Practical Lithium Research Articles

“Dead Lithium” Formation and Mitigation Strategies in Anode‐Free Li‐Metal Batteries

AbstractThin lithium‐metal foil is a promising anode material for next‐generation batteries due to its high theoretical specific capacity and low negative potential. However, safety issues linked to dendrite growth, low‐capacity retention, and short cycle life pose significant challenges. Also, it has excess energy that must be minimized in order to reduce the battery costs. To limit excess lithium, practical lithium metal batteries need a negative‐to‐positive electrode ratio as close to 1 : 1 as possible, which can be achieved through limiting excess lithium or using an “anode‐free” metal battery design. However, both designs experience fast capacity fade due to the irreversible loss of active lithium in the cell, caused by the formation of the solid electrolyte interphase (SEI), dendrite formation and “dead lithium,” – refers to lithium that has lost its electronic connection to the anode electrode or current collector. The presence of dead lithium in batteries negatively affects their capacity and lifespan, while also raising internal resistance and generating heat. Additionally, dead lithium encourages the growth of lithium dendrites, which poses significant safety hazards. Within this fundamental review, we thoroughly address the phenomenon of dead lithium formation, assessing its origins, implications on battery performance, and possible strategies for mitigation. The transition towards environmentally friendly and high‐performance metal batteries could be accelerated by effectively tackling the challenge posed by dead lithium.

Direct contact pre-lithiation for practical lithium ion batteries: Focus review

Pre-lithiation methods address the challenges of low initial coulombic efficiency (ICE) and reduced energy density in lithium-ion batteries (LIBs) by adding additional lithium sources to compensate for initial irreversible Li+ losses. The direct contact pre-lithiation (DC-Pr) method has garnered extensive attention due to its simplicity, convenience as well as significant effects on the improved cycling durability. Considering the most important factors, i.e., effectiveness and uniformity, this review focuses on the anode DC-Pr method for LIBs with the lithium sources from Li foil, stabilized lithium metal powder (SLMP), lithium-rich alloys, and physical vapor deposition of lithium metal. After summarizations and discussions, the review overviews the challenges and prospects for DC-Pr methods, aiming to provide guidance for the construction and developments of practical LIBs.

Synergistic Effect of High Donor Electrolyte and Catalytic Separator for Practical Lithium–Sulfur Batteries

Synergistic Effect of High Donor Electrolyte and Catalytic Separator for Practical Lithium–Sulfur Batteries

Practical Lithium–Sulfur Batteries: Beyond the Conventional Electrolyte Concentration

Practical Lithium–Sulfur Batteries: Beyond the Conventional Electrolyte Concentration

Designing Cooperative Ion Transport Pathway in Ultra‐Thin Solid‐State Electrolytes toward Practical Lithium Metal Batteries

AbstractSolid polymer electrolytes (SPEs) are promising for high‐energy‐density solid‐state Li metal batteries due to their decent flexibility, safety, and interfacial stability. However, their development was seriously hindered by the interfacial instability and limited conductivity, leading to inferior electrochemical performance. Herein, we proposed to design ultra‐thin solid‐state electrolyte with long‐range cooperative ion transport pathway to effectively increase the ionic conductivity and stability. The impregnation of PVDF−HFP inside pores of fluorinated covalent organic framework (CF3−COF) can disrupt its symmetry, rendering rapid ion transportation and inhibited anion immigration. The functional groups of CF3−COF can interact with PVDF−HFP to form fast Li+ transport channels, which enables the uniform and confined Li+ conduction within the electrolyte. The introduction of CF3−COF also enhances the mechanical strength and flexibility of SPEs, as well as ensures homogeneous Li deposition and inhibited dendrite growth. Hence, a remarkably high conductivity of 1.21×10−3 S cm−1 can be achieved. Finally, the ultra‐thin SPEs with an extremely long cycle life exceed 9000 h can be obtained while the NCM523/Li pouch cell demonstrates a high capacity of 760 mAh and 96 % capacity retention after cycling, holding great promises to be utilized for practical solid‐state Li metal batteries.

