Li-Rich Li2 [Ni0.8 Co0.1 Mn0.1 ]O2 for Anode-Free Lithium Metal Batteries

An Ultralight Composite Current Collector Enabling High-Energy-Density and High-Rate Anode-Free Lithium Metal Battery

Anode-free lithium (Li) metal batteries are promising alternatives to current Li-ion batteries due to their advantages such as high energy density, low cost, and convenient production. However, the copper (Cu) current collector accounts for more than 25 wt% of the total weight of the anode-free battery without capacity contribution, which severely reduces the energy and power densities. Here, a new family of ultralight composite current collectors with a low areal density of 0.78 mg cm-2, representing significant weight reduction of 49%-91% compared with the Cu-based current collectors for high-energy Li batteries, is presented. Rational molecular engineering of the polyacylsemicarbazide substrate enables enhanced interfacial interaction with the sputtered Cu layer, which results in excellent interfacial stability, flexibility, and safety for the obtained anode-free batteries. The battery-level energy density has been significantly improved by 36%-61%, and a maximum rate capability reaches 5 C (10 mA cm-2) attributed to the homogeneous Li+ flux and smooth Li deposition on the nanostructured Cu layer. The results not only open a new avenue to improve the energy and power densities of anode-free batteries via composite current collector innovation but, in a broader context, provide a new paradigm to pursue high-performance, high-safety, and flexible batteries.

Designer Lithium Reservoirs for Ultralong Life Lithium Batteries for Grid Storage

The minimization of irreversible active lithium loss stands as a pivotal concern in rechargeable lithium batteries, particularly in the context of grid-storage applications, where achieving the utmost energy density over prolonged cycling is imperative to meet stringent demands, notably in terms of life cost. Departing from conventional methodologies advocating electrode prelithiation and/or electrolyte additives, a new paradigm is proposed here: the integration of a designer lithium reservoir (DLR) featuring lithium orthosilicate (Li4SiO4) and elemental sulfur. This approach concurrently addresses active lithium consumption through solid electrolyte interphase (SEI) formation and mitigates minor yet continuous parasitic reactions at the electrode/electrolyte interface during extended cycling. The remarkable synergy between the Li-ion conductive Li4SiO4 and the SEI-favorable elemental sulfur enables customizable compensation kinetics for active lithium loss throughout continuous cycling. The introduction of a minute quantity of DLR (3 wt% Li4SiO4@S) yields outstanding cycling stability in a prototype pouch cell (graphite||LiFePO4) with an ampere-hour-level capacity (≈2.3 Ah), demonstrating remarkable capacity retention (≈95%) even after 3000 cycles. This utilization of a DLR is poised to expedite the development of enduring lithium batteries for grid-storage applications and stimulate the design of practical, implantable rechargeable batteries based on related cell chemistries.

Programmable DNA Interphase Layers for High-Performance Anode-Free Lithium Metal Batteries

Anode-free lithium (Li) metal batteries are promising candidates for advanced energy storage, attributed to their appealing characteristics such as high energy density, low cost, and convenient production. However, their major challenges lie in the poor cycling and rate performance owing to the inferior reversibility and kinetics of Li plating and stripping, which significantly hinder their real-world applications. Here, it is demonstrated that deoxyribonucleic acid (DNA), the most important genetic material in nature, can serve as a highly programmable interphase layer for innovation of anode-free Li metal batteries. It is found that the abundant base pairs in DNA can contribute transient Li-N bonds that facilitate homogeneous Li+ flux, thus resulting in excellent Li plating/stripping kinetics and reversibility even at a harsh areal current of 15 mA cm-2. The anode-free LiFePO4 full batteries based on an ultrathin (0.12 µm) and ultralight (≈0.01 mg cm-2) DNA interphase layer show high CEs (≈99.1%) over 400 cycles, corresponding to an increase of ≈186% compared with bare copper (Cu) foil. These results shed light on the excellent programmability of DNA as a new family of interphase materials for anode-free batteries, and provide a new paradigm for future battery innovation toward high programmability, high sustainability, and remarkable electrochemical performance.

