Unstable Solid Electrolyte Interphase Layer Research Articles

Effect of Water–Soluble Polyimide (w-PI) Type Binders on the Performance of High-Capacity Silicon Anodes of Lithium-Ion Batteries

In order to enhance rapid charging and driving range for electric vehicles, the high-capacity of lithium-ion batteries (LIBs) is imperative. Commercially available graphite as an anode material has long cycle life, abundance, and low cost. However, it has a limitation in its theoretical specific capacity (372 mAh g−1).To overcome this limitation, much attention has been paid to silicon (Si), which offers a high theoretical specific capacity of 4,200 mAh g−1. Nevertheless, silicon suffers from excessive volume expansion, resulting in issues such as pulverization of active alloy particles, delamination, and the formation of an unstable Solid Electrolyte Interphase layer. This lead to a limitation to use the silicon in large amount in an electrode. A polymeric binder has a critical role in improving the high-capacity Si anode. Conventional polyimide (PI), one of various super-engineering plastics, was applied to the Si anodes, but it is still challenged to water-insolublity and high temperature imidization process around 300 oC. In this study, a water-soluble PI (w-PI) is designed by the polycondensation between dianhydrides and diamine in water environment. In addition, a relatviely low-temperature imidization temperature below 200 oC will be appled by the introduction of dimethylimidazole. This study will briefly outline the direction for implementing a w-PI binder and improving electrochemical performance of high-capacity anode compared to conventional binders such as PVdF and CMC/SBR. Keyword: high-capacity Si anode; dianhydrides and diamine; Polyimide (PI); and water-soluble PI Figure 1

The Influence of Cathode Degradation Products on the Anode Interface in Lithium-Ion Batteries.

Degradation of cathode materials in lithium-ion batteries results in the presence of transition metal ions in the electrolyte, and these ions are known to play a major role in capacity fade and cell failure. Yet, while it is known that transition metal ions migrate from the metal oxide cathode and deposit on the graphite anode, their specific influence on anode reactions and structures, such as the solid electrolyte interphase (SEI), is still quite poorly understood due to the complexity in studying this interface in operational cells. In this work we combine operando electrochemical atomic force microscopy (EC-AFM), electrochemical quartz crystal microbalance (EQCM), and electrochemical impedance spectroscopy (EIS) measurements to probe the influence of a range of transition metal ions on the morphological, mechanical, chemical, and electrical properties of the SEI. By adding representative concentrations of Ni2+, Mn2+, and Co2+ ions into a commercially relevant battery electrolyte, the impacts of each on the formation and stability of the anode interface layer is revealed; all are shown to pose a threat to battery performance and stability. Mn2+, in particular, is shown to induce a thick, soft, and unstable SEI layer, which is known to cause severe degradation of batteries, while Co2+ and Ni2+ significantly impact interfacial conductivity. When transition metal ions are mixed, SEI degradation is amplified, suggesting a synergistic effect on the cell stability. Hence, by uncovering the roles these cathode degradation products play in operational batteries, we have provided a foundation upon which strategies to mitigate or eliminate these degradation products can be developed.

Hybrid Dynamic Covalent Network-Based Protecting Layer for Stable Li-Metal Batteries.

Metallic lithium (Li) is considered as the "Holy Grail" anode material for next-generation energy storage systems due to its extremely high theoretical capacity and low electrochemical potential. Before the commercialization of the Li electrode, dendritic Li growth and the unstable solid electrolyte interphase layer should be conquered. Herein, a hybrid covalent adaptable polymer network (HCAPN) is prepared via the random copolymerization of poly(ethylene glycol) methyl ether methacrylate and -acetoacetoxyethyl methacrylate, followed by chemical cross-linking with polyethylenimine (PEI) and amine-modified silicon dioxide (SiO2). Such a hybrid network, where PEI and amine-modified SiO2 formed a vinylogous urethane-based dynamic covalent bond with the copolymer, respectively, shows improved mechanical properties, solvent resistance, and excellent healability/recyclability. As the protecting layer on the Li electrode, the assembled HCAPN@Li||HCAPN@Li symmetric cell shows a long cycle life of 800 h with low overpotential at a current density of 1 mA cm-2, and superior electrochemical performance can be achieved in the HCAPN@Li||LiFePO4 full cell (capacity retention of 77% over 400 cycles at 1.5 C) and HCAPN@Li||NCM811 cell (capacity retention of 79% after 300 cycles). Surface morphology analysis is also performed for physical insight into their role as protecting layer. This work provides a new perspective for constructing a hybrid dynamic covalent network-based polymer protecting layer for inhibiting Li dendrite growth.

