Stable Anode-Free All-Solid-State Lithium Battery through Tuned Metal Wetting on the Copper Current Collector

In Situ Grown Li2Te Enhanced Lithium Metal Anode Interfacial Kinetics

Lithium metal anode (LMA) is expected to be the ideal anode material for future high-energy-density batteries, but regulating the complex electrolyte-anode interface remains a challenge. In this work, a stable Li2Te coating is formed on the surface of commercial copper mesh (LTCM) using a simple and quick method to improve lithium metal anode interfacial kinetics. Li2Te possesses a strong affinity for both Li+ and TFSI- anions, which reduces the lithium nucleation barrier and guides the formation of inorganic-rich SEI, accelerates the diffusion of Li+, and promotes the growth of lithium metal along the plane. The highly conductive Li2Te and Cu generated by in situ lithiation reaction together constitute an effective electron-conducting network, which synergistically enhances the interfacial kinetics and the cycling stability of LMA. As a result, the LTCM maintains high Coulombic efficiency (98%) even after 2200 cycles at 1 mA cm-2, whereas the symmetric cell has a long cycle life of over 5400 h at 1 mA cm-2. In addition, the full cells with LFP display a high capacity retention ratio (80%) after 480 cycles at 1 C and the corresponding pouch cell can cycle steadily more than 464 cycles at 1 C, which has good application prospects.

Anode-free post-Li metal batteries

Anode-free metal batteries (AFMBs) are a new architecture of battery technology that relies solely on current collectors (CCs) at the anode side, eliminating the need for traditional metal anodes. This approach can pave the way for higher energy densities, lower manufacturing costs, and lower environmental footprints associated with metal batteries. This comprehensive review provides an in-depth exploration of AFMB technology, extending its scope beyond lithium and into a broader range of metals (sodium Na, potassium K, magnesium Mg, zinc Zn and aluminum Al). The concept of "metal-philicity" is discussed, which plays a pivotal role in understanding and controlling metal plating behavior within AFMBs, and also computational studies that employ first-principles calculations. This novel notion offers valuable insights into the interactions between metals and CC surfaces, which are essential for designing efficient battery systems. Moreover, the review explores various materials and experimental methods to enhance metal plating efficiency while mitigating issues such as dendrite formation through the realm of surface modifications and coatings on CCs. By providing a deeper understanding of strategies for optimizing anode-free post-Li metal battery technologies, this review aims to contribute to developing more efficient, sustainable, and cost-effective energy storage for the near future.

Win-Win Strategies Enable Efficient Anode-Less Zinc-Ion Hybrid Supercapacitors

Boosting the energy and power densities of electrochemical energy storage (EES) devices to broaden their practicality is of great significance and emergently desirable. Recently, the EES cells with an anode-free concept have been announced to realize those targets. Herein, 20 μm of a zincophilic layer prepared by blending ZIF-8 and sodium alginate (SA) is uniformly coated on Cu foil (Z8-SA@Cu) as an alternative anode for anode-less zinc-ion hybrid supercapacitors (ALZHSCs). Contributing by the distinctive features evidenced by electrochemical measurements and post-mortem analyses: (1) less nucleation barrier and overpotential, (2) limited zincate formation, (3) improved Zn2+ flux and (4) efficient Zn plating/stripping, the as-prepared Z8-SA@Cu is rationally considered to be a promising anode for ALZHSCs. Encouragingly, the assembled ALZHSC device not only delivers an impressive rate capability (40 mAh/g at 1 mA/cm2 and 34 mAh/g at 10 mA/cm2) but also achieves the excellent cycling stability (capacity retention: 88 % after 12,000 cycles at 5 mA). Most importantly, the ALZHSC device also reveals significant increases in gravimetric energy density and high-power ability as compared to the traditional ZHSCs.

