62 research outputs found
Nontraditional Approaches To Enable High-Energy and Long-Life LithiumāSulfur Batteries
ConspectusLithiumāsulfur
(LiāS)
batteries are promising for
automotive applications due to their high theoretical energy density
(2600 Wh/kg). In addition, the natural abundance of sulfur could mitigate
the global raw material supply chain challenge of commercial lithium-ion
batteries that use critical elements, such as nickel and cobalt. However,
due to persistent polysulfide shuttling and uncontrolled lithium dendrite
growth, LiāS batteries using nonencapsulated sulfur cathodes
and conventional ether-based electrolytes suffer from rapid cell degradation
upon cycling. Despite significant improvements in recent decades,
there is still a big gap between lab research and commercialization
of the technology. To date, the reported cell energy densities and
cycling life of practical LiāS pouch cells remain largely unsatisfactory.Traditional approaches to improving LiāS performance are
primarily focused on confining polysulfides using electronically
conductive hosts. However, these micro- and mesoporous hosts suffer
from limited pore volume to accommodate high sulfur loading and the
associated volume change during cycling. Moreover, they fail to balance
adsorptionāconversion of polysulfides during chargeādischarge,
leading to the formation of massive dead sulfur. Such hosts are themselves
electrochemically inactive, which decreases the practical energy density.
In contrast, a series of nontraditional approaches, paired with advances
in multiscale mechanistic understanding, have recently demonstrated
exciting performance outcomes not only in conventional coin cells
but also in practical pouch cells.In this Account, we first
introduce our novel cathode design strategies
to overcome polysulfide shuttling and sluggish redox kinetics in thick
S cathodes via seleniumāsulfur chemistry and cathode host engineering.
Next, we gain a mechanistic understanding of LiāS batteries
in various types of electrolytes via a series of spectroscopic, nuclear
magnetic resonance, and electrochemical methods. Meanwhile, a novel
cathode solid electrolyte interphase encapsulation strategy via nonviscous
highly fluorinated ether-based electrolyte is introduced. The established
selection rule by investigating how solvating power retards the shuttle
effect and induces robust cathode/solid-electrolyte interphase formation
is also included. We then discuss how the synergistic interactions
between rational cathode structures and electrolytes can be exploited
to tailor the reaction pathways and kinetics of S cathodes under high
mass loading and lean electrolyte conditions. In addition, a novel
interlayer design to simultaneously overcome degradation processes
(polysulfide shuttling and lithium dendrite formation) and accelerate
redox reaction kinetics is presented. Finally, this Account concludes
with an overview of the challenges and strategies to develop LiāS
pouch cells with high practical energy density, long cycle life, and
fast-charging capability
Electrode Surface Film Formation in Tris(ethylene glycol)-Substituted TrimethylsilaneāLithium Bis(oxalate)borate Electrolyte
One of the silicon-based electrolytes, tris(ethylene glycol)-substituted trimethylsilane (1NM3)ālithium bis(oxalate)borate (LiBOB), is studied as an electrolyte for the LiMn<sub>2</sub>O<sub>4</sub> cathode and graphite anode cell. The solid electrolyte interface (SEI) characteristics and chemical components of both electrodes were investigated by X-ray photoelectron spectroscopy and X-ray diffraction. It was found that SEI components on the anode are similar to those using carbonateāLiBOB electrolyte, which consists of lithium oxalate, lithium borooxalate, and Li<sub><i>x</i></sub>BO<sub><i>y</i></sub>. Moreover, we demonstrated that 1NM3āLiPF<sub>6</sub> electrolyte, which lacks an SEI formation function, could not maintain the graphite structure during the electrochemical process. Therefore, it is evident that the 1NM3āLiBOB combination and its suitable SEI film formation capability are vital to the lithium ion battery with graphite as the anode
Mechanistic Study of Electrolyte Additives to Stabilize High-Voltage CathodeāElectrolyte Interface in Lithium-Ion Batteries
Current developments
of electrolyte additives to stabilize electrodeāelectrolyte
interface in lithium-ion batteries highly rely on a trial-and-error
search, which involves repetitive testing and intensive amount of
resources. The lack of understandings on the fundamental protection
mechanisms of the additives significantly increases the difficulty
for the transformational development of new additives. In this study,
we investigated two types of individual protection routes to build
a robust cathodeāelectrolyte interphase at high potentials:
(i) a direct reduction in the catalytic decomposition of the electrolyte
solvent; and (ii) formation of a ācorrosion inhibitor filmā
that prevents severely attack and passivation from protons that generated
from the solvent oxidation, even the decomposition of solvent cannot
be mitigated. Effect of two exemplary electrolyte additives, lithium
difluoroĀ(oxalato)Āborate (LiDFOB) and 3-hexylthiophene (3HT), on LiNi<sub>0.6</sub>Mn<sub>0.2</sub>Co<sub>0.2</sub>O<sub>2</sub> (NMC 622)
