Anode-Free Sodium Battery through in Situ Plating of Sodium Metal

Sodium-ion batteries (SIBs) have been pursued as a more cost-effective and more sustainable alternative to lithium-ion batteries (LIBs), but these advantages come at the expense of energy density. In this work, we demonstrate that the challenge of energy density for sodium chemistries can be overcome through an anode-free architecture enabled by the use of a nanocarbon nucleation layer formed on Al current collectors. Electrochemical studies show this configuration to provide highly stable and efficient plating and stripping of sodium metal over a range of currents up to 4 mA/cm², sodium loading up to 12 mAh/cm², and with long-term durability exceeding 1000 cycles at a current of 0.5 mA/cm². Building upon this anode-free architecture, we demonstrate a full cell using a presodiated pyrite cathode to achieve energy densities of ∼400 Wh/kg, far surpassing recent reports on SIBs and even the theoretical maximum for LIB technology (387 Wh/kg for LiCoO₂/graphite cells) while still relying on naturally abundant raw materials and cost-effective aqueous processing

Ultrafast Solvent-Assisted Sodium Ion Intercalation into Highly Crystalline Few-Layered Graphene

A maximum sodium capacity of ∼35 mAh/g has hampered the use of crystalline carbon nanostructures for sodium ion battery anodes. We demonstrate that a diglyme solvent shell encapsulating a sodium ion acts as a “nonstick” coating to facilitate rapid ion insertion into crystalline few-layer graphene and bypass slow desolvation kinetics. This yields storage capacities above 150 mAh/g, cycling performance with negligible capacity fade over 8000 cycles, and ∼100 mAh/g capacities maintained at currents of 30 A/g (∼12 s charge). Raman spectroscopy elucidates the ordered, but nondestructive cointercalation mechanism that differs from desolvated ion intercalation processes. In situ Raman measurements identify the Na⁺ staging sequence and isolates Fermi energies for the first and second stage ternary intercalation compounds at ∼0.8 eV and ∼1.2 eV

Role of Nitrogen-Doped Graphene for Improved High-Capacity Potassium Ion Battery Anodes

Potassium is an earth abundant alternative to lithium for rechargeable batteries, but a critical limitation in potassium ion battery anodes is the low capacity of KC₈ graphite intercalation compounds in comparison to conventional LiC₆. Here we demonstrate that nitrogen doping of few-layered graphene can increase the storage capacity of potassium from a theoretical maximum of 278 mAh/g in graphite to over 350 mAh/g, competitive with anode capacity in commercial lithium ion batteries and the highest reported anode capacity so far for potassium ion batteries. Control studies distinguish the importance of nitrogen dopant sites as opposed to sp³ carbon defect sites to achieve the improved performance, which also enables >6× increase in rate performance of doped <i>vs</i> undoped materials. Finally, <i>in situ</i> Raman spectroscopy studies elucidate the staging sequence for doped and undoped materials and demonstrate the mechanism of the observed capacity enhancement to be correlated with distributed storage at local nitrogen sites in a staged KC₈ compound. This study demonstrates a pathway to overcome the limitations of graphitic carbons for anodes in potassium ion batteries by atomically precise engineering of nanomaterials

Polysulfide Anchoring Mechanism Revealed by Atomic Layer Deposition of V₂O₅ and Sulfur-Filled Carbon Nanotubes for Lithium–Sulfur Batteries

Despite the promise of surface engineering to address the challenge of polysulfide shuttling in sulfur–carbon composite cathodes, melt infiltration techniques limit mechanistic studies correlating engineered surfaces and polysulfide anchoring. Here, we present a controlled experimental demonstration of polysulfide anchoring using vapor phase isothermal processing to fill the interior of carbon nanotubes (CNTs) after assembly into binder-free electrodes and atomic layer deposition (ALD) coating of polar V₂O₅ anchoring layers on the CNT surfaces. The ultrathin submonolayer V₂O₅ coating on the CNT exterior surface balances the adverse effect of polysulfide shuttling with the necessity for high sulfur utilization due to binding sites near the conductive CNT surface. The sulfur loaded into the CNT interior provides a spatially separated control volume enabling high sulfur loading with direct sulfur-CNT electrical contact for efficient sulfur conversion. By controlling ALD coating thickness, high initial discharge capacity of 1209 mAh/g_S at 0.1 C and exceptional cycling at 0.2 C with 87% capacity retention after 100 cycles and 73% at 450 cycles is achieved and correlated to an optimal V₂O₅ anchoring layer thickness. This provides experimental evidence that surface engineering approaches can be effective to overcome polysulfide shuttling by controlled design of molecular-scale building blocks for efficient binder free lithium sulfur battery cathodes

Ultrafine Iron Pyrite (FeS₂) Nanocrystals Improve Sodium–Sulfur and Lithium–Sulfur Conversion Reactions for Efficient Batteries

Nanocrystals with quantum-confined length scales are often considered impractical for metal-ion battery electrodes due to the dominance of solid-electrolyte interphase (SEI) layer effects on the measured storage properties. Here we demonstrate that ultrafine sizes (∼4.5 nm, average) of iron pyrite, or FeS₂, nanoparticles are advantageous to sustain reversible conversion reactions in sodium ion and lithium ion batteries. This is attributed to a nanoparticle size comparable to or smaller than the diffusion length of Fe during cation exchange, yielding thermodynamically reversible nanodomains of converted Fe metal and Na_<i>x</i>S or Li_<i>x</i>S conversion products. This is compared to bulk-like electrode materials, where kinetic and thermodynamic limitations of surface-nucleated conversion products inhibit successive conversion cycles. Reversible capacities over 500 and 600 mAh/g for sodium and lithium storage are observed for ultrafine nanoparticles, with improved cycling and rate capability. Unlike alloying or intercalation processes, where SEI effects limit the performance of ultrafine nanoparticles, our work highlights the benefit of quantum dot length-scale nanocrystal electrodes for nanoscale metal sulfide compounds that store energy through chemical conversion reactions