Designing Cooperative Ion Transport Pathway in Ultra-Thin Solid-State Electrolytes toward Practical Lithium Metal Batteries.

Solid polymer electrolytes (SPEs) are promising for high-energy-density solid-state Li metal batteries due to their decent flexibility, safety, and interfacial stability. However, their development was seriously hindered by the interfacial instability and limited conductivity, leading to inferior electrochemical performance. Herein, we proposed to design ultra-thin solid-state electrolyte with long-range cooperative ion transport pathway to effectively increase the ionic conductivity and stability. The impregnation of PVDF-HFP inside pores of fluorinated covalent organic framework (CF3-COF) can disrupt its symmetry, rendering rapid ion transportation and inhibited anion immigration. The functional groups of CF3-COF can interact with PVDF-HFP to form fast Li+ transport channels, which enables the uniform and confined Li+ conduction within the electrolyte. The introduction of CF3-COF also enhances the mechanical strength and flexibility of SPEs, as well as ensures homogeneous Li deposition and inhibited dendrite growth. Hence, a remarkably high conductivity of 1.21×10-3 S cm-1 can be achieved. Finally, the ultra-thin SPEs with an extremely long cycle life exceed 9000 h can be obtained while the NCM523/Li pouch cell demonstrates a high capacity of 760 mAh and 96 % capacity retention after cycling, holding great promises to be utilized for practical solid-state Li metal batteries.

Remodeling Highly Fluorinated Electrolyte via Shielding Agent Regulation toward Practical Lithium Metal Batteries.

Highly fluorinated electrolytes have proved effective in improving electrochemical stability of lithium metal batteries. However, excessive fluorination not only detrimentally impacts the electrolyte ionic conductivity, but also inevitably forms the over-fluorinated interphases with sluggish ion diffusivity. Herein, a strategy on remodeling Li+ solvation structure in highly fluorinated electrolyte aided is proposed by fluorinated amide (FDMA), which denoted as "shielding agent". Benefitting from FDMA's high donor number (DN)value (22.1), the Li+-dipole (fluoroethylene carbonate (FEC) or trans-4,5-Difluoroethylenecarbonate (DFEC)) interaction is interrupted and the participation of FDMA in primary solvation sheath fructify the solid-electrolyte interphase without scarifying the privilege of fluorinated electrolyte on interphase chemistry. Eventually, the optimal high-fluorinated electrolyte (FDMA/DFEC + 1.0mol L-1 LiTFSI) with this unique shielding effect displays high ionic conductivity and rapid Li+ desolvation behavior, enabling Li||LiNi0.6Co0.2Mn0.2O2 (Li||NCM622) to achieve an ultralong cycle-life of 2000 cycles at 1C with 84.7% capacity retention. Even under extreme conditions (NCM622: 10mg cm-2; electrolyte: 20µL; Li: 50µm), the Li||NCM622 displays excellent electrochemical performance. Additionally, 447Wh kg-1 Li||LiNi0.8Co0.1Mn0.1O2 (Li||NCM811) pouch cells have been successfully fabricated and demonstrate an exceptional cycle-life over 150 cycles. The proposed "shielding" strategy to modulate the solvation structure paves the way for developing practical LMBs with fluorinated electrolytes.

