Suppress Dendrite Growth Research Articles

Synchronous Healing of Li Metal Anode via Asymmetrical Bidirectional Current.

SummaryThe creation of Li metal anodes while minimizing dendrite growth is an important challenge for developing high-energy density batteries. Dendrites can originate from an inhomogeneous charge distribution or an irregular substrate, and often, the way to suppress dendrite growth is to avoid their formation altogether (ion-uniform mechanism over a shelf time). Herein, we propose a different route to eliminate dendrite formation, called an asymmetrical bidirectional current mode (ABCM) of charging, leading to a healable Li metal anode and resulting in a positive feedback cycle. This mode allows for a stable cyclic performance and suppresses dendrite formation effectively (while holding the polarization ∼27 mV for over 1,000 h), and provides a better result than suppressing Li dendrites via weakening of the Li dendrite (ion-uniform mechanism). These results indicate that ABCM may be a promising way to stabilize the Li anode of Li metal batteries, without any chemical/physical modification of the anode.

A Dual-Functional Conductive Framework Embedded with TiN-VN Heterostructures for Highly Efficient Polysulfide and Lithium Regulation toward Stable Li-S Full Batteries.

Lithium-sulfur (Li-S) batteries are strongly considered as next-generation energy storage systems because of their high energy density. However, the shuttling of lithium polysulfides (LiPS), sluggish reaction kinetics, and uncontrollable Li-dendrite growth severely degrade the electrochemical performance of Li-S batteries. Herein, a dual-functional flexible free-standing carbon nanofiber conductive framework in situ embedded with TiN-VN heterostructures (TiN-VN@CNFs) as an advanced host simultaneously for both the sulfur cathode (S/TiN-VN@CNFs) and the lithium anode (Li/TiN-VN@CNFs) is designed. As cathode host, the TiN-VN@CNFs can offer synergistic function of physical confinement, chemical anchoring, and superb electrocatalysis of LiPS redox reactions. Meanwhile, the well-designed host with excellent lithiophilic feature can realize homogeneous lithium deposition for suppressing dendrite growth. Combined with these merits, the full battery (denoted as S/TiN-VN@CNFs || Li/TiN-VN@CNFs) exhibits remarkable electrochemical properties including high reversible capacity of 1110 mAh g-1 after 100 cycles at 0.2 C and ultralong cycle life over 600 cycles at 2 C. Even with a high sulfur loading of 5.6 mg cm-2 , the full cell can achieve a high areal capacity of 5.5 mAh cm-2 at 0.1 C. This work paves a new design from theoretical and experimental aspects for fabricating high-energy-density flexible Li-S full batteries.

Suppressing Dendrite Growth of a Lithium Metal Anode by Modifying Conventional Polypropylene Separators with a Composite Layer

Lithium metal is a promising candidate anode for next generation high energy density batteries. However, the Li dendrite growth results in electrode degradation and safety hazards, obstructing its ...

Vertically Aligned Carbon Nanofibers on Cu Foil as a 3D Current Collector for Reversible Li Plating/Stripping toward High‐Performance Li–S Batteries

AbstractA vertically aligned carbon nanofiber (VACNF) array with unique conically stacked graphitic structure directly grown on a planar Cu current collector (denoted as VACNF/Cu) is used as a high‐porosity 3D host to overcome the commonly encountered issues of Li metal anodes. The excellent electrical conductivity and highly active lithiophilic graphitic edge sites facilitate homogenous coaxial Li plating/stripping around each VACNF and forming a uniform solid electrolyte interphase. The high specific surface area effectively reduces the local current density and suppresses dendrite growth during the charging/discharging processes. Meanwhile, this open nanoscale vertical 3D structure eliminates the volume changes during Li plating/stripping. As a result, highly reversible Li plating/stripping with high coulombic efficiency is achieved at various current densities. A low voltage hysteresis of 35 mV over 500 h in symmetric cells is achieved at 1 mA cm−2 with an areal Li plating capacity of 2 mAh cm−2, which is far superior to the planar Cu current collector. Furthermore, a Li–S battery using a S@PAN cathode and a lithium‐plated VACNF/Cu (VACNF/Cu@Li) anode with slightly higher capacity (2 mAh cm−2) exhibits an excellent rate capability and high cycling stability with no capacity fading over 600 cycles.

