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Cobalt telluride anchored to nitrogen-rich carbon dodecahedra (CoTe@NCD) as high-rate potassium and sodium ion battery anodes.

A strategy for modifying the structure of solid-state electrolytes (SSEs) to reduce the cation diffusion activation energy is presented. Two heavily W-doped sodium thioantimonate SSEs, Na2.895 W0.3 Sb0.7 S4 and Na2.7 W0.3 Sb0.7 S4 are designed, both exhibiting exceptionally low activation energy and enhanced room temperature (RT) ionic conductivity; 0.09 eV, 24.2 mS/cm and 0.12 eV, 14.5 mS/cm. At -15 °C the Na2.895 W0.3 Sb0.7 S4 displays a total ionic conductivity of 5.5 mS/cm. The 30 % W content goes far beyond the 10-12 % reported in the prior studies, and results in novel pseudo-cubic or orthorhombic structures. Calculations reveal that these properties result from a combination of multiple diffusion mechanisms, including vacancy defects, strongly correlated modes and excessive Na-ions. An all-solid-state battery (ASSB) using Na2.895 W0.3 Sb0.7 S4 as the primary SSE and a sodium sulfide (Na2 S) cathode achieves a reversible capacity of 400 mAh g-1 .

A stable anode-free all-solid-state battery (AF-ASSB) with sulfide-based solid-electrolyte (SE) (argyrodite Li

Laser processing is employed to fabricated zinc-ion battery (ZIB) anodes with state-of-the-art electrochemical performance from commercial zinc foils. Lasers are widely utilized for industrial surface finishing but have received minimal attention for zinc surface modification. Laser lithography patterned zinc foils “LLP@ZF” are hydrophilic, with an electrolyte contact angle of 0°. This is due to the concave-convex surface geometry that enhances wetting (periodic crests, ridges and valleys, roughness 16.5 times planar). During electrodeposition LLP@ZF's surface geometry generates a periodic electric field and associated current density distribution that suppresses tip growth (per continuum simulations). Per Density Functional Theory (DFT) its surface oxide is zincophilic, resulting in low nucleation barriers during plating (e.g. 3.8 mV at 1 mA cm−2). A combination of these attributes leads to stable dendrite-free plating/stripping behavior and low overpotentials at fast charge (e.g. 48.2 mV at 8 mA cm−2 in symmetric cell). Cycling is possible at an unprecedented areal capacity of 50 mA h cm−2, with 400 h stability at 1 mA cm−2. Moreover, exceptional aqueous zinc battery (AZB) performance is achieved, with MnO2-based cathode loading 10 mg cm−2 and corresponding anode capacity 7.6 mA h cm−2. A broad comparison with literature indicates that LLP@ZF symmetric cell and full battery performance are among most favorable.\ud \ud

Lithium metal–selenium (Li–Se) batteries offer high volumetric energy but are limited in their cycling life and fast charge characteristics. Here a facile approach is demonstrated to synthesize hierarchically porous hollow carbon spheres that host Se (Se@HHCS) and allow for state-of-the-art electrochemical performance in a standard carbonate electrolyte (1 M LiPF6 in 1 : 1 EC : DEC). The Se@HHCS electrodes display among the most favorable fast charge and cycling behavior reported. For example, they deliver specific capacities of 442 and 357 mA h g−1 after 1500 and 2000 cycles at 5C and 10C, respectively. At 2C, Se@HHCS delivers 558 mA h g−1 after 500 cycles, with cycling coulombic efficiency of 99.9%. Post-mortem microstructural analysis indicates that the structures remain intact during extended cycling. Per GITT analysis, Se@HHCS possesses significantly higher diffusion coefficients in both lithiation and delithiation processes as compared to the baseline. The superior performance of Se@HHCS is directly linked to its macroscopic and nanoscale pore structure: the hollow carbon sphere morphology as well as the remnant open nanoporosity accommodates the 69% volume expansion of the Li to Li2Se transformation, with the nanopores also providing a complementary fast ion diffusion path.