Self-Limiting Phase Transition Enabling Reversible Overstoichiometric Li Storage in Ni-Rich Cathodes

Ni-rich cathodes are some of the most promising candidates for advanced lithium-ion batteries, but their available capacities have been stagnant due to the intrinsic Li+ storage sites. Extending the voltage window down can induce the phase transition from O3 to 1T of LiNiO2-derived cathodes to accommodate excess Li+ and dramatically increase the capacity. By setting the discharge cutoff voltage of LiNi0.6Co0.2Mn0.2O2 to 1.4 V, we can reach an extremely high capacity of 393 mAh g-1 and an energy density of 1070 Wh kg-1 here. However, the phase transition causes fast capacity decay and related structural evolution is rarely understood, hindering the utilization of this feature. We find that the overlithiated phase transition is self-limiting, which will transform into solid-solution reaction with cycling and make the cathode degradation slow down. This is attributed to the migration of abundant transition metal ions into lithium layers induced by the overlithiation, allowing the intercalation of overstoichiometric Li+ into the crystal without the O3 framework change. Based on this, the wide-potential cycling stability is further improved via a facile charge-discharge protocol. This work provides deep insight into the overstoichiometric Li+ storage behaviors in conventional layered cathodes and opens a new avenue toward high-energy batteries.

Design of High-Entropy Tape Electrolytes for Compression-Free Solid-State Batteries

Advanced solid electrolytes with strong adhesion to other components are the key for the successes of solid-state batteries. Unfortunately, traditional solid electrolytes have to work under high compression to maintain the contact inside owing to their poor adhesion. Here, a concept of high-entropy tape electrolyte (HETE) is proposed to simultaneously achieve tape-like adhesion, liquid-like ion conduction, and separator-like mechanical properties. This HETE is designed with adhesive skin layer on both sides and robust skeleton layer in the middle. The significant properties of the three layers are enabled by high-entropy microstructures which are realized by harnessing polymer-ion interactions. As a result, the HETE shows high ionic conductivity (3.50 ± 0.53 × 10-4 S cm-1 at room temperature), good mechanical properties (toughness 11.28 ± 1.12 MJ m-3, strength 8.18 ± 0.28 MPa), and importantly, tape-like adhesion (interfacial toughness 231.6 ± 9.6 J m-2). Moreover, a compression-free solid-state tape battery is finally demonstrated by adhesion-based assembling, which shows good interfacial and electrochemical stability even under harsh mechanical conditions, such as twisting and bending. The concept of HETE and compression-free solid-state tape batteries may bring promising solutions and inspiration to conquer the interface challenges in solid-state batteries and their manufacturing.

Toward maximum energy density enabled by anode-free lithium metal batteries: Recent progress and perspective

Owing to the emergenceof energy storage and electric vehicles, the desire for safe high-energy-density energy storage devices has increased research interest in anode-free lithium metal batteries (AFLMBs). Unlike general lithium metal batteries (LMBs), in which excess Li exists to compensate for the irreversible loss of Li, only the current collector is employed as an anode and paired with a lithiated cathode in the fabrication of AFLMBs. Owing to their unique cell configuration, AFLMBs have attractive characteristics, including the highest energy density, safety, and cost-effectiveness. However, developing AFLMBs with extended cyclability remains an issue for practical applications because the high reactivity of Li with limited inventory causes severely low Coulombic efficiency (CE), poor cyclability, and dendrite growth. To address these issues, tremendous effort has been devoted to stabilizing Li metal anodes for AFLMBs. In this review, the importance and challenges of AFLMBs are highlighted. Then, diverse strategies, such as current collectors modification, advanced electrolytes, cathode engineering, and operation protocols are thoroughly reviewed. Finally, a future perspective on the strategy is provided for insight into the basis of future research. It is hoped that this review provides a comprehensive understanding by reviewing previous research and arousing more interest in this field.

Unveiling the Role of Fluorination in Hexacyclic Coordinated Ether Electrolytes for High-Voltage Lithium Metal Batteries

Fluorinated ethers have become promising electrolyte solvent candidates for lithium metal batteries (LMBs) because they are endowed with high oxidative stability and high Coulombic efficiencies of lithium metal stripping/plating. Up to now, most reported fluorinated ether electrolytes are -CF3-based, and the influence of ion solvation in modifying degree of fluorination has not been well-elucidated. In this work, we synthesize a hexacyclic coordinated ether (1-methoxy-3-ethoxypropane, EMP) and its fluorinated ether counterparts with -CH2F (F1EMP), -CHF2 (F2EMP), or -CF3 (F3EMP) as terminal group. With lithium bis(fluorosulfonyl)imide as single salt, the solvation structure, Li-ion transport behavior, lithium deposition kinetics, and high-voltage stability of the electrolytes were systematically studied. Theoretical calculations and spectra reveal the gradually reduced solvating power from nonfluorinated EMP to fully fluorinated F3EMP, which leads to decreased ionic conductivity. In contrast, the weakly solvating fluorinated ethers possess higher Li+ transference number and exchange current density. Overall, partially fluorinated -CHF2 is demonstrated as the desired group. Further full cell testing using high-voltage (4.4 V) and high-loading (3.885 mAh cm-2) LiNi0.8Co0.1Mn0.1O2 cathode demonstrates that F2EMP electrolyte enables 80% capacity retention after 168 cycles under limited Li (50 μm) and lean electrolyte (5 mL Ah-1) conditions and 129 cycles under extremely lean electrolyte (1.8 mL Ah-1) and the anode-free conditions. This work deepens the fundamental understanding on the ion transport and interphase dynamics under various degrees of fluorination and provides a feasible approach toward the design of fluorinated ether electrolytes for practical high-voltage LMBs.