Interdependence of Support Wettability - Electrodeposition Rate- Sodium Metal Anode and SEI Microstructure

This study examines how current collector support chemistry (sodiophilic intermetallic Na2Te vs. sodiophobic baseline Cu) and electrodeposition rate affect microstructure of sodium metal and its solid electrolyte interphase (SEI). Capacity and current (6 mAh cm-2, 0.5-3 mA cm-2) representative of commercially relevant mass loading in anode-free sodium metal battery (AF-SMBs) are analyzed. Synchrotron X-ray nanotomography and grazing-incidence wide-angle X-ray scattering (GIWAXS) are combined with cryogenic ion beam (cryo-FIB) microscopy. Highlighted are major differences in film morphology, internal porosity, and crystallographic preferred orientation e.g. (110) vs. (100) and (211) with support and deposition rate. Within the SEI, sodium fluoride (NaF) is more prevalent with Te-Cu versus sodium hydride (NaH) and sodium hydroxide (NaOH) with baseline Cu. Due to competitive grain growth the preferred orientation of sodium crystallites depends on film thickness. Mesoscale modeling delineates the role of SEI (ionic conductivity, morphology) on electrodeposit growth and onset of electrochemical instability.

Thermodynamics, Adhesion, and Wetting at Li/Cu(-Oxide) Interfaces: Relevance for Anode-Free Lithium-Metal Batteries

A rechargeable battery that employs a Li metal anode requires that Li be plated in a uniform fashion during charging. In "anode-free" configurations, this plating will occur on the surface of the Cu current collector (CC) during the initial cycle and in any subsequent cycle where the capacity of the cell is fully accessed. Experimental measurements have shown that the plating of Li on Cu can be inhomogeneous, which can lower the efficiency of plating and foster the formation of Li dendrites. The present study employs a combination of first-principles calculations and sessile drop experiments to characterize the thermodynamics and adhesive (i.e., wetting) properties of interfaces involving Li and other phases present on or near the CC. Interfaces between Li and Cu, Cu2O, and Li2O are considered. The calculations predict that both Cu and Cu2O surfaces are lithiophilic. However, sessile drop measurements reveal that Li wetting occurs readily only on pristine Cu. This apparent discrepancy is explained by the occurrence of a spontaneous conversion reaction, 2 Li + Cu2O → Li2O + 2 Cu, that generates Li2O as one of its products. Calculations and sessile drop measurements show that Li does not wet (newly formed) Li2O. Hence, Li that is deposited on a Cu CC where surface oxide species are present will encounter a compositionally heterogeneous substrate comprising lithiophillic (Cu) and lithiophobic (Li2O) regions. These initial heterogeneities have the potential to influence the longer-term behavior of the anode under cycling. In sum, the present study provides insights into the early stage processes associated with Li plating in anode-free batteries and describes mechanisms that contribute to inefficiencies in their operation.

Conformal 3D Li/Li13Sn5 Scaffolds Anodes for High-Areal Energy Density Flexible Lithium Metal Batteries

Achieving a high depth of discharge (DOD) in lithium metal anodes (LMAs) is crucial for developing high areal energy density batteries suitable for wearable electronics. Yet, the persistent growth of dendrites compromises battery performance, and the significant lithium consumption during pre-lithiation obstructs their broad application. Herein, A flexible 3D Li13Sn5 scaffold is designed by allowing molten lithium to infiltrate carbon cloth adorned with SnO2 nanocrystals. This design markedly curbs the troublesome dendrite growth, thanks to the uniform electric field distribution and swift Li+ diffusion dynamics. Additionally, with a minimal SnO2 nanocrystals loading (2 wt.%), only 0.6 wt.% of lithium is consumed during pre-lithiation. Insights from in situ optical microscope observations and COMSOL simulations reveal that lithium remains securely anchored within the scaffold, a result of the rapid mass/charge transfer and uniform electric field distribution. Consequently, this electrode achieves a remarkable DOD of 87.1% at 10 mA cm-2 for 40 mAh cm-2. Notably, when coupled with a polysulfide cathode, the constructed flexible Li/Li13Sn5@CC||Li2S6/SnO2@CC pouch cell delivers a high-areal capacity of 5.04 mAh cm-2 and an impressive areal-energy density of 10.6 mWh cm-2. The findings pave the way toward the development of high-performance LMAs, ideal for long-lasting wearable electronics.