cathode were investigated to validate our hypothesis. It is demonstrated
that understandings of both electrolyte additives and solvent are
essential and careful balance between the cathode protection mechanism
of additives and their side effects is critical to obtain optimum
results. More importantly, this study opens up new directions of rational
design of functional electrolyte additives for the next-generation
high-energy-density lithium-ion chemistries
Stable Nanostructured Cathode with Polycrystalline Li-Deficient Li<sub>0.28</sub>Co<sub>0.29</sub>Ni<sub>0.30</sub>Mn<sub>0.20</sub>O<sub>2</sub> for Lithium-Ion Batteries
The lithium-ion battery,
a major renewable power source, has been
widely applied in portable electronic devices and extended to hybrid
electric vehicles and all-electric vehicles. One of the main issues
for the transportation application is the need to develop high-performance
cathode materials. Here we report a novel nanostructured cathode material
based on air-stable polycrystalline Li<sub>0.28</sub>Co<sub>0.29</sub>Ni<sub>0.30</sub>Mn<sub>0.20</sub>O<sub>2</sub> thin film with lithium
deficiency for high-energy density lithium-ion batteries. This film
is prepared via a method combining radio frequency magnetron sputtering
and annealing using a crystalline and stoichiometric LiCo<sub>1/3</sub>Ni<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub> target. This lithium-deficient
Li<sub>0.28</sub>Co<sub>0.29</sub>Ni<sub>0.30</sub>Mn<sub>0.20</sub>O<sub>2</sub> thin film has a polycrystalline nanostructure, high
tap density, and higher energy and power density compared to the initial
stoichiometric LiCo<sub>1/3</sub>Ni<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub>. Such a material is a promising cathode candidate for high-energy
lithium-ion batteries, especially thin-film batteries
Interactions of Dimethoxy Ethane with Li<sub>2</sub>O<sub>2</sub> Clusters and Likely Decomposition Mechanisms for LiāO<sub>2</sub> Batteries
One
of the major problems facing the successful development of LiāO<sub>2</sub> batteries is the decomposition of nonaqueous electrolytes,
where the decomposition can be chemical or electrochemical
during discharge or charge. In this paper, the decomposition pathways
of dimethoxy ethane (DME) by the chemical reaction with the major
discharge product, Li<sub>2</sub>O<sub>2</sub>, are investigated using
theoretical methods. The computations were carried out using small
Li<sub>2</sub>O<sub>2</sub> clusters as models for potential sites
on Li<sub>2</sub>O<sub>2</sub> surfaces. Both hydrogen and proton
abstraction mechanisms were considered. The computations suggest that
the most favorable decomposition of ether solvents occurs on certain
sites on the lithium
peroxide surfaces involving hydrogen abstraction followed by reaction
with oxygen, which leads to oxidized species such as aldehydes and
carboxylates as well as LiOH on the surface of the lithium peroxide.
The most favorable site is a LiāOāLi site that may be
present on small nanoparticles or as a defect site
on a surface. The decomposition route initiated by the proton abstraction
from the secondary position of DME by the singlet cluster (OāO
site) requires a much larger enthalpy of activation, and subsequent
reactions may require the presence of oxygen or superoxide. Thus,
pathways involving proton abstraction are less likely than that involving
hydrogen abstraction. This type of electrolyte decomposition (electrolyte
with hydrogen atoms) may influence the cell performance including
the crystal growth, nanomorphologies of the discharge products, and
charge overpotential
Cathode Material with Nanorod StructureīøAn Application for Advanced High-Energy and Safe Lithium Batteries
We have developed a novel cathode
material based on lithiumānickelāmanganeseācobalt
oxide, where the manganese concentration remains constant throughout
the particle, while the nickel concentration decreases linearly and
the cobalt concentration increases from the center to the outer surface
of the particle. This full concentration gradient material with a
fixed manganese composition (FCGāMn-F) has an average composition
of LiĀ[Ni<sub>0.60</sub>Co<sub>0.15</sub>Mn<sub>0.25</sub>]ĀO<sub>2</sub> and is composed of rod-shaped primary particles whose length reaches
2.5 Ī¼m, growing in the radial direction. In cell tests, the
FCGāMn-F material delivered a high capacity of 206 mAh g<sup>ā1</sup> with excellent capacity retention of 70.3% after
1000 cycles at 55 Ā°C. This cathode material also exhibited outstanding
rate capability, good low-temperature performance, and excellent safety,
compared to a conventional cathode having the same composition (LiĀ[Ni<sub>0.60</sub>Co<sub>0.15</sub>Mn<sub>0.25</sub>]ĀO<sub>2</sub>), where
the concentration of the metals is constant across the particles
High Capacity O3-Type Na[Li<sub>0.05</sub>(Ni<sub>0.25</sub>Fe<sub>0.25</sub>Mn<sub>0.5</sub>)<sub>0.95</sub>]O<sub>2</sub> Cathode for Sodium Ion Batteries
In this work we report NaĀ[Li<sub>0.05</sub>(Ni<sub>0.25</sub>Fe<sub>0.25</sub>Mn<sub>0.5</sub>)<sub>0.95</sub>]ĀO<sub>2</sub> layered
cathode materials that were synthesized via a coprecipitation method.