Sodium metal battery (SMB, NMB) anodes can become dendritic due to an electrochemically unstable native Na-based solid electrolyte interphase (SEI). Herein Li-ion activated tin sulfide graphene nanocomposite membrane (A-SnS–G) is employed as an artificial SEI layer, allowing cyclability of record-thin 100 μm Na metal foils. The thin Na metal is prepared by a self-designed metallurgical rolling protocol. A-SnS–G is initially placed onto the polypropylene (PP) separator but becomes in situ transferred onto the Na metal surface. Symmetric metal cells protected by A-SnS–G achieve low-overpotential extended high-rate cycling in a standard carbonate electrolyte (EC : DEC = 1 : 1, 5% FEC). Accumulated capacity of 1000 mA h cm−2 is obtained after 500 cycles at 4 mA cm−2, with accumulated capacity-to-foil capacity (A/F) ratio of 90.9. This is among the most favorable cycle life, accumulated capacity, and anode utilization combinations reported. Protection by non-activated SnS–G membrane yields significantly worse cycling, albeit still superior to the baseline unprotected sodium. Post-mortem and dedicated light optical analysis indicate that metal swelling, dendrite growth and dead metal formation is extensive for the unprotected sample, but is suppressed with A-SnS–G. Per XPS, post-100 cycles near-surface structure of A-SnS–G is rich in metallic Sn alloys and inorganic carbonate salts. Even after 300 cycles, Li-based SEI components ROCO2-Li, Li2CO3 and LiF are detected with A-SnS–G. As a proof of principle, an SMB with a high mass loading (6 mg cm−2) NVP cathode and a A-SnS–G protected anode delivered extended cyclability, achieving 74 mA h g−1 after 400 cycles at 0.4C.

The shuttling of soluble lithium polysulfides (LiPS) and the sluggish Li-S conversion kinetics are two main barriers toward the practical application of lithium-sulfur batteries (LSBs). Herein, we propose the addition of copper selenide nanoparticles at the cathode to trap LiPS and accelerate the Li-S reaction kinetics. Using both computational and experimental results, we demonstrate the crystal phase and concentration of copper vacancies to control the electronic structure of the copper selenide, its affinity toward LiPS chemisorption, and its electrical conductivity. The adjustment of the defect density also allows for tuning the electrochemically active sites for the catalytic conversion of polysulfide. The optimized S/Cu1.8Se cathode efficiently promotes and stabilizes the sulfur electrochemistry, thus improving significantly the LSB performance, including an outstanding cyclability over 1000 cycles at 3 C with a capacity fading rate of just 0.029% per cycle, a superb rate capability up to 5 C, and a high areal capacity of 6.07 mAh cm-2 under high sulfur loading. Overall, the present work proposes a crystal phase and defect engineering strategy toward fast and durable sulfur electrochemistry, demonstrating great potential in developing practical LSBs., The authors thank the support from the projects ENE2016-77798-C4-3-R and NANOGEN (PID2020-116093RB-C43), funded by MCIN/AEI/10.13039/501100011033/and by “ERDF A way of making Europe”, by the “European Union”. D.Y., M.L., X.H., and C.Z. thank the China Scholarship Council for the scholarship support. ICN2 acknowledges the support from the Severo Ochoa Programme (MINECO, grant no. SEV-2017-0706). IREC and ICN2 are both funded by the CERCA Program/Generalitat de Catalunya. This project received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 823717-ESTEEM3. Calculations at UT Austin were supported by the Welch Foundation (F-1841) and the Texas Advanced Computing Center. Part of the present work has been performed in the framework of Universitat Autònoma de Barcelona Materials Science PhD program. J.L. is a Serra Húnter Fellow and is grateful to MICINN/FEDER RTI2018-093996-B-C31, GC 2017 SGR 128, and to the ICREA Academia program.

In this work, the Na-K liquid alloy with a charge selective interfacial layer is developed to achieve an impressively long cycling life with small overpotential on a sodium super-ionic conductor solid-state electrolyte (NASICON SSE). With this unique multi-cation system as the platform, we further propose a unique model that contains a chemical decomposition domain and a kinetic decomposition domain for the interfacial stability model. Based on this model, two charge selection mechanisms are proposed with dynamic chemical kinetic equilibrium and electrochemical kinetics as the manners of control, respectively, and both are validated by the electrochemical measurements with microscopic and spectroscopic characterizations. This study provides an effective design for high-energy-density solid-state battery with alkali Na-K anode, but also presents a novel approach to understand the interfacial chemical processes that could inspire and guide future designs.

