Nano-rods in Ni-rich layered cathodes for practical batteries.

Lithium transition metal oxide layers, Li[Ni1-x-yCox(Mn and/or Al)y]O2, are widely used and mass-produced for current rechargeable battery cathodes. Development of cathode materials has focused on increasing the Ni content by simply controlling the chemical composition, but as the Ni content has almost reached its limit, a new breakthrough is required. In this regard, microstructural modification is rapidly emerging as a prospective approach, namely in the production of nano-rod layered cathode materials. A comprehensive review of the physicochemical properties and electrochemical performances of cathodes bearing the nano-rod microstructure is provided herein. A detailed discussion is regarding the structural stability of the cathode, which should be maximized to suppress microcrack formation, the main cause of capacity fading in Ni-rich cathode materials. In addition, the morphological features required to achieve optimal performance are examined. Following a discussion of the initial nano-rod cathodes, which were based on compositional concentration gradients, the preparation of nano-rod cathodes without the inclusion of a concentration gradient is reviewed, highlighting the importance of the precursor. Subsequently, the challenges and advances associated with the nano-rod structure are discussed, including considerations for synthesizing nano-rod cathodes and surface shielding of the nano-rod structure. It goes on to cover nano-rod cathode materials for next-generation batteries (e.g., all-solid-state, lithium-metal, and sodium-ion batteries), inspiring the battery community and other materials scientists looking for clues to the solution of the challenges that they encounter.

Mechanism Behind the Loss of Fast Charging Capability in Nickel-Rich Cathode Materials.

Fast charging technology for electric vehicles (EVs), offering rapid charging times similar to conventional vehicle refueling, holds promise but faces obstacles owing to kinetic issues within lithium-ion batteries (LIBs). Specifically, the significance of cathode materials in fast charging has grown because Ni-rich cathodes are employed to enhance the energy density of LIBs. Herein, the mechanism behind the loss of fast charging capability of Ni-rich cathodes during extended cycling is investigated through a comparative analysis of Ni-rich cathodes with different microstructures. The results revealed that microcracks and the resultant cathode deterioration significantly compromised the fast charging capability over extended cycling. When thick rocksalt impurity phases form throughout the particles owing to electrolyte infiltration via microcracks, the limited kinetics of Li+ ions create electrochemically unreactive areas under high-current conditions, resulting in the loss of fast charging capability. Hence, preventing microcrack formation by tailoring microstructures is essential to ensure stability in fast charging capability. Understanding the relationship between microcracks and the loss of fast charging capability is essential for developing Ni-rich cathodes that facilitate stable fast charging upon extended cycling, thereby promoting widespread EV adoption.

Non-Flammable Electrolyte Enables High-Voltage and Wide-Temperature Lithium-Ion Batteries with Fast Charging.

Electrolyte design has become ever more important to enhance the performance of lithium-ion batteries (LIBs). However, the flammability issue and high reactivity of the conventional electrolytes remain a major problem, especially when the LIBs are operated at high voltage and extreme temperatures. Herein, we design a novel non-flammable fluorinated ester electrolyte that enables high cycling stability in wide-temperature variations (e.g., -50 °C-60 °C) and superior power capability (fast charge rates up to 5.0 C) for the graphite||LiNi0.8 Co0.1 Mn0.1 O2 (NCM811) battery at high voltage (i.e., >4.3 V vs. Li/Li+ ). Moreover, this work sheds new light on the dynamic evolution and interaction among the Li+ , solvent, and anion at the molecular level. By elucidating the fundamental relationship between the Li+ solvation structure and electrochemical performance, we can facilitate the development of high-safety and high-energy-density batteries operating in harsh conditions.

Intergranular Shielding for Ultrafine-Grained Mo-Doped Ni-Rich Li[Ni0.96 Co0.04 ]O2 Cathode for Li-Ion Batteries with High Energy Density and Long Life.

