Alkali-ion Batteries Research Articles

In-situ investigation and application of cyano-substituted organic electrode for rechargeable aqueous Na-ion batteries

Rechargeable aqueous alkali-ion batteries are of great interest in cost-effective, risk-free and green energy-storage technologies. Although redox-active organic compounds are regarded as a kind of promising electrode materials, the limited capacity and low charge-transfer capability still hinder their applications in aqueous alkali-ion batteries. Herein, we have designed a cyano-substituted diquinoxalinophenazine (3CN-DPZ) organic electrode. For the first time, in-operando monitoring techniques, i.e., in-situ Raman and in-situ FTIR investigations, combined with the theoretical calculations are thoroughly carried out to explore the role of electron-withdrawing cyano substituents in 3CN-DPZ organic electrode for aqueous Na+ storage. It is demonstrated that the introduced cyano groups provide redox-active sites for the 3CN-DPZ organic electrode upon Na+ uptake/removal and have the strong electron absorption ability coordinated with Na+ in aqueous electrolyte. Therefore, the 3CN-DPZ organic electrode delivers a large specific capacity of 305.1 mAh/g at 1 A/g, a high rate capability of 211.3 mAh/g at 64 A/g, and an exceptional cycling retention of ∼ 97.9 % over 5000 cycles. Furthermore, a high-performance aqueous Na-ion battery (ANIB) has been fabricated with considerable energy/power characteristics and long cycling lifespan, revealing its potential scalable applications in satisfying the various requirements of high-safety and low-cost energy storage systems.

Polymorphic Phosphorus Applied to Alkali-Ion Battery Electrodes.

The polymorphic phosphorus materials such as amorphous red and black ones have been used as the anodes for alkali-ion batteries. As the research field of 2D materials is pioneered, the fibrous red and violet phosphorus begin to be investigated and predicted for various devices. Meanwhile, they are not only applied to the active materials of electrodes but also the formation of protective layers for battery application. This article briefly introduces the primary allotropes of phosphorus, their research progress, and their potential for the application of alkali-ion batteries. Next, the recent studies concerning their applications of electrodes and protective layers for alkali-ion batteries are discussed in detail. Finally, the merits and drawbacks of preparation approaches, the strategies for improvement of battery performance, and the urgent challenges as well as possible solutions for future development of alkali-ion batteries using the electrodes or protective layers made from phosphorus materials, are summarized.

Multiple redox-active cyano-substituted organic compound integrated with MXene for high-performance flexible aqueous K-ion battery

Aqueous alkali-ion batteries are a kind of risk-free and low-cost energy storage devices for portable equipment and wearable products. Even though phenazine-based organic compounds have π-conjugated aromatic structures and contain N heteroatoms with redox-active centers, the limited capacity performance still hinders their application as the electrode material for aqueous alkali-ion batteries. Herein, we firstly designed a novel cyano-substituted diquinoxalinophenazine (6CN-DQPZ) organic compound, which was further integrated with MXene to construct a self-supported and binder-free 6CN-DQPZ@MXene electrode. Theoretical calculation and in-situ Raman analysis demonstrate that the introduction of cyano electron-withdrawing groups not only optimizes the electronic structure of 6CN-DQPZ to enhance its electrochemical activity, but also provides additional redox-active sites for 6CN-DQPZ upon K+ uptake/removal, thereby endowing a rapid, ultra-stable and efficient aqueous K+ storage behavior for the 6CN-DQPZ@MXene electrode, especially a considerably large reversible capacity of 477.6 mAh cm−3 (or 238.8 mAh/g) and exceptional cycle performance with a high capacity retention of ∼ 98.9 % over 2000 cycles. For actual applications, a high-performance flexible aqueous K-ion battery (AKIB) has been fabricated with considerable energy/power characteristics and long lifespan under the straight and bending states, revealing its potential application as a reliable and efficient flexible energy storage device for portable/wearable electronics.

