11 research outputs found
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/cm<sup>2</sup>, sodium loading up to
12 mAh/cm<sup>2</sup>, and with long-term durability exceeding 1000
cycles at a current of 0.5 mA/cm<sup>2</sup>. 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 LiCoO<sub>2</sub>/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<sup>+</sup> 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 KC<sub>8</sub> graphite intercalation compounds
in comparison to conventional LiC<sub>6</sub>. 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 sp<sup>3</sup> 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 KC<sub>8</sub> 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 V<sub>2</sub>O<sub>5</sub> 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 V<sub>2</sub>O<sub>5</sub> anchoring
layers on the CNT surfaces. The ultrathin submonolayer V<sub>2</sub>O<sub>5</sub> 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<sub>S</sub> 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 V<sub>2</sub>O<sub>5</sub> 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 (FeS<sub>2</sub>) 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 FeS<sub>2</sub>, 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<sub><i>x</i></sub>S or Li<sub><i>x</i></sub>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<sub>S</sub> at 0.1C rates, maintaining 370
mAh/g<sub>S</sub> at 10 times higher rates of 1C. Cycling at 1C rates
reveals retention of over 300 mAh/g<sub>S</sub> 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 steeltwo 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 (V<sub>2</sub>O<sub>5</sub>), 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 V<sub>2</sub>O<sub>5</sub> 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 V<sub>2</sub>O<sub>5</sub>, 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 V<sub>2</sub>O<sub>5</sub>. 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