Progress and Perspectives on the Development of Pouch-Type Lithium Metal Batteries

Lithium (Li) metal batteries (LMBs) are the "holy grail" in the energy storage field due to their high energy density (theoretically >500 Wh kg-1 ). Recently, tremendous efforts have been made to promote the research & development (R&D) of pouch-type LMBs toward practical application. This article aims to provide a comprehensive and in-depth review of recent progress on pouch-type LMBs from full cell aspect, and to offer insights to guide its future development. It will review pouch-type LMBs using both liquid and solid-state electrolytes, and cover topics related to both Li and cathode (including LiNix Coy Mn1-x-y O2 , S and O2 ) as both electrodes impact the battery performance. The key performance criteria of pouch-type LMBs and their relationship in between are introduced first, then the major challenges facing the development of pouch-type LMBs are discussed in detail, especially those severely aggravated in pouch cells compared with coin cells. Subsequently, the recent progress on mechanistic understandings of the degradation of pouch-type LMBs is summarized, followed with the practical strategies that have been utilized to address these issues and to improve the key performance criteria of pouch-type LMBs. In the end, it provides perspectives on advancing the R&Ds of pouch-type LMBs towards their application in practice.

Long-Life Quasi-Solid-State Anode-Free Batteries Enabled by Li Compensation Coupled Interface Engineering

Initially, anode-free Li metal batteries present a promising power source that merges the high production feasibility of Li-ion batteries with the superb energy capabilities of Li-metal batteries. However, their application confronts formidable challenges of extremely short lifespan due to the inadequacy of zero-Li-excess cell configuration against irreversible Li loss. A Li compensation coupled interface engineering strategy is reported for realizing long-life quasi-solid-state anode-free batteries. The Li2 S is utilized as a sacrificial Li supplement to effectively counterbalance irreversible Li loss without damage to cell chemistry. Meanwhile, it demonstrates remarkable efficacy in establishing a robust yet slender inorganic-organic hybrid solid-state interphase for inhibiting cell degradation by dead and dendritic Li. This strategy enables quasi-solid-state anode-free batteries with a long lifespan of 500 cycles. The Ah-scale quasi-solid-state pouch cells, featuring a high-loading LiFePO4 cathode and lean gel polymer electrolyte, exhibit a high specific energy of 300 Wh kgcell -1 . This achievement translates into an improvement of 46% in gravimetric energy and 94% in volumetric energy compared to LiFePO4 ||graphite batteries while outperforming LiFePO4 ||Li-metal batteries by 22-47% in volumetric energy. Such quasi-solid-state anode-free cells also demonstrate good safety, showcasing remarkable resistance against nail penetration in ambient air without failure, smoke, or fire accidents.

Scalable fabrication of ultra-fine lithiophilic nanoparticles encapsulated in soft buffered hosts for long-life anode-free Li2S-based cells

Minimizing the amount of metallic lithium (Li) to zero excess to achieve an anode-free configuration can help achieve safer, higher energy density, and more economical Li metal batteries. Nevertheless, removal of excess Li creates challenges for long-term cycling performance in Li metal batteries due to the lithiophobic copper foils as anodic current collectors. Here, we improve the long-term cycling performance of anode-free Li metal batteries by modifying the anode-free configuration. Specifically, a lithiophilic Au nanoparticle-anchored reduced graphene oxide (Au/rGO) film is used as an anodic modifier to reduce the Li nucleation overpotential and inhibit dendrite growth by forming a lithiophilic LixAu alloy and solid solution, which is convincingly evidenced by density functional theory calculations and experimentally. Meanwhile, the flexible rGO film can also act as a buffer layer to endure the volume expansion during repeated Li plating/stripping processes. In addition, the Au/rGO film promotes a homogeneous distribution of the electric field over the entire anodic surface, thus ensuring a uniform deposition of Li during the electrodeposition process, which is convincingly evidenced by finite element simulations. As expected, the Li||Au/rGO-Li half-cell shows a highly stable long-term cycling performance for at least 500 cycles at 0.5 mA cm-2 and 0.5 mA h cm-2. A Li2S-based anode-free full cell allows achieving a stable operation life of up to 200 cycles with a capacity retention of 63.3%. This work provides a simple and scalable fabrication method to achieve anode-free Li2S-based cells with high anodic interface stability and a long lifetime.

