Lithium metal anode on a copper dendritic superstructure

Anode-Free Li Metal Batteries: Feasibility Analysis and Practical Strategy

Energy storage devices are striving to achieve high energy density, long lifespan, and enhanced safety. In view of the current popular lithiated cathode, anode-free lithium metal batteries (AFLMBs) will deliver the theoretical maximum energy density among all the battery chemistries. However, AFLMBs face challenges such as low plating-stripping efficiency, significant volume change, and severe Li-dendrite growth, which negatively impact their lifespan and safety. This study provides an overview and analysis of recent progress in electrode structure, characterization, performance, and practical challenges of AFLMBs. The deposition behavior of lithium is categorized into two stages: heterogeneous and homogeneous interface deposition. The feasibility and practical application value of AFLMBs are critically evaluated. Additionally, key test models, evaluation parameters, and advanced characterization techniques are discussed. Importantly, practical strategies of different battery components in AFLMBs, including current collector, interface layer, solid-state electrolyte, liquid-state electrolyte, cathode, and cycling protocol, are presented to address the challenges posed by the two types of deposition processes, lithium loss, crosstalk effect and volume change. Finally, the application prospects of AFLMBs are envisioned, with a focus on overcoming the current limitations and unlocking their full potential as high-performance energy storage solutions.

One-stone, two birds: One step regeneration of discarded copper foil in zinc battery for dendrite-free lithium deposition current collector

The ever-growing requirement for electrochemical energy storage has exacerbated the production of spent batteries, and the recycling of valuable battery components has recently received a remarkable attention. Among all battery components, copper foil is widely utilized as a current collector for stable zinc platting and stripping in zinc metal batteries (ZMBs) due to the perfect lattice matching of between metal copper and zinc, which is accompanied by the formation of multiple copper-zinc alloy components during the cycling process. Herein, a novel "two birds with one-stone" strategy through a one simple heat treatment step to revive the discarded copper foil in zinc metal battery is reported to further obtain a lithiophilic current collector (CuxZny-Cu) with multiple copper-zinc alloy components on the surface of the discarded copper foil. Such revived CuxZny-Cu current collector greatly reduces the lithium nucleation overpotential and realizes uniform lithium deposition and further inhibits lithium dendrites growth. The formed multiple CuxZny alloy phases on the surface of discarded copper foil exhibit a low Li nucleation overpotential of only 15 mV at 0.5 mA cm-2 for the first cycle. Moreover, such a CuxZny-Cu current collector could achieve stable cycle for 220 cycles at 0.5 mA cm-2 and 110 cycles at 1 mA cm-2 with a Li plating capacity of 1 mAh cm-2. Theoretical calculations indicate that, compared with pure Cu foil, the formed multiple alloy components of CuZn5, CuZn8, Cu0.61Zn0.39 and CuZn have low adsorption energy of -2.17, -2.55, -2.16 and -2.35 eV with lithium atoms, respectively, which result in reduced lithium nucleation overpotential. The full cell composed of CuxZny alloy current collector with deposition of 5 mAh cm-2 metal Li anode coupled with LiFePO4 (LFP) cathode exhibits a reversible capacity of 125.6 mAh/g after 110 cycles at a current of 0.5 C with capacity retention of 85.1 %. This work proposed a promising strategy to regenerate the discarded copper foil in rechargeable batteries.

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.

Ultrathin Lithiophilic 3D Arrayed Skeleton Enabling Spatial-Selection Deposition for Dendrite-Free Lithium Anodes

Lithium metal batteries are promising to become a new generation of energy storage batteries. However, the growth of Li dendrites and the volume expansion of the anode are serious constraints to their commercial implementation. Herein, a controllable strategy is proposed to construct an ultrathin 3D hierarchical host of honeycomb copper micromesh loaded with lithiophilic copper oxide nanowires (CMMC). The uniquely designed 3D hierarchical arrayed skeletons demonstrate a surface-preferred and spatial-selective effect to homogenize local current density and relieve the volume expansion, effectively suppressing the dendrite growth. Employing the constructed CMMC current collector in a half-cell, >400 cycles with 99% coulombic efficiency at 0.5 mA cm^-2 is performed. The symmetric battery cycles stably for >2000 h, and the full battery delivers a capacity of 166.6 mAh g^-1 . This facile and controllable approach provides an effective strategy for constructing high-performance lithium metal batteries.

Rate-Dependent Failure Mechanisms and Mitigating Strategies of Anode-Free Lithium Metal Batteries

Anode-free lithium (Li) metal batteries (AFLMBs) could provide a specific energy over 500 Wh/kg, but their cycle life requires improvement. In this work, we propose a new method to calculate the real Coulombic efficiency (CE) of the Li metal during the cycling of AFLMBs. Through this approach, we find low rate discharging unfavorable for Li CE, which is mitigated through electrolyte optimization. In contrast, high rate discharging boosts Li reversibility, indicating AFLMBs to be intrinsically suited for high power use cases. However, AFLMBs still fail rapidly, due to the Li stripping overpotential buildup, which is mitigated by a zinc coating that enables a better electron/ion transferring network. We believe well-targeted strategies need to be better developed to synergize with the intrinsic features of AFLMBs to enable their commercialization in the future.