A Sugar-Derived Room-Temperature Sodium Sulfur Battery with Long Term Cycling Stability

We demonstrate a room-temperature sodium sulfur battery based on a confining microporous carbon template derived from sucrose that delivers a reversible capacity over 700 mAh/g_S at 0.1C rates, maintaining 370 mAh/g_S at 10 times higher rates of 1C. Cycling at 1C rates reveals retention of over 300 mAh/g_S capacity across 1500 cycles with Coulombic efficiency >98% due to microporous sulfur confinement and stability of the sodium metal anode in a glyme-based electrolyte. We show sucrose to be an ideal platform to develop microporous carbon capable of mitigating electrode–electrolyte reactivity and loss of soluble intermediate discharge products. In a manner parallel to the low-cost materials of the traditional sodium beta battery, our work demonstrates the combination of table sugar, sulfur, and sodium, all of which are cheap and earth abundant, for a high-performance stable room-temperature sodium sulfur battery

Solution Assembled Single-Walled Carbon Nanotube Foams: Superior Performance in Supercapacitors, Lithium-Ion, and Lithium–Air Batteries

We demonstrate a surfactant-free, solution processing route to form three-dimensional freestanding foams of pristine single-walled carbon nanotubes (SWCNTs) and explore the diverse electrochemical energy storage applications of these materials. This route utilizes SWCNT dispersions in organic <i>n</i>-methylpyrrolidone solvents and subsequent electrophoretic assembly onto a metal foam sacrificial template which can be dissolved to yield surfactant-free, binder-free freestanding SWCNT foams. We further provide a comparison between surfactant-free foams and conventional surfactant-based solvent processing routes and assess performance of these foams in supercapacitors, lithium-ion batteries, and lithium–air batteries. For pristine SWCNT foams, we measure up to 83 F/g specific capacitance in supercapacitors, specific capacity up to 2210 mAh/g for lithium-ion batteries with up to 50% energy efficiency, and specific discharge capacity up to 8275 mAh/g in lithium–air batteries. For lithium–air batteries, this corresponds to a total energy density of 21.2 and 3.3 kWh/kg for the active mass and total battery device, respectively, approaching the 12.7 kWh/kg target energy density of gasoline. In comparison, SWCNT foams prepared with surfactant exhibit poorer gravimetric behavior in all devices and compromised Faradaic storage that leads to depreciated amounts of usable, stored energy. This work demonstrates the broad promise of SWCNTs as lightweight and highly efficient energy storage materials but also emphasizes the importance of clean nanomanufacturing routes which are critical to achieve optimized performance with nanostructures

From the Junkyard to the Power Grid: Ambient Processing of Scrap Metals into Nanostructured Electrodes for Ultrafast Rechargeable Batteries

Here we present the first full cell battery device that is developed entirely from scrap metals of brass and steeltwo of the most commonly used and discarded metals. A room-temperature chemical process is developed to convert brass and steel into functional electrodes for rechargeable energy storage that transforms these multicomponent alloys into redox-active iron oxide and copper oxide materials. The resulting steel–brass battery exhibits cell voltages up to 1.8 V, energy density up to 20 Wh/kg, power density up to 20 kW/kg, and stable cycling over 5000 cycles in alkaline electrolytes. Further, we show the versatility of this technique to enable processing of steel and brass materials of different shapes, sizes, and purity, such as screws and shavings, to produce functional battery components. The simplicity of this approach, building from chemicals commonly available in a household, enables a simple pathway to the local recovery, processing, and assembly of storage systems based on materials that would otherwise be discarded

All Silicon Electrode Photocapacitor for Integrated Energy Storage and Conversion

We demonstrate a simple wafer-scale process by which an individual silicon wafer can be processed into a multifunctional platform where one side is adapted to replace platinum and enable triiodide reduction in a dye-sensitized solar cell and the other side provides on-board charge storage as an electrochemical supercapacitor. This builds upon electrochemical fabrication of dual-sided porous silicon and subsequent carbon surface passivation for silicon electrochemical stability. The utilization of this silicon multifunctional platform as a combined energy storage and conversion system yields a total device efficiency of 2.1%, where the high frequency discharge capability of the integrated supercapacitor gives promise for dynamic load-leveling operations to overcome current and voltage fluctuations during solar energy harvesting

Tunable Mechanochemistry of Lithium Battery Electrodes

The interplay between mechanical strains and battery electrochemistry, or the tunable mechanochemistry of batteries, remains an emerging research area with limited experimental progress. In this report, we demonstrate how elastic strains applied to vanadium pentoxide (V₂O₅), a widely studied cathode material for Li-ion batteries, can modulate the kinetics and energetics of lithium-ion intercalation. We utilize atomic layer deposition to coat V₂O₅ materials onto the surface of a shapememory superelastic NiTi alloy, which allows electrochemical assessment at a fixed and measurable level of elastic strain imposed on the V₂O₅, with strain state assessed through Raman spectroscopy and X-ray diffraction. Our results indicate modulation of electrochemical intercalation potentials by ∼40 mV and an increase of the diffusion coefficient of lithium ions by up to 2.5-times with elastic prestrains of <2% imposed on the V₂O₅. These results are supported by density functional theory calculations and demonstrate how mechanics of nanomaterials can be used as a precise tool to strain engineer the electrochemical energy storage performance of battery materials