Effect of the N,S-Codoped Carbon Layer on the Rate Performance of Air-Stable Lithium Iron Oxide Prelithiation Additives

Lithium iron oxide (Li5FeO4, LFO) holds great promise in cathode prelithiation additives for lithium-ion batteries. However, it is hard to make full use of the power under high current rates due to its poor air stability and electronic conductivity. The carbon protective layer is an effective approach, and introducing heteroatoms would be beneficial to further improving Li+ kinetics. However, the interplay between the dopants and Li+ is always ignored. Herein, we aim to reveal the interaction among Li+ ions and the defects of carbon layers from nitrogen/sulfur dopants and the corresponding influence on delithiation performances of LFO. It is found that the codoping of nitrogen and sulfur on carbon layers contributes to the boosted capacity and rate capability. The modified SNC@LFO presents a large irreversible capacity (779.3 mAh g-1 at 0.1 C) and excellent rate performance (537.1 mAh g-1 at 1 C), which is up to 16.6 and 64.0%, respectively, compared to LFO.

Hexacyclic Chelated Lithium Stable Solvates for Highly Reversible Cycling of High-Voltage Lithium Metal Battery

Ether-based electrolytes that are endowed with decent compatibility towards lithium anode have been regarded as promising candidates for constructing energy-dense lithium metal batteries (LMBs), but their applications are hindered by low oxidation stability in conventional salt concentration. Here, we reported that regulating the chelating power and coordination structure can remarkably increase the high-voltage stability of ether-based electrolytes and lifespan of LMBs. Two ether molecules of 1,3-dimethoxypropane (DMP) and 1,3-diethoxypropane (DEP) are designed and synthesized as solvents of electrolytes to replace the traditional ether solvent (1,2-dimethoxyethane, DME). Both computational and spectra reveal that the transition from five- to six-membered chelate solvation structure by adding one methylene on DME results in the formation of weak Li solvates, which increase the reversibility and high-voltage stability in LMBs. Even under lean electrolyte (5 mL Ah-1 ) and low anode to cathode ratio (2.6), the fabricated high-voltage Li||LiNi0.8 Co0.1 Mn0.1 O2 LMBs using electrolyte of 2.30 M Lithiumbisfluorosulfonimide (LiFSI)/DMP still show capacity retention over 90 % after 184 cycles. This work highlights the importance of designing the coordination structures in non-fluorine ether electrolytes for rechargeable batteries.

A Molecularly Engineered Cathode Lithium Compensation Agent for High Energy Density Batteries

Prelithiating cathode is considered as one of the most promising lithium compensation strategies for practical high energy density batteries. Whereas most of reported cathode lithium compensation agents are deficient owing to their poor air-stability, residual insulating solid, or formidable Li-extracting barrier. Here, this work proposes molecularly engineered 4-Fluoro-1,2-dihydroxybenzene Li salt (LiDF) with high specific capacity (382.7 mAh g^-1 ) and appropriate delithiation potential (3.6-4.2 V) as an air-stable cathode Li compensation agent. More importantly, the charged residue 4-Fluoro-1,2-benzoquinone (BQF) can synergistically work as an electrode/electrolyte interface forming additive to build uniform and robust LiF-riched cathode/anode electrolyte interfaces (CEI/SEI). Consequently, less Li loss and retrained electrolyte decomposition are achieved. With 2 wt% 4-Fluoro-1,2-dihydroxybenzene Li salt initially blended within the cathode, 1.3 Ah pouch cells with NCM (Ni92) cathode and SiO/C (550 mAh g^-1 ) anode can keep 91% capacity retention after 350 cycles at 1 C rate. Moreover, the anode free of NCM622+LiDF||Cu cell achieves 78% capacity retention after 100 cycles with the addition of 15 wt% LiDF. This work provides a feasible sight for the rational designing Li compensation agent at molecular level to realize high energy density batteries.

Li2Se as a Cathode Prelithiation Additive for Lithium-Ion Batteries

In conventional lithium-ion batteries (LIBs), active lithium (Li) ions, which function as charge carriers and could only be supplied by the Li-containing cathodes, are also consumed during the formation of the solid electrolyte interphase. Such irreversible Li loss reduces the energy density of LIBs and is highly desired to be compensated by prelithiation additives. Herein, lithium selenide (Li₂Se), which could be irreversibly converted into selenide (Se) at 2.5-3.8 V and thus supplies additional Li, is proposed as a cathode prelithiation additive for LIBs. Compared with previously reported prelithiation reagents (e.g., Li₆CoO₄, Li₂O, and Li₂S), the delithiation of Li₂Se not only delivers a high specific capacity but also avoids gas release and incompatibility with carbonate electrolytes. The electrochemical characterizations show that with the addition of 6 wt % Li₂Se to the LiFePO₄ (LFP) cathodes, a 9% increase in the initial specific capacity in half Li||LFP cells and a 19.8% increase in the energy density (based on the total mass of the two electrodes' materials) could be achieved without sacrificing the other battery performance. This work demonstrates the possibility to use Li₂Se as a high-efficiency prelithiation additive for LIBs and provides a solution to the high-energy LIBs.