Advanced Material Engineering to Tailor Nucleation and Growth towards Uniform Deposition for Anode-Less Lithium Metal Batteries

Anode-less lithium metal batteries (ALMBs), whether employing liquid or solid electrolytes, have significant advantages such as lowered costs and increased energy density over lithium metal batteries (LMBs). Among many issues, dendrite growth and non-uniform plating which results in poor coulombic efficiency are the key issues that viciously decrease the longevity of the ALMBs. As a result, lowering the nucleation barrier and facilitating lithium growth towards uniform plating is even more critical in ALMBs. While extensive reviews have focused to describe strategies to achieve high performance in LMBs and ALMBs, this review focuses on strategies designed to directly facilitate nucleation and growth of dendrite-free ALMBs. The review begins with a discussion of the primary components of ALMBs, followed by a brief theoretical analysis of the nucleation and growth mechanism for ALMBs. The review then emphasizes key examples for each strategy in order to highlight the mechanisms and rationale that facilitate lithium plating. By comparing the structure and mechanisms of key materials, the review discusses their benefits and drawbacks. Finally, major trends and key findings are summarized, as well as an outlook on the scientific and economic gaps in ALMBs.

Porous Metal Current Collectors for Alkali Metal Batteries

Alkali metals (i.e., Li, Na, and K) are promising anode materials for next-generation high-energy-density batteries due to their superior theoretical specific capacities and low electrochemical potentials. However, the uneven current and ion distribution on the anode surface probably induces undesirable dendrite growth, which leads to significant safety hazards and severely hinders the commercialization of alkali metal anodes. A smart and versatile strategy that can accommodate alkali metals into porous metal current collectors (PMCCs) has been well established to resolve the issues as well as to promote the practical applications of alkali metal anodes. Moreover, the proposal of PMCCs can meet the requirement of the dendrite-free battery fabrication industry, while the electrode material loading exactly needs the metal current collector component as well. Here, a systematic survey on advanced PMCCs for Li, Na, and K alkali metal anodes is presented, including their development timeline, categories, fabrication methods, and working mechanism. On this basis, some significant methodology advances to control pore structure, surface area, surface wettability, and mechanical properties are systematically summarized. Further, the existing issues and the development prospects of PMCCs to improve anode performance in alkali metal batteries are discussed.

Brushed Metals for Rechargeable Metal Batteries

Battery designs are swiftly changing from metal-ion to rechargeable metal batteries. Theoretically, metals can deliver maximum anode capacity and enable cells with improved energy density. In practice, these advantages are only possible if the parasitic surface reactions associated with metal anodes are controlled. These undesirable surface reactions are responsible for many troublesome issues, like dendrite formation and accelerated consumption of active materials, which leads to anodes with low cycle life or even battery runaway. Here, a facile and solvent-free brushing method is reported to convert powders into films atop Li and Na metal foils. Benefiting from the reactivity of Li metal with these powder films, surface energy can be effectively tuned, thereby preventing parasitic reaction. In-operando study of P₂ S₅ -modified Li anodes in liquid electrolyte cells reveals a smoother electrode contour and more uniform metal electrodeposition and dissolution behavior. The P₂ S₅ -modified Li anodes sustain ultralow polarization in symmetric cell for >4000 h, ≈8× longer than bare Li anodes. The capacity retention is ≈70% higher when P₂ S₅ -modified Li anodes are paired with a practical LiFePO₄ cathode (≈3.2 mAh cm^-2 ) after 340 cycles. Brush coating opens a promising avenue to fabricate large-scale artificial solid-electrolyte-interphase directly on metals without the need for organic solvent.

2D PdTe2 Thin-Film-Coated Current Collectors for Long-Cycling Anode-Free Rechargeable Batteries

The practical implementation of anode-free batteries is limited by factors such as lithium dendrite growth and low cycling Coulombic efficiency (CE). In this study, the improvement in the electrochemical performance of anode-free rechargeable lithium batteries bearing a Cu current collector (CC) coated with PdTe₂ thin films is reported. The optimized thickness and sputtering heating conditions of the PdTe₂ layer are 15 nm and 473.15 K, respectively. Upon deposition on a CC, PdTe₂ works as a seed layer that considerably improves the CE in half-cells, owing to its unique 2D structure that reduces the nucleation overpotential. A further contribution to the high performance is brought about by a CuTe interphase between the coating layer and Cu CC formed during heating. Such an interphase contributes to the high CE by improving the uniformity of the current density distribution on the CC that suppresses lithium dendrite growth. A low nucleation overpotential and uniform current density distribution, in turn, result in a smooth morphology of the plated Li. The full cell obtained with the PdTe₂-coated CC exhibits a capacity retention of 70.7% after the 100th cycle, with an average CE of 99.65% at a 0.2C rate─an outstanding result in view of the rapid development of lithium-ion batteries.