Enhancing the performance of metallic lithium anode in batteries through water-resistant and air-stable coating

The limited reversibility and high reactivity of lithium metal with the liquid electrolyte in lithium batteries hinder its widespread adoption. The formation of an unstable solid electrolyte interphase layer and the sensitivity of lithium metal to moisture and air are major issues that need to be addressed. To overcome the practical challenges associated with the application of lithium anodes in lithium metal batteries, a well-thought-out design of a protective layer is proposed. Here, we have developed a composite coating comprising polyvinylidene fluoride, fumed colloidal silica, and paraffin wax as a protective layer for lithium metal anodes. The coating exhibits excellent electrochemical stability, high ionic conductivity, and mechanical stability, effectively suppressing dendrite growth and accommodating lithium volume changes during cycling. Moreover, the hydrophobic wax component can mitigate the atmospheric sensitivity of metallic lithium anodes. The coating process employed is facile and economically viable, significantly enhancing the scalability of lithium metal batteries. Experimental characterizations confirm the structure and composition of the coating, and electrochemical measurements demonstrate the improved electrochemical performance and cyclability of the coated lithium metal anodes. The results indicate that the developed composite coating has great potential for enhancing the electrochemical and processing stability of metallic lithium anodes for lithium metal batteries.

LiF-Rich Interfacial Protective Layer Enables Air-Stable Lithium Metal Anodes for Dendrite-Free Lithium Metal Batteries.

Lithium (Li) metal is considered as a promising anode candidate for high-energy-density batteries. However, the high reactivity of Li metal leads to poor air stability, limiting its practical application. Additionally, the interfacial instability, such as dendrite growth and an unstable solid electrolyte interphase layer, further complicates its utilization. Herein, a dense lithium fluoride (LiF)-rich interfacial protective layer is constructed on the Li surface through a simple reaction between Li and fluoroethylene carbonate (denoted as LiF@Li). The LiF-rich interfacial protective layer consists of both organic (ROCO2Li and C-F-containing species, which only exist on the outer layer) and inorganic (LiF and Li2CO3, distribute throughout the layer) components with a thickness of ∼120 nm. Specifically, chemically stable LiF and Li2CO3 play an important role in blocking air and hence improve the air durability of LiF@Li anodes. Notably, LiF with high Li+ diffusivity facilitates uniform Li+ deposition, while organic components with high flexibility relieve volume change upon cycling, thereby enhancing the dendrite inhibition capacity of LiF@Li. Consequently, LiF@Li exhibits remarkable stability and excellent electrochemical performance in both symmetric cells and LiFePO4 full cells. Moreover, LiF@Li maintains its initial color and morphology even after air exposure for 30 min, and the air-exposed LiF@Li anode still retains its superior electrochemical performance, further establishing its outstanding air-defendable capability. This work proposes a facile approach in constructing air-stable and dendrite-free Li metal anodes toward reliable Li metal batteries.

A Series of Hybrid Multifunctional Interfaces as Artificial SEI Layer for Realizing Dendrite Free, and Long‐Life Sodium Metal Anodes

AbstractSodium metal (Na) anodes are considered the most promising anode for high‐energy‐density sodium batteries because of their high capacity and low electrochemical potential. However, Na metal anode undergoes uncontrolled Na dendrite growth, and unstable solid electrolyte interphase layer (SEI) formation during cycling, leading to poor coulombic efficiency, and shorter lifespan. Herein, a series of Na‐ion conductive alloy‐type protective interface (Na‐In, Na‐Bi, Na‐Zn, Na‐Sn) is studied as an artificial SEI layer to address the issues. The hybrid Na‐ion conducting SEI components over the Na‐alloy can facilitate uniform Na deposition by regulating Na‐ion flux with low overpotential. Furthermore, density functional study reveals that the lower surface energy of protective alloys relative to bare Na is the key factor for facilitating facile ion diffusion across the interface. Na metal with interface layer facilitates a highly reversible Na plating/stripping for ≈790 h, higher than pristine Na metal (100 h). The hybrid self‐regulating protective layers exhibit a high mechanical flexibility to promote dendrite free Na plating even at high current density (5 mA cm−2), high capacity (10 mAh cm−2), and good performance with Na3V2(PO4)3 cathode. The current study opens a new insight for designing dendrite Na metal anode for next generation energy storage devices.