Prolonged lifespan of initial-anode-free lithium-metal battery by pre-lithiation in Li-rich Li2Ni0.5Mn1.5O4 spinel cathode

Anode-free lithium metal batteries (AF-LMBs) can deliver the maximum energy density. However, achieving AF-LMBs with a long lifespan remains challenging because of the poor reversibility of Li⁺ plating/stripping on the anode. Here, coupled with a fluorine-containing electrolyte, we introduce a cathode pre-lithiation strategy to extend the lifespan of AF-LMBs. The AF-LMB is constructed with Li-rich Li₂Ni_0.5Mn_1.5O₄ cathodes as a Li-ion extender; the Li₂Ni_0.5Mn_1.5O₄ can deliver a large amount of Li⁺ in the initial charging process to offset the continuous Li⁺ consumption, which benefits the cycling performance without sacrificing energy density. Moreover, the cathode pre-lithiation design has been practically and precisely regulated using engineering methods (Li-metal contact and pre-lithiation Li-biphenyl immersion). Benefiting from the highly reversible Li metal on the Cu anode and Li₂Ni_0.5Mn_1.5O₄ cathode, the further fabricated anode-free pouch cells achieve 350 W h kg^-1 energy density and 97% capacity retention after 50 cycles.

In Situ Electrochemically Oxidative Activation Inducing Ultrahigh Rate Capability of Vanadium Oxynitride/Carbon Cathode for Zinc-Ion Batteries

As a promising candidate for large-scale energy storage, aqueous zinc-ion batteries (ZIBs) still lack cathode materials with large capacity and high rate capability. Herein, a spherical carbon-confined nanovanadium oxynitride with a polycrystalline feature (VN_xO_y/C) was synthesized by the solvothermal reaction and following nitridation treatment. As a cathode material for ZIBs, it is interesting that the electrochemical performance of the VN_xO_y/C cathode is greatly improved after the first charging process viain situ electrochemically oxidative activation. The oxidized VN_xO_y/C delivers a greatly enhanced reversible capacity of 556 mAh g^-1 at 0.2 A g^-1 compared to the first discharge capacity of 130 mAh g^-1 and a high capacity of 168 mAh g^-1 even at 80 A g^-1. The ex situ characterizations verify that the insertion/extraction of Zn²⁺ does not affect the crystal structure of oxidized VN_xO_y/C to promise a stable cycle life (retain 420 mAh g^-1 after 1000 cycles at 10 A g^-1). The experimental analysis further elucidates that charging voltage and H₂O in the electrolyte are curial factors to activate VN_xO_y/C in that the oxygen replaces the partial nitrogen and creates abundant vacancies, inducing a conversion from VN_xO_y/C to VN_x-mO_y+2m/C and then resulting in considerably strengthened rate performance and improved Zn²⁺ storage capability. The study broadens the horizons of fast ion transport and is exceptionally desirable to expedite the application of high-rate ZIBs.

Facile One-Step Heat Treatment of Cu Foil for Stable Anode-Free Li Metal Batteries

The anode-free lithium metal battery (AFLMB) is attractive for its ultimate high energy density. However, the poor cycling lifespan caused by the unstable anode interphase and the continuous Li consumption severely limits its practical application. Here, facile one-step heat treatment of the Cu foil current collectors before the cell assembly is proposed to improve the anode interphase during the cycling. After heat treatment of the Cu foil, homogeneous Li deposition is achieved during cycling because of the smoother surface morphology and enhanced lithiophilicity of the heat-treated Cu foil. In addition, Li₂O-riched SEI is obtained after the Li deposition due to the generated Cu₂O on the heat-treated Cu foil. The stable anode SEI can be successfully established and the Li consumption can be slowed down. Therefore, the cycling stability of the heat-treated Cu foil electrode is greatly improved in the Li|Cu half-cell and the symmetric cell. Moreover, the corresponding LFP|Cu anode-free full cell shows a much-improved capacity retention of 62% after 100 cycles, compared to that of 43% in the cell with the commercial Cu foil. This kind of facile but effective modification of current collectors can be directly applied in the anode-free batteries, which are assembled without Li pre-deposition on the anode.