Accelerating sulfur redox kinetics by rare earth single-atom electrocatalysts toward efficient lithium–sulfur batteries

Toward practical lithium−sulfur (Li−S) batteries, there is a pressing need to improve the rate performance and longevity of cells. Herein, we report developing a cathode electrocatalyst Lu SA/NC, capable of accelerating sulfur redox kinetics with a high specific capacity of 1391.8 mAh g−1 at 0.1 C, and a low-capacity fading rate of 0.049 % per cycle over 1000 cycles even with a high sulfur loading (5.96 mg cm−2). The unparalleled cathodes are built upon the unique structure in which single-atoms of rare earth metals are doped in nitrogen-doped porous carbon (RM SAs/NC). The theoretical and experimental studies reveal that the rare earth Lu atom has an unrivaled adsorption capacity for polysulfides and can promote facile deposition and dissolution reactions in charge-discharge processes. The in-situ Raman experiments provide direct evidence for its promotion of polysulfide transformation to eliminate the shuttle effect. The theoretical calculations suggest that the presence of f-d-p hybridization enables accelerating sulfur reduction kinetics and enhancing lithium−sulfur battery performance. The strategic paradigm introduced in this study underscores significant practical potential in the exploration of rare earth single-atom catalysts for high performance Li−S batteries.

Rolling strategy for highly efficient preparation of phosphating interface enabled the stable lithium anode

Lithium metal anode has an ultra-high theoretical specific capacity and the lowest reduction potential, regarded as the next-generation anode material for high-energy-density batteries. However, the lithium metal anode suffers from the severe side reaction and Li dendrite growth caused by the inhomogeneous deposition of Li+ on the anode during the electrochemical cycling. Herein, a strategy is proposed to design an artificial solid electrolyte interface (SEI) by rolling with the organic phosphating lubricant. The obtained phosphating interface with high surface energy and surface Young’s modulus significantly induces the dense deposition of Li+ and results in a stable cycling. The phosphating interface enables the symmetric cells to cycle stably for 750 h at 1 mA cm−2 with 1 mA h cm−2 and for 450 h at 3 mA cm−2 with 3 mA h cm−2 using ester-based electrolyte. The full cell with high single-side mass loading (10 mg cm−2) of LiCoO2 achieves a capacity retention rate of 77.7 % after 165 cycles at 1 C and 75.6 % after 120 cycles at 2 C. This work paves a path to construct a green fluorine-free interface and provide a large-scale modification for practical lithium strips.

Boosting High-Voltage Practical Lithium Metal Batteries with Tailored Additives

HighlightsFGN-182 electrolytes exhibit highly reversible Li plating/stripping with an average Coulombic efficiency reaching up to 99.56% determined from Auerbach’s test.The gas-evolution process of LiNO3 in high-voltage lithium cobalt oxide (LCO) cathodes is revealed by in situ differential electrochemical mass spectrometry.Pouch cells equipped with high-loading LCO (3 mAh cm−2) cathodes, ultrathin Li chips (25 μm), and lean electrolytes (5 g Ah−1) using optimized electrolyte (FGN-182 + 1%HTCN) demonstrate outstanding cycling performance.

Coupling interfacial effect in heterogeneous RuP2-RuP for accelerating sulfur reduction reaction of lithium sulfur batteries

The cathodic host for practical lithium sulfur (Li–S) batteries needs to meet numerous requirements, such as outstanding electron conductivity, desirable lithium polysulfide (LiPSs) adsorption ability, and efficient catalytic effect towards the redox of sulfur. Given the above considerations, an N, P, S tri-doped 3D interconnected porous carbon embedded with heterogeneous ruthenium phosphides (RuP2-RuP@NPSC) was constructed to serve as a sulfur host for high-performance and practical Li–S battery. Strong interfacial coupling effect in the RuP2-RuP heterojunctions endowed the active sites with favorable LiPSs adsorption ability and boosted sulfur reduction reaction. The density functional theory calculation suggested that the electronic tuning of the constructed heterojunction interface could enhance the electron transport and LiPSs adsorption ability. The higher current response of symmetric cells, larger Li2S deposition and dissolution capacity of RuP2-RuP@NPSC in comparison to other counterparts of RuP@NPSC, RuP2@NPSC, and NPSC further verified the great catalytic capability of RuP2-RuP heterojunctions. As a result, corresponding cells with RuP2-RuP@NPSC/S electrodes delivered an impressive reversible capacity of 565 mAh g−1 at 6 C, and an ultralow capacity decay rate of 0.019 % per cycle after 1000 cycles was achieved at the current of 2 C. The commercial level high sulfur loading pouch cells further confirmed the feasibility and practicability of RuP2-RuP@NPSC/S based Li–S battery