Hybrid Dynamic Covalent Network as a Protective Layer and Solid-State Electrolyte for Stable Lithium-Metal Batteries.

Lithium (Li) metal is a highly promising anode material for next-generation high-energy-density batteries, while Li dendrite growth and the unstable solid electrolyte interphase layer inhibit its commercialization. Herein, a chemically grafted hybrid dynamic network (CHDN) is rationally designed and synthesized by the 4,4'-thiobisbenzenamine cross-linked poly(poly(ethylene glycol) methyl ether methacrylate-r-glycidyl methacrylate) and (3-glycidyloxypropyl) trimethoxysilane-functionalized SiO2 nanoparticles, which is utilized as a protective layer and hybrid solid-state electrolyte (HSE) for stable Li-metal batteries. The presence of a dynamic exchangeable disulfide affords self-heability and recyclability, and the chemical attachment between SiO2 nanoparticles and the polymer matrix enables the homogeneous distribution of inorganic fillers and mechanical robustness. With integrated flexibility, fast segmental dynamics, and autonomous adaptability, the as-prepared CHDN-based protective layer enables superior electrochemical performance in half cells and full cells (capacity retention of 83.7% over 400 cycles for the CHDN@Li/LiFePO4 cell at 1 C). Furthermore, benefiting from intimate electrode/electrolyte interfacial contact, CHDN-based solid-state cells deliver excellent electrochemical performance (capacity retention of 89.5% over 500 cycles for the Li/HSE/LiFePO4 cell at 0.5 C). In addition, the Li/HSE/LiFePO4 pouch cell exhibits superior safety, even exposing various physical damage conditions. This work thereby provides a fresh insight into a rational design principle for dynamic network-based protective layers and solid-state electrolytes for battery applications.

Are Porous Polymers Practical to Protect Li‐Metal Anodes? ‐ Current Strategies and Future Opportunities

AbstractThe practical application of lithium (Li) metal batteries (LMBs) is significantly hindered by the uncontrolled Li dendrite growth and unstable solid electrolyte interphase layer, which leads to low Coulombic efficiency and short cycling lifetime. Constructing protective layers on Li metal surface is demonstrated as a facile and efficient approach to tackle these issues. With superior chemical/electrochemical stability, mechanical robustness, high current density tolerance, and low cost, porous polymers are considered promising candidates as the protective layers toward practical Li‐metal battery applications. In this review, the fundamental mechanisms in stabilizing Li‐metal electrodes, design principles, scalable processing, and recent progress of porous polymers toward practical batteries are thoroughly reviewed and discussed. The purpose of the current review is to analyze whether applying porous polymers as the protective layers is a more promising option of LMBs, and it also discusses how to practically achieve low cost, high‐energy‐density, safe, and long cycle life batteries.

Advances of polymer binders for silicon‐based anodes in high energy density lithium‐ion batteries

AbstractConventional lithium‐ion batteries (LIBs) with graphite anodes are approaching their theoretical limitations in energy density. Replacing the conventional graphite anodes with high‐capacity Si‐based anodes represents one of the most promising strategies to greatly boost the energy density of LIBs. However, the inherent huge volume expansion of Si‐based materials after lithiation and the resulting series of intractable problems, such as unstable solid electrolyte interphase layer, cracking of electrode, and especially the rapid capacity degradation of cells, severely restrict the practical application of Si‐based anodes. Over the past decade, numerous reports have demonstrated that polymer binders play a critical role in alleviating the volume expansion and maintaining the integrity and stable cycling of Si‐based anodes. In this review, the state‐of‐the‐art designing of polymer binders for Si‐based anodes have been systematically summarized based on their structures, including the linear, branched, crosslinked, and conjugated conductive polymer binders. Especially, the comprehensive designing of multifunctional polymer binders, by a combination of multiple structures, interactions, crosslinking chemistries, ionic or electronic conductivities, soft and hard segments, and so forth, would be promising to promote the practical application of Si‐based anodes. Finally, a perspective on the rational design of practical polymer binders for the large‐scale application of Si‐based anodes is presented.image