Combined sulfur and nitrogen (S ​= ​12.9 ​at.%, N ​= ​9.9 ​at.%) rich carbons are synthesized for potassium ion anode applications. The low-surface-area carbons (56 ​m2 ​g−1) have sulfur covalently bonded to the structure, with minimum unbound “free” sulfur. This allows for exceptional rate capability and stability: Capacities of 437, 234 and 72 mAh g−1 are achieved at 0.1, 1 and 10 ​A ​g−1, with 75% retention at 2 ​A ​g−1 after 3000 cycles. These are among the most favorable capacity-cyclability combinations reported in potassium ion battery carbon literature. As a proof of principle, the carbons are incorporated into a potassium ion capacitor with state-of-the-art energy and power (e.g. 110 ​W ​h ​kg−1 at 244 ​W ​kg −1). According to XPS analysis, the reaction of nitrogen with K+ is distinct from that of K+ with sulfur. The N and N–O moieties undergo a series of complex multi-voltage reactions that result in both reversible and irreversible changes to their structure. The K–S reactions involve a combination of reversible adsorption and reversible formation of sulfides, thiosulfate and sulfate. GITT and EIS analysis indicate that incorporation of S into the N-rich carbon increases the K+ solid-state diffusion coefficient by factors ranging from ~3 to 8, depending on the voltage. The diffusivities are asymmetric with charging vs. discharging, signifying distinct reaction pathways. The covalently bound sulfur also has a positive influence on the solid electrolyte interphase (SEI) formation, at early and at prolonged cycling.

We synthesized Co2P nanoparticle encapsulated N-doped carbon nanocages through one-step carbonization–phosphidation of ZIF-67. As potassium ion battery (KIB, PIB) anodes, the Co2P@NCCs display state-of-the-art electrochemical performance, including the most favorable fast charge characteristics reported. The single-nanometer thick carbon cage yields rapid solid-state K-ion diffusion and prevents aggregation/pulverization of 40 nm cobalt phosphide.

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal-sulfur batteries remain challenged by several factors, including polysulfides' (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li-S and the emerging Na-S and K-S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li-S are relatively mature, less progress has been made with Na-S and K-S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal-selenium and the metal-selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal-sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li-S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (

Sodium-ion batteries (SIBs) have been regarded as one of the most promising alternatives to lithium-ion batteries (LIBs) due to their analogous working mechanism but greater abundance. The cost-effectiveness of Na batteries is expected to overtake that of LIBs in terms of electromobile applications if their energy densities can reach 200 Wh kg-1. In an anode-free configuration, all active sodium is stored in the cathode while anode only contains current collector with zero excess sodium, therefore achieving maximized energy density, significantly reduced cost, and simplified manufacture procedures. However, the anode-free batteries often suffer rapid capacity decay due to the absence of a reservoir to replenish the Na loss during cycling. In this work, we employed repeated cold rolling and folding to fabricate a metallurgical composite of sodium-antimony-telluride Na2(Sb2/6Te3/6Vac1/6) dispersed in electrochemically active sodium metal, termed “NST-Na”. This new intermetallic has a vacancy-rich thermodynamically stable fcc structure and enables state-of-the-art electrochemical performance in widely employed carbonate and ether electrolytes. NST-Na achieves 100% depth-of-discharge (DOD) in 1 M NaPF6 in G2, with 15 mAh cm-2 at 1 mA cm-2 and CE of 99.4%, for 1000 hours of plating/stripping. Sodium metal batteries (SMB, NMB) with NST-Na and Na3V2(PO4)3 (NVP) or sulfur cathodes give significantly improved energy, cycling and CE (> 99%). Anode-Free battery with NST collector and NVP obtains 0.23% capacity decay per cycle. Imaging and tomography using (cryo-)FIB sectioning, (cryo-)SEM, and (cryo-)TEM imaging indicate that sodium metal fills the open space inside the self-supporting sodiophilic NST skeleton, resulting in dense (pore-free and SEI-free) metal deposits with flat surfaces. The baseline Na deposit consists of filament-like dendrites and Dead Metal, intermixed with pores and SEI. Density functional theory (DFT) calculations show that uniqueness of NST lies in the thermodynamic stability of Na atoms (rather than clusters) on its surface that leads to planar wetting, and in its own stability that prevents decomposition during cycling. Figure 1

We combined advanced TEM (HRTEM, HAADF, EELS) with solid-state (SS)MAS NMR and electroanalytical techniques (GITT, etc.) to understand the site-specific sodiation of selenium (Se) encapsulated in a nanoporous carbon host. The architecture employed is representative of a wide number of electrochemically stable and rate-capable Se-based sodium metal battery (SMB) cathodes. SSNMR demonstrates that during the first sodiation, the Se chains are progressively cut to form an amorphous mixture of polyselenides of varying lengths, with no evidence for discrete phase transitions during sodiation. It also shows that Se nearest the carbon pore surface is sodiated first, leading to the formation of a core-shell compositional profile. HRTEM indicates that the vast majority of the pore-confined Se is amorphous, with the only localized presence of nanocrystalline equilibrium Na