Seed-Free Selective Deposition of Lithium Metal into Tough Graphene Framework for Stable Lithium Metal Anode.

Graphene has been wildly used as a host to suppress dendrite growth to stabilize the lithium metal anode. However, the high overpotential of lithium deposition on pure graphene has to be lowered by doping or employing precious metals. Additionally, the soft nature of graphene rendered itself to aggregate, consequently squeezing room for lithium accommodation. Herein, a tough graphene framework composed of 3D periodic hollow spheres was reported as a free-standing host to stabilize lithium metal anodes. The prepared 3D periodic hollow structure not merely reinforces the framework to maintain hollow structure under pressure caused by assembling battery, but also lowers the overpotential without the help of dopant or precious metals. It is worthy to note that high efficiency of ion diffusion, thanks to the channels interconnecting hollow spheres by holes on the walls, benefits both suppression of lithium dendrite and rate capability. The properties of low density and high mechanical strength make graphene frameworks electrode a promising lightweight Li host material, which reveals a new avenue for designing high-energy density electrode materials.

Dendrites in Lithium Metal Anodes: Suppression, Regulation, and Elimination.

With the increasing diversification of portable electronics and large-scale energy storage systems, conventional lithium-ion batteries (LIBs) with graphite anodes are now approaching their theoretical limits. Lithium metal, as the "Holy Grail" electrode for next-generation rechargeable batteries, is being revisited to meet the booming demand for high energy density electrodes due to its ultrahigh theoretical specific capacity and negative redox potential. Nevertheless, typical issues like notorious dendrite growth still hamper the bulk application of Li metal anodes. Dendrite growth renders increased surface area of the lithium metal, causing persistent depletion of the electrolyte and active materials, facilitating catastrophic failure of the battery, and even inducing fatal safety hazards. The consequences become more serious during operation at high current densities and over long cycling life. Therefore, it is urgent to suppress and even eliminate dendrite formation during the Li plating/stripping process. This Account highlights several innovative strategies for dendrite suppression, dendrite regulation, and dendrite elimination from the perspective of interface energy and bulk stresses. First, we review the fundamental mechanism of dendrite formation and growth in Li metal anodes. We show that the dendrite morphology could be substantially ameliorated, in theory, by homogenizing the electric field distribution, lowering the Li ion concentration gradient, and facilitating mechanical blocking. Next, we address the problem of dendrite suppression by applying two-dimensional (2D) materials to Li metal systems and preventing dendrite penetration through stress release and mechanical blocking. Graphene with a high specific area and vermiculite sheets (VSs) with a large physical rigidity were demonstrated to be efficacious in reinforcing Li anodes and polymer electrolytes separately. However, Li dendrite growth is a continuous process and remains inevitable with increasing current density and cycling life. Instead of suppressing dendrite growth, we focus on how to regulate homogeneous Li dendrite formation and growth. Dendrite regulation means to allow dendrite growth but take steps to transform it into Li with a smooth morphology. We introduce two main strategies to regulate Li growth: (i) guiding Li nucleation and (ii) controlling the Li growth pathways and directions. These processes greatly rely on the interface energy between the substrate and Li atoms. Elimination of the dendrites, which is the most formidable challenge for dendrite control, can also be achieved by dynamically engineering the force, such as deflecting the electric field by Lorentz force in a magnetic field, enhancing the integrated yield stress by the design of bulk nanostructured materials, and reducing the lateral Li diffusion barrier by a biomimetic co-deposition process. Solutions to the challenges of dendrite control in Li metal anodes can provide safe next-generation rechargeable lithium metal batteries that have a long cycling life. We also hope that our strategies presented in this Account can offer promise for other metal batteries.