Chemomechanics Engineering Promotes the Catalytic Activity of Spinel Oxides for Sulfur Redox Reaction

AbstractCooperative catalysis is a promising approach to enhance the sluggish redox kinetics of lithium polysulfides (LiPSs) for practical lithium–sulfur (Li–S) batteries. However, the elusory synergistic effect among multiple active sites makes it challenging to accurately customize the electronic structure of catalysts. Herein, a strategy of precisely tailoring eg orbitals of spinel oxides through chemomechanics engineering is porposed to regulate LiPSs retention and catalysis. By manipulating the regulable cations in MnxCo3‐xO4, it is theoretically and experimentally revealed that the lattice strain induced by the Jahn–Teller active and high‐spin Mn3+ at octahedral (Oh) sites can increase the eg occupancy of low‐spin Co3+Oh, which effectively regulates the chemical affinity toward LiPSs and establishes an unblocked channel for intrinsic charge transfer. This leads to a volcano‐type correlation between the eg occupancy at Oh sites and sulfur redox activity. Benefitting from the cooperative catalysis of dual‐active sites, MnCo2O4 with an average eg occupancy of 0.45 affords the most appropriate adsorption strength and rapid redox kinetics toward LiPSs, leading to remarkable rate performance and capacity retention for the assembled Li–S batteries. This work demonstrates the promise of chemomechanics engineering for optimizing the eg occupancy to achieve efficient sulfur redox catalysts.

Hybridizing carbonate and ether at molecular scales for high-energy and high-safety lithium metal batteries

Commonly-used ether and carbonate electrolytes show distinct advantages in active lithium-metal anode and high-voltage cathode, respectively. While these complementary characteristics hold promise for energy-dense lithium metal batteries, such synergy cannot be realized solely through physical blending. Herein, a linear functionalized solvent, bis(2-methoxyethyl) carbonate (BMC), is conceived by intramolecularly hybridizing ethers and carbonates. The integration of the electron-donating ether group with the electron-withdrawing carbonate group can rationalizes the charge distribution, imparting BMC with notable oxidative/reductive stability and relatively weak solvation ability. Furthermore, BMC also offers advantages including the ability to slightly dissolve LiNO3, excellent thermostability and nonflammability. Consequently, the optimized BMC-based electrolyte, even with typical concentrations in the single solvent, demonstrates high-voltage tolerance (4.4 V) and impressive Li plating/stripping Coulombic efficiency (99.4%). Moreover, it fulfills practical lithium metal batteries with satisfactory cycling performance and exceptional tolerance towards thermal/mechanical abuse, showcasing its suitability for safe high-energy lithium metal batteries.

Electrochemical Lithium Deposition on LixTi5O12.

Lithium metal batteries (LMBs) have been regarded as one of the most promising next-generation high-energy-density storage devices. However, uncontrolled lithium dendrite growth leads to low Coulombic efficiencies and severe safety issues, hindering the commercialization of LMBs. Reducing the diffusion barrier of lithium is beneficial for uniform lithium deposition. Herein, a composite is constructed with Li4Ti5O12 as the skeleton of metallic lithium (Li@LixTi5O12) because Li4Ti5O12 is a "zero-strain" material and exhibits a low lithium diffusion barrier. It was found that the symmetric cells of Li@LixTi5O12 can stably cycle for over 400 h at 1 mA cm-2 in the carbonate electrolyte, significantly exceeding the usual lifespan (∼170 h) of the symmetric cell using a lithium metal electrode. In a full cell with Li@LixTi5O12 as the anode, the cathode LiFePO4 delivers a capacity retention of 78.2% after 550 cycles at 3.6C rate and an N/P ratio = 8.0. This study provides new insights for designing a practical lithium anode.

