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.

Dual Additives for Stabilizing Li Deposition and SEI Formation in Anode-Free Li-Metal Batteries

Anode-free Li-metal batteries are of significant interest to energy storage industries due to their intrinsically high energy.However,the accumulative Li dendrites and dead Li continuously consume active Li during cycling.That results in a short lifetime and low Coulombic efficiency of anode-free Li-metal batteries.Introducing effective electrolyte additives can improve the Li deposition homogeneity and solid electrolyte interphase(SEI)stability for anode-free Li-metal batteries.Herein,we reveal that introducing dual additives,composed of LiAsF6 and fluoroethylene carbonate,into a low-cost commercial carbonate electrolyte will boost the cycle life and average Coulombic efficiency of NMC‖Cu anode-free Li-metal batteries.The NMC‖Cu anode-free Li-metal batteries with the dual additives exhibit a capacity retention of about 75%after 50 cycles,much higher than those with bare electrolytes(35%).The average Coulombic efficiency of the NMC‖Cu anode-free Li-metal batteries with additives can maintain 98.3%over 100 cycles.In contrast,the average Coulombic efficiency without additives rapidly decline to 97%after only 50 cycles.In situ Raman measurements reveal that the prepared dual additives facilitate denser and smoother Li morphology during Li deposition.The dual additives significantly suppress the Li dendrite growth,enabling stable SEI formation on anode and cathode surfaces.Our results provide a broad view of developing low-cost and high-effective functional electrolytes for high-energy and long-life anode-free Li-metal batteries.

SEI/dead Li-turning capacity loss for high-performance anode-free solid-state lithium batteries

Anode-free solid-state lithium metal batteries(AF-SSLBs)have the potential to deliver higher energy density and improved safety beyond lithium-metal batteries.However,the unclear mechanism for the fast capacity decay in AF-SSLBs,either determined by dead Li or solid electrolyte interface(SEI),limits the proposal of effective strategies to prolong cycling life.To clarify the underlying mechanism,herein,the evolution of SEI and dead Li is quantitatively analyzed by a solid-state nuclear magnetic resonance(ss-NMR)technology in a typical LiPF6-based polymer electrolyte.The results show that the initial capacity loss is attributed to the formation of SEI,while the dead Li dominates the following capacity loss and the growth rate is 0.141 mA h cm^(−2)cycle−1.To reduce the active Li loss,the combination of inorganic-rich SEI and self-healing electrostatic shield effect is proposed to improve the reversibility of Li deposition/dissolution behavior,which reduces the capacity loss rate for the initial SEI and following dead Li generation by 2.3 and 20.1 folds,respectively.As a result,the initial Coulombic efficiency(ICE)and stable CE increase by 15.1%and 15.3%in Li-Cu cells,which guides the rational design of high-performance AF-SSLBs.

Stoichiometric Ti_(3)C_(2)T_(x)Coating for Inhibiting Dendrite Growth in Anode-Free Lithium Metal Batteries

Lithium metal batteries(LMBs)and anode-free LMBs(AFLMBs)present a solution to the need for batteries with a significantly superior theoretical energy density.However,their adoption is hindered by low Coulombic efficiency(CE)and rapid capacity fading,primarily due to the formation of unstable solid electrolyte interphase(SEI)layer and Li dendrite growth as a result of uneven Li plating.Here,we report on the use of a stoichiometric Ti_(3)C_(2)T_(x)(S-Ti_(3)C_(2)T_(x))MXene coating on the copper current collector to enhance the cyclic stability of an anode-free lithium metal battery.The S-Ti_(3)C_(2)T_(x)coating provides abundant nucleation sites,thereby lowering the overpotential for Li nucleation,and promoting uniform Li plating.Additionally,the fluorine(-F)termination of S-Ti_(3)C_(2)T_(x)participates in the SEI formation,producing a LiF-rich SEI layer,vital for stabilizing the SEI and improving cycle life.Batteries equipped with S-Ti_(3)C_(2)T_(x)@Cu current collectors displayed reduced Li consumption during stable SEI formation,resulting in a significant decrease in capacity loss.AFLMBs with S-Ti_(3)C_(2)T_(x)@Cu current collectors achieved a high initial capacity density of 4.2 mAh cm^(-2),70.9%capacity retention after 50 cycles,and an average CE of 98.19%in 100 cycles.This innovative application of MXenes in the energy field offers a promising strategy to enhance the performance of AFLMBs and could potentially accelerate their commercial adoption.