Non-Woven rGO Fibers Attached to Non-Woven Aramid Separator for High-Speed Charging and Discharging of Li Metal Anode

Li metal is one of the best candidate anode materials for next-generation Li ion batteries (LIBs) and the most promising anode material that can replace the carbonaceous anode currently in use because of its high theoretical specific capacity and low redox potential (vs. SHE). Nevertheless, in order to apply Li metal to LIBs as an anode, issues such as those related to the cycle characteristics such as the life span and C-rate capability need to be resolved. These issues arise owing to the solid electrolyte interphase (SEI) formed on the surface of the Li metal anode (LMA). Unlike the conventional graphite anode, which exhibits a stable intercalation/de-intercalation mechanism, the Li metal anode, which utilizes a lithiation-delithiation mechanism known as hostless electrochemical plating/stripping to charge/discharge, undergoes repeated formation/collapse of an unstable SEI layer on its surface. Thus, the LMA is continuously exposed to undesirable interfacial reactions with the liquid electrolyte. The continuous occurrence of these side-reactions deteriorates the cycle characteristics of the LMA. In particular, this phenomenon gradually intensifies as the applied current increases, leaving the LMA operative within limited cycles at a high current density. Thus, the surface of the LMA needs to be subjected to additional treatments, based on studies of interfacial phenomena, for introducing it to LIBs, which many research groups attempted. Of the many approaches, studies that stabilization of the LMA surface by the introduction of a conductive interlayer between the LMA and separator or by applying a functional separator provided excellent results and the advantage using Li metal without structural modification. Similarly, a good interlayer or functional separator should be able to control undesirable interfacial reactions by the formation of the stable SEI layer, which prevents accumulation of an inactive layer and liquid electrolyte depletion, maintaining the cycle characteristics of LMA. In particular, when there is a conductive interlayer above the LMA, the conductive interlayer at the top structurally meets the Li+ ion flux first during the plating step. Therefore, the SEI layer formed is more stable on the conductive interlayer than on the LMA surface and could thus ensure surface stability of the LMA, preventing repeated SEI formation/collapse, dendritic growth, and liquid electrolyte depletion. In consideration of this point, in this work, we proposed non-woven type reduced graphene oxide fibers attached to aramid paper (rGOF-A) as an advanced separator to solve the aforementioned issues presented by an unstable SEI layer. When the rGOF side of rGOF-A contacts the Li metal anode, it functions effectively as a conductive frame, so the electrons can migrate from the underlying the LMA to the rGOF as the current is applied. Thus, the rGOF first meets the Li+ ion flux rather than the LMA, and the SEI layer, which has different chemical characteristics than those of the LMA surface, forms more stably mainly on rGOF in strong reductive conditions. In other words, rGOF can act a conductive layer and induces formation of the SEI layer in rGOF, not the LMA, helping toward stable operation of the LMA. In addition, this formed stable SEI layer can be effectively confined within the rGOF frame to have a high modulus. Moreover, as the electrolyte is consumed to form the SEI layer on the surface of rGOF, chemically reactive C–F bonds are generated at the surface of rGOF and the partially fluorinated rGOF surface induces the formation of LiF known as the component of the stable SEI during the Li+ ion plating process. LiF is a key component in a stable SEI layer on the LMA because it has a wide electrochemical stability window and improves the surface diffusion of ions, which can lead to smooth Li plating. Thus, LiF protects the LMA from further repeated SEI layer formation/collapse processes and helps the LMA to operate reliably. This passivation effect of rGOF on the LMA surface allows the LMA to maintain its cycle characteristics for a rapid charging/discharging condition (20 mA cm-2, 1 mAh cm-2) as well as at a higher areal capacity (20 mA cm-2,20 mAh cm-2) than practical application condition. Thus, the rGOF-A functional separator ensures cycling stability of the LMA without any deteriorating factor, which contributes to large Li source irreversibility, and this does not involve a structural change for the LMA or additional treatments such as those involving additives to maintain to the cycle characteristics or lifespan. Figure 1

TiO2 as a multifunction coating layer to enhance the electrochemical performance of SiOx@TiO2@C composite as anode material