Deploying Ni-enriched (Ni≥95 %) layered cathodes for high energy-density lithium-ion batteries (LIBs) requires resolving a series of technical challenges. Among them, the structural weaknesses of the cathode, vigorous reactivity of the labile Ni4+ ion species, gas evolution and associated cell swelling, and thermal instability issues are critical obstacles that must be solved. Herein, we propose an intuitive strategy that can effectively ameliorate the degradation of an extremely high-Ni-layered cathode, the construction of ultrafine-scale microstructure and subsequent intergranular shielding of grains. The formation of ultrafine grains in the Ni-enriched Li[Ni0.96 Co0.04 ]O2 (NC96) cathode, achieved by impeding particle coarsening during cathode calcination, noticeably improved the mechanical durability and electrochemical performance of the cathode. However, the buildup of the strain-resistant microstructure in Mo-doped NC96 concurrently increased the cathode-electrolyte contact area at the secondary particle surface, which adversely accelerated parasitic reactions with the electrolyte. The intergranular protection of the refined microstructure resolved the remaining chemical instability of the Mo-doped NC96 cathode by forming an F-induced coating layer, effectively alleviating structural degradation and gas generation, thereby extending the battery's lifespan. The proposed strategies synergistically improved the structural and chemical durability of the NC96 cathode, satisfying the energy density, life cycle performance, and safety requirements for next-generation LIBs.

Synergistic Engineering of Se Vacancies and Heterointerfaces in Zinc-Cobalt Selenide Anode for Highly Efficient Na-Ion Batteries.

The exploitation of effective strategies to accelerate the Na+ diffusion kinetics and improve the structural stability in the electrode is extremely important for the development of high efficientcy sodium-ion batteries. Herein, Se vacancies and heterostructure engineering are utilized to improve the Na+ -storage performance of transition metal selenides anode prepared through a facile two-in-one route. The experimental results coupled with theoretical calculations reveal that the successful construction of the Se vacancies and heterostructure interfaces can effectively lower the Na+ diffusion barrier, accelerate the charge transfer efficiency, improve Na+ adsorption ability, and provide an abundance of active sites. Consequently, the batteries based on the constructed ZnSe/CoSe2 -CN anode manifest a high initial Coulombic efficiency (97.7%), remarkable specific capacities (547.1 mAh g-1 at 0.5 A g-1 ), superb rate capability (362.1 mAh g-1 at 20 A g-1 ), as well as ultrastable long-term stability (1000 cycles) with a satisfied specific capacity (535.6 mAh g-1 ) at 1 A g-1 . This work facilitates an in-depth understanding of the synergistic effect of vacancies and heterojunctions in improving the Na+ reaction kinetics, providing an effective strategy to the rational design of key materials for high efficiency rechargeable batteries.

Lithium-Oxygen Batteries and Related Systems: Potential, Status, and Future.

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO2 emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation. Present lithium-ion technologies are preparing the public for this inevitable change, but their maximum theoretical specific capacity presents a limitation. Their high cost is another concern for commercial viability. Metal-air batteries have the highest theoretical energy density of all possible secondary battery technologies and could yield step changes in energy storage, if their practical difficulties could be overcome. The scope of this review is to provide an objective, comprehensive, and authoritative assessment of the intensive work invested in nonaqueous rechargeable metal-air batteries over the past few years, which identified the key problems and guides directions to solve them. We focus primarily on the challenges and outlook for Li-O2 cells but include Na-O2, K-O2, and Mg-O2 cells for comparison. Our review highlights the interdisciplinary nature of this field that involves a combination of materials chemistry, electrochemistry, computation, microscopy, spectroscopy, and surface science. The mechanisms of O2 reduction and evolution are considered in the light of recent findings, along with developments in positive and negative electrodes, electrolytes, electrocatalysis on surfaces and in solution, and the degradative effect of singlet oxygen, which is typically formed in Li-O2 cells.

A lithium-oxygen battery based on lithium superoxide.