Locally Fluorinated Electrolyte Medium Layer for High-Performance Anode-Free Li-Metal Batteries

Low cycling Coulombic efficiency (CE) and messy Li dendrite growth problems have greatly hindered the development of anode-free Li-metal batteries (AFLBs). Thus, functional electrolytes for uniform lithium deposition and lithium/electrolyte side reaction suppression are desired. Here, we report a locally fluorinated electrolyte (LFE) medium layer surrounding Cu foils to tailor the chemical compositions of the solid-electrolyte interphase (SEI) in AFLBs for inhibiting the immoderate Li dendrite growth and to suppress the interfacial reaction. This LFE consists of highly concentrated LiTFSI dissolved in a fluoroethylene carbonate and/or succinonitrile plastic mixture. The CE of Cu||LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) AFLB increased to a high level of 99% as envisaged, and the cycling ability was also highly improved. These improvements are facilitated by the formation of a uniform, dense, and LiF-rich SEI. LiF possesses high interfacial energy at the LiF/Li interface, resulting in a more uniform Li deposition process as proved by density functional theory (DFT) calculation results. This work provides a simple yet utility tech for the enhancement of future high-energy-density AFLBs.

An Electric-Field-Reinforced Hydrophobic Cationic Sieve Lowers the Concentration Threshold of Water-In-Salt Electrolytes

High-concentration water-in-salt (WIS) electrolytes expand the stable electrochemical window of aqueous electrolytes, leading to the advent of high-voltage (above 2 V) aqueous Li-ion batteries (ALIBs). However, the high lithium salt concentration electrolytes of ALIBs result in their high cost and deteriorate kinetic performance. Therefore, it is challenging for ALIBs to explore aqueous electrolytes with appropriate concentration to balance the electrochemical window and kinetic performance as well as the cost. In contrast to maintaining high concentrations of aqueous electrolytes (>20 m), a small number of hydrophobic cations are introduced to a much lower electrolyte concentration (13.8 m), and it is found that, compared with WIS electrolytes, ALIBs with these concentration-lowered electrolytes possess a compatible stable electrochemical window (3.23 V) and achieve better kinetic performance. These findings originate from the added cations, which form an electric-field-reinforced hydrophobic cationic sieve (HCS) that blocks water away from the anode and suppresses the hydrogen evolution reaction. Meanwhile, the lower electrolyte concentration provides significant benefits to ALIBs, including lower cost, better rate capability (lower viscosity of 18 cP and higher ionic conductivity of 22 mS cm^-1 at 25 °C), and improved low-temperature performance (liquidus temperature of -10.18 °C).

CNT/PVDF Composite Coating Layer on Cu with a Synergy of Uniform Current Distribution and Stress Releasing for Improving Reversible Li Plating/Stripping

The uncontrollable formation of polymorphous Li deposits, e.g., whiskers, mosses, or dendrites resulting from nonuniform interfacial current distribution and internal stress release in the upward direction on the conventional current collector (e.g., Cu foil) of Li metal rechargeable batteries with a lithium-metal-free negatrode (LMFRBs), leads to rapid performance degradation or serious safety problems. The 3D carbon nanotubes (CNTs) skeleton has been proven to effectively reduce the current density and eliminate the internal accumulated stress. However, remarkable electrolyte decomposition, inherent Li source consumption due to repeated SEI formation, and Li⁺ intercalation in CNTs limit the application of 3D CNTs skeleton. Thus, it is necessary to avoid the side effects of the 3D CNTs skeleton and retain uniform interfacial current distribution and stress mitigation. In this work, we integrate the CNTs network with a soft functional polymer polyvinylidene fluoride (PVDF) to form a relatively dense coating layer on Cu foil, which can shield the contact between the internal surface of the 3D CNTs framework and the electrolyte. Simultaneously, the Li-F-rich SEI resulting from the partial reduction of PVDF with deposited Li and the soft nature of the coating layer release the accumulation of internal stress in the horizontal direction, resulting in mosses/whisker-free Li deposition. Thus, improved Li deposition/dissolution and stable cycling performance of the LMFRBs can be achieved.