We report a new approach for nanosilicon-graphene hybrids with uniquely stable solid electrolyte interphase. Expanded graphite is gently exfoliated creating "defect-free" graphene that is non-catalytic towards electrolyte decomposition, simultaneously introducing high mass loading (48 wt. %) Si nanoparticles. Silane surface treatment creates epoxy chemical tethers, mechanically binding nano-Si to CMC binder through epoxy ring-opening reaction while stabilizing the Si surface chemistry. Epoxy-tethered silicon pristine-graphene hybrid "E-Si-pG" exhibits state-of-the-art performance in full battery opposing commercial mass loading (12 mg cm-2 ) LiCoO2 (LCO) cathode. At 0.4 C, with areal capacity of 1.62 mAh cm-2 and energy of 437 Wh kg-1 , achieving 1.32 mAh cm-2 , 340.4 Wh kg-1 at 1 C. After 150 cycles, it retains 1.25 mAh cm-2 , 306.5 Wh kg-1 . Sputter-down XPS demonstrates survival of surface C-Si-O-Si groups in E-Si-pG after repeated cycling. The discovered synergy between support defects, chemical-mechanical stabilization of Si surfaces, and SEI-related failure may become key LIB anode design rule.

We report a bifunctional sodium metal battery (SMB) and lithium metal battery (LMB) cathode based on 63 wt.%SeS covalently bonded to a co-pyrolyzed polyacrylonitrile (PAN) host, termed “SeSPAN”. This dense, low surface area, fully-amorphous electrode offers a highly favorable combination of reversible capacity, rate capability, and cycling life: At a fast charging rate of 1 A g−1, the reversible capacities with Na and Li are 632 and 749 mAh g−1 (based on active SeS), with cycle 1 CE of 81% in both cases. At an ultra-fast charging rate of 4 A g−1 (∼5C) the reversible capacities with Na and Li are 453 and 604 mAh g−1. Li-SeSPAN degrades 3% at cycle 500, while with Na-SeSPAN degrades by 17% after 150 cycles at 0.5 A g−1. Both Na and Li cells display a uniquely low voltage hysteresis (210 and 200 mV at a current density of 0.2 A g−1), indicative of facile charge-discharge kinetics. Analysis of the post-cycled anodes shows negligible S or Se crossover, with neither species being detected in the Li-SEI after extended cycling.

This comprehensive Review focuses on the key challenges and recent progress regarding sodium-metal anodes employed in sodium-metal batteries (SMBs). The metal anode is the essential component of emerging energy storage systems such as sodium sulfur and sodium selenium, which are discussed as example full-cell applications. We begin with a description of the differences in the chemical and physical properties of Na metal versus the oft-studied Li metal, and a corresponding discussion regarding the number of ways in which Na does not follow Li-inherited paradigms in its electrochemical behavior. We detail the major challenges for Na-metal systems that at this time limit the feasibility of SMBs. The core Na anode problems are the following interrelated degradation mechanisms: An unstable solid electrolyte interphase with most organic electrolytes, "mossy" and "lath-like" metal dendrite growth for liquid systems, poor Coulombic efficiency, and gas evolution. Even solid-state Na batteries are not immune, with metal dendrites being reported. The solutions may be subdivided into the following interrelated taxonomy: Improved electrolytes and electrolyte additives tailored for Na-metal anodes, interfacial engineering between the metal and the liquid or solid electrolyte, electrode architectures that both reduce the current density during plating-stripping and serve as effective hosts that shield the Na metal from excessive reactions, and alloy design to tune the bulk properties of the metal per se. For instance, stable plating-stripping of Na is extremely difficult with conventional carbonate solvents but has been reported with ethers and glymes. Solid-state electrolytes (SSEs) such as beta-alumina solid electrolyte (BASE), sodium superionic conductor (NASICON), and sodium thiophosphate (75Na2S·25P2S5) present highly exciting opportunities for SMBs that avoid the dangers of flammable liquids. Even SSEs are not immune to dendrites, however, which grow through the defects in the bulk pellet, but may be controlled through interfacial energy modification. We conclude with a discussion of the key research areas that we feel are the most fruitful for further pursuit. In our opinion, greatly improved understanding and control of the SEI structure is the key to cycling stability. A holistic approach involving complementary post-mortem, in situ, and operando analyses to elucidate full battery cell level structure-performance relations is advocated.

