Recent Advances in Structural Optimization and Surface Modification on Current Collectors for High‑Performance Zinc Anode:Principles,Strategies,and Challenges

The last several years have witnessed the prosperous development of zinc-ion batteries(ZIBs),which are considered as a promising competitor of energy storage systems thanks to their low cost and high safety.However,the reversibility and availability of this system are blighted by problems such as uncontrollable dendritic growth,hydrogen evolution,and corrosion passivation on anode side.A functionally and structurally well-designed anode current collectors(CCs)is believed as a viable solution for those problems,with a lack of summarization according to its working mechanisms.Herein,this review focuses on the challenges of zinc anode and the mechanisms of modified anode CCs,which can be divided into zincophilic modification,structural design,and steering the preferred crystal facet orientation.The possible prospects and directions on zinc anode research and design are proposed at the end to hopefully promote the practical application of ZIBs.

Status and Opportunities of Zinc Ion Hybrid Capacitors: Focus on Carbon Materials, Current Collectors, and Separators

Zinc ion hybrid capacitors(ZIHCs), which integrate the features of the high power of supercapacitors and the high energy of zinc ion batteries, are promising competitors in future electrochemical energy storage applications. Carbon-based materials are deemed the competitive candidates for cathodes of ZIHC due to their cost-effectiveness, high electronic conductivity, chemical inertness, controllable surface states, and tunable pore architectures. In recent years, great research efforts have been devoted to further improving the energy density and cycling stability of ZIHCs. Reasonable modification and optimization of carbon-based materials offer a remedy for these challenges. In this review, the structural design, and electrochemical properties of carbon-based cathode materials with different dimensions, as well as the selection of compatible, robust current collectors and separators for ZIHCs are discussed. The challenges and prospects of ZIHCs are showcased to guide the innovative development of carbon-based cathode materials and the development of novel ZIHCs.

A pre-strain strategy of current collectors for suppressing electrode debonding in lithium-ion batteries

The interfacial debonding between the active layer and the current collector has been recognized as a critical mechanism for battery fading,and thus has attracted great efforts focused on the related analyses.However,much still remains to be studied regarding practical methods for suppressing electrode debonding,especially from the perspective of mechanics.In this paper,a pre-strain strategy of current collectors to alleviate electrode debonding is proposed.An analytical model for a symmetric electrode with a deformable and limited-thickness current collector is developed to analyze the debonding behavior involving both a pre-strain of the current collector and an eigen-strain of the active layers.The results reveal that the well-designed pre-strain can significantly delay the debonding onset(by up to 100%)and considerably reduce the debonding size.The critical values of the pre-strain are identified,and the pre-strain design principles are also provided.Based on these findings,this work sheds light on the mechanical design to suppress electrode degradation.

Surface-roughened current collectors for anode-free all-solid-state batteries

Anode-free all-solid-state batteries(AFASSBs), composed of a fully lithiated cathode and a bare current collector(CC) that eliminates excess lithium, can maximize the energy density(because of a compact cell configuration) and improve the safety of solid-state systems. Although significant progress has been made by modifying CCs in liquid-based anode-free batteries, the role of CCs and the mechanism of Li formation on CCs in AFASSBs are still unexplored. Here, we systematically investigate the effect of the surface roughness of the CCs on the Li plating/stripping behavior in AFASSBs. The results show that the moderately roughened CC substantially improves the Coulombic efficiency and cycle stability of AFASSBs owing to the increased contact points between the solid electrolyte and the roughened CC. In contrast, the excessively roughened CC deteriorates the performance owing to the contact loss.Moreover, an ex situ interface analysis reveals that the roughened surface of the CC could suppress the interfacial degradation during the Li ion extraction from a sulfide solid electrolyte to a CC. This provides an indication to the origin that hinders the electrochemical performance of AFASSBs. These findings show the potential for the application of surface-engineered CCs in AFASSBs and provide guidelines for designing advanced CCs.

Contribution to the understanding of the performance differences between commercial current collectors in Li–S batteries