Abstract SiOx-based anode materials suffer from inherent defects of volume expansion, high initial capacity loss, and the huge electron and ion resistance in the unstable solid electrolyte interphase layer impede their commercialization. Surface coating is the most prevalent strategy for resolving the key concerns. In this paper, we present a dual-shell coating structural composite (denoted as SiOx@TiO2@C) through a two-step process. By introducing a high-quality anatase-phase TiO2 layer, a highly stable interface and decreased resistance to electron and ion diffusion of composite are achieved and investigated systematically. Additionally, the side reactivity is studied firstly. Moreover, the enhanced safety of the electrode is evaluated. The as-prepared composite exhibites a high initial discharge capacity of 1624.7 mAh g−1 with an initial coulombic efficiency (ICE) of 81.2%, capacity retention of 89.5% (vs 2nd discharge) after 800 cycles, and a reversible capacity of 949.7 mAh g−1 at 10 A g−1. The assembled full-cell exhibites an initial area capacity of 2.6 mAh cm−2 with an ICE higher than 90%; the exceeding 106 times and 60 times increase in electron conductivity and Li+ conductivity facilitate electron and ion diffusion particularly at high rates. The approximately 1.5 times higher energy barrier implies the blocking effect of the TiO2 layer on the side reaction. The almost 4 times decrease in the accumulated enthalpy reveals the positive effect of the anatase-phase TiO2 layer on thermal stability. The probable reasons associated with the interface stability are discussed and proposed in this paper.

Emerging Potassium Metal Anodes: Perspectives on Control of the Electrochemical Interfaces.

ConspectusPotassium metal serves as the anode in emerging potassium metal batteries (KMBs). It also serves as the counter electrode for potassium ion battery (KIB) half-cells, with its reliable performance being critical for assessing the working electrode material. This first-of-its-kind critical Account focuses on the dual challenge of controlling the potassium metal-substrate and the potassium metal-electrolyte interface so as to prevent dendrites. The discussion begins with a comparison of the physical and chemical properties of K metal anodes versus the much oft studied Li and Na metal anodes. Based on established descriptions for root causes of dendrites, the problem should be less severe for K than for Li or Na, while in fact the opposite is observed. The key reason that the K metal surface rapidly becomes dendritic in common electrolytes is its unstable solid electrolyte interphase (SEI). An unstable SEI layer is defined as being non-self-passivating. No SEI is perfectly stable during cycling, and all SEI structures are heterogeneous both vertically and horizontally relative to the electrolyte interface. The difference between a "stable" and an "unstable" SEI may be viewed as the relative degree to which during cycling it thickens and becomes further heterogeneous. The unstable SEI on K metal leads to a number of interrelated problems, such as low cycling Coulombic efficiency (CE), a severe impedance rise, large overpotentials, and possibly electrical shorting, all of which have been reported to occur as early as in the first 10 plating/stripping cycles. Many of the traditional "interface fixes" employed for Li and Na metal anodes, such as various artificial SEIs, surface membranes, barrier layers, secondary separators, etc., have not been attempted or optimized for the case of K. This is an important area for further exploration, with an understanding that success may come harder with K than with Li due to K-based SEI reactivity with both ether and ester solvents.The second critical problem with K metal anodes is that they do not thermally or electrochemically wet a standard (untreated) Cu foil current collector. Published experimental and modeling research directly highlights the weak bonding between the K atoms and a Cu surface. Existing surface treatment approaches that achieve improved K wetting are discussed, along with the general design rules for future studies. Also discussed are geometry-based methods to tune nucleation as well dual approaches where nucleation and SEI structure are tuned through complementary schemes to achieve extended half-cell and full battery stability. We hypothesize that K metal never achieves a planar wetting morphology even at cycle one, making the dendrites "baked-in". We propose that classical thin film growth models, Frank van der Merwe (F-M), Volmer-Weber (V-W), and Stranski-Krastanov (S-K), can be employed to describe early stage plating behavior. It is demonstrated that islandlike V-W growth is the applicable description for the natural plating behavior of K on pristine Cu. Moving forward, there are three inter-related thrusts to be pursued: First, K salt-based electrolyte formulations have to mature and become further tailored to handle the increased reactivity of a metal rather than an ion anode. Second, the K-based SEI structure needs to be further understood and ultimately tuned to be less reactive. Third, the energetics of the K metal-current collector interface must be controlled to promote planar wetting/dewetting throughout cycling.