Enabling rapid charging lithium metal-based rechargeable batteries through suppression of dendrite growth and ion depletion in the electrolyte via surface acoustic wave-driven mixing

Lithium metal is an attractive material for use as anodes in batteries due to its high energy density. However, it is unstable during recharging, with non-uniform Li deposition that leads to porosity, dendrites, rechargeable lithium metal batteries (LMB) have been unrealistic for fifty years with serious safety problems. Over this time, research on chemistry modifications have produced modest improvements, but none that have justified considering LMB over lithium-ion batteries in rechargeable applications. Nonuniform Li deposition during charging occurs due to a Li ion depletion layer adjacent to the anode, especially at high charge rates. By including a small surface acoustic wave device (SAW) into the LMB that produces intense acoustic waves in the electrolyte, rapid submicron boundary layer mixing flow may be generated during charging. This flow largely eliminates the Li ion depletion layer, and because the SAW device is small, solid state, and requires only 10 mW h/cm2 during battery charging, there is a realistic possibility of incorporating this technology into current batteries under consideration for an electric vehicle, consumer device, and medical applications. The elimination of the ion depletion layer furthermore allows high-rate charging, as we will demonstrate in our electrochemistry and morphological results. The underlying physics will be explained using a closed-form model formed from intermediate asymptotics, and will show the crucial impact of the Peclet number in avoiding the ion depletion layer.

A Lightweight 3D Cu Nanowire Network with Phosphidation Gradient as Current Collector for High-Density Nucleation and Stable Deposition of Lithium.

Lithium metal anodes with high energy density are important for further development of next-generation batteries. However, inhomogeneous Li deposition and dendrite growth hinder their practical utilization. 3D current collectors are widely investigated to suppress dendrite growth, but they usually occupy a large volume and increase the weight of the system, hence decreasing the energy density. Additionally, the nonuniform distribution of Li ions results in low utilization of the porous structure. A lightweight, 3D Cu nanowire current collector with a phosphidation gradient is reported to balance the lithiophilicity with conductivity of the electrode. The phosphide gradient with good lithiophilicity and high ionic conductivity enables dense nucleation of Li and its steady deposition in the porous structure, realizing a high pore utilization. Specifically, the homogenous deposition of Li leads to the formation of an oriented texture on the electrode surface at high capacities. A high mass loading (≈44 wt%) of Li with a capacity of 3 mAh cm-2 and a high average Coulombic efficiency of 97.3% are achieved. A lifespan of 300 h in a symmetrical cell is obtained at 2 mA cm-2 , implying great potential to stabilize lithium metal.

High Dielectric, Robust Composite Protective Layer for Dendrite‐Free and LiPF6 Degradation‐Free Lithium Metal Anode

AbstractThe development of lithium metal anodes for next generation batteries remains a challenge. Uncontrolled Li dendrite growth not only induces severe safety issues but also leads to capacity fading by continuously consuming the electrolyte. This study demonstrates the design and fabrication of a composite protective layer composed of a high dielectric polymer, inorganic particles, and an electrolyte to overcome these obstacles. This layer not only suppresses dendrite growth, but also prevents LiPF6 degradation. The electrolyte introduced in the protective layer remains within the coating layer after solvent removal and acts as an ion transport channel at the interface. This enables the protective layer to exhibit high ionic conductivity and mechanical strength. The composite protective layer, which exhibits synergistic soft‐rigid characteristics, is placed on the Li metal anode and facilitates superior interfacial stability during long‐term cycles. LiMn2O4/coated lithium full cells using the composite protective layer show a superior rate capability and enhanced capacity retention compared to the cells using a bare lithium anode. The proposed strategy opens new avenues to fabricate a sustainable composite protective layer that affords superior performance in lithium metal batteries.

Improvement of the Li Dissolution/Deposition Reversibility Under Oxygen Atmosphere By Employment of LiNO3⁻based Electrolyte