Stable anode-free zinc-ion batteries enabled by alloy network-modulated zinc deposition interface

Newly-proposed anode-free zinc-ion batteries(ZIBs)are promising to remarkably enhance the energy density of ZIBs,but are restricted by the unfavorable zinc deposition interface that causes poor cycling stability.Herein,we report a Cu-Zn alloy network-modulated zinc deposition interface to achieve stable anode-free ZIBs.The alloy network can not only stabilize the zinc deposition interface by suppressing 2D diffusion and corrosion reactions but also enhance zinc plating/stripping kinetics by accelerating zinc desolvation and nucleation processes.Consequently,the alloy network-modulated zinc deposition interface realizes high coulombic efficiency of 99.2%and high stability.As proof,Zn//Zn symmetric cells with the alloy network-modulated zinc deposition interface present long operation lifetimes of 1900 h at 1 m A/cm^(2)and 1200 h at 5 m A/cm^(2),significantly superior to Zn//Zn symmetric cells with unmodified zinc deposition interface(whose operation lifetime is shorter than 50 h),and meanwhile,Zn3V3O8cathodebased ZIBs with the alloy network-modified zinc anodes show notably enhanced rate capability and cycling performance than ZIBs with bare zinc anodes.As expected,the alloy network-modulated zinc deposition interface enables anode-free ZIBs with Zn3V3O8cathodes to deliver superior cycling stability,better than most currently-reported anode-free ZIBs.This work provides new thinking in constructing high-performance anode-free ZIBs and promotes the development of ZIBs.

In-situ construction of high-mechanical-strength and fast-ion-conductivity interphase for anode-free Li battery

The solid electrolyte interphase(SEI)with strong mechanical strength and high ion conductivity is highly desired for Li metal batteries,especially for harsh anode-free batteries.Herein,we report a pragmatic approach to the in-situ construction of high-quality SEI by applying synergistic additives of Li NO_(3)and ethylene sulfite(ES)in the electrolyte.The obtained SEI exhibits a high average Young’s modulus(9.02GPa)and exchanging current density(4.59 mA cm^(-2)),which are 3.0 and 1.2 times as large as those using the sole additive of LiNO_(3),respectively.With this improved SEI,Li-dendrite growth and side reactions are effectively suppressed,leading to an ultra-high Coulombic efficiency(CE)of 99.7%for Li plating and stripping.When applying this improved electrolyte in full cells,it achieves a high capacity retention of 89.7%for over 150 cycles in a LiFePO_(4)||Li battery(~12 mg cm^(-2)cathode,50μm Li)and of 44.5%over 100 cycles in a LiFePO_(4)||Cu anode-free battery.

Iodine Promoted Ultralow Zn Nucleation Overpotential and Zn-Rich Cathode for Low-Cost, Fast-Production and High-Energy Density Anode-Free Zn-Iodine Batteries

The anode-free design is a promising strategy to increase the energy density of aqueous Zn metal batteries(AZMBs).However,the scarcity of Zn-rich cathodes and the rapid loss of limited Zn greatly hinder their commercial applications.To address these issues,a novel anode-free Zniodine battery(AFZIB)was designed via a simple,low-cost and scalable approach.Iodine plays bifunctional roles in improving the AFZIB overall performance:enabling high-performance Zn-rich cathode and modulating Zn deposition behavior.On the cathode side,the ZnI_(2) serves as Zn-rich cathode material.The graphene/polyvinyl pyrrolidone heterostructure was employed as an efficient host for ZnI_(2) to enhance electron conductivity and suppress the shuttle effect of iodine species.On the anode side,trace I_(3)^(−) additive in the electrolyte creates surface reconstruction on the commercial Cu foil.The in situ formed zincophilic Cu nanocluster allows ultralow-overpotential and uniform Zn deposition and superior reversibility(average coulombic efficiency>99.91% over 7,000 cycles).Based on such a configuration,AFZIB exhibits significantly increased energy density(162 Wh kg^(−1)) and durable cycle stability(63.8% capacity retention after 200 cycles)under practical application conditions.Considering the low cost and simple preparation methods of the electrode materials,this work paves the way for the practical application of AZMBs.

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.

Dynamically lithium-compensated polymer artificial SEI to assist highly stable lithium-rich manganese-based anode-free lithium metal batteries

Owing to the unique structure,anode-free lithium metal batteries(AFLMBs)have higher energy density and lower production cost than traditional lithium metal batteries(LMBs)or lithium-ion batteries(LIBs),However,AFLMBs suffer from an inherently finite Li reservoir and exhibit poor cycle stability,low Coulombic efficiency(CE)and severe dendrite growth.In this work,polydiallyl lithium disulfide(PDS-Li)was successfully synthesized and coated on Cu current collector by electrochemical polymerization.The PDS-Li acts as an additional lithium resource to compensate for the irreversible loss of lithium during cycling.In addition,the special structure and lithiophilicity of PDS-Li contribute to lower nucleation overpotential and uniform lithium deposition.When coupled with Li-rich manganese-based(LRM)cathode of Li1.2Mn0.54Ni0.13Co0.13O2,the anode-free full cell exhibits significantly improved cycle stability over 100 cycles and capacity retention of 63.3%and 57%after 80 and 100 cycles,respectively.We believe that PDS-Li can be used to ensure stable cycling performance and high-energy-density in AFLMBs.