Oxidative Molecular Layer Deposition of Amine-Containing Conjugated Polymer Thin Films

Conjugated polymers such as polyethylenedioxythiophene (pEDOT), polypyrrole (pPy), and polyaniline (pAni) exhibit high electrochemical capacities, making them appealing as electrode materials for energy storage, electrochemical desalination, and chemical sensing. Recent work has established the growth of thin films of pEDOT using alternating gas-phase exposures of the EDOT monomer and a metal chloride (e.g., MoCl5) oxidant in a process termed oxidative molecular layer deposition (oMLD). Here, we describe the first demonstration of oMLD of amine-containing conjugated polymers. We find that pyrrole (Py) and MoCl5 undergo self-limiting surface reactions during oMLD exposures to form conformal pPy thin films, but oMLD using aniline (Ani) and p-phenylenediamine (PDA) monomers yields unexpected azo functionality. The formation of azo groups is attributed to an MoCl5-amine surface adduct that spatially constrains polymerization reactions near the amine group and produces azo groups when coupling two primary amines. pPy grown by oMLD exhibits a record-breaking 282 mAh/g capacity in an aqueous electrolyte, and PDA/MoCl5 oMLD yields azo polymers of interest as anode materials for alkali-ion batteries. Alternating between Py and PDA monomers during oMLD produces molecularly assembled copolymers with qualitatively different electrochemical responses from the isolated monomer structures. This work lays the foundation for the growth of conformal thin films of conjugated amine polymers with molecular-level control of composition and thickness.

A novel silicon-doped 2D Ti2C MXene monolayer as high capacity stable anode material for lithium ion batteries: Insight from density functional theory study

Although MXene is still considered as the newcomer of the 2D nanomaterials family for energy storage application, pristine MXene is unable to satisfy the capacity demand of energy storage devices like alkali-ion batteries. Here, we present a DFT based investigation with GGA-PBE exchange-correlation functional on pristine and Si-doped Ti2C system for potential application as anode materials in lithium ion batteries. This work explores the structural, electronic and adsorption behavior of pristine and Si-doped Ti2C nanosheets. All predictedSi-doped Ti2CMXenes adsorbed Li-atoms with favorableadsorption energy (Ead)without any structural deformation, exhibiting good structural stability. For three distinct adsorption sites, the Eadare calculated as −1.48 eV, −1.55 eV and −1.57 eV which indicates thatEadis higher when lithium ion is adsorbed at the titanium atomic sites. The calculated specific capacity for pristine Ti2C is 331.6 mAh/g, which is less than conventional graphite anode material. But after doping Si atoms, the specific capacity increases up to 439.4 mAh/g for Si-doped Ti2C and enhance the storage capacity up to 32% for lithium ion batteries. The predicted Vocfor pristine nanosheet is 2.26 V and for the mono- and di-Si doped nanosheets 2.24 V and 2.14 V, respectively. Besides, the nanosheets remain metallic during lithiation process after doping silicon.

Boosting K-ion kinetics by interfacial polarization induced by amorphous MoO3- for MoSe2/MoO3-@rGO composites

Ø The K-ion storage of MoSe 2 @rGO is enhanced by incorporating amorphous MoO 3- x with oxygen vacancies. Ø A built-in electric field benefits for electron-transfer and K-ion migration across the hetero-junction interface. Ø Larger dielectric polarization induced by MoO 3- x reduces charge transfer resistance and enhance K-ion migration across electric double-layer. Promoting interfacial reaction kinetics is highly desirable for achieving high-performances of anode material in alkali-ion batteries. Herein, flower-like MoSe 2 /MoO 3- x @rGO composites are fabricated by a facile solvothermal method involving a thermal-treatment at 800°C. When evaluated as an anode material for potassium ion batteries, MoSe 2 /MoO 3- x @rGO delivers 248.2 mA h g −1 after 50 cycles at 0.2 A g −1 with a capacity retention of 84.6% and 182.9 mA h g −1 after 150 cycles at 1.0 A g −1 with a capacity retention of almost 61.2%, superior to those of bare MoSe 2 or MoSe 2 @rGO composites. Analysis from electrochemical measurements, the amorphous MoO 3- x containing oxygen vacancies could not only effectively buffer the self-aggregation of MoSe 2 nanosheets but also provides lots of accessible active sites for potassium ion storage. Additionally, the open channels in the amorphous MoO 3- x phase lead to easier ion hopping and smaller diffusion barriers. Furthermore, the built-in electric field at the interface would be beneficial for electron transfer and K-ion migration across the hetero-junction interface. Moreover, larger dielectric polarization induced by the high relative permittivity of amorphous MoO 3- x would reduce charge transfer resistance and enhance K-ion migration across electric double-layer. Our work provides new insight into the enhanced performance of anode material coated by an amorphous layer with large relative permittivity.

