping over the cycle life of zero excess LMBs operating in ambient conditions.
... Nevertheless, an increased DoD may adversely affect the cycling performance due to challenges in forming a stable lithium reservoir. 99 Typically, aer the initial deep charge and discharge (1.25 V-4.5 V), anode-free batteries undergo cycling within a standard voltage range (3.5-4.5 V). 100 The lithium initially extracted from the cathode during the rst charging cycle is deposited onto the current collector, creating a lithium reservoir. This reservoir compensates for lithium loss during cycling, consequently improving the battery's longevity. ...
... An intermittent high DoD protocol has been developed by researchers, where the battery predominantly cycles at a lower discharge depth of 50% and periodically experiences deeper discharges of 80%. 100 This strategy represents a balance between improving energy density and maintaining the lithium reservoir to extend the battery's cycle life. An alternative method involves a steady DoD, while implementing an asymmetric charging protocol that features a slower charge rate compared to the discharge rate. ...
The anode-free lithium metal battery is characterized by light weight, low cost, high-energy density, and high safety and shows great potential for the application of flexible devices.
... 14 Similarly, the Dahn group examined using asymmetric charge protocols such as C/5-D/2 and were able to increase the cycle lifetime compared to symmetric or fast charge-slow discharge protocolslikewise, they were able to greatly improve the lithium plating and stripping morphology. 15 Beyene et al. demonstrated that a prolonged 24 h rest after the first deposition allows for a more uniform SEI formation via the reduction of the fluorinated solvent, resulting in 64% capacity retention after 50 cycles compared to almost zero capacity retention of the control group. 16 There have also been numerous attempts to modify the current collector surface to improve performance; Lin et al. explored using a tri-alloy of gallium, indium, and tin to promote epitaxial lithium plating on the current collector surface and a Li-F-rich SEI layer. ...
As demand for extended range in electric vehicles and longer battery lifetimes in consumer electronics has grown, so have the requirements for higher energy densities and longer cycle lifetimes of the cells that power them. One solution to this is the implementation of an “anode‐free” battery. By removing the anode and plating lithium directly onto the current collector, it is possible to access the same capacities and voltage windows as traditional lithium metal batteries, with the entirety of the lithium source coming from the cathode. Herein, a copper foil current collector coated with niobium oxide or lithium niobium oxide through atomic layer deposition (ALD) is applied to extend the cycling life of the anode‐free batteries by reducing dendrite formation and improving the stability of the lithium metal surface throughout cycling. The ALD coatings are able to extend the cycle lifetime in full coin cells from 20 cycles to 80% capacity retained in the bare copper controls to 50 and 115 cycles for the NbO and LiNbO coatings, respectively. Over the lifetime of the cells, the ALD‐LiNbO is able to cumulatively offer a staggering improvement of an additional 100 kWh L ⁻¹ compared to the bare copper control.
... In particular, several investigations have empirically demonstrated the improvement of cycle life in LMBs by adopting a relatively higher-rate discharge protocol, commonly referred to as an asymmetric chargedischarge protocol. [16][17][18] For instance, Louli et al. have elucidated that during high-rate discharge, the development of a Li + concentration gradient enables an increased current density at the tips of the Li deposits. [17] This phenomenon leads to preferential stripping from the tips, effectively removing nonuniform deposits. ...
... [16][17][18] For instance, Louli et al. have elucidated that during high-rate discharge, the development of a Li + concentration gradient enables an increased current density at the tips of the Li deposits. [17] This phenomenon leads to preferential stripping from the tips, effectively removing nonuniform deposits. Consequently, an anodeless LMB exhibits a longer cycle life due to higher CE achieved at relatively higher discharge currents. ...