Introduction Rechargeable non-aqueous Li-air batteries (LABs) have attracted much attention as one of the next-generation batteries because of their potential for possessing large specific energy (theoretical value: 3.5 kWh kg-1) more than 5 times of those of Li-ion batteries [1]. For practical use, some technical problems have to be overcome; during discharging, the choking of air electrode by the Li2O2 generated; during charging, the requirement of applying high overpotential for the electrochemical oxidation of Li2O2 or the short circuit of LAB cells caused by Li dendrite growth on Li electrode. Li dissolution/deposition reactions using various Li salts, solvents, and additives have been investigated under oxygen free condition, which is far from practical use, to find that the repetition of the reaction provides Li deposition on Li electrode non-uniformly with clear boundary. This is probably caused by the chemical composition and uniformity of the solid electrolyte interphase (SEI) films formed on Li electrode. Such Li deposition can raise the problems mentioned above. These remaining problems, moreover, restrict the Li dissolution/deposition reactions only at low depth of charge/discharge though LABs are promising due to their large specific energy. We have reported that the presence of oxygen improved the Li dissolution/deposition reversibility, due to the formation of proper SEI films [2]. In this study, focusing on not only presence of oxygen gas but also LiNO3-based electrolyte [3], we evaluated the reversibility of Li | Li symmetric cell and Li-air (Li | O2) cell at relatively high state of charge/discharge. Experimental Li | Li symmetric cells was constructed with Li metal foils (thickness：0.5 mm) used for both electrodes, a separator (Celgard 2400), and 1.0 M glyme-based electrolytes containing LiSO3CF3 (LiOTf), LiN(SO2CF3)2 (LiTFSI) or LiNO3 in an Ar-filled dry box. Li-air (Li | O2) cells were constructed in the similar method but Ketjen Black-loaded carbon paper was used as an air electrode, the positive electrode. Li dissolution/deposition tests were conducted under Ar or O2 atmosphere. The applied current density and maximum discharge/charge capacity were 0.20 mA cm−2 and 2.0 mAh cm−2 (corresponding to 10 μm of Li dissolution/deposition), respectively, in the cut off voltage range of −2.0 to 2.0 V. The Li metal electrodes after 15 cycles of the tests were rinsed with tetraglyme to remove Li salts, and the obtained electrodes were analyzed using scanning electron micrograph (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) to characterize the resulting SEI films. Results and Discussion Fig. 1 showed the surface and cross-sectional SEM images of Li electrodes of Li | Li symmetric cells after 15 cycles of Li dissolution/deposition reactions at 2.0 mAh cm−2. In the case of LiTFSI-based electrolyte, oxygen suppressed crack and Li dendrite growth (thick deposition) compared to oxygen free condition. In addition, oxygen suppressed the decomposition of the electrolyte, LiOTf tetraglyme solution, and enhanced the deposition of Li2O, which works as a protective layer, though rather non-uniformly. These are indicated by chemical compositions determined by EDS (F and S contents are lower under oxygen atmosphere) and XPS spectra (O1s, Li1s, C1s, and F1s spectra). In the case of LiNO3-based electrolyte under oxygen, larger overpotential was observed than that in the case of LiOTf and LiTFSI but the suppression of dendrite growth and the uniform Li2O deposition were observed on the Li electrodes. These must contribute to improve the reversibility. The similar tendency was also observed for Li-air (Li | O2) cells. The cell using LiNO3 tetraglyme solution as an electrolyte showed the suppression of Li dendrite growth and the uniform deposition of Li2O, though the charge/discharge reversibility was slightly improved in this experimental condition. These results can be associated with the formation of uniform Li2O protective layer on Li negative electrode, probably promoted by NO3 -: NO3 -+ 2Li →NO2 -+ Li2O [4]. Of particular note is that these Li dissolution/deposition reactions using LiNO3-based electrolyte, which showed the suppression of Li dendrite growth and the uniform deposition of Li2O, were performed at high depth of charge/discharge, where the thickness of dissolved/deposited layer reached about 10 μm, comparable to practical use.

A New Developed Fluorinated Electrolyte for Anode-Free Lithium Metal Battery

The glob is in need of efficient energy storage materials with an affordable cost, better energy density, safe and extended cycle life. To this end, scholars are investigating an alternative idea to boost the energy density, safety and minimize cost to satisfy the need of the society. One of the new ideas is the use of alternative design such as anode-free rechargeable lithium metal battery. In anode-free, the absence of Li+ host anode material reduces the cell weight and space required for the anode as a result; energy density of the cell will therefore be, significantly larger compared to the conventional Li-ion batteries. Nevertheless, realizing this anode-free battery in practical applications is still handicapped. The major reason for the failure of this system is depletion of the active Li and consumption of electrolyte solvents during repair of the solid electrolyte interphase. To mitigate this issue developing a functional electrolyte is therefore the key solution to bring it into practical application. Therefore, here we developed cost effective, highly fluorinated interphases forming new electrolyte solution of carbonate-ether mixed fluorinated electrolyte design with the standardized commercial salt LiPF6 which is stable at wider potential (2.5-4.5 V). The designed electrolyte suppresses dendrite growth, form conductive and stable LiF dominated solid electrolyte interface (SEI) for anode-free lithium metal battery using Cu‖LiNi0.3Mn0.3Co0.3O2. It shows stable cyclic performance with high average Coulombic efficiency > 98.7 % and high retention capacity for long cycles with 0.5 mA/cm2 current density both in the anode free system and NMC/MCMB full cell. The enhanced cycle life and well retained in capacity using the as-prepared electrolyte is mainly because of the synergistic effect of the partially fluorinated carbonated and ether based functional groups in which on contributes to the higher voltage and the other contributes to the higher efficiency. This is electrolyte combination is new and the best electrolyte ever reported for anode-free lithium metal battery to our knowledge. Keywords: SEI ; anode-free Lithium metal battery ; carbonate-ether mixed solvent ; copper foil, Fluorinated Interphase