A Versatile Strategy for Achieving Fast‐Charging Batteries via Interfacial Engineering: Pseudocapacitive Potassium Storage without Nanostructuring

The rapid transport of alkali ions in electrodes is a long-time dream for fast-charging batteries. Though electrode nanostructuring has increased the rate-capability, its practical use is limited because of the low tap density and severe irreversible reactions. Therefore, development of a strategy to design fast-charging micron-sized electrodes without nanostructuring is of significant importance. Herein, a simple and versatile strategy to accelerate the alkali ion diffusion behavior in micron-sized electrode is reported. It is demonstrated that the diffusion rate of K+ ions is significantly improved at the hetero-interface between orthorhombic Nb2 O5 (001) and monoclinic MoO2 (110) planes. Lattice distortion at the hetero-interface generates an inner space large enough for the facile transport of K+ ions, and electron localization near oxygen-vacant sites further enhances the ion diffusion behavior. As a result, the interfacial-engineered micron-sized anode material achieves an outstanding rate capability in potassium-ion batteries (KIBs), even higher than nanostructured orthorhombic Nb2 O5 which is famous for fast-charging electrodes. This is the first study to develop an intercalation pseudocapacitive micron-sized anode without nanostructuring for fast-charging and high volumetric energy density KIBs. More interestingly, this strategy is not limited to K+ ion, but also applicable to Li+ ion, implying the versatility of interfacial engineering for alkali ion batteries.

Fast charging of alkali-ion batteries at the single-particle level: the impact of particle geometry on diffusional and kinetic bottlenecks in voltammetry

Fast charging of alkali-ion batteries at the single-particle level: the impact of particle geometry on diffusional and kinetic bottlenecks in voltammetry

Designing Advanced Liquid Electrolytes for Alkali Metal Batteries: Principles, Progress, and Perspectives

The ever‐growing pursuit of high energy density batteries has triggered extensive efforts toward developing alkali metal (Li, Na, and K) battery (AMB) technologies owing to high theoretical capacities and low redox potentials of metallic anodes. Typically, for new battery systems, the electrolyte design is critical for realizing the battery electrochemistry of AMBs. Conventional electrolytes in alkali ion batteries are generally unsuitable for sustaining the stability owing to the hyper‐reactivity and dendritic growth of alkali metals. In this review, we begin with the fundamentals of AMB electrolytes. Recent advancements in concentrated and fluorinated electrolytes, as well as functional electrolyte additives for boosting the stability of Li metal batteries, are summarized and discussed with a special focus on structure–composition–performance relationships. We then delve into the electrolyte formulations for Na‐ and K metal batteries, including those in which Na/K do not adhere to the Li‐inherited paradigms. Finally, the challenges and the future research needs in advanced electrolytes for AMB are highlighted. This comprehensive review sheds light on the principles for the rational design of promising electrolytes and offers new inspirations for developing stable AMBs with high performance.