Dual‐gradient Engineering of Urchin‐like Silver@Copper Oxide Heterostructures for Highly Stable Lithium Metal Anodes

AbstractLithium‐metal anodes with excellent theoretical specific capacities (3680 mAh g−1) have attracted considerable attention for overcoming the capacity bottleneck of conventional graphite anodes. However, they often suffer from uncontrolled dendrite growth and undesirable side reactions, considerably limiting their practical application in lithium‐metal batteries. In this study, urchin‐like silver@copper oxide (Ag@CuO) heterostructures with gradient electrical conductivity and lithiophilicity are prepared using a facile liquid‐phase reduction method. The unique amphiphilic lithium mechanism of the alloying and conversion reactions effectively reduces the nucleation overpotential of the lithium metal anode and promotes a uniform lithium deposition process. Meanwhile, the in situ‐generated Li2O‐rich solid electrolyte interphase (SEI) film can further induce uniform and reversible lithium plating/stripping. All these characteristics endow the Ag@CuO anode with a high Coulombic efficiency of 98.89%, even after 1200 cycles, and long cycle life of 2800 h at a current density of 0.2 mA cm−2, thus demonstrating that such modified Li metal anodes exhibit superior compatibility with major commercial cathode materials, such as LiCoO2 (LCO) and LiNi0.8Co0.1Mn0.1O2 (NCM‐811). Hence, this study provides an effective strategy for developing practical lithium metal anodes.

Copper Current Collector: The Cornerstones of Practical Lithium Metal and Anode-Free Batteries.

Comparing with the commercial Li-ion batteries, Li metal secondary batteries (LMB) exhibit unparalleled energy density. However, many issues have hindered the practical application. As an element in lithium metal and anode-free batteries, the role of current collector is critical. Comparing with the cathode current collector, more requirements have been imposed on anode current collector as the anode side is usually the starting point of thermal runaway and many other risks, additionally, the anode in Li metal battery very likely determines the cycling life of full cell. In the review, we first give a systematic introduction of copper current collector and the related issues and challenges, and then we summarize the main approaches that have been mentioned in the research, including Cu current collector with 3D architecture, lithophilic modification of the current collector, artificial SEI layer construction on Cu current collector and carbon or polymer decoration of Cu current collector. Finally, we give a prospective comment of the future development in this field.

Improving Rate Performance of Encapsulating Lithium‐Polysulfide Electrolytes for Practical Lithium−Sulfur Batteries

AbstractThe cycle life of high‐energy‐density lithium−sulfur (Li−S) batteries is severely plagued by the incessant parasitic reactions between Li metal anodes and reactive Li polysulfides (LiPSs). Encapsulating Li‐polysulfide electrolyte (EPSE) emerges as an effective electrolyte design to mitigate the parasitic reactions kinetically. Nevertheless, the rate performance of Li−S batteries with EPSE is synchronously suppressed. Herein, the sacrifice in rate performance by EPSE is circumvented while mitigating parasitic reactions by employing hexyl methyl ether (HME) as a co‐solvent. The specific capacity of Li−S batteries with HME‐based EPSE is nearly not decreased at 0.1 C compared with conventional ether electrolytes. With an ultrathin Li metal anode (50 μm) and a high‐areal‐loading sulfur cathode (4.4 mgS cm−2), a longer cycle life of 113 cycles was achieved in HME‐based EPSE compared with that of 65 cycles in conventional ether electrolytes at 0.1 C. Furthermore, both high energy density of 387 Wh kg−1 and stable cycle life of 27 cycles were achieved in a Li−S pouch cell (2.7 Ah). This work inspires the feasibility of regulating the solvation structure of LiPSs in EPSE for Li−S batteries with balanced performance.