An Interfacial Layer Based on Polymers of Intrinsic Microporosity to Suppress Dendrite Growth on Li Metal Anodes

The performance and safety of lithium (Li) metal batteries can be compromised owing to the formation of Li dendrites. Here, the use of a polymer of intrinsic microporosity (PIM) is reported as a feasible and robust interfacial layer that inhibits dendrite growth. The PIM demonstrates excellent film-forming ability, electrochemical stability, strong adhesion to a copper metal electrode, and outstanding mechanical flexibility so that it relieves the stress of structural changes produced by reversible lithiation. Importantly, the porous structure of the PIM, which guides Li flux to obtain uniform deposition, and its strong mechanical strength combine to suppress dendrite growth. Hence, the electrochemical performance of the anode is significantly enhanced, promising excellent performance and extended cycle lifetime for Li metal batteries.

Combining polymeric membranes with inorganic woven fabric: Towards the continuous and affordable fabrication of a multifunctional separator for lithium-ion battery

The close relationship between separators and the performances of lithium-ion batteries (LIBs) has motivated considerable R&D passions. However, commercial polyolefin-based separators are often limited by their inferior electrolyte wettability and poor thermal stability, whilst advanced polymeric/inorganic separators are confined in laboratory due to the use of expensive starting materials and complicated manufacture process. Here we report a sandwich separator fabricated by continuously sandwiching a glass fiber fabric with two layers of polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) microporous membranes. SiO2 powders are incorporated in the middle layer to improve thermal stability and suppress dendrite growth. The separator inherits not only robust mechanical strength (≥20 MPa) and thermal stability (against both long-term heating and combustion) from inorganic fabric, but also high porosity and electrolyte affinity (electrolyte uptake ~369%) from polymeric membrane, thus possessing extraordinary electrochemical performances. The existence of SiO2 powders further extends the service life of LIB, in that the discharge capacity retains at 157.7 mA hg−1 after 100 cycles at 1.0C. More attractively, fabrication of such separators does not require a tedious procedure or sophisticated equipment, and all materials involved are of affordable price, making us anticipate the great commercial potential of this sandwich separator.

Good riddance, dendrites

Understanding dendrite formation is key to advancing high-energy-density and safe metallic lithium batteries. With the help of cryogenic electron microscopy, heat is now suggested to play a crucial role in stabilizing lithium metal electrodes by suppressing dendrite growth.

In Situ NMR Studies of Li Microstructure Formation

Lithium metal is an attractive anode for next-generation, high-energy batteries but it suffers from both capacity fading and safety problems associated with microstructural and dendritic growth. A detailed understanding of the fundamental processes that lead to an uneven Li deposition is necessary to develop new and effective strategies to mitigate dendrite growth. The morphology of Li deposits is highly dependent on the choice of electrolyte system with improved cycling performance attributed to a more uniform, robust and conductive solid electrolyte interphase (SEI). [1] In this work we use in situ nuclear magnetic resonance (NMR) spectroscopy in combination with electrochemical characterisation techniques and scanning electron microscopy (SEM). With in situ NMR we are able to monitor and quantify the microstructures that form during lithium deposition. As a result of the ‘skin depth issue’ of metals, that is the electromagnetic RF field excites only the surface of the Li metal, NMR is a sensitive and quantitative method for microstructure formation.[2] Furthermore, the resonance of the microstructural peak gives an indication of the morphology of the growing deposits. [3] This allows for an effective comparison of different electrolyte systems and lithium plating conditions. [2,3] Superconcentrated electrolytes are investigated in detail as their suppression of dendrite growth has been reported in many studies. [1,4] Different electrochemical cycling parameters are investigated including the relatively unexplored method of applying pulsed current as to ascertain the role of the concentration gradients in the SEI layer. Reference s : [1] Liu, B. et al. Joule 2, 833–845 (2018). [2] Bhattacharyya, R. et al. Nat. Mater. 9, 504–510 (2010). [3] S. Chandrashekar, et al. Nat. Mater. 11, 311-315 (2012). [4] Qian, J. et al. Nano Energy 15, 135–144 (2015).