Batteries based on sodium superoxide and on potassium superoxide have recently been reported. However, there have been no reports of a battery based on lithium superoxide (LiO2), despite much research into the lithium-oxygen (Li-O2) battery because of its potential high energy density. Several studies of Li-O2 batteries have found evidence of LiO2 being formed as one component of the discharge product along with lithium peroxide (Li2O2). In addition, theoretical calculations have indicated that some forms of LiO2 may have a long lifetime. These studies also suggest that it might be possible to form LiO2 alone for use in a battery. However, solid LiO2 has been difficult to synthesize in pure form because it is thermodynamically unstable with respect to disproportionation, giving Li2O2 (refs 19, 20). Here we show that crystalline LiO2 can be stabilized in a Li-O2 battery by using a suitable graphene-based cathode. Various characterization techniques reveal no evidence for the presence of Li2O2. A novel templating growth mechanism involving the use of iridium nanoparticles on the cathode surface may be responsible for the growth of crystalline LiO2. Our results demonstrate that the LiO2 formed in the Li-O2 battery is stable enough for the battery to be repeatedly charged and discharged with a very low charge potential (about 3.2 volts). We anticipate that this discovery will lead to methods of synthesizing and stabilizing LiO2, which could open the way to high-energy-density batteries based on LiO2 as well as to other possible uses of this compound, such as oxygen storage.

Critical Role of Functional Groups Containing N, S, and O on Graphene Surface for Stable and Fast Charging Li-S Batteries.

Lithium-sulfur (Li-S) batteries are considered one of the most promising energy storage technologies, possibly replacing the state-of-the-art lithium-ion (Li-ion) batteries owing to their high energy density, low cost, and eco-compatibility. However, the migration of high-order lithium polysulfides (LiPs) to the lithium surface and the sluggish electrochemical kinetics pose challenges to their commercialization. The interactions between the cathode and LiPs can be enhanced by the doping of the carbon host with heteroatoms, however with relatively low doping content (<10%) in the bulk of the carbon, which can hardly interact with LiPs at the host surface. In this study, the grafting of versatile functional groups with designable properties (e.g., catalytic effects) directly on the surface of the carbon host is proposed to enhance interactions with LiPs. As model systems, benzene groups containing N/O and S/O atoms are vertically grafted and uniformly distributed on the surface of expanded reduced graphene oxide, fostering a stable interface between the cathode and LiPs. The combination of experiments and density functional theory calculations demonstrate improvements in chemical interactions between graphene and LiPs, with an enhancement in the electrochemical kinetics, power, and energy densities.

Nano/Microstructured Silicon-Carbon Hybrid Composite Particles Fabricated with Corn Starch Biowaste as Anode Materials for Li-Ion Batteries.

Silicon has a great potential as an alternative to graphite which is currently used commercially as an anode material in lithium-ion batteries (LIBs) because of its exceptional capacity and reasonable working potential. Herein, a low-cost and scalable approach is proposed for the production of high-performance silicon-carbon (Si-C) hybrid composite anodes for high-energy LIBs. The Si-C composite material is synthesized using a scalable microemulsion method by selecting silicon nanoparticles, using low-cost corn starch as a biomass precursor and finally conducting heat treatment under C3H6 gas. This produces a unique nano/microstructured Si-C hybrid composite comprised of silicon nanoparticles embedded in micron-sized amorphous carbon balls derived from corn starch that is capsuled by thin graphitic carbon layer. Such a dual carbon matrix tightly surrounds the silicon nanoparticles that provides high electronic conductivity and significantly decreases the absolute stress/strain of the material during multiple lithiation-delithiation processes. The Si-C hybrid composite anode demonstrates a high capacity of 1800 mAh g-1, outstanding cycling stability with capacity retention of 80% over 500 cycles, and fast charge-discharge capability of 12 min. Moreover, the Si-C composite anode exhibits good acceptability in practical LIBs assembled with commercial Li[Ni0.6Co0.2Mn0.2]O2 and Li[Ni0.80Co0.15Al0.05]O2 cathodes.

Engineering Sodium-Ion Solvation Structure to Stabilize Sodium Anodes: Universal Strategy for Fast-Charging and Safer Sodium-Ion Batteries.

