Dendrite-Free Lithium Anodes Enabled by a Commonly Used Copper Antirusting Agent

Air Corrosion of Layered Cathode Materials for Sodium-Ion Batteries: Cation Mixing and a Practical Suppression Strategy

Layered oxide cathodes of sodium-ion batteries (SIBs) are considered promising candidates due to their fascinating high capacity, good cyclability, and environmental friendliness. However, the air sensitivity of layered SIB cathodes causes high electrode manufacturing costs and performance deterioration, hampering their practical application. Herein, a commercial O3-type layered Na(Ni1/3Fe1/3Mn1/3)O2 (NNFM) material is adopted to investigate the air corrosive problem and the suppression strategy. We reveal that once the layered material comes in contact with ambient air, cations migrate from transition metal (TM) layers to sodium layers at the near surface, although Na+ and TM ions show quite different ion radii. Experimental results and theoretical calculations show that more Ni/Na disorder occurs in the air-exposed O3-NNFM materials, owing to a lower Ni migration energy barrier. The cation mixing results in detrimental structural distortion, along with the formation of residual alkali species on the surface, leading to high impedance for Na+ diffusion during charge/discharge. To tackle this problem, an ultrathin and uniform hydrophobic molecular layer of perfluorodecyl trimethoxysilane is assembled on the O3-NNFM surface, which significantly suppresses unfavorable chemistry and structure degradation during air storage. The in-depth understanding of the structural degradation mechanism and suppression strategy presented in this work can facilitate high-energy cathode manufacturing from the perspective of future practical implementation and commercialization.

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.

Exploiting Zirconium-Based Metallic Glass Thin Films for Anode-Free Lithium-Ion Batteries and Lithium Metal Batteries With Ultra-Long Cycling Life

Coating Zr-based metallic glass, Zr53 Cu31 Ni11 Al5 (Zr-MG), on a Cu current collector (CC) and Li metal anode (LMA) significantly improves the cycle performance of both types of Li-ion batteries, namely, anode-free Li-ion batteries (AFLBs) and Li metal batteries (LMB). The inherent isotropy and homogeneity of the Zr-MG significantly improve the surface uniformity of the CC and LMA. A 12 nm-thick Zr-MG thin film coating on the CC reduces the overpotential in the AFLB, leading to a more uniform Li plating morphology. The Li film covers almost the entire surface of the Zr-CC, whereas it only covers ≈75% of the bare CC during charging. An LFP||Zr-CC full-cell exhibits a capacity retention of 63.6% after the 100th cycle, with an average CE of 99.55% at a 0.2 C rate. In the case of the LMB, a 12 nm-thick Zr-MG thin film-coated LMA (Zr-LMA) exhibits a stable capacity of up to 1500 cycles. An LFP||Zr-LMA full-cell exhibits capacity retention and CE after 1500 cycles of 66.6% and 99.97%, respectively, at a 1 C rate. Zirconium-MG thin films with atomic-level uniformity, outstanding corrosion resistance, lithiophilic characteristics, and high diffusivity result in superior AFLB and LMB performances.

Constructing 3D Skeleton on Commercial Copper Foil via Electrophoretic Deposition of Lithiophilic Building Blocks for Stable Lithium Metal Anodes

Lithium (Li) metal has been regarded as the "Holy Grail" of Li battery anodes thanks to its high theoretic specific capacity and low reduction potential, but uneven formation of Li dendrites and uncontrollable Li volume changes hinder the practical applications of Li metal anodes. A three-dimensional (3D) current collector is one of the promising strategies to address the above issues if it can be compatible with current industrialized process. Here, Au-decorated carbon nanotubes (Au@CNTs) are electrophoretically deposited on commercial Cu foil as a 3D lithiophilic skeleton to regulate Li deposition. The thickness of the as-prepared 3D skeleton can be accurately controlled by adjusting the deposition time. Benefitting from the reduced localized current density and improved Li affinity, the Au@CNTs-deposited Cu foil (Au@CNTs@Cu foil) achieves uniform Li nucleation and dendrite-free Li deposition. Compared with bare Cu foil and CNTs deposited Cu foil (CNTs@Cu foil), the Au@CNTs@Cu foil exhibits enhanced Coulombic efficiency and better cycling stability. In the full-cell configuration, the Au@CNTs@Cu foil with predeposited Li shows superior stability and rate performance. This work provides a facial strategy to directly construct a 3D skeleton on commercial Cu foils with lithiophilic building blocks for stable and practical Li metal anodes.

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.