Application of electrodeposited Cu-metal nanoflake structures as 3D current collector in lithium-metal batteries

Since uncontrolled lithium (Li) dendrite growth and dendrite-induced dead Li severely limit the development of Li metal batteries, 3D Cu current collectors can effectively alleviate these problems during Li plating/stripping. Herein, one-step galvanostatic electrodeposition method is employed to fabricate a new current collector on Cu foam decorated with large-scale and uniform 3D porous Cu-based nanoflake (NF) structures (abbreviated as 3D Cu NF@Cu foam). This 3D structure with large internal surface areas not only generates lithophilic surface copper oxides and hydroxides as charge centers and nucleation sites for Li insertion/extraction, but also endows abundant space with interlinked NFs for buffering the cell volume expansion and increasing battery performance. As a result, Li-deposited 3D Cu NF@Cu foam current collector can realize stable cycling over 455 cycles with an average Coulombic efficiency of 98.8% at a current density of 1.0 mA cm^-2, as well as a prolonged lifespan of >380 cycles in symmetrical cell without short-circuit, which are superior to those of blank Cu foam current collector. This work realizes Li metal anode stabilization by constructing 3D porous Cu NFs current collectors, which can advance the development of Li metal anode for battery industries.

Remedies to Avoid Failure Mechanisms of Lithium-Metal Anode in Li-Ion Batteries

Rechargeable lithium-metal batteries (LMBs), which have high power and energy density, are very attractive to solve the intermittence problem of the energy supplied either by wind mills or solar plants or to power electric vehicles. However, two failure modes limit the commercial use of LMBs, i.e., dendrite growth at the surface of Li metal and side reactions with the electrolyte. Substantial research is being accomplished to mitigate these drawbacks. This article reviews the different strategies for fabricating safe LMBs, aiming to outperform lithium-ion batteries (LIBs). They include modification of the electrolyte (salt and solvents) to obtain a highly conductive solid–electrolyte interphase (SEI) layer, protection of the Li anode by in situ and ex situ coatings, use of three-dimensional porous skeletons, and anchoring Li on 3D current collectors.

Uniform Deposition of Li-Metal Anodes Guided by 3D Current Collectors with In Situ Modification of the Lithiophilic Matrix

The lithium (Li)-metal anode is deemed as the "holy gray" of the next-generation Li-metal system because of its high theoretical specific capacity, minimal energy density, and lowest standard electrode potential. Nevertheless, its commercial application has been limited by the large volume variation during charge and discharge, the unstable interface between the Li metal and electrolyte, and uneven deposition of Li. Herein, we present a 3D host (Cu) with lithiophilic matrix (CuO and SnO₂) in situ modification via a facile ammonia oxidation method to serve as a current collector for the Li-metal anode. The 3D Cu host embellished by CuO and SnO₂ is abbreviated as 3D CSCC. By increasing interfacial activity, lowering the nucleation barrier, and accommodating changes in volume of the Li metal, the 3D CSCC electrode effectively demonstrates a homogeneous and dendrite-free deposition morphology with an excellent cycling performance up to 3000 h at a 1.0 mA cm^-2 current density. Additionally, the full cells paired with Li@3D CSCC anodes and LiCoO₂ cathodes show good capacity retention performance at 0.2 C.

Laser-Induced Silicon Oxide for Anode-Free Lithium Metal Batteries

The development of a rechargeable Li metal anode (LMA) is an important milestone for improved battery technology. Practical issues hindering LMAs are the formation of Li dendrites and inactive Li during plating and stripping processes, which can cause short circuits, thermal runaway, and low coulombic efficiency (CE). Here, the use of a laser-induced silicon oxide (LI-SiO_x ) layer derived from a commercial adhesive tape to improve the reversibility of Li metal batteries (LMBs) is studied. The silicone-based adhesive of the tape is converted by a commercial infrared laser into a homogeneous porous SiO_x layer deposited directly over the current collector. The coating results in superior performance by suppressing the formation of Li dendrites and inactive Li and presenting higher average CE of 99.3% (2.0 mAh cm^-2 at 2.0 mA cm^-2 ) compared to bare electrodes. The thickness and morphology of the deposited Li is investigated, revealing a different mechanism of Li deposition on coated electrodes. The laser coating affords a method that is fast and avoids the use of toxic organic solvents and extensive drying times. The improved performance with the SiO_x coating is demonstrated in LMB with a zero-excess ("anode-free") configuration where a 100% improved performance is verified.