Single-atomic Zn-(C/N/O)lithiophilic sites induced stable lithium plating/stripping in anode-free lithium metal battery

For anode-free lithium metal battery,lithiophilic surface modification on the current collector can effectively reduce the lithium nucleation barrier,so as to regulate the electrodeposition of lithium.Here,atomically dispersed Zn-(C/N/O)lithiophilic sites in the amorphous carbon medium were introduced onto Cu by an in-situ induced ion coordination chemistry strategy to get the modified Zn@NC@RGO@Cu current collector.X-ray absorption spectroscopy(XAS)combined with scanning transmission electron microscopy in high angle annular dark field(STEM-HAADF)analysis proved the single atomic state of the zinc sites surrounded by C,N,and O with a coordination number of~3.According to the electrochemical tests and first principle calculations,the ultra-uniformly dispersed Zn-(C/N/O)sites at the atomic level can effectively improve the lithium affinity,reduce the energy barrier for lithium nucleation,homogenize the lithium nucleation,and enhance an inorganic lithium compounds rich solid electrolyte interphase layer.As a result,the nucleation overpotential of lithium on the modified current collector was reduced to 7.7 mV,which was 5.4 times lower than that on bare Cu.Uniform lithium nucleation and deposition enabled stable Li plating/stripping and elevated Coulombic efficiency of 98.95%in Li||Cu cell after>850 cycles.Capacity retention of 89.7%was successfully achieved in the anode-free lithium metal battery after 100 cycles.

Zinc battery goes to anode-free

The zinc(Zn)batteries have challenges include uncontrollable dendritic growth,unreasonable negative to positive ratio and limited areal capacity.This highlight presents the latest development to resolve the uncontrollable Zn dendrite formation at high areal capacities of 200 mAh·cm^(-2) through a two-dimensional metal/metal-Zn alloy heterostructured interface.The anode-free Zn batteries with an attractive and practical pouch cell energy density of 62 Wh·kg^(-1) enlighten an arena towards their commercialization.

Microstructural evolution in lithium plating process and its effect on the calendar storage life

The growing demand for electric vehicles highlights the need for energy storage solutions with higher densities,spotlighting Li metal anodes as potential successors to traditional Li-ion batteries(LIBs).Achieving longer calendar aging life for Li metal anodes is crucial for their practical use,given their propensity for corrosion due to a low redox potential,which leads to compromised cycling stability and significant capacity loss during storage.Recent research investigated that this susceptibility is mainly dependent on the surface area of Li metal anode and the properties of the solid electrolyte interphase(SEI),particularly its stability and growth rate.Our research adds to this understanding by demonstrating that the amount of Li plating is a key factor in its corrosion during open-circuit storage,as assessed across various electrolytes.We discovered that increasing the Li plating amount effectively reduces Coulombic efficiency(C.E.)loss during aging,due to a lower surface area-to-Li ratio.This implies that the choice of electrolyte for optimal storage life should consider the amount of Li plating,with higher capacities promoting better storage characteristics.

Anode-less all-solid-state batteries:recent advances and future outlook

While all-solid-state batteries have built global consensus with regard to their impact in safety and energy density,their anode-less versions have attracted appreciable attention because of the possibility of further lowering the cell volume and cost.This perspective article summarizes recent research trends in anode-less all-solid-state batteries(ALASSBs)based on different types of solid electrolytes and anticipates future directions these batteries may take.We particularly aim to motivate researchers in the field to challenge remaining issues in ALASSBs by employing advanced materials and cell designs.

Design Principle,Optimization Strategies,and Future Perspectives of Anode‑Free Configurations for High‑Energy Rechargeable Metal Batteries

Metal anodes(e.g.,lithium,sodium and zinc metal anodes)based on a unique plating/stripping mechanism have been well recognized as the most promising anodes for next-generation high-energy metal batteries owing to their superior theoretical specific capacities and low redox potentials.However,realizing full utilization and the theoretical capacity of metal anodes remains challenging because of their high reactivity,poor reversibility,and nonplanar metal evolution patterns,which lead to irreversible loss of active metals and the electrolyte.To minimize the above issues,excess metal sources and flooded electrolytes are generally used for laboratory-based studies.Despite the superior cycling performance achieved for these cells,the metal-anode-excess design deviates from practical applications due to the low anode utilization,highly inflated coulombic efficiency,and undesirable volumetric capacity.In contrast,anode-free configurations can overcome these draw-backs while reducing fabrication costs and improving cell safety.In this review,the significance of anode-free configurations is elaborated,and different types of anode-free cells are introduced,including reported designs and proposed feasible yet unexplored concepts.The optimization strategies for anode-free lithium,sodium,zinc,and aluminum metal batteries are summarized.Most importantly,the remaining challenges for extending the cycle life of anode-free cells are discussed,and the requirements for anode-free cells to reach practical applications are highlighted.This comprehensive review is expected to draw more attention to anode-free configurations and bring new inspiration to the design of high-energy metal batteries.