Molecular precursor driven synthesis of phase pure tin sulfide nanosheets and investigation of their photoresponsive behaviour

Tin Sulfide (SnS) has emerged as an important semiconductor for photovoltaics, thermoelectric and as high-capacity anode material for alkali-ion batteries. However, producing phase pure SnS free from higher tin sulfides (SnS2 and Sn2S3) having different optoelectronic properties, is a challenging task. In this report, we present a structurally characterized single source molecular precursor (SSP), [tBu2Sn(SpymMe2)2], for the facile synthesis of phase pure orthorhombic SnS nanosheets in different high boiling solvents (oleylamine, octadecene, dodecanthiol) with varying coordination ability. As-prepared SnS nanosheets were thoroughly checked for its phase purity, elemental composition and morphology through pXRD and electron microscopic techniques. A distinct variation in crystallite size, morphology and band gap of nanosheets as function of reaction solvent was observed during investigation. Finally, the as prepared SnS nanosheets derived from SSP exhibit high photoresponsitivity and photostability which make them promising candidate for alternative low-cost photon absorber material.

Carbon/Pyropolymer-based Electrode Materials for Alkali Ion Storage

Carbon materials have large numbers of redox-active sites for alkali-ion storage, such as Stone-Wales, vacancy, edge, and pseudo-edge defect sites as well as extrinsic defects. The topological defects can be a redox host in anodic voltage regions, while the extrinsic defects can store alkali ions in a cathodic voltage range. Therefore, carbon materials can be a great candidate for both anode and cathode for alkali ion batteries. In this study, alkali ion storage behaviors of different carbon materials, highly defective graphene-based nanosheet (GNS), well-ordered graphite nanoplate (GNP), hard carbon series samples, and nanoporous pyropolymers which are a kind of carbon materials including numerous defects, are reviewed, and their potentials as both anode and cathode for alkali ion batteries are discussed.

Self-Sacrifice Template Construction of Uniform Yolk-Shell ZnS@C for Superior Alkali-Ion Storage.

Secondary batteries have been widespread in the daily life causing an ever‐growing demand for long‐cycle lifespan and high‐energy alkali‐ion batteries. As an essential constituent part, electrode materials with superior electrochemical properties play a vital role in the battery systems. Here, an outstanding electrode of yolk–shell ZnS@C nanorods is developed, introducing considerable void space via a self‐sacrificial template method. Such carbon encapsulated nanorods moderate integral electronic conductivity, thus ensuring rapid alkali‐ions/electrons transporting. Furthermore, the porous structure of these nanorods endows enough void space to mitigate volume stress caused by the insertion/extraction of alkali‐ions. Due to the unique structure, these yolk–shell ZnS@C nanorods achieve superior rate performance and cycling performance (740 mAh g−1 at 1.0 A g−1 after 540 cycles) for lithium‐ion batteries. As a potassium‐ion batteries anode, they achieve an ultra‐long lifespan delivering 211.1 mAh g−1 at 1.0 A g−1 after 5700 cycles. The kinetic analysis reveals that these ZnS@C nanorods with considerable pseudocapacitive contribution benefit the fast lithiation/delithiation. Detailed transmission electron microscopy (TEM) and X‐ray diffraction (XRD) analyses indicate that such yolk–shell ZnS@C anode is a typical reversible conversion reaction mechanism accomplished by alloying processes. This rational design strategy opens a window for the development of superior energy storage materials.

Hollow CoS/C Structures for High-Performance Li, Na, K Ion Batteries.

Alkali ion (Li, Na, and K) batteries as a new generation of energy storage devices are widely applied in portable electronic devices and large-scale energy storage equipment. The recent focus has been devoted to develop universal anodes for these alkali ion batteries with superior performance. Transition metal sulfides can accommodate alkaline ions with large radius to travel freely between layers due to its large interlayer spacing. Moreover, the composite with carbon material can further improve electrical conductivity of transition metal sulfides and reduce the electron transfer resistance, which is beneficial for the transport of alkali ions. Herein, we designed zeolitic imidazolate framework (ZIF)–derived hollow structures CoS/C for excellent alkali ion (Li, Na, and K) battery anodes. The porous carbon framework can improve the conductivity and effectively buffer the stress-induced structural damage. The ZIF-derived CoS/C anodes maintain a reversible capacity of 648.9, and 373.2, 224.8 mAh g−1 for Li, Na, and K ion batteries after 100 cycles, respectively. Its outstanding electrochemical performance is considered as a universal anode material for Li, Na, and K ion batteries.