Li Dynamics in Mixed Ionic-Electronic Conducting Interlayer of All-Solid-State Li-metal Batteries

Lithium-metal (Li0) anodes potentially enable all-solid-state batteries with high energy density. However, it shows incompatibility with sulfide solid-state electrolytes (SEs). One strategy is introducing an interlayer, generally made of a mixed ionic-electronic conductor (MIEC). Yet, how Li behaves within MIEC remains unknown. Herein, we investigated the Li dynamics in a graphite interlayer, a typical MIEC, by using operando neutron imaging and Raman spectroscopy. This study revealed that intercalation-extrusion-dominated mechanochemical reactions during cell assembly transform the graphite into a Li-graphite interlayer consisting of SE, Li0, and graphite-intercalation compounds. During charging, Li+ preferentially deposited at the Li-graphite|SE interface. Upon further plating, Li0-dendrites formed, inducing short circuits and the reverse migration of Li0. Modeling indicates the interface has the lowest nucleation barrier, governing lithium transport paths. Our study elucidates intricate mechano-chemo-electrochemical processes in mixed conducting interlayers. The behavior of Li+ and Li0 in the interlayer is governed by multiple competing factors.

Self-assembled hydrated copper coordination compounds as ionic conductors for room temperature solid-state batteries

As the core component of solid-state batteries, neither current inorganic solid-state electrolytes nor solid polymer electrolytes can simultaneously possess satisfactory ionic conductivity, electrode compatibility and processability. By incorporating efficient Li+ diffusion channels found in inorganic solid-state electrolytes and polar functional groups present in solid polymer electrolytes, it is conceivable to design inorganic-organic hybrid solid-state electrolytes to achieve true fusion and synergy in performance. Herein, we demonstrate that traditional metal coordination compounds can serve as exceptional Li+ ion conductors at room temperature through rational structural design. Specifically, we synthesize copper maleate hydrate nanoflakes via bottom-up self-assembly featuring highly-ordered 1D channels that are interconnected by Cu2+/Cu+ nodes and maleic acid ligands, alongside rich COO- groups and structural water within the channels. Benefiting from the combination of ion-hopping and coupling-dissociation mechanisms, Li+ ions can preferably transport through these channels rapidly. Thus, the Li+-implanted copper maleate hydrate solid-state electrolytes shows remarkable ionic conductivity (1.17 × 10-4 S cm-1 at room temperature), high Li+ transference number (0.77), and a 4.7 V-wide operating window. More impressively, Li+-implanted copper maleate hydrate solid-state electrolytes are demonstrated to have exceptional compatibility with both cathode and Li anode, enabling long-term stability of more than 800 cycles. This work brings new insight on exploring superior room-temperature ionic conductors based on metal coordination compounds.

A Tailored Interface Design for Anode-Free Solid-State Batteries

Anode-free solid-state batteries (AFSSBs) are considered to be one of the most promising high-safety and high-energy storage systems. However, low Coulombic efficiency stemming from severe deterioration on solid electrolyte/current collector (Cu foil) interface and undesirable Li dendrite growth impede their practical application, especially when rigid garnet electrolyte is used. Here, an interfacial engineering strategy between garnet electrolyte and Cu foil is introduced for stable and highly efficient AFSSBs. By utilizing the high Li ion conductivity of LiC6 layer, interfacial self-adaption ability arising from ductile lithiated polyacrylic acid polymer layer and regulated Li deposition via Li-Ag alloying reaction, the garnet-based AFSSB delivers a stable long-term operation. Additionally, when combined with a commercial LiCoO2 cathode (3.1 mAh cm-2 ), the cell also exhibits an outstanding capacity retention due to the tailored interface design. The strategies for novel AFSSBs architecture thus offer an alternative route to design next-generation batteries with high safety and high density.