Sodium-ion batteries are promising alternatives for lithium-ion batteries due to their lower cost caused by global sodium availability. However, the low Coulombic efficiency (CE) of the sodium metal plating/stripping process represents a serious issue for the Na anode, which hinders achieving a higher energy density. Herein, we report that the Na+ solvation structure, particularly the type and location of the anions, plays a critical role in determining the Na anode performance. We show that the low CE results from anion-mediated corrosion, which can be tackled readily through tuning the anion interaction at the electrolyte/anode interface. Our strategy thus enables fast-charging Na-ion and Na-S batteries with a remarkable cycle life. The presented insights differ from the prevailing interpretation that the failure mechanism mostly results from sodium dendrite growth and/or solid electrolyte interphase formation. Our anionic model introduces a new guideline for improving the electrolytes for metal-ion batteries with a greater energy density.

WO3 Nanowire/Carbon Nanotube Interlayer as a Chemical Adsorption Mediator for High-Performance Lithium-Sulfur Batteries.

We developed a new nanowire for enhancing the performance of lithium-sulfur batteries. In this study, we synthesized WO3 nanowires (WNWs) via a simple hydrothermal method. WNWs and one-dimensional materials are easily mixed with carbon nanotubes (CNTs) to form interlayers. The WNW interacts with lithium polysulfides through a thiosulfate mediator, retaining the lithium polysulfide near the cathode to increase the reaction kinetics. The lithium-sulfur cell achieves a very high initial discharge capacity of 1558 and 656 mAh g-1 at 0.1 and 3 C, respectively. Moreover, a cell with a high sulfur mass loading of 4.2 mg cm-2 still delivers a high capacity of 1136 mAh g-1 at a current density of 0.2 C and it showed a capacity of 939 mAh g-1 even after 100 cycles. The WNW/CNT interlayer maintains structural stability even after electrochemical testing. This excellent performance and structural stability are due to the chemical adsorption and catalytic effects of the thiosulfate mediator on WNW.

Na2V6O16·3H2O Barnesite Nanorod: An Open Door to Display a Stable and High Energy for Aqueous Rechargeable Zn-Ion Batteries as Cathodes.

Owing to their safety and low cost, aqueous rechargeable Zn-ion batteries (ARZIBs) are currently more feasible for grid-scale applications, as compared to their alkali counterparts such as lithium- and sodium-ion batteries (LIBs and SIBs), for both aqueous and nonaqueous systems. However, the materials used in ARZIBs have a poor rate capability and inadequate cycle lifespan, serving as a major handicap for long-term storage applications. Here, we report vanadium-based Na2V6O16·3H2O nanorods employed as a positive electrode for ARZIBs, which display superior electrochemical Zn storage properties. A reversible Zn2+-ion (de)intercalation reaction describing the storage mechanism is revealed using the in situ synchrotron X-ray diffraction technique. This cathode material delivers a very high rate capability and high capacity retention of more than 80% over 1000 cycles, at a current rate of 40C (1C = 361 mA g-1). The battery offers a specific energy of 90 W h kg-1 at a specific power of 15.8 KW kg-1, enlightening the material advantages for an eco-friendly atmosphere.

Microstructural Degradation of Ni-Rich Li[Nix Coy Mn1 -x-y ]O2 Cathodes During Accelerated Calendar Aging.

Because electric vehicles (EVs) are used intermittently with long resting periods in the fully charged state before driving, calendar aging behavior is an important criterion for the application of Li-ion batteries used in EVs. In this work, Ni-rich Li[Nix Coy Mn1 -x-y ]O2 (x = 0.8 and 0.9) cathode materials with high energy densities, but low cycling stabilities are investigated to characterize their microstructural degradation during accelerated calendar aging. Although the particles seem to maintain their crystal structures and morphologies, the microcracks which develop during calendar aging remain even in the fully discharged state. An NiO-like phase rock-salt structure of tens of nanometers in thickness accumulates on the surfaces of the primary particles through parasitic reactions with the electrolyte. In addition, the passive layer of this rock-salt structure near the microcracks is gradually exfoliated from the primary particles, exposing fresh surfaces containing Ni4+ to the electrolyte. Interestingly, the interior primary particles near the microcracks have deteriorated more severely than the outer particles. The microstructural degradation is worsened with increasing Ni contents in the cathode materials, directly affecting electrochemical performances such as the reversible capacities and voltage profiles.