Ion Transport Mechanism in Polymer Electrolytes - Bridging the Scales Via Molecular Simulations and Theory

Solid polymer electrolytes (SPEs) consisting of a salt in a polymer matrix are considered as safe alternatives to liquid electrolytes. However, at ambient temperatures, their conductivity is still too low for an efficient use in modern energy storages. To overcome this deficiency, several strategies have been proposed. For instance, it was demonstrated that the addition of a low-molecular-weight additive such as an ionic liquid (IL) results in improved transport properties [1]. To unravel the mechanisms how the ion transport is enhanced at the molecular level, molecular dynamics (MD) simulations are an extremely powerful tool. In case of classical SPEs based on poly(ethylene oxide) (PEO), three different microscopic transport mechanisms can generally be identified from MD simulations [2]: First, diffusion of coordinating lithium ions along the PEO backbone, second, cooperative motion of the ions with the PEO dynamics, and third, ion transfer processes between distinct PEO chains (see sketch). However, due to the limited size of the simulation system (in particular the length of the polymer chains), the comparison between experiments and the numerical data alone can be made only qualitatively. To bridge the gap between the different length and time scales characteristic for experiments and simulations, we devised an analytical framework based on polymer theory that allows us to extrapolate the numerical data to experimental scales. To illustrate this concept, we demonstrate that the way in which an IL may enhance the lithium mobility can in principle be twofold: First, the IL can act as a plasticizer, enhancing the dynamics of the polymer segments and thus also the motion of the attached lithium ions [3,4], and second, for specifically designed IL molecules that directly coordinate to the lithium ions (such as pyrrolidinium ions with chemically bound oligoether chains [5]), the IL may serve as a molecular shuttle detaching the lithium ions from the slow polymer chains [6], resulting in a much larger enhancement of the lithium ion transport. In a second step, we focus on SPEs based on diblock copolymers, consisting of a mechanically stable block and an ionically conducting PEO domain. Due to their increased overall rigidity, these electrolytes tend to suppress dendrite growth more efficiently, and thus are considered to be key candidates for lithium metal batteries. Special emphasis is again placed on the role of low-molecular-weight additives that recently have been studied experimentally [7], and on their impact on the molecular transport mechanism. [1] M. Joost, M. Kunze, S. Jeong, M. Schönhoff, M. Winter, S. Passerini, Electrochim. Acta 2012, 86, 330-338[2] D. Diddens, A. Heuer, O. Borodin, Macromolecules 2010, 43(4), 2028-2036[3] D. Diddens, A. Heuer, ACS Macro Lett. 2013, 2(4), 322-326[4] D. Diddens, A. Heuer, J. Phys. Chem. B 2014, 118(4), 1113-1125[5] J. von Zamory, G. A. Giffin, S. Jeremias, F. Castiglione, A. Mele, E. Paillard, S. Passerini, Phys. Chem. Chem. Phys. 2016, 18(31) 21539-21547[6] D. Diddens, E. Paillard, A. Heuer, J. Electrochem. Soc. 2017, 164(11), E3225-E3231[7] T. S. Dörr, A. Pelz, P. Zhang, T. Kraus, M. Winter, H.-D. Wiemhöfer, Chem. Eur. J. 2018, 24(32), 8061-8065 Figure 1

Uniform nucleation of sodium in 3D carbon nanotube framework via oxygen doping for long-life and efficient Na metal anodes