An unstable solid electrolyte interphase (SEI) and accompanying Li metal dendrites are the key impediments to commercialization of high-energy lithium metal batteries (LMBs). We employ a strontium fluoride (SrF2) microsphere coated polypropylene (PP) separator to stabilize the SEI and to prevent dendrites from growing. This approach is tested with Li‖Cu half-cells, Li‖Li symmetrical cells, and Li‖NMC full LMBs, there being a major improvement in each case. The Li‖Cu cell with SrF2 maintains a stable coulombic efficiency (CE) of 80% after 100 cycles, when tested at 0.25 mA cm−2 to a capacity of 0.5 mA h cm−2. By comparison, the uncoated PP reference has a CE of 10% in cycle 60. The Li‖Li cell with SrF2 exhibits a markedly smaller voltage polarization and is able to stably cycle for approximately 340 h vs. the reference which begins to display severe voltage instability at 200 h. The Li‖NMC full LMB with SrF2 shows an initial discharge capacity of 173 mA h g−1, with 167 mA h g−1 (96.5%) being retained after 200 cycles at 200 mA g−1 (1C rate). The SrF2 containing LMB also has a substantially improved rate capability over the reference, the difference being drastic even at the highest testing rate of 20C. First-principles calculations based on DFT indicate that lithium ions prefer to adsorb onto the SrF2 surface, which should create a more uniform ion flux and reduce the propensity for dendrite nucleation. In parallel, the SrF2 spheres bind with the SEI layer, creating a tough in situ formed composite membrane that mechanically stabilizes a planar metal interface.

Lithium metal battery systems (LMBs) are being sought as an ultimate replacement to LIBs, potentially increasing the cell energy by over fifty percent due to the high capacity and low voltage of the metal anode. Analogous improvement in energy is possible with sodium metal batteries (NMBs) and with potassium metal batteries (KMBs), where existing ion insertion anodes can be replaced by plating/stripping metal. However, in all three cases safety and performance are compromised by an unstable solid electrolyte interphase (SEI) that consumes metal ions and electrolyte, and ultimately leads to dendrites. This presentation provides a series of case studies derived from the group's LMB, NMB and KMB research on the microstructural design principles that provide for long-term cycling and fast-charge stability of metal anodes. The approaches may be categorized as the following: a) design of plating/stripping supports and templates with tuned geometry and functionality; b) design of secondary interlayers placed between the metal anode and the separator; and c) design of multifunctional hybrid separators to replace the conventional polymer separators employed with LIBs. It is demonstrated that despite appearing distinct, the efficacy of each in enabling electrochemical stability originates from three fundamental features that are directly interrelated. The wetting behavior of the electrolyte on the anode must be optimized, the wetting/stripping behavior of the metal anode on the current collector must be controlled, and a geometrically and chemically modified SEI must be established. Simultaneously achieving all three leads to stable plating/stripping, while missing even one leads to rapid dendrite growth. Cryogenic FIB cross sections and cryo-TEM are combined to yield new insight regarding film wetting behavior and early dendrite formation in optimized versus baseline specimens, analyzing growth in several representative electrolytes.

Electrochemical capacitors charge and discharge more rapidly than batteries over longer cycles, but their practical applications remain limited due to their significantly lower energy densities. Pseudocapacitors and hybrid capacitors have been developed to extend Ragone plots to higher energy density values, but they are also limited by the insufficient breadth of options for electrode materials, which require materials that store alkali metal cations such as Li+ and Na+. Herein, we report a comprehensive and systematic review of emerging anion storage materials for performance- and functionality-oriented applications in electrochemical and battery-capacitor hybrid devices. The operating principles and types of dual-ion and whole-anion storage in electrochemical and hybrid capacitors are addressed along with the classification, thermodynamic and kinetic aspects, and associated interfaces of anion storage materials in various aqueous and non-aqueous electrolytes. The charge storage mechanism, structure-property correlation, and electrochemical features of anion storage materials are comprehensively discussed. The recent progress in emerging anion storage materials is also discussed, focusing on high-performance applications, such as dual-ion- and whole-anion-storing electrochemical capacitors in a symmetric or hybrid manner, and functional applications including micro- and flexible capacitors, desalination, and salinity cells. Finally, we present our perspective on the current impediments and future directions in this field.