Sodium-ion batteries: present and future.

Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.

Self-Rearrangement of Silicon Nanoparticles Embedded in Micro-Carbon Sphere Framework for High-Energy and Long-Life Lithium-Ion Batteries.

Despite its highest theoretical capacity, the practical applications of the silicon anode are still limited by severe capacity fading, which is due to pulverization of the Si particles through volume change during charge and discharge. In this study, silicon nanoparticles are embedded in micron-sized porous carbon spheres (Si-MCS) via a facile hydrothermal process in order to provide a stiff carbon framework that functions as a cage to hold the pulverized silicon pieces. The carbon framework subsequently allows these silicon pieces to rearrange themselves in restricted domains within the sphere. Unlike current carbon coating methods, the Si-MCS electrode is immune to delamination. Hence, it demonstrates unprecedented excellent cyclability (capacity retention: 93.5% after 500 cycles at 0.8 A g-1), high rate capability (with a specific capacity of 880 mAh g-1 at the high discharge current density of 40 A g-1), and high volumetric capacity (814.8 mAh cm-3) on account of increased tap density. The lithium-ion battery using the new Si-MCS anode and commercial LiNi0.6Co0.2Mn0.2O2 cathode shows a high specific energy density above 300 Wh kg-1, which is considerably higher than that of commercial graphite anodes.

2,4-Dimethoxy-2,4-dimethylpentan-3-one: An Aprotic Solvent Designed for Stability in Li-O2 Cells.

In this study, we present a new aprotic solvent, 2,4-dimethoxy-2,4-dimethylpentan-3-one (DMDMP), which is designed to resist nucleophilic attack and hydrogen abstraction by reduced oxygen species. Li-O2 cells using DMDMP solutions were successfully cycled. By various analytical measurements, we showed that even after prolonged cycling only a negligible amount of DMDMP was degraded. We suggest that the observed capacity fading of the Li-O2 DMDMP-based cells was due to instability of the lithium anode during cycling. The stability toward oxygen species makes DMDMP an excellent solvent candidate for many kinds of electrochemical systems which involve oxygen reduction and assorted evaluation reactions.

A Long-Life Lithium Ion Battery with Enhanced Electrode/Electrolyte Interface by Using an Ionic Liquid Solution.

In this paper, we report an advanced long-life lithium ion battery, employing a Pyr14 TFSI-LiTFSI non-flammable ionic liquid (IL) electrolyte, a nanostructured tin carbon (Sn-C) nanocomposite anode, and a layered LiNi1/3 Co1/3 Mn1/3 O2 (NMC) cathode. The IL-based electrolyte is characterized in terms of conductivity and viscosity at various temperatures, revealing a Vogel-Tammann-Fulcher (VTF) trend. Lithium half-cells employing the Sn-C anode and NMC cathode in the Pyr14 TFSI-LiTFSI electrolyte are investigated by galvanostatic cycling at various temperatures, demonstrating the full compatibility of the electrolyte with the selected electrode materials. The NMC and Sn-C electrodes are combined into a cathode-limited full cell, which is subjected to prolonged cycling at 40 °C, revealing a very stable capacity of about 140 mAh g(-1) and retention above 99 % over 400 cycles. The electrode/electrolyte interface is further characterized through a combination of electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) investigations upon cell cycling. The remarkable performances reported here definitively indicate that IL-based lithium ion cells are suitable batteries for application in electric vehicles.

Study on the Catalytic Activity of Noble Metal Nanoparticles on Reduced Graphene Oxide for Oxygen Evolution Reactions in Lithium-Air Batteries.