The demand for practical implementation of lithium metal batteries (LMBs) is increasing due to their superior energy density. However, poor cycle life and safety concerns regarding dendrite formation remain significant challenges. Recent studies have shown empirical improvements in cycle life through the use of high‐rate discharge protocols, but the precise mechanism behind this enhancement is still unclear due to difficulties in analyzing the lithium electrode, especially in LMB cells with high energy density designs. In this study, X‐ray computed tomography (XCT) analysis, a non‐destructive technique, was employed to investigate the lithium metal electrode in pouch‐type cells with a cell‐level energy density exceeding 350 Wh kg⁻¹. XCT analysis revealed significant volume expansion of the lithium electrode during charge/discharge cycles, particularly under high‐rate charging conditions, which promoted dendritic growth due to inhomogeneous current distribution. However, such undesired volume expansion was largely suppressed during high‐rate discharge, leading to improved cycle life. This study underscores the importance of non‐destructive techniques in comprehending the degradation mechanisms of high‐energy‐density LMBs.
... 21,22 These losses stem from the formation of solid electrolyte interphases (SEI) through reactions between the Li metal and the liquid electrolyte. [21][22][23][24] Moreover, the inhomogeneity of the Li deposition/dissolution causes the growth of high surface area Li (HSAL) such as Li dendrites that expose fresh Li surfaces to the electrolyte, inciting further Li-consuming SEI formation. Aer repeated cycling, the individual HSAL protrusions can get isolated from the electrode surface, which leads to further Li loss through the formation of electrochemically inactive "dead" Li. [21][22][23][24][25][26] Another detrimental factor is the recurrent volume uctuation because of the frequent electrochemical deposition and redissolution of the temporary Li metal layer. ...
... [21][22][23][24] Moreover, the inhomogeneity of the Li deposition/dissolution causes the growth of high surface area Li (HSAL) such as Li dendrites that expose fresh Li surfaces to the electrolyte, inciting further Li-consuming SEI formation. Aer repeated cycling, the individual HSAL protrusions can get isolated from the electrode surface, which leads to further Li loss through the formation of electrochemically inactive "dead" Li. [21][22][23][24][25][26] Another detrimental factor is the recurrent volume uctuation because of the frequent electrochemical deposition and redissolution of the temporary Li metal layer. This uctuation causes mechanical stress that can wear down cell components, reducing the cycle life of the battery. ...
... 21 To achieve increased CEs and a prolonged cycle life for ZELMBs, a homogeneous and reversible Li charge/discharge behavior and reduced decomposition reactions in the cell are desirable. 21 In this regard, a lot of attention has been devoted to the electrolyte design [29][30][31][32][33][34][35][36][37] and optimized cycling conditions for ZELMBs, 18,24,38 as well as functional coatings and surface modications for the negative electrode. 27,[39][40][41][42][43][44][45][46] Table S2 (ESI †) summarizes the capacity retention improvements that were achieved in several recent studies using ZELMBs with optimized Cu-based negative electrode substrates. ...
In zero-excess lithium metal batteries (ZELMBs), also termed “anode-free” LMBs, Li from the positive electrode is electrodeposited onto a bare current collector instead of the Li metal negative electrode commonly used in LMBs. This enables high theoretical energy density and facile, safe, and low-cost assembly. To tackle coulombic inefficiencies during Li deposition/dissolution, 3D structured current collectors can be used instead of 2D foil materials. This study elucidates the Li deposition behavior in custom-made open-porous Cu micro-foams from nucleation to large scale deposition. For the first time in ZELMBs, surface and sub-surface Li deposits in open-porous 3D materials are compared to deposits on 2D foils using cryogenic focused ion beam scanning electron microscopy (cryo-FIB-SEM). The results highlight that Cu micro-foams can store substantial amounts of dendrite-free Li in their open-porous 3D structure, minimizing detrimental volume changes during Li deposition/dissolution. Electrochemical analyses and simulations reveal that current density distribution over the large surface area of the Cu micro-foams reduces the Li nucleation overvoltage by ≈40%. Also, charge/discharge cycling in ZELMBs shows increases in coulombic efficiency, capacity retention, and cycle life. Overall, this work explains how open-porous Cu micro-foam current collectors improve the Li deposition behavior to boost the cycling characteristics of ZELMBs.