Facile Electroless Plating Method to Fabricate a Nickel-Phosphorus-Modified Copper Current Collector for a Lean Lithium-Metal Anode

The compatibility of current collectors with reactive Li is key to inducing stable Li cycling and prolonged cycle life of lean Li-metal batteries. Herein, a thin and uniform layer of Ni-P complex was built on the surface of a Cu current collector (NiP@Cu) via an efficient, controllable, and cost-effective electroless plating method. The thickness, morphology, composition, and roughness of the Ni-P deposition were successfully regulated. Lithiophilicity of the current collector was greatly improved by Ni-P deposition, which effectively reduced the Li nucleation overpotential and suppressed the Li dendrite growth. In addition, NiP@Cu promoted an inorganic LiF/Li₃P-rich solid electrolyte interphase to facilitate interfacial charge transfer and eliminate excessive side reactions between Li and the electrolyte. As a result, the Coulombic efficiency of half-cells remained above 98.5% for more than 400 cycles at 0.5 mA/cm² and 98.2% for more than 250 cycles at 1 mA/cm². Full cells with NiP@Cu also showed superior performance compared to those with bare Cu. This work proposes a promising surface modification method to develop a stable, dendrite-free, and cost-effective anode current collector for high-energy-density lean Li-metal batteries.

Rational Engineering of Anode Current Collector for Dendrite-Free Lithium Deposition: Strategy, Application, and Perspective

Lithium metal anodes have attracted extensive attention due to their high theoretical capacity and low redox potential. However, low Coulombic efficiency, serious parasitic reaction, large volume change, and dendrite growth during cycling have hindered their practical application. The engineering of an anode current collector provides important advances to solve these problems, eliminate excess lithium usage, and substantially increase the energy density. In this review, we summarize the engineering strategies of an anode current collector with emphasis on different methods and applications in lithium metal-based systems. Finally, the perspectives and challenges of current collector engineering for lithium metal anode are discussed.

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.

Achieving a dendrite-free lithium metal anode through lithiophilic surface modification with sodium diethyldithiocarbamate

Sodium diethyldithiocarbamate (DDTC) monolayer self-assembly on Cu foil can be used to construct a lithiophilic surface modification layer, which can help to achieve a robust and stable SEI and guide homogeneous and dendrite-free Li deposition.

Self-Assembled Monolayers for Batteries

Current studies in the Li-battery field are focusing on building systems with higher energy density than ever before. The path toward this goal, however, should not ignore aspects such as safety, stability, and cycling life. These issues frequently originate from interfacial instability, and therefore, precise surface chemistry that allows for accurate control of material surface and interfaces is much in demand for advanced battery research. Molecular self-assembly as a surface chemistry tool is considered to surpass many conventional coating techniques due to its intrinsic merits such as spontaneous organization, molecular-scale uniformity, and structural diversity. Recent publications have demonstrated the power of self-assembled monolayers (SAMs) in addressing pressing issues in the battery field such as the chemical stability of Li, but many more investigations are needed to fully explore the potential and impact of this technique on energy storage. This perspective is the first of its kind devoted to SAMs in batteries and related materials. Recent research progress on SAMs in batteries is reviewed and mainly falls in two categories, including the improvement of chemical stability and the regulation of nucleation in conversion electrode reactions. Future applications and consideration of SAMs in energy storage are discussed. We believe these summaries and outlooks are highly stimulative and may benefit future advancements in battery chemistry.

Stable Lithium-Carbon Composite Enabled by Dual-Salt Additives

Lithium metal is regarded as the ultimate negative electrode material for secondary batteries due to its high energy density. However, it suffers from poor cycling stability because of its high reactivity with liquid electrolytes. Therefore, continuous efforts have been put into improving the cycling Coulombic efficiency (CE) to extend the lifespan of the lithium metal negative electrode. Herein, we report that using dual-salt additives of LiPF₆ and LiNO₃ in an ether solvent-based electrolyte can significantly improve the cycling stability and rate capability of a Li-carbon (Li-CNT) composite. As a result, an average cycling CE as high as 99.30% was obtained for the Li-CNT at a current density of 2.5 mA cm^-2 and an negative electrode to positive electrode capacity (N/P) ratio of 2. The cycling stability and rate capability enhancement of the Li-CNT negative electrode could be attributed to the formation of a better solid electrolyte interphase layer that contains both inorganic components and organic polyether. The former component mainly originates from the decomposition of the LiNO₃ additive, while the latter comes from the LiPF₆-induced ring-opening polymerization of the ether solvent. This novel surface chemistry significantly improves the CE of Li negative electrode, revealing its importance for the practical application of lithium metal batteries.