Enhancing Li+ Transport in NMC811||Graphite Lithium-Ion Batteries at Low Temperatures by Using Low-Polarity-Solvent Electrolytes

LiNi_x Co_y Mn_z O₂ (x+y+z=1)||graphite lithium-ion battery (LIB) chemistry promises practical applications. However, its low-temperature (≤ -20 °C) performance is poor because the increased resistance encountered by Li⁺ transport in and across the bulk electrolytes and the electrolyte/electrode interphases induces capacity loss and battery failures. Though tremendous efforts have been made, there is still no effective way to reduce the charge transfer resistance (R_ct ) which dominates low-temperature LIBs performance. Herein, we propose a strategy of using low-polarity-solvent electrolytes which have weak interactions between the solvents and the Li⁺ to reduce R_ct , achieving facile Li⁺ transport at sub-zero temperatures. The exemplary electrolyte enables LiNi_0.8 Mn_0.1 Co_0.1 O₂ ||graphite cells to deliver a capacity of ≈113 mAh g^-1 (98 % full-cell capacity) at 25 °C and to remain 82 % of their room-temperature capacity at -20 °C without lithium plating at 1/3C. They also retain 84 % of their capacity at -30 °C and 78 % of their capacity at -40 °C and show stable cycling at 50 °C.

Opportunities and Challenges of Li2 C4 O4 as Pre-Lithiation Additive for the Positive Electrode in NMC622||Silicon/Graphite Lithium Ion Cells

Silicon (Si)-based negative electrodes have attracted much attention to increase the energy density of lithium ion batteries (LIBs) but suffer from severe volume changes, leading to continuous re-formation of the solid electrolyte interphase and consumption of active lithium. The pre-lithiation approach with the help of positive electrode additives has emerged as a highly appealing strategy to decrease the loss of active lithium in Si-based LIB full-cells and enable their practical implementation. Here, the use of lithium squarate (Li₂ C₄ O₄ ) as low-cost and air-stable pre-lithiation additive for a LiNi_0.6 Mn_0.2 Co_0.2 O₂ (NMC622)-based positive electrode is investigated. The effect of additive oxidation on the electrode morphology and cell electrochemical properties is systematically evaluated. An increase in cycle life of NMC622||Si/graphite full-cells is reported, which grows linearly with the initial amount of Li₂ C₄ O₄ , due to the extra Li⁺ ions provided by the additive in the first charge. Post mortem investigations of the cathode electrolyte interphase also reveal significant compositional changes and an increased occurrence of carbonates and oxidized carbon species. This study not only demonstrates the advantages of this pre-lithiation approach but also features potential limitations for its practical application arising from the emerging porosity and gas development during decomposition of the pre-lithiation additive.

Commercially Viable Hybrid Li-Ion/Metal Batteries with High Energy Density Realized by Symbiotic Anode and Prelithiated Cathode

The energy density of commercial lithium (Li) ion batteries with graphite anode is reaching the limit. It is believed that directly utilizing Li metal as anode without a host could enhance the battery's energy density to the maximum extent. However, the poor reversibility and infinite volume change of Li metal hinder the realistic implementation of Li metal in battery community. Herein, a commercially viable hybrid Li-ion/metal battery is realized by a coordinated strategy of symbiotic anode and prelithiated cathode. To be specific, a scalable template-removal method is developed to fabricate the porous graphite layer (PGL), which acts as a symbiotic host for Li ion intercalation and subsequent Li metal deposition due to the enhanced lithiophilicity and sufficient ion-conducting pathways. A continuous dissolution-deintercalation mechanism during delithiation process further ensures the elimination of dead Li. As a result, when the excess plating Li reaches 30%, the PGL could deliver an ultrahigh average Coulombic efficiency of 99.5% for 180 cycles with a capacity of 2.48 mAh cm^-2 in traditional carbonate electrolyte. Meanwhile, an air-stable recrystallized lithium oxalate with high specific capacity (514.3 mAh g^-1) and moderate operating potential (4.7-5.0 V) is introduced as a sacrificial cathode to compensate the initial loss and provide Li source for subsequent cycles. Based on the prelithiated cathode and initial Li-free symbiotic anode, under a practical-level 3 mAh capacity, the assembled hybrid Li-ion/metal full cell with a P/N ratio (capacity ratio of LiNi_0.8Co_0.1Mn_0.1O₂ to graphite) of 1.3 exhibits significantly improved capacity retention after 300 cycles, indicating its great potential for high-energy-density Li batteries.

A Better Choice to Achieve High Volumetric Energy Density: Anode-Free Lithium-Metal Batteries

Volumetric energy density is a critical but easily neglected index of lithium-metal batteries (LMBs). Compared with gravimetric energy density, the volumetric energy density (VED) of LMBs is much more sensitive to the anode/cathode (A/C) ratio due to the low density of lithium (Li) metal and the volume expansion of the Li-metal anode owing to its pulverization during cycles. Anode-free LMBs (AF-LMBs) have high theoretical VED due to the absence of an anode and high retention with relatively low cell expansion. Because Li plating highly depends on the mother substrate, Li plating on copper (Cu) substrates is more reversible and denser than that on Li substrates during cycling, which is beneficial for maintaining high volumetric capacity and efficient Li utilization. Therefore, considering that excess Li must be strictly limited to achieve competitive energy density, AF-LMBs (with bare Cu foil as the anode current collector) for high-volumetric-density batteries are recommended.