... Meanwhile, in practical cell applications, it is required to increase the loading of active material, decrease the amount of electrolyte, Figure 1. Designs of anode-free lithium-ion battery based on cathodes categorization and the strategies for the performance improvement [19][20][21][22][23][24][25]. Reprinted with permission from Ref. [20] (Copyright 2021, John Wiley and Sons); Ref. [21] (Copyright 2021, Springer Nature); Ref. [22] (Copyright 2019, RSC Pub); Ref. [23] (Copyright 2019, American Chemical Society); Ref. [24] (Copyright 2019, Elsevier). ...
... The mod- Figure 1. Designs of anode-free lithium-ion battery based on cathodes categorization and the strategies for the performance improvement [19][20][21][22][23][24][25]. Reprinted with permission from Ref. [20] (Copyright Batteries 2023, 9,381 3 of 19 2021, John Wiley and Sons); Ref. [21] (Copyright 2021, Springer Nature); Ref. [22] (Copyright 2019, RSC Pub); Ref. [23] (Copyright 2019, American Chemical Society); Ref. [24] (Copyright 2019, Elsevier). ...
... Cycling protocols including charge and discharge current density [25], cut-off age [63], temperature [46], external pressure [64,80], etc. are also important for impr the electrochemical performance of AFLBs. These protocols are beneficial to mech investigation but may not be suitable for application in real life. ...
Anodes equipped with limited lithium offer a way to deal with the increasing market requirement for high-energy-density rechargeable batteries and inadequate global lithium reserves. Anode-free lithium-ion batteries (AFLBs) with zero excess metal could provide high gravimetric energy density and high volumetric energy density. Moreover, the elimination of lithium with a bare current collector on the anode side can reduce metal consumption, simplify the cell technological procedure, and improve manufacturing safety. However, some great challenges, such as insufficient cycling stability, significant lithium dendrite growth, as well as unstable solid electrolyte interface, impede the commercial application of AFLBs. Fortunately, significant progress has been made for AFLBs with enhanced electrode stability and improved cycling performance. This review highlights research on the design of anode-free lithium-ion batteries over the past two decades, presents an overview of the main advantages and limitations of these designs, and provides improvement strategies including the modification of the current collectors, improvement of the liquid electrolytes, and optimization of the cycling protocols. Prospects are also given to broaden the understanding of the electrochemical process, and it is expected that the further development of these designs can be accelerated in both scientific research and practical applications.
... Additionally, the repetitive formation and breakdown of the solid electrolyte interphase (SEI) layer over an increasing number of cycles may affect the Coulombic efficiency (CE) and stability of the cells. [7][8][9][10][11][12][13][14][15] These side reactions could lead to critical safety hazards. Thus, several approaches have been proposed to address the challenges posed by lithium metal anodes, including the addition of electrolyte additives, the application of artificial coatings on the metal surface, the incorporation of lithium host structures, and the introduction of lithiophilic alloy metals [7,8,10,11,16] More recently, anode-less or anode-free lithium metal batteries (AFLMBs), which do not utilize any form of anode active material, have received significant attention. ...
Anode‐free lithium metal batteries (AFLMBs) show promise as a means of further enhancing the energy density of current lithium‐ion batteries, as they do not require conventional graphite anodes. The anode‐free configuration, however, suffers from inferior chemical stability of the solid electrolyte interphase (SEI) layer and experiences inhomogeneous lithium deposition during charge/discharge processes, resulting in rapid capacity fading. To address these issues, a carbonized polydopamine (CPD) coating is applied to the copper current collector. The CPD‐coated copper current collector promotes highly efficient and reversible lithium plating and stripping processes, resulting in a densely packed lithium deposition that significantly improves cycling stability. The anode‐free full cell, consisting of CPD‐coated copper current collector and a LiFePO 4 cathode, demonstrates significantly improved electrochemical performance, with a capacity retention of more than 63% after 100 cycles at a current rate of 0.3C. The stability of the SEI layer and the presence of lithiophilic sites are verified through a range of techniques, including optical microscopy, Raman spectroscopy, X‐ray photoelectron spectroscopy, chronoamperometry, and electrochemical impedance spectroscopy. Based on these collective findings, it can be inferred that the use of CPD coating provides a simple way to enhance the electrochemical performance of AFLMBs.