This is the first report of molybdenum carbide-based electrocatalyst for sulfur-based sodium-metal batteries. MoC/Mo

It is a major challenge to achieve fast charging and high reversible capacity in potassium ion storing carbons. Here, we synthesized sulfur-rich graphene nanoboxes (SGNs) by one-step chemical vapor deposition to deliver exceptional rate and cyclability performance as potassium ion battery and potassium ion capacitor (PIC) anodes. The SGN electrode exhibits a record reversible capacity of 516 mAh g-1 at 0.05 A g-1, record fast charge capacity of 223 mA h g-1 at 1 A g-1, and exceptional stability with 89% capacity retention after 1000 cycles. Additionally, the SGN-based PIC displays highly favorable Ragone chart characteristics: 112 Wh kg-1at 505 W kg-1 and 28 Wh kg-1 at 14618 W kg-1 with 92% capacity retention after 6000 cycles. X-ray photoelectron spectroscopy analysis illustrates a charge storage sequence based primarily on reversible ion binding at the structural-chemical defects in the carbon and the reversible formation of K-S-C and K2S compounds. Transmission electron microscopy analysis demonstrates reversible dilation of graphene due to ion intercalation, which is a secondary source of capacity at low voltage. This intercalation mechanism is shown to be stable even at cycle 1000. Galvanostatic intermittent titration technique analysis yields diffusion coefficients from 10-10 to 10-12 cm2 s-1, an order of magnitude higher than S-free carbons. The direct electroanalytic/analytic comparison indicates that chemically bound sulfur increases the number of reversible ion bonding sites, promotes reaction-controlled over diffusion-controlled kinetics, and stabilizes the solid electrolyte interphase. It is also demonstrated that the initial Coulombic efficiency can be significantly improved by switching from a standard carbonate-based electrolyte to an ether-based one.

We synthesized Co2P nanoparticle encapsulated N-doped carbon nanocages through one-step carbonization-phosphidation of ZIF-67. As potassium ion battery (KIB, PIB) anodes, the Co2P@NCCs display state-of-the-art electrochemical performance, including the most favorable fast charge characteristics reported. The single-nanometer thick carbon cage yields rapid solid-state K-ion diffusion and prevents aggregation/pulverization of 40 nm cobalt phosphide.

Graphite is ubiquitous as the anode material in lithium-ion batteries, but offers relatively low volumetric capacity (330 to 430 mAh cm-3). By contrast, Tellurene (Te) is expected to alloy with alkali metals with high volumetric capacity (~2620 mAh cm-3), but to date there is no detailed study on its alloying behavior. In this work, we have investigated the alloying response of a range of alkali metals (A = Li, Na or K) with few-layer Te. In-situ transmission electron microscopy and density functional theory both indicate that Te alloys with alkali metals forming A2Te. However, the crystalline order of alloyed products varied significantly from single-crystal (for Li2Te) to polycrystalline (for Na2Te and K2Te). It is well established that typical alloying materials (e.g., silicon, tin, black phosphorous) lose their crystallinity when reacted with Li. The ability of Te to retain its crystallinity is therefore surprising. Nudged elastic band calculations and ab-initio molecular dynamics simulations reveal that compared to Na or K, the migration of Li is highly “isotropic” in Te, enabling its crystallinity to be preserved. Such isotropic Li transport is made possible by Te’s peculiar structure comprised of chiral chains bound by van der Waals forces. To evaluate the electrochemical performance of Te, we tested Te electrodes in half-cells vs Li/Na/K metal. While alloying with Na and K showed poor performance, with Li, the Te electrode exhibited a volumetric capacity of ~700 mAh cm-3, which is about two-times the practical capacity of commercial graphite. Such Te based batteries could play an important role in applications where high volumetric energy and power density are of paramount importance.