The NaĀ[Li<sub>0.05</sub>(Ni<sub>0.25</sub>Fe<sub>0.25</sub>Mn<sub>0.5</sub>)<sub>0.95</sub>]ĀO<sub>2</sub> electrode exhibited an exceptionally
high capacity (180.1 mA h g<sup>ā1</sup> at 0.1 C-rate) as
well as excellent capacity retentions (0.2 C-rate: 89.6%, 0.5 C-rate:
92.1%) and rate capabilities at various C-rates (0.1 C-rate: 180.1
mA h g<sup>ā1</sup>, 1 C-rate: 130.9 mA h g<sup>ā1</sup>, 5 C-rate: 96.2 mA h g<sup>ā1</sup>), which were achieved
due to the Li supporting structural stabilization by introduction
into the transition metal layer. By contrast, the electrode performance
of the lithium-free NaĀ[Ni<sub>0.25</sub>Fe<sub>0.25</sub>Mn<sub>0.5</sub>]ĀO<sub>2</sub> cathode was inferior because of structural disintegration
presumably resulting from Fe<sup>3+</sup> migration from the transition
metal layer to the Na layer during cycling. The long-term cycling
using a full cell consisting of a NaĀ[Li<sub>0.05</sub>(Ni<sub>0.25</sub>Fe<sub>0.25</sub>Mn<sub>0.5</sub>)<sub>0.95</sub>]ĀO<sub>2</sub> cathode
was coupled with a hard carbon anode which exhibited promising cycling
data including a 76% capacity retention over 200 cycles
High-Capacity Sodium Peroxide Based NaāO<sub>2</sub> Batteries with Low Charge Overpotential via a Nanostructured Catalytic Cathode
The
superoxide based NaāO<sub>2</sub> battery has circumvented
the issue of large charge overpotential in LiāO<sub>2</sub> batteries; however, the one-electron process leads to limited capacity.
Herein, a sodium peroxide based low-overpotential (ā¼0.5 V)
NaāO<sub>2</sub> battery with a capacity as high as 7.5 mAh/cm<sup>2</sup> is developed with Pd nanoparticles as catalysts on the cathode
Solid-State Li-Ion Batteries Using Fast, Stable, Glassy Nanocomposite Electrolytes for Good Safety and Long Cycle-Life
The development of safe, stable,
and long-life Li-ion batteries is being intensively pursued to enable
the electrification of transportation and intelligent grid applications.
Here, we report a new solid-state Li-ion battery technology, using
a solid nanocomposite electrolyte composed of porous silica matrices
with in situ immobilizing Li<sup>+</sup>-conducting ionic liquid,
anode material of MCMB, and cathode material of LiCoO<sub>2</sub>,
LiNi<sub>1/3</sub>Co<sub>1/3</sub>Mn<sub>1/3</sub>O<sub>2</sub>, or
LiFePO<sub>4</sub>. An injection printing method is used for the electrode/electrolyte
preparation. Solid nanocomposite electrolytes exhibit superior performance
to the conventional organic electrolytes with regard to safety and
cycle-life. They also have a transparent glassy structure with high
ionic conductivity and good mechanical strength. Solid-state full
cells tested with the various cathodes exhibited high specific capacities,
long cycling stability, and excellent high temperature performance.
This solid-state battery technology will provide new avenues for the
rational engineering of advanced Li-ion batteries and other electrochemical
devices
A Mo<sub>2</sub>C/Carbon Nanotube Composite Cathode for LithiumāOxygen Batteries with High Energy Efficiency and Long Cycle Life
Although lithiumāoxygen batteries are attracting considerable attention because of the potential for an extremely high energy density, their practical use has been restricted owing to a low energy efficiency and poor cycle life compared to lithium-ion batteries. Here we present a nanostructured cathode based on molybdenum carbide nanoparticles (Mo<sub>2</sub>C) dispersed on carbon nanotubes, which dramatically increase the electrical efficiency up to 88% with a cycle life of more than 100 cycles. We found that the Mo<sub>2</sub>C nanoparticle catalysts contribute to the formation of well-dispersed lithium peroxide nanolayers (Li<sub>2</sub>O<sub>2</sub>) on the Mo<sub>2</sub>C/carbon nanotubes with a large contact area during the oxygen reduction reaction (ORR). This Li<sub>2</sub>O<sub>2</sub> structure can be decomposed at low potential upon the oxygen evolution reaction (OER) by avoiding the energy loss associated with the decomposition of the typical Li<sub>2</sub>O<sub>2</sub> discharge products
- ā¦