... This cycling protocol help to minimize lithium inventory loss during Li plating and stripping. [49] As shown in Figure 8a, the discharge capacity decreased. However, higher capacity retention of 60% after 100 cycles was demonstrated, with a similar average CE of 98.2% (Figure 8b). ...
Anode‐free Li‐metal batteries are of significant interest to energy storage industries due to their intrinsically high energy. However, the accumulative Li dendrites and dead Li continuously consume active Li during cycling. That results in a short lifetime and low Coulombic efficiency of anode‐free Li‐metal batteries. Introducing effective electrolyte additives can improve the Li deposition homogeneity and solid electrolyte interphase (SEI) stability for anode‐free Li‐metal batteries. Herein, we reveal that introducing dual additives, composed of LiAsF6 and fluoroethylene carbonate, into a low‐cost commercial carbonate electrolyte will boost the cycle life and average Coulombic efficiency of NMC||Cu anode‐free Li‐metal batteries. The NMC||Cu anode‐free Li‐metal batteries with the dual additives exhibit a capacity retention of about 75% after 50 cycles, much higher than those with bare electrolytes (35%). The average Coulombic efficiency of the NMC||Cu anode‐free Li‐metal batteries with additives can maintain 98.3% over 100 cycles. In contrast, the average Coulombic efficiency without additives rapidly decline to 97% after only 50 cycles. In situ Raman measurements reveal that the prepared dual additives facilitate denser and smoother Li morphology during Li deposition. The dual additives significantly suppress the Li dendrite growth, enabling stable SEI formation on anode and cathode surfaces. Our results provide a broad view of developing low‐cost and high‐effective functional electrolytes for high‐energy and long‐life anode‐free Li‐metal batteries.
... This is the more demanding condition since it has been reported that slower discharge than charge can lead to higher surface area Li morphology. 38 The improvement seen in F2DEM under a slower discharge rate potentially indicates that F2DEM can facilitate the formation of a more stable SEI. Under symmetric C/2 charge rate and C/2 discharge rate, 1.75 M LiFSI / F2DEM yielded similar cycling performance as the two reference electrolytes (Figure 4e-f). ...
High degree of fluorination for ether electrolytes has resulted in improved cycling stability of lithium metal batteries (LMBs) due to stable SEI formation and good oxidative stability. However, the sluggish ion transport and environmental concerns of high fluorination degree drives the need to develop less fluorinated structures. Here, we introduce bis(2-fluoroethoxy)methane (F2DEM) which features monofluorination of the acetal backbone. High coulombic efficiency (CE) and stable long-term cycling in Li||Cu half cells can be achieved with F2DEM even under fast Li metal plating conditions. The performance of F2DEM is further compared with diethoxymethane (DEM) and 2-[2-(2,2-Difluoroethoxy)ethoxy]-1,1,1-Trifluoroethane (F5DEE). The structural similarity of DEM allows us to better probe the effects of monofluorination, while F5DEE is chosen as the one of the best performing LMB electrolytes for reference. The monofluorine substitution provides improved oxidation stability compared to non-fluorinated DEM, as demonstrated in the linear sweep voltammetry (LSV) and voltage holding experiments in Li||Pt and Li||Al cells. Higher ionic conductivity compared to F5DEE is also observed due to the decreased degree of fluorination. Furthermore, 1.75 M lithium bis(fluorosulfonyl)imide (LiFSI) / F2DEM displays significantly lower overpotential compared with the two reference electrolytes, which improves energy efficiency and enables its application in high-rate conditions. Comparative studies of F2DEM with DEM and F5DEE in anode-free (LiFePO4) LFP pouch cells and high-loading LFP coin cells with 20 {\mu}m excess Li further show improved capacity retention of F2DEM electrolyte.