Lithium Oxalate as a Lifespan Extender for Anode-Free Lithium Metal Batteries

Anode-free lithium metal batteries (AFLMBs) have been extensively studied due to their intrinsic high energy and safety without a metallic Li anode in cell design. Yet, the dendrite and dead-Li buildup continuously consumes the active Li upon cycling, leading to the poor lifespan of AFLMBs. Here, we introduce lithium oxalate into the cathode as an electrode additive providing a Li reservoir to extend the lifespan of AFLMBs. The AFLMB using 20% lithium oxalate and a LiNi0.3Co0.3Mn0.3O2 composite cathode exhibits >80 and 40% capacity retention after 50 and 100 cycles, respectively, outperforming the poor cycle life of fewer than 20 cycles obtained from the cell using a pure LiNi0.3Co0.3Mn0.3O2 cathode. Surprisingly, the average Coulombic efficiency of AFLMBs is found to improve as the amount of lithium oxalate increases in the composite cathode. This abnormal phenomenon could be attributed to the as-formed carbon dioxide after the first activation cycle forming a Li2CO3-rich solid-electrolyte interphase and improving the Li deposition and stripping efficiency. The findings in this work provide a new strategy to delay the capacity roll-over of AFLMBs from an electrode engineering perspective, which can be coupled with other approaches such as functional electrolytes synergistically to further improve the cycle life of AFLMBs for practical application.

Co-Solvent Electrolyte Engineering for Stable Anode-Free Zinc Metal Batteries

Anode-free metal batteries can in principle offer higher energy density, but this requires them to have extraordinary Coulombic efficiency (>99.7%). Although Zn-based metal batteries are promising for stationary storage, the parasitic side reactions make anode-free batteries difficult to achieve in practice. In this work, a salting-in-effect-induced hybrid electrolyte is proposed as an effective strategy that enables both a highly reversible Zn anode and good stability and compatibility toward various cathodes. The as-prepared electrolyte can also work well under a wide temperature range (i.e., from -20 to 50 °C). It is demonstrated that in the presence of propylene carbonate, triflate anions are involved in the Zn²⁺ solvation sheath structure, even at a low salt concentration (2.14 M). The unique solvation structure results in the reduction of anions, thus forming a hydrophobic solid electrolyte interphase. The waterproof interphase along with the decreased water activity in the hybrid electrolyte effectively prevents side reactions, thus ensuring a stable Zn anode with an unprecedented Coulombic efficiency (99.93% over 500 cycles at 1 mA cm^-2). More importantly, we design an anode-free Zn metal battery that exhibits excellent cycling stability (80% capacity retention after 275 cycles at 0.5 mA cm^-2). This work provides a universal strategy to design co-solvent electrolytes for anode-free Zn metal batteries.

Highly reversible Li-ion full batteries using a Mg-doped Li-rich Li1.2Ni0.28Mn0.468Mg0.052O2 cathode and carbon-decorated Mn3O4 anode with hierarchical microsphere structures

Microsphere structured Mg-doped Li-rich Li1.2Ni0.28Mn0.468Mg0.052O2 cathode and carbon-decorated Mn3O4 anode materials were prepared for application to lithium-ion full batteries. As-assembled lithium-ion full batteries exhibited enhanced electrochemical performances like high charge/discharge capacity, and long-term capacity retention.

Electronic Effect and Regiochemistry of Substitution in Pre-sodiation Chemistry

The low oxidation potential of a pre-sodiation cathode additive intrinsically prevents decomposition of the electrolyte. Although the introduction of electron-donating substitution reduces the oxidation potential, the additional molecular weight restricts the output capacity. Herein, as theroretically predicted, the electrochemical oxidation potential of sodium carboxylate is manipulated by the electronic effect and regiochemistry of the functionality, in which the stronger electron-donating substituent, p-π conjugation, and optimized regiochemistry can dramatically lead to the lower potential originated from the elevation of the highest occupied molecular orbital level. Thus, benefiting from the para-NH₂ unit accompanied by a conjugated aromatic architecture, molecularly engineered sodium para-aminobenzoate (PABZ-Na) presents a reduced oxidation plateau of 3.45 V. Triggered by the positive compensation merit, sodium-based electrochemical storage systems manifest excellent electrochemical performances. This breakthrough sheds light into the correlation between the electronic effect of the functional group and the oxidation potential of the organic additive, affording in-depth insights into the fundamental guidance of pre-sodiation chemistry.