Realization of high cycle life bismuth oxychloride Na-ion anode in glyme-based electrolyte

Two-dimensional bismuth oxychloride (BiOCl) is recently explored as an anode in rechargeable alkali-ion batteries because its layered structure facilitates ionic diffusion and higher specific capacities. However, its application is mainly challenged by rapid capacity decay originating from particle pulverization and unstable solid electrolyte interphase (SEI). Herein, we demonstrate the higher cycling stability of BiOCl anode in Na-ion batteries (NIBs) by simply coupling it with diglyme-based electrolyte. The BiOCl anode delivers reversible capacities greater than 295 mA h g−1 for 650 cycles at 100 mA g−1. It also displays excellent rate performances (∼278 and 267 mA h g−1 at 200 and 500 mA g−1, respectively) and higher durability under different current rates. Such stellar performance of BiOCl anode is attributed to the formation of stable SEI and maintenance of electrode integrity as revealed by the post-mortem studies. Besides, the electrochemical (de)sodiation mechanism of BiOCl anode is also clarified through in-operando X-ray diffraction (XRD) studies, which reveals the reversible formation of Bi ↔ NaBi ↔ cubic-Na3Bi phases. This report emphasizes the importance of electrolyte engineering as an excellent way to build stable SEI and achieve high-performance advanced alloy anodes for NIB application.

Steric modulation of Na2Ti2O3(SiO4)·2H2O toward highly reversible Na ion intercalation/deintercalation for Na ion batteries

Sodium-ion batteries (SIBs) require the development of novel anode materials due to the incompatibility of graphite anode. Herein, we explore the titanosilicate Na2Ti2O3SiO4·2H2O (STOS) as a potential anode material for SIBs. Controlling the content of crystal water in the lattice of STOS through dehydration significantly enhanced its electrochemical performances including coulombic efficiency, reversible capacity, cyclic stability and rate capability. By combining various structural analyses, the mechanism behind the enhancement was successfully clarified. Upon dehydration, the host framework is rearranged to create extra diffusion channels along the a and b axes as well as the additional vacant sodium sites previously occupied by crystal water in the original channels. Compared with the one-directional channels along the c axis in STOS, the channel of dehydrated homologue is three-dimensional with larger space finally enabling rapid sodium-ion diffusion and higher reversible capacity with the relieved lattice strains during charge/discharge. This strategy opens a new avenue and can be broadly applied to other electrode materials containing crystal water in the lattice to not only uncover their hidden potential but also suggest new realm of electrode materials for alkali ion batteries.

Manganese-Based Tunnel-Type Cathode Materials for Secondary Li-Ion and K-Ion Batteries.

The rational design of novel cathode materials remains a key pursuit in the development of (post) Li-ion batteries. Considering the relative ionic and Stokes radii and open frameworks with large tunnels, Na-based compounds can act as versatile cathodes for monovalent Li-ion and post-Li-ion batteries. Here, tunnel-type sodium insertion material Na0.44MnO2 is demonstrated as an intercalation host for Li-ion and K-ion batteries. The rod-shaped Na0.44MnO2 was synthesized by a solution combustion method assuming an orthorhombic structure (space group Pbam), which led to Na0.11K0.27MnO2 (NKMO) and Na0.18Li0.51MnO2 (NLMO) cathodes for K-ion batteries and Li-ion batteries, respectively, via facile electrochemical ion exchange from Na0.44MnO2. These new compositions, NKMO and NLMO, exhibited capacities of ∼74 and 141 mAh g-1, respectively (at a rate of C/20), with excellent cycling stability. The underlying mechanistic aspects (structural changes and charge storage mechanism) in these cathode compositions were probed by combining ex situ structural, spectroscopy, and electrochemical tools. Tunnel-type Na0.44MnO2 forms a versatile cathode material for non-aqueous alkali-ion batteries.