Lithium–sulfur batteries have been recognised as highly promising next-generation batteries, due to their low cost and high theoretical energy density. Despite numerous advances in this technology over the last decade, its commercialisation is still a challenge that has not yet been achieved. Many efforts have been made to improve the problems that these batteries present, mainly by investigating different cathode manufacturing strategies, testing novel Li anodes, new additives in the electrolytes, and modified separators or interlayers. However, the characteristics of the current collectors used in the preparation of the electrodes have been rarely addressed. Three commercial collectors are commonly used in basic research on Li–S batteries: Al foil, carbon coated Al foil (Al-C), and carbon paper (gas diffusion layer, GDL). In this work, a detailed study of the electrochemical response of these commercial collectors has been carried out. The tests were carried out on two S composites formed by carbons of a different natures, commercial carbon black and synthetic N-doped graphene. In addition, the S impregnation method was different, using either melt diffusion at 155 ℃ or ethylenediamine as S solvent, respectively. In both systems, the results were similar – the electrodes supported on GDL delivered higher specific capacities than those supported on Al and Al-C, with minimal differences between the two. Of the different collector properties examined to explain this behaviour, namely Al corrosion, electrical conductivities, surface-level composition, and surface texture, only the latter had a significant effect in the performance of GDL-based electrodes. SEM images revealed a rough and cracked surface formed by the agglomerated carbon particles that give rise to a complex pore system, predominantly consisting of macropores. All of these features are beneficial for a better anchoring of the active material on the collector surface, in addition to enhancing the wettability of the electrolyte and favouring reaction kinetics. In contrast, the Al-based collector possesses a very smooth and non-porous surface, detrimental to both the active material-substrate interface and the active material impregnation by the electrolyte.

Performance evaluation of the incorporation of different wire meshes in between perforated current collectors and membrane electrode assembly on the Passive Direct methanol fuel cell

Passive Direct methanol fuel cells(DMFC)are more suitable for charging small capacity electronic devices.In passive DMFC,the fuel and oxidant are supplied by diffusion and natural convection process on the anode and cathode sides respectively.Current collectors(CC)play a vital importance in fuel cell performance.This paper presents the combined impact of perforated and wire mesh current collectors(WMCC)on passive DMFC performance.Three types of open ratios of perforated current collectors(PCC),such as 45.40%,55.40%and 63.40%and two types of wire mesh current collectors with open ratios of 38.70%and 45.40%were chosen for the experimental work.A combination of TaguchiL9 rule is considered.A combination of three PCC and two WMCC on both anode and cathode was used.Methanol concentration was varied from 1 mol·L^(-1)-5 mol·L^(-1)for nine combinations of PCC and WMCC.From the experimental results,it is noticed that the combination of PCC and WMCC with an open ratio of 55.40%and 38.70%incorporated passive DMFC produced peak power density at 5 mol·L^(-1)of methanol concentration.The passive DMFC performance was evaluated in terms of maximum power density and maximum current density.The combined current collectors of PCC and WMCC open ratios of 55.40%+38.70%have more stable voltage than single PCC of open ratio 63.40%at 4 mol·L^(-1)of methanol concentration.

Constructing nanoporous Ni foam current collectors for stable lithium metal anodes

Lithium metal,as the most ideal anode material for high energy density batteries,has been researched for several decades.However,the dendrite formation and large volume change during repetitive lithium plating/stripping lead to a serious safety issue and impede the practical application of lithium metal anode.Herein,a nanoporous Ni foam current collector with high surface area and surface flaws is constructed via a facile oxidation-reduction method.The inherent macropore structure of Ni foam can partly accommodate the volume variation during Li plating/stripping.The well-distributed nanopores on the skeleton of Ni foam can effectively reduce the local current density,regulate the uniform lithium nucleation and deposition with homogenous distribution of Li^(+) flux.Moreover,the surface flaws induce the formation of ring Li structures at initial nucleation/deposition processes and concave Li metal spontaneously formed based on the ring Li structures during cycling,which can direct the even Li plating/stripping.Therefore,highly stable Coulombic efficiency is achieved at 1 mA cm^(-2) for 200 cycles.The symmetrical cell,based on the nanoporous Ni foam current collector,presents long lifespans of 1200 and 700 h respectively at different current densities of 0.5 and 1 mA cm^(-2) without short circuit.In addition,the LiFePO4 full cell,with the Li metal anode based on the nanoporous Ni foam current collector,shows excellent cycling performance at 1 C for 300 cycles and rate performance.

Powder metallurgical 3D nickel current collectors with plasma-induced Ni3N nanocoatings enabling long-life and dendrite-free lithium metal anode

Building three-dimensional(3D) current collectors is a promising strategy to surmount the bottlenecks of lithium metal anodes(LMAs), but the regulation methodology of a 3D current collector has seldom been considered comprehensively concerning both skeleton architectures and surface coatings. Herein, a robust porous 3D nickel skeleton(NS) with lithiophilic NiN nanocoatings(NiN@NS) is synthesized via an integrative route of powder metallurgy/plasma-enhanced nitridation technics. The facile powder metallurgical method facilitates the adjustment of NS architectures toward sufficient electrolyte adsorption and even current density distribution, while the followed plasma-enhanced chemical vapor deposition(PECVD) method can induce compact NiN nanocoatings on NS, which reduces the Li nucleation overpotential, accelerates the Li-ion transfer, and facilitates a highly reversible oriented texture of Li deposition morphology owing to the dense and homogenous deposition of Li into the pores. The optimized NiN@NS current collector shows a high averaged Coulombic efficiency(CE) of 98.8% over 350cycles, a prolonged lifespan of 1000 h(at 2 mA cm^(-2)) in symmetrical cells, together with the significant performance in full cells. The ingenious methodology reported in this work can also be broadly applicable for the controllable production of other 3D skeletons with nitride nanocoatings for various applications.