The Na metal anode has long been considered as one of the most promising anode types due to its high theoretical capacity and its having the lowest electrochemical potential. Safety concerns, low efficiency, and large volume changes are severe hurdles blocking its practical application, however, especially in the case of high areal capacity. Herein, an oxygen-doped carbon nanotube framework (a-CNTs) obtained after acidification has been adopted as the Na plating matrix to regulate the homogeneous nucleation of Na metal and suppress dendrite growth. The oxygenic functional groups on the carbon nanotubes induce them “sodiophilic”, which guides the homogeneous nucleation and uniform deposition of Na. In addition, the cross-conductive network and high specific surface area of a-CNTs further enhance the electrochemical performances. As a result, a-CNTs have enabled reversible plating/stripping for 1000 cycles with coulombic efficiency of 99.8% at 3 mA cm−2 for 1 mA h cm−2. Furthermore, the symmetrical cells could run stably for 1650 cycles at 3 mA cm−2 for 1 mA h cm−2, and even could run for more than 300 h at 5 mA cm−2 at 8 mA h cm−2, which has rarely been achieved under such aggressive working conditions.

Interface Engineering on Solid-State Ceramic Electrolyte By Graphene-like Coating for Electrochemically Stable Sodium Metal Batteries

Rechargeable sodium (Na) based battery can be a cost-effective successor of lithium (Li) ion battery owing to the natural abundance of Na resource and high capacity of metallic Na anode. However, liquid electrolytes pose critical safety issue that arises from their flammable organic solvent component and Na dendrite formation upon repeated electrochemical charge/discharge cycles. Solid electrolytes not only can eliminate the abovementioned safety concerns, they can also enhance electrochemical stability, broaden operating temperature range and prolong cycling life. One of the greatest challenges for solid electrolyte is the large interfacial resistance between electrolyte and electrode. Various optimization techniques for reducing interfacial resistance have been reported. Nevertheless, all-solid-state batteries still face stagnant advancements due to the limited effectiveness. Na3Zr2Si2PO12 (NASICON) ceramic electrolyte remains to be a promising solid-state electrolyte for Na batteries because of its high ionic conductivity and excellent electrochemical and thermal stability. However, the pairing of pristine NASICON with high-capacity metallic Na anode gives rise to large NASICON/Na interfacial resistance and poor interface wettability that result in non-uniform Na+ flux across the interface. Specifically, Na+ ions tend to plate preferentially along the grain boundaries of NASICON where the Na+ flux is locally intensified, leading to detrimental dendrite-like nucleation on Na anode over repeated charge/discharge cycles. Theoretically, a homogeneous and stable interlayer with superior Na anode compatitability and ion conductivity can facilitate uniform Na+ flux across the interface, therefore effectively decrease the interfacial resistance and suppress unregulated dendrite-like Na formation during cycling. Past research efforts to implement such an interlayer on ceramic electrolyte include the employment of polymer layer, applying molten metal on ceramic electrolyte, and coating a layer of metal oxide using relatively expensive method of atomic layer deposition. This motivated us to solve the challenges of large interfacial resistance and non-uniform plated Na for solid-state Na metal batteries through a facile and scalable approach. Graphene, with its unique properties of chemical inertness, mechanical flexibility and structural rigidness, has attracted great interests in various energy storage applications. Recent study demonstrated the use of ultrathin graphene film coating on Na metal as a stable artificial solid electrolyte interphase (SEI) layer in conventional liquid electrolyte to suppress the dendrite growth, in which the graphene defects network act as an efficient Na+ transport pathway. Therefore, graphene can be a promising interlayer for solid-state Na metal batteries to improve Na+ conductivity between the ceramic electrolyte and Na metal. The abundantly distributed defects network on graphene-like interlayer can enable uniform Na+ flux across the electrode/electrolyte interface, circumventing the preferential Na metal plating along the grain boundaries of NASICON and therefore suppress dendrite growth. However, direct growth of graphene on ceramic electrolyte has not yet been reported, largely due to the non-catalytic nature of ceramic electrolyte. In this work, we report the direct growth of ultrathin graphene-like layer on NASICON ceramic electrolyte, hereafter referred as G-NASICON, to significantly decrease the interfacial resistance, improve Na plating/stripping cycling stability and enable uniform Na plating and minimize the unregulated dendrite-like Na formation on Na anode after repeated stripping/plating cycles. Graphene growth on NASICON was carried out in a chemical vapor deposition system. CVD growth of graphene materials towards energy-related applications is highly attractive due to the outstanding properties of graphene materials, as well as the scalability of CVD method. The formation mechanism of graphene-like layer on the ceramic substrate is based on the carbothermic reduction occurring at ceramic surface to initiate nucleation and growth. Optimized graphene-like layer on NASICON effectively decreases the NASICON/Na interfacial resistance more than ten-fold, from 524 Ω cm2 to 46 Ω cm2. The Na/G-NASICON/Na symmetric cells delivered remarkably stable Na stripping/plating cycling behavior at a current density of 1 mA/cm2 with 1 mAh/cm2 capacity over 1000 hours that, to the best of our knowledge, represents the best performance in solid-state Na symmetric cell systems. The surface of Na electrode after 1000 hours of cycling obtained from Na/G-NASICON/Na remained smooth because of uniform Na+ flux across graphene-coated-NASICON/Na interface enabled by the abundant graphene defects network for efficient Na+ transport. Solid-state room temperature battery consists of graphene-regulated NASICON electrolyte, Na3V2(PO4)3 cathode and Na anode delivered a reversible initial capacity of 108 mAh/g at 1C current density for 300 cycles with 85% capacity retention, far superior than the battery with pristine NASICON. This work can be a valuable contribution towards a safe and stable solid-state Na metal battery system, and provide insights for solid-state lithium metal batteries as well.