Endowing the Lithium Metal Surface with Self-Healing Property via an in Situ Gas-Solid Reaction for High-Performance Lithium Metal Batteries.

The property of the solid electrolyte interphase (SEI) layer is of prime importance for the performance of lithium metal anodes. Replacing the spontaneously formed inhomogeneous and unstable SEI layer with a high-performance artificial SEI is an effective strategy. Herein, a self-healing SEI layer with high lithium-ion conductivity and a stable framework to address the issues of poor performance of lithium metal anodes is achieved. C, Li2S, and LiI are uniformly distributed on the lithium surface via a "sauna" reaction between CS2-I2 mixed steam and metal lithium, which has the potential to be applied to large-scale preparation. The obtained SEI layer possesses high mechanical strength and facilitated lithium-ion transport capability, which are inherited from the amorphous C and lithium compounds (Li2S and LiI). Most importantly, the LiI component can migrate through the electrolyte and cover the exposed lithium caused by flaws and cracks, leading to a self-healing property. As a result, the C-Li2S-LiI@Li electrode exhibits excellent electrochemical performance with low overpotential and long lifespan.

A critical study on a 3D scaffold-based lithium metal anode

Three-dimensional (3D) conductive scaffolds have attracted intensive interest recently for Li metal anode due to the capability of suppressing Li-dendrite growth. However, there is a lack of comprehensive understanding of its multiple roles including any side effects, which is critical for lithium metal anode technology. Here, we fabricate a type of Au-coated polyimide nanofabric as the scaffold for Li-metal anode and study the lithium plating/stripping behavior with different current densities. Different from reported studies which usually only discussed the benefits of 3D scaffolds, this study reveals unstabilized solid-electrolyte-interphase (SEI) with 3D architectures. It is found that 3D scaffold tends to form unstable SEI layer at high current density, which finally results in a short cell life due to continuous SEI accumulation and fast consuming of liquid electrolyte. To better understand this new finding, we propose an electrochemomechanical failure model for lithium metal anode, which will be instructive for designing advanced structures to electrochemomechanically stabilize Li-metal composite anode.

Lead-Carbon Nanofiber Based ANODE for High Performance LI-ION Battery

Lead-carbon (Pb-C) nanofibrous anodes for lithium-ion batteries were prepared via the electrospinning method. The use of lead-based anodes with high amounts of carbon has been shown to improve the cycling performance of batteries through increased capacity retention and electrical conductivity. This is attributed to the Pb-C accommodation to volume change during lithiation/de-lithiation upon cycling as well as suppressed formation of the unstable solid-electrolyte interphase layer. By preparing the anode via electrospinning, an increase in specific area and active material content can be achieved with significant improvement to the battery performance. In this report, significant enhancement of battery performance in terms of specific capacity and cyclability is made using the prepared Pb-C nanofiber anodes. The Pb-C nanofiber anode exhibits a high specific capacity of 637 mAh g-1 with excellent cycling performance.

Surface Gradient Ti-Doped MnO2 Nanowires for High-Rate and Long-Life Lithium Battery.

Cryptomelane-type α-MnO2 has been demonstrated as a promising anode material for high-energy Li-ion batteries because of its high capacity and intriguing [2 × 2] tunnel structure. However, applications of MnO2 electrode, especially at high current rates and mass active material loading, are limited by the poor mechanical stability, unstable solid electrolyte interphase layer, and low reversibility of conversion reactions. Here, we report a design of homogeneous core-shell MnO2 nanowires (NWs) created by near-surface gradient Ti doping (Ti-MnO2 NWs). Such a structurally coherent core-shell configuration endowed gradient volume expansion from the inner core to the outer shell, which could effectively release the stress of the NW lattice during cycling and avoid pulverization of the electrode. Moreover, the gradiently doped Ti is able to avoid the Mn metal coarsening, reducing the metal particle size and improving the reversibility of the conversion reaction. In this way, the Ti-MnO2 NWs achieved both high reversible areal and volumetrical capacities (2.3 mA h cm-2 and 991.3 mA h cm-3 at 200 mA g-1, respectively), a superior round-trip efficiency (Coulombic efficiency achieved above 99.5% after only 30 cycles), and a long lifetime (a high capacity of 742 mA h g-1 retained after 3000 cycle at 10 A g-1) at a high mass loading level of 3 mg cm-2. In addition, the detailed conversion reaction mechanism was investigated through in situ transmission electron microscopy, which further evidenced that the unique homogeneous core-shell structure could largely suppress the separation of core and shell upon charging and discharging. This new NW configuration could benefit the design of other large-volume-change lithium battery anode materials.