Copper-coated Porous Polyimide as Ultralight and Safe Current Collectors for Advanced LIBs

Metallic copper is widely used as current collector(CC) for graphite anode of lithium-ion batteries(LIBs) due to its high electrical conductivity and electrochemical stability. However, the large volume density of commercial copper foil(~8.9 g·cm^(-3)) limits the increase of energy density of battery. Here, copper-coated porous polyimide(Cu@PPI) was prepared by vacuum evaporation as collector for the graphite anode. The sandwich structure connects the copper metal on both sides of the collector with excellent electrical conductivity. Compared to commercial Cu foil, Cu@PPI has lighter mass(≤3.9 mg for disc of 12 mm diameter versus 9.9 mg of ~10 μm Cu foil) and lower volume density(≤3.3 g·cm^(-3)). In addition, the porous structure allows of better adhesion of reactive substances and electrochemical properties than pure Cu foils. It is estimated that the energy density of Cu@PPI should be much higher than that of Cu foil. This strategy should be applicable for other current collectors.

Present and future of functionalized Cu current collectors for stabilizing lithium metal anodes

Li metal has been recognized as the most promising anode materials for next-generation high-energy-density batteries,however,the inherent issues of dendrite growth and huge volume fluctuations upon Li plating/stripping normally result in fast capacity fading and safety concerns.Functionalized Cu current collectors have so far exhibited significant regulatory effects on stabilizing Li metal anodes(LMAs),and hold a great practical potential owing to their easy fabrication,low-cost and good compatibility with the existing battery technology.In this review,a comprehensive overview of Cu-based current collectors,including planar modified Cu foil,3D architectured Cu foil and nanostructured 3D Cu substrates,for Li metal batteries is provided.Particularly,the design principles and strategies of functionalized Cu current collectors associated with their functionalities in optimizing Li plating/stripping behaviors are discussed.Finally,the critical issues where there is incomplete understanding and the future research directions of Cu current collectors in practical LMAs are also prospected.This review may shed light on the critical understanding of current collector engineering for high-energy-density Li metal batteries.

Current collectors based on multiwalled carbon-nanotubes and fewlayer graphene for enhancing the conversion process in scalable lithium-sulfur battery

We investigated herein the morphological,structural,and electrochemical features of electrodes using a sulfur(S)-super P carbon(SPC)composite(i.e.,S@SPC-73),and including few-layer graphene(FLG),multiwalled carbon nanotubes(MWCNTs),or a mixture of them within the current collector design.Furthermore,we studied the effect of two different electron-conducting agents,that is,SPC and FLG,used in the slurry for the electrode preparation.The supports have high structural crystallinity,while their morphologies are dependent on the type of material used.Cyclic voltammetry(CV)shows a reversible and stable conversion reaction between Li and S with an activation process upon the first cycle leading to the decrease of cell polarization.This activation process is verified by electrochemical impedance spectroscopy(EIS)with a decrease of the resistance after the first CV scan.Furthermore,CV at increasing scan rates indicates a Li+diffusion coefficient(D)ranging between 10^(−9) and 10^(−7) cm^(2)·s^(−1)in the various states of charge of the cell,and the highest D value for the electrodes using FLG as electron-conducting agent.Galvanostatic tests performed at constant current of C/5(1 C=1675 mA·g_(s)^(−1))show high initial specific capacity values,which decrease during the initial cycles due to a partial loss of the active material,and subsequently increase due to the activation process.All the electrodes show a Coulombic efficiency higher than 97%upon the initial cycles,and a retention strongly dependent on the electrode formulation.Therefore,this study suggests a careful control of the electrode in terms of current collector design and slurry composition to achieve good electrode morphology,mechanical stability,and promising electrochemical performance in practical Li-S cells.

Revisiting aluminum current collector in lithium-ion batteries:Corrosion and countermeasures

With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.