Impact of Pressure Distribution and Magnitude on the Performance of Lithium Metal Anodes

Li metal anodes are a critical battery technology due to their ability to substantially increase the energy density of Li-based batteries. It is well known that pressure greatly impacts the performance of a Li-metal anode. However, precisely how the pressure value and distribution of pressure affect performance is unclear. Furthermore, the solid-electrolyte interphase composition that forms under varying pressure distributions remains a key parameter for practical lithium metal anodes. In this work, different pressure distributions were employed by using differently shaped and oriented mechanical springs in the coin cells, resulting in varying contact points. Pressure-sensitive films were used to spatially map the pressure and correlate it to the performance. It was found that higher average pressure does not necessarily have a positive effect on performance. When high pressure is paired with poor pressure uniformity, the performance is in fact worse likely due to the current focusing effect, rendering unsatisfied cycling stability. This work points to the importance of controlling the relationship between average pressure and pressure uniformity.

Porous Magnesium Hydride Nanoparticles Uniformly Coated by Mg‐Based Composites toward Advanced Lithium Storage Performance

Magnesium hydride (MgH2) has been recognized as a promising anode material of lithium‐ion batteries (LIBs) owing to its ultrahigh specific capacity. The low conductivity and the structural pulverization induced by large volume expansion, however, has long limited its practical lithium storage performance. Herein, a series of yolk‐shell‐like structures, composed of porous MgH2 nanoparticles (NPs) decorated with Mg‐based composites through in‐situ solid‐gas reaction using MgH2 as both the reactant and the structural template, have been fabricated and uniformly dispersed on electronically conductive graphene. It could not only physically accommodate the volume change of MgH2 owing to the physical protection of Mg‐based composites and the formation of void space inside MgH2 NPs, but also effectively facilitate the transportation of electrons throughout the whole electrode. Particularly, the uniform decoration of ultrathin Mg(BH4)2 as the shell with thermodynamically favorable intercalation of lithium ions and low kinetic barrier for the lithium‐ion diffusion promotes facile transportation of lithium ions into active MgH2, which, coupled with the porous structure constructed by flexible graphene, effectively improves the ion conductivity of the electrode. The synergistic improvement in electronic and ionic conductivity leads to a high reversible capacity of 1651 mAh g−1 at 200 mA g−1 after 380 cycles.

Beyond LiF: Tailoring Li2O-Dominated Solid Electrolyte Interphase for Stable Lithium Metal Batteries.

The components and structures of the solid-electrolyte interphase (SEI) are critical for stable cycling of lithium metal batteries (LMBs). LiF has been widely studied as the dominant component of SEI, but Li2O, which has a much lower diffusion barrier for Li+, has rarely been investigated as the dominant component of SEI. The effect of Li2O-dominated SEI on electrochemical performance still remains elusive. Herein, an ultrastrong coordinated cosolvation diluent, 2,3-difluoroethoxybenzene (DFEB), is designed to modulate solvation structure and tailor Li2O-dominated SEI for stable LMBs. In the DFEB-based LHCE (DFEB-LHCE), DFEB intensively participates in the first solvation shell and synergizes with FSI- to tailor an Li2O-dominated inorganic-rich SEI which is different from the LiF-dominated SEI formed in conventional LHCE. Benefiting from this special SEI architecture, a high Coulombic efficiency (CE) of 99.58% in Li||Cu half cells, stable voltage profiles, and dense and uniform lithium deposition, as well as effective inhibition of Li dendrite formation in the symmetrical cell, are achieved. More importantly, the DFEB-LHCE can be matched with various cathodes such as LFP, NCM811, and S cathodes, and the Li||LFP full cell using DFEB-LHCE possesses 85% capacity retention after 650 stable cycles with 99.9% CE. Especially the 1.5 Ah practical lithium metal pouch cell achieves an excellent capacity retention of 89% after 250 cycles with a superb average CE of 99.93%. This work unravels the superiority of the Li2O-dominated SEI and the feasibility of tailoring SEI components through modulation of solvation structures.