A high-performance lithium anode based on N-doped composite graphene

Lithium (Li) metal is the most promising electrode for next-generation rechargeable batteries. In order to push the commercialization of the lithium metal batteries, a kind of nitrogen(N)-doped composite graphene (NCG) adopted as the Li plating host was prepared to regulate Li metal nucleation and suppress dendrite growth. Furthermore, a new kind of sandwich-type composite lithium metal (STCL) electrode was developed to improve its application. The STCL electrode can be used as convenient as a piece of Li foil but no dendrite growth. In a symmetric battery, the STCL electrode cycled for more than 4500 h with the overpotential of less than 40 mV. And due to the creative design, the STCL promises the Li–S battery with a prolonged cycling lifespan.

The effects of anode additives towards suppressing dendrite growth and hydrogen gas evolution reaction in Zn-air secondary batteries

In our continual effort to develop a cost effective rechargeable Zn-air batteries, herewith, we demonstrated Zn anodes comprising of (i) 30 wt.% Zn: 3 wt.% bismuth oxide: 10 wt.% potassium sulfide (ZBK), (ii) 30 wt.% Zn: 3 wt.% bismuth oxide: 5 wt.% lead (II) oxide (ZBP), and (iii) 30 wt.% Zn: 3 wt.% bismuth oxide: 10 wt.% potassium sulfide: 5 wt.% lead (II) oxide additives (ZBKP) in 6 M KOH aqueous solutions and 1.88 wt.% polyacrylic acid as the gelling agent. KOH gel constituted the remaining mass of the anode wt.%. Results were confirmed via cycle voltammetry (CV), Tafel, electrochemical impedance spectroscopy (EIS), etc., measurements. Among the various Zn anodes analyzed, ZBKP showed a superior cathodic peak of − 1.805 and 1.950 V vs. Hg/HgCl at 5th and 40th cycles during electrochemical cycle voltammetry. Tafel fitting on linear polarization test shows that ZBK exhibits the highest corrosion behavior followed by ZBP while ZBKP has the lowest corrosion behavior with an estimated corrosion inhibition efficiency of 36.06%. Furthermore, ZBKP displays the lowest dendrite growth, least corrosion rate, and superior capacity even at 60th cycles compared to ZBK and ZBP. In view of our finding, ZBKP has a higher positive electrode potential compare to ZBK and ZBP electrodes. Thus, ZBKP is the most suitable for aqueous battery due to its low minimal side effect. Field emission-scanning electron microscopy/energy dispersive x-ray spectroscopy (FE-SEM/EDS) images confirm that the various elemental additives were evenly deposited on the Zn anode surface. Ex situ spectroscopy and electrochemical performance studies also verified that the dendrite-free nature of improved Zn anode and the modified interfaces between electrolyte and Zn play vital roles towards advancing the energy storage performance. With all this indices and yard stick, the level of improvement we demonstrated in this current study is attractive for the design of an advanced secondary zinc-air batteries.