The Effects of the Geometry of a Current Collector with an Equal Open Ratio on Output Power of a Direct Methanol Fuel Cell

The open ratio of a current collector has a great impact on direct methanol fuel cell(DMFC)performance.Although a number of studies have investigated the influence of the open ratio of DMFC current collectors,far too little attention has been given to how geometry(including the shape and feature size of the flow field)affects a current collector with an equal open ratio.In this paper,perforated and parallel current collectors with an equal open ratio of 50%and different feature sizes are designed,and the corresponding experimental results are shown to explain the geometry effects on the output power of the DMFC.The results indicate that the optimal feature sizes are between 2 and 2.5 mm for both perforated and parallel flow field in the current collectors with an equal open ratio of 50%.This means that for passive methanol fuel cells,to achieve the highest output power,the optimal feature size of the flow field in both anode and cathode current collectors is between 2 and 2.5 mm under the operating mode of this experiment.The effects of rib and channel position are also investigated,and the results indicate that the optimum pattern depends on the feature sizes of the flow field.

Nickel nanopore arrays as promising current collectors for constructing solid-state supercapacitors with ultrahigh rate performance

In this work, nickel nanopore arrays with a highly-oriented nanoporous structure inherited from por- ous alumina membranes were used as nanostructured current collectors for constructing ultrahigh rate solid-state supercapacitors. A thin layer of poly（3,4-ethylenediox- ythiophene） （PEDOT） as electroactive materials was conformally coated onto nickel nanopores to form heterostructured electrodes. The as-prepared electrodes have a large specific surface area to ensure a high capacity, and the highly-oriented nanoporous structure of nickel nanopores reduces the ion transport resistance, allowing the ions in the solid-state electrolytes to quickly access the PEDOT surface during the fast charge-discharge process. As a result, the assembled solid-state supercapacitor in a symmetric configuration exhibits an ideal capacitive behavior and a superior rate capability even at an ultrahigh scan rate of 50 V· s^-1.

Laser irradiation of graphite foils as robust current collectors for high-mass loaded electrodes of supercapacitors

Conductive substrates with low cost,lightweight,and chemical stability have been highly recognized as alternative current collectors for energy storage devices.Graphite foil is promising to fulfill these requests,whereas the inert surface chemistry denies its possibility as the carrier with high-mass loading active species.Herein,we report a facile yet efficient laser-mediated strategy to fast regulate graphite foils for robustly loading active species.The smooth and hydrophobic graphite foil surface turned to be a rough,super-hydrophilic one containing oxygen-rich clusters after lasering.The reconstructed surface affords anchors for active species,such as nanostruetured MnO_(2),FeOOH,and Fe_(2)O_(3),with the highest loading mass of 20 mg·cm^(-2).The high-mass loading MnO_(2)electrode offers an areal capacitance of 3933 mF·cm^(-2)at 1 mA·cm^(-2).Then,the asymmetric supercapacitor,fabricated by MnO_(2)and Fe_(2)O_(3)deposited laser-irradiated graphite foils,exhibits improved performance with high energy density,large power capability,and long-term stability.The strategy suggests a reliable way to produce alternative current collectors for robust energy storage devices.

Recent Advances in Carbon-Based Current Col lectors/Hosts for Alkali Metal Anodes

The urgent demand for high-energy-density storage systems evokes the research upsurge on the alkali metal batteries with high theoretical capacities.However,the utilization of alkali metal anodes,including Li,Na,and K,is significantly hindered by notorious dendrite growth,undesirable corrosion,and unstable solid electrolyte interface.In order to resolve these issues,the carbon materials for the rational design of current collector/host that can regulate the plating/stripping behavior of alkali metal have been exploited.These carbon-based current collectors/hosts are featured with many pivotal advantages,including mechanical integrity to accommodate the volume change,superior electronic/ionic conductivity,large available surface area,and rich functionalization chemistries to increase the affinity to alkali metal.In this review,the recent progress on various dimensional carbon-based current collectors/hosts with different chemical components in stabilizing the alkali metal anodes through the regulation of initial deposition and subsequent growth behavior during plating/stripping process is provided.The nanostructured carbon scaffolds with self-affinity to alkali metals,as well as the carbon frameworks with internal/external affinitive sites to alkali metals,catalogued by various dimensions,are discussed in this review.Therefore,these appealing strategies based on the carbon-based current collectors/hosts can provide a paradigm for the realization of high-energy-density alkali metal batteries.