A new approach is employed to boost the electrochemical kinetics and stability of vanadium oxygen hydrate (VOH, V2O5·nH2O) employed for aqueous zinc-ion battery (ZIB) cathodes. The methodology is based on electrically conductive polyaniline (PANI) intercalated-exfoliated VOH, achieved by preintercalation of an aniline monomer and its in situ polymerization within the oxide interlayers. The resulting graphene-like PANI-VOH nanosheets possess a greatly boosted reaction-controlled contribution to the total charge storage capacity, resulting in more material undergoing the reversible V5+ to V3+ redox reaction. The PANI-VOH electrode obtains an impressive capacity of 323 mAh g-1 at 1 A g-1, and state-of-the-art cycling stability at 80% capacity retention after 800 cycles. Because of the facile redox kinetics, the PANI-VOH ZIB obtains uniquely promising specific energy-specific power combinations: an energy of 216 Wh kg-1 is achieved at 252 W kg-1, while 150 Wh kg-1 is achieved at 3900 W kg-1. Electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) analyses indicate that with PANI-VOH nanosheets, there is a simultaneous decrease in the charge transfer resistance and a boost in the diffusion coefficient of Zn2+ (by a factor of 10-100) vs the VOH baseline. The strategy of employing PANI for combined intercalation-exfoliation may provide a broadly applicable approach for improving the performance in a range of oxide-based energy storage materials.

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.

The capacity-voltage fade phenomenon in lithium iron phosphate (LiFePO4) lithium ion battery cathodes is not understood. We provide its first atomic-scale description, employing advanced transmissi...

Hybrid ion capacitors are held back by the discrepancy of the fast kinetics in “capacitor-like” ion adsorption cathodes versus the sluggish kinetics of “battery-like” ion insertion anodes. We demonstrate a novel lithium ion capacitor (LIC) architecture that circumvents this problem. This is achieved by employing an identical porous carbon for both positive and negative electrodes with structure and chemistry optimized for power and cyclability. In fact, the architecture does not require a separate source of Li ions apart from the electrolyte salt, reducing the danger of large-scale Li plating and dendrite growth. An optimized device yields excellent Ragone characteristics: 127 Wh kg–1 at 332 W kg–1 (74 W h L–1 at 193 W L–1) while at the very high power of 33,573 W kg–1 the energy remains solid at 40 Wh kg–1 (23 W h L–1 at 19 472 W L–1) (based on total active material). The latter is equivalent to a 6 s full charge or discharge on par or superior in rate to classical supercapacitors. The LICs are uniquely ...

This review focuses on carbon-based sodium ion battery (NIB) negative electrodes, emphasizing the internal structure – Na storage mechanisms – electrochemical performance relations. We bring a unique vantage to the ever-expanding field of NIB anode literature: To quantify the critical emphasis on the structure – properties interdependence, we provide comprehensive data comparisons of representative published studies. This is accomplished through a series of “Master Plots”, which rather than focusing on an individual publication, combine the data by broad features first outlined in the taxonomy section. The advantage of such an approach is that it transcends the paper-to-paper differences in electrochemical performance in a given class of anodes, providing generalizable comparisons that are statistically significant. For instance, we manage to demonstrate that, while N-doped carbons have a slight advantage in terms of capacity, their rate performance at higher currents is unchanged over that of undoped carbons. To our knowledge such broad high-level data analysis has not been done in past reviews on either NIB or LIB carbon anodes. Furthermore, we also discuss a wide range of individual microstructures and chemistries, offering critical analysis when appropriate.

In this critical Review we focus on the evolution of the hybrid ion capacitor (HIC) from its early embodiments to its modern form, focusing on the key outstanding scientific and technological questions that necessitate further in-depth study. It may be argued that HICs began as aqueous systems, based on a Faradaic oxide positive electrode (e.g., Co3O4, RuOx) and an activated carbon ion-adsorption negative electrode. In these early embodiments HICs were meant to compete directly with electrical double layer capacitors (EDLCs), rather than with the much higher energy secondary batteries. The HIC design then evolved to be based on a wide voltage (∼4.2 V) carbonate-based battery electrolyte, using an insertion titanium oxide compound anode (Li4Ti5O12, LixTi5O12) versus a Li ion adsorption porous carbon cathode. The modern Na and Li architectures contain a diverse range of nanostructured materials in both electrodes, including TiO2, Li7Ti5O12, Li4Ti5O12, Na6LiTi5O12, Na2Ti3O7, graphene, hard carbon, soft carbo...