Study of ionic conduction, dielectric relaxation, optical and electrochemical properties of AgPO3/graphene glasses for magnesium battery applications

Developing suitable cathode material for alkali ion batteries is the most significant challenge facing commercialization. The effect of graphene nanoplatelets (GNP) on the physical and optical properties of AgPO3 glass is demonstrated. For the first time, AgPO3/Graphene glasses have been synthesized by melt-quenching method to assess the physical and the electrochemical performance as a cathode for a Magnesium ion battery. The complex impedance method determines bulk conductivity; the bulk conductivity increases with increasing temperature and graphene content. AgPO3_2 wt%GNP (sample 2) shows the optimum stoichiometric ratio with linear conductivity-temperature growth up to fast-ionic conductivity ∼ 1.79×10−2 (ohm. cm)−1 at 150 °C. The study of frequency dependence of both dielectric constant and dielectric loss have been explained based on ion hopping beside the ionic polarization mechanism. Optical properties such as the refractive index, optical energy gap, molar refractivity, molecular polarizability, dispersion, and oscillator energy of AgPO3 glass with different graphene nanoplatelets are investigated. The data reveal the lowest energy gap for the glass sample (AgPO3/2 wt%GNP). On the contrary, the values of refractive index, dispersion energy, molar refractivity and molecular polarizability are the highest for (AgPO3_2%wt%GNP) sample. The coin cell has been fabricated with the cell configuration Mg//electrolyte//AgPO3 and Mg//electrolyte//AgPO3_2 w%GNP. The cell with AgPO3_2 wt% GNP electrode has a high initial discharge capacity of ∼187 mAh/g compared with AgPO3 electrodes of ∼100 mAh/g.

Understanding of electrochemical K+/Na+ exchange mechanisms in layered oxides

Ion-exchange reactions are commonly used to develop novel metastable electrode materials for alkali-ion batteries that cannot be synthesized using direct chemical reactions. In this study, the electrochemical K to Na ion-exchange reaction mechanisms in a layered KxCoO2 cathode as a model system were investigated using operando and ex situ structure characterization techniques. Some level of K ions was observed to remain in the layered structure during the electrochemical ion-exchange reactions. Interestingly, the K ions are well separated from the Na-rich phases in the discharged state, and they form an intermediate phase in which K and Na ions are mixed at the top of charge. We discovered that such residual K ions prevent the collapse of the layered structure in the high-voltage regime, thereby improving the cycling stability in a Na-battery system.

Exploration of CrPO4@N-doped carbon composite as advanced anode material for potassium-ion batteries

Metal phosphates are attracting great attention as anode materials for alkali-ion batteries due to their chemical stability, low working voltage, and high theoretical capacity. However, there are few reports on the application of metal phosphate as potassium-ion batteries (PIBs) anode material, and the potassium storage mechanism remains mysterious. Herein, a core–shell chromium phosphate@N-doped carbon (denoted as CrPO4@NC) composite is newly synthesized and demonstrated as conversion-type anode material for PIBs. The N-doped carbon coating layer effectively relieves the mechanical strain and improves electrical conductivity during repetitive cycling. The formed P–C bonding between CrPO4 core and nitrogen-doped carbon shell can help to maintain structural integrity and accelerate charge transfer. As a consequence, the CrPO4@NC composite exhibits a decent capacity (304.6 mAh g−1 at 50 mA g−1), good rate capability (135.1 mAh g−1 at 500 mA g−1), and superior stability (133.2 mAh g−1 at 200 mA g−1 after 100 cycles). Particularly noteworthy, we also provide experimental evidence that a conversion reaction occurs at CrPO4@NC electrode with metallic Cr and K3PO4 formed during the potassiation process. This work illustrates that CrPO4 may be a kind of anode material for applications in energy storage systems.

Headway towards contemporary 2D MXene-based hybrid electrodes for alkali-ion batteries

This review provides a comparative study of contemporary MXene-based hybrid electrode materials in different alkali ion batteries.