Among many challenges present in Li-air batteries, one of the main reasons of low efficiency is the high charge overpotential due to the slow oxygen evolution reaction (OER). Here, we present systematic evaluation of Pt, Pd, and Ru nanoparticles supported on rGO as OER electrocatalysts in Li-air cell cathodes with LiCF3SO3-tetra(ethylene glycol) dimethyl ether (TEGDME) salt-electrolyte system. All of the noble metals explored could lower the charge overpotentials, and among them, Ru-rGO hybrids exhibited the most stable cycling performance and the lowest charge overpotentials. Role of Ru nanoparticles in boosting oxidation kinetics of the discharge products were investigated. Apparent behavior of Ru nanoparticles was different from the conventional electrocatalysts that lower activation barrier through electron transfer, because the major contribution of Ru nanoparticles in lowering charge overpotential is to control the nature of the discharge products. Ru nanoparticles facilitated thin film-like or nanoparticulate Li2O2 formation during oxygen reduction reaction (ORR), which decomposes at lower potentials during charge, although the conventional role as electrocatalysts during OER cannot be ruled out. Pt-and Pd-rGO hybrids showed fluctuating potential profiles during the cycling. Although Pt- and Pd-rGO decomposed the electrolyte after electrochemical cycling, no electrolyte instability was observed with Ru-rGO hybrids. This study provides the possibility of screening selective electrocatalysts for Li-air cells while maintaining electrolyte stability.

Highly Cyclable Lithium-Sulfur Batteries with a Dual-Type Sulfur Cathode and a Lithiated Si/SiOx Nanosphere Anode.

Lithium-sulfur batteries could become an excellent alternative to replace the currently used lithium-ion batteries due to their higher energy density and lower production cost; however, commercialization of lithium-sulfur batteries has so far been limited due to the cyclability problems associated with both the sulfur cathode and the lithium-metal anode. Herein, we demonstrate a highly reliable lithium-sulfur battery showing cycle performance comparable to that of lithium-ion batteries; our design uses a highly reversible dual-type sulfur cathode (solid sulfur electrode and polysulfide catholyte) and a lithiated Si/SiOx nanosphere anode. Our lithium-sulfur cell shows superior battery performance in terms of high specific capacity, excellent charge-discharge efficiency, and remarkable cycle life, delivering a specific capacity of ∼750 mAh g(-1) over 500 cycles (85% of the initial capacity). These promising behaviors may arise from a synergistic effect of the enhanced electrochemical performance of the newly designed anode and the optimized layout of the cathode.

Anatase titania nanorods as an intercalation anode material for rechargeable sodium batteries.

For the first time, we report the electrochemical activity of anatase TiO2 nanorods in a Na cell. The anatase TiO2 nanorods were synthesized by a hydrothermal method, and their surfaces were coated by carbon to improve the electric conductivity through carbonization of pitch at 700 °C for 2 h in Ar flow. The resulting structure does not change before and after the carbon coating, as confirmed by X-ray diffraction (XRD). Transmission electron microscopic images confirm the presence of a carbon coating on the anatase TiO2 nanorods. In cell tests, anodes of bare and carbon-coated anatase TiO2 nanorods exhibit stable cycling performance and attain a capacity of about 172 and 193 mAh g(-1) on the first charge, respectively, in the voltage range of 3-0 V. With the help of the conductive carbon layers, the carbon-coated anatase TiO2 delivers more capacity at high rates, 104 mAh g(-1) at the 10 C-rate (3.3 A g(-1)), 82 mAh g(-1) at the 30 C-rate (10 A g(-1)), and 53 mAh g(-1) at the 100 C-rate (33 A g(-1)). By contrast, the anode of bare anatase TiO2 nanorods delivers only about 38 mAh g(-1) at the 10 C-rate (3.3 A g(-1)). The excellent cyclability and high-rate capability are the result of a Na(+) insertion and extraction reaction into the host structure coupled with Ti(4+/3+) redox reaction, as revealed by X-ray absorption spectroscopy.