Advanced Current Collectors for Alkali Metal Anodes

High-energy-density batteries are in urgent need to solve the ever-increasing energy stroage demand for portable electronic devices,electric vehicles,and renewable solar and wind energy systems.Alkali metals,typically lithium(Li),sodium(Na)and potassium(K),are considered as the promising anode materials owing to their low electrochemical potential,low density,and high theoretical gravimetric capacities.However,the problem of dendrite growth of alkali metals during their plating/stripping process will lead to low Coulombic efficiencies,a short lifespan and huge volume expansion,eventually hindering their practical commercialization.To resolve this issue,a very effective approach is engineering the anodes on structured current collectors.This review summarizes the development of the alkali metal batteries and discusses the recent advances in rational design of anode current collectors.First,the challenges and strategies of suppressing alkali-metal dendrite growth are presented.Then the special attention is paid to the novel current collector design for dendrite-free alkali metal anodes.Finally,we give conclusions and perspective on the current challenges and future research directions toward advanced anode current collectors for alkali metal batteries.

Regulating lithium nucleation and growth by zinc modified current collectors

Lithium metal is commonly regarded as the“Holy Grail”anode material for high energy density rechargeable batteries.However,the uncontrollable growth of Li dendrites has posed safety concerns and thus greatly hindered its large-scale application.Here we have modified the surface of a commercial anode current collector,Cu foil,with a thin layer of Zn by a facile electroplating method,in order to regulate the Li nucleation and the following growth processes.Because of the formation of a solid solution buffer layer and Li-Zn alloy phases,the Li nucleation overpotential was dramatically reduced,realizing a uniform Li nucleation and a smooth Li plating morphology.As a result,significantly improved long-term cycling performance with a high Coulombic efficiency was achieved by the lithiophilic Zn coated Cu foil as a current collector.Full cells of Li-LiFePO4 and Li-S using the Li deposited on the Zn modified Cu as the anode,showed increased capacity with low voltage hysteresis and greatly enhanced cycling stability,ascribed to the uniform Li deposition and formation of a stable SEI layer.This work demonstrates the feasibility of employing lithiophilic modified Cu foils as Li metal current collectors for practical applications.

Plowing-Extrusion Processes and Performance of Functional Surface Structures of Copper Current Collectors for Lithium-Ion Batteries

Most copper current collectors for commercial lithium-ion batteries(LIBs)are smooth copper foils,which cannot form a stable and effective combination with electrode slurry.They are likely to deform or fall off after long-term operation,resulting in a sharp decline in battery performance.What is worse is that this condition inevitably causes internal short circuits and thus brings about security risks.In this study,a process route of fabricating the functional surface structures on the surface of a copper collector for LIBs by twice-crisscross micro-plowing(TCMP)is proposed,which provides a new idea and an efficient method to solve the above problems from the perspective of manufacturing.The finite element simulation of TCMP combined with the cutting force test and morphological characterization is conducted to verify the forming mechanism of the surface structures on a copper sheet and its relationship with the processing parameters.The influence of several key processing parameters on the surface characteristics of the copper sheet is comprehensively explored.A series of functions is tested to obtain the optimal parameters for performance improvement of the current collector.Results show that the structured copper sheet with the cutting distance of 250μm,cutting depth of 80μm,and cutting crossing angle of 90°enables the best surface features of the current collector;the contact angle reaches 0°,the slurry retention rate is up to 89.2%,and the friction coefficient reaches 0.074.The battery using the as-prepared structured copper sheet as the current collector produces a specific capacity of 318.6 mAh/g after 50 cycles at a current density of 0.2 C,which is 132.7%higher than the one based on a smooth surface.The capacity reversibility of the sample with the new current collector is much better than that of the traditional samples,yielding a lower impedance.

Vertical graphene nanosheetsmodiBed Al current collectors for high-performance sodium-ion batteries

Rechargeable sodium-ion batteries(SIBs)are promising candidates for large-scale energy storage owing to their excellent high-power performance.However,Al-based current collectorsat both anodes and cathodes of SIBs,which widely influence the power properties of a variety of electrodes in SIBs,have rarely been investigated.Here,we demonstrate that vertical graphene nanosheets grown on commercial Al foil by the plasma-enhanced chemical vapor deposition(PECVD)method,form a robust connection with the carbon-based conductive network of the electrode,thereby significantly reducing the electrode current collector interfacial resistance.For sodium vanadium phosphate(NVP)anodes with vertical graphenenanosheetmodified Al foil(G-AI)current collectors,the interfacial resistance between the electrode and current collector is reduced 20-fold compared with that in the case of Al foil.The G-AI current collector reduces the polarization and improves the rate capability compared with that of Al current collectors within both cathodes and anodes of SIBs.At a high rate of 5 C,the capacity retention of NVP cathode with G-AI current collector is 74%,which is much higher than that with AI foil(22%).We believe that the obtained results support the prospect for the widespread use of G-AI current collectors in the further improvement of high-power profiles of SIBs.