Functionalizing Separator by Coating a Lithiophilic Metal for Dendrite-Free Anode-free Lithium Metal Batteries

A stable anode-free lithium metal battery (AFLMB) is accomplished by the adoption of a facile fabricated amorphous antimony (Sb)-coated separator (SbSC). The large specific surface area of the separator elevates lithium (Li)-Sb alloy kinetic, improving Li wetting ability on pristine copper current collector (Cu). When tested with LiNi0.8 Mn0.1 Co0.1 O2 (NMC811) as cathode, the full cell with SbSC demonstrates low nucleation overpotential with compact, dendrite-free and homogeneous Li plating, and exhibits a notable lithium inventory retention rate (LIRR) of 99.8 % with capacity retention of 93.6 % after 60 cycles at 0.5 C-rate. Conversely, full cells containing pristine separator/Cu (i. e., SC) and pristine separator/Sb-coated current collector (i. e., SSbC) display poor cycling performances with low LIRRs. Density functional theory corroborates the nucleation behaviours observed during in-situ half-cell Li deposition. Functionalizing polymeric separator by metallic coating in AFLMB is a novel approach in improving the cycle life of an AFLMB by promoting homogeneous Li plating behavior. This innovative approach exemplifies a promising applicability for uniform Li-plating behavior to achieve a longer cycle life in AFLMB.

Design Strategies for Aqueous Zinc Metal Batteries with High Zinc Utilization: From Metal Anodes to Anode-Free Structures

Aqueous zinc metal batteries (AZMBs) are promising candidates for next-generation energy storage due to the excellent safety, environmental friendliness, natural abundance, high theoretical specific capacity, and low redox potential of zinc (Zn) metal. However, several issues such as dendrite formation, hydrogen evolution, corrosion, and passivation of Zn metal anodes cause irreversible loss of the active materials. To solve these issues, researchers often use large amounts of excess Zn to ensure a continuous supply of active materials for Zn anodes. This leads to the ultralow utilization of Zn anodes and squanders the high energy density of AZMBs. Herein, the design strategies for AZMBs with high Zn utilization are discussed in depth, from utilizing thinner Zn foils to constructing anode-free structures with theoretical Zn utilization of 100%, which provides comprehensive guidelines for further research. Representative methods for calculating the depth of discharge of Zn anodes with different structures are first summarized. The reasonable modification strategies of Zn foil anodes, current collectors with pre-deposited Zn, and anode-free aqueous Zn metal batteries (AF-AZMBs) to improve Zn utilization are then detailed. In particular, the working mechanism of AF-AZMBs is systematically introduced. Finally, the challenges and perspectives for constructing high-utilization Zn anodes are presented.

Insight into Dendrites Issue in All Solid-State Batteries with Inorganic Electrolyte: Mechanism, Detection and Suppression Strategies

All solid-state batteries (ASSBs) are regarded as one of the promising next-generation energy storage devices due to their expected high energy density and capacity. However, failures due to unrestricted growth of lithium dendrites (LDs) have been a critical problem. Moreover, the understanding of dendrite growth inside solid-state electrolytes is limited. Since the dendrite process is a multi-physical field coupled process, including electrical, chemical, and mechanical factors, no definitive conclusion can summarize the root cause of LDs growth in ASSBs till now. Herein, the existing works on mechanism, identification, and solution strategies of LD in ASSBs with inorganic electrolyte are reviewed in detail. The primary triggers are thought to originate mainly at the interface and within the electrolyte, involving mechanical imperfections, inhomogeneous ion transport, inhomogeneous electronic structure, and poor interfacial contact. Finally, some of the representative works and present an outlook are comprehensively summarized, providing a basis and guidance for further research to realize efficient ASSBs for practical applications.