β-SnSb is known to be a highly stable anode for sodium ion batteries during cycling, but its sodiation–desodiation alloying reactions are poorly understood. Combining in situ TEM with electroanalytical methods, we demonstrate that β-SnSb forms Na3Sb and Na15Sn4 in sequence upon sodiation and re-forms as β-SnSb upon desodiation. The negative enthalpy of mixing for Sn and Sb is sufficient to cause sequentially deposited bilayers of Sn/Sb to transform into β-SnSb, resulting in comparable cycling stability. The good cycling stability of β-SnSb results from the complex two-phase amorphous–nanocrystalline microstructure in the partially charged–discharged states, as well as the intrinsic mechanical toughness of the β phase. Per the in situ TEM results, the sequential phase transformation shows minimal fracturing of the β-SnSb, indicating facile buffering of stresses. Extensively cycled specimens eventually show crystalline Sn phase segregation, which may be the source of the ultimate capacity fade in the alloy and bilayers.

While zirconium-based coatings are known to improve the cycling stability of a number of lithium ion battery cathodes, the microstructural origin of this enhancement remains uncertain. Here we combine advanced transmission electron microscopy (high-resolution transmission electron microscopy, high-angle annular dark field, electron energy loss spectroscopy, and energy-dispersive X-ray spectroscopy) with electrochemical impedance analysis to provide new insight into the dramatic role of Zr surface modification on the electrochemical performance of Li- and Mn-rich (LMR) cathodes (Li[Li0.2Ni0.13Co0.13Mn0.54]O2). It is demonstrated that a Zr-based rock-salt structure layer with a thickness of 1–2 nm is formed on the surface of the LMR. This layer is effective in suppressing the deleterious phase transformation of LMR from initial layered composite combining Li2MO3 and LiMO2 to the disordered rock-salt phase, leading to an enhanced long-term cycling performance and rate capability. Electrochemical impedance sp...

This is the first report of a multifunctional separator for potassium-metal batteries (KMBs). Double-coated tape-cast micro-scale AlF3 on polypropylene (AlF3 @PP) yield state-of-the-art electrochemical performance: Symmetric cells are stable after 1,000 cycles (2,000 hours) at 0.5 mA cm-2 and 0.5 mAh cm-2 , with 0.042 V overpotential. Stability is maintained at 5.0 mA cm-2 for 600 cycles (14,400 minutes), with 0.138 V overpotential. Post-cycled plated surface is dendrite-free, while stripped surface contains smooth SEI. Conventional PP cells fail rapidly, with dendrites at plating, and "Dead Metal" and SEI clumps at stripping. Potassium hexacyanoferrate(III) cathode KMBs with AlF3 @PP display the enhanced capacity retention (91% at 100 cycles versus 58%). AlF3 partially reacts with K to form an artificial SEI containing KF, AlF3 and Al2 O3 phases. The AlF3 @PP promotes complete electrolyte wetting and enhances uptake, improves ion conductivity, and increases ion transference number. The higher of K+ transference number is ascribed to the strong interaction between AlF3 and FSI- anions, as revealed through 19 F NMR. The enhancement in wetting and performance is general, being demonstrated with ester- and ether-based solvents, with K-, Na- or Li- salts, and with different commercial separators. In full batteries AlF3 prevents Fe crossover and cycling-induced cathode pulverization. This article is protected by copyright. All rights reserved.

Repeated cold rolling and folding is employed to fabricate a metallurgical composite of sodium-antimony-telluride Na2 (Sb2/6 Te3/6 Vac1/6 ) dispersed in electrochemically active sodium metal, termed "NST-Na." This new intermetallic has a vacancy-rich thermodynamically stable face-centered-cubic structure and enables state-of-the-art electrochemical performance in widely employed carbonate and ether electrolytes. NST-Na achieves 100% depth-of-discharge (DOD) in 1 m NaPF6 in G2, with 15 mAh cm-2 at 1 mA cm-2 and Coulombic efficiency (CE) of 99.4%, for 1000 h of plating/stripping. Sodium-metal batteries (SMBs) with NST-Na and Na3 V2 (PO4 )3 (NVP) or sulfur cathodes give significantly improved energy, cycling, and CE (>99%). An anode-free battery with NST collector and NVP obtains 0.23% capacity decay per cycle. Imaging and tomography using conventional and cryogenic microscopy (Cryo-EM) indicate that the sodium metal fills the open space inside the self-supporting sodiophilic NST skeleton, resulting in dense (pore-free and solid electrolyte interphase (SEI)-free) metal deposits with flat surfaces. The baseline Na deposit consists of filament-like dendrites and "dead metal", intermixed with pores and SEI. Density functional theory calculations show that the uniqueness of NST lies in the thermodynamic stability of the Na atoms (rather than clusters) on its surface that leads to planar wetting, and in its own stability that prevents decomposition during cycling.