Dendrite-free lithium electrode cycling via controlled nucleation in low LiPF6 concentration electrolytes

Lithium metal electrodes are not widely used in rechargeable batteries as dendritic lithium growth and electrolyte reactions raise serious stability and safety concerns. In this study, we show that reproducible two-dimensional lithium deposition can be realized using a lithium salt concentration of 0.020 M, an added supporting salt, and a short lithium nucleation pulse. This approach, which is common in electrodeposition of metals, increases the lithium nuclei density on the electrode surface and decreases the extent of Li+ migration favoring dendritic lithium growth. Contrary to common belief, ascribing the dendrite problem to heterogeneous lithium nucleation due to an unstable solid electrolyte interphase layer, we show that the main lithium deposition problem stems from the difficulty to obtain two-dimensional deposition at the low lithium deposition overpotentials encountered in conventional high-lithium concentration electrolytes. The present results hence clearly demonstrate that two-dimensional lithium deposition can be realized in lithium-metal-based batteries.

Confined silicon nanospheres by biomass lignin for stable lithium ion battery

Biomass lignin, as a significant renewable resource, is one of the most abundant natural polymers in the world. Here, we report a novel silicon-based material, in which lignin-derived functional conformal network crosslinks the silicon nanoparticles via self-assembly. This newly-developed material could greatly solve the problems of large volume change during lithiation/delithiation process and the formation of unstable solid electrolyte interphase layers on the silicon surface. With this anode, the battery demonstrates a high capacity of ∼3000 mA h g−1, a highly stable cycling retention (∼89% after 100 cycles at 300 mA g−1) and an excellent rate capability (∼800 mA h g−1 at 9 A g−1). Moreover, the feasibility of full lithium-ion batteries with the novel silicon-based material would provide wide range of applications in the field of flexible energy storage systems for wearable electronic devices.

Inorganic-Organic Coating via Molecular Layer Deposition Enables Long Life Sodium Metal Anode.

Metallic Na anode is considered as a promising alternative candidate for Na ion batteries (NIBs) and Na metal batteries (NMBs) due to its high specific capacity, and low potential. However, the unstable solid electrolyte interphase layer caused by serious corrosion and reaction in electrolyte will lead to big challenges, including dendrite growth, low Coulombic efficiency and even safety issues. In this paper, we first demonstrate the inorganic-organic coating via advanced molecular layer deposition (alucone) as a protective layer for metallic Na anode. By protecting Na anode with controllable alucone layer, the dendrites and mossy Na formation have been effectively suppressed and the lifetime has been significantly improved. Moreover, the molecular layer deposition alucone coating shows better performances than the atomic layer deposition Al2O3 coating. The novel design of molecular layer deposition protected Na metal anode may bring in new opportunities to the realization of the next-generation high energy-density NIBs and NMBs.

Practical considerations of Si-based anodes for lithium-ion battery applications

Using Si-based anodes in Li-ion batteries is one of the most feasible approaches to achieve high energy densities despite their disadvantages, such as low conductivity and massive volume expansion, which cause unstable solid electrolyte interphase layers with mechanical failure. The forefront in research and development to address the above challenges suggests the possibility of fully commercially viable cells using various structural and interfacial modifications. In particular, we present a discussion of each dimension of Si-based anodes in multiple controlled systems, including plain, hollow, porous, and uniquely engineered structures, which are further evaluated based on their anode performances, such as initial reversibility, capacity retention for extended cycles with its efficiency, degree of volume expansion tolerance, and rate capabilities, by several practical standards in half cells. With these practical considerations, multi-dimensional structures with uniform size distributions (micrometers, on average) are strongly desired to satisfy the rigorous requirements for widespread applications. Furthermore, we closely examined several full cells composed of Si-based multicomponent anodes coupled with suitable cathodes based on practical standards to propose future research directions for Si-based anodes to keep pace with the rapidly changing